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DMC-1700/1800 Chapter 6 Programming Motion • 129
Homing
The Find Edge (FE) and Home (HM) instructions may be used to home the motor to a mechanical reference. This
reference is connected to the Home input line. The HM command initializes the motor to the encoder index pulse in
addition to the Home input. The configure command (CN) is used to define the polarity of the home input.
The Find Edge (FE) instruction is useful for initializing the motor to a home switch. The home switch is connected
to the Homing Input. When the Find Edge command and Begin is used, the motor will accelerate up to the slew
speed and slew until a transition is detected on the Homing line. The motor will then decelerate to a stop. A high
deceleration value must be input before the find edge command is issued for the motor to decelerate rapidly after
sensing the home switch. The Home (HM) command can be used to position the motor on the index pulse after the
home switch is detected. This allows for finer positioning on initialization. The HM command and BG command
causes the following sequence of events to occur.
Stage 1:
Upon begin, the motor accelerates to the slew speed specified by the JG or SP commands. The
direction of its motion is determined by the state of the homing input. If _HMX reads 1 initially,
the motor will go in the reverse direction first (direction of decreasing encoder counts). If _HMX
reads 0 initially, the motor will go in the forward direction first. CN is the command used to
define the polarity of the home input. With CN,-1 (the default value) a normally open switch will
make _HMX read 1 initially, and a normally closed switch will make _HMX read zero.
Furthermore, with CN,1 a normally open switch will make _HMX read 0 initially, and a normally
closed switch will make _HMX read 1. Therefore, the CN command will need to be configured
properly to ensure the correct direction of motion in the home sequence.
Upon detecting the home switch changing state, the motor begins decelerating to a stop.
Note: The direction of motion for the FE command also follows these rules for the state of the
home input.
Stage 2:
The motor then traverses at 256 counts/sec in the opposite direction of Stage 1 until the home
switch toggles again. If Stage 3 is in the opposite direction of Stage 2, the motor will stop
immediately at this point and change direction. If Stage 2 is in the same direction as Stage 3, the
motor will never stop, but will smoothly continue into Stage 3.
Stage 3:
The motor traverses forward at 256 counts/sec until the encoder index pulse is detected. The
motor then stops immediately.
The DMC-1700/1800 defines the home position as the position at which the index was detected
and sets the encoder reading at this point to zero.