Functional Evaluation and Operational Adaptation of Bipedal Robotic Platform

Transcription

1 Contemporary Engineering Sciences, Vol. 10, 2017, no. 22, HIKARI Ltd, Functional Evaluation and Operational Adaptation of Bipedal Robotic Platform Edwin Valbuena, Diego Perdomo and Fredy Martínez District University Francisco José de Caldas Technological Faculty, Bogotá D.C., Colombia Copyright c 2017 Edwin Valbuena, Diego Perdomo and Fredy Martínez. This article is distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Objectives: To perform a structural analysis on the design of the SIROBI3 robotic platform that matches the mechanical strengths on each of its parts for differents materials in order to make design adjustments and define manufacturing characteristics. Methods: The prototype performance is evaluated from its model in SolidWorks Motion and SolidWorks Simulation, for three different materials, analyzing physical and morphological behavior, under static conditions. We use mechanical performance in terms of torque requirements and total mass of the structure as a criterion for the selection of construction materials. Findings: The final result, i.e., the performance of the prototype with the optimum material, showed a significant reduction of the mass and weight of the robot, thus obtaining the reduction of efforts of the actuators and servomotors. In addition, the speed and mobility of the platform was increased. Novelty: The use of computer models to simulate the behavior of the robot under real operating conditions. Keywords: robot, deformation, mechanical model, structural analysis 1 Introduction The advancement and development of humanoid robots from the XIX century to date has progressed exponentially, this has generated much interest in certain companies which see the future of technology in humanoid robots.

2 1058 Edwin Valbuena, Diego Perdomo and Fredy Martínez Some of these are: Honda, Boston Dynamics, Humanoid Mex-One, NASA and research groups such as the Massachusetts Institute of Technology. What is sought is an independent humanoid who can perform the basic tasks (walking, running, taking objects, transporting) and can serve people [2]. It is expected that in about 20 years the new humanoid robots will be made of plastic and fluids to be more flexible and will replace the heavy engines and aluminum parts (bio-mimetic). The bipedal structures are called humanoid robots. These parts fulfill the function of modeling a part of the human body, in principle, to function in human environments. The bipedal structure is a great option to replace limbs whose parts are absent in people. This encourages the construction of prototypes with the same movement, strength and elasticity of these parts [10]. These characteristics or movements must be similar (or equal) to the part of the body that is to be replaced, so that the mechanical stresses are not flawed and fully comply with the movements that they want to meet. It is noteworthy that the greater the number of movements, or greater complexity of robot mobility, the proportion of the method used to model such movements increases proportionately. This is why it is important to determine how robust the robot is, and to try to use in its design the movements that are strictly necessary. Many researchers are still trying to determine new algorithms, structures, designs, and control parameters that will help meet all of the features [7]. The parameterization of dynamic equations can be modeled through several methods. Some examples are the Lagrange-Euler method with three degrees of freedom (DOF) that has been proven to be efficient for modeling walking movements [6]. The Newton-Euler method, among others, is used for different degrees of freedom, which would represent the number of movements that prototypes could implement. Another important aspect is the correct distribution of forces. For this in the design must take into account the type of material in which the prototype is built, the mechanical stresses that must be supported and the wear that would have the joints [5]. There are many motion simulation software tools at present. These tools represent a very significant help for researchers, since they can reduce many tests and errors. In addition, it is possible to identify and correct (if necessary) more easily the imperfections and details to be modified in the prototype [1]. The District University Francisco José de Caldas, through the ARMOS research group, developed the design of a biped robot prototype (Fig. 1). A first approach to this structure and its control, specifically focused on the process of walking of the platform called SIROBI1 was presented in 2010 [3]. The basic design architecture has been maintained and improved until its latest improvement with the new design developed in 2013 [4]. This research seeks to continue improving this design, particularly in rela-

3 Adaptation of bipedal platform 1059 Figure 1: Biped robot, District University ARMOS Research group [4] tion to the mechanical design and selection of materials, considering the requirements of movement, stability and weight for different loading conditions [9, 8]. In Figs. 2 and 3 the general characteristics of the design are shown. 2 Problem statement The paper documents the improvement and optimization of the biped robot prototype developed by the ARMOS research group at the District University Francisco José de Caldas [4]. The objective is to review the structure Figure 2: Upper part of the bipedal robot, ARMOS Research group

4 1060 Edwin Valbuena, Diego Perdomo and Fredy Martínez Figure 3: Lower part of the bipedal robot, ARMOS Research group and design of the pieces considering their actual operation in the prototype for different materials. The materials to be considered are those that for their manipulability, access and cost are viable for the construction of the prototype. Among the tests applied we documented the tests of stress, deformation, displacement, percentage of damage according to activities and useful life. From the test results we determine which of the materials under study is the most optimal to develop each and the biped prototype parts. The study process was developed in the following stages: Research on the different types of materials suitable for manufacturing that were not considered in the prototype design. Analysis and evaluation of materials available for the prototype using SolidWorks software from SolidWorks Corporation. Perform structural analysis tests determining the results of Von Mises stress, static displacement and static strain of each piece with each type of material, and establish the strength and rigidity of the design. Carry out the performance evaluation by analyzing the damage tests and the useful life of each of the pieces with the different materials. Determination of the type of material that best fits each part of the design, taking into account parameters of speed, mobility and performance expected in the final prototype. 3 Materials and Methods The materials selected for the study were: PET, PLA and ABS, in addition to the aluminum alloys known as Duralumin, Alclad and 6061 aluminium alloy.

5 Adaptation of bipedal platform 1061 Table 1 shows some characteristics of these materials. We perform a structural analysis of each of the pieces with different types of materials. The study gives results of the behavior of the pieces depending on the material in which they are constructed. For this we define the total mass of the prototype and the estimated forces that would support the pieces. The total weight of the robot was estimated at 80 kg. Table 1: Characteristics of materials suitable for the prototype One of the tests applied is the Von Mises stress test. Von Mises stress is proportional to the energy of distortion. In structural engineering this is used in the context of failure theories as an indicator of good design for ductile materials. According to the results of the Von Mises test, we also analyze the degrees of displacement at the most critical points of the pieces, showing the results in millimeters. Finally we perform a unitary strain analysis, that is, the relationship between the total deformation and the initial length of each piece. This analysis allows to determine the deformation of the element subjected to tensile stresses or axial comprehension. 4 Results and Discussion ABS (Acrylonitrile Butadiene Styrene) is a very common and very resistant plastic ideal for the printing of mechanical parts. It is a plastic sensitive to changes in temperature. The advantages of this material is that it is very easy to manipulate, can be polished, sanded, filed, drilled, painted and glued without any problem. It is extremely strong and has little flexibility. Aluminium 6061 is a hardened aluminum alloy containing as main elements aluminum, magnesium and silicon. It was originally called 61S alloy. It has good mechanical properties and for use in welding. It is one of the most common aluminum alloys for general use. PET (Polyethylene Terephthalate) is a recycled material with which most commonly used bottles are made. It is a material more resistant than ABS, not flexible and not expensive. In each simulation we apply the characteristics considered as normal operation in activity (number of fasteners, type of applied load and estimated value) as initial conditions, and we applied three types of studies: static analysis nodal tension, static displacement and static unit deformation. Figs. 4 and 5 show some of the results.

6 1062 Edwin Valbuena, Diego Perdomo and Fredy Martínez Figure 4: (a) Static analysis nodal tension, central femoral bar. (b) Static displacement, central femoral bar. (c) Static unitary deformation, central femoral bar. ABS material Figure 5: (a) Static analysis nodal tension, the ankle disk joining the bottom of the robot. (b) Static displacement, top part of the restraint between the hip and the femur. (c) Static unitary deformation, top part of the restraint between the hip and the femur. ABS material

7 Adaptation of bipedal platform 1063 For the evaluation of performance of the materials we carry out studies of percentage of damage and useful life. For this we applied a linear analysis for aluminum and a nonlinear analysis for plastic materials, due to the behavior of each of the materials. Fig. 6 shows one of the results. Table 2 shows the summary of material selection for each of the pieces according to the results of the analysis. The table includes the mass and estimated weight of each piece. Figure 6: Non-linear fatigue analysis, useful life, PET material Table 2: Results of material selection 5 Conclusions This article defines the construction material for each of the parts of the SIROBI3 robot of the ARMOS research group. The selection of the material is based on the mechanical design of the robot, the definition of its movements, and an analysis of stresses (displacements, movements and tensions) and fatigue of material (number of repetitions and percentage of damage) to which

8 1064 Edwin Valbuena, Diego Perdomo and Fredy Martínez is subjected each of the part. Simulations are made with different materials beforehand considered as suitable according to their cost and availability. Acknowledgments This work was supported by District University Francisco José de Caldas. The views expressed in this paper are not necessarily endorsed by District University. The authors thank the research group ARMOS for the evaluation carried out on prototypes of ideas and strategies. References [1] E. Dean-Leon, S. Nair and A. Knoll, User friendly matlab-toolbox for symbolic robot dynamic modeling used for control design, 2012 IEEE International Conference on Robotics and Biomimetics (ROBIO), (2012), [2] O. E. Gonzalez R. and D. M. Acero Soto, Robot semi-autónomo para el transporte de pacientes con movilidad reducida, Tekhnê, 13 (2016), no. 2, [3] F. Martínez, D.M. Acero and M. Castiblanco, Hybrid fuzzy-sliding scheme for the balance control of a biped robot, Lecture Notes in Computer Science, Vol. 6216, Springer Berlin Heidelberg 2010, [4] F. Martínez, W. Arias and D. Zarate, Especificación, diseño y simulación de un prototipo de robot bípedo para investigación en control, CIIMA 2014 III Congreso Internacional de Ingeniería Mecatrónica y Automatización, (2014), 1-6. [5] L. Mostefai, M. Denai and Y. Hori, Robot joint friction compensation based on a local modeling technique, th IEEE International Workshop on Advanced Motion Control, (2008), [6] J. K. Rai, R. P. Tewari and D. Chandra, An optimal control of bio-robotic leg for human-like walking, 2010 International Conference on Industrial Electronics Control Robotics (IECR), (2010),

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