KR20070035333A - Displacement measuring device by using the focus splitting and method thereof - Google Patents

Abstract

The present invention relates to a displacement measuring apparatus and a measuring method for measuring the displacement of a target object by using a focus division method so as to accurately measure the displacement to the object in processing or inspecting the object.

Displacement measuring apparatus and method according to the present invention detects the light passing through the pinhole disposed before the focus and the pinhole disposed after the focus by the optical sensor based on the focus position divided by the beam splitter, respectively, and the difference in the amount of light detected Displacement to the measurement object can be measured through the difference of the electrical signals generated by the optical sensor, and the influence on the reflectance of the measurement object is minimized by normalizing the difference of the calculated electrical signals to the sum of the electrical signals. In addition, since the linearity of the signal can be secured, highly accurate displacement measurement is possible when processing or inspecting various electronic products such as semiconductors and LCDs and various mechanical products.

In addition, it is possible to measure the displacement more precisely than the conventional displacement measuring method by maximizing the sensitivity to the change of displacement, so it can be applied to the method and device for the auto focusing device to keep the distance between the object and the measurement optical system constant. Do.

Displacement measuring device, displacement measuring method, pinhole, optical sensor, laser

Description

Displacement measuring device by using the focus splitting and method

1 is a schematic diagram showing a configuration of a displacement measuring apparatus using a focus division method according to an embodiment of the present invention;

2 is a schematic view for explaining a focus position of light according to the displacement of the measurement object according to the present invention;

3A is a graph showing the relationship between the displacement of a measurement object and the optical sensor output;

3b is a graph of differentially amplifying the optical sensor output of FIG.

3c is a graph showing the relationship between voltage and distance,

Fig. 4 is a schematic diagram showing the configuration of an autofocus apparatus using the focus division displacement measuring method according to the second embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10: light source 20: displacement measuring device

21: parallel optical lens unit 24: condensing lens unit

25: second beam splitter 26A: first pinhole

26B: second pinhole 28A: first optical sensor

28B: second optical sensor 29: signal processor

The present invention relates to a displacement measuring apparatus and a measuring method for measuring the displacement of a target object by using a focus division method so as to accurately measure the displacement to the object in processing or inspecting the object.

Recent rapid technological developments across industries have required precise machining and rapid and accurate inspection in the fields of semiconductors, MEMS, display devices, optical components, and micromechanical components.

Since these parts require precise handling in the manufacturing process, precision optical devices such as microscopes and interferometers are frequently used for processing, assembly, and inspection.

For example, flatness inspection in flat panel display packaging or flip chip, a kind of semiconductor chip, MEMS and other engineering precision products. It is very important to accurately measure the displacement to the measuring object and to adjust the displacement.

Currently, in the processing, assembly and inspection of precision parts and equipment, the shape of the workpiece or inspected object is also changed from a simple two-dimensional shape to a complex three-dimensional shape, and also the need for in-process inspection. Increasingly, in precision optics, the importance of rapid and accurate distance measurement techniques to complex shaped objects is further emphasized.

In general, a method of determining a displacement to a focal length in a precision optical device, a method using an ultrasonic sensor, a method using an infrared sensor, a TTL phase difference detection method, a method using a laser beam, and the like.

Displacement measuring method using ultrasonic sensor is to measure displacement by emitting ultrasonic wave and calculating the return time. The use frequency is from tens of kilohertz to hundreds of kilohertz, and the use frequency is determined by the resonance frequency of ultrasonic sensor. . The higher the resonance frequency of the ultrasonic sensor, the higher the accuracy.

Ultrasonic sensors are inexpensive, easy to manufacture and install, and have faster information processing than other sensors, but the uncertainty of the sensor's own information is large, and there is a lot of false information due to the mirror effect. There is a problem that is greatly affected by the environment, such as humidity.

The displacement measuring method using an infrared sensor basically consists of a light emitting part emitting light of a certain frequency and a light receiving part receiving light emitted from the light emitting part, and when the infrared light emitted from the light emitting part hits an object and is reflected, the light receiving part reflects the light. The distance to the object is measured by detecting the light. Infrared sensors are inexpensive and can be shot in the dark, but are limited in the distance measurement.

Displacement measurement method using an infrared sensor is mainly applied to the automatic focusing device of the video camera, as shown in the Republic of Korea Patent Publication No. 0130002.

Next, displacement measurement by TTL phase difference detection focuses on the point where the difference in luminance or contrast on the surface of the subject visible through the lens, that is, the surface where the focus sensor is placed, is maximized. It is a method of calculating the difference in luminance and inferring it by distance. In principle, this method does not measure when there is no difference in luminance on the surface or when the focus is focused on white near 100% of the reflectance, and cannot be measured even in a dark situation where the reflectance is near zero.

Finally, a displacement measuring method using a laser beam projects a laser beam output from a light emitting source onto a part to be inspected placed on a reference plane such as a stage, and receives a reflected light beam with a light receiving unit. The displacement is specified by measuring the level of.

Since the displacement measuring method using the conventional laser beam basically uses a triangulation method, the laser light source and the light receiving part are separated from each other by a certain distance, so that the light emitting beam and the light receiving beam must be configured to maintain a constant angle, thereby making the equipment compact. There is a problem that the measurement accuracy depends on the constraints and the positioning state of the part.

The technical problem to be achieved by the present invention is to find a novel displacement measuring method and apparatus having a completely different concept from the conventional displacement measuring method having the above problems, and an object of the present invention is to provide a simple optical configuration using a focus division method. It is to provide a displacement measuring method and a measuring device which accurately and quickly measure the position of an object only by processing and signal.

The present invention is to introduce a new measuring method and signal processing method to perform accurate and rapid displacement measurement by a simple mechanism, the result of the object displacement measurement is inaccurate according to the reflectivity of the object that can occur in the conventional displacement measurement method By eliminating the problem of deterioration, it is possible to measure the displacement of the measurement object more precisely.

In addition, the displacement measuring method and apparatus of the present invention is designed to be applied as an auto focusing device for maintaining a constant focal length between an object and a measuring optical system and a method for implementing the same.

In order to achieve the above technical problem, the displacement measuring apparatus according to the present invention includes light passing through a pinhole disposed before focus and a pinhole disposed after focus based on a focus position divided by a beam splitter, respectively. It is characterized by measuring the displacement to the measurement object through the electrical signal difference between the optical sensors generated by the difference in the amount of light detected, and it is derived from the time series describing the steps in which these components are operated Displacement measuring method according to the invention.

Displacement measuring device according to the invention and a light source for emitting light; A parallel light lens unit for irradiating light emitted from the light source in parallel; A first beam splitter for changing a path of light irradiated in parallel by the parallel light lens unit; An objective lens unit for focusing light whose path is changed by the first beam splitter to a measurement object; A condensing lens unit for condensing the reflected or scattered light after focusing on the measurement object by the objective lens unit; A second beam splitter for dividing the light focused by the condenser lens unit into two; A first pinhole focused by the condensing lens unit and positioned on one optical path divided by a second beam splitter and installed in front of a focus position of the light; A second pinhole focused by the condensing lens unit and disposed on another light path divided by the second beam splitter and installed at a rear of a focus position of light; A first optical sensor focused by the condenser lens unit and measuring an amount of light passing through the first pinhole; A second optical sensor focused by the condenser lens unit and measuring an amount of light passing through the second pinhole; A signal processing unit for acquiring and processing signals from the first and second optical sensors is provided in a basic configuration.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail.

1 is a block diagram for explaining a displacement measuring apparatus using a focus division according to the present invention.

Referring to FIG. 1, the displacement measuring apparatus 20 according to the present invention has a light having arbitrary waveforms in the form of continuous, pulsed or sine curves generated and emitted from the light source 10 through the parallel optical lens unit 21. After passing through the first beam splitter 23 and the objective lens unit 22 in the form of a beam to reach the measurement object 100 to measure the displacement, the object lens unit 22 is reflected from the measurement object 100. After passing through the first beam splitter 23, the light beam is split through the first beam splitter 23 to form a single focal point through the condenser lens unit 24, and a second beam splitter 25 is disposed on the rear surface of the condenser lens unit 24. It is installed so that the light beam passing through the condenser lens unit 24 is divided into two. That is, the light passing through the condenser lens unit 24 is divided into two light beams to form two focal points.

A first pin hole 26A is installed in front of the focal position of one divided light beam, and a second pin hole 26B is installed in the back of the focal position of another divided light beam, wherein the pin hole may have a slit shape. The distance between the focal position of the lens and the pinhole position, the shape of the pinhole, the thickness of the pinhole forming member, the material of the pinhole forming member, and the like are appropriately selected according to the measurement performance and the measurement range.

In addition, the first optical sensor 28A is installed at the rear of the first pin hole 26A in pairs with each pin hole, and the second optical sensor 28B is installed at the rear of the second pin hole 26B to pass through each pin hole. The amount of light is measured at each optical sensor paired with a pinhole.

The signal processor 29 obtains an electrical signal value from the first optical sensor 28A and the second optical sensor 28B, converts the difference between the electrical signal values into a distance, and the displacement of the measurement object 100 is increased. Allow measurement.

FIG. 2 shows the focal position of the light beam passing through the condensing lens unit 24 when the displacement of the measurement object 100 moves by the displacement -d to + d based on the focal length A. FIG.

When the displacement of the measurement object 100 is at the focal length A, the light reflected from the measurement object 100 passes through the condenser lens part 24 to be collected at a point B at the focal length of the condenser lens part 24. The focus position of the light beam varies according to the displacement to the subject.

The amount of light passing through the pinhole changes according to the focus position, and the light passing through the pinhole located in directions opposite to each other with respect to the focus causes the signal values of the respective optical sensors to change in opposite directions.

In more detail with reference to Fig. 2, when the focal position is located behind the displacement A by the displacement d (displacement -d), the light passing through the condenser lens unit focuses the light at a distance less than the focal position B. Will be concluded.

The light with the displacement -d passes through each pinhole and enters the sensor paired with the pinhole so that the amount of light is measured. In the case of the first sensor, since the light of the displacement -d passes through the first pinhole, the value is 1 ( If 100% passes, the reference value is 1), and in the case of the second sensor, since the light of the displacement -d does not pass through the second pinhole, the amount of light measured by the second sensor does not pass. Less than one.

When the focus is located at the focus position A and the displacement + d, the light passing through the condenser lens part is focused at the rear of the focus position B, and the amount of light measured by each sensor is the first pinhole in the case of the first sensor. Since there is light that does not pass, the value does not reach 1, and in the case of the second sensor, the value is 1 since all light passes through the second pinhole.

Figure 3a shows the difference between the above-described displacement and the output signal from each sensor, and shows the output for each optical sensor according to the displacement of the measurement object.

The optical sensor used in the present invention is a general optical sensor that measures the amount of light passing through the pinhole, and converts the amount of current according to the amount of light into an electrical size and outputs the value as a signal.

If the light passes through all the pinholes, the value will be 1, and if the light does not pass through the pinholes, the value output from the photosensor will be closer to 0 as the amount of light that does not pass increases.

By differentially amplifying the signal values of the first optical sensor 28A and the second optical sensor 28B according to the displacement of the measurement object, an optical sensor signal of positive voltage and an optical sensor signal of negative voltage are obtained. When the differential signal is 0, the distance between the measurement object 100 and the objective lens unit 22 is dropped by the focal length of the objective lens unit 22, and thus the displacement is based on the calculated voltage value. The distance from the objective lens unit 22 to the measurement object 100 can be converted.

FIG. 3B is a graph obtained by differentially amplifying the output values of the first optical sensor 28A and the second optical sensor 28B according to the displacement of FIG. 3A. The signal values shown in this graph may be expressed by Equation 1 below.

Signal value = first optical sensor signal-second optical sensor signal [Equation 1]

When the size or location of the pinhole is determined, a characteristic graph as shown in FIG. 3B can be completed. Therefore, when a signal value is determined for an arbitrary subject, a displacement corresponding to the signal value can be determined through the characteristic graph. will be.

However, as can be seen from the graph, the displacement values corresponding to the maximum signal value and the minimum signal value are not determined as one value. When the displacement increases, a very small change in the signal value actually represents a very large displacement difference. The displacement calculation by this graph is only possible for very narrow displacements.

In addition, when the displacement is calculated based on the signal value according to [Equation 1], when the light passes through all the pinholes and the light sensor signal is weak, that is, when the reflectivity of the subject is very low, the relationship between the pinhole and the focus is different. Irrespective of the amount of light itself, it is not possible to measure accurate displacement.

Therefore, in the present invention, in order to secure the linearity of the signal graph and to remove the influence of the reflectivity according to the measurement object, a normalized signal is calculated as a signal value. That is, in order to secure the linearity of the signal, the final displacement signal value is obtained by dividing the difference of each signal by the sum of the respective signals.

This is expressed as equation (2).

[수학식 2]

[Equation 2]

Figure 3c shows the above equation (2) as a graph, showing that the displacement of the measurement object 100 can be obtained by converting the displacement signal value into a distance.

As a result, the displacement measuring apparatus and the measuring method based on the present invention are based on a graph as shown in FIG. 3C. When the final displacement signal value is obtained, the displacement represented by the graph is calculated based on this value.

4 is combined with a drive device for driving an optical device for use as an autofocusing device and method for maintaining a constant focal length between an object and an optical system using the displacement measuring device and method using the focus division method of the present invention. It is a block diagram which shows the structure schematically.

As described in detail above, the optical system 10 includes a light source 10, a parallel light lens unit 21, an objective lens unit 22, a condenser lens unit 24, a first beam splitter 23, and a second beam splitter 25. The first pin hole 26A, the second pin hole 26B, the first optical sensor 28A, the second optical sensor 28B, and the like are organically coupled and modularized or assembled.

Focus division displacement measuring apparatus or method of the present invention can also be used as a device for auto focus or a method for auto focus, as shown in Figure 4, the final calculated from the electrical values output from the two optical sensors The optical signal 58 engaged with the drive system is moved back and forth by converting the displacement signal value into a control signal capable of controlling the motor 54 by the signal processor 29 and applying the control signal to the motor 54 to drive the drive system. It is possible to configure the feedback control to maintain a constant state between the measurement object and the lens.

In addition, the lens unit used in the present invention may be formed of a lens group as well as a single lens.

Although the preferred embodiments of the present invention have been described as described above, those skilled in the art may variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims. It will also be within the scope of the invention.

As described above, according to the displacement measuring apparatus and method using the focus division method according to the present invention, it is possible to measure the exact displacement to the measurement object, and also to make the distance between the object and the measuring optical system to be the focal length of the optical system. You can implement autofocus and autofocus to keep it constant.

In addition, according to the displacement measuring apparatus and method according to the present invention, the influence of the reflectivity of the measurement target is additionally eliminated, and the linearity of the signal is secured, so that the measurement can be more reliable than the displacement measuring apparatus and method using a conventional optical system.

Claims (5)

The light reflected from the measurement object and focused through the condenser lens unit is divided into two condensed beams using a beam splitter disposed at the rear side of the condenser lens unit. Pass through the pinholes placed in front, and the other focused light passes through the pinholes placed at the back of the focus position, and outputs the amount of light passing through each pinhole as an electrical signal from the optical sensor paired with each pinhole. The final displacement signal value is determined as a signal value obtained by dividing the electrical signal value of each optical sensor by the sum of the electrical signal values of each optical sensor, and the displacement is calculated based on this value. Displacement measurement method using a focus division method characterized in that to make. The method of claim 1, By converting the final displacement signal value into a control signal capable of controlling the motor driving the drive system for driving the optical system to control the motor to realize a method of automatically focusing by adjusting the focal length between the measurement object and the lens Displacement measurement method using a focus division method characterized in that. A light source for emitting light; A parallel light lens unit for irradiating light emitted from the light source to the measurement object in parallel; A first beam splitter for changing a path of light irradiated in parallel by the parallel light lens unit; An objective lens unit for focusing light whose path is changed by the beam splitter to a measurement object; A condensing lens unit for condensing the reflected or scattered light after focusing on the measurement object by the objective lens unit; A second beam splitter for splitting the light focused by the condenser lens unit into two; A first pinhole focused by the condensing lens unit and positioned on a path of light as one light divided by a second beam splitter, and installed in front of a focus position of the light; A second pinhole that is focused by the condensing lens unit and is another light split by the second beam splitter, the second pinhole being positioned on a path of the light and installed behind the focus position of the light; A first optical sensor focused by the condenser lens unit and measuring an amount of light passing through the first pinhole; A second optical sensor focused by the condenser lens unit and measuring an amount of light passing through the second pinhole; A processor which receives a signal from the first optical sensor and the second optical sensor, obtains a final displacement signal value obtained by dividing the difference between the signal values of the two optical sensors by the sum of the signal values, and calculates a corresponding displacement; Displacement measuring device using a focus division method characterized in that provided. The method of claim 3, The calculated final displacement signal value is converted into a control signal capable of controlling the motor 54 by the signal processor 29, and the control signal is applied to the motor 54 to drive the drive system to engage the optical system 58 engaged with the drive system. Displacement measuring device using a focus division method characterized in that the autofocusing device for automatically focusing between the measuring object and the lens to be moved back and forth. The method according to claim 3 to 4, The light source is a displacement measuring apparatus using a focus division method, characterized in that for driving the laser in one of the waveform form of continuous, pulsed, sign.

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