Patent Publication Number: US-6988769-B2

Title: Spring toggle furniture mechanism

Description:
FIELD OF THE INVENTION 
     Conventionally, reclining type articles of furniture (i.e., chairs, sofas, loveseats, and the like) require a mechanism to bias a leg rest assembly in the extended and stowed positions. The mechanisms provided by the prior art include a large number of moving parts that tend to increase the manufacturing time and costs associated with the furniture. 
     BACKGROUND OF THE INVENTION 
     Conventionally, reclining type articles of furniture (i.e., chairs, sofas, loveseats, and the like) require a mechanism to bias a leg rest assembly in the extended and stowed positions. The mechanisms provided by the prior art include a large number of moving parts that tends to increase the manufacturing time and costs associated with the furniture. 
     Moreover, because these parts move to extend and stow the leg rest assembly the parts require alignment relative to one another to ensure proper operation. Additionally, the large number of parts adds weight to the furniture thereby making the furniture difficult to move and transport. Additionally, the occupant of the seat must overcome the biasing force to begin extending the leg rest assembly. Since one of the purposes of providing the leg rest assembly is to increase user comfort, overcoming a large biasing force tends to detract from the user&#39;s enjoyment of the furniture. 
     Once the occupant does overcome the biasing force of the mechanism, though, the large number of moving parts tends to generate noise as the user extends (or stows) the assembly. Also, as the assembly nears its fully extended (or retracted) position, the prior art mechanisms suddenly accelerate (or jerk) to the fully extended position. Again, these disadvantages of the prior art mechanisms detract from the occupant&#39;s comfort and enjoyment of the furniture. 
     Finally, the large number of parts also exposes the furniture to an increased risk of mechanical failure, particularly of those parts subject to cyclic stress (i.e., fatigue). Thus, a need exists to simplify and improve the prior art leg rest mechanisms. 
     SUMMARY OF THE INVENTION 
     A biasing assembly is provided by the present invention for an article of furniture having a seat assembly supported from a chair frame and an actuation mechanism for enabling a leg rest assembly to move between a stowed position and an extended position. The mechanism includes a support shaft, a drive rod spaced apart from the support shaft, and a toggle link coupled to the drive shaft. The biasing assembly includes a spring with a first and a second end. The spring is adapted to attach to the toggle link at the first end. The spring also includes an engagement member at the second end adapted to engage the support shaft while remaining free to slide along the axis of the support shaft. Thus, the spring aligns itself on the support shaft. 
     In another embodiment, the present invention provides an actuation mechanism for an article of furniture having a seat assembly supported from a chair frame and a leg rest assembly. The leg rest assembly is moveable between a stowed position and an extended position. The actuation mechanism enables the movement of the leg rest assembly and includes a support shaft; a drive rod spaced apart from the support shaft; a toggle link coupled to the drive shaft; and a biasing assembly. The biasing assembly includes a spring with a first and a second end. The spring is attached to the toggle link at the first end and includes an engagement member at the second end that engages the support shaft while remaining free to slide along the axis of the support shaft. Thus, the spring aligns itself on the support shaft. In yet another embodiment, the present invention provides an article of furniture including such a mechanism. 
     In another form, the present invention provides a method of assembling an article of furniture. The assembled article of furniture will have a seat assembly supported from a chair frame and an actuation mechanism for enabling a leg rest assembly to move between a stowed position and an extended position. Moreover, the assembled mechanism will include a support shaft, a drive rod spaced apart from the support shaft, and a toggle link coupled to the drive shaft. Furthermore, the method includes attaching a spring of a spring assembly to the toggle link at a first end of the spring and engaging a member of the spring assembly at a second end of the spring to the support shaft while remaining free to slide along the axis of the support shaft. Accordingly, the spring aligns itself on the support shaft. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view of a chair with upholstery, springs and other parts removed from the pre-assembled components for illustrating an improved actuation mechanism; 
         FIG. 2  is a top plan view of a leg rest mechanism of the chair of  FIG. 1  in accordance with a preferred embodiment of the present invention; 
         FIG. 3  is an elevation view of a leg rest mechanism of the chair of  FIG. 1  in accordance with a preferred embodiment of the present invention; 
         FIG. 4  is an exploded perspective view of a spring toggle assembly of the mechanism of  FIG. 1 ; 
         FIG. 5  is an elevation view of the spring toggle assembly of the mechanism of  FIG. 4  in a retracted position; and 
         FIG. 6  is an elevation view of the spring toggle subassembly of the mechanism of  FIG. 4  in an extended position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with the teachings of the present invention, an improved actuation mechanism  10  for use in single and multi-person articles of furniture  12  (i.e. chairs and sofas or loveseats) is disclosed. In addition, the present invention is also directed to a method of assembling the improved actuation mechanism of an article of furniture having a leg rest assembly (e.g., a recliner or the like). As will be described, the actuation mechanism  10  contains fewer parts and is accordingly simpler, lighter, and more reliable than the prior art actuation mechanisms. Concomitantly, the present invention facilitates application of highly efficient fabrication and assembly processes. 
     The actuation mechanism  10  of the present invention includes a single spring mechanism  14  to bias the leg rest assembly  16  in the stowed and extended positions. Moreover, the single spring mechanism  14  simplifies the assembly process and improves the reliability of the actuation mechanism  10 . In the disclosed embodiments, the article of furniture  12  includes a pre-assembled actuation mechanism  10  and various upholstered frame components (not shown). Moreover, since the actuation mechanism  10  of the present invention is relatively compact in size, the use of loose upholstered cushions, which is an important feature in marketing various styles of chair, sofa or loveseat furniture, is also possible. 
     With particular reference now to the drawings, the functional and structural aspects of actuation mechanism  10 , shown operably suspended from the various pre-upholstered box-like frame components of a chair  12  (partially shown), will now be described. For purposes of clarity,  FIG. 1  shows the various pre-assembled frame components with their upholstery, padding, springs, etc. removed to better illustrate the interdependency of the frame components construction which can be rapidly and rigidly assembled in a relative easy and efficient manner. Therefore, all of the frame components can be individually fabricated or sub-assembled to include the requisite brackets, springs, padding and upholstery on an “off-line” batch-type basis. Thereafter, the various pre-assembled and upholstered frame components are assembled for totally integrating actuation mechanism  10  therein. 
     As seen in  FIGS. 1 through 3 , actuation mechanism  10  of chair  12  is integrated into and operably suspended from left and right side frame assemblies  18 . In addition to side frame assemblies  18 , chair  12  also includes front and rear rail assemblies  20 ,  22 , respectively, which when interconnected define a rigid “box-like” chair frame. Seat assembly  24  is supported within the side frame assemblies  18  and an actuation mechanism  10 . As will be described in greater detail hereinafter, actuation mechanism  10  is pre-assembled to include a drive rod  26  and front support shaft  28 , both of which are spatially oriented to be precisely located and “suspended” from left and right side frame assemblies  18 . 
     Actuation mechanism  10  is shown to support leg rest assembly  16  thereon. More specifically, leg rest assembly  16  includes left and right pantograph linkage mechanisms  30  and the single spring-assisted toggle mechanism  14  which is operably associated with drive rod  26  and front support shaft  28  to selectively actuate leg rest assembly  16 . A rigid cross-brace  32  is secured between drive rod  26  and support shaft  28  for providing structural rigidity within actuation mechanism  10 . One end of cross-brace  32  is journally supported on drive rod  26  while the opposite end thereof is configured as a bracket  34  which is fixedly secured (such as by a suitable threaded fastener) to an inner surface of front rail assembly  20 . Furthermore, support shaft  28  is fixed to an intermediate portion of cross-brace  32  to inhibit rotation of support shaft  28  upon rotation of drive rod  26 . In the preferred construction, drive rod  26  is an elongated square shaft having a handle portion (not shown) provided adjacent an upholstered exterior portion of one of side frame assemblies  18  that can be easily reached by a person seated in chair  10  for convenient actuation thereof. 
     As best seen in  FIG. 1 , most of the structural frame components such as side frame assemblies  18 , front rail assembly  20 , rear rail assembly  22 , seat assembly  24 , and leg rest frame board  36  are each constructed in a manner which enables them to support springs, padding, upholstery, etc. in order to complete a decorative and stylish chair  12 . Preferably, each of these frame components is fabricated from one or more wood panels and/or rails that are fixedly secured together by suitable fasteners, such as dowels, staples, nails and screws, and which may be reinforced at critical joints by metal reinforcement plates or brackets and/or wood corner blocks in a known manner. As previously noted, each frame component is individually pre-assembled for subsequent assembly into the chair  12 . However, it is to be understood that the specific construction shown for each frame component is merely exemplary in nature. 
     Leg rest assembly  16  is shown to include frame board  36  having an outer surface that is padded and upholstered. Frame board  36  is supported and moved by identical left and right hand pantograph linkages  30 . Pantograph linkages  30  may be similar in function and structure to that shown in  FIG. 3  of U.S. Pat. No. 3,096,121, assigned to the common Assignee of the present invention, with the exception that pantograph linkages  30  are operably suspended about the second set of “fixed” suspension points defined by support shaft  28 . 
     As best seen in  FIGS. 2 and 3 , the single spring-assisted toggle assembly  14  is provided which works coactively with leg rest pantograph linkages  30 . Toggle assembly  14  provides means for securely holding frame board  36  of leg rest assembly  16  in a fully retracted position against front rail assembly  20 . Toggle assembly  14  is also operable to supply a spring force for biasingly urging leg rest assembly  16  toward one of its extended and retracted positions. More particularly, toggle assembly  14  includes a toggle lever  38  with a square hole  40  which is mounted by means of the square hole  40  on square drive rod  26  for rotation therewith. Toggle lever  38  is pivotally connected at pivot  42  to rear leg  44  of a C-shaped toggle link  46  that curves around, below and to the rear of drive rod  26  where its front leg  48  has an opening  50  to which an attachment means  56  in the form of a hook at one end of a helical coil spring  52  is attached. The toggle lever  38  of toggle assembly  14  is positively located on drive rod  26  by means of a fastener  58  for maintaining the toggle assembly  14  in place on drive rod  26 . The configuration of aperture  40  in combination with the use of fastener  58  having the advantage of integrally coupling the toggle lever  38  with the drive rod  26 . Thus, the spring  52  will not cause the toggle lever  38  to jump as the toggle assembly  14  rotates over center. 
     The opposite end of spring  52  includes an engagement member  54  that is slidably engaged with the support shaft  28 . More specifically, the engagement member  54  is configured to couple the spring  52  with the support shaft  28  while remaining free to slide along the axis of the support shaft  28 . Taken together, the spring  52 , the engagement member  54 , and attachment means  56  at the other end of the spring  52  may be referred to as a biasing element that may also be formed as one continuous part such as by forming the biasing assembly from a suitable wire. However, the biasing element may be formed by multiple components. A tension adjustment means (not shown) may be optionally provided for adjusting the tension in spring  52 . For example, the tension in spring  52  can be adjusted by relatively increasing or decreasing the length and hence the preload in the spring. 
     Operation of toggle assembly  14  will now be described in detail. The location of pivot  42  above drive rod  26  and the line of action of spring  52  are such that in the retracted position of leg rest assembly  16 , the spring force acts to blazingly hold or “retain” leg rest assembly  16 . As leg rest  16  is initially extended upon slight rotation of drive rod  26 , pivot  42  moves down and over center of an imaginary line between about the center of the engagement member  54  (e.g., hook) and the axis of drive rod  26 . Once pivot  42  is over-center, tension loading on spring  52  assists in drivingly rotating drive rod  26  for extending leg rest assembly  16  as front leg  48  of link  46  is pulled toward engagement member  54 . In addition, spring  52  assists the seat occupant in pivoting handle (not shown) through the required actuation angle. In similar fashion, toggle assembly  14  is adapted to utilize the spring biasing force of spring  52  to assist in returning leg rest assembly  16  to its stowed position upon reverse rotation of the drive rod  26 . 
     Now with reference to  FIGS. 5 and 6 , more differences between the stowed and retracted positions of the leg rest assembly  16  are illustrated. First, the C shaped toggle link  46  has rotated about the drive shaft  26  from the retracted position (see  FIG. 5 ) to the extended position (see  FIG. 6 ). As can be see, in the retracted position about half of the C-shaped toggle link  46  is shown on the side of the drive shaft  26  opposite that of the spring  52  whereas in the extended position substantially all of the C-shaped toggle link  46  is on the same side of the drive shaft  26  as the spring  52 . Thus, the spring  52  is stretched less in the extended position than in the retracted position. Accordingly, the biasing force developed by the spring in the retracted position exceeds the biasing force developed in the extended position. However, in another embodiment the extended biasing force exceeds the retracted biasing force. 
     From a comparison of  FIGS. 5 and 6 , it can be seen that the toggle assembly  14  and in particular the toggle lever  28  rotates through about 145° of rotation from the retracted position to the extended position and cross the over center position after about 50° of rotation. In this manner, the kinematics of the toggle assembly is timed to provide a force balanced through the range of motion (i.e., retraction to extension and visa versa) which results in a smoothly operating leg rest assembly. 
     With continuing reference now to  FIGS. 5 and 6 , the spring  52  with member  54  slidably engaged on the support shaft  28  is also illustrated. In particular, a portion  60  of the support shaft  28  is shown in  FIGS. 3 and 4 . The portion  60  is generally free from obstructions, which would otherwise prevent the engagement member  54  from sliding along the portion  60 . Generally, portion  60  is positioned on the support shaft  28  opposite the location of the fastener  58  on the drive rod  26 . 
     Accordingly, the spring  52  acting in tension will tend to pull the engagement member  54  toward the center of the portion  60 . Thus, the spring  52  will slide along the length of the support shaft  28  and align itself between the drive rod  26  and the support shaft  28  where the spring  52  is at a minimum installed length. In other words, the spring  52  can be deemed a self-aligning member of the mechanism  10 . An anti-friction agent such as wax or oil may be provided locally on the portion  60  of support shaft  28  to promote self-alignment. Because of the self-alignment of the spring  52 , the spring  52  will experience a lower, and more predictable, level of cyclic stress during operation. Accordingly, the spring  52  (and similarly stressed components) will last longer than non self-aligning springs that experience a similar stress environment. Though, of course, the single spring  52  is generally sized to provide the desired biasing forces without requiring a second or subsequent springs. 
     By way of comparison, the prior art devices typically use one or more wires, spacers, springs, retaining clips, and the like to maintain multiple spring toggles in alignment with the other components of the recliner  12 . Thus, movement of the prior art spring toggles caused all of these various components to move and vibrate. Accordingly, operation of the prior art recliners produces more noise than the chairs  12  of the present invention. In contrast, the spring toggle assembly  14  provided by the present invention requires no aids to align the single spring toggle  14 . Accordingly, the present invention provides quieter operation. Additionally, by eliminating the alignment aids and reducing the number of spring toggles to one (and only one spring toggle in a preferred embodiment) the present invention significantly reduces the part count of the chair  12 . Thus, the chair  12  is simpler, lighter, less expensive, and more reliable than the prior art recliners. 
     Turning now to a detailed discussion of the load points of the spring  52 , those skilled in the art will appreciate that the upholstery and padding applied to the leg rest assembly  16  may cause relatively minor forces to act on the actuation mechanism  16 . Some of these forces will tend to move the leg rest assembly  16  toward either the retracted or the extended positions. Thus, it should be noted herein that the term biasing force refers to the force developed specifically by the spring  52  unless expressly stated otherwise. 
     With regard to the load points of the spring  52 , it has been found that occupants of the chair  12  prefer an actuation mechanism  10  that they perceive as operating smoothly (e.g., without sudden acceleration or jerks of the leg rest assembly  16 ). Thus, in a preferred embodiment, the spring is 5.8 inches long in a completely neutral state and has a spring rate of 30 pounds per inches and an initial pre load of 17 pounds. Additionally, the spring  52  may be placed relative to the drive rod  26  and the support shaft  28  such that the spring is elongated by about 7.75 inches in the extended position. Thus, the preferred extended biasing force is about 83 pounds. In the retracted position the spring may be likewise be elongated about 7.0 inches to provide a biasing force of about 54 pounds. Presently, the spring  52  is designed for a maximum extension of 8.5 inches. 
     Meanwhile, in the over center position (relative to the drive rod axis) the spring  52  may be preloaded to about 17 pounds. Note that in the current embodiment, the over center position corresponds to about a 67% extension of the leg rest assembly  16 . Thus, when the spring  52  is over center, the preload tends to act through the axis of the drive shaft  26  thereby tending to move the leg rest assembly  16  in neither direction. As the drive shaft  26  rotates from the over center point, it causes the spring force to act on the end of the toggle lever  38  at a short moment arm (i.e., distance perpendicular to the spring force) from the axis of the drive shaft  26 . Accordingly, the moment applied to the drive shaft  20  by the spring  52  is relatively small near the over center position due to the relatively short moment arm. As the drive shaft  20  continues to rotate, the moment arm increases in proportion to the sine of the increasing drive shaft  26  angle from the over center position. Therefore, the spring  52  smoothly develops an increasingly large biasing force as the drive shaft  26  rotates towards the extended or retracted positions. 
     While the preferred embodiment has been described with particularity of the springs parameters and force generation, one skilled in the art will recognize that the specification of a given toggle assembly are dictated by the parameters of a given chair. For example, the spring rates may be increased to accommodate a chaise-type leg rest mechanism that tends to be heavier than non-chaise-type leg rest. Likewise, the kinematics of the toggle assembly may be such that the moment arm at the extended position (I e ) and at the retracted position (I r ) provide a different force balance, thereby requiring modification of the spring parameters. 
     Moreover, because the spring  52  is loaded at all times (even at the over center point,) the spring tends to draw the drive rod  26 , the support shaft  28 , and the components of the spring toggle assembly  14  firmly together. Thus, the pre-load reduces relative movement and backlash between these components. Accordingly, the present invention provides a quieter, smoother actuation mechanism  10  than the prior art. Note should also be made, that for a given article of furniture  12 , the preferred biasing forces and preload (discussed below) may be determined empirically. 
     In another embodiment, the engagement member  54  includes a hook to slidably engage the support shaft  28 . While a hook  54  with a diameter d 1  equal to a diameter d 2  of the support shaft  28  may be employed, a diameter d 1  exceeding the diameter d 2  is preferred. More particularly, it has been found that hooks  54  with the diameter d 1  equal to diameter d 2  tend to fail at a portion  62  of the spring  52  adjacent the hook  54  (i.e., adjacent the support shaft  28 ). In contrast, hooks  54  with diameters d 1  larger than d 2  provide reliable and predictable service life when exposed to the designed level of cyclic stress. A diameter d 1  between about 130% and about 170% of the diameter d 2  is desirable. As presently preferred, a hook having a diameter of ¾ inches is used over a support shaft having a diameter of ½ inches. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.