how to apply notch filter in the PID control

[iyearning]

Dear all,

I am using PID control in my positioning stage but the output is every noisy with some fixed frequencies(30,50,150Hz). I want to add a notch filter to take off those noise. However, I do not know how to apply the notch filter to the PID module. Could anyone tell me how and show me example if you have?

Thanks

best

[GerdW]

Hi iyearning,

how fast does your stage move?

Wouldn't it be easier to apply a "simple" low pass filter instead of filtering 3 different frequencies of your position signal?

[johnsold]

How fast is your stage moving? How fast does the PID loop run? How are you measuring the frequencies of the "noisy" output?

Filters usually apply to an array of numbers, not a single value. You need multiple points to even define a frequency.

I agree with GerdW that something simpler may be adequate.

Lynn

[iyearning]

Dear Gerdw,

I hope the stage can move with frequency of around 60 Hz. So I think I have to use a notch filter rather than a low pass filter.

Thanks

best

[iyearning]

Dear Zealot,

The natural frequency of the stage is 30Hz. The frequency of the PID loop is now set as 10 Hz. I measure the position information and use FFT to get the frequency information. For each loop, there are 200 numbers, I think it may be enough for the filters. I hope I can increase the PID loop frequency upto 60Hz. I think I need to add both the notch filter and lead-lag filter into the controller.

Thanks

best

[johnsold]

If the natural frequency of the stage is 30 Hz, you may have difficulty getting good control over the 0-60 Hz range. You did not mention the type of stage or provide any specifications. Many devices undergo large rapid phase changes near their natural frequencies. A transfer function like that may create major challenges for the controller. Even if you are able to tune the controller and one or more filters to get it to work, any change in the loading of the stage may shift the natural frequency enough to detune things.

Lynn

[iyearning]

Hi LYnn,

I am sorry for my late reply. My stage is driven by a voice coil actuator (VCA). The VCA as a resolution of 1 um and range of 6 mm. The NF of the stage does shift when the load is changing. Do you have any advice for controlling such kind of stage?

BTW, as far as I see, the control frequency is determined in the DAQ Assistant settings and its value is equal to "Sampling rate"/"Samples to read", am I right?

Thanks

best

[iyearning]

Here is the link that will give you more description of my system and my problem.

minimize the chattering of a linear stage driven by a voice coil actuator(VCA)

Thanks

best