scholarly journals Design and Analysis of a Novel Variable Stiffness Joint for Robot

2018 ◽  
Vol 249 ◽  
pp. 03005
Author(s):  
Xiang Zhang ◽  
Twan Capehart ◽  
Carl A. Moore
Keyword(s):  
High Frequency ◽  
Joint Stiffness ◽  
Variable Stiffness ◽  
Robotic Systems ◽  
Compliant Joint ◽  
Variable Transmission ◽  
Application Requirements ◽  
Base Application ◽  
Robotic Applications ◽  
Human Robotic Interaction

As people pay more attention to the safety of human-robotic interaction, the flexibility of machine joints is becoming more and more important. To address the needs of future robotic applications, many kinds of variable stiffness mechanisms have been designed by scientists. But most of the structures are complex. By studying and comparing many different mechanism designs of variable stiffness joint, we recognize the need to miniaturization and reduce weight of variable stiffness joints with high frequency operation. To address this, need a continuously Variable Compliant Joint (CVCJ) was designed. The core of the joint is based on the structure of the spherical continuously variable transmission (SCVT) which is the catalyst to change the stiffness continuously and smoothly. In this paper, we present a compact variable stiffness joint structure to meet the volume and weight requirements of the future robotic systems. We show the connection between the joint stiffness coefficient and the structure parameters by making mathematical analysis, modelling and simulation for the system to verify the ability to satisfy the base application requirements of the compliant joint.

Variable Transmission Compliance With an MR Damper

Aerospace ◽  
2004 ◽  
Author(s):  
E. R. Westervelt ◽  
J. P. Schmiedeler ◽  
G. Washington
Keyword(s):  
Force Control ◽  
Position Control ◽  
Joint Stiffness ◽  
Mr Damper ◽  
Robotic Systems ◽  
Transmission Design ◽  
Task Requirements ◽  
Variable Transmission ◽  
In Series ◽  
The Magnetic Field

This paper presents a novel transmission design that consists of a parallel combination of an MR damper and a compliant element together acting in series with an actuator. By adjusting the magnetic field to vary the amount of damping, the transmission can be switched between compliant and effectively rigid modes. Transmission compliance between an actuator and its load has several benefits: It enables (1) storage of elastic energy to improve efficiency, (2) filtering of shocks acting on the load that would otherwise be transmitted to the actuator, and (3) facilitation of force control by converting it to a position control problem. Despite these benefits, the design objective for most robotic systems remains to minimize transmission compliance to improve transmission bandwidth, improving the ability to control the position of the load with high precision. With the new transmission presented in this paper, compliance becomes a tunable quantity allowing joint stiffness to be optimized based upon the task requirements.

Variable Stiffness Mechanisms Using Spherical Continuously Variable Transmissions

2015 ◽  
Author(s):  
Twan Capehart ◽  
Carl A. Moore
Keyword(s):  
Real World ◽  
Variable Stiffness ◽  
Rolling Friction ◽  
Vibration Mitigation ◽  
Primary Mechanism ◽  
Continuously Variable Transmissions ◽  
Variable Transmission ◽  
Shock Resistance ◽  
Friction Dynamics ◽  
Robotic Applications

Some robot developers are considering elasticity to provide compliance for better adaption to a changing environment, shock resistance and safer human-robotic interactions (HRI). In this study we simulate a spherical continuously variable transmission (CVT) to validate its ability as the primary mechanism in a variable stiffness device for a 1D robotic hopper. The spherical CVT has been used in many robotic applications including cobots by Peshkin et al. [1] and as the driving unit in the load sensitive mechanism by Tadakuma et al. [2]. A CVT based variable stiffness/damping device intended for vibration mitigation was presented by Little [3]. That paper presented the kinematics and experiments of the CVT based variable stiffness/damping device for the specific application of vibration mitigation. This study considers the dynamics of the CVT based variable stiffness/damping device and modifies the device based on previous studies. We use ADAMS to simulate the modified system because it captures many of the real world dynamics arising from the CVT’s rolling friction dynamics. Finally we present a conceptual design of the variable stiffness CVT and briefly discuss its use in a 1D legged hopper application.

Study on the stiffness property of a variable stiffness joint using a leaf spring

2018 ◽  
Vol 233 (3) ◽  
pp. 1021-1031 ◽  
Author(s):  
Lijin Fang ◽  
Yan Wang
Keyword(s):  
Geometric Nonlinearity ◽  
Large Deflection ◽  
Elliptic Integral ◽  
Joint Stiffness ◽  
Variable Stiffness ◽  
Leaf Spring ◽  
Stiffness Property ◽  
Force Structure ◽  
Leaf Springs ◽  
Application Requirements

Variable stiffness joints designed to ensure physical safety or adjust stiffness actively have attracted much attention in recent years. Springs are used in the internal kinematic structures of variable stiffness joints to achieve the compliance. In this paper, the stiffness property of a variable stiffness joint using a leaf spring is studied on the basis of geometric nonlinearity associated with large deflections of leaf springs. A new end structure is used in the variable stiffness joint to exert the external force on the leaf spring. Based on the elliptic integral solution to large deflection problems of cantilever beams, the effects of different end exertion force structures and geometric nonlinearity of leaf springs on the stiffness property are analyzed when the deflected angle of the joint is larger. It is found that the end exertion force structure and large deflection of leaf springs have a great impact on the changes of the joint stiffness during the joint deflection. A new variable stiffness joint using two leaf springs is proposed to meet different application requirements by changing the end exertion force structure. The experiment of the proposed joint is carried out to verify the validity of the stiffness analysis results.

scholarly journals Development of an Exoskeleton-Type Assist Suit Utilizing Variable Stiffness Control Devices Based on Human Joint Characteristics

Actuators ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 17
Author(s):  
Seigo Kimura ◽  
Ryuji Suzuki ◽  
Katsuki Machida ◽  
Masashi Kashima ◽  
Manabu Okui ◽  
...  
Keyword(s):  
Joint Stiffness ◽  
Knee Extensor ◽  
Artificial Muscle ◽  
Variable Stiffness ◽  
Lower Limbs ◽  
Joint Characteristics ◽  
Standing Up ◽  
Maximum Decrease ◽  
Control Devices ◽  
The Relationship

In this paper, the prototype of the assistive suit for lower limbs was developed. The prototype was based on an assist method with joint stiffness and antagonized angle control. The assist method comprises a system consisting of a pneumatic artificial muscle and a pull spring, which changes the joint stiffness and the antagonized angle to correspond to the movement phase and aims at coordinated motion assistance with the wearer. First, the characteristics of the developed prototype were tested. It was confirmed that the measured value of the prototype followed the target value in the relationship between torque and angle. In addition, there was hysteresis in the measured value, but it did not affect the assist. Next, the evaluation of standing-up and gait assist by measuring electromyography (EMG) of the knee extensor muscle was conducted using the prototype. In all subjects, a decrease in EMG due to the assist was confirmed. In one subject, the maximum decrease rate at the peak of the EMG was about 50% for standing-up motion and about 75% for gait motion. From the results of these assist evaluations, the effectiveness of the assist method based on the joint stiffness and antagonistic angle control using the prototype was confirmed.

A Geometric Parametric Analysis of a Magnetorheological Engine Mount

2010 ◽  
Author(s):  
Walter Anderson ◽  
Constantine Ciocanel ◽  
Mohammad Elahinia
Keyword(s):  
High Frequency ◽  
New Technology ◽  
Low Frequency ◽  
Variable Stiffness ◽  
Small Displacement ◽  
Element Analysis ◽  
Mr Fluid ◽  
Wide Range ◽  
Engine Mount ◽  
Vehicle Technology

Engine vibration has caused a great deal of research for isolation to be performed. Traditionally, isolation was achieved through the use of pure elastomeric (rubber) mounts. However, with advances in vehicle technology, these types of mounts have become inadequate. The inadequacy stems from the vibration profile associated with the engine, i.e. high displacement at low frequency and small displacement at high frequency. Ideal isolation would be achieved through a stiff mount for low frequency and a soft mount for high frequency. This is contradictory to the performance of the elastomeric mounts. Hydraulic mounts were then developed to address this problem. A hydraulic mount has variable stiffness and damping due to the use of a decoupler and an inertia track. However, further advances in vehicle technology have rendered these mounts inadequate as well. Examples of these advances are hybridization (electric and hydraulic) and cylinder on demand (VCM, MDS & ACC). With these technologies, the vibration excitation has a significantly different profile, occurs over a wide range of frequencies, and calls for a new technology that can address this need. Magnetorheological (MR) fluid is a smart material that is able to change viscosity in the presence of a magnetic field. With the use of MR fluid, variable damping and stiffness can be achieved. An MR mount has been developed and tested. The performance of the mount depends on the geometry of the rubber part as well as the behavior of the MR fluid. The rubber top of the mount is the topic of this study due to its major impact on the isolation characteristics of the MR mount. To develop a design methodology to address the isolation needs of different hybrid vehicles, a geometric parametric finite element analysis has been completed and presented in this paper.

A bio-inspired robotic climbing robot to understand kinematic and morphological determinants for an optimal climbing gait

2021 ◽  
Author(s):  
Hendrik Beck ◽  
Johanna J Schultz ◽  
Christofer J Clemente
Keyword(s):  
Optimal Parameter ◽  
Legged Locomotion ◽  
Robotic Systems ◽  
Climbing Robot ◽  
Kinematic Parameters ◽  
Phase Dynamics ◽  
Complex Interactions ◽  
Optimal Dynamic ◽  
Speed Stability ◽  
Robotic Applications

Abstract Robotic systems for complex tasks, such as search and rescue or exploration, are limited for wheeled designs, thus the study of legged locomotion for robotic applications has become increasingly important. To successfully navigate in regions with rough terrain, a robot must not only be able to negotiate obstacles, but also climb steep inclines. Following the principles of biomimetics, we developed a modular bio-inspired climbing robot, named X4, which mimics the lizard’s bauplan including an actuated spine, shoulders, and feet which interlock with the surface via claws. We included the ability to modify gait and hardware parameters and simultaneously collect data with the robot’s sensors on climbed distance, slip occurrence and efficiency. We first explored the speed-stability trade-off and its interaction with limb swing phase dynamics, finding a sigmoidal pattern of limb movement resulted in the greatest distance travelled. By modifying foot orientation, we found two optima for both speed and stability, suggesting multiple stable configurations. We varied spine and limb range of motion, again showing two possible optimum configurations, and finally varied the centre of pro- and retraction on climbing performance, showing an advantage for protracted limbs during the stride. We then stacked optimal regions of performance and show that combining optimal dynamic patterns with either foot angles or ROM configurations have the greatest performance, but further optima stacking resulted in a decrease in performance, suggesting complex interactions between kinematic parameters. The search of optimal parameter configurations might not only be beneficial to improve robotic in-field operations but may also further the study of the locomotive evolution of climbing of animals, like lizards or insects.

Design of a Novel Variable Stiffness Series Elastic Actuator for Extended Linearity

2019 ◽  
Author(s):  
Seung Ho Lee ◽  
Hyeok Jin Lee ◽  
Kyeong Ha Lee ◽  
Ji Min Baek ◽  
Ja Choon Koo
Keyword(s):  
Linear Relationship ◽  
Variable Stiffness ◽  
Linear Series ◽  
Torque Sensor ◽  
Industrial Automation ◽  
Linear Relations ◽  
Series Elastic Actuator ◽  
Robotic Applications ◽  
Adjustable Compliance ◽  
Series Elastic

Abstract Recently, Series Elastic Actuator (SEA) has been popularly used as a torque sensor thanks to its notable ability to calibrate the relation between torque and displacement. It has been applied to many robotic applications and used in a various industrial automation fields. However, most of the current SEAs have nonlinear torque-displacement characteristics which could not be easily alleviated. In order to be utilized as a feasible torque sensor, the wide linearity of a SEA in torque-displacement relationship is not an option. Also, adjustable compliance is needed to implement a mechanism with different stiffness, depending on the various cases where SEA can be applied. In this paper, we designed a Variable Stiffness Linear Series Elastic Actuator (VLSEA) mechanism that can achieve variable stiffness with a linear relationship between torque and displacement. At first, a design with a four-bar link was proposed for linear relations, but it was difficult to implement variable stiffness. We modified the design using the Scotch Yoke mechanisms for the model to have variable stiffness. Simulation of the designed model then verifies that the model can properly implement linearity and variable stiffness.

A Compact 3 Degree of Freedom Spherical Joint

2011 ◽  
Vol 3 (3) ◽  
Author(s):  
Mark L. Guckert ◽  
Michael D. Naish
Keyword(s):  
Control Systems ◽  
Degrees Of Freedom ◽  
Closed Loop ◽  
Degree Of Freedom ◽  
Robotic Systems ◽  
Closed Loop Control ◽  
Spherical Joint ◽  
Experimental Assessment ◽  
Loop Control ◽  
Robotic Applications

Spherical joints have evolved into a critical component of many robotic systems, often used to provide dexterity at the wrist of a manipulator. In this work, a novel 3 degree of freedom spherical joint is proposed, actuated by tendons that run along the surface of the sphere. The joint is mechanically simple and avoids mechanical singularities. The kinematics and mechanics of the joint are modeled and used to develop both open- and closed-loop control systems. Simulated and experimental assessment of the joint performance demonstrates that it can be successfully controlled in 3 degrees of freedom. It is expected that the joint will be a useful option in the development of emerging robotic applications, particularly those requiring miniaturization.

Multilayered Structures for Electro Bonded Laminates

2011 ◽  
Author(s):  
Luigi Di Lillo ◽  
Dario Albino Carnelli ◽  
Andrea Bergamini ◽  
Paolo Ermanni
Keyword(s):  
Electrical Properties ◽  
Experimental Evidence ◽  
High Frequency ◽  
Mechanical Response ◽  
Variable Stiffness ◽  
Electric Properties ◽  
Multilayered Structures ◽  
Electric Model ◽  
Normal Forces ◽  
Insulating Properties

This paper reports on the investigation and optimization of the electric properties of a geometry based variable stiffness concept. The concept relies on the combination of electrostatic normal forces and friction between the layers of a multi-layer beam to develop structures, electro bonded laminates (EBL), with an actively tuneable bending stiffness. Previous studies have detailed the connection between the mechanical response of these system and the electrical properties of its polymer constitutive films. Particularly, they pointed out the need to improve both the dielectric and the insulating properties of these films in order to have an enhancement of the bending tunability range of the system. In this paper a multilayer polymer configuration is considered as a possible answer to this need and it is put forward together with the electric model and the relatively high frequency experimental evidence of the proposed solution.

Sign in / Sign up

Export Citation Format

Share Document