Harmonic reducers are generally supported by flexible bearings. The elastic deformation of the flexible bearing enables the harmonic reducer to satisfy high reduction ratio performance. By considering the flexible outer ring and non-circular inner ring of the bearing, a general analytic model was developed to calculate the ball load distribution of flexible bearings. The validity of the proposed analytic model was proved by studying two types of flexible bearing mounted on elliptical cam and four-force action type cam, respectively. Several results validate the use of proposed analytic model to assess the ball load distribution instead of more time consuming FEM. Influences of design parameters in the flexible bearing on the load distribution were investigated, which makes reference for the optimal design of the flexible bearing.

The study of the relationship between the desired system dynamics and the actuation wrench producing those dynamics is important for robotic system analysis. For traditionally actuated robots, the quality indices of dexterity and manipulability quantify this relationship. However, for unilaterally actuated robots (UARs), such as grasping hands and cable-driven parallel robots (CDPRs), these indices cannot be applied due to the unilateral actuation constraint. In this paper, the quality indices of unilateral dexterity ( UD ) and unilateral maximum force amplification (UMFA) are established for UARs with arbitrary number of actuators. It is shown that these quality indices provide task-independent quantifications of the physical properties of robustness and force amplification for UARs, and they can measure the mechanism’s capability both in singular and nonsingular poses. With these indices, manipulability ellipsoid-derived measures can be applied to arbitrary UARs. The significance of the quality indices for robot synthesis and motion generation analysis is illustrated through two case studies: a five-fingered grasp selection problem and the workspace analysis of a spatial CDPR.

The paper describes an innovative fixture created within the AUTORECON project of the European Commission's 7th Framework Program. The fixture is designed to respond to the automotive industry's needs of high modularity and full flexibility, by allowing the secure multishape grasping of a very wide range of (often large and heavy) metal workpieces typical for car-assembly operations. The fixture is used as an end-effector of an industrial robot, which in turn acts in cooperation with other machines, such as other robots performing machining or other processes on the part. The fixturing device is both a highly reconfigurable structure and a robotic mechanism: moving as a programmable robot to reconfigure and acting as a supporting structure once a hold on the part has been established. This dual functioning has been made possible by the development of a key component, a stepless lockable revolute joint, described herein. In order to get a readily modifiable system, all parts of the fixture are designed as modules. Prototypes of the main parts and the whole fixture have been fabricated and experiments validating the design are reported.

This paper presents a longitudinal analysis through bibliometrics from three perspectives: geospatial analysis of research productivity, citation network analysis of journals, and top productive researchers with research communities. The purpose of these analyses is to detect the development and research trends of mechanism and machine theory (MMT) field. The results indicate that the productivity of MMT publications shows a growing trend. The United States (U.S.) has dominated MMT publications, but its ratio has dropped off approximately twenty percent in the past three decades, while China (CN) has rapidly grown in its quantity and ratio of MMT publications. The concentration of MMT publications among various countries has declined over time. Through citation network analysis, the relationships between journals in the MMT field are identified and their variations over periods are derived. The citations have been centered between five related journals and three core journals. Additionally, the evolution of research communities corresponding to the top 30 productive researchers and the distribution of the publications in each community among countries are identified.

Shape-control in an architectural context is expected to provide unique opportunities for buildings with enhanced functionality, flexibility, energy performance, and occupants comfort. An architectural concept is proposed which consists of a parallel arrangement of planar n-bar mechanisms formulating its skeleton structure and a membrane material stretched over it to define the building envelope. Overall shape changes involve coordinated motion of the individual planar mechanisms. Each linkage is equipped with one motion actuator as well as brakes installed on every joint. Reconfigurations of the building are based on the “effective 4-bar (E4B)” concept allowing stepwise adjustments. Each intermediate step involves the selective locking of (n − 4) joints on each closed-loop linkage effectively reducing it to a single degrees-of-freedom (DOF) 4-bar mechanism, the configuration of which can be adjusted using the available motion actuator. A reconfiguration of the mechanism can be realized through alternative control sequences and an optimal one can be selected based on specific criteria. The paper reports the fundamental design and control concepts. A simulation and an experimental study are presented to demonstrate the implementation of the general reconfiguration approach and examine relevant issues.

This paper presents performance charts that map the design space of a bio-inspired robotic condylar hinge joint. The joint mimics the design of the human knee joint by copying the condylar surfaces of the femur and tibia and by copying the four-bar motion of the cruciate ligaments. Four aspects of performance are modeled: peak mechanical advantage, RMS (root mean square) mechanical advantage, RMS sliding ratio, and range of movement. The performance of the joint is dependent on the shape of the condylar surfaces and the geometry of the four-bar mechanism. The design space for the condylar hinge joint is large because the four-bar mechanism has a very large number of possible configurations. Also, it is not intuitive what values of design parameters give the best design. Performance graphs are presented that cover over 12,000 different geometries of the four-bar mechanism. The maps are presented on three-dimensional graphs that help designers visualize the limits of performance of the joint and visualize tradeoffs between individual aspects of performance. The maps show that each aspect of performance of the joint is very sensitive to the geometry of the four-bar mechanism. The trends in performance can be understood by analyzing the kinematics of the four-bar mechanism and the shape of the condylar surfaces.

This paper presents the mechanical design of a novel surgical robotic platform, specifically developed for single-port laparoscopy (SPL). The greatest constraint is the small size of the skin incision through which the robot must operate. Several technical and technological challenges have been tackled to meet the stringent requirements imposed by the surgical procedure at hand. In this paper, a detailed mechanical description of the system is provided, fulfilling the necessary design requirements. The main outcome of this work is a compact, light-weight (total weight approximately 6 kg) and highly dexterous bimanual robot capable of overcoming the current drawbacks experienced in SPL when using traditional medical devices. The system has been assessed in terms of tracking accuracy, resulting in satisfactory and promising performance.

The complex kinematic structure of a human thumb makes it difficult to capture and control the thumb motions. A further complication is that mapping the fingertip position alone leads to inadequate grasping postures for current robotic hands, many of which are equipped with tactile sensors on the volar side of the fingers. This paper aimed to use a data glove as the input device to teleoperate the thumb of a humanoid robotic hand. An experiment protocol was developed with only minimum hardware involved to compensate for the differences in kinematic structures between a robotic hand and a human hand. A nonlinear constrained-optimization formulation was proposed to map and calibrate the motion of a human thumb to that of a robotic thumb by minimizing the maximum errors (minimax algorithms) of fingertip position while subject to the constraint of the normals of the surfaces of the thumb and the index fingertips within a friction cone. The proposed approach could be extended to other teleoperation applications, where the master and slave devices differ in kinematic structure.

Correct evaluation of robot performance has been a problem in the field of robotics. Many scholars have proposed a variety of performance indices, such as manipulability, condition number, and minimum singular value, to describe quantitatively the kinematic performance of a robotic mechanism. However, two questions remain: (1) how to describe the kinematic performance completely for the design of a robotic mechanism, and (2) how to comprehensively describe the global performance distribution characteristics in the workspace. This paper presents a global performance index system for kinematic optimization of a robotic mechanism based on Jacobian matrix, manipulability ellipsoid, and descriptive statistics theory that can comprehensively describe the kinematic performance and the performance distribution characteristics in a robot's workspace. First, the Jacobian matrix, a linear mapping from the joint space to the task space of a robotic mechanism, is analyzed, and the kinematic transmission ability indices and the kinematic transmission accuracy index are determined. Second, four indices, including global average value, global volatility, global skewness, and global kurtosis, are presented to describe the global performance index's distribution in the workspace. Third, the global performance index system is established to evaluate a robot's global kinematic performance based on the above analysis. Finally, a two-degrees of freedom (DOF) robotic mechanism is designed based on the global performance index system as a case, analysis of which shows that the final mechanism has good kinematic performance in the workspace. This demonstrates that the global performance index system proposed in this paper can be useful for the evaluation of the kinematic performance and kinematic optimization of a robotic mechanism.

This paper presents an innovative solution for bounce reduction between a robotic leg and the ground by means of a semi-active compliant foot. The aim of this work is to enhance the controllability and the balance of a legged robot by improving the traction between the foot tip and the ground. The compliant foot is custom-designed for quadruped walking robots and it consists of a linear spring and a magnetorheological (MR) damper. By utilizing magnetorheological technology in the damper element, the damping coefficient of the compliant foot can be altered across a wide range without any additional moving parts. The content of this paper is twofold. In the first part the design, a prototype and a model of the semi-active compliant foot are presented, and the performance of the magnetorheological damper is experimentally studied in quasi-static and dynamic cases. Based on the quasi-static measurements, the damping force can be controlled in a range from 15 N to 310 N. From the frequency response measurements, it can be shown that the controllable damping force has a bandwidth higher than 100 Hz. The second part of this paper presents an online stiffness identification algorithm and a mathematical model of the robotic leg. A critical damping control law is proposed and implemented in order to demonstrate the effectiveness of the device that makes use of smart materials. Further on, drop tests have been carried out to assess the performance of the proposed control law in terms of bounce reduction and settling time. The results demonstrate that by real-time control of the damping force 98% bounce reduction with settling time of 170 ms can be achieved.

Reconfigurable robotic systems can enhance productivity and save costs in the ever growing flexible manufacturing regime. In this work, the idea to synthesize robotic mechanisms with dynamic properties that are reconfigurable is studied, and a methodology to design reconfigurable mechanisms with this property is proposed, named reconfigurable dynamics (Re-Dyn). The resulting designs have not only the kinematic properties reconfigurable, such as link lengths, but also properties that directly affect the forces and accelerations, such as masses and inertias. A 2-degree of freedom (DOF) parallel robot is used as a test subject. It is analyzed and redesigned with Re-Dyn. This work also presents the robots forward dynamic model in detail, which includes the force balancing mediums. The connection method is directly utilized for this derivation, which is well suited for multibody dynamics and provides insight for design parameters (DPs). Dynamic performance indices are also briefly discussed as related to the Re-Dyn method. After redesigning the robot, a full simulation is conducted to compare performances related to a flexible manufacturing situation. This illustrates the advantages of the proposed method.

Flapping-wing robotic platforms based on Dipteran insects have demonstrated lift to weight ratios greater than 1, but research into regulating the aerodynamic forces produced by their wings has largely focused on active wing trajectory control. In an alternate approach, a flapping-wing drivetrain design that passively balances aerodynamic drag torques is presented. A discussion of the dynamic properties of this millimeter-scale underactuated planar linkage accompanies an experimental test of an at-scale device. This mechanism introduces a novel strategy for regulating forces and torques from flapping wings, using passive mechanical elements to potentially simplify control systems for mass and power limited flapping-wing robotic platforms.

This paper presents the design and evaluation of a platform for the assessment of the performance of compliant or underactuated hands. The position of objects relative to the hand can be varied in order to assess the successful grasp region. The boundary positions of this region can be measured with a precision of 3 mm. In addition, the force required to pull an object all the way out of the hand from a stable initial configuration is measured with a precision of 0.2 N for frictionless grasping. These experiments are proposed as benchmark tests to quantify the functional performance of compliant or underactuated robotic hands. This platform considers planar symmetrical grasps, where objects can move along the line of symmetry. An innovative approach to emulate frictionless grasps of circular objects is proposed as well.

The article describes the design of a robotic wrist able to perform spherical motions: Its mechanical architecture is based on parallel kinematics and is suitable to be realized at the mini- or microscale by means of flexible joints. In view of the preliminary design, a rigid-body model has been studied first and the direct and inverse kinematic analyses have been performed, allowing for the determination of theoretical workspace and passive joints’ displacements. The rigid-body dynamic behavior and the operative ranges of the machine have been assessed through the development of an inverse dynamics model. Then, the microparts have been designed with the help of finite element method (FEM) and multibody software and the study has been focused on the flexures: Since the analyses showed that the center of the spherical motion moves around several millimeters in the workspace, the original kinematic concept has been modified with the introduction of a ball joint constraining the mobile platform to frame so as to prevent unwanted translations.

A device reminiscent of the mammalian spine has been designed and built with the ability to lock each individual joint in a string of ball joints. The assembly may be controlled in a manner similar to other hyper-redundant robots, with the added advantage of locking in a straight or axial position. Locking is achieved by orienting two mating collars in a singular configuration that forces compression against neighboring collars and prohibits bending or rotation. Locking is desirable for added strength in supporting objects, as well as for stabilization and power efficiency when bending is not necessary. The split locking mechanism represents a biologically inspired structure with added strength and stability for use in robotics.

This paper investigates the equivalent mechanism structure of origami cartons and for the first time proposes a quantitative model of cartons and the interactive configuration space for folding origami cartons. With an analysis of the equivalent mechanism, gusset vertexes of cartons are investigated based on their equivalent spherical linkages and identified as guiding linkages that determine folding. Having established a kinematics model, a configuration control vector is characterized to control carton manipulation. The information of this configuration control vector is passed to the tip of a robotic finger, and the finger configuration space is hence identified. The paper further introduces configuration transformation and creates a carton interactive configuration space, leading to generating trajectories of all four configuration control vectors and, subsequently, to finger operation trajectories. This results in making use of four robotic fingers for folding origami cartons. The interactive technique is further used for final tucking carton flaps. A novel rig with robotic fingers is then presented to demonstrate the principle and concept.