Parallel Kinematic Machine Tool Research Articles

パラレルメカニズム型工作機械における重力に起因する運動誤差の補正法(パラレルメカニズム)

パラレルメカニズム型工作機械における重力に起因する運動誤差の補正法(パラレルメカニズム)

Compensation of Gravity-Induced Errors on a Hexapod-Type Parallel Kinematic Machine Tool

This paper presents a methodology to compensate contouring errors introduced by the gravity on a Hexapod-type parallel kinematic machine tool with the Stewart platform. Unlike conventional serial kinematic feed drives, the gravity imposes a critical effect on the positioning accuracy of a parallel kinematic feed drive, and its effect significantly varies depending on the position and the orientation of the spindle. We first present a kinematic model to predict the elastic deformation of struts caused by the gravity. The positioning error at the tool tip is given as the superposition of the deformation of each strut. It is experimentally verified for a commercial parallel kinematic machine tool that the machine's contouring error is significantly reduced by compensating gravity-induced errors on a reference trajectory.

R-Test, a New Device for Accuracy Measurements on Five Axis Machine Tools

When rotary axes (rotary tables and/or swivelling axes) are used in combination with linear axes, the position and the orientation of the rotary axes have to be known accurately, because these parameters strongly influence the accuracy of the machined work piece. The new device measures X, Y., Z deviations of circular and spherical movements simultaneously on continuous paths. These deviations are used to calibrate parameter errors like backlash, positioning error, squareness, parallelism, etc. The uncertainty budget of the measurements is presented and effects of thermal influences are shown. Measurement results on a serial five-axis machine and on the parallel kinematic machine tool Hexaglide are shown and discussed in detail.

Disturbance Estimation on a Hexapod-Type Parallel Kinematic Machine Tool by Using A Disturbance Observer

This paper presents a disturbance estimation methodology on a Hexapod-type parallel kinematic machine tool of the Stewart platform. The disturbance estimation by monitoring an armature current of servo motors has been commonly done on conventional serial mechanism feed drives. On a parallel mechanism feed drive, a disturbance observer must have a more complex structure with a precise model of the gravity effect on servo motor loads, which significantly varies depending on the position and the orientation of a spindle unit. The estimation performance of the proposed disturbance observer is validated through static load tests and cutting experiments. As an application example, the proposed disturbance estimation scheme is applied to the compensation of the tool deflection in end milling processes by tilting the spindle.

Post-Processor Development of a Hybrid TRR-XY Parallel Kinematic Machine Tool

A hybrid 5-degrees-of-freedom parallel kinematic machine tool constructed using the TRR-XY mechanism has been used to investigate the theory of post-processing. The effects of the cutter shapes and machine construction on the post-processing are investigated. Some specific parameters only are required to modify the post-processing for the different tools used in real cutting. The tilt angle and yaw angle of the cutter relative to the normal direction of the cutting surface are included in the investigation. The parametric representations of different cutter shapes defined by the DIN standard were also adopted in the derivation. The generality of the post-processor theory developed was then increased. Finally, NC code has been generated using LABVIEW software. Simulations are performed to verify the correctness of the work based on several designed tool paths.

Design optimization of the linkage dimension for a hybrid-type parallel kinematic machine tool

The parallel kinematic machine tool has many advantages including excellent loading capacity, high structural stiffness and small accumulated error of linkage. It has become one of the most important research fields for machine tools. In the present research, a principle for the optimization of the dimensional design parameters of a parallel kinematic machine tool is proposed. A five-degree-of-freedom (5DOF) parallel kinematic machine tool with a TRR-XY hybrid mechanism is chosen for investigating the design procedures and the optimization results. The inverse kinematics of the hybrid mechanism is first investigated. Then, the inverse solution is used to analyse and create the workspaces of the machine tool. The design parameters of the mechanical components are further optimized for constructing the maximum workspace.

Effects of design dimensions on the driving force variation of a hybrid TRR’XYparallel kinematic machine tool

Using parallel-link mechanism as the basic structure of the parallel kinematic machine (PKM) tool is a new design concept and has become one of the most important research fields, attracting many previous researchers. Research on the actuator driving force variation of a PKM tool is essential for the applications of a PKM tool to real machining processes. For machining a component, the smaller actuator driving force required means that the PKM tool has a higher machining performance. To improve the machining performance, understanding of the required actuator driving is very important. A generalized force analysis of the developed system was obtained using the Denavit-Hartenberg (D-H) notation method. The force reactions on the joints and actuator driving forces are obtained on the basis of various cutter locations and a given external cutting force. The prediction of the cutter location with the singularity condition can be also obtained on the basis of the infinite force of the joints. The geometry relationship between the tool platform and the links is adopted to verify the singularity conditions of the system. The driving force variation of the hybrid TRR- XY five-degree-of-freedom machine tool is further investigated.

Accuracy issues of parallel kinematic machine tools

Parallel kinematic machines (PKMs) have been attracting attention in research institutes as well as in the machine tool industry because of their structural rigidity due to their closed kinematic loops and their conceptual capabilities in high dimensional accuracy. During performance evaluation of the first prototypes of parallel machine tools, it turned out that their accuracy has not yet reached industrial application level. Against this background, the accuracy behaviour of a hexapod milling machine, located at the Laboratory for Machine Tools and Production Engineering (WZL) at Aachen University of Technology, and accuracy-related design issues have been extensively studied. Based on these investigations, strategies for kinematic calibration and error compensation have been developed.

Parallel Kinematic Machine Tools – Current State and Future Potentials

Parallel kinematics have recently attracted attention as machine tools because of their conceptual potentials in high motion dynamics and accuracy combined with high structural rigidity due to their closed kinematic loops. This paper, prepared with input from CIRP colleagues as well as of machine manufacturers and end-users involved in PKM, attempts to review the development of parallel kinematics for machine tools, their practical application and their performance compared to classical machine tools.

Nonlinearity for a parallel kinematic machine tool and its application to interpolation accuracy analysis

This paper is concerned with the kinematic nonlinearity measure of parallel kinematic machine tool (PKM), which depends upon differential geometry curvature. The nonlinearity can be described by the curve of the solution locus and the equal interval input of joints mapping into inequable interval output of the end-effectors. Such curing and inequation can be measured by BW curvature. So the curvature can measure the nonlinearity of PKM indirectly. Then the distribution of BW curvature in the local area and the whole workspace are also discussed. An example of application to the interpolation accuracy analysis of PKM is given to illustrate the effectiveness of this approach.

Approach of fast avoiding link interference of the 6 DOF parallel kinematic machine tool

Approach of fast avoiding link interference of the 6 DOF parallel kinematic machine tool