Hot-swap assembly for computers

An assembly that engages a component to a computer system includes a cover adapted to retain the component and to be inserted within a chassis of the computer system. A slide movably coupled to the cover has a proximal position associated with inserting the cover into the chassis and a distal position associated with withdrawing the cover from the chassis. A detector coupled to a lock and to the slide detects movement of the slide to actuate the lock. The lock is coupled to the slide and to the detector, and blocks movement of the slide towards the distal point when the lock is in an engaged state.

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 such connecting and
 disconnecting components while the computer system 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, 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, with components that require significant
 force for engagement and disengagement, human operators may damage
 delicate parts of system while applying the force for engagement or
 disengagement.
 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 of the computer system, and reduces the
 mechanical force needed to be applied by operators for the engagement and
 disengagement of components. Thus, an operator expects to apply a
 relatively light force to remove or insert a component on the computer
 system. The light force applied minimizes the chance of mechanical damage
 to the system. Also, the mechanism is able to block attempted removal of a
 component if the electrical processes necessary for hot swap have yet to
 complete. The combination results in a substantially more reliable system,
 less prone to damage during the hot swap operation.
 According one aspect of the invention, a module is provided for computer
 system. The computer system includes a chassis having one or more slots
 for accepting the module. Processing resources associated with removing
 and inserting modules during operation are included in the computer
 system. The module according to the present invention comprises a cover
 adapted to fit within the slot in the chassis. A system component, such as
 a controller circuit board, disk drive array, or other data-processing
 resource is mounted with the cover. A connector coupled to the component
 includes a plurality of connection elements adapted to mate with
 corresponding elements in the computer system on the chassis. Means for
 preventing mishandling, such as those described in more detail below, are
 included. Such means include mechanical and electrical components which
 provide leverage for engaging and disengaging the component, and which
 communicate with the host system to prepare for electrical disengagement
 and engagement of the component. Also, such means include a lock or other
 mechanism for preventing the mechanical disengagement of a component when
 the system has yet to electrically prepare for the disengagement.
 According to one embodiment of the invention, a mechanism for providing
 leverage for engagement and disengagement of the component in the cover is
 included. The mechanism includes a slide mounted on the cover. A pivotal
 connection is provided near a distal end of the slide. The proximal end of
 the slide is adapted to extend outside the cover, and act as a handle for
 an operator. The lever system is coupled to and actuated by movement of
 the slide. The lever system provides for balanced engagement of the
 component with the connectors in the host system.
 In one preferred embodiment, the slide is movable among an inserted
 position, at least one intermediate position and an extended position. The
 lever system translates movement of the slide in the direction from the
 intermediate position to the extended position into force causing
 disengagement of the connector, and translates movement of the slide in
 the direction from the extended position to the intermediate position into
 force for engagement of the connector. A portion of the motion from the
 inserted position toward the intermediate position provides a dead region,
 in which no force is translated from the slide through the lever system to
 tend to disengage the component. This dead region is utilized for sensing
 motion, to enable electronic lock to prevent further disengagement if the
 system has not prepared for it.
 In another preferred embodiment a lock is included which prevents motion of
 the slide from being translated to disengagement force. The lock is
 coupled to the host system, and engages the slide when the host system has
 not finished preparing for the disengagement. In one preferred system,
 power is normally not applied to the lock. In this embodiment, the lock
 includes a mechanical stop which prevents motion until the operator
 applies an enabling act, such as depressing a spring loaded tongue
 element. When the enabling act is executed, power is applied to the lock.
 Unless the system signals that it is ready for disengagement, the lock
 prevents further disengagement action.
 The lever system in a preferred embodiment comprises first and second lever
 arms coupled to a pivotal connection near the distal end of the slide. The
 first lever arm extends toward a first lateral edge of the cover. The
 first lever arm is coupled to a fulcrum near the first lateral edge. The
 opposite end of the lever arm is coupled to an engagement member adapted
 to engage with a mechanical stop on the chassis. The second lever arm
 extends to the second lateral edge of the cover. The second lever arm is
 coupled to a fulcrum near the second lateral edge. The opposite end of the
 second lever arm is coupled to a second engagement member. For balanced
 operation, the first and second lever arms are essentially the same length
 and apply substantially equal force in response to motion of the slide.
 The engagement member in this embodiment is connected near the lateral
 ends of the respective lever arm. The engagement member is biased via a
 spring to swing outward to engage a mechanical stop on the chassis. During
 engagement, the spring tends to force the engagement member to extend
 outside the cover and engage the mechanical stop. The lever arm acts to
 apply an engagement force against the mechanical stop. During
 disengagement, the lever arm acts to reverse the engagement force. Also
 first and second retraction arms are coupled respectively with the first
 and second lever arms. A retraction arm is coupled to the engagement
 member and to a pivotal connection on the slide, such as the same pivotal
 connection to which the lever arm is connected. The retraction arm acts in
 response to motion of the slide towards the retracted position to pull
 against the force of the spring and withdraw the engagement member inside
 the cover to allow removal of the component.
 In yet another embodiment, the host system includes a graphical user
 interface or other interface allowing an operator to signal the system of
 an intention to remove a component. In response to the operator signal,
 the host system performs power management and communication management
 routines to prepare the system for a hot swap operation. Until the power
 and communication management routines have been completed, the lock
 associated with the component to be removed is set in a position to
 prevent removal.
 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.

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 in the chassis 100. The components are engaged to
 communicate with the host processor through a corresponding slot or
 opening in the face 145 of the chassis 100. The data processing resources
 in a preferred system 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 in the chassis 100 further includes processing
 resources associated with removing and inserting modules during operation
 of the host.
 The components are mounted in covers that are removably mounted on 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. For applications having connectors with large
 numbers of I/O pins, a handle is coupled with a mechanism providing
 leverage for insertion force.
 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 operator of the device. The interface is
 monitored by control processes in the host system 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 within the host system 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 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 cover. The cover includes 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 is included with the cover which is engaged to
 prevent removal of the module unless the system has released the lock.
 FIGS. 2-7 illustrate one embodiment of the cover. FIGS. 8-11 illustrate an
 alternative embodiment of the cover. Both embodiments include means for
 engaging and disengaging the a module according to the present invention.
 The illustrated means constitute preferred embodiments of the present
 invention. Other mechanisms based on a lever system, and an engagement
 member coupled to the lever system are also suitable alternatives. Also, a
 lock mechanism is provided for preventing operation of the lever system
 under system control.
 FIG. 2 illustrates one embodiment of a cover 200 according to the present
 invention. The cover 200 includes a front face 201 which includes a
 variety of structures (e.g. 202, 203) which provide openings for switches,
 connectors and indicators intended to be visible through the cover. The
 cover 200 includes a back face 204 against which an array 205 of
 connectors is mounted for establishing electrical communication with the
 host system bus. The cover includes a left side wall 206 and a right side
 wall 207. The cover 200 includes a base plate on which guides 208 and 209
 are mounted. A slide 210 is positioned between the guides 208 and 209, and
 is moveable between an inserted position as illustrated in FIG. 2, an
 intermediate position, and a withdrawn position as illustrated in FIG. 3.
 A pivot 211 is mounted on the slide 210. The pivot 211 is constructed using
 a riser secured to the slide 210 and extending upward from the plane of
 the drawing. The pivot 211 is adapted to receive a first lever arm 212 and
 a second lever arm 213. The first lever arm 212 extends from the pivot 211
 through a fulcrum 214 near the left side 206 of the cover. Opposite the
 fulcrum 214, a second end 216 of the first lever arm 212 is connected to
 an engagement member 218. The engagement member 218 includes a hook 220
 adapted to engage a mechanical stop (not shown) on the chassis. In a
 similar fashion, the lever arm 213 extends through a fulcrum 215 on the
 right lateral side 207 of the cover. A second end 217 of the lever arm 213
 is coupled to an engagement member 219. The engagement member 219 includes
 a hook 221 adapted to engage a second mechanical stop (not shown) on the
 chassis.
 Structural plates 250 and 251 secure the fulcrums 214 and 215 for the lever
 system. The lever system illustrated in FIG. 2 provides gain in force
 between 10 to 1 and 20 to 1. This gain is important for engagement of
 covers and components that include large arrays of connectors 205, such as
 hundreds of connectors, which require engagement force on the orders of
 tens to hundreds of pounds. Other lever systems are suitable for use as
 well. Also in some systems which require less engagement force, the
 mechanical gain is not as important.
 The use of the first and a second lever arms 212, 213 provides for
 essentially balanced operation of the engagement members 218, 219.
 Although not shown in FIGS. 2 and 3, the first lever arm 212 and second
 lever arm 213 have elongated openings near the pivot 211 which allow for
 sliding engagement with the pivot 211.
 As can be seen, operation of the slide 210 causes the lever arms 212 and
 213 to rotate on the respective fulcrums 214, 215. In the inserted
 position as shown in FIG. 2, the engagement members 218 and 219 are pulled
 toward the front face 201 of the cover under an engagement force caused by
 the lever action. As the slide 210 is withdrawn from the cover, the
 engagement members 218 and 219 are pushed away from the front face 201,
 allowing disengagement of the hooks 220, 221 from a chassis.
 Retraction arms 222 on the left side and 223 on the right side are also
 coupled to the pivot 211. These retraction arms could be coupled to other
 pivot points associated with the slide 210 if desired. The retraction arm
 222 is coupled to a spring 224 which tends to pull the lateral end 226 of
 the retraction arm 222 toward the back face 204 of the cover. The lateral
 end 226 of the retraction arm 222 is coupled to the engagement member 218
 at a pivot 228. The spring 224 through this connection tends to rotate the
 engagement member 218 in a counter-clockwise direction out of the side 206
 of the cover in order to engage the chassis.
 The retraction arm 223 extends to the right side engagement member 219, and
 is coupled to a spring 225 at a lateral end 227. Also, the lateral end 227
 is connected to a pivot 229 on the engagement member 219. The action of
 the spring 225, connected in this manner, tends to drive the engagement
 member 219 in a clockwise direction out the side 207 of the cover.
 The system shown in FIG. 2 also includes a lock mechanism 260 generally
 coupled with the slide 210. The lock mechanism includes a pawl 261 mounted
 on a pivot 262 coupled to the slide 210. A spring 263 tends to cause the
 pawl 261 to rotate in a counter-clockwise direction. A mechanical stop 264
 is mounted on the cover 200 adjacent the slide 210. The rail 209 includes
 an angular surface 265 against which the pawl 261 tends to rotate as the
 slide 210 is withdrawn. A solenoid 266 is mounted above the pawl 261. The
 solenoid 266 includes a pin not shown which is normally in a withdrawn
 position. When the pin is withdrawn, the pawl will rotate outward and
 engage the mechanical stop 264 to prevent withdrawal of the slide 210. If
 the solenoid 266 is engaged, the pin will extend downward, and prevent the
 pawl 261 from rotating outward to engage the stop 264. Thus, when the pin
 is extended, the slide 210 will be freely withdrawn past the lock
 mechanism, and allow disengagement action of the lever arms and retraction
 arms as described above. Otherwise, the lock will act to prevent
 disengagement of the cover until the pin on the solenoid 266 is extended.
 The lock also includes a spring loaded tongue element 267, or other element
 requiring an operator action to begin the withdrawal process. A switch 268
 is coupled with the tongue element 267. The tongue element 267 includes a
 ridge 269 which tends to engage a bar on the cover, or the chassis, and
 prevent motion of the slide 210. When an operator the presses the tongue
 element 267, the ridge 269 is lowered below the bar on the cover and the
 switch 268 is engaged. The switch 268 enables the solenoid 266. A signal
 provided by the host system controls the solenoid 266 so that it remains
 in the withdrawn position unless the system is ready for withdrawal of the
 component on the cover. If the system is ready for withdrawal, the
 solenoid 266 extends the pin downward and allows withdrawal of the slide
 210.
 As the slide 210 is withdrawn from the fully inserted position as shown in
 FIG. 2 to the intermediate position at which the pawl 261 engages the
 mechanical stop 264, there is essentially no disengagement force applied
 to the engagement members 218, 219 because of the sliding engagement of
 the lever arms 212, 213 with the pivot 211, and the relatively small
 distance traversed by the slide. Furthermore, because little force is
 needed to cause motion of the slide, the operator will not tend to pull
 too hard and damage the system. The motion from the fully inserted
 position to the intermediate position allows for detection of the
 attempted withdrawal of the component, and prevention of that withdrawal
 if the system has not prepared for it.
 FIG. 3 illustrates the cover and lever assembly of FIG. 2 with the slide
 210 in the withdrawn position. In this position, the lever arms 212, 213
 pivot around the respective fulcrums 214, 215 and cause the engagement
 members 218, 219 to be pushed away from the front face 201 to release the
 engagement force. The retraction arms 222, 223 are extended to the end of
 the slots 270, 271 at the ends near the pivot 211. This pulls against the
 springs 224, 225 and causes the engagement member 218 to rotate in a
 clockwise direction, and the engagement member 219 to rotate in a
 counter-clockwise direction, withdrawing engagement members away from the
 chassis, and allowing the cover 200 to be removed from the chassis.
 As a module is inserted, the action of the retraction arms 222 and 223
 tends to allow the engagement members 218, 219 to rotate outward and
 engage the chassis. The action of the lever arms 212,213 applies
 engagement force against the chassis to secure the connectors 205 with
 corresponding connectors in the chassis.
 FIG. 4 is a view of the back end 204 of the cover 200 showing a component
 connector 420 used to couple a memory module with the computer system 100.
 The component connector 420 is mounted on the cover 200, or alternatively
 formed for example on a circuit board in the cover, as an extension of the
 mounted component. The cover 200 provides a back panel 410 through which
 the component connector 420 extends to engage with the corresponding
 mating connector (not shown) of the computer system 100. The component
 connector 420 may have either male or female connector elements. The
 individual pins are not shown in FIG. 4, to avoid crowding in the drawing.
 In one example, the component comprises a memory module including a large
 pin connector, such as ones suitable for employment with arrays of FLASH
 EPROM modules that store many gigabytes of information. FIG. 4 illustrates
 an embodiment incorporating a large male or female pin connector on the
 cover 200, where the pins/holes are arranged in clusters 421, including
 four or more rows of pins. The large pin connector 420 may include over
 1500 pins/holes and several ground and power contacts which engage a
 mating connector within the chassis. For large pin connectors such as one
 illustrated by FIG. 4, a force greater than 200 pounds may be necessary to
 engage the memory module with the computer system 100.
 Multiple guide pins 430 are also incorporated into the component connector
 420, or in the back panel 410, to guide the component connector into
 engagement with the mating connector of the chassis. In this example,
 three guide pins 430 are spaced horizontally to extend from the back end
 204 of the cover 200. The guide pins may be positioned on either the back
 panel 410 or on an interface surface of the component connector. The guide
 pins 430 align the component connector 420 with respect to the slot or
 opening of the chassis when an insertion force is applied to the cover
 200. In particular, large pin connectors used with the component connector
 420 benefit from guide pins 430 because the guide pins more readily ensure
 alignment between the memory module and the computer system when the
 insertion force is applied to the component connector.
 FIGS. 5A-5C provide a close-up illustration of the lock mechanisms 260 on
 the slide 210. First with reference to FIG. 5A, the slide 210 is in a
 fully inserted position. The tongue element 267 tends by its spring action
 to lift away from the slide 210. A ridge 535 engages a bar 516 on the
 front face of the cover and prevents withdrawal of the slide. The pawl 261
 is shown in a position such that the solenoid 266 may engage a pin 555
 with the pawl 261 by extending downward. A stop 530 positions the pawl 261
 in the manner shown to let the pin extend past the top surface of the pawl
 so that a side 532 of the pawl will ride along the pin. If the pin is not
 extended, then the side 532 of the pawl will ride adjacent the guide
 member 209 in the region 265 as described before.
 The proximal end 506 of the slide 210 is formed to provide a handle for the
 operator. The mechanical stop 264 is reinforced with structural members
 544 and 534.
 The tongue element 267 is secured to the slide 210 by elements 522 which
 may be screws, welded joints or other structural connectors. The tongue
 element has a region 520 which is normally inside the wall 516. The ridge
 535 is formed in the region 520. Also, a switch contact 524 is formed on
 the tongue element 267 in the region 520. The switch contact 524 is
 adapted to contact a switch 268 mounted on the bar 516 on the cover. When
 the contact 524 is spaced away from the switch 268, the system enables the
 solenoid 266 as mentioned before.
 FIG. 5B illustrates the lock 260 with the pawl 261 engaged at the
 mechanical stop 264. Skis occurs if the pin 555, shown in FIG. 5A is
 withdrawn from the solenoid to 266, allowing the surface 532 of the pawl
 261 to ride along the wall in region 545 of the guide 209. In order to
 reach this position, the tongue element 267 must be depressed, causing the
 ridge 535 to slip under the bar 516, and the contact 524 to lose contact
 with the switch 268.
 FIG. 5C illustrates the lock mechanism 260 in substantially the same
 position as that of FIG. 5B, except that the solenoid 266 is engaged to
 prevent the pawl 261 from engaging the mechanical stop. Thus, the slide is
 in a position to be withdrawn from the cover. It can be seen in FIG. 5C
 that the pin 555 of the solenoid 266 is extended downward, and the surface
 532 of the pawl rides on the pin 555 to prevent engagement with the
 mechanical stop 264.
 The lock mechanism shown in FIGS. 5A-5C is characterized by a solenoid 266
 which has a normally extended pin 555. In this manner, when the power is
 off for the system, the pin is extended, and the slide may be withdrawn.
 Thus, a lock which allows withdrawal of the system when power is off is an
 advantageous aspect of the invention.
 Other configurations of locks can be utilized, including solenoid having
 normally withdrawn pins, other electromagnetically actuated components, or
 other electromechanical configurations which allow for system control of
 the lock during hot swap operations.
 FIGS. 6A-6C illustrate the engagement member 218 in engaged and disengaged
 positions. As can be seen in FIG. 6A, the lever arm 212 is secured through
 a fulcrum 214 to the engagement member 218 at pivot 216. The fulcrum 214
 is secured to the cover by structure 250. The retraction arm 222 is
 secured to the engagement member 218 at pivot 655. The spring 224 is
 coupled between the retraction arm 222 and the cover. As shown in the
 drawing, the engagement member has a hook region 220 which is engaged with
 a mechanical structure 610 on the chassis. Structure 610 includes a
 surface 612 within a cut out area 615, against which the hook 220 applies
 engagement force. The head 650 of the engagement member 218 fits within
 the cut out area 615 of the member 610. This member is engaged along the
 left side 206 of the cover in the example shown. In FIG. 6B, the lever arm
 212 has been moved to the intermediate position against the stop on the
 tongue member. In this illustration can be seen that the head 650 of the
 engagement member 218 remains within the cut out area 615, and little or
 no disengagement force is applied. In FIG. 6C the lever arm 212 is moved
 toward the fully retracted position, releasing the head 650 of the
 engagement member 218, so that the hook 220 does not engage the member
 612. The retraction arm 222 pulls against spring 224 to withdraw the head
 650 from the member 610 allowing reaction of the component.
 The engagement member and lever system illustrated can be replaced with a
 variety of other mechanisms, including mechanically operated and
 magnetically operated engagement devices. The present system allows for
 significant leverage action to apply insertion force for large connector
 components, using smooth, easy action withdrawing and inserting the slide.
 FIG. 7 illustrates the pivot 211 on the slide 210, and the manner in which
 the lever arms 212 and 213 and the retraction arms 222 and 223 are engaged
 with the pivot 211. In FIG. 7, the slide is in the withdrawn position,
 such that the distal end of the slide is adjacent the solenoid 266. The
 retraction arms 223 and 222 include slots 710. When the slide 210 is in
 the withdrawn position as shown in FIG. 7, with the distal end of the
 slide near the solenoid 266, the pivot 211 engages the ends of the slots
 710, and applies force to withdraw the engagement member inside the cover
 as described above.
 The lever arms 212 and 213 also include slots which couple with the pivot
 211. The slots allow for the linear slide to drive arcuate motion of the
 lever arms, and for movement of the slide from the fully inserted position
 to the intermediate position without applying significant lever force to
 the engagement members.
 FIGS. 8, 9, 10, and 11 illustrate an alternative configuration of the lever
 assembly and mechanical lock for a module cover 800 according to the
 present invention, adapted for systems which require lower engagement and
 disengagement forces than are developed using the configuration of FIGS. 2
 and 3. The cover 800 includes a front wall 801 and a back wall 802. A left
 side wall 803 and a right side wall 804 are formed on the cover 800. The
 chassis includes mechanical stop structures 805 and 806 on the left and
 right sides, respectively, of the slot in the chassis which receives the
 cover 800.
 The mechanism includes a slide structure 810 which has a left extending arm
 811 and a right extending arm 812. The left end of the left extending arm
 811 includes a guide surface 813 which is adapted to slide along a
 receiving surface 815 on the left side wall 803. The end of the right
 extending arm includes a guide surface 814 which is adapted to slide along
 a receiving surface 816 on the right side wall 804. Also, the slide 810 is
 secured by a riser 820 within a slot 821. The slot 821 establishes the
 maximum inserted position and the maximum withdrawn position of the slide
 810. Although not shown in the drawing, a spring loaded switch, like the
 tongue assembly 267 of FIGS. 2 and 3, and in FIGS. 5A-5C, is mounted by
 fasteners at the fastener receiving holes 822 on the slide. A mechanical
 lock including a pawl 823 is also mounted on the slide 810 in the manner
 discussed above with respect to FIGS. 5A-5C. The pawl 823 is adapted to
 strike a stop member 824 on the cover 800 unless a solenoid pin is
 extended to drive the pawl to a position which avoids contact with the
 stop 824, as described above. This structure is placed in a different
 location on the slide 810 than the similar structure describes above with
 respect to FIGS. 5A-5C. The mechanical lock can be positioned at any
 convenient location on the slide as suits the need of the particular
 embodiment, and adopt a variety of mechanical and electromechanical
 structures.
 The slide includes a handle structure 850 at the proximal end of the slide.
 The distal end of the slide 850 is adapted to extend long enough to hold
 the pawl 823 and improve structural integrity during sliding from inserted
 to withdrawn positions of the slide 810.
 The assembly includes a left lever arm 830 and a right lever arm 831. The
 left lever arm 830 is coupled to a fulcrum 832. The right lever arm 831 is
 coupled with fulcrum 833. The lever arms 830, 831 include respective
 inside curved surfaces 834 and 835. Likewise, the lever arms 830, 831
 include respective outside curved surfaces 836 and 837. In the inside
 curved surfaces 834 and 835 are adapted to engage with pivot 838 and bar
 840 on the left, and a pivot 839 and bar 841 on the right. The outside
 curved surfaces 836 and 837 are adapted to engage with pivots 842 and 843
 on the left and right sides respectively. The left lever arm 830 includes
 an engagement end 844 adapted to apply engagement force against the stop
 805 in the chassis. The right lever arm 831 includes an engagement end 845
 adapted to fit with the stop 806 in the chassis.
 Operation of the lever assembly can be understood with respect to FIGS. 9,
 10, and 11, which use the same reference numbers as FIG. 8. As can be seen
 in FIG. 8, the inside curved surfaces 834, 835 of the lever arms 830, 831
 contact outside surfaces of the bars 840 and 841 which are parallel to the
 direction of motion of the slide. The outside curved surfaces 836 and 837
 of the left and right lever arms contact pivots 842 and 843 respectively.
 The engagement ends 844 and 845 of the lever arms 830 and 831 apply force
 against the stops 805 and 806, which force tends to hold the mechanism in
 the chassis.
 In FIG. 9, the slide 810 is shown withdrawn to an intermediate position.
 Between the position of FIG. 8 and the position of FIG. 9, there is no
 cover movement. The inside surfaces 834 and 835 of the lever arms ride
 against the bars 840 and 841 until the position indicated in FIG. 9. The
 engagement ends 844 and 845 continue to apply engagement force against the
 stops 805 and 806 respectively.
 FIG. 10 illustrates a position in which the slide 810 is near a fully
 withdrawn position. As the slide moves from the position of FIG. 9 to the
 position of FIG. 10, the inside surfaces of the lever arms 830, 831 rotate
 about the pivots 838 and 839. The pivots 842 and 843 engage the outside
 surfaces 836 and 837. As the lever arms move through the position of FIG.
 10, they apply leverage to overcome the connector resistance and cause the
 engagement ends 844 and 845 to apply disengagement force against the stops
 805 and 806.
 FIG. 11 illustrates the slide 810 in the fully withdrawn position. This
 position, the riser 820 is against the distal end of the slot 821 on the
 slide 810. The lever arms 830 and 831 rotate so that the engagement ends
 844 and 845 are withdrawn relative to the cover 800, allowing removal of
 the cover from the chassis without resistance from the stops 805 and 806.
 The outside curved surfaces 836 and 837 rotate on the pivots 842 and 843
 during the final lever transition.
 As the component is inserted, the lever system goes through low leverage
 transition between positions of FIG. 11 and FIG. 10, and begins to apply
 higher leverage after the position of FIG. 10. In the transition from the
 position of FIG. 10 to the position of FIG. 9, the lever system overcomes
 the connector resistance. In the position of FIG. 9, the component is
 fully engaged. As the slide is inserted from the position of FIG. 9 to the
 position of FIG. 8, there is no component movement.
 In the region of movement of the slide between the inserted position of
 FIG. 8 and the intermediate position of FIG. 9, there is essentially no
 movement of the engagement ends 844 and 845 of the lever arms. The
 detector mechanism described above operates to detect attempted removal of
 the component in this region of no movement. This allows the
 electromechanical lock to engage if the system is not prepared for removal
 of the component, or to allow removal if the system is prepared.
 Computer systems incorporating principles of this invention provide several
 advantages. In particular, the invention provides an assembly that allows
 for modules engaged with a computer system to be safely and easily
 hot-swapped. For example, the cover 200, 800 under this system may only be
 removed when the logic of the computer system confirms that the module is
 ready to be disengaged from the system. Moreover, the cover 200, 800 may
 include safeguards that prevent damage to the lock, module, or computer
 system by users who suddenly apply significant forces to prematurely
 disengage the module. In addition, the cover may include a leveraged
 translational mechanism including a combination of levers, retraction arms
 and engagement members which allow for easy engagement and disengagement
 of the module from the computer system. In an embodiment of the invention,
 the translational mechanism may leverage a force applied to a slide 210,
 810 of the cover 200, 800 to allow users to easily insert and engage
 modules requiring significant insertion forces.
 Two separate issues with regard to hot swapping modules in computer systems
 include:
 1. Plugging or unplugging cards requires the system bus be "stopped" or
 noise could cause data or program corruption.
 2. Data in the card could be lost if a card were removed without giving the
 system time to store the data.
 To prevent unexpected extraction of a card, a mechanical and electrical
 lock using a solenoid in one example is used. The solenoid is used to lock
 the lever mechanism on each board module. The solenoid is energized by the
 module power supply thus preventing the energized module from being
 removed. In order to reduce energy consumption a switch on the release
 latch turns on the solenoid only when moved, i.e., when someone is trying
 to remove the module. A short pin on the bus connector can be polled to
 ensure the card release latch. Removal of a card is done using the front
 panel display management interface or the management interface remotely.
 The LEDs on the boards not ready to be removed can flash amber while the
 LED on board that is ready to be extracted is unlit. Note that the bus
 will continue to operate until a user squeezes the release latch to the
 card. This operates a switch in the latch that alerts the system the card
 is being unplugged. Bus activity is suspended.
 The embodiments shown are advantageous for reasons including:
 1. The solenoid is powered from the onboard DC/DC power supply in the
 module.
 2. Non-operating (de-energized) boards may be removed at any time.
 3. A switch on the release latch alerts the system when a board is being
 unplugged.
 4. To save power and reduce heat the solenoid only operates when the
 release latch is squeezed.
 5. No force is applied to the solenoid when the module is locked and a user
 attempts to remove the module.
 6. Only a small force is applied to the solenoid when the system is
 unlocked. This allows the use of a very small solenoid.
 The foregoing description of preferred embodiments of the present invention
 has been provided for the purposes of illustration and description. It is
 not intended to be exhaustive or to limit the invention to the precise
 forms disclosed. Obviously, many modifications and variations will be
 apparent to practitioners skilled in this art. The embodiments were chosen
 and described in order to best explain the principles of the invention and
 its practical applications, thereby enabling others skilled in the art to
 understand the invention for various embodiments and with various
 modifications as are suited to the particular use contemplated. It is
 intended that the scope of the invention be defined by the following
 claims and their equivalents.