Abstract:
A receiving module applied in a rangefinder. The receiving module, receiving beams of different incident angles, includes a light pipe having a receiving end, an emitting end and a reflecting surface connecting the receiving end and the emitting end. The light pipe also has an optical axis perpendicular to the receiving and the emitting ends. When beams of different incident angles from different positions enter the light pipe, the light pipe confines the beams to a certain area. Using the receiving module of the invention, the rangefinder can measure targets from all ranges.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a receiving module, and more particularly, to a receiving module applied in a rangefinder.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIG. 1 schematically shows a conventional optical rangefinder, disclosed in U.S. Pat. No. 6,441,887. The optical rangefinder  1  includes an emitter  2 , a telescopic system  3  and a receiving system  4 . Referring to FIG. 1, a beam from the emitter  2  passes through the telescopic system  3 , incident on the target. Next, a beam reflected by the target enters the receiving system  4 .  
           [0005]    [0005]FIG. 2A schematically shows the rangefinder of FIG. 1, measuring a target at 100 m, and FIG. 2B schematically shows the rangefinder of FIG. 1, measuring a target at 1 m. Referring to FIGS. 1 and 2A, the interval between the receiving system  4  and the telescopic system is about 7 cm, and the distance from target T to the optical rangefinder  1  is around 100 m. The receiving system  4 , target T, and telescopic system  3  form an included angle θ 1 . The included angle  31  is around 0.0007 radians. Referring to FIGS. 1 and 2B, the receiving system  4 , target T, and telescopic system  3  form another included angle θ 2 . The included angle θ 2  is around 0.07 radians.  
           [0006]    However, when the included angle increases from 0.0007 radians to 0.07 radians, the reflected beam Br 2  from the target T has difficulty entering the receiving system  4 . In general, by increasing the diameter of the receiving system, the reflected beam Br 2  enters the receiving system  4  easily. However, the reflected beam Br 2  cannot be received by the light sensor even though the reflected beam Br 2  enters the receiving system  4 .  
           [0007]    In addition, the U.S. Pat. No. 5,815,251 discloses another range finder using many ways to receive the reflecting beam. However, the complex mechanism is difficult to execute.  
         SUMMARY OF THE INVENTION  
         [0008]    To solve the above problems, it is an object of the present invention to provide a receiving module applied in a rangefinder for measuring short range and long distances.  
           [0009]    According to the object of the invention, the receiving module includes an object lens, a light pipe and a light sensor. The object lens has an optical axis, and the light pipe has a receiving end, an emitting end and a reflecting surface, respectively connected the receiving and emitting ends. After a beam, not parallel to the optical axis, passes the object lens, the object lens alters the beam to approximately parallel to the optical axis. Next, the beam enters the light pipe via the receiving end and is reflected several times by the reflecting surface. The beam from the emitting end of the light pipe converges on one area, in which the light sensor is located.  
           [0010]    The receiving module of the invention is applied in an optical rangefinder, further comprising an emitter and another object lens.  
           [0011]    The light pipe comprises a plurality of mirrors, or can comprise a solid rod with a reflecting surface is coated with a reflecting film. When a beam enters the light pipe, the beam is reflected by the reflecting surface and leaves the light pipe from the emitting end.  
           [0012]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 schematically shows a conventional optical rangefinder as disclosed in U.S. Pat. No. 6,441,887;  
         [0015]    [0015]FIG. 2A schematically shows the optical rangefinder of FIG. 1, measuring a target at 100 m;  
         [0016]    [0016]FIG. 2B schematically shows the optical rangefinder of FIG. 1, measuring a target at 1 m;  
         [0017]    [0017]FIG. 3 schematically shows beams entering an object lens at different angles;  
         [0018]    [0018]FIG. 4 schematically shows a light pipe guiding beams to a convergence area;  
         [0019]    [0019]FIG. 5A schematically shows a receiving module of the invention;  
         [0020]    [0020]FIG. 5B schematically shows another receiving module of the invention;  
         [0021]    [0021]FIG. 5C schematically shows another receiving module of the invention;  
         [0022]    [0022]FIG. 6A schematically shows a rangefinder utilizing the receiving module of the invention;  
         [0023]    [0023]FIG. 6B schematically shows another rangefinder utilizing the receiving module of the invention; and  
         [0024]    [0024]FIGS. 7A to  7 C schematically show all different light pipe types. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    [0025]FIG. 3 schematically shows beams entering an object lens at different angles. As shown in FIG. 3, the distance between point A and the positive lens CV exceeds the distance between point B and the positive lens CV, with the incident angle of the beam  1   a  from point A to the positive lens CV less than the incident angle of the beam  1   b  from point B to the positive lens CV. According to Snell&#39;s law, the beam  1   a  travels through the positive lens CV and reaches a point A′ of an optical axis OA of the positive lens CV, and the beam  1   b  travels through the positive lens CV and reaches a point B′ of an optical axis OA of the positive lens CV. Thus, beams from different light source reach different points by passing the positive lens CV. The distance between points A′ and B′ is represented as L.  
         [0026]    [0026]FIG. 4 schematically shows a light pipe guiding beams to a convergence area. Referring to FIG. 4, the light pipe  10  has a length L, and a receiving end  11 , emitting end  12 , and enclosed reflecting surface  13 , connecting the receiving end  11  and the emitting end  12 . In the invention, the receiving end  11  of the light pipe  10  is located at point B′, and the emitting end  12  point A′. The optical axes of light pipe  10  and positive lens CV are coaxial.  
         [0027]    As shown in FIG. 4, the beam  1   a  from point A passes the positive lens CV according to Snell&#39;s law, and the beam  1   a  enters the light pipe  10  via the receiving end  11 . Next, the beam  1   a  from point A intersects the optical axis OA at point A′.  
         [0028]    As shown in FIG. 4 the beam  1   b  from point B passes the positive lens CV according to Snell&#39;s law, and intersects the optical axis OA at point B′. The point B′ is located on the receiving end  11 , such that beam  1   b  from point B is reflected by the reflecting surface  13  and travels forward in light pipe  10 . Thus, according to the light tracing shown in FIG. 4, the beam  1   b  from point B intersects the optical axis OA at point A′ again. Beams emitted from different positions pass the positive lens CV and travel forward in light pipe  10 , and then intersect the optical axis OA in substantially the same position.  
         [0029]    [0029]FIG. 5A schematically shows a receiving module of the invention. As shown in FIG. 5A, the receiving module  20  of the invention includes a positive lens  21 , a light pipe  10  and a detector  22 , wherein the positive lens  21  and the light pipe  10  have the same optical axis OA. When two different beams  1   a ,  1   b  travel through the positive lens  21  and the light pipe  10 , the beams  1   a ,  1   b  respectively intersect the optical axis OA at two neighboring points, forming an area A′. The detector  22  is located in area A′ to receive beams  1   a ,  1   b  from different light sources. Referring to FIG. 5A, the light pipe  10  confines the beams from different light sources to the area A′, smaller than the area of the detector for receiving the beams. FIG. 5B schematically shows another receiving module of the invention. As shown in FIG. 5B, the receiving module  20 ′ further includes an aspherical lens  23  located near the emitting end  13  of the light pipe  10 , to reduce area A′, ensuring that detector  22  receives the beams from all ranges. Referring to FIG. 5B, the aspherical lens  23  confines beams from different light source to the area, smaller than area A′ and the area of the detector for receiving the beams. FIG. 5C schematically shows another receiving module of the invention. As shown in FIG. 5C, the receiving module  20 ″ further includes a concave mirror  24 , by which the beams  1   a ,  1   b  passing the positive lens are reflected. The reflected beams  1   a ,  1   b  enter the light pipe  10  via the receiving end  11  and propagate forward by reflection in the light pipe  10 . Next, beams  1   a ,  1   b  from the emitting end  12  of the light pipe  10  are received by detector  22 . In this invention, the surface of the concave mirror is preferably aspherical, and beams from the light pipe  10  can be further confined to a smaller area, ensuring that detector  22  receives the beams from all ranges.  
         [0030]    [0030]FIG. 6A schematically shows a rangefinder utilizing the receiving module of the invention shown in FIG. 5B. As shown in FIG. 6A, the optical system of the rangefinder  100  includes an emitting module  30  and receiving module  20 ′. The emitting module  30  includes an emitting device  32  and a collimating lens  31 . After the emitting device  32  emits a beam of narrow-band  1   0 , the beam of narrow-band  1   0  is converted to form a collimated beam  1   1  by passing the collimating lens  31 . The collimated beam  1   1  is incident on a target (not shown), and reflected thereby to form a reflected collimated beam  1   2 . A portion of reflected beam  1   2  enters the receiving module  20 ′ via the positive lens  21 . No matter the distance to the target, the reflected beam  1   2  from the target is confined to one area by the light pipe  10 . Next, the area is reduced by an aspherical lens  23 , and the detector  22  receives the reflected beam  1   2 . FIG. 6B schematically shows another rangefinder utilizing the receiving module shown in FIG. 5C. As shown in FIG. 6B, the optical system of the rangefinder  100 ′ includes an emitting module  30  and the receiving module  20 ″. The emitting module  30  includes an emitting device  32  and the collimating lens  31 . The emitting device  32  emits a beam of narrow-band  1   0 , which is then converted to collimated beam  1   1  by passing the collimating lens  31 , and is incident on a target (not shown), and reflected thereby to form a reflected collimated beam  1   2 . A portion of reflected beam  1   2  enters the receiving module  20 ″ via the positive lens  21 . No matter the distance to the target, the reflected beam  1   2  from the target is confined to one area by the concave mirror  24  and the light pipe  10 . The area can be further reduced by an aspherical lens, with the detector  22  receiving the reflected beam  1   2 .  
         [0031]    [0031]FIGS. 7A to  7 C schematically show a variety of light pipes. As shown in FIG. 7A, the area of the receiving end  11 ′ of the light pipe  10 ′ is smaller then the area of the emitting end  12 ′. As shown in FIG. 7B, the area of the receiving end  11  of the light pipe  10  is equal to the area of the emitting end  12 ′. As shown in FIG. 7C, the area of the receiving end  11 ″ of the light pipe  10 ″ is larger then the area of the emitting end  12 ″. In the invention, the light pipe can be a solid rod with a reflecting surface coated with a reflecting film. In addition, the light pipe can be a hollow rod and comprises a plurality of mirrors.  
         [0032]    The receiving module of the invention receives beams of different incident angle, for confinement beams to an area not larger than the area of the detector. Thus, the detector receives the beams from different positions.  
         [0033]    No matter the distance to the target, the receiving module of the invention applied to the rangefinder receives reflected beams, assuring measurement of distance to the target.  
         [0034]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.