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Printer-friendly | Three fork sensors in a rowTwo sets of three fork sensors monitor the correct feeding of assembly partsThree consecutive red light fork sensors, type FGL 80-RK, check the feeding and position of small parts in a production line for AC adaptors. Practical details such as a light-weight, plastic housing, flexible mounting with a dovetail and clearly visible status LEDs at the end of the fork arms, were decisive factors for the choice of this SensoPart product. It is one of industry’s common applications: small assembly parts are fed via a transport rail, collected by a gripper and taken to the assembly point. For a manufacturer of power adapters and battery chargers in Germany’s Münsterland, this production step is used for the assembly of AC adapters, and is a double station: a gripper is supplied alternately with small parts from two feed belts. The actual presence and correct alignment of the parts in question must be checked before the gripper arrives. “The client wanted a preferably uncomplicated and low-priced solution for this application task“, reported SensoPart application engineer Thomas Worms. Simple and reliable The automated solution using a series of three fork sensors on each of the two feed rails proved to be as simple as it was reliable: The fork sensor at the end of the rail checks whether the part is conveyed right up to the stop plate, the middle sensor “looks to see” whether the part is in the correct position (it must be lying flat) and the first fork sensor in the conveying direction signals whether the space is free for the next part. On the first two fork sensors, the LED lights up to signal the correct status. With the stop plate check on the other hand, the LED light signals an error. In this case, the parent control system receives an appropriate signal and the gripper arm stops. As the LEDs are fitted on the (rounded) ends of the fork sensors, the status is clearly visible to the machine operator from any direction. “The production line is quite complicated and eye-catching signals are important“, emphasises Thomas Worms.
Teach-in instead of potentiometer SensoPart’s fork sensors were also quickly set-up: instead of the widely-used conventional potentiometer, the sensors offer the user a dynamic teach-in system enabling configuration even during a running process. The sensors “learn“ the size and reflectance properties of the parts to be detected directly on a moving object: the teach button is pressed for three seconds until the status LED flashes; the button is then held pressed whilst the object to be detected runs through the fork sensor, the setting is saved when the button is released. “The two sets of three fork sensors were mounted and set-up on both feed rails, ready for operation, in just a few minutes“, explained Thomas Worms. Error-free for over two years Possible alternatives to the fork sensors were also examined, but were rejected mainly for cost reasons. A vision sensor or optical fibre system would not only have been much more expensive due to the purchasing cost but would also have required more complex mounting and set-up work. The fork alignment also has advantages over the classical retro-reflective light barrier, as the sensor and reflector are permanently attached and thus always perfectly aligned. A proximity switch, in turn, could have caused problems with changing part surfaces (black, shiny metallic). The fork sensor finally proved to be the optimum solution in every respect – function, complexity, cost. The solution described here has been in use for over two years now, error-free. The fork sensor FGL-RK from SensoPart
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