When an axis has been defined as sinusoidally commutated, the controller must have an
estimate for commutation phase. When hall sensors are used, the controller automatically
estimates this value upon reset of the controller. If no hall sensors are used, the controller
will not be able to make this estimate and the commutation phase must be set before
enabling the motor.
If Hall Sensors are Not Available:
To initialize the commutation without Hall effect sensor use the command, BZ. This function drives
the motor to a position where the commutation phase is zero, and sets the phase to zero.
The BZ command argument is a real number which represents the voltage to be applied to the
amplifier during the initialization. When the voltage is specified by a positive number, the
initialization process will end up in the motor off (MO) state. A negative number causes the process to
end in the Servo Here (SH) state.
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 <CR>
will drive the 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:
SH <CR>
Enable X axis motor
PRX=-1*(_BZX) <CR>
Move X motor close to zero commutation phase
BG <CR>
Begin motion on X axis
AM <CR>
Wait for motion to complete on X axis
BZX=-1 <CR>
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
DMC-14x5/6
Chapter 2 Getting Started
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