Abstract:
A device for measuring a lens, comprising a first interferometer having a first optical axis and carried on a first adjustment base, a lens holder for holding the lens having a first surface having a first lens optical axis and a second surface having a second lens optical axis, and a platen having a sliding rail and carrying the first adjustment base and the lens holder thereon, wherein the lens holder is movable on the sliding rail, wherein each of the first adjustment base and the lens holder has a tetra-axis adjustment mechanism through which a relative positional relationship of the first optical axis of the first interferometer and the first lens optical axis of the first surface of the lens is adjustable.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a technology for measuring a lens, and more particular to a technology for measuring decenter and tilt amounts of a lens by an interferometer. 
     BACKGROUND OF THE INVENTION 
     For the recent years, the vigorous development of the electro-optic industry, particularly the digital camera and the cellular phone camera, has placed a larger and larger demand for the optical devices. Of the optical elements, the optical lens can be the most essential and important one. In terms of the product characteristics, the optical lens may be categorized into a refractive device (e.g. a lens and a prism), a reflective device, a diffractive device, a hybrid device, among others, which are each related to a specific material and manufacturing process. Among the optical lens, the aspherical optical devices have found more and more applications and are more and more required. This is because the aspherical lens can have a good imaging quality as compared to the spherical lens. Further, when the aspherical optical device is applied to an optical system, the number of the optical device required and the overall cost for the system may be reduced. 
     For the manufacturing reason, the aspherical lens is prone to a decenter or tilt issue with respect to the optical axes of its two side surfaces, leading to a deviation of the optical characteristics thereof. To obviate the deficient lens products, whether the decenter and tilt issues existing on the two axes of the aspherical lens are required to be measured or inspected, so that the lens itself can be corrected in optical design or manufacturing. In this regard, how to precisely and rapidly measure the aspherical lens is apparently an important issue to the manufacturing and design of the aspherical lens. 
     For the spherical lens, the optical axis is a line connecting the both curvature centers of the two side surfaces thereof, which is shown in  FIG. 7A . For the lens with only a single spherical surface, all lines extending from the curvature center to the spherical surface can be taken as the optical axis, which is shown in  FIG. 7B . For the spherical lens, the optical axis is a common line among the optical axes of the two side surfaces and thus the line connected between the two spherical curvature centers. In the spherical lens, the decenter and tilt issues do not exist between the two optical axes but only exists between the optical axes and the geometrical centerlines, which is shown in  FIG. 7C . This is conventionally measured by a collimator. In the aspherical lens, a line formed by connecting the curvature centers of all the curvatures of the spherical surfaces is the optical axis and only this optical axis exists therein, which is shown in  FIG. 7D . Thus, the aspherical lens is provided with an optical axis at each of the two side surfaces thereof. The two optical axes possibly do not coincide with each other due to the manufacturing error problem. Accordingly, the decenter and tilt issues exist between the two optical axes, which are shown in  FIG. 7E . This is generally measured by a reflective collimator. However, the aspherical lens is mostly formed by glass molding or plastic injection and thus burrs and mouse bites might be found at the rim portion thereof, which can cause a disturbance for the rotation of the lens, required when being measured by a collimator, or an error with respect to the measurement. 
     In view of the above, there is a need to provide a method and device for measuring the decenter and tilt amounts between the two side surfaces of the lens by using an interferometer. After a long intensive series of experiments and research, the inventor finally sets forth such method and device. As compared to the prior art, the method and device of the present invention may not only be used for the spherical lens but also for the aspherical lens, and the optical lens may be precisely and rapidly measured. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a device for measuring a lens, comprising a first interferometer having a first optical axis and carried on a first adjustment base, a lens holder for holding the lens having a first surface having a first lens optical axis and a second surface having a second lens optical axis, and a platen having a sliding rail and carrying the first adjustment base and the lens holder thereon, wherein the lens holder is movable on the sliding rail, wherein each of the first adjustment base and the lens holder has a tetra-axis adjustment mechanism through which a relative positional relationship of the first optical axis of the first interferometer and the first lens optical axis of the first surface of the lens is adjustable. 
     In an embodiment, the tetra-axis adjustment mechanism comprises two translation axes and two rotation axes. 
     In an embodiment, the lens holder has a 180 degrees overturn mechanism through which the first and second lens optical axes of the first and second surfaces are calibrated in turn with respect to the first optical axis of the first interferometer. 
     In an embodiment, the device further comprises a second interferometer having a second optical axis and disposed on a second adjustment base on the platen to measure a relative positional relationship of the second lens optical axis of the second surface and the second optical axis of the second interferometer. 
     In an embodiment, the device is used to measure a decenter and a tilt of the lens. 
     It is another object of the present invention to provide a method for measuring a decenter amount and a tilt amount of a lens, comprising the steps of providing an interferometer having an optical axis and the lens, wherein the lens has a first lens optical axis and a second lens optical axis, arranging the optical axis of the interferometer and the first lens optical axis of the first surface into having a first specific relative positional relationship therebetween, rotating the lens by 180 degrees, adjusting the second optical axis of the lens and the optical axis of the interferometer into having a second specific relationship therebetween and recording a first adjusted translation amount Δy, a second adjusted translation amount Δz, a first adjusted angular amount Δθ y  and a second adjusted angular amount Δθ z  required to be adjusted, and calculating the respective one of the decenter amount δ and the tilt amount Δθ existing between the first and second lens optical axes according to the first and second adjusted translation amounts Δy and Δz and the first and second adjusted angular amounts Δθ y  and Δθ z . 
     In an embodiment, each of the first and second specific relationships is a relationship where the optical axis of the interferometer and the first and second lens optical axes of the first and second surfaces totally coincide with each other. 
     In an embodiment, the optical axis of the interferometer and the first and second lens optical axes of the first and second surfaces are adjusted to totally coincide with one another by observing the formed interferogram of each surface of the lens. 
     In an embodiment, a distance between the surface of lens and the interferometer is adjusted to present the interfering fringes of the interferogram of the each surface of lens. 
     In an embodiment, the optical axis of the interferometer and the first and second lens optical axes of the lens are adjusted to totally coincide with one another by observing whether the interfering fringes are formed as concentric rings and whether the concentric rings are positioned at a center of the interferogram. 
     In an embodiment, the first and second specific relationships are identical to each other. 
     In accordance with an aspect of the present invention, a method for measuring a decenter amount and a tilt amount of a lens is disclosed, which comprises the steps of providing a first interferometer having a first optical axis, a second interferometer having a second optical axis and the lens, wherein the lens has a first surface having a first lens optical axis and a second surface having a second lens optical axis, and the first and second interferometers face the first and second surfaces of the lens respectively, adjusting the first interferometer and the lens so that the first lens optical axis of the first surface and the first optical axis of the first interferometer have a first specific relative positional relationship therebetween, adjusting the second lens optical axis of the second surface of the lens and the second optical axis of the second interferometer into having a second specific relative positional relationship therebetween and recording a first adjusted translation amount Δy, a second adjusted translation amount Δz, a first adjusted angular amount Δθ y  and a second adjusted angular amount Δθ z , and calculating the decenter amount δ and the tilt amount Δθ existing between the first and second lens optical axes of the first and second surfaces according to the first and second specific relative positional relationships and the first and second adjusted translation amounts Δy and Δz and the first and second adjusted angular amounts Δθ y  and Δθ z . 
     In an embodiment, each of the first and second specific relationships is a relationship where the first and second optical axes of the first and second interferometers and the first and second lens optical axes of the first and second surfaces totally coincide with one another. 
     In an embodiment, the optical axes of the first and second interferometers and the first and second lens optical axes of the first and second surfaces are adjusted to totally coincide with one another by observing the formed interferogram of each surface of the lens. 
     In an embodiment, a first distance between the first surface of the lens and the first interferometer and a second distance between the second surface of the lens and the second interferometer are adjusted respectively to present the interfering fringes of the interferogram of the each surface of lens. 
     In an embodiment, the optical axes of the first and second interferometers and the first and second lens optical axes of the first and second surfaces are adjusted to totally coincide with one another by observing whether the interfering fringes are formed as concentric rings and whether the concentric rings are positioned at a center of the interferogram. 
     In an embodiment, the first and second specific relationships are identical to each other. 
     Other objects, features and efficacies will be further understood when the following description is read with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above contents and the advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed descriptions and accompanying drawings, in which: 
         FIGS. 1A and 1B  are each a diagram of an arrangement of a combination of a lens of a specific type and an interferometer when the lens is measured by the interferometer according to an embodiment of the present invention; 
         FIGS. 2A through 2D  are diagrams illustrating how to obtain a relationship of optical axes of the lens and an optical axis of the interferometer according to the present invention; 
         FIG. 3  is a diagram of a lens measuring device with a single interferometer according to a first embodiment of the present invention; 
         FIGS. 4A through 4D  are diagrams for illustrating steps of measuring decenter and tilt amounts of the lens by using the lens measuring device shown in  FIG. 3 ; 
         FIG. 5  is a diagram of a lens measuring device with dual interferometers according to a second embodiment of the present invention; 
         FIGS. 6A  through  FIG. 6C  are diagrams for illustrating steps of measuring the decenter and tilt amounts of the lens by using the lens measuring device shown in  FIG. 5 ; and 
         FIGS. 7A through 7E  are diagrams for illustrating the decenter and tilt existing on the optical axes of the lens according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention discloses a lens measuring method and device for determining decenter and tilt amounts of a lens, which will now be described more specifically by way of the following embodiments with reference to the annexed drawings. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purposes of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
     Referring to  FIGS. 1 and 2 , which are each a diagram of an arrangement of a combination of a lens of a specific type and an interferometer when the lens is measured by the interferometer according to an embodiment of the present invention. As shown, when the lens  10 A to be measured is a convex lens, the lens  10 A has to be placed within a focus range of the interferometer  20  so that interfering bands can be generated on the lens  10 A. In the case of a concave lens, the lens  10 B has to be placed outside the focus range of the interferometer  20  so that the corresponding interfering bands can be generated on the lens  10 B. Namely, each of the lenses l 0 A,  10 B has to be placed at a proper position (the position shown in  FIGS. 1A  and the position shown in  FIG. 1B , respectively) with respect to the interferometer  20  so that the interfering bands can be generated as a reference for the measurement scheme in this invention for the lens  10 A,  10 B. 
     Referring to  FIGS. 2A through 2D , which are diagrams illustrating how to obtain a relationship of optical axes of the lens and an optical axis of the interferometer according to the present invention. When an optical axis of one of the two surfaces of the lens coincides with an optical axis of the interferometer, the interfering fringes shown in  FIG. 2A , where a spherical lens is used, and  FIG. 2B , where a aspherical lens is used, and which are arranged as concentric circles with a center thereof located central to the interferogram.  FIG. 2C  is a diagram of interfering fringes obtained when decenter or tilt is presented between the optical axes of the spherical lens and the interferometer.  FIG. 2D  is a diagram of interfering fringes obtained when decenter or tilt is presented between the optical axes of the aspherical lens and the interferometer. 
     It may be known from the above description that a relationship of the optical axes of the lens and the optical axis of the interferometer can be obtained by observing the interfering fringes of the surface of lens. Therefore, the decenter and tilt amounts of the lens can be respectively known by finding a difference between the decenter and tilt amounts of the two optical axes of the lens with respect to the optical axis of the interferometer, respectively. 
     The following will be dedicated to the lens measuring device according to the present invention.  FIG. 3  shows a lens measuring device with a single interferometer according to a first embodiment of the present invention. The lens measuring device  100  comprises an interferometer  20 , a lens  10  to be measured and a platen  40 . The interferometer  20  is mounted on an adjustment base  22  on the platen  40 . The lens is mounted on the platen  40  through a lens holder  12 . On the platen  40 , there is also a sliding rail  42  through which the lens holder  12  is movable along a straight line on the platen  40 . To make it possible to measure the two surfaces of the lens  10  by the interferometer  20 , the lens holder  12  is designed to have a 180 degrees overturn mechanism so that the two optical axes of the lens  10  can be aligned with respect to the optical axis of the interferometer  20 . In addition, to make it possible to obtain the decenter and tilt amounts of the lens by comparing the optical axis of the interferometer  20  and the optical axes of the lens  10 , each of the adjustment base  22  and the lens holder  12  is provided with a tetra-axis adjustment mechanism (not shown) so that the optical axes of the lens  10  and the interferometer  20  may be adjusted when required. In operation, one of the tetra-adjustment mechanisms may be used to adjust the adjustment base  22  or the lens holder  12  in four directions, including two translational directions and two rotative directions. When the direction of the sliding rail  42  is defined as X-axis in three dimensional space, the two translational directions are Y-axis and Z-axis directions. Thus, the relationship of the optical axis of the interferometer  20  and the optical axes of the lens  10  may be represented with two translational amounts Δy and Δz and two angular amounts Δθ y  and Δθ z  of the adjusted one of the two tetra-axis adjustment mechanisms. 
     Referring to  FIGS. 4A through 4D , steps for measuring the decenter and tilt of a lens by using the lens measuring device with a single interferometer shown in  FIG. 3  is shown therein. 
     As shown in  FIG. 4A , the lens measuring device  100  with a single interferometer is first provided and a standard planar lens  10 ′ is provided on the lens holder  12  so that a calibrating process for the interferometer  20  may be done before the measuring process for a lens begins. In the calibrating process, the lens holder  12  is caused to move on the platen  40  backward and forward. If the same interfering fringes, which are parallel, are presented before and after the lens holder  12  and thus the standard planar lens  10 ′ moves, it means that the interferometer  20  has been finished with the calibrating process with respect to the platen  40 . Next, providing the lens  10  to be measured in place of the standard planar lens  10 ′. Then, the measuring process for the lens  10  may be launched. As shown in  FIG. 4B , the optical axis of the interferometer  20  is made to coincide with the optical axis of the first surface of the lens  10  by operating the tetra-axis adjustment mechanism (not shown) on the lens holder  12 . Next, the lens  10  is caused to overturn 180 degrees by using the 180 degree overturn mechanism described above. At this time, the second surface  102  faces the interferometer  20  (as shown in  FIG. 4C ). At the same time, the optical axis of the interferometer  20  still coincides with the optical axis of the first surface  101 . Referring next to  FIG. 4D , the optical axis of the second surface  102  is adjusted to coincide with the optical axis of the interferometer  20  by operating the tetra-axis adjustment mechanism on the lens holder  12 . At this time, translational amounts Δy and Δz and adjusted angular amounts Δθ y  and Δθ z  of the tetra-axis adjustment mechanism in the Y and Z directions, respectively, required to move the optical axis of the second surface  102  from the original position when the optical axis of the first surface  101  to the final position when the optical axis of the second surface  102  coincides with the optical axis of the interferometer  20 , are recorded. With the parameters of Δy, Δz, Δθ y  and Δθ z , the decenter and tilt amounts δ and θ existing between the first and second surfaces  101 ,  102  can be found, wherein δ=√{square root over (δ y   2 +δ z   2 )} and Δθ=√{square root over (Δθ y   2 +Δθ z   2 )}. 
     Referring to  FIG. 5 , a diagram of the lens measuring device with dual interferometers according to a second embodiment of the present invention is shown therein. The lens measuring device  200  is identical to the lens measuring device of the above embodiment except that a second interferometer  30  further included therein. The second interferometer  30  is also mounted on the platen  40  through an adjustment base  32 . Similarly, the second interferometer  30  may also be adjusted in position, for measurement reason, with translational amounts Δy and Δz and adjusted angular amounts Δθ y  and Δθ z  in the Y and Z directions, respectively, of the adjustment base  32  involved. Further, the second interferometer  30  may also move forward and backward on the platen  40 . 
       FIGS. 6A  through  FIG. 6C  are diagrams for illustrating steps of measuring the decenter and tilt amounts of the lens by using the lens measuring device shown in  FIG. 5 . 
     At first, the lens measuring device having the two interferometers  200  shown in  FIG. 5  is provided and a standard planar lens  10 ′ is provided on the lens holder  12 . As such, a calibrating process like that described with respect to  FIG. 4A  may be conducted. Namely, the first interferometer  20  is first calibrated with respect to the platen  40  with the second interferometer  30  being ignored. Then, the second interferometer  30  is calibrated with respect to the platen  40 . In calibrating the second interferometer  30 , the second interferometer  30  has to be translated and rotated, which have to be performed by operating the adjustment base  32 . If the same interfering fringes, which are parallel, are presented before and after the standard planar lens  10 ′ moves, it means that the interferometer  30  has been finished with the calibrating process with respect to the platen  40 . At this time, it also means that the optical axes of the first and second interferometers  20 ,  30  coincide with each other. After the calibrating process, the lens  10  to be measured is provided in place of the standard planar lens  10 ′ and then the measuring process for the decenter and tilt amounts of the lens is ready to be performed. As shown in  FIG. 6B , the optical axis of the first surface  101  of the lens  10  to be measured is made to coincide with the optical axis of the first interferometer  20  by using the tetra-axis mechanism (not shown) on the lens holder  12 . Next, referring to  FIG. 4C  where the optical axis of the lens  10  to be measured is made to coincide with the optical axis of the second interferometer  30  by using the adjustment base  32  associated with the second interferometer  30  or the tetra-axis mechanism (not shown) on the lens holder  12 . At this time, translational amounts Δy and Δz and angular amounts Δθ y  and Δθ z  of the tetra-axis adjustment mechanism or the adjustment base  32  in the Y and Z directions, respectively, required to make the optical axis of the second surface  102  from the original position when the optical axis of the first surface  101  coincides with the optical axis of the first interferometer  20  to the final position when the optical axis of the second surface  102  coincides with the second interferometer  30 , are recorded. With the parameters of Δy, Δz, Δθ y  and Δθ z , the decenter and tilt amounts δ and θ existing between the first and second surfaces  101 ,  102  can be found, wherein δ=√{square root over (δ y   2 +δ z   2 )} and Δθ=√{square root over (Δθ y   2 +Δθ z   2 )}. 
     In the above embodiments, the decenter and tilt amounts of the lens are determined by making the optical axes of the lens coincide with the optical axis of the interferometer, which is served as a measurement basis. However, those skilled in the related art may also determine the decenter and tilt amounts of the lens by setting other measurement bases. In this regard, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. 
     While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention need not to be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.