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15. ABSOLUTE POSITION DETECTION SYSTEM
15.8 Examples of use
15.8.1 MELSEC-A1S (A1SD71)
(1) Instructions
The absolute coordinate system (programmable controller coordinate system) of the A1SD71 (AD71)
only covers the range in which the address increases (positive coordinate values) on moving away from
the machine home position (the position reached in the home position return operation). Therefore, if
the motor enters the range where the coordinate value is negative due to the load torque or a fall on a
vertical axis when the power is turned ON/OFF at a point near the machine home position, the system
fails to detect the absolute position. To prevent this problem, it is necessary to set the home position
(operation home position) for positioning in addition to the machine home position.
(a) The home position should be set in the direction in which the position address of the programmable
controller coordinate system increases on moving away from machine home position, as illustrated
below. Note that the home position for positioning must be more than one revolution of the servo
motor shaft from the machine home position.
If the address of the machine home position is changed to any value other than "0", the home
position should be set in the direction in which the position address increases on moving away from
the machine home position (machine home position after changing the home position address) and
at a point removed from the machine home position by more than one revolution of the motor shaft.
0
010000
50000
50000 0
010000
50000
20000
Machine home position
Home position
(operation home position)
Programmable
controller coordinate
system
A
BS
coordinate
system
a) If revolution direction parameter (Pr. 14) 0 b) If revolution direction parameter (Pr. 14) 1
Programmable
controller coordinate
system
ABS
coordinate
system
Direction in which
address increases
Direction in which
address increases
More than 1 revolution
of motor shaft
More than 1 revolution
of motor shaft
Machine home
positionHome position
20000
50000
(b) In the range where the address decreases on moving away from the machine home position, do not
turn the power supply to the programmable controller or the servo amplifier, the servo-on
pushbutton switch, or the PC-RESET switch, ON/OFF. If any of these operations are attempted,
the ABS coordinate error (Y4B) is output since the absolute position cannot be detected.
020000
0 10000
50000
50000 0
010000
50000
50000 20000
Machine home position Home position
A
BS
coordinate
system
a) If revolution direction parameter (Pr. 14) 0
Programmable
controller coordinate
system
ABS
coordinate
system
Direction in which
address increases
Absolute position data can be
detected
ABS coordinate
value error occurs
if power is turned
on within this range
ABS coordinate
value error occurs
if power is turned
on within this range
Machine
home positionHome position
Direction in which
address increases
Absolute position data can be
detected
b) If revolution direction parameter (Pr. 14) 1
Programmable
controller coordinate
system