Electricity: motive power systems – Positional servo systems – With particular motor control system responsive to the...
Reexamination Certificate
2001-09-27
2003-08-05
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Positional servo systems
With particular motor control system responsive to the...
C318S696000
Reexamination Certificate
active
06603282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a DC motor control device and a DC motor control method especially for use as a countermeasure against heat generated at a carriage of a serial printer driven by a DC motor.
2. Related Background Art
First explained are general configuration of an ink jet printer using a DC motor control device and its control method.
FIG. 1
is a block diagram that shows general configuration of an ink jet printer.
The ink jet printer shown in
FIG. 1
includes a paper feed motor (hereinafter also called a PF motor)
1
that feeds paper; a paper feed motor driver
2
that drives the paper feed motor
1
; a carriage
3
that supports a head
9
fixed thereto to supply ink onto printing paper
50
and is driven to move in parallel to the printing paper
50
and vertically of the paper feeding direction; a carriage motor (hereinafter also called a CR motor)
4
that drives the carriage
3
; a CR motor driver
5
that drives the carriage motor
4
; a DC unit
6
that outputs a D.C. current for controlling the CR motor driver
5
; a pump motor
7
that controls the draft of ink for the purpose of preventing clogging of the head
9
; a pump motor driver
8
that drives the pump motor
7
; a head driver
10
that drives and controls the head
9
; a linear encoder
11
fixed to the carriage
3
; a linear encoder coding plate
12
having slits in predetermined intervals; a rotary encoder
13
for the PF motor
1
; a paper detecting sensor
15
that detects the terminal position of each sheet of paper under printing; a CPU
16
that controls the whole printer; a timer IC
17
that periodically generates interruption signals to the CPU
16
; an interface portion (hereinafter also called IF)
19
that exchanges data with a host computer
18
; an ASIC
20
that controls the character resolution, driving waveform of the head
9
, and so on, in accordance with character information sent from the host computer
18
through the IF
19
; a PROM
21
, a RAM
22
and an EEPROM
23
that are used as an operation area of the ASIC
20
and the CPU
16
and a program storage area; a platen
25
that supports the printing paper
50
; a transport roller
27
driven by the PF motor
1
to transport the printing paper
50
; a pulley
30
attached to a rotating shaft of the CR motor
4
; and a timing belt
31
driven by the pulley
30
.
The DC unit
6
controls and drives the paper feed motor driver
2
and the CR motor driver
5
in response to a control instruction sent from the CPU
16
and outputs of the encoders
11
,
13
. Both the paper feed motor
1
and the CR motor
4
are DC motors.
FIG. 2
is a perspective view that illustrates configuration around the carriage
3
of the ink jet printer.
As shown in
FIG. 2
, the carriage
3
is connected to the carriage motor
4
by the timing belt
31
via the pulley
30
, and driven to move in parallel with the platen
25
under guidance of a guide member
32
. The carriage
3
has the recording head
9
projecting from its surface opposed to the printing paper and having a row of nozzles for releasing black ink and a row of nozzles for releasing color ink. These nozzles are supplied with ink from the ink cartridge
34
and release drops of ink onto the printing paper to print characters and images.
In a non-print area of the carriage
3
, there is provided a capping device
35
for shutting nozzle openings of the recording head
9
when printing is not executed, and a pump unit
36
having the pump motor
7
shown in FIG.
1
. When the carriage
3
moves from the print area to the non-print area, it contacts a lever, not shown, and the capping device
35
moves upward to close the head
9
.
When any of the nozzle openings of the head
9
is clogged, or ink is forcibly released from the head
9
just after replacement of the cartridge
34
, the pump unit
36
is activated while closing the head
9
, and a negative pressure from the pump unit
36
is used to suck out ink from the nozzle openings. As a result, dust and paper powder are washed out from around the nozzle openings, and bubbles in the head
9
, if any, are discharged together with the ink to the cap
37
.
FIG. 3
is a diagram schematically illustrating configuration of the linear encoder
11
attached to the carriage
3
.
The encoder
11
shown in Gig.
3
includes a light emitting diode
11
a
, collimator lens
11
b
and detector/processor
11
c
. The detector/processor
11
c
has a plurality of (four) photo diodes
11
d
, signal processing circuit
11
e
, and two comparators
11
fA
,
11
fB
.
When a voltage V
CC
is applied across opposite ends of the light emitting diode
11
a
through a resistor, light is emitted from the light emitting diode
11
a
. This light is collimated into parallel beams by the collimator lens
11
b
, and the beams pass through the coding plate
12
. The coding plate
12
has slits in predetermined intervals (for example, in intervals of {fraction (1/180)} inch).
Parallel beams passing through the coding plate
12
enter into photo diodes
11
d
through fixed slits, not shown, and are converted into electric signals. Electric signals output from these four photo diodes
11
d
are processes in the signal processing circuit
11
e
. Signals output from the signal processing circuit
11
e
are compared in the comparators
11
fA
,
11
fB
, and comparison results are output as pulses. Pulses ENC-A, ENC-B output from the comparators
11
fA
,
11
fB
are outputs of the encoder
11
.
FIGS. 4A and 4B
are timing charts showing waveforms of two output signals from the encoder
11
during normal rotation of the CR motor and during its reverse rotation.
As shown in
FIGS. 4A and 4B
, in both normal rotation and reverse rotation of the CR motor, the pulse ENC-A and the pulse ENC-B are different in phase by 90 degrees. The encoder
4
is so configured that the pulse ENC-A is forward in phase by 90 degrees relative to the pulse ENC-B as shown in
FIG. 4A
when the CR motor
4
rotates in the normal direction, i.e., when the carriage
3
is moving in its main scanning direction whereas the pulse ENC-A is behind in phase by 90 degrees relative to the pulse ENC-B as shown in
FIG. 4B
when the CR motor
4
rotates in the reverse direction. Then, one period T of these pulses corresponds to each interval of the slits of the coding plate
12
(for example, {fraction (1/180)} inch), and it is equal to the time required for the carriage
3
to move from a slit to another.
On the other hand, the rotary encoder
13
for the PF motor
1
has the same configuration as the linear encoder
11
except that the former is a rotatable disc that rotates in response to rotation of the PF motor
1
, and the rotary encoder
13
also outputs two output pulses ENC-A, ENC-B. In ink jet printers, in general, slit interval of a plurality of slits provided on a coding plate of the encoder
13
for the PF motor
1
is {fraction (1/180)} inch, and paper is fed by {fraction (1/1440)} inch when the PF motor rotates by each slit interval.
FIG. 5
is a perspective view showing a part related to paper feeding and paper detection.
With reference to
FIG. 5
, explanation is made about the position of the paper detecting sensor
15
shown in FIG.
1
. In
FIG. 5
, a sheet of printing paper
50
inserted into a paper feed inlet
61
of a printer
60
is conveyed into the printer
60
by a paper feed roller
64
driven by a paper feed motor
63
. The forward end of the printing paper
50
conveyed into the printer
60
is detected by an optical paper detecting sensor
15
, for example. The paper
50
whose forward end is detected by the paper detecting sensor
15
is transported by a paper feed roller
65
driven by the PF motor
1
and a free roller
66
.
Subsequently, ink is released from the recording head (not shown) fixed to the carriage
3
which moves along the carriage guide member
32
to print something on the printing paper
50
. When the paper is transported to a predetermined position, the terminal end of the printing paper
50
currently under p
Dang Khanh
Seiko Epson Corporation
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