Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2001-11-13
2003-12-02
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S244000
Reexamination Certificate
active
06657651
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical writing head, in particular to an optical writing head in which the deviation of a line of light spots due to manufacturing dispersion of a rod-lens array. The present invention further relates to a method of correcting the deviation of a line of light spots.
BACKGROUND ART
A writing head of an optical printer, i.e. an optical writing head is a light source for exposing a photosensitive drum and comprises a line of light-emitting points consisting of a light-emitting element array. The structure of an optical printer including an optical writing head is shown in FIG.
1
. An optically conductive material (photosensitive material) such as amorphous Si is provided on the surface of a cylindrical drum
2
, which is rotated at the printing speed. The surface of the photosensitive material is uniformly charged with an electrostatic charger
4
. Then, light corresponding to a dot image being printed with an optical writing head
6
is projected onto the surface of the photosensitive material to neutralize the charge on the area to which the light is projected. Next, a developer
8
deposits the toner on the photosensitive material surface in accordance with the charged pattern on the photosensitive material surface. The transfer unit
10
transfers the toner on a paper sheet
14
fed from a cassette
12
. The toner on the paper sheet is thermally fixed by the heat applied by a fixer
16
, and the paper is sent to a stacker
18
. Upon completion of transfer, on the other hand, the charge on the drum is neutralized over the entire surface with an erasing lamp
20
, and the remaining toner is removed by a cleaner
22
.
The construction of the optical print head
6
is shown in FIG.
2
. This optical print head comprises a light-emitting element array
24
and a rod-lens array
26
, and the lens is adapted so as to focus on the photosensitive drum
2
. The rod-lens array be composed of alternately stacked rod lenses, for example.
The inventors of the present invention have interested in a three-terminal light-emitting thyristor having a PNPN-structure as an element of the light-emitting element array, and have already filed several patent applications (see Japanese Patent Publication Nos. 1-238962, 2-14584, 2-92650, and 2-92651.) These patent publications have disclosed that a self-scanning function for light-emitting elements may be implemented, and further have disclosed that such self-scanning light-emitting element array has a simple and compact structure for the light source of a printer, and has smaller array pitch of thyristors.
The inventors have further provided a self-scanning light-emitting element array having such structure that an array of light-emitting thyristors having transfer function is separated from an array of light-emitting thyristors having writable function (see Japanese Patent Publication No. 2-263668.)
Referring to
FIG. 3
, there is shown an equivalent circuit diagram of a fundamental structure of this self-scanning light-emitting element array (two-phase driving and cathode common type). According to this structure, the light-emitting element array comprises transfer elements T
1
, T
2
, T
3
. . . and writable light-emitting elements L
1
, L
2
, L
3
. . . , these elements consisting of three-terminal light-emitting thyristors. The structure of the portion of an array of transfer elements includes diode D
1
, D
2
, D
3
. . . as means for electrically connecting the gate electrodes of the neighboring transfer elements to each other. V
GK
is a power supply (normally 5 volts), and is connected to all of the gate electrodes G
1
, G
2
, G
3
. . . of the transfer elements via a load resistor R
L
, respectively. Respective gate electrodes G
1
, G
2
, G
3
. . . are correspondingly connected to the gate electrodes of the writable light-emitting elements L
1
, L
2
, L
3
. . . . A start pulse ø
S
is applied to the gate electrode of the transfer element T
1
, transfer clock pulses ø
1
and ø
2
are alternately applied to all of the anode electrodes of the transfer elements, and a write signal ø
I
is applied to all of the anode electrodes of the light-emitting elements.
The operation of this self-scanning light-emitting device will now be described briefly. Assume that as the transfer clock ø
1
is driven to a high level, the transfer element T
2
is now turned on. At this time, the voltage of the gate electrode G
2
is dropped to a level near zero volt from 5 volts. The effect of this voltage drop is transferred to the gate electrodes G
3
via the diode D
2
to cause the voltage of the gate electrode G
3
to set about 1 volt which is a forward rise voltage (equal to the diffusion potential) of the diode D
2
. On the other hand, the diode D
1
is reverse-biased so that the potential is not conducted to the gate G
1
, then the potential of the gate electrode G
1
remaining at 5 volts. The turn on voltage of the light-emitting thyristor is approximated to a gate electrode potential+a diffusion potential of PN junction (about 1 volt.) Therefore, if a high level of a next transfer clock pulse ø
2
is set to the voltage larger than about 2 volts (which is required to turn-on the transfer element T
3
) and smaller than about 4 volts (which is required to turn on the transfer element T
5
), then only the transfer element T
3
is turned on and other transfer elements remain off-state, respectively. As a result of which, on-state is transferred from T
2
to T
3
. In this manner, on-state of transfer elements are sequentially transferred by means of two-phase clock pulses.
The start pulse ø
S
works for starting the transfer operation described above. When the start pulse ø
S
is driven to a low level (about 0 volt) and the transfer clock pulse ø
2
is driven to a high level (about 2-4 volts) at the same time, the transfer element T
1
is turned on. Just after that, the start pulse ø
S
is returned to a high level.
Assuming that the transfer element T
2
is in the on-state, the voltage of the gate electrode G
2
is lowered to almost zero volt. Consequently, if the voltage of the write signal ø
I
is higher than the diffusion potential (about 1 volt) of the PN junction, the light-emitting element L
2
may be turned into an on-state (a light-emitting state.)
On the other hand, the voltage of the gate electrode G
1
is about 5 volts, and the voltage of the gate electrode G
3
is about 1 volt. Consequently, the write voltage of the light-emitting element L
1
is about 6 volts, and the write voltage of the light-emitting element L
3
is about 2 volts. It follows from this that the voltage of the write signal ø
I
which can write into only the light-emitting element L
2
is in a range of about 1-2 volts. When the light-emitting element L
2
is turned on, that is, in the light-emitting state, the amount of light thereof is determined by the write signal ø
I
. Accordingly, the light-emitting elements may emit light at any desired amount of light. In order to transfer on-state to the next element, it is necessary to first turn off the element in on-state by temporarily dropping the voltage of the write signal ø
I
down to zero volts.
The self-scanning light-emitting element array described above may be fabricated by arranging a plurality of light-emitting element array chips in one line so as to have a desired number of light-emitting points.
In an optical writing head using such self-scanning light-emitting element array, there is a problem in that a line of light spots which are projected on the photosensitive drum is deviated from a straight line in a sub-scanning direction due to the manufacturing dispersion of a rod-lens array.
FIG. 4
shows the condition where a line of light spots is deviated in a sub-scanning direction. The light
41
emitted from each light-emitting point
40
of a straight-line light-emitting element array
28
passes through a rod-lens array
26
constructed by alternately stacked rod-lenses
27
. The light passed through the rod-lens array is projected onto the photosensitive drum (not
Nippon Sheet Glass Co. Ltd.
Pham Hai
RatnerPrestia
LandOfFree
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