AB Micro 1400 PID w/1024 Encoder/DC Motor

dave k

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Join Date
Jan 2011
Location
ny
Posts
26
Team,
I have a micro 1400 and a 1024 encoder using HSC function to control a 0-10Vdc DC Drive (1/3 Hp Motor) for a simple material take up. Material speed is about 10"/min.
I am trying to use the PID instruction to control Speed, however I am not able to tune no matter what variables I use within the PID Instruction. It ramps up and then down and then just continues the cycle.
It is not in a STI Routine and is setup for Timed Mode.
Maybe I do not have the correct pieces.

any ideas suggestions would be greatly appreciated.

thanks
o_O
 
Speed control using a HSC is not going to be particularly effective, as you have to poll the HSC at irregular, comparitively slow intervals, then calculate how many pulses were counted since the last poll. In other words, you don't have instant or accurate feedback. If you can tell us more about the process, we may be able to help find another solution.

Also, how familiar are you with PID Tuning on RS500?
 
The application is basically a material winder. I seem to get a good feedback, in/min.
I start a 1 second timer and get the number of encoder pulses and then calculate the position traveled and the speed at which it traveled.
I am not a PID expert but have some experience, also I am trying to use Loop Pro Tuner

the dc drive is just a little KB electronics with a 0-10VDC input

thanks for the input
 
It won't work. I can provide a lot of reasons why.
Get a real motion controller that can sample at 1KHz at consistent intervals. The derivative gain is critical when there is no velocity loop in the amplifier. The derivative gain is useless with a high counts per revolution and consistent sampling intervals.
Tuning a small motor should take 2 minutes.
http://deltamotion.com/peter/Videos/AutoTuneTest2.mp4
I was actually testing the Screen Flow picture in picture and inserting the title screen.
I knew the auto tuning would work. The motor in the video is a DC motor with a small amplifier with no velocity loop so the controller must use lots of derivative gain to dampen the system.
 
I currently use the RMC70 for a hydraulic press and it works awesome. however spending $2000 on a controller to turn a DC motor seems like over kill.
What do you think with the parts I have would get me the best results? meaning as close as I can get. Basically all I am doing is ramping to a speed and holding it
With the Micrologic PLC the high speed counter can be read up to 100Khz and if I put it in an STI routine my update will be easily in Milliseconds.
Should I sample the encoder as fast as I can or should I sample at a slower rate?
Maybe use a direct output until close to setpoint and then turn on PID Control?
any suggestions would be appreciated,
Delta Controllers by far are awesome.
thanks for feedback.
 
I currently use the RMC70 for a hydraulic press and it works awesome. however spending $2000 on a controller to turn a DC motor seems like over kill.
Over kill definitely! We like over kill. Over kill means you would be done by now. How much is your time worth?
How much is your time in the future and lost production worth?

Here is a video where I tune a small 200W DC motor with no velocity loop in the amplifier. It takes 2 minutes. BTW, I wasn't testing the RMC. I was testing the picture in picture capability of the screen flow software.
The amplifier only converts the voltage from the controller to current and the resulting torque. You can see the control output is proportional to the acceleration and deceleration, not velocity like a hydraulic system or motor connected to a drive with a velocity loop.
http://deltamotion.com/peter/Videos/AutoTuneTest2.mp4

There are two routes to take.
1: Buy a real motion controller with a sample time of 1Khz that has a PID and velocity and acceleration feedforwards. The controller will need to do the job of the velocity loop like in my video.
2: Buy a small drive with the velocity loop. You may be able to get by with the PLC you are using.

The derivative gain is critical. The derivative gain must be somewhere you your control loop. In option 1 the controller must have a derivative gain. In option 2 the velocity loop's proportional gain is the position loops derivative gain.

Adjust the velocity loop or derivative gain first depending on the option you take. The derivative gain adds damping and will reduce oscillation.

The encoder is key to using the derivative gain or velocity loop. Ideally, you want to be at the upper limit of the count rate. At 100KHz your PLC could get as many as 1000 counts in 10 ms. That is good because a little variation in the counts per second due to sprockets etc will change the reading by 1 count per 1/1000. At your current number of counts per revolution you will get 10 counts per scan and if that varies by 1 count the measured speed will vary by 10%. This is not good. The other item people forget is that during the housekeeping time of the PLC the interrupts are turned off. This means the time between reading could be 10.5 milliseconds and the next scan 9.5 millisecond. That will cause bad velocity measurements that will look like noise and limit the ability to use the derivative gain.

The RMC uses a FPGA to latch data every millisecond with no sample jitter. There is only a quantizing error due to resolution of the encoder.
 
Any suggestions on a DC drive, you may recommend? your second suggestion would be best for me to use a small drive with a velocity loop
 
We have used Elmo drives in the past but I think they are no longer available unless you are a OEM. Now use Maxon drives for our demo units.

The motor in the video powered by a transconductance amplifier. Transconductance means it coverts voltage to current. There is no smarts. I don't call dumb amplifiers drives.
 

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