Abstract:
The present invention relates to a voice coil module (VCM), and more particularly, to a VCM used for lens fixation and displacement measurement in order to prevent and control power consumption. Accordingly, in the VCM, power is not additionally consumed in order to maintain a specific position of the lens in a state that a focus of the lens is adjusted. Further, the lens is not moved and an optical axis is not distorted when a vibration occurs while an image is captured. Furthermore, the lens can be accurately controlled by measuring the present position of the lens.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a voice coil module (VCM), and more particularly, to a VCM used for lens fixation and displacement measurement in order to prevent and control power consumption. 
   2. Description of the Related Art 
   A voice coil module (VCM) generally includes a permanent magnet and a coil. An attractive force or a repulsive force is produced between an induced magnetic field generated by a current flowing through the coil and a magnetic filed generated by the permanent magnet. Displacement of a lens occurs due to a spring force as well as the attractive force or the repulsive force. 
   The VCM advantageously has a simple structure and a low manufacturing cost. Therefore, the VCM is widely used in a driving unit of an automatic focusing device provided to a small image sensor. The driving unit of the automatic focusing device may be implemented with a stepping motor or an ultrasonic motor. 
   Manufacturing of a small stepping motor requires a high cost and a difficult technique. Therefore, a small automatic focusing device is generally driven by using the ultrasonic motor or the VCM. 
     FIG. 1  illustrates a structure of a conventional VCM. 
   A lens  110  is fixed to a vertically movable lens barrel  120 . A coil  140  that generates a magnetic field in response to an input current is disposed to the lens barrel  120 . The lens barrel  120  is connected with a casing  130  and a spring  150 . A permanent magnet  160  is fixed to the casing  130 . A current  180  is supplied to the coil  140  through an input terminal  170  while changing its direction and magnitude. In this case, the lens barrel  120  moves to an equilibrium point between a spring force and a magnetic force exerted between the permanent magnet  160  and the coil  140 . 
   According to the magnitude and direction of the input current, a displacement  190  of the lens barrel  120  is regulated. In the VCM having this structure, a current having a constant magnitude and direction has to be continuously provided so that the lens  110  can maintain a constant position, resulting in a significant amount of power loss. 
   That is, although the VCM can be manufactured in a small size due to its cost competitiveness, simply operation, and simple structure, the conventional VCM has a demerit in that power loss is more significant than the ultrasonic motor since, in order to fix the lens  110  to a specific position, a constant current has to be continuously supplied to a driving coil. Such power loss is a major stumbling block when it comes to put the VCM to the market for a small-sized product using a battery. 
   Furthermore, the conventional VCM is not provided with a method for determining whether the VCM is correctly controlled and for measuring a present position of the VCM. Therefore, a problem lies in that it is difficult to accurately control the VCM, and an erroneous operation cannot be prevented. 
   SUMMARY OF THE INVENTION 
   In order to solve the aforementioned problems, an object of the present invention is to provide a voice coil module (VCM) in which power loss can be avoided in a state that a lens is fixed to a specific position, an unclear image can be avoided by preventing vibration of the lens when a minute vibration occurs while an image is captured or by preventing distortion of an optical axis, accurate control can be achieved by measuring a present displacement according to operations of the VCM, and an erroneous operation can be avoided. 
   According to an aspect of the present invention, there is provided a VCM comprising: a lens barrel to which the lens is attached and which is vertically movable along with the lens; a lens barrel fixing pin which is provided to left and right sides of the lens barrel so as to fix the lens barrel; a casing which includes the lens barrel in its center; a first spring which is attached to the casing at a lower end of the lens barrel; a second spring which is joined between the lens barrel fixing pin and an inner surface of the casing; and a lens barrel fixing pin driving coil which is attached to an outer surface of the casing and an extended line from the lens barrel fixing pin. 
   In the aforementioned aspect of the present invention, the VMC may further comprise: a first position measuring coil which is attached to the outer surface of the lens barrel; a second position measuring coil which is attached to the outer surface of the casing in a right-angle direction with respect to the lens barrel fixing pin driving coil; a current input terminal which supplies a current to either the first position measuring coil or the second position measuring coil; and a position measuring voltage output terminal which is connected to one of the first and second position measuring coils which is not connected to the current input terminal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a structure of a conventional voice coil module (VCM). 
       FIG. 2  illustrates a lens fixing unit of a VCM according to an embodiment of the present invention. 
       FIG. 3  illustrates a lens fixing unit of a VCM according to another embodiment of the present invention. 
       FIG. 4  illustrates a lens displacement measuring unit of a VCM according to another embodiment of the present invention. 
       FIG. 5  illustrates a lens fixing unit and a lens displacement measuring unit of a VCM according to another embodiment of the present invention. 
       FIG. 6  is a graph for comparing a current in the present of a lens barrel fixing pin and a current in the absent of the lens barrel fixing pin. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 2  illustrates a lens fixing unit of a VCM according to an embodiment of the present invention. The lens fixing unit includes a lens  210 , an lens barrel  220 , a casing  230 , an lens barrel fixing pin  250 , a coil  240  for driving the lens barrel fixing pin  250 , a first spring  290  for supporting the lens barrel  220 , and a second spring  260 . 
   The lens barrel  220 , which is vertically movable along with the lens  210 , is held by the lens barrel fixing pin  250  by a strength of the second spring  260  fixed to the casing  230 . The lens barrel fixing pin  250  is a ferromagnetic body or a paramagnetic body. A direct connection  280  is made between the lens barrel fixing pin  250  and the casing  230 . Further, the lens barrel fixing pin  250  is connected with the casing  230  and the second spring  260  so that the lens barrel fixing pin  250  can move only in a horizontal direction. Accordingly, the lens barrel  220  and the lens  210  are fixed by the lens barrel fixing pin  250  and the second spring  260  without power loss. 
   If there is a need for moving the lens  210 , the coil  240  fixed to the casing  230  and a current input terminal  270  through which a current is supplied to the coil  240  are used. A moving operation of the lens  210  will now be described. 
   A magnetic field is generated when a current is supplied to the coil  240  fixed to the casing  230  through the current input terminal  270 . The magnetic field allows the lens barrel fixing pin  250  to be moved towards the coil  240 . Then, the lens barrel  220  is in a free state. As shown in  FIG. 1 , the lens barrel  220  vertically moves due to the attractive force or the repulsive force exerted between a magnetic field generated by the current flowing through the lens barrel driving coil  140  and a magnetic field generated by the permanent magnet  160 , and the strength of the first spring  290  for supporting the lens barrel  220 . 
     FIG. 3  illustrates a lens fixing unit of the VCM according to another embodiment of the present invention. The lens fixing unit includes an lens barrel  320 , a casing  330 , an lens barrel fixing pin  350  that is a ferromagnetic body or a paramagnetic body and has elasticity, and a supporter  360 . 
   The lens barrel  320 , which is vertically movable along with the lens  310 , is held by the lens barrel fixing pin  350  fixed to the casing  330 . The lens barrel fixing pin  350  is a ferromagnetic body or a paramagnetic body having elasticity. The lens barrel fixing pin  350  is fixed by the supporter  360 . 
   Accordingly, the lens barrel  320  and the lens  310  are fixed by means of the lens barrel fixing pin  350  without power loss. 
   A moving operation of the lens  310  is the same as described above with reference to  FIG. 2  except that the second spring  260  connected to the lens barrel fixing pin  250  is replaced with the lens barrel fixing pin  350  having elasticity. 
     FIG. 4  illustrates a lens displacement measuring unit of the VCM according to another embodiment of the present invention. The lens displacement measuring unit is provided in order to solve the problem of the VCM, in which, an erroneous operation may occur when a present position of a lens cannot be measured, and thus the VCM cannot determine whether accurate control is achieved or not. 
   A lens  410  is fixed to a vertically movable lens barrel  420 . The lens barrel  420  is connected to a casing  430  by means of a spring  450 . A coil  440  is fixed to the lens barrel  420  so as to move along with the lens barrel  420 . A coil  460  is fixed to the casing  430 . Each of the coils  440  and  460  includes a current input terminal  470  and a voltage output terminal  480 . 
   In order to measure a displacement  490  of the lens barrel  420 , an alternating current having a constant magnitude is supplied to the coil  440  fixed to the lens barrel  420 . Then, a voltage induced to the coil  460  fixed to the casing  430  is measured. 
   When the displacement  490  of the lens barrel  420  is changed due to a current flowing through the driving coil  140  and the permanent magnet  160 , changes occur in an area overlapping between the two coils  440  and  460  which face each other. In the case that each of the two coils  440  and  460  has a fixed width, the overlapping area is in proportion to a length  495  in which the two coils  440  and  460  overlap each other. 
   Therefore, the voltage induced to the coil  460  fixed to the casing  430  is in proportion to the length  495  in which the two coils  440  and  460  overlap each other. Accordingly, the length  495  in which the two coils  440  and  460  overlap each other can be measured by using a magnitude of the measured voltage, thereby determining whether accurate control can be achieved or not. 
   In this case, the locations of the two coils  440  and  460  can be switched each other. One of the two coils  440  and  460 , which is connected to the current input terminal  470 , may be the driving coil  140  of the VCM. That is, when an alternating current having a high frequency and a small amplitude is provided instead of a direct current for driving the driving coil  140  of the VCM, it is possible to induce a voltage in proportion to the aforementioned length  495 . 
     FIG. 5  illustrates a lens fixing unit and a lens displacement measuring unit of the VCM according to another embodiment of the present invention. 
   A lens  510  and a lens barrel driving coil  540  are fixed to a lens barrel  520 . A coil  560 , which drives a permanent magnet  550  and a lens barrel fixing pin  570 , and a position measuring voltage output coil  580  are fixed to a casing  530 . An end of the lens barrel fixing pin  570  is fixed to the casing  530 . 
   While a current flows through the lens barrier fixing pin driving coil  560 , the location of the lens barrel  520  is changed due to a direct current flowing through the lens barrel driving coil  540 . A voltage is induced to the position measuring voltage output coil  580  due to a minute alternating current having a high frequency and flowing through the lens barrel driving coil  540 . The present position of the lens barrel  520  can be measured according to a magnitude of the voltage which induced to the position measuring voltage output coil  580 . 
     FIG. 6  is a graph for comparing a current in the present of a lens barrel fixing pin and a current in the absent of the lens barrel fixing pin. 
   When the lens barrel fixing pin is absent, after a lens barrel reaches a predetermined point by a supply of a current indicated by a current curve  610 , a constant current has to be continuously supplied to a driver stage in order to fix a position of the lens barrel. On the other hand, when the lens barrel fixing pin is present, the supply of a current indicated by a current curve  620  supplied to the driver stage can be stop almost at the same time as the supply of a current indicated by a current curve  630  to the lens barrel fixing pin, thereby reducing power loss. 
   Accordingly, in a voice coil module (VCM) of the present invention, power loss can be avoided in a state that a lens is fixed to a specific position, an unclear image can be avoided by preventing vibration of the lens when a minute vibration occurs while an image is captured or by preventing distortion of an optical axis, accurate control can be achieved by measuring a present position, and an erroneous operation can be avoided.