JP2016095543A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent non-uniform conveyance of subsequent sheets without reducing productivity or affecting conveyance of a preceding sheet and image formation even if recording material is conveyed successively by one driving source, to obtain an excellent image.SOLUTION: In an image forming apparatus for driving a cassette pickup roller 17 and a registration roller 18 with the same driving source, a paper feed conveyance control part 221 starts controlling conveyance speed of a subsequent sheet supplied after a preceding sheet, which has been supplied earlier from a paper feed position, when determination is made that a rear end of the preceding sheet has passed through the registration roller 18.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser printer.

  An image forming apparatus (for example, a copying machine or a printer) using an intermediate transfer member forms a toner image on a photosensitive drum by a developing roller, and transfers the toner image to the intermediate transfer member (hereinafter referred to as primary transfer). Thereafter, the toner image is collectively transferred onto a recording material such as paper (hereinafter referred to as secondary transfer) to obtain an image. In such an image forming apparatus, when the recording material is fed into the image forming apparatus and transported to the secondary transfer position, the stacking amount in the cassette, the take-out amount by the preceding paper, the wear state of the feeding roller, the media Depending on the type or the like, slippage occurs and variation occurs. Here, the variation means that the timing to reach a predetermined position varies. If variation occurs from the start of paper feeding to the secondary transfer position, the toner image cannot be transferred to an appropriate position on the recording material, and a high-quality image cannot be formed.

  Therefore, in the prior art, for example, the following control is performed. That is, by measuring the dispersion time of the recording material conveyed using the paper detection sensor provided on the conveyance path to the secondary transfer position, and carrying out the conveyance control based on the measured time, Control is performed to transfer the toner image to an appropriate position (see, for example, Patent Document 1). Specifically, the variation time and the reference time without variation are compared, and the conveyance speed is accelerated or decelerated from the difference, and the conveyance time is conveyed to the secondary transfer position. As a result, variations can be eliminated and a good image can be obtained. Hereinafter, such control is referred to as conveyance speed control.

JP 2007-101666 A

  In the prior art, the conveyance speed control execution timing is determined only at the timing when the recording material is detected by the paper detection sensor. In this case, for example, when the recording material is continuously conveyed in an image forming apparatus in which conveyance from the start of paper feeding to the secondary transfer position is performed by one drive source, there are the following cases. That is, if the conveyance speed control is performed at the timing when the recording material is detected by the paper detection sensor as in the prior art, the conveyance speed of the preceding paper during the secondary transfer may change, and normal image formation may not be performed. For this reason, it is always ensured that the succeeding sheet reaches the sheet detection sensor after the preceding sheet has passed through the most downstream conveying unit operating with the same drive source so as not to affect the conveyance of the preceding recording material. The paper feed interval is increased to control. However, with such control, the interval between image formations increases, and the productivity of the image forming apparatus decreases.

  The present invention has been made under such circumstances, and even when the recording material is continuously conveyed by the same driving source, it affects the conveyance of the preceding paper and the image formation without reducing the productivity. An object of the present invention is to obtain a good image by suppressing variations in the conveyance of the following paper without giving it.

  In order to solve the above-described problems, the present invention has the following configuration.

(1) A first transport unit for feeding a recording material from a paper feeding position onto a transport path, and a front end or a rear end of the recording material provided downstream of the first transport unit in the recording material transport direction. A first detecting means for detecting the recording medium; a second conveying section provided downstream of the first detecting means for conveying the recording material to the transfer position; and upstream of the transfer position and the second Second detection means provided on the downstream side of the conveyance unit and detecting the leading edge or the trailing edge of the recording material, and the toner image on the image carrier at the transfer position is transferred to a predetermined position on the recording material. And a control means for controlling the conveyance speed of the recording material based on the detection result of the recording material by the first detection means or the second detection means, and the first conveyance section and the second conveyance section are the same The image forming apparatus is driven by a driving source of The conveyance speed control of the second recording material fed subsequent to the first recording material fed in advance from the feeding position is performed after the rear end of the first recording material passes through the second conveyance unit. An image forming apparatus which starts.

  (2) A first transport unit for feeding the recording material from the paper feed position onto the transport path, and a front end or a rear end of the recording material provided downstream of the first transport unit in the recording material transport direction. Detecting means for detecting the toner, a second conveying portion provided on the downstream side of the detecting means for conveying the recording material to the transfer position, and a toner image on the image carrier at the transfer position at a predetermined position of the recording material. Control means for controlling the recording material conveyance speed based on the detection result of the recording material by the detection means, so that the first conveyance unit and the second conveyance unit are the same. The image forming apparatus is driven by the driving source, and the control unit controls the conveyance speed of the second recording material fed following the first recording material fed in advance from the feeding position. Starting after the trailing edge of the first recording material has passed through the second conveying section An image forming apparatus comprising and.

  According to the present invention, even when the recording material is continuously conveyed by the same drive source, the variation in the conveyance of the subsequent sheet is suppressed without affecting the conveyance of the preceding sheet and the image formation without reducing the productivity. A good image can be obtained.

1 is an overall configuration diagram of an image forming apparatus according to a first embodiment. 1 is a system configuration diagram of an image forming apparatus according to a first embodiment. Conventional transport speed control timing chart for comparison with Example 1 (separate drive / same drive) Transport speed control timing chart of Embodiment 1 Transfer speed control flowchart of the first embodiment Configuration diagram of transport section of image forming apparatus of embodiment 2 Transport speed control timing chart of embodiment 2 Conveyance speed control flowchart of the second embodiment Transfer speed control timing chart of embodiment 3 (deceleration processing) Transport speed control timing chart of the third embodiment (acceleration processing) Conveyance speed control flowchart of Embodiment 3 Transfer speed control timing chart of embodiment 4 Example 4 Conveying Speed Control Flowchart

  The mode for carrying out the present invention will be described in detail below with reference to examples.

In the first exemplary embodiment, in an image forming apparatus in which conveyance from the start of paper feeding to the secondary transfer position is performed by one drive source, two sheets are detected between the paper feeding position and the secondary transfer position (transfer position). The following method will be described when two sensors are continuously printed with a sensor. That is, the conveyance of the succeeding paper is performed using the result detected by the paper detection sensor (hereinafter referred to as the downstream paper detection sensor) on the downstream side in the conveyance direction of the recording material (hereinafter referred to as the downstream paper detection sensor). A method for implementing the speed control will be described. Note that the preceding paper (first recording material) is a paper that is fed in time before the recording material when the recording material is transported on the transport path, and is transported prior to the recording material. This means the recording material conveyed immediately before among the recording materials conveyed on the road. Further, the succeeding paper (second recording material) refers to a recording material that is fed in time after the preceding paper and is transported on the transport path following the preceding paper. That is, a certain recording material is a succeeding sheet when viewed from the preceding sheet. Of the both ends of the recording material being conveyed, the end on the downstream side in the conveyance direction is referred to as the front end, and the end on the upstream side in the conveyance direction is referred to as the rear end.

[Image forming apparatus]
In FIG. 1, the overall configuration of a laser printer as an image forming apparatus will be described. In the following description, the first station is a station for forming a yellow (Y) color toner image and is represented by symbol a, and the second station is a station for forming a magenta (M) color toner image and represented by symbol b. ing. Further, the third station is represented by a symbol c as a cyan (C) toner image forming station, and the fourth station is represented by a symbol d as a black (K) toner image forming station.

(Image forming part)
The first station will be described. The photosensitive drum 1a is formed by laminating a plurality of functional organic materials including a carrier generation layer that generates a charge by exposure on a metal cylinder, a charge transport layer that transports the generated charge, and the like. The outermost layer of the photosensitive drum 1a has a low electrical conductivity and is almost insulated. The photosensitive drum 1a is configured, for example, by applying OPC (organic photoconductor layer) to the outer peripheral surface of an aluminum cylinder. Both ends of the photosensitive drum 1a are rotatably supported by flanges, and are driven to rotate counterclockwise with respect to the drawing by transmitting a driving force from a driving motor (not shown) to one end. The charging roller 2a as a charging unit is in contact with the photosensitive drum 1a and uniformly charges the surface of the photosensitive drum without being driven to rotate as the photosensitive drum 1a rotates. The charging roller 2a is a conductive roller formed in a roller shape. The charging roller 2a is brought into contact with the surface of the photosensitive drum 1a, and a charging voltage is applied by the charging voltage power source 20a, so that the surface of the photosensitive drum 1a is made uniform. Charge. The charging roller 2a is applied with a DC voltage or a voltage superimposed with an AC voltage, and discharge occurs in a small air gap upstream and downstream from the contact nip portion between the surface of the charging roller 2a and the photosensitive drum 1a. 1a is charged.

  The cleaning unit 3a cleans toner remaining on the photosensitive drum 1a after transfer (hereinafter referred to as transfer residual toner). The developing unit 8a as developing means includes a developing roller 4a that is in contact with the photosensitive drum 1a, a non-magnetic one-component developer (hereinafter referred to as toner) 5a, and a developer coating blade 7a. The developing unit 8a includes a toner storage unit that stores toner of each color of yellow, magenta, cyan, and black. The developing roller 4a is adjacent to the surface of the photosensitive drum, is driven to rotate by a driving unit (not shown), and performs development by applying a developing voltage from a developing voltage power source 21a. The above-described 1a to 8a are integrated process cartridges 9a that are detachable from the image forming apparatus.

  The exposure apparatus 11a, which is an exposure means, has a rotating polygon mirror (not shown), and the rotating polygon mirror is irradiated with image light corresponding to an image signal from a laser diode (not shown). The exposure device 11a is composed of a scanner unit or an LED array that scans laser light with a rotating polygon mirror, and irradiates a scanning beam 12a modulated on the basis of an image signal onto the photosensitive drum 1a.

The charging roller 2a is connected to a charging voltage power source 20a that is a voltage supply means to the charging roller 2a. The developing roller 4a is connected to a developing voltage power source 21a that is a voltage supply unit to the developing roller 4a. The primary transfer roller 81a is connected to a primary transfer voltage power supply 84a which is a voltage supply means to the primary transfer roller 81a. The above is the configuration of the first station, and the second, third, and fourth stations have the same configuration, and b, c, and d are appended to the same number, and description thereof is omitted.

  Inside the intermediate transfer belt 80 (image carrier), which will be described later, primary transfer rollers 81a to 81d that are in contact with the intermediate transfer belt 80 are provided to face the four photosensitive drums 1a to 1d, respectively. These primary transfer rollers 81a to 81d are connected to primary transfer voltage power supplies 84a to 84d. A positive voltage is applied to the primary transfer rollers 81a to 81d, and the negative color toner images on the photosensitive drum 1 are sequentially transferred to the intermediate transfer belt 80 in contact with the photosensitive drum 1 to form a multicolor image. Is done.

  The intermediate transfer belt 80 is supported by three rollers, that is, a secondary transfer counter roller 86, a driving roller 14, and a tension roller 15 as a stretching member, and an appropriate tension is maintained. By driving the driving roller 14, the intermediate transfer belt 80 moves in the forward direction at substantially the same speed with respect to the photosensitive drums 1a to 1d. The intermediate transfer belt 80 rotates in the arrow direction (clockwise direction), and the primary transfer roller 81a is disposed on the opposite side of the photosensitive drum 1a with the intermediate transfer belt 80 interposed therebetween. Further, a static elimination member 23a is disposed on the downstream side of the primary transfer roller 81a in the rotation direction of the intermediate transfer belt 80. The driving roller 14, the tension roller 15, the static eliminating member 23a, and the secondary transfer counter roller 86 are electrically grounded. Hereinafter, symbols a to d are omitted unless necessary.

  The multi-color image formed on the intermediate transfer belt 80 (on the image carrier) is recorded by the secondary transfer roller 82 by the secondary transfer roller 82 in synchronism with the recording material P fed and conveyed from a feeding unit described later. (Also referred to as secondary transfer). The toner remaining on the intermediate transfer belt 80 without being transferred to the recording material P is removed by a belt cleaning roller 88 to which a voltage is applied by a cleaning voltage power supply 89.

(Feeding department)
When paper is fed from the main body cassette 16, the cassette pickup roller 17 (first transport unit) is driven, and the main body cassette bottom plate 29 is raised to push up the recording material P installed in the main body cassette 16. The uppermost recording material P pushed up contacts the cassette pickup roller 17, and the recording material P is separated and fed one by one by the rotation of the cassette pickup roller 17, and the registration roller 18 (second transport unit). It is conveyed to. The cassette pickup roller 17 and the registration roller 18 are driven and rotated by the same drive source (not shown) (stepping motor or the like) to convey the recording material P. A pre-registration sensor 35a (first detection means) and a registration sensor 35b (second detection means), which are paper detection sensors for detecting the recording material P, are installed on the conveyance path. In the present embodiment, for example, the pre-registration sensor 35 a is installed on the downstream side of the cassette pickup roller 17, and the registration sensor 35 b is installed on the downstream side of the registration roller 18. This ensures that the trailing edge of the recording material P passes through the cassette pickup roller 17 at the timing when the trailing edge of the recording material P is detected by the pre-registration sensor 35a. Similarly, at the timing when the registration sensor 35b detects the trailing edge of the recording material P, it is guaranteed that the trailing edge of the recording material P passes through the nip formed by the registration roller 18 and the conveyance path.

For example, when the recording material P is not detected, the pre-registration sensor 35a and the registration sensor 35b output a low level signal. When the leading edge of the recording material P reaches the pre-registration sensor 35a and the registration sensor 35b, for example, the output of these sensors rises and outputs a high level signal. The pre-registration sensor 35a and the registration sensor 35b continue to output, for example, a high level signal while the recording material P passes, and when the trailing end of the recording material P passes, the outputs of these sensors fall and output a low level signal. To do. The signal output from the sensor depending on the presence or absence of the recording material P is not limited to the above-described configuration, and may be any signal that can distinguish the arrival of the front end of the recording material P from the passage of the rear end.

(Recording material conveyance control)
The fed recording material P is conveyed by the registration roller 18, and the leading edge of the image and the leading edge of the recording material are aligned at a position 35c and conveyed to the secondary transfer portion. Hereinafter, the position 35c is referred to as a merge point. The intermediate transfer belt 80 constituting the secondary transfer unit is stretched and supported by three rollers, that is, a secondary transfer counter roller 86, a driving roller 14, and a tension roller 15, and is arranged to face all the photosensitive drums 1a to 1d. It is installed. The intermediate transfer belt 80 is circulated and moved by the driving roller 14 and electrostatically adsorbs the toner image on the outer peripheral surface facing the photosensitive drum 1. As a result, a multicolor image is formed on the outer periphery of the intermediate transfer belt 80, and the image formed on the intermediate transfer belt 80 is a contact portion (secondary transfer) between the secondary transfer roller 82 and the intermediate transfer belt 80 that are the secondary transfer positions. (Transfer section).

  When transporting the recording material P, a voltage is applied to the secondary transfer roller 82 by the secondary transfer voltage power supply 85, thereby forming an electric field on the secondary transfer counter roller 86 disposed oppositely. In addition, dielectric polarization is generated between the intermediate transfer belt 80 and the recording material P to generate an electrostatic attracting force therebetween.

(Fixing part)
A fixing device 19 as fixing means applies heat and pressure to an image formed on a recording material to fix the toner image, and has a fixing belt (not shown) and an elastic pressure roller (not shown). The elastic pressure roller sandwiches the fixing belt and forms a fixing nip portion with a predetermined width with a predetermined pressure contact force with a belt guide member (not shown). In a state where the fixing nip rises to a predetermined temperature and is temperature controlled, the recording material P on which the unfixed toner image conveyed from the image forming unit is formed is between the fixing belt and the elastic pressure roller in the fixing nip. The image surface is introduced upward, that is, facing the fixing belt surface. Then, the image surface is brought into close contact with the outer surface of the fixing belt in the fixing nip portion, and the fixing nip portion is nipped and conveyed together with the fixing belt. In the process in which the recording material P is nipped and conveyed together with the fixing belt through the fixing nip portion, the fixing belt heats the unfixed toner image on the recording material. The fixed recording material P is discharged to the paper discharge tray 36.

[System configuration of image forming apparatus]
FIG. 2 is a block diagram for explaining the entire system configuration of the image forming apparatus. The controller unit 201 can communicate with the host computer 200 and the engine control unit 202. The controller unit 201 receives image information and a print command from the host computer 200, analyzes the received image information, and converts it into bit data. The controller unit 201 transmits a print reservation command, a print start command, and a video signal for each recording material to the CPU 211 and the image processing GA 212 via the video interface unit 210.

  The controller unit 201 transmits a print reservation command to the CPU 211 via the video interface unit 210 in accordance with a print command from the host computer 200, and transmits a print start command to the CPU 211 when printing is possible. The CPU 211 prepares for execution of printing in the order of print reservation commands from the controller unit 201 and waits for a print start command from the controller unit 201. When receiving the print start command, the CPU 211 instructs each control unit (the image control unit 213, the fixing control unit 214, and the paper transport unit 215) to start the print operation in accordance with the information of the print reservation command.

  When receiving the start of the printing operation, the image control unit 213 starts preparation for image formation. When the CPU 211 receives from the image control unit 213 that preparation for image formation has been completed, the CPU 211 outputs a / TOP signal as a reference timing for outputting a video signal to the controller unit 201. When the controller unit 201 receives the / TOP signal from the CPU 211, the controller unit 201 outputs a video signal based on the / TOP signal. When receiving a video signal from the controller unit 201, the image processing GA 212 transmits image formation data to the image control unit 213. The image control unit 213 performs image formation based on the image formation data received from the image processing GA 212.

  The paper transport unit 215 starts the paper feeding operation when receiving the printing operation start. The paper feed transport control unit 221 of the paper transport unit 215 rotates the stepping motor 223 via the paper feed transport motor driver IC 222. The paper feed conveyance control unit 221 instructs the paper feed pickup solenoid 224 to start driving (shown as a drive instruction) at the paper pick-up timing, and rotates the cassette pick-up roller 17. The paper feeding / conveying control unit 221 detects the position of the recording material according to the output results of the pre-registration sensor 35a and the registration sensor 35b (illustrated as sensor ON / OFF), and performs the conveyance speed control to the recording material up to the secondary transfer position. Transport.

  The fixing control unit 214 starts fixing preparation when it receives the start of the printing operation. The fixing control unit 214 starts temperature control according to the information of the print reservation command in accordance with the timing when the recording material on which the secondary transfer has been performed is conveyed. The fixing control unit 214 fixes the image on the recording material and conveys the recording material to the outside of the apparatus.

[Conventional transport speed control]
FIG. 3A and FIG. 3B are timing charts for conventional transport speed control for comparison with the present embodiment. FIG. 3A is a timing chart when the cassette pickup roller 17 and the registration roller 18 are driven and rotated by separate drive sources (stepping motors or the like). FIG. 3B is a timing chart when the cassette pickup roller 17 and the registration roller 18 are driven and rotated by the same drive source.

  FIG. 3 shows from the top the output timing of the / TOP signal (300a), the arrival timing of the image leading edge (310a) to each position, and the timing (320a) for driving the cassette pickup roller 17 (shown as a cassette pick). Subsequently, the actual measurement value (330a) of the output timing of the pre-registration sensor 35a, the theoretical value (340a) of the output timing of the pre-registration sensor 35a, the actual measurement value (350a) of the output timing of the registration sensor 35b, and the theoretical output timing of the registration sensor 35b. The value (360a) is indicated. Furthermore, the state (370a) of the first recording material (first sheet), the state (380a) of the second recording material (second sheet), and the speed (390a) of the paper feeding / conveying unit are shown. Here, the actual measurement value of the output timing of each sensor is measured by starting a timer (not shown) at the timing when the CPU 211 outputs the / TOP signal, for example. In addition, the theoretical value of the output timing of each sensor is assumed to be stored in advance in, for example, a memory (not shown), and so on.

(In the case of separate drive sources (FIG. 3A))
FIG. 3A will be described. The CPU 211 outputs a / TOP signal corresponding to the first recording material (hereinafter simply referred to as the first sheet) (301a), and starts an image forming operation (311a) corresponding to the first sheet. Further, the CPU 211 instructs the paper transport unit 215 to start the printing operation, and the paper feed transport control unit 221 of the paper transport unit 215 starts the paper feed operation (321a) by the cassette pickup roller 17 (in 370a, “paper feed” "). The paper feed conveyance control unit 221 conveys the first sheet until reaching the registration sensor 35b (351a) (shown as “registration conveyance” in 370a). Note that 331a indicates an actual value of arrival at the first pre-registration sensor 35a, and 341a indicates a theoretical value of arrival at the first pre-registration sensor 35a. At this time, the conveyance speed of the recording material controlled by the paper conveyance unit 215 is a steady speed (steady speed) V. The paper feed conveyance control unit 221 stops the conveyance control at the timing when the leading edge of the recording material (referred to as the paper leading edge) reaches the registration sensor 35b (351a) (shown as “image leading edge waiting” 371a in 370a). At this time, the paper transport unit 215 controls the recording material transport speed to decelerate from the steady speed V to 0 (stop). The paper feed conveyance control unit 221 controls the conveyance of the first recording material that has been stopped by the registration sensor 35b in accordance with the image on the intermediate transfer belt 80, that is, at the timing when the leading edge of the image (310a) reaches 312a. Is resumed (312a). In addition, 312a illustrates “registration sensor ON virtual position on the belt”. Here, the “registration sensor ON virtual position on the belt” means the time for the leading edge of the image to reach the secondary transfer portion from that position on the intermediate transfer belt 80, and the leading edge of the recording material from the position of the registration sensor 35b to the secondary transfer. It is a position where the time to reach the part becomes equal. The speed of the paper transport unit is accelerated from 0 to a steady speed V (shown as “re-feed transport” in 370a).

  The CPU 211 outputs the / TOP signal of the second sheet after the time corresponding to the image size (302a) + the margin between images (image interval (303a)) has elapsed from the first sheet / TOP signal output timing (301a) ( 304a). Here, the image size (302a) is the size of the toner image in the conveyance direction, and the image interval (303a) is the toner image corresponding to the first sheet when the toner image is formed on the intermediate transfer belt 80. This is the interval between the trailing edge of the toner image and the leading edge of the toner image corresponding to the second sheet.

The paper feed conveyance control unit 221 starts the second paper feed operation at the paper feed timing (322a) determined from the output timing (304a) of the second / TOP signal (shown as "paper feed" in 380a). ). At the time (332a) when the leading edge of the second sheet reaches the pre-registration sensor 35a, the paper feed / conveyance control unit 221 is the difference time Δt between the theoretical value (342a) of the pre-registration sensor arrival timing and the actual measurement value (332a). ₁ (334a) is calculated. The theoretical value here is the timing when the recording material is conveyed without variation from the start of paper feeding to the pre-registration sensor 35a. The paper feed conveyance control unit 221 performs conveyance speed control so that the difference time Δt ₁ can be eliminated before reaching the registration sensor (conveyance speed control A (382a)) (in “380a,“ registration conveyance (conveyance speed control A) ”). ").

  Here, the conveyance speed control A will be described in detail. For example, when the leading edge of the succeeding sheet reaches the pre-registration sensor 35a earlier than the theoretical value (theoretical value (342a)> measured value (332a)), for example, when the succeeding sheet is taken out by the preceding sheet, the transport speed is set to Decelerate (391a (solid line)). On the other hand, when the paper leading edge of the succeeding paper reaches the pre-registration sensor 35a later than the theoretical value due to slippage of the cassette pickup roller 17 and the paper (theoretical value (342a) <measured value (333a)) Like that. That is, the conveyance speed is accelerated (392a (broken line)), and the speed is returned to the steady speed immediately before reaching the registration sensor. Hereinafter, a method for calculating the speed at which the recording material is conveyed by the conveyance speed control A will be described.

For example, when the conveyance speed is decelerated (391a; solid line)
T _{reg_preg} ... time from the pre-registration sensor 35a to the registration sensor 35b Δt ₁ ... difference time (334a) between the sensor theoretical value before registration (342a) and the actual measurement value (332a)
T _down ··· from the time T _up ··· transport speed of up to transport speed is decelerated from the steady speed V to the transport speed control speed _{V ctrl} is the conveying speed control speed _{V ctrl} to accelerate to a steady speed V time T ·・ ・_Assuming that the transfer speed is controlled at the transport speed control speed _Vctrl , the time for carrying the transport speed control is:
T _{reg_preg} + Δt ₁ = T _down + T + T _up (Formula 1)
Is established.

In addition, the section (distance) for carrying speed control is
V... Steady speed V _ctrl ... Transport speed control speed S1... Recording material transport distance from when the leading edge of the recording material reaches the pre-registration sensor 35a until reaching the registration sensor 35b.
S1 =
((V + _Vctrl ) × _Tdown ) / 2 + (T × _Vctrl ) + ((V + _Vctrl ) × _Tup ) / 2 (Formula 2)

S1 is a transport distance (= T _{reg_preg} × V) when the leading edge of the recording material reaches the pre-registration sensor 35a and the registration sensor 35b at an ideal timing (that is, the recording material is transported at a steady speed V without transport speed control). Because it is the same,
T _{reg_preg} × V =
((V + _Vctrl ) × _Tdown ) / 2 + (T × _Vctrl ) + ((V + _Vctrl ) × _Tup ) / 2 (Formula 3)
Is established.

Here, when acceleration of the stepping motor and acceleration at the time of deceleration are g,
During deceleration:
_Vctrl = V-g * _Tdown (Formula 4)
During acceleration:
V = _Vctrl + g × _Tup (Formula 5)
Is established.

As described above, _Vctrl and T are calculated from the formulas (1) to (5), and the conveyance speed control A is performed. The acceleration g varies depending on the characteristics of the stepping motor, the control method, and the like. For this reason, it is assumed that the information is stored in a memory (not shown) of the CPU 211 in advance, and the information on the acceleration g is output from the CPU 211 to the paper feed conveyance control unit 221. Note that the sheet feeding / conveying control unit 221 may include a memory (not shown), and the acceleration g information may be stored in advance in the memory.

  In the case of accelerating the conveyance speed (392a), it is assumed that the timing of reaching the second pre-registration sensor 35a is the actual measurement value 333a (dashed line).

Δt ₂ ... Difference time between sensor theoretical value before registration and measured value (335a)
Then,
T _{reg_preg −Δt 2} = T _up + T + T _down (Formula 6)
It becomes.

In addition, the section (distance) for carrying speed control is
V _ctrl2 ... Transport speed control speed S2... Recording material transport distance from when the leading edge of the recording material reaches the pre-registration sensor 35a until it reaches the registration sensor 35b.
S2 =
_{((V + V ctrl2) ×} T up) / 2 + (T × V ctrl2) + ((V + V ctrl2) × T down) / 2 ( Equation 7)

S2 is a transport distance (= T _{reg_preg} × V) when the leading edge of the recording material reaches the pre-registration sensor 35a and the registration sensor 35b at an ideal timing (that is, the recording material is transported at a steady speed V without transport speed control). Because it is the same,
T _{reg_preg} × V =
_{((V + V ctrl2) ×} T up) / 2 + (T × V ctrl2) + ((V + V ctrl2) × T down) / 2 ( Equation 8)
Is established.

As described above, _Vctrl2 and T are calculated from the formulas (4) to (8), and the conveyance speed control A is performed.

  The conveyance speed control A eliminates variations in the arrival timing before the registration sensor when the recording material is conveyed from the sheet feeding start position to the registration before sensor 35a. Here, examples of the paper feed start position include the position of the leading end portion of the recording material P stacked on the top of the main cassette 16 and the nip portion where the cassette pickup roller 17 is in contact with the conveyance path. Variations in the arrival timing of the pre-registration sensor are caused by paper stacking amount, take-out amount of preceding paper, and slippage of the cassette pickup roller 17 and paper (hereinafter referred to as paper feeding variation).

  After that, the sheet feed control unit 221 calculates a difference time between the theoretical value (363a) of the registration sensor arrival timing and the actual measurement value (353a) when the leading edge of the second sheet reaches the registration sensor 35b. The paper feed conveyance control unit 221 performs conveyance speed control so that this difference can be eliminated by the time when the merge point 35c is reached (313a) (conveyance speed control B (383a)) (the 380a includes "merge point conveyance (conveyance speed)". Control B) ”).

  The transport speed control B performs the same control as the transport speed control A described above. Thereafter, the paper feed conveyance control unit 221 returns the conveyance speed to the steady speed V before the leading edge of the paper reaches the merge point 35c (313a) (denoted as "merge point virtual position on the belt" in 310a).

  The conveyance speed control B eliminates variation in the arrival timing of the registration sensor when the recording material is conveyed from the pre-registration sensor 35a to the registration sensor 35b. When the recording material is transported to the registration roller 18 by the cassette pickup roller 17, the recording material is not sandwiched between the transporting rollers, and therefore, slippage occurs depending on the surface state of the recording material and variations in the feed roller system (wear state). (Conveyance variation (slip)). The variation in the registration sensor arrival timing is caused by the conveyance variation (slip).

  Thereafter, after the leading edge of the paper reaches the merge point 35c, the paper feed conveyance control unit 221 conveys the recording material at a constant speed V, fixes the image by the fixing control unit 214, and discharges the recording material outside the apparatus. (384a) (illustrated as “conveyance” in 380a). Incidentally, 381a indicates that the second sheet 380a is transported before registration. Further, 352a is an actual measurement value of the timing when the rear end of the first sheet passes the registration sensor 35b, 361a is a theoretical value of the timing when the leading edge of the first sheet reaches the registration sensor 35b, and 362a is a theoretical value of the timing when the first sheet reaches the registration sensor 35b. Is the theoretical value of the timing of passing through.

  In the conventional example shown in FIG. 3A, as described above, the cassette pickup roller 17 and the registration roller 18 are driven and rotated by separate drive sources (stepping motors or the like), and the recording material is conveyed. For this reason, when the transport speed control of the succeeding paper is performed, the transport control of the preceding paper is not affected.

(In the case of the same drive source)
FIG. 3B is a timing chart for conventional conveyance speed control when the cassette pickup roller 17 and the registration roller 18 are driven and rotated by the same drive source (stepping motor or the like) to convey the recording material. . Here, description of the same control as in FIG. 3A is omitted, and the difference from the control described in FIG. In FIG. 3B, a symbol b is attached corresponding to the symbol a in FIG.

  In FIG. 3B, the cassette pickup roller 17 and the registration roller 18 are driven and rotated by the same drive source (stepping motor or the like), and the recording material is conveyed. Therefore, as described with reference to FIG. 3A, when the conveyance speed control is performed on the second subsequent sheet at the pre-registration sensor arrival timing (FIG. 3A 332a or 333a), it is the first sheet. This will affect the conveyance of the preceding paper. This is because when the drive and rotation are performed by the same drive source, the speed of the registration roller 18 driven by the same drive source also changes. That is, since the conveyance speed control A indicated by 382a in FIG. 3A starts before the timing 352a when the trailing edge of the first sheet passes the registration sensor 35b, The first sheet conveyed by the registration roller 18 is affected.

  Therefore, as in the example of FIG. 3B, the paper feed interval so that the trailing edge of the preceding sheet always passes the registration sensor 35b (352b) by the sensor arrival timing (332b) at the leading edge of the succeeding sheet. It is necessary to widen (323b) in advance (304b). As a result, not only the image interval (303b) described with reference to FIG. 3A is provided, but also the image formation interval is increased by the preceding sheet registration sensor passage waiting correction sheet interval (304b). The CPU 211 waits for a time corresponding to the image size (302b) + image interval (303b) + preceding paper registration sensor passage waiting time (304b) from the output of the first / TOP signal (301a) to the / TOP signal of the second sheet. The signal (305b) is output. For this reason, when the cassette pickup roller 17 and the registration roller 18 are driven by the same drive source, the productivity is reduced as compared with the case of driving by another drive source.

[Conveyance speed control of this embodiment]
FIG. 4 shows a timing chart of two-sheet continuous printing in this embodiment. In the present embodiment, a method for eliminating variations in feeding and conveying recording materials without widening the image interval even when the conveying unit from the start of feeding to the secondary transfer position is driven by the same drive source will be described. Each signal in the timing chart of FIG. 4 corresponds to FIG. In FIG. 4, reference numerals 400 are assigned in correspondence with reference numerals 300 in FIG. 3. However, in FIG. 4, regarding the pre-registration sensor 35a, the passage timing of the rear end of the first sheet is 432, the arrival timing of the front end of the second sheet is 433, and a difference time Δt ₃ described later is 434.

  The CPU 211 outputs the first / TOP signal (401) and starts the first image forming operation (411). Further, the CPU 211 instructs the paper transport unit 215 to start a printing operation, and the paper feed transport control unit 221 of the paper transport unit 215 starts the paper feed operation (421). The paper feed conveyance control unit 221 conveys the first sheet until the leading edge of the first sheet reaches the registration sensor 35b (451). At the timing when the leading edge of the first sheet reaches the registration sensor 35b (451), the sheet feeding / conveying control unit 221 decelerates the sheet feeding / conveying unit speed from the steady speed V and stops conveying control. Then, the sheet feed control unit 221 waits for the first image until the leading edge of the image reaches the registration sensor ON virtual position 412 on the intermediate transfer belt 80 (471). When the leading edge of the image reaches the registration sensor ON virtual position 412 on the intermediate transfer belt 80, the sheet feeding and conveyance control unit 221 resumes recording material conveyance control in accordance with the image on the intermediate transfer belt 80 (412). That is, the sheet feeding / conveying section speed is returned to the steady speed V, and the first sheet is resumed (represented as “re-feeding conveyance” in 470).

The CPU 211 outputs the / TOP signal of the second sheet after the time corresponding to the image size (402) + the margin between images (image interval (403)) has elapsed since the first sheet / TOP signal output timing (401) ( 404). This is different from the conventional control shown in FIG. 3B in which a preceding paper registration sensor passage waiting correction sheet interval (304b) is provided. The CPU 211 instructs the paper transport unit 215 to start a printing operation at the output timing (404) of the second sheet / TOP signal, and the paper feed transport control unit 221 supplies the feed determined from the output timing (404) of the / TOP signal. The sheet feeding operation for the second sheet is started at the sheet timing (422). The paper feed conveyance control unit 221 does not perform the conveyance speed control A at the timing (433) when the leading edge of the second sheet reaches the pre-registration sensor 35a, and the theoretical value (442) and actual measurement value (pre-registration sensor arrival timing). 433) and a difference time Δt ₃ (434) are calculated. Then, the paper feed conveyance control unit 221 conveys the first and second sheets at a constant speed V until the timing (452) when the trailing edge of the first sheet as the preceding sheet passes the registration sensor 35b (481). ) (Illustrated as “register transfer (steady speed)” on 480).

The paper feeding / conveying control unit 221 starts from the timing (433) when the leading edge of the second sheet, which is the paper, reaches the pre-registration sensor 35a, and the timing (452) when the trailing edge of the first sheet, which is the preceding sheet, exits the registration sensor 35b. The time T ₁ (491) until is measured with a timer (not shown), for example. Then, the paper feed conveyance control unit 221 performs the conveyance speed control A (482) of the second recording material at the timing (452) when the trailing edge of the preceding paper passes the registration sensor 35b.

(Conveyance speed control A)
Hereinafter, a method for calculating the speed at which the recording material is conveyed by the conveyance speed control A will be described.
T ₁ ... preceding paper (first sheet) registration sensor passage time (491)
Then, the time for carrying the conveyance speed control A is expressed by the following equation.
T _{reg_preg} + Δt ₃ −T ₁ = T _down + T + T _up (Equation 9)
V... Steady speed V _ctrl ... Transport speed control speed S3... Recording material transport distance from when the leading edge of the succeeding paper reaches the pre-registration sensor 35a until the trailing edge of the preceding paper passes the registration sensor 35b S4: Assuming the recording material conveyance distance of the subsequent sheet conveyed by the conveyance speed control A,
S3 = V × T ₁
S4 =
((V + _Vctrl ) * _Tdown ) / 2 + (T * _Vctrl ) + ((V + _Vctrl ) * _Tup ) / 2

The sum of the recording material conveyance distance (S3) and the recording material conveyance distance (S4) conveyed by the conveyance speed control A is the conveyance distance when the leading edge of the recording material reaches the pre-registration sensor 35a and the registration sensor 35b at an ideal timing. It is the same as (= T _{reg_preg} × V). Here, the ideal timing is when the recording material is conveyed at the steady speed V without the conveyance speed control. Therefore,
T _{reg_preg} × V
= S3 + S4
_{= (V × T 1) +} ((V + V ctrl) × T down) / 2 + (T × V ctrl) + ((V + V ctrl) × T up) / 2 ( equation 10)
Is established.

From (Equation 4), (Equation 5), (Equation 9), and (Equation 10), _Vctrl and T are calculated and the conveyance speed control A is performed. The acceleration g is as described above.

The recording material conveyance distance S1 conveyed by the conventional conveyance speed control A is equal to the recording material conveyance distance S3 conveyed by the conveyance control from the pre-registration sensor 35a to the conveyance speed control start and the conveyance speed control of the present embodiment. It becomes equal to the sum of the recording material conveyance distance S4 conveyed by A. That is, T _{reg_preg} × V = S1 = S3 + S4.

  The paper feed conveyance control unit 221 performs the conveyance speed control B at the timing (453) when the leading edge of the second recording material reaches the registration sensor 35b (483).

(Conveying speed control B)
Details of the conveyance speed control B will be described below. First, in 453, the difference between the actual value (453) of the registration sensor arrival timing of the second recording material detected by the registration sensor 35b and the predefined theoretical value (463) is calculated. The paper feed conveyance control unit 221 executes the conveyance speed control by accelerating or decelerating the conveyance speed by the paper feed conveyance control unit 221 so that this difference (variation in conveyance) can be eliminated by the time when the merge point 35c is reached (413). . Note that the conveyance speed control B performs control so that the second recording material returns to the steady speed V immediately before the leading edge of the recording material reaches the merge point 35c. The conveyance speed is calculated by the same method as in the conventional example described with reference to FIG.

  The paper feed conveyance control unit 221 switches the conveyance speed control B to the steady speed V before the leading edge of the second sheet reaches the merge point 35c (413), and conveys the recording material. The CPU 211 fixes the image by the fixing control unit 214. The recording material is discharged outside the apparatus (484).

[Recording material conveyance control process of this embodiment]
FIG. 5 shows a flowchart in the present embodiment. The flowchart of FIG. 5 is a flowchart regarding the recording material conveyance control of the second sheet (subsequent sheet) which is the object of conveyance speed control. Details of the control are shown below. In step (hereinafter referred to as “S”) 500, the sheet feeding / conveying control unit 221 detects two sheets to be controlled by the cassette pickup roller 17 at a predetermined timing from the output of the / TOP signal (FIG. 4404) from the CPU 211. The feeding of the recording material for the second eye is started (422 in FIG. 4). In step S501, the paper feed conveyance control unit 221 determines whether the leading edge of the second sheet has been detected by the pre-registration sensor 35a, that is, whether the subsequent sheet has reached the pre-registration sensor 35a. In S501, when the sheet feeding / conveying control unit 221 determines that the succeeding sheet has not reached the pre-registration sensor 35a, the process returns to S501. In S501, when the paper feeding / conveying control unit 221 determines that the leading edge of the second sheet, which is a subsequent sheet, has reached the pre-registration sensor 35a (433 in FIG. 4), a timer (not shown) is started in S502, and the preceding sheet registration sensor is detected. The measurement of the passage time T ₁ (491) is started (502).

In step S503, the paper feed conveyance control unit 221 determines whether the trailing edge of the first sheet, which is the preceding sheet, is detected by the registration sensor 35b, that is, whether the preceding sheet has passed the registration sensor 35b. In S503, when the paper feed conveyance control unit 221 determines that the preceding paper has not passed the registration sensor 35b, the process returns to S503. In S503, when the paper feed control unit 221 determines that the trailing edge of the first sheet, which is the preceding sheet, has passed the registration sensor 35b (FIG. 4452), the timer started in S502 is stopped and the preceding sheet registration sensor is detected in S504. The measurement of the passage time T ₁ (491) is terminated. In step S505, the paper feed conveyance control unit 221 starts the conveyance speed control A described above. Here, as described above, the paper feed conveyance control unit 221 calculates _Vctrl , T from (Equation 4), (Equation 5), (Equation 9), and (Equation 10), and _performs the conveyance speed control A. Implement (Figure 482).

  In step S506, the paper feed conveyance control unit 221 determines whether the registration sensor 35b has detected the leading edge of the second recording material, that is, whether the subsequent sheet has reached the registration sensor 35b. If the paper feed control unit 221 determines in S506 that the subsequent paper has not reached the registration sensor 35b, the process returns to S506. If the paper feeding / conveying control unit 221 determines in S506 that the leading edge of the succeeding paper has reached the registration sensor 35b (FIG. 4453), it carries the conveying speed control B in S507 (FIG. 4483).

As described above, according to the present exemplary embodiment, when a recording material is continuously conveyed in an image forming apparatus in which conveyance from the start of sheet feeding to the secondary transfer position is performed by one drive source, the following is performed. Control. That is, the conveyance speed control of the subsequent recording material is performed at the timing when it is detected that the recording material conveyed in advance passes through the conveyance path moving by the drive source. As a result, it is possible to suppress variations in paper feeding and conveyance without affecting the conveyance and secondary transfer of the recording material conveyed in advance, and to obtain a good image without reducing productivity. Become. In the present embodiment, an example in which two sheet detection sensors are used and the conveyance speed control is divided into two times A and B has been described. This is based on the spirit of the present invention. Variations are possible and are not excluded from the scope of the invention.

  As described above, according to the present embodiment, even when recording materials are continuously conveyed by the same drive source, variations in conveyance of subsequent paper without affecting productivity and image formation without reducing productivity. And an excellent image can be obtained.

  In the first exemplary embodiment, the conveyance speed control A is performed after the trailing edge of the preceding sheet passes the registration sensor 35b in order to perform the conveyance speed control A after the preceding sheet has passed the registration roller 18. However, the registration sensor 35 b can detect the trailing edge of the recording material when the trailing edge of the recording material reaches a position downstream of the nip portion of the registration roller 18. FIG. 6 is a diagram illustrating a main part of the conveyance path from the paper feeding unit to the secondary transfer unit. As shown in FIG. 6, at the timing (600) when the trailing edge of the recording material (shown as “paper”: dark solid line) passes through the registration sensor 35b, the trailing edge of the recording material is downstream from the nip portion of the registration roller 18 by a distance 601. Will be transported.

  Therefore, in the second embodiment, a method of predicting the position of the preceding paper by the pre-registration sensor 35a and performing the conveyance speed control A immediately after the trailing edge of the recording material of the preceding paper has passed the registration roller 18 will be described. . Note that the overall configuration and system block diagram of the laser printer as the image forming apparatus are the same as in the first embodiment (FIGS. 1 and 2), and a description thereof will be omitted.

[Recording material conveyance control of this embodiment]
FIG. 7 shows a timing chart of two-sheet continuous printing in this embodiment. Since the first image formation and the recording material conveyance control in the timing chart shown in FIG. 7 are the same as those in the first embodiment, the description thereof will be omitted, and the second recording material conveyance control will be described below. Each signal in the timing chart of FIG. 7 corresponds to FIG. 4, and the reference number 700 is attached corresponding to the reference number 400 in FIG. 4.

The sheet feed control unit 221 measures the time until the trailing edge of the preceding sheet passes the nip portion of the registration roller 18 at the timing (732) when the trailing edge of the preceding sheet has passed the pre-registration sensor 35a. Measurement of the preceding paper registration roller passage time T ₂ (792) is started. Here, since the distance from the pre-registration sensor 35a to the registration roller 18 and the recording material conveyance speed are known, it is unique when the preceding sheet that has passed the pre-registration sensor 35a passes the nip portion of the registration roller 18. It is decided. That is, from the distance between the pre-registration sensor 35a and the registration roller 18 and the conveyance speed (steady speed V) of the preceding paper, the trailing edge of the preceding paper passes the registration roller 18 after passing the pre-registration sensor 35a. It is possible to calculate a time T ₂ (passing time of the preceding paper registration roller) until the time. Thus, the trailing edge of the preceding sheet is to start a timer for example (not shown) when passing through the pre-registration sensor 35a, be considered as the preceding sheet has passed through the nip portion of the registration roller 18 when the time T ₂ has elapsed it can. In FIG. 7, this timing is set to 793.

After the trailing edge of the first sheet, which is the preceding sheet, has passed through the pre-registration sensor 35a (732), the leading end of the second sheet, which is the sheet that has been fed, reaches the pre-registration sensor 35a. The time (733) (the time between sensor paper before registration) Δt _blank (791) is measured until it is done. The paper feed / conveyance control unit 221 determines the difference time Δt ₄ between the theoretical value (742) of the pre-registration sensor arrival timing and the actual measurement value (733) at the timing (733) when the leading edge of the succeeding paper reaches the pre-registration sensor 35a. 734) is calculated, and the execution timing of the conveyance speed control A is determined.

Hereinafter, a method for calculating the speed at which the recording material is conveyed by the conveyance speed control A will be described.
T ₂ ... preceding paper registration roller passage time (792)
Δt _blank・ ・ ・ Time between sensor paper before registration (791)
Δt ₄ ... Difference time (734) between the theoretical value (742) of the arrival timing before the second registration and the actual measurement value (733).
Then, the time for carrying speed control is
T _{reg_preg} + Δt ₄
= (T ₂ −Δt _blank ) + T _down + T + T _up (Formula 11)
It becomes.

In addition, the section (distance) for carrying speed control is
V: Steady speed V _{ctrl: Conveying} speed control speed S5: After the leading edge of the second recording material reaches the pre-registration sensor 35a, the trailing edge of the preceding sheet passes through the nip portion of the registration roller 18. The recording material conveyance distance until the recording material is conveyed. S6...
S5 = V × (T ₂ −Δt _blank )
S6 = ((V + _Vctrl ) × _Tdown ) / 2 + (T × _Vctrl ) + ((V + _Vctrl ) × _Tup ) / 2

The sum of the recording material conveyance distance (S5) and the recording material conveyance distance (S6) conveyed by the conveyance speed control A is the conveyance distance when the leading edge of the recording material reaches the pre-registration sensor 35a and the registration sensor 35b at an ideal timing. It is the same as (= T _{reg_preg} × V). Therefore,
T _{reg_preg} × V
= S5 + S6
= V × (T ₂ −Δt _blank ) + ((V + _Vctrl ) × T _down ) / 2 + (T × _Vctrl ) + ((V + _Vctrl ) × T _up ) / 2 (Formula 12)
Is established.

As described above, _Vctrl and T are calculated from (Expression 4), (Expression 5), (Expression 11), and (Expression 12), and the conveyance speed control A is performed (782).

  The paper feed conveyance control unit 221 performs the conveyance speed control B at a timing (753) when the leading edge of the second sheet reaches the registration sensor 35b (783). The conveyance speed control B is calculated by the same method as the conventional example described with reference to FIG. The paper feed conveyance control unit 221 conveys the recording material by switching from the conveyance speed control B to the steady speed before the leading edge of the paper reaches the merge point 35c (713), and the CPU 211 fixes the image by the fixing control unit 214. The recording material is discharged outside (784).

[Recording material conveyance control process of this embodiment]
FIG. 8 shows a flowchart in the present embodiment. The flowchart of FIG. 8 is a flowchart regarding the recording material conveyance control of the second sheet (subsequent sheet) that is the object of conveyance speed control. Details of the control are shown below.

In step S800, the paper feed / conveyance control unit 221 starts feeding the second recording material, which is the succeeding paper to be controlled by the conveyance speed (FIG. 7 722). In step S801, the paper feed conveyance control unit 221 determines whether the trailing edge of the first sheet, which is the preceding sheet, has passed the pre-registration sensor 35a. In S801, if the paper feed conveyance control unit 221 determines that the trailing edge of the preceding paper has not passed the pre-registration sensor 35a, the process returns to S801. In S801, if the paper feed conveyance control unit 221 determines that the trailing edge of the preceding paper has passed the pre-registration sensor 35a (732 in FIG. 7), the process proceeds to S802. In step S <b> 802, the paper feed conveyance control unit 221 starts a timer (not shown) and measures the time T ₂ for measuring the time until the trailing edge of the preceding paper passes the nip portion of the registration roller 18 (FIG. 7793). Start measurement.

In step S <b> 803, the paper feed conveyance control unit 221 determines whether or not the leading edge of the second sheet of recording material is detected by the pre-registration sensor 35 a, that is, whether or not the leading edge of the subsequent sheet has reached the pre-registration sensor 35 a. to decide. In step S803, if the paper feed conveyance control unit 221 determines that the leading edge of the subsequent sheet has not reached the pre-registration sensor 35a, the process returns to step S803. In S803, when the paper feed conveyance control unit 221 determines that the leading edge of the succeeding paper has reached the pre-registration sensor 35a (733 in FIG. 7), the process proceeds to S804. In step S <b> 804, the paper feed conveyance control unit 221 measures the pre-registration sensor paper interval time Δt _blank . Further, sheet transportation control unit 221 determines the previous sheet registration roller passing time T ₂ as described above as a transport speed control A start timing. Δt _blank may refer to the value of the timer started in S802, or may be measured by a timer different from the timer started in S802.

In step S <b> 805, the paper feed conveyance control unit 221 determines whether it is time to start the conveyance speed control A. If the sheet feed control unit 221 determines in S805 that it is not the timing to start the transport speed control A, the process returns to S805. In S805, when it is determined that the start timing of the conveyance speed control A is reached (FIG. 7793), the paper feed conveyance control unit 221 executes the conveyance speed control A in S806 (FIG. 7782). Incidentally, the paper feed conveyance control unit 221, if it is determined "(from pre-registration sensor 35a resist distance to the roller 18) / constant speed V" with reference to the timer, which is measured starting at S802 and the time T ₂ has elapsed Then, it is determined that it is the start timing of the conveyance speed control A. That is, the start timing of the conveyance speed control A is the timing 793 in FIG. 7, and is the timing at which the trailing edge of the preceding paper is predicted to have passed the registration roller 18. Further, as described above, the sheet feed conveyance control unit 221 calculates _Vctrl and T from (Equation 4), (Equation 5), (Equation 11), and (Equation 12), and _performs the conveyance speed control A. To do.

  In step S807, the paper feed conveyance control unit 221 determines whether or not the leading edge of the second sheet, which is the subsequent sheet (the sheet), has reached the registration sensor 35b, and determines that the leading edge of the subsequent sheet has not reached the registration sensor 35b. If so, the process returns to S807. If it is determined in S807 that the leading edge of the succeeding paper has reached the registration sensor 35b (FIG. 7753), the paper feed control unit 221 executes the conveyance speed control B in S808 (FIG. 7783).

  As described above, according to the present exemplary embodiment, in the image forming apparatus in which conveyance from the start of paper feeding to the secondary transfer position is performed by one drive source, when the recording material is continuously conveyed, The conveyance speed control is performed as follows. That is, it is performed at the timing when it is detected that the recording material conveyed in advance passes through a position on the conveyance path where a roller or the like moving by one drive source is installed. As a result, it is possible to suppress variations in paper feeding and conveyance without affecting the conveyance and secondary transfer of the recording material conveyed in advance, and to obtain a good image without reducing productivity. Become. Unlike the first embodiment, the conveyance speed control A is performed by predicting the timing at which the preceding sheet passes the registration roller 18. As a result, a large number of correctable sections can be secured by the distance (601) between the registration roller 18 and the registration sensor 35b, and more paper feed variations can be corrected.

Further, in the present embodiment, an example in which the conveyance speed control is divided into two times A and B using two recording material detection sensors has been described, but this is various in accordance with the spirit of the present invention. These modifications are possible and are not excluded from the scope of the present invention.

  As described above, according to the present embodiment, even when recording materials are continuously conveyed by the same drive source, variations in conveyance of subsequent paper without affecting productivity and image formation without reducing productivity. And an excellent image can be obtained.

  The third embodiment is configured such that the positions of the pre-registration sensor 35a and the registration sensor 35b are shorter than the image interval for continuous printing, and the acceleration-side conveyance speed control is performed from the pre-registration sensor 35a. A method of performing speed control from the registration sensor 35b will be described. In the present embodiment, it is possible to secure a large number of acceleration-correctable sections by carrying out acceleration-side transport speed control from the pre-registration sensor 35a. On the other hand, by carrying out deceleration-side conveyance speed control from the registration sensor 35b, it is possible to reduce conveyance variation between the pre-registration sensor 35a and the registration sensor 35b. The overall configuration and system block diagram of the laser printer as the image forming apparatus are the same as in the first and second embodiments (FIGS. 1 and 2), and the description thereof is omitted.

[Recording material conveyance control of this embodiment]
9 and 10 are timing charts for two-sheet continuous printing in the present embodiment. Since the image formation and recording material conveyance control of the first sheet (preceding sheet) in the timing charts shown in FIGS. 9 and 10 are the same as those in the first and second embodiments, the description thereof will be omitted. Or, the recording material conveyance control of the paper will be described. The signals in the timing charts of FIGS. 9 and 10 correspond to FIG. 4 and are assigned the numbers 900 and 1000 corresponding to the numbers 400 in FIG. 4, respectively.

(Deceleration-side transfer speed control)
In FIG. 9, the sheet feed control unit 221 determines that the timing (933) when the leading edge of the succeeding sheet reaches the pre-registration sensor 35a is earlier than the theoretical value (942) (predetermined timing) of the pre-registration sensor arrival timing. Judgment is as follows. That is, the paper feed conveyance control unit 221 determines that the conveyance variation can be sufficiently eliminated by performing the conveyance speed control from the timing (953) when the leading edge of the succeeding paper reaches the registration sensor 35b. The timing at which the paper feed conveyance control unit 221 starts conveyance speed control is the timing (953) at which the leading edge of the succeeding paper reaches the registration sensor 35b, and therefore the trailing edge of the preceding paper has passed through the registration sensor 35b.

Next, the paper feed conveyance control unit 221 calculates a difference time Δt ₅ between the theoretical value (963) of the registration sensor arrival timing and the actual measurement value (953) at the timing (953) when the leading edge of the succeeding paper reaches the registration sensor 35b. To do. The paper feed conveyance control unit 221 performs conveyance speed control so that the difference time Δt ₅ can be eliminated by the time when the merge point 35c is reached (913) (983).

Below, the calculation method of the speed conveyed by conveyance speed control is demonstrated.
T _{marg_reg} ... time from the _registration sensor 35b to the merge point Δt ₅ ... The time for carrying out the conveyance speed control when the difference time between the theoretical value (963) of the registration sensor arrival timing and the actual measurement value (953) is
T _{marg_reg} + Δt ₅ = T _down + T + T _up (Formula 13)
It becomes.

In addition, the section (distance) for carrying speed control is
V... Steady speed V _ctrl ... Transport speed control speed S7... Recording material transport distance transported by transport speed control
S7 =
((V + _Vctrl ) * _Tdown ) / 2 + (T * _Vctrl ) + ((V + _Vctrl ) * _Tup ) / 2

The recording material conveyance distance (S7) conveyed by the conveyance speed control is the same as the conveyance distance (= T _{marg_reg} × V) when the leading edge of the recording material reaches the registration sensor 35b and the merge point 913 at an ideal timing.
T _{marg_reg} × V =
((V + _Vctrl ) * _Tdown ) / 2 + (T * _Vctrl ) + ((V + _Vctrl ) * _Tup ) / 2 (Formula 14)
Is established.

As described above, _Vctrl and T are calculated from (Equation 4), (Equation 5), (Equation 13), and (Equation 14), and the conveyance speed control is performed.

  The paper feed conveyance control unit 221 switches the conveyance speed control from the conveyance speed control to the steady speed V before reaching the merge point 35c (913) at the leading edge of the succeeding paper, and the CPU 211 causes the fixing control unit 214 to fix the image. The recording material is discharged out of the apparatus (984).

(Acceleration-side transfer speed control)
Next, FIG. 10 will be described. In FIG. 10, the paper feed conveyance control unit 221 determines that the timing (1033) at which the leading edge of the succeeding paper reaches the pre-registration sensor 35a is later than the theoretical value (1042) (predetermined timing) of the pre-registration sensor arrival timing. Judgment is as follows. That is, the paper feed conveyance control unit 221 determines that the conveyance speed control is to be performed from the timing (1033) when the leading edge of the second sheet reaches the pre-registration sensor 35a. In this case, the distance between the pre-registration sensor 35a and the registration sensor 35b is shorter than the image interval (1003), and the conveyance of the subsequent paper before registration (1081) is delayed. For this reason, it may be considered that the trailing edge of the preceding paper has already passed the registration sensor 35b at the timing when the paper feed conveyance control unit 221 starts conveyance speed control (1052).

The paper feed conveyance control unit 221 calculates a difference time Δt ₆ between the theoretical value (1042) of the pre-registration sensor arrival timing and the actual measurement value (1033), and uses this difference time Δt ₆ until the merge point 35c is reached (1013). Carrying speed control will be implemented so that it can be resolved.
Δt ₆ ... Assuming that the difference time between the theoretical value (1042) of the sensor arrival timing before registration and the actual measurement value (1033), the time for carrying speed control is
T _{marg_reg} + T _{reg_preg −Δt 6}
= T _up + T + T _down (Formula 15)
It becomes.

In addition, the section (distance) for carrying speed control is
V ... steady speed V _ctrl ... transport speed control speed S8 ... recording material transport distance transported by transport speed control
S8 =
((V + _Vctrl ) × T _up ) / 2 + (T × _Vctrl ) + ((V + _Vctrl ) ×
T _down ) / 2

The recording material conveyance distance (S8) conveyed by the conveyance speed control is the conveyance distance when the leading edge of the recording material reaches the pre-registration sensor 35a, the registration sensor 35b, and the merge point 1013 at an ideal timing (= (T _{margin_reg} + T _{reg_preg} )). XV), so
(T _{marg_reg} + T _{reg_preg} ) × V =
((V + _Vctrl ) * _Tup ) / 2 + (T * _Vctrl ) + ((V + _Vctrl ) * _Tdown ) / 2 (Formula 16)

As described above, _Vctrl and T are calculated from (Expression 4), (Expression 5), (Expression 15), and (Expression 16), and the conveyance speed control is performed.

  The paper feed conveyance control unit 221 switches the conveyance speed control from the conveyance speed control to the steady speed before reaching the merge point 35c (1013) at the leading edge of the succeeding paper, and the CPU 211 fixes the image by the fixing control unit 214. The recording material is discharged outside (1084).

[Recording material conveyance control process of this embodiment]
FIG. 11 shows a flowchart in the present embodiment. The flowchart of FIG. 11 is a flowchart relating to recording material conveyance control of the second sheet (subsequent sheet or the sheet) that is the object of conveyance speed control. Details of the control are shown below.

  In step S1100, the paper feeding / conveying control unit 221 starts feeding the second recording material to be controlled in the conveyance speed (FIG. 9922, FIG. 101022). In step S1101, the paper feed conveyance control unit 221 determines whether the leading edge of the succeeding sheet has been detected by the pre-registration sensor 35a, that is, whether the succeeding sheet has reached the pre-registration sensor 35a. In S1101, if the paper feeding / conveying control unit 221 determines that the subsequent sheet has not reached the pre-registration sensor 35a, the process returns to S1101. In S1101, when the paper feeding / conveying control unit 221 determines that the leading edge of the succeeding sheet has reached the pre-registration sensor 35a (FIG. 9933, FIG. 101033), the actual measured value of the pre-registration sensor arrival time of the succeeding sheet is calculated in S1102. Judge whether it is faster than the value.

In step S1102, if the paper feed conveyance control unit 221 determines that the measured value of the sensor arrival time before registration of the subsequent sheet is earlier than the theoretical value (FIG. 9933), the conveyance speed control on the deceleration side is controlled by the leading edge of the second sheet. It is assumed that the operation is performed at the timing when the registration sensor 35b is reached (FIG. 9953). In step S1103, the paper feed conveyance control unit 221 determines whether the registration sensor 35b has detected the leading edge of the subsequent sheet, that is, whether the subsequent sheet has reached the registration sensor 35b. In S1103, if the paper feed conveyance control unit 221 determines that the succeeding sheet has not reached the registration sensor 35b, the process returns to S1103. In step S1103, when the sheet feeding / conveying control unit 221 determines that the succeeding sheet has reached the registration sensor 35b (FIG. 9953), the processing proceeds to step S1104. In step S1104, the paper feed conveyance control unit 221 calculates a difference time Δt ₅ between the measured value and the theoretical value of the registration sensor arrival time, and starts conveyance speed control based on the difference time Δt _{5 in step} S1105 (FIG. 9983, merge point). Transport). That is, as described above, the sheet feed conveyance control unit 221 calculates _Vctrl , T from (Equation 4), (Equation 5), (Equation 13), and (Equation 14), and thereby the conveyance speed on the deceleration side. Implement control.

In step S1102, if the paper feed control unit 221 determines that the measured value of the sensor arrival time before registration of the subsequent sheet is later than the theoretical value (FIG. 101033), the process proceeds to step S1106. In step S1106, the paper feed conveyance control unit 221 calculates a difference time Δt ₆ between the measured value and the theoretical value of the sensor arrival time before registration, and starts the conveyance speed control based on the difference time Δt _{6 in step} S1107 (FIG. 10, 1083). Cash register / merge point transport). As described above, the paper feed conveyance control unit 221 calculates _Vctrl and T from (Equation 4), (Equation 5), (Equation 15), and (Equation 16), and _performs acceleration-side conveyance speed control. carry out.

  As described above, according to the present embodiment, the conveyance from the start of paper feeding to the secondary transfer position is performed by one drive source, and the distance between the two recording material detection sensors is set to a position shorter than the image interval of continuous printing. The arranged image forming apparatus has the following effects. That is, the conveyance speed control on the acceleration side is performed from the upstream sensor (pre-registration sensor 35a), and the conveyance speed control on the deceleration side is performed from the downstream sensor (registration sensor 35b). As a result, it is possible to secure a large number of acceleration-correctable sections and reduce conveyance variations to downstream sensors (registration sensors).

  In this embodiment, the two recording material detection sensors have been described on the conveyance path, with the upstream sensor as the pre-registration sensor and the downstream sensor as the registration sensor, but various modifications can be made based on the spirit of the present invention. These are not excluded from the scope of the present invention.

  As described above, according to the present embodiment, even when recording materials are continuously conveyed by the same drive source, variations in conveyance of subsequent paper without affecting productivity and image formation without reducing productivity. And an excellent image can be obtained.

  In the third embodiment, the method of performing the conveyance speed control on the acceleration side from the pre-registration sensor and the method of performing the conveyance speed control on the deceleration side from the registration sensor has been described. In the fourth embodiment, depending on whether or not the conveyance variation amount detected by the pre-registration sensor 35a is larger than the variation correction amount (predetermined amount) that can be corrected between the registration sensor 35b and the merge point 35c, as follows. A method of determination will be described. That is, a method of determining whether to perform the conveyance speed control from the pre-registration sensor 35a or to perform the conveyance speed control from the registration sensor 35b based on the conveyance variation amount detected by the pre-registration sensor 35a will be described. In this case, even if the acceleration-side conveyance speed control of the third embodiment is performed from the pre-registration sensor 35a, it can be performed from the registration sensor 35b depending on the conveyance variation amount.

  When the conveyance variation amount detected by the pre-registration sensor 35a is smaller than the variation correction amount that can be corrected between the registration sensor 35b and the merge point, the conveyance speed control is performed from the registration sensor 35b. As a result, in the image forming apparatus having a hardware configuration in which variation occurs between the pre-registration sensor 35a and the registration sensor 35b, the conveyance variation between the pre-registration sensor 35a and the registration sensor 35b is larger than that of the configuration of the third embodiment. It becomes possible to reduce. The overall configuration and system block diagram of the laser printer as the image forming apparatus are the same as in the first, second, and third embodiments (FIGS. 1 and 2), and the description thereof is omitted.

[Recording material conveyance control of this embodiment]
FIG. 12 shows a timing chart for continuous printing of two sheets in this embodiment. Since the image formation and recording material conveyance control of the first sheet (preceding sheet) in the timing chart shown in FIG. 12 are the same as those in the first and second embodiments, the description thereof will be omitted. ) Recording material conveyance control will be described. Each signal in the timing chart of FIG. 12 corresponds to FIG. 4, and the reference number 1200 is assigned to correspond to the reference number 400 in FIG.

In FIG. 12, the sheet feeding / conveying control unit 221 performs a theoretical value (1242) and an actual measurement value (pre-registration sensor arrival timing) at the timing (1233) when the leading edge of the second sheet, which is the subsequent sheet, reaches the pre-registration sensor 35a. 1233) to calculate the difference time Δt ₇ with. The paper feed conveyance control unit 221 determines whether the conveyance variation can be sufficiently eliminated by performing the conveyance speed control from the timing (1253) when the leading edge of the succeeding paper reaches the registration sensor 35b.

Hereinafter, a method for determining whether or not the conveyance variation can be sufficiently eliminated by performing the conveyance speed control from the registration sensor 35b will be described. The difference time between the theoretical value (1263) of the arrival timing of the registration sensor 35b and the actual measurement value (1253) of the subsequent sheet is the same assuming that there is no variation in conveyance between the pre-registration sensor 35a and the registration sensor 35b. The difference time Δt ₇ is used.
Δt ₇ : Difference time between the theoretical value (1242) of the arrival timing of the pre-registration sensor 35a and the registration sensor 35b and the actual measurement value (1233) S9: Distance corresponding to the amount of variation in conveyance at the registration sensor 35b (simply conveyance) Called variation)
S10 recording material conveyance distance from ... registration sensor 35b can be corrected by the conveying speed control of the acceleration side at a maximum speed _{V max} of the motor (variation correction amount)
V: Steady speed V _max: Maximum speed
S9 = V × Δt ₇ (Expression 17)
S10 =
((V + V _max ) × T _up ) / 2 + (T × V _max ) + ((V + V _max ) × T _down ) / 2 (Formula 18)

Conveying the variation amount in the registration sensor 35b (S9) than the recording material feeding distance can be corrected by the conveying speed control of the acceleration side at a maximum speed _{V max} of the motor from the registration sensor 35b (variation correction amount) (S10) may be larger (S9 <S10)
V × Δt ₇ <
((V + V _max ) × T _up ) / 2 + (T × V _max ) + ((V + V _max ) × T _down ) / 2 (Formula 19)

Above, sheet transportation control unit 221, (Equation 4), (5), if (19) holds than Delta] t _7, fully solve the conveyance variation by the conveying speed control performed by the registration sensor 35b Judge that you can.

Here, assuming that there is no conveyance variation between the pre-registration sensor 35a and the registration sensor 35b, the following description has been given. That is, the difference between the theoretical value (1242) of the arrival timing of the pre-registration sensor 35a and the actual measurement value (1233) and the difference between the theoretical value (1263) of the arrival timing of the registration sensor 35b and the actual measurement value (1253) are the same Δt. ₇ explained. When there is a conveyance variation between the pre-registration sensor 35a and the registration sensor 35b, from the variation variation data, (Equation 17) is calculated as S9 = V × (Δt ₇ + Δt _margin ) (Equation 20)
To replace the left side of (Equation 19) with (Equation 20).

The presence / absence of conveyance variation and the amount of conveyance variation from the pre-registration sensor 35a to the registration sensor 35b vary depending on the individual image forming apparatuses, and can be obtained by experiments in advance. If there is a transport variation, the transport variation data is measured by experiment, and the maximum value of the measured value, a value obtained by adding a margin to the maximum value, or the like is set as Δt _margin , and a memory (not shown) Just remember it.

[Recording material conveyance control process of this embodiment]
FIG. 13 shows a flowchart in the present embodiment. The flowchart of FIG. 13 is a flowchart relating to the recording material conveyance control of the second sheet (subsequent sheet or the sheet) that is the object of conveyance speed control. Details of the control are shown below.

In step S1300, the paper feed / conveyance control unit 221 starts feeding the second recording material, which is the succeeding paper to be controlled by the conveyance speed (1222 in FIG. 12). In step S1301, the paper feed conveyance control unit 221 determines whether the leading edge of the succeeding sheet has been detected by the pre-registration sensor 35a, that is, whether the succeeding sheet has reached the pre-registration sensor 35a. In S1301, if the sheet feeding / conveying control unit 221 determines that the subsequent sheet has not reached the pre-registration sensor 35a, the process returns to S1301. In S1301, if the sheet feeding / conveying control unit 221 determines that the succeeding sheet has reached the pre-registration sensor 35a (FIG. 12 1233), the process proceeds to S1302. In step S1302, the paper feed conveyance control unit 221 calculates a difference time Δt ₇ between the measured value (FIG. 12 1233) and the theoretical value (FIG. 12 1242) of the pre-registration sensor arrival time, and in step S1303, the difference time Δt ₇ (formula 19) is calculated. ) Is a value that holds. Here, in the case of an image forming apparatus in which there is no variation in conveyance between the pre-registration sensor 35a and the registration sensor 35b, the sheet feeding and conveyance control unit 221 sets the left side of (Equation 19) as (Equation 17). In the case of an image forming apparatus in which there is a conveyance variation between the pre-registration sensor 35a and the registration sensor 35b, the paper feed / conveyance control unit 221 sets the left side of (Equation 19) as (Equation 20).

Sheet transportation control unit 221 in S1303 subsequent, when determining the difference time Delta] t ₇ as a value (19) is satisfied, whether or not it is detected that the leading end of the subsequent sheet by the registration sensor 35b at S1304, i.e., the registration sensor 35b Determine if the paper has arrived. In S1304, if the paper feed conveyance control unit 221 determines that the subsequent sheet has not reached the registration sensor 35b, the process returns to S1304. In step S1304, when the sheet feeding / conveying control unit 221 determines that the succeeding sheet has reached the registration sensor 35b (FIG. 12 1253), the process proceeds to step S1305. In step S1305, the paper feed conveyance control unit 221 calculates a difference time Δt ₇ ′ between the actual value (FIG. 12 1253) and the theoretical value (FIG. 12 1263) of the registration sensor arrival time, and in step S1306, the conveyance speed control is performed based on Δt ₇ ′. (FIG. 12 1283, merge point conveyance). The difference time Delta] t 7 _'is in the image forming apparatus is not conveyed variation between the registration sensor 35b from the pre-registration sensor 35a, a difference time Delta] t _7.

Sheet transportation control unit 221 in S1303, if the difference time Delta] t ₇ is (Formula 19) was determined to be a value that does not hold, to start based on the conveying speed control difference time Delta] t ₇ in S1307. In other words, the paper feed conveyance control unit 221 determines that the conveyance variation amount cannot be corrected even if the conveyance speed control is performed at the maximum speed V _max after the leading edge of the succeeding sheet reaches the registration sensor 35b. Start from the front sensor 35a.

  As described above, according to this embodiment, the conveyance from the start of feeding to the secondary transfer position is performed by one drive source, and the distance between the two recording material detection sensors is shorter than the image interval of continuous printing. The image forming apparatus is configured as follows. That is, the conveyance speed control is minimized from the upstream sensor (pre-registration sensor), and the conveyance speed control is performed from the downstream sensor (registration sensor) as much as possible. As a result, it is possible to secure a large number of acceleration-correctable sections and reduce conveyance variations to downstream sensors (registration sensors).

  In this embodiment, the two recording material detection sensors have been described with the upstream sensor as the pre-registration sensor 35a and the downstream sensor as the registration sensor 35b on the conveyance path. However, various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

  As described above, according to the present embodiment, even when recording materials are continuously conveyed by the same drive source, variations in conveyance of subsequent paper without affecting productivity and image formation without reducing productivity. And an excellent image can be obtained.

[Other Examples]
In Examples 1 to 4, two rollers (cassette pickup roller 1) are driven by the same drive source.
However, the present invention is also applicable to a configuration in which three or more rollers between the paper feed start position and the secondary transfer unit are driven by the same drive source. In this case, among the plurality of rollers driven by the same drive source between the paper feed start position and the secondary transfer unit, the timing of the succeeding sheet is determined at the timing when the trailing edge of the preceding sheet has passed through the most downstream roller. Carry out the conveyance speed control.

  In the first to fourth embodiments, the conveyance speed control of the succeeding paper is performed using two recording material detection sensors (pre-registration sensor 35a and registration sensor 35b) between the paper feed start position and the secondary transfer unit. explained. However, the present invention is also applicable to a configuration in which three or more recording material detection sensors are provided between the paper feed start position and the secondary transfer unit. In this case, using the two recording material detection sensors of the plurality of recording material detection sensors, one recording material detection sensor detects the trailing edge of the preceding paper, and another recording material detection sensor detects the leading edge of the succeeding paper. What is necessary is just to detect.

  In Embodiments 1 to 4, the paper feed conveyance control unit 221 calculates the start timing of the conveyance speed control using the detection result of the recording material detection sensor. However, the detection result of the recording material detection sensor may be output to the CPU 211, and the CPU 211 may calculate the start timing of the conveyance speed control.

  In Embodiments 1 to 4, the case of two-sheet continuous printing has been described, but the present invention can also be applied to three or more sheets of continuous printing.

In the first to fourth embodiments, the conveyance speed control of the succeeding paper is performed using two recording material detection sensors (pre-registration sensor 35a and registration sensor 35b) between the paper feed start position and the secondary transfer unit. explained. However, at least one sensor for detecting the leading edge and the trailing edge of the recording material is provided on the downstream side of the cassette pickup roller 17 and the upstream side of the registration roller 18, that is, on the conveyance path between the cassette pickup roller 17 and the registration roller 18. It is good also as a structure provided. In this case, the distance from the sensor between the cassette pickup roller 17 and the registration roller 18 (hereinafter referred to as sensor A) to the registration roller 18 and the recording material conveyance speed are known. Therefore, it is uniquely determined when the preceding sheet that has passed the sensor A passes the nip portion of the registration roller 18. That is, from the distance between the sensor A and the registration roller 18 and the conveyance speed (steady speed V) of the preceding paper, the time from the trailing edge of the preceding paper passing through the sensor A to passing through the registration roller 18 it can be calculated T _a. Therefore, it is the rear end of the preceding sheet is to start a timer for example (not shown) when passing through the sensor, considered preceding sheet when the elapsed time T _A has passed the nip portion of the registration roller 18. That is, based on the detection result of the sensor A, the timing at which the preceding paper passes the registration roller 18 is predicted, and the conveyance speed control A is performed. Other controls are the same as in the second embodiment, for example.

  In the first to fourth embodiments, the image forming apparatus having the configuration illustrated in FIG. 1 has been described. However, in order to synchronize the timing when the toner image is transferred to the recording material, the image forming is performed so that the conveyance speed of the recording material is controlled. Any device can be applied. In this case, in the image forming apparatus that directly transfers the toner image on the photosensitive drum to the recording material, the photosensitive drum corresponds to the image carrier. In an image forming apparatus that transfers a toner image on a photosensitive drum to an intermediate transfer belt and transfers the toner image on the intermediate transfer belt to a recording material, the intermediate transfer belt corresponds to an image carrier.

  As described above, in the other embodiments, even when the recording material is continuously conveyed by the same drive source, the conveyance of the subsequent sheet can be performed without affecting the conveyance of the preceding sheet and the image formation without reducing the productivity. Variation can be suppressed and a good image can be obtained.

17 Cassette pick-up roller 18 Registration roller 35a Pre-registration sensor 35b Registration sensor 221 Feed control unit

Claims (9)

A first transport unit for feeding the recording material from the paper feed position onto the transport path;
A first detection unit that is provided downstream of the first conveying unit in the recording material conveyance direction and detects the leading edge or the trailing edge of the recording material;
A second transport unit provided on the downstream side of the first detection unit, for transporting the recording material to the transfer position;
A second detection means provided on the upstream side of the transfer position and on the downstream side of the second transport unit, and detects the leading edge or the trailing edge of the recording material;
The conveyance speed of the recording material based on the detection result of the recording material by the first detection means or the second detection means so that the toner image on the image carrier is transferred to a predetermined position of the recording material at the transfer position. Control means for performing the control;
An image forming apparatus that drives the first transport unit and the second transport unit by the same drive source,
The control means controls the conveyance speed of the second recording material fed subsequent to the first recording material fed in advance from the paper feeding position, and the rear end of the first recording material is the second recording material. An image forming apparatus, which starts after passing through a conveyance unit.   The control means determines that the rear end of the first recording material has passed through the second transport unit by detecting the rear end of the first recording material by the second detection means. The image forming apparatus according to claim 1.   The control means predicts the timing at which the trailing edge of the first recording material passes through the second transport unit based on the timing at which the trailing edge of the first recording material is detected by the first detection means. The image forming apparatus according to claim 1, wherein:   After the first recording material has passed through the second conveying portion, the control means detects the conveying speed of the second recording material and the timing at which the second recording material is detected by the first detecting means or the second detecting means. The image forming apparatus according to claim 1, wherein the image forming apparatus accelerates or decelerates based on the image quality. When the distance on the conveyance path between the first detection means and the second detection means is shorter than the distance between the trailing edge of the toner image corresponding to the first recording material and the leading edge of the toner image corresponding to the second recording material. ,
When the control means determines that the leading edge of the second recording material has reached earlier than a predetermined timing based on the detection result of the leading edge of the second recording material by the first sensing means, the second sensing means causes the The conveyance speed control is started at the timing when the leading edge of the second recording material is detected, and when it is determined that the leading edge of the second recording material has arrived later than the predetermined timing, the second detection material causes the second detection material to The image forming apparatus according to claim 1, wherein the conveyance speed control is started at a timing when the leading edge of the recording material is detected. When the distance on the conveyance path between the first detection means and the second detection means is shorter than the distance between the trailing edge of the toner image corresponding to the first recording material and the leading edge of the toner image corresponding to the second recording material. ,
When the first detecting means detects that the leading edge of the second recording material has arrived, the control means calculates the amount of conveyance variation based on the detection result of the leading edge of the second recording material by the first detecting means. The calculated conveyance speed control is started at a timing when the leading end of the second recording material is detected by the second detection unit when the calculated conveyance variation amount is smaller than a predetermined amount. The image forming apparatus according to 1. A first transport unit for feeding the recording material from the paper feed position onto the transport path;
A detecting means provided on the downstream side of the first conveying section in the conveying direction of the recording material, and detecting the leading edge or the trailing edge of the recording material;
A second transport unit that is provided on the downstream side of the detection unit and transports the recording material to the transfer position;
Control means for controlling the conveyance speed of the recording material based on the detection result of the recording material by the detection means so that the toner image on the image carrier is transferred to a predetermined position of the recording material at the transfer position;
An image forming apparatus that drives the first transport unit and the second transport unit by the same drive source,
The control means controls the conveyance speed of the second recording material fed subsequent to the first recording material fed in advance from the paper feeding position, and the rear end of the first recording material is the second recording material. An image forming apparatus, which starts after passing through a conveyance unit.   The control means predicts the timing at which the trailing edge of the first recording material passes through the second transport unit based on the timing at which the trailing edge of the first recording material is detected by the detection means. The image forming apparatus according to claim 7.   The control unit accelerates or decelerates the conveyance speed of the second recording material after the first recording material passes through the second conveyance unit based on the timing when the second recording material is detected by the detection unit. The image forming apparatus according to claim 7, wherein the image forming apparatus is an image forming apparatus.

Images