Abstract:
An endoscope apparatus comprises: an insertion section including a distal end; a power changing movable lens that makes observational magnification variable, the power changing movable lens being movably built in an objective optical system provided at the distal end; a linear transmission member that drives the power changing movable lens, the linear transmission member being disposed from a drive section provided at a position other than the insertion section to the distal end; a focus adjusting movable lens that achieves automatic focusing function, the focus adjusting movable lens being movably built in the objective optical system separately from the power changing movable lens; and an actuator that drives the focus adjusting movable lens, the actuator being arranged in the distal end.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an endoscope apparatus and, in particular, to a structure of an endoscope that performs automatic focus control simultaneously with acquisition of an optically enlarged image of an object to be observed. 
     2. Description of the Related Art 
     A electronic endoscope apparatus includes an electronic endoscope (scope) having a CCD (Charge Coupled Device) and the like, which is a solid-state image pickup device, at a distal end thereof, a processor device, and a light source device, and displays an image of an object to be observed on a monitor by picking up an image of an object to be observed by the solid-state image pickup device on the basis of light illumination from the light source device and performing image processing with respect to picture signals by the processor device. 
       FIG. 6  shows a structure of a distal end of an endoscope with an objective lens moving mechanism in the related art which is applied to electronic endoscopes of this type. In  FIG. 6 , an observation window  3  is provided at a distal end surface of a supporting section  2  of a distal end  1  of the endoscope, and a CCD  6 , which is a solid-state image pickup device, is arranged on the back side of the observation window  3  on an optical path with the intermediary of a prism  4  and a cover glass  5 . The picture signals obtained by the CCD  6  are transmitted to the processor device via a signal line  7 . 
     Arranged between the observation window  3  and the prism  4  is a first movable lens  9  and a second movable lens  10  which constitute an objective optical system, and hence a varifocal optical system is established. A holding frame  11  of the first movable lens  9  and a holding frame  12  of the second movable lens  10  are mounted to a cylindrical cam shaft  13  by fitting engaging holes  11 A,  12 A thereof on an outer periphery of the cam shaft  13 . The engaging hole  11 A is formed with a cam pin  15 , and the engaging hole  12 A is formed with a cam pin  16  so as to project therefrom, and the cam shaft  13  is formed with cam grooves  17 ,  18  at different inclination angles with respect to the axial line thereof. The cam pin  15  is engaged with the cam groove  17  and the cam pin  16  is engaged with the cam groove  18 . 
     A linear transmission member  19  formed of a multicoil spring is connected to the cam shaft, and the other end of the linear transmission member  19  is mounted to a motor or the like provided in an operating unit. Therefore, by rotating the cam shaft  13  via the linear transmission member  19  by driving the motor or the like, the first movable lens  9  and the second movable lens  10  move in the fore-and-aft direction in the direction of the optical axis by engagement between the cam grooves  17 ,  18  and the cam pins  15 ,  16 , whereby optical change in magnification power (enlargement) or the like is achieved. 
     On the other hand, as regards the endoscope, there exist a type in which focusing is achieved by driving a focusing lens by a rapid deformation piezoelectric actuator by operating an operating switch of an operating unit as disclosed in JP-A-6-22903. 
     Alternatively, as shown in JP-A-2002-263058, an endoscope having an automatic focusing mechanism is also manufactured. This automatic focusing mechanism is adapted to drive a movable lens for automatic focusing on the basis of focus estimating signals (high-frequency signals) extracted from the picture signals (predetermined distance measurement area). With the control of the automatic focusing mechanism, the automatically focused object to be observed can be observed on a monitor. 
     In the case of the endoscope apparatus in which the magnification power is changed optically as described in conjunction with  FIG. 6 , the magnification power is changed optically (observational distance, observational depth, and focal distance or the like are variable) by moving the second movable lens  10  in association with the movement of the first movable lens  9 . In association with the change of the focal point, positional adjustment such as to reduce the distance between the object to be observed and the distal end of the electronic endoscope (scope) and correction of the focus are necessary. However, in an enlarged position, focusability is limited due to the observational depth. Therefore, if further detailed focusing can be performed automatically, an enlarged and clear image of the object to be observed can easily be acquired. In other words, in the related art, when being out of focus, it is necessary to perform focus adjustment operation by minutely moving the distal end of the endoscope for changing the distance with respect to the object to be observed, and such an operation is quite complicated. 
     On the other hand, since the diameter of the distal end of the endoscope is aimed to be small, an efficient structure and arrangement must be employed in order to provide an automatic focusing mechanism for performing focusing operation automatically in addition to the optical magnification power change mechanism. 
     SUMMARY OF THE INVENTION 
     In view of such problems, it is an object of the present invention to provide an endoscope apparatus in which a focused enlarged image can be acquired automatically and easily by arranging an automatic focusing mechanism efficiently in a distal end of a small diameter independently from an optical magnification power change mechanism. 
     In order to achieve the above-described object, the invention according to a first aspect of the invention is an endoscope apparatus comprising: an insertion section including a distal end; a power changing movable lens that makes observational magnification variable, the power changing movable lens being movably built in an objective optical system provided at the distal end; a linear transmission member that drives the power changing movable lens, the linear transmission member being disposed from a drive section provided at a position other than the insertion section to the distal end; a focus adjusting movable lens that achieves automatic focusing function, the focus adjusting movable lens being movably built in the objective optical system separately from the power changing movable lens; and an actuator (which is compact and is capable of high-velocity driving) that drives the focus adjusting movable lens, the actuator being arranged in the distal end. 
     The invention according to a second aspect of the invention further comprises an automatic focus control circuit that sets the focus adjusting movable lens to an initial position by the actuator when starting a focusing operation with the automatic focusing function, and controls a movement of the focus adjusting movable lens from the initial position to a focused position. 
     According to the structure in the first aspect of the invention, with the provision of the focus adjusting movable lens for driving with the rapid actuator separately from the power changing movable lens, fine focusing can be achieved automatically. 
     According to the structure in the second aspect of the invention, since the focus adjusting movable lens is set to the initial position at the time of focusing operation and the lens movement (position) is controlled from the initial position by controlling the drive pulse of the actuator or by measuring the drive time of the same, automatic focusing control is enabled without providing a specific position detection sensor. 
     According to the endoscope apparatus of the present invention, while the power changing movable lens is driven by the linear transmission member, the focus adjusting movable lens is driven by the compact actuator arranged in the distal end. Therefore, the automatic focusing mechanism, which is independent from the optical magnification power change mechanism, is arranged efficiently in the distal end of reduced diameter, and a focused enlarged image can be acquired automatically and easily. 
     According to the structure in the second aspect of the invention, since the automatic focusing control is performed without using the position detection sensor or the like, reduction of the diameter of the endoscope is advantageously achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the structure of a distal end of an endoscope with a portion other than a prism and an image pickup device in cross-section taken along the line I-I in  FIG. 2 ; 
         FIG. 2  is a drawing of the distal end of the invention when viewed from the front; 
         FIG. 3  is a drawing showing a structure and an operational range of a piezoelectric actuator that drives the movable lens for adjusting the focus according to the embodiment; 
         FIG. 4  is a drawing showing a general structure of an electronic endoscope device according to the embodiment; 
         FIGS. 5A and 5B  are drawings showing voltage (drive pulse) waveforms for driving the piezoelectric actuator according to the embodiment; and 
         FIG. 6  is a cross-sectional view showing a structure of the distal end of the electronic endoscope in the related art. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A structure of an electronic endoscope apparatus according to an embodiment is shown in  FIG. 1  and  FIG. 4 .  FIG. 1  shows the structure of a distal end of an endoscope with a portion other than a prism and an image pickup device in cross-section taken along the line I-I in  FIG. 2 . In  FIG. 1 , an observation window (lens)  22   a , a fixed lens  22   b , a first movable lens  23   a  and a second movable lens  23   b  for changing the magnification power that are each configured as a varifocal lens, a fixed lens  22   c  and a third movable lens  23   c  for focusing are arranged in sequence from the front as an objective optical system at a distal end  20  of the electronic endoscope (scope). A CCD  26  which is a solid state image pickup device is arranged on the backside of the third movable lens  23   c  with the intermediary of a prism  24  and a cover glass  25 . Signals picked up by the CCD  26  are supplied to a processor device via a circuit board  27  and a signal line  28 . 
     The first movable lens  23   a  is held by a holding frame  30  having an engaging hole  30 A, and the second movable lens  23   b  is held by a holding frame  31  having an engaging hole  31 A, and the respective lenses  23   a ,  23   b  are attached to a cylindrical cam shaft  33  in a state in which the engaging holes  30 A,  31 A are fitted on the outer periphery of the cam shaft  33 . The engaging hole  30 A is formed with a cam pin  35 , and the engaging hole  31 A is formed with a cam pin  36  so as to project therefrom, and the cam shaft  33  is formed with cam grooves  37 ,  38  at different inclination angles with respect to the axial line thereof. The cam pin  35  is engaged with the cam groove  37 , and the cam pin  36  is engaged with the cam groove  38 . 
     A linear transmission member  39  formed of a multicoil spring or the like is connected to the cam shaft  33 , and the other end of the linear transmission member  39  is mounted to a motor shaft of a drive unit  40  ( FIG. 4 ) provided in a operating unit. Therefore, by rotating the cam shaft  33  via the linear transmission member  39  by driving the motor, the first movable lens  23   a  and the second movable lens  23   b  are moved in the fore-and-aft direction by the amounts different from each other by engagement of the cam grooves  37 ,  38  and the cam pins  35 ,  36 , whereby the optical magnification power change (enlargement) is achieved. In other words, the first and the second movable lenses  23   a ,  23   b  constitutes the varifocal optical system, and the power magnification is changed optically (observational distance, observational depth, and focal distance are variable) by relatively moving in the fore-and-aft direction. In association with the change of the focal point due to the movement, positional adjustment such as to reduce the distance between the object to be observed and the distal end of the electronic endoscope is performed and then correction of focus is performed, whereby the magnification power on the monitor screen is changed (enlarged). 
     On the other hand, in order to drive the third movable lens  23   c  for focusing, a compact and rapid actuator  42  employing a piezoelectric element is mounted to the supporting portion  43 , and an engaging hole  45 A of a holding frame  45  is movable fitted and arranged on the outer periphery of the drive shaft  42 A of the actuator  42 . In the actuator  42 , as shown in  FIG. 3 , a piezoelectric element  42 B is mounted to the drive shaft  42 A, and by moving the drive shaft  42 A by the piezoelectric element  42 B in the fore-and-aft direction at varying speed, the third movable lens  23   c  can be moved in the fore-and-aft direction. Other compact linear actuator such as electrostatic actuator may be used as the actuator  42 . The present invention will be further illustrated with examples below. Reference numeral  44  in  FIG. 3  is a stopper for stopping the third movable lens  23   c  at an initial position a 1 . 
     As shown in  FIG. 2 , in addition to the structure shown in  FIG. 1 , a light guide, illumination windows  46 A,  46 B for illuminating light supplied from the light guide, an operative instrument insertion channel  47  and so on are disposed within the distal end  20 . 
       FIG. 4  shows a circuit structure of the electronic endoscope apparatus according to an embodiment, which includes a CDS (relative double sampling)/AGC (automatic gain control) circuit  51  for performing relative double sampling and automatic gain control by inputting the output signal of the above-described CCD  26 . On the downstream of the CDS/AGC circuit  51 , a A/D converter  52 , a DSP (Digital Signal Processor)  53  for performing various image processing, an image memory  54  for storing one frame of image data, D/A converter  55 , and a monitor  56  are arranged. 
     A BPF (Band-Pass Filter) unit  58  that inputs output image signals from the A/D converter  52  and extracts high-frequency components of the picture signals (brightness signals and the like) are provided. In the BPF unit  58 , high-frequency components (two types of high-frequency detected signals) for evaluating the focus (or contrast) by two BPF having different pass bands are extracted. In addition, a micro computer  60  for generally managing the control of the electronic endoscope or the processor apparatus is provided, and an auto focus (AF) control unit  60   a  of passive system is provided in the microcomputer  60 . A magnification power change switch  62  for changing the magnification power is provided in the operating unit of the electromagnetic endoscope, and the operating signals are supplied to the microcomputer  60 . 
     The embodiment is configured as described above. In this apparatus, the image of the object to be observed is picked up by the CCD  26  in  FIG. 4 , and is subjected to the image processing by the circuit from the CDS/AGC circuit  51  to D/A converter  55  on the downstream thereof, whereby the image of the object to be observed is displayed on the screen of the monitor  56 . On the other hand, when the magnification power change switch  62  is operated, the linear transmission member  39  is rotated via the drive unit  40 , and the cam shaft  33  shown in  FIG. 1  is rotated. Accordingly, the first movable lens  23   a  and the second movable lens  23   b  are driven and are moved to positions where desired magnification power is provided. In accordance with the change of the position of the focal point due to the movement, the positional adjustment such as to reduce the distance between the object to be observed and the distal end of the electronic endoscope and correction of the focus is performed. Consequently, the optically enlarged image to be observed is picked up by the CCD  26 , and an image of the enlarged object to be observed is displayed on the screen of the monitor  56 . 
     In this manner, in the state in which the object to be observed and the distal end of the electronic endoscope are close to each other, the operation for correcting the focus is complicated due to the observational depth, and in a case in which the object to be observed is pulsating, it is specifically difficult to maintain the focused state constantly. Therefore, in the embodiment, the automatic focusing control by the third movable lens  23 C for automatic focusing is performed simultaneously with the magnification power changing operation. In other words, in the BPF unit  58  in  FIG. 4 , the high-frequency components which is a focal point evaluation value is extracted from the image signals, and the movement control of the third movable lens  23   c  is performed by supplying the high-frequency components to the automatic focus control unit  60   a . Then, in this automatic focusing control, the third movable lens  23   c  is set to an initial position at the beginning, and then movement is started from this initial position. 
     In  FIG. 5 , a voltage waveform to be applied to the piezoelectric element  42 B of the actuator  42  is shown.  FIG. 5A  shows a waveform when the lens  23   c  is moved backward (assuming that the side of the observation window is the front),  FIG. 5B  shows a waveform when the lens  23   c  is moved toward the front. In other words, the lens  23   c  moves backward at an initial rise where the voltage pulse is slow in  FIG. 5A , and moves forward at a fall time where the voltage pulse is slow in  FIG. 5B . In the embodiment, for example, the third movable lens  23   c  is adapted to move one step with one saw-tooth wave in  FIGS. 5A and 5B  so that the third movable lens  23   c  can move a range between positions a 1  to a n  including n steps (10 steps, for example) as shown in  FIG. 3 . In the embodiment, by applying 10 or more saw-tooth waves shown in  FIG. 5A  to the piezoelectric element  42 B, the third movable lens  23   c  is moved to the initial position a 1  in  FIG. 3  (where it is stopped by a stopper  44 ) irrespective of the current position of the third movable lens  23   c.  Accordingly, the initial position a 1  of the third movable lens  23   c  is specified, and hence the position detection sensor is not necessary. The above-described initial position may be a n  at the front end. 
     Then, by moving the third movable lens  23   c  in the direction in which the focal point evaluation value increases after having moved from the initial position a 1  to the predetermined position, so called climbing action is performed, and then the third movable lens  23   c  is moved to the focal point by the maximum focal point evaluation value. In this manner, in the embodiment, focusing is achieved by the third movable lens which is separate from the first and second movable lenses  23   a ,  23   b  for optically changing the magnification power, finer focusing than in the related art is enabled. 
     In other words, in the above-described magnification power change function as well, focusing is achieved in a predetermined distance (range) by the first movable lens  23   a  and the second movable lens  23   b . However, depending on the distance between the object to be observed and the distal end of the electronic endoscope, it may go out of focus (in particular, when the scale of enlargement is high). Therefore, the automatic focusing control functions effectively in such a case, and hence the operation and work for moving the distal end of the electronic endoscope to the position where it comes into focus is not any longer necessary. 
     The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.