Electricity: motive power systems – Open-loop stepping motor control systems
Reexamination Certificate
1999-09-30
2001-02-06
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Open-loop stepping motor control systems
Reexamination Certificate
active
06184646
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to stepping motor control units and image forming apparatuses, and more particularly to a stepping motor control unit which controls a stepping motor of an equipment such as an image forming apparatus, and to an image forming apparatus which uses such a stepping motor control unit. The present invention is particularly suited for controlling the speed and the like of a stepping motor which accurately transports a recording medium such as paper in printers, facsimile machines and copying machines.
2. Description of the Related Art
FIG. 1
is a system block diagram generally showing a printer control system. The printer control system shown in
FIG. 1
includes an image data storage part
61
which stores image data, an image data processing controller
62
, a printer control unit
63
, a driving system equipment
64
such as a stepping motor, a heating system equipment
65
such as a heat roller fixing unit, an optical system equipment
66
such as a laser head, other equipments
67
, and sensors
68
which are required to control the various equipments. For example, the image data stored in the image data storage part
61
are obtained by an input from a personal computer, a facsimile signal, an input from an image scanning or the like.
The image processing controller
62
obtains the image data from the image data storage part
61
, and converts the image data into a format which can be understood by the printer control unit
63
before supplying the image data to the printer control unit
63
. The printer control unit
63
controls the equipments
64
through
67
in order to print the image data supplied thereto. The printer control unit
63
reads outputs of the sensors
68
during the print control process, and switches the control operation.
FIG. 2
is a diagram generally showing an example of a printer. The printer shown in
FIG. 2
includes a resist motor
70
, a resist roller
71
which is driven by the resist motor
70
and transports paper, a pickup roller
72
which picks up the paper from a paper cassette
79
, an eject roller
73
, a transport path
74
, a photo sensor
75
for detecting the position of the paper, a photoconductive drum
76
, a laser optical system unit
77
for forming a latent image on the photoconductive drum
76
by writing an optical image, a heat roller fixing unit
78
for fixing a toner image on the paper, and the paper cassette
79
. The illustration of a developing part and a fixing part of the printer is omitted in FIG.
2
.
The resist roller
71
, the pickup roller
72
and the eject roller
73
shown in
FIG. 2
are driven by a stepping motor. A description will be given of a speed control of the resist motor
70
which drives the resist roller
71
. When a print start instruction is input, the pickup roller
72
rotates and picks up the paper from the paper cassette
79
, and in addition, the resist motor
70
is rotated to transport the paper. The resist motor
70
is accelerated to a predetermined speed and thereafter assumes a constant speed state by maintaining the predetermined speed. For example, when the resist motor
70
is in the constant speed state and the trailing edge of the paper passes the photo sensor
75
, an output of the photo sensor
75
changes from an ON state to an OFF state, that is, falls to a low level, thereby decelerating the resist motor
70
.
FIG. 3
is a system block diagram showing a conventional stepping motor control unit of the printer. The stepping motor control unit shown in
FIG. 3
includes a processor (CPU)
1
, a timer resistor and down counter
2
, a mutual excitation waveform output circuit
3
, a motor driving circuit
4
, a stepping motor
5
, an interrupt generating circuit
6
, an input port
7
for inputting a paper position state information signal from a sensor, and a ROM
8
which stores motor speed control data.
The processor
1
is located within the printer control unit
63
shown in FIG.
1
. The processor
1
writes a time value in the timer register and down counter
2
, and also control other parts of the printer. These other parts of the printer include the driving system equipment
64
, the heating system equipment
65
, the optical system equipment
66
, and the other equipments
67
. The timer register and down counter
2
outputs a time completion pulse when the time value instructed by the processor
1
is measured. This time completion pulse is input to the mutual excitation waveform output circuit
3
. When the time completion pulse is input, the mutual excitation waveform output circuit
3
switches the mutual excitation waveform. An output of the mutual excitation waveform output circuit
3
is subjected to a power amplification in the motor driving circuit
3
before being applied to the stepping motor
5
.
The time completion pulse is also input to the interrupt generating circuit
6
. The interrupt generating circuit
6
turns ON an interrupt signal S when the time completion pulse is input. When the interrupt signal S is turned ON, the processor
1
executes a processing program for controlling the stepping motor
5
. The processing program for controlling the stepping motor
5
controls the stepping motor
5
by referring to the data stored in the ROM
8
and the sensor output received via the input port
2
.
The ROM
8
includes an acceleration table
8
a
and a deceleration table
8
b.
In the acceleration table
8
a,
“phase-A and 10 &mgr;s” are written at an address
0
as shown in
FIG. 4
, indicating that the phase-A is to be excited first and that the time value is 10 &mgr;s. In addition, in the acceleration table
8
a, “
8 &mgr;s” is written at an address
1
, “6 &mgr;s” is written at an address
2
, and “4 &mgr;s” is written at an address
3
. In addition, “2 &mgr;sF” is written at an address
4
to indicate that the time value is 2 &mgr;s and this data is the last data in the acceleration table
8
a.
On the other hand, in the deceleration table
8
b, “
4 &mgr;s” is written at an address
0
, “6 &mgr;s” is written at an address
1
, and “8 &mgr;s” is written at an address
2
. Further, “10 &mgr;sF” is written at an address
3
to indicate that the time value is 10 &mgr;s and that this data is the last data in the deceleration table
8
b.
FIGS. 5 and 6
are diagrams for explaining example of an acceleration control, a constant speed control, and a deceleration control of the stepping motor
5
.
FIG. 5
shows excitation pulses during each period, and
FIG. 6
shows a mutual excitation waveform for each phase during a start control and a constant speed control of a 2-phase excitation type stepping motor. In
FIG. 6
, an interrupt signal SS shown below the interrupt signal S is obtained by the present invention, as will be described later.
FIG. 7
is a diagram for explaining signal exchanges between the timer register down counter
2
and the mutual excitation waveform output circuit
3
. The time value is written in a timer register of the timer register and down counter
2
by the processor
1
. When the processor
1
outputs a timer start trigger signal, the value in the timer register of the timer register and down counter
2
is loaded into a down counter of the timer register and down counter
2
, and the value of the down counter is decremented by 1 every time a time clock is input thereto. After outputting the timer start trigger signal, the processor
1
writes the next time value in the timer register of the timer register and down counter
2
. The processor
1
supplies an output enable signal to the mutual excitation waveform output circuit
3
at the same time as supplying the timer start trigger signal to the timer register and down counter
2
. As a result, the mutual excitation waveform output circuit
3
excites a phase specified by the processor
1
, such as a phase &phgr;A, for example.
When the down counter of the timer register and down counter
2
outputs a time completion pulse, the value of the timer register of the timer register and d
Kobayashi Takakazu
Yagoshi Teruaki
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Ro Bentsu
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