Effect of compliance location in series elastic actuators

Robotica ◽  
2013 ◽  
Vol 31 (8) ◽  
pp. 1313-1318 ◽  
Author(s):  
Jonathon W. Sensinger ◽  
Lawrence E. Burkart ◽  
Gill A. Pratt ◽  
Richard F. ff. Weir
Keyword(s):  
Gear Ratio ◽  
Large Gear ◽  
Class 1 ◽  
In Series ◽  
Ratio Dependent ◽  
Series Elastic Actuators ◽  
Series Elastic ◽  
Instrumentation Design

SUMMARYSeries elastic actuators have beneficial properties for some robot applications. Several recent implementations contain alternative placements of the compliant element to improve instrumentation design. We use a class 1 versus class 2 lever model and energy-port methods to demonstrate in this paper that these alternative placements should still be classified as series elastic actuators. We also note that the compliance of proximal series elastic actuators is reflected by an augmented gear ratio dependent on the nominal gear ratio, which is significant for small gear ratios and approaches unity for large gear ratios. This reflected compliance is shown to differ depending on the sign of the gear ratio. We demonstrate that although the reflected compliance is only marginally influenced by the magnitude of the gear ratio, there are several notable differences, particularly for small gear ratios.

Modeling and Control of Four-bar Mechanism with Series Elastic Actuators

2020 ◽  
Author(s):  
Felipe R. Lopes ◽  
Marco A. Meggiolaro
Keyword(s):  
Human Interaction ◽  
Robotic Manipulation ◽  
Modeling And Control ◽  
Lqr Control ◽  
In Series ◽  
Flexible Behavior ◽  
Series Elastic Actuators ◽  
New Generation ◽  
And Control ◽  
Series Elastic

A new generation of robots that work in cooperation with humans (called collaborative robots) needs some flexibility to adapt to the environment and activities with people. That is why the Series Elastic Actuator (SEA) has been a breakthrough in actuator technologies. The idea of inserting an elastic element in series with a motor allows a lower output impedance, consequently a flexible behavior in the manipulator, in addition to providing torque feedback to better compensate disturbances caused e.g. by friction losses. This article presents a four-bar mechanism with SEA for the purpose of robotic manipulation. Its kinematics and dynamicsare studied, as well as its regulation and trajectory control. The behavior of the decoupled four-bar mechanism and the characteristics of the SEA are also analyzed. Then the regulation control of the complete system is carried out using LQR control. Finally, a circular trajectory is controlled in a simulation to validate the proposed control strategy. The simulation results show the effectiveness of the proposed controller for the mechanism in the presence of SEAs estimating torque and providing the desired compliance for human interaction.

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.

Design of a Parallel Architecture Robotic Spine Exoskeleton With Series Elastic Actuators

2017 ◽  
Author(s):  
Chawin Ophaswongse ◽  
Rosemarie C. Murray ◽  
Sunil K. Agrawal
Keyword(s):  
Degrees Of Freedom ◽  
Human Subjects ◽  
Parallel Architecture ◽  
Six Degrees Of Freedom ◽  
In Series ◽  
Machine Interface ◽  
Position And Orientation ◽  
Human Usage ◽  
Series Elastic Actuators ◽  
Series Elastic

This paper proposes a novel methodology for the design of series elastic actuators in parallel-actuated platforms which have full six degrees-of-freedom in position and orientation. Series elastic actuators can potentially contribute to lower power consumption and provide a better human-machine interface for the user. This is an important consideration in the use of a robotic spine exoskeleton for human subjects, which motivates this work. In the study of parallel-actuated systems with full six degrees-of-freedom, the effect of compliance in series with actuators has not been adequately studied from the perspective of kinematics and wrench capabilities. These analyses are performed in this paper with the goal to improve the design of the robotic spine exoskeleton (ROSE) and its human usage.

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.

STIFFNESS ANALYSIS OF TWO COMPLIANT PIVOTS USED IN SERIES ELASTIC ACTUATORS

2012 ◽  
Vol 36 (3) ◽  
pp. 315-328
Author(s):  
Shusheng Bi ◽  
Tao Qiao ◽  
Hongzhe Zhao ◽  
Jingjun Yu
Keyword(s):  
Mechanical Design ◽  
Design Method ◽  
Special Kind ◽  
Nonlinear Finite Element ◽  
Element Analysis ◽  
Stiffness Analysis ◽  
Leaf Springs ◽  
In Series ◽  
Series Elastic Actuators ◽  
Series Elastic

A compliant pivot used in series elastic actuators (SEAs) can be of great practical use for saving structure space. The analysis of load-deflection behavior for such pivots can provide an analytical mechanical design method. In this paper, two pivots are proposed for the corresponding implementation. Based on the Awtar accurate approximations, the two annulus compliant pivots are further simplified to linear stiffness behavior for the SEAs applications. Specifically, an annulus compliant pivot based on parallel leaf-springs is firstly analyzed. After that, we focus on a special kind of annulus compliant pivot whose degree of constraint (DOC) was released. Finally, the accuracy characteristics of the models are identified by comparing with the results obtained by nonlinear finite element analysis.

scholarly journals Wrench Capability of a Stewart Platform With Series Elastic Actuators

2018 ◽  
Vol 10 (2) ◽  
Author(s):  
Chawin Ophaswongse ◽  
Rosemarie C. Murray ◽  
Sunil K. Agrawal
Keyword(s):  
Degrees Of Freedom ◽  
Stewart Platform ◽  
Six Degrees Of Freedom ◽  
In Series ◽  
Novel Method ◽  
Machine Interface ◽  
Position And Orientation ◽  
Human Usage ◽  
Series Elastic Actuators ◽  
Series Elastic

This paper proposes a novel method for analyzing linear series elastic actuators (SEAs) in a parallel-actuated Stewart platform, which has full six degrees-of-freedom (DOF) in position and orientation. SEAs can potentially provide a better human–machine interface for the user. However, in the study of parallel-actuated systems with full 6DOF, the effect of compliance in series with actuators has not been adequately studied from the perspective of wrench capabilities. We found that some parameters of the springs and the stroke lengths of the linear actuators play a major role in the actuation limits of the system. This is an important consideration when adding SEAs into a Stewart platform or other parallel-actuated robots to improve their human usage.

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