Robotics software systems

A robotics software “system” is defined here as one which allows robot users to program robot tasks in terms of key states of the task, instead of manipulator motions. It consists of two subsystems: a language system and a planning system. The language system involves the design of syntax and semantics of a robot programming language whereas the planning system determines specific manipulator movements for a given task defined in a task-level language. This paper describes the major components of a robotics software system and reviews principal research findings in the related aspects including programming languages, manipulator and world modelings, motion planning, and graphic simulation. Underlying research issues are addressed at the end.     

Hybrid fuzzy control of robotics systems

This paper presents a new approach towards optimal design of a hybrid fuzzy controller for robotics systems. The salient feature of the proposed approach is that it combines the fuzzy gain scheduling method and a fuzzy proportional-integral-derivative (PID) controller to solve the nonlinear control problem. The resultant fuzzy rule base of the proposed controller can be decomposed into two layers. In the upper layer, the gain scheduling method is incorporated with a Takagi-Sugeno (TS) fuzzy logic controller to linearize the robotics system for a given reference trajectory. In the lower layer, a fuzzy PID controller is derived for all the locally linearized systems by replacing the conventional PI controller by a linear fuzzy logic controller, which has different gains for different linearization conditions. Within the guaranteed stability region, the controller gains can be optimally tuned by genetic algorithms. Simulation studies on a pole balancing robot and a multilink robot manipulator demonstrate the effectiveness and robustness of the proposed approach.     

Fast replanning for navigation in unknown terrain

Mobile robots often operate in domains that are only incompletely known, for example, when they have to move from given start coordinates to given goal coordinates in unknown terrain. In this case, they need to be able to replan quickly as their knowledge of the terrain changes. Stentz' Focussed Dynamic A/sup */ (D/sup */) is a heuristic search method that repeatedly determines a shortest path from the current robot coordinates to the goal coordinates while the robot moves along the path. It is able to replan faster than planning from scratch since it modifies its previous search results locally. Consequently, it has been extensively used in mobile robotics. In this article, we introduce an alternative to D/sup */ that determines the same paths and thus moves the robot in the same way but is algorithmically different. D/sup */ Lite is simple, can be rigorously analyzed, extendible in multiple ways, and is at least as efficient as D/sup */. We believe that our results will make D/sup */-like replanning methods even more popular and enable robotics researchers to adapt them to additional applications.     

The autonomy-safety-paradox of service robotics in Europe and Japan: a comparative analysis

Service and personal care robots are starting to cross the threshold into the wilderness of everyday life, where they are supposed to interact with inexperienced lay users in a changing environment. In order to function as intended, robots must become independent entities that monitor themselves and improve their own behaviours based on learning outcomes in practice. This poses a great challenge to robotics, which we are calling the “autonomy-safety-paradox” (ASP). The integration of robot applications into society requires the reconciliation of two conflicting aspects: increasing machine autonomy and ensuring safety in end-use. As the level of robot autonomy grows, the risk of accidents will increase, and it will become more and more difficult to identify who is responsible for any damage incurred. However, emphasizing safety impairs the autonomous functioning of the robot. This problem implies the need for a broadened concept of product safety. Our comparative study shows that the institutional framing of the ASP as well as concrete solutions to this problem differs between Europe and Japan in two respects: (1) the understanding of robot agency and (2) the concept of “appropriate” user–robot interaction.     

Human–robot collision model with effective mass and manipulability for design of a spatial manipulator

As the use of service robots becomes more popular, many solutions to ensure human safety during human–robot collision have been proposed. In this paper, we address one of the most fundamental solutions to design an inherently safe robot manipulator. A collision model is developed to evaluate the collision safety of any spatial manipulator. Most collision studies have focused on collision analysis and safety evaluation, but not on the use of evaluation results to design a safer robot arm. Therefore, we propose a collision model that relates design parameters to collision safety by adopting effective mass and manipulability. The model was then simplified with several assumptions. Furthermore, experimental results from biomechanical literature were employed to describe a human–robot collision. The major advantage of this collision model is that it can be used to systemically determine the design parameters of a robot arm.     

Robot accuracy and stiffness—An experimental study

Investigations in robotics have been mainly directed toward the design of robots with a significant degress of intelligence, capable of high adaptability. However, very little research has been done on the design of a robot manipulator as an executive mechanism of the intelligent control system, whose high quality design will allow the sophisticated functions imposed by the control system.

Experimental investigations of robot accuracy show unacceptable results which limit their future wider application. This is the reason why the off-life programming of robots has not been widely used, without which it is impossible to imagine a more significant integrationof robots in the CIM environment.

The object of our study has been to find out the causes of low degreee of robot accuracy, emphasizing the non-corresponding choice of the robot coordinate system, algorithmic and computational errors and drive and transmission element design. Comparison with corresponding results gained from investigations of CNC machine tools cannot be avoided because of the fact that robots are also machines from which accuracy is required. What is missing in robotics today, but which inevitably is required, is the establishment of a standard methodology for testing robot accuracy and other performance.     

Evaluation of head-collision safety of a 7-DOF manipulator according to posture variation

As the need for the improvement of the productivity in the manufacturing process grows, industrial robots are brought out of the safety fences and used in the direct collaborative operation with human workers. Consequently, the intended and/or unintended contact between the human and the robot in the collaborative operation is no longer an extraordinary event and is a mundane possibility. The level of the risk of the collision depends on various quantities associated with the collision, for example, inertia, velocity, stiffness, and so on. MSI (manipulator safety index) which is based on HIC (head injury criteria) conventionally used in the automotive industry is one of the practically available measures to estimate the risk of the collision between the human and the manipulator. In this paper MSI is applied to evaluate the collision safety of a 7-DOF articulated human-arm-like manipulator. The risk of the collision could be reduced by choosing different postures without deviating from the given end-effector trajectory using the redundant degree of freedom in the 7-DOF manipulator. The paper shows how the redundant degree of the freedom is utilized to design safer trajectories and/or safer manipulator configurations among many available. A parametric analysis and simulation results for a given trajectory illustrate the usefulness of the concept of the trajectory design for alleviating the risk of the manipulator operation in the human–robot coexisting workspace.     

Automatically composing and parameterizing skills by evolving Finite State Automata

We propose a robotics algorithm that is able to simultaneously combine, adapt and create actions to solve a task. The actions are combined in a Finite State Automaton whose structure is determined by a novel evolutionary algorithm. The actions parameters, or new actions, are evolved alongside the FSA topology. Actions can be combined together in a hierarchical fashion. This approach relies on skills that with which the robot is already provided, like grasping or motion planning. Therefore software reuse is an important advantage of our proposed approach. We conducted several experiments both in simulation and on a real mobile manipulator PR2 robot, where skills of increasing complexity are evolved. Our results show that (i) an FSA generated in simulation can be directly applied to a real robot without modifications and (ii) the evolved FSA is robust to the noise and the uncertainty arising from real-world sensors.     

Development and control of a series elastic actuator equipped with a semi active friction damper for human friendly robots

Compliance is increasingly being incorporated in the transmission of robotics actuation systems to cope with unpredictable interactions, improve the robustness of the robot and in some cases its efficiency. However, compliance also introduces some drawbacks as e.g. reduced bandwidth of the controlled system and typically underdamped vibration modes which decrease the accuracy and stability margin of the controlled system. To tackle these issues, variable physical damping has recently been incorporated in such actuation systems. This paper presents the analysis, development, control, identification and experimental evaluation of a novel actuation system which embodies transmission characteristics such as passive compliance and variable physical damping. The first part of this paper introduces an analysis on how these two physical properties affect the performance of the actuation system with the second part analysing the mechatronic design and control in detail. Furthermore, a novel damping estimation method is presented. Results are presented to validate the results obtained in the analysis section advantages gained by employing such actuation approach and to show the effectiveness of the actuation unit in replicating and estimating desired mechanical impedance values.     

Symbolic modeling in robotics: Genesis,applicaton, and future prospects

This survey article gives an overview of software packages for generating numerically efficient manipulator models in symbolic form, i.e. as computer programs written in a high-level language such as C or FORTRAN. We chronicle the history of computational robot dynamics and, to some extent, multibody systems dynamics. We survey several mechanical computer-aided engineering software packages because they have charted the course for symbolic robot modeling software. The attractive features of various programs regarding areas of application (vehicles, robots, satellites, etc.) and design possibilities (kinematic and dynamic analysis, modal analysis, optimization of mechanical design, numerical efficiency of generated symbolic models, etc.) are emphasized. Finally, as an example, we present the SYM program package in more detail and point out the new strategic area of robotics which has emerged during the last two years: computer-aided generation of control laws.     

Canonical transformations used to derive robot control laws from a port-controlled Hamiltonian system perspective

This paper addresses the problem of deriving control laws for robot manipulators in the framework of port-controlled Hamiltonian systems via canonical transformations and passivity-based control. The control design is focused on the presentation of a new energy-shaping methodology for tracking control based on the introduction of virtual non-homogeneous fields where a desired energy is defined to compensate for the actual energy of the robot manipulator while a virtual field forces the system to track a general reference trajectory. This requires use of the Legendre-Fenchel transformation and allows for the derivation standard control laws in the robotics field such as PD control with gravity compensation or PD with precompensation. Finally, the passivity of the input-output mapping of the non-autonomous Hamiltonian system is analyzed in detail, resulting in new Lyapunov candidate functions having their roots in physics.     

Concurrent design of controller and passive elements for robots with impulsive actuation systems

There are some biological evidences showing that the actuation system in legged animals is impulsive; it is not continuous. As opposed to continuous control/actuation, the control actions occur in specific intervals, and from the instant of one actuation until the start of the next one, passive elements guarantee the stability of the robotic system and govern its natural dynamics. In this paper, we present an analytical method for concurrent design of impulsive controller and passive elements (compliance and damper) for robotic systems; e.g., manipulators and legged-robots. To optimize the force profiles of passive elements, three different cost functions are presented which optimize the natural dynamics and energy consumption of the robot. The presented method can be applied to both cyclic and non-cyclic (explosive) tasks so as to attain energy efficient and bio-inspired motions. The method is applied to three biological models: a simulated human arm for throwing an object, a swing leg for drawing an oval, and a 3D quadruped robot for performing walking gait. Our findings in the simulation studies are in line with the hypothesis of impulsive actuation in nature and show the applicability of our method in robotics.     

Modeling development process of skill-based system for human-like manipulation robot

The importance of system integration is widely recognized in robotics. This motivates the application of Model-Based Systems Engineering (MBSE) approaches to improve the development process of robot systems. This paper models a development process to achieve given task goals using a human-like upper body robot based on MBSE approach. For this purpose, we focus on the domain knowledge of tasks and skills in robotics. Since MBSE is a general methodology, there is a lot of flexibility on the way of proceeding with the analysis and design, and how to utilize models there. Using the concept of tasks and skills is helpful for better uderstanding of the development process. Our process is based on three main concepts: (1) stakeholders of User and Developer, (2) coordination between User and Developer using skills as communication interface, (3) extension development. Making the process explicit helps many stakeholders such as robot makers, system integrators, and engineers in various application domains to join the system development. It is also effective for accumulating experiences and work products of the development. In addition, we can expect that better understanding of the engineering process results in the improvement of the process performed by automation tools and humans cooperatively.     

Cable-Direct-Driven Robot (CDDR) with Passive SCARA Support: Theory and Simulation

This article presents a new planar translational cable-direct-driven robot (CDDR) with actuation redundancy and supported against loading normal to the motion plane with a passive planar two-degree-of-freedom SCARA-type (Selective Compliance Assembly Robot Arm) serial manipulator. This allows the robot to resist cable sag without being supported on the motion plane. The proposed robot architecture may assure high payload-to-weight ratio, resistance to forces normal to the plane of motion, and a potentially large workspace. Another benefit is that the passive SCARA has structure to provide end-effector moment resistance, which is not possible with many proposed translational CDDRs. Moreover, the passive robot can also serve as an independent Cartesian metrology system. This article derives the kinematics and dynamics models for the proposed hybrid serial/parallel architecture. Additionally it proposes a dynamic Cartesian controller always ensuring positive cable tensions while minimizing the sum of all the torques exerted by the actuators. Simulation examples are also presented to demonstrate the novel CDDR concept, dynamics, and controller.Category (7) – System Modelling/Simulation/Control/Computer–Aided Design/Robot Control/Teleoperation/Moving Robots     

A Highly-Maneuverable Demining Autonomous Robot: an Over-Actuated Design

Based on the well-known advantages of using an over-actuated mechanism for robots, this research proposes a holonomic highly-maneuverable autonomous robot design for demining service applications. The proposed approach provides an interesting compromise between the design requirements of the demining robot applications and the over-actuated autonomous robots. The robot body is mainly divided into two parts: the first part provides the robot with its required locomotion and it consists of a driving/steering subsystem with four driving wheels (4WD), four steering mechanisms (4SW), and a passive suspension subsystem. The second part is a manipulator with three degrees of freedom that is designed based on two parallelogram mechanisms. The proposed design insures many advantages over existing designs, including stability, maneuverability, autonomous navigation, and simplicity of the control effort constraints. The robot model and its corresponding stability analysis were conducted and simulated in order to evaluate the motion of the robot over different environments rough terrains and slanted surfaces. Moreover, a prototype of the proposed robot was developed and built and different types of sensors were used in order to help it take precise actuation decisions for navigation and control. The prototype was experimentally tested for different scenarios and environments in order to validate the proposed design. The testing results demonstrated decent performance of the robot in autonomous navigation and in localizing the detected objects.     

Concurrent design of a three-link manipulator prototype

This paper presents an affordable and comprehensive robotic model of critical aid to any engineering school involved in teaching robotics. We present the stages of designing a three-link robot manipulator prototype that was built as part of a research project for establishing a prototyping environment for robot manipulators. Building this robot helped to determine the required subsystems and interfaces for building the prototyping environment, and provided hands-on experience for real problems and difficulties that are addressed and solved using this environment. The robot is now successfully used as an educational tool in robotics and control classes.     

Self-reconfigurable robots

In this article, the concept of a cellular robot that is capable of reconfiguring itself is reviewed. This "self-reconfigurable (SR) robot" exemplifies a new trend in robotics, indeed, we can now build various kinds of SR robots with off-the-shelf technologies of processors, actuators, and sensors. These SR robots, based on modern mechatronics, are still not as adaptable as the liquid metal robot in The Terminator 2 but are just as flexible as any conventional robots     

Kinematic-Sensitivity Indices for Dimensionally Nonhomogeneous Jacobian Matrices

Numerous performance indices have been proposed to compare robot architectures based on their kinematic properties. However, none of these indices seems to draw a consensus among the robotics community. The most notorious indices, which are manipulability and dexterity, still entail some drawbacks, which are mainly due to the impossibility to define a single invariant metric for the special Euclidean group. The natural consequence is to use two distinct metrics, i.e., one for rotations and one for point displacements, as has already been proposed by other researchers. This is the approach used in this paper, where we define the maximum rotation sensitivity and the maximum point-displacement sensitivity. These two indices provide tight upper bounds to the end-effector rotation and point-displacement sensitivity under a unit-magnitude array of actuated-joint displacements. Therefore, their meaning is thought to be clear and definite to the designer of a robotic manipulator. Furthermore, methods for the computation of the proposed indices are devised, some of their properties are established and interpreted in the context of robotic manipulator design, and an example is provided.      

Control of flexible manipulators via singular perturbations and distributed vibration damping

A composite control strategy for a two-link flexible manipulator is analyzed which combines hub actuation with distributed vibration control. The hub actuation is based upon an integral manifold approach in which the system dynamics are approximately linearized to any order of a small parameter E representing stiffness of the robot arms. A polymer film is proposed as a distributed actuator to dampen vibrations due to elasticity in the links. Simulation results are provided which show that the addition of the distributed actuator significantly reduces the displacement and velocity of the first flexible mode in each link compared to hub actuation alone. Editor: T. Vincent     

Door-opening behavior of an autonomous mobile manipulator by sequence of action primitives

A goal of this research is to accomplish a long distance navigation task by an autonomous mobile manipulator, including a behavior of “Passing through a doorway.” In our approach to this problem, we apply the concept of action primitives to the mobile manipulator control system. Action primitives are defined as unit elements of a complex behavior (such as door opening behavior), which control a robot according to a sequence of planned motion primitives. An important feature of the concept is that each action primitive is designed to include an error adjustment mechanism to cope with the accumulated position error of the mobile base. In this article, we report on the design and implementation of action primitives for a door opening task, and show experimental results for “Passing through a doorway” by an autonomous mobile manipulator using sequences of action primitives. © 1996 John Wiley & Sons, Inc.