JPH04213015A - Method and apparatus for detecting rotating amount of feed screw in screw feeding mechanism - Google Patents

Abstract

PURPOSE:To measure the amount of rotation of a feed screw accurately. CONSTITUTION:Light is emitted from a spot light source or a linear light source 1 on a grid pattern 3A formed on the outer surface of a cylindrical part of the end part of a feed screw 3. The cylindrical part is not related to the a screw feeding function. The shaded pattern corresponding to the grid pattern 3A is generated. The displacement of the shaded pattern caused by the rotation of the feed screw 3 is detected with an optical sensor 2, and the amount of rotation of the feed screw 3 is detected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for detecting the amount of rotation of a feed screw in a screw feed mechanism.

0002

2. Description of the Related Art Various types of screw feeding mechanisms, such as ball screws, static pressure screws, and slide screws, are used as precision positioning means in precision machining and precision measurement.

In a screw feed mechanism, a method for detecting the amount of rotation of the feed screw is to attach a scale to the feed screw using a coupling member, and to detect the amount of rotation of the scale as the feed screw rotates optically or magnetically. There is a known method for detecting this using an encoder.

[0004] In the case of the above-mentioned rotation amount detection method, there is a possibility that a slight "play" exists between the coupling member and the feed screw from the beginning, or that play occurs over time due to temperature changes, vibrations, and shocks. This is likely to occur, and if such backlash exists, the rotation of the feed screw and the rotation of the scale will not strictly match, making it impossible to detect the accurate amount of rotation of the feed screw.

In addition, in the case of conventional optical or magnetic encoders, it is necessary to set the relative positional relationship between the sensor and the scale with extremely high precision, and if vibration or impact distorts the positional relationship, There was a problem that the accuracy of rotation amount detection decreased.

[0006]

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a novel feed screw rotation amount that can accurately detect the amount of rotation of the feed screw and is less susceptible to the effects of vibrations and shocks. The purpose is to provide a detection method and device.

[0007]

SUMMARY OF THE INVENTION The present invention is a method and apparatus for detecting the amount of rotation of a "feed screw" in a screw feed mechanism, such as the above-mentioned slide screw, ball screw, or static pressure screw.

The “feed screw rotation amount detection method” of the present invention is as follows:
"A lattice pattern is formed on the circumferential surface of a cylindrical portion not involved in the screw feeding function at the end of the feed screw of the screw feeding mechanism, with the lattice arrangement direction perpendicular to the generatrix of the circumferential surface so as to surround the screw rotation axis," Irradiating the grating pattern with light from a point light source or a linear light source, generating a shadow pattern corresponding to the grating pattern using reflected light flux, and detecting displacement of the shadow pattern as the feed screw rotates using an optical sensor, Detects the amount of rotation of the feed screw.

The "feed screw rotation amount detection device" of the present invention is a device for implementing the above method, and includes a grating pattern, a light source, and a light sensor. The "lattice pattern" is a lattice pattern that surrounds the screw rotation axis on the peripheral surface of the cylindrical part of the feed screw end of the screw feeding mechanism that is not involved in the screw feeding function, with the direction perpendicular to the generatrix of the peripheral surface being the lattice arrangement direction. It is formed. The "light source" is a point light source or a linear light source, which irradiates the grid pattern with light and generates a silhouette pattern corresponding to the grid pattern using reflected light flux. "Light sensor"
detects the displacement of the shadow pattern as the feed screw rotates.

[0010] The grating pattern can be formed by well-known photolithography, but a particularly suitable forming method is magnetic lithography (claim 3).
).

[0011]

[Operation] A shadow pattern corresponding to the grid pattern is generated by irradiating the light beam from a point light source or a linear light source onto the grid pattern, and the displacement of the shadow pattern due to the movement of the grid pattern is detected by an optical sensor. A method for measuring the amount of movement of a pattern is known (Japanese Patent Application Laid-open No. 63
-47616, Japanese Patent Application Laid-Open No. 1-297513)
.

Since the present invention utilizes the above shadow picture pattern, the shadow picture pattern will first be briefly explained below.

In FIG. 3, reference numeral 10 indicates a linear light source, and reference numeral 1
Reference numeral 2 indicates a grid pattern, and reference numeral 14 indicates a screen. A grating pattern is one in which changes in transmittance or reflectance are repeated in a single period in one direction, but in the grating pattern 12 shown in FIG. 3, changes in transmittance are repeated in a single period in the vertical direction of the figure. It is something. Regarding the grating pattern, the "direction in which the change in transmittance or the change in reflectance is repeated in a single period" is called "the grating arrangement direction". In FIG. 3, the vertical direction of the figure is the lattice arrangement direction of the lattice pattern 12. The grating pattern 12 has ξ as a grating pitch, that is, a period of transmittance change in the grating arrangement direction.

The linear light source 10 has a length d in the lattice arrangement direction of the lattice pattern 12. For example, as a linear light source,
It is preferable to use a semiconductor laser made of AlGaAs or GaAs whose light emitting part is parallel to the lattice arrangement direction, but in this example, the light emitting part is circular with a diameter d.

[0015] The light beam from the linear light source 10 is arranged in a grating pattern 1.
2, diffracted lights L1, L2, L3, L4, L5, etc. are generated from each irradiated portion of the grating pattern 12. Interference fringes as shown by reference numeral 20 appear in the region where these diffracted lights interfere with each other.

Length d of linear light source 10 and grating pattern 12
When the grating pitch ξ satisfies the following condition: (1/10)≦(d/ξ)≦4 (1), the interference fringes 20 are called a “shadow pattern”. This shadow picture pattern is generated as if an ideal point light source was placed at the position of the linear light source 10 and the grating pattern 12 was enlarged as a geometric optical shadow picture. That is, the distance between the linear light source 10 and the grating pattern 12 and the distance between the grating pattern 12 and the screen 14 are respectively b1 and b as shown in the figure.
2, the silhouette pattern 20 is the lattice pattern 12 expanded by {(b1+b2)/b1} times in the lattice arrangement direction. Moreover, when the linear light source 10 is fixed and the grid pattern 12 is moved in the direction of the grid arrangement, the shadow picture pattern 2
0 is also displaced in the same direction as the grid pattern 12 while maintaining the silhouette relationship with the grid pattern 12. Therefore, the amount of movement D of the grid pattern is determined by the shadow picture pattern 20 as {(b1+b2)/b
1}D, and by using the silhouette pattern, extremely minute displacements of the grating pattern itself can be measured with high precision.

The dimension of the linear light source 10 in the direction perpendicular to the drawing of FIG. 3 is not particularly limited. In addition, coherent light is ideal for the light irradiated onto the grid pattern from a linear light source, but
Even with an incoherent light beam from a light source such as an LED, a slit with a length d as shown in Figure 4 ((I) in the same figure)
), an aperture (II) with an elliptical aperture whose major or minor axis is d, or an aperture (III) with a circular aperture whose diameter is d and irradiates the grid pattern. , if the relationship between the above d and the grating pitch ξ satisfies the above (1), a shadow pattern can be generated.

Although the case where a shadow pattern is generated by light from a linear light source has been described above, the above-mentioned JP-A-6
As disclosed in detail in Publication No. 3-47616,
Even if a grating pattern is irradiated with divergent coherent light from a point light source (which can be realized by matching the width direction of the light emitting part of the semiconductor laser with the lattice arrangement direction of the lattice pattern), a shadow pattern can be generated. can. In the present invention, the amount of rotation of the feed screw is detected using such a shadow pattern.

Since the grid pattern for generating the silhouette pattern is formed on the feed screw itself, the amount of rotation of the grid pattern is strictly equal to the amount of rotation of the feed screw itself. The rotation of the grid pattern is then magnified by the silhouette pattern.

[0020]

[Example] Specific examples will be described below. FIG. 1(I) shows only the essential parts of one embodiment of the present invention. The ball screw 3 serving as a feed screw is configured to feed a piece 4 screwed into its threaded portion in the direction of the rotation axis by rotation. One end of the ball screw 3 has a cylindrical portion that does not participate in the feeding function, and a lattice pattern 3A is formed in this portion. That is, the lattice pattern 3A is formed so as to surround the rotation axis 3B of the screw, with the lattice arrangement direction being in a direction perpendicular to the generatrix of the cylindrical portion.

When this lattice pattern 3A is irradiated with a coherent light beam from the linear light source 1, a shadow pattern as described above is generated and is rotationally displaced as the ball screw 3 rotates. The linear light source 1 is a semiconductor laser arranged so that the longitudinal direction of its light emitting part corresponds to the lattice arrangement direction.

[0022] When the optical sensor 2 is fixedly disposed at a portion where the shadow picture pattern is generated and outputs a photoelectric conversion output, this output changes oscillatingly in accordance with the displacement of the shadow picture pattern. Assuming that one pitch of the grating pattern corresponds to an angle δθ when viewed from the axis of the ball screw 3, one period of the output of the optical sensor 2 corresponds to the rotation angle δθ of the ball screw 3. Of course, the rotational speed and rotational acceleration can also be detected by performing an arithmetic operation of differentiating the detected amount of rotation with respect to time.

For example, as shown in FIG. 2, the output of the optical sensor 2 is amplified by an amplifier 6, the rotation amount and rotation speed are calculated by an arithmetic circuit 7, and the results are preset in the comparator circuit 8. The control circuit 9 controls the motor 1 so that the calculated rotation amount or rotation speed matches the set rotation amount or rotation speed.
1 to control the rotation of the ball screw 3, it is possible to give the ball screw 3 a desired rotation amount or rotation speed.

FIG. 1 (II) shows an LED 1 as a linear light source.
The figure shows a state where the light from ' is taken out through the slit 5 as shown in FIG. 4(I) and is irradiated onto the grating pattern 3A. As described above, a silhouette pattern can also be generated in this manner, and the amount of rotation can be detected in the same manner as in the above embodiment.

Finally, a method using magnetic lithography will be described as an example of a method for forming a lattice pattern on the cylindrical portion at the end of the feed screw. Fe3O4 and C are added to the end of the feed screw where the lattice pattern is to be formed.
A magnetized film of oCr is formed to a thickness of several thousand angstroms, and a lattice pattern is written on this magnetized film using a magnetic head to form a magnetized pattern corresponding to the lattice pattern. Subsequently, a fluid in which fine powder of iron oxide having a particle size of about 50 to 200 Å is dispersed in a light or thermosetting resin together with a surfactant is applied to the magnetized pattern. The fine powder of iron oxide gathers at the boundaries of the magnetic domains in the magnetization pattern and visualizes the magnetization pattern, so all you have to do is irradiate the resin with light or heat it to solidify the resin to obtain the desired lattice pattern. can.

[0026]

As described above, according to the present invention, a novel method and device for detecting the amount of rotation of a feed screw in a screw feed mechanism can be provided. Since the present invention is configured as described above, the amount of rotation of the feed screw can be detected easily and reliably. In addition, the relative positional relationship between the optical sensor that detects the displacement of the shadow pattern and the grid pattern does not require as much precision as compared to conventional encoders, and even if the positional relationship is slightly shifted due to vibration or impact, the displacement of the shadow pattern will not change. can be detected well.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining a configuration for controlling the rotation amount or rotation speed of a feed screw using the above embodiment.

FIG. 3 is a diagram for explaining a silhouette pattern and its generation conditions.

FIG. 4 is a diagram for explaining the shape of an opening of a light-shielding plate for generating a shadow pattern with light from an incoherent light source.

[Explanation of symbols]

1 Linear light source 2 Optical sensor 3 Ball screw 3A as a feed screw
lattice pattern

Claims (3)

[Claims] Claim 1: A lattice pattern is formed on the circumferential surface of a cylindrical portion not involved in the screw feeding function at the end of the feed screw of the screw feeding mechanism, with the lattice arrangement direction being perpendicular to the generatrix of the circumferential surface, so as to surround the screw rotation axis. irradiating the lattice pattern with light from a point light source or a linear light source to generate a silhouette pattern corresponding to the lattice pattern using the reflected light beam;
A method for detecting the amount of rotation of a feed screw in a screw feed mechanism, characterized in that the amount of rotation of the feed screw is detected by detecting the displacement of the silhouette pattern as the feed screw rotates using an optical sensor. [Claim 2] A lattice arrangement direction is formed on the circumferential surface of a cylindrical portion not involved in the screw feeding function at the end of the feed screw of the screw feeding mechanism so as to surround the screw rotation axis, with the direction perpendicular to the generatrix of the circumferential surface being the lattice arrangement direction. a point light source or a linear light source for irradiating light onto the lattice pattern and generating a shadow picture pattern corresponding to the lattice pattern by means of a reflected light beam; 1. A feed screw rotation amount detection device in a screw feed mechanism, comprising an optical sensor for detecting displacement. 3. A feed screw rotation amount detection device in a screw feed mechanism according to claim 2, wherein the grating pattern is formed by magnetic lithography.