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Imaging apparatus for fully automatic screen printer

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Title: Imaging apparatus for fully automatic screen printer.
Abstract: An imaging apparatus for fully automatic screen printer including two stacked light sources, two stacked beamsplitters, two stacked optical reflectors, two stacked imaging lens and two stacked image sensors, wherein the two stacked optical reflectors and the two stacked light sources are correspondingly disposed on two different sides of the two beamsplitters, the two stacked imaging lens are disposed on another side of the beamsplitters different from that of the optical reflectors and the light sources, the two stacked image sensors are disposed behind the imaging lens; the optical reflectors are provided with an upward reflection plane and a downward reflection plane, the optical axes of the imaging lenses are orthogonal to that of the light sources. The imaging apparatus is of two independent optical paths which capture the image of the printed circuit board and that of the screen respectively. Furthermore, the imaging apparatus is of compact structure, high acquiring speed and optical paths easy to be adjusted. ...


Inventors: Xianmin Zhang, Yongcong Kuang, Yuequan Tang
USPTO Applicaton #: #20120098956 - Class: 348 86 (USPTO) - 04/26/12 - Class 348 


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The Patent Description & Claims data below is from USPTO Patent Application 20120098956, Imaging apparatus for fully automatic screen printer.

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RELATED APPLICATION

This Application is a Divisional of U.S. patent application Ser. No. 11/836,497, filed Aug. 9, 2007.

BACKGROUND OF THE INVENTION

The present invention relates to an imaging apparatus, specially relates to an imaging apparatus for the reference mark measurement and inspecting the paste solder printing; more specially relates to an imaging apparatus for the reference mark measurement of the screen and the printed circuit board during the paste solder printing of the printed circuit board of the screen printing process, and for the inspection of the screen and the printed circuit board during the paste solder printing.

During the paste solder printing of the printed circuit board of the screen printing process, in order to apply the solder paste to the printed circuit board accurately, the portions of the printed circuit board desired to be printed are required to be corresponding to the holes of the screen. Reference mark measurement is usually used for the alignment of the screen and the printed circuit board, that is to say, signs are marked on both the screen and the printed circuit board so as to ensure that the portions of the printed circuit board desired to be printed are corresponding to the holes of the screen when the relevant signs of the screen are calibrated with respect to that of the printed circuit board. The simplest method of the alignment is mechanical positioning, in which the reference marks are the holes formed on the printed circuit board, and the sinker bars of the pistons of one or more cylinder-piston means are inserted into the positioning holes of the printed circuit board when positioning. However, this method is of the defects including low precision, low speed and even that there is no positioning hole due to the different positioning aperture of different printed circuit board. Therefore, this method is difficult to adapt to the development of the SMT production with high density, large output and high precision, and will fall into disuse gradually.

With the development of the electronic component in the direction of micromation, chip type and high density, the screen printer is required to be of higher precision, speed and reliability. Currently, in the SMT product line of the printed circuit board with high density, most of the defects come from the printing faults of the solder paste. The quality inspection of the solder-paste printing is mainly carried out by manual inspection. The manual inspection may have the problems including strong subjectivity, poor

reproducibility, misjudgment and overlook due to vision fatigue, etc. The manual inspection is hardly qualified for the inspection requirement of SMT product line.

A screen printer utilizing machine vision technique can realize simultaneously both alignment with respect to the reference mark in high speed and high precision, and printing quality inspection during printing. At present, the imaging apparatus of the screen printer of this type normally includes a low-angle ring light source, two light sources, a beamsplitter, an optical reflector, an imaging lens and an image sensor. During the operation, the two light sources on different horizontal planes illuminate at different time, the light sources irradiate on the screen or the printed circuit board through the beamsplitter, and then the beams of light are reflected back to the beamsplitter and refracted to the imaging lens by the beamsplitter, and finally imaging on the image sensor is obtained. This method is of the advantages including simple light path and low cost. However, acquiring the images at different time may result in that the image acquiring positions of the lower image and the upper image are inconsistent; and the dimension of the imaging apparatus in the direction of the upward and downward light path is too large, so that the distance between the printed circuit board and the screen is accordingly large when acquiring the image.

SUMMARY

OF THE INVENTION

An object of the present invention is to provide an imaging apparatus with compact structure, in which the light path is easy to adjust and the images can be acquired from the same position in upward and downward directions. The imaging apparatus is used for image acquiring during the reference mark measurement of the screen and the printed circuit board, and during the inspection in the solder-paste printing process.

The above object of the present invention is achieved by the following technical solutions:

An imaging apparatus for fully automatic screen printer including two stacked light sources, two stacked beamsplitters, two stacked optical reflectors, two stacked imaging lens and two stacked image sensors, wherein the two stacked optical reflectors and the two stacked light sources are correspondingly disposed on two different sides of the two beamsplitters, the two stacked imaging lens are disposed on another side of the beamsplitters different from that of the optical reflectors and the light sources, the two stacked image sensors are disposed behind the imaging lens; the optical reflectors are provided with an upward reflection plane and a downward reflection plane, the optical axes of the imaging lenses are orthogonal to that of the light sources.

Preferably, the two stacked optical reflectors and the two stacked light sources are disposed on two opposite sides of the two beamsplitters, the imaging apparatus forms a T-shaped structure.

Preferably, the two stacked optical reflectors and the stacked imaging lens are correspondingly disposed on two opposite sides of the two stacked beamsplitters, the two stacked light sources are disposed on another side of the two stacked beamsplitters different from that of the optical reflectors and the imaging lens, the imaging apparatus forms a L-shaped structure.

Preferably, the angles of the light-splitting planes of the beamsplitters with respect to the axes of the imaging lenses and the axes of the light source are both 45°.

Preferably, the beamsplitter may be formed of two right angular prisms; or the beamsplitter may be formed of one or two light-splitting plates

Preferably, the optical reflector may be formed of an isosceles right angle prism or two reflection lens or a right angle prism with two reflection planes.

Preferably, the image sensor may be formed of an analog or digital CCD camera or CMOS camera.

Preferably, the imaging apparatus further includes a ring light source, the ring light source is formed of a LED ring light source between a printed circuit board and the optical reflector in order to provide lateral illumination for the printed circuit board, the beam of light reflected downwards by the optical reflector travels through the central hole of the ring light source and then irradiates on the printed circuit board.

Preferably, the light source and the image sensor are connected to the camera controller of the image acquiring control and processing device so as to control the switching of the light source and accordingly control the image acquiring of the screen and the printed circuit board; the video signal output end of the image sensor is connected to the image acquiring card of the image acquiring control and processing device, so as to convert the acquired image video signals into digital signals.

The advantages of the present invention:

The imaging apparatus according to the present invention can simultaneously capture the images in downward direction (i.e. the screen) and upward direction (i.e. the printed circuit board), so that the relative movement of the printed circuit board and the screen is minimized. Moreover, the combination of the coaxial illumination and the side illumination can improve the quality of the reference mark image of the printed circuit board and the inspection image of the solder paste, which adapts to the image acquiring during the reference mark measurement of the screen and the printed circuit board, and during the inspection in the solder-paste printing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of the first embodiment showing a T-type imaging apparatus with two lenses for fully automatic screen printer;

FIG. 2 is the top view of the imaging apparatus shown in FIG. 1;

FIG. 3 is the front view of the imaging apparatus shown in FIG. 1 during operation;

FIG. 4 is the bottom view of the imaging apparatus shown in FIG. 1;

FIG. 5 is the right view of the imaging apparatus shown in FIG. 1;

FIG. 6 is the schematic view showing the structure formed of the T-type imaging apparatus with two lenses as shown in FIG. 1, and the image acquiring control and processing device, along with the positioning device; and

FIG. 7 is a schematic perspective view of the second embodiment showing a L-type imaging apparatus with two lenses for fully automatic screen printer.

Wherein,

the first reflector;

the second reflector;

low-angle LED ring light source;

the first beamsplitter;

the second beamsplitter;

the first LED light source;

the second LED light source;

the first imaging lens;

the first image sensor;

the second imaging lens;

the second image sensor;

imaging apparatus;

screen;

printed circuit board;

positioning device;

image acquiring control and processing device.

DETAILED DESCRIPTION

OF THE INVENTION

The above characteristics and spirit of the present invention will be more clearly understood by the detailed description of the preferred embodiments accompanying the drawings, which are given as example only without intention to limit the protection scope of the present invention.

Embodiment 1

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stats Patent Info
Application #
US 20120098956 A1
Publish Date
04/26/2012
Document #
13092677
File Date
04/22/2011
USPTO Class
348 86
Other USPTO Classes
348E07085
International Class
04N7/18
Drawings
9



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