JPH04351914A - Linear magnetic encoder - Google Patents

Abstract

PURPOSE:To enhance the reliability and life of a linear magnetic encoder by using a thin film containing barium ferrite magnetic powder in a magnetic field generating medium within a linear scale. CONSTITUTION:A linear scale 6 is provided with a thin film 3 formed on a scale substrate 2 made of metals or plastics in such a way that barrium ferrite magnetic powders are dispersed in an epoxy resin. By applying external magnetic field in the thin film 3, magnetization is performed so that magnetic poles, having predetermined pitches in the longitudinal direction, are formed. Then a stable magnetization pattern can be realized by selecting the coersive force of the magnetic thin film 3 in the range from 400Oe to 4000Oe. Since the surface of the magnetized thin film 3 generates stray magnetic field, a needle position detecting signal is obtained by detecting it with a magnetic sensor 1 mounted opposite to the thin film 3. Since the magnetic sensor 1 is not influenced by the effects of oil, moisture, and dust, its reliability can be enhanced and its life can be lengthened.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear magnetic encoder used for positioning a movable element of a linear motor that moves linearly.

0002

[Prior Art] A linear motor is constructed by providing a coil on a movable element that moves linearly along a guide rail, and placing a permanent magnet along the rail, making use of the magnetic interaction between the two. be done. At this time, an optical encoder was used to position the mover and detect the position of the magnet that became the stator (U.S. Patent 41514
47).

0003

[Problems to be Solved by the Invention] When the optical encoder described above is used in an environment with a lot of dust, oil vapor, or moisture, the light emitting part of the encoder may be covered with the dust, oil vapor, or moisture.
Furthermore, since the surface of the linear scale that transmits or reflects light becomes cloudy, there is a drawback that the position detection signal from the encoder is not output. An object of the present invention is to provide a linear encoder that can output stable position detection signals even in such an environment with a lot of dust, oil, and moisture.

0004

[Means for Solving the Problems] According to the present invention, a linear scale, which is a component of a linear encoder, is formed of a scale base and a magnetic film, and a detection head is formed of a magnetic sensor consisting of a Hall element or a magnetoresistive element. This is a linear magnetic encoder featuring: A linear scale is constructed by forming a thin film of barium ferrite magnetic powder dispersed in an epoxy resin on a scale base made of metal or plastic. By applying a magnetic field to this thin film from the outside, it is magnetized and magnetic poles having a predetermined pitch in the longitudinal direction are formed. At this time, by setting the coercive force of this magnetic thin film between 400 Oe and 4000 Oe, a stable magnetization pattern can be obtained. A stray magnetic field is generated from the surface of the magnetized thin film, and is detected by a magnetic sensor placed opposite the thin film to obtain a movable element position detection signal. At this time, the magnetic sensor serving as the detection head is fixed to one of the movable element or the stator, and the linear scale provided with a thin film is fixed to the other.

[0005]

Embodiment FIG. 1 shows an embodiment of the present invention. The linear magnetic encoder is composed of a linear scale 6 and a detection head 20. The detection head 20 consists of a magnetic sensor 1 such as a Hall element or a magnetoresistive element and a necessary signal extraction terminal 7, and if necessary, a signal processing circuit for obtaining a digital signal may be provided in the section 7. The linear scale 6 consists of depositing a thin film 3 with a thickness in the range of 1 μm to 500 μm using a mixture of epoxy resin and barium ferrite on a scale base 2 made of metal, plastic, or ceramics. Consisted of. This thin film is magnetized according to the type of output signal necessary for the linear magnetic encoder, and magnetized tracks 4 and 5 are formed. Track 4 is an incremental track in which north poles and south poles are alternately magnetized at a predetermined pitch between 5 μm and 5 mm. Track 5 is an index track, and one or more N-S pole pairs are provided in each track at prespecified positions for the purpose of serving as an origin or a signal detection starting point. Note that, if necessary, an absolute track, which is a third track, may be provided in parallel with these tracks. The incremental or index magnetization pitch is determined in accordance with the positioning resolution of the output signal of the linear magnetic encoder. The coercive force of the thin film 3 containing barium ferrite magnetic powder is limited to a certain predetermined value within the range of 400 Oe to 4000 Oe. This means that the coercive force of the thin film is 400 Oe.
In the following cases, the recorded magnetization on the track after magnetization will be easily destroyed by the noise magnetic field from the outside, while on the other hand, in the case of a coercive force exceeding 4000 Oe, it will not be possible to magnetize at a predetermined pitch. This is because it is impossible. This relationship is shown in FIG. FIG. 2 shows FIG. 1 from the side. The linear scale 6 does not come into contact with the magnetic sensor 1 and is installed so as to move relative to the detection head while always maintaining a constant distance. With this method, there is no mechanically worn part between the head and the scale, resulting in a long life. Furthermore, in a linear magnetic encoder, a highly reliable and stable signal output can be obtained because the magnetic field is not affected by an atmosphere containing a lot of oil or moisture. In FIG. 2, the orientation of barium ferrite is not shown in detail. However, barium ferrite magnetic powder has a hexagonal plate shape, and the axis of easy magnetization is perpendicular to its surface. Therefore, by aligning this axis of easy magnetization with the direction perpendicular to the surface of the thin film of the scale substrate, the magnetic field can be reduced. Since it can be emitted farther from the scale surface, the voids 21 can be increased compared to a thin film without such orientation. In FIG. 2, the width of the scale is shorter than the length of the sensor element 1 in order to avoid contact between the linear scale 6 and the solder terminal part 8 for signal extraction of the magnetic sensor 1. It is also possible to provide a step in the portion facing the solder terminal portion 8. FIG. 3 shows an embodiment in which a signal processing circuit for converting an analog output into a digital signal is provided behind the magnetic sensor 1. A circuit board 10 is provided inside the signal processing circuit storage section 9,
The structure is such that the final output after being converted into a digital signal is taken out to the outside via the connection connector 12. FIG. 5 shows an example in which a linear magnetic encoder is attached to a linear motor. Mover 1 on linear guide 17
3 is provided with a moving coil 14, and moves back and forth as a unit. At this time, the magnetic sensor 1 is attached to the side of the mover 13.
is attached, and a linear scale 6 is provided opposite to this together with a thin film containing variferrite. In this example, the signal processing circuit 10 is not provided behind the magnetic sensor, but is provided on the upper surface of the mover, and both are connected by a cable 7. FIG. 6 shows another embodiment of the present invention, in which a part of the linear motor body is also used as a linear scale base by forming a thin film containing barium ferrite on the side surface of the fixing yoke 15 of the linear motor. be. In this case, the magnetic sensor 1 and the signal processing circuit 10
is provided on the movable element 13. In FIG. 6, since there is no need to provide a base for the linear scale outside the motor, the entire linear motor can be further downsized.

[0006]

Effects of the Invention According to the present invention, the reliability of the linear encoder, which was insufficient in the past, can be improved by improving the reliability of the magnetic sensor.
This is greatly improved since it is not affected by dust, and the lifespan of the linear encoder can be extended. Further, when a linear magnetic encoder is used, it is possible to have a structure in which the linear scale and the movable element or the movable element part of the linear motor are used together, so that the linear magnetic encoder and the linear motor can be significantly miniaturized.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a linear magnetic encoder according to the present invention.

FIG. 2 is a side view of FIG. 1;

FIG. 3 is a side view showing another embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between coercive force and magnetization pitch of a thin film according to the present invention.

FIG. 5 is a diagram showing an embodiment of the linear magnetic encoder of the present invention attached to a linear motor.

FIG. 6 is a diagram showing an embodiment of the linear magnetic encoder of the present invention attached to a linear motor.

[Explanation of symbols]

1 Magnetic sensor 2 Scale base 3 Magnetic thin film 4 Incremental track 5 Index track 6 Linear scale 7 Cable 8 Solder terminal 9 Circuit storage section 10 Circuit board 11 Circuit parts 12 Connector for connection 13 Mover 14 Mover coil 15 York 16 Linear scale support part 17 Linear guide 18 Stator magnet 19 Base 20 Detection head 21 Voids

Claims (4)

[Claims] Claim 1: A scale base for a linear scale;
A linear magnetic encoder used for detecting the position of a mover of a linear motor that is equipped with a medium that generates a magnetic field within a linear scale, characterized in that the medium that generates a magnetic field within the linear scale has a thin film containing barium ferrite magnetic powder. linear magnetic encoder. 2. The linear magnetic encoder according to claim 1, further comprising a linear scale made of a thin film containing magnetic powder such that the barium ferrite magnetic powder has a coercive force in the range of 400 Oe to 4000 Oe. linear magnetic encoder. 3. Mixing the magnetic powder according to claim 1 or 2 with an epoxy resin, forming a thin film magnetic recording medium on a scale substrate using the same, and then magnetizing it at a predetermined pitch. A linear magnetic encoder that has a linear magnetic scale as a component. 4. The linear magnetic encoder according to claim 1, wherein the scale base for the linear scale is a part of a linear motor main body.