Abstract:
An avionics LRU having multiple circuit cards therein which are arranged in readily accessible slots and have insertion/extraction apparatuses coupled thereto which use a rack and pinion arrangement to provide a relatively high insertion force over an increased displacement.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to aviation electronics, or avionics, and more particularly relates to multi-card avionics boxes, and even more particularly relates to a system and method for extracting circuit cards from avionics boxes having blind mated circuit cards therein. 
     BACKGROUND OF THE INVENTION 
     In the past, designers of avionics systems have endeavored to provide systems with improved reliability and improved serviceability. One crucial element in such systems has been the use of spare component parts, including field replaceable spare circuit cards. These field replaceable circuit cards allow for repair of avionics equipment without extended downtimes which are often associated with sending an avionics LRU to a service center for repair. One common method of assisting in quick removal of circuit cards has been the use of pivoting cam extractors, which are attached to the circuit card and pivoted to create a camming action, causing motion of the circuit card away from a connector in the LRU. 
     While these pivoting camming extractors have many advantages, often including low cost and ease of manufacture, they also have significant drawbacks. 
     First of all, the pivoting camming extractors often result in extraction or insertion forces which have significant components in directions other than the desired direction of insertion or extraction. 
     Secondly, the insertion and extraction forces often approach or exceed the force limits of these cam extractors, especially with circuit cards having high pin counts and limited displacements. Consequently, there exists a need for improvement in systems and methods for inserting and extracting circuit cards. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide enhanced reliability for avionics boxes having extractable circuit cards therein. 
     It is a feature of the present invention to include a multi-tooth rack and pinion arrangement. 
     It is an advantage of the present invention to reduce the undesired extraction forces in a direction other than the primary direction of travel of the circuit card during the insertion and/or extraction process. 
     It is another advantage of the present invention to increase the mechanical advantage of the extractor for generating strong insertion and extraction forces required for circuit cards with high pin counts, and at the same time, maintaining or increasing the displacement insertion or extraction. 
     It is yet another advantage of the present invention to improve the reliability of avionics boxes by reducing pin damage during insertion. 
     The present invention is an apparatus and method for inserting circuit cards in circuit card cases, such as, but not limited to, avionics LRUs, which are designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features, and achieve the already articulated advantages. The present invention is carried out with a “cam-less extractor” in a sense that the amount of undesired pivoting of the circuit card during insertion and extraction has been greatly reduced. 
     Accordingly, the present invention is a system and method for inserting and extracting circuit cards from a case by use of a multi-toothed rack in association with a pivoting toothed member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more fully understood by reading the following description of the preferred embodiments of the invention, in conjunction with the appended drawings wherein: 
     FIG. 1 is a simplified perspective diagram of an extractor and environment of the prior art. 
     FIG. 2 is a perspective view of a pair of extractors of the present invention, together with the environment in which they would be used. 
     FIG. 3 is an enlarged perspective view of an extractor of the present invention in a disengaged state. 
     FIG. 4A is a side view of an extractor of FIG. 2 shown disposed in a disengaged state. 
     FIG. 4B is a side view of an extractor of FIG. 2 shown disposed in a state intermediate of that shown in FIGS. 2 and 3, and intermediate of that shown in FIGS. 4A and 4C. 
     FIG. 4C is a side view of an extractor of FIG. 2 shown disposed in a state intermediate of that shown in FIGS. 2 and 3, and intermediate of that shown in FIGS. 4B and 4D. 
     FIG. 4D is a side view of an extractor of FIG. 2 shown disposed in an engaged state. 
     FIG. 5 is a cutaway view of portions of an aircraft of the prior art. 
    
    
     DETAILED DESCRIPTION 
     Now referring to the drawings, wherein like numerals refer to like matter throughout, and more particularly to FIG. 1, there is shown a system of the prior art, generally designated  100 , which includes a circuit card  101  for insertion into an avionics box, not shown. A lever handle  102  is coupled through lever handle pivot pin  104  to circuit card  101 , and a camming action occurs when lever handle  102  pivots about lever handle pivot pin  104  and lever handle tooth  106  engages chassis rack  110  with a chassis rack tooth  112  thereon. These camming extractors are well known in the art. 
     Now referring to FIG. 2, there is shown an avionics box  200  of the present invention having a chassis slot  220  therein for coupling with a circuit card  201 . Coupled to circuit card  201  is a lever handle  202 . FIG. 2 shows the circuit card  201  having bottom and top extractors which are preferably identical to each other and are disposed adjacent to avionics box bottom  226  and avionics box top  228  respectively. The description herein is equally applicable to either the top or bottom of circuit card  101 . Lever handle  202  pivots about lever handle pivot pin  204 , thereby causing lever handle first tooth  206  to interact with chassis rack member  210  and chassis rack member first tooth  212  thereon. Circuit card  201  is shown in a chassis slot  220 . Two chassis slots are shown; however, it should be understood that numerous chassis slots may be included depending upon the particular design requirements. Circuit card  201  slides through a rack slot  222 , which is an interstice between adjacent chassis rack members  210  and then is further slid into chassis slot  220 . 
     Now referring to FIG. 3, there is an enlarged perspective view of the apparatus of FIG. 2, showing additional detail. The apparatus is shown in a disengaged state, meaning that the circuit card  201  is free to slide in chassis slot  220  because there is no contact between lever handle first tooth  206 , lever handle second tooth  207 , and lever handle third tooth  208  and the chassis rack member  210 . Together lever handle first tooth  206 , lever handle second tooth  207 , lever handle third tooth  208 , and lever handle  202  may be viewed as a pinion for cooperation with a rack. Chassis rack member  210  is shown having a chassis rack member first tooth  212 , which is preferably wider than chassis rack member second tooth  214  and chassis rack member third tooth  216 . The purpose of the extra width of chassis rack member first tooth  212  is to assure that proper alignment of lever handle first tooth  206  occurs with respect to the chassis rack member  210 . Chassis rack member first tooth  212  is of sufficient girth that it will mesh with initial lever handle gap  209 , but it will not mesh with second lever handle gap  211 . This prevents a situation where circuit card  201  might otherwise be inserted into chassis slot  220  while lever handle  202  is already disposed in a partially closed orientation where one of lever handle second tooth  207  or lever handle third tooth  208  might have been the initial gear tooth which meshes with chassis rack member  210 . This would typically result in an insertion of circuit card  201  to a point which is less than a normal full insertion. Chassis rack member fourth tooth  218  is included for assistance in extraction of said circuit card  201 . Lever handle first tooth  206 , lever handle second tooth  207 , and lever handle third tooth  208  may have a lever handle gear tooth width dimension  224  which is in excess of a width characteristic of rack slot  222 , so that lever handle first tooth  206 , lever handle second tooth  207 , and lever handle third tooth  208  are capable of engaging adjacent chassis rack members  210  (see FIG.  2 ). Circuit card  201  has a predetermined level of insertion forces and displacement necessary to fully insert circuit card  201  via chassis slot  220  into avionics box  200 . The pitch radius  230  is designed to provide the appropriate level of mechanical advantage to result in the necessary insertion forces. The dimensions of lever handle radius  232  and pitch radius  230  are effectively matched to the predetermined level of necessary insertion forces for said circuit card  201 . 
     In operation, and now referring to FIGS. 4A-4D, the present invention operates as follows: 
     Circuit card  201  is inserted into chassis slot  220  with lever handle  202  disposed as shown in FIG.  4 A. Lever handle first tooth  206  is not yet meshed with chassis rack member  210 . As lever handle  202  is progressively raised through positions shown in FIG.  4 B and FIG. 4C, circuit card  201  is caused to translate along chassis rack member  210  until it reaches its desired location when lever handle  202  is disposed as shown in FIG.  4 D. The details of dimensions and relative locations of the various parts of the apparatus of the present invention are expected to be tailored in well-known ways to accommodate predetermined levels of insertion forces and predetermined levels of mechanical advantage and displacement. 
     Now referring to FIG. 5, there is shown a cutaway view of an aircraft of the prior art, generally designated  500 , having a cutaway portion  501  exposing a structural frame  502  and an avionics rack  504  having at least one avionics receiving station  506  therein for receiving a typical avionics line replaceable units (LRUs) or an avionics box  200  of the present invention, which preferably has connectors thereon which are similar, if not identical, to connectors for coupling prior art avionics LRUs with avionics rack  504 . The present invention is described herein in an aviation and avionics environment because it is believed that the beneficial aspects of the invention will be readily appreciated in such an environment. However, it should be understood that the circuit card insertion apparatus and slots, etc. of the present invention, can be used in any type of electronics equipment, and it is the intention of the present invention to include these other non-avionics equipment types. 
     It is thought that the method and apparatus of the present invention will be understood from the foregoing description and that it will be apparent that various changes may be made in the form, construct steps, and arrangement of the parts and steps thereof without departing from the spirit and scope of the invention or sacrificing all of their material advantages. The form herein described is merely a preferred exemplary embodiment thereof.