Design of a Multi-Point Kinematic Coupling for a High Precision Telescopic Simultaneous Measurement System

This paper covers the design of a new multi-point kinematic coupling specially developed for a high precision multi-telescopic arm measurement system for the volumetric verification of machine tools with linear and/or rotary axes. The multipoint kinematic coupling allows the simultaneous operation of the three telescopic arms that are registered at the same time to a sphere fixed on the machine tool spindle nose. Every coupling provides an accurate multi-point contact to the sphere, avoiding collisions and interferences with the other two multi-point kinematic couplings, and generating repulsion forces among them to ensure the coupling’s fingers interlacing along the machine tool x/y/z travels in the verification process. Simulation presents minimal deformation of the kinematic coupling under load, assuring the precision of the sphere-to-sphere distance measurement. Experimental results are provided to show that the multi-point kinematic coupling developed has repeatability values below ±1.2 µm in the application.

Kinematics-based five-axis trochoidal milling process planning for deep and curved 3D slots

Trochoidal (TR) milling is a popular means for slotting operation. Attributing to its unique circular shaped path pattern, TR milling avoids the full tool-workpiece engagement, which helps reduce the cutting heat accumulation and hence slow down the tool wear. While traditionally TR milling is only used for machining 2.5D cavities, it has now been extended to machining genuine 3D curved cavities under the realm of five-axis machining. However, since for a typical five-axis machine tool the rotary axes have a much larger moment of inertial than the three linear axes, to reduce both the total machining time and the consumed electric energy (for driving the machine tool), it is desirable to minimize the use of the two rotary axes (particularly the one with the worst moment of inertial) when planning a TR tool path for a given 3D cavity. Unfortunately, due to the newness of five-axis TR machining, there has no published reports on this subject. In this paper, we present a five-axis TR tool path planning algorithm for machining an arbitrary 3D curved cavity, which will consider the kinematical characteristics of the five-axis machine tool and try to minimize the use of the kinematically worst rotary axes, while tending to all the required constraints such as the threshold on the cutting force. Both computer simulation and physical cutting experiments of the proposed method have been conducted, and the results give a preliminary confirmation on the feasibility and advantages of the proposed method.

Generation of Efficient Iso-Planar Printing Path for Multi-Axis FDM Printing

The emerging multi-axis fused deposition modeling (FDM) printing process is a powerful technology for fabricating complicated 3D models that otherwise would require extensive support structures or suffer the severe stair-case effect if printed on a conventional three-axis FDM printer. However, because of the addition of two rotary axes which enables the printing nozzle to change its orientation continuously, and the fact that the printing layer is now curved, determining how a nozzle printing path to cover the layer becomes a non-trivial issue, since the rotary axes of the printer in general have a much worse kinematic capacity than the linear axes. In this paper, specifically targeting robotic printing, we first propose an efficiency indicator called the material deposition rate which considers both the local geometry of the layer surface and the kinematic capacities of the printer. By maximizing this indicator globally, a best drive plane direction is found, and then the classic iso-planar method is adopted to generate the printing path for the layer, which not only upholds the specified printing quality but also strives to maximize the kinematic capacities of the printer to minimize the total printing time. Preliminary experiments in both computer simulation and physical printing are carried out and the results give a positive confirmation on the proposed method.

Optimization of the setup position of a workpiece for five-axis machining to reduce machining time

Five-axis machining is commonly used for complicated features due to its advantage of rotary movement. However, the rotary movement introduces nonlinear terms in the kinematic transform. The nonlinear terms are related to the distance between the cutter location (CL) data and the intersection of the two rotary axes. This research studied the possible setup positions after the toolpaths have been generated, and the objective was to determine the optimal setup position of a workpiece with minimal axial movements to reduce the machining time. We derived the kinematic transform for each type of five-axis machines, and then, defined an optimization problem that described the relationship between the workpiece setup position and the pseudo-distance of the axial movements. Eventually, an optimization algorithm was proposed to search for the optimal workpiece setup position within the machinable domain, which is already concerned with over-traveling and machine interference problems. In the end, we verified the optimal results with a case study with a channel feature, which was real cutting on a table-table type five-axis machine. The results show that we can save the axial movements up to 16.76% and the machining time up to 10.70% by setting up the part at the optimal position.

Configuring of 3-axis vertical CNC Machine for Rapid Prototyping with two Translatory and one Rotary Axes

This paper describes the configuration of a 3-axis vertical CNC machine tool for rapid prototyping with one rotary and two translational axes. The machine works in a polar-cylindrical coordinate system. The structure of the machine is C’OXZ. The virtual machine model is configured in the PTC Creo software environment. After configuring the virtual machine, the simulation of the CLFbased was performed in the mentioned software environments, and then the verification according to the G-code program in the Vericut software environment was performed. Programming and control of the configured prototype machine are realized in the LinuxCNC software environment, which is based on the PC platform. Also, in this paper, digital twin of machine realized in a python software environment is shown. The presented results show the proper functioning of the whole system.

Highly efficient and accurate calibration method for the position-dependent geometric errors of the rotary axes of a five-axis machine tool

This paper proposes a calibration method for continuous measurements with a double ball bar (DBB) used to identify the position-dependent geometric errors (PDGEs) of the rotary axes of five-axis machine tools. The different DBB installation modes for the rotary axes of the spindle and workbench are established, and the same initial DBB installation position is used for multiple tests. This approach minimizes the number of required DBB installations, which increases the measurement efficiency of the PDGEs of the rotary axes and reduces installation errors. PDGEs identification based on the adaptive least absolute shrinkage and selection operator (LASSO) method is proposed. By assigning coefficients to the PDGEs polynomial, the ill-conditioned problem of the identification process can be effectively avoided, thereby improving the identification accuracy. The measurement and identification methods proposed in this paper are verified by experiments on a five-axis machine tool. After compensation, the PDGEs are obviously reduced and the accuracy indexes of the circular trajectory tests performed under multiaxis synchronous control are obviously improved.