Image reading device

Abstract

To provide an image reading device that prevents a reduction in the accuracy of reading an image caused by electrification of a light guide.SOLUTION: An image reading device comprises: a document table glass on which a document is placed; an LED 408 that emits light to irradiate the document; a light guide 207 that guides the light emitted from the LED 408 to the document; an LED array substrate 206 on which the LED 408 is mounted; an image sensor that receives the light reflected on the document to read an image of the document; a ground pattern 409 that is provided on the LED array substrate 206 and is grounded; and a resistor 410 that is connected with the ground pattern 409 at one terminal 514. The distance Δx1 from the light guide 207 to the other terminal 515 of the resistor 410 is shorter than the distance Δx2 from the light guide 207 to a terminal 510 of the LED 408.SELECTED DRAWING: Figure 5

Description

Technical Field

[0005]

[0001] The present invention relates to an image reading apparatus that reads an image from a document.

Background Art

[0002] An image reading apparatus irradiates light onto a document and receives the reflected light to read an image. Patent Document 1 discloses an image reading apparatus having, as an illumination mechanism, an LED array in which a plurality of light-emitting diodes (LEDs) are linearly arranged on a substrate. Patent Document 2 describes an image reading apparatus having a configuration in which a light guide that guides light emitted from an LED is brought into close contact with the LED and the light irradiated from the LED is condensed onto the paper surface of the document with high efficiency.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, an image reading apparatus includes a document table glass on which a document is placed, and a pressure plate that presses the document on the document table glass to prevent the document from floating during reading. In such an image reading apparatus, due to user operations such as placing the document and opening and closing the pressure plate, friction and peeling operations between the pressure plate and the document occur. As a result, the pressure plate may become charged.

[0005] When a charged pressure plate is closed while the reading unit, which includes an LED board with LEDs mounted on it and a light guide, is directly below the document glass, the charged pressure plate can inductively charge the light guide. When the light guide becomes charged, a discharge may occur between the light guide and the LED terminals. Furthermore, the discharge from the charged light guide may not be limited to the LED terminals, but may also occur at the wiring of the LED board or the terminals of other mounted electronic components.

[0006] If a discharge occurs at the terminals of an LED or other electronic component, the LED or the semiconductor device that controls its operation may malfunction. If the LED or semiconductor device malfunctions, the image reading device may not be able to obtain sufficient light emission to read the image accurately.

[0007] In view of the above-mentioned problems, the primary objective of the present invention is to suppress the decrease in image reading accuracy caused by the light guide becoming charged. [Means for solving the problem]

[0008] The image reading device of the present invention comprises a document glass on which a document is placed, a light-emitting means for emitting light to irradiate the document, a light guide for guiding the light emitted from the light-emitting means to the document, a substrate on which the light-emitting means is mounted, a light-receiving means for receiving reflected light from the document and reading an image of the document, a grounding pattern provided on the substrate and grounded, and a surface-mount component with one terminal connected to the grounding pattern, wherein the surface-mount component is arranged such that the distance from the light guide to the other terminal of the surface-mount component is shorter than the distance from the light guide to the terminal of the light-emitting means. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the decrease in image reading accuracy caused by the light guide becoming charged. [Brief explanation of the drawing]

[0010] [Figure 1] Diagram showing the configuration of the image reading device. [Figure 2] Diagram illustrating the configuration of the reading unit. [Figure 3] Controller diagram. [Figure 4] Detailed diagrams illustrating the LED array substrate and LED control substrate. [Figure 5] (a) and (b) are detailed diagrams of the LED array unit. [Figure 6] (a) and (b) are detailed diagrams of the LED array unit. [Modes for carrying out the invention]

[0011] Preferred embodiments of this invention will be described in detail below with reference to the drawings.

[0012] (Image reading device) Figure 1 is a diagram showing the configuration of the image reading device according to this embodiment. The image reading device 100 comprises a reading unit 101, a belt 102, a motor 103, a document glass 104, and a pressure plate 105. The belt 102 is rotationally driven by the motor 103, moving the reading unit 101 in the direction of the arrow (scanning direction). The document 106 is placed on the document glass 104 and pressed down by the pressure plate 105. The pressure plate 105 is attached to the document glass 104 so as to be openable and closable. The reading unit 101 reads an image from the document 106 placed on the document glass 104 while being moved in the scanning direction by the belt 102.

[0013] (Reading unit 101) Figure 2 is an explanatory diagram of the configuration of the reading unit 101. The reading unit 101 comprises an LED array unit 201 which is a light-emitting part, a plurality of planar mirrors 202a to 202d, an imaging lens 203, an image sensor 204 which is a light-receiving part, and an image sensor substrate 205 on which the image sensor 204 is mounted. The LED array unit 201 is composed of an LED array substrate 206 on which a plurality of side-view type LEDs are mounted as light-emitting elements, and a light guide 207 which is a light guide that guides the light emitted from the LEDs to the document 106.

[0014] The reading unit 101 illuminates the document 106 placed on the document glass 104 with light using the LED array unit 201. The light is reflected by the document 106. The reflected light from the document 106 is guided to the imaging lens 203 by the plane mirrors 202a to 202d and is imaged onto the light-receiving surface of the image sensor 204. The image sensor 204 performs photoelectric conversion of the received light and outputs an electrical signal representing the scanned image. The electrical signal is processed by the image sensor substrate 205 and converted into image data representing the image of the document, which is then output.

[0015] (controller) Figure 3 is an explanatory diagram of the controller of the image reading device 100. The image reading device 100 is equipped with a CPU (Central Processing Unit) 300 as its controller. The CPU 300 controls the overall operation of the image reading device 100. Figure 3 describes a configuration in which the CPU 300 controls the light emission of the reading unit 101 (LED array unit 201).

[0016] The reading unit 101 includes an LED array substrate 206 and an LED control substrate 302. The LED array substrate 206 is mounted with an LED array 301 in which a plurality of LEDs for irradiating light onto the document 106 are arranged in series. The LED control substrate 302 is mounted with an LED control unit 303. The LED control unit 303 is connected to the LED array 301 and the CPU 300. The LED control unit 303 is an electronic circuit that controls the light emission of each LED in the LED array 301 by supplying the power supplied from the power source to each LED in the LED array 301 based on the LED lighting control signal acquired from the CPU 300.

[0017] (LED array substrate 206 and LED control substrate 302) FIG. 4 is a detailed explanatory diagram of the LED array substrate 206 and the LED control substrate 302. The LED control substrate 302 includes an LED lighting unit 402 and current control units 404, 405, and 406 as the LED control unit 303. Power is supplied to the LED control substrate 302 from the power source via a connector 401, and an LED lighting control signal is input from the CPU 300. The LED array substrate 206 includes an LED array 301 composed of a plurality of LEDs 408a to 408l and a ground pattern 409 (a wiring pattern for grounding). Power is supplied to the LED array substrate 206 from the LED control substrate 302 via a connector 407. In the LED array 301 of the present embodiment, three columns of a plurality of LEDs connected in series are provided.

[0018] The LED lighting unit 402 supplies the power supplied from the power source to the LED array substrate 206 via a connector 403. At that time, the LED lighting unit 402 controls the supply and cutoff of the power based on the LED lighting control signal. Such an LED lighting unit 402 is composed of a switch circuit such as a FET (Field Effect Transistor) that supplies and cuts off the power.

[0019] The current control units 404, 405, and 406 control the current flowing through the LED array 301. The light irradiated on the document 106 needs to have a constant emission amount. However, since the forward voltage (VF) of the LEDs 408a to 408l varies for each individual, variations in the emission amount occur only by controlling the applied voltage. The current control units 404, 405, and 406 suppress such variations in the emission amount by controlling the amount of current supplied to the LED array 301. The current control units 404, 405, and 406 are provided in a number corresponding to the number of columns of the LEDs (LEDs 408a to 408d, 408e to 408h, 408i to 408l) of the LED array 301. In the present embodiment, since there are three columns of LEDs, three current control units 404, 405, and 406 are provided. The current control units 404, 405, and 406 are constant current circuits composed of, for example, operational amplifiers, current limiting resistors, and the like.

[0020] The LED array substrate 206 applies the power supplied from the LED control substrate 302 via the connector 407 to the LEDs at the head of each column of the LED array 301. In the present embodiment, power is applied to the anode terminals of the LEDs 408a, 408e, and 408i. The cathode terminals of the LEDs 408d, 408h, and 408l at the rear end of each column are connected to the corresponding current control units 404, 405, and 406 of the LED control substrate 302 via the connector 407. The emission amount of the column of LEDs 408a to 408d is controlled by adjusting the amount of current by the current control unit 404. The emission amount of the column of LEDs 408e to 408h is controlled by adjusting the amount of current by the current control unit 405. The emission amount of the column of LEDs 408i to 408l is controlled by adjusting the amount of current by the current control unit 406.

[0021] In the present embodiment, the LED array 301 has a configuration in which four columns of LEDs connected in series are connected in parallel in three rows. The LED array 301 can be freely set the number of LEDs connected in series and the number of columns of LEDs according to the range to be irradiated. The larger the irradiation range, the more the number of LEDs connected in series and the number of columns of LEDs.

[0022] The grounding pattern 409 is a conductive member connected to the ground of the LED control board 302 via connectors 407 and 403. Therefore, the grounding of the LED control board 302 and the LED array board 206 are common. Multiple chip-type components (chip components), such as resistors 410a, 410b, 410c, ... 410m, are connected to the grounding pattern 409.

[0023] Each resistor 410a, 410b, 410c, ... 410m has low resistance, for example, a resistance value of 0 [Ω]. Each resistor 410a, 410b, 410c, ... 410m has one terminal connected to the ground pattern 409 and the other terminal open and not connected anywhere. Each resistor 410a, 410b, 410c, ... 410m makes precise contact with the light guide 207 with the other terminal that is not connected anywhere. In other words, resistors 410a to 410m can be chip components (surface mount components) whose terminal potential is at ground potential and which can conduct current. Each resistor 410a, 410b, 410c, ... 410m is placed one by one between the multiple LEDs 408 and even further outside the outermost LED 408. Therefore, the number of resistors 410a, 410b, 410c, ... 410m is one more than the number of LEDs 408.

[0024] (Configuration of LED array unit 201) Figure 5 is a detailed configuration diagram of the LED array unit 201. Figure 5(a) is a view of the LED array unit 201 from the document glass 104 side (top side). Figure 5(b) is a cross-sectional view taken along line A-A' in Figure 5(a). The LED array unit 201 has a light guide 207 arranged on an LED array substrate 206. The LED array substrate 206 is, for example, a printed circuit board.

[0025] The LED array board 206 is mounted with LEDs 408a to 408h, a grounding pattern 409, a wiring pattern 501, a connector 407, and resistors 410a to 410i. The grounding pattern 409 is electrically grounded. The wiring pattern 501 electrically connects LEDs 408a to 408h. The connector 407 is electrically connected to the external LED control board 302. The resistors 410a to 410i are electrically connected to the grounding pattern 409. The rows of LEDs 408a, 408b, 408c, and 408d are connected in series by the wiring pattern 501. The rows of LEDs 408e, 408f, 408g, and 408h are connected in series by the wiring pattern 501. The rows of LEDs 408a, 408b, 408c, and 408d are connected in parallel to the rows of LEDs 408e, 408f, 408g, and 408h.

[0026] The light guide 207 is positioned to face the light-emitting surface 513 of the side-view type LED 408 (LED 408a to 408h) and the LED array substrate 206, and guides the light emitted from the LED 408 toward the document 106. The wiring pattern 501 is a conductive member formed on both sides of the LED array substrate 206. It is preferable that the wiring pattern 501 is not formed in the area in contact with the light guide 207 in order to prevent discharge from the light guide 207. For example, in the vicinity of the light guide 207, the wiring pattern 501 is connected via via to the wiring pattern 501 on the side of the LED array substrate 206 opposite to the side in contact with the light guide 207. With this configuration, the wiring pattern 501 is not formed in the area in contact with the light guide 207.

[0027] In Figure 5(b), since LEDs 408a to 408h are located in approximately the same position when viewed in cross-section, LEDs 408a to 408h are collectively referred to as LED 408. Similarly, resistors 410a to 410i are collectively referred to as resistor 410. As shown in Figure 5(b), LED 408 is mounted on the upper side of the LED array substrate 206 (the side facing the document glass 104). A terminal 510 for connecting to the wiring pattern 501 of the LED array substrate 206 is provided on the mounting surface of LED 408. The terminal 510 is soldered to a land pattern 511, which is part of the wiring pattern 501 on the surface of the LED array substrate 206.

[0028] The grounding pattern 409 is formed on the upper side of the LED array substrate 206. One terminal 514 of the resistor 410 is soldered to the grounding pattern 409. The other terminal 515 of the resistor 410 is not soldered anywhere and is in contact with the light guide 207. Strictly speaking, due to variations in mounting precision, not all terminals 515 of the resistor 410 will be in contact with the light guide 207. If the other terminal 515 were soldered to the light guide 207, the solder fillet would prevent accurate contact. To prevent this, the other terminal 515 is not soldered to the light guide 207.

[0029] The distance Δx1 between terminal 515 of resistor 410 and light guide 207 is extremely small compared to the distance Δx2 between the light-emitting surface 513 of LED 408 and light guide 207. In other words, terminal 515 of resistor 410 is positioned closer to the light guide 207 than terminal 510 of LED 408.

[0030] When a discharge occurs from a charged object to another object via the air, the object to which the discharge occurs is determined by the "potential difference between the charged object and the discharge destination" and the "distance between the charged object and the discharge destination." In this embodiment, as the charge of the light guide 207 increases, the potential difference with the candidate discharge destinations (terminal 510 of the LED 408 and terminal 515 of the resistor 410) increases. At that time, since terminal 515 of the resistor 410 is closer to the light guide 207 than terminal 510 of the LED 408, the potential difference required for discharge is smaller, and discharge occurs to terminal 515 of the resistor 410 first. As a result of the discharge from the light guide 207, the charge of the light guide 207 decreases. The resistor 410 releases the charge obtained by the discharge to the ground.

[0031] In other words, no potential difference greater than the potential difference required for discharge occurs between the light guide 207 and the terminal 515 of the resistor 410. Also, no large potential difference sufficient to cause discharge occurs between the light guide 207 and the terminal 510 of the LED 408. Because the light guide 207 is an insulator, the amount of charge generated when the pressure plate 105 becomes charged is not uniform. However, the light guide 207 can suppress discharge from the LED 408 to the terminal 510 by arranging multiple resistors 410 near the point where the terminal 515 makes contact.

[0032] In the example shown in Figure 5(a), resistors 410a to 410i are placed one by one between the multiple LEDs 408a to 408h arranged in a straight line, and further outside the outermost LEDs 408a and 408h in the arrangement. The arrangement of resistors 410a to 410i is not limited to this. The number of resistors can be adjusted as long as it is possible to prevent the light guide 207 from becoming charged to the terminals 510 of the LED 408. The amount of charge on the light guide 207 varies depending on its material and shape. The likelihood of discharge from the light guide 207 to the LED 408 and resistor 410 varies depending on the shape of each terminal, the distance, etc. For this reason, one resistor 410 may be placed for every two LEDs 408. Furthermore, the effects of this embodiment may be obtained even if the number of resistors 410 is further reduced.

[0033] Figure 6 is a detailed configuration diagram of the LED array unit 201 with an adjusted number of resistors.

[0034] Figure 6(a) shows an example where resistor 410 is placed every other LED 408. Near resistors 410a, 410c, 410e, 410g, and 410i, the charge level of the light guide 207 is kept to a level at which a discharge occurs between it and resistors 410a, 410c, 410e, 410g, and 410i. For this reason, near LEDs 408a to 408h, the charge level of the light guide 207 is kept below a level at which a discharge occurs between it and LEDs 408a to 408h.

[0035] Furthermore, even if a discharge occurs between the mounted components, if the mounted components have sufficient voltage resistance, a failure will not occur. For example, if the LED lighting unit 402 and LED 408 have high voltage resistance, and the current control units 404, 405, and 406 have low voltage resistance, failure of the LED array unit 201 can be prevented by preventing discharge to the paths connected to the current control units 404, 405, and 406. In this case, as illustrated in Figure 6(b), resistors 410e and 410i only need to be placed near the cathode terminals of LEDs 408d and 408h connected to the current control units 404 and 405.

[0036] Thus, even if the pressure plate 105 becomes charged due to user actions or other reasons, the discharge occurs between the light guide 207 and the terminal 515 of the resistor 410 because the light guide 207 is in contact with the terminal 515 of the resistor 410, which is electrically at ground level. In other words, discharge from the light guide 207 to the terminal 510 of the LED 408 and the wiring pattern 501 is suppressed. This prevents discharge from the light guide 207 to the terminal 510 of the LED 408 and the wiring pattern 501, and prevents failure of the LED 408 and mounted components on the LED control board 302. As a result, the image reading device 100 can accurately read the image of the document 106 even when the pressure plate 105 is charged. That is, it is possible to suppress the decrease in image reading accuracy caused by the charging of the light guide 207.

Claims

1. The document glass on which the document is placed, A light-emitting means that emits light to irradiate the aforementioned manuscript, A light guide that guides the light emitted from the light-emitting means onto the original document, A substrate on which the light-emitting means is mounted, A light receiving means that receives the reflected light from the aforementioned document and reads the image of the document, A grounding pattern provided on the aforementioned substrate and grounded, The grounding pattern includes a surface-mount component to which one terminal is connected, The surface-mount component is arranged such that the distance from the light guide to the other terminal of the surface-mount component is shorter than the distance from the light guide to the terminal of the light-emitting means. Image reading device.

2. The other terminal of the surface mount component is characterized by not being connected to anything. The image reading device according to claim 1.

3. The aforementioned light-emitting means are arranged in a linear fashion in multiple locations. The surface-mount components are characterized by being arranged one at a time between the plurality of light-emitting means and one further outside the outermost light-emitting means in the array. The image reading device according to claim 1 or 2.

4. The aforementioned light-emitting means are arranged in a linear fashion in multiple locations. The surface-mount components are characterized in that they are arranged alternately with respect to the plurality of light-emitting means. The image reading device according to claim 1 or 2.

5. The substrate further includes a connector for connecting to another substrate on which a control means for controlling the emission of light from the light-emitting means and a current control means for controlling the current flowing through the light-emitting means are mounted. The surface-mount component is characterized by being positioned near the terminals of the light-emitting means connected to the current control means. The image reading device according to claim 1 or 2.

6. The light-emitting means is an LED, The surface-mount component is characterized by being positioned near the cathode terminal of the LED. The image reading device according to claim 5.

7. The aforementioned LEDs are arranged in series in multiples. The current control means controls the current flowing through a plurality of LEDs arranged in series, The surface-mount component is characterized by being positioned near the cathode terminal of the LED connected to the current control means. The image reading device according to claim 6.

8. The grounding pattern is characterized in that it shares a common ground with the other boards via the connector. The image reading device according to claim 5.

9. The surface-mount component is characterized by being a resistor. The image reading device according to claim 1.

10. The light-emitting means has a side-view type light-emitting surface, The light guide is positioned on the substrate so as to face the light-emitting surface. The grounding pattern is characterized by being provided between one terminal of the surface mount component and the substrate. The image reading device according to claim 1.

11. The surface mount component is characterized in that it is arranged such that the distance from the light guide to the other terminal of the surface mount component is shorter than the distance from the light guide to the light-emitting surface of the light-emitting means. The image reading device according to claim 10.

12. The surface-mount component and the ground pattern overlap when viewed from the direction normal to the surface of the substrate on which the light-emitting means is mounted. The image reading device according to claim 1.

13. The grounding pattern is provided on the substrate, and one terminal of the surface mount component is provided on the grounding pattern, characterized in that The image reading device according to claim 12.

14. The aforementioned light-emitting means are arranged in a linear fashion in multiple locations. The present invention is characterized in that, when viewed from the direction in which the multiple light-emitting means are arranged, the multiple light-emitting means and the surface-mount components overlap, while the light guide and the surface-mount components do not overlap. The image reading device according to claim 1.

15. The aforementioned light-emitting means are arranged in a linear fashion in multiple locations. The grounding pattern is characterized by being formed continuously in the direction in which the plurality of light-emitting means are arranged. The image reading device according to claim 1.

Images