Joint Structural Parameters Research Articles

The biomechanical influence of facet joint parameters on corresponding segment in the lumbar spine: a new visualization method

Facet joints have been discussed as influential factors in the development of lumbar degeneration, which includes disc herniation and degenerative lumbar spondylolisthesis. Facet orientation (FO) and facet tropism (FT) are two important structural parameters of the lumbar facet joints. Many previous studies have focused on single parameter analysis of the lumbar spine. Owing to the correlation between independent variables, single-factor analysis cannot reflect the interaction between variables; however, there has been no corresponding biomechanical method developed to address this problem. To investigate the complex biomechanical influences on the lumbar spine when vertebral FO and FT are varied using finite element analysis (FEA) and contour maps visualization, and analyze the biomechanical role of facet joint structural parameters in the process of lumbar degenerative diseases. A biomechanical modelling, analysis, and verification study was performed. A three-dimensional non-linear FEA model of 3 denucleated intervertebral discs (L2-3, L3-4, L4-5) with adjacent vertebral bodies (L2-L5) was created. Previously performed in vitro experiments provided experimental data for the range of motion in each load direction that was used for calibration. For 12 lumbar models, different facet joint angles relative to the sagittal plane at both L3-4 facet joints were simulated for 35°≤FO≤50° and 0°≤FT≤15°. By modifying different values of FO and FT, FEA simulation of different lumbar spine models was performed. Contour maps were used to visualize the FO- and FT-relevant data. Under flexion, extension, and torsion moments, facet joint contact force and intradiscal stress increased with increasing FT. In the condition where FT remained 0° and increasing FO values, facet joint contact force and intradiscal stress remained low with no apparent increasing or decreasing trend when the model was under flexion, extension, and torsion moments. In the condition where FO and the FT values were varied at the same time, the highest force and stress regions in the contour maps were observed when all three types of moments were applied. Stress distributions of the L3-4 disc with different FT and FO values showed disc stress increased significantly with increases of FT and was concentrated on the ipsilateral region of the facet joint with the more sagittal orientation. The combination of FO and FT has an important impact on the corresponding disc and facet joints, but FT played a more significant role. Moreover, disc stress was concentrated on the ipsilateral region of facet joint with greater sagittal orientation when FT existed. FT with high sagittal orientation may increase risk of recurrent LDH due to increase ipsilateral disc pressure. These biomechanical findings may help clinicians to understand the prognosis of some lumbar degenerative conditions.

Ultra-lightweight space arm DELIAN: mechatronic analysis and joint control design

This paper deals with the design of the control system for a joint prototype of ESA space manipulator DELIAN. A joint model is developed, focusing on assessment of joint structural parameters and most important torque disturbances, mainly related to dependence of friction on velocity, position and temperature. Then, analysis and design of the P/PI controller are carried out, giving stability conditions, and proposing an optimal tuning for velocity and position loops, with respect to setpoint tracking and disturbance rejection requirements.

Study on the Error Transfer of Articulated Arm Coordinate Measuring Machines

The articulated arm coordinate measuring machine (AACMM) is a new type coordinate measuring machine (CMM) base on the linkage structure. The kinematic model of a 6-DOF AACMM with DH method was established, and from the kinematic model the coordinate systems and joint structural parameters of the AACMM are obtained. The Jacobian matrix was deduced by differential transformation from the kinematic model of the AACMM, and according to the Jacobian matrix, the error transfer coefficients of the joint structural parameters were calculated. Then with the calculation results the influence of the joint structural parameters on the measuring accuracy of the AACMM was analyzed, which provides a theoretical basis for calibration, tolerance distribution of the joint parts and components' selection of the AACMM. DOI: http://dx.doi.org/10.11591/telkomnika.v11i2.1987

An identification method for joint structural parameters using an FRF-based substructuring method and an optimization technique

A new method is proposed to identify the joint structural parameters of complex systems using a frequency response function (FRF)-based substructuring method and an optimization technique. The FRF method is used to estimate the joint parameters indirectly by minimizing the difference between the reference and calculated responses using a gradient-based optimization technique with analytical gradient information. To assess the robustness of the identification method with respect to noisy input data, FRFs contaminated by uniformly distributed random noise were tested in a numerical example. The effects of the random noise and the magnitude of the connection stiffness values on the accuracy of the method were investigated while identifying the joint parameters. When the FRFs were contaminated with random noise, the proposed procedure performed well when used to identify the stiffness values, but the accuracy of identification is deteriorative when used to identify the damping coefficients. The joint parameters of a real bolted structure were also identified by the proposed method. The results show that it can be applied successfully to real structures, and that a hybrid approach using both calculated and measured FRFs in the substructure model can enhance the quality of the identification results.

Joint structural parameter identification using a subset of frequency response function measurements

The dynamic characteristics of a structure composed of substructures are affected considerably by the properties of the joints. To conduct an accurate dynamic analysis it is first necessary to model the joints accurately. Their structural parameters can then be identified from experiments. This paper proposes a method of identifying joint structural parameters using subset frequency response function (FRF) measurements. For the most part, it is impractical to obtain all the FRFs since the responses at joint related degrees of freedom (dofs) are difficult to measure correctly. Thus, the unmeasured FRFs are estimated from measured FRFs and the joint excluded structure analytical model. Then, assuming a model of joint, the joint structural parameters are extracted from partly measured and partly estimated FRFs. To avoid the influence of measured noise, the output error method is used in an iterative way. The validity and feasibility of the proposed method are demonstrated both numerically and experimentally. The results show that joint structural parameters can be identified accurately even when the measurements are contaminated by noise. Thus, this method can be applied to real structures usually having rotational and inaccessible dofs.

Identification of linearised joint structural parameters by combined use of measured and computed frequency responses

The necessity of accurate prediction of structural dynamics has led to extensive studies on identification of joint structural parameters. The present paper proposes an effective identification scheme for linearised joint parameters of a structure, which makes use of not only the measured frequency response functions (FRFs) of the structure but also the computed FRFs of an auxiliary model. The auxiliary model is constructed such that it possesses the same properties as the test structure except the joint structural parameters to be determined. The fundamental assumption is that the dynamic properties of the structure other than the joint parameters to be identified are completely known. The proposed identification scheme is straighforward and cost-effective, requiring neither modal parameters nor any condensation techniques for the model.

Identification of the Joint Structural Parameters of Machine Tool by DDS and FEM

A unique methodology is proposed to identify the joint structural parameters of the machine tool by combining the Dynamic Data System (DDS) methodology with the Finite Element Method (FEM). The structural parameter identification of a simple system with complete modal matrix is introduced together with the modal analysis by the DDS method. The simulation study of a two degree-of-freedom system shows the high accuracy of the identification procedure. The identification of joint parameters of a general system with an incomplete mode shape is analyzed next. The condensation and digital filtering techniques are developed for this purpose. In a shaft model experiment the joint parameters are identified when the response data at boundary points are difficult to be measured. Furthermore, a column model experiment revealed the ability of the proposed identification technique to deal with a large number degree-of-freedom system.