Mitsubishi Electric MELSEC-L LD75P User Manual page 778

Term
STEPPING MOTOR
STEP FUNCTION
STOP WITH STOPPER
STROKE
STROKE LIMIT
776
A motor that rotates a given angle (example: 0.15) when 1 pulse is generated.
For that reason, a rotation proportional to the No. of pulses can be obtained. 2-phase to 5-phase stepping motors
are available. In the 3-phase type, the rotor rotates in order from A to C when a voltage is applied. Often found in
compact motors, stepping motors rotate accurately without feedback. Be careful of step out when overloaded.
C B
N A A S
B C
1) First, the A phase is excited
by a pulse.
C B
A A
B C
3) The nearest tooth to the
B phase is attracted, and the
rotation stops.
When the operation is designed so that several positioning data Nos. are consecutively run, this function can be
used to carry out a test operation for 1 data item at a time.
This is one machine OPR method. With this method, a stopper is established at the OP, and the operation is
stopped when the machine presses against it. Motor burning would occur or the stopper would be damaged if the
machine were left in that state.
There are two methods to prevent this; a timer can be used to shut OFF the motor after a fixed time, or the motor
can be stopped by limiting sudden increase in the motor torque when the machine presses against the stopper.
Machine OPR
The stroke is the variation in the operation by the distance from a stopped state to the next stopped state after a
movement.
This is the range in which a positioning operation is possible, or the range in which the machine can be moved
without damage occurring. (Movement outside this range is possible in the manual operation.) For operations
using a worm gear, the stroke limit is determined by the length of the screw. For operations using a fixed-feed, it
is determined by the max. dimension to be cut.
The upper/lower limits are set in the parameters, but a separate limit switch should be established and an
emergency stop circuit outside the programmable controller should be created. Refer to the term "LIMIT
SWITCH".
Lower limit
0
Positioning possible in a 3m (9.84feet) range
Description
C
A A
C
2) When the B phase is then excited,
the force works in the direction
shown by the arrows.
C B
A A
B C
4) As the excitation phase is
continuously changed, the rotor
rotates in a clockwise direction.
OP
Stopper
Limit switch
for emergency
stop
Upper limit
3m (9.84feet)