3.1.8 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
Cyclic modes
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
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
Quick stop
Diagnostics opmode Used for triggering diagnostic OS commands.
Switching the modes Describes how the modes can be selected.
Extended control functionalities These features can be used to enhance performance:
Cogging Torque Compensation Removes 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 linearly over the speed range.
Anti-Windup Control An Anti-Windup alogorithm is used to prevent the Integrator part to accumulate
beyond acceptable boundaries.
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.
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