Position feedback is core to any servo application, and most rotary servo motors employ an integrated feedback device with a physical link back to the servo drive, allowing the drive to read the motor’s position and correct any errors between the commanded and actual positions. Two interfaces that facilitate the communication between the motor feedback device and the servo drive are Hiperface and Hiperface DSL.

Hiperface: The hybrid solution for absolute and incremental feedback

Hiperface (an amalgamation of HIgh PERformance InterFACE) is a motor feedback protocol developed specifically for digital drives and introduced in 1996 by Sick Stegmann. Its key benefit is its simplicity, combining a digital channel (according to the RS-485 standard) for absolute position information with an analog channel for incremental position and speed feedback, all in one, eight-wire cable (two wires for the digital RS-485 communication, four for the differential sine/cosine signals, and two for power). The hybrid design allows the transmission of absolute position information at startup and incremental positioning for normal operation.

Hiperface DSL: The all-digital, single cable feedback protocol

In 2011, Sick introduced a new protocol under the Hiperface name: Hiperface DSL (Digital Servo Link) — an all-digital feedback protocol that uses just two wires for bi-directional digital communication and encoder power. These two digital feedback wires are bundled with the motor power into a single cable, which decreases cable cost and complexity, especially for applications with multiple servo drives. The use of just one cable, and therefore, one connector on the motor, is also ideal for very small servo motors, where space for electrical connections is extremely limited.

Like the original protocol, Hiperface DSL complies with the RS-485 standard and allows cable lengths up to 100 meters. Data can be transmitted cyclically at 9.375 Mbaud, or synchronously with the controller clock, with cycle times as low as 12 μs. Hiperface DSL can provide up to 23 bits of resolution per revolution for single-turn encoders and up to 12 bits for multi-turn encoders.

The Hiperface DSL architecture also establishes channels for the transfer of motor parameter data, condition monitoring, and integrated safe motion, transmitting the necessary data over the two digital communication wires. The parameter channel transmits information such as electronic “type plate” data, while the process data channel transmits position and speed information. Two safety channels transmit absolute safe position information as well as encoder status. This redundancy and error-checking make the Hiperface DSL interface compliant with SIL2 (PLd) and SIL3 (PLe) safety standards, per IEC 61508 and EN/ISO 13849-1.

Finally, a SensorHub channel transmits data from other sensors located within the motor — temperature, vibration, acceleration, or humidity, for example — to enable condition monitoring, predictive maintenance, and diagnostics. These capabilities make Hiperface DSL a key component for Industry 4.0 applications and the IIoT.

In 2016, Sick opened the Hiperface DSL interface, providing a licensing model for any drive or motor manufacturer to integrate the technology into their product offering.