Long-distance inductive sensors ensure fast and reliable assembly of automotive stereos

A plastics manufacturer tests batches of control knobs for in-car audio systems before shipment to automotive assembly plants. Each knob contains a small metal washer that can occasionally become dislodged and therefore a custom-built testing machine tests that they are present. Contrinex long-distance inductive sensors, positioned directly below a tray of 70 knobs, confirm the presence of a washer in each assembly, enabling fast and reliable testing.

Application

In operation, plastic control knobs for in-car audio systems are retained in position by small spring washers; during manufacture, a washer is fitted to each knob after moulding. The manufacturer transports batches of knobs to automotive assembly plants in transit trays, each containing 70 knobs. Occasionally, washers are omitted or become dislodged, resulting in rejection of entire batches of knobs by the customer. Manual inspection of each knob is neither practical nor cost-effective so a sensor system must test each knob in-situ in the transit tray. The size and position of the washers makes the task particularly demanding. Each 10mm-diameter washer is formed from 1mm-diameter steel wire and in a batch of knobs, these are located at 45mm centres in a transit tray, where washers lie more than 10 millimetres above the sensors. The sensors must operate reliably in close proximity to one another, sensing the presence of the washers through the plastic tray.

Solution

Contrinex Extra Distance inductive sensors are ideal for this application; M18-diameter units from the Basic range operate reliably at sensing distances up to 12mm. Quasi-embeddable with chrome-plated brass bodies and PBTP sensing faces, these devices allow a minimum clearance between sensors of only 44mm, comfortably accommodating the required spacing. A bank of 70 sensors, mounted in a custom-built testing fixture, aligns exactly with the positions of the knobs in the transit tray. Locating lugs position the tray correctly and clamps secure it during the testing cycle; checking the presence of a washer in each of the 70 knobs is accomplished in a few seconds and in the event that a washer is missing, the position of the faulty knob is immediately identified.

This Contrinex inductive sensor has an industry-standard PNP normally-open interface and an integral M12 connector, allowing easy removal and replacement of individual sensors for maintenance. Connection to the customer’s test equipment is via a flexible PVC-sheathed cable.