Aerotech UNIDEX 600 Series, User Manual

Page: 129 / 354

AerTune U600 User’s Guide
5-10
Aerotech, Inc.
Version 1.4
5.3.7. Computing Torque (Closed-Loop Torque Mode)
The torque applied to the motor (in torque mode) may be easily calculated for brush or
brushless motors if you know a few parameter values and the K
t
(motor torque constant).
The UNIDEX 600/650 Controllers have a 16 bit Digital-to-Analog converter used to
convert a signed 16 bit number (+32,767 through –32,767) to an analog voltage in the
range of +10 volts through –10 volts. This voltage is applied to the command input of the
servo amplifier (knowing the G
m
(transconductance) value of the servo amplifier allows
the current (Amps) output to be calculated). Aerotech’s amplifiers typically (model
dependant) have a peak output of 20 or 30 amps. Simply meaning, a +/- 10 volts in to the
amplifier will be equal to +/- x amps, where x is the peak output current of the servo
amplifier. This current produces a torque generated by the motor, equal to the current
multiplied by the K
t
of the motor. For example, if the peak output command (or
instantaneous output command) from DAC was 16,385 (+5 volts), the amplifier produced
30 amps for an input of 10 volts, and the motor had a K
t
of 16 oz-in (ounce-inches) per
amp, then:
(5 volt command / 10 volt, max amps input command) * 30 amps (max
I output) * 16 oz-in K
t
= 240
or
5/10 * 30 *16 = 240
Figure 5-6. Closed-Loop Torque Mode
16 Bit
Number
DAC
(+32,767)
+10
-10
(-32,767)
G
m
Servo Amplifier
+X
-X
Current
K
t
Torque
UNIDEX 600