Wednesday 23 May 2012

Automotive: rotary selectors

A typical car dashboard features several rotary selectors. Temperature, vents, blowers, and headlights are operated by rotating dial-type switches. Automotive manufacturers test these components to determine whether the torque required to operate them is within acceptable limits.

A selector can be neither too stiff nor too slack. If too stiff, the driver will struggle to operate it efficiently and safely; if too slack, selection will be uncertain and slippage could result. Rotary selectors must also provide definite tactile feedback, to provide indication of the selector's position when visual contact is a problem, such as when the vehicle is in motion and the driver cannot be distracted. Working from carefully derived ergonomics parameters, manufacturers define torque ranges for their selectors. Samples of the finished component will undergo testing as part of the quality control process. The test will obtain measurement of the torque required to rotate the selector, so the test device must emulate the human motions involved and capture an accurate picture of the selector's torque performance.

In this photo, a rotary selector (temperature dial) is undergoing torque testing on a Vortex torque tester.
The long pegs grip the switch’s housing securely to the lower platen, so that unwanted movement does not influence the torque reading. Accurate torque measurement is possible only if the switch's axis, the tester's drive shaft, and the transducer are in direct alignment. While the alignment of transducer and drive shaft are engineered into the design of the Vortex and are unchangeable, the switch's axis is potentially variable, especially if the switch's surrounding housing is irregular in form. The housing must be held level and stable throughout the test. The holding mechanism could be component-specific or adjustable. An adjustable mechanism, such as that shown here, is a more economical solution for manufacturers who have a range of components and require short setup times and easy, simple reconfiguration of the test device. The Vortex's adjustable pegs and mounting table allow components of various shapes to be held level and central so that correct axial alignment can be achieved.

The switch's selector bar is gripped by the upper set of pegs. These upper pegs (also adjustable for neat, secure gripping of the selector bar) are fixed to a static platen and hold the selector immobile while the component housing is revolved by the lower platen. Together, these platens, via their fixtures, apply to the rotary selector the pinching and twisting motions performed by the human user.

The upper, static platen is connected to the torque-sensing transducer. The transducer reads the torque experienced by the switch during the test and sends this to a display or computer, where it is reported in graph form for analysis and stored.

(Axial alignment of stalk-mounted rotary selectors can be difficult, but the adjustable holding mechanism fitted to this Vortex-xt provides an effective solution.)

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