Feature: Sensors


ASIC-underpinned position


sensors for robots By Dr Mike Coulson, Analogue Design Manager, Swindon Silicon Systems


I


n 2020, the International Federation of Robotics calculated that three million industrial robots were operating in factories around the world. Each of these robots relies on numerous


position sensors, which in turn depend on sophisticated application-specific integrated circuits, or ASICs. “Position sensor” is a broad term


covering a range of technologies. Here we will consider sensors that measure rotation and linear displacement. For example, a rotary encoder might measure the angle of a robotic arm


16 April 2022 www.electronicsworld.co.uk


joint, whilst a linear encoder might report the position of a cartesian robot along a particular axis. A cartesian robot has three principal axes of control that are linear and at right angles to each other. In each case, an encoder moves across a precisely-manufactured scale, often graduated with sophisticated ‘redundant’ patterns.


Position sensor electronics The encoder includes a sensing element that converts a physical stimulus into a weak electronic signal. In an inductive encoder, his is a coil detecting a


changing magnetic environment – say, a slotted ferrous metal scale. In an optical encoder the sensing element may be a phototransistor. Each type features an excitation circuit to create the stimulus, and a signal-conditioning circuit to amplify the weak electrical response. Most encoders then digitise the signal using an analogue-to-digital converter (ADC), with its output then passed on to a processing unit such as a CPU or microcontroller that decides what to do with the signal. This CPU then calculates the position from the scale encoding, before serialising the


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