WO2005022247A2

WO2005022247A2 - An apparatus and a method for alignment of a line sensor camera by laser

Info

Publication number: WO2005022247A2
Application number: PCT/IL2004/000772
Authority: WO
Inventors: Hillel Avni; Nir Weissberg
Original assignee: Panoptes Ltd
Priority date: 2003-09-03
Filing date: 2004-08-24
Publication date: 2005-03-10
Also published as: WO2005022247A3

Abstract

An apparatus for alignment of a line sensor camera (110) by laser. The apparatus provides line-by-line photographic frames of a material below, these lines being along an axis transverse to a linear axis in the direction of movement. The apparatus includes a line sensor camera (250). The line sensor camera (250) includes a front cover (220) having a pair of pinholes (241 and 242), wherein a first pinhole (242) is for absolute linear and transverse alignment and a second pin hole (241) is oblong for final transverse adjustment leeway. The front cover also has a pair of screw holes. The apparatus also includes a laser harness (300) that includes a pair of lasers for illuminating a precise line on the material along the transverse axis, the line defined by a pair of illuminated points, each point corresponding to one of the lasers.

Description

AN APPARATUS AND A METHOD FOR ALIGNMENT OF A LINE SENSOR CAMERA BY LASER

FIELD OF THE INVENTION

The present invention relates to an apparatus and a method for machine vision systems. More particularly, the present invention relates to an apparatus and a method for alignment of a line sensor camera by laser.

BACKGROUND OF THE INVENTION When photographing with a line camera, there is a problem determining the exact position being imaged, especially when the medium being photographed is generally homogeneous. For homogeneous materials, such as woven and non-woven textile fabrics, paper, plastic and metal foils during various stages of the production process, it is important maintain a photographic record during various stages of processing. The series of video frames can then be accessed in the form of a defect map, along with any defects recognized during or after recording. It is important to precisely coordinate and synchronize pinpoint lighting of the moving material with the camera image. Fabric defects include holes, a thick thread, strongly contrasted thread color, etc, for example, with respect to repeated patterns. It is important to set defect thresholds correctly as to quantity and size, and to know the exact location and maximize information about the geometry and nature of each defect. The processing must be fast, accurate, automated, interruptible and resumable when necessary. Prior art systems and methods have concentrated on the fault detection and identification (FDI) aspects of defect imaging. Little ingenuity has been applied to the absolute determination of defect location, and the need to accurately synchronize pinpoint lighting. For example, if the lighting and the image being photographed are not precisely coordinated, an image of variant brightness may be recognized by the system. This may lead to a false defect determination. Thus, there is a need to accurately synchronize and establish each aspect of the location of each image frame, both along the line of processing and transverse to it.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention to overcome the limitations of the prior art, and provide a method and an apparatus for fast, accurate, interruptible and resumable alignment of a line sensor camera by laser.

It is another object of the present invention to provide an improved system for surface inspection. It is yet another object of the present invention to provide an improved system for inspection of the surface of woven and non-woven materials.

An apparatus is disclosed for alignment of a line sensor camera by laser. The apparatus provides line-by-line photographic frames of a material below, these lines being along an axis transverse to a linear axis in the direction of movement. The apparatus includes a line sensor camera. The line sensor camera includes a front cover having a pair of pinholes, wherein a first pinhole is for absolute linear and transverse alignment and a second pin hole is oblong for final adjustment leeway and having a pair of screw holes. The camera also includes a lens affixed to the front cover and adjusted to see a focal line on the material, a line sensor to convert light to electric charge, a mechanical housing to align the lens to the line sensor and a stack of printed circuit board (PCB) slots, one of the slots housing the line sensor and the remaining slots housing peripherals, wherein the stack of slots is covered by a dark substance. The apparatus also includes a laser harness that includes a pair of lasers for illuminating a precise line on the material along the transverse axis, the line defined by a pair of illuminated points, each point corresponding to one of the lasers. The laser harness also includes a pair of pins for precisely affixing the laser harness to the front cover by insertion in the pair of pinholes and a pair of screws for insertion in the screw holes and for locking the harness to the front cover subsequent to being precisely affixed, wherein an installation mechanism allows said front cover of the camera to be aligned to the slot that holds the line sensor. Additional features and advantages of the invention will become apparent from the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention in regard to the embodiments thereof, reference is made to the accompanying drawings and description, in which like numerals designate corresponding elements or sections throughout, and in which:

Fig. 1 is a schematic illustration of a front view and top view of the smart camera configuration, according to an exemplary embodiment of the present invention;

Fig. 2a is an isometric illustration of the computer/camera, in combination with a lens, constructed according to the principles of an exemplary embodiment of the present invention;

Fig. 2b is an front view illustration of the computer/camera, without the lens, constructed according to the principles of an exemplary embodiment of the present invention; and

Figs. 3a and 3b are isometric view and side view illustrations of the dual laser harness, constructed according to the principles of an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

References to like numbers indicate like components in all of the figures. The present invention provides a system and method for helping the user establish the exact position when the medium being photographed is generally homogeneous. This is done using two precision laser beams, based on the principle that two points determine a line. The system includes a laser harness and a method for synchronizing it with a line camera. Fig. 1 is a schematic illustration of a front view and top view of the smart camera 110 configurations 100, according to an exemplary embodiment of the present invention. Camera 110 of the present invention is used to inspect production lines and other installations, wherein the material being produced is moving in a straight line as shown by directional arrow 105 in the top view. A video camera is used to photograph the material, line-by-line, and these lines being transverse to the direction of movement. Camera 110, having a lens 120, is a video camera in the sense that a series of images is taken over time. Camera 110 is typically 2 meters above the material. Two pinpoints of laser light 142 are shown in the top view, as described with reference to Fig. 3b below. An adjustment 140 in the right side laser point is seen to bring the line defined by the two lasers into alignment with the line of the material 130 being photographed. The same action could be applied independently to the left side.

Fig. 2a is an isometric illustration of the computer/camera 220, in combination with a lens 210, constructed according to the principles of an exemplary embodiment of the present invention. Attached lens 210, has behind it an exemplary linear charge coupled device (CCD) sensor, which is one pixel in width and typically from 2k to 8k pixels in length in an exemplary embodiment. Alternatively, other types of line sensors can be used. At time t, the photo is taken at coordinate x along the line of movement. At some time later, t + Δ, the photo is taken at coordinate x + Δ. Over time, a video photo is accumulated of lines and frames. Lens 210 is adjusted to see a focal line. A dual laser harness is attached to a pair of laser flanges 232, each having a pinhole 241 (only one is visible).

Fig. 2b is an front view illustration of the computer/camera, without the lens, constructed according to the principles of an exemplary embodiment of the present invention. The exemplary line sensor 250, described with reference to Fig. 2a, is shown in the center of a dark material that covers an exemplary stack of printed circuit board (PCB) slots 260. Typically from 3 to 6 slots contain line sensor 250 and peripherals. The exemplary side view shows 3 slots 263. Line sensor 250 is on the frontmost slot, as seen in Fig. 2b. Line sensor 250 converts light to electric charge. Of pin holes 241 and 242, only left-hand pin hole 241 is shown to be oblong for final adjustment leeway. An installation mechanism allows the front cover of camera 220 to be aligned to the slot that holds line sensor 250. This is accomplished by means of the fit between the front cover and the laser device. The purpose of this alignment and fit are to place the slot with line sensor 250 along the x, y and z axes of the lens and laser device. Looking at the laser from the back side, next to each screw there is a pin - the left side pin fits into oblong hole 242, and the right side pin fits into round accurate hole 241. Together the two pins against the holes give the correct position. The screws against the knurled holes provide for locking the laser handle in that position. The holes are on the front cover of the camera case. Oblong hole 242 provides freedom of adjustment on the axis of the line sensor, while enforcing an accurate adjustment on the perpendicular axis. Because of physical variations in the production process of the system of the present invention, the following adjustments are desirable, because the pinpoints will not show the exact line, but often there will be an unacceptable amount of deviation.

Figs. 3a and 3b are isometric view and side view illustrations of the dual laser harness 300, constructed according to the principles of an exemplary embodiment of the present invention. Dual laser harness 300 is mounted by means of a pair of knurled-handled screws 350 to screw holes shown in Fig. 2, such that its unified construction provides a threaded lens aperture 360, in which to mount lens 210 (lens only shown in Figs. 1 and 2). The emanation of light from one laser is illustrated by arrow 310, as it shines from its laser housing 312. Each laser can be adjusted up and down 314, by rotating about pivot point 316, to achieve the alignment described with reference to Fig. 1 above. The ease with which the laser is pivoted is controlled by means of a pair of friction plates 372 (only one shown), typically made of Teflon™. Another adjustment can be made along the line sensor axis to widen the distance between the laser points so that they could be at the edges of the photographed frame. This serves to fit any angle of adjaustment that may be necessary, and reduces the deviation of the actual line that is created between the laser pinpoints relative to the optimal desired line. The deviations are created because both the line and the pinpoints are not infinitey small.

In summary: To achieve synchronization between the camera, the sensor and the lasers, the following steps are necessary: a. synchronize the lasers with the camera and then lock the lasers; b. synchronize the camera to photograph the exact line on the surface, put camera in a fixed position and lock the camera in place; and c. optionally disassemble the laser harness from the camera, because it is needed only for initial alignment. a. is achieved by the laser harness mechanism, that allows the laser pinpointing to be adjusted to the photographed line as described above. b. is achieved by adjusting the camera to the desired spot on the surface guided by the laser pinpoints. 4. is done by releasing screws 350 while the camera stands still.

Having described the present invention with regard to certain specific embodiments thereof, it is to be understood that the description is not meant as a limitation, since further modifications will now suggest themselves to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the appended claims.

Claims

We claim: 1. An apparatus for alignment of a line sensor camera by laser, the apparatus provides line- by-line photographic frames of a material below, these lines being along an axis transverse to a linear axis in the direction of movement, the apparatus comprising: a line sensor camera comprising: a front cover comprising: a pair of pinholes, wherein a first pinhole is for absolute linear and transverse alignment and a second pin hole is oblong for final adjustment leeway; and a pair of screw holes; a lens affixed to said front cover and adjusted to see a focal line on the material, a line sensor to convert light to electric charge; a mechanical housing to align said lens to said line sensor; a stack of printed circuit board (PCB) slots, one of said slots housing said line sensor and the remaining slots housing peripherals, said stack of slots covered a by dark substance; and a laser harness comprising: a pair of lasers for illuminating a precise line on the material along said transverse axis, said line defined by a pair of illuminated points, each of said points corresponding to one of said lasers; a pair of pins for precisely affixing said laser harness to said front cover by insertion in said pair of pinholes; and a pair of screws for insertion in said screw holes and for locking said harness to said front cover subsequent to being precisely affixed, wherein an installation mechanism allows said front cover of said camera to be aligned to said slot that holds said line sensor.

2. The apparatus according to claim 1, wherein said sensor is a linear charge coupled device (CCD) sensor.

3. The apparatus according to claim 1 , wherein said screws are knurled-handled screws.

4. The apparatus according to claim 1 , wherein each of said lasers can be adjusted up and down by rotation about a pivot point.

5. The apparatus according to claim 4, wherein the ease with which each of said lasers can be adjusted up and down is controlled by a friction plate.

6. The apparatus according to claim 5, wherein said friction plates are fabricated from Teflon™.

7. The apparatus according to claim 1 , wherein a further adjustment is provided along the transverse axis to vary the distance between said illuminated laser points, so that said illuminated laser points could be preferably at the edges of the photographic frames.

8. The apparatus according to claim 1 , wherein a further adjustment is provided along an axis orthogonal to both the transverse axis and the linear axis to vary the distance between each of said lasers and said corresponding illuminated laser points.

9. A method for taking at least one photograph centered on an exact horizontal line on a surface, by providing synchronization between a camera, a sensor and two lasers used for alignment along the line defined by the pinpoints of the intersection of the beams of the two lasers with the surface, the method comprising: a first synchronizing step of synchronizing the lasers with the camera, wherein the lasers are lockied, and wherein said first sychronizating is achieved by a laser harness mechanism, attached by a set of screws to the camera, thereby allowing the laser pinpointing to be adjusted to the photographed line; and a second synchronizing step of synchronizing the camera to photograph relative to the exact line on the surface, wherein the camera is put in a fixed position and locked in place, and wherein said second synchronizing step is achieved by adjusting the camera to the desired spot on the surface guided by the laser pinpoints, such that the photograph is centered on the exact horizontal line on the surface.

10. The method according to claim 9, further comprising disassembling said laser harness mechanism from the camera, by releasing said set of screws while the camera stands still.

11. The method according to claim 9, further comprising adjusting each of said lasers up and down by rotation about a pivot point.

12. The method according to claim 11, wherein the ease with which each of said lasers can be adjusted up and down is controlled by a friction plate.

13. The method according to claim 12, wherein said friction plates are fabricated from Teflon™.

14. The method according to claim 9, further comprising adjusting along the transverse axis to vary the distance between said illuminated laser points, so that said illuminated laser points could be preferably at the edges of the photographic frames.

15. The method according to claim 9, further comprising adjusting along an axis orthogonal to both the transverse axis and the linear axis to vary the distance between each of said lasers and said corresponding illuminated laser points.