JPS59226807A - Linear displacement measuring instrument - Google Patents

Abstract

PURPOSE:To hold a scale at right angles regardless of the curvature of a frame body and to measure with high precision by adhering a scale holding member which has guide surfaces and a projection to the frame body, and pressing and adhering a main scale to the member with a rubber rod. CONSTITUTION:The main scale holding member 30 which has the two guide surfaces 30A and 30B and guide projection 30c is adhered and fixed to the frame body 14 at specific pitch with an elastic adhesive 32. Then, the main scale 10 while pressed against the guide surface 30A with the rubber rod 12 is adhered fixedly to the holding member with an elastic adhesive 34. Consequently, even if there is a slight error in the bending angle theta of the member 30, the bottom surface of the scale 10 abuts on the guide surface 30B securely, and even if the frame body 14 curves, the scale 10 is held at right angles and the difference in thermal expansion between the frame body 14 and scale 10 is absorbed, so taking a high-precision measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a linear displacement measuring machine, and particularly to a linear displacement measuring machine having a relatively short main scale. a frame body connected to one of the two objects 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;
an index scale connected to the other of the objects to be measured and moved along the main scale, and configured to measure relative displacement between the two objects to be measured from relative movement of the main scale and the index scale. Concerning the improvement of the linear displacement measuring machine.

Generally speaking, in a measuring machine that measures the length of an object, when measuring the amount of movement of something that moves relative to the 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 amount of relative displacement between the frame body and the detector is read by, for example, an optical method or an electromagnetic method.

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 adhesively fixed to the frame 14 using an elastic adhesive 16 or the like while being pressed against the guide surfaces 14A and 14B of the frame 14, so that the main scale 10 is elastically held.

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 configured as shown in FIG.
The index scales 26 and 28 on which vertical striped scales similar to those shown in FIG.

However, due to the manufacturing method used to form the frame 14, the extruded aluminum material is already subject to bending and twisting of, for example, about 0.03111 m per 300 mm of length, that is, about 30 times the scale resolution of 1 μm. It is difficult in practice to correct these irregularities and achieve a finish with a high y1 degree comparable to that of main scale 10.In addition, during use, heat may be generated due to temperature changes. Therefore, in the past, in order to obtain a scale resolution of about 1 μm, for example, the main scale 1
No matter how precisely the main scale 10 is finished and processed, when the main scale 10 is fixed to the frame 14 with adhesive, the main scale 10 will adapt to the bending of the frame 14 and deform.
There was a problem in that the scale was enlarged or reduced, resulting in a significant drop 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
Since A does not coincide with the neutral plane C of the main scale 10, the curvature of the main scale 10 is as shown in FIG.
When the bend 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 △θ, the length before the bending occurs, that is, the length of the neutral plane C, and the scale plane 10A
When the length of is taken as LO, the error ε between the two is approximately expressed by the following equation.

ε=Lo −L , (1) LO
−← (R+j/2) △ θ ,,,(2
(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-RCO3(Δθ/2) R[1-(1-(1/2 +)X(Δθ/2)
2)] =R(Δθ)2/8 =LΔθ/8, (4) Therefore,
The error ε is expressed by the following equation using this δ.

ε: (t/2) 80 ÷ (t / 2)
mm, thickness [is 5 mm, and δ is 0.06+nm, the error ε is about 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 defect in a linear displacement measuring machine that requires measurement accuracy of 1 μm or less.

In order to alleviate such problems, when fixing the main scale 10 to the frame 14 by adhesive, for example, use a test indicator, an electric micrometer, etc., and touch the electric micrometer, etc. to two sides of the main scale 10. It is also possible to position the main scale 10 by measuring the accuracy in the longitudinal direction and inserting shims between the main scale 10 and the frame 14 according to the irregularities, but this is not possible. This method not only has extremely low efficiency, but also has problems in that accurate positioning is extremely difficult.

The present invention has been made to solve the above-mentioned conventional problems, and has the objective of holding the main scale straight regardless of bending of the frame, and absorbing the difference in thermal expansion between the main scale and the frame. Therefore, an object of the present invention is to provide a linear displacement measuring device that can perform highly accurate measurements.

The present invention includes: a frame connected to one of two objects to be measured whose relative displacement is to be measured; a main scale held by the frame and made of a material having a coefficient of thermal expansion different from that of the frame;
an index scale connected to the other of the objects to be measured and moved along the main scale, and configured to measure relative displacement between the two objects to be measured from relative movement of the main scale and the index scale. In the linear displacement measuring device, a main scale holding member having two guide surfaces corresponding to and covering two intersecting surfaces of the main scale is provided, while maintaining the straightness of the guide surfaces.
Covering the frame with adhesive and fixing at a predetermined pitch in the longitudinal direction of the frame, and adhesively fixing the main scale to the main scale holding member while being pressed against the guide surface of the main scale holding member by a pressing means, The above objective has been achieved.

According to the present invention, the main scale has two guide surfaces corresponding to the two intersecting surfaces thereof, and the main scale holding member is adhesively fixed to the frame while maintaining the straightness of the guide surfaces. The main scale can be held straight regardless of the bending of the frame. Furthermore, since the main scale holding members are adhesively fixed at predetermined pitches in the longitudinal direction of the frame, the difference in thermal expansion between the main scale and the frame can be easily absorbed.

Further, in an embodiment of the present invention, a guide protrusion is formed in the central part of the guide surface in the thickness direction of the main scale, so that even if the shape accuracy of the main scale holding member is not high, the main scale can be held therein. This allows it to be held stably on an elevated surface.

Furthermore, in another embodiment of the present invention, the pressing means is an elastic member, and the contact area of the elastic member to the main scale is
The area of contact between the main scale and the main scale holding member is made smaller than that of the main scale to prevent an unbalanced moment from being generated.

Further, in still another embodiment of the present invention, the ratio of the guide surface length of the main scale holding member to the main scale holding member arrangement interval is set to 1 to 1:11, so that even when the main scale holding member is roughly handled during transportation, This is to prevent problems such as misalignment of the main scale.

Embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in Figures 4 and 5, this embodiment uses one of the two objects whose relative displacement is to be measured, for example, a frame made of an aluminum extrusion that is fixed to the bed of a machine tool. A main scale 10 held by the frame body 14 and made of a material having a coefficient of thermal expansion different from that of the frame body 14, such as glass, is connected to the other object to be measured, such as a workpiece or a tool. , an index scale (not shown) that is moved along the main scale 10, and the relative displacement between the two objects to be measured can be measured from the relative movement between the main scale 10 and the index scale. In the linear displacement measuring device, a main scale holding section 113 holds two guide surfaces 30A and 30B corresponding to two orthogonal surfaces of the main scale 10.
0 is adhesively fixed 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 and 30B, and the main scale 10 is attached to a rubber plate serving as a pressing means. The rod 12 is pressed against the guide surface 30A of the main scale holding member 30, and the elastic adhesive 34 is used to adhesively fix the main scale holding member 30 to the main scale holding member 30.

As shown in detail in FIG. 6, the main scale holding member 30 has an abbreviated shape, with one guide surface 30B.
There is a guide protrusion 30C in the center of the main scale in the thickness direction.
is formed. This is to ensure that even if there is a slight error in the bending angle θ of the main scale holding member 30, the bottom surface of the main scale 10 will surely come into contact with the guide surface 30B. Note that if the main scale holding member 30 can be bent with high precision, the guide protrusion 30C may be omitted.

The contact area of the rubber rod 12 to the main scale 10 is:
Main scale holding member 30 of the main scale 10
The area of contact is smaller than that of the contact area. 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 front stage interval P is 1 near to 1:
It is said to be in the range of 11. This is the main scale 10
It absorbs the difference in thermal expansion 11sI between the frame body 14 and the frame body 14, thereby preventing damage to the main scale 10 due to thermal stress, reducing hysteresis in measured values due to temperature changes during measurement, and further preventing rough handling during transportation. This is to prevent problems such as misalignment of the main scale due to

That is, as the applicant has already proposed in Japanese Patent Application No. 57-57604, the main scale 10 is, for example, 1500 m long.
If there is a long scale C of about m ~ 4500 nv, the main scale 1 is placed in the longitudinal direction of the main scale 10.
0. An elastic member non-joint part is provided with a pitch and length determined by the materials of the frame 14 and the elastic joint member and the length of the main scale 10, and when the temperature changes, the elastic member is applied to the main scale 10 through the elastic joint part side. Reducing thermal stress By covering the main scale 10, it is possible to prevent damage to the main scale 10 due to thermal stress and to reduce hysteresis in measured values due to temperature changes during measurement. In the case of a long object, the guide 1IIi length 1 of the main scale holding part < 430 and the main scale holding member arrangement 1i1
The ratio of 1 interval P can be in the range of 1=15 to 1:20. On the other hand, the length of the main scale 10 is, for example, 150 mm.
If it is relatively short, 0+nm or less, it is light;
Since it is easy to carry, it is less likely to be handled roughly during transportation, so the arrangement should be made to prevent the packaging from falling, and for example, the maximum allowable external force should be set at around 12G for a long scale, whereas for a short scale, the There is an 8-double that raises it to about 20-50G.

The inventor said that the effective length is 160CHnm and 1800mm, respectively.
, 2000mm, 2200mm, 2400vn, 260
For a linear displacement measuring machine with main scale 10 of 0 mm, 2800 mm, and 3000 mm, the diameter is 3 m.
m rubber rod 12 made of nitrile rubber (hardness 60), one mating part has a length of 15 ± 2 m + n, and the unjoined part has a width of 135 n + m.
When an experiment was conducted by arranging them at equal pitches, the experimental results shown in Table 1 below were obtained, and it was confirmed that all of them were sufficient.

C Cor 10 Be] ρ kume\/%:/+:=M1 table, F<+/2) is the maximum tension of the main scale 1o when the temperature changes by 70°C (unit: kg: standard value) 330kg
/mn+), agmax C, also the maximum stress of main scale 1o (unit: kg/man2: standard value 3 kc
l/1111112), (l rmaX rubber rod 12
Maximum stress (t2-42kg/n+m2: NA4flr
M0.8-/nu++2), λ(1> is the difference in thermal expansion between the frame 14 and the main scale 10 (unit: mm)
, λ' (1) is also the rubber rod 1 of the main scale 1o.
2 (unit: μm), λ-1 (1) is the elongation of the rubber rod 12 (unit: im), λ(1)) is the hysteresis against temperature (unit: μm), n is the maximum allowable It is an external force (unit: G).

As is clear from Table 1, the maximum allowable external force is 2°G ~ 50
G is secured, and the hysteresis against temperature is also 16
In the case of 00mm, it is relatively small at 4.4μm, and
It can be seen that packaging costs are significantly improved.

In addition, when the amount of hysteresis with respect to temperature was calculated in the same way, the amount of hysteresis was 1.7 μm when the effective length of the main scale was 1000 mm, and the effective length was 12
00mm, the amount of hysteresis is 2.5μm
When one effective length was 1400 mm, the hysteresis value was 3.4 μm, which was a problem-free amount.

Specifically, the attachment of the main scale 10 to the frame body 14 in this embodiment is performed, for example, as follows. 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 points of the main scale 10, which is provided corresponding to at least the arrangement position of the main scale holding part tJ30. The main scale holding member 30 is suctioned and fixed at a predetermined pitch. Next, the frame body 14 is adhesively fixed with an elastic adhesive 32 to the main scale holding part +J 30 which is suction-fixed to the positioning jig. Further, the target positioning jig is removed and, instead, the main scale 10 is adhesively fixed to the main scale holding portion U30 using an elastic adhesive 34. Thereby, the main scale holding member 30 can be easily adhesively fixed to the frame 14 while maintaining the straightness of the guide surfaces 30A and 30B.

In this embodiment, 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 1o. The effect of absorbing the difference in thermal expansion between the frame body 14 and the frame body 14 is particularly high. Note that the types of adhesives are not limited to these, and for example, it is also possible to use adhesives in which one or both of the adhesives do not have elasticity.

In the above embodiments, the present invention was applied to a linear displacement measuring machine that used an aluminum frame and a glass main scale, but the scope of the present invention is not limited to this, and other It is clear that the method can also be applied to a linear displacement measuring machine using a frame body main scale made of

As described above, according to the present invention, the main scale can be held straight regardless of bending of the frame, and the difference in thermal expansion between the main scale and the frame can be absorbed. Therefore, it has an excellent effect of being able to obtain high measurement accuracy.

[Brief explanation of the drawing]

Fig. 1 is a J cross-sectional view showing the holding structure of the main scale in an example of a conventional linear displacement measuring machine, and 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. , FIG. 3 is a plan view of a device for measuring measurement errors caused by bending of the main scale in the thickness direction, and FIG. A sectional view showing the main school holding structure in the embodiment of the linear displacement measuring machine according to the present invention, FIG.
FIG. 6 is a cross-sectional view taken along line -v, showing the shape of the main scale holding part H used in the embodiment. 10...main scale, 12...rubber, 1
4... Frame body, 24... Index scale, 30... Main scale holding member, 30A, 30B... Guide surface, 30G... Guide protrusion, 32.34... Elastic adhesive, P ...Main scale holding member arrangement interval. Agent Takaya Ron (1 idiot)

Claims (4)

[Claims] (1) a frame connected to one of two objects to be measured whose relative displacement is to be measured; 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 objects to be measured and moved along the main scale, and the relative displacement between the two objects to be measured is measured from the relative movement of the main scale and the index scale. In the linear displacement measuring device, a main scale holding member having two guide surfaces corresponding to two intersecting surfaces of the main scale extends in the longitudinal direction of the frame while maintaining the straightness of the guide surfaces. In addition to being adhesively fixed at a predetermined pitch,
A linear displacement measuring device, wherein the main scale is adhesively fixed to the main scale holding member while being pressed against a guide surface of the main scale holding member by a pressing means. (2) The linear displacement measuring device according to claim 1, wherein a guide protrusion is formed at the center of the guide surface in the thickness direction of the main scale. (3) A patent claim in which the pressing means is an elastic member, and the area of contact of the elastic member with the main scale is smaller than the area of contact of the main scale with the main scale holding member. Linear displacement measurement unit as described in item 1. (4) The ratio of the length of the guide surface of the main scale holding member to the spacing between the main scale holding parts is 1 near to 1:11.
A linear displacement measuring device according to claim 1.