JPS61219818A - Length measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a high preciseness length measuring apparatus, by fixing a length measuring scale to the mount reference surface formed to a case under pressure by an elastic member through a lubricating member. CONSTITUTION:A lubricating member 3 is inserted between a length measuring scale 1 and a case 2, and the scale 1 is pressed and held to the mount surface 6 of the case 2 in the side opposite to the member 3 by the elastic member 4 provided between the scale 1 and the case 2. A detection head 8 has the light source provided to one graduation surface of the scale 1 and the index scale and light receiving element provided to the other graduations surface thereof and is constituted of a detection part 8a moving to the direction vertical to the surface of paper in opposed relation to the graduations surface, the base part 8b fixed to the other 11 of an article to be measured and the arm part 8c connected the detection part 8a and the base part 8b. When temp. change is generated, the length of the scale 1 changes but the scale 1 slides along the surface of the member 3 and receives no effect of the case 2. Therefore, measuring accuracy becomes stable.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a length measuring device that measures the amount of relative displacement between two relatively displaced objects.

(Background of the Invention) This type of device uses a detection head that uses photoelectric means to detect a length measurement scale that has a lattice-like scale, that is, a scored band, on one side of a transparent material such as glass. It is known as a length measuring device that reads the amount of movement.

Generally, in this type of photoelectric length measuring device, a glass plate as described above is used as the sub-length scale, and an extruded aluminum alloy material is used as the case for holding and housing the length measuring scale. As a method of holding the length measuring scale, a conventional method is disclosed in US Pat. No. 4,031,595 in which the length measuring scale is pressed against the reference surface of the case with a rubber string 4. This method has the disadvantage that the length measurement accuracy changes due to the difference in thermal expansion coefficient between glass and aluminum alloy when there is a temperature change. That is, there is a coefficient of friction between the length measuring scale and the case, and when the length measuring scale and the case try to move relative to each other, a frictional force acts due to the pressing force of the rubber string. Due to this frictional force, when there is a temperature change, the length measurement scale will expand or contract due to the thermal expansion of the case, and the amount that the length measurement scale would normally expand or contract due to thermal expansion will be expanded or contracted.
There was a drawback that the length measurement accuracy changed significantly.

To explain in more detail, in a length measuring device with a conventional mounting structure as shown in Fig. 2, the length measuring direction (
(direction perpendicular to the page) K It is assumed that no frictional force acts between the length measuring scale 1 and the case 2. Assume that the length of the length measurement scale l is 1 m. Next, if the room temperature rises to 30°C, case 2 made of aluminum alloy has a coefficient of thermal expansion of 22
×10-1/°C, compared to room temperature of 20°C, 0.
If the coefficient of thermal expansion of the glass of length measurement scale 1 is 8 x 10 = /'C, then the length should be 0.08 rxyx longer than when the length measurement scale IH room temperature is 20°C. However, in reality, as mentioned above, since the frictional force acts, the length measurement scale IFi case 2) causes it to be further stretched and becomes longer. Since there is a limit to the frictional force, if the measuring scale 1 is stretched beyond a certain amount,
There is no possibility that a slippage will occur between the length measuring scale 1 and the case 20, and the length measuring scale 1 will be stretched by the same amount as the case 2. In this way, the thermal expansion coefficient of the length measuring scale 1 is determined to be between the thermal expansion coefficient of case 2 and that of the length measuring scale 1 alone, and the value is not constant.

Then, when the temperature returns to 20℃, length measurement scale 1 is case 2.
It will remain compressed. For this reason, there was a drawback that the accuracy was unstable. Japanese Patent Publication No. 51-106458 is a technique for improving this drawback. This is intended to provide an elastic adhesive layer 12 between the length measuring scale 1 and the case 2 to alleviate distortion caused by thermal expansion. (See FIG. 3) However, this structure has the drawback that it is difficult to fix the length measurement scale in an ideal state, that is, in a straight position, resulting in poor length measurement accuracy.

(Objective of the Invention) The present invention solves these drawbacks, and provides a length measuring device that is highly accurate, has little change in accuracy even when temperature changes, and has a coefficient of thermal expansion that is very close to the original value of the length measuring scale. The purpose is to obtain.

A case fixed to one of the objects to be measured is made to hold a length measurement scale having a different coefficient of thermal expansion from that of the case, and a detection head is mounted on the other object to be measured to move along the length measurement scale and detect the amount of displacement. In a fixed length measuring device,
The length measuring device is characterized in that a mounting reference surface for the length measuring scale is formed in the case, and the length measuring scale is pressed and fixed to the mounting reference surface by an elastic member via a lubricating member.

(Embodiment) FIG. 1 shows an embodiment of the present invention, in which a lubricating member 3 made of, for example, a Teflon plate is inserted between a length measuring scale l and a case 2. The sub-length scale 1 is pressed against the mounting reference surface 6 of the case 2 and held by an elastic member 4 such as a rubber string provided between the length measurement scale 1 and the case 2 on the opposite side of the lubricating member 3. The elastic member 4 is made of adhesive 5, 5'
It is adhesively fixed to the case 2 and length measuring scale 1 by. With this structure, the lubricating member 3 prevents frictional force from acting between the length measuring scale 1 and the case 2. The adhesive 5 prevents the length measuring scale 1 from falling off the case 2. The elastic member 4 is made of, for example, a rubber string as described above, and its elastic modulus is sufficiently smaller than that of the length measurement scale 1 and case 2, so that stress that deforms the length measurement scale to the extent that it causes problems in length measurement accuracy is not generated. ,. In addition, the adhesive 7 has one narrow area (length measurement scale IFi
The length measurement direction is perpendicular to the paper surface), and by adhesively fixing the length measurement scale 1 and case 2 in one narrow area in that direction (for example, the center), the length measurement scale 1 and case 2 can be fixed.
When the case 2 is attached to one side 10 of the object to be measured, the relative positional relationship between the one side 10 of the object to be measured and the length measuring scale 1 is stabilized. In addition to the Teflon plate, solid lubricant, lubricating oil, rollers, etc. can be used as the lubricating member 3.

A detection head 8 is provided to read scales formed on the length measurement scale l in a direction perpendicular to the paper surface.

The detection head 8 has a light source on one side of the graduation surface of the length measurement scale l, and an index scale and a light receiving element on the other side.
, a base portion 8b fixed to the other side 11 of the object to be measured, and an arm portion 8C that connects the detection portion 8a inside the case 2 and the base portion 8b outside the case 2. A through hole is formed in the case 2 in the direction perpendicular to the page to allow movement of the arm portion 8C in the direction perpendicular to the page.Through this through hole, oil, dirt, etc. can be leaked from the outside of the case 2 to the inside of the case 2. To prevent intrusion, seal members 9 a +9b are provided from both sides between the case 2 and the arm 8C to cover the through hole and allow the arm 8C to move in the direction perpendicular to the plane of the paper.

Because of this structure, when the other object 11 of the object to be measured moves in the direction perpendicular to the plane of the paper relative to the one object 10 of the object to be measured, the light-receiving element of the detection section 8a responds to the displacement I of the other object 11, as is well known. A sinusoidal signal is output. For example, by counting the number of cycles, the amount of displacement can be determined.

When a temperature change occurs, the length of the measuring scale 1 changes, but since it slides on the surface of the measuring scale 1#-i lubricating member 3 and is not affected by case 2, the change in length is It depends only on the coefficient of thermal expansion of the material of the length measurement scale l. Therefore, measurement accuracy becomes stable. Furthermore, by performing correction calculations on measured values using temperature information obtained by the temperature detector, a length measuring device with high measurement accuracy can be obtained.

In the above embodiments, a photoelectric transmissive length measuring device using glass as the length measuring scale was used as an example, but a photoelectric reflective length measuring device with a metal length measuring scale was used. Furthermore, it goes without saying that the present invention can be similarly applied to a magnetic length measuring device in which the length measuring scale is made of a magnetic material or the like.

(Effects of the Invention) As described above, according to the present invention, high accuracy can be obtained because the length measurement scale is attached following the reference surface of the case, and the coefficient of friction between the length measurement scale and the case is small, and the length measurement scale is attached along the reference surface of the case. Since the frictional force acting on the scale is very small, the coefficient of thermal expansion is very close to the original value of the measuring scale, and the device of the present invention has the advantage that there is little change in accuracy even when there is a temperature change. It is effective because high precision and stable accuracy can be obtained if it is incorporated into machine tools, measuring devices, etc. and used for positioning and length measurement.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the device according to the present invention, FIG. 2 is a cross-sectional view showing a length measuring scale mounting structure in the prior art, and FIG. 3 is a cross-sectional view showing a length measuring scale mounting structure in another prior art. A sectional view shown. (Explanation of symbols of main parts) 1... Length measurement scale, 2... Case, 3... Lubricating member, 4... Elastic member, 6... ...Mounting reference surface, 8...
detection head.

Claims (1)

[Claims] 1) A case fixed to one of two relatively displaced objects to be measured is made to hold a length measurement scale having a different coefficient of thermal expansion from that of the case, and the other object to be measured is made to hold a length measurement scale having a different coefficient of thermal expansion from that of the case. In a length measuring device having a fixed detection head that moves along a scale and detects displacement, a mounting reference surface for the length measuring scale is formed in the case, and the length measuring scale is lubricated by an elastic member. A length measuring device, characterized in that it is press-fixed to the mounting reference surface via a member. 2) The length measuring device according to claim 1, wherein the elastic member is a rubber cord adhesively fixed to the length measuring scale and the case. 3) The length measuring device according to claim 1 or 2, wherein the main scale is bonded to the case in one narrow area. 4) The length measurement according to any one of claims 1 to 3, wherein any one of a Teflon plate, a solid lubricant, a lubricating oil, and a roller is used as the lubricating member. Device.