Keywords: magnetic rotary encoder, FEM and servo motorServomotors used in semiconductor manufacturing equipment and in ultra-precise machining applications are required to be very small with fast and precise controllability. The sensors for detecting rotational speed and position hence need to be very small and have high resolution. In many applications, the absolute type sensors are preferred over the incremental type. Rotary encoders are mainly classified as optical and magnetic types that use magneto-resistive (MR) devices. Optical encoders comprise of light emitting diodes (LED), photo diodes (PD) and a rotary disc with slits. Slits are precisely formed using semiconductor process technology. Hence, in general, optical encoders have high resolution. However, in smaller than 10 mm size, the resolution becomes unfavorable due to the limitations imposed by the slit width and the size of LED and PD.A new magnetic rotary encoder is proposed that addresses these problems. Fig. 1. shows a perspective view of the proposed magnetic rotary encoder for detecting the absolute position of a rotating body. It consists of a disc magnet magnetized in one direction with all its magnetic domain aligned parallel to each other, hall effect devices in the air gap, and a fixed body formed by a ring-shaped magnetically soft material. The accuracy of the encoder depends on the distortion of pseudosinusoidal output waveform from the hall sensors. Therefore, for achieving high accuracy the distortion of the output waveform should be minimal. To obtain an encoder with high accuracy, a study of the parameters that influence the shape and material of an encoder head was carred out using FEM analysis.An encoder based on the proposed method having a width of 10 mm, a height of 10 mm, and a depth of 3 mm was developed. The photograph of a disassembled rotary magnetic encoder is shown in Fig. 2. The output waveforms of phase A and B are shown in Fig.3. Significantly improved sinusoidal waveforms with distortion levels less than 0.6% of the fundamental was achieved. The prototype encoder has a high resolution of 4,096 ppr and is capable of detecting absolute angular position. The construction is very simple, resulting in a highly reliable encoder from vibration and operating temperature points of view. Non-memberKoji Uemura * * Non-memberIkuma Murokita * Non-memberMotomichi Ohto * Member A new type of a magnetic rotary encoder for servomotors is proposed. A salient feature of the proposed encoder is its small size, high resolution, and simple construction. An encoder based on the proposed method having a width of 10 mm, a height of 10 mm, and a depth of 3 mm was developed and is reported here. In addition, the developed encoder has a high resolution of 4096 ppr and is capable of detecting absolute angular position. The proposed encoder comprises of a disc magnet magnetized in one direction with all the magnetic domains in the material parallel to each other, a stationary body made up of a magnetically soft material, and four Hall effect dev...
Keywords-Shearing force sensor; displacement sensor; friction; robot hand; optical sensor.I.
In this paper, we propose a torque measurement device embedded in robot arms. The device uses an integrated microdisplacement sensor and trapezoidal frame. The sensor tip of 3 mm area and 0.7 mm thickness measures the mirror tilt angle on the underside of the frame caused by a torque applied to the frame. We have successfully measured a linear output change for the torque and found that the gradient of the output change differed largely from the material and the corner angle of the frame.
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