development of a piezoelectric tool actuator for precision turning

138 Pages·2009·8.82 MB·English

DEVELOPMENT OF A PIEZOELECTRIC TOOL ACTUATOR
FOR PRECISION TURNING
by
Andrew Stanley Woronko
B.A.Sc. (Mechanical Engineering), ,1999
University of Waterloo
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE
in
THE FACULTY OF GRADUATE STUDIES
MECHANICAL ENGINEERING
We accept this thesis as conforming
to the required standard
THE UNIVERSITY OF BRITISH COLUMBIA
December 2001
© Andrew Stanley Woronko, 2001
In presenting this thesis in partial fulfillment of the requirements for an advanced degree at
the University of British Columbia, I agree that the Library shall make it freely available for refer
ence and study. I further agree that permission for extensive copying of this thesis for scholarly
purposes may be granted by the head of my department or by his or her representatives. It is
understood that copying or publication of this thesis for financial gain shall not be allowed with
out my written permission.
DEPARTMENT OF MECHANICAL ENGINEERING
The University of British Columbia
2324 Main Mall
Vancouver, BC, Canada
V6T 1Z4
Date: Ths (2^ x>i ,
Abstract
Precision turning as an alternative to conventional finish machining operations of cylindri
cal components offers significant reductions in manufacturing cost and cycle time. In this thesis
the development of a piezoelectric tool actuator for precision turning of shafts is presented. A
review of research conducted in the areas of precision turning, piezoelectric actuator develop
ment, and micropositioning systems design is presented. Mounted to a conventional turning
machine, the tool actuator overcomes the limitations of machine tool feed drives by providing
precise control of the finishing depth of cut. In this manner part tolerances are achieved in one
setup on a single machine, without the need for subsequent finishing operations.
Design of the actuator system was driven by constraints on motion range and resolution,
size, and structural properties. Tool motion is provided through the use of a high voltage piezo
electric translator housed within a monolithic solid flexure. A capacitive position sensor provides
feedback of tool motion to the controller. In order to be practical in an industrial setting the actu
ator design is compact, and provides an interface for exchangeable tooling. The specifications of
the actuator are 36 micron stroke, 370 N/micron stiffness, and 3200 Hz natural frequency (radial
direction). A sliding mode control scheme was implemented to regulate tool position, and reject
disturbances due to cutting forces and actuator non-linearity.
The actuator was experimentally verified through machining tests in both laboratory and
industrial sites. Results showed that positioning resolution of 20 nm is achievable in precision
finishing, and that the commanded controller position was accurately reflected on the machine
workpiece. Average surface roughness for 4340 steel (36-40 HRC) was less than 0.3 microns,
and less than 0.15 microns for hardened 4320 steel (58-62 HRC).
ii
Table of Contents
Abstract ii
Table of Contents iii
List of Figures vi
List of Tables ix
Acknowledgements x
Nomenclature xi
1 Introduction 1
2 Literature Review 4
2.1. Overview 4
2.2. Precision turning 5
2.2.1. Geometry and forces in turning 5
2.2.2. Accuracy of machine tool feed drives 7
2.2.3. Part quality 8
2.2.3.1. Form errors 9
2.2.3.2. Surface roughness 10
2.2.4. Hard turning 15
2.3. Piezoelectric tool actuator development 17
2.4. Design of micropositioning systems 20
3 Actuator Design and Analysis 26
3.1. Introduction 26
3.2. Design objectives and constraints 26
iii
3.3. Design overview 28
3.4. Precision turning process 35
3.5. Component design and analysis 37
3.5.1. Tool assembly 37
3.5.2. Piezoelectric driving element 40
3.5.3. Guiding Unit 42
3.5.3.1. Analytical model of flexures 44
3.5.3.2. Finite element model of flexures 49
3.5.4. Position sensor assembly 53
3.5.5. Support plates 56
3.5.6. Clamping Units 57
3.6. Summary 60
4 System Identification and Control 62
4.1. Introduction 62
4.2. Instrumentation and system setup 62
4.3. Piezoelectric actuator non-linearities 64
4.4. Actuator modal properties 66
4.5. Displacement sensor 70
4.6. Actuator system model 75
4.7. Sliding mode controller design 76
4.8. System response 81
4.9. SMC and feedforward force control 83
4.10. Summary 85
5 Experimental Results 86
5.1. Introduction 86
5.2. Experimental setup 86
iv
5.3. Position control 88
5.4. Micro profiling 93
5.5. Surface roughness 99
5.6. Industrial application 1: Pratt & Whitney Canada 104
5.7. Industrial application 2: Caterpillar Technical Center 107
5.8. Summary 113
6 Conclusions and Recommendations 114
6.1. Conclusions 114
6.2. Recommendations for future research 116
References 117
v
List of Figures
Figure 2.1 : Turning process and cutting forces [1] 6
Figure 2.2 : Geometry of the turning tool [1] 6
Figure 2.3 : Axis feed drive of a CNC machine tool 8
Figure 2.4 : Unfiltered, roughness, and waviness profiles of a turned surface 11
Figure 2.5 : Feed marks left on the workpiece surface during the turning process 12
Figure 2.6 : Effect of feedrate and tool nose radius on the fraction of the uncut chip area
in which h< hj 14
mn
Figure 2.7 : Examples of solid flexure mechanisms transmitting linear motion 22
Figure 2.8 : Solid flexure hinge profiles 24
Figure 2.9 : Circular solid flexure hinge geometry 25
Figure 3.1 : Actuator mounted to a Hardinge lathe turret 30
Figure 3.2 : Actuator external views and major components 31
Figure 3.3 : Exploded view of the actuator assembly 32
Figure 3.4 : Internal view of actuator with support plates removed 33
Figure 3.5 : Actuator overall dimensions (in mm) 34
Figure 3.6 : Actuator covers for use with cutting fluids 34
Figure 3.7 : Steps in the actuator assisted precision turning operation 36
Figure 3.8 : Actuator tool assembly 37
Figure 3.9 : Komet ABSN25 clamping system (dimensions in mm) 38
Figure 3.10 : Force sensor arrangement for measurement of radial cutting forces 39
Figure 3.11 : Bare and preloaded piezostack configurations 41
Figure 3.12 : Actuator Guiding Unit and flexure hinge profile 43
Figure 3.13 : Guiding Unit model for equivalent linear stiffness based on flexure hinge
flexibility in rotational and axial directions 47
Figure 3.14 : Superposition of a single hinge bending and axial stiffness to obtain the
equivalent linear stiffness 48
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Figure 3.15 : Guiding unit stiffness versus hinge radius for varying hinge thickness 49
Figure 3.16 : Mode shapes of the Guiding Unit flexures determined from FE model 51
Figure 3.17 : Finite element result for Guiding Unit stresses under maximum radial load 54
Figure 3.18 : Capacitive position sensor assembly 55
Figure 3.19 : Finite element result for first bending mode of the sensor probe bracket 56
Figure 3.20 : Finite element result for first three Bottom Plate vibration modes 57
Figure 3.21 : Clamping Unit assembly details 58
Figure 4.1 : System instrumentation and signal flow 63
Figure 4.2 : Piezoelectric actuator hysteresis 65
Figure 4.3 : Piezoelectric actuator creep 66
Figure 4.4 : Direct transfer functions for the x, y, and z directions, undamped mode 68
Figure 4.5 : Direct transfer functions for the x, y, and z directions, clamped mode 69
Figure 4.6 : Capacitive displacement sensor calibration 70
Figure 4.7 : Block diagram of the sensor dynamics 72
Figure 4.8 : Simulated bode diagram of the sensor dynamics 72
Figure 4.9 : Magnitude and phase of direct transfer function obtained using the
displacement sensor 73
Figure 4.10 : Real and imaginary parts of the transfer function obtained using the
displacement sensor 74
Figure 4.11 : Block diagram of the translator-flexure system 75
Figure 4.12 : Block diagram of the sliding mode controller with parameter adaptation 79
Figure 4.13 : Open loop System response to a step voltage input 82
Figure 4.14 : Closed loop system response to a unit displacement step input 82
Figure 4.15 : Block diagram of the feedforward force controller 83
Figure 4.16 : Block diagram of sliding mode controller with feedforward force control 84
Figure 5.1 : Experimental setup on the Hardinge lathe at MAL-UBC 88
Figure 5.2 : Radial cutting force and tool positioning for a 0.1 mm depth of cut 90
Figure 5.3 : Radial cutting force and tool positioning for a 0.005 mm depth of cut 91
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Figure 5.4 : Position control using feedforward force compensation for a 0.1 mm depth of cut..92
Figure 5.5 : Step change in depth of cut, actuator control 94
Figure 5.6 : Step change in depth of cut, machine CNC control 95
Figure 5.7 : Tapered profile for both actuator and CNC control 97
Figure 5.8 : Convex and concave surface profiles 98
Figure 5.9 : Surface roughness of 4340 steel at 150 m/min 102
Figure 5.10 : Surface roughness for 4340 steel at 200 m/min 102
Figure 5.11 : Surface roughness for 4320 steel at 150 mm.min 103
Figure 5.12 : Surface roughness for 4320 steel at 200 m/min 103
Figure 5.13 : Actuator setup at Pratt & Whitney Canada 104
Figure 5.14 : Diameter reductions for PWC tests 106
Figure 5.15 : Average roughness values for PWC tests 106
Figure 5.16 : Actuator setup at Caterpillar Technical Center 108
Figure 5.17 : Average roughness for Caterpillar tests, 0.4 mm nose radius 110
Figure 5.18 : Average roughness for Caterpillar tests, 0.8 mm nose radius 110
Figure 5.19 : Roundness errors for tests conducted at Caterpillar Ill
Figure 5.20 : Straightness errors for tests conducted at Caterpillar Ill
Figure 5.21 : Surface microstructure at 125 m/min, 0.4 mm nose radius 112
Figure 5.22 : Surface microstructure at 185 m/min, 0.4 mm nose radius 112
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List of Tables
Table 3.1 : Actuator design constraints 28
Table 3.2 : Single axis force sensor specifications 40
Table 3.3 : Driving piezoelectric actuator specifications 41
Table 3.4 : Titanium alloy (Ti-A16-V4) material properties [55] 42
Table 3.5 : Guiding Unit stiffness determined from finite element model 50
Table 3.6 : Capacitive position sensor specifications 55
Table 3.7 : Specifications of the Clamping Unit piezostack 59
Table 4.1 : Specifications of the Spectrum F3 DSP board 64
Table 4.2 : Physik Instrumente P-270 high voltage amplifier specifications 64
Table 4.3 : Identified actuator modal parameters 67
Table 5.1 : Inserts used for the cutting tests 87
Table 5.2 : Workpiece material specifications 87
Table 5.3 : Surface roughness results for 4340 steel (35-40 HRC) 101
Table 5.4 : Surface roughness results for 4320 steel (58-62 HRC) 101
ix