626 research outputs found
Analisi di posizione e spazio di lavoro di una piattaforma di Gough-Stewart modificata
No full textIn questo lavoro gli autori presentano una soluzione dell’analisi di posizione di-retta di una piattaforma di Gough-Stewart modificata che, rispetto alla piattaforma classi-ca, presenta alcuni vantaggi. La soluzione dell’analisi di posizione diretta del manipolato-re è basata su una parametrizzazione che porta ad un sistema di quattro equazioni di chiusura
A Sequential Approach for Modelling the Knee Joint Stiffness
No full textMathematical models of the knee joint are important tools which have both theoretical and practical
applications. Many models have been presented in the literature as a confirmation of their
scientific and practical relevance (Hefzy and Cooke, 1996). Some of them are purely kinematic
and a few of these (Wilson and O’Connor, 1997; Parenti-Castelli and Di Gregorio, 2000; Sancisi
and Parenti-Castelli, 2007) simulate the knee passive motion, i.e. the tibia-femur relative motion
under virtually unloaded conditions. Others are kinetostatic (Blankevoort et al., 1991) or dynamic
(Pandy et al., 1997). In some cases these models are defined from average data taken from
the literature, otherwise they are based on experimental data and try to fit a particular required
task.
In this paper a novel approach is proposed to define more and more sophisticated models of
a human articulation. In particular, a stiffness model of the knee is developed starting from a
simple although efficient kinematic model of the passive motion recently presented in (Parenti-
Castelli and Di Gregorio, 2000). The results obtained from the stiffness model are presented and
then compared with published experimental data
Rotation axis identification at the human tibio-talar and talo-calcaneal joints by the Burmester theory
No full textA correct identification of the human joint rotation axes is important in several applications, such as prosthesis and exoskeleton design, and multibody modelling of the human body. This identification is particularly difficult at the ankle joint, where two different articulations are observed, namely the tibio-talar joint (connecting the tibia and talus) and the talo-calcaneal joint (connecting the talus and calcaneus). The motion of both these joints could be approximated to some extent with a rotation about a single axis; thus, the ankle requires the identification of two distinct axes in order to correctly describe the joint motion. A new method is proposed in this study for the identification of the tibio-talar and talo-calcaneal rotation axes that does not require the measure of the talus motion. This feature is particularly important for in vivo measurements, since non-invasive experimental techniques do not allow the talus motion to be obtained, due to the inaccessibility of this bone. The method also exhibits other advantages: the rotation axes are identified simultaneously and thus their identification accuracy is independent; the method is not based on optimization techniques and thus it does not require the definition of an objective function; it is robust; it makes it possible to obtain the talus motion. The theoretical bases of the method are presented and a case study is used to assess the potentiality of the identification procedure
A simple rig for precise measurements of the knee and ankle joint motion under static loading conditions
No full textIn this paper a rig for the analysis of the motion of the knee and ankle joints under static loading conditions is presented and described. The rig is simple, versatile and precise: experimental tests can be performed both on the knee and ankle joints, by a wide range of anatomical specimen sizes; the loads applied to the joints during tests can be measured and controlled with a high precision; specimen position and orientation can be precisely set. Thus, this structure makes it possible to measure precise and repeatable experimental data on the joint motion under static loading conditions, by means of a stereophotogrammetric device. Such experimental data are generally not available in the literature, where all details on the loading conditions are generally not reported, but are necessary in many applications, such as joint modelling and prosthesis and orthosis design
A procedure for the definition of a patient-specific kinematic model of the knee joint: an in-vivo validation
No full textThe capability to model human joint motion is a fundamental step towards the definition of effective treatments and medical devices, with an increasing request to adapt the devised models to the specificity of each subject. We present an approach for the definition of subject-specific models of the knee natural motion. The approach is the result of a combination of two different techniques and exploits the advantages of both. It relays upon non invasive measurements that can be performed in vivo, based on which a kinematic model of the natural motion is built, suitable to be extended to the definition of static and dynamic models. Comparison of the model outcomes with in-vivo measurements performed on one subject shows promising results supporting the proposed approach
Measurement of articular angles and ground forces in the sit-to-stand movement
No full textIn this paper, two motion protocols are presented that describe the sequence of movements to be complied with by a subject to perform a sit-to-stand movement. In gait analysis, the sit-to-stand movement is the movement a patient does when he/she gets up from a chair and stands in upright position. The protocols are intended to obtain repeatable and reproducible results that can be compared among different studies. The first protocol (standard) is closer to other studies in the literature, in order to improve comparison with previous experimental results. The second protocol (natural) reproduces a sit-to-stand movement more similar to natural conditions. The main differences between the two protocols are in the knee angle, the pose of the arms and the torso at the beginning of the test. The two motion protocols are tested by a volunteer on a gait lab. Results of experimental tests in terms of joint and foot-ground angles, ground reaction force and center of pressure show both the repeatability of the tests and the differences between standard and natural movement during sit-to-stand
A preliminary study for a kinematic model of the complex tibia-fibula-talus-calcaneus
No full textThe relevance of the articulation passive motion, i. e. the motion in virtually unloaded condition, for the study of human diarthrodial joints has been widely recognized. In particular, passive motion makes it possible to better understand the basic role of the main anatomical structures that guide the relative motion between the articular elements. Recently, it has been shown that equivalent mechanisms allow obtaining fisical-mathematical models that can well replicate the articular passive motion. These models represent also a useful tool for both pre-operation planning and prosthesis design. Although the human ankle joint has been extensively investigated for its strategic importance in human physical activities, studies that examine the kinematic behavior of the tibio-talar joint also outlining the motion of the fibula bone, which is directly involved in the ankle motion, are still lacking. This paper presents a preliminary study for the development of a 3D passive motion model of the articulation that involves four bones, namely tibia, fibula, talus and calcaneus. In this anatomical complex, called TFC for simplicity, the ankle joint is a fundamental part. In particular, this model targets to evaluate the fibula role
Stiffness analysis of spatial strip-driven devices
No full textOrthoses and exoskeletons require simple yet accurate devices to assist human joints in their motion. This paper presents the stiffness analysis of a spatial-strip driven device suitable for this application. The device features two cylinders guided by three flexible strips, so that a pure rolling relative motion between the two cylinders is generated. The analysis is conducted by defining analytical models to predict the equilibrium position of the device under different loading conditions. Only axial stiffness of the flexible strips is considered, while the effects of flexural and torsional stiffness are ignored as well as friction
Robust, Fast and Accurate Solution of the Direct Position Analysis of Parallel Manipulators by Extra-Sensors
No full textParallel manipulators (PMs) are closed kinematic chains with one or more loops where only some pairs are actuated while the remaining are passive. In particular, they feature a fixed link (base) and an output moving link (platform) interconnected by at least two independent kinematic chains (legs) to form one loop. The most well known and commonly employed PMs (hereafter called UPS-PMs) feature n variable-length legs of type UPS (where U, P and S are for universal, spherical and prismatic pairs respectively). Equivalently, a revolute pair R could be used instead of the prismatic pair P in order to make the leg length variable (in this case the leg would be of type URS). These leg topologies provide the platform with six degrees of freedom with respect to the base.
Although the definition of UPS-PMs requires n  2, in practice, neglecting overconstrained and redundantly-actuated manipulators, performance issues recommend 3  n  6. Indeed, UPS-PMs with only two UPS legs might exhibit a low stiffness against torques acting along the line joining the centers of the two spherical pairs, and their control would require the in-series placement of at least three actuators/sensors (one of them placed to control/measure at least one out of the three degrees of freedom of the spherical pairs) which reduces the overall manipulator dynamic and accuracy capabilities. On the other side, the use of more than six legs reduces the exploitable manipulator workspace for the increase of leg interference.
Different sub-classes of manipulator architectures can be obtained according to the location of the centers of the U and S pairs in the base and in the platform respectively (Innocenti & Parenti-Castelli, 1994; Faugere & Lazard, 1995). General UPS-PM architectures feature distinct joint centers. Special architectures can be devised by setting some of the joint centers to be coincident.
A schematic of a 6-DOF UPS-PM having six legs (n = 6) and general architecture is shown in Fig. 1. In the figure, the U pairs (connecting the legs to the base) and S pairs (connecting the legs to the platform) are depicted as grey and white dots respectively. Points Bi and Pi (i = 1, ..., 6) represent the centers of the U and S pairs of the i-th leg on the base and on the platform respectively. The six legs of type UPS are represented by the telescopic rods BiPi (i = 1, ..., 6). Accordingly, the length of the i-th leg is defined as the distance li = Pi - Bi.
Manipulators with less than six DOF can be obtained from UPS-PMs by suitably eliminating or locking some of the leg kinematic pairs. For instance, considering a 6-DOF UPS-PM having six legs, elimination of four P pairs yields a 2-DOF PM having two legs of type UPS and four legs of type US.
Well-known examples of UPS-PMs are as follows: 1) the 6-DOF UPS-PMs (Gough & Whitehall, 1962; Stewart, 1965; Cappel, 1967); 2) the 3-DOF spherical PMs (Innocenti & Parenti-Castelli, 1993); 3) the 2-DOF spherical PMs (Vertechy & Parenti-Castelli, 2006); and 4) the 1-DOF helicoidal PMs (Jacobsen, 1975). Because of their parallel architecture, UPS-PMs exhibit large payload-to-weight ratio, high accuracy, high structural rigidity and high dynamic capabilities, which make them excel as: a) fast and high precision robots in vehicle simulators (Gough & Whitehall, 1962; Stewart, 1965; Cappel, 1967), machine tools (Charles, 1995) and positioning systems (Schmidt-Kaler, 1992); b) passive Cartesian input devices in joysticks, master-slave teleoperation systems (Daniel et al., 1993) and other tracking devices (Geng & Haynes, 1994); c) force/torque sensors and generators in multi-axis sensors and motors (Gaillet & Reboulet, 1983; Nguyen et al., 1991; Lewis et al., 2002); d) mechanical transmissions in motion converters (Jacobsen, 1975); and e) orthopedic devices in fixations systems (Taylor & Taylor, 2000; Di Gregorio & Parenti-Castelli, 2002).
Practical use of UPS-P..
Improved rig for the analysis of knee behaviour under dynamic motion tasks
No full textThe evaluation of the knee joint behaviour is of great interest for medicine. A new rig to test knees in vitro in loaded and unloaded conditions is presented in this paper. Its loading system based on a cable-driven parallel manipulator allows the application of general loads typical of common daily activities. Its force-control permits the evaluation of the joint natural response to the loads in terms of movement, measured thanks to a stereophotogrammetric system. In addition, the principal muscles that control the knee flexion and extension can be simulated and their contributions to the joint equilibrium can be evaluated thanks to a dedicated control system. The rig is an evolution of a previously presented version, of which it preserves the low cost and simplicity, together with the versatility and accuracy
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