JPH036422A - Encoder - Google Patents

Abstract

PURPOSE:To lessen an error in measurement by a method wherein, with a reference substance rotated, a scanning track formed by a probe is adjusted so that it may accord with the direction of a crystal lattice of the surface of the reference substance. CONSTITUTION:A modulated component of a frequency formed by scanning by a probe 103 on a reference scale 104 of a scale period (p) provided on a rotary table 11 is superposed on a tunnelling current 107 flowing between the probe 103 and the reference scale 104 by vibrations of the probe 103. When an object 101 and an object 102 move mutually in the lateral direction herein, the modulated component of the frequency superposed on the current 107 causes a phase shift in relation to a signal serving as a reference, e.g. a probe vibration signal 2A. The phase shift in one period, i.e. 2pi, of the signal corresponds to the lateral shift of the probe 103 from a base for the period of the scale 104, and by detecting this phase shift, therefore, the amount of the relative shift in the lateral direction of the object 101 from the object 102 can be detected accurately.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to position information measurement in micro-positioning, dimension measurement, distance measurement, speed, measurement, etc. This invention relates to an encoder used for measurement.

[Prior Art] Conventionally, this type of encoder is composed of a reference scale having information regarding position or angle, and a detection means for detecting information regarding position or angle by moving eight times relative to the reference scale. They are classified into several types depending on the reference scale and detection means, such as optical encoders, magnetic encoders, and capacitance encoders.

Further, as an encoder capable of obtaining even higher resolution, an encoder using the principle of a scanning tunneling microscope (STM) and using an atomic arrangement as a reference scale has been proposed (Japanese Patent Application Laid-open No. 209302/1989).

In this 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 and a tunnel current is caused to flow, the tunnel current changes exponentially depending on the distance. This is what was used. For example, when a sharp probe is used to two-dimensionally scan a sample surface made of a conductive material while keeping the distance between the probe and the sample surface constant, a tunneling current may occur due to the atomic arrangement or uneven shape of the surface. changes, so an image of the sample surface can be obtained based on this ("Solid State Physics J Vo
L, 22 No. 31987 PP, 176-186
).

In other words, when a sample with a regular atomic arrangement or a periodic uneven shape is used as a reference scale, and a relative positional shift occurs between the reference scale and the probe along the direction of the reference scale, the tunnel current periodically changes depending on the relative positional deviation between the reference scale and the probe. It is possible to construct an encoder that has the resolution of several atomic oniders by taking advantage of this change.

[Problem to be solved by the invention] However, in the above conventional example, graphite (HOPG or K15h graphite) is used as the reference scale.
Although a crystal lattice such as the one shown in FIG.
According to b), the detected tunnel current changes as shown in waveforms 7a' to 7b' in FIG. 5(B). For example, if the trajectory of the probe rests on the peak of the crystal lattice as shown by arrow 7a, a uniform output signal with a large amplitude and good signal-to-noise ratio as shown in waveform 7a' can be obtained, but as shown in arrow 7b As shown, when the crystal lattice is tilted to the alignment direction, the waveform 7b'
As shown in the figure, the amplitude is large at the peaks and small at the valleys, making it impossible to obtain a uniform output signal, resulting in an error in the encoder output.

If the encoder is actually configured as in the conventional example above,
Although it is desirable for the probe to follow a trajectory as shown by the arrow 7a, the probe does not necessarily follow such a trajectory when a reference scale using a crystal lattice is set on the encoder. Furthermore, it is not absolute that the orientation of the crystal lattice has the same orientation throughout the entire area within the plane of the reference scale. For example, in a location where the probe detects tunneling current, if the probe is brought closer to the reference scale, moved away from it, and then brought closer again, the former and the latter are likely to cause a detection position shift on the order of microns. At the same time, it is thought that an orientation change within the reference scale plane using the crystal lattice occurs.

Therefore, there is no guarantee that the path will follow the trajectory shown by the arrow 7a in FIG. 7(A), which causes an error in the encoder output as described above.

In view of the problems of the prior art, an object of the present invention is to
The objective is to reduce measurement errors in encoders.

[Means for Solving the Problems] In order to achieve this object, the encoder of the present invention includes a conductive reference object, a conductive probe whose tip is placed close to the surface of the reference object, and a conductive probe disposed with its tip close to the surface of the reference object. A means for vibrating relative to a reference object in a relative displacement detection direction, a means for applying a voltage between the reference object and the probe, and a means for detecting a tunnel current flowing between the reference object and the probe. and a means for detecting a phase shift between the tunnel current signal detected by the detection means and a reference signal, and detecting the amount of relative displacement between the reference object and the probe and the direction of the relative displacement based on this. and means for rotating the reference object.

[Function] In this configuration, the displacement between the probe and the reference object is determined by causing the probe to vibrate in the relative displacement detection direction while passing a tunnel current between them, and based on the phase shift of the modulation component of the tunnel current caused by the vibration. Detected. This phase shift is influenced by the S/N ratio of the detected tunnel current, and this S
In order to increase the N ratio and perform accurate measurements, it is necessary that the scanning locus of the probe coincide with the crystal lattice direction of the surface of the reference object. Therefore, in the present invention, during measurement,
The reference object is rotated by the means for rotating the reference object, and the scanning locus of the probe is adjusted to match the crystal lattice direction of the surface of the reference object, thereby performing accurate measurements.

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

FIG. 1 is a block diagram of an encoder according to an embodiment of the present invention, and FIGS. 2 and 3 show signals obtained in each component of the apparatus shown in FIG. 1. FIG. 4(a) is a plan view showing details of the rotation mechanism of the encoder in FIG.
b) is a sectional view taken along line A-A.

As shown in FIG. 1, in this encoder, a target object 101 and a target object 102 are installed so that they can be relatively displaced only in the horizontal direction (left and right directions in the drawing).
1 is provided with a conductive probe 103, and the object 102 is provided with a rotary table 11 having a reference scale 104.

A bias power supply 106 is connected between the probe 103 and the rotary table 11.
A bias voltage is applied, and the tip of the probe 103 and the reference scale 104 on the rotary table 11 are brought close to each other (approximately 1 nanometer or less) to the extent that a tunnel current 107 flows between them. Tunnel current 107 is detected by tunnel current detection circuit 108.

During measurement, the probe 103 is activated by the probe vibration drive signal 2A, which is a triangular wave with a frequency f, output from the oscillation circuit 109, and by the probe vibration means 110, which is driven in accordance with the probe vibration drive signal 2A.
is vibrated at a frequency f and an amplitude d in the direction of relative change between the object 101 and the object 102. The vibration speed at this time is object 1
It is sufficiently larger than the relative displacement speed of 01 and 102. Note that instead of vibrating the probe 103, a substrate vibrating means may be provided on the object 102 to vibrate the substrate 105.

Due to the vibration of the probe 103, the tunnel current 107 flowing between the probe 103 and the reference scale 104 of the scale period P on the rotary table 11 includes a frequency object 101 caused by scanning the reference scale 104 with the probe 103. When the object 102 and the object 102 move laterally relative to each other, the tunnel current 107 described above increases.
A phase shift occurs with respect to the superimposed bone, for example, the probe vibration signal 2A. Since a phase shift of one period of the signal, that is, 2π, corresponds to a lateral shift between the probe 103 and the substrate 105 corresponding to the period of the reference memory 104, by detecting this phase shift, the difference between the objects 101 and 102 can be determined. A relative amount of lateral deviation can be detected.

The signal processing method will be explained below. In the above configuration, the tunnel current 107 is superimposed on the tunnel 108 and the filter takes out the tunnel current modulation signal 2p as a tunnel current modulation signal 2p. However, the amplitude of the probe vibration drive signal 2A applied to the probe vibration means 110 is adjusted so that □=n (n is a natural number), and the frequency of the tunnel current modulation signal 2D is brought to nf. On the other hand, the reference signal generating circuit 111 multiplies the frequency of the signal with the frequency f from the transmitting circuit 109 by n, converts the waveform into a sine wave, outputs the motion amount reference signal 2B, and further changes the phase by π/ The motion direction reference signal 2C is output with a shift of 2. Then, the phase comparison circuit 112 compares the phases of the tunnel current modulation signal 2D and the motion amount reference signal 2B, and outputs a motion amount phase comparison signal 2E. On the other hand, the phase comparison circuit 113 compares the phases of the tunnel current modulation signal 2D and the motion direction reference signal 2C, and outputs a motion direction phase comparison signal 2F. The motion amount phase comparison signal 2E and the motion direction phase comparison signal 2F are
01 and the object 102 are displaced in the lateral direction, the signals change to signals 3A and 3C shown in FIG. 3, respectively, depending on the amount of displacement. The signals 3A and 3C are binarized into a binary motion amount phase comparison signal 3B and a binary motion direction phase comparison signal 3D, respectively, and the counter 114 operates as follows based on these signals 3B and 3D. Detects relative displacement.

That is, as shown in FIG. 3, the pulse rising points (3b, 3b2, 3b
In 3), if the sign of the motion direction phase comparison binary signal 3D is + (plus), the counter 114 adds the number of pulses, and conversely, the pulse rising point of the signal 3B (3b43
In b5), if the sign of the signal 3D is - (minus), the counter 114 subtracts the number of pulses and outputs the relative displacement amount signal 3E. Here, one pulse in the counter 114 corresponds to one modulation in the tunnel current modulation signal 2D.
This corresponds to a phase shift corresponding to a period, that is, a relative displacement amount between the objects 101 and 102 corresponding to a period (p) of the periodic structure of the reference scale 104. Therefore, by using a reference scale whose period p is known in advance, it is possible to detect the relative displacement between the objects 101 and 102 based on the relative displacement signal 3E output by the counter 114.

Next, the rotation mechanism portion will be explained using FIG. 4.

FIG. 3(a) is a plan view of this rotation mechanism, and FIG. 2(b) is a sectional view taken along line AA in FIG. In the figure, 11 is a rotary table having a reference scale 104, 102 is an object, 13 is a bearing, 14 is a nut, 15 is a gear firmly fixed to the shaft of the rotary table 11, and 16 is a gear for rotating the gear 15. 1-Mugia, 17 is a washer. The rotary table 11 is pressed and fixed to the object 102 by a bearing 13, a nut 14, and a washer 17 with a force smaller than the force that allows the rotary table 11 to rotate by frictional sliding.

To rotate the rotary table 11, the ohm gear 16 is rotated and its rotational force is transmitted to the gear 15. The worm gear 16 is rotated by a rotation drive means such as a DC motor or a stepping motor, but it may be rotated manually, and is not particularly limited.

Next, a specific example using a rotation mechanism will be described with reference to FIGS. 1 and 5. As described above, the reference port 1 graduation 104 is set on the encoder device, and the probe 1° 3 is brought close to the reference graduation 104 until the tunnel current 107 can be detected. Then, the probe 103 is vibrated using the probe vibrating means 110, and the tunnel current 107 at this time is
It is assumed that the locus of the probe and the detection signal when the tunnel current detection circuit 108 detects a change in the current are as shown by the arrow 7b and the signal 7b' in FIG. 5(A). In this case, although the counter 114 operates, the actual amount of movement cannot be detected because the SN ratio is poor. So, in this case, −
The distance between the degree probe 103 and the reference scale 104 is set at about 1 mm, and the rotary table 11 is rotated, for example, by about 8 degrees clockwise in FIG. 5(A) by rotation of the gear 15. Next, the distance between the probe 103 and the reference scale 104 is brought close to the distance where the tunnel current 107 disappears, and the probe 103 is vibrated. As a result, the probe draws a trajectory as shown by the arrow 7a in FIG. 7(A), and a detection signal as shown by the waveform 7a' in FIG. 7(B) can be obtained.

2. In order to match the direction of vibration for detecting the amount of movement of the probe 103 with the direction of the scale of the reference scale 104, first, the probe 103 is scanned two-dimensionally, and the surface image is determined by image processing. , the direction of the reference scale 104 is automatically adjusted by detecting an angular deviation in the direction and applying feedback control to the DC motor or the like that drives the above-mentioned rotation mechanism so as to rotate it by an angle corresponding to the directional deviation.

If there is no angular deviation, no rotation operation is performed.

[Effects of the Invention] As explained above, according to the present invention, in a high-resolution encoder applying the principle of a scanning tunneling microscope (STM), a mechanism for rotating the reference scale is installed, so that the reference scale can be rotated to the encoder. It becomes possible to easily adjust the angular error when mounted and the azimuth deviation in the reference scale plane as desired, which has the effect of reducing encoder output errors and improving reliability.

[Brief explanation of the drawing]

1 is a configuration diagram of an encoder according to an embodiment of the present invention, FIGS. 2 and 3 are output waveform diagrams of the encoder of FIG. 1, and FIG. 4 is a rotation mechanism of the encoder of FIG. 1. A partial detailed view, FIG. 5, is an explanatory diagram showing the operating direction and output waveform within the reference scale plane. 11, rotary table 13: bearing 101: object 102: object 103: probe 104, reference scale 106, bias power supply 108/tunnel current detection circuit 109, oscillation circuit 110: probe vibration means reference signal generation circuit/phase comparison circuit, Phase comparison circuit: counter

Claims (1)

[Claims] (1) a conductive reference object, a conductive probe disposed with its tip close to the surface of the reference object, and means for vibrating the probe relative to the reference object in a relative displacement detection direction; A means for applying a voltage between the reference object and the probe, a means for detecting a tunnel current flowing between the reference object and the probe, a signal of the tunnel current detected by the detection means, and a signal serving as a reference. An encoder comprising means for detecting a phase shift between the reference object and the probe, and detecting the relative displacement amount and direction of the relative displacement between the reference object and the probe based on the detected phase shift, and means for rotating the reference object. .