Sheet loading device and image forming system

Abstract

Improve the positional accuracy of the loading trays. [Solution] The system comprises a loading section for loading sheets, a motor that outputs a driving force to raise and lower the loading section, a rotation detection section that detects the amount of rotation of the motor, and a control unit that sets a target rotation amount for the motor when lowering the loading section as a sheet is loaded onto it, and provides feedback control of the motor based on the target rotation amount and the detection result of the rotation detection section. The control unit changes the control parameters (G0, G1) of the feedback control in response to the weight of the sheet loaded onto the loading section changing from a first weight (0) to a second weight (1000) which is heavier than the first weight.

Description

Technical Field

[0001] The present invention relates to a sheet loading device for loading sheets and an image forming system to which this is applied.

Background Art

[0002] In recent years, with the speeding up of image forming processing in image forming apparatuses, in a sheet loading device as well, in order to load sheets that are discharged at high speed, there is a demand for speeding up the sheet loading process corresponding to the sheet discharge speed and for good alignment of the stacked sheet bundles. Further, with an increase in the loading capacity of the sheet loading device due to handling long sheets and the like, the weight of the loaded sheets is increasing. When loading sheets in a sheet loading device, a loading tray (loading section) for loading the sheets is lowered in accordance with sheet discharge. Further, in order to take out the sheets loaded on the loading tray, the loading tray is moved up and down. At the time of taking out the sheets loaded on such a loading tray, control for changing the lifting speed of the loading tray based on the sheet loading weight is disclosed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the sheet loading device described in Patent Document 1, control based on the sheet loading weight is not performed during sheet loading. For this reason, there is a problem that during sheet loading, as the number of stacked sheets increases and the sheet loading weight becomes heavier, the variation in the position of the actual loading tray with respect to the target lowering amount of the loading tray becomes larger.

[0005] The present invention aims to provide a sheet loading device and an image forming system that can improve the positional accuracy of the loading tray. [Means for solving the problem]

[0006] One aspect of the present invention is a sheet loading device comprising: a loading section for loading sheets; a motor that outputs a driving force for raising and lowering the loading section; a rotation detection section for detecting the amount of rotation of the motor; and a control unit that sets a target rotation amount for the motor and performs feedback control of the motor based on the target rotation amount and the detection result of the rotation detection section when lowering the loading section as a sheet is loaded onto the loading section, wherein the control unit changes the control parameters of the feedback control in response to the weight of the sheets loaded onto the loading section changing from a first weight to a second weight that is heavier than the first weight.

[0007] Another aspect of the present invention is a sheet loading device comprising: a loading section for loading sheets; a motor that outputs a driving force for raising and lowering the loading section; a height detection section for detecting the height of the loading section; and a control unit that sets a target height for the loading section and provides feedback control of the motor based on the target height and the detection result of the height detection section when lowering the loading section as a sheet is loaded onto the loading section, wherein the control unit changes the control parameters of the feedback control in response to the height of the loading section changing from a first height to a second height lower than the first height.

[0008] Another aspect of the present invention is an image forming system characterized by comprising an image forming apparatus for forming an image on a sheet, and a sheet loading apparatus for receiving the sheet on which the image has been formed by the image forming apparatus and loading it onto the loading section. [Effects of the Invention]

[0009] According to the present invention, the positional accuracy of the loading tray can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing an image forming system according to the first embodiment. [Figure 2] This is a cross-sectional view showing an exhaust module according to the first embodiment. [Figure 3] A control system block diagram for the discharge module according to the first embodiment. [Figure 4] Block diagram showing the feedback control system of the discharge module according to the first embodiment. [Figure 5] This is a time chart showing the control procedure for the discharge module according to the first embodiment. [Figure 6] This is a flowchart showing the control procedure for the discharge module according to the first embodiment. [Figure 7] This is a time chart showing the control procedure for the discharge module according to the second embodiment. [Figure 8] This flowchart shows the control procedure for the discharge module according to the second embodiment. [Modes for carrying out the invention]

[0011] <First Embodiment> The first embodiment will be described below with reference to Figures 1 to 6. This embodiment describes the case where an image forming system is applied to an inkjet recording system 1. Figure 1 is a schematic diagram showing an example of the general configuration of the inkjet recording system 1. This inkjet recording system 1 is a sheet-fed inkjet recording system that produces a recording material by forming an ink image on a sheet S using two liquids, a reaction liquid and ink. As shown in Figure 1, the inkjet recording system 1 consists of a feeding module 100, a print module 200, a drying module 300, a fixing module 400, a cooling module 500, an inversion module 600, and a stacking module 700. The cut sheet S supplied from the feeding module 100 is transported along the transport path, processed in each module, and stacked in the stacking module 700. In this embodiment, the sheet refers to the recording material and includes paper such as sheets and envelopes, plastic films such as overhead projector sheets (OHP), cloth, etc. Furthermore, in this embodiment, the sheet transport direction Df is positioned so that it is in the left-right direction of the inkjet recording system 1, and the right side is denoted as the right direction R, the left side as the left direction L, the upper side as the upper direction U, and the lower side as the lower direction D.

[0012] The feeding module 100 is connected to the print module 200 and transports sheets to supply sheets to the print module 200, and transfers sheets between the print module 200 and the feeding module 100. The feeding module 100 has a first feeding unit 111, a second feeding unit 112, and a third feeding unit 113 as a sheet feeding unit that houses and feeds sheets S. The first feeding unit 111 has a first housing section 111a that houses sheets S and a first feeding section 111b that feeds sheets S from the first housing section 111a. The second feeding unit 112 has a second housing section 112a that houses sheets S and a second feeding section 112b that feeds sheets S from the second housing section 112a. The third supply unit 113 has a third storage section 113a for storing sheets S, and a third feeding section 113b for feeding sheets S from the third storage section 113a. The first storage section 111a, the second storage section 112a, and the third storage section 113a are each capable of storing multiple sheets and are configured to be pull out towards the front of the device. The sheets S are separated in the first storage section 111a, the second storage section 112a, and the third storage section 113a by the first feeding section 111b, the second feeding section 112b, and the third feeding section 113b, and fed one sheet at a time to be transported to the print module 200. Note that the supply unit is not limited to three units, and may have one, two, or four or more units. The feeding module 100 will be described later.

[0013] The print module 200 is an example of an image forming apparatus and includes a pre-image registration correction unit (not shown), a print belt unit 220, and a recording unit 230, which transport the sheet S. The sheet S transported from the feed module 100 has its tilt and position corrected by the pre-image registration correction unit and is transported to the print belt unit 220. The recording unit 230 is positioned opposite the print belt unit 220 with respect to the transport path. The recording unit 230 performs a recording process (printing) on ​​the transported sheet S from above using a recording head to form an image. Multiple recording heads are arranged along the transport direction. In this embodiment, in addition to the four colors Y (yellow), M (magenta), C (cyan), and Bk (black), there are a total of five line-type recording heads corresponding to the reaction solution. Note that the number of colors is not limited to four, and the number of recording heads is not limited to five. The inkjet method can employ a method using a heating element, a method using a piezoelectric element, a method using an electrostatic element, a method using a MEMS element, etc. Each color of ink is supplied to the recording head from an ink tank (not shown) via an ink tube. The sheet S printed in the recording unit 230 is transported by a print belt unit 220, ensuring clearance with the recording head. The sheet S printed in the recording unit 230 is scanned for image misalignment and color density by an inline scanner (not shown) located downstream of the recording unit in the sheet transport direction. The detection results are used to correct the printed image.

[0014] The drying module 300 includes a decoupling section 320, a drying belt unit 330, and a hot air blowing section 340. It reduces the liquid content of the ink applied to the sheet S by the recording section 230 of the print module 200, thereby improving the adhesion between the sheet S and the ink. The sheet S printed by the recording section 230 of the print module 200 is transported to the decoupling section 320 located upstream of the sheet transport direction in the drying module 300. In the decoupling section 320, the sheet S can be transported from above by air pressure and belt friction, and by weakly holding and transporting the sheet S on the belt, it prevents the sheet S on the print belt unit 220, which forms the ink image, from shifting. The drying belt unit 330 is located below the belt, and the hot air blowing section 340 is located above the belt, facing each other across the belt. The sheet S transported from the decoupling section 320 is transported by suction in the drying belt unit 330, and at the same time, the ink-applied surface is dried by hot air from the hot air blowing section 340. In addition to the method of applying hot air, the drying method may also be configured by combining a method of irradiating the surface of the sheet S with electromagnetic waves (such as ultraviolet or infrared rays) or a conductive heat transfer method using contact with a heating element.

[0015] The fixing module 400 has a fixing belt unit 410. The fixing belt unit 410 has an upper belt unit and a lower belt unit, and the ink can be fixed to the sheet S by passing the sheet S conveyed from the drying module 300 between the heated upper belt unit and the lower belt unit.

[0016] The cooling module 500 has multiple cooling units 510 and cools the high-temperature sheet S that has been transported along the sheet transport path from the fixing module 400. The cooling units 510 are configured to cool the sheet S by drawing in outside air into the cooling box with a fan, increasing the pressure inside the cooling box, and blowing air from nozzles formed in the transport guide onto the sheet S. The cooling units 510 are positioned both above and below the transport path to cool the sheet S from both sides.

[0017] Further, the cooling module 500 has a conveyance path switching unit 520, and can switch the conveyance path of the sheet S according to whether the sheet S is conveyed to the inversion module 600 or to the duplex conveyance path used during duplex printing. During duplex printing, the sheet S is conveyed to the conveyance path below the cooling module 500. In this case, from the cooling module 500, it is further conveyed along the duplex conveyance paths of the fixing module 400, the drying module 300, the printing module 200, and the feeding module 100. A first inversion unit 420 for inverting the front and back of the sheet S is provided in the duplex conveyance path of the fixing module 400. Then, again, it is conveyed from the feeding module 100 to the pre-image registration correction unit, the print belt unit 220, and the recording unit 230 of the printing module 200, and is printed by the recording unit 23^{}

[0018] [[ID=]4]The inversion module 600 has a second inversion unit 640, can invert the front and back of the conveyed sheet S, and can change the front and back orientation of the discharged sheet S. The stacking module 700 is an example of a sheet stacking device, and has a top tray 720 and a stacking unit 750, and aligns and stacks the sheet S conveyed from the inversion module 600.

[0019] [Stacking module] Next, the configuration of the stacking module 700 will be described with reference to FIG. 2. FIG. 2 is a schematic cross-sectional view showing the stacking module 700. When a sheet is discharged from the inversion module 600, the sheet is carried into the conveyance roller 201 and conveyed through the conveyance path 202. The carried-in sheet is conveyed with the conveyance direction switched by a switching unit 203 that switches the sheet conveyance path by rotation according to a selection instruction from a main body operation unit (not shown) or the like. The switching unit 203 is switched by a solenoid 203a (see FIG. 3).

[0020] If the user specifies the top tray 720 on the top surface of the loading module 700 as the destination for sheet discharge, the control unit 701 (see Figure 3) drives the switching unit 203 with a solenoid 203a, and the switching unit 203 is rotated so that its tip faces downward. Guided by the switching unit 203, the sheet is transported to the top tray 720 and discharged.

[0021] If the user designates a loading unit 750 located downstream of the loading module 700 as the destination for sheet discharge, the control unit 701 drives and controls the switching units 203, 204, 205, and 206. Switching unit 204 is switched by solenoid 204a (see Figure 3), switching unit 205 is switched by solenoid 205a (see Figure 3), and switching unit 206 is switched by solenoid 206a (see Figure 3). Switching units 203, 204, 205, and 206 are all rotated so that their tips face upward. Guided by the switching units 203, 204, 205, and 206, the sheet is transported from the discharge roller pair 207 to the loading unit 750 and discharged. In other words, the discharge roller pair 207 is an example of a discharge section that transports sheets and discharges them onto the loading tray 251. Upstream of the discharge roller pair 207 in the sheet transport direction, a discharge sensor 216 is provided to detect sheets.

[0022] Furthermore, if the user specifies an unshown post-processing device connected downstream of the loading module 700 as the destination for sheet discharge, the control unit 701 drives and controls the switching units 203 and 204. The sheet is transported (discharged) to the unshown post-processing device by the guidance of the switching units 203 and 204, or, if necessary, the switching units 205 and 206.

[0023] Downstream from the discharge roller pair 207 to the loading unit 750, in the retraction direction X which is the sheet discharge direction, a transfer mechanism 705, which is an example of a transfer section, is provided. This transfer mechanism 705 has a drive pulley 211, a driven pulley 210, and a gripper belt 208 suspended between them. The gripper belt 208 is rotationally driven in the direction of arrow 212 by the driving force of a gripper belt motor (not shown) being transmitted to the drive pulley 211 by a gear mechanism or the like. The gripper belt 208 is rotationally driven so that the speed at which its surface moves is the same as the sheet transport speed.

[0024] Furthermore, in the transfer mechanism 705, grippers 209a and 209b are attached to the gripper belt 208, which engage with the leading edge of the sheet discharged from the discharge roller pair 207 and grip it between themselves and the gripper belt 208. Grippers 209a and 209b are examples of gripper members and engage with the leading edge of the sheet discharged from the discharge roller pair 207. Grippers 209a and 209b move together with the gripper belt 208 in the direction of arrow 212 at the same speed as the sheet transport speed. Then, the sheet S is transported (conveyed) above the loading unit 750 along the sheet discharge direction to a predetermined position as its leading edge is gripped by grippers 209a and 209b. Specifically, the transfer mechanism 705 has grippers 209a and 209b, and by rotating the grippers 209a and 209b, it transfers the sheet engaged with the grippers 209a and 209b to a predetermined position above the loading tray 251 and hands it over to the retraction section 214.

[0025] The tip stopper 213 abuts against the tip of the sheet S, positioning the sheet S. The tip stopper 213 includes an inclined surface 213a against which the sheet gripped by the grippers 209a and 209b makes contact, and a retraction section 214 consisting of rollers or the like that pulls in the sheet S. When the grippers 209a and 209b, which are gripping the sheet S, move toward the tip stopper 213 due to the rotation of the gripper belt 208, the tips of the sheet S gripped by the grippers 209a and 209b come into contact with the inclined surface 213a of the tip stopper 213. When the tips of the sheet S come into contact with the inclined surface 213a, the grippers 209a and 209b release their grip.

[0026] After the sheet S is released from the grippers 209a and 209b, it is discharged toward the retraction section 214, and the leading edge of the sheet S comes into contact with the contact surface 213b of the tip stopper 213 by the retraction section 214, thereby positioning the leading edge of the sheet. In this embodiment, the retraction section 214 is a rotating roller, but it is not limited to this and may be a rotating belt or the like. That is, the retraction section 214 is positioned above the loading tray 251 and moves to pull in the retraction direction X by contacting the uppermost sheet among the sheets loaded on the loading tray 251. The contact surface 213b is an example of a stopper, positioned downstream of the retraction section 214 in the retraction direction X, and contacts and positions the leading edge of the sheet pulled in by the retraction section 214. As a result, the sheet S is transported to a predetermined position above the loading unit 750 (a position where the leading edge of the sheet S is aligned with the contact surface 213b). This predetermined position can be arbitrarily set by setting the position of the tip stopper 213 to any position above the loading unit 750. In this embodiment, the tip stopper 213 is described as being fixed, but when loading the sheet S onto the loading unit 750 while offsetting it, the tip stopper 213 may be moved each time the sheet is offset using a moving mechanism or the like.

[0027] Meanwhile, the rear end of the sheet separates from the discharge roller pair 207, and the sheet is loaded onto the loading tray 251 with its front end position restricted. The loading tray 251 is an example of a loading section on which sheets are loaded. As sheets are loaded, it is necessary to lower the loading tray 251. For this reason, when the sheet surface detection sensor 215 located in the front stopper 213 detects the loaded sheet 240, the tray lifting motor 323 (see Figure 3) is driven to repeatedly perform tray lowering control, lowering the loading tray 251 by a predetermined amount.

[0028] When it is necessary to remove the loaded sheets after the job is completed or during the job, the loading tray 251 is lowered to a position where the sheets can be removed. A trolley 260 is provided at the lowered position on which the loading tray 251 is placed, and the loading tray 251 with the loaded sheets is removed from the loading module 700 along with the trolley 260.

[0029] [Control System] Next, the control configuration of the loading module 700 will be explained using Figure 3. The control unit 701 has a CPU, memory, etc., and controls each part of the loading module 700. The control unit 701 communicates with the main CPU 303, which controls the entire inkjet recording system 1. The control unit 701, following the instructions of the main CPU 303, comprehensively controls the loading module 700, mainly driving each load within the loading module 700 and processing sensor signals, and is responsible for executing sequence control of the module.

[0030] The control unit 701 communicates with the FPGA 301. The control unit 701 supplies the necessary control signals from the FPGA 301 to the solenoid drive circuit 310, the stepping motor drive circuit 311, and the brushless motor drive circuit 313, driving the solenoids 203a to 206a, the transport motor 321, and the tray lifting motor 323. The tray lifting motor 323 is an example of a motor and outputs a driving force to raise and lower the loading tray 251.

[0031] The control unit 701 can sequentially control each load according to the input signals of each sensor by receiving signals from the transport sensor, the sheet surface detection sensor 215, and the encoder 324. Here, the encoder 324 is an example of a rotation detection unit that detects the amount of rotation of the tray lifting motor 323, and is a sensor that detects the rotation of the tray lifting motor 323. The tray lifting motor 323 is a brushless motor using a PWM (Pulse Width Modulation) control method. By providing a PWM signal from the FPGA 301 to the brushless motor drive circuit 313, the brushless motor drive circuit 313 changes the voltage applied to the tray lifting motor 323 according to the duty cycle of the PWM signal.

[0032] Next, the control method for the tray lifting motor 323 controlled by the control unit 701 will be explained using Figure 4. As shown in Figure 4, the control unit 701 performs position feedback control of the tray lifting motor 323, using PID control as the control method. That is, the control unit 701 performs feedback control by PID control, which calculates the deviation between the target rotation amount and the detection result of the encoder 324 and performs proportional control, integral control, and differential control. When the control unit 701 moves the tray lifting motor 323 by a predetermined amount, it increases the target movement amount r with each control cycle until it reaches the predetermined amount. The control unit 701 detects the rotational movement amount y of the tray lifting motor 323 with each control cycle using the encoder 324 attached to the tray lifting motor 323, and inputs the deviation e between the target movement amount r and the detected rotational movement amount y to the PID controller 312.

[0033] The PID controller 312 multiplies the deviation e directly by the proportional gain Kp in the P (proportional term), multiplies the integrated value obtained by accumulating the deviations e in the I (integral term) by the integral gain Ki, and multiplies the difference value obtained by taking the difference between the deviation e and the previous deviation in the D (derivative term) by the derivative gain Kd. The PID controller 312 then adds up the calculated values ​​of each term and uses the sum of these values ​​as the DUTY value of the PWM signal supplied to the brushless motor drive circuit 313. As a result, the brushless motor drive circuit 313 applies a voltage corresponding to the DUTY value to the tray lifting motor 323, operating the tray lifting motor 323. When the tray lifting motor 323 operates, the amount of rotational movement y detected by the encoder 324 changes, so the voltage applied to the tray lifting motor 323 changes according to the rotational state. Specifically, when the loading tray 251 is lowered as a sheet is loaded onto it, the control unit 701 sets a target rotation amount for the tray lifting motor 323. Then, based on the target rotation amount and the detection result of the encoder 324, the control unit 701 performs feedback control of the tray lifting motor 323.

[0034] [Tray lowering control] Next, the tray lowering control, which lowers the loading tray 251 by a predetermined amount, will be explained using Figure 5. Figure 5 is a timing chart of the tray lowering control, which lowers the loading tray 251 by a predetermined amount as sheets are loaded. As shown in Figure 5, the control unit 701 starts the tray lowering control triggered by the detection of the rear end of a sheet by the discharge sensor 216. Here, the discharge sensor 216 represents the detection state of the sheet as a low level, and the timing at which it switches from a low level to a high level, for example time t1, is the timing at which the discharge sensor 216 detects the rear end of a sheet. Since the discharge sensor 216 is a transport sensor located upstream of the loading tray 251 in the sheet transport direction, the detection of the rear end of a sheet by the discharge sensor 216 is the timing at which a sheet is loaded onto the loading tray 251, which is equivalent to an increase in the number of loaded sheets.

[0035] The control unit 701 determines at time t2, after a predetermined time has elapsed from time t1, whether or not the sheet surface detection sensor 215 has detected the sheet surface. If the control unit 701 determines that the sheet surface has been detected, it starts driving the tray lifting motor 323 using the feedback control described above, and stops driving it at time t3, after a predetermined time has elapsed, thereby lowering the loading tray 251 by a predetermined amount. Here, the state in which the sheet surface detection sensor 215 has detected the sheet surface and the state in which the tray lifting motor 323 is being driven are represented by a high level, respectively.

[0036] In the example shown in Figure 5, the sheet enters the tip stopper 213 where the sheet surface detection sensor 215 is located between time t1 and time t2. Since the sheet surface detection sensor 215 may detect the flapping of the sheet when it enters the stopper, the control unit 701 performs sheet surface detection at time t2, when the sheet loading is complete and the sheet's behavior has stabilized. If the control unit 701 determines that the sheet surface detection sensor 215 has not detected the sheet surface at a time when the sheet's behavior has stabilized, such as at time t5, it does not drive the tray lifting motor 323.

[0037] When the control unit 701 stops driving the tray lifting motor 323 at time t3, the loading tray 251 will continue to descend due to its inertia, but since the tray lifting motor 323 is stopped, it will vibrate. If the next sheet is loaded while the loading tray 251 is vibrating, proper sheet surface detection will not be possible. Therefore, it is necessary to stop driving the tray lifting motor 323 at time t3, before time t4, when the next sheet is loaded onto the loading tray 251.

[0038] Due to the aforementioned constraints on the start time t2 and stop time t3 of the tray lifting motor 323, the operating time of the tray lifting motor 323 for the loading tray 251 is short. Because the operating time is short, the loading tray 251 will stop operating before it can stably track the target lowering amount. For this reason, the control gain is adjusted in advance so that the amount of movement is at a predetermined value at the stopping timing of the tray lifting motor 323.

[0039] On the other hand, as the number of stacked sheets increases and the weight of the stacked sheets 240 increases, the inertia on the motor shaft of the tray lifting motor 323 increases, so the change in the amount of movement at the start of motor operation changes. Specifically, the start of tray movement is delayed, the amount of overshoot (exceeding the target amount of movement) or undershoot (exceeding the target amount of movement) increases, and vibration also increases. As a result, as the weight of the stacked sheets 240 increases, the amount of movement of the tray lifting motor 323 when stopped changes, and there is a risk that the amount of descent of the stacked tray 251 will vary.

[0040] If the downward movement is less than the target movement, the gap between the retraction section 214 and the loading tray 251 becomes smaller relative to the thickness of the sheet being transported, and the contact pressure between the retraction section 214 and the transported sheet increases, which may cause wrinkles or buckling in the sheet. If the downward movement is greater than the target movement, the gap between the retraction section 214 and the loading tray 251 becomes larger relative to the thickness of the sheet being transported, and the contact pressure between the retraction section 214 and the transported sheet decreases, which may prevent the sheet from being retracted and aligned.

[0041] To avoid these risks, it is effective to change the control gain of the feedback control of the tray lifting motor 323 as the weight of the loading sheets 240 increases, i.e., as the number of loaded sheets increases. The control gain is a parameter that determines the responsiveness of the PID controller 312. Therefore, by changing the control gain in accordance with the change in the responsiveness of the controlled object due to the increase in the weight of the loading sheets 240, it is possible to adjust the transient vibration of the rotational movement amount y of the tray lifting motor 323.

[0042] As a result, variations in the amount the loading tray 251 descends can be suppressed. In Figure 5, the control gain is set to G0 when the number of loaded sheets is 0, the control gain is changed to G1 at time t6 when the number of loaded sheets reaches 1000, and the control gain is changed to G2 at time t7 when the number of loaded sheets reaches 2000. Here, the weight of the loaded sheets 240 is the value obtained by multiplying the number of loaded sheets by the weight of each sheet, and the weight of each sheet is determined by the sheet size and sheet basis weight, so the number of loaded sheets for which the control gain is changed is changed according to the sheet size and sheet basis weight. That is, the control unit 701 changes the control gain, which is an example of a control parameter for feedback control, in response to the weight of the sheets loaded on the loading tray 251 changing from a first weight (for example, the weight of one sheet) to a second weight (for example, the weight of 1000 sheets) which is heavier than the first weight.

[0043] Here, as the weight of the controlled object increases, the system's response slows down, potentially causing vibrations and overshoot. Therefore, when the weight of the seat increases, the feedback control parameters for tray lifting and lowering are modified to increase the response speed to tray lowering and suppress overshoot and vibration. Specifically, this can be done by increasing the proportional gain Kp to increase the response speed, decreasing the integral gain Ki to suppress overshoot, and increasing the differential gain Kd to suppress vibrations. However, excessively increasing the proportional gain Kp will cause vibrations, excessively decreasing the integral gain Ki will cause positional deviations due to steady-state errors, and excessively increasing the differential gain Kd will make the system sensitive to external noise, so appropriate adjustment is necessary.

[0044] Therefore, in this embodiment, as an example of changing the control gain G, the proportional gain Kp is increased, the integral gain Ki is decreased, and the differential gain Kd is increased according to the number of sheets stacked. That is, the control unit 701 performs feedback control to speed up the response by increasing the proportional gain Kp as a control parameter in response to an increase in the weight of the sheets stacked on the stacking tray 251. The control unit 701 also performs feedback control to reduce overshoot by decreasing the integral gain Ki as a control parameter in response to an increase in the weight of the sheets stacked on the stacking tray 251. The control unit 701 also performs feedback control to reduce vibration by increasing the differential gain Kd as a control parameter in response to an increase in the weight of the sheets stacked on the stacking tray 251.

[0045] Specifically, when the number of stacked items is 0, the proportional gain Kp, integral gain Ki, and differential gain Kd are all set to 1. In this case, when the number of stacked items is 1000 or more, the proportional gain Kp is set to 2, the integral gain Ki to 0.5, and the differential gain Kd to 2. When the number of stacked items is 2000 or more, Kp is set to 4, the integral gain Ki to 0.25, and the differential gain Kd to 4. In this way, by appropriately adjusting the control gain G in accordance with the increase in the number of stacked items, the stability and responsiveness of the system can be maintained. In this embodiment, the proportional gain Kp, integral gain Ki, and differential gain Kd are all changed, but this is not limited to this, and it is sufficient to change at least one of them.

[0046] Next, the operation procedure of the control unit 701 will be explained using the flowchart shown in Figure 6. Each control step is performed in the control unit 701. This flow starts when power is turned on to the control unit 701 and it starts up. The control unit 701 sets the control gain of the tray lifting motor 323 to the initial value G0 (S1). The control unit 701 determines whether or not the sheet surface detection sensor 215 is ON (S2). If the control unit 701 determines that the sheet surface detection sensor 215 is NOT ON (S2; NO), it determines again whether or not the sheet surface detection sensor 215 is ON (S2).

[0047] If the control unit 701 determines that the sheet surface detection sensor 215 is ON (S2; YES), it determines whether the acquired number of stacked sheets × sheet size × sheet basis weight is equal to or greater than a predetermined value N2 (S3). If the control unit 701 determines that the number of stacked sheets × sheet size × sheet basis weight is equal to or greater than a predetermined value N2 (S3; YES), it sets the control gain to G2 (S4) and determines again whether the sheet surface detection sensor 215 is ON (S2).

[0048] If the control unit 701 determines that the number of stacked sheets × sheet size × sheet basis weight is not equal to or greater than a predetermined value N2 (S3; NO), it determines whether the acquired number of stacked sheets × sheet size × sheet basis weight is equal to or greater than a predetermined value N1 (S5). If the control unit 701 determines that the number of stacked sheets × sheet size × sheet basis weight is equal to or greater than a predetermined value N1 (S5; YES), it sets the control gain to G1 (S6) and determines again whether the sheet surface detection sensor 215 is ON or OFF (S2). If the control unit 701 determines that the number of stacked sheets × sheet size × sheet basis weight is not equal to or greater than a predetermined value N1 (S5; NO), it determines again whether the sheet surface detection sensor 215 is ON or OFF (S2).

[0049] In this embodiment, the gain setting is set to three stages: G0, G1, and G2. However, it is not limited to this, and the number of stages may be changed according to the product configuration. Furthermore, even within the same product, the gain may be changed according to the sheet type, temperature and humidity environment, loading speed, and other loading conditions.

[0050] As described above, according to this embodiment, the control unit 701 monitors the sheet surface detection sensor 215 and changes the control gain of the tray lifting motor 323 according to the number of sheets stacked × sheet size × sheet basis weight, i.e., the weight of the stacked sheets. In other words, in this embodiment, the control unit 701 changes the control gain of the feedback control in response to an increase in the weight of the sheets stacked on the stacking tray 521. This makes it possible to optimize the stability and responsiveness of the motor control system, improve the consistency of the stacked sheets, suppress stacking errors, and improve the positional accuracy of the stacking tray 251.

[0051] In the above-described embodiment, the control unit 701 was described as performing feedback control using PID control, but this is not the only case. For example, instead of using all three types of control—proportional control, integral control, and differential control—two of them may be combined or even just one of them may be used.

[0052] Furthermore, in the above-described embodiment, the control unit 701 was described as calculating and obtaining the weight of the stacked sheets by multiplying the number of stacked sheets by the sheet size and the sheet basis weight, but it is not limited to this. For example, a sensor that can directly detect the weight of the sheets stacked on the stacking tray 251 may be provided.

[0053] Furthermore, in the above-described embodiment, the motor control gain is changed in software in the control unit 701. However, the system is not limited to this, and equivalent functionality may be implemented in hardware using transistors or discrete ICs.

[0054] Furthermore, although the above-described embodiment described the application to a loading module 700 as an example of a sheet loading device, it is not limited to this, and can be applied to, for example, locations where a large number of sheets are loaded. Specifically, it can be applied to devices that load sheets without using a gripper belt, such as large-capacity stackers, finisher discharge trays, and large-capacity feeding decks.

[0055] Furthermore, although the above-described embodiment described the case in which the image forming system is applied to an inkjet recording system 1 of the inkjet recording method, it is not limited to this and may also be applied to an electrophotographic image forming apparatus.

[0056] <Second Embodiment> Next, a second embodiment will be described using Figures 7 and 8. This embodiment differs from the first embodiment in that it uses a control period instead of a control gain as a control parameter. However, the other components are the same as in the first embodiment, so the same reference numerals are used and detailed explanations are omitted.

[0057] In this embodiment, the control block is the same as in the first embodiment, so we will explain it using the control block diagram in Figure 4. In the first embodiment, the control gain of the PID controller 312 was changed based on the sheet load weight, but in the second embodiment, the control gain of the PID controller 312 is not changed based on the sheet load weight, but instead the control period for calculating the PID control is changed. By changing the control period, the cumulative value of the deviation e and the difference value between the deviation e and the previous deviation change, and an effect equivalent to changing the control gain can be obtained.

[0058] [Tray lowering control] The tray lowering control, which lowers the loading tray 251 by a predetermined amount, will be explained using Figure 7. Figure 7 is a timing chart of the tray lowering control in this embodiment, which lowers the loading tray 251 by a predetermined amount as sheets are loaded. The difference from Figure 5 is that the parameter that changes with increasing number of loaded sheets has changed from control gain to control period. The other configurations are the same as in the first embodiment.

[0059] Therefore, in the first embodiment, as an example of changing the control gain G, the proportional gain Kp is increased, the integral gain Ki is decreased, and the differential gain Kd is increased according to the number of sheets stacked. That is, the control unit 701 performs feedback control to speed up the response by increasing the proportional gain Kp as a control parameter in response to an increase in the weight of the sheets stacked on the stacking tray 251. The control unit 701 also performs feedback control to reduce overshoot by decreasing the integral gain Ki as a control parameter in response to an increase in the weight of the sheets stacked on the stacking tray 251. The control unit 701 also performs feedback control to reduce vibration by increasing the differential gain Kd as a control parameter in response to an increase in the weight of the sheets stacked on the stacking tray 251.

[0060] In this case, with respect to proportional control, shortening the control period increases the update speed of the detected deviation e, thus improving responsiveness. Therefore, shortening the proportional control period and increasing the proportional gain Kp have equivalent effects. For this reason, the control unit 701 uses feedback control to speed up the response by shortening the control period of proportional control as a control parameter in response to an increase in the weight of the sheets loaded on the loading tray 251.

[0061] Regarding integral control, increasing the control period reduces the accumulation speed of the detected deviation e, thereby suppressing overshoot. Therefore, increasing the integral control period and decreasing the integral gain Ki have equivalent effects. For this reason, the control unit 701 performs feedback control to reduce overshoot by increasing the control period of integral control as a control parameter in response to an increase in the weight of the sheets loaded on the loading tray 251.

[0062] Regarding differential control, shortening the control period increases the update speed of the detected deviation e, thus increasing sensitivity to noise. Therefore, shortening the differential control period and increasing Kd have equivalent effects. For this reason, the control unit 701 performs feedback control to reduce vibration by shortening the control period of the differential control as a control parameter in response to an increase in the weight of the sheets loaded on the loading tray 251.

[0063] Therefore, as an example of changing the control period, the proportional control period is decreased, the integral control period is increased, and the differential control period is increased depending on the number of stacked items. For example, as shown in Figure 7, the control period when the number of stacked items is 0 is set to T0, the control period is changed to T1 at time t6 when the number of stacked items reaches 1000, and the control period is changed to T2 at time t7 when the number of stacked items reaches 2000.

[0064] Specifically, when the number of stacked items is 0, the proportional control period, integral control period, and differential control period are all set to 2 ms. When the number of stacked items is 1000 or more, the proportional control period is set to 1 ms, the integral control period to 4 ms, and the differential control period to 1 ms. Furthermore, when the number of stacked items is 2000 or more, the proportional control period is set to 0.5 ms, the integral control period to 8 ms, and the differential control period to 0.5 ms. In this way, the stability and responsiveness of the system can be maintained by appropriately adjusting the control period in accordance with the increase in the number of stacked items. In this embodiment, all three of the proportional control period, integral control period, and differential control period are changed, but this is not limited to this; it is sufficient to change at least one of these.

[0065] Next, the operation procedure of the control unit 701 will be explained using the flowchart shown in Figure 8. Each control step is performed in the control unit 701. This flow starts when power is turned on to the control unit 701 and it starts up. The control unit 701 sets the control cycle of the tray lifting motor 323 to the initial value T0 (S11). The control unit 701 determines whether or not the sheet surface detection sensor 215 is ON (S2). If the control unit 701 determines that the sheet surface detection sensor 215 is NOT ON (S2; NO), it determines again whether or not the sheet surface detection sensor 215 is ON (S2).

[0066] If the control unit 701 determines that the sheet surface detection sensor 215 is ON (S2; YES), it determines whether the number of stacked sheets × sheet size × sheet basis weight is equal to or greater than a predetermined value N2 (S3). If the control unit 701 determines that the number of stacked sheets × sheet size × sheet basis weight is equal to or greater than a predetermined value N2 (S3; YES), it sets the control cycle to T2 (S14) and determines again whether the sheet surface detection sensor 215 is ON (S2).

[0067] If the control unit 701 determines that the number of sheets × sheet size × sheet basis weight is not equal to or greater than a predetermined value N2 (S3; NO), it determines whether the number of sheets × sheet size × sheet basis weight is equal to or greater than a predetermined value N1 (S5). If the control unit 701 determines that the number of sheets × sheet size × sheet basis weight is equal to or greater than a predetermined value N1 (S5; YES), it sets the control cycle to T1 (S16) and determines again whether the sheet surface detection sensor 215 is ON or OFF (S2). If the control unit 701 determines that the number of sheets × sheet size × sheet basis weight is not equal to or greater than a predetermined value N1 (S5; NO), it determines again whether the sheet surface detection sensor 215 is ON or OFF (S2).

[0068] In this embodiment, the gain setting is set to three stages: T0, T1, and T2. However, this is not limited to these stages, and the number of stages may be changed according to the product configuration. Furthermore, even within the same product, the gain settings may be changed according to the sheet type, temperature and humidity environment, loading speed, and other loading conditions.

[0069] As described above, according to this embodiment, the control unit 701 monitors the sheet surface detection sensor 215 and changes the control cycle of the tray lifting motor 323 according to the number of sheets stacked × sheet size × sheet basis weight, i.e., the weight of the stacked sheets. In other words, in this embodiment, the control unit 701 changes the control cycle of the feedback control in response to the increased weight of the sheets stacked on the stacking tray 521. This makes it possible to optimize the stability and responsiveness of the motor control system, improve the consistency of the stacked sheets, suppress stacking errors, and improve the positional accuracy of the stacking tray 251.

[0070] In the embodiments described above, the control unit 701 changes the control parameters according to the weight of the loaded sheets, but it is not limited to this, and for example, the control parameters may be changed according to the height of the loading tray 251. That is, if the weight of the sheets loaded on the loading tray 251 increases, the height of the loading tray 251 decreases, so the correlation between sheet weight and the height of the loading tray 251 can be utilized.

[0071] For example, a height detection sensor 261 (see Figure 2) is provided as an example of a height detection unit that detects the height of the loading tray 251. The control unit 701 may set a target height for the loading tray 251 when lowering it, and then perform feedback control of the tray lifting motor 323 based on the target height and the detection result of the height detection sensor 261. In this case, the control unit 701 changes the control parameters of the feedback control in response to the height of the loading tray 251 changing from a first height to a second height lower than the first height. The control parameters may be a control gain, as in the first embodiment, or a control period, as in the second embodiment. [Explanation of Symbols]

[0072] 1…Inkjet recording system (image forming system), 200…Print module (image forming apparatus), 207…Discharge roller pair (discharge section), 209a,209b…Gripper (gripper member), 213b…Contact surface (stopper), 214…Retraction section, 251…Loading tray (loading section), 261…Height detection sensor (height detection section), 323…Tray lifting motor (motor), 324…Encoder (rotation detection section), 700…Loading module (sheet loading apparatus), 701…Control unit, 705…Transfer mechanism (transfer section)

Claims

1. A loading section for loading sheets, A motor that outputs a driving force to raise and lower the aforementioned loading section, A rotation detection unit for detecting the amount of rotation of the motor, The system includes a control unit that sets a target rotation amount for the motor and performs feedback control of the motor based on the target rotation amount and the detection result of the rotation detection unit when the loading unit is lowered as a sheet is loaded onto the loading unit, The control unit changes the control parameters of the feedback control in response to the weight of the sheets loaded in the loading section changing from a first weight to a second weight that is heavier than the first weight. A sheet loading device characterized by the following features.

2. The control unit performs feedback control to increase the response speed by increasing the proportional gain as a control parameter in response to the weight of the sheet loaded in the loading section changing from the first weight to the second weight. The sheet loading device according to feature 1.

3. The control unit performs feedback control to reduce overshoot by decreasing the integral gain as a control parameter in response to the weight of the sheets loaded in the loading section changing from the first weight to the second weight. The sheet loading device according to feature 1.

4. The control unit performs feedback control to reduce vibration by increasing the differential gain as a control parameter in response to the weight of the sheets loaded on the loading section changing from the first weight to the second weight. The sheet loading device according to feature 1.

5. The control unit, in response to the change in the weight of the sheets loaded in the loading section from the first weight to the second weight, performs feedback control to increase the response speed by shortening the control period of proportional control as a control parameter. The sheet loading device according to feature 1.

6. The control unit, in response to the change in the weight of the sheets loaded in the loading section from the first weight to the second weight, performs feedback control to reduce overshoot by lengthening the control period of the integral control as a control parameter. The sheet loading device according to feature 1.

7. The control unit, in response to the change in the weight of the sheets loaded in the loading section from the first weight to the second weight, performs feedback control to reduce vibration by shortening the control period of the differential control as a control parameter. The sheet loading device according to feature 1.

8. The control unit calculates the deviation between the target rotation amount and the detection result of the rotation detection unit and performs feedback control using PID control, which involves proportional control, integral control, and differential control. The sheet loading device according to feature 1.

9. The motor is a brushless motor. The sheet loading device according to feature 1.

10. The control unit obtains the weight of the sheets loaded in the loading section based on the sheet size, basis weight, and number of sheets. The sheet loading device according to feature 1.

11. A retraction unit is positioned above the loading unit and moves to contact the uppermost sheet among the sheets loaded on the loading unit and retract it in the retraction direction, The system includes a stopper positioned downstream of the retraction section in the aforementioned retraction direction, which contacts and positions the leading edge of the sheet retracted by the retraction section. The sheet loading device according to feature 1.

12. A discharge unit that transports the sheets and discharges them to the loading unit, The system includes a transfer unit having a gripper member that engages with the leading edge of the sheet discharged from the discharge unit, and which rotates the gripper member to transfer the sheet engaged with the gripper member to a predetermined position above the loading unit and hand it over to the retraction unit. The sheet loading device according to feature 11.

13. A loading section for loading sheets, A motor that outputs a driving force to raise and lower the aforementioned loading section, A height detection unit for detecting the height of the loading section, The system includes a control unit that, when the loading section is lowered as a sheet is loaded onto it, sets a target height for the loading section and provides feedback control to the motor based on the target height and the detection result of the height detection unit, The control unit changes the control parameters of the feedback control in response to the height of the loading section changing from a first height to a second height lower than the first height. A sheet loading device characterized by the following features.

14. An image forming apparatus that forms an image on a sheet, A sheet stacking device according to any one of claims 1 to 13, which receives a sheet on which an image has been formed by the image forming device and stacks it in the stacking section, An image forming system characterized by the following features.

Images