[MITSUBISHI SERVO] Home Position keeps shifting after the machine is restarted.

[jagadeeshr]

Hardware

PLC: Mitsubishi Q06UDV

Servo Module: Mitsubishi QD77MS2

Servo Amplifier: Mitsubishi MR-JE Series Amplifier

Customer has restarted their production after 1.5 months of lock-down.

Yesterday, I got a call that a servo is not returning to its home position. This servo uses 'Data Set' method as home position return method. The servo is moved to the home position (indicated by a proximity sensor) and a 'Set as Home Pos.' button is pressed on the HMI screen. The current position of the servo is set as 0.

Yesterday, during an auto cycle, the servo had completed its positioning, but had stopped 20 mm below the home position. When the servo was moved to the home position, the position was -21.60 mm. After teaching the home position, we ran a 5 cycles, there were no issues.

Today, when the machine was switched ON, the home position had shifted from 0 to -81.3 mm.

In addition, the servo has a bunch of hardware problems: heating, noise, jerk, and motor current is 40% during idle and > 100% during operation.

I'm not sure what the exact issue is?

Edit: Talked to the programmer who had installed this machine. He mentioned that there was some issue with the encoder cable that was causing the motor to heat up.

Edited May 21, 2020 by jagadeeshr

[MitsProgrammer]

Good day Sir

It sounds like you have a battery issue. Please check and replace the battery. 

[jagadeeshr]

I'll mention this to the maintenance engineer at the site.

Is it possible to diagnose or monitor the battery status? When I monitored the servo through the Simple Motion Module Setting Tool, there was an occasional warning about positioning start command. Other than this there was nothing else.

Edited May 21, 2020 by jagadeeshr

[MitsProgrammer]

Good day Sir

You can check the battery status by using the I/O monitoring in MR Configurator 2

The Bit BWNG is a battery warning bit. 

Another test you can do is to leave the machine on overnight, if the servo have not lost position then you know the battery is faulty.