JP2019018364A - Inkjet recording device - Google Patents

Abstract

To provide an inkjet recording device configured so that one sensor can detect a distance between a recording medium and the sensor and a density of an image.SOLUTION: An inkjet recording device 100 comprises a recording head 34, a carrying part 4, a sensor 7 and a control part 9. The sensor 7 is arranged at an upstream side in a carrying direction D3 of a paper P with respect to the recording head 34. The sensor 7 executes a first detection operation for detecting a distance HS between the sensor 7 and the paper P and a second detection operation for detecting a density D of an image formed in the paper P. The control part 9 comprises a first detection part 901 and a second detection part 902. The first detection part 901 controls the sensor 7 so that the sensor 7 executes the first detection operation. The carrying part 4 carries the paper P, without reversing the paper P, from a downstream side in the carrying direction D3 of the paper P with respect to the recording head 34 to an upstream side in the carrying direction D3 of the paper P with respect to the recording head 34. The second detection part 902 controls the sensor 7 so that the sensor 7 executes the second detection operation.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ink jet recording apparatus.

  The ink jet recording apparatus described in Patent Document 1 includes a recording head, a distance sensor, an actuator, and a control unit. The distance sensor detects a distance between the recording head and the upper surface of the substrate. The actuator moves the recording head in the vertical direction. The controller controls the actuator based on the detection result of the distance sensor to adjust the distance between the recording head and the upper surface of the substrate.

JP 11-291475 A

  However, in the ink jet recording apparatus described in Patent Document 1, it is necessary to arrange a density sensor in order to detect the density of an image. Therefore, it is necessary to dispose the distance sensor and the density sensor, and the manufacturing cost increases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ink jet recording apparatus in which a single sensor can detect a distance from a recording medium and an image density.

  An ink jet recording apparatus according to the present invention includes a recording head, a transport mechanism, a sensor, and a control unit. The recording head forms an image on a recording medium. The transport mechanism is configured so that the front and back of the recording medium are not reversed from the downstream side in the transport direction of the recording medium to the upstream side in the transport direction of the recording medium with respect to the recording head. Transport the recording medium. The sensor is disposed upstream of the recording head in the conveyance direction of the recording medium and on the same side as the recording head with respect to the mounting surface of the recording medium. The placement surface indicates a surface on which the recording medium is placed when the recording head forms an image on the recording medium. The sensor is configured to be capable of executing a first detection operation for detecting a distance between the sensor and the recording medium and a second detection operation for detecting the density of the image formed on the recording medium. . The control unit controls the sensor so that the sensor performs the first detection operation and the second detection operation.

  According to the ink jet recording apparatus of the present invention, one sensor can detect the distance to the recording medium and the image density.

1 is a diagram illustrating a configuration of an ink jet recording apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the control part which concerns on embodiment of this invention. It is a figure which shows the structure of a sensor. (A) It is a figure which shows the change of a 1st voltage and a 2nd voltage. (B) It is a figure which shows the change of a voltage difference. It is a figure which shows the relationship between distance and a voltage difference. It is a flowchart which shows the process of a control part. It is a flowchart which shows the density | concentration detection process of a control part. It is a flowchart which shows the head raising / lowering process of a control part.

  Embodiments of the present invention will be described below with reference to the drawings (FIGS. 1 to 8). In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof is not repeated.

  First, an ink jet recording apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration of an inkjet recording apparatus 100 according to the present embodiment. As shown in FIG. 1, the inkjet recording apparatus 100 includes a housing 1, a feeding unit 2, an image forming unit 3, a transport unit 4, a discharge unit 5, a discharge tray 6, a sensor 7, a lifting mechanism 8, and a control unit 9. Prepare. The housing 1 accommodates a feeding unit 2, an image forming unit 3, a conveying unit 4, a discharging unit 5, a sensor 7, an elevating mechanism 8 and a control unit 9.

  The feeding unit 2 is disposed below the inside of the housing 1. The feeding unit 2 includes a feeding cassette 21 and a feeding roller 22. The feeding cassette 21 stores paper P and is detachable from the housing 1. The feeding unit 2 feeds the paper P to the transport unit 4. The paper P corresponds to an example of “recording medium”.

  The image forming unit 3 is disposed above the feeding unit 2. The image forming unit 3 forms an image on the paper P. The image forming unit 3 includes a pressing roller 31, a conveyance belt 32, a recording head 34, and a head base 35. The recording head 34 includes a recording head 34a, a recording head 34b, a recording head 34c, and a recording head 34d.

  The presser roller 31 presses the paper P sent from the transport roller pair 411 toward the transport belt 32, and sends the paper P to the recording head 34.

  The conveyance belt 32 sends the paper P sent from the conveyance roller pair 411 to the discharge unit 5 via the lower side of the recording head 34.

  The recording head 34a stores cyan ink. The recording head 34b stores magenta ink. The recording head 34c stores yellow ink. Black ink is stored in the recording head 34d. A color image is formed on the paper P by the recording heads 34a to 34d.

  The head base 35 supports the recording head 34. The head base 35 is a flat plate-like member extending along the transport direction D3 of the paper P. On the head base 35, recording heads 34a to 34d are arranged in order along the transport direction D3 of the paper P.

  The transport unit 4 transports the paper P fed from the feeding unit 2. The transport unit 4 includes a first transport unit 41, a second transport unit 42, a third transport unit 43, a fourth transport unit 44, a fifth transport unit 45, and a sixth transport unit 46. The transport unit 4 corresponds to an example of a “transport mechanism”.

  The first transport unit 41 transports the paper P fed from the feeding unit 2 to the image forming unit 3. The first transport unit 41 includes a transport roller pair 411. The conveyance roller pair 411 sends the paper P to the image forming unit 3 in accordance with the image forming timing.

  The second transport unit 42 transports the paper P discharged from the discharge unit 5 to the third transport unit 43 or the fourth transport unit 44. Specifically, when the paper P is reversed, the second transport unit 42 transports the paper P to the third transport unit 43. If the paper P is not reversed, the second transport unit 42 transports the paper P to the fourth transport unit 44.

  The third transport unit 43 inverts the paper P sent from the second transport unit 42 and sends it to the fourth transport unit 44. The third transport unit 43 includes a reverse roller pair 431. The reversing roller pair 431 is configured to be capable of forward rotation and reverse rotation. First, the reverse roller pair 431 transports the paper P sent from the second transport unit 42 in the direction D1 by rotating forward. A direction D1 indicates a direction away from the reversing roller pair 431 (right direction in FIG. 1). Then, the reverse roller pair 431 stops in a state where the upstream end in the direction D1 of the paper P is sandwiched. Next, the reverse roller pair 431 is rotated in the reverse direction to convey the paper P in the direction D <b> 2 and send the paper P to the fourth conveyance unit 44. The direction D2 indicates a direction opposite to the direction D1.

  The fourth transport unit 44 transports the paper P sent from the second transport unit 42 and the third transport unit 43 to the fifth transport unit 45 or the sixth transport unit 46. Specifically, the fourth transport unit 44 transports the paper P to the fifth transport unit 45 when discharging the paper P, and the fourth transport unit when transporting the paper P to the image forming unit 3. 44 conveys the paper P to the sixth conveyance unit 46.

  The fifth transport unit 45 transports the paper P sent from the fourth transport unit 44 toward the discharge tray 6. The fifth transport unit 45 includes a discharge roller pair 451. The discharge roller pair 451 discharges the paper P to the discharge tray 6.

  The sixth transport unit 46 transports the paper P transported by the fourth transport unit 44 to the image forming unit 3. The pair of transport rollers 411 sends the paper P transported by the sixth transport unit 46 to the image forming unit 3 in accordance with the image formation timing.

  Since the transport unit 4 includes the second transport unit 42, the third transport unit 43, the fourth transport unit 44, and the sixth transport unit 46, the transport direction of the paper P with respect to the recording head 34 is as follows. The paper P can be transported from the downstream side of D3 to the upstream side in the transport direction D3 of the paper P with respect to the recording head 34. The conveyance direction D3 indicates a direction from the press roller 31 toward the discharge unit 5 (left direction in FIG. 1).

  Specifically, by sequentially transporting the paper P by the second transport unit 42, the fourth transport unit 44, and the sixth transport unit 46, recording is performed from the downstream side in the transport direction D3 of the paper P with respect to the recording head 34. The sheet P can be transported upstream of the head 34 in the transport direction D3 of the sheet P. Further, by sequentially transporting the paper P by the second transport unit 42, the fourth transport unit 44, and the sixth transport unit 46, the paper P does not pass between the recording head 34 and the transport belt 32. The paper P can be conveyed without turning the front and back of the paper.

  Further, by sequentially transporting the paper P by the second transport unit 42, the third transport unit 43, the fourth transport unit 44, and the sixth transport unit 46, the downstream side of the transport direction D3 of the paper P with respect to the recording head 34. Thus, the paper P can be transported upstream of the recording head 34 in the transport direction D3 of the paper P. Further, the paper P passes between the recording head 34 and the transport belt 32 by sequentially transporting the paper P by the second transport unit 42, the third transport unit 43, the fourth transport unit 44, and the sixth transport unit 46. Therefore, the paper P can be transported with the front and back sides of the paper P reversed. By reversing the paper P, the front and back of the paper P are reversed, and the upstream end of the paper P and the downstream end of the paper P when the paper P is conveyed to the recording head 34 are reversed.

  The discharge unit 5 sends the paper P on which an image has been formed by the recording head 34 to the second transport unit 42.

  The discharge tray 6 places the paper P discharged from the discharge roller pair 451.

  The sensor 7 is disposed upstream of the recording head 34 in the transport direction D3 of the paper P and on the same side as the recording head 34 with respect to the placement surface SP of the paper P. The same side as the recording head 34 corresponds to the upper side of the mounting surface SP in FIG. The placement surface SP indicates a surface on which the paper P is placed when the recording head 34 forms an image on the paper P. Specifically, the placement surface SP indicates a surface of the outer peripheral surface of the transport belt 32 that faces the recording head 34.

  The sensor 7 emits light to an image (or paper P) formed on the paper P, and detects a first component and a second component of reflected light from the image (or paper P). The polarization planes of the first component and the second component are orthogonal to each other. Specifically, the first component represents a P wave (P polarization) component PP, and the second component represents an S wave (S polarization) component PS.

  The elevating mechanism 8 elevates and lowers the recording head 34 in a direction approaching and separating from the mounting surface SP. For example, the elevating mechanism 8 elevates and lowers the head base 35 and the recording head 34 integrally in a direction approaching and separating from the mounting surface SP. The elevating mechanism 8 includes a wire and a motor. The motor is configured to be capable of forward rotation and reverse rotation. One end of the wire is fixed to the head base 35, and the other end of the wire is wound around the rotating shaft of the motor. As the motor rotates forward, the head base 35 is raised through the wire. That is, the recording head 34 moves in the direction D5. When the motor is reversed, the head base 35 is lowered through the wire. That is, the recording head 34 moves in the direction D4.

  The control unit 9 includes a processor 91 and a storage unit 92. The processor 91 includes, for example, a CPU (Central Processing Unit). The storage unit 92 includes a memory such as a semiconductor memory, and may include an HDD (Hard Disk Drive). The storage unit 92 stores a control program.

  Next, with reference to FIG.1 and FIG.2, the structure of the control part 9 which concerns on this embodiment is demonstrated. FIG. 2 is a diagram illustrating a configuration of the control unit 9. As shown in FIG. 2, the control unit 9 includes a first detection unit 901, a second detection unit 902, a conveyance control unit 903, a lift control unit 904, an instruction unit 905, and a distance storage unit 921. Specifically, the processor 91 functions as a first detection unit 901, a second detection unit 902, a conveyance control unit 903, a lift control unit 904, and an instruction unit 905 by executing a control program. The storage unit 92 functions as the distance storage unit 921.

  The distance storage unit 921 stores the distance difference ΔH in association with the voltage difference ΔV. The distance difference ΔH indicates a difference obtained by subtracting the reference distance HA from the distance HM. The distance HM indicates a distance HS (see FIG. 1) detected based on the P wave component PP and the S wave component PS. The reference distance HA indicates a preset distance HS. The distance HS indicates the distance between the sensor 7 and the paper P. When the distance HS matches the reference distance HA, the recording head 34 can form a high-quality image on the paper P. The reference distance HA is 6 mm, for example. The voltage difference ΔV will be described in detail with reference to FIG.

  The first detection unit 901 controls the sensor 7 so that the sensor 7 performs the first detection operation. The first detection operation is an operation for detecting the distance HM between the sensor 7 and the paper P. The distance HM indicates a detection value of the distance HS. Further, the first detection unit 901 detects a distance HR (see FIG. 1) between the lower surface of the recording head 34 and the paper P based on the distance HM. The calculation method of the distance HM will be described in detail with reference to FIG.

The second detection unit 902 controls the sensor 7 so that the sensor 7 performs the second detection operation. The second detection operation is an operation for detecting the density D of the image formed on the paper P. The second detection unit 902 detects the density D of the image formed on the paper P based on the P wave component PP and the S wave component PS obtained by the second detection operation. Specifically, the second detection unit 902 detects the concentration D based on the following formula (1).
D = {1− (VP−VS) / (VP0−VS0)} × 100 (1)
Here, the first voltage VP indicates the P wave component PP, and the second voltage VS indicates the S wave component PS. The first voltage VP0 indicates a P-wave component PP at a portion where a toner image is not formed (for example, the surface of the conveyance belt 32), and the second voltage VS0 is a portion where a toner image is not formed (for example, conveyance) The S wave component PS on the surface of the belt 32 is shown.

  The conveyance control unit 903 controls the conveyance belt 32, the conveyance unit 4, and the discharge unit 5 so that the conveyance belt 32, the conveyance unit 4, and the discharge unit 5 convey the paper P.

  The lift control unit 904 controls the lift mechanism 8 so that the lift mechanism 8 moves the recording head 34 up and down. Specifically, the lifting control unit 904 controls the lifting mechanism 8 so that the lifting mechanism 8 moves the recording head 34 up and down based on the distance HM.

  The instruction unit 905 controls the image forming unit 3 so that the image forming unit 3 forms an image on the paper P.

  As described above with reference to FIGS. 1 and 2, in the embodiment of the present invention, the sensor 7 is arranged on the upstream side in the transport direction D <b> 3 of the paper P with respect to the recording head 34. The first detection unit 901 controls the sensor 7 so that the sensor 7 performs the first detection operation. The sensor 7 detects the distance HS by the first detection operation. The transport unit 4 does not reverse the front and back of the paper P from the downstream side in the transport direction D3 of the paper P with respect to the recording head 34 toward the upstream side of the transport direction D3 of the paper P with respect to the recording head 34. The paper P is conveyed. The second detection unit 902 controls the sensor 7 so that the sensor 7 performs the second detection operation. The sensor 7 detects the density D by the second detection operation. Therefore, the sensor 7 can detect the distance HS and the concentration D. Therefore, the manufacturing cost can be reduced. Further, since the sensor 7 is disposed on the upstream side in the conveyance direction D3 of the paper P with respect to the recording head 34, the distance HS can be detected before an image is formed by the recording head 34. Therefore, the possibility that the paper P collides with the recording head 34 can be reduced.

  Further, since the lifting control unit 904 controls the lifting mechanism 8 so that the lifting mechanism 8 moves the recording head 34 up and down based on the distance HS, a clear image can be formed on the paper P. Specifically, before forming an image on the paper P, the recording head 34 can be raised and lowered according to the distance HS so that the distance HR between the recording head 34 and the paper P can be adjusted to a predetermined distance. Therefore, a clear image can be formed on the paper P. The predetermined distance indicates the value of the distance HR when the distance HS substantially matches the reference distance HA.

  Next, with reference to FIGS. 1-3, the structure of the sensor 7 which concerns on embodiment of this invention is demonstrated. FIG. 3 is a diagram illustrating a configuration of the sensor 7. As shown in FIG. 3, the sensor 7 includes a light emitting element 71, a first beam splitter 72, a second beam splitter 73, and a detection unit DT. The detection unit DT detects the P wave component PP and the S wave component PS of the reflected light. The detection unit DT includes a first light receiving element 74 and a second light receiving element 75.

  The light emitting element 71 emits light W1 to the image N or the paper P formed on the paper P. The light emitting element 71 includes, for example, an LED (Light Emitting Diode).

  The first beam splitter 72 transmits the light W2 of the P wave component out of the light W1 from the light emitting element 71 and reflects the light of the S wave component. The P-wave component light W2 is incident on the image N or the paper P formed on the paper P.

  The P-wave component light W2 is reflected by the image N or the paper P formed on the paper P, and the reflected light W3 is generated. The reflected light W3 has a regular reflection component and a diffuse reflection component. The regular reflection component is a P wave component PP, and the diffuse reflection component is an S wave component PS.

  The second beam splitter 73 transmits the light W4 of the P wave component PP among the reflected light W3, and reflects the light W5 of the S wave component PS.

  The first light receiving element 74 detects the light W4 of the P wave component PP. Specifically, the first light receiving element 74 outputs an electric signal having a voltage corresponding to the light amount of the light W4. The first light receiving element 74 includes, for example, a photodiode.

  The second light receiving element 75 detects the light W5 of the S wave component PS. Specifically, the second light receiving element 75 outputs an electric signal having a voltage corresponding to the light amount of the light W5. The second light receiving element 75 includes, for example, a photodiode.

  As described above with reference to FIGS. 1 to 3, in the embodiment of the present invention, the second beam splitter 73 converts the reflected light W3 into the light W4 of the P wave component PP and the light W5 of the S wave component PS. To separate. The first light receiving element 74 detects the amount of light W4 of the P wave component PP. The second light receiving element 75 detects the amount of light W5 of the S wave component PS. Therefore, it is possible to accurately detect the light amount of the light W4 of the P wave component PP of the reflected light W3 and the light amount of the light W5 of the S wave component PS of the reflected light W3.

  Next, the first voltage VP, the second voltage VS, and the voltage difference ΔV will be described with reference to FIGS. FIG. 4A is a diagram illustrating a change between the first voltage VP and the second voltage VS. The horizontal axis represents time T, and the vertical axis represents the first voltage VP and the second voltage VS. The first voltage VP indicates a voltage output from the first light receiving element 74, and the second voltage VS indicates a voltage output from the second light receiving element 75. That is, the first voltage VP indicates the amount of light of the P wave component PP, and the second voltage VS indicates the amount of light of the S wave component PS. FIG. 5A further shows a graph G11 and a graph G12. A graph G11 shows a change in the first voltage VP. The graph G12 shows the change of the second voltage VS.

  In a period PD1 from time T1 to time T2 shown in FIG. 4A, the sensor 7 detects the reflected light W3 reflected from the cyan image N. In the period PD1, the value of the first voltage VP is the voltage value VP1. In the period PD1, the value of the second voltage VS is the voltage value VS1.

  In the period PD2 from time T3 to time T4, the sensor 7 detects the reflected light W3 reflected from the magenta image N. The density D of the magenta image N matches the density D of the cyan image N. In the period PD2, the value of the first voltage VP is the voltage value VP2. In the period PD2, the value of the second voltage VS is the voltage value VS2.

  As shown in the graph G11 and the graph G12, the voltage value VP2 is larger than the voltage value VP1, and the voltage value VS2 is larger than the voltage value VS1. That is, the reflected light W3 reflected by the magenta paper P has a larger amount of P wave component PP and S wave component PS than the reflected light W3 reflected by the cyan image N.

FIG. 4B is a diagram illustrating changes in the voltage difference ΔV. The horizontal axis indicates time T, and the vertical axis indicates voltage difference ΔV. The voltage difference ΔV is expressed by the following equations (2) and (3).
ΔV = ΔVP−ΔVS (2)
ΔV = (VP−VPA) − (VS−VSA) (3)
That is, the voltage difference ΔV indicates a difference obtained by subtracting the second voltage difference ΔVS from the first voltage difference ΔVP. The first voltage difference ΔVP indicates a difference obtained by subtracting the first reference voltage VPA from the first voltage VP. The second voltage difference ΔVS indicates a difference obtained by subtracting the second reference voltage VSA from the second voltage VS. The first reference voltage VPA indicates the value of the first voltage VP when the distance HS matches the reference distance HA. The second reference voltage VSA indicates the value of the second voltage VS when the distance HS matches the reference distance HA.

  FIG. 4B further shows a graph G2. Graph G2 shows the change in voltage difference ΔV. As shown in the graph G2, the value of the voltage difference ΔV1 in the period PD1 matches the value of the voltage difference ΔV2 in the period PD2. That is, as the color of the image N changes, the value of the first voltage VP and the value of the second voltage VS change, but the value of the voltage difference ΔV does not change.

Next, processing of the first detection unit 901 will be further described with reference to FIGS. FIG. 5 is a diagram showing the relationship between the distance difference ΔH and the voltage difference ΔV, and shows a graph G3. The distance difference ΔH is expressed by the following equation (4).
ΔH = HM-HA (4)
That is, the distance difference ΔH indicates a difference obtained by subtracting the reference distance HA from the distance HM.

The horizontal axis in FIG. 5 represents the distance difference ΔH, and the vertical axis represents the voltage difference ΔV. Graph G3
The relationship between the distance difference ΔH and the voltage difference ΔV is shown. As shown in the graph G3, the voltage difference ΔV increases monotonously as the distance difference ΔH increases. That is, the voltage difference ΔV and the distance difference ΔH have a one-to-one correspondence. When the distance difference ΔH is zero, the voltage difference ΔV is zero.

  The relationship between the voltage difference ΔV and the distance difference ΔH shown in the graph G3 is stored in the distance storage unit 921. Specifically, the distance storage unit 921 stores the distance difference ΔH in association with the voltage difference ΔV. The distance storage unit 921 stores, for example, a table that associates the distance difference ΔH with the voltage difference ΔV.

  The first detection unit 901 detects the distance HM based on the P wave component PP and the S wave component PS. Specifically, the first detection unit 901 acquires the first voltage VP and the second voltage VS from the sensor 7. And the 1st detection part 901 calculates voltage difference (DELTA) V using Formula (3). Further, the first detection unit 901 reads the distance difference ΔH corresponding to the voltage difference ΔV from the distance storage unit 921. The first detection unit 901 detects the sum of the distance difference ΔH and the reference distance HA as the distance HM.

  As described above with reference to FIGS. 2 to 5, in the embodiment of the present invention, the first detection unit 901 calculates the distance HM based on the difference between the P wave component PP and the S wave component PS. To do. Specifically, the first detection unit 901 calculates the distance HM based on the voltage difference ΔV. Further, the voltage difference ΔV and the distance difference ΔH have a one-to-one correspondence. Therefore, the distance HM between the sensor 7 and the paper P can be accurately calculated based on the difference between the P wave component PP and the S wave component PS.

Next, processing of the control unit 9 will be described with reference to FIGS. FIG. 6 is a flowchart showing the processing of the control unit 9.
As shown in FIG. 6, first, in step S101, the control unit 9 determines whether or not the density D is detected.
If the controller 9 determines that the density D is detected (YES in step S101), the process proceeds to step S103.
In step S103, the control unit 9 executes the “density detection process”, and the process ends. “Density detection process” indicates a process executed by the control unit 9 to detect the density D.
If the control unit 9 determines that the density D is not detected (NO in step S101), the process proceeds to step S105.
In step S105, the control unit 9 determines whether to detect the distance HM.
If the control unit 9 determines that the distance HM is not detected (NO in step S105), the process returns to step S101. If the control unit 9 determines that the distance HM is detected (YES in step S105), the process proceeds to step S107.
In step S107, the transport unit 4 transports the paper P to the lower side of the sensor 7, and the first detection unit 901 detects the distance HM. Specifically, the transport unit 4 stops transporting the paper P when the leading end in the transport direction D3 of the paper P reaches a position directly below the sensor 7.

Next, in step S109, the elevation control unit 904 determines whether the distance HM satisfies the following expression (5).
| HM-HA | ≦ ΔHS (5)
Here, the reference distance difference ΔHS defines a range of a distance HM in which the recording head 34 can form a high-quality image N on the paper P.
If the elevation control unit 904 determines that the distance HM does not satisfy Expression (5) (NO in step S109), the process proceeds to step S111.
In step S111, the lift control unit 904 executes the “head lift process”, and then the process proceeds to step S113. “Head lifting / lowering process” indicates a process of moving the recording head 34 up and down so that the recording head 34 can form a high-quality image N on the paper P.
If the elevation control unit 904 determines that the distance HM satisfies Expression (5) (YES in step S109), the process proceeds to step S113.
In step S113, the conveyance belt 32 conveys the sheet P in the conveyance direction D3 of the sheet P, and the image forming unit 3 forms the image N on the sheet P. Thereafter, the sheet P is conveyed sequentially through the discharge unit 5, the second conveyance unit 42, the fourth conveyance unit 44, and the fifth conveyance unit 45, and the sheet P is discharged to the discharge tray 6 to complete the processing.

Next, the “density detection process” of the control unit 9 will be described with reference to FIGS. FIG. 7 is a flowchart showing the “density detection process” of the control unit 9.
As shown in FIG. 7, first, in step S <b> 201, the transport unit 4 transports the paper P to the lower side of the sensor 7, and the first detection unit 901 detects the distance HM. Specifically, the transport unit 4 stops transporting the paper P when the leading end in the transport direction D3 of the paper P reaches a position directly below the sensor 7.
Next, in step S203, the elevation control unit 904 determines whether the distance HM satisfies Expression (5).
If the elevation control unit 904 determines that the distance HM does not satisfy Expression (5) (NO in step S203), the process proceeds to step S205.
In step S205, the lift control unit 904 executes the “head lift process”, and then the process proceeds to step S207.
If the elevation control unit 904 determines that the distance HM satisfies Expression (5) (YES in step S203), the process proceeds to step S207.
In step S207, the conveyance belt 32 conveys the sheet P in the conveyance direction D3 of the sheet P, and the image forming unit 3 forms a density adjustment image on the sheet P. The density adjustment image indicates an image N formed on the paper P in order to confirm whether or not the recording head 34 has formed the image N at a predetermined density D.

Next, in step S <b> 209, the transport unit 4 does not reverse the paper P, and the downstream side of the transport direction D <b> 3 of the paper P with respect to the recording head 34. The paper P is conveyed toward the upstream side. Specifically, the discharge unit 5, the second transport unit 42, the third transport unit 43, the fourth transport unit 44, and the sixth transport unit 46 sequentially transport the paper P.
Next, in step S211, the conveyance belt 32 conveys the paper P to the lower side of the sensor 7, and the first detection unit 901 detects the distance HM. Specifically, the transport belt 32 transports the paper P so that the paper P passes under the sensor 7. Thereafter, the discharge unit 5, the second transfer unit 42, the fourth transfer unit 44, and the fifth transfer unit 45 sequentially transfer the sheet P, discharge the sheet P to the discharge tray 6, and the process ends.

  As described above with reference to FIGS. 2 to 7, in the embodiment of the present invention, the sensor 7 executes the first detection operation to detect the distance HM between the sensor 7 and the paper P, and the image The forming unit 3 forms an image N on the paper P. Next, the conveyance unit 4 does not reverse the sheet P from the downstream side in the conveyance direction D3 of the sheet P with respect to the recording head 34 toward the upstream side in the conveyance direction D3 of the sheet P with respect to the recording head 34. The paper P is conveyed. Then, the sensor 7 executes the second detection operation to detect the density D of the image N formed on the paper P. Therefore, for example, according to the distance HM, the recording head 34 can be moved up and down so that the distance HM between the recording head 34 and the paper P can be adjusted to the reference distance HA. Therefore, a clear image N can be formed on the paper P.

Next, the “head lifting process” of the control unit 9 will be described with reference to FIGS. FIG. 8 is a flowchart showing the “head lifting process” of the control unit 9.
As shown in FIG. 8, in step S301, the elevation control unit 904 determines whether or not the distance HM is less than the reference distance HA.
If the elevation control unit 904 determines that the distance HM is not less than the reference distance HA (NO in step S301), the process proceeds to step S309. If the elevation controller 904 determines that the distance HM is less than the reference distance HA (YES in step S301), the process proceeds to step S303.
In step S <b> 303, the lifting mechanism 8 raises the recording head 34.
Next, in step S305, the elevation control unit 904 determines whether the distance HM satisfies Expression (5).
If the elevation control unit 904 determines that the distance HM does not satisfy Expression (5) (NO in step S305), the process returns to step S303. If the elevation control unit 904 determines that the distance HM satisfies Expression (5) (YES in step S305), the process proceeds to step S307.
In step S307, the lifting mechanism 8 stops raising the recording head 34, and the process returns.

If NO in step S301, the elevating mechanism 8 lowers the recording head 34 in step S309.
Next, in step S311, the elevation controller 904 determines whether or not the distance HM satisfies Expression (5).
If the elevation control unit 904 determines that the distance HM does not satisfy Expression (5) (NO in step S311), the process returns to step S309. If the elevation control unit 904 determines that the distance HM satisfies Expression (5) (YES in step S311), the process proceeds to step S313.
In step S313, the lifting mechanism 8 stops the lowering of the recording head 34, and the process returns.

  As described above with reference to FIGS. 2 to 8, in the embodiment of the present invention, the lifting mechanism 8 moves the recording head 34 up and down so that the distance HM satisfies the formula (5). Therefore, a clear image N can be formed on the paper P.

  The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof (for example, (1) to (2) shown below). For ease of understanding, the drawings schematically show each component as a main component, and the thickness, length, number, etc. of each component shown in the drawings are different from the actual for convenience of drawing. There is a case. Moreover, the shape, dimension, etc. of each component shown by said embodiment are an example, Comprising: It does not specifically limit, A various change is possible in the range which does not deviate substantially from the structure of this invention.

  (1) In the embodiment of the present invention, as described with reference to FIGS. 1 to 4, the sensor 7 includes the first beam splitter 72 and the second beam splitter 73, but the present invention is not limited to this. . The sensor 7 may include the second beam splitter 73. For example, the sensor 7 may include a polarizing plate instead of the first beam splitter 72.

  (2) In the embodiment of the present invention, as described with reference to FIGS. 2 to 5, the first detection unit 901 reads the distance difference ΔH corresponding to the voltage difference ΔV from the distance storage unit 921. The invention is not limited to this. The first detection unit 901 may detect the distance difference ΔH based on the voltage difference ΔV. For example, the first detection unit 901 may detect the distance difference ΔH with reference to a graph G3 illustrated in FIG.

  The present invention relates to an ink jet recording apparatus and has industrial applicability.

DESCRIPTION OF SYMBOLS 100 Inkjet recording device 3 Image forming part 34, 34a-34d Recording head 4 Conveyance part (conveyance mechanism)
41 1st conveyance part 42 2nd conveyance part 43 3rd conveyance part 44 4th conveyance part 45 5th conveyance part 46 6th conveyance part 7 Sensor 71 Light emitting element 72 1st beam splitter 73 2nd beam splitter DT detection part 74 4th 1 light receiving element 75 second light receiving element 8 lifting mechanism 9 control unit 91 processor 92 storage unit 901 first detection unit 902 second detection unit 903 transport control unit 904 lift control unit 905 instruction unit 921 distance storage unit D concentration D3 transport direction HA Reference distance HM Detection distance HS distance P Paper (recording medium)
PPP wave component (first component)
PS S wave component (second component)
VP 1st voltage VS 2nd voltage ΔH Distance difference ΔV Voltage difference SP Mounting surface

Claims (5)

A recording head for forming an image on a recording medium;
The recording medium is transported from the downstream side in the transport direction of the recording medium with respect to the recording head to the upstream side in the transport direction of the recording medium with respect to the recording head without reversing the front and back of the recording medium. A transport mechanism;
A sensor disposed upstream of the recording head in the conveyance direction of the recording medium and on the same side as the recording head with respect to the mounting surface of the recording medium;
A control unit,
The mounting surface indicates a surface on which the recording medium is mounted when the recording head forms the image on the recording medium. The sensor detects a distance between the sensor and the recording medium. And a second detection operation for detecting the density of the image formed on the recording medium.
The ink jet recording apparatus, wherein the control unit controls the sensor so that the sensor executes the first detection operation and the second detection operation. The sensor is
A light emitting element that emits light;
A beam splitter that separates the reflected light into a first component and a second component;
A first light receiving element for detecting the first component;
The inkjet recording apparatus according to claim 1, further comprising a second light receiving element that detects the second component.   The inkjet recording apparatus according to claim 2, wherein the control unit detects the distance based on a difference between the first component and the second component obtained by the first detection operation.   The sensor and the transport so that the sensor performs the second detection operation after the sensor performs the first detection operation and the transport mechanism transports the recording medium from the downstream side to the upstream side. The inkjet recording apparatus according to any one of claims 1 to 3, wherein the mechanism is controlled. An elevating mechanism for elevating the recording head in a direction approaching and separating from the mounting surface;
5. The inkjet recording apparatus according to claim 4, wherein the control unit controls the lifting mechanism so that the lifting mechanism moves the recording head up and down based on the distance detected by the first detection operation.

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