Abstract:
The present invention provides a zoom lens unit and a photographic device using the same, wherein the zoom lens unit can readily achieve position accuracy and slope accuracy of the lens, and reduce the required number of parts to lower the costs. The zoom lens unit of the present invention comprises a plurality of lens sets constituting an optical system wherein at least two lens sets thereof are movable, stepping motors for separately driving each of the at least two lens sets, and a shutter module installed in the center of the optical system, wherein the at least two lens sets and the shutter module are installed within an integral box body.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a construction of a zoom lens unit and a photographic device using the same.  
       BACKGROUND OF THE INVENTION  
       [0002]     Recently, it is desired that the increasingly popular digital cameras, video cameras, and photographic devices with built-in digital camera (such as mobile phones with built-in digital camera and music players with built-in digital camera) become thinner and lighter. In view of such trends, a “flection-type” zoom lens unit is widely used in the above-mentioned device, which is characterised in that a prism is installed behind the object lens and the optical axis is rotated by 90°, resulting in increased height and reduced thickness of the entire lens unit.  
         [0003]      FIG. 1  is a cross sectional view of a conventional construction of the above-mentioned flection-type zoom lens unit. The flection-type zoom lens unit has lens sets constituting the optical system, wherein the lens sets comprise at least two movable lens sets  108 , as shown in  FIG. 1 . In addition, in order to drive the two lens sets  108 , two stepping motors  113  are employed, and a shutter module  104  is located in the center of the optical system.  
         [0004]     Conventionally, the structure shown in  FIG. 1  takes a shutter module  104  as a center, and the top and bottom portions thereof are the structure made of the top box body  106 A and the bottom box body  106 B. For example, protrusions are provided on the shutter module  104 , and guide holes are formed on the top and bottom box bodies ( 106 A,  106 B). The positioning of the structure is achieved through the engagement between the protrusions and the guide holes. On the top end of the top box body  6 A, an object lens  101  and a prism  102  are disposed. On the bottom end of the bottom box body  106 B, an image detector  110  is disposed.  
         [0005]     The movable lens mounts  107 A and  107 B may move upwards and downwards, being supported respectively by two guide rods ( 105 A,  105 A′, and  105 B,  105 B′) on the right and left respectively. The actuating force of the movement comes from the assembly of a bolt  109  and a nut  111  coupled to a stepping motor  103 . To detect the upper and lower limited positions of the moving range of the movable lens mounts, two photo-interrupters PI are disposed on each of the box bodies respectively. a mask  113  extending into the gap of the photo-interrupters is disposed on the lens movable mount  107 .  
         [0006]      FIG. 2  is a side view of the zoom lens unit in  FIG. 1  (the motors and the guide rods are omitted). The light passing through the object lens  101  are reflected into a downward direction by the prism  102 .  
         [0007]      FIG. 3  shows the zooming action of the zoom lens unit in  FIG. 1 .  FIG. 3  depicts the position relationship between the two zoom lenses  108 , which locate at the focal length sites. Generally, one part moves in a linear manner, and the other part moves along a curve.  
         [0008]     Additionally, in conventional zoom lens, cams carved with linear and curved grooves control the movement of the two lenses; whereas, in the flection-type zoom lens, two stepping motors  103  are used to actuate the two lenses  108 .  
         [0009]      FIG. 4  is a schematic diagram showing the CPU and motor driver for actuating the conventional zoom lens unit in  FIG. 1 . The actuation of the stepping motor  108  is controlled by the CPU. The position relationship between the two zoom lenses  108  are set in the program for the CPU.  
         [0010]      FIG. 5  is a diagram showing the relationship between the moving range of the two lens sets  108  and the four photo-interrupters (PI). The origin positions of the two movable lenses  108  are determined by the four photo-interrupters (PI). In the case of the lenses being driven by the stepping motors  103 , the origin positions of the lenses must be determined. When the power is ON, the signal of the photo-interrupter PI is detected as a position-setting reference for each movable lens  108 . To achieve the above-mentioned objects, one photo-interrupter can be disposed on each movable lens. Further, when the stepping motor  103  can not operate properly due to certain reason, the movable lenses  108  can be prevented from moving beyond designed range by installing four photo-interrupters (PI). If the movable lens moves beyond the normal range, the movable lenses  108  would collide with the box body or other lenses. Then, the bolt and the nut may engage together too firmly that the movable lenses  108  are stuck in the position and cannot be moved to other positions by the stepping motor  103 . The above must be prevented at all cost. Thus, two photo-interrupters (PI) are respectively disposed adjacent to the two ends for the normal moving range of the movable lens, for monitoring the movements of the movable lens  108 ; should the movable lens  108  move beyond the position, the position of the lens  108  may be reset by the control program.  
         [0011]     The above-mentioned zoom lens is characterized by driving two lens sets with stepping motors, as compared to more conventional zoom lens in which the movement of the two lenses are controlled by the cam carved with linear and curved grooves. Accordingly, the structure is simplified, and expensive parts may be omitted, and the assembling of the lens unit is simplified. However, the following problems still exist.  
         [0012]      FIG. 6  is a cross sectional view of a conventional zoom lens, which is made by assembling the top and bottom box bodies with bad precision such that the top and bottom box bodies displaced slightly toward right and left respectively. As shown in  FIG. 6 , a shutter module  104  is located in the center of the zoom lens optical system. Since the shutter module  104  is formed into a structure combined by separate constructions at the top and bottom thereof, the position error of each lens set readily occurs, which causes the optical performance impaired. If the differences in position and size between the protrusions on the above-mentioned shutter modules  104  and the guide holes on the box body ( 106 A,  106 B) cause the dislocation between the top and bottom box bodies ( 106 A,  106 B) in the horizontal direction, the displacement of the optical axis also takes place. In addition, if position dislocation occurs between the box bodies ( 106 A,  106 B) and the shutter module  104 , the guide rod  105  disposed between them and the lens mount  107  assembled on the guide rod may be sloped. These cases are rather bad in optics, which may cause the problems such as deteriorated image resolution for the image detector  110 , and hazy image corners.  
         [0013]     In addition, since the length of the supporter of the lens mount  107  that jacketed on the guide rod  105  is limited by the shutter module  104  located in the center position, thus being insufficient, the lens mount  107  is prone to be sloped, which may cause the optical performance impaired. In particular, as shown in  FIG. 7 , the relationship between the movable lens mount  107  and the guide rod  105  is illustrated, and circular holes are formed on the supporter in  FIG. 7  for the guide rod  105  to pass through. The diameter of the hole needs to be larger than that of the guide rod  105 . If the diameter of the hole is smaller that that of the guide rod  105 , the lens mount  107  may be fixed, likewise, if the diameter of the hole is equal to that of the guide rod  105 , the guide rod  105  cannot move smoothly either. That is, it should be assembled in such a way that there is a gap between the frame and guide rod  105 . Since there are gaps, the lens mount  107  may be slightly sloped relative to the guide rod  105 , and if the length of the supporter becomes short, the slope may become larger.  
         [0014]     In addition to the above-mentioned problems, in the conventional flection-type zoom lens, there are two sets of movable lens mounts and a total of four photo-interrupters are installed, thus the costs for both assembling-and parts increase, making cost a problem.  
         [0015]     The present invention is created to solve the problems in the above-mentioned conventional flection-type zoom lens, with the object that positioning accuracy and slope accuracy could be readily achieved in flection-type zoom lens unit, and the required number of parts is decreased to lower the costs.  
       SUMMARY OF THE INVENTION  
       [0016]     In order to achieve the above-mentioned objects, the present invention provides a zoom lens unit comprising a plurality of lens sets constituting an optical system wherein at least two lens sets thereof are movable, stepping motors for separately driving each of the at least two lens sets, and a shutter module installed in the center of the optical system, wherein the at least two lens sets and the shutter module are installed within an integral box body.  
         [0017]     It is preferred that three guide rods are mounted on a top plate and a bottom plate of the integral box body, and each of the at least two lens sets are coupled respectively to at least two of said three guide rods in a way such that each of the lens sets can move freely along the optical axis direction and that one of said three guide rods is commonly coupled to said at least two lens sets.  
         [0018]     The aforementioned shutter module does not completely divide the inner space of the integral box body into upper and lower parts, but instead is mounted in such a way that spaces are left beside said shutter module for the guide rods and supporters of the at least two lens sets which are movable to pass through.  
         [0019]     Photo-interrupters are disposed to detect the positions of the above-mentioned two movable lens sets. Preferably, at least one of the photo-interrupters is commonly used to detect the positions of the two movable lens sets.  
         [0020]     The above-mentioned zoom lens may further comprise an object lens and a prism installed behind the object lens such that the optical axis is rotated by 90° and the lens sets can be installed on the rotated optical axis direction, so as to increase the height and the decrease thickness of the entire unit.  
         [0021]     The subject invention also provides photographic device comprising the above zoom lens unit. The photographic device may be, for example, a digital camera, video camera, or any device with built-in digital camera. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a cross sectional view of the typical structure of a conventional flection-type zoom lens.  
         [0023]      FIG. 2  is a side view of the conventional zoom lens unit in  FIG. 1 .  
         [0024]      FIG. 3  shows the zooming action of the conventional zoom lens unit in  FIG. 1 .  
         [0025]      FIG. 4  is a schematic diagram showing the CPU and motor driver for actuating the conventional zoom lens unit in  FIG. 1 .  
         [0026]      FIG. 5  is a diagram showing the relationship between the moving range of two lens sets and four photo-interrupters (PI).  
         [0027]      FIG. 6  is a cross sectional view of the conventional zoom lens, which is assembled with the top and bottom box bodies thereof displaced slightly toward right and left respectively.  
         [0028]      FIG. 7  is a diagram illustrating the relationship between movable lens mount and guide rods.  
         [0029]      FIG. 8  is a cross sectional view of a zoom lens unit of the present invention.  
         [0030]      FIG. 9  shows the action of four photo-interrupters in a conventional zoom lens.  
         [0031]      FIG. 10  shows the action of three photo-interrupters according to present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]      FIG. 8  is a cross sectional view of a preferred zoom lens unit according to the present invention. As shown in  FIG. 8 , a prism box  15  is installed on the top end of the zoom lens, and an object lens  1  is installed within the prism box; and behind the object lens  1 , a prism  2  is installed to rotate the optical axis by 90°. The lens sets constituting the zoom lens optical system are disposed on the optical axis direction. The lens sets comprise two movable lens sets  8 . The two lens sets  8  are actuated by two stepping motors  3  which are controlled by a CPU, and the position relationship between the two lens sets  8  have been set in the programs for the CPU.  
         [0033]     The box body  6  accommodating the two movable lens sets  8  is formed as an integral box. As compared with the assembled box body in the conventional zoom lens, the integral construction can achieve a box body with higher accuracy.  
         [0034]     Within the integral main box body  8 , a shutter module  4  and three guide rods ( 5 A,  5 B,  5 C) are disposed. The shutter module  4  does not divide the inner space of the integral box body into upper and lower portions completely, but is instead mounted in such a way that spaces are left beside the shutter for the guide rods ( 5 A,  5 B,  5 C) and the supporters (casing pipe) of the frame ( 7 A,  7 B) of the movable lens sets to pass through.  
         [0035]     For the two movable lenses, the movable lens mount  7 A is disposed on the guide rod  5 A, and the movable lens mount  7 B is disposed on the guide rod  5 B, which lens mounts can move upwards and downwards. A guide rod  5 C is used for inhibiting the rotation of the lens mounts ( 7 A,  7 B), which is shared by both lens mounts ( 7 A,  7 B). The main box body  6  is formed as an integral box, which can prevent the possible positional dislocation of the guide rods in the top and bottom direction in the assembled construction, thus avoiding the sloping problem of the guide rods. And three disposed guide rods ( 5 A,  5 B,  5 C) are not prone to be sloped.  
         [0036]     Further, dedicated guide rod  5 A and guide rod  5 B are disposed respectively on the two movable lens mounts ( 7 A,  7 B). And there is a distance between the positions of the guide rods in the front and behind directions to avoid the conflicts between the two rods. The combination of the two movable lens mounts ( 7 A,  7 B) and the dedicated guide rods ( 5 A,  5 B) are conducted by assembling the casing pipes of the two movable lens mounts ( 7 A,  7 B) onto the dedicated guide rods ( 5 A,  5 B) respectively. Thereby, the supporters (casing pipe) of the movable lens mounts ( 7 A,  7 B) can maintain sufficient length. The length of the supporters (casing pipe) can be calculated by subtracting the inner height of the integral main box body  6  with the moving amount of lens. As a result, the slope caused by the gap between the movable lens mounts ( 7 A,  7 B) and guide rods ( 5 A,  5 B) is reduced.  
         [0037]     Also, as compared with the four photo-interrupters (PI) installed for detecting the moving ranges of the lens in the conventional zoom lens, there are only three photo-interrupters in the present invention. As illustrated above, since the space within the main box body  6  is not divided completely into upper and lower portions by the shutter module  4 , the central photo-interrupter among the three photo-interrupters can be shared to detect the positions of both the top movable lens set  8  and the bottom movable lens set  8 . The three photo-interrupters are one less than the four photo-interrupters required in conventional devices, thus, the costs for such part is reduced, and the assembling process is also simplified further.  
         [0038]      FIG. 9  shows the action of four photo-interrupters in a conventional zoom lens.  FIG. 9A  depicts that when the zoom lens is set in the Wide position in which the focal length is the shortest, the mask plates  113  interlocked with set A and set B reach the positions of the photo-interrupters P 1  and P 2  respectively, and the photo-interrupters are in an ON state.  FIG. 9B  depicts that when the zoom lens is set in the Tele position in which the focal length is the longest, the mask plates  113  interlocked with set A and set B approach the photo-interrupters P 3  and P 4  respectively, which are not in an ON state.  FIG. 9C  depicts that when set A moves downward beyond the Tele position, the mask plate interlocked with set A reaches the position of P 3 . Then the state of P 3  is detected, and if it is ON, it can be determined that driving abnormality occurs to set A.  FIG. 9D  depicts that when set B moves upward beyond the Tele position, the mask plate interlocked with set B reaches the position of P 4 . Then the state of P 4  is detected, and if it is ON, it can be determined that driving abnormality occurs to set B. Through the above steps, the problem that the position cannot be shifted by the stepping motor  103  can be avoided, but since four photo-interrupters are needed, it is disadvantageous in terms of costs.  
         [0039]      FIG. 10  shows the action of three photo-interrupters in the present invention.  FIG. 10A  depicts that when the zoom lens is set in the Wide position, the mask plates  13  interlocked with set A and set B reach the positions of photo-interrupters P 1  and P 2  respectively, and the photo-interrupters are in an ON state.  FIG. 10B  depicts that when the zoom lens is set in the Tele position, both mask plates  13  interlocked with set A and set B approach the photo-interrupter P 3 , but P 3  is not in an ON state.  FIG. 10C  depicts that when set A moves downward beyond the Tele position, the mask plate  13  interlocked with set A reach the position of P 3 . Then the state of P 3  is detected, and if it is ON, it can be determined that driving abnormality occurs to set A.  FIG. 10D  depicts that when set B moves upward beyond the Tele position, the mask plate  13  interlocked with set B reach the position of P 3 . Then the state of P 3  is detected, and if it is ON, it can be determined that driving abnormality occurs to set B.  
         [0040]     As mentioned above, although the construction according to the present invention comprises only three photo-interrupters, if the state of P 3  is detected to be ON, it can be determined that driving abnormality occurs to either set B or set A. Although it is impossible to know for sure which one of set A and set B having driving abnormality, actually no problems will arise. When driving abnormality is detected, simply by moving set A and set B into the positions of P 1  and P 2  for resetting, the lens system can resume its normal state. In addition, omitting one photo-interrupter from four photo-interrupters can reduce the costs. And since the action and detection of three photo-interrupters are simpler, the costs for the assemblage and developing control software are reduced.  
         [0041]     As mentioned above, according to the detailed descriptions of the present invention, a zoom lens unit with high lens position accuracy can be provided, and high slope accuracy can be achieved therein. Furthermore, the construction of the zoom lens is simplified, and the number of parts is reduced, so with the costs.