AXIS_SERVO_DRIVE Diagrams

AXIS_SERVO_DRIVE diagrams include:

Motor Position Servo

The Motor Position Servo configuration provides full position servo control using only the motor mounted feedback device to provide position and velocity feedback. This servo configuration is a good choice in applications where smoothness and stability are more important that positioning accuracy. Positioning accuracy is limited due to the fact that the controller has no way of compensating for non-linearity in the mechanics external to the motor.

Note that the motor mounted feedback device also provides motor position information necessary for commutation. Synchronous input data to the servo loop includes Position Command, Velocity Offset, and Torque Offset. These values are updated at the coarse update rate of the associated motion group.

The Position Command value is derived directly from the output of the motion planner, while the Velocity Offset and Torque Offset values are derived from the current value of the corresponding attributes. These offset attributes may be changed programmatically via SSV instructions or direct Tag access which, when used in conjunction with future Function Block programs, provides custom ‘outer’ control loop capability.

Auxiliary Position Servo

The Auxiliary Position Servo configuration provides full position servo control using an auxiliary (that is, external to the motor) feedback device to provide position and velocity feedback. This servo configuration is a good choice in applications positioning accuracy is important. The smoothness and stability may be limited, however, due to the mechanical non-linearities external to the motor.

Note that the motor mounted feedback device is still required to provide motor position information necessary for commutation. Synchronous input data to the servo loop includes Position Command, Velocity Offset, and Torque Offset. These values are updated at the coarse update rate of the associated motion group.

The Position Command value is derived directly from the output of the motion planner, while the Velocity Offset and Torque Offset values are derived from the current value of the corresponding attributes. These offset attributes may be changed programmatically via SSV instructions or direct Tag access which, when used in conjunction with future Function Block programs, provides custom ‘outer’ control loop capability.

Dual Position Servo

This configuration provides full position servo control using the auxiliary feedback device for position feedback and the motor mounted feedback device to provide velocity feedback. This servo configuration combines the advantages of accurate positioning associated with the auxiliary position servo with the smoothness and stability of the motor position servo configuration.

Note that the motor mounted feedback device also provides motor position information necessary for commutation. Synchronous input data to the servo loop includes Position Command, Velocity Offset, and Torque Offset. These values are updated at the coarse update rate of the associated motion group.

The Position Command value is derived directly from the output of the motion planner, while the Velocity Offset and Torque Offset values are derived from the current value of the corresponding attributes. These offset attributes may be changed programmatically via SSV instructions or direct Tag access which, when used in conjunction with future Function Block programs, provides custom ‘outer’ control loop capability.

Motor Dual Command Servo

The Motor Dual Command Servo configuration provides full position servo control using only the motor mounted feedback device to provide position and velocity feedback. Unlike the Motor Position Servo configuration, however, both command position and command velocity are applied to the loop to provide smoother feedforward behavior. This servo configuration is a good choice in applications where smoothness and stability are important. Positioning accuracy is limited due to the fact that the controller has no way of compensating for non-linearities in the mechanics external to the motor.

Note that the motor mounted feedback device also provides motor position information necessary for commutation. Synchronous input data to the servo loop includes Position Command, Velocity Command, and Velocity Offset. These values are updated at the coarse update rate of the associated motion group.

The Position and Velocity Command values are derived directly from the output of the motion planner, while the Velocity Offset value is derived from the current value of the corresponding attributes. The velocity offset attribute may be changed programmatically via SSV instructions or direct Tag access which, when used in conjunction with future Function Block programs, provides custom ‘outer’ control loop capability.

Auxiliary Dual Command Servo

The Auxiliary Dual Command Servo configuration provides full position servo control using only the auxiliary mounted feedback device to provide position and velocity feedback. Unlike the Auxiliary Position Servo configuration, however, both command position and command velocity are applied to the loop to provide smoother feedforward behavior. This servo configuration is a good choice in applications where positioning accuracy and good feedforward performance is important. The smoothness and stability may be limited, however, due to the mechanical non-linearities external to the motor.

Note, that the motor mounted feedback device is still required to provide motor position information necessary for commutation. Synchronous input data to the servo loop includes Position Command, Velocity Command, and Velocity Offset. These values are updated at the coarse update rate of the associated motion group.

The Position and Velocity Command values are derived directly from the output of the motion planner, while the Velocity Offset value is derived from the current value of the corresponding attributes. The velocity offset attribute may be changed programmatically via SSV instructions or direct Tag access which, when used in conjunction with future Function Block programs, provides custom ‘outer’ control loop capability.

Dual Command Feedback Servo

The Motor Dual Command Feedback Servo configuration provides full position servo control using the auxiliary feedback device for position feedback and the motor mounted feedback device to provide velocity feedback. Unlike the Dual Feedback Servo configuration, however, both command position and command velocity are also applied to the loop to provide smoother feedforward behavior. This servo configuration is a good choice in applications where smoothness and stability are important as well as positioning accuracy.

Note, that the motor mounted feedback device is still required to provide motor position information necessary for commutation. Synchronous input data to the servo loop includes Position Command, Velocity Command, and Velocity Offset. These values are updated at the coarse update rate of the associated motion group.

The Position and Velocity Command values are derived directly from the output of the motion planner, while the Velocity Offset value is derived from the current value of the corresponding attributes. The velocity offset attribute may be changed programmatically via SSV instructions or direct Tag access which, when used in conjunction with future Function Block programs, provides custom ‘outer’ control loop capability.

Velocity Servo

The Velocity Servo configuration provides velocity servo control using the motor mounted feedback device. Synchronous input data to the servo loop includes Velocity Command, Velocity Offset, and Torque Offset. These values are updated at the coarse update rate of the associated motion group. The Velocity Command value is derived directly from the output of the motion planner, while the Velocity Offset and Torque Offset values are derived from the current value of the corresponding attributes. These offset attributes may be changed programmatically via SSV instructions or direct Tag access which, when used in conjunction with future Function Block programs, provides custom ‘outer’ control loop capability.

Torque Servo

The Torque Servo configuration provides torque servo control using only the motor mounted feedback device for commutation. Synchronous input data to the servo loop includes only the Torque Offset. This values are updated at the coarse update rate of the associated motion group.

The Torque Offset value is derived from the current value of the corresponding attribute. This offset attribute may be changed programmatically via SSV instruction or direct Tag access which, when used in conjunction with future Function Block programs, provides custom 'outer' control loop capability.

Drive Gains

Rockwell Automation

servo drives use Nested Digital Servo Control Loop such as shown in the block diagrams above, consisting typically of a position loop with proportional, integral, and feed-forward gains around a digitally synthesized inner velocity loop, again with proportional and integral gains for each axis.

These gains provide software control over the servo dynamics, and allow the servo system to be completely stabilized. Unlike analog servo controllers, these digitally set gains do not drift. Furthermore, once these gains are set for a particular system, another SERCOS module programmed with these gain values will operate identically to the original one.