A CNC machining center with Fanuc 6M CNC control system, the speed control unit shows TGLS alarm while 4^th axis reference return under JOG mode.

TGLS alarm of speed control unit means “speed measuring system off”, so below should be checked:

1-      Check pulse encoder inside the motor, and it is fine.

2-      Check couplings of the motor and drivers, all is good.

3-      Measure the connection of motor cables, nothing wrong.

4-      Exchange the driver control board and they are ok.

Then restart the machining center, the alarm gone, but it come again when trying to zero-return of the rotary table.

To find out what is the problem and considering this machining center using semi-close-loop servo system, so disconnect the motor and ball screw, then restart the machine and try, machine is working fine, this means the problem must be come from the mechanical parts of the rotary table.

Check carefully then find out the gear of the rotary table was drifted, fixed it then the alarm gone and the machining center back to normal.