Galil DMC-2X00 - Manual (Page 39)

WARNING: This command must move the motor to find the zero commutation phase. This
movement is instantaneous and will cause the system to jerk. Larger applied voltages will cause
more severe motor jerk. The applied voltage will typically be sufficient for proper operation of the
BZ command. For systems with significant friction, this voltage may need to be increased and for
systems with very small motors, this value should be decreased. For example:
BZ –2, 0,1
will drive both A and C axes to zero, will apply 2V and 1V respectively to A and C and will end up
with A in SH and C in MO.
Step F - part 2 (Systems with Hall Sensors Only). Set Zero Commutation Phase
With Hall sensors, the estimated value of the commutation phase is good to within 30 °. This
estimate can be used to drive the motor but a more accurate estimate is needed for efficient
motor operation. There are 3 possible methods for commutation phase initialization:
Method 1. Use the BZ command as described above.
Method 2. Drive the motor close to commutation phase of zero and then use BZ command.
This method decreases the amount of system jerk by moving the motor close to zero
commutation phase before executing the BZ command. The controller makes an estimate for
the number of encoder counts between the current position and the position of zero
commutation phase. This value is stored in the operand _BZn. Using this operand the
controller can be commanded to move the motor. The BZ command is then issued as
described above. For example, to initialize the A axis motor upon power or reset, the
following commands may be given:
SHA ;Enable A axis motor
PRA=-1*(_BZA) ;Move A motor close to zero commutation phase
BGA ;Begin motion on A axis
AMA ;Wait for motion to complete on A axis
BZA=-1 ;Drive motor to commutation phase zero and leave
;motor on
Method 3. Use the command, BC. This command uses the Hall transitions to determine the
commutation phase. Ideally, the Hall sensor transitions will be separated by exactly 60
° and
any deviation from 60 ° will affect the accuracy of this method. If the Hall sensors are
accurate, this method is recommended. The BC command monitors the Hall sensors during a
move and monitors the Hall sensors for a transition point. When that occurs, the controller
computes the commutation phase and sets it. For example, to initialize the A axis motor upon
power or reset, the following commands may be given:
SHA ;Enable A axis motor
BCA ;Enable the brushless calibration command
PRA=50000 ;Command a relative position movement on A axis
BGA ;Begin motion on A axis. When the Hall sensors
; detect a phase transition, the commutation phase is
;re-set.
DMC-2X00 Chapter 2 Getting Started y 29