Trinamic Discussion Groups

mbowman · Posted: Fri Dec 15, 2006 11:27 pm Post subject: Motor Noise

I have a stepper motor running back and forth, controlled by the TMCM-303 controller. Intermittently it makes a "clack" sound when accelerating or deaccelerating. How can I eliminate this sound?
_________________
M Bowman
Controls Engineer
Applied Robotics, Inc.

B. Dwersteg (TRINAMIC) · Posted: Sat Dec 16, 2006 10:44 am Post subject:

This is not a normal behaviour. It might be, that your motor triggers the short circuit detection in the TMCM-303, if you work with full current. Please try with slightly reduced current, or try using a different motor output of the 303. Perhaps also it is a mechanical effect and the motor is defective.

mbowman · Posted: Mon Dec 18, 2006 8:59 pm Post subject: low-speed resonance?

I was wondering if the noise may be due to resonance at low speed, as the motor is accelarating to running speed. From "Electric Motors and Drives" by Austin Hughes: "In practice, measured torque-speed curves frequently diaplay severe dips at or around certain stepping rates. The magnitude and location of the torque dips depend in a complex way on the characteristics of the motor, the drive, the operating mode and the load. There are two distinct mechanisms which cause the dips. The first is a straightforward 'resonance-type' problem which manifests itself at low stepping rates, and originates from the oscillatory nature of the single-step response. Whenever the stepping rate coincides with the natural frequency of rotor oscillations, the oscillations can be enhanced, and this in turn makes it more likely that the rotor will fail to keep in step with the advancing field."

My running speed was 2000. The StallGuard profiler shows a lot of yellow areas up to speed 545, and red from 545 to 609, more yellow to 800, red from 1099 to 1243.
_________________
M Bowman
Controls Engineer
Applied Robotics, Inc.

B. Dwersteg (TRINAMIC) · Posted: Tue Dec 19, 2006 11:47 am Post subject:

Did you turn off mixed decay? It should be turned on, except when doing StallGuard homing or optionally in stand still. Mixed decay will eliminate most resonance up to a certain degree.

mbowman · Posted: Tue Dec 19, 2006 8:14 pm Post subject: Set Mixed Decay On

Mixed decay (parameter 203) was set to 100. I set it to -1 (permanently on, also in the rising part of the microstep wave) and the sound disappeared. The motor is used in a gripper. When I am gripping (stalled, velocity zero), should I set the mixed decay to zero?
_________________
M Bowman
Controls Engineer
Applied Robotics, Inc.

Andrew · Master Joined: 06 Nov 2006 Posts: 258 Location: Europe

You do hear some noise.
But did you check whether the motor misses steps either routinely, or occasionally?

We just have discussed this prolem, and how to work around it here:
http://www.trinamic.com/ttdg/viewtopic.php?t=263
Please read there for suggestions how to jump over and between bad speeds.

As you have established yourself, there are a lot of bad speeds, which your mechanical set up cannot maintain.
Those speeds are mostly resonant.

According to the discussion linked above, you would need to find a way to skip bad speeds, and still not to upset the inertia of your load.

Speed 2000 is quite high. Current in motors usually fall down significantly at this speed. So you would have a hard time running without missed steps.
Most probably even when the motor reaches the speed 2000, it still has occasional missed steps.
Mind, that Stall Guard detects most but not all missed steps.

You might need to stay content with far slower speeds.
When the top speed is slow enough, there's only one range of bad speeds below it, which is far easier to jump over, than having to jump over several bad ranges to higher top speeds.

In general, the first bad range, usually the worst, could be jumped over by setting a higher starting speed (the bottom speed). But TMCM will ignore it on deceleration or acceleration (don't remember which), and still pass through the bad slow speed.

As I wrote in that linked discussion, TMCM is quite poor at seting the bottom speed. So, it can't easily jump over the bad low speeds. Also mid range bad speeds can't be easily avoided. Hence the many problems.

Avoiding bad speeds still can be done. E.g. by turning off acceleration/deceleration. When I have time, I write how to do that. Or you try and figure that out yourself, and write here for us.
Meanwhile read the linked discussion for more suggestions.

This problem is very common. Many users achieve great speeds, and simply because it runs more or less smoothly, they think it is a good speed, and stubbornly refuse to ackknoledge defeat, when resonance manifests at various speeds below, or occasionally at that supposedly nice speed.

B. Dwersteg (TRINAMIC) · Posted: Wed Dec 20, 2006 10:23 am Post subject:

It is good to hear that the problem is solved with mixed decay set to -1.

I think, the problem with the mixed decay setting of 100 is, that mixed decay switches on with some delay, caused by software. This might be the clicking sound. The delay time has been improved with the newer firmware revisions (V3.29 or higher). When using a mixed decay setting of -1 (i.e. continuously on), you may want to switch off mixed decay in stand still, to save some power and reduce motor noise. Just try.