Hand-held instant bar code reader system with automated focus based on distance measurements

We claim as our invention:

1. In a bar code reader system, a hand-held bar code reader positionable by hand at varying distances from a bar code to be read and operable for reading bar codes at distances from said reader within a certain operative range, said reader comprising:

bar code sensor means for generating an output signal in accordance with a bar code image incident thereon,

distance measurement means for automated reading of distances of a bar code from the hand-held bar code reader over a certain measurement range which exceeds said certain operative range for reading of bar codes,

reading distance adaption means for automatically adapting the reader to the reading of a bar code at varying distances therefrom within the said operative range by causing an image of the bar code to be substantially focused at the image sensor means,

enabling means for enabling a bar code reading operation, and

control means coupled with said enabling means and said distance measuring means and operative in response to enabling of a bar code reading operation by said enabling means and in response to reading by said distance measurement means of distances within said operative range for automatically controlling the reading distance adaptation means during movement of the reader relative to a bar code within said operative range to tend to establish and maintain a focused bar code image at the image sensor means.

2. In a bar code reader according to claim 1,

said image sensor means comprising a solid state photoelectric sensor array capable of resolving elements of a complete bar code simultaneously incident thereon.

3. In a bar code reader according to claim 2, said solid state photoelectric sensor array having an elongated photosensing region with a resolution of about five thousand pixels so as to be capable of the instantaneous reading of a bar code having a minimum bar size of about five thousandths of an inch and a length greater than seven inches.

4. In a bar code reader according to claim 1, said control means being automatically operable to repeatedly actuate said reading distance adaptation means as the bar code reader is moved toward the bar code from a distance of at least two inches in front of the reader.

5. In a bar code reader according to claim 1, said reading distance adaptation means being automatically controllable by said control means to automatically adapt the reader to the reading of bar codes over a range from about zero to about three inches in front of the bar code reader.

6. In a bar code reader according to claim 1, aiming indicator means operatively associated with the reading distance adaptation means for indicating an optimum aiming relationship of the reader relative to a bar code in any adjustment of said adaptation means.

7. In a bar code reader according to claim 6, said reading distance adaptation means comprising an axially movable lens system, and said aiming indicator means comprising indicator light source means for producing a marker beam extending through the lens system from interiorly of the reader to the exterior thereof.

8. In a bar code reader according to claim 6, said aiming indicator means comprising means for directing respective marker beams for representing the lateral margins of a bar code field of view of the image sensor means.

9. In a bar code reader according to claim 8, said aiming indicator means providing marker beam paths extending from opposite margins of the image sensor means.

10. In a bar code reader according to claim 6, said aiming indicator means comprising light reflector elements at opposite margins of the image sensor means and indicator light source means for directing light beams toward the respective reflector elements such that marker beams are directed from the reflector elements reversely to the path of reflected light from a bar code in the reader for delineating lateral margins of a field of view of the image sensor means exterior to the reader.

11. In a bar code reader according to claim 10, said indicator light source means providing visible light beams of respective different colors.

12. In a bar code reader according to claim 6, said control means responding to a manually generated signal to turn on only said aiming indicator means without activation of said reading distance adaptation means when said distance measurement means provides a distance reading showing that the reader is at a distance from a bar code outside said operative range.

13. In a bar code reader according to claim 6, said reader having flashable illuminator means, said aiming indicator means being operable upon deactivation of said flashable illuminator means following a flash illumination therefrom.

14. In a bar code reader according to claim 13, said reader having manual actuator means for enabling said aiming indicator means and said flashable illuminator means such that when the actuator means is held in actuated condition, the flashable illuminator means and the aiming indicator means can be automatically repeatedly alternately activated until a valid bar code reading is obtained.

15. In a bar code reader according to claim 6, said aiming indicator means generating visible light beams of respective different colors for indicating the margins of a field of view with respect to said bar code image sensor means.

16. In a bar code reader according to claim 6, said reader having manually operated means operative for activating said aiming indicator means in advance of a bar code reading operation when the reader is outside said operative range of said reading distance adaptation means.

17. In a bar code reader according to claim 1, said enabling means including a manual actuator for signalling for a bar code reading operation, said control means being operative to activate said distance measurement means in response to manual actuation of said actuator.

18. In a bar code reader according to claim 1, said distance measurement means measuring the distance between the reader and a bar code at plural points along the length of a bar code, and said control means automatically adjusting the reading distance adaptation means according to the distances measured by said distance measurement means at said plural points.

19. In a bar code reader according to claim 1, said reader having flashable illuminator means for instantaneously illuminating a bar code, and reflected light sensor means for providing a measure of average light reflected from at least a substantial part of a bar code during activation of the flashable illuminator means.

20. In a bar code reader according to claim 19, said reflected light sensor means being disposed in the vicinity of the bar code image sensor means for receiving reflected light transmitted from at least six elements of a bar code.

21. In a bar code reader according to claim 19, said flashable illuminator means having energy supply means for supplying activating energy to the flashable illuminator means, and switch means controlling the supply of activating energy from the energy supply means for interrupting activation of the flashable illuminator means in dependence upon the reflected light measured by said reflected light sensor means.

22. In a bar code reader according to claim 1, said bar code image sensor means having image signal receiving means for receiving an integrated bar code image signal after a selectable integration interval during which reflected light from a bar code acts on the bar code image sensor means, and reflected light sensor means for providing a measure of light reflected from a bar code during a reading operation and controlling said image signal receiving means to receive an integrated bar code image signal after a selected amount of light has impinged on the reflected light sensor means.

23. In a bar code reader according to claim 22, said reflected light sensor means being disposed in the vicinity of the bar code image sensor means for averaging the reflected light transmitted from at least a substantial number of elements of a bar code.

24. In a bar code reader according to claim 22, said reflected light sensor means comprising a plurality of reflected light sensors associated with respective segments of the reader field of view and individually selectable for controlling transfer of an instantaneous bar code image signal to said image signal receiving means after respective individually controlled integration times.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The present invention is particularly concerned with improvements in instant bar code readers of the type shown in U.S. Pat. Nos. 4,282,425 and 4,570,057. The disclosures of these U.S. patents are incorporated herein by reference by way of background.

The instant type of bar code reader with flashable illuminator means has proved to be extremely desirable for portable applications because of its unique simplicity and compact design. A significant goal of the present invention is to retain the major advantages of the present commercial instant bar code readers with flashable illuminator means while enhancing the capacity for reading bar codes of substantially greater length. An important related aspect of the invention is to enable the reading of such large labels by illuminating the same with an instantaneous flash of light while the labels are at a greater distance from the frontal end of the reader. A further development goal is to more effectively adapt the reading operation both to close up bar code labels of high reflectivity and to labels at greater distances and of curved configuration.

SUMMARY OF THE INVENTION

The present invention is therefore particularly directed to the provision of an instant bar code reader which, while retaining the advantages of simplicity, ease of hand operation and ruggedness, achieves enhanced versatility by its ability to read bar codes of greater length and to adapt to a greater range of reading distances.

Such enhanced versatility is realized by providing the reader with an automatically controlled lens system and operating such control in accordance with a measure of reading distance. Further improvements are achieved by monitoring an average of reflected light from the bar code during a reading operation, and terminating integration of the reflected light from a bar code after an optimum measurement sample of the reflected light image has been received.

Aiming of the reader may be carried out with the assistance of visible marker light beams directed into the field of view of the reflected light image sensor. In an ideal embodiment, the marker beams extend from opposite ends of the bar code image sensor through the reflected light optics so that the beams delineate the desired locations for the opposite ends of a bar code in the reader field of view.

For the sake of energy conservation during portable operation, automatic control of the lens system may be disabled until such time as the bar code is within a effective reading range. Where a capacitor discharge energizes a flashable illuminator, the capacitor discharge current may be interrupted as soon as an adequate amount of reflected light has been received; this not only reduces battery drain but also speeds up the capacitor recharging cycle. By monitoring the charge on the capacitor, a new reading cycle can be initiated after a minimum time lapse, should an initial reading cycle be unsuccessful.

Accordingly, it is an object of the invention to provide a bar code reader configuration particularly suited to hand held operation while exhibiting increased versatility.

A more specific object is to provide a bar code reader capable of reading a wider range of bar code sizes without sacrifice of essential simplicity and ease in hand held operation.

Another object is to provide a bar code reader capable of rapid and efficient alignment with bar codes located at substantial distances from the reader.

A further object of the invention is to provide an instant bar code reader which achieves the foregoing objects while minimizing energy consumption so as to retain a capacity for extended portable operation.

A feature of the invention resides in the provision of an adaptive bar code image sensor system enabling a succession of readings of a given bar code with reflected light from respective different segments of such bar code controlling respective integration times. This feature is applicable for example to bar code labels of a curvature such that a bar code reading with a single integration time would not effectively sample reflected light from all segments of the label.

Further features leading to enhanced adaptability of the code image sensor system comprise individually operable flash illumination means enabling more rapid flash sequences, and/or enabling improved illumination of irregular or curved code configurations and/or of code configurations of greater extent, and/or enabling respective individually controlled flash durations immediately following each other, and e.g. adapted to respective different segments of a code configuration.

Still further features of an adaptive code image sensor system relate to simultaneous reading of code segments at markedly different depths of field and/or multiple depth measurement sensors for assessing the depth of respective segments of a code configuration, and/or selectable image sensors effectively adapted to read code configurations at respective overlapping depth ranges for instantaneous adaptation to a code configuration at any depth over a wide range without the use of moving parts. In one implementation, the depth of field of a lens system is greatly increased by providing multiple optical image paths of respective different lengths in the reader which lead through the lens system to respective independently controllable image sensors.

Another feature resides in the provision of a marker beam indicator system for delineating the optimum location for a bar code in the reader field of view so that the reader can be positioned rapidly and efficiently even while at substantial distances from a bar code.

Various method features will be apparent from the following disclosure. For example, in a case where a curved bar code label has a central segment within the focal depth of the lens system, but the marginal segments are actually outside the focal depth, one exemplary method of programmed operation may provide for a second flash automatically after the lens system has automatically focused at a selected greater depth. By assembling the two readings, e.g. pixel by pixel, a good bar code reading may be obtained with e.g. valid start and stop characters being obtained from the second reading.

In another method of programmed operation, a display forming part of the operator input/output means can instruct the operator to take first a reading of the left hand portion of a severely curved label, then a central portion and then a right hand portion, with the processor assembling the pixels of the respective readings to obtain a complete bar code image reading. The operator could, in another mode, advise the reader processor e.g. by the selective actuation of function keys or the like, of a particular reading sequence to be input to the reader processor for extremely long or sharply curved labels. The function keys could be part of a keyboard associated with the reader itself and/or a keyboard associated with a host computer unit directly mechanically coupled with the reader housing, or coupled via any suitable remote linkage means such as a cable or a radio frequency channel.

In certain instances, the reader processor may assemble the pixels of successive readings not only with the assistance of internal check characters and pre-knowledge of code formats and the like and/or of specific reading sequences, but further with the assistance of measurements from multiple distance measurement sensors defining the general bar code spacial configuration. Utilizing multiple flashable illuminators and/or multiple intensity sensors may enable valid reading of different segments while avoiding in all cases, any saturation of CCD charge wells or the like of an image sensor. Saturation of any part of a CCD shift register may adversely affect subsequent operation of an image sensor.

Other objects, features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying sheets of drawings, and from the features and relationships of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a preferred embodiment of the present invention;

FIG. 2 is a diagrammatic view useful for explaining certain features of a specific exemplary embodiment of the invention;

FIG. 3 is a somewhat diagrammatic partial longitudinal sectional view for indicating the application of certain features of the present invention to an instant bar code reader generally as shown in U.S. Pat. No. 4,570,057;

FIG. 4 is a somewhat diagrammatic plan view illustrating an adaptive bar code image sensor system in accordance with the present invention, and also illustrating an alternative label guide indicator arrangement for the reader of FIG. 3;

FIGS. 5, 6 and 7 are electric circuit diagrams for illustrating an exemplary implementation of component 11 of FIG. 1;

FIGS. 6A through 6F show waveforms useful for explaining the operation of the circuit of FIG. 6;

FIGS. 8 and 9 show an exemplary implementation of components 15, 16 and 17 of FIG. 1;

FIG. 10 is an electric circuit diagram for illustrating an exemplary implementation for component 121 in FIG. 1; and

FIGS. 11 and 12 are diagrammatic illustrations for indicating an exemplary implementation of component 20 in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates a preferred instant bar code reader system for extending the versatility of a commercial bar code reader such as shown in U.S. Pat. No. 4,570,057.

Component 10, FIG. 1, may represent a control and processing means for the system and may include a central processing unit, memory units and analog to digital conversion channels.

The central processing unit and associated memory form the main control portion of the system. The other functional blocks of FIG. 1 may be inputs or outputs with respect to the central processing unit.

The central processing unit may be a microprocessor that executes the program to control the operation of the reader. The microprocessor acts as a microcontroller with the capability of sensing and controlling the functional elements of the bar code reader, and decoding the bar code as supplied from a bar code image sensor means 11. Where the reader is coupled on line with a host computer system, (for example by a host connection means in the form of a flexible cable), the decoded bar signal is transmitted to the host under the control of the central processing unit. The microprocessor is capable of static operation with shut-down for power conservation. Wake-up of the processor will occur when an operator actuates a scan switch 12.

An electrically erasable read only memory of component 10 may be utilized to store parameters and special modifiable decoding sequences for the bar code reader operation. Examples of these parameters would be label code, and input/output speed and control format.

Component 10 may also include a random access memory for data collection, decoding work space and buffer storage of the decoded label data for transmission to a host computer, for example. The random access memory can be internal to the microprocessor chip or reside on a data bus.

The analog/digital channels are for receiving the bar code signals generated by the bar code image sensor mean 11 and for other purposes as will be hereafter explained.

The image sensor means 11 may, for example, include a photosensor array indicated diagrammatically at 13 having a one dimensional linear array of photodiodes for detecting the bar code reflection image. To read labels with bar code lengths of greater than seven inches with high resolution requires that the array have relatively high resolution. By way of example, the array 13 may comprise five thousand photodiode circuits (5,000 pixels) and provide approximately three photodiode circuits (3 pixels) for each five mils (0.005 inch) of a bar code length. (Each pixel of array 13 may have a length of about seven microns.) A charge coupled device (CCD) shift register may be arranged to receive bar code signal elements from the respective photodiode circuits after a suitable integration interval. Once the bar code signal elements have been transferred to the shift register, the signal elements are retained independently of further exposure of the photodiodes to reflected light from the bar code.

In the embodiment of FIG. 1, an intensity sensor 14 is provided and may comprise a photodiode that will determine the relative amount of light exposure of the photosensor array 13. If component 10 operates at sufficiently high speed, the signal from the intensity sensor 14 may be supplied exclusively to component 10 via an analog/digital channel so that the control and processing means can determine the optimum point for transfer of the bar code image signals to the shift register.

In a presently preferred implementation, however, the intensity sensor means 14 is directly coupled with the hardware control circuits of the flashable illuminator means and of the bar code image sensor means, and this is indicated by dash lines L1 and L2 in FIG. 1; in this case, line L is used only so that the processor component 10 is advised that a flash has actually occurred. In a preferred embodiment wherein a flashable illuminator 15 is driven by capacitor discharge current, a component 16 may effect interruption of the flow of current from the capacitor based directly on the signal supplied via L1 from intensity sensor 14. In this way, energy is conserved, and recharging of the capacitor speeded up. Component 16 may comprise a flash current interrupter switch means, e.g. a solid state switch which is controlled to interrupt discharge of the capacitor of high voltage generation unit 17 and thus to terminate the flash of light from the flashable illuminator 15 when intensity sensor 14 indicates that adequate reflected light has been received from a bar code.

The system of FIG. 1 is also indicated as including a reading distance adaptation means 20, label guide indicator means 21 and reading distance sensor means 22. These components are best understood by reference to a specific example as shown in FIG. 2. FIG. 2 illustrates an exemplary configuration wherein the label guide indicator means 21 is provided by a pair of marker light emitting diodes 24 and 25 which produce light beams 26 and 27 extending from opposite ends of the photosensor array 13 through the lens system indicated at 30 so as to delineate by means of marker light spots at 28 and 29 on the label the field of view of the reader. FIG. 2 illustrates a situation where label 31 has a bar code with a length greater than seven inches and is located at a distance D from a frontal window part 33 of the reader of greater than two inches, for example, three inches. By way of example in FIG. 2, flashable illuminator 15 of FIG. 1 is illustrated as being implemented by two flash tubes 35 and 36 directed obliquely outwardly relative to a central axis 37 of the reader.

FIG. 2 also illustrates the provision of an ultrasonic transducer 38 for implementing component 22 of FIG. 1. For example, transducer 38 may emit an ultrasonic pulse along an axis 39 aligned with the reader central plane such that the time of arrival of a reflected pulse from the bar code label 31 provides a measure of reading distance. In place of or in addition to distance sensor 38, infrared distance measurement sensors 38-1 and 38-2 are provided in FIG. 2, with axes arranged to intersect a curved label generally at a mean distance (e.g. at D.sub.o equal to one-half the sum of the maximum distance D1 and the minimum distance D11). By way of example, adaptation means 20 may include motor driven focus adjustment means 40 coupled with the lens system 30 for adjusting the lens system parallel to the central optical axis 37, as represented by the double-headed arrow 41.

In the example of U.S. Pat. No. 4,570,057, the reader has a width dimension at its frontal wall which is greater than the extent of the exit light path at the plane of such frontal wall. However, in the specific configuration of FIG. 2, it will be observed that marginal light rays 43 and 44 from the flash tubes 35 and 36 are transmitted by transparent side walls 45 and 46 of the reader housing so that in this case the illumination field has a total extent at the plane of the reader frontal wall which is substantially greater than the width dimension of such frontal wall.

In FIG. 2, a photodiode intensity sensor 50 corresponding to component 14 of FIG. 1 is indicated as being mounted centrally as defined by a plane intersecting the optical axis 37, but offset from photosensor array 13 so as not to obstruct light incident thereon. (Optical axis 37 intersects photodiode array 13.) Intensity sensor 50 is preferably placed so as to intercept light of maximum intensity as reflected from the label 31. By way of example, intensity sensors such as 50, 51 and 52 may be located at respective different locations adjacent sensor array 13 as indicated, and successive ones of the sensors may be selected for actual control of bar code image integration time during successive bar code reading operations for a given curved bar code configuration as will be hereafter explained.

In the example of FIG. 2, mirror elements 53 and 54 are mounted at opposite ends of photosensor array 13 for reflecting light from the sources 24 and 25 along the beam paths 26 and 27.

Components such as 11, 14, 15, 20, 21 and 22 of FIG. 1 may be implemented as shown in FIG. 3. FIG. 3 may be taken as supplementing FIG. 2, and corresponding reference numerals have been used in FIGS. 2 and 3 to designate similar parts.

Referring to the physical arrangement of parts as indicated in FIG. 3, the location of the intensity sensors such as 51 to one side of a central optical axis 60 is indicated. Considering the plane which intersects the photosensor array 13 and coincides with the optical axis 60, it will be understood that mirrors such as 53 will each have a location centered on such plane. As indicated in FIG. 3, ultrasonic transducer 38 may be located just above window 33 with its axis 39 directed generally parallel to the optical axis 64 (which indicates the axis for the reflected light entering the reader).

In conformity with FIG. 2, the reader is shown as having transparent side wall portions such as 46 at the respective sides o the reader, corresponding to the transparent portions 45 and 46 in FIG. 2. Each of the flash lamp tubes 35 and 36 may be provided with a housing 75 and an interior reflector 76 with a configuration as described as U.S. Pat. No. 4,570,057. At a depth of approximately three inches in front of the window 33, the flash illumination means 35 and 36 may effectively illuminate a sensing region having an extent greater than seven inches, for example.

Reflected light from a bar code label 31 follows an optical path at indicated at 64, 80, 81 and 60 in FIG. 3 by virtue of the arrangement of mirrors 82, 83 and 84. These mirrors are fixed relative to reader housing 86, while a lens barrel 90 carrying optical lenses is axially adjustable relative to the reader housing. Also preferably forming part of the adjustable lens barrel assembly 90 are an infrared rejecting filter 97 and a rectangular aperture element analogous to that of U.S. Pat. No. 4,570,057. For the sake of diagrammatic indication, barrel assembly 90 is shown as having a series of gear teeth 101 meshing with a worm gear drive 102 which is driven from an adjustment motor 103 via a right angle drive coupling assembly 105. The barrel assembly 90 may have a range of adjustment so as to accommodate bar code labels closely adjacent to the frontal window 33 and at progressively greater distances in front of the window 33 up to reading distances of at least three inches.

In FIG. 3, a bearing for the shaft of worm gear 102 is indicated at 111. Guide means for lens barrel 90 are indicated as comprising flanges such as 112 for riding in cooperating slot-like low friction guideways such as 114. An alternative location for the light emitting diodes 24 and 25 is indicated at 24-1 in FIG. 3.

An analog to digital conversion channel of component 10, FIG. 1, may be utilized to monitor charge build-up in the high voltage generation component 17 so that a flash of the illuminator means 15 will take place only when the desired amount of flash driving current is available.

Other analog to digital conversion channels may read the light intensity values accumulated by intensity sensors 50, 51 and 52, so that such intensity values can determine respective bar code image integration times, where desired.

Component 120 in FIG. 1 represents desired audio and visual status indicators for facilitating operation of the reader unit. For example, a red-light-emitting diode indicator may be energized whenever a thumb actuator controlling read enable switch 12 is pressed and the reading distance sensor means 22 determines that a bar code label is beyond the maximum reading distance of the reading distance adaptation means 20. At such a distance outside of the operative reading range, the lens adjustment motor 103, FIG. 3, may be disabled, e.g., by the programming of control and processing means 10 to conserve power. When the reader is within the operative range, if the thumb operated switch 12 is actuated, motor 103 is essentially continuously controlled according to successive distance readings. If a good bar code reading is accomplished, means 120 may produce a relatively long single beep and turn on a green-light-emitting indicator diode. Where a bad bar code reading situation is determined, e.g., after a selected number of reading attempts, means 120 may generate three short beeps, for example. The programming may be such that once a good reading or bad reading condition is determined, the user must release the thumb switch and depress it again to initiate another read sequence. Indicator lamps and a beeper have been shown in the seventh figure of U.S. Pat. No. 4,570,057 and are described therein at column 11, lines 37-43. The indicator lights may be physically located forwardly of the thumb switch as can be seen in the first figure of U.S. Pat. No. 4,570,057.

FIG. 1 also indicates an input/output buffer component 121 for coupling the control and processing means 10 with a host processor or the like. A connection means 122 may directly receive a host processor so that the host processor housing is physically attached with the reader housing. As another example, connection means 122 may comprise a cable containing six conductors. Preferably, such a cable would be detachable at the reader. In this second example, all needed voltages may be generated in the reader from plus five volts supplied by two of the six conductors (+5 V, GND). The other four signal lines of the cable are preferably independently programmable as inputs or outputs. By way of example, the host processor may be part of a

held computer such as shown in U.S. Pat. Nos. 4,455,523 and 4,553,081. The rechargeable batteries of the portable computer may supply all needed power to the reader unit of the present invention. In the second example, a host computer unit can be carried in a belt holster for example during extended use of the reader unit of the present invention.

FIG. 4 is a somewhat diagrammatic top plan view of an exemplary bar code image sensor means 11 such as indicated only schematically in FIG. 1. In FIG. 4, the sensor housing 124 is shown as having a light transparent cover window 125 overlying the photodiode array 13. Where the photodiode array comprises five thousand individual elements or pixels, each with a dimension of about seven microns, the intensity sensors 50, 51 and 52 may each have a length of about one-tenth inch or more so as to span many bars of a reflected bar code image, e.g., at least six bar code elements, and reliably sense an average intensity value which is essentially independent of any specific bar code sequence. By way of example, the intensity sensors may be cemented to the exterior surface of window 125 at successive locations along photodiode array 13 but offset from the light entrance path to the photodiode array.

Mirrors 53 and 54, FIG. 2, may be cemented in place on the glass 125 as indicated for mirrors 53' and 54' in FIG. 4. The light sources 24' and 25' in FIG. 4 may be located in wall 130, FIG. 3, at a section as indicated 24-1 in FIG. 3. The mirrors 53' and 54' are secured at angles such that the marker beams will extend parallel to the image path at 60, 81, 80 and 64 and will produce spots of visible light, e.g., of red color, corresponding to spots 28 and 29 in FIG. 2, and spot 28 as indicated in FIG. 3.

In a preferred mode of operation of the embodiments of FIGS. 1-4, manual actuation of the read enable switch 12 will initiate a flash of the illuminator means 1