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The quiet revolution

A quiet digital revolution in the control and application of brushless servo motors and drives is promising a step-change in technology and could be accepted as a new industry standard

speed regulation and enable a more compact motor design. These advances will benefit not only the motor and drive manufacturers themselves, but also machine builders and systems integrators who are demanding smaller and more efficient motors. End-users are set to benefit from lower costs and improved operator safety. At the centre of the advance is a fully-digital encoder


interface protocol which eliminates the problem of electro- magnetic interference encountered in previous analogue systems and therefore the risk of signal degradation. The Hiperface DSL (Digital-Servo-Link) motor feedback interface was introduced in mid 2011, and four significant manufacturers – Beckhoff, Parker, Robox and Selema – have all launched enabled drives and motors. Its developer Sick anticipates further announcements during 2012. The new digital interface is so robust that cores inside

the motor power cable can be used for the communication of feedback data to the drive. The twisted pair traditionally used for the temperature winding sensor in a standard motor power cable is used for the Hiperface DSL communication. The result is the need for a separate dedicated feedback cable is completely eliminated. This, together with the loss of connectors to the motor and drive, promises major cost reductions – savings which enable motor manufacturers to be more competitive in pricing as well as significantly reducing error possibilities for connector and cable faults. Commissioning times are also reduced significantly. Hiperface DSL also offers significant benefits for operator

safety, having been developed with safe drive systems in mind. It incorporates the redundancy and error checking


he benefits of a new, completely, digital communications protocol for carrying servo data from the motor to the drive electronics are significant. They promise to save costs, improve

required to achieve both SIL2 (PLd) and SIL3 (PLe) levels for safe speed and safe position functions. To fully understand the significance of the achievement,

it is worth taking a moment to consider the role and progress of the encoder in servo motors. First of all, the encoder must provide angular positional information to enable the drive to form the correct commutation signals required to make the motor turn. In addition it provides high resolution speed information to enable the drive to accurately regulate the speed of motion. Finally, it generates absolute positional information over multiple revolutions for precise positioning of the servo axis. Before the advent of Hiperface DSL, this typically required an eight, ten, twelve or even fourteen-core feedback cable as well as a power cable, which included twin cores for temperature sensing. Potentially analogue feedback signals (continuous sine wave) were subject to degradation and loss due to the ‘noisy’ electromagnetic environment created by the motor power cable.

EMC interference Adequate shielding was bulky and expensive and physical separation of the two cables could be difficult, so some ‘noise’ was tolerated. Additionally, data degradation was potentially a problem when considering safety integration at SIL3 levels. The advantage of the Hiperface DSL technology is that the protocol contains sufficient redundancy and error checking capabilities to make it much less susceptible to EMC interference. Hiperface DSL will operate over up to 100 metres of

cable although, at longer than 20 metres, the impedance of the cable has to be carefully specified to avoid affecting the high data exchange rate. The Sick Hiperface DSL interface comprises an enabled encoder on the motor and software to program the servo drive via the standard Field

Programmable Gate Array (FPGA). The encoders also provide opportunities for improved condition monitoring and preventative maintenance. Temperature, speed and rotation information will be logged inside the encoder with all information accessible via Hiperface DSL. Open accessibility to this information will enable plant operators and maintenance engineers to plan maintenance more effectively, enabling increased plant availability and reducing machine downtime. In the case of drives connected to the Internet, the data log can be remotely accessed by engineering teams located anywhere in the world, providing opportunities for enhanced plant support. Drive manufacturers will find it very easy to implement

the new interface to take advantage of the improved data comms potential and the newly-equipped motors. The Intellectual Property is downloaded from the supplied CD ROM to set the drive up via the FPGA. The motor specific data can be stored into the encoders during motor assembly, enabling the automatic uploading of the essential motor characteristics to the drive during commissioning. There will be a hardware saving on the drive too, as the requirement for a separate feedback connector is eliminated. Another benefit lies in the potential for improved control

and condition monitoring of the motor, via the drive and into the Distributed Control System (DCS) for the plant. As well as the temperature sensing already integrated, the interface supports the transmission of acceleration, torque and vibration data providing opportunities for enhanced control of the complete motor axis. A development of Sick’s previous Hiperface

technology which is already a standard in motor and drive manufacture worldwide, the new interface has been developed closely with Sick customers to ensure a robust step-change in technology with the reliability expected of a system set to become adopted as a standard in the years to come. Sick expects this new and innovative solution to be taken up most quickly in robotic and automated machinery applications as well as for integration into process and packaging equipment.


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