Renishaw scanning technology

Renishaw scanning technology
Renishaw’s innovative approach to scanning system design compared with conventional solutions The presentation explains how Renishaw designs its scanning systems, as well as providing comparisons of Renishaw’s solutions with those from other metrology suppliers. Issue 2 technology

Questions to ask your metrology system supplier
Do my measurement applications require a scanning solution? how many need to be scanned? how many need discrete point measurement? If I need to scan, what is the performance of the system? scanning accuracy at high speeds total measurement cycle time, including stylus changes If I also need to measure discrete points, how fast can I do this? These questions were the conclusion of the CMM inspection fundamentals presentation. These should be considerations for any potential user of a scanning system. Throughout the rest of this presentation, probing solutions from Renishaw and other suppliers should be considered in light of these fundamental business needs.

Questions to ask your metrology system supplier
Will I benefit from the flexibility of an articulating head access to the component sensor and stylus changing What are the lifetime costs? purchase price what are the likely failure modes and what protection is provided? repair / replacement costs and speed of service These questions were the conclusion of the CMM inspection fundamentals presentation. These should be considerations for any potential user of a scanning system. Throughout the rest of this presentation, probing solutions from Renishaw and other suppliers should be considered in light of these fundamental business needs.

Probing applications - factors
Manufacturers need a range of measurement solutions. Why? machining processes have different levels of stability: stable form : therefore control size and position discrete point measurement form variation significant : therefore form must be measured and controlled scanning How stable are your manufacturing processes? In general, you should measure your components only as often as required to ensure the stability of your manufacturing processes. In reality, this involves focussing on key features on your components - those that are critical to its function - to work out the best process control strategy. Your choice of manufacturing technique for these features will be a critical factor in the choice of process control method: If, for example, you machine a critical bore with a process that reliably produces features with good form, it's size or position may vary. In this case, control of the size and position will be important, but not control of the roundness or cylindricity. By contrast, if you use a machining process that produces features with significant form variation (i.e. the variability of the form is a significant proportion of the form tolerance), then understanding form errors will become important.

Probing applications - factors
Manufacturers need a range of measurement solutions. Why? Features have different functions: for clearance or location form is not important Discrete point measurement for functional fits form is critical and must be controlled Scanning Features that have functional fits Some features on your components will need to mate with other parts for your product to work correctly. In many cases, the form or profile of these features will be critical to the functional fit. This is where scanning is the ideal measurement technology Other features Most of the features on your parts will not have such exacting tolerances. Many will be clearance holes, location features or drilled holes. In these cases, measuring discrete points might be the best approach, since it can be faster and simpler than scanning such features, and it avoids excess stylus wear The pragmatic approach Typically you will want to use a combination of scanning and discrete point measurement to control your production processes. On most parts, there will be some features that you want to scan, whilst many others can be controlled by discrete point measurement This practical approach will give you the right amount of information for control, without incurring unnecessary measurement time and expense. Measured values Best fit circle Maximum inscribed (functional fit) circle

Scanning Typical scanning routines to measure form
Scanning should be used where measurement of form is required. This example shows inspection of an F1 cylinder block, in which precision surfaces are critical to the performance of the race engine. Scanning provides much more information about the form of a feature than discrete point measurement Spiral scanning of a cylinder bore gathers data about feature size, position, orientation and form

Renishaw scanning - our objectives
speed and accuracy design sensors with high dynamic response to provide high accuracy data at high speed accurate through use of sophisticated probe calibration match styli materials to applications for best results flexibility probe changing stylus changing articulation cost effectiveness innovative hardware and scanning techniques reduce complexity robust designs and responsive service for lower lifetime costs Renishaw provides fast, accurate and cost-effective solutions by considering all the elements of the scanning system: Sensors - Renishaw scanning sensors are designed to support high speed, accurate measurement. They are compact and light, with excellent dynamic response. They are passive probes to avoid unnecessary system complexity and to improve measurement performance. Articulating heads - provide flexibility and automation, whilst reducing measurement cycle time, since indexing is quicker than stylus changing. Due to the lightweight sensor design, heads can themselves be compact and light, thus minimising dynamic loads on the CMM. Probe and stylus changing - providing flexibility and optimisation of sensor choice for each measurement task, reducing the need for clumsy stylus clusters. This improves measurement accuracy and allows components to be scanned on smaller, and hence less expensive, CMMs. Sensor calibration - Renishaw uses a patented and sophisticated compensation process, derived from a rapid calibration routine. The following factors are also important to scanning system design and are covered in more detail under Renishaw CMM motion control: Dynamic motion control - providing fast scanning cycles without compromising accuracy. Tight integration of sensor and machine control optimises inspection processes. Our control and calibration methods are applicable to any type of CMM. Machine calibration - reducing measurement errors whilst keeping machine costs down. Calibration covers static and dynamic sources of error to allow rapid and accurate inspection.

Renishaw scanning systems
Active and passive scanning probe design Renishaw scanning sensor design Performance styli for scanning The main topics in this presentation are: Active and passive scanning probe design - a head-to-head comparison of Renishaw’s passive scanning technology with ‘active’ scanning systems from other metrology suppliers. This highlights differences in design and explains the influence of these on scanning performance, system robustness and lifetime costs. Scanning sensor design - a closer look at key features of Renishaw scanning probes, explaining how these benefit scanning performance. Performance scanning for styli - styli design contributes to scanning accuracy, and material selection to match the application is critical. Articulating heads - indexing and servo solutions for scanning on CMMs that provide flexible access to the part, focussing on key design features. Probe and stylus changing - solutions that increase probing flexibility - key features that ensure a reliable and cost-effective product. Articulating heads Probe and stylus changing

Active or passive sensors?
Active sensors Complexity 3 force generators 3 dampers LVDTs mounted on stacked axes Simplicity no motor drives no locking mechanism no tare system no electromagnets no electronic damping Design active sensors are large, heavy and complex passive sensors are small and relatively simple

Passive sensors Simple, compact mechanism
no motor drives no locking mechanism no tare system no electromagnets no electronic damping springs generate contact force force varies with deflection Passive sensor technology Passive scanning probes use a simple mechanism to sense stylus deflection in 3 axes. During measurement the springs in the suspended probe mechanism generate a force to match the deflection. This contact force varies with deflection, but it is highly repeatable. Typical scanning deflection Force Deflection

Active sensors Complex, larger mechanism force generators in each axis
force is modulated in probe not constant at stylus tip* deflection varies as necessary longer axis travels Displacement sensor Axis drive force generator Active scanning technology Active scanning sensors use a motorised mechanism that is able to control the stylus deflection and modulate the contact force with the component. Force generators modulate the contact force, rather than springs. This arrangement attempts to avoid the non-linear force / deflection characteristics of the sensor by limiting their effect through mechanical design. Note that the force is modulated within the body of the probe, not at the stylus tip. Between the force generators and the stylus is a complex mechanism that is not perfectly stiff and which will exert some uncontrolled damping, hence the rapidly changing force commanded in the probe will be different from that seen at the stylus tip. This approach uses a complex electro-mechanical design to try to avoid accuracy problems, with relatively simple compensation. The result is a large, expensive and more fragile sensor. Force Controlled force range Deflection * see next slide

Active sensors Errors in force modulation at stylus tip
force is modulated at each stacked axis mechanism & stylus mass, plus stylus stiffness connect force generator to stylus tip errors that lead to uncontrolled stylus force: inertial acceleration of stylus mass error in estimating probe acceleration (d2xp/dt2) error in estimating probe velocity (dxp/dt) error in estimating quill acceleration (d2xq/dt2) force feedback error (eFp) Force Fp controlled here Modulation of probe force results in uncontrolled stylus force Active sensors use stacked axis mechanisms, with force generators, dampers and position sensors on each moving stage. The force generators are modulated during scanning to a narrow force range. However, it should be noted that this force modulation may be occurring 500 mm or more from the point of contact, and that there are substantial masses between the force generator and the stylus tip. These factors mean that the contact force between the stylus and the part is not, in fact, constant. Using a perfect control system, the only factor that contributes to uncontrolled stylus force is the inertial acceleration of the effective stylus mass. This becomes more significant the faster you go and the heavier the stylus (large heavy styli are the norm for active sensors). Moreover, perfect control conditions do not prevail, and so additional errors creep in. The acceleration and velocity of the axis stages are derived by differentiation of the stage position - a process which is prone to error (especially estimation of acceleration, involving two differentiations). The same issues apply to the acceleration of the CMM quill, which have a substantial effect on the heavy probe mechanism. Also, the force feedback sensing will not be perfect. Each of these factors results in uncontrolled differences between the force at the stylus tip and that which is being controlled in the probe. In the CMM XY plane the uncontrolled stylus force is different for each direction. Even if the errors in estimating stage acceleration are of the same magnitude, because there is significantly greater moving mass in one axis (the axes are stacked, remember), there is significantly greater uncontrolled stylus force. It is also interesting to note that there can be different effective moving stylus masses in the two directions when large stylus trees are needed. Since the principle mode of access to parts for this type of probe is through the use of large & complex stylus clusters, this is an important issue. What matters is force Fs here Fp cp Quill Probe mechanism mass Stylus mass Fs kp ks xq xp xs

Compact passive sensor
Method of control Passive sensors Active sensors simple device senses deflection no powered motion measurements taken using machine to control stylus deflection 3 axes under servo control new devices take advantage of modern CMM motion control effectively a miniature CMM ‘force generators’ control the deflection to modulate the force on the stylus 6 axes under servo control conceived in 1970s to accommodate poor machine motion control Compact passive sensor The first active sensors were developed in the 1970s, an era when CMMs were relatively slow and when computers were not able to tightly control the motion of the machine. Since then, CMM structures have been revolutionised by new materials and construction techniques, and motion systems have been transformed by better motor technology and massive increases in computing power. It is now possible to control the motion of the stylus tip much more precisely, enabling the use of simpler, passive sensors. Complex active sensor

Sensor design and calibration
Passive sensors Active sensors smaller axis travels required at 300 mm/sec, deflections can be held within a 100 µm range* stylus bending compensated by sophisticated calibration routine large probe travel needed to keep the contact force steady during scanning direction- dependent stylus bending variations minimised by controlling the contact force Compact passive sensor Complex active sensor * using adaptive scanning

Dynamic response Passive sensors Active sensors light weight
high natural frequency suspension system motorised stylus carrier driven on internal servo loop Modern CMMs are able to move very quickly - often faster than 500 mm/sec - and can generate high accelerations - sometimes more than 0.5g. Yet scanning on conventional scanning systems is typically performed at a tiny fraction (less than 5%) of this potential. These slow scanning moves offset most of the gains in cycle time made by having a fast measuring machine. Clearly there is scope for significant cycle time improvements if some of this untapped potential can be released. Renishaw has met this challenge with its innovative Renscan DCTM technology. This is explained in the Renishaw CMM motion control presentation. Probe suspension responds whilst scan vector is adjusted Motors adjust stylus position to modulate contact force

Scanning probe calibration
Constant force does not equal constant stylus deflection although active sensors provide modulated probe force, stylus bending varies, depending on the contact vector stylus stiffness is very different in Z direction (compression) to in the XY plane (bending) if you are scanning in 3 dimensions (not just in the plane of the stylus), this is important e.g. valve seats e.g. gears F  F High deflection when bending Constant force does not mean constant deflections Some active sensors are promoted on the basis that they provide a constant contact force, which implies better measurement performance. In reality, of course, force is not constant - it is modulated within a range. This does not necessarily result in better performance. 2D scanning The key is stylus bending. When the contact force is perpendicular to the axis of the stylus (e.g. probing a circle aligned with the axis of the stylus), the stylus is under a bending load. It deflects according to the formula  = F.L3 / 3EI (where F = force, L = stylus length, E = Young’s modulus of stem material, I = moment of inertia of stylus cross-section). Stiffness in this plane is relatively low. Variation in the bending of the stylus during scanning in the XY plane is indeed low if the force is modulated (active sensors), or if a probe with low spring rate and low deflection is used (passive probes). This approach allows for accurate measurement with a simple assumption of constant stylus bending. 3D scanning However, as soon as the contact vector introduces a component in the Z direction, things change significantly. Stiffness in the probe’s Z direction is far higher than in the XY plane, since the stylus is in compression rather than bending. This results in far lower deflections under scanning loads in this direction. When scanning a sphere, for instance, the deflection reduces with the angle  as shown in the graph. The constant force = constant stylus bending assumption breaks down when tougher measurement tasks are faced. Both active and passive sensors have to cope with non-linear stylus bending when measuring in three dimensions. Minimising contact force variation is helpful since deflections are related to this force. Active sensors modulate the contact force directly, whereas Renishaw passive sensors use low spring rates to minimise force variation over their operating range. In both cases, calibration is needed to prevent significant measurement errors and the calibration method used is critical. Deflection Low deflection in compression  90 180

Scanning probe calibration
 modulated force does not result in better accuracy passive & active sensors must both cope with non-linear stylus bending how the probe is calibrated is important Passive sensors passive probes have contact forces that are predictable at each {x,y,z} position scanning probe axis deflections are driven by the contact vector sensor mechanism and stylus bending calibrated together Active sensors contact force is controlled, and therefore not related to {x,y,z} position calibration must linearise output of readheads, mechanism motion and stylus bending longer styli increase bending variation Both active and passive sensors have to cope with non-linear stylus bending when measuring in three dimensions. Minimising contact force variation is helpful since deflections are related to this force. Active sensors modulate the contact force directly, whereas Renishaw passive sensors use low spring rates to minimise force variation over their operating range. In both cases, calibration is needed to prevent significant measurement errors and the calibration method used is critical. Passive sensor calibration The mechanism of a passive probe is moved under contact forces between the stylus and the component. As it moves, springs resist the contact force until equilibrium is reached. As such, any deflection of the probe is the result of a predictable contact force for any one stylus configuration. With a passive mechanism and ‘isolated optical metrology’ sensor system, it is possible to calibrate the characteristics of the probe mechanism (e.g. small errors in position feedback and any inter-axis and non-linear effects) at the same time as compensating for stylus bending. Both sources of potential measurement error can be detected and removed in one process. Active sensor calibration By contrast, an active sensor controls the force between the stylus and the component, moving the sensor mechanism as appropriate to achieve this. The contact force is modulated within a range, whatever the position of the stylus within the probe’s frame of reference. The probe calibration process must linearise the motion of the probe mechanism, the readhead outputs and stylus bending. Active sensors are quill mounted and therefore need longer styli to access many features. Since bending is related to stylus length, this exacerbates 3D bending variation effects.

Effective calibration for superior 3D scanning
SP80 testing at Renishaw sub micron 2D and 3D scanning performance 2D: 0.3 m 3D: 1.0 m ISO unknown path raw data - no data filtering Test details: CMM spec L/1000 Test time 97 secs Controller UCC1 Filter None Stylus length 50 mm Scanning performance testing Renishaw’s tests use the paths defined in the ISO international standard for acceptance and reverification for CMMs used in scanning measuring mode. This is a demanding test, requiring the probe to perform four paths around and across a calibration sphere, during which time the contact vector moves through a full range of angles. The test result shows the span of readings around the true spherical surface. The values quoted are raw data - I.e. no data filtering has been applied. This shows the basic performance of the sensor, machine controller, machine frame and sensor calibration. Data filtering can further improve the figures and would be used in normal working conditions. Figures for Renishaw probes are quoted for unknown path (THN), whilst active sensor scan performance is only available for known path scans (THP). The SP80 probe used was a pre-production unit. 2D and 3D performance The 2D figure is the value from the A circle in the ISO test. This involves measurement around the equator of a 25 mm (1 inch) diameter datum sphere. The 3D figure is computed from four scans which cover all planes of motion, and include compound angle contact vectors.

Measurement performance
Passive sensors Active sensors low inertia probe holds surface at high speeds fast discrete point measurement cycles with 'extrapolate to zero' routines no heat sources for improved stability 500 mW power consumption < 1ºC temperature change inside probe motorised probe mechanism enables high speed scanning slow discrete point measurement cycles due to the need to servo and static average probe data heat sources: motors and control circuits generate heat that must be measured and compensated Probe inertia A high natural frequency can be achieved, even with low spring rates, due to the low suspended mass of Renishaw’s compact scanning probes. In active sensors, masses are much higher but not suspended on springs, so motorised control is used to allow the stylus to track the surface quickly. Discrete point measurement Active sensors measure discrete points by driving the stylus against the surface, holding machine position steady and then using the probe’s motors to modulate the contact force. With six axes under simultaneous servo control, there are oscillations that must be accounted for by averaging the probe output for a period of time. Only then can the probe be moved off the surface. This whole process can take several seconds. Passive sensors do not need to go through such a complex or time-consuming process. The probe is simply moved so that the stylus meets the surface and reaches a specified deflection. The probe’s deflection is monitored throughout. As the probe moves off the surface, the probe’s readings during the period of contact can be examined to find the true surface position by ‘extrapolating back to zero’ - effectively the same as static averaging except that it is done on the move. This process typically takes less than one second per point. Heat soak Renishaw scanning probes consume little electrical power since there is no requirement to drive the stylus carrier, or lock the axes. With a peak power consumption of less than 1W, the SP600 family do not have significant internal heat sources. Experiments show that temperature variations inside the probe are less then 1 ºC. Active sensors, by contrast, need to measure and accommodate significant internal heat sources.

Minimum inspection cycle times
High speed measurement High speed scanning A dynamically responsive sensor, combined with adaptive scanning algorithms, allows high speed scanning whilst coping with unexpected obstacles. The first video shows very high speed scanning on a regular feature. The second video shows high speed measurement on a contoured surface in which the probe must adapt rapidly to changing contours. High speed scanning on a large component Scanning a complex surface at high speed

Minimum inspection cycle times
High speed measurement Video commentary scanning probe taking discrete points at high speed ‘extrapolate to zero’ routines high speed scanning Discrete point measurement With SP600 and extrapolate to zero measurement routines, cycle times for discrete point measurement approach those achievable with tough-trigger probes. The video shows a scanning probe taking discrete points on a bore, and then shows a scanning cycle on the same feature for comparison. It is important for a scanning probe to be able to measure discrete points quickly, as well as to scan at high speed, since many features are best controlled with discrete points. Discrete point measurement also minimises stylus wear. Active scanning sensors measure discrete points more slowly since they need to adjust the contact force once the stylus has been positioned on the surface of the component. Rapid discrete point measurement and scanning combined

Robustness Passive sensors Active sensors simplicity
position feedback system is only electro-mechanical element no moving wires kinematic stylus changing and patented Z over-travel bump stop provide robust crash protection probe will survive most accidents simpler motion control more things to go wrong force generators locking mechanism tare system electromagnets electronic damping control hardware for the above limited crash protection if the stylus is deflected beyond its limits more complex motion control Kinematic stylus changing provides a low force ‘break joint’ which causes the stylus to detach in XY collisions. In the Z direction, a patented ‘bump stop’ prevents damage to the probe mechanism. The chances are, a Renishaw scanning probe will survive most crashes and still work to spec. In more than 8 years of sales, no SP600 field failures returned the Renishaw can be attributed to crash damage. The same cannot be said for active sensors that do not provide robust crash protection features. Plus, crash damage to active sensors tends to be more costly due to their complexity and high repair charges.

Robustness Crash protection Video commentary overtravel in XY plane
causes stylus module to unseat stop signal generated stylus reseats as machine backs off surface probe still operational Renishaw scanning sensors are equipped with a unique kinematic stylus changing system, allowing for rapid swapping between styli and crash protection for the scanning probe. Accidents do happen, and you will want to minimise their impact on your scanning system. Renishaw's patented stylus changing systems use a magnetically retained kinematic joint, giving excellent repeatability and a high speed stylus changing mechanism A key benefit is crash protection - in the event of a collision the stylus detaches from the probe, without inducing forces in the sensor that could damage the sensing mechanism. You may have to pick up your stylus, but at least the probe should be OK. Video commentary In the video, the scanning probe is first overtravelled in the Z direction, causing the kinematic stylus to unseat from its magnetic coupling. An alarm signal causes the machine to stop, and the stylus module reseats as the machine backs off. The probe is still operation and measures normally without any need to re-qualify the stylus. The same process is repeated in the XY plan - once again the probe is OK to continue measuring. Scanning probes with high attachment forces do not offer the same level of crash protection, either for the stylus or for the component. Detachable styli allow stylus overtravel without damage to the probe or component

Lifetime costs Passive sensors Active sensors lower purchase costs
simple and cost-effective to purchase lower running costs crash protection for greater reliability 50,000+ hours operating life advance replacement service at discounted price customer-replacement on site due to simple fittings less downtime cost-effective repair higher purchase costs complex and high cost sensor higher running costs complex sensor limited crash protection vendor technician needed to remove damaged sensor more downtime high repair charges Renishaw service Renishaw’s RBE facility enables customers to quickly replace faulty product with one that is rebuilt to factory specification, at a heavily discounted price. Renishaw’s objective is to make the cost of ownership affordable, both in terms of service charges and in terms of costly downtime. Robustness SP600 probes have exceeded 50,000 hours of service with no failures. This is more than twice the MTBF claimed for active sensors.

Renishaw scanning sensor design
Renishaw design objectives: optimised for high speed measurement accurate position sensing without stacked axis errors compact and light, with excellent dynamic response models for quill mounting and use with articulating heads passive design to avoid unnecessary system complexity SP600M mounted on a PH10M indexing head

Renishaw scanning probes - quill mounted
Renishaw provides a range of quill-mounted scanning probes, suitable for all sizes of machine. SP80 The world’s most accurate scanning solution, the SP80 is a quill-mounted probe suitable for scanning deep features on larger CMMs. The unique digital readheads and isolated optical metrology of the SP80 provide exceptional accuracy, even with styli as long as 500 mm (19.7 in). Sub 1 micron ISO performance is achievable with suitable probe calibration. SP600Q A quill-mounted version of the SP600, this provides the smallest and affordable scanning solution for machines where Z axis travel is limited. SP80 quill-mounted digital readheads for ultra-high accuracy very long styli SP600Q in-quill version of SP600 reduced impact on working volume suitable for any quill size

Renishaw scanning probes - for articulating heads
Renishaw provides a range of articulating head-mounted scanning probes, suitable for all sizes of machine and all types of scanning application. SP600M This head-mounted probe provides a highly flexible scanning solution, enabling access to features on all faces of the component without the need for large and complex styli. A further advantage is the ability to switch sensors to other types of probe, such as touch-trigger or optical sensors, for even greater measurement flexibility. SP25M The SP25M provides the same benefits of flexibility and sensor changing as the SP600M, but does so in a smaller package. Module and stylus changing are included, enabling the use of different scanning modules, each optimised for a specific stylus length, plus a touch-trigger probing module, which interfaces to TP20 stylus modules. SP600M styli up to 300 mm flexible part access robust changeable with other sensors SP25M ultra-compact design (25 mm diameter) styli up to 200 mm interchangeable with touch-trigger probing

Renishaw scanning probes - key characteristics
Passive sensor - no force generators minimal heat source for greater stability no electro-mechanical wear reduced vibration during discrete point measurement No heat soak The SP600 has no motors for driving or locking its axes, and therefore has no heat sources within it. 'Active' probes have up to 6 motors inside them, resulting in heat soak that can affect measurement performance. Mechanical simplicity and longevity 'Active’ probes are effectively measuring machines, featuring powered motion of the axes. Such sensors add complexity to the scanning system, calling for more control and more maintenance. There are many more powered components that could fail By contrast, the SP600 probe is a passive device, acting merely as a means of position feedback. It is much simpler than an 'active' probe - the only power required is for the readheads. This makes for inherent reliability, leading to much lower lifetime costs SP600 has a life expectancy in excess of 50,000 hours, more than twice as long as quoted values for active sensors. Reduced vibration With no motors and hence no servo control within the probe itself, passive sensors rely only on the machine’s servo performance. Active sensors have another set of servo controlled axes to contend with, adding to overall servo noise during scanning.

Box spring mechanism - SP600 and SP80 unique design compact mechanism - fits inside Ø50 mm (2 in) probe low inertia rapid dynamic response low spring rates single 3D ferrofluid damper Compact dimensions - 50 mm diameter, 89 mm length Compact dimensions are valuable since they allow the probe itself to enter deep features, thus reducing the length of stylus needed to access the surface. It is always sensible to minimise stylus length to reduce stylus bending and to minimise suspended mass, thus maximising the dynamic response of the probe. The SP600 is much smaller than probes fitted to conventional scanning systems. Light weight - SP600M weighs just 216g (7.6 oz) The light overall weight of Renishaw scanning probes means that versions can be mounted on articulating heads for flexible part access. Renishaw's SP600M is the only scanning probe that can be mounted on an articulating head. When mounted on a PH10 indexing head, the combined weight is less than 1 kg (2.2 lbs). Even on fixed probes, a light mass reduces the dynamic loads on the CMM quill during scanning. Here, the compact size of the SP600Q makes it ideal for use on small CMMs where the measurement volume is limited. The SP600Q weighs 299g (10.5 oz). By contrast, 'active' probes are heavy - some weigh more than 5 kg (11 lbs). This can increase the inertial loads on the machine quill, limiting scanning accuracy at higher speeds. Parallel acting springs

Pivoting probe mechanism - SP25M patented, pivoting mechanism featuring ‘isle of Man’ spring ultra-compact mechanism - fits inside a Ø25 mm (1 in) probe very low inertia very low spring rates (< 60 g/mm) high natural frequency (rigid member) when in contact with the component ‘Isle of Man’ spring creates XY pivot point Compact dimensions - 25 mm diameter The SP25M is the world’s smallest scanning probe. The SP25M features a patented pivoting mechanism using an 'Isle of Man' spring (see diagram). When in contact with the part, the mechanism is extremely stiff, whilst its light mass requires very low spring rates to suspend it. When the stylus is in contact with the part, a rigid member connects the stylus tip with the measurement system, resulting in a high natural frequency. Unlike complex active probes, Renishaw's passive sensors do not require motors, independent dampers or locking mechanisms, all of which add to the mass and inertia of the sensor. Renishaw's unique design results in a high natural frequency and the capability to handle rapid changes in surface without hitting the bump-stops or losing the surface. A dynamically responsive mechanism, combined with tight machine motion control, allows Renishaw probes to scan at very high speeds. Another advantage of high speed response is that the maximum stylus travel of the probe can be smaller, thus reducing probe size and probe mass - all to the benefit of high speed scanning performance. Second spring allows translation in all direction

Z pos Isolated optical metrology - SP600 readheads attached to probe housing measures deflection of whole mechanism, not just one axis eliminates inter-axis errors picks up thermal and dynamic effects probes with stacked axes cannot measure inter-axis errors directly Y pos Readheads attached to probe body X pos A scanning probe has three axes of deflection - X, Y and Z. The probes use parallel-acting springs to allow each axis to move relative to one another. Each axis moves in an arc, resulting in a small amount of motion in a direction perpendicular to the axis that is moving. This small deflection - or inter-axis error - must be accounted for to ensure that the position of the stylus is accurately known. In a Renishaw scanning probe, the three axes are arranged to form a unique 'box spring', making for a very compact design. The transduction (position sensing) system is located behind the spring assembly. By contrast, a tower probe features stacked axes, making the probe much longer. A position sensing device is mounted on each axis. Isolated optical metrology Renishaw's SP600 probe mechanism features a transduction system with readheads fixed to the body of the probe, measuring the deflection in each direction on a target mounted to the moving mechanism. This arrangement means that any inter-axis errors caused by the arc motion of each pair of parallel-acting springs are directly measured by the sensor system - the deflection in each direction is measured 'back to earth'. The motion of the stylus is measured directly by the readheads, meaning that the system is not reliant on the mechanical design of the structure for its accuracy. The illustration on this slide shows a schematic of an SP600 mechanism featuring position sensitive detectors (PSDs) lit by LEDs shining through precision slits. By contrast, probes that feature position sensing devices mounted to each axis can only measure linear deflections relative to the axis above. They cannot detect inter-axis errors, nor errors of squareness of the probe axes. Whilst these errors can be compensated, this is not necessary for a Renishaw scanning probe. Isolated optical metrology systems can detect sources of variable error such as thermal and dynamic effects. Stacked axis probes cannot detect these and so perform less well in real world conditions, or when scanning quickly. Illustration shows SP600 mechanism with PSDs Inter-axis error

Isolated optical metrology - SP80 SP80 features digital readheads with m resolution reading precision gratings accuracy defined by straightness of lines on each grating and calibrated squareness of gratings, not by probe mechanical design ISO test data: ISO Diff: 0.6 m ISO Tij: 1.0 m CMM spec L / 1000 Test time 61 secs Controller UCC1 Filter None Stylus 50 mm, 9 mm, ceramic The SP80 quill-mounted probe also features isolated optical metrology. The larger size of this probe allows for a more sophisticated sensor system - the SP80 uses digital readheads and precision gratings as the basis for its position feedback. This allows for even greater precision. The digital readheads are each matched to a grating, which contains a series of precisely straight and parallel lines. Three gratings are attached to the moving mechanism, each one aligned with an axis of motion. The squareness of these gratings is calibrated, so that any slight misalignments are corrected in the probe output. The readheads interpolate the signal from the gratings to produce a digital output at 20 nm resolution. The accuracy of the overall {x.y.z} deflection of the probe is reliant on the straightness of the lines on the grating surface, and on the performance of the readheads, not on the design of the probe mechanism. The performance results speak for themselves. Note: ISO Tij is the result generally quoted for scanning probes. It is the the total span of readings in the measured data set. Renishaw also quotes ISO Diff values - the maximum radial error from the calibrated perfect sphere to the measured values. Note that these results are for unknown path scans and are raw data with no filter applied. When a 60Hz harmonic filter is used, the Tij value for SP80 in this test fell to 0.6 microns. Other details for the ISO test: Scanning speed = 5 mm/sec Scanning deflection = 0.5 mm Total points taken = 2,619 Note - results quoted are for unknown path scans.

SP25M probe body Isolated optical metrology - SP25M IREDs in probe body reflect light off mirrors in stylus module back onto PSDs non-linear outputs compensated by sophisticated 3rd order polynomial algorithms 2 PSDs detect stylus deflection IRED ISO test data: ISO Diff: 1.3 m ISO Tij: 2.6 m CMM spec L / 1000 Test time 57 secs Controller UCC1 Filter None Stylus 50 mm, 5 mm, ceramic Mirror The SP26M uses a very different mechanism to SP80 and SP60, and a different optical scheme. Like those probes, however, the SP25M features isolated optical metrology, where the light sources (IREDs) and detectors (PSDs) are attached directly to the probe body, and therefore are able to measure the total deflection of the probe mechanism directly. The IREDs direct light onto two mirrors, mounted to the moving mechanism in the stylus module (the housings and kinematics are not shown for clarity). These mirrors can pivot and translate relative to the probe body and cause the reflected light patches to move on the PSDs. The XY location of both reflected beams are analysed and the resulting data can be used to compute the {x,y,z} deflection of the stylus. The relationship between the location of the reflected spots on the PSDs and the position of the stylus tip is complex and non-linear. However, Renishaw’s sophisticated compensation algorithms, featuring 3rd order polynomials to linearise the output, enable high accuracy scanning data to be extracted from this compact mechanism. The ISO test results show excellent performance for such a compact probe. Note: ISO Tij is the result generally quoted for scanning probes. It is the the total span of readings in the measured data set. Renishaw also quotes ISO Diff values - the maximum radial error from the calibrated perfect sphere to the measured values. Note that these results are for unknown path scans and are raw data with no filter applied. When a 60Hz harmonic filter is used, the Tij value for SP80 in this test fell to 1.3 microns. Other details for the ISO test: Scanning speed = 5 mm/sec Scanning deflection = 0.3 mm Total points taken = 2,281 Kinematic joint between probe body and stylus module (not shown)

Kinematic stylus changing optimise stylus and hence repeatability for each feature: minimum length Longer styli degrade repeatability maximum stiffness minimum joints maximum ball size Maximum effective working length repeatable re-location no need for re-qualification passive no signal cables easy installation Renishaw scanning sensors are equipped with a unique kinematic stylus changing system, allowing for rapid swapping between styli and crash protection for the scanning probe. Using Renishaw’s new modular rack system, any number of stylus changing ports can be fitted to a CMM, allowing great flexibility in your choice of styli. This allows you to select the best stylus for each measurement task, resulting in more repeatable measurements. Video commentary The video shows how quick and simple an automatic stylus change is. In just 10 seconds, the stylus is switched and the probe is ready to measure again. The repeatable kinematics mean that the stylus can be changed many times and will always be in the same position relative to the probe, so there is no need to re-qualify after each change. Kinematic stylus changing in around 10 seconds means that you can pick the best stylus for each feature

Feature access - SP80 SP80 can support very long and complex styli 500 mm (19.7 in) 500 g (17.6 oz) suitable for measurement of deep features on large components no need for counter-balancing full measurement range is maintained irrespective of stylus mass and orientation Whilst stylus length should be kept to a minimum, there are applications where a long stylus is essential to access deep features. The SP80 is designed to meet this challenge, with the capability to carry long and heavy styli without an unacceptable loss in measuring performance. As with all Renishaw scanning probes, the SP80 is designed to provide its full quoted measurement range with the need for stylus counter-balancing. Even if a heavy stylus is mounted to the probe, any deflection caused in the mechanism still leaves sufficient travel to provide the full measuring range. The travel (the distance over which each axis can move and sense position) is larger than the measuring range (the control limits within which the probe is kept during scanning). Active sensors, by contrast, use a mechanical tare system to keep the stylus positioned around a ‘sweet spot’ in the travel.

Feature access - SP80 Video commentary 500 mm (20 in) stylus cranked stylus no counter-balancing needed scanning deep features in F1 engine block In this video, an SP80 is scanning a feature deep inside a cylinder block, using a long stylus. Styli of up to 500 mm (20 in) can be used. SP80 scanning with a 500 mm (20 in) stylus for access to deep features

Feature access - SP80 deep bore measurement - cranked / star styli VDI / VDE test data: CMM spec: L / 1000 Test speed: 5 mm/sec Controller: UCC1 Filter: 50 Hz Values: Unknown path V2 m 1.75 1.5 1.25 1.0 The chart shows how the scanning performance of the SP80 varies with stylus length using a variety of cranked styli. In this test, a 50 mm diameter ring gauge, orientated at 90 degrees to the CMM quill, was measured with styli of different lengths. Styli up to 400 mm in length were used, in all cases showing V2 performance of better than 2 microns. 0.75 0.5 0.25 50 100 150 200 250 Stylus length (mm)

Feature access - SP600 family Video commentary 200 mm (8 in) stylus scanning deep features in a cylinder block compact probe dimensions further extend the reach of the probe styli up to 280 mm (11.0 in) can be used with SP600 probes In this video, an SP600M is scanning a feature deep inside a cylinder block, using a long stylus. Styli of up to 280 mm (11.0 in) can be used. The small diameter of the SP600 means that it can itself be inserted into many deep features, further extending the reach of the measurement system. SP600 scanning with a 200 mm (8 in) stylus for access to deep features

Feature access - SP25M three scanning modules, each optimised for a range of stylus lengths same measuring range and accuracy in all orientations stiff carbon fibre stylus extensions provide excellent effective working length with M3 styli styli up to 200 mm (7.9 in) The SP25M supports three different scanning modules, each with gains and spring rates optimised to carry different length styli. By repositioning the ‘isle of Man’ spring, which provides the pivot point, relative to the readheads, and by adjusting the spring rates, excellent measurement performance can be achieved across a wide range of stylus lengths. The SM25-1 module carries styli up to 50 mm long The SM25-2 module carries styli between 50 mm and 100 mm long The SM25-3 module carries styli between 100 mm and 200 mm long

Feature access - SP25M ISO test data accurate form measurement, even with long styli ISO Tij m ISO test data: CMM spec: L / 1000 Test speed: 5 mm/sec Controller: UCC1 Filter: None / 60 Hz Values: Unknown path 3.5 3.0 2.5 2.0 This chart shows the results of a series of ISO scanning tests using a SP25M probe fitted to a PH10M head, with different stylus configurations. Two ISO Tij values are quoted for each stylus length: raw data and data that has been subject to a 60 Hz harmonic filter, designed to remove high frequency noise from the probe and machine position feedback systems. Three different scanning modules are used, each of which has been designed to work with a range of stylus lengths, with optimised gains and spring rates to deliver the best scanning accuracy: Module Stylus SM mm long, stainless steel stem, 3 mm ball - shortest scanning stylus SM mm long, ceramic stem, 5 mm ball - typical ‘short’ stylus SM mm long, graphite fibre stem, 6 mm ball - typical ‘long’ stylus SM mm long, graphite fibre stem, 6 mm ball - extreme length stylus Note that SP25M’s small size means that the probe itself can gain access to many deep features, extending the reach of the probe. Filtered (60 Hz harmonic) 1.5 No filter (raw data) 1.0 22: 3 mm, SS stem 50: 5 mm, ceramic stem 100: 6 mm, GF stem 200: 6 mm, GF stem 0.5 22 50 100 200 Stylus length (mm)

Feature access - SP25M probe is small enough to be inserted into many features total reach can be extended, with a probe extension, to nearly 400 mm (15.7 in) including length of probe body In this video, an SP25M is scanning a counter-bore, using the compact size of the probe to gain access to this deep feature without resorting to an excessively long stylus. SP25M inspecting a deep counter-bore

Feature access - SP25M probe can be mounted on an articulating head means that many features can be accessed with fewer styli lower stylus costs shorter cycle times The SP25M’s compact size and low mass makes it ideal for mounting on a PH10M indexing head, enabling flexible access to numerous features around the part, without changing styli. Combined with module and stylus changing, this makes it the most versatile scanning system available.

Crash protection stylus change joint has low release force over-travel in XY causes stylus to detach Z crash protection outer housing provides a ‘bump stop’ to prevent probe mechanism and readhead damage Renishaw's kinematic stylus changing system provides crash protections when the stylus travel is exceeded in a lateral direction (X or Y). However, this does not provide full protection for crashes in the Z direction A feature of Renishaw scanning probes is a Z 'bump stop' that transfers any compression forces into the probe body before the Z travel of the scanning mechanism is exceeded. This means that in the event of an uncontrolled Z movement of the machine, the probe stylus and the probe body take the load whilst protecting the box spring and readheads from damage. Stylus deforms in a severe Z crash, whilst probe mechanism is protected Note - same principles apply to pivoting probes like SP25M.

Crash protection Video commentary steel stylus crushed against SP600 more severe than any Z crash since E Stop would prevent continued force bump-stop protection system saves probe mechanism probe was still functional after test completed This video shows a Renishaw scanning probe being deliberately ‘crashed’ and still measuring accurately afterwards. The stylus is crushed against the probe, causing it to buckle. In a real Z crash, the emergency stop facility on the CMM would cut in to limit the force applied to the quill, meaning that the forces applied to the probe would be lower and less sustained than in this test.. The patented bump stop takes the force of the impact and protects the probe mechanism and electronics. The probe still functioned normally and was found to meet specification following a recalibration cycle. Renishaw scanning probes are robust - even after bending or breaking the stylus, they still work!

Circle C Compression test data Circle B Stylus ball shatters Circle A Circle D Force (N) ISO CMM spec L / 250 Test time secs Controller UCC1 Filter None Stylus length mm (All data in m) Circle Before After A B C D Result The chart shows the force / deflection profile during the compression test. The peak force applied to the probe was over 1,630 N (365 lb), which occurs at the point where the ball shattered. The force then builds up again as the stylus starts to buckle. An ISO Part 4 scanning test was performed on the probe before and after the compression test. There is no degradation in performance as a result of the compression test. Deflection (mm)

Stylus selection for scanning
Styli choice affects performance the stylus is a critical element in any scanning system affects: feature access (stylus length and configuration, effective working length) speed (weight affects dynamic response) repeatability (stiffness, joints) accuracy over time (wear, pick-up on stylus) choice of stylus configuration and materials must be driven by the application The stylus is a critical element of any scanning system, since it is the part of the system that must detect and transmit surface information to the probe mechanism and readheads, whilst introducing the minimum of noise and error. Stylus selection affects: Feature access - styli must be chosen that allow the probe to access the features that are to be inspected. Styli must have sufficient reach, be the right shape and orientation to enter and measure the target feature, and be stiff and straight enough to give enough working length to prevent ‘shanking out’ on the feature. Speed - heavy styli increase the suspended mass of the system and therefore reduce the dynamic response. Scanning can be done faster when styli are light and stiff. Repeatability - measurements will be more repeatable if the stylus is stiff. Joints reduce stiffness and introduce hysteresis, and so should be avoided if possible. Accuracy over time - before it can be used to measure features, a stylus must be calibrated. When scanning, the stylus is dragged over the surface (unlike touch-trigger probing), and so the behaviour of the stylus tip over time must be understood if errors are not to accumulate. Key issues are wear and pick-up, both of which result in the stylus ball changing shape slightly, resulting in measurement errors. The choice of tip material must be driven by the component material (see later slide). To summarise - it is the measurement application that must drive the choice of stylus. If you measure a wide range of parts, then you will need a range of suitable styli and an efficient means to change them.

Configuration keep styli as short and as stiff as possible avoid joints articulating heads reduce the need for long styli where longer styli are essential, choose single-piece styli made from performance materials (e.g. M5 range for SP80): graphite fibre stems (light and stiff) titanium fittings Long graphite fibre stylus Joints reduce stiffness and can therefore affect measurement repeatability. The need for complex styli, and hence joints, can be reduced by the use of articulating heads, which permit the probe to be reorientated to suit the feature, thus enabling simple, straight styli to be used for most measurement tasks. Renishaw’s SP25M and SP600M can be mounted to indexing and servo heads, giving greater flexibility of feature access with simple styli. In some applications, access to deep features demands a long stylus. Rather than building a stylus up from a kit of parts, it is best to select a single-piece design for optimum stiffness. Renishaw’s M5 range for the SP80 scanning probe provide lengths of up to 500 mm, manufactured from titanium and graphite fibre for minimum suspended mass. Similarly, longer styli for the SP25M are also made with graphite fibre stems for lighter mass and the maximum effective working length.

Effects of continuous scanning on stylus balls
Three phenomena that can affect scanning accuracy in touch trigger probing, the stylus ball comes into temporary contact with the measured surface scanning results in a different and more aggressive type of surface interaction between the stylus and the workpiece testing at Renishaw has revealed three interactive phenomena: 1. Debris 2. Adhesive wear 3. Abrasive wear Compared to touch trigger probing applications where the stylus ball comes into temporary contact with the measured surface, contact scanning results in a different and more aggressive type of surface interaction between the stylus and the workpiece. Contact scanning is not a new application, having been used for very high precision measurement since the late 1970's, and the industry standard ball material, ruby, has been successfully applied with only a few limitations. In some extreme applications, particularly when scanning aluminium, a phenomenon known as ’adhesive wear' (or pick-up) has been observed. This is now believed by some to become a problem as scanning applications become faster and more widespread. Renishaw has undertaken a programme of extensive investigation and testing to study the effects of prolonged contact scanning over a number of common engineering surfaces with different stylus ball materials. By understanding the material interactions and processes involved, Renishaw is able to offer its customers the optimum product and application advice to achieve maximum performance from their scanning tasks. The following slides provide a brief overview of our findings. They indicate that there is not one but three different interactive phenomena involved in contact scanning. These are: 1) debris, 2) adhesive wear and 3) abrasive wear Sliding interaction between ball and surface

Phenomenon 1 - debris any contamination present on the scanning path will collect on the stylus ball as it passes over the surface metal oxide particles on the surface air-born debris such as coolant mist or paper dust debris can be removed by wiping the ball with a dry, lint-free cloth a periodic cleaning regime for the stylus ball is the only solution to avoid a build up of debris debris is practically unavoidable with any contact scanning application and is independent of the stylus ball or scanned surface material Any contamination present on the scanning path will collect on the stylus ball as it passes over the surface. Unless the component has been scrupulously cleaned and inspection is being carried out in a clean room environment, then debris will be present. This can be made up of oxide particles of a metal surface as it is exposed to the air or air borne debris such as coolant mist or paper dust from a printer. The key characteristic of debris is that it can be easily and totally removed by simply wiping the ball with a dry lint-free cloth. Consequently, a periodic cleaning regime for the stylus ball is the only solution to avoid a build up of debris, which may eventually effect the measurements being taken. Collection of debris is practically unavoidable with any contact scanning application and will occur almost regardless of the stylus ball or scanned surface material. Typical debris collected on a stylus ball after scanning

Phenomenon 2 - adhesive wear adhesive wear (sometimes referred to as pick-up) involves the transfer of material from one surface to another local welding (adhesion) at microscopic contact points break off during sliding minute particles from one surface are transferred to the other surface material adhesion is permanent and cannot be removed through normal cleaning techniques as the surface material from the workpiece starts to adhere to the ball, it is the attached material which is now in contact with the surface as like materials attract, rapid build up can occur will eventually degrade the form of the stylus ball compromised measuring results In Tribology, the study of material interaction, adhesive wear (sometimes referred to as Pick-up) is characterised by the transfer of material from one surface to another. When the two surfaces come into contact and slide over one another, interaction and local welding (adhesion) occurs at microscopic contact points between the surfaces, which break off during sliding. This results in minute particles from one surface being transferred to the other surface. Unlike debris, the material adhesion is permanent and cannot be removed through normal cleaning techniques. Consequently, as the surface material starts to adhere to the ball, it is that material which is now in contact with the surface. As like materials attract, rapid build up can occur which will eventually degrade the form of the stylus ball to such a level as to compromise measuring results.

Phenomenon 2 - adhesive wear factors affecting adhesive wear: contact force distance scanned hardness of surfaces (if stylus is much harder than surface being measured) affinity between ball and surface materials … is it a similar material? single point contact such conditions apply when scanning an aluminium surface with a relatively hard ruby (aluminium oxide) stylus ball significant wear only occurs after long periods scanning the same part in most real applications, the amount of material transfer is negligible on the form of the stylus ball (< 0.1 m) and cannot be quantified, even with the highest precision measuring equipment Factors affecting adhesive wear: The degree of adhesive wear is directly proportional to the: - contact force - distance scanned - hardness of surfaces The rate of adhesive wear is also worsened if there is an affinity between the two materials (ball and surface) or if the relative hardness of each surface is significantly different. Such conditions apply when scanning an aluminium surface with a relatively hard ruby (aluminium oxide) stylus ball. However, with the continuous distances scanned and probing forces encountered in this application, although adhesive wear does occur, the amount of material transfer is minute and immeasurable on the form of the stylus ball, even with the highest precision measuring equipment.

Phenomenon 2 - adhesive wear significant errors only occur in unrepresentative situations: Unrepresentative experiences There is however, one application that can significantly increase adhesive wear. This occurs typically during repetitive test cycles or with exhibition demos where the stylus ball is scanned over the same material path time and time again where intimate bare material contact occurs. In many such applications, the material build up is sometimes seen as a ring around the ball equator. The problem can be exacerbated further by limiting contact to a single point on the ball. In this case, material build up can grossly deform the form of the sphere and will significantly influence measuring results. Examples The first image shows adhesive wear visible on a ruby stylus ball that has been scanned with a single point contact on aluminium with a 15 g contact force for a continuous distance of 350 m. Although visible, the material pick up is so small that it could not be measured on high precision roundness measuring equipment. Compare this with the material pick up shown in the second image where, under the same conditions, the ball was repeatedly scanned over the same path several hundred times to achieve the scanning distance. The resulting patch is much larger (approx. 200 µm x 500 µm) and measurable in height at approximately 2 µm. Although this is an extremely harsh test and totally unrepresentative of any real scanning measurement task, it does illustrate the effects of adhesive wear. Test conditions: ruby stylus on aluminium 15 g contact force, single point contact 350 m scan path over new material Results: small patch where adhesion occurs negligible impact on ball form Test conditions: ruby stylus on aluminium 15 g contact force, single point contact 350 m scan path over repeated path Results: 200 m x 500 m adhesion patch 2 m impact on ball form

Phenomenon 3 - abrasive wear abrasive wear involves removal of material from both surfaces small particles from both surfaces break and adhere to each surface harder stylus particles attached to the component surface begin to act as an abrasive where there is little atomic attraction between the two materials, wear rather than material build up occurs Test conditions: ruby on stainless steel 15 g contact force, single point contact 5,600 m scan path over new material very extreme - unrepresentative of most applications Results: flat on ball surface approx. 150 m diameter form error of 1.5 m Abrasive wear is characterised by removal of material from both surfaces. The rate of wear on each surface will depend upon their relative hardness. Rather like a benign form of adhesive wear, small particles from both surfaces break and adhere to each surface. However, as in the case of ruby and steel, the harder ruby particles attached to the steel surface begins to act as an abrasive. As there is little atomic attraction between these two materials, wear rather than material build up occurs. Once again, the form of the stylus ball has changed which can result in scanning measurement error. This is made significantly worse by single point contact. The illustration shows the results of wear on a ruby stylus ball scanning on a steel surface with a contact force of 15 g for 5,600 m. The flat is approximately 150 µm in diameter, resulting in a 1.5 µm form error of the ball. Note that material will also be removed from the steel surface (slightly more as steel is less hard than ruby), however this will be from a much larger surface of material and not all from one spot as on the ball, so it is not significant. As with the conditions given in the illustration of abrasive wear, the tests are extreme and totally unrepresentative of any real application. However, they serve to illustrate the effects of wear.

Ball material - conclusions from testing at Renishaw ruby can suffer adhesive wear (pick-up) on aluminium under extreme conditions, but performs well in most applications ruby is the best material on stainless steel Ruby stylus used in touch-trigger mode The conclusions are from testing at Renishaw, which is still ongoing: Ruby suffers from pick-up (adhesive wear) on aluminium under extreme conditions, such as where a newly machined feature (i.e. where the surface has not yet oxidised) is repeatedly scanned using the same contact point . For most scanning applications, which involve a variety of features and therefore different contact points, ruby performs well. For instance, ruby styli have been used for digitising applications for many years without any problems. Ruby is the best choice for stainless steel, suffering very low abrasive wear and no adhesive wear. Silicon nitride is the best choice for aluminium, but suffers high levels of abrasive wear on steel and cast iron. Zirconia is ideal for cast iron, and gives acceptable performance on aluminium and steel Tungsten carbide performs well with cast iron parts Once again, the message is: understand the application before choosing a stylus.

Ball material - conclusions from testing at Renishaw silicon nitride is a good substitute for ruby in extreme aluminium applications, but suffers from abrasive wear on stainless steel and cast iron Silicon nitride stylus tip scanning an aluminium component The conclusions are from testing at Renishaw, which is still ongoing: Ruby suffers from pick-up (adhesive wear) on aluminium under extreme conditions, such as where a newly machined feature (i.e. where the surface has not yet oxidised) is repeatedly scanned using the same contact point . For most scanning applications, which involve a variety of features and therefore different contact points, ruby performs well. For instance, ruby styli have been used for digitising applications for many years without any problems. Ruby is the best choice for stainless steel, suffering very low abrasive wear and no adhesive wear. Silicon nitride is the best choice for aluminium, but suffers high levels of abrasive wear on steel and cast iron. Zirconia is ideal for cast iron, and gives acceptable performance on aluminium and steel Tungsten carbide performs well with cast iron parts Once again, the message is: understand the application before choosing a stylus.

Ball material - conclusions from testing at Renishaw zirconia is the optimum choice for scanning cast iron components tungsten carbide also performs well on cast iron Zirconia is often used where a large diameter tip is required The conclusions are from testing at Renishaw, which is still ongoing: Ruby suffers from pick-up (adhesive wear) on aluminium under extreme conditions, such as where a newly machined feature (i.e. where the surface has not yet oxidised) is repeatedly scanned using the same contact point . For most scanning applications, which involve a variety of features and therefore different contact points, ruby performs well. For instance, ruby styli have been used for digitising applications for many years without any problems. Ruby is the best choice for stainless steel, suffering very low abrasive wear and no adhesive wear. Silicon nitride is the best choice for aluminium, but suffers high levels of abrasive wear on steel and cast iron. Zirconia is ideal for cast iron, and gives acceptable performance on aluminium and steel Tungsten carbide performs well with cast iron parts Once again, the message is: understand the application before choosing a stylus. Zirconia stylus tip and graphite fibre stem

Articulation or fixed sensors?
Articulating heads are a standard feature of most computer- controlled CMMs heads are the most cost-effective way to measure complex parts Fixed probes are best suited to small machines on which simple parts are to be measured ideal for flat parts where a single stylus can access all features Articulating heads allow users to reorientate the probe without the need to re-qualify the stylus. This alone increases flexibility and saves time that fixed probe spend changing styli. Fixed probes are only the optimum choice when the range of parts to be measured is small and the parts themselves are simple.

Renishaw articulating heads
Increased flexibility… easy access to all features on the part repeatable re-orientation of the probe reduced need for stylus changing optimise stylus stiffness for better metrology Reduced costs… indexing is faster than stylus changing less expensive than active scanning systems reduced stylus costs simpler programming Flexibility Articulation brings the key benefit of simpler stylus arrangements that can be used to probe features in almost any orientation. In many cases, one stylus is all you need to inspect a whole component By contrast, fixed probe systems typically require several styli to inspect a part, particularly where features can not be accessed by a straight stylus mounted vertically. This need for multiple styli makes fixed sensors slower to use than probes mounted on articulating heads - since indexing is faster than stylus changing. Reduced costs and higher throughput Articulating heads allow you to measure more features with the same stylus, reducing the need for stylus changes. This means that you can spend more time inspecting and less time getting ready to measure.

Renishaw articulating heads for scanning
PH10M indexing head the industry standard PH10MQ in-quill version of PH10M reduced impact on working volume needs 80 mm quill PHS1 servo positioning head infinite range of orientations longer extension bars

Articulating head applications
Flexible probe orientation PH10M offers 7.5° increments in 2 axes - is this enough? prismatic parts generally few features at irregular angles use a custom stylus to suit the angle required fixed scanning probes also need customer styli for such features Knuckle joint needed to access features at irregular angles The PH10 family of indexing heads provide sufficient flexibility of probe positioning for all but the most specialised inspection tasks. With 7.5° increments in each axis, PH10 heads allow the probe to be orientated at the optimum angle for most features. Whilst it is possible to provide smaller increments, this provides little real world advantage and serves to increase the complexity and mass of the articulating head. Where features are orientated at an irregular angle on a prismatic part, then the best course of action is to configure a custom stylus to suit that feature. Renishaw provides a range of knuckle joints and stylus accessories to build up such special configurations. Note that a fixed probe also needs to use custom styli to measure the same feature.

Articulating head applications
Flexible probe orientation PH10M offers 7.5° increments in 2 axes - is this enough? sheet metal / contoured parts many features at different irregular angles stylus must be perfectly aligned with surface in each case no indexing head is suitable fixed probes also unsuitable due to need for many stylus orientations need continuously variable head (PHS1) Cylindrical stylus must be perfectly aligned with hole In the case of sheet metal or contoured parts, where there are numerous surfaces and features at irregular angles, then using custom styli is not a cost-effective solution. In sheet metal work inspection (e.g. body-in-white) it is essential to have perfect alignment between the stylus and the part. This is where an infinitely variable servo head such as the Renishaw PHS1 is useful. Whilst such a head could be used for all measurements on all features, the PHS1's extra size and mass compared to the PH10 family makes it best suited to larger CMMs. Sheet metal

PH10M indexing head - design characteristics
Head repeatability test results: Method: 50 measurements of calibration sphere at {A45,B45}, then 50 with an index of the PH10M head to {A0,B0} between each reading TP200 trigger probe with 10mm stylus Results: Comment: indexing head repeatability has a similar effect on measurement accuracy to stylus changing repeatability Result Span fixed Span index  [Span]  [Repeatability] X ± Y ± Z ± Test spec: Machine Specification: U1 = L / 1000 U3 = L / 1000 Controller: Renishaw UCC-1 Controller. Head: PH10MQ. Extension Bar: None. Probe: TP200. Stylus: 10x4mm Stainless Steel Software: Virtual DMIS V3.8.5 Test method: Machine underwent a 90 minute warm-up cycle. 50 measurements were made on a calibration sphere (13 points per measurement) with the head fixed at angle A45, B45. This establishes a baseline repeatability for the machine. Another set of measurements were made, with an index to A0, B0 and back again between each. The same qualification data was used throughout. Spans and standard deviations for the sphere centre position were established for both set of readings. Increases in span and standard deviation can be attributed to head index repeatability. Repeatability is defined as a 2 sigma value (i.e. 95% of readings will fall within this amount of the mean). Increases in repeatability were less than 0.4 microns in each direction (increase in 3D repeatability was approx 0.5 microns) - typically not a significant part of allowable measurement error.

Indexing repeatability affects the measured position of features Size and form are unaffected Most features relationships are measured ‘in a plane’ Feature positions are defined relative to datum features in the same plane (i.e. the same index position) Datum feature used to establish a part co-ordinate system Therefore indexing typically has no negative impact on measurement results, but many benefits Although indexing repeatability is very small, it is sometimes argued that it will have a detrimental effect on measurement accuracy. This can be demonstrated to be untrue in almost all instances. The repeatability of indexing will affect the position of the stylus tip. It will not, of course, affect the size and shape of the tip, nor the measurement characteristics of the CMM. Consequently, indexing repeatability has no impact on the measured size or form of component features. In the case of measured position, this effect is also zero in most cases. Complex parts with features in many different orientations are generally toleranced relative to datum features in the same plane. Thus it is a simple matter to inspect the datum feature and establish a part co- ordinate system (PCS), thus eliminating the small effect of indexing repeatability. All the features in that plane can then be measured relative to the PCS with the articulating head locked in that orientation.

Light weight 650 g (1.4 lbs) lightest indexing head available total weight of < 1 kg including scanning probe Fast indexing typical indexing time is 2 to 3 seconds indexes can occur during positioning moves no impact on measurement cycle time Using a single probe and simple stylus combination to measure features in several orientations saves time. Re-orientating the sensor takes bout 2 to 3 seconds - and can be performed during positioning moves - thus having no impact on cycle times By contrast, using a quill mounted scanning probe could require a clumsy stylus cluster or demand multiple stylus arrangements. To change styli, the quill must be moved to a docking position at the stylus rack, a change operation must occur, and the probe must then be positioned back to the part. If a complex stylus is used, time is wasted on longer clearance moves around the part With Renishaw's kinematic stylus changing system, this time is minimised. Conventional stylus changing systems are slower. Indexing can be up to 10 times faster than stylus changing, with the extra benefit on proven programs of combining indexing with positioning moves.

Flexible part access This video shows scanning features in three different orientations, using a single, simple stylus. The probe is fitted to a PH10M indexing head, which allows rapid reorientation of the probe to allow access to the three features. In this instance, the head reorientations are programmed to occur during positioning moves, meaning that they have no impact on the measurement cycle time. By contrast, a fixed sensor would need either a large, complex stylus arrangement or a time-consuming stylus change to measure these features. Rapid indexing during CMM positioning moves give flexible access with no impact on cycle times

Autojoint programmable sensor changing with no manual intervention required use scanning and touch-trigger probes in the same measurement cycle Sensor changing Having access to a range of different types of probe can be invaluable if you have many different types of parts to inspect. For some parts, a touch-trigger probe will be ideal, whilst others will need a scanning sensor (to inspect complex forms, for instance), and yet others may need an optical sensor (where the material to be inspected is soft). In some cases you may need an extension bar to offset the probe from the quill to allow access to a deep feature A probe changing rack allows you to store different sensors and automatically change between them. This increases your flexibility and allows you to pick the best extension / probe / stylus combination for each key feature on your components. Autojoint features kinematic connection for high repeatability

PHS1 servo head - design characteristics
Servo positioning for total flexibility full 360° rotation in two axes for total flexibility of part access resolution of 0.2 arc sec equivalent to 0.1µm at 100mm radius servo control of both axes for infinitely variable positioning and full velocity control speeds of up to 150° per second 5-axis control required The PHS1 is a servo head, rather than an indexing head like the PH10 family. This means that the probe can be positioned at any angle, rather than a finite number of indexing positions. This can be advantageous in some sheet metal applications where features are orientated at many different angles. For prismatic parts with precision geometric features, the PHS1 provides no significant advantage over indexing heads. The greater size and mass of the PHS1 servo head makes it suited to larger CMMs, whereas the PH10 is ideal for small to medium measuring machines.

High torque for long reach extension bars of up to 750 mm (30 in) ideal for auto body inspection touch-trigger probes only Autojoint for use with SP600M powerful motors generate 2 Nm torque 4 times more than a PH10 carry probes and extension bars of up to 1 kg (2.2 lbs) The PHS1 is ideally suited to specialist inspection applications like auto body measurement. It is here that the ultimate positioning flexibility is required, whilst the PHS1's extra reach (up to mm) is also valuable. The PHS1 can support a SP600M scanning probe.

Infinitely variable positioning This video shows how an infinitely variable positioning head can be used to control precisely the position of the probe stylus throughout a measurement routine. In this case, the motion of the PHS1 head is coordinated with the motion of the CMM to keep the probe tip close to the calibration sphere, whilst accessing the sphere from several different orientations. PHS1’s motion can be combined with the CMM motion to generate blended 5 axis moves

ACR3 probe changer for use with PH10M
4 or 8 changer ports store a range of sensors, extensions and stylus configurations Passive mechanism CMM motion used to lock and unlock the Autojoint for secure and fully automatic sensor changes Sensor changing Having access to a range of different types of probe can be invaluable if you have many different types of parts to inspect. For some parts, a touch-trigger probe will be ideal, whilst others will need a scanning sensor (to inspect complex forms, for instance), and yet others may need an optical sensor (where the material to be inspected is soft). In some cases you may need an extension bar to offset the probe from the quill to allow access to a deep feature The ACR3 probe changing rack allows you to store up to 8 different sensors and automatically change between them. This increases your flexibility and allows you to pick the best extension / probe / stylus combination for each key feature on your components. Compact rack with minimal footprint

New ACR3 probe changer for use with PH10M
Probe changing Video commentary new ACR3 sensor changer no motors or separate control change is controlled by motion of the CMM The ACR3 is a simple, passive device that uses the machine motion to affect the unlocking and locking actions needed to change sensors. The lateral movement of the rack causes the Autojoint to lock or unlock, disconnecting the old sensor and connecting the new one. In this instance, a scanning sensor is swapped for a touch-trigger probe, highlighting how different types of sensor can be integrated into a single probing routine. Quick and repeatable sensor changing for maximum flexibility

ACR2 probe changer for use with PHS1
Probe module changing flexible storage of probes and extension bars The ACR2 changer rack can hold up to 6 different PHS probe modules. These are attached using kinematic mounts to the lower rotary axis of the PHS1 head. Modules can support touch- trigger probes on extension bars up to 750 mm (30 in) long, the SP600M scanning probe and non-contact probes.

FCR25 module and stylus changing for SP25M
Passive rack enables both module and stylus changing modular rack system switch between scanning modules to suit application switch between scanning and touch-trigger modules Two sensors in one - switching between scanning and touch-trigger probing modules SP25M module and stylus changing The SP25M is unique in that it supports both kinematic stylus changing and module changing using a single, modular rack system. Users can switch between a total of four modules - three scanning modules optimised for different stylus lengths, plus a touch-trigger module incorporating the TP20 sensor. Users can then select from a range of scanning styli, or from the full range of TP20 modules and extensions. The result is a highly flexible measurement system, that can provide the right combination of probe, extension and stylus to suit almost any dimensional measurement task. The video shows module changing using the FCR25 modular rack system.

FCR25 module and stylus changing for SP25M
Passive rack enables both module and stylus changing change styli to suit measurement task scanning styli up to 200 mm full range of TP20 modules combine with ACR3 for sensor changing Typical changing routine: stow TTP stylus stow TTP module pick up scan module pick up scan stylus SP25M module and stylus changing The SP25M is unique in that it supports both kinematic stylus changing and module changing using a single, modular rack system. Users can switch between a total of four modules - three scanning modules optimised for different stylus lengths, plus a touch-trigger module incorporating the TP20 sensor. Users can then select from a range of scanning styli, or from the full range of TP20 modules and extensions. The result is a highly flexible measurement system, that can provide the right combination of probe, extension and stylus to suit almost any dimensional measurement task. The video on this slide shows a typical changing routine in which styli and modules are both changed.

SP600 stylus changing Passive rack simple design rapid stylus changes
storage for up to 4 stylus modules any number of racks can be used in a system kinematic stylus changing mechanism highly repeatable connection between stylus and probe, styli can be stored and re-used without the need for qualification crash protection from an overtravel mechanism in the base of the rack Rapid stylus changing with the passive SCR600 stylus change rack Stylus changing Unless you are measuring a simple component, you will need to change your stylus configuration to suit different measurement tasks. This can be done manually using a threaded connection, but probe systems are now available with a repeatable, automated means to switch styli This greatly increases your flexibility by allowing you to access features that demand long or complex styli, as well as using different tips (sphere, disc, cylinder) needed for different surface configurations. With automated stylus changing, all of this can be achieved automatically, reducing operator intervention and increasing measurement throughput. The video shows how quick and simple an automatic stylus change can be. In just 10 seconds, the stylus is switched and the probe is ready to measure again. The repeatable kinematics mean that the stylus can be changed many times and will always be in the same position relative to the probe, so there is no need to re-qualify after each change.

Renishaw scanning - our offering
the fastest and most accurate scanning passive scanning probes with dynamically superior mechanisms sophisticated probe calibration performance styli to match your application the most flexible and productive solution probe changing stylus changing articulation the lowest ownership costs innovative hardware and scanning techniques reduce complexity robust designs and responsive service for lower lifetime costs Renishaw’s approach to scanning system design delivers the best performing and most cost-effective solution available.

Responsive service and expert support
Application and product support wherever you are Renishaw has offices in over 20 countries responsive service to keep you running optional advance RBE (repair by exchange) service on many products we ship a replacement on the day you call trouble-shooting and FAQs on Service facility at Renishaw Inc, USA

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