JP2013071831A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire a detected result in a stable period of time when a feeding sheet upper surface position of a printing sheet hardly fluctuates so that the feeding sheet upper surface position is stably kept at an upper limit position.SOLUTION: The image forming apparatus includes a side feeding sheet tray 120 which sends a plurality of printing sheets 10 one by one to a feeding sheet path with a pickup roller 220a and a scraper roller 220b, a feeding sheet table drive motor 210 which changes a relative position to the scraper roller 220b of the printing sheet 10, an upper limit detection sensor 401 which detects a feeding sheet upper surface position of the printing sheet 10, a sequence operation section 335c which controls the start of operation of the feeding sheet table drive motor 210 based on the detection results with the upper limit detection sensor 401, and a time step determination section 335a which determines a time step being a time interval to acquire the detection results by the upper limit detection sensor 401 out of time steps stored in a memory 334 among periodical operating cycles, wherein the upper limit detection sensor 401 acquires the detection results by the upper limit detection sensor 401 during a period of each time step.

Description

  The present invention relates to an image forming apparatus that has a paper feed path for feeding a recording medium from a paper feed tray to a conveyance path and forms an image on a recording medium conveyed on the conveyance path.

  2. Description of the Related Art Conventionally, an image forming apparatus is provided with a paper feed tray for storing printing paper for printing, and the printing paper stacked on the paper feeding tray is picked up one by one by a paper feed mechanism such as a pick-up roller, It is sent out to the image forming unit via the conveyance path.

  Such a sheet feeding mechanism generally has a structure in which a sheet feed table disposed at the bottom of the sheet feed tray moves up and down in accordance with the remaining amount of printing paper. Specifically, an upper limit sensor is provided for detecting that the upper surface position of the printing paper stacked on the paper feed tray has reached the upper limit position that is a position to be supplied to the transport path. The table is moved up and down to raise the printing paper to an appropriate upper limit position (for example, Patent Document 1).

  In the technique described in Patent Document 1, it is detected whether or not the printing paper loaded on the paper feed tray is at a predetermined supply position, and if it is determined that the print paper is not at the upper limit position for a predetermined time. The sheet feeding upper surface position is continuously detected and the sheet feeding table is raised until it is detected that the sheet feeding table is at the upper limit position. In the case of using an upper limit detection sensor that detects the position of the sheet feed table as in the technique disclosed in Patent Document 1, it is important that the detection accuracy of the upper surface position of the sheet feed by the upper limit detection sensor is high. Yes.

JP 2006-21867 A

  However, between the time when the printing paper is sent out from the paper feeding tray and the time when the next printing paper is sent out, the upper surface position of the paper feeding may be lowered even if the paper feeding tray is stationary. is there. Specifically, when picking up printing paper from the paper feed tray, the pickup roller is rotated while being pressed against the printing paper, so that the paper feed tray is not moving up and down while the pickup roller is pressed. However, the upper surface of the paper feed has been lowered.

  On the other hand, in the conventional mechanism that captures the detection state of the upper limit detection sensor at a constant interval during the printing operation, the upper surface detection position is changed by the upper limit detection sensor when the pickup roller starts to be driven by lowering the paper supply upper surface position. The drive motor of the paper feed table is driven until no detection is made and the paper feed upper surface position is raised to the original position. On the other hand, when the pressing force associated with the raising of the pickup roller is released, the upper surface of the sheet feeding that has been pushed down by the pickup roller also rises again by the amount lowered. However, since the paper feed tray has already been moved up, the upper surface of the paper feed is positioned higher than the normal upper limit as much as the paper feed tray is moved up. As a result, the pickup roller contacts the front of the paper. The pressure became too high, causing paper feed defects such as paper jams and printing position misalignment.

  Further, while the motor for driving the pickup roller and the motor for driving the intermediate conveyance roller disposed downstream of the conveyance path are driven, the vibration of these motors acts on the sheet feeding table and the pickup roller. As a result, since the upper surface position of the printing paper is fluctuated, the same problem as described above has occurred.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of stably keeping the upper surface position of a recording medium (printing paper) at an appropriate position.

In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention provides:
An image forming apparatus having a paper feed path for feeding a recording medium from a paper feed tray to a conveyance path, and forming an image on the recording medium conveyed on the conveyance path,
Pick-up means for picking up the recording media stacked on the paper feed tray one by one and sending them to the paper feed path;
Lifting and lowering means for raising the laminated recording medium so as to approach the pickup means;
Detecting means for detecting an upper surface position of the laminated recording medium;
A detection result for obtaining a detection result of the detection means at an interval between sheets after the pickup means finishes sending the recording medium to the paper feed path and starts sending the next recording medium to the paper feed path. Acquisition means;
Based on the detection result of the detection means acquired by the detection result acquisition means, an elevation control unit that controls the start of the raising operation of the recording medium by the elevation means;
It is characterized by providing.

  According to the image forming apparatus of the first aspect of the present invention, the position of the upper surface of the recording medium may fluctuate due to the influence of the pickup means during the feeding of the recording medium to the paper feed path. On the other hand, since the recording medium is not sent out by the pickup means during the paper interval, the upper surface position of the recording medium is relatively stable. Therefore, the detection result of the detection means is acquired during the paper interval, and based on this, it is determined whether or not it is necessary to start raising the recording medium by the elevating means. The ascending operation of the recording medium can be avoided. As a result, the upper surface position of the recording medium can be stably maintained at an appropriate position by the elevating means, and the recording medium can be stably sent to the paper feed path.

  The image forming apparatus of the present invention described in claim 2 is the image forming apparatus of the present invention described in claim 1, wherein the interval between sheets is an operation period of a motor for driving a roller in the pickup means. The period is at least excluded.

  According to the image forming apparatus of the present invention described in claim 2, in the image forming apparatus of the present invention described in claim 1, while the roller in contact with the recording medium in the pickup means is driven by the motor, The upper surface position of the recording medium may fluctuate due to the influence of roller vibration. Thus, by excluding the operation period of the motor for driving the roller from the period for obtaining the detection result of the detection means, it is possible to avoid erroneous detection of the upper surface position of the recording medium due to the influence of the vibration of the roller.

  Further, in the image forming apparatus of the present invention described in claim 3, in the image forming apparatus of the present invention described in claim 1 or 2, the interval between sheets is a period excluding at least an operation period of the pickup means. It is characterized by that.

  According to the image forming apparatus of the present invention described in claim 3, in the image forming apparatus of the present invention described in claim 1 or 2, the pickup unit is in contact with the recording medium while the pickup unit is operating. Even if the roller is not driven by a motor, the vibration generated when the recording medium is sent out to the paper feed path is transmitted to the recording medium, and the upper surface position of the recording medium may fluctuate. Therefore, not only the operation period of the motor for driving the roller but also the operation period of the pickup means is excluded from the period for acquiring the detection result of the detection means, thereby affecting the influence of vibration generated when the recording medium is sent to the paper feed path. Can prevent erroneous detection of the upper surface position of the recording medium.

The image forming apparatus of the present invention described in claim 4 is the image forming apparatus of the present invention described in claim 1, 2, or 3,
The paper feed path is
A registration roller that adjusts the feeding timing of the recording medium with respect to the transport path;
An intermediate transport roller group for transporting the recording medium between the pickup means and the registration rollers;
The paper interval is a period excluding at least an operation period of the registration roller and the intermediate conveyance roller group.
It is characterized by that.

  According to the image forming apparatus of the present invention described in claim 4, in the image forming apparatus of the present invention described in claim 1, 2 or 3, the paper feed path includes a registration roller and a group of intermediate transport rollers. While these rollers are driven, the vibration is transmitted to the recording medium, and the upper surface position of the recording medium may fluctuate. Therefore, by excluding the operation period of the registration roller and the intermediate conveyance roller group in the sheet feeding path from the period for acquiring the detection result of the detection unit, the registration roller and the intermediate conveyance roller group in the sheet feeding path convey the recording medium. It is possible to avoid erroneous detection of the upper surface position of the recording medium due to the influence of vibration generated on the recording medium.

  Furthermore, the image forming apparatus of the present invention described in claim 5 is the image forming apparatus of the present invention described in claim 1, 2, 3 or 4, wherein the elevating control unit is configured to perform the elevating / lowering of the inter-paper interval. Controlling the start of the rising operation of the recording medium based on the detection result of the detecting means acquired by the detection result acquiring means during a non-rising period excluding the period during which the recording medium is being raised by the means. To do.

  According to the image forming apparatus of the present invention described in claim 5, in the image forming apparatus of the present invention described in claim 1, 2, 3, or 4, the raising operation of the recording medium by the elevating means is performed from the paper feed tray. This is started during the interval between sheets so as not to interfere with the operation of sending the recording medium to the sheet feeding path. Therefore, even during the interval between sheets, the upper surface position of the recording medium fluctuates while the recording medium is being lifted by the elevating means. Therefore, the upper surface position of the recording medium can be correctly detected by acquiring the detection result of the detection means only during the non-raising period of the recording medium by the elevating means in the paper interval.

  The image forming apparatus of the present invention described in claim 6 is the image forming apparatus of the present invention described in claim 5, wherein the period during the ascending operation by the elevating means is based on the average speed of the ascending operation. The average speed is determined based on the transport speed of the recording medium in the paper feed path, the paper size in the transport direction of the recording medium, the paper interval, and the paper thickness of the recording medium. It is characterized by that.

  According to the image forming apparatus of the present invention described in claim 6, in the image forming apparatus of the present invention described in claim 5, the lifting means can be used to raise the recording medium by a stroke corresponding to one recording medium. The time is determined by the transport speed of the recording medium in the paper feed path, the paper size in the transport direction of the recording medium, and the paper interval. Assuming that all of this time is spent and the lifting / lowering means lifts the recording medium by one stroke of the recording medium, the average speed of the lifting operation by the lifting / lowering means is determined by factors including the sheet thickness of the recording medium. it can.

  Then, the period of the ascending operation in which the elevating unit raises the recording medium when the upper surface position of the recording medium is not in an appropriate position based on the detection result of the detecting unit can be determined based on the above-described average speed of the ascending operation. . Therefore, by correctly determining the average speed of the ascending operation by the elevating means, the recording medium elevating operation period (or non-ascending period) by the elevating means is accurately specified in the paper interval, and the detection result of the detecting means is obtained. It can be acquired in an appropriate period to correctly detect the upper surface position of the recording medium.

  According to the present invention, the upper surface position of the recording medium can be stably maintained at an appropriate position by the elevating means, and the recording medium can be stably sent to the paper feed path.

It is the schematic which shows the outline | summary of the printing paper conveyance path | route of the printing apparatus which concerns on one Embodiment of this invention. FIG. 2 is an enlarged side view showing a part of a paper feed system conveyance path in FIG. 1. FIG. 2 is a perspective view showing a side paper feed tray provided in the printing apparatus of FIG. 1. FIG. 2 is a block diagram illustrating modules relating to sheet feeding mechanism control of the arithmetic processing unit in FIG. 1. FIG. 5 is a time chart showing sheet feeding mechanism control in FIG. 4. It is a block diagram which shows the module regarding the switching control of the operation speed in the arithmetic processing part of FIG. (A) is a graph which shows the transition diagram of the setting pattern regarding the driving force of FIG. 6, (b) is a graph which shows the time function of FIG.

(Overall configuration of printing device)
An image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings, taking a printing apparatus using an inkjet line color printer as an example. FIG. 1 is a schematic diagram showing an outline of a printing paper conveyance path of a printing apparatus according to an embodiment of the present invention. In the figure, the number of rollers constituting the drive unit is omitted as appropriate.

  A printing apparatus 100 (image forming apparatus) according to the present embodiment illustrated in FIG. 1 includes a plurality of ink heads on which a large number of nozzles are formed. Then, the printing apparatus 100 discharges black or color ink from each ink head to perform printing in line units, and forms a plurality of images on the recording paper on the transport belt so as to overlap each other.

  The printing apparatus 100 forms an image on the printing paper 10 that is conveyed on an annular conveyance path. This transport path includes a paper feed system transport path FR for supplying paper, a normal path CR from the paper feed system transport path FR through the head unit 110 to the paper discharge path DR, and a reversal connected to the normal path CR. The route SR is roughly configured.

  As a paper feeding mechanism for supplying the printing paper 10 in the paper feeding system conveyance path FR, a side paper feeding tray 120 that is disposed outside the side of the housing and stores the printing paper 10 in a stacked manner, and the inside of the housing And a plurality of paper feed trays (130a, 130b, 130c, 130d).

  The printing paper 10 fed from one of the side paper feeding tray 120 and the paper feeding tray 130 is conveyed along a paper feeding system conveyance path FR in the housing by a driving mechanism such as a roller, and the printing paper. 10 is led to the resist portion R which is the reference position of the top portion of the ten. Then, the printing paper 10 is supplied to the registration rollers of the registration unit R by driving the rollers upstream of the registration rollers.

  On the other hand, an image forming unit is provided downstream of the registration unit R in the transport direction. The image forming unit is provided with a head unit 110 having a plurality of print heads. The printing paper 10 is image-formed line by line with ink ejected from each printing head while being conveyed at a speed determined by printing conditions by a conveying belt 160 provided on the opposite surface of the head unit 110. The printed printing paper 10 is further conveyed on the normal route CR by a driving mechanism such as a roller. A discharge port 140 is branched and connected to the normal route CR as a discharge mechanism for discharging the printed printing paper 10.

  In the case of single-sided printing in which printing is performed only on one side of the printing paper 10, the printing paper 10 is directly discharged to the paper discharge outlet 140 through the paper discharge path DR and received by the paper discharge outlet 140. The paper is stacked on a paper discharge table 150 provided as a table with the printing surface facing down. The paper discharge table 150 has a tray shape protruding from the housing, and has a certain thickness. The paper discharge table 150 is inclined, and the printing paper 10 discharged from the paper discharge port 140 is naturally arranged and overlapped by a wall formed at a lower position of the inclination.

  On the other hand, in the case of double-sided printing in which printing is performed on both sides of the printing paper 10, the front side (the first printed side is “front side” and the next printed side is “back side”). Without being guided to the side, it is further transported in the housing and sent out to the reversing path SR. A switching mechanism 170 for switching the transport path for back side printing is provided at a branch point between the paper discharge path DR and the reversal path SR, and the printing paper 10 that has not been sent to the discharge path by the switching mechanism 170 is provided. , Is pulled into the reversal path SR.

  In the reversing path SR, the sheet is delivered from the normal path CR, and so-called switchback is performed in which the sheet is reversed by reciprocating the sheet. Then, it is returned to the normal route CR via the switching mechanism 172 by a driving mechanism such as a roller, and is fed again via the registration portion R, and the back side is printed by the same procedure as the front side. Thereafter, the printing paper 10 on which the back side is printed and the images are formed on both sides is guided to the paper discharge port 140 through the paper discharge route DR and discharged, and is discharged as a receiving tray for the paper discharge port 140. It is loaded on the paper table 150. In the present embodiment, switchback at the time of duplex printing is performed using a space provided in the paper discharge tray 150. The space provided in the paper discharge tray 150 is configured to be covered so that the printing paper 10 cannot be taken out from the outside during switchback.

  In the printing apparatus 100, the printing paper 10 that has already been printed on one side is also re-fed to the registration portion R that is the reference position of the leading portion of the fed printing paper 10 during duplex printing. For this reason, at the portion immediately before the registration portion R, there is a merging point where the feeding path of the newly fed printing paper 10 and the re-feeding path where the back-side printing paper is circulated and conveyed. It is formed. Then, the registration unit R sends out the paper on the downstream side of the merging point between the paper feed conveyance path FR and the normal path CR.

  In the present embodiment, after a certain printing paper 10 is fed, the next printing paper 10 is not fed after waiting for the printing on the printing paper 10 to be discharged, but by scheduling. Before the preceding printing paper 10 is discharged, the succeeding printing paper 10 can be fed and continuously printed at a predetermined interval. Therefore, in normal scheduling at the time of duplex printing, a space is secured in advance so as to secure a position where the sheet returned from the reversing path SR is inserted when feeding the front sheet. Thereby, in this apparatus, printing on the front surface and printing on the back surface can be performed in parallel, and productivity equivalent to that for single-sided printing can be ensured in terms of print surface.

  The conveying belt 160 is wound around a driving roller 161 and a driven roller 162 disposed at the front end and the rear end of the surface facing the head unit 110 in the normal path CR. Rotate and move. Further, on the upper surface of the transport belt 160, ink heads of four colors are arranged side by side along the belt moving direction, and a head unit 110 that forms a color image so as to overlap a plurality of images is opposed to the head unit 110. Yes.

  Further, as illustrated in FIG. 1, the printing apparatus 100 includes an arithmetic processing unit 330 that is an arithmetic module. The arithmetic processing unit 330 is configured by a processor such as a CPU or DSP (Digital Signal Processor), hardware such as a memory and other electronic circuits, software such as a program having the function, or a combination thereof. The The arithmetic processing unit 330 virtually constructs various functional modules by appropriately reading and executing the program. Each constructed functional module performs processing related to image data, operation control of each unit, and various processing for user operations. In addition, an operation panel 340 is connected to the arithmetic processing unit 330, and an instruction and a setting operation by a user can be received through the operation panel 340.

(Conveying mechanism in the paper feed path)
Next, the paper feed system conveyance path FR will be described. FIG. 2 is an explanatory diagram showing an enlargement of a part of the paper feed system conveyance path FR according to the present embodiment.

  As shown in FIG. 2, the paper feed mechanism of the present invention is a mechanism that is provided as a part of the above-described paper feed system conveyance path FR and sends the print paper 10 to the registration unit R. In the paper feed mechanism of the present embodiment, the paper is supplied to the registration unit R through the paper feed path FR1 for newly feeding paper from the side paper feed tray 120 disposed outside the side surface of the housing.

  In the registration unit R, registration rollers 240a and 240b are arranged upstream of the head unit 110 in the normal path CR. The registration rollers 240a and 240b temporarily hold the printing paper 10 entering the normal route CR from the paper feeding system conveyance path FR side, and adjust the sending timing of the printing paper 10 to the head unit 110. In the registration portion R, pre-registration rollers 230a and 230b are arranged adjacent to the upstream side of the conveyance path with respect to the registration rollers 240a and 240b. The pre-registration rollers 230a and 230b send the printing paper 10 from the paper feed path FR1 to the registration rollers 240a and 240b.

  The registration rollers 240 a and 240 b are driven and controlled by a registration driving motor 240. The registration drive motor 240 is disposed upstream of the image forming unit (head unit 110) in the conveyance path. The registration driving motor 240 is a driving unit that holds the printing paper 10 related to paper feeding by a pair of rollers (registration rollers 240a and 240b) and adjusts the sending timing of the printing paper 10 to the image forming unit. The registration drive motor 240 is controlled by the drive control unit 335 to start and stop the operation and the operation speed, and the acceleration at the time of startup and the deceleration acceleration at the time of deceleration are controlled.

  The pre-registration rollers 230a and 230b are driven and controlled by a pre-registration drive motor 230. The pre-registration drive motor 230 is disposed upstream of the registration rollers 240a and 240b in the conveyance path. The pre-registration drive motor 230 holds the printing paper 10 related to paper feeding by a pair of rollers (pre-registration rollers 230a and 230b), adjusts the timing of sending the printing paper 10 to the image forming unit, It is a drive means which performs "abutting correction control". In the “butting correction control”, the skew of the paper is corrected by correcting the orientation of the printing paper 10 conveyed obliquely to be straight and sending it to the subsequent stage (conveying belt 160).

  Further, a resist sensor 513 is provided in the resist portion R. The registration sensor 513 is installed close to the upstream side of the registration rollers 240a and 240b, and is a sensor that detects the arrival of the printing paper 10 to the registration rollers 240a and 240b. In the present embodiment, a reflection sensor, a transmission sensor, and other various sensors can be used as the resist sensor 513.

  The paper feed path FR <b> 1 is a path through which the printing paper 10 stacked and stored in the side paper feed tray 120 is fed to the registration unit R. In the paper feed path FR1, a plurality of intermediate transport rollers 251 (251a, 251b), 252 (252a, 252b), 253 (253a) that transport the printing paper 10 between the pickup roller 220a and the pre-registration roller 230a (230b). , 253b) is provided along the paper feed path, and the printing paper 10 picked up from the side paper feed tray 120 is sent to the registration unit R.

  In the present embodiment, these intermediate transport rollers 251, 252, and 253 are directly driven by the intermediate transport drive motor 250 only for the intermediate transport roller 251 located on the upstream side of the paper feed path, and the other intermediate transport rollers 252 Reference numeral 253 is driven to rotate by the power transmitted by the belt pulley mechanism. In this embodiment, the pre-registration rollers 230a and 230b and the intermediate conveyance rollers 251, 252, and 253 are components of the intermediate conveyance roller group.

  An intermediate conveyance drive motor 250 for the intermediate conveyance rollers 251, 252, and 253 is disposed in the sheet feeding path FR 1, and a plurality of disposed rollers (intermediate conveyance rollers 251 (251 a, 251 b), 252 (252 a, 252 b), 253). (253a, 253b)) is a driving unit that holds the printing paper 10 for feeding and adjusts the sending timing of the printing paper 10 to the registration portion R.

  The intermediate transport roller group is provided with an intermediate inlet sensor 511 and an intermediate outlet sensor 512. The intermediate inlet sensor 511 is a sensor that is installed in the vicinity of the upstream intermediate conveyance roller 251 in the paper feed path FR1 and detects the arrival of the printing paper 10 to the paper feed path FR1. The intermediate exit sensor 512 is a sensor that is installed in the vicinity of the downstream intermediate conveyance roller 253 in the paper feed path FR1 and detects the passage of the printing paper 10 from the paper feed path FR1.

  The side paper feed tray 120 located upstream of the paper feed path FR1 is provided with a paper feed mechanism according to the present invention. FIG. 3 is a perspective view illustrating a paper feed mechanism provided in the printing apparatus according to the embodiment.

  More specifically, the paper feed mechanism according to the present invention is a mechanism for sending the printing paper 10 loaded in the side paper feed tray 120 to the paper feed system conveyance path FR. Specifically, this paper feed mechanism includes a side paper feed tray 120, a pickup drive motor 220, a paper feed stand drive motor 210, a lower limit detection sensor 402, and an upper limit detection sensor 401. The side paper feed tray 120 is a box for storing a large number of printing papers 10 in a stacked state, and the side paper feed tray 120 is provided with a paper feed table 121 and a driving force transmission unit 125.

  The pickup drive motor 220 is a drive unit that is located above the side paper feed tray 120 and picks up the printing paper 10 stacked on the side paper feed tray 120 and sends it to the registration unit R. The pickup drive motor 220 directly rotates the pickup roller 220a and indirectly rotates the scraper roller 220b via a belt pulley mechanism. Specifically, the pickup roller 220a and the scraper roller 220b are driven to rotate by the rotational force of the pickup drive motor 220 being transmitted through the rotation shaft 222 of the pickup roller 220a. The pickup roller 220a and the scraper roller 220b pick up and take in the uppermost printing paper 10 one by one from among the stacked printing papers 10, and send it out to the paper feeding path FR1 through the registration portion R.

  The sheet feeding table drive motor 210 is a lifting means that is attached to the sheet feeding table 121 and moves up and down together with the sheet feeding table 121 by the driving force to change the relative position of the stacked printing paper 10 with respect to the scraper roller 220b. It is a self-propelled drive mechanism. The sheet feeding table drive motor 210 raises the upper surface position of the printing paper 10 to an upper limit position where pickup can be performed under the control of the arithmetic processing unit 330. The sheet feeding table drive motor 210 transmits driving force to the side sheet feeding tray 120 via the driving force transmission unit 125 (pinion 125a and rack 125b), moves up and down together with the sheet feeding table 121, and loads on the sheet feeding table 121. The printed printing paper 10 is moved up and down.

  The paper feed table 121 is a bottom plate member that is provided on the bottom surface of the side paper feed tray 120 and on which the print paper 10 is stacked. The print paper 10 is stacked on the paper feed table 121. In addition, a driving force transmission unit 125 is provided outside the sheet feeding table 121, and the driving force of the sheet feeding table driving motor 210 is transmitted to the sheet feeding table 121 via the driving force transmission unit 125. The driving force transmission unit 125 is a rack and pinion member that converts the rotational force of the sheet feeding table driving motor 210 into the vertical movement of the sheet feeding table 121.

  Further, an upper limit detection sensor 401 and a lower limit detection sensor 402 are provided above and below the side paper feed tray 120. As shown in FIG. 2, the upper limit detection sensor 401 uses the shaft of the pickup roller 220a as a fulcrum, and the printing paper 10 loaded on the paper feed table 121 by the position of the shielding plate 221 that moves up and down according to the vertical position of the scraper roller 220b. This is a sensor for detecting the upper surface position of the paper feed. As the upper limit detection sensor 401, for example, a transmission type sensor whose optical axis is shielded by the shielding plate 221 can be used. In the present embodiment, when the printing paper 10 is present (when the shielding plate 221 blocks the optical axis), the state is High (ON), and when there is no printing paper 10 (when the shielding plate 221 does not block the optical axis). It becomes Low (OFF) state. However, the upper limit detection sensor 401 is not limited to this form, and for example, a reflection type sensor may be used.

  On the other hand, a lower limit detection sensor 402 shown in FIG. 3 is a sensor that is installed below the side paper feed tray 120 and detects whether the position of the paper feed tray 121 is at the lower limit position. As the lower limit detection sensor 402, for example, a reflective sensor that detects the presence or absence of the paper feed tray 121 can be used. Of course, a transmission type sensor may be used for the lower limit detection sensor 402.

(Paper feed control mechanism)
In this embodiment, the control of the sheet feeding operation from the side sheet feeding tray 120 is performed by the arithmetic processing unit 330 described above. FIG. 4 is a block diagram showing modules relating to paper feed control of the arithmetic processing unit 330, and FIG. 5 is a time chart showing detection control by paper feed mechanism control. The “module” used in the description indicates a functional unit for achieving a predetermined operation, which is configured by hardware such as an apparatus or a device, software having the function, or a combination thereof. .

  As shown in detail in FIG. 4, the arithmetic processing unit 330 mainly includes a job data receiving unit 331, a paper type acquisition unit 332, an operation signal acquisition unit 333, an upper layer command unit 337, and an image processing unit 336. A drive control unit 335 and a storage unit 334 are provided.

  The job data receiving unit 331 is a communication interface that receives job data that is a series of print processing units, and is a module that passes data included in the received job data to the upper layer command unit 337 and the image processing unit 336. The communication here includes, for example, short-range communication such as infrared communication as well as LAN such as intranet (intra-company network) and home network based on 10BASE-T, 100BASE-TX, and the like.

  The upper layer command unit 337 is a module that determines the speed of image formation and the operation speed, order, and timing of each drive unit based on job data. Based on the schedule determined by the upper layer command unit 337, the image formation control unit 336a and the drive control unit 335 execute an image formation process and a conveyance operation.

  The image processing unit 336 is an arithmetic processing device that performs digital signal processing specialized for image processing, and is a module that performs conversion of image data necessary for printing and executes printing. The image processing unit 336 includes an image formation control unit 336a and a color conversion circuit 336b.

  The color conversion circuit 336b is a circuit that converts an RGB print image into a CMYK print image, and causes the image formation control unit 336a to execute printing based on the print image for each color. The image formation control unit 336a is a module that controls the operation of the ink head of each color and the operation of the driving unit of the transport path, and controls the entire image formation processing. The timing and printing according to the scheduling by the upper layer command unit 337 Image formation is performed at a speed.

  The operation signal acquisition unit 333 is a module that receives an operation signal from the user from the operation panel 340 or the communication interface 341. The operation signal acquisition unit 333 analyzes the received operation signal and causes another module to execute processing according to the user operation.

  The paper type acquisition unit 332 is a module that acquires paper type data such as the size, type, or thickness of the printing paper 10 that is detected by the paper size detection mechanism 530 or the operation signal acquisition unit 333. Then, the paper type acquisition unit 332 transmits the acquired paper type data to the drive control unit 335 during the printing process.

  The paper size detection mechanism 530 is a module that acquires the size of the paper that is to be transported in the paper feed system transport path FR. Specifically, the paper size detection mechanism 530 includes information on the paper feed trays 130 (130a to 130d) of the paper feed source, the intermediate inlet sensor 511 and the intermediate outlet sensor 512 of the paper feed path FR1, and the printing paper 10 of the registration sensor 513. The paper size is acquired based on the passage information.

  On the other hand, the operation signal acquisition unit 333 acquires the paper size related to the conveyance process by reading out the printer driver performed by the user, the paper setting in the operation panel 340, the paper size sensor of the paper feed tray in the printing apparatus 100, and the like. To do. The paper size detection mechanism 530 and the operation signal acquisition unit 333 transmit the acquired paper type data to the paper type acquisition unit 332.

  The printer driver is an application or middleware executed by each client PC on the network when the printing apparatus is used like a network printer, for example. The printer driver is connected via a communication interface 341 such as a LAN. Print data and an execution command can be transmitted to the printing apparatus 100. In this embodiment, the printer driver is provided with an interface for setting the paper type. Therefore, the user can select the paper type by selecting an item on this interface. The operation signal acquisition unit 333 acquires information such as a paper type, a paper thickness, and a paper size according to the selection of the paper type.

  The storage unit 334 is a memory device that stores and holds various data and programs. In the present embodiment, the time during which the upper limit detection sensor 401 acquires the detection result in the periodic operation cycle from when the printing paper 10 is sent out from the side paper feed tray 120 to when the next printing paper 10 is sent out. Data of time steps that are intervals are stored. The time step stored in the storage unit 334 is referred to by the drive control unit 335 during the printing process.

  This time step is determined based on at least the average ascending speed of the paper feed tray 121. The time that the sheet feeding table drive motor 210 can spend to raise the sheet feeding upper surface position (sheet feeding table 121) of the printing paper 10 by the thickness (stroke) of one sheet of the printing paper 10 is the feeding path. It is determined by the conveyance speed of the printing paper 10 in FR1, the paper size of the printing paper 10 (dimension in the conveyance direction), and the idling time (inter-paper interval) inserted while the two printing papers 10 are conveyed before and after. Assuming a case where all of this time is spent and the paper feed stand drive motor 210 raises the print paper 10 (paper feed stand 121) by the thickness (stroke) of one print paper 10, the paper feed stand drive motor The average speed of the ascending operation by 210 can be specified by an element that further considers the paper thickness of the printing paper 10.

  Then, when the paper feed upper surface position of the printing paper 10 is not at an appropriate position, the operation period during which the paper feeding platform drive motor 210 raises the printing paper 10 can be determined based on the above-described average speed of the raising operation. it can. Therefore, by correctly determining the average speed of the ascending operation by the sheet feed table drive motor 210, the period of the ascending operation of the sheet feed table drive motor 210 in the interval between sheets can be accurately specified. As a result, the above-described time step is appropriately set during a period when the ascending operation by the paper feed drive motor 210 is not performed (non-ascending period), and the detection result of the upper limit detection sensor 401 is acquired during an appropriate period. Thus, it is possible to correctly detect the upper surface position of the printing paper 10. The time step described above is determined in consideration of the following points (a) to (d).

  (A) The time interval for acquiring the detection result of the upper limit detection sensor 401 is from the trailing edge of the printing paper 10 passing through the pickup roller 220a until the next pickup drive motor 220 is started.

  (B) The start timing of the time step for obtaining the detection result of the upper limit detection sensor 401 is synchronized with the operation timing of the pickup drive motor 220.

  (C) It is assumed that the time interval for acquiring the detection result of the upper limit detection sensor 401 is when the paper feed table drive motor 210 is not driven and when the pickup drive motor 220 is not driven.

  (D) When an intermediate conveyance roller is included, the timing for obtaining the detection result of the upper limit detection sensor 401 is when the paper feed table driving motor 210 and the pickup driving motor 220 are not driven, and the driving means for the intermediate conveyance roller group It is assumed that it is performed at a time interval that is a stop time.

The operation cycle S [sec] is when the sheet length [m] is P, the sheet interval [sec] is B, and the speed [m / s] of the conveyor belt 160 is V.
S = P / V + B
Is calculated from

When the paper thickness [m] is T, the average ascent speed A [m / s] of the paper feed table is
A = T / S
Is calculated from

  In this time step, a plurality of types are prepared depending on the type of recording medium such as size and paper quality, are determined as appropriate according to the type of paper, and are stored in the storage unit 334 at the time of factory shipment or maintenance.

  The drive control unit 335 is a module that controls the conveyance of each conveyance path, and switches the control of each drive unit based on the conveyance condition for each printing paper 10 to control the operation speed of each drive unit. In the present embodiment, the drive control unit 335 includes a time step determination unit 335a, an operation mode selection unit 335b, a sensor detection unit 338, and a sequence operation unit 335c as an elevating function of the side paper feed tray 120. A current control unit 335d.

  The time step determination unit 335a extracts a time step suitable for the type of the printing paper 10 acquired by the paper type acquisition unit from the time step recorded in the storage unit 334, and acquires the output of the upper limit detection sensor 401 as a period. This is a module to decide. Specifically, the paper size to be used is acquired from the paper type data detected by the paper size detection mechanism 530 and the operation signal acquisition unit 333, and the schedule in the upper layer command unit 337 is collated and stored in the storage unit 334. A suitable time step is selected from the set time steps. Then, the selected time step is transmitted to the sensor detection unit 338 and the operation mode selection unit 335b.

  The sensor detection unit 338 is a module that detects the position of the top surface of the printing paper 10 loaded on the paper feed table 121 based on the detection result of the upper limit detection sensor 401 stacked on the paper feed table 121. This detected signal is notified to the sequence operation unit 335c. In particular, in the present embodiment, the detection result is acquired as upper limit position detection data based on the time step input from the time step determination unit 335a.

  The operation mode selection unit 335b is a module that determines whether to raise or lower the side paper feed tray 120 based on job data input from the upper layer command unit 337. Further, the operation mode selection unit 335b includes a servo function for controlling the object position, orientation, orientation, and the like so as to follow the target value. The operation mode determined by the operation mode selection unit 335b is input to the sequence operation unit 335c.

  The sequence operation unit 335c is a module that drives and controls the sheet feeding mechanism based on the selection operation from the operation mode selection unit 335b and the detection result acquired from the sensor detection unit 338. Specifically, when the upper limit detection sensor 401 detects the position of the upper surface of the sheet feeding after a predetermined time after raising the sheet feeding table 121, the sequence operation unit 335c sends a brake instruction to the driver and stops the sheet feeding table 121. Let When the printing paper 10 is conveyed and the upper limit detection sensor 401 is not detected, the sequence operation unit 335c sends a normal rotation (or reverse) signal to the driver and resumes the control to raise the paper feed table. Thereafter, the operation is repeated until the printing process is stopped. At this time, the sequence operation unit 335c sends a signal to the current control unit 335d to set a current for driving the motor.

  The current control unit 335d is a module that sets the motor current so that a predetermined starting current straight line or curve is obtained when the motor is started based on the control signal input from the sequence operation unit 335c.

(Operation speed switching control module)
Note that the sequence operation unit 335c described above performs operation speed switching control when driving the sheet feeding mechanism. Next, operation speed switching control will be described. FIG. 6 is a block diagram illustrating a module related to switching control of the operation speed of the arithmetic processing unit 330. FIG. 7A is a graph illustrating a transition diagram of a constant speed pattern of the driving force calculated by the timing calculation unit 362. (B) is a graph showing a shift pattern.

  The sequence operation unit 335c includes a print processing operation detection unit 361, a timing calculation unit 362, and a process selection unit 363 as an operation speed switching control module group.

  The print processing operation detection unit 361 is a module that detects execution of print processing in the printing apparatus 100 based on a control signal sent from the image processing unit 336. Then, the print processing operation detection unit 361 notifies the process selection unit 363 of the detected execution state of the print processing.

  The timing calculation unit 362 is a module that calculates speed data for operating the sheet feed table driving motor 210 at a predetermined speed based on the measurement value stored in the storage unit 334. Specifically, the timing calculation unit 362 reads from the storage unit 334 the driving force of the sheet feed table driving motor 210 acquired by the sensor detection unit 338 and stored in the storage unit 334 in the previous paper supply operation.

  The timing calculation unit 362 includes a pattern selection unit 362a. The pattern selection unit 362 a selects an operation speed pattern optimal for the sheet feeding operation from the storage unit 334 based on the paper type data from the paper type acquisition unit 332 and the switching timing calculated by the timing calculation unit 362. This is the module to read. The read operation speed pattern is transferred to the drive control unit 335.

  In the present embodiment, this operation speed pattern includes two patterns: a constant speed pattern with a constant speed and a speed change pattern that accelerates or decelerates. The constant speed pattern is inclination data indicating the rate of change of driving force per time as shown in FIG.

  The other operation speed pattern is speed data for controlling the sheet feed table drive motor 210 and driving the sheet feed table 121 upward in accordance with a time function for changing the operation speed as shown in FIG. This time function is an exponential function that defines the relationship between the passage of time and the control amount of the driving force, and is a cube function in this embodiment. Specifically, when the upper limit detection sensor 401 is in the OFF state, the ascent of the sheet feeding base 121 is started, the upper limit detection sensor 401 is in the ON state, and the driving force at the time T until the ascent operation is stopped by the brake. Defines the changes. Note that a plurality of time functions are prepared according to the paper type, the type data of the printing paper 10 from the paper type acquisition unit 332 is input, the shift pattern stored in the storage unit 334 is selected, and the time The function is input to the execution processing unit 363.

  The storage unit 334 stores a measured value of the driving force of the sheet feed table drive motor 210 at the time when the sensor detection unit 338 detects the sheet feed upper surface position, and the previous sheet feed table drive motor 210 is stored for each printing operation. Is sent to the timing calculation unit 362. The storage unit 334 stores an operation speed pattern of the paper feed table drive motor 210 and an elapsed drive time of the paper feed table drive motor 210 in association with each other. Note that a plurality of types of operation speed patterns are prepared depending on the type of the printing paper 10 such as the size and quality of the printing paper 10 and are appropriately selected according to the paper type. The operation speed pattern is stored in the storage unit 334 at the time of factory shipment or maintenance.

  In the present embodiment, the sensor detection unit 338 detects the position of the upper surface of the printing paper 10 stacked on the paper feeding table 121 based on the detection result of the upper limit detection sensor 401, and calculates the timing of the detected signal. Notification to the unit 362. In addition, the sensor detection unit 338 causes the storage unit 334 to store the measurement value detected by the elevation of the paper feed tray 121 for calculation of the next switching timing.

  The execution processing unit 363 selects either the constant speed pattern or the shift pattern calculated by the timing calculation unit 362, and controls the sheet feeding table drive motor 210 according to the selected constant speed pattern or the shift pattern. This is a module for driving the paper feed table 121 upward. The constant speed pattern or the shift pattern is selected in accordance with, for example, a user operation from the operation panel 340, a load amount of the printing paper 10, or a time interval until the next pickup driving time. Also good. At this time, a current control signal for driving the sheet feeding table 121 upward is transmitted to the current control unit 335d.

  Here, when each constant speed pattern is input, as shown in FIG. 7A, a large amount of printing paper 10 is loaded on the paper feed tray 121 under the control of the sequence operation unit 335c and the current control unit 335d. When the paper is loaded, the paper feed table 121 is moved by the driving force with a certain inclination to reach the upper limit position.

  On the other hand, when a shift pattern is input, as shown in FIG. 7B, the sequence operation unit 335c changes the operation speed of the drive unit according to the drive elapsed time T of the paper feed table drive motor 210. Therefore, when the load amount of the printing paper 10 loaded on the paper feed tray 121 is large, the weight is increased, and a torque is required to raise the paper feed tray 121, and the drive elapsed time becomes long. Since the time function is defined so as to rise in a quadratic curve, the driving force of the sheet feed table driving motor 210 is increased as the driving elapsed time T becomes longer. Here, when the loading amount of the printing paper 10 is large, the rising speed does not increase too much due to the weighting, and the upper limit position of the loading paper can be reached at an appropriate speed.

  On the other hand, when the load amount of the printing paper 10 loaded on the paper feed tray 121 is small, the weight is reduced, and the drive elapsed time Tn when the paper feed tray 121 is raised is shorter than T. Since the time function is defined so as to rise in a quadratic curve, the driving force of the sheet feed table driving motor 210 can be reduced as the driving elapsed time Tn becomes shorter. Here, when the loading amount of the printing paper 10 is small, since the weight is small, the rising speed is easily increased. However, since the upper limit position is reached in a short time, the rising speed is not excessively increased. The upper limit position of the loaded paper can be reached at an appropriate speed.

(Action / Effect)
According to the present embodiment, since the sequence operation unit 335c acquires the detection result from the upper limit detection sensor 401 based on the time step, in the stable interval that is a time interval in which the paper feed upper surface position does not vary, The output of the upper limit detection sensor 401 can be taken in to determine whether or not the paper feed upper surface position has been lowered. As a result, it is possible to prevent erroneous detection of the paper feed upper surface position drop.

  Specifically, the fluctuation range of the paper feed upper surface position in the case where the output of the upper limit detection sensor 401 is captured in the stable section and the case where the output of the upper limit detection sensor 401 is captured in the section where the fluctuation of the paper feed upper surface position is large will be described. . Note that FIG. 5 shows a time chart of paper feed mechanism control when sequentially feeding 1 to 11 print sheets 10. The solid line in FIG. 5 shows the output waveform of each part according to the present embodiment, and the dotted line shows the output waveform of each part when the upper surface position of the paper feed is detected at a predetermined interval as in the conventional example.

  The horizontal axis in FIG. 5 represents time transition (Sec), and the vertical axis represents the detection state of the upper limit detection sensor 401 (paper present = ON / paper absent = OFF) and the current (A) of the paper feed drive motor. State, deviation distance (mm) of the paper feed upper surface position, and PU paper presence / absence state (whether passing = ON / not passing = OFF) indicating whether or not the printing paper 10 passes the pickup roller 220a, respectively. Is shown. Here, the detection state of the upper limit detection sensor 401 represents the ON state with a numerical value 3 on the right axis, and the OFF state with a numerical value 2. Further, the current (A) of the sheet feeding table drive motor represents the intensity of the current with each numerical value on the right axis, and the PU paper presence / absence state represents the state with paper with the numerical value minus 6 on the right axis, and the numerical value minus 7 represents a state of no paper. Further, the deviation distance (mm) of the paper feed upper surface position is a numerical value on the left axis and represents the magnitude of the distance.

  More specifically, in the conventional example, since the detection by the upper limit detection sensor 401 is performed at regular intervals, as shown in FIG. 5, the sensor signal is instantaneous even in a section where the fluctuation is large (PU paper presence / absence state is ON). Is turned ON (in the figure: P3). This indicates that the upper limit detection sensor 401 erroneously recognizes that the upper surface position of the paper feed is at the upper limit position by driving or rotating the scraper roller 220b and the pickup roller 220a. For this reason, even if the current (fluctuating current) of the paper feed table drive motor 210 becomes zero corresponding to the momentary ON of the sensor signal, the upper limit detection sensor 401 does not immediately output the upper surface detection signal. Accordingly, the paper feed table drive motor 210 is re-driven, and the current of the paper feed table drive motor 210 increases (P4 in the figure).

  As described above, when the output of the upper limit detection sensor 401 is acquired even in a section where the fluctuation is large (the PU paper presence / absence state is ON), it is detected whether the upper surface position of the paper feed is in the upper limit position. The paper feed table drive motor 210 is driven from time to time regardless of the decrease in the print paper 10 on the tray, and the fluctuation of the paper feed upper surface position due to the stop of the drive of the pickup drive motor 220 is added. In this way, the upper surface position of the paper feed varies greatly (in the figure: P1).

  However, according to the present embodiment, the time step determined by the time step determination unit 335a becomes a stable section that is a section in which the paper feed upper surface position does not vary. When the output of the upper limit detection sensor 401 is acquired only in this stable section and it is detected whether or not the upper surface position of the paper feed is at the upper limit position, the paper feed tray is only provided when the paper on the paper feed tray is reduced. Since the drive motor 220 is driven, as shown in FIG. 5, the fluctuation range of the paper feed upper surface position becomes small (in the figure: P2).

  In the present embodiment, since the output of the upper limit detection sensor 401 is captured only at the time intervals of the stable section in this way to determine whether or not the paper feed upper surface position has been lowered, the waveform of the paper feed front surface position is reduced in the paper feed upper surface position. As a result, the upper surface position of the paper feed can be stably maintained at the upper limit position.

  In particular, in this embodiment, the time step determination unit 335a synchronizes the start timing of the time step with the operation timing of the pickup roller 220a. Therefore, by setting the start time and end time from the operation timing, the rear end of the printing paper 10 passes through the pickup roller 220a, and the next pickup driving motor 220 is activated (that is, the next printing paper 10 is The detection result from the upper limit detection sensor 401 can be acquired at a time interval until the pickup roller 220a passes through the pickup roller 220a. As a result, the detection result can be acquired in a stable section that is a section in which the paper upper surface position does not fluctuate, and the paper feed upper surface position is set to a stable upper limit position by raising and lowering the paper feed tray according to the detection result. Can keep.

  In particular, in the present embodiment, the time step determination unit 335a calculates from each condition such as the sheet size, the conveyance speed, the sheet interval, or the sheet thickness, and the average ascending speed obtained from these conditions. A stable time interval within the operation cycle can be calculated according to each condition for conveying the printing paper 10.

  In the present embodiment, the time step determination unit 335a sets a time interval when the paper feed table drive motor 210 is not driven and when the pickup drive motor 220 is not driven as a time step. Therefore, the upper limit is detected only at a stable time interval in which the paper feed stand 121 moves up and down and the upper surface position of the printing paper 10 is unstable is eliminated and the fluctuation of the upper surface position of the printing paper is less. The output of the sensor 401 can be taken in to determine whether or not the paper feed upper surface position has decreased. As a result, it is possible to prevent erroneous detection of the lowering of the paper feed upper surface position.

  In this embodiment, when the intermediate transport rollers 251, 252, and 253 are provided, the influence of vibration generated by the drive motor 250 of the intermediate transport rollers 251, 252, and 253 and the pickup roller 220a It is possible to exclude the influence of so-called “spinning” that idles in accordance with the conveyance of the paper by the conveyance rollers 251, 252, and 253. For this reason, it is possible to determine whether or not there is a decrease in the upper surface position of the paper sheet only at a stable time interval with less fluctuation in the upper surface position of the paper sheet 10 to be fed. Therefore, it is possible to stably keep the upper surface position of the sheet feeding upper surface position.

DESCRIPTION OF SYMBOLS 10 Printing paper 100 Printing apparatus 110 Head unit 120 Side paper feed tray 121 Paper feed stand 125 Driving force transmission part 125a Pinion 125b Rack 130 Paper feed tray 140 Paper discharge port 150 Paper discharge stand 160 Conveying belt 161 Drive roller 162 Drive roller 170, 172 Switching mechanism 210 Paper feed drive motor 220 Pickup drive motor 220a Pickup roller 220b Scraper roller 230 Pre-registration drive motor 230a Pre-registration roller 230a, 230b Pre-registration roller 240 Registration drive motor 240 Intermediate conveyance rollers 240a, 240b Registration roller 250 Intermediate conveyance Drive motor 251, 252, 253 Intermediate transport roller 330 Arithmetic processing unit 331 Job data receiving unit 332 Paper type acquisition unit 333 Operation signal acquisition unit 334 Storage unit 335 Drive control unit 335a Time step determination unit 335b Operation mode selection unit 335c Sequence operation unit 335d Current control unit 336 Image processing unit 336a Image formation control unit 336b Color conversion circuit 337 Upper layer command unit 338 Sensor detection unit 340 Operation panel 341 Communication interface 361 Print processing operation detection unit 362 Timing calculation unit 362a Pattern selection unit 363 Process selection unit 401 Upper limit detection sensor 402 Lower limit detection sensor 511 Intermediate inlet sensor 512 Intermediate outlet sensor 513 Registration sensor 530 Paper size detection mechanism CR Normal path DR Ejection Paper path FR Paper feed system transport path R Registration section SR Reverse path

Claims (6)

An image forming apparatus having a paper feed path for feeding a recording medium from a paper feed tray to a conveyance path, and forming an image on the recording medium conveyed on the conveyance path,
Pick-up means for picking up the recording media stacked on the paper feed tray one by one and sending them to the paper feed path;
Lifting and lowering means for raising the laminated recording medium so as to approach the pickup means;
Detecting means for detecting an upper surface position of the laminated recording medium;
A detection result for obtaining a detection result of the detection means at an interval between sheets after the pickup means finishes sending the recording medium to the paper feed path and starts sending the next recording medium to the paper feed path. Acquisition means;
Based on the detection result of the detection means acquired by the detection result acquisition means, an elevation control unit that controls the start of the raising operation of the recording medium by the elevation means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the interval between sheets is a period excluding at least an operation period of a motor that drives a roller that contacts the recording medium in the pickup unit.   3. The image forming apparatus according to claim 1, wherein the interval between sheets is a period excluding at least an operation period of the pickup unit. The paper feed path is
A registration roller that adjusts the feeding timing of the recording medium with respect to the transport path;
An intermediate transport roller group for transporting the recording medium between the pickup means and the registration rollers;
The paper interval is a period excluding at least an operation period of the registration roller and the intermediate conveyance roller group.
The image forming apparatus according to claim 1, 2 or 3.   The elevating control unit is based on the detection result of the detecting unit acquired by the detection result acquiring unit during a non-ascending period excluding a period during the elevating operation of the recording medium by the elevating unit in the paper interval. The image forming apparatus according to claim 1, wherein the start of the raising operation of the recording medium is controlled.   The period during the raising operation of the recording medium by the raising / lowering means is determined based on the average speed of the raising / lowering operation, and the average speed is determined by the conveyance speed of the recording medium in the paper feed path, the recording medium The image forming apparatus according to claim 5, wherein the image forming apparatus is determined based on a paper size in the transport direction, an interval between the papers, and a paper thickness of the recording medium.

Images