Printing – Processes – Transfer or offset
Reexamination Certificate
1999-12-07
2002-03-12
Eickholt, Eugene (Department: 2854)
Printing
Processes
Transfer or offset
C347S037000, C400S279000
Reexamination Certificate
active
06354216
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving mechanism for a scanning head which travels along a scanning surface and reads an image or writes an image, and to an image recording device which includes such a scanning head.
2. Description of the Related Art
In recent years, there have been developed a number of image recording devices equipped with an image scanning device of a digital exposure system. As an example, as is shown in
FIG. 14
, there is provided an image scanning device which has a scanning head
28
which moves parallel to a rotational axis
12
of an exposure drum
14
to scan and expose an exposure surface.
This scanning head
28
slides along shafts
16
and
18
(main scanning), writes an image on a photosensitive material which is wound around the exposure drum
14
by using a light beam modulated in accordance with image data and outputted from an optical semiconductor
36
(for example, a laser diode, an LED, or the like), and then the exposure drum
14
is rotated so as to be moved in steps (sub-scanning). The above-described movements are repeated in a sequential order.
The scanning head
28
is structured such that driving force is transmitted thereto from a timing belt
46
trained around sprockets
118
and
120
which are rotated by a stepping motor
52
, so that the scanning head
28
slides along the shafts
16
and
18
. However, due to deviation of a rotational shaft of the stepping motor
52
or other mechanical factors of the driving mechanism (the sprockets, a timing belt, or a reduction gear), cyclic speed variations of the scanning head
28
are caused (that is, the speed varies at the same position).
Due to such variations of the scanning speed of the scanning head
28
as described above, as in waveforms L
1
and L
2
which are shown in
FIG. 12A
, vibrations, which have amplitudes and periods whose phases correspond to each other, are caused in each of a forward scanning and a reverse scanning of the scanning head
28
within an exposure range thereof.
In this state, if the scanning head
28
writes an image, due to density variations (density unevenness) which are generated in a direction intersecting a scanning direction of the scanning head
28
(i.e., which are generated in the sub-scanning direction), vertical stripes are formed at fixed positions (for example, position C in FIG.
12
A), thus deteriorating image quality noticeably.
Moreover, as shown in
FIG. 15
, the scanning head
28
starts being driven from a stopping position S which is located outside a writing range, is accelerated and thereafter attains a constant speed in the writing range. Then, outside of the writing range, the speed of the scanning head is reduced, and the scanning head stops at a stopping position E. However, when driving is started, vibration is generated in the scanning head
28
.
Since the vibration phases correspond to each other per scan in the forward or reverse direction, if writing of an image is carried out in such a state, vertical stripes due to density variations are generated in the scan direction and the direction orthogonal thereto, deteriorating the image quality considerably.
For example, if the frequency of the vibration is 50 HZ and the scanning speed of the scanning head
28
is 600 mm/s, vertical stripes are generated at a 12 mm pitch.
SUMMARY OF THE INVENTION
In view of the aforementioned, an object of the present invention is to shift vibration periods or phases of a scanning head so as to reduce visibility of vertical stripes caused by variations in density.
In a first aspect of the present invention, there is provided a scanning head which travels along a scan surface and reads or writes an image. For each scan in which the scanning head travels and reads or writes an image, at least one of the period of and phase of the vibration generated at the scanning system is shifted. In this way, the visibility of vertical stripes caused by fluctuations in density can be reduced.
In a second aspect of the invention, the driving control mechanism changes a driving starting position of the scanning head or an acceleration starting position of the scanning head, either outside of the image reading range or outside of the image writing range.
In the aforementioned structure, not by shifting the driving starting positions randomly (it is of course allowable to shift the driving starting positions randomly), but by shifting the driving starting position per scan in case of reciprocating scans and by shifting the driving starting position per even-numbered scan in the case of one-way scans, it is ensured that the phases of the vibration of the scanning head can be shifted and visibility of vertical stripes can be reduced.
In a third aspect of the present invention, the driving mechanism for a scanning head of the first aspect further comprises: an acceleration pattern which generates vibrations at the scanning head at an arbitrary position during acceleration of the scanning head, in each scan for one of reading an image and writing an image; and a mechanism for changing the acceleration pattern, which changes the position at which vibrations are generated.
In this way, sudden changes in acceleration are applied to the scanning head during acceleration at a different position for each scan. Thus, the phase of the vibration is different for each scan, and vertical stripes are therefore less visible.
In a fourth aspect, the driving starting position or acceleration starting position is input in advance, on the basis of data on vibration periods when the scanning head is driven. The data on vibration periods may be measured and input in a memory for every machine type prior to shipping. Also, data input means may be provided in an image recording device, and, by using a test chart, positions where vertical stripes are produced may be actually identified visually, and the driving starting position or acceleration starting position may be shifted per scan. In this way, the driving mechanism for a scanning head of the present invention can cope with variations in the vibration periods that occur as time passes.
In a fifth aspect, data on vibration periods during driving of the scanning head is measured, and on the basis of the measured data, the one of the driving starting position and the acceleration starting position of the scanning head is calculated, and the calculated one of the driving starting position and the acceleration starting position of the scanning head is inputted. As the measuring means, for example, a linear encoder may be attached to the scanning head, or a rotary encoder may be attached to a rotational shaft of a sprocket which transmits driving force to the scanning head, to measure the data.
As described above, by measuring data per scan and calculating the driving starting position or the acceleration starting position, the driving mechanism for a scanning head of the present invention can cope with variations in vibration periods that occur due to disturbances.
In a sixth aspect, the drive control mechanism changes the stopping position of the scanning head, and, from the stopping position, driving of the scanning head is started.
In the aforementioned structure, if the stopping position of the scanning head is controlled and the scanning head is driven from the stopping position, the driving starting position or acceleration starting position can of course be shifted. Therefore, compared with a controlling method in which the stopping position is fixed and the driving starting positions are shifted when driving is started, control can be simplified.
In a seventh aspect of the present invention, for each scan in which an image is read or written, the phase of the vibration period is varied between the forward direction and the reverse direction by superposing fine driving on the driving pulse of the pulse motor which drives the scanning head.
An eighth aspect of the present invention is a driving mechanism for a scanning head which moves reciprocatingly so as to one of read
Eickholt Eugene
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
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