Abstract:
A precessional device having independent control of the output torque generated by the device and the oscillation rate of the device is disclosed. The device comprises a rotor supported by an axle wherein the ends of the axle are supported by a circular race. The circular race is rotatable, and may be driven by a motor or other means, thereby controlling the oscillation rate of the device independently of the output torque arising from the rotation rate of the rotor. The motor may be controlled by a control program that adjusts the rotation rate of the circular race to modify the shape of the resistance curve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of U.S. application Ser. No. 11/549,642, filed on 14 Oct. 2006 and entitled “Precessional Device and Method”, which is a Continuation of U.S. application Ser. No. 10/428,761, filed 2 May 2003, entitled “Precessional Device and Method”, and issued as U.S. Pat. No. 7,181,987. Both applications are incorporated in their entirety by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to precessional devices. More specifically, the invention relates to a device and method which utilize precessional forces in a controlled manner. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    Exercise Most existing precessional devices are passive devices that require a deflecting torque from an external source to generate a precessional torque. A common example of this type of precessional device is the gyroscopic heading indicator used for aviation navigation. The spinning rotor inside such a device does not generate precessional torque on its own, rather, it simply responds to the torque exerted on it (by the directional changes of the aircraft) by maintaining its original heading relative to the magnetic compass. 
         [0004]    In contrast to this passive type of precessional device, U.S. Pat. No. 6,401,556 issued to Hamady on Jun. 11, 2002, herein incorporated by reference in its entirety, discloses a precessional device which generates a precessional torque without requiring an externally inputted deflecting torque. The disclosed device employs rotors which precess along a circular race or track. Axles run through each rotor making contact at either end with the surface of the tracks. The rotors&#39; spin rate, ω s , is directly proportional to the rotational velocity, ω r , which is defined as the frequency of the rotors&#39; precession around the track. The relationship between ω r  and ω s  is determined by the ratio of the diameter of the axle tips such that ω s =ω r d track /d axle  The practical implication of this direct relationship is that the rotor speed (and resulting net precessional output torque) can not be increased without a corresponding increase in the oscillation frequency (Hz) of the net output torque. This limits the devices usefulness in applications such as resistive exercise where high resistance is often associated with slower movements and low resistance exercise is often associated with faster movements. Therefore, there remains a need for a device where ω s  may be increased beyond the constraints defined by ω s =ω r d track /d axle , including but not limited to, a device where ω s  and ω r  may be controlled independently of each other. 
       SUMMARY OF THE INVENTION 
       [0005]    One embodiment of the present invention is directed to an apparatus comprising: a rotor spinning at a rotor spin rate about a spin axis; an axle supporting the rotor, the axle having a first axle tip, a second axle tip, and a longitudinal axis aligned with the spin axis of the rotor; a rotatable circular race in rolling contact with the first axle tip and in rolling contact with the second axle tip at a point on the circular race diametrically opposite the first axle tip; a motor for rotating the circular race; and a controller for controlling the rotation of the circular race independently of the rotor spin rate. 
         [0006]    Another embodiment of the present invention is directed to an apparatus comprising: a rotor spinning about a rotor axle at a rotor spin rate; a track assembly in rolling contact with the rotor axle during precessional movement of the rotor; and means for rotating the track assembly independently of the rotor spin rate. 
         [0007]    Another embodiment of the present invention is directed to an apparatus comprising: a first rotor spinning about a first spin axis and rotating about a first rotational axis inside a first rotatable track assembly, the first track assembly having a first tract rotation axis coincident with the first rotational axis; a second rotor spinning about a second spin axis and rotating about a second rotational axis inside a second rotatable track assembly the second track assembly having a second tract rotation axis coincident with the second rotational axis; and a housing supporting the first rotatable track assembly and the second track assembly, wherein neither spin axes are parallel to the rotational axes. 
         [0008]    Another embodiment of the present invention is directed to a method for modifying a resistance curve characterized by a periodicity, the resistance curve generated by a precessional device, the method comprising: providing a precessional device comprising a rotor spinning at a spin frequency capable of precessional rotation at a precessional frequency in a track assembly; and rotating the track assembly to modify the periodicity of the resistance curve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will be described by reference to the preferred and alternative embodiments thereof in conjunction with the drawings in which: 
           [0010]      FIG. 1  is a perspective view of one embodiment of the present invention; 
           [0011]      FIG. 2  is a section view of the axle and track assembly in another embodiment of the present invention; 
           [0012]      FIG. 3  is a schematic diagram of the controller for the embodiment shown in  FIG. 1 ; 
           [0013]      FIG. 4   a  is a perspective view of the embodiment shown in  FIG. 1  housed in a hand-held exercise device; 
           [0014]      FIG. 4   b  is a perspective view of another embodiment of the present invention; 
           [0015]      FIG. 5  is a graph illustrating a sinusoidal and modified resistance curve generated by one embodiment of the present invention; 
           [0016]      FIG. 6   a  is perspective rendering illustrating another embodiment of the present invention; 
           [0017]      FIG. 6   b  is a side view rendering illustrating the embodiment shown in  FIG. 6   a;    
           [0018]      FIG. 6   c  is a section view of a detail of the embodiment shown in  FIGS. 6   a  and  6   b ; and 
           [0019]      FIG. 7  is a perspective view of another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  is an illustration of one embodiment of the present invention. The device illustrated in  FIG. 1  includes two flywheel assemblies. Each assembly  100  consists of a flywheel, or rotor  110 , supported by an axle  115  that extends at either end into a circular race or “track”  120 . Bearing mounts  125  disposed toward each end of the axle  115  generate a preload that causes the flywheel/rotor assembly to cant at an angle, θ. In some embodiments, a motor  130  drives each track  120  through a transmission  140  that causes the tracks  120  to counter-rotate. The motor  130  may be permanently attached to the device or may be external to the device and applied to rotate the tracks during the start-up of the device. Other means for driving the rotation of the tracks  120  such as, for example, manually rotating the tracks should be apparent to one of skill in the art and are intended to be encompassed within the scope of the present invention. The motor  130  may be engaged to initially bring the track rotation and rotor spin rate to an operational range and disengaged once the track rotation and rotor spin rate are within their respective operational range. In the embodiment shown in  FIG. 1 , the tracks are vertically aligned or “stacked.” 
         [0021]    A locking solenoid  150 , when engaged to a lock plate  155 , keeps the position of the axle  115  fixed. The locking solenoid  150  and lock plate  155  act as a clutch such that when the locking solenoid  150  is engaged with the lock plate  155 , the rotation of the motor driven track  120  provides a driving force to increase or decrease the spin rate of the rotor  110  about the rotor axis. Disengaging the locking solenoid  150  from the lock plate  155 , allows the spinning rotor  110  to rotate, or precess, about the rotation axis of the rotatable track  120 . 
         [0022]      FIG. 2  is a section view of a detail of  FIG. 1  showing the axle tip configuration in the circular race. Referring to  FIG. 2 , axle  115  is supported by bearing mount  125 , which is supported by the axle tip support  210 . The axle  115  is canted at an angle, θ, from horizontal such that the axle tip  225  is in rolling contact with the lower surface  230  of the track  120 . Although not shown in  FIG. 2 , the opposite end of the axle  115  contacts the upper surface of the track  120 . The profile of the axle tip  225  is configured to allow rolling contact with the track surfaces  230  and is not limited by the exemplar profile shown in  FIG. 2 . In  FIG. 2 , the profile of the axle tip is cylindrical and is matched to an angled track surface that corresponds to the cant angle of the axle. Other profiles such as, for example, a tapered axle tip having a taper angle approximately the same as the cant angle of the axle may be matched to a horizontal, with respect to the orientation shown in  FIG. 2 , track surface and should be understood to be encompassed within the scope of the present invention. 
         [0023]      FIG. 3  is a schematic block diagram illustrating one embodiment of the controller for the precessional device. CPU  310  controls a user display  312 , user input devices such as, for example, a keypad  314  or user controls  316 . Memory  318 , such as for example, flash memory provides storage for the control program and data structures executed by the CPU  310 . Audio or visual alarms, such as for example, a beeper  320  are also controlled by the CPU  310  and provide feedback to the user. CPU  310  provides power control  330  for the regenerative motor  130 . The power source for the motor may be supplied by batteries  332  in the device or by an external power supply  334 . Retro-reflective opto-electronic sensor  160 , positioned on the axis of precession, provides the speed of each rotor  110  to the CPU  310 . An encoder within the track drive motor  130  provides track speed data to the CPU  310 . The current in the motor coil may be measured via a current sensor such as, for example, a sense resistor and provided to the CPU  310 . The current sensor may be calibrated by the control program executing on the CPU  310 . The deflection angle indicating the angular position of the axle tip  225  along the circumference of the track  120  is provided to the CPU  310  by a sensor such as, for example, a piezoelectric gyro or goniometer. 
         [0024]    The frictional contact between the moving track  120  and the axle tips causes the flywheel  110  to rotate about the axle  115 . In one embodiment, the rotor may accelerate to thousands of RPM as they are driven by the frictional contact between the flywheel axle tips and the moving track driven by the motor  130 . No precessional torque is generated during the spin-up of the flywheel, however, because travel of the tips within the track  120  is prevented by the engaged locking solenoid  150 . 
         [0025]    At a preset rotor speed sufficient to generate a noticeable output torque, the locking solenoid  150  disengages and current to the motor  130  driving the tracks  120  is cut. When current is cut to the motor  130 , the motor  130  acts as an electronic brake, braking the rotation of the tracks. In a preferred embodiment, the low transmission ratio from the tracks to the motor multiplies the braking effect of the motor thereby quickly stopping the rotating tracks. The rotational inertia of the spinning flywheel coupled by the frictional contact between axle tips and track causes the rotor assembly to precess around the track. 
         [0026]    The precession of the rotor assembly  100  around the track  120  acts as a deflecting torque on the spinning flywheel thereby generating a precessional torque that is perpendicular to both the deflecting torque and the axis of rotation. In the embodiment shown in  FIG. 1 , the precessional torque generates a force that is normal to the surface of the track such that the axle tip is pressed into the surface of the track, as shown in  FIG. 2 . The combined, net torque generated by the rotor assemblies, provides the resistive force that the user must overcome. In other words, the operator exercises against this resistive force. 
         [0027]    When the user inputs a deflecting torque against the rotor-generated precessional torque, causing the track surfaces to push back on the axle tips, a second precessional torque is generated in the direction of the rotation of the rotor assemblies. The second precessional torque causes an acceleration of the rotor assemblies around their respective tracks. The increased rotational velocity around the track, and the corresponding increase in spin velocity, increases the rotor-generated precessional torque according to the formula τ=|ω s ω r , where | is the rotational inertia of the rotors, ω s  is the spin velocity of the rotors, and ω r  is the rotational velocity of the rotor around the track. 
         [0028]    The preferred range for spin velocity of the rotor depends on the size and mass of the rotor and on the desired torque output from the device. In some embodiments, the rotor spins at an operational angular speed of between approximately 2,000-15,000 RPM, preferably between 4,000-12,000 RPM, and most preferably between 8,000-10,000 RPM. In some embodiments, the precession of the axle tip in the circular race  120  is between about 0.25-2.0 Hz. Once operational speed has been reached, the rotational energy of the rotor assemblies drives the tracks&#39; counter-rotation. The track motor continues to act as an electronic brake, siphoning energy out of the system to recharge the batteries. 
         [0029]      FIG. 4   a  is an illustration of one embodiment of the present invention. The precessional engine  410  may be packaged in a housing  420  that allows for safe and comfortable manipulation by a user. The housing  420  provides secure support for the precessional engine  410  and transmits the internal forces generated by the precessional engine  410  through the detachable outer handle  425  or other outer attachment accessories. The device produces a smooth, harmonic oscillating net torque that can be used as the basis for resistive exercise including concentric and eccentric muscle exertions and aerobic and anaerobic exercises. 
         [0030]      FIG. 4   b  is an illustration of another embodiment of the present invention. The housing provides for ergonomically designed inputs  428  for the user to control operations. 
         [0031]    As previously described, the torque sensed by a user interacting with the device is defined by: τ=|ω s ω r , where | is the inertia of the rotors (a function of their shape and mass), ω s  is the rotor spin velocity (about the axis of the rotor axle) and ω r  is the rotational velocity of the rotor assemblies around the track. The rotational velocity, ω r , also referred to herein as the precessional velocity, determines the oscillation rate (Hz) of the net torque generated by the device. 
         [0032]    In known precession devices, there is a fixed relationship, or ratio, between the rotor spin velocity, ω s , and the rotational velocity, ω r . The ratio, ω s /ω r , may be determined by assuming pure rolling of the axle tip on a fixed track surface, resulting in the relation, ω s /ω r =D t /D a , where D t  is the diameter of the track and D a  is the diameter of the axle tip. Both D t  and D a  are fixed and therefore ω s /ω r  is also fixed once D t  and D a  are specified. Thus, in known precession devices, a given ω s  corresponds to a given ω r  An increase in ω s  results in a proportional increase in ω r  The user may increase ω r  by manipulating the device at a higher tempo, which increases the deflecting torque on the rotors, causes an angular acceleration of the rotor assemblies around the track, and produces a higher torque output, τ. The fixed ratio of ω s /ω r , however, requires an increase in ω r . Therefore, as the output torque is increased, the oscillation rate of the output torque must also increase. For the expected range of output torques useful in exercise devices, the oscillation rate is usually higher than the 0.5-1.5 Hz oscillation rate preferred for resistive exercise. 
         [0033]    In contrast to the fixed relation between the output torque and oscillation rate of the output torque of prior art devices, the present invention allows independent control of the output torque and oscillation rate regardless of the ratio of the track diameter to the axle diameter. The decoupling of the output torque from the oscillation rate of the present invention allows for a more compact precessional engine that provides sufficient resistive exercise over a wider range of resistive forces and oscillation rates. 
         [0034]    In a preferred embodiment, the track  120  is rotatable and may be counter-rotated relative to the precession of the rotor. Counter-rotation of the track relative to the precession of the rotor allows for a greater effective rotor spin velocity with a smaller track diameter, allowing for more compact device designs than previously achievable. The relative precession rate, ω rp , is the rate of rotation of the rotor assembly relative to the track surface and is given by ω rp =ω r +ω t , where ω t  is the rotation rate of the track. In the rotating track system, a relative precession rate of 4 Hz, for example, may be achieved as a combination of actual rotor assembly rotation relative to the device as a whole ω r , and the rate of track counter-rotation ω t . For example, if ω r  is 1 Hz and ω t  is 3 Hz, the relative precession rate, ω rp , is 4 Hz. The resulting output torque, τ, is 4 times greater than it would be if the track were stationary, since ω rp  is 4 times greater than ω r . The user may therefore control torque output during operation by increasing or decreasing the track counter-rotation rate, ω t . 
         [0035]      FIG. 5  is a graph illustrating a resistance curve of one embodiment of the present invention. A typical resistance curve  510  is shown as a solid line in  FIG. 5  and exhibits sinusoidal variation in the torque as a function of time. The sinusoidal variation arises from the precession of the rotor assembly along the circumference of the track. In many instances, however, it is desirable to modify the shape of the resistance curve to other than a perfect sinusoid. 
         [0036]    In some embodiments, the present invention allows for modification of the sinusoidal resistance curve  520  by computer control of the motorized rotor, precession, and track speed. The sinusoidal resistance curve may be modified by, for example, reducing the precession rate near the peak output, which flattens the force output and generates a more constant resistance force across each oscillation. 
         [0037]    As an illustrative example, the track speed may be controlled on a real-time basis to accelerate track counter-rotation when the net torque curve nears its peak. If the rotor spin rate, ω s , is constant, the relative precession rate, ω rp , will also remain constant. As the track rotation rate, ω t , is increased, ω r  must decrease in order to maintain constant ω rp . As ω r  decreases, however, the output torque is also reduced thereby flattening the resistance curve. 
         [0038]    Independent control of the track rotation may be used to quickly stop the precession of the rotor assembly if the user loses control of the device. A pressure sensor may be disposed on the handle of the device such that when the user breaks contact with the handle, a signal from the pressure sensor is transmitted to the CPU indicating loss of contact with the handle. In response to the receipt of the signal from the pressure sensor, the control program may disengage the motor from the track, thereby allowing the track to free-wheel. The free-wheeling track will accelerate to match the precessional rotation rate, ω rp , such that ω r  quickly approaches zero. Alternatively, the motor may be engaged to counter-rotate the track such that the precession of the rotor assembly is offset by the counter-rotation of the track. 
         [0039]      FIG. 6   a  is a rendering of another embodiment of the present invention. In the embodiment shown in  FIG. 6   a , the motor  630  drives the rotation of the track assembly  620  via track drive shaft  638  and the rotor assembly  625  via rotor drive shaft  636 . Rotor  610  and axle  615  spins about an axis coincident with the axle&#39;s longitudinal axis. The spinning axle  615  is supported by rotor bearing  612 , which is supported by the rotor assembly  625 . 
         [0040]      FIG. 6   b  is a side view of the embodiment shown in  FIG. 6   a . The motor drive shaft  635  is connected through a series of drive belts to the rotor drive shaft  636  and the track drive shaft  638 . Transmission  640  couples the rotor drive shaft  636  to the track drive shaft  638  such that the track drive shaft  638  counter-rotates to the rotor drive shaft  636 . In addition, transmission  640  fixes the ratio between the track rotation frequency and the rotor rotation frequency. The gear ratio of the transmission may be changed to better suit the intended use of the precessional engine. 
         [0041]      FIG. 6   c  is a section view of the axle and track assembly showing the axle tip configuration in the circular track. Referring to  FIG. 6   c , axle  615  is supported by rotor bearing  622 , which is supported by the rotor bearing mount  625 . In the compact design shown in  FIG. 6   c , the track  620  is supported by a housing-track bearing  640  that allows the track  620  to rotate relative to the housing chassis  650 . The track  620  is also coupled to the rotor bearing mount  625  through a track-rotor assembly bearing  645  that allows rotational movement of the track  620  relative to the rotor bearing mount  625 . The rotor bearing mount  625  is supported by a rotor assembly-housing bearing  647 . In some embodiments, bearings  640 ,  645 , and  647  are precision ring bearings that allow for a lightweight but very powerful precessional engine. The embodiment shown in  FIG. 6   c  may be appropriate for specialized environments such as, for example, high-end rehabilitation market at a relatively high cost. For a broader market segment, designs incorporating inexpensive bearings or alternative methods may be incorporated using design methods readily available to one of skill in the art. 
         [0042]    The configuration shown in  FIGS. 6   a ,  6   b  and  6   c  show the track assemblies having a coincident rotation axis. It should be understood, however, that the present invention is not limited to such a configuration. The vertical alignment of the track assemblies enables a single motor to drive both track assemblies  620  and both rotor assemblies  625 . Other embodiments within the scope of the present invention include, but are not limited to, multiple motors with each motor individually driving a single track or rotor assembly. When each track or rotor assembly is driven by its own motor, a transmission is not required and the rotation axes of the track assemblies may be parallel but not coincident. 
         [0043]    The use of separate motors to drive the rotor and track assemblies allows independent control of ω s  and ω r  thereby allowing independent control of the output torque and torque oscillation frequency. The advantage of a single motor driving both the rotor and track assemblies through a transmission is reduced cost while still allowing high output torque at a suitable oscillation frequency. For a rotatable track, the relation between ω s  and ω r  is given by ω s =ω r (1+G)(d track /d axle ) where G is the ratio, G=ω t /ω r . For prior art systems having a non-rotatable track, ω t =0 and G=0. Counter-rotating the track results in a positive G thereby generating a higher output torque at the same oscillation frequency. Rotating the track in the same direction as the rotation of the spinning rotor results in a negative G thereby reducing the output torque at the same oscillation frequency. 
         [0044]      FIG. 7  is a perspective view illustrating another embodiment of the present invention. A rotor  710  and axle  715  spin about a spin axis that is coincident with the longitudinal axis of the axle  715 . The tips of the axle  715  travel along the surface of a rotatable track assembly  720 . The rotatable track assembly  720  is supported by a housing  750  that allows the track to rotate in the housing  750 . An external driving force may be applied to the rotor such that the rotor  710  and axle  715  begin to spin about the spin axis. The external driving force may be a rotating motor shaft applied to the circumferential edge of the rotor or any mechanical or manual means for imparting a tangential force to the circumferential edge of the rotor. A portion of the rotational energy of the spinning rotor  710  may be transferred to the track via the frictional force of the spinning rotor tip against the track surface. The energy imparted by the spinning rotor may cause the track to counter-rotate to the rotation direction of the spinning rotor. A resistance force developed between the rotating track and housing reduces the rotation rate of the track thereby causing the rotor assembly to rotate in a direction opposite to the rotation of the track. 
         [0045]    Having thus described at least illustrative embodiments of the invention, various modifications and improvements will readily occur to those skilled in the art and are intended to be within the scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.