Mode parameterisation according to SoE

Parametrization of the IDN S-0-0032

Cascaded control structure

The diagram shows a typical control structure with higher-level position controller and subordinate speed and current controller.

A cascaded controller structure consisting of current, speed and position controllers has proven to be necessary for achieving high dynamics and positioning accuracy. The diagram illustrates the time constants of the individual control loops, rising from inside to outside. Two operating modes are suitable for positioning: velocity set value specification or position set value specification.

For the position of operation, 2 modes are:

• • speed setpoint (speed interface):
  Cyclic speed setpoints are sent from the controller to the drive. Of the Position controller is in this case on the side of the controller (NC) implemented.
• • Position setpoint. (Position interface):
  Cyclic setpoint positions are sent from the controller to the drive. The position controller is here implemented in the drive. In the control (NC) only the setpoint profile is calculated. Here is a higher bandwidth in the position control achieved (no EtherCAT dead in closed Loop). This mode should always be used when the controller enables.

Profile generator

The profile generator generates curve profile of a positioning job of the PLC function block MC_MoveAbsolute. In each NC cycle, at a specified time (node T1 - Tn), the Setpoints this positioning task passed to the axis control. Thus, the servo amplifier optimally can proceed, the target values of the profile generator with the SAF task of the EtherCAT fieldbus must be triggered. The SAF task ensures that the support points (T1 - Tn) to the servo amplifier be transported.

MC_MoveAbsolute is primarily used for linear axis systems. This PLC function block, let to axes with a speed v process of starting to target positions.

For further informations, please look at the following link: PLC ( Libs ( TwinCAT 3 PLC lib: Tc2_MC2 ( Motion-Function block ( Point to Point Motion

Position interface

The position calculated by the profile generator is transferred to the drive via the EtherCAT fieldbus. This gives the drive a new position setpoint in each SAF cycle. The position controller in the drive (see cascaded control structure) eliminates the EtherCAT dead time in the position control loop. By using the position controller in the drive, the position controller has no effect in the NC (parameterization in the TCDrivemanager). The "Control Kp factor" in the NC online window of the CD driver manager therefore has no effect.

The actual position of the feedback system is mapped to the NC. Here it makes sense to select the standard (default) lag distance, which is calculated by the drive (automatically when reading in a standard Sercos axis). This lag distance provides the real position differences. The following distance can also be calculated internally via the NC. However, this calculation includes the dead time of the fieldbus (EtherCAT) and is thereby falsified.

This operating mode is configured via parameter S-0-0032. In addition to the internal position controller, a speed pre-control can be activated. If no precontrol is used, the setpoint of the speed controller is composed exclusively of the product control difference and the amplification of the position controller.

As a rule, pilot control makes sense. Depending on the application, the weighting of this variable between 0 and 100% can be influenced.

Speed interface

If the servo amplifier does not have a position controller or if the setpoint speed must be influenced with additional components, the position controller can be transferred to the controller. The setpoint speed calculated by the profile generator is supplemented by the amount that the TwinCAT PTP position controller calculates due to a tracking error.

The interpolation points of the velocity setpoints have, as with the position specification, a temporal resolution which is determined by the interpolation clock (task time of the SAF task of the NC).

This operating mode is configured via parameter S-0-0032.

Another operating mode is torque control. In this operating mode, the nominal torque is specified. The actual torque is transmitted as feedback signal. The torque control is performed by the drive. If an external measuring point is regarded as an actual value, a control (generation of setpoints) must be provided in the controller.