Motion Control
Precision MicroControl Corp.
112
i
The following MCCL example uses the
D
efine
H
ome (
aDHn
) command to
redefine the encoder position of a closed loop system.
; MCCL linear stage homing sequence using the positive limit sensor
MD1,1LM2,1LN3,MJ10
;call
homing
macro
MD10,1VM,1DI0,1GO,LU”STATUS”,1RL@0,IS10,MJ11,NO,JR-5
;move
and
poll
the
Limit
+
sensor
MD11,1WS0.01,1MN,1DI1,1SV1000,1GO,LU”STATUS”,1RL@0,IC28,MJ12,NO,JR-5
;move
negative
until
limit
+
inactive
MD12,1AB,1WS.1,1DH0,1PM,1MN,1MA-100
;stop immediately when limit + not active,
;define position as 0. Move to position –
100.
Homing open loop steppers
Open loop steppers are typically homed based on the position of a home sensor. Unlike servos that use a
precision reference index mark, steppers are more prone to homing inaccuracies due the lower
repeatability of the single electro mechanical home sensor. To achieve the highest possible repeatability;
reduce the velocity of the axis and always approach the home sensor from the same direction. Here is a
typical linear axis controlled by an open loop stepper motor. A home sensor defines the home position of
the axis. End of travel or Limit Switches are used to protect against damage of the mechanical
components.
Stepper motor
Lead screw
Home sensor
Positive Limit
sensor
Negative Limit
sensor
Stage
When power is applied or the controller is reset, the position of the stage is unknown. The following
command sequence will move the stage in the positive direction. If the positive limit sensor is activated
before the Home sensor the stage will change direction, until home sensor is located. When the Home
sensor is activated the
MCEdgeArm ( )
and
MCIsEdgeFound ( )
functions are used to capture the
position of the Home sensor active edge.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
