Mitsubishi Electric MELSEC-L02SCPU User Manual page 51

(8) Movement amount and speed of a worm gear system
This section describes methods of calculations required for positioning control by using worm gear system. The
worm gear consists of a balls lined up in an engagement part, just like a ball bearing. The ball screw has no
backlash and can rotate with a small force.
The calculations are performed based on the system described below.
Pulse generator (PLG)
Servomotor
(a) Movement amount per pulse
Calculated from the worm gear lead, deceleration ratio, and pulse generator resolution.
L
(mm/pulse)
A=
R n
The movement amount is calculated by (Number of output pulses) x (Movement amount per pulse).
(b) Command pulse frequency
Calculated from the movable section speed and movement amount per pulse.
V
(pulse/s)
Vs =
A
(c) Deviation counter droop pulse amount
Calculated from the command pulse frequency and position loop gain
Vs
(pulse)
=
K
*1 Ratio of the command pulse frequency to the number of deviation counter droop pulses. A desired position loop gain can
be set adjusting the drive unit. To improve the stopping accuracy, increase the gain. Note, however, that an excessively
high gain may cause overshooting (beyond the target position) and make the operation unstable. An excessively low
gain increases the stopping error, although the movement becomes smoother at stopping.
Internal thread
V
Workpiece
Worm gear
R
Table
L
P
P0
CHAPTER 7 POSITIONING FUNCTION
External thread
A : Movement amount per pulse (mm/pulse)
Vs : Command pulse frequency (pulse/s)
n : Pulse generator resolution (pulse/rev)
L : Worm gear lead (mm/rev)
R : Deceleration ratio
V : Movable section speed (mm/s)
N : Motor speed (r/min)
K : Position loop gain (1/s)
: Deviation counter droop pulse amount
P0 : OP (pulse)
P : Address (pulse)
*1
.
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