The fundamental operating principle of the capacitive encoder is capacitive modulation between two dielectric plates based on their relative position. Variations in capacitance are detected by transmitting a high-frequency reference signal from a stationary dielectric and detecting the modulated signal at the receiver using sinusoidal patterns.
The following image illustrates the principle of operation as implemented in the FREE™ technology platform. The different KappaSense encoder products use the same principle in different ways. (see also: Micro Linear Encoder)
The scale is a printed circuit board (PCB) on which a periodic field pattern is printed. A high-frequency phase shifted reference signal is generated through this pattern.
The readhead is a printed circuit board on which conductive sinusoidal patterns are printed.
During operation, the scale transmits a periodic, high-frequency, carrier signal. The readhead moving relative to the scale creates a variable capacitor whose capacitance changes with relative position of the readhead to the scale, and the sinusoidal pattern on the readhead modulates the high-frequency signal of the transmitter in a predictable way. The position of the readhead relative to the scale can thus be calculated. KappaSense use proprietary algorithms implemented in standard electronic components. (see also: FREE™ Cable-less encoder)
The readhead location relative to the scale dictates the capacitance and therefore the signal amplitude and modulation. The relative position between the readhead and the scale can therefore be calculated.
Absolute position calculation is enabled by adding a lower resolution sinusoidal pattern on the readhead PCB. The high-frequency signal of the transmitter is thus modulated by two different sinusoidal patterns on the readhead.
See also: Capacitive Encoders