A program was awarded under the Air Force Machine Tool Sensor Improvements Program Research and Development Announcement to develop and demonstrate the use of a Capacitance Sensor System including Capacitive Non-Contact Analog Probe and a Capacitive Array Dimensional Measurement System to check the dimensions of complex shapes and contours on a machine tool or in an automated inspection cell. The manufacturing of complex shapes and contours and the subsequent verification of those manufactured shapes is fundamental and widespread throughout industry. The critical profile of a gear tooth; the overall shape of a graphite EDM electrode; the contour of a turbine blade in a jet engine; and countless other components in varied applications possess complex shapes that require detailed and complex inspection procedures. Current inspection methods for complex shapes and contours are expensive, time-consuming, and labor intensive

Resnick, Ralph

English

NASA Technical Reports Server

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ON MACHINE CAPACITANCE DIRaENSIONAL AND 
SURFACE PROFILE MEASUREMENT SYSTEM 
Ralph Resnick 
Extrude None Corporation 
8075 Pennsylvania Avenue 
Irwin, PA 15642 
ABSTRACT 
A program was awarded under the Air Force Machine Tool Sensor Improvements Program Research 
md Development Announcement to develop and demonstrate the use of a Capacitance Sensor System 
ancluding Capacitive Non-Contact Analog Probe and a Capacitive Array Dimensional Measurement 
System to check the dimensions of complex shapes and contours on a machine tool or in an automated 
anspectnon cell. The manufacturing of complex shapes and contours and the subsequent verification of 
those manufactured shapes is fundamental and widespread throughout industry. The critical profile of a 
gear tooth; tile overall shape of a graphite EDM electrode; the contour of a turbine blade in a jet engine; 
md count3ess other components in varied applications possess complex shapes that require detailed and 
complex inspection procedures. Current inspection methods for complex shapes and contours are 
expewsuve, time-consuming, and labor intensive. 
An effort entitled "On-Machine Capacitance Dimensional and Surface Profile Measurement System" 
funded by the U.S. Air Force Wright Patterson Laboratories PRDA Program and performed by the MetreX 
Davisaon of Extrude Hone Corporation seeks to address the needs of complex shape measurement and 
mpsove upon the use of the present technologies for performing those measurements. Recent advances in 
capacatance dimensional and surface roughness measurement provide a potential methodology for the 
iderafieation of complex shapes. By building a capacitance probe or array and then scanning the workpiece, 
valuable information can be obtained about the surface under the sensor(s). This data can then be 
assnmllated, translated, and transferred to the machining process controller for setup or corrective action. 
Slr~ce the cost per capacitance sensor is low and processing time is short, full form verification could be 
done quackly and inexpensively. Careful design and integration would permit the new measurement 
system to be swstalled in or near process. 
The objective of this program is to develop and demonstrate a system to check and quantify 
dimensional ~g~formation about complex workpiece shapes in a process environment on an automated 
machisac 8001. The proposer has established a partnership with Carrier Corporation of United 
Technologies on this program to establish key requirements, to review approaches and programs, to 
provide components, and to test results in a present process. Researchers at the University of Washington 
are working on design and analyzing mathematical models of the system as well as performing the 
eravironmensal testing. The National Institute of Standards and Technology is providing the temperature, 
stabnlr;ty asad dynamic testing and defined interface standards based on recently implemented Dimensional 
Meaurement Inspection Specifications (DMIS). 
PURPOSE AND OBJECTIVE 
Identification of the Problem 
The verification and inspection of complex shapes is far-reaching and significant. An improper 
profile on a gear can cause misalignment increasing gear noise and decreasing gear life. A cam with the 
wrong coaltour can cause erratic engine performance. The aircraft engine industry has many important 
complex shapes on important components and is highly representative of the requirements of industry in 
general. Aircraft turbine engine components require that their geometric form be accurate and consistent. 
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More efficient and predictable engine performance can be established if the engine components are 
maintained within the design criteria. To guarantee the components will meet performance specifications 
requires that the specific engine parts be gauged to the design criteria. For some simple components this 
gauging task is straightforward and easily performed; however, on complex components with intricate 
shapes and contours, specifically turbine blades and disks, Integrally Bladed Rotors (IBR's), and 
impellers, the gauging and design verification is detailed and complicated. Since the production of these 
components is performed on complicated machines with complex parts programs or intricate processes, 
the feedback of this test information is vital 'and timely for process and program control. 
Present techniques for form measurement of complex aircraft engine components include Coordinate 
Measurement Machines (CMM's), Light Sectioning, SigmaFlex gauges, and even templates and feeler 
gages. All of these techniques are complex and/or labor intensive. The procedures are performed off- 
machine, at times even off-site, complicating the ability to transfer the valuable correction data to the 
manufacturing cell. Fixturing, programming and setup requirements are extremely time consuming and 
expensive. It has been estimated that the post-process dimensioning of a workpiece roughly accounts for 
between 20 to 40 percent of the total time to complete a machining operation. depending upon the 
complexity of the cut and the number of tools used in the manufacturing process.l 
Since these parts are often processed on highly sophisticated and accurate machine tools, subsequcna 
removal of a fixrured workpiece from the machine and transfer to a separate inspection device seems 
redundant and unnecessary. A more efficient and straightforward approach would be to instrument the 
machine tool performing the process with adequate probes and sensors that would easily interface, both In 
hardware and software, to the machine and would thus utilize the inherent accuracy capabilities of the 
machine tool to be the verification bed for the part. Potential errors inherent in the machine to inspection 
device transfer (and possible repetition) such as fixturing orientation could be avoided. Obvious time 
savings would be realized. In fact, in a recent study by Southwest Regional Institute for a project entitled 
"High Productivity and Precision Machining Program" for the National Center for Manufacturing 
Sciences (NCMS), the highest priority focus area with 81% of the surveyed in favor was In-Process 
Dimensional Measurement. This survey was conducted among numerous NCMS members which include 
a vast majority of the most noted domestic machine tool  builder^.^ 
The successfu1 completion of the MetreX effort will help to strengthen the U.S. machine tool indusaa-y 
and help to build more efficient, higher performance aircraft turbine engines at more affordable costs, and 
help the entire U.S. manufacturing base by mnking possible the economic production of complex 
shapesfundamental elements in a wide range of components used for military, industrial. scientific and 
medical purposes. 
Research Obiectives 
The project is directed to the development and demonstration of a Capacitive Non-Contact Analog 
Probe (CNAP) and a Capacitive Array Dimcnsional Measurement (CADM) system for inspecting 
complex contours. This system incorporates technology developed by Extrude Hone's MetreX Division, 
and will provide a fast, low cost method of measuring complex shapes. In the case of the CADM, the 
gauge will measure a large number of points over a surface array that is electrically scanned in 
milliseconds, the time required being substantially less than existing methods. The technology is being 
further developed to be used on the machine tool, on-site, and consideration is being given to the 
requirements of measurement in various processing environments. Direct software interfacing techniques 
Air Force Wright Aeronautical Laboratories, "AFWAL-TR-88-4177 Final Report for 1 October 1987 - 
31 December 1988," Manufacturing Technology Program Assessment of New Sensor Terhnologiesfor she 
U.S. Machine Tool Industry, Sept. 1988. 
Mechanical Technology Inc., Nigh Protluctivity and Precision Machining Program: Integration Pian, 
NCMS-89-PE-4.1 (Ann Arbor: National Center for Manufacturing Sciences, 1990), p. 1-3. 
axe being researched and if necessary, developed to provide logical and straightforward communication to 
new or existing machine tools. 
The project is validating the ability of the capacitance sensors to accurately and repeatedly measure 
the complex shape of a workpiece. Mathematical modeling of the designed sensorts) and probes is being 
performed and analyzed. A demonstration lab unit and specifications for the equipment design with 
interfacing protocol to as wide a range of machine tool controls as practical to perform the inspection 
procedure ow the machine tool are being established. In addition, the system's ability to withstand the 
rigors of a hostile machine tool environment are being tested. The research will culminate in the design, 
fabrication and test of the entire system, the integration of the system with a machine tool process, the 
optimization of the process and the demonstration of the total system capabilities. 
Benefits 
'me opportunities to improve the performance of products and to permit innovative new designs for 
producrs that are dependent on components with complex shapes are limited by the high costs of 
producing the components and verifying their shapes. For example, involute gears are very sensitive to 
gear misalignment. If the profile of the gear is manufactured incorrectly, the subsequent misalignment 
will cause the shift of the be'uing conhct toward the edge of the gear tooth surfaces and transmission 
errors khaa cause gear noise. Much time and expense is spent in the design and engineering, as well as the 
manufilcture of these gears simply to overcome the control variations of the gear producing process. An 
innovat~on 80 improve the manufacturing of gears by providing timely verification and subsequent 
correction sf the process would provide a welcome technology edge to producers, end-users, as well as 
U.S. manufacturers of gear machine tools. 
The need to verify complex shapes and accordingly correct their manufacturing processes has been 
recogrlized by the aircraft turbine engine industry. Numerous components in a jet engine including turbine 
blades, impellers, and Integrally Bladed Rotors (IBR's) possess complex contours and shapes and require 
very derailed and complicated inspection procedures. An inspection system incorporating dimensional and 
tolerance data. measurement in a timely fashion as close to the manufacturing process as possible would 
Wead  to reduced inspection time and costs, higher standards of accuracy, increased workpiece throughput, 
and reduced machining labor costs. 
As devices continually and increasingly employ complex shapes and near net-processed components 
gain populsity, the need to verify these components' complex shapes will grow accordingly. If the 
proposed system of near-process verification of those shapes finds successful integration, the subsequent 
growth of complex shapes and their manufacturing processes would be compounded. The expanded 
design oppoaunities for new products with special capabilities will offer significant performance and 
strategic benefits in a range of applications including turbine engine components, gears, and cutting tools. 
RELATED WORK 
Capxilance sensing technology has been used since the 1950's for measuring the thickness of metal 
sh-ips and coatings, the expansion and fatigue of metals, and the size, depth and cylindricity of precision 
bores and shafts. One of the important benefits of capacitance in these and other applications lies in its 
ability to measure such parameters without actually contacting the workpiece surface. Other advantages 
anclu~de a high frequency response, excellent linearity and resolution, and convenient portability. Typical 
configurations of conventional capacitance dimensional measurement systems are singular or differential 
in application. Extrude Hone's MetreX Division has pioneered the effort to develop capacitance 
technology for surface finish evaluations, and has recently developed basic capacitance sensor array 
capabilities for shape, edges, proximity, and slip under a Phase I1 Department of Energy SBIR project. 
The Division is currently working on a Phase I1 SBIR grant sponsored by NASA to demonstrate the 
feasibility oif integrating all of the tactile attributes into a single sensor array, to develop software to 
control sensor scanning schemes and to establish adaptive grasping control algorithms. 
One phase of the current Air Force project is to build on the results of this program to integrate the 
dimensional measurement capabilities of a capacitance array and probe to check the conformity of a 
complex workpiece shape to a known reference shape on the machine tool. 
The Division was granted a license to patents and know-how covering the use of fringe-field 
capacitive technology developed at the University of Washington. The technology supplements the 
Division's existing techniques with surface profilometry and dimensional measurement capabilities. The 
Division has been working to incorporate this technology for those applications which require more than 
average surface roughness measurements. The advantages of current capacitance metrology including fast 
response time and rugged sensors for in-process inspection are enhanced and strengthened by this 
technology. 
This technology was one of three selected for evaluation for the Automated Disk Slot Inspection 
System (ADSIS), an Industrial Modernization Incentives Program (IMIP) through Garrett Engine 
Division of Allied Signal Aerospace Company. The objective of the program was to develop an automated 
system of inspecting gas turbine engine disk slots using advanced inspection technologies to achieve 
enhanced accuracy, repeatability, and flexibility coupled with faster data acquisition. Under this program, 
a spherical capacitance prototype probe designed to interface to a Coordinate Measuring Machine was 
delivered. This single sensor probe provides noncontact dimensional data on turbine disk slots in a 
scanning mode without contacting the part. After initial evaluation by both Garrett and the National 
Institute of Standards and Technology (NIST), the capacitance probe was selected as one of the prime 
sensing technologies . The other technologies, conventional touch trigger and laser triangulation probes, 
were deemed too slow and not capable of being configured small enough to reach into the limited access 
areas required. 
This Air Force effort is building on the results of these programs to establish the feasibility of 
integrating the measurement capabilities of this Capacitance Non-Contact Analog Probe to measure 
dimensions, features and surface characteristics in conjunction with an appropriate machine tool. 
Bibliography 
Garbini, J.L., L.J. Albrecht. J.E. Jorgensen and G.F. Mauer, "Surface Profilometry Based on Fringing 
Capacitance Measurement," ASME Journal of Dynamic Systems, Measurement and Control, Vol. 107(3), 
(September, 1985). 
Garbini, J.L., F.T. O'Neill and J.E. Jorgensen, "A High Speed Fringe-Field Capacitive Hole Inspection 
System," Modeling, Sensing and Control of Manufacturing Processes, ASME, DSC-Vol.4, (1986). 
Mathias, R.A. and J.L. Garbini, An Advanced Force Sensor System for Unmanned and Flexible 
Manufacturing, presented at the Sensor Technology for Untended Manufacturing Conference, Chicago, 
Illinois, SME Paper No. MS84-910, (1984). 
Tsukamaki, T., J.L. Garbini and J.E. Jorgensen, "An Algorithm for the Control of a Bi-Stable Multi- 
Segmented Manipulator," presented at the Fifth IASTED International Symposium on Robotics and 
Automation, (November 12, 1984). 


On Machine Capacitance Dimensional and Surface Profile Measurement System

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