Image reading device and image forming apparatus

Abstract

To accurately locate a carriage at a home position and enable the positioning in relatively short time without providing a sensor dedicated to detecting that the carriage has reached the home position.SOLUTION: An image forming apparatus 1 comprises a control unit 100. The control unit 100 arranges a carriage to a home position search starting position ST, subsequently, determines whether a read image indicated by image data sequentially read by an image sensor is white on the basis of the image data, while moving the carriage in a first direction DR1 to bring the carriage closer to a downstream-side end DE1 of a first white reference plate 164 from the home position search starting position ST, and moves the carriage in the first direction DR1 by a predetermined first distance D1 and stops the carriage, with the position of the carriage when the read image is determined to be white (end DE1) as a reference point to thereby locate the carriage at the home position.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image reading device that reads an original placed on a contact glass, and an image forming apparatus equipped with the same. [Background technology]

[0002] Some image reading devices are equipped with a contact glass for placing a document on it, a light source that irradiates light along the main scanning direction toward the document placed on the contact glass, a carriage that is arranged on the underside of the contact glass opposite the top surface on which the document is placed and that can move back and forth in a sub-scanning direction that is perpendicular to the main scanning direction, and an image sensor that receives reflected light from the light source and reads the image of the document placed on the contact glass.

[0003] The carriage is moved in the sub-scanning direction by a drive mechanism powered by a stepping motor, etc. By controlling the operation of this stepping motor, an initial operation is performed to position the carriage at a specified position such as the home position, and then the carriage is moved in the sub-scanning direction to read the image of a document placed on the contact glass.

[0004] In order to position the carriage at the home position, an image reading device is provided with a dedicated sensor such as a photo interrupter (PI) sensor to detect when the carriage has reached the home position, but this increases the number of parts, which is undesirable. Cost reduction is especially important for budget models. Therefore, various technologies have been proposed for positioning the carriage at the home position without using a dedicated sensor such as a PI sensor (see, for example, Patent Documents 1 and 2 listed below). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-152965 [Patent Document 2] Japanese Patent Publication No. 2022-049279 Summary of the Invention [Problem to be solved by the invention]

[0006] When returning the carriage to the home position immediately after the image reading process of the document placed on the contact glass is completed, it is theoretically possible to return the carriage to the home position by moving the carriage in the opposite direction a distance equal to the distance it moved from the home position during the reading process.

[0007] However, the stepping motor excitation method may differ between operation during the reading process and operation during return. For example, if W1-2 phase excitation is used during the reading process and 1-2 phase excitation is used during return, phase alignment is required. If phase alignment is not performed, a phase shift will occur, and it will be difficult to accurately position the carriage to the home position during return, even if the carriage is moved the same distance as during the reading process.

[0008] Furthermore, even after the carriage has stopped at the home position, when returning from an energy saving mode (e.g., sleep mode) to a normal mode, it is preferable to position the carriage at the home position in order to accurately detect the carriage position at that time.

[0009] The above-mentioned Patent Documents 1 and 2 describe that an image sensor detects that the carriage has reached the boundary line (white reference plate edge) between the white area (white reference plate) and the black area, and the carriage is positioned at the home position by moving the carriage a predetermined distance from the edge of the white reference plate and then stopping it.

[0010] However, the inventions described in the above Patent Documents 1 and 2 may require a very long time to position the carriage at the home position. For example, if the carriage is far away from the edge of the white reference plate, it takes a very long time for the carriage to reach the edge of the white reference plate.

[0011] The present invention has been made in consideration of the above circumstances, and aims to enable accurate positioning of a carriage to its home position without providing a dedicated sensor for detecting that the carriage has reached the home position, and to enable this positioning to be achieved in a relatively short time. [Means for solving the problem]

[0012] An image reading device according to one aspect of the present invention includes a contact glass on which an original is placed, a light source that irradiates light along a main scanning direction toward the original placed on the contact glass, a carriage that is disposed on the lower surface of the contact glass opposite to the upper surface on which the original is placed and that moves back and forth in a sub-scanning direction that is perpendicular to the main scanning direction, a drive mechanism that moves the carriage in the sub-scanning direction, an image reading unit that receives reflected light from the light source and reads an image of the original placed on the contact glass, and a drive mechanism that drives the carriage. a control unit that controls the operation of the image reading unit and the carriage to move the carriage in the sub-scanning direction and cause the image reading unit to read an image of a document placed on the contact glass; an outer edge member that is arranged on the outer edge of the contact glass; and a first white reference plate that is arranged within an arrangement area of ​​the contact glass, with its long side extending in the main scanning direction, and is arranged to be overlapped on the outer edge member in a plane, wherein the first white reference plate is arranged in a position from one end of the contact glass to an original placement area on the contact glass in the sub-scanning direction, and the control unit and a control unit for controlling the carriage to move the carriage to a predetermined home position search start position that is set within an area where the first white reference plate is disposed and serves as a standby position of the carriage after causing the image reading unit to read an image of the document placed on the contact glass, the control unit controls the operation of the drive mechanism to move the carriage to a predetermined home position search start position that is on the document placement area side with respect to the area where the first white reference plate is disposed and stop the carriage, and while moving the carriage in a first direction from the home position search start position toward the area where the first white reference plate is disposed, executes a first determination process for determining whether a read image indicated by image data that is outside the document placement area in the main scanning direction and that is sequentially read by the image reading unit is white, and, using the position of the carriage at the time when it is determined that the read image is white as a base point, moves the carriage a predetermined distance in the first direction from the side edge of the first white reference plate on the document placement area side to the position of the home position and stops the carriage.The carriage is positioned at the home position.

[0013] An image forming apparatus according to one aspect of the present invention includes the image reading apparatus according to the above aspect of the present invention, and an image forming section that forms an image obtained by reading by the image reading apparatus on a recording medium. [Effects of the Invention]

[0014] According to the present invention, the carriage can be accurately positioned at the home position without providing a dedicated sensor for detecting that the carriage has reached the home position, and the positioning can be achieved in a relatively short time. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view showing the appearance of an image forming apparatus according to an embodiment of the image reading apparatus of the present invention; [Figure 2] 1A is a cross-sectional front view schematically showing a document feeding section and a document reading section, and FIG. 1B is a plan view schematically showing the document reading section. [Figure 3] 3 is a cross-sectional view of the document reading unit taken along line III-III in FIG. 2(B). [Figure 4] FIG. 2 is a functional block diagram illustrating a main internal configuration of the image forming apparatus. [Figure 5] 10A and 10B are diagrams illustrating an example of control for positioning a carriage to a home position. [Figure 6] 10 is a table showing the relationship between the average value of image data for each color and the black-and-white discrimination result. [Figure 7] 10 is a flowchart illustrating an example of a process for positioning a carriage to a home position, which is performed by a control unit of the image forming apparatus. [Figure 8] 10A and 10B are diagrams illustrating an example of a processing flow for positioning a carriage at a home position. [Figure 9] 10A and 10B are diagrams illustrating an example of control until the carriage is positioned at a home position search start position. [Figure 10] 10A and 10B are diagrams illustrating an example of a processing flow for positioning a carriage at a home position. [Figure 11] 10A and 10B are diagrams illustrating an example of control until the carriage is positioned at a home position search start position. DETAILED DESCRIPTION OF THE INVENTION

[0016] An image reading apparatus and an image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a perspective view showing the appearance of an image forming apparatus according to an embodiment of the image reading apparatus of the present invention.

[0017] The image forming device 1 is a multifunction device that combines multiple functions, such as a copy function, a printer function, a scanner function, and a facsimile function, and is configured to include a document feeding unit 6, a document reading unit 5, an image forming unit 12, a paper feeding unit 14, and an operation unit 47.

[0018] The document feed unit 6 is configured to be openable and closable by a hinge or the like (not shown) on the top surface of the document reading unit 5, and functions as a document pressing cover when reading a document placed on a contact glass 161 (FIG. 2, etc.) described later. The document feed unit 6 also includes a document placement tray 61 on which documents are placed, and a document discharge tray 62 provided below the document placement tray 61. The document feed unit 6 supplies the documents placed on the document placement tray 61 to the document reading unit 5 one by one, and discharges the documents to the document discharge tray 62.

[0019] The document reading unit 5 includes a scanner and the like, and reads the document fed from the document feeding unit 6, or reads the document placed on the contact glass 161. The document reading unit 5 is also capable of sequentially reading multiple document images sent from the document feeding unit 6.

[0020] The following describes the case where a document reading operation is performed in the image forming apparatus 1. The document reading unit 5 optically reads an image of a document supplied to the document reading unit 5 by the document feeding unit 6 or a document placed on the contact glass 161, and generates image data. The image data generated by the document reading unit 5 is stored in an image memory or the like (not shown).

[0021] The following describes an image forming operation performed by the image forming apparatus 1. The image forming unit 12 is equipped with a photosensitive drum, charging device, exposure device, developing device, and primary transfer device for each color, and is a mechanism for forming an image on recording paper as a recording medium by secondary transfer via an intermediate transfer belt. The image forming unit 12 forms a toner image on recording paper fed from the paper feed unit 14 based on image data generated by a document reading operation, image data stored in an image memory, etc., and image data received from a computer connected via a network, to create a printed matter.

[0022] The recording paper on which the toner image has been formed by the image forming unit 12 undergoes a fixing process in a fixing unit 13 (FIG. 4) described later, and the recording paper after the fixing process is discharged onto a discharge tray 151.

[0023] The paper feed unit 14 includes a plurality of paper feed cassettes 141, and further includes a pickup roller that picks up recording paper from the paper feed cassettes 141 and feeds it to the image forming unit 12, a transport roller, a transport path, and a rotation drive mechanism for each roller.

[0024] The operation unit 47 has various hard keys operated by the user, and in response to the operation of the hard keys, receives instructions from the user, such as an instruction to execute an image forming operation, for various operations and processes that can be executed by the image forming apparatus 1. For example, the operation unit 47 receives an instruction to read a document (a scan instruction or a copy instruction).

[0025] The operation unit 47 includes a display unit 473 that displays operation guides and the like to the operator. The operation unit 47 also receives input of instructions from the user based on the user's operation (touch operation) on the screen displayed on the display unit 473 via a touch panel that the display unit 473 has.

[0026] The display unit 473 is composed of an LCD (Liquid Crystal Display) or the like. The display unit 473 is equipped with a touch panel. When the operator touches a button or key displayed on the screen, the touch panel receives an instruction associated with the touched position. In this case, the touch panel functions as an operation unit.

[0027] 2(A) is a cross-sectional front view that schematically shows the document feeding unit 6 and the document reading unit 5. FIG. 2(B) is a plan view that schematically shows the document reading unit 5. The document reading unit 5 includes a contact glass 161, an outer edge member 162, a first white reference plate 164, a second white reference plate 165, and a carriage 51.

[0028] The carriage 51 includes a light source 52 that emits light in the main scanning direction toward a document placed on the document placement area A1 of the contact glass 161 or a document transported by the document feeder 6 and passing through the contact glass 161 (transported document reading area A2), and an image reading unit 53 that receives reflected light from the light source 52 and reads an image of the document placed on the document placement area A1 or the document passing through the contact glass 161 (transported document reading area A2). The image reading unit 53 is, for example, an image sensor such as a CIS (contact image sensor). The direction in which the image reading unit 53 extends (the lengthwise direction of the image reading unit 53; in the example shown in FIG. 2B, the Y direction) is defined as the main scanning direction, and the direction perpendicular to the main scanning direction (the movement direction of the carriage 51; in the example shown in FIG. 2B, the X direction) is defined as the sub-scanning direction.

[0029] Here, one side of the contact glass 161 in the sub-scanning direction is one end 161A, and the other side on the opposite side is the other end 161B. The document placement area A1 is an area of ​​the contact glass 161 that is closer to the other end 161B of the contact glass 161 in the sub-scanning direction than the separator 163 and the first white reference plate 164.

[0030] The carriage 51 is provided so as to be movable back and forth in a sub-scanning direction perpendicular to the main scanning direction along an unillustrated rail, and is moved in the sub-scanning direction by a known drive mechanism 121 (FIG. 4) powered by, for example, a stepping motor (not shown).

[0031] The document feeder 6 includes a document placement tray 61 , a document discharge tray 62 , a paper feed roller 63 , a registration roller 64 , a plurality of transport rollers 65 , a discharge roller 66 , and a back surface reading unit 67 .

[0032] The back side reading unit 67 is a unit that reads the image on the back side of the document transported by the document feeder 6, and has a light source and an image sensor, similar to the carriage 51. The image sensor of the back side reading unit 67 reads the image on the back side of the document, while the image sensor of the carriage 51 reads the image on the front side of the document. Therefore, the carriage 51, facing the back side reading unit 67, can also be said to be a front side reading unit.

[0033] The outer edge member 162 is disposed on the outer edge of the contact glass 161 and has a separator 163 that separates the contact glass 161 into a document placement area A1 and a transport document reading area A2.

[0034] The first white reference plate 164 and the second white reference plate 165 are white plates with a predetermined color tone that are used when performing shading correction. The first white reference plate 164 is a white reference plate for the carriage 51, which is the front side reading unit, and the second white reference plate 165 is a white reference plate for the back side reading unit 67.

[0035] The first white reference plate 164 is disposed below the separator 163. That is, the first white reference plate 164 is disposed closer to one end 161A of the contact glass 161 (to the left in FIG. 2) in the sub-scanning direction than the document placement area A1. Furthermore, the first white reference plate 164 is disposed so that its long side extends in the main scanning direction and overlaps the outer edge member 162 on a plane.

[0036] A first white reference plate 164 is disposed at a position from one end 161A of the contact glass 161 to the document placement area A1 on the contact glass 161 in the sub-scanning direction.

[0037] The second white reference plate 165 is disposed at a position spaced apart from the first white reference plate 164 in the sub-scanning direction, and is disposed closer to one end 161A of the contact glass 161 than the first white reference plate 164. The second white reference plate 165 is disposed so that its long side extends in the main scanning direction and overlaps the outer edge member 162 on a plane.

[0038] 3 is a cross-sectional view of the document reading unit 5 taken along line III-III in FIG. 2(B). Width W1 indicates the width of the first white reference plate 164 in the sub-scanning direction (e.g., 9.6 mm), and width W2 indicates the width of the second white reference plate 165 in the sub-scanning direction (e.g., 17.9 mm).

[0039] The home position HP is set at the location of the first white reference plate 164 in the sub-scanning direction (within the placement area of ​​the first white reference plate). In this embodiment, the home position HP is set at a position a predetermined distance L1 (e.g., 2.0 mm) from an end DE1 of the first white reference plate 164 on the document placement area A1 side in the sub-scanning direction. The length L2 indicates the distance (e.g., 10.6 mm) between the home position HP and an end DE2 of the second white reference plate 165 on the document placement area A1 side. The length L3 indicates the length (e.g., 41.6 mm) between the position closest to the end 161A of the range in which the carriage 51 can move in the sub-scanning direction and the end DE1 of the first white reference plate 164 on the document placement area A1 side.

[0040] 4 is a functional block diagram showing a schematic diagram of the main internal configuration of image forming apparatus 1. Image forming apparatus 1 includes a control unit 10, a document feed unit 6, a document reading unit 5, an image forming unit 12, a fixing unit 13, a paper feed unit 14, an operation unit 47, and a storage unit 8.

[0041] The image forming unit 12 includes a drive mechanism 121 that moves a carriage 51 (FIG. 2) in the sub-scanning direction, and an image reading unit 53.

[0042] The fixing unit 13 is a fixing device equipped with a heat roller, a pressure roller, and a drive mechanism for rotating these rollers. The fixing unit 13 heats and presses the recording paper on which the toner image has been formed by the image forming unit 12 at the nip between the two rollers, fixing the toner image to the recording paper. The recording paper that has been fixed is then discharged to the discharge tray 151 (Figure 1).

[0043] The storage unit 8 is a large-capacity storage device such as a hard disk drive (HDD) or a solid state drive (SSD), and stores various control programs and the like.

[0044] The control unit 10 includes a processor, a RAM (Random Access Memory), a ROM (Read Only Memory), and a dedicated hardware circuit. The processor may be, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), or an MPU (Micro Processing Unit). The control unit 10 includes a control unit 100.

[0045] The control unit 10 functions as the control unit 100 by the operation of the processor in accordance with the control program stored in the storage unit 8. However, the control unit 100 can also be configured by a hardware circuit, without relying on the operation in accordance with the control program by the control unit 10. Unless otherwise stated below, the same applies to each embodiment.

[0046] The control unit 100 is responsible for overall operational control of the image forming apparatus 1. The control unit 100 is connected to the document feed unit 6, the document reading unit 5, the image forming unit 12, the fixing unit 13, the paper feed unit 14, the operation unit 47, and the storage unit 8, and performs drive control of each of these units. For example, the control unit 100 controls the operation of the light source 52, the drive mechanism 121, and the image reading unit 53, moves the carriage 51 in the sub-scanning direction, and causes the image reading unit 53 to read the image of the document placed on the contact glass 161. The control unit 100 also controls the operation of the image forming unit 12, etc., and executes various processes required for image formation by the image forming apparatus 1.

[0047] 5 is a diagram illustrating an example of positioning control of the carriage 51 to the home position HP. When positioning the carriage 51 at the home position HP, the control unit 100 controls the operation of the drive mechanism 121 to move and stop the carriage 51 at a predetermined home position search start position ST within a range of a predetermined distance DA (for example, 4 mm) from the end DE1 in the sub-scanning direction of the first white reference plate 164. This positions the carriage 51 at the home position search start position ST. In this embodiment, an example is shown in which the home position search start position ST is set at a position that is a distance DB (≦distance DA) from the downstream end DE1 of the first white reference plate 164.

[0048] Thereafter, the control unit 100 moves the carriage 51 in a first direction DR1 (upstream direction) from the home position search start position ST toward the edge DE1 of the first white reference plate 164, and executes a first determination process based on image data of an area outside the document placement area A1 in the main scanning direction (for example, line III-III shown in FIG. 2B) sequentially read by the image reading unit 53 to determine whether the read image represented by the image data is white. For example, the control unit 100 executes the first determination process based on pixel values ​​of each color component (red, green, blue) of the read image using the image reading unit 53 (e.g., CIS) whose reading area extends to a position where it overlaps the outer edge member 162 on a plane. In other words, only a portion of the read image by the image reading unit 53 is used, rather than the entire image.

[0049] Until the carriage 51 reaches the end DE1 of the first white reference plate 164, the read image will not be the white of the first white reference plate 164, but will be a color other than white, for example, black. In other words, when the read image becomes white, it means that the carriage 51 has reached the downstream end DE1 of the first white reference plate 164. For example, if the distance DB is approximately 3 mm and the movement amount of the carriage 51 per drive pulse of the motor of the drive mechanism 121 is 0.042328 mm, and if two pulses constitute one step, the movement amount of the carriage 51 is approximately 0.085 mm, so the carriage 51 will reach the downstream end DE1 of the first white reference plate 164 after 36 movements (≒0.085 × 36).

[0050] The method for determining whether a scanned image is white will be described below. The control unit 100 calculates the average value of the image data of each color component (red, green, blue) obtained from the image scanning unit 53 (CIS), determines whether each calculated average value is equal to or greater than a predetermined threshold value set for determining white, and determines whether the scanned image is white based on the determination result.

[0051] Figure 6 is a table showing the relationship between the average value of image data for each color and the black-and-white discrimination result. "Low" in the figure indicates a value below the threshold, "High" in the figure indicates a value above the threshold, and "Any" in the figure indicates that the value is not related to the threshold. As can be seen from the table shown in Figure 6, for example, when the average value of green image data (Ave G) is "High" or when the average value of blue image data (Ave B) is "High," the scanned image is determined to be white.

[0052] The control unit 100 sets the position of the carriage 51 when it determines that the read image is white (downstream end DE1 of the first white reference plate 164) as the base point, moves the carriage 51 from here a predetermined first distance D1 (first distance D1 = length L1 between end DE1 of the first white reference plate 164 and the home position HP) in the first direction DR1, stops the carriage 51, and positions the carriage 51 at this position as the home position HP. If the length L1 is set to approximately 2 mm, the carriage 51 is moved by 48 pulses (≈0.042328 × 48).

[0053] Next, the process of positioning carriage 51 at home position HP, which is performed by control unit 10 of image forming apparatus 1, will be described with reference to the flowchart shown in Fig. 7. This process is performed when control unit 100 causes image reading unit 53 to read the image of the document placed in document placement area A1 of contact glass 161, and then positions carriage 51 at home position search start position ST.

[0054] While moving carriage 51 in first direction DR1 (upstream direction) from home position search start position ST, control unit 100 determines whether the read image represented by the image data is white, based on image data outside document placement area A1 in the main scanning direction that is sequentially read by image reading unit 53. Here, control unit 100 controls the operation of drive mechanism 121 to first move carriage 51 in first direction DR1 (upstream direction) by two pulses (S1), and then controls the operation of image reading unit 53 to obtain image data outside document placement area A1 and determine whether the read image represented by the image data is white (S2).

[0055] If the control unit 100 determines that the scanned image is white (YES in S2), this means that the carriage 51 has reached the downstream end DE1 of the first white reference plate 164, and so it controls the operation of the drive mechanism 121 to move the carriage 51 from its current position in the first direction DR1 (upstream direction) by 48 pulses (S3). The position after this movement becomes the home position HP. Then, the process ends.

[0056] On the other hand, if the control unit 100 determines that the read image is not white (NO in S2), the carriage 51 has not reached the downstream end DE1 of the first white reference plate 164, so the control unit 100 returns to S1 and controls the operation of the drive mechanism 121 to move the carriage 51 by two pulses in the first direction DR1. Thereafter, the control unit 100 repeats the process of S2.

[0057] Next, we will explain the process of positioning carriage 51 again at home position HP after stopping carriage 51 at home position HP through the above positioning and before having image reading unit 53 read the image of the document placed in document placing area A1 of contact glass 161 (for example, when image forming apparatus 1 returns from energy saving mode to normal mode (standby mode)).

[0058] As a result of the control of the drive mechanism 121 by the control unit 100 described above, the carriage 51 is positioned at the home position HP immediately after the image reading process is completed. In this state, when the control unit 100 transitions the operation mode of the image forming apparatus 1 to the energy saving mode and then returns the operation mode to the normal mode (standby mode), it is assumed that the carriage 51 is positioned at the home position HP, but there is a possibility that the carriage 51 may have moved slightly in the sub-scanning direction during the energy saving mode period. Therefore, when the operation mode returns to the normal mode, the control unit 100 again positions the carriage 51 at the home position HP before causing the image reading unit 53 to read the image of the document placed in the document placement area A1.

[0059] When positioning in this manner, the control unit 100 determines whether the read image represented by the image data is white, based on image data that is outside in the main scanning direction from the document placement area A1 read by the image reading unit 53. When the control unit 100 determines that the read image is white, it moves the carriage 51 in the first direction DR1 a predetermined second distance D2 (second distance D2>length L2 between the home position HP and the end DE2 of the second white reference plate 165, second distance D2<length L2+width W2 of the second white reference plate 165 in the sub-scanning direction) and stops the carriage 51.

[0060] Thereafter, the control unit 100 determines whether the read image represented by the image data read by the image reading unit 53 outside the document placement area A1 in the main scanning direction is white, based on the image data. When the control unit 100 determines that the read image is white, the control unit 100 moves the carriage 51 in a second direction DR2 opposite to the first direction DR1 a predetermined third distance D3 (third distance D3 > second distance D2 + length L1) and stops the carriage 51, setting this stopped position as the home position search start position ST. Then, the control unit 100 positions the carriage 51 at the home position HP by executing the process shown in FIG. 7.

[0061] Fig. 8 is a diagram illustrating an example of processing when, after carriage 51 has been stopped at home position HP as described above, carriage 51 is repositioned at home position HP before image reading unit 53 reads the image of the document placed in document placement area A1 on contact glass 161. Fig. 9 is a diagram illustrating an example of control until carriage 51 is positioned at home position search start position ST.

[0062] <Step 1> The control unit 100 performs a black-and-white determination (second determination process) on the read image at the current stop position of the carriage 51. If the image is white, the process proceeds to step 2; if the image is black, the process proceeds to step S11 (FIG. 10) described later.

[0063] <Step 2> The control unit 100 moves the carriage 51 in the first direction DR1 a second distance D2 (355 pulses), and then performs a black-and-white determination (third determination process) on the read image.If the image is white, the process proceeds to step S3; if the image is black, the process proceeds to step S11.

[0064] <Step 3> The control unit 100 moves the carriage 51 in the second direction DR2 a third distance D3 (473 pulses), and then performs a black-and-white determination (fifth determination process) on the read image. If the read image is white, the process proceeds to step S11; if the read image is a color other than white, for example, black (it is determined that the carriage 51 has reached the home position search start position ST), the process proceeds to step S4.

[0065] <Step 4> The control unit 100 moves the carriage 51 in the first direction DR1 a distance of two pulses, then performs a black-and-white determination (first determination process) on the read image. If the image is white (it is determined that the carriage 51 has reached the downstream end DE1 of the first white reference plate 164), the control unit 100 moves the carriage 51 in the first direction DR1 a first distance D1 (48 pulses). This completes positioning of the carriage 51 to the home position HP. If the image is black, step S4 is repeated.

[0066] Next, we will explain the process of repositioning the carriage 51 to the home position HP when it is unclear whether the carriage 51 has been stopped at the home position HP as described above (for example, when the power to the image forming apparatus 1 is turned on from off).

[0067] When the control unit 100 is uncertain whether the carriage 51 has been stopped at the home position HP as described above and repositions the carriage 51 at the home position HP, it moves the carriage 51 in the second direction DR2 a predetermined fourth distance D4 (fourth distance D4 > length L3 from one end 161A of the contact glass 161 to the end DE1 of the first white reference plate 16 on the document placing area A1 side) and stops the carriage 51, thereby positioning the carriage 51 closer to the document placing area A1 than the first white reference plate 164.

[0068] Thereafter, the control unit 100 moves the carriage 51 in the first direction DR1 by a predetermined fifth distance D5 (fifth distance D5<width W1 of the first white reference plate 164 in the sub-scanning direction) and executes a fourth determination process to determine whether the read image indicated by the image data is white, based on the image data outside the document placement area A1 read by the image reading unit 53. If the control unit 100 determines in the fourth determination process that the read image is not white, it moves the carriage 51 again by the fifth distance D5 in the first direction DR1 and executes the fourth determination process again.

[0069] On the other hand, when the control unit 100 determines in the fourth determination process that the scanned image is white, it moves the carriage 51 again in the second direction DR2 by a fifth distance D5 and stops it, and sets the stopped position as the home position search start position ST. Then, the control unit 100 positions the carriage 51 at the home position HP by executing the process shown in FIG.

[0070] Fig. 10 is a diagram illustrating an example of the flow of processing for positioning the carriage 51 at the home position HP, which is performed when it is assumed that the carriage 51 is stopped at a position other than the home position HP. Fig. 11 is a diagram illustrating an example of control until the carriage 51 is positioned at the home position search start position ST.

[0071] <Step 11> The control unit 100 moves the carriage 51 in the second direction DR2 by a fourth distance D4 (1064 pulses), and then performs a black-and-white determination on the scanned image. If the scanned image is a color other than white, for example, black, the process proceeds to step S12. In theory, it is impossible for the scanned image to be determined as white. The control unit 100 controls the display on the display unit 473 to notify the user of the error.

[0072] <Step 12> The control unit 100 moves the carriage 51 a fifth distance D5 (189 pulses) in the first direction DR1, bringing the carriage 51 closer to the first white reference plate 164. Thereafter, a black-and-white determination (fourth determination process) is performed on the read image, and if the image is black, step S12 is repeated to bring the carriage 51 even closer to the first white reference plate 164. If the image is white, the carriage 51 has reached the first white reference plate 164, so the control unit 100 moves the carriage 51 a fifth distance D5 (189 pulses) in the second direction DR2, placing the carriage 51 downstream in the sub-scanning direction from the first white reference plate 164, and then proceeds to step S13.

[0073] <Step 13> The control unit 100 sets the current position as the home position search start position ST, moves the carriage 51 a distance of two pulses in the first direction DR1, and then performs a black-and-white determination (first determination process) on the read image. If the read image is white, the control unit 100 moves the carriage 51 a first distance D1 (48 pulses) in the first direction DR1. This completes the positioning of the carriage 51 to the home position HP. If the read image is a color other than white, for example, black, step S13 is repeated.

[0074] 10 and 11 is a process that is performed when it is unclear whether the carriage 51 has stopped at the home position HP as described above. As an example of this case, the number of black and white determinations (black and white detections) that are performed before the carriage 51 is positioned at the home position HP will be explained, taking as an example a case where the carriage 51 is stopped at the home position HP when the power is turned on.

[0075] The control unit 100 performs one black-and-white determination after the movement (1064 pulses, 45.04 mm) in <Step 11>. The carriage 51 is positioned approximately 43 mm (= 45.04 - 2) downstream in the sub-scanning direction from the downstream edge DE1 of the first white reference plate 164. The control unit 100 detects a white image during the sixth movement (189 pulses, 8.0 mm) in <Step 12>, resulting in six black-and-white determinations. The home position search start position ST is set to a position approximately 3 mm from the downstream edge DE1 of the first white reference plate 164, and the carriage 51 is moved 0.085 mm at a time toward the downstream edge DE1 of the first white reference plate 164. Therefore, the carriage 51 reaches the downstream edge DE1 of the first white reference plate 164 during the 36th black-and-white determination (≒ 3 mm / 0.085 mm). Therefore, the number of black and white determinations in this case is 43 (=1+36+6).

[0076] In addition, if the control unit 100 determines that the read image is not white in the second judgment process, if it determines that the read image is not white in the third judgment process, or if it determines that the read image is white in the fifth judgment process, it may perform the process described above when positioning the carriage 51 at the home position HP again when it is unclear whether the carriage 51 has stopped at the home position HP.

[0077] According to the above embodiment, the carriage 51 can be accurately positioned at the home position HP without providing a dedicated sensor for detecting that the carriage 51 has reached the home position HP. Also, because the carriage 51 is first positioned at the home position search start position ST and then positioned at the home position HP, the time required for positioning can be shortened. Therefore, without providing a dedicated sensor, the carriage 51 can be accurately positioned at the home position HP, and the required time can also be shortened.

[0078] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible. Furthermore, in the above embodiment, the configuration and processing shown in the above embodiment using Figures 1 to 11 are merely one embodiment of the present invention, and it is not intended that the present invention be limited to these configurations and processing. [Explanation of symbols]

[0079] 1. Image forming device 12 Image forming unit 51 Carriage 52 Light source 53 Image reading unit 121 Drive mechanism 161 Contact Glass 162 Outer edge member 164 1st white reference plate 165 2nd white reference plate

Claims

1. a contact glass for placing a document thereon; a carriage that has a light source that irradiates light along a main scanning direction toward a document placed on the contact glass, and that is disposed on the lower surface of the contact glass opposite to the upper surface on which the document is placed, and that moves back and forth in a sub-scanning direction that is perpendicular to the main scanning direction; a drive mechanism that moves the carriage in a sub-scanning direction; an image reading unit that receives reflected light of light emitted from the light source and reads an image of a document placed on the contact glass; a control unit that controls operations of the light source, the drive mechanism, and the image reading unit to move the carriage in the sub-scanning direction and cause the image reading unit to read an image of a document placed on the contact glass; an outer edge member disposed on the outer edge of the contact glass; a first white reference plate that is arranged within an arrangement area of ​​the contact glass, has a long side extending in the main scanning direction, and is arranged so as to overlap the outer edge member in a plane; the first white reference plate is disposed at a position from one end of the contact glass to a document placement area on the contact glass in the sub-scanning direction; The control unit after causing the image reading unit to read the image of the document placed on the contact glass, when positioning the carriage at a home position in the sub-scanning direction that is set within an area where the first white reference plate is placed and that serves as a standby position for the carriage, controlling the operation of the drive mechanism to move the carriage to a predetermined home position search start position that is on the document placement area side with respect to the area where the first white reference plate is placed and stop the carriage; While moving the carriage in a first direction from the home position search start position toward an area where the first white reference plate is placed, a first determination process is executed to determine whether a read image indicated by the image data is white, based on image data that is read sequentially by the image reading unit and that is outside the document placement area in the main scanning direction; An image reading device that positions the carriage at the home position by moving the carriage a predetermined distance from the side end of the first white reference plate on the document placement area side in the first direction to the home position position, using the position of the carriage at the time when the read image is determined to be white in the first judgment process as a base point, and then stopping the carriage.

2. a second white reference plate that is spaced apart from the first white reference plate in the sub-scanning direction, that is closer to the one end of the contact glass than the first white reference plate in the sub-scanning direction, and that has a long side extending in the main scanning direction and is arranged to overlap the outer edge member in plan view, When the control unit stops the carriage at the home position by the positioning and then positions the carriage at the home position again before causing the image reading unit to read an image of the document placed on the contact glass, executes a second determination process to determine whether a read image indicated by the image data read by the image reading unit outside the document placement area is white; When it is determined in the second determination process that the read image is white, the carriage is moved in the first direction by a predetermined second distance D2, which is longer than a length L2 between the home position and the side end of the second white reference plate on the document placement area side and shorter than the sum of the length L2 and a width W2 of the second white reference plate in the sub-scanning direction, and then stopped. executes a third determination process to determine whether a read image indicated by the image data outside the document placement area read by the image reading unit at the stopped position is white, 2. The image reading device of claim 1, wherein when the third judgment process determines that the read image is white, the carriage is moved in a second direction opposite to the first direction by a predetermined third distance D3 longer than the second distance D2 + length L1 and stopped, and the first judgment process and the positioning are performed using this stopped position as the home position search start position.

3. When the control unit performs positioning of the carriage to the home position again when it is unclear whether the carriage has been stopped at the home position by the positioning, the carriage is moved in a second direction opposite to the first direction by a predetermined fourth distance D4 that is longer than a length L3 from the one end of the contact glass to a side end of the first white reference plate on the document placement area side, and then stopped; and the carriage is disposed closer to the document placement area than the first white reference plate; After the placement, the carriage is moved in the first direction by a predetermined fifth distance D5 that is shorter than the width W1 of the first white reference plate in the sub-scanning direction, and a fourth determination process is executed to determine whether or not the read image indicated by the image data is white based on the image data outside the document placement area that is read by the image reading unit at this time; When it is determined in the fourth determination process that the read image is not white, the carriage is moved again in the first direction by the fifth distance D5, and the fourth determination process is executed again; 2. The image reading device of claim 1, wherein when the read image is determined to be white, the carriage is moved a fifth distance D5 in the second direction and stopped, and the stopped position is used as the home position search start position, and the first judgment process and the positioning are performed.

4. An image reading device according to any one of claims 1 to 3; an image forming unit that forms an image obtained by reading with the image reading device on a recording medium;

Images