The German encoder manufacturer Sick has developed a new digital interface technology for linking servodrives to brushless servomotors that, it hopes, will become a standard for these connections. The Hiperface DSL (digital servo link) encoder interface allows one cable to carry both power and encoder signals, so motors only need a single connector, thus cutting cabling time and costs significantly.

Sick also claims that the interface is the only one available that supports encoders to SIL3 levels for safe speed and safe position functions. Initial products will probably support SIL2, but the technology is certified to SIL3.

The protocol will allow digital sensor data to be transmitted over distances of up to 100m using two or four wires in a motor’s power cable. The twisted-pair wires traditionally used for motor winding temperature sensors can now be used for digital communications. Encoders supporting the new protocol will have an optional input for digitising temperature signals and transmitting them to the drive with the encoder data, thus eliminating the need for a dedicated feedback cable.  

For distances up to 20m, standard cables can be used; for longer distances, the cables must meet specified impedance criteria.

The interface conforms to the RS-485 standard and offers a transmission rate of 9.216Mbd. It transmits data in synchronisation with the drive cycle, which can be as short as 12.15μs – about five times quicker than the fastest drives.

The encoders can also be used to log temperature, speed and rotation data for maintenance purposes. Hiperface DSL can also add other sensor information – such as torque, vibration and acceleration – to provide enhanced dynamic control.

“The combination of improved speed regulation and functionality with greater operator safety, and at a reduced cost, marks a significant step forward,” says Darren Pratt, Sick’s UK encoder specialist. “Hiperface DSL is set to be the new standard for high- to low-performance applications.”

The first encoders supporting the new protocol are to be launched within a few months. Several leading servomotor and drive manufacturers are expected to launch systems using Hiperface DSL before the end of 2011.