Advancement of Legged Locomotion Models by Including Nonlinear Damping

Accurately predicting human locomotion has been a goal of various mathematical models. Early canonical models of locomotion were developed to predict the basic features of ground reaction forces (GRF). More recently, modified hip actuated and leg damped locomotion models have been developed to better predict the stability and robustness of human and animal locomotion. Such improvements have resulted in the loss of the characteristic GRF predicted by earlier models. Historically, GRF are among the most common measures to experimentally study human locomotion. Thus, it is important to develop new mathematical models that predict both accurate stability of motion, as well as GRF. We hypothesized that by replacing linear damping models with nonlinear leg damping, we can better replicate human GRF. We then derived the equations of motion for this new type of locomotion model and analyzed the system behavior. GRF from the modified model were compared with published human GRF data. Stability and robustness were also studied through the use of numerical analysis to make sure that the ability to predict stable motion was not compromised. We found that the modified model with nonlinear leg damping provides a significantly better prediction of GRF, especially in the early part of stance. Further, the model\u27s ability to predict the stability of locomotion is similar to the actuated model with linear damping. As a result, we expect that stable actuated models of locomotion can generally be combined with nonlinear leg damping models to better predict human locomotion GRF and stability

Our Journey Into Learning Innovation and Competency-Based Education

Short Abstract: In 2013 a learning innovation incubator began with a question “what might an education addressing next-generation skills look like?” A result was the first competency-based undergraduate program at a main campus of a major university. This talk provides insights into a process involving learning and policy innovation. Full Abstract: In 2013 a learning innovation incubator began to consider the question “what might an education addressing next-generation skills look like?” Faculty from technology, mathematics, science, and various disciplines in the humanities met weekly for six months establishing trust with the help of a learning innovation coach using open dialog in areas such as empathy, belonging, and vulnerability. With the help of experts from Cal Poly San Luis Obispo and Olin College, two learning experiences (courses) were created and developed in the spring and summer of 2014. The learning experiences intentionally integrated the humanities with STEM fields using self-awareness and open-ended wicked problems as cornerstones to foster and develop individual student learning and metacognition. A competency-based learning model was adopted to assess student agency and learning in a more holistic way. Over the next three years a cohort of students navigated requirements for their declared major while participating in these new and evolving learning experiences, and the process of obtaining necessary degree approvals

The Unfortunate Role of Farm Subsidies as a Stimulus for Inequality and Obesity

Governmental expenditures are directed at a particular objective, but their effects have consequences far beyond the named target of the expenditures. Specific farm subsidies, for example, encourage consumption of particular foods by reducing the costs of producing these foods. To what extent do these subsidies affect the American obesity epidemic? How do the subsidies create disparate negative effects on those in poverty? Exploring these questions stimulates us to take greater care when designing legislation to take a broader look at the stakeholders affected by any particular governmental expenditure

Design of Stabilizing Arm Mechanisms for Carrying and Positioning Loads

Stabilizing arm mechanisms are used to support and position a load with minimal force from the user. Further, stabilizing arm mechanisms enable operators to stabilize the motion of the load while walking or running over variable terrain. Although existing stabilizing arm mechanisms have reached fairly broad adoption over a range of applications, it remains unknown exactly how the spring properties and geometric parameters of the mechanism enable its overall performance. We developed a simplified model to analyze the vertical dynamics of stabilizing arms to determine how the spring properties and mechanism geometry affect the natural frequency of the load mass, the range of load masses that can be supported, and the equilibrium position of the load mass. We found that decreasing the unstretched spring free length is the most effective way to minimize the natural frequency; the spring lever arm can be used to adjust for a desired load mass range, and the linkage length can be used to adjust the range of motion of the stabilizing arm. The spring stiffness should be selected based on the other parameters. This work provides a systematic design study of how the parameters of a stabilizing arm mechanism affect its behavior and fundamental design principles that could be used to improve existing mechanisms, and enable the design of new mechanisms

Resilient Communities: Understanding Networks for Post-Disaster Recovery

Community response and recovery from a disaster can vary widely based on community characteristics. Many disasters leave little time for preparation prior to arrival and can cause widespread death and destruction. Regardless of the impact of the disaster, response and recovery rates vary based upon several factors including resource availability, social and physical infrastructure, and policies in each community

Towards Robustly Stable Musculo-Skeletal Simulation of Human Gait: Merging Lumped and Component-Based Modeling Approaches

The objective of work presented in this paper is to increase the center-of-mass stability of human walking and running in musculo-skeletal simulation. The approach taken is to approximate the whole-body dynamics of the low-dimensional Spring-Loaded Inverted Pendulum (SLIP) model of locomotion in the OpenSim environment using existing OpenSim tools. To more directly relate low-dimensional dynamic models to human simulation, an existing OpenSim human model is first modified to more closely represent bilateral above-knee amputee locomotion with passive prostheses. To increase stability further beyond the energy-conserving SLIP model, an OpenSim model based upon the Clock-Torqued Spring-Loaded-Inverted-Pendulum (CT-SLIP) model of locomotion is also created. The result of this work is that a multi-body musculo-skeletal simulation in Open-Sim can approximate the whole-body sagittal-plane dynamics of the passive SLIP model. By adding a plugin controller to the OpenSim environment, the Clock-Torqued-SLIP dynamics can be approximated in OpenSim. To change between walking and running, only one parameter representing the preferred period of a stride is changed. The result is a robustly stable simulation of the center-of-mass locomotion for both walking and running that could serve as a first step toward increasingly anatomically accurate and robustly stable musculo-skeletal simulations.</jats:p

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The spring-loaded inverted pendulum (SLIP) is a simple, passivelyelastic two-degree-of-freedom model for legged locomotion that describes the center-of-mass dynamics of many animal species and some legged robots. Conventionally, SLIP models employ a single support leg during stance and, while they can exhibit stable steady gaits when motions are confined to the sagittal plane, threedimensional gaits are unstable to lateral toppling. In this paper it is shown that multiple stance legs can confer stability. Three SLIPinspired models are studied: a passive bipedal kangaroo-hopper, an actuated insect model, and passive and actuated versions of a hexapedal robot model. The latter models both employ tripod stance phases. The sources of lateral stability are identified and, for the passive systems, analytical estimates of critical parameters are provided. Throughout, rotations are ignored and only center-of-mass translational dynamics are considered. KEY WORDS—legged locomotion, spring-loaded inverted pendulum, three-dimensional motion, multiple legs, periodic gait, Poincaré map, stability 1

Analytic-Holistic Two-Segment Model of Quadruped Back-Bending in the Sagittal Plane

Back-bending in the sagittal plane is common in many animals during legged locomotion and could be useful for robots. However, to our knowledge, there exists no analytical mechanistic model of sagittal-plane back bending legged locomotion of quadrupeds. Such a mechanistic model and knowledge derived from it is expected to enable direct analysis and insight into back bending locomotion and can be applied to the study of biomechanics or the design of robots. Here a whole-body mechanistic model is developed and governing equations of motion are derived to provide insight into the mathematical structure of the system dynamics. The model is energy conserving, consisting of massless elastic legs pinned to two body segments. The two body segments are pin-joined together with a rotational spring. The massless legs are returned to a resting angle relative to the body during swing phase. We discover: 1) Whole-body configuration variables simplify the resulting equations of motion. 2) The sagittal-plane back-bending two-segment model of legged locomotion yields stable periodic gaits.</jats:p