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btxsistemas
09-06-2012, 06:21 PM
Hi all, I'm new here, and I've a question.
I'm using a Yaskawa servodrive with his 1.27Nm servomotor, and trying to get a short distance position with it in a very short time, I'm talking about 15mSeg to turn about only 1/20 of the full 360 deg.
My problem is that the servodrive is taking too much time to do this, although I try to adjust many parameters of the drive, I can't get it run faster.
Any ideas ?
In example, to turn the servodrive three complete turns of 360 deg each, I get the positioning complete, arround in the double time, comparin when I only want to turn 1/20 of turn (sounds crazy... no ?).
Hope is clear explained my problem.
Thank you in advance.
Alberto.
http://www.mig-welding.co.uk/forum/images/buttons/edit.gif (http://www.mig-welding.co.uk/forum/editpost.php?do=editpost&p=369381)

Jonathan
09-06-2012, 11:34 PM
Can you provide an exact model number for the servo-drive and motor? Does it allow you to adjust the PID constants as that will affect the response time, but could have a detrimental affect in other areas.

What are you using to signal the drive to move the motor this distance? The acceleration setting, if there is one, may be too low. Neglecting acceleration 1/20th of a turn in 15ms requires only 200rpm. Perhaps there is some other delay in the system lowering the response time. How are you measuring the time?

btxsistemas
10-06-2012, 12:06 AM
Can you provide an exact model number for the servo-drive and motor? Does it allow you to adjust the PID constants as that will affect the response time, but could have a detrimental affect in other areas.

What are you using to signal the drive to move the motor this distance? The acceleration setting, if there is one, may be too low. Neglecting acceleration 1/20th of a turn in 15ms requires only 200rpm. Perhaps there is some other delay in the system lowering the response time. How are you measuring the time?

Thank you so much for answer Jonathan.

1-Servo motor is Yaskawa (Japan) SGMAV-04ADA61

2-Servo Drive is Yaskawa (Japan) SGDV-2R8A01A
I'm sending pulses with a board of my design. That board apply aceleration and desaceleration ramps, although, you can avoid them using Pn216 and Pn217 parameters of the drive. I'm sending the pulses enough fast to get a position time lower that I need. I'm using pulses/dir config, and open collector scenary for them. I also have other motors in the machine working well, doing different tasks, from 5.39Nm to 8.34Nm.


My servodrive in this case is for a 1.27Nm motor, I've run the SigmaWin software, and give me a inertia ratio of about 27 of the system, if I not remember well.
I did the tunning of the system while it was running in the real application, but I'd not good results.
Also I've change some parameters by hand, while doing some graphics of the time responses, the /COIN signal in the graphic report a position time of 15ms, but positioning error signal is more large, but in real time, looking at the motor, you can see clearly that is running so slow.
And the job that the motor should do, confirm that, I need more speed.

My application is a bit strange, I should move a wire, to be cut after the positioning, in a machine that get pieces of this wire at a specific lenght.
I should move only 25 pulses of the motor while it is set at 400 step/rev.

What I see, is: in that low quantity of pulses, I get a very low speed of turn, but,..... in example if move about 1200 pulses, then I get a positioning time about twice as the 25 pulses I get. That's what is getting me crazy.
I strongly need more and more instant aceleration, that the drive don't give me.
I can't believe that such a servodrive can't do the task, and a stepper that I have near, do it perfect. http://www.mig-welding.co.uk/forum/images/smilies/sad.gif
Hope I was clear... English is not my natural language.

I've also adjust by hand the gains in some parameters without luck.
Also I've contact my Yaskawa distributor, but only said me that should work, not how http://www.mig-welding.co.uk/forum/images/smilies/icon_biggrin.gif

Thank you again.!!!

Jonathan
10-06-2012, 01:18 PM
I'm sending pulses with a board of my design. That board apply aceleration and desaceleration ramps, although, you can avoid them using Pn216 and Pn217 parameters of the drive.

What I see, is: in that low quantity of pulses, I get a very low speed of turn, but,..... in example if move about 1200 pulses, then I get a positioning time about twice as the 25 pulses I get. That's what is getting me crazy.
I strongly need more and more instant aceleration, that the drive don't give me.

From what you've said there it does sound like the problem is the acceleration being too low, as otherwise moving 1200 pulses would not be much different to moving 25.

Have you changed the Pn216 and Pn217 parameters? It seems they are used to smooth sudden changes in acceleration, so if the time constant is set too high that will stop the motor accelerating fast enough. I would try setting both these to a lower number (but not so low as to make the motor stall), perhaps zero, and stop your board applying acceleration/deceleration ramps. If that works you can enable the acceleration setting on your board and gradually increase it to make the motion smoother.

If that doesn't help you could try increasing the proportional gain a little. The motor speed is determined (partially) by multiplying the proportional gain by the position error. Since you're only commanding the motor to move 25 pulses, the position error is quite small so unless the gain is high the motor speed will be quite low, resulting in a slow response. The problem is you may get too much overshoot.

Section 6.5.3 in the servo driver manual (http://support-omron.fr/pdf/SIEPC80000045C%20SigmaV%20User_Manual_Design_Maint enance_Rotational_Motor.pdf), page 239 looks useful...

Do you have an oscilloscope? If so you could use it to measure the actual response time accurately.

btxsistemas
10-06-2012, 03:54 PM
From what you've said there it does sound like the problem is the acceleration being too low, as otherwise moving 1200 pulses would not be much different to moving 25.

Have you changed the Pn216 and Pn217 parameters? It seems they are used to smooth sudden changes in acceleration, so if the time constant is set too high that will stop the motor accelerating fast enough. I would try setting both these to a lower number (but not so low as to make the motor stall), perhaps zero, and stop your board applying acceleration/deceleration ramps. If that works you can enable the acceleration setting on your board and gradually increase it to make the motion smoother.

If that doesn't help you could try increasing the proportional gain a little. The motor speed is determined (partially) by multiplying the proportional gain by the position error. Since you're only commanding the motor to move 25 pulses, the position error is quite small so unless the gain is high the motor speed will be quite low, resulting in a slow response. The problem is you may get too much overshoot.

Section 6.5.3 in the servo driver manual (http://support-omron.fr/pdf/SIEPC80000045C%20SigmaV%20User_Manual_Design_Maint enance_Rotational_Motor.pdf), page 239 looks useful...

Do you have an oscilloscope? If so you could use it to measure the actual response time accurately.

Jonathan.
As you wrote, the problem is the aceleration is too low for me in this case.
I've being palying with Pn216 and Pn217 an with the ramps of my board, but no luck, although Pn216/217 are in zero, the system wont run faster.
Now, you're near my actual problem, it is that the gains Pn100 and Pn102 haven't variations in my positioning graphics. Except that if I move them too differents, I get overshooting or excesive vibration.
What is strange for me, is that I never get more speed while increasing the gain.. why ???, I've being playing with a wide set of values for them, and the motor seems to not change it speed.
Since it is my first experience with this drives...I'm asking to me.... Is there any "Pn or Fn" value that produce the gain is not responding ? Reading the manual in page 239....I'm asking to me in what tuning level I've my Pn170 now.... good point.
You know, first I did the auto tuning, and then, I modified the gains and Pn216/217 while running interactively. But I can't never change the speed position doing that. Except if the values of Pn216/217 are increased and speed goes down (of course).
Next Tuesday, I'll have a tektronix near the machine, or, maybe I will replace the drive for a stepper, to let my customer work with the machine, while I try again the servodrive in my office, with the motor and driver and the oscilloscope under the table.

Thank you so much.

btxsistemas
17-06-2012, 01:44 AM
Hi Jonathan.
After a hard work week. Today I've tried some modifications in the servodrive parameters, and I get very good results, also solving the problem.
I've noticed that Pn141 (Model Following Control Gain) and Pn147 (Model Following Control Speed Feedforward Compensation) have very good effect in the final motor speed.
With Pn147 I get reduce my positioning time considerably and with Pn141 I get avoid the oscillation of the axis, arround the final position.
So it was a goal for me, and all is working fine now.
Thank you so much again for your help.