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rotary encoders for robotics

Robotics: Must-know benefits of inductive rotary encoders

By measuring joint rotation, rotary encoders ensure that a robot’s arm and tool center point are where they need to be. These measuring devices come in an assortment of sizes and scanning technologies. Although optical scanning is currently in vogue, inductive scanning technology offers many benefits that designers and product managers ought to consider.

Inductive scanning

Inductive scanning technology uses copper-nickel graduation structures applied to a PCB carrier material. Receiver coils evenly distributed around the encoder generate signals that provide the absolute position value. These high-frequency signals induced by the graduation structures are modulated in their amplitude and phase position. Absolute position information is instantly available upon power-up, thereby making reference runs unnecessary.

Inductive rotary encoders are available in both singleturn and multiturn variants. Multiturn versions can measure angles greater than ±180° as well as count the number of revolutions. The benefits of inductive rotary encoders include their easy mounting and high immunity to environmental factors.

HEIDENHAIN receiver transmitter encoders

Figure 1: View of the stator with the coils of the scanning unit (on the left) and the rotor with its shielding surface of the circular scale (on the right)

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Axial mounting tolerances

A benefit of inductive rotary encoders is their relatively wide mounting tolerances. Once mounted, HEIDENHAIN rotary encoders have an axial tolerance of ±0.4 mm on the motor shaft and ±0.3 mm on the output shaft. The nominal gap is 1.0 mm.

What’s more, inductive rotary encoders do not require unique pairing between a specific scanning unit and a specific circular scale. Every scanning unit has been calibrated to a reference circular scale and can therefore be used with any rotor of the same type. This is technologically possible thanks to the wide mounting tolerances.

Mechanical loading

The wide tolerance for the scanning gap also mitigates the effect of eccentricity that may arise from load-induced shaft deformation. Thermal expansion, which occurs during continuous operation and under extreme environmental conditions, has a negligible effect. Full-disk inductive scanning is resilient to rotor wobble. Built-in encoder electronics can also compensate for any mounting inaccuracy between the rotor and the scanning unit.

Figure 2: The rotor’s shielding surface passes over the windings of the receiver coil, where a high-frequency signal is induced that modulates a sine or cosine signal.

Noise immunity

Finally, the inductive scanning principle is largely immune to magnetic fields, which are found in some specialized production environments. Inductive rotary encoders also have large function reserves for handling contamination such as oil vapors, high humidity and motor brake dust, delivering a clear advantage over optical rotary encoders with an LED and photosensor.

Summary

Rotary encoders are a key factor in achieving high repeatable positioning accuracy. Because robots typically contain multiple rotary encoders, the benefits of the chosen encoder design have a cumulative effect.

Rotary encoders with inductive full-disk scanning, such as the HEIDENHAIN KBI and KCI series, feature wide mounting tolerances that can simplify robot design and reduce assembly costs. Their resilience to mechanical loading, extreme environments and particulate contamination ensures high reliability.

We are happy to provide more information about our encoders, as well as advise you regarding your specific application. Please get in touch!

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DR. JOHANNES HEIDENHAIN GmbH develops and produces linear encoders, angle encoders, rotary encoders and CNC controls for demanding positioning tasks. Rounding out its product portfolio are touch probes, camera systems, length gauges, digital readouts, signal converters, testing devices and inspection devices. What’s more, its practical software solutions for the Digital Shop Floor empower end users to fully digitalize their manufacturing ecosystem.

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