CA2131327C

CA2131327C - Lens changeable image scanner and lens position control device in the same

Info

Publication number: CA2131327C
Application number: CA002131327A
Authority: CA
Inventors: Tadao Ohtsuka; Masao Shoda
Original assignee: Microtek International Inc
Current assignee: Microtek International Inc
Priority date: 1993-01-12
Filing date: 1994-01-12
Publication date: 1999-04-13
Anticipated expiration: 2014-01-12
Also published as: US5610755A; EP0635966A1; US5535040A; EP0635966B1; EP0635966A4; WO1994016518A1; DE69413156T2; CA2131327A1; DE69413156D1

Abstract

A lens position control mechanism and method in an image scanner converts a reading line density by changing over lenses. A base rotatable in a plane parallel to an original table is provided, and the lenses are supported on the base so that their optical axes are in a plane parallel to the base surface and intersect each other at a pivot. A proper kind of lens can be arranged at a proper position by controlling the rotation of the base in such a manner that a reference pattern is provided at a position at which it is readable by an image receiving element through the lens and a lens existing in an optical path is judged on the basis of a received image of the reference pattern to confirm the position of the lens. Thereby, an image scanner capable of changing over lenses at a high precision can be obtained without increasing the height of the image scanner.

Description

; l7/7 ''...t.~ 7 DESCRIPTION

LENS CHANGEABLE IMAGE SCANNER AND LENS POSITION
CONTROL DEVICE IN THE SAME

TECHNICAL FIELD
The present invention relates to an image sc~nner, and more particularly to an image scanner in which a re~ing line density or the like can be con-verted by changing over lenses and to a lens positioncontrol structure and method in such an image scanner.

BACKGROUND ART
A resolving power required in an image ~ ;
scanner is regarded as being different in accordance lO with an original, for example, 400 dpi (dots per inch) :~
for re~;ng an A3-size sketch or the like, 600 dpi for re~ing an A4-size document having a high freguency of -~
use as a simple print original, and 1200 dpi for read- --. ~:
ing a transparent original up to 4 x 5 i nches . :
In the conventional method respon~1ng to such reguirements, a plurality of kinds of lenses having different magnifying factors are selectively :

used in order to change a line density in an image scanner. A general structure of a lens change-over structure in such an image scanner includes, for exam-ple, a structure in which each lens is mounted on a : :
slider capable of moving on a rail so that it is selec-.

tively positioned in front of an image receiving ele-ment such as a CCD ~or charge-coupled device) by motor-driving the slider or a structure in which each lens is held on a rotatable disk-like holder so that it is selectively positioned in front of an image receiv-ing element by motor-driving the holder. In such a structure, the positioning of the lens for the image receiving element is made using a limit switch or a proximity sensor.
However, the lens as mentioned above re-quires a high precision for its optical position rela-tionship. Therefore, for example, in the case of the type in which the slider holding each lens thereon is line~rly moved on the rail, a certain degree of preci-sion for the installation of the rail is required over the whole of a moving range of the slider and hence the rail assembling work is liable to become troublesome.
Also, in the image scanner as mentioned above, it is general that a sCAnni ng unit scans along a horizontal -~
original table mounted with an original sheet and an image received by a mirror is reflected parallel to the original table and is then received by the image re-ceiving element. Accordingly, it is desired in view of operability that the size of the image scanner in a direction of height thereof or a direction perpendic-ular to the original table should be made as small as possible. However, in the case of the type in which the disk-like holder holding each lens thereon is k .~: - ~ . ~ . . .

~ t~ 3~7 rotated, the disk-like holder is rotated in a plane perpendicular to an optical path and hence the holder projects in the above-mentioned height direction, which provides a problem that the whole of the image scanner be~ ?~ large in size and the operability thereof is deteriorated.
Further, a positional relationship between the act~al lens and the image receiving element differs for every lens due to problems inclusive of the preci-sion of assembly. Therefore, in order to accuratelymake the optical positioning of the lens and the image receiving element by use of the limit switch or the proximity sensor as mentioned above, the position of each sensor itself must be adjusted for every image 15 sC~nn~r. ~his work is liable to be troublesome. ;~
A principal object of the present invention made in light of the above-mentioned problems of the prior art is to provide an image scanner in which the -~
high-precision positioning of a plurality of lenses upon change-over is possible with a simple structure and the size of the whole of a device is not increased.
Another principal object of the present invention is to provide a lens position control struc-ture and con~lol method in an image scanner in which the kinds and/or positions of a plurality of lenses can be accurately detected and controlled with a simple structure.

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-DISCLOSURE OF INVENTION
According to the present invention, the above first object is achieved by providing an image scanner comprising a table on which an object is ar-ranged to take in an image of the object by an imagereceiving element, sc~nni ng means for relatively scan-ning a surface of the table, a reflecting optical ~yst for directing an image from the sc~nn;ng means toward the image receiving element so that it is paral-lel to the table, and a plurality of kinds of lensescapable of being used in a change-over ~nn~r, wherein there is provided a base which has a pivot and is rotatable in a plane parallel to the table surface, and the lenses are supported on the base so that the opti-cal axes of the lenses are positioned on the same planeand intersect each other at the position of the pivot, whereby one of the lenses to be used can be selected by rotating the base.
With such a construction, since each lens is ;~
~20 thus SUppOl ~ed on the rotatable base with the pivot, -~ the precision of the positioning of each lens can be ensured if only the precision of the pivot is ensured.
Also, since the direction of rotation of the base is -~
parallel to the surface of the original table, the size in a height direction is substantially the same as that in the case of a single lens.
According to the present invention, the above secon~ object is achieved by providing a lens -- s -position control structure in an image scanner in which a plurality of lenses can be used in a change-over ~nner to take in the image of an object by an image receiving element, the structure comprising a reference pattern provided at a predete, ~ ne~ position at which it is readable through the lens, and means for detect-ing the kind of the lens from image data of the refer-ence pattern read by the image receiving element pro-vided in an optical path, and by providing a lens -position control method in an image sC~nner in which a plurality of lenses can be used in a change-over manner to take in the image of an object by an image receiving el~ ~rt, the method comprising a step of re~ng image ;;
data of a reference pattern provided at a predetel ine~
position at which it is readable through the lens, and a step of detecting the kind of the lens from the image data. Particularly, it is preferable that the position of the lens is detected from the image data of the reference pattern read by the image receiving element. -With such a construction, since the kind and/or position of the lens used is detected from the image of the reference pattern which is actually re-ceived or obtained, it is possible to accurately and easily perform the lens position control.

BRIEF DESCRIPTION OF DRAWINGS
Fig. 1~ is a block diagram showing a schemat-ic structure of an image scanner according to an em-s~

bodiment to which the present invention is applied;
Fig. 2 is a plan view of a lens unit shown in Fig. 1;
Fig. 3 is front views showing examples of a reference pattern shown in Fig. 1;
Fig. 4 is a block diagram showing the gist of the operation of the image sc~nner of the present embodimznt; and Fig. 5 is a diagram representing a relation-ship between the size of an original and a desiredresolving power.

BEST MODE FOR CARRYING OUT THE INVENTION
A preferred ~ ~o~; -nt of the present inven-tion will now be explained in detail in reference to the ~ nying drawings.
Fig. 1 is a block diagram showing a ~ch~ -t-ic structure of an image sc~nn~r to which the present invention is applied. An original table 2 is provided at an upper surface portion of a casing 1. A sc~nn;ng unit 3 including a lamp 3a for reflected illumination and a mirror 3b is provided on the lower surface side of the orig;n~l table 2, and a lamp 4 for transmitted illumlnation interlocking with the sc~nn;ng unit 3 is provided on the upper surface side thereof. Further, at a position opposite to the mirror 3b of the SC~nning unit 3 is provided a movable mirror unit 5 including a pair of mirrors 5a and 5b for reflecting light from the _7~ 2 7 scanning unit 3 toward an image receiving element 7 so that it is parallel to the original table 2. The sc~nn;ng unit 3, the lamp 4 for transmitted illumina-tion and the movable mirror unit 5 move and scan paral-lel to the original table 2. Particularly, the mirrorunit 5 moves interlocking with the sC~nni ng unit 3 by a distance which is one half of the moving distance of the sC~nn; ng unit 3. Thereby, a distance between the original table 2 and the image receiving element 7 0 heS- 9S always the same.
The image receiving element 7 including a ;-CCD for receiving the image of an original placed on ~-the original table 2 from the sC~nn~ ng unit 3 is pro-vided at a position opposite to the mirror 5b of the ;~
mirror unit 5 through a lens unit 6 including three lenses with different magnifying factors which can be changed over. Output lines of the image receiving element 7 are connected to an image processor unit 8.
An image received by the image receiving element 7 from the original table 2 through the sc~nn;~g unit 3, the mirror unit 5 and the lens unit 6 is subjected to a process~ng by the image processor unit 8, which will be mentioned later on, and is then outputted therefrom to the exterior.
The sC~nn~ ng unit 3, the lamp 4 for trans-mitted illumination, the movable mirror unit 5 and the lens unit 6 are driven and controlled by a controller 9. The controller 9 also controls the process; ~g ~ 8 -- r~"
performed by the image processor unit 8.
The lens unit 6 includes a sector-shaped base 10 having a central portion at which a pivot lOa is provided and a peripheral portion lOb the vicinity of which is slidably supported by a circular rail 18.
With this construction, the base 10 is rotatable in a plane parallel to the original table 2. The lens unit 6 further includes three lenses 11 to 13 which have different magnifying factors and are arranged on the base 10 so that the centers of their optical axes coincide with each other upon change-over, and a driv-ing unit 14 composed of a pair of pulleys 16, a motor 17 and a wire 15 which is engaged with the peripheral ~:
portion lOb for wire-driving the base 10 right and left 15 in the above - tioned plane. By controlling the motor ~ :
17 in accordance with a procedure which will be men- ~ ~
tioned later on, each of the lenses 11 to 13 is selec- ~:
tively arranged between the mirror 5b of the mirror unit 5 and the image receiving element 7. If the driving unit 14 is provided on the pivot lOa side opposite to the peripheral portion lOb and the wire 15 ~-is laid over to enclose the base 10, no excess space is not required for the installation of the driving unit and hence there results in a compact construction as a whole.
In Fig. 1, a reference pattern 19 for de-tecting which one of the lenses ll to 13 of the lens unit 6 is arranged between the mirror 5b and the image , .. ,,. . " .. . ,, . ,, , . , ~ ,.., .. . . . . . - - . :

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_g_ receiving element 7 and whether or not its optical axis coincides with the optical path, is downward provided at a waiting position of the sc~nni ng unit 3 or at a proper position other than a sc~nni ng range of the original table 2. The reference pattern 19 includes two white stripes depicted with a predetel ;ned inter- -val on a black ground. Accordingly, which one of the lenses 11 to 13 is arranged between the mirror 5b and the image receiving element 7 can be checked by re~ing the reference pattern 19 received by the image receiv-ing element 7 when the sc~nni ng unit 3 is at the wait- -~
ing position and measuring the positions of the two white stripes and an interval therebetween to check whether or not they coincide with conditions beforehand given. Also, whether or not the optical axis of the arranged lens coincides with the optical path can be -che~kefl by measuring a deviation in position of the white stripe. The check can be made without using a limit switch, a proximity sensor or the like. It is needless to say that the actual reference pattern may comprise a pattern including only one stripe, a pattern - including a black stripe depicted on a white ground, and so forth, as shown in (a) to (h) of Fig. 3 by way - of example. The result of check thus obtained is based on the final output of a detecting optical xy~t Therefore, the result of check involves all errors included on the way.

When it is detel inP-d on the basis of the ~l3~ 27 result of check that a proper lens is not arranged, the motor 17 is driven to wind up the wire 15 clockwise or counterclockwise so that a desired one of the lenses 11 to 13 is selectively arranged between the mirror 5b of -~
the mirror unit 5 and the image receiving element 7 and the fine positioning of the lens is made. In this case, with the structure in which the sector-shaped base 10-is rotated around the pivot lOa, no deviation in a radial direction is generated and a positional deviation in a rotational direction can be cancelled through a feedback control. Therefore, a high preci-slon can be obtained easily as compared with a struc-ture in which a l; nP~r sliding is made.
The image receiving element 7 is provided at a proper position on the lower stream of the optical path than the mirror 5b and may be placed at the posi-tion of the pivot lOa.
Fig. 4 is a block diagram showing the sim-plified processi ng procedure of the present image scanner. First, an image is received by the CCD image receiving el r ~ t 7 from the original table 2 through the ~C~nn;ng unit 3, the mirror unit 5 and the lens unit 6. R, G and B signals correspon~i ng to the re-ceived image are outputted from the CCD element 7 to the image processor unit 8. The image processor unit 8 converts the received analog R, G and B signals into digital s;gn~ls, respectively. With this A/D conver-sion, the subsequent signal process; ng can be performed by a digital operation. The image processor unit 8 performs a shading processing and a gradation conver-sion (or 7 correction) for the digital R, G and B
signals and may further perform a line density conver-sion, as required.
Though the number of bits of the A/D conver-sion deter ;n~s the scale of the digital operation, the number of bits in the present embodiment is large as 12 ~-bits for each ~h~nnPl Therefore, a Sh~Ai ng correction method based on a LUT (look-up table) system used in the conventional image scanner is not preferable since a required - -_y capacity is e~ ? 1 y increased.
Also, it is difficult to ; ove the precision of the line density conversion.
The image processor unit 8 further performs an MTF ( ~d~ tion transfer function) correction and a color correction for the image signal subjected to the above-mentioned processing and thereafter outputs it to the exterior through an interface. The signal is subjected to an image processing by a computer or the like (not shown) and is then outputted to an output device such as a plotter.
Each lens is selected in accordance with a line density required by the processor side. In the present embodiment, the base 10 is rotated by the wire 15. Means for rotating the base 10 in a plane may include, for example, a method using a gear or toothed wheel, a method using a direct coupling to a motor -12~ 2 7 shaft, and so forth.
In the present embodiment, there is used a ~ -construction in which the table having an object placed thereon is stationary whereas the sc~nn;ng means and the reflecting optical system including mirrors therein are moved. However, there may be used a construction in which the sc~nning means and the reflecting optical sy~t- are stationary whereas the table is moved.

INDUSTRIAL APPLICABILITY
As apparent from the foregoing explanation, in an image scanner according to the present invention, since each lens is su~ol~ed on a rotatable base with a pivot, the high precision of positioning is ensured upon change-over of a plurality of lenses if only the pivot is mounted with a high precision. Also, since the direction of rotation of the base is along the surface of an original table, the size in a height direction is substantially the same as that in the case of a single lens and the size of the whole of a device is not increased.
In a lens control structure and control method according to the present invention, since the kind and/or position of a lens used is detected from the image of a reference pattern which is actually re-ceived, a lens position detecting sensor or the like isnot required. Namely, the ~ r of parts is reduced and a process upon ass~ ~ly is simplified, thereby improving the assembling work. Further, it is possible to accurately and easily perform a lens position con-trol.
In a scanner to which the present invention is applied, optical lenses are automatically or manual-ly changed over in accordance with the size of an original so that the resolving power can be changed with no deterioration of an image. Fig. 5 is a diagram showing a relationship between the resolving power and the original.
For example, it is preferable that the image of an A3-size Griginal having a longitu~;nRl ~1 an~ion of 297 mm and f~ll;ng between lines Q1 and ~ should be read with a resolving power of 400 dpi. Also, it is preferable that the image of an A4-size original having a longitu~;nAl fl; --cion of 210 mm and falling between lines Q2 and Q6 should be read with a resolving power of 600 dpi. Further, it is preferable that the image of a so-called 4 x 5 inch size original having a longi-tu~i n~l and lateral ~; -nc;ons of 101.6 mm and 127 mm and falling between lines Q3 and Q5 or within 101.6 mm should be read with a resolving power of 1200 dpi.
If a user places an original of Q3 - Q5 size on the original table surface of the scanner, the scanner dete~ ;nes from the size of the original that the resolving power of 1200 pdi is suitable. Thereby, a change-over to a lens for 1200 dpi is made and the original is automatically read with 1200 dpi.

In the case where a certain portion of an A4-size original includes a photograph or the like and it is desired that only the correspon~ng portion should be read with the resolving power of 1200 dpi, the setting may be made in such a -nner that the correspon~i ng portion is placed on the Q3 - Q5 area and 1200 dpi is selected through a ~nllal operation.
Thereby, even in the case of an original with a size other than a defined size, an image can be read with 1200 dpi.
The lens may be determined by an operator's selection.

..... ~ , .. ~ . . . . . . . . .. ; . :

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An image scanner comprising:
a table on which an object is arranged;
scanning means for scanning said object on said table;
a reflecting optical system for directing light from said scanning means toward said image receiving element so that the reflected light is parallel to said table;
a plurality of different lenses being changeable;
and a base for supporting said lenses;
wherein said base is rotatable in a plane parallel to the surface of said table around a pivot, so that the optical axes of said lenses are positioned on the plane and intersect each other on said pivot, whereby one of said lenses can be selected by rotating said base for focusing said reflected light.

2. An image scanner according to Claim 1, wherein said table is stationary and said scanning means moves parallel to the surface of said table when the scanning is being made.

3. An image scanner according to Claim 1, wherein said scanning means is stationary and said table makes a parallel movement when the scanning is being made.