CABLE

The end user assumes that the cable will function correctly in every application. However, this is not always the case. Cables are protected in several ways from electrical influences and also partially against mechanical faults. As well as the outer jacket, individual cores are also surrounded with various materials. The insulation or protective layers are wound in tape form around the wire or the braid. Depending on application requirements, the material consists of either kapton, teflon, mica, polyester, copper or glass fibre yarn.
The unsheathed wire is fed into the banding machine from one side. Depending on the configuration, there are one or two banding units here. These units consist of a receiver for the banding material, which is wound on a roll. The receiver is also called a bobbin. There is a housing around the bobbin, also called a head, which takes over the guidance of the tape. The wire runs in the centre of this unit. When the wire is moving through the machine, the bobbin and head are constantly rotating in order to band the wire with the inserted material. Depending on which cable has to be produced, it is possible to let the tape overlap slightly, to change the winding pitch or to vary the tensile force with which the tape is wound. This is possible because the head and bobbin can rotate separately from each other and therefore achieve different tensile forces and angles. If a second banding unit is installed, the wire can be wrapped again and also in the opposite direction to the first wrapping if required.

New sensor solution

In order to control the tension during the complete banding process, it is important to know the current diameter of the bobbin. Previous attempts to measure the diameter made use of a reflection light barrier. The sensor unit was attached to a mechanism that constantly pivoted to the bobbin. If the existing diameter of the bobbin penetrated this light barrier, a pulse was generated, which could be used as a value for the diameter.
However, as the mechanism for this solution was too complicated, the company, Lukas Anlagenbau, looked for a new solution. It found what it was looking for at measurement technology company Micro-Epsilon, who solved this task using its non-contact laser triangulation sensor.
The laser sensor is now mounted in the machine next to the drum. It continuously measures the current diameter of the drum from this position. The recorded measurement data is transmitted to a winding processor, which then calculates the desired torque of the bobbin drive. The problem with this application is the fact that different materials are being measured, from shiny to transparent materials, which can be located on the drum. Shiny metals present a problem for many laser sensors due to their direct reflection characteristics. The tapes used have a thickness of around 0.1mm and are 6 to 8mm wide. Micro-Epsilon’s “optoNCDT 1401” laser sensor has a measuring range of 200mm and competently performs this measurement. The laser spot reflects onto the coil surface and calculates the precise diameter of the coil. For data acquisition, it must be noted that the head has many vertical cross members for the tape guide. These continuously stray across the measuring range of the sensor and must be suppressed by software so that only the diameter value is provided as the measurement result.

Two systems for different requirements

Depending on application requirements, two basic types of system are available, which ensure that the tape does not unwind unnecessarily in the case of a stoppage or production slowing down and therefore interrupting the production process downstream. Tapes can be inserted in the standard version, which can tolerate tensile loads of more than 4N. The required tape tension is achieved by braking the bobbin with a torque-controlled drive. The winding processor determines the required torque for the drive from the measurement data obtained by the laser sensor.
Another version with a driven bobbin is available as a second variant for more sensitive tapes from a tape tension of 1N. In this system, the spindle diameter is also measured by the laser sensor. A torque measurement is also made. Both measurements are used in the winding processor for calculating the correct torque or tension. External influences such as friction and different storage temperatures are negated with this more sensitive regulation. Therefore, the system can be more precisely regulated and controlled and can therefore produce a high quality final product.
Working closely with Micro-Epsilon, Lukas Anlagenbau, founded in 1959, has created an innovative solution for measuring the diameter of banding spindles. This simple and convenient solution makes complex mechanisms redundant . It is still debatable as to what extent laser measurement technology can be used by Lukas for other products.

About the subject: Laser triangulation

A laser projects a spot of light, which is monitored by a light-sensitive element, onto the surface to be measured. If the distance between the sensor and the surface changes, the angle also changes at which the camera records the light spot. This change of distance can be determined very accurately using simple trigonometric calculations. The resolution possible with this method is in the sub-micrometer range.
Fast exposure regulation, which controls the exposure time and the laser intensity for each measurement pulse, is required for accurate measurement results and also for challenging objects. The innovative RTSC function of Micro-Epsilon’s laser sensors perform these tasks in real-time. Therefore, maximum signal quality is ensured for each measured value.

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