scholarly journals Design, Dynamics Analysis, and Real-Time Stiffness Control of a Variable Stiffness Joint

Electronics ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 973
Author(s):  
Yang Yu ◽  
Shimin Wei ◽  
Qiunan Ji ◽  
Zheng Yang
Keyword(s):  
Real Time ◽  
Elastic Deformation ◽  
Simulation Analysis ◽  
Mechanical Design ◽  
Dynamic Stiffness ◽  
Variable Stiffness ◽  
Dynamical Model ◽  
Adjustment Process ◽  
Stiffness Control ◽  
Stiffness Adjustment

This paper proposes a variable stiffness joint based on a symmetrical crank slider mechanism (SCM-VSJ). Firstly, the mechanical design and the working principle of the variable stiffness joint is described, and its stiffness regulation characteristics are studied. Secondly, the dynamical model of variable stiffness joint including joint motor, harmonic reducer and stiffness adjustment motor is established, in addition, the transmission mechanism of the crank slider mechanism and the elastic deformation of the spring bar are considered in the dynamic modeling. Finally, in order to control the dynamic stiffness of the variable stiffness joint in real time, a kind of improved PID (proportional-integral-derivative) control algorithm based on feed-forward and feedback closed-loop is proposed on the basis of the existing dynamical model, and the simulation analysis of real-time tracking control of dynamic stiffness for sinusoidal wave expected stiffness signal and random expected stiffness signal is carried out respectively. The research shows that the real-time stiffness control of SCM-VSJ can be realized effectively, and during the stiffness adjustment process, the output torque of the stiffness adjustment motor will be affected by the elastic deformation of the spring bar.

A new variable stiffness robot joint

2015 ◽  
Vol 42 (4) ◽  
pp. 371-378 ◽  
Author(s):  
Yong Tao ◽  
Tianmiao Wang ◽  
Yunqing Wang ◽  
Long Guo ◽  
Hegen Xiong ◽  
...  
Keyword(s):  
Design Methodology ◽  
Dynamic Stiffness ◽  
Variable Stiffness ◽  
System Behavior ◽  
Pivot Point ◽  
Content Type ◽  
Wide Range ◽  
Variable Stiffness Actuators ◽  
Stiffness Adjustment ◽  
Elastic Elements

Purpose – This study aims to propose a new variable stiffness robot joint (VSR-joint) for operating safely. More and more variable stiffness actuators are being designed and implemented because of their ability to minimize large forces due to shocks, to safely interact with the user and their ability to store and release energy in passive elastic elements. Design/methodology/approach – The design of VSR-joint is compact and integrated highly and the operating is simply. The mechanics, the principle of operation and the model of the VSR-joint are proposed. The principle of operation of VSR-joint is based on a lever arm mechanism with a continuously regulated pivot point. The VSR-joint features a highly dynamic stiffness adjustment along with a mechanically programmable system behavior. This allows an easy adaption to a big variety of tasks. Findings – Preliminary results are presented to demonstrate the fast stiffness regulation response and the wide range of stiffness achieved by the proposed VSR-joint design. Originality/value – In this paper, a new variable stiffness joint is proposed through changing the cantilever arm to change the performance of the elastic element, which is compact, small size and simple adjustment.

scholarly journals 3D Printing Adjustable Stiffness External Fixator for Mechanically Stimulated Healing of Tibial Fractures

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Hongwei Li ◽  
Dichen Li ◽  
Feng Qiao ◽  
Lei Tang ◽  
Qi Han
Keyword(s):  
External Fixator ◽  
Tibial Fracture ◽  
Block Structure ◽  
Dynamic Stiffness ◽  
Healing Process ◽  
Treatment Phase ◽  
Variable Stiffness ◽  
Tibial Fractures ◽  
Patient Specific ◽  
Stiffness Adjustment

External fixation is a long-standing but well-established method, which has been widely used for the treatment of fractures. To obtain the maximum benefit from the mechanical stimulus, the stiffness of the external fixator should be adjusted properly throughout the treatment phase. Nevertheless, the lack of a valid dynamic adjustable fixation device impedes this possibility. Based on the stiffness adjustment tolerance of the healing callus, this paper proposes an active-dynamic stiffness adjustable external fixator design method to meet stiffness requirements at different stages of the tibial fracture healing process. A novel external fixator with an adjustable stiffness configuration was designed, and the finite element method was used to simulate the stress distribution between fixator and fracture gap. The stiffness adjustment tolerance was determined based on previous studies. According to this tolerance, the optimal block structure dismantling sequence was sought and the corresponding stiffness was calculated through topology optimization for the entire external fixator model. The appropriate amount of variable stiffness at the fracture gap was applied by dismantling the configuration of the block structure external fixator during the healing process. A novel patient-specific adjustable stiffness external fixator for mechanically stimulated tibial fracture reduction and therapy was proposed. This enables surgeons to tailor the construction of the external fixator frame to the clinical needs of each patient. The presented dismantling approach of the block structure to produce conformable stiffness provides a new clinical treatment strategy for tibial fractures.

scholarly journals Simultaneous position and stiffness control of a revolute joint using a biphasic media variable stiffness actuator

2019 ◽  
Vol 1 (2) ◽  
pp. 80-97
Author(s):  
Jesus H Lugo
Keyword(s):  
Control Method ◽  
Variable Stiffness ◽  
Industrial Processes ◽  
Revolute Joint ◽  
Additional Information ◽  
Physical Prototype ◽  
Stiffness Control ◽  
Variable Stiffness Actuator ◽  
Control Fluid ◽  
And Control

Safe interactions between humans and robots are needed in several industrial processes and service tasks. Compliance design and control of mechanisms is a way to increase safety. This article presents a compliant revolute joint mechanism using a biphasic media variable stiffness actuator. The actuator has a member configured to transmit motion that is connected to a fluidic circuit, into which a biphasic control fluid circulates. Stiffness is controlled by changing pressure of control fluid into distribution lines. A mathematical model of the actuator is presented, a model-based control method is implemented to track the desired position and stiffness, and equations relating to the dynamics of the mechanism are provided. Results from force loaded and unloaded simulations and experiments with a physical prototype are discussed. The additional information covers a detailed description of the system and its physical implementation.

scholarly journals Equivalent Electronic Circuit of a System of Oscillators Connected With Periodically Variable Stiffness

2022 ◽  
Author(s):  
Soumyajit Seth ◽  
Grzegorz Kudra ◽  
Krzysztof Witkowski ◽  
Jan Awrejcewicz
Keyword(s):  
Mechanical System ◽  
Electronic Circuit ◽  
Mechanical Design ◽  
Variable Stiffness ◽  
State Variables ◽  
Fixed Point Attractor ◽  
Point Attractor ◽  
Magnetic Resistance ◽  
Nonlinear Behaviors ◽  
Resistance Forces

In this paper, we have shown the electronic circuit equivalence of a mechanical system consists of two oscillators coupled with each other. The mechanical design has the effects of the magnetic, resistance forces and the spring constant of the system is periodically varying. We have shown that the system’s state variables, such as the displacements and the velocities, under the effects of different forces, lead to some nonlinear behaviors, like a transition from the fixed point attractor to the chaotic attractor through the periodic and quasi-periodic attractors. We have constructed the equivalent electronic circuit of this mechanical system and have verified the numerically obtained behaviors using the electronic circuit.

Variable stiffness control of series elastic actuated biped locomotion

2018 ◽  
Vol 11 (3) ◽  
pp. 225-235 ◽  
Author(s):  
Jianwen Luo ◽  
Shuguo Wang ◽  
Ye Zhao ◽  
Yili Fu
Keyword(s):  
Variable Stiffness ◽  
Biped Locomotion ◽  
Stiffness Control ◽  
Series Elastic
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