Optimal Design of a Micro Series Elastic Actuator

2010 ◽  
Author(s):  
Ozan Tokatli ◽  
Volkan Patoglu
Keyword(s):  
Optimal Design ◽  
Force Control ◽  
Pareto Front ◽  
Position Control ◽  
Compliant Mechanism ◽  
Tracking Error ◽  
Movement Direction ◽  
Design Criteria ◽  
Coupling Element ◽  
Series Elastic

We propose using series elastic actuation (SEA) in micro mechanical devices to achieve precise control of the interaction forces. Using μSEA for force control removes the need for high-precision force sensors/actuators and allows for accurate force control through simple position control of the deflection of a compliant coupling element. Since the performance of a μSEA is highly dependent on the design of this compliant coupling element, we employ a design optimization framework to design this element. In particular, we propose a compliant, under-actuated half-pantograph mechanism as a feasible kinematic structure for this coupling element. Then, we consider multiple design objectives to optimize the performance of this compliant mechanism through dimensional synthesis, formulating an optimization problem to study the trade-offs between these design criteria. We optimize the directional manipulability of the mechanism, simultaneously with its task space stiffness, using a Pareto-front based framework. We select an optimal design by studying solutions on the Pareto-front curve and considering the linearity of the stiffness along the actuation direction as a secondary design criteria. The optimized mechanism possesses high manipulability and low stiffness along the movement direction of the actuator; hence, achieves a large stroke with high force resolution. At the same time, the mechanism has low manipulability and high stiffness along the direction perpendicular to the actuator motion, ensuring good disturbance rejection characteristics. We model the behavior of this compliant mechanism and utilize this model to synthesize a controller for μSEA to study its dynamic response. Simulated closed loop performance of the μSEA with optimized coupling element indicates that force references can be tracked without significant overshoot and with low tracking error (about 1.1%) even for periodic reference signals.

Many-Objective Optimal Design of Sliding Mode Controls

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Yousef Sardahi ◽  
Jian-Qiao Sun
Keyword(s):  
Optimal Design ◽  
Pareto Front ◽  
Sliding Mode ◽  
Design Method ◽  
Tracking Error ◽  
Control Design ◽  
Processing Algorithm ◽  
Order System ◽  
Post Processing ◽  
Control Effort

This paper presents a many-objective optimal (MOO) control design of an adaptive and robust sliding mode control (SMC). A second-order system is used as an example to demonstrate the design method. The robustness of the closed-loop system in terms of stability and disturbance rejection are explicitly considered in the optimal design, in addition to the typical time-domain performance specifications such as the rise time, tracking error, and control effort. The genetic algorithm is used to solve for the many-objective optimization problem (MOOP). The optimal solutions known as the Pareto set and the corresponding objective functions known as the Pareto front are presented. To assist the decision-maker to choose from the solution set, we present a post-processing algorithm that operates on the Pareto front. Numerical simulations show that the proposed many-objective optimal control design and the post-processing algorithm are promising.

Design and Measurement Error Analysis of a Low-Friction, Lightweight Linear Series Elastic Actuator

2013 ◽  
Author(s):  
Bryce Lee ◽  
Viktor Orekhov ◽  
Derek Lahr ◽  
Dennis Hong
Keyword(s):  
Measurement Error ◽  
Error Analysis ◽  
Measurement Errors ◽  
Position Control ◽  
Force Measurement ◽  
Compliant Mechanism ◽  
Load Cell ◽  
Low Friction ◽  
Linear Guide ◽  
Series Elastic

Series elastic actuators (SEAs) have many benefits for force controlled robotic applications. Placing an elastic member in series with a rigid actuator output enables more-stable force control and the potential for energy storage while sacrificing position control bandwidth. This paper presents the design and measurement error analysis of a low-friction, lightweight linear SEA used in the Shipboard Autonomous Fire Fighting Robot (SAFFiR). The SAFFiR SEA pairs a stand-alone linear actuator with a configurable compliant member. Unlike most electric linear actuators, this actuator does not use a linear guide, which reduces friction and weight. Unlike other SEAs which measure the force by measuring the spring deflection, a tension and compression load cell is integrated into the design for accurate force measurements. The configurable compliant member is a titanium cantilever with manually adjustable length. The final SEA weighs 0.82[kg] with a maximum force of 1,000[N]. The configurable compliant mechanism has in a spring constant range of 145–512[kN/m]. Having no linear guide and incorporating the load cell into the universal joint both introduce measurement errors. The length error across a parallel ankle joint is less than 0.015[mm] and the force measurement error is less than 0.25% of the actual force. Finally, several changes are suggested for the next iteration of the SEA to improve its usability on future robots.

scholarly journals Field-based optimal-design of an electric motor: a new sensitivity formulation

Open Physics ◽  
2017 ◽  
Vol 15 (1) ◽  
pp. 924-928 ◽  
Author(s):  
Paolo Di Barba ◽  
Maria Evelina Mognaschi ◽  
David Alister Lowther ◽  
Sławomir Wiak
Keyword(s):  
Optimal Design ◽  
Electric Motor ◽  
Pareto Front ◽  
Switched Reluctance Motor ◽  
Design Criteria ◽  
New Approach ◽  
Switched Reluctance ◽  
Reluctance Motor ◽  
Robust Optimal Design

AbstractIn this paper, a new approach to robust optimal design is proposed. The idea is to consider the sensitivity by means of two auxiliary criteria A and D, related to the magnitude and isotropy of the sensitivity, respectively. The optimal design of a switched-reluctance motor is considered as a case study: since the case study exhibits two design criteria, the relevant Pareto front is approximated by means of evolutionary computing.

Multi-objective optimal design of flexible-joint parallel robot

2018 ◽  
Vol 35 (8) ◽  
pp. 2775-2801 ◽  
Author(s):  
Fabian Andres Lara-Molina ◽  
Didier Dumur ◽  
Karina Assolari Takano
Keyword(s):  
Optimal Design ◽  
Position Control ◽  
Structural Parameters ◽  
Design Procedure ◽  
Parallel Robot ◽  
Performance Criteria ◽  
Design Criteria ◽  
Flexible Joints ◽  
Content Type ◽  
Multi Objective

Purpose This paper aims to present the optimal design procedure of a symmetrical 2-DOF parallel planar robot with flexible joints by considering several performance criteria based on the workspace size, dynamic dexterity and energy of the control. Design/methodology/approach Consequently, the optimal design consists in determining the dimensional parameters to maximize the size of the workspace, maximize the dynamic dexterity and minimize the energy of the control action. The design criteria are derived from the kinematics, dynamics, elastodynamics and the position control law of the robot. The analysis of the design criteria is performed by means of the design space and atlases. Findings Finally, the multi-objective design optimization derived from the optimal design procedure is solved by using multi-objective genetic algorithms, and the results are analyzed to assess the validity of the proposed approach. Originality/value An alternative approach to the design of a planar parallel robot with flexible joints that permits determining the structural parameters by considering kinematic, dynamic and control operational performance.

scholarly journals A Sliding Mode Force and Position Controller Synthesis for Series Elastic Actuators

Robotica ◽  
2019 ◽  
Vol 38 (1) ◽  
pp. 15-28 ◽  
Author(s):  
Emre Sariyildiz ◽  
Rahim Mutlu ◽  
Haoyong Yu
Keyword(s):  
Force Control ◽  
Dynamic Models ◽  
Position Control ◽  
Sliding Mode ◽  
Dynamic Environment ◽  
Industrial Robots ◽  
Motion Controller ◽  
Mismatched Disturbances ◽  
Series Elastic Actuators ◽  
Series Elastic

SummaryThis paper deals with the robust force and position control problems of series elastic actuators (SEAs). It is shown that an SEA’s force control problem can be described by a second-order dynamic model which suffers from only matched disturbances. However, the position control dynamics of an SEA is of fourth order and includes matched and mismatched disturbances. In other words, an SEA’s position control is more complicated than its force control, particularly when disturbances are considered. A novel robust motion controller is proposed for SEAs by using disturbance observer (DOb) and sliding mode control. When the proposed robust motion controller is implemented, an SEA can precisely track desired trajectories and safely contact with an unknown and dynamic environment. The proposed motion controller does not require precise dynamic models of environments and SEAs. Therefore, it can be applied to many different advanced robotic systems such as compliant humanoids, industrial robots and exoskeletons. The validity of the proposed motion controller is experimentally verified.

Non-Overshooting Force Control of Series Elastic Actuators

2010 ◽  
Vol 166-167 ◽  
pp. 421-426
Author(s):  
Ozan Tokatli ◽  
Volkan Patoglu
Keyword(s):  
Force Control ◽  
Position Control ◽  
Force Sensor ◽  
Force Sensors ◽  
Element Orders ◽  
Interaction Forces ◽  
Controlled Systems ◽  
Important Challenge ◽  
Mechanical Devices ◽  
Series Elastic

Whenever mechanical devices are used to interact with the environment, accurate control of the forces occurring at the interaction surfaces arises as an important challenge. Traditionally, force controlled systems utilize stiff force sensors in the feedback loop to measure and regulate the interaction forces. Series elastic actuation (SEA) is an alternative approach to force control, in which the deflection of a compliant element (orders of magnitude less stiff than a typical force sensor) placed between motor and the environment is controlled to regulate the interaction forces. The use of SEAs for force control is advantageous, since this approach possesses inherent robustness without the need for high-precision force sensors/actuators and allows for the accurate control of the force exerted by the actuator through position control of the deflection of a compliant coupling element. Here, a non-overshooting force controller is proposed to be embedded into the control structure of SEAs. Such controller architecture ensures safe operations of SAEs by making sure that the force applied to the environment are always bounded from above by the reference forces commanded to the controller.

Exploiting the instability of eccentric tube robots for distal force control in minimally invasive cardiac ablation

2021 ◽  
pp. 095440622110075
Author(s):  
Hessa Alfalahi ◽  
Federico Renda ◽  
Conor Messer ◽  
Cesare Stefanini
Keyword(s):  
Minimally Invasive ◽  
Force Control ◽  
Motion Tracking ◽  
Heart Surgery ◽  
Compliant Mechanism ◽  
Heart Rhythm ◽  
Disease Recurrence ◽  
Optimal Level ◽  
Design Parameters ◽  
Cardiac Ablation

While the dilemma of motion tracking and force control in beating-heart surgery is previously addressed using active control architectures and rigid robotic actuators, this work leverages the highly controllable mechanical properties of concentric tube robots for intelligent, design-based force control in minimally invasive cardiac ablation. Briefly, cardiac ablation is the conventional procedure for treating arrhythmia patients, by which exposing the diseased cardiac tissue to Radio-Frequency (RF) energy restores the normal heart rhythm. Yet, the procedure suffers low success rate due to the inability of existing flexible catheters to maintain a consistent, optimal contact force between the tip electrode and the tissue, imposing the need for future repeat surgeries upon disease recurrence. The novelty of our work lies in the development of a statically-balanced compliant mechanism composed of (1) distal bi-stable concentric tubes and (2) a compliant, torsional spring mechanism that provides torque at tubes proximal extremity, resulting in an energy-free catheter with a zero-stiffness tip. This catheter is expected to maintain surgical efficacy and safety despite the chaotic displacement of the heart, by naturally keeping the tip force at an optimal level, not less and not more than the surgical requirement. The presented experimental results of the physical prototype, reflect the feasibility of the proposed design, as well as the robustness of the formulated catheter mathematical models which were uniquely deployed in the selection of the optimal design parameters.

scholarly journals Neural Network Based Contact Force Control Algorithm for Walking Robots

Sensors ◽  
2021 ◽  
Vol 21 (1) ◽  
pp. 287
Author(s):  
Byeongjin Kim ◽  
Soohyun Kim
Keyword(s):  
Neural Network ◽  
Contact Force ◽  
Force Control ◽  
Control Algorithm ◽  
Position Control ◽  
Linear Quadratic Regulator ◽  
Walking Robots ◽  
Test Model ◽  
Linear Quadratic ◽  
Contact Force Control

Walking algorithms using push-off improve moving efficiency and disturbance rejection performance. However, the algorithm based on classical contact force control requires an exact model or a Force/Torque sensor. This paper proposes a novel contact force control algorithm based on neural networks. The proposed model is adapted to a linear quadratic regulator for position control and balance. The results demonstrate that this neural network-based model can accurately generate force and effectively reduce errors without requiring a sensor. The effectiveness of the algorithm is assessed with the realistic test model. Compared to the Jacobian-based calculation, our algorithm significantly improves the accuracy of the force control. One step simulation was used to analyze the robustness of the algorithm. In summary, this walking control algorithm generates a push-off force with precision and enables it to reject disturbance rapidly.

scholarly journals Fractional-Order PII1/2DD1/2 Control: Theoretical Aspects and Application to a Mechatronic Axis

2021 ◽  
Vol 11 (8) ◽  
pp. 3631
Author(s):  
Luca Bruzzone ◽  
Mario Baggetta ◽  
Pietro Fanghella
Keyword(s):  
Fractional Order ◽  
Position Control ◽  
Tracking Error ◽  
Experimental Tests ◽  
Maximum Torque ◽  
Control Effort ◽  
Tuning Method ◽  
Alternative Approach ◽  
Remarkable Reduction ◽  
Distributed Order

Fractional Calculus is usually applied to control systems by means of the well-known PIlDm scheme, which adopts integral and derivative components of non-integer orders λ and µ. An alternative approach is to add equally distributed fractional-order terms to the PID scheme instead of replacing the integer-order terms (Distributed Order PID, DOPID). This work analyzes the properties of the DOPID scheme with five terms, that is the PII1/2DD1/2 (the half-integral and the half-derivative components are added to the classical PID). The frequency domain responses of the PID, PIlDm and PII1/2DD1/2 controllers are compared, then stability features of the PII1/2DD1/2 controller are discussed. A Bode plot-based tuning method for the PII1/2DD1/2 controller is proposed and then applied to the position control of a mechatronic axis. The closed-loop behaviours of PID and PII1/2DD1/2 are compared by simulation and by experimental tests. The results show that the PII1/2DD1/2 scheme with the proposed tuning criterium allows remarkable reduction in the position error with respect to the PID, with a similar control effort and maximum torque. For the considered mechatronic axis and trapezoidal speed law, the reduction in maximum tracking error is −71% and the reduction in mean tracking error is −77%, in correspondence to a limited increase in maximum torque (+5%) and in control effort (+4%).

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