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gjmontagner

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  1. Hello, good morning. I'm facing a problem in controlling a device using a deltatau controller (Faraday Powerbrick LV IMS). The motor is a Nanotec L4118S1404-M6x1 two phase stepper The encoder is an absolute Renishaw 32 bits linear encoder the device is an uncooled in-flange slit ASM0239 by FMB-Oxford (find drawing attached) As seen on the attached image, for one axis of the device, when I try to make a negative movement, we find some recurring noise on the position error signal( which can also be heard). At the end of the movement, the position error oscillates by +-50 counts, which corresponds to 2,5 micrometers. This happens only at certain positions on the axis course. The solution I found for this was to lower the servo frequency, after which the oscillations had their amplitude lowered to +-5 counts. Then I applied a deadband with outdbon=3 and outdboff=5. However, I'd like to pursue a better solution. One thing we noted is that when we move the motor in open loop, we cannot find the same oscillation signal in the encoder position signal while the motor moves. Because of that, we came up with the idea of implementing a "re-iterated open-loop control". The idea is: Whenever a movement is requested for the axis, a cycle is activated. The cycle goes like this: First, the motor is moved in open-loop, by a small quantity, towards the desired position. After the movement, the system checks the encoder position, and, if it is not close enough to the desired position, another open-loop movement is issued. This cycle repeats itself until the desired position is reached, within a pre-determined position band. By doing this, the movement would not be prone to noise and oscillations as observed in closed-loop control, since it would be based now in open-loop control. We can adjust the open-loop increments in order to minimize time to target and prevent introducing new oscillations in the system when the motor is close to its desired position, due to the nature of the technique. The question is: Is this doable in a deltatau controller? Is there a native solution to implement such a technique? How can I best approach this solution, in order to try it out? Thank you very much for your attention.
  2. Hi Dave, first of all thank you for your response. I see. The voltage mode was already implemented for an older device, so I carried on. But I observed that when I turn it off, there is more in-position noise. Also, the oscillations kept happening with the current loop enabled. Do you have a good-practices guide as to how to configure voltage mode control, so that we can aim for the best techniques to avoid oscillations? Basically we set Phasemode = 8, and: IiGain=0 IpfGain=2 IpbGain=0 Also, PhaseCtrl=6 We also tried to use notch filters to mitigate the oscillations, but whenever we applied a filter for one frequency, another one appeared up, as seen on the attachments (Three fft images: Before the first filter, after the first filter on 85Hz, and after the double filter adding a notch at 295Hz. The noise itself is a high frequency chirp which had 12 counts of amplitude at first, but after the notch filters were applied, was amplified to 100 counts of amplitude). Do you know why this is happening? Am I using the notch filter correctly? Thanks in advance
  3. Hello, good morning. I am facing an issue when trying to control a motor with a power pmac. What happens is I get an oscillatory motion when the motor reaches its desired position, as you can see in the first two attachments (the first one showing the oscillation, and the second one showing its details, on encoder position and servo effort). This happens in certain specific positions of the motor course, at the end of the course which is farther from the motor (the motor drives a linear actuator). At the opposite end of the course (near the motor), I got a FeFatal error, for one of the problematic motors. Also, I am driving these motors with "Voltage mode", but I am not familiar with this setup. Are there any pitfalls when using this control mode that I may not be aware of? Also, what could be a possible guideline to do the control loop tuning, as to try to eliminate these oscillations, while still being able to control the motor for the whole course? I tried to lower Kp gain, which apparently reduced these oscillations (which have approximately 15Hz frequency) but then I start to get a 0,5Hz low frequency oscillation on position error when moving in one direction, as can be seen on the third attachment. This oscilation has a 1mm period, for the speed currently being used. Thanks in advance. Guilherme
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