Advanced Mechanics in Robotic Systems

This chapter is based within the study of the humanoid robots world and focuses specifically on the mechatronic study of them. From a scientific standpoint, will be represented mechanically this anthropomorphic robots (from now, called humanoid robots) as a final link in the evolutionary chain in robotics area. Likewise, the design of humanoid robots is based on a wide range of mechatronic disciplines (such as material science, mechanics, and even biomechanics), and we will try to describe them in this chapter. Therefore, the aim of this chapter is to approach progressively the problem of the humanoid robot design, using physical and mechanics concepts, interacting through analogies with the human body. The chapter begins making a further description of the humanoid robots world, showing the evolutionary process that have undergone this type of robots in recent years. With this run-through of the main important points, we try to describe a general procedure to find a key criteria for successful process design of humanoid robots. This “robot-making” process to explain an analysis with initial theoretical calculations that result in the selection of the various mechanical components of a humanoid robot (actuators, motors until structural components). Then, the objetive of this chapter is to present the comprehensive analysis of mechanical design of a humanoid robot that allows to know and quantify the variables you will encounter along the design process of this type of machines.

One of the main objectives of the robotic is to make the systems able to interact, modify, transmit and receive information from the human environment. They reach the possibility to replace the human being in simple and basic functions with better results. In this way, robotic hands play a relevant role since they can perform different tasks, such as holding and manipulating, reaching visual communication and obtaining direct contact with the environment, interacting and even modifying it. When we refer to robotic hands the first thing that comes up to our mind is a robotic system that tries to imitate, in the closest way, the skills and shapes that human hands have. There are many different robotic hands and each of them marks a determined improvement in a specific aspect, due to new technology used in its development, since it has been designed from an innovative mechanic system or mechanism. Technology and mechanics applied to robotics help in improving faster. These two concepts, as it is going to be detailed in this Chapter, must be closely related because the efficient use of one of them depends on the improvement of the other. Basing in our classification, it is possible to divide robotic hands in to two types: the multi-actuated robotic hands, directed by technology and helped by special mechanisms, and the underactuated robotic hands, focused on complex and innovative mechanic systems. The second classification adds a new system concept that allows generating several and independent tasks fulfilled with only one actuator, referring to a new generation of robotic hands able to manipulate in a more dextrous way. In this Chapter, robotic hands will be analysed from its technological and mechanical aspects. First, there will be a brief explanation of robotic hands that have incorporated innovative mechanisms or new technology. Afterwards, the Chapter will focus on functional problems that can be found in the robotic hands development. Finally, some solutions will be detailed through mechanical systems and how they can affect the development of new robotic hands, studying the case of underactuated architectures.

This chapter presents an introduction to mobile robots in the field of the service robots, paying special attention to the mechanical structure of wheeled, legged, hybrid and tracked robots. The issues regarding to the maneuverability and capability of overcoming obstacles are discussed for the wheeled robots. A classification of the wheeled robots is made according to the way they are steered and driven, exposing the forward kinematics equations for every basic scheme. The common characteristics of hybrid and tracked robots are also presented, together with their advantages and drawbacks. A classification of legged robots is also included, focusing mainly on the structure of the leg and discussing relevant issues regarding controlability and efficiency.

Nowadays parallel robots have been extensively studied and new prototypes have been patented and commercialized for a large number of industrial and non industrial applications. A recent trend in parallel manipulators concerns with the emerging area of modular re-configurable parallel robots. This class can not only be referred to classical parallel manipulators, but also to cable-based systems. Recently, a new class of parallel robots has been developed, namely the cable-based parallel ones, and they have attracted the attention of the Robotics community because of their potential advantages over conventional parallel robots. In this context, a survey is presented on recent developments on modular re-configurable parallel robots, both classical manipulators and cable-based ones. A case study of a re-configurable cable-based parallel manipulator is presented.

Mechatronics is an applied interdisciplinary science that aims to integrate mechanical elements, electronics and parts of biological organisms. Mechatronics’ end goal is to design useful products. When those products are focused in human welling, helping them or by restoring lost capabilities, any mechatronics solution should consider at the beginning of the design process that all the mechanics, control and electronics must work cooperatively with and for human. Several challenges related to control issues and the role of human and machine in the control loop could be better achieved if human centered mechanical design approaches are assumed. From a mechanical point of view the development of robots that could operate in close interaction with human is a big challenge. Soft human–robot interaction is the branch that covers those topics. To analyze this fact, in this chapter, a general classification of the different types of robotic systems that currently could be found as well as actuators commonly used. The safety of the robotic assistant, working in close cooperation with humans, is currently a topic of interest in the robotics community. There are many ways to design and conduct intrinsically safe systems, from those that use complex sensory systems to monitor the user within the working environment to avoid contact, even the most sophisticated seeking to minimize the inertia of its moving parts (links) in order to reduce damage in case of accidental collision. Safety mechanisms will be reviewed based on variable stiffness actuators, novel designs of all-gear-motor shaft, etc. The study will include risk assessment and safety for the user. Risk and safety standards will be reviewed. Taking into account undesired collision, two types of safety strategies are reported: pre-contact and post-contact strategies. The first minimize the possible effect of the accident before it occurs. The latter should minimize the consequences of that accident. Those new advances in the design techniques are being applied for ultra-light weight robotics arms and also prosthesis combined with new solutions in kinematic synthesis, materials, geometry and shape of mechanical components, actuators technologies and new thermal and FEM analysis techniques to validate them.

Modern research prevents interdisciplinary activities, in which experts of several fields work together in order to obtain a final solution with high performance characteristics. The main fields in robotics are control, electronics and mechanics. These areas are highly close and they must collaborate together in robotic projects deciding the most suitable solution of every sub-system for a successful operation as an integrate system. For example, a suitable mechanical design can simplify the requirements of control and electronics. This chapter deals with the importance of the mechanical design in the development of mechatronic devices as easy-operation systems. Low-cost robots are related to new emerging application areas and they can be also operated in a simpler way compared to the typical industrial robots. The synthesis process of mechanism that composed the robotic structures represents a key phase in the mechanical design of easy-operation prototypes. The main idea is to obtain dynamic systems in which their transfer functions do not present undesirable characteristics from the control point of view, for instance, all poles equal to zero or non linearity of inputs. For this goal, the mechanical designer should consider the recommendation from the control strategist during the mechanism synthesis. Similar, backlash, hysteresis, shafts offset and fiction are also undesirable mechanical characteristics for non complex control architecture. Some tips are reported in this chapter for a mechanical design in which these undesirable characteristics are reduced as much as possible.