Joint Stiffness Parameters Research Articles

Active Vibration Control of a Modular Robot Combining a Back-Propagation Neural Network with a Genetic Algorithm

In this paper, a genetic algorithm based back-propagation neural network suboptimal controller is developed to control the vibration of a nine-degrees-of-freedom modular robot. A finite-element method is used to model the modules of the robot, and the entire system dynamic equation is established using the substructure synthesis method. Then the joint stiffness parameters are identified based on the experimental modal analysis experiment. After modeling the whole structure with the models of the robotic modules and the joint parameters, simulations of the vibration control for the modular robot in several configurations are carried out. It is shown that the control method presented in this paper is effective at suppressing the residual vibrations of the modular robot.

Effects of keyswitch design and finger posture on finger joint kinematics and dynamics during tapping on computer keyswitches

Objective. To examine the effects of postural and keyswitch characteristics on musculoskeletal tissue loading during tapping on computer keyswitches. Design. We hypothesized that joint torques, stiffness and work parameters differ across keyswitch designs and finger postures typical of those observed during computer keyboard typing. We experimentally measured joint kinematics and calculated joint torques while tapping on different keyswitches in different postures, and analyzed the data using mechanical impedance models. Methods. Sixteen human subjects tapped with the index finger on computer keyswitches mounted on a sensor which measured vertical and horizontal forces. Miniature electro-optical goniometers mounted dorsally across each finger joint measured joint kinematics. Joint torques were calculated from endpoint forces and joint kinematics using an inverse dynamics algorithm. A linear spring-damper impedance model was fitted to joint torque, position, and velocity during the contact period of each tap. Subjects tapped in three postures approximating those employed during tapping on three rows of a computer keyboard, on four different keyswitches, resulting in 12 conditions. Results. More extended finger posture was associated with greater joint torques, energies, and stiffnesses, despite minimal differences in endpoint forces across posture. Greater keyswitch make forces were associated with increased forces, joint torques and joint stiffnesses, however this relationship was not monotonic. Conclusions. Joint torques and stiffness parameters differed across keyswitch designs and finger postures. Estimates of joint impedance and work provided a unique perspective into finger dynamics. Relevance Determining the causes of work-related musculoskeletal disorders is facilitated by characterizing workplace task biomechanics, which can be linked to specific injury mechanisms.

Increased musculoskeletal stiffness during load carriage at increasing walking speeds maintains constant vertical excursion of the body center of mass

The primary objective of this research was to determine changes in body and joint stiffness parameters and kinematics of the knee and body center of mass (COM), that result from wearing a backpack (BP) with a 40% body weight load at increasing speeds of walking. It was hypothesized that there would be speed and load-related increases in stiffness that would prevent significant deviations in the COM trajectory and in lower-extremity joint angles. Three independent biomechanical models employing kinematic data were used to estimate global lower-extremity stiffness, vertical stiffness and knee joint rotational stiffness in the sagittal plane during walking on a treadmill at speeds of 0.6–1.6 m s −1 in 0.2 m s −1 increments in BP and no backpack conditions. Kinematic data were collected using an Optotrak, three-dimensional motion analysis system. Knee angles and vertical excursion of the COM during the compression (loading phase) increased as a function of speed but not load. All three estimates of stiffness showed significant increases as a function of both speed and load. Significant interaction effects indicated a convergence of load-related stiffness values at lower speeds. Results suggested that increases in muscle-mediated stiffness are used to maintain a constant vertical excursion of the COM under load across the speeds tested, and thereby limit increases in metabolic cost that would occur if the COM would travel through greater vertical range of motion.

914 ニューラルネットワークを用いた結合部の設計パラメータ推定法 : 部材 2 本からなる結合部

In this paper, the method, which estimates the design parameters (thickness, shape of cross section, length of partition, position of flange etc.) using neural network, is described. We deal with simple joined part models composed of 2 beams as an antomobile body structure. At first, some learning data are prepared by changing the design parameters. Next, the relation between joint stiffness and design parameter is constructed by using neural network. Once the trained neural network is given, the design parameter can be estimated by only inputting the some values of joint stiffness into the trained neural network. It was shown that the design parameters were obtained from the values of joint stiffness by using the trained neural network.

00/01289 Method and catalysts for the preparation of di-tertiary amines by the aminomethylation of nonconjugated dienes with synthesis gas and secondary amines

This paper presents an effecient method of modelling faulted rock using the multiregion boundary element method. The boundary element method is ideally suited for modelling problems in rock mechanics because of the requirement to descretize surfaces only. This contrasts with the volume discretization needed for the finite element method, finite difference method and the distinct element method. The disadvantage of the boundary element method is that the rock mass is assumed to be isotropic and elastic. However, it is possible to model the non-linear behaviour on fault planes by using the concept of multiple regions and by connecting these regions via non-linear springs or Goodman type joint elements. The disadvantage of this method has been that joint stiffnesses have to be specified and that a great number of iterations are needed because the stiffness coefficient of a spring may change very rapidly from a very high value (for example when a joint is in compression) to a very low value (when a joint is in tension). This paper describes a novel method for the treatment of faults with the boundary element method which eliminates the need to specify joint stiffness parameters and which is able to model signi fault movement with very few iterations. The numerical scheme makes very effecient use of computer resources because the non-linear iterations only involve degrees of freedom at the interfaces. Examples of applications of the new model to practical problems in mining and geological engineering are given.

Analysis of No. 50 Taper Joint Stiffness Under Axial and Radial Loading

This paper is concerned with the joint stiffness characteristics of the standard 7/24 taper interface. Experimental identification of joint stiffness parameters is performed on No. 50 tapers, using a special test setup, by implementing a frequency response function (FRF) based method for joint parameter identification, in conjunction with finite element modeling of the substructure. The effects of axial and radial loading as well as taper wear on the taper joint stiffness are examined. It is shown that taper joint stiffness nonuniformly increases with axial preloading and decreases with radial loading. Validation of the identified stiffness values is given by comparing the predicted natural frequencies of the taper assembly with experimentally measured values.

Efficient numerical modelling of faulted rock using the boundary element method

This paper presents an effecient method of modelling faulted rock using the multiregion boundary element method. The boundary element method is ideally suited for modelling problems in rock mechanics because of the requirement to descretize surfaces only. This contrasts with the volume discretization needed for the finite element method, finite difference method and the distinct element method. The disadvantage of the boundary element method is that the rock mass is assumed to be isotropic and elastic. However, it is possible to model the non-linear behaviour on fault planes by using the concept of multiple regions and by connecting these regions via non-linear springs or Goodman type joint elements. The disadvantage of this method has been that joint stiffnesses have to be specified and that a great number of iterations are needed because the stiffness coefficient of a spring may change very rapidly from a very high value (for example when a joint is in compression) to a very low value (when a joint is in tension). This paper describes a novel method for the treatment of faults with the boundary element method which eliminates the need to specify joint stiffness parameters and which is able to model signi fault movement with very few iterations. The numerical scheme makes very effecient use of computer resources because the non-linear iterations only involve degrees of freedom at the interfaces. Examples of applications of the new model to practical problems in mining and geological engineering are given.

The control of hand equilibrium trajectories in multi-joint arm movements.

According to the equilibrium trajectory hypothesis, multi-joint arm movements are achieved by gradually shifting the hand equilibrium positions defined by the neuromuscular activity. The magnitude of the force exerted on the arm, at any time, depends on the difference between the actual and equilibrium hand positions and the stiffness and viscosity about the equilibrium position. The purpose of this paper is to test the validity and implications of this hypothesis in the context of reaching movements. A mathematical description of the behavior of an arm tracking the equilibrium trajectory was developed and implemented in computer simulations. The joint stiffness parameters used in these simulations were derived from experimentally measured static stiffness values. The kinematic features of hand equilibrium trajectories which were derived from measured planar horizontal movements gave rise to the suggestion that the generation of reaching movements involves explicit planning of spatially and temporally invariant hand equilibrium trajectories. This hypothesis was tested by simulating actual arm movements based on hypothetical equilibrium trajectories. The success of the predicted behavior in capturing both the qualitative features and the quantitative kinematic details of the measured movements supports the equilibrium trajectory hypothesis. The control strategy suggested here may allow the motor system to avoid some of the complicated computational problems associated with multi-joint arm movements.

Objective measurement of joint stiffness in rheumatoid arthritis.

SummaryA brief description of a method for measurement of joint stiffness originally described by Wright and Johns is given. We have used this method with slight modifications in studying joint stiffness in normal cases and in patients with rheumatoid arthritis. Morning stiffness and its relation to grip power and pinching has been studied and the effect of temperature changes and synovectomy is illustrated. A comparison between objective and subjective joint stiffness is made with special reference to the use of the Lansbury systemic index as a disease activity parameter in rheumatoid arthritis. The relation between joint stiffness and other disease activity parameters in rheumatoid arthritis is discussed.We have found this method for objective measurement of joint stiffness to be useful in the clinical assessment of patients with rheumatoid arthritis in Steinbrocker Stages I and II. In more advanced stages anatomical damage of the metacarpophalangeal joint usually makes it difficult to get reproduceable...