Electrophotography – Control of electrophotography process – Control of fixing
Reexamination Certificate
2001-04-23
2003-09-02
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of fixing
Reexamination Certificate
active
06615005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus which performs printing on both faces of a recording medium, a control method for the image forming apparatus, and a storage medium.
2. Related Background Art
In recent years, an image forming apparatus which transfers yellow, magenta, cyan and black images on a sheet (a recording medium) in an electrophotographic process, fixes formed toner images to the sheet by a fixing roller, and then discharges the sheet to perform two-faced printing is widespread.
As shown in
FIG. 6
, in case of the two-faced printing by the image forming apparatus, for example, a transportation roller
326
is reversed after the trailing edge of the sheet passed a sheet discharge sensor
324
, the sheet is thus switched back, and then the image is again formed on the back face of the sheet through a reverse rotation path
325
.
FIG. 7
is a block diagram showing a control structure of the conventional image forming apparatus. Hereinafter, the control structure of the conventional image forming apparatus will be explained.
In
FIG. 7
, numeral
401
denotes a CPU which controls the image forming apparatus as a whole, and numeral
402
denotes a DC (direct current) brushless motor which drives a photosensitive drum for yellow (called a Y photosensitive drum). The DC brushless motor
402
drives each roller of an yellow (Y) cartridge
314
, a Y photosensitive drum
306
, and a transfer roller for yellow (called a Y transfer roller)
310
shown in FIG.
6
.
Numeral
403
denotes a DC brushless motor which drives a photosensitive drum for magenta (called an M photosensitive drum). The DC brushless motor
403
drives each roller of a magenta (M) cartridge
315
, an M photosensitive drum
307
, and a transfer roller for magenta (called an M transfer roller)
311
shown in FIG.
6
.
Numeral
404
denotes a DC brushless motor which drives a photosensitive drum for cyan (called a C photosensitive drum). The DC brushless motor
404
drives each roller of a cyan (C) cartridge
316
, a C photosensitive drum
308
, and a transfer roller for cyan (called a C transfer roller)
312
shown in FIG.
6
. Numeral
405
denotes a DC brushless motor which drives a photosensitive drum for black (called a Bk photosensitive drum). The DC brushless motor
405
drives each roller of a black (Bk) cartridge
317
, a Bk photosensitive drum
309
, and a transfer roller for black (called a Bk transfer roller)
313
shown in FIG.
6
.
Numeral
406
denotes a high voltage control circuit which applies a high voltage based on the electrophotographic process to the photosensitive drums, the cartridges, the transfer rollers and an electrostatic belt and controls the applied voltage. The high voltage control circuit
406
contains control circuits for four colors. Numeral
407
denotes a scanner control circuit which scans the photosensitive drum with a laser beam. Also, the scanner control circuit
407
contains control circuits for the four colors.
Numeral
408
denotes a fixing control circuit which controls a temperature of a fixing heater, and numeral
409
denotes a sheet discharge sensor. Numeral
410
denotes a DC brushless motor which drives the fixing roller and the electrostatic belt. Namely, the DC brushless motor
410
controls an electrostatic belt
305
and a fixing roller
322
shown in FIG.
6
. Numeral
411
denotes a pulse motor which drives a sheet feed roller. Namely, the pulse motor
411
drives a sheet feed roller
303
shown in FIG.
6
. Numeral
412
denotes a pulse motor which is used to perform the two-faced printing. Namely, the pulse motor
412
drives the transportation roller
326
shown in FIG.
6
.
Numerals
413
and
414
denote driver (D/V) IC's for the pulse motors. Each of the D/V IC's
413
and
414
performs constant current control to flow a desired current in a desired excitation phase on the basis of an excitation signal supplied from the CPU.
Numeral
415
denotes an interface which communicates with a not-shown host computer.
As above, the color image forming apparatus includes the plural driving motors, and uses them according to an object. The respective motors are started, controlled and stopped by the control CPU.
FIG. 8
is a block diagram showing a circuit structure of the conventional DC brushless motor.
In
FIG. 8
, numeral
501
denotes a motor unit, numeral
502
denotes a control IC, and numeral
503
denotes a three-phase motor. Numeral
504
denotes a Hall sensor which detects a position of a main pole in a rotor. Numeral
505
denotes an FG sensor which detects a pattern adhered magnetically to the rotor, and outputs
36
pulses per one rotation of the motor.
Numeral
506
denotes an oscillator, numeral
507
denotes a current detection resistor, numeral
508
denotes a control unit, numeral
509
denotes a driver unit, numeral
510
denotes a current limiter detection unit, numeral
511
denotes a speed control unit, numeral
512
denotes a frequency divider, and numeral
513
denotes an integrating amplifier. Numerals
514
and
516
denote resistors which are integrating amplifier constants, and numerals
515
and
517
denote capacitors which are also integrating amplifier constants.
Numeral
518
denotes a control signal line which is used to drive and stop the motor from a not-shown microcomputer, and numeral
519
denotes a ready signal line which is activated when the number of rotations of the motor reaches a predetermined value. Further, a motor brake signal line is provided to supply a motor brake signal.
Next, an operation will be explained.
When a motor driving instruction is issued through the control signal line
518
by controlling the image forming apparatus, the control unit
508
detects the position of the main pole in the rotor of the three-phase motor
503
by using the Hall sensor
504
, creates a three-phase excitation pattern to rotate the motor in a desired rotation direction, and transmits an excitation signal to a driver unit
509
.
In response to the excitation signal, the driver unit
509
excites a not-shown output transistor to change the current direction for the coil of the three-phase motor
503
to obtain desired excitation. On the other hand, when the rotor of the three-phase motor
503
is rotated, a predetermined pulse is generated by the FG sensor
505
, and the generated pulse is transferred to the speed control unit
511
. The speed control unit
511
compares a reference clock generated by the oscillator
506
and the frequency divider
512
with the pulse detected by the FG sensor
505
, and then outputs a difference obtained in the comparison.
The reference clock is set to be the object number of rotations of the motor. Namely, when the FG sensor outputs 30 pulses per one rotation of the motor, the reference clock only needs 600/60×30=300 Hz to rotate the motor by 600 rpm.
The difference from the object speed obtained by the speed control unit
511
is integrated by the integrating amplifier
513
and transferred to the driver unit
509
. At this time, a gain and a phase compensation value are determined by the resistors
514
and
516
and the capacitors
515
and
517
.
Such constants are called servo constants.
FIG. 9
is a timing chart showing switchback control timing in sheet feed, sheet transportation and two-faced printing of the conventional image forming apparatus.
In
FIG. 9
, numeral
601
denotes sheet feed motor driving timing, numeral
602
denotes photosensitive drum driving timing for each color, numeral
603
denotes fixing roller driving timing, numeral
604
denotes sheet discharge sensor output timing, and numeral
605
denotes reverse rotation motor driving timing.
First, when a printing start is triggered at a time
606
, the photosensitive drum, the transfer roller, the cartridge driving roller and the electrostatic belt are driven at a time
607
. Then, the sheet feed motor is driven at a time
608
to feed and transport the sheet.
After the sheet is transported, when a desired
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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