Mechatronics Linear Motors Advantages : Precise High forces Few parts video Disadvantages : Limited stroke Space occupancy Cost Complex to build/assemble.

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Linear MotorsLinear 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

Motori LineariMotori Lineari

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Linear Electric MotorsAdvantages:•Performances•Compact•IP65-67 animazione1 animazione2

Disadvantages:•Cost•Limited Stroke•Complex Assembly and New Know How

Motori LineariMotori Lineari

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Pneumatic Cylinders

Advantages:•Force•Cost

Disadvantages:•Low Accuracy, Repeatability•Limited Stroke•“Air supply” issue

Motori LineariMotori Lineari

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Solenoids

Advantages:•Cost•Compact•High Speed

Disadvantages:•Very low accuracy, repeatability (bang-bang)

Motori LineariMotori Lineari

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Linear Motors: Performances & Costs

Motori LineariMotori Lineari

Cost, Performance

Belt BallScrew

MotorThe best when concerning kinematicsThe best when concerning forceThe best when concerning cost,The worst when concerning accuracy

animazione

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Differences with respect to rotary motors (1)

Suppliers of linear motors sell force [N].

Suppliers of linear encoderssell accuracy [m and bandwidth: Hz].

Then it’s necessary to assemble it, put a case, maybe a brake, etc..

Motori LineariMotori Lineari

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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/cm2 of gap.

Motori LineariMotori Lineari

Differences with respect to rotary motors (2)

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Motori LineariMotori Lineari

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.

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Motori LineariMotori Lineari

The competitive solution: positioning

X cartesian axis L=2000 mm, 50 kg load, pinion/rack or linear motor?

Motor cost 5 Nm = 100Gearbox cost = 150Encoder in the motor =30Rack and pinion =120Alignments, mounting

procedure =100

Result: 2 m/sec, 1g, settling time ~ 100 msec, accuracy ~0.1 mm

Total cost = 500

Motor cost 400/1000 N = 300Magnetic encoder cost = 50Alignments, mounting procedure = 50

Result : 4 m/sec, 2g, settling time=20 msec, accuracy 0.02 mmTotal cost = 400And each year the linear motors cost decrease…

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Different Types of Linear Motors:

Iron-CoreIron-Core

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Different Types of Linear Motors:

Air-CoreAir-CoreOr Epoxy-CoreOr Epoxy-Core

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Different Types of Linear Motors:

Slot-lessSlot-less

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Different Types of Linear Motors:

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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

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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: 0.1 - 0.25mm typical

LinMot Rod-like motor(link)

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LinMot SW Tool

C=ki; I=(V-k)/R

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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

Motori CoppiaMotori Coppia

Torque MotorsTorque 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

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Motori CoppiaMotori Coppia

Epicyclical Motors (Motori Epiciclici)

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Motori CoppiaMotori Coppia

Existing TechnologiesSingle 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.

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Motori CoppiaMotori Coppia

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 37000 Nm

• From 85 to 570 mm

diameter