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Zheng Liang
Zheng Liang
Associate III
June 23, 2017
Question

Performance with voltage mode on powerSTEP01

  • June 23, 2017
  • 3 replies
  • 1219 views
Posted on June 23, 2017 at 05:53

I'm testing the powerSTEP01 with 

http://www.st.com/content/st_com/en/products/ecosystems/stm32-open-development-environment/stm32-nucleo-expansion-boards/stm32-ode-move-actuate-hw/x-nucleo-ihm03a1.html

 connected Arduino UNO, and I set parameters with BEMF compensation software. This is the first time I use voltage mode and I faced some problemes with this mode:
  1. Is this mode could noly work at low speed? I run the motors with 1300step/s, the current wave is nice, but at 1500step/s, the wave is distortion, although the motor is runing, but it would like to shake the desk damaged, here is what I captured:

    0690X00000602TiQAI.bmp

    More speed I increased, the motor will be stall and stop.

    In my application, I need to run the motor at 2000step/s, and I get it worked with current mode, but I prefer the low noise performance under voltage mode.
  2. If question 1 is yes, so what approximate speed range it would be? or if not, what the parameters shoud I adjust for this achievement?
  3. At low speed under voltage mode, in range of like 10~200step/s , the current is not constant, less speed will get less current amplitude, I used to with current mode, the current will be constant in this range, so is this normal under voltage mode? What I'm worrying is the output torque of motor.

PS:I got question 1 from this youtube video: 

https://www.youtube.com/watch?v=fihUgqWpz3s

 and my test, but I found that L6470/L6480 is pure voltage control, so I'm confused now.

Hope get your response.

Thanks,

Zheng

#powerstep01
This topic has been closed for replies.

3 replies

Zheng Liang
Zheng LiangAuthor
Associate III
June 24, 2017
Posted on June 24, 2017 at 08:16

I solved question 1 with grip friction like follow gesture on an old disk.

0690X00000603u7QAA.jpg

So, another question is floated to the surface, is this mode couldn't run with light load scenario?

Ram Krishan Sharma
Ram Krishan Sharma
Associate
June 25, 2017
Posted on June 25, 2017 at 10:32

Hello Zheng,

Q1 & 2

The Voltage mode have limitation of not able to control the field weakening ,as your rpm is increasing the Back emf is proportionally increasing and it constantly tries to reduce the current flowing in the stator .

Hence with voltage mode you cannot take the motor above the rated speed that may be around 1300 -1400 steps per second .

if you try to make motor run over rated voltage it will stall as Eb > V and Back emf will stop current flow.

Hence near the Peak Rated RPM zone your motor starts to shake as the back emf is reducing effect of your applied voltage and the system is not able to compensate as voltage has reached to rated voltage.

You are able to run in current mode because in this mode it can do

https://www.quora.com/What-is-field-weakening-in-motor

hence it can allow you to operate at RPM ranges greater than rated.

Q3

The current must be more or less constant in voltage mode as well this indicated that you need to recalibrate the back emf compensation in the voltage mode . 

Your system is Over Compensated.

Zheng Liang
Zheng LiangAuthor
Associate III
June 28, 2017
Posted on June 28, 2017 at 17:21

Hi, Ram

Thanks, your reply helps me a lot to understand the principle of voltage mode, I will use mixed mode in my application. so the voltage mode couldn't run over rated speed, but chip L6470/L6480 is pure voltage mode controlled, I just curious about  how could these work with high speed?

Regard,

Zheng

estie
estie
Associate III
February 4, 2018
Posted on February 04, 2018 at 08:57

I think some of these chips are aimed at automotive market for things like window winder motors, where higher speed is not required.

If your initial tests were with a bare motor that is very unstable mechanically and will stall easily. You should add some inertia to the system. Connect to a drive shaft or whatever you intend to drive, or just a cylindrical mass. Stepper motors are a mechanically resonant system and will tend to go unstable and stall in a mid-range resonant band which is often around the speeds you are indicating.

You either need to blast through it before the resonance has time to build up or change the mechanics of the system to move where the resonant frequency lies.

Frictional damping can help but you are throwing away torque and it is pretty hard to get a decent current into to motor with these chips.

If that motor has 6 wires you can try half coil connection, that changes the way it reacts quite a lot and may get you the range you need.

You can see the results of monitoring the sense resistor voltage under the two connection modes in my post here:

https://community.st.com/message/183011-current-limit-on-powerstep

Sorry it's so long since you posted. You will have realised there's not much action on these 'communities' at ST.

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