WO1998011577A1

WO1998011577A1 - Electrical switch

Info

Publication number: WO1998011577A1
Application number: PCT/US1997/015519
Authority: WO
Inventors: Michael L. Harris
Original assignee: Smith & Nephew, Inc.
Priority date: 1996-09-13
Filing date: 1997-09-04
Publication date: 1998-03-19
Also published as: AU4178997A

Abstract

An electrical switch is secured by a friction fit within a recess in a base. The base may, for example, comprise a camera head for an endoscope, or may be part of the endoscope itself. The switch includes a switching element and an actuator for the switching element. A portion of the actuator is disposed in the recess and is radially spaced from the recess wall. A retainer is radially disposed between and engages that portion of the actuator and the recess wall to provide an interference fit therebetween. No external mounting hardware (such as a cover plate held in place by screws over the switch) or adhesives are needed to retain the switch within the base or prevent contaminants from leaking past the switch into the recess. As a result, the switch is small and is well suited for use in applications - such as with endoscopes and camera heads - where space is at a premium and where contamination must be avoided.

Description

ELECTRICAL SWITCH

This invention relates to electrical switches, and more particularly to electrical switches for use with an endoscope or other remote visualization device (such as a borescope).

An endoscope typically includes an elongated flexible or rigid outer tube which carries optical fibers for illuminating a remote area (such as a body cavity) with light from an external source. An optical system mounted at the distal end of the tube receives an image of an illuminated object in the body cavity, and transmits the image through the tube to a camera head mounted to the proximal end of the endoscope. The camera head typically houses a solid state imaging device, such as a charge-coupled-device (CCD), and associated electrical circuitry. The CCD produces electrical signals which represent the optical image and are passed to a camera processor connected to the camera head, which in turn processes the signals for display on a video monitor.

Some camera heads are equipped with electrical pushbutton switches actuated by the user to control various operating parameters of the system (such as camera shutter speed). Typically, each switch is mounted within a pocket in the camera head and is secured in place by a rigid (e.g., steel) cover plate which is screwed into the head over the switch actuator.

In some endoscopes (known as electronic endoscopes) the CCD is located at the distal end of the tube, which eliminates the need for a separate camera head. In this case, the pushbutton switches are mounted on the proximal end of the endoscope itself.

This invention features an electrical switch that is secured by a friction fit within a recess in a base. The base may, for example, comprise a camera head for an endoscope, or may be part of the endoscope itself.

Among other advantages, the invention eliminates the need for external mounting hardware (such as a cover plate held in place by screws over the switch) or adhesives to retain the switch within the base or prevent contaminants from leaking past the switch into the recess. As a result, the switch is small and thus is suited for use in applications - such as with endoscopes and camera heads - where space is at a premium and where contamination must be avoided.

Accordingly, an electrical switch configured to be secured within a recess defined by a wall in a base, comprising a switching element, an actuator for said switching element, a portion of said actuator being disposed in the recess and radially spaced from the wall, and a retainer radially disposed between and engaging said portion of said actuator and the wall to provide an interference fit between said actuator and the base.

Preferred embodiments may include one or more of the following features.

The actuator includes a sealing surface, and the retainer engages the actuator to compress the sealing surface against a portion of the recess wall. This provides a fluid- and gas-tight seal between the actuator and the base. In addition, the actuator and the retainer are made from materials selected to withstand sterilization and disinfection. As a result, a camera head or an endoscope equipped with the switch may be sterilized and/or disinfected without the risk of the sterilizing or disinfecting agents leaking past the switch to damage other components. Moreover, the interference fit eliminates the need for adhesives that might be damaged during the sterilization/disinfection process.

The actuator may include a circular, elastomeric body having an upper wall engaged by a user to actuate the switching element and an axially-extending side wall. The retainer is a ring that surrounds the body and engages the side wall to provide the interference fit. The side wall terminates at the sealing surface, which is oriented radially with respect to said side wall. Preferably, the sealing surface is located on the underside of a radially- extending, annular flange at the end of the side wall. The retainer engages the flange and compresses the sealing surface against a radial portion of the recess wall. A surface feature (such as a ridge) on the sealing surface engages a complementary feature (e.g., a groove) on the radial portion of the recess wall. This further enhances the face seal provided between the actuator and the base.

The body may include an axially extending post on an underside of its upper wall. The post is positioned to actuate the switching element when the actuator is depressed by the user. The post may be radially spaced from the side wall by an annular channel within which fits a support member, e.g., an annular ferrule. The ferrule helps prevent a user from accidentally collapsing the body or otherwise disrupting the interference fit by, e.g, applying excessive pressure. The switching element may include a conductive member disposed adjacent to a pair of electrical contacts. The actuator is positioned to, when actuated by a user, move the conductive member from a first position, in which the conductive member isolates the electrical contacts from each other, to a second position, in which the conductive member interconnects the electrical contacts. Preferably, the conductive member is resilient to resume the first position when the user releases the actuator.

The electrical switch is particularly useful for controlling an operating parameter of an endoscopic system. For example, the switch (or multiple switches) can be connected for controlling an operating parameter of a camera (whether the camera is mounted in the endoscope or in a separate camera head). Alternatively, or in addition, the switch can be used to control an operating parameter of an image display device (such as a video monitor, etc.). The switch can be connected to a processor in the endoscopic system or to the camera.

The switch is reliable and is simple to make. (Indeed, the switch is preferably built as its components are installed, one by one, into the recess.) Because the switch is secured in place by an interference fit, the recess can be significantly more shallow than in prior approaches in which hardware such as screwed-in mounting plates were required. As a result, the switch is lightweight and compact and can be used in a variety of applications in which space is at a premium.

Other features and advantages will become apparent from the following detailed description, and from the claims. _Fig. 1 shows a remote visualization system. Fig. 2 illustrates a camera head used with an endoscope in the system of Fig. 1.

Figs. 3 and 4 are exploded isometric and cross-sectional views, respectively, of an electrical switch on the camera head of Fig. 2.

Fig. 5 is a cross-sectional view of the assembled electrical switch.

Referring to Fig. 1 , remote visualization system 10 includes an endoscope 12 the proximal end 13 of which is mounted to a camera head 14. Endoscope 12 includes an elongated tube 16 (which is rigid or flexible, as desired) configured for insertion into a remote area, such as a body cavity. Tube 16 carries optical fibers 18 which deliver light produced by a light source 20 to the remote area. An optical system 22 (represented schematically in Fig. 1 by a lens) mounted in the distal end of tube 16 receives an optical image of an illuminated object in the body cavity, and transmits the image through tube 16 to camera head 14.

Camera head 14 houses a camera, which includes a CCD 24 and its associated control circuitry 26. CCD 24 converts the image into electrical signals, which are processed by control circuitry 26 and transmitted via a cable 28 to a camera processor 30. One example of camera head 14 is described in a copending patent application EP 0669756, assigned to the present assignee.

Camera processor 30 processes the electrical signals to generate a video image that is displayed on a display device, such as a video monitor 32. The video signals produced by camera processor may also be sent to other display devices (such as a video cassette recorder (VCR) 33 or a printer 34), or other accessory devices. A pair of electrical switches 40a, 40b (sometimes referred to collectively below with reference numeral 40) are mounted on camera head 14. The user actuates switches 40 to control various operating parameters of system 10. For example, switch 40a is used to control video accessories (such as monitor 32, VCR 33, and printer 34). Various camera functions (such as shutter speed, automatic gain control, white balance, etc.) are controlled with switch 40b. Switches 40 are connected directly to camera processor 30 via cable 28.

Referring also to Fig. 2, camera head 14 includes a sealed, sterilizable plastic housing 44. Switches 40 are thin, momentary contact devices that are sealed within an upper wall 46 of housing so as to be impenetrable by liquids during sterilization and disinfection of housing 44. For example, switches 40 can withstand chemical sterilization (such as with ethylene oxide gas, searic acid liquid, and hydrogen peroxide plasma) and cold-soak disinfectants. The front end of housing 44 is equipped with a threaded mount 48 for attachment to endoscope 12. A window 50 sealed within mount 48 passes the optical image from endoscope 12 to CCD 24, which is located immediately behind window 50 in housing 44. Cable 28 enters the rear of housing 44 at a sealed joint 52.

Referring to Figs. 3 and 4, each switch 40 is mounted with an interference fit within a circular recess 56 in housing wall 46. Switch 40 is assembled as its components are placed into recess 56 and, when completed, is self-securing and self-sealing within recess 56 without the need for adhesives or any additional mounting hardware (such as screws). The switching element of switch 40 includes a circular printed circuit board 60 the upper surface of which includes a pair of concentric, electrical contacts 61a, 61b separated by an insulating ring 62. Wires 63 (Fig. 4) are soldered to electrical contacts on the underside of board 60, which are in turn connected to contacts 61a,

61b by conductive feedthroughs (not shown) through board 60.

Wires 63 extend through the bottom of recess 56 and are connected to cable 28 (Fig. 1). Board 60 is supported within recess 56 on an annular shelf 57 and is placed on shelf 57 after the electrical connections to wires 63 are made.

A metallic "snap dome" 64 (commercially available from Westlake Components International of Westlake, California, part no. 4L-08.5S-2.6F-D) includes a set of four circumferentially spaced legs 65 which rests on contact 61b on the upper surface of board 60 and a central region 66 which overlies contact 61a. When switch 40 is in the "open" position, snap dome 64 is in the configuration shown in, e.g., Fig. 4, with central region 66 spaced from the upper surface of board 60 and contact 61a. In this position, snap dome 64 electrically isolates contacts 61a, 61b from each other. When the user actuates switch 40 (as described below) snap dome central region 66 "snaps" to a flattened position against the upper surface of board 60 and bridges contacts 61a, 61b, thereby "closing" switch 40. As discussed above, switch 40 is a momentary contact device, and thus when the user releases switch 40 snap dome 64 resiliently returns to its original position. The "snap" action of snap dome 64 gives the user a tactile feel when operating switch 40.

The actuating member of switch 40 is a resilient circular button 68 the upper wall 70 of which has a curved exterior surface to give button 68 an overall dome shape. Button 68 is made from an elastomeric material (such as polyurethane) that can withstand repeated sterilization and disinfection of the kinds discussed herein without breaking down. The cylindrical side walls 72 of button 70 extend axially downwardly from upper wall 70 and terminate at a radially oriented flange 74. The outer diameter of flange 74 is slightly smaller than the inner diameter defined by the side walls 47 of recess 56 so that button 68 can easily be inserted placed into recess 56.

The lower annular surface 76 of flange 74 forms a sealing surface which engages an annular, radially extending surface 49 of wall 46 in recess 56. For additional sealing purposes, surface 76 includes a surface feature, such as a semicircular ridge 76a, that fits within a complementary-shaped circular groove 49a in surface 49. As discussed in more detail below, the engagement of flange surface 76 against recess surface 76 provides a high pressure (e.g., 15 psi gauge) face seal that is impermeable to gas and liquid.

A cylindrical post 78 projects axially from the center of button upper wall 68 to depress snap dome 64 when switch 40 is actuated. Post 78 is radially spaced from button side walls 72 by an annular channel 80, which allows upper wall 70 to flex downwardly when the user pushes down button 68 to actuate switch 40. An annular ferrule 82 (made from, e.g., plastic or other nonmetal) is disposed within channel 80 as a support member for button 68, as described below.

It will be appreciated from Fig. 4 that button side walls 72 are radially spaced from side walls 47 of recess 56. Switch 40 includes a plastic retaining ring 84 which frictionally fits within this space to provide a sealed interface between button 68 and housing wall 46. Put another way, retaining ring 84 is sized to provide tight interference fits between its exterior surface 86 and recess side walls 47 and between its interior surface 88 and button side walls

72. The nominal interference fit between exterior surface 86 and recess side walls 47 is 0.18mm ± 0.051mm (0.007 ±0.002 inches); the nominal interference fit between interior surface 88 and button side walls 72 is 0.077mm ± 0.026mm (0.003 ±0.001 inches).

Exterior surface 86 is beveled 90 at the lower end of retaining ring

84 to facilitate assembling ring 84 into recess 56.

Referring also to Fig. 5, switch 40 is assembled into recess

56 as follows. First, circuit board 60 is connected to wires 63 and is installed on shelf 57. Then, snap dome 64 is placed on board 60, with legs 65 disposed on contact 61b and central region 66 in registry with contact 61a. Ferrule 82 is slid around post 78 of button

68 and is fitted in place by engaging a set of (e.g., four) circum- ferentially-spaced teeth 83 into complementary detents 73 formed in the interior surface of button side walls 72 (Fig. 5). The upper surface 85 of ferrule 82 is beveled to provide a space between ferrule 82 and the underside of button upper wall 70 that allows button 68 to flex downwardly when depressed by the user.

Button 68 and ferrule 82 are placed as a unit into recess 56 so that flange 76 meets recess surface 49 (and ridge 76a fits within groove 49a). Then, retaining ring 84 is placed over button 68 onto housing wall 46 so that button upper surface 70 protrudes through a central opening 92 in ring 84. Next, retaining ring 84 is driven into recess 47 (e.g., using a hand tool with a sleeve that fits over button 68 and engages the upper surface of 87 of ring 84) until ring upper surface 87 is flush with the upper surface 51 of housing wall 46 and lower annular surface 94 of ring 84 (Fig. 4) firmly engages the upper surface of button flange 74. In this position, retaining ring 84 compresses button flange 74 against recess surface 49 and firmly seats ridge 76a within groove 49a to provide a liquid- and gas-tight face seal between button 68 and housing wall 46.

As discussed, the outer diameter of retaining ring 84 is slightly larger than the inner diameter defined by recess side wails

47. As a result, a secure interference fit is obtained between exterior surface 86 of retaining ring 84 and recess side walls 47. Moreover, the size differential causes retaining ring 84 to compress inwardly as it is driven into recess 56, thereby providing a secure interference fit between its interior surface 88 and side walls 72 of button 68. Accordingly, retaining ring 72 serves the additional purpose of retaining the components of switch 40 together within recess 56.

Thus, when fully assembled, switch 40 itself provides a secure, sealed interface with camera head housing 44 without the need for adhesive or additional mounting hardware. Further, there are no cracks or crevices between button 68 and camera housing 44 within which dirt or other contaminants could accumulate. Camera head 14 can then be sterilized (repeatedly, as necessary over its operating lifetime) without fluid or gas leakage at the switch 40 interface.

As shown in particular in Fig. 5, switch 40 is also a thin device, requiring only a shallow recess 56 in camera head housing 44. For example, with the components described above, recess 56 need have a depth D between shelf 57 and upper surface 51 of housing wall 46 of only 3.8mm (0.150 inches). The depth to surface 49 is 2.70mm (0.105 inches), and circuit board 60 is 0.77mm (0.030 inches thick), which leaves a space of 0.38mm (0.015 inches) for snap dome 64. Preferably, the lower surface of button post 78 just touches the upper surface of snap dome 64 (which minimizes the required amount of travel of button 68).

During an endoscopic procedure, switch 40 is used to control any desired operating parameter of system 10 (Fig. 1). As discussed, switch 40a is used to control video accessories (such as monitor 32, VCR 33, and printer 34), while switch 40b controls various camera functions (such as shutter speed, automatic gain control, white balance, etc.). The user actuates switch 40 simply by pressing down on and then releasing button 68. When button 68 is depressed, post 78 (Fig. 5) deflects snap dome central region 66 downwardly, thereby electrically interconnecting contacts 61a, 61b and closing switch 40. Snap dome 64 returns to its original position and opens switch 40 when the user releases button 68.

Camera processor 30 senses closing (and subsequent opening) of switch 40 via wires 63 and cable 28 and responds by performing the appropriate processing function. For parameters that are adjusted incrementally (such as camera shutter speed), the user simply repeatedly depresses and releases switch 40 for each desired incremental change in the operating parameter.

The tight interference fit that retaining ring 84 makes with button 68 and housing wall 46 blocks contaminants from entering recess 56 when the user actuates switch 40. Ferrule 82 helps maintain the integrity of the interference fit if the user applies excessive force to button 68 or presses button 68 from the side rather than vertically (e.g., diagonally from corner 71 between upper wall 70 and side walls 72 of button 68). That is, because ferrule 82 is disposed in channel 80 against button side walls 72 and is made from a stiff material (relative to button 68), ferrule 82 prevents side walls 72 from pulling inwardly away from retaining ring 84 in response to sideways pressure. Moreover, upper surface 85 of ferrule 82 supports button 68 if the user applies excessive pressure to button 68, and thus prevents button 68 from collapsing within recess 56.

Other embodiments are within the scope of the following claims.

For example, camera head 14 may include more or fewer than two switches 40a, 40b, as desired. Indeed, because of its reduced size and lack of external mounting hardware, switch 40 is ideally suited for applications in which space is at a premium. Thus, more than two switches 40 can be mounted on even relatively small devices such as camera head 14. Switches 40 can control other functions of system 10, and in fact the function of switches 40 can be programmable via, e.g., camera processor 30.

Either (or both) switches 40 can alternatively be connected to CCD control circuitry 26 to control CCD 24 directly or to adjust another function of camera head 14.

Switches 40 can be mounted directly on endoscope 12. This configuration is particularly useful when endoscope 12 is an electronic endoscope, in which the camera is disposed at the distal tip of insertion tube 16. In this case, there is no need for a separate camera head; rather, endoscope proximal end 13, which is integral with the remainder of endoscope 12, provides the base in which switches 40 are secured. One example of an electronic endoscope is described in EP 0592194 entitled "Endoscope with Focussing

Mechanism," filed on October 9, 1992 by Jed Kennedy, assigned to the present assignee.

Switches 40 can be used on devices other than endoscopes and camera heads. For example, switches 40 can be used on a motorized handpiece for a powered surgical instrument. For devices such as these, which are often sterilized by autoclaving, the switch components should be selected to withstand the autoclaving process. An example of a powered surgical instrument handpiece is described in copending patent application serial no. 08/630,537, entitled "Surgical Instrument Handpiece and System," filed on April 10, 1996 by Douglas Sjostrom et al., assigned to the present assignee.

The relative positions of groove 49a and ridge 76a can be reversed. That is, the groove can be formed as a surface feature on the underside of flange 74 to receive a complementary ridge on recess surface 49.

Claims

1. An electrical switch configured to be secured within a recess defined by a wall in a base, comprising a switching element, an actuator for said switching element, a portion of said actuator being disposed in the recess and radially spaced from the wall, and a retainer radially disposed between and engaging said portion of said actuator and the wall to provide an interference fit between said actuator and the base.

2. The electrical switch of claim 1 wherein said actuator includes a sealing surface, said retainer engaging said actuator to compress said sealing surface against a portion of the recess wall.

3. The electrical switch of claim 1 wherein said actuator includes a body having an upper wall engaged by a user to actuate said switching element and an axially-extending side wall, said retainer engaging said side wall to provide said interference fit.

4. The electrical switch of claim 3 wherein said side wall terminates at a sealing surface oriented radially with respect to said side wall, said retainer engaging said actuator to compress said sealing surface against a radial portion of the recess wall.

5. The electrical switch of claim 4 wherein said side wall terminates at a radially-extending flange, said sealing surface being disposed on an underside of said flange and said retainer engaging an upper side of said flange to compress said sealing surface against the radial portion of the recess wall.

6. The electrical switch of claim 5 further comprising a surface feature on said sealing surface configured to engage a complementary feature on the radial portion of the recess wall.

7. The electrical switch of claim 6 wherein said surface feature includes a ridge.

8. The electrical switch of claim 3 wherein said body is circular, said retainer comprising a ring that surrounds said body.

9. The electrical switch of claim 3 wherein said body includes an axially extending post on an underside of said upper wall and positioned to actuate said switching element when said actuator is depressed by a user.

10. The electrical switch of claim 9 wherein said post is radially spaced from said side wall, and further comprising a support member disposed therebetween.

11. The electrical switch of claim 10 wherein said body is circular and includes an annular channel radially between said post and said side wall, said support member comprising an annular ferrule disposed in said channel.

12. The electrical switch of claim 3 wherein said body is made from an elastomeric material.

13. The electrical switch of claim 1 wherein said actuator and said retainer are made from materials selected to withstand sterilization and disinfection.

14. The electrical switch of claim 1 wherein said switching element includes a conductive member disposed adjacent to a pair of electrical contacts, said actuator being positioned to, when actuated by a user, move said conductive member from a first position, in which said conductive member isolates said electrical contacts from each other, to a second position, in which said conductive member interconnects said electrical contacts.

15. The electrical switch of claim 14 wherein said conductive member is resilient to resume said first position when the user releases said actuator.

16. A device for use in an endoscopic system, comprising a housing for attachment to an endoscope and for connecting the endoscope to a processor for causing an optical image received by the endoscope to be displayed, an electrical switch secured within a recess defined by a wall in said housing and including a switching element connectable to the processor for controlling an operating parameter of said endoscopic system, an actuator for said switching element, a portion of said actuator being disposed in said recess and radially spaced from the wall, and a retainer radially disposed between and engaging said portion of said actuator and said wall to provide an interference fit between said actuator and said housing.

17. The device of claim 16 wherein said device comprises a camera head constructed to be attached to the endoscope.

18. The device of claim 16 wherein said device is a portion of the endoscope.

19. The device of claim 16 further comprising multiple said electrical switches secured within corresponding recesses in said housing.

20. The device of claim 16 wherein said recess is circular, said actuator comprising a circular body and said retainer comprising a ring disposed around said body.

21. The device of claim 20 wherein said body includes a sealing surface, said retainer engaging said actuator to compress said sealing surface against a portion of the recess wall.

22. The device of claim 21 wherein said body has an upper wall engaged by a user to actuate said switching element and an axially- extending side wall that terminates at a sealing surface oriented radially with respect to said side wall, said retainer engaging said side wall to provide said interference fit and engaging said sealing surface to compress said sealing surface against said portion of the recess wall.

23. The device of claim 16 further comprising a camera for producing electrical signals representative of an image of an object observed by the endoscope, said operating parameter being an operating parameter of said camera.

24. The device of claim 16 wherein said operating parameter is an operating parameter of an image display device associated with the processor.

25. A camera head for use with an endoscope, comprising a housing for attachment to the endoscope, a camera disposed within said housing for producing electrical signals representative of an image of an object observed by the endoscope, and an electrical switch secured within a recess defined by a wall in said housing and including a switching element for providing a control signal for an operating parameter of said camera, an actuator for said switching element, a portion of said actuator being disposed in said recess and radially spaced from the wall, and a retainer radially disposed between and engaging said portion of said actuator and said wall to provide an interference fit between said actuator and said housing.