Type Synthesis Method Research Articles

Force-Motion Coupled Mechanism Synthesis Method of Heavy Load Parallel Kinematic Mechanism for Multi-DoF Forming Process

Abstract At present, the design of parallel kinematic mechanism (PKM) generally starts from type synthesis based on the motion pattern and then the dimensions are synthesized based on performance requirements The synthesized type of PKM with optimal load-bearing capacity is hard to determine because the above type synthesis is just based on the motion pattern and the number of synthesized types of PKM is huge. Therefore, this paper aims to investigate a force-motion coupled mechanism synthesis method for heavy load PKM with optimal motion performance and load-bearing capacity. First, the optimal load-bearing conditions for PKM are derived, namely, the wrench screw of a limb is parallel to the external force acting on the moving platform and is reciprocal with the wrench of the actuator. Furthermore, a novel force-motion coupled type synthesis method is proposed, in which the wrench of the limb is added to the constrained screw system. In this situation, the synthesized PKM is singular. Therefore, dimension synthesis is carried out based on the workspace, and a near-singular 6-PHSS PKM is then synthesized. Finally, a novel multi-DoF forming machine with a forming force of 6000 kN is developed. Compared with the Stewart platform (6-UPS PKM), the maximum forces of the actuator and limb of the new near-singular 6-PHSS PKM were reduced by 80% and 10%, respectively, validating the proposed force-motion coupled synthesis method for heavy load PKM.

Type synthesis of 3-DOF spherical hybrid mechanisms with fixed centers of rotation

To improve the load-bearing capacity and the rotation range about the normal of the moving platform in a spherical parallel mechanism (SPM), a type synthesis method for spherical hybrid mechanisms (SHMs) with fixed centers of rotation is proposed by coupling a serial transmission chain with the central passive limb chain of the SPM near its center area. Based on the analysis of the spherical mechanism configuration’s research status with a fixed rotation center, a method for systematically synthesizing SHMs is given, and four types of limb chains are developed. The possible limb constraint systems provided by each type of limb chain are analyzed via screw theory, and the type synthesis of each type of limb chain is carried out. Screening rules are proposed to obtain the preferred limb chains from the limb chain configuration results. By selecting and permuting preferred limb chains based on the mechanism’s center position of rotation and the constraint type, a series of SHMs that rotate unrestricted about the normal of the moving platform are produced. Selecting the RBR-2RRR SHM as an example, its workspace, singularity, dexterity, and stiffness are analyzed to verify the effectiveness of the research. This work enriches the configuration types of SHMs and provides theoretical support for the design and applications of SHMs in engineering.

Configuration design of movable heavy-duty reconfigurable posture adjustment platform with dual motion modes

AbstractThe existing single-mode posture adjustment equipment for solar wing docking is only suitable for a limited number of satellite dimensions; it could not meet the diverse development trends of satellite models. The working range requirements are different when different-sized satellites dock with the solar wing, and the docking process is divided into two stages in this paper. While the DOFs required for the two stages are different, a movable heavy-load reconfigurable redundant posture adjustment platform (RrPAP) with dual motion modes is proposed in this paper. The RrPAP consists of a wheeled mobile platform and a reconfigurable parallel posture adjustment mechanism (PAM). The micro-motion PAM limb types are synthesized, and the comprehensive load-bearing index is proposed to select the mechanism types for heavy-load conditions. A decentralized four-limb six-degree-of-freedom (6-DOF) parallel micro-motion PAM is designed. In the macro-motion stage, for the PAM to still have a defined motion after being released from ground constraints, a serial coupling sub-chain is designed between adjacent limbs to restrict relative movement between them. A type synthesis method for symmetrically coupled mechanisms based on mechanism decoupling and motion distribution is proposed. Four types of symmetrically coupled mechanisms with multi-loop consisting of serial coupling sub-chains are synthesized by using this method. The feasibility of the proposed method is demonstrated through an example using the constraint synthesis method based on screw theory. This work provides a foundation for subsequent refinement and expansion of type synthesis theories and the selection of new types of mechanisms.

Research on the Type Synthesis of a Regular Hexagonal Prism Rubik’s Cube Mechanism

The Rubik’s Cube mechanism (RCM) is a kind of reconfigurable mechanism with multiple characteristics such as multiple configurations, variable topology, strong coupling, and reconfigurability. Crossover research on the RCM with mathematics, chemistry, cryptography, and other disciplines has led to important breakthroughs and progress. It is obvious that the invention and creation of a new RCM can provide important ideological inspiration and theoretical guidance for the accelerated iterative updating of Rubik’s Cube products and the expansion of their applications. This paper investigates the type synthesis method for a regular hexagonal prism (RHP) RCM (RHPRCM). Through analysis of the reconfigurable movement process of the RCM, two mechanism factors are abstracted, a type synthesis process for the RHPRCM is proposed, a symmetry layout method for the RCM’s revolute axis based on the RHP space polyhedron is proposed, and an analysis method for the intersection of the revolute pair contact surfaces (RPCSs) based on the adjacency matrix is proposed. Taking a revolute axis passing through the center of an RHP and having only one RPCS for each revolute axis as an example, an RHPRCM with different topological structures is synthesized. The relevant research in this paper can provide methodological guidance for the synthesis of other spatial RCMs.

Type Synthesis Method for Parallel Robots With Special Topologies

Type Synthesis Method for Parallel Robots With Special Topologies

Type Synthesis of Modular Polyhedral Mechanisms Based on the Generalized Mechanism Models of Regular Polyhedron

Abstract An integrated type synthesis method for polyhedral mechanisms based on polyhedron is proposed. The properties of the polyhedron are considered and the corresponding generalized mechanism is built based on strategies that geometric components are regarded as construction members. Topological graph and configuration matrix are used to describe the generalized mechanism. The target mechanism and its descriptions are obtained from the generalized mechanism via designing the construction members appropriately. Possible types are then enumerated using set operations according to the configuration matrix. The axes of the kinematic pairs are set based on the geometric properties of the polyhedron. Degrees-of-freedom (DOFs) of those possible types are calculated using the modified G–K criterion based on screw theory, and the type synthesis results with DOF more than 0 are obtained. Tetrahedral mechanisms with revolute and sliding pairs are synthesized, and they have 135 configuration results with lower-mobility, which validates the accuracy and effectiveness of the proposed method. Some application examples of the tetrahedral mechanisms are further illustrated for potential values of synthesized mechanisms in robot field.

Deployable polyhedral mechanisms with radially reciprocating motion based on novel basic units and an additive-then-subtractive design strategy

This paper is to deal with the mechanism design problem for constructing deployable polyhedral mechanisms on the basis of novel basic units with an additive-then-subtractive design strategy. The aimed deployable polyhedral mechanisms can be, but are not limited to, Platonic and Archimedean solids. The basic units involved in the type synthesis process refer to one-degree-of-freedom regular polygonal prisms, whose deployable performance has been already proven to be excellent. To show the procedure of the type synthesis method, the case study on a deployable regular-tetrahedron mechanism is presented as a design example. The mobility properties of the proposed deployable regular-tetrahedron mechanism are then confirmed with the combination of screw theory and line geometry. In addition, the kinematic model is presented to study the deployable performance of deployable polyhedral mechanisms. By adopting the proposed type synthesis method, novel deployable Platonic and Archimedean polyhedral mechanisms are proposed with wider-margin radially reciprocating motion. This work not only provides the design and analysis method but also contributes new types of mechanisms, hoping to have a reference for the research of deployable polyhedral mechanisms.

A family of RCM mechanisms: Type synthesis and kinematics analysis

• Propose a novel family of 2-DOF remote center-of-motion parallel mechanism. • The RCM points can be located at variable positions by deforming linkages. • Propose a type synthesis method for RCM and 2T mechanisms. • Propose a combined Jacobian matrix to analyze the complex kinematics. • The non-constrained RCM points contribute to more adaptable MIS manipulators. The remote center-of-motion (RCM) mechanism plays an important role in surgery robotics, exoskeleton robots, haptic devices, pointing mechanisms and so on because of the movements of their end-effector through a fixed point. However, the positions of RCM points are always constrained by the joints. In this paper, a family of two-degree-of-freedom (2-DOF) RCM mechanisms are proposed based on the two translational DOFs (2T) parallel mechanism and the redundant constraint linkage. The RCM points of the proposed mechanisms can be located at any position without constraints, which highlights the remote feature of RCM and contributes to more adaptable manipulators. The redundant constraint linkage of the mechanisms is bestowed a new function as an end-effector. A type synthesis method for the family of RCM mechanisms is proposed by the screw theory. As a subprocedure, 2T parallel mechanisms with a spherical surface shaped workspace can be generated innovatively and classified by the overconstrained dimensions. Finally, different RCM mechanisms are constructed to prove the type synthesis method and discussed by kinematics analysis.

Design and development of a Schönflies-motion parallel robot with articulated platforms and closed-loop passive limbs

The Delta-like parallel robot, which contains three open-ended Pa(4S)1 passive limbs, plays an important role in high-speed pick-and-place operations. To meet the demand in high-speed and high-precision applications, this paper presents a novel articulated-platform parallel robot TH-HR4 with Schönflies motion under the guidance of a modified type synthesis method based on Grassmann Line Geometry and Line Graph. With the benefit of the adopted closed-ended revolute/universal joints, the inherent error of the closed-loop passive limb in the presented parallel robot is avoided when compared with that of the open-ended passive limb caused by elastic deformation. Robot design and kinematics are then provided. To investigate the characteristics of motion/force transmissibility and constrainability of the presented articulated-platform parallel robot, the equivalent transmission and constraint wrenches analysis is presented by considering that the transmission and constraint wrenches in the articulated-platform parallel robots should be applied to the end-effector but not the sub-platforms. Then, the motion/force performance indices which include the input transmission index (ITI), the modified output transmission index (MOTI), the medial transmission index (MTI), and the constraint transmission index (CTI) are extended to evaluate the kinematic performance of the proposed articulated-platform parallel robot. Dimension synthesis of the TH-HR4 robot is carried out, by adopting the performance atlas method, to make the robot realize a good transmission and constraint workspace. Based on these foundations, a prototype of the TH-HR4 parallel robot with optimal geometrical parameters has been developed. Performance tests and applications indicate that the HR4 parallel robot can generate high-precision and high-speed operations.

Novel closed-loop deployable mechanisms and integrated support trusses for planar antennas of synthetic aperture radar

Synthetic aperture radar (SAR) is indispensable electronic equipment in modern life, which has been widely used in the field of geological exploration, disaster monitoring, and environmental observation. With the increasing complexity of earth observation tasks, a higher receiving resolution of SAR is required, which needs the area of the radar antenna to be increased. However, there is a contradiction between the small launch space and the large working area. The deployable antenna mechanism is expected to meet the challenge. In this paper, a graphical type synthesis method is proposed to carry out the mechanism design of deployable mechanisms. According to the structural analysis and design requirements, the articulated form is adopted to carry sub-planes of planar antennas and provide one kinematic chain of the deployable mechanism. Then, different designed kinematic chains are synthesized to construct novel closed-loop deployable mechanisms. Mobility verification of a selected closed-loop deployable mechanism is carried out by screw theory to demonstrate the validity of type synthesis results. By sharing the provided kinematic chain and symmetrical design of two deployable mechanisms, deployable units with the driving unit are proposed as basic modules of support trusses for planar antennas. As a result, three novel deployable support trusses integrated by a series of deployable units and assembly mechanisms are proposed as the platforms for planar antennas. The deployable mechanisms and integrated support trusses proposed in this paper provide candidates for planar antennas of SAR.

Accurate detection mechanism synthesis and robot-assisted recognition method for ankle instantaneous motion

The latest rehabilitation robot based on generalized spherical parallel mechanism (GSPM) forces higher requirements for the accurate ankle motion description, but the talus, ankle core component, is hidden within soft tissue and difficult to be directly observed and described. For this problem, the accurate detection robot and robot-assisted instantaneous motion recognition method for ankle based on it are proposed. Firstly, a foot-talus coupled motion model based on ankle bone structure is established, functional requirements of the detection robot are clarified. Secondly, a type synthesis method of variable GSPM is proposed based on screw theory, and partially decoupled under-actuated GSPMs are constructed. This method can directly determine the actuators and sensors arrangement during the non-instantaneous limb synthesis to avoid complex judgment and screening. Then, the principle and method of robot-assisted ankle instantaneous motion recognition are revealed and summarized by clarifying kinematic mapping relationship of human-machine system. This method can accurately recognize talus orientation and drive repetitive foot motion to weaken subjects' fatigue factors. Finally, based on the established virtual prototype, the rationality and feasibility of the robot-assisted recognition method are verified.

A Novel Method for Type Synthesis of Parallel Mechanism Without Parasitic Motion Based on 2R1T Parallel Mechanism with Rotational Bifurcation

The parasitic motion has been widely recognized as the major drawback of the parallel mechanism. Therefore a class of 2R1T PMs (parallel mechanism) without parasitic motion has been synthesized. However, these PMs can only rotate around two axes in sequential order. It decreases the performance of the balancing adjustment of the end-effector. In this paper, a family of 2R1T PMs without parasitic motion was reconstructed by using a novel method based on the remarkable properties of rotational bifurcation mechanisms, which can rotate in sequential order. Furthermore, some PMs rotating around two continuous axes in an arbitrary order are established by adding single joints. Taking the practicability of these structures into consideration, the workspace of 3-PRPS PM was analyzed as an example. Moreover, this study explores the practical application of the PMs without parasitic motion in developing balance mechanisms in rough-terrain fire-fighting robots. During the climbing process, the tank is adjusted to be parallel to the horizontal plane in real-time. It is proved that this kind of structure realizes continuous rotation around two rotation axes on the premise of no parasitic motion.

Type Synthesis Based on Modular Combination with Virtual Rotation Center and Application

Type synthesis of mechanical structure is of great significance to the realization of mechanism target function, systematization, and stability of mechanical device. The type synthesis method of multilinkage robot has been given high demands with increasing number of degrees of freedom and high flexibility in special occasions. In order to improve the workspace and flexibility of mechanism, this paper studies the existing type synthesis theory and proposes a type synthesis method of modular combination with virtual rotation centers. Firstly, modular units are built. Secondly, modular units are expanded according to the needed paths. In the end, the expanded modular units are combined to form the kinematic linkages. Based on the proposed method, the configuration design of the aerial working platform and the self-adaptive levelling platform is completed. The stabilities of two platforms are checked by modal analysis. The prototype products are manufactured, respectively, for further verifying validity of the method. The designed aerial working platform with virtual rotation centers can achieve 360° rotating large workspace, more compact mechanical structure, and short arrival time at the same height than the common scissor-type and mast-type aerial working platforms. The designed adaptive levelling platform is tested that ensures the levelling of the upper surface at different inclinations. The method can provide new idea for the mechanism configuration and expand the application scope of new mechanisms.

Type synthesis of 2R1T remote center of motion parallel mechanisms with a passive limb for minimally invasive surgical robot

In view of the demands for medical imaging compatibility and efficient space occupation around the surgical site, this paper proposes remote center of motion (RCM) parallel mechanisms (PMs) with a passive limb to enable more flexible arrangement of the limbs and actuators in a RCM surgical manipulator. A type synthesis method is proposed to design the 2R1T RCM PMs with a passive limb based on the Lie group. The motion requirements for the RCM mechanism are first expressed in the form of Lie group. The motion arrangement and kinematic structure development are then implemented to obtain the active and passive limbs. By means of this approach, numerous 2R1T RCM PMs with a passive limb are synthesized. The actuated joints are then selected, and a few qualitative evaluation indices are proposed. Finally, the motion configurations of two generated mechanisms are validated through simulation. The proposed method is universally effective for the type synthesis of multi-degree of freedom RCM PMs with a passive limb.

Constraint characteristics and type synthesis of two families of 1T2R parallel mechanism

AbstractPU- and P*U*-equivalent parallel mechanisms (PMs) are critical families of PMs with one translational and two rotational (1T2R) degree of freedoms and have always been a research hotspot among lower mobility PMs. However, researches on these two families of PMs remain to be inadequate, and existing types are few and uncomprehensive. In this study, first, general wrench systems of PU-equivalent are derived based on virtual-chain approach and screw theory, revealing its constraint characteristics under general configuration. Cause of one parasitic motion is put forward and general wrench systems of P*U*-equivalent PMs with one parasitic motion are obtained. In addition, constraint analysis has been carried out to figure out constraint characteristics of P*U*-equivalent PMs with three parasitic motions. Second, branch chains are divided by generating constraints, and their structures are synthesized based on the presented rules. Then, the process for type synthesis of PU-equivalent PMs and P*U*-equivalent PMs and a series of novel 1T2R PMs are attained based on this. Finally, a novel PU-equivalent PM, 2PRU-PRUPc, and a novel P*U*-equivalent PM with one parasitic motion, 2PRU-PUU PM, are analyzed, demonstrating the effectiveness of the proposed type synthesis method.

6-DOF wheeled parallel robot and its automatic type synthesis method

Wheeled parallel robots combine the advantages of wheeled mobile robots and traditional parallel robots. In this paper, we have introduced wheels in parallel robots as kinematic pairs for the first time. Moreover, a new definition of the incidence matrix of the spatial branched chain is proposed and extended, and the incidence matrix of the wheel is given. Furthermore, we present an automatic type synthesis method for parallel robots with wheels. We synthesized 80 types of open-loop spatial chains with wheels. For the first time, we synthesized two kinds of wheeled parallel robots having six degrees of freedom (6-DOF) with new kinematic characteristics. In addition, a prototype of this 6-DOF wheeled parallel robot was successfully developed with a rated load up to 5 tons. These wheeled parallel robots can be widely used in the field of heavy equipment manufacturing, such as parts processing, transportation, orientation adjustment, automatic assembly, and other industrial operations.

Type synthesis of reconfiguration parallel mechanisms transforming between trusses and mechanisms based on friction self-locking composite joints

This paper proposes a concept of the reconfiguration parallel mechanism (RePM) based on friction self-locking composite joints, which can transform between a truss and a mechanism. This kind of RePMs not only have infinite continuous locking configurations, high payload and impact resistance capabilities, but also decrease energy consumption. The type synthesis method of the RePMs is proposed, including four stages: 1, determination of the motion characteristics of the task; 2, motion design of limbs, including the special and common parts; 3, assembly of limbs and selection of actuated joints; 4, qualitative type evaluation. Based on the friction force principle, a family of self-locking composite joints are presented, including the translation self-locking joint (JSLT), revolution self-locking joint (JSLR) and JSLTr joint. Two applications of the mechanisms with self-locking joints are executed. For application I, some RePMs for in-situ robots are proposed, which have high payload capability and save energy in the locked configuration. For application II, numerous novel RePMs for legged landers with terrain-adaptive landing capability are proposed, which have the infinite continuous landing configurations for landing on various uneven terrains. The proposed concept and design method of RePMs with self-locking joints have wide potential applications in the robots with high payload or impact resistance capabilities.

Design and analysis of a novel hinged boom based on cable drive

Hinged booms are widely used in astrophysics missions; however, the trajectory and deployment velocity are difficult to control because they are usually driven by springs, which limits their application in narrow spaces. Thus, a novel hinged boom is highly required to achieve motion controllability. Through an equivalent substitution between the cable drive loop and the binary link in topology, a type synthesis method for the cable-driven single-degree-of-freedom chain is proposed based on the single-open-chain (SOC) adding method. According to the configuration design, a novel cable-driven hinged boom is proposed, aiming to achieve boom synchronism. Then, to preload easily, a method that preload is applied and measured at the cable ends is adopted and the relationship between the initial preload and the target preload is deduced. By analyzing the distribution of cable tension, a new stiffness model is proposed thus a stiffness equation is obtained. Finally, the dynamic simulation analysis and zero-gravity deployment experiment of the hinged boom is carried out to verify its reliability. This research provides a new way for the type synthesis of cable-driven single-degree-of-freedom chain and a new model for analyzing cable-driven stiffness. Moreover, the novel cable-driven hinged boom obtained in this study can be well-applied in the field of aerospace.

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.

A New Method for Type Synthesis of 2R1T and 2T1R 3-DOF Redundant Actuated Parallel Mechanisms with Closed Loop Units

The current type synthesis of the redundant actuated parallel mechanisms is adding active-actuated kinematic branches on the basis of the traditional parallel mechanisms, or using screw theory to perform multiple getting intersection and union to complete type synthesis. The number of redundant parallel mechanisms obtained by these two methods is limited. In this paper, based on Grassmann line geometry and Atlas method, a novel and effective method for type synthesis of redundant actuated parallel mechanisms (PMs) with closed-loop units is proposed. Firstly, the degree of freedom (DOF) and constraint line graph of the moving platform are determined successively, and redundant lines are added in constraint line graph to obtain the redundant constraint line graph and their equivalent line graph, and a branch constraint allocation scheme is formulated based on the allocation criteria. Secondly, a scheme is selected and redundant lines are added in the branch chains DOF graph to construct the redundant actuated branch chains with closed-loop units. Finally, the branch chains that meet the requirements of branch chains configuration criteria and F&C (degree of freedom & constraint) line graph are assembled. In this paper, two types of 2 rotational and 1 translational (2R1T) redundant actuated parallel mechanisms and one type of 2 translational and 1 rotational (2T1R) redundant actuated parallel mechanisms with few branches and closed-loop units were taken as examples, and 238, 92 and 15 new configurations were synthesized. All the mechanisms contain closed-loop units, and the mechanisms and the actuators both have good symmetry. Therefore, all the mechanisms have excellent comprehensive performance, in which the two rotational DOFs of the moving platform of 2R1T redundant actuated parallel mechanism can be independently controlled. The instantaneous analysis shows that all mechanisms are not instantaneous, which proves the feasibility and practicability of the method.