PRECISION ENGINEERING AND MOTION CONTROL n adding a rotary encoder – also known as a shaft encoder – which converts the angular position of the shaft to analogue or digital output signals. Such encoders are the most common option for adding feedback to SMLAs. Fig 2 shows how adding an encoder to an SMLA can provide feedback to the controller and share important motion data such as position, speed or direction. Encoder choices There are two main types of rotary encoder: incremental and absolute (Fig 3). The former use a rotating disk connected to a shaft and positioned between a light source and a photo sensor. Multiple slits arranged around the perimeter of the disk allow light to pass to the sensor in patterns of pulses representing motion characteristics. For applications requiring more detailed motion data or an added level of protection if power is lost, an absolute encoder offers benefits. Like incremental encoders, absolute devices are centremounted to spin with the motor shaft between a light source and a photo sensor. But, instead of using uniformly arranged slits, absolute encoders use an intricate arrangement of unique openings over a much larger disk area. These interrupt the light signals in patterns that a detector chip can read as higher-fidelity representations of every angular position of the stroke – even without a homing device. Encoders can be integrated with all three types of SMLA. The encoder body simply has to be bolted onto a flat surface, and the optical disk mounted on a shaft, which must be an extension of the original motor shaft so that the disk can rotate with it to capture the motor’s motion accurately. While open-loop SMLA systems are suitable for many applications, users wanting real-time feedback on load position should consider adding encoders to their stepper motors. They can provide position feedback, real-time data on speed, direction and other characteristics, while improving control and monitoring of the load. For basic positioning feedback, you should specify incremental encoders, but if high precision is required, or the ability to maintain position once the equipment is powered on, you should consider absolute encoders. n Fig 2: Adding an encoder to an SMLA can provide feedback to the controller Fig 3: Key elements of incremental (left) and absolute encoders (right) products and solut We specialise in p ncod tions for oviding e r & se n s o r s - g ea rboxes - ders servo &stepper drive automating - couplings - a c t u a t o r s - supe s & motors - motion control & your world since 1985 ps er metering pum & HMIs Motor Technolog your specific ne products and solu T. +44 (0)161 2 gy td. eeds. ions for L t E. info@m 2177100 www.m motec.co.uk motec.co.uk Fig 1: An automated pipetting machine using an encoder on its horizontal axis.
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