JP4176007B2 - Code reader having distance measuring function - Google Patents

Description

  The present invention reads a one-dimensional or two-dimensional code represented by a mark formed by a difference in reflectance, specular reflection, or diffuse light, and is printed on a seal-like medium or directly formed on an object surface. In particular, the present invention relates to a code reading device having a distance measuring function for measuring a distance to a code to be read and a distance measuring method thereof.

  In recent years, in order to recognize management information of products and parts in a short time, one-dimensional or two-dimensional codes in which product and part numbers, product names, prices, and other information are symbolized by black and white stripes are widely used. ing. A code (also referred to as “label” or “mark”) having encoded information, such as a one-dimensional code or a two-dimensional code represented by a code formed by a difference between these different reflectances or specular reflections and diffused light. For example, in a one-dimensional code, a series of numbers is represented by a combination of line width ratios, and various pieces of information such as product and part numbers are replaced with the above numbers. Such a code reader that optically reads a one-dimensional code composed of a one-dimensional bar or a secondary code composed of a two-dimensional cell is a hand-held type that an operator uses while holding the device, There is a stationary type fixed at a predetermined position on the road.

  A light-emitting diode is mainly used as a hand-held type light source, and a laser beam is mainly used as a stationary light source. Hand-held code readers are frequently used at supermarkets and department stores as a point-of-sale (POS) system, and are also used in the manufacturing and distribution stages.

  On the other hand, stationary code readers are used in distribution distribution centers and the like. For example, in a distribution center, an article with a random destination and type is conveyed by a conveying means such as a belt conveyor, and information on a label attached to the surface of the conveyed article is imaged by an imaging means. A code is read by processing an image, and various articles are automatically sorted by a sorting device based on the information.

FIG. 11 is an external view showing an example of a hand-held type code reader that images a region in a two-dimensional area and reads a code. The main body 7 of the code reading device has a substantially rectangular parallelepiped shape with a cross-sectional cross-section. A code reading unit 7a is provided at the tip of one end of the main body 7, and a numeric keypad 7b for inputting commands such as registration, deletion, display, and guidance of the read code data on the upper surface of the other end of the main body 7. In addition, a display unit 7c made of liquid crystal or the like for displaying predetermined items is provided. When using this code reading device, the user holds the holding portion of the main body 7 with one hand and presses the operation switch 7d. By pressing the operation switch 7d, for example, two points of visible light, cross-shaped visible light, X-shaped visible light, or rectangular-shaped visible light is irradiated as a guide light for checking a reading area, using a laser diode as a light source. Is done. When the operator aligns the guide light with the code to be read and then presses the operation switch 7d again to instruct the start of reading, the light reflected from the reading area is incident on the lens system , and the image formed is an image sensor or the like. The image is picked up by the image pickup means. A code is recognized (decoded) from the image data (see, for example, Patent Document 1).

  In a hand-held code reader having such a code recognition function, an object is generally read by a fixed focus lens. For example, when a code is read correctly, a sound is emitted to the operator. If the information is not read correctly due to the notification and the distance to the code is too close or too far, the operator needs to repeat the reading operation.

  In order to cover the drawbacks of such a fixed focus type code reader, an autofocus mechanism may be provided. However, if an autofocus mechanism employed in a camera that captures an image of a person or a landscape is used, high There is a disadvantage that it becomes price.

  The above-mentioned code reader for barcodes, etc., requires a high-performance autofocus function with higher distance measurement accuracy and focus adjustment accuracy than cameras that capture images of people and landscapes. No. For this reason, it is desirable to install an inexpensive autofocus device in the above-described code reading device even if the accuracy is somewhat inferior.

  As an apparatus for measuring the distance to an object, for example, using a laser beam or radio wave, the distance or distance to the object is measured by measuring the time difference until the signal reaches the object and is reflected back. There are also those for vehicles such as those that measure the rate of change (see, for example, Patent Document 2) and those that measure the distance to an object by the principle of triangulation using two image sensors (see, for example, Patent Document 3). Can be mentioned. However, even if these distance measurement methods are applied, it is difficult to realize an autofocus device that can be focused at high speed and a small size, light weight, and a code reading device having the function at low cost.

  In view of this, the present applicant has proposed a hand-held reading apparatus and a distance measurement method having an autofocus function that can be realized with an inexpensive configuration in Patent Document 4. In the device disclosed in Patent Document 4, a light beam having a predetermined angle with respect to the optical axis of the lens system of the image pickup means is irradiated, and the displacement of the image position of the light beam with respect to the optical axis of the lens system is used. Measurement of the distance to the object and determination of the moving position of the lens system in autofocus control are performed. As a preferred mode, the above-described light beam is also used as a guide light indicating a reading position / range of a reading target such as a barcode, thereby adding a distance to the target such as a sensor. It can be measured without any problems. As for autofocus control, the lens system or the image sensor is moved in accordance with the distance calculated from the displacement amount of the image position of the light beam, and the focal position is adjusted (see, for example, Patent Document 4).

JP-A-8-227437 Japanese Patent Publication No. 61-6349 JP-A-4-262500 JP 2002-56348 A

  In the above-described device disclosed in Patent Document 4, a distance measuring method for measuring the distance to an object based on the amount of displacement of the image position of the light beam with respect to the optical axis of the lens system is employed. However, when the distance measuring light beam is also used as the guide light, it is assumed that the light beam of the guide light is inclined with respect to the light receiving axis of the imaging means. Therefore, there is a problem that it cannot be applied to a code reading device that projects guide light parallel to the light receiving axis of the imaging means. In addition, in the distance measuring method described in Patent Document 4, when imaging is performed in a state where the imaging surface is inclined with respect to the surface to which the code is attached, the position of the light beam also changes according to the inclination angle. An error occurs. For this reason, when applied to a hand-held code reader, the distance cannot be measured accurately depending on the imaging state, and the code recognition accuracy is lowered because focus is not achieved. Even in a stationary code reader, if the article to which the code is applied is not placed straight on the conveyance path (surface of a belt conveyor or the like), the distance cannot be measured accurately and the focus is not achieved. Therefore, there is a drawback that the code recognition accuracy is lowered.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to measure the distance to a code to be read without adding a device such as a dedicated sensor for distance measurement. An object of the present invention is to provide a code reading device having a distance measuring function and a distance measuring method thereof capable of measuring a distance with a small error even if there is an angle between a surface to which a code is applied and an imaging surface.

The present invention relates to an imaging means for capturing an image of the object to be read with a one-dimensional or two-dimensional code represented by a mark formed by a difference in reflectance or specular reflection or diffuse light, A code reader comprising: an optical pointer light projecting unit that projects an optical pointer having a predetermined shape that indicates an imaging position of a reading target; and a code decoding unit that processes an image captured by the image capturing unit and decodes the code The object of the present invention is to obtain image information of the optical pointer imaged by the imaging means in a state where the optical pointer is projected, and in accordance with a projection area of the optical pointer. A% of the maximum density value calculated by comparing the density value of each pixel in the measurement window with a predetermined pixel range set in advance as the measurement window is used as the first threshold value. And B <A, B% of the maximum density value is set as a second threshold value, and the number of pixels whose density value exceeds the first threshold value in the measurement window is set as a first pointer. The image width is counted, and the number of pixels having a density value exceeding the second threshold in the window is counted as a second pointer image width to approximately represent the spread of the optical pointer image. A ratio of the second pointer image width to the first pointer image width is calculated as a pointer image spread degree, and the code is calculated using a table or a function formula that defines the relationship between the pointer image spread degree and the distance to the code. made reach by the further comprising a distance measuring means for calculating the distance to.

Furthermore , the object of the present invention is to obtain image information of the optical pointer imaged by the imaging means in a state where the optical pointer is projected, and is preset according to a projection area of the optical pointer. Counting the number of pixels whose density value exceeds a predetermined threshold in the measurement window using a certain pixel range as a measurement window, and using the counted value as first distance measurement information, the measurement window A% of the maximum density value calculated by comparing the density values of each pixel in the inside is set as the first threshold, and B <A is set as B% of the maximum density value as the second threshold, The number of pixels whose density value exceeds the first threshold in the measurement window is counted as the first pointer image width, and the number of pixels whose density value exceeds the second threshold in the window. The second point Counting as the image width, the ratio of the second pointer image width to the first pointer image width is used as second distance measurement information, and the first distance measurement information approximately represents the shape of the optical pointer. This can also be achieved by providing distance measuring means for calculating the distance to the code based on the information and the second distance measurement information that approximately represents the spread of the image of the optical pointer.

Furthermore, the measurement window is more effectively achieved by being a window having a constant width set corresponding to a pixel row traversing the image of the optical pointer in a predetermined direction .
Further, the light beam of the optical pointer for projecting light through said optical pointer light projecting means, are parallel light beam with respect to the light receiving axis of the imaging means, the imaging according to the distance calculated by said distance measuring means A lens moving unit that automatically adjusts the focus by moving the lens system or the image pickup element of the unit in the optical axis direction, and a plurality of steps that are set in advance according to the focal depth of the lens system at each imaging distance From the focal length, the focal distance at the corresponding stage corresponding to the distance calculated by the distance measuring means is obtained, and the lens moving means is controlled to place the lens system or the image sensor at the focal distance at the relevant stage. It is provided with a focus adjustment control means for instantaneously moving, the stage of the focal length is two stages or three stages, and the code reading device is on the surface of the article continuously conveyed along the conveyance path. A stationary type code reading device that reads the generated code in real time, and when the distance calculated by the distance measuring means falls within the distance of the focus of the imaging means, the code decoding image is read It further comprises imaging timing control means for imaging by the imaging means, and the imaging timing control means is more effective by stopping the projection of the optical pointer before imaging the code decoding image. Achieved.

  According to the present invention, by using an optical pointer indicating the imaging position of the reading target, the shape of the pointer image that changes according to the distance to the reading target (the image of the size of the pointer image or the focus shift, etc.) Because the distance to the object is measured and the focus adjustment control is performed based on the amount of change), without adding a dedicated sensor for distance measurement, etc. Measurement of the distance to the code to be read and accurate focusing can be performed. In addition, a method for measuring a distance based on a count value of pixels in which a density value exceeds a predetermined threshold in a window including a predetermined pixel range set in advance according to the shape of the optical pointer Compared to the conventional method of distance measurement based on the amount of displacement of the image position (point or line segment) of the light beam, the distance to the reading object can be measured at a higher speed and a code is attached. It is possible to reduce the measurement error of the distance that occurs when there is an angle between the current surface and the imaging surface.

  The present invention can be applied to a code reader having a general hardware configuration, and guide light (hereinafter referred to as an optical pointer) indicating an imaging position of a reading target without adding a device such as a distance sensor. And a function for measuring the distance to the code reading surface. In the best mode described below, the amount of change in the image shape of the optical pointer that changes in accordance with the distance to the reading target is obtained, and the distance from the amount of change to the reading surface of the code is measured. .

  The “pixel density value” referred to in the present invention means a monochrome or color output from an image pickup device (an image pickup device for picking up a black and white image, a CCD type or CMOS type color image pickup device) of a code reader. A density value obtained by processing a pixel signal (an analog value or a digital value indicating the density of an image obtained according to the image plane illuminance).

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. In the embodiments described below, a case where the present invention is applied to a one-dimensional / two-dimensional code reading apparatus will be described as an example. The optical pointer used for distance measurement in the present invention is a guide light for confirming the imaging position projected from a general code reader to a reading target, and the shape and direction of the light beam are particularly limited. However, the light beam of the optical pointer is preferably a light beam parallel to the light receiving axis of the imaging means.

  FIG. 1 is a block diagram showing a configuration example of a code reading apparatus according to the present invention. Since the external configuration of this code reader is the same as that of the code reader shown in FIG. 11, the description thereof is omitted here.

  A code reading device 10 shown in FIG. 1 includes an image pickup unit 11 for picking up an image to be read, an optical pointer light projecting unit 12 for projecting an optical pointer indicating an image pickup position of the read target 1, and an image pickup. Lens moving means 13 for adjusting the focus by moving the lens system of means 11, code decoding means 14 for decoding the code by processing the image of the code to be read, and the image of the optical pointer being picked up Is provided with a distance measuring means 15 for calculating the distance to the reading object and a control means 16 comprising a CPU, a memory, an input / output interface and the like for controlling each means based on a predetermined program.

  As the image pickup means 11, an image pickup device (for example, a CCD type or CMOS type image pickup camera or a line sensor in which color image elements are linearly arranged) including an image pickup element and a lens for picking up a black and white or color image is used. The The optical pointer light projecting means 12 is a means for irradiating the imaging target with a light beam having a predetermined shape as a guide light (optical pointer) from the light emitting element, and indicating the imaging position to the operator. A semiconductor laser or the like is used. The lens moving means 13 may be composed of a stepping motor or servo and may move the lens system in a stepless manner. However, the lens moving means 13 is composed of an electromagnetic actuator composed of a coil, an electromagnet, etc. It is desirable that the lens system be moved instantaneously by controlling an electromagnetic actuator to a plurality of positions (about two or three stages) of focal length. The code decoding means 14 and the distance measuring means 15 may be configured by either software or hardware in the present embodiment, but hereinafter software (computer program executed under the control of the CPU of the control means 16). The case where it is configured as described above will be described as an example.

  The control means 16 includes optical pointer light projection control by the optical pointer light projection means 12, illumination light illumination control by drive control of an illumination means (additional configuration) not shown, image pickup control by the image pickup means 11, and image pickup means 11. Distance measurement processing based on image information of the captured optical pointer, focus adjustment control by driving control of the lens moving means 14, decoding processing of the read code (decoding processing), transmission processing of decoded data to the host system 20 Various controls are performed.

  In addition to the function of transmitting data to the host system 20 via the communication network or the like, the control means 16 delivers code decoding data (or raw image data) to a memory, PC card, flash memory, or the like. A data storage function for storing and recording in a possible storage medium 15 is provided.

  In the configuration as described above, first, the distance measuring method of the code reading apparatus according to the present invention will be described. In the present invention, as shown in FIG. 2, an optical pointer composed of a light beam parallel to the light receiving axis R of the image pickup device 11b of the image pickup means (or a light beam close to parallel) is used as the light emitting element of the optical pointer light projecting means. The reading surface 1A (1B, 1C) is irradiated from 12a, and the image of the optical pointer imaged through the lens system 11a is picked up by the image pickup device 11b. The distance measuring unit 15 obtains a distribution of pixels whose density value exceeds a predetermined threshold (density distribution of each pixel constituting the optical pointer image) based on the imaged image data of the optical pointer, and the distribution. Based on the information, the distance to the code reading surface 1A (1B, 1C) is calculated.

  The “density distribution representing the shape of the optical pointer” used for the distance measurement described above varies depending on the imaging distance. Therefore, if the density distribution of the optical pointer is obtained, the distance to the code can be calculated using a table or a function formula that defines the relationship between the density distribution and the distance to the code. For example, if all the density distributions of the optical pointer are analyzed, the shape of the optical pointer can be obtained with a certain degree of accuracy, but it is not necessary to recognize the exact shape in order to calculate the distance to the code. Therefore, in the present invention, a value (amount) that approximately represents a partial shape such as the width of the optical pointer image is calculated, and the distance to the code is measured based on the calculated value.

  In the following, (1) a method of measuring the distance to the code using a value that approximately represents the shape of the optical pointer as distance measurement information, and (2) a value that approximately represents the spread of the image due to focus shift. A method for measuring the distance to the code as the business information will be described with specific examples.

  First, as a first embodiment of the distance measuring method, a method for measuring the distance to the code using a value that approximately represents the shape of the optical pointer as distance measurement information will be described.

  3A, 3B, and 3C show the optical pointer when the reading surface 1A, the reading surface 1B, and the reading surface 1C in FIG. 2 are imaged with the optical pointer projected. Examples of images (G1A, G1B, G1C) are shown. When the optical pointer is not diffused light, the size of the optical pointer on the reading surface is substantially the same even if the distance is changed. However, as shown in the images G1A, G1B, and G1C, the same angle of view is obtained. The shape of the pointer image in the screen imaged in (1) changes in accordance with the imaging distance so that it becomes smaller as the reading target is separated. Therefore, the distance measuring unit 15 counts the number of pixels in which the density value obtained from the image signal captured by the imaging unit 11 exceeds a predetermined threshold, for example, as a value that approximately represents the shape of the optical pointer. Then, the distance to the reading surface is calculated using a table or a function formula that defines the relationship between the count value, which is distance measurement information, and the distance to the reading surface (code).

  When obtaining the distance measurement information, the image information of the entire screen may be targeted. However, in order to avoid natural light other than the optical pointer and perform calculation at high speed, as shown in FIG. 3, a predetermined pixel area (pixel range) preset according to the projection area of the optical pointer. Is set as the measurement window W (W1 or W2), and it is preferable to target the pixel group in the measurement window W. Further, rather than using a two-dimensional measurement window W2 as shown in FIGS. 3A to 3C, the optical pointer image as shown in FIG. 3A is traversed in a predetermined direction. The calculation can be performed at higher speed by using a linear window W1 having a constant width set corresponding to the pixel column.

  FIG. 4 shows the count value (number of pixels) and the code up to the code, with the count value (number of pixels) of the pixels whose density value exceeds a predetermined threshold in the measurement window W1 as the vertical axis and the distance (mm) as the horizontal axis. It is the figure which showed the correlation with these distances with the graph. FIG. 5 shows the count values (pixel numbers) actually measured at distances of 50 mm, 100 mm, and 150 mm. As shown in FIG. 4, it can be seen that the correlation between the count value approximately representing the shape of the optical pointer and the distance is inversely proportional. In the distance measuring means 15, a table or a function formula as shown in FIG. 5 that defines the correlation between the count value of a pixel whose density value exceeds a predetermined threshold and the distance to the code within a certain measurement window. Use to calculate the distance to the code.

  4 and 5, the density value of each pixel is compared in the measurement window to obtain a density peak (maximum density value), and the half value (50% of the maximum density value) is set as a threshold value. A value obtained by counting pixels exceeding the threshold value (hereinafter referred to as “half-value width”) is used as distance measurement information, but the threshold value used for counting pixels may be fixed. Further, the reference value (for example, the number of pixels in the table of FIG. 5) used when the distance is obtained by the distance measuring means 15 is the same when distance measurement is performed by other methods described later. For example, it is preferable to set, as a reference value, a count value (measured value) calculated in advance in a state where an optical pointer is projected onto the code surface of the sample. Also, a function expression indicating the relationship between the count value and the distance to the code may be a function expression based on an actual measurement value (concentration distribution) instead of a logical expression.

  As described above, the distance measuring unit 15 obtains image information of the optical pointer imaged by the imaging unit 11 (imaging device) in a state where the optical pointer is projected, and is preset according to the projection area of the optical pointer. The measured pixel W is used as a measurement window W, and the number of pixels whose density value exceeds a predetermined threshold in the measurement window W is counted, and the pixel count value approximately represents the shape of the optical pointer. The distance to the code is calculated using a table or a function formula that defines the relationship between the code and the distance to the code.

  In the case of a code reading device having a zoom function, an image of an optical pointer is picked up with the lens system moved so as to be the zoom amount when the reference value is set. Or, without moving the lens system, the reference value or the calculated value is corrected by the ratio between the zoom amount at the time when the reference value is set and the current zoom amount, and the amount of change after the correction is changed to the reading surface. Calculate the distance. Further, even if there is a slight inclination between the surface of the object and the imaging surface, there is no problem in the focus adjustment processing or the like, but the distance may be measured more accurately in consideration of the inclination. For example, in the case of an optical pointer having a striped projection shape as shown in FIG. 3, the inclination is obtained from the distortion of the shape of the entire contour portion or the edge portion of each bar, the interval between the bars, etc. If the image component amount is corrected from the obtained amount of inclination, a more accurate change amount and distance can be calculated. In addition, even in other shapes (circular, cross-shaped, rectangular, optical pointers composed of line segments having a certain width, etc.), the distortion of the geometric shape of the optical pointer caused by the inclination is imaged. If obtained by processing, the inclination can be calculated from the information of the distortion.

  Next, as a second embodiment of the distance measuring method, a method for measuring the distance to a code using a value that approximately represents the spread of an image due to a focus shift as distance measurement information will be described.

  As described above, the size of the optical pointer image changes according to the imaging distance. By the way, when an image is taken out of focus, the image of the optical pointer spreads and a blurred image is taken. In the first embodiment of the distance measurement method, an example is described in which distance measurement is performed based on the count value of pixels whose density value exceeds a predetermined threshold value. However, in the first embodiment, two threshold values are set. The width of the two positions of the pointer image is obtained, and the distance is measured with the ratio of the widths as “a value that approximately represents the spread of the optical pointer image”.

  FIG. 6 is a diagram showing the density distribution of the image portion of the optical pointer with each pixel in the measurement window as the horizontal axis and the pixel density as the vertical axis. L1, L2, and L3 in FIG. 6 indicate density distributions at distances of 50 mm, 100 mm, and 150 mm, respectively. The shape of the optical pointer image shown in FIG. 3 (an optical pointer composed of three line segments having a predetermined width) has a pulse waveform if it is in focus, but is not in focus. 6, the optical pointer image spreads to form a wavy waveform as shown in FIG.

  In the present embodiment, for example, the density value of each pixel is compared in the aforementioned measurement window to obtain a density peak (maximum density value), and A% (for example, half value: A = 50) of the maximum density value. ) As the first threshold value, B <A, and B% of the maximum density value (for example, B = 13.5) is set as the second threshold value, and the density value is set to the first threshold value in the measurement window. The number of pixels exceeding the threshold value is counted as the first pointer image width. If the ratio of the second pointer image width to the first pointer image width is obtained, the spread of the optical pointer image can be approximately expressed. The distance to the code is calculated by using a table or a function formula that defines the relationship between the pointer image spread degree and the distance to the code, using the ratio of the pointer image widths as the pointer image spread degree.

  FIG. 7 is a graph showing the correlation between the pointer image spread degree and the distance to the code, with the pointer image spread degree as the vertical axis and the distance (mm) as the horizontal axis. FIG. 8 shows values (the above-mentioned pointer image spread degrees) indicating the spread degrees measured at distances of 50 mm, 100 mm, and 150 mm as percentages. As shown in FIG. 7, the correlation between the distance of the pointer image spread and the distance that approximately represents the spread of the optical pointer image is approximately 100 mm at a distance of 100 mm, and the spread is approximately 100 mm at a distance of 100 mm. When the distance becomes shorter, the spread degree increases near the distance, and the spread degree increases as the distance becomes longer. With this correlation, the distance cannot be calculated uniquely from the degree of spread. However, when an image of an optical pointer is picked up, the distance can be uniquely calculated from the degree of spread if it is picked up at a focal position where only the left-up part or the right-up part in FIG. 7 is obtained. This focal position may be set as an initial setting value of the image pickup means, or may be automatically adjusted when an image of the optical pointer is picked up.

  As described above, in the second embodiment, the distance measuring unit 15 obtains image information of the optical pointer imaged by the imaging unit 11 (imaging device) in a state where the optical pointer is projected, and the optical pointer is obtained. A% of the maximum density value calculated by comparing the density values of the respective pixels in the measurement window is set as a first threshold value using a predetermined pixel range preset according to the projection area as a measurement window. At the same time, B <A is set and B% of the maximum density value is set as the second threshold value, and the number of pixels whose density value exceeds the first threshold value in the measurement window is counted as the first pointer image width. In addition, the number of pixels whose density value exceeds the second threshold value in the measurement window is counted as the second pointer image width, and the first pointer approximately representing the spread of the image of the optical pointer. Image width A ratio (second table as shown in FIG. 8) or a function formula that calculates the ratio of the second pointer image width to the “pointer image spread” and defines the relationship between the pointer image spread and the distance to the code Is used to calculate the distance to the code.

  In the above-described first or second embodiment, when measuring the density value in the measurement window, for example, the density signal is input from the image signal captured by the imaging unit 11 and the two-dimensional A density histogram in the vertical (and) or horizontal direction is created by adding the density values of the horizontal (and) or vertical pixels in the measurement window, and its waveform (waveform showing the density distribution shown in FIG. 6). The distance may be obtained by collating with the basic pattern. However, since the distance cannot be measured at a high speed, it is optimal to perform the distance measurement in the first and second embodiments.

  In the above-described embodiment, (1) the method for measuring the distance to the code using the value that approximately represents the shape of the optical pointer as distance measurement information is the first embodiment; The method of measuring the distance to the code using the value that approximately represents the spread of the image by the distance measurement information has been described as the second embodiment, but the shape of the optical pointer of (1) above is approximately The value to be represented is the first distance measurement information, the value (2) approximately representing the spread of the image is the second distance measurement information, and based on the first and second distance measurement information. If the distance to the cord is measured, the distance measurement information of both of them complement each other, and a more accurate distance can be measured. In this case, the first distance measurement information (the count value of the pixels whose density value exceeds a predetermined threshold in the measurement window) and the second distance measurement information (the first pointer image width and the first value described above). The distance to the code may be calculated using a function expression having a variable (the ratio of the pointer image width of 2) as a variable, and the first and second ranging information are obtained by a predetermined arithmetic expression. The distance to the code may be calculated using a table that defines the relationship between the distance and the distance. In addition, an optimum value is selectively selected based on one of the distance measurement information, such as the first distance measurement information when the calculated image spread degree is small and the second distance measurement information when it is large. The distance to the code may be calculated using a table that defines the relationship between the value and the distance.

  Next, the use of the distance obtained by the distance measuring means 15 will be described.

  The distance obtained by the distance measuring means 15 is used as, for example, information for adjusting the focus, and control information for imaging timing in a stationary code reader.

  First, the focus adjustment method will be described. The focus adjustment is performed by moving the lens system (or the image sensor) of the imaging unit 11 in the optical axis direction according to the distance calculated by the distance measuring unit 15.

  FIG. 9 shows the relationship between the imaging distance and the focal depth of the optical system, and the moving system of the lens system (or imaging element) in autofocus control will be described with reference to FIG. In the present invention, the focus position is adjusted using the distance obtained by the distance measuring means 15 as the focus adjustment information. At that time, the autofocus is not continuous, and the moving position is in a plurality of stages according to the focal depth of the lens system at each imaging distance, for example, the moving position with respect to the far, middle and near three stages as shown in FIG. Is set, and the lens system (or image sensor) is moved relatively in the optical axis direction to the moving position corresponding to the change amount of the image component of the optical pointer or the distance to the reading target. Position.

  In the example of FIG. 9, the focal depths of 40 mm to 140 mm are “near”, 80 mm to 230 mm are “medium”, and 170 mm to 400 mm are “far”. A fixed position (focus position) of 3 positions is set as the movement position. For example, when the standard position of the lens system is the “medium” focal position and the distance to the reading object is determined to be “far”, the lens moving means (electromagnetic actuator) 13 is driven and controlled to be “far”. When the lens system 11a is moved to the focal position and it is determined that the distance to the reading target is “near”, the lens moving unit 13 is driven and controlled to move the lens system 11a to the “near” focal position. As described above, by using the change amount or distance of the image component of the optical pointer obtained by the distance measuring means 15 as the focus adjustment information and performing the stepwise autofocus control, the focus adjustment can be performed with an inexpensive configuration. It can be performed at high speed.

  Next, an operation example of the code reader according to the present invention will be described with reference to the flowchart of FIG.

  When an instruction to start reading the code is issued by pressing the operation switch, an optical pointer (guide light) for reading position confirmation and distance measurement is projected from the guide light projector of the code reader. As the optical pointer, for example, a light beam composed of a laser pattern having a predetermined shape showing the field of view of the imaging unit 11 is emitted through a diffraction grating. For example, a guide light beam composed of a pattern as shown in FIG. A light beam parallel to the light receiving axis and / or a light beam having a predetermined angle is irradiated onto the reading surface. The optical pointer light projecting means 12 for generating an optical pointer having such a pattern is fixed at a predetermined position in the housing of the imaging means 11, but may be configured so that the diffraction grating unit can be detachably loaded. Here, a case where a light beam parallel to the light receiving axis of the imaging unit is projected will be described as an example. (Step S1).

  The operator adjusts the position to the reading target (in this example, one-dimensional or two-dimensional code) while viewing the visual field position indicated by the optical pointer 1, and then presses the operation switch again to instruct the start of reading (step S2). . In response to this reading start instruction, an image of the guide light is picked up (step S3), and the distance measuring means 15 calculates the pixel count value (or pointer image spread degree) approximately representing the shape of the optical pointer described above for the distance measurement information. Is calculated as (step S4), and the distance to the code is calculated using a table or a function formula that defines the relationship between the pixel count value (or pointer image spread degree) and the distance to the code (step S5). . Then, the moving position of the lens system for adjusting the focus is determined based on the distance (or the pixel count value or the pointer image spread degree) (step S6).

  In this embodiment, in order to realize high-speed focus adjustment, for example, as described above, for example, a plurality of stages (in this example, “ Focus is automatically adjusted at high speed by instantaneously moving the lens system by driving and controlling the electromagnetic actuator to the position of the focal length (near, middle, or far). It is configured to do. By performing such focus adjustment, in the conventional hand-held type code reader using the fixed-viewpoint imaging means, the reading depth is about 80 mm to 230 mm at the aperture F10, for example. In the example, the reading depth is about 40 mm to 400 mm. As a result, it is possible to operate without worrying about the distance to the reading object, the reading success rate can be increased, and various reading objects can be handled (step S7).

  The control means 16 performs the above-described focus adjustment control, stops the projection of the optical pointer, and images the code to be read in a state where the optical pointer is not projected (step S8). Then, the code is decoded by the code decoding means 14 (step S9). If the decoding of the code is completed, the operator is notified by a buzzer sound, light (for example, LED display) or the like (step S10), and the operation related to the code reading process is ended.

  The code data decoded as described above is stored and recorded in a storage medium. When processing by the host system, the storage medium is loaded into the host system side apparatus for batch processing, or data is acquired from the storage medium by cable connection with the code reader and processed. In a code reader having a wireless communication function, data is transmitted to the host system side in real time, for example, when the decoding process is completed. Further, in a code reading apparatus having a storage function and a communication function, an operator operates a processing mode (for example, a first mode for storing, a second mode for transmitting in real time, and a third mode for storing and transmitting in real time). May be selected. Furthermore, the data stored in the storage medium may be fetched collectively or selectively by a transmission request from the higher system side.

  Next, a description will be given of a case where the distance obtained by the distance measuring unit 15 is used for imaging timing control information in a stationary code reader.

  In the case of a stationary code reader that reads in real time a code attached to the surface of an article that is continuously conveyed along the conveyance path, the distance calculated by the distance measuring means 15 and the distance range in which the focus is in focus And when the calculated distance falls within the in-focus range (or the optimum distance according to the size of the object to be read, etc.) It is possible to automatically pick up an in-focus image. In this case, it is not necessary to move the lens.

It is a block diagram which shows the structural example of the code reader which concerns on this invention. It is a figure for demonstrating the distance measuring method which concerns on this invention. It is a figure which shows the example of the image of the optical pointer which concerns on this invention, and the example of the window for a measurement. It is a figure which shows the correlation of the count value and distance which are used for 1st Embodiment of the ranging method in this invention. It is a figure which shows an example of the table used for 1st Embodiment of the ranging method in this invention. It is a figure which shows density distribution of the image part of an optical pointer. It is a figure which shows the correlation of the pointer image spread degree and distance used for 2nd Embodiment of the ranging method in this invention. It is a figure which shows an example of the table used for 2nd Embodiment of the ranging method in this invention. It is a figure for demonstrating the moving system of the lens system based on this invention. It is a flowchart for demonstrating the operation example of the code reader which concerns on this invention. It is an external view which shows an example of a general hand-held type code reader.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reading object 10 Code reader 11 Imaging means 11a Lens system 11b Image pick-up element 12 Optical pointer light projection means 13 Lens moving means 14 Code decoding means 15 Distance measuring means 16 Control means 20 Host system

Claims (9)

Imaging means for taking an image of the reading object with a one-dimensional or two-dimensional code represented by a mark formed by a difference in reflectance, specular reflection, or diffuse light, and imaging of the reading object In a code reading apparatus comprising: an optical pointer light projecting unit that projects an optical pointer having a predetermined shape indicating a position; and a code decoding unit that processes an image captured by the image capturing unit and decodes the code.
Image information of the optical pointer imaged by the imaging means in a state where the optical pointer is projected is obtained, and a certain pixel range preset according to the projection area of the optical pointer is used as a measurement window. A% of the maximum density value calculated by comparing the density values of the respective pixels in the measurement window is set as the first threshold value, and B <A is set, and B% of the maximum density value is set as the second threshold value. The number of pixels whose density value exceeds the first threshold in the measurement window is counted as a first pointer image width, and the density value in the window is set to the second threshold. The number of pixels exceeding this is counted as the second pointer image width, and the ratio of the second pointer image width to the first pointer image width that approximately represents the spread of the image of the optical pointer is determined as the pointer image width. And a distance measuring means for calculating the distance to the code using a table or a function formula that defines a relationship between the degree of spread of the pointer image and the distance to the code. A code reader having a distance function. Imaging means for taking an image of the reading object with a one-dimensional or two-dimensional code represented by a mark formed by a difference in reflectance, specular reflection, or diffuse light, and imaging of the reading object In a code reading apparatus comprising: an optical pointer light projecting unit that projects an optical pointer having a predetermined shape indicating a position; and a code decoding unit that processes an image captured by the image capturing unit and decodes the code.
Image information of the optical pointer imaged by the imaging means in a state where the optical pointer is projected is obtained, and a certain pixel range preset according to the projection area of the optical pointer is used as a measurement window. In the measurement window, the number of pixels whose density value exceeds a predetermined threshold is counted, and the counted value is used as first distance measurement information.
A% of the maximum density value calculated by comparing the density values of the respective pixels in the measurement window is set as the first threshold value, and B <A is set, and B% of the maximum density value is set as the second threshold value. The number of pixels whose density value exceeds the first threshold in the measurement window is counted as a first pointer image width, and the density value in the window is set to the second threshold. The number of pixels exceeding the second pointer image width is counted, and the ratio of the second pointer image width to the first pointer image width is used as second distance measurement information.
Based on the first distance measurement information that approximately represents the shape of the optical pointer and the second distance measurement information that approximately represents the spread of the image of the optical pointer, up to the code A code reading device having a distance measuring function, characterized by comprising distance measuring means for calculating a distance. The measurement window, code reading apparatus having a distance measurement function according to claim 1 or 2 which is the window of a constant width which is set corresponding to the pixel columns across an image of said optical pointer in a predetermined direction. The code reading having a distance measuring function according to any one of claims 1 to 3 , wherein a light beam of the optical pointer projected by the optical pointer light projecting unit is a light beam parallel to a light receiving axis of the imaging unit. apparatus. Furthermore any of claims 1 to 4 comprising a lens moving means for automatically adjusting the lens system or focus by moving the image sensor in the optical axis direction of the imaging means according to the distance calculated by said distance measuring means A code reader having a distance measuring function described in 1. The lens moving means obtains the focal distance at the stage corresponding to the distance calculated by the distance measuring means from a plurality of focal lengths set in advance according to the focal depth of the lens system at each imaging distance. The code reading apparatus according to claim 5 , further comprising: a focus adjustment control unit that controls the lens system to instantaneously move the lens system or the image sensor to the position of the focal length at the stage. The code reader according to claim 6 , wherein the focal length stage is in two stages or three stages. The code reading device is a stationary code reading device that reads in real time a code attached to the surface of an article that is continuously conveyed along a conveying path, and the distance calculated by the distance measuring unit is the imaging unit. ranging function according to any one focus of claims 1 to 7 further comprising an imaging timing control means for imaging by the imaging means to decode image of the code when it becomes within the range of the distance to focus of A code reader. 9. The code reader according to claim 8 , wherein the imaging timing control unit stops the projection of the optical pointer before imaging the code decoding image.

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