FR2736180A1 - DEVICE FOR READING DATA SYMBOLS - Google Patents

Abstract

Data symbol reading device (1, 1 '), wherein the image of a data symbol (38) in a symbol reading area (36) is formed on an image forming member (43) by means of an optical system, which includes a zoom lens system, a zoom lens control circuit, a stepping motor (11), and a limit switch (14, 14a). During reading processing, if the reading of the data symbol is not successful, the magnification of the zoom lens (46) is increased by one step from the minimum magnification end to 'so that the data symbol can be successfully read (until an appropriately decoded data is obtained). As a variant, you can initially set the magnification of the zoom lens to maximum magnification and, if the reading of the data symbol is not successful, then decrease it by one step at a time from the end of maximum magnification.

Description

DEVICE FOR READING DATA SYMBOLS

  The present invention relates to a device for reading data symbols for reading information coded as symbols for

two-dimensional data.

  Point of Sale (POS) systems generally use some form of barcode system to read and identify product codes that are marked on each product. These barcode systems allow fast and efficient entry of data into a data management system. However, conventional bar codes may contain only a limited amount of information since the data is

  stored in a one-dimensional arrangement of bars.

  To solve this problem, symbols have been developed as a means of containing more information, with a mosaic or checkerboard pattern, in which a black and white pattern is arranged in two dimensions. Data symbol reading devices can be broadly classified to read two-dimensional data symbols into two groups: those in which an image forming element (area sensor) is used to read the data symbol pattern simultaneously in two dimensions; and those in which the reader and the data symbol move relative to each other in a direction perpendicular to the main scan direction to perform an auxiliary scan (secondary scan), and in which a

  rectilinear sensor performs a main scan of the two-dimensional symbol.

  Reading devices that use an imaging element (a surface sensor) do not require relative movement between the reading module and the data symbol, and can read the

symbols in a shorter time.

  However, with reading devices that use an imaging element (a surface sensor), if a relatively small data symbol is used, the symbol is difficult to read and the data pattern difficult to decode. In particular, since the individual cells of the two-dimensional pattern are small, it may not be possible to correctly recognize these cells and errors in reading data symbols

  may occur, causing unacceptable reading delays.

  It is therefore an objective of the present invention to provide an improved data symbol reading device in which

  a data symbol is magnified automatically during reading.

  The present invention relates to a device for reading data symbols which satisfies this need. According to one aspect of the present invention, a data symbol reading device comprises an image forming element for receiving images, and a variable magnification optical system for forming an image of a symbol reading area on the image. imaging element. A driving device modifies the magnification of the variable magnification optical system, and a decoding device decodes an image of the data symbol inside the image of the symbol reading area received by the training element d 'picture. An evaluation device evaluates whether the decoding device has successfully decoded the image of the data symbol, and a drive control device, associated with the evaluation device, controls the drive device to vary the magnification towards a magnification where the decoding device successfully decodes the image of the

data symbol.

  In this way, if the data symbol cannot be read, 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 controller initially controls the drive to adjust the magnification to minimum magnification of the variable magnification optical system. Then, the drive controller controls the drive device to increase the magnification until the evaluation device evaluates that the decoding device

  successfully decoded the image symbol image.

  This embodiment makes it possible to magnify data symbols

  relatively small until the symbol is readable.

  In another embodiment, the drive controller initially controls the drive device to adjust the magnification to maximum magnification of the variable magnification optical system, and the drive controller controls the drive device to decrease the magnification until the evaluation device evaluates that the decoding device

  decodes the image of the data symbol successfully.

  In this embodiment, the symbol at the highest magnification is read for which the symbol is entirely inside the symbol reading zone, allowing good precision and decoding.

specific.

  Preferably, the data symbol reading device according to this aspect of the present invention further comprises a light source for illuminating the symbol reading area and a light source driving circuit for driving the source of light at an adjustable lighting level. In this case, the drive controller further controls the light source driver circuit to drive the light source at a lighting level set in accordance with the magnification of the variable magnification optical system. This allows for

  correct exposures even if the magnification varies.

  According to another aspect of the present invention, a data symbol reading device comprises: an image forming element for capturing an image and a variable magnification optical system for forming an image of a symbol reading area on the imaging element. A variable magnification device changes the 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 evaluation device evaluates whether the image symbol of data within the symbol reading area is successfully decoded. A controller sets the magnification modifier to an initial minimum magnification, and controls the magnification modifier to increase the magnification by the value of a predetermined magnification step until the evaluator evaluates that the image of the data symbol has

been successfully decoded.

  Therefore, if a relatively small data symbol is unreadable, the data symbol reader can automatically increase the magnification of the image until the data symbol

data becomes readable.

  In this case, the magnification modification device preferably comprises a switch for detecting the minimum magnification of the optical system with variable magnification. In addition, the magnification modification device preferably includes a step-by-step device for varying the magnification of the magnification optical system.

variable step by step.

  According to yet another aspect of the present invention, a data symbol reading device comprises: an image forming element for capturing an image and a variable magnification optical system for forming an image of a symbol reading area on the imaging element. A variable magnification device changes the 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 evaluation device evaluates whether the image symbol of data within the symbol reading area is successfully decoded. A controller sets the magnification modifier to an initial maximum magnification, and controls the magnification modifier to decrease the magnification by the value of a predetermined magnification step until the evaluator evaluates that the image of

  data symbol has been successfully decoded.

  Therefore, if a data symbol is unreadable due to a high magnification level, and exceeds outside the symbol reading area s, the data symbol reading device can automatically decrease the magnification of the data symbol. until the data symbol becomes readable. We therefore read the symbol at the highest magnification at which the symbol is completely inside the reading area of

  symbol, thereby improving accuracy.

  In this case, the magnification modification device preferably comprises a switch for detecting the maximum magnification of the optical system with variable magnification. In addition, the magnification modification device preferably includes a step-by-step device for varying the magnification of the magnification optical system.

variable step by step.

  According to yet another aspect of the present invention, a data symbol reading device comprises: a CCD image forming element for receiving images and a variable magnification optical system, including a zoom lens, for forming a picture

  a symbol reading area on the CCD image forming member.

  A zoom lens drive changes the 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 which decodes an image of a data symbol within the image of the symbol reading area received by the CCD imaging element, and a device evaluation which evaluates whether the decoding device successfully decodes the image of the data symbol. The control circuit controls the zoom lens drive to change the magnification of the zoom lens until the evaluation device successfully evaluates that the decoding device has

  successfully decoded the data symbol image.

  The characteristics and advantages of the invention will also emerge

  of the description which will follow by way of example with reference to the drawings

  attached, in which: FIG. 1 is a perspective view of a device for reading data symbols according to the invention; Figure 2 is a sectional side view of the data symbol reading device shown in Figure 1, taken along line 1-11 of Figure 1; Figure 3 is a bottom view of the head portion of the symbol reading device shown in Figure 1; Figure 4 is a block diagram showing a circuit arrangement for the data symbol reader shown in Figure 1; FIGS. 5A and 5B are diagrams showing the relationship between the magnification of a zoom lens and a data reading area; FIG. 6 is a flowchart showing the control operations of a first embodiment of a device for reading data symbols according to the invention; and FIG. 7 is a flowchart showing the control operations of a second embodiment of a reading device

  data symbols according to the invention.

  FIG. 1 is a perspective view of a device for reading data symbols 1 according to the invention. FIG. 2 is a side view in section of the data symbol reading device 1 shown in FIG. 1, FIG. 3 is a bottom view of a head portion 22 of the data symbol reading device 1 shown in FIG. Figure 1, and Figure 4 is a block diagram of a circuit arrangement of the reading device.

  data symbols 1 shown in Figure 1.

  As shown in FIGS. 1 to 4, the device for reading data symbols 1 comprises a housing 2 with a handle part 21, a head part 22 and a housing 3. The handle part 21 is elongated so that it can be grasped by hand, and it houses a control circuit 50. The head part 22 is formed at the front end of the handle part 21 by creating an L-shape and it houses a reading module 4. The housing 3 is formed at the end of the head portion 22, extending from the reading module 4 in the direction of a symbol reading area 36. An opening

  front 31 is formed at the front end of the housing 3.

  The exterior of the housing 2 is provided with an operating switch 19, and an indication section 18. The operating switch 19 is used to activate the reading function of the symbol reading device data 1, and it is arranged in an easily accessible position on one side of the handle part 21. The indication section 18 provides information to the operator and is in an easily visible position on the upper face from the end of the handle part 21. In this embodiment the indication module 18 is an LCD (liquid crystal display), however, any suitable indication device could be used, such as a transmitting diode light (LED) or a group of LEDs. The reading module 4 comprises two light sources 41 (for example, LEDs (light-emitting diodes), light valves or halogen lamps), a charge-coupled device (CCD) 43 as an element of image detection, an optical system 44, to form an image on the CCD, and a support element 48. The support element 48 constitutes

  a mount for the other components of the reading module 4.

  The optical system 44 forms an image on the CCD 43 from the light reflected by the symbol reading area 36. The optical system 44 comprises a mirror 45 for deflecting the light path 47 from the light reflected by the reading area of symbol 36, and a zoom lens (a group of lenses) 46 causes the formation of an image by light

  reflected by the mirror 45 on the CCD 43.

  The two light sources 41 are placed in a substantially symmetrical manner with respect to the light path 47, at the lower end of the support element 48. The light sources 41 are connected to a source driving circuit. light 42 (shown in Figure 4). A diffusion plate (not shown) can be installed on the light emission side of the light sources 41, to make the luminance more uniform in line with the symbol reading area 36. As a variant, a diffusion part can be formed in frosting part

  a transparent plate 7 (described above).

  CCD 43 has many photodiode picture elements arranged in an array. Each of the picture elements accumulates an electric charge corresponding to the quantity of light received, and the CCD 43 is controlled to sequentially transfer these charges. The charges

  transferred are image signals (analog) that can be read.

  The symbol reading area 36 is formed on a reference plane 37, the reference plane 37 representing the surface on which the data symbol 38 is placed. The symbol reading area 36 is a predetermined area illuminated by the sources of light 41 and readable by the CCD 43. The light reflected by the symbol reading area 36 is sent to the CCD 43. Although the symbol reading area 36 varies according to the magnification and the angle of field of the zoom lens 46, the symbol reading area 36 at minimum magnification and maximum field angle substantially coincides with, or includes, the front aperture 31

housing 3.

  The housing 3 serves as a guide for keeping the reading module 4 at a predetermined distance (an optical path length) relative to the symbol reading zone 36. In other words, the housing 3 fixes a distance to form ( 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 lighting light coming from the sources of light 41 and the light path 47 of the light reflected by the symbol reading area 36. The housing 3 has a section

  transverse rectangular parallel to the symbol reading area 36.

  A transparent plate 7 is installed inside the housing 3 perpendicular to the light path 47, on the inside of the front opening 31. The transparent plate 7 separates the internal space of the housing 3 and the head part 22 into a space 4a on the side of the front opening 31 and a space 4b on the side of the reading module 4. The transparent plate can be made of 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 described above, part of the transparent plate may possibly

  serve as a diffuser for light sources 41.

  As shown in FIG. 3, in this example, the data symbol 38 is includes a checkerboard matrix pattern of black and white (or alternately black and transparent) cells, the matrix being at least 2 by 2, but, preferably considerably larger. Each cell represents 0 or 1 binary, and information is thus coded in the cell pattern. However, the data symbol 38 is not limited to the arrangement shown so that it is readable by the data symbol reading device. In addition, it is preferable that there are no other marks capable of forming images, other than the data symbol 38, within a predetermined area equal to or greater than the

symbol reading area 36.

  As shown in Figure 4, the control circuit 50 comprises a signal processing circuit 5, a zoom lens drive circuit 10, a stepper motor 1 1, the light source drive circuit 42, a transmission drive circuit 16, an implementation switch circuit 13 for the implementation switch 19, a limitation switch 14, and an indication module 18. The energy for the data symbol reading device can be supplied to the control circuit using batteries internal to device 1, or from a source

  external as a central computer 17.

  The signal processing circuit 5 includes a CCD driving circuit 6, an amplification circuit 8, a binary shaping circuit 9, a memory 12, and a central processing unit (CPU) 15, as a means control. The CCD driver circuit 6 drives the CCD, and produces and outputs 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 sent by the CCD driver to the CPU 1 5.

  The CPU 15 is also connected to the zoom lens drive circuit 10, the light source driver 42, the transmission driver 16, the power switch circuit

  work 1 3, to the limit switch 14, and to the indication module 18.

  The zoom lens drive circuit 10, the zoom lens 46, and the stepper motor 11 are part of a drive means for varying

  the magnification of the optical system (at variable magnification) 44.

  The zoom lens 46 (the lens group) is a conventional mechanically compensated zoom lens arrangement, using a cam ring to move the lens elements to (i) change the focal length and (ii) compensate for the offset image, that is to say, defocus. The zoom lens drive circuit 10 is connected to the stepping motor 11 and controls the stepping motor 11 to drive the zoom lens 46 (by means of the cam ring, not shown) between a minimum focal length (minimum magnification, at the wide-angle end) and a maximum focal distance (maximum magnification). The stepper motor 1 1 turns step by step forwards or backwards and, for each instruction received, drives the objective 46 by a unitary step in the direction towards the end of minimum magnification or in the direction towards maximum magnification tip. The predetermined unit step value is determined by dividing, equally, the distance between the minimum magnification end and the maximum magnification end, in N equal parts (N being at least

  minus 2). For example, the N equal parts can be 20 equal parts.

  The limit switch 14 is (in this example) a normally open switch which closes when operated. The limit switch 14 closes when the zoom lens 46 is placed at the minimum magnification end. The limit switch 14 opens when the zoom lens 46 deviates from the minimum magnification end.

  CPU 15 monitors the status of limit switch 14 (i.e.

  say, whether it is closed or open) and determines the magnification (focal length) of the zoom lens 46, for the two states of the limit switch 14, and the importance and direction of the drive of the stepper motor 11. That is, in the first embodiment, the CPU 15 determines that the zoom lens 46 is set to minimum magnification when the limit switch 14 is closed. When the limit switch 14 is open, the CPU 15 determines the magnification of the zoom lens 46 from the number of steps in which the drive motor 11 has been

  driven since the limit switch 14 was opened.

  The magnification of the zoom lens 46 is used by the CPU 15 to control the zoom lens driver circuit 10, to adjust the amount of light emitted by the light sources 41, and it is also used in the

decoding processing.

  Figure 5A is a diagram showing a symbol reading area 91 when the magnification of the zoom lens 46 is set to the minimum magnification, and Figure 5B is a diagram showing a symbol reading area 192 when the magnification of the zoom lens 46 is

  larger than the minimum magnification.

  As shown in FIG. 5A, if a relatively small data symbol 38 is read, and if the reading is carried out with the minimum magnification, the data symbol 38 (in particular, the individual cells which constitute the data symbol 38) is small compared to the symbol reading area 191, and the reading and decoding accuracy of the

  data symbol 38 is not optimal.

  However, as shown in Figure 5B, if we change the plane of the zoom lens 46 to a greater focal length and read at a higher magnification, we magnify the data symbol 38 at a more readable size (compared to the symbol reading area 1 92), and this improves the reading and decoding accuracy of the

data symbol 38.

  The device for reading data symbols 1 is activated when the operating switch 19 is closed. The CPU 15 first orders the light source driver 42 to switch on the light sources 41. The light emitted by the light sources 41 illuminates the symbol reading area 36, and the light reflected by 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 driver 42 to adjust the amount of light emitted as a function of the current magnification level. That is, the CPU 15 determines the magnification of the zoom lens 46 and controls the light source driver 42 to adjust the amount and duration of the light emitted.

  by light sources 41 for appropriate exposure.

  The CPU 15 also activates the CCD driver 6 when the operating switch is closed 19. The CCD driver 6 outputs a CCD driver to the CCD 43 horizontal and a vertical CCD attack pulse to control the accumulation and

  charge transfer to CCD 43.

  Amplification circuit 8 amplifies the image signals (analog) 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 part (from analog to digital) of the amplification circuit 8 and they then enter the

binary 9.

  The binary formatting circuit 9 compares the digital image signals for each picture element with a predetermined threshold data, and sets a value of "1" or "0", accordingly. For example, a data value in binary form of "1" corresponds to a black part of the data symbol 38 while a value of "O" corresponds to a white part. The binary data (image data) output from the binary circuit 9 are stored at determined addresses of the memory 12 by means of an address counter included in the CPU 15. This counter is attacked address by composite clock signals (described above)

  from the CCD 6 driver circuit.

  The CPU 15 then accesses the memory 12 and performs the necessary image processing on the image data, for example, an image inversion, a symbol extraction (the extraction of the only information that concerns the symbol of data 38), fading correction, rotation, and the like. The data in the memory 12 are read sequentially as a function of the addresses indicated by the address counter mentioned above (the reading order can be reversed with respect to the order of storage in the memory 12). In addition, the CPU 15 decodes the image data according to the particular system used to code the

data symbol 38.

  During this read processing, if the data symbol cannot be decoded precisely, the CPU 15 changes the magnification by means of a feedback control process. That is, the magnification of the zoom lens 46 increases by one step at a time from the minimum magnification until the data symbol 38 can be read. treatments, we first take a first image

  at minimum magnification (at the largest angle) of the zoom lens 46.

  Image processing and decoding are then carried out, and the CPU 15 determines whether an appropriate decoded data item has been obtained (that is, whether the symbol has been read correctly or not). data 38). If the appropriate decoded data has not been obtained, the zoom lens 46 is taken one step in the direction of the increase in magnification and a new image is taken. The CPU 15 again performs the prescribed image processing and decoding, and determines whether an appropriate decoded data has been obtained. The operations are repeated until an appropriate decoded data item is obtained (i.e., until the data symbol 38 is read appropriately) or until the zoom lens 46 reaches the

maximum magnification.

  When an appropriate decoded datum has been obtained, the decoded datum is entered via the transmission driver 16 into the central computer 17, which can be, for example, a personal computer or a work station. . The central computer 17 stores, tabs,

etc., the decoded data.

  Figure 6 is a flowchart showing the first mode of

  realization of a device for reading data symbols according to the invention.

  In step S 101, the CPU 15 gives the zoom lens drive circuit 10 the order to drive the zoom lens 46 to the minimum magnification position (to adjust the angle of view at the angle of view

maximum).

  In step S 102, the CPU 15 gives the CCD driver 6 the order to capture an image of the symbol reading area 36. Step S 102 comprises the adjustment of a level d lighting suitable for current magnification, the attack of light sources 41 by the drive circuit of light sources 42 at the fixed lighting level, the entry of the image by the CCD 43, the shaping binary image signals

  analog, and writing image data to memory 1 2.

  In step S 103, the CPU 15 performs a data symbol extraction processing. For example, in the extraction processing, 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). We find the outline of the data symbol 38 and we try to follow it. For example, if tracking the image data corresponding to the image elements of the outline of the data symbol 38 results in a closed loop starting at 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 carried out successfully. On the other hand, if the tracking cannot be started (i.e., if no image element can be found) or finished (i.e., if the outline does not not a closed loop), tracking failed. The extraction will fail if, for example, the data symbol 38 protrudes outside the symbol reading area 36, or if the data symbol 38 is not inside the symbol reading area 36 (for example, when the magnification of the zoom lens 46 is too high). If the outline is complete, then the area inside

  of the contour is in the decoding area.

  In step S 104, the CPU 15 checks whether the extraction of the symbol (i.e.

  say, the outline in the example described) has been successfully completed. If the symbol extraction failed (NO in step S 104), the failed extraction is treated as an error. For example, a warning to the operator, indicating that the extraction has failed, may be displayed in

  using the indication module 18.

  If it has been determined that the extraction of the symbol has been carried out successfully (YES in step S 104), the CPU 15 attempts to decode the symbol of

data 38, in step S 105.

  In step S 106, the CPU 15 checks whether the decoding has been carried out successfully. If the CPU 15 determines that the decoding has been carried out successfully (YES in step S 106), the decoded data is transmitted to the central computer 17 via the transmission drive circuit 16, at 1 step S 109, the zoom lens is brought back to the minimum magnification at

  step S 110, and the processing ends.

  A decoding error (i.e., unsuccessful decoding) will occur if, for example, the magnification of the zoom lens 46 is too low to correctly recognize the cells making up the data symbol 38, and it will not be possible to obtain suitable decoded data. If the decoding of the symbol 38 has not been carried out successfully and if a suitable decoded data has not been obtained (NO at step S 106), the CPU 15 determines whether the magnification of the objective at zoom 46 is set to

  maximum magnification, in step S 107.

  If the CPU 15 determines that the magnification of the zoom lens 46 is set to maximum magnification (YES in step S 107), the result at maximum magnification is treated as an error, (again, it can be displayed using the indication module 18 a warning indicating that

  decoding was not successful even at maximum magnification).

  If the CPU 15 determines that the magnification of the zoom lens 46 is not set to the maximum magnification (NO in step S 107), the CPU 15, in step S 108, gives the attack 10, the order to train the target to

  zoom 46 by one step in the direction of higher magnification.

  The processing loops back to step S 102, by performing a new image capture of the symbol reading area. In this way, the magnification of the zoom lens 46 increases incrementally (in step S 108) until the cells of the data symbol 38 are successfully decoded (i.e. we obtain a suitable decoded data), or until we reach the maximum magnification. If suitable decoded data is obtained, the CPU 15 determines, in step S 106, that the decoding has been successful, and step S 109 is executed to send the decoded data. If the maximum magnification is reached without having obtained suitable decoded data, the CPU 15 determines, in step

  S 107, that an error has occurred, and performs error processing.

  Thus, with the device for reading data symbols 1 of the first embodiment, since the magnification of the zoom lens 46 is modified during the reading processing to obtain an appropriate magnification with which the data symbol 38 can be read. , errors in reading the data symbol 38 are avoided and the accuracy of reading the data symbol 38 is improved, whatever the size of the

data symbol 38.

  In addition, since the magnification of the zoom lens 46 varies automatically, the implementation of the device for reading data symbols 1 is simplified, and it is possible to read more quickly and more

specifies the data symbol 38.

  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 drive, instead of the switch 14 at the minimum magnification end in the first embodiment. The first and second embodiments are similar, and we will describe below only the structural and circuit parts of the data symbol reading device of the second embodiment which are different from the first embodiment.

production.

  Referring again to FIG. 4, the device for reading data symbols 1 ′ according to the second embodiment comprises a limitation switch 14a. The limit switch 14a is (in this second example) a normally open switch which closes when it is operated. The limit switch 14a closes when the zoom lens 46 is placed at the maximum magnification end. The limit switch 14a opens when the zoom lens 46 deviates from the end of the

maximum magnification.

  The CPU 15 monitors the status of the limit switch 14a (i.e.

  say, if it is closed or open) and determines the magnification (the focal length) of the zoom lens 46, for the two states of the limitation switch 14a, and the importance and the direction of the drive of the stepper motor 11. That is, in the second embodiment, the CPU 15 determines that the zoom lens 46 is set to maximum magnification when the limit switch 14a is closed. When the limit switch 14a is open, the CPU 15 determines the magnification of the zoom lens 46 from the number of steps of which the drive motor 11 has been

  driven since the limit switch 14a was opened.

  The magnification of the zoom lens 46 is used by the CPU 15 to control the zoom lens driver circuit 10, to adjust the amount of light emitted by the light sources 41, and it is also used in the

decoding processing.

  The general operation of the data symbol reading device 1 ′ is similar to that of the first embodiment. The data symbol reading device 1 ′ is actuated when the operating switch 19 is closed. During the reading processing, if the data symbol cannot be decoded precisely, the CPU 15

  changes the magnification using a reverse order process

  reaction. That is, the magnification of the zoom lens 46 decreases one step at a time from the maximum magnification until

  can read data symbol 38.

  That is to say that we first take a first image at maximum magnification (at the narrowest angle) of the zoom lens 46. We then carry out image processing and decoding, and the CPU 15 determines whether an appropriate decoded data item has been obtained (i.e., whether or not the data symbol 38 has been read correctly). If the appropriate decoded data has not been obtained, the zoom lens 46 is taken by one step in

  the direction of the decrease in magnification and we take a new image.

  CPU 15 performs image processing and decoding again

  prescribed, and it determines whether an appropriate decoded data has been obtained.

  The operations are repeated until an appropriate decoded data item is obtained (i.e., until the data symbol 38 is read appropriately) or until the zoom lens 46 reaches the

minimum magnification.

  When an appropriate decoded datum has been obtained, the decoded datum is entered via the transmission driver 16 into the central computer 17, which can be, for example, a personal computer or a work station. . The central computer 17 stores, tabs,

etc., the decoded data.

  Figure 7 is a flowchart showing the second mode of

  realization of a device for reading data symbols according to the invention.

  In step S 201, the CPU 15 gives the zoom lens drive circuit 10 the order to drive the zoom lens 46 to the position of maximum magnification (to adjust the angle of view at the minimum field of view). In step S 202, the CPU 15 gives the CCD driver 6 the order to capture an image of the symbol reading area 36. Step S 202 comprises the adjustment of a level d lighting suitable for current magnification, the attack of light sources 41 by the drive circuit of light sources 42 at the fixed lighting level, the entry of the image by the CCD 43, the shaping binary image signals

  analog, and writing image data to memory 1 2.

  In step S 203, the CPU 15 performs a data symbol extraction processing as described above with reference to the first embodiment. In step S 204, the CPU 15 attempts to decode the symbol

data 38.

  In step S 205, the CPU 15 checks whether the decoding has been carried out successfully. If the CPU 15 determines that the decoding has been carried out successfully (YES in step S 205), the decoded data is transmitted to the central computer 17 via the transmission driver circuit 16, at 1 step S 208, the zoom lens is brought back to the maximum magnification at

  step S 209, and the processing ends.

  Decoding error (i.e. unsuccessful decoding) will occur if, for example, the magnification of the zoom lens 46 is too

  strong to correctly detect the outline of data symbol 38 (i.e.

  that is, if the data symbol 38 protrudes outside of the symbol reading area 36, or if the data symbol 38 is not inside the symbol reading area 36). If the decoding of the symbol 38 has not been carried out successfully and if a suitable decoded data has not been obtained (NO at step S 206), the CPU 15 determines whether the magnification

  of the zoom lens 46 is set to the minimum magnification in step S 206.

  If the CPU 15 determines that the magnification of the zoom lens 46 is set to the minimum magnification (YES in step S 206), the result at the minimum magnification is treated as an error, (it can be displayed using the module d 'indication 18 a warning that the

  decoding was not successful even at minimum magnification).

  If the CPU 15 determines that the magnification of the zoom lens 46 is not set to the minimum magnification (NO in step S 206), the CPU 15, in step S 207, gives the attack 10, the order to train the target to

  zoom 46 by one step in the direction of lower magnification.

  The processing loops back to step S 202, by performing a new image capture of the symbol reading area. In this way, the magnification of the zoom lens 46 decreases incrementally (in step S 207) until the cells of the data symbol 38 are successfully decoded (i.e. a suitable decoded data is obtained), or until the minimum magnification is reached. If suitable decoded data is obtained, the CPU 15 determines, in step S 208, that the decoding has been successful, and step S 208 is executed to send the decoded data. If the minimum magnification is reached without having obtained suitable decoded data, the CPU 15 determines, in step

  S 206, that an error has occurred, and performs error processing.

  Thus, with the data symbol reading device 1 ′ of the second embodiment, as with the data symbol reading device 1 of the first embodiment described above, errors in reading the data symbol 38 are avoided and the accuracy of reading the data symbol 38 is improved, whatever the size of the

data symbol 38.

  In addition, since the magnification of the zoom lens 46 varies automatically, the implementation is simplified, and one can read

  quickly and accurately the data symbol 38.

  Furthermore, with the device for reading data symbols 1 ′, since the reading is carried out at a magnification of the zoom lens 46 which is the greatest magnification at which the data symbol 38 is found at inside the symbol reading area 36, we will further improve

  the accuracy of reading the data symbol 38.

  Although the device for reading data symbols of the invention has been described by means of the embodiments shown, the embodiments can undergo various modifications without going out of the mind or

the scope of the invention.

  For example, ambient light can be used to illuminate the symbol reading area 36. In this case, the light sources can be suppressed or the light sources can be used to compensate for a lack of ambient lighting. The device for reading data symbols i can be designed with one or more transparent openings or windows on the sides of the housing 3, so that the

  position of data symbols 38 and that ambient light can enter.

  In particular, if the data symbol 38 is placed closer to the center of the symbol reading area 36, the data symbol 38 can be magnified further, and the accuracy of reading the symbol of the symbol is further improved.

given 38.

Claims (14)

  1. Device for reading data symbols (1, 1 ') comprising: an image-forming element (43) for receiving images, characterized in that it further comprises: an optical system with variable magnification (44 ) for forming an image of a symbol reading area (36) on said image forming member (43); drive means (11, 14, 15) for changing the magnification of said variable magnification optical system (44); decoding means (15) for decoding an image of the data symbol (38) within the image of said symbol reading area (36) received by said image forming element (43) means evaluation (15) to evaluate whether said decoding device (15) has successfully decoded said image of said data symbol (38); and drive control means (10, 15), associated with said evaluation means (1 5), for controlling said drive means (11, 1 4, 15) to vary said magnification to a magnification o said decoding means (15) successfully decodes said image of said symbol of given (38).   2. Device for reading data symbols according to claim 1, characterized: in that said drive control means (10, 15) initially controls said drive means (11, 14, 15) to adjust said magnification to a minimum magnification of said variable magnification optical system (44); and in that said drive control means (10, 15) controls said drive means (11, 14, 15) to increase said magnification until said evaluation means (15) evaluates that said means decoding (15) decoded said image of said data symbol (38) successfully.   3. Device for reading data symbols according to claim 1, characterized: in that said drive control means (10, 15) initially controls said drive means (11, 14, 15) to adjust said magnification to maximum magnification of said variable magnification optical system (44); and in that said drive control means (10, 15) controls said drive means (11, 14, 15) to decrease said magnification until said evaluation means (1 5) evaluates that said decoding means (15) decoded said image of said data symbol (38) successfully.   4. Device for reading data symbols according to claim 1, characterized in that it further comprises: a light source (41) for lighting said symbol reading area (36); and a light source driver (42) for driving said light source   light source (41) at an adjustable lighting level.   5. Device for reading data symbols according to claim 4, characterized in that said drive control means (10, 15) controls, in addition, said light source driving circuit (42) to drive said light source (41) at a lighting level adjusted according to said magnification of said system   variable magnification optics (44).   6. Device for reading data symbols (1) comprising an image forming element (43) for capturing an image characterized in that it further comprises: a variable magnification optical system (44) for forming a image of a symbol reading area (36) on said image forming member (43); a magnification modification means (1 1, 14, 15) for modifying the magnification of said variable magnification optical system (44); decoding means (15) for decoding an image of the data symbol (38) within the image of said symbol reading area (36); evaluation means (15) for evaluating whether said image of said data symbol (38) within said symbol reading area (36) has been successfully decoded; and control means (50) for setting said magnification modification means (11, 14, 15) to an initial minimum magnification, and for controlling said magnification modification means (11, 14, 15) for increasing said magnification the value of a predetermined magnification step until said evaluation means (1 5) evaluates that said   image of said data symbol (38) has been successfully decoded.   7. Device for reading data symbols according to claim 6, characterized in that said magnification modification means (11, 14, 15) comprises a switch (14) for detecting said   minimum magnification of said variable magnification optical system (44).   8. Device for reading data symbols according to claim 6, characterized in that said magnification modification means (11, 14, 15) comprises a step-by-step device (11) for varying said magnification of said optical system with magnification. variable (44) in a step-by-step manner.   9. Device for reading data symbols (1 ′) comprising an image forming element (43) for capturing an image characterized in that it further comprises: a variable magnification optical system (44) for forming an image of a symbol reading area (36) on said image forming member (43); magnification modifying means (11, 14a, 15) for modifying the magnification of said variable magnification optical system (44); decoding means (15) for decoding an image of the data symbol (38) within the image of said symbol reading area (36); evaluation means (15) for evaluating whether said image of said data symbol (38) within said symbol reading area (36) has been successfully decoded; and control means (50) for adjusting said magnification modification means (11, 14a, 15) to an initial maximum magnification, and for controlling said magnification modification means (11, 14a, 15) for decreasing said magnification of the value of a predetermined magnification step until said evaluation means (15) evaluates that said   image of said data symbol (38) has been successfully decoded.   10. Device for reading data symbols according to claim 9, characterized in that said magnification modification means (11, 14a, 15) comprises a switch (14a) for detecting said maximum magnification of said optical system with variable magnification (44).   11. Device for reading data symbols according to claim 9, characterized in that said magnification modification means (11, 1 4a, 15) comprises a step-by-step device (1 1) for varying said magnification of said optical system with variable magnification (44) in a step-by-step manner.   12. A device for reading data symbols (1, 1 ') comprising: a CCD image forming element (charge coupled device) (43) for receiving images; characterized in that it further comprises a variable magnification optical system (44), including a zoom lens (46), for forming an image of a symbol reading area (36) on said lens forming element CCD image (43); a zoom lens drive (11, 14, 15) for changing the magnification of said zoom lens (46); and a control circuit (50) connected to said zoom lens drive and said CCD imaging element (43), said control circuit (50) comprising: a decoding device (15) which decodes an image a data symbol (38) within said image of said symbol reading area (36) received by said CCD image forming element (43); and an evaluation device (15) which evaluates whether the decoding device (15) successfully decodes said image of said data symbol (38), said control circuit (50) controlling said zoom lens drive to modify said magnification of said zoom lens (46) until said evaluation device (15) successfully evaluates that said   decoding (15) has successfully decoded the image of said data symbol (38).   13. Device for reading data symbols according to claim 12, characterized: in that said control circuit (50) initially controls said zoom lens (46) to adjust said magnification to a minimum magnification of said zoom lens; and in that said control circuit (50) controls said zoom lens to increase said magnification until said evaluation device (1 5) evaluates that said decoding device (1 5) has decoded said   image of said data symbol (38) successfully.   14. Device for reading data symbols according to claim 12, characterized: in that said control circuit (50) initially controls said zoom lens (46) to adjust said magnification to a maximum magnification of said zoom lens; and in that said control circuit (50) controls said zoom lens to decrease said magnification until said evaluation device (15) evaluates that said decoding device (15) has decoded said   image of said data symbol (38) successfully.