title: Dynamically variable negative stiffness structures.
abstract: Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness-based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators.
authors.affiliation: HRL Laboratories LLC, Malibu, CA 90265, USA.
authors.forename: Christopher B
authors.identifier: 0000-0002-2976-3146
authors.initials: CB
authors.lastname: Churchill
authors.affiliation: HRL Laboratories LLC, Malibu, CA 90265, USA.
authors.forename: David W
authors.initials: DW
authors.lastname: Shahan
authors.affiliation: HRL Laboratories LLC, Malibu, CA 90265, USA.
authors.forename: Sloan P
authors.initials: SP
authors.lastname: Smith
authors.affiliation: HRL Laboratories LLC, Malibu, CA 90265, USA.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Keefe
authors.affiliation: HRL Laboratories LLC, Malibu, CA 90265, USA.
authors.forename: Geoffrey P
authors.initials: GP
authors.lastname: McKnight
mesh_terms: D000818:Animals; D057005:Bioengineering / Q000295:instrumentation* / Q000706:statistics & numerical data; D001696:Biomechanical Phenomena; D006801:Humans; D012371:Robotics; D014732:Vibration; D016474:Weight-Bearing
keywords: Vibration isolation; impedance control; negative stiffness; nonlinear structures