Cyclic synchronous operating modes: CSP, CSV, CST
What are cyclic-synchronous operating modes?
Cyclic synchronous modes are EtherCAT-based control modes in accordance with CiA 402, in which the master sends a new setpoint to the drive in each communication cycle. The master handles trajectory planning, while the drive executes the local control loops.
Why is this important?
In robotics, CNC machines, and multi-axis systems, it is not enough to simply give the drive a target position and let it move there on its own. The master must centrally calculate the coordinated path planning for all axes and transmit each individual intermediate point to the drives:
- Full control over the motion path — complex trajectories (S-curves, splines, circular interpolation) are calculated in the master
- Multi-axis synchronization — all axes receive their setpoints in the same communication cycle
- Deterministic execution — EtherCAT guarantees the temporal consistency of setpoint transmission
- Flexibility — the master can adjust the movement at any time without relying on the drive's internal trajectory generator.
How does it work?
Three operating modes cover the three control variables:
CSP — Cyclic Synchronous Position (Mode 8): The master sends target positions. The drive performs position, speed, and torque control. In addition, velocity offset (0x60B1) and torque offset (0x60B2) can be sent as feedforward signals.
CSV — Cyclic Synchronous Velocity (Mode 9): The master sends target speeds. The drive performs speed and torque control. Interpolation between cycles ensures smooth transitions.
CST — Cyclic Synchronous Torque (Mode 10): The master sends target torques. The drive only performs torque control. Ideal for force/impedance control.
Comparison with profile modes (PP, PV, PT): In profile modes (PP=1, PV=3, PT=4), the drive's internal trajectory generator takes over path planning. The master only specifies a target and movement parameters. This is simpler, but does not offer cross-axis coordination.
The mode is selected via OD object 0x6060 (Modes of Operation). Modes can be changed dynamically in the "Operation enabled" state — provided that all required PDO data has been mapped.
How does SOMANET implement this?
All SOMANET servo drives support CSP, CSV, and CST as primary operating modes. The internal sampling cycle is 250 µs (4 kHz), and the recommended EtherCAT cycle time is between 250 µs and 8 ms. Distributed clocks ensure synchronization in multi-slave systems.
Three controller variants are available in CSP mode: Cascaded PID, Single PID, and Dual Encoder Cascade Control. Command smoothing and interpolation compensate for slower master cycle times.
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