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A kinematic characterization of human walking by using CaTraSys

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A kinematic characterization of human walking by using CaTraSys
  1 Varela, M.J., Ceccarelli, M., Flores, P., A kinematic characterization of human walking by using CaTraSys. Mechanism and Machine Theory, Vol. 86, pp. 125-139, 2015   A kinematic characterization of human walking by using CaTraSys Maria João Varela a , Marco Ceccarelli  b,* , Paulo Flores a a  CT2M/DSM Department of Mechanical Engineering, University of Minho Azurém Campus, 4800-058 Guimarães, Portugal Email:;  b  LARM: Laboratory of Robotics and Mechatronics DICeM, University of Cassino and South Latium Via Di Biasio 43, 03043 Cassino (Fr), Italy Email: Abstract  This paper presents an experimental characterization of the biomechanics of human gait by means of Cassino Tracking System (CaTraSys). CaTraSys is a passive cable- based parallel manipulator that is used to determine pose and exerted force of mechanical systems along large trajectories. It is a low-cost easy-operable system that has been utilized in the present work for a clinical application as an assessing device for diagnosis and rehabilitation procedures. A methodology for experimental tests and data analysis is outlined, which includes mean extrapolation of acquired trajectory data. Basic characteristics of two-dimensional (2D) and three-dimensional (3D) resulting gait  patterns are discussed. Using spatiotemporal parameters, different test conditions and anthropometric characteristics are evaluated in order to assess their influence on the human walking from the kinematic point of view. Keywords: Biomechanics, Human gait, Experimental mechanics, CaTraSys 1. Introduction It is known that the methods that are used in gait research frequently include pressure and force plates [1, 2], video or optoelectronic-based analysis systems [3], accelerometers, gyroscopes [4], instrumented shoes [5] and pressure and force sensitive footswitches [6, 7]. These systems are utilized to acquire kinematic and kinetic gait data, such as trajectories or ground reaction forces. In the Robotics field, cable-based parallel manipulators have been considered to be interesting systems. This type of systems is cable actuated in which cables are connected to the end-effector from a stationary frame. They ensure very good kinematic and dynamic characteristics and are characterized by an easy set-up, transportability and good inertial behavior due to small moving masses consisting of cables and light end-effectors. Another important feature is that the calibration procedure must be performed when any component of the system is changed and periodically. A drawback associated with these robotic manipulators deals with the requirement of operating in a reduced *  Corresponding author: Telephone: +39-0776-2993663; Fax: +39-0776-2993989  2 workspace in order to avoid cables interference. The most important characteristics are the low cost and easy operation that can be considered very important for a possible commercial system [8, 9]. All these features are also suitable for clinical applications [10]. Besides allowing to record gait information, these manipulators can be utilized to guide movement of human limbs, which make them attractive even as rehabilitation devices. In addition, cable-based systems can be reconfigured for different therapies. The cables in opposition to the rigid links reduce the constraints [8, 9, 11]. CaTraSys [12] is a passive cable-based parallel manipulator with possible application in clinical fields as an assessing device. Experimental tests of a patient limb  performance could give the clinicians information towards diagnosis and rehabilitation  procedures. Iida and Yamamuro [13] studied patients performance before and after joint replacement, and they observed that the 3D displacements curves of the body centre of gravity that were initially distorted, tended to normalize after the clinical procedure. These results can be seen as a proof of the clinical potential of CaTraSys. Thus, the  purpose of the present work deals with the experimental characterization of human gait using CaTraSys. In this process, the mean trajectory pattern of the gait tests is evaluated and a kinematic analysis is carried out from experimental acquired data. Four different test settings and anthropometric features are evaluated utilizing spatiotemporal  parameters.   2. CaTraSys for motion tracking CaTraSys, presented in Fig. 1a, was developed at the Laboratory of Robotics and Mechatronics (LARM), Department of Civil and Mechanical Engineering (DICeM) of the University of Cassino and South Latium, in 1993. Since then it has been continuously evolved in operation and design and it has been successfully utilized in different applications for determination of workspace, kinematic parameters and force exerted by robots and human limbs [12]. CaTraSys is constituted by mechanical and electronic components together with a software package, as it is illustrated in Fig. 1b. The Trilateral Sensing Platform (TSP) is constituted by a metal stationary platform on which are fixed six position sensors ! !   ( ! =1…6) (cable extension transducers celesco TM  PT101 [14]) and six force sensors ! !   ( ! =1…6) (tension/compression load cells LAUMAS ®  SA [15]). Each cable is attached to a spring of a position sensor, such that it is conducted through the pair of pulleys and finally reaches the end-effector structure (see Fig. 2). The moving platform is the end-effector for CaTraSys and allows the system to track the movement. Pose of the end-effector and tension applied to pull it are determined through the position and force sensors, respectively. The signals from the position and force sensors are conducted to the six amplifiers  ! !   ( ! =1…6) (analog weight transmitters LAUMAS ®  TPS [16]), which provide signal amplification. Then, a data acquisition (DAQ) board (National Instruments TM  USB-6210 [17]) and the software packages Laboratory Virtual Instrument Engineering Workbench (LabVIEW TM ) and MATrix LABoratory (MATLAB ® ) are utilized for the  purpose of data acquisition and data processing. The voltage is provided by a direct current (DC) power supply [18]. The springs and pulleys contribute to maintain the tension of the cables. The tension has a range limit since, on one hand, they need a minimum value to avoid its slackness and, on the other hand, a maximum value to minimize elastic and inelastic effects [8]. The pulleys are considered with the purpose of obtaining a compact system where the cables can move in a relatively large range, without the risk of cable folding, wrapping or damaging [18].  3 In the present work, regarding the moving platform, six steel cables are utilized in a 3-3 configuration, as it is illustrated in Fig. 3a. End-effectors are tightly strapped to the legs around two measurement points, namely at the medium line of the knee and close to the ankle. The proper positioning at the location of interest is ensured by Velcro ® custom straps, which are soft, flexible and adaptable. However, the straps can be source of some inaccuracy in the measurements. It is important to note that CaTraSys formulation considers knee and ankle end-effectors as two points moving in the workspace (see points !  and  !  in Fig. 3a). (a) (b) Figure 1 - (a) Photography of the CaTraSys prototype; (b) Schematic representation of CaTraSys components [18]. Figure 2 - Installation of CaTraSys components. Cable   Position   Sensor   Force Sensor O 1   End-Effector Pulleys   Fixed Platform  4 CaTraSys can be modeled as a six degrees-of-freedom (DOFs) parallel manipulator since cables can be considered as extensible legs connecting the platform and base by means of spherical and universal joints, respectively. CaTraSys is a passive cable system since the input motion is given through the action on the end-effector. The system can be used to identify the six DOFs of a body in space, being capable to give 3D pose (position and orientation) and force information [8]. (a) (b) Figure 3 - CaTraSys 3-3 configuration: (a) A treadmill gait assessment in which the end-effectors are strapped to the knee and ankle {adapted from [18]}; (b) A corresponding trilateration scheme. The main objective of CaTraSys developments is to combine the low-cost, the easy-operability and the mechanical robustness features. It is considered a low-cost system when compared to other available commercial measuring systems, such as video capture systems. This is possible because CaTraSys only uses commercial off-the-shelf mechanical components, which makes it an economical and robust system. The intuitive and fast operation of CaTraSys is due to the simplicity of the trilateration method, which is the base of determining pose of the moving platform, and to the simple calibration. In addition, CaTraSys works in real-time allowing for the immediate evaluation of the test results [12]. CaTraSys is also very adaptable to different robotic schemes. The parallel architecture of CaTraSys moving platform can be utilized in diverse configurations, i.e., different number of end-effectors and cables. Additional relevant features of CaTraSys are the following, the position of the sensors in the stationary platform can be changed, the system can be used along with other measurement instruments, different rigid mechanical systems can be easily attached and movements can be performed in different planes [8]. The Virtual Instrument (VI) uses the DAQ software to collect, at a sample rate of 40 Hz, and calibrate the length and force data. The formula node does the trilateration and forces computations, of which result the knee and ankle trajectory as well as the force components (total of six positions and six forces). Figure 3b depicts the trilateration scheme corresponding to the CaTraSys walking test of Fig. 3a. Cables one, two and three are attached to the knee point !   and cables four, five and six are connected to the ankle point  ! . Points   ! ! , ! !  and ! !   are the base  points of the cables, while ! ! , ! !  and   ! !  represent the distance between points !  and   ! ! , ! !  and ! ! . With the purpose of determining the coordinates of a point it is necessary, at least, to know the location of three fixed points together with three distances, which, in this work, are measured by the position sensors. In short, if at a specific instant of time, the coordinates of points ! ! , ! !  and ! !  and the distances ! ! , ! !   K A d 1     0 5  X 0 4  0 1  d 5  d 2  d 3  Y 0 6  0 3  0 2  d 4  Z A K d 6  
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