Extended distance inductives ‘as cute as a button’

In an automotive equipment test application, Contrinex extended-distance 500 Series inductive sensors quickly identify any production faults.

The demanding quality standards of the automotive industry require a manufacturer to inspect the control knobs they manufacture for in-car audio systems, before shipment to the car assembly plants. The presence of a small metal washer that can occasionally become dislodged from inside each knob is therefore checked using a custom-built testing machine.

An array of Contrinex extended-distance 500 Series inductive sensors are positioned directly below a tray of 70 knobs, to confirm the presence of a washer in each radio button, enabling fast and reliable testing.

During manufacture, the spring-washer is fitted to each knob after it has been moulded, and it is this washer which holds the control knob onto the in-car audio system. The manufacturer transports batches of knobs to automotive assembly plants in plastic transit trays which each contain 70 knobs. Occasionally, washers are omitted or become dislodged, resulting in the rejection of entire batches of the knobs by the automotive plant and potential penalties.

Manual inspection of each knob is neither practical nor cost-effective, so a sensor system was required that could test each knob in-situ within the transit trays used to deliver the knobs to the customer.

The small size and position of the washers make the task particularly demanding. There is only a small amount of metal present in each of the 10mm-diameter washers, as they are formed from 1mm-diameter steel wire. The washers lie more than 10mm above the bottom of the plastic tray which is the only feasible sensor location. The transit trays tightly pack the knobs together at 45mm centres, and so the inductive sensors must reliably check the presence of the washers through the plastic tray, without interference from the other nearby sensors.

Contrinex extended distance 500 Series inductive sensors meet the needs of this application, with the M18-diameter units operating reliably at sensing distances up to 12mm. The quasi-embeddable sensors feature chrome-plated brass bodies and PBTP sensing faces. They allow a minimum clearance between sensors of only 44mm, achieving the 45mm between centres requirement of the existing transit trays.

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. 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, which allows the easy removal and replacement of individual sensors for maintenance.