Abstract:
A disclosure for a limited motion exerciser has been provided. The device as presently conceived is entirely driven by the user in a sitting position only. It would be placed on the floor, slightly forward of the knees such that movement of either leg away from the chair will be met with a predetermined resistance. Its physical size dictates a stroke of approximately 10 inches. Two traction elements are provided, one positioned beneath each foot. The elements are mechanically independent, allowing use of one or the other. Ideally both feet and lower legs would be active, employing equal and opposite motion, similar to normal walking. As designed, there is sufficient interior volume to install a user-adjustable load resistance that will be battery powered and recharged by the energy expended by the user. This feature (user-adjustability) will be covered by a subsequent patent application and is not detailed herein.

Description:
BACKGROUND 
       [0001]    This machine was originally conceived on Oct. 7, 1991 by Lani R. Arst, a US citizen, who at that time was living at 10945 Rose Avenue, Apartment 110, Los Angeles, Calif. 
         [0002]    It is intended to be used by people who spend the greater part of their work day sitting at a desk or for those who find themselves with limited physical mobility and are chair-bound. It would especially apply to those with poor circulation in the lower extremities but are otherwise in good physical condition, able to walk without support. Leg, thigh and gluteous maximus muscles normally associated with movement of the legs will benefit from use of this device. 
         [0003]    In the original disclosure document, reference was made to a platform 16 inches in length and 14 inches in width; this was accompanied by a sketch showing two movable belts, each of which were held in tension by a spring-loaded, telescoping support. This support would also provide a low-friction pad that would engage the weight of the legs while in use. 
         [0004]    In the original disclosure document, under “Description of Invention”, reference was made to an adjustable feature that would enable the user to increase or decrease the tension of the back and forth motion. As this was not detailed in the initial submission, it will not be included in the substitute specification; no new matter is offered. 
       SUMMARY OF THE INVENTION 
       [0005]    This device is intended to provide the user with a passive resistance to normal motion of the back of the thigh muscles, the lower legs (calves) and ankles while sitting. Since the motion is a reciprocating action, similar to walking, little or no motion would be transmitted to the chair. This device is intended for use only while in a sitting position, and standing while operating will be highly discouraged. Low initial cost and long service life are a high priority. For this reason, internal part count and weight will be minimized. As longevity is greatly influenced by wear, the design will minimize the use of friction in all moving parts. By design intent, the device will meet all advertised claims for a period of three years with no scheduled maintenance. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0006]      FIG. 1  (of 2) shows the front view of the device which identifies the three principle components: a base assembly (item  1 . 0 ), a top cover (item  2 . 0 ) and the two identical traction elements (items  3 . 0 ). 
           [0007]      FIG. 2  (of 2) shows three cross-sectional views, taken from the longitudinal direction. Two of the cross sections, each identified in  FIG. 1  as section A-A and B-B, are cuts through the two roller assemblies and one of the two traction elements. The roller assemblies (items  4 . 1  and  4 . 2 ) will be similar in size and shape but have subtle differences relating to functionality. The third sectional view, identified as section C-C, is a cut through and parallel to the rotational axis of the front roller assemble (item  4 . 1 ). 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Base assembly (item  1 .) serves as the primary structure wherein all vertical and horizontal loads are reacted by, and transferred through, the base into the floor or ground plain. It is designed to allow easy assembly of all working components during manufacturing as well as during shop servicing. 
         [0009]    Material selection—the material to be used in the fabrication of the base will be of glass fiber reinforced bulk molding compound (BMC). If available, a recyclable base polymer will be specified. The chosen material will be able to withstand a minimum of 15 drops from a height of 36 inches (as part of the finished product) without cracking or damage to any of the internal parts. 
         [0010]    Structural design—the base will be designed to support a maximum static (non-operating) load of 250 pounds, evenly distributed over each of the two traction elements (item  3 . 0 )—125 pounds per element. Loads passed through the base will be reacted by four elastomeric pads bonded into cavities formed during the molding process. Material thickness and sections will be determined by allowable deflections based on anticipated external, as well as internal, loading. The two housings, item  1 . 0  base, and item  2 . 0  cover, are designed to snap together as shown in  FIG. 2 , section B-B. This feature enables operation without concern by the user should the mechanical fasteners become lost. Four clips, two across the front and two across the back, are essential assembly aids prior to insertion of the fasteners. Threaded self-locking inserts will be integrally molded in place at four corners (the top cover, item  2 . 0 , will be provided with matching clearance holes). Details of these mounting bosses have been omitted from the figure for clarity. 
         [0011]    Cover (item  2 . 0 ) serves to protect all internal components from liquid spills and damage from falling objects. As depicted in  FIG. 1 , all features are generously radiused to prevent injury during handling or transport. The parting line between the base (item  1 . 0 ) and cover (item  2 . 0 ) will be held to a profile tolerance of 0.005 inches per inch of length to minimize gaps. Clearance between the cover and the two traction elements (item  3 . 0 ) will be no larger than necessary to avoid intimate contact while in use (approximately 0.125 inches). 
         [0012]    The material to be used in the fabrication of the cover will be the same as used for the base (item  1 . 0 ). Exterior finish will be as molded. The material will be inherently stain-resistant and non-reactive to all commonly available solvents and detergents. Post processing will be limited to light deburring and flash removal during manufacture. 
         [0013]    The cover will be designed to withstand overhead drops of a 1 pound steel object one time at any location without cracking through. Minor imperfections will be accepted after impact. By design, the cover will not be required to react any external loads. Therefore sections (wall thickness) will be sufficient to withstand the impact test and the drop test discussed in the paragraph just previous to this one. 
         [0014]    Two traction elements, or belts, will be required for normal operation. The device will also operate normally with forces applied to only one of the two elements. The design is unique in that the inner surface is contoured to run within notches at the center of each roller (for guidance) and is surfaced with a low-friction layer (such as Teflon™) to minimize wear. The belts will also be manufactured with continuous loops of stranded cording to resist stretching over time under the influence of the tensioning springs (item  11 . 0 ). 
         [0015]    The elastomer base material will be made of ethylene propylene diene monomer (EPDM) compound reinforced with carbon fiber. Lateral ribs, shown in  FIG. 1 , will be molded to provide comfortable contact with bare feet and facilitate bending around the two rollers (items  4 . 1  and  4 . 2 ) without cracking. 
         [0016]    The traction elements will be designed to fail by separation of the cord reinforcement at or above 150 pounds (roller separating force). Limit loading will be based on a cyclic fatigue life of 10 8  cycles in one direction (90° around a 1.4 inch radius) while under a tensile load of 50 pounds total separating force. Cold-flow, or slow stretching under a continuous load of 20 pounds, will be less than 0.1 inches per year. The unit will operate as expected up to a total stretch of 0.25 inches providing a service life of 2.5 years, or 14.3×10 6  cycles. 
         [0017]    Reference is made to the roller assemblies (items  4 . 1  and  4 . 2 ). Two forward and two aft rollers are required, one of each type for each traction element. Each roller assembly will include two ball bearings (item  8 . 0 ), two bearing retainers (item  8 . 1 ), an inner core (item  9 . 0 ), and an outer shell (item  10 . 0 ). The “V” notch, shown in  FIG. 2 , section C-C, serves two important functions. The first is guidance of each traction element where engagement is over 180° of arc. The second function is to activate the separating load via rolling contact on center with transfer bearing (item  7 . 0 ). 
         [0018]    Both forward and aft roller assemblies (items  4 . 1  and  4 . 2 ) are identical with the sole exception of surface treatment. Aft rollers ( 4 . 2 ) will be coated with a layer of titanium-nitride for wear resistance. Initially thickness of the coating will be specified at 0.0005 to 0.0015 inches. All bearings (item  8 . 0 ) will be self-lubricated ceramic ball type and sealed to reduce likelihood of contamination. Bearing retainers (item  8 . 1 ) will be of non-magnetic cres and fitted with O.D. threads to enable a light axial bearing preload. Staking after assembly will prevent disengagement. The inner support (item  9 . 0 ) will be injection molded from 30 percent glass fiber reinforced polyetheretherketone (PEEK) with section properties sized to permit insertion and axial support of bearing inner races. 
         [0019]    Common roller housings (item  10 . 0 ) will be machined from through-hardened, 3 inch diameter bar stock. A high-quality alloy steel, 9310 or 4340, will be specified. Heat treatment of the outer support (item  5 . 0 ) may be specified if necessary to reduce wear. 
         [0020]    The rollers will be sized to control deflection at the midpoint between bearings at less than 0.005 inches maximum with a point load of 50 pounds. 
         [0021]    The outer support shown in  FIG. 2 , section B-B, serves three functions:
       A. Uniform support and roll axis stabilization for loads imposed by the user;   B. Guidance and support of the inner support which telescopes inside (item  6 . 0 ) in  FIG. 2 , section B-B); and   C. A resistance to motion by bearing on the aft roller (item  4 . 2 ) outside diameter.       
 
         [0025]    The outer support will be formed into a rectangular cross-section with one end closed in the form of a cylinder. The radius of curvature will be approximately 0.02 inches larger than the roller radius in order to ensure initial wear occurs on center with line contact. With use, this surface (softer than the roller) will expand slowly to area contact and polish over time. 
         [0026]    The load cylinder will be fabricated from 4130 or 4340 alloy steel from standard sheet stock and welded into a rectangular box section. After welding the radiused end, the entire part will be powder-coated to prevent corrosion 
         [0027]    Material thickness will be determined by finite element analysis of the assembly (item  6 . 0  installed in item  5 . 0 ). Criteria will be no permanent deformation when supported in the base (item  1 . 0 ) and loaded to 125 pounds over a distributed surface of 4 square inches. 
         [0028]    Reference is made to the inner support assembly (item  6 . 0 ). This assembly consists of a rectangular section sized to fit within the outer support (item  5 . 0 ). On one end rests a helically-wound spring (item  11 . 0 ). On the opposite end, a retained bearing and shaft is fitted in a slotted yoke. The rectangular section will be designed to slip into the outer support (item  5 . 0 ) with a clearance fit of 0.010, +/−0.005 (0.005 per side) inches. The yoke section serves as a reaction point for the spring and a sliding support for the follower bearing (item  7 . 0 ). Once installed, the separating force created by spring (item  11 . 0 ) will be reacted at one end by roller (item  4 . 2 ) and at the opposite end by roller (item  4 . 1 ), creating the tensile load on the traction element (item  3 . 0 ) and frictional drag between the aft roller and load housing (item  5 . 0 ). All external surfaces of the inner support in contact with the outer support (item  5 . 0 ) will be machined to a profile of 0.005 inches and electro-polished. 
         [0029]    The inner support will be fabricated using a combination of both sheet and bar stock. Bar stock 4130 or equivalent, will be machined to form the yoke section. This will be mechanically fastened by welding to the rectangular section. After all machining and polishing, this detail will be powder coated to prevent corrosion. 
         [0030]    All load paths will be designed with a factor of safety of 1.5 on yield strength and 3.0 on ultimate strength. Deflection allowable will control section properties. Analysis of vertical deflections will assume uniform and distributed load sharing between item  5 . 0  and item  6 . 0  assembled normally. 
         [0031]    Reference is made to the bearing follower assembly (item  7 . 0 ). The bearing follower assembly consists of two closed-end needle bearings, a shaft and a roller follower machined to fit within, and guided by the “V” groove formed on the roller (item  10 .) outside surface. The roller follower will be pressed onto a standard 0.5 inch shaft (gauge stock). Motion of the shaft/roller follower will be carried by 2¾ inch O.D. closed-end needle bearings. Grease, mobil 28, or equivalent, gear lubricant, will be applied during assembly of the exerciser. 
         [0032]    All materials will be corrosion-resistant as commercially available. Torrington needle bearings will be protected by additives in the lubricant. A machinable grade of Cres will be used for the follower and tool steel for the shaft. 
         [0033]    The roller follower will be cut at an angle that is 4 to 6 degrees larger than the roller groove, gradually forming area contact that will stabilize with use. This solution assures lateral stabilization and guidance over the life of the unit. 
         [0034]    Reference is made to the load spring (item  11 . 0 ). In order to manufacture this helical-coil compression spring, the following data will be provided:
       Material and its condition   Wire size (wire diameter, d)   End treatment   Total number of turns or coils (N)   Coil diameter (O.D.), and   Free length (l f )       
 
         [0041]    After choosing a standard wire gauge from published data (such as Washburn and Moen), free length spring rate will be calculated. Constraints will be load at loaded length (9⅞ inches from  FIG. 2  section B-B) and outside diameter (1¾ inches, also from  FIG. 2 ), end condition will be ground and square. Existing spring design computer software will be used to optimize the design for the lowest possible volume and cost. The final design will be accepted for this application (static service) if the following criteria are satisfied: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Spring Index (C = D/d) 
                 3 ≦ C ≦ 12 
               
               
                   
                 Number of active turns 
                 10 ≦ N ≦ 25 
               
               
                   
                 Factor of safety at closure 
                 1.1 ≦ η ≦ 1.4 
               
               
                   
                 Spring rate is defined as 
                 (k = d 4  · G/8 · D 3  · N) 
               
               
                   
                 Where Helix diameter 
                 (D = O.D. − d) 
               
               
                   
                 Sheer modulus 
                 (G = 11.5 × 10 6  PSI) 
               
               
                   
                 Force at closure 
                 (F s  = k · Y s ) 
               
               
                   
                 Where (Y s ) free length stacked height 
               
               
                   
                 Sheer stress at closure 
                 (τ = 8 · Ks · Fs · D/πd 3 ) 
               
               
                   
                 Where K s  = 1 + 0.5/C 
               
               
                   
                 Sheer yield strength 
                 (S sy  = 0.577 · 0.75 · S u ) 
               
               
                   
                 Where S u  is the ultimate tensile strength 
               
               
                   
                 Factor of safety at closure 
                 (η s  = S sy /τ S   
               
               
                   
                   
               
             
          
         
       
     
         [0042]    Common alloy spring material will be specified such as 1085 music wire or 1066 cold-drawn spring wire. 
         [0043]    Much of the design criteria includes strength considerations. The principal concern will be margins for buckling and tolerances suitable for manufacturability. The design will allow for reasonable variation on helix diameter (+/−0.030 inches) and free length (+/−0.15 inches).