Mitsubishi Electronics QD75P, QD75D Position control, Speed control, Designated distance

1 PRODUCT OUTLINE

MELSEC-Q

The principle of "position control" and "speed control" operation is shown below.

Position control

The total No. of pulses required to move the designated distance is obtained in the following manner.

Total No. of pulses required to move designated distance

Designated distance

=Movement amount of machine (load) side when motor rotates once

No. of pulses required for motor to rotate once

The No. of pulses required for the motor to rotate once is the "encoder resolution" described in the motor catalog specification list.

When this total No. of pulses is issued from the QD75 to the servo amplifier, control to move the designated distance can be executed.

The machine side movement amount when one pulse is issued to the servo amplifier is called the "movement amount per pulse". This value is the min. value for the workpiece to move, and is also the electrical positioning precision.

Speed control

The "Total No. of pulses" mentioned above is invariably required for controlling the distance. For positioning or speed control, the speed must be controlled as well. The speed is determined by the frequency of pulses sent from the QD75 to the drive unit.

Positioning	Servo	Servo
module	amplifier	motor

Detector (Pulse encoder)

Speed = Pulses frequency	Feedback pulses
Movement amount = No.of pulses
Feedback pulses =
Pulses generated by detector

Pulse frequency

[pps] This area is the total No. of commanded

pulses.

A

ta td (s)

0.4 1.2 0.4

Movement amount t = 2

Fig. 1.1 Relationship between position control and speed control

POINT

The QD75 controls the position with the "total No. of pulses", and the speed with the "pulse frequency".

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