Unloaded Motion Research Articles

VARIATION OF THE ANKLE MOTION WITH THE PIVOT-POINT POSITION AS PREDICTED BY A SPHERICAL MODEL OF THE JOINT

Recent studies proved that the ankle unloaded motion is nearly spherical and can be accurately modeled by one degree-of-freedom spatial spherical mechanisms. Starting from relevant experimental data measured on nine specimens, the global optimal pivot-point (PP) position, i.e., the center of this spherical motion, is obtained in this study and the effect on ankle motion of the changing position of this PP is analyzed.

A three-dimensional ankle kinetostatic model to simulate loaded and unloaded joint motion.

A kinetostatic model able to replicate both the natural unloaded motion of the tibiotalar (or ankle) joint and the joint behavior under external loads is presented. The model is developed as the second step of a sequential procedure, which allows the definition of a kinetostatic model as a generalization of a kinematic model of the joint defined at the first step. Specifically, this kinematic model taken as the starting point of the definition procedure is a parallel spatial mechanism which replicates the ankle unloaded motion. It features two rigid bodies (representing the tibia-fibula and the talus-calcaneus complexes) interconnected by five rigid binary links, that mimic three articular contacts and two nearly isometric fibers (IFs) of the tibiocalcaneal ligament (TiCaL) and calcaneofibular ligament (CaFiL). In the kinetostatic model, the five links are considered as compliant; moreover, further elastic structures are added to represent all the main ankle passive structures of the joint. Thanks to this definition procedure, the kinetostatic model still replicates the ankle unloaded motion with the same accuracy as the kinematic model. In addition, the model can replicate the behavior of the joint when external loads are applied. Finally, the structures that guide these motions are consistent with the anatomical evidence. The parameters of the model are identified for two specimens from both subject-specific and published data. Loads are then applied to the model in order to simulate two common clinical tests. The model-predicted ankle motion shows good agreement with results from the literature.

J2410101 移乗動作における腰部負担軽減のための表面筋電計を用いた動的評価法に関する実験的検討

Low back pain of caregiver has serious problem in welfare field. Transfer motion is thought as a cause of the low back pain, and it is necessary to reduce the lumbar burden. Also practical quantification method of lumbar burden is required strongly. This study aims to develop a practical and dynamic evaluation method of lumber burden by measuring surface muscle potential of the Erector spine muscle. This study delas with transfer motion and divide it into three motions, "lifting motion", "rotation a motion" and "unloading motion". Experiments have been conducted to show that "lifting motion" and "rotation a motion" can be evaluated by the surface muscle potential of the erector spine muscle by previous studies. This paper focuses on the "unloading motion" and, the relationship between the load and the "surface muscle potential of the erector spine muscle" is confirmed by experiments. It is also shown that the lumbar burden during "unload motion" is possible to be evaluated by using the surface muscle potential. In addition, this study evaluates, whether dynamic evaluation by using the proposed evaluation method is possible. Because caregivers are required to slow down during the "unoad motion", inertial force increass the load during decelerated motion. For an example, a dynamic evaluation in the case of deceleration during the "unloading motion" were confirmed by experiments. Conducting experiments, we found that the value of the potential of the surface of the erector spine was increased during slow down motion. This result indicates that the lumbar burden can be increased by decelerated motion. This study showed the effectiveness of the dynamic evaluation method by surface muscle potential.

Long-term outcome (20 to 33 years) of radial shortening osteotomy for Kienböck’s lunatomalacia

Radial shortening osteotomy (RSO) as treatment for Kienböck's disease usually improves patient symptoms for several years. Four small series have also shown that the effect may last for decades, but only two studies have used a patient-based assessment. We examined 16 patients, with a mean age at operation of 32 years, evaluating clinical and radiological results at a mean 25 (range 20 to 33) years after surgery. Three patients had progressive lunate collapse, of whom one patient needed a silicone implant arthroplasty 2 years after RSO and one patient a wrist fusion 16 years after RSO. The time between onset of symptoms and osteotomy in the remaining 14 patients averaged 20 months. The mean VAS for pain was 0.9 at rest, 0.9 with unloaded motion, 1.7 with slight, and 3.0 with heavy exertion. Two patients had marked wrist pain. Compared with the contralateral wrist the mean range of motion was 88%, grip strength was 95%, and key pinch 107%. The Disabilities of the Arm, Shoulder, and Hand score averaged 6.1, and the Mayo wrist score, 79.3. The Lichtman stage remained unchanged in 56% of patients. The inner structure of the lunate improved in all patients, and its shape remained unchanged in half of the cases. Radial shortening osteotomy provides decade-long improvement in 75% of patients and seems to be a reasonable treatment for symptomatic Kienböck's disease.

The Stress and Strain States of the Posterior Annulus Under Flexion

Experimental measurement of bovine caudal annulus fibrosus (AF) biaxial stress-strain states for unloaded motion segments and those loaded in flexion combined with axial compression. To measure AF biaxial stress-strain states for motion segments free of external loads and those loaded in flexion combined with axial compression. In vitro, cyclically loaded flexion is associated with the complete rupture of the AF in acute cases. However, currently little is known about the tissue-level stress and strain states in this damaging load configuration. Surface strains of the posterior annulus were measured, during loading of intact bovine caudal motion segments in flexion combined with axial compression, using the unloaded motion segment as a reference. Planar annulus specimens were excised from the motion segments, and the measured strains from the unloaded and flexed intact discs were applied to the excised specimens in a planar biaxial stress-strain device to determine the stress state in each condition. The annulus strain state of the flexed disc was input into a previously developed nonlinear strain energy function with additive terms that directly represent the structural features of the AF. The AF posterior surface strain for motion segments in flexion combined with compression was -0.1087 (circumferential) and 0.1051 (axial) on average. This strain state corresponded to average biaxial stresses in the annulus of 0.046 MPa (circumferential) and 0.224 MPa (axial). The planar AF specimens contracted after sectioning, resulting in small negative strains. In the absence of external loads on a motion segment, the annulus was approximately in a state of equibiaxial tensile stress. The theoretical analysis indicated that collagen crosslinks store a greater portion of the strain energy than the matrix or collagen fibers. In flexion combined with compression, the posterior AF stress state is biaxial and is much larger in the axial direction in bovine caudal discs.

Novel peroxide‐vulcanized NBR‐PAni.DBSA blends, part 2: Effects of conductive filler particles alignment

AbstractDicumyl peroxide (DCP) vulcanized poly(butadiene‐co‐acrylonitrile)‐polyaniline dodecylbenzenesulfonate [NBR‐PAni.DBSA] blends were successfully prepared by using the practical thermomechanical mixing method. The effect of alignment of PAni.DBSA particles on the mechanical and electrical properties of vulcanized blends was studied (by passing the blends through a two roll‐mills). All vulcanized blends strained parallel to the flow direction when passed through the two roll‐mills had their electrical conductivities enhanced with increasing strain in tension. Good historical memory in term of the electrical conductivities during three cycles of straining (with 300 times of strain loading and unloading motion for each cycle) was observed for all vulcanized blends (99% retention of original value before straining). These vulcanized blends also showed better mechanical properties (i.e., higher tensile strength and tear strength) than the ones strained perpendicularly to the flow direction. With the ideal mechanical properties and reversible electrical behavior, this type of blend can potentially emerge as a new class of flexible smart material. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The steady state responses of s.d.o.f. viscous elasto-plastic oscillator under sinusoidal loadings

Depending on the values of the parameters identified, the long-term behaviour of s.d.o.f. viscous elasto-plastic oscillator under sinusoidal loadings may be periodic with or without intermediate unloading, or elastic shakedown (including purely elastic). A new phase-plane estimation method for the steady state elasto-plastic solutions is presented. We identify three dimensionless ratios, namely damping ratio ζ, force ratio r f and frequency ratio r w, as well as an elastic-phase duration variable y. The new estimate offers closed-form formulae for the force ratio r f and for the ductility ratio μ in terms of ζ, r w and y. Applying numerical method to the function r f= r f( ζ, r w, y), we can obtain the inverse function y= y( ζ, r w, r f), such that the variation of μ in terms of ζ, r w and r f can be evaluated. Alternatively, for a given ductility ratio, we can solve μ= μ( ζ, r w, y) numerically for y and then obtain the curves of r f versus r w to meet specified ductility ratio. The proposed method can estimate the steady state responses for any applied load and forcing frequency. The results calculated are in very good agreement with the exact time-marching solutions. A simple criterion of parameters values for elastic shakedown is derived, by which we can calculate the maximum driving force amplitude to avoid structures oscillating in the plastic range. It is found that there exists a best driving force amplitude for maximizing dissipation efficiency. The distribution of periodic points with and without intermediate unloading in the parametric plane ( r w,1/ r f) for given damping ratio is clarified. The intermediate unloading motion region locates within the range of r w ⩽ 1−ζ 2 /3 , and its size decreases when damping ratio increases.

A Spatial Mechanism With Higher Pairs for Modelling the Human Knee Joint

By generalizing a previous model proposed in the literature, a new spatial kinematic model of the knee joint passive motion is presented. The model is based on an equivalent spatial parallel mechanism which relies upon the assumption that fibers within the anterior cruciate ligament (ACL), the medial collateral ligament (MCL) and the posterior cruciate ligament (PCL) can be considered as isometric during the knee flexion in passive motion (virtually unloaded motion). The articular surfaces of femoral and tibial condyles are modelled as 3-D surfaces of general shapes. In particular, the paper presents the closure equations of the new mechanism both for surfaces represented by means of scalar equations that have the Cartesian coordinates of the points of the surface as variables and for surfaces represented in parametric form. An example of simulation is presented in the case both femoral condyles are modelled as ellipsoidal surfaces and tibial condyles as spherical surfaces. The results of the simulation are compared to those of the previous models and to measurements. The comparison confirms the expectation that a better approximation of the tibiofemoral condyle surfaces leads to a more accurate model of the knee passive motion.

A general formulation for the calculation of the load sharing and transmission error under load of spiral bevel and hypoid gears

This paper presents the basis of a Loaded Tooth Contact Analysis (LTCA) program predicting the motion error of spiral bevel gear sets under load, and explores some of the influences of the unloaded motion error curve shape and amplitude over the kinematical behaviour under load. The effects of tooth composite deflection caused by bending and shearing, tooth contact deformation and initial profile separation due to profile mismatch are considered in the development. Due to the complex geometry of spiral bevel gear teeth, the tooth bending stiffness is calculated by finite elements. Classical Hertz theory is used to calculate the contact deformation. Numerical examples are presented to illustrate the behaviour of spiral bevel gear motion error under load as the unloaded motion error is modified. Results show that under general circumstances, low contact ratio spiral bevel gears with parabolic unloaded motion error may produce undesirable kinematics under load, while parabolic motion error high contact ratio spiral bevel gears are likely to produce acceptable kinematics under a larger load range. It is also shown that the governing factors, in loaded motion error, are the contact ratio, thus combined mesh stiffness, and the amplitude of unloaded motion error curve which is linked to load sharing between adjacent tooth pairs.

The Generating Space for Parabolic Motion Error Spiral Bevel Gears Cut by the Gleason Method

Because of their inherent pseudo-conjugate natures, spiral bevel gears cut by the Gleason method basically transmit motion in a nonuniform manner. This motion nonuniformity, or motion error, repeated at each tooth engagement and at high speeds and loads, can cause vibrations in transmissions and contact-entry impact loads on gear teeth which affect the life of a gearset. It is customary to make small changes to machine settings in order to produce gear pairs with vastly improved kinematics. Therefore, machine setting changes must be carefully chosen such as to produce appropriate unloaded kinematical motion error that will cancel tooth bending deflection and contact deformation at a given load, and thus reduce noise and vibrations due to motion nonuniformity. This paper presents a study on the effects of machine settings, such as cutter tilt, machine center to back and offset, on the unloaded kinematical motion error. Applying CAD Boolean operations on the results, it is found that, for a given speed ratio, an infinite number of cutter tilt, work offset and machine center to back combinations will produce gear sets with convex parabolic motion error curve of any desired amplitude. Moreover, the amplitude of motion error curves can be linked directly to contact bias on the tooth flank. Thus, gear sets with any parabolic motion error in the unloaded state can be produced, such as to cancel tooth bending deflection and contact deformation in the loaded state.

Environmental correlates of Arctic ice-edge noise

Temporal variations of low-frequency, broadband ambient noise measured in early summer under drifting ice floes of the marginal ice zone (MIZ) are cross correlated with local environmental forces and ice field descriptors. Surface gravity wave forcing is the primary correlate of the noise; its interaction with ice floes generates sound, most likely via flexural floe failure, and unloading motion, within a few kilometers of the ice edge. Ice concentration is also well correlated with the noise, most likely parametrically. That is, as ice concentration increases, so does the density of potential sound sources in the ice field. Ice stress, ice moment, and wind stress magnitude, while highly correlated with low-frequency noise in the fully ice-covered Arctic, are poor correlates in the MIZ. Lateral melt rate, as a surrogate for thermally induced ice stress, is also poorly correlated with low-frequency MIZ noise. When surface wave forcing is weak, about 1/2 the time in this experiment, episodes of high noise are sometimes observed. These episodes are roughly 3–6 h in duration and 12 h in periodicity. Evidence suggests that they are related to the formation and advection of bands of highly concentrated ice by internal waves during off-ice winds.

荷役作業における作業者の運動動作解析と評価の研究 (第2報)

A system is established to analyze and evaluate three-dimensional human body motions, which is applied to analyze simple loading and unloading operations. A three-dimensional model of human body consisting of seventeen equivalent rigid cylinders is proposed and the equations of motion are derived. A sequence of loading and unloading motion in both the frontal and the sagittal planes were taken simultaneously employing a 16 mm movie camera with use of a life-size mirror placed in front of the subject. The three-dimensional information of the motion is taken into a minicomputer via a graphic tablet. The threedimensional computer graphics are utilized to display the motion patterns of the operation, the loci of the body center of gravity and the correlations of the angles among the major body joints for detailed analysis of the operation. The forces and torques acting at individual joints are also estimated for quantitative examinations of the motion by solving the equations of motion based on the motion data.