GB2302754A

GB2302754A - Data symbol reading device

Info

Publication number: GB2302754A
Application number: GB9613613A
Authority: GB
Inventors: Takeharu Shin; Shuzo Seo; Nobuhiro Tani; Makoto Nukui; Yukihiro Ishizuka
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1995-06-28
Filing date: 1996-06-28
Publication date: 1997-01-29
Also published as: GB9613613D0; JPH0916702A; FR2736180A1; DE19626056A1; GB2302754A8

Description

2302754 DATA SYMBOL READING DEVICE The present invention relates to a data

symbol reading device for reading coded information such as two-dimensional data symbols.

Point of Sale (POS) systems generally use some form of bar code system for reading and identifying the product codes that are marked on each product. These bar code systems allow the fast and efficient entry of data into a data management system. However, conventional bar codes can only hold a limited amount of information because data is stored in a one dimensional arrangement of bars.

To overcome this problem, symbols with a mosaic or tessellated pattern, in which a black and white pattern is arranged in a two-dimensional manner, have been developed as a means for holding more information. Data symbol reading devices for reading two dimensional data symbols may be generally classified into two groups: those in which an imaging element (an area sensor) is used to read the data symbol pattern 'in two dimensions simultaneously; and those in which the data reading unit and data symbol are moved relative to each other for auxiliary (sub) scanning, and a line sensor main scans the two- dimensional symbol.

Data symbol reading devices which use a two-dimensional imaging element (area sensor) do not require relative movement between the reading unit and the data symbol, and symbols can be read in a shorter time.

However, with a conventional data symbol reading devices using a twodimensional imaging element (area sensor), if a relatively small data symbol is to be read, the symbol is difficult to read and the data pattern difficult to decode. In particular, since individual cells in the two dimensional pattern are small, it may not be possible to recognize these cells properly and data symbol reading errors may occur, causing unacceptable delays in reading.

It is therefore an object of the present invention to provide an improved data symbol reading device for alleviating problems associated with known devices.

According to one aspect of the present invention there is provided, a data symbol reading device comprising an imaging element for receiving images, and a variable magnification optical system for forming an image of a symbol reading area on the imaging element. A driving device varies a magnification of the variable magnification optical system, and a decoding device decodes an image of the data symbol within the image of the symbol reading area received by the imaging element. An evaluating device evaluates if the decoding device successfully decodes the image of the data symbol, and a drive control device, associated with the evaluating device, controls the driving device to vary the magnification to a magnification where the decoding device successfully decodes the image of the data symbol.

in this manner, if the data symbol is unreadable, the data symbol reading device can automatically adjust the magnification of the image so that the data symbol becomes readable.

In one embodiment, the drive control device initially controls the driving device to set the magnification to a minimum magnification of the variable magnification optical, system. Subsequently, the drive control device controls the driving device to increase the magnification until the evaluating device evaluates that the decoding device successfully decodes the image of the data symbol.

This embodiment allows relatively small data symbols to be magnified until the symbol is readable.

In another embodiment, the drive control device initially controls the driving device to set the magnification to a maximum magnification of the variable magnification optical system, and wherein the drive control device controls the driving device to decrease the magnification until the evaluating device evaluates that the decoding device successfully decodes the image of the data symbol.

In this embodiment, the symbol is read at the highest magnification in which the symbol is fully within the symbol reading area, allowing good accuracy and accurate decoding.

Preferably, the data symbol reading device according to this aspect of the present invention further includes a light source for illuminating the symbol reading area, and a light source driver for driving the light source at a settable illumination level. In this case, the drive control device further controls the light source driver to drive the light source at an illumination level set according to the magnification of the variable magnification optical system. This allows proper exposures to be made even when the magnification is changed.

According to another aspect of the present invention, there is provided a data symbol reading device including: an imaging element for capturing an image and a variable magnification optical system for forming an image of the symbol reading area on the imaging element. A magnification varying device varies a magnification of the variable magnification optical system, and a decoding device decodes an image of the data symbol within the image of the symbol reading area. An evaluating device evaluates if the image of the data symbol within the symbol reading area is successfully decoded. A control device sets the magnification varying device to an initial minimum magnification, and controls the magnification varying device to increase the magnification by a predetermined magnification step size until the evaluating device evaluates that the image of the data symbol is successfully decoded.

Accordingly, if a relatively small. data symbol is unreadable, the data symbol reading device can automatically increase the magnification of the image until the data symbol becomes readable.

In this case, the magnification varying device preferably includes a switch for detecting the minimum magnification of the variable magnification optical system. Furthermore, the magnification varying device preferably includes a stepping device for varying the magnification of the variable magnification optical system in a stepwise fashion.

In still another aspect of the present invention, there is provided a data symbol reading device including:

an imaging element for capturing an image, and a variable magnification optical system for forming an image of the symbol reading area on the imaging element. A magnification varying device varies a magnification of the variable magnification optical system, and a decoding device decodes an image of the data symbol within the image of the symbol reading area. An evaluating device evaluates if the image of the data symbol within the symbol reading area is successfully decoded. A control device sets the magnification varying device to an initial maximum magnification, and controls the magnification varying device to decrease the magnification by a predetermined magnification step size until the evaluating device evaluates that the image of the data symbol is successfully decoded.

Accordingly, if a data symbol is unreadable because of a high magnification level, and protrudes outside the symbol reading area, the data symbol reading device can automatically decrease the magnification of the image until the data symbol becomes readable. The symbol is therefore read at the highest magnification in which the symbol is fully within the symbol reading area, enhancing accuracy.

In this case, the magnification varying device preferably includes a switch for detecting the maximum magnification of the variable magnification optical system. Furthermore, the magnification varying device preferably includes a stepping device for varying the magnification of the variable magnification optical system in a stepwise fashion.

In yet still another aspect of the present invention, there is -provided a data symbol reading device including a CCD imaging element for receiving images and a variable magnification optical system, including a zoom lens, for forming an image of a symbol reading area on the CCD imaging element. A zoom lens drive varies a magnification of the zoom lens, and a control circuit is connected to the zoom lens drive and the CCD imaging element. The control circuit includes a decoding device that decodes an image of a data symbol within the image of the symbol reading area received by the CCD imaging element, and an evaluating device that evaluates if the decoding device successfully decodes the image of the data symbol. The control circuit controls the zoom lens drive to vary the magnification of the zoom lens until the evaluating device successfully evaluates that the decoding device has successfully decoded the image of the data symbol.

Examples of the present invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a perspective view of a data symbol reading device 'of - the invention; Fig. 2 is a sectional side view of the data symbol reading device shown in Fig. 1, taken along the line II-Ii of Fig. 1; Fig. 3 is a bottom view of a head part of the data symbol reading device shown in Fig. 1; Fig. 4 is a block diagram showing a circuit arrangement for the data symbol reading device shown in Fig. 1; Figs. 5A and 5B are schematic diagrams showing the relationship between magnification of a zoom lens and a symbol reading area; Fig. 6 is a flowchart showing control operations of a first embodiment of a data symbol reading device according to the invention; and Fig. 7 is a flowchart showing control operations of a second embodiment of a data symbol reading device of the invention.

1 Fig. 1 is a perspective view of a data symbol reading device 1 of the invention, Fig. 2 is a sectional side view of the data symbol reading device 1 taken along the line II-II of Fig. 1), Fig. 3 is a bottom view of a head 9 - part 22 of the data symbol reading device 1 shown in Fig. 1, and Fig. 4 is a block diagram of a circuit arrangement of the data symbol reading device 1 shown in Fig. 1.

As shown in Figs. 1 through 4,the data symbol reading device 1 includes a casing 2 with a grip part 21, a head part 22 and a housing 3. The grip part 21 is elongated so that it can be gripped with the hand, and houses a control circuit 50. The head part 22 is formed at the front end of the grip part 21 to create an L-shape, and houses a reading unit 4. The housing 3 is formed at the end of the head part 22, extending from the reading unit 4 toward a symbol reading area 36. A front opening 31 is formed at the front end of the housing 3.

The exterior of the casing 2 is provided with an operation switch 19 and an indication unit 18. The operation switch 19 is used for activating the data symbol reading device 1, and is provided in an easily accessible position at one side of grip part 21. The indication unit 18 provides information to the operator, and is provided in an easily visible position on the upper face of the end of grip part 21. in this embodiment the indication unit 18 is an LCD (liquid crystal display), however, any suitable indication device may be used, such as a light emitting diode (LED) or group of LED's.

The reading unit 4 includes a pair of light sources 41 (for example, LED's, light valves, or halogen lamps), a charge coupled device (CCD) 43 as an imaging element (in this embodiment, an optical system 44 for forming an image on the CCD, and a supporting member 48. The supporting member 48 provides a frame for the other components of the reading unit 4.

The optical system 44 forms an image on the CCD 43 from light reflected from the symbol reading area 36. The optical system 44 includes a mirror 45 for bending the light path 47 of the reflected light from symbol reading area 36, and a zoom lens (a lens group) 46, which forms the light reflected by the mirror 45 into an image on the CCD 43.

The two light sources 41 are substantially symmetrically positioned with respect to the path of light 47 at the lower end of the supporting member 48. The light sources 41 are connected to a light source driving circuit 42 (shown in Fig. 4). A diffuser plate (not shown) may be installed at the light emitting side of the light sources 41 to make the luminance at the symbol reading area 36 more uniform. Alternatively, a diffuser portion can be provided by roughening a part of a transparent plate 7 (described below).

The CCD 43 includes a plurality of photodiode picture elements disposed in an array. Each of the picture elements accumulates an electrical charge corresponding to the amount of light received, and the CCD 43 is controlled to sequentially transfer these charges. The transferred charges are readable (analog) image signals.

The symbol reading area 36 is formed on a reference plane 37, the reference plane 37 representing the surface upon which a data symbol 38 is positioned. The symbol reading area 36 is a predetermined area illuminated by the light sources 41 and readable by the CCD 43. The light reflected from the symbol reading area 36 is sent to the CCD 43. Although the symbol reading area 36 changes in accordance with the magnification and field angle of the zoom lens 46, the symbol reading area 36 at the minimum magnification and maximum field angle substantially coincides with, or includes, the front opening 31 of the housing 3.

The housing 3 acts as a guide for maintaining the reading unit 4 at a predetermined distance (optical path length) with respect to the symbol reading area 36. In other words, the housing 3 sets a distance for forming (via the optical system 44) an image of a data symbol 38 (in the symbol reading area 36) on the CCD 43. The housing 3. surrounds the light path of the illuminating light from the light sources 41 and the light path 47 of the light reflected from the symbol reading area 36. The housing 3 has a rectangular cross section parallel to the symbol reading area 36.

A transparent plate 7 is installed in the interior of the housing 3 perpendicular to the light path 47, at the inner side of the front opening 31. The transparent plate 7 partitions the internal space of the housing 3 and the head part 22 into a space 4a at the front opening 31 side and a space 4b at the reading unit 4 side. The transparent plate can be made from glass or plastic. The main purpose of the transparent plate 7 is to prevent the entry of foreign matter (dust, lint, moisture and the like) into the space 4b. However, as previously described, a portion of the transparent plate may alternatively act as a diffuser for the light sources 41.

As shown in Fig. 3, in this example, the data symbol 38 includes a tessellated array pattern of black and white (or, alternatively, black and transparent) cells, the array being at least 2 by 2, but preferably considerably larger. Each cell expresses binary 0 or 1, and information is thereby encoded in the pattern of cells. However, the data symbol 38 is not restricted to the illustrated arrangement in order to be readable by the data symbol reading device. Further, it is preferable for there to be no other imageable markings other than the data symbol 38 within a predetermined area equal to or larger than the symbol reading area 36.

As shown in Fig. 4, the control circuit 50 includes a signal processing circuit 5, a zoom lens driving circuit 10, a stepping motor 11, the light source driving circuit 42, a communication driver 16, an operation switch circuit 13 for the operation switch 19, a limit switch 14, and an indication unit 18. Power for the data symbol reading device can be supplied to the control circuit using batteries internal to the device 1, or from an external source such as a host computer 17.

The signal processing circuit 5 includes a CCD driving circuit 6, an amplification circuit 8, a binarization circuit 9, a memory 12, a central processing unit (CPU) 15 as a control means. The CCD driving circuit 6 drives the CCD, and generates and transmits clock signals to the CPU 15. For example, composite clock signals, having a horizontal synchronization signal and a vertical synchronization signal combined with a clock signal, are transmitted from the CCD driving circuit to the CPU 15.

The CPU 15 is also connected to the zoom lens driving circuit 10, the light source driving circuit 42, the communication driver 16, the operation switch circuit 13, the limit switch 14, and the indication unit 18.

The zoom lens driving circuit 10, the zoom lens 46, and the stepping motor 11 form a portion of a driving means for varying the magnification of the (variable magnification) optical system 44. The zoom lens 46 (lens group) is a conventional mechanically compensated zoom lens arrangement, using a cam ring to move lens elements to (i) change focal length and to (ii) compensate for image shift, i.e., defocusing. The zoom lens driving circuit 10 is connected to the stepping motor 11 and controls the stepping motor 11 to drive the zoom lens 46 (via the cam ring, not shown) between a minimum focal length (minimum magnification, at the wide angle end) and a maximum focal length (maximum magnification). The stepping motor 11 advances or reverses in a step-wise fashion, and for each command received, drives the zoom lens 46 by one unit step in a direction toward the minimum magnification end or in a direction toward the maximum magnification end. The predetermined unit step size is determined by dividing the driving distance between the minimum magnification end and the maximum magnification end equally into N equal parts (N being at least 2). For example, N equal parts may be 20 equal parts.

The limit switch 14 is (in this example) a normallyopen switch that is turned ON when actuated. The limit switch 14 is turned ON when the zoom lens 46 is positioned at the minimum magnification end. When the zoom lens 46 moves away from the minimum magnification end, the limit switch 14 turns OFF.

The CPU 15 monitors the condition of the limit switch 14 (i.e. ON or OFF) and determines the magnification (focal length) of the zoom lens 46 from both the condition of the limit switch 14, and the amount and direction of driving of the stepping motor 11. That is, in the first embodiment, the CPU 15 determines that the zoom lens 46 is set to the minimum magnification when the limit switch 14 is ON. When the limit switch 14 is OFF, the CPU 15 determines the magnification of the zoom lens 46 from the number of steps by which the stepping motor 11 was driven since the limit switch 14 was turned OFF.

The magnification of the zoom lens 46 is used by the CPU 15 to control of the zoom lens driving circuit 10, to adjust of the quantity of light emitted by the light sources 41, and in the decoding process.

Fig. SA is a schematic diagram showing a symbol reading area 191 when the magnification of the zoom lens 46 is set to the minimum magnification, and Fig. 5B is a schematic diagram showing a symbol reading area 192 when the magnification of the zoom lens 46 is higher than the minimum magnification.

As shown in Fig. SA, if a relatively small data symbol 38 is read, and the reading is performed with the minimum magnification, the data symbol 38 (in particular, the individual cells which comprise the data symbol 38) is small with respect to the symbol reading area 191, and the accuracy of reading and decoding of the data symbol 38 is not optimum.

However, as shown in Fig. 5B, if the zoom lens 46 is zoomed to a larger focal length and reading is performed at a higher magnification, the data symbol 38 is magnified to more readable size (with respect to the symbol reading area 192) and the accuracy of reading and decoding of the data symbol 38 is thereby improved.

The data symbol reading device 1 is activated when the operation switch 19 is turned ON. The CPU 15 first instructs the light source driving circuit 42 to turn on the light sources 41. The light emitted from the light sources 41 illuminates the symbol reading area 36, and the reflected light from the symbol reading area forms an image (via the optical system 44 including the zoom lens 46) on the CCD 43.

The CPU 15 controls the light source driving circuit 42 to set the quantity of light emitted according to the current magnification level. That is, the CPU 15 determines the magnification of the zoom lens 46, and controls the light source driving circuit 42 to adjust the quantity and duration of light emitted by the light sources 41 for an appropriate exposure.

The CPU 15 also activates the CCD driving circuit 6 when the operation switch 19 is turned ON. A horizontal CCD driving pulse and a vertical CCD driving pulse are output from the CCD driving circuit 6 to the CCD 43, to control the accumulation and transfer of charge at the CCD 43.

The amplification circuit 8 amplifies the (analog) image signals output sequentially from the CCD 43. The analog image signals are converted into digital image signals (for example., 8-bit image signals) by an A/D converter portion of the amplification circuit 8, and are then input into the binarization circuit 9.

The binarization circuit 9 compares the digital image signals for each picture element with predetermined threshold data, and sets a value of "l" or "Off accordingly. For example, a binarized data value of I'll, corresponds to a black part of the data symbol 38 while a value of "0" corresponds to a white part. The binarized data (image data) output from the binarization circuit 9 are stored, according to an address counter in the CPU 15, in prescribed addresses of the memory 12. This address counter is driven by composite clock signals (as previously described) from the CCD driving circuit 6.

The CPU 15 then accesses the memory 12 and performs the necessary image processing on the image data, for example, image inversion, symbol extraction (extraction of only the information concerned with the data symbol 38), dropout correction, rotation, and the like. The data in memory 12 are read out sequentially in accordance with the addresses designated by the abovementioned address counter (the order - is - of readout may be reversed with respect to the order of storage into memory 12). Furthermore, the CPU 15 decodes the image data in accordance with the particular system used to encode the data symbol 38.

During this reading process, if the data symbol cannot be accurately decoded, the CPU 15 varies the magnification through a feedback control process. That is, the magnification of the zoom lens 46 is increased one step at a time from the minimum magnification, until the data symbol 38 can be read.

To carry out these processes, an image is first taken at the minimum magnification (widest angle) of the zoom lens 46 set. Image processing and decoding are then carried out, and the CPU 15 determines if appropriate decoded data have been obtained (i.e. whether or not the data symbol 38 has been read correctly). If appropriate decoded data have not been obtained, the zoom lens 46 is driven by one step in the direction of increasing magnification and a new image is taken. The CPU 15 again performs the prescribed image processing and decoding, and determines if appropriate decoded data have been obtained. The operations are repeated until appropriate decoded data are obtained (i.e. until the data symbol 38 is read appropriately) or until the zoom lens 46 reaches the maximum magnification.

When appropriately decoded data have been obtained, the decoded data are output by the communication driver 16 to the host computer 17, which may be, for example, a personal computer or a work station. The decoded data are stored, tabulated, and the like by the host computer 17.

Fig. 6 is a flowchart describing the first embodiment of a data symbol reading device of to the invention.

In step S101, the CPU 15 instructs the zoom lens driving circuit 10 to drive the zoom lens 46 to the minimum magnification position (the field angle is set to the maximum field angle).

In step S102, the CPU 15 instructs the CCD driving circuit 6 to capture an image of the symbol reading area 36. Step S102 includes the setting of an appropriate illumination level for the current magnification, the driving of the light sources 41 by the light source driving circuit 42 to the set illumination level, the intake of the image by the CCD 43, the binarization of the analog image signals, and the writing of the image data into the memory 12.

In step S103, the CPU 15 performs a data symbol extraction process. For example, in the extraction process the CPU 15 reads the image data from the memory 12 to find the outline of the data symbol 38 (for example, a border of the symbol 38). The outline of the data symbol 38 is found and tracing is attempted. For example, if the tracing of the image data corresponding to the picture elements of the outline of the data symbol 38 results in a closed loop starting from an origin and returning to the origin (i.e. if the complete outline of the data symbol 38 has been detected), the extraction of the data symbol 38 is determined to have been performed successfully. On the other hand, if the tracing cannot be started (i.e., no picture elements could be found) or completed (i.e., the outline does not make a closed loop), the tracing is =successful. An unsuccessful extraction will occur if, for example, the data symbol 38 protrudes outside the symbol reading area 36, or if the data symbol 38 is not within the symbol reading area 36 (e.g., when the magnification of zoom lens 46 is too high). If the outline is complete, then the area within the outline is the decoding area.

In step S104, the CPU 15 checks if the extraction of the symbol (i.e., the outline in the described example) has been successfully carried out. If the symbol extraction is unsuccessful (N at step S104), the unsuccessful extraction is processed as an error. For example, a warning indicating the unsuccessful extraction to the operator can be displayed using the indication unit 18.

If the extraction of the symbol is determined to have been successful (Y at step S104), the CPU 15 attempts to decode the data symbol 38 in step S105.

In step S106, the CPU 15 checks if the decoding has been carried out successfully. If the CPU 15 determines that the decoding has been performed successfully (Y at step S106), the decoded data are transmitted to the host computer 17 via the communication driver 16 at step S109, the zoom lens is reset to the minimum magnification at step S110, and the process ends.

A decoding error (i.e., unsuccessful decoding) will occur if, for example, the magnification of the zoom lens 46 is too low to properly recognize the cells comprising the data symbol 38, and appropriate decoded data cannot be obtained. If the decoding of the data symbol 38 has not been carried out successfully and appropriate decoded data are not obtained (N at step S106), the CPU 15 determines if the magnification of the zoom lens 46 is set to the maximum magnification at step S107.

If the CPU 15 determines that the magnification of the zoom lens 46 is set to the maximum magnification (Y at step S107), the maximum magnification result is processed as an error (again, a warning indicating that the decoding was unsuccessful even at the maximum magnification can be displayed using the indication unit 18).

If the CPU 15 determines that the magnification of the zoom lens 46 is not set to the maximum magnification (N at step S107), the CPU 15 instructs the zoom driving circuit 10 to drive the zoom lens 46 one step in the higher magnification direction at step S108.

The process the loops back to step S102, performing a new image capture of the symbol reading area. in this manner, the magnification of the zoom lens 46 is incrementally increased (at step S108) until the cells of the data symbol 38 are successfully decoded (i.e. appropriate decoded data is obtained) or until the maximum magnification is reached. If appropriate decoded data is obtained, the CPU 15 determines at step S106 that decoding is successful and step S109 is executed to send the decoded data. If the maximum magnification is reached without having obtained appropriate decoded data, the CPU 15 determines at step S107 that an error has occurred and proceeds with the error processing.

Thus, with the data symbol reading device 1 of the first embodiment, sincethe magnification of the zoom lens 46 is changed during the reading process to obtain an appropriate magnification at which the data symbol 38 can be read, errors in the reading of the data symbol 38 are prevented and the accuracy of the reading of the data symbol 38 is improved, regardless of the size of the data symbol 38.

Furthermore, since the magnification of the zoom lens 46 is changed automatically, the operation of the data symbol reading device 1 is simplified, and the data symbol 38 can be read more quickly and accurately.

In a second embodiment of a data symbol reading device according to the invention, a switch 14a is actuated at the maximum magnification end of the zoom lens driving, instead of the switch 14 at the minimum magnification end in the first embodiment. The first and second embodiments are similar, and only structural and circuit portions of the data symbol reading device according to the second embodiment different from the first embodiment are described hereinafter.

Again referring to Fig. 4, the data symbol reading device 1' according to the second embodiment includes a limit switch 14a. The limit switch 14a is (in this second example) a normally-open switch that is turned ON when actuated. The limit switch 14a is turned ON when the zoom lens 46 is positioned at the maximum magnification end. When the zoom lens 46 moves away from the maximum magnification end, the limit switch 14a turns OFF.

The CPU 15 monitors the condition of the limit switch 14a (i.e. ON or OFF) and determines the magnification (focal length) of the zoom lens 46 from both the condition of the limit switch 14a, and the amount and direction of driving of the stepping motor 11. That is, in the second embodiment, the CPU 15 determines that the zoom lens 46 is set to the maximum magnification when the limit switch 14a is ON. When the limit switch 14a is OFF, the CPU 15 determines the magnification of the zoom lens 46 from the number of steps by which the stepping motor 11 was driven since the limit switch 14a was turned OFF.

The general operation of the data symbol reading device 11 is similar to that of the first embodiment. The data symbol reading device 11 is activated when the operation switch 19 is turned ON. During the reading process, if the data symbol cannot be accurately decoded, the CPU 15 varies the magnification through a feedback control process. That is, the magnification of the zoom lens 46 is decreased one step at a time from the maximum magnification, until the data symbol 38 can be read.

That is, an image is first taken at the maximum magnification (narrowest angle) of the zoom lens 46 set. Image processing and decoding are then carried out, and the CPU 15 determines if appropriate decoded data have been obtained (i.e. whether or not the data symbol 38 has been read correctly). If appropriate decoded data have not been obtained, the zoom lens 46 is driven by one step in the direction of decreasing magnification and a new image is taken. The CPU 15 again performs the prescribed image processing and decoding, and determines if appropriate decoded data have been obtained. The operations are repeated until appropriate decoded data are obtained (i.e. until the data symbol 38 is read appropriately) or until the zoom lens 46 reaches the minimum magnification.

Fig. 7 is a flowchart describing the second embodiment of a data symbol reading device according to the invention.

In step S201, the CPU 15 instructs the zoom lens driving circuit 10 to drive the zoom lens 46 to the maximum magnification position (the field angle is set to the minimum field angle)-

In step S202, the CPU 15 instructs the CCD driving circuit 6 to capture an image of the symbol reading area 15. Step S202 includes the setting of an appropriate illumination level for the current magnification, the driving of the light sources 41 by the light source driving circuit 42 to the set illumination level, the intake of the image by the CCD 43, the binarization oil the analog image signals, and the writing of the image data into the memory 12.

In step S203, the CPU 15 performs a data symbol extraction process as previously described with reference to the first embodiment. In step S204, the CPU 15 attempts to decode the data symbol 38.

In step S205, the CPU 15 checks if the decoding has been carried out successfully. If the CPU 15 determines that the decoding has been performed successfully (Y at step S205), the decoded data are transmitted to the host computer 17 via the communication driver 16 at step S208, the zoom lens is reset to the maximum magnification at step S209, and the process ends.

A decoding error (i.e., unsuccessful decoding) will occur if, for example, the magnification of the zoom lens 46 is too high and the outline of the data symbol 38 cannot be properly detected (i.e., if the data symbol 38 is protruding outside the symbol reading area 36, or the data symbol 38 is not within the symbol reading area 36). if the decoding of the data symbol 38 has not been carried out successfully and appropriate decoded data are not obtained (N at step S206), the CPU 15 determines if the magnification of the zoom lens 46 is set to the minimum magnification at step S206.

If the CPU 15 determines that the magnification of the zoom lens 46 is set to the minim= magnification (Y at step S206), the minimum magnification result is processed as an error (a warning indicating that the decoding was unsuccessful even at the minimum magnification can be displayed using the indication unit 18).

If the CPU 15 determines that the magnification of the zoom lens 46 is not set to the minimum magnification (N at step S206), the CPU 15 instructs the zoom driving circuit 10 to drive the zoom lens 46 one step in the lower magnification direction at step S207.

The process the loops back to step S202, performing a new image capture of the symbol reading area. In this manner, the magnification of the zoom lens 46 is incrementally decreased (at step S207) until the cells of the data symbol 38 are successfully decoded (i.e. appropriate decoded data is obtained) or until the minimum magnification is reached. If appropriate decoded data is obtained, the CPU 15 determines at step S205 that decoding is successful and step S208 is executed to send the decoded data. If the minimum magnification is reached without having obtained appropriate decoded data, the CPU 15 determines at step S206 that an error has occurred and proceeds with the error processing.

Thus, with the data symbol reading device la of the second embodiment, as with the data symbol reading device 1 off the first embodiment described earlier, errors in the reading of the data symbol 38 are prevented and the accuracy of the reading of the data symbol 38 is improved, regardless of the size of the data symbol 38.

Furthermore, since the magnification of the zoom lens 46 is changed automatically, the operation is simplified, and the data symbol 38 can be read quickly and accurately.

Still further, with the data symbol reading device 11, since reading is performed at a magnification of the zoom lens 46 which is the largest magnification at which the data symbol 38 is within the symbol reading area 36, the accuracy of the reading of the data symbol 38 will be improved further.

Although the data symbol reading device of the invention has been described by way of the illustrated embodiments, the embodiments may undergo various modifications without departing from the scope of the invention.

For example, ambient light may be used to illuminate the symbol reading area 36. in this case, the light sources may be omitted or the light sources may be used to compensate for a lack of ambient illumination. The data symbol reading device 1 may be designed with one or more openings or transparent windows on the sides of the housing 3, so that the position of the data symbol 38 can be checked and so that ambient light may enter. In particular, if the data symbol 38 is positioned closer to the center of the symbol reading area 36, the data symbol 38 may be magnified more, and the accuracy of the reading of the data symbol 38 is further improved.

Claims

1. A data symbol reading device comprising: an imaging element for receiving images; a variable magnification optical system for forming an image of a symbol reading area on said imaging element; driving means for varying a magnification of said variable magnification optical system; decoding means for decoding an image of a data symbol within said image of said symbol reading area received by said imaging element; evaluating means for evaluating if said decoding means successfully decodes said image of the data symbol, and drive control means associated with said evaluating means, for controlling said driving means to vary said magnification to a magnification where said decoding means can successfully decode said image of the data symbol.

2. A data symbol reading device according to claim 1, wherein said drive control means initially controls said driving means to set said magnification to a minimum magnification of said variable magnification optical system, and wherein said drive control means controls said driving means to increase said magnification until said evaluating means evaluates that said decoding means can successfully decode said image of the data symbol.

3. A data symbol reading device according to claim 1, wherein said drive control means initially controls said driving means to set said magnification to a maximum magnification of said variable magnification optical system, and wherein said drive control means controls said driving means to decrease said magnification until said evaluating means evaluates that said decoding means can successfully decode said image of the data symbol.

4. A data symbol reading device according to any preceding claim further comprising:

light source for illuminating the symbol reading area; and light source driver for driving said light source at a settable illumination level.

5. A data symbol reading device according to claim 4, wherein said drive control means further controls said light source driver to drive said light source at an illumination level set according to said magnification of said variable magnification optical system.

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6. A data symbol reading device comprising: an imaging element for capturing an image; a variable magnification optical system for forming an image of a symbol reading area on said imaging element; magnification varying means for varying a magnification of said variable magnification optical system; decoding means for decoding an image of a data symbol within said image of the symbol reading area; evaluating means for evaluating if said image of the data symbol within the symbol reading area is successfully decoded; control means for setting said magnification varying means to an initial minimum magnification, and for controlling said magnification varying means to" increase said magnification by a predetermined magnification step size until said evaluating means evaluates that said image of the data symbol is can be successfully decoded.

7. A data symbol reading device according to claim 6, wherein said magnification varying means includes a switch for detecting said minimum magnification of said variable magnification optical system.

8. A data symbol reading device according to claim 6 or 7, wherein said magnification varying means includes a stepping device for varying said magnification of said variable magnification optical system in a stepwise fashion.

9. A data symbol reading device comprising: an imaging element for capturing an image; a variable magnification optical system for forming an image of a symbol reading area on said imaging element; magnification varying means for varying a magnification of said variable magnification optical system; decoding means for decoding an image of a data symbol within said image of the symbol reading area; evaluating means for evaluating if said image of the data symbol within the symbol reading area is successfully decoded; control means for setting said magnification varying means to an initial maximum. magnification, and for controlling said magnification varying means to decrease said magnification by a predetermined magnification step size until said evaluating means evaluates that said image of the data symbol can be successfully decoded.

10. A data symbol reading device according to claim 9, wherein said magnification varying means includes a switch for detecting said maximum magnification of said - 34 variable magnification optical system.

11. A data symbol reading device according to claim 9 or 10, wherein said magnification varying means includes a stepping device for varying said magnification of said variable magnification optical system in a stepwise fashion.

12. A data symbol reading device comprising: a CCD imaging element for receiving images; a variable magnification optical system including a zoom lens, for forming an image of a symbol reading area on said CCD imaging element; a zoom lens drive for varying a magnification of said zoom lens; and a control circuit connected to said zoom lens drive and said CCD imaging element, said control circuit including: a decoding device for decoding an image of a data symbol within said image of said symbol reading area received by said CCD imaging element; an evaluating device for evaluating if said decoding device successfully decodes said image of the data symbol, wherein said control circuit controls said zoom lens drive to vary said magnification of said zoom lens until said evaluating device successfully evaluates that said decoding device can successfully decode said image of the data symbol.

13. A data symbol reading device according to claim 12, wherein said control circuit initially controls said zoom lens drive to set said magnification to a minimum magnification of said zoom lens, and wherein said control circuit controls said zoom lens drive to increase said magnification until said evaluating device evaluates that said decoding device can successfully decode said image of the data symbol..

14. A data symbol reading device according to claim 12, wherein said control circuit initially controls said zoom lens drive to set said magnification to a maximum magnification of said zoom lens, and wherein said control circuit controls said zoom lens drive to decrease said magnification until said evaluating device evaluates that said decoding device can successfully decode said image of the data symbol.

15. A data symbol reading device comprising: an imaging element for receiving images; a magnification optical system for forming an image of a symbol reading area on said imaging element; and means for varying a magnification of said magnification optical system.

16. A data symbol reading device substantially as herein described with reference to the accompanying drawings.