Patent Publication Number: US-9428948-B2

Title: Air spring counterbalance

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of the previously filed U.S. patent application Ser. No. 14/467,081, filed on Aug. 25, 2014, to be issued as U.S. Pat. No. 9,103,149, which application is a continuation of the previously filed U.S. patent application Ser. No. 14/079,716, filed on Nov. 14, 2013, now issued as U.S. Pat. No. 8,813,429, which application is a divisional of the previously filed U.S. patent application Ser. No. 13/628,691, filed on Sep. 27, 2012, now issued as U.S. Pat. No. 8,590,209, each of which is incorporated by reference in their entirety as though fully rewritten herein. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to movable barrier operators and more particularly to devices used to counter the weight of a movable barrier. 
     BACKGROUND 
     Movable barrier operators of various kinds are known in the art. Such movable barrier operators often work in conjunction with a corresponding movable barrier such as a single panel or segmented garage door, a rolling shutter, a pivoting, swinging, or sliding gate or arm barrier, and so forth. In particular, the movable barrier operator typically responds to user inputs (often as input via a remotely located user interface) to effect selective movement of a corresponding movable barrier (for example, to transition the movable barrier back and forth between a closed and an opened position). 
     A variety of mechanisms may serve to effect the movement of a movable barrier, including electric motors linked to the movable barrier through chain, belt, or screw driven mechanisms. Fluid-based operators that rely upon a rigid cylinder are also known in the art as a way to effect the movement of a movable barrier. These systems rely upon either hydraulic or pneumatic pressure to actuate a piston mechanically linked to the movable barrier. When hydraulic or pneumatic pressure increases in the rigid cylinder, the piston extends from the cylinder. Fluid-based operators have not gained popular success, however. Expense of the system components, labor intensive installation, specialized knowledge or tools required for installation, and the large amount of space required for such systems have prevented their popular adoption. Rigid piston and cylinder mechanisms are expensive to manufacture, requiring tight tolerances and specialized materials. Fluid-based operators also rely upon complicated mechanisms to translate the motion of a rigid cylinder into motion of the movable barrier. In many cases, these mechanisms require large amounts of space and are difficult to install and calibrate. Some of the known fluid-based movable barrier operators rely upon a second rigid cylinder to counterbalance the weight of the door. This configuration increases the costs associated with the fluid-based operator, because it requires duplication of expensive piston and cylinder components. 
     In conjunction with vertically lifted movable barriers, for example single panel or segmented garage doors and rolling shutters, counterbalance mechanisms are typically provided to reduce the effort required to lift the movable barrier. Counterbalance mechanisms that rely upon mechanical springs, such as torsion or extension springs, are known in the art, as are pneumatic mechanisms that rely upon a rigid piston and cylinder acting as an energy storage device. 
     An example prior art counterbalance mechanism will be described with reference to  FIG. 10 , which illustrates a vertically lifted garage door  1001 , installed using methods known in the art. The garage door  1001  has rollers  1010  that run along tracks  1020  at either side of the door. The tracks  1020  guide each segment  1002 ,  1003 ,  1004 , and  1005  of the door  1001  as the door  1001  is raised or lowered. The tracks comprise a horizontal portion  1021  generally parallel to the ceiling of the garage and a vertical portion  1022  generally parallel to the door opening. The segments  1002 ,  1003 ,  1004 , and  1005  are connected to one another by hinges  1009 . A jackshaft  1030  (sometimes also referred to as a torsion bar) is mounted above the garage door  1001 . Cables  1032  attach at either side of the bottom of the garage door  1001  and run vertically along the sides of the garage door  1001 . The cables  1032  are spooled around drums  1040  at either end of the jackshaft  1030 . The interaction of the cables and the drums cause the jackshaft to rotate as the garage door is raised or lowered. As the door  1001  lowers, the cables  1032  unspool from the drums  1040  and extend down with the door  1001 . Similarly, as the door  1001  is lifted, the cables re-spool around the drums  1040 . A torsion spring  1035  is coiled around the jackshaft  1030  and exerts a rotational force on the jackshaft  1030  such that the shaft  1030  has a tendency to re-spool the cables  1032 . Through the cables  1032 , the spring  1035  pulls against the weight of the door  1000 , which makes it easier to raise the door  1000 . In effect, the arrangement of the torsion spring  1035 , jackshaft  1030 , drums  1040 , and cables  1032  reduce the weight of the door  1000 . 
     A garage door opener  1050  lifts and lowers the garage door  1001  by pulling a carriage  1051  along a lift track  1052  using a chain, belt, or screw. The carriage  1051  is connected to the garage door  1001  through a linkage  1053 . As the garage door is raised, the weight of the segments  1002 ,  1003 ,  1004 , and  1005  becomes supported as they move from the vertical portion  1022  to the horizontal portion  1021  of the garage door track  1020 . In this way, the force required to lift the garage door  1001  becomes less as more segments pass along the horizontal portion  1021  of the garage door track. The prior art torsion spring  1035  accommodates this decrease in the weight of the garage door  1000  because it exerts less force as it relaxes. The torsion spring  1035  must be sized appropriately so that the reduction in its force corresponds correctly to the position of the garage door. Any one of several sizes of torsion spring  1035  could be required, based on the width of the garage door  1001  and the relative weight of the garage door  1001 . For example, different springs  1035  would be required for a two-car garage than for single car garages. Likewise, wood doors are substantially heavier than foam-cored metal doors and therefore require different springs  1035 . Because this type of counterbalance mechanism is a commonly installed system, there is a need for counterbalance mechanisms that can be retrofitted on these types of existing movable barriers systems. 
     Counterbalance mechanisms that rely upon mechanical springs are known to have sudden failures that can be disturbing for people in the vicinity. If the spring is not adequately secured during installation, or if the spring loosens during ordinary operation, it may snap loose as the movable barrier is lowered. Further, mechanical springs typically have a relatively short lifespan. The mechanical springs known in the art and used to counterbalance the weight of movable barriers commonly fail after as few as 10,000 cycles. Particularly in industrial and commercial door installations, the limited lifespan of mechanical springs requires frequent replacement of the springs. Replacing these mechanical springs is a labor intensive procedure that requires disassembly of the entire jack-shaft assembly. The mechanical spring is coiled around the outside of the jackshaft, so the only way to replace the spring is to remove the jackshaft completely and slide the spring off the end of the shaft. 
     When used as counterbalance mechanisms, mechanical springs require careful selection to match the weight of the door. The characteristics of the spring, such as spring constant and/or the displacement the spring is capable of, must be selected according to the weight and size of the door. Because these characteristics are fixed in a mechanical spring, manufacturers must stock a variety of springs. 
     Pneumatic counterbalance mechanisms that rely upon a rigid piston and cylinder suffer from the high costs associated with fluid-based movable barrier operators. The system components are expensive to manufacture and install for many of the same reasons discussed above. 
     In light of these disadvantages of the known current counterbalance and movable barrier operator systems, there is a need for a counterbalance mechanism and movable barrier operator that is robust and capable of a longer lifespan, that may be easily installed on existing jackshaft mechanisms, that reduces risks during installation and the likelihood of failure during use, and that may be installed using commonly available tools and knowledge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above needs are at least partially met through air spring counterbalance approaches described in the following detailed description, particularly when studied in conjunction with the drawings, wherein: 
         FIG. 1  comprises a perspective view of an example air spring counterbalance mechanism; 
         FIG. 2  comprises a side view of the air spring counterbalance mechanism of  FIG. 1 ; 
         FIG. 3  comprises a cross-section side view of the air spring counterbalance mechanism of  FIG. 1  along line  3 - 3 ; 
         FIG. 4  comprises a front view of the air spring counterbalance mechanism of  FIG. 1 ; 
         FIG. 5  comprises a perspective view of the bottom of an example air spring counterbalance mechanism; 
         FIG. 6  comprises a side view of an example air spring counterbalance mechanism illustrating additional supporting structures; 
         FIG. 7  comprises a front view of the air spring counterbalance mechanism of  FIG. 6 ; 
         FIG. 8  comprises a perspective view of another example air spring counterbalance mechanism; 
         FIG. 9  comprises a side view of another example air spring counterbalance mechanism; 
         FIG. 10  comprises a perspective view illustrating installation of a prior art device; 
         FIG. 11  comprises a perspective view illustrating installation of an example air spring counterbalance mechanism; 
         FIG. 12  comprises several plots showing forces exerted by a typical air spring over a range of displacements of the air spring; 
         FIG. 13  comprises a conceptual illustration of an example control system for an air spring counterbalance; 
         FIG. 14  comprises a perspective view illustrating an example multi-door installation of air spring counterbalance mechanisms; 
         FIG. 15  comprises a flow chart illustrating an example method for installing an air spring counterbalance mechanism; and 
         FIG. 16  comprises a flow chart illustrating an example method for using an air spring counterbalance mechanism to control the position of a movable barrier. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. 
     DETAILED DESCRIPTION 
     Generally speaking, pursuant to these various embodiments, an air spring is mechanically connected to support the weight of a movable barrier. For example, the air spring is configured to exert a linear force, which is converted through a mechanical coupling into a rotational force that counterbalances the weight of the movable barrier through a jackshaft. More specifically, a fluid-based spring counterbalance mechanism including an elastic flexible fluid-based spring disposed between two surfaces is used to support some or all of the weight of a movable barrier. A linkage mechanism comprising at least one rotatable shaft is configured to receive rotational motion from a jackshaft associated with the movable barrier. A translational mechanism coupled to the at least one rotating shaft and coupled to at least one of the two surfaces is configured to compress the flexible fluid-based spring between the two surfaces in response to rotation of the rotatable shaft. By compressing the fluid-based spring, the counterbalance mechanism provides a force that partially or fully supports the weight of the movable barrier. 
     So configured, a single type of fluid-based spring such as an air spring can be configured to work with a variety of barrier types because the fluid-based spring&#39;s counterbalance effect can be controlled by adjusting the pressure within the spring. Accordingly, a minimal number of types of fluid-based spring systems can be applied to a large number of barrier types such that the spring to barrier matching problem is largely reduced or eliminated. Moreover, typical fluid-based springs can be expected to have a longer expected lifetime than the 10,000 cycle lifetime expected of typical mechanical torsion springs. Additionally, fluid-based springs are less likely to fail in a sudden event, instead gradually losing the ability to maintain a pressure sufficient to counterbalance a barrier. Such a failure mode provides an opportunity to replace a fluid-based spring before total failure of the system. These and other benefits will become apparent through study of the following description and accompanying figures. 
     Turning to the figures, an example air spring counterbalance mechanism  100  for a movable barrier is shown in  FIGS. 1, 2, 3, and 4 . A flexible fluid-based spring such as an air spring  110  is disposed between two surfaces. In this example, the two surfaces include a fixed plate  120  and a movable plate  130 . A linkage mechanism includes at least one rotatable shaft  180  that is configured to rotate in response to movement of a movable object, such as the movable barrier. A translational mechanism is coupled to the at least one rotating shaft  180  and to at least one of the two surfaces  120  and  130 . The translational mechanism is configured to compress the flexible fluid-based spring between the two surfaces  120  and  130  in response to rotation of the rotatable shaft  180  such that the counterbalance mechanism is configured to provide a force opposed to movement of the movable object. 
     In the illustrated example, the translational mechanism includes a cable  150  made of metallic wire rope or other suitably strong and flexible connecting material that is fixed at its first end  151  to the fixed plate  120 . In other approaches, the cable  150  is fixed to the movable plate  130 . The cable  150  passes through a hole  131  in the moveable plate  130  and over a pulley  160  having a groove  161  configured to support the cable  150 . The pulley  160  rolls on a shaft  162  that is supported by flanges  132  that protrude from the bottom of the movable plate  130 . In another approach, the flanges  132  supporting the pulley  160  protrude from the top of the movable surface  130 , alongside the air spring  110 . The second end  152  of the cable  150  is coupled to a drum  170 . As the drum  170  rotates, it takes up the cable  150  and causes the movable plate  130  to compress the air spring  110  by reducing the distance between the fixed plate  120  and the movable plate  130 . The combination of the two plates  120  and  130 , along with the cable  150  and the drum  170 , comprise a translational mechanism designed to compress the air spring  110 . 
     In this example, the drum  170  is coupled through a planetary gear mechanism  171  to a rotatable shaft  180 . The rotatable shaft  180  is supported by flanges  123  that protrude from the top surface of the fixed plate  120 . The rotatable shaft  180  may include a keyway  181  or other indexing feature used to link the shaft  180  to other shafts, including the jackshaft  1130  described with respect to  FIG. 11 . 
     With brief reference to the example of  FIG. 11 , the shaft  180  is configured to be coupled to the motion of a movable barrier  1101  such that the shaft  180  rotates as the movable barrier  1101  is lowered and raised. In this arrangement, when the shaft  180  rotates in a first direction associated with lowering the movable barrier  1101 , it causes the causes the drum  170  to take up the cable  150  and compress the air spring  110 . Similarly, when the shaft  180  rotates in the opposite direction while opening the movable barrier  1101 , it unspools the cable  150  from the drum  170  and allows the air spring  110  to relax. The planetary gear mechanism  171  serves to couple the drum  170  to the shaft  180  and to reduce the rotational speed of the drum  170  relative to the rotational speed of the shaft  180 . In this way, the planetary gear  171  serves as a linkage mechanism between the drum  170  and a movable barrier. The fixed plate  120  includes a mounting bracket  121 . The mounting bracket  121  includes through holes  122  such that the mounting bracket can be fixed to a garage wall (e.g.,  1160  in  FIG. 11 ). 
     With reference to  FIG. 3 , a cut-away view that illustrates the inner workings of the example air spring  110  will be described. Section lines appear on  FIG. 1  to illustrate the nature of the cut-away illustrated in  FIG. 3 . Air springs have been known in the art relating to vehicle suspension systems since the 1930&#39;s. In one approach, a flexible fluid-based spring includes a rubberized bladder in a substantially cylindrical configuration disposed between two surfaces, wherein the bladder is configured to receive and contain a fluid, such as gas or air. An example air spring suitable for use in various applications described herein is a GOODYEAR® air spring, model number 1S4-008. Air springs typically consist of an air-tight flexible member  111  fixed between a bead plate  113  and a piston  112 . The end closure  114  is molded to the flexible member to form an air-tight seal at one end of the flexible member  111 . At the other end, the flexible member  111  is crimped to the bead plate  113  to form an air-tight seal. As the piston  112  is displaced toward the bead plate  113 , the piston  112  drives into the volume of air contained in the flexible member  111 , causing that volume to reduce and therefore compressing the air inside the flexible member  111 . Thus, an increasing force is required to displace the piston  112  further towards the bead plate  113 , in much the same way a mechanical coil spring requires increasing force to accomplish greater displacement. In some air springs, a bumper  115  is included to provide a stop that prevents the piston  112  from contacting the bead plate  113 . This description of a typical air spring is merely exemplary and not intended to limit the types of air spring used in the disclosed approaches. In addition, although air is discussed herein, any compressible fluid could be used to fill the flexible member  111 . For example, a variety of pure or mixed gases could be used instead of air. 
     The use of the air spring  110  in this mechanism provides several benefits over a traditional coil spring. The force generated by the air spring  110  at a given displacement is capable of adjustment by increasing or reducing the air pressure within the air spring  110 . A nozzle  116  allows air to be added or removed from the air spring  110  to adjust air spring&#39;s  110  internal air pressure. The nozzle  116  preferably incorporates a one-way valve or other mechanism to capture the air pressure added to the air spring  110 . Because the air spring&#39;s  110  internal air pressure correlates to its output force, the air spring counterbalance mechanism  100  can be adjusted simply by adjusting the air spring&#39;s  110  air pressure to accommodate many different sizes and weights of movable barrier. Thus, a single air spring counterbalance mechanism  100  can serve to replace multiple mechanical springs. Instead of stocking an inventory of different torsion springs for different door-weights, a single air spring mechanism can be installed and then adjusted to accommodate a given movable barrier. 
     Another benefit of the air spring, as compared to traditional coil springs, is the reduced likelihood of a sudden failure in the counterbalance mechanism. Mechanical springs have a tendency to fail suddenly and with little warning. In contrast, air springs are most likely to fail gradually, typically through loss of pressure over time due to a gradual leak. This provides ample warning of the imminent failure. When complete failure occurs, the spring gradually goes limp rather than suddenly and uncontrollably releasing energy. In addition, air springs are known to have substantially longer cycling lifespans than the mechanical torsion springs commonly used in movable barrier counterbalance mechanisms. 
       FIG. 5  is a bottom perspective view that illustrates an alternative approach of the air spring counterbalance mechanism  500 , in which cables  550  are routed in a cross-wise fashion over four pulleys  560  mounted on the bottom of the movable plate  530 . Each cable passes over two pulleys  560 . This approach serves to balance the load on the cables  550  and reduces the overall weight supported by each pulley  560 . 
     The air spring  510  is mounted between a fixed plate  520  and a movable plate  530 . The cables  550  are fixed at a first end  551  to the fixed upper surface and route through holes  531  in the movable plate  530 . The cables pass over pulleys  560  and through a second set of holes  531  in the movable plate  530 . The pulleys  560  rotate on shafts  562  that are supported by a housing  533  that extends from the bottom surface of the movable plate  530 . The cables  550  then route through holes  524  in the fixed plate  520  and are mounted to a drum ( 570  shown in  FIG. 8 ). The drum is mounted to a rotatable shaft  580  that is configured to interface with a jack shaft (not shown). As the shaft  580  is rotated, the cable is spooled or unspooled from the drum  570 , causing the air spring  510  to be compressed or released, respectively. 
     Other approaches of the translational mechanism are possible, as would be envisioned by a person having ordinary skill in the art. These might include, but would not be limited to, various methods of fixing the cable  550  to the plates  520  and  530 , the use of multiple drums  570  to take up the cable  550 , and designs in which the pulleys  560  are eliminated by fixing the cables  550  to the movable surface  530 . 
       FIGS. 6 and 7  illustrate an example counterbalance mechanism  600  with supporting structures provided to maintain the correct orientation of the air spring  110 . Except as described further here, the features of the mechanism  600  are the same as described with respect to  FIGS. 1-4 . Side plates  624  attach to either side of the fixed plate  120 . A vertical stabilizer  625  is fixed to each side plate  624 . The vertical stabilizers run parallel to the air spring  110 . Each vertical stabilizer has a first surface  626  and a second surface  627  that are parallel to one another. 
     Bottom side plates  633  extend vertically from the movable plate  630 . Four guide rollers  634  are mounted on each of the bottom side plates  633 . The guide rollers  634  are supported by shafts  635  that extend outwardly from the bottom side plates  633 . The rollers  634  are mounted such that they bear against the vertical stabilizers  625 . In this way, the rollers  634  and the vertical stabilizers  625  keep the movable plate  130  substantially parallel to the fixed plate  120 . 
       FIG. 8  further illustrates the example supporting structures described with respect to  FIGS. 6 and 7 . A counterbalance mechanism  800  contains features previously described with respect to  FIG. 5 , specifically including pulleys  560  mounted such that the cables  550  are routed below the movable surface  530  in a cross-wise fashion. Instead of a planetary gear mechanism (e.g.,  171  of  FIG. 1 ), the counterbalance mechanism  800  has a gear  882  mounted to the rotatable shaft  580 . A chain  883  drives the gear  882 . This approach is discussed in more detail below with respect to  FIG. 9 . In this example, the drum  570  is directly mounted to the rotatable shaft  580 . 
     As discussed with respect to  FIGS. 6 and 7 , the vertical stabilizer  625  provides surfaces  626  and  627  against which the rollers  634  bear. The rollers  634  constrain the movable plate  530  to a position that is substantially parallel to the fixed plate  520 , even as the cables  550  compress the air spring  510 . The support structures, including the vertical stabilizer  625 , bottom side plates  633 , rollers  634 , and other ancillary components illustrated on the left hand side of  FIG. 8 , could also be duplicated on the right hand side of the mechanism  800  although they are not depicted in  FIG. 8 . 
       FIG. 9  illustrates a chain-driven alternative approach to a fluid-based counterbalance system  900  having the linkage mechanism to the movable barrier including a first shaft and a second shaft operatively coupled to the first shaft through at least one gear. A sprocket  984  is mounted to the jackshaft  985 . The jackshaft  985  is coupled to a movable barrier (e.g.,  1101  in  FIG. 11 ), such that the jackshaft  985  rotates as the movable barrier is raised or lowered. A chain  983  couples the sprocket  984  to a gear  982 . The gear  982  is coupled to the drum (e.g.,  870  in  FIG. 8 ) such that the drum rotates and takes up the cable  950  as the movable barrier is lowered. In this approach, the sprocket  984  and gear  982  serve to reduce the rotation of the drum relative to the rotation of the shaft  985 . Other approaches to designing the linkage mechanism are possible, as would be envisioned by a person having ordinary skill in the art. These would include any gear, chain, belt, or other similar mechanism. The remaining features illustrated in  FIG. 9  are substantially the same as have been described with respect to  FIGS. 1-4 , above. 
     Turning to  FIG. 11 , an example interface between the air spring counterbalance and a common movable barrier configuration will be discussed. The air spring counterbalance  1100  interfaces with the jack shaft  1130  of a garage door  1101 . Any movable barrier may be counterbalanced by the air spring counterbalance  1100 , including a single panel or segmented garage door, a rolling shutter or other barrier that may be opened and closed by lifting the movable barrier against the force of gravity. The garage door  1101  includes features of the garage door  1001 , depicted in  FIG. 10 , including panels  1002 ,  1003 ,  1004 ,  1005 , hinges  1009 , and rollers  1010 , which run along tracks  1020 . The drums  1140  are fixed on either end of the jackshaft  1130 . In some installations the drums  1140  are placed at intermediate locations along the jack shaft  1130 . As described with respect to  FIG. 10 , the drums  1140  rotate with the jackshaft  1130  and take up cables  1132  that run from the drum to at the base of the door  1101 . In this system, when the jackshaft  1130  rotates in a first direction, it raises the garage door  1101  by spooling up the cables. If the jackshaft  1130  rotates in the opposite direction, the garage door  1101  lowers as the cables  1132  are unspooled from the drums  1140 . In addition to being coupled to the jackshaft  1130 , the air spring counterbalance mechanism  1100  is rotatably fixed. A bracket plate (e.g.,  121  in  FIG. 1 ) located at the fixed end of the air spring counterbalance is affixed to the wall  1160  using screws or bolts. A person of ordinary skill in the art will recognize that many other means may be appropriate for affixing the counterbalance mechanism  1100  to the wall  1160 . 
     The air spring counter balance  1100  is intended to replace other counterbalancing mechanisms such as the mechanical torsion spring (e.g.,  1035  in  FIG. 10 ) frequently used to counterbalance the weight of a garage door  1101 , although in one approach the counter balance  1100  could also serve as a supplement to these other counterbalancing mechanisms. In another approach, the air spring counter balance  1100  may be installed on the opposite end of the jackshaft  1130 . In still another approach, one or more air spring counter balances  1100  are installed at either or both ends of the jackshaft  1130 , for example, to compensate for heavy or wide garage doors. In yet another approach, the air spring counterbalance  1100  includes adaptations that allow more than one air spring counterbalance to couple together in series. The rotatable shafts (e.g.,  180  in  FIG. 1 ) of the respective air spring counterbalance mechanisms are coupled together via a coupling device to accommodate series installation. In this way, counterbalance mechanisms may be added modularly to accommodate a variety of movable barriers, based on the weight, size, or orientation of the barrier. 
     The design of the air spring counterbalance mechanism is advantageous over the mechanical torsion springs that are typically used as movable barrier counterbalance mechanisms. Because the air spring counterbalance mechanism can be installed at the end of the jackshaft, the jackshaft does not need to be disassembled and removed when the air spring counterbalance mechanism is installed or replaced. This reduces the time and labor required to install or replace the air spring counterbalance mechanism, which is a benefit to any owner of a movable barrier system. The reduction in time and labor is a particular benefit for owners of commercial and industrial movable barriers, which are subject to more frequent use and consequently more frequent replacement. 
     The relationship between displacement, force, and pressure within the Goodyear® 1S4-008 air spring is plotted in  FIG. 12 . The chart  1200  shows the force exerted by the air spring on the y-axis  1201 , and the height of the air spring on the x-axis  1202 . One of skill in the art understands “height” of the air spring to mean the distance between compression ends of the air spring. For example, in the air spring illustrated in  FIG. 3 , the height is the distance H between the top of the movable plate  130  and the bottom surface of the fixed plate  120 . The “height” of the air spring changes with the physical compression of the air spring. The plot lines  1210 ,  1220 ,  1230 ,  1240 , and  1250  show the force exerted by the air spring at a given displacement, for different initial fluid pressures. For example, the plot line  1250  indicates the load on the spring assuming 21 psig of air pressure is applied before the spring is compressed. Although 21 psig is the starting air pressure, the air pressure within the air spring will increase as the spring is compressed, requiring an increasing force to further displace the spring. The plot line  1240  illustrates a force-displacement curve for an initial pressure of 39 psig, and lines  1230 ,  1220 , and  1210  illustrate curves respectively associated with 60 psig, 82 psig, and 92 psig. By changing the fluid pressure within the air spring, the characteristics of the spring can be manipulated, as illustrated by the plot lines  1210 ,  1220 ,  1230 ,  1240 , and  1250 . The dashed line  1260  represents the initial height of the air spring. The intersections of the dashed line and the various plot lines  1220 ,  1230 ,  1240 , and  1250  are labeled, respectively, as  1261 ,  1262 ,  1263 ,  1264 , and  1265 . The effect of changing the air pressure is well illustrated by looking at the intersections  1261  and  1263 , which show that reducing the air pressure from 92 psig to 60 psig reduces the force exerted by the spring from approximately 700 lbf (pounds of force) to 425 lbf. 
     The variable force exerted by an air spring is one advantage associated with various ones of the described designs. By adjusting the fluid pressure in the air spring, the air spring counterbalance can be adjusted to match the force needed to balance the weight of the movable barrier, which offers several benefits. Because the force exerted by the air spring counterbalance mechanism corresponds to the pressure of the air in the air spring, the counterbalance mechanism can be installed in a de-energized state and later pre-loaded by pressurizing the air spring, reducing the level of skill and training required to install the counterbalance device. In contrast, mechanical torsion springs must be pre-loaded before they are secured, or as part of the process of securing the spring. If the mechanical spring is improperly secured after pre-loading, the spring may snap loose suddenly and release its stored energy. 
     Further, as illustrated in  FIG. 12 , changing the initial pressure within an air spring changes the slope of the plot lines. This slope corresponds to the spring rate, in pounds per inch (lb./in.), of the air spring. Spring rate is a design characteristic that must be selected when choosing mechanical springs, however an air spring allows the spring rate to be adjusted based on the unique needs of any particular installation. 
     Additionally, by varying the pressure within the air spring, the air spring counterbalance can be used to move a garage door (e.g.,  1101  depicted in  FIG. 11 ).  FIG. 13  is a conceptual view of an air spring counterbalance and an exemplary control system used to vary the fluid pressure within the air spring of the counterbalance. The physical embodiments of this system might be incorporated in a single unit or distributed among separate elements, as shown. A valve  1310  controls air flow through a hose  1311  connected to the flexible fluid-based spring, here an air spring, via the connector valve  116 . The valve  1310  includes an outlet port  1312 , an exhaust port  1313 , and an inlet port  1314 . Preferably, the valve  1310  is a three position valve with an open state, an exhaust state, and a no-flow state. In another approach, the valve could be a two position valve with an open state and an exhaust state. A compressed air hose  1315  provides high pressure air from an air compressor  1320 . The compressor  1320  includes a compressor unit  1321  and a pressure tank  1322 . The compressed air hose  1315  attaches to the compressor at an outlet port  1323 . One of skill in the art would recognize that the compressor  1320  can be replaced with any source of pressurized fluid or air. 
     Operating circuitry is configured to control a position of a movable barrier by effecting adding pressurized fluid to the flexible fluid-based spring from the source of pressurized fluid coupled to the flexible fluid-based spring or by effecting removal of pressurized fluid from the spring via a release mechanism operably controlled by the operating circuitry. In the illustrated example, the operating circuitry includes control electronics  1330  that provide signals to the valve  1310  and the compressor  1320  to control the operation of those devices. The valve control wire  1331  provides a signal that indicates to the valve  1310  to go to the open state, or the exhaust state, or to a no-flow state. In the open state, air is added to the air spring  110 , and the pressure in the air spring is consequentially increased. In the exhaust state, air flows from the air spring  110  through the exhaust port  1313  of the valve  1310 , reducing the pressure in the air spring  110 . Preferably, the exhaust port  1313  includes a constriction that limits the amount of air exiting the air spring  110  to a controlled rate. In the no-flow state, the air spring  110  is closed off and maintains whatever pressure is already in the air spring  110 . In one approach, the signal transmitted via the wire  1333  is a digital electronic signal (e.g. 12V, −12V, or 0V). Alternative approaches could include analog electronic signals or any communication signal known in the art. In one alternative approach, the valve  1310  is replaced with a pressure regulator, such that the electronic signal sent over the wire  1331  commands the regulator to maintain a certain pressure within the air spring  110 . The compressor control wire  1332  provides a signal that indicates to the compressor  1320  that the compressor should run. As with the signal sent to the valve  1310 , a digital signal is preferred for control of the compressor  1320 , but other signals could be used in alternative approaches. In still other approaches, the signal may indicate the desired pressure that the compressor  1320  should generate. 
     The control electronics  1330  also receive signals. A pressure gauge  1340  is mounted inline in the hose  1311  between the valve  1310  and the air spring counterbalance  100 . The pressure gauge  1340  provides a signal via a pressure signal wire  1333 , so that the control electronics  1330  knows what pressure exists within the air spring counterbalance  100 . In other approaches, a wire  1337  connected to a strain gauge on the cable  150  might provide information about the force exerted by the air spring counterbalance. Similarly, a wire  1338  connected to a torque sensor mounted to the shaft  180  might indicate the output torque generated by the air spring counterbalance. The control electronics  1330  receive command signals, either through electro-magnetic radiation such as radio or light-based signals or through a wired connection  1334  to a command button. Door position sensors provide position information for the garage door  1101  to the control electronics  1330  via wires  1335  and  1336 . The door position sensors may alternatively be proximity sensors or digital encoders, and additional wires may be added to the system to accommodate these different sensors. In alternative approaches, any of the signals received by the control electronics  1330  could be received via a wireless communications protocol. 
     The control electronics comprises a processor capable of receiving command signals and pressure signals. The processor is also capable of acting upon those signals based on predetermined logic and providing output signals to the valve and the compressor such that those devices modulate the pressure in the air spring and therefore operate the air spring to move a garage door (e.g.,  1101  in  FIG. 11 ). Upon receipt of a command signal, the control electronics  1330  evaluate the current position of the garage door according to signals received on the wires  1335  and  1336 . The control electronics also evaluate the pressure, force, or torque within the air spring counterbalance  100  to determine how to command the valve  1310  and the compressor  1320 . For example, the control electronics might detect that a high pressure already exists within the air spring  110 , which indicates that the valve should be commanded to the exhaust state to release pressure from the air spring  110  and lower the garage door  1101 . Alternative examples of the control electronics  1330  could comprise a processor located remotely from the control electronics, or would rely upon electronic circuits to provide the operating logic instead of a processor. 
       FIG. 14  illustrates an example multi-door installation in which an air spring counterbalance mechanism  1400  is installed on each of the doors  1401 . Each air spring counterbalance mechanism  1400  is connected to a source of pressurized fluid. An air compressor and central control unit  1490  provides pressurized air to each counterbalance mechanism  1400 . Preferably, a central air compressor provides a ready source of compressed air. By varying the air pressure in the counterbalance mechanisms  1400 , the mechanisms can serve not only to counter the weight of the doors  1401  but also as operators to raise or lower the doors  1401 . When used in this fashion as an operator, the pressure of the air spring counterbalance preferably falls within the range of operating pressures produced by common industrial air compressors. Typically, industrial air compressors are known to provide up to 175 psig (pounds per square inch gauge). Alternatively, a dedicated compressor  1490  may be provided for use with each air spring counterbalance mechanism, as illustrated in  FIG. 13 . In this example, the air spring operating pressure may be higher according to the capabilities of the dedicated compressor. 
     Each of the counterbalance mechanisms  1400  is connected to a low voltage control line  1492  and a compressed air line  1491 . The low voltage control line  1492  may comprise wiring for digital or analog signals, or any wired communication known to a person having skill in the art. Wireless communications are also possible. Each counterbalance mechanism  1400  has a valve (e.g.,  1310  depicted in  FIG. 13 ) and control electronics (e.g.,  1330  depicted in  FIG. 13 ). In this example, the control module  1490  receives signals including a command to operate any one of the movable barriers  1400 . Based on the signals, the control module  1490  sends command signals via the low voltage control line  1492  to the control electronics at the proper counterbalance mechanism  1400 . The control electronics open the barrier by opening the valve to allow compressed air into the air spring counterbalance mechanism  1400 , from the compressed air line  1491 . To close the barrier, the control electronics control the value to open the interior of the air spring to a lower pressure line or to the outside to lower the pressure of the air spring counterbalance mechanism. With the lower internal pressure, the barrier&#39;s weight causes the barrier to close. 
     Each counterbalance mechanism  1400  has position sensors  1402  and  1403  capable of determining the position of the door. Position sensors  1402  and  1403  may include proximity sensors, light beams, encoders or any other sensors known to a person having ordinary skill in the art. In one approach, the low voltage control line  1492  transmits signals to the control unit  1490  from the sensors  1402  and  1403  located at the counterbalance mechanisms  1400 . In another approach, the sensors  1402  and  1403  are configured to send signals to the control electronics for the corresponding counterbalance mechanism, which can control the movement of the barrier at least in part in response to the signals from the sensors  1402  and  1403 . In another approach, the counterbalance mechanism  1400  may include an encoder or other sensor designed to determine the position of the drum  1404 . 
       FIG. 15  describes a method for installing an air spring counterbalance in which the adjustment of air pressure in the air spring is used to accommodate a variety of movable barriers based on the weight, size, or orientation of the barrier. In steps  1510  and  1520 , the air spring counterbalance mechanism (e.g.,  1100 ) is coupled to the jackshaft (e.g.,  1130 ) and affixed to the wall (e.g.,  1160 ) or other support structure as described above. In step  1530 , the pressure in the air spring is increased by adding air to the air spring (e.g.,  110 ) via a connector valve (e.g.,  116 ). Air may be added in discrete quantities or continuously. As described with reference to  FIG. 12 , the force exerted by the air spring increases as the pressure in the air spring increases. This force offsets the weight of the movable barrier, which reduces the effort required for a person or an automated barrier operator to move the barrier. According to step  1540 , air is added until the barrier moves. Movement of the barrier indicates that the weight of the barrier has been fully offset by the force exerted by the air spring. In step  1550 , the final air pressure is set by allowing a fixed volume of air to escape from the air spring, by observing a predetermined reduction of the air pressure in the air spring or by reducing the air pressure until the barrier returns to its prior position. 
     Optionally, as described in step  1560 , the air spring is connected to a source of pressurized air. The pressurized air source may optionally be used at step  1570  to maintain the pressure in the air spring. This is accomplished by periodically adding a volume of air to the air spring, by using a pressure regulated valve to maintain a constant pressure in the air spring or by adding pressure or volume based on ambient temperature or the observed position of the door. The pressure source should be configured in step  1550 , to the extent any of these mechanisms, or some other mechanism, is used to maintain the pressure in the air spring. These alternative approaches are implemented through hardware described with respect to  FIG. 13 . In one approach, the control electronics  1330  are configured to periodically open the valve  1310  to add pressure to the air spring  110 . Alternatively, the control electronics  1330  are configured to maintain pressure within the air spring  110  by observing the input from the pressure gauge  1340  and opening the valve  1310  whenever the pressure in the air spring drops below a threshold set at step  1550 . In yet another alternative, the control electronics  1330  comprise a temperature sensor and logic that causes the control electronics  1330  to add pressure to the air spring  110  in relation to the temperature at the air spring  110 . As discussed with respect to  FIG. 13 , the control electronics  1330  receive position information from input wires  1335  and  1336 . The control electronics  1330  may alternatively use the position information to determine the correct pressure for the air spring  110 , and operate the valve  1310  to set that pressure. 
     In addition to setting the fluid pressure to counterbalance the weight of the movable barrier, the fluid pressure may be controlled dynamically to operate the movable barrier. By controlling the fluid pressure in the air spring, the barrier may be raised or lowered. In this mode of operation, the air spring counterbalance serves as both a counter balance mechanism and as a movable barrier operator. This system offers many advantages because it replaces both the movable barrier operator (e.g.,  1050  in  FIG. 10 ) and the counterbalance mechanism (e.g.,  1035  in  FIG. 10 ) currently used. 
       FIG. 16  describes a method for operating a movable barrier, using the air spring counterbalance mechanism. Starting from step  1600 , control electronics (e.g.,  1330  described in  FIG. 13 ) evaluate whether they have received a command signal that indicates the barrier should be moved. If the signal is received, the system proceeds to step  1610  where it evaluates whether the door should be raised or lowered. In one alternative, the command signal simply indicates that the barrier should be moved without indicating what direction. In this alternative, the control electronics  1330  determine the present state of the barrier either by evaluating position sensor inputs  1335  and  1336 , by evaluating a state stored in memory, or by testing movement in one direction to determine if movement in that direction is possible. In another alternative, the command signal itself indicates which direction the door should move and the control electronics proceed according to that command. 
     If the control electronics  1330  determines that the barrier is to be raised, the system proceeds to step  1620  and fluid is added to the air spring, by opening the valve  1310  discussed in  FIG. 13 . Fluid can either be added continuously or in discrete increments, by identifying a target pressure or by opening an input valve for a pre-determined period of time. The amount of fluid to be added may be predetermined, for instance by using a learning system that identifies how much fluid must be added or what pressure would be sufficient to raise the door to the desired position. For example, the pressure sensor  1340  discussed in  FIG. 13  might be used by the control electronics  1330  to close the control loop so that the control electronics can close the valve  1310  when a predetermined pressure is achieved. At step  1625  the control electronics  1330  evaluate whether the barrier is at the raised position. If not, the system proceeds back to step  1620  and opens the valve  1310  and adds more fluid. If the barrier has been raised to the desired position, the system may optionally proceed to a maintenance loop starting at step  1640 . At step  1640  the system continuously monitors whether the barrier is at the desired position. Part of this step might include maintaining a certain fluid pressure, as discussed with respect to step  1570  in  FIG. 15 . If the barrier is at the desired position the system proceeds to step  1600 . If not, the system proceeds to step  1610 , where it evaluates whether to raise or lower the door. 
     If the control electronics  1330  determines that the barrier is to be lowered, the system proceeds to step  1630  and fluid is released from the air spring by putting the valve in the exhaust state, as discussed with respect to  FIG. 13 . Fluid can either be released continuously or in discrete increments, by identifying a target pressure or by opening a release valve for a period of time. As discussed above, the control electronics  1330  may use the pressure sensor  1340  discussed with respect to  FIG. 13  to determine when a predetermined pressure has been achieved. The amount of fluid to be released may be predetermined, for example by using a learning system that identifies how much fluid must be released or what pressure would be sufficient to lower the door to the desired position. Step  1635  evaluates whether the barrier is at the lowered position. If not, the system proceeds back to step  1630  and releases more fluid. If the barrier has been lowered to the desired position, the system may optionally proceed to step  1640 , where it enters the same position maintenance loop discussed above. Additional steps might be added to this process, and the process could be limited to include only steps  1600 ,  1610 ,  1620 , and  1625  or limited to include only steps  1600 ,  1610 ,  1630 , and  1635 . 
     Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept. This will also be understood to encompass various combinations and permutations of the various components that have been set forth in these teachings.