Facsimile and static presentation processing – Facsimile – Picture signal generator
Reexamination Certificate
2000-01-12
2003-03-18
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C358S497000, C358S474000
Reexamination Certificate
active
06535305
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a transmission mechanism for optical scanner and particularly to a scanner transmission mechanism that uses a screw bar to drive screw nuts to perform scanning operation.
2. Description of the Prior Art
Optical scanner is a widely used computer peripheral device which uses a chassis to capture image and a transmission mechanism to move the chassis for scanning a document.
FIG. 1
illustrates a conventional scanner transmission mechanism which generally includes a screw bar
10
, a nut
20
and a chassis
30
fastened to the nut
20
. The screw bar
10
is an elongate bar with threads
101
formed on outside surface. One end of the screw bar
10
engages with a motor
103
which may drive the screw bar
10
to rotate when activated.
The nut
20
has a round internal opening with internal threads (not shown in the figure) formed inside and is engageable with the threads
101
. When the motor
103
is activated and rotates, the screw bar
10
will be turned and moves the nut
20
linearly which in turn moves the chassis
30
reciprocally to perform scanning operation.
However due to machining limitation, there will be tolerance between the threads
101
and the internal threads
202
of the nut
20
(the gap between thread
101
and
202
shown in FIG.
2
). This gap will cause impact and vibration between the screw
10
and nut
20
during scanning operation.
For instance, when driving force is large, the screw bar
10
moves ahead and causes the front surface of the threads
202
making contact with the front surface of the threads
101
and result in a thread gap formed in the rear portion (shown in FIG.
2
A). When friction resistance is large, the contact surface will take place between the rear surface of the threads
101
and
202
, and result in a gap forming at the front position (shown in FIG.
2
B). During scanning operation, the nut
20
will be moved reciprocally along the screw bar
20
. The existence of the gap between the threads will cause vibration, which have negative impact on scanning quality and will lower scanner durability. The turning of the screw bar
10
also tends to tilt the nut
20
skew angularly (as shown in
FIG. 2C
) which may further down grade scanning quality. All of this begs for improvement.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a transmission mechanism for scanner that does not have reciprocal vibration between the screw bar and nut for achieving higher quality scanning.
It is another object of this invention to provide a transmission mechanism for scanner that is free of vibration between the screw bar and nut for enhancing durability of the scanner.
It is a further object of this invention to provide a transmission mechanism for scanner that may prevent the nut from tilting angularly for enhancing scanning quality.
The transmission mechanism according to this invention includes a screw bar, a first nut, a second nut, a retainer, a first spring and a second spring. The screw bar is an elongate bar with threads formed on outside surface and has one end engaged with and driven by a motor for rotation. The first and second nut have internal threads engageable with the threads of the screw bar. The first nut is located between the motor and second nut.
The retainer is a hollow casing for housing the first and second nut inside. It has a front wall making contact with the first nut. The first spring is located and compressed between the first and second nut. The second spring is located and compressed between the second nut and a rear wall of the retainer. The second spring has greater spring force than the first spring. Hence the first nut is pressed with the rear surface of the internal threads making close contact with the threads of the screw bar. By the same token, the front surface of the internal threads of the second nut is making close contact with the threads of the screw bar. Therefore even when there is variation in driving or friction force in the transmission mechanism, the relative position between the first and second nut remains constant in the retainer. Vibration between the nuts and the screw bar thus may be avoided. Better scanning quality may be obtained and scanner durability may be improved. Furthermore, the retainer helps to prevent the nuts from tilting angularly which may further improve scanning quality.
REFERENCES:
patent: 4651229 (1987-03-01), Coli
patent: 5264949 (1993-11-01), Stemmle
patent: 5467111 (1995-11-01), Furukawa et al.
patent: 5771059 (1998-06-01), Kerr et al.
patent: 5973717 (1999-10-01), Kerr et al.
patent: 5997119 (1999-12-01), Kerr
patent: 6049348 (2000-04-01), Spurr
patent: 6208368 (2001-03-01), Kerr
patent: 6384897 (2002-05-01), Tsuji
patent: 6476849 (2002-11-01), Kerr
Chang Tsang-Huai
Fang Po-Hua
Lee Cheukfan
Troxell Law Office PLLC
UMAX Data Systems Inc.
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