Lecture Description:

Features are becoming standard in servo drives for automation:
- Heidenhain has expanded their fully digital encoder protocol EnDat for safety-critical
applications.
- Sick Stegmann introduced the first fully digital 2-wire interface for encoders in 2011: Hiperface
Digital Servo Link (HDSL). A separate encoder cable with connectors, etc. is no longer required,
which is why Beckhoff Automation introduces drives using this technology under the name One
Cable Technology (OCT).
- Concerning functional safety, the black-channel technology known from the safety extensions of
the fieldbuses has become common for safety-related encoder protocols.
- For the electrical connection, the 2-wire interface with a 7 - 12 V direct current power supply has
become a standard for motor integrated encoders.
The manufacturers of servo drives have the challenge to support these different encoder interfaces.
This support is very simple concerning the electrical interface since the 2-wire circuitries are almost
identical. The data transmission is done with 10 - 25 Mbit via standard RS-485 transceivers.
Sometimes with 8B10B coding, sometimes with Manchester code to allow a DC-free half-duplex
transmission without an extra clock signal. The encoders can thus be supplied with power via the
same 2 wires.
Looking at the development of low-cost FPGAs in recent years, the cost per logic element is hardly
decreasing, especially for "smaller" devices. However, the devices are equipped with ever-larger onchip memory areas.
Therefore, a universal encoder interface for FPGAs was developed in such a way that a dual-port
memory is used as a common encoder protocol-independent interface in the direction of motion
control and also in the direction of safe logic. This enables particularly simple integration of different
encoder protocols in servo drives. Connection to a higher-level central safety controller for multi-axis applications is also easy to implement, even if different safety-related encoder protocols are used in one system.
In terms of functional safety, the multi-protocol encoder-interface IP is part of the black-channel, which significantly simplifies system integration.