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Chapter 6: Motor Wiring
The amp enable and amp fault connections are discussed in the chapter 7, “I/O Wiring.” Any
unused lines should be left unconnected.
6.4.5 Step-and-Direction Controlled Servo Motors
Some brushless servos are controlled by step-and-direction pulses. With this type of motor, the
position information is communicated by step pulses, and the PID loop is handled internally by
the drive itself.
To avoid possible instability caused by conflict between the drive PID loop and the controller’s
PID loop, it is best to operate step-and-direction servos as open-loop step motors. The controller
will send step pulses and a direction pulse to the drive, which will handle the PID servo control
internally.
6.5 Wiring Step Motors
6.5.1 Open-Loop Step Motors
DSPpro controllers can control step motors in both open-loop (no encoder) and closed-loop
configurations. In the open-loop configuration the step pulse output (connected to the driver) is
fed back into the controller and used to keep track of the “actual position.” Thus the DSP closes
the loop internally on a pair of axes when the open-loop step configuration is selected. Full/half
and micro stepping drives are compatible with the boards.
Filter
PID
D/A
Voltage
to
Frequency
Converter
Analog Output
Active if Stepper Axis
Output
Step
Encoder
Inputs
Active if Closed-Loop Axis
Active if Open-Loop Axis
Figure 6-11. Internal Architecture to Control Step Motors
Most step drives require three wires for operation: step, direction and ground (or + 5 volts). The
board provides a TTL level step pulse(+) output and dir) output for each axis. In
addition, the complements of the step and direction signals are also provided (step(-) and dir(-)).
Some drives allow differential inputs in which both step + and step - lines are connected for
higher noise immunity. If in doubt, fax the driver data sheets or driver pin-outs to MEI Technical
Support along with any questions.
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