Wiper mechanism for rotary miniature variable resistor or capacitor - has toothed wheel of deformable metal turned by worm gear which cannot be overtightened

摘要

The resistor is a conducting track on an insulating substrate. A central, common electrode leads to a printed circuit pad. The moving wiper contact is attached to a rotor with a toothed wheel. The teeth of the wheel mesh in the helical thread of a worm gear. The toothed wheel is made of an elastically deformable metal such as steel or phosphor-bronze. The rotor has a radial notch which constitutes a stop-block when it comes into contact with a fixed block. When the thread is turned (using a screwdriver) the wheel and rotor turn until the two blocks meet. The position of the radial block is such that, when it comes into contact with the fixed block, the last tooth on the wheel is in the thread groove on the gear. Further turning force results in the tooth being forced out of the groove and the wheel and rotor are prevented from turning further without increased restraining force.