Abstract:
An improved elastic motor is disclosed having a constant torque characteristic. The motor utilizes a reel with elastic stretched to its maximum tension. Each unit length of the elastic is allowed to relax back to its normal state while generating work in a process that will continue until the wheel is fully unwound. The present invention will ease design of mobile devices and the like by providing a power source having a predictable and stable output characteristic.

Description:
CROSS REFERENCE TO OTHER APPLICATIONS  
       [0001]    This application is filed as a continuation-in-part of co-pending Application Ser. No. 09/578,419 entitled “Elastic Motor” filed May 25, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to elastic motors, and more specifically, to an improved elastic motor having constant torque characteristics.  
         BACKGROUND OF THE INVENTION  
         [0003]    Elastic motors have been employed for centuries and have found particular application in model airplanes for over 150 years. Typical prior art elastic motors, such as those used in a model airplane, generally comprise a rubber loop threaded through a hook on a propeller shaft and is further attached to another hook at the tail of the craft. As the motor is wound up it first twists the elastic into a skein, then a row of knots form and spread along the whole length. A third stage occurs when a row of knots forms in the already knotted skein. When this row is complete the rubber is substantially stretched to its limit.  
           [0004]    Upon release of propeller, there is a burst of power. When this is spent, a period of slowly declining torque follows for the majority of the motor run and is followed by a decline to zero torque.  
           [0005]    The torque characteristics of the prior art elastic motor devices, like those described above, make model airplane design a considerable challenge. Clearly, this is because it is difficult for a designer to properly construct design constraints when the source of propulsion has such wavering torque characteristics. Aside from model airplane design, conventional elastic motors have undesirable performance in other applications as well. The knotting of the rubber introduces internal friction in the wound skein that can be eased somewhat by lubrication. Lubrication, however, drastically reduces the useful life of the rubber.  
           [0006]    Therefore, the shortcomings of the prior art suggest a strong need for an elastic motor design that has a constant torque characteristic and does not damage the elastic material.  
           [0007]    One particular U.S. Patent which aims to answer this need for a constant torque producing elastic motor is McAneny U.S. Pat. No. 4,629,438 which discloses a rubber band powered motor for a model airplane. McAneny teaches of a method of providing an extended flight through means of producing a more stable torque to improve upon designs comprising a wind up rubber band with a sudden burst output. Thus, the elastomeric members are either fully stretched, fully relaxed, in brief stretching mode or in brief relaxing mode. As a result, McAneny relies on tapes and gears, coupled to the multiple number of elastomeric members, to absorb the sudden bursts and function to produce a more stable torque output. However, McAneny teaches of an approximately steady torque output which extends the period of decay but does not provide for a periodic torque output which can be approximated as constant under certain heavy loads. Additionally, McAneny relies upon components, namely gears and tapes, which may add significant weight, cost and size to the design, all of which are undesirable characteristics for most applications.  
           [0008]    Thus, there exists a need for an elastic motor which can provide an approximately constant torque output while still retaining desirable and practical characteristics such as light weight, low cost and small size.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is directed towards an elastic motor, more specifically, to an elastic motor having a constant torque characteristic.  
           [0010]    The motor system of an embodiment of the present invention starts with a reel which is wound with elastic stretched to its maximum tension. Each unit length of the elastic is allowed to relax back to its normal state while generating torque in a process that continues until the reel is fully unwound. The process may be seen as analogous to a steam engine which has a supply of steam at constant pressure. Portions of steam are fed to a cylinder where they expand to generate work (pressure times change in volume) by pushing a cylinder back to turn a wheel. When the expansion is complete the steam is exhausted and the process repeated. In the case of the present invention, a unit length of stretched elastic is connected into a system and allowed to contract to its unstressed state while turning a wheel and developing work. When fully contracted the relaxed elastic is fed to a take up reel and a new unit length of stretched elastic is taken. The process is continued until all the stretched elastic is used up. There is no twisting or knotting of the elastic and no need to lubricate it to prevent binding and wear as in a twisted skein, although some lubrication may assist operation.  
           [0011]    Additionally, similar results can be obtained through the use of more than one spool, wherein each spool has a corresponding elastic member of which its transition from a tense state to a relaxed state represents one torque period, and all torque periods collectively yielding an approximate torque output. In such an embodiment, sensing means may allow for the spools to release the tension of their corresponding elastic members in series whereupon each new torque period begins when the previous spool reaches a certain level of low tension.  
           [0012]    Furthermore, certain applications may be enhanced through the use of an elastic motor of the present invention with a minimum number of moving parts. Such a design may comprise the continuous transfer of an elastic member between two spools. This concept may be realized through the inclusion of a flat drive spool whereupon an elastic member is stretched and releases tension upon each rotation in a periodic fashion. Pinch rollers may be included to yield a desired tension in the elastic member as the portions of the elastic member that have released tension are left slack beyond the pinch rollers. Optionally, a take up spool may be included in addition to, or in place of, pinch rollers.  
           [0013]    Hence, it is an object of the invention to provide an improved elastic motor.  
           [0014]    Furthermore, it is an object of the invention to provide an improved elastic motor having a constant torque characteristic.  
           [0015]    Further, it is an object of the invention to provide an improved means of powering portable devices.  
           [0016]    Additionally, it is an object of the invention to provide an elastic motor having increased elastic material life.  
           [0017]    Further, it is an object of the invention to provide an improved means of driving a dynamo.  
           [0018]    Furthermore, it is an object of the invention to provide an improved means of powering wind-up toys and devices.  
           [0019]    These and other objects will become apparent to those skilled in the art upon study of the following drawings and detailed description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    A further understanding of the present invention can be obtained by reference to a preferred embodiment set forth in the illustrations of the accompanying drawings. Although the illustrated embodiment is merely exemplary of systems for carrying out the present invention, both the organization and method of operation of the invention, in general, together with further objectives and advantages thereof, may be more easily understood by reference to the drawings and the following description. The drawings are not intended to limit the scope of this invention, which is set forth with particularity in the claims as appended or as subsequently amended, but merely to clarify and exemplify the invention.  
         [0021]    For a more complete understanding of the present invention, reference is now made to the following drawings in which:  
         [0022]    [0022]FIG. 1 (FIG. 1) depicts an elastic motor typical of the prior art.  
         [0023]    [0023]FIG. 2 (FIG. 2) depicts the torque characteristics of an elastic motor typical of the prior art.  
         [0024]    [0024]FIG. 3A (FIG. 3A) depicts an elastic motor, in accordance with the present invention, in wind up mode.  
         [0025]    [0025]FIG. 3B (FIG. 3B) depicts an elastic motor, in accordance with the present invention, in the start of operating mode.  
         [0026]    [0026]FIG. 3C (FIG. 3C) depicts an elastic motor, in accordance with the present invention, at the end of the first cycle of operation.  
         [0027]    [0027]FIG. 3D (FIG. 3D) depicts the behavior of the elastic material in an elastic motor in accordance with the present invention.  
         [0028]    [0028]FIG. 3E (FIG. 3E) depicts the torque characteristics of an elastic motor in accordance with the present invention.  
         [0029]    [0029]FIG. 4A (FIG. 4A) depicts an alternate embodiment of an elastic motor in accordance with the present invention.  
         [0030]    [0030]FIG. 4B (FIG. 4B) depicts an alternate embodiment of an elastic motor in accordance with the present invention, in operational mode.  
         [0031]    [0031]FIG. 5A (FIG. 5A) depicts an alternate embodiment of an elastic motor in accordance with the present invention utilizing crossbars in the elastic.  
         [0032]    [0032]FIG. 5B (FIG. 5B) depicts a detail of the elastic used in the device of FIG. 5A.  
         [0033]    [0033]FIG. 6 (FIG. 6) depicts an embodiment of a multiple spool elastic motor in accordance with the present invention.  
         [0034]    [0034]FIG. 7 (FIG. 7) depicts a detail of the transition between a leading and following reel in an embodiment of a multiple spool elastic motor in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    As required, a detailed illustrative embodiment of the present invention is disclosed herein. However, techniques, systems and operating structures in accordance with the present invention may be embodied in a wide variety of forms and modes, some of which may be quite different from those in the disclosed embodiment. Consequently, the specific structural and functional details disclosed herein are merely representative, yet in that regard, they are deemed to afford the best embodiment for purposes of disclosure and to provide a basis for the claims herein which define the scope of the present invention. The following presents a detailed description of a preferred embodiment (as well as some alternative embodiments) of the present invention.  
         [0036]    Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “in” and “out” will refer to directions toward and away from, respectively, the geometric center of the device and designated and/or reference parts thereof. The words “up” and “down” will indicate directions relative to the horizontal and as depicted in the various figures. The words “clockwise” and “counterclockwise” will indicate rotation relative to a standard “right-handed” coordinate system. Such terminology will include the words above specifically mentioned, derivatives thereof and words of similar import.  
         [0037]    Referring first to FIG. 1, depicted is a typical prior art elastic motor in a model airplane. A rubber loop  101  is threaded through a hook  102  on the propeller shaft  103  and is attached to another hook  104  at the tail. As the motor is wound up it first twists into a skein, then a row of knots form and spread along the whole length. A third stage occurs when a row of knots forms in the already knotted skein. When this row is complete the rubber is generally stretched to its limit.  
         [0038]    Upon release of propeller  105  there is a burst of power, A to B as depicted on the torque characteristic of FIG. 2. When this is spent, a period of slowly declining torque B to C follows for the majority of the motor run and is followed by a decline to zero torque, points C to D.  
         [0039]    [0039]FIG. 3A through 3D show a first embodiment of the present invention. FIG. 3A shows an elastic motor in accordance with the present invention in wind up mode. Fully relaxed elastic  301  passes through movable rollers  302  as reel  303  rotates in a clockwise direction  305 . The elastic  304  is wound at constant tension and is fully stretched.  
         [0040]    In FIG. 3B, an elastic motor in accordance with the present invention at the start of operating mode is depicted. Movable rollers  302  grab the elastic  301  close to the reel  303 . Bar  307  is coupled to the reel  303  and is used to prevent slip of the stretched elastic  304 . The length of the elastic between  307  and  302  is NL where L is a unit length of relaxed elastic. The operation cycle allows this to be relaxed back to its relaxed length L while the tension in the elastic provides torque to turn reel  303  and supply power to a load. Reel  303 , upon release, will begin to rotate in a counterclockwise direction  306 .  
         [0041]    [0041]FIG. 3C depicts an elastic motor in accordance with the present invention at the end of the first operating cycle. Reel  303  is allowed to release, causing counterclockwise rotation  306 . The length between rollers  302  and bar  307  shortens to unit length L as the tension in the elastic  308  decreases until complete relaxation.  
         [0042]    [0042]FIG. 3D depicts an elastic motor in accordance with the present invention that is capable of multiple operating cycles. This is accomplished by introducing an additional bar  309  and disengaging bar  307 . In FIG. 3D( 1 ), the elastic motor is shown at the end of the first operating cycle, as described above in FIG. 3C. In FIG. 3D( 2 ), rollers  302  are first backed up and the elastic  308  is released. Bar  307  remains engaged to maintain secure contact between elastic  308  and reel  303 . Reel  303  continues to rotate in counterclockwise direction  306 . In FIG. 3D( 3 ) the changeover point between cycles is shown. While the elastic remains released between reels  302 , additional bar  309  is introduced between bar  307  and elastic  308 . Reel  303  is poised to continue rotation in counterclockwise direction  306 . In FIG. 3D( 4 ) the start of the second cycle is shown. Pinch rollers  307  and  309  are moved to position  302  and new clamping bar  315  is placed in the initial position of  307  as in FIG. 3B. Clamping rollers  307  and  309  are opened and elastic  308  is released. This cycle is identical to the start of the first operating cycle described in FIG. 3B, with bar  307  replaced with bar  315 . Reel  303  is now ready to continue rotating in counterclockwise direction  306  until bar  315  approaches clamping rollers  307  and  309  in position  302 . At that point, the cycle repeats with bar  315  in position of  307  of FIG. 3D( 1 ). The pinch rollers  302  and clamping bars  307 ,  315  and  309  recycle their functions with each ensuing cycle.  
         [0043]    [0043]FIG. 3E depicts the output torque characteristics of the elastic motor just described. Torque is plotted on axis  311  versus time on axis  312 . Peak values  310  are equal to the elastic tension multiplied by the reel radius. The average output torque is half that amount and is constant throughout operation.  
         [0044]    Another embodiment of the present invention comprises two reels, one for relaxed elastic, the other for stretched elastic. The two reels may be the same size, but it is not necessary. Differing diameters or geometries can provide different output characteristics. FIG. 4A depicts an exemplary motor  400  in accordance with this embodiment of the present invention. Motor  400  is shown in wind up mode. Reel  406  is loaded with relaxed rubber  401 , the end of which is connected to opposing reel  407 . Reel  406  rotates in a clockwise direction  403  and reel  407  rotates in counterclockwise direction  403 . The elastic  404  wound on reel  407  is stretched to n times its lengthened, and optimally, is at full tension. Thus reel  407  turns n times as fast as reel  406 . Roller  405  prevents the elastic  401  on reel  406  from slipping over itself and ruining the tension relationship.  
         [0045]    [0045]FIG. 4B depicts the motor  400  in operational mode, wherein the device is producing work. Reel  407  has two bars  408  and  409  pressing against the elastic  404  to prevent slippage. Reel  407  rotates in clockwise direction  410  taking bars  408  and  409  with it. Opposing reel  406  rotates in counterclockwise direction  411 . When bar  408  approaches roller  405 , the elastic  404  between bar  408  and roller  405  is in its relaxed state. At this point, roller  405  is disengaged to allow bar  408  to pass and further allow elastic  404  to wind onto reel  406 . After bar  408  passes, roller  405  is put back in place. Bar  408  is now removed and the elastic  404  between bar  407  and roller  405  undergoes the same process. At this point, bar  408  is replaced and is ready for the next cycle. Motor  400  is capable of multiple operating cycles.  
         [0046]    Such a device  400  as described can achieve the required operation, however, the need to remove and replace bars  408  and  409  and roller  405  complicates operation. Thus, an alternate embodiment is depicted in FIG. 5A. An elastic sheet  501  is used comprising integral crossbars that engage in slots  502 ,  507  and  508  on reel end plates  503  and  504  to maintain the high and low tension zones in the elastic  501  and allow automatic transfer between the two reels  505  and  506  without the need for any other moving parts. The two reels  505  and  506  are fitted with slotted end plates  503  and  504 . Reel  505  rotates in counterclockwise direction  510  n times as fast as reel  506  rotates in clockwise direction  511 . Reel  506  has two slots  507  and  508  in its end plates. Reel  505  has 2n slots  502  in its end plates  503 . The end plates  503  and  504  overlap at point  509  so that the elastic  501  can transfer between the reels  505  and  506  without any slipping and thus maintain the tension relationship. Rotating reel  506  counterclockwise will automatically stretch the elastic  501  to n times its original length. The two reels  505  and  506  could be coupled together by a gear box or a cog belt to have an n to 1 speed ratio and assist in maintaining accurate alignment. Coupling the two reels  505  and  506  together reduces the output torque to [1−(1/n)] of the maximum. Thus, the higher the value of n, the higher the system efficiency.  
         [0047]    [0047]FIG. 5B depicts a detail of the elastic used in device  500 . Elastic  501  comprises an elastic strip  515  and integral crossbars  516 . Crossbars  516  articulate with slots  502 ,  507  and  508  to constrain the movement of reels  505  and  506  and thus maintain the tension relationship.  
         [0048]    [0048]FIG. 6 depicts a multiple spool elastic motor with four spools A 1 -A 4 , although any number of spools may be used with this design for changing the duration of operation and without parting from the spirit and scope of the present invention. These spools A 1 -A 4  rotate freely on drive shaft F. Said spools A 1 -A 4  have corresponding elastic members E 1 -E 4 . Primary pawls Bl-B 3  correspond to adjacent spools A 2 -A 4 . Primary pawl B 4  is drawn only for consistency and is only used if a fifth spool is added to the present embodiment. Primary pawls B 1 -B 3  function to prevent clockwise movement of spools A 2 -A 4  upon tension of elastic members E 2 -E 4 . One end of each of elastic member E 1 -E 4  is attached to a corresponding spool A 1 -A 4 , while the other end is wrapped around a pawl projection G 1 -G 4  and secured around fixed elastic attachment bar J. This configuration results in an increasing downward force on primary pawls B 1 -B 4  proportional to an increased tension in elastic members E 1 -E 4 . Pawl lift H produces a constant upward force upon said primary pawls B 1 -B 4 , which rotate independently on pivot rod K. When the tension in elastic members E 1 -E 3  increases, primary pawls B 1 -B 3  lower and engage spool cuts I 2 -I 4 , thus, resisting clockwise movement of spools A 2 -A 4 . An increase in tension of elastic member E 4  would result in the lowering of primary pawl B 4  to engage a spool cut I 5  (not shown) if a fifth spool is added to the present embodiment. Molded pawls D 1 -D 4  are joined to the outer side of spools A 1 -A 4  on the section comprising spool cuts I 1 -I 4 . It should be noted that molded pawls D 2 -D 4  are not shown due to their being hidden between said spools A 1 -A 4 . Ratchets C 1 -C 4 , placed on the outside of spools A 1 -A 4 , connect with molded pawls D 1 -D 4  to provide high resistance for clockwise movement and negligible resistance for counter-clockwise movement of said spools A 1 -A 4 . It should also be noted that ratchets C 2 -C 4  are not shown due to their being hidden between spools A 1 -A 4 . Coupling one of spools A 1 -A 4  with its respective ratchet C 1 -C 4  yields the coupling of said one of said spools A 1 -A 4  to drive shaft F.  
         [0049]    During initial stages, spools A 1 -A 4  are wound counterclockwise simultaneously and tension in elastic members E 1 -E 4  increases. This motion is transmitted to said spools A 1 -A 4  by ratchets C 1 -C 4  and molded pawls D 1 -D 4  which spring into engagement. As elastic members E 1 -E 4  stretch on spools A 1 -A 4  they will slip over themselves and it is contemplated that a lubricant could be used to reduce friction. Primary pawls B 1 -B 3  are pulled downwards by tension in elastic members E 1 -E 3  to engage spool cuts C 2 -C 4  and impede clockwise movement of spools A 2 -A 4 . Additionally, spool A 1  is free to rotate clockwise in the present design, but may be prevented to do so by inserting a pin into ratchet C 1 .  
         [0050]    Upon removal of said pin, spool A 1  begins to turn clockwise and molded pawl D 1  and ratchet C 1  function to turn drive shaft F clockwise. A clockwise torque is produced at drive shaft F by said spool A 1 . As spool A 1  turns clockwise, tension in elastic member E 1  decreases and at some level of decreased tension the upward force from pawl lift H exceeds the downward force from tension in elastic member E 1 . At this point, primary pawl B 1  raises above spool cut I 2  on spool A 2  and as a result, said spool A 2  begins to provide a clockwise torque to drive shaft F. Upon the activation of said spool A 2 , elastic member E 1  has been completely relaxed and spool A 1  is no longer providing torque to drive shaft F.  
         [0051]    The process described continues until all elastic members E 1 -E 4  become fully relaxed. With each spool being turned, a naturally decaying torque cycle is produced at drive shaft F. Over the course of the entire operation, however, a periodic torque is produced wherein the relaxation of each spool A 1 -A 4  represents one torque period, or cycle. Therefore, said periodic torque output at drive shaft F can be approximated as a constant torque.  
         [0052]    [0052]FIG. 7 depicts a detail of the transition between a leading and following reel in an embodiment of a multiple spool elastic motor in accordance with the present invention. In this figure, elastic member E 1  on spool A 1  has released its tension and no longer provides torque to drive shaft F. Primary pawl B 1 , thus, raises as the upward force placed upon said primary pawl B 1  by pawl lift H exceeds the downward force placed upon pawl projection G 1  by said elastic member E 1 . As primary pawl B 1  raises, said primary pawl B 1  disengages spool cut I 2  and spool A 2  begins to rotate clockwise as tension in elastic member A 2  begins to be released. As spool A 2  rotates clockwise, molded pawl D 2  springs into action with ratchet C 2 . Said ratchet C 2  is further coupled with said spool A 2  to provide a clockwise torque to drive shaft F.  
         [0053]    The multiple spool elastic motor embodiment detailed in FIGS. 6 and 7 may operate as a single unit or may comprise additional elements. For example, other types of elastic motors may be coupled in a manner similar to that of the multiple spool elastic motor of FIGS. 6 and 7, or other types of elastic motors may function as individual elements along drive shaft F of FIGS. 6 and 7. One such element may be a pin rubber elastic motor design as in FIGS. 5A and 5B, wherein a plurality of spools are coupled to one another in a manner such as that of the multiple spool elastic motor of FIGS. 6 and 7 to provide operation for longer periods of time. An embodiment such as this, may comprise crossbars on an elastic sheet, such as the embodiment described in FIGS. 5A and 5B, or may comprise a variety of other plurality of continuous engaging and disengaging elements. Embodiments such as those which would comprise a plurality of the disclosed elements may provide such a multiplexing of elastic motors that large motors may be assembled which can operate for long periods of time.  
         [0054]    While the present invention has been described with reference to one or more preferred embodiments, such embodiments are merely exemplary and are not intended to be limiting or represent an exhaustive enumeration of all aspects of the invention. The scope of the invention, therefore, shall be defined solely by the following claims. Further, it will be apparent to those of skill in the art that numerous changes may be made in such details without departing from the spirit and the principles of the invention. It should be appreciated that the present invention is capable of being embodied in other forms without departing from its essential characteristics.