JPH04115119A - Encoder - Google Patents

Abstract

PURPOSE:To measure relative displacement accurately and stably by relatively scanning a probe along the surface of a reference graduation, and correcting the deviation of the probe along the direction perpendicular to the detecting direction of the relative displacement. CONSTITUTION:An x-direction probe-driving signal 3a generated in a reference- signal oscillator 111 is applied on the x-direction driving electrode of an x-y-z direction probe-driving element 103 through an amplifier 112. A y-direction probe-driving signal 3b is applied to the y-direction driving electrode of the element 103 through an adder 113 and an amplifier 114. Then, the tip of a probe 104 scans a reference graduation 105 in a circle drawing pattern. In gate circuits 115 and 116, an input signal 3b from a current/voltage converter circuit 107 is gated with a gate signal whose phase is shifted in synchronization with signals 3a and 3b outputted from the oscillator 111. Thus, signals 3k and 3l are outputted. These signals are averaged in averaging circuits 117 and 118 and binary-coded in binary-coding circuits 119 and 120. Thus, a relative moving amount signal 4a and a moving direction signal 4b are obtained. An x-direction relative displacement amount 4c are further computed in an up and down counter 121.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is applicable to position information measurement in micro-positioning, dimension measurement, distance measurement, speed, measurement, etc., particularly on the atomic order (0, 1
This invention relates to encoders used for measurement control that require resolution of nanometers.

[Prior Art] Conventionally, this type of encoder has been composed of a reference scale having information regarding position or angle, and a detection means that moves relative to the reference scale to detect information regarding position or angle. It is classified into several types depending on this reference scale and detection means, such as optical encoder,
There were magnetic encoders, capacitive encoders, etc.

In addition, as a displacement measurement device that can obtain even higher resolution, we have proposed a parallel displacement detection device using the principle of a scanning tunneling microscope (STM) with the atomic arrangement as a reference scale, a scanning tunnel current pressure detection device, and a positioning device. (Japanese Unexamined Patent Publication No. 62-209302, 1989 Japan Society for Precision Engineering Autumn Conference Academic Lecture 1 Tora Meeting Proceedings P153). In a scanning tunneling microscope, when a voltage is applied between a conductive sample and a conductive probe and the probe is brought close to a distance of about 1 nm, a tunnel current flows, and the tunnel current changes exponentially depending on the distance. When a sharp probe is used to scan two-dimensionally while maintaining a constant distance from the surface of a sample made of a conductive material, the tunneling current changes depending on the atomic arrangement or the shape of the irregularities on the surface. It is possible to obtain images of the surface [G, B1nn1g et al, Phys, Re
v. Lett, 49 (1982) 57].

When a sample with a regular atomic arrangement or a periodic uneven shape is used as a reference scale, and there is a relative positional deviation between the reference scale and the probe along the direction of the reference scale, a tunnel current periodically occurs. By taking advantage of this change, it is possible to construct a displacement measuring device having an atomic-order resolution of about 0.1 nanometer.

[Problem to be solved by the invention] However, in the above conventional example, a crystal lattice such as graphite (HOPG or K15h graphite) can be used as a reference scale, but the actual STM image of graphite is shown in Fig. 6 (A ), the tunneling current is observed in a triangular lattice shape, and the detected tunnel current changes as shown in FIG. 6(B) depending on the trajectory of the probe (arrow in the figure). For example, in the case of the trajectory 6a when the probe rests on the peaks of the crystal lattice as shown in the figure, a signal with a thick amplitude and good S/N as shown in waveform 6a'' can be obtained, but if In the case of trace 6b, the amplitude is very small as in waveform 6b', and the S/N is poor.In addition, in the case of trace 6c, which is tilted with respect to the alignment direction of the crystal lattice, it rides on a mountain as in waveform 6c'. The amplitude is large at certain points and becomes small at points where it crosses the valley, resulting in pressure errors.

In fact, when a displacement measuring device is configured as in the conventional example above, it is desirable that the trajectory of the probe passes along the trajectory 6a in FIG. Holding the probe and the reference scale so that they do not deviate relative to each other in the direction (referred to as the X direction) perpendicular to the relative displacement detection direction (referred to as the Due to temperature drift in the open state, stress relaxation, relative displacement due to external vibration, non-linearity of the relative movement support mechanism, angular error between the direction of relative movement and the crystal lattice direction of the reference scale, etc. It was difficult.

In addition, in the conventional positioning device described above, there are
Errors are caused by local defects in the crystal lattice.

Furthermore, in the conventional scanning tunnel current detection device described above, it is necessary to vibrate the probe laterally at different frequencies in the x and y directions, which causes a problem in that the tracking speed as an encoder becomes low.

In view of the above-mentioned problems in the prior art, it is an object of the present invention to provide an encoder with a resolution of 0.1 nanometer order, in which the probe and the reference scale are relative to each other in a direction perpendicular to the relative movement detection direction. The purpose of the present invention is to realize an encoder with a high follow-up speed and a high tracking speed.

[Means for Solving the Problems] In order to achieve the above object, the encoder of the present invention has a reference scale having a periodic pattern surface fixed to a first object, and a second scale whose tip is brought close to the reference scale. A probe placed on the object, a probe driving means that scans the probe in a relatively closed curve along the surface of the reference scale, and a signal corresponding to the information on the reference scale detected through the probe. a signal detecting means for detecting a relative displacement in a predetermined direction between the first and second objects based on a signal detected by the signal detecting means during scanning by the probe driving means; a deviation detection means for detecting a relative deviation in a direction perpendicular to the displacement detection direction; and a deviation detection means for detecting a relative deviation in a direction perpendicular to the displacement detection direction; and relative moving means for moving.

The probe driving means is such that the amplitude of the component in the relative displacement detection direction is equal to the amplitude of the component in the direction between the reference scales in the relative displacement detection direction or the probe is made to scan in a closed curve shape orthogonal to the relative displacement detection direction. is preferred.

As the closed curve, for example, a circle or an ellipse is used.

The amount of relative displacement in a direction orthogonal to the relative displacement detection direction may be detected from the control state of the relative displacement means.

[Function] In this configuration, when the probe is scanned relatively in a circular or elliptical manner along the surface of the reference scale, the tip of the probe is parallel to the relative displacement detection direction and the center of the scanning circle or ellipse. The magnitude of the tunnel current at two locations crossing the straight line passing through changes depending on the relative position of the probe and the scale row of the reference scale in the relative displacement detection direction. In other words, the magnitude of the tunnel current signal is maximum when the probe is directly above the scale row,
It is at its minimum when it is between the scale rows, and changes periodically in accordance with the scale rows. Therefore, when detecting the amount of relative displacement, the scale rows are counted based on the signals at the two locations mentioned above, and the direction of movement is detected using the other signal.

The magnitude of the tunnel current at two locations where the tip of the probe crosses a straight line that is perpendicular to the relative displacement detection direction and passes through the center of the scanning circle or ellipse is determined by the reference scale and the probe in the direction perpendicular to the relative displacement detection direction. It changes depending on the deviation from the needle. Therefore, the relative displacement between the reference scale and the probe is corrected so that the signal magnitudes at the two locations described above are the same, and the center of probe scanning is parallel to the relative displacement detection direction. is kept on a certain scale row on a standard reference scale.

[Example code] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram showing the configuration of an encoder according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the principle of this encoder, and FIGS. 3 and 4 show each component of this encoder. A waveform diagram showing the signal obtained in FIG. 5 is as follows.
FIG. 7 is an explanatory diagram showing another probe scanning method and a reference scale.

As shown in FIG. 1, this encoder has an xyz direction probe drive element 103 fixed to an object 101, which is one of two objects, and a conductive element attached to the tip of the element 103 to detect the amount of relative displacement. A probe 104 is provided with a conductive two-dimensional reference scale 105 fixed on the other object 102 so as to oppose the tip of the probe 104 . Examples of the two-dimensional reference scale 105 include a carbon atomic lattice on a cleavage plane of graphite, a gold atomic lattice on an epitaxial growth surface of gold on a cleavage plane substrate of mica, and a carbon atomic lattice on an epitaxial growth plane of gold on a cleavage plane substrate of mica. ) Uses a periodic two-dimensional arrangement of atoms and molecules, such as the molecular arrangement of the cleavage plane of a crystal. A bias voltage is applied between the probe 1°4 and the reference scale 105 by a bias power supply +06, and the distance between the tip of the probe 104 and the reference scale 105 is brought close to the extent that a tunnel current flows by the probe driving element 103. It looks like this. This tunnel current is converted into voltage by the current-voltage conversion circuit 107, and is used to
4 and the reference scale 105 are controlled so that the average interval remains constant when they move relative to each other. That is, the output signal 3g of the current-voltage conversion circuit 107 is manually inputted to the average tunnel current setting circuit 108, and an error signal with a set tunnel current value having a desired interval is detected.Based on the detected signal, the low-pass filter 109 and A control voltage is applied to the X-direction drive electrode of the probe drive element 103 via the amplifier 11o. The cutoff frequency of the low-pass filter +09 removes the fast modulation component of the tunnel current that is generated when the probe 104 scans the reference scale of 1°5 and the distance between the probe and the reference scale changes due to the peak of the reference scale. is selected to pass the direct current component of the tunneling current. As a result, the probe 104 is driven and controlled in the X direction by the probe drive element 103 so that the average distance from the reference scale 105 is constant.

Further, a reference signal oscillator 111 that generates an X-direction probe drive signal 3a that is a cosine wave signal of frequency f, a y-direction probe drive signal 3b that is a sine wave signal of frequency f, and gate signals 3c to 3f; An amplifier 112 amplifies the X-direction probe drive signal 3a and applies it to the X-direction drive electrode of the probe drive element 103, and adds the y-direction probe drive signal 3b and the y-direction control signal from the y-direction control circuit 127. Adder 113
, an amplifier that amplifies the pressure and applies it to the y-direction driving N pole of the probe driving element 1゜3] 14. Current: Positive conversion circuit 107
The output signal 3g from the reference signal oscillator 111 is ANDed with the gate signals 30 to 3d from the reference signal oscillator 111, respectively, and
3m.

Gate circuit 115122, 1 that outputs 3u and 3n
16. 123, A word No. 3, 3
Averaging circuits 117.124.118.125 and 117.125 average and output m3ρ and 3n, respectively.
Each of the outputs of 118 is binarized to obtain a relative B movement signal 4a.
and a binarization circuit 119 that outputs the moving direction signal 4b.
120, an up/down counter 121 that calculates the X-direction relative displacement position based on the signals 4a and 4b and outputs the X-direction relative displacement amount signal 4c, and a subtractor 126 that calculates and outputs the difference between the outputs of the averaging circuits 124 and 125. , and subtractor 12
A y-direction control circuit 127 is provided which outputs a y-direction control signal to the adder 13 so that the difference signal from 6 becomes zero.

Next, the operation of detecting the relative displacement amount (relative movement amount and relative movement direction) between the object 101 (probe side) and the object 102 (reference scale side) will be described.

X-direction probe drive signal 3 generated by the reference signal oscillator 111
a is applied to the X-direction drive electrode of the probe drive element 103 via the amplifier 112, and the Y-direction probe drive signal 3b is applied to the X-direction drive electrode of the probe drive element 103.
is connected to the probe driving element 1 via an adder 113 and an amplifier 114.
When the voltage is applied to the X-direction drive electrode 03, the tip of the probe 104 scans the reference scale 105 in a circle 201, as shown in FIG. At this time, if the diameter of the circle of the trajectory of the tip of the probe 104 is D, and the lattice spacing of the atomic arrangement of the reference scale is d, then D=(N±-)d (N=1.2, 3...) The amplitudes of the cosine wave signal (X-direction probe drive signal 3a) and the sine wave signal (y-direction probe drive signal 3b) are adjusted so that As a result, the moving direction signal 4b in the X direction, which will be described later, becomes maximum.

In FIG. 2, points A to E are object 101 and object 1.
02 indicates the center of the trajectory of the tip of the probe 104 at each point in time when relative movement occurs in the X direction. The center of circular motion of the tip of the probe 104 is from point A to E along the X axis.
, the output signal of the current-voltage conversion circuit 107 changes from signals 3g to 3j to 3g.

Now, assuming that the center is at point A, the gate circuits 115 and 116 output from the reference signal oscillator 111,
The human power signal 3g from the current-voltage conversion circuit 107 is gated by the gate signals 3c and 3e, which are synchronized with the x and X-direction probe drive signals 3a3b and are out of phase with each other, and the signal 3u is output as the signal 3. These signals are shown in Figure 3 (k).
, (Il), are averaged by averaging circuits 117 and 118 as shown by broken lines, and are then averaged by a binarization circuit 119.
．． In step 120, the relative displacement amount signal 4a and the moving direction signal 4b are binarized, and roughly based on these signals, the X-direction relative displacement amount 4c is calculated in the up/down counter 121. The calculation is performed as follows.

That is, the pulse falling point of the relative movement amount signal pulse 4a, , D2. In D3, if the sign of the movement direction signal 4b is + (plus), the counter 121 adds the number of pulses, and if it is - (minus), it subtracts it. Further, if the sign is - (minus) at the pulse rising points U, U2, the number of pulses is added, and if it is + (plus), the number of pulses is subtracted. In this way, the X-direction relative displacement amount 4
It is possible to find c.

Regarding the amount of relative displacement in the y direction, assuming that the center is now at point A, the gate circuit 122123 synchronizes with the x and Kate signal 3 shifted
d and 3f are applied to the human power signal 3g from the current-voltage conversion circuit 107, and signals 3m and 3n are output. These signals are averaged by an averaging circuit 124125 as shown by broken lines in FIGS. 3(m) and (n),
The subtracter 126 calculates the difference between them, and the X-direction control signal is sent from the X-direction control circuit 127 to drive the probe drive element 103 in the X-direction via the adder 113 and amplifier 114 so that the difference signal becomes zero. The voltage is applied to the electrode, thereby controlling the probe position in the X direction.

In this way, when a relative displacement occurs between the object 101 and the object 102, the probe 104 does not make a rotational movement.
The center will move along one atomic arrangement in the X direction of the reference scale 105 (tracking),
Even if the objects 101 and 102 produce a relative displacement in the X direction, the tip of the probe 104 produces a relative displacement in the X direction (other than the X direction component of rotational motion) with respect to the reference scale 105. do not.

The X-direction control signal at this time is a signal applied to the probe drive element 103 in order to make the tip of the probe 104 follow the reference scale 105 in the X direction. It is possible to calculate the amount of relative displacement. At the same time, the probe 104 moves (tracks) along one atomic arrangement in the X direction of the reference scale 105, so when detecting the amount of relative movement in the X direction,
There is no detection error due to lateral deviation in direction.

In this embodiment, the reference scale 105 has an atomic arrangement or a triangular lattice, and the locus of movement of the tip of the probe 104 is circular. For example, without limitation, FIG. 5(A)
And as shown in (B), the locus of movement of the tip of the probe is
An ellipse 501 may also be used. In this case, the grid spacing in the X direction is dx
,'! If the directional grid spacing is dY, search is performed so that the X-axis diameter Dx and Y-axis diameter DY of the ellipse are respectively the same, so that the 8 direction signals in the X direction and the tracking difference signal in the X direction are maximized. The amplitudes of the cosine wave signal and the sine wave signal applied to the needle drive element 103 are adjusted.

Further, as shown in FIG. 5(C), the same applies when the atomic arrangement of the reference scale 105 is a square lattice.

[Effects of the Invention] As explained above, according to the present invention, an atomic arrangement or the like is used as a reference scale, a signal corresponding to information on the reference scale is detected via a probe, and the relative position of the probe and the reference scale is detected. In an encoder that detects deviation, the probe is scanned in a relatively closed curve along the surface of the reference scale, and based on the obtained signal,
Control is performed to correct the deviation of the probe along the direction perpendicular to the direction of relative displacement detection, which eliminates temperature drift of the device, external vibration, nonlinearity of the relative movement support mechanism, and angle setting error of the reference scale. It becomes possible to correct the relative displacement in the direction orthogonal to the relative displacement detection direction caused by such factors, and to accurately and stably measure the relative displacement.

Furthermore, since the probe scans in a closed curve shape such as a circumferential shape or an elliptical shape, it is possible to increase the speed and realize an encoder with a high tracking speed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an encoder according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the principle of the encoder of the present invention, and FIGS. The figure is a waveform diagram showing the signals obtained in each component of the device in Figure 1, Figures 5 (A) to (C) are explanatory diagrams showing other probe scanning methods and reference scales, and Figures (A) and (B) are explanatory diagrams of a length measurement waveform according to a conventional example. 101 - Target object, 102: Target object, 103: xyz direction probe drive element, 104 - Probe, 105: Reference scale, 10
6: Hias power supply, 1.07 current voltage conversion circuit, 108
Average tunnel current setting circuit, 109: Low-pass filter, 110. Amplifier, 111: Reference signal oscillator, 112
・Amplifier, 113 Adder, 114: Amplifier, 115
Gate circuit, ]16. Kate circuit, 117. Averaging circuit, 118: Averaging circuit, 119: Binarization circuit, 120,
Binarization circuit, 121 Up/down counter, 122.
gate circuit, 123 gate circuit, 124/averaging circuit, 125: averaging circuit, 126: subtracter, 127: y-direction control circuit.

Claims (4)

[Claims] (1) A reference scale with a periodic pattern surface fixed to a first object, a probe placed on a second object with its tip close to the reference scale, and a probe placed on the surface of the reference scale. a probe driving means for scanning in a relatively closed curve along the probe;
A signal detection means detects a signal according to information on a reference scale via the probe; and a signal detection means detects a signal in a predetermined direction between the first and second objects based on the signal detected by the signal detection means during scanning by the probe drive means. Displacement detection means for detecting relative displacement; Displacement detection means for detecting relative displacement in a direction orthogonal to the relative displacement detection direction by the displacement detection means; An encoder comprising a relative moving means for relatively moving a reference scale and a probe so as to correct a relative deviation. (2) The probe driving means is such that the amplitude of the component in the relative displacement detection direction is 1/4 or more of the interval between the reference scales in the relative displacement detection direction, and the amplitude of the component in the direction orthogonal to the relative displacement detection direction is relative to the relative displacement detection direction. 1 of the interval between the reference scales in the direction orthogonal to the displacement detection direction
2. The encoder according to claim 1, wherein the probe scans in a closed curve shape so that the angle is greater than or equal to /2. (3) The encoder according to claim 1 or 2, wherein the closed curve is a circle or an ellipse. (4) The encoder according to any one of claims 1 to 4, further comprising means for detecting a relative displacement amount in a direction perpendicular to a relative displacement detection direction from a control state of the relative movement means.