Patent Application
20070154241
(i) Technical Field
The present invention relates to an image scanner for reading image information of a document. And the invention relates to an image scanner which is not only used alone but also used as, in particular, an image reading unit of an image forming apparatus such as a copier or a multifunction machine which utilizes image information read from a document.
(ii) Related Art
As one example of image scanners used in copiers and multifunction machines, there is one in which two carriages mounted with optical components such as an illumination lamp and reflection mirrors in a distributed manner are reciprocated under the bottom surface of a platen glass as a document stage (document placement surface) inside a case to which the platen glass is attached and an image of image information of a document placed on the platen glass is formed on an image sensor such as a CCD (charge-coupled device) linear sensor or directly formed an image carrying body such as a photoreceptor body via optical components such as an image forming lens. There is another image scanner in which even the image sensor is mounted on the carriages.
In the above image scanners, in general, the two carriages are supported so as to run on rails that are disposed along the read scanning direction which is parallel with the surface of the platen glass, and a wire drive mechanism is employed which reciprocates, at a movement distance ratio, the carriages which are connected to wires each of which is wound on and stretched between plural pulleys.
However, in this case, since the carriages are merely held by the wire on the rails, they may swing widely when vertical vibration is applied to them, as a result of which the reflection mirrors mounted thereon may be damaged, deviated in position, or subjected to other trouble. Such trouble most likely occurs when, for example, an image scanner is transported after its manufacture or in changing its installation location because unexpected impact may be exerted on it many times as external force in such a situation.
As for the carriage locations, for example,
In the image scanner of the related art, in the transport position mode, since as shown in
In the transport position mode, since the other carriage 20 merely kept in a state that it is stopped and fixed on the rails via wires 41, it may move in the read scanning direction X2 when impact is exerted on it during a transport. If this carriage is moved in the read scanning direction X2, wire portions connected to it are also moved and loosened. Those wire portions may come off the closest pulleys (e.g., the pulleys 44) on which those wire portions are wound.
One countermeasure is such that the other carriage is also fixed completely in position by pressing it against a fixedly disposed member. However, in this case, impact occurring during a transport is transmitted to the carriage via the fixedly disposed member without being weakened and may adversely affect the optical components mounted on the carriage.
According to an aspect of the invention, there is provided a image for a document, comprising:
a case having a document placement surface on which a document is placed;
rails disposed inside the case along a read scanning direction which is parallel with the document placement surface;
two carriages comprising a first carriage and a second carriage which have optical components and move by running on the rails;
a fixedly disposed member disposed on one end side in the read scanning direction, the fixedly disposed member stopping and fixing one of the two carriages;
a wire drive mechanism having a plurality of pulleys and wires each of which is wound on and stretched between the plurality of pulleys, the wire drive mechanism reciprocating the two carriages which are coupled to the wires; and
a movement restricting member that restricts a maximum movement distance of the first carriage in a stationary position mode to about 1.6d or less, d being a groove depth of pulleys in mm and the maximum movement distance being a distance by which the first carriage is allowed to move in the read scanning direction in the stationary position mode in which the first carriage is kept stopped and fixed via the wires by moving the second carriage by causing the wire drive mechanism to operate so that the second carriage hits the fixedly disposed member to be stopped and fixed.
An exemplary embodiment of the invention will be discussed with reference to the accompanying drawings.
First, the reason why, as described above, the maximum movement distance which is attained by the movement restricting member is set at about 1.6d or less in the image scanner according to an exemplary embodiment of the invention is as described below. The maximum movement distance L at least does not include zero (0<L). It is better that the maximum movement distance L be smaller than or equal to (π/2)d, and it is even better that the maximum movement distance L be smaller than or equal to d. Restricting the maximum movement distance L to such better values makes it possible to prevent, more reliably, the wires from coming off the pulleys, as well as to make even shorter the distance by which the other carriage is allowed to move in the read scanning direction in the stationary position mode. The depth d of the pulley groove is the height-direction distance from the bottom of the pulley groove to the flange tops (see
No particular limitations are imposed on the structure, the location, etc. of the movement restricting member as long as it can restrict the maximum movement distance in the read scanning direction. However, from the viewpoints of the cost, reduction in the number of components, etc., it is advantageous, over a case of providing the movement restricting member as a new component, to form the movement restricting member as a portion of the case. The movement restricting member is only required to restrict (the distance of) movement of the other carriage at least in one of the two directions of the read scanning direction, the one direction being such that the wires may come of the pulleys if a movement occurs in that direction. That is, there is no particular reason to restrict movement in both directions.
Furthermore, the movement restricting member may be a drawn projection that is formed by bending a portion of the case (e.g., a portion of a frame that is located on such a side as to face the other carriage being located at the stationary position). In this case, since the drawn projection is connected to the case at two locations, it is higher in mechanical strength than a bent portion that is erected by cutting the case and is connected to the case at only one end. Should the other carriage hits the drawn projection, the drawn projection is never deformed or damaged.
Usually, the other carriage is a carriage that is mounted with optical components including a reflection mirror and a light source for illuminating a document. However, it may be a carriage that is not mounted with a light source. Usually, the fixedly disposed member is part of the case (e.g., a frame that is located on such a side as to face the one carriage being located at the stationary position). However, the invention is not limited to such a case. For example, it may be a member that is not part of the case and is fixed to the case. For example, the stationary position mode is used in transporting the image scanner or moving it in changing its installation location.
An exemplary embodiment of the invention will be hereinafter described in more detail.
As shown in
The first carriage 20 includes a carriage main body 20a and brackets 20b and 20c which are attached to the main body 20a at both ends, and is a full-rate scanning movement body which is reciprocated at the same speed as a movement speed on first slide rails 24 (see
The second carriage 25 includes a main body 25a and brackets 25b and 25c which are attached to the main body 25a at both ends, and is a half-rate movement body which is reciprocated in link with the movement of the first carriage 20 at a speed that is a half of the speed of the first carriage 20 in the same read scanning direction on second slide rails 29 (see
In the reading unit 30, an image-forming lens 32 for forming an image of the reflection light H originating from the document and reflected by the reflection mirrors 26 and 27 of the second carriage 25 and an imaging device 33 such as a CCD line sensor for reading, through photoelectric conversion, the reflection light H originating from the document and image-formed by the image-forming lens 32 are mounted at positions (close to outward-to-homeward reversing positions of reciprocation movements of the carriages 20 and 25) located on the bottom surface side of the case 10. Of the above components, the imaging device 33 is mounted on a circuit board 35 for driving it, and the circuit board 35 is fixed to the case 10 via a bracket or the like (not shown). In the reading unit 30, part of the image-forming lens 32 and the imaging device 33 are covered with a shield cover 38 (the image-forming lens 32 and the imaging device 33 are reading optical components of the reading unit 30).
The wire drive mechanism 40 mainly includes two wires 41, plural pairs of pulleys 42, 43, and 44 on and between which the wires 41 are wound and stretched, and a drive motor 45.
In the wire drive mechanism 40 of this exemplary embodiment, as shown in
The two wires 41 are wound around the two respective drive pulleys 42 plural times (in
In the wire drive mechanism 40, the drive motor 45 is rotated at a speed in a direction. Resulting rotary motive power is transmitted to the first carriage 20 and the second carriage 25 via the wires 41 which are wound on and stretched between the plural pairs of pulleys 42-44, and reciprocates the first carriage 20 and the second carriage 25 in the read scanning direction X. In
In the image scanner 1, as shown in
Basic image reading by the above-configured image scanner 1 is performed as follows.
First, when a document 2 as a subject of reading is placed on the platen glass 11 with its information-bearing surface down manually or by an automatic document feeder, the first carriage 20 and the second carriage 25 start to be moved with a timing from the home positions in the arrow direction X1 (outward path). As they are moved, the information-bearing surface of the document 2 is illuminated by the lamp 21 and a scan is performed in the main scanning direction which is perpendicular to the read scanning direction X. A scan is also performed in the auxiliary scanning direction (read scanning direction X) as the first carriage 20 and the second carriage 25 are moved in the arrow direction X1 (outward path) because of operation of the wire drive mechanism 40.
While the above scans are performed, reflection light H from the document 2 being illuminated shines on the image-forming lens 32 after passing the mirror 23 and the mirrors 26 and 27 in this order, whereby image information of the document 2 is read electrically. The image information of the document that is read by the imaging device 33 (i.e., a resulting electrical signal) is sent to an image processing section of a copier main body via the circuit board 35.
In the image scanner 1, movement of the first carriage 20 and the second carriage 25 to the transport positions is performed as follows.
In an operation of movement to the transport positions, first, the drive motor 45 of the wire drive mechanism 40 is operated and rotated in such a direction that the drive pulleys 42 take up wire portions 41c that are wound on the fixed pulleys 43 while paying out wire portions 41d that are connected to the first carriage 20 and wound on the double-groove pulleys 44. As a result, the first carriage 20 and the second carriage 25 which have been located at the home positions (see
Then, as shown in FIGS. 3B and 8-10, the drive operation of the wire drive mechanism 40 is stopped as soon as the second carriage 25 hits the outer frame 12B of the case 10. As a result, the second carriage 25 is kept in a state that it is stopped and fixed by means of the wires 41 while being in contact with the outer frame 12B of the case 10. On the other hand, the first carriage 20 is kept in a state that it is stopped and fixed by the stopped and fixed second carriage 25 via the wires 41 (i.e., the wire end portions 41d extending from the rotation-stopped drive pulleys 42 past the double-groove pulleys 44 to the wire fixedly attaching portions 15) without being brought in contact with the outer frame 12B of the case 10 (an interval S is formed). In
The first carriage 20 and the second carriage 25 are stopped and fixed at the transport positions in the above-described manner. In this state, the first carriage 20 and the second carriage 25 are kept not prone to move at least in the vertical direction even when external impact or vibration is applied to them when the image forming apparatus 1 is transported or moved.
However, as described above, when located at the home position, the first carriage 20 is stopped without being brought in contact with the outer frame 12B of the case 10 (an interval S is formed). Therefore, even though located at the home position, the first carriage 20 can move in the read scanning direction X (strictly, in the direction of arrow X2) when the image scanner 1 receives strong external force such as impact. It is inferred that this is due to the facts that the first carriage 20 is merely placed on the slide rails 24 and prevented from moving in the read scanning direction X by the wires 41, and that the wires 41 can move to provide the same effect as would be obtained when they were made longer because their one end portions 41b are attached elastically via the tension springs 47 and the drive pulleys 42 are in such a state as to be able to rotate though slightly. If the first carriage 20 is moved from the transport position in the read scanning direction X2, the wires 41 are moved together with it, as a result of which, in the worst case, as described above, the wires 41 come off the closest double-groove pulleys 44 (large-diameter pulleys 44a).
In view of the above, in the image scanner 1, a movement restricting member 50 is provided which restricts, to about 1.6d or less, the maximum movement distance L by which the first carriage 20 is allowed to move from the transport position in the read scanning direction X (in this example, strictly, in the direction of arrow X2), where d (mm) is the depth of the grooves 48 of the pulleys 44 (large-diameter pulleys 44a).
In this exemplary embodiment, as shown in
The reason (hypothesis) whey the maximum movement distance L by which the movement restricting member 50 allows the first carriage 20 to move in the read scanning direction X is set at “about 1.6d or less” (L≦1.6d) is as follows.
It is assumed that, as shown in
First, it will be discussed whether or not the wire 41 comes off when, as shown in
Incidentally, the circumferential elongation length is given by the following equation. In the equation, r is the radius of the bottom 48a of the pulley groove.
(Circumferential elongation length due to movement of distance that is the same as groove depth d)
=(2πr/2)+d=πr+d
That is, in this case, it is inferred that the wire 41 does not come off or is not prone to come off because the circumference-elongated wire portion 41g is engaged with an upper groove bottom 48a(1) and a lower groove bottom 48a(2) and exists in the groove 48 as a whole (in other words, the wire 41 is engaged with the flanges).
It is then inferred that the wire 41d that extends from the first carriage 20 and is wound on the pulley 44 actually comes off (the groove 48 of) the pulley 44 at a high probability if the wire 41d in a state of
Based on the above discussion, the movement distance N of the first carriage 20 in a state that the wire 41d projects from the flanges of the pulley 44 over a quarter or more of the circumference is calculated according to the following equation:
(Movement distance N of first carriage 20)
=(J1−J2)+α
In this equation, J1 is the length of the wire portion 41h from the upper groove bottom 48a(1) to the lower groove bottom 48a (2) in a state that it projects from the flanges over a quarter or more of the circumference and is given by J1={π(2r+d)}/2. The parameter J2 is the length of the wire portion 41m that is that portion of the wire 41d which is wound being in contact with the groove bottom 48a, and is given by J2=2rπ/2. The parameter α is the elongation length (of a wire portion W2) when a wire portion W1 extending from the end position P of the wire fixedly attaching portion 20e to the upper groove bottom 48a(1) runs onto a flange top 44f. For example, the elongation length α is given by
α=W2−W1=(W1/cos θ)−W1=(d/sin θ)−W1
where θ is the angle formed by the normal wire portion W1 and the wire portion W2 that runs onto the flange top 44f.
Substituting the above into the calculation formula of the movement distance N of the first carriage 20, we obtain
(Movement distance N of first carriage 20)
=(J1−J2)+α
=[{π(2r+d)}/2−πr]+α
=(π/2)d+α.
Since, as this result shows, the movement distance N of the first carriage 20 is given by N=(π/2)d+α, the wire 41 comes off the pulley 44 if N exceeds this value. Therefore, satisfactory results should be obtained formally as long as the maximum movement distance L is set less than or equal to N=(π/2)d+α. However, in this case, the term α can be eliminated because it is much smaller than (π/2)d. Furthermore, since (π/2)=1.5707963 . . . , it can be approximated as 1.6. This can also be understood as including the deviation α to some extent.
Based on the above discussion, it has been decided, as a general rule, to set the maximum movement distance L so that it satisfies L≦1.6d.
Actual image scanner 1 were prepared according to the exemplary embodiment in which the groove depth d of the pulleys 44 (a) was 1.5 mm and the maximum movement distance L was set at 2.4 mm and 0.7 mm by means of the drawn projection 51 (movement restricting member). Whether or not the wires came off the pulleys 44 (large-diameter pulleys 44a) was checked by applying artificial vibration of the same conditions. The wires did not come off in either case.
Furthermore, in the image scanner 1, as shown in
Although in this exemplary embodiment the movement restricting member 50 is provided on the outer frame 12B of the case 10, it may be provided on the first carriage 20. The invention is not limited to the case that only one movement restricting member 50 is provided; plural movement restricting members 50 may be provided. And the position of the movement restricting member 50 is not limited to the position in the exemplary embodiment; the movement restricting member 50 may be provided at another position if necessary.
The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| P.2005-363092 | Dec 2005 | JP | national |
