Magnetically coupled actuator

Abstract: A lens surrounded by a sealed protective chamber is focused by utilising a magnetically coupled actuator associated with the lens to adjust the position of the lens within the chamber. By using a magnetic field to adjust the lens position, it is not necessary to employ mechanical actuation means which have to pass through the walls of the chamber. The chamber is thereby completely sealed and contaminants are prevented from contacting the lens.

Description: This invention is related to magnetic coupling and more particularly to optical lens focusing systems employing a magnetic actuation coupler to move and focus a lens. The invention also relates to surgical and medical devices incorporating such magnetically coupled actuator systems. Physicians frequently use optical devices to facilitate examining an area that might otherwise be difficult to observe. For example, when performing arthroscopic knee surgery, a surgeon inserts an arthroscope through a small incision in the patient's leg and manipulates the arthroscope to various areas of interest. The arthroscope uses optical fibres to illuminate the area of interest inside the patient's knee and an optical assembly for picking up an image and transmitting it either for direct observation by the surgeon or to a video camera for display on a TV monitor. Because the surgeon will be moving the arthroscope to various areas of interest throughout the procedure, the distance between the arthroscope's distal tip and the area of interest will vary. It is therefore necessary to provide some mechanism for focusing the image picked up by the arthroscope in order to produce a high quality view on the monitor. Such a focusing mechanism typically consists of at least one focusing lens whose position can be adjusted by the surgeon during the procedure. The focusing lens is placed in a chamber in order to minimise the intrusion of contaminants and to prevent it from fogging during the procedure. The chamber also protects the lens when the device is being cleaned and sterilised between surgical procedures. Cleaning is typically achieved by washing in soaps and disinfecting solutions. Sterilisation is accomplished usually by exposure to ethylene oxide gas or by steam autoclaving (the application of superheated steam under high pressure to the medical instrument). Since it is necessary to move the focusing lens within the chamber to achieve a desired focus, a mechanical adjustment mechanism which is coupled to the lens (or some structure supporting the lens) extends through to the exterior of the sealed chamber to enable the surgeon to manually move the lens. The point at which the mechanism penetrates the chamber must be sealed as tightly as possible to keep the lens clean and fog-free. German document DE-U-8810044 discloses an apparatus for adjusting the position of a lens, comprising: a lens (2a); a sealed chamber (1, 3, 4, 5) surrounding the lens, the chamber including a window (4) to permit light to enter the said chamber and pass through the lens; an actuator (2, 7) held inside the chamber, the actuator being coupled to the lens (2a) and movable with respect to the chamber thereby to cause motion of the lens when the actuator is moved; and an element (7a) held outside the chamber and magnetically coupled to the actuator through a surface of the chamber, the element (7a) being movable relative to the chamber to cause movement of the actuator to thereby adjust the position of the lens. The present invention aims to provide an apparatus for adjusting the position of a lens which provides "tight" coupling between the outside magent and the interior lens carrier which is accomplished by the use of a strong magnet and the design of the magnet washers mated with the carrier projections. The present invention thus provides apparatus comprising: a lens (20); a sealed chamber (16) surrounding said lens (20), said chamber (16) including a window (18) to permit light to enter said chamber (16) and pass through said lens (20); an actuator held inside said chamber (16), said actuator being coupled to said lens (20) and movable with respect to said chamber (16) thereby to cause motion of said lens (20) when said actuator is moved; and an element held outside said chamber (16) and magnetically coupled to said actuator through a surface of said chamber (16), said element being movable relative to said chamber (16), to cause movement of said actuator to thereby adjust the position of said lens (20), said element comprising a magnet (36) and said actuator comprising a ferromagnetic material or a magnet, characterised in that said actuator and said element define a closed flux path, said actuator comprises projections (28, 30, 32 and 34) which define part of said flux path, said projections (28, 30, 32 and 34) being in sliding contact with an inner surface of said chamber (16), and said apparatus further comprising two ferromagnetic washers (38, 40), respectively positioned adjacent the poles of said magnet (36) respectively aligned with said projections (28, 30, 32 and 34) and configured to conduct the flux radially. The present invention also provides medical or surgical devices which comprise the lens adjustment apparatus of the invention. In a preferred form of this embodiment the device is an endoscope coupled to a viewing device in which the lens adjustment apparatus of the invention functions as a coupler between the endoscope and viewing device. In accordance with a further aspect of the present invention there is also provided a method for the operation of a medical or surgical device incorporating the lens adjustment apparatus of the invention which includes moving the element which is held outside the sealed chamber thereby to move the ferromagnetically coupled actuator and its associated lens system and to focus the light moving in a path through the chamber and lens. In the invention, a lens surrounded by a protective chamber is focused by utilising a magnetic field to adjust the position of the lens within the chamber. By using a magnetic field to adjust the lens position, it is not necessary to pass a mechanical actuator device through the wall of the chamber, thereby allowing the chamber to be completely sealed to prevent contaminants from contacting the lens. In general, in one aspect, the invention features adjusting the position of a lens to thereby adjust the focus of light passing through the lens. The lens is surrounded by a sealed protective chamber. The chamber includes a window to permit light to enter the chamber and the lens; an actuator held inside the chamber and movable with respect to the chamber, the actuator being arranged to cause motion of the lens when the actuator is moved; and an element held outside the chamber and ferromagnetically coupled to the actuator through a surface of the chamber, the element being movable relative to the chamber to cause movement of the actuator to thereby adjust the position of the lens. The invention also generally features a method for moving a focusing lens having a protective chamber surrounding the lens, the chamber including a window to permit light to enter the chamber and the lens, the chamber comprising an actuator positioned inside the chamber and arranged to cause motion of the lens when the actuator is moved, the method comprising moving an element that is ferromagnetically coupled to the actuator and positioned outside the chamber to cause the actuator to move thereby adjusting the position of the lens. In preferred embodiments, the magnet is supported by a magnet support that has a stabilisation member to restrict the movement of the magnet. The magnet is preferably a ring-shaped permanent magnet and can be moved in a direction that is parallel to an axis of the chamber. Alternatively, the actuator and the element can both be magnets. or the element can be ferromagnetic and the actuator can be a magnet. The chamber is preferably cylindrical, non-magnetic and is sealed at each of its ends by a window through which light may pass. The curved surface of the cylindrical chamber is continuous and free of apertures through which debris or other contaminants could pass. The sealed chamber prevents motion from being transmitted mechanically through the wall of the chamber. The apparatus may be a medical device such as an endoscope coupler for coupling an endoscope to another device (eg. a video monitor). The apparatus may also be eg. a video arthroscope, which is designed to couple directly to a video camera without an auxiliary coupler; a camera with integral focusing optics; a beam splitter type coupler, which provides simultaneous viewing of an image through an ocular as well as a video system; or coupler designed to permit photography through endoscopes. The video system may comprise means for converting light to a video signal such as a charged coupled device (CCD) which is coupled to means for processing and displaying the video signal. The CCD may be coupled remotely to the video processing system by a suitable flexible cable. The invention may also be a device which moves an apparatus contained within a sealed chamber other than a lens. The invention will now be illustrated by reference to the accompanying drawing which is a cross-sectional view of an endoscope coupler. Referring to the drawing, endoscope coupler 10 includes a front housing 12 and a rear housing 14. The apparatus may be a medical device such as an endoscope coupler for coupling an endoscope to another device (eg. a video monitor). Front housing 12 includes a spring operated variable split ring clamp that can attach to endoscopes of various diameters. Light 17 from an endoscope 19 enters a sealed non-magnetic cylindrical tube 16 through a front window 18, passes through focusing lens 20 and exits tube 16 through a rear window 22 and into a video head assembly 23 for viewing on a monitor. Lenses 20 are mounted in a support structure 24 that includes a generally cylindrical permeable steel, ferromagnetic support 26 and a pair of non-magnetic tubes 27, 29. Ferromagnetic support 26 includes radial projections 28, 30, 32 and 34 each of which is in sliding contact with the inner surface of tube 16 to allow ferromagnetic support 26 to slide freely (arrow 31) within tube 16 thereby moving lenses 20 toward and away from front window 18 and the source of the light for focusing. Projections 28 and 34 are thicker than projections 30, 32 to provide stable supporting surfaces for support structure 24 within tube 16. Windows 18, 22 are sealed to tube 16 either by adhesives or by a solder or braze connection. Tube 16 is fixed at opposite ends to housing 12, 14 either by adhesives or by mechanical means such as an interference press fit, threads or by a solder or braze connection. A ring shaped permanent magnet 36 surrounds tube 16 and has retaining permeable steel flux conducting washers 38, 40 adjacent to its north (N) and south (S) poles, respectively. The inner diameter of magnet 36 is slightly larger than the outside diameter of tube 16 so that magnet 36 may slide freely along tube 16. The length of magnet 36 together with the two retaining washers 38, 40 is equal to the spacing of the two projections 30, 32. Magnet 36 and washers 38, 40 are supported by a support structure 42 which receives a screw 44 in its radially outermost surface. The support structure may be attached to magnet 36 by adhesives, threads, interference press or a retaining ring. The head of screw 44 fits within a helical groove 46 formed in a cylindrical focusing sleeve 48. Focusing sleeve 48 is mounted within and may be rotated by rotating a cylindrical focusing ring 50 attached to sleeve 48 by adhesives or threads. An anti-rotation or stabilising rod 52 is secured at one end to magnet support 42 by a press fit and at its other end is received in a hole 54 formed in housing 14. Endoscope coupler 10 also includes a wave spring 56, floating washers 58, 60 and 62, support 64 and nut 66. The washers are made of a dimensionally stable material with low coefficient of friction, such as bronze or a polyamide-imide plastic. In operation, light representing an image that passes through tube 16 is focused onto an imaging sensor (not shown) in head assembly 23 by lenses 20, the focus being adjustable by moving lenses 20 toward and away from the imaging sensor. To achieve the adjustment, focusing ring 50 is rotated to thereby rotate focusing sleeve 48. The head of screw 44 will move within helical groove 46 as focusing sleeve 48 is rotated and will therefore move either toward front housing 12 or toward rear housing 14, depending on the direction of rotation of focusing ring 50. The movement of screw 44 will cause magnet support 42, magnet 36, and washers 38, 40 to move outside of tube 16. Stabilisation rod 52 stabilises magnet 36 and prevents magnet 36 from rotating with focusing sleeve 48. Since support 26 is ferromagnetic, a flux path is established between the north and south poles of magnet 36 via washers 38, 40, projections 30, 32 and the tubular part of support 34. As a result, as magnet 36 moves, lens support 24 and lenses 20 will also move, thereby adjusting the focus of the image passing through tube 16. The washers function as bearings for the entire assembly. This prevents "cocking" or binding and prevents abrasive contact between the magnet assembly and tube 16. Wave spring 56 functions to prevent "end-play" (ie. axial movement). The primary sliding surfaces are the surfaces of washers 58 and 60. Because focus is achieved without the need to extend any mechanical components through the surface of sealed tube 16, no debris or steam can enter the tubes in which the lenses are housed. Conventional focusing devices use a direct mechanical connection between the lenses and some external adjustment such as the above described focusing ring. It is therefore necessary to have apertures in the chamber that contains the lenses to admit the mechanical components of the adjustment mechanism. Although the apertures are typically sealed as well as possible, dirt, disinfecting solutions and water vapour are still sometimes able to penetrate into the chamber causing the lenses to become dirty or fogged, degrading performance of the device and necessitating a difficult and time consuming cleaning of the lenses which is typically done by the manufacturer, making the device unavailable to the physician. In the present invention, the lenses will remain dirt and fog-free throughout the surgical procedure. Furthermore, when the device is cleaned and sterilised between surgical operations such as by autoclaving, the steam will not be able to penetrate into the chamber thereby preventing the lenses from fogging. In other embodiments of the invention, for example, instead of using a single lens assembly and moving the lens axially to achieve the desired focus, multiple lenses can be selectively moved into the path of the light passing through the chamber with each lens providing a different predetermined focus.

Claims: Apparatus comprising: a lens (20); a sealed chamber (16) surrounding said lens (20), said chamber (16) including a window (18) to permit light to enter said chamber (16) and pass through said lens (20); an actuator held inside said chamber (16), said actuator being coupled to said lens (20) and movable with respect to said chamber (16) thereby to cause motion of said lens (20) when said actuator is moved; and an element held outside said chamber (16) and magnetically coupled to said actuator through a surface of said chamber (16), said element being movable relative to said chamber (16), to cause movement of said actuator to thereby adjust the position of said lens (20), said element comprising a magnet (36) and said actuator comprising a ferromagnetic material or a magnet, characterised in that said actuator and said element define a closed flux path, said actuator comprises projections (28, 30, 32 and 34) which define part of said flux path, said projections (28, 30, 32 and 34) being in sliding contact with an inner surface of said chamber (16), and said apparatus further comprising two ferromagnetic washers (38, 40), respectively positioned adjacent the poles of said magnet (36) respectively aligned with said projections (28, 30, 32 and 34) and configured to conduct the flux radially. Apparatus as claimed in claim 1 wherein said element comprises a magnet and a magnet support secured to said magnet, said magnet support including a stabilisation member to restrict rotational movement of said magnet. Apparatus as claimed in any one of claims 1 to 2 wherein said chamber is cylindrical. Apparatus as claimed in claim 3 wherein said cylindrical chamber is sealed at each of its ends by a window through which said light may pass. Apparatus as claimed in claim 3 or claim 4 wherein the curved surface of said cylindrical chamber is continuous and free of apertures through which debris or other contaminants could pass. Apparatus as claimed in any one of claims 1 to 5 wherein said element is adapted to be moved in a direction parallel to an axis of said chamber. Apparatus is claimed in any one of claims 1 to 6 wherein said magnet is ring-shaped. Apparatus as claimed in any one of claims 1 to 7 wherein said magnet comprises a permanent magnet. Apparatus as claimed in any one of claims 1 to 8 wherein said chamber is formed from a non-magnetic material. Apparatus as claimed in any one of claims 1 to 9 wherein said lens is adapted to move along an optical axis on which said lens lies. Medical or surgical devices comprising apparatus as claimed in any one of claims 1 to 10. A device as claimed in claim 11 wherein the apparatus is an endoscope coupler and the device further comprises an endoscope and a viewing device coupled or adapted to be coupled to said endoscope coupler. A device as claimed in claim 12 wherein the viewing device comprises means for converting light to a video signal means for processing the video signal and means for viewing the process video signal. A method of operating a medical or surgical device as claimed in any one of claims 11 to 13 comprising moving said element held outside said chamber thereby to move said magnetically coupled actuator and lens and focus light moving in a path through the chamber and lens.

Inventors: CHINNOCK RANDALL B, DIONNE NORMAN J, CHINNOCK, RANDALL B., DIONNE, NORMAN J.
Applicants: SMITH & NEPHEW DYONICS, SMITH & NEPHEW DYONICS INC
Application year: 1991
Main classification: G02B7
IPC codes: H02K33, A61B1, G02B7, G02B23