Patent Application
20080086033
Referring to
For the purposes of this disclosure, the term “hermetic life” refers to the number of autoclaving cycles to which a device can be exposed while maintaining an acceptable hermetic level, for example, enduring a helium leak test at one atmosphere differential pressure with a leak rate less than or equal to about 1×10−9 cubic centimeters of helium per second (cc/s He), where an autoclaving cycle is defined as an exposure to saturated steam at a temperature of about 137° C. for a period of about thirty minutes.
Explosion welding—also referred to as explosion bonding or cladding; or explosive welding, bonding or cladding—permits the joining of dissimilar metals, including metals with highly differing properties. Explosion welding is a nonconventional solid-state welding process by which flat metal plates or concentric cylinders are joined by the controlled force of explosives. In contrast to conventional welding methods, the base metals are not melted during explosion welding; instead, a progressive detonation force accelerates one or both of the plates into each other, resulting in a high-velocity, high-interfacial-pressure impact [e.g., about 5,000 to about 7,000 feet per second (ft/s) and about 100 to about 600 thousand pounds per square inch (kpsi)] that forms a durable, high-strength metallurgical bond between the two base metals.
Generally, a layer of explosive material such as a plastic explosive (e.g., ammonium nitrate) is placed over a surface of a cladding plate, which is separated by a small stand-off distance from an adjacent, base plate that is resting on an anvil plate. Then, the explosive material is detonated from one edge of the cladding plate. As the detonation front progresses across the cladding plate, the cladding plate is thrust toward the base plate and a metal surface plasma jet is ejected ahead of the collision front between the two plates, effectively removing oxides and contaminants from the two surfaces, which allows bonding between dissimilar metals that cannot be welded by conventional means. Thus, explosion welding is used to join metals such as aluminum, copper, nickel, alloys containing these metals, stainless steel, Kovar, low-carbon steel, or iron-nickel alloys, or the like to dissimilar metals such as aluminum, copper, nickel, alloys containing these metals, stainless steel, Kovar, iron-nickel alloys, titanium, molybdenum, zirconium, tantalum, niobium, or the like.
In addition, a metal plate can be explosion welded to a dissimilar metal in order to form a bridge that can be used to bond or join additional components that are composed of one or both of the metals, or additional components that are composed of other metals that can be joined to the two metals by conventional means. For example, a stainless steel plate can be explosion welded to an aluminum plate to form a joint, after which an aluminum component can be conventionally welded to the aluminum plate and a stainless steel component can be conventionally welded to the stainless steel plate. Similarly, as another example, a stainless steel plate can be explosion welded to a flat surface of an aluminum component, after which the composite component can be machined and an additional stainless steel component can be conventionally welded to the surface of the stainless steel plate.
As depicted in
However, some higher-thermal-conductivity metals and other materials having relatively high thermal conductivity, for example, greater than about 25 W/m K, including aluminum, cannot be welded to stainless steel by conventional welding techniques because of dissimilar properties with respect to stainless steel. For example, the bridge 28 made from stainless steel cannot be welded to the housing 26 made from aluminum using conventional welding. Thus, explosive welding is employed at an interface 27 between the bridge 28 and the housing 26.
The endoscopic system 24 further includes an imaging device in the form of the video camera head 22, or endocamera, to produce a digital electronic image from an optical image of a target subject transmitted by way of an endoscope 32, a light source 34, a digital image processor 36 and a display 38. The light source 34 can be coupled to the endoscope 32 by an optical link 40, for example, a fiber optic cable, to illuminate the target subject under observation beyond the tip of the endoscope 32. In addition, the video camera head 22 can be optically coupled to the endoscope 12 by a coupler 42 to receive an optical image, and electrically coupled to the image processor 36 by an electrical link 44 to transmit a resulting digital image. The image processor 36 can perform signal processing to further refine the digital image, which can then be transmitted by way of another electrical link 46 for display on the display 38, for example, a cathode ray tube (CRT) display or flat panel liquid crystal display (LCD).
As shown in
In order to protect the electronic components 48 of the video camera head 22 during autoclaving, the housing 26 is made from materials having substantial resistance to steam corrosion. The housing 26 is hermetically sealed to the bridge 28 and the bridge 28 is hermetically sealed to the window 30 via the methods as mentioned above. The resulting hermetically-sealed video camera head 22 can withstand numerous repeated autoclave cycles, for example, between about one hundred cycles and about one thousand cycles, greater than about one hundred cycles, greater than about two hundred fifty cycles, greater than about five hundred cycles, greater than about one thousand cycles, or more cycles.
Furthermore, in order to accommodate video camera electronic components 48 that generate heat energy at a relatively high rate compared to some standard video cameras, the housing 26 is composed of a material with relatively high thermal conductivity, for example, greater than about 25 Watts per meter kelvin (W/m K), such as aluminum or an aluminum alloy. As a result, the housing 26 dissipates heat at a rate sufficient to maintain an internal ambient at an acceptable working temperature for the electronic components 48. In addition, aluminum or an aluminum alloy provides a relatively light-weight, low-cost housing 26 with favorable machining properties.
Similarly, the optical window 30 not only has acceptable optical characteristics, but also is able to withstand repeated autoclaving cycles. Thus, the optical window 30 includes an optical ceramic material that is highly transparent and resistant to steam etching, such as optical sapphire (monocrystalline aluminum oxide, or alumina, Al2O3).
Referring to
A hermetic seal 58 is formed between the optical element 56 and the mount 54 by way of a brazing or soldering process, and a hermetic seal 59 is formed between the mount 54 and the bridge 28 by way of a conventional welding process, such as laser welding. Another hermetic seal 60 is formed at the bond interface 62 coupling the main body 50 and the front body 52 by way of a conventional welding process, such as laser welding. An additional hermetic seal 64 is formed at the bond interface 66 coupling the bridge 28 and the front body 52 by way of explosion welding. In this manner the dissimilar metals comprising the housing 26 and the mount 54 are effectively hermetically joined by way of the bridge 28, facilitating the hermetic joining of the mount 54 to the optical element 56 in order to form the complete hermetically-sealed autoclavable video camera head 22.
Referring to
A hermetic seal 58 is formed between the optical element 56 and the mount 54 by way of a brazing or soldering process, and a hermetic seal 76 is formed between the mount 54 and the front body 74 by way of a conventional welding process, such as laser welding. Another hermetic seal 82 is formed at the bond interface 84 coupling the front body 74 and the bridge member 70 by way of a conventional welding process, such as laser welding. An additional hermetic seal 86 is formed at the bond interface 88 coupling the bridge member 70 and the main body 72 by way of explosion welding. In this manner, the metal comprising the bulk of the housing 26 (that is, the main body 72) is effectively hermetically joined to the dissimilar metal of the front body 74 and the mount 54 by way of the bridge 70, facilitating the hermetic joining of the mount 54 to the optical element 56 in order to form the complete hermetically-sealed autoclavable video camera head 22.
Then, in step 92, the bridge and the front housing are machined to provide an opening for a window to allow an optical image to pass into the interior of the video camera housing. Next, in step 94, a hermetic joint is formed by way of soldering or brazing at an interface between an optical element, which is composed of an optical ceramic material such as sapphire, and the mount.
Subsequently, in step 96, a hermetic joint is formed by way of a bonding method, such as laser welding, at an interface between the mount and the bridge. Then, in step 98, a hermetic joint is formed by a bonding method, such as laser welding, at an interface between the front body and a main body of the video camera housing, which is also composed of the high-thermal-conductivity metal.
Then, in step 102, the main body and the bridge are machined to provide a partial housing of the video camera housing. Next, in step 104, the optical element, which is composed of sapphire, is brazed to the mount, which is composed of the dissimilar metal, such as stainless steel. Subsequently, in step 106, a hermetic seal is formed by means such as laser welding at an interface between a window mount and the front body, which are composed of the dissimilar metal. In this implementation, the front housing has been previously machined in a preliminary process to provide an opening for a window to allow an optical image to pass into the interior of the video camera housing. Next, in step 108, a hermetic joint is formed by a bonding method, such as laser welding, at an interface between the front body of the housing and the bridge member.
Additionally, alternative implementations of the autoclavable video camera head and method of manufacture include an optical element composed of any suitable natural or synthetic optical ceramic material, for example, sapphire, spinel (magnesium aluminum oxide, MgAl2O4), nitrogen-stabilized aluminum oxide (aluminum oxynitride or ALON™, Al23O27N5), or the like. Moreover, alternative implementations include a housing partially or wholly composed of any suitable material having relatively high thermal conductivity, for example between about 25 W/m K and about 100 W/m K, greater than about 25 W/m K, greater than about 50 W/m K, greater than about 100 W/m K, or more. Examples of materials having relatively high thermal conductivity include aluminum (Al), copper (Cu), silver (Ag), gold (Au) and alloys of these metals, such as bronze, phosphor bronze, brass, constantan and 2024-T6, 6061 and 4047 aluminum alloys.
It will be understood that various modifications may be made. For example, useful results still could be achieved if steps of the disclosed techniques were performed in a different order and/or if components in the disclosed systems were combined in a different manner and/or replaced or supplemented by other components. Accordingly, other implementations are within the scope of the following claims.
