Compensation System for Thermal Deformations of Ballscrews

2014 ◽  
Author(s):  
Michał Kowal ◽  
Roman Staniek
Keyword(s):  
Thermal Expansion ◽  
Machine Tools ◽  
Kinematic Chain ◽  
Indirect Measurement ◽  
Cnc Machine Tools ◽  
Positioning Error ◽  
Cnc Machine ◽  
Measurement Systems ◽  
Drive Systems ◽  
Precise Machine

Accurate ballscrews are vital components of precise machine tool drive systems. As determined by direct measurement systems, the ballscrew positioning error has no bearing on the final positioning accuracy of the axis. For economical reasons, however, most machine tools are equipped with indirect measurement systems, in which errors stemming from thermal expansion of the ballscrew constitute approximately 60% of the kinematic chain error sum. Moreover, the currently observed boost in productivity of modern CNC machine tools leads to significant amplification of energy dispersal values in the nut-screw systems, due to the increased positioning velocity of the controlled axes. This, in turn, contributes to a rise of positioning error values through thermal expansion of the aforementioned ballscrews. This article deals with technological and constructional problems of screw lengthening compensation. It enumerates methods of thermal expansion-based error compensation as attained through utilization of indirect measurement systems. Finally, it presents experimental data indicating the possibility of effective screw lengthening compensation, thus proposing an alternative to the currently applied compensation systems.

scholarly journals Positioning Errors Measurement of CNC Machine Tools Based on J-DBB Method

2021 ◽  
Vol 11 (24) ◽  
pp. 11770
Author(s):  
Tao Sun ◽  
Wen Wang ◽  
Zhanfeng Chen ◽  
Yewen Zhu ◽  
Kaifei Xu ◽  
...  
Keyword(s):  
Machine Tool ◽  
Machine Tools ◽  
Degree Of Freedom ◽  
Ball Screw ◽  
Cnc Machine Tools ◽  
Positioning Error ◽  
Cnc Machine Tool ◽  
Spherical Joint ◽  
Cnc Machine ◽  
Positioning Errors

Due to the errors of the servo system and the errors of the ball screw drive system, the positioning errors inevitably occur in the process of CNC machine tools. The measurement of traditional equipment is limited by a fixed measurement radius and a single degree of freedom, which can only be measured within a fixed plane. In this paper, four different positioning errors of CNC machine tools are first measured at full scale by using J-DBB (a modified double ball bar with one spherical joint connecting two bars) method. The J-DBB device uses a three-degree-of-freedom spherical joint as a connecting part, which realizes that the measurement radius can be continuously changed, and the measurement space is a spatial sphere. First, the principle of the J-DBB method is briefly introduced. Next, four typical positioning errors of CNC machine tools are analyzed and examined, which contain the uniform contraction error of ball screw and linear grating, periodic error of the ball screw and linear grating, interference of measurement devices error, and opposite clearance error. In the end, the trajectories of the CNC machine tool spindle with a single positioning error are simulated by using the J-DBB method. The results reveal that this method can be used for the positioning error of machine tools, which helps to better understand the spatial distribution of CNC machine tool errors and provides guidance for the reasonable selection of working areas to improve the machining accuracy of parts.

Identification of 5-Axis Machine Tools Feed Drive Systems for Contouring Simulation

2011 ◽  
Vol 5 (3) ◽  
pp. 377-386 ◽  
Author(s):  
Burak Sencer ◽  
◽  
Yusuf Altintas ◽  
Keyword(s):  
Transfer Function ◽  
Machine Tools ◽  
Closed Loop ◽  
Cnc Machine Tools ◽  
Cnc Machine ◽  
Feed Drive ◽  
Model Transfer ◽  
Drive Systems ◽  
Feed Drive System ◽  
Model Transfer Function

An identification technique is introduced for identifying closed loop transfer function of machine tool’s feed drive systems to be used in simulation of the tracking and contouring performance of Computer Numerical Controlled (CNC) machine tools. The identification is performed from air-cutting tests utilizing only standard G-codes containing linear motion commands. A general transfer function model is derived for representing the closed loop tracking response of the feed drive system. The model considers the drive to be controlled by commonly used controller schemes such as P-PI Cascade, PID or the Sliding Mode Controller (SMC) with feed-forward dynamic and friction compensation. The parameters of the model transfer function are fitted tominimize the discrepancy between the actual and predicted axis position on the axis. In order to guarantee the stability of the identified model transfer function, bounds on the pole locations are imposed. The resultant constrained non-linear optimization problem is solved efficiently using the Particle Swarm Optimization (PSO) method. For achieving reliable convergence of the stochastic PSO algorithm, a parameter tuning strategy is presented. Simulation and experimental studies show that the identified feed drive model captures the fundamental dynamics of the drives system accurately for simulating their closed loop response. Combined with the kinematics of the machine, contouring errors of 5-axis CNC machine tools during simultaneous multi-axis motion are predicted.

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