A manufacturer of dancer systems for web tension control uses an inductive sensor with analog output to register constant, small changes in web tension and transmit them to the tension control system, which in turn provides continuous feedback to a variable speed drive.
- Long service life
- Direct interface to a controller (0 – 10 VDC or 4 – 20 mA)
- Simple installation
- Non-contact solution
- Immune to dirty environments
- Long sensing distances compared to market standard
- Excellent repeating accuracy
As a web unwinds and feeds material into the process, the control system must compensate for minor changes in tension. These may be due not only to inherent material properties, but also to slight deformation of the unwind roll, worn bearings, alignment issues, acceleration/deceleration ramps and start/stop functions. The web tension control system registers these tension changes via a dancer roll, which rises and falls constantly in small increments (‘dancing’). In the past, either a feedback potentiometer or an encoder-type product has been used by the customer to provide a signal to the machine controller, which adjusts drive speed/braking accordingly.
However, both alternatives involve a moving shaft coupled to the pivoting dancer arm of the system. Both are therefore subject to wear and tear on delicate bearing surfaces. To avoid this problem in the systems offered, the customer seeks a non-contact solution.
Inductive sensors from the Extra Distance family, Analog Output range (series 509) are ideal for this application. Available in a range of standard housings, their Condist® oscillator technology ensures much longer operating distances than standard (up to 40 mm). The sensors’ analog output provides resolution in the µm range with excellent temperature stability and repeat accuracy. The continuous, non-digitized output of these sensors is perfectly suited to recording the precise movement of a constantly ‘dancing’ roll.
The approach using an analog inductive sensor requires no mechanical contact but merely an elliptical metal target or direct view of the moving dancer arm. It is then possible to interface the sensor output directly to a controller, with several switch points included in a single device. This greatly simplifies installation, while the problems of wear and tear associated with mechanical contact are also avoided.