Omron CJ1W-MA - REV 10-2008, Operation Manual

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Coordinate System and Present Position Section 7-3
Depending on the PLC’s cycle time and MECHATROLINK communications
cycle, short-term changes in status of the Servo Drive may not be monitored
successfully.
7-3 Coordinate System and Present Position
The PCU uses a single coordinate system based on the origin determined for
each axis using the origin defining functions. This coordinate system provides
two types of present positions for each axis: a feedback present position and
a command present position.
Feedback/Command
Present Position The Servo Drive uses a rotary encoder to detect Servomotor rotations (pro-
viding feedback), and the Servomotor is controlled so that the deviation
between the feedback and command values is compensated to 0. Therefore,
while a position deviation remains in the Servo Drive, a difference equivalent
to the position deviation between the position command value and the inte-
grated value of the feedback, which indicates the actual machine (Servomo-
tor) position, should exist.
The PCU outputs to the I/O memory area allocated for each axis in the CPU
Unit the amount of feedback indicating the actual position of the machine
(Servomotor) as the feedback present position and the position given in the
command as the command present position.
Note When executing speed control and torque control commands, there is no
command present position because a positioning loop is not configured. A
command present position calculated from the position deviation assumed
from the current speed is output as monitor information.
Present Position
Upper/Lower Limits The feedback present position and command present position can be dis-
played as values in the range
−
2,147,483,648 to 2,147,483,647 (command
units). When an operation in a fixed direction without a target position using
jogging, speed control, or torque control is continued, the present value that
exceeds the above range and is not limited by limit input signals or software
limits is given as follows:
t1
Position
Target position
(position command
value)
Speed
Target speed
(speed command
value)
Position deviation
Start
Time
Time
Time
Solid line: Command speed
Broken line: Servomotor's actual speed
Solid line: Command present position
Broken line: Feedback present position
(Servomotor's actual position)
Command present
position at t1
Feedback present
position at t1