Prognostic Diagnosis of Hollow Ball Screw Pretension on Preload Loss Through Sensed Vibration Signals
The pretension for a ball screw is a way to improve the position accuracy. Hollow ball screw without a cooling system has the thermal deformation effect due to increase in temperature. It will reduce precision accuracy in machine tool when the ball screw
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Abstract The pretension for a ball screw is a way to improve the position accuracy. Hollow ball screw without a cooling system has the thermal deformation effect due to increase in temperature. It will reduce precision accuracy in machine tool when the ball screw nut preload or ball screw pretension is lost. The purpose of this study is to use vibration signals for the prognostic analysis for the ball screw pretension. Features of different pretension conditions by 0, 5, 10, and 20 μm are discriminated by empirical mode decomposition (EMD), fast Fourier transform (FFT), and marginal frequency method. Temperature effects with long-term operation were discussed. This study experimentally extracts the characteristic frequencies for bettering pretension through the vibration signals. This diagnosis results realize the purpose of prognostic effectiveness on knowing the hollow ball screw preload loss based on pretension data and utilizing convenience. Keywords Hollow ball screw • Vibration signals • Hilbert–Huang transform • FFT
1 Introduction High-lead ball screw is used widely in industrial machines and equipment for linear actuation. The positioning accuracy of feed system is an important factor in machine tools. However, the ball screw thermal displacement is a key factor. When a machine has been operated for a long time, it produces thermal displacement effects as general. There are two conventional ways to improve the thermal displacement: control the temperature rise and compensate the thermal displacement. Controlling the temperature rise is the most efficient way.
Y.-C. Huang (*) • Y.-S. Chen • S.-L. Sun • K.-H. Peng Department of Mechatronics Engineering, National Changhua University of Education, Changhua 50007, Taiwan e-mail: [email protected] J. Juang and Y.-C. Huang (eds.), Intelligent Technologies and Engineering Systems, Lecture Notes in Electrical Engineering 234, DOI 10.1007/978-1-4614-6747-2_111, # Springer Science+Business Media New York 2013
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But it is costly and difficult to maintain the temperature variation. The use of the thermal displacement compensation method is as follows. First is to let the temperature of the machine reach a steady state by warming up the machine. Then the motor encoder or the optical scale signals are manipulated and can be feedback to the controller. Last but not least is to do the ball screw pretension for absorbing the thermal displacement caused by temperature rise. Pretension is effective to improve the thermal displacement. However, discussion for monitoring the status of the pretension failure is less in recent years. Large pretension may cause preload loss. Therefore, predicting the signals to determine the onset of pretension loss or preload loss of ball screws has recently become an urgent necessity in the industry. These signals often require conventional fast Fourier transform (FFT), short-time Fourier transform, or discrete wavelet transform for fault diagnosis in the frequency and time domains [1]. Huang and coworkers [2,
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