Image forming apparatus using an ink-jet method

Abstract

 An image forming apparatus (100; 200) using an ink jet method includes an ink jet head (15) including a nozzle, configured to discharge ink from the nozzle to form an image on a recording medium (S), a carriage (14) configured to convey the ink jet head in a main scanning direction so that the ink jet head mounted thereon forms the image in the main scanning direction, a platen (12) configured to support the recording medium, wherein the recording medium is conveyed along the platen so that the image is formed in a sub-scanning direction, a jam detection mechanism (101, 102, 103) configured to detect a jam of the recording medium, and a vary mechanism (122, 130; 208, 209) configured to vary a distance between the ink jet head and the platen according to the jam detection performed by the jam detection mechanism.

Description

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a mechanism for removing a jammed sheet therein.

[0002] A background image forming apparatus which adopts an ink jet method and discharges ink from a nozzle hole to form an image on a recording sheet has been widely used and dominating as a printer.

[0003] FIG. 1 is a cross section view of a background image forming apparatus and schematically illustrates a configuration thereof. As shown in FIG. 1, an image forming apparatus 10 includes a pair of conveyance rollers 11, a platen 12, a guide rod 13, a carriage 14, an ink jet head 15, conveyance rollers 16, and conveyance gears 17. The pair of conveyance rollers 11 conveys a recording sheet S so that the recording sheet S travels on the platen 12 in a conveyance direction. The carriage 14 travels in a main scanning direction, which is perpendicular to the conveyance direction, along the guide rod 13. While the carriage 14 travels in the main scanning direction, the ink jet head 15 mounted on the carriage 14 performs recording on the recording sheet S on the platen 12. After the recording is performed, the recording sheet S is discharged by the conveyance rollers 16 and the conveyance gears 17. In the configuration of the image forming apparatus 10, as the distance between the recording sheet S and the ink jet head 15 becomes smaller, quality of an image to be formed by the image forming apparatus 10 becomes higher. However, since curling and floating of the recording sheet S needs to be taken into account, a small gap is arranged between the recording sheet S and the ink jet head 15.

[0004] FIG. 2 is a cross section view of the image forming apparatus 10 shown in FIG. 1, and schematically illustrates a jam occurred while the recording sheet S is conveyed between the platen 12 and the ink jet recording head 15. As shown FIG. 2, the recording sheet S needs to be removed by being pulled in a direction of an arrow A.

[0005] This patent specification describes an image forming apparatus using an ink jet method and including an ink jet head having a nozzle, configured to discharge ink from the nozzle to form an image on a recording medium, a carriage configured to convey the ink jet head in a main scanning direction so that the ink jet head mounted thereon forms the image in the main scanning direction, a platen configured to support the recording medium, wherein the recording medium is conveyed along the platen so that the image is formed in a sub-scanning direction, a jam detection mechanism configured to detect a jam of the recording medium, and a vary mechanism configured to vary a distance between the ink jet head and the platen according to the jam detection performed by the jam detection mechanism.

[0006] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a cross section view of a background image forming apparatus, and schematically illustrates a configuration thereof;

FIG. 2 is a cross section view of the background image forming apparatus shown in FIG. 1, and schematically illustrates a jam occurred while recording is performed;

FIG. 3 is a cross section view of an image forming apparatus, and schematically illustrates a configuration of an exemplary jam detection mechanism included therein;

FIG. 4 is a flowchart of an exemplary jam detection operation of the image forming apparatus shown in FIG. 3;

FIG. 5 is a flowchart of another exemplary jam detection operation of the image forming apparatus shown in FIG. 3;

FIG. 6 is a flowchart of another exemplary jam detection operation of the image forming apparatus shown in FIG. 3;

FIG. 7 is a flowchart of another exemplary jam detection operation of the image forming apparatus shown in FIG. 3;

FIG. 8 is a flowchart of another exemplary jam detection operation of the image forming apparatus shown in FIG. 3;

FIG. 9 is a flowchart of another exemplary jam detection operation of the image forming apparatus shown in FIG. 3;

FIG. 10 is a flowchart of another exemplary jam detection operation of the image forming apparatus shown in FIG. 3;

FIG. 11 is a flowchart of another exemplary jam detection operation of the image forming apparatus shown in FIG. 3;

FIG. 12 is a cross section view of the image forming apparatus shown in FIG. 3, and schematically illustrates ascent and descent of a carriage included therein;

FIGs. 13A and 13B are cross section views of the image forming apparatus shown in FIG. 3, and schematically illustrate a configuration of a carriage elevation mechanism according to an embodiment of the present invention;

FIGs. 14A and 14B are cross section views of the image forming apparatus shown in FIG. 3, and schematically illustrate another configuration of the carriage elevation mechanism;

FIG. 15 is a cross section view of the image forming apparatus shown in FIGs. 13A and 13B, and a solenoid actuator;

FIGs. 16A and 16B are cross section views of an ink jet head and recording mediums;

FIG. 17 is a cross section view of the image forming apparatus shown in FIGs. 13A and 13B, and a motor;

FIG. 18 is a flowchart of a jammed-sheet removal operation of the image forming apparatus shown in FIG. 15;

FIGs. 19A and 19B are cross section views of an image forming apparatus, and schematically illustrate a configuration of a platen elevation mechanism according to another embodiment of the present invention; and

FIGs. 20A an 20B are cross section views of the image forming apparatus, and schematically illustrate another configuration of the platen elevation mechanism.

[0007] In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to FIG. 3, an image forming apparatus according to an exemplary embodiment of the present invention is described.

[0008] FIG. 3 is a cross section view of an image forming apparatus 100, and schematically illustrates a configuration of an exemplary jam detection mechanism included therein. In FIG. 3, the components represented by the same reference numerals as in FIGs. 1 and 2 are the same components as in the background image forming apparatus 10 shown in FIGs. 1 and 2.

[0009] The configuration of the exemplary jam detection mechanism of the image forming apparatus 100 is described below referring to FIG. 3.

[0010] As shown in FIG. 3, the image forming apparatus 100 includes the pair of conveyance rollers 11, the platen 12, the guide rod 13, the carriage 14, the ink jet head 15, the conveyance rollers 16, and the conveyance gears 17 shown in FIGs. 1 and 2. The image forming apparatus 100 further includes an entry sensor 101, a registration sensor 102, an exit sensor 103, and a timer (not shown).

[0011] The entry sensor 101, the registration sensor 102, and the exit sensor 103 are located above a conveyance path for conveying a recording sheet S. A sensing position of the entry sensor 101 on the conveyance path is located at a predetermined distance L1 in an upstream direction from a sensing position of the registration sensor 102. The sensing position of the registration sensor 102 is located immediately upstream of a print area of the image forming apparatus 100. A sensing position of the exit sensor 103 is located downstream of the print area, and at a predetermined distance L2 from the sensing position of the registration sensor 102.

[0012] The image forming apparatus 100 having the jam detection mechanism performs a jam detection operation. Exemplary flows of the jam detection operation are described below referring to FIGs. 4 to 11.

[0013] FIG. 4 is a flowchart of an exemplary jam detection operation of the image forming apparatus 100. As shown in FIG. 4, in step S101, the image forming apparatus 100 checks whether or not the entry sensor 101 has sensed a front end of the recording sheet S. When the image forming apparatus 100 judges that the entry sensor 101 has sensed the front end of the recording sheet S (YES in step S101), the timer starts timekeeping in step S102. When the image forming apparatus 100 judges that the entry sensor 101 has not yet sensed the front end of the recording sheet S (NO in step S101), step S101 is repeated.

[0014] In step S103, time t2 needed for conveying the front end of the recording sheet S for the distance L2 is derived on the basis of print conditions such as the length of the recording sheet S in a longitudinal direction, an image quality mode, and the amount of print data. Further, time T1 is derived by adding the time t2 to predetermined time t1 needed for conveying the front end of the recording sheet S for the distance L1 at a predetermined conveyance speed.

[0015] In step S104, the image forming apparatus 100 checks whether or not the time T1 has passed. When the image forming apparatus 100 judges that the time T1 has passed (YES in step S104), the image forming apparatus 100 checks whether or not the exit sensor 103 has sensed the front end of the recording sheet S (step S105). When the image forming apparatus 100 judges that the time T1 has not yet passed (NO in step S104), step S104 is repeated.

[0016] When the image forming apparatus 100 judges that the exit sensor 103 has not sensed the front end of the recording sheet S (NO in step S105), the image forming apparatus 100 judges that a jam has occurred in step S106. When the image forming apparatus 100 judges that the exit sensor 103 has sensed the front end of the recording sheet S (YES in step S105), the image forming apparatus 100 judges that no jam has occurred in step S107.

[0017] FIG. 5 is a flowchart of another exemplary jam detection operation of the image forming apparatus 100.

[0018] As shown in FIG. 5, in step S201, the image forming apparatus 100 checks whether or not the entry sensor 101 has sensed a rear end of the recording sheet S. When the image forming apparatus 100 judges that the entry sensor 101 has sensed the rear end of the recording sheet S (YES in step S201), the timer starts timekeeping in step S202. When the image forming apparatus 100 judges that the entry sensor 101 has not yet sensed the rear end of the recording sheet S (NO in step S201), step S201 is repeated.

[0019] In step S203, time T2 needed for conveying the rear end of the recording sheet S for the distance L1 added with the distance L2, which is the distance between the sensing position of the entry sensor 101 and the sensing position of the exit sensor 103, is derived on the basis of print conditions such as the length of the recording sheet S in the longitudinal direction, the image quality mode, and the amount of print data.

[0020] In step S204, the image forming apparatus 100 checks whether or not the time T2 has passed. When the image forming apparatus 100 judges that the time T2 has passed (YES in step S204), the image forming apparatus 100 checks whether or not the exit sensor 103 has sensed the rear end of the recording sheet S (step S205). When the image forming apparatus 100 judges that the time T2 has not yet passed (NO in step S204), step S204 is repeated.

[0021] When the image forming apparatus 100 judges that the exit sensor 103 has not sensed the rear end of the recording sheet S (NO in step S205), the image forming apparatus 100 judges that a jam has occurred in step S206. When the image forming apparatus 100 judges that the exit sensor 103 has sensed the rear end of the recording sheet S (YES in step S205), the image forming apparatus 100 judges that no jam has occurred in step S207.

[0022] FIG. 6 is a flowchart of another exemplary jam detection operation of the image forming apparatus 100. As shown in FIG. 6, in step S301, the image forming apparatus 100 checks whether or not the entry sensor 101 has sensed a front end of the recording sheet S. When the image forming apparatus 100 judges that the entry sensor 101 has sensed the front end of the recording sheet S (YES in step S301), the timer starts timekeeping in step S302. When the image forming apparatus 100 judges that the entry sensor 101 has not yet sensed the front end of the recording sheet S (NO in step S301), step S301 is repeated.

[0023] In step S303, time T3 needed for a rear end of the recording sheet S to pass the entry sensor 101 after the front end thereof passes the entry sensor 101 is derived on the basis of print conditions such as the length of the recording sheet S in a longitudinal direction, an image quality mode, and the amount of print data.

[0024] In step S304, the image forming apparatus 100 checks whether or not the time T3 has passed. When the image forming apparatus 100 judges that the time T3 has passed (YES in step S304), the image forming apparatus 100 checks whether or not the entry sensor 101 has sensed the rear end of the recording sheet S (step S305). When the image forming apparatus 100 judges that the time T3 has not yet passed (NO in step S304), step S304 is repeated.

[0025] When the image forming apparatus 100 judges that the entry sensor 101 has not sensed the rear end of the recording sheet S (NO in step S305), the image forming apparatus 100 judges that a jam has occurred in step S306. When the image forming apparatus 100 judges that the entry sensor 101 has sensed the rear end of the recording sheet S (YES in step S305), the image forming apparatus 100 judges that no jam has occurred in step S307.

[0026] FIG. 7 is a flowchart of another exemplary jam detection operation of the image forming apparatus 100. As shown in FIG. 7, in step S401, the image forming apparatus 100 checks whether or not the entry sensor 101 has sensed a front end of the recording sheet S. When the image forming apparatus 100 judges that the entry sensor 101 has sensed the front end of the recording sheet S (YES in step S401), the timer starts timekeeping in step S402. When the image forming apparatus 100 judges that the entry sensor 101 has not yet sensed the front end of the recording sheet S (NO in step S401), step S401 is repeated.

[0027] In step S403, the image forming apparatus 100 checks whether or not time T4 needed for conveying the front end of the recording sheet S for the distance L1 at the predetermined conveyance speed (i.e. T4 = t1) has passed. When the image forming apparatus 100 judges that the time T4 has passed (YES in step S403), the image forming apparatus 100 checks whether or not the exit sensor 103 has sensed the front end of the recording sheet S (step S404). When the image forming apparatus 100 judges that the time T4 has not yet passed (NO in step S403), step S403 is repeated.

[0028] When the image forming apparatus 100 judges that the exit sensor 103 has not sensed the front end of the recording sheet S (NO in step S404), the image forming apparatus 100 judges that a jam has occurred in step S405. When the image forming apparatus 100 judges that the exit sensor 103 has sensed the front end of the recording sheet S (YES in step S404), the image forming apparatus 100 judges that no jam has occurred in step S406.

[0029] FIG. 8 is a flowchart of another exemplary jam detection operation of the image forming apparatus 100.

[0030] As shown in FIG. 8, in step S501, the image forming apparatus 100 checks whether or not the entry sensor 101 has sensed a rear end of the recording sheet S. When the image forming apparatus 100 judges that the entry sensor 101 has sensed the rear end of the recording sheet S (YES in step S501), the timer starts timekeeping in step S502. When the image forming apparatus 100 judges that the entry sensor 101 has not yet sensed the rear end of the recording sheet S (NO in step S501), step S501 is repeated.

[0031] In step S503, time T5 needed for conveying the rear end of the recording sheet S for the distance between the sensing position of the entry sensor 101 and the sensing position of the registration sensor 102 is derived on the basis of print conditions such as the length of the recording sheet S in the longitudinal direction, the image quality mode, and the amount of print data.

[0032] In step S504, the image forming apparatus 100 checks whether or not the time T5 has passed. When the image forming apparatus 100 judges that the time T5 has passed (YES in step S504), the image forming apparatus 100 checks whether or not the registration sensor 102 has sensed the rear end of the recording sheet S (step S505). When the image forming apparatus 100 judges that the time T5 has not yet passed (NO in step S504), step S504 is repeated.

[0033] When the image forming apparatus 100 judges that the registration sensor 102 has not sensed the rear end of the recording sheet S (NO in step S505), the image forming apparatus 100 judges that a jam has occurred in step S506. When the image forming apparatus 100 judges that the registration sensor 102 has sensed the rear end of the recording sheet S (YES in step S505), the image forming apparatus 100 judges that no jam has occurred in step S507.

[0034] FIG. 9 is a flowchart of another exemplary jam detection operation of the image forming apparatus 100.

[0035] As shown in FIG. 9, in step S601, the image forming apparatus 100 checks whether or not the registration sensor 102 has sensed a front end of the recording sheet S. When the image forming apparatus 100 judges that the registration sensor 102 has sensed the front end of the recording sheet S (YES in step S601), the timer starts timekeeping in step S602. When the image forming apparatus 100 judges that the registration sensor 102 has not yet sensed the front end of the recording sheet S (NO in step S601), step S601 is repeated.

[0036] In step S603, time T6 needed for conveying the front end of the recording sheet S for the distance between the sensing position of the registration sensor 102 and the sensing position of the exit sensor 103 is derived on the basis of print conditions such as the length of the recording sheet S in a longitudinal direction, an image quality mode, and the amount of print data.

[0037] In step S604, the image forming apparatus 100 checks whether or not the time T6 has passed. When the image forming apparatus 100 judges that the time T6 has passed (YES in step S604), the image forming apparatus 100 checks whether or not the exit sensor 103 has sensed the front end of the recording sheet S (step S605). When the image forming apparatus 100 judges that the time T6 has not yet passed (NO in step S604), step S604 is repeated.

[0038] When the image forming apparatus 100 judges that the exit sensor 103 has not sensed the front end of the recording sheet S (NO in step S605), the image forming apparatus 100 judges that a jam has occurred in step S606. When the image forming apparatus 100 judges that the exit sensor 103 has sensed the front end of the recording sheet S (YES in step S605), the image forming apparatus 100 judges that no jam has occurred in step S607.

[0039] FIG. 10 is a flowchart of another exemplary jam detection operation of the image forming apparatus 100.

[0040] As shown in FIG. 10, in step S701, the image forming apparatus 100 checks whether or not the registration sensor 102 has sensed a rear end of the recording sheet S. When the image forming apparatus 100 judges that the registration sensor 102 has sensed the rear end of the recording sheet S (YES in step S701), the timer starts timekeeping in step S702. When the image forming apparatus 100 judges that the registration sensor 102 has not yet sensed the rear end of the recording sheet S (NO in step S701), step S701 is repeated.

[0041] In step S703, time T7 needed for conveying the rear end of the recording sheet S for the distance between the sensing position of the registration sensor 102 and the sensing position of the exit sensor 103 is derived on the basis of print conditions such as the length of the recording sheet S in the longitudinal direction, the image quality mode, and the amount of print data.

[0042] In step S704, the image forming apparatus 100 checks whether or not the time T7 has passed. When the image forming apparatus 100 judges that the time T7 has passed (YES in step S704), the image forming apparatus 100 checks whether or not the exit sensor 103 has sensed the rear end of the recording sheet S (step S705). When the image forming apparatus 100 judges that the time T7 has not yet passed (NO in step S704), step S704 is repeated.

[0043] When the image forming apparatus 100 judges that the exit sensor 103 has not sensed the rear end of the recording sheet S (NO in step S705), the image forming apparatus 100 judges that a jam has occurred in step S706. When the image forming apparatus 100 judges that the exit sensor 103 has sensed the rear end of the recording sheet S (YES in step S705), the image forming apparatus 100 judges that no jam has occurred in step S707.

[0044] FIG. 11 is a flowchart of another exemplary jam detection operation of the image forming apparatus 100. As shown in FIG. 11, the carriage 14 is provided with a travel signal in step S801. In step S802, the image forming apparatus 100 checks whether or not a linear sensor (not shown) has sensed traveling of the carriage 14.

[0045] When the image forming apparatus 100 judges that the linear sensor has not sensed the traveling of the carriage 14 (NO in step S802), the image forming apparatus 100 judges that a jam has occurred in step S803 because the recording sheet S contacts the ink jet head 15 and prevents the carriage 14 from traveling. When the image forming apparatus 100 judges that the linear sensor has sensed the traveling of the carriage 14 (YES in step S802), the image forming apparatus 100 judges that no jam has occurred in step S804.

[0046] Next, a jammed-sheet removal mechanism of the image forming apparatus 100 according to the embodiment of the present invention is described below in detail.

[0047] When the image forming apparatus 100 judges that a jam has occurred as described above, a jammed sheet is removed by using the jammed-sheet removal mechanism so that the jammed sheet does not contact the ink jet head 15. As the jammed sheet does not contact the ink jet head 15, a nozzle is prevented from being clogged with dust. As a result, an occurrence of deficit imaging can be prevented.

[0048] As described above, the time used for judging whether or not a jam has occurred is derived on the bases of print conditions such as the length of the recording sheet S in the longitudinal direction, the image quality mode, and the amount of print data in the embodiment of the present invention. Alternatively, the time may be previously determined including a tolerance, and the judgment may be made when the predetermined time has passed. Alternatively, the judgment may be made without setting time. In the case, a sensor may be arranged in a position where the recording sheet S is expected to arrive, and the judgment may be made according to a result of sensing performed by the sensor.

[0049] FIG. 12 is a cross section view of the image forming apparatus 100, and schematically illustrates ascent and descent of the carriage 14.

[0050] The image forming apparatus 100 further includes a carriage elevation mechanism (not shown). As shown in FIG. 12, when the recording sheet S jams while being conveyed on the platen 12, the carriage elevation mechanism moves up the carriage 14 in a direction of an arrow B so that a distance between the carriage 14 and the platen 12 is increased. The jammed recording sheet S is pulled in a direction of an arrow A, and can be pulled out without contacting the ink jet head 15. After the jammed recording sheet S is removed from the image forming apparatus 100, the carriage elevation mechanism moves down the carriage 14 into an original position.

[0051] The carriage elevation mechanism for causing the carriage 14 to move up and down is described in detail below referring to FIGs. 13A to 17.

[0052] FIGs. 13A and 13B are cross section views of the image forming apparatus 100.

[0053] As shown in FIG. 13A, the image forming apparatus 100 further includes a guide plate 121 and a side plate having a hole (not shown). The carriage elevation mechanism of the image forming apparatus 100 includes the lever 122 and a bearing 130 for swingably supporting the lever 122. The guide plate 121 functions as a guide member for guiding the carriage 14 to move substantially vertical under positional restrictions. The position of the carriage 14 is kept by the guide rod 13 and the guide plate 121. The bearing 130 is inserted to the hole formed on the side plate. The guide rod 13 has, for example, a D-shape so as not to rotate, and is inserted to the bearing 130.

[0054] The center of the bearing 130 is located off the center of the guide rod 13. Therefore, when the lever 122 (i.e. input force) engaged with the bearing 130 is caused to swing in a direction of an arrow C in FIG. 13A, the bearing 130 rotates as a fulcrum, and the guide rod 13 (i.e. output force) moves up, thereby lifting the carriage 14. Since the guide plate 121 is fixed, the carriage 14 substantially vertically moves up and down along the guide plate 201.

[0055] The distance between the carriage 14 and the platen 12 can be increased as described above by using the carriage elevation mechanism, and the jammed recording sheet S can be removed from the image forming apparatus 100 without contacting the ink jet head 15 as shown in FIG. 13B. Further, the carriage 14 can be returned into the original position after the jammed recording sheet S is removed.

[0056] Alternatively, the carriage elevation mechanism of the image forming apparatus 100 may be configured as described below referring to FIGs. 14A and 14B. Descriptions of the same configuration as the carriage elevation mechanism shown in FIGs. 13A and 13B are omitted.

[0057] FIGs. 14A and 14B are cross section views of the image forming apparatus 100.

[0058] The position of the carriage 14 is kept by only the guide rod 13. The guide plate 121 is not needed. The guide rod 13 has, for example, the D-shape or a square shape so as not to rotate along with the bearing 130.

[0059] The center of the bearing 130 is located on the center of the guide rod 13. Therefore, when the lever 122 engaged with the bearing 130 is caused to swing in the direction of the arrow C in FIG. 14A, the bearing 130 and the guide rod 13 rotate as the fulcrum and the output force. As a result, the carriage 14 engaged with the guide rod 13 is pivotably lifted centering on an axis of the guide rod 13.

[0060] The distance between the carriage 14 and the platen 12 can be increased as described above by using the carriage elevation mechanism, and the jammed recording sheet S can be removed from the image forming apparatus 100 without contacting the ink jet head 15 as shown in FIG. 14B. Further, the carriage 14 can be returned into the original position after the jammed recording sheet S is removed.

[0061] The carriage elevation mechanism may include a solenoid actuator for causing the lever 122 to swing.

[0062] FIG. 15 is a cross section view of the image forming apparatus 100 having the carriage elevation mechanism shown in FIGs. 13A and 13B, and a solenoid actuator 123.

[0063] As shown in FIG. 15, the solenoid actuator 123 is connected to the lever 122, and drives the lever 122 to move up and down. The solenoid actuator 123 pulls down the lever 122 to lift the guide rod 13 and the carriage 14 as described above referring to FIGs. 13A and 13B. The solenoid actuator 123 pushes up the lever 122 so that the carriage 14 is returned into the original position.

[0064] FIGs. 16A and 16B are cross section views of the ink jet head 15 and recording mediums, and schematically illustrate recording on the recording mediums.

[0065] Although it is preferable that the ink jet head 15 and the recording sheet S are closely located, the carriage 14 is configured such that the ink jet head 15 is located at a distance of x from a thick recording sheet ST as shown in FIG. 16A. In the case of recording on, for example, an envelope, since component pieces of paper are pasted threefold or fourfold, the envelope is likely to contact the ink jet head 15. Therefore, as shown in FIG. 16B, the carriage 14 needs to be lifted in order to keep the distance of x between the ink jet head 15 and a recording envelope SE. Therefore, the image forming apparatus 100 includes a height adjustment lever 124 arranged such that the height adjustment lever 124 can be operated from outside a housing 125 of the image forming apparatus 100. The height adjustment lever 124 is operated according to types of the recording sheet S to move up or down the carriage 14 so that a constant distance is kept between the ink jet recording head 15 and the platen 12. Further, the moving distance of the carriage elevation mechanism and a platen elevation mechanism described below is variable, and is determined according to the thickness and the type of a recording sheet so that a sufficient space is provided for removing a jammed recording sheet. The carriage elevation mechanism is configured such that an operating angle y° of the height adjustment lever 124 is smaller than an operation angle z° of the lever 122 (i.e. y° < z°).

[0066] As described above, the lever 122 is caused to swing by the solenoid actuator 123 in carriage elevation mechanism shown in FIG. 15. Alternatively, the carriage elevation mechanism may include a motor for causing the lever 122 to swing.

[0067] FIG. 17 is a cross section view of the image forming apparatus 100 having the carriage elevation mechanism shown in FIGs. 13A and 13B, and a motor 126.

[0068] As shown in FIG. 17, the image forming apparatus 100 further includes a worm gear 207 connected to a shaft of the motor 206. An end portion of the lever 122 has teeth to serve as a gear, and is engaged with the worm gear 127. When the motor 126 is activated, the motor 126 drives the lever 122 to swing so that the carriage 14 is moved up and down. In the case, the moving distance of the carriage 14 may be varied by controlling the driving of the motor 126. As a result, the carriage 14 may be moved up into an appropriate position according to the thickness and the type of the recording sheet.

[0069] FIG. 18 is a flowchart of a jammed-sheet removal operation of the image forming apparatus 100 having the solenoid actuator 123 shown in FIG. 15.

[0070] Steps of the jammed-sheet removal operation are describe below referring to FIG. 18.

[0071] When a jam occurs, the jam is detected in step S901. In step S902, the image forming apparatus 100 checks whether or not a cover thereof is opened by an operator to remove a jammed sheet. When the image forming apparatus 100 does not detect opening of the cover (NO in step S902), step S902 is repeated. When the image forming apparatus 100 detects opening of the cover (YES in step S902), the image forming apparatus 100 turns on the solenoid actuator 123 in step S903. In step S904, the carriage 14 is moved up to increase the distance between the ink jet head 15 and the platen 12. In step S905, the operator removes the jammed sheet. In step S906, the image forming apparatus 100 turns off the solenoid actuator 123 so that the carriage 14 is returned into the original position. The solenoid actuator 123 remains on only when necessary so that electric power is prevented from being wasted. In step S907, the image forming apparatus 100 checks whether or not the cover is closed. When the image forming apparatus 100 does not detect closing of the cover (NO in step S907), step S907 is repeated. When the image forming apparatus 100 detects closing of the cover (YES in step S907), the image forming apparatus 100 checks whether or not a sensor for monitoring removal of a jammed sheet is in a normal state in which no sheet is detected in step S908. When the image forming apparatus 100 judges that the sensor is in the normal state (YES in step S908), the carriage 14 is moved down into a stand-by position, and is turned into a stand-by state in which a moisture retention cap is put on the ink jet head 15 in step S909. In step S910, a maintenance operation such as head cleaning is performed. Even when dust adheres to the ink jet head 15, the dust can be removed by the head cleaning, thereby preventing a nozzle thereof from being clogged with the dust. On the other hand, when the image forming apparatus 100 judges that the sensor is not in the normal state, in other words, the jammed sheet has not yet been removed (NO in step S908), the image forming apparatus 100 displays an error message to the extent that the jam has not been cleared to prompt the operator to remove the jammed sheet in step S911.

[0072] It is preferable that the carriage 14 is moved into the stand-by position or a position in which injection is performed without using actual ink before the carriage 14 is moved up, because when in the positions, the carriage 14 is located outside a print area, and removal of a jammed sheet may be easily performed.

[0073] An image forming apparatus 200 according to another embodiment of the present invention is described below referring to FIGs. 19A to 20B. The same components as the image forming apparatus 100 are represented by the same reference numerals.

[0074] FIGs. 19A and 19B are cross section views of the image forming apparatus 200 including a platen elevation mechanism.

[0075] As shown in FIGs. 19A and 19B, the image forming apparatus 200 includes the platen 12, the guide rod 13, the carriage 14, and the ink jet head 15. The image forming apparatus 200 further includes a plurality of link members 208 and a lever 209, which serve as the platen elevation mechanism of the present invention.

[0076] The plurality of link members 208 have respective rotation axes, and swingably support the platen 12. The lever 209 is connected to one of the rotation axes of the link members 208. When the lever 209 is pulled up in a direction of an arrow D shown in FIG. 19A, the platen 12 swings to increase the distance between the platen 12 and the ink jet head 15 as shown in FIG. 19B.

[0077] Alternatively, the platen elevation mechanism may include only the lever 209. FIGs. 20A an 20B are cross section views of the image forming apparatus 200 having the platen elevation mechanism including only the lever 209. In the case, the platen 12 is swingably supported by a supporting member, and the lever 209 is directly connected to a rotation axis of the supporting member. When the lever 209 is pulled up in the direction of the arrow D shown in FIG. 20A, the platen 12 swings to increase the distance between the platen 12 and the ink jet head 15 as shown in FIG. 20B.

[0078] In the embodiment of the present invention, the lever 209 of the image forming apparatus 200 is manually pulled up. Alternatively, the lever 209 may be moved up and down by using a solenoid actuator or a motor as in the embodiment described above referring to the image forming apparatus 100.

[0079] The present invention is not limited to the above embodiments. The mechanism for increasing the distance between the platen 12 and the ink jet head 15 may adopt various modifications or replacements within the scope of the claims of the present invention.

[0080] This patent specification is based on Japanese patent applications, No. JP2005-338303 filed on November 24, 2005, in the Japan Patent Office, the entire contents of which are incorporated by reference herein.

Claims

1. An image forming apparatus,(100; 200) using an ink jet method, comprising:

an ink jet head (15) including a nozzle, configured to discharge ink from the nozzle to form an image on a recording medium (S);

a carriage (14) configured to convey the ink jet head in a main scanning direction so that the ink jet head mounted thereon forms the image in the main scanning direction;

a platen (12) configured to support the recording medium, wherein the recording medium is conveyed along the platen so that the image is formed in a sub-scanning direction;

a jam detection mechanism (101, 102, 103) configured to detect a jam of the recording medium; and

a vary mechanism (122, 130; 208, 209) configured to vary a distance between the ink jet head and the platen according to the jam detection performed by the jam detection mechanism.

2. The image forming apparatus (100) according to claim 1, wherein the vary mechanism (122, 130) includes a carriage elevation mechanism (122, 130), and is configured to move the carriage (14) away from and toward the platen (12).

3. The image forming apparatus (100) according to claim 2, wherein the carriage elevation mechanism (122, 130) is configured to move up and down the carriage (14) in a substantially vertical direction.

4. The image forming apparatus (100) according to either claim 2 or claim 3, wherein the carriage elevation mechanism (122, 130) includes a pivot mechanism, and is configured to cause the carriage (14) to swing up and down on a pivot.

5. The image forming apparatus (200) according to any one of the preceding claims, wherein the vary mechanism (208, 209) includes a platen elevation mechanism (208, 209), and is configured to move the platen (12) away from and toward the ink jet head (15) mounted on the carriage (14).

6. The image forming apparatus (200) according to claim 5, wherein the platen elevation mechanism (208, 209) is configured to move up and down the platen (12) while keeping the platen substantially parallel to the ink jet head (15) mounted on the carriage (14).

7. The image forming apparatus (100; 200) according to any one of claims 4 or 6, wherein the pivot mechanism includes a drive mechanism having a solenoid actuator (123) or a motor (126).

8. The image forming apparatus (100; 200) according to any one of claims 1 through 7, wherein a distance at which the carriage (14) is caused to move up and down by the carriage elevation mechanism (122, 130) or a distance at which the platen (12) is caused to move up and down by the platen elevation mechanism (208, 209) is variable, and is determined according to at least one of a thickness and a type of the recording medium (S).

Drawing