Structural design and stiffness matching control of bionic variable stiffness joint for human–robot collaboration

The physical compliance of interaction is an important requirement for safe and efficient collaboration between robots and humans,and the realization of human–robot compliance requires robot joints with variable stiffness similar to those of human joints.In this study,based on the tissue structure and driving principle of the human arm muscle ligament,a robot joint with variable stiffness is designed,consisting of an elastic belt and serial elastic actuator in parallel.The variable stiffness of the joint is realized by adjusting the tension length of the elastic belt.Surface electromyography(sEMG)signals of the human arm are used as the characterization quantity of joint stiffness to establish the pseudostiffness model of the elbow joint.The stiffness of the robot joints is adjusted in real-time to match the human arm stiffness based on the changes in sEMG signals of the human arm during operation.Real-time compliant interaction of human–robot collaboration is realized based on an end stiffness matching strategy.Additionally,to verify the effectiveness of the human joint stiffness matching-based compliance control strategy,a human–robot cooperative lifting experiment was designed.The bionic variable stiffness joint shows good stiffness adjustment,and the human–robot joint stiffness matching strategy based on human sEMG signals can improve the effectiveness and comfort of human–robot collaboration.

Parametric formulae for axial stiffness of CHS X-joints subjected to brace axial tension

Recent research has shown that circular hollow section(CHS) joints may exhibit non-rigid behavior under axial load or bending. The non-rigid behavior significantly affects the mechanical performance of structures. This paper is concerned with the parametric formulae for predicting axial stiffness of CHS X-joints while braces are in tension. The factors influencing the axial stiffness of CHS X-joints under brace axial tension are investigated,including the joint geometric parameters,the axial force of the chord,and bending moments of braces in two directions,etc. Effects of various parameters on axial stiffness of CHS X-joints are examined by systematic single-parameter nonlinear analysis using shell finite element methods. The analysis is implemented in a finite element code,ANSYS. The observed trends form the basis of the formulae for calculating the joint axial stiffness under brace axial tension by multivariate regression technique. In order to simplify the formulae,two non-dimensional variables are introduced. The proposed formulae can be used to calculate the joint axial stiffness in the design of single-layer steel tubular structures.

Traditional Chinese medicine nursing protocols for knee osteoarthritis

ABSTRACT:Knee osteoarthritis(KOA),a complicated peripheral joint disorder,can be caused by non-modifiable and modifiable risk factors.At present,the treatment for osteoarthritis is mainly to manage symptoms and improve quality of life.Although some patients with osteoarthritis may choose pharmacological agents for pain relief,it has been confirmed that a variety of preparations and doses of pharmacological agents were ineffective.In recent years,Traditional Chinese medicine(TCM)has been shown unique superiorities in the treatment of osteoarthritis,including KOA.Therefore,this article primarily investigated the key points of common syndromes,TCM nursing methods and healthy guidance of KOA,aiming at maintaining and developing the strengths of TCM,improving its efficacy and standardizing its behavior.

Acceleration-Dependent Analysis of Vertical Ball Screw Feed System without Counterweight

The distinguishing feature of a vertical ball screw feed system without counterweight is that the spindle system weight directly acts on the kinematic joints.Research into the dynamic characteristics under acceleration and deceleration is an important step in improving the structural performance of vertical milling machines.The magnitude and direction of the inertial force change significantly when the spindle system accelerates and decelerates.Therefore,the kinematic joint contact stiffness changes under the action of the inertial force and the spindle system weight.Thus,the system transmission stiffness also varies and affects the dynamics.In this study,a variable-coefficient lumped parameter dynamic model that considers the changes in the spindle system weight and the magnitude and direction of the inertial force is established for a ball screw feed system without counterweight.In addition,a calculation method for the system stiffness is provided.Experiments on a vertical ball screw feed system under acceleration and deceleration with different accelerations are also performed to verify the proposed dynamic model.Finally,the influence of the spindle system position,the rated dynamic load of the screw-nut joint,and the screw tension force on the natural frequency of the vertical ball screw feed system under acceleration and deceleration are studied.The results show that the vertical ball screw feed system has obviously different variable dynamics under acceleration and deceleration.The influence of the rated dynamic load and the spindle system position on the natural frequency under acceleration and deceleration is much greater than that of the screw tension force.