In many production processes, material webs are continuously fed to various processing steps. One example is the stamping of sheet metal electrical connectors for the automotive industry. The web of material here consists of a metal strip, which is delivered on large rolls. The processing speed is high. The tape material is unwound on one side and on the other side rolled up. Both is carried out with electric motors. Depending on the actual diameter of the rolls the required winding speed is different.
A traditional method for proper speed control of the reels is the sag. It provides a uniform supply of material. Between un- and upwinder slack loops are generated intentially. With sensors, the sag is measured and kept constant by controlling. If the sag is too small, the speed of the following electric motor is reduced until the slack is back as desired.
Earlier so called dancers were used, which had direct contact with the strip material. Today one uses ultrasonic sensors to measure a distance. Because the tapes have often very high speed and are strongly fluttering, ultrasonic sensors are ideal. They detect even in harsh environment.
Typically ultrasonic sensors with analogue output are used, such as UPK or UPR series.