To improve the positioning performance when the position reference is changing dynamically, an additional velocity offset is available in the cascaded controller.
The working principle of this feature is based on the two different loops (position loop and velocity loop) that the cascaded control structure consists of: While the velocity controller generates the actual reference torque, the position controller generates the reference for the velocity controller.
Therefore any change in the reference position first has to go through the position loop before reaching the velocity loop.
To skip this step and thus improve the overall control performance, the velocity controller takes a velocity offset that is added to its reference value. It is typically gained by computing the derivative of the reference position and can be multiplied with a factor.
NOTE: This velocity offset must be computed by the master, it is not computed on the slave.
This object provides the offset for the velocity value. The offset is given in [rpm]. In cyclic synchronous position mode, this object contains the input value for velocity feed forward. In cyclic synchronous velocity mode (see Clause 18), it contains the commanded offset of the drive device.
NOTE The value itself is absolute and thus independent of how often it is transmitted over the communication system, for example transmitted twice does not mean double value. Since the additive velocity value represents an offset to the target velocity, it can be also used to control the drive with relative values with regard to the target velocity.
|Name||Index:Sub||Type||Bit Size||Min Data||Max Data||Default Data||Unit||Access||PDO Mapping|
|Velocity offset||0x60B1:0||DINT||32||0||readwrite||Transmit or Receive PDO|