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Panometric
Panometric
Associate III
October 24, 2020
Question

Recommendations for a synchronous linear motor or PMLSM

  • October 24, 2020
  • 2 replies
  • 1974 views

I'm looking to build a small linear motor, that could move or just accelerate an incoming load with permanent magnets attached along a path, like a touchless conveyor belt.

https://en.wikipedia.org/wiki/Linear_motor

It might have as few as 3 or as many as 8 phases in the 10-100 watt range total. The loads will be a wide variety of weights and speeds, and keeping acceleration smooth is very important. So I'm looking to sense, calculate and apply just the right force.

I have developed a potential a sensor system already that would control the force applied, but if the solution was also able to sense the incoming load that may also be advantageous.

Is the PowerStep01 flexible enough to work like this in kind of a one pass mode rather then repeated rotations?

If not, what parts might be a good fit for this, and are there any other resources like software libraries that might make it easier to get started?

Thanks.

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2 replies

Laurent Ca...
Laurent Ca...
Senior III
October 26, 2020

Dear @Panometric​ 

Do you use MC SDK tools?

Best regards

Laurent Ca...

Panometric
PanometricAuthor
Associate III
October 28, 2020

I looked at them briefly, there is so much on rotational motors, it maybe hard to see the trees through the forest. Do the tools support this motor topology?

More specifically, is the PowerStep01 appropriate?

Enrico Poli
Enrico Poli
ST Employee
November 4, 2020

Hi @Panometric​ ,

The POWERSTEP01 is designed to drive stepper motors, so it drives two motor phases imposing two sinusoidal currents with a phase relation of 90°.

For this reason I think it could fit 2 phase linear motors only.

Using multiple devices you may be able to drive linear motors with a number of phases multiple of 2 managing in the proper way the phase shifting (at least from the theoretical point of view).

For example, in an 8 phase motor you should have 4 pairs of phases where the target current should be 90° each other. You drive each pair using a POWERSTEP01 and you set the phase relation between each pair initializing in the proper way the EL_POS register (electrical angle imposed by the controller).

If you want the full control of the current driven by the POWERSTEP01 you could use the StepClock mode where the STCK input directly controls the microstepping sequencer and you can adjust the current amplitude through the TVAL_HOLD/KVAL_HOLD registers.

In this operating mode the POWERSTEP01 takes care of the current control of the motor phases (amplitude and phase relation of the two currents) and your external algorithm should define the proper torque (target current) and the motion profile (acceleration, deceleration, etc.)

Do you think this could fit your needs?

Kind Regards

Enrico

Panometric
PanometricAuthor
Associate III
November 10, 2020

Thanks Enrico. I am looking for 6 phases. So it sounds like an odd fit, since you are saying I would need 3. Is there another ST motor product for 3 phase BLDCs that might also work?

Enrico Poli
Enrico Poli
ST Employee
November 16, 2020

Dear @Panometric​

For 3 phase driving I can suggest you the new STDRIVE101

It is a very compact 3-phase gate driver (4x4 mm) with overcurrent protection and Vds monitoring. However in this case the current control is all in your hands.

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