[Project78]

Hi everyone,

I am retrofitting my 1981 Enshu Accumill with LinuxCNC, Mesa 7i43, Mesa 7i33TA and AMC 12a8e servo drives.

I have everything set up and I am configuring the system. When testing the motors I noticed something strange on my Y axis. If I command a positive direction it barely moves. Once the command ends, it reverses in the opposite direction at full speed.

I currently have the drive in Voltage mode. I have checked all voltages to and from the drive with the motor disconnected. It is all correct. The command voltage is correct and the output voltage is correct in both directions. I also confirmed it is not the motor since I tried different motors and the problem persisted.

Since the voltages are correct, I am starting to think the current output of the drive is a problem. Perhaps the drive is broken?

Have any of you experienced this problem or have suggestions?

Thanks!

[Al_The_Man]

Try the drive open loop with a 0-10v command on the analogue input, try both polarities, I have a dual 9v battery box set up with bi-directional control for testing.
Al.

[Project78]

Hi Al,

Thanks for the quick reply.

I believe I am testing it in open loop. There is no feedback to the drive. I am using my DAC card to send +10v to -10v to the drive and I measure the output in Voltage mode. The drives velocity loop integration is also off.

I can see when the +10v is applied I get my full 62-63 volt output and it returns to 0 when 0v is applied. The reverse is true too. This is measured when the motor is disconnected.

I just checked the voltage when it is attached to the motor. In the positive direction at 10v it only outputs at 38 volts. Once I remove voltage it reverses at -26 volts even though no command voltage is present. 38 plus 26 is 64 which is very close to my systems max voltage. This is very strange.

Any ideas?

[Al_The_Man]

I assume the 38v and -26 is at the motor?
Did you try by substituting the drive and or motor?
Are the DIP switches set right?
Did you do a Null adjustment with the zero offset?
Does the motor perform OK direct on a 12v automotive battery in both polarities, for example?
Al.

[Project78]

Hi Al,

Thanks again for your response. I have answers below.

I assume the 38v and -26 is at the motor? Yes, at the motor. I am taking this reading from the power output of the drive that goes to the motor. I also checked it after the AMC filter card too.
Did you try by substituting the drive and or motor?Yes. Both. The motor is not the problem. The problem only occurs with the particular drive in question.
Are the DIP switches set right? I believe so. It is set up exactly the same as the other drives that function fine.
Did you do a Null adjustment with the zero offset? Yes, I did. With no motor load the voltages in both directions are perfect. However, the problem only presents itself after the motor is connected and moved. After the move the drive begins to and continues to output -26 volts.
Does the motor perform OK direct on a 12v automotive battery in both polarities, for example? I haven't tried this but the motor woks normally when connected to another drive.

I fear it is a drive malfunction. Any other thoughts?

[Al_The_Man]

Sounds like a drive problem to me?
Al.

[Project78]

Thanks Al. It was helpful to get a second opinion before replacing the drive. Thanks again.