JPH0814485B2 - Scale accuracy measuring device and measuring method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a scale accuracy measuring device and method, and more particularly to improvement of a scale holding mechanism.

[Prior Art] Conventionally, a linear encoder that detects the relative movement amount of two moving bodies is well known, and since the movement amount can be measured with high accuracy and high resolution, the shape of various measured objects such as a three-dimensional measuring device can be measured. Alternatively, it is used in a device for measuring dimensions.

The linear encoder includes a magnetic type, a photoelectric type, a capacitance type, and the like, but each has two scales that are arranged to face each other, and various scales are provided on the scale surface in order to capture the relative movement amount of the scale as a physical quantity change. A pattern is formed.

For example, in a photoelectric linear encoder, the scale is formed with a scale pattern in which light non-transmissive portions and light transmissive portions made of thin film chrome or the like are alternately provided on a glass substrate at predetermined intervals.

Then, the two scales are moved relative to each other in accordance with the relative movement of the moving body, the light from the light emitter is transmitted / blocked by the scale pattern of the scale, and the light receiving device arranged opposite to the light emitter is placed across the scale. The amount of relative movement of the moving body is detected by the output of the container.

Therefore, the scale pattern formation accuracy of the scale directly leads to the measurement accuracy of the linear encoder, and in order to correspond to the recent higher accuracy and higher resolution of the linear encoder, more accurate and finer scale pattern formation and accuracy inspection are required. Is essential.

FIG. 4 shows a schematic configuration of a conventional scale accuracy measuring device.

In the figure, the measuring device 10 is installed in an incubator 12 made of polyurethane or the like.

Further, the measuring device 10 is fixed to the bed 14, a table 18 formed on the bed 14 through rolling balls 16 so as to be relatively movable with respect to the bed 14 with a light sliding force, and fixed to the table 18. And a scale holding means 22 for holding the glass scale 20.

Further, the table 18 is provided with a moving mechanism thereof, and the moving mechanism includes a motor 24, a table feed screw 26 interlocked with the shaft of the motor 24, and a table feed screw 26 that meshes with the table feed screw 26. A feed member 28 for feeding and moving the table 18 in the direction of arrow I by rotation.

Therefore, the scale 20 can be positioned at a predetermined position by externally drivingly controlling the motor 24.

Further, a reflector 30 made of a corner cube or the like for positioning and holding the scale 20 at a predetermined position is provided at the left end portion of the table 18 in the figure, and the table 18 cooperates with a laser interferometer (not shown). Detect the movement amount of.

Further, a scale reading means 32 such as a photoelectric microscope is arranged so as to face the scale 20a of the scale 20, and the scale 20a of the scale 20 moving relative to the scale reading means 32 can be read.

The scale accuracy measuring apparatus according to the illustrated example is roughly configured as described above, and its operation will be described below.

First, the measurer causes the scale holding means 22 to hold the scale 20.

Here, as shown in FIG. 5, the scale holding means 22 has a pressing arm 34 that can be screwed (or spring pressed), and a scale is provided via a pressing rubber 36 provided on the pressing arm 34. Holds 20

However, in the recently required high-accuracy measurement, the difference in the temperature distribution between the scale 20 itself or the parts has a great influence on the measurement accuracy.

Therefore, aging is performed for a long time in the environment of 20 ° C. to uniformly bring the temperature of each part of the scale 20 to 20 ° C.

Then, by driving the motor 24, the scale is
The 20 predetermined measurement positions are made to face the scale reading means, and the scale 20 is slightly fed at the measurement positions to measure the scale pitch on the scale 20.

[Problems to be Solved by the Invention] Problems with the Prior Art However, due to the extremely high precision demands of precision measuring machines and the like in recent years, the scale precision has a deviation from the true value of 0.1.
μm or less, σ = 0.01μ per 1,000 mm repeated measurement accuracy
m is required, and a highly accurate scale accuracy measuring device corresponding thereto is required.

However, conventionally, this type of scale accuracy measuring device has a problem in that it has a large error and cannot sufficiently meet the required measurement accuracy.

This is because there is friction between the scale holding means 22 and the scale 20, so that the thermal stress generated during the aging period cannot be released, which causes a measurement error due to strain.

That is, in the conventional scale accuracy measuring device, the material of the scale and the material of the scale holding means, or other measuring device parts are different, so when the temperature of each part is equilibrated by aging, thermal stress occurs due to temperature change during that time and strain. Will occur.

For example, the material of the photoelectric encoder scale is glass (coefficient of thermal expansion α = 7.5 × 10 ⁻⁶ / ° C.), whereas the material of ordinary scale holding means is steel (coefficient of thermal expansion α
= 11.5 × 10 ^-6 / ° C), and even if the temperature is the same before aging, a difference in expansion degree occurs due to a temperature change during aging, resulting in strain.

Furthermore, when performing such precision measurements, it is necessary to install the device in an unmanned incubator in consideration of temperature changes due to the body temperature of the measurer. The member was used to fix the scale, and the flexure of the elastic member absorbed the strain of the scale generated during aging.

However, even by such a method, the restoring force of the flexure generated in the elastic member acts on the scale, and it is difficult to maintain the strain completely in a non-strained state.

This distortion has a great influence on the measurement accuracy of the scale accuracy measuring device and must be removed somehow.

OBJECT OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide a scale accuracy measuring device and a measuring method thereof capable of reading the scale accuracy of the scale sufficiently accurately and efficiently. is there.

[Means for Solving the Problem] In order to achieve the above-mentioned object, a scale accuracy measuring device according to the present invention is characterized by comprising a vacuum suction mechanism and a temporary peeling means.

Here, the vacuum suction mechanism is provided in the scale holding means and firmly holds the scale loosely held in the holding means.

The temporary peeling means peels the scale from the scale holding means.

In the present invention, it is preferable that the temporary peeling means comprises a peeling piezoelectric element whose one end is in contact with the end of the scale.

Further, the scale accuracy measuring method according to the present invention includes an aging step, a scale distortion removing step, and a measuring step.

In the aging step, the scale is vacuum-adsorbed and held by the scale holding means and aged until a predetermined temperature is reached.

In the scale strain removing step, after the aging step is completed, the vacuum suction of the scale is temporarily released to remove the thermal stress of the scale due to the thermal expansion.

In the measuring step, the scale is again vacuum-sucked on the scale holding means to read the scale.

[Operation] Since the scale accuracy measuring device according to the present invention has the vacuum suction mechanism of the scale as described above, the scale can be easily held and peeled by adjusting the degree of vacuum, and the heat generated during aging can be easily generated. Easy release of stress is possible.

At the time of this temporary scale peeling, the scale is stretchably and loosely held by the scale holding means, and the strain of the scale generated during the aging can be removed.
Moreover, the scale can be re-adsorbed.

Moreover, the temporary peeling means can surely peel the scale when the thermal stress is removed, so that the measurement accuracy can be greatly improved.

Here, if the temporary peeling means is composed of a peeling piezoelectric element provided in the scale holding means, it is possible to keep the measurement environment constant without generating unnecessary heat.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a scale accuracy measuring apparatus according to an embodiment of the present invention, (A) is a front view and (B) is a side view.

It should be noted that the reference numeral 100 is added to the portion corresponding to the above-mentioned conventional technique and the description thereof is omitted.

In this embodiment, a table 118 is placed on a bed 114 via rolling balls 116 such as linear bearings, and the table can be moved to an appropriate position by rotating the feed screw 126 with a pulse motor or the like. There is. Then, the scale holding means 122 is movably mounted on the table 118 via a vertical load receiving ball 150 and a horizontal constraining ball 152.

One vertical load receiving ball 150 (150
a), two pieces (150b, 150c) are arranged on the right side in the figure, and the scale holding means 122 is supported at three points.

Two horizontal restraining balls 152 are installed on each of the restraining stands 154a, 154b, 154c, 154d arranged on the left, right, front and back of the table 118. In addition, each restraint 154 is screw 1
The position can be adjusted by 56, and the scale holding means 122 is moved in the direction of arrow II to perform the predetermined positioning of the scale 120.

As shown in FIG. 2 in an enlarged manner, the scale holding means 122 has a vacuum suction mechanism for the scale, and the vacuum suction mechanism has a suction groove 158 provided on the surface facing the scale 120. The pipe 160 is connected to a vacuum pump (not shown) that is drawn out from the approximate center of the suction groove.

Further, along the lower edge of the scale 120, peeling piezoelectric elements 162a and 162b are arranged at two places on the left and right of the scale holding means 122 as temporary peeling means.

The peeling piezoelectric element 162 has a laminated piezoelectric actuator element, that is, a laminated structure of piezoelectric ceramic plates, and can expand and contract by about 15 μm by adjusting the voltage.

This piezoelectric element has the advantages that it is small, does not generate unnecessary heat, and can be operated more freely than outside the temperature-controlled room.

Therefore, even when the scale 120 is not peeled from the scale holding means 122 when the vacuum degree of vacuum suction is reduced, the scale is pushed from below by the extension of the piezoelectric element and can be surely peeled.

It should be noted that such a peeling means is not limited to the piezoelectric element, and may be a means for blowing a small amount of air from the suction groove. In addition,
At this time, the scale 120 can release the thermal stress by expanding and contracting near the scale holding means 122 and the scale retainer 172.

Further, the scale retainer 172 does not move the scale position even after the temporary peeling, and re-holding by suction is extremely easy.

On the other hand, as shown in FIG.
A minute feed mechanism 164 is provided at the left end of 118.

The minute feed mechanism 164 has a minute feed piezoelectric element 166 whose one end contacts the left end of the table 118, a positioning screw 168 whose tip contacts the other end of the piezoelectric element 166, and the scale holding means 1.
It is composed of a tension coil spring 170 for pulling 22 to the left in the drawing.

Then, on the left side of the scale holding means 122 in the figure, the reflector 130 is provided at substantially the same height as the position of the scale scale 120a.
Is provided, and the amount of movement of the scale holding means 122 with respect to the base 114 can be measured by receiving and reflecting the laser light from the laser interferometer installed on the base 114.

As shown in FIG. 1, the laser interferometer includes a laser oscillator 180, a beam splitter 182, a second reflector 184,
A laser oscillator consisting of a detector 186 such as a photoelectric converter
A laser beam from 80 is projected toward the reflector 130, and a beam splitter 182 is arranged on the optical path with an inclination of 45 degrees.

The laser light reflected by the beam splitter 182 travels in a direction orthogonal to the optical path, is reflected by a second reflector 184 provided on the optical path, passes through the beam splitter 182, and is directed to a detector 186. Incident.

On the other hand, the reflector 1 attached to the scale holding means 122
The reflected light from 30 is reflected by the beam splitter 182, interferes with the reflected light from the second reflector 184, and the detector 1
It is incident on 86.

According to such an interferometer, when the scale holding means 122 moves in the longitudinal direction, the optical path length from the beam splitter to the reflector 130 changes, so that by detecting the wavelength of the laser light incident on the detector 186, 0.01 The amount of movement of the scale holding means 122 can be measured with an accuracy of μm.

In the present invention, since highly accurate measurement is performed in this manner, the scale holding means 122 is made lightweight so as to be able to sufficiently follow minute changes in the piezoelectric element, and is also affected by minute deformation based on the radius due to the load. Therefore, the three-tiered structure is adopted to enable the coarse movement of the table 118 and the fine movement of the scale holding means 122 for the removal thereof.

A scale reading means 132 such as a photoelectric microscope is installed on the base or the like so as to face the scale 120a of the scale 120.

The scale accuracy measuring apparatus according to the present embodiment is configured as described above, and the scale accuracy is measured as follows.

Aging Step First, the measurer holds the scale 120 on the scale holding surface of the scale holding means 122.

A scale retainer 172 is arranged so as to face the scale holding surface.

In this state, when a vacuum pump (not shown) is driven, the scale 120 is sucked by the suction groove 158 and firmly held by the scale holding means 122.

Here, in the prior art, in order to hold the scale, as shown in FIG. 5, the scale is brought into contact with the scale holding means, and the scale is configured to be pressed by pressing rubbers arranged at several places in the longitudinal direction. , The scale was sometimes bent, but according to the vacuum adsorption method in which at least one groove is provided on the scale mounting surface of the scale holding means and the void in the groove is diluted as in the present embodiment. ,
The scale properly adheres to the flat surface of the scale holding means and does not deform.

Further, the measurer operates the positioning screw 168 to determine the initial positions of the minute feed piezoelectric element 166 and the scale 120.

Then, after that, aging is performed in a thermostat in the same manner as in the conventional method until the temperature of each part of the scale 120 becomes uniform.

Scale distortion removing step Then, when the aging is completed, the vacuum degree of the suction groove 158 is lowered.

At the same time, a drive voltage is applied to the peeling piezoelectric element 162,
When extended, the scale 120 is reliably peeled off from the scale holding means 122.

As a result, the thermal stress generated during the aging between the scale 120 and the scale holding means 122 and the strain caused thereby are removed.

Measurement Step Next, the voltage application to the peeling piezoelectric element is stopped and the vacuum pump is driven again.

Then, the scale 120 is sucked into the suction groove 158, and the scale pitch of the scale 120 is read by the scale reading means 132 such as a photoelectric microscope.

 The scale is measured as follows.

Table coarse movement process First, the operator operates the feed screw 126 to move the table 118.

Then, the scale reading means 132 is opposed to the measurement starting point of the scale 120.

Fine feed step Next, the fine feed mechanism is operated to measure the scale pitch of the scale.

That is, a voltage is applied to the minute feed piezoelectric element 166, and the extension thereof causes the scale holding means 122 and the scale 120 to be minute feed.

Here, as is well known, the piezoelectric element has a degree of expansion proportional to an applied voltage, and by controlling the applied voltage, minute feeding of an accurate scale is performed at an extremely low speed.

Therefore, by increasing or decreasing the voltage applied to the piezoelectric element 166, the element is continuously expanded or contracted, and the scale holding means 122 is moved at a low speed.

When the scale reading means 132 detects the edge of the scale or the center of the scale at the measurement start point, the signal of the laser interferometer is used as the measurement start point, the scale moves one pitch, and the scale edge at the other end is detected. By setting the signal of the laser interferometer as the end point of the measurement, the pitch of the scale 120 can be measured with extremely high accuracy.

The amount of movement by the piezoelectric element is about 15 μm, and the feed rate is about 0.01 μm / sec to 1 μm / sec, 8/1000 μm
It is possible to measure the scale pitch.

Then, when the scale pitch measurement at the measurement position is completed, the next measurement position is opposed to the scale reading means by screw feeding.

At this time, the voltage application to the minute feed piezoelectric element is stopped, but the tension spring 170 is contracted as the minute feed piezoelectric element contracts.
As a result, the scale holding means 122 is pulled back and returned to the initial position.

The scale pitch at each measurement point is measured by repeating the above measurement operation.

Length Measuring Process Next, the length measuring process for measuring the length between certain scale scales according to the present embodiment will be described.

The measurer first operates the feed screw 126 to make the scale reading means 132 face the measurement start point position of the scale 120.

Then, the minute feed mechanism 164 is operated to detect the edge of the scale graduation at the measurement starting point or the like by the graduation reading means 132 as in the pitch measurement, and the signal of the laser interferometer at that time is used as the starting point until the length to be measured next time. Lead screw 126
Then, the table 118 and the scale holding means 122 are moved.

During this time, the reflector 130 also moves, so the interferometer continues to measure the amount of movement.

Next, when the measurement end position of the scale 120 faces the scale reading means 132, the feeding is stopped, and the end edge of the scale is measured by using the minute feeding mechanism 164 in the same manner as when the scale reading edge 132 of the starting point is detected by the scale reading means 132. Etc. are detected.

Then, by reading the value of the interferometer when the edge or the like at the end point is detected, the accuracy of the scale at the desired length can be measured with extremely high accuracy.

Here, the reflector 130 is set at the same height as the scale of the scale so that an Abbe error does not occur.

Further, since the minute feed piezoelectric element 166 is arranged below the scale holding means 122, an unreasonable force is not applied during feeding.

[Effects of the Invention] Since the present invention is configured as described above, the following effects are achieved.

In the invention described in claim 1, since the scale is sucked and held by the vacuum suction mechanism and the scale strain is removed by the temporary peeling mechanism before the measurement, the scale can be held and peeled without contact, It is possible to release the thermal stress generated during aging and perform accuracy measurement without distortion in the scale.

In the invention described in claim 2, since the piezoelectric element whose one end is in contact with the end of the scale is the temporary peeling mechanism, by driving the piezoelectric element at the time of peeling the scale, unnecessary heat is not generated from the scale. Reliable peeling is performed.

According to the third aspect of the invention, since the vacuum adsorption is temporarily released after the aging is finished to release the thermal stress generated in the scale, the scale graduation measurement can be performed without distortion.

[Brief description of drawings]

FIG. 1 is an external view of a scale accuracy measuring device according to an embodiment of the present invention, FIG. 2 is an enlarged view of a main part of a vacuum suction mechanism of the device shown in FIG. 1, and FIG. 1 is an explanatory view of a minute feed mechanism of the apparatus shown in FIG. 1, FIG. 4 is an external view of a conventional scale accuracy measuring apparatus, and FIG. 5 is an explanatory view of a scale holding mechanism of the conventional apparatus. 10,110 …… Scale accuracy measuring device 18,118 …… Table 20,120 …… Scale 22,122 …… Scale holding means 158 …… Suction groove (vacuum suction mechanism) 162 …… Peeling piezoelectric element (temporary peeling means) 166 …… Small feed piezoelectric element ( Micro feed mechanism)

Claims (3)

[Claims] 1. A scale holding means provided on a table for loosely holding a scale so that it can expand and contract, and a scale reading means arranged to face a scale forming surface of the scale, the scale holding means and the scale reading means. While relatively moving the and along the scale pattern formed on the scale surface, in the scale accuracy measuring device for measuring the scale accuracy of the scale surface by the scale reading means, provided in the scale holding means, in the scale holding means A scale accuracy measuring device comprising: a vacuum suction mechanism that firmly suctions and holds a loosely held scale; and a temporary peeling unit that peels the scale from the scale holding unit. 2. The scale accuracy measuring device according to claim 1, wherein the temporary peeling means comprises a peeling piezoelectric element provided on the scale holding means and having one end abutting against the scale holding means. . 3. A scale pattern formed on a scale surface, comprising scale holding means provided on a table for loosely holding the scale so that the scale can expand and contract, and scale reading means arranged opposite to the scale forming surface of the scale. In the scale accuracy measuring method for measuring the scale accuracy of the scale surface by the scale reading means while relatively moving along the scale, the scale is vacuum suction-held on the scale-holding means, and an aging step of aging until reaching a predetermined temperature, After the aging process is completed, the vacuum suction of the scale is temporarily released, and the scale strain removal means that removes the thermal stress generated in the scale due to thermal expansion, and the scale is again vacuum-sucked to the scale holding means and the scale is read. A scale accuracy measuring method comprising: a measuring step.