Abstract:
A passive/reactive device protects a Payload from injury or damage due to the shock caused by impact or explosion. When the vehicle or structure mounting the Payload receives a shock pulse, the invention limits the acceleration transmitted from the vehicle or structure to the Payload to an acceptably low, user-adjustable level which is substantially constant or is some other user-adjustable force-displacement function. The invention is capable of doing so even when the peak magnitude of the imposed shock is on the order of thousands of G&#39;s, with a rise time to peak on the order of microseconds. The invention can be embodied to operate passively, without any external source of power, sensor system, or CPU, although they can be added to improve certain usability features. The invention also absorbs or dissipates the shock energy in substantially the minimum distance possible without exceeding the user-defined acceleration limit on the Payload. The invention can also react when a shock-producing impact is imminent by repositioning the Payload away from the impact site. The Payload can be a person or persons, or shock-vulnerable equipment. The shock can be created in a number of ways, including an explosion, an impact or collision, the slamming on high-performance boats and some off-road vehicles, earthquake, or even intentional shocks on an amusement thrill ride. The ability of the invention to protect against shock is limited only by its ability to absorb or dissipate the energy of the shock pulse on the Payload. The device can be implemented to protect against shock from any arbitrary direction. The name Shock-Limiting Interface, Compact (SLIC) is coined for this invention.

Description:
The present invention claims the priority of Provisional Patent Application 60/345,275 filed Jan. 2, 2002, and Provisional Patent Application 60/402,522 filed Aug. 09, 2002, the disclosures of which are incorporated herein by reference in their entireties. 
   The present invention is a new concept in protecting a Payload from injury or damage due to the shock of impact experienced by the Payload&#39;s vehicle (or structure). The present invention is installed as an interface between the Payload and vehicle, and limits the force transmitted to the Payload while absorbing the energy of the shock pulse. The invention can be embodied in many ways, including as a seating system, a passenger platform, an equipment mounting system, a crash protection capsule, a blast-proof chamber, or a thrill ride. 
   The invention is unusually adept at protecting against shock. Unlike other shock-absorbing approaches which reduce the transmitted shock to a percentage of the excitation shock, this invention unequivocally limits the force transmitted from the vehicle (or structure) to the Payload to a low, user-adjustable value. It does this virtually independently of the magnitude of the impact acceleration or jerk (d 3 x/dt 3 ). In addition, the invention accomplished this using the minimum possible relative displacement between Payload and vehicle, consistent with not exceeding the limit on acceleration transmitted to the Payload. 

   BACKGROUND OF THE INVENTION 
   Planing boats operating in rough water may experience significant vertical shocks when the boat and wave impact one another. The most powerful shocks occur after a boat has become airborne flying off the crest of a wave, when the boat lands onto a wave face with its keel substantially parallel to the wave surface. Shock impulses on the order of 50 Gs with pulse durations in excess of 40 milliseconds are not uncommon, and suck shock is more than enough to cause serious injury. Documented injuries include sprains to the back, neck, hip, knee, and shoulder, kidney damage, and broken ribs and limbs. 
   Typically, naval architects have attempted to reduce this shock by deepening and narrowing the hull, and pointing the bow. These deep-vee hulls impact the water more gradually and with less peak acceleration than shallower, flatter hulls. But deep-vee hulls require deeper water for safe navigation may have roll stability issues, and generally require more fuel for a given speed than shallow-vee hulls. Moreover, they cannot unquestionably limit the acceleration on the Payload in all cases of boat-water impact. 
   Boat operators typically attempt to reduce shock by either slowing down considerably in rough water, or slowing down somewhat while attempting to steer and throttle around the biggest waves while avoiding becoming airborne. The drawback of these approaches is the speed reduction. Military and law-enforcement boats often cannot slow too much without risking mission failure. Offshore power boats cannot slow too much without risking the race. 
   A number of hardware devices have been developed and are in use, including several that have been patented. All have drawbacks. Perhaps the most serious drawback of previous approaches is that they cannot protect the Payload if the incident shock peak or its rate of rise is too large. Many of these devices work reasonably well provided the peak shock amplitude is fairly low, for example, shock peak under 10 G&#39;s with jerk under 100 G&#39;s per second. But the performance of these same devices degrades as the rate of rise and/or peak amplitude of the acceleration increases. Faster boat speeds and rougher seas create sharper, more powerful shocks, with peaks on the order of 50 G&#39;s and jerk on the order of 1,000 G&#39;s per second. Previous approached are generally based on viscous dampers and springs. A viscous damper&#39;s force is a function of the relative velocity of its endpoints. Even if actively controlled, a viscous damper transmits forces to the Payload which depend on the peak load and loading rate of the shock pulse. 
   A problem related to protection from boat shock is protection from explosive shock. Explosive devices generate accelerations on the order of thousands of G&#39;s with jerk on the order of tens of millions of G&#39;s per second. Explosions have such short pulse durations, as small as a fraction of a millisecond, that an active protection system would require an extremely high sampling rate, some very rapid processing algorithms to discriminate between noise and an actual explosion, and very rapid actuators to effect protection of the Payload, making an active protection system very expensive, if it could be made at all. Current approaches using passive viscous damping systems would either break or dump fluid out their relief valve under such extreme forces. Traditional approaches to protecting against shock differ somewhat depending, upon the nature of the Payload. If the Payload consists of equipment, the traditional approaches have been to either harden it or mount it on resilient mounts. Hardening generally results in increased weight and volume, and often impacts accessibility or maintenance and convective cooling. Resilient mounting often exacts volume penalty in order to accommodate sway and surge of the equipment during shock. In cases where the Payload is personnel, there have also been two similar traditional approaches. The first is to brace for shock, generally involving bending the legs and holding onto handrails while tensing the muscles. The other approach has been some type of resilient interface such as padded seating or heavy sponge rubber deck covering on a ship traversing a suspected minefield. No systematic, engineered approach which can unequivocally protect a Payload from explosive shock has been developed. Another drawback of many previous approaches is an inability to adjust to the weights of various Payloads. These devices are either overly stiff or overly-soft depending upon the Payload-mass. Overly stiff devices obviously transmit too much force to the Payload. But overly soft devices may also be inadequate in that they expend all available relative displacement between Payload and vehicle without absorbing all the shock energy. The Payload then bottoms out, spiking the acceleration. Even if the Payload does not bottom out, an overly soft interface takes up more volume than required, impacting its usefulness, particularly in high-performance vehicles. A further drawback of previous devices is a slow reset time. If the device cannot restore the Payload to its original position before the next shock hits, then the next shock may cause it to bottom out. 
   The purpose of the present invention is to protect the Payload (personnel and sensitive equipment) firm shock. It does so by limiting the force transmitted to the Payload to a low, user-adjustable value, regardless of the peak amplitude or rise rate of the imposed shock on the vehicle or structure. Another purpose of the present invention is to provide adjustment of the force transmitted to the Payload from the vehicle or structure to accommodate the masses of various Payloads without being overly stiff or bottoming out. Anther purpose of the present invention is to have a quick reset time so that it can be fully recovered in time for each subsequent shock events. BRIEF DESCRIPTION OF THE INVENTION In accordance with the foregoing purposes and other purposes and intents, the invention is based upon three, required principles and one optional principle. The first principle is limiting the acceleration upon the Payload regardless of the peak shock imposed upon the vehicle. 
   The second principle is that the displacement required to dissipate the shock energy be minimized. The third principle is adjustability to accommodate range of Payload masses. The fourth principle is optional and is the ability to react to an impending shock by repositioning the Payload to gain more displacement over which to dissipate the shock energy. A number of useful ways to implement the above principles are conceived. Various seating systems, equipment foundations, cockpit enclosures, platforms, and even entire chambers can be isolated from their surroundings by the present invention. The invention is generically comprised of four required assemblies, plus one optional assembly. 
   (1) The Frame Assembly (FA) mounts directly to the vehicle. It provides Structural support to the other major assemblies, constraining their movement to within acceptable limits, and enabling them to function properly. 
   (2) The Payload Interface Assembly (PIA) directly interfaces with the Payload. It directly supports and restrains the Payload. It provides monitoring and control capabilities for the invention. 
   (3) The Suspension Assembly (SA) supports the PIA. During a shock, the SA works with the EDA to allow the PIA to move just enough to avoid exceeding the acceleration limit on the Payload, and then recovers the PIA. 
   (4) The Energy Dissipating Assembly (EDA) dissipates the shock energy. 
   (5) The optional Shock Anticipating Assembly (SAA) is a reactive assembly which repositions the PIA just prior to shock so that more displacement is available to absorb or dissipate the shock. According to one aspect of the invention, a limiting interface for supporting a payload relative to a structure includes a frame assembly attached to the structure, a payload interface assembly for receiving the payload, a suspension between assembly disposed between the frame assembly and the payload interface assembly, and an energy dissipating, assembly disposed between the frame assembly and the payload interface assembly. The energy dissipating assembly is adapted to dissipate energy transmitted to the structure, so as to limit a parameter of interest transmitted to the payload. Depending on the particular application, in various embodiments, the parameter of interest can be displacement, time integrals of displacement including velocity, acceleration and jerk, as well as vibration, force, energy, and shock. Based on an event that causes an input to the structure, the limiting interface can be configured to attenuate the energy, so ask to transmit to the payload a predetermined maximum parameter of interest in a predetermined manner. For example, in one embodiment, a force displacement profile of the payload interface assembly is substantially linear. Alternatively or additionally, in another embodiment, the force-displacement profile of the payload interface assembly is substantially constant. In yet another embodiment, the force displacement profile of the payload interface assembly is substantially a square wave. The limiting interface may optionally include an anticipating assembly disposed between the frame assembly and the payload interface assembly that repositions the payload interface assembly relative to the structure from a neutral position in anticipation of an event. In one such embodiment, the anticipating assembly increases a range of travel of the payload interface assembly relative to the structure in anticipation of an event. In various embodiments of the invention, the suspension assembly permits relative movement between the payload interface assembly and the structure in a first direction only, when acceleration or other parameter of interest transmitted to the payload is about to exceed a predetermined value. In still other embodiments of the invention, the suspension assembly permits relative movement between the payload interface assembly and the structure in a first direction only, for as long as acceleration or other parameter of interest transmitted to the payload is about to exceed a predetermined value. According to one embodiment, the limiting interface and the energy dissipating assembly are capable of accommodating a plurality of events. The limiting interface may be reset automatically or, alternatively, manually. In various embodiments of the resetting type, after at least one event, the payload interface assembly is returned to a neutral position by the suspension assembly. In other embodiments, the energy dissipating assembly is capable of accommodating a single event, and can be rebuilt or refurbished to restore functionality. 
   In various embodiments, whether multiple event, single event, resettable or refurbishable, the energy dissipating assembly may be configured to convert kinetic energy transmitted to the structure at least partially into thermal energy. In some embodiments, the energy dissipating assembly may be configured to deform an element, elastically and, optionally, plastically. The energy dissipating assembly may be a friction brake, of any of a variety of configurations. The limiting interface may advantageously be adjustable, to accommodate payloads of various configurations and mass, including equipment and personnel. In those instances where the payload is a person, the payload interface assembly may be a platform, bench, seat, or any suitable supporting structure for a person. Similarly, the structure may be any of a variety of structures, including aeronautic-based, land-based, or water-based vehicles. 
   According to another aspect of the invention, a method for supporting a payload relative to a structure includes, in one embodiment, the steps of providing a limiting interface attached to the structure and adapted to receive the payload and dissipating energy transmitted to the structure, so as to limit a parameter of interest transmitted to the payload. In one embodiment, the limiting interface does so by converting at least a portion of kinetic energy transmitted to the structure to substantially a square wave force-displacement profile transmitted to the payload. Alternatively or additionally, a magnitude of the force-displacement profile may be substantially constant. In general, the magnitude of the square wave force-displacement profile is less than a predetermined value. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram of the Payload, a generic SLIC device, and the vehicle (or structure). 
       FIG. 2  shows a basic SLIC device implemented as a seating system which uses a straight-mounted SA actuator and “Check-Clamp” type EDA. 
       FIG. 3  shows details of the Check-Clamp EDA used in the SLIC device of  FIG. 2 . 
       FIG. 4  shows a vector diagram of the clamping force in the Check-Clamp EDA of  FIG. 3 . 
       FIG. 5  shows a variant of the FA from the SLIC device of  FIG. 2 , in which the rails are tipped backwards. 
       FIG. 6  shows a SLIC device in which the SA actuator has been mounted at an angle with respect to the direction of movement of the PIA. 
       FIG. 7  shows a SLIC device using twin pneumatic actuators mounted at mirror angles to one another to support the Payload Pan. 
       FIG. 8  shows a SLIC device similar to that of  FIG. 7 , but using twin matched gas charged lift supports. 
       FIG. 9  shows a SLIC device in which the FA uses a four-bar linkage to constrain the movement of the PIA. 
       FIG. 10  is a different view the SLIC device of  FIG. 9 . 
       FIG. 11  shows a SLIC device featuring a bell crank and linkage to amplify the movement and reduce the force of the SA actuator on the Payload Pan. 
       FIG. 12  shows a Check-Clamp type EDA similar to that of  FIG. 4  but with springs mounted at angles replacing the counterweights, drop stops, and spring. 
       FIG. 13  shows a Check Clamp type EDA which uses a lever to amplify the clamping force of the EDA actuator, a roller bearing replacing the linkage on one side, and a more sensitive mechanism for adjusting the engagement/disengagement of the clamping feature. 
       FIG. 14  shows a Check Clamp type EDA in which both pressure pads are mounted on roller bearings. 
       FIG. 15  shows details of the pivot adjusting mechanism used in  FIG. 14 . 
       FIG. 16  shows how the required clamping force in a Check-Clamp type EDA can be reduced by adding additional suspension bars and associated brake components. 
       FIG. 17  shows details of some components of the multiple suspension bar Check-Clamp type EDA of  FIG. 16 . 
       FIG. 18  shows a simple SAA arrangement. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In accordance with the foregoing purposes and other purposes and intents, the invention is based upon three required principles and one optional principle, a more expanded discussion of which follows. 
   Principles of Operation 
   The first principle is limiting the acceleration on the Payload to a level below that which would cause injury or damage. To this end, a SLIC device is designed so that is cannot sustain a force between the Payload and vehicle greater than that which would cause injury or damage. No matter how large the force or acceleration on the vehicle, the SLIC device only transmits an acceptably low force to the Payload. 
   The second principle is that the change in relative displacement between the Payload and vehicle is kept to a minimum. This makes the device as compact as is substantially possible without violating the first principle. To achieve this substantially minimum displacement, the SLIC device does not allow relative movement between Payload and vehicle in response to shock unless the acceleration on the Payload is about to exceed the injury or damage limit, and then allows only as much movement as is substantially necessary to absorb or dissipate all the shock energy, imposed on the Payload. 
   The third principle is adjustability to accommodate the masses of various Payloads. More massive Payloads must be supported with more force than less massive Payloads to achieve equal accelerations and thus equal protection from shock. 
   The optional fourth principle is that the invention react to an impending shock by repositioning the Payload to provide more relative displacement at impact. Since energy is force integrated over distance, more relative displacement means that the energy of a given shock pulse can be dissipated at a lower force. 
   A corollary principle that follows from the above is that the force-displacement output of the invention upon the Payload be substantially a square wave. The magnitude of a square wave approaches but does not exceed the limiting force, and its pulse width is the shortest possible given the amount of energy to be absorbed. It is the most efficient profile for absorbing any given shock pulse with out exceeding the limiting force on the Payload. The invention is unique in that it can transform a shock impulse of thousands of G&#39;s peak amplitude and jerk (d 3 x/dt 3 ) on the order of tens of millions of G&#39;s per second into a force-displacement profile which is substantially a square wave, of adjustable and substantially constant magnitude. 
   Another corollary principle is that the present invention can slow a person to a complete stop, safely, in a minimum distance, from speeds of almost arbitrary magnitude. 
   There are two limits on the capability of the invention to protect against any arbitrary shock. The first limit is in regards to the strength of the FA. The FA must be designed strong enough to withstand two conditions. The first condition is the ability to withstand without significant deformation, the body force resulting from the perhaps thousands of G&#39;s acceleration experienced by the vehicle, which is also experienced by the FA. The second condition is that the FA be strong enough to support the force resulting from the user-adjusted acceleration of the masses of the Payload, PIA, SA, EDA, and SSA (if implemented), which must be supported by the FA. The second limit on the capability of the invention is its capacity to fully absorb or dissipate to energy in the shock pulse directed upon the Payload. This is an energy balance criterion. In the time domain, the integral over time of the output acceleration of the SLIC device must be equal to the integral over time of the input acceleration of the shock. In the space domain, the available relative displacement of the Payload with respect to the vehicle must exceed that required to fully absorb the shock. If all the energy is not fully absorbed, then the device will bottom out, spiking the acceleration felt by the Payload. 
   Concepts of Embodiment 
   A number of useful shock-limiting applications for conceived. The invention has applications for protecting a Payload housed in a structure as a Payload riding in a vehicle. Various seating systems, equipment foundations, cockpits, standing platforms, even entire chambers can be isolated from their host vehicle or their other surroundings. The invention can also be implemented on the exterior of a vehicle, as a shock-limiting to reduce the impact force of a head-on collision. The invention could be installed on the exterior of a fixed structure, such a bridge abutment, to limit the force on the structure which may result from accidental vehicle impact. An amusement park thrill ride offering a vertical free-fall of several hundred feet and a “sudden” thrill stop at the end could be implemented. Another application is as a bumper system on the front end of a vehicle 
     FIG. 1  shows a block diagram of a SLIC device  100  mounted functionally between the Payload and the vehicle (or structure). The SLIC device is shown to be composed of the four required major assemblies, the Frame Assembly (FA)  95 , the Payload Interface Assembly (PIA)  96 , the Suspension Assembly (SA)  97 , and the Energy Dissipating Assembly (EDA)  98 , plus the optional fifth major assembly, the Shock Anticipating Assembly (SAA)  99 . Each of these assemblies shall be discussed here in generic terms, and later in more detail, with several examples of typical embodiments. 
   The FA  95  provides structural support to the other major assemblies, and mounts directly to the vehicle or structure. The FA  95  generally constrains the movement of the other major assemblies to within certain geometric bounds, enabling them to function properly. Since the FA  95  is fastened directly, to the vehicle, it experiences whatever shocks the vehicle does. The shock on the FA  95  may be attenuated somewhat by plastic deformation of the vehicle frame, but may also possibly be exacerbated by elastic spring-back of the vehicle frame. 
   The PIA  96  directly interfaces between the Payload and the other major assemblies. It touches and supports the Payload and provides monitoring and control capabilities for the invention. The heart of the PIA  96  is the Payload Pan (not shown in  FIG. 1 ), which is a structural assembly to which the other components of the PIA  96  are attached. The Payload Pan is constrained by the FA  95  to move within certain limits, and is connected to the SA  97  and EDA  98 , and also the SAA  99  when implemented. If the Payload consists of shock-vulnerable equipment, the PIA  96  consists of the Payload Pan, the connecting components enabling smooth low-friction movement within the FA  95 ; the joints and connections to the other major assemblies, appropriate hardware to fasten the equipment, and an Interface Monitoring and Control Panel (IMCP) assembly, which is used to monitor and adjust the performance of the invention. If the Payload is a person or persons, the equipment mounting fasteners would be replaced by various human interface components such as seat pad(s), seat back(s), seat belt(s) and harness(es), a standing platform, arm rest(s), hand rail(s), footrest(s), leg rest(s), lumbar support(s), head rest(s), neck support(s), and other sundry comfort amenities. Depending upon the severity of the shock environment, the PIA may also mount a Vehicle Monitoring and Control Panel (VMCP) assembly used to navigate and pilot the vehicle. This is to fully isolate the personnel, reduce operator fatigue, and improve performance. For military or law-enforcement applications, a communications panel, a weapons control panel, or other mission-specific items, may also be included, for example. 
   The SA  97  mounts between the PIA  96  and FA  95 , except when the optional SAA  99  is incorporated. The SA  97  supports the PIA  96  at the Neutral Position. The Neutral Position is the normal, user-adjustable position of the Payload with regard to the shock vector, for example, the seat height in regards to an upwardly-directed shock. After a shock, the SA  97  operates on conjunction with the EDA before the next shock pulse hits. During a shock event, the SA  97  operates in conjunction with the EDA  98  to provide a substantially constant force output between the PIA  96  and FA  95  over the full range of motion of the PIA  96 . There are three methods for the SA  97  to function with the EDA  98 . One method hereafter known as “SA/EDA Method 1” is for the SA  97  to provide only a nominal supporting force while the EDA  98  provides the bulk of the resistive force as it dissipates energy during the shock stroke. The EDA  98  then disengages, and the SA  97  recovers the PIA  96  to the Neutral Position using the same nominal supporting force, but with damping as it approaches the Neutral Position, to avoid launching the Payload out of the PIA  96 . The second method, hereafter known as “SA/EDA Method 2”, is for the SA  97  to provide the bulk of the resistive force while it stores the shock energy during the shock stroke, while the EDA  98  is disengaged. The SA  97  then recovers the PIA  96  to the Neutral Position at a force reduced by the EDA  98 , which engages to dissipate the stored energy. The third method, “SA/EDA Method 3” combines the first two methods. 
   The EDA  98  dissipates the shock energy. It works with the SA  97  as described above. 
   The SAA  99  is the optional assembly. It may be included when the timing and direction of the shock vector can be predicted with reasonable accuracy. The SAA  99  mounts interposed between the PIA  96  and the SA  97 , with the EDA  98  mounted around them. Nominally a reactive assembly, the SAA  99  repositions the PIA  96  relative to the FA  95  just prior to shock so that a greater displacement distance is available to dissipate or absorb the shock energy at impact. This provides two significant advantages. The most obvious advantage is that the shock energy can be absorbed and dissipated at a lower force than would be possible than over a shorter distance. The second advantage is that the Payload&#39;s average position is maintained closer to the Neutral Position, assuming that the Payload sweeps through the Neutral Position as a result of the shock. Note that when an SAA  99  is included in the SLIC device  100 , the SA  97  and EDA  98  function together under SA/EDA Method 2. 
   In one of its simplest embodiments, for example as part of a seating system aboard a high-performance planing boat, the SAA  99  simply reacts to the free-fall period before impact. In this example, the SAA  99  provides a continuous upward force upon the PIA  96  at a fraction of the combined weights of the Payload, PIA  96 , and the parts of the SA  97  and EDA  98  moving with them. During the time intervals between shocks, the PIA  96  simply remains at the Neutral Position, since the upward force of the SAA  99  is too weak to exceed the weight of the components. As the boat becomes airborne speeding off the crest of a wave, an impact shock with some other part of the seaway is imminent. Neglecting aerodynamics, the boat accelerates downward at −1.0 G. The SAA  99  reacts to the free-fall, raising the PIA  96  and Payload upwards with respect to the falling boat, creating extra displacement beyond that inherent in the Neutral Position. At impact, the EDA  98  uses the extra displacement to dissipate energy. 
   An example of a much more sophisticated embodiment of an SAA  99  would use a set of powered actuators to reposition the PIA  96 . The actuators would have to receive their commands of when and where to reposition the PIA from a CPU, which in turn would be fed from a sensor array and/or communication is link. The sensors would have to be capable of detecting potential shock threats and the CPU would have to be capable of resolving the sensor data in real time to discriminate real shock threats from false ones. The communications link would presumably tell of the onset of a real, perhaps massive shock threat such as an earthquake or nuclear blast. Since electrons move faster than shock waves, there is the possibility that a suitable sensor array networked across the epicenter or ground zero and linked to an appropriate CPU could detect a massive shock event in time to warn nearby SLIC devices so that they could reposition their PIA&#39;S. 
   In general, the SLIC device  100  will function most effectively when the constrained movement of the PIA  96  is aligned with the shock vector. Supporting the PIA  96  with three of mutually orthogonal sets of SA  97  and EDA  98  will protect the Payload from any arbitrarily oriented shock. Alternatively, the entire SLIC device  100  can be mounted in a gimbaled assembly. 
   Embodiment of the Invention 
   A Typical SLIC Device 
     FIG. 2  shows an embodiment of a typical SLIC device implemented as a vehicle seat intended to protect against an upwardly-oriented shock. The Payload Pan  20  rides up and down on rails,  10   a  and  10   b , and is equipped with rollers  21  to reduce friction. The rails are fastened at their upper ends to crossmember  11 , and at their bottom ends to foundation  12 , which is fastened to the deck of the vehicle. Braces  13   a ,  13   b ,  13   c ,  13   d ,  13   e , and  13   f  (shown in phantom) help the crosshead  11  and foundation  12  maintain alignment of the rails  10   a  and  10   b . Similar braces (not shown) leading to the foundation or vehicle deck forward and/or backward stabilize the rails  10   a  and  10   b  from swaying forward or backward (into or out of the paper), and together with the foundation  12  and the other braces  13   a–f  provide torsional stiffness as well. The Payload Pan  20  supports the Payload, in this case, a person. In this case then, several typical seat features are mounted to the Payload Pan  20  such as a seat bottom, seat back, lumbar support, padding, armrests, footrests, seatbelt, shoulder harness, etc. All these features are considered typical of many seating systems and are omitted from the drawing for clarity. An important assembly mounted to the Payload Pan  20  in a spot convenient to the user is the Interface Control Panel (ICP)  27 , which has been drawn to the side of the FA for clarity. The ICP  27  enables the user to monitor and adjust the performance of the SLIC device. In this particular embodiment, the components of the ICP  27  are the SA accumulator fill  41 , SA accumulator bleed valve  42 , SA pressure gage  44 , flow control valve  47 , EDA fill valve  61 , EDA bleed valve  62 , and EDA pressure gage  64 , each of which shall be discussed more fully later. The Payload Pan  20  is supported by the SA actuator  30 , which is mounted to the Foundation  12  at clevis bracket  16   a , and attached to the Payload Pan  20  at clevis bracket  32 . The SA actuator  30  supports the Payload Pan  20  at the Neutral Position  37 . The upward support force developed by the SA actuator  30  is a function of its piston area and the pressure of the gas in the SA accumulator  40 . The gas in the cap end of the SA actuator  30  and SA accumulator  40  are in free communication through appropriate hose and piping  49   f . The SA accumulator  40  provides extra gas volume to lessen the pressure rise due to compression of the SA actuator  30  as the Payload Pan  20  strokes downward. The user can monitor the pressure in the SA actuator  30  at the ICP  27  using the SA pressure gage  44 . The user can raise the initial pressure in the Sa actuator  30  by opening the SA fill valve  41 , allowing higher-pressure gas from the flask  45  to enter through appropriate piping and hose  49   a  and  49   b . Similarly, the user can reduce the SA actuator  30  pressure by opening the SA bleed valve  42 , allowing some gas to escape to the atmosphere through appropriate piping and hose  49   b  and  49   d . On this type of SLIC device where the EDA  98   a , fully discussed later, provides the bulk of the resistance versus shock, the initial pressure in the SA actuator  30  would typically be adjusted to provide an upward force of between 1.2 to 1.4 times the combined weight of the Payload plus PIA. After initial adjustment, the pressure can be readjusted as desired to counteract pressure changes due to temperature change or leakage. The SA actuator  30  provides all the force during the upward stroke restoring the Payload Pan  20  to the Neutral Position  37 . Over-pressurization of the SA accumulator  40  is prevented by the SA relief valve  43 . To reduce contamination of the head-end chamber of the SA actuator  30  when the piston strokes downward, makeup air comes from a plenum  48  which is connected through appropriate hose and piping  49   e . A flow control valve  47  is installed in the piping  49   e  which allows free flow of gas into the head-end chamber but throttles the gas coming out. The user can adjust the position of the flow control valve  47  to control the rate of ascent of the Payload Pan  20  back to the Neutral Position  37 . The flask  45  is charged from a separate air source such as an onboard compressor through appropriate supply piping  49   g  by opening the flask supply valve  46 . The pressure in the EDA accumulator  60  is monitored at the ICP  27  using the EDA pressure gage  64 . The EDA accumulator  60  pressure can be adjusted by opening either the EDA fill valve  61  to increase gas charge from the flask  45 , or opening he EDA bleed valve  62  to allow some gas to escape to atmosphere. The EDA Accumulator  60  supplies pressure to the EDA actuator ( 65 , in  FIG. 3 ) which is part of EDA  98   a  and will be discussed more fully in  FIG. 3 . The SA and EDA are arranged to work in SA/EDA Method 1, described above. A spring snubber  34  is mounted to a bracket  16   d  attached to the foundation  12  to prevent excessively hard impact or bottoming out the SA actuator  30  in case of hose rupture or other cause of pressure loss in the SA actuator  30 . The suspension bar  17  is fastened to the crossmember  11  at clevis bracket  16   c  and attached to the foundation  12  at clevis bracket  16   b . The EDA  98   a  is fastened to the Payload Pan  20 . 
     FIG. 3  shows the details of EDA  98   a  from  FIG. 2 . We coin the term “Check-Clamp” to describe this type of EDA because of the way it functions. EDA  98   a  dissipates energy at an adjustable, substantially constant force when the relative movement of the EDA  98   a  relative to the suspension bar  17  is downward, and allows free movement of the EDA  98   a  at only nominal force when its relative movement is upward. The top end of the suspension bar  17  is fastened to the crosshead  11  (shown in part) at clevis bracket  16   c , and its bottom end is attached to the foundation  12  (shown in part) at clevis bracket  16   b . The suspension bar  17  passes through the EDA framework  50  though milled slots  50   a  and  50   b . The EDA framework  50  is fastened to the Payload Pan  20  (not shown in this Figure). Pressure pads  51   a  and  51   b  have been fitted with brake shoes  52   a  and  52   b  which have brake linings  53   a  and  53   b  bonded to them. The brake shoes  52   a  and  52   b  are fastened to the pressure pads  51   a  and  51   b  using threaded fasteners  59   a  and  59   b . One of the pressure pads  51   a  is attached to one end of the EDA actuator  65  by bushed clevis pin  55   a . The EDA actuator  65  is fitted with a body trunnion mount, the trunnion pins  55   c  of which pivot in bushings at an intermediate point along lever  67 . The upper end of lever  67  is attached to the EDA framework  50  at clevis bracket  50   c  using bushed clevis pin  55   e . The lower end of lever  67  is tapped to accept jackscrew  66   a . The other end of jackscrew  66   a  bears on the EDA framework  50  at a hardened point  57   c , so turning the jackscrew  66   a  in or out will adjust the position of the lower end of the lever  67 , which in turn adjusts the position of the trunnion pins  55   c , which is the pivot point for the EDA actuator  65 . A periodic maintenance adjustment of the jackscrew  66   a  is needed to compensate for wear in the brake linings  53   a  and  53   b . The jackscrew  66   a  is equipped with jam nut  66   b  to lock it in position once adjusted. A spring  66   c  keeps the jackscrew  66   a  in contact with the EDA framework  50  to stabilize the adjusted position of the bushed clevis pin  55   c , and prevent peening damage to either the hard point  57   c  or the end of the jackscrew  66   a . A counterweight  69   a  is fastened to the other end of the EDA actuator  65  in order to approximately balance the moments of the FDA actuator  65 , the pressure pad  51   a , the brake shoe  52   a , the brake lining  53   a , the fastener  59   a , and the bushed clevis pin  55   a  about the bushed trunnion pins  55   c . This prevents gravity or other body forces from causing rotation of the EDA actuator  65  about the bushed trunnion pins  55   c . The other pressure pad  51   b  is attached to one end of the linkage  54  using bushed clevis pin  55   b . The linkage  54  is attached at an intermediate point to the EDA framework  50  at clevis bracket  50   d  using bushed clevis pin  55   d . A counterweight  69   b  is fastened to the other end of the linkage  54  and performs a balancing function similar that of counterweight  69   a . The cap end chamber of the EDA actuator  65  is pressurized from the EDA accumulator  60  (shown in  FIG. 2 ) through piping/hose  49   i . The EDA actuator  65  can therefore clamp the brake linings  53   a  and  53   b  onto the suspension bar  17  at a specific normal force equal to the product of the piston area of the EDA actuator  65  times the pressure of the EDA accumulator 60 times the sine of the angle made between the EDA actuator  65  and the suspension bar  17 . But this clamping only occurs when the suspension bar  17  rises with respect to the EDA framework  50 , which happens during the shock down stroke. At all other times, the brake linings  53   a  and  531   b  are in contact at with the suspension bar  17  but at a much smaller normal force provided by the tension in spring  68  and counterweights  69   a  and  69   b  (see below for more details). During the downward shock stroke, friction between the brake linings  53   a  and  53   b  and the suspension bar  17  cause the brake linings to stick to the suspension bar. As the suspension bar  17  rises, the EDA actuator  65  and linkage  54  pivot upwards with it, bringing the upper surfaces of the pressure pads  51   a  and  51   b  into contact with the hardened surfaces  57   a  and  57   b  on the EDA framework  50 . The EDA  98   a  will continue to move downward on the suspension bar  17  only if the downward force on it exceeds the frictional resistance between brake linings  53   a  and  53   b  and the suspension bar  17 . The frictional resistance is equal to two times the product of the clamping force normal to the suspension bar  17  times the coefficient of friction between the brake linings  53   a  and  53   b  and the suspension bar  17 . The EDA  98   a  continues to move downward until the all the shock energy has either been dissipated by friction or stored in the increased enthalpy of the gas in the SA accumulator, SA actuator, and associated piping and hoses ( 40 ,  30 , etc. in  FIG. 2 ). Then, the SA actuator ( 30  in  FIG. 2 ) applies a net upward force on the Payload Pan ( 20  in  FIG. 2 ), which raises the EDA  98   a  with respect to the suspension bar  17 . The friction of the brake linings  53   a  and  53   b  with the suspension bar  17  causes the EDA actuator  65  and linkage  54  to rotate downwards. The downwards rotation is aided by the obtuse angles that the EDA actuator  65  and linkage  54  make with the suspension bar  17 . After a few degrees of downward rotation, the EDA actuator  65  bottoms out, totally releasing the clamping force of the pressure pads  51   a  and  51   b  on the suspension bar  17 . Excessive downward rotation is prevented by the tension in spring  68 , and stop bars  58   a  and  58   b  which are fastened to the EDA framework  50  by threaded fasteners  59   c  and  59   d , and fastened to the tapped holes in bushed clevis pins  55   a  and  55   b  by threaded fasteners  59   e  and  59   f . The EDA  98   a  therefore provides only the minimal frictional resistance due to the spring  68  clamping force as it is raised up with respect to the suspension bar  17 . The tension spring  68  provides enough force to maintain continuous contact between the brake linings  53   a  and  53   b  and the suspension bar  17 , so that when another shock hits, the whole clamping process will be repeated. 
   More on Some of the Concepts Presented in the SLIC Device of  FIGS. 2 and 3 . 
   The counterweights  69   a  and  69   b  only need to approximately balance the EDA actuator  65  (and attached components) about bushed trunnion pins  55   c  and linkage  54  (and attached components). It is preferred to make the counterweights slightly heavier than would be required to balance precisely. This is so that the shock vector will tighten rather than loosen the pressure pads  51   a  and  51   b  upon the suspension bar  17 . As the brake linings  53   a  and  53   b  wear away the imbalance becomes even more favorable. While slightly overloading the counterweights  69   a  and  69   b  implies that negative-G body forces (free fall for example) will tend to loosen the clamping, the tension spring  68  can easily be made strong enough to maintain the brake linings  53   a  and  53   b  in firm contact with the suspension bar  17 . Alternatively, counterweights would not be needed at all if the spring  68  were made stiff enough, but this would increase the resistance during the recovery. 
   It is important that pressure pads  51   a  and  51   b  stop at the hardened surfaces  57   a  and  57   b  prior to cam-locking over center. This ensures prompt and easy disengagement from the suspension bar  17 . Stopping the rotation about five degrees short of locking over center is a good design point. 
     FIG. 4  shows the vectors involved in clamping the Pressure Pads  51   a  and  51   b  to the suspension bar  17 . It is important that the brake linings  53   a  and  53   b  stick and not slide on the suspension bar  17  at initial engagement at the start of a shock pulse. The maximum angle that the EDA actuator  65  and linkage  54  can rotate to and still clamp is θmax. Examining the geometry of one side of the clamping mechanism, we can resolve the thrust vector F of the EDA actuator  65  into a vertical component Fsinθ and the horizontal component Fcosθ. The vertical component tends to make the brake lining slip on the suspension bar  17 , and the horizontal component multiplied by the frictional coefficient tends to make it stick. Though the brake linings  53   a  and  53   b  would typically have a somewhat higher static coefficient than dynamic, we shall use the dynamic coefficient to be conservative in case there may be some slipping before full clamping. Typical brake lining material has a minimum dynamic frictional coefficient of 0.35 or greater depending upon the material. This results in a maximum drop angle θmax of 19.3 degrees to ensure clamping. The preferred embodiment uses a conservative design value of no more than thirteen degrees for θmax. This corresponds to a frictional coefficient of 0.23, or a 34% safety margin to allow for slight degradation of the brake lining material due to contamination, pitting, etc. 
   Bottoming out the EDA actuator  65  at or before θmax is important to the proper disengaging of the clamping action. 
   As the brake linings  53   a  and  53   b  wear away, the clamping action will disengage at a smaller and smaller angle θ, and would eventually approach five degrees (i.e., no clamping at all) if the jackscrew  66   a  and jam nut  66   b  were not adjusted to compensate. Strictly speaking, the jackscrew  66   a  and jam nut  66   b  would not have to be readjusted until the brake linings  53   a  and  53   h  have worn the clamping angle θ down to 5+ degrees, but this would be imprudent. However, readjusting too frequently would seem burdensome. A reasonable compromise is to readjust the jackscrew  66   a  and jam nut  66   b  when the clamping angle θ has worn down to about ten degrees, and to readjust it back to thirteen degrees. 
   In general, whenever a clevis joint is specified, it may be replaced by a spherically-mounted bearing. 
   In general, all clevis pins are bushed with an appropriate friction-reducing and/or anti-corrosion bushing fitted to the ID of the clevis pieces and OD of the clevis pin. Bushings may be deleted if an analysis of the load, friction, wear, and corrosion circumstances of the clevis joint warrant. 
   The adjustment and retainer features provided by the jackscrew  66   a , jam nut  66   b , and spring  66   c  can just as effectively be provided in a variety of other common ways familiar to those practiced in the art. All of these other common ways are conceived. 
   The adjustments of the valves  41  and  42  to maintain pressure in the SA actuator  30  can be automated. There are several ways to do this, each of which involves electronically (digitally) sampling either the average pressure or the pressure at a specific Payload Pan  20  position (the Neutral Position  37 , for example) and comparing it to a reference signal corresponding to the initially-adjusted pressure value. If the measured signal differs from the reference signal by more than a specific amount, a control algorithm can trigger solenoids or similar actuators attached to valves  41  and  42  to admit or release gas and restore the pressure to the initial value. 
   The volume of the SA accumulator  40  in comparison to the swept volume of the SA actuator  30  affects the increase in the SA actuator force as it strokes. As a first-order approximation, the compression and expansion of the gas in the SA actuator  30  and the rest of the gas-filled components connected to it can be modeled as adiabatic. If air is used as the working fluid, then if the volume of the accumulator  40  and all connected hosing and piping  49   a ,  49   b ,  49   c ,  49   d , and  49   f  is on the order of twenty times the swept volume of the SA actuator  30 , then the upward force exerted by the SA actuator  30  will remain substantially constant throughout its stroke range (within about 3.5% of its mean value, or within about 7% of its initial value). This is shown by Table  1  and  FIG. 4  of the Provisional Patent Application filed 02 Jan. 2002. 
   The spring  68  is shown as a tension spring, and is shown mounted over the axial centerlines of bushed clevis pins  55   a  and  55   b . Neither of these is required for satisfactory operation. Other ways are conceived for performing the same function (maintaining the brake linings in contact with the suspension bar) by use of one or more compression springs, tension springs, leaf springs, rotary springs, etc., attached at various points, allowing the pressure pads to tilt with respect to the suspension bar  17 . 
   The use of a pneumatic actuator to support a load subject to shock is not novel. The use of a pneumatic actuator in conjunction with various mechanisms and mounting schemes to attempt to make the support substantially constant is novel. The use of such a support arrangement with a separate device which is intended to dissipate the shock energy at a substantially constant force is also novel. The use of such a combined mechanism with another mechanism designed to anticipate a shock event and increase the displacement available for absorbing/dissipating the shock energy by repositioning the Payload is also novel. 
   In  FIGS. 2 and 3 , the FA is composed of parts  10   a ,  10   b ,  11 ,  12 ,  13   a ,  13   b ,  13   c ,  13   d ,  13   e ,  13   f ,  16   a ,  16   b ,  16   c ,  16   d ,  17 , the fasteners used for mounting to the vehicle, the (unpictured) support braces running into the paper, an (unpictured) cover plate to keep hands away from moving machinery, and (unpictured) maintenance access hatches in the cover plate. For simplicity of illustration the rails  10   a  and  10   b  are shown as providing only lateral and roll support to the Payload Pan  20  through the rollers  21 . The rails actually provide support in the surge (fore and aft), yaw, and pitch directions as well. The rails only allow motion of the Payload Pan in the heave (vertical) direction. 
   In  FIGS. 2 and 3 , the PIA is composed of parts  20  and  21 , and the assembly  27 . It is to be understood that several mundane features common to seats are not shown for ease of illustration. Though only one roller is called out in piece  21 , it is to be understood that a number of rollers are required, in each of the movement directions restrained by the rails  10   a  and  10   b . The important function of piece  21  is to reduce friction in the allowable movement direction (heave) and support the loads restraining the Payload Pan  20  in all other directions. Piece  21  could therefore be embodied by a linear bearing, wheels on axles mounted to the Payload Pan  20 , wheels on axles mounted to the rails  10   a  and  10   b , or even by low-friction skid surfaces. 
   In  FIG. 2 , the SA is composed of parts  30 ,  32 ,  34 ,  40 ,  43 ,  48 , and the hoses  49   b ,  49   c ,  49   e , and  49   f . Parts  41 ,  42 ,  44 ,  47  and piping manifold  49   d  are parts of the IMCP assembly  27 , which is part of the PIA. 
   In  FIGS. 2 and 3 , the EDA is assembly  98   a , which is fully discussed in  FIG. 3 . 
   The SLIC device depicted in  FIGS. 2 and 3  do not have an SAA. 
   More Concepts 
     FIG. 5  shows one way in which the rails  10   a ′ and  10   b ′ can be tipped backwards by ten to fifteen degrees in order to align them more closely with the orientation of the shock vector on a high-performance boat. Studies have shown that the sharpest shock vectors are often tipped backwards by about ten to fifteen degrees.  FIG. 5  also shows one type of channel which provides the type of support needed to allow only one-degree of freedom movement of the PIA. Channels with cross-sections other than U-shapes are conceived. The important thing is that the channel and friction-reducing bearing work together to restrain the PIA in all directions but one, and in that direction, to allow low-friction movement. 
     FIG. 6  shows a SLIC device similar to that of  FIG. 2 , but with some differences in the SA. First, the SA actuator  130  is mounted at the angle θ with respect to the direction of movement of the Payload Pan  120 . Second, it is attached to the Payload Pan  120  at a different location, clevis bracket  132 . Third, the volume of the SA accumulator  140  is smaller than the volume of the SA accumulator  40  of  FIG. 2 . The SA accumulator  140  is smaller to increase the pressure rise as the SA actuator  130  strokes. The upward component of the SA actuator  130  force vector is diminished by the cosine of the angle θ. Fourth, the SA Actuator  130  must have a larger piston area than that of SA actuator  30 , just to equalize the lift force on the Payload Pan  120 . Alternatively, the initial system pressure could be increased, or a combination of each. Fifth, the stroke of the SA actuator  130  may be, but does not have to be, shorter than the stroke of the SA actuator  30 , because of the angle mounting. Sixth, the FA has to be stronger to withstand the extra side loading imposed by the horizontal component of the SA actuator  130 . Several design dependencies flow from the decision to mount the SA actuator  130  at an angle. The larger the mounting angle θ, the smaller the SA accumulator  140  must be in order to maintain the same vertical lift component on the Payload Pan  120 . The larger the mounting angle θ, the stronger the FA has to be to withstand the unbalanced lateral load. The larger the mounting angle θ, the greater the increase in piston area of the SA actuator  130  must be as compared to a simple straight-mounted SA actuator  30 , or alternatively, the greater the increase in initial system pressure must be. The larger the mounting angle θ, the shorter the stroke of the SA actuator  130  may be as compared to a simple straight-mounted SA actuator  30 . The larger the mounting angle θ, the greater the transient pressure rise in the pneumatic system, so care must be taken to avoid over-pressurizing the system. The larger the mounting angle θ, the greater the transient temperature increase in the pneumatic system, so care must be taken to ensure that any temperature-sensitive components such as seals, gaskets, or hoses are not damaged. Using the above guidelines, it is possible to tailor a suitable SA design optimized for particular performance attributes within the capabilities of he components selected. 
     FIG. 7  shows another SLIC device. Here, two matched SA actuators  230   a  and  230   b  have been mounted as mirror images to one another. They support the Payload Pan  220 , and cancel each other&#39;s lateral loadings. The components of the FA, including rails  210   a  and  210   b  can therefore be made less strong and lighter, etc. Another variation, which may or may not be advantageous from an arrangements standpoint, is the relocation of the SA accumulator  240  to within the FA boundaries. In general, however, keeping the components closer together helps save space and may improve performance by reducing weight, reducing time lag due to friction, etc. Note also that the pneumatic hosing must branch to supply both SA actuators  230   a  and  230   b.    
   The rendering of  FIG. 7  and the renderings in the Appendices of the Provisional Patent Filings have been simplified to enhance clarity. Most components common to the previous devices have been omitted from the Figure. The rails  210   a  and  210   b , though illustrated as simple flat surfaces capable of providing restraint in only the lateral and roll directions, in fact are channel sections or similar and provide restraint to the Payload Pan  220  in every direction except linear movement along their long axes. Similarly, the roller wheels  221  are illustrated in only one direction when in fact they must roll along the rails  210   a  and  210   b  to transfer the restraining forces to the Payload Pan  220  and reduce friction of its movement. Only the back frame of the Payload Pan  120  is illustrated. 
     FIG. 8  shows a SLIC device which uses a matched set of gas charged lift supports  330   a  and  330   b  as the SA actuator. These actuators are pre-charged with gas to provide a certain force output which increases with the compression stroke. They can be purchased with self-contained damping, which can be implemented on either the compression or extension stroke, or both. For this purpose, damping on compression is unneeded and undesirable. It would disrupt the substantially constant force upon the Payload Pan  320 , making it dependent upon the relative velocities of the Payload Pan  320  and rails  310   a  and  310   b . A certain amount of damping on the extension stroke is desirable, as it allows deletion of the flow control valve, plenum, and hosing which are required to perform the damping function in the device of  FIG. 2 . This is an advantage which also saves space, weight, and cost, as is the capability to delete about half of the remaining pneumatic system, as compared to the SLIC device of  FIG. 2 . The disadvantage is that adjustability of force and damping is limited.  FIG. 8  shows one way of providing some adjustability in force, by using a turnbuckle-like screw  335   a . One end of the screw  335   a  has a left hand thread, the other a right hand thread. Each end of the screw threads into one of the clevis blocks,  336   a  and  336   b  to which the lower ends of each support  330   a  and  330   b  are pinned. A stabilization piece  333  supports the vertical load of the gas charged supports  330   a  and  330   b , relieving the screw  335   a  of that duty so it only has to support the laterally-directed loads. The stabilization piece  333  also prevents the clevis blocks  336   a  and  336   b  from rotating with the screw  335   a . The screw  335   a  is supported radially by a bushing  335   d  at one end, and radially and axially by a combination bushing/thrust bearing  335   e  at the other end. When the handle  335   b  and crank  335   c  are turned, the turnbuckle screw  335   a  rotates, which either draws clevis blocks  336   a  and  336   b  closer together or further apart, depending upon the direction of rotation. This changes the angle of each gas charged support  330   a  and  330   b , changing the vertical component of their support on the Payload Pan  320 . Note that since the handle  335   b  is used to control the performance of this SLIC device, it is functionally part of the PIA, within the IMCP  327 . 
   Although not illustrated, another way of adjusting the support force on the Payload Pan  320  on this or similar types of SLIC devices is to add or subtract gas charged supports. One way of implementing this is to mount one clevis bracket on the Payload Pan  320  and one clevis bracket on the FA for each gas charged actuator potentially desired, then simply quick-pin each support into or out of each clevis place as needed. The lower clevis brackets can be mounted on the turnbuckle screw  335   a  in the manner of clevis blocks  336   a  and  336   b  for added adjustability once pinned in place. The other shortcoming is lack of damping adjustability. The supports are factory-sealed and the damping is not field-adjustable. If the damping is too high, the PIA will not recover to the Neutral Position  337  before the next shock. Therefore, supports should be procured with acceptably-low damping. If extra damping is needed, a separate, adjustable damping device can be added externally. 
   Though gas charged lift supports are designed for static lift situations such as holding open the rear hatch on a minivan or opening the engine cover on a boat, they can be used as an SA actuator provided they are not used to dissipate the energy of the shock pulse. The heat buildup will cause premature failure. Therefore, when used, gas charged lift supports should be implemented by SA/EDA Method 1. 
   The discussion above assumes that the use of gas charged supports which develop force while extending, which is the only configuration normally available. All the above would still apply to supports which develop force while retracting, but tailored to the new configuration. 
     FIG. 9  shows a SLIC device with a substantially different FA which incorporates a four-bar linkage instead of the rails and rollers presented previously. Since the characteristics of motion of four-bar linkages are so well known to those skilled in the art, additional detailed discussion on that aspect of the device will not be necessary here. However, two points are worthy of note. The first is that device is designed to take heavy side loads (into and out of the paper). Since a four bar linkage is nominally a planar mechanism, the extra strength in the side direction comes from the design of the brackets  421   a ,  421   b ,  431   a , and  431   b , the linkages  434   a  and  434   b  and the foundation  412  and Payload Pan  420  to which they are attached. The laterally-oriented gusset plates help stiffen the brackets against side forces, and the linkages are designed to resist deformation under torsion. The second point is the nominal range of motion of the Payload Pan  420 . Established as approximately plus or minus 30 degrees from horizontal (which is not necessarily the Neutral Position), plus or minus 30 degrees of movement is a good compromise between strict linear motion and ease of manufacture, which translates as cost for the consumer. Using a length of six inches between pivot points for the linkages  434   a  and  434   b , a vertical range of six inches is achieved while only allowing a fore-aft variance of 0.8 inches. This angular range is usually acceptable. 
   In  FIG. 9 , the SA is the same type as for the SLIC device in  FIG. 8 , a matched pair of gas charged lift supports  430   a  and  430   b  are mounted at mirror images to one another with respect to the vertical, and are attached at their base to clevis bracket  432  and at their upper ends to clevis blocks  436   a  and  436   b . The upward force of these supports is adjusted in the same manner as for  FIG. 8 . Turning handle  435   b  attached to crank  435   c  rotates turnbuckle-threaded screw  435   a  which draws the clevis blocks  436   a  and  436   b  closer or further away from one another, changing the magnitude of the upward vector component of the gas charged supports  430   a  and  430   b . The upward force of the clevis blocks  436   a  and  436   b  press on the stabilization crosshead  433 , which takes the bending moment off the turnbuckle screw  435   a  and also prevents the clevis blocks  436   a  and  436   b  from rotating excessively with the turnbuckle screw  435   a . The turnbuckle screw  435   a , etc. have been oriented to provide easier access to the handle  435   b . The turnbuckle screw is supported at one end by a radial bushing  435   d  and at the other end by a combination thrust/radial bushing  435   e , each mounted in appropriate brackets. A snubber piece (or snubbers)  409  prevents hard impact between the Payload Pan  420  and foundation  412  in case of an exceptionally energetic shock in comparison to the adjusted resistance of the EDA  498  and upward force-displacement of the SA actuators  430   a  and  430   b.    
     FIG. 10  shows the same SLIC device as in  FIG. 9 , from a different perspective. The EDA  498  is shown at the rear of the device. This EDA uses the same one-way clamping principle as the previous EDA&#39;s, but it has a difference in that it uses a push-bar  417  instead of the suspension bar to transfer the force to the FA. The push bar  417  is attached to the FA at the foundation  412  at clevis bracket  416  using clevis pin  455   c . The EDA  498  is attached to the Payload Pan  420  at clevis bracket  456  using trunnion pins  455   a  and  455   b . The clevis brackets  416  and  456  are oriented to accommodate the rotation of the EDA  498  and push bar  417  through the angle θ EDA , as the four bar Cage swings through the angle θ FA , and the vertical displacement d. Adequate space must be provided to allow freedom of movement. Also, suitable cover panels (not shown) should be installed over the moving machinery parts to protect personnel from pinch or chafe hazards, etc. 
   Using a push bar such as  417  has the advantage that the FA can be shorter, saving weight and space, and possibly improving aesthetics. The FA does not have to extend upwards just to hang the suspension bar. However, unlike the suspension bar, the push bar  417  is subject to buckling, and thus needs to be designed stiff enough to not buckle under the maximum expected load. The maximum expected load is the product of the sum of the weight of the PIA plus the weight of the heaviest passenger plus his gear, times the maximum user-adjustable G-loading for the device. 
   The ends of each SA actuator, the gas charged supports  430   a  and  430   b  require freedom of movement in two rotational directions, pitch and roll (assuming the seat faces fore-aft). As such, a spherically-mounted clevis bearing, spherically-mounted bearing, resiliently-bedded clevis joint or similar joint is required to ensure standard service life. 
   Because the four-bar linkage moves the PIA in an arc instead of linear motion and because the EDA  498  is of the push rather than pull type, the issue of EDA  498  alignment with the push bar  417  must be addressed. In general, the EDA  498  should always be aligned to the push bar  417  to ensure optimum performance and normal service life. Many simple ways of doing this are conceived and will be immediately familiar to those skilled in the art. Methods include use of a linear bearing between the push bar  417  and EDA  498  housing similar to that used in the head end of a hydraulic actuator. Various other bearings and bushings, spring-loaded sliding shoes, etc. are also conceived. The preferred embodiment uses bushings  408   a  and  408   b  to between the Push bar  417  and EDA  498  housing to alleviate friction and provide some stability, combined with locating the trunnion pins  455   a  and  455   b  between the EDA center of resistance  418  and the far end clevis pin  455   c  of the push bar  417 . Alignment and stability of the pushing force vector is then assured to be collinear between the trunnion pins  455   a  and  455   b  and the clevis pin  455   c . The EDA center of resistance  418  is the point where the EDA force can be considered to act upon the push bar  417 , which in practical terms is the center of EDA clamping force on the pressure pads. If desired to help alleviate vibration and farther minimize pitching of the EDA  498 , one or more springs or snubbers,  419   a  and  419   b  can be interposed between the Payload Pan  420  and the EDA housing  498 . 
     FIG. 11  shows a SLIC device featuring a bell crank and linkage to amplify the movement and reduce the force of the SA actuator on the Payload Pan. Most components common to previous SLIC devices have been omitted for clarity. SA actuator  530  is connected at one end to foundation  512  at clevis bracket  516  and clevis pin  532   e . The other end of the SA actuator  530  is connected to bell crank  531   a  at an intermediate point by clevis pin  532   d . One end of the bell crank  531   a  is attached to the FA at clevis bracket  536  and clevis pin  532   c . The other end of bell crank  531   a  is pinned to one end of linkage  531   b  by clevis pin  532   b . The other end of linkage  531   b  is attached to the Payload Pan  520  at clevis bracket  536  using clevis pin  532   a . The Payload Pan  520  translates along the rails  510   a  and  510   b  supported by the rollers  521  in the standard way of previous SLIC devices. One advantage of using the bellcrank  531   a  and linkage  531   b  mechanism is to transform the force-displacement output of the SA actuator  530  into one that is more desirable. This may be done by adjusting, either by design or by user adjustment, the location of clevis pin  532   d  in relation to the other pins  532   b  and  532   c  and the overall length of the bellcrank  531   a . Another advantage is that standard-off-the-shelf pneumatic actuators or gas charged supports can be used for the SA actuator  530 . Gas charged supports are available only in certain strokes, dimensions, and force outputs, yet there is an advantage to using them when possible so that about half of the otherwise-required pneumatic system can be deleted. The disadvantage is that the extra components (bellcrank  531   a , linkage  531   b , etc.) add weight, require more volume, and cost more than using just the gas charged support alone. 
   Several other concepts for substantially constant-force SA&#39;s are detailed in the Provisional Patent Applications in Appendices A, B, C, and D. Each of these concepts basically combines a force-producing component with one or more techniques and/or mechanisms which transforms its force-displacement output into a substantially constant force over its range of motion. It is felt that these additional concepts are straight forward enough to be clearly understood by those skilled in the art without explanation beyond that provided herein and in the Provisional Applications. 
   The definition of “substantially constant force” requires clarification. Substantially constant means maintained within a certain range, such as within thirty percent, ten percent, or four percent of the mean value. In general, for SLIC devices using SA/EDA Method 1 can maintain an output force constant to within the difference between the static and sliding coefficients of friction between the brake linings (×53 series) and the suspension bar or push bar (×17 series). Since the static coefficient of friction is generally larger than the sliding coefficient, the force peaks just before sliding starts. For best efficiency, its best to choose a brake lining material where the static and sliding coefficients are very close. SA/EDA Method 1 SLIC devices depend on the EDA to provide the bulk of their resistance to shock. While sliding, the frictional force is very steady. For SLIC devices which use SA/EDA Method 2, in which the SA provides the bulk of the support force during the shock pulse, the variance in support force can generally be kept within ±3.5 percent of the median value over the fill range of PIA movement. There are several ways of doing this, some more complicated than others, and several ways are detailed in the Provisional Patent Application of 2 Jan. 2002. The claim of substantially constant force is therefore warranted, especially considering that most traditional shock-handling techniques are functions of the shock magnitude and rise rate, and hence vary widely in their force-displacement response depending upon the shape of the shock pulse. 
   In general, handling the shock using S/EDA Method 1 saves space, weight, and cost over devices using SA/EDA Method 2. The most intuitive explanation for this is that Method 1 devices simply dissipate the energy, whereas Method 2 devices have to both store and dissipate the energy. 
     FIG. 12  shows a Check-Clamp type EDA which is similar to one in  FIG. 3 , but the counterweights  69   a  and  69   b , spring  68 , and drops stops  58   a  and  58   b  have been replaced by springs  168   a  and  168   b  mounted at the angle θ by fasteners  168   a  and  168   b . The clevis bracket  150   d  supporting the right end of the linkage  154  is also simplified. The advantage of this EDA over the one in  FIG. 2  is that it is simpler and lighter. Its important that the springs  168   a  and  168   b  provide enough upward force that they will maintain the brake linings  153   a  and  153   b  in contact with the suspension bar  117  even when subjected to the maximum body force (which is user-adjustable) on the respective unbalanced loads about clevis pins  155   c  and  155   d . Note that a weaker spring can be used if the mounting angle θ is decreased, and that the mounting angle can be zero or negative if desired. 
     FIG. 13  shows a Check Clamp type EDA similar to the others but with a lever  267   a  to amplify the clamping force of the EDA actuator  265 , a mechanism which makes adjusting the drop angle (θ in  FIG. 3 ) easier by making it less sensitive to rotation of the jackscrew  266   a , and a roller bearing  269  replacing the linkage under one of the pressure pads  251   b . The clamping force exerted upon the pressure pads  251   a  and  251   b  is the product of the EDA actuator  265  force multiplied by the lever ratio of lever  267   a , which is the length between axes of bushed clevis pins  255   c  and  255   d  divided by the length between axes of bushed clevis pins  255   b  and  255   c . The movement distance at the pressure pads is the movement at the EDA actuator  265  divided by the lever ratio of lever  267   a . This makes adjustment of the engagement/disengagement of the clamping feature easier, since it is less sensitive to rotations of the jackscrew  266   a . The adjustment is made easier still (by being made less sensitive to improper angular position of jackscrew  266   a ) through the action of lever  267   b . The movement at the EDA actuator is the movement at the jackscrew  266   a  divided by the lever ratio of lever  267   b . On the right side of  FIG. 13 , the pressure pad  251   b  is supported by a roller bearing  269  (or similar feature such as low-friction skid surface, etc.) to assist in disengaging the clamping feature. The pressure pad  251   b  bears on a section of the EDA framework  250 X and is held in place by restraining fasteners  259   e  and  259   f . The pressure pad  251   b  is restrained from movement in any direction except parallel to the suspension bar  217 , and is restrained from excessive movement in that direction as well by making contact with hard points on the EDA framework  257  and  258 . Replacing the linkage with the roller bearing  269  helps save space to the right of the suspension bar  217 . Note that each of the above three changes could have been implemented independently of the others. 
     FIG. 14  shows a Check Clamp type EDA which uses a plunger  354  to apply the clamping force on the pressure pads  351   a  and  351   b . Brake shoes  352   a  and  352   b  are fastened to the pressure pads using fasteners  359   a  and  359   b  and have brake lining material  353   a  and  353   b  bonded to them respectively. The pressure pads  351   a  and  351   b  ride on roller bearings (or ball beatings, low-friction skid pads, etc.)  369   a  and  369   b  respectively, and are held in place and constrained to linear motion by their interfering geometry with the EDA framework  350  or plunger  354  and fasteners  359   a ,  339   b ,  359   c , and  359   d . One or both of the roller paths of bearings  369   a  and/or  369   b  are positioned at an angle θ p  with respect to the long axis of suspension bar  317 . Springs  368   a  and  368   b  are mounted by fasteners  359   c ,  359   f ,  359   g , and  359   h  in order to maintain contact between the brake linings  353   a  and  353   b  and the suspension bar  317  once the clamping pressure is disengaged. The plunger  354  is fastened to the lever  367  at an intermediate point by clevis pin  355   a . The plunger  354  is constrained to linear motion only by sliding in an appropriate slot cut in the EDA framework  350 . A force F is applied at one end of lever  367  at clevis pin  355   c . The other end of lever  367  is pinned to an adjusting assembly  901  by clevis is pin  355   b . The adjusting assembly  901  is used to adjust the drop angle at which the clamping feature engages and disengages, and to compensate for wear in the brake lining material  353   a  and  353   b . Adjusting Assembly  901  is fully discussed in  FIG. 15 . The lever  367  is constrained to rotate through arc θ L , which constrains the plunger  354  to move only through displacement δ L . The length of the arc θ L  can be adjusted by turning jackscrew  366   a  which passes through a hole or slot in lever  367  and threads into tapped boss  350   b  on EDA framework  350 . The rotational position of the jackscrew  366   a  can be locked by tightening jam nut  366   b . The EDA is shown with its clamping feature fully engaged, with the pressure pads  351   a  and  351   b  pressing on surfaces  357   a  and  357   b  respectively and the force F fully applied to lever  367 . To disengage the clamping feature, the EDA framework  350  has to move upward relative to suspension bar  317 . The angle θ P  assists this disengagement by effecting an upwardly-directed vertical component of the clamping force upon the EDA framework  350 . Friction causes the brake pads  353   a  and  353   b  to stick to the suspension bar  317  as the EDA framework  350  rises. The distance between the bearing races for the pressure pads  351   a  and  351   b  increases as the EDA framework  350  rises, so the plunger  354  moves to the right. This allows the lever  367  to rotate counterclockwise until it makes contact with the jackscrew  366   a  on surface  357   c , relieving the clamping force. The EDA framework  350  can continue to move upwards as the brake linings slide up the suspension bar  317  being resisted by a small friction force due to the action of springs  368   a  and  368   b  (and its weight, etc.). 
   Note that the method of stopping the lever  367  at surface  357   c  to redirect the force F off the pressure pads  351   a  and  351   b  can also be used to disengage the clamping feature on the previously-discussed EDA&#39;s, instead of using the bottoming-out of the EDA actuator to relieve the clamping force. 
     FIG. 15  shows details of the adjusting assembly  901  used in the EDA of  FIG. 14 . Jackscrew  902  inserts through a washer/thrust bearing  903 , through a hole in bracket  905 , through the coils of spring  904 , and into tapped hole  906  in one end of slider  907 . Slider  907  is constrained to linear movement by the gussets of bracket  905 . The opposite end of the slider  907  has a hole drilled through it fitted with a bushing  908  in order to accept a clevis pin. Longitudinal position of the slider  907  is adjusted by rotational position of the jackscrew  902 . Lockwire or other locking device can be used to prevent inadvertent rotation of jackscrew  902 . 
     FIG. 16  shows a way of decreasing the required clamping force of a Check-Clamp type EDA while maintaining its resisting force. In this example, the required clamping force is halved as compared to one of the EDA&#39;s previously discussed. A second suspension bar  417   b  has been added, along with a third brake shoe  452   c  which has brake lining material  453   c  and  453   d  bonded to either side of it. A pair of teeth plates  455   a  and  455   b , have ridges which engage with ridges on the sides of brake shoes  452   a ,  452   b , and  452   c  to hold them aligned with one another. The teeth plates  455   a  and  455   b  are capable of transmitting shear loads developed in the center brake shoe  452   c  to the other brake shoes and also to the EDA framework  450 . The arrangement substantially shares the total resistive force of the EDA equally among the four brake linings  453   a ,  453   b ,  453   c , and  453   d . Note that since two of the brake linings  453   c  and  453   d  are bonded to the center brake shoe  452   c , brake shoe  451   c  takes substantially half of the total resistive force of the EDA, and the teeth plates  455   a  and  455   b  have to be designed accordingly. The teeth plates have holes and slots milled through them to accept machine screws  459   a ,  459   b ,  459   c , and  459   d  which hold the teeth plates and brake shoes  452   a ,  452   b , and  452   c  in continuous engagement, but lateral movement is unrestricted so as not to impact the engagement and disengagement of the clamping feature. 
     FIG. 17  shows selected components from  FIG. 16  in an isometric view. 
   Additional suspension bars could be added using the method shown in  FIGS. 16 and 17 , interleaved with additional brake shoes, etc., as may be desired. 
   If a Check-Clamp type EDA is to be used in a pushing motion, as was described in  FIGS. 9 and 10 , additional push bars may be added in a similar method to that shown in  FIGS. 16 and 17 . 
     FIG. 18  shows a simple arrangement for a type of SAA usable when the primary shock direction imposed on the vehicle is oriented vertically upward. The upper end of the SAA actuator  670  is attached to the FA crosshead  611  at clevis bracket  616 . The lower end is attached to the upper end of the SA actuator  630 . The lower end of the SA actuator  630  is attached to the Payload Pan  620  at clevis bracket  626 . The head-end chambers of the SAA actuator  670  and the SA actuator  630  are pneumatically connected to one another and to the SA accumulator (not shown) and associated IMCP (not shown) piping by hosing  649   a  and are thus at the same pressure. The cap end chambers of the SAA actuator  670  and the SA actuator  630  are pneumatically connected to one another and to the plenum (not shown) and associated IMCP piping (not shown) by hosing  649   a  and are thus at the same pressure. The SAA actuator  670  and the SA actuator  630  apply an upward force on the Payload Pan according ot the pressure in the SA accumulator and their respective piston areas. The piston area of the SAA actuator  670  is set to about three to six times the piston area of the SA Actuator  630 , depending upon the application. The upward force from the SAA actuator  670  should be weak enough that the Payload Pan  620  remains at the Neutral Position  637  unless the vehicle experiences significant negative acceleration, such as becoming airborne. This is to prevent nuisance rising of the Payload Pan  620  when traversing bumpy seas or terrain that are not severe enough to require additional relative displacement to absorb the shock. The stroke of the SAA actuator  670  is d SAA  and may be established independently of the stroke length d SA  of the SA actuator  630 . 
   Numerous other embodiments of the SAA actuator are conceived, many of which are similar on concept to the suspension concepts usable for the SA. When an SAA is used, it is usually easiest and simplest to incorporate the SA and EDA in SA/EDA Method 1. 
   The Check-Clamp type EDA can have a variable controllable force by using a solenoid to apply the clamping force. The force can be controlled by adjusting the solenoid voltage, in response to a G-sensor mounted on the FA.