Speed monitoring with encoders

TWK (Germany) offers rotary encoders for speed monitoring. They support CANopen.

In a press release, TWK stated: Measuring speeds is an increasingly important requirement in machines and systems. They are used to reach certain positions. The drives are precisely controlled. It is usually possible to travel between the end points - for example, in the case of a crane. When the target point is approaching, the speed is reduced. Servo drives with integrated sensors can perform this task. In many cases, however, a separate encoder must be used. Especially when it comes to safety-oriented applications in which additional position and speed detection by functionally safe sensors is required. It serves to protect the environment, people, and machines, said the company.

In many cases, for example, the speed of automated guided vehicles (AGVs) is measured directly at the wheels in order to meet safety requirements. In addition to the control aspect, there is also the task of speed monitoring, e.g. for the rotor of a wind turbine. Here, it must be ensured that a certain speed is not exceeded. If it does, the turbine must be switched off - or at least an alarm must be triggered. In other words, the requirements for a reliable output signal are high, the company added.

TWK has been active in the field of sensor technology for machines and plants for a long time and has been offering functionally sensors for years. These are mainly rotary encoders, electronic cam switches, and inclination sensors, including a special version, the rotor hub sensor. What they all have in common is that they are certified according to ISO 13849 as well as IEC 61508 - with level PLd or SIL2. Depending on the product, various flange and shaft shapes as well as stainless steel versions are available. In terms of encoders, there are several latest releases from TWK.

For example, the TRK38/S3 single turn safety encoder has been launched. It has a diameter and housing length of 38 mm. With the Fail-Safe-over-Ethercat interface (FSoE), it offers SIL2/PLd performance with a resolution of up to 16 bits/360°. The quality of the speed signal has been improved, said the company: the accuracy of the position detection on the time scale is now approx. 1 µs. This equidistance is important for precise speed, which is based on the calculation of the position difference per time unit (adjustable), they explained. The absolute encoders have CiA 406 profile for encoders implemented. The CiA 406 profile series specifies the application interface for absolute rotary and linear encoders.

But also with regard to classic encoders with CANopen safety interface, TWK has a certified encoder with safe position and speed signal in its portfolio with the TRN/S4. A positive-locking mechanical connection between the customer’s shaft and the sensor shaft ensures that the magnet in the sensor shaft reflects the rotation of the customer’s shaft. With the TBN model, one rotation (i.e. max. 65 536 steps) is recorded. With the subsequent absolute transmission, the TRN shaft encoder reaches a measuring range of up to 4096 rotations. The position and speed values (PDO - Process Data Object) are output via the CANopen protocol.

The company concluded: With the help of these devices, a functionally safe detection/monitoring of the speed in the most diverse variations can be realized in order to make machines and systems safer.

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