Mitsubishi Electric GENERAL PURPOSE AC SERVO MR-E- A/AG Instruction Manual page 154

10. TROUBLESHOOTING
(2) How to find the cause of position shift
Positioning unit
(a) Output pulse
counter
Q
(C) Servo-on (SON),
stroke end
(LSP/LSN) input
When a position shift occurs, check (a) output pulse counter, (b) cumulative command pulse display, (c)
cumulative feedback pulse display, and (d) machine stop position in the above diagram.
(A), (B) and (C) indicate position shift causes. For example, (A) indicates that noise entered the wiring
between positioning unit and servo amplifier, causing pulses to be mis-counted.
In a normal status without position shift, there are the following relationships:
1) Q P (positioning unit's output counter
CMX(parameter No.3)
2) P
CDV(parameter No.4)
C (cumulative command pulses
3) C M (cumulative feedback pulses
Check for a position shift in the following sequence:
1) When Q P
Noise entered the pulse train signal wiring between positioning unit and servo amplifier,
causing pulses to be miss-counted. (Cause A)
Make the following check or take the following measures:
Check how the shielding is done.
Change the open collector system to the differential line driver system.
Run wiring away from the power circuit.
Install a data line filter.
CMX
When
2) P
CDV
During operation, the servo-on signal (SON) or forward/reverse rotation stroke end signal was
switched off or the clear signal (CR) and the reset signal (RES) switched on. (Cause C)
If a malfunction may occur due to much noise, increase the input filter setting (parameter No. 1).
3) When C
Mechanical slip occurred between the servo motor and machine. (Cause B)
Servo amplifier
Electronic gear (parameters No. 3, 4)
CMX
P
CDV
(A)
(b) Cumulative command
pulses
C
M
C
(c) Cumulative
feedback pulses
servo amplifier's cumulative command pulses)
electronic gear cumulative feedback pulses)
travel per pulse
10 - 3
Machine
Servo motor
L
SM
(d) Machine stop
position M
(B)
Encoder
machine position)