Safety-critical accelerator pedal sensor assembled in just 9 seconds

Citation

(2003), "Safety-critical accelerator pedal sensor assembled in just 9 seconds", Assembly Automation, Vol. 23 No. 1. https://doi.org/10.1108/aa.2003.03323aaf.008

Safety-critical accelerator pedal sensor assembled in just 9 seconds

Safety-critical accelerator pedal sensor assembled in just 9 seconds

Keywords: Assembly, Automotive industry

Modular Automation has designed an assembly system for Wabash Technologies that can assemble accurately the eight components of a safety-critical throttle position sensor, and check the component's function, all with a cycle time of just 9 s (Plate 6).

Plate 6 Modular Automation has designed and built system that can assemble the eight components of a safety-critical throttle sensor in just 9 s

The sensor is for a leading Tier 1 pedal manufacturer whose generic throttle pedal design positions it well to meet the requirements of many major OEM's. The sensor provides electronic throttle control that is more accurate and more reliable than cables. Electronic control is also maintenance free.

The process is essentially automatic but requires two operators to load critical components. Each operation is checked to make sure that it took place correctly; any incorrect assemblies are flagged on the pallet and pass through without further work. Laser trimming calibrates the resistance of the unit and an electronic test also ensures that each completed assembly works correctly.

The operator first loads a housing and rotor onto a flagged pallet. The first automatic station then loads the substrate, ensures that it is laid flat and heat stakes it into position. The system checks only that the substrate is present, not that it performs correctly. Electronic testing is carried out later in the process. This maintains a practical outlook on testing to ensure that every component is tested adequately, yet avoid duplication.

Further operations load the spring, rotor and cover, which is heat staked into position to complete the assembly. There are, however, three operations that are particularly technically demanding: wire bonding, spring contact assembly, and laser trimming.

The wire bonding station uses a proprietary wire bonder to weld nine hair-thin wire contacts into position to link the substrate with the electrical contacts moulded into the sensor body. This is a very delicate operation that must be completed perfectly for the sensor to operate correctly.

The spring contact assembly positions three twin-spoked contacts and heat stakes them to secure. The contacts are only 4mm wide and only 75 mm thick and must be secured without deformation. The system uses a force gauge to measure the pressure exerted by every spoke of the contact on the substrate track - too little force would cause a bad connection, too much would wear the track and result in premature failure of the component.

Laser trimming of the substrate track calibrates the final assembly to ensure it as the correct resistance at a zero mechanical position. The system checks the resistance before and after the trimming process. Again this is a critical operation that ensures the correct operation of the sensor.

For further information contact: David Cockayne, Modular Automation, Talbot Way, Small Heath Business Park, Birmingham, B10 OHS, UK. Tel: 0121 766 7979NI; Fax: 0:121 766 6385.