Active chatter control in a milling machine

Abstract

IThe use of active feedback compensation to mitigate cutting instabilities in an advanced milling machine is discussed in this paper. A linear structural model delineating dynamics significant to the onset of cutting instabilities was combined with a nonlinear cutting model to form a dynamic depiction of an existing milling machine. The model was validated with experimental data. Modifications made to an existing machine model were used to predict alterations in dynamics due to the integration of active feedback compensation. From simulations, subcomponent requirements were evaluated and cutting enhancements were predicted. Active compensation was shown to enable more than double the metal removal rate over conventional milling machines.Keywords: milling, controls, chatter INTRODUCTIONMaximum metal removal rate is a quantitative measure of the productive capacity of a machine tool. This measure, which is machine as well as tool dependent, is limited by the onset of machining in~tabilities',~,~,~. Machining instabilities are minimized by enhancing the stability of structural vibratory modes significant to cutting dynamics.Active methods can be used to enhance the stability of pertinent structural vibratory modes for a variety of machining configurations. Although active methods are relatively immature5, potential performance enhancements resulting from active implementation overshadow performance enhancements resulting from current passive innovations.Active methods can be categorized into activelpassive, process control, and feedback compensation methods. Activelpassive methods actively tune or mimic stabilizing passive absorber^^^^^^. Process control methods alter or modulate operating parameters (spindle speed, feed rate, etc.) to locate, or oscillate between, predetermined stability domains9i10, and feedback compensation methods actively modify machine dynamics such that domains of stability are enlarged".'2713.Presented within this paper is the design of an active feedback compensator which will actively modify machine dynamics such that domains of stability are enlarged. This design process entails; 1) development and validation of a model, 2) modification of the model for active compensation, and 3) performance evaluation.In section 2, modeling and validation is discussed. In section 3, the modeling of dynamics essential for active compensation is discussed. And in section 4, performance earnings are presented. MODEL DEVELOPMENTA machine model is a set of mathematical relationships relating dynamic response parameters (displacement of tool tip center, force on tool, etc ...) to a set of process parameters (spindle speed, number of teeth on tool, etc ...). The goal of modeling is to create mathematical relationships which are sufficiently accurate for the purpose of prediction. Model accuracy is quantified by comparison with experimental data. The model discussed in this section is shown to compare well with experimental data.The machine model is the unification of a cutting model and a structural ...

Piezoelectric active control for workpiece chatter reduction during milling

“…Three control strategies were investigated: strain rate feedback, active vibration absorber, and positive position feedback. The strain rate feedback controller consisted of a differentiator, low pass filter, and gain term: (6) The behaviour of the PZT will therefore be similar to that of a single PZT connected to a passive resistance circuit [10]. Initially the gain K SRF was chosen arbitrarily to achieve satisfactory damping performance.…”

“…Much of this work has focussed on controlling the vibrations of the cutting tool, since traditionally, this has been the most flexible element in the system. Examples include the work by Browning [5], Dohner [6], Segalman [7], Lei [8] and their respective colleagues.…”

Active vibration control of a rotor-bearing-actuator system using robust eigenvalue placement method

“…The rotor vibrations caused by unbalances, process forces and system instabilities affect the machining accuracy and machine reliability, so an increasing amount of research is focused on the effective vibration control method for rotary machine. [1][2][3][4][5] Considering the advantages such as wide application and high stability, the active control is more suitable for adjusting to a myriad of load conditions and machinery configurations compared with the passive control. 6 The dynamical model of rotor system is essential for active vibration control design.…”

Dynamics Analysis of Unbalanced Motorized Spindles Supported on Ball Bearings

“…Due to the complexity of the reliability and performance problems caused by profound high speed effects [1][2][3], the machine tools capable of achieving the high speed cutting were first introduced commercially in 1980s, which lags behind the theory of high speed metal cutting by 50 years [4]. Motorized spindles are the core components of CNC machine tools and greatly improve the cutting speed, while the inevitable unbalance of the spindle system caused by unexpected errors during manufacturing and installation process strongly influences the machining productivity and finish quality of workpieces in high speed operating conditions [5][6][7][8][9][10][11]. Therefore, it is necessary to deeply study the dynamic properties of unbalanced machine tool motorized spindle systems.…”