Motor rotation information such as position, speed, and direction must be highly accurate in order to control precise drivers and mechanisms across a wide variety of emerging applications—for example, in pick-and-place machines that mount microscopic components in the limited PCB area. The challenge for designers is to meet the high accuracy requirement of the position feedback sensor in a high-speed application, while at the same time infusing all components into the limited PCB space to be fit inside tiny enclosures, such as a robotic arm.
There are a few components of a motor control feedback system that must work in concert in order to achieve optimal performance. The motor control loops are composed of a motor, a controller, and a position-feedback interface. One of the most precise position sensors is the optical encoder. An optical encoder is composed of an LED light source, a marked disc attached to the motor shaft, and a photodetector. As the shaft and disc rotate, light from the LED is either refracted or passed through the disc, resulting in the photodetector producing small sine or cosine signals. These signals are then passed through an amplifier such as the ADA4940-2, then through an analog to digital converter such as the AD7380, both from Analog Devices. Afterward, the signal can be processed by the main control computer.
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