CANopen Programmer's Manual - Maccon.de

CANopen Programmer’s Manual 5: Stepper Mode Support
5.1: Stepper Mode Operation
Copley Controls Amplifiers and Stepper Mode Operation
Copley Controls supports the use of stepper motors over a CANopen network.
The Stepnet amplifier can drive a two-phase stepper motor in stepper or servo mode.
The Accelnet and Xenus amplifiers can drive a three-phase stepper motor in stepper mode.
Stepper vs. Servo
In a closed-loop servo system, sensors feed back the actual position and/or velocity of the motor,
and the amplifier calculates how much torque to apply to the motor to move it to the target
destination.
An open-loop stepper system does not typically have sensors to feed back actual position or
velocity information. Nor does it use the position and velocity loops used in servo systems.
Instead, the amplifier moves the motor in steps by applying fixed current to the motor’s windings in
measured intervals. Position and velocity commands can be derived but not measured.
Microstepping
The type of stepper motor supported by the Copley Controls Stepnet amplifier has two windings. It
can be driven using the simple full stepping method or the more precise microstepping method.
Copley Controls supports microstepping as described in Microstepping (p. 159).
The Accelnet and Xenus amplifiers support three-phase, three-winding stepper motors. The
Accelnet and Xenus also use microstepping to drive these three-phase stepper motors.
Microstepping
Copley Controls’ microstepping amplifiers provide a much higher degree of control over a motor’s
position than does a full stepping system. The microstepping amplifier applies varying amounts of
current into both windings of the motor at the same time, making it possible to rest the motor not
only at the full step locations, but at points between them, and thus allowing a high degree of
control over the motor’s position.
In microstepping mode it is necessary to program the following CANopen objects:
Object Description
Motor Pole Pairs
(Index 0x2383, Sub-Index 2, p. 91)
Microsteps/Rev
(Index 0x2383, Sub-Index 29, p. 96)
Number of motor pole pairs (electrical phases) per rotation. For example, for
a 1.8 deg/step motor, set Motor Pair Polls to 50.
Microsteps per revolution.
There is virtually no limit on the number of microsteps/rev. Programming a very high value does
not mean that the amplifier can actually move the motor to that many distinct positions, because
the ability to control current in the windings is limited. The practical limit depends on the motor, but
something on the order of 1000 microsteps/electrical cycle is generally reasonable. It is
sometimes advantageous to program a large number of microsteps, so the system works as
expected when connected to a high resolution encoder.
Some drive manufacturers require that the number of microsteps/rev be an integer multiple of the
number of electrical cycles. Copley Controls amplifiers do not have such a limitation.
Copley Controls 159