Image scanner

An image scanner is provided and includes a case having a document placement surface, two carriages which are mounted with optical components and move by running on rails, a wire drive mechanism for reciprocating the two carriages which are coupled to wires, and a movement restricting member for restricting a maximum movement distance of the first carriage in a stationary position mode to about 1.6 d 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.

BACKGROUND

(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,FIG. 3Ashows a state that carriages20and25are located at home positions andFIG. 3Bshows a state that the carriages20and25are located at transport positions.

In the image scanner of the related art, in the transport position mode, since as shown inFIG. 3Bat least the one carriage25is located at the very end position in the read scanning direction so as to be set close to the pulleys43, its swing width can be minimized even when vertical vibration is exerted on it. However, the following phenomenon may occur.

In the transport position mode, since the other carriage20merely kept in a state that it is stopped and fixed on the rails via wires41, it may move in the read scanning direction X2when 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 pulleys44) 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.

SUMMARY

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 1.6 d 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.

DETAILED DESCRIPTION

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 1.6 d 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 (seeFIG. 11) in the case where the wire is wound so as to be brought in contact with the bottom of the pulley groove.

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.

FIGS. 2-6mainly show fundamental components of the image scanner according to an exemplary embodiment of the invention. For example, the image scanner according to an exemplary embodiment is used as an image reading unit of a digital copier.

As shown inFIGS. 2-4etc., the image scanner1has a box-shaped case10which is opened on the top side. A platen glass11on which a document2is placed with its information-bearing surface down is fitted in the top opening portion of the case10. In the image scanner1, a first carriage20and a second carriage25which constitute a reduction image-forming optical system, a reading unit30for finally reading image information of the document2, and a wiring drive mechanism40for reciprocating the carriages20and25are disposed in the internal space of the case10which is located under the platen glass11. The case10is mainly formed by outer frames12A,12B,12C, and12D (four walls; the outer frames12A and12D are not shown), a top plate frame13which is disposed on the top side of the outer frames and is formed with the above-mentioned top opening portion, and a bottom frame14which is disposed under the outer frames. An exterior cover is finally attached to the outer frames12, and plural fixing holes18for attachment of the exterior cover are formed in the outer frames12(seeFIG. 4).

The first carriage20includes a carriage main body20aand brackets20band20cwhich are attached to the main body20aat both ends, and is a full-rate scanning movement body which is reciprocated at the same speed as a movement speed on first slide rails24(seeFIGS. 4 and 9) which are provided inside the case10along the read scanning direction (auxiliary scanning direction) X which is parallel with the surface of the platen glass11. In the carriage20, the bottom surfaces of the brackets20band20care provided with plural sliding legs20d. The carriage20is moved as the sliding legs20dslide on the slide rails24(seeFIGS. 6,7, etc.). (The main body20aof) the first carriage20is mainly mounted with a lamp (e.g., halogen lamp or fluorescent lamp)21as a light source for illuminating the information-bearing surface of the document2and a reflection mirror23for reflecting, to the second carriage25, reflection light H (a broken line H inFIG. 2indicates its optical axis) coming from the document2being illuminated by the lamp21.

The second carriage25includes a main body25aand brackets25band25cwhich are attached to the main body25aat both ends, and is a half-rate movement body which is reciprocated in link with the movement of the first carriage20at a speed that is a half of the speed of the first carriage20in the same read scanning direction on second slide rails29(seeFIGS. 4 and 9) which are provided inside the case10along the read scanning direction X. In the carriage25, the bottom surfaces of the brackets25band25care provided with plural sliding legs25d. The carriage25is moved as the sliding legs25dslide on the slide rails29(seeFIGS. 6,7, etc.). (The main body25aof) the second carriage25is mounted with two reflection mirrors26and27for reflecting, to the reading unit30, the reflection light H originating from the document2and reflected by the reflection mirror23.

In the reading unit30, an image-forming lens32for forming an image of the reflection light H originating from the document and reflected by the reflection mirrors26and27of the second carriage25and an imaging device33such 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 lens32are mounted at positions (close to outward-to-homeward reversing positions of reciprocation movements of the carriages20and25) located on the bottom surface side of the case10. Of the above components, the imaging device33is mounted on a circuit board35for driving it, and the circuit board35is fixed to the case10via a bracket or the like (not shown). In the reading unit30, part of the image-forming lens32and the imaging device33are covered with a shield cover38(the image-forming lens32and the imaging device33are reading optical components of the reading unit30).

The wire drive mechanism40mainly includes two wires41, plural pairs of pulleys42,43, and44on and between which the wires41are wound and stretched, and a drive motor45.

In the wire drive mechanism40of this exemplary embodiment, as shown inFIGS. 3A and 3B,FIG. 5, etc., two drive pulleys42are attached to a drive shaft46which is disposed rotatably so as to be parallel with the direction Z (main scanning direction, perpendicular to the read scanning direction X) in an end portion inside the case10where the imaging device33of the reading unit30is disposed. Two fixed pulleys43are disposed rotatably at such positions as to be opposed to the two respective pulleys42in an end portion inside the case10that is opposite to the end portion where the drive pulleys42are disposed. Two double-groove pulleys44are rotatably attached to both end portions (brackets25band25c) of the second carriage25. The drive motor45is a stepping motor, for example, and its rotary drive shaft is connected to the above-mentioned drive shaft46directly or via a drive transmission mechanism.

The two wires41are wound around the two respective drive pulleys42plural times (inFIG. 5etc., each wire is not drawn so as to be wound on the associated drive pulley plural times). One wire end portion41aof each wire is connected to the first carriage20, then wound on a large-diameter-groove pulley44aof the double-groove pulley44, and finally attached (fixed) to a fixedly attaching portion15of the case10. The wires41are strongly fixed by means of wire fixedly holding portions25ewhich are provided on the bottom surfaces of the brackets25band25cof the first carriage20, respectively. The other wire end portion41bof each wire is wound on the fixed pulley43, then wound on a small-diameter-groove pulley44bof the double-groove pulley44, and finally attached the case10via a tension spring47in a state that it is led outside the outer frame12B of the case10.

In the wire drive mechanism40, the drive motor45is rotated at a speed in a direction. Resulting rotary motive power is transmitted to the first carriage20and the second carriage25via the wires41which are wound on and stretched between the plural pairs of pulleys42-44, and reciprocates the first carriage20and the second carriage25in the read scanning direction X. InFIG. 1etc., arrow directions X1and X2correspond to an outward path and a homeward path of a reciprocation movement, respectively. In the wire drive mechanism40, the pulleys42-44are disposed and the wires41are wound and stretched in the above-described manner so as to utilize the principle of the movable pulley. Therefore, the displacement of the half-rate second carriage25is a half of that of the full-rate first carriage20when they are moved.

In the image scanner1, as shown inFIGS. 3A,5,6, etc., the two carriages20and25are moved to their home positions (standby reference positions) and stopped there by operating the wire drive mechanism40(drive motor45) by a control operation of a control section (not shown; includes sensors for detecting position information of the carriages). Furthermore, as shown inFIGS. 3B,7,8, etc., the two carriages20and25are moved to their transport (stationary) positions and stopped and fixed there by operating the wire drive mechanism40. Movement to the transport positions is performed by selecting a transport position mode and making an input (instruction) through an information input section (e.g., input keys and switches on an operating panel) for the control section of the image scanner1.

Basic image reading by the above-configured image scanner1is performed as follows.

First, when a document2as a subject of reading is placed on the platen glass11with its information-bearing surface down manually or by an automatic document feeder, the first carriage20and the second carriage25start 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 document2is illuminated by the lamp21and 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 carriage20and the second carriage25are moved in the arrow direction X1(outward path) because of operation of the wire drive mechanism40.

While the above scans are performed, reflection light H from the document2being illuminated shines on the image-forming lens32after passing the mirror23and the mirrors26and27in this order, whereby image information of the document2is read electrically. The image information of the document that is read by the imaging device33(i.e., a resulting electrical signal) is sent to an image processing section of a copier main body via the circuit board35.

In the image scanner1, movement of the first carriage20and the second carriage25to the transport positions is performed as follows.

In an operation of movement to the transport positions, first, the drive motor45of the wire drive mechanism40is operated and rotated in such a direction that the drive pulleys42take up wire portions41cthat are wound on the fixed pulleys43while paying out wire portions41dthat are connected to the first carriage20and wound on the double-groove pulleys44. As a result, the first carriage20and the second carriage25which have been located at the home positions (seeFIGS. 3A,6, etc.) receive motive power from the wires41and are moved on the slide rails24and29in the arrow direction X2of the read scanning direction.

Then, as shown in FIGS.3B and8-10, the drive operation of the wire drive mechanism40is stopped as soon as the second carriage25hits the outer frame12B of the case10. As a result, the second carriage25is kept in a state that it is stopped and fixed by means of the wires41while being in contact with the outer frame12B of the case10. On the other hand, the first carriage20is kept in a state that it is stopped and fixed by the stopped and fixed second carriage25via the wires41(i.e., the wire end portions41dextending from the rotation-stopped drive pulleys42past the double-groove pulleys44to the wire fixedly attaching portions15) without being brought in contact with the outer frame12B of the case10(an interval S is formed). InFIGS. 9,10, etc., symbol43cdenotes a shaft or its bearing portion of the fixed pulleys43and symbol44cdenotes a shaft or its bearing portion of the double-groove pulleys44.

The first carriage20and the second carriage25are stopped and fixed at the transport positions in the above-described manner. In this state, the first carriage20and the second carriage25are 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 apparatus1is transported or moved.

However, as described above, when located at the home position, the first carriage20is stopped without being brought in contact with the outer frame12B of the case10(an interval S is formed). Therefore, even though located at the home position, the first carriage20can move in the read scanning direction X (strictly, in the direction of arrow X2) when the image scanner1receives strong external force such as impact. It is inferred that this is due to the facts that the first carriage20is merely placed on the slide rails24and prevented from moving in the read scanning direction X by the wires41, and that the wires41can move to provide the same effect as would be obtained when they were made longer because their one end portions41bare attached elastically via the tension springs47and the drive pulleys42are in such a state as to be able to rotate though slightly. If the first carriage20is moved from the transport position in the read scanning direction X2, the wires41are moved together with it, as a result of which, in the worst case, as described above, the wires41come off the closest double-groove pulleys44(large-diameter pulleys44a).

In view of the above, in the image scanner1, a movement restricting member50is provided which restricts, to about 1.6 d or less, the maximum movement distance L by which the first carriage20is 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 grooves48of the pulleys44(large-diameter pulleys44a).

In this exemplary embodiment, as shown inFIGS. 1,8,9, etc., the movement restricting member50is a drawn projection51formed by bending, inward, by a degree, a portion, opposed to the first carriage20, of the outer frame12B (to which the second carriage25is to hit) of the case10. The drawn projection51is formed by forming parallel cuts over and under a portion of the outer frame12B and bending that portion by pressing it inward from outside the frame, and the drawn projection51remains continuous with the outer frame12B at both ends. The first carriage20is formed in such a manner that the side surfaces, facing the outer frame12B, of the main body20aand the brackets20band20care in the same plane.

The reason (hypothesis) whey the maximum movement distance L by which the movement restricting member50allows the first carriage20to move in the read scanning direction X is set at “about 1.6 d or less” (L≦1.6 d) is as follows.

It is assumed that, as shown inFIG. 11, the depth d of the groove48of each pulley44(large-diameter pulley44a) is defined as the height-direction distance from the bottom48aof the pulley groove48to the flange tops44f. In the example ofFIG. 11, the wire41having a diameter m is wound so as to be in contact with the bottom48aof the pulley groove48.

First, it will be discussed whether or not the wire41comes off when, as shown inFIG. 12, the first carriage20is moved by the distance that is the same as the depth d of the pulley grooves48from the transport position in the read scanning direction (direction X2). In this case, it is predicted that the movement of the carriage20will directly cause movement of the wire41din the direction of arrow X2and finally result in circumferential elongation of a wire portion41ethat is wound on the pulley44. A two-dot chain line in the figure indicates a predicted state of a circumference-elongated wire portion41g, and symbol P denotes the position of the pulley-44-side wire end of the wire fixedly attaching portion20e.

Incidentally, the circumferential elongation length is given by the following equation. In the equation, r is the radius of the bottom48aof 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 wire41does not come off or is not prone to come off because the circumference-elongated wire portion41gis engaged with an upper groove bottom48a(1) and a lower groove bottom48a(2) and exists in the groove48as a whole (in other words, the wire41is engaged with the flanges).

It is then inferred that the wire41dthat extends from the first carriage20and is wound on the pulley44actually comes off (the groove48of) the pulley44at a high probability if the wire41din a state ofFIG. 13, that is, in a state that the wire41dprojects from the flanges (their tops44f) of the pulley44over a quarter or more of the circumference (wire portion41h). Based on this inference, we think that the difference between the length of the wire portion41hbeing in the above state and the length of a normal wire portion41m(the first carriage20is not moved) is equal to the movement distance N of the first carriage20, that is, the above-mentioned maximum movement distance L.

Based on the above discussion, the movement distance N of the first carriage20in a state that the wire41dprojects from the flanges of the pulley44over a quarter or more of the circumference is calculated according to the following equation:

(Movement distance N of first carriage20)
=(J1−J2)+α

In this equation, J1is the length of the wire portion41hfrom the upper groove bottom48a(1) to the lower groove bottom48a(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 J2is the length of the wire portion41mthat is that portion of the wire41dwhich is wound being in contact with the groove bottom48a, and is given by J2=2rπ/2. The parameter α is the elongation length (of a wire portion W2) when a wire portion W1extending from the end position P of the wire fixedly attaching portion20eto the upper groove bottom48a(1) runs onto a flange top44f. 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 W1and the wire portion W2that runs onto the flange top44f.

Substituting the above into the calculation formula of the movement distance N of the first carriage20, we obtain

Since, as this result shows, the movement distance N of the first carriage20is given by N=(π/2)d+α, the wire41comes off the pulley44if 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≦1.6 d.

Actual image scanner1were prepared according to the exemplary embodiment in which the groove depth d of the pulleys44(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 projection51(movement restricting member). Whether or not the wires came off the pulleys44(large-diameter pulleys44a) was checked by applying artificial vibration of the same conditions. The wires did not come off in either case.

Furthermore, in the image scanner1, as shown inFIG. 4, through-holes17as escape holes are formed in the outer frame12B at positions that face the attachment boundaries between the main body25aand the brackets25band25cof the second carriage25. With this measure, even if weld projections (weld beads)4exist at the attachment boundaries between the main body25aand the brackets25band25cof the second carriage25so as to project from the surfaces of the main body25aand the brackets25band25cto the outer frame12B side, the weld projections4can escape into the through-holes17without hitting the frame12B when the second carriage25hits the outer frame12B in the transport position mode as shown inFIGS. 9,10, etc.

Although in this exemplary embodiment the movement restricting member50is provided on the outer frame12B of the case10, it may be provided on the first carriage20. The invention is not limited to the case that only one movement restricting member50is provided; plural movement restricting members50may be provided. And the position of the movement restricting member50is not limited to the position in the exemplary embodiment; the movement restricting member50may be provided at another position if necessary.