Abstract:
A mechanism that prevents premature disengagement of a component from a computer system is provided. Through a graphical user interface, the user signals to logic associated with the computer system to ready a component for removal from the computer system chassis. A trigger recessed in a handle is depressed to mechanically free the handle to pivot from the engaged position outward. The trigger activates a lock, which is coupled to logic associated with the computer system, which is capable of deactivating the lock. The lock prevents disengagement of the component from the computer system by preventing a handle arm, to which the handle is attached, from pivoting outward. When the lock is deactivated, the handle arm is actually free to pivot. When pivoting, the handle arm engages a hub, which rotates as the handle arm pivots. The hub is coupled to a first lever arm which moves and pivots a first engagement member. This engagement member may include a catch which engages insertion and extraction stops mounted on the chassis of the computer system. In one aspect of the invention, the action of the first lever arm and first engagement member may be substantially balanced by a second lever arm and second engagement member. In another aspect of the invention, an indicator light may be provided on or proximate to the component, to signal the user which component is ready for removal, decreasing the chance that the wrong component will be removed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mechanical and electrical apparatus for connecting and disconnecting components of a computer system. More particularly, the present invention relates to a mechanism engaging and disengaging components from the system while it is operating. 
     2. Description of Related Art 
     Computer systems such as file servers and storage servers in computer networks are relied upon by large numbers of users. When a file server or storage server is out of operation, for example, because of maintenance or service, many people are inconvenienced. Thus, technology has been developed which supports maintenance and service of computer systems while they remain operational. One part of maintenance and service includes the replacement of components. So-called “hot swap” technology allows the replacement of components without turning off the power or resetting the computer system as a whole. 
     Typical hot swap technology employs resources for signaling the system and components in the system about an intention to remove or replace a component. Also, the technology includes routines that stabilize communications among the components, and manage the distribution of power to components during the exchange. 
     The exchange of components on computer systems for maintenance and repair requires human operators. Human operators are prone to misuse or abuse the mechanical and electrical resources associated with hot swap technology. For example, an operator may attempt to withdraw a component from a computer chassis without first executing hot swap electrical routines to prepare the component. Also, when a system includes multiple interchangeable components, an operator may attempt to remove the wrong component. 
     Therefore, is desirable to provide a mechanism that reduces the possibility of misuse or abuse by human operators of mechanisms for engaging and disengaging components, and mechanisms for managing the electrical hot swap processes. 
     SUMMARY OF THE INVENTION 
     The present invention provides a mechanism that prevents premature disengagement of components the computer system. An indicator shows that a component is ready to be removed and positively identifies which of multiple identical components should be removed. The mechanism is able to block attempted removal of the wrong component or of a component if the electrical processes necessary for hot swap have yet to complete. Thus, for a component that is ready to be removed, an operator expects to apply a relatively light force to remove or insert the component. The light force applied minimizes the chance of mechanical damage to the system. The result is a substantially more reliable system, that is less prone to damage during hot swap operation and less prone to removal of the wrong component. 
     In one embodiment, the present invention includes a module for a computer system, the system including a chassis having at least one compartment for accepting the module, and processing resources, comprising: a carrier adapted to fit within the compartment in the chassis with a component mounted inside; a connector adapted to mate with a corresponding element in the computer chassis upon engagement of the module; and means, coupled with the carrier, for engaging and disengaging the component with the system. In various embodiments, the means for engaging may leverage an insertion force applied to the carrier to mate the connector with the corresponding elements in the chassis. It may include a pivotal handle arm coupled to the carrier defining a travel guide; a rotatable hub coupled with the carrier having a protrusion which engage the travel guide; a first lever arm, coupled between the hub and a first engagement member, the engagement member positioned near the lateral edge of the carrier to engage the chassis when the handle arm is moved to an inserted position. The movement of the handle arm toward the inserted position rotates the hub and directs the first lever arm to rotate the engagement member to engage the chassis. The first engagement member may include a catch which engages insertion and extraction stop mounted on the chassis. 
     In a further aspect of the present invention, the first lever arm and first engagement member may be mirrored by a second lever arm coupled to the hub and a second engagement member coupled to the second lever arm. These elements positioned on opposing lateral edges of the carrier may form a structure adapted to apply a substantially balanced force. 
     Another feature of the present invention includes a lock in communication with the processing resources which prevents disengagement of the carrier absent an enable signal provided by the processing resources. 
     An alternative embodiment of the present invention is an assembly for engaging a component to a computer system, the assembly comprising: a carrier adapted to retain the component and to be inserted within the chassis of the computer system; a handle arm coupled to the carrier; a detector coupled to the carrier and the handle arm, the detector detecting movement to actuate a lock; and a lock blocking movement of the carrier when engaged. This embodiment may further include logic associated with a computer system and coupled to the lock to selectively override the detector and de-actuate the lock when the component is ready for removal. The detector may provide a signal to actuate the lock and the logic may provide a control signal to selectively de-actuate the lock. In addition, there may be a handle mounted on the handle arm and a trigger mounted on the handle, the trigger having a released position in which it is biased and a depressed position, the trigger applying a force to the detector when the trigger is in its released position. In an embodiment, the detector is coupled to the trigger by a detector surface having a biased distal end that extends to meet the trigger, the biased distal end having a raised position in which it is biased and a depressed position, the biased distal end being coupled to actuate the lock when in its raised position. 
     An aspect of the invention is that the lock alternatively comprises a cam and a solenoid or it comprises a solenoid secured to the carrier and having a rod, the rod being slidable between an extended position in which it is biased and a retracted position, and a cam secured to the handle arm and movable between a locked position for resisting movement of the handle arm and an extended position, the cam adapted to engage the rod and move into the unlocked position when the rod is in the extended position. The cam may be pivotal in a plane that is substantially parallel to the handle arm. The logic should include resources for receiving a request to remove component and resources for determining whether the component is ready for removal from the computer system. Preferably, the logic is coupled to a graphic user interface. The logic may includes resources for enabling an indicator light proximate to the component being removed to signal when the component is ready for removal. 
     In another embodiment, the present invention includes an assembly for engaging a component to computer system, comprising: a carrier having a front end and a back end, adapted to retain the component and to be inserted within the chassis coupled with the component and a connector adapted to mate with a corresponding element in the computer chassis; a pivotal handle arm defining a travel guide; a rotatable hub coupled with the carrier and having a protrusion engaging the travel guide; a first lever arm coupled between the hub and a first engagement member, positioned to engage the chassis when the handle arm is moved to the inserted position; a lock coupled to the handle arm to prevent movement of the handle arm when the lock is engaged; and a detector for detecting movement to actuate and engage the lock. There may be logic associated with the computer system and coupled to the lock to selectively override the detector and de-actuate the lock when the component is ready for removal. Alternatively, there may be logic associated with the computer system to provide a control signal the lock to selectively de-actuate a lock when the component is ready for removal. 
     An aspect of this embodiment may be that movement of the handle arm toward an inserted position rotates the hub, moves the first lever arm, rotates the engagement member and engages the chassis. The first engagement member may include a catch which engages insertion and extraction stop mounted on the chassis. 
     In a further aspect of the present invention, the first lever arm and first engagement member may be mirrored by a second lever arm coupled to the hub and a second engagement member coupled to the second lever arm. These elements positioned on opposing lateral edges of the carrier may form a structure adapted to apply a substantially balanced force. 
     As part of the detector, there may be a handle mounted on the handle arm and a trigger mounted on the handle, the trigger having a released position in which it is biased and a depressed position, the trigger applying a force to the detector when the trigger is in its released position. In an embodiment, the detector is coupled to the trigger by a detector surface having a biased distal end that extends to meet the trigger, the biased distal end having a raised position in which it is biased and a depressed position, the biased distal end being coupled to actuate the lock when in its raised position. 
     Aspects of the lock, logic and indicator light in this embodiment may be as summarized above for other embodiments. 
     In a further embodiment, this invention includes an assembly for engaging a component to a computer system having a chassis, comprising: a carrier adapted to retain the component and to be inserted within the chassis to couple the component to a connector associated with the computer system; a lock coupled to the carrier to prevent removal of the carrier from the chassis when the lock is engaged; and logic associated with computer system to determine whether the component is ready to be disengaged from computer system, logic being coupled to the lock to selectively engage or disengage a lock when the computer system is operational. This embodiment may further include a detector, aspects of which are set forth above. 
     Alternatively, the concepts of the present invention may be embodied in a module for a computer system, having a chassis with at least one compartment, and processing resources, comprising: a carrier adapted to fit within the compartment in the chassis; a component mounted in the carrier; a connector adapted to mate with a corresponding element in the; a pivotal handle arm coupled; a translation mechanism to translate movement of the handle arm into force causing disengagement of the module from the chassis; a detector coupled with the handle arm which detects movement; a lock preventing movement of the handle arm past an intermediate position when locked; and logic coupled with processing resources and the detector, which locks the lock upon detection of motion unlocks and which causes the lock to enter the unlocked state upon receipt of a signal from the processing resources. 
     In aspects of this invention, the translation mechanism includes a hub which rotates upon movement of the handle arm between the intermediate position and the inserted position. Preferably, the lock assumes the unlocked state when not powered. 
     Aspects of the handle arm, hub and engagement member summarized above may also be found in this embodiment, as may be aspects of the detector, lock, logic and indicator. 
     The present invention provides mechanical and electrical components which improve the reliability of systems with hot swap capability, and make such operations more easily executed. 
     Further aspects and advantages of the present invention can be seen upon review of the figures, the detailed description, and the claims which follow. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a front view of computer system employing the concepts of this invention. 
     FIG. 2 is a face-on isometric view of a module or assembly. 
     FIG. 3 is a right front isometric view of a module or assembly, with the handle in the inserted position with respect to the carrier. 
     FIG. 4 is an isometric view of the handle arm, hub, first and second lever arms, first and second engagement members, the cam and solenoid, without the carrier. 
     FIG. 5 is a lower right back isometric view of a module or assembly, with the handle in the inserted position. 
     FIG. 6 is a reverse isometric view of a module or assembly, with a face of the carrier removed to reveal the component mounted inside the carrier. 
     FIG. 7A is a right back isometric view of a module or assembly, with the handle moving outward rotated less than 15 degrees from the inserted position and a surface of the cam riding on the solenoid rod, to clear the lock stop. 
     FIG. 7B is a reverse isometric view of a module or assembly, in the same state as FIG.  7 A. 
     FIG. 7C is a reverse isometric view of a module or assembly, with the handle rotated 15 degrees from the inserted position and a surface of the cam riding on the solenoid rod, having cleared the lock stop. 
     FIG. 7D is a right back isometric view of a module or assembly, with the handle rotated less than 15 degrees from the inserted position and the cam engaged with the lock stop, in its locked position. 
     FIG. 8 is a right back isometric view of a module or assembly, with the handle rotated 15 degrees from the inserted position and a surface of the cam riding on the solenoid rod, having cleared the lock stop. 
     FIG. 9A is a right back isometric view of a module or assembly, with the handle rotated 30 degrees from the inserted position and the cam beginning to extend through a slot in the cover. 
     FIG. 9B is a reverse isometric view of a module or assembly, in the same state as FIG. 9 a.    
     FIG. 10A is a right back isometric view of a module or assembly, with the handle rotated 45 degrees from the inserted position and the engagement members clearing the extraction stops. 
     FIG. 10B is a reverse isometric view of a module or assembly, in the same state as FIG. 10 a.    
     FIG. 11 is a right front isometric view of a module or assembly, with the handle moving from the extended position inward, the handle being rotated 30 degrees from the inserted position and the protrusion from the hub following the travel guide in the handle arm. 
     FIG. 12 is a right front isometric view of a module or assembly, with handle moving from the extended position inward, the handle being rotated 15 degrees from the inserted position and the protrusion from the hub following the travel guide in the handle arm. 
    
    
     DETAILED DESCRIPTION 
     A detailed description of embodiments of the present invention is provided with reference to the figures, in which FIG. 1 shows a computer system chassis  100  having a plurality of modules and a graphic user interface  160  according to the present invention. The computer system chassis  100  has a face  145  through which components are added to and communicate with the host processing system  105  in the chassis  100 . The components are engaged to communicate with the host processor  107  in compartments accessible through corresponding slots or openings in the face  145  of the chassis  100 . The date processing resources in a preferred provide storage services for a network of computers. In such preferred system, the components include memory modules, such as large arrays of flash EPROMs or disk drives storing large amounts of information. In addition, network interface components are included supporting a network architecture to provide memory services to many users. The host system  105  in the chassis  100  further include processing resources  109  associated with removing and inserting modules during operation of the host. 
     The components are mounted in carriers that are removably mounted in compartments of the chassis  100  through the slots in the face  145 . Such components include controller circuit boards, disk drives, memory circuit boards and other devices having resources for communicating with the host system. In the simplified example shown in FIG. 1, modules  110 ,  115  and  120  are arranged vertically in the face  145 . The modules  110 ,  115  and  120  each include handles  111 ,  116 ,  121 , and respective covers as shown in more detail in FIG.  2 . The handles  111 ,  116 ,  121  are engaged with a mechanism on the respective cover for locking the component within the chassis  100  when the host system is operational. 
     As represented schematically in FIG. 1, other modules  125 ,  130 ,  135  are shown in the face  145 . These modules are formed in alternative configurations, such as in a horizontal alignment relative to the chassis  100 . Such alternative modules may include disk drive arrays or other types of components designed for operation with the host system. In the example shown the additional modules  125 ,  130  and  135  include handles  126 ,  131  and  136  adapted for coupling with a locking mechanism and an assembly for translating motion of the handle into insertion and removal force for the component. 
     Also shown in FIG. 1 is a graphic user interface GUI  160 . The GUI  160  provides an interface for the operator of the device. The interface is monitored by control processes in the host system  105  for managing hot swap operations. Thus, the GUI includes a module select window having graphical buttons  161 ,  162  and  163  by which users are able to select modules and functions related to such modules for execution by the processes in the host system. Thus logic  175  within the host system  105  is coupled to the interface for managing the preparation of communication systems and power management resources for removal and insertion of components. In one embodiment, the GUI  160  also acts to signal the operator when the component is ready for removal, and the host system  105  is no longer overriding the lock mechanism on the component. 
     The modules, such as module  110  of the system include a component mounted within a carrier. The carrier includes a structure for securing a connector for connection of the component to the system communication structure, and a mechanism for engaging and disengaging the module with the system chassis. Also. a mechanical lock  185  is included with the carrier which is engaged to prevent removal of the module unless the system has released the lock  185 . Also, each lock  185  is coupled with a respective detector  187 . 
     FIG. 2 is a front isometric view of an embodiment of the present invention. The module or assembly is labeled  200 . A movable handle  201  operates the engagement and disengagement mechanism of the module. Cover  205  is on the front end of the module carrier, as depicted in subsequent figures. Three indicator lights  202 ,  203  and  204  are proximate to the module. In this embodiment, they are mounted directly on the cover of the module. In other embodiments, some or all of the indicator lights could be mounted on the chassis near the module. One or more of these indicator lights are coupled to logic associated with the computer system (not shown) which controls a lock and the indicator light. This logic is able to provide an enable control signal selectively to de-actuate the lock and also a signal to enable the indicator light indicating that the module is ready to be removed. 
     FIG. 3 depicts a module for a computer system, also referred to as an assembly for engaging a component to a computer system. This module is adapted to fit within a compartment or slot in the chassis of a computer system. The carrier  300  for the module or assembly has a lateral edge  302 , an opposing lateral edge  304 , a front end at the cover  205  and a back end opposite the front end. The carrier  300  has an inside where the component  306  is mounted, and an outside. To aid in insertion of the carrier into the chassis, a top guide  310  with leaf springs  312  and  313  are provided, which electronically ground the module. The guide and springs fit into a slot in the chassis. As will be seen in later figures, the top guide and springs are matched by a bottom guide and springs in this embodiment. The cover  205  is secured to the carrier by clips  306  and  307 . Collectively, a handle arm  320 A and  320 B, a hub  330 , a first lever arm  340  and a first engagement member  350  provide means, coupled with the carrier, for an engaging and disengaging the carrier and its component with the computer system. The connections among these elements are described below. 
     A handle arm  320 A and  320 B is pivotally secured to the carrier at  321 . As will be seen in later figures, the handle arm in this embodiment includes two flat surfaces substantially parallel to each other with a bend between the surfaces so that the two surfaces are offset. One extent of the handle arm  320 A extends through a slot in cover  205 . The handle arm has a handle  201  attached outside the front cover. The handle arm moves from an inserted position through an intermediate position to an extended position in an arc of approximately 45 degrees. FIG. 3 illustrates the handle in its inserted position. The prongs of handle  320 B may straddle handle arm  320 A and are rotatably coupled to the carrier  300 . The handle arm  320 B defines a travel guide, which is a cut-out in the shape of right triangle with a concave hypotenuse and rounded comers. This travel guide engages a protrusion  332  on the hub  330  which is rotatably attached to the carrier at  331 . A tubular rivet may be used at  331 . Various approaches can be taken to prevent protrusion  332  from escaping the travel guide. Finger  333  of hub  330  can serve as a keeper. A washer can be mounted on protrusion  332  so that the travel guide of arm  320 B is between hub  330  and the washer. In some embodiments, one or more support bearing surfaces behind hub  330  and in front of arm  320 B can be used to assure that those components remain in the desired plane of rotation. In FIG. 3, the hub rotates clockwise as the handle arm moves from its inserted to its extended position. When the handle arm is in its inserted position, as depicted in FIG. 3, the hub is somewhat over rotated counter-clockwise so that force applied to the hub to disengage the component tends to over-rotate the hub counter-clockwise, rather than rotating it clockwise toward disengagement. 
     The hub  330  is pivotally attached at  334  to a first lever arm  340 . It is also pivotally attached to a second lever arm  345  at a point not visible in this figure. The first and second lever arms may pass through slots in the lateral edge  302  of the carrier and the opposing lateral edge  304  of the carrier. In FIG. 3, slot  359  in the opposing lateral edge  304  can be seen. The first lever arm  340  is pivotally attached at  341  to a first engagement member  350 . The first engagement member is pivotally attached to the carrier at fulcrum  351 , which leverages the force applied to the handle to engage the component and mate respective connectors on the component and the chassis. In some embodiments, a coplaner bearing surface may be provided adjacent to the first and second lever arms or the first and second engagement members to assure that their movement remains in the intended plane, without twisting or torquing. Movement of the handle arm toward the inserted position rotates the hub and directs the lever arm to rotate the engagement members to engage the chassis. The first engagement member is positioned with respect to the lateral edge  302  of the carrier so that it engages the chassis of the computer system when the handle arm is moved to its inserted position. In this embodiment, the first engagement member includes a catch which engages an insertion stop  353  and an extraction stop  352 . As can be seen in other figures, the second engagement member  355  also has a catch which engages a second insertion stop  358  and a second extraction stop  357 . FIG. 3 shows that the second engagement member  355  is positioned with respect to the opposing lateral edge  304  of the carrier so it engages the chassis when the handle arm is moved to the inserted position. FIG. 3 also shows that the second engagement member rotates through a slot  359  in opposing lateral edge  304  to engage the chassis. In one embodiment of the present invention, the first and second engagement members are positioned on opposing lateral edges of the carrier so as to apply a substantially balanced force to the first and second engagement members and, thus, to the respective positions of the chains or stops on the chains which they engage. 
     This embodiment also includes a lock, comprising a cam  360 , a protrusion  362 , a spring  363 , surface on the cam  364 , a solenoid  370 , a rod (not shown) in the solenoid, and a stop (not shown). This lock is coupled with a detector  187  to detect movement and actuate the lock and to logic associated with the computer system to selectively override the detector and de-actuate the lock when the component is ready for removal. The detector may provide a signal to actuate the lock and the logic may provide a control signal to selectively de-actuate the lock. The lock is coupled with the means for engaging and disengaging and is in communication with processing resources which prevent the disengagement of the carrier absent an enabled or control signal from the processing resources. When the lock is in its locked position, the cam  360  engages the chassis or a stop on the chassis for resisting movement of the handle arm and removal of the component. When the lock is in its unlocked position, the cam  360  clears the chassis and stop, permitting the handle arm to move to its extended position and permitting the component to disengage from the system. In this embodiment, the elements of the lock are assembled as follows: the cam  360  is pivotally coupled to the handle arm  320 A at  361 . A tubular rivet may serve as a pivot axis. A protrusion  362  from the handle arm  320 A engages an arc guide defined in the cam  360 . The arc guide in this embodiment describes an arc through which cam  360  pivots. Spring  363  mounted on the cam  360  engages the protrusion  362  to bias the cam towards its locked position. One skilled in the art will, of course, recognize that there are many other ways to bias the cam. The surface  364  of the cam is adapted to engage with a rod (not shown) of the solenoid  370 . When the solenoid rod is in its normal extended position, the cam surface  364  rides over the road and will clear a stop (not shown). With the movement of the handle arm  320 A, the cam  360  engages the rod and assumes its unlocked position. If the solenoid  370  is actuated and the rod is in its retracted position, instead of its extended position, the cam  360  will be biased to assume its locked position and to engage with the chassis or a stop on the chassis. The solenoid  370  is coupled to the carrier, as is the stop which cannot be seen in this figure. 
     To prevent accidental rotation of handle arm  320 , one embodiment provides a trigger including a finger bearing surface (not shown) accessible by reaching under and behind handle  201  and actuated by pressing upward. Pressing the trigger rotates trigger arm  325  which includes tab  326 . Trigger arm  325  is biased by leaf spring  323  which is mechanically coupled to the trigger arm and captured by keeper  322 . Tab  326  engages the plunger of a two pole switch (not shown) which actuates the solenoid  370 . This switch detects movement of the handle arm. It also powers on the solenoid, which allows the solenoid to remain unpowered when the arm is in its inserted position. As the unpowered solenoid is biased in an unlocked position, the lock will not be engaged when the system is unplugged or unpowered. 
     FIG. 4 is a close-up isometric view of elements of this embodiment which translate movement of the handle arm  320 A into engagement of the catches on  350  and  355  with the chassis or stops on the chassis. In FIG. 4, the handle arm is in its inserted position. The engagement members  350  and  355  are in position to engage the chassis or stops on the chassis. The numbering of this figure corresponds to FIG.  3 . However, some of the pivotal connection points are depicted as voids in members, rather than fulcrums, pivots, protrusions or other elements for pivotal connection the travel guide defined in the handle arm  320 B appears in an alternative configuration which is better adapted to use of a washer mounted on protrusion  322 . Visible in FIG. 4, but not in the previous figures, is the rod  471  of the solenoid  370 . The engagement of surface  364  of the cam with the rod  471  of the solenoid can readily be seen. Also visible are two pole switch  590  and finger bearing surface  828 . 
     FIG. 5 is a lower right back isometric view of the module or assembly, again with the handle arm in its inserted position. The numbering of this figure corresponds to the numbering of previous figures. This figure illustrates the mounting of indicator lights  202 ,  203  and  204  through the cover  205  of the chassis. The attachment of the cover with clips  306  and  307  to the chassis is clear. A few additional features not previously visible are also apparent. At the front end of the carrier, slot  509  through the cover  205  is visible. The handle arm  320 A passes through the slot  509 . Along the opposing lateral edge  304 , the bottom guide  510  and leaf springs  512  and  513  are visible. On the outside of the carrier, at the back end, a connector  580  appears. This connector is coupled to component  306 . This connector includes at least one connection element adapted to mate with a corresponding element associated with the computer system (not shown), optically mounted on the chassis upon engagement of the module. The connector  580  may be mounted on the outside of the carrier or on the component. It is coupled with the component to provide an electrical connection between the component and the computer system. At the front end of the carrier, along the bottom, opposing lateral edge, there is a top  575  which engages cam  360  when the cam is in its locked position to resist removal of the component. The location of switch  590 , which engages tab  326  of trigger arm  325  is apparent. This switch may include a plunder biased in a first position which engages the tab  326  and is movable to a second position by the tab. This plunger has a detector surface which detects engagement with tab  326 . 
     FIG. 6 is a reverse isometric view of the module, with the face of the carrier  300  cut away to reveal the elements mounted inside the carrier. In this view, connector  580  and its coupling to component  306  is clear. The profile of hub  330  is revealed in this figure. The pivotal connection between the hub  330  and second lever arm  345  at  635  is also revealed. The engagement of surface  364  of the cam  360  with the rod  471  can be seen. The over-rotation of the hub when the handle arm  320 A and  320 B is in its inserted position can be seen, by visualizing an axis between pivotal couplings  351  and  334 , as compared to an axis between  351  and the pivotal coupling of the hub at  331 . The same is true for an axis between pivotal connections  356  and  635 , as compared to an axis between  356  and the pivotal coupling of the hub at  331 . This over-rotation is advantageous because removal force supplied to the carrier will not tend to disengage the engagement members. Applying removal force to the carrier would press the catch of the engagement member  350  against extraction stop  352 , causing rotation. Through pivotal connection  351 , the first lever arm  340  would tend to rotate the hub in the opposite direction as would be required to move the first lever arm toward its disengaged position. The form of trigger arm  325  is better revealed in this figure and its pivot point  361  is apparent. The form of switch  590  and its position adjacent to the trigger arm can be seen. 
     FIGS. 7A,  7 B,  7 C and  7 D illustrate the interaction of the cam  360  and the solenoid  370  as the handle arm  320   a  moves from its inserted to its extracted position. The numbering in these figures is as in the previous figures. In FIG. 7A, the handle  201  and the handle arm  320 A have been pulled out less than 15 degrees from their inserted position to an intermediate position. It is apparent that the rod  471  (not shown) of the solenoid  370  is in its normal extended position, as the cam  360  is rotated in opposition to the biasing spring  363  and is in the unlocked position where it will clear stop  575 . The cam is rotated because surface  364  is riding on the rod. FIG. 7B is a reverse isometric view with handle  201  in the same position as in FIG.  7 A. The contact between surface  364  and rod  471  is shown. FIG. 7C illustrates handle  201  and handle arm  320 A rotated 15 degrees from their inserted position to an intermediate position. The contact between surface  364  and rod  471  is again apparent. In FIGS. 7A,  7 B and  7 C, the cam  360  is in an unlocked position. FIG. 7D shows the cam in its locked position. Rod  471 , not visible in FIG. 7D, must be retracted, as cam  360  is securely engaged against stop  575 . 
     FIG. 8 illustrates the handle  201  and handle arm  320 A and  320 B rotated 15 degrees from the inserted position. This 15 degree rotation is approximately the extent of free travel of the handle arm before the travel guide engages protrusions  332  and begins to rotate hub  330 . This figure shows that the lever arm and hub are still in their over-rotated position. The protrusion  332  has begun to engage the travel guide defined by handle arm  320 B. Additional rotation will cause the travel guide to apply force to the protrusion, thereby tending to rotate the hub clockwise toward a disengage position. Finger bearing surface  828 , coupled to trigger arm  325 , is revealed in this figure and is easily seen in FIG.  9 A. 
     FIGS. 9A and 9B are isometric and reverse isometric views of this translation mechanism, with the handle  201  and handle arm  320 A rotated  30  degrees from the inserted position. These figures demonstrate that force applied by the travel guide defined in handle arm  320 B to the protrusion  332  translates movement of the handle arm into rotation of the hub, which causes movement of the lever arms and rotation of the engagement members. Movement of the handle arm from the intermediate position to the extended position causes force to be applied by the catches of the first engagement arm  350  and the second engagement arm  355  to the chassis or to insertion stops  353  and  358 , promoting disengagement of the module from chassis. 
     FIGS. 10A and 10B are isometric and reverse isometric views of this translation mechanism with the handle  201  and handle arm  320   a  rotated 45 degrees to the extended position. 
     These figures again show how movement of the handle arm from the intermediate position to the extended position translates into force causing disengagement of the module from chassis. In these figures, the catches of the disengagement members  350  and  355  have rotated so that there is clearance between the catches and the extraction stops  352  and  357 . A dentate (not shown) in the handle arm or the trigger arm may be supplied to support the handle in its fully extended position. 
     FIG. 11 depicts this embodiment of the translation mechanism when the handle  201  and handle arm  320 A are being pushed from their extended position to an intermediate position. Due to the shape of the travel guide defined in handle arm  320 B, this embodiment of the present invention reacts differently when the handle arm is at 30 degrees on a path toward its inserted position than it does when the handle arm is at 30 degrees on a path toward its extended position. As the handle is pushed in, at 30 degrees the protrusion  332  engages the side of the travel guide proximal to the front end of the carrier. The travel guide applies force to the hub, causing it to rotate the toward its engaged position. 
     FIG. 12 shows the translation mechanism as the handle  201  and handle arm  320 A reach an angle of 15 degrees, on a path from an intermediate position toward the inserted position. The hub is approaching its over-rotated, inserted and engaged position. The protrusion  332  has nearly reached the end of its travel along the edge of the travel guide proximal to the front end of the carrier. 
     The embodiments shown are advantageous for reasons including: The solenoid is powered from the chassis through a connection to the module. Non-operating (de-energized) boards may be removed at any time. A switch on the release latch alerts the system when a board is being unplugged. The second pole of the switch controls power to solenoid, avoiding the delay otherwise resulting from software control. To save power and reduce heat the solenoid only operates when the release latch is squeezed. No force is applied to the solenoid when the module is locked and a user attempts to remove the module. Only a small force is applied to the solenoid when the system is unlocked. This allows the use of a very small solenoid. The indicator light directs the user to the module being removed. The graphical user interface assists the user in requesting removal of a component. The amount of resistance to removal gives the user a tactile indication of whether the component is ready for removal. 
     The foregoing description of various embodiments of the invention have been presented for purposes of illustration and description. The description is not intended to limit the invention to the precise forms disclosed. Many modifications and equivalent arrangements will be apparent to people skilled in the art.