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Szacowanie błędu trajektorii narzędzia w 5-osiowej obróbce współbieżnej

Stryczek R., Szczepka W.

Pomiary Automatyka Kontrola

2013

R. 59, nr 7

667--670

Artykuł prezentuje możliwości zwiększenia produktywności frezarek z dwoma jednostkami obróbczymi, wyposażonymi w wielokanałowy układ sterowania. Metoda opiera się na możliwości współbieżnej pracy dwóch jednostek obróbczych, realizujących złożone trajektorie, każda w 3 osiach, przy czym oś X jest wspólną osią dla obu jednostek. Zaprezentowano możliwości przechwytywania osi pomiędzy kanałami, funkcje synchronizacji pracy wielokanałowej, narzędzia do tablicowania złożonych trajektorii ruchu, funkcje sprzężenia osi, holowania, śledzenia ruchu i diagnostyki w tym zakresie. Przedstawiono przykład modelu szacowania błędów trajektorii narzędzia.

Error analysis in realization of complex trajectories of the tool movement of a multi-axis lathe is currently an issue widely discussed in the literature [1, 2, 3, 4]. However, this literature does not include particular cases, such as machining by means of a bridge type mill with two machining units equipped with a multi-channel CNC system – Sinumerik 840D. There is a possibility of simultaneous work of two machining units which realize complex trajectories; three axes per each unit; moreover, they both share axis X (Fig. 1). There are presented the standard programmatic tools necessary for such movements (axis replacement between the channels, data transfer between the channels, program coordination in multi-channel operations), the tools for defining curve tables in order to realize complex trajectories, the functions of coupled motions between the leading and following axis as declaration well as the possibilities of movement control and system diagnostics [5]. The method of declaration and initiation of external procedures in the leading channel (Fig. 2) is discussed. The worked out procedure for tabling the motion on the regular curve (Fig. 3, 4) necessary for simultaneous, double circular interpolation controlled by one channel is presented. The analysis of the tool trajectory errors and the chart for error estimation (Fig. 5) are also contained in the paper. The method was verified on a practical example of rail machining. The productivity of the machine tool in that particular case increased by 20-30%.

An analytic model for tool trajectory error in 5-axis machining

So B. S., Park D. H., Cho Y., Kim T. J., Song T. S., Ko T. J.

Journal of Achievements in Materials and Manufacturing Engineering

2008

Vol. 31, nr 2

570-575

Purpose: This paper proposes an analytical method of evaluating the maximum error by modeling the exact tool path when the tool traverses singular region in five-axis machining. Design/methodology/approach: It is known that the Numerical Control (NC) data obtained from the inverse kinematic transformation can generate singular positions, which have incoherent movements on the rotary axes. Such movements cause unexpected errors and abrupt operations, resulting in scoring on the machined surface. To resolve this problem, previous methods have calculated several tool positions during a singular operation, using inverse kinematic equations to predict tool trajectory and approximate the maximum error. This type of numerical approach, configuring the tool trajectory, requires a lot of computational time to obtain a sufficient number of tool positions in the singular region. We have derived an analytical equation for the tool trajectory in the singular area by modeling the tool operation, by considering linear and nonlinear parts that are a general form of the tool trajectory in the singular area and that are suitable for all types of five-axis machine tools. In addition, evaluation of the maximum tool-path error shows high accuracy, using our analytical model. Findings: In this study, we have separated the linear components of the tool trajectory from the nonlinear ones, to propose a tool trajectory model that is applicable to any kind of 5-axis machine. We have also proposed a method to calculate the maximum deviation error based on the proposed tool trajectory model. Practical implications: The algorithms proposed in this work can be used for evaluating NC data and for linearization of NC data with singularity. Originality/value: Our algorithm can be used to modify NC data, making the operation smoother and reducing any errors within tolerance.