Introduction into sercos interface
The sercos interface meets all the requirements by employing a fiber-optic ring structure. Fiber optic cables were chosen to provide high immunity against electromagnetic interference. In industrial applications, unforeseen noise levels must be expected in cable ducts. Furthermore, HF interference resulting from power control by pulse-width modulation, and separately-sited AC line and ground connections on controllers and drives must be reliably eliminated. The ring structure has the smallest number of fiber optic cables and requires no complicated T-branches.
The length of each transmission section can be up to 50 meters with plastic fiber optic cables and up to 250 meters with glass fiber cables. The maximum number of subscribers per fiber optic ring is 254. The maximum number of drives that can be operated per fiber optic cable depends on the required communication cycle time, the chosen amount of operating data and the data rate. The graph shows the number of drives which can be connected to each fiber optic ring for a typical CNC application with speed control and position control modes. The number of drives per controller can be extended as required by using several fiber optic rings.
Specification
The transmission medium is a fiber-optic ring. The maximum transmission rate with the new SERCON 816 ASIC is 2, 4, 8, 16Mbit/s, depending on the version. This interface lets you implement 3 different communication options between CNC and digital drive controllers:
- Transfer of target position
- Transfer of target speed or
- Transfer of target torque
Here, the transfer of target positions has proven itself as the best solution for fast and highly-precise applications. In a fiber-optic ring, up to 6 axes can be supplied simultaneously and cyclically with new position target values (target positions) every 0.5 ms. All of the in-drive data, parameters, and diagnoses can be displayed and entered via the sercos interface using a CNC compatible with sercos.
