Patent Publication Number: US-2012029283-A1

Title: Guide assembly for endoscope

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a guide assembly for an endoscope. More particularly, the present invention relates to a guide assembly capable of causing an endoscope to enter a body cavity smoothly, and keeping a steering device in the endoscope steerable readily even with a self-propelled structure for guiding. 
     2. Description Related to the Prior Art 
     An endoscope is used to diagnose a body cavity, such as a large intestine in a gastrointestinal tract. Manipulation of the endoscope is a difficult process, because the large intestine is a tortuous organ in a human body, and some body parts are very changeable in the position in the body, such as a sigmoid colon and a transverse colon. Learning the manipulation of the endoscope of the large intestine requires much experience and time. If a doctor is insufficiently skilled in the manipulation, physical load to the body of a patient will be very large. 
     U.S. Pat. Nos. 6,971,990 and 7,736,300 (corresponding to JP-A 2009-513250) disclose a self-propelled apparatus for propelling the endoscope in the axial direction in the body cavity to facilitate the manipulation even for an unskilled operator or doctor. The self-propelled apparatus of the documents includes a movable endless track device or crawler device or toroidal device. The endless track device is driven to turn around for the endoscope to travel mechanically. Force of propulsion is created by the endless track device contacting a wall of the large intestine, so as to guide the endoscope deeply in the body cavity. 
     However, U.S. Pat. Nos. 6,971,990 and 7,736,300 disclose the self-propelled apparatus in which a support or housing of the endless track device longitudinally extends in the axial direction of the elongated tube. There is a problem in that the steering of the steering device is obstructed by the combined use of the guide assembly or the self-propelled apparatus, and that flexibility of the elongated tube may be lower. Accordingly, the manipulation may be more difficult. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems, an object of the present invention is to provide a guide assembly capable of causing an endoscope to enter a body cavity smoothly, and keeping a steering device in the endoscope steerable readily even with a self-propelled structure for guiding. 
     In order to achieve the above and other objects and advantages of this invention, a guide assembly of a self-propelled type for an endoscope including a section of an elongated tube for entry in a body cavity is provided. The elongated tube has a portion of a steering device on a distal side with a variable direction. At least first and second self-propelled units are mounted about the steering device, arranged with one another, for contacting a wall of the body cavity for propulsion. The first and second self-propelled units include respectively first and second driving devices, actuated with force by an external drive source, for converting the force into force for the propulsion. 
     The first self-propelled unit includes a first transmission device for transmitting the force from the drive source to the first driving device. The second self-propelled unit includes a second transmission device for transmitting the force from the drive source to the second driving device discretely from the first transmission device. 
     The first self-propelled unit is fixedly mounted on the steering device. 
     The first self-propelled unit is disposed on a distal side from the second self-propelled unit. Furthermore, a connecting coil structure connects the second self-propelled unit to the first self-propelled unit. 
     The connecting coil structure includes at least two coils having diameters different from one another, and combined by containing a first one in a second one thereof so that winding directions thereof are opposite to one another. Furthermore, a flexible tubular cover covers the connecting coil structure. 
     In one preferred embodiment, furthermore, the second self-propelled unit is fixedly mounted on the steering device. 
     Each of the at least first and second self-propelled units includes an endless track device, having an annular surface, driven by the first or second driving device with the force, for endlessly moving on an endless track in the axial direction. 
     Each of the at least first and second self-propelled units includes a worm gear sleeve, secured to the steering device, and rotated thereabout by the first or second transmission device. Each of the first and second driving devices includes an engagement roller, having teeth, rotatable about an axis perpendicular to the axial direction, meshed with the worm gear sleeve, for moving the endless track device. 
     The first self-propelled unit further includes a bearing sleeve for supporting the worm gear in a rotatable manner about the steering device. The worm gear of the second self-propelled unit is supported about the steering device in a rotatable manner with a small clearance. 
     In another preferred embodiment, each of the at least first and second self-propelled units further includes a bearing sleeve for supporting the worm gear in a rotatable manner about the steering device. 
     Each of the first and second driving devices includes a first ring sleeve disposed around the worm gear. A first through opening is formed in a wall of the first ring sleeve, for supporting the engagement roller in a rotatable manner. A second ring sleeve is disposed around the first ring sleeve, for movably supporting the endless track device. A second through opening is formed in a wall of the second ring sleeve. An idler roller is secured in the second through opening, for rotating about an axis perpendicular to the axial direction, and nipping the endless track device in cooperation with the engagement roller. 
     The idler roller is constituted by a pair of idler rollers, and the engagement roller is disposed between the idler rollers. 
     Each of the first and second transmission devices includes a torque coil structure having a proximal end connected to the drive source for transmitting torque. A pinion is secured to a distal end of the torque coil structure, for applying the torque to the first or second driving device when the drive source operates. 
     The endless track device is formed from fluid-impermeable material, and internally charged with liquid. 
     In one preferred embodiment, the endless track device is formed from fluid-impermeable material, and internally charged with gel. 
     In another preferred embodiment, the endless track device is formed from biocompatible plastic material. 
     The second self-propelled unit is operated remotely. 
     Consequently, it is possible to keep a steering device in the endoscope steerable readily even with a self-propelled structure for guiding, because of the combination of the two self-propelled units driven discretely. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent from the following detailed description when read in connection with the accompanying drawings, in which: 
         FIG. 1  is a plan illustrating an endoscope system; 
         FIG. 2  is a perspective view illustrating a guide assembly; 
         FIG. 3  is an exploded perspective view illustrating the guide assembly; 
         FIG. 4  is a vertical section illustrating the guide assembly; 
         FIG. 5  is a vertical section illustrating another preferred guide assembly without a connecting coil structure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE PRESENT INVENTION 
     In  FIG. 1 , an endoscope system  2  includes an endoscope  10  and a self-propelled type of guide assembly  11 . The endoscope  10  has a handle device  12  and an elongated tube  13  or guide tube disposed to extend from the handle device  12  for entry in a body cavity, for example, a large intestine of a gastrointestinal tract. A universal cable  14  is disposed to extend from the handle device  12 . Connection plugs (not shown) are disposed at a proximal end of the universal cable  14  for connection with a light source apparatus and a processing apparatus (not shown) in a removal manner. 
     The handle device  12  includes steering wheels  15 , an air/water button  16  and a suction button  17 . The air/water button  16  is operable for supplying air or water through a distal end of the elongated tube  13 . An instrument channel  18  is formed through the handle device  12  and the elongated tube  13  for receiving entry of a forceps, electrocautery device or other medical instrument. 
     The elongated tube  13  includes a flexible device  19 , a steering device  20  and a head assembly  21  in a sequence in a distal direction from the handle device  12 . The flexible device  19  has a length as great as several meters for reach of the head assembly  21  to an object of interest in a body cavity. The steering device  20  bends up and down and to the right and left in response to operation of the steering wheels  15  of the handle device  12 . Thus, the head assembly  21  can be steered in a desired direction in the patient&#39;s body. 
     An imaging window  30  is formed in the head assembly  21  for imaging of a body part in the body. See  FIG. 2 . The head assembly  21  contains objective optics and an image sensor or solid-state image pickup device for imaging, such as CCD and CMOS image sensors. The image pickup device is connected to the processing apparatus by a signal line, which extends through the elongated tube  13 , the handle device  12  and the universal cable  14 . An object image of the body part is focused on a reception surface of the image pickup device, and is converted into an image signal. The processing apparatus processes the image signal from the image pickup device through the signal line by image processing, and obtains a video signal by conversion after the image processing. The object image is output and displayed on a monitor display panel (not shown) according to the video signal. 
     Various openings are formed in the head assembly  21  as illustrated in  FIG. 2 . Among those, a lighting window  31  passes illumination light from a light source apparatus toward an object of interest. An air/water nozzle  32  supplies air or water toward the imaging window  30  from an air/water supply device in the light source apparatus in response to depression of the air/water button  16 . An instrument opening  33  causes a distal end of a medical instrument from the instrument channel  18  to appear distally. 
     The guide assembly  11  is a device mounted on the endoscope  10 , for assisting forward and backward movement of the elongated tube  13  of the endoscope  10  in a body cavity. There is an external drive source  22  which drives the guide assembly  11 . The drive source  22  includes motors  22   a  and  22   b . A torque coil structure  54   a  of a multi component type or three component type is connected with an output shaft of the motor  22   a . A torque coil structure  54   b  of a multi component type or three component type is connected with an output shaft of the motor  22   b . See  FIG. 3 . A protection sheath  23   a  receives entry of the torque coil structure  54   a  at its full length for covering. A protection sheath  23   b  receives entry of the torque coil structure  54   b  at its full length for covering. Torque of the motors  22   a  and  22   b  is transmitted to the torque coil structures  54   a  and  54   b . Each of the torque coil structures  54   a  and  54   b  rotates inside the protection sheaths  23   a  and  23   b  responsively as transmission devices or wire devices. 
     An overtube  24  is used to cover the elongated tube  13 , and is ready to expand and shrink in an axial direction of an axis A of the elongated tube  13 . The protection sheaths  23   a  and  23   b  are entered between the overtube  24  and the elongated tube  13 . 
     A controller (not shown) controls the drive source  22 . A button panel (not shown) is connected to the controller. The button panel includes a command button for inputting command signals for forward movement, backward movement and stop of the self-propelled type of guide assembly  11 , and a speed button for changing a moving speed of the guide assembly  11 . Note that a control program can be prepared suitably for an object to be imaged. The drive source  22  can be actuated according to the control program without manipulating the button panel, so as to actuate the guide assembly  11  automatically. 
     In  FIG. 2 , the guide assembly  11  includes a first self-propelled unit  11   a  and a second self-propelled unit  11   b  or guide structures. The first self-propelled unit  11   a  is positioned on a distal side from the second self-propelled unit  11   b . Those are secured to the steering device  20  of the elongated tube  13  of the endoscope  10 . Each of the self-propelled units  11   a  and  11   b  includes a movable endless track device  34  or crawler device or toroidal device, and a driving device  35  or support device or barrel device with a rotating mechanism. The endless track device  34  has a hollow shape with an annular surface, is movable on an endless track, and is formed from a biocompatible plastic material having flexibility and fluid-impermeability. An example of the biocompatible plastic material is polyvinyl chloride. Also, polyamide resin, fluorocarbon resin, polyurethane resin and the like can be used. The inside of the endless track device  34  is filled with suitable fluid, such as liquid, gel, gas, or a combination of at least two of liquid, gel and gas. 
     The endless track device  34  of the first self-propelled unit  11   a  is driven by the motor  22   a , and endlessly turns around in the axial direction of the axis A. The endless track device  34  of the second self-propelled unit  11   b  is driven by the motor  22   b , and endlessly turns around in the axial direction. When an outer surface  34   a  of the endless track device  34  contacts an inner wall of a body cavity, propelling force occurs in the self-propelled units  11   a  and  11   b  to move the elongated tube  13  along the axis A. 
     To propel the elongated tube  13  in the distal direction, the elongated tube  13  is moved by the turn around of the endless track device  34  in an endless manner to orient the outer surface  34   a  in the proximal direction. To move the elongated tube  13  in the proximal direction, the endless track device  34  is turned around endlessly to orient the outer surface  34   a  in the distal direction. 
     In  FIGS. 3 and 4 , the driving device  35  includes a first ring sleeve  40  and a second ring sleeve  41 . Both of the first and second ring sleeves  40  and  41  are cylindrical, and have an equal size along the axis A. A diameter of the first ring sleeve  40  is smaller than that of the second ring sleeve  41 . The first ring sleeve  40  is contained in and surrounded by the second ring sleeve  41 . In  FIG. 3 , the endless track device  34  is not depicted. 
     Through openings  40   a  are formed in a wall of the first ring sleeve  40 . An engagement roller  42  or drive roller or toothed roller has teeth, is disposed inside each of the through openings  40   a , and rotates about an axis perpendicular to the axis A. The engagement roller  42  is disposed at the middle of the first ring sleeve  40  in the direction of the axis A. Three engagement rollers  42  are arranged at a pitch of 120 degrees in the circumferential direction of the first ring sleeve  40 . 
     Through openings  41   a  are formed in a wall of the second ring sleeve  41 . A pair of idler rollers  43  or driven rollers are disposed inside respectively the through openings  41   a . Each of the idler rollers  43  is rotatable about an axis parallel to the axis of the engagement roller  42 . Three pairs of idler rollers  43  are arranged at a pitch of 120 degrees in the circumferential direction of the second ring sleeve  41 . When the first ring sleeve  40  is contained in the second ring sleeve  41 , the second ring sleeve  41  is positioned relative to the first ring sleeve  40  to set the engagement roller  42  between the idler rollers  43 . The endless track device  34  is mounted about the second ring sleeve  41  by passage in its end openings. The endless track device  34  is nipped between the engagement roller  42  and the idler rollers  43 . An inner surface  34   b  of the endless track device  34  is contacted by the idler rollers  43 , which are rotated by endless turn around of the endless track device  34 . 
     Specifically, the endless track device  34  is prepared in the following manner. At first, a plastic tube having two open ends with flexibility and elasticity is initially formed from a sheet or film of the above-described suitable material. The plastic tube is halfway inserted in a sleeve lumen of the second ring sleeve  41 . Then a portion of the plastic tube outside the sleeve lumen is bent back externally and extended to cover the periphery of the second ring sleeve  41 . A first side line of the inserted half of the plastic tube is opposed to a second side line of the bent half to the plastic tube, so that the halves are attached together along the first and second side lines by adhesion, welding or other suitable method. Finally, the toroidal shape of the endless track device  34  is obtained. 
     A worm gear  44  or worm thread is contained in the first ring sleeve  40 . The worm gear  44  is included in a worm gear sleeve (worm drive or worm sleeve). A bearing sleeve  45   a  or holding sleeve supports the worm gear  44  in the first self-propelled unit  11   a . An inner sleeve  45   b  supports the worm gear  44  in the second self-propelled unit  11   b . A bore of the inner sleeve  45   b  is larger than that of the bearing sleeve  45   a . The elongated tube  13  of the endoscope  10  is entered in center holes of the bearing and inner sleeves  45   a  and  45   b . The elongated tube  13  is tightly fitted in the bearing sleeve  45   a . Thus, the bearing sleeve  45   a  is fixedly mounted on the steering device  20 . The head assembly  21  projects distally from the bearing sleeve  45   a  upon mounting the bearing sleeve  45   a  on the elongated tube  13 . The inner sleeve  45   b  is connected with the bearing sleeve  45   a . Although the bearing sleeve  45   a  is immovable on the steering device  20 , the inner sleeve  45   b  is rotatable on the steering device  20 . Thus, the inner sleeve  45   b  is prevented from dropping away from the steering device  20 . A worm thread of the worm gear  44  rotates about the bearing sleeve  45   a  or with the inner sleeve  45   b  along the axis A. The worm gear  44  is meshed with the engagement roller  42 , which is rotated by the worm gear  44 . 
     A rear end ring  46  is attached to the first ring sleeve  40  of the second self-propelled unit  11   b . A flange  46   a  is a portion of the rear end ring  46  at its peripheral edge. The flange  46   a , when the rear end ring  46  is attached to the first ring sleeve  40 , contacts a rear edge of the first ring sleeve  40 . The inner sleeve  45   b  is fitted in an inner hole of the rear end ring  46  in a tight manner without dropping. 
     A front end ring  47  is attached to the first ring sleeve  40  of the first self-propelled unit  11   a . A flange  47   a  is a portion of the front end ring  47  at its peripheral edge. The flange  47   a , when the front end ring  47  is attached to the first ring sleeve  40 , contacts a front edge of the first ring sleeve  40 . An end of the bearing sleeve  45   a  is fitted in an inner hole of the front end ring  47  in a tight manner without dropping. 
     A connecting ring  50  is fitted on the first ring sleeve  40  in the first self-propelled unit  11   a  by entry from a side opposite to the front end ring  47 . Similarly, another connecting ring  50  is fitted on the first ring sleeve  40  in the second self-propelled unit  11   b  by entry from a side opposite to the rear end ring  46 . The connecting ring  50  includes a small diameter portion  50   a  and a large diameter portion  50   b , which are circular with different diameters. The small diameter portion  50   a  is firmly positioned in the first ring sleeve  40 . The large diameter portion  50   b  is engaged with an edge of the first ring sleeve  40  upon fitting the small diameter portion  50   a  in the first ring sleeve  40 . Recesses  50   c  are formed in the connecting ring  50  at front and rear ends. When the small diameter portion  50   a  is fitted in the first ring sleeve  40 , each of the bearing and inner sleeves  45   a  and  45   b  is engaged with the inner surface of one of the recesses  50   c . This prevents drop of the bearing and inner sleeves  45   a  and  45   b . There is a connecting coil structure  51  of a multi component type or three component type, which has one end retained into a second one of the recesses  50   c . A center opening  50   d  is formed in the connecting ring  50 , and receives entry of the elongated tube  13 . 
     The connecting coil structure  51  includes a first coil spring  51   a , a second coil spring  51   b  and a third coil spring  51   c . The first coil spring  51   a  is positioned externally. The second coil spring  51   b  has an outer diameter substantially equal to an inner diameter of the first coil spring  51   a . The third coil spring  51   c  has an outer diameter substantially equal to an inner diameter of the second coil spring  51   b . The coil springs  51   a ,  51   b  and  51   c  are combined in a multi layer form in such a state that their winding directions are different from one another. Specifically, the first and third coil springs  51   a  and  51   c  have turns wound in the counterclockwise direction. The second coil spring  51   b  has turns wound in the clockwise direction. 
     When the connecting coil structure  51  is rotated in the counterclockwise direction, the first and third coil springs  51   a  and  51   c  are shifted and tightened in an inward direction, the second coil spring  51   b  being shifted and loosened in an outward direction. When the connecting coil structure  51  is rotated in the clockwise direction, the first and third coil springs  51   a  and  51   c  are shifted and loosened in the outward direction, the second coil spring  51   b  being shifted and tightened in the inward direction. Thus, changes in relative positions of the first ring sleeve  40  in the first self-propelled unit  11   a  and the first ring sleeve  40  of the second self-propelled unit  11   b  can be prevented about the axis A even though the inner sleeve  45   b  in the second self-propelled unit  11   b  is not fixed to the steering device  20 . 
     A tubular cover  52  is flexible along the axis A of the elongated tube  13 , and has one end to which the connecting ring  50  is secured. The tubular cover  52  covers the connecting coil structure  51 , and prevents body fluid from contacting the connecting coil structure  51 . In  FIG. 3 , the tubular cover  52  is not depicted. 
     Spur gear teeth  53  or a driven gear is formed with a proximal end of the worm gear  44  in the second self-propelled unit  11   b , the teeth being arranged about the axis A. A through hole (not shown) is formed in the rear end ring  46  in the direction of the axis A, and receives entry of the torque coil structure  54   a . A pinion  55  is secured to an end of the torque coil structure  54   a  extending through the through hole. Thus, the pinion  55  is rotated together with the torque coil structure  54   a . A cutout  46   b  is formed in the rear end ring  46 , and contains the pinion  55 . An axis of the pinion  55  is parallel to the axis A. The torque coil structure  54   a  includes three coil springs combined in a multi layer form in such a state that their winding directions are different from one another. The torque coil structure  54   a  can transmit torque even upon rotating in any of the forward and backward directions. The pinion  55  is meshed with the spur gear teeth  53 . When the torque coil structure  54   a  rotates, the pinion  55  rotates responsively, to rotate the spur gear teeth  53 . 
     In the first self-propelled unit  11   a , the spur gear teeth  53  are formed with a distal end of the worm gear  44  and are arranged about the axis A. A receiving hole (not shown) is formed in the front end ring  47  in the direction of the axis A, and receives entry of the torque coil structure  54   b . A pinion  55  is secured to an end of the torque coil structure  54   b  extending in the receiving hole. Thus, the pinion  55  is rotated together with the torque coil structure  54   b . A cutout  47   b  is formed in the front end ring  47 , and contains the pinion  55 . An axis of the pinion  55  is parallel to the axis A. In a manner similar to the connecting coil structure  51 , the torque coil structure  54   b  includes three coil springs combined in a multi layer form in such a state that their winding directions are different from one another. The torque coil structure  54   b  can transmit torque even upon rotating in any of the forward and backward directions. The pinion  55  is meshed with the spur gear teeth  53 . When the torque coil structure  54   b  rotates, the pinion  55  rotates responsively, to rotate the spur gear teeth  53 . A receiving hole  50   e  is formed in each connecting ring  50  and penetrates in the direction of the axis A. A receiving hole  46   c  is formed in the rear end ring  46  and penetrates in the direction of the axis A. The receiving holes  46   c  and  50   e  receive entry of the torque coil structure  54   b . Thus, the torque coil structure  54   b  extends between the worm gear  44  and the first ring sleeve  40  in the second self-propelled unit  11   b , between the connecting coil structure  51  and the tubular cover  52 , and between the worm gear  44  and the first ring sleeve  40  in the first self-propelled unit  11   a.    
     The operation of the endoscope system  2  is described now. At first, the overtube  24  is retained on the elongated tube  13  of the endoscope  10 . The elongated tube  13  is entered in the bearing and inner sleeves  45   a  and  45   b  to mount the guide assembly  11  on the elongated tube  13 . 
     After securing the overtube  24  and the guide assembly  11  to the endoscope  10 , a power source of the processing apparatus, light source apparatus and controller is turned on. Then personal information of the patient is input. The elongated tube  13  of the endoscope  10  is entered in his of her body cavity. 
     After the head assembly  21  is advanced to a predetermined body part, for example, slightly short of a sigmoid colon, then the button panel is operated to turn on a power source for the drive source  22  of the self-propelled type of guide assembly  11  to drive the motors  22   a  and  22   b . Then a command signal for start is input with the button panel. The motors  22   a  and  22   b  rotate the torque coil structures  54   a  and  54   b  in a predetermined direction. The pinion  55  is rotated by rotation of the torque coil structures  54   a  and  54   b . The worm gear  44  in each of the self-propelled units  11   a  and  11   b  is rotated by the pinion  55  discretely. 
     When the worm gear  44  rotates together with the self-propelled units  11   a  and  11   b , the engagement roller  42  is rotated responsively. Thus, the endless track device  34  endlessly turns around in each of the self-propelled units  11   a  and  11   b . The guide assembly  11  advances in the axial direction of the elongated tube  13  when the outer surface  34   a  of the endless track device  34  contacts a wall of a body cavity. Consequently, the head assembly  21  advances along the wall of the body cavity. 
     When a command signal for a change is input by operating the button panel, the motors  22   a  and  22   b  change a rotational speed of the torque coil structures  54   a  and  54   b . Thus, a moving speed of the self-propelled type of guide assembly  11  is changed. When a command signal for return is input by operating the button panel, the motors  22   a  and  22   b  cause the torque coil structures  54   a  and  54   b  to rotate in a backward direction, to move the guide assembly  11  and the head assembly  21  backwards. When a command signal for a stop is input by operating the button panel, the motors  22   a  and  22   b  stop to stop moving the guide assembly  11 . It is possible to propel the head assembly  21  through the body cavity to an object of interest by suitably repeating those steps of the movement. 
     A doctor or operator steers the steering device  20  of the endoscope  10  by manipulating the steering wheels  15 , to bend the head assembly  21  in a desired direction. Force for driving is applied to the second self-propelled unit  11   b  in the guide assembly  11  discretely from the force applied to the first self-propelled unit  11   a . Thus, the self-propelled units  11   a  and  11   b  can follow the steering of the steering device  20 . This is effective in keeping the steering device  20  free from being obstructed by the guide assembly  11 . In the second self-propelled unit  11   b , a clearance space exists between the inner surface of the inner sleeve  45   b  and the steering device  20 , so as to facilitate smooth steering of the steering device  20 . The second self-propelled unit  11   b  is connected to the first self-propelled unit  11   a  by the connecting coil structure  51 . So the steering device  20  can operate for steering without being obstructed by the guide assembly  11 . 
     In the above embodiment, the first self-propelled unit  11   a  is fixedly mounted on the steering device  20 . The second self-propelled unit  11   b  is connected to the first self-propelled unit  11   a  by the connecting coil structure  51 . In contrast, another preferred embodiment having the self-propelled units  11   a  and  11   b  discretely mounted on the steering device  20  is illustrated in  FIG. 5 . 
     The connecting coil structure  51  is not present in the embodiment. To mount the self-propelled units  11   a  and  11   b  on the steering device  20 , the bearing sleeve  45   a  in the second self-propelled unit  11   b  is mounted on the elongated tube  13 . The bearing sleeve  45   a  is fixedly positioned on the steering device  20  without the play of the inner sleeve  45   b  above. The first self-propelled unit  11   a  is retained on the steering device  20  discretely from the second self-propelled unit  11   b . Consequently, it is possible to reduce a manufacturing cost of the guide assembly  11  by eliminating the connecting ring  50  and the connecting coil structure  51 . 
     In the embodiment, the connecting coil structure  51  is used between the two worm gears  44  in the self-propelled units  11   a  and  11   b . However, other elements may be used between the two and having flexibility along the axis A, for example, only one coil spring, a rubber tube or the like. 
     Although the self-propelled units  11   a  and  11   b  are disclosed in the above embodiment, the number of the self-propelled units or guide structures may be three or more. Also, the number of the drive sources or motors for the self-propelled units may be one or three or more. 
     In the above embodiments, the self-propelled type of guide assembly is used with the endoscope for a medical use. Also, the guide assembly of the invention can be used with an endoscope for industrial use, an ultrasonic probe, or other instruments for imaging in a cavity. Although the movable endless track device or crawler device or toroidal device is turned around in the guide assembly, a guide assembly of the invention can be any mechanical type for entry in a body cavity as a component for an instrument for imaging. 
     Although the present invention has been fully described by way of the preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those having skill in this field. Therefore, unless otherwise these changes and modifications depart from the scope of the present invention, they should be construed as included therein.