JPH0244368B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a linear displacement measuring machine, and particularly to a linear displacement measuring machine equipped with a relatively short main scale. A frame body to be connected,
a main scale held by the frame and made of a material having a coefficient of thermal expansion different from that of the frame; and an index scale connected to the other of the object to be measured and moved along the main scale; The present invention relates to an improvement of a linear displacement measuring machine that measures the relative displacement between the two objects to be measured from the relative movement of the main scale and the index scale.

[Conventional technology]

Generally speaking, in a measuring machine that measures the length of an object, when measuring the amount of relative movement of something that moves relative to the main body, such as the amount of movement of the probe relative to the main body, the amount of movement of the slider relative to the column, etc., the main scale is held on one side. A displacement measuring device is known in which a frame body is fixed to the other side and a detector including an index scale is fixed to the other side, and the relative displacement between the frame body and the detector is read by, for example, an optical method or an electromagnetic method. There is. In such displacement measuring machines, especially in linear displacement measuring machines equipped with a transmission-type displacement detecting device, the frame body is generally complicated in shape, and is designed to improve sealability, nonflammability, and weight reduction of the detection part. Because the main scale is made of extruded aluminum, and the main scale held in the frame is made of glass, there is a difference in the amount of thermal expansion when the temperature changes, causing the main scale to deform and reduce measurement accuracy. However, in severe cases, the main scale may be destroyed. Therefore, conventionally, for example, as shown in FIG.
The main scale 10 is directly adhered to the frame body 14 using an elastic adhesive 16 or the like while being pressed against the guide surfaces 14A and 14B of the frame body 14, thereby elastically holding the main scale 10. Ta. In FIG. 1, 20 is moved in the longitudinal direction of the main scale 10 while maintaining a predetermined positional relationship with the main scale 10 by a sliding piece 22 that slides on the surface of the main scale 10. The slider 24, which is configured as shown in FIG. A light emitting element and a light receiving element are fixed to the slider 20, sandwiching the main scale 10 and the index scale 24, respectively.

[Problems to be solved by the invention]

However, due to the manufacturing method, the aluminum extruded material forming the frame 14 is already, for example, about 0.03 mm per 300 mm of length, that is,
For example, bending, twisting, waviness, etc. of about 30 times the scale resolution of 1 μm occur irregularly, and it is practically difficult to correct this and achieve the same level of precision as the main scale 10. Furthermore, during use, thermal deformation occurs due to temperature changes. Therefore, in the past, no matter how highly precisely the main scale 10 is finished in order to obtain a scale resolution of, for example, about 1 μm, when the main scale 10 is bonded to the frame 14, the main scale 10 is attached to the frame 14. There was a problem in that the scale would be deformed by adapting to the bends in the curve, etc., and the scale would be enlarged or reduced, resulting in a significant decrease in measurement accuracy. Now, when estimating the effect on measurement accuracy when the main scale 10 is bent due to the bending of the frame 14, for example, as shown in FIG. If the main scale 10 is formed symmetrically with respect to the main scale 10, no error will occur when the main scale 10 bends in the height direction as shown by the arrow B. However, normally, the scale face 10 on which the scale 10B is formed
A does not coincide with the neutral plane C of the main scale 10, so as shown in FIG.
When a bend of 0 occurs in the thickness direction, the radius of the bend is R, the expected angle of the unit section for which the error should be evaluated is Δθ, and the length before the bend occurs, that is, the length of the neutral plane C. L and the length of the scale surface 10A are _L0 , the error ε between the two is approximately expressed by the following equation. ε=L ₀ −L (1) L ₀ ≒(R+t/2)Δθ (2) L≒RΔθ (3) Here, t is the thickness of the main scale 10. By the way, the maximum deformation amount δ at the center of the neutral plane C is approximately expressed by the following equation. δ≒R−Rcos(Δθ/2)=R[1−{1−(
1/2! ) × (Δθ/2) ² }] = R (Δθ) ² /8 = L
Δθ/8 (4) Therefore, the error ε is expressed by the following equation using this δ. ε≒(t/2)Δθ≒(t/2)×(8δ/L
)≒4tδ/L…(5) Therefore, the length L of the error evaluation unit section of the main scale 10 is 300 mm, the thickness t is 5 mm, and δ is 0.06 mm.
When , the error ε is approximately 4 μm. Therefore, for example, in the case of a main scale with a total length of 900 mm, an error of 12 μm will occur, which is a fatal flaw in a linear displacement measuring machine that requires measurement accuracy of 1 μm or less. In order to alleviate such problems, when bonding the main scale 10 to the frame body 14, for example,
54-48574, the accuracy is measured in the longitudinal direction using a test indicator, an electric micrometer, or the like, for example, by bringing the electric micrometer or the like into contact with two sides of the main scale 10. Adjust the adjustment screw according to the unevenness,
It is also possible to position the main scale 10 by inserting a shim between the main scale 10 and the frame 14, but this is not only extremely inefficient, but also makes accurate positioning extremely difficult. The problem was that it was difficult. The present invention has been made in order to solve the above-mentioned conventional problems, and does not use the frame as a position reference at all. Therefore, the main scale can be held straight regardless of the bending of the frame, etc. It is an object of the present invention to provide a linear displacement measuring machine that can absorb the difference in thermal expansion between a frame body and a main scale, and therefore can perform highly accurate measurements.

[Means to solve the problem]

The present invention provides a frame body connected to one of two objects to be measured whose relative displacement is to be measured, a main scale held by the frame body and made of a material having a coefficient of thermal expansion different from that of the frame body; and an index scale connected to the other of the objects to be measured and moved along the main scale, so that relative displacement between the two objects to be measured is measured from relative movement between the main scale and the index scale. In the linear displacement measuring machine, the main scale is
A plurality of main scale holding members are provided for holding the main scale at a plurality of locations in the longitudinal direction, and the main scale holding member is arranged on one side of the graduation face of the main scale or its back face, and the side face of the scale along the longitudinal direction. and a main scale locking part formed integrally with the guide surfaces, and the frame body has two guide surfaces corresponding to the back surfaces of the two guide surfaces of the main scale holding member. Two adhesive surfaces are provided, and the back surfaces of the two guide surfaces of each main scale holding member are adhered to the adhesive surfaces of the corresponding frames, and the main scale is pressed using the main scale locking part. Each of the main scale holding members is adhered to the plurality of main scale holding members while being pressed against one of the two guide surfaces of each main scale holding member by a means, and the main scale holding member and the frame are bonded and the main scale and The above object is achieved by at least one of the adhesives of the main scale holding member being elastic adhesive.

[Effect]

According to the present invention, since the main scale is held without using the frame as a position reference, the main scale can be held straight regardless of the bending of the frame. Further, the main scale holding member is adhered to the frame body at a plurality of locations in the longitudinal direction of the frame body, and at least one of the adhesion between the main scale holding member and the frame body and the adhesion between the main scale and the main scale holding member. Since one side is elastically bonded, the difference in thermal expansion between the main scale and the frame is easily absorbed. Further, in an embodiment of the present invention, the pressing means is a rubber rod inserted between the main scale locking portion of the main scale holding member and the surface of the main scale, so that the main scale is surely held. This is what I did. Furthermore, in another embodiment of the present invention, the configuration is simplified such that the pressing means is the main scale locking portion itself of the main scale holding member having spring characteristics.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIGS. 4 and 5, the first embodiment of the present invention is made of one of two objects whose relative displacement is to be measured, for example, an extruded aluminum member fixed to the bed of a machine tool. frame 1
4, a main scale 10 held by the frame 14 and made of a material having a coefficient of thermal expansion different from that of the frame 14, such as glass; It has an index scale (not shown) that is moved along the scale 10, and the main scale 10
In the linear displacement measuring machine, the relative displacement between the two objects to be measured is measured from the relative movement of the main scale 1 and the index scale.
Two guide surfaces 30 corresponding to two orthogonal surfaces of 0
A, 30B and the main scale holding member 30 having the main scale locking portion 30C are held at a predetermined pitch in the longitudinal direction of the frame body 14 with an elastic adhesive 32 while maintaining the straightness of the guide surfaces 30A, 30B. At the same time as adhering, the main scale 1
0 is pressed against the guide surface 30A of the main scale holding member 30 by the rubber rod 12, which is a pressing means using the main scale locking part 30C, and adhered to the main scale holding member 30 with an elastic adhesive 34. It is designed to be fixed. The main scale holding member 30 is approximately U-shaped. The contact area of the rubber rod 12 with the main scale 10 is made smaller than the contact area of the main scale 10 with the main scale holding member 30. This is to prevent an unbalanced moment from occurring. The ratio of the guide surface length 1 of the main scale holding member 30 to the main scale holding member arrangement interval P is in the range of 1:7 to 1:11. This absorbs the difference in thermal expansion between the main scale 10 and the frame 14, and causes the main scale 10 to expand due to thermal stress.
This is to prevent damage to the scale, reduce hysteresis in measured values due to temperature changes during measurement, and prevent problems such as misalignment of the main scale due to rough handling during transportation. That is, as the applicant has already proposed in JP-A-58-174806, the main scale 10 is, for example,
In the case of a long scale of approximately 1,500 mm to 4,500 mm, the pitch and pitch are determined in the longitudinal direction of the main scale 10 by the materials of the main scale 10, the frame 14, and the elastic joint member, and the length of the main scale 10. By providing a long elastic member non-bonded portion to reduce the thermal stress applied to the main scale 10 through the elastic bonding member during temperature changes, damage to the main scale 10 due to thermal stress can be prevented, and It is possible to reduce hysteresis in measured values due to temperature changes. Therefore, when the main scale 10 is a long object of 1500 mm or more, for example, the ratio of the guide surface length 1 of the main scale holding member 30 to the main scale holding member arrangement interval P is 1:15 to 1:15. It can be in the range of 1:20. On the other hand, if the length of the main scale 10 is relatively short, for example, 1500 mm or less, it is light and easy to carry, so it is easy to be handled roughly during transportation. The maximum allowable external force needs to be increased from about 12G for long scales to about 20G to 50G for short scales. Therefore, in this case, the ratio of the guide surface length l of the main scale holding member 30 to the main scale holding member arrangement interval P is set in the range of 1:7 to 1:11. Frame 1 of main scale 10 in this embodiment
Specifically, the attachment to 4 is performed as follows, for example. That is, first, a positioning jig made of a magnetic material is attached to a positioning jig including a magnet portion having a shape corresponding to two perpendicular surfaces of the main scale 10, which is provided at least in correspondence with the arrangement position of the main scale holding member 30. Main scale holding member 3
0 is suctioned and fixed at a predetermined pitch. Next, the frame body 14 is attached to the main scale holding member 30 suction-fixed to the positioning jig using an elastic adhesive 32.
Adhesive. Furthermore, the positioning jig is removed, and the main scale 10 is adhered to the main scale holding member 30 using an elastic adhesive 34 instead. With this, the guide surfaces 30A, 30
The main scale holding member 30 can be easily adhered to the frame body 14 while maintaining the straightness of B. In this embodiment, the pressing means is the main scale locking portion 3 of the main scale holding member 30.
Since the rubber rod 12 is inserted between the 0C and the surface of the main scale 10, the main scale 10 can be held securely. Next, a second embodiment of the present invention will be described in detail. This embodiment is a linear displacement measuring machine having a main scale 10, a frame 14, a main scale holding member 30, etc., similar to the first embodiment, as shown in FIG.
The main scale locking portion 30C of 0 has spring characteristics, and the main scale locking portion 30C itself having the spring characteristics presses the main scale 10 in the direction of the guide surface 30A of the main scale holding member 30. This is what I did. The other points are the same as those of the first embodiment, so the explanation will be omitted. In this embodiment, since the pressing means is the main scale locking portion 30C of the main scale holding member 30 which has spring characteristics, the configuration is greatly simplified. In the above embodiments, elastic adhesives 32 and 34 are used to bond the frame 14 and the main scale holding member 30, and to bond the main scale holding member 30 and the main scale 10. Main scale 10 and frame 14
It is particularly effective in absorbing the difference in thermal expansion between the two. Note that the type of adhesive is not limited to this, and for example, it is also possible to use an adhesive that does not have elasticity for either one. In all of the above embodiments, the present invention
Although the present invention has been applied to a linear displacement measuring machine that uses an aluminum frame and a glass main scale, the scope of application of the present invention is not limited to this, and can also be applied to a frame and main scale made of other materials. It is clear that the method can be similarly applied to the linear displacement measuring device used.

【Effect of the invention】

As described above, according to the present invention, the main scale can be positioned without using the frame as a position reference, and the main scale can be held straight regardless of the bending of the frame.
Furthermore, the difference in thermal expansion between the frame and the main scale can be absorbed. Therefore, it has an excellent effect of being able to obtain high measurement accuracy.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a main scale holding structure in an example of a conventional linear displacement measuring machine, FIG. 2 is a front view showing an example of the relationship between the scale forming position and the bending direction on the main scale, Figure 3 is
Figure 4 is a plan view for calculating measurement errors caused by bending of the main scale in the thickness direction.
A fifth cross-sectional view showing the main scale holding structure in the first embodiment of the linear displacement measuring device according to the present invention.
The figure is a sectional view taken along line V-V in FIG. 4, and FIG. 6 is a sectional view showing a main scale holding structure in a second embodiment of the linear displacement measuring device according to the present invention. 10...Main scale, 12...Rubber bar, 1
4... Frame body, 24... Index scale, 3
0...Main scale holding member, 30A, 30B
...Guide surface, 30C...Main scale locking portion, 32, 34...Elastic adhesive.

Claims (1)

[Claims] 1. A frame connected to one of two objects to be measured whose relative displacement is to be measured;
a main scale made of a material having a coefficient of thermal expansion different from that of the frame; and an index scale connected to the other of the object to be measured and moved along the main scale; A linear displacement measuring device configured to measure the relative displacement between the two objects to be measured from movement, comprising a plurality of main scale holding members for holding the main scale at a plurality of locations in its longitudinal direction; The main scale holding member includes two guide surfaces corresponding to the graduation surface of the main scale or its back surface, and one surface of the scale side surface along the longitudinal direction, and a main scale integrally molded with the guide surface. The frame body is provided with two adhesive surfaces corresponding to the back surfaces of the two guide surfaces of the main scale holding member, and the back surface of the two guide surfaces of each main scale holding member is , each of the main scales is adhered to the adhesive surface of the corresponding frame, and the main scale is pressed against one of the two guide surfaces of each main scale holding member by a pressing means using the main scale locking part. the plurality of main scale holding members, and at least one of the adhesion between the main scale holding member and the frame and the adhesion between the main scale and the main scale holding member is elastic adhesion. Linear displacement measuring machine. 2. The linear displacement measuring device according to claim 1, wherein the pressing means is a rubber rod inserted between the main scale locking portion of the main scale holding member and the surface of the main scale. 3. The linear displacement measuring device according to claim 1, wherein the pressing means is the main scale locking portion itself of the main scale holding member having spring characteristics.