Instrumentation Monthly Test | Measurement | Control
A manufacturer of textile handling machines trusts the speed, precision and reliability of Contrinex’s long-range Analogue Inductive sensors to measure the small changes in the position of a ‘dancer’ roller or ‘follower’, which follows the fabric web’s position and so indicates the web’s tension. The sensor’s precision measurement is fed into a tension control system, which in turn provides continuous feedback to a variable speed drive.
Customer application
As the textile web is unwound and fed into the machine, the control system must compensate for minor changes in tension. These can be due to variations in the properties of the fabric and from within the machine itself, such as slight deformation of the rollers, worn bearings, alignment issues, and the requirement to enable acceleration/deceleration to make speed changes.
A web tension control system registers these tension changes via a dancer roller, which rises and falls constantly in small increments (‘dancing’). Encoder or precision potentiometers are typically used by the customer to measure the ‘dancer’ roller’s position, providing a signal to the machine controller, which adjusts drive speed/braking accordingly.
Encoders and potentiometers have a moving shaft coupled to the pivoting dancer arm of the dancer system and are therefore subject to wear and tear on delicate bearing surfaces and well as limitations in the service life of the encoders and potentiometers in a dusty or fluffy environment. To avoid these problems the customer was looking for a non-contact solution.
Customer solution
Contrinex analogue inductive sensors from their Extra Distance 509 Series family, available from PLUS Automation, provided the perfect solution for this application and the dusty environment. Their Condist oscillator technology ensures excellent temperature stability and repeat accuracy which is required for precision measurement at longer operating distances (up to 40 mm) to a resolution in the µm range.
Their excellent speed, resolution and continuous non-digitised output is particularly suitable for fast precise measurement of the constantly ‘dancing’ roll in this feedback control system.
The use of an analogue 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.
