Mechatronics Linear Motors Advantages : Precise High forces Few parts video Disadvantages : Limited stroke Space occupancy Cost Complex to build/assemble (basically new know-how needed) Types of linear actuators: Electrical Linear Motors Pneumatic Cylinders Solenoids

Mechatronics Linear Electric Motors Advantages: Performances Compact IP65-67 animazione1 animazione2animazione1animazione2 Disadvantages: Cost Limited Stroke Complex Assembly and New Know How

Mechatronics Pneumatic Cylinders Advantages: Force Cost Disadvantages: Low Accuracy, Repeatability Limited Stroke “Air supply” issue

Mechatronics Solenoids Advantages: Cost Compact High Speed Disadvantages: Very low accuracy, repeatability (bang-bang)

Mechatronics Linear Motors: Performances & Costs Cost, Performance Belt Ball Screw Motor The best when concerning kinematics The best when concerning force The best when concerning cost, The worst when concerning accuracy animazione

Mechatronics Linear Motors: which applications? The linear motor eliminates the mechanical transmission: Possibility to have higher bandwidth and gains, lower settling time No speed limit No limit-cycles or backlashes No maintenance But… if we have no transmission, then… No inertia: accuracy and stiffness depends on the servo control The position sensor have to be on the load directly, not hidden in the motor

Mechatronics Differences with respect to rotary motors (1) Suppliers of linear motors sell force [N]. Suppliers of linear encoders sell accuracy [  m and bandwidth: Hz]. Then it’s necessary to assemble it, put a case, maybe a brake, etc..

Mechatronics In a linear motor only the windings that are close to the slider works, then, with respect to a rotary motor, with the same weight, the avilable force is lower. In other words, while in a rotary motor all the windings and permanent magnets work, in the linear one is not the case. The rod-like motors reduce the problem, but they don’t eliminate it. Avilable forces: 5-8N/cm 2 of gap. Differences with respect to rotary motors (2)

Mechatronics The correct and incorrect applications: Applications where the cycle time is relevant, the stroke is long, obtain the maximum advantage: Load/unload, transfer, positioning indexing, packaging in general robots textile, paper, laser Where the forces are very high and continuous (the linear motor is milited in continuous force), and the bandwidth is limited and cannot be improven (for example because is limited by the load or other external factors), the linear motor can be a useless… and expensive… solution.

Mechatronics The linear motor is a part of the mechanics of the machine The machine has to be designed together with the motor: High ratio stiffness/mass (if I double the stifness and the mass I have the same resonance frequency) Reduce the masses distributing the motor on the machine The position sensor choice is fundamental (linear encoder sin/cos) the precision (and cost) are determined by the senosr The stiffness is determined by the sensor’s resolution (never higher than the needed positioning accuracy)

Mechatronics Which applications do fail? If the machine is limited by mechanical resonances, insufficient stiffness, the linear motor will not provide any improvement. If the control system is not fast enough, it will be the bottle neck and the full machine will not have desired performences. If the deisred stiffness is high and the bandwidth limited, the gearbox is the only solution. If the accuracy offered by the position sensor is not needed, then the linear motor is an expensive solution.

Mechatronics The competitive solution: positioning X cartesian axis L=2000 mm, 50 kg load, pinion/rack or linear motor? Motor cost 5 Nm = 100 Gearbox cost = 150 Encoder in the motor =30 Rack and pinion =120 Alignments, mounting procedure =100 Result: 2 m/sec, 1g, settling time ~ 100 msec, accuracy ~0.1 mm Total cost = 500 Motor cost 400/1000 N = 300 Magnetic encoder cost = 50 Alignments, mounting procedure = 50 Result : 4 m/sec, 2g, settling time=20 msec, accuracy 0.02 mm Total cost = 400 And each year the linear motors cost decrease…

Mechatronics Different Types of Linear Motors: Iron-Core

Mechatronics Different Types of Linear Motors: Air-Core Or Epoxy-Core

Mechatronics Different Types of Linear Motors: Slot-less

Mechatronics Different Types of Linear Motors:

Mechatronics Different Types of Linear Motors:

Mechatronics Linear Motor example:

Mechatronics Tubolar Linear Motors: Symmetrical Design Compact cross section, similar to ball screw 1mm nominal anular airgap (Non-critical gap for easy installation) Enclosed Magnets & Coils Not easily damaged Force transferred directly to load High mechanical stiffness Integral Heat Sink Fins (No added cooling required) Copley (PullTab) Thrust Tube

Mechatronics Sensor-less linear motors They replace the normal external position encoder (normally up to half the total cost of the complete motor) with integral Hall position sensing Accuracy is, of course, worse tha encoder- equipped motors: mm typical LinMot Rod-like motor (link)

Mechatronics LinMot SW Tool C=ki; I=(V-k  )/R

Mechatronics Torque Motors (Motori Coppia) are just motors providing huge torques, generally with a very high pole pairs number and in direct-drive application with very low speed Torque Motors How to go beyond the torque/dimensions limit today reached by the permanent magnets brushless motors? Conventional Motor: windings on several slots, inserted in the slot in chaotic way. Epicyclical Motor: each teeth has one-and-only-one winding around it, very short motor length

Mechatronics Epicyclical Motors (Motori Epiciclici)

Mechatronics Existing Technologies Single teeths, micro-impressed, wind-up and laser soldered Layered winding on the teeth Wounded teeths are joined and re-soldered All connections are done outside Complex process. High cogging. Low teeth number. Star-shaped stator (open toward the external side) done with metal sheets, cut and pasted Complex process. Low cogging. Conventional Stator, windings inserted in the slot Complex (often manual) operation Not efficient slot filling Used in big-diamater motors. High cogging.

Mechatronics With brushless PM technology, high number of poles, low speed, they provide high performances if integrated in the machine Direct-Drive Torque Motors From 10 to Nm From 85 to 570 mm diameter