Keywords
Robust stability, Multi-Dimensional Bisection Method (MDBM), turning, process damping
IntroductionThe determination of the stability of dynamical systems with time delay is of high importance for many industrial and research applications. The investigation of the dynamics of turning processes is such a typical industrial problem. In order to reach high process efficiency the material removal rate (MRR) has to be maximized. The major limitation for increasing the MRR is the so-called chatter vibration. The origin of these self-excited vibrations is the surface regeneration effect, which can be described by linear delayed differential equations (DDEs) [1,2]. Another example is human balancing, which is often modelled by a simple inverted pendulum in the presence of reflex delay [3,4,5], which is a relevant issue to human motion control [6]. A similar problem is the remote control of periodic robotic motions, when the delay in the information transmission system is not negligible [7,8].The most important qualitative property of the corresponding dynamical system is the stability of the equilibrium or periodic motions. This is usually presented in the form of the socalled stability chart, that identifies those ranges of parameters where the linear system is stable.Many well-known computational techniques are available to determine the stability chart of DDEs [9,10,11,12,13,14].In many cases, especially for machining operations at low spindle speed, the computation of the stability boundary requires very high computational effort and unnecessarily high resolution, due to the dense and sharp line segments of the stability boundary (see Fig. 1). In these cases, the computation of the lower envelope of the dense stability lobe structure would be adequate.In case of time-domain computations [10,13,15,16,17], really high degree of discretization is required for proper results. In frequency domain computations [14,18,19,20], the determination of the very dense lobe structure in the unstable domain is unnecessary and also high resolution is required to determine the chatter frequency parameter, which is also a required computational step.Traditional computational methods consider exact models of the system, and do not take into account the uncertainty of