Increased safety for direct drives
By Kathrin Kritzer, Motor Feedback Systems/Motion Control Sensors Product Manager, SICK STEGMANN GmbH, Donaueschingen
Wednesday, 23 May, 2018
Excellent dynamic performance, low inertia, gearless operation and long service life are just four of the benefits OEMs are looking to achieve when they install direct drives in their machines. Rotative direct drives are the optimal choice for applications, with fast cycles and very high standards for positioning accuracy in particular. With its new motor feedback systems in the SES/SEM 70 and 90 series, SICK is now also introducing safety technology and built-in direct multiturn to the world of direct drives.
Within state-of-the-art production processes, close interaction between human and machine continues to progress, creating opportunities for human-robot collaboration within a cyber-physical working environment. As we see the boundaries between automation and workers becoming more and more blurred, brand-new options for interaction are opening up. However, all of this comes with a whole host of questions relating to safety that we have not needed to consider before now. The only way to provide personal protection within a production setting that no longer involves fixed safety fences or cordoned-off areas is to introduce reliable safety technology with fast response times.
SICK envisions new applications for the hollow shaft variant in the SES/SEM 70 and 90 series, primarily to be within the field of torque motors and rotary tables as well as in the diverse area of direct drives within robot applications, injection moulding machines, woodworking centres, semiconductor technology and handling systems.
No battery buffer
The new SES/SEM 70 and 90 motor feedback systems are available in a singleturn and multiturn variant, which marks true innovation on the market. Rather than relying on a revolution counter with a battery buffer to measure revolutions, SICK has integrated a gear mechanism into the encoder for this purpose, which is hugely beneficial regarding both installation and maintenance. For one thing, the SES/SEM system does not require an additional power supply through the battery buffer of the connected drive. This cuts back on the wiring required, as there is no need for a cable between the drive and the motor feedback system.
The significant benefits afforded by the lack of the battery buffer are also particularly evident during operation. Once batteries reach the end of their life cycle, they inevitably have to be replaced, which is costly and necessitates machine downtime. By cutting out this step, the availability and productivity levels of the whole machine will increase, while material and staffing costs associated with monitoring and maintenance will drop.
The SICK solution instead transmits the revolutions recorded by the mechanical multiturn, along with positioning information to the connected drive via the HIPERFACE interface. The mechanical multiturn can capture up to 4096 revolutions. The motor feedback system is installed directly on the motor shaft, without the need for extra strap connections or mechanical couplings. The entire system has an impressively long service life with fewer wear-and-tear parts, rendering it maintenance-free.
With the view of meeting requirements for safety technology, SICK is currently working towards achieving functional safety certification in line with Safety Integrity Level 2 (SIL2) under EN 61508 and Performance Level d (PLd) under EN ISO 13849 for the new HIPERFACE devices within the SES/SEM 70 and 90 product family. These motor feedback systems have been designed specifically for rotative direct drives (such as torque motors), opening up new opportunities for configuring machines with direct drives and safety technology with relative ease. SICK supplying the new encoders with certification will make life easier for machine manufacturers performing final acceptance on a system as far as safety technology is concerned.
In terms of different motor sizes, SICK is providing the new hollow shaft encoder for direct drives with shaft diameters of 25 millimetres (SES/SEM70 model) and 50 millimetres (SES/SEM90 model). The smart size of the hollow shaft encoder with HIPERFACE interface is keeping with the current trend of manufacturing machines and systems that are as compact as possible. The motor feedback systems are suitable for hollow shaft motors operating at high speeds. The SES/SEM70 can be used up to a maximum speed of 8500 rpm, while the SES/SEM90 is compatible with speeds of up to 6000 rpm.
From a functional point of view, the motor feedback system is based on capacitive measurement principle with holistic sensing. The core element of the SES/SEM product family is the bearing-free sensor element, consisting of a sender and receiver printed circuit board and a sinusoidal rotor. The rotation of the rotor, which is installed on the motor shaft, alters the dielectric between the sender and receiver printed circuit board. The change to the electric field is converted into sine-cosine signals and transmitted to the drive via the HIPERFACE interface.
The holistic sensing is incredibly robust and resistant to dust, moisture and mechanical influences in comparison to optical systems with ball bearings, code disks and light sources. Regarding control quality, the new motor feedback system features a finely resolving track with 32 sine-cosine periods per revolution (SES/SEM70) or 64 sine-cosine periods per revolution (SES/SEM90). The hollow shaft diameter of 25 millimetres or 50 millimetres allows for cables, cooling lines and other connections to be fed through the motor shaft with ease. When designing machines, this property offers unprecedented levels of flexibility, which can be beneficial within collaborative robot applications, for instance.
The motor feedback systems in the SES and SEM product family are quick and easy to install without the need for any special adjustment tools. Just attach and rotate them, and you are good to go. Once a system is installed, the SOPAS software can be used to check the position of the rotor, which can be used to ensure correct attachment directly. This is a reliable way of identifying installation errors before delivery of the motor.
Direct drives are currently an undeniable trend in the field of electrical drive technology. The countless reasons behind this include their long service life, increased immediacy, lack of backlash, energy efficiency and compact design. Having identified this trend early, SICK decided to develop motor feedback systems for torque motors and linear drives. Mechanical multiturn and safety technology have been added to the properties of the new SES/SEM70 and 90 product family, allowing SICK to deliver a full portfolio of motor feedback systems with HIPERFACE interface for direct drives.
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