scholarly journals A General Framework for Minimizing Energy Consumption of Series Elastic Actuators With Regeneration

2017 ◽  
Author(s):  
Edgar Bolívar ◽  
Siavash Rezazadeh ◽  
Robert Gregg
Keyword(s):  
Energy Consumption ◽  
Elastic Element ◽  
Close Contact ◽  
Reference Trajectory ◽  
Ankle Motion ◽  
Natural Motion ◽  
Actuator Constraints ◽  
Natural Dynamics ◽  
Series Elastic Actuators ◽  
Series Elastic

The use of actuators with inherent compliance, such as series elastic actuators (SEAs), has become traditional for robotic systems working in close contact with humans. SEAs can reduce the energy consumption for a given task compared to rigid actuators, but this reduction is highly dependent on the design of the SEA’s elastic element. This design is often based on natural dynamics or a parameterized optimization, but both approaches have limitations. The natural dynamics approach cannot consider actuator constraints or arbitrary reference trajectories, and a parameterized elastic element can only be optimized within the given parameter space. In this work, we propose a solution to these limitations by formulating the design of the SEA’s elastic element as a non-parametric convex optimization problem, which yields a globally optimal conservative elastic element while respecting actuator constraints. Convexity is proven for the case of an arbitrary periodic reference trajectory with a SEA capable of energy regeneration. We discuss the optimization results for the tasks defined by the human ankle motion during level-ground walking and the natural motion of a single mass-spring system with a nonlinear spring. For all these tasks, the designed SEA reduces energy consumption and satisfies the actuator’s constraints.

Design of a Compact, Lightweight, Electromechanical Linear Series Elastic Actuator

2014 ◽  
Author(s):  
Coleman Knabe ◽  
Bryce Lee ◽  
Viktor Orekhov ◽  
Dennis Hong
Keyword(s):  
Elastic Element ◽  
Load Capacity ◽  
Ball Screw ◽  
Leaf Spring ◽  
Load Range ◽  
Compression Load ◽  
Design Changes ◽  
Series Elastic Actuators ◽  
Future Work ◽  
Series Elastic

Series Elastic Actuators (SEAs) have several benefits for force controlled robotic applications. Typical SEAs place an elastic element between the motor and the load, increasing shock tolerance, allowing for more accurate and stable force control, and creating the potential for energy storage. This paper presents the design of a compact, lightweight, low-friction, electromechanical linear SEA used in the lower body of the Tactical Hazardous Operations Robot (THOR). The THOR SEA is an evolutionary improvement upon the SAFFiR SEA [1]. Design changes focused on reducing the size and fixed length of the actuator while increasing its load capacity. This SEA pairs a ball screw-driven linear actuator with a configurable elastic member. The elastic element is a titanium leaf spring with a removable pivot, setting the compliance to either 650 or 372 [kN/m]. The compliant beam is positioned parallel to the actuator, reducing overall packaging size by relocating the space required for spring deflection. Unlike typical SEAs which measure force through spring deflection, the force applied to the titanium beam is measured through a tension/compression load cell located in line with each actuator, resulting in a measurable load range of +/−2225 [N] at a tolerance of +/−1 [N]. A pair of universal joints connects the actuator to the compliant beam and to the robot frame. As the size of each universal joint is greatly dependent upon its required range of motion, each joint design is tailored to fit a particular angle range to further reduce packaging size. Potential research topics involving the actuator are proposed for future work.

Configurable Compliance for Series Elastic Actuators

2013 ◽  
Author(s):  
Viktor Orekhov ◽  
Derek Lahr ◽  
Bryce Lee ◽  
Dennis Hong
Keyword(s):  
Force Control ◽  
Joint Stiffness ◽  
Variable Stiffness ◽  
Effective Length ◽  
In Series ◽  
Primary Advantage ◽  
Variable Compliance ◽  
Natural Dynamics ◽  
Series Elastic Actuators ◽  
Series Elastic

Variable compliance has been a growing topic of interest in legged robotics due to recent studies showing that animals adjust their leg and joint stiffness to adjust their natural dynamics and to accommodate changes in their environment. However, existing designs add significant weight, size, and complexity. Series Elastic Actuators, on the other hand, are designed with a set stiffness usually tuned for actuator performance. We propose a new concept for implementing a physical spring in series with a linear SEA using a cantilevered spring. A movable pivot is used to adjust the stiffness by changing the effective length of the cantilever. While the proposed design does not allow for variable compliance, it does retain many of the benefits of passive spring elements such as absorbing impacts, storing energy, and enabling force control. The primary advantage of the design is the ability to adjust the stiffness of each joint individually without the increased weight and complexity of variable stiffness designs. This paper introduces the motivation for configurable compliance, describes the proposed design concept, explains the design methods, and presents experimental data from a completed prototype.

scholarly journals Energy Implications of Torque Feedback Control and Series Elastic Actuators for Mobile Robots

2018 ◽  
Author(s):  
Stephen P. Buerger ◽  
Anirban Mazumdar ◽  
Steven J. Spencer
Keyword(s):  
Energy Consumption ◽  
Feedback Control ◽  
Best Practices ◽  
Energy Efficient ◽  
Mechanical Impedance ◽  
Gear Ratio ◽  
Spring Stiffness ◽  
Feedback Analysis ◽  
Series Elastic Actuators ◽  
Series Elastic

Torque feedback control and series elastic actuators are widely used to enable compact, highly-geared electric motors to provide low and controllable mechanical impedance. While these approaches provide certain benefits for control, their impact on system energy consumption is not widely understood. This paper presents a model for examining the energy consumption of drivetrains implementing various target dynamic behaviors in the presence of gear reductions and torque feedback. Analysis of this model reveals that under cyclical motions for many conditions, increasing the gear ratio results in greater energy loss. A similar model is presented for series elastic actuators and used to determine the energy consequences of various spring stiffness values. Both models enable the computation and optimization of power based on specific hardware manifestations, and illustrate how energy consumption sometimes defies conventional best-practices. Results of evaluating these two topologies as part of a drivetrain design optimization for two energy-efficient electrically driven humanoids are summarized. The model presented enables robot designers to predict the energy consequences of gearing and series elasticity for future robot designs, helping to avoid substantial energy sinks that may be inadvertently introduced if these issues are not properly analyzed.

Design of Elastic Element and Controller Algorithm

2014 ◽  
Author(s):  
Zhuohua Shen ◽  
Junming Zhang ◽  
Manish Anand ◽  
Jared Schwartzentruber ◽  
Justin Seipel
Keyword(s):  
Elastic Element ◽  
Dynamic Properties ◽  
Steel Strip ◽  
Low Cost ◽  
Spring Steel ◽  
Control Series ◽  
Series Elastic Actuators ◽  
Strip Length ◽  
Elastic Elements ◽  
Series Elastic

Recent development of series elastic actuators have revealed a capability to mimic muscle-like properties and achieve accurate force control. Series elastic actuators have also been widely used in humanoid and surgical robotic devices. The design of the elastic elements are critical and complex. This tends to increase costs and complexity of designing and controlling series elastic actuators. Here, we present a novel low cost and easy-to-fabricate design for a series elastic element that also has adjustable stiffness. The design consists of simple shaft couplers and spring steel plates. During the test, the stiffness of the designed elastic elements is very close to linear (R2 = 0.999) when the clamped spring-steel strip length is sufficiently long. As the clamped strip length shortens, the resulting torque deflection curve becomes slightly quadratic but remains largely linear. Also, the designed elastic element exhibits little hysteresis during loading and unloading. The stiffness of the designed elastic element can be tuned to achieve a range of stiffness values, thus it is suitable for different applications with different stiffness requirements. We also design a simple control algorithm and develop a simulation based on the dynamic properties of the designed elastic element. In simulation, the controller is able to accurately track the commanded torque values. Overall, this design could help reduce the cost and development time required for series elastic actuators.

Hopping frequency influences elastic energy reuse with joint series elastic actuators

2021 ◽  
Vol 119 ◽  
pp. 110319
Author(s):  
A. Mohammadi Nejad Rashty ◽  
M. Grimmer ◽  
A. Seyfarth
Keyword(s):  
Elastic Energy ◽  
Series Elastic Actuators ◽  
Series Elastic

scholarly journals Contractile behavior of the gastrocnemius medialis muscle during running in simulated hypogravity

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Charlotte Richter ◽  
Bjoern Braunstein ◽  
Benjamin Staeudle ◽  
Julia Attias ◽  
Alexander Suess ◽  
...  
Keyword(s):  
Elastic Element ◽  
Muscle Wasting ◽  
Space Station ◽  
Vigorous Exercise ◽  
Gastrocnemius Medialis ◽  
Gravitational Forces ◽  
Series Elastic Element ◽  
Applied Loading ◽  
Exercise Countermeasures ◽  
Series Elastic

AbstractVigorous exercise countermeasures in microgravity can largely attenuate muscular degeneration, albeit the extent of applied loading is key for the extent of muscle wasting. Running on the International Space Station is usually performed with maximum loads of 70% body weight (0.7 g). However, it has not been investigated how the reduced musculoskeletal loading affects muscle and series elastic element dynamics, and thereby force and power generation. Therefore, this study examined the effects of running on the vertical treadmill facility, a ground-based analog, at simulated 0.7 g on gastrocnemius medialis contractile behavior. The results reveal that fascicle−series elastic element behavior differs between simulated hypogravity and 1 g running. Whilst shorter peak series elastic element lengths at simulated 0.7 g appear to be the result of lower muscular and gravitational forces acting on it, increased fascicle lengths and decreased velocities could not be anticipated, but may inform the development of optimized running training in hypogravity. However, whether the alterations in contractile behavior precipitate musculoskeletal degeneration warrants further study.

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