Chapter 6: Motor Wiring
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6.4 Wiring Servo Motors
DSPpro controllers can control brush servo motors, brushless servo motors, or linear brushless
motors. Basic connections require an analog output signal (from the board to the amplifier) and
an encoder input (from the motor to the board).
6.4.1 Velocity/Torque Mode
Most amplifiers support either Velocity mode (voltage control), Torque mode (current control),
or both. The DSPpro motion controllers can be used with either Velocity or Torque controlled
servo motor/amplifier packages.
When the amplifier is in Velocity mode, the velocity of the motor is proportional to the analog
input voltage (-10 volts to +10 volts). When the amplifier is in Torque mode the current applied
to the motor is proportional to the analog input voltage (-10 volts to +10 volts). Generally,
Velocity mode is more stable than Torque mode.
6.4.2 Encoder Input
DSPpro motion controllers accept TTL level (0v to 5v, 40mA max) encoder input from either
differential or single-ended encoders. Differential encoders are preferred due to their excellent
noise immunity. When used with differential encoders, the differential line receiver
(LM26LS32) on the controller reads the difference between A+ and A- and between B+ and B-.
By reading the difference between the square wave inputs any significant noise is canceled out.
The connections for a single ended encoder are identical to a differential encoder except channel
A- and channel B- should be left unconnected (floating). The A- and B- lines are pulled up
internally to 2.5 volts.
The controller also reads the index pulse (either single ended or differential). Typically, there is
one index pulse per revolution of the encoder (rotary type), which can be used for homing.
Encoder signals are read in quadrature. This means every line on the encoder will produce a
rising edge and a falling edge on channels A+ and B+ which are interpreted by the DSPpro as
four encoder counts.
The amp enable and amp fault connections are discussed in chapter 7, “Dedicated I/O”. Any
unused lines should be left unconnected.
6.4.3 Brush Servo Motors
The minimum required connections for brush type servo motors are:
Analog signal (+/- 10 V)
Signal Ground
Encoder Channel A +
Encoder Channel B +
+5 volts
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