Design Innovation Papers

Novel Contact Sensor for High-Speed Machining

[+] Author and Article Information
Valéry Bourny

Associated Professor
e-mail: valery.bourny@u-picardie.fr

Florent Swingedouw

e-mail: florent.swingedouw@u-picardie.fr

Thierry Capitaine

Associated Professor
e-mail: thierry.capitaine@u-picardie.fr

Aurélien Lorthois

e-mail: aurelien.lorthois@u-picardie.fr

Jérôme Dubois

Associated Professor
e-mail: jerome.dubois@u-picardie.fr

Jacky Senlis

e-mail: jacky.senlis@u-picardie.fr
Laboratoire des Technologies Innovantes (LTI, EA3899),
Université de Picardie Jules Verne (UPJV),
80000 Amiens, France

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received September 21, 2011; final manuscript received September 28, 2012; published online December 7, 2012. Assoc. Editor: Robert Gao.

J. Manuf. Sci. Eng 134(6), 065001 (Dec 07, 2012) (10 pages) doi:10.1115/1.4007781 History: Received September 21, 2011; Revised September 28, 2012

This work presents a method implemented in an embedded system to detect the first contact between a high-speed machine tool and a workpiece surface with high accuracy, reliability and ease-of-use. This method is based on impedance magnitude variation measurements and the computation of a correlation function. A specific sensor was designed from this method for testing purposes in actual industrial conditions. This work is focused on the detection of the first contact between the tool and the workpiece surface. The purpose of this paper is to explore the efficiency of impedance spectroscopy and to identify a method to detect the first contact between a tool and a workpiece efficiently in high-speed machining operations and for the finishing process in particular.

Copyright © 2012 by ASME
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Fig. 1

Oscilloscope-based impedance spectroscopy measurements. By recording the voltage UZ(ω) (Y2 trace) and the current IZ(ω) (as the voltage drop across a series resistance RS,Y1–Y2 trace) with a twin-trace oscilloscope the magnitude |Z(ω)| and the phase angle arg Z(ω) of the probed impedance Z(ω) can be determined.

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Fig. 2

Experimental impedance spectroscopy measurements setup implemented (a) on a five-axis high-speed vertical tooling machine Huron K2X8-Five. (b) An electrical insulator (epoxy material) is between machine turntable and workpiece.

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Fig. 3

The high-speed machine model with the corresponding impedances

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Fig. 4

Impedance spectra ZST (a) magnitude and (b) phase angle of ZST. The observed impedance plot exhibits nonstandard power-law behavior with frequency.

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Fig. 5

Equivalent resistance R// (a) and capacitance C// (b) of ZST determined from Fig. 4. Both exhibit unusual power-law variations [10].

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Fig. 6

Impedance spectra ZWM (between the workpiece and the machine table) as functions of the frequency f (a) magnitude and (b) phase angle of ZWM. Both exhibit usual behavior in a broad frequency range equivalent to an ideal capacitance.

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Fig. 7

Magnitude of the impedance before contact, |ZBeforeContact|, and at the contact, |ZContact| (a). The linear fitting algorithm gives -1.041±0.020ΩHz-1 and -0.794±0.020ΩHz-1 for the slope of |ZBeforeContact| and |ZContact|, respectively. From these experimental results the ratio a is obtained (b).

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Fig. 8

Electrical analogy of the Fig. 3 before and at first tool-worpiece contact. The switch characterizes the contact detection.

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Fig. 9

Voltage signals before (a) and at first contact (b) between the tool and the workpiece surface: generator voltage in yellow (f = 500 Hz), U(t) voltage in blue and RSI(t) voltage in red (RS=10kΩ). The speed of the tool is v = 1000 rpm.

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Fig. 10

Modulus of the impedance Z at f = 100 kHz to the docking for different spindle speed

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Fig. 11

Voltage signals before (a) and at contact (b): generator voltage in yellow (f = 500 Hz), U(t) voltage in blue and RSI(t) voltage in red (RS=10kΩ). The speed of the tool is v = 1000 rpm.

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Fig. 12

UBeforeContact and Ucontact voltages as functions of time. U = 10 V, f = 1 kHz, RS=10kΩ, v = 1000 rpm.

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Fig. 13

CBeforeContact and Ccontact correlation product. U = 10 V, f = 1 kHz, RS=10kΩ, v = 1000 rpm.

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Fig. 14

The parameters of signal processing with the particular case K = 1

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Fig. 16

PWM generator with timer compare functionality

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Fig. 17

Principle of PWM frequency change

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Fig. 18

Correlation process synchronization

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Fig. 19

X and Y RAM blocks




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