Parallel Kinematic Research Articles

The implementation of an optical computer mouse as a low-cost displacement sensor

The accurate measurement of distance, position or displacement is a requirement in many robotics projects. This paper presents the investigation of a HP M-UAE96 optical mouse as a low-cost displacement sensor. Various resolutions were obtained on a Windows operating system in conjunction with MATLAB®. The Arduino IDE was used with a linear actuator module to accurately produce predetermined linear movements. The most suitable resolution was found to be 0.2 mm/pixel and was implemented on a parallel kinematic manipulator in a case study. Surface contact and length of measurement were significant factors that influenced measurement accuracy.

A Spatial Parallel Kinematic Manipulator with Nested Kinematic Chains and High Rotational Range

A Spatial Parallel Kinematic Manipulator with Nested Kinematic Chains and High Rotational Range

Mechatronic Coupling System for Cooperative Manufacturing with Industrial Robots

Rising product variants and shortened product life cycles require more flexible and universally utilizable production systems and machines. Consequently, it can be expected that the importance of industrial robots in production will continuously increase, due to their suitability to take over the role of a universal production machine. However, robots are not yet able to fulfill this role. Industrial use of robots has so far been limited mainly to simple transport and handling tasks in the context of human-robot collaboration as well as highly repetitive automated tasks in the context of manufacturing and assembly. For universal use, robots must be capable to perform more demanding tasks in manufacturing with higher requirements on mechanical stiffness and accuracy. Therefore, this paper presents a mechatronic system to couple two robots to a parallel kinematic system to temporarily increase the mechanical stiffness. The coupled state of the robots allows load sharing, higher process forces and eventually higher precision. The overall goal is to enable robots to perform more demanding manufacturing tasks and thus to be utilized in a wider range of applications. Design requirements, the development approach and optimization methods of the first coupling module prototype will be presented and discussed. The next development steps, a future demonstration system and possible use cases for the coupling module will be shown in the outlook.

Adaptive RISE Feedback Control for Robotized Machining With PKMs: Design and Real-Time Experiments

The development of high-precision tasks, such as machining, needs a positioning device for the cutting tool with the smallest possible error. Multiple design factors need to be considered to ensure a mechatronic device successfully performs such tasks. One of these factors may be attributed to the control scheme, which is responsible for controlling the position of the machine. In view of the importance of designing a good control scheme for a robotic system, in this article, we propose a new extension of the robust integral sign of the error (RISE) for the positioning device a parallel kinematic machine (PKM). This extension consists in including a nominal feedforward term based on the inverse dynamic model of the robot and replacing the RISE fixed feedback gains with adaptive ones. The RISE part of the proposed controller ensures semiglobal asymptotic stability. Moreover, it can accommodate sufficiently smooth bounded disturbances. The feedforward part cancels the nonlinearities of the system, improving the tracking performance of the controller. The adaptive feedback gains produce corrective actions when an increase in the tracking errors is due to the contact forces that occur during the machining process. A Lyapunov-based stability analysis is conducted to prove the semiglobal asymptotic stability of the proposed control solution. To show its effectiveness, real-time experiments are performed for two case studies; the first one is on a free motion trajectory and the second on machining experiments under three different forward speeds on SPIDER4, a redundantly actuated PKM.

가공용 위치 보상 2축 스테이지 최적설계

Recent, manufacturing industry has demand that a robot milling system with higher DOF than CNC milling due to an increase in demand for processing complex and flexible shapes. However, a disadvantage of low surface quality exists owing to vibrations caused by the low rigidity of the robot. The main reason for the low surface quality of a target workpiece is the resonant frequency of the robot occurring below 200 Hz . To overcome this problem, we developed a 2-DOF position compensation stage that has high dynamics. In this study, the stage of parallel kinematics using an L-shaped flexible hinge was presented and optimized for rigidity higher than that of the serial kinematics structure. The optimally designed stage through the crab-leg structure was designed with high stiffness with a moving range of 26.1 μm and natural frequency of 513.54 Hz.

Innovative Delta Robot Sample Scanner

Synchrotron Endstations typically use a stack of coarse and fine motion stages to position and scan a sample in the beam. The serial nature of this design causes a low resonant frequency and hence limits the position stability. The combination of multiple stages also adds motion control and data analysis complexity. A large range parallel kinematic cartesian sample scanner has been designed, built, tested and installed to address these limitations. The stage combines a 3 mm travel range with < 3 nm RMS position jitter in the scan directions and < 1 nm/minute thermal drift during scanning. This paper describes and demonstrates the mechatronic design process of Dynamic Error Budgeting. The stage is installed and fully operational on beamline I14 at the Diamond Light Source being used for nanoscale XRF mapping, imaging and ptychography.

Novel Reconfigurable Walking Machine Tool Enables Symmetric and Nonsymmetric Walking Configurations

Current research on walking robots strives to achieve a higher efficiency, a better load capacity, and an increased adaptability. Parallel kinematic manipulators (PKMs) are characterized by high payload and accuracy, but conventional PKMs with fixed configurations are limited to constrained workspaces in known structured environments. In this article, we propose a parallel reconfigurable walking machine tool that overcomes these limits by adapting its configuration and gaits to different scenarios. A lightweight and compact positioning system with shape memory alloy actuation is presented to achieve reconfiguration capabilities. Furthermore, kinematic, stability, and force analyses are reported to determine the optimal walking gaits in three different scenarios (with inclined slopes at different angles) and four robot configurations. Finally, a set of experiments with the physical prototype validates the proposed models. The results show that symmetric configurations present a better performance at lower ground inclinations (0.5% error), whereas asymmetric configurations can climb on slope conditions that would prevent the use of conventional PKMs (18% or 10°).

STRUCTURAL - MORPHOLOGICAL SYNTHESIS OF PARALLEL KINEMATICS-BASED HYBRID 3D-PRINTER AND CONNECTION WITH THE CHALLENGES OF INDUSTRY 4.0

This article highlights the application of a systematic method, a structural - morphological approach to the synthesis of new technical solutions in the field of additive technologies to meet the challenges of Industry 4.0, namely the synthesis of a hybrid, fully automated 3D printer with parallel kinematic structures.

Design and Performance of a Spatial 6-RRRR Compliant Parallel Nanopositioning Stage

Piezoelectric actuators (PEAs) and compliant parallel mechanisms (CPMs) are advantageous for designing nanopositioning stages (NPSs) with multiple degrees of freedom (multi-DOFs). This paper proposes a new NPS that uses PEAs and CPMs with multiple spatial DOFs. First, the design of the mechanism is introduced. Six parallel kinematics revolute-revolute-revolute-revolute (RRRR) branched chains were used to create a 6-RRRR CPM for superior mechanical performance. Three in-plane and three out-of-plane chains were combined using a two-in-one structure to ensure fabrication feasibility. A two-in-one 6-RRRR CPM was employed to build the proposed NPS. Second, the mechanical performance was analyzed. High-efficiency finite-element modeling approaches were derived using the compliance-based matrix method (CMM) and a pseudo-rigid body model (PRBM). The model included both 6-RRRR CPM and NPS. The simulation results validated the static and dynamic performance, and the experimental results verified the kinematics. Based on the newly designed mechanism and verified mechanical performance, the proposed 6-RRRR NPS contributes to the development of spatial multi-DOF NPSs using PEAs and CPMs.

A new fast nonlinear model predictive control of parallel manipulators: Design and experiments

High-speed parallel manipulators are characterized by fast sampling rates and challenges owing to the presence of constraints, high nonlinearities, uncertainties, and fast dynamics. The development of a reliable nonlinear model predictive control (NMPC) approach for this type of robotic systems is challenging because of the complex dynamics that involves high computational burden. To address this control problem, this paper proposes a new fast NMPC strategy applied to high-speed parallel robots. Based on (i) a parameterization technique, (ii) a fast gradient solver, (iii) a proportional integral derivative (PID) control term, (iv) a nonlinear dynamic model, and (v) an artificial neural network (ANN) model, two fast NMPC frameworks were developed to reduce the computational cost of the classical NMPC and address online implementation. In this study, we focus on improving the performance of the standard predictive control strategy outside of the range of its classical applicability by developing a fast NMPC controller for high-speed parallel kinematic manipulators (PKMs). Numerical simulations and real-time experimental results were presented and discussed to validate the relevance of the proposed controllers. Experiments were conducted on a four-degree-of-freedom (4-DOF) PKM called VELOCE developed in our laboratory. The results show that the proposed solution outperforms the original scheme in terms of real-time tracking performance.

Geometric modeling with small defects of over-constrained Parallel Kinematic Machine

In the case of over-constrained mechanisms, the system can only be assembled or move under strict geometric conditions. A crucial step is to identify these conditions from the geometric model. Classically, the geometric model of a robot is computed from the Denavit–Hartenberg formalism. However, when imperfect mechanisms are studied, this formalism does not introduce exhaustively small geometric defects. In this article, a formalism based on kinematic joint invariants is preferred to describe the geometric behavior. The efficiency of this formalism is demonstrated for the accuracy improvement of a serial robot. A stationarity analysis of the geometric model is then performed to determine the geometric constraints induced by the over-constrained systems and to reduce the number of geometric parameters initially introduced. The methodology is first illustrated on an over-constrained slider–rod–crank system. Then, it is applied to the over-constrained mechanism of the Tripteor X7, a Parallel Kinematic Machine-tool. The benefit of our methodology is validated by a comparison of the geometric model obtained with a CAD model and a previous geometric model proposed in the literature. Finally, the identification of the parameters of the defined geometric model is conducted in order to quantify the potential accuracy benefit.

Research on the End Effector and Optimal Motion Control Strategy for a Plug Seedling Transplanting Parallel Robot

Due to the phenomenon of holes and inferior seedlings in trays, it is necessary to remove and replenish unqualified seedlings. The traditional operation is labor-intensive, and the degree of mechanization is low. This paper took broccoli seedlings as the research object and developed an image recognition system suitable for seedling health recognition and pose judgement, researched and designed a plug-in end effector that reduces leaf damage, and conducted orthogonal tests to obtain a substrate parameter combination containing the moisture content, seedling age, and transplanting acceleration suitable for culling operations. A parallel robot kinematics and dynamics model was built. The fifth degree B-spline curve was used to construct the joint space motion curve for seven nodes, and the motor speed, torque, and end-effector acceleration were used to construct the joint space motion curves. The end-effector acceleration was the constraint condition to plan the optimal trajectory of the joint space in time, and the optimal time was obtained using the artificial fish swarm–particle swarm hybrid optimization algorithm. A single operation time was greatly reduced; the whole machine was systematically built; the average time of single-time seedling removal was measured; and the transplanting efficiency of the whole machine was high. In the seedling damage rate gap test, the leaf damage rate was low. This research provides a reference for the localized development of greenhouse high-speed and low-loss seedling removal equipment.

Object-oriented modeling, simulation and control of a 6-DoF parallel kinematic manipulator for remote handling in DONES facility

This paper describes the modeling and simulation activities performed, within the EUROfusion framework, to support the engineering design and the development of the control system of the DONES Parallel Kinematic Manipulator (PKM), a 6-DoF parallel robot part of the Remote Handling System of the DONES facility. The main tasks of the PKM are the planned annual replacement of the Target Assembly and the High Flux Test Module, two of the crucial and most activated components of DONES. The PKM model, developed using the Modelica object-oriented language, is able to simulate the dynamics of the entire robots, including the main non-linear effects due to backlashes and static friction. The simulator is employed to support the preliminary design of the control system, based on an independent-joint approach with dual-loop cascade-PID logic. Simulations are then conducted to assess robot performances in terms of resolution, accuracy, repeatability and generated forces.

Comparative Study Using CAD Optimization Tools for the Workspace of a 6DOF Parallel Kinematics Machine

This paper deals with an up-to-date topic among robotic industrial applications that require a high degree of speed, rigidity, and orientation. Currently, when technology and software applications reach a high level of performance, in various robotic industrial applications that start from certain concepts, the implementation of efficient structures has proven to be challenging. New structures such as the parallel kinematic machine (PKM) category has proven its efficiency through its structure in terms of high inertia rigidity and high speeds during processes. This paper deals with the subject of PKM-type structures in terms of the optimal design workspace of such a structure. The calculation of the workspace is considered the premise from which it starts in terms of its implementation in a robotic production line. The entire process of calculating the workspace for a given PKM structure is carried out through modern CAD applications that have specific modules in place in this direction. CATIA V5 offers the possibility through the product engineering optimizer module, simulation and calculation of different scenarios aimed at identifying the volume of the workspace for a PKM structure. In the article, we demonstrate the relations between the robot workspace and the design parameters, a method that can also be applied for other parallel structures. The method is useful for robot designers in the optimization of parallel robots with regard to the workspace by using CAD tools. Previous research in the field refers of the usage of CAD tools only for visual representation and not for optimizing the workspace, while this study and test results show that CAD tools are suitable for analyzing and optimizing the robot workspace of the 6DOF parallel robot, due to its easiness in application and fast implementation time.

Kinematic error model of a 3-PUU parallel mechanism for translational motion

Accuracy of parallel kinematic machine (PKM) is affected by geometric parameters (GPs) and non-geometric parameters (NGPs). For GPs, the use kinematic error model (KEM) to calibrate these errors has been studied, but few of them have considered the influence of the linkage posture. In this paper, link-orientation-based joint error model (LOBJEM) and sensitivity analysis are presented. In LOBJEM, the original KEM, which is constant joint error model (CJEM), is derived first. The angle between each link and the Z axis is considered as the parameter to adjust the KEM to derive LOBJEM and it can cause the value of joint error to vary with the position of end effector. The calibration process includes measuring the positioning error by a laser interferometer, identifying the error terms using least square method and compensating by the numerical control code (NC-code). The error model and calibration process have been realized on the delta robot 3D printer. Compared with the CJEM, the residual error of LOBJEM was reduced from 75% to 60% of the original error. To estimate the positioning errors caused by NGPs, we constructed a backpropagation neural network model, which can reduce the final residual error to 25% of the original error.

パラレルメカニズムを用いた小形三次元座標測定機

パラレルメカニズムを用いた小形三次元座標測定機

THE NEW IMPLEMENTATION METHODS MANAGEMENT MECHANICAL CUTTING AND VIBRO PROCESS

The problem of ensuring the required quality and operation of the properties of machine parts is becoming increasingly important in mechanical engineering. However, to date, no generalized theoretical relationships between surface quality parameters, machining accuracy, performance properties of parts and parameters of machining processes, which allow to solve the problem of technological support of the specified performance properties of parts. The control of the surface formation process with the required properties is carried out mainly by using partial experimental dependences and tables of processing modes. The complexity of the problem is that when machining parts it is necessary to establish such processing conditions that would provide a set of requirements for tool wear, machining accuracy, surface quality characteristics, productivity and more. Working machines of special and general purpose, their separate knots and mechanisms are constantly improved, thus increase of a technical level of machines is carried out by introduction of new technical decisions, use of modern technologies and scientific developments. The experience of development and operation of mechanisms of parallel kinematics confirms their high efficiency and prospects of this direction of mechanical engineering. Due to the design features of the layout, the mechanisms of parallel kinematics have closed kinematic chains that form spatial structures. As a rule, these structures are based on triangular rod systems. They have high rigidity characteristics, provide high speeds and acceleration of working bodies. Accordingly, these capabilities can significantly increase the static and dynamic accuracy of positioning mechanisms. The lack of theoretical foundations for the development of mechanisms, in particular high-precision mechanisms, hinders the widespread introduction of parallel kinematics mechanisms. Improving accuracy requires a comprehensive study of kinematics and work processes, taking place in their main nodes. Therefore, studies aimed at improving the parameters of static and dynamic accuracy of spatial mechanisms of parallel kinematics are relevant.

A Tethered Façade Cleaning Robot Based on a Dual Rope Windlass Climbing Mechanism: Design and Experiments

Cleaning tasks for vertical structures, such as building façades and walls on construction sites, are dangerous; there is a high risk of fall accidents among workers engaged in such tasks. Hence, research on the automation of wall-cleaning tasks based on robotics technology has been actively conducted in recent years. However, existing wall-cleaning robots have limitations, such as poor mobility performance or the need for additional infrastructure for operation. In this article, we designed a novel rope-driven wall-cleaning robot Edelstro-M2 with two innovative characteristics. First, both vertical and horizontal movements on the wall are possible by implementing a dual rope climbing mechanism and parallel kinematics. Second, except for a rope fixing arrangement, additional infrastructure, such as winch and building management unit systems, is not required for operation. A prototype model was developed, and real-world experiments were conducted to verify the mobility and cleaning performance of the robot. In the experiment, the robot was controlled by manual remote control. We plan to study automatic control of the robot in the future works.

A constraint embedding approach for dynamics modeling of parallel kinematic manipulators with hybrid limbs

Parallel kinematic manipulators (PKM) are characterized by closed kinematic loops, due to the parallel arrangement of limbs but also due to the existence of kinematic loops within the limbs. Moreover, many PKM are built with limbs constructed by serially combining kinematic loops. Such limbs are called hybrid, which form a particular class of complex limbs. Design and model-based control requires accurate dynamic PKM models desirably without model simplifications. Dynamics modeling then necessitates kinematic relations of all members of the PKM, in contrast to the standard kinematics modeling of PKM, where only the forward and inverse kinematics solution for the manipulator (relating input and output motions) are computed. This becomes more involved for PKM with hybrid limbs. In this paper a modular modeling approach is employed, where limbs are treated separately, and the individual dynamic equations of motions (EOM) are subsequently assembled to the overall model. Key to the kinematic modeling is the constraint resolution for the individual loops within the limbs. This local constraint resolution is a special case of the general constraint embedding technique. The proposed method finally allows for a systematic modeling of general PKM. The method is demonstrated for the IRSBot-2, where each limb comprises two independent loops.

Determination of the argon spectral function from(e,e′p)data

The E12-14-012 experiment, performed in Jefferson Lab Hall A, has measured the $(e, e'p)$ cross section in parallel kinematics using a natural argon target. Here, we report the full results of the analysis of the data set corresponding to beam energy 2.222 GeV, and spanning the missing momentum and missing energy range $15 \lesssim p_m \lesssim 300$ MeV/c and $12 \lesssim E_m \lesssim 80$ MeV. The reduced cross section, determined as a function of $p_m$ and $E_m$ with $\approx$4\% accuracy, has been fitted using the results of Monte Carlo simulations involving a model spectral function and including the effects of final state interactions. The overall agreement between data and simulations turns out to be quite satisfactory ($\chi^2$/n.d.o.f.=1.9). The resulting spectral function will provide valuable new information, needed for the interpretation of neutrino interactions in liquid argon detectors.