Atmospheric Single-Arm Robot
Operation
User’s Manual
Moving and Homing a Robot Axis
Brooks Automation
Revision 1
6-3
Moving and Homing a Robot Axis
The range of travel of each axis is physically limited by mechanical hard stops and,
with the exception of the arm axes, is electronically guarded by two limit switches.
The negative and positive limit switches are located within the full travel of the hard
stops. The negative limit switch is also the home switch for the Theta and Z-axes. The
R axis has one limit switch, the negative limit or home switch. Software limits are log-
ical limits that apply to programmed motions.
A DC servo motor, a servo driver or amplifier, and a motion control board control the
robot axis. The servo motor is directly connected to an optical encoder. The encoder
and limit switch signals are input to the Galil motion control board.
The Galil motion control board monitors the motor position by reading the optical
encoder and outputs a signal that controls the servo amplifier current. The amplifier
module amplifies the signal and sends the power to the motor. The encoder on the
motor provides feedback to the motion control board to create the next output signal.
You can home the robot axis with a standard homing macro (HOM) or with the
HOME command. During the robot homing sequence:
1.
The robot axis moves towards the home switch at the Home speed defined in
your robot parameters file (*.par file).
2.
When the robot axis reaches the home switch, the home flag interrupts the limit
switch.
3.
With the switch interrupted, the robot axis moves away from the home switch
until the controller senses the first index pulse from the encoder.
4.
The encoder outputs one index pulse for each revolution. The motion control
board uses the encoder signals to generate a quadrate signal for the CPU. This
first index pulse provides a zero reference point that is more repeatable than
the home switch used to home the robot when the system is initialized.
5.
The motion control board zeroes the position counter, which is then used as
the zero or home position.
6.
The Home offset is read from the Robot Parameter File and written to the
motion control board register. The Home offset is stored in encoder or quad-
rate counts.
7.
The robot axis then moves to the Customized home position, which is also
defined in the Robot Parameter File. The default for the customized home
position is 0, but you can re-define it.
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