Chapter 2 Getting Started • 28 USER MANUAL
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
;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.