ClassID:

178230

G03G2215/0141 - CPC Classification

Classification description:

Apparatus for electrophotographic processes for producing multicoloured copies; Plural electrographic recording members; Linear arrangement adjacent plural transfer points primary transfer to a recording medium carried by a transport belt the linear arrangement being horizontal

Recent Application in this class:
#1
20260072390
2026-03-12

IMAGE FORMING APPARATUS, NON-TRANSITORY COMPUTER READABLE MEDIUM STORING PROGRAM, AND IMAGE FORMING METHOD

#2
20240353775
2024-10-24

DEVELOPING CARTRIDGE INCLUDING HOUSING AND GEAR

#3
20230068807
2023-03-02

Image forming apparatus with a reduced dimension in a horizontal direction

#4
20230066747
2023-03-02

Image forming apparatus with geometric configuration that reduces misregistration of images

#5
20220050405
2022-02-17

Developing cartridge including housing and gear

#6
20210311415
2021-10-07

Developing cartridge including housing and gear

#7
20210116835
2021-04-22

Image forming apparatus including multiple photosensitive drums and multiple developing rollers

#8
20200326643
2020-10-15

Developing cartridge including housing and gear

#9
20200241438
2020-07-30

IMAGE FORMING APPARATUS AND CONTROL METHOD OF IMAGE FORMING APPARATUS

#10
20200209781
2020-07-02

Image forming apparatus

#11
20200133155
2020-04-30

Image forming apparatus and control method of image forming apparatus

#12
20190204763
2019-07-04

Developing cartridge including housing and gear

#13
20180173133
2018-06-21

Image forming apparatus

#14
20180157194
2018-06-07

Developing cartridge including housing and gear

#15
20180150023
2018-05-31

Developer cartridge

#16
20180120755
2018-05-03

Image forming apparatus

#17
20180101125
2018-04-12

Image forming apparatus and tandem type photosensitive unit

#18
20170285505
2017-10-05

Developer cartridge

#19
20170277119
2017-09-28

Image forming apparatus having electrical contact

#20
20170277118
2017-09-28

Developer container, developer unit and image forming apparatus

#21
20170261906
2017-09-14

Image forming apparatus

#22
20170261881
2017-09-14

Lens unit, light-exposure apparatus, and image forming apparatus

#23
20170097580
2017-04-06

Member for electrophotography, developing apparatus, and electrophotographic apparatus

#24
20170090345
2017-03-30

Image forming apparatus

#25
20170003639
2017-01-05

Image-forming apparatus having structure for stably supporting belt unit

#26
20160320743
2016-11-03

Image forming apparatus and tandem type photosensitive unit

#27
20160291535
2016-10-06

Image forming apparatus

#28
20160291528
2016-10-06

Image forming apparatus and drum unit

#29
20160291527
2016-10-06

Image forming apparatus and drum unit with conveying unit for conveying toner removed from photosensitive drum

#30
20160291526
2016-10-06

Image forming apparatus having photosensitive members and blades in contact with respective photosensitive members

#31
20160291524
2016-10-06

Image forming apparatus providing stable engagement between gears upon attachment of drum unit to housing

#32
20160275389
2016-09-22

Printer with paper conveyance control upon paper jam

#33
20160274519
2016-09-22

Fixing device and electrophotographic image forming apparatus including the same

#34
20160266529
2016-09-15

Fixing device including heater, resin frame and metal frame having wall disposed between resin frame and heater

#35
20160259283
2016-09-08

Image forming apparatus having photosensitive body and charging device

#36
20160238991
2016-08-18

Image forming apparatus having developer cartridges and cartridge supporting member

#37
20160231693
2016-08-11

Image forming apparatus configured to use a common driving source for image bearing members

#38
20160224872
2016-08-04

Image forming apparatus, control method and non-transitory computer-readable medium

#39
20160216681
2016-07-28

Image forming apparatus

#40
20160216658
2016-07-28

Image heating apparatus having a rubbing rotatable member

#41
20160202656
2016-07-14

Image forming apparatus having cartridges

#42
20160152062
2016-06-02

Image forming apparatus

#43
20160147166
2016-05-26

Toner, two-component developer, and color-image forming apparatus

#44
20160144646
2016-05-26

Image forming apparatus

#45
20160131988
2016-05-12

Receiver materials with color toner images and fluorescent highlights

#46
20160116877
2016-04-28

Temperature-based rotational speed control for a developing roller in an image forming apparatus

#47
20160109822
2016-04-21

Optical writing control device for reducing driving power of optical writing device

#48
20160091858
2016-03-31

Image forming apparatus

#49
20160091857
2016-03-31

Image-forming apparatus provided with interlocking mechanism for inputting drive force to drive roller of belt unit

#50
20160091845
2016-03-31

Fixing device

#51
20160077465
2016-03-17

Developer cartridge

#52
20160054702
2016-02-25

Developer cartridge having developing roller and electrode

#53
20160026112
2016-01-28

Image forming apparatus

#54
20160018782
2016-01-21

Photosensitive drum access configuration for an image-forming apparatus

#55
20160011556
2016-01-14

Image forming apparatus, image forming method and non-transitory computer-readable storage device having image forming program

#56
20160004210
2016-01-07

Image-forming apparatus having structure for stably supporting belt unit

#57
20150338822
2015-11-26

Image forming apparatus having first cover and second cover

#58
20150338776
2015-11-26

Image forming apparatus having developer cartridge and cartridge supporting member

#59
20150331384
2015-11-19

Cleaning blade and image forming apparatus

#60
20150317545
2015-11-05

Image forming apparatus with re-conveyance mechanism

#61
20150277363
2015-10-01

Image forming apparatus and tandem type photosensitive unit

#62
20150277324
2015-10-01

Image forming apparatus and method for adjusting forming condition of image forming apparatus

#63
20150277284
2015-10-01

Developing cartridge positioning portions for relative positioning of developing roller, supply roller and housing

#64
20150277261
2015-10-01

Image forming apparatus having a developer carrier that separates from a photosensitive member during sheet re-conveyance

#65
20150261158
2015-09-17

Image forming apparatus, image forming method, and computer-readable storage medium that change data lengths of first data and second data according to a condition of image formation

#66
20150242733
2015-08-27

Image forming apparatus and method of forming images

#67
20150241837
2015-08-27

Image forming apparatus having process unit including photosensitive member and member for removing substances from photosensitive member

#68
20150156376
2015-06-04

Method for controlling color separations registration

#69
20150153700
2015-06-04

Image forming apparatus having panel unit

#70
20150147097
2015-05-28

Image forming unit and image forming apparatus

#71
20150117927
2015-04-30

Image processing apparatus including two portions for receiving discharged sheet

#72
20150110511
2015-04-23

Image forming apparatus having conveying body and transfer units

#73
20150104740
2015-04-16

Full-color toner set, full-color developer set, image-formation method using same, and image-formation device

#74
20150104223
2015-04-16

Developer cartridge having developing roller

#75
20150086246
2015-03-26

Developer cartridge

#76
20150086245
2015-03-26

Developer cartridge

#77
20150086224
2015-03-26

Developer cartridge

#78
20150003855
2015-01-01

Image forming apparatus capable of adjusting black and color print densities and control program for adjusting such densities

#79
20150003845
2015-01-01

Image forming apparatus that performs inspection of printed matter, method of controlling the same, and storage medium

#80
20150002600
2015-01-01

Image forming apparatus

#81
20140376961
2014-12-25

Image forming apparatus having developer cartridge and cartridge supporting member

#82
20140376958
2014-12-25

Image forming apparatus

#83
20140376957
2014-12-25

Frame-enhancing structure for a frame to support an image forming unit in an image forming apparatus

#84
20140376956
2014-12-25

Image forming apparatus with frame having hollowly-formed connecting frames

#85
20140334842
2014-11-13

Image forming apparatus

#86
20140321889
2014-10-30

Image formation apparatus and method of controlling image formation apparatus that utilizes misregistration amount detection patterns

#87
20140321874
2014-10-30

Cleaner, image forming apparatus using the cleaner, and voltage setting device

#88
20140314440
2014-10-23

Image forming apparatus

#89
20140305838
2014-10-16

Packing device

#90
20140294476
2014-10-02

Duplex printer with a unidirectional drive source and a gear train with a partially toothed gear

#91
20140294438
2014-10-02

Image forming apparatus having supporting member for supporting cartridges

#92
20140294437
2014-10-02

Image forming apparatus having supporting member with rigidity

#93
20140294425
2014-10-02

Image forming apparatus having movable supporting member for supporting cartridge

#94
20140286661
2014-09-25

Image forming apparatus

#95
20140270827
2014-09-18

Image forming apparatus

#96
20140255056
2014-09-11

Image forming apparatus

#97
20140248065
2014-09-04

Image forming apparatus having a controller to control the current flowing between a cleaning member and a collecting member

#98
20140241749
2014-08-28

Image forming apparatus having cartridges

#99
20140241746
2014-08-28

Image forming apparatus which controls fixing drive motor according to pressure roller diameter

#100
20140241743
2014-08-28

Circuit board configuration for image forming apparatus

#101
20140241736
2014-08-28

Image forming apparatus including cartridge for protecting photosensitive drum

#102
20140227006
2014-08-14

Image forming apparatus

#103
20140212642
2014-07-31

Enhanced color toner images using fluorescing magenta toners

#104
20140212169
2014-07-31

Image forming apparatus

#105
20140212158
2014-07-31

Image forming apparatus provided with cleaning member capable of reliably cleaning image bearing member

#106
20140205320
2014-07-24

Image forming apparatus having front cover and top cover

#107
20140205319
2014-07-24

Image forming apparatus

#108
20140204167
2014-07-24

Image forming apparatus having exposing unit positioning member

#109
20140147164
2014-05-29

Image forming apparatus

#110
20140147159
2014-05-29

Photosensitive member cartridge

#111
20140112671
2014-04-24

Image forming apparatus

#112
20140093275
2014-04-03

Image forming apparatus

#113
20140093274
2014-04-03

Image formation apparatus

#114
20140086658
2014-03-27

Image forming apparatus

#115
20140086645
2014-03-27

Temperature sensor and frame configuration for an image forming apparatus

#116
20140086644
2014-03-27

Fixing device and image forming apparatus

#117
20140079429
2014-03-20

Image forming apparatus

#118
20140076491
2014-03-20

Resin sheet manufacturing apparatus and resin sheet manufacturing method

#119
20140072319
2014-03-13

Image formation apparatus

#120
20140056616
2014-02-27

Electrographic printing of tactile images

#121
20140056615
2014-02-27

Developer cartridge

#122
20140044460
2014-02-13

Moving-member detecting device and image forming apparatus

#123
20140037350
2014-02-06

Sheet conveyer device and image forming apparatus

#124
20140037322
2014-02-06

Image forming device capable of reliably collecting matter deposited on endless belt in storage member and facilitating maintenance of storage member

#125
20140037321
2014-02-06

Image forming device capable of reliably recovering matter deposited on endless belt and ensuring smooth operations of retaining member

#126
20140037311
2014-02-06

Image forming device

#127
20140029978
2014-01-30

Image forming apparatus

#128
20140016979
2014-01-16

Image forming apparatus

#129
20140016964
2014-01-16

Image forming apparatus and tandem type photosensitive unit

#130
20140016963
2014-01-16

Image forming apparatus capable of easily drawing image forming unit from main casing

#131
20140010569
2014-01-09

Image forming apparatus including holder for holding photosensitive drums

#132
20130295498
2013-11-07

Enhancing color toner images with fluorescing magenta toners

#133
20130294801
2013-11-07

Highlighting color toner images with fluorescing toners

#134
20130259494
2013-10-03

Printing apparatus

#135
20130242318
2013-09-19

Image forming apparatus and method for controlling the same

#136
20130195521
2013-08-01

Producing gloss-watermark pattern on fixing member

#137
20130195520
2013-08-01

Producing gloss-watermark pattern on fixing member

#138
20130164041
2013-06-27

Developer storage container, image forming unit and image forming apparatus

#139
20130164033
2013-06-27

Photosensitive drum access configuration for an image forming apparatus

#140
20130164023
2013-06-27

Photosensitive member unit

#141
20130108330
2013-05-02

Developing device and image forming apparatus using the same

#142
20130108302
2013-05-02

Edge printing printer

#143
20130108289
2013-05-02

Image forming apparatus

#144
20130101322
2013-04-25

Image forming apparatus

#145
20130101308
2013-04-25

Airflow management method for corona charger

#146
20130084110
2013-04-04

Image forming device equipped with oblique motion prevention mechanism

#147
20130084109
2013-04-04

Image forming apparatus including image forming calibration

#148
20130084100
2013-04-04

Process cartridge and image forming apparatus

#149
20130084099
2013-04-04

Image forming apparatus

#150
20130084096
2013-04-04

Image forming apparatus having paper dust cleaning unit movably provided on photosensitive member unit

#151
20130084089
2013-04-04

Image forming apparatus and method of setting exposure amount

#152
20130077986
2013-03-28

Grounding configuration for an image forming apparatus

#153
20130071162
2013-03-21

COLOR TONER FOR OPTICAL FIXING AND IMAGE FORMING APPARATUS

#154
20130071138
2013-03-21

Development device and image formation apparatus

#155
20130064590
2013-03-14

Image-forming device

#156
20130058684
2013-03-07

Developing device capable of precisely positioning thickness-regulating member

#157
20130051857
2013-02-28

Developing device provided with developing roller and supply roller

#158
20130051856
2013-02-28

Process unit and image formation apparatus having a cleaning member in contact with a projection portion

#159
20130051852
2013-02-28

Developer cartridge having developing roller

#160
20130051816
2013-02-28

Cartridge having detection body

#161
20130028632
2013-01-31

Image forming apparatus and developer cartridge

#162
20130028631
2013-01-31

Image forming apparatus having developer cartridge moving mechanism

#163
20130011171
2013-01-10

Image forming apparatus with fixing unit adapted to fix toner including pressure-induced phase transition toner

#164
20120315063
2012-12-13

Process cartridge including developing roller and electrophotographic photosensitive member that can be contacted to and spaced from each other

#165
20120308259
2012-12-06

Image forming apparatus and process unit that form images by using photosensitive bodies and developing units

#166
20120301199
2012-11-29

Image formation device and belt unit therefor

#167
20120288305
2012-11-15

Developer cartridge

#168
20120275811
2012-11-01

COLOR IMAGE FORMING APPARATUS INCLUDING FUNCTION OF CORRECTING COLOR DRIFT OF IMAGE AND COLOR IMAGE FORMING METHOD

#169
20120269536
2012-10-25

Image forming apparatus

#170
20120262750
2012-10-18

Method of compensating for errors caused by a print head using skew correction

#171
20120256998
2012-10-11

Light emitting device, print head, and image forming apparatus

#172
20120251209
2012-10-04

Image forming device

#173
20120251192
2012-10-04

IMAGE FORMING APPARATUS

#174
20120251177
2012-10-04

Image formation apparatus

#175
20120251176
2012-10-04

ROTATING PRINTER PHOTORECEPTORS HAVING FIXED-POSITION FEATURES

#176
20120251164
2012-10-04

Image-forming apparatus

#177
20120251162
2012-10-04

Developing device provided with developing roller and thickness regulating blade

#178
20120251161
2012-10-04

Image forming device equipped with cleaning time determination unit

#179
20120249712
2012-10-04

Light-emitting chip, print head, and image forming apparatus

#180
20120243014
2012-09-27

Image forming apparatus for performing image adjustment that reduces time to print when mark formation and printing are required at the same time

#181
20120237232
2012-09-20

Printing apparatus

#182
20120229585
2012-09-13

Image forming apparatus, image forming method, and computer program product

#183
20120224898
2012-09-06

Gloss applier and image forming apparatus incorporating same

#184
20120224162
2012-09-06

Image forming apparatus

#185
20120219314
2012-08-30

Image forming apparatus including chargers around which air passes

#186
20120207522
2012-08-16

Image forming apparatus having an intermediate transfer belt

#187
20120207504
2012-08-16

Image forming apparatus

#188
20120201552
2012-08-09

Image forming apparatus capable of reducing image density irregularity

#189
20120195622
2012-08-02

Paper particle removing device, and image formation device provided with paper particle removing device

#190
20120195621
2012-08-02

Developing cartridge capable of providing stabilized electrical power supply to developing roller

#191
20120183332
2012-07-19

Image forming apparatus

#192
20120183325
2012-07-19

Image forming apparatus

#193
20120183324
2012-07-19

Image forming apparatus with movable exposure units

#194
20120183323
2012-07-19

Image forming apparatus

#195
20120183322
2012-07-19

Image forming apparatus

#196
20120183321
2012-07-19

Image forming apparatus having supporting member configured to hold developing sections

#197
20120183320
2012-07-19

Image forming apparatus

#198
20120183319
2012-07-19

Image forming apparatus

#199
20120183318
2012-07-19

Image forming apparatus having interlocking mechanism configured to interlock developing-section displacement mechanism and photosensitive-member displacement mechanism with cover

#200
20120163844
2012-06-28

Image forming apparatus and control program for detecting and correcting positional offset

#201
20120163843
2012-06-28

Image forming apparatus

#202
20120163842
2012-06-28

Image forming apparatus and method for controlling image forming apparatus

#203
20120148296
2012-06-14

Image forming apparatus comprising a plurality of process units

#204
20120134699
2012-05-31

Image forming apparatus having a configuration to prevent electric discharge in a cleaning member

#205
20120128382
2012-05-24

Image forming apparatus

#206
20120107017
2012-05-03

Image forming apparatus

#207
20120093524
2012-04-19

METHOD FOR PRINTING AN IMAGE ONTO A SHEET IN A PRINTER

#208
20120087697
2012-04-12

Image forming apparatus that includes a first developing device that holds a black developer and a second developing device that holds a gray developer

#209
20120082484
2012-04-05

IMAGE FORMING APPARATUS AND IMAGE FORMING METHOD

#210
20120076527
2012-03-29

Image forming device

#211
20120063829
2012-03-15

Sheet supplying device and image forming apparatus incorporating same

#212
20120057900
2012-03-08

Tandem-type process unit removably loaded in image forming device

#213
20120057888
2012-03-08

Developing voltage control using a deboost circuit in an image forming apparatus

#214
20120051762
2012-03-01

Image forming apparatus

#215
20120051759
2012-03-01

Determining developer toner concentration in electrophotographic printer

#216
20120039623
2012-02-16

Bias application control in an image forming apparatus

#217
20120027449
2012-02-02

Image forming device

#218
20120020704
2012-01-26

Toner cartridge having linearly movable shutter member and image forming device provided with the same

#219
20120020679
2012-01-26

Image forming apparatus having preference control unit

#220
20120002990
2012-01-05

IMAGE FORMING APPARATUS AND IMAGE FORMING METHOD

#221
20120002982
2012-01-05

IMAGE FORMING APPARATUS AND IMAGE FORMING METHOD

#222
20110318078
2011-12-29

Image forming apparatus and control method for the same

#223
20110318055
2011-12-29

Tandem drum unit having resiliently movable abutment portions

#224
20110318035
2011-12-29

Image forming apparatus having a controllable drive coupling

#225
20110317182
2011-12-29

Image forming apparatus

#226
20110311275
2011-12-22

Image forming apparatus

#227
20110286766
2011-11-24

Image forming apparatus having detachable process units

#228
20110280617
2011-11-17

Image formation apparatus

#229
20110279876
2011-11-17

Image processing apparatus

#230
20110255905
2011-10-20

Image forming apparatus having exposing unit positioning member

#231
20110242589
2011-10-06

Printing apparatus to determine correction on suspended image data

#232
20110236043
2011-09-29

Image forming apparatus with a plurality of image forming units

#233
20110222902
2011-09-15

Image forming device having cleaning member for cleaning belt

#234
20110217068
2011-09-08

Image forming apparatus having toner cartridge with movable shutter

#235
20110211861
2011-09-01

Image forming apparatus with a seamless belt and a tensile force applying mechanism for the seamless belt

#236
20110211853
2011-09-01

Image forming apparatus and storing medium

#237
20110199417
2011-08-18

Recording apparatus and method for controlling the recording apparatus

#238
20110164900
2011-07-07

Image forming apparatus

#239
20110164897
2011-07-07

Electrophotographic image forming apparatus with contacting and spacing member

#240
20110157613
2011-06-30

Image forming device that performs reverse-transfer operation in accordance with image forming condition

#241
20110135360
2011-06-09

Image forming unit with developer collector contacting image carrier at predetermined contact pressure, and image forming device

#242
20110123202
2011-05-26

Image forming apparatus

#243
20110097110
2011-04-28

Image forming apparatus having structure for securing removable unit

#244
20110091247
2011-04-21

Image forming apparatus

#245
20110076050
2011-03-31

Image forming apparatus having body-side contacts and unit-side contacts

#246
20110069981
2011-03-24

Belt drive device and image forming apparatus

#247
20110064463
2011-03-17

Developer cartridge

#248
20110064457
2011-03-17

Image forming apparatus and tandem type photosensitive unit

#249
20110026982
2011-02-03

Image forming apparatus

#250
20100329703
2010-12-30

Image forming apparatus for controlling disposal of developer

#251
20100310284
2010-12-09

Velocity detecting device and multi-color image forming apparatus

#252
20100303528
2010-12-02

Image forming apparatus and driver

#253
20100290810
2010-11-18

Image forming apparatus

#254
20100266311
2010-10-21

Image forming apparatus

#255
20100266301
2010-10-21

Image forming apparatus and image forming method

#256
20100247162
2010-09-30

Developer station for an electrographic printer having reduced developer agitation

#257
20100245865
2010-09-30

Image forming apparatus having a function for adjustment of image forming conditions

#258
20100239330
2010-09-23

Image forming apparatus having driving roller for automatic steering of intermediate image transfer belt

#259
20100226695
2010-09-09

Image forming apparatus having misregistration correction of the toner image formed by each image forming unit

#260
20100226694
2010-09-09

Image forming apparatus

#261
20100224090
2010-09-09

Methods of reducing grain and texture in a printed image

#262
20100209157
2010-08-19

Image-forming device having cleaning unit opposing belt

#263
20100189485
2010-07-29

Image forming apparatus

#264
20100178083
2010-07-15

Image forming apparatus and auto color registration method thereof

#265
20100178076
2010-07-15

Image forming apparatus

#266
20100166462
2010-07-01

Image forming apparatus including separation member for separating photosensitive member from endless belt

#267
20100166455
2010-07-01

Image forming apparatus

#268
20100158585
2010-06-24

Belt member feeding device and image forming apparatus provided with the same

#269
20100158568
2010-06-24

Belt member feeding device and image forming apparatus provided with the same

#270
20100158559
2010-06-24

Color electrophotographic image forming apparatus

#271
20100124430
2010-05-20

Image forming apparatus

#272
20100124155
2010-05-20

Rotary disk eccentricity measurement method, rotary encoder, and image forming apparatus including the rotary encoder

#273
20100104336
2010-04-29

Method and apparatus for printing embossed reflective images

#274
20100098465
2010-04-22

Image forming apparatus with belt adjustment

#275
20100098445
2010-04-22

Image forming apparatus having control unit

#276
20100092217
2010-04-15

Transferring unit and image forming apparatus including the same

#277
20100080581
2010-04-01

Image-forming device

#278
20100074638
2010-03-25

Image forming apparatus

#279
20100054813
2010-03-04

Image forming apparatus including positioning member for exposure unit

#280
20100054808
2010-03-04

Image forming device whose upper cover is provided with discharge roller and pinch roller

#281
20100053638
2010-03-04

Image-forming device

#282
20100021201
2010-01-28

Image forming apparatus having detachable process units

#283
20100021186
2010-01-28

IMAGE FORMING APPARATUS

#284
20100003059
2010-01-07

Bearing member, belt unit, and image forming device

#285
20090325097
2009-12-31

Developer, developer container, and image forming apparatus

#286
20090324280
2009-12-31

Tandem type photosensitive unit and image forming apparatus

#287
20090324275
2009-12-31

Tandem-type process unit removably loaded in image forming device

#288
20090317101
2009-12-24

Image forming apparatus

#289
20090297176
2009-12-03

Image forming apparatus with drive control unit

#290
20090269091
2009-10-29

Image forming device and image forming method thereof

#291
20090263148
2009-10-22

Image forming using a transparent toner image

#292
20090257779
2009-10-15

Image forming apparatus

#293
20090256615
2009-10-15

Pulse signal generating device, transport device, image forming apparatus, and pulse generating method

#294
20090245894
2009-10-01

Image forming apparatus belt having a detecting portion for position detection

#295
20090244567
2009-10-01

Image forming apparatus

#296
20090226229
2009-09-10

Image forming apparatus

#297
20090226225
2009-09-10

Image forming apparatus

#298
20090214274
2009-08-27

Image forming apparatus having removable belt

#299
20090208229
2009-08-20

Image Forming Apparatus

#300
20090202280
2009-08-13

Endless belt, transfer unit, and image forming apparatus