JPH064247Y2 - Moving distance measuring device - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a measuring device equipped with an optical interferometer as a sensor for accurately measuring a moving distance of a moving table, and particularly to detecting rotation of the moving table. By doing so, the present invention relates to a moving distance measuring device for a moving stand, which prevents an error in moving distance measurement.

[Conventional technology]

In a moving distance measuring device that measures the amount of movement of an XY biaxial moving table using a conventional optical interferometer, a corner in which the directions of an incident beam and an outgoing beam coincide with each other is used as a movable mirror that constitutes the optical interferometer. Since the cube was not available, a plane mirror was used. In such an apparatus, tilting of the movable mirror may occur due to rotation of the movable base due to yawing or pitching, and depending on the selection of the measurement point position on the movable base, the movable base may move. Since an error will occur in the moving distance measurement, in order to prevent such a measuring error, until now, two high-performance optical interferometers have been used to perform precise moving distance measurement that compensates for rotation of the moving table. There was a device.

[Problems to be solved by the invention]

However, the moving distance measuring device for a moving table configured as above has the following problems. As described above, in the moving distance measuring device for a movable table using a plane mirror as the movable mirror, when the movable table rotates, tilt variation occurs in the movable table, and as a result, unnecessary fringes are generated and the amount of received light is reduced. As a result, the S / N of the interference signal is reduced.

Further, the above-described rotation causes an error in measuring the moving distance of the moving table depending on the position of the measuring point selected on the moving table.

More specifically, when the movable mirror is tilted by θ due to yawing of the movable table or the like, the reflected light M from the movable mirror is 2θ relative to the reflected light F from the fixed mirror, as shown in FIG. Interference with a crossing angle. In this case, the photoelectric converter or the light receiver D
Optical path difference d = y ・ sin2
θ occurs, and the interference light I is generally expressed as I = Ia · cos (4πx / λ + 2πd / λ + φ _O ) + Ib. Where λ is the wavelength, Ia is the amplitude component, and Ib
And φ _O represent a constant light quantity and transport difference.

The moving displacement amount x to be detected is expressed as a cosine-type phase term, and includes a phase difference (2πd / λ) that differs at the position in the y direction due to the optical path difference.

The received light signal is expressed as a value obtained by integrating the amount of received light (I in the above equation) at each point in the x and y directions on the light receiving surface. When the phase difference 2πd / λ is large, cos 4π x
There is a problem that the signal component of / λ cannot be obtained.

On the other hand, if the light-receiving surface is made smaller, the above problem is solved, but a decrease in signal level is unavoidable, and there is a problem that a special means must be taken to improve the S / N.

To give a specific numerical example, for example, the size of the photodetector D is y
_{When 1} = 2 mm and the tilt angle is θ = 0.16 mrad, the phase difference at both ends is 633 when the wavelength λ of the He-Ne laser light is 633.
Since it is nm, y ₁ (sin2θ) / λ≈1 and 2π
y ₁ (sin 2θ) / λ≈2π.

Further, in a precise distance measuring device that compensates for the rotation of the moving table by using a plurality of high-performance optical interferometers, there is a problem that it becomes large in size and complicated in structure and expensive. It was

The present invention solves the above-mentioned problem, and the purpose thereof is to detect yawing and pitching of a mobile stand, which can be applied to a mobile stand with inferior performance due to calculation correction, and high-precision measurement is possible. Another object of the present invention is to provide a moving distance measuring device for a moving table.

[Means for solving problems]

According to the present invention, as the light source, the orthogonal dual frequency laser light source in which the parallel polarized light flux and the vertically polarized light flux oscillate at different optical frequencies is used, and the light receiving surface is divided into a plurality of light receivers. An optical interferometer adopting a method of obtaining a detection signal of d / λ and controlling the angle of the fixed mirror by this signal is constructed. Then, the detected phase difference 2π d
The problem is solved by controlling the angle of the fixed mirror so that / λ is always 0, and yawing and pitching are detected from the angle control amount to enable highly accurate movement distance measurement. Is.

[Action]

In the case of the moving distance measuring device of the movable table provided with such means, the polarized light beam emitted from the orthogonal dual frequency light source is split into two light beams by the non-polarizing beam splitter, and one light beam is converted into the first photoelectric conversion. An electric signal FF having a difference frequency between the two polarized light beams is generated by receiving the electric signal from the container, and this electric signal can be used as a reference signal for phase detection. Further, another light flux is introduced into the polarization interferometer, and the light flux including the position and tilt angle information of the movable mirror provided on the movable table is received by the second photoelectric converter whose light receiving surface is divided into two. Two electrical signals SF, SS
Can be A phase difference can be detected from the two electric signals SF and SS, and an actuator for driving the fixed mirror of the polarization interferometer can be controlled based on the detected phase difference. By controlling this actuator so that the detected phase difference becomes zero, the rotation of the movable table can be compensated. On the other hand, the electric signal FF
Then, the moving distance of the mobile table can be calculated based on the electric signal FS obtained by passing the electric signal through the π / 2 phase shifter and the electric signal SF.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a moving distance measuring device for a moving table as an embodiment. However, the optical system is shown in a plan view, and is for explaining the tilt detection and the rotation compensation of the movable table with the vertical direction as the rotation axis.

First, the parallel polarized light flux 2 emitted from the orthogonal dual frequency light source 1,
And the vertically polarized light beam 3 are split by the non-polarized beam splitter 4, and the interference signal F is divided by the analyzer 5 and the first photoelectric converter 6.
Get F. When the difference frequency between the two polarized light beams is f, this signal FF can be expressed as FF = Ia ₁ cos (2πft + φ ₁ ) + Ib ₁ and serves as a reference signal for phase detection. On the other hand, the transmitted light flux of the non-polarization beam splitter 4 is the polarization interferometer 3
It is incident on 0 to detect the moving displacement amount x of the moving table 7.

The polarization interferometer 30 includes a polarization beam splitter 8 and two
It is composed of quarter wave plates 9A and 9B, a movable mirror 10, a fixed mirror 11, and an analyzer 12. The output signal from this polarization interferometer is detected by the second photoelectric converter 13 whose light-receiving surface shown in FIG. 3 is divided into two, and generates two signals SF and SS. These signals SF and SS are SF = Ia ₂ cos (2πft + 4π x / λ + φ ₂ ) + Ib ₂ SS = Ia ₃ cos (2πft + 4π x / λ + 2π d / λ +
φ ₂ ) + Ib _3, and the signal SS includes a phase term 2π d / λ due to the inclination θ of the movable mirror 10 with reference to the signal SF.
Here, when the distance between the two light receiving surfaces is P _y , this phase term is 2π d / λ = 2 as the phase difference between the two signals SF and SS.
It is expressed as π P _y (sin 2 θ) / λ≈4 π P _y θ / λ, but if there is a tilt θ of the movable mirror, different phase differences occur in the y direction on the light receiving surface, so that the above invention is intended to solve If θ is large as described in the section of the problem of cos (2
The signal component of (πft + 4π x / λ) is significantly reduced.

In order to detect the tilt θ of the movable mirror 10, a method of obtaining 4π P _y θ / λ by the phase difference detection circuit 20 from the output signals SF and SS of the second photoelectric converter 13 whose light receiving surface is divided into two is used. To use.

The phase difference detection circuit 20 uses the filtered signals SF and S.
A circuit for converting S into a pulse at zero cross and converting the rise time difference and fall time difference of the two signals into voltage values can detect a phase difference from -π to + π.
Further, as another phase difference detection method, when the moving speed of the moving table is slow and the frequency due to 4πx / λ is sufficiently lower than the difference frequency f of the two polarized light beams, one of the signals SS or SF is not shown in the figure. The phase difference detection circuit 20 is replaced by a synchronous detection circuit (not shown) instead of the phase difference detection circuit 20.
There is a method of obtaining π P _y θ / λ.

In FIG. 1, reference numeral 21 is an angle control unit that controls the angle of the fixed mirror 11. Here, the detected phase difference 4π
P _y θ / λ is integrated to generate a signal of 4π P _y θ / λ = 0 as a drive signal for the actuator 23. The actuator 23 is a rotation correction device using an electrostrictive element, and is driven by the output of the high voltage amplifier 22 to give the fixed mirror 11 an inclination angle corresponding to the drive signal. Therefore, when the tilt of θ is generated in the movable mirror 10 by the integral control for setting the detected phase difference to 0, the fixed mirror 1
1 also follows and causes an inclination of θ, and the phase difference on the light receiving surface becomes uniform. In this control method, even if the phase difference detection is nonlinear as 4πP _y θ / λ as described above, the angle control unit 2
The output of 1 is proportional to the inclination θ of the movable mirror 10, and even if the detection range is narrow, a value of θ over a wide range up to the operation range of the actuator 23 can be obtained. The output of the angle control unit 21 can be fetched into the data processing unit 24, and the tilt information of the moving table can be used for the correction calculation of the positioning of the moving table.

The above description is about the tilt (yawing) detection and the rotation compensation of the moving table with the vertical axis as the rotation axis.
By tilting the light receiving surface of the second photoelectric converter 13 into four as shown in FIG. 4 and using the actuator 23 for two axes, the inclination (pitching) with the horizontal axis as the rotation axis.
Detection and rotation compensation can also be added.

Further, the object to be compensated for the tilt of the movable table is not limited to the fixed mirror, and an actuator may be attached to the movable mirror for compensation. Since the center of rotation of the movable mirror is fixed, it is possible to uniquely know how the movable table tilts while moving, and no inconvenience occurs.

The signal FF and SF signals are used for the output processing of the moving displacement amount x of the moving table. First, unnecessary frequency components such as a DC component are removed by a film, and the π / 2 phase shifter 15 generates a signal FS. Next, low frequency components are generated by the first and second synchronous detection circuits (16, 17) using the signals SF and FS as input signals and the signals SF and FF as input signals.
Obtain the sin (4π x / λ) and cos (4π x / λ) components.
It is possible to determine the moving direction of the moving table 7 by these two signals, and normally, a pulse for positive / negative counting is generated at every phase π / 4, that is, at the optical path length λ / 8 step, and this pulse is counted by the reversible counter 19. Then, the displacement amount x of the moving table
That is, the moving distance can be measured.

[Effect of device]

As described above, according to the moving distance measuring device for a moving table of the present invention, it is possible to eliminate an error in measuring the moving distance due to an angle variation of the moving table, and yawing and pitching the moving table with a simple means. Can be detected. Therefore, even with a moving table made with a simple mechanism with poor performance,
High-precision distance measurement of 0.5 μm is possible. This means that even if a high-performance mobile stand cannot be introduced in an electron beam system due to various conditions such as volume or magnetism, the device of the present invention can measure the moving distance or position of the mobile stand. It is applicable as a length measuring device for alignment.

Further, according to the device of the present invention, it is not necessary to use a plurality of high-performance optical interferometers to compensate for the rotation of the movable table, so that it is structurally compact, simple, and inexpensive.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory view for explaining an optical path difference due to a tilt of a movable mirror, and FIG. 3 is an explanatory view of a light receiving surface of a yaw detecting photoelectric converter. ,
FIG. 4 is an explanatory view of the light receiving surface of the photoelectric converter for detecting yawing and pitching. 1 ... Orthogonal dual frequency light source, 4 ... Non-polarization beam splitter, 6 ... First photoelectric converter, 7 ... Moving stage, 8 ... Polarization beam splitter, 9 ... 1/4 wavelength plate, 10 ... … Movable mirror, 11 …… Fixed mirror, 13 …… Second photoelectric converter, 15
...... π / 2 phase shifter, 16 …… First synchronous detection circuit, 17
...... Second synchronous detection circuit, 18 ...... Phase discrimination circuit, 19
...... Reversible counter, 20 ...... Phase difference detection circuit, 23 ......
Actuator, 24 ... Data processing unit, 30 ... Polarization interferometer, 40 ... Signal processing means

Claims (1)

[Scope of utility model registration request] 1. A quadrature dual-frequency light source (1) which emits a light flux composed of two polarizations having different frequencies and orthogonal to each other; a light flux emitted by the quadrature dual-frequency light source to travel to first and second optical paths. An optical element (4) for splitting into one light beam; a first photoelectric converter (6) for receiving a light beam traveling to the first optical path and obtaining an electric signal FF having a difference frequency between the two polarized light beams
And; a phase shifter (15) that outputs a second signal FS having a phase difference of π / 2 from the output signal FF of the first photoelectric converter; and a light beam that passes through the second optical path, A polarization interferometer (30) that emits a light beam with deviation information on the position and angle of a reflecting mirror provided on the movable table; and a light beam emitted from the polarization interferometer that has a light-receiving surface divided into at least two. A second photoelectric converter (13) for converting the signal into at least two electric signals; and a phase difference detection circuit (20) for detecting a phase difference between two predetermined signals of the output signals of the second photoelectric converter. An actuator (23) for controlling the position and angle of one of the reflecting mirrors that compose the polarization interferometer based on the detected phase difference
A first synchronous detection circuit (16) having a predetermined one of the output signals of the second photoelectric converter and one of the output signals of the phase shifter as input signals; A second synchronous detection circuit (17) which receives the output signal of the converter and a predetermined one of the output signals of the second photoelectric converter as input signals; and of the first and second synchronous detection circuits A moving distance measuring device for a moving table, which comprises a signal processing means (40) for comparing the output signals to determine the moving direction of the moving table and calculating the moving distance.