KR20000065493A - optical fiber laser triangulation device for measurement of 3 degrees-of-freedom displacements - Google Patents

Abstract

PURPOSE: A super-fine displacement sensor of a multiple degree of freedom is provided to perform a fine measuring process by using optical method, finely measures 3 freedom-degree displacement of a spatial rigid substance by using a non-contact and an optical method. CONSTITUTION: An optical signal generator outputs an optical signal through an optical fiber according to an input control signal. A first measurement part illuminates the optical signal on a surface of a measured object, and measures a light quantity of a reflective light. Second measurement parts are symmetrically positioned to each other centering around an output terminal of the first measurement part, measures a focus distance change of the reflective light from the object's surface and a light quantity variation of the reflective light, and outputs them to the outside. A signal processor(1104) measures a displacement of the object's surface by using a measured focus distance variation, and measures a main angle and of the object's surface(1109) and a pitch angle of the object's surface by using a measured light quantity variation measured by the first and second measurement parts.

Description

Optical fiber laser triangulation device for measurement of 3 degrees-of-freedom displacements

The present invention relates to a displacement sensor, and more particularly, to a multi-degree of freedom ultra-precision displacement sensor using an optical fiber capable of precisely measuring three-degrees-of-freedom displacement of a rigid body in space by a non-contact and optical method.

As the performance of various semiconductor equipment, actuators of ultra-fine exercise equipment, electromechanical complex systems, precision processing systems, and the like have been improved, interest in measuring equipment capable of measuring the movement thereof has increased.

Among the various measuring equipments, the devices that apply the optical principle are non-contact, and the resolution of the wavelength unit of light is compared to the conventional touch measuring equipments, and is being applied to various industrial devices.

In general, examples of displacement measuring devices using optical principles widely used in industrial fields include interferometers, optical triangular sensors, and optical fiber sensors.

In the drawings, Figure 1 is a block diagram of a conventional optical triangular sensor, Figure 2 is an exemplary view for explaining the principle of measuring the displacement of the object using the conventional optical triangular sensor.

Referring to Figures 1 and 2, the basic principle of the optical triangulation method is described as follows.

Light from the laser passes through lens 1 and collects at the point labeled focus 1 on the surface to be measured.

The surface to be measured has diffuse reflection characteristics (reflection of light in all directions, such as white paper), and reflect light in all directions.

Among them, only the light passing through the lens 2 is used to calculate the position information. Light passing through the lens 2 is collected on the position sensitive element located at the focal length of the lens 2.

If the surface to be measured moves up and down with displacement as shown in FIG. 2, the position of the focus 2 on the position sensitive element is changed.

Measuring the displacement using this is the measuring principle of the phototriangular sensor.

That is, as shown in FIG. 2, when the surface to be measured is located at position 1, the light collected on the position-sensitive device becomes 1, and when the surface is position 2, the position of light on the position-sensitive device is 2. ,

Position-sensitive devices are devices that can detect the position of light.

Such a sensor is widely used in the related art, and its application field is as follows.

1) Non-contact displacement measuring device

2) Probe in 3D Measuring Machine

3) Non-contact surface shape measuring device

4) machine vision system

However, optical triangular sensors have fundamental problems, and one of them is that optical triangular sensors can measure only one degree of freedom translational motion.

That is, there is a limitation that only translational motion in one direction can be measured.

In other words, the reliability of the measurement is lowered when the surface to be measured is inclined with respect to the incident optical axis.

This will be described in detail with reference to FIG. 3 as follows.

In the drawings, Figure 3 is an exemplary view for explaining the principle of the error that occurs when measuring the rotation of the object using a phototriangular sensor according to the prior art.

As shown in the figure, the displacement of the measurement target surface is fixed and the position of the light on the position sensitive element should not change at all when the measurement target surface is rotated around the point of focus 1.

That is, the sensor should not react to the rotation of the surface to be measured.

But in reality this is not the case,

That is, in the situation shown in FIG. 3, no response should be made to the rotation of the surface to be measured, but if the actual triangulation sensor is made and operated, the sensor output will change when the surface to be measured rotates.

This is a situation that is very difficult to explain theoretically, which leads to a decrease in the reliability of displacement measurement and a situation in which rotation measurement is also impossible.

Also, theoretically, only one degree of freedom of motion is measured (assuming the ideal case that the sensor output does not change for rotation). This can cause problems if you want to measure motion of several degrees of freedom at the same time. .

It is assumed that all movements occur purely in one direction, but in reality they are not.

In the example of a stage widely used in an industrial field, a user assumes that the stage moves in only one direction, but due to various error factors there is not only movement in one direction but also movement in multiple directions simultaneously. will be.

In order to correct and correct the error caused by these various directions of motion, a sensor capable of measuring the motions in various directions is essential.

However, to measure it with the phototriangular sensor which is widely used in the industrial field, it becomes troublesome to measure several points.

In addition, a widely used method for measuring such multi-degree of freedom motion is a method using three or more phototriangular sensors.

However, to summarize the problems of this method is as follows.

1) The problem of cost

2) The problem of space layout

3) Signal Processing Problem

The problem of cost is caused by having to use several sensors, and the problem of space arrangement refers to a problem of placing three sensors on the surface to be measured.

If the size of the surface to be measured is large, there is no problem, but the current trend of industrial development tends to be ultra-precision and ultra-small, because it is difficult to assume that the surface to be measured is large.

The problem with signal processing is that because the signals from the three sensors must be processed in real time, the technique is complicated and inevitably increases the cost.

As a way to solve this problem, the following can be considered.

1) Design of sensor that can measure multiple degrees of freedom with one device

2) Solve the space layout problem by developing a compact 1 degree of freedom sensor

3) Development of new signal processing techniques

Among the above considerations, as a design of a sensor capable of measuring multiple degrees of freedom, many ideas about multi-degree-of-freedom sensors have been developed.

In the figure, Figure 4 is a block diagram of a multi-degree of freedom phototriangular sensor according to the prior art.

As shown in the figure, the configuration of the multi-degree-of-freedom phototriangular sensor according to the prior art installs two position sensitive elements symmetrically.

In the above situation, the distance information read from the position sensitive element 1 and the position sensitive element 2 is the same.

However, the intensity (light quantity) of the light read by the position sensitive element 1 and the position sensitive element 2 is different.

When the surface to be measured is inclined to the right as described above, the amount of light reaching the position sensitive element 2 is greater than the amount of light reaching the position sensitive element 1.

In other words, if the position-sensitive device is used for position-sensitivity, which is the purpose of its development, and read out the amount of light through proper operation, it is possible to find out how inclined the surface to be measured is inclined, and not only the distance but also the tilt. Even luggage can be measured.

To recap, position detection is based on traditional phototriangular principles, but reading out tilted information uses a means of comparing the amount of light reaching the position sensitive element.

The actual measurement target surface is not only tilted left and right in a plane as shown in FIG. 4 but also tilted in a free position in space.

Therefore, in order to comprehensively read the inclined information, a method of arranging four position sensitive elements as shown in FIG. 5 is used.

5 is a block diagram of a multi-degree of freedom phototriangular sensor using four position-sensitive elements.

As shown in the figure, four position-sensitive elements were arranged in a circle around the laser to read information about which direction the surface to be measured was inclined.

However, the prior art can measure the attitude of the measurement target surface only by arranging four position-sensitive elements in the module, which causes a problem that the size of the module called the sensor head must be increased.

Ultimately, there is a problem in that there is a limit in solving the problem of spatial arrangement, signal processing, and economic problem.

Meanwhile, another optical fiber sensor, which is another position measuring device, will be described below.

6 is an exemplary view for explaining the principle of the optical fiber displacement sensor according to the prior art.

The optical fiber is a fiber (fiber) for passing light, and the light emitted from the optical fiber end is essentially spread as shown in FIG. 6.

Since the light spreads at the end of the optical fiber more than 20 degrees, the light from the end of the optical fiber is less than 1mm and spreads.

The sensors required by the industry attach an optical fiber collimator to the end of the optical fiber because its operating range must be turned on.

An optical fiber collimator is a device that directs light from an optical fiber to a far distance.

Since the size is a little larger than the optical fiber diameter, it is a very small device having a size between 0.2 mm and 0.5 mm.

Now, an optical fiber directional coupler, which is an essential device for understanding an optical fiber sensor, will be described with reference to FIG. 7.

7 is a block diagram of an optical fiber directional coupler used in the prior art.

Fiber-optic directional couplers are simply dividers, simply splitting light.

Ports 1, 2, 3 and 4 of the optical fiber directional coupler are all composed of optical fibers.

The word "directionality" is given for the following reasons: Light entering port 1 never splits into port 2 but splits into port 3 and port 4.

In addition, the light coming from port 2 goes out to port 3 and port 4, on the contrary, the light from port 3 is divided into port 1 and port 2, and the same is true of light entering port 4.

That is, the directional optical coupler serves to divide the light from one port into two ports on the opposite side.

Next, an optical fiber connector is simply a device for connecting two optical fibers.

8 is a configuration diagram of an optical fiber sensor according to the prior art.

In the optical fiber displacement sensor, the light from the semiconductor laser enters the optical fiber first.

Through optical fiber directional coupler 1, optical fibers 3 and 4 enter.

Light that went to optical fiber 4 goes out to photodiode 2.

Photodiodes are devices that measure the amount of incoming light.

By measuring the signal from photodiode # 2, you can measure the amount of light from the semiconductor laser.

The fiber optic directional coupler splits the signal by 1: 1.

That is, if the amount of light from the semiconductor laser is 100, 50 light goes to the optical fiber No. 3, 50 light goes to the optical fiber No. 4, and the amount of light detected by the second photodiode is 50.

Light that went to optical fiber 3 is collected in parallel light by the optical fiber collimator.

Light from the optical fiber collimator is projected onto the surface to be measured and reflects off the surface to be measured.

The light reflected from the surface to be measured again enters the optical fiber three times.

In the laser described above, the amount of light of 100 is 50 light to the third optical fiber, and the amount of light 50 from the optical fiber collimator is reflected from the surface to be measured and enters the optical fiber again.

When the amount of light 50 is shot on the surface to be measured, the amount of reflected light is only about 1-2.

Then, the light entering the optical fiber 3 is again divided into the optical fiber 1 and the optical fiber 2 by the optical fiber directional coupler.

For convenience, if the amount of reflected light is 1, the amount of light going through optical fiber 3 to optical fiber 2 will be 0.5, and the amount of light detected by photodiode 1 will be 0.5.

The important point here is that the amount of light reflected back varies by the distance between the optical fiber collimator and the surface being measured.

The relationship is shown graphically in FIG.

In the figure, FIG. 9 is a graph showing the relationship between the distance and the amount of light used in the conventional optical fiber sensor.

The graph of FIG. 9 shows the distance between the optical fiber collimator and the surface to be measured by knowing the amount of light entering the photodiode 1 through the optical fiber no. 2.

The reason why the second photodiode is required in the related art is that although the amount of light emitted from the laser is generally constant, the amount of light changes to some extent during the optical fiber.

Therefore, it is necessary to know clearly whether the amount of light emitted from the photodiode No. 1 changes due to a change in distance or because of optical fiber waveguide characteristics while passing through the optical fiber.

Therefore, photodiode No. 2 is needed because the signal from Photodiode No. 2 is divided by the signal from Photodiode No. 1 (normalized) to obtain accurate distance information.

However, in the conventional optical fiber displacement sensor, the amount of light entering the photodiode No. 1 is changed by the distance between the surface to be measured and the optical fiber collimator. As a result, there was a problem that it is difficult to determine whether the signal from the first photodiode is a signal due to tilting or a signal due to a distance change.

10 is a block diagram of an improved optical fiber sensor according to the prior art.

The colored part in the drawing is an optical fiber that emits light, and the colored part is an optical fiber that receives light.

In solution 1, if light is emitted from the optical fiber in the middle, light is received from the optical fiber on both sides.

If the surface to be measured is tilted, the amount of light entering the optical fibers on both sides will be different, and the tilt can be measured using this.

However, the problem is that the spatial inclination cannot be measured and only the two-dimensional inclination can be measured.

The solution to this problem is solution 2.

By emitting light from the optical fiber in the middle and light from the six optical fibers around it, spatial tilt can be detected.

It is remarkable that the sensor using the optical triangulation method uses the amount of light received by arranging several position-sensitive elements in order to read the information about the tilt, and the method of reading the information about the tilt The same is true for optical fiber sensors and optical triangular sensors.

The biggest advantage of the optical fiber sensor is as follows.

1) Since it uses optical fiber of hair thickness, it is very small compared to other size sensors.

2) Due to the rapid development of communication (optical communication) using optical fibers, the price of various optical fiber elements is very low.

Since the measuring devices have a precision of μm or less and can measure the change in distance or orientation without changing the physical quantity of the object to be measured, existing contact displacement measuring devices are being replaced at a high speed.

In addition, the measurement principle of the measurement equipment using the optical principle is based on the projection of light on the object to be measured and converting the phase, amount of light, and position of the reflected light into displacement.

However, the measurement apparatuses according to the related art are inefficient in terms of space, require a large number of expensive measurement instruments, additionally require a posture converting circuit, and have many limitations due to difficulty in real time measurement.

In this regard, it is essential to develop a device capable of measuring in real time three degrees of freedom motion in space using a single measuring device at a relatively low cost.

The present invention has been made to meet the requirements as described above, by guiding the light from the laser diode to the optical fiber to be projected on the measurement object to reduce the size of the sensor head, by utilizing the optical fiber itself as a displacement measuring sensor It is an object of the present invention to provide a multi-degree-of-freedom displacement sensor using an optical fiber that obtains distance information by using a conventional optical triangulation method and at the same time processes a signal from a position-sensitive device to obtain an excessive information on azimuth. .

1 is a block diagram of a phototriangular sensor according to the prior art,

2 is an exemplary view for explaining the principle of measuring the displacement of an object using a phototriangular sensor according to the prior art,

3 is an exemplary view for explaining the principle of the error occurred in the measurement of the rotation of the object when using a conventional triangular sensor,

4 is a block diagram of a multi-degree of freedom optical triangular sensor according to the prior art,

5 is a configuration diagram of a multi-degree-of-freedom phototriangular sensor using four position-sensitive elements,

6 is an exemplary view for explaining the shape of light spreading from the end of the optical fiber,

7 is a configuration diagram of an optical fiber directional coupler used in the prior art,

8 is a configuration diagram of an optical fiber displacement sensor according to the prior art,

9 is a graph showing the basic relationship between the distance and the amount of light used in the optical fiber displacement sensor according to the prior art,

10 is a block diagram of an improved optical fiber multi-degree of freedom sensor according to the prior art,

11 is a block diagram of a multi-degree of freedom ultra-precision displacement sensor using an optical fiber according to an embodiment of the present invention,

12 is an exemplary diagram for explaining a relation between a surface normal vector and a yaw angle and a pitch angle,

FIG. 13 is an exemplary diagram for describing a distance and light quantity measurement using the position sensitive device of FIG. 11;

14 is an exemplary waveform diagram of a generated signal of a laser diode driver used in the present invention.

♠ Explanation of symbols on the main parts of the drawings.

1101, 1113: round aperture 1102, 1114: lens

1103, 1115: position sensitive element 1104: signal processor

1105: laser diode driver 1106: laser

1107, 1108: photodiode 1109: surface to be measured

1110: directional coupler 1111: optical fiber collimator

1112: optical fiber

According to the present invention for achieving the object as described above, the optical signal generating means for generating an optical signal according to the input control signal to output through the optical fiber; First measuring means for measuring and outputting the amount of reflected light after transmitting the optical signal input from the optical signal generating means to the measurement target surface; A pair of symmetrically positioned around the output terminal of the first measuring means for measuring and outputting a focal length change and light quantity change of the reflected light from the measurement target surface of the optical signal output from the first measuring means Second measuring means; And measuring the displacement of the surface to be measured using the focal length change measured by the pair of second measuring means, and using the change in the amount of light measured by the first and second measuring means And a signal processing means for measuring a change in pitch angle, there is provided a multi-degree of freedom ultra-precision displacement sensor using an optical fiber.

Now, a preferred embodiment of the multi-degree of freedom displacement sensor using the optical fiber of the present invention will be described in detail with reference to the drawings.

11 is a block diagram of a multi-degree of freedom displacement sensor according to an embodiment of the present invention.

As shown in the figure, the multi-degree of freedom displacement sensor according to an embodiment of the present invention, the first and second circular aperture (1101, 1113), the first and second lenses (1102, 1114), the first and Second position sensitive elements 1103, 1115, signal processor 1104, laser diode driver 1105, laser 1106, first photodiode 1107, second photodiode 1108, directional coupler 1110 And an optical fiber 1112 for connecting the optical fiber collimator 1111 and the laser 1106 and the directional coupler 1110 and for connecting the directional coupler 1110 and the optical fiber collimator 1111.

Now, the operation of the multi-degree of freedom displacement sensor according to an embodiment of the present invention will be described in detail.

First, the laser diode driver 1105 generates a driving signal for driving the laser 1106 according to a control signal input from the signal processor 1104 and outputs the driving signal to the laser 1106.

The laser 1106 oscillates according to the driving signal input from the laser diode driver 1105 to generate and output an optical signal.

The directional coupler 1110 divides and outputs an optical signal input from the laser 1106 into an optical fiber collimator 1111 and a second photodiode 1108.

The second photodiode 1108 measures and outputs light intensity of the optical signal input from the directional coupler 1110.

The optical fiber collimator 1111 prevents the spread of the optical signal output from the directional coupler 1110 and projects it onto the measurement target surface.

At the same time, the optical fiber collimator 1111 receives the reflected light from the measurement target surface of the projected optical signal and outputs it to the first photodiode 1107.

Then, the first photodiode 1107 measures the light intensity of the input reflected light signal and outputs it to the signal processor 1104.

The first and second circular apertures 1101 and 1113 pass reflected light of the optical signal output from the optical fiber collimator 1111, and the first and second lenses 1102 and 1114 pass through the first and second circular apertures 1101. And condenses and outputs the optical signal passing through 1114.

The first and second position-sensitive devices 1103 and 1115 measure the change amount of focus and the amount of light of the optical signals passed from the first and second lenses 1102 and 1114 and output the measured amount of change to the signal processor 1104.

Then, the signal processor 1104 may include information about the amount of light received from the first photodiode 1107, information about the amount of light received from the second photodiode 1108, and the first and second position sensitive devices 1103 and 1115. The yaw angle and the pitch angle are measured and output using the information of the amount of change of the light quantity inputted from Measure and output.

In the drawings, FIG. 2 is an exemplary view for explaining the relationship between the surface normal vector and the yaw angle and pitch angle.

As shown in the figure, the surface normal vector is defined as the longitude α, latitude β on the cylindrical coordinate system.

The longitude α represents a yaw angle, and the latitude β represents a pitch angle.

Thus, the yaw angle and pitch angle can be used to find the surface normal vector of the surface to be measured.

In the drawings, FIG. 13 is an exemplary view for explaining distance and light quantity measurement using the position sensitive device of FIG. 11.

When the surface to be measured moves in space and has an arbitrary posture, light emitted from the optical fiber collimator passes through the objective lenses 1102 and 1114 to the position sensitive elements 1103 and 1115 from the surface to be measured, which is characterized by diffuse reflection. When the focal point 50 is formed, the focal point 50 of the position sensitive elements 1103 and 1115 moves in accordance with the change of the distance d on the z-axis.

As shown in the figure, the output currents of the position sensitive elements 1103 and 1115 vary in magnitude of the current signals I ₁ and I ₂ obtained depending on the position of the position focal point 50.

Using this, the distance d can be converted. Further, in accordance with the change degree of the 12 θ so it varies the amount of light passing through the circular aperture (14, 15), by using the signal I ₀ can be obtained information about the amount of change of θ.

In the drawings, FIG. 14 is an exemplary waveform diagram of a generated signal of a laser diode driver used in the present invention.

As shown in the figure, the generated signal of the laser diode driver used in the present invention is a pulse signal having a duty to prevent degradation of the entire system and to reduce noise.

As described above, the multi-degree-of-freedom displacement sensor using the optical fiber of the present invention can measure three-degrees-of-freedom motion in real time with one measuring device, which requires ultra-precision multi-degree of freedom displacement measurement within a limited space area and a limited budget. There is an effect that can be effectively applied to various vibration measuring fields, micro photovoltaic complex system, various semiconductor equipment.

In addition, the multi-degree-of-freedom displacement sensor using the optical fiber of the present invention configures a light source using the optical fiber, and since the optical fiber portion is used as the displacement sensor, the size of the sensor head is very small, so that measurement can be performed without any spatial constraints. It is effective.

In addition, the multi-degree-of-freedom displacement sensor using the optical fiber of the present invention can be manufactured at low cost by reducing the number of elements required for multi-degree of freedom measurement by applying the position-sensitive element to the measurement of each change as well as the position of the focus It works.

The technical concept of the multi-degree of freedom displacement sensor using the optical fiber of the present invention has been described above with the accompanying drawings, but this is by way of example and not by way of limitation. In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (4)

Optical signal generating means for generating an optical signal according to the input control signal and outputting the optical signal through the optical fiber; First measuring means for measuring and outputting the amount of reflected light after transmitting the optical signal input from the optical signal generating means to the measurement target surface; A pair of symmetrically positioned around the output terminal of the first measuring means for measuring and outputting a focal length change and light quantity change of the reflected light from the measurement target surface of the optical signal output from the first measuring means Second measuring means; And The displacement of the surface to be measured is measured by using a change in focal length measured by the pair of second measuring means, and the yaw angle and A multi-degree of freedom ultra-precision displacement sensor using an optical fiber, comprising signal processing means for measuring a change in pitch angle. The method of claim 1, The pair of second measuring means, A circular aperture positioned symmetrically about an output terminal of the first measuring means to receive reflected light of the surface to be measured of the output optical signal of the first measuring means; An objective lens for condensing the optical signal incident on the circular aperture; And And a position sensitive element for measuring and outputting a focal length change amount and a light amount change amount of the focused light located at a focal length of the objective lens. The method according to claim 1 or 2, The first measuring means, A directional coupler for dividing and outputting the signal coming from the signal generating means, and for dividing and outputting the reflected light from the measurement target surface; A first photodiode for measuring and outputting an amount of reflected light input from the directional coupler; A second photodiode for measuring and outputting an intensity of light amount of transmitted light input from the directional coupler; And And an optical fiber collimator for preventing the spread of the transmitted light input from the directional coupler and for receiving the reflected light on the surface to be measured. The method of claim 3, wherein The optical signal generating means, A laser diode driver for generating and outputting a laser diode driving signal in accordance with a control signal input from the signal processing means; And And a laser for generating an optical signal according to the driving signal input from the laser diode driver and outputting the optical signal to the optical fiber.