Mitsubishi MELSEC-F Training Manual page 17

Positioning Control
2) Positioning method and stop precision
Velocity
V elocity
H eavy
load
S m all
inertia
S top com m and
Velocity
High speed
Speed reduction command
Stop command
S peed reductio n start
T im e delay
S top
Dispersion in
speed reduction
distance
Stop command
< Limit switch method >
- When automatically stopping a moving
part driven by a motor, stop the motor by a
position signal, detected by a limit switch
Coasting
distance
(in general conditions, turn on the brake at
the same time).
- The moving part continues by a coasting
distance until it completely stops, after the
Time
stop command is given. The coasting
Stop
distance is shaded in the figure.
- The stop precision is equivalent to the
dispersion in the shaded area as shown in
the figure on the left.
The dispersion is affected by the speed
Light load
when the stop command is given, the load
Large inertia
size and the time delay since the stop
D ispersion
command is given, until speed reduction
in stop
actually starts.
T im e
S top
- If the required stop precision is not
satisfactory w hen stopping from the
normal operation speed, the most effective
method to improve the stop precision is to
reduce the operation speed.
Dispersion
in stop
- However, if the operation speed is simply
reduced, the machine efficiency may also
be reduced. In actual operation, the motor
Time speed can be reduced from high speed to
low speed once, then the motor stopped.
The World of Positioning Control 1
1-5