AU703614B2

AU703614B2 - Multiple optical lens system with auto-focus calibration

Info

Publication number: AU703614B2
Application number: AU12505/97A
Authority: AU
Inventors: Henry Peng; Wen-Tso Tseng; Kelvin Yang
Original assignee: Umax Data System Inc
Current assignee: Veutron Corp
Priority date: 1997-02-04
Filing date: 1997-02-04
Publication date: 1999-03-25
Anticipated expiration: 2017-02-04
Also published as: AU1250597A

Description

-1- MULTIPLE OPTICAL LENS SYSTEM WITH AUTO- FOCUS

CALIBRATION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system with multiple optical lenses, and more particularly, to a system with capability of auto-focus calibration including sharpness and magnification adjustment, and also furthermore, to achieve the purpose of obtaining more accuracy in focus adjusting than conventionally manual operations, and of upgrading the yield rate of the system with multiple lenses.

2. Description of the Prior Art 15 A In the present days, many kinds of products are produced and modified each day.

A similar progress also occurs in optical systems such as scanners. A requirement of higher resolution than ever has brought about an optical system with multiple lenses.

Unfortunately, even finer optical instruments still have some manufacture errors, such as 9o*the focus length of the lens can not exactly fit with its theoretical focus length, or summation error derived from assembling kinds' manufacture errors after assembly. In °order to upgrade the accuracy and yield rate of the optical systems, some adjustments are required for calibrating the system.

Conventional schemes for of sharpness and magnification calibration for a scanner are achieved by using manual adjusting. Not only the system accuracy depends on the operator's experiments and is out of control, but is inconsistent with the requirements of auto-producing procedures. An improvement to the traditional schemes of adjusting becomes an eager desire for upgrading the yield rate with higher efficiency.

SUMMARY OF THE INVENTION The principal object of the present invention is to provide an optical system such as a scanner with multiple lenses to be capable of automatically calibrating the focus of the lenses inside the system without applying manual adjusting.

The other object of the invention is to provide the optical system being capable of upgrading the accuracy and yield rate of the optical system.

I:\Share S&ILIBCC\960238e2doc 00009 A further object of the invention is to provide the optical system being capable of following an auto-producing procedure for achieving the higher efficiency purpose.

The optical system according to the invention is composed of at least a test chart, a lot of optical lenses, micro-sensors, home-sensors, a base control motor, an image sensor, a lens switch motor for switching the optical lenses, and an imaging control motor for moving the image sensors.

The optical system according to the invention applies the imaging control motor and the base control motor for controlling the movements of the image sensors and the optical lenses, respectively, and obtains information derived from the image sensors for sharpness and magnification calibration. This procedure repeats until the optical system S passes both the sharpness and magnification calibration criteria.

15 9 ~BRIEF DESCRIPTION OF THE DRAWINGS 9 9The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to oo9 the following detailed description, when taken in conjunction with the accompanying 20 drawings, wherein: 9 9 FIG. 1 represents a drawing of an optical system having multiple lenses and S •capability of auto-focus calibration according to the present invention, and a condition of 1220 dpi (Dot-Per-Inch) resolution is calibrated; FIG. 2 is a drawing of the optical system that a condition of the 3048 dpi resolution is calibrated; and FIG. 3 shows a flow chart for describing the operations of the auto-focus calibration according to the present invention.

DESCRIPTION OF THE PREFERRED

EMBODIMENT

FIG. 1 displays a drawing of an optical system having multiple lenses and capability of auto calibrating the focus of the lenses (referring to "auto-focus calibration system" for short). Furthermore, the FIG. 1 also represents a condition of the 1220 dpi (Dot-Per-Inch) resolution is calibrated.

According to the schematic diagram of the FIG. 1, the auto-focus calibration Ssystem is basically composed of a test chart 101, lenses 102 and 109, home-sensors 103 I:\Share S&\LIB3CC\960238e2.doc and 105, micro-sensors 104 and 108, a charge coupled device (CCD) 106, a CCD control motor 107, a lens switch motor 110 for switching the lenses 102 and 109, and a base control motor 111 for moving the base of the auto-focus calibration system.

Both of the bases of the auto-focus calibration system and the CCD 106 must return to their initial conditions before the auto-focus calibration procedure starts. The home-sensors 103 and 105 detect whether the base and the CCD 106 return to their initial states, respectively. The lens switch motor 110 switches the lenses 102 and 109 based on the calibrated resolution to make the optical path passes through the test chart 101, the lens 102 or 109 to the CCD 106. Calibration information is then derived from the CCD 106. Based on the calibration information, sharpness and magnification calibration can be achieved by using the base control motor 111 and the CCD control motor 107 for properly moving the bases of the auto-focus calibration system and the CCD 106, respectively.

i Please note that the base control motor 111 can only move the base of the auto :calibration system. The movement of the CCD 106 is under controlled by the CCD control motor 107. In addition, the image sensor is not being constrained to a specific device. For example, the CCD 106 in the preferred embodiment can be replaced by S 20 another kind of image sensor such as CIS (Contact Image Sensor) in accordance with proper modification in structure.

••o*a Furthermore, the lenses 102 and 109 represent different resolution, and they are o• °"switched by the lens switch motor 110. Information detected by the micro-sensors 104 or 108 is used to notify the auto-focus calibration system that which lens is under calibrated.

SThe test chart 101 contains special patterns designed beforehand for adjusting purpose, and forms a clear image with known magnification when a calibrated lens forms an image on its focus exactly.

According to calibration procedure described in the FIG. 1, the lens switch motor 110 switches the lens 102 to center of the auto-focus calibration system, and to make the optical path pass through the test chart 101, the lens 102 to the CCD 106. Calibration information can be derived from the CCD 106. In the mean time, the of the micro-sensor 108 is off, but the micro-sensor 104 is on. It implies that the lens 102 is under calibrated.

After the calibration information is obtained, the base control motor 111 moves the base of the auto-focus calibration system properly for purpose of focus adjustment of the lens I:\Share S&F\LIBCC\960238e2doc 102. The magnification adjustment is achieved via the movements of the CCD 106 by using the CCD control motor 107.

FIG. 2 describes a calibration procedure when calibrating the resolution 3048 dpi.

Similarly to the condition of the resolution 1220 dpi, the lens switch motor 110 switches the lens 109 to the center of the auto-focus calibration system, and makes the optical path pass through the test chart 101, the lens 102 to the CCD 106. Calibration information is also derived from the CCD 106. In the mean time, the micro-sensor 104 is off, but the micro-sensor 108 is on. It implies that the lens 109 is under calibrated. After the calibration information is obtained, the base control motor 111 moves the base of the auto-focus calibration system properly for the purpose of focus adjustment of the lens 102. The magnification adjustment is achieved also via the movements of the CCD 106 by using the CCD control motor 107.

FIG. 3 is a flow chart representative of the operations of the auto-focus calibration according to the present invention. After all the components of the auto-focus system returns to their initial states, a calibrated resolution must be decided for selecting a relative lens (step 301). The lens switch motor 110 can implement this task of selecting the specified lens. For example, the 1220 dpi resolution applies the lens 102, and resolution of the 3048 dpi applies the lens 109.

Sharpness calibration is performed in step 303. Because each optical instrument has somewhat manufacture error, the calibrated lens can not avoid itself to have any such error. However, an incorrect focus will generate a blurring image. It is important to make the lens for imaging on its focus as exactly as possible. Furthermore, an optical system such as a scanner can be seemed as a transferring system for converting plane imaging signals into digital signals. A desire for an image evaluation scheme to estimate the system performance is certainly needed up.

In the preferred embodiment, the scheme for evaluating the sharpness quality of the auto-focus calibration system is MTF (Modulation Transfer Function) technology that applies a test chart with a half resolution to the calibrated system. For example, a test chart with 100 lppi resolution is used for a scanner with 400 dpi resolution. After the calibration information is obtain, R (Red), G (Green), B (Blue) channels are analyzing separately for ensuring them can pass a preset criterion of shaipness measurement. In the preferred embodiment, the evaluation of the preset criterion is 40%. If the auto-focus L\Share S&F\LIBCC\960238edoc calibration system fails in MTF measurement, the base control motor 111 will move the base of the auto-focus calibration system to force the lenses 102 or 109 being properly moved until the auto-focus calibration system passes the MTF evaluation (step 304).

Please note that the CCD 106 is motionless in the step 304.

Magnification calibration is performed after the sharpness adjusting is completed (step 305). An image generated by the proper focus may be clear but fails in magnification after the sharpness calibration (it also caused by the manufacture errors of the optical instrument). That is the reason why the magnification calibration is needed.

Assume the theoretical magnification of the lens is known as M, and the current magnification is being M. In the preferred embodiment, the deviation of the current magnification M is defined as: 15 I-IM*-MI S. M* 9 where the I M*-M I represents the absolute value of the difference between M* and M.

i The deviation of the current magnification I can not be greater than 0.005 in the preferred embodiment. Furthermore, if the value of I M*-Mlis smaller, the 20 magnification is closer to the theoretical magnification.

When the detecting magnification fails in the measurement mentioned above, the CCD must be moved for the purpose of modifying the current magnification M (step "306). This can be done by using the CCD control motor 107 to move the CCD 106.

When the deviation of the current magnification I is less than the preset criterion 0.005, 9 the auto-focus calibration system goes back to step 303 for sharpness calibration because the sharpness may have been changed. The auto-focus calibration system repeats the above procedure from steps 303 to 306 until the system passes both criteria of the sharpness and magnification calibrations.

In some cases, the calibration procedure described in the FIG. 3 may trap in an infinite loop for some optical system having larger manufacture errors. To avoid this, a timer is used for counting the calibration time when the procedure starts. When the calibrating time is over than a preset criterion, the auto-focus calibration system will stop automatically for the optical system fails in the calibration procedure. This also achieves the requirement of auto-testing process.

I:\Share S&RLIBCC\960238e2.doc 6- In conclusion, the present invention discloses an auto-focus calibration system for adjusting sharpness and magnification in an optical system having multiple lenses. Not only the purpose of modern auto-producing procedure is achieved, but also increases the yield rate and production effect.

As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.

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The claims defining the invention are as follows: 1. An optical system having multiple lenses with auto-focus calibration capability, each of said lenses is concerned with a resolution, said system comprises: home-sensing means for notifying whether a base of said system returns to an initial condition; testing means responsive to a light source of said system for generating testing signals; a plurality of lenses, said testing signals penetrating a calibrated lens selected from said plurality of lenses; imaging means responsive to said testing signals penetrating said calibrated lens S 1 for generating calibration images representative of information for said sharpness and said is" magnification calibration; "a plurality of micro-sensing devices for notifying which one of said plurality of lenses is calibrated; e• •base controlling means responsive to said calibration images for moving said base to control movements of said calibrated lens; and imaging controlling means responsive to said calibration images for controlling movements of said imaging means.

0000 2. The system according to claim 1, wherein said testing means comprises a test chart.

3. The system according to claim 1, wherein a total quantity of said lenses is equal to a total number of said micro-sensing devices.

4. The system according to claim 1, wherein said imaging means comprises a CCD (Charge Coupled Device).

An optical system having two lenses with auto-focus calibration capability, each of said lens is concerned with a resolution, said system comprises: testing means responsive to a light source of said system for generating testing signals; a first lens for making said testing signals to penetrate said first lens when said I:\Share S&F\II3CC\960238edoc

Claims

7. The system according to claim 5, wherein said imaging means comprises a CCD (Charge Coupled Device).
8. A method for calibrating sharpness and magnification in an optical system with multiple lenses, said method comprising the steps of: selecting a resolution to be calibrated; selecting a lens according to said selected resolution; I:\Share S&F\LIBCC\96238e2.doc -9- performing a sharpness calibration procedure to ensure a sharpness deviation of said optical system is less than a sharpness threshold value; performing a magnification calibration procedure to ensure a magnification deviation of said optical system is less than a magnification threshold value; and repeating said performing said sharpness calibration procedure and said performing magnification calibration procedure steps a plurality of times until said optical system pass both said sharpness calibration and said magnification calibration.
9. The method according to claim 8, wherein said sharpness calibration procedure comprising the steps of: producing a sharpness adjusting information representative of a sharpness calibration measurement of said optical system; moving said selected lens by using said sharpness adjusting information; and S1repeating said producing and said moving steps a plurality of times until said 15 sharpness deviation of said optical system is less than said sharpness threshold value. The method according to claim 9, wherein said sharpness adjusting information is obtained by using a MTF (Modulation Transfer Function) scheme.
11. The method according to claim 10, wherein said sharpness threshold value is 4%
12. The method according to claim 8, wherein said magnification calibration procedure comprising the steps of: detecting a current magnification; comparing a theoretical magnification of said selected lens and said current magnification to obtain a comparing information; moving an image sensor of said optical system by using said comparing information; and repeating said detecting, said comparing, and said moving steps a plurality of times until said magnification deviation of said optical system is less than said magnification threshold value.
13. The method according to claim 12, wherein said comparing information is obtained by the steps of: calculating a difference between said theoretical magnification and said current I:\Share S&F\LIBCC\960238e2.doc 10 magnification; calculating an absolute value of said difference; calculating a quotient of said absolute value dividing said theoretical magnification; and outputting said quotient to be said comparing information.
14. The method according to claim 13, wherein said preset criterion of magnification measurement is 0.005.
15. The method according to claim 12, wherein said image sensor comprises a CCD (Charge Coupled Device).
16. The method according to claim 8, said repeating step further comprising a step of counting all calibration time used by said method, said method stops when said 15 calibration time is over than a preset criterion.
17. The method according to claim 8, further comprising a step of returning said -e optical system to initial conditions of said optical system before performing said step of o"o selecting said resolution to be calibrated.
18. An optical system having multiple lenses with auto-focus calibration capability, S: substantially as described herein with reference to the accompanying drawings. DATED this Second Day of February 1999 Umax Data Systems Inc. Patent Attorneys for the Applicant SPRUSON FERGUSON I:\Share S&RLIBCC\960238edoc Multiple Optical Lens System with Auto-Focus Calibration ABSTRACT The present invention discloses an optical system with multiple optical lens having capability of auto-focus calibration, instead of conventional scheme of manual operations. The optical system disclosed by the invention basically includes a number of home-sensors (104,108) and micro-sensors (103,105), a number of lens (102,109), an image sensor (106), an imaging control motor (107), a lens switch motor (110) for switching the lens, and a base control motor (111) for switching base of the optical system. By using the imaging control motor (107) and the base control motor (111) to control motions of the imaging device (106) and the lens (102,109), auto sharpness and magnification calibration is easily achieved. Vt i* ,t 4* i* S .4. [N:\LIBU]09005:JED