1,720,983 research outputs found
A technique based on adaptive extended jacobians for improving the robustness of the inverse numerical kinematics of redundant robots
No full textThe extended Jacobian is a technique for solving the redundancy of redundant robots. It is based on the definition of secondary tasks, through constraint functions that are added to the mapping between joint rates and end-effector's twist. Several approaches showed its potential, applications, and limitations. In general, the constraint functions are a linear combination of basic functions with constant coefficients. This paper proposes the use of adaptive coefficients in such functions by using the conditioning index of the extended Jacobian as a quality measure. A good conditioning index of the extended Jacobian keeps the robot far from singularities and contributes to the solution of the inverse kinematics. In this paper, initially, the extended Jacobian and the proposed algorithm are discussed, and then, two tests in different circumstances are presented in order to validate the proposal
Smooth transition for collision avoidance of redundant robots: An on-line polynomial approach
No full textThe presence of cooperation between robots and machines in the industrial environment improved the solution for several manufacturing problems. With cooperation, new challenges emerged, and among these stands out the collision avoidance between such robots and machines. Collision avoidance can be dealt with in several ways, taking into account the computational effort to make a decision and the quality of the calculated trajectory for the robots, evaluated, for instance, by smooth profiles avoiding sudden variations in joints’ velocities or acceleration. In these circumstances, the involved robots need to be redundant since new movements are necessary for avoiding collisions. The strategies for collision avoidance are offline (i.e., based on pre-programming the task), or online (i.e., implemented while the robot performs the main task). In online collision avoidance strategies, numerical performance must ensure the time requirements of the main task performed by the robot; so, numerically efficient solutions are the most appropriate. This paper presents a proposal for the collision avoidance treatment from fixed obstacles for redundant robots, based on polynomial functions. The proposed solution allows achieving smooth trajectories according to criteria based on the continuity of derivatives in trajectory curve transitions. When the robot is out of the imminent collision, it is proposed to solve the inverse kinematics through the Adaptive Extended Jacobians. Throughout the text, the mathematical developments based on polynomials are presented, and in the end, a case study graphically shows comparative results
A Novel Method to Design Translational Parallel Manipulators With an Assigned Maximum Orientation Error
No full textGeometric Design and Tolerancing (GD&T) is the language that specifies several design features and, in this paper, is used to deal with the tolerances of Translational Parallel Manipulators (TPMs). TPMs intend to make a platform have only translational motion with respect to the frame (base), but, in practice, TPMs' platforms present undesirable rotation motions due to unavoidable geometric errors in links' sizes. During the machine-element design, geometric errors can be limited by imposing given tolerances on links' sizes and the tighter tolerances are the higher manufacturing costs are. Therefore, dealing with tolerances is the key for designing a TPM with assigned requirements in terms of platform's rotation limits. In this context, this paper moves from the fact that machining processes generate link sizes with values distributed according to Gaussian distributions, whose mean values are the nominal sizes and whose standard deviations depend on the machining process accuracy, to build a novel method that makes a designer able to satisfy an assigned maximum orientation error on the TPM platform. The proposed method consists of two main phases: (a) identification of the geometric parameters that affect platform's position and orientation, and (b) an analysis, based on numerical simulations, that relates the tolerances assigned to the identified parameters and the positioning precision of the platform. The method can be adapted to other types of lower-mobility robots (LMRs). A case study is also discussed to better illustrate the method
Collision Avoidance for Redundant 7-DOF Robots Using a Critically Damped Dynamic Approach
No full textThe presence of collaborative robots in industrial environments requires that their control strategies include collision avoidance in the generation of trajectories. In general, collision avoidance is performed via additional displacements of the kinematic chain that make the robot move far from the objects that are occasionally inserted into its safety workspace. The variability of the coordinates of the collision points inside the safety volume leads to abrupt movements for the robot. This paper presents a general method for smoothing abrupt movements in robots with one degree of redundancy for collision-avoidance trajectories, employing a second-order digital filter designed with adjustable critical damping. The method is illustrated by applying it to a redundant robot with a spherical–revolute–spherical type (SRS-type) kinematic chain, which is a benchmark used to test the algorithms ideated for solving this problem. This paper also presents an alternative algorithm for the inverse kinematics of the SRS-type robot and the computational experiments that show the collision avoidance proposal’s performance and its properties through graphical results
Workspace Analysis and Dimensional Synthesis of the PRRS-RRC Shoenflies-Motion Generator
No full textSchoenflies-motion generators (SMGs) are 4-degrees-of-freedom (DOF) manipulators whose end effector can perform translations along three independent directions and rotations around one fixed direction (Schoenflies motions). Pick-and-place tasks are typical industrial applications that can be accomplished by these manipulators. In a previous paper, one of the authors proposed a novel single-loop not-overconstrained SMG of type PRRS-RRC with actuators on or near the base and decoupled kinematics, and presented its kinematic analysis. Here, its workspace analysis and its dimensional synthesis are addressed
Mecanismos Paralelos De Dois Graus De Liberdade Para Acionamento De Uma Estação Total Robotizada
No full textThe present invention relates to a robotic total station (or laser tracker), widely used for measuring large structures and at great distances. The objective of the invention is to use parallel mechanisms with mobility equal to two (pan and tilt) to drive a robotic total station (or laser tracker). A robotic total station (or laser tracker) has two drives, one to rotate the telescope horizontally (a movement known as pan) and one to rotate the telescope vertically (a movement known as tilt). The objective of using parallel mechanisms in the robotic total station (or laser tracker) is to meet the requirements of the robotic total station (or laser tracker), which are: pan and tilt, speed and precision. The parallel mechanisms proposed in the present application, because they have two legs, allow the motors to be fixed to the base and the battery to power the motors to be placed on the base as well. This means that the only moving masses are the links and joints of the mechanism and the telescope
Wriflex: Design and Kinematic Analysis of a Self-aligning Parallel Wrist
No full textThis paper presents a new self-aligning parallel wrist called Wriflex. Wriflex is composed of four legs: one of RRR type and the remaining three of PRRS type that connect a moving platform to a fixed platform (base). Leg RRR is a passive-motion-constraint leg designed to generate the spherical movement of the end-effector. The three prismatic (P) pairs, one for each PRRS leg, are the only actuated joints and are located on the base. Here, the kinematic analysis of Wriflex is studied. In particular, the forward and the inverse position analyses are solved in closed form. Then, its instantaneous kinematics is addressed till to identify all its singularities. Eventually, its self-aligning capability is proved by employing the Conditioning Index as kinetostatic-performance measure
Instantaneous Kinematics and Free-from-Singularity Workspace of 3-XXRRU Parallel Manipulators
No full text3-XXRRU parallel manipulators (PMs) constitute a family of six-degrees-of-freedom (DOF) PMs with three limbs of type XXRRU, where R and U stand for revolute pair and universal joint, respectively, and XX indicates any actuated two-DOF mechanism that moves the axis of the first R-pair. The members of this family share the fact that they all become particular 3-RRU structures when the actuators are locked. By exploiting this feature, the present paper proposes a general approach, which holds for all the members of this family, to analyze the instantaneous kinematics, workspace, and kinetostatic performances of any 3-XXRRU PM. The results of this study include the identification of singularity conditions without reference to a specific actuation system, the proposal of two specific dimensionless performance indices ranging from 0 to 1, the determination of the optimal actuation system, and the demonstration that 3-XXRRU PMs, when appropriately sized and actuated, possess a broad singularity-free workspace that is also fully isotropic. These findings hold significance in the context of the dimensional synthesis and control of 3-XXRRU PMs. Moreover, when combined with the closed-form solutions for their positional analysis, as demonstrated in a previous publication by the same authors, 3-XXRRU PMs emerge as intriguing alternatives to other six-DOF PMs. The efficacy of the proposed approach is further illustrated through a case study
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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