23 Jul 2024


Tech combines the best of optical and magnetic encoders

Nidec says that its AC servomotor fitted with the Zignear position-sensing technology performs with a similar accuracy to a conventional 17-bit AC servomotor.

Nidec has developed a technology for detecting the position of motor rotors that, it claims, combines the high accuracy of optical encoders with the low costs and component counts of magnetic encoders.

Nidec and its Nidec Sankyo subsidiary have incorporated the patented technology into an AC servomotor that has a resolution of 17 bits, and a maximum accuracy of better than ±0.02 degrees. The motor is aimed, in particular, at applications requiring high precision and responsive controls, such as industrial robots and AGVs (automated guided vehicles).

Brushless DC motors have traditionally needed encoders because it has been difficult to detect their rotor positions accurately due to inconsistencies in the mounting and sensitivity of magnetic sensors – especially Hall sensors. Nidec has developed an algorithm that corrects these inconsistencies, improving the position-detection accuracy using general-purpose microcomputers.

Conventional optical and magnetic encoders have strengths and weaknesses:
• Despite optical encoders’ high accuracy and their ability to operate in strong magnetic fields, they can be expensive because of their installation costs and need for code wheels and other components. Also, their performance can deteriorate in adverse environments where dust or oil are present.
Magnetic encoders can operate reliably is such environments and are cost-competitive because they work with a relatively inexpensive chips, but their accuracy is lower than that of optical devices.

Like magnetic encoders, Nidec’s new Zignear sensors need few components – only a Hall-effect device and a general-purpose microcomputer. They detect rotor positions using a magnet attached to the motor in combination with software. Their tracking capabilities are said to be similar to those of optical encoders. In tests, the technology is said to have achieved position accuracies of better than ±0.1 degrees in temperatures from –40 to +125℃.

The sensors have the same ring shape as a magnetic encoder, making replacements easy. They have an outer diameter of about 30mm and are about 2mm thick. They can output ABZ pulses, like optical encoders, as well as serial data, voltage and PWM signals, which are common with magnetic encoders.

Nidec says that it has demonstrated that an AC servomotor equipped with the Zignear technology can power an AGV with a similar accuracy to a conventional 17-bit AC servomotor.

It has also tested a stepper motor equipped with Zignear in a sewing machine application where the motor has to feed cloth using repeated high-speed forward and reverse rotations. The company says the sewing machine operated normally and demonstrated a high-speed response.

Nidec is planning to test the technology in other applications such as industrial robots and power tools.

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