Mitsubishi MELSEC-Q Series User Manual page 22

1
PRODUCT OUTLINE
(2) Movement amount and speed in a system using ball screw
Pulse encoder(PLG)
Servomotor
1
- 6 1.2 Outline of Positioning Control and Count Operation
1.2.2 Design outline of positioning control system
(b) Output pulse from the QD72P3C3
1) As shown in Figure 1.3, the number of pulses in a pulse train is small at the
start, and then the number increases as the servomotor accelerates and its
speed approaches the command speed.
2) The pulse frequency stabilizes once the speed reaches the command speed.
3) To decelerate the servomotor, the QD72P3C3 decreases the number of pulses
in a pulse train before it finally stops the output.
The servomotor actually decelerates and stops its rotation with little delay from
the command pulse stop.
This time difference in deceleration and stop between pulse output from the
QD72P3C3 and the servomotor is called the "stop settling time" and
necessary for ensuring stopping accuracy.
Speed V
Droop pulse
amount
Accele-
ration
Few
Pulse train
pulses
Figure 1.3 Output pulse from the QD72P3C3
V
Workpiece
Feed screw
Table
R
L
P0
Figure 1.4 System using ball screw
In the system shown in Figure 1.4, the movement amount per pulse, command
pulse frequency, and deviation counter droop pulse amount are determined in the
following manner.
Servomotor speed
Pulse
distribution
Decele-
ration
Few
Many pulses
pulses
A: Movement amount per pulse (mm/pulse)
Vs: Command pulse frequency (pulse/s)
n: Pulse encoder resolution (pulse/rev)
L: Feed screw lead (mm/rev)
R: Deceleration ratio
V: Movable section speed (mm/s)
N: Rotation frequency of motor (r/min)
K: Position loop gain (1/s )
P
: Deviation counter droop pulse amount
P0: OP (pulse)
P: Address (pulse)
Time t
Stop settling
time