A stiffness adjustment mechanism maximally utilizing elastic energy of a linear spring for a robot joint

This paper presents a parallel compliance device with variable translational stiffness properties. The variation of endpoint stiffness depends on the change of the spring stiffness in each limb. A synthesis algorithm for realizing the desired force compliance performance is built. Based on the proposed algorithm, a group of optimal spring stiffness can be derived. For the implementation of this device, an electromagnetic linear spring with current-controlled stiffness is developed. After testing the mechanical characteristics of the electromagnetic spring, a prototype of the parallel compliance device is built. The endpoint stiffness under different combinations of spring stiffness values is exhibited in the form of stiffness ellipsoids. A case is studied and verifies the ability of the presented compliance device to realize the desired endpoint stiffness. As the stiffness adjustment range of electromagnetic spring is limited, the bound of physically realizable stiffness of the presented compliance device is also discussed.

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ON IMPROVING BIPEDAL WALKING ENERGETICS THROUGH ADJUSTING THE STIFFNESS OF ELASTIC ELEMENTS AT THE ANKLE JOINT

International Journal of Humanoid Robotics ◽

10.1142/s0219843609001656 ◽

2009 ◽

Vol 06 (01) ◽

pp. 23-48 ◽

Cited By ~ 3

Author(s):

REZA GHORBANI ◽

QIONG WU

Keyword(s):

Ankle Joint ◽

Model Simulation ◽

Bipedal Walking ◽

Walking Robots ◽

Walking Robot ◽

Energy Feedback ◽

Linear Spring ◽

Elastic Form ◽

The Impact ◽

Stiffness Adjustment

Impact at each leg transition is one of the main causes of energy dissipation in most of the current bipedal walking robots. Minimizing impact can reduce the energy loss. Instead of controlling the joint angle profiles to reduce the impact, which requires a significant amount of energy, installing elastic mechanisms (with adjustable stiffness) on the robots structure is proposed in this paper, enabling the robot to reduce the impact, and to store part of the energy in the elastic form and return it to the robot. The conceptual design of an adjustable stiffness artificial tendon is proposed which is added to the ankle joint of a bipedal walking robot model. Simulation results on the stance phase demonstrate significant improvements in the energetics of the bipedal walking robot by proper stiffness adjustment of the tendon as compared to using a single linear spring. A controller based on energy feedback is designed to automatically adjust the stiffness of the tendon. Computer simulations illustrate improvements in performance of the energetics of the bipedal walking robot in consecutive walking steps while the stiffness of the tendon is adjusted properly.

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Indirect actuation reduces flight power requirements in Manduca sexta via elastic energy exchange

10.1101/727743 ◽

2019 ◽

Cited By ~ 1

Author(s):

Jeff Gau ◽

Nick Gravish ◽

Simon Sponberg

Keyword(s):

Manduca Sexta ◽

Elastic Energy ◽

Energy Exchange ◽

Viscoelastic Model ◽

Additional Energy ◽

Mechanical Coupling ◽

Exchange Performance ◽

Frequency Independent ◽

Linear Spring ◽

Deformation Mechanics

AbstractIn the vast majority of flying insects, wing movements are generated indirectly via the deformations of the exoskeleton. Indirect measurements of inertial and aerodynamic power requirements suggest that elastic energy exchange in spring-like structures may reduce the high power requirements of flight by recovering energy from one wingstroke to the next. We directly measured deformation mechanics and elastic energy storage in a hawkmoth Manduca sexta thorax by recording the force required to deform the thorax over a frequency range encompassing typical wingbeat frequencies. We found that a structural damping model, not a viscoelastic model, accurately describes the thorax’s linear spring-like properties and frequency independent dissipation. The energy recovered from thorax deformations is sufficient to minimize flight power requirements. By removing the passive musculature, we find that the exoskeleton determines thorax mechanics. To assess the factors that determine the exoskeleton’s spring-like properties, we isolated functional thorax regions, disrupted strain in an otherwise intact thorax, and compared results to a homogeneous hemisphere. We found that mechanical coupling between spatially separated thorax regions improves energy exchange performance. Furthermore, local mechanical properties depend on global strain patterns. Finally, the addition of scutum deformations via indirect actuation provides additional energy recovery without added dissipation.

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A Stiffness Adjustment Mechanism Based on Negative Work for High-efficient Propulsion of Robotic Fish

Journal of Bionic Engineering ◽

10.1007/s42235-018-0021-0 ◽

2018 ◽

Vol 15 (2) ◽

pp. 270-282 ◽

Cited By ~ 5

Author(s):

Dong Xu ◽

Haining Zeng ◽

Xiang Peng ◽

Ziqing Zhao ◽

Jingmeng Liu

Keyword(s):

Robotic Fish ◽

Adjustment Mechanism ◽

Negative Work ◽

High Efficient ◽

Stiffness Adjustment

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Hopping with degressive spring stiffness in a full-leg exoskeleton lowers metabolic cost compared with progressive spring stiffness and hopping without assistance

Journal of Applied Physiology ◽

10.1152/japplphysiol.01003.2018 ◽

2019 ◽

Vol 127 (2) ◽

pp. 520-530

Author(s):

Stephen P. Allen ◽

Alena M. Grabowski

Keyword(s):

Elastic Energy ◽

Metabolic Cost ◽

Spring Stiffness ◽

Metabolic Power ◽

Metabolic Demand ◽

Nonlinear Spring ◽

Vertical Stiffness ◽

Leg Stiffness ◽

Linear Spring ◽

Stiffness Profile

When humans hop with a passive-elastic exoskeleton with springs in parallel with both legs, net metabolic power (Pmet) decreases compared with normal hopping (NH). Furthermore, humans retain near-constant total vertical stiffness ( ktot) when hopping with such an exoskeleton. To determine how spring stiffness profile affects Pmet and biomechanics, 10 subjects hopped on both legs normally and with three full-leg exoskeletons that each used a different spring stiffness profile at 2.4, 2.6, 2.8, and 3.0 Hz. Each subject hopped with an exoskeleton that had a degressive spring stiffness (DGexo), where stiffness, the slope of force vs. displacement, is initially high but decreases with greater displacement, linear spring stiffness (LNexo), where stiffness is constant, or progressive spring stiffness (PGexo), where stiffness is initially low but increases with greater displacement. Compared with NH, use of the DGexo, LNexo, and PGexo numerically resulted in 13–24% lower, 4–12% lower, and 0–8% higher Pmet, respectively, at 2.4–3.0 Hz. Hopping with the DGexo reduced Pmet compared with NH at 2.4–2.6 Hz ( P ≤ 0.0457) and reduced Pmet compared with the PGexo at 2.4–2.8 Hz ( P < 0.001). ktot while hopping with each exoskeleton was not different compared with NH, suggesting that humans adjust leg stiffness to maintain overall stiffness regardless of the spring stiffness profile in an exoskeleton. Furthermore, the DGexo provided the greatest elastic energy return, followed by LNexo and PGexo ( P ≤ 0.001). Future full-leg, passive-elastic exoskeleton designs for hopping, and presumably running, should use a DGexo rather than an LNexo or a PGexo to minimize metabolic demand. NEW & NOTEWORTHY When humans hop at 2.4–3.0 Hz normally and with an exoskeleton with different spring stiffness profiles in parallel to the legs, net metabolic power is lowest when hopping with an exoskeleton with degressive spring stiffness. Total vertical stiffness is constant when using an exoskeleton with linear or nonlinear spring stiffness compared with normal hopping. In-parallel spring stiffness influences net metabolic power and biomechanics and should be considered when designing passive-elastic exoskeletons for hopping and running.

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