GB2313450A

GB2313450A - Apparatus for providing a movable beam of light

Info

Publication number: GB2313450A
Application number: GB9610500A
Authority: GB
Inventors: Yona Newman
Original assignee: Motorola Israel Ltd
Current assignee: Motorola Solutions Israel Ltd
Priority date: 1996-05-18
Filing date: 1996-05-18
Publication date: 1997-11-26
Also published as: GB9610500D0

Abstract

An apparatus (10) for providing a movable beam of light (12) includes an array of liquid crystal material (14) having a plurality of zones (16) which are selectively energisable to be changed from a first state (18) to a second state (20) of light transmissibility, a light source (22) illuminating one face (24) of the array and a control device (26) for selectively energising the zone (28) to provide a transparent region (30) by means of which light from the light source passes through the array and an opaque region, the selective energisation being such as to vary the size and or locating of the transparent region (30) to provide a moving beam of light (12).

Description

APPARATUS FOR PROVIDING A MOVABLE BEAM OF LIGHT AND METHOD OF OPERATION Field of the Invention This invention relates to an apparatus for providing a movable beam of light. The invention is applicable but not limited to scanners.

Background of the Invention Scanners are widely used today for many applications such as bar-code reading, fingerprint scanning and for the capture of text and or graphics.

There are two families of bar-code scanners, one family is used for reading the now familiar One-Dimensional (1-D) bar-codes and the other family is used for reading a newer type of bar-code called Dense Codes, also known as Two-Dimensional (2-D) bar-codes.

1-D bar-codes are composed of an alternating pattern of bars and spaces in one direction. The information is encoded by varying the width of the bars and spaces within acceptable parameters. The identical pattern is repeated in the other direction, providing for a reduction in aiming accuracy and label failure redundancy. 1-D bar-codes are scanned using'either a laser diode or a linear Charged-Coupled-Devices (CCD). The laser scanner sweeps å laser beam (created by a laser diode) over the length of the bar-code. The sweeping motion is usually created by reflecting the laser beam on a rotating mirror.

The reflected light is collected and focused and then digitised. 'The digitised image is then input into a decode engine. Because many types of surfaces may reflect alternating patterns of bars and spaces, the bar-code is specified as having a "quiet zone" at its beginning and end. The sensed presence of this zone is typically used to begin the decoding process in the engine.

CCD scanners accomplish the scanning of the bars and spaces by illuminating the area of interest with supplemental ill\:hnination (typically Light Emitting Diodes - LED's). The reflected light is focused onto the CCD elements where the presence of a space is detected because a space reflects a relatively large amount of light, while the presence of a bar is detected because a bar reflects relatively little light. Once the sensing line has been captured, a sampling circuit determines a threshold and decides whether each pixel is a zero or a one. The pixels are then read out in concatenated fashion and fed to the decoder in a manner similar to that used by laser systems.

2-D bar-codes have to be scanned by area. The scanning laser technique is not normally used because of the mechanical and optical complexity of two axis scanning, instead a CCD area array is used with supplementary illumination to capture an image of the whole area being scanned.

Fingerprints are scanned by area with a CCD area array in a similar way to 2-D bar-codes.

Two methods are presently in use for scanning text or graphics. The first method is a single row hand-held scanners using a CCD strip with an illumination source that is manually moved over the page with the text or graphics to be captured. The axis of movement is from top to bottom. The second method is employed in flat-bed scanners and uses a CCD strip under an illuminated transparent plate (or "bed") with the material to be scanned placed face-down on the bed. The CCD strip is then mechanically moved from top to bottom of the bed. A variant on this, which can only be used on suitable material, is to mechanically feed the material over a stationary CCD strip.

This is also the method used in facsimile machines.

A disadvantage of the scanners described above is that they are optomechanical and the sweeping motion of the beam of light is created by reflecting the beam of light on a rotating mirror. Each method of scanning uses different mechanism for sweeping the beam of light over the object surface. Thus the scanners are complex and hence expensive to make.

This invention seeks to provide a apparatus which mitigates the above mentioned disadvantages.

Summarv of the Invention According to a first aspect of the invention there is provided apparatus for providing a movable beam of light comprising: an array of liquid crystal material having a plurality of zones which are selectively energisable to be changed from a first state to a second state of light transmissibility; a light source illuminating one face of the array; and a controller for selectively energising the zones to provide a transparent region by means of which light from the light source passes through the array and an opaque region, the selective energisation being such as to vary the size and or location of the transparent region to provide a moving beam of light.

In essence, the invention provides a "shutter" (the transparent or transmissive region) which has no moving mechanical parts but is generated electronically. This makes the apparatus easier to manufacture, lighter, more reliable and less expensive than previous arrangements. It also provides an arrangement which is easily modified to offer different movements or configurations of the beam of light by modifvingthe way in which the controller selectively energises the zones.

The invention is particularly applicable to scanning arrangements having a detector for detecting light reflected of an object to be scanned.

Preferably, the detector is arranged to receive light reflected back by the object through the transparent region of the array. This is preferable since the same array can be used to provide a "shutter' for the detector as well as the illuminating beam.

Preferably, the light source illuminates the array of liquid crystal material substantially uniformly. This will ensure that the beam does not vary in intensity as a consequence of the location of the transparent zone.

Conveniently, the light detector is located between the light source and the illuminated face of the array.

The preferred location for the light detector is on an optical axis of the scanner although other locations may be feasible, for example offset from the optical axis.

Advantageously the apparatus will include a lens operable coupled to a control device for focusing the reflected light. This will have the advantage of allowing the apparatus to be used at wide range of distances away from the object to be scanned with the reflected light being "automatically" focused onto the detector.

Preferably, the lens directs the reflected light through the transparent region of the array to the detector. Of course where the detector is located at some other position the lens will be arranged to direct the light to it in some other direction.

The apparatus will find particular application in bar-code scanning and for such operations it will preferably include means to process a bar-code scanned from the object.

Many different types of detector may be used but in the preferred embodiment the detector is a charged coupled device.

Preferably, the array of liquid crystal material is a dot matrix transmissive array of liquid crystal material. This may be a monochrome array but alternatively a colour liquid crystal material may be used. Coloured liquid crystal material will advantageously permit a variation in the wavelength of the light beam produced which will assist scanning operations off certain objects. Where the light passes back through the array to the detector the coloured array will act as a filter favouring the wavelength of the illuminating beam.

Preferably the apparatus will include a memory for storing data defining at least one configuration of the opaque and transmissive regions of the array which data being accessible to the controller. This will permit faster operation since the configuration does not have to be generated prior to each use. More than one configuration could be stored and the most appropriate one in the circumstances chosen for use. The selection could be based on whether or not a scan has been produced which satisfies a quality criterion such as the signal to noise ratio.

Preferably, the apparatus includes a processor for processing an output of the detector to determine whether the output is satisfactory and a controller responsive to the processor for adjusting at least one operating parameter of the scanner. The parameters that can be varied can include the intensity of the light of the beam, the configuration, or the wavelength of the light or a combination of these factors.

In accordance with a second aspect of the invention there is provided a method for providing a movable beam of light comprising the steps of: providing an array of liquid crystal material having a plurality of zones which are selectively energisable to be changed from a first state to a second state of light transmissibility; providing a light source illuminating one face of the array; and selectively energising the zones to provide a transparent region by means of which light from the light source passes through the array and an opaque region, the selective energisation being such as to vary the size and or location of the transparent region to provide a moving beam of light.

Whilst the before mentioned aspects of the invention provide apparatus and a method for generating a light beam, in accordance with a further aspect of the invention there is provided apparatus for detecting ; ght received from an object of interest comprising: a light detector; an array of material having a plurality of selectively energisable zones to change light transitivity of the zones from a first state to at least a second state different to the first; an array controller for selectively energising the zones to provide a first region which is relatively opaque and a second region which is relatively transmissive of light; wherein the array is disposed between the object and the detector.

A preferred embodiment of the invention will now be described by way of example only, with reference to the drawings.

Brief Description of the Drawings FIG. 1 is an apparatus for providing a movable beam of light in accordance with the invention.

FIG. 2 is a block diagram of a scanner including the apparatus of FIG.

1 according to a preferred embodiment of the invention.

FIG. 3 is a flow chart showing a method for capturing and decoding objects images according to a preferred embodiment of the invention.

FIG. 4 is an explanatory diagram Detailed Descnption of the Drawings As is shown in FIG. 1, an apparatus 10 for providing a movable beam of light 12 includes an array of liquid crystal material 14 having a plurality of zones 16 which are selectively energisable to be changed from a first state 18 to a second state 20 of light transmissibility, a light source 22 illuminating one face 24 of the array and a control device 26 for selectively energising the zone 28 to provide a transparent region 30 by means of which light from the light source passes through the array and an opaque region, the selective energisation being such as to vary the size and or location of the transparent region 30 to provide a moving beam of light 12.

FIG. 2 shows a scanner 40 incorporating the apparatus 10 of FIG. 1.

The scanner 40 utilises the apparatus 10 for providing a moving beam of light 12 for scanning an object 50. The scanner 40 also includes a power source 51, a light switch 53, a light detector 42 for detecting light 48 reflected from the object 50, and lens 46 for focusing the reflected light 48 on the ligwht detector 42.

The control device 26 of the apparatus 10 includes a microprocessor 56, a LCD controller 58, an analog to digital (A/D) converter 59, a program memory 52, a picture memory 54 and a lens focus control 57.

In operation, the microprocessor 56, executes a program stored in program memory 52. The microprocessor 56, by means of data and control lines, controls the LCD controller 58. A required scan pattern for the LCD 14 is stored in a picture memory 54. This allows the microprocessor 56 to carry out other functions whilst the scanner 40 is scanning the object 50 because it does not have to generate the scan pattern. The reflected light 48 from the object 50 is detected by light detector 42 and suitably amplified, filtered and converted from an analog signal to a digital signal by the A/D converter 59, before being fed into the microprocessor 56. The light source 22 may be switched by a light switch 53 under the control of the microprocessor 56 so as to minimise drain on the battery. The lens 46 is also operably coupled to the control device 26 for focusing the reflected light 48. The microprocessor 56 controls the lens 46 with the lens focus control 57 so as to provide autofocusing. The lens 46 is used to focus the scanning pattern onto the object 50.

The position of the lens 46 can be altered during the scanning process so as to dynamically change the focus point. This optimises the capture of the desired information. Thus, the same lens and controller is used to focus bqth the illuminating and reflected light.

In this embodiment of the invention, the array is a liquid crystal display, that is to say, a dot matrix transmissive type monochrome LOD. The light source 22 is an electro minescent panel is arranged to illuminate the LCD 14 with uniformly bright light 47. The LCD 14 used is a graphics type, having a vertical and horizontal resolution - that is to say a number of individual elements or pixels. The number density of the pixels should be compatible with the resolution required for the type of object image to be scanned. The light reflected back from the object is then detected and processed as in current scanners, for example by a light detector or by a CCD strip.

The light detector 42 is mounted behind the LCD 14 which is the best position to intercept the reflected light 48. In conventional scanners the detector can only be mounted where it will not interfere with, or be in the shadow of, the scan generator mechanism. It is located on an optical axis 60 of the scanner 40.

The method of operation of the scanner 40 will now be described with reference to FIG. 3.

In a first step 100, the scanner 40 is activated by a user and the light source 22 switched on. The next step is step 102 in which microprocessor 56 instructs the LCD controller 58 to initiate a scan. In the scanning step, the LCD controller 58 downloads the scan pattern from memory 54 and selectively activates the zones 16 of the display as will now be described with reference to FIG. 4.

FIG. 4(a) shows the LCD 14 prior to energisation of the zones. The zones are represented as square pixels and in the figure they are an array of 16 rows R1 to R16 and 16 columns C1 to C16 although in reality there are many more rows and colllmns than are illustrated.

FIG. 4(b) shows the LCD 14 at a first sub-step in the scanning step 102.

In this sub-step the pixels in R1 and R3 to R16 are energised and become opaque and thus block light from the light source 22. Pixels R2 C1, R2 C2, R2 C15, R2 C16 are also energised and made opaque and also block light from the light source 22. This leaves pixels R2 C3 to R2 C14 transparent and it is through this transmissive zone that light passes from the scanner to the object 50 via the lens 46.

FIG. 4(c) shows the next sub-step in the scanning. In this stsep, pixels R2 CQ to R2 C14 are energised so making them opaque and pixels R3 C3 to R3 C14 are de-energised making them transmissive to light from the light source 22. Again light passes through the transmissive zone to the object 50 via the lens 46.

FIG. 4(d) shows the next sub-step and it can be seen that the transmissive region has migrated one row down by energising pixels R3 C3 to R3 C14 and de-energising pixels R4 C3 to R4 014.

Further sub-steps are shown in FIG.4(e) to FIG. 4(F). FIG. 4(g) shows the final sub-step prior to the return to the first sub-step shown in FIG. 4(b).

Some of the subsets between 4(g) and 4(f) having been omitted for brevity.

Thus, it will now be appreciated that one scan is performed by creating an "aperture" in the LCD 14 which is made to migrate from top to bottom of the array by selective energisation and de-energisation of pixels that form the array. A scanning beam is thus created which moves in a corresponding manner.

Light which is incident to the object 50 is reflected back to the lends 46 where it is focused and directed through the transmissive region (where ever it is currently located) to the detector 42. In essence, this presents to the detector 42 a "strip" of an image of the object 50, each strip corresponding to one location of the "aperture". Each strip is passed by the detector 42 via the analogue to digital converter 59 and microprocessor 56 to memory 52. This comprises a step of measuring and storing, step 103 of Fig.3.

After the completion of one scan by the above described sub-steps a complete image is stored in memory 52 and is available for subsequent analysis.

In step 104 the stored image is analysed by the microprocessor 56 to determine whether it is adequate, that is to say, has a satisfactory signal to noise ratio. A scan parameter is varied in step 105 if the scan is unsatisfactory and the scan repeated again by returning to step 100. In this case, the parameter varied is the source intensity in conjunction with varying the focus of the lens 46. Should this still fail to achieve a satisfactory scan, the colour of the light transmissive region or aperture is varied. This gives a light filtering effect which will favour the colour of light selected for the scan.

For example, the LCD 14 could be energised in the transmissive region to provide a red aperture providing red illuminating light and passing primarily red reflected light back to the detector 42.

A final variation of a scan parameter is the selection of an alternative scan pattern from the memory 54. The alternative scan pattern is in this case a pattern in which an "aperture" is formed in one column that is to say at right angles to the "aperture" of the first pattern. The "aperture" thus formed is caused to migrate from C2 to C15 as shown in the figures that is to say left to right. Again the other scanning variations can be carried out until a successful scan is achieved the image stored in memory 52 is processed by microprocessor 56 to extract the required information. The information can then be displayed on the LCD 14 by the microprocessor 56 instructing the controller 58. A user will then be able to visually verify that the scan is satisfactory.

In alternative embodiments of the invention, the scan parameters that are varied may include the scan speed that is to say the rate at which the "aperture" is made to migrate. The earlier described order of factors that are varied may also be varied for example the colour of the aperture could be varied prior to varying the light intensity. This will yield particuarly immediate gains in image resolution and subsequent analysis due to the different reflectance properties of different materials forming the object without perhaps unnecessarily illuminating the object with high intensity light which will cause a greater power drain. This may be of particular significance where the scanner is battery powered.

The scan patterns could be varied for example by arranging the pattern diagonally across the LCD and migrating the pattern from one corner to an opposite corner. Whilst, the described patterns are linear in nature they could be provided as different shapes such as cruciform. Two scan patterns could be utilised simultaneously such as vertically and horizontally migrating patterns, thus alleviating the need to switch from one pattern to the other.

After inspection of the information displayed on the LCD the user could vary some or all of the scan parameters by manual adjustment of control knobs prior to a new scan or set of scans being performed.

In alternative embodiments of the invention, the light source can instead of electro-luminescent panel be an incandescent lamp, LED array, hot or cold cathode fluorescent lamps or a discharge lamp of the like.

Although in the described embodiment the light used is in the visible part of the spectrum other wavelengths of light could be used.

Claims

1. An apparatus for providing a movable beam of light comprising: an array of liquid crystal material having a plurality of zones which are selectively energisable to be changed from a first state to a second state of light transmissibility; a light source illuminating one face of the array; and a controller for selectively energising the zones to provide a transparent region by means of which light from the light source passes through the array and an opaque region, the selective energisation being such as to vary the size and or location of the transparent region to provide a moving beam of light.

2. A scanner arrangement for, in use, scanning an object which arrangement including apparatus as claimed in claim 1 and further comprising: a detector for detecting light reflected of the object.

3. The scanner as claimed in claim 2 wherein the detector is arranged to receive light reflected back by the object through the transparent region of the array.

4. The scanner according to claim 2 or to claim 3 wherein the light source illuminates the array of liquid crystal material substantially uniformly.

5. The scanner according to any one of claims 2, 3 or 4 wherein the light detector is located between the light source and the illuminated face of the array.

6. The scanner according to claim 5 wherein the light detector is located on an optical axis of the scanner.

7. The scanner according to any one of the preceding claims, further comprising: a lens operably coupled to a control device for focusing the reflected light.

8. The scanner according to claim 7 wherein the lens directs zhe reflected light through the transparent region of the array to the detector.

9. The scanner according to any one of the preceding claims including means to process a bar-code scanned from the object.

10. The scanner according to any one of the preceding claims wherein the detector is a charged coupled device.

11. The scanner according to any of the preceding claims, wherein the array of liquid crystal material is a dot matrix transmissive array of liquid crystal material.

12. The scanner according to any of the preceding claims, wherein the dot matrix transmissive array of liquid crystal material is a colour array of liquid crystal material.

13. The scanner as claimed in any one of the preceding claims including a memory for storing data defining at least one configuration of the opaque and transmissive regions of the array which data being accessible to the.

controller.

14. The scanner according to any one of the preceding claims further comprising a processor for processing an output of the detector to determine whether the output is satisfactory and a controller responsive to the processor for adjusting at least one operating parameter of the scanner.

15 The scanner according to claim 14 in which the light source is responsive to the controller such that the intensity is varied when the output is determined as being unsatisfactory.

16. The scanner according to claim 14 when dependant on claim 13 in which the controller selects from the data to provide more than one configuration such that the configuration is varied when the output is determined as being unsatisfactory.

17. The scanner according to claim 14 when dependant on claim 12 wherein the colour of the liquid crystal display is varied to give a change in operating parameter.

18. A method for providing a movable beam of light comprising the steps of: providing an array of liquid crystal material having a plurality of zones which are selectively energisable to be changed from a first state to a second state of light transmissibility; providing a light source illuminating one face of the array; and selectively energising the zones to provide a transparent region by means of which light from the light source passes through the array and an opaque region, the selective energisation being such as to vary the size and or location of the transparent region to provide a moving beam of light.

19. The method according to claim 18, wherein the step of selectively energising further comprises the steps of: selecting at least one scanning pattern; and selectively energising the zones to vary the size and or location of the transparent region according to the selected scanning pattern to provide the moving beam of light.

20. The method according to claim 18 or claim 19 including a step of illuminating an object with the beam of light and detecting light reflected back by the object.

21. The method according to claim 20 including a step of providing a focusing arrangement for focusing the reflected light onto the detector.

22. The method according to claim 20 or 21 including a step of analysing the detected light and varying an operating parameter in response to the analysis.

23. The method according to claim 22 wherein the operating parameter that is varied is at least one of: an intensity of the light beam; a wavelength of the light beam; a scanning pattern; a variation in the focus of the focusing arrangement; and a speed of movement of the light beam.

24. The method according to any one of the preceding claims including the step of displaying on the array of liquid crystal material.

25. A method for producing a moving beam of light substantially as hereinbefore described with reference to and as illustrated by any one or any combination of the figures of the drawings.

26. Apparatus for producing a moving beam of light substantially as hereinbefore described with reference to and as illustrated by any one or any combination of the figures of the drawings.

27. Apparatus for detecting light received from an object of interest comprising: a light detector; an array of material having a plurality of selectively e'nergisable zones to change light transitivity of the zones from a first state to at least a second state different to the first; and an array controller for selectively energising the zones to provide a first region which is relatively opaque and a second region which is relatively transmissive of light; wherein the array is disposed between the object and the detector.

28. Apparatus as claimed in claim 27 wherein the selective energisation is such as to vary at least one of size or location of the regions.

29. Apparatus for detecting light received from an object substantially as hereinbefore described with reference to and as illustrated by any one or any combination of the drawings.