University of Tehran 1 Interface Design Omid Fatemi

University of Tehran 2 Typical Interface Design Connect ComputeConveyCooperate Sense Reality Touch Reality Connect Transform Embedded Systems Micros Assembler, C Real-Time Memory Peripherals Timers DMA PC interfaces HCI Busses Protocols Standards PCI IEEE488 SCSI USB & FireWire CAN

University of Tehran 3 Sensors : Review voltage source –directly measured variable resistance –can be converted to a voltage and measured –voltage divider for coarser measurements –wheatstone bridge for finer measurements variable capacitance variable inductance variable signal

University of Tehran 4 Touch Reality “adding to the real world”

University of Tehran 5 Motors coils of conductive wire magnetic fields rotational motion –except for linear induction motor everywhere from the very large (LRT) to the very small (toys) electrical energy converted to mechanical

University of Tehran 6 Stepper Motors more accurately controlled than a normal motor allowing fractional turns or n revolutions to be easily done low speed, and lower torque than a comparable D.C. motor useful for precise positioning for robotics Servomotors require a position feedback signal for control

University of Tehran 7 Stepper Motor Diagram

University of Tehran 8 Stepper Motor Types –Variable Reluctance –Unipolar/Bipolar Permanent Magnet

University of Tehran 9 Variable Reluctance Motors

University of Tehran 10 Variable Reluctance Motors This is usually a four wire motor – the common wire goes to the +ve supply and the windings are stepped through Our example is a 30 o motor The rotor has 4 poles and the stator has 6 poles Example

University of Tehran 11 Variable Reluctance Motors To rotate we excite the 3 windings in sequence –W –W –W This gives two full revolutions

University of Tehran 12 Unipolar Motors

University of Tehran 13 Four Phase Stepper Motor

University of Tehran 14 Unipolar Motors This is usually a 5 or 6 wire motor – with a centre tap on each of the two windings – the two taps are typically wired to the +ve Our example is a 30 o motor The rotor has 6 poles and the stator has 4 poles Example

University of Tehran 15 Unipolar Motors To rotate we excite the 2 windings in sequence –W1a –W1b –W2a –W2b This gives two full revolutions

University of Tehran 16 Basic Actuation Wave Forms

University of Tehran 17 Unipolar Motors To rotate we excite the 2 windings in sequence –W1a –W1b –W2a –W2b This gives two full revolutions at 1.4 times greater torque but twice the power

University of Tehran 18 Enhanced Waveforms better torque more precise control

University of Tehran 19 Unipolar Motors The two sequences are not the same, so by combining the two you can produce half stepping –W1a –W1b –W2a –W2b

University of Tehran 20 Torque vs. Speed

University of Tehran 21 Motor Control Circuits Fundamentally a circuit as below is required

University of Tehran 22 Motor Control Circuits We must deal with the inductive kick when the switches are turned off. We can shunt this using diodes.

University of Tehran 23 Motor Control Circuits In order to interface the stepper motor with a μP (or similar) we need a TTL compatible circuit. The 5v control should be well regulated. The motor power will not require regulation.

University of Tehran 24 Motor Control Circuits For low current options the ULN200x family of Darlington Arrays will drive the windings direct.

University of Tehran 25 Interfacing to Stepper Motors

University of Tehran PPI

University of Tehran 27 Stepper Motor Step Angles

University of Tehran 28 Terminology Steps per second, RPM –SPS = (RPM * SPR) /60 Number of teeth 4-step, wave drive 4-step, 8-step Motor speed (SPS) Holding torque

University of Tehran 29 Vector Generation Hardware solutions –Logic design –State machine Software solutions –Microprocessor and output ports –timing

University of Tehran 30 Example

University of Tehran 31 Solenoids and Coils coils of conductive wire magnetic field pushes or pulls used in speaker coils, door bell strikers, pin ball machines electrical to mechanical motion interface small linear motion

University of Tehran 32 Piezoelectric crystalline structure; locked, repetitive distribution of molecules and charge a small amount of uneven force on the material will produce a charge imbalance in the matrix and create a voltage potential which can be measured and used as a sensor conversly, a voltage potential can be applied across it and it will cause the crystal to deform –small speakers, beepers

University of Tehran 33 Heaters, Coolers electricity through wire generates heat because the conductance is not infinite power = V*V/R –hair dryers, pipe heaters, seat warmers electricity through a thermocouple can generate heat –if applied in reverse, it can absorb heat or cool »electric coolers for cars

University of Tehran 34 Thermal Shape Memory Effect A shape memory alloy is capable of remembering a previously memorized shape. It has to be deformed in its low temperature phase Martensite and subsequently heated to the high temperature phase Austenite, e.g. in hot water or with an electrical current. The alloy generates a high force during the phase transformation. Thus, it can be used as an actuator in a multitude of different applications. The shape change is not restricted to just pure bending. The most suitable actuation mode has proved to be the linear contraction of a straight wire actuator. In contradiction to the mechanical shape memory effect, the thermal shape memory effect is related to a heat stimulus, with which the Memory-Metal is capable of delivering a high amount of work output per material volume.

University of Tehran 35 Mechanical Shape Memory Effect: Superelasticity Shape memory alloys are able to show an obviously elastic deformation behaviour which is called Mechanical Shape Memory Effect or Superelasticity. This deformation can be as high as 20x of the elastic strain of steel. Reason for the superelasticity is the stress induced phase transformation from the high temperature phase Austenite into the low temperature phase Martensite. The strain related to this phase transformation is fully reversible after removing the stress. The commercial NiTinol alloys show as much as 8% of superelastic strain. Temperature changes are not necessary for the superelasticity.

University of Tehran 36 Martensite Deformability The martensitic low temperature phase can be deformed similar to pure Tin: it can be bent back and forth without strain hardening. Thus, the risk of breakage of a component made from martensitic NiTinol is significantly lower as for instance in stainless steel. And finally when heated into the austenitic phase, the alloy recovers its initial shape. The metallurgical reason for the martensite deformability is the twinned structure of the low temperature phase: the twin boundaries can be moved without much force and without formation of dislocations, which can be considered as being the initiator of fracture

University of Tehran 37 Shape Memory Alloy also known as: muscle wire, nitinol, flexinol nickle/titanium alloy metal crystalline structure undergoes shape change with a change in temperature two stable states: martensite (cooled state), austenite (heated state) can generate enough force to move thousands of times its own weight

University of Tehran 38 SMA continued silent linear movement has life like quality –no motors required for robotic limbs low voltage, easily interfaced to a microcontroller wire length shrinks by up to 8% but typically 5% is used wire can snap from overheating caused by excessive current or by over stressing it

University of Tehran 39 Making SMA

University of Tehran 40 SMA Cycle

University of Tehran 41 Bias Forces

University of Tehran 42 Wire Length vs Temperature

University of Tehran 43 Photons electricity can be turned into light directly (LEDs) or indirectly through heat –LEDs can be combined to create a multisegment display for alphanumerics –all colors available now –coherent light beams can be made from laser diodes vacuum tubes still most common form of display for TV and computers