connecting UMI 7764

[marmut]

Hi,

I'm just setting up my motion control system, using 7344 card and umi 7764 connected to a third party drive but it's currently not working. I've read the online forums about connecting the inhibit output and command signal from the 7764 to a third party drive, and I followed the exact steps. My motor is a brush servo, with single ended optical encoder. I'm trying to use the MAX to configure and test the system, so I've been using the 1-D interactive feature, but the drive does not seem to be enabled. I checked the voltages across the terminals (+5V and the Inhibit out, which are connected to the drive's enable and digital ground) and the voltage is 5V when the motion is stopped/inhibited, which is right (polarity is active low) but when I tried to run the motor and press the play, the voltage across drops to only 3.6V, which might not be low enough to enable the drive as the enable function is also set to active low. I'm just using axis 1 of the card and the umi as well. I checked other axes, and the voltage drops slightly more, to about 1.5V, but I'm not sure if that's low enough. What might be wrong with my system?

The motor does not lock when it's in halt mode, but this might be due to the drive being disabled? When I press the run button, there's also DAC voltage spike to 10V for about 50 ms then it'll go to zero again. The MAX also listed the encoders as unconfigured even though the encoders are connected and when i turn the motor the count changes in the MAX. I'm attaching the picture of the DAC output and the axis 1 i/o mapping.

Thank you

[A_Person]

Hi marmut:

It sounds like you may have the inhibit out and the drive's enable level mixed up.  Try switching the polarity of the inhibit output in MAX and see if that enables the drive properly.

You are correct about the motor locking.  With the drive disabled, the motor will be free.

The screenshot of MAX you posted shows the encoder as unconfigured under Output Mapping.  This would be used if you were mapping the encoder output to another device.  It doesn't sound like this is the case in your situation though so you shouldn't have anything to worry about.

[marmut]

Hi Person,

Thanks a lot for the feedback. I tweaked the connection and the polarity slightly and it's able to enable the drive now. However, there are still problems:

1. As soon as I hit the run button in MAX 1-D interactive, the motor will power up and straight away kill off the axis, since there is always following error. Do you know how I can fix that? I set the mode to absolute position, and I tried relative position as well, but it did not help.

2. The DAC command for run and halt is always in the same direction, and they alternate. I'm attaching another screenshot for reference. Even when the axis is killed, and I hit the halt button, the motor will run. This should not be the case as the motor should lock instead when the drive is enabled, right? I think without the following error the motor might run wild upon enabling the drive.

Regards,

marmut

 

[marmut]

Hi,

I already managed to solve my problem. There was some problem with the drive setting, and probably some conflicting command from the controller and the driver. However, I have more questions regarding the DAC read vi, as there seems to be a lot of noise when I used the vi to read the DAC output. Strangely, the DAC output in 1-D interactive in MAX shows something that's a lot smoother. Secondly, the reading from DAC read is very high, can reach up to thousands in amplitude. I don't think it's in volts (3000 volts in really really high), is there something wrong with the vi, or is the unit different? I'm using LabView 7.1.

[A_Person]

Hi marmut:

Glad to hear that you got the first issue resolved.

I'm not sure about the noise you are seeing, perhaps you could post a screen shot.

As far as using the Read DAC VI, the issue is that the output is just a 16-bit integer value representing the voltage.  The help file for the VI lists the scale as +32,767 for a +10 V output and -32,768 for -10 V.  All other voltage values can be found based on that linear scale.