JP2006118962A - Magnetic encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep the magnetic flux density of magnetic poles nearly constant to perform position detection for a mobile unit stably for a long term by preventing ambient magnetic powder such as iron powder from adhering to a magnetic scale by magnetically adsorbing it with magnetic adsorption members. <P>SOLUTION: Covers 13/15 covering the magnetic scale 9 are attached to either the magnetic scale 9 or a magnetic detection member 11 which constitute a magnetic encoder 1. The magnetic adsorption members 23/25 are attached to openings 19/21 formed between the magnetic detection member 11 and the covers 13/15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic encoder that detects a moving position and a moving amount of a moving body that moves linearly in, for example, a robot or a machine tool (hereinafter, the moving position and moving amount are referred to as a moving position unless otherwise specified). Relates to a magnetic encoder for preventing magnetic substance powder such as iron powder in a factory atmosphere from adhering to a magnetic scale and deteriorating the accuracy of detecting the moving position of the moving object.

  For example, as shown in Patent Document 1, in order to detect a moving position of a moving body that moves linearly on a main body frame of a machine tool, different magnetic poles (N pole and S pole) having a desired detection resolution width are provided on the main body frame. The magnetic scale alternately magnetized is attached along the moving direction of the moving body, and the moving body is attached with a magnetic detection member such as a hall element that detects a magnetic field change from the magnetic scale and outputs an electric signal. There is known a magnetic encoder that detects a moving position of a moving body based on an electric signal output from a magnetic detection member along with the movement.

  The magnetic encoder described above has features that it can detect the moving position of a moving body with high accuracy and stability over a long period of time, with fewer position detection errors due to dust and the like than optical encoders using LEDs and laser light. ing.

However, in a magnetic encoder such as a machine tool installed in a factory where a large amount of magnetic powder such as iron powder is generated, the iron powder in the factory atmosphere is likely to be magnetically attracted to the magnetic scale. When the powder is magnetically attracted, the magnetic flux density of each magnetic pole in the magnetic scale becomes low, and an electric signal having a lower current value than that in the normal state is output from the magnetic detection member. For this reason, when the current value of the electrical signal is equal to or less than the predetermined threshold value set for outputting the position detection signal, the position detection cannot be performed without outputting the position detection signal, and the predetermined threshold value is set. Even in the above case, the time width may be shortened and the position detection operation may become unstable.
Japanese Patent Laid-Open No. 2004-191261

  The problem to be solved is that the magnetic substance such as iron powder in the factory atmosphere adheres to the magnetic scale and the magnetic flux density of each magnetic pole becomes low, so the position detection becomes impossible or the position detection accuracy deteriorates. The position of the moving body cannot be detected stably over a long period of time.

  In the present invention, a cover that covers the magnetic scale is attached to one of the magnetic scale and the magnetic detection member constituting the magnetic encoder, and a magnetic adsorption member is attached to an opening formed between the magnetic detection member and the cover. Is the most important feature.

  The present invention maintains the magnetic flux density of each magnetic pole substantially constant by magnetically adsorbing magnetic powder such as iron powder in the atmosphere by the magnetic adsorption member and preventing it from adhering to the magnetic scale, thereby detecting the position of the moving body. Can be stably performed over a long period of time.

  In the present invention, a configuration in which a magnetic adsorption member is attached to an opening formed between a cover that covers the magnetic scale and the magnetic detection member is the best mode.

The present invention will be described below with reference to the drawings showing embodiments.
1 to 3, the moving device 3 to which the magnetic encoder 1 is attached is configured by, for example, an industrial robot or a machine tool so that the moving body 7 is linearly moved in the longitudinal direction on the main body frame 5. A magnetic scale 9 constituting a part of the magnetic encoder 1 is attached to the main body frame 5 in parallel with the moving direction of the moving body 7.

  The magnetic scale 9 has a length corresponding to the moving distance of the moving body 7, and magnetic poles (N pole and S pole) having different widths according to the moving position detection resolution of the moving body 7 with respect to the longitudinal direction are in the longitudinal direction. Are alternately magnetized. The moving body 7 is controlled to reciprocate in the longitudinal direction on the main body frame 5 by, for example, a servo motor and a linear moving mechanism (not shown) connected thereto.

  A magnetic sensor 11 as a magnetic detection member constituting a part of the magnetic encoder 1 is attached to the moving body 7 via a mounting bracket 12 so as to be opposed to the magnetic scale 9 with a minute gap capable of detecting a magnetic field. It has been. The magnetic sensor 11 is composed of, for example, a magnetodielectric magnetic sensor, a Hall element, a magnetic diode, a magnetoresistive element, and the like. From this, a sine wave electrical signal for setting the next S pole to 360 ° is output to detect the moving position of the moving body 7.

  In the above description, each magnetic pole width in the magnetic scale 9 is set to a width corresponding to the moving position detection resolution of the moving body 7. However, by dividing the electric signal output according to each magnetic pole by a desired number, The moving position detection resolution of the moving body 7 can be improved.

  Covers 13 and 15 are attached to the main body frame 5 so as to cover the entire magnetic scale 9 and allow the moving body 7 to move. One cover 13 has one end fixed to the main body frame 5 above the magnetic scale 9 and the other end extending to the side of the magnetic sensor 11 attached to the moving body 7 and then being attached to one surface of the mounting bracket 12 (illustrated). And a gap 19 for allowing the moving body 7 to move.

One end of the other cover 15 is fixed to the main body frame 5 below the magnetic scale 9, and the other end allows the moving body 7 to move with respect to the other surface (the left surface in the drawing) of the mounting bracket 12. It is configured to have a gap 21. Then, the magnetic attracting members 23 and 25 are disposed at the other ends of the covers 13 and 15 facing the respective surfaces of the mounting bracket 12 and are not in contact with the moving body 7 with a length extending over the entire length of the covers 13 and 15. It is installed in the state of. Each of the magnetic attracting members 23 and 25 may be a rod-like permanent magnet, a synthetic resin magnetic sheet mixed with permanent magnet powder, or a magnetic rubber sheet. Any magnetic field strength that does not affect is sufficient. The openings at both ends in the longitudinal direction of the covers 13 and 15 are closed by a closing plate 14.

Next, the operation of the magnetic encoder 1 will be described.
First, the outline of the movement position (movement amount) detection operation of the moving body 7 will be described. When the moving body 7 is linearly moved with respect to the main body frame 5, the magnetic sensor 11 detects the magnetic field from each magnetic pole in the magnetic scale 9. Then, a sine wave electrical signal shown in FIG. 4 is output. A position detection control circuit (not shown) outputs a position detection signal when the current value of the electric signal is equal to or greater than a preset threshold value, and sequentially increments a counter circuit (not shown) based on the position detection signal. Thus, the moving position of the moving body 7 is detected.

Now, in an environment where a large amount of magnetic powder such as iron powder floats in the atmosphere where the moving device 3 is installed, the iron powder in the atmosphere is magnetically attracted to each magnetic pole of the magnetic scale 9. . When iron powder is magnetically attracted to the magnetic scale 9, the magnetic flux density of each magnetic pole in the magnetic scale 9 becomes low, and the current value of the electric signal output from the magnetic sensor 11 of the moving body 7 that moves along the magnetic scale 9. However, it is lower than normal.

As a result, when the current value of the electrical signal output from the magnetic sensor 11 is lower than a predetermined threshold value for outputting the position detection signal, as shown by the one-dot chain line in FIG. 4, the position detection signal is output. Cannot detect the position. Further, as shown by a two-dot chain line in FIG. 4, even if the current value of the electric signal is equal to or greater than the threshold value, the time width becomes short and the output state of the position detection signal becomes unstable. There is a possibility that the moving position cannot be reliably detected or the position detection accuracy is deteriorated.

In the present embodiment, in order to prevent this, the moving body 7 is allowed to move, and the magnets 19 and 21 are formed in the gaps 19 and 21 formed between the covers 13 and 15 and the mounting bracket 12 that cover the entire magnetic scale 9. The adsorbing members 23 and 25 are attached, and the magnetic adsorbing members 23 and 25 magnetically adsorb the iron powder to enter the space covered with the covers 13 and 15 to restrict the adhering to the inside. This prevents adhesion to the magnetic scale 9. This stabilizes the electric signal output from the magnetic sensor 11 while keeping the magnetic flux density of each magnetic pole in the magnetic scale 9 substantially constant, and makes it possible to stably detect the moving position of the moving body 7 by the magnetic sensor 11 over a long period of time. enable.

In the above description, the magnetic scale 9 is fixedly attached to the main body frame 5 and the magnetic sensor 11 is attached to the moving body 7 that moves, and the magnetic scale 9 and the magnetic sensor 11 are relatively moved. 5 may be configured such that the magnetic sensor 11 is fixedly attached to 5 and the magnetic scale 9 is attached to the moving body 7 that moves and the two are relatively moved. In this case, as shown in FIG. 5, a mounting plate 63 extending in the longitudinal direction is mounted on a bracket 61 mounted on the moving body 7, and a mounting plate facing the magnetic sensor 11 mounted on the main body frame 5. A long magnetic scale 9 is attached to the surface 63. Further, covers 65 and 67 are attached to attachment plates 63 corresponding to the upper and lower portions of the magnetic scale 9 so as to cover the entire magnetic scale 9, and the magnetic attracting members 69 and 67 are attached to the surfaces of the covers 65 and 67 facing the main body frame 5. What is necessary is just to make it the structure which attached 71 in the non-contact state.

In the above description, the configuration in which the moving position of the moving body 7 is detected by one magnetic sensor 9 is described as an example. Of course, it may be.

It is explanatory drawing which shows the outline of the moving apparatus to which a magnetic encoder is attached. It is explanatory drawing which expands and shows a magnetic encoder location. FIG. 3 is a longitudinal sectional view taken along line AA in FIG. 2. It is a wave form diagram of the electric signal output from a magnetic sensor. It is explanatory drawing which shows the modified Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic encoder 7 Moving body 9 Magnetic scale 11 Magnetic sensor 13 * 15 as a magnetic detection member Covers 19 * 21 Gap 23 * 25 Magnetic adsorption member

Claims (5)

A magnetic scale in which different magnetic poles are alternately arranged with respect to the longitudinal direction and a magnetic detection member that is arranged so as to face the magnetic scale with a desired gap and outputs an electric signal based on a change in the magnetic field, In the magnetic encoder for detecting the moving position of the moving body in accordance with the relative movement of the magnetic scale and the magnetic detection member, a cover that covers the magnetic scale is attached to either the magnetic scale or the magnetic detection member, and the magnetic detection member and the cover A magnetic encoder having a magnetic attracting member attached to an opening formed therebetween. 2. The magnetic encoder according to claim 1, wherein the cover is fixed to the magnetic scale side so as not to interfere with the magnetic detection member. 2. The magnetic encoder according to claim 1, wherein the cover is fixed to the magnetic detection member side so as not to interfere with the magnetic scale. The magnetic attraction member according to claim 1 is a magnetic encoder attached so as to be in a non-contact state by providing a minute gap with respect to an opposing magnetic scale or magnetic detection member. 2. The magnetic encoder according to claim 1, wherein the magnetic adsorption member is a magnetic sheet.

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