Masayuki Nashiki

A new flux-barrier-type reluctance motor with a slit rotor

A reluctance motor, with a rotor which has many slits, is proposed. The slits are used to generate magnetic flux in the d-axis direction. In practice, the rotor, which has a fewer number of slits, is desired to increase productivity. With a fewer number of slits, torque ripple becomes large. Therefore, torque ripple reduction methods are also proposed. In simulations and experiments, rated torque of the proposed motor is 1.7/spl times/ as much as that of the conventional brushless DC motor with ferrite permanent magnets. The peak-to-peak (p-p) torque ripple is 1.5% p-p of the rated torque at the rated torque. The efficiency is 91% and the power factor is 61%, at the rated torque and 1200 min/sup -1/. The characteristics of the field weakening and the constant power control are also shown. The breakpoint frequency of speed controls is about 200 Hz. Therefore, the proposed reluctance motor is feasible for general applications.

Optical encoder using a slit-width-modulated grating

Abstract In this paper we propose a simple optical encoder using slit-width-modulated gratings. The distortion of the encoder signal (harmonic noise) is reduced by using the slit-width-modulated gratings to obtain a sinusoidal curve. The intensity of the light transmitted through the superimposed gratings was investigated by the Fresnel diffraction theory. The Fourier coefficient of the gratings was analysed in order to reduce the distortion of the encoder signal. For practical use, the slit width of the gratings was designed to reduce the third and fifth harmonics of the encoder signal. In the experiment, the slit-width-modulated gratings were fabricated by optical lithography. It was confirmed that the signal distortion was reduced and virtually independent of the air gap between the two gratings. Since the interpolation error is considerably suppressed, the proposed technique will be useful in precision machining.

Pitch-modulated phase grating and its application to displacement encoder

Abstract A binary phase grating with modulated pitch is investigated for a simple displacement encoder. The grating consists of a binary phase grating to eliminate the zeroth-order diffraction, and the pitch of the grating is modulated to compensate the higher harmonics of the encoder displacement signal. Therefore, an undistorted sinusoidal signal as a function of displacement is obtained by simply superimposing a conventional binary grating on the pitch-modulated phase gratings for any air gap between the gratings. The characteristics of the proposed gratings and the encoder signal are investigated by the Fresnel diffraction theory. The proposed grating has been fabricated lithographically, and the signal was examined experimentally. Considering these results, the proposed technique can suppress interpolation error and will be useful for an encoder in precision machining.

A Study on the Improvement of Motion Accuracy of Hexapod type Parallel Mechanism Machine Tool(1st Report). The method of Kinematic Calibration without Gravitation Deformation.

This paper describes a method to obtain the kinematic parameter for the hexapod machine tools by using telescoping ball bar device. This method deals with length error of struts, positional errors of base and platform joints as kinematic parameters. For finding a better set of ball bar measurement conditions, Fourier transformation is applied to explain error trace patterns of the circular test. Although it is difficult to identify all kinematic parameter errors with about fifteen circles of ball bar measurement, the machines motion error can be decreased to one sixth when this method is applied. However, in this report, the deformations of struts are not taken into consideration.

Compact optical encoder using modulated-pitch phase grating: suppression of harmonic noise and contrast change

In this paper, we investigate the combination of two gratings for a compact optical displacement encoder. The modulated pitch gratings are considered to obtain the sinusoidal signal as a function of displacement. In addition, the phase grating with the pitch modulation is examined to suppress the contrast change of the encoder signal as a function of the gap between the index and main scales. By these investigations, we find some combinations of gratings to satisfy the above requirements.

High precision and full digital servo system.

This paper reports new servo control technology to realize high precision and high speed machining of machine tool. The conventional analogue servo control technology, due to its generic errors such as non-linearity, offset (drift) and insufficient resolution, has its limitation in high precision and high speed machining. A full digital servo control method, a high resolution absolute position encoder and brushless servo motors have been developed and the high resolution of 0.1 μm and high speed machining of 56 m/min have been achieved.