Magneto-Rheological Actuators for Human-Safe Robots: Modeling, Control, and Implementation

In recent years, research on physical human-robot interaction has received considerable attention. Research on this subject has led to the study of new control and actuation mechanisms for robots in order to achieve intrinsic safety. Naturally, intrinsic safety is only achievable in kinematic structures that exhibit low output impedance. Existing solutions for reducing impedance are commonly obtained at the expense of reduced performance, or significant increase in mechanical complexity. Achieving high performance while guaranteeing safety seems to be a challenging goal that necessitates new actuation technologies in future generations of human-safe robots. In this study, a novel two degrees-of-freedom safe manipulator is presented. The manipulator uses magneto-rheological fluid-based actuators. Magneto-rheological actuators offer low inertia-to-torque and mass-to-torque ratios which support their applications in human-friendly actuation. As a key element in the design of the manipulator, bi-directional actuation is attained by antagonistically coupling MR actuators at the joints. Antagonistically coupled MR actuators at the joints allow using a single motor to drive multiple joints. The motor is located at the base of the manipulator in order to further reduce the overall weight of the robot. Due to the unique characteristic of MR actuators, intrinsically safe actuation is achieved without compromising high quality actuation. Despite these advantages, modeling and control of MR actuators present some challenges. The antagonistic configuration of MR actuators may result in limit cycles in some cases when the actuator operates in the position control loop. To study the possibility of limit cycles, describing function method is employed to obtain the conditions under which limit cycles may occur in the operation of the system. Moreover, a connection between the amplitude and the frequency of the potential limit cycles and the system parameters is established to provide an insight into the design of the actuator as well as the controller. MR actuators require magnetic fields to control their output torques. The application of magnetic field however introduces hysteresis in the behaviors of MR actuators. To this effect, an adaptive model is developed to estimate the hysteretic behavior of the actuator. The effectiveness of the model is evaluated by comparing its results with those obtained using the Preisach model. These results are then extended to an adaptive control scheme in order to compensate for the effect of hysteresis. In both modeling and control, stability of proposed schemes are evaluated using Lyapunov method, and the effectiveness of the proposed methods are validated with experimental results

Hybrid Magneto-Rheological Actuators for Human Friendly Robotic Manipulators

In recent years, many developments in the field of the physical human robot interaction (pHRI) have been witnessed and significant attentions have been given to the subject of safety within the interactive environments. Ensuring the safety has led to the design of the robots that are physically unable to hurt humans. However, Such systems commonly suffer from the safety-performance trade-off. Magneto-Rheological (MR) fluids are a special class of fluids that exhibit variable yield stress with respect to an applied magnetic field. Devices developed with such fluids are known to provide the prerequisite requirements of intrinsic safe actuation while maintaining the dynamical performance of the actuator. In this study, a new concept for generating magnetic field in Magneto-Rheological (MR) clutches is presented. The main rationale behind this concept is to divide the magnetic field generation into two parts using an electromagnetic coil and a permanent magnet. The main rationale behind this concept is to utilize a hybrid combination of electromagnetic coil and a permanent magnet. The combination of permanent magnets and electromagnetic coils in Hybrid Magneto-Rheological (HMR) clutches allows to distribute the magnetic field inside an MR clutch more uniformly. Moreover, The use of a permanent magnet dramatically reduces the mass of MR clutches for a given value of the nominal torque that results in developing higher torque-to-mass ratio. High torque-to-mass and torque-to-inertia ratios in HMR clutches promotes the use of these devices in human-friendly actuation

Conception et validation expérimentale d’un robot manipulateur 6 DDL actionné par des embrayages magnétorhéologiques semi-délocalisés

L’utilisation de robots manipulateurs est un standard en industrie pour automatiser deschaînes de production. Ces robots sont précis, robustes et rapides. Pour atteindre leurperformance, ils sont conçus avec des actionneurs puissants et ils sont faits de pièces mas-sives. Lorsqu’ils sont en utilisation, ces robots doivent être placés dans une zone clôturéepuisqu’ils représentent un danger pour les travailleurs. Pour pallier ce problème, l’industriese tourne vers les robots collaboratifs. Ces robots normalisés sont conçus pour être sansdanger pour les utilisateurs ce qui permet une intégration facile et abordable. Plusieursstratégies comme l’utilisation d’algorithmes de contrôle et des designs mécaniques sontutilisés pour réduire le danger d’un robot manipulateur pour un utilisateur.Ce mémoire présente un manipulateur de 6 degrés de liberté (DDL) actionné par des em-brayages magnétorhéologiques (MR) semi-délocalisés. Le manipulateur a été conçu pouratteindre ou dépasser les performances des bras robots collaboratifs commerciaux dans lebut de valider la capacité des actionneurs MR pour des applications en robotique colla-borative. Le manipulateur a été dimensionné pour avoir des spécifications similaires auxrobots collaboratifs UR5 et WAM. Les spécifications ont été validées par les mesures ex-périmentales. Le manipulateur a une masse en mouvement de seulement 5.3 kg et il peutdéplacer une masse de 4.5 kg à 1 m/s avec une portée de 0.885 m. De plus, la bandepassante en force est au-dessus de 50 Hz et la friction des joints est de maximum 10 % ducouple maximum du joint. Aussi, le manipulateur est intrinsèquement sécuritaire et tolé-rant aux impacts. En somme, il est possible de dire qu’un actionnement MR semi-délocaliséest une solution prometteuse pour la robotique collaborative, mais d’autres mesures ex-périmentales avec le manipulateur sont nécessaires pour que la technologie MR atteigneson plein potentiel en robotique. En autre, il serait nécessaire de mesurer la capacité dumanipulateur à produire des murs virtuels, de mesurer la précision du positionnement dumanipulateur et de mesurer l’énergie transmise par le bras au moment d’un impac

有効なトルク制御が可能で安全なロボットのための可変トルクリミッタの設計と評価

早大学位記番号:新7966早稲田大

Active Collision Avoidance for Human-Robot Interaction With UKF, Expert System, and Artificial Potential Field Method

With the development of Industry 4.0, the cooperation between robots and people is increasing. Therefore, man—machine security is the first problem that must be solved. In this paper, we proposed a novel methodology of active collision avoidance to safeguard the human who enters the robot's workspace. In the conventional approaches of obstacle avoidance, it is not easy for robots and humans to work safely in the common unstructured environment due to the lack of the intelligence. In this system, one Kinect is employed to monitor the workspace of the robot and detect anyone who enters the workspace of the robot. Once someone enters the working space, the human will be detected, and the skeleton of the human can be calculated in real time by the Kinect. The measurement errors increase over time, owing to the tracking error and the noise of the device. Therefore we use an Unscented Kalman Filter (UKF) to estimate the positions of the skeleton points. We employ an expert system to estimate the behavior of the human. Then let the robot avoid the human by taking different measures, such as stopping, bypassing the human or getting away. Finally, when the robot needs to execute bypassing the human in real time, to achieve this, we adopt a method called artificial potential field method to generate a new path for the robot. By using this active collision avoidance, the system can achieve the purpose that the robot is unable to touch on the human. This proposed system highlights the advantage that during the process, it can first detect the human, then analyze the motion of the human and finally safeguard the human. We experimentally tested the active collision avoidance system in real-world applications. The results of the test indicate that it can effectively ensure human security

Modeling and Testing of a Series Elastic Actuator with Controllable Damping

Compliant Actuators are much safer than traditional stiff joint actuators, but at the cost of high overshoot, positional accuracy, and speed. A damper that varies its damping torque during motion is introduced to alleviate these downsides. The equations of motion for the system are derived and simulated. The simulations demonstrated a decrease in the overshoot and ringing time. A physical proof of concept was manufactured and tested. The results from the physical model were inconclusive due to a fault in the physical model. A more accurate physical test model is proposed, and is simulated

磁性流体を用いたバックドライブ可能な油圧アクチュエータの開発

早大学位記番号:新7478早稲田大

Advanced Mobile Robotics: Volume 3

Mobile robotics is a challenging field with great potential. It covers disciplines including electrical engineering, mechanical engineering, computer science, cognitive science, and social science. It is essential to the design of automated robots, in combination with artificial intelligence, vision, and sensor technologies. Mobile robots are widely used for surveillance, guidance, transportation and entertainment tasks, as well as medical applications. This Special Issue intends to concentrate on recent developments concerning mobile robots and the research surrounding them to enhance studies on the fundamental problems observed in the robots. Various multidisciplinary approaches and integrative contributions including navigation, learning and adaptation, networked system, biologically inspired robots and cognitive methods are welcome contributions to this Special Issue, both from a research and an application perspective

Advances of Italian Machine Design

This 2028 Special Issue presents recent developments and achievements in the field of Mechanism and Machine Science coming from the Italian community with international collaborations and ranging from theoretical contributions to experimental and practical applications. It contains selected contributions that were accepted for presentation at the Second International Conference of IFToMM Italy, IFIT2018, that has been held in Cassino on 29 and 30 November 2018. This IFIT conference is the second event of a series that was established in 2016 by IFToMM Italy in Vicenza. IFIT was established to bring together researchers, industry professionals and students, from the Italian and the international community in an intimate, collegial and stimulating environment