In a closed-loop system, a load is driven by a motor, and an encoder measures the position of the load. There is no shortage of encoder options including magnetic encoders, capacitive encoders, resolvers, and optical encoders. However, there are key performance requirements that optical encoder deliver compared to other encoder options. In many applications, encoders need to provide very high resolution and accuracy with low power consumption from the overall system. While transmissive encoders are most common in the industry due to accessibility, optical encoders offer the highest resolution and accuracy.
This video presentation covers key concepts of interferential optical encoders including coherent light, wave interference, and diffraction gratings. Leading to the explanation of talbot imaging in optical encoders.
Talbot imaging allows for very simple construction – a laser light source, grating, and sensor – making it a low cost, low power consumption, lightweight option for closed-loop systems. The talbot image is essentially a replica of the grating created through the interference of higher order diffractions, therefore the sensors detect an approximate square wave. To achieve a pure sinewave that is needed to interpolate the signal, the talbot image is filtered through geometric sensors and propagation filtering. This sine wave is then used to interpolate the signal and reach very high resolution.