US 20060118210 A1
Devices and methods which store and selectively release relatively substantial amounts of energy for enabling individuals to undertake superior performance in locomotion and other physical activities. The different embodiments include a hyperelastic SMA element which stores and releases energy in a differential pulley set, in a hinged knee, and in a pogo stick.
1. An energy storage device comprising a hyperelastic shape memory alloy element which changes to one shape while storing energy responsive to a stress, and a structure which applies the stress to the element, the structure being selected from the group consisting of a differential pulley mechanism, a knee brace and a pogo stick.
2. A device as in
3. A device as in
4. A device as in
5. A device as in
6. A device as in
7. A method of storing and selectively releasing energy in a device that can be carried by an individual, the method comprising the steps of providing a hyperelastic shape memory alloy element, applying a stress to the element which stores energy in the element which when release is sufficient to enable the individual to undertake superior performance in locomotion and other physical activities, and releasing the energy.
8. A method as in
This application claims the benefit under 35 USC §119(e) of U.S. provisional patent applications Ser. No. 60/615,846 filed Oct. 4, 2004; 60/637,741 filed Nov. 22, 2004; and 60/658,862 filed Mar. 7, 2005.
1. Field of the Invention
The invention relates to the storage and release of mechanical energy by portable devices.
2. Description of the Related Art
A warfighter on foot must carry equipment and is often required to move fast and over terrain that requires increased physical effort. It is recognized that increasing the mobility of the footsoldier makes him or her more effective in combat and other situations.
Exoskeletons have been demonstrated that provide super strength for individuals. Driven by electrical stepper motors, these require a source of energy, usually batteries which are too heavy to be practical for operational use.
The idea of storing mechanical energy to enhance the physical capabilities is incorporated in an invention by Nicholas Zagn of Saint Petersburg Russia in 1890. His apparatus used conventional springs that are limited to less than one percent strain, and have varying force according to Hooke's law. This does not provide an optimum energy source for locomotion.
The prior art has not provided a compact, light-weight and portable device for storing sufficient amounts of potential energy which can be quickly released into kinetic energy for enhancing human locomotion and other physical activities.
The need has therefore been recognized for compact, light-weight and portable devices that obviate the foregoing and other limitations and disadvantages of prior art devices of the type described. Despite the various devices of the type in the prior art, there has heretofore not been provided a suitable and attractive solution to these problems.
A general object of this invention is to provide devices and methods that store substantial amounts of potential energy which can be quickly released into kinetic energy sufficient for enhancing human locomotion and other physical activities.
Another object is to provide a portable ‘passive’ device which can store sufficient energy to lift individuals to a specified height, or alternatively to absorb the equivalent potential energy of descent from such a height.
The invention in summary provides devices and methods which store and selectively release relatively substantial amounts of energy for enabling individuals to undertake superior performance in locomotion and other physical activities.
The invention provides devices and methods which enable an individual, such as a warfighter, to carry heavier loads and run faster without increasing demands on physical stamina; and to enable a person of ordinary ability to leap high enough to clear a high obstacle and thus to escape from a dangerous situation. When combined with suitable exoskeleton components, the devices and methods will enable a person to jump from a building or make a rapid descent by parachute without suffering injury due to sudden deceleration. It is particularly desirable that the devices not require electrical power, i.e. they are a ‘passive’ system that uses and amplifies human effort. The individual is enabled to function on the ground with the equipment in place. The devices are neither too heavy or bulky nor too restrictive or awkward. Otherwise it would have negative impact on the individual's mobility and effectiveness.
The invention provides an individual/warfighter with extraordinary abilities to run, carry heavy loads, and leap onto and from structures. The devices of the different embodiments are characterized in being compact while enabling the release of a sufficient quantity of mechanical energy to boost a human to heights not achievable by human muscle alone. Acceleration is constant during boost, and limited to tolerable levels. One embodiment described in detail in connection with
CuAlNi single crystal provides a dense storage for kinetic energy in the form of crystal phase change. The force exerted is constant during excursion of a hyperelastic plateau during extension and contraction. The devices of the invention are characterized in that they: a) of modest weight, b) are of a size and shape practical for an individual/warfighter to carry and c) store enough energy to significantly boost jumping ability.
Physical Considerations: Mass (of the Individual and of the Device) and Energy Requirements
One example for employing a device in accordance with the invention is: (a) for use with a payload of 180 lbs (80 kg) and (b) for a jump height of 12 feet (4 meters). There is to be no external heating or cooling during the cycle. The design is for an energy storage device only. It is assumed that this device will be combined with additional specialized mechanical components for performance of specific tasks. The design may be scaled to larger or smaller dimensions, for example to provide a projectile launcher.
Assuming the 80-kilogram load and a jump height of 4 meters it is necessary that the mechanism store at least 3200 joules of energy. Shape memory alloys, which transform from one solid crystal structure to another, are capable of energy storage at greater densities than elastic materials. In hyperelastic transformations, the energy is absorbed and released at nearly constant force, so that constant acceleration is attainable.
Materials for Storing and Releasing the Required Energy
The preferred material for use as the energy store/release element in devices the invention is copper-aluminum-nickel single crystal hyperelastic alloy. CuAlNi sustains repeated strains of more than 9% as demonstrated in the stress-strain isotherm of
Physical data for the preferred hyperelastic CuAlNi SMA are listed in Table I of
An example of one cycle of operation is as follows: a mass falls under influence of gravity and lands. Deceleration compresses a spring made of hyperelastic CuAlNi alloy. The alloy releases heat as the stress increases to the plateau and stress-induced martensite is formed. The alloy is then cooled (by external means) to its austenite finish temperature as the stress diminishes to zero. The spring is then returned to its original configuration. This cycle is depicted in
During the deceleration phase of the cycle, i.e. Path (a) of
In the chart of
In the chart of
Differential Pulley Mechanism
The embodiment of
The differential pulley embodiment of
In operation of device 80, energy is stored by applying a downward stress on distal end 98. The figure shows this step by using gravity on mass 99 to create the stress. Other means could be used to apply the stress, such as a small hand crank, not shown. The stress causes the paired pulleys 82, 84 to rotate anticlockwise as viewed in the figure. The differential diameters of the two pulleys causes the SMA wire to elastically stretch and absorb energy. After stretching, the gear set could be locked against rotation by a suitable latch or detent, not shown, until energy release is desired. When the gear set is unlocked by the user, the wire contracts and releases the energy as the gear set rotates clockwise. The released energy could be employed to do work, such as by using the rotating axles 86 and/or 90 to rotate a cutting tool, drill or the like.
Technical Design: Calculations, Dimensions, Forces, Strength of Materials.
Table II of
This table uses the equations of motion of a differential pulley system to calculate physical sizes of the components, and to keep these within reasonable limits. Many possible solutions can be calculated that meet the stated goals, but not all are practical.
Two cases are presented, each capable of delivering 3200 joules of mechanical energy. Each has been derived to produce a half turn of the pulley assembly. In the first case, having a stroke of 4 meters and a lifting force of 80 kg, the cable is wound on a drum that is too large to be practical. In the second case, the stroke has been reduced by one half, and the lifting force doubled. This results in a drum radius that is reasonable for being carried in a back-pack. This design presumes that the application will contain a lever arm to increase the stroke by a factor of two.
Knee Hinge Device
In the embodiment of
During operation, as the person's legs stride forward before a launch, one knee flexes by bending so that the thigh and calf pivot toward each other. The weight and forward momentum of the person causes SMA wire 110 to stretch during the flexing and store energy. As the person's weight is shifted to the other leg and momentum is lost, the wire contracts and releases most of the stored energy, causing the knee to flex back and straighten the leg while forcefully propelling the person forward and/or up.
Pogo Stick Device
Technical discussion of CuAlNi Single Crystal Hyperelastic Alloy: Why it is Superior, How it Works, and How it is Made.
Hyperelastic shape memory alloys comprise an enabling technology providing dense energy storage, constant force, and simple implementation. Conventional elastic spring material may be strained about 0.5 percent without permanent deformation. In contrast, mechanical energy is stored by a crystalline phase change in hyperelastic SMA, allowing complete recovery of more than 9 percent, a twenty-fold increase. Deformation and recovery take place at constant stress so that forces and hence accelerations are limited and predictable.
Conversion of high-temperature crystalline phase to stress-induced martensite permits a very large amount of mechanical energy to be stored, and, as the single crystal is not plastically deformed, complete shape recovery takes place at nearly the same level of stress.
This material is created by pulling single crystals from melt in a process known as the Stepanov method, similar to the Czochralski method of fabricating silicon boules for microelectronics manufacture.
Background of Hyperelastic Shape Memory Alloys
SMA materials have become popular for use as actuators due to their ability to generate substantial stress during shape recovery of large strains during temperature-induced phase transformation. The energy density of such actuators is high compared to other alternatives, such as electromagnetic, electrostatic, bimetals, piezoelectric, and linear
and volume thermal expansion effects of ordinary materials. The operating cycle of an SMA actuator includes deformation during or after cooling, and subsequent heating which results in a temperature-induced phase transformation and recovery of the deformation. SMA actuation is favored where relatively large force and small displacements are required in a device that is small in size and low in mass.
Shape memory is the ability of certain alloys to recover plastic deformation, which is based on a diffusionless solid-solid lattice distortive structural phase transformation. The performance of shape memory alloy based actuators strongly depends on the amount of recoverable deformation. In turn, recoverable deformation itself is a function of the lattice distortions which take place during martensitic phase transformation in the particular SMA. For an individual grain (single crystal) of SMA, the amount of possible recoverable strain after uniaxial loading, depends on the particular crystallographic orientation of the deformation tensor relative to the crystallographic axes of the high temperature (austenite) phase and the sign of applied load (tension or compression).
For a given deformation mode, the recoverable strain is strongly orientation dependent, and for the various crystallographic directions it differs by approximately a factor of two.
The recoverable deformation of these polycrystalline SMA alloys, due to the lattice distortion during diffusionless solid-solid phase transition, is substantially lower than is theoretically possible for a given material. The main reason for this is that for a conglomerate of randomly oriented grains (as is normally the case for polycrystalline materials), the average deformation will always be less than the maximum available value for a given grain. The diffusionless nature of phase transitions in SMA results in strict lattice correspondence between the high temperature (austenite) and low temperature (martensite) lattices. As the symmetry of the martensite lattice is lower than that of austenite, maximum deformation in each grain can only be attained in one particular crystallographic direction. This means that for randomly oriented grains (as normally is the case for polycrystalline materials), the average deformation will be at least a factor of two less than the maximum.
The restrictions imposed on a polycrystalline body by the deformation mechanism is another reason for diminished recoverable deformation in polycrystals as compared with a single crystal. To maintain integrity of the polycrystal, deformation of each particular grain has to be less than that corresponding to the theoretical limit for lattice distortion.
Therefore, for polycrystalline material, resultant recovery is the vector sum of particular grain deformations over the whole range of grain orientations, and is significantly smaller than the maximum value for an individual single crystalline grain.
By comparison, recoverable deformation close to the theoretical value (lattice distortion) can be achieved in single crystalline SMA. In addition to the substantially increased recoverable deformation, absence of grain boundaries results in increased strength and longer fatigue life. Specifically, as a single crystal, the strength of the grain for CuAlNi SMA can be as high as 800 MPa with the practical limit for recoverable deformation up to 9 percent and potentially even higher for special deformation modes. An additional advantage of a single crystal SMA is that not only the thermally induced phase transformation may contribute to the recoverable deformation, as in the case for polycrystals, but also stress-induced martensite-to-martensite phase transitions. Depending on the material, this additional contribution may be up to 15 percent. Therefore the total theoretical recovery can be as high as 24 percent.
The graphs of FIGS. 6(a) and 6(b) show stress-strain curves for a CuAlNi single crystal SMA and a polycrystal TiNi SMA. Curve 20 shows the single crystal SMA in its austenitic phase while curve 22 shows the martensitic phase. Curve 24 shows the polycrystal SMA in its austenitic phase while curve 26 shows the martensitic phase.
Hyperelastic single crystal SMA is an enabling technology for mechanical energy storage. It has the following advantages over polycrystal SMA for mechanical devices:
Since single crystals cannot be processed by conventional hot or cold mechanical formation without breaking single crystallinity, a special procedure is required for shaping single crystals in the process of growth as the crystal is pulled from melt, resulting in finished shape.
Single crystal SMA is fabricated in a special crystal-pulling apparatus. A seed of the desired alloy is lowered into a crucible containing a melted ingot of the alloy composition, and gradually drawn up. Surface tension pulls the melted metal along with the seed. The rising column cools as it leaves the surface of the melt. The rate of drawing is controlled to correspond with the rate of cooling so that a solid crystal is formed at a region that becomes a crystallization front. This front remains stationary while the crystal, liquid below and solid above, travels through it. The top surface of the melt can contain a die (of the desired cross-sectional shape) that forms the shape of the crystal as it grows. This procedure generally is known as the Stepanov method of making single crystals. The principal elements are shown in
After the ingot is melted the crucible with the metal is lifted up until the hydrostatic pressure pushes the molten metal almost to the upper edge of the shape-forming die. The metal should be overheated above the melting point for about 10-15 C. After the temperature becomes stable the seed is lowered into the die opening until it reaches the surface of the molten metal. This operation requires a port for visual observation. The seed material melts and the column of molten metal confined by the capillary forces rises above the upper edge of the shape-forming die. The combination of the proper pressure (defined by the vertical position of the crucible), metal temperature (defined by the power applied to the heater) and capillary forces will maintain the corresponding shape of the molten material and at the same time prevent it from spilling. Now the pulling mechanism is turned on and the seed starts moving up, away from the shape-forming die. The column of molten material becomes longer until its length gets stabilized with the crystallization front at the top few millimeters above the edge of the shape-forming die. Continuous adjustment of pressure and temperature is needed to stabilize the shape of the molten column of the metal for a given pulling rate.
The shape and size of the single crystal produced according to method described above are defined by the geometry of the shape-forming die, the pressure of liquid at the edge of the shape-forming die, and the position of the crystallization front relative to the shape-forming die. There is no specific physical limitation on the length of the pulled single crystal. However, technically it is limited by the stroke of the pulling mechanism.
From the known Cu—Al phase diagram, rapid cooling (quenching) of the drawn crystal is necessary for production of single crystal beta phase that has the desired hyperelastic properties. Starting with beta phase at 850-1000 Celsius, if the alloy is cooled slowly the beta phase precipitates as beta+gamma, and at lower temperatures, as alpha+gamma−2. Single crystal beta phase, which requires that Al remains in solution at room temperature, is formed by rapid cooling in salt water from 850 Celsius. At elevated temperatures, above 300 Celsius, some decomposition gradually occurs; in fact, beta phase is not entirely stable at room temperatures but the time constant for decay is many years. The known phase diagram for the ternary CuAlNi alloy has similar characteristics.