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
will drive the X axis to zero, using a 2V signal. The controller will then leave the
motor enabled. For systems that have external forces working against the motor,
such as gravity, the BZ argument must provide a torque 10x the external force. If the
torque is not sufficient, the commutation zero may not be accurate.
If Hall Sensors are Available:
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 _BZx.
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 X axis
motor upon power or reset, the following commands may be given:
SHX
Enable X axis motor
PRX=-1*(_BZX)
Move X motor close to zero commutation phase
BGX
Begin motion on X axis
AMX
Wait for motion to complete on X axis
BZX=-1
Drive motor to commutation phase zero and leave
the
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 X axis motor upon power or reset, the
following commands may be given:
SHX
Enable X axis motor
BCX
Enable the brushless calibration command
PRX=50000
Command a relative position movement on X axis
BGX
Begin motion on X axis. When the hall sensors
detect a phase transition, the commutation phase is re-set.
22
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Chapter 2 Getting Started
DMC-1600
