1. Field of the Invention
The present invention relates to an image reading lens module; in particular, it relates to an image reading lens module comprising two lenses and designed with regards to the wide field of angle requirement in compact scanning device applications.
2. Description of Related Art
Typically, the essential objective of a scanning device is to read an image with an image reading lens module and form an image onto an image sensor which then converts the image into electronic signals transferred to the outside. In order to prevent distortions in imaging processes or to compensate for light rays of different wavelengths, the design of optical reading lens plays a critical role.
For example, as disclosed in U.S. Pat. No. 6,147,816, a double-lens image reading lens module uses two meniscus lenses to constitute such an image reading lens module applicable to image scanners or facsimile machines. As shown in
An image reading lens module for the bar code reader machine is disclosed in US Patent Publication US 2009/0140048 which adopts a receiving lens positioned at the diffractive end of a compound parabolic concentrator thereby increasing the field of angle; whereas it is challenging to fabricate its lens structure and the receiving lens has a significant length thus adversely affecting the purpose of miniaturization. Furthermore, ROC Patent TWM306698 also discloses a single-pieced image reading lens module which is more convenient to manufacture, but requires even longer reception distance thus reducing the usability thereof
Hence, in order to improve the quality of the received image, U.S. Pat. No. 5,917,661 discloses an image reading lens module using two optical lenses, as shown in
Regarding to the design of image reading lens module suitable for high resolution bar code reader machines, as the four lens image reading lens module disclosed in U.S. Pat. No. 7,477,460 or US Patent Publication US2007/0097522, better compensation in astigmatic aberration can be achieved but the integral length thereof is nonetheless too long, and more lenses are needed, which is not cost-effective.
At present, on the development trend in bar code reader machines, intensive user needs for small-sized, short range operations between the bar code reader machine and the bar code exist, it is therefore advantageous to fulfill such demands with an image reading lens module featuring a shortened lens module length (entire length), wide angle of view, reduced back focal length as well as high resolution through effective astigmatic aberration corrections.
Considering the aforementioned issues found in prior art, one main objective of the present invention lies in providing a reading optical lens module which enables a wider angle of view, shorter back focal length and better corrected astigmatic aberration for applications on the bar code reader machine requiring small size and short range scanning. The reading optical lens module comprises a first lens, a second lens and an image sensor arranged sequentially from the object side to the image side and along an optical axis.
Herein the first lens is a meniscus lens whose object side optical surface is a convex surface facing toward the object side, and the object side optical surface and the image side optical surface of the first lens are both aspherical surfaces. Herein the second lens is a meniscus lens whose object side optical surface is a concave surface facing toward the object side, and the object side optical surface and the image side optical surface of the second lens are both aspherical surfaces. Moreover, the first lens and the second lens are selected to have the same refractive Index Nd. Herein the image sensor is disposed on an imaging plane formed after combination of the first lens and the second lens, and the reading optical lens module satisfies the following conditions:
62.0°<2ω<89.5° (1)
1.50<TL/D1/2=2.20 (2)
wherein 2ω denotes the diagonal angle of the field of view for the reading optical lens module (in degrees), TL denotes the distance between the object side optical surface of the first lens and the imaging plane, and D1/2 represents half of the length of the diagonal line in the effective sensing area provided by the image sensor.
Another objective of the present invention lies in providing a reading optical lens module as previously described, which comprises a first lens, a second lens and an image sensor arranged sequentially from the object side to the image side and along an optical axis, and further satisfies one of the following conditions or a combination thereof:
1.0<|f/f1|+|f/f2|<2.1 (3)
1.10<R1/R2<1.50 (4)
1.35<(R3+R4)/(R3−R4)<2.50 (5)
wherein f denotes the focal length of the reading optical lens module, f1 denotes the focal length of the first lens, f2 denotes the focal length of the second lens, R1 denotes the paraxial radius of curvature on the object side optical surface of the first lens, R2 denotes the paraxial radius of curvature on the image side optical surface of the first lens, R3 denotes the paraxial radius of curvature on the object side optical surface of the second lens and R4 denotes the paraxial radius of curvature on the image side optical surface of the second lens.
According to another main objective of the present invention, a reading optical lens module is provided which enables a wider angle of view, shorter back focal length and better corrected astigmatic aberration for applications on the bar code reader machine requiring small size and short range scanning. From the object side to the image side, the reading optical lens module comprises a first lens, an aperture stop, a second lens and an image sensor arranged along an optical axis sequentially.
Herein the first lens is a meniscus lens whose object side optical surface is a convex surface facing toward the object side, and the object side optical surface and the image side optical surface of the first lens are both aspherical surfaces. Herein the aperture stop is a middle aperture diaphragm for blocking stray light. Herein the second lens is a meniscus lens whose object side optical surface is a concave surface facing toward the object side, and the object side optical surface and the image side optical surface of the second lens are both aspherical surfaces. Herein the image sensor is disposed on the imaging plane formed after combination of the first lens and the second lens, and the reading optical lens module further satisfies the following condition in addition to the aforementioned conditions of conditions (1) and (2):
0.58<BFL/TL<0.79 (6)
wherein BFL denotes the back focal length of the reading optical lens module, and TL denotes the distance from the object side optical surface of the first lens to the imaging plane on the optical axis.
According to yet another objective of the present invention, a reading optical lens module for the bar code reader machine as previously described is provided for facilitating the generation of chromatic dispersion due to light rays of different wavelengths in the reading optical lens module for the bar code reader machine, further satisfying the following condition in addition to the aforementioned conditions of conditions (1) and (2):
|v
d1
−v
d2
|/v
d1<0.08 (7)
where vd1 denotes the coefficient of dispersion in the first lens and vd2 denotes the coefficient of dispersion in the second lens. Furthermore, to reduce material preparations in manufacture processes, the first lens and the second lens may be made of the material having the same dispersion coefficient Vd.
In the reading optical lens module according to the present invention, the first lens and the second lens may be made of the glass or plastic material, and the present invention is not limited thereto.
In summary of the above-said descriptions, the reading optical lens module according to the present invention features one or more of the following advantages:
(1) the reading optical lens module according to the present invention allows to increase the amplitude of refraction, adjust the spherical aberration and the astigmatic field curving as well as correct the distortion through two meniscus lenses combined in different directions;
(2) the reading optical lens module according to the present invention can achieve a wider angle of view by means of restrictions indicated in condition (1) thereby successful reading the bar code image at a closer distance; further through the limitation of condition (2), it is possible to reduce the distance from the object side optical surface of the first lens to the imaging plane (TL) with half of the diagonal line of the effective sensing area of the image sensor in the unit length (D1/2) thus achieving the objective of miniaturization of the reading optical lens module; and also based on the additional limitation of condition (6) and the additional limitation of a middle aperture stop, the back focal length (BFL) of the reading optical lens module can be advantageously reduced with the same distance from the object side optical surface of the first lens to the imaging plane (TL) so as to facilitate the miniaturization (slimness) of the reading optical lens module;
(3) the reading optical lens module according to the present invention allows to, by means of additional limitation of condition (3), regulate the refraction power between the first lens and the second lens such that the distribution of the refraction power can be more balanced in order to reduce the sensitivity of the integral system and occurrence of aberration thereby fulfilling the goal of good imaging feature. Furthermore, by means of additional limitation of condition (4), it is possible to enhance the refraction power of the first lens so as to shorten the entire length of the reading optical lens module; and via additional restriction described in condition (5), the profile of the second lens can be advantageously confined in order to facilitate manufacturing.
(4) the reading optical lens module according to the present invention allows to, with regards to further limitations of condition (7), generate the chromatic dispersion to increase the resolution of the image, such as a barcode, due to light rays of different wavelengths, further enabling the use of material having the identical dispersion coefficient for the first lens and the second lens thereby simplifying manufacture materials and reducing manufacture costs.
Referring initially to
The object side optical surface 111 and the image side optical surface 112 of the first lens 11 can be aspherical surfaces, and the object side optical surface 121 and the image side optical surface 122 of the second lens 12 can be aspherical surfaces as well. The aspherical optical surfaces of the first lens 11 and the second lens 12 can be constructed based on the following aspherical surface formula (8):
wherein Z denotes the distance from any point on the lens in the direction of optical axis to the tangential plane of the center of the lens (SAG); c denotes the curvature; r denotes the height of the lens perpendicular to the optical axis, K denotes the conic constant; and α1˜α8 denotes the aspherical coefficient for the second to the sixteenth order, respectively.
The reading optical lens module 10 according to the present invention will now be described in details through the subsequent embodiments in conjunction with the appended drawings.
Refer to
The object side optical surface of the first lens 111, the image side optical surface of the first lens 112, the object side optical surface of the second lens 121 and the image side optical surface of the second lens 122 are all aspherical surfaces constituted by means of the aspherical surface formula (8), whose aspherical coefficients are shown as below in Table 2.
In the reading optical lens module of the first embodiment, the focal length of the entire reading optical lens module 10 is f=8.59 (mm), the f-number of the constructed reading optical lens module is Fno=3.2, and the diagonal angle for the field of view (FOV) is 2ω=64.7 (in unit of degrees).
Refer back to Table 1, wherein, in the present embodiment, the dispersion coefficient for the first lens 11 of the reading optical lens module is represented as vd1, the dispersion coefficient for the second lens 12 is represented as vd2, with the following relationship: |vd1−vd2|/vd1=0, which satisfies condition (7), as using the same material in design of the two lenses. On the optical axis, the distance from the object side optical surface of the first lens 111 to the imaging surface 14 is TL=15.01, and the half of the diagonal length in the effective sensing area of the image sensor is D1/2=7.215, with TL/D1/2=2.08 which satisfies condition (2). The back focal length of the reading optical lens module of the present embodiment is BFL=11.27, with BFL/TL=0.75 which satisfies condition (6). Furthermore, the focal length of the first lens 11 is f1=−19.07 and the focal length of the second lens 12 is f2=5.97, with |f/f1|+|f/f2|=1.89 which satisfies condition (3).
Referring to Table 1, in the present embodiment, the first lens 11 and the second lens 12 respectively satisfies conditions (4) and (5): R1/R2=1.40 and (R3+R4)/(R3−R4)=1.64.
It can be seen from the optical data listed in Table 1 and the astigmatic aberration curve shown in
The astigmatic aberration curve for the second embodiment of the present invention can be referred to
The object side optical surface of the first lens 111, the image side optical surface of the first lens 112, the object side optical surface of the second lens 121 and the image side optical surface of the second lens 122 are all aspherical surfaces constituted by means of the aspherical surface formula (8) whose aspherical coefficients are shown as below in Table 4.
In the reading optical lens module of the second embodiment, the focal length of the entire reading optical lens module 10 is f=8.17 (mm), the f-number of the constructed reading optical lens module is Fno=3.2, and the diagonal angle for the field of view (FOV) is 2ω=69.3 (in unit of degrees).
Refer back to Table 3, wherein, in the present embodiment, the dispersion coefficient for the first lens 11 of the reading optical lens module is represented as vd1, the dispersion coefficient for the second lens 12 is represented as vd2, with the following relationship: |vd1−vd2|/vd1<0.018, which satisfies condition (7), as using the same material in design of the two lenses. On the optical axis, the distance from the object side optical surface of the first lens 111 to the imaging surface 14 is TL=13.63, and the half of the diagonal length in the effective sensing area of the image sensor is Dv2=7.215, with TL/D1/2=1.89 which satisfies condition (2). The back focal length of the reading optical lens module of the present embodiment is BFL=10.53, with BFL/TL=0.77 which satisfies condition (6). Furthermore, the focal length of the first lens 11 is f1=−24.43 and the focal length of the second lens 12 is f2=5.925 with |f/f1|+|f/f2|=1.71 which satisfies condition (3).
Referring to Table 3, in the present embodiment, the first lens 11 and the second lens 12 respectively satisfies condition (4) and (5): R1/R2=1.31 and (R3+R4)/(R3−R4)=1.66.
It can be seen from the optical data listed in Table 3 and the astigmatic aberration curve shown in
The astigmatic aberration curve for the third embodiment of the present invention can be referred to
The object side optical surface of the first lens 111, the image side optical surface of the first lens 112, the object side optical surface of the second lens 121 and the image side optical surface of the second lens 122 are all aspherical surfaces constituted by means of the aspherical surface formula (8) whose aspherical coefficients are shown as below in Table 6.
In the reading optical lens module of the third embodiment, the focal length of the entire the reading optical lens module 10 is f=7.84 (mm), the f-number of the constructed the reading optical lens module is Fno=3.2, and the diagonal angle for the field of view (FOV) is 2ω=88.3 (in unit of degrees).
Refer back to Table 5, wherein, in the present embodiment, the dispersion coefficient for the first lens 11 of the reading optical lens module is represented as vd1, the dispersion coefficient for the second lens 12 is represented as vd2, with the following relationship: |vd1−vd2|/vd1<0.065, which satisfies condition (7), as using the same material in design of the two lenses. On the optical axis, the distance from the object side optical surface of the first lens 111 to the imaging surface 14 is TL=12.05, and the half of the diagonal length in the effective sensing area of the image sensor is D1/2=7.215, with TL/D1/2=1.67 which satisfies condition (2). The back focal length of the reading optical lens module of the present embodiment is BFL=7.23, with BFL/TL=0.60 which satisfies condition (6). Furthermore, the focal length of the first lens 11 is f1=588.1 and the focal length of the second lens 12 is f2=6.80, with |f/f1|+|f/f2|=1.167 which satisfies condition (3).
Referring to Table 5, in the present embodiment, the first lens 11 and the second lens 12 respectively satisfies conditions (4) and (5): R1/R2=1.157 and (R3+R4)/(R3−R4)=2.306.
It can be seen from the optical data listed in Table 5 and the astigmatic aberration curve shown in
The aforementioned descriptions are exemplary rather than being restrictive. All effectively equivalent changes, alternation or substitutions made thereto without departing from the spirit and scope of the present invention are deemed to be encompassed by the present invention as delineated in the following claims.
Number | Date | Country | Kind |
---|---|---|---|
099146970 | Dec 2010 | TW | national |