| CPC G02B 21/025 (2013.01) [G02B 21/361 (2013.01)] | 11 Claims |
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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”) which is equipped with an optical microscope, and a control device;
wherein, the CCD 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 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 of the optical microscope in the CCD via the control device, the control device transmits the magnification of the optical microscope input by the user to the central processing device which then transmits a received magnification of the optical microscope to the CCD, the CCD adjusts a current magnification of the optical microscope 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 is reflected by the light reflector towards the micro cantilever, the CCD receives image on the micro cantilever, and transmits the image to the central processing device; the central processing device processes the image to identify an abscissa of an extreme edge of the micro cantilever, and according to a relationship between a driving arm displacement distance and a pixel position variation in the image and based on the abscissa of the extreme edge of the micro cantilever, controls the driving device to drive the driving arm to move the micro cantilever such that a light spot reflected from the micro cantilever to the four-quadrant photodetector stays at a center of the four-quadrant photodetector;
wherein the CCD transmits the image to the central processing device, and the central processing device processes the image to identify the abscissa of the extreme edge of the micro cantilever, which comprises following steps:
Step 1: the central processing device converts a 3-channel 24-bit image collected by the CCD 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, 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:
 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 a threshold T is assigned any value selected within [0, N−1], and a value of the threshold T corresponding to a maximum value of the inter-class variance σ2 is set as a best threshold value, a micro cantilever area is marked above the probe on the four-quadrant photodetector according to the coordinates;
wherein the central processing device obtains the relationship between the driving arm displacement distance and the pixel position variation in the image, which comprises following steps:
Step 1: the abscissa of the extreme edge of the micro cantilever area segmented based on the best threshold value corresponding to the maximum value of the inter-class variance σ2 is used as a reference point X0;
Step 2: a stepping distance of the driving arm is kept below 100 μm, wherein at a first moment, the driving arm is driven to move a predetermined displacement distance |L0|, and an actual abscissa of the extreme edge of the micro cantilever area is X1, the abscissa has a variation of ΔX0=|X1−X0|, with all the above values being absolute values;
Step 3: at a second moment, the driving arm is driven to move a predetermined displacement distance |L1|, and an actual abscissa of the extreme edge of the micro cantilever area is X2, the abscissa has a variation of ΔX1=|X1−X2|; at a third moment, the driving arm is driven to move a predetermined displacement distance |L2|, and an actual abscissa of the extreme edge of the micro cantilever area is X3, the abscissa has a variation of ΔX2=|X2−X3|; with all the above values being absolute values, the relation between the image pixel variation and the displacement distance of the driving arm is as follows:
 wherein, AT in the above formula is a transpose of a matrix A, wherein an interval between the first moment and the second moment is identical with that between the second moment and the third moment, and a and b are coefficients to be solved, with the matrix A being
 and the matrix B being
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