Image scanning apparatus and method, and mirror drive method and mechanism

The present invention enables to scan in a sub scan direction an image on a scan medium placed on a flat plane using a simple configuration of a one-dimensional image sensor at a fixed position in combination with a reflecting mirror. A drive source having a constant rpm is used to rotate the reflecting mirror at an angular velocity changing in a non-linear way. The rotation of the drive source is transmitted to a drive mechanism linked to a four-node link mechanism to rotate the reflecting mirror at an angular velocity changing in a non-linear way, so that the scan position on the scan medium is shifted in the sub scan direction at a constant linear velocity.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an image scanning apparatus and method for
 scanning an image on a reading medium such as a sheet of paper, and a
 mirror drive method and mechanism for rotating a reflecting mirror.
 2. Description of the Related Art
 Conventionally, a flat bed type image scanner has been widely used for
 reading/scanning an image on a surface of a reading medium such as a
 manuscript. This flat bed type image scanner normally has a contact glass
 arranged in a horizontal direction as medium placement means. Below this
 contact glass, there is provided an image scanning mechanism.
 This image scanning mechanism includes, for example, an image sensor having
 a number of photo elements arranged in a main scanning direction and a
 support body for supporting the image sensor at a position parallel to the
 contact glass in such a manner that the image sensor can be moved in a sub
 scanning direction. In this flat bed type image scanner, the image on a
 reading medium placed on the contact glass can be scanned as a number of
 main scanning lines continuous in the sub scanning direction.
 It should be noted that as such a flat bed type image scanner, there is a
 model in which the image sensor is fixed and a pair of scanning mirrors is
 moved in the sub scanning direction for scanning an image on a reading
 medium. Moreover, there is an image scanning apparatus in which the image
 sensor is fixed and the contact glass is moved in the sub scanning
 direction. Furthermore, there is an image scanning apparatus in which the
 image sensor is fixed and a manuscript as the reading medium is moved in
 the sub scanning direction by a sheet feed mechanism.
 In the aforementioned image scanning apparatuses using the contact glass,
 the reading medium is placed with its image downward on the contact glass
 and a user cannot observe the image which is being scanned.
 Moreover, in the model having a fixed image sensor, a reading medium is
 placed with its image upward on a sheet feeding mechanism and a user can
 observe the image which is being scanned. However, a jam may be caused in
 the sheet feeding mechanism when comparatively thin sheets of paper are
 set on the sheet feeding mechanism.
 These problems are solved by image scanning apparatuses disclosed in
 Japanese Patent Applications No. 6-13307 and No. 6-294160. These image
 scanning apparatuses includes a table as medium arrangement means on which
 a reading medium is placed, and above this table, there is provided a
 scanner head supported by a support arm.
 The scanner head has an image sensor, an image formation optical system,
 and a reflecting mirror which are built in the scanner head. The
 reflecting mirror is rotatably supported on a rotary shaft which is
 arranged in parallel to the main scanning direction. The reflecting mirror
 reflects an image light, i.e., a reflected light or transmitting light
 from the reading medium, into a predetermined direction which vertically
 intersects the main scanning direction.
 This image sensor has one-dimensional structure consisting of a number of
 photo elements arranged in the main scan direction so as to read a main
 scan line consisting of a number of dots. Furthermore, reflecting mirror
 is rotated so that the main scan line reading position is shifted in the
 sub scan direction. Thus, a two-dimensional image is read/scanned by the
 number of main scan lines continuous in the sub scan direction.
 In the image scanning apparatus having the aforementioned configuration, a
 reading medium is placed with its image facing upward on the table. That
 is, a user can observe the image while it is being scanned. Moreover,
 there is no need of feeding a reading medium by a feeding mechanism.
 Accordingly, there is no problem in reading an image on a very thin sheet
 of paper or on a page of a thick book.
 In the aforementioned image scanning apparatus, there is a problem that
 during the sub scanning on the scan medium carried out by the rotation of
 the reflecting mirror, the sub scan speed of the scan position on the scan
 medium is fluctuated if the reflecting mirror is rotated at a constant
 angular velocity.
 That is, at a center position where an image is scanned at a right angle,
 the sub scan linear velocity becomes smallest, and the linear velocity is
 increased as the scan position is shifted from the center to the end
 portion of the manuscript. If the image sensor reads main scan lines at a
 constant interval in this state, the image data obtained is such that a
 center potion is expanded and the both end portions are contracted.
 For example, it is possible to electronically control the image sensor scan
 interval corresponding to the rotation angle of the reflecting mirror or
 to correct by way of data processing the image data scanned. However,
 these require a complicated processing operation. In the former case, the
 light reception amount of the image sensor is varied and in the latter
 case, the resolution of the image data is finally lowered.
 In order to solve the aforementioned problems, conventionally, the angular
 velocity of the reflecting mirror is changed in a non-linear way so that
 the scan position on the scan medium is moved in the sub scan direction is
 a constant linear velocity. Thus, for controlling the angular velocity of
 the reflecting mirror, a voice coil motor has been used as a drive source
 for servo control of the reflecting mirror rotation. However, this
 complicates the circuit configuration, reducing the productivity and
 disabling to reduce the apparatus size.
 SUMMARY OF THE INVENTION
 It is therefore an object of the present invention to provide an image
 scanning method and apparatus employing a reflecting mirror rotation for
 the sub scanning, an angular velocity of which is controlled with a simple
 configuration to be non-linear so that the sub scan speed is constant.
 The image scanning method according to the present invention comprising
 steps of: reflecting with a reflecting mirror an image light generated
 from an image of a medium arranged in a plane continuous in a main scan
 direction and in a sub scan direction, into a predetermined direction
 vertically intersecting the main scan direction; introducing the reflected
 image light to an image formation optical system so as to obtain an image
 formation at position of an image sensor consisting of a number of photo
 elements arranged in a direction parallel to the main scan direction; and
 rotating with a drive force of a drive source the reflecting mirror
 pivotally supported by a rotary shaft parallel to the main scan direction
 so that a scan position of the image sensor on the medium is moved in the
 sub scan direction;
 wherein the drive source provides rotation of a constant angular velocity
 which is converted by a four-node link mechanism into the rotation of the
 reflecting mirror having an angular velocity changed in a non-linear way,
 so that the scan position on the scan medium by the image sensor is moved
 in the sub scan direction at a constant linear velocity.
 Thus, an image light generated from a scan image is reflected by the
 reflecting mirror to a predetermined direction vertically intersecting the
 main scan direction so that an image formation is obtained at a light
 reception position of the image sensor by the image formation optical
 system and the image light is read as a main scan line by a number of
 photo elements of the image sensor. Here, the reflecting mirror is rotated
 so that a scan position of the image sensor on the scan medium is shifted
 in the sub scan direction. Thus, a two-dimensional image is scanned as a
 number of main scan lines continuous in the sub scan direction. A constant
 angular velocity of the drive source is changed by a four-node link
 mechanism into a non-linearly changing angular velocity of rotation of the
 reflecting mirror, so that a scan position of the image sensor on the scan
 medium is shifted in the sub scan direction at a constant linear velocity.
 It should be noted that the term "image light" represents a light flux
 corresponding to an image on the scan medium such as a reflected light
 from the scan medium or the light which has transmitted through the scan
 medium. Moreover, the main scan direction represents a direction of the
 photo elements arranged in the image sensor, and the sub scan direction
 vertically intersects the main scan direction projected on the surface of
 the scan medium.
 The image scanning apparatus according to the present invention comprises:
 medium placing means for placing a scan medium having on its surface an
 image to be scanned, on a flat plane continuous in a main scan direction
 and in a sub scan direction; a reflecting mirror for reflecting an image
 light generated from the image of the medium arranged by the medium
 setting means, into a predetermined direction vertically intersecting the
 main scan direction; an image formation optical system for image formation
 at a predetermined position from the reflected image light; an image
 sensor provided at the image formation position of this image formation
 optical system and consisting of a number of photo elements arranged in a
 direction parallel to the main scan direction; a drive source for
 generating a predetermined drive force; a mirror support mechanism having
 a rotary shaft for supporting the reflecting mirror so as to be rotatable
 in a direction parallel to the main scan direction; and a mirror drive
 mechanism linked to the drive source for rotating the reflecting mirror at
 an angular velocity changing in a non-linear way so that a scan position
 of the image sensor on the medium is moved in the sub scan direction at a
 constant linear velocity.
 Thus, a scan medium is arranged on a plane of the manuscript area
 continuous in the main scan direction and in the sub scan direction. An
 image light generated by an image on the scan medium is reflected by the
 reflecting mirror in a predetermined direction vertically intersecting the
 main scan direction. The image light reflected is focused by the image
 formation optical system at a predetermined position. The image light is
 for the image formation is read as a one-dimensional main scan line by a
 number of photo elements arranged in the main scan direction of the image
 sensor.
 Here, the reflecting mirror supported by the mirror support mechanism on a
 rotary shaft parallel to the main scan direction is rotated by a the
 mirror drive mechanism driven by the drive source so that a scan position
 of the image sensor on the scan image is shifted in the sub scan
 direction. Thus, a two-dimensional image is read/scanned as a number of
 main scan lines continuous in the sub scan direction. It should be noted
 that rotation of the drive source having a constant angular velocity is
 converted by the mirror drive mechanism into the rotation of the
 reflecting mirror having an angular velocity that changes in a non-linear
 way, so that the scan position of the image sensor on the scan medium is
 shifted in the sub scan direction at a constant linear velocity.
 According to another aspect of the present invention, the mirror drive
 mechanism comprises a four-node link mechanism. This four-node link
 mechanism converts the rotation of the drive source having a constant
 angular velocity into the rotation of the reflecting mirror having an
 angular velocity changing in a non-linear way.
 According to still another aspect of the present invention, the link
 mechanism has: a drive link of a small crank shape linked to the drive
 source; a follower link of a long crank shape linked to the reflecting
 mirror; and an interlock link for linking between an end portion of the
 drive link and an end portion of the follower link, wherein the drive link
 is approximately at a right angle to the interlock link when an optical
 path of an image light coming into the reflecting mirror intersects the
 scan image approximately at a right angle.
 Thus, when the drive link linked to the drive source is rotated with a
 constant angular velocity, the follower linked to the interlock link is
 also rotated. The interlock link moves with a velocity which is at its
 maximum when the interlock link is approximately at a vertical position to
 the drive link. In this state, the follower link also has a maximum
 angular velocity.
 The mirror drive method accoridng to the present invention drives a
 rotatable reflecting mirror for reflecting an optical path penetrating a
 predetermined point and a predetermined plane in such a manner that an
 intersecting point of the optical path and the plane is shifted in a
 linear way, wherein a rotation of a constant angular velocity is converted
 into a rotation of an angular velocity changing in a non-linear way, so
 that the intersecting point is shifted at a constant linear velocity.
 Thus, rotation of a constant angular velocity is converted by the four-node
 link mechanism into the rotation of the reflecting mirror having an
 angular velocity changing in a non-linear way, so that the intersecting
 point of the optical path on the plane is shifted at a constant linear
 velocity.
 The mirror drive mechanism according to the present invention comprises: a
 drive link of a short crank shape which is driven to rotate at a constant
 angular velocity; a follower link of a long crank shape which is linked to
 a reflecting mirror supported on a rotary shaft; and an interlock link for
 linking an end portion of the drive link to an end portion of the follower
 link, wherein if an optical path reflected by the reflecting mirror is
 assumed to penetrate a predetermined point and a predetermined plane, the
 drive link is approximately vertical to the interlock link when the
 optical path intersects the plane approximately vertically.
 Thus, when the drive link is rotated at a constant angular velocity, the
 follower link linked via the interlock link is also rotated. When the
 interlock link is approximately at a vertical position to the drive link,
 the interlock link has the maximum velocity of movement. In this state,
 the follower link also has a maximum angular velocity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Description will now be directed to a stand scanner as an image scanning
 apparatus according to an embodiment of the present invention with
 reference to the attached drawings. It should be noted that FIG. 1 is a
 cross sectional view showing an internal configuration of a scanner head
 which is an essential portion of the stand scanner. FIG. 2 is a plan view
 and FIG. 3 is a front view showing an external view of the entire scanner.
 FIG. 4 schematically shows an image data scanned from an image to be
 scanned. FIG. 4A shows a state of the image data prior to a pincushion
 correction and FIG. 4B shows a state of the image data after the
 pincushion correction. FIGS. 5 to 7 shows a change of the internal state
 of the scanner head in a scanning procedure. FIG. 5 shows an initial
 stage, FIG. 6 shows an intermediate stage, and FIG. 7 shows a final stage
 of the scanning procedure.
 The stand scanner 1 according to the present embodiment, as shown in FIG. 2
 and FIG. 3, includes a manuscript table 2 on which a medium is to be
 placed. A manuscript area 3 is arranged in a left portion of this table.
 In FIG. 2, a manuscript placed has its leading edge at the top and
 trailing edge at the bottom. The main scan direction is from left to right
 and the sub scan direction is from top to bottom of the manuscript area,
 thus defining a continuous plane.
 A scanner head 5 is mounted on a support arm 4 extending in a perpendicular
 direction from outside of the upper left of this manuscript area. As shown
 in FIG. 3, the scanner head 5 includes a box-shaped scanner block 7 and a
 support block 6 connected to the support arm 4. The scanner block 7 has a
 housing 8 in which a scan window 9 is formed corresponding to an upper
 left corner of the manuscript area in FIG. 2.
 Referring to FIG. 1, the scanner block 7 of the scanner head 5 includes a
 reflecting mirror 11 provided above the scan window 9. This reflecting
 mirror is supported so that its reflection surface defines approximately
 45 degrees to the horizontal direction of the scanner head 5 as well as to
 the vertical direction down to the manuscript area. Note that this
 reflecting mirror 11 is rotatably supported by a mirror support mechanism
 12. This mirror support mechanism 12 has a rotary shaft 13 provided in
 parallel to the main scan direction, i.e., in the direction from left to
 right of the manuscript area.
 A mono-focus lens 14 is adjacent to this reflecting mirror. The mono-focus
 lens 14 serves as an image formation optical system having an optical axis
 extending in a direction parallel to the sub scan direction. This
 mono-focus lens 14 is supported by a member support mechanism (not
 depicted) consisting of a guide rail and a mirror cylinder in such a
 manner that the mono-focus lens 14 can move in a direction parallel to the
 sub scan direction.
 The scanner block 7 also includes an image sensor 15 arranged at the depth
 of the scanner block. The image sensor 15 includes a number of photo
 elements 16 consisting of charge coupled devices (CCD) or the like which
 are arranged in one-dimensional structure corresponding to the main scan
 direction.
 In the stand scanner 1 according to the present embodiment, a scan optical
 path is formed from the manuscript area 3 on the manuscript table 3 to the
 reflecting mirror 11 and from the reflecting mirror via the mono-focus
 lens 14 to the image sensor 15. The image sensor 15 is arranged at a
 position where an image is formed by the mono-focus lens 14 from the image
 scanned in the manuscript area.
 Moreover, in the stand scanner 1 according to the present embodiment, the
 scanner block 7 of the scanner head 5 includes a built-in stepping motor
 21 as a drive source of a constant angular velocity. This stepping motor
 21 is linked via a gear set to a link mechanism 23 and to a cam mechanism
 24.
 The link mechanism 23 is linked to the rotatable reflecting mirror 11.
 Thus, the gear set 22 and the link mechanism 23 constitute a mirror drive
 mechanism 25 for rotating the reflecting mirror 11. The cam mechanism is
 linked to the mono-focus lens 14 which can be displaced. The cam mechanism
 24 and the link mechanism 23 are both linked to the gear set 22.
 Accordingly, the cam mechanism 24 serves as a displacement correction
 mechanism for displacing the mono-focus lens 14 in association with the
 rotation of the reflecting mirror 11.
 More specifically, a final gear 26 in the gear set 22 has a sector shape
 and makes only a reciprocal movement with a predetermined angle. This
 final gear 26 has a rotary shaft 27 which is linked to the link mechanism
 23, constituting a four-node linkage.
 That is, the rotary shaft 27 of the final gear 26 of the gear set 22 is
 linked directly to a drive link 28 which is comparatively short, whereas
 the mirror support mechanism 12 has a rotary shaft 13 which is directly
 linked to a follower link 29 which is comparatively long.
 The bottoms of these links 28 and 29 are connected via a interlock link 30.
 When the image sensor 15 scans a position in the manuscript area
 immediately below the reflecting mirror 11, the links 28 and 29 are
 positioned almost in a perpendicular direction. That is, this link
 mechanism 23 is constructed so that the links 28 and 29 are approximately
 vertical to the interlock link 30 when the optical path from the
 reflecting mirror 11 is approximately perpendicular to the surface of the
 manuscript area 3.
 With the link mechanism 23 having the aforementioned configuration, the
 angular velocity of rotation of the reflecting mirror 11 is changed even
 if the angular velocity of the stepping motor 21 and that of the final
 gear 26 are constant. That is, in the stand scanner 1 of the present
 embodiment, as has been described above, the scan window 9 of the scanner
 head 5 is positioned directly above the upper left corner of the
 manuscript area 3. The link mechanism 23 is constructed so that when the
 scan position on the manuscript area 3 is immediately below the scan
 window 9, the reflecting mirror 11 has a highest angular velocity, and the
 angular velocity of the reflecting mirror 11 is decreased as the scan
 position on the manuscript area 3 moves apart from the position
 immediately below the scan window.
 Moreover, a cam 33 of a modified configuration is linked directly to a
 rotary shaft 32 of an idler gear 31 which is the last but one in the gear
 set 22. This cam 33 is in abutment with a cam follower 34. The cam 33 has
 a spiral configuration having an outer circumferential surface which
 gradually departs from a cam center. The cam follower 34 is in abutment
 with this outer circumferential surface.
 The cam follower 34 is formed in an longitudinal arm configuration
 extending approximately in a perpendicular direction. The cam follower 34
 is supported at its bottom so that the cam follower 34 can make a
 reciprocal movement. The cam follower 34 is urged toward the cam 33 by an
 elastic mechanism such as a coil spring (not depicted). Thus, the cam
 follower 34 has a top end brought into abutment with the outer
 circumeferential surface of the cam 33 and a center portion linked to the
 mono-focus lens 14.
 The high-speed cam mechanism 24 having the aforementioned configuration is
 constructed so as to bring the mono-focus lens 14 into a reciprocal
 movement at a non-constant velocity even if the stepping motor 21 and the
 idler gear 31 are rotated in a constant direction at a constant velocity
 with respect to an image scanning. That is, in the stand scanner 1
 according to the present embodiment, as has been described above, the scan
 window 9 of the scanner head 5 is positioned above the upper left of the
 manuscript area 3. The cam mechanism 24 is constructed as follows. When
 the scan position to be scanned in the manuscript area 3 is immediately
 below the scan window 9, the distance between the mono-focus lens 14 and
 the image sensor 15 is shortest, and the distance becomes greater as the
 scan position moves apart from the upper left corner of manuscript area 3.
 It should be noted that, as shown in FIG. 2, the stand scanner 1 according
 to the present embodiment includes a built-in impact printer 42. This
 impact printer 42 has at its end a position guide 43 which corresponds to
 the upper end of the manuscript area 3. Moreover, at the right of the
 impact printer 42 and the manuscript area 3, there is provided a working
 area 44 for handling manuscripts.
 Moreover, in the stand scanner 1 according to the present invention, as has
 been described above, the scanner block 7 of the scanner head 5 includes
 various built-in optical parts and movable mechanisms which are controlled
 to be driven by a drive control circuit board (not depicted) contained in
 the support block 6 of the scanner head 5 together with an image
 processing circuit board (not depicted). Wiring of the built-in circuits
 in this support block 6 is contained in the support arm 4 and is connected
 to an interface (not depicted) arranged on or at a side of the manuscript
 table 2.
 As has been described above, in the stand scanner 1 according to the
 present invention, the scanner block 7 of the scanner head 5 is positioned
 above the upper left corner of the manuscript area 3. Accordingly, as
 shown in FIG. 4A, an image data obtained from a scan is such that the
 lower end of the manuscript is displaced leftward. A control program and
 processing parameters for restoring this image data into a correct
 configuration as shown in FIG. 4B are contained, for example, in an image
 processing circuit built in the support block 6 of the scanner head 5.
 The aforementioned image processing is often called as a pincushion. The
 scanner head scans a manuscript, i.e., an image data with a resolution
 higher than required at a final stage. A digital data of the main scan is
 subjected to a data processing using a conversion table corresponding to
 the sub scan position so that an image data deformed as shown in FIG. 4A
 is corrected into a normal rectangular configuration so as to obtain a
 uniformity in the entire length of the main scan line.
 Furthermore, in the stand scanner 1 according to the present embodiment, as
 has been described above, the scanner head 5 is supported by the support
 arm 4 so as to be positioned above the upper left corner of the manuscript
 area 3. The support arm 4 is supported by an arm pivotal support mechanism
 (not depicted) built in the manuscript table, in such a manner that the
 support arm 4 can be rotated in a horizontal direction, and is fixedly
 held by an arm lock mechanism (not depicted) so that the scanner block 7
 is positioned above the upper left corner of the manuscript area 3. When
 this arm lock mechanism is released, the support arm 4 can be rotated in
 the horizontal direction together so as to move the scanner head 5 from
 above the upper left corner of the manuscript area toward the back of the
 printer.
 A user of this stand scanner 1, for example, can sit in front of the
 manuscript table 2 and read a manuscript 45 while it is scanned. The
 manuscript 45 need not be fed by a feed mechanism which may cause a jam.
 The manuscript 45 placed in the manuscript area 3 is scanned by the scanner
 block 7 of the scanner head 5 supported by the support arm 4. Here, the
 main scan lines are scanned by the one-dimensional image sensor 15 fixed
 in the scanner block 7 while the scan position is moved in the sub scan
 direction by rotation of the reflecting mirror 11. Thus, the scanner block
 7 need not move over the manuscript area.
 As has been described above, the scanner block 7 in a fixed position moves
 the scan position in the sub scan direction through rotation of the
 reflecting mirror 11 and accordingly, the optical path length for the scan
 varies according to the rotation of the reflecting mirror 11. In the stand
 scanner 1 according to the present invention, the mono-focus lens 14 is
 interlocked with the rotation of the reflecting mirror 11 so as to be
 displaced in the optical axis direction, thus always enabling a preferable
 image formation on the image sensor 15.
 More specifically, FIG. 5 shows an initial position of the reflecting
 mirror 11, where the reflecting mirror 1 is at a greatest angle to a
 horizontal plane and the scan optical path is slightly slanting from the
 perpendicular direction. In this state, the scanner block 7 scans the top
 of the manuscript.
 Here, in the link mechanism 23, the lower ends of the links 28 and 29 are
 held at a back position. In the cam mechanism 24, the cam follower 34 is
 in abutment with the greatest diameter portion of the cam 33. Accordingly,
 the mono-focus lens 14 is slightly moved away from the image sensor 15. In
 this state, the image formation position of the manuscript area by the
 mono-focus lens 14 is matched with the light reception position of the
 image sensor 15, and an image scanned from the manuscript is preferably
 formed at the position of the image sensor 15.
 The scan operation is started from the aforementioned initial state, and as
 shown in FIG. 6, the reflecting mirror 11 is rotated to decrease the angle
 to the horizontal plane and the optical path is positioned in a
 perpendicular direction. The reflecting mirror 11 is further rotated to
 decrease the angle to the horizontal plane and as shown in FIG. 7, and the
 optical path is positioned to be slanting to scan the bottom of the
 manuscript. Thus, the scan position on the manuscript 45 is moved from the
 top to the bottom.
 Here, in the link mechanism 23, the lower ends of the links 28 and 29 are
 displaced in the sub scan direction as the cam 33 is rotated in the
 clockwise in the figure. The cam follower 34 is in abutment with a smaller
 diameter portion of the cam 33 and again brought into abutment with the
 greatest diameter portion of the cam 33. Accordingly, the mono-focus lens
 14 approaches the image sensor 15 and then retrieves.
 As has been described above, in the stand scanner 1 according to the
 present embodiment, while scanning the manuscript 45 from its top to the
 bottom, the optical path length is firstly reduced slightly and then
 increased. Thus, an image scanned is always formed preferably at the
 position of image sensor 15. That is, the scanner block 7 fixedly
 supported can preferably scan the entire manuscript placed in the
 manuscript area.
 Moreover, in the stand scanner according to the present embodiment, the
 angular velocity of the rotation of the reflecting mirror 11 is firstly
 increased and then decreased so that the linear velocity of the sub scan
 on the manuscript is constant. Accordingly, if the image sensor 15 carries
 out a reading operation at a constant interval, it is possible to read
 main scan lines from the image on the manuscript 45 with a constant
 interval.
 Furthermore, in the stand scanner 1 according to the present invention, as
 has been described above, the reflecting mirror is rotated with a velocity
 changing in a non-linear way and the mono-focus lens 14 is caused to make
 a reciprocal movement at a velocity changing in a non-linear way. These
 operations are realized by the link mechanism 23 and the cam mechanism 24
 driven by the stepping motor 21 rotating at a constant velocity.
 Consequently, operations the aforementioned reflecting mirror 11 and the
 mono-focus lens 14 need not be controlled with an electronic control. It
 is possible to accurately control the positions of the reflecting mirror
 11 and the mono-focus lens 14 with a simple configuration. Moreover, the
 link mechanism 23 for rotating the reflecting mirror 11 and the cam
 mechanism 24 for moving the mono-focus lens 14 are mechanically
 interlocked and driven by a single stepping motor 21. This enables to
 reduce the number of parts required and reduce the total weight of the
 apparatus as well as enhance the production efficiency. Thus, the
 aforementioned configuration enables to appropriately interlock the
 operation of the reflecting mirror 11 with the operation of the mono-focus
 lens 14 which is different from the operation of the reflecting mirror 11.
 The stand scanner 1 according to the present embodiment uses the mono-focus
 lens 14 as a single image formation optical system for image formation on
 the image sensor 15 from a scanned image from the manuscript area 3. That
 is, the optical system is also significantly simple. The focal point
 position is corrected only by displacement of a single optical part, i.e.,
 the mono-focus lens 14. This simple configuration enables to reduce the
 load of the stepping motor 21.
 It should be noted that in the stand scanner 1 according to the present
 invention, as has been described above, the impact printer 42 is arranged
 behind the manuscript area 3 and the working area 44 is provided at the
 right. This assures a preferable workability for a user. Moreover, a
 position guide 43 is provided at the front end of the impact printer 42
 and enables to set a manuscript 45 accurately in the manuscript area 3.
 Furthermore, in the stand scanner 1 according to the present embodiment,
 the scanner head 5 for scanning the manuscript 45 in the manuscript area 3
 is positioned not above the center of the manuscript area 3 but in the
 upper left corner of the manuscript area 3. This assures a preferable
 workability when replacing the manuscript 45 manually.
 Moreover, the support arm 4 on which the scanner head 5 is supported can be
 rotated. If necessary, the arm lock mechanism can be released to rotate
 the support arm 4 so that the scanner head 5 is positioned out of the
 manuscript area 3. Thus, when no manuscript is to be scanned, the
 manuscript area 3 can be used as a work area continuous to the work area
 44. This also improves the workability.
 Moreover, because the scanner head 5 is arranged above a position displaced
 from the center of the manuscript area 3, as shown in FIG. 4, the image
 data is deformed when scanned, but the image data is subjected to the
 pincushion correction in the image processing circuit. Thus, it is
 possible to externally output the image data in a normal state.
 Furthermore, in the stand scanner 1 according to the present embodiment,
 the scanner block 7 is connected via the support block 6 to the support
 arm 4. This support block 6 used to appropriately position the scanner
 block 7 also contains various circuits. Thus, the internal space of the
 support block 6 is effectively utilized, reducing the entire space
 required.
 It should be noted that the present invention is not to be limited to the
 aforementioned embodiment but can be modified in various ways within the
 scope of the invention. For example, in the aforementioned embodiment, the
 scanner head 5 is arranged above the manuscript table 2 so that the image
 on the surface of the manuscript can be observed by a user while it is
 scanned.
 However, it is also possible to reverse the internal configuration of the
 aforementioned scanner head 5 and arrange the scanner head 5 below a
 contact glass, thus constituting a flat-bed type image scanner (not
 depicted). In this case, the configuration below the contact glass can be
 reduced because there is no need of moving the image sensor 15 and a pair
 of scan mirrors.
 Moreover, in the aforementioned embodiment, the mono-focus lens 14 is moved
 to correct the focal point position corresponding to the sub scan position
 on the manuscript 45. Alternatively, it is also possible to displace the
 image sensor 15 without displacing the mono-focus lens 14, or to displace
 both of the mono-focus lens 14 and the image sensor 15. However, it is not
 advantageous to displace the image sensor 15 connected to various wires,
 and it is preferable to displace the mono-focus lens 14 as has been
 described above.
 Furthermore, in the aforementioned embodiment, the image formation optical
 system includes only one mono-focus lens 14, simplifying the
 configuration. Alternatively, it is also possible to constitute this image
 formation optical system with a plurality of lenses. However, it is
 preferable that the image formation optical system include only one
 mono-focus lens 14 for this requires displacement only one part.
 Moreover, in the aforementioned embodiment, the mirror 11 is rotated by the
 link mechanism 23 at a velocity varying in a non-linear way, whereas the
 mono-focus lens 14 is displaced by the cam mechanism 24 at a velocity
 changing in a non-linear way. Alternatively, it is also possible to rotate
 the reflecting mirror 11 with a cam mechanism and to displace the
 mono-focus lens 14 with a link mechanism.
 Moreover, in the aforementioned embodiment, the image sensor 15 has photo
 elements 16 arranged in one array in the main scan direction.
 Alternatively, it is also possible to arrange the photo elements in a
 plurality of arrays for simultaneously scanning a plurality of main scan
 lines, or to arrange the photo elements 16 in a checker arrangement so as
 to increase the resolution by way of time division scan.
 Furthermore, in the aforementioned embodiment, the scanner head is
 positioned above the upper left corner of the manuscript area 3, so as to
 enhance the workability while the image data is subjected to the
 pincushion correction. Alternatively, it is also possible to arrange the
 scanner head 5 above a desired position on the manuscript area 3.
 For example, if the scanner head 5 is arranged above the upper center of
 the manuscript area 3, the image data is symmetric between right and left,
 simplifying the correction procedure. If the scanner head 5 is arranged
 above the center of the manuscript area 3, the image data is symmetric not
 only between right and left but also between the top and bottom, further
 simplifying the correction procedure.
 In case the scanner head 5 is arranged above the center of the manuscript
 area, the image data is symmetric between right and left and between the
 top and bottom, but from the workability viewpoint such as replacement of
 the manuscript, it is preferable that the scanner head 5 be arranged above
 the upper left corner of the manuscript area 3.
 Moreover, in the aforementioned embodiment, the stepping motor 21 rotating
 at a constant velocity is connected via the gear set 33 to the link
 mechanism 23 and the mirror drive mechanism 25 so as to rotate the
 reflecting mirror 11 at an angular speed changing in a non-linear ways so
 that the manuscript area 3 is scanned by the image sensor 15 in the sub
 scan direction at a constant velocity.
 The aforementioned mirror drive mechanism 25 can also be used for scanning
 a reflected light of a laser beam emitted from a laser source, so as to
 realize a laser printer (not depicted) for writing the main scan line on
 the surface of the photo sensitive body at a constant linear velocity
 without using a f.theta. lens, an image projection apparatus (not
 depicted) for displaying the main scan lines on a wall surface at a
 constant velocity.
 The present invention having the aforementioned configuration have effects
 as follows.
 The image scanning method according to an embodiment of the present
 invention comprises steps of: reflecting with a reflecting mirror an image
 light generated from an image of a medium arranged in a plane continuous
 in a main scan direction and in a sub scan direction, into a predetermined
 direction vertically intersecting the main scan direction; introducing the
 reflected image light to an image formation optical system so as to obtain
 an image formation at position of an image sensor consisting of a number
 of photo elements arranged in a direction parallel to the main scan
 direction; and rotating with a drive force of a drive source the
 reflecting mirror pivotally supported by a rotary shaft parallel to the
 main scan direction so that a scan position of the image sensor on the
 medium is moved in the sub scan direction; wherein the drive source
 provides rotation of a constant angular velocity which is converted by a
 four-node link mechanism into the rotation of the reflecting mirror having
 an angular velocity changed in a non-linear way, so that the scan position
 on the scan medium by the image sensor is moved in the sub scan direction
 at a constant linear velocity.
 Consequently, it is possible to shift the scan position of the image sensor
 on the scan medium in the sub scan direction at a constant linear
 velocity, enabling to preferably scan an image on the scan medium with a
 simple configuration.
 The image scanning apparatus according to an embodiment of the present
 invention comprises: medium placing means for placing a scan medium having
 on its surface an image to be scanned, on a flat plane continuous in a
 main scan direction and in a sub scan direction; a reflecting mirror for
 reflecting an image light generated from the image of the medium arranged
 by the medium setting means, into a predetermined direction vertically
 intersecting the main scan direction; an image formation optical system
 for image formation at a predetermined position from the reflected image
 light; an image sensor provided at the image formation position of this
 image formation optical system and consisting of a number of photo
 elements arranged in a direction parallel to the main scan direction; a
 drive source for generating a predetermined drive force; a mirror support
 mechanism having a rotary shaft for supporting the reflecting mirror so as
 to be rotatable in a direction parallel to the main scan direction; and a
 mirror drive mechanism linked to the drive source for rotating the
 reflecting mirror at an angular velocity changing in a non-linear way so
 that a scan position of the image sensor on the medium is moved in the sub
 scan direction at a constant linear velocity.
 Consequently, it is possible to shift the scan position of the image sensor
 on the scan medium in the sub scan direction at a constant linear
 velocity, enabling to preferably scan an image on the scan medium with a
 simple configuration.
 According to another aspect of the invention, the image scanning apparatus
 is further characterized in that the mirror drive mechanism comprises a
 four-node link mechanism.
 The four-node link mechanism enables to easily convert the rotation of the
 drive source having a constant angular velocity into the rotation of the
 reflecting mirror having an angular velocity changing in a non-linear way.
 According to another aspect of the invention, the image scanning apparatus
 is further characterized in that the link mechanism has: a drive link of a
 small crank shape linked to the drive source; a follower link of a long
 crank shape linked to the reflecting mirror; and an interlock link for
 linking between an end portion of the drive link and an end portion of the
 follower link, wherein the drive link is approximately at a right angle to
 the interlock link when an optical path of an image light coming into the
 reflecting mirror intersects the scan image approximately at a right
 angle.
 Thus, with a simple configuration, it is possible to obtain a constant
 linear velocity of the scan position on the scan medium.
 The mirror drive method according to the present invention drives a
 rotatable reflecting mirror for reflecting an optical path penetrating a
 predetermined point and a predetermined plane in such a manner that an
 intersecting point of the optical path and the plane is shifted in a
 linear way, wherein a rotation of a constant angular velocity is converted
 into a rotation of an angular velocity changing in a non-linear way, so
 that the intersecting point is shifted at a constant linear velocity.
 Thus, with a simple configuration, it is possible to shift the intersecting
 point of the optical path with the plane at a constant linear velocity.
 The mirror drive mechanism according to the presnet invention comprises: a
 drive link of a short crank shape which is driven to rotate at a constant
 angular velocity; a follower link of a long crank shape which is linked to
 a reflecting mirror supported on a rotary shaft; and an interlock link for
 linking an end portion of the drive link to an end portion of the follower
 link, wherein if an optical path reflected by the reflecting mirror is
 assumed to penetrate a predetermined point and a predetermined plane, the
 drive link is approximately vertical to the interlock link when the
 optical path intersects the plane approximately vertically.
 Thus, with a simple configuration, it is possible to shift the intersecting
 point of the optical path with the plane at a constant linear velocity.
 The invention may be embodied in other specific forms without departing
 from the spirit or essential characteristic thereof. The present
 embodiments are therefore to be considered in all respects as illustrative
 and not restrictive, the scope of the invention being indicated by the
 appended claims rather than by the foregoing description and all changes
 which come within the meaning and range of equivalency of the claims are
 therefore intended to be embraced therein.
 The entire disclosure of japanese patent application no. 09-253348 (filed
 on Sep. 18.sup.th, 1997) including specification, claims, drawings and
 summary are incorporated herein by reference in its entirety.