JP2016173412A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent extra frequent changes in conveyance speed.SOLUTION: When it is determined that predetermined requirements are satisfied, size information is stored in a first memory, thereby preventing conveyance speed from being change frequently more than necessary. For example, after the size of a sheet actually conveyed is detected, even if the size of a sheet to be conveyed next is different from that of the sheet conveyed previously, size information is not stored unless it is determined that the predetermined requirements are satisfied. Extra frequent changes in conveyance speed can be prevented, accordingly.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  For example, in the image forming apparatus described in Patent Document 1, when the size of a sheet (hereinafter referred to as a designated size) included in an image forming command signal issued from a host (computer) to the image forming apparatus is a small size. When the sheet is transported in the low speed mode and the designated size is other than the small size, the sheet is transported in the normal speed mode in which the transport speed is higher than that in the low speed mode. That is, the image forming apparatus described in Patent Document 1 has a configuration in which the conveyance speed can be switched in accordance with the size of the conveyed sheet.

JP 2003-076117 A

  By the way, there is a case where the size of the actually conveyed sheet is different from the designated size. For this, a sheet sensor is provided in the sheet conveyance path, a sheet size is detected using a signal output from the sheet sensor, and a conveyance speed is switched according to the detected sheet size. And it is sufficient.

  However, in the above configuration, there is a possibility that the transfer speed switching operation occurs more frequently than necessary. If the switching operation frequently occurs, there is a possibility that an image cannot be formed efficiently. The switching operation frequently occurs when, for example, the size of the sheet that is actually conveyed is detected, and then the sheet that is conveyed next has a size different from the size of the sheet that has been conveyed first. For example, it is detected that there is.

  In view of the above points, an object of the present invention is to suppress occurrence of a switching operation of a conveyance speed more frequently than necessary.

  In the present application, a housing (3), a paper feed tray (17), an image forming mechanism (5) provided in the housing (3) for forming an image on a sheet, a paper discharge tray (3A), A transport mechanism (15, 19) having a transport path from the paper feed tray (17) to the paper discharge tray (3A) via the image forming mechanism (5), and transporting the sheet along the transport path; A sheet sensor (S1) that is provided in the path and outputs signals of different levels depending on whether or not a sheet is present at a predetermined position in the conveyance path, a memory (M1), and a control unit (20) are provided.

  The control unit (20) is predetermined by size detection processing for detecting the size of the sheet based on a signal output from the sheet sensor (S1), determination processing for determining whether a predetermined requirement set in advance is satisfied, and determination processing. When it is determined that the requirement is satisfied, the size information indicating the size detected in the size detection process is stored in the memory (M1), and the size information stored in the memory (M1) in the size storage process is the first size information. When it is determined that the first size is the first size or the first size is determined by the first size determination process and the first size determination process, the first speed is set and the first size is determined. When it is determined in the size determination process that the size is the second size, the speed setting process for setting a second speed different from the first speed, and the transport mechanism (15, 19 at the speed set in the speed setting process). And executes the operating process for operating the.

  In the present invention, when it is determined that the predetermined requirement is satisfied, the size information indicating the size detected in the size detection process is stored in the memory (M1), so that the conveyance speed switching operation is performed more frequently than necessary. Generation | occurrence | production can be suppressed.

  That is, in the present invention, for example, after the size of the actually conveyed sheet is detected, the next conveyed sheet is detected to be a size different from the size of the previously conveyed sheet. If it is determined that the predetermined requirement is not satisfied, the size information indicating the size detected in the size detection process is not stored in the memory (M1). Therefore, it can be suppressed that the switching operation of the conveyance speed occurs more frequently than necessary.

  Incidentally, the reference numerals in parentheses for each of the above means are examples showing the correspondence with the specific means described in the embodiments described later, and the present invention is indicated by the reference numerals in the parentheses of the above respective means. It is not limited to specific means.

1 is a central sectional view of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a control system of the image forming apparatus 1 according to the embodiment of the present invention. It is a flowchart which shows main control. It is a flowchart which shows conveyance speed determination control. It is a flowchart which shows a size information initialization system. It is a flowchart which shows the size information update control which concerns on 1st Embodiment. It is a flowchart which shows the size information update control which concerns on 2nd Embodiment. It is a flowchart which shows the size information update control which concerns on 3rd Embodiment. It is a flowchart which shows the size information update control which concerns on 4th Embodiment.

(First embodiment)
The “embodiment of the invention” described below shows an example of the embodiment. In other words, the invention specific items described in the claims are not limited to the specific means and structures shown in the following embodiments.

  In this embodiment, the present invention is applied to a monochrome image forming apparatus. The image forming apparatus according to this embodiment is used by being connected to a computer. At least one member or part described with at least a reference numeral is provided, except where “plurality”, “two or more”, and the like are omitted. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
1. Outline of Mechanical Configuration of Image Forming Apparatus As shown in FIG. 1, an image forming mechanism 5 is accommodated in a housing 3 of the image forming apparatus 1. The image forming mechanism 5 forms an image on a sheet. The image forming mechanism 5 is an electrophotographic system having a developing cartridge 7, a photosensitive drum 8, an exposure device 9, a fixing device 11, and the like.

  The developing cartridge 7 has a developing roller 7A, a storage portion 7B, and the like. The photosensitive drum 8 carries a developer image. The charger 8A charges the photosensitive drum 8. The exposure device 9 exposes the charged photosensitive drum 8. Thereby, an electrostatic latent image is formed on the photosensitive drum 8.

  The developing roller 7A supplies the developer stored in the storage unit 7B to the photosensitive drum 8. As a result, a developer image is formed on the photosensitive drum 8. A transfer roller 13 is disposed at a position facing the photosensitive drum 8.

  The transfer roller 13 transfers the developer image carried on the photosensitive drum 8 onto the sheet. The fixing device 11 fixes the developer transferred to the sheet to the sheet. The fixing device 11 includes a heating roller 11A, a pressing roller 11B, and the like.

  The heating roller 11A heats the developer directly or indirectly. The pressing roller 11B presses the sheet against the heating roller 11A. The fixing device 11 conveys the sheet toward the sheet discharge tray 3A. A sheet on which an image is formed is placed on the paper discharge tray 3A.

  A first feeder mechanism 15A and a second feeder mechanism 15B are provided upstream of the image forming mechanism 5 in the sheet conveying direction. The first feeder mechanism 15A sends out the sheets placed on the first paper feed tray 17A one by one toward the image forming mechanism 5 side.

  The second feeder mechanism 15B sends out the sheets placed on the second paper feed tray 17B one by one toward the image forming mechanism 5 side. The first paper feed tray 17 </ b> A and the second paper feed tray 17 </ b> B can be displaced with respect to the apparatus main body such as the housing 3 on the lower side of the image forming mechanism 5 in the apparatus main body.

  Hereinafter, the first paper feed tray 17A and the second paper feed tray 17B are collectively referred to as the paper feed tray 17. The first feeder mechanism 15A and the second feeder mechanism 15B are collectively referred to as a feeder mechanism 15.

  Note that the paper feed tray 17 according to the present embodiment is detachably attached to the apparatus main body. For this reason, the user can attach and detach the paper feed tray 17 with respect to the apparatus body when replenishing the paper feed tray 17 or changing the sheet placed in the paper feed tray 17. .

  The sheet placed on the paper feed tray 17 is transported along a transport path (transport path) Lo from the paper feed tray 17 through the image forming mechanism 5 to the paper discharge tray 3A. The feeder mechanism 15 and the pair of registration rollers 19 form a conveyance mechanism that conveys the sheet along the conveyance path.

  The pair of registration rollers 19 is provided upstream of the image forming mechanism 5 (photosensitive drum 8) in the sheet conveying direction and corrects the posture of the sheet fed to the image forming mechanism 5. A sheet sensor S1 is provided upstream of the image forming mechanism 5 in the sheet conveyance direction.

  The sheet sensor S1 outputs a signal for detecting whether or not there is a sheet at a predetermined position in the conveyance path. That is, the sheet sensor S1 outputs a signal corresponding to the presence or absence of a sheet. The sheet sensor S1 according to the present embodiment outputs a low (Lo) level signal when detecting the presence of a sheet, and outputs a high (Hi) level signal when detecting the absence of a sheet.

2. Outline of Electrical Configuration of Image Forming Apparatus The operation of the transport mechanism is controlled by the control unit 20 as shown in FIG. In the present embodiment, the operation of the image forming mechanism 5 is also controlled by the control unit 20. The control unit 20 is configured by a microcomputer having a CPU, a ROM, a RAM, and the like. A program for controlling the transport mechanism and the image forming mechanism 5 is stored in advance in a nonvolatile storage unit such as a ROM.

  The control unit 20 (image forming apparatus 1) starts and controls the operations of the transport mechanism and the image forming mechanism 5 in response to an image forming command from the computer. The image formation command is information including at least image data and designated size information.

  Image data is data relating to an image formed on a sheet. The designated size information is information indicating the sheet size on which an image is to be formed. The designated size information is size information set by the user via software such as a printer driver incorporated in the computer.

  The control unit 20 receives signals output from the sheet sensor S1, the first tray sensor S2, and the second tray sensor S3. The first tray sensor S2 outputs a signal for detecting whether or not the first paper feed tray 17A is mounted at the proper position. The second tray sensor S3 outputs a signal for detecting whether or not the second paper feed tray 17B is mounted at a regular position.

  The regular position refers to a position where a sheet can be fed from the sheet feed tray 17 (the first sheet feed tray 17A and the second sheet feed tray 17B) to the image forming mechanism 5. For this reason, when the sheet feeding tray 17 is located at a position shifted from a normal position (hereinafter also referred to as a feeding position) with respect to the housing 3 (apparatus main body), the sheet is directed toward the image forming mechanism 5. It cannot be fed.

  The first tray sensor S2 and the second tray sensor S3 output a signal according to whether or not the paper feed tray 17 is at the feeding position. The first tray sensor S2 and the second tray sensor S3 according to this embodiment output a low (Lo) level signal when the paper feed tray 17 is at the feed position, and the paper feed tray 17 is at the feed position. If not, a high (Hi) level signal is output.

  A first memory M1 and a second memory M2 are connected to the control unit 20. In the first memory M1, information indicating the sheet size (hereinafter referred to as size information) is stored in a state corresponding to each of the first paper feed tray 17A and the second paper feed tray 17B.

  Hereinafter, the size information of the sheet fed from the first paper feed tray 17A is referred to as first size information. The size information of the sheet fed from the second paper feed tray 17B is referred to as second size information. The first size information and the second size information are collectively referred to as size information.

  The second memory M2 stores a conveyance speed when the sheet is conveyed by the conveyance mechanism. That is, the control unit 20 controls the operating speeds of the transport mechanism and the image forming mechanism 5 so that the sheet is transported at the transport speed (hereinafter referred to as a set speed) stored in the second memory M2.

  The first memory M1 and the second memory M2 are rewritable nonvolatile storage units, and information is written (stored) and read by the control unit 20. A storage device in which the first memory M1 and the second memory M2 are integrated with the control unit 20 may be used.

3. 3. Control Operation by Control Unit 3.1 Outline of Control FIGS. 3 to 6 are flowcharts showing the control operation by the control unit 20. A program for executing the control shown in each flowchart is stored in advance in a nonvolatile storage unit such as a ROM. The controller 20 (CPU) reads these programs and controls the operations of the transport mechanisms 15 and 19 and the image forming mechanism 5.

  The control shown in FIG. 3 (hereinafter referred to as main control) is activated when an image forming command is sent to the image forming apparatus 1 from a computer or the like. The control shown in FIG. 4 is a sub-control (referred to as conveyance speed determination control) that is activated in the main control. Specifically, the control is for determining a setting speed (hereinafter referred to as a scheduled writing setting speed) to be stored in the second memory M2 using the size information stored in the first memory M1. Control.

  The control shown in FIGS. 5 and 6 is a control that starts and operates independently of the main control. Specifically, the control is to acquire information on the size information to be stored in the first memory M1, determine the size information using the acquired information, and write the size information in the first memory M1. Control.

3.2 Main control (see Fig. 3)
When an image formation command is issued from the computer or the like to the image forming apparatus 1 and this control program is started, after the conveyance speed determination control is executed (S1), it is determined whether it is necessary to switch the set speed. (S3).

  Specifically, in S3, it is determined whether or not the current set speed, that is, the set speed currently written in the second memory M2 is the same as the scheduled write setting speed determined in S1. Is done.

  If it is determined in S3 that the set speed needs to be switched (S3: YES), it is determined whether or not the number of sheets required to form an image is less than a predetermined number (S5). That is, at the time when the number determination process of S5 is executed, it is determined whether or not the remaining number of sheets on which an image needs to be formed is less than a predetermined number set in advance.

  When it is determined that the remaining number of sheets is not less than the predetermined number (S5: NO), a sheet on which an image is currently formed or a sheet already fed from the sheet feed tray 17 is placed in the sheet discharge tray 3A. It is determined whether or not the discharge has been completed, that is, whether or not the discharge has been completed (S7).

  If it is determined that the discharge has not been completed (S7: NO), S7 is executed again. When it is determined that the discharge is completed (S7: YES), the transport mechanisms 15 and 19 are stopped and the sheet transport is stopped (S9).

  Next, after the set speed stored in the second memory M2 is rewritten to the writing scheduled set speed determined in S1 and the carry speed is switched (S11), the carry mechanism is updated at the updated set speed. 15 and 19 are activated, and sheet feeding is started (S13).

  If it is determined in S3 that it is not necessary to switch the set speed (S3: NO), and if it is determined in S5 that the remaining number of sheets is less than the predetermined number (S5: YES) ), S7 to S11 are not executed, and sheet feeding / conveyance is started (S13). That is, in this case, the sheet is fed / conveyed at the set speed stored in the second memory M2 when S3 or S5 is executed without updating the set speed.

  When the sheet is fed / conveyed (S13), it is determined whether or not there is a next page, that is, whether or not the sheet needs to be further fed (S15). If it is determined that there is a next page (S15: YES), S1 is executed. When it is determined that there is no next page (S15: NO), this control ends.

3.3 Transfer speed judgment control (see Fig. 4)
When the conveyance speed determination control is activated, it is determined whether or not the designated size included in the image formation command is the first size (S21). The first size refers to a size smaller than a normal size (for example, A4 size). Hereinafter, a size larger than the first size (for example, a normal size) is referred to as a second size.

  If it is determined that the designated size is the first size (S21: YES), it is determined that the writing preset speed is the first speed (S23). The first speed is a conveyance speed that is smaller than the conveyance speed (hereinafter referred to as the second speed) when conveying the second size sheet. Specifically, the first speed is about ½ of the second speed.

  If it is determined that the designated size is not the first size (S21: NO), it is determined whether or not the paper feed tray 17 as the paper feed source is the first paper feed tray 17A (S25). When it is determined that the paper supply source is the first paper supply tray 17A (S25: YES), it is determined whether or not the first size information is the first size (S27).

  When it is determined that the first size information is the first size (S27: YES), it is determined that the writing preset speed is the first speed (S29). When it is determined that the first size information is not the first size, that is, the first size information is the second size (S27: NO), it is determined that the writing preset speed is the second speed ( S31).

  If it is determined that the paper source is not the first paper tray 17A, that is, the paper source is the second paper tray 17B (S25: NO), whether or not the second size information is the first size. Is determined (S33).

  When it is determined that the second size information is the first size (S33: YES), it is determined that the writing preset speed is the first speed (S35). When it is determined that the second size information is not the first size, that is, the second size information is the second size (S33: NO), it is determined that the writing preset speed is the second speed ( S37).

3.4 Size information initialization control (see Fig. 5)
The size information initialization control starts when a power switch (not shown) of the image forming apparatus 1 is turned on and stops when the power switch is turned off.

  When the size information initialization control is activated, a signal output from the first tray sensor S2 indicates whether or not the first paper feed tray 17A has been opened, that is, whether or not the first paper feed tray 17A has shifted from the feeding position. It is determined using (S41).

  If it is determined that the first paper feed tray 17A has been opened (S41: YES), initialization is performed to set the first size information to the second size (S43). If it is determined that the first paper feed tray 17A is not opened (S41: NO), whether or not the second paper feed tray 17B has been opened is determined using a signal output from the second tray sensor S3. (S45).

  If it is determined that the second paper feed tray 17B has been opened (S45: YES), initialization is performed with the second size information as the second size (S47). If it is determined that the second paper feed tray 17B is not opened (S45: NO), S41 is executed.

As is clear from the size information initialization control, the second size is stored in the first memory M1 as size information unless updated by the size information update control (see FIG. 6).
3.5 Size information update control (see Fig. 6)
The size information update control is executed when an image formation command is issued to the image forming apparatus 1, that is, when printing (image formation) is started (S51).

  When image formation is started and a sheet is fed from the sheet feed tray 17 (S51: YES), the size of the sheet is detected (measured) using a signal output from the sheet sensor S1 (S53). In other words, by multiplying the set speed by the time when the low level signal is output from the sheet sensor S1, the dimension (size) of the part parallel to the conveying direction is measured among the outer dimensions of the sheet.

  When the size measurement is completed (S53: YES), it is determined whether or not the paper supply source tray 17 is the first paper supply tray 17A (S55). When it is determined that the paper supply source is the first paper supply tray 17A (S55: YES), it is determined whether or not the size measured in S53 (hereinafter referred to as the measurement size) is the first size. (S57).

  When it is determined that the measurement size is the first size (S57: YES), the first size is stored in the first memory M1 as the first size information (S59). When it is determined that the measurement size is not the first size, that is, the measurement size is the second size (S57: NO), the second size is stored in the first memory M1 as the first size information (S61). .

  If it is determined that the paper feed source is not the first paper feed tray 17A, that is, the paper feed source is the second paper feed tray 17B (S55: NO), whether or not the measurement size is the first size is determined. It is determined (S63).

  When it is determined that the measurement size is the first size (S63: YES), the first size is stored in the first memory M1 as the second size information (S65). When it is determined that the measurement size is not the first size, that is, the measurement size is the second size (S63: NO), the second size is stored in the first memory M1 as the second size information (S67). .

  When the measurement size information is stored in the first memory M1 as size information, it is determined whether or not the paper feed tray 17 as the paper feed source has been switched (S69). When it is determined that the paper feed tray 17 as the paper feed source has been switched (S69: YES), S53 is executed.

  If it is determined that the paper supply source tray 17 has not been switched (S69: NO), it is determined whether or not image formation has ended (S71), and when image formation has ended (S71). : YES), this control is finished.

4). Characteristics of Image Forming Apparatus According to this Embodiment In this embodiment, when it is determined that a predetermined requirement is satisfied, the measurement size is stored in the first memory M1 as size information, so the conveyance speed is switched more frequently than necessary. It can suppress that operation | movement will generate | occur | produce.

  In the present embodiment, “satisfying the predetermined requirement” means that (a) when sheet feeding is started (see FIG. 6), (b) after feeding from the first sheet feeding tray 17A, When the paper is fed from the second paper feed tray 17B (see FIG. 6), or fed from the second paper feed tray 17B and then fed from the first paper feed tray 17A (FIG. 6). (C) When the presence of a sheet from the sheet feeding tray 17 is detected using the first tray sensor S2 or the second tray sensor S3 (see FIG. 5).

  Therefore, in the present embodiment, for example, after the size of the actually conveyed sheet is measured, the next conveyed sheet is detected to be a size different from the size of the previously conveyed sheet. However, when it is determined that the predetermined requirement is not satisfied, the size information is not updated. Therefore, it can be suppressed that the switching operation of the conveyance speed occurs more frequently than necessary.

  In the present embodiment, it is possible to suppress an excessive increase in temperature at the non-sheet passing portion of the fixing device 11 (heating roller 11A). That is, since the first speed has a low conveyance speed, the time during which the fixing device 11 is in contact with the sheet can be lengthened. For this reason, the sheet and the developer can be sufficiently heated without greatly increasing the temperature of the fixing device 11 and increasing the temperature difference between the fixing device 11 and the sheet.

  The non-sheet passing portion of the fixing device 11 refers to a portion of the fixing device 11 (heating roller 11A) that does not contact the sheet. That is, the size of the fixing device 11, that is, the dimensions of the heating roller 11A and the pressing roller 11B in the axial direction are adapted to the dimensions of the maximum size sheet that can be conveyed.

  For this reason, when a sheet of a size (first size in the present embodiment) smaller than the maximum size sheet (second size in the present embodiment) is conveyed, the fixing device 11 (heating roller 11A) A part that does not contact the sheet is generated.

  Further, since the first speed is low in the conveyance speed, the heat of the non-sheet passing portion of the fixing device 11 can be diffused to the paper passing portion of the fixing device 11, so that the temperature excessively increases in the non-sheet passing portion. Can be suppressed. That is, since the non-sheet passing portion is a portion that does not contact the sheet, the cooling effect due to contact with the sheet is small.

  However, as described above, in this embodiment, it is not necessary to greatly increase the temperature of the fixing device 11, so that the heat of the non-sheet passing portion of the fixing device 11 can be diffused to the sheet passing portion of the fixing device 11. Although the second speed has a high conveyance speed, the temperature of the non-sheet passing portion does not increase excessively because the range of the sheet passing portion is large.

  In the present embodiment, when the designated size is the first speed, the set speed is the first speed, and when the designated size is not the first speed, the measurement size is set as the set speed. Generation can be suppressed.

  That is, as the conveying speed increases, images can be formed on many sheets in a short time. However, the higher the conveyance speed, the higher the possibility that a conveyance defect will occur. On the other hand, in the present embodiment, when the designated size is the first size, the set speed is the first speed, so that the occurrence of a conveyance failure can be suppressed.

  When the designated size is not the first size, the measurement size is set as the set speed, so that an appropriate conveyance speed can be set as the set speed. Therefore, it is possible to suppress the occurrence of conveyance failure.

  In the present embodiment, the size information is stored in a state corresponding to each of the first paper feed tray 17A and the second paper feed tray 17B. As a result, even when the paper feed tray 17 to which the sheet is supplied is changed, it is possible to obtain size information corresponding to the sheet size of the sheet placed on the paper feed tray 17.

(Second Embodiment)
As shown in FIG. 7, the present embodiment is a modification of the size information update control (FIG. 6). In FIG. 7, the same processes as those in FIG. 6 are denoted by the same reference numerals as those in FIG. Hereinafter, only processing different from FIG. 6 (size information update control according to the first embodiment) will be described.

  If it is determined in S71 that image formation has not ended (S71: NO), it is determined whether or not the size information of the paper feed tray 17 currently being fed is the first size (S73). ). If it is determined that the size information is the first size (S73: YES), S69 is executed. When it is determined that the size information is not the first size, that is, the size information is the second size (S73: NO), S53 is executed.

Accordingly, in the present embodiment, priority is given to “conveying the sheet at the first speed”, so that the occurrence of a conveyance failure can be suppressed.
(Third embodiment)
This embodiment is a modification of the size information update control (FIG. 6) as shown in FIG. In FIG. 8, the same processes as those in FIG. 6 are denoted by the same reference numerals as those in FIG. Hereinafter, only processing different from FIG. 6 (size information update control according to the first embodiment) will be described.

  If it is determined in S71 that the image formation has not ended (S71: NO), it is determined whether or not the size information of the paper feed tray 17 currently being fed is the second size (S75). ). When it is determined that the size information is the second size (S75: YES), S69 is executed. When it is determined that the size information is not the second size, that is, the size information is the first size (S75: NO), S53 is executed.

Thereby, in this embodiment, it is possible to achieve both “high-speed printing that forms an image on many sheets in a short time” and “characteristics of occurrence of conveyance failure”.
(Fourth embodiment)
This embodiment is a modification of size information update control as shown in FIG.

  When image formation is started and a sheet is fed from the sheet feed tray 17 (S81: YES), the size of the sheet is measured using a signal output from the sheet sensor S1 (S83). When the size measurement is completed (S83: YES), it is determined whether or not the paper feed tray 17 as the paper feed source is the first paper feed tray 17A (S85).

  When it is determined that the paper supply source is the first paper supply tray 17A (S85: YES), the size measurement process (S83) is performed on the sheet supplied from the first paper supply tray 17A. The number of times (hereinafter referred to as “T1 sheet size measurement number”) is increased by 1 (S87).

  The number of T1 sheet size measurements is stored in a rewritable nonvolatile storage device (not shown). In the present embodiment, the T1 sheet size measurement count is written in an area provided in the first memory M1.

  Next, it is determined whether or not the measurement size is the first size (S89). When it is determined that the measurement size is the first size (S89: YES), the number of times the first size sheet is fed from the first paper feed tray 17A (hereinafter referred to as “T1 first size measurement count”). Is increased by one (S91). In the present embodiment, the T1 first size measurement count is also written in an area provided in the first memory M1.

  When it is determined that the measurement size is not the first size, that is, the measurement size is the second size (S89: NO), the number of times the second size sheet has been fed from the first paper feed tray 17A (hereinafter referred to as “second size”) , “T1 second size measurement count”) is incremented by one (S93). In the present embodiment, the T1 second size measurement count is also written in an area provided in the first memory M1.

  Next, it is determined whether or not the T1 sheet size measurement count is equal to or greater than a preset predetermined count (for example, 5 times) (S95). If it is determined that the T1 sheet size measurement count is equal to or greater than the predetermined count (S95: YES), it is determined whether the T1 first size measurement count is greater than the T1 second size measurement count (S97).

  When it is determined that the T1 first size measurement count is larger than the T1 second size measurement count (S97: YES), the first size is stored in the first memory M1 as the first size information (S99). When it is determined that the T1 first size measurement count is equal to or less than the T1 second size measurement count (S97: NO), the second size is stored in the first memory M1 as the first size information (S101).

  Next, it is determined whether or not the image formation is completed (S119). When the image formation is completed (S119: YES), this control is ended. If it is determined that the T1 sheet size measurement count is not equal to or greater than the predetermined count (S95: NO), S119 is executed.

  When it is determined in S85 that the paper source is not the first paper tray 17A, that is, the paper source is the second paper tray 17B (S85: NO), paper is fed from the second paper tray 17B. The number of times the size measurement process (S83) is performed on the sheet that has been executed (hereinafter referred to as “T2 sheet size measurement count”) is increased by one (S103).

  The T2 sheet size measurement count is stored in a rewritable nonvolatile storage device (not shown). In the present embodiment, the T2 sheet size measurement count is written in an area provided in the first memory M1.

  Next, it is determined whether or not the measurement size is the first size (S105). When it is determined that the measurement size is the first size (S105: YES), the number of times the first size sheet is fed from the second paper feed tray 17B (hereinafter, “T2 first size measurement count”). Is increased by one (S107). In the present embodiment, the T2 first size measurement count is also written in an area provided in the first memory M1.

  When it is determined that the measurement size is not the first size, that is, the measurement size is the second size (S105: NO), the number of times the second size sheet has been fed from the second paper feed tray 17B (hereinafter referred to as “second size”) , “T2 second size measurement count”) is incremented by one (S109). In the present embodiment, the T2 second size measurement count is also written in an area provided in the first memory M1.

  Next, it is determined whether or not the T2 sheet size measurement count is greater than or equal to a preset predetermined count (for example, 5 times) (S111). If it is determined that the T2 sheet size measurement count is greater than or equal to the predetermined count (S111: YES), it is determined whether the T2 first size measurement count is greater than the T2 second size measurement count (S113).

  When it is determined that the T2 first size measurement count is larger than the T2 second size measurement count (S113: YES), the first size is stored in the first memory M1 as the second size information (S115). When it is determined that the T2 first size measurement count is equal to or less than the T2 second size measurement count (S113: NO), the second size is stored in the first memory M1 as second size information (S117).

  Next, it is determined whether or not the image formation is completed (S119). When the image formation is completed (S119: YES), this control is ended. If it is determined that the T2 sheet size measurement count is not equal to or greater than the predetermined count (S111: NO), S119 is executed.

  In the size information initialization control according to the present embodiment, when the initialization process (S43 and S47 in FIG. 5) is executed, in addition to the initialization process in which the size information is the first size, the T1 sheet An initialization process is also performed to set the size measurement count, T1 first size measurement count, T1 second size measurement count, T2 sheet size measurement count, T2 first size measurement count, and T2 second size measurement count to zero.

  As a result, in the present embodiment, “whether the ratio of the number of times the first size is detected is larger than a predetermined ratio” is stored as the size information in the first memory M1 as a predetermined requirement. It can be suppressed that the switching operation of the conveyance speed frequently occurs.

(Other embodiments)
In the above-described embodiment, “an exchange sensor that outputs different signals depending on whether or not there is a sheet in the sheet feeding tray 17 when the sheet feeding tray 17 is in a position where the sheet can be fed to the image forming mechanism 5. ”, The first tray sensor S2 and the second tray sensor S3 are used, but the present invention is not limited to this.

  Specifically, for example, an “empty sensor” that detects whether or not there is a sheet in the sheet feeding tray 17 may be used as the replacement sensor. That is, when the paper feed tray 17 is not at the feeding position, even if a sheet is placed on the paper feed tray 17, the “empty sensor” outputs a signal indicating “no sheet”.

  The image forming apparatus 1 according to the above-described embodiment is a monochrome electrophotographic system, but the present invention is not limited to this, and can be applied to a color electrophotographic system or an ink jet system image forming apparatus. .

  Further, the present invention is not limited to the above-described embodiment as long as it matches the gist of the invention described in the claims.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 3A ... Discharge tray 3 ... Housing 5 ... Image forming mechanism 7 ... Developing cartridge 7A ... Developing roller 7B ... Storage part 8 ... Photosensitive drum 8A ... Charger 9 ... Exposing device 11 ... Fixing device 11A ... Heating Roller 11B ... Pressing roller 13 ... Transfer roller 15A ... First feeder mechanism 15B ... Second feeder mechanism 17A ... First paper feed tray 17B ... Second paper feed tray 19 ... Registration roller 20 ... Control unit S1 ... Seat sensor S2 ... First tray sensor S3 ... Second tray sensor M1 ... First memory M2 ... Second memory

Claims (14)

An image forming mechanism for forming an image on a sheet;
A housing for housing the image forming mechanism;
A paper feed tray on which a sheet conveyed to the image forming mechanism is placed;
A paper discharge tray on which a sheet on which an image is formed is placed;
A transport mechanism having at least a part of a transport path from the paper feed tray to the paper discharge tray via the image forming mechanism, and transporting a sheet along the transport path;
A sheet sensor for detecting whether or not there is a sheet at a predetermined position in the conveyance path, and outputting a signal corresponding to the presence or absence of the sheet;
A memory capable of storing information;
A control unit capable of controlling at least the transport mechanism;
The controller is
A size detection process for detecting the size of the sheet by a signal output from the sheet sensor;
A determination process for determining whether or not a predetermined requirement set in advance is satisfied;
A size storage process for storing size information indicating the size detected in the size detection process in the memory when it is determined that the predetermined requirement is satisfied in the determination process;
A first size determination process for determining whether the size information stored in the memory in the size storage process is a first size or a second size larger than the first size;
An operation process for operating the transport mechanism at a set speed;
If the first size is determined to be the first size in the first size determination process, the first speed is set as the set speed, and the first size determination process is determined to be the second size. In this case, an image forming apparatus that executes a speed setting process for setting a second speed different from the first speed as the set speed.   The image forming apparatus according to claim 1, wherein in the operation process, a sheet placed on the paper feed tray is fed at the set speed. The control unit can execute an image forming process for operating the image forming mechanism to form an image based on image data;
The image forming apparatus according to claim 1, wherein in the size detection process, size detection is performed on a sheet on which an image is formed in the image formation process. A plurality of the paper feed trays;
In the size storing process, a sheet feeding tray to which the sheet subjected to the size detection process is fed and the size information of the sheet fed from the sheet feeding tray are associated with each other and stored in the memory. The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus. When any one of the plurality of sheet feeding trays is a first sheet feeding tray and a sheet feeding tray different from the first sheet feeding tray is a second sheet feeding tray,
In the determination process, “whether or not a sheet is fed from the second sheet feeding tray after the sheet is fed from the first sheet feeding tray” can be determined as the first predetermined requirement.
In the size storing process, when it is determined that the first predetermined requirement is satisfied, the size information of the subsequent sheet detected in the size detecting process is stored in the memory. Item 5. The image forming apparatus according to Item 4. The paper feed tray is displaceable relative to the housing;
An exchange sensor that outputs different signals depending on whether or not there is a sheet in the sheet feeding tray when the sheet feeding tray is in a position where the sheet can be fed to the image forming mechanism;
The control unit executes a replacement detection process for detecting presence or absence of a sheet at the position where the sheet can be fed by a signal output from the replacement sensor,
In the determination process, it is possible to determine “whether or not a sheet is detected from no sheet in the replacement detection process” as the second predetermined requirement,
In the size storing process, after it is determined that the second predetermined requirement is satisfied, the size information of the sheet first detected in the size detecting process is stored in the memory. Item 6. The image forming apparatus according to any one of Items 3 to 5.   After the size information is stored in the memory in the size storage process, the control unit performs the size information until it is detected in the replacement detection process whether there is a sheet at the feedable position. The image forming apparatus according to claim 6, wherein a storage stop process for stopping storage of the data in the memory is executed.   After the control unit detects the presence of a sheet from the absence of a sheet at the feedable position in the replacement detection process, after the size information indicating the first size is first stored in the memory 7. The storage stop process for stopping the storage of the size information in the memory until the presence / absence of a sheet at the relative position is detected in the replacement detection process. Image forming apparatus. The paper feed tray is displaceable relative to the housing;
An exchange sensor that outputs different signals depending on whether or not there is a sheet in the sheet feeding tray when the sheet feeding tray is in a position where the sheet can be fed to the image forming mechanism;
The controller is
An exchange detection process for detecting the presence or absence of a sheet at a position where the sheet can be fed by a signal output from the exchange sensor;
Each time the size detection process detects the size of the sheet conveyed to the image forming mechanism after the replacement detection process detects the presence of a sheet to the presence of a sheet, the number of executions of the size detection process is counted. Whether or not a first size ratio, which is a ratio of the number of times the first size is detected in the size detection process to a value counted in the count process, is greater than a predetermined ratio set in advance. Execute the rate determination process to determine,
The determination process can determine whether the value counted in the count process has reached a predetermined value as the third predetermined requirement,
In the size storage process, when it is determined by the determination process that the third predetermined requirement is satisfied, and when it is determined by the ratio determination process that the first size ratio is larger than the predetermined ratio. The size information indicating the first size is stored in the memory,
In the size storage process, when the determination process determines that the third predetermined requirement is satisfied, and the ratio determination process determines that the first size ratio is equal to or less than the predetermined ratio The image forming apparatus according to claim 3, wherein the size information indicating the second size is stored in the memory. The first speed is smaller than the second speed;
The image forming mechanism is an electrophotographic system having a fixing device that heat-fixes a developer image transferred to a sheet,
The controller is
An image forming process for forming an image based on image data by operating the image forming mechanism;
An acquisition process that includes the image data and designated size information indicating a sheet size, and acquires image formation request information requesting the image formation process;
A second size determination process for determining whether the specified size information is the first size or the second size; and when the first size is determined in the second size determination process, the first size The second operation process for setting the set speed to the first speed and operating the fixing device at the first speed regardless of the size determination process is performed. The image forming apparatus according to any one of the above. The paper feed tray is displaceable relative to the housing;
An exchange sensor that outputs different signals depending on whether or not there is a sheet in the sheet feeding tray when the sheet feeding tray is in a position where the sheet can be fed to the image forming mechanism;
The controller is
An exchange detection process for detecting the presence or absence of a sheet at the position where the sheet can be fed by a signal output from the exchange sensor, and a size stored in the memory when no sheet is detected in the exchange detection process. The image forming apparatus according to claim 10, wherein an initialization process is performed to set information as the second size. The controller is
A speed determination process for determining whether or not the set speed needs to be reset; and when the speed determination process determines that the set speed needs to be reset, the operation of the transport mechanism is stopped. Execute transport stop processing to
The operation process or the second operation process is executed after the set speed is reset after the operation of the transport mechanism is stopped by the transport stop process. The image forming apparatus described. The controller is
Performing a sheet number determination process for determining whether or not the number of sheets necessary to form an image in the image processing is less than a predetermined number;
In the operation process or the second operation process, when it is determined in the number determination process that the number is less than the predetermined number, the set speed is not reset, and the current set speed is set. The image forming apparatus according to claim 12, wherein the conveyance mechanism operates.   14. The image forming apparatus according to claim 12, wherein the sheet sensor is provided upstream of the image forming mechanism in a sheet conveying direction and detects the presence or absence of a sheet.