Hybrid Manipulator Research Articles

Design of a planar hyper-redundant lockable mechanism for shape morphing using a centralized actuation method

This work presents a type of kinematically hyper-redundant manipulators, namely serial-parallel manipulators (S-PMs), for shape morphing control. The proposed S-PMs use a centralized actuation method to significantly reduce the number of actuators. The basic design concept is to use flexible limbs to actuate a serial manipulator made of passively lockable rigid parallel manipulator (PM) modules of 3-DOFs. To implement shape morphing control, a shape parametric method is proposed to establish a relationship between a morphing shape and the DOFs of the S-PMs, based on which the kinematics of this hybrid manipulator is derived. The proposed method is applied to design and control a morphing airfoil wing with specific structure and motion requirements. The achieved results demonstrate the effectiveness of the proposed method.

Development of a novel 6-DOF hybrid serial-parallel mechanism for pose adjustment of large-volume components

In this paper, a novel 6-degrees-of-freedom (DOF) hybrid mechanism is proposed to realize position and posture adjusting for large-volume equipment. The designed hybrid manipulator is composed of the lower and upper modules, namely, a 3-DOF redundant spatial parallel mechanism (SPM) and a 3-DOF planar parallel mechanism (PPM), which has three rotational and three translational DOFs. According to the step-by-step pose adjusting strategy, the kinematics analyses of the lower and upper modules have been carried out systematically. For the whole hybrid mechanism, a complete kinematic model has been established; and visualized workspace of the kinematic model with regular shape and large volume demonstrates profound application prospects in engineering. In order to evaluate the performance of the proposed mechanism, experimental tests have been conducted in an automated docking system for pose adjustment of large and heavy components. The analysis results demonstrate the effectiveness and practicability of the new mechanism.

Analysis of Contact force optimization for a hybrid manipulator

A novel hybrid manipulator is designed. Based on the fact that the sum of the external force vector for the object is zero, the criterion of the stability of the object is derived. The formula for calculating contact force of fingers was deduced by matrix theory. The maximum frictional force was taken as boundary condition, then the contact force of fingers was optimized. The advanced CAD software was used to simulate the process of grasping the object. The stability of the object at a certain time was verified. Finally, the contact force between fingers and objects was optimized. It provides a theoretical basis for the application of the hybrid manipulator.

A Novel Modular Approach for Kinematic Modeling and Analysis of Planar Hybrid Manipulators

Abstract For customized design of a hybrid manipulator for a specific application, selection of an appropriate configuration is always a challenge. To assist in this foremost decision in data-driven synthesis, a novel approach is proposed for modular formation of quick configurations. Majorly, a unified methodology is presented for the development of respective kinematic models and differential relations for their performance analyses. This unified modular approach utilizes modular primitives to define planar hybrid configurations. Three types of primitives are introduced as modular components, and the pattern study is detailed. Modeling results from the proposed approach are also compared with normally used partial differentiation with respect to the computational efforts, streamlined modular implementations, and applicability in optimal design approaches. The comparison highlights how the column-wise approach is appropriate for modular methodology. The strategy will help a designer as a tool for analyzing several configurations. Two realistic case studies are demonstrated in this article for application of the methodology in the medical robotics field.

TriRhino: A Five-Degrees-of-Freedom of Hybrid Serial–Parallel Manipulator With All Rotating Axes Being Continuous: Stiffness Analysis and Experiments

Abstract This paper studies the stiffness and experiment of a five-degrees-of-freedom (DOF) hybrid, serial–parallel, manipulator, with all rotating axes being continuous: TriRhino. First, the motion principle of the hybrid manipulator is introduced and the structural design is presented. Next, the stiffness analysis of the hybrid manipulator is carried out. Specifically, a stiffness test, based on prototype and loading device, is performed, proving that the real stiffness is lower than that obtained by the finite element analysis. Following, the main geometric parameters, involving error, are determined, while the real values of the parameters with an error are identified, through performed calibration experiments. Finally, the measurement results show that the positioning accuracy of the manipulator is significantly improved, after kinematic calibration. Moreover, machining experiments on a workpiece show the great ability of the proposed manipulator, in machining parts with curved surface; thus, great application prospects, in the machining of structural parts with complex surfaces, are quite realistic.

Type Synthesis of 2T1R Planar Parallel Mechanisms and Their Moduling Development Applications

The two translational degrees-of-freedom (DOF) and one rotational DOF (2T1R) planar parallel mechanisms (PMs) have the characteristics of simple structures, simple kinematic and dynamic models, and ease of control and allow for a variety of application prospects. This paper concentrates on the derivations of the 5-DOF hybrid manipulators based on the synthesized mechanisms. To understand the effect of the constraint on the motion of a rigid body clearly, the method of reciprocal product between the wrench screw (constraint) and the twist screw (motion) is used and the relationships between the constraint and the motion of a rigid body are analyzed as well. The results are extended to the relationships between the limb constraint and the axes of limb joints. Then, limbs are divided into planar motion and spatial motion limbs in view of their motion characteristics, and some common limbs with constraint are listed. After that, based on the type synthesis method, a class of 2T1R planar PMs with common limbs is carried out. Meanwhile, some typical planar closed chains with two same limbs are obtained in the process of type synthesis. Finally, a 2T1R kinematically redundancy planar PM and two 2R1T spatial PMs are derived by making simple changes to the obtained mechanisms, and detailed derivations of three 5-DOF hybrid manipulators with the ability of processing spatial complex surface are given. Proved by the test parts, the accomplishment of deriving novel robot configurations with regard to expectant motion are quite valuable and practical.

Kinematics and workspace analysis of a robotic device for performing rehabilitation therapy of upper limb in stroke-affected patients

Exoskeleton robots generally have multi-functions and one such function is doing rehabilitation therapy in upper limb and lower limb in stroke-affected patients. A novel hybrid (serial-parallel) robot manipulator was proposed in this paper for rehabilitation of upper limb and its kinematics are studied systematically. This robot manipulator intends to perform wrist flexion, wrist extension, wrist radial deviation, wrist ulnar deviation, elbow flexion, elbow extension, elbow pronation and elbow supination motions. The contemporary mechanical designs especially the kinematic structure of upper limb exoskeleton robots have a unique feature that is, almost all of them use serial manipulators, and few others used parallel manipulators. The kinematic structure of the proposed robot is that of a hybrid manipulator (two parallel manipulators connected in series) which has 4-degrees-of-freedom. It is composed of an upper 3SPS-type parallel manipulator and 2SPR-type parallel manipulator connected in series. The Jacobian and Hessian Matrix method was used to derive the manipulator kinematic formula for solving the displacement, velocity and acceleration. A 3D model of the robotic arm was constructed and analyzed by simulation. The positioning workspace of manipulator was constructed and analyzed. The 3SPS-type parallel manipulator has good kinematic characteristics while performing wrist motions. The 2SPR-type parallel manipulator produced singular configuration, while performing the desired rehabilitation elbow motions, it was found to not be suitable for usage in performing rehabilitation therapy in stroke-affected patients.

A critical review of modelling methods for flexible and rigid link manipulators

Mathematical modelling plays an important role for robotic manipulators in order to design their particular controllers. Also, it is hard challenge to obtain an accurate mathematical model or obtain a suitable modelling method in such vast field. Thus, this critical review is advantageous and indispensable for researchers who are interested in the area to gain fruitful knowledge on the mathematical modelling methods. This paper is classified based on the type of robotic manipulators such as flexible link manipulators (FLMs), rigid link manipulators (RLMs) and hybrid manipulators which involves rigid links and flexible links. The used modelling methods for FLMs are the assumed mode method, the finite element method, and the lumped parameter method as approximation techniques which are well explained and reviewed. The Lagrangian method has inclusive explanation and review which is widely participated for obtaining the dynamic equations of FLMs, and it is appropriate and commonly employed for modelling RLMs. The Newtonian method, the forward kinematic, and the inverse kinematic are also well discussed and reviewed which are suitable and commonly employed for modelling RLMs. The critical discussion of 170 articles reported in this paper guides researchers to select the suitable method for modelling. This paper reviews the published articles in the period of 2010–2020 except for few older articles for the need of providing essential theoretical knowledge. The advantages and disadvantages of each method are well summarized at the end of the paper. The intelligent identification methods are briefly discussed due to the lack of publications especially on the period of 2010–2020.

A Hybrid Underwater Manipulator System With Intuitive Muscle-Level sEMG Mapping Control

Soft-robotic manipulators, with their closed-chamber elastomeric actuators, natural water-sealing and inherent compliance, are ideal for underwater applications for compact, lightweight, and dexterous manipulation tasks. However, their low structure rigidity makes soft robots highly prone to underwater disturbances, rendering traditional control methods unreliable, substantially increasing the challenges for high-dexterity control. To address this issue, we proposed an intuitive underwater hybrid manipulator system with a muscle-level mapping design concept. The manipulator was designed to construct an actuator-configuration which could directly map to the main muscles group in the human forearm. Exploiting this analogy, an electromyography-based wearable controller was developed using continuous bio-sensory data from the operator's arm to complement the intuitive manipulator control. A prototype of the proposed manipulator was constructed and validated in various experiments, where a human user could effectively use muscle activations to proportionally drive the soft-robotic manipulator in free-space motions, as well as performing object manipulation tasks both in air and underwater, only using visual feedback, with consistent performances under various time delays. The promising results of this work have demonstrated that the muscle-level analogy of soft robotics could lead to intuitive and effective underwater manipulation with simple structure and low control effort.

Reconsideration of terminal constraint/mobility and kinematics of 5-DOF hybrid manipulators formed by one 2R1T PM and one RR SM

Hybrid manipulators formed by one 2R1T parallel manipulator (PM) and one RR serial manipulator (SM) have been widely studied. However, the previous researches only focused on the PM part. The basic terminal constraint/mobility and kinematics issues of the integrated hybrid manipulators have been ignored and thus should be reconsidered. The paper studies the basic motion and constraint issues of the integrated hybrid manipulators by using the Exechon hybrid manipulator as a case. First, using Grassmann–Cayley algebra(GCA), a method for deriving the terminal constraint of the 5-DOF hybrid manipulator is proposed and the terminal DOF property is solved. Second, the terminal position and orientation coupling relation in the hybrid manipulator is revealed based on the elimination method and the inverse displacement is solved. Third, the 6 × 6 form full Jacobian containing all actuation and constraint information of the manipulator is derived. The established models in this paper are applicable for the 5-DOF hybrid manipulators.

Inverse displacement analysis of a novel hybrid humanoid robotic arm

The application of hybrid mechanisms in the field of humanoid robots has attracted significant attention. A novel eight-degree-of-freedom hybrid manipulator is proposed to realize a kinematic function similar to that of the human arm. A general method for solving the inverse displacement problem of hybrid mechanisms is given, and the proposed humanoid robotic arm is taken as an example to demonstrate the solution process of this method. Furthermore, a closed-form solution for the inverse displacement problem of the hybrid humanoid robotic arm is derived by using the given method based on screw theory, exponential product formula, and Paden–Kahan subproblems. In addition, the problem of verifying and selecting the appropriate solutions according to the starting postures is also illustrated in a series of simulation experiments. Simulation experiment results show that there are (at most) 32 sets of solutions for the proposed humanoid robotic arm according to the same target position-orientation matrix and the given redundant input variables, and the accuracy of the proposed method for solving the inverse displacement problem is verified.

Impedance control of three dimensional hybrid manipulator

The hybrid manipulators are always found to be of great use in industries due to the major shortcoming of serial manipulators (lesser accuracy and heavy structure) and parallel manipulators (small workspace). Henceforth, a three-dimensional hybrid manipulator is presented in this paper and this hybrid manipulator connects two parallel manipulators in a serial arrangement. Afterwards, the theory of impedance control with some changes is applied for an operation on a three dimensional L-shaped path having some restrictions imposed on the interactive forces when the manipulator is interacting with an object in its environment along with an approach to eliminate amnesia i.e. difference between the actual trajectory and the command trajectory. The overwhelming controller is used between the actual system and the inverse controller. It is observed from the result that there is always some amnesia during force control and some time is provided before the next phase of force control to remove this difference in trajectory.

Coupling analysis of a 5-degree-of-freedom hybrid manipulator based on a global index.

Parallel kinematic machines have been applied in aerospace and automotive manufacturing due to their potentials in high speed and high accuracy. However, there exists coupling in parallel kinematic machines, which makes dynamic analysis, rigidity enhancement, and control very complicated. In this article, coupling characteristics of a 5-degree-of-freedom (5-dof) hybrid manipulator are analyzed based on a local index and a global index. First, velocity analysis as well as acceleration analysis of the robot is conducted to provide essential information for dynamic modeling. Then the dynamic model is built based on the principle of virtual work. Whereas the mass matrix is off-diagonal, a local coupling index as well as a global index is defined, based on which coupling characteristics of the robot are analyzed. Results show that distributions of coupling indices are symmetric due to its structural features. And dimensional parameters, structural parameters, as well as mass parameters have a large influence on the system's coupling characteristics. Research conducted in the article is of great help in optimal design and control. Meanwhile, the method proposed in the article can be applied to other types of parallel kinematic machines or hybrid manipulators.

Application of a Novel Elimination Algorithm with Developed Continuation Method for Nonlinear Forward Kinematics Solution of Modular Hybrid Manipulators

SUMMARYThis paper addresses the application of a novel elimination algorithm with a newly developed homotopy continuation method (HCM) for forward kinematics of a specific hybrid modular manipulator known as n-(6UPS). First, the kinematic model of n-(6UPS) was extracted using a homogenous transformation matrix method. Then, a novel algebraic elimination algorithm was developed to transform the highly nonlinear proposed kinematic model into a system of polynomial equations for each module. Next, the HCM is considered to solve the system of equations. Comparison of the results from the proposed approach with experimental data and other methods demonstrates the efficiency of the proposed contribution.

Kinematic calibration methodology of hybrid manipulator containing parallel topology with main limb

There is a class of parallel kinematic mechanisms (PKMs) containing so-called “main limb”, the kinematic characteristics of which are the same as those of their main limbs. This paper proposes a kinematic calibration method for hybrid manipulators containing parallel topology with main limb. We propose a kinematic equivalent limb (KEL) of the hybrid manipulator and then establish the error model of the KEL. After that, the calibration model of the entire manipulator is derived by integrating the differential error of the parallel part. Using the presented method, the calibration of a seven degrees-of-freedom (DOFs) hybrid manipulator is studied as an example. The error models of both the KEL and the entire hybrid robot are established. The calibration experiment for the hybrid manipulator is carried out. The kinematic parameter errors of the prototype are identified. The errors of the hybrid manipulator decreased by 85% after calibrating, which validates the calibration method.

Workspace analysis and trajectory tracking of a planar hybrid manipulator with ball screw feed drive

The hybrid manipulators have benefits of both serial as well as parallel manipulators. In this paper, a planar hybrid manipulator with six degrees-of-freedom is proposed; it consists of two parallel manipulators each having three degrees-of-freedom. The models for forward and inverse dynamic analysis of this manipulator are presented with bond graph approach. The actuators of the manipulator have ball screw feed drive mechanism to convert rotary motion into linear motion. There are basically three problems addressed in the paper. First, the models are simulated for trajectory tracking of a semi-circular path traced by the lower manipulator initially and then tracking of another semi circular path by upper manipulators. The second problem addressed is to develop the bond graph model of the hybrid manipulator with proportional control to reach a desired position from an initial position with an unity slope after few seconds. Finally, workspace analysis for given semi-circular trajectory is done with calculation of area of the workspace of lower, upper and hybrid manipulators. It is observed from the simulation that the response follows the desired trajectory within the permissible limit. The result indicates that manipulator follows nearly tangential path. It is seen from the result that the desired trajectory lies within the workspace boundary.

Dynamics and control of a 7-DOF hybrid manipulator for capturing a non-cooperative target in space

This paper proposes a 7-DOF hybrid serial-parallel manipulator for capturing a non-cooperative target in space and discusses its dynamics and control. The hybrid manipulator is connected in a series by a 3-DOF parallel part with 1-PU&2-PUS configurations and a 4-DOF serial part with a 4R configuration. First, the UP-RRRR equivalent serial mechanism is presented for the kinematic analysis of the hybrid manipulator. Utilizing the Newton-Euler method, the dynamic model of the equivalent serial mechanism is derived in a recursive form. Then the dynamic equations of the parallel part in recursive form are also developed using the Newton-Euler method. Based on the complete dynamic model, we propose a control scheme for a hybrid robot to capture a non-cooperative target in a zero-gravity environment, including three modules: admittance control, motion estimation of the target satellite, and feedforward of the reaction forces. Finally, experimental results of full physical experiments based on air-bearing testbeds confirm the validity of the proposed control scheme for the hybrid robot to capture a non-cooperative target in space.

A Transformation Method to Generate the Workspace of an n(3RRS) Serial–Parallel Manipulator

Abstract This paper presents a transformation method to generate the workspace of an n(3RRS) serial–parallel manipulator (S–PM). Firstly, the boundary of the workspace of the 3RRS parallel manipulator (PM) is obtained using the boundary search method and verified by MATLAB/SimMechanics simulation. Secondly, the workspace of the 2(3RRS) S–PM is obtained using the proposed method and verified by MATLAB/SimMechanics simulation. Finally, the workspace of the 3(3RRS) S–PM is obtained using the proposed method. The results indicate that the n(3RRS) S–PM can significantly expand its workspace with the increase in the number of PMs connected in series, and the proposed method can generate the workspaces of n(3RRS) S–PMs efficiently with the advantages of simple operation, high efficiency, and high accuracy. The proposed method is applicable to all S–PMs that are composed of PMs, and it provides a reference for solving the workspaces of other types of redundantly hybrid manipulators.

Optimization design for a compact redundant hybrid parallel kinematic machine

Abstract Designing a machine tool that simultaneously satisfies the requirements of high rigidity, large dexterous workspace and small footprint is challenging. This paper proposed a redundant hybrid manipulator as a machine tool with these features. The design attempted to integrate the advantages of a PKM (parallel kinematic mechanism), SKM (serial kinematic mechanism) and redundancy mechanism. The geometric parameters of the manipulator were elaborately tuned to overcome intrinsic and extrinsic singularities with an optimal machining plane. High-accuracy and complex-shape machine results have been experimentally verified. The advantage is the ability to shorten the required strokes of the linear actuators effectively. This change not only improves the performance in terms of rigidity, accuracy and dynamics of the entire mechanism but also reduces the cost of the materials and the performance ratio. The second is to decrease the overall machinery-footprint-to-workspace ratio and lower the manufacturing cost via occupied floor space reduction and layout flexibility of the production line.

Compliance analysis and lightweight design of a two-degree-of-freedom rotating head

This article presents an approach for the compliance analysis and lightweight design of a two-degree-of-freedom rotating head by considering both gravity and joint/link compliances, which provides a comprehensive understanding on the posture adjustment mechanism of five-degree-of-freedom hybrid manipulator. A kinetostatic analysis is carried out to consider both externally applied wrench imposed upon the end-effector and gravity of all movable components. Then, a deflection analysis integrating both joint and link compliances and formulation of component compliance matrices are completed by using a semi-analytical approach. Finally, the lightweight design of two-degree-of-freedom rotating head is realized by considering the deflection constraints. This approach enables to effectively evaluate the deflections of end-effector caused by both payload and gravity under given operation conditions. Moreover, the established method provides reliable guidelines for the design of two-degree-of-freedom rotating head with superior static rigidities and dynamic behaviors.