MOTION SYSTEM APPLICATIONS
New encoders wrap around axes MYRIAD
features have been added to all rotary-encoder subtypes in recent years. These rotary encoders include those that output incremental or absolute signals to provide feedback on position and speed. Incremental signals are trains of high and low waves indicating movement but not specific position. In contrast, absolute encoders do indicate position of the rotary axis being tracked along with movement. Mechanical encoders are actually more like rotary switches but with a digital output. They are common in consumer products for knob tracking and in medical and fitness equipment and avionics. Resolution is defined in terms of angle of throw — for a number of positions — such as 30 positions for a 360° turn for example. Rotary encoders for true motion-control applications include capacitive encoders employing low current. These are an efficient option using a high-frequency transmitter that sends signals intermittently modulated by an etched disc before they get to a receiver. That receiver reads the capacitance variations and an ASIC translates them into angular values with resolution to forty ninety-six steps per revolution. The most common rotary encoders today though are optical encoders. Early versions had fragile glass discs between a light source and sensing head. Increasingly common today are more rugged versions. The disc can be etched metal, marked tempered glass, or engineered plastic.
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Sp Robotics demand very high levels of repeatability — even down to 0.1 mm in some cases. POSITAL FRABA hollow-shaft encoders can deliver this performance on six-axis articulated (SCARA) industrial robots and cobots. They have center bores of 30 or 50 mm (to route cables and media hoses) and are 17.8 mm thick with an O.D. of 80 mm and weight of only 110 g.
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DESIGN WORLD — MOTION
11 • 2020
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