CA2190189C - Method and apparatus for illumination and imaging of a surface - Google Patents

Abstract

An apparatus for illumination and imaging of a surface includes an apparatus for illuminating the surface, an apparatus for obtaining an image of the illuminated surface and providing an output signal representative of the obtained image, and an apparatus for limiting the exposure time of the image-obtaining apparatus to a selected fast exposure time less than the video frame rate of the image-obtaining apparatus. The image-obtaining apparatus may be a CCD-based camera (40). The CCD-based camera and the illumination apparatus may be mounted in a shroud (20) having an opaque side wall. A first polarizing film (100) may be provided intermediate the illumination apparatus and the surface, and a second polarizing film (102), having a polarization orientation orthogonal to that of the first polarizing film, may be provided intermediate to the surface and the image-obtaining apparatus. Tip switches (130, 132) may be provided to prevent activation of the illumination apparatus and the image obtaining apparatus except when a loser edge of the shroud side wall is in contact with the surface.

Description

2 ~ 90 ~ ~9 MT`THOD AND APPARATUS FOR IT TTTMTNATION AND IMAGING OF A SURFAC~

Backqround of the Invention. --This invention relates to methods and devices forilluminating a surface and obtaining an image of the surface, and particularly to hand-held illumination and imaging devices for ~:
the purpose of reading labels having information in a code, such as a bar code, or an ~lr~A - ic format.

Devices for imaging of surfaces provide an electronic representation of an image of the surface of an object. The representation in electronic form is then stored or transmitted to an appropriate data processing apparatus. If information is stored in the label in alphanumeric format, the image would be transmitted to a data processing apparatus having character recognition capacity. Typically, however, routine information is printed in a code format. A common example is a bar code label affixed to the surface of a package. The bar code label contains information about the package's origin, destination, order number, and the like. To retrieve the information from the bar code label, an appropriate imaging device electronically creates a digitized image of the bar code label. That image is then transferred to a processing computer. The processing computer deciphers the desired information from the digitized image.

An imaging device can be either machine-mounted or hand-held. Portable hand-held devices are ~CpC-'IAlly useful when processing is required at remote locations. Such devices are . . .
also useful when the objects to which labels have been applied may be in a variety of sizes or positions.

The ability to retrieve data from the surface of an object depends largely on the quality of the digital image obtained by the imaging device. Glares, shadows and non-uniformity in illumination on the surface during the imaging process result in degradation of th~ digital image. More speci-fically, image processing software may be unable to reliably identify the optical characteristics (such as color) of every portion of the label. As a result, data will be lost. Uniform illumination over a surface is ~p~ l l y important when reading inform2tion on an alphanumeric label or in a two-dimensional encoded format where there is a minimum of redundancy.

Non-uniform ambient light is one source of non-uniformity in illumination. A second problem, which is particu-larly common in shipping of packages and letters, results from the practice of placing a shiny protective layer, such as trans-parent tape, over the label. Such tape will cause specular reflection from the surface, which will obscure the image of the underlying label.

A desirable goal in obtaining images of labels is to obtain the image as ouickly as possible. I'his goal mzkes it desirable to be able to capture the entire image of a two-dimensional label substantially instantaneously.

219018~
. --The use of charge-coupled device based cameras has been proposed for obtaining images of labels. ~lowever, CCD-based cameras are subject to the drawback that the photo-charges in the potential wells in the CCD array can exceed the capacity of the potential wells in the presence of intense illumination. Charges spill over into adjacent potential wells, which rh~- is known as blooming. Blooming, of course, results in loss of inf ormation .

Furthermore, relative motion of the camera and the substrate can cause blurring of the obtained image. For example, a normal video exposure time is 0.033 seconds. In that time, an object moving at 5 inches per second moves 0.165 inches, which, in 100 dpi image resolution, is 16.5 pixels. Such a pixel shift will provide a very blurred image, with resulting loss of data.

It is an object of this invention to provide a method and apparatus for illumination and imaging of a surface which obtains accurate images in a short amount of time.

It is a particular object of this invention to provide a method and apparatus for illumination and imaging of a surface which employs a CCD-based camera which is not subject to ~looming or to blurring.

It is a further particular object of this invention to provide an appar~tus and method for illumination and imaging of a ~ 2l90189 . .
surface which is not subject to 6pecular reflection from the surface .

Additional objects and advantages of the invention will become apparent from the detailed description of a preferred ~--h~ nt which follows.

., Summarv of the Invention.

An apparatus for illumination and imaging of a surface includes means for illuminating the surface, means for obtaining an image of the illuminated surface and providing an output signal representative of the obtained image, and shutter means for limiting the exposure time of the image obtaining means to a selected fast exposure time less than the video frame rate.

An apparatus for illumination and imaging of a surface includes a shroud having an op2S~ue side wall, a lower edge of which side wall defines a bottom opening, me2ns, mounted in the shroud, for illuminating the surface through the bottom opening, and means, comprising a CCD-based camera mounted in the shroud, for obtaining an im2ge of the illuminated surface and providing an output signal representative of the obtained image.

An apparatus for illumination and imaging of a surface includes means for illuminating the surface, means for obtaining an image of the illuminated surface and providing an output signal representative of the obtained image, first light ~- 21~189 -polarizing means intermediate the illuminating means and the illuminated surface, and second light polarizing means, orthogo-nal to the first light polarizing means, intermediate the illumi-nated surface and the image obtaining means.

A method for illumination and imaging of a surface includes the steps of illuminating the surface, obtaining an image of the illuminated surface while selectively limiting the exposure time to a selected fast exposure time less than the video frame rate and providing an output signal representative of the obtained image.

A method for illumination and imaging of a surface, includes the steps of providing a shroud having an opac~ue side wall, a lower edge of which defines a bottom opening, employing a light source mounted in the shroud to illuminate the surface through the bottom opening, and employing a CCD-b2sed camera mounted in the shroud for obtaining an image of the illuminated surface and providing an output signal representative of the obtained image.

A method for illumination and imaging of a surface includes the steps of illuminating the surface with light polar-ized in a first direction, polarizing light reflected from the surface in a second direction, orthogonal to the first direction, obtaining an image of the illuminated surf~ce from the polarized - 219~189 reflected light and providing an output signal representative of the obtained image.

Brief Desc~iPtion of the Fiqures.

Figure 1 is a perspective view with partial cutaway of an apparatus of the invention in use.

Figure 2 is an exploded perspective view of an appara-tus according to the invention.

Figure 3 is a flow chart illustrating operation of a shutter circuit in an apparatus according to the invention.

Figure 4 is a block diagram showing a controller, and signal processor as used with an apparatus according to the invention .

~etailed Pescri~tion of a Preferred Fmhr-~ir '.

~ e~erring now to Figure 1, there is depicted an illuminating and imaging ~pparatus lO according to the invention in use illuminating and imaging a label 14 applied to a planar upper sur~ace of a package 12 . F~ef erring to Figure 2, apparatus lo includes shroud 20, camera 40, handle 60, and illumination apparatus 80. Shroud 20 has an opaque, vertical sidewall 22.
Vertical sidewall 22 has a lower edge which defines a bottom opening 24, and has a top opening 26. In the ~ t ~ 219û189 illustrated in the figures, sidewall 22 includes four planar panels, 60 as to provide a square cross-section. It will be understood that the form of vertical sidewall 22 may be selected as desired. For example, the vertical sidewall 22 may be rectan-gular, or cylindrical in plan. Ordinarily, vertical sidewall 22 wil; be selected so that the shape of bottom opening 24 is the same as the shape of a surface to be illuminated. The shape of the bottom opening 24 may also be selected so as to be the same as the shape of the array of an imaging deYice. It will also be appreciated that vertical sidewall 22 need not be precisely vertical .

Camera 40, which in the illustrated ~"~hoAir- t has a substantially cylindrical housing, is disposed through top opening 26 in shroud 20. Camera 40 is mounted in an upper portion of shroud 20 by bracket 42 on the side of the housing of camera 40. Camera 40 is secured to shroud 20 by a fastener 44 disposed through hole 28 through sidewall 22. Camera 40 is an app~ratus that ohtains an image of a surface, such as the surface of package 12 illustrated in Pigure 1, and produces a signal representative of the obtained image of the surface. Camera 40 may be, for example, a CCD-based camera. An example of a suit-able CCD-based camera is a Pulnix T~-7X, with a Tamron ~ . 5 mm.
lens. Appropriate power and signal lines are provided through cable 70 to an external power supply (not shown), controller 110 and signal proce~sor 120 (shown schematically in Figure 4). The , .. , . . . .... _ _ . ... . .. . ... _ .. .... . .. . ... ...

2~901~39 power supply provides electrical power for operation of camera 40 and illumination apparatus 80. The signal lines in cable 70 transmit control signals from controller 110 to camera 40 and trigger 85, and transmit from camera 40 to signal p~uc~ssoL 120 an output signal representative of the image obtained by camera 40 .

Referring again to Figures 1 and 2, handle 60 is mounted on the upper face of the housing of camera 40. E~andle 60 i5 generally cylindrical, and provides a convenient hand grip ~or an operator. Preferably, there is provided a hand switch 62, which an operator can use for providing a signal to controller to begin the sequence of illuminating the surface and obtaining the image. Hand switch 62 may be an omnidirectional switch.

Illumination apparatus device 80 is mounted in an upper po~tion of shroud 20, mounted on horizontal plate 72, which is preferably mounted within an upper portion of shroud 20 about a lens of camera 40. In the illustrated embodiment, lighting apparatus 80 is a linear xenon flash lamp or strobe light.
Illumination apparatus 80 includes a flash lamp tube 82, which is mounted in a reflector 84. Reflector 84 may have a surface of } ub~le alzac, or reflective aluminum. Suitable electrical connections (not shown) provide current to cause the flash lamp tube 82 to flash. Horizonal planar support plate 72 is provided with an aperture 74 therethrough for permitting light from the - ~ 21~0l89 .

surface to pass through to camera 40. Suitable conventional fixtures may be provided for mounting flash tube 82 in ref1ector 84 .

There are further provided first polarizing film, or pol~arizer, 100 and second polarizing film, or analyzer, 102.
First polarizing film 100 is provided beneath illumination apparatus 80. First polarizing film lO0 is so positioned that all light emitted by illumination apparztus 80 is transmitted through first polarizing film lO0 before reaching an illuminated surface through bottom opening 24 of shroud 20. Second polariz-ing film 102 is mounted on the aperture of camera 40. Second polarizing film 102 is thus so mounted that light reflected from a surface will pass through second polarizing film 102 before entering camera 40. First polarizing film 100 has a first selected polarization orientation, and second polarizing film 102 has a second selected polarization orientation, 90- from the polarization orientation of first polarizing film 100. The use of the combination of first polarizing film lO0 in the path of light from illumination apparatus 80 to the surface, and second polarizing film 102, having a polarization orientation at a go-angle from the polarization orientation of first polarizing film lO0, in the path of light reflected from the illuminated surface to the camera 40, eliminates the effect of specular reflection of light from the surface. The use of first polarizing film loo and second polarizing film 102 is particularly advantageous where _g_ apparatus 10 is used to read labels that may be covered with a shiny coating such as a transparent tape.

Tip switches 130, 132 are provided at two opposite points on the lower edge of shroud 20. Tip switches 130, 132 are clcsed when the respective points on the lower edge of shroud 20 engage a surface. As shown in Figure 4, tip switches 130, 132 are connected in series with hand switch 62. The signal from hand switch 62 will only be transmitted when both lower edges of shroud 20 are in contact with a surface, such as the surface of package 12 of Figure 1. As a result, tip switches 130, 132 serve to prevent activation of illumination device 80 and of camera 40, except when the lower edge of shroud 20 is in contact with the surface .
This configuration of tip switches 130, 132 serves both safety and image S~uality goals. First, illumination apparatus 80 cannot be inadvertently activated while directed at someone ' s eyes. 3ecause the flash lamp intensity is high, eye discomfort could be caused if the device were activated while directed at someone's eyes. Second, the configuration of tip switches 130, 132 assumes that the camera cannot be activated while a gap exists between the ~oints on the lower edge of shroud 20 w~ere tip switches 130, 132 are located, and a surface. As a result, the ~uantity of ambient light reaching the surface will be minimized. If, as shown, the lower edge of shroud 20 lies in a -` 2190189 pl2ne, this configuration of tip 5witc~.e5 130, 132 aSaUres that 6ubstantially no aroient light will reach r planar 5ur~ace ~ithin the ~hroud.

An electronic shutter is pr~ferably provided ~or control Of th~ CCD-bssed car~era. A ccD-ba5ed ca~era convention-ally zllows ~harge to accu=ulate in the potential walls ~or a p~riod o~ ti~e e~}ual to the video ~ra ~le rate. At the end o~ this period of ti~e r the charge i5 r~ad out in accordance with conven-tion~l techniquQs. The video ~ra~e rate (or video ~ra~e len~th or video exposure ti~"e) is conventionally 1~30 8econd5. ~owever, it has b~en ~ound by the inventor~, in using device 10, that the illu=ination produced by illur~lnation ~ppar~ltus 80 is GO great that th~ photo-charyes in rany o~ the potential wells o~ a CCD
arr~y will exceed the czpacity of the potential wells, if charges are p~r~;tted to accu3ulate for a tire ec~ual to thG video ~rame r~te. In addition, it is desir~ble to reduce the exposure tlme as 21uch as possLble to prevant ~05S oi clarity caused by relative ove~ent o~ the ca=era and the lz~el.

~ ef errir.g now to Figure 3, there is shown a ~low chzrt illustrzting the se~uence Or oper~tion o~ an electronic shutter accor~ing to the inYention. qhe electronic shutter is pre~erzbly provided in cont~oller llo, eith~r in so~tware or hardware. At box 305, label~ld "S~RT VIDE0 FRA~5E (T--0) ," a new video ~rame has --11-- , -- 219018~
., .
btarted. At the start of the video frame, at time T = O, there i5 no charge stored in any of the elements of the CCD array.
_ Immediately after time T = O, each element in the CCD
array i5 maintained in a shorted condition, so that no charge can accumulate in any of the elements of the CCD array. In other words, the electronic shutter is closed. This step is illustra-ted by box 310, laoeled MAINTAIN CCD SHORTED.

The time T from the beginning of the video fr2me is then continuously compared to a time equal to the length of a video frame less a selected fast exposure time. This is illus-trated by box 315, labeled T = VIDEO FRAME LENGTH - SELECTED FAST
Expos~rRE TIME? If the time T is less than the video frame rate less the selected fast exposure time, the controller continues to maintain the elements in the CCD arr2y shorted, as indicated by the arrow marked "NO" leading from box 315.

If the time T is equal to the video frame length less the selected fast exposure time, then, as indicated by box 320, labeled "ACTIVATE CCD ARRAY AND TrTTTMTNATION APPARATUS," the controller provides a signal so that the elements of the CCD
array are no longer shorted, and the elements begin to accumulate charge. Simultaneously, illumination apparatus 80 is activated by a signal provided from the controller to trigger 85. As a result, the elements in the CCD array will be exposed to light reflected during illumination of the surface and will accumulate charge .

Time T is comp~red to the length of the video frame, as shown by box 325, labeled T = VIDEO FRANE LENGTE~?. As long as the time T is less than the video frame length, the CCD array remains activated, and individual elements accumulate charge as light impinges on them. Thls is indicated by the arrow marked ~o from box 325 to box 320. As shown by the arrow marked YES from box 325 to box 330, when the time is equal to the video frame length, the CCD array is read out, as ir.:'icated by box 330, labeled ~tEAD OUT CCD A~AY. The process is then at an end, as indicated by box 3 3 5 .

It will be understood that by the foregoing process, the time that the elements in the CCD array are accumulating charge is maintained as short as possible. This will prevent blurring, due to relative moYement of appar~tus 10 and the surface, and will also prevent blooming due to excessive exposure time. The use of an electronic shutter provides precise control over the selected fast exposure time. In addition, the use of the electronic shutter, combined ~ith activation of the illumina-tion apparatus simultaneously with the opening of the electronic shutter, assures that the light reflected from the surface is primarily light generated by the illumination apparatus. The use of an electronic shutter thereby minimizes the influence of . 2190l89 a~ient light. This in particular a86ure5 that, wlth the u5e oS
first nd s-cond polarizing films 100, 102, oriented at a nlnety degree ~ngle to ooe ano~her, as ~ a;n^d a_ove, th_ glare fro~
the 6ur~acQ will be eli~Lnated or -~ n~mi zor~, ~ t i6 pre~erred that the selected fa5t exposurs tl~e be substantially shorter than the video ~rare rate, and preferably a~ fa~t a~ po88ible, provided t~lat ttne illurlnat~on intenslty is great enough. In ~ te~tod ~-ho~; t, a ~elected rast exposure ti~:e of one mi~ nnrl providQd good re8ults. ~his selected f~st eYposure tl~e is thus 1/33 the video fr~:e rate. The 6elected ~act exposure time l:ay be set, on an empirical bzsis, by those o~ sklll in the art. ~f, after using a s_lected f~st exposure time, bloomLn~ or blurring are observed, then the selected fast exposure tlme should be shortened. I~ after using A ~elected fast e~cposure ti~e, obtained inten3ity levels were too low to di5tinguish diSferent optical pro,.er~ies, the selected ~ast exposure time sho~lld be increased.

R~ferrin~ no~ to FlgUre 4, there i6 illustr ~ted a block di~gram o~ an appr~r~tus according to the invention with its controller and signal pL~ _ooOl~ Controller 110 provides control signals to camera 40 and illumination ~aL~.~s trigger circuit 8s. ~ip switches 130, 132, are disposed in the circuit lnterr~ediate switch 62 ~nd controller 110. As explained above, thc control si~nals Srom controller llo provide for an electronic shutt~r to ti:~e op~ration of ca~era 40,, as well as for timing o~

.

-2l90l8~
. . .
the triggering of illumination apparatus 80. Trigger circuit 85 customarily includes an electrical energy 5torage device!_such as one or more capacitors. I~pon receipt of a signal from controller 110, trigger circuit 85 allows current to flow from such capaci-tors to illumination apparatus 80. Camera 40 provides a signal, representative of the light reflected from the surface, to signal processor 120.

Many variations are possi~le within the scope of the invention. For example, the light source illumination apparatus 80 need not be a flash lamp. Illumination apparatus 80 may include, for example, an array of light-emitting diodes, a diffuse light source, or any other type of light source. An intense light source, such as a flash lamp, is advantageous in that it will tend to minimize the influence o~ ambient light on the total illumination of the surface. As a result, non-unifor-mities in ambient illumination will contribute relatively little to total illumination. Intense illumination, such as that from a flash lamp, also permits the aperture of the camera lens to be adjusted to 2 minimum, to provide the greatest depth of field.
Depth of field is particularly useful when a label is applied to a curved surface, such as a tube.

Shroud 20, in combination with illumination apparatus 80 and camera 40, is highly advantageous. Shroud 20, is opaque, and in operation has only bottom opening 24. As a result shroud _ _ _ . _ _ _ _ _ _ _ _ _ _ _ . . .. . . . .. ..

-~ 2l90189 20 substantially eliminates the illumination of the surface by ambient light. As a result, illumination of the sur~ace will be substantially entirely as a result of lighting apparatus 80.
Thus, uniformity of illumination may be controlled. In addition, polarization of light illuminating the surface may be controlled, to reduce specular reflection. Control of the intensity of illumination is also achieved. This assures that the apparatus may successfully be used even where ambient illumination is very intense, such as in direct sunlight. The distance between the lens of camera 40 and the surface is maintained constant, thereby eliminating the need to refocus the camera. The device according to the invention can be implemented in a hand-held conf iguration .

It will also ~e appreciated that a CCD-based camera, while advantageous, is not necessarily required for practice of certain ~ho~i Ls of the invention. Rather, other devices may be used which obtain an image of the illuminated surface and provides an electronic output signal representative of the obtained image. A vidicon or similar device may conceivably also be employed.

Tn a particularly preferred ~hoAi--nt, given only by way of example, camera 4 0 is mounted three inches above the bottom edge of the shroud, and has a field of view 2.5 inches across . The shroud has ~ nC of 3 . 75 inches in height. The reflector 84 has an inner diameter of 0.8 inches, and extends in ~ 219018~
an arc of 225 . The axis of the lamp is mounted 1. 45 inches 2way from the camera optical center, and 0 . 234 inches radially from the axis of the reflector 80. The selected short exposure time may be about 1 In; 1 1 i eP~nnrl~

- It will be ~ppreciated that there are considerable variations that can be accomplished in a method and apparatus of the invention without departing from its scope. As a result, al-though a preferred embodiment of the method and apparatus of the invention has been described above, it is emphasized that the invention is not limited to ~ preferred ~ and there exist other alternative ~ i nts that are fully Dn~ CSD~
within the invention ' s scope, which is intended to be limited only by the scope o~ the ~rpDnrlD~ claims.

Claims (14)

WE CLAIM:

1. An apparatus for illumination and imaging of a surface, comprising:
a. a shroud having an opaque side wall, a lower edge of said side wall defining a bottom opening;
b. means, mounted in said shroud, for illuminating the surface through said bottom opening; and c. means, mounted in said shroud, comprising a CCD-based camera, for obtaining an image of the illuminated surface and providing an output signal representative of said obtained image.

2. The apparatus of claim 1, wherein said illuminating means and said image obtaining means are mounted in an upper portion of said shroud.

3. The apparatus of claim 1, further comprising means for preventing activation of said illumination means and said image obtaining means except when said lower edge of said shroud side wall is in contact with the surface.

4. A method for illumination and imaging of a surface, comprising the steps of:
a. providing a shroud having an opaque side wall, a lower edge of said side wall defining a bottom opening;
b. illuminating the surface through said bottom opening by employing a light source mounted in said shroud; and c. obtaining an image of the illuminated surface, employing a CCD-based camera mounted in said shroud, and providing an output signal representative of the obtained image.

5. The method of claim 4, wherein said CCD-based camera and said light source are mounted in an upper portion of said provided shroud.

6. The method of claim 4, further comprising the steps of providing means for preventing carrying out of said steps (b) and (c) except when the lower edge of said side wall is in contact with the surface, and before said steps of illuminating the surface and obtaining an image, engaging the surface with said lower edge of said shroud side wall.

7. The apparatus of claim 1, wherein said lower edge of said side wall lies in a plane.

8. The apparatus of claim 3, wherein said activation preventing means is adapted to prevent activation of said illumination means and said image obtaining means except when two substantially opposite points on said lower edge of said shroud side wall are in contact with the surface.

9. The apparatus of claim 8, wherein said lower edge of said side wall lies in a plane.

10. The apparatus of claim 8, further comprising an activation switch mounted thereon for activation of said illumination means and said image obtaining means, and a circuit defined intermediate said activation switch and said illumination means and said image obtaining means, wherein said activation preventing means comprises two tip switches mounted on said shroud side wall at said two substantially opposite points, said tip switches being connected in series in said circuit, whereby said circuit can only be closed when both of said tip switches are closed.

11. The method of claim 4, wherein said lower edge of said side wall lies in a plane.

12. The method of claim 6, wherein said preventing means is adapted to prevent carrying out of said steps (b) and (c) except when two substantially opposite points on said lower edge of said shroud side wall are in contact with the surface, and wherein said step of engaging the surface comprises contacting the surface with said lower edge of said shroud side wall at said two substantially opposite points.

13. The method of claim 12, wherein said lower edge of said side wall lies in a plane.

14. The method of claim 12, further comprising the steps of providing an activation switch and a circuit, said activation switch being adapted to close said circuit to cause said steps (b) and (c) to take place, wherein said preventing means comprises two tip switches mounted on said shroud side wall at said two substantially opposite points, said tip switches being connected in series in said circuit, whereby said circuit can only be closed when both of said tip switches are closed.