The Octahedral Hexarot - a novel 6-DOF parallel manipulator

A novel 6-DOF parallel kinematic manipulator named the Octahedral Hexarot is presented and analyzed. It is shown that this manipulator has the important benefits of combining a large positional workspace in relation to its footprint with a sizable range of platform rotations. These features are obtained by combining a rotation-symmetric actuating arm system with links in an octahedral-like configuration. Thus the manipulator consists of a central cylindrical column with six actuated rotating upper arms that can rotate indefinitely around the central column. Each upper arm is connected to a manipulated platform by one 5-DOF lower arm link. The link arrangement of the Octahedral Hexarot is inspired by the original Gough platform. The manipulated platform is an equilateral triangle and the joint positions on the upper arms approximately form an equilateral triangle. A task dependent optimization procedure for the structural parameters is proposed and the workspace of the resulting manipulator is analyzed in depth.

Kinematic analysis and workspace determination of hexarot-a novel 6-DOF parallel manipulator with a rotation-symmetric arm system

Parallel mechanisms possess several advantages such as the possibilities for high acceleration and high accuracy positioning of the end effector. However, most of the proposed parallel manipulators suffer from a limited workspace. In this paper, a novel 6-DOF parallel manipulator with coaxial actuated arms is introduced. Since parallel mechanisms have more workspace limitations compared to that of serial mechanisms, determination of the workspace in parallel manipulators is of the utmost importance. For finding position, angular velocity, and acceleration, in this paper, inverse and forward kinematics of the mechanism are studied and after presenting the workspace limitations, workspace analysis of the hexarot manipulator is performed by using MATLAB software. Next, using the obtained cloud of points from simulation, the overall borders of the workspace are illustrated. Finally, it is shown that this manipulator has the important benefits of combining a large positional workspace in relation to its footprint with a sizable range of platform rotations.

An introduction to utilising the redundancy of a kinematically redundant parallel manipulator to operate a gripper

Although parallel manipulators provide several benefits compared to similar-sized serial manipulators, they typically exhibit a limited rotational workspace. One approach to designing a parallel manipulator with infinite range of tool rotation around one axis is to introduce kinematic redundancy. This is typically achieved by extending a non-redundant mechanism with an additional actuator and a supplemental degree of freedom, while the degrees of freedom of the tool platform remain the same. The main drawback of this approach is the cost of the additional actuator. In this paper, we discuss the possibility of harvesting the motion in the additional degree of freedom to operate a gripper. The benefits of the proposed idea include saving the cost of a gripper actuator and reducing the mass of the manipulated platform. Additionally, the requirement to provide the manipulated platform with compressed air or electric power is removed. Several variants of a kinematically redundant manipulated platform with five degrees of freedom are introduced along with conceptual mechanical designs for transforming the redundant platform motion into the opening and closing of a gripper.

A comparison of the yaw constraining performance of SCARA-tau parallel manipulator variants via screw theory

The SCARA-Tau parallel manipulator was derived with the objective to overcome the limited workspace-to-footprint ratio of the DELTA parallel manipulator while maintaining its many benefits. The SCARA-Tau family has later been extended and a large number of variants have been proposed. In this paper, we analyse four of these variants, which together encompass the main differences between all the proposed SCARA-Tau manipulators. The analysed manipulator variants utilise an identical arrangement of five of the six linkages connecting the actuated arms and the manipulated platform and exhibit the same input-output Jacobian. The normalised reciprocal product between the wrench of the sixth linkage and the twist of the platform occurring without this linkage provides a measure on how effectively the sixth linkage constrains the manipulated platform. A comparison of the manipulator variants with respect to this measure demonstrates each variants suitability for specific applications.

Heavy tools manipulation by low powered direct-drive five-bar parallel robot

This paper presents a simple and available system for manipulation of heavy tools by low powered manipulator for industrial applications. In the heavy manufacturing industries, sometimes, heavy tools are employed for different types of work. But the application of robots with heavy tools is not possible due to the limited torque limits of actuators. Suspended tool systems (STS) have been proposed to manipulate heavy tools by low powered robot-arm for this purpose. A low powered five-bar direct-drive parallel manipulator is designed and constructed to manipulate heavy tools suspended from a spring balancer. The validity, usefulness, and effectiveness of the suspended tool system are shown by experimental results.

Inverse kinematics analysis of 6-RRCRR parallel manipulators

This paper presents a solution to the inverse kinematics of 6-RRCRR parallel manipulators with orthogonal non-intersecting RR-joint configuration. The inverse kinematics solution of such parallel robots compared with that of parallel robots with orthogonal intersecting RR-joint or universal joint configuration is more complex due to the existence of RR-joint variables. A novel methodology is established to define 6 independent variables of the actuators and 12 dependent RR-joint variables using the pose of the mobile platform with respect to the base frame. The constraint of RR-joints are analysed and the numerical algorithm to obtain joint variables is assessed. The forward kinematics of a 6- RRCRR parallel manipulator is modelled and computational analysis is performed in order to numerically verify the accuracy and effectiveness of the proposed methodology for the inverse kinematics analysis. Numerical results of a trajectory tracking simulation are provided. The results verify high accuracy for the proposed inverse kinematics solution of this special family of parallel micromanipulators.

A method for extending planar axis-symmetric parallel manipulators to spatial mechanisms

This paper investigates axis-symmetric parallel manipulators, composed of a central base column and an arm system able to rotate around this column. The arm system includes several actuated upper arms, each connected to a manipulated platform by one or more lower arm linkages. Such manipulators feature an extensive positional workspace in relation to the manipulator footprint and equal manipulator properties in all radial half-planes defined by the common rotation-axis of the upper arms. The similarities between planar manipulators exclusively employing 2-degrees-of-freedom (2-DOF) lower arm linkages and lower mobility spatial manipulators only utilising 5-DOF lower arm linkages are analysed. The 2-DOF linkages are composed of a link with a 1-DOF hinge on both ends whilst the 5-DOF linkages utilise 3-DOF spherical joints and 2-DOF universal joints. By employing a proposed linkage substitution scheme, it is shown how a wide range of spatial axis-symmetric parallel manipulators can be derived from a limited range of planar manipulators of the same type.

On the feasibility of utilising gearing to extend the rotational workspace of a class of parallel robots

Parallel manipulators provide several benefits compared to serial manipulators of similar size. These advantages typically include higher speed and acceleration, improved position accuracy and increased stiffness. However, parallel manipulators also suffer from several disadvantages. These drawbacks commonly include a small ratio of the positional workspace relative to the manipulator footprint and a limited rotational capability of the manipulated platform. A few parallel manipulators featuring a large ratio of the positional workspace relative to the footprint have been proposed. This paper investigates the feasibility of employing gearing to extend the range of the end-effector rotation of such mechanisms. The objective is to achieve parallel manipulators where both the positional and rotational workspace are comparable to that of serial manipulators.

Analysis of the inverse kinematics problem for 3-DOF axis-symmetric parallel manipulators with parasitic motion

 Determining an analytical solution to the inverse kinematics problem for a parallel manipulator is typically a straightforward problem. However, lower mobility parallel manipulators with 2-5 degrees of freedom (DOFs) often suffer from an unwanted parasitic motion in one or more DOFs. For such manipulators, the inverse kinematics problem can be significantly more difficult. This paper contains an analysis of the inverse kinematics problem for a class of 3-DOF parallel manipulators with axis-symmetric arm systems. All manipulators in the studied class exhibit parasitic motion in one DOF. For manipulators in the studied class, the general solution to the inverse kinematics problem is reduced to solving a univariate equation, while analytical solutions are presented for several important special cases.

Mathematical modelling of linear motion error for Hexarot parallel manipulators

Hexarot is a robotic manipulator that belongs to the family of axis symmetric parallel mechanisms. The robot is able to move the robot platform or tool center point in six degrees of freedom (DOF). This paper presents the kinematics model of the robot including the inverse and forward kinematics, and its time derivatives. Then using the kinematics formulations, investigation of the nonlinear motion of the Hexarot robot for a desired linear motion path is performed. For this purpose, the concept of curvature of the robot path is used for measuring the nonlinearity of the actual motion of the robot. The nonlinear motion error of the robot is analyzed for the scenario where the platform moves on a linear path between two arbitrary points of the robot workspace. The effects of different parameters on the nonlinear motion error of the mechanism are demonstrated and strategies for motions with low error values are proposed.

Kinematic and dynamic modeling of a robotic head with linear motors

Our present research focuses on kinematic and dynamic modeling of a 3-DOF robotic cutting head for the next generation of CNC machines. The robotic cutting head is one kind of parallel manipulator of 3-PUU type, which has a high flexibility of motion in three-dimensional space. The parallel manipulator consists of three linear servomotors, which drive three connecting rods independently according to the cutting strategy. Being a parallel manipulator, the robotic cutting head has higher stiffness and position accuracy; consequently, higher velocities and accelerations can be achieved. A very suitable application of this mechanism is as a cutting head of a precision machine tool for three-dimensional cutting problems.

Supporting scientists in re-engineering sequential programs to parallel using model-driven engineering

Developing complex computational-intensiveand data-intensive scientific applications requires effectiveutilization of the computational power of the availablecomputing platforms including grids, clouds, clusters, multicoreand many-core processors, and graphical processingunits (GPUs). However, scientists who need to leverage suchplatforms are usually not parallel or distributed programmingexperts. Thus, they face numerous challenges whenimplementing and porting their software-based experimentaltools to such platforms. In this paper, we introduce asequential-to-parallel engineering approach to help scientistsin engineering their scientific applications. Our approach isbased on capturing sequential program details, plannedparallelization aspects, and program deployment details usinga set of domain-specific visual languages (DSVLs). Then, usingcode generation, we generate the corresponding parallelprogram using necessary parallel and distributedprogramming models (MPI, OpenCL, or OpenMP). Wesummarize three case studies (matrix multiplication, N-Bodysimulation, and signal processing) to evaluate our approach.