JP2008070808A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that reduces a first printout time, even if switching a speed related to image formation from a first speed to a second speed, which is different from the first speed. <P>SOLUTION: The image forming apparatus includes a plurality of primary transfer control sequences that are prepared every image forming mode for controlling the output of a first transfer means to conditions suitable for image formation prior to the image formation. Also, the apparatus includes a first transfer control sequence selection means for selecting and executing one primary transfer sequence among the plurality of primary transfer control sequences depending on the image forming mode. When the image forming mode is switched during the execution of a selected primary transfer control sequence, the apparatus stops the primary transfer control sequence in execution and executes the primary transfer control sequence based on the switched image forming mode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a plurality of image forming modes and performing image formation by selecting an optimal image forming mode according to the type of recording medium.

  In image forming apparatuses such as electrophotographic copying machines and laser printers, as a high-speed and advantageous method, cartridges as image forming units for yellow, magenta, cyan, and black are arranged on a straight line, and each color has a certain time difference. There is an in-line method that sequentially performs image formation.

  Further, among inline type image forming apparatuses, there is an intermediate transfer belt type image forming apparatus. In this image forming apparatus, before transferring the toner image to the recording medium, the toner images of the respective colors formed by the respective image forming portions are temporarily superimposed on the intermediate transfer belt and primarily transferred. Next, the toner images of each color on the intermediate transfer belt are collectively transferred to a recording medium, and then the recording medium is transported to a fixing device, where the toner image is fixed on the recording medium by heat and pressure. Form.

  On the other hand, in recent years, there has been known an image forming apparatus that automatically determines the type of a recording medium and selects an optimal print condition according to the determination result. For example, an image forming apparatus has been proposed that has a plurality of image forming modes, discriminates the type of recording medium by a medium discriminating unit, and selects an appropriate image forming mode according to the result (see Patent Document 1). ).

  In general, the media discriminating means for discriminating the type of the recording medium is arranged by placing a sensor called a media sensor on the paper conveyance path, and stops the recording medium when the recording medium reaches the media sensor. Is configured to determine. The print condition, specifically the print speed, is selected based on the detection result of the media sensor. For example, if the detection result is plain paper, printing is performed at a normal speed (1/1 speed), and if the detection result is thick paper, printing is performed at a speed half that of the normal speed (1/2 speed).

  As described above, the main purpose of changing the printing speed depending on the type of the recording medium is to reduce the speed of passing the recording medium through the fixing device, that is, the fixing speed, and also reduce the speed of the image forming unit in the same manner. It is to improve color and ensure color mixing.

  In order to achieve this object, a method is conceivable in which only the fixing speed is set to 1/2 speed and the speed of the image forming unit is kept to 1/1 speed. However, since a mechanism for decelerating the recording medium and a larger conveying distance are required after the image is formed on the recording medium and before the recording medium is conveyed to the fixing device, the apparatus becomes complicated and large. The fact is that it is rarely adopted.

  The automatic discrimination mode of the type of recording medium is often called an auto mode and is frequently used. An image forming apparatus having an auto mode is excellent in usability because an image is formed under optimum print conditions without a user specifying the type of recording medium. In the auto mode, generally, the print operation is not started after the medium is determined, but the print preparation operation (hereinafter referred to as pre-rotation) is started at a normal speed in advance, and the medium is determined later. . If the determination result is plain paper, printing is continued at the normal speed, and if the determination result is thick paper, the printing speed is changed from 1/1 speed to 1/2 speed from that point.

  One of the pre-rotation operations of printing is primary transfer bias control. This is a control performed to determine an optimum transfer bias (voltage) at the time of primary transfer, and is a control called ATVC (Active Transfer Voltage Control). The transfer bias needs to be optimally controlled according to the state of the image forming apparatus, and should be determined in consideration of the environment in which the image forming apparatus is placed and the usage state thereof (for example, the deterioration state of the photosensitive drum). There is. Therefore, ATVC is performed prior to the primary transfer operation. The control is, for example, the following processing.

  First, a primary transfer bias is applied to the primary transfer roller, and a primary transfer current flowing at that time is detected by a current detection circuit. Next, the primary transfer power supply is controlled (constant current control) so as to be equal to a preset target current. This is continued for one rotation of the transfer roller, an average voltage is calculated during this rotation, and this average voltage is adopted as the primary transfer bias during image formation.

  This is an example of primary transfer bias control, and there are other methods. For example, by continuing to apply a primary transfer bias of a predetermined voltage, the primary transfer current flowing at that time is detected, the impedance of the transfer portion that can be calculated from the voltage value and the current value is obtained, and from this impedance, the impedance at the time of image formation is determined. There is a method for obtaining a primary transfer bias.

JP-A-2005-338362

  In the above conventional example, the pre-rotation of 1/1 speed printing is started in the auto mode, but when the speed switching to 1/2 speed is necessary, the primary transfer bias is deviated from the optimum value, resulting in an image defect. The problem that occurs occurs. In order to cope with this problem, it is often the case that ATVC is performed at each of a plurality of speeds of the transfer portion and an optimum primary transfer bias is set at each speed.

  However, if the ATVC for 1/2 speed is repeated after the ATVC for 1/1 speed is performed, the time until the printed image is obtained, the so-called FPOT (First Print Out Time) is delayed. There was a problem that.

  The present invention has been made to solve such a problem, and an object of the present invention is to change a speed related to image formation from a first speed to a second speed different from the first speed. An object of the present invention is to provide an image forming apparatus capable of shortening the FPOT even when switching to.

  In order to achieve such an object, the present invention provides a latent image forming unit for forming a latent image on a first image carrier, a developing unit for developing the latent image as a toner image, and the toner image. A first transfer unit for primary transfer onto the second image carrier, and a step of primary transfer of the toner image onto the second image carrier by the first transfer unit. Is repeated to form a plurality of color toner images on the second image carrier, and the plurality of color toner images are collectively secondarily transferred onto a recording medium by a second transfer unit. The image forming mode includes a plurality of primary transfer control sequences prepared for each image forming mode for controlling the output of the first transfer unit to a condition suitable for image forming prior to image formation. According to the plurality of primary transfer control sequences. A primary transfer control sequence selection unit that selects and executes one primary transfer control sequence, and when the image forming mode is switched during execution of the primary transfer control sequence selected by the primary transfer control sequence selection unit; The primary transfer control sequence being executed can be interrupted, and the primary transfer control sequence corresponding to the switched image forming mode can be executed.

  According to the present invention, even when the speed relating to image formation is switched from the first speed to the second speed different from the first speed, the primary transfer control is switched to a different mode in a shorter time. It becomes possible. Therefore, the first printout time (FPOT) can be shortened.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to the present embodiment.
The image forming apparatus 128 is a full-color laser printer that includes four photosensitive drums 101, 102, 103, and 104 and an intermediate transfer belt 123. Further, the image forming apparatus 128 is provided with process cartridges 115, 116, 117, and 118. Further, these process cartridges include charging rollers 111, 112, 113, and 114, laser scanners 109 and 110 as exposure apparatuses, and development rollers 105, 106, 107, and 108 as development apparatuses. With these process cartridges, yellow, magenta, cyan, and black toner images are formed. The photosensitive drums 101, 102, 103, and 104 are rotatable in the direction of the arrow in the figure.

  The toner image formed on each photosensitive drum is transferred to an intermediate transfer belt (belt-shaped image carrier) adjacent to the photosensitive drum in a primary transfer portion having primary transfer rollers 119, 120, 121, and 122. ) Sequential transfer (primary transfer) onto 123. Next, the image transferred onto the intermediate transfer belt 123 is transferred (secondary transfer) to a recording medium such as paper in a second transfer unit having a secondary transfer roller 126.

  Hereinafter, the process cartridge 115 described above will be described in more detail. Since the other three process cartridges 116, 117, and 118 have the same configuration, description thereof will be omitted. The process cartridge 115 is for yellow, 116 is for magenta, 117 is for cyan, and 118 is for black toner.

  The process cartridge 115 includes a photosensitive drum 101 that is rotatably supported. The photosensitive drum 101 has a basic configuration of a conductive substrate such as aluminum and a photoconductive layer formed on the outer periphery thereof. This is a general organic photosensitive drum. The photosensitive drum 101 is rotationally driven by a driving unit (not shown) in the direction of the arrow shown in the drawing.

  A charging roller 111 is disposed above the photosensitive drum 101. The charging roller 111 is in contact with the surface of the photosensitive drum 101, and the surface is uniform in a predetermined polarity (minus in the present embodiment) and potential. It is charged in the form of a roller. The charging roller 111 is composed of a conductive metal core disposed at the center and a conductive layer formed on the outer periphery thereof, and is rotatably supported. Further, the charging roller 111 is disposed substantially in parallel to the photosensitive drum 101 and is pressed toward the center of the photosensitive drum 101 by a pressing unit (not shown). Are pressed against each other with a predetermined pressing force. The charging roller 111 rotates following the rotation of the photosensitive drum 101 in the arrow direction. A bias voltage is applied to the charging roller 111 by a high-voltage power supply for charging (not shown), whereby the surface of the photosensitive drum 101 is uniformly contact-charged.

  A laser beam L1 from the laser scanner 109 is irradiated on the downstream side of the charging roller 111 along the rotation direction of the photosensitive drum 101. The laser scanner 109 scans, for example, laser light on / off based on image information to expose the surface of the photosensitive drum 101, and changes the potential of the exposed portion, so that it corresponds to the image information. An electrostatic latent image is formed. The laser scanner 109 performs black and magenta exposure, and the laser scanner 110 performs cyan and yellow exposure.

  Further, a developing roller 105 is rotatably installed on the downstream side of the irradiation position of the laser beam L1. The developing roller 105 is supplied with toner as a developer from a developer container (not shown). By applying a developing bias voltage to the developing roller 105 by a developing high voltage power source (not shown), the toner adheres to the exposed portion of the surface of the photosensitive drum, and the electrostatic latent image is developed as a toner image.

  A transfer roller 119 is disposed on the downstream side of the developing roller 105 and below the photosensitive drum 101 with the intermediate transfer belt 123 interposed therebetween. This transfer roller 119 includes a grounded cored bar and a conductive layer formed in a cylindrical shape on the outer peripheral surface thereof. Further, both ends of the transfer roller 119 are pressed toward the center of the photosensitive drum 101 by a pressing member such as a spring (not shown). Accordingly, the conductive layer of the transfer roller 119 is pressed against the surface of the photosensitive drum 101 via the intermediate transfer belt 123 with a predetermined pressing force, and a transfer nip portion is formed between the photosensitive drum 101 and the transfer roller 119. It is formed. An intermediate transfer belt 123 is sandwiched between the transfer nip portions, and toner that is negatively charged due to a potential difference between the surface of the photosensitive drum 101 and the transfer roller 119 is transferred from the surface of the photosensitive drum 101 to the intermediate transfer belt 123. Transferred to the surface. This transfer is called primary transfer. From the photosensitive drum 101 after the transfer of the toner image, deposits such as residual toner are removed by a cleaner (not shown).

  The intermediate transfer belt 123 is stretched by three rollers including a counter roller of the secondary transfer roller 126 and a tension roller 125, and is rotationally driven in the direction of the arrows of these rollers.

  The intermediate transfer belt 123 can be formed of a dielectric resin such as PC, PET, or PVDF. The transfer roller 119 is formed of a conductive urethane sponge.

  As described above, the toner images of the respective colors formed on the photosensitive drum 101 are sequentially transferred onto the intermediate transfer belt 123, and then conveyed to the secondary transfer portion as the intermediate transfer belt 123 rotates.

  The paper feed cassette 1 140, the paper feed cassette 2 141, the paper feed cassette 3 142, and the paper feed cassette 4 143 accommodate recording media. Hereinafter, an operation of feeding and transporting a recording medium from the paper feed cassette 1 will be described. This operation is the same for the paper feed cassettes 2, 3, and 4.

  As the toner image on the intermediate transfer belt 123 is conveyed to the secondary transfer unit, the recording medium taken out from the paper feed cassette 1 is supplied to the conveyance rollers 148 and 152 and the registration roller 160 via the pickup roller 144. Is done. Next, in the secondary transfer portion, the above-described toner image is transferred onto the recording medium by a secondary transfer bias applied between the secondary transfer roller 126 and the opposite roller of the secondary transfer roller 126. The residual toner on the intermediate transfer belt 123 is removed and collected by an intermediate transfer belt cleaner (not shown). Moreover, the secondary transfer inner roller 126 has a conductive urethane solid layer.

  The fixing device 127 includes a fixing roller 157 that is rotatably arranged and a pressure roller 156 that rotates while being pressed against the fixing roller 157. A heater (not shown) such as a halogen lamp is disposed inside the fixing roller 157, and the surface temperature of the fixing roller 157 is adjusted by controlling the power supplied to the heater. When the recording medium is conveyed in this state, the fixing roller 157 and the pressure roller 156 are rotated at a constant speed, and the recording medium is almost from both the front and back sides when passing between the fixing roller 157 and the pressure roller 156. Pressurized and heated at a constant pressure and temperature. As a result, the unfixed toner image on the surface of the recording medium is melted and fixed on the recording medium to form a full-color image.

  In addition, the image forming apparatus 128 includes a control unit 139 as a control unit that controls the entire image forming apparatus 128. The control unit 139 includes a CPU that executes processing operations such as various calculations, control, and determination. The control unit 139 has a ROM that stores a control program executed by the CPU, such as a process described later with reference to FIGS. Further, the control unit 139 includes a RAM that temporarily stores data during CPU processing, input data, and the like.

  The above is a schematic description of image formation in a color laser printer.

  Hereinafter, switching of the primary transfer bias control (ATVC) when the image forming mode is switched, which is a characteristic part of the present embodiment, will be described. In this embodiment, after starting the printing operation in the auto mode, the image forming speed is changed from the standard speed (1/1 speed) to a half of the standard speed according to the detection result of the media sensor that detects the type of the recording medium. A case of switching to (1/2 speed) will be described.

FIG. 2 is a flowchart showing a flow of operations from the start of pre-rotation (start of paper feeding) to the start of image formation according to an embodiment of the present invention.
FIG. 3 is a timing chart from the start of pre-rotation (start of paper feeding) to the start of image formation according to an embodiment of the present invention.

  First, when an instruction for printing in the auto mode is issued, the image forming apparatus 128 starts pre-rotation at the standard image forming speed (1/1 speed) (S201). When performing the pre-rotation, a sequence called a pre-rotation sequence is generally executed in which a series of processes to be performed in the pre-rotation are sequentially performed in time series. Each arrow in a portion 301 surrounded by a solid line in FIG. 3 represents typical processing performed in this pre-rotation sequence. One of the pre-rotation sequences includes a motor start 308, which is a start-up at a 1/1 speed of a belt motor (not shown) that drives the intermediate transfer belt 123, and a drum motor that drives the photosensitive drum 101 ( (Not shown) represents the start at 1/1 speed. After the rotation of the photosensitive drum and the intermediate transfer belt 123 is stabilized (0.67 seconds after the start of the previous rotation), the primary transfer ATVC of each color is sequentially performed. In this embodiment, the order is yellow (309), magenta (310), cyan (311), and black (312).

  The primary transfer ATVC for each color is sequentially performed in accordance with the order of the normal image forming sequence for each color. By doing so, it is not necessary to provide a separate sequence for the ATVC operation, so that the control can be simplified.

  Several methods have been proposed for ATVC. Here, primary transfer high-voltage power supplies 131, 132, 133, and 134 that can change the primary transfer voltage (primary transfer bias) and primary transfer current detection means 135, 136, 137, and 138 that detect the primary transfer current are used. The primary transfer high-voltage power supplies 131, 132, 133, and 134 are connected to the primary transfer rollers 119, 120, 121, and 122 in order to apply the primary transfer voltage to the primary transfer rollers 119, 120, 121, and 122. . The primary transfer high-voltage power supply is controlled by the control unit 139 so that the primary transfer current becomes a predetermined target current while charging the photosensitive drum 101 to a predetermined charging potential using these. Further, this control is continued while the primary transfer roller 119 rotates once, and the average primary transfer voltage at this time is calculated. The average primary transfer voltage is used when transferring. Therefore, the time required for ATVC is 0.67 seconds, which is the time required for one rotation of the primary transfer roller 119 for one color, and this is sequentially performed for each color.

  FIG. 6 shows the time from the start of the pre-rotation of each color to the start of the ATVC and the time from the end when the pre-rotation sequence is 1/1 speed. Since the time difference between the start of ATVC in each color is 0.5 seconds, the start timing and end timing of ATVC for each color are the times shown in FIG.

  On the other hand, the image forming apparatus 128 starts feeding the recording medium from the paper feeding cassette almost simultaneously with the start of the pre-rotation (S202). Thereafter, the media sensor 161 automatically determines the type of the recording medium.

  FIG. 5 shows the time from the start of paper feed to the end of media detection in each paper feed cassette when the paper feed speed is 1/1 speed.

  There are four paper feed cassettes, and the distance from each paper feed cassette to the media sensor 161 is different. For this reason, the time from the start of paper feed to the end of media detection also differs for each paper feed cassette.

  The media sensor 161 is arranged downstream of the recording medium conveyance direction from the point where the recording medium conveyance paths from the respective paper feeding cassettes merge into one place, and the recording from each paper feeding cassette is performed. Media identification can be done with one media sensor. By arranging the media sensor in this way, it is possible to switch the mode of the primary transfer control at an optimum timing according to each paper feed port.

  In the present embodiment, it is assumed that the recording medium is fed from the paper feed cassette 1140. In other words, the user can operate the input unit (not shown) of the image forming apparatus 128 to select the paper feed cassette 1 to feed paper from the paper feed cassette 1140. In this case, sheet cassette information indicating which sheet cassette is the selected sheet cassette is stored in the RAM of the control unit 139. That is, the paper feed cassette information is information indicating that the selected paper feed cassette is the paper feed cassette 1140. When the user operates the input unit to input an operation start instruction, the CPU feeds paper from the paper feed cassette 1140 based on the paper feed cassette information.

  Further, in an image data supply apparatus such as a computer connected to the image forming apparatus 128, the user may select a paper feed cassette. In this case, the image data supply apparatus attaches the paper feed cassette information to the print job, and transmits the paper feed cassette information to the image forming apparatus 128 together with the print job. Upon receiving the paper cassette information, the image forming apparatus 128 stores it in the RAM, and the CPU feeds paper from the selected paper cassette according to the paper cassette information.

  When the leading edge of the recording medium is detected by the media sensor 161, the fed recording medium is conveyed to a predetermined position in front of the secondary transfer roller 126, and then the conveyance is temporarily stopped. Next, the image forming apparatus 128 determines the type of the recording medium using the media sensor 161. The next operation is not started until this determination is finished (S203).

When the determination of the type of the recording medium is completed, the image forming apparatus 128 determines whether there is a change to the image forming speed at 1/2 speed (S204). Specifically, if it is determined that the type of recording medium is thick paper having a basis weight of 120 [g / m ² ] or more, it is determined that the image forming speed needs to be changed to 1/2 speed. If it is determined that the image forming speed is not changed to 1/2 speed, the image forming apparatus 128 waits for the end of the pre-rotation sequence without changing the image forming speed (S215), and starts image formation (S215). S216).

  The time until this determination is made is 0.8 seconds from the start of feeding as shown in FIG. At this time, as shown in FIG. 6 and FIG. 3, the pre-rotation sequence is in progress of yellow ATVC. Therefore, when the image forming speed is changed to 1/2 speed, the image forming apparatus 128 determines that the paper is fed from the paper feeding cassette 1 (S205), and then the yellow ATVC is finished. (S208). When the yellow ATVC is finished, the 1/1 speed pre-rotation sequence is finished (S212). Next, the image forming apparatus 128 activates a speed switching sequence to 1/2 speed (S213).

  If it is determined in S204 that there is a change to 1/2 speed, the image forming apparatus 128 determines from which paper feed cassette the paper is fed based on the paper feed cassette information stored in the RAM. To do. In the present embodiment, as described above, the paper feed cassette information is information indicating that paper is fed from the paper feed cassette 1 140. Therefore, the image forming apparatus 128 feeds from the paper feed cassette 1 140 in S205. Judge that it is paper. Note that processing when paper is fed from other paper feed cassettes 2, 3, and 4 instead of from the paper feed cassette 1 will be described later.

  The speed switching sequence to the 1/2 speed is a sequence in which the 1/1 speed pre-rotation sequence is redone at the 1/2 speed. That is, the belt motor and the drum motor are started at 1/2 speed, and ATVC is started when the rotation is stabilized. In order to perform ATVC at 1/2 speed, time twice as long as ATVC at 1/1 speed is required. Each arrow in a portion 302 surrounded by a solid line in FIG. 3 represents typical processing performed in the speed switching sequence to 1/2 speed. Typical processing includes motor activation 303 and temporary transfer ATVC for each color. In this embodiment, the processing is performed in the order of yellow (304), magenta (305), cyan (306), and black (307). As shown in FIG. 3, the speed switching sequence of 1/2 speed ends after 7.0 seconds from the start of the first pre-rotation. At this timing, the speed switching sequence ends (S214), and image formation starts. It becomes possible (S216). The image formation start is a timing at which exposure by the above-described exposure apparatus is started. An electrostatic latent image is formed on the photosensitive drum 101 with reference to this timing, and primary transfer to the intermediate transfer belt 123 is performed. .

  Next, as the toner image on the intermediate transfer belt 123 reaches the position of the secondary transfer roller 126, the conveyance of the recording medium for which the medium detection is completed is resumed, and the secondary transfer to the recording medium is performed. After the secondary transfer to the recording medium, the toner image is fixed by the fixing device 127 and discharged onto the paper discharge tray 129 as a color print image.

FIG. 4 is a timing chart from the start of pre-rotation (feed start) to the start of image formation according to the conventional method.
In the conventional system, the 1/1 speed pre-rotation sequence is not interrupted and the 1/2 speed speed switching sequence is not immediately executed, but instead of the 1/1 speed pre-rotation sequence. After execution to the end, the speed switching sequence to 1/2 speed is started.

  As shown in FIG. 4, in the conventional method, the time from the start of the pre-rotation (start of paper feeding) to the start of image formation takes 8.5 seconds. Therefore, the first printout time can be shortened by 1.5 seconds by using the method of this embodiment.

  In this embodiment, an example in which paper is fed from the paper feeding cassette 1 is shown, but the same control is performed when paper is fed from another paper feeding cassette. However, since the distance from each paper feed cassette to the media sensor is different, the reduction time of the first printout time is different.

Next, a case where paper is fed from the paper cassette 2 141 will be described. In this case, the paper feed cassette information is information indicating that the selected paper feed cassette is the paper feed cassette 2 141.
The image forming apparatus 128 performs S201 to S203 in the same manner as described above, and if it is determined in S204 that there is a change to 1/2 speed, the process proceeds to S205, based on the sheet cassette information stored in the RAM. It is determined whether or not paper is being fed from the paper cassette 1. If it is determined that the paper is not fed from the paper cassette 1, the process proceeds to S206, and it is determined whether or not the paper is fed from the paper cassette 2 based on the paper cassette information stored in the RAM. In this case, since the paper feed cassette information is information indicating that the selected paper feed cassette is the paper feed cassette 2 141, the process proceeds to S209.

  In this case, the media detection for the recording medium to be fed ends 1.5 seconds after the start of feeding as shown in FIG. At this time, in the 1/1 speed pre-rotation sequence, as shown in FIGS. 3 and 6, magenta ATVC is being executed. Therefore, the image forming apparatus 128 waits for the end of magenta ATVC (S209), ends the 1/1 speed pre-rotation sequence, and subsequently starts the speed switching sequence to 1/2 speed. By doing so, the time until the start of image formation becomes 7.5 seconds, and the first printout time can be shortened by 1.0 seconds.

Next, a case where paper is fed from the paper feed cassette 3 142 will be described. In this case, the paper feed cassette information is information indicating that the selected paper feed cassette is the paper feed cassette 3142.
The image forming apparatus 128 performs S201 to S203 in the same manner as described above, and if it is determined in S204 that there is a change to 1/2 speed, the process proceeds to S205, based on the sheet cassette information stored in the RAM. It is determined whether or not paper is being fed from the paper cassette 1. If it is determined that the paper is not fed from the paper cassette 1, the process proceeds to S206, and it is determined whether or not the paper is fed from the paper cassette 2 based on the paper cassette information stored in the RAM. If it is determined that the paper is not fed from the paper cassette 2, the process proceeds to S207, where it is determined whether the paper is fed from the paper cassette 3 based on the paper cassette information stored in the RAM. . In this case, since the paper feed cassette information is information indicating that the selected paper feed cassette is the paper feed cassette 3142, the process proceeds to S210.

  In this case, the media detection for the recording medium to be fed ends after 2.0 seconds from the start of feeding as shown in FIG. At this time, as can be seen from FIGS. 3 and 6, in the 1/1 speed pre-rotation sequence, cyan ATVC is being executed. Therefore, the image forming apparatus 128 waits for the end of cyan ATVC (S210), ends the 1 / 1-speed pre-rotation sequence, and subsequently starts the speed switching sequence to 1/2 speed. By doing so, the time until the start of image formation is 8.0 seconds, and the first printout time can be shortened by 0.5 seconds.

Next, a case where paper is fed from the paper cassette 4143 will be described. In this case, the paper feed cassette information is information indicating that the selected paper feed cassette is the paper feed cassette 4143.
The image forming apparatus 128 performs S201 to S203 in the same manner as described above, and if it is determined in S204 that there is a change to 1/2 speed, the process proceeds to S205, based on the sheet cassette information stored in the RAM. It is determined whether or not paper is being fed from the paper cassette 1. If it is determined that the paper is not fed from the paper cassette 1, the process proceeds to S206, and it is determined whether or not the paper is fed from the paper cassette 2 based on the paper cassette information stored in the RAM. If it is determined that the paper is not fed from the paper cassette 2, the process proceeds to S207, where it is determined whether the paper is fed from the paper cassette 3 based on the paper cassette information stored in the RAM. . In this case, since the paper feed cassette information is information indicating that the selected paper feed cassette is the paper feed cassette 4143, the process proceeds to S211.

  In this case, the media detection for the recording medium to be fed ends 2.5 seconds after the start of feeding as shown in FIG. At this time, in the 1/1 speed pre-rotation sequence, as shown in FIGS. 3 and 6, the black ATVC is being executed. Therefore, the image forming apparatus 128 waits for the end of the black ATVC (S211), ends the pre-rotation sequence of 1/1 speed, and subsequently starts the speed switching sequence to 1/2 speed. By doing so, the time to start image formation is 8.5 seconds. However, this does not reduce the first printout time.

  As described above, it can be seen that the closer the paper feed cassette is to the media sensor, the greater the effect of reducing the first printout time. On the other hand, it can be seen that if the distance from the media sensor to the paper feed cassette is more than a certain distance, the effect of reducing the first printout time is lost. Actually, since the media sensor and the paper feed cassette are often arranged at close positions, the effect of shortening the first printout time is effective for most image forming apparatuses.

(Second Embodiment)
FIG. 7 is a flowchart showing the flow of operations from the start of pre-rotation (start of paper feed) to the start of image formation according to the present embodiment. FIG. 8 shows the start of pre-rotation (start of paper feed) according to this embodiment. ) To the start of image formation.

  In the present embodiment, unlike the first embodiment, when an instruction for printing in the auto mode is issued, the image forming apparatus 128 starts pre-rotation at 1/2 speed (S701). The auto mode does not always start at the standard image forming speed (1/1 speed). For example, as in the present embodiment, a case where a 1/2 speed pre-rotation that is 1/2 the standard image forming speed is used in the auto mode can be considered. For example, in an image forming apparatus in which the image forming speed of the last print job is set to be the pre-rotation speed of the next auto mode, the print job performed immediately before the auto mode is set to the 1/2 speed mode. This is the case. In addition, in an image forming apparatus configured to be able to specify the pre-rotation speed in the auto mode for each paper feed cassette, it may be possible to feed paper from a paper feed cassette in which the auto mode is set to 1/2 speed.

In the present embodiment, the image forming apparatus 128 first starts printing fed from the paper cassette 1 in the auto mode, performs the 1 / 2-speed pre-rotation sequence (S701), and the 1 / 2-speed feed. Paper (S702) is performed. Next, it is determined that the type of the recording medium is plain paper having a basis weight of about 75 [g / m ² ] (S703), and the image forming speed is switched to 1/1 speed. That is, after the 1/2 speed pre-rotation sequence is completed (S712), the speed switching sequence to 1/1 speed is started (S713).

FIG. 9 shows the time from the start of paper feed to the end of media detection in each paper feed cassette when the paper feed speed is 1/2 speed.
FIG. 10 shows the time from the start of the pre-rotation of each color to the start of the ATVC and the time to the end when the pre-rotation sequence is 1/2 speed.

  In this embodiment, since the pre-rotation and the paper feed speed are 1/2 speed, as shown in FIGS. 9 and 10, the time from the paper feed start to the end of the media detection, and from the start of the pre-rotation to the start of ATVC. The time and the time until the end are approximately twice those of the 1/1 speed. Other control methods are the same as those in the first embodiment, and detailed description thereof is omitted.

FIG. 11 is a timing chart from the start of pre-rotation (feed start) to the start of image formation according to the conventional method.
In the conventional method, the 1 / 2-speed pre-rotation sequence is not interrupted and the 1 / 1-speed speed switching sequence is not immediately executed. After executing to the end, the speed switching sequence to 1/1 speed is started.

  As shown in FIG. 11, in the conventional method, the time from the start of the pre-rotation (start of paper feeding) to the start of image formation takes 8.5 seconds.

  If the system of this embodiment is used, as shown in FIG. 8, the time from the start of the pre-rotation to the start of image formation is 5.17 seconds when paper is fed from the paper feed cassette 1. Therefore, the first printout time can be shortened by 3.33 seconds.

  Similarly, when paper is fed from the paper cassette 2, the time from the start of the previous rotation to the start of image formation is 6.17 seconds. Therefore, the first printout time can be shortened by 2.33 seconds.

  When paper is fed from the paper feed cassette 3, the time from the start of the previous rotation to the start of image formation is 7.17 seconds. Therefore, the first printout time can be reduced by 1.33 seconds.

  As described above, the effect of shortening the first printout time is effective even when the pre-rotation and the paper feed speed are switched from the low speed to the high speed.

(Third embodiment)
The image forming apparatus according to the present embodiment has two modes, a mode in which the control described in the first embodiment or the second embodiment is executed and a mode in which the control is not executed, and the user can select one of the modes. It is comprised as follows.

  The mode in which the above-described control is not executed is a mode in which ATVC is executed for all colors at the speed before the change even when the image forming speed is changed in the auto mode, and ATVC is not performed again at the speed after the change. is there. For example, when printing starts at a higher image forming speed and you do not want to lower the image forming speed depending on the recording medium, that is, when priority is given to the time to print completion rather than image quality improvement There is. In this case, by selecting a mode in which the above-described control is not executed, it is possible to shorten the time until printing is completed. In order to prioritize image quality, a mode for executing the above-described control may be selected. By doing so, it is possible to provide an image forming apparatus with a wide range of user selection and excellent usability.

(Fourth embodiment)
The image forming apparatus according to the present embodiment compares the bias setting conditions set for each image forming mode before and after switching the image forming mode, and the first and second embodiments have been described depending on the comparison result. The switching control is not performed. For example, if the target primary transfer current during ATVC, which is the bias setting condition, is not different before and after switching the image forming mode, the primary transfer bias value determined as a result of performing ATVC at the speed before switching is changed even at the speed after switching. Can be used. In this case, even if the image forming mode is switched in the auto mode, it is not necessary to perform ATVC again. Therefore, it is not necessary to perform switching control, and the first printout time can be shortened.

  Up to now, only two image forming modes, 1/1 speed and 1/2 speed, have been described, but the image forming speed is not limited to these. That is, speeds such as 1/3 speed and 3/4 speed are also conceivable. For example, there may be a case where the target primary transfer current is the same at 1/1 speed and 3/4 speed and is different at 1/2 speed or 1/3 speed. In such a case, the switching control is not performed when the image forming mode is switched from 1/1 speed to 3/4 speed, and when the image forming mode is switched from 1/1 speed to 1/2 speed or 1/3 speed, It is possible to perform control such as switching control.

  By doing so, a waiting time for switching the image forming mode is generated only when necessary, and when it is not necessary, the waiting time is eliminated, so that the usability can be further improved.

1 is a schematic cross-sectional view of an image forming apparatus that can implement the present invention. 6 is a flowchart showing a flow of operations from the start of pre-rotation (feeding start) to the start of image formation according to an embodiment of the present invention. 6 is a timing chart from the start of pre-rotation (start of paper feeding) to the start of image formation according to an embodiment of the present invention. 10 is a timing chart from the start of pre-rotation (start of paper feeding) to the start of image formation according to a conventional method. FIG. 6 is a diagram illustrating a time from the start of paper feed to the end of media detection in each paper feed cassette when the paper feed speed is 1/1 speed. It is a figure showing the time from the pre-rotation start of each color to the start of ATVC and the time to the end when the pre-rotation sequence is 1/1 speed. 6 is a flowchart illustrating a flow of operations from the start of pre-rotation (start of paper feeding) to the start of image formation according to an embodiment of the present invention. 6 is a timing chart from the start of pre-rotation (start of paper feeding) to the start of image formation according to an embodiment of the present invention. FIG. 10 is a diagram illustrating a time from the start of paper feed to the end of media detection in each paper feed cassette when the paper feed speed is 1/2 speed. It is a figure showing the time from the pre-rotation start of each color to the start of ATVC and the time to the end when the pre-rotation sequence is 1/2 speed. 10 is a timing chart from the start of pre-rotation (start of paper feeding) to the start of image formation according to a conventional method.

Explanation of symbols

301 1/1 speed pre-rotation sequence 302 speed switching sequence to 1/2 speed 303 1/2 speed motor start-up process 304, 305, 306, 307 1/2 speed ATVC
308 1/1 speed motor start-up process 309, 310, 311, 312 1/1 speed ATVC
313 Media detection end timing of the paper feed cassette 1 314 Media detection end timing of the paper feed cassette 2 315 Media detection end timing of the paper feed cassette 3 316 Media detection end timing of the paper feed cassette 4

Claims (8)

A latent image forming means for forming a latent image on the first image carrier;
Developing means for developing the latent image as a toner image;
First transfer means for primary transfer of the toner image onto a second image carrier,
The process of primary transfer of the toner image onto the second image carrier by the first transfer unit is repeated for the toner image of a plurality of colors to form a toner image of a plurality of colors on the second image carrier. And
An image forming apparatus for performing secondary transfer of the plurality of color toner images collectively onto a recording medium by a second transfer unit,
Prior to image formation, it has a plurality of primary transfer control sequences prepared for each image formation mode for controlling the output of the first transfer means to conditions suitable for image formation,
A primary transfer control sequence selection unit that selects and executes one primary transfer control sequence of the plurality of primary transfer control sequences according to an image forming mode;
When the image forming mode is switched during execution of the primary transfer control sequence selected by the primary transfer control sequence selecting means, the primary transfer control sequence being executed is interrupted halfway, and the switched image forming mode is set. An image forming apparatus that executes a corresponding primary transfer control sequence. Media detection means capable of identifying the characteristics of the recording medium;
Automatic image formation mode selection means for automatically selecting an image formation mode suitable for image formation from among a plurality of image formation modes according to the characteristics of the recording medium detected by the media detection means. The image forming apparatus according to claim 1, wherein: Voltage control means for constant voltage control of the first transfer means;
Output current detection means for detecting an output current value at the time of constant voltage control by the voltage control means,
The primary transfer control sequence includes a constant voltage value controlled by the constant voltage control unit and an output current value detected by the output current detection unit based on a bias setting condition prepared for each image forming mode. The image forming apparatus according to claim 1, wherein transfer bias control is performed to calculate and determine an output voltage to the first transfer unit.   4. The inline system in which the first image carrier, the developing unit, and the first transfer unit are arranged in series by the number of colors necessary for image formation. The image forming apparatus according to any one of the above.   5. The image forming apparatus according to claim 3, wherein in the primary transfer control sequence, the transfer bias control is sequentially performed in an arrangement order of colors to be primarily transferred. 6. A plurality of paper supply units for storing recording media, wherein the media detection unit is a recording medium conveyance path of the image forming apparatus, and the recording media fed and conveyed from the plurality of paper supply units It is located downstream from the point where it joins one place,
The image forming apparatus according to claim 1, wherein the recording medium can be identified from all of the paper feeding units by one of the media detecting units.   The image forming apparatus according to claim 1, wherein the user can select whether or not to execute a primary transfer control sequence different from the primary transfer control sequence being executed.   Comparing bias setting conditions prepared for each image forming mode before and after switching the primary transfer control sequence, it is determined whether or not to execute a primary transfer control sequence different from the primary transfer control sequence being executed. The image forming apparatus according to claim 1.

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