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 
   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 
   This invention relates generally to elastic motors, and more specifically, to an improved elastic motor having constant torque characteristics. 
   BACKGROUND OF THE INVENTION 
   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. 
   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. 
   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. 
   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. 
   One particular invention which aims to answer this need for a constant torque producing elastic motors is disclosed in McAneny U.S. Pat. No. 4,629,438 which describes a rubber band powered motor for a model airplane. McAneny teaches a method of providing an extended flight by producing a more stable torque. 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 multiple elastomeric members, to absorb the sudden bursts and function to produce a more stable torque output. 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. 
   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 
   The present invention is directed towards an elastic motor, more specifically, to an elastic motor having a constant torque characteristic. 
   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. 
   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. 
   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. 
   Hence, it is an object of the invention to provide an improved elastic motor. 
   Furthermore, it is an object of the invention to provide an improved elastic motor having a constant torque characteristic. 
   Further, it is an object of the invention to provide an improved means of powering portable devices. 
   Additionally, it is an object of the invention to provide an elastic motor having increased elastic material life. 
   Further, it is an object of the invention to provide an improved means of driving a dynamo. 
   Furthermore, it is an object of the invention to provide an improved means of powering wind-up toys and devices. 
   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 
     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. 
     For a more complete understanding of the present invention, reference is now made to the following drawings in which: 
       FIG. 1  ( FIG. 1 ) depicts an elastic motor typical of the prior art. 
       FIG. 2  ( FIG. 2 ) depicts the torque characteristics of an elastic motor typical of the prior art. 
       FIG. 3A  ( FIG. 3A ) depicts an elastic motor, in accordance with the present invention, in wind up mode. 
       FIG. 3B  ( FIG. 3B ) depicts an elastic motor, in accordance with the present invention, in the start of operating mode. 
       FIG. 3C  ( FIG. 3C ) depicts an elastic motor, in accordance with the present invention, at the end of the first cycle of operation. 
       FIG. 3D  ( FIG. 3D ) depicts the behavior of the elastic material in an elastic motor in accordance with the present invention. 
       FIG. 3E  ( FIG. 3E ) depicts the torque characteristics of an elastic motor in accordance with the present invention. 
       FIG. 4A  ( FIG. 4A ) depicts an alternate embodiment of an elastic motor in accordance with the present invention. 
       FIG. 4B  ( FIG. 4B ) depicts an alternate embodiment of an elastic motor in accordance with the present invention, in operational mode. 
       FIG. 5A  ( FIG. 5A ) depicts an alternate embodiment of an elastic motor in accordance with the present invention utilizing crossbars in the elastic. 
       FIG. 5B  ( FIG. 5B ) depicts a detail of the elastic used in the device of FIG.  5 A. 
       FIG. 6  ( FIG. 6 ) depicts an embodiment of a flat drive spooled elastic motor of the present invention. 
       FIG. 7  ( FIG. 7 ) depicts a sequence of an elastic motor of the present invention in a wind up process. 
       FIG. 8  ( FIG. 8 ) depicts a sequence of an elastic motor of the present invention in operation. 
       FIG. 9  ( FIG. 9 ) depicts an embodiment of a flat drive spooled elastic motor of the present invention with pinch rollers. 
       FIG. 10  ( FIG. 10 ) depicts an elastic member with a surface pattern. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   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. 
   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. 
   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. 
   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. 
     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. 
   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 . 
     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. 
     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.  3 D( 1 ), the elastic motor is shown at the end of the first operating cycle, as described above in FIG.  3 C. In FIG.  3 D( 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.  3 D( 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.  3 D( 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.  3 B. 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.  3 D( 1 ). The pinch rollers  302  and clamping bars  307 ,  315  and  309  recycle their functions with each ensuing cycle. 
     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. 
   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  402  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. 
     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. 
   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.  5 A. 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. 
     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. 
   Referring next to  FIG. 6 , depicted is an embodiment of an elastic motor of the present invention with a flat drive spool H. This elastic motor J operates with one end of elastic member E attached to flat drive spool H and the other end of elastic member E attached to take up spool D. To initiate tension in elastic member E, winding sequence begins by winding crank A clockwise. Winding crank A is coupled to flat drive spool H to yield elastic member being tightly wound around flat drive spool H. Upon completion of the wind up sequence winding crank A may be removed. As shown, take up spool D is coupled to take up shaft G and functions to collect relaxed elastic member E upon the release of tension in elastic member E. Also, flat drive spool H is coupled to drive shaft F, which is further coupled to take up shaft G, and thus take up spool D, by means of coupling belt B. This configuration results in flat drive spool H operating complementary with take up spool D, whereupon take up spool D turns counterclockwise to collect elastic member E as a counterclockwise rotation of flat drive spool H occurs during the operating period of the elastic motor. Likewise, upon flat drive spool H rotating clockwise during wind up sequence, take up spool D turns clockwise as it releases elastic member E. Drive shaft F provides a torque output during operation. 
   While elastic motor J may successfully operate with all features described above, without certain modifications this design is prone to slippage of elastic member E around take up spool D. For example, if elastic member E on take up spool D tightens during operation it will not be fully relaxed for the next wind up sequence and would lead to overstretching and breakage of elastic member E upon additional wind up sequences. Thus, additional features are discussed in the following which will lead to proper functioning of elastic motor J throughout many cycles of use. 
   One important feature is to design the texture of elastic member E such that it will not interlock or slip upon the wind up sequence. The texture of elastic member E may take the form of transverse ribs, in that elastic member E will comprise ridges on one side, or it may have ridges on both sides. Additionally, the shape of take up spool D may be made flat, similar to drive spool H, so that elastic member E will bind on the ends of take up spool D rather than slip around the edges. Furthermore, elastic member E may pass through pinch rollers to better control the tension of elastic member E during wind up and operating sequences to provide for proper operation. An embodiment with such pinch rollers is detailed later in FIG.  9 . 
   Referring next to  FIG. 7 , depicted is a sequence of an exemplary elastic motor of the present invention in a wind up process. As in  FIG. 6 , one end of elastic member E is attached to take up spool D and the other end of elastic member E is attached to an end of flat drive spool H. Elastic member E is initially wound up in its relaxed state around take up spool D. In  FIG. 7A , elastic member E is attached to the end of drive spool H at point A and the initial position of the outermost portion of elastic member E still remaining on take up spool D is identified at point B. In  FIG. 7B , elastic member E is stretched along one side of drive spool H as said drive spool H is rotated clockwise. As shown, the end of elastic member E connected at point A remains at the end of drive spool H as said elastic member E is stretched.  FIG. 7C  depicts the wind up sequence after flat drive spool H has been rotated approximately 90 degrees clockwise. Nearing a 180 degree rotation of flat drive spool H,  FIG. 7D  depicts the next step of the wind up process, in which distance A to B is less than the length of flat drive spool H.  FIG. 7E  then depicts the wind up sequence after flat drive spool H is rotated approximately 180 degrees clockwise. The length of stretched elastic member E from point A to point B extends approximately as long as the length of flat drive spool H. The wind up sequence then repeats with new starting point C at the outermost portion of elastic member E still remaining on take up spool D, and with point B of the elastic member E located at the other end of flat drive shaft H. The described winding procedure continues until all of elastic member E is transferred from take up spool D to flat drive spool H. 
     FIG. 8  depicts a sequence of an exemplary elastic motor of the present invention in operation. After the wind up sequence has been completed and flat drive spool H has been engaged to rotate counterclockwise, the tension in elastic member E begins to turn flat drive spool H clockwise.  FIG. 8A  depicts initial counterclockwise rotation of flat drive spool H. Next,  FIG. 8B  depicts a section of elastic member E being pulled off one side of flat drive spool H and transferred to take up spool D.  FIG. 8C  then depicts the operational sequence after flat drive spool H has rotated approximately 90 degrees counterclockwise. Next,  FIG. 8D  depicts the transferring of elastic member E from flat drive spool H to take up spool D, wherein the release of tension in elastic member E continues to rotate flat drive spool H counterclockwise. Finally,  FIG. 8E  depicts the beginning of the removal of another section of elastic member E from flat drive shaft H. The preceding operation sequence repeats until all of elastic member E is transferred from flat drive spool H to take up spool D. 
     FIG. 9  depicts an exemplary elastic motor with flat drive spool H and pinch rollers P. One end of elastic member E is attached to flat drive spool H and the end of elastic member E remains slack and may be attached to take up means (such as take up spool as in  FIG. 6 ) or left unattached. Elastic member E is wound under tension around flat drive spool H. Pinch rollers P provide means for creating this tension by pinching elastic member E between them as flat drive spool H is wound. Pinch rollers may take the form of cog wheels that trap elastic member E between its teeth to prevent slippage. Furthermore, the cog wheels, or gear wheels may be made elliptical in order to vary the rate at which elastic member E is taken up during each revolution. 
     FIG. 10  depicts a textured surface  1201  upon elastic member E. By adding texture to elastic member E, slippage between the elastic member and the spools can be prevented. Textured surface  1201  may comprise any surface pattern which prevents slippage without departing from the scope of the present invention. 
   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.