JPH02243918A - Displacement detector - Google Patents

Abstract

PURPOSE:To measure displacement with high resolution by counting periodic ruggedness presenting in one direction on the surface of a reference scale and measuring the quantity of displacement of an object to be measured. CONSTITUTION:A micrometer 7 is adjusted manually and a probe 10 is put close to the reference scale 5 until a tunnel current can be detected. The other end of a wire 4 is fixed to the moving part of the object and when the moving part moves by delta (<10mm), a stage 2 is drawn in an X direction through the wire 4. Consequently, the stage 2 moves in an X direction because of the characteristic of a leaf spring 3. When this stage 2 moves, a signal corresponding to the ruggedness of the surface of the reference scale 5 is obtained. This signal is inputted to an edge detector to obtain positive/negative pulse which is counted to enable a counter to count displacement which is about 1/2 as large as the pitch P of the scale 4, so that the displacement is displayed with a display device.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a displacement measuring device, and in particular, detects the pitch of a reference scale using a tunnel current, and measures the displacement of the scale over several 108 or more points based on the Δ reference. It is replaced by a displacement detection device that can be determined.

(Conventional technology) Conventionally, the following displacement detectors are known.

Conventional example 1 (3rd Selengforum (April 1986)
718 and 9), "Ultra-high resolution digital scale using semiconductor laser °, p, 87) is a displacement detector using a reference scale, similar to this invention. In this method, the GraLing (
irradiating the scale with a laser beam using a diffraction grating,
The interference signal of the diffracted light is interpolated to provide a high-resolution pulse (1n
m) has been obtained.

Conventional example 2 (Japanese Patent Application No. 62-209802) is a parallel movement amount detection device using tunnel current, similar to the present invention. Here, a single crystal such as Sl, Go, or quartz is used as the reference scale.

However, Conventional Examples 1 and 2 have the following problems.

(Conventional Example 1) This method uses a diffraction grating as a reference scale, but there are currently two methods for manufacturing the diffraction grating: a method using lithography and a machining method using a ruling engine. In principle, the latter may yield a narrower pitch.

In addition, the average number of commercially available products is 2,000 lines/m+m, and even at the research level it is 18,000 lines/■ (pitch -56 m+n), and there is a possibility of further miniaturization in the future. That is, the most important parameter in the reference scale is the pitch (P), and it is important to reduce this P in order to achieve high accuracy of the scale. However, in Conventional Example 2, the condition for diffraction to occur is slnθ-λ/P (see FIG. 9), and for this to have a solution, λ/P<1, that is, λ<P. However, since the practical wavelength is limited to around λ-250nm, P = 250na+ in the diffraction method.
is the limit of the reference scale, and the rest has no choice but to rely on interpolation to obtain high resolution.

(Conventional example 2) ① When 81 etc. are used as a reference scale, oxidation occurs on the surface of Sl etc. in the atmosphere, and a high vacuum is required to use tunnel current.

■Generally, the surface atoms of crystals are ReRe-C0n5traC
1LIarlr1 rearrangement) occurs, and the atomic arrangement is likely to be disordered.

■81 etc. have two-dimensional regularity, so it is true that the probe manipulates only the top of the atom as described in the text.9. l: Impossible. For this reason, it is necessary to consider what will happen when the device is operated diagonally, such as by providing a movement ratio calculating device.

(Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances, and is used to accurately measure the position of a prong moving melon or the stage of a processing machine when measuring the dimensions of a product with high accuracy. Another object of the present invention is to provide a displacement detection device which is small in size and has a simple structure, and which can determine displacement as ΔPI with high resolution.

[Structure of the Invention] (Means for Solving the Problems) The present invention includes a reference scale having four conductivity, a stage that moves the reference scale one-dimensionally, and a probe having conductivity with respect to the reference scale. A coarse movement mechanism that brings the needle closer together,
It is equipped with a fine movement mechanism for driving the probe by a minute amount with respect to the reference scale, a control circuit for maintaining a constant tunnel current flowing through the reference scale and the probe 181, and a circuit for displaying the signals of the control circuit in a numerical manner. This is a displacement detection device that counts periodic irregularities existing in one direction on the surface of a reference scale and determines the amount of displacement of an Al11 constant by 7iPI.

The first void of the present invention is the use of tunnel current, and the second point is the configuration of the reference scale. The Kisō scale will be explained below with reference to FIGS. 1O (A) and (B). This figure is an excerpt from the drawing of Conventional Example 2, and the same figure (A) shows the wall interface of the Nb5c3 single crystal as ST.
An analog diagram observed with M, the same figure (B) shows Nb in NbSe3.

FIG. 3 is a plan view of the interface of So atoms. That is, when observing the cracked surface of a single crystal of niobselenium Nb Se 3 using STM, a signal with periodicity at the atomic level is detected. This period, that is, the pitch is 1.529±0.02 mff1, and if this value or 1/2 of this value is used, a pulse with a resolution of 1 nIm or less can be obtained.

However, when using this NbSe3 crystal as a reference scale, a low temperature of 77K (Kelvin) is required, and this A
The Pj meter itself must be operated in a low temperature chamber using liquid HO or the like. However, unlike conventional example 2, 1
Since a single crystal with dimensional periodicity is used, a meaningful periodic signal can be obtained even if the probe does not run perpendicular to the atomic array.

In addition, a single crystal diffraction grating (l'lΩc p1tc) (
Conductive surface coated with gold, etc.)
You can also use In this case, at present there is a pitch of about GOnm, but in the future there is a possibility of a pitch of several n11. The total length of the scale at this time is several tens of ma.
It seems that several 10a+rA is possible from +.

Note that it is obvious that the reference scale has one-dimensional periodicity in this case as well.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 is a schematic perspective view of a displacement detection device according to this embodiment.

1 in the figure is, for example, 100mm (length) x
The housing is made of aluminum and measures 50+nm (width) x 20mm (height). Inside this housing 1, a hollow stage 2 is arranged. This housing 2 is made of phosphor bronze or spring steel and has a thickness of 0.05 to 0.
．． It is connected to the housing 1 at four points via thin plates (plate springs) 3 of 2 mm and 72 degrees. Here, each leaf spring 3 is parallel. At one end of the stage 2,
A wire 4 made of boron fiber or carbon fiber with extremely low elongation is fixed. This wire 4
is drawn out from a through hole 1a provided in the side wall of the housing 1. The other end of this wire 4 is
It is fixed to a constant object (not shown), that is, to the stage of a dimension measuring machine or processing machine whose displacement is to be determined by /1111. This fixation is configured so that displacement is transmitted to the stage 2. On the top surface of the stage 2,
A reference scale 5 having NbSe3 crystals interposed between the walls is fixed by adhesives, screws, or the like.

An aluminum L-shaped arm 6 shown in FIG. 2 is attached to the housing 1. As shown in FIG. This arm 6 is provided with a micrometer 7 (one scale is 1 to 0.1 μm) for coarse movement. This micrometer 7 has a micro moving section 8.
is attached, and by manually rotating the micrometer 7, the micro-moving section 8 moves in the 16Z direction.

Here, the micrometer 7 and the micro moving part 8
These are collectively called the fine movement mechanism. The tip of the micro-movement section 8 is, for example, of a laminated type and has a displacement characteristic of 5 μm/100 V (total applied voltage) (that is, a maximum of 5 μm at 100 μm).
A piezoelectric element (fine movement mechanism) 9 is provided. At the tip of this piezoelectric cord 9, a probe 10 is attached.
is installed. This method of fixing the probe 10 is, for example, a method in which an aluminum block with a hole into which the probe 10 is inserted is glued to the tip of the piezoelectric cord 9, and the probe 10 is inserted into this hole and fixed with a screw. .

FIG. 4 is a circuit diagram showing an electrical control system of a displacement detection device having such a structure. This control system includes a bias voltage source 21 for obtaining tunnel current, a current-voltage conversion circuit 22 for detecting tunnel current, a logarithmic amplifier 23, and a differential amplifier '52.
4, an integrator 25, an amplifier 26, a high voltage amplifier 'S, 27, an edge detector 28, a counter 29, a display 30, etc.

Next, the operation of the displacement detection device having the above structure will be explained.

(1) First, manually adjust the coarse movement micro 7 to bring the probe lO close to the reference scale 5 to the extent that a tunnel current can be detected. Note that this tunnel current is self-evident based on the principle of a scanning tunneling microscope (STM), so a description thereof will be omitted. Here, the probe 10 is fed back by the control circuit shown in FIG. 4, similar to the STM, and the reference scale 5
It is kept in the vicinity of several nrp from the surface.

■On the other hand, the wire 4 is attached to the moving part of the
The other end is fixed, and the movable part is 6 (ku10+
u+) When the stage 2 moves, the stage 2 is pulled in the X direction via the wire 4. As a result, the stage 2 moves in parallel in the X direction as shown in FIG. 3 due to the characteristics of the leaf spring 3. Note that in this method, stage 2 does not move in the y and z directions (
There is very little vertical or horizontal movement). Furthermore, the pitching, yawing, and 0-ring components of so-called stage 2 are extremely small and can be maintained for several seconds or less. When the stage 2 moves, similar to the principle of STM, as shown in the signal S in FIG. 5, 2! A signal corresponding to the irregularities on the surface of the quasi-scale 49 is obtained (the irregularities reach the atomic level).

(2) Furthermore, this signal is input to the edge detector 2B to obtain positive and negative pulses (E) as shown in FIG. By counting these pulses, approximately 1/2 of the pitch P of the reference scale 4 is calculated.
The displacement can be counted by a counter 29 and displayed by a display 30.

Therefore, the displacement detection device according to the above embodiment has Nb5o
A reference scale 5 with two crystals between the walls, this reference scale 5
a stage 2 that moves the probe 10 in parallel to the reference scale 2, a coarse movement mechanism that brings the probe 10 closer to the reference scale 2, a fine movement mechanism that moves the probe 10 by a minute amount with respect to the reference scale 5, and a stage 2 that moves the probe 10 in parallel with the reference scale 5; It is equipped with a control circuit that keeps the tunnel current flowing between the needles 10 constant and a circuit that counts and displays the signals of this control circuit, and counts periodic irregularities existing in one direction on the surface of the basic scale 5. The structure is such that the lower quantity of the object to be measured is determined by 71pj. Therefore, it has the effects listed below.

1) Although a tunnel current method is used, the current flow is extremely small (0.1V/nA), so temperature drift can be avoided (101J times more stable than the optical method in Conventional Example 2). On the other hand, in the conventional method of applying light to a diffraction grating and electrolyzing a periodic signal, the diffraction grating is warmed by the light and thermally expands, making it impossible to obtain sufficient precision (accuracy of measurement).

2) When observing the interwall surface of a single crystal of NbSe3 using STM, a signal with periodicity at the atomic level is obtained. This period, that is, the pitch is 1.529±0.02 mm, and by using this value or 1/2 of this value, a pulse with a resolution of 1 nm or less can be obtained.

In contrast, in the conventional method of shining light onto a diffraction grating, ln
Although a resolution of i is obtained, the accuracy of this resolution depends on the periodicity of the peak shape of the diffraction grating. Therefore, 1n
+n accuracy cannot be guaranteed at present.

That is, 3) The entire device can be made small enough to fit in the palm of your hand. On the other hand, in the case of the conventional method of shining light onto a diffraction grating, the entire apparatus becomes large because an optical distance is required.

4) The control circuit is extremely simple. On the other hand, in the case of Conventional Example 2, extremely complicated electric circuits such as an AD converter and a CPU are required.

In the above embodiments, a case has been described in which the stage is connected to the object to be measured by a wire, but the present invention is not limited to this. For example, any material such as a connecting rod or a metal tape may be used as long as it can transmit the displacement of the object to be measured to the displacement of the stage without expansion or contraction.

In the above embodiment, a case has been described in which the stage and the housing are connected by mutually parallel leaf springs, but the present invention is not limited to this. For example, as shown in Figures 7 and 8, it may be of the type cut out from an aluminum alloy block by wire-cut electrical discharge machining or the like, and it is not limited to parallel springs, but any mechanism that can move the reference scale in parallel in the X direction. Other mechanisms may also be used.

In the above embodiment, a case has been described in which the arm is provided with a micrometer for coarse movement, but the present invention is not limited to this. For example, any mechanism that can perform positioning with an accuracy of 1 to 0.1 μm may be used.

In the above embodiment, a logarithmic amplifier was used in the electrical control system, but
If feedback can be performed, this logarithmic amplifier may be omitted. Furthermore, in the same control system, the edge detector 28 generates pulses for the signal S shown in FIG. A Schmitt circuit is required, and the resolution in this method is twice that of light).

[Effects of the Invention] As detailed above, according to the present invention, it is possible to use high-resolution 71111 when measuring the prong movement amount when determining the dimensions of a product with high precision and the position of the stage of a processing machine with high precision. We can provide a displacement detection device that is small and has a simple structure that can measure low levels.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of a displacement detection device according to a fourth embodiment of the present invention, FIG. 2 is a perspective view of an arm used in this device, and FIG. 3 is a stage that is one component of the device shown in FIG. FIG. 4 is a circuit diagram showing the electrical control system of the device shown in FIG. 1, FIG. 5 is a waveform diagram of signal S, FIG. 6 is a pulse diagram of signal E, and FIGS. Figure 8 is a perspective view showing modified examples of the stages, Figure 9 is an explanatory diagram showing the relationship between wavelength, incident angle, and pitch, and Figure 10 is a case where the wall interface of a single crystal of Nb Se 3 is observed by STM. FIG. DESCRIPTION OF SYMBOLS 1... Housing, 2... Stage, 3... Leaf spring, 4... Wire, 5... Reference scale, 6...
Arm, 7... micrometer, 8... micro moving part, 9... piezoelectric element, IO... probe. Applicant's Representative Patent Attorney Takehiko Suzue Arm

Claims (1)

[Claims] A conductive reference scale, a stage that moves the reference scale one-dimensionally, a coarse movement mechanism that brings the conductive probe closer to the reference scale, and a minute movement mechanism that moves the probe closer to the reference scale. It is equipped with a fine movement mechanism for driving, a control circuit for keeping the tunnel current flowing between the reference scale and the probe constant, and a circuit for counting and displaying the signals of this control circuit, and is provided in one direction on the surface of the reference scale. A displacement detection device that measures the amount of displacement of an object by counting periodic irregularities.