Image forming apparatus

Abstract

To provide an image forming apparatus capable of reducing the number of times of elevating / lowering a head unit.SOLUTION: The image forming apparatus 1 includes a head unit 5 disposed above a conveyance path 21a, an elevating device 7 configured to raise the head unit 5 from a height at which an image can be formed on a sheet, a carry-in detection sensor 9 configured to detect a sheet carried in below the head unit 5 after an image forming operation is started once, a carry-out detection sensor 11 configured to detect a sheet carried out below the head unit 5 after the image forming operation is started once, and a controller 10 configured to store the number of carry-in sheets detected by the carry-in detection sensor 9 after the image forming operation is started once and the number of carry-out sheets detected by the carry-out detection sensor 11 after the image forming operation is started once. And a control part 51 for driving the lifting device 7 to lift the head unit 5 only when the stored number of sheets to be carried in and the number of sheets to be carried out do not coincide with each other when a power source is turned on after the image forming operation is started and the power source is turned off.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus equipped with a head unit that can be raised and lowered. [Background technology]

[0002] In an image forming apparatus using an inkjet head or the like, if paper remains on the transport path when the power is turned on, paper being transported may interfere with the remaining paper, causing transport problems such as paper jams or damage to the head unit. For this reason, image forming apparatuses are sometimes equipped with a means for detecting paper remaining on the transport path when the power is turned on. For example, the image forming apparatus described in Patent Document 1 displays a warning and then starts warming up if recording paper is present in the apparatus when the power is turned on. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-236956 Summary of the Invention [Problem to be solved by the invention]

[0004] Inkjet image forming devices are equipped with a head unit that ejects ink onto paper transported on a transport belt to form an image. The head unit is supported so that it can be raised from a predetermined image formation height. When a paper jam occurs, the head unit is raised to open the transport belt and remove the jammed paper.

[0005] Such image forming devices are equipped with a sensor that detects paper being transported on a transport belt. When the sensor detects a paper jam, the transport belt stops moving, and the head unit is raised to clear the paper jam.

[0006] However, when the power is turned on after being turned off due to a power outage or other reason during image formation, the sensor cannot detect whether paper remains on the conveyor belt. If the image formation operation is resumed with paper remaining on the conveyor belt, there is a risk of paper transport failure or damage to the head unit, as described above. For this reason, when the power is turned on, it is necessary to raise the head unit and visually check whether paper remains on the conveyor belt. However, considering the durability and lifespan, it is preferable to raise and lower the head unit as few times as possible.

[0007] Therefore, taking the above circumstances into consideration, the present invention aims to provide an image forming device that can reduce the number of times the head unit is raised and lowered by detecting the presence or absence of paper on the transport path when the power is turned on after being turned off during image forming operation. [Means for solving the problem]

[0008] In order to achieve the above object, the image forming apparatus of the present invention is characterized by comprising: a transport path along which paper is transported in a predetermined transport direction; a head unit arranged above the transport path and which ejects ink onto paper transported along the transport path to form an image; an elevator device which raises the head unit from a height at which an image can be formed on the paper; an inlet detection sensor which is arranged upstream of the head unit in the transport direction and which detects paper transported below the head unit after a single image forming operation has been started; an outlet detection sensor which is arranged downstream of the head unit in the transport direction and which detects paper transported from below the head unit after the image forming operation has been started; and a control unit which stores the number of inlet sheets of paper detected by the inlet detection sensor and the number of outlet sheets of paper detected by the outlet detection sensor after the image forming operation has been started, and which drives the elevator device to raise the head unit only if the stored number of inlet sheets and the stored number of outlet sheets do not match when the power is turned on after the power has been turned off after the image forming operation has been started.

[0009] In the present invention, the conveying path may have a number of through holes penetrating in the thickness direction and be formed by a conveying belt running in the conveying direction, and the input detection sensor and the output detection sensor may be optical sensors having a light-emitting element and a light-receiving element arranged on either side of the through holes in the conveying belt, and the number of input sheets and the number of output sheets may be detected as the conveying belt runs during the image forming operation.

[0010] In the present invention, the time when the power is turned on after the image forming operation is completed may include the time when the power is turned on at startup and when power is restored after a power outage.

[0011] In the present invention, the number of sheets carried in and the number of sheets carried out may be stored in a nonvolatile memory. [Effects of the Invention]

[0012] According to the present invention, when the power is turned off, it is determined whether paper remains on the transport path below the head unit, and the head unit is raised only if paper remains, thereby reducing the number of times the head unit is raised and lowered. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a front view schematically illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 2 is a block diagram showing a control unit of the image forming apparatus according to the embodiment of the present invention; FIG. [Figure 3] 10 is a flowchart showing steps for calculating the number of sheets of paper carried under a head unit in an image forming apparatus according to an embodiment of the present invention. [Figure 4] 10 is a flowchart showing steps for calculating the number of sheets of paper to be conveyed out from under the head unit in the image forming apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] An image forming apparatus according to an embodiment of the present invention will now be described with reference to the drawings.

[0015] First, the configuration of the image forming apparatus 1 will be described with reference to Fig. 1. Fig. 1 is a front view showing a schematic internal configuration of the image forming apparatus 1.

[0016] The image forming apparatus 1 includes a transport unit 3 that transports paper along a transport direction X, a head unit 5 that forms an image on the paper transported by the transport unit 3 using an inkjet method, a lifting device 7 that raises and lowers the head unit 5, an input detection sensor 9 that is arranged upstream of the head unit 5 in the transport direction X, and an output detection sensor 11 that is arranged downstream of the head unit 5 in the transport direction X.

[0017] First, the conveying unit 3 will be described. The conveying unit 3 includes an endless conveying belt 21, a conveying plate 23 disposed in the hollow portion of the conveying belt 21, and a suction device 25. The conveying belt 21 has a large number of through holes formed therethrough in the thickness direction. The large number of through holes are preferably arranged at equal intervals along the conveying direction X and the width direction (a direction intersecting with the conveying direction X).

[0018] The conveyor belt 21 is wound around a drive roller 27 and a driven roller 29. The drive roller 27 is driven to rotate by a motor (not shown), causing the conveyor belt 21 to run counterclockwise in Fig. 1. The outer surface of the conveyor belt 21 running on the upper track is the conveyor surface 21a (also called the conveyor path) along which the paper is conveyed.

[0019] The conveying plate 23 is in contact with the inner peripheral surface (the surface behind the conveying surface 21a) of the conveying belt 21 that runs on the upper track. When the conveying belt 21 runs, the inner peripheral surface of the conveying belt 21 slides along the upper surface of the conveying plate 23. The conveying plate 23 has a large number of through holes formed all over its surface that penetrate in the thickness direction. The suction device 25 is disposed below the conveying plate 23. When the suction device 25 is driven, air is sucked in through the through holes of the conveying belt 21 and the conveying plate 23. This attracts the paper to the conveying surface 21a.

[0020] An upstream guide plate 31 and a downstream guide plate 33 are arranged on the upstream and downstream sides of the transport unit 3 in the transport direction X. The paper is transported from the upstream guide plate 31 to the transport unit 3, and then from the transport unit 3 to the downstream guide plate 33.

[0021] Next, the head unit 5 will be described. The head unit 5 includes four head units 5Bk, 5C, 5M, and 5Y (collectively referred to as head unit 5) corresponding to four colors of ink (black, cyan, magenta, and yellow). The four head units 5Bk, 5C, 5M, and 5Y are lined up in order along the transport direction X. Each head unit 5 includes three print heads 41 and a plate 43 that supports the three print heads 41. The three print heads 41 are arranged in a staggered pattern along the width direction so that they are approximately the same as the width of the paper, and are supported by the plate 43.

[0022] Each print head 41 has a number of nozzles and a piezoelectric element attached to each nozzle. The nozzle outlets open to the bottom surface of the print head 41. When a voltage is applied to the piezoelectric element, the piezoelectric element deforms, causing ink in the nozzle to be ejected downward from the outlet.

[0023] 1, the head unit 5 is disposed above the transport surface 21a of the transport belt 21 of the transport unit 3. A predetermined gap allowing paper to pass through is provided between the lower surface of the head unit 5 (the ink ejection ports of the print head 41) and the transport surface 21a of the transport belt 21. The height of the head unit 5 at the predetermined gap from the transport surface 21a is defined as the image formation height.

[0024] Next, the lifting device 7 will be described. The lifting device 7 raises the head unit 5 to a retraction height that is higher than the image formation height. The lifting device 7 is a rack-and-pinion mechanism that has a rack that is provided on the head unit 5 and extends in the vertical direction, and a pinion that is supported on the housing of the image forming apparatus 1 and engages with the rack. By rotating the pinion in one direction, the rack, i.e., the head unit 5, rises from the image formation height to the retraction height (see the two-dot chain line in Figure 1). By rotating the pinion in the other direction, the head unit 5 descends from the retraction height to the image formation height.

[0025] Next, the carry-in detection sensor 9 will be described. The carry-in detection sensor 9 is disposed above the upstream guide plate 31 and in close proximity to the transport unit 3. The carry-in detection sensor 9 is a reflective optical sensor equipped with a light emitter and a light receiver. The light emitter emits light toward the downstream upstream guide plate 31, and the light receiver receives the light reflected by the upstream guide plate 31. The detection result of the carry-in detection sensor 9 (the amount of light received by the light receiver) is input to the control unit 51 (see FIG. 2).

[0026] Next, the discharge detection sensor 11 will be described. The discharge detection sensor 11 is disposed above the downstream guide plate 33 and in the vicinity of the transport unit 3. The discharge detection sensor 11 is also a reflective optical sensor equipped with a light emitter and a light receiver. The light emitter emits light downward toward the downstream guide plate 33, and the light receiver receives the light reflected by the downstream guide plate 33. The detection result of the discharge detection sensor 11 (the amount of light received by the light receiver) is input to the control unit 51 (see FIG. 2).

[0027] Next, the control unit 51 will be described with reference to the block diagram of Fig. 2. The control unit 51 includes a non-volatile memory 53 for storing data.

[0028] The control unit 51 controls the pinion of the lifting device 7 to rotate the pinion to raise the head unit 5 from the image formation height to the retraction height, or to lower the head unit 5 from the retraction height to the image formation height.

[0029] As described above, the control unit 51 also receives detection results from the carry-in detection sensor 9 and the carry-out detection sensor 11. The control unit 51 determines the presence or absence of an object based on the amount of light received. In other words, when no paper is being transported through the upstream guide plate 31 or the downstream guide plate 33, the light emitted from the light emitter is reflected by both guide plates and received by the light receiver. On the other hand, when paper is being transported through the upstream guide plate 31 or the downstream guide plate 33, the light emitted from the light emitter is reflected by the paper and received by the light receiver. Because the reflectance of the guide plates and the paper differ, the presence or absence of paper is detected based on the difference in the amount of light received.

[0030] When the incoming detection sensor 9 detects paper, the control unit 51 determines that paper has been brought in below the head unit 5, and when the outgoing detection sensor 11 detects paper, the control unit 51 determines that paper has been transported out from below the head unit 5. Furthermore, from this determination result, the control unit 51 calculates the number of sheets of paper that have been brought in below the head unit 5 (number of incoming sheets) and the number of sheets of paper that have been transported out from below the head unit 5 (number of outgoing sheets) after one image forming operation has started.

[0031] Next, a method for calculating the number of sheets carried in and the number of sheets carried out after a single image forming operation has started will be described with reference to the flowcharts in Figures 3 and 4. When the image forming operation starts, the control unit 51 lowers the head unit 5 to the image formation height. The control unit 51 drives the motor of the transport unit 3 to move the transport belt 21. The paper is transported from the upstream guide plate 31 to the transport belt 21. Then, ink is ejected from each print head 41 of the head unit 5 in accordance with image data, and an image is formed on the paper. The paper with the image formed is transported from the head unit 5 to the downstream guide plate 33.

[0032] First, calculation of the number of sheets carried in will be described with reference to Fig. 3. When the image forming operation starts, in step S1, the number of sheets carried in N is set to zero (N = 0). Next, in step S2, it is determined whether or not a sheet has been carried in below the head unit 5 using the method described above, based on the detection result of the carry-in detection sensor 9. If it is determined in step S2 that a sheet has been carried in below the head unit 5, in step S3, the number of sheets carried in N is incremented (N = N + 1). Control unit 51 repeats the processing of step S2 until it is determined that a sheet has been carried in below the head unit 5.

[0033] Next, in step S4, control unit 51 stores the number of sheets carried in N in nonvolatile memory 53 of control unit 51. Then, proceeding to step S5, control unit 51 determines whether or not the power to image forming apparatus 1 has been turned off. Control unit 51 repeats the determination in step S5 until it is determined in step S5 that the power has been turned off.

[0034] As a result, the nonvolatile memory 53 stores the number N of sheets of paper that have been conveyed below the head unit 5 from the time the image forming operation is started until the power is turned off.

[0035] Next, calculation of the number of sheets to be conveyed will be described with reference to FIG. 4. When the image forming operation starts, in step S11, the number of sheets to be conveyed M is set to zero (M=0). Next, in step S12, it is determined whether or not the paper has been conveyed from below the head unit 5 using the method described above, based on the detection result of the conveyance detection sensor 11. If it is determined in step S12 that the paper has been conveyed from below the head unit 5, in step S13, the number of sheets to be conveyed M is incremented (M=M+1). The control unit 51 repeats the process of step S12 until it is determined that the paper has been conveyed from below the head unit 5.

[0036] Next, in step S14, control unit 51 stores the number of sheets to be discharged M in nonvolatile memory 53 of control unit 51. Then, the process proceeds to step S15, where control unit 51 determines whether or not the power supply to image forming apparatus 1 has been turned off. Control unit 51 repeats the determination in step S15 until it is determined in step S15 that the power supply has been turned off.

[0037] As a result, the nonvolatile memory 53 stores the number M of sheets of paper that have been conveyed out from below the head unit 5 from the time the conveyor belt 21 starts to run until the power is turned off.

[0038] The operation of image forming apparatus 1 having the above configuration after the power is turned off after the start of image forming operation will be described. After the image forming operation has started, if the power is turned off due to a power outage, for example, the image forming operation will end. When the power is turned on to resume the image forming operation, first, control unit 51 reads the number of sheets N that have been carried in and the number of sheets M that have been calculated as described above and stored in nonvolatile memory 53, and determines whether the number of sheets N that have been carried in and the number of sheets M that have been carried out match.

[0039] If they match, the control unit 51 resumes the image forming operation. In other words, since the number of sheets carried in and the number of sheets carried out are the same, all of the sheets carried in below the head unit 5 have been carried out from below the head unit 5. In other words, no sheets remain below the head unit 5. Therefore, there will be no problem if the image forming operation is started and the conveyor belt 21 is made to run.

[0040] On the other hand, if they do not match, the control unit 51 determines that paper remains on the transport surface 21a. In other words, if the number of sheets carried in is greater than the number of sheets carried out, it is possible that some of the sheets carried in below the head unit 5 have not been carried out from below the head unit 5, and that paper remains below the head unit 5. Therefore, if the image formation operation is resumed as is, the remaining paper will interfere with the newly transported paper, causing transport problems. Therefore, in this case, the control unit 51 controls the elevator device 7 to raise the head unit 5 and open the transport surface 21a. Then, the paper remaining on the transport surface 21a is removed. Thereafter, the control unit 51 controls the elevator device 7 to lower the head unit 5 to the image formation height and resume the image formation operation. Specifically, the transport belt 21 is caused to run. When the image formation operation is resumed, the control unit 51 rewrites the number of sheets carried in N and the number of sheets carried out M stored in the non-volatile memory to zero (N=0, M=0).

[0041] As is clear from the above explanation, according to the present invention, it is possible to determine whether or not paper remains on transport surface 21a below head unit 5 when the power is turned off, without raising head unit 5. Then, only if paper remains, head unit 5 is raised to remove the paper remaining on transport surface 21a, and then image formation operation is resumed. In other words, if no paper remains on transport surface 21a below head unit 5 when the power is turned off, head unit 5 is not raised, so the number of times head unit 5 is raised and lowered can be reduced.

[0042] Furthermore, since the number of sheets carried in and the number of sheets carried out are stored in the nonvolatile memory 53, the data on the number of sheets carried in and the number of sheets carried out is stored even after the power of the image forming apparatus 1 is turned off.

[0043] In the above embodiment, the case where the power is turned on to resume image forming operation after being turned off due to a power outage has been described, but when the power is turned on at startup, the remaining paper may also be determined from the number of sheets brought in and the number of sheets taken out, as described above.

[0044] The carry-in detection sensor 9 and the carry-out detection sensor 11 may be disposed above the conveying surface 21 a of the conveyor belt 21 on the upstream side and downstream side of the head unit 5 .

[0045] In this case, a transmission-type optical sensor may be used instead of a reflective optical sensor. When a transmission-type optical sensor is used, in addition to the aforementioned through-holes for attracting paper, detection through-holes are formed in the conveyor belt 21. The detection through-holes have a larger diameter than the paper-attracting through-holes and are formed at predetermined intervals along the conveyance direction X. The light-emitting unit and light-receiving unit of the transmission-type optical sensor are arranged with the detection through-hole in the conveyor belt 21 in between. When light emitted from the light-emitting unit passes through the detection through-hole, it is received by the light-receiving unit, but when it is irradiated onto the conveyor belt 21, it is not received by the light-receiving unit.

[0046] The detection through-holes are formed at predetermined intervals, so that the light receiving unit receives light at a constant cycle when the conveyor belt 21 moves. On the other hand, when paper is conveyed onto the conveying surface 21a of the conveyor belt 21, the detection through-holes are blocked by the paper, and the light receiving cycle of the light receiving unit changes. The control unit 51 detects the paper based on this change in cycle and calculates the number of sheets fed in and the number of sheets fed out.

[0047] Although the present invention has been described with reference to specific embodiments, the present invention is not limited to the above embodiments, and those skilled in the art may modify the above embodiments without departing from the scope and spirit of the present invention. [Explanation of symbols]

[0048] 1. Image forming device 5 Head Unit 7 Lifting device 9. Loading detection sensor 11. Carry-out detection sensor 21a Conveying surface (conveying path) 51 Control section 53 Non-volatile memory

Claims

1. a conveyance path along which the paper is conveyed in a predetermined conveyance direction; a head unit disposed above the transport path and configured to eject ink onto paper transported along the transport path to form an image; an elevating device that elevates the head unit from a height at which an image can be formed on paper; an input detection sensor that is disposed upstream of the head unit in the transport direction and detects paper that is input below the head unit after a single image forming operation has started; a conveyance detection sensor that is disposed downstream of the head unit in the conveyance direction and detects paper that has been conveyed out from below the head unit after the image forming operation has started; an image forming apparatus characterized by comprising: a control unit that stores the number of sheets of paper introduced detected by the input detection sensor and the number of sheets of paper taken out detected by the output detection sensor after the image forming operation has started, and that drives the lifting device to raise the head unit when the power is turned on after being turned off after the image forming operation has started, only if the stored number of sheets introduced and the number of sheets taken out do not match.

2. 2. The image forming apparatus according to claim 1, wherein the power-on time includes a start-up time and a recovery time from a power outage.

3. 2. The image forming apparatus according to claim 1, wherein the control unit includes a nonvolatile memory for storing the number of sheets carried in and the number of sheets carried out.

Images