Experimental Physics and
Industrial Control System

Hi Joey,

    That controller is designed to control either a stepper motor or a DC motor with an encoder, aka a servomotor. So you either need to add an encoder (looks like the motor vendor will sell you one) or switch to a stepper motor. A DC motor alone has no idea where it is, so its position can't be controlled without help.

Pete.

Hi everyone,

I appreciate all of your responses. 

Peter: The type of motor that we have is a DC motor and the part is specified here.

Tim: The controller we have is a DMC-4080 from Galil and is not homemade. The VBAS = 0, VELO = 25000, and ACCL = 1, and these are default values. The website for this controller is found here.

Best,

Joey Thai

On Mon, Feb 13, 2017 at 11:26 AM, D Peter Siddons <[email protected]> wrote:

Hi Joey,

To be clear, what kind of motor is that? Is it a simple DC motor or a stepper motor. It seems to have a fairly complex controller. What kind of controller is that? Is it commercial or home-made?

Pete.

On 02/13/2017 02:01 PM, Joey Thai wrote:

Hi Tim,

I am also a student at the University of Washington working on the same project as Matthew. We greatly appreciated your response and found it consistent with the "Motor Record and related software" documentation provided by this website: http://www.aps.anl.gov/bcda/synApps/motor/R6-9/motorRecord.html

The problem we have is that the VAL field seems to change the speed of the coreless brushed motor's rotation. The YouTube video below demonstrates the speed of the motor when we set the VAL field to 100, then 30:

https://www.youtube.com/watch?v=xR7BVMfGruQ

Notice that the speed of the motor when VAL is set to 30 is noticeable slower than the speed when VAL is set to 100. Since the motor we are using is not using an encoder, the motor does not know its current position. As Matthew said earlier, VAL seems to affect the speed of the motor's rotation.

I guess my question is, is there some sort of hidden relationship between the VAL field and the speed of a motor's rotation?

Best Regards,

Joey Thai

On Sat, Feb 11, 2017 at 11:29 PM, Mooney, Tim M. <[email protected]> wrote:

Hi Matthew,

The VAL field is the position you want the motor to move to.  You choose the units you want for the VAL field, and then you set the MRES (motor resolution) field to be the distance, in those units, that the motor will move when it's driver gets one step pulse. (You should also set the EGU field to some string that will tell the user what units you chose for the VAL field.  The EGU field isn't used for any other purpose.)

Other background information: the motor's running speed (VELO) is in EGUs per second.  The motor's acceleration time (ACCL) is the number of seconds you want it to take for the motor to get from its base speed (VBAS) to its running speed (VELO). Stepper motors have a resonant speed that you want to avoid.  If you set VBAS to be higher than the resonant speed, the motor will leap immediately to the base speed, avoiding the resonance, and then accelerate from there to the running speed.  This is why short moves are slow, and longer moves are faster.

Tim Mooney ([email protected]) (630)252-5417
Beamline Controls Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab

---

From: [email protected] [[email protected]] on behalf of Matt Dentinger [[email protected]]
Sent: Saturday, February 11, 2017 8:52 PM
To: [email protected]
Subject: VAL field in Motor record Default unit

Dear Tech-Talk,

   Hi, I am a student at the University of Washington and I am learning how to navigate and use EPICS programming.  For the task at hand I will not be able to use encoders, making use of absolute positioning impossible, so I was wondering what default unit the VAL field was in.  Through some testing it seems the larger the value, the faster the motor moves so I guessed that it might be a number that somehow represents revolutions per second (or another given time).  Hope you can shed some light on my issue.  Also, haven't subscribed yet, but I may have to depending on how this project continues.  Thanks again.

  Best,

  
     Matthew Dentinger

-- 
D. Peter Siddons
Detector Development Group Leader
Photon Science Division, NSLS-II,
Bldg. 535B
Brookhaven National Laboratory
Upton, NY 11973

email: [email protected]
Phone: (631) 344-2738

-- 
D. Peter Siddons
Detector Development Group Leader
Photon Science Division, NSLS-II,
Bldg. 535B
Brookhaven National Laboratory
Upton, NY 11973

email: [email protected]
Phone: (631) 344-2738