Specifications

LA Series Linear Servo Amplifier Technical Reference Manual

11 Balancing

Motor phase balancing is performed to minimize torque ripple in the motor caused by impedance

variations in the motor windings and to compensate for component tolerance variations in the amplifier

drive circuits. The intent of this adjustment is to get the three motor voltages approximately equal taking

into account polarity. Once the drive is balanced, the setting should not need to be changed as long as the

drive operates with the same motor and at the same baseplate temperature as when the balance was

performed

NOTE: Be sure the amplifier is at operating temperature when performing any balancing procedures. To

achieve operating temperature, enable the amplifier with the motor load connected and monitor the

baseplate temperature, either at TP2 (10°C/Volt) or using the “L” serial command.

There are two methods that can be used to balance the output phases, Autobalance and Manual

Balance. For most cases, the Autobalance feature will balance the phases to an acceptable level. For

other cases where the motor resistance may be very high, or exact phase balance must be obtained, the

manual method should be used after the Autobalance to further “tweak” the offsets.

11.1 Autobalance

The drive has the ability to autobalance the phase offsets using an internal algorithm. The algorithm is

initiated by holding the push button for longer than 1 second. The “B” command can also be used from the

serial interface. Once started, the algorithm will display a “-“ middle bar on the LED display. Depending on

the amount of offset, the phase voltage and the load resistance, the amount of time spent in the

Autobalance routine varies from about 5 seconds to about 30 seconds.

If the drive is unable to balance the phases, the routine exits and reports and Autobalance Fault

(4) on the LED display.

Note: Be sure the motion controller is set to output 0vdc to the command input(s) and the motion controller

is set for open loop mode (no feedback loop). This is very important, as the motor will not be able to move

during this procedure.

The procedure for using the Autobalance feature:

1) Connect the motor in the normal manner.

2) Apply power to the system (Bias and Bus).

3) Set the motion controller to open loop mode (no feedback loop)

4) Set the motor so no motion is possible (lock down the stage).

5) Set the command input(s) to 0 volts and Enable the amplifier.

6) Press the Reset button S1 and hold for greater than 1 second. Confirm the middle bar on the LED

display is showing. Release the button.

7) Once the procedure completes, the display will either show Enabled (0) or Autobalance Fault (4). If

the drive is Enabled, the process has completed successfully. If a fault is shown, the phases will

have to be balanced manually.

Note: The Autobalance function is typically able to balance a load with a resistance that falls within the

range of 1 ohm to 10 ohms. The Autobalance function may not consistently balance loads outside this

range. This does not indicate a problem with the amplifier. It means the load may need to be manually

balanced. This is especially true if the manual balance pots have been moved from their factory center

position. Once the load has been manually balanced and the pots re-centered, the Autobalance function

will most likely work.