CN112965231A

CN112965231A - Piezoelectric crystal-based microscope system and automatic focusing method thereof

Info

Publication number: CN112965231A
Application number: CN202110214359.9A
Authority: CN
Inventors: 覃翠; 张健; 何睿清; 魏峘; 赵静; 余辉龙
Original assignee: Nanjing Institute of Technology
Current assignee: Nanjing Institute of Technology
Priority date: 2021-02-26
Filing date: 2021-02-26
Publication date: 2021-06-15

Abstract

The invention discloses a piezoelectric crystal-based microscopic system and an automatic focusing method thereof in the field of microscopic vision technology. Between the measured object and the objective lens of the microscope system, it is used to change the imaging position of the measured object; the voltage control circuit is electrically connected to the computer and the piezoelectric crystal, and is used to change the effect on the piezoelectric crystal according to the control instructions of the computer. voltage value. In the invention, a piezoelectric crystal is added between the microscope objective lens and the shooting target, and the thickness of the crystal is controlled by voltage, so as to change the optical distance between the shooting target and the microscope objective lens, so as to adjust the position of the focus to realize automatic focusing, and has the advantages of focusing. It has the characteristics of high speed, high precision, and low manufacturing and use costs.

Description

Piezoelectric crystal-based microscope system and automatic focusing method thereof

Technical Field

The invention belongs to the technical field of microscopic vision, and particularly relates to a piezoelectric crystal-based microscopic system and an automatic focusing method thereof.

Background

Microscopic vision is widely applied to the fields of medicine, IC manufacturing, bioengineering, micro electro mechanical system assembly and the like, and has the characteristics of small field of view, short depth of field and the like. Microscopic vision must acquire sharp images by focusing. The automatic focusing technology is the core function of an automatic control microscopic vision system, is the high-precision measurement basis of microscopic vision, and is the key of the automatic focusing technology for accurate and rapid focusing. At present, the automatic focusing mainly determines the out-of-focus state by observing the image characteristics of a shot target or the distance between a lens and the target, and then adjusts the relative position of an objective lens or the whole equipment and a wafer through mechanical movement, thereby achieving the aim of focusing. Although the method can quickly realize focusing, the focusing process and the focusing precision of the method depend on the precision and the speed of mechanical movement, so that the cost is high.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a microscope system based on piezoelectric crystals and an automatic focusing method thereof, which have the characteristics of high focusing speed, high precision, low manufacturing and using cost and the like.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

in a first aspect, there is provided a microscopy system comprising: the microscope system is used for acquiring the image of the measured object and transmitting the image to the computer; the piezoelectric crystal is arranged between the object to be measured and the objective lens of the microscope system and is used for changing the imaging position of the object to be measured; and the voltage control circuit is respectively electrically connected with the computer and the piezoelectric crystal and is used for changing the voltage value acted on the piezoelectric crystal according to the control instruction of the computer.

Further, the piezoelectric crystal is polycrystalline piezoelectric ceramic.

Further, the microscope system employs a CCD or CMOS camera.

In a second aspect, there is provided an auto-focusing method for a microscope system, which uses the microscope system of the first aspect, including: based on the deformation characteristics of the piezoelectric crystal under the action of the electric field, changing the voltage value acting on the piezoelectric crystal according to the set voltage difference, thereby changing the thickness of the piezoelectric crystal; when the piezoelectric crystal is at different voltage values, respectively acquiring images of a measured object and calculating a definition evaluation function of the images to obtain a definition evaluation function value; and adjusting the voltage value acting on the piezoelectric crystal based on the definition evaluation function value until the automatic focusing is completed.

Further, the adjusting of the voltage value applied to the piezoelectric crystal based on the sharpness evaluation function value until the automatic focusing is completed specifically includes: if the definition evaluation function value is increased, the voltage applied to the piezoelectric crystal is continuously increased according to the set voltage difference delta V; until the definition evaluation function value is reduced, the voltage acting on the piezoelectric crystal is reduced by delta V, and the focusing is considered to be performed at the moment; if the value of the sharpness evaluation function decreases, the voltage applied to the piezoelectric crystal continues to decrease according to the set voltage difference Δ V until the value of the sharpness evaluation function decreases, and the voltage applied to the piezoelectric crystal increases by Δ V, and it is considered that the focus is achieved.

Further, the piezoelectric crystal has deformation characteristics under the action of an electric field, specifically:

X＝eE (2)

wherein E is the piezoelectric coefficient of the crystal, E is the electric field, and X is the strain capacity of the piezoelectric crystal.

Compared with the prior art, the invention has the following beneficial effects: the invention adds a piezoelectric crystal between the microscope objective and the shooting target, and controls the thickness of the crystal through voltage, thereby changing the optical path between the shooting target and the microscope objective, adjusting the position of the focus to realize automatic focusing, and having the characteristics of high focusing speed, high precision, low manufacturing and using cost, and the like.

Drawings

FIG. 1 is a schematic diagram illustrating a focusing principle of a microscope system according to an embodiment of the present invention;

fig. 2 is a schematic system structure diagram of a microscope system according to an embodiment of the present invention.

Detailed Description

The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

The first embodiment is as follows:

as shown in fig. 1, when the focal length of the convex lens 1 is f, and a piezoelectric crystal 2 with thickness d and refractive index n is added between the convex lens and the focal point, the position L where the convex lens 1 focuses becomes:

that is, the object to be measured is at this position, and focusing can be achieved.

When the piezoelectric crystal is acted by external force along a certain direction, the polarization phenomenon can be generated inside the piezoelectric crystal, so that charged particles are relatively displaced, and charges with equal size and opposite signs are generated on the surface of the crystal; when the external force is removed, the state of the battery is restored to the uncharged state. The charge quantity generated by the crystal under the action of force is in direct proportion to the magnitude of the external force. Conversely, if an electric field is applied to the crystal, the crystal is mechanically deformed in a certain direction; when the applied electric field is removed, the deformation disappears, and this phenomenon is called inverse piezoelectric effect, also called electrostrictive effect.

The method for judging the defocusing in the traditional automatic focusing, such as a method for calculating the image definition, is utilized to determine whether the defocusing exists. And generating signals, changing the voltage of the electric field, and adjusting the deformation of the piezoelectric crystal, thereby changing the focusing position, realizing focusing and obtaining a clear image.

The piezoelectric crystal has the following deformation characteristics under the action of an electric field:

X＝eE (2)

wherein E is the piezoelectric coefficient of the crystal, E is the electric field, and X is the strain capacity of the piezoelectric crystal; the electric field is a controllable variable. By changing the value of the voltage, the amount of strain can be changed, so that the position of the focus is changed, and the change of the focus position is realized.

Based on the above, the present embodiment provides a microscope system, as shown in fig. 2, including: the microscope system 3 is used for acquiring the image of the measured object 4 and transmitting the image to the computer 5; the piezoelectric crystal 2 is arranged between the object to be measured 4 and the objective lens 31 of the microscope system and is used for changing the imaging position of the object to be measured 4; and the voltage control circuit 6 is respectively electrically connected with the computer 5 and the piezoelectric crystal 2 and is used for changing the voltage value acted on the piezoelectric crystal 2 according to the control instruction of the computer 5.

In this embodiment, the piezoelectric crystal is a polycrystalline piezoelectric ceramic.

In this embodiment, the microscope system 3 employs a CCD or CMOS camera 33. When the object is photographed by a microscope, the light reflected by the object 4 to be measured is transmitted to the CCD through the objective lens 31 and the barrel lens 32 of the camera, and after the CCD is exposed, the photodiode is excited by the light to release charges, and an electric signal of the photosensitive element is generated.

In the embodiment, the piezoelectric crystal 2 is additionally arranged between the microscope objective and the object to be measured (shooting target) 4, and the thickness of the crystal is controlled by voltage, so that the optical path between the shooting target and the objective 31 is changed, the position of a focus is adjusted to realize automatic focusing, and the device has the characteristics of high focusing speed, high precision, low manufacturing and using cost and the like.

Example two:

based on the microscope system described in the first embodiment, the present embodiment provides an auto-focusing method for a microscope system, including: based on the deformation characteristics of the piezoelectric crystal under the action of the electric field, changing the voltage value acting on the piezoelectric crystal according to the set voltage difference, thereby changing the thickness of the piezoelectric crystal;

when the piezoelectric crystal is at different voltage values, respectively acquiring images of a measured object and calculating a definition evaluation function of the images to obtain a definition evaluation function value;

adjusting a voltage value acting on the piezoelectric crystal based on the definition evaluation function value until the automatic focusing is completed, specifically comprising:

if the definition evaluation function value is increased, the voltage applied to the piezoelectric crystal is continuously increased according to the set voltage difference delta V; until the definition evaluation function value is reduced, the voltage acting on the piezoelectric crystal is reduced by delta V, and the focusing is considered to be performed at the moment;

if the value of the sharpness evaluation function decreases, the voltage applied to the piezoelectric crystal continues to decrease according to the set voltage difference Δ V until the value of the sharpness evaluation function decreases, and the voltage applied to the piezoelectric crystal increases by Δ V, and it is considered that the focus is achieved.

In this embodiment, the specific working process of the automatic focusing method of the microscope system is as follows:

1. placing the object to be measured in front of the objective lens of the microscope system as shown in fig. 2;

2. plus an initial voltage V₀To obtain an initial electric field E₀The thickness of the initial piezoelectric crystal is d;

3. shooting a microscopic picture by a camera, and calculating an image definition evaluation function; .

4. Increasing voltage delta V, increasing electric field delta E, increasing thickness delta d, shooting again, and calculating an evaluation function;

and (4) adopting a definition evaluation function, and if the function value is increased, continuing to increase the voltage delta V and increasing the thickness. Until the function value drops, the voltage is reduced by Δ V, at which point it is considered to be in focus. If the function value decreases, the voltage Δ V is decreased, the thickness is decreased, and the function value is increased until the function value decreases, and the voltage Δ V is increased, and it is considered that the focus is present.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims

1. a microscopic system, is characterized in that, comprises:

Microscope system, which is used to collect the image of the measured object and transmit it to the computer;

Piezoelectric crystal, set between the object to be measured and the objective lens of the microscope system, to change the imaging position of the object to be measured;

The voltage control circuit is electrically connected with the computer and the piezoelectric crystal respectively, and is used for changing the voltage value acting on the piezoelectric crystal according to the control instructions of the computer.

2 . The microscope system according to claim 1 , wherein the piezoelectric crystal is a polycrystalline piezoelectric ceramic. 3 .

3. The microscope system according to claim 1, wherein the microscope system adopts a CCD or a CMOS camera.

4. An automatic focusing method for a microscope system, wherein the microscope system according to any one of claims 1 to 3 is adopted, comprising:

Based on the deformation characteristics of the piezoelectric crystal under the action of the electric field, the voltage value acting on the piezoelectric crystal is changed according to the set voltage difference, thereby changing the thickness of the piezoelectric crystal;

When the piezoelectric crystals are at different voltage values, the images of the object to be measured are collected respectively and the sharpness evaluation function of the image is calculated to obtain the sharpness evaluation function value;

Adjust the voltage value applied to the piezoelectric crystal based on the value of the sharpness evaluation function until the autofocus is completed.

5. The automatic focusing method of a microscope system according to claim 4, wherein the adjustment of the voltage value acting on the piezoelectric crystal based on the sharpness evaluation function value until the automatic focusing is completed, specifically comprising:

If the value of the definition evaluation function increases, continue to increase the voltage acting on the piezoelectric crystal according to the set voltage difference ΔV; until the value of the definition evaluation function decreases, reduce the voltage acting on the piezoelectric crystal by ΔV , it is considered to be in focus at this time;

If the value of the definition evaluation function decreases, continue to reduce the voltage acting on the piezoelectric crystal according to the set voltage difference ΔV until the value of the definition evaluation function decreases, then increase the voltage acting on the piezoelectric crystal by ΔV , it is considered to be in focus at this time.

6. The autofocusing method of a microscope system according to claim 4, wherein the deformation characteristics of the piezoelectric crystal under the action of the electric field are specifically:

X=eE (2)

Among them, e is the piezoelectric coefficient of the crystal, E is the electric field, and X is the strain amount of the piezoelectric crystal.