Stiffness analysis of biped humanoid robot WABIAN-RIV

Abstract

In this paper, a humanoid robot named as WABIAN-RIV (WAseda BIpedal humANoid Refined IV) is analyzed in terms of stiffness characteristics. This paper proposes basic models and a formulation in order to deduce the stiffness matrix as a function of the most important stiffness parameters of the WABIAN architecture. The proposed formulation is useful for numerical estimation of stiffness performances. An evaluation of stiffness performances is carried out by numerically implementing the proposed formulation. An experimental validation of the numerical results is also carried out on WABIAN-RIV humanoid robot.

Introduction

The development of robots that are able to imitate the human movements is one of the most fascinating activities of the researchers in the field of Robotics. The interest on this field is not only due to intention of replacing humans in dangerous tasks, but also due to the desire to create something that is similar to the man himself [1].

A humanoid robot is a robot able to complete movements and to guarantee performances similar to those that are performed by the human body [2]. Humanoid robots are complex mechatronic systems requiring developments in kinematic/mechanical design, sensory systems, Artificial Intelligence, computing, control, communications and actuation/power systems [3]. This complexity makes their construction a substantial challenge for designers in many branches of Science and Engineering. Many research groups work for the development of humanoid robots. Significant prototypes are SDR-4X II by Sony [4], ELVIS by Chalmers University in Goteburg [5], ASIMO by Honda Motor Corporation [6], PINO by Kitano Symbiotic Systems [7], EYEBOT by University of Western Australia [8], AMI by KAIST [9]. They are shown in Fig. 1(a)–(f), respectively. Details on several other humanoid projects can be found in [10].

As regards the mechanical design of a humanoid robot, stiffness performance is a very important aspect that has to be considered as pointed out for example in [11], [12], [13], [14], [15]. In fact, in a robot if the stiffness of links and joints are inadequate, external forces and moments may cause large deflections in the links, which are undesirable from the viewpoint of both accuracy and payload performances. Therefore, a stiffness analysis is carried out on different types of robots in order to evaluate their stiffness performances. Significant examples can be found in [13], [14], [15], [16], [17], [18], [19], [20]. Moreover, once a proper stiffness model and formulation have been defined they can be used also for design purposes in order to find an optimum compromise between weight of links and stiffness performance as proposed for example in [20], [21], [22], [23]. The above-mentioned considerations strongly suggest to perform stiffness analysis also for humanoid robots.

This paper describes a stiffness analysis of the humanoid robot WABIAN-RIV as based on proper kinematic, stiffness and static models. By using these models a formulation is proposed to deduce the overall stiffness matrix. This formulation has been numerically implemented in order to obtain the stiffness matrix and an estimation of the stiffness performance. Experimental tests have been carried out in order to validate the proposed formulation. Some preliminary numerical and experimental results have been also reported in [24], [25].