Mitsubishi Electric MELSEC iQ-R-RD75P4 User Manual page 223

Movement amount per pulse
[Pr.2] No. of pulses per rotation (Ap), [Pr.3] Movement amount per rotation (Al), and [Pr.4] Unit magnification (Am) are the
items for determining how many rotations (equivalent to how many pulses) a motor should operate to move a machine for the
movement amount set in the program.
The drive unit controls the positioning to a motor with the number of pulses.
The following shows the control details of the RD75.
RD75
CPU module, Command
engineering tool value
*1 For the RD75P, the upper limit of the command pulse frequency is 200kpulse/s, and for the RD75D, the upper limit is 5Mpulse/s.
*2 For a drive unit without the electronic gear function, or when the electronic gear function is not used, this value is 1.
• Consider a system with a motor connected to a ball screw as shown in the figure above. The electronic gear of the drive
unit is 1.
• The movement amount of the machine is in units of mm or inches. Set the command value in units of mm or inches to the
RD75 for the CPU module program.
• The motor is controlled by the drive unit in units of pulses. Therefore, since the command value in units of mm or inches is
converted in units of pulses, set Ap, Al, and Am so that the following relational expression is satisfied. In this case, the
machine movement amount for the command 1 pulse output from the RD75 is calculated by the following calculation
formula.
Movement amount per pulse (A) =
Item
Number of pulses per rotation of motor
Movement amount per rotation of motor
Movement amount per pulse
The command frequency from the RD75 is limited. If the command frequency exceeds the upper limit,
increase Movement amount per pulse (A) greater (N times) to decrease the command frequency.
In this case, the electronic gear on the drive unit must be increased by N times as well.
The command pulse from the RD75 is changes to 1/N times. Therefore, multiply it by N on the drive unit side
to keep the number of rotations of the motor.
Since Movement amount per pulse (A) is increased, the position accuracy (command resolution) for the
command 1 pulse from the RD75 decreases.
Consider to decrease the command speed when the position accuracy is required.
Command
Drive unit
pulse
*1
Electronic
Ap
gear
Al × Am
Al × Am
Ap
Motor
*2
Reduction gear
Rotates the motor
depending on the number
of pulses.
Symbol
Ap
Al  Am
A
7.3 Function to Compensate Control
Lead
Machine
Ball screw
7 CONTROL SUB FUNCTIONS
7
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