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Following Error
« on: February 15, 2010, 02:07:03 PM »
I am experiencing following errors on a gantry router running Panasonic servo drives, I have tried tuning the drives and have got them to a point just before instability sets in. The following error is around 900 counts on the drives. The motors are capable of 3000 RPM and are running a 25 to 1 planetry gearbox with a 50mm spur gear onto a rack, Mach is tuned for 312 pulses per mm with a velocity of 8000 mm/min, in order to achieve the velocity, the drives are running an electronic gearing of 1 to 5. The computer is a core 2 duo 2 Ghz set at a kernel speed of 60KHz (anything higher causes jitters in the pulse train) in order to achieve an acceptable 90deg x to y transition, linear speed needs to be kept below 2000mm/min.
Any suggestions would be appreciated 

Offline Hood

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Re: Following Error
« Reply #1 on: February 16, 2010, 02:57:15 AM »
It  to me sounds either like your tuning is still not perfect or that you are trying to accelerate/decelerate too fast and may need to drop that in Machs motor tuning. Can you control the axis via the drives software to see how things run from it? Another possibility is the 60KHz may not be giving you a stable enough pulse stream.
 I personally dislike electronic gearing for an axis and when I set up my lathe it was my only option, now however I use the SmoothStepper and it has allowed me to have no electronic gearing and also increase the rapid speed 4 times even without that gearing. The pulse from the SmoothStepper is very likely to be much better than anything you will ever get from a parallel port.
 Where are you located?
Hood
Re: Following Error
« Reply #2 on: February 16, 2010, 03:41:33 AM »
Dear Hood

The acceleration for the y Axis is set to 500 and the X and Slaved A Axis are set to 300, the following error is apparent even when running a constant traverse of say 2 meters. I am based in Johannesburg South Africa.

Regards Brian

Offline Hood

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Re: Following Error
« Reply #3 on: February 16, 2010, 05:11:34 AM »
Doesnt sound excessive but if the following error is throughout all motion then it certainly suggests its tuning issue. With my drives I have to tune two loops, the Velocity has to be done first and I usually find the AutoTune gets that fairly close but usually I have to manually tweak the Position Tuning to get the best.
Hood
Re: Following Error
« Reply #4 on: February 16, 2010, 06:18:30 AM »
When I tried auto tune it appeared to be way too loose, it is also difficult to do auto tune on the gantry which has a slaved axis, is it possible that I need to drop the velocity gain and go up on the position? I have only tried to get them both as high as possible. The Z axis is the worst due to the uneven load for up versus down travel.

Offline Hood

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Re: Following Error
« Reply #5 on: February 16, 2010, 06:27:11 AM »
My drives software has an oscilloscope function in it and I can watch real time all types of signals as I adjust, for instance when doing the position tuning I can watch the Position command, the position feedback and the position error all at the same time, it makes tuning a bit easier. Does your drive have such a feature?

Hood
Re: Following Error
« Reply #6 on: February 16, 2010, 08:32:33 AM »
I do not have the software or programming cable, and have just programmed the drive from the user keypad, interestingly I have reduced the speed gain and increased the position gain and have managed a 50% improvement in the error. Am I correct in thinking that the electronic gearing would multiply the error by the gearing factor?

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Re: Following Error
« Reply #7 on: February 16, 2010, 02:10:14 PM »
I dont think it would  as the drive is still sending the same position signal out and reading the feedback.

Hood