JP4703376B2 - Linear encoder - Google Patents

Description

  The present invention relates to an optical linear encoder suitable for measuring a relative movement amount during machining of a machine tool or the like, and more particularly to an optical linear encoder having a structure for preventing a measurement error due to the influence of thermal expansion. Is.

  In a machine tool or the like, it is extremely important to accurately measure the relative movement amount of a tool with respect to a workpiece, and various measuring apparatuses for this purpose have been commercialized.

  As one of them, an optical scale using moire fringes obtained by superposing two optical gratings is conventionally known. This optical scale has a main scale provided with a grid (marked line) on one surface of a reflective glass scale so that a transparent portion and a non-transparent portion are arranged at a predetermined pitch, and a transparent surface provided on the surface of the sensor portion. It has an index scale with a grid (scribing line) on one surface of the glass so that the light transmitting and non-light transmitting portions are arranged at a predetermined pitch, and the main scale and the index scale are opposed to each other with a minute interval. The index scale grating is arranged so as to be tilted at a minute angle with respect to the main scale grating.

  When the grating moves by 1 pitch P, the moire fringes are displaced by the interval of the stripes, and the amount of movement within 1 pitch is accurately measured by reading the changes in the transmitted light and reflected light of the slits within the interval. Will be able to.

  A specific configuration of such a conventional optical scale, that is, a linear encoder is shown in FIGS. FIG. 6 is a front view of the conventional linear encoder 1, and FIG. 7 is a cross-sectional view taken along the line A-A '. The illustrated linear encoder 1 includes a slider unit 4 that slides on a glass scale 3 and a head carrier 6 that is attached to a movable part (not shown) such as a machine tool.

  As described above, the slider unit 4 includes a sensor unit 41 having an index scale and an optical sensor that are arranged opposite to the glass scale 3 and provided with a lattice (scribing line), and a left and right for sliding the glass scale 3 with less vibration. Side guide roller 42, lower guide roller 43, and side lower guide roller 45. When used, as shown in FIG. 7, the glass scale 3 and the slider unit 4 are accommodated in the scale base 11 and the opening thereof is sealed by the first seal member 14 and the second seal member 15. The structure prevents oil and dust from entering.

  The head carrier 2 is attached to a movable part such as a machine tool, which is the object to be measured, and is connected to the slider unit 4 via the connection column 21 and has a degree of freedom that can follow the operation of the object to be measured to some extent. It has a structure.

  One end side of the slider holding spring 44 is fixed to the slider holding portion 22 held by the head carrier 2 body via the column 21, and the other end side is fixed to the slider unit 4. The slider holding spring 44 is a wire-like spring having elasticity such as a piano wire and urges and holds the slider unit 4 from the slider holding portion 22 toward the glass scale 3 side. For this reason, the sensor unit 41 of the slider unit 4 can move while facing the glass scale 3 at a constant distance, and can also follow the vibration from the machine tool. .

  As shown in FIG. 7, the glass scale 3 is mounted in a mounting groove 11 a inside the scale base 11 with a string-like or cylindrical round rubber 5 and an adhesive 6. That is, in the structure of the illustrated example, the glass scale 3 is housed so as to be pressed against the left side of the mounting groove 11a in the drawing, and the adhesive 6 and the string-like or columnar round rubber 5 are embedded in the remaining space. Thus, the glass scale 3 is bonded and held while being urged by the elasticity of rubber in the right side surface direction, and can be adapted to the influence of vibration and thermal expansion. At this time, it is assumed that the glass scale 3 is attached to the scale base 11 while maintaining straightness.

  The glass scale 3 is usually attached to the machine tool and the length measuring device at the time of shipment from the factory, and the glass scale 3 is kept straight by vibrations or shocks so that the glass scale 3 is not dropped from the mounting groove 11a. It is attached.

  In this example, the string-like or columnar round rubber 5 is embedded in the central portion and both end portions of the glass scale 3, respectively, and an adhesive is applied to the space portion between them to be bonded and fixed. The mounting position and number of round rubbers vary depending on the size and shape of the glass scale 3.

  The linear encoder 1 is attached to a fixed part of a machine tool (not shown) by screwing a scale base 11 with an intermediate support 12 and attachment parts 13 at both ends, and a head carrier 2 is attached to a movable part of the machine tool. It is done. Then, the movement amount (displacement) of the movable part is detected as the relative movement amount of the glass scale 3 and the sensor unit 41 of the slider unit 4.

  However, in the linear encoder 1 having such a configuration, the scale base 11, the glass scale 3, the string-like or cylindrical round rubber 5, and the adhesive 6 that are constituent members thereof have different thermal expansion coefficients. Yes. For this reason, along with the temperature change of the installation environment of the linear encoder 1, each member causes expansion and contraction due to different temperature coefficients. The different expansion / contraction for each member causes the following problems.

  In other words, aluminum is usually used for the constituent members of the scale base, but this aluminum has low rigidity and is not easily affected by temperature changes because there is no mechanism for suppressing shrinkage due to temperature changes. For this reason, the glass scale is pulled by the expansion and contraction of the scale base having a large thermal expansion coefficient due to the temperature change.

  On the other hand, the round rubber for fixing the glass scale 3 to the surface pressure contact is often twisted when inserted between the mounting groove and the glass scale, which accumulates unnecessary stress inside. And, in the behavior due to the difference in temperature coefficient between the scale base and the glass scale as described above, the internal stress causes more frictional resistance and stress.

  As a result, even when the temperature change region shifts to the stable region, the glass scale may behave irregularly. That is, even when the temperature once changes and then returns to the original temperature, there is a problem that the same accuracy is not exhibited. In addition, there is a problem that the accuracy error of the glass scale increases when the temperature changes, and the accuracy error is not stable.

  The structure for fixing the glass scale using the string-like or columnar round rubber as described above is disclosed in, for example, Japanese Utility Model Laid-Open No. 55-157713 (Patent Document 1) and Japanese Patent Application Laid-Open No. 58-174806 (patent). Document 2), Japanese Patent Application Laid-Open No. 59-226807 (Patent Document 3), Japanese Patent Application Laid-Open No. 59-226809 (Patent Document 4), and the like.

However, none of the documents mentions the influence of stress due to the twist of the round rubber, and there is no description suggesting this.
Japanese Utility Model Publication No. 55-157713 JP 58-174806 A JP 59-226807 A JP 59-226809 A

  An object of the present invention is to provide a linear scale that eliminates the problems caused by the stress inherent in the elastic member for fixing the glass scale and has little measurement error due to temperature change or variation in measurement accuracy.

That is, the above object is achieved by the following configuration of the present invention.
(1) a glass scale, a slider unit that scans the glass scale to obtain a position measurement value, and a hollow scale base that accommodates the glass scale and the slider unit,
A part of the glass scale is stored in a mounting groove of the scale base,
The elastic member is arranged in a partial region of the space where the stored glass scale and the mounting groove side face, and the glass scale is fixed by arranging an adhesive in the other space region,
The elastic member is a linear encoder in which a plurality of the elastic members are arranged in a spherical shape or a flat spherical shape.
(2) The linear encoder according to (1), wherein the elastic member is a spherical NBR rubber.

  According to the present invention, it is possible to provide a linear scale in which the stress inherent in the elastic member for fixing the glass scale is reduced as much as possible to eliminate the problems caused thereby, and the measurement error due to temperature change or the variation in measurement accuracy is small. it can.

  As shown in FIG. 1, for example, the linear encoder of the present invention includes a glass scale 3, a slider unit (not shown) that scans the glass scale 3 to obtain a position measurement value, and the glass scale 3 and the slider unit. And a part of the glass scale 3 is stored in the mounting groove 11a of the scale base 11, and the stored glass scale 3 and the mounting groove side surface 11a face each other. The elastic member 7 is disposed in a partial region of the space to be operated, and the adhesive is disposed in the other space region and the glass scale 3 is fixed. The elastic member 7 has a spherical shape or a flat spherical shape. A plurality of these are arranged side by side. Preferably, the elastic member is a spherical NBR rubber. Here, FIG. 1 is a schematic sectional perspective view showing the basic configuration of the linear encoder of the present invention.

  As described above, the elastic member for fixing the glass scale 3 has a spherical shape or a flat spherical shape, so that it can be easily mounted without any unnecessary stress at the time of mounting, and the glass scale has a different thermal expansion coefficient. Therefore, the displacement stress between the scale base 11 and the glass scale 3 can be stably maintained even under a predetermined temperature cycle condition. Therefore, it is possible to provide a linear encoder with little measurement error due to temperature change or variation in measurement accuracy.

  In this invention, an elastic member is arrange | positioned in a part of space area where the attachment groove side surface of a scale base and the accommodated glass scale oppose. As such an elastic member, a metal spring such as a spring obtained by bending a metal plate or a coil spring can be used. However, in the present invention, an elastic member such as an elastomer is used from the viewpoint of cost and handling. The shape is spherical or flat.

  Here, the spherical shape is a sphere having a circular cross section from any direction of the elastic body, and the sphericity is preferably 10 to 200 μm, more preferably about 10 to 100 μm. Here, the sphericity is measured by measuring the contours of two or three equator surfaces that form one sphere at 90 degrees with a roundness measuring instrument, and the radial distance from each minimum circumscribed circle to the steel ball surface. It can be obtained as the maximum value. Alternatively, one ball is placed between the 90-degree and 120-degree V-grooves and a probe perpendicular thereto, and the maximum value of the movement of the probe when measured in a different direction is divided by 2. Also good. In addition, the roundness of the radius method is obtained by the maximum radius-minimum radius. l

  In addition, in the present invention, it may be recognized as spherical at first glance, and may be flat spherical. Here, the flat spherical shape means a shape having a circular section and an elliptic section, such as a rugby ball. In other words, by using these elastic members, what has been a linear contact point in the past becomes a point-like contact point, which increases the degree of freedom of movement between the contacting member and the elastic member itself, and resistance during movement. It becomes difficult to accumulate extra stress.

  Such an elastic member is not particularly limited as long as it is a material such as a resin having a predetermined elastic modulus, but is preferably classified as an elastomer. Such elastomers include natural rubber, styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), neoprene rubber (NR), olefin elastomer, nylon elastomer, urethane rubber, acrylic rubber, silicone rubber, and fluoro rubber (FPM). ), Ethylene-propylene-diene rubber (EPDM), chloroprene rubber, or at least an elastic force equivalent to these. Among these, particularly those having a natural frequency far from the natural frequency of the encoder and excellent in damping properties are preferable, and nitrile butadiene rubber (NBR) is particularly preferable.

  The size of the cross-section (minimum cross-section) of the elastic member may be set to such a size that the elastic member is deformed to the extent that it is inserted into the gap and that the elasticity can generate a pressing force enough to fix the glass scale. Further, the number of elastic members arranged at one place and the interval between them may be determined to be the optimum number and interval in consideration of the size of the glass scale, the pressing force necessary for holding the glass scale, and the like. As a specific interval, it is desirable to select between an interval at which the elastic members are in contact with each other or an interval at which the elastic members are not in contact with an interval from one elastic member to another.

In the present invention, an adhesive is disposed in at least a part of the region other than the region where the elastic member in the space region where the side surface of the mounting groove of the scale base and the accommodated glass scale face each other. As such an adhesive, an adhesive having a low adhesive strength is preferable in order to absorb the deviation between the scale base and the glass scale to some extent. Specifically, the tensile shear force according to JIS K6850 is preferably 11 Mpa (N / mm ² ) or less, more preferably 10 Mpa (N / mm ² ) or less, and particularly 6 Mpa (N / mm ² ) or less. In some cases, it is desirable that the pressure be ³ Mpa (N / mm ² ) or less. In addition, the lower limit is required to have a strength that regulates and maintains the scale, but it can be used if it is at least about 0.6 Mpa (N / mm ² ).

  Further, the hardness (Shore D hardness) is preferably less than 70 and 10 or more, and more preferably 50 or less and 20 or more. If the adhesive is too hard, it becomes difficult to absorb the difference in thermal expansion between the glass scale and the scale base, and stress tends to accumulate inside.

  An example of such an adhesive is a silicone-based adhesive. Examples of silicone adhesives include “PM100”, “PM155”, “PM165”, “PM300”, “PM200”, “PM155”, “EP001”, etc., manufactured by CEMEDINE CO., LTD. Furthermore, Three Bond Co, Ltd. “1220”, “1221”, “1230”, GE Toshiba Silicone Corporation “TSE392”, “TSE3925”, “TSE397” “TSE3971”, “TSE3972”, “TSE3975”, “TSE399” and the like.

  A more specific configuration of such an optical scale, that is, a linear encoder is shown in FIGS. FIG. 2 is a front view of the linear encoder 1 according to the present invention, and FIG. The illustrated linear encoder 1 includes a slider unit 4 that slides on a glass scale 3 and a head carrier 6 that is attached to a movable part (not shown) such as a machine tool.

  The slider unit 4 is, as is well known, a sensor unit 41 having an index scale and an optical sensor disposed opposite to the glass scale 3 and provided with a lattice (engraving line), and left and right sides for smoothly sliding the glass scale 3. A part guide roller 42, a lower guide roller 43, and a side lower guide roller 45. When used, as shown in FIG. 3, the glass scale 3 and the slider unit 4 are accommodated in the scale base 11, and the opening is sealed by the first seal member 14 and the second seal member 15. The structure prevents oil and dust from entering.

  The head carrier 2 is attached to a movable part such as a machine tool, which is the object to be measured, and is connected to the slider unit 4 via the connection column 21 and has a degree of freedom that can follow the operation of the object to be measured to some extent. It has a structure.

  One end side of the slider holding spring 44 is fixed to the slider holding portion 22 held by the head carrier 2 body via the column 21, and the other end side is fixed to the slider unit 4. The slider holding spring 44 is a wire-like spring having elasticity such as a piano wire and urges and holds the slider unit 4 from the slider holding portion 22 toward the glass scale 3 side. For this reason, the sensor unit 41 of the slider unit 4 can move while facing the glass scale 3 at a constant distance, and can also follow the vibration from the machine tool. .

  As shown in FIG. 3, the glass scale 3 is mounted in a mounting groove 11 a inside the scale base 11 with a spherical elastic member 7 and an adhesive 6. That is, in the structure of the illustrated example, the glass scale 3 is housed so as to be pressed against the left side of the mounting groove 11a in the drawing, and the adhesive 6 and the spherical elastic member 7 are embedded in the remaining space portions, respectively. The scale 3 is adhered and held while being urged by the elasticity of rubber in the right side surface direction, so that it can be adapted to the effects of vibration and thermal expansion. At this time, it is assumed that the glass scale 3 is attached to the scale base 11 while maintaining straightness.

  The glass scale 3 is usually attached to the machine tool and the length measuring device at the time of shipment from the factory, and the glass scale 3 is kept straight by vibrations or shocks so that the glass scale 3 is not dropped from the mounting groove 11a. It is attached.

  In this example, a plurality of spherical rubbers, which are spherical elastic members, are embedded at appropriate intervals in both ends and the center of the glass scale 3, and a space between them is made of a low adhesive such as silicone. An adhesive having a low strength and a relatively low hardness is applied and fixed. The mounting position and number of the ball rubbers vary depending on the size and shape of the glass scale 3 as described above.

  Such a linear encoder 1 is attached to a fixed part of a machine tool (not shown) by, for example, a scale base 11 being screwed to an intermediate support 12 and attachment parts 13 at both ends, and a head is attached to a movable part of the machine tool. A carrier 6 is attached. Then, the movement amount (displacement) of the movable part is detected as the relative movement amount of the glass scale 3 and the sensor unit 41 of the slider unit 4.

  A linear encoder configured as shown in FIGS. 2 and 3 was prepared as an inventive sample, and a linear encoder configured as shown in FIGS. 6 and 7 was prepared as a comparative sample. The glass scale has a nominal reading length of 320 mm, and the elastic member is a spherical NBR rubber (sphericity: 150 to 100 μm or less). Stowed. As the adhesive, a silicone-based adhesive [one-component type silicone sealant (alcohol type)], manufactured by Toray Dow Corning Co., Ltd. (former Toray Dow Corning Silicone Co., Ltd.) and trade name SE 9176 CLEAR were used. In the comparative sample, cylindrical NBR round rubber was used.

  These inventive samples and comparative samples were examined for scale displacement under a temperature cycle of 20 ° C. → 50 ° C. → 20 ° C. → 0 ° C. → 20 ° C. For detection of displacement, slider units were arranged at both ends and the center of the glass scale, respectively, and the displacement of the glass scale relative to the scale base was detected by these three slider units. The results are shown in FIGS.

  As is apparent from FIGS. 4 and 5, in FIG. 4 of the conventional sample, when the reference temperature is raised from 20 ° C. to 50 ° C., the amount of change on the right side of the scale is larger than that on the left side, and the central portion is also on the right side. It has changed by 10 μm or more. In addition, when the temperature is returned to 20 ° C. again, it can be seen that the output from the left sensor part has shifted by about 10 microns to the left from the original position. Furthermore, when the temperature is lowered to 0 ° C., the amount of change on the right side of the scale is as large as 40 microns or more, whereas on the left side, it is understood that the balance is unbalanced at about a dozen microns. The central part is also shifted to the left by several microns. And when it returns to the original temperature, it turns out that it has shifted | deviated to the left of several microns-20 microns as a whole. Thus, in the conventional configuration, when a thermal cycle is applied, the glass scale is displaced with respect to the scale base and cannot be reproduced in the original state.

  On the other hand, in the invention sample of FIG. 5, the amount of change during and after the thermal cycle of 20 ° C. → 50 ° C. → 20 ° C. → 0 ° C. → 20 ° C. is the same amount of change on both the left and right when the temperature changes. At the reference temperature of 20 ° C., there is only a deviation of about several microns, and the amount of deviation is substantially equal on the left and right, indicating that the reproducibility is extremely excellent.

  INDUSTRIAL APPLICABILITY The present invention can be applied not only to a linear encoder that measures a relative movement amount during machining of a machine tool or the like, but also to a linear encoder that requires measurement of various linear distances, movement amounts, and displacement amounts. The unit is not limited to the structure of the above-described embodiments, and can be applied to various structures and systems.

It is a front view which shows the specific structure of the linear encoder of this invention. It is a front view which shows the specific structure of the linear encoder of this invention. It is an AA cross-sectional arrow view of FIG. It is the graph which showed shift | offset | difference of the right-and-left detection head in the thermal cycle of a comparative sample. It is the graph which showed shift | offset | difference of the right-and-left detection head in the thermal cycle of an invention sample. It is a front view which shows the specific structure of the conventional linear encoder. It is an AA cross-sectional arrow view of FIG.

Explanation of symbols

1 Linear encoder 3 Glass scale 4 Slider unit 5 Round rubber (string or cylindrical)
6 Adhesive 7 Elastic member (ball rubber)
11 Scale base 11a Mounting groove

Claims (2)

A glass scale, a slider unit that scans the glass scale to obtain a position measurement value, and a hollow scale base that houses the glass scale and the slider unit,
A part of the glass scale is stored in a mounting groove of the scale base,
The elastic member is arranged in a partial region of the space where the stored glass scale and the mounting groove side face, and the glass scale is fixed by arranging an adhesive in the other space region,
The elastic member is a linear encoder in which a plurality of the elastic members are arranged in a spherical shape or a flat spherical shape.   The linear encoder according to claim 1, wherein the elastic member is a spherical NBR rubber.

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