FX
3S
/FX
3G
/FX
3GC
/FX
3U
/FX
3UC
PLC User's Manual - Positioning Control Edition
Built-in Positioning Functions
6 Mechanical Zero Return - DSZR/ZRN Instruction
6.2 DOG Search Zero Return (DSZR Instruction)
B - 108
6.2.4 Important Points
For important programming points, refer to Section 4.7.
• Detection of (the rear end and the front end of) the near-point signal (DOG) will be affected by the input
filter and the scan time of the sequence program.
Secure 1 scan time or more from the rear end of the DOG to turning ON of the zero-point signal.
• Since the zero-phase signal of the servo motor is used, adjust the relation between the rear end of the
DOG and the zero-phase signal as shown in the following figure. If fine adjustment of the origin position is
needed, adjust the position of the near-point signal (DOG).
• Properly set the DOG so that the near-point signal (DOG) can be kept at the ON status until the speed is
reduced to the creep speed.
This instruction will start speed reduction at the front end of the DOG, and will stop the operation at the rear
end of the DOG or at detection of the first zero-phase signal after passing the rear end of the DOG.
The current value register will then be cleared (reset to "0").
If the speed is not reduced to the creep speed before detecting the rear end of the DOG, the operation may
not be stopped at the specified position.
• Use the near-point signal (DOG) between the reverse rotation limit 1 (LSR) and the forward rotation limit 1
(LSF).
The intended operation may not be performed if the relationship among the near-point signal (DOG),
reverse rotation limit 1 (LSR) and forward rotation limit 1 (LSF) is not as shown in the figure below.
• The input device specified for the near-point signal or the zero-phase signal cannot be used
for the following items:
- High-speed counter
- Input interruption
- Pulse catch
- SPD instruction
- DVIT instruction
*1
- ZRN instruction
*1. O
nly available for FX3U and FX3UC PLCs.
• The creep speed should be sufficiently slow.
The zero return instruction will not decelerate at the stop point. Therefore, if the creep speed is not slow
enough, the operation may not stop at the specified position due to inertia.
• If an operand is changed during instruction execution, the change will be ignored and the operation will not
be affected. To change the operation, turn off the command contact of the instruction, and then turn it on
again.
• If the instruction activation contact is turned off during the zero return operation, the speed will decelerate
and the operation will stop. In this case, the "Instruction execution complete" flag (M8029) will not be
turned on.
• If the "pulse output monitor" (BUSY/READY) flag is on, a positioning instruction (including PLSR and
PLSY) that uses the same output cannot be executed.
If the "pulse output monitor" (BUSY/READY) flag is still on after the instruction activation contact is turned
off, do not execute a positioning instruction (including PLSR and PLSY instructions) that uses the same
output number.
DOG
Rear end
Zero-phase signal
Front end
Operation direction
Longer than
1 scan time
Reverse rotation limit 2
(Servo amplifier side)
Reverse rotation limit 1
(Programmable
controller side)
LSR
Forward rotation limit 2
(Servo amplifier side)
Forward rotation limit 1
(Programmable
controller side)
LSF
Reverse rotation Forward rotation
Servo motor
DOG
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