February 2021

39 www.drivesncontrols.com February 2021 are insensitive to temperature and have a low sensitivity to external fields. As an encoder rotates, it generates two square-wave outputs (A and B) that are usually 90 degrees out-of-phase with each other. By measuring the phase shift of the A and B outputs, the encoder’s direction can be determined. To measure distance of travel or speed, the encoder’s resolution must also be taken into account. Resolution is the number of points of measurement within a 360-degree revolution of the shaft, also known as the duty cycle or period. Generally, the greater the number of points – measured as lines per revolution (LPR) or pulses per revolution (PPR) – the greater the accuracy. Magnetic encoders typically have up to 1,024 LPR. Each output switches between high and low values. The two bits of information thus create four times the number of counts for each line or pulse. This is known as quadrature decoding and can increase resolution by up to four times – for example, turning 512 lines into 2,048 counts or angular steps. In addition to the A and B output channels, a third channel (Z) is sometimes included and is used to determine the reference position. Encoders are crucial for many applications. Taking our original example of insulin administration, drug delivery systems need to dispense precise amounts of medication at specified rates. Encoders can confirm that the exact dose is delivered. This example shows how more lines for increased encoder resolution can help ensure precision. Gripping Another application where encoders can play a vital role is robotic grippers, which need to be able to handle delicate components. It is essential that the right amounts of pressure and speed are applied avoid damaging the components. Encoders allow a gripper’s operation to be optimised by controlling the speed and position of its motor, depending on the component it is handling. Similarly, pick-and-place systems used to assemble electronic equipment need high- speed motion control to detect the size and weight of components quickly and repeatedly, and to place them precisely. Encoders enable the high-speed, high- accuracy control needed to achieve manufacturing quality and productivity. n SENSORS AND ENCODERS n Optical encoders such as Portescap’s E9 can achieve accurate, precise positioning, and are unaffected by magnetic interference. Contact us at Drives & Controls Damien Oxlee 01732 370342 damien.oxlee@dfamedia.co.uk Andy Wylie 01732 370341 andy.wylie@dfamedia.co.uk IF YOU’RE READING THIS, THEN SO ARE 60,000+ ENGINEERS. IMAGINE THE IMPACT YOUR ADVERTISEMENT COULD HAVE.