Accuracy issues of parallel kinematic machine tools

In the development of robots and machine tools, in addition to conventional and serial structures, parallel mechanism-based kinematic structures have been used over a longer period of time. Aside from a number of advantages, the irregular shape and relatively small dimensions of the workspace formed by parallel mechanisms rank among the major weaknesses of their application. Accordingly, this fact has to be taken into consideration in the process of designing parallel mechanism-based robots or machine tools. This paper describes the categorization of criteria for the conceptual design of parallel mechanism-based robots or machine tools, resulting from workspace analysis as well as the procedure of their defining. Furthermore, it also presents the designing methodology that was implemented into the program for the creation of a robot or machine tool space model and the optimization of the resulting solution. For verification of the criteria and the programme suite, three common (conceptually different) mechanisms with a similar mechanical structure and kinematic characteristics were used.

A review of parallel kinematic machine tools: Design, modeling, and applications

This research is investigated on the multi-objective performance optimization of a parallel robotic machine tool which is expected to be applied as a next generation of computer numerical control (CNC) machine. The system configuration and the kinematic model are detailed introduced. The performance maps including dexterity and workspace are generated and illustrated. The multi-objective optimal performance indices are investigated based on the integration of the evolutionary algorithm and Pareto frontier sets. The developed technologies and approaches are generic and also feasible for the design, modeling and improvement of other parallel kinematic machines.

Machining capability of a 2-D of parallel kinematic machine tool and conventional CNC milling machine

A 5-Degree of Freedom (DOF) 5-UPS/PRPU fully parallel machine tool (PMT) was introduced. Based on the original edition of CNC system, the concise motion control algorithm was deduced by analyzing the identical feature between two Euler angles of 5-UPS/PRPU PMT and two swing angles of conventional 5-axis cutter swing machine tool. Then by using the formula of the inverse kinematic solution of the PMT, the length of the driving axis in the joint space can be calculated. The new CNC system software based on this algorithm was developed and it has been applied successfully to the 5-DOF PMT in our laboratory.

This paper took a 3-UPS Parallel Machine Tool (PMT) as the object of research; it mainly introduced the process of establishing the compensation strategy for this PMT. Firstly the kinematics equations on driving chain and constraint chain was established on the basis of kinematics analysis. Then according to the structural characteristics and the results of kinematics analysis, the error compensation strategy of feedback correction type with the semi-closed loop control mode was used in the error compensation for this PMT by the method of installing respectively the encoders on the each joint of parallelogram mechanism, namely the compensation way of “parallel driving and series feedback” was adopted. Finally this paper has also deduced the theoretical model of error compensation. The research results in this paper provided a theoretical basis for realizing error compensation of this PMT, and had important practical significance for improving machining precision of PMT

This paper examines the competitive characteristics of U.S. manufacturers in the machine tool (MT) industry. After several decades of decline, this industry has recently shown signs of a modest but sustained recovery. Empirical evidence from a national survey of 104 MT producers suggests that the revival of this sector has been driven by a combination of factors, including renewed export involvement, improved customer support, and better product design. Although most MT companies are small-to-medium-sized enterprises (SMEs), the survey data show that very small SMEs are poorly represented in the recovery thrust of the industry as a whole. Our principal conclusion is that the MT industry has been following an export-led path toward stabilization, but that certain types of small producers are unlikely to thrive for very long. The most serious problems facing small producers include shrinking local markets, import competition, shortages of skilled labor, and cyclical demand.

A novel 6-SSP parallel machine tool and a novel 4SPS+UPU parallel machine tool are presented, and a novel CAD approach is proposed to machine a 3D free-form surface in its normal direction by using the two parallel machine tools. First, by adopting the CAD geometry constraint and dimension-driving technique, the simulation mechanisms of a 6-SSP parallel manipulator with 6-DOF and a 4SPS+UPU parallel manipulator with 5-DOF are created. Second, a 3D free-form surface and a guiding plane of tool path are constructed above the moving platform of the two simulation mechanisms. Third, the tool axis of simulation parallel machine tool is retained perpendicular to the 3D free-form surface. In the light of two prescribed tool paths, the driving limbs and the pose of the moving platform of parallel machine tools are solved automatically and visualized dynamically.

A deformation model of a parallel kinematic machine tool

The Department of Manufacturing Engineering and Operations Management at The University of Nottingham was the first research establishment in Europe to acquire a Parallel Link Mechanism (PLM) Machine tool. The machine, purchased as part of a 4 year research initiative1, is Giddings and Lewis’ first production Variax Hexacenter™. To properly ascertain the full capability of a machine tool a variety of tests are required and for this purpose a number of standards have been established and widely accepted. These test procedures have been developed over the years to suit serial kinematic mechanism machines and at present there are no acceptance standards designed specifically for PLM Machine tools. Some of the standard tests are suitable for comparison with conventional machines but there is definite scope for additional tests designed to be more revealing for PLM machines.

A fuzzy interpolation method is proposed to simplify the calibration process for parallel machine tools. Either inverse or forward kinematic models need to be used in the traditional calibration methods to perform the identification and compensation of the pose errors for parallel machine tools. Instead of using a model, the proposed method presents a modeless technique combined with the fuzzy interpolation method to obtain the same or higher calibration accuracy when a small workspace is adopted.

This paper deals with possible new concepts for machine tools based on parallel kinematics for advanced manufacturing. Parallel kinematics machines (PKM) enable the mechanical properties of manufacturing machines to be improved. This has been proven by several new machine tool concepts. However, this potential can be and must be increased by applying the principle of redundant actuation. This paper deals with the extension of the concepts of redundantly actuated parallel kinematics structures for five-sided five-axis machine tools and for a free-forming sheet metal forming machine. The design principles of previous successful PKMs are summarized and new concepts are proposed. The most important requirement criteria are summarized. The proposed concepts are qualitatively and initially quantitatively evaluated according to these criteria.

Unchained from the confines of controller limitations, the industrial application of parallel kinematic machines in manufacturing is beginning to emerge. The launch of commercially available hexapod machine tools at the 1994 International Manufacturing Technology Show in Chicago represented the first radical departure in machine tool design since the introduction of numerical controls. The parallel actuator technology promises to offer manufacturers a number of advantages relative to conventional machine tools, such as a higher stiffness-to- mass ratio, higher speeds, higher accuracy, reduced installation requirements, and mechanical simplicity. Several machine tool makers in the U.S. and around the world are pursuing parallel actuator technology, while their prospective customers — manufacturers — are beginning to contemplate what the novel multi-axis machining technology might mean for their operations.

Firstly, structure component of the 6PUS-UPS PMT (Parallel Machine Tool) was introduced. Secondly, errors during the machine tool debugging were analyzed and measured, and those determined by the 6PUS-UPS PMT structure character were focused on, including the clearance error between the slider and the guide way, the vibration error and the verticality error and so on. Lastly, the verticality error was measured using the digital display micrometer and the frame level, which has great influence on the 6PUS-UPS PMT precision

Heavy-load Nonapod: A novel flexible redundant parallel kinematic machine for multi-DoF forming process