Parallel Machine Tool Research Articles

Kinematical calibration of a hybrid machine tool with Regularization method

The hybrid machine tools, combining the advantages of serial and parallel type machine tools, provide more and more application opportunities for less-freedom parallel mechanism. Accuracy performance is still an important index of hybrid machine tool for industry application. In this study, configuration of a 3-P(4R)S-XY hybrid machine tool is first introduced. The 3-P(4R)S parallel mechanism can be simplified to a 3-PRS mechanism on kinematical calibration. Based on that, error model and error kinematics are derived to introduce all possible manufacturing and assembling errors into calibration. Then, identification matrix is derived by differentiating kinematical equations. Combining the advantages of calibration schemes based on both inverse and forward kinematics model, a new measurement scheme is put forward, in which not all freedoms of motions needs to be measured and error identification could be efficiently accomplished in one time measurement. In order to solve the ill-posed problem in error identification, practical Regularization methods are adopted. Finally, the kinematical calibration experiment of the prototype machine tool is performed with a combined measuring tool. The results of RTCP accuracy test reveal that the positioning accuracy is less than 0.05 mm in the 30° cone workspace. Calibration experiments for the prototype verify feasibility and effectivity of the more precise kinematical error model, the low-cost measurement scheme, and the error identification solution with Regularization method.

Accuracy Analysis and Simulation of Three Degrees of Freedom Parallel Machine Tool

This paper proposes a novel three degrees of freedom parallel machine tool. The parallel machine tool consists of three serial chains and a fixed base and a moving platform which can be moved in a pose space corresponding to the three degrees of freedom. By using matrix methods, a error model of the parallel machine was developed. The explicit solution of the error of joint and the stroke error of telescopic link were solved for analysis of influence factors of error on the position of moving platform. It provided a theoretical foundation for error compensation of parallel machine tool.

The Lower Control System Development of 3 DOF Parallel Machine Tool CNC System Based on DSP

The 3 DOF parallel machine tool CNC system based on DSP takes 3-HUU configuration of parallel machine tool as the control object, and adopts TMS320F2812 of TI DSP as control core of the CNC system. This paper mainly studies hardware design and software design of the lower control system of the 3 DOF parallel machine tool, and does practical test which shows that the CNC system can well control the parallel machine tool and finish machining movement.

Kinematics Analysis of a New 5 DOF Parallel-Serial Machine Tool Based on the Vector Method

A 5-axis parallel-serial machine tool is proposed, which consists of a 3-DOF parallel mechanism and a 2-DOF serial mechanism, and the kinematics analysis is discussed in detail based on the vector method. The size of the velocity transformation matrix is decreased. The problem of parameter coupling is resolved by adopting identity matrix and four-element vector. The relationship between the velocity and acceleration of the movable platform and the input parameters of the parallel mechanism is established. These algorithms are verified correct through ADAMS (Automatic Dynamic Analysis of Mechanical System) and can be referenced by kinematics analysis, dynamics analysis of parallel or parallel-serial machine tools, which have coupling kinematics parameters.

Tracking Error Transform in Parallel Kinematic Machining

Parallel kinematic machine tools (PKM) are developed to increase dynamic parameters for high speed and high accuracy machining to gain short lead times and high productivity. One of the most important components of machine tools is the numerical controller (NC). Most NCs are organized in a cascaded structure, comprising the position, velocity and current loops. Commonly applied servo controllers generate tracking errors in each axis. These tracking errors are a significant factor that affects machining accuracy, beside geometric machine errors, vibrations, temperature changes and tool errors. In this paper the contour error originated from servo tracking controller in Cartesian kinematic machine tools (CKM) with perpendicular arranged machine axes and PKM is presented. The effects of the forward transformation of the tracking errors in PKM are addressed with experiment and simulation results. The servo tracking effect on trace accuracy is discussed by a tripod mechanism and radial deviations are measured with double ball bar method (DBB).

Commande vision/force de robots parallèles

In this paper, force and position control of parallel kinematic machines is discussed. Cartesian space computed torque control is applied to achieve force and position servoing directly in the task space within a sensor based control architecture. The originality of the approach resides in the use of a vision system as an exteroceptive pose measurement of a parallel machine tool for force control purposes.

Development of NC System of the 3-PUU Parallel Machine Tool Based on PMAC

In this paper, a PUU parallel machine tool with three translational degrees of freedom (DOF) is designed which is usually used in the complex grain machining of the solid rocket engine.， and its numerical control system is described in detail. The so-called “PC+PMAC” is used as the hardware platform, and Windows as the software one, the parallel machine tool NC system is built. The features, such as multi-axis motion control and fast real time communication of PMAC, software resources and efficient data processing of PC are utilized such that Man Machine Interface, position servo control, real time measurement of cutter configuration and closed loop control of the parallel machine tool are realized.

Approximate Feedback Linearization Control for High Precision Hydraulic Parallel Machine Tool

Traditional feedback linearization approach (TFL) requires a priori knowledge of plant, which is difficult and the computational efficiency of controller is low due to complex dynamics of plant. In order to improve the tracking performance of hydraulic parallel machine tool and limit the drawbacks of TFL, a novel approximate feedback linearization approach is proposed in this paper. The mathematical models of hydraulic parallel machine tool are established using Kane method and hydromechanics. The approximate feedback linearization control is designed for the parallel machine tool in joint space, with the position and the stored data in the previous time step are employed, as a learning tool to yield improved performance. Under Lyapunov theorems, the stability of the presented algorithm is confirmed in the presence of uncertainties. Simulation results show the proposed control is readily and effective to realize path tracking, it exhibits excellent performance and high efficiency without a precision dynamics of plant. Moreover, the presented algorithm is well suitable for most industrial applications.

Research on Static Stiffness Characteristics of Parallel Machine Tool

The static stiffness characteristic of parallel machine tool is an important factor and reference for machine design and optimization. The static stiffness characteristic of 3-TPT parallel machine tool is researched in this paper. The structural analytical model of machine tool is built by ANSYS software, which has two different work positions and three kinds of different workloads. The details of analytical process and method are provided, and the deformation conditions and the laws of stiffness variation are got. The main factors of static stiffness are obtained, so it provides an important reference for modifying structure of machine tool and relative research.

Simulation of normal machining of 3D free-form surface by an orthogonal 3-leg parallel machine tool with 5-DOF

A novel orthogonal 3-leg parallel machine tool (PMT) with 5 DOFs is designed for normal machining a 3D free-form surface s. A CAD variation geometry approach is adopted for pre-solving the extension/rotation of the linear/rotational actuators and the pose of this PMT. First, a simulation mechanism of this PMT is created by using the CAD variation geometry technique. Second, a s and a guiding plane of the tool path are constructed, the tool axis of the PMT is kept perpendicular to s, and then a simulation PMT is created. Third, in the light of the two kinds of prescribed tool paths, the extension/rotation of the linear/rotational actuators and the pose of the PMT are pre-solved automatically and visualized dynamically.

The Error Modeling on a Kind of Parallel Machine Tool in Considering the Joint Gap

This paper takes a kind of 3-UPS Parallel Machine Tool (PMT) as the objective of research. First, the kinematic analysis is carried out to the machine and the kinematics equation is obtained. Then, the mathematical model on tool posture error of this machine is established in considering the joint gap based on the kinematics equation. According to the mathematical model expression, the posture error of tool tip point can be calculated when the specific values to the length error of the driving rod and the position error of the joint point are known. The establishment of error model has important theoretical significance to the design as well as the error analysis and compensation of this Parallel Machine Tool.

Research on Vibration Behaviors Simulation for a Novel High-Speed PMT

In order to grasp the vibration characteristics of a novel High-Speed 4-HPS-HPH PMT(parallel machine tool), A vibration behaviors analysis method using virtual prototype simulation was put forward. By the united application of CAD, CAE and visual technologies, the rigid-flexible vibration model of 4-HPS-HPH PMT was constructed. Then the dynamic response of the tool tip, including vibration displacement, vibration velocity, vibration acceleration, and maximum dynamic stresses of driving limbs were realized. The simulation results show that the rigid-flexible vibration model proposed can indicate the vibration behaviors of parallel machine tool. This research provides necessary guidance for dynamic performance analysis, optimization design and control of this 4-HPS-HPH PMT.

Study on Parameter Optimization Based on Workspace of 3-DOF Parallel Machine Tool

This paper proposes an optimization method which makes the structural parameters are minimum and the workspace is maximum based on 3-DOF parallel machine tool. By analysis the conditions of boundary, parameters optimization model is built and gives out the explicit solution of dexterous workspace. Analysis the effect of structural parameters on workspace. The results show the workspace is a unsingularity space.

Simulation of parallel kinematic machine tools with minimal effort

New innovative machine tool concepts like parallel kinematics require the development process to be continuously supported by simulation. Otherwise it will be impossible to exploit their full potential due to the complexity of the kinematic and dynamic behavior. Nevertheless, machine tool manufacturers often refrain from employing simulation tools because of the high effort and expenses expected for the introduction of this technology. It is against this backdrop that the paper presents a method to support the development process of parallel kinematic machine tools with a minimum of effort. An analysis of the development process identifies the machine characteristics that have to be determined for each stage. A simulation method is developed based on these results and on the requirements for a seamless integration of the simulation techniques into the different stages of the process. It is implemented and tested by the example of a parallel kinematic machine tool that has already been successfully introduced in industry.

Enhancing PKM Accuracy by Separating Actuation and Measurement: A 3DOF Case Study

This paper proposes an approach for enhancing parallel kinematics machine accuracy by separating actuation and measurement. We describe the interest of the separation actuation and measurement concept and define the sensor redundancy used for designing the measurement device. Then, we present the design of a parallel machine-tool prototype with an independent measuring system, MoM3, as well as the optimization of its measuring system. Lastly, we present the control schemes used on the prototype, and provide experimental results to show the efficiency of separation actuation and measurement applied to a machine-tool.

Special Issue on Parallel Structures in Manufacturing and Robotics

The first parallel robot – a hexapod – although invented and built in 1947 by Dunlop Tyres’ Dr. Eric Gough, is still commonly known as the Steward Platform after Dr. D. Steward, who published the first research paper on the parallel structure. This opened a new era in parallel structures, which find applications in numerous industries thanks to their many advantages over their serial counterparts, including high-speed, high-accuracy operations, high rigidity, and use in limited workspace. The most noticeable of these are flight and vehicle simulators and high-speed, high-precision machining applications. After decades of use limited due to the structure’s close-loop nature, however, challenges remain, including optimizing layouts, finding optimal workspace, determining structural manipulability, ascertaining structural validation, and developing robust control. This special issue of Automation Technology addresses these vital issues. The seven articles present here deal with research on parallel structures including proposals of mechanisms for extending workspace for existing structures and their new applications, proposals, and kinematic analyses of new structures with enlarged workspace and calibration proposals for parallel machine tool mechanisms. The control of redundant mechanisms, which provide ways to increase mechanism workspace and flexibility, is also explored. These articles are sure to provide researchers in parallel structures with stateof- the-art information useful in their own work. They are also certain to prove both interesting and informative to general readers and specialists in other fields. I would like to express my deep appreciation to the authors, reviewers, and editors for their invaluable contributions for this issue.

Research on Dynamic Behaviors for a Parallel Machine Tool Considering Elastic Component

In order to obtain dynamic behaviors of a spatial rigid-flexible coupling system of PMT(parallel machine tool) without the construction of mathematical model, a new method for dynamic behaviors simulation, which integrates CAD, CAE and visual technologies, was presented. The solid model of PMT was built in SolidWorks and transmitted to ADAMS, the modal neutral file of flexible body including driving limbs and spherical joints were generated in ANSYS, and introduced into ADAMS, then the rigid-flexible coupling model of PMT was build. Based on the rigid-flexible coupling model, the dynamic behaviors, which includes displacements error output response, dynamic stress of driving limbs and natural frequency, were realized. The simulation results show that the rigid-flexible coupling model established can indicate the dynamic behaviors of PMT. The flexibility of driving limbs and spherical joints are demonstrated to have significant impact on dynamics characteristics of PMT. This research can provide the important theoretical base of the optimization design of dynamic parameters for PMT.

Statics Analysis of a Novel 5-DOF Parallel Manipulator

A novel orthogonal 5-DOF parallel manipulator was proposed, and the statics equations of the 5-DOF parallel manipulator were derived in closed forms based on its layout feature, then the statics transmission indices wer defined, and discussed in detail. It can provide theoretical base for the applications of the 5-DOF parallel machine tool. The novel 5-DOF parallel manipulator can be used as the precision platform in which the requirements for high stiffness, high accuracy and good technological efficiency.

Modeling of Position and Pose Error of Stewart Machine Tool Based on D-H Transforming Matrix

The kinematical equation of the moving platform of Stewart parallel machine tool is established with D-H transformation matrix,the equation contains the pose parameters of hinge joints and the D-H parameters of component parts in all branches of parallel mechanism. Based on the equation,an new computation model of position-pose error of parallel machine tool is set up by means of the differential method of matrix. It is demonstrated that not only the effects of all geometrical parameter errors on the accuracy of machine tool are reflected in the model,but also the linear,explicit formula are derived approximately from the nonlinear,implicit correlation between machine position-pose error and all geometric errors. To verify the linear model,another model is derived from the length formula of branches of mechanism,which can reflect much exactly the nonlinear correlation between machine position-pose error and all geometric errors. A simulation demonstrates the effectiveness of linear model because its results approximate satisfactorily those of nonlinear model. Therefore the linear model can be applied to Stewart type parallel machine tool in accuracy analysis or integration,and kinematical identification due to its advantages in analysis. The simulation also demonstrates that the influence of all D-H geometric errors on the machine tool position and pose should be considered when high accuracy of the position and pose is required.

Hybrid kinematics machine tool for drilling applications: precision prediction using advanced software tools

We present a new approach for precision prediction of parallel kinematics machine tools by virtual prototyping (VP) using advanced software tools. VP modelling and kinematics simulation using MSC/ADAMS was carried out for the proposed parallel drilling module mounted on a serial milling machine base, to perform a 3-PRS-PP hybrid-mechanism-based machine tool. The related kinematic analysis, such as the displacement and velocity analysis of the drilling tool end, the rotation angle analysis of the ball joints, the linear movements of the prismatic joints, is obtained. Kinematics analyses and simulations were carried out with and without manufacturing and assembly deviations. The effects of deviations on machine performances were analysed using two-dimensional probability distribution analysis. We present the application of a virtual prototype simulation approach in the parametric design process, structural design and error budget determination for new types of machine tools.