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The following quote was obtained by the news editors from the background information supplied by the inventors: "This invention is directed to a micro-electrical discharge machine (.mu.EDM) based metrology system using a styli and sensing at pica joule energy levels. The micro-electrical discharge machine based metrology system is a non-contact, non-destructive, and on-board metrology system capable of in-process quality assurance/quality control (QA/QC).
"Many industries, including semiconductor, medical, automotive, defense and aerospace have an increasing need for parts with dimensions measured in microns, commonly known as microstructures. However, known methods for measuring these microstructures have various short-comings which often result in the need to scrap parts which are manufactured out of specification.
"When a conventionally-sized part is manufactured, the part can be removed from the machining platform and measured. If a dimension is found to be out of tolerance, the part can be placed back onto the machining platform for additional work. However, as machined parts are reduced in size to microns with even smaller tolerances, it is impractical for these parts to be re-positioned on the machine after measuring with the necessary accuracy. Accordingly, in order to maintain reference points on the machined part, the part must be measured on the machining platform prior to removal. If a part is removed from the machine to be measured and found to be out of specification, the part must be scrapped as it is very difficult to reposition in the machine with the accuracy necessary for additional machining. The machining process must then be modified and a new part fabricated. This costs time, money, and results in material waste.
"Known on-machine metrology devices can cut this drop-out rate by 90%, resulting in substantial savings to the manufacturer, supplier, and consumer. However, these known metrology platforms are expensive, have fragile sensors and have a limited scope of measurement.
"Known on-machine micro-metrology systems are generally divided into two types, tactile or optical systems. Optical systems, either visible or laser, are limited by line-of-sight restrictions (if it can't see it, it can't measure it). While tactile based systems have delicate sensors with limited ranges with respect to aspect ratios, sidewalls, and overhangs. Tactile sensors also rely on surface contact with the part, surface contact can leave witness marks, scratches or blemishes that can render a part unusable for an intended purpose. As an example, one type of ultra-high precision probe will contact a surface with 0.300 Nm/.mu.m of force. This force is 15 billion times greater than the smallest force from the sensor of this invention.
"Both tactile and optical systems are also adversely affected by machine oils and other machining residues. For either of these systems to be effective, additional cleaning steps are necessary both inside and outside of the machining platform prior to use.
"As such, there is a need for an improved metrology system for measuring micro-sized components that avoids the short-comings of known metrology systems."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "A general object of the invention is to provide a metrology system that uses electrical discharge sensing to measure a component's size.
"Electrical discharge machining (EDM) is currently a purely material erosion manufacturing process whereby electric sparks are used to erode material from a work piece to form a desired shape. A tool-electrode and a work piece-electrode are subjected to an electric voltage and in a dielectric. Initially, as the tool-electrode approaches the work piece-electrode the dielectric acts as an insulator. As the tool-electrode moves closer to the work piece an electric field breaks down the dielectric, forming a plasma bubble between the tool-electrode and the work piece-electrode. The plasma bubble conducts a flow of energy, a spark, between the work piece-electrode to the tool-electrode, evaporating material from the work piece and a smaller amount of material from the tool. This flow of energy depletes the charge stored in the system, and equalizes an electric potential between the tool-electrode and work piece-electrode, collapsing the electric field and ending the spark event. Particles of evaporated material cool and are flushed away with the dielectric fluid. With the electrical flow broken, the capacitor recharges and the electric field is reestablished. Table 1 lists the traditional energy levels used by conventional EDM and .mu.EDM systems. It is traditionally held that EDM circuits will not function with a bias of less than 60 volts.
"TABLE-US-00001 TABLE 1 Voltage (V) Capacitance (pF)
"Instead of the conventional focus of an EDM described above, the metrology machine of the present invention uses a lower energy level so as to not remove any material from the surface of the work piece.
"In a preferred embodiment, the micro-electrical discharge based metrology system for non-contact, non-destructive, on-board metrology includes a pica joule energy level .mu.EDM sensing circuit and a reliable spindle probe sensor that is electrically isolated and mountable in a variety of conventional EDM machines. Sensing with these energy levels using a .mu.EDM formed styli is a reversal of the process behind EDM. Such minute energy levels, combined with high frequency response electronics, will create a non-destructive, non-contact electrical sensor for in situ metrology. The system of this invention will not only have the ability for micro-metrology, but will have the added benefit of a .mu.EDM's innate capability to self-manufacture its own probe sensors, as well as the standard .mu.EDM functionality for manufacturing micro-holes, contoured forming, and de-burring of conductive materials.
"In a preferred embodiment, the micro-electrical discharge based metrology system of this invention includes a tank to hold a work piece, preferably in a dielectric fluid. Preferably, the tank includes a support surface and a mechanism to reposition the work piece in at least two dimensions and preferably three dimensions. The work piece preferably comprises a conductive material, for example, but not limited to, metallic materials including stainless steel, platinum, titanium, gold and molybdenum. However, the work piece need not be a metallic material and may comprise any conductive material including, but not limited to, ceramic materials, doped silicon, impregnated ceramics, and thin-film covered, non-conductive materials.
"The micro-electrical discharge based metrology system of this invention further includes a probe with a mechanism for positing the probe in proximity to the work piece. The mechanism is preferably a computer numerical control (cnc) machine that is capable of moving the probe in at least two dimensions and preferably in three dimensions. The probe preferably comprises one of a traditional coordinate measuring machine (CMM) stylus, a cylindrical stylus, an ultra-smooth stylus, a rectangular stylus, a wheel or disk stylus, and a tapered stylus. However, this invention is not limited to the listed styli and may be any type of stylus known to a person of skill in the art.
"The micro-electrical discharge based metrology system of this invention further includes a control unit with a sensing circuit (also known as a discharge circuit) and a controller for the cnc machine. The sensing circuit is electrically connected to the probe and the work piece. The sensing circuit preferably comprises a resistor-capacitor (RC) circuit that runs on a natural frequency of the chosen component values. Alternatively, the sensing circuit may comprise a pulsed direct current (DC) generator with a frequency selected by a waveform generator.
"In operation, the cnc machine moves the probe in proximity to the work piece, as a gap between the work piece and the probe becomes sufficiently small a dielectric breakdown occurs and a position of at least one of the probe and the work piece is recorded, preferably on a recordable medium in the control unit and/or the cnc machine. The cnc machine then moves the probe to another position in proximity to the work piece to record another position. This process is repeated until the work piece is dimensioned, as needed. In a preferred embodiment, a spark energy resulting from the dielectric breakdown does not cause damage to a surface of the work piece. In an embodiment, the spark energy resulting from the dielectric breakdown is less than 2.0 nanojoules (nJ). In another embodiment, the spark energy resulting from the dielectric breakdown is less than 0.500 nanojoules. In another embodiment, the spark energy resulting from the dielectric breakdown is less than 0.020 nanojoules.
"In another preferred embodiment of this invention, the micro-electrical discharge machine for non-contact measuring of this invention is a stand-alone machine that includes an isolated probe system, a stand-alone control box, a control cable and coded instructions to interface with a third-party micro electrical discharge machine and/or a third-party cnc machine. In another embodiment, the micro-electrical discharge machine can be retrofit onto existing .mu.EDM as well as licensed and distributed with new .mu.EDM platforms.
BRIEF DESCRIPTION OF THE DRAWINGS
"These and other objects and features of this invention will be better understood from the following detailed description taken in conjunction with the drawings, wherein:
"FIG. 1 is a schematic drawing of a micro-electrical discharge based metrology system according to one embodiment of this invention;
"FIG. 2 shows a sensing circuit according to a preferred embodiment of this invention;
"FIG. 3 shows a preferred embodiment of a probe that may be used with the micro-electrical discharge based metrology system of FIG. 1;
"FIGS. 4.1 to 4.7 show various alternative probes that may be used with the micro-electrical discharge based metrology system of FIG. 1;
"FIGS. 5.1 and 5.2 show a pair of probes that may be used with the micro-electrical discharge based metrology system of FIG. 1 and surface deformations resulting from each probe;
"FIG. 6 shows a pair of graphs showing measurement repeatability of the micro-electrical discharge based metrology system of this invention; and
"FIG. 7 shows a carbide nozzle and a 3-D mapping of the carbide nozzle."
URL and more information on this patent application, see: Mraz, Jerry;
Keywords for this news article include: Smaltec International Llc.
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