Coded data generation or conversion – Digital pattern reading type converter – Magnetic – inductive or capacitive
Patent
1990-04-19
1992-05-19
Williams, Howard L.
Coded data generation or conversion
Digital pattern reading type converter
Magnetic, inductive or capacitive
341 8, 34087031, H03M 122, G01D 518
Patent
active
051152398
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
This application may be related to International Application PCT/JP89/00506.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic-type absolute position encoder and, more particularly, to a magnetic-type absolute position encoder capable of detecting, as an absolute position, the rotational position, etc., of a rotary shaft of a motor or the like driving a machine tool.
2. Description of Related Art
Many encoders of optical-type have been proposed as absolute position encoders (for example, see International Application PCT/JP89/00506). An optical absolute position encoder of this kind has a rotary coding disk and a fixed coding disk, with the rotary coding disk being formed so as to obtain sinusoidal and cosinusoidal outputs the numbers of cycles per revolution of which differ from one another in each of a plurality of channels. The sinusoidal and cosinusoidal outputs in each channel enter respective A/D converters and are converted into digital data in order to successively generate information (angle information) indicative of the angular position of the rotary coding disk. Thereafter, the digital data obtained by A/D-converting the sinusoidal and cosinusoidal outputs in each channel are combined channel by channel and the result is used as address information of a ROM storing position information. A predetermined number of items of position information are interpolated in one wavelength of each channel. It is assumed that the number of channels is four, that one, 16, 256 and 4096 cycles of the sinusoidal and cosinusoidal outputs are generated per revolution in each channel, and that 2.sup.4 items of position information are interpolated in one wavelength of each channel, in which case the foregoing absolute position encoder is capable of detecting absolute position at a resolution of 360.degree./2.sup.16.
A magnetic-type absolute position encoder has not been employed in the prior art. The reason will now be explained. FIG. 6 is a diagram showing the construction of a magnetic rotation sensor (MR sensor), in which numeral 61 denotes a magnetic drum. The drum is provided with a magnetic material 62 forming a number of small poles. Numeral 63 denotes a magnetic reluctance element disposed in close proximity to the magnetic drum 61 to sense the magnetic flux of the magnetic material 62.
The magnetic drum 61 consists of a non-magnetic cylinder with a diameter of 50 mm having a magnetic paint baked onto its side face, and the magnetic paint is magnetized to have a number of poles having a pitch of amount 120 .mu.m. The magnetic reluctance element 63 comprises a magnetic reluctance element main body consisting of a permalloy thin-film pattern formed on glass, and a wiring pattern for forming a magnetic circuit. The shape and dimensions of the pattern on the main body correspond to the magnetization pattern on the drum. Thus an output signal in accordance with the amount of rotation of the drum can be obtained.
The operating principle of the magnetic rotation sensor will be described with reference to FIG. 7. The characteristic of the magnetic reluctance element 63 is such that an electrical resistance value R, which prevails when a current is passed through the pattern in the longitudinal direction thereof, decreases when a magnetic field H orthogonal to the pattern is present. Accordingly, when the pattern of the magnetic reluctance element 63 is disposed to correspond to the magnetization pattern of the drum, or in other words, when magnetic reluctance elements 63a, 63b are disposed so as to be out of phase by .lambda./4 (where .lambda. is the magnetized pattern pitch), as shown in FIG. 7(a), the resistance values of the magnetic reluctance elements 63a, 63b become smaller in alternating fashion in accordance with the movement of the magnetization pattern. In the state shown in FIG. 7(a), the resistance value of the magnetic reluctance element 63a becomes smaller and that of the magnetic reluctance element 63b becomes larger.
REFERENCES:
patent: 2926335 (1960-02-01), Bower
patent: 3553466 (1971-01-01), Johnston
patent: 4628298 (1986-12-01), Hafle et al.
patent: 4764767 (1988-08-01), Ichikawa et al.
patent: 4882536 (1989-11-01), Meyer
patent: 4951048 (1990-08-01), Ichikawa et al.
Fanuc Ltd.
Williams Howard L.
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