Structure Optimization of Wheel Force Transducer Based on Natural Frequency and Comprehensive Sensitivity

The current research of wheel force transducer （WFT） mainly focuses on test signal processing and decoupling methods based on signal itself, while the WFT structure optimization research related to decreasing the mass and increase the natural frequency and comprehen- sive sensitivity is not enough. In order to improve the WFT test accuracy, a structure optimization method based on natural frequency and comprehensive sensitivity indicators is put forward. The WPT with 8-beam elastic body is used for the finite element modeling （FEM）, in which the fol- lowing variations are taken into consideration： the con- nection type of elastic body with modified rim, the number of connection holes, and the respects of strain beam including the shape, the cross sectional area and the length, etc.. The test results shows that the natural frequency of the connecting block type is increased by 65.5% compared with the connecting seat type of elastic body ＆ modified rim, and the main channel sensitivity is improved as well. The results show that the connecting block type will achieve the best comprehensive performance when the number of connecting holes between the elastic body and the modified rim is 20. And the thinner and longer strain beam with smaller cross section area is preferable within the scope of elastic body mechanical strength. This research proposes a novel structure optimization method for WFT which contributes to improve the measurement performance of WFT.

OPTIMAL DESIGN OF A 6-AXIS FORCE TRANSDUCER BASED ON STEWART PLATFORM RELATED TO SENSITIVITY ISOTROPY

The design method of a 6-axis force robot's transducer based on the Stewartplatform is detailed. For this purpose, the sensitivity isotropy evaluation criteria of thetransducer are defined, and by the aid of computer, the relationships between the criteria and theparameters of all the transducers based on the Stewart platform are investigated within thegeometric model of the solution space, which can provide the theoretical background for the optimalconstruction design of the 6-axis force transducer related to the sensitivity isotropy.

Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology

Inside the second experimental wave energy converter (WEC) launched at the Lysekil research site on the Swedish west coast in March 2009 a number of sensor systems were installed for measuring the mechanical performance of the WEC and its mechanical subsystems. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Two measurement periods, separated by 2.5 month, are presented in this paper. One measurement is made two weeks after launch and another 3 months after launch. Comparisons and correlations are made between different sensors measuring simultaneously. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period. Vibration frequencies due to wear are recognized by comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is a sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.

DETERMINATION OF QUADRICEPS FORCES IN SQUAT AND ITS APPLICATION IN CONTACT PRESSURE ANALYSIS OF KNEE JOINT

While the quadriceps muscles of human body are quite important to the daily ac-tivities of knee joints,the determination of quadriceps forces poses significant challenges since it cannot be measured in vivo.Here,a novel approach is presented to obtain the forces in squat through the combination of motion photography,force transducers measuring,multi-rigid-body theory and finite element analysis.Firstly,the geometrical and angular data of human for squat process were obtained through the analysis of photographed pictures for human squat with cam-era.At the same time,force transducers were used to measure the reaction forces from feet and to determine the center of gravity for identical squat process.Next,based on the multi-rigid-body dynamics,a mathematical model for human right leg and foot was established in order to determine the quadriceps torques under different squat angles.Then,so as to determine the quadriceps forces along with varied squat angles,a simplified three-dimensional finite element model was built,including tibia,fibula,patella,patella ligament and quadriceps tendon.Finally,the contact pressure of knee joint was analyzed for the squat with the established model of knee joint involving the obtained quadriceps forces from finite element analysis.And it showed that in the 0-90 degree squat process,the peak value of contact pressure of articular cartilages and menisci is increased with the increased squat angle.This study can be referenced for further un-derstanding of the biomechanical behaviors of knee,contact pressure effects of daily activities on knee,and is significantly instructive for sports rehabilitation.