Image pickup unit for endoscope

According to this invention, there is provided an image pickup unit for an endoscope, including a lens barrel portion includes a movable lens holding barrel that holds the movable lens and is movable to advance and retract and a drive mechanism portion which is disposed at a side surface portion of the lens barrel portion and drives the movable lens holding barrel. The unit has a holding portion which is disposed at the side surface portion of the lens barrel portion and is configured to position and hold the drive mechanism portion, a gap between the lens barrel portion and the drive mechanism portion is filled with an adhesive which is made to have a difference in hardness such that hardness is lower on a proximal end side than on a distal end side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup unit for an endoscope having a movable lens drive section which is disposed at a distal end portion of an endoscope insertion portion and moves some or all of objective lenses.

2. Description of the Related Art

Endoscopes which can be introduced from outside of a living body or a structure into an inside and include an image pickup unit for picking up an optical image are utilized in, e.g., fields of medicine and industry in order to observe a spot difficult to observe, such as an inside of a living body or an inside of a structure.

An image pickup unit of an endoscope includes an objective lens which forms an object image and an image pickup device (typically, a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor) sensor) which is disposed at an image formation surface of the objective lens.

For example, Japanese Patent Application Laid-Open Publication No. 2007-229155 discloses an image pickup unit for an endoscope which has a movable lens among objective lenses and is provided with a function of changing a photographing magnification by moving the movable lens in an optical axis direction (a variable-power function or a zoom function).

In a technique disclosed in Japanese Patent Application Laid-Open Publication No. 2007-229155, the image pickup unit for an endoscope is configured to include a lens barrel portion including a movable lens holding barrel which holds the movable lens and is capable of moving to advance and retract in the optical axis direction and an image pickup device and a drive mechanism portion which is disposed at a side portion of the lens barrel portion. An arm portion protruding outwardly in a radial direction is provided at the movable lens holding barrel. The drive mechanism portion is configured to drive the movable lens holding barrel in the optical axis direction by pushing and pulling the arm portion. The lens barrel portion and the drive mechanism portion of the image pickup unit for an endoscope are shaped to extend in a direction toward a proximal end separately from each other.

SUMMARY OF THE INVENTION

An image pickup unit for an endoscope according to one aspect of the present invention is an image pickup unit for an endoscope, including a lens barrel portion which is configured to hold an objective lens including a movable lens disposed on a distal end side and an image pickup device disposed closer to a proximal end side than the objective lens and includes a movable lens holding barrel that holds the movable lens and is movable to advance and retract and a drive mechanism portion which is disposed at a side surface portion of the lens barrel portion and drives the movable lens holding barrel, wherein the unit has a holding portion which is disposed at the side surface portion of the lens barrel portion and is configured to position and hold the drive mechanism portion, the drive mechanism portion is shaped to extend in a direction toward a proximal end with a gap with the lens barrel portion on a side closer to the proximal end than the holding portion, and the gap between the lens barrel portion and the drive mechanism portion is filled with an adhesive which is made to have a difference in hardness such that hardness is lower on a proximal end side than on a distal end side.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described below with reference to the drawings. Note that each constituent element is differently scaled in the individual drawings used in a following description such that the constituent element has a recognizable size on the drawings and that the present invention is not limited only to the quantity of constituent elements, shapes of constituent elements, size ratios among constituent elements, and relative positional relationships among individual constituent elements described in the drawings.

An example of an embodiment of the present invention will be described below. An example of a configuration of an endoscope101including an image pickup unit1for an endoscope according to the present invention will first be described with reference toFIG. 1. Note that the image pickup unit1for an endoscope will be simply referred to as the image pickup unit1hereinafter. The endoscope101according to the present embodiment can be introduced into a subject, such as a human body, and is configured to optically pick up an image of a predetermined site to be observed inside a subject. Note that a subject into which the endoscope101is to be introduced is not limited to a human body and may be another living body or an artifact, such as a machine or a building structure.

The endoscope101is mainly composed of an insertion portion102which is to be introduced into an inside of a subject, an operation portion103which is located at a proximal end of the insertion portion102, and a universal cord104which extends from a side portion of the operation portion103.

The insertion portion102is composed of a distal end portion110disposed at a distal end, a bendable bending portion109disposed closer to a proximal end side than the distal end portion110, and a flexible tube portion108with flexibility disposed closer to the proximal end side than the bending portion109and connected to a distal end side of the operation portion103, which are provided so as to be continuous. Note that the endoscope101may be in a form of a so-called rigid endoscope not including a part with flexibility at an insertion portion.

As will be described in detail later, the image pickup unit1and an illuminating light emitting portion113(not shown inFIG. 1) are provided at the distal end portion110. An angle operation knob106for operating the bending portion109such that the bending portion109is bent is provided at the operation portion103. A variable-power operation portion107which is a lever switch for ordering action of a drive mechanism portion30(to be described later) and performing an action of changing an image pickup magnification of the image pickup unit1is disposed at the operation portion103. Note that the variable-power operation portion107may take any other form, such as a rotary switch, a push switch, or a touch sensor.

An endoscope connector105which is connected to an outside apparatus120is provided at a proximal end portion of the universal cord104. The endoscope101also includes an electrical cable115and an optical fiber bundle114(not shown inFIG. 1) which are inserted so as to extend through the universal cord104, the operation portion103, and the insertion portion102.

The electrical cable115is configured to electrically connect the connector portion105and the image pickup unit1. The image pickup unit1is electrically connected to the outside apparatus120via the electrical cable115when the connector portion105is connected to the outside apparatus120. Via the electrical cable115, supply of power from the outside apparatus120to the image pickup unit1and communication between the outside apparatus120and the image pickup unit1are performed.

The optical fiber bundle114is configured to propagate light, which is given off from a light source portion of the outside apparatus120, to the illuminating light emitting portion113of the distal end portion110. Note that the light source portion may be disposed at the operation portion103or the distal end portion110of the endoscope101.

The outside apparatus120is configured to include, for example, the light source portion, a power source portion120a, an image processing unit120b, and an image display portion121. The power source portion120ais configured to output power that causes the drive mechanism portion30of the image pickup unit1to act in response to a user's operation of the variable-power operation portion107. As will be described in detail later, by way of example, the power source portion120ais configured to apply current to a shape memory alloy wire (hereinafter abbreviated as an SMA wire)41which is a wire-like piece of shape memory alloy of the drive mechanism portion30in the present embodiment.

The image processing unit120bis configured to generate a video signal on the basis of an image pickup device output signal outputted from the image pickup unit1and output the video signal to the image display portion121. That is, an optical image picked up by the image pickup unit1is displayed as video on the image display portion121. Note that some or all of the power source portion120a, the image processing unit120b, and the image display portion121may be disposed not at the outside apparatus120but at the endoscope101.

A configuration of the distal end portion110will be described. As shown inFIG. 2, the image pickup unit1and the illuminating light emitting portion113are disposed at the distal end portion110.

By way of example, in the present embodiment, the image pickup unit1is disposed along a longitudinal direction (an insertion axis direction) of the insertion portion102which is indicated by an arrow A inFIG. 2so as to perform image pickup in a direction toward the distal end. More specifically, the image pickup unit1is disposed such that an optical axis O of objective lenses11is along the longitudinal direction of the insertion portion102. Note that the image pickup unit1may be disposed such that the optical axis O forms a predetermined angle with the longitudinal direction of the insertion portion102.

The illuminating light emitting portion113is configured to emit light which is emitted from a distal end of the optical fiber bundle114such that an object for the image pickup unit1is illuminated with the light. In the present embodiment, the illuminating light emitting portion113is configured to emit light in the direction toward the distal end from a distal end face of the distal end portion110along the longitudinal direction of the insertion portion102.

The image pickup unit1and the illuminating light emitting portion113are held by a holding portion111which is provided at the distal end portion110. The holding portion111is a rigid member which is exposed at the distal end face of the distal end portion110and is provided with through-holes111aand111bwhich are pierced along the longitudinal direction of the insertion portion102. Inside the through-holes111aand111b, the image pickup unit1and the illuminating light emitting portion113are fixed by a method, such as adhesive or screwing. The optical fiber bundle114is inserted from a proximal end side and is fixed inside the through-hole111b.

A configuration of the image pickup unit1according to the present embodiment will be described. As shown inFIGS. 2 and 3, the image pickup unit1is configured to include a lens barrel portion20which holds the objective lenses11and an image pickup device11disposed closer to an image side than the objective lenses11and the drive mechanism portion30that is disposed at a side portion of the lens barrel portion20.

As shown in a cross-sectional view inFIG. 4, the objective lenses11are composed of a plurality of optical system members, such as lenses, which form an object image. The objective lenses11according to the present embodiment are configured to include a fixed lens11awhich is composed of one or a plurality of lenses with fixed positions inside the lens barrel portion20and a movable lens11bwhich is composed of one or a plurality of lenses movable in a direction of the optical axis O inside the lens barrel portion20. By way of example, in the present embodiment, the objective lenses11are configured such that the photographing magnification increases (an angle of view decreases) with increase in proximity of the movable lens11bto the image side.

Note that although the objective lenses11according to the present embodiment are formed such that the photographing magnification increases with increase in the proximity of the movable lens11bto the image side, the objective lenses11may be formed such that the photographing magnification decreases with increase in the proximity of the movable lens11bto the image side. In the present embodiment, the fixed lenses11aare disposed in front of and behind the movable lens11b. The movable lens11bmay, however, be disposed closest to an object side among the objective lenses11or be disposed closest to the image side among the objective lenses11. The objective lenses11may be configured to include any other optical system member, such as a diaphragm, a prism, or an optical filter.

The image pickup device12has a plurality of light-receiving elements in an array which photoelectrically convert incident light. For example, an image pickup device referred to as, e.g., a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor) sensor or any of various other image pickup devices can be generally used as the image pickup device12. The image pickup device12is disposed such that the light-receiving devices are located at an image formation surface of the objective lenses11.

Cover glasses13are glued with adhesive to a light-receiving surface, at which the light-receiving devices are disposed, of the image pickup device12. A circuit substrate14is electrically connected to the image pickup device12. The circuit substrate14is electrically connected to the electrical cable115.

A configuration of the lens barrel portion20will first be described. The lens barrel portion20that holds the objective lenses11and the image pickup device12described above is configured to include a fixed barrel21, an object-side lens holding barrel22, a movable lens holding barrel23, and an image-side lens holding barrel24. The fixed barrel21, the object-side lens holding barrel22, and the image-side lens holding barrel24are members with quasi-cylindrical shapes, respectively, and positions of the components are fixed by, e.g., adhesive or press fitting.

The cover glasses13are fixed with adhesive to a proximal end side of the fixed barrel21. That is, the image pickup device12is fixed to the proximal end side of the fixed barrel21via the cover glasses13.

A circular cylindrical portion21awith a quasi-circular cylindrical shape is provided on a distal end side of the fixed barrel21. A slit21bthat is a through-hole in which an arm portion23bof the movable lens holding barrel23(to be described later) is inserted so as to extend through the through-hole is formed in a side surface portion of the circular cylindrical portion21a. The slit21bis a long hole, a longitudinal direction of which is substantially parallel to the optical axis O.

A holding portion21cwhich protrudes outwardly in a radial direction (a direction orthogonal to the optical axis O) in an arm-like manner is provided closer to the proximal end side than the slit21bon a side surface of the fixed barrel21. The slit21band the holding portion21care provided in substantially same circumferential directions relative to the optical axis O, as seen from the direction of the optical axis O. As will be described in detail later, the holding portion21cis a part which positions and holds a distal end portion of a guide pipe33constituting the drive mechanism portion30. More specifically, a through-hole21dwhich is substantially parallel to the optical axis O is formed in the holding portion21c, and the substantially circular cylindrical guide pipe33is fixed while being inserted so as to extend through the through-hole21d. As will be described in detail later, a pressing portion32is disposed inside the guide pipe33so as to be movable to advance and retract in the direction of the optical axis O.

The object-side lens holding barrel22is fixed on a distal end side of the circular cylindrical portion21aof the fixed barrel21. The object-side lens holding barrel22is a substantially circular cylindrical member which holds the fixed lens11athat is located closer to the object side than the movable lens11bamong the objective lenses11.

A restraining convex portion22awhich protrudes outward in the radial direction (the direction orthogonal to the optical axis O) in an arm-like manner is provided at a side surface of the object-side lens holding barrel22. The restraining convex portion22ais provided in a substantially same circumferential direction as the circumferential direction for the slit21bto the optical axis O, as seen from the direction of the optical axis O. As will be described in detail later, the restraining convex portion22ais a part constituting a portion of the drive mechanism portion30. A flat portion22bwhich is substantially orthogonal to the optical axis O is formed on a proximal end side of the restraining convex portion22a. A substantially circular concave portion22cwhich is provided to be recessed in the direction of the optical axis O is formed in the flat portion22b. The concave portion22cis disposed such that a center position of the concave portion22cdeviates from a center position of the through-hole21dthat is provided in the holding portion21cof the fixed barrel21, as seen from the direction of the optical axis O. More specifically, the concave portion22cis disposed inside the through-hole21dof the fixed barrel21in the radial direction, as seen from the direction of the optical axis O.

Inside the circular cylindrical portion21aof the fixed barrel21, the movable lens holding barrel23is disposed so as to be movable to advance and retract in the direction of the optical axis O. The movable lens holding barrel23is a member which holds the movable lens11bamong the objective lenses11. As shown inFIG. 5, the movable lens holding barrel23is configured to have a substantially circular cylindrical lens holding portion23aand an arm portion23bwhich protrudes outward from a side surface of the lens holding portion23ain the radial direction (the direction orthogonal to the optical axis O) in an arm-like manner.

The lens holding portion23ais capable of holding the movable lens11binside. The lens holding portion23ahas an outer diameter which is set such that the lens holding portion23afits in the circular cylindrical portion21aof the fixed barrel21with a predetermined gap with the circular cylindrical portion21aand is configured to be slidable in the direction of the optical axis O inside the circular cylindrical portion21a. In a state in which the lens holding portion23afits in the circular cylindrical portion21a, the arm portion23bis inserted so as to extend through the slit21b. Rotation of the movable lens holding barrel23about the optical axis O is regulated by the arm portion23binserted so as to extend through the slit21b.

In the state in which the lens holding portion23afits in the circular cylindrical portion21a, the arm portion23bprotrudes outward from the circular cylindrical portion21ain the radial direction. More specifically, the arm portion23bhas a length enough to protrude outward in the radial direction to a position which overlaps with a center of the through-hole21dthat is provided in the holding portion21cof the fixed barrel21.

The arm portion23bis provided so as to abut on the flat portion22bof the restraining convex portion22ain the object-side lens holding barrel22before the lens holding portion23aabuts when the movable lens holding barrel23is moved to a distal end side (the object side).FIG. 4shows a state in which the arm portion23babuts on the flat portion22bof the restraining convex portion22a, and the movable lens holding barrel23is located closest to the distal end side within a movable range. The arm portion23bis provided so as to abut on a part (not shown) of the fixed barrel21or a spacer (not shown) fixed to the fixed barrel21before the lens holding portion23aabuts when the movable lens holding barrel23is moved to a proximal end side (the image side).FIG. 6shows a state in which the arm portion23babuts on the fixed barrel21or the spacer, and the movable lens holding barrel23is located closest to the proximal end side within the movable range. As described above, in the present embodiment, the movable range in the direction of the optical axis O of the movable lens holding barrel23is defined to extend to a point where the arm portion23babuts on the fixed part of the fixed barrel21.

The movable lens holding barrel23moves in the direction toward the distal end when the arm portion23bis pressed by the pressing portion32(to be described later). The pressing portion32is disposed along the guide pipe33that is inserted so as to extend through the through-hole21dof the holding portion21cso as to be movable to advance and retract in the direction of the optical axis O. If the center positions of the concave portion22cand the through-hole21dsubstantially coincide with each other, as seen from the direction of the optical axis O, when the movable lens holding barrel23is located at a most distal end of the movable range, the arm portion23bmay enter the concave portion22c, and the movable lens holding barrel23may be tilted. The tilt of the movable lens holding barrel23may cause deviation in field of view or focus deviation. For the reason, in the present embodiment, an area over which the flat portion22band the arm portion23babut on each other is widened by deviating the center positions of the concave portion22cand the through-hole21dfrom each other, as described above. With the configuration, the movable lens holding barrel23is prevented from being tilted.

A chamfered sloping portion23dis formed at a corner on a proximal end side at an outer end portion in the radial direction of the arm portion23b. The proximal end side of the arm portion23bis a part which is urged toward the distal end side by the pressing portion32(to be described later). The press on the arm portion23bseparate from the optical axis O causes torque to be imparted to the movable lens holding barrel23. If the torque is high, so-called “twisting” meaning that the movable lens holding barrel23is tilted inside the fixed barrel21may occur to cause the movable lens holding barrel23to fail at sliding. For the reason, in the present embodiment, a barycenter of a contact surface of the arm portion23band the pressing portion32is brought close to the optical axis O by providing the sloping portion23dsuch that the torque to be imparted to the movable lens holding barrel23is low.

A concave portion23cis provided in a surface on a distal end side of the arm portion23b. A columnar core bar25is fitted in the concave portion23cso as to protrude in a direction substantially parallel to the optical axis O. The core bar25is fixed with an adhesive26which is provided at a bottom portion of the concave portion23cto the arm portion23c. The core bar25is provided at a position where the core bar25protrudes into the concave portion22cprovided in the restraining convex portion22aof the object-side lens holding barrel22. The core bar25is a part for preventing buckling of a first spring31constituting the drive mechanism portion30(to be described later).

A film made of lubricant is formed in a region of the outer circumferential face, where an outer circumferential face of the movable lens holding barrel23is in contact with other members. By way of example, in the present embodiment, a fluorine coating agent is applied to an outer circumferential face in contact with the fixed barrel21of the lens holding portion23aof the movable lens holding barrel23. The application of the fluorine coating agent to the outer circumferential face of the movable lens holding barrel23allows the movable lens holding barrel23to smoothly move to advance and retract in the direction of the optical axis O.

Inside the circular cylindrical portion21aof the fixed barrel21, the image-side lens holding barrel24is fixed closer to the proximal end side than the movable lens holding barrel23and closer to the object side than the cover glasses12. The image-side lens holding barrel24is a substantially circular cylindrical member which holds the fixed lens11athat is located closer to the image side than the movable lens11bamong the objective lenses11.

In a region closer to the proximal end side than the fixed barrel21, the image pickup device12, the circuit substrate14, and a distal end portion of the electrical cable115are surrounded by a cylindrical shielding frame15which is made of a metallic thin plate, and the shielding frame15is filled with an electrically insulating sealing resin. The shielding frame15and the distal end portion of the electrical cable115are sheathed with a heat-shrinkable tube17.

The movable lens holding barrel23described above of the lens barrel portion20is driven to advance and retract in the direction of the optical axis O by the drive mechanism portion30disposed at the side portion of the lens barrel portion20.

A configuration of the drive mechanism portion30is not particularly limited as long as the drive mechanism portion30is disposed at the side portion of the lens barrel portion20and can drive the movable lens holding barrel23in the direction of the optical axis O. For example, the drive mechanism portion30may be a mechanism in which a distal end portion of a wire routed along the electrical cable115is fixed to the arm portion23band which drives the movable lens holding barrel23by pushing and pulling the wire by the lever provided at the operation portion103of the endoscope101. Alternatively, for example, the drive mechanism portion30may be configured to drive the movable lens holding barrel23by a linear motor.

By way of example, in the present embodiment, the drive mechanism portion30is configured to drive the movable lens holding barrel23in the direction of the optical axis O through expansion and contraction of an SMA wire41. The configuration of the drive mechanism portion30according to the present embodiment will be described below.

The drive mechanism portion30is configured to have a drive force transmitting portion30awhich is disposed at the side portion of the lens barrel portion20, a drive force generating portion30bwhich is disposed closer to the proximal end side than the drive force transmitting portion30a, and a coupling portion30cwhich connects the drive force transmitting portion30aand the drive force generating portion30b.

The drive mechanism portion30is configured to include the restraining convex portion22a, the first spring31, the pressing portion32, the guide pipe33, a second spring34, a first outer tube35, and an inner wire36.

The guide pipe33is a circular cylindrical pipe and is fixed to the holding portion21cwhile the distal end portion is inserted so as to extend through the through-hole21dprovided in the holding portion21cof the fixed barrel21. The guide pipe33is positioned and fixed at a side portion of the fixed barrel21by the holding portion21csuch that a central axis is substantially parallel to the optical axis O.

The first outer tube35is connected to a proximal end of the guide pipe33. The first outer tube35is a pipe which is made of a synthetic resin, such as polyether ether ketone resin (PEEK). The inner wire36is inserted so as to extend through the first outer tube35. The first outer tube35is configured to be bendable according to a manner in which the bending portion109of the insertion portion102in the endoscope101bends and resist tension added to the inner wire36inserted so as to extend through the first outer tube35.

Inside the guide pipe33, the piston-like pressing portion32is disposed to be freely slidable in an axial direction. The pressing portion32protrudes from a distal end of the guide pipe33in the direction toward the distal end and abuts on the arm portion23bof the movable lens holding barrel23. A distal end of the inner wire36is fixed to the pressing portion32.

The second spring34that urges the pressing portion32in the direction toward the distal end is disposed inside the guide pipe33. In the present embodiment, the second spring34is a compression coil spring. Thus, if tension is not added to the inner wire36, the pressing portion32presses the arm portion23bof the movable lens holding barrel23in the direction toward the distal end by urging force of the second spring34.

The first spring31is disposed so as to urge the movable lens holding barrel23in a direction toward the proximal end. In the present embodiment, the first spring31is a compression coil spring and is disposed in the concave portion22cprovided in the restraining convex portion22aof the object-side lens holding barrel22. The first spring31is thus disposed across the arm portion23bof the movable lens holding barrel23from the pressing portion32.

The first spring31is configured here such that force urging the arm portion23bin the direction toward the proximal end is weaker than force urging the arm portion23bin the direction toward the distal end of the second spring34. Thus, if tension is not added to the inner wire36, the arm portion23bmoves in the direction toward the distal end by the urging force of the second spring34to abut on the restraining convex portion22a, as shown inFIG. 4. That is, if tension is not added to the inner wire36, the movable lens holding barrel23is located at a distal end of the movable range.

If tension is added to the inner wire36, the second spring34contracts, and the pressing portion32moves in the direction toward the proximal end, the arm portion23bmoves toward the proximal end side by urging force of the first spring31, as shown inFIG. 6. That is, the drive force transmitting portion30ais configured such that the pressing portion32moves to advance and retract in the direction of the optical axis O in response to change in the tension of the inner wire36and is configured to move the movable lens holding barrel23in the direction of the optical axis O by the urging force of the first spring31.

The drive force generating portion30bis configured to produce tension to be added to the inner wire36. The drive force generating portion30bis configured to include the SMA wire41, a second outer tube42, an electric wire43, and a lead wire44. By way of example, in the present embodiment, the drive force generating portion30bis provided so as to be located closer to the proximal end side than the bending portion109of the insertion portion102in the endoscope101.

The second outer tube42is a pipe which is made of a synthetic resin, such as polyether ether ketone resin (PEEK), and the SMA wire41is inserted so as to extend through the second outer tube42. The second outer tube42is configured to be bendable according to a manner in which the flexible tube portion108of the insertion portion102in the endoscope101bends and resist tension produced by the SMA wire41inserted so as to extend through the second outer tube42.

A distal end of the second outer tube42is connected to a proximal end of the first outer tube35via a coupling pipe51of the coupling portion30c. The coupling pipe51is a metallic tube. The proximal end of the first outer tube35and a distal end of the coupling pipe51are fixed with adhesive. A proximal end of the coupling pipe51and a proximal end of the second outer tube42are fixed through so-called swaging that presses hard on the coupling pipe51.

The SMA wire41is configured to contract when temperature rises. A distal end of the SMA wire41is connected to a proximal end of the inner wire36inside the coupling pipe51. The distal end of the SMA wire41and the proximal end of the inner wire36are connected by, for example, fixation through swaging that presses hard on the wire coupling portion52while both the ends are inserted so as to extend through the metallic tubular wire coupling portion52.

A distal end of the electric wire43is electrically connected to a distal end portion of the SMA wire41. More specifically, the distal end of the electric wire43is fixed to the coupling pipe51through soldering, and the electric wire43and the coupling pipe51are electrically connected. Inside the coupling pipe51, the lead wire44for electrically connecting the coupling pipe51and the SMA wire41is disposed. The lead wire44has one end fixed to the coupling pipe51through soldering and the other end fixed to the distal end portion of the SMA wire41through soldering. The lead wire44is disposed with some slack so as to be capable of following motion of the distal end portion of the SMA wire41that moves to advance and retract in an axial direction inside the coupling pipe51.

The electric wire43has a proximal end provided at the endoscope connector105and is configured so as to be electrically connectable to the power source portion120avia the endoscope connector105.

Although not shown, a proximal end of the SMA wire41is fixed to a proximal end of the second outer tube42such that a position in the longitudinal direction is not changed. A distal end of an electric wire (not shown) is electrically connected to a proximal end portion of the SMA wire41. The electric wire electrically connected to the proximal end portion of the SMA wire41has a proximal end provided at the endoscope connector105and is configured so as to be electrically connectable to the power source portion120avia the endoscope connector105.

In the present embodiment, the SMA wire41is configured so as to be electrically connectable to the power source portion120avia the one pair of electric wires, and current outputted from the power source portion120ais applied to the SMA wire41.

The SMA wire41generates heat corresponding to applied current and contracts according to the generated heat. The contraction of the SMA wire41causes tension to be added to the inner wire36connected to the distal end of the SMA wire41. As described above, the drive force generating portion30bis configured to generate driving force that drives the movable lens holding barrel23.

A configuration of the drive mechanism portion30which maintains watertightness of the coupling portion30cwill be described. As shown inFIG. 4, in the coupling portion30c, an outer circumference of a connection portion of the proximal end of the first outer tube35and the distal end of the coupling pipe51is sheathed with a first heat-shrinkable tube55. A space between an inner circumferential face of a distal end portion of the first heat-shrinkable tube55and an outer circumferential face of the first outer tube35and a space between an inner circumferential face of a proximal end portion of the first heat-shrinkable tube55and an outer circumferential face of the coupling pipe51are filled with an adhesive58. With the configuration, watertightness at the connection portion of the proximal end of the first outer tube35and the distal end of the coupling pipe51is realized.

A portion from the outer circumferential face of the first outer tube35to an outer circumferential face of the first heat-shrinkable tube55is sheathed with a second heat-shrinkable tube56. A proximal end portion of the second heat-shrinkable tube56is fixed with an adhesive59with which a space between the proximal end portion and the outer circumferential face of the first heat-shrinkable tube55is filled.

A portion from the outer circumferential face of the first heat-shrinkable tube55to an outer circumferential face of the second outer tube42in a region closer to the proximal end side than the second heat-shrinkable tube56is sheathed with a third heat-shrinkable tube57. A distal end portion of the third heat-shrinkable tube57is fixed with the adhesive59, with which a space between the distal end portion and the outer circumferential face of the first heat-shrinkable tube55is filled.

As described above, a heat-shrinkable tube with which the drive mechanism portion30is sheathed in order to maintain watertightness in the drive mechanism portion30according to the present embodiment is divided at the coupling portion30cinto two, the second heat-shrinkable tube56and the third heat-shrinkable tube57.

A heat-shrinkable tube, with which a part inserted so as to extend through the bending portion109of the drive mechanism portion30is sheathed, is large in the amount of deformation and is relatively susceptible to damage. For example, in the case of a conventional configuration in which a whole of a drive mechanism portion is sheathed with one heat-shrinkable tube, watertightness in the drive mechanism portion cannot be maintained if a hole is formed in the heat-shrinkable tube. In contrast, in the present embodiment, even if a hole is formed in, for example, the second heat-shrinkable tube56, watertightness in the coupling portion30cis ensured by the first heat-shrinkable tube55and the third heat-shrinkable tube57.

Since a portion where the proximal end of the coupling pipe51and the proximal end of the second outer tube42are fixed is a portion which is fixed through swaging, moisture is likely to enter the coupling portion30cthrough the portion. The part, through which moisture is likely to enter the coupling portion30c, is sheathed with the third heat-shrinkable tube57that is not disposed inside the bending portion109and is insusceptible to damage, and watertightness in the coupling portion30ccan thus be reliably maintained.

As has been described above, the image pickup unit1according to the present embodiment is configured to include the lens barrel portion20and the drive mechanism portion30disposed at the side portion of the lens barrel portion20. In the present embodiment, a gap is formed between the lens barrel portion20and the drive mechanism portion30.

More specifically, a portion closer to the proximal end side than the holding portion21cof the drive mechanism portion30has a quasi-circular cylindrical shape extending toward the proximal end side in the direction of the optical axis O. An outer diameter of the portion with the circular cylindrical shape extending toward the proximal end side of the drive mechanism portion30is substantially same to the coupling portion30c, though the outer diameter becomes somewhat large due to presence of the second heat-shrinkable tube56. The shielding frame15closer to the proximal end side than the holding portion21cof the lens barrel portion20becomes smaller in diameter toward the proximal end side in order to avoid interference with components incorporated in the bending portion109and the flexible tube portion108. The tendency becomes more remarkable due to reduction in size of the image pickup device12and the circuit substrate14.

For the reason, a gap forms between the shielding frame15that becomes smaller in diameter toward the proximal end side and the drive mechanism portion30that extends linearly with a substantially same outer diameter toward the proximal end side. More specifically, the gap formed between the shielding frame15and the drive mechanism portion30becomes wider toward the proximal end side.

In the image pickup unit1according to the present embodiment, the gap formed between the shielding frame15and the drive mechanism portion30is filled with an adhesive60. The adhesive60is made to have a difference in hardness after curing between a distal end side and a proximal end side and is configured such that hardness on the proximal end side is lower than hardness on the distal end side.

A configuration for making the hardness of the adhesive60lower on the proximal end side than on the distal end side is not particularly limited. By way of example, in the present embodiment, the gap is filled on the distal end side with a high-hardness adhesive60awhich is relatively high in hardness after curing and is filled on the proximal end side with a low-hardness adhesive60bwhich is lower in hardness after curing than the high-hardness adhesive60a. Note that the number of types of adhesives different in hardness is not limited to two. The number may be three or more.

In other words, in the present embodiment, the gap formed between the shielding frame15and the drive mechanism portion30is filled with the adhesive60, the hardness of which increases with increase in proximity to a root of the drive mechanism portion30that extends from a side surface portion of the lens barrel portion20to fix the lens barrel portion20and the drive mechanism portion30.

According to the image pickup unit1described above of the present embodiment, the drive mechanism portion30can be firmly fixed to the lens barrel portion20at a predetermined position without misregistration by filling a portion of the gap which is close to the root of the drive mechanism portion30extending from the side surface portion of the lens barrel portion20with the high-hardness adhesive60a.

If a force for moving a proximal end side of the drive mechanism portion30is added to the lens barrel portion20, as indicated by an arrow F inFIG. 7, the low-hardness adhesive60b, with which the proximal end side of the gap is filled and which is low in hardness and is relatively flexible, is deformed to follow movement of the proximal end side of the drive mechanism portion30without exfoliating. The deformation of the low-hardness adhesive60balleviates a force added to the high-hardness adhesive60athrough the movement of the proximal end side of the drive mechanism portion30.

For example, if work of inserting the image pickup unit1into the through-hole111ain the holding portion111is performed at the time of assembly of the endoscope101, a worker grasping the image pickup unit1may cause a force which moves the proximal end side of the drive mechanism portion30relative to the lens barrel portion20, as indicated by the arrow F inFIG. 7, to be added to the image pickup unit1. However, according to the present embodiment, since the force is alleviated through deformation of the low-hardness adhesive60b, and the portion where the shielding frame15and the drive mechanism portion30are fixed is firmly fixed with the high-hardness adhesive60a, exfoliation of the high-hardness adhesive60aand breakage of an adhesive portion which fixes the holding portion21cof the fixed barrel and the guide pipe33can be prevented.

In contrast to the present embodiment, for example, if the gap formed between the shielding frame15and the drive mechanism portion30is filled with an adhesive relatively high in hardness and uniform in hardness, when a force which moves the proximal end side of the drive mechanism portion30relative to the lens barrel portion20is added to the image pickup unit1, the adhesive is not deformed and exfoliates from the proximal end side. For example, if the gap formed between the shielding frame15and the drive mechanism portion30is filled with an adhesive relatively low in hardness and uniform in hardness, when a force which moves the proximal end side of the drive mechanism portion30relative to the lens barrel portion20is added to the image pickup unit1, a whole of the adhesive is deformed, and the drive mechanism portion30moves relative to the lens barrel portion20. For the reason, the adhesive portion that fixes the holding portion21cof the fixed barrel21and the guide pipe33may be broken or the holding portion21cmay be broken.

Since a high-hardness adhesive generally has low viscosity and high flowability before curing, it is relatively difficult to fill the high-hardness adhesive into a wide gap and cure the high-hardness adhesive. In the present embodiment, the gap is narrow at a spot where the high-hardness adhesive60ais filled, and work can be easily performed.

Note that although a plurality of types of adhesives different in hardness is used in the above-described embodiment to decrease the hardness of the adhesive60to be filled into a gap formed between the lens barrel portion20and the drive mechanism portion30toward the proximal end side, the present invention is not limited to the configuration. For example, if the adhesive60is an adhesive having hardness after curing which varies according to cure temperature, the present invention can be realized by filling the gap with one type of adhesive and curing the adhesive with different cure temperatures for the distal end side and the proximal end side.

Note that the present invention is not limited to the above-described embodiment and can be appropriately changed without departing from the scope or spirit of the invention readable from the claims and the entire specification. An image pickup unit for an endoscope which involves such changes is also included in the technical scope of the present invention.