Delta Tau controller issue

[CimUser2000]

I am in the process of retrofitting a cnc machine with the ISA PMAC Delta Tau motion controller card. The milling machine has ballscrews and DC servos. I installed three new Kollmorgen amplifiers to drive the X, Y, and Z axis's and tuned the amplifiers according to the instructions. They work great. When I supply + or - 10 volts to the inputs, the machine will rapid traverse. When I remove any voltage, the servos hold position perfectly. When I hook up the Delta Tau motion controller card, all three axis's start to drift. I have Delta Tau tuning software that refuses to tune the parameters correctly in "open loop" mode. I have a second Delta Tau card that reacts the same way. The motion controller card obviously is supplying a voltage to the amplifiers which makes them drift. Does anybody know what adjustments I have to make on the card to get the output to the amplifiers zero volts? I beleive there has to be parameters to adjust this?

[Al_The_Man]

I am not that familier with the Delta-Tau, but have have experience with Galil and Acroloop.
The analogue signal on these type of cards are either a a pot or parameter, but either way it should be zero when no signal commanded.
I am assuming this is what you are trying to do? The manual on the card should be show the method, But I would disconnect everything from the card to do this adjustment, including the analogue to the drives and any encoder feedback.
Have you hooked up the servo's in the closed loop method with everything connected?
Al.

[MetLHead]

You should be able to put the PMAC card into closed loop even with some offset on the analog outputs. The card will still hold position, you will just have some following error when the motors are sitting still. You can then adjust the DAC offsets with I-Variables Ix29.

I129 = X DAC offset
I229 = Y DAC offset
I329 = Z DAC offset

Adjust these values with the motors on and the card holding position. Change these values until the motor following errors reach zero.

Regards,
Scott

[CimUser2000]

Thanks for your replies....I have not put it into closed loop mode yet. I thought to properly tune the card, I had to get open loop mode tuned first. Scott, what is "following error" while the servo motors are sitting still? Do the servos oscillate during this condition? As Al mentioned, would I be better off adjusting some parameters without the amplifiers connected until I get a zero voltage on the output to the amps? If so, do you happen to know which parameters?

Thanks,
John

[kaye7877]

The PMAC controller is so flexible that it can be difficult to work with if you are not intimately familiar with it.

Do you have the encoder or resolver feedback connected to the PMAC card? Is is running in closed loop? No matter how hard you try, if you are running in open loop, the servos will not stay perfectly still.

You say you tuned the amplifiers? With the PMAC card, you would usually run the amplifier in torque mode and close the servo loop on board the PMAC. No real tuning would take place on the drive itself.

I may be off base, but it sounds like you only have feedback to your amplifiers/drives and are closing the loop there. The PMAC is sending an analog signal and the drive is trying to follow it in Speed mode. Post a schematic of what you are doing so we can help a little more.

[kaye7877]

Looks like I was typing my reply at the same time.

Don't worry about getting open loop mode tuned first. Go though the PMAC setup software to get each axis moving. You will tune the servos from there.

PMAC's auto tune doesn't work very in my opinion. Only on the most stiff and simple of systems will it work well.

[CimUser2000]

kaye7877,
When you say "tune the servos from there", do you mean tune them through the PMAC parameters or tune the actual potentiometers on the amplifiers?

[kaye7877]

Tune through the PMAC parameters. PMAC has parameters for each axis. You will need to know these as you go throught the setup software.

See attached spreadsheet for my last setup. This was for one of four PMACs I used to control a 20 coordinated axis machine. Maybe this will help you. Go though the manual so you can understand each variable. The spreadsheet will make sense after that.

Do you have the PMAC setup software? Make sure you have your home and limit switches setup correctly. Start by concentrating on one axis. In the PMAC software, you can do simple moves that show following error. I could write a LOONNGGG chapter on this part of the tuning. Once you get there, we can discuss that part of it.

[Ron22]

CimUser2000,
I agree with kaye7877 that the PMAC card is not the easiest to set up but it is very versatile and powerful.
Download this if you do not already have it
PMAC Software Maunal
Did you enable the axis? I100 = 1, I200 = 1 or I300 = 1. Depending on what axis you have set up.
You either need the limits, fault and amp enable hooked up or disabled. Look at Ix25.
In PEWIN there is an auto tuning function. This is not the best but will get you going. There is also a DAC calibration that will adjust the output (+/-10 Ix29) for you. You should not really need to do that.
Play with the auto tuning you should be able to get the motor to move and hold its own position in closed loop.

Now for the questions.
What software are you using (PEWIN PMAC-NC)? You can download 30 day trials from their web page.
What Kollmorgen amplifiers do you have?
What mode do you have them set to (torque, velocity, speed)?
What is the feedback (encoder, resolver)?
Are the motors off the machine (safer to play with at first)?

[kaye7877]

Ron22 has a good point. Take the motors off the machine.....

[CimUser2000]

Ron22,
Yes, I have enabled the axis's. The CNC machine was originally set up with the limit switches configured for "Normally Open". The Delta Tau manual suggests "Normally Closed", so I changed it to that way. I hooked up the "Amp Enabled" connection on the amplifier to a toggle On/Off switch to ground so that I can control each axis independantly. I can get the auto-tune software to move the axis's, but it seems like no matter what I do, the machine axis will not hold position steady...it drifts. But that is in Open Loop mode. I will close the loop and start debugging from there.

To answer your questions:
The CNC machine is a 1981 Wells-Index Model 810 (looks like a manual bridgport model). Travel is X28.5 Y11.7 Z5.0. It had a Sharnoa controller on it which had its limitations, plus the boards where not that reliable. I got tired of dumping money into an obsolete controller.
The amps are Kollmorgen Model KXA-175 (I bought off of E-Bay - Brand new). I have it set to Velocity Mode since I have Tachometer Input.
The servos are ElectroCraft (original equipment)and are rated @ 2000 RPM no load. The CNC spec has a rapid traverse speed of 150"/minute. The ballscrews are .200"/rev.
I am using PEWIN for setting up the PMAC ISA card (running WindowsXP). I am going to use PMAC-NC (not the newest version). I bought DPRAM for the 8 axis card since it didn't have it and I read it is required if I was going to use PMAC-NC.
The machine has optical rotary encoders coupled to the end of the ballscrews that have 1000 lines/rev resolution.
The motors are on the machine right now. I don't plan on taking them off for debugging. I have been using my X-Axis for debugging first (with 28 inches of travel, theres a lot of room for me to stop a runaway axis!
I bought the PMAC 8-axis card off of E-bay with the amplifiers as a set. When I went to buy the DPRAM, I found a whole Delta Tau Advantage 600 Pendant w/ a computer and a 4-axis PMAC ISA card which I ended up buying also. That setup came with the PMAC software and PMAC-NC software. I swapped out the 4-axis card with the 8-axis card. After I had problems trying to tune the axis's, I put the 4-axis card back in and had the same results. The 8-axis card is back in now.
This is a hobby machine for me. I thought I was at the point where I would have to pay the big bucks to get a Delta Tau technician in so that this doesn't become a "boat anchor"! You guys have given me direction to continue on. I really appreciate your help.

John

[Ron22]

Do you know the PMAC has an Amp enable output? You could just hook up the one you want. This way when you kill the axis in PEWIN it will disable the amp for you.
I would play with the auto tuning and closed loop. You really do not need to worry too much about open loop because the PMAC can disable the drive when in open loop.
I usually use Torque mode and do not hook up the Tach wires but that is just my personal preference.
Since you have the motors on the machine and are doing testing you do have the big red panic button hooked up

Just to warn you Delta Tau PMAC-Nc is not the easiest to set up either. Is it NC 2.36 I hope this is probably the most stable version they have. First get the axis tuned and moving using PEWin. Fight one battle at a time. You will also find out a lot of the Delta Tau experts/technicians do not know much about NC it is a very small percent of what they do.

Good luck and keep us informed