From chrisr@galilmc.com Wed Jun 18 12:05:44 2003 Date: Wed, 18 Jun 2003 14:17:54 -0700 From: Chris Richtsmeier To: denault@jeans.ifa.hawaii.edu Subject: RE: Question on DMC 1800 & JG Tony, Below are the responses to your questions. 1. Your understanding of IP is correct in that IP is used to make position corrections, however there are some nuances with the command. For example if you are in jog mode and you issue the IP command, it will instantly try to servo to the new position for example if you are at 2000 when you issue IP ten, then the new commanded position is 2010 instantly. The PID loop will cause the voltage to change to make this position change happen. 2. Changes in jog velocity are blended, however the change in velocity due to IP is not blended. Both acceleration and velocity are assumed to be infinte as the position change is to be instantaneous. 3. Yes you can correct the controller at any time using both the IP and JG commands. 4. The jog mode may or may not be the best mode for your application. >From my understanding of the application you need to be jogging along, and at some point, you need to slightly alter the position. My question is do you need that small change to be smooth or profiled? If it does not need to be smooth, then perhaps jog mode is the best. If it does need to be very smooth, then you could command a jog move on the virtual axis of the controller, and gear for that axis. You can then use the IP command to change position in a very smooth fashion. If you have any questions about this, please give me a call. 5. If you were to move from one mode to the other then it is necessary to decelerate and then accelerate. If you blend them through gearing on the virtual axis, then it is possible to blend the two together. It is also possible to use the jog mode similar to a position mode, for example you can use trip points such as AD to wait for a certain position, and then do something. For example, you might want to move close to position 10000, you could go to position 950 and then issue the ST command, the controller would then decelerate which could bring you very close to 10000. I would recommend giving me a call to more directly discuss your application. Regards, Chris Richtsmeier Applications Engineer Galil Motion Control 800-377-6329 x120 -----Original Message----- From: Technical Support [mailto:support@galilmc.com] Sent: Wednesday, June 18, 2003 9:06 AM To: chrisr@galilmc.com Subject: Fwd: Question on DMC 1800 & JG ----- Forwarded message from Tony Denault ----- Date: Tue, 17 Jun 2003 15:43:15 -1000 (HST) From: Tony Denault Reply-To: denault@jeans.ifa.hawaii.edu Subject: Question on DMC 1800 & JG To: support@galilmc.com Hello Galil Support, We are evaluating the DMC 1800 for a telescope control servo system. This system will drive a telescope at a slow velocity (300 counts/sec) but high resolution (1 count = 0.05 arcseconds). Driving a telescope is an unusually servo task because endpoint of a move is not known. Traditional servo motions with acceleration-deceleration profiles can not be used. For telescope control, a computer will calculate a motor position based on the exact time, star coordinates (RA, Dec). This calculation happen every 50 to 100 ms. Normally the velocity would be constant, however other external event (guiding camera, joystick adjustment) can make position adjustment randomly. As a result the computer only knows it's where it should be now, and based on past calculations loops, it can estimate it velocity using a simple linear interpolation. I know of other telescopes driving their motor using a JOG modes, every 100 or 50 ms comparing the motor position with the calculated position. Any errors (motor - calculated) are taken care of by trying to adjust the velocity of the JOG. I find this unfortunate as the computer is trying to do servo correction. We have been searching for motor controller that can provide additional features to support our application. You DMC 1800 seen attractive. I noticed that your JOG mode has the ability to adjust the target position register using the IP command. 1. As I understand your manual, the IP command is used ot make incremental correction for the actual target position. The JOG velocity is continuous, and the controller would adjust the velocity to correct the IP adjustment. For example, if a motor is moving at a constant rate, and an IP command is given it would act as an offset correction. For example, if I had was jogging a 1000 c/s, and noticed I had a 10 count error at the following table illustrate what would happen: Time IP Motor position t0 1000 t0 + 1 s 10 2000 <- caculated I should be at 2010 moving at 1000 c/s t0 + 2 s 3010 t0 + 3 s 4010 2. I assume changes in jog velocity are blended smoothly. Is this correct? 3. At any instant, I can adjust correct the controller using both the IP and JG commands. 4. I am assuming the JG mode is best for my application. Have I overlooked another mode? 5. Is it possible to smoothly transistion between modes. Like do a absolute positon (PA), then JG. If I want to go to PA 10000 at 500c/s, then jog at 100 c/s. Would the PA decelerate 500->0 velocity at its destination, then the JG velocity accelerates (0->100)? 6. If written answers are too time consuming, perhaps I can call and talk to an application engineer? Thanks, Tony /----------------------------------------------------------------------- \ | Tony Denault | Email: denault@irtf.ifa.hawaii.edu | | Institute for Astronomy | Phone: (808) 932-2378 | | 640 North Aohoku Place | Fax: (808) 933-0737 | | Hilo, Hawaii 96720-2700 | | \----------------------------------------------------------------------- / ----- End forwarded message -----