# US 2021/0333531 A1 · System of automatic adjustment of laser reflection path

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- Number: US 2021/0333531 A1
- Document ID: US20210333531A1
- Status: Published application
- Kind: A1
- Application number: 17/236,353
- Filed: 2021-04-21
- Published: 2021-10-28
- Earliest claimed: 2020-04-28
- Assignees: North University of China
- Applicants: North University of China
- Inventors: Jun Liu; Zongmin Ma; Jun Xu; Jun Tang; Yunbo Shi; Huanfei Wen; Cheng Dong; Huiyun Wang
- Web page: https://patentgrep.com/patent/US20210333531A1

## CPC

- G02B 21/025: {with variable magnification (variable magnification G02B15/00)}
- G01Q 20/02: by optical means
- G02B 21/361: {Optical details, e.g. image relay to the camera or image sensor (G02B21/364 takes precedence; illumination details G02B21/06 and subgroups)}
- G02B 21/365: {Control or image processing arrangements for digital or video microscopes (G02B21/361, G02B21/362 take precedence)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G01Q: SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]

## Abstract

A system of automatic adjustment of a laser reflection path, comprising a central processing device, a driving device, a four-quadrant photodetector, a driving arm, a micro cantilever, a sample, a sample placing table, a light reflector, a laser, a CCD equipped with an optical microscope, a vibration sensor, a signal processing circuit, a display device, a storage device, and a control device; a system of automatic adjustment of the laser reflection path is controlled by the control device, wherein a laser beam is emitted by the laser, an image collected by the CCD equipped with the optical microscope is processed by the central processing device to identify the micro cantilever, and then a driving arm is driven by a driving device to drive the micro cantilever to move to the center of a laser spot, during which vibration signals of the driving arm are also under monitoring.

## Claims

### Claim 1

A system of automatic adjustment of a laser reflection path, comprising a central processing device, a driving device, a four-quadrant photodetector, a driving arm, a micro cantilever, a sample placing table, a light reflector, a laser, a charge-coupled device (“CCD”) equipped with an optical microscope, and a control device;
wherein, the CCD equipped with the optical microscope is disposed right above the sample placing table, a sample is placed on the sample placing table, a laser emission terminal of the laser has the light reflector arranged in front of the same, the four-quadrant photodetector and the laser are arranged on a same horizontal plane, the driving device drives the driving arm, the micro cantilever is positioned below the driving arm, the CCD equipped with the optical microscope is bidirectionally connected with the central processing device, an input terminal of the laser and an input terminal of the driving device are both connected with an output terminal of the central processing device, an output terminal of the four-quadrant photodetector is connected with an input terminal of the central processing device, and an output terminal of the control device is connected with an input terminal of the central processing device;
wherein, a user inputs a magnification value of the CCD equipped with the optical microscope via the control device, the control device transmits the magnification value of the CCD equipped with the optical microscope input by the user to the central processing device which then transmits a received magnification value of the CCD equipped with the optical microscope to the CCD equipped with the optical microscope, the CCD equipped with the optical microscope adjusts its magnification to the received magnification accordingly, the user controls the central processing device via the control device to enable the laser to emit laser beams which pass through the light reflector and are reflected onto the micro cantilever, the CCD equipped with the optical microscope receives image information on the micro cantilever, and transmits the collected image information to the central processing device; the central processing device processes the received image information to identify the micro cantilever, obtains a relationship between a driving arm displacement distance and a pixel position variation in the CCD image, and controls the driving device to drive the driving arm to move the micro cantilever to a central position of a laser beam spot reflected by the light reflector.

### Claim 2 (depends on 1)

The system of automatic adjustment of the laser reflection path according to claim 1, further comprising: a vibration sensor, a signal processing circuit, a display device and a storage device, wherein the vibration sensor is disposed on the driving arm, an output terminal of the vibration sensor is connected with an input terminal of the signal processing circuit, an output terminal of the signal processing circuit is connected with an input terminal of the central processing device, an input terminal of the display device and an input terminal of the storage device are both connected with the output terminal of the central processing device, when the driving device drives the driving arm to move, the vibration sensor collects vibration signals of the driving arm during displacement, and transmits the collected vibration signals to the signal processing circuit which processes and then transmits the received vibration signals to the central processing device, the central processing device transmits the received vibration signals to the display device for display and transmits the received vibration signals to the storage device for storage, the user gets to know the vibration signals via the display device, and, if the vibration signals are greater than a pre-set threshold, sends a stop instruction to the central processing device through the control device, the central processing device receives the stop instruction, controls the laser to stop it from emitting laser beams, and the driving device stops operation.

### Claim 3 (depends on 1)

The system of automatic adjustment of the laser reflection path according to claim 1, wherein the control device transmits the magnification value of the CCD equipped with the optical microscope input by the user to the central processing device, and the magnification value is 3 times.

### Claim 4 (depends on 2)

The system of automatic adjustment of the laser reflection path according to claim 2, wherein the central processing device also contains a signal processing module which extracts characteristic quantities from the received vibration signals, wherein the extraction comprises the following specific steps:
Step 1: vibration signals collected in time T are segmented according to pre-set sampling time periods, wherein the pre-set sampling time periods are identical for segmenting time T into n sampling time periods, and the vibration signals in a first time period are X1·sin(ω1t), the vibration signals in a second time period are X2·sin(ω2t), and so on, the vibration signals in an nth time period are Xn·sin(ωnt); wherein Xn is an amplitude in the nth time period and con is a frequency in the nth time period;
Step 2: vibration signals in the synthesized time T are X·sin(ωt), wherein X is a characteristic value of the amplitude of the vibration signals in the synthesized time T, and ω is a frequency characteristic value of the amplitude of the vibration signals in the synthesized time T, so that
Step 3: the vibration signals X·sin(ωt) are superposed in frequency, so that
X·ω2·sin(ωt)=X1·ω12·sin(ω1t)+X2·ω22·sin(ω2t)+ . . . +Xn·ωn2·sin(ωnt);
Step 4: characteristic parameters are solved so that
ω
=
∑
i
=
1
n
⁢
[
X
i
·
ω
i
2
·
sin
⁡
(
ω
i
⁢
t
)
]
∑
i
=
1
n
⁢
[
X
i
·
sin
⁡
(
ω
i
⁢
t
)
]
X
=
∑
i
=
1
n
⁢
[
X
i
·
sin
⁡
(
ω
i
⁢
t
)
]
sin
⁡
(
ω
i
⁢
t
)
wherein pre-set thresholds are ω max and X max, and if ω>ω max or X>X max for a vibration signal, the user sends a stop instruction to the central processing device through the control device, the central processing device receives the stop instruction, controls the laser to stop it from emitting laser beams, and the driving device stops operation.

### Claim 5 (depends on 1)

The system of automatic adjustment of the laser reflection path according to claim 1, wherein the CCD equipped with the optical microscope transmits the collected image information to the central processing device, and the central processing device processes the received image information to identify the micro cantilever, which comprises the following steps:
Step 1: the central processing device converts a 3-channel 24-bit image collected by the CCD equipped with the optical microscope into a single-channel 8-bit image as the following formula:
I(x,y)=0.3×IR(x,y)+0.59+IG(x,y)+0.11×IB(x,y);
wherein, IR(x,y), IG(x,y), and IB(x,y) are respectively red, green and blue components of the image collected by the CCD equipped with the optical microscope, I(x,y) is a grey value of the converted image, and (x,y) represents horizontal and vertical coordinates of the image;
Step 2: the grey value I(x,y) is enhanced as the following formula:
G
0
⁡
(
x
,
y
)
=
255
×
∑
i
=
0
k
⁢
n
i
n
wherein, G0(x,y) is a grey value of the enhanced image, k is a coefficient of a grey enhancement adjustment, ni is a number of pixels of the grey value I, and n is a number of total pixel values of the image;
Step 3: for images with different brightness, regions with high contrast ratios are identified for segmenting the image of the micro cantilever as the following formula:
σ2=ω0(μ0−μ)2+ω1(μ1−μ)2.
wherein, ω0 represents a proportion of target pixels, ω1 represents a proportion of background pixels, μ0 represents a grey average of target pixels, μ1 represents a grey average of background pixels, μ represents a grey average of the whole image, and σ2 represents an inter-class variance;
wherein, the image has N grey levels in total, and while selecting a threshold T within [0, N−1] and setting a maximum σ2 to the best threshold, a micro cantilever area is marked above the probe on the four-quadrant photodetector according to the coordinates.

### Claim 6 (depends on 5)

The system of automatic adjustment of the laser reflection path according to claim 5, wherein the central processing device processes the received image information to identify the micro cantilever, obtains a relationship between a driving arm displacement distance and the pixel position variation in the CCD image, which comprises the following steps:
Step 1: an abscissa of an extreme edge of the micro cantilever area is used as the reference point X0 when the maximum σ2 acts as the best threshold;
Step 2: a stepping distance of the driving device is kept below 100 μm, wherein at the first time, when an actual abscissa of the extreme edge of the micro cantilever area is X1, the abscissa has a variation of ΔX0=|X1−X0|, and the displacement distance |L0| of the driving device is obtained, with all the above values being absolute values;
Step 3: the above Step 2 is repeated to obtain the other two groups of corresponding relational expressions: ΔX1=|X1−X2|, |L1|, ΔX2=|X2−X3|, |L2|, so that the relation between the image pixel variation and the displacement distance of the driving device is as follows:
[
a
b
]
=
[
A
T
⁢
A
]
-
1
⁢
A
T
⁢
B
wherein, in the above formula, at the second time, the actual abscissa of the extreme edge of the micro cantilever area is X2, and the displacement distance |L1| of the driving device is obtained; at the third time, the actual abscissa of the extreme edge of the micro cantilever area is X3, and the displacement distance |L2| of the driving device is obtained, wherein an interval between the first time and the second time is identical with that between the second time and the third time, and a and b are coefficients to be solved, with the matrix A being
[
L
0
1
L
1
1
L
2
1
]
and the matrix B being
[
Δ
⁢
⁢
X
0
Δ
⁢
⁢
X
1
Δ
⁢
⁢
X
2
]
.

### Claim 7 (depends on 2)

The system of automatic adjustment of the laser reflection path according to claim 2, wherein the vibration sensor collects a vibration signal of the driving arm during displacement, converts the collected vibration signal into a voltage signal V0, and transmits the voltage signal V0 to the signal processing circuit; wherein V1 is a voltage signal processed by the signal processing circuit, the signal processing circuit comprises a signal amplifying unit and a signal filtering unit, the output terminal of the vibration sensor is connected with an input terminal of the signal amplifying unit; an output terminal of the signal amplifying unit is connected with an input terminal of the signal filtering unit, and an output terminal of the signal filtering unit is connected with the input terminal of the central processing device.

### Claim 8 (depends on 7)

The system of automatic adjustment of the laser reflection path according to claim 7, wherein the signal amplifying unit comprises operational amplifiers A1-A2 and resistors R1-R7;
wherein, the output terminal of the vibration sensor is connected with one end of a first resistor R1 where the first resistor R1 is also connected with one end of a third resistor R3, a second end of the first resistor R1 is also connected with an output terminal of a first operational amplifier A1, the second end of the first resistor R1 is also connected with one end of a second resistor R2, a second end of the second resistor R2 is connected with an inverting input terminal of the first operational amplifier A1, a second end of the third resistor R3 is connected with an inverting input terminal of a second operational amplifier A2, the second end of the third resistor R3 is connected with one end of a seventh resistor R7, one end of a fourth resistor R4 is grounded, a second end of the fourth resistor R4 is connected with an in-phase input terminal of the second operational amplifier A2, one end of a fifth resistor R5 is connected with the second end of the second resistor R2, a second end of the fifth resistor R5 is connected with an output terminal of the second operational amplifier A2, one end of a sixth resistor R6 is connected with an in-phase input terminal of the first operational amplifier A1, a second end of a sixth resistor R6 is grounded, a second end of a seventh resistor R7 is connected with the output terminal of the second operational amplifier A2, the output terminal of the second operational amplifier A2 is connected with an input terminal of the signal filtering unit; and the signal filtering unit comprises resistors R8-R14, capacitors C1-C2, and operational amplifiers A3-A4;
wherein, the output terminal of the signal amplifying unit is connected with one end of the first capacitor C1 where the first capacitor C1 is also connected with one end of an eighth resistor R8, a second end of the eighth resistor R8 is connected with a second end of the capacitor C1, one end of a ninth resistor R9 is grounded, a second end of the ninth resistor R9 is connected with the second end of the eighth resistor R8, the second end of the first capacitor C1 is connected with an in-phase input terminal of a third operational amplifier A3, one end of a tenth resistor R10 is connected with one end of a second capacitor C2, a second end of the tenth resistor R10 is connected with an in-phase input terminal of a third operational amplifier A3, the one end of the tenth resistor R10 is also connected with an output terminal of the fourth operational amplifier A4, the second end of the second capacitor C2 is connected with an inverting input terminal of the operational amplifier A3, one end of a slide rheostat R11 is connected with the inverting input terminal of the operational amplifier A3 where the slide resistor R11 is also connected with an inverting input terminal of a fourth operational amplifier A4 and with the slide rheostat R11 connected with the second end of the second capacitor C2, one end of a twelfth resistor R12 is connected with a second end of the slide rheostat R11, a second end of the twelfth resistor R12 is connected with an output terminal of the operational amplifier A3, one end of a fourteenth resistor R14 is connected with the one end of the resistor R8, a second end of the fourteenth resistor R14 is connected with an in-phase input terminal of the operational amplifier A4 where the fourteenth resistor R14 is also connected with one end of a thirteenth resistor R13, a second end of the thirteenth resistor R13 is connected with the second end of the twelfth resistor R12 where the thirteenth resistor R13 is also connected with the output terminal of the third operational amplifier A3, the output terminal of the third operational amplifier A3 is connected with the input terminal of the central processing device, and the signal filtering unit transmits the voltage signal V1 to the central processing device.

### Claim 9 (depends on 1)

The system of automatic adjustment of the laser reflection path according to claim 1, wherein the control device is a touch control-instruction input device.

### Claim 10 (depends on 1)

The system of automatic adjustment of the laser reflection path according to claim 1, wherein the driving device comprises a stepping motor, a first lead screw (4) and a second lead screw (3), wherein the first lead screw (4) and the second lead screw (3) are connected through a connector, the driving arm (2) is connected with the first lead screw (4) in a threaded manner, the micro cantilever (1) is connected with the driving arm (2), the driving arm (2) may be driven by the first lead screw (4) to enable fine adjustments left and right, the second lead screw (3) may drive the micro cantilever (1), the driving arm (2) and the first lead screw (4) to enable fine adjustment up and down, and the second lead screw (3) and the first lead screw (4) are connected with the stepping motor at their ends so as to provide high-precision micro actuation for the lead screws.

### Claim 11 (depends on 2)

The system of automatic adjustment of the laser reflection path according to claim 2, wherein the control device transmits the magnification value of the CCD equipped with the optical microscope input by the user to the central processing device, and the magnification value is 3 times.

### Claim 12 (depends on 2)

The system of automatic adjustment of the laser reflection path according to claim 2, wherein the CCD equipped with the optical microscope transmits the collected image information to the central processing device, and the central processing device processes the received image information to identify the micro cantilever, which comprises the following steps:
Step 1: the central processing device converts a 3-channel 24-bit image collected by the CCD equipped with the optical microscope into a single-channel 8-bit image as the following formula:
I(x,y)=0.3×IR(x,y)+0.59×IG(x,y)+0.11×IB(x,y);
wherein, IR(x,y), IG(x,y), and IB(x,y) are respectively red, green and blue components of the image collected by the CCD equipped with the optical microscope, I(x,y) is a grey value of the converted image, and (x,y) represents horizontal and vertical coordinates of the image;
Step 2: the grey value I(x,y) is enhanced as the following formula:
G
0
⁡
(
x
,
y
)
=
255
×
∑
i
=
0
k
⁢
n
i
n
wherein, G0(x,y) is a grey value of the enhanced image, k is a coefficient of the grey enhancement adjustment, ni is a number of pixels of the grey value I, and n is a number of total pixel values of the image;
Step 3: for images with different brightness, regions with high contrast ratios are identified for segmenting the image of the micro cantilever as the following formula:
σ2=ω0(μ0−μ)2+ω1(μ1−μ)2.
wherein, ω0 represents a proportion of target pixels, ω1 represents a proportion of background pixels, ω0 represents the grey average of target pixels, μ1 represents a grey average of background pixels, μ represents a grey average of the whole image, and σ2 represents an inter-class variance;
wherein the image has N grey levels in total, and while selecting a threshold T within [0, N−1] and setting a maximum σ2 to the best threshold, a micro cantilever area is marked above the probe on the four-quadrant photodetector according to the coordinates.

### Claim 13 (depends on 12)

The system of automatic adjustment of the laser reflection path according to claim 12, wherein the central processing device processes the received image information to identify the micro cantilever, obtains a relationship between a driving arm displacement distance and the pixel position variation in the CCD image, which comprises the following steps:
Step 1: an abscissa of an extreme edge of the micro cantilever area is used as the reference point X0 when the maximum σ2 acts as the best threshold;
Step 2: a stepping distance of the driving device is kept below 100 μm, wherein at the first time, when an actual abscissa of the extreme edge of the micro cantilever area is X1, the abscissa has a variation of ΔX0=|X1−X0|, and the displacement distance |L0| of the driving device is obtained, with all the above values being absolute values;
Step 3: the above Step 2 is repeated to obtain the other two groups of corresponding relational expressions: ΔX1=|X1−X2|, |L1|, ΔX2=|X2−X3|, |L2|, so that the relation between the image pixel variation and the displacement distance of the driving device is as follows:
[
a
b
]
=
[
A
T
⁢
A
]
-
1
⁢
A
T
⁢
B
wherein, in the above formula, at the second time, the actual abscissa of the extreme edge of the micro cantilever area is X2, and the displacement distance |L1| of the driving device is obtained; at the third time, the actual abscissa of the extreme edge of the micro cantilever area is X3, and the displacement distance |L2| of the driving device is obtained, wherein an interval between the first time and the second time is identical with that between the second time and the third time, and a and b are coefficients to be solved, with the matrix A being
[
L
0
1
L
1
1
L
2
1
]
and the matrix B being
[
Δ
⁢
⁢
X
0
Δ
⁢
⁢
X
1
Δ
⁢
⁢
X
2
]
.

### Claim 14 (depends on 2)

The system of automatic adjustment of the laser reflection path according to claim 2, wherein the driving device comprises a stepping motor, a first lead screw (4) and a second lead screw (3), wherein the first lead screw (4) and the second lead screw (3) are connected through a connector, the driving arm (2) is connected with the first lead screw (4) in a threaded manner, the micro cantilever (1) is connected with the driving arm (2), the driving arm (2) may be driven by the first lead screw (4) to enable fine adjustments left and right, the second lead screw (3) may drive the micro cantilever (1), the driving arm (2) and the first lead screw (4) to enable fine adjustment up and down, and the second lead screw (3) and the first lead screw (4) are connected with the stepping motor at their ends so as to provide high-precision micro actuation for the lead screws.