why only Axis 1 is permanently active?

[Gram]

I have four step motors, controlled by 7334 controller via a UMI-7764. Each step motor is hooked up to one Axis in UMI-7764 terminal block. However, I can only drive the motor on Axis 1 regardless of different Axis number I set in LabVIEW vi. What would possibly be the reasons? Thanks!

[Jochen]

Please check the following using 1D interactive in MAX:

- Do you receive an error when you try to move another axis?
- Are the other axes activated and configured properly?
- Are the axes powered after the controller was initialized (do you feel static torque when you try to turn the motors manually?)
- Is your UMI powered?
- Can you measure steps being generated at the other outputs using a scope?
- What's the state of the axes that can't be moved?
- What type of amplifier do you use?

Best regards,

Jochen Klier
National Instruments Germany

[Gram]

Thanks a lot! I fixed the problem using 1D interactive in MAX following your instructions. Some configuration problems have been detected for the axes that were not working. Now, all motors on four axes can be driven by the controller.

I encounter another problem at the moment. I need simultaneously run two motors along a vector move path in a 2D space. Although I specified the velocity along this path, the two motors sometimes did not work simultaneously. As a result, a constant velocity along the prescribed path cannot fully be maintained. Besides, large nosie and vibration were generated, which in turn cause problems . All the motors are open loop stepper. Can you also advise on it? Thanks again.

[Jochen]

Again here comes a bunch of questions:
- Which version of NI-Motion are you using? 6.1.5 is the latest version please upgrade to this version if you haven't installed it, yet
- When the axes don't follow the defined vector do they reach their target position, though? If not this would mean they are loosing steps.
- Does the problem occurr no matter which values are set for acceleration and velocity? Does this problem also occurr at very low accel. and velocity values?
- If you are really loosing steps, are there any mechanical problems (friction, twisting, high inertia)? Is there a way to increase the motor current to get more torque?

Regards,

Jochen

[Gram]

Thanks Jochen,

I have kept trying the system. I find that there is no occurrence of losing step, although it stops sometimes during the move. Seems that a constant velocity is unattainable, even specified in the program. The lower the velocity, the more unsteady the move is. Most of the problems are caused by mechanical constrain, e.g. friction, twisting, vibration, and noise as you mentioned. I have discussed the problems with colleagues to minimise constrain associated (release mechanical constrain, lubrication, etc.). It is better now, yet, further modification is still required.

[Gram]

I am still working on the system. So far, we modified the mechanical parts of the system and it is now running more smoothly with less noise and vibration. I set motors in a half-step mode, which also help smooth the move. However, even though I specified a fixed velocity (the maximum velocity attainable for the motor), the system (mechanical components) still cannot run continuously, i.e, stop sometimes for a while, and then run again. Can you give me further suggestion on that, as a stable and continuous move is vitally important for our application?

[Jochen]

I remember a similar situation where the problem was caused by a current limit in the drive. Please make sure that the drive delivers enough current for your motor. Maybe there are some dip switches that can be changed.

Best regards,

Jochen Klier
National Instruments Germany

[Gram]

Thanks for your help. I increase the phase current to the motor by setting the on board switches. The problem still occurs. I notice that although the mechanical parts stop moving, the current trajectory data keep updating.

[Rodj]

Since you are running the 7334 in open loop stepper mode, I am not surprised that the board continues to output the steps even when the axes stop. Since it has no feedback from the system, it always generates the steps according to the trajectory setting.

Is your drive getting a fault condition?
Have you considered microstepping at a higher rate? This will increase the smoothness of the motion, but does reduce the maximum torque.
Have you tried slower velocities and accelerations? If stepper motors are accelerated too quickly, or are commanded a too high of a velocity, they will "slip". Which will look like they have stopped. Then when the stop "slipping", the motor will start turning again.
Also a motor running in whole step or half step mode, may need to use a base velocity. At really low velocities, motors commanded in whole step mode may not move. If you can though I recommend you use microstepping.

Rodger S.

[Gram]

Many thanks, Rodger,

No fault condition/error is found from the drive.
I set the motor running in a half step mode. Basically, the motors are two 23HSX and one 34HSX series hybrid stepper motors from Mclennan Servo Supplies Ltd. They all provide 200 steps/rev when used with full step drives or 400 steps/rev in half step mode and are controlled through PM546 bipolar stepper motor translator from the same company. I am not so sure about microstepping, does that mean I will introduce gear box device into the system.
I have tried slower velocities and accelerations, as it is also required in this application to output slow movement of the mechanical system. Say, if I set velocity to be 5 rpm, I do not know what would be appropriate value for acceleration/deceleration? What is the basic velocity for an application like this?