The Improved DLR Wrist: Design and Analysis of 2-Degrees-of-Freedom Rotational Mechanism Using Spatial Antiparallelogram Linkages

2020 ◽  
Vol 143 (5) ◽  
Author(s):  
Dukchan Yoon ◽  
Long Kang ◽  
Sajjad Manzoor ◽  
Youngjin Choi
Keyword(s):  
Kinematic Analysis ◽  
Degrees Of Freedom ◽  
Structural Modification ◽  
Angular Displacement ◽  
Rolling Motion ◽  
Robot Arm ◽  
Screw Axis ◽  
Parasitic Motion ◽  
Instantaneous Screw Axis ◽  
Instantaneous Screw

Abstract This article presents a kinematic analysis and modification of a wrist mechanism of the DLR robot arm, which is based on antiparallelogram linkages. This mechanism is modified to improve the range of motion (ROM), to reduce the parasitic motion, and to approximately perform the decoupled output motion. For these purposes, the elliptical rolling motion of an overconstrained antiparallelogram is first investigated in consideration of its structural modification. Also, a specific joint that has a relatively small movement is developed as a flexible hinge by further minimizing its angular displacement for design simplification. The axode analysis of the instantaneous screw axis for wrist movements is conducted to compare the rotational performance between the original and modified mechanisms. Moreover, their workspace qualities are evaluated through analyses of the workspace and the kinematic isotropy index. Finally, the improved DLR wrist of the final modification is prototyped, and its wide circumduction is demonstrated.

Axodes Analysis of the Multi DOF Parallel Mechanisms and Parasitic Motion

2013 ◽  
Author(s):  
Ziming Chen ◽  
Huafeng Ding ◽  
Wenao Cao ◽  
Zhen Huang
Keyword(s):  
Jacobian Matrix ◽  
Parallel Mechanisms ◽  
Screw Axis ◽  
Spatial Mechanism ◽  
Parasitic Motion ◽  
Screw Motions ◽  
Instantaneous Screw Axis ◽  
Moving Platform ◽  
Instantaneous Screw ◽  
General Motion

The general motion of a spatial mechanism is a screw motion about an instantaneous screw axis (ISA). The locus of a series of ISAs will form a ruled surface, which can be called as an axode. For a spatial mechanism with only one degree of freedom (DOF), the ISAs or the axodes of the moving platform are unique. However, the axodes of the parallel mechanisms (PMs) with multi DOF are related to the specific motion which has various possibilities. In this paper, the ISAs of the multi DOF PMs are studied using the jacobian matrix which is changing with the configurations of the moving platform. The axodes of the multi DOF PMs with different inputs or outputs are obtained using this method. Based on the analyzed results, it is very clear that the general motions of the PMs are screw motions or rotations about a series of ISAs. In the end, the parasitic motion of the PMs is studied. For a PM, the parasitic motion will exist if the rotational freedoms are not rotations about a fixed point or axis.

Generating Swept Volumes With Instantaneous Screw Axes

1994 ◽  
Author(s):  
Zeng-Jia Hu ◽  
Zhi-Kui Ling
Keyword(s):  
Moving Object ◽  
Ruled Surfaces ◽  
Screw Axis ◽  
Spherical Surfaces ◽  
Swept Volumes ◽  
Instantaneous Screw Axis ◽  
Swept Volume ◽  
Instantaneous Screw ◽  
Plane Polygon ◽  
Boundary Surfaces

Abstract The instantaneous screw axis is used in the generation of the swept volume of a moving object. The envelope theory is used to determine the boundary surfaces of the swept volume. Specifically, the envelope surfaces generated by a plane polygon, cylindrical and spherical surfaces are presented. Furthermore, the ruled surfaces generated by edges of the moving object are discussed.

scholarly journals Conceptual mechanical design of antagonistic variable stiffness joint based on equivalent quadratic torsion spring

2020 ◽  
Vol 103 (3) ◽  
pp. 003685042094129
Author(s):  
Jishu Guo
Keyword(s):  
Degrees Of Freedom ◽  
Modular Design ◽  
Angular Displacement ◽  
Variable Stiffness ◽  
Human Robot Interaction ◽  
Design Calculation ◽  
Robot Arm ◽  
Compact Structure ◽  
Torsion Spring ◽  
Stiffness Characteristics

The variable stiffness joint is a kind of flexible actuator with variable stiffness characteristics suitable for physical human–robot interaction applications. In the existing variable stiffness joints, the antagonistic variable stiffness joint has the advantages of simple implementation of variable stiffness mechanism and easy modular design of the nonlinear elastic element. The variable stiffness characteristics of antagonistic variable stiffness joints are realized by the antagonistic actuation of two nonlinear springs. A novel design scheme of the equivalent nonlinear torsion spring with compact structure, large angular displacement range, and desired stiffness characteristics is presented in this article. The design calculation for the equivalent quadratic torsion spring is given as an example, and the actuation characteristics of the antagonistic variable stiffness joint based on the equivalent quadratic torsion spring are illustrated. Based on the design idea of constructing the antagonistic variable stiffness joint with compact structure and high compliance, as well as the different design requirements of the joints at different positions of the multi–degrees of freedom robot arm, nine types of mechanical schemes of antagonistic variable stiffness joint with the open design concept are proposed in this article. Finally, the conceptual joint configuration schemes of the robot arm based on the antagonistic variable stiffness joint show the application scheme of the designed antagonistic variable stiffness joint in the multi–degrees of freedom robot.

scholarly journals Estimating the Instantaneous Screw Axis and the Screw Axis Invariant Descriptor of Motion by Means of Inertial Sensors: An Experimental Study with a Mechanical Hinge Joint and Comparison to the Optoelectronic System

Sensors ◽  
2019 ◽  
Vol 20 (1) ◽  
pp. 49 ◽  
Author(s):  
Andrea Ancillao ◽  
Maxim Vochten ◽  
Erwin Aertbeliën ◽  
Wilm Decré ◽  
Joris De Schutter
Keyword(s):  
Inertial Sensors ◽  
High Sensitivity ◽  
Helical Axis ◽  
Screw Axis ◽  
Invariant Representation ◽  
Optoelectronic System ◽  
Hinge Joint ◽  
Instantaneous Screw Axis ◽  
The Mean ◽  
Instantaneous Screw

The motion of a rigid body can be represented by the instantaneous screw axis (ISA, also known as the helical axis). Recently, an invariant representation of motion based on the ISA, namely, the screw axis invariant descriptor (SAID), was proposed in the literature. The SAID consists of six scalar features that are independent from the coordinate system chosen to represent the motion. This method proved its usefulness in robotics; however, a high sensitivity to noise was observed. This paper aims to explore the performance of inertial sensors for the estimation of the ISA and the SAID for a simple experimental setup based on a hinge joint. The free swing motion of the mechanical hinge was concurrently recorded by a marker-based optoelectronic system (OS) and two magnetic inertial measurement units (MIMUs). The ISA estimated by the MIMU was more precise, while the OS was more accurate. The mean angular error was ≈2.2° for the OS and was ≈4.4° for the MIMU, while the mean standard deviation was ≈2.3° for the OS and was ≈0.2° for the MIMU. The SAID features based on angular velocity were better estimated by the MIMU, while the features based on translational velocity were better estimated by the OS. Therefore, a combination of both measurements systems is recommended to accurately estimate the complete SAID.

Instantaneous Screws of Weight-Bearing Knee: What Can the Screws Tell Us About the Knee Motion

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Alon Wolf
Keyword(s):  
Screw Theory ◽  
Weight Bearing ◽  
Theoretical Background ◽  
Geometrical Method ◽  
Screw Axis ◽  
Knee Motion ◽  
3D Space ◽  
Instantaneous Screw Axis ◽  
Instantaneous Screw ◽  
Insight Into

There are several ways to represent a given object's motion in a 3D space having 6DOF i.e., three translations and three rotations. Some of the methods that are used are mathematical and do not provide any geometrical insight into the nature of the motion. Screw theory is a mathematical, while at the same time, geometrical method in which the 6DOF motion of an object can be represented. We describe the 6DOF motion of a weight-bearing knee by its screw parameters, that are extracted from 3D Optical Reflective motion capture data. The screw parameters which describe the transformation of the shank with respect to the thigh in each two successive frames, is represented as the instantaneous screw axis of the motion given in its Plücker line coordinate, along with its corresponding pitch and intensity values. Moreover, the Striction curve associated with the motion provides geometrical insight into the nature of the motion and its repeatability. We describe the theoretical background and demonstrate what the screw can tell us about the motion of healthy subjects' knee.

A Generalized Kinematic for Calculating and Evaluating Surface Geometry of Gears and Cutting Tools

1992 ◽  
Author(s):  
J. Grill ◽  
K. H. Hirschmann ◽  
G. Lechner
Keyword(s):  
General Equation ◽  
Cutting Tools ◽  
Grinding Process ◽  
Spatial Motion ◽  
Line Geometry ◽  
Surface Geometry ◽  
Screw Axis ◽  
On Line ◽  
Instantaneous Screw Axis ◽  
Instantaneous Screw

Abstract A new method for simulating the cutting and grinding process of gears has been developed. The procedure, implemented on a workstation, allows to describe the most general case of spatial motion based on line coordinates. The meshing of two gears is replaced by the motion of two axodes, rolling and sliding on each other about and along the instantaneous screw axis. A general equation of meshing has been developed, also based on line geometry. Velocity, acceleration and jerk can be determined, which are used for calculating the generated surfaces and their derivatives.

Velocity Analysis of Truss-Type Manipulators

1996 ◽  
Author(s):  
Stephen L. Canfield ◽  
R. Randall Soper ◽  
Scott L. Hendricks ◽  
Charles F. Reinholtz
Keyword(s):  
Ad Hoc ◽  
A Priori ◽  
Velocity Analysis ◽  
General Description ◽  
Screw Axis ◽  
Output Plane ◽  
The Past ◽  
Instantaneous Screw Axis ◽  
Instantaneous Screw ◽  
Variable Geometry Truss

Abstract A generalized method for the velocity analysis of truss-type manipulators is presented. This analysis relies on a priori knowledge of the position analysis for the manipulator. The approach uses a connectivity chart to define the equations required to determine the velocities of the nodal points of the truss. The problem of determining the nodal velocities is formulated as a linear algebraic relationship for ease of analytical and numerical manipulation. Once each nodal velocity is known, a general description of the overall manipulator velocity is formed by determining the instantaneous screw axis for the output plane. An analytical method for characterizing this output velocity in terms of the instantaneous screw axis is presented. Analysis of each of the four basic variable geometry truss modules (tetrahedron, octahedron, decahedron, and dodecahedron) is presented. Although ad hoc velocity analyses of many of these manipulators have been presented in the past, the technique presented in this paper is unified for any truss-type manipulator.

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