GB2089604A - Rotary disc type magnetic encoder - Google Patents

Abstract

A rotary disc type magnetic encoder (10) is constituted by a rotary disc substrate and a magnetic medium (12) coated on one surface of the substrate. The magnetic medium (12) forms a plurality of concentric tracks adapted to store information bits. Each track includes a plurality of arcuate information sections (0, 1, 2, 3....) each storing one digit of a Gray decimal binary code, and at least one of the arcuate information segments is magnetized perpendicularly of the plane of the disc to store an information bit "1" or "0". According to this invention it is possible to prevent short circuited magnetic field distribution, and to increase the density of stored information. <IMAGE>

Description

SPECIFICATION Rotary disc type magnetic encoder This invention relates to a magnetic encoder, and more particularly a rotary disc type magnetic encoder.

When recording sounds with various types of audio or video devices a horizontal magnetizing system has been generally used in which the sounds are magnetically recorded on one surface of a magnetic medium in the form of a tape or disc.

Where an angular scale display board of a rotary magnetic encoder is prepared by using such a horizontal magnetizing system, a magnetic medium coated on one surface of a disc is parallelly magnetized such that adjacent portions will have opposite polarities. According to this method, a so-called floating display type rotary magnetic encoder is obtained, in which an angle is displayed by a difference between relative numbers of the scales without determining any specific reference point.

Where it is desired to obtain an absolute display type rotary encoder, displaying an amount of displacement from a given point, by using a similar magnetizing system, the magnetic medium coated on the disc is magnetizied such that concentric annulartracks correponding to respective digits or orders of magnitude will be formed. In this case, respective tracks are constituted by magnetized regions which are alternately magnetized in lateral opposite directions.

However, in the rotary encoder prepared in this manner, the most significant digit, that is a magnetized region located at a portion nearest the center of a circle of an address for displaying a rotational angle becomes substantially U shaped.

Accordingly, the magnetic lines of force concen trade to short-circuitthe opposite ends of the U shaped region, and near the magnetically neutral point at the central portion of that region, the intensity of the magnetic field is extremely weakened, whereby a magnetic sensor does not produce any output, thus causing erroneous counting. Even when the deformation of the regions is not so large, the angles subtended by the magnetized sectors increase toward the center of the circle, so that the magnetic lines of force would concentrate on a line interconnecting the opposite sectors on the side near the center, so as to pass through the minimum distance between two magnetic poles, so that it is impossible to produce uniform magnetic field.

Where the length of the outer periphery of a given magnetized region becomes largerthan the diamet rical dimension, the tendency of the erroneous counting becomes large that can not be neglected.

Accordingly, it is the principal object of this invention to provide an improved rotary disc type magnetic encoder.

Another object of this invention is to provide a novel rotary disc type magnetic encoder having annular information segments that do not form short-circuited magnetic field distribution causing an erroneous encoding.

Still another object of this invention is to provide a rotary disc type magnetic encoder that can increase the density of the stored informations.

A further object of this invention is to provide a rotary disc type magnetic encoder in which a magnetic medium on a disc can be readily magnetized according to predetermined codes.

Still further object of this invention is to provide a rotary disc type magnetic encoder capable of decreasing as far as possible erroneous encoding.

Yet another object of this invention is to provide an improved rotary disc type magnetic encoder capable of providing a desired magnetic flux distribution.

According to this invention, there is provided a rotary disc type magnetic encoder which comprises a rotary disc substrate, having on one surface thereof a coating of a magnetic medium forming a plurality of concentric tracks adapted to store information, each track including a plurality of arcuate information segments each adapted to store one digit of a Gray decimal binary code, wherein at least one of said arcuate information segments is magnetized perpendicularly to the plane of the disc to store an information bit "1 " or "0".

In the accompanying drawings: Fig. lisa plan view showing one embodiment of the rotary disc type magnetic encoder embodying the invention; Fig. 2 is an enlarged sectional view of a portion of the rotary disc type encoder shown in Fig. 1; Fig. 3 is a connection diagram showing one exslm- ple of a magnetic sensor utilized for the rotary disc type magnetic encoder shown in Figs. 1 and 2; and Figs. 4 and 5 are enlarged sectional view of portions of modified rotary disc type encoders embodying the invention.

A preferred embodiment of the rotary disc type magnetic encoder of this invention shown in Figs. 1 and 2 comprises a magnetic disc 10 utilizing a nonmagnetic rotary disc substrate 11 made of such nonmagnetic material as an aluminium alloy, or a 6-NYLON (trade name registered by Du Pont) type plastic. On the upper surface of the substrate 11 is coated a magnetic medium 12, for example a composite anisotropy medium composed of double layers of Fe-Ni and Cu - Cr alloy thin films, or a powder of r - Fe2O3 or s Fe - Co alloy. The rotary magnetic disc 10 constructed as above described is generally used in combination with a magnetic sensor 13 (see Fig. 3) made of a well known magnetoresistive element or the like.Thus,as the rotary disc 10 rotates, information bits "1" or "0" stored in a plurality of tracks located immediately' beneath the magnetic sensor 13 are read out and then encoded.

According to this invention, the magnetic medium 12 is magnetized in a direction perpendiculartothe surface of the disc as diagrammatically shown in Fig.

2, and the information bits "1" or "0" are stored according to the direction of magnetization. Since such perpendicular magnetization can reduce substantially to zero the distance necessary for inverting the direction of magnetization (that is the recording wavelength), it is possible to store the information at a high density, thus greatly improving the accuracy of encoding. With this method it is possible to pro vide magnetic field having a uniform intensity over the entire surface of respective magnetized regions on the main surface of the magnetic medium.

More particularly, when magnetized perpendicu larly with respectto the main surface of the magnetic medium 12 in a manner as above described, in each magnetized region, a magnetic path would be formed between the front surface (or rear surface) of the magnetic medium and the rear (or front) surface around the periphery of each magnetized region.

Accordingly, even when an information segment of each track on the main surface of each magnetized region takes the form of a U or an arcuate segment, the magnetic field does not concentrate to such a degree that causes short circuiting of both ends of that segment. Accordingly, when the magnetic sensor is moved along the surface of the magnetized disc 10, it is always possible to produce a constant voltage signal corresponding to the configuration of the segment of the magnetized region.

In this example, the magnetization in a direction from the front surface to the rear surface of the sheet of drawing corresponds to an information "1", whereas the magnetization in the opposite direction corresponds to an information "0".

This example is also characterized in that it utilizes Gray decimal binary codes as shown in the following table.

Table

&verbar; Decimal Gray decimal binary code 0 000000 1 000001 2 000011 3 000010 4 000110 5 001110 6 001010 7 001011 8 001001 9 001000 10 011000 11 011001 12 011011 13 011010 14 0 1111 0 15 010110 16 010010 17 010011 18 010001 19 010000 20 110000 21 110001 22 110011 23 110010 24 11 0 11 0 25 11111 0 26 111 0 1 0 27 111011 28 111001 29 111000 30 101000 31 101001 32 1 0 1 0 11 33 1 0 1 0 1 0 34 101110 35 100110 36 100010 37 100011 38 100001 39 100000 Although these codes are well known, these codes are charecterized in that adjacent codes are different by only one bit, so that they can be advantageously used for increasing the rate of magnetization thus correctly reading out the information by magnetizing perpendicularly. As can be noted from Fig. 1 the lower order bits are arranged in the outermost track, and as the tracks approach the center the orders of bits are shifted toward upper orders. For example, a decimal code "0"meansthatthe bit regions in all radial directions are "0", that is these regions are magnetized in a direction from the front surface to the rear surface of the sheet of drawing. On the other hand, a decimal code "1" means that the leastsignif- icant bit is "1", that is this bit is magnetized in a direction from the rear surface to the front surface of the sheet of drawing, and the other bits are the same as the bit regions of binary code "0". In the same manner, Gray decimal codes are arranged for respective decimal codes.

As above described when the magnetic medium is magnetized in the vertical direction, and where powders of r - Fe2O3 and Fe - Co alloys are used as the magnetic medium, although it is difficult to orient the magnetic medium in the lateral direction it is easy not only to orient it in the vertical direction but also to manufacture the disc.

As above described in the rotary disc type magnetic encoder embodying the invention, since a rotary magnetic disc magnetized perpendicularly is used, there is no fear of concentrating magnetic field art a portion of the main surfaces of respective magnetized regions as in the prior art horizontally magnetized disc, whereby magnetic field having substantially uniform intensity can be obtained over the entire surface irrespective of the configuration thereof.This readily enables an absolute value display which has been difficult, due to the occurrence of erroneous countings at higher order digits, Moreover, according to this invention, the information stored in the arcuate information segments in respective tracks is constituted by Gray decimal binary codes so that when the codes are arranged in the foregoing example, the code conversion between adjacent code regions is only one bit, so that it is possible to read out information from the rotary magnetic disc of this invention with a magnetic sensor without any error.

This characteristic is advantageous when the rotary disc type magnetic encoder of this invention is incorporated into a robot machine ora numerical control device.

Fig. 3 shows one example of a magnetic sensor utilized in combination with the rotary disc type magnetic encoder of this invention which comprises a pair of magnetoresistive elements 21 and 22 sen- ally connected across a source of supply E, a waveForm shaping circuit 23 connected to the junction between the resistors 21 and 22, and cascadeconnected amplifiers 24 and 25, which amplify the output of the waveform shaping circuit 23 to obtain an output. The magnetoresistive elements 21 and 23 are arranged to alternately detect magnetic field.

Although not shown, a plurality of magnetic sensors are provided for respective tracks on the magnetic disc 10. If necessary, the output in the form of Gray decimal binary codes are converted into normal binary codes by using well known exclusive-OR logic gates.

Where it is difficu It to obtain positive and negative signals according to the type of the polarity when the main surfaces of the perpendicularly magnetized regions are scanned, it is preferabie to construct the tracks by alternately disposing perpendicularly magnetized regions and non-magnetized regions so as to make the presence and absence of the magnetic field correspond to "1" and "0".

Figs. 4 and 5 illustrate examples of such a construction. Thus, Fig. 4 shows a case wherein all magnetized regions 31,32 and 33 are magnetized in the same direction and wherein non-magnetized regions 34,35 and 36 are disposed alternately with the magnetized regions. Fig. 5 shows a case wherein magnetized regions 41,42 and 43 and nonmagnetized regions 45,46 and 47 are disposed alternately, and alternately magnetized regions 41, 42 and 43 are magnetized on opposite and parallel directions. The widths of the horizontal regions may be varied as desired.

While in the foregoing embodiments, all magnetic tracks corresponding to respective orders of magnitude were constituted by perpendicularly magnetized regions, it should be understood that the invention is not limited to such specific construction. It is possible to constitute only the tracks located near the center of a circle, where the intensity of magnetic field becomes nonuniform to an extent at which the possibility of erroneous counting becomes significant, by perpendicularly magnetized regions, and to constitute other regions by horizontally magnetized regions.

Claims (7)

1. A rotary disc type magnetic encoder which comprises a rotary disc substrate having on one surface thereof a coating of a magnetic medium forming a plurality of concentric tracks adapted to store information, each track including a purality of arcuate information segments each adapted to store one digit of a Gray decimal binary code, wherein at least one of said arcuate information segments is magnetized perpendicularly to the plane of the disc to store an information bit "1" or "0".

2. An encoder as claimed in Claim 1 wherein the information bits "1 " and "0" stored in said arcuate information segments are constituted by regions magnetized in opposite and parallel directions.

3. An encoder as claimed in Claim 2 wherein said regions magnetized in opposite and parallel directions are disposed alternately.

4. An encoder as claimed in Claim 1 wherein one of the infs. n mation bits "1 " ond "0" stored in said arnua' information segments is constituted by a region magnetized perpendicularly to the plane of the disc while the other informtion bit is constituted by a non-magnetized region.

5. An encoder as claimed in Claim 4 wherein said magnetized regions and non-magnetized regions are alternately disposed.

6. An encoder as claimed in Claim 1 wherein one of the information bits "1 " and "0" stored in said arcuate information segments is constituted by a pair of regions magnetized in opposite and parallel directions, and the other information bit is constituted by non-magnetized regions.

7. An encoder as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying Drawings.