US20130097810A1

US20130097810A1 - Elastic load suspension

Info

Publication number: US20130097810A1
Application number: US13/648,994
Authority: US
Inventors: Jeffrey K. Ackerman; Justin E. Seipel
Original assignee: Purdue Research Foundation
Current assignee: Purdue Research Foundation
Priority date: 2011-10-10
Filing date: 2012-10-10
Publication date: 2013-04-25

Abstract

Elastic load suspension systems and methods are disclosed. Embodiments include handles with springs to reduce peak forces and reduce the overall energy required to carry a load. Some embodiments include handles that connect to loads, where the effective spring length statically deflects at least 2.5 and at most 18 inches, and in some embodiments approximately 5 inches, when carrying the load. Alternate embodiments include elastic suspension handles that are lightly damped, such as those with a damping ratio of at most 0.5. Still further embodiments include elastic suspension handles that elastically suspend loads and have a natural frequency that is less than the locomotive frequency of the object carrying the handle, such a less than the typical human walking frequency of 2 Hertz.

Description

This application claims the benefit of U.S. Provisional Application No. 61/545,407, filed Oct. 10, 2011, the entirety of which is hereby incorporated herein by reference.

GOVERNMENT RIGHTS

This invention was made with government support under 1131423 awarded by the National Science Foundation. The government has certain rights in the invention.

FIELD

Embodiments of this disclosure relate generally to carrying loads, a particular example including suspending loads being carried in order to minimize the forces exerted on the individual carrying the load and/or to reduce the energy required to carry the load.

BACKGROUND

Energy is required to move of an object and an objects being moved imparts forces to the device or person moving the object. As an example, a person carrying an object, such as a suitcase, expends energy to move the object. In addition to the energy required to move the object horizontally from place to place, additional energy is typically expended as the object moves up and down as the person walks. The object being moved, the suitcase in this example, also imparts forces onto the person while it is being moved, and these forces may vary with time reaching periodic maximum values, which may occur when the object reaches the bottom of its up and down motion while being carried.

SUMMARY

Embodiments of the present disclosure provide an improved elastic load suspension apparatuses and methods.
Embodiments of the present disclosure provide reduced peak forces and/or increased locomotive efficiency.
Some embodiments include handles with springs, where in some embodiments the effective spring length statically deflects at least 2.5 and at most 18 inches, at least 4 inches and at most 10 inches, and in some embodiments approximately 5 inches, when carrying the load.
Alternate embodiments include elastic suspension handles that are lightly damped, such as those with a damping ratio of at most 0.5, those with a damping ratio of at least 0.1 and at most 0.3, and those with a damping ratio of at least 0.01 and at most 0.1.
Still further embodiments include elastic suspension handles that elastically suspend loads and have a natural frequency that is less than the locomotive frequency of the object carrying the handle, such a less than the typical human walking frequency of 2 Hertz.
This summary is provided to introduce a selection of the concepts that are described in further detail in the detailed description and drawings contained herein. This summary is not intended to identify any primary or essential features of the claimed subject matter. Some or all of the described features may be present in the corresponding independent or dependent claims, but should not be construed to be a limitation unless expressly recited in a particular claim. Each embodiment described herein is not necessarily intended to address every object described herein, and each embodiment does not necessarily include each feature described. Other forms, embodiments, objects, advantages, benefits, features, and aspects of the present disclosure will become apparent to one of skill in the art from the detailed description and drawings contained herein. Moreover, the various apparatuses and methods described in this summary section, as well as elsewhere in this application, can be expressed as a large number of different combinations and subcombinations. All such useful, novel, and inventive combinations and subcombinations are contemplated herein, it being recognized that the explicit expression of each of these combinations is unnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the figures shown herein may include dimensions or may have been created from scaled drawings. However, such dimensions, or the relative scaling within a figure, are by way of example, and not to be construed as limiting.

FIG. 1 is a double-mass coupled oscillator model for analyzing elastically suspended loads according to one embodiment of the present description.

FIG. 2 is a bode plot of the oscillator model depicted in FIG. 1 with k2=650 N/M and b2=22 N/S/M.

FIG. 3 is a depiction reflecting the total peak forces on the main mass m1 are less with an elastically suspended load versus a rigidly attached load for k2<1050 N/M.

FIG. 4 is a depiction reflecting the energy cost of locomotion is less for a system with an elastically suspended load versus a rigidly attached load for k2<1050 N/M.

FIG. 5 is a plot reflecting increased damping reduces the effectiveness of elastically suspended loads by reducing the out-of-phase amplitude of the load mass m2.

FIG. 6 is a plot reflecting that increasing load M2 increases the relative energy savings potential.

FIG. 7 is a plot reflecting that increasing locomotion frequency ω increases the relative energy savings potential.

FIG. 8 is a plot reflecting that the stability of a system with an elastically suspended load is lower than a system with a rigidly attached load.

FIGS. 9A and 9B are plots of the net center of mass of a locomotion system with an elastically suspended load and a rigidly attached load, respectively, with the net center of mass of the elastically suspended load being reduced due to the vertical motion of the load being between 90-180 degrees out of phase with the main mass.

FIG. 10 is a side elevational view of a typical handle for carrying loads.

FIG. 11 is a side elevational of a handle for carrying elastically suspended loads according to one embodiment of the present disclosure.

FIG. 12 is a side elevational view of an elastic load suspension system for a robot according to another embodiment of the present disclosure.

FIG. 13 is a diagrammatical representation of a person running and a damped mass system used to analyze the dynamics of a person running according to another embodiment of the present disclosure.

FIG. 14 is a plot of the predicted average power consumption for an embodiment of the system depicted in FIG. 1.

FIG. 15 is a plot of the maximum load force of an embodiment of the system depicted in FIG. 1.

FIG. 16 is a plot of the static deflection of the load mass in an embodiment of the system depicted in FIG. 1.

FIG. 17 is a plot comparing the predicted average power consumption of an elastically suspended load and a rigidly attached load of the system depicted in FIG. 1.

FIG. 18 is a plot comparing the maximum load force of an elastically suspended load and a rigidly attached load of the system depicted in FIG. 1.

FIG. 19 is an cantilever elastic load suspension handle according to one embodiment of the present disclosure, to which additional cantilever springs may be added in series.

FIG. 20 is an elastic suspension handle with adjustable stiffness according to another embodiment of the present disclosure.

FIG. 21 is a side elevational view of a cantilever stretcher handle with a pre-tensioning mechanism according to another embodiment of the present disclosure.

FIG. 22 is a side elevational view of an elastic suspension handle with a pulley and elastic cord according to a further embodiment of the present disclosure.

FIG. 23 is a perspective view of a cantilever elastic suspension handle with a torsion spring inside according to still another embodiment of the present disclosure.

FIGS. 24A and 24B are perspective and side elevational views, respectively, of an elastic suspension handle with a user selectable option to lock the handle and to fold the handle if desired according to still a further embodiment of the present disclosure.

FIGS. 25A and 25B are perspective and side elevational views, respectively, depicting details of a torsion mechanism usable with the embodiments depicted in FIGS. 24A and 24B according to yet a further embodiment of the present disclosure.

FIG. 26 is an elastic suspension handle with a torsion spring and tension adjustment mechanism according to yet a further embodiment of the present disclosure.

FIG. 27 is a perspective view of an elastic suspension handle for a baby carrier or infant car seat type device according to yet a further embodiment of the present disclosure.

FIG. 28 includes a side elevational views of a pre-tensioning mechanism for the elastic suspension handle depicted in FIG. 27 in various operational states.

FIG. 29 is a perspective view of an elastic suspension handle with a hook according to still another embodiment of the present disclosure.

FIG. 30 includes detailed depictions of the pre-tensioning mechanism depicted in FIG. 29.

FIG. 31 depicts a cantilever or torsion spring type suspension handle according to one embodiment of the present disclosure.

FIG. 32 depicts a cantilever or torsion spring type suspension handle according to another embodiment of the present disclosure.

FIG. 33 depicts a cantilever type suspension handle with torsion springs at the joints a further to another embodiment of the present disclosure.

FIG. 34 depicts a torsion spring handle with two torsion springs (one on either side) according to yet another embodiment of the present disclosure.

FIG. 35 depicts a clock-spring type suspension handle (somewhat similar to a dog leash) according to still another embodiment of the present disclosure.

FIG. 36 depicts a torsion spring handle with load connection linkages according to yet a further embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to one or more embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended; any alterations and further modifications of the described or illustrated embodiments, and any further applications of the principles of the disclosure as illustrated herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. At least one embodiment of the disclosure is shown in great detail, although it will be apparent to those skilled in the relevant art that some features or some combinations of features may not be shown for the sake of clarity.
Any reference to “invention” within this document is a reference to an embodiment of a family of inventions, with no single embodiment including features that are necessarily included in all embodiments, unless otherwise stated. Furthermore, although there may be references to “advantages” provided by some embodiments, other embodiments may not include those same advantages, or may include different advantages. Any advantages described herein are not to be construed as limiting to any of the claims.
Specific quantities (spatial dimensions, temperatures, pressures, times, force, resistance, current, voltage, concentrations, wavelengths, frequencies, heat transfer coefficients, dimensionless parameters, etc.) may be used explicitly or implicitly herein, such specific quantities are presented as examples only and are approximate values unless otherwise indicated. Discussions pertaining to specific compositions of matter, if present, are presented as examples only and do not limit the applicability of other compositions of matter, especially other compositions of matter with similar properties, unless otherwise indicated.
Carrying loads during locomotion can be energetically costly. Load carrying has static and dynamic components and peak forces can be high due to dynamic loads. Compared to rigidly attached loads, elastically suspended loads, such as using a compliant spring, can reduce peak forces during locomotion, increase energy efficiency (especially for a walking or running person carrying a load), and reduce the forces acting on the load, which has advantages when carrying delicate items, such as babies, animals, and delicate equipment.
A double-mass coupled-oscillator model, such as the system depicted in FIG. 1, was used to evaluate the effect of elastically-suspended loads on the peak forces and energy cost during locomotion and to investigage the effect of elastically-suspended loads (including weakly coupled loads) on the stability of locomotion, which can affect the efficiency and control task of carrying an elastically-suspended load. The stability of a system with elastically-suspended loads may also affect the maneuverability of a system and locomotion over rough or uneven terrain. Reduction of the peak forces and energy costs of locomotion was also evaluated to find an optimal coupling of the two masses.
The equations of motion for the double-mass coupled-oscillator system are shown as follows.
Main mass M1 stance phase:
$\begin{matrix} {\ddot{X}}_{1} = \frac{1}{M_{1}} (- (B_{1} + B_{2}) {\dot{X}}_{1} - (K_{1} + K_{2}) X_{1} + B_{2} {\dot{X}}_{2} + K_{2} X_{2} + B_{1} \dot{L} (t) + K_{1} L (t) - g) & (1) \end{matrix}$
Load mass m2 stance and flight phase:
$\begin{matrix} {\ddot{X}}_{2} = \frac{1}{M_{1}} (- B_{2} {\dot{X}}_{2} - K_{2} X_{2} + B_{2} {\dot{X}}_{1} + K_{2} X_{1} - g) & (2) \end{matrix}$
Where the parameters are as defined in Table 1.

	TABLE 1

	K1	Leg stiffness
	B1	Leg damping
	K2	Suspension stiffness
	B2	Suspension damping
	M1	Main mass
	M2	Load mass
	ω	Locomotion frequency
	L(t)	Leg length forcing function
	x₁	Position of main mass M1
	{dot over (x)}₁	Velocity of main mass M1
	x₂	Position of load mass M2
	{dot over (x)}₂	Velocity of load mass M2

Lift-off condition:
The parameter values M1=75 kg (main mass), K1=28,000 N/m (leg stiffness), and B1=950 Ns/m (leg damping) approximate those of an average human. The leg length forcing function L(t) used to simulate the effective springy-leg length when a person bends at the knee during locomotion is shown below.
L(t)=L ₀ +A sin(ωt) (3)
The parameters I₀=0.9 m (approximate unstretched leg length from foot to hip), A=0.025 m (amplitude of oscillation of the hip during locomotion, 5/2 cm), and ω=2π rad/s (approximate walking frequency, 1 Hz) were selected to approximate the motion of a person's center of mass during locomotion. One of ordinary skill can readily adapt this analysis for different walking frequencies by substituting the desired walking frequency in place of the 1 Hz (2π rad/s) that is used in the following paragraphs. For example, a more accurate approximation of the adult human walking frequency of 2 Hz (4π rad/s) may be substituted in for ω, while still other examples can use a frequency of locomotion of approximately 3 Hz (6π rad/s) to estimate the frequency for a running person. The load M2=25 kg is used to estimate a relatively heavy load (being one-third of the main mass M1), but other loads may also be analyzed.
Using these parameters, the system approximates a human walking with elastically-suspended loads. This model can provide valuable insight into locomotion with elastically-suspended loads from first principles.
The initial conditions of the simulation were adjusted for the system to achieve stable periodic motion. The effect of an elastically-suspended load versus a rigidly-attached load was determined by graphical and numerical comparison. The peak forces on the main mass M1 were calculated from the spring and damping forces acting on the main mass M1 as shown below.
Leg Spring Force=−K ₁(X ₁−(L ₀ +A sin(ωt)))
Leg Damping Force=−B ₁({dot over (X)} ₁ −ωA cos(ωt)))
Load Suspension Spring Force=−K ₂(X ₁ −X ₂))
Load Suspension Damping Force=−B ₂({dot over (X)} ₁ −{dot over (X)} ₂))
Peak Force on Main Mass M ₁=max(ΣF _M ₁) (4)
The energy cost of locomotion was estimated by determining the average positive power from the leg length forcing function required for the system to maintain a periodic motion at steady state. We only used the average positive power because we assume the leg length actuator cannot store and return energy for purposes of illustration.
P=FV
P=({dot over (X)} ₁ −ωA cos(ωt)))(K ₁(X ₁ −L ₀ −A sin(ωt))+B ₁({dot over (X)} ₁ −ωA cos(ωt))) (5)
Although presently not well understood, attempts have been made to understand the stability of the elastic-suspension handles to determine the effects of these handles on stability. While the analysis is ongoing, initial results appear to indicate that systems with elastic suspension handles can be rather stable, although potentially slightly less stable than systems with rigidly attached handles. Initial results also appear to indicate that elastic suspension handles may enhance stability, especially when the user is traversing rough terrain, such as when a user is carrying an elastically suspended load up or down stairs.
The stability of a system can be defined as the ability of a system to return to a stable limit cycle or equilibrium point after perturbation. To quantify the rate of recovery from a perturbation (the stability), a linearized version of the mapping function that maps all possible perturbations from one cycle to the next produces an n×n return map (the Jacobian), where n is the number of states. The eigenvalues of the n×n Jacobian matrix are stability values, or the percentage of the perturbation remaining after each cycle. For a discrete system, eigenvalues greater than one generally indicate that the cycle is unstable, eigenvalues equal to one generally indicate that the cycle is marginally stable, and eigenvalues less than one generally indicate that the cycle is stable. The stability of the system in this model was calculated by perturbing the initial conditions of the system (δx₁₀, δ{dot over (x)}₁₀, δx₂₀, δ{dot over (x)}₂₀), estimating the partial derivatives using finite differences for the mapping from the period x(p) to x(p+1), and calculating the eigenvalues of the resulting Jacobian matrix.
$\begin{matrix} J = [\begin{matrix} \frac{δ x_{1}}{δ x_{10}} & \frac{δ x_{1}}{δ {\dot{x}}_{10}} & \frac{δ x_{1}}{δ x_{20}} & \frac{δ x_{1}}{δ {\dot{x}}_{20}} \\ \frac{δ {\dot{x}}_{1}}{δ x_{10}} & \frac{δ {\dot{x}}_{1}}{δ {\dot{x}}_{10}} & \frac{δ {\dot{x}}_{1}}{δ x_{20}} & \frac{δ {\dot{x}}_{1}}{δ {\dot{x}}_{20}} \\ \frac{δ x_{2}}{δ x_{10}} & \frac{δ x_{2}}{δ {\dot{x}}_{10}} & \frac{δ x_{2}}{δ x_{20}} & \frac{δ x_{2}}{δ {\dot{x}}_{20}} \\ \frac{δ {\dot{x}}_{2}}{δ x_{10}} & \frac{δ {\dot{x}}_{2}}{δ {\dot{x}}_{10}} & \frac{δ {\dot{x}}_{2}}{δ x_{20}} & \frac{δ {\dot{x}}_{2}}{δ {\dot{x}}_{20}} \end{matrix}] & (6) \end{matrix}$
The suspension stiffness and damping parameters K2 and B2 were adjusted to find a parameter range such that the system with elastically-suspended loads exhibits reduced peak forces and reduced energy cost of locomotion compared to a rigidly attached load. The rigidly-attached load was simulated by setting the suspension parameters to large values (K2=10*K1 and B2=10*B1). For the given human parameters, the parameter range necessary for the system with elastically-suspended loads to exhibit both reduced peak forces and reduced energy cost of locomotion was K2<885 N/m. High suspension damping B2 reduces the effect of elastically-suspended loads because the motion of the load M2 is reduced, so the damping was kept low (B2<25 Ns/m). To illustrate the peak forces and energy cost in this low K2 region and compare them with those at higher K2 and B2 values, a parameter sweep of 25 N/m≦K2≦2000 N/m in increments of 25 N/m was chosen; B2 was simultaneously varied from 10 Ns/m to 50 Ns/m in increments of 0.5 Ns/m. The value of the suspension damping B2 was increased along with the suspension stiffness K2 to simulate how stiffer suspension springs may have larger damping values. Once the parameter range was established, the stability of the system over this range was calculated.
It was discovered that the peak forces and energy cost during locomotion with elastically-suspended loads are reduced for low K2 and B2 values compared to a rigidly-attached load. These values represent a load suspension with compliant springs and low damping. Low K2 values weakly-couple the motion of the elastically-suspended load M2 from the motion of the main mass M1. Weak-coupling corresponds to a maximum phase shift of approximately 180 degrees. This concept can be best viewed in the frequency domain with a Bode plot as depicted in FIG. 2. In this figure, the weakly-coupled elastically-suspended load is nearly 180 degrees out-of-phase at the locomotion frequency ω=2π.
As can be seen in FIG. 3, elastically suspending loads reduce the peak magnitude of forces acting on the main mass M1 for low K2 (<1050 N/m) and B2 values compared to a rigidly-attached load. Specifically, the peak forces of the main mass M1 acting on the leg and the load M2 acting on the main mass M1 were reduced. Summing these forces yields the overall reduction in peak forces on the main mass Ml. For a given set of parameters, there is an optimal value K2=850 N/m that can minimize the total peak forces acting on the main mass M1.
Referring now to FIG. 4, the power input required to maintain stable periodic motion was reduced for an elastically-suspended load for low K2 (<885 N/m) and B2 values versus a rigidly-attached load. For the given set of parameters, there was an optimal value K2=650 N/m that minimized the power input required to achieve periodic motion.
The total peak forces and the energy cost during locomotion depend on the suspension damping B2. See FIG. 5. Small values of the suspension damping B2 enhance the effectiveness of elastically-suspended loads by reducing the peak forces and the energy cost of locomotion for low K2 values and lowering the absolute minimum peak forces and peak power input during locomotion. Large values of B2 reduce the out-of-phase amplitude of M2, thereby inhibiting the effectiveness of elastically-suspended loads.
Increasing load M2 (FIG. 6) and increasing locomotion frequency ω (FIG. 7) increase the effectiveness of elastically-suspended loads by lowering the absolute minimum power required for steady locomotion, which increases the relative energy savings potential, and increases the range of suspension stiffness K2 values such that locomotion with an elastically-suspended load has a lower power input than a rigidly-attached load.
The stability of the system is somewhat reduced with an elastically-suspended load versus a rigidly-attached load over the low K2 and B2 parameter range in which the peak forces and energy cost of locomotion are reduced. See FIG. 8. This figure plots the eigenvalues of a system with an elastically-suspended load. The stability of a discrete system is quantified by perturbing the initial conditions of a stable limit cycle and measuring the eigenvalues of the Jacobian matrix; eigenvalues greater than one generally indicate that the cycle is unstable, eigenvalues equal to one generally indicate that the cycle is marginally stable, and eigenvalues less than one generally indicate that the cycle is stable. From this figure, the system with an elastically-suspended load is clearly stable, but is less stable (has larger eigenvalues) than a system with a rigidly-attached load. The destabilization effect appears to be due to the load M2 position and velocity; this effect can be seen in the eigenvectors of the system over this parameter range.
For elastically-suspended loads to be effective, the motion of the load mass M2 should be weakly-coupled to the motion of the main mass M1. This requires a spring of sufficiently low stiffness K2 and low suspension damping B2. During periodic motion under these conditions, the load M2 oscillates with approximately the same amplitude as the main mass M1 and the motion of the load M2 is nearly 180 degrees out of phase with the motion of the main mass M1. In some embodiments, the compliant suspension stiffness K2 necessary to weakly-couple the load can be obtained with compliant coil springs or bungee cords and the damping B2 can be kept low by using low friction bearings and springs with low damping. Furthermore, in alternate embodiments where the static deflection of a load suspended with compliant springs is significant, large suspension spring travel is required.
It should be appreciated that the design objective for elastically-suspended loads is generally different than that of tuned vibration absorbers. The parameters of tuned vibration absorbers are adjusted such that the forcing function frequency ω is at the anti-resonance peak of the system to minimize the motion of the main mass M1. However, selecting a K2 value such that the leg length forcing function frequency ω is at the anti-resonance peak of the double-mass coupled-oscillator system is not desirable for some elastically suspended load embodiments. For the set of human walking parameters given above, the K2 value that adjusts the input frequency ω to the anti-resonance peak is 986 N/m. At this value, the motion of the main mass M1 is minimized, but the peak forces and energy cost of locomotion are increased, which may not be desirable in some embodiments of the present disclosure.
Reducing peak forces can be important in load carrying devices to reduce stress on humans, animals, and robots.
For a system with elastically-suspended load, the optimal value of the suspension stiffness that minimizes the total peak forces on the main mass M1 (e.g., K2=850 N/m) and an optimal value of the suspension stiffness that minimizes the energy cost during locomotion (e.g., K2=650 N/m) may be a different values. In these systems, the minimum total peak forces cannot simultaneously exist with the minimum energy cost during locomotion. This is a tradeoff inherent in the tuning of many systems with elastically-suspended loads. Some embodiments of the present disclosure minimize the energy cost of locomotion with some reduction in peak forces, which may have advantages over the embodiments that minimize peak forces while reducing the energy cost of locomotion.
Although minimal suspension damping B2 is generally desirable, it may be advantageous to have some damping in the system, such as a sufficient amount of damping to avoid detrimental resonance effects. For example, if the damping is too low, the resonance peak of the system can become significant and can potentially excite oscillations of the load M2, especially if the system is mistuned. This type of situation could reduce the effectiveness of elastically suspending a load and potentially cause damage to a compliant suspension system. In certain embodiments, some amount of damping B2 will be inherently present and advantages may be realized by minimizing the damping inherent in the system. In alternate embodiments, the damping ratio is at most 0.5. In other embodiments, the damping ratio is at least 0.1 and at most 0.3. In still further embodiments, the damping ratio is at least 0.01 and at most 0.1.
When walking with a standard backpack load, the mass-specific gross metabolic power increases curvilinearly with speed and is directly proportional to the load at any speed. The model results show the same trend when walking with a rigidly-attached load. When walking with an elastically-suspended load, the potential energy savings may increase with increasing load and speed. Furthermore, since changing the load M2 and locomotion frequency ω can shift the range of low K2 values sufficient to weakly-couple the load and increase the effectiveness of elastically-suspended loads, there exists an opportunity for the suspension stiffness K2 and damping B2 parameters of an elastically-suspended load to be dynamically tuned for optimal system performance based on knowledge of M2 and ω.
Preliminary analysis appears to indicate that the stability of a system with an elastically-suspended load may be somewhat reduced as compared to a rigidly-attached load over the low K2 and B2 parameter range. As such, a trade-off may exist for locomotion with elastically-suspended loads. A system with elastically-suspended loads can reduce the peak forces and peak power input during locomotion, but this may potentially be at the cost of slightly reduced stability. Although the reduction in stability may not be so significant that the system becomes unstable, the relative stability of a system with an elastically-suspended load appears to be marginally lower than a system with a rigidly-attached load.
Although the effects of elastically-suspended loads on stability are not fully understood, decreased stability can potentially have negative implications for the locomotion of systems with elastically-suspended loads, such as when traveling over rough terrain. If the relative stability of a system with an elastically-suspended load is reduced for locomotion over level terrain, the stability over rough terrain can be poor and can even result in locomotion failure. This may increase the difficulty of the control effort for a human or animal to maintain stable locomotion over rough terrain. However, as the terrain gets increasingly rough, the stability of a system with elastically-suspended loads appears to improve.
The maneuverability of a system is generally defined as a measure of how quickly a system can change direction, e.g., turn. Since increased maneuverability has been linked to decreased dynamic stability, elastically-suspended loads may increase the maneuverability of locomotion systems.
One can elastically-suspend a load on a human, animal, robot, or vehicle that has a vertical component of motion during locomotion. The motion of interest is generally in the vertical direction because the center of mass of humans, animals, and robots is displaced by some amount during locomotion. For instance, the center of mass (CoM) of a human is displaced by about 5-7 cm while walking. When a human, animal, or robot carries a load during locomotion, the load must undergo the same displacement as the center of mass (unless some actuation is used to control the load displacement, which costs energy). For such a rigidly-attached load, the human, animal, or robot must be able to lift the mass of the main body plus the mass of the load during every stride.
To elastically-suspend a load, one needs to couple a load to the main body with a spring. A spring (which may take different forms such as torsion springs, leaf springs, cantilevered springs, coil springs, volute springs, tension springs, air springs, compliant mechanism springs, etc.) can be used to achieve a phase difference of 90-180 degrees between the vertical motion of the load and the main body. With a spring at the interface, the main body and the load can be effectively decoupled (or “weakly-coupled”) from each other. Doing so can reduce the motion of the net center of mass of the system, reducing the amount of work required during each stride. Thus, the energy cost and peak forces of locomotion can be reduced. Moreover, since the vertical motion of the load can also be reduced, elastically-suspending a load can help protect sensitive packages inside the load. Depicted in FIGS. 9A and 9B is a comparison of the net CoM movement in a locomotion system with an elastically-suspended load and a rigidly-attached load, reflecting that the movement of the elastically-suspended load can be reduced with the motion of the load being between 90 and 180 degrees out of phase with the main mass.
Depicted FIG. 10 is a rigid handle. Depicted in FIG. 11 is a handle 100 for elastically suspending a load according to one embodiment of the disclosure. The handle 100 for elastic load includes a spring 105 to suspend a load 110 from the hand grip 115. The spring 105 achieves a phase shift of 90-180 degrees between the load 110 and the hand grip 115 to decouple the motion of the masses.
By elastically-suspending a load, the handle increases the energy efficiency and decreases the peak forces during locomotion compared to a standard (rigid) handle. Both the gain in energy efficiency and the reduction in peak forces depend on the load. For increasing load, the relative energy efficiency gain increases and the relative reduction in peak forces decrease. Stated differently, increasing the load increases the effectiveness of elastically-suspended loads versus rigidly-attached load during locomotion.
Significant benefits can be achieved from elastically-suspending a load. For example, a backpack with a load suspension (27 kg load) was shown to reduce the energy cost of locomotion (increase the energy efficiency) by 6.2% and reduce the peak accelerative vertical force by 82% and the total peak vertical forces by 33% compared to a rigidly-attached load. Suspending a load (32% body mass) on a prototype robot with a weakly-damped elastic suspension system can reduce the energy cost (increased the energy efficiency) by up to 24%. Although a handle such as the one depicted in FIG. 11 will typically suspend smaller loads (for example, a 25 lb load, which is a reasonable weight for a person to carry with a single hand, is about 15% of a 170 lb person's weight), there is nevertheless a substantial benefit from elastically suspending loads.
Some embodiments include a compact handle mechanism. Since compliant springs are beneficial, a long suspension travel may be used to statically support a given load with linear springs (Hooke's Law). To accommodate the long suspension travel, the springs can be pre-stressed or rotation/torsion springs can be used. Rotational/torsion springs are particularly useful in some embodiments because they are compact and undergo rotational displacement instead of linear displacement. Various embodiments utilize various types of springs, such as elastic bands, coil springs, coiled metal watch springs, air springs, and/or compliant mechanisms.
Tuning of the springs can be useful. The double-mass coupled-oscillator model described above can help select the approximate spring stiffness required to realize, and to potentially optimize, the benefits of elastically-suspended loads.
The applications of the elastic handle are numerous. One embodiment includes a “universal” handle for elastic load suspension that can be used to pick up grocery bags, shopping bags, buckets, rugs, briefcases, laptop cases, purses, luggage, toolboxes, military cargo, salt bags, etc. In alternate embodiments, an “integrated” handle for elastic load suspension could be integrated into carrying cases, luggage, toolboxes, military cargo, baby seats/carriers, dog carriers, etc.
In still further embodiments, a weakly-coupled robot load suspension capable of elastically suspending loads inside of a robot (such as batteries, electronics, and fuel) as well as external loads. Such a suspension system can increase the energy efficiency and reduce the peak forces during robot locomotion compared to rigidly-attached loads. In one embodiment, the robot load suspension can use a linear spring and a rotational bell crank to change the direction of a suspension springs deflection. As such, the robot load suspension can utilize the length of a robot with a long horizontal suspension system rather than a tall vertical suspension system that could have a negative impact on the pitching dynamics of the robot during locomotion. This concept is particularly useful for robots that are long relative to their height.
In one embodiment, the elastic load suspension is attached to a hexapod robot as depicted in FIG. 12. The load (e.g., the battery which may or may not power the robot) is attached to one end of an aluminum bell-crank lever arm. The bell crank is mounted on a shaft that allows the bell crank to rotate. An elastic band is attached to the other end of the bell-crank and is tuned by changing its length. The elastic band travels around a small pulley mounted on a wooden plank extending off the back of the robot. The wooden plank allows for the pulley to be a sufficient distance from the bell crank lever arm to enable the compliant elastic band to significantly deflect and statically support the battery load. The other end of the elastic band is tied and fixed to the bell crank shaft. The bell crank shaft is mounted such that the battery load is statically supported by the elastic band over the center of mass of the robot. In some embodiments, the load is centered above the robot's center of mass to reduce the effect of the oscillating load on the pitching dynamics of the robot.
The bell crank mechanism enables a load to be elastically suspended over the robot. The mechanism does not require a large amount of vertical space for the load to be statically supported and oscillate about the static equilibrium point. When the bell crank arm supporting the load is vertical, the elastic band does not support the load. As the bell crank arm supporting the load rotates toward the front of the robot, the elastic band supports an increasing proportion of the load. This results in a non-linear elastically-suspended load. For the small oscillations of a tuned elastically-suspended load that is nearly horizontal, the non-linear effect of the bell crank rotation is assumed to be negligible.
One aspect of embodiments of the present disclosure is the tuning of the elastic suspension system. Using, for example, a human that is walking or running carrying a load, the human's motion may be approximated by the action of a pogo stick. See FIG. 13. While walking and running, the human body moves vertically up and down by approximately 4-7 cm (about 2 in). If one is carrying a load, one needs to vertically lift the load by approximately this same distance. The accelerations from lifting the load during each stride increases the peak forces on the body by approximately 2-3 times the weight of the load itself. Furthermore, the energetic cost of locomotion increases in proportion to the load being carried.
As previously mentioned, if a load can be elastically-suspended from the body with a compliant suspension, then the motion of the load can be decoupled from the motion of the body and reduce the peak forces and energetic cost of locomotion. Using a linear two degree-of-freedom vertical hopping model to investigate this phenomenon (see, e.g., FIG. 1), it can be seen that the forcing function L(t)=a*sin(wt) oscillates the effective spring-leg with the approximate amplitude and frequency (w=2 Hz) of human walking. Embodiments of the disclosure include handles with natural frequencies below that expected while the load is being carried, which for human walking is below 2 Hz (which is also below the typical human running frequency of approximately 3 Hz).
FIG. 14 depicts the results of walking at 2 Hz with a 20 lb load and a load suspension damping ratio of 0.1. This figure depicts the qualitative reduction in the average power of walking while carrying a load when the suspension stiffness is below the resonant frequency of human walking. This occurs when the suspension stiffness K2 is less than 1400 N/m. Also note the point at which the energetic cost is minimized.
A similar trend is observed with the peak dynamic forces on the body, but the tuning is different. As depicted in FIG. 15, the peak dynamic forces are reduced when the suspension stiffness is below 1000 N/m and the peak dynamic forces are minimized when the stiffness is minimized.
Choosing such low suspension stiffness requires a large static deflection, which increases exponentially as the suspension stiffness is minimized (based on Hooke's law, F=kx). See FIG. 16. However, designing a handle suspension that can accommodate very large static deflections can be mechanically challenging.
FIG. 17 shows the average power with respect to the effective linear static deflection of the load suspension. The minimum power occurs when the static deflection is approximately 3 inches. The power decreases relative to a rigidly-attached load as the static deflection increases, but there are diminishing returns.
FIG. 18 depicts the peak force of the load on the body with respect to the static deflection. The load force is minimized as the effective linear static deflection is maximized, but again, there are diminishing returns.
In some embodiments, the handle suspension is tuned for a given load such that the minimum effective linear static deflection is at least 2.5 inches and at most 18 inches. In other embodiments, the handle suspension is tuned for a given load such that the minimum effective linear static deflection is at least 4 inches and at most 10 inches. In still further embodiments, the handle suspension is tuned for a given load such that the minimum effective linear static deflection is approximately 5 inches. In some embodiments the extension of the load below the normal resting position of the handle may be at least 2.5 inches and at most 18 inches, at least 4 inches and at most 10 inches, or approximately 5 inches; while in other embodiments the effective spring length statically deflects at least 2.5 inches and at most 18 inches, at least 4 inches and at most 10 inches, or approximately 5 inches.
Different load masses may require different tuning. A 15 lb load will generally require one stiffness and a 30 lb load will generally require another stiffness. If the suspension is linear and a 15 lb load has 5 in of travel, then a 30 lb load could have 10 in of travel. If the 15 lb load instead has 10 in of travel, then the 30 lb load would have 20 in, which could be a problem for the mechanism to accommodate. As such, various embodiments tune the handle suspension for a particular load mass. Some embodiments may be able to accommodate only a certain range of loads (a typical range may include 15-30 lbs), although other embodiments incorporate a suspension with an adjustable tension that can accommodate multiple load masses, which may be accomplished manually or with an actuator.
Limiting the static load deflection of the handle spring can have adverse consequences. For example, if an elastic suspension mechanism results in a small static defection of the load, such as less than 2.5 inches, the natural frequency of the handle can inadvertently be higher than the natural frequency of locomotion and actually increase peak forces and decrease locomotive energy efficiency (increase locomotive energy cost).
Depicted in FIG. 19 is a cantilever elastic load suspension handle according to one embodiment of the present disclosure. The handle includes a grip portion and cantilever members (for example leaf springs) that are connected together at an intermediate position and suspend a load below the grip portion.
FIG. 20 depicts an elastic suspension handle with adjustable stiffness according to another embodiment of the present disclosure. This handle includes a grip portion and cantilever members that are connected to one another with a mechanism that varies the connection point between the cantilever members. The cantilever members are also attached to the load so that the load may be suspended below the grip portion while being carried.
Depicted in FIG. 21 is a cantilever pretension mechanism that may be used to pretension the spring. One advantage of pre-tensioning the spring is that it is possible to maintain a sufficient effective spring deflection while decreasing the actual separation between the grip and the load to suspend the load below the grip portion. The stretcher member is useful in creating and maintaining the appropriate pretension.
Depicted in FIG. 22 is an elastic suspension handle utilizing one or more elastic cords and one or more pulleys to elastically suspend the load below the grip portion.
FIG. 23 depicts a suspension handle with an internal torsion spring according to yet a further embodiment of the present disclosure. This handle allows the user to selectively lock the handle to create a rigid load suspension device or to permit the load to be elastically suspended from the grip portion. In the illustrated embodiment, the grip portion is rotatable between two positions, one corresponding to an elastic suspension and the other corresponding to a rigid suspension of the load. In still further embodiments, the grip portion may be used to adjust the pre-tensioning of the spring.
FIG. 24A depicts details of the options selectable with the rotatable grip portion in FIG. 23. FIG. 24B depicts an alternate embodiment in which the suspension handle is hinged with respect to the load connection portion.
FIGS. 25A and 25B depict a detailed close-up of a torsion mechanism that may be utilized with the handle depicted in FIG. 23.
FIG. 26 depicts a torsion handle with a torsion spring and tension adjustment mechanism according to yet a further embodiment of the present disclosure. This handle includes a grip portion, a torsion spring, a tension adjustment, a pulley connected to the torsion spring, and an idler pulley. The tension adjustment mechanism may be used to compensate for varying load masses or other situations as would be understood by one of ordinary skill in the art.
FIG. 27 depicts an elastic suspension handle that may be used with devices similar to baby carriers or infant-type car seats. As the grip portion is raised, the suspension handle elongates creating the appropriate effective deflection of the spring-type handle as depicted in FIG. 28. Pre-tensioners may also be utilized to effect the actual extension of the grip portion above the basket while maintaining a suitable effective static spring deflection.
FIG. 29 depicts a circular-type suspension handle according to still a further embodiment of the present disclosure. The circular-type suspension handle includes optional pre-tensioners that can provide a proper effective static spring deflection when carrying a load as depicted in FIG. 30. This handle also includes an optional hook that may be used to attach a load.
FIG. 31 depicts a cantilever suspension handle according to another embodiment of the present invention. This handle includes a grip portion connected to a mounting structure that is connected to cantilever (or optionally torsional) members that are connected to the load.
FIG. 32 depicts another cantilever (or torsion) spring suspension handle according to another embodiment of the present disclosure. This handle includes a grip cantilever or torsion member similar to the cantilever (or torsion) member depicted in FIG. 31 but with a more direct connection between the cantilever (or torsion) member and the grip portion.
FIG. 33 depicts a handle with a grip portion and a scissor-type arrangement with torsion springs connected at the joints of the parallelogram-shaped figure.
FIG. 34 depicts a torsion spring handle with two torsion springs located within the grip portion (one located on either side of the grip portion) and a load connection member being connected to the torsion springs.
FIG. 35 depicts a clock spring type suspension handle according to still another embodiment of the present invention. This handle includes a coiled up spring within the grip portion similar to some dog leashes, with the spring being connected to the load.
FIG. 36 depicts a suspension handle according to yet another embodiment of the present invention. This handle includes a grip portion connected to a torsion spring which is attached to a load via a linkage. As the user pulls up on the grip portion, the torsion spring deflects resulting in an elastically suspended load.
Alternate embodiments of the present disclosure include an elastically-suspended satchel as a hip-supported load carrying device that can suspend a load with a compliant spring near the center of mass of a human, animal, or robot. Alternate embodiments can use linear spring deflection or rotational spring deflection, space saving advantages being realized with the latter. These embodiments It can increase the energy efficiency and reduce the peak forces during locomotion compared to a standard rigidly-attached satchel.
Alternate embodiments apply the concept of tuned elastically-suspended loads to vehicles. For large loads outside the optimal range of the vehicles suspension, additional elastic load suspension mechanisms can help improve the energy efficiency of the vehicles' motion.
Alternate embodiments include universal handles for carrying grocery/shopping bags, briefcases, laptop computer cases, purses, luggage, toolboxes, military cargo, etc. Still other embodiments include integrated handles for carrying briefcases, luggage, toolboxes, military cargo, baby seats/carriers, pet carriers, etc.
Still further embodiments utilize one or more torsion springs to suspend a load from a handle.
If there is some optimal range of load suspension stiffness values for different parameters of the locomotion system (load, speed, morphology), there is also an opportunity to dynamically tune the load suspension stiffness during locomotion. This can be accomplished with an actuator that can change the suspension stiffness during locomotion given a control signal input, maintaining the optimal load suspension stiffness.
The reference system used herein may refer generally to various directions (e.g., upper, lower, forward and rearward), which are merely offered to assist the reader in understanding the various embodiments of the disclosure and are not to be interpreted as limiting. Other reference systems may be used to describe various embodiments, such as referring to the direction of projectile movement as it exits the firearm as being up, down, rearward or any other direction.
While examples, one or more representative embodiments and specific forms of the disclosure have been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive or limiting. The description of particular features in one embodiment does not imply that those particular features are necessarily limited to that one embodiment. Features of one embodiment may be used in combination with features of other embodiments as would be understood by one of ordinary skill in the art, whether or not explicitly described as such. One or more exemplary embodiments have been shown and described, and all changes and modifications that come within the spirit of the disclosure are desired to be protected.

Claims

What is claimed is:

1. A carrying handle, comprising:

a grip portion;

a connecting member for connecting the grip portion to a load; and

a spring connected to the grip portion and to the connecting member, wherein the effective spring length statically deflects at least 2.5 and at most 18 inches when carrying the load.

2. The carrying handle of claim 1, wherein the effective spring length statically deflects at least 4 inches and at most 10 inches when carrying the load.

3. The carrying handle of claim 1, wherein the effective spring length statically deflects 5 inches when carrying the load.

4. The carrying handle of claim 1, wherein the spring is pretensioned and the physical displacement between the handle and the carried object is reduced.

5. The carrying handle of claim 1, wherein the natural frequency of the spring is less than 2 Hertz.

6. The carrying handle of claim 1, wherein the damping ratio of the carrying handle is at most 0.5.

7. The carrying handle of claim 1, wherein the stiffness of the spring is adjustable by the user.

8. The carrying handle of claim 1, wherein the spring is a nonlinear spring.

9. The carrying handle of claim 1, wherein the spring is a leaf spring, a torsion spring, a coil spring, an air spring, an elastic cord, an elastic band, or a compliant plastic mechanism.

10. The carrying handle of claim 1, comprising:

a locking mechanism with at least two user selectable configurations including

a rigid suspension configuration, wherein the spring is restrained from deflecting, and

an elastic suspension configuration, wherein the spring deflects when carrying the load.

11. A method for carrying a load, comprising:

extending the effective length of a spring connected to a handle and a load, the effective spring length extending at least 2.5 inches and at most 18 inches;

suspending the load below the extended handle;

lightly damping oscillations of the suspended load with a damping ratio equal to at most 0.5.

12. The method of claim 11, wherein said extending extends the effective length of the spring at least 4 and at most 10 inches.

13. The method of claim 11, wherein said extends the effective length of the spring 5 inches.

14. The method of claim 11, wherein said lightly damping is accomplished with a damping ratio equal to at most 0.1.

15. The method of claim 11, comprising:

restricting non-vertical motion of the suspended load.

16. The method of claim 11, comprising:

extending the load below the handle and reaching a static equilibrium point approximately 5 inches below the handle.

17. A method of manufacturing a handle, comprising:

selecting an elastic member that will have an effective static deflection of at least 2.5 inches and at most 18 inches when a predetermined load is suspended by the elastic member;

connecting the elastic member to a grip adapted for grasping; and

connecting the elastic member to a load attachment portion, the load attachment portion including a mechanism for attaching to the predetermined load.

18. The method of claim 17, wherein said selecting includes selecting an elastic member that will have an effective static deflection of at least 4 inches and at most 10 inches when the predetermined load is suspended by the elastic member

19. The method of claim 17, wherein said selecting includes selecting an elastic member that will have an effective static deflection of approximately 5 inches when the predetermined load is suspended by the elastic member

20. The method of claim 17, comprising:

selecting an elastic member that will have a damping ratio of at most 0.5 when connected to the grip and the load attachment portion and suspending the predetermined load.