阅读说明：本技术 一种用于立体内窥镜的光学成像系统及立体内窥镜 (Optical imaging system for stereoscopic endoscope and stereoscopic endoscope ) 是由 不公告发明人 于 2021-11-02 设计创作，主要内容包括：一种用于立体内窥镜的光学成像系统及立体内窥镜,所述光学成像系统由物方至像方依次包括第一透镜、第二透镜、第三透镜、第四透镜、第五透镜和第六透镜,其中：所述第一透镜为负光焦度透镜；所述第二透镜、所述第三透镜和所述第四透镜为正光焦度透镜；所述第五透镜为正光焦度透镜,所述第六透镜为负光焦度透镜,并且所述第五透镜和第六透镜构成胶合透镜组。该光学成像系统具有大视场、小口径、短尺寸、大景深、高分辨率的优点。(An optical imaging system and stereoscopic endoscope for stereoscopic endoscope, the optical imaging system includes first lens, second lens, third lens, fourth lens, fifth lens and sixth lens from object side to image side in proper order, wherein: the first lens is a negative focal power lens; the second lens, the third lens and the fourth lens are positive focal power lenses; the fifth lens is a positive power lens, the sixth lens is a negative power lens, and the fifth lens and the sixth lens form a cemented lens group. The optical imaging system has the advantages of large view field, small caliber, short size, large depth of field and high resolution.)

1. An optical imaging system for a stereoscopic endoscope, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens in order from an object side to an image side, wherein:

the first lens is a negative focal power lens;

the second lens, the third lens and the fourth lens are positive focal power lenses;

the fifth lens is a positive power lens, the sixth lens is a negative power lens, and the fifth lens and the sixth lens form a cemented lens group.

2. The optical imaging system of claim 1, wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are all spherical glass lenses.

3. The optical imaging system of claim 1, further comprising a stop disposed between the third lens and the fourth lens.

4. The optical imaging system of claim 1, wherein a ratio of a focal length of the first lens to a focal length of the optical imaging system satisfies: 0.95< | f1/f | <1.05, wherein f1 is the focal length of the first lens, and f is the focal length of the optical imaging system.

5. The optical imaging system of claim 1, wherein the focal length of the second lens and the focal length of the third lens satisfy: 0.52< | f2/f3| <0.62, wherein f2 is the focal length of the second lens and f3 is the focal length of the third lens.

6. The optical imaging system of claim 1, wherein the focal length of the fifth lens and the focal length of the sixth lens satisfy: 0.85< | f5/f6| <0.92, wherein f5 is the focal length of the fifth lens and f6 is the focal length of the sixth lens.

7. The optical imaging system of claim 1, wherein the optical imaging system further satisfies at least one of the following conditions: the refractive index of the first lens is greater than or equal to 1.72, and the abbe number of the first lens is greater than or equal to 50; the refractive index of the second lens is greater than or equal to 1.75, and the abbe number of the second lens is less than or equal to 26; the refractive index of the third lens is greater than or equal to 1.75, and the abbe number of the third lens is less than or equal to 25; the refractive index of the fourth lens is less than or equal to 1.65, and the abbe number of the fourth lens is greater than or equal to 60; the refractive index of the fifth lens is less than or equal to 1.65, and the dispersion coefficient of the fifth lens is greater than or equal to 48; the refractive index of the sixth lens is greater than or equal to 1.84, and the abbe number of the sixth lens is less than or equal to 25.

8. The optical imaging system of claim 1, wherein the optical imaging system has an overall optical length greater than or equal to 14.1mm and less than or equal to 15.2 mm.

9. The optical imaging system of claim 1, wherein the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are each less than 3.5mm in diameter.

10. The optical imaging system of claim 1, wherein a ratio of a half-image height of the optical imaging system to an optical overall length of the optical imaging system is less than or equal to 0.12.

11. The optical imaging system of claim 1, wherein a ratio of an effective aperture of the first lens to a half-image height of the optical imaging system is less than 2.0.

12. The optical imaging system of claim 1 or 7, wherein a ratio of a back focal length of the optical imaging system to an effective focal length of the optical imaging system is greater than 1.75 and less than or equal to 1.95.

13. A stereoscopic endoscope, comprising:

the optical imaging system of any one of claims 1 to 12; and

an image sensor disposed at an image side of the optical imaging system for converting an optical signal via the optical imaging system into an electrical signal.

Technical Field

The present invention relates generally to the field of optical imaging, and more particularly to an optical imaging system for a stereoscopic endoscope and a stereoscopic endoscope.

Background

Minimally invasive surgery in the world has become the development of various fields of surgical medicine today. The minimally invasive surgery has the advantages of small damage to patients, reduction of pain of the patients during the surgery, short postoperative rehabilitation time and the like, and is more and more widely applied.

With the continuous development of science and technology, the surgical robot can replace a surgeon to perform minimally invasive surgery as a novel minimally invasive surgery platform. The precision of the surgery surpasses the limit of a human hand, is a revolutionary leap for the concept of the whole surgery, and is widely applied to the field of minimally invasive surgery such as urology surgery, thoracic surgery, gynecology, abdominal surgery and the like.

In order to precisely control the position of the surgical instrument, the surgical robot observes the diseased tissue using a stereoscopic endoscope. For stereoscopic endoscopes or laparoscopes, a large field of view is required to view a wide range of surgical fields. Meanwhile, due to the size limitation of the distal end portion of the stereoscopic endoscope, the aperture of the objective optical imaging system for the endoscope constituting each optical channel is required to be as small as possible. In addition, it is desirable to clearly view images in a certain range before and after the focusing position during the operation, and an endoscope objective optical imaging system is required to have a large depth of field and a high resolution.

Therefore, an endoscope optical imaging system with large field of view, small caliber, short size, large depth of field and high resolution is provided, and has great significance for a stereoscopic endoscope.

Disclosure of Invention

In this summary, concepts in a simplified form are introduced that are further described in the detailed description. This summary of the invention is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In view of the deficiencies of the prior art, an aspect of the present invention provides an optical imaging system, which comprises, in order from an object side to an image side, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens, wherein:

the first lens is a negative focal power lens;

the second lens, the third lens and the fourth lens are positive focal power lenses;

the fifth lens is a positive power lens, the sixth lens is a negative power lens, and the fifth lens and the sixth lens form a cemented lens group.

In one embodiment, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are all spherical glass lenses.

In one embodiment, the optical imaging system further comprises a diaphragm disposed between the third lens and the fourth lens.

In one embodiment, a ratio of a focal length of the first lens to a focal length of the optical imaging system satisfies: 0.95< | f1/f | <1.05, wherein f1 is the focal length of the first lens, and f is the focal length of the optical imaging system.

In one embodiment, the focal length of the second lens and the focal length of the third lens satisfy: 0.52< | f2/f3| <0.62, wherein f2 is the focal length of the second lens and f3 is the focal length of the third lens.

In one embodiment, the focal length of the fifth lens and the focal length of the sixth lens satisfy: 0.85< | f5/f6| <0.92, wherein f5 is the focal length of the fifth lens and f6 is the focal length of the sixth lens.

In one embodiment, the refractive index of the first lens is greater than or equal to 1.72, the Abbe number of the first lens is greater than or equal to 50; the refractive index of the second lens is greater than or equal to 1.75, and the abbe number of the second lens is less than or equal to 26; the refractive index of the third lens is greater than or equal to 1.75, and the abbe number of the third lens is less than or equal to 25; the refractive index of the fourth lens is less than or equal to 1.65, and the abbe number of the fourth lens is greater than or equal to 60; the refractive index of the fifth lens is less than or equal to 1.65, and the dispersion coefficient of the fifth lens is greater than or equal to 48; the refractive index of the sixth lens is greater than or equal to 1.84, and the abbe number of the sixth lens is less than or equal to 25.

In one embodiment, the optical imaging system has an overall optical length greater than or equal to 14.1mm and less than or equal to 15.2 mm.

In one embodiment, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens are each less than 3.5mm in diameter.

In one embodiment, a ratio of a half-image height of the optical imaging system to an optical overall length of the optical imaging system is less than or equal to 0.12.

In one embodiment, a ratio of an effective aperture of the first lens to a half-image height of the optical imaging system is less than 2.0.

In one embodiment, a ratio of a back focal length of the optical imaging system to an effective focal length of the optical imaging system is greater than 1.75 and less than or equal to 1.95.

Another aspect of an embodiment of the present invention provides a stereoscopic endoscope, including: an optical imaging system as described above; and an image sensor disposed at an image side of the optical imaging system.

The optical imaging system of the embodiment of the invention has the advantages of large field of view, small caliber, short size, large depth of field and high resolution, and the stereoscopic endoscope of the embodiment of the invention has similar advantages because of adopting the optical imaging system.

Drawings

The following drawings of the invention are included to provide a further understanding of the invention. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

In the drawings:

FIG. 1 shows a schematic diagram of an optical imaging system according to one embodiment of the invention;

FIG. 2 shows a modulation transfer function plot for an optical imaging system according to one embodiment of the present invention;

FIG. 3 shows a graph of chromatic aberration of magnification of an optical imaging system according to one embodiment of the invention;

FIG. 4 shows a through focus plot of an optical imaging system according to one embodiment of the invention;

FIG. 5 shows a graph of modulation transfer function versus field of view for an optical imaging system in accordance with one embodiment of the present invention.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.

It is to be understood that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

For a better understanding of the present application, various aspects of the present application will be described in more detail with reference to the accompanying drawings. It should be understood that the detailed description is merely illustrative of exemplary embodiments of the present application and does not limit the scope of the present application in any way. Like reference numerals refer to like elements throughout the specification. The expression "and/or" includes any and all combinations of one or more of the associated listed items.

It should be noted that in this specification, the expressions first, second, third, etc. are used only to distinguish one feature from another, and do not represent any limitation on the features. For example, the first lens discussed below may also be referred to as the second lens or the third lens without departing from the teachings of the present application.

In the drawings, the thickness, size, and shape of the lens have been slightly exaggerated for convenience of explanation. In particular, the shapes of the spherical or aspherical surfaces shown in the drawings are shown by way of example. That is, the shape of the spherical surface or the aspherical surface is not limited to the shape of the spherical surface or the aspherical surface shown in the drawings. The figures are purely diagrammatic and not drawn to scale.

Herein, the paraxial region refers to a region near the optical axis. If the lens surface is convex and the convex position is not defined, it means that the lens surface is convex at least in the paraxial region; if the lens surface is concave and the concave position is not defined, it means that the lens surface is concave at least in the paraxial region. The surface of each lens closest to the subject is referred to as the object side of the lens, and the surface of each lens closest to the image side is referred to as the image side of the lens.

It will be further understood that the terms "comprises," "comprising," "has," "having," "includes" and/or "including," when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, elements, components, and/or groups thereof. Moreover, when a statement such as "at least one of" appears after a list of listed features, the entirety of the listed features is modified rather than modifying individual elements in the list. Furthermore, when describing embodiments of the present application, the use of "may" mean "one or more embodiments of the present application. Also, the term "exemplary" is intended to refer to an example or illustration.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.

An optical imaging system according to an embodiment of the present invention will be described in detail with reference to fig. 1 to 5. In the following description, a lens has a positive optical power, indicating that it is convergent in refraction of light; the lens has a negative power, indicating that its refraction of light is divergent. Convex lens surface means that the radius of curvature of the lens is positive, whereas concave lens surface means that the radius of curvature is negative. If the lens surface is convex and the convex position is not defined, it means that the lens surface can be convex at the paraxial region; if the lens surface is concave and the concave locations are not defined, this means that the lens surface can be concave at the paraxial region. If the power or focal length of the lens does not define its zone location, it means that the power or focal length of the lens may be the power or focal length of the lens at the paraxial region.

As shown in fig. 1, an optical imaging system 100 according to an embodiment of the present invention includes six lenses, which are, in order from an object side to an image side, a first lens 101, a second lens 102, a third lens 103, a fourth lens 104, a fifth lens 105, and a sixth lens 106. Light from an object passes through the first lens 101, the second lens 102, the third lens 103, the fourth lens 104, the fifth lens 105 and the sixth lens 106 in sequence and then is imaged on an imaging surface on the image side of the sixth lens 106.

Wherein, the first lens 101 is a negative power lens, preferably a plano-concave negative power lens; the fourth lens of the second lens 102, the third lens 103 and 104 is a positive power lens; the fifth lens is a positive power lens, the sixth lens 106 is a negative power lens, and the fifth lens 105 and the sixth lens 106 are a cemented lens group. More specifically, the object-side surface of the first lens 101 is a plane, and the image-side surface is a concave surface; the object-side surface of the second lens element 102 is a plane, and the image-side surface thereof is a convex surface; the object-side surface and the image-side surface of the third lens element 103 are convex; the object-side surface and the image-side surface of the fourth lens element 104 are convex; the object-side surface and the image-side surface of the fifth lens element 105 are convex; the object-side surface of the sixth lens element 106 is concave and the image-side surface thereof is convex, and the object-side surface of the sixth lens element 106 and the image-side surface of the fifth lens element 105 have complementary shapes and are cemented together. According to the embodiment of the invention, through reasonable optical setting of the six lenses, the optical imaging system 100 has the advantages of large depth of field, large field of view, small caliber and short size while ensuring high resolution, and can meet the use requirements of the stereoscopic endoscope.

In one embodiment, the six lenses are all spherical glass lenses. The optical imaging system 100 of the embodiment of the invention adopts a design scheme of a global surface glass lens, so that the optical imaging system is easy to process and low in manufacturing cost, and compared with an aspheric surface, the optical imaging system effectively reduces the assembly error and improves the assembly yield. And the spherical glass lens has better universality, and the difficulty of later maintenance is reduced.

The first lens 101 is a negative power lens and can provide a large field angle. In one embodiment, the ratio of the focal length f1 of the first lens to the focal length f of the optical imaging system 100 as a whole satisfies: 0.95< | f1/f | < 1.05. The first lens 101 is a plano-concave negative power lens, and diverges the off-axis incident light, so that the included angle between the large-view-angle light and the optical axis is reduced, and aberration correction is easier.

The second lens 102 to the fourth lens 104 are all positive power lenses for sufficiently converging the light refracted by the first lens 101. Most of the negative refractive power required for the optical imaging system 100 is taken charge of by the first lens 101. Since the negative refractive power of the first lens 101 is large and thus large aberrations are generated, the second lens 102 to the fourth lens 104 help to appropriately correct the aberrations generated by the first lens.

In the embodiment of the invention, the second lens 102 and the third lens 103 are biconvex lenses, so that the light rays refracted by the first lens 101 can be converged quickly. In the embodiment of the invention, the fourth lens 104 is a biconvex lens, which can further converge light and reduce the height of an incident image plane of the light, and meanwhile, the fourth lens 104 can also act together with a diaphragm arranged between the third lens 103 and the fourth lens 104 to effectively correct aberration formed by the spherical glass lens.

In the embodiment of the present invention, the fifth lens 105 and the sixth lens 106 are configured as a cemented lens group, and the use of the cemented lens group is beneficial to reducing or eliminating chromatic aberration to the maximum extent and improving imaging quality.

The optical imaging system 100 of the embodiment of the present invention further includes at least one stop for reducing stray light and improving image quality. The diaphragm may be an iris diaphragm or a non-iris diaphragm. The more forward the stop is located, the more favorable the correction of the chief ray angle, and the more backward the stop is located, the larger the field angle of the system is, which is favorable for satisfying the wide-angle characteristic of the optical imaging system, and in order to achieve a better balance between the two, in one embodiment, the stop may be disposed between the third lens 103 and the fourth lens 104.

In one embodiment, a filter element is further disposed between the sixth lens 106 and the imaging surface. The filter element includes an infrared filter for filtering out infrared band light entering the optical imaging system 100, so as to prevent the infrared light from irradiating the image sensor to generate noise. The material of the filter element comprises glass, and the material does not affect the focal length of the optical imaging system.

In one embodiment, the focal length f2 of the second lens and the focal length f3 of the third lens satisfy: 0.52< | f2/f3| <0.62, and 0.85< | f5/f6| <0.92 is satisfied between the focal length f5 of the fifth lens and the focal length f6 of the sixth lens. By making the relationship between the focal lengths of the second lens 102 and the third lens 103, and the relationship between the focal lengths of the fifth lens 105 and the sixth lens 106 satisfy the above conditions, the effective focal lengths of the lenses can be optimized, which is beneficial to adjusting the light focusing position and controlling the total length of the optical imaging system 100.

Further, the refractive index and the abbe number of the first lens 101 to the sixth lens 106 also satisfy at least one of the following conditions: the refractive index nd1 of the first lens 101 satisfies: nd1 is more than or equal to 1.72, and the abbe number v1 of the first lens 101 satisfies: v1 is more than or equal to 50; the refractive index nd2 of the second lens 102 satisfies: nd2 is more than or equal to 1.75, and the abbe number v2 of the second lens 102 satisfies: v2 is less than or equal to 26; the refractive index nd3 of the third lens 103 satisfies: nd3 is more than or equal to 1.75, and the abbe number v3 of the third lens 103 satisfies: v3 is less than or equal to 25; the refractive index nd4 of the fourth lens 104 satisfies: nd4 is less than or equal to 1.65, and the abbe number v4 of the fourth lens 104 satisfies: v4 is more than or equal to 60; the refractive index nd5 of the fifth lens 105 satisfies: nd5 is less than or equal to 1.65, and the abbe number v5 of the fifth lens 105 satisfies: v5 is more than or equal to 48; the refractive index nd6 of the sixth lens 106 satisfies: nd6 is more than or equal to 1.84, and the dispersion coefficient v6 of the sixth lens 106 satisfies: v6 is less than or equal to 25. Satisfying the above conditions is advantageous for eliminating chromatic aberration and aberration.

Further, the total optical length L of the optical imaging system 100 satisfies: l is more than or equal to 14.1mm and less than or equal to 15.2 mm. Further, the diameters of the first lens 101, the second lens 102, the third lens 103, the fourth lens 104, the fifth lens 105, and the sixth lens 106 are each less than 3.5mm, and preferably less than or equal to 3 mm. The optical imaging system meeting the conditions has the advantages of small caliber and short size, and meets the requirement of the three-dimensional endoscope on miniaturization.

Further, the half-image height H and the total optical length L of the optical imaging system 100 satisfy: H/L is less than or equal to 0.12. Further, the effective aperture D1 of the first lens 101, the half-image height H of the optical imaging system 100, and the optical total length L of the optical imaging system 100 also satisfy the following conditions: D1/H < 2.0. Satisfying the above conditions is advantageous for achieving compactness and miniaturization of the optical imaging system 100 while also enabling high pixel performance of the optical imaging system 100.

Further, the back focal length BFL of the optical imaging system 100 and the effective focal length f of the optical imaging system 100 satisfy the following condition: BFL/f is more than 1.75 and less than or equal to 1.95.

The structural parameters of each lens of the optical imaging system according to an embodiment of the present invention are specifically shown in table 1. In table 1, the front surface represents the object side surface of the lens, and the back surface represents the image side surface of the lens; f represents the effective focal length of the optical imaging system, L represents the total optical length of the optical imaging system, FOV represents the field angle, D1 represents the effective aperture of the first lens, H represents the half-image height of the optical imaging system, and BFL represents the back focal length of the optical imaging system; the unit of curvature radius and thickness in table 1 is mm; when the radius of curvature of the surface of any of the lens, the diaphragm, and the infrared filter in table 1 is infinity, the surface is a plane.

TABLE 1

Referring to fig. 2-5, wherein fig. 2 shows Modulation Transfer Function (MTF) plots at 150lp/mm for an optical imaging system according to an embodiment of the present invention; FIG. 3 is a graph of chromatic aberration of magnification of an optical imaging system according to an embodiment of the invention; FIG. 4 is a defocus plot of an optical imaging system of an embodiment of the present invention; FIG. 5 is a graph of MTF versus field of view for an optical imaging system of an embodiment of the present invention at 60lp/mm, 100lp/mm, 150lp/mm, and 200lp/mm, respectively.

As can be seen from FIG. 2, at 150lp/mm, the MTF value of the full field of view of the optical imaging system of the embodiment of the invention is more than 0.4, and is concentrated, thereby meeting the requirement of high definition use.

As can be seen from FIG. 3, the chromatic aberration of magnification of the optical imaging system of the embodiment of the invention is less than 1.5 μm, and within the Airy radius, it can be regarded as no chromatic aberration.

As can be seen from fig. 4, the optical imaging system of the present embodiment has a large depth of focus, and when the defocus is 0.04mm, the MTF values are all above 0.4, so that the optical imaging system has a large depth of field.

As can be seen from FIG. 5, the MTF of the optical imaging system of the embodiment of the invention changes smoothly with the field of view at 60lp/mm, 100lp/mm, 150lp/mm and 200lp/mm, which shows that the MTF values of the full field of view are concentrated, the change of the resolution from the center to the edge is small, and the optical imaging system meets the use requirements of a high-definition wide-angle lens.

In summary, the optical imaging system of the embodiment of the invention has at least the following advantages:

(1) all lenses in the optical imaging system are spherical glass lenses, the processing is easy, compared with an aspheric surface, the assembling error is effectively reduced, and the assembling yield is improved;

(2) through reasonable optical design of the six lenses, the optical imaging system has the advantage of large depth of field while ensuring high resolution;

(3) the aperture of the optical imaging system can be smaller than 3mm, the horizontal field angle can reach 78.5 degrees, and the optical imaging system is very suitable for being used as a camera module of a three-dimensional endoscope;

(4) the optical imaging system 100 of the embodiment of the invention is an image space telecentric system, the telecentricity is less than 5 degrees, the edge illumination is favorably improved, meanwhile, the definition can be still ensured when the image plane of the sensor deviates from the optimal image plane to a certain extent, and the focusing difficulty in assembly is reduced.

The optical imaging system 100 of the embodiment of the present invention can be applied to a stereoscopic endoscope. Therefore, the embodiment of the invention can also provide a stereoscopic endoscope. The stereoscopic endoscope of the embodiment of the present invention includes the optical imaging system 100 as described in the various embodiments above, and an image sensor provided at the image side of the optical imaging system 100.

The image sensor may provide an imaging surface on which light refracted through the lens is imaged. In addition, the image sensor may convert the optical signals imaged on the imaging surface into electrical signals for use by a computer or other suitable stereoscopic endoscope. The image sensor may be a Complementary Metal Oxide Semiconductor (CMOS) image sensor or a Charge-coupled Device (CCD) image sensor, and the embodiment of the present invention is not limited thereto.

Because the optical imaging system adopted by the stereoscopic endoscope has the characteristic of miniaturization, when the diameter of each lens is smaller than 3mm, the outer diameter of the sleeve of the stereoscopic endoscope can be smaller than 10mm through reasonable structural design, and the clinical requirement is met. Other advantageous technical effects of the stereoscopic endoscope according to the embodiment of the present invention are similar to those of the optical imaging system 100, and therefore, are not described herein again.

It will be understood by those skilled in the art that all of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where such features are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Furthermore, those skilled in the art will appreciate that while some embodiments described herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments may be used in any combination.

Technical terms used in the embodiments of the present invention are only used for illustrating specific embodiments and are not intended to limit the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, the use of "including" and/or "comprising" in the specification is intended to specify the presence of stated features, integers, steps, operations, elements, and/or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. The embodiments described herein are further intended to explain the principles of the invention and its practical application and to enable others skilled in the art to understand the invention.

The flow chart described in the present invention is only an example, and various modifications can be made to the diagram or the steps in the present invention without departing from the spirit of the present invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted or modified. It will be understood by those skilled in the art that all or a portion of the above-described embodiments may be practiced and equivalents thereof may be resorted to as falling within the scope of the invention as claimed.