Image forming device

Abstract

To provide an image formation device which enables reduction of failure, such as color drift, caused by temperature.SOLUTION: An image formation device includes: an inter-device heater 53 which heats the interior of a housing; recording heads which are housed in the housing and provided for each color of inks; head heaters 85 which are respectively provided at the recording heads and heat the inks housed in the recording heads; temperature sensors 83 which detect temperatures of the respective recording heads; and a control unit 101 which drives the inter-device heater 53 until the temperatures of the inks based on the detection results of the temperature sensors 83 reach a print permission temperature and controls driving of the head heaters 85 so as to maintain the print permission temperature after the temperatures reach the print permission temperature.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an ink jet type image forming apparatus having a recording head provided for each color of ink. [Background technology]

[0002] In an inkjet image forming apparatus, various problems such as color misregistration (print position misalignment) and ink ejection failure can occur depending on the temperature inside the apparatus.

[0003] For example, color misregistration occurs as follows. Generally, the recording heads are arranged along the conveying direction of the sheet conveyed by the conveying belt. The timing of ink ejection from each recording head is set based on the running speed of the sheet within a predetermined temperature range. However, when the temperature inside the machine is lower than the predetermined temperature range, the head base holding the recording head shrinks, causing the position of the recording head in the conveying direction to deviate from the predetermined position, or the diameter of the driving roller or driven roller around which the conveying belt is wrapped shrinks, causing the running position of the sheet to change, causing the relative positional relationship between the recording head and the sheet in the conveying direction to change from the predetermined positional relationship. Then, as described above, the position of the ink ejected at a constant ejection timing deviates from the predetermined position in the conveying direction, causing color misregistration (printing position deviation). Also, when the ink is low in temperature, the viscosity is high, causing ejection failure.

[0004] Regarding the problem of color misregistration, Patent Document 1 discloses an image forming apparatus that detects the amount of fluctuation in the angular velocity of a rotating body (corresponding to a drive roller) to reduce color misregistration in the transport direction. Patent Document 2 discloses a printing device (corresponding to an image forming apparatus) that corrects color misregistration by comparing a printed test pattern with a print. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-301768 A [Patent Document 2] JP 2016-182759 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the image forming apparatuses disclosed in Patent Documents 1 and 2, no consideration is given to color misregistration and ink ejection defects caused by temperature.

[0007] SUMMARY OF THE PRESENT DISCLOSURE In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of reducing defects such as color shift caused by temperature. [Means for solving the problem]

[0008] In order to solve the above problems, the image forming apparatus of the present invention is characterized in that it comprises an in-machine heater that heats the inside of a housing, a recording head housed in the housing and provided for each color of ink, a head heater provided in each of the recording heads and heats the ink contained in the recording head, a temperature sensor that detects the temperature of each of the recording heads, and a control unit that drives the in-machine heater until the temperature of the ink based on the detection result of the temperature sensor reaches a print-permitted temperature, and after the print-permitted temperature is reached, controls the drive of the head heater so as to maintain the print-permitted temperature.

[0009] In the image forming apparatus according to the present invention, the control unit may start a printing operation after each of the inks has reached the print-allowing temperature.

[0010] In the image forming apparatus of the present invention, an operation unit may be further provided that enables a user to select a print priority mode that permits printing even when the ink has not reached the permissible print temperature, and the operation unit may be characterized in that a message indicating that print quality is not guaranteed is displayed when the print priority mode is selected. Effect of the Invention

[0011] According to the present invention, in the case of a low-temperature environment, printing operations are started after the temperature inside the device (including the temperature of the ink in each recording head) has uniformly increased to the print-permitting temperature, thereby reducing the occurrence of color misregistration. [Brief description of the drawings]

[0012] [Figure 1] 1 is a front view showing a schematic internal structure of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a perspective view showing a schematic diagram of a head unit in the image forming apparatus according to one embodiment of the present invention. [Figure 3A] 1 is a cross-sectional view showing a recording head in an image forming apparatus according to an embodiment of the present invention. [Figure 3B] 2 is a cross-sectional view showing a discharge unit of a recording head in an image forming apparatus according to one embodiment of the present invention. FIG. [Figure 4] 2 is a block diagram showing a control unit of the image forming apparatus according to the embodiment of the present invention; [Diagram 5] 11 is a graph showing an example of a relationship between the amount of color misregistration and the elapsed time from power-on. [Figure 6] 5 is a graph showing the relationship between the temperature change of the head and the elapsed time from power-on in the image forming apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[0014] The image forming apparatus 1 will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a front view showing a schematic internal configuration of the image forming apparatus 1, and Fig. 2 is a perspective view showing the head unit 25. Fr, Rr, L, and R in each drawing indicate the front, rear, left, and right sides of the image forming apparatus 1.

[0015] The image forming apparatus 1 includes a box-shaped housing 3. The lower portion of the housing 3 accommodates a paper feed tray 5 for storing sheets, and a paper feeder 7 for feeding sheets from the paper feed tray 5 and transporting them to a first transport path 9. The first transport path 9 is formed at the right end inside the housing 3, extending upward from the paper feeder 7.

[0016] Above the paper feed tray 5, the first conveying section 11 and the second conveying section 13 are arranged side by side. The first conveying section 11 includes an endless first conveying belt 15 wound around a driving roller and a driven roller, and a suction unit 17 arranged in a hollow part of the first conveying belt 15. The first conveying belt 15 circulates and runs in a counterclockwise direction in FIG. 1. The second conveying section 13 includes an endless second conveying belt 19 wound around a driving roller and a driven roller, and a suction unit 21 arranged in a hollow part of the second conveying belt 19. The second conveying belt 19 circulates and runs in a counterclockwise direction in FIG. 1. The sheet conveyed along the first conveying path 9 is sucked by the upper running surface of the first conveying belt 15 and the upper running surface of the second conveying belt 19 by the suction units 17 and 21, respectively, and is conveyed along the running direction. In the following description, the upstream side and the downstream side refer to the upstream side and the downstream side in the sheet conveying direction. The direction perpendicular to the sheet conveying direction is defined as the width direction.

[0017] A head unit 25 is provided above the first transport section 11. As shown in Fig. 2, the head unit 25 includes four line heads 27 corresponding to four colors of ink (yellow, magenta, cyan, and black), and a base plate 29 that supports the four line heads 27. The four line heads 27 are arranged in parallel along the sheet transport direction X (left-right direction) and are supported by the base plate 29.

[0018] Each line head 27 includes three recording heads 31. Each recording head 31 has a rectangular parallelepiped shape that is long in the width direction Y (front-rear direction), and is arranged in a staggered pattern along the width direction Y. Each recording head 31 includes a large number of nozzles that are arranged in the transport direction X and the width direction Y. The recording heads 31 will be described later. Each recording head 31 ejects ink downward from the nozzles to form an image on the sheet transported by the first transport belt 15.

[0019] 1 again, a second transport path 37 is provided between the downstream side of the second transport unit 13 and a discharge opening 35 formed on the left side surface of the housing 3. A discharge tray 39 is supported below the discharge opening 35 on the left side surface of the housing 3. The sheet transported along the second transport path 37 is discharged from the discharge opening 35 and stacked on the discharge tray 39.

[0020] The second transport path 37 branches into a third transport path 41 upstream of the discharge port 35. The third transport path 41 has a switchback path. The third transport path 41 merges with the first transport path 9 upstream of the first transport section 11. A manual feed transport path 47 is formed between the junction of the first transport path 9 and the third transport path 41 and a manual feed port 45 formed on the right side surface of the housing 3. A manual feed tray 49 is supported below the manual feed port 45 on the right side surface of the housing 3.

[0021] Furthermore, ink containers 51 that contain four colors of ink are disposed in the housing 3. Each ink container 51 is connected to a corresponding line head 27 via a sub-ink tank (not shown). An in-machine heater 53 is provided near the ink container 51. The in-machine heater 53 includes a ceramic heater 55 and a fan 57, and generates hot air directed toward the inside of the housing 3 to heat the inside of the machine. An in-machine temperature sensor 59 is also provided inside the housing 3.

[0022] Next, the printing operation will be briefly described. A sheet fed from the paper feed cassette 5 by the paper feed device 7 and conveyed along the first conveying path 9, or a sheet fed from the manual feed tray 49 and conveyed from the manual feed port 45 along the manual feed conveying path 47, is conveyed to the first conveying section 11. In the first conveying section 11, the sheet is sucked onto the upper running surface of the first conveying belt 15 by the suction unit 17, and conveyed along with the movement of the first conveying belt 15. At this time, ink is discharged from the nozzles of the recording heads 31 of each line head 27 of the head unit 25, and an image is formed on the sheet. The sheet on which the image has been formed is conveyed to the second conveying section 13. In the second conveying section 13, the sheet is sucked onto the upper running surface of the second conveying belt 19 by the suction unit 21, and conveyed along with the movement of the second conveying belt 19. The sheet is conveyed from the second conveying section 13 along the second conveying path 37, discharged from the discharge port 35, and stacked on the discharge tray 39.

[0023] In the case of double-sided printing, a sheet with an image formed on one side thereof is transported from the second transport path 37 to the third transport path 41. The sheet is turned over while being transported along the third transport path 41, and then transported to the first transport section 11, where ink is ejected from the nozzles of the recording heads 31 of each line head 27 of the head unit 25 to form an image on the other side of the sheet. The sheet with the image formed thereon is transported from the second transport section 13 along the second transport path 37, discharged from the discharge port 35, and stacked on the discharge tray 39.

[0024] Next, the recording head 31 will be described with reference to Figures 3A and 3B. Figure 3A is a cross-sectional view of the recording head 31, and Figure 3B is a cross-sectional view of the recording head 31.

[0025] As shown in FIG. 3A, the recording head 31 has an ink containing portion 31a formed along the width direction Y, and an ink ejection portion 31b provided below the ink containing portion 31a.

[0026] An ink reservoir 71 is provided in the ink storage section 31a. The ink reservoir 71 is divided into upper and lower compartments by a filter 73. An inlet tube 77 is connected to one end of the upper wall of the ink storage section 31a in the width direction Y, and an outlet tube 79 is connected to the other end. Both tubes 77, 79 communicate with the upper compartment of the ink reservoir 71. Ink supplied to the upper compartment of the ink reservoir 71 through the inlet tube 77 passes through the filter 73 and is supplied to the lower compartment. Meanwhile, ink that does not pass through the filter 73 is discharged through the outlet tube 79.

[0027] In addition, a head temperature sensor 83 is provided on the top wall of the ink containing section 31a. The head temperature sensor 83 detects the temperature of the side wall. Furthermore, a head heater 85 is provided on the side wall of the ink containing section 31a. The head heater 85 is, for example, a tip heater, and heats the side wall to heat the ink in the ink reservoir 71.

[0028] The ink ejection section 31b has a common flow path 75 that communicates with a section below the ink reservoir 71 of the ink storage section 31a. In the common flow path 75, a plurality of ejection units 81 are provided side by side in the width direction Y and the transport direction X.

[0029] As shown in FIG. 3B, each ejection unit 81 has a pressure chamber 91 that communicates with the common flow path 75, and a nozzle 93 that opens downward from the pressure chamber 91. An actuator 95 is provided in the pressure chamber 91. The actuator 95 is, for example, a piezoelectric element. When a voltage is applied to the piezoelectric element, the piezoelectric element is deformed due to the inverse piezoelectric effect. The deformation of the piezoelectric element is transmitted to the pressure chamber 91, which is compressed. As a result, ink sent from the common flow path 75 to the pressure chamber 91 is pressurized and ejected from the nozzle 93.

[0030] Next, the control unit 101 will be described with reference to the block diagram of Fig. 4. Detection results are sent to the control unit 101 from the in-machine temperature sensor 59 (see Fig. 1) and the head temperature sensor 83 (see Fig. 3A). The control unit 101 estimates the in-machine temperature and the temperature of the ink in the line head 27 based on the detection results sent from both temperature sensors 59, 83. The control unit 101 is also electrically connected to the in-machine heater 53 and the head heater 85, and turns on or off (drives) the in-machine heater 53 and the head heater 85 based on the estimated in-machine temperature and ink temperature.

[0031] An example of temperature control of the image forming apparatus 1 having the above configuration will be described with reference to Fig. 1, Fig. 3A, etc. When the image forming apparatus 1 is turned on from a power-off state, the control unit 101 first turns on the in-machine heater 53. When the in-machine heater 53 is driven, the temperature inside the housing 3 rises, and the temperatures of the housing 3 itself, the head unit 25 described above, and each part such as the drive roller and driven roller of the first and second transport belts 15 and 19 of the first and second transport units 11 and 13 rise.

[0032] The control unit 101 permits the start of printing operation after the ink temperature estimated based on the detection result of the head temperature sensor 83 reaches the print-permitted temperature (e.g., 26°C) in all recording heads 31. After the printing operation is started, the control unit 101 turns the head heater 85 on or off based on the detection result of the head temperature sensor 83 to maintain the ink temperature at the print-permitted temperature. In addition, the control unit 101 turns the in-machine heater 53 on or off based on the temperature detected by the in-machine temperature sensor 59 to maintain the in-machine temperature constant.

[0033] 1, the head unit 25 is relatively far from the in-machine heater 53, and furthermore, the ink reservoir 71 (see FIG. 3A) of the recording head 31 in which the ink used for printing is stored is provided inside the recording head 31, so the temperature of the ink in the ink reservoir 71, i.e., the ink used for printing, is less likely to rise compared to other parts. For this reason, as described above, if the temperature inside the machine is lower than a predetermined temperature, color shift (print position shift) is likely to occur.

[0034] An example of color misregistration will be described with reference to the graph in Fig. 5. The vertical axis of the graph indicates the amount of color misregistration (dots), and the horizontal axis indicates the time (minutes) elapsed since the power was turned on (internal heater 53 was turned on). In this example, a case will be described where the environmental temperature is a low temperature (15°C) lower than the reference temperature (20 to 23°C).

[0035] As shown in the graph, the color shift is large, about 1 dot, immediately after the power is turned on. The color shift gradually decreases as time passes, and becomes almost zero after about 150 minutes.

[0036] That is, when the internal heater 53 is turned on, the temperature inside the device rises, and the temperatures of the above-mentioned housing 3 itself, the head unit 25, and each part such as the drive roller and driven roller of the first and second transport belts 15 and 19 of the first and second transport sections 11 and 13 gradually rise, but it can be seen that a certain time (150 minutes in this example) is required until color misregistration is zero, that is, until the ink temperature reaches the appropriate printable temperature. To prevent color misregistration, it is necessary to start the printing operation after the entire image forming apparatus 1 (including the above-mentioned parts and ink) has reached a uniform printable temperature.

[0037] Next, the temperature rise tendency of each part of the image forming apparatus 1 will be described with reference to the graph in Fig. 6. The vertical axis of the graph indicates temperature change (°C), and the horizontal axis indicates elapsed time (min). The two-dot chain line in the graph indicates the detection result of the head temperature sensor 83 when the in-machine heater 53 and head heater 85 are turned on simultaneously with the power being turned on, the dashed line indicates the detection result of the temperature sensor (not shown) arranged around the recording head 31 when the in-machine heater 53 is turned on simultaneously with the power being turned on, and the solid line indicates the detection result of the head temperature sensor 83 when the in-machine heater 53 is turned on simultaneously with the power being turned on. The environmental temperature is 14°C.

[0038] As shown by the two-dot chain line in the graph, when the internal heater 53 and head heater 85 are turned on at the same time as the power is turned on, the temperature detected by the head temperature sensor 83 rises rapidly, rising by 12°C after about three minutes and almost reaching the printable temperature. When the head heater 85 is turned on in this way, the temperature of the recording head 31 rises rapidly and reaches the printable temperature, but as explained with reference to the graph in Figure 5, the components inside the housing 3 are not sufficiently heated and do not reach the printable temperature. For this reason, if a printing operation is performed under these circumstances, color shifts may occur.

[0039] Also, as shown by the dashed line in the graph, when the internal heater 53 is turned on at the same time as the power is turned on, the temperature around the recording head 31 rises, but the degree of rise is not uniform and there is a large amount of variation. For this reason, for example, if the start of a printing operation is determined based on the temperature around the recording head 31, the printing operation may be performed before the entire image forming apparatus 1 (including the above-mentioned components and ink) has necessarily reached a uniform print-permitted temperature.

[0040] On the other hand, as shown by the solid line in the graph, when the internal heater 53 is turned on at the same time as the power is turned on, the temperature detected by the head temperature sensor 83 gradually rises at an almost uniform rate, and the amount of fluctuation is small. In other words, the temperature around the ink reservoir 71 of the recording head 31 starts to rise later than the surrounding area, in other words, it is difficult to heat up, but it is less affected by the external environment, and the temperature rises in proportion to the temperature rise caused by the internal heater 53. Also, since the difficult-to-heat areas rise to the printable temperature in this way, it can be estimated that the entire inside of the machine has almost reached the printable temperature. Therefore, it is preferable to determine that the entire image forming apparatus 1 (including the above-mentioned components and ink) has reached a uniform printable temperature based on the detection result of the head temperature sensor 83, and then execute the printing operation.

[0041] After the printing operation has started, the control unit 101 turns on or off the in-machine heater 53 based on the detection result of the in-machine temperature sensor 59 to maintain the temperature inside the machine at a predetermined temperature. Meanwhile, the control unit 101 turns on or off the head heater 85 based on the detection result of the head temperature sensor 83 to maintain the temperature of the ink at a predetermined temperature. As shown by the two-dot chain line in the graph in Figure 6, the ink has high sensitivity to the head heater 85, so the ink temperature can be adjusted with good sensitivity.

[0042] As described above, according to the present invention, in a low-temperature environment, printing operation is started after the temperature inside the device (including the temperature of the ink in each recording head 31) has uniformly risen to the printable temperature, so the occurrence of color misregistration can be reduced. In addition, after the temperature has risen to the printable temperature, the temperature of each recording head 31 is adjusted by turning the head heater 85 on and off, so the ink temperature can be adjusted with high sensitivity.

[0043] As described with reference to the graph in FIG. 5, a certain time (150 minutes in the above example) is required to raise the temperature inside the device until color misregistration no longer occurs. However, there may be cases where the user wishes to start the printing operation before the certain time has elapsed. In this case, the control unit 101 may permit the printing operation regardless of the ink temperature. In this case, a print priority mode that permits the printing operation regardless of the ink temperature is provided in the operation unit 1a (see FIG. 1) of the image forming apparatus 1, and when the print priority mode is selected, a message indicating that the quality is not guaranteed is displayed on the operation unit 1a. When the user selects the print priority mode, the control unit 101 permits the printing operation regardless of the detection result of the head temperature sensor 83.

[0044] 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]

[0045] 1. Image forming device 1a Control section 3. Chassis 31 Recording head 53 In-flight heater 83 Head temperature sensor (temperature sensor) 85 Head heater 101 Control section

Claims

1. A housing provided with a transport path along which a sheet is transported; an internal heater that generates hot air directed toward the inside of the housing to heat the inside of the housing including the conveying path; a recording head housed in the housing and provided for each color of ink; a head heater provided in each of the recording heads for heating the ink contained in the recording head; a temperature sensor for detecting the temperature of each of the recording heads; a control unit that drives the in-machine heater until the temperature of the ink based on the detection result of the temperature sensor reaches a printable temperature, and after the printable temperature is reached, controls the drive of the head heater so as to maintain the printable temperature.

2. 2. The image forming apparatus according to claim 1, wherein the control unit starts a printing operation after each of the inks reaches the print-allowing temperature.

3. an operation unit that enables a user to select a print priority mode that permits printing even when the ink has not reached the print permission temperature; 2. The image forming apparatus according to claim 1, wherein a message is displayed on the operation unit, indicating that print quality is not guaranteed when the print priority mode is selected.

Images