07/26/2005 • Automation • Drive Tech • Sensor Technology

Wire-draw encoders: path measurement and position detection ”round the corner”

The new wire-draw encoders of the BTF/PRF series from SICK-Stegmann provide a precise and robust solution in many situations where positions are to be determined or paths measured but the measurement section goes round a corner. The devices – a combination of wire-draw mechanism and a choice of absolute or incremental encoder – are available for a variety of measurement lengths up to 50 m.

Elevating platforms, hydraulic drives, measurement stands, construction machines, or cranes are typical examples of plants whose control systems require precise positional and path information – but which do not have a continuous measurement path as a result of articulated or hinged mechanisms. The new BTF/PRF wire-draw encoders offer tailor-made opportunities for precise path measurement and position detection.

Drum rotations are the measure of all things

With wire-draw encoders, a rust-free steel cord led along the measurement path is wound in or out of a drum in a single layer. The number of drum rotations (proportional to the length) is counted by an encoder and converted to a measurement signal. Even without a straight linear path this provides precise positional and path data, and thus information e.g. on the platform height of an elevating platform, the movement of travelling mechanisms, the position of a dredging shovel, or that of a crane’s gripper. In order to allow the device to ignore the demanding application conditions, these wire-draw encod-ers have a robust housing with an enclosure rating of IP 64, a dirt scraper, and an inte-grated chamber for cable grease.

Available with absolute or incremental encoder

Depending on the preferred measurement length and the desired position formation, the user can choose between BTF absolute wire-draw encoders (a combination of an MRA-F wire-draw mechanism with an ATM60 series absolute encoder) and PRF incremental wire-draw encoders (a combination of an MRA-F wire-draw mechanism with a DRS60 series incremental encoder). With Profibus, CANopen or DeviceNet fieldbus technolo-gies; the SSI interface; the absolute and HTL or TTL interfaces of incremental wire-draw encoders, the appropriate interface for data transmission is available for any particular application.

Wide range of uses
The wide variety of types of BTF/PRF wire-draw encoders available opens up numerous application opportunities, such as for presses, extrusion machines, high-bay ware-houses, theatre stages, medical technology, locks and barrage systems, and in numer-ous other applications and branches.
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