1. Field of the Invention
This invention relates to an apparatus and a method for sensing the position of a device on a cassette, more particularly for sensing the position of the cassette handling apparatus on a cassette holding liquid sterilant.
2. Description of the Related Art
U.S. Pat. No. 4,643,876, incorporated herein by reference, discloses a sterilization system in which a vaporizable germicide, such as hydrogen peroxide, is introduced into an evacuated sterilization chamber. The vaporizable germicide vaporizes and is allowed to disperse throughout the chamber and onto the items to be sterilized. After a desired period of time electrical energy is applied to an electrode to form a plasma to complete the sterilization cycle.
This system has been successfully commercialized as the STERRAD(copyright) Sterilization System and is available from Advanced Sterilization Products, a Division of Ethicon, Inc., Irvine, Calif. The system is used in hospitals and other environments where it is operated repeatedly throughout the day by personnel having a widely varying range of understanding of the apparatus. In order to insure safeguards in the event of operator error, the system employs an automated delivery system for delivering the liquid vaporizable germicide to the sterilization chamber. Measured portions of the liquid germicide, for example hydrogen peroxide, are provided in rupturable cells within a rigid cassette housing. The cassette and operation of the delivery system are more fully described in the Williams et al. patents, U.S. Pat. No. 4,817,800 issued Apr. 4, 1989; U.S. Pat. No. 4,913,196 issued Apr. 3, 1990; U.S. Pat. No. 4,938,262 issued Jul. 3, 1990; and U.S. Pat. No. 4,941,518 issued Jul. 17, 1990, all of which are incorporated herein by reference. In the above-referenced patents, the operator manually grasps the cassette housing and inserts it into the sterilizer. When spent, the cassette is ejected.
Prior methods of sterilization utilized heat, steam, or toxic, flammable chemicals, such as ethylene oxide. Heat or steam can damage delicate medical equipment. Use of toxic chemicals for sterilization poses risks to workers. Sterilization of equipment with hydrogen peroxide and plasma with the cassette system provide many advantages over the prior sterilization systems. The hydrogen peroxide and plasma kill a wide range of bacteria, viruses, and spores at low temperatures, minimizing the chance of damaging delicate temperature-sensitive instruments. Further, hydrogen peroxide decomposes to water and oxygen after exposure to plasma, avoiding the need to dispose of any toxic byproducts. Finally, the cassette isolates the operator from the liquid hydrogen peroxide in the cells in the cassette.
U.S. Pat. No. 5,882,611 issued Mar. 16, 1999 and U.S. Pat. No. 5,887,716 issued Mar. 30, 1999 to Williams et al., herein incorporated by reference, describe an improved cassette and delivery system, in which the cassette is encased in a protective sleeve. The sleeve isolates the cassette from the operator""s hands during all stages of handling and absorbs any drops of liquid hydrogen peroxide which might be left on the exterior of the spent cassette, protecting the operator from contact with any sterilant which escapes from the cassette. The delivery system automatically extracts the cassette from the sleeve, delivers the liquid germicide to the sterilization chamber, and reinserts the spent cassette into the sleeve, all without any handling by the operator. Further, the delivery system checks the cassette before processing to insure that the cassette is not already used or that the cassette is expired.
Although the delivery system described in U.S. Pat. No. 5,882,611 offers many advantages over the previous delivery systems, opportunities for improvement remain. The delivery system is complex and expensive. Further, the delivery system depends on a timer to determine which cell is in the injector rather than directly sensing the position of the cassette in the delivery system.
There is thus a need for a delivery system which is simpler and less expensive than the previously described systems while retaining the advantage of minimizing operator handling. Further, there is a need for a delivery system in which the position of the delivery system and injection system on the cassette may be determined with more certainty than simply relying on a timer.
The cassette sensing mechanism and delivery system of the present invention provide a positive indication of the location of the cassette in the delivery and injection system. Further, the delivery system is far less complex than the previous delivery system. Finally, the delivery system of the present invention retains the advantages of the prior delivery and injection system in extracting the cassette from a sleeve, delivering the liquid sterilant to the sterilization chamber, and reinserting the spent cassette into the sleeve without the requirement for operator intervention.
One aspect of the invention involves a sensing mechanism for detecting the unevenness of a surface on a device, where there is at least a first path and a second path on the surface. The sensing mechanism contains at least one connector, a first pawl, a second pawl, and a sensor mounted on the first pawl or the second pawl. The first end of the first pawl is connected to the connector in a manner allowing movement of the first pawl and the second end of the first pawl contacts a portion of the first path on the surface. The first end of the second pawl is connected to the connector in a manner allowing movement of the second pawl and the second end of the second pawl contacts a portion of the second path. The sensor detects the position of the first pawl relative to the second pawl.
Advantageously, the first path and said second path are noncoincident. Preferably, the device is a cassette. In an embodiment, the cassette contains germnicide. Advantageously, the germicide contains hydrogen peroxide. Preferably, the connector is a pivot, where the first pawl and said second pawl rotate about the pivot. Advantageously, the movement of the first pawl and the second pawl is due to gravity. In another embodiment, the movement of the first pawl and the second pawl is due to one or more springs.
The unevenness of the surface may be on the top, bottom, or side of the device. The sensor may be a photoelectric sensor, an electromechanical sensor, or a proximity sensor. Advantageously, the first path is adjacent to second path. Preferably, the mechanism also contains a control unit.
Another aspect of the invention involves a sensing mechanism for detecting the position of a cassette having a first path and a second path, where the first path has at least one groove and the second path is relatively smooth. The mechanism includes at least one connector, a first pawl, a second pawl, and a sensor mounted on the first pawl or the second pawl. The first end of the first pawl is connected to the connector in a manner allowing movement of the first pawl and the second end of the first pawl contacts a portion of the first path on the surface. The first end of the second pawl is connected to the connector in a manner allowing movement of the second pawl, while the second end of the second pawl contacts a portion of the said second path. The sensor detects the position of the first pawl relative to the second pawl, to detect the position of the cassette.
Preferably, the cassette contains germicide. Advantageously, the germicide is hydrogen peroxide. Preferably, the connector is a pivot, where the first pawl and said second pawl rotate about the pivot. In an embodiment, the movement of the pawls is due to gravity. In another embodiment, the movement of the pawls is due to a moving mechanism, such as a hydraulic mechanism, pneumatic mechanism, or one or more springs.
Another aspect of the invention involves a method for positioning a cassette for injection of germicide to a sterilization system. The method includes providing a cassette with a surface having a first path and a second path, where the first path has at least one groove and the second path is relatively smooth. The method also includes providing a sensing mechanism having at least one connector, two pawls connected to the connector in a manner allowing movement of the pawls, and a sensor mounted on one of the pawls. The method also includes inserting the cassette into the sensing mechanism in the sterilization system. The end of one pawl contacts a portion of the first path on the surface of the cassette and the end of the other pawl contacts a portion of the second path on the surface of the cassette. The relative position of the two pawls is determined with the sensor, thereby determining the position of the end of the pawl on the first path on the surface of the cassette. The method also includes moving the cassette until the pawl contacts the groove in the first path on the surface of the cassette, positioning the cassette for injection of germicide into said sterilization system.
Advantageously, the determining and moving steps are repeated. Preferably, the cassette contains germicide. In an embodiment, the method also includes injecting the germicide into the sterilization system. Preferably, the sensor is a photoelectric sensor, an electromechanical sensor, or a proximity sensor. Advantageously, the first path and the second path are noncoincident. Preferably, the germicide is hydrogen peroxide.