Programme
Microscale surface and form profilometry using a standing wave probe
Dr. Marcin B. Bauza
InsituTec Inc - USA
Presentation abstract
Measurement of both microscale parts and larger parts with microscale features remains a challenging problem. Most microscale probing systems which currently exist are generally based on a similar principle of operation compared to larger probes applied to macroscale measurements, or are based on sharp tips attached to relatively large cantilevers as is the case for stylus profilometry and scanned probe techniques. In particular, these types of probing systems often embody a probe in the form of a shank which attaches a precision microscale sphere or spherical contact on the end. As a result of manufacturing complexities, the aspect ratio of these probes can be small, scanning speeds low and adhesion related problems are usually difficult to overcome. Contact forces of many of these touch probes are often greater than 1 µN and, for small probe tip radii, can elastically or even plastically deform the measured surface. In practice, characterization of surface topography and dimensional features remains a significant challenge for the micromanufacturing industry. The impact to quality control for microscale manufacturing is widespread ranging from components for medical, aero space, automotive, electronics, optical, micro molding, precision micro mechanics, free form diamond turned parts, and many more applications.
The aim of this presentation is to discuss an emerging microscale probing technology using a patented standing wave probe methodology. The probing and scanning technology discussed in this presentation demonstrates the ability to measure both dimensional features and surface finish simultaneously in the same data set that are normally impractical to measure with surface profilometers.
In general, the probe consists of a 500:1 aspect ratio fiber with a 7 µm diameter attached at one end to an oscillator with the free end comprising the measurement ‘tip’. The oscillator produces a standing wave in the oscillating probe shank compared to conventional probes that use a microscale sphere on the end of a rigid shank. As a result of the standing wave formed in steady state vibration, the free end of the shank generates an amplitude of oscillation greater than the probe shank diameter. Thus, the probe does not require a spherical ball to serve as the contact point and simply uses the contact diameter of the free end of the vibrating shank. This methodology is referred to as a virtual probe tip. During scanning, the probe has two sensitivity regions referred to as near-field (out of contact) scanning and contact scanning. The contact scanning mode for example contacts with 100 nN maximum force and is low enough to not damage highly precise parts such as precision optics. The sensor is only sensitive in one axis and is thus referred to as a one dimensional (1D) sensor. The probe is expanded to multi-dimensional measurements by adapting the probe to the free end of an articulating or precision spindle gauge head that is located on the quill of a CMM. The spindle rotates the probe’s sensitive axis such that it continues to remain normal to the surface of the part. The gauge head used is referred to as AccuSurf 3D and offers the ability to profile 3D objects and extract both surface finish and form.
Examples of measurements of calibrated surface finish artifacts (supplied by NIST) are shown below to quantify the probe’s ability to measure surface finish, Figure 1. In addition, we will discuss many examples ranging from microscale holes (Figure 2), conical holes (Figure 3a), aerogels, optically finished concave and convex surfaces (Figure 3b) and thickness of microscale foils (thicknesses of 60 µm) will be presented. Videos will also be presented showing the fibers functionality and scanning capability. Next steps discussed for this work will include integration with a Zeiss CMM and scaling affects.
- Weckenmann A., Estler T., Peggs G., McMurtry D. Probing Systems in Dimensional Metrology. Annals of the CIRP 53 (2004) 657-684.
- Yang F. Adhesive contact of axisymmetric suspended miniature structure. Sensors and Actuators A104 (2003) 44-52.
- Bhushan B. Nanoscale tribophysics and tribomechanics Wear 225-229 (1999) 465-492.
- Bauza M.B., Hocken R.J., Smith S.T., Woody S.C., Development of a virtual probe tip with an application to high aspect ratio microscale features. Rev. Sci. Instrum. 76, 095112 (2005)
- Bauza M.B., Woody B.A., Woody S.C., Smith S. T., 3D Surface Profilometry of high aspect ratio features, Proc of 12th Met and Props, 2009.
Information about the speaker
Dr. Marcin Bauza completed a MSc. in Mechanical Engineering specializing in Polymer Science in 2000 and in 2001 he completed a second MSc. in Mechanical Engineering specializing in Metrology at Poznan University of Technology. During his study, he was co-author of several publications in a field of Polymer Science. In spring 2005 he completed his Ph.D. in Mechanical Engineering at the Center for Precision Metrology at University of North Carolina at Charlotte. During the past 8 years he was focused on development of microscale force probes, picometer motion platforms, ultra-precise spindles, microscale tweezers and various real time high accuracy measuring systems. His expertise is in Labview controls and FPGA programming, electronics circuit design and assembly, CAD design, FEA analisys, instrumentation assembly, integration and characterization. Dr. Bauza currently manages projects in microscale dimensional metrology and high speed scanning. He also worked on several developments including nanopositioning stages, self sensing micro-tweezers, prultraprecision spindles, custom metrology gauge heads and various industrial as well as national lab contracts. As a consequence, these investigations have accumulated multiple patents, as well as peer reviewed publications and many conference proceedings. Additionally, Dr. Bauza serves as reviewer on Precision Engineering Journal.