This paper introduces a new mechanism that will be classified as an RR-RP hybrid serial-parallel mechanism with variable topology. A mechanism with variable topology is a mechanism that can change its topology due to a change it its joints constraint geometric profile. The RR-RP is unique in that it combines the functionality of both an RR and RP serial manipulator without the need for an additional actuator, leading to a lower weight, lower cost, and more efficient mechanism. The new mechanism and its topology are presented, followed by a workspace analysis, derivation of the forward and inverse kinematics, and velocity analysis of the new mechanism.

Industrial manipulators often interact with large and complex objects for a variety of automation tasks. Finding a feasible path for the robot end-effector that ensures task success is often non-trivial due to considerations such as reachability, singularity avoidance, and collision avoidance. This paper proposes an approach to expand the search space for feasible robot trajectories (and search for an optimal solution) by taking advantage of task redundancy for certain tasks while ensuring task completion. The effort builds on previous work enabling virtual fixture generation for complex shapes given CAD or scan data. The proposed method has been developed into a trajectory planning library on the ROS (Robot Operating System) framework and tested by simulating an interaction of a six-axis industrial robot with an aircraft fuselage. Results show increased coverage of task area with minimal robot base placements.

In this paper, an artificial neural network (ANN) based transfer learning approach of inverse displacement analysis of robot manipulators is studied. ANNs with different structures are applied utilizing data from different end effector paths of a manipulator for training purposes. Four transfer learning methods are proposed by applying pretrained initial parameters. Final training results of ANN with transfer learning are compared with those of ANN with random initialization. To investigate the rate of convergence of data fitting comprehensively, different values of performance targets are defined. The computing epochs and performance measures are compared. It is presented that, depending on the structure of ANN, the proposed transfer learning methods can accelerate the training process and achieve higher accuracy. Depending on the method, the transfer learning improves the performance differently.

This paper is focused on the development of an effective hardware and software architecture that is useful to improve the performance of slender parallel manipulators. The latter can perform high acceleration in fast pick and place applications, but their features can be also exploited in more advanced operations, where path following is a central issue. A simple and effective approach to model the elastodynamic behavior of flexible parallel manipulator is proposed, conceived to be fast and easy to implement in model-based control schemes. Moreover, a workbench architecture based on camera acquisitions is essential to calibrate the elastodynamic model and provide all the required information that are needed to improve path following of flexible mechanims.

Electron beam lithography (EBL) is an important lithographic process of scanning a focused electron beam to direct write a custom pattern with nanometric accuracy. Due to the very limited e-beam field of the focused election beam, a motion stage is needed to move the sample to the e-beam field for processing large patterns. In order to eliminate the stitching error induced by the existing “step and scan” process, we in this paper propose a large range compliant nano-manipulator so that the manipulator and the election beam can be moved in a simultaneous manner. We also present an optimization design for the geometric parameters of the compliant manipulator under the vacuum environment.

In order to make robot manipulators work more compliantly when contacting with the environment, it is necessary to reduce the contact force caused by positioning errors. One effective way to solve this problem is impedance control, which makes the robot manipulator a second-order mass-spring-damping system in principle. In this paper, a position-based fractional-order impedance control design method is proposed for the robot manipulator force control. The end-effector/environment contact model is established, and the closed-loop system is analyzed with the reference force as input. A fractional-order impedance parameters design method is proposed for better force-control performance, which calculates and optimizes parameters through frequency-domain specifications (i.e., phase margin and gain crossover frequency) and time-domain specification (i.e., the minimum J ITSE ). With the Robotics ToolBox for MATLAB (RTB), the performance comparison between integer-order and fractional-order impedance controls is illustrated in simulation. The fractional-order impedance control system has a faster response, smaller overshoot, and better resistance to external disturbances from the environment.

This paper presents the gravity balancing reliability and sensitivity analysis of robotic manipulators with uncertainties. The gravity balancing reliability of the robot is defined as the probability that the reduction torque ratio of the robot reduces below a specified threshold. This index is of great importance for assessing and guaranteeing the balancing performance of the robot in the presence of uncertainties in input parameters. In this work, the balancing design for an industrial robot using the gear-spring modules (GSMs) is proposed with the adoption of a simulation-based analysis of the gravity effect of the robot. The Monte Carlo Simulation (MCS) method with normally distributed variables (i.e., link dimensions, masses, and spring stiffness coefficients) is employed to analyze and simulate the reliability. A case study with an industrial robot is then given to illustrate the reliability performance and the sensibility of the uncertain parameters. It is found that the gravity balancing behavior is achieved even when the uncertainties are applied. The uncertainties could deteriorate the balancing performance when increasing the standard deviations by more than seven percent of their means. The dimensional parameters enjoy the most critical influence on the balancing performance.

The essential characteristics of machining robots are their stiffness and their accuracy. For machining tasks, serial robots have many advantages such as large workspace to footprint ratio, but they often lack the stiffness required for accurately milling hard materials. One way to increase the stiffness of serial manipulators is to make their joints using closed-loop or parallel mechanisms instead of using classical prismatic and revolute joints. This increases the accuracy of a manipulator without reducing its workspace. This paper introduces an innovative two degrees of freedom closed-loop mechanism and shows how it can be used to build serial robots featuring both high stiffness and large workspace. The design of this mechanism is described through its geometric and kinematic models. Then, the kinematic performance of the mechanism is analyzed, and a serial arrangement of several such mechanisms is proposed to obtain a potential design of a machining robot.

This paper presents a consistent analytic kinematic formulation of the 3-PRS parallel manipulator (PM) with a parasitic motion by embedding the velocity level structural constraint equation into the motion expression. Inverse rate kinematics (IRK) is solved with a simple constraint compatible velocity profile, which is obtained by projecting the instantaneous restriction space onto the motion space. Moreover, the systematic method to reveal the parasitic motion is introduced. Thus, the parasitic terms are automatically identified from the main motions. Unlike the usual approach, this study does not consider any explicit parasitic motion expression. Consequently, the derivation of constraint compatible input velocity, which comprises the parasitic term, is simplified. To incorporate the parasitic motion into the task velocity, constraint Jacobian of the manipulator is analytically obtained first. The manipulator Jacobian is extended to incorporate the passive joint’s information apart from the active joints and structural constraint. Hence, the dimension of the Jacobian matrix used to solve IRK is 9 × 6. The validity of the IRK is proved by the Bordered Gramian based forward rate kinematics (FRK). Then, an accurate numerical integration, RK4, is applied to the joint velocity of IRK to obtain the manipulator’s joint values. Consequently, the moving plate’s pose is obtained via forward position kinematics computed using integrated active and passive joint values for validation. The projection matrix used to get compatible constraint motion adjusts our input velocity and makes it compatible with the structural constraint policy, and the parasitic motion is embedded easily. Thus, an explicit formulation of the parasitic motion equation is not required, as the usual practice. Finally, the study presented numerical simulations to show the validity of the outlined resolutions. This paper’s result and analysis can be uniformly applied to other parallel manipulators with less than 6 DoFs.

The design of XY compliant parallel manipulators (CPMs) remains challenging considering the tradeoff between the mirror-symmetry for better constrained undesired rotations and the small footprint, although a significant number of XY CPMs have been reported in extensive applications. This paper presents a new XY CPM using mirror-symmetry without increasing its footprint, mainly aiming to reduce the undesired parasitic rotations of input and output motion stages. The concept of higher degree of stiffness centre symmetry is deployed to tackle the parasitic rotations, leading to a multi-layer compact XY CPM design with each layer being a rotation-symmetrical design. A nonlinear and analytical model of the proposed XY CPM is derived using free body diagrams and the Beam Constrained Model (BCM) to accurately analyse its performance characteristics over a large range of motion. The designed XY CPM is then verified by the nonlinear finite element analysis (FEA) method. Finally, the proposed multi-layer design is comprehensively compared with the well-received single-layer rotation-symmetrical design. It is shown in the new design that the parasitic rotations of input and output stages along with the actuator isolation are significantly reduced and that the out-of-plane-stiffness is also significantly increased.

Kinematic error model plays an important role in improving the positioning accuracy of robot manipulators by kinematic calibration. The identifiability of kinematic parameters in the error model directly affects the positioning accuracy of the mechanism. And the number of identifiable kinematic parameters determines how many parameters can be accurately identified by kinematic calibration, which is one of the theoretical basis of kinematic error modeling. For serial mechanisms, a consensus has been reached that the maximum number of identifiable kinematic parameters is 4R + 2P + 6, where R and P represent the numbers of revolute and prismatic joints, respectively. Due to complex topologies of parallel mechanisms, there is still no agreement on the formula of the maximum number of identifiable parameters. In this paper, a comprehensive numerical study on the number of identifiable kinematic parameters of parallel mechanisms is conducted. The number of identifiable parameters of 3802 kinds of limbs with different types or actuation arrangements are analyzed. It can be concluded that the maximum number of identifiable kinematic parameters is Σ i = 1 n 4R i + 2P i + 6 − C i − 2(PP) i /3(PPP 1 ) i /(2R i + 2P i )(PPP) i , where C i represents the number of joints whose motion cannot be measured and n denotes the number of limbs in a parallel mechanism; (PP) i , (PPP 1 ) i , and (PPP) i represent two consecutive unmeasurable P joints, three consecutive P joints in which two of them cannot be measured, and three unmeasurable P joints, respectively.

This paper deals with the workspace of a closed-loop manipulator having three rotary-linear (R-L) actuators on ground-mounted cylindric joints, plus three revolute and three spheric pairs [1]. The workspace is defined as the reachable region of the origin of the moving coordinate system embedded in the six-degree-of-freedom platform of the manipulator. The regions in the workspace where the platform can rotate in any direction, cannot rotate or can rotate in only some directions have been defined as complete rotatability workspace (CRW), nonrotatability workspace (NRW) and partial rotatability workspace (PRW). Equations of the workspace of the platform which has a) complete theoretical rotatability and b) nonrotatability (when its center is on the boundary of the workspace) are respectively derived. The reachable region of the center of the platform, where this center remains in a plane with a given platform orientation, is also studied.

Robotic manipulators for use in space have flexible structures and as a result have special control problems. These manipulators change their vibrational characteristics as they change in orientation. The Space Shuttle Remote Manipulator System (RMS) was chosen as a typical system and experiments were performed using the Draper Laboratory software model of the arm (DRS). First, the workspace of the manipulator was characterized in terms of the robot’s first two modes of vibration. Next, some feedforward experiments were performed on the computer model to show the promise of vibration reduction using feedforward control.

This paper presents an efficient algorithm for guidance of a convex rigid body in-between non-convex polygonal objects in a Computer-Aided Design (CAD) environment. A shrinking procedure is used that separates the kinematic from the shape constraints by reducing the problem to that of guidance of a line segment in an expanded environment. A slicing technique together with an algorithm for decomposition of the interface channel between the non-convex objects is used to generate the motion program for the line segment. The results can be applied to model based guidance of mobile robots or automatic motion planning for robot manipulators.

The design of modern mechanical hands requires a choice for the kinematic structure of the finger. The typical finger is a planar manipulator with one, two, or three independently controllable joints. Each controllable joint requires a motor and sensor system which increases the weight of the hand. There is a desire to minimize the number of degrees of freedom in a mechanical hand because the payload capacity of a manipulator is limited. Two degrees of freedom provides the required positioning capability of a finger tip (though not the ability to control contact angle). Three joints are required to provide the ability to enclose grasped objects. This paper considers the design of fingers which are planar manipulators with three joints but only two degrees of freedom. In addition to the fully coupled design, twelve classes of finger designs with varying degrees of de-coupling are presented. It happens that one of these classes includes the human finger, a mechanical model of which is presented in detail.

A 3 DOF closed chain kinematic structure particularly well suited to robot manipulators is explored. The structure has a number of distinct geometries, two of which are analyzed to reveal the geometric and Jacobian relationships, singularities and the workspace volume. These relationships are found to be much simpler than for other parallel actuated spatial structures with 3 or more DOFs. The geometries studied can have large workspace volumes. An optimization procedure is applied to select link lengths for which the Jacobian is relatively homogeneous. Singularities can be restricted to the boundary of the workspace. The proposed geometries can achieve speeds and accuracies unattainable with similar serial link designs.

A statically-balanced direct drive robot manipulator is being constructed at the University of Minnesota for analysis of manufacturing tasks such as deburrlng and grinding when Impedance Control (8, 10, 11) is used to control the robot. This mechanism using a four bar linkage is designed without extra counterweights. As a result of elimination of the gravity forces on the drive system, smaller actuators (and consequently smaller amplifiers) are chosen to guarantee the acceleration of about 5g without overheating the motors. This mechanism results in closed-form solution for Inverse kinematics. The closed-form solutions for dynamic and Inverse kinematic have been derived. High torque, low speed brush-less AC synchronous motors are used to power the robot. The relatively “large” workspace of this configuration is suitable for manufacturing tasks. Graphite epoxy composite material is being used for the construction of the robot links.

In this paper, the design of a spherical three-degree-of-freedom parallel manipulator is considered from a kinematic viewpoint. Three different design criteria are established and used to produce designs having optimum characteristics. These criteria are i )symmetry ii )workspace maximization, and iii )isotropy. The associated problems are formulated and their solutions, one of them requiring to resort to a numerical method, are provided. Optimum designs are thereby obtained. A dicussion on singularities is also included.

The use of a computer-controlled multirobot system with sensors in batch manufacturing and assembly tasks offers a number of significant advantages. These include cost savings, reliability, tolerance of working environments unacceptable to humans, and an adaptability to both structured and unstructured environments through simple reprogramming. The end results are improved productivity, efficiency, and flexibility in manufacturing and automation. However, the use of two or more cooperating robots has not been fully exploited to date. Current industrial practice employs simple time-space coordination which does not allow more than one robot working in a common workspace, such coordination and control results in under-utilization of robots. With the increasing demand for high performance manipulators and efficient multirobot manufacturing cells, there is a vital need to develop theoretical and design methodologies that will solve the generic problems faced by industrial robots working cooperatively. If multirobot systems are to be used in manufacturing and assembly tasks, a thorough knowledge of the dynamics of such systems is essential. This paper formulates the dynamics of two robots cooperating to move a rigid body object. The analysis is based on Newtonian mechanics with screw calculus and dual transformation matrices.

The end effector deflections of robotic manipulators may be minimized by optimizing the geometric shape and the dimensions of their links. A multiple posture static performance criterion for the prediction of the shape optimum design is presented. An efficient optimization algorithm is developed for the solution of the problem using finite element modeling to predict the compliance of the robotic arm. The method is applied to an existing robotic arm, and the results demonstrate that simple alterations to the dimensions and the shape of the links can greatly improve, not only the stiffness, but also the stiffness/mass ratio and consequently the vibrational response of the manipulator structure.