Motion Control

To make you motion system perform in an optimal way, it is necessary to understand the basic concepts behind motion via EtherCAT, more specifically the CiA 402 Drive Profile and the SOMANET specific extensions:

• Control Loops

  • Current and Torque Control Loop

  • Velocity Control Loop

  • Position Control Loop

  • Dual Loop Cascaded Postion Control

• Modes of operation: SOMANET supports several modes of operation according to CiA 402

  • Cyclic modes: In cyclic synchronous modes, the trajectory must be computed by the master.

    • Cyclic synchronous torque control (CST): In torque control mode the master sends desired torques to the drive.

    • Cyclic synchronous velocity control (CSV): In velocity control modes the master sends desired velocities to the drive.

    • Cyclic synchronous position control (CSP): In position control modes the master sends desired positions to the drive.

  • Profile modes: In profile modes, the trajectory is computed on the slave.

    • Profile position mode: In profile position mode the trajectory to a target point is generated on the drive.

    • Profile velocity mode: In profile velocity mode the motor will rotate at a target velocity.

    • Profile torque mode: In profile torque mode the drive sends a target torque to the motor.

  • Homing modes: Homing can be used to center an axis.

  • Switching the modes: Describes how the modes can be selected.

• Extended control functionalities: These features can be used to enhance performance:

  • Cogging compensation: Feature for compensating ripples caused by magnetic interaction between motor rotor and stator.

  • Field weakening: The velocity range of electric motors can be extended by weakening the magnetic field of the rotor.

  • Anti-windup control: An Anti-Windup algorithm is used to prevent the integrator part to accumulate too much.

  • Gain scheduling: Applies controller gains which will change dynamically regarding the current speed.

  • Motor overload protection (i2t): This feature limits the overcurrent injected to the motor to prevent damage from overheating.

  • Velocity feed forward: To increase the velocity of the robot’s reaction, the target position signal can bypass the position controller.

  • Torque Offset: A desired offset torque can be added to the reference torque.

  • Velocity Offset: An additional velocity offset can be used to improve the positioning performance.

  • Filtering: Digital filters can be used to remove unwanted frequencies such as noise or nonlinear effects.

  • Control supervision: Allows to supervise the work of the control loops

  • Distributed clocks: Allows to synchronize the system time for enhanced performance.