Mitsubishi MELSEC-F, Training Manual

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Positioning Control The World of Positioning Control 1
1-6
< Pulse count method >
- When a pulse encoder is attached to a moving part, and the motor speed is controlled by
a number steps while the pulse number is counted, the movement quantity per pulse is
determined in accordance with the relationship between the pulse number generated by
one rotation of the encoder, and the movement quantity of the moving part (workpiece)
realized by one rotation of the motor. The movement quantity per pulse is regarded as
the minimum unit for the stop command.
- However, the coasting distance at stop is not eliminated.
< Pulse command method >
- In this method using a servo system, the weak points described above are improved. A
pulse encoder is attached to the servo motor, detecting the motor rotation quantity
(workpiece movement distance), to continuously and directly control the speed from the
high-speed operation to the target position, which allows the workpiece to stop with good
precision.
- As the coasting distance at stop is eliminated, the positioning precision is improved.