Velocity Control Mode

In Velocity Control application mode, the application control program and motion planner provide a setpoint value to the CIP Motion device using the cyclic data connection. The velocity control method can be either open loop or closed loop.

Open Loop Velocity Control Method

A motor control device configured for open loop velocity control is traditionally referred to as Variable Frequency, or V/Hz, or VFD, drive.

A feedback device for this configuration is optional. In the absence of a feedback device, the drive estimates the actual velocity and returns it to the controller.

Closed Loop Velocity Control Method

A motor control device configured for closed loop velocity control is traditionally referred to as velocity loop drive or velocity servo drive. A closed loop velocity control drive implies an inner torque/current control loop and therefore is sometimes referred to as a vector drive.

A feedback device for the velocity loop drive configuration is optional. You can achieve tighter speed regulation when using a feedback device, particularly at low speed. When the feedback device is included, it may be used to return actual position, velocity, and acceleration data to the controller using the cyclic data connection. When the feedback device is not included, only the estimated velocity can typically be returned to the controller.

In addition to Command Velocity, the controller can also pass Command Acceleration for the purposes of forward control.

Acceleration Control Method

While not a mainstream control mode in the industry nor mentioned in the IEC standard, the acceleration control mode is included here to complete the dynamic progression from velocity control to torque control and because the Motion Control Axis Object can support an Acceleration Command, potentially derived from the controller's motion planner. In the acceleration control mode, the application control program and motion planner provide acceleration setpoint values to the CIP Motion device using the cyclic data connection. The drive converts the acceleration set-point into a torque command using the estimated system inertia. Acceleration control works in concert with the inner torque/current control loop as shown in the diagram.

A feedback device for the acceleration control configuration is mandatory and may be used to return actual position, velocity, and acceleration data to the controller using the cyclic data connection.