Capacitive-Type Flexible Linear Encoder With Untethered Slider Using Electrostatic Induction

A novel capacitive linear encoder characterized by its untethered slider is presented. The main components are made of flexible printed circuit films measuring 0.2 mm in thickness that allows the sensor to be set up in thin interspaces or on curved surfaces. The sensor consists of a long receiver film and a short transmitter film, respectively containing four-phase and two-phase electrodes; the transmitter is used as a slider and the receiver as a stator. To realize an untethered slider, the sensor employs a unique approach; electric power is supplied to the transmitter film by electrostatic induction, which removes electric wires from the slider. This untethered slider can facilitate sensitive applications where a mechanical disturbance caused by an electric wire can be a problem. The principle was verified using a prototype encoder, which showed an error of ± 4 ¿ m.