Source: http://www.google.com/patents/US7560657?dq=3798360
Timestamp: 2013-12-06 10:37:13
Document Index: 414039283

Matched Legal Cases: ['art 320', 'art 320', 'art 320', 'art 320', 'arts 320', 'arts 320', 'Art63', 'art 1']

Patent US7560657 - Plasma-assisted processing in a manufacturing line - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Advanced Patent Search | Sign inAdvanced Patent SearchPatentsMethods and apparatus are provided for plasma-assisted processing multiple work pieces in a manufacturing line. In one embodiment, the method can include placing the work pieces in movable carriers, moving the carriers on a conveyor into an irradiation zone, flowing a gas into the irradiation zone, igniting...http://www.google.com/patents/US7560657?utm_source=gb-gplus-sharePatent US7560657 - Plasma-assisted processing in a manufacturing linePublication numberUS7560657 B2Publication typeGrantApplication numberUS 10/513,605PCT numberPCT/US2003/014055Publication dateJul 14, 2009Filing dateMay 7, 2003Priority dateMay 8, 2002Fee statusLapsedAlso published asUS20060081567Publication number10513605, 513605, PCT/2003/14055, PCT/US/2003/014055, PCT/US/2003/14055, PCT/US/3/014055, PCT/US/3/14055, PCT/US2003/014055, PCT/US2003/14055, PCT/US2003014055, PCT/US200314055, PCT/US3/014055, PCT/US3/14055, PCT/US3014055, PCT/US314055, US 7560657 B2, US 7560657B2, US-B2-7560657, US7560657 B2, US7560657B2InventorsMichael L. Dougherty, Sr., Devendra Kumar, Satyendra KumarOriginal AssigneeBtu International Inc.Patent Citations (103), Non-Patent Citations (99), Referenced by (1), Classifications (11), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetPlasma-assisted processing in a manufacturing lineUS 7560657 B2Abstract Methods and apparatus are provided for plasma-assisted processing multiple work pieces in a manufacturing line. In one embodiment, the method can include placing the work pieces in movable carriers, moving the carriers on a conveyor into an irradiation zone, flowing a gas into the irradiation zone, igniting the gas in the irradiation zone to form a plasma (e.g., by subjecting the gas to electromagnetic radiation in the presence of a plasma catalyst), sustaining the plasma for a period of time sufficient to at least partially plasma process at least one of the work pieces in the irradiation zone, and advancing the conveyor to move the at least one plasma-processed work piece out of the irradiation zone. Various types of plasma catalysts are also provided.
1. A method of plasma-assisted processing a plurality of work pieces within a localized irradiation zone that occupies some portion of a radiation chamber, the method comprising:
placing each of the plurality of work pieces in or on a corresponding movable carrier that is disposed within the radiation chamber;
sequentially moving each of the movable carriers on a conveyor into the localized irradiation zone of the radiation chamber;
flowing a gas into the localized irradiation zone;
igniting the gas in the localized irradiation zone to form a hot plasma;
sustaining the hot plasma for a period of time sufficient to at least partially plasma-process at least one of the work pieces in the localized irradiation zone; and
advancing the conveyor to move the at least one plasma-processed work piece out of the localized irradiation zone and into a portion of the radiation chamber in which the at least one plasma-processed work piece is not exposed to the plasma-forming localized irradiation zone.
2. The method of claim 1, wherein the plasma-processing is at least one of sintering, annealing, normalizing, spheroiding, tempering, age hardening, case hardening, joining, doping, nitriding, carburizing, decrystallizing, carbo-nitriding, cleaning, sterilizing, vaporizing, coating and ashing.
3. The method of claim 1 wherein at least one of the work pieces comprises a plurality of parts to be joined.
4. The method of claim 1, wherein the conveyor comprises at least one of a belt, a track, a robot, a turntable, a roller, a wheel, a chain, a bucket, a tray, a guide rail, a lift, a screw, a push bar, a ribbon screw, a rail system, an under floor system, a roller system, a slider system, a slat system, a gravity feed system, a chain on edge system, a cable system, a magnetic conveyor, a pulley system, a reciprocating conveyor, and any other mechanism capable of moving the work pieces from one location to another.
5. The method of claim 1 wherein the work piece includes at least one of a metal, a non-metal, a ceramic, a glass, an organic material, and a non-organic material.
6. The method of claim 1, wherein the irradiation zone includes a housing for adjoining the carrier.
7. The method of claim 6, wherein the housing and the carrier cooperate to form a cavity.
8. The method of claim 7, wherein the housing includes at least a top portion.
9. The method of claim 7, wherein the housing includes an inlet for conveying gas to the cavity.
10. The method of claim 6, further comprising moving the carrier to a position adjacent the housing.
11. The method of claim 6, further comprising moving the housing to a position adjacent the carrier.
12. The method of claim 1, further comprising igniting the plasma using a plasma catalyst.
13. The method of claim 12, wherein the catalyst is at least one of an active catalyst and a passive catalyst.
14. The method of claim 13, wherein the catalyst comprises at least one of metal, inorganic material, carbon, carbon-based alloy, carbon-based composite, electrically conductive polymer, conductive silicone elastomer, polymer nanocomposite, and an organic-inorganic composite.
15. The method of claim 14, wherein the catalyst is in the form of at least one of a nanoparticle, a nano-tube, a powder, a dust, a flake, a fiber, a sheet, a needle, a thread, a strand, a filament, a yarn, a twine, a shaving, a sliver, a chip, a woven fabric, a tape, and a whisker.
16. The method of claim 15, wherein the catalyst comprises carbon fiber.
17. The method of claim 13, wherein the catalyst is in the form of at least one of a nano-particle, a nano-tube, a powder, a dust, a flake, a fiber, a sheet, a needle, a thread, a strand, a filament, a yarn, a twine, a shaving, a sliver, a chip, a woven fabric, a tape, and a whisker.
18. The method of claim 13, wherein the plasma catalyst comprises an active plasma catalyst including at least one ionizing particle.
19. The method of claim 18, wherein the at least one ionizing particle comprises a beam of particles.
20. The method of claim 18, wherein the particle is at least one of an x-ray particle, a gamma ray particle, an alpha particle, a beta particle, a neutron, and a proton.
21. The method of claim 18, wherein the at least one ionizing particle is a charged particle.
22. The method of claim 18, wherein the ionizing particle comprises a radioactive fission product.
23. The method of claim 1, wherein the housing comprises a waveguide.
24. The method of claim 1, wherein at least one of the plurality of work pieces is exposed to a substantially larger amount of plasma than other of the plurality of work pieces.
25. The method of claim 1, wherein the zone includes a housing that cooperates with at least one of the plurality of work pieces to form a cavity.
26. The method of claim 1, wherein the sequentially moving includes moving at least one of the movable carriers continuously.
27. The method of claim 1, wherein the sequentially moving includes moving a plurality of the movable carriers into the zone in batches.
28. The method of claim 1, wherein the sustaining comprises directing an amount of electromagnetic radiation having a frequency less than about 333 GHz into the zone.
29. A method of plasma-assisted processing a plurality of work pieces within a localized irradiation zone that occupies some portion of a radiation chamber, the method comprising:
sequentially conveying a plurality of work pieces into the localized irradiation zone of the radiation chamber;
sequentially conveying the plurality of work pieces out of the localized irradiation zone into a portion of the radiation chamber that is not exposed to the plasma-forming localized irradiation zone.
30. The method of claim 29, further comprising placing the plurality of work pieces on a plurality of movable carriers before sequentially conveying the plurality of work pieces into the irradiation zone.
31. The method of claim 30, wherein the irradiation zone includes a housing configured to adjoin at least one of the plurality of carriers, and wherein the method further comprises forming a plasma cavity in the irradiation zone by moving the housing and the at least one of the plurality of carriers closer together.
32. The method of claim 31, wherein the housing includes at least a top portion, and wherein the moving comprises moving the at least one of the plurality of carriers toward the top portion.
33. The method of claim 31, wherein the housing includes at least a top portion, and wherein the moving comprises moving the top portion toward the at least one of the plurality of carriers.
34. The method of claim 29, wherein the igniting the gas comprises exposing the gas to the electromagnetic radiation at a frequency less than about 333 GHZ in the presence of a plasma catalyst at a gas pressure of at least about atmospheric pressure.
35. The method of claim 34, wherein the plasma catalyst is at least one of an active plasma catalyst and a passive plasma catalyst.
36. The method of claim 31, wherein the housing comprises a waveguide.
37. The method of claim 29, wherein the sequentially conveying into the irradiation zone is at least one of continuous and batched.
38. The method of claim 29, wherein the conveying comprises moving the work pieces along a manufacturing line.
39. The method of claim 29, further comprising applying an electric bias to the work piece during the sustaining.
40. The method of claim 39, wherein the applying comprises applying at least one of a DC bias, an AC bias, a pulsed bias, and a continuous bias. Description
FIELD OF THE INVENTION This invention relates to methods and apparatus for plasma-assisted processing of work pieces in a manufacturing line.
BACKGROUND OF THE INVENTION Plasmas can be used to assist in a number of processes, including the joining and heat-treating of materials. However, igniting, modulating, and sustaining plasmas for these purposes can be difficult for a number of reasons.
For example, it is known that a plasma can be ignited in a cavity by directing a large amount of microwave radiation into the cavity containing a gas. If the radiation intensity is large enough, the plasma can ignite spontaneously. However, radiation sources capable of supplying such large intensities can have several disadvantages; they can be expensive, heavy, bulky, and energy-consuming. Moreover, these large radiation sources normally require large electrical power supplies, which can have similar disadvantages.
One way of igniting a plasma with a lower radiation intensity is to reduce the pressure in the cavity. However, vacuum equipment, which can be used to reduce this pressure, can limit manufacturing flexibility, especially as the plasma chambers become large and especially in the context of manufacturing lines.
A sparking device can also be used to ignite a plasma using a lower radiation intensity. Such a device, however, only sparks periodically and therefore can only ignite a plasma periodically, sometimes causing an ignition lag. Moreover, conventional sparking devices are normally powered with electrical energy, limiting their use and position in many manufacturing environments.
BRIEF SUMMARY OF A FEW ASPECTS OF THE INVENTION A method of plasma-assisted processing a plurality of work pieces can be provided. In one embodiment, a method of plasma-assisted processing a plurality of work pieces is provided. The method can include sequentially conveying a plurality of work pieces into an irradiation zone, flowing a gas into the irradiation zone, igniting the gas in the irradiation zone to form a plasma, sustaining the plasma for a period of time sufficient to at least partially plasma process at least one of the work pieces in the irradiation zone, and sequentially conveying the plurality of work pieces out of the irradiation zone.
In another embodiment, the method can include placing each of the plurality of work pieces in a plurality of movable carriers, sequentially moving each of the movable carriers on a conveyor into an irradiation zone, flowing a gas into the irradiation zone, igniting the gas in the irradiation zone to form a plasma, sustaining the plasma for a period of time sufficient to at least partially plasma process at least one of the work pieces in the irradiation zone, and advancing the conveyor to move the at least one plasma-processed work piece out of the irradiation zone.
Apparatus for plasma-assisted processing a plurality of work pieces may also be provided. In one embodiment, an apparatus can include a radiation source, a radiation housing through which radiation passes from the source, a conveyor for sequentially moving the work pieces into and out of an irradiation zone adjacent the housing in the presence of a plasma. The apparatus may also include a gas inlet for conveying gas into the irradiation zone to enable plasma formation in the irradiation zone.
A plasma catalyst for initiating, modulating, and sustaining a plasma is also provided. The catalyst can be passive or active. A passive plasma catalyst can include any object capable of inducing a plasma by deforming a local electric field (e.g., an electromagnetic field) consistent with this invention, without necessarily adding additional energy. An active plasma catalyst, on the other hand, is any particle or high energy wave packet capable of transferring a sufficient amount of energy to a gaseous atom or molecule to remove at least one electron from the gaseous atom or molecule in the presence of electromagnetic radiation. In both cases, a plasma catalyst can improve, or relax, the environmental conditions required to ignite a plasma.
FIG. 9 shows an illustrative embodiment of a portion of a plasma-assisted processing system for directing ionizing radiation into a radiation chamber consistent with this invention;
FIG. 10 shows a perspective view of illustrative apparatus for plasma-assisted processing of multiple work pieces consistent with this invention;
FIG. 11 shows another perspective view of the illustrative apparatus of FIG. 10 consistent with this invention;
FIG. 12 shows a top plan view of an illustrative conveyor that can be used with the apparatus of FIG. 10 consistent with this invention;
FIG. 13 shows a cross-sectional view of the illustrative conveyor of FIG. 12, taken along line 13-13 of FIG. 12, along with various additional components and work pieces, consistent with this invention;
FIG. 14 shows a cross-sectional view of another illustrative conveyor with recesses in which work pieces can be placed consistent with this invention; and
FIG. 15 shows a flow-chart for an illustrative method of plasma-processing a plurality of work pieces consistent with this invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS This invention relates to methods and apparatus for plasma-assisted processing in a manufacturing line and can be used to lower energy costs and increase manufacturing flexibility.
The following commonly owned, concurrently filed U.S. patent applications are hereby incorporated by reference in their entireties: U.S. patent application Ser. No. 10/513,229, U.S. patent application Ser. No. 10/513,313, PCT Application US03/14132, now expired, U.S. patent application Ser. No. 10/513,394, U.S. patent application Ser. No. 10/513,607, U.S. patent application Ser. No. 10/449,600, PCT Application US03/14034, now expired, U.S. patent application Ser. No. 10/430,416, U.S. patent application Ser. No. 10/430,415, PCT Application US03/14133, now expired, U.S. patent application Ser. No. 10/513,606, U.S. patent application Ser. No. 10/513,309, U.S. patent application Ser. No. 10/513,220, PCT Application US03/14122, now expired, U.S. patent application Ser. No. 10/513,397, U.S. patent application Ser. No. 10/513,605, PCT Application US03/14137, now expired, U.S. patent application Ser. No. 10/430,426, PCT Application US03/14121, now expired, U.S. patent application Ser. No. 10/513,604, and PCT Application US03/14135.
FIG. 1 shows illustrative plasma system 10 consistent with one aspect of this invention. In this embodiment, cavity 12 is formed in a vessel that is positioned inside radiation chamber (i.e., applicator) 14. In another embodiment (not shown), vessel 12 and radiation chamber 14 are the same, thereby eliminating the need for two separate components. The vessel in which cavity 12 is formed can include one or more radiation-transmissive insulating layers to improve its thermal insulation properties without significantly shielding cavity 12 from the radiation. As described more fully below, system 10 can be used to generate a plasma and can be included in a manufacturing line consistent with this invention.
In one successful experiment, a plasma was formed in a partially open cavity inside a first brick and topped with a second brick. The cavity had dimensions of about 2 inches by about 2 inches by about 1.5 inches. At least two holes were also provided in the brick in communication with the cavity: one for viewing the plasma and at least one hole for providing the gas. The size of the cavity can depend on the desired plasma process being performed. Also, the cavity can at least be configured to prevent the plasma from rising/floating away from the primary processing region.
Cavity 12 can be connected to one or more gas sources 24 (e.g., a source of argon, nitrogen, hydrogen, xenon, krypton) by line 20 and control valve 22, which may be powered by power supply 28. Line 20 may be tubing (e.g., between about 1/16 inch and about � inch, such as about ⅛″), but could be any device capable of delivering gas. Also, if desired, a vacuum pump can be connected to the chamber to remove fumes that may be generated during plasma processing. In one embodiment, gas can flow in and/or out of cavity 12 through one or more gaps in a multi-part vessel. Thus, gas ports consistent with this invention need not be distinct holes and can take on other forms as well, such as many small distributed holes.
Radiation source 26, which may be powered by electrical power supply 28, can direct radiation energy into chamber 14 through one or more waveguides 30 or by using a coaxial cable. It will be appreciated by those of ordinary skill in the art that source 26 can be connected directly to cavity 12 or chamber 14, thereby eliminating waveguide 30. The radiation energy entering cavity 12 is used to ignite a plasma within the cavity. This plasma can be substantially sustained and confined to the cavity by coupling additional radiation with the catalyst
The invention may be practiced with microwave sources at, for example, both 915 MHz and 2.45 GHz provided by Communications and Power Industries (CPI), although radiation having any frequency less than about 333 GHz can be used. The 2.45 GHz system provided continuously variable microwave power from about 0.5 kilowatts to about 5.0 kilowatts. A 3-stub tuner allowed impedance matching for maximum power transfer and a dual directional coupler was used to measure forward and reflected powers. Also, optical pyrometers were used for remote sensing of the sample temperature.
As mentioned above, radiation having any frequency less than-about 333 GHz can be used consistent with this invention. For example, frequencies, such as power line frequencies (about 50 Hz to about 60 Hz), can be used, although the pressure of the gas from which the plasma is formed may be lowered to assist with plasma ignition. Also, any radio frequency or microwave frequency can be used consistent with this invention, including frequencies greater than about 100 kHz. In most cases, the gas pressure for such relatively high frequencies need not be lowered to ignite, modulate, or sustain a plasma, thereby enabling many plasma-assisted processes to occur at atmospheric pressures and above in any manufacturing environment.
The equipment was computer controlled using LabView 6 i software, which provided real-time temperature monitoring and microwave power control. Noise was reduced by using sliding averages of suitable number of data points. Also, to improve speed and computational efficiency, the number of stored data points in the buffer array were limited by using shift-registers and buffer-sizing techniques. The pyrometer measured the temperature of a sensitive area of about 1 cm2, which was used to calculate an average temperature. The pyrometer sensed radiant intensities at two wavelengths and fit those intensities using Planck's law to determine the temperature. It will be appreciated, however, that other devices and methods for monitoring and controlling temperature are also available and can be used consistent with this invention. For example, control software that can be used consistent with this invention is described in commonly owned, concurrently filed PCT Application US03/14135, now expired, which is hereby incorporated by reference in its entirety.
In one embodiment, the powder catalyst can be carried into the cavity and at least temporarily suspended with a carrier gas. The carrier gas can be the same or different from the gas that forms the plasma. Also, the powder can be added to the gas prior to being introduced to the cavity. For example, as shown in FIG. 1A, radiation source 52 can supply radiation to radiation cavity 55, in which plasma cavity 60 is placed. Powder source 65 can provide catalytic powder 70 into gas stream 75. In an alternative embodiment, powder 70 can be first added to cavity 60 in bulk (e.g., in a pile) and then distributed in the cavity in any number of ways, including flowing a gas through or over the bulk powder. In addition, the powder can be added to the gas for igniting, modulating, or sustaining a plasma by moving, conveying, drilling, sprinkling, blowing, or otherwise, feeding the powder into or within the cavity.
A predetermined ratio profile can be used to simplify many plasma processes. In many conventional plasma processes, the components within the plasma are added as necessary, but such addition normally requires programmable equipment to add the components according to a predetermined schedule. However, consistent with this invention, the ratio of components in the catalyst can be varied, and thus the ratio of components in the plasma itself can be automatically varied. That is, the ratio of components in the plasma at any particular time can depend on which of the catalyst portions is currently being consumed by the plasma. Thus, the catalyst component ratio can be different at different locations within the catalyst And, the current ratio of components in a plasma can depend on the portions of the catalyst currently and/or previously consumed, especially when the flow rate of a gas passing through the plasma chamber is relatively slow.
Unlike a single-mode cavity, a multi-mode cavity can support several propagation modes simultaneously, which, when superimposed, result in a complex field distribution patter. In such a pattern, the fields tend to spatially smear and, thus, the field distribution usually does not show the same types of strong minima and maxima field values within the cavity. In addition, as explained more fully below, a mode-mixer can be used to �stir� or �redistribute� modes (e.g., by mechanical movement of a radiation reflector). This redistribution desirably provides a more uniform time-averaged field distribution within the cavity.
Whether or not a single or multimode cavity is used consistent with this invention, it will be appreciated by those of ordinary skill in the art that the cavity in which the plasma is formed can be completely closed or partially open. For example, in certain applications, such as in plasma-assisted furnaces, the cavity could be entirely closed. See, for example, commonly owned, concurrently filed PCT Application No. US03/14133, now expired. In other applications, however, it may be desirable to flow a gas through the cavity, and therefore the cavity must be open to some degree. In this way, the flow, type, and pressure of the flowing gas can be varied over time. This may be desirable because certain gases, such as argon, which facilitate formation of plasma, can be easier to ignite but may not be needed during subsequent plasma processing.
For many plasma-assisted applications, a cavity containing a uniform plasma is desirable. However, because radiation can have a relatively long wavelength (e.g., several tens of centimeters), obtaining a uniform distribution can be difficult to achieve. As a result, consistent with one aspect of this invention, the radiation modes in a multi-mode cavity can be mixed, or redistributed, over a period of time. Because the field distribution within the cavity must satisfy all of the boundary conditions set by the inner surface of the cavity, those field distributions can be changed by changing the position of any portion of that inner surface.
Thus, even if the initial orientation of the catalyst is perpendicular to the electric field, the redirection of the electric field vectors can change the ineffective orientation to a more effective one. Those skilled in the art will appreciated that mode-mixing can be continuous, periodic, or preprogrammed.
In addition to plasma ignition, mode-mixing can be useful during subsequent plasma processing to reduce or create (e.g., tune) �hot spots� in the chamber. When a radiation cavity only supports a small number of modes (e.g., less than 5), one or more localized electric field maxima can lead to �hot spots� (e.g., within cavity 12). In one embodiment, these hot spots could be configured to coincide with one or more separate, but simultaneous, plasma ignitions or processing events. Thus, the plasma catalyst can be located at one or more of those ignition or subsequent processing positions.
Illustrative Plasma-Assisted Processing in a Manufacturing Line
Methods and apparatus for plasma-assisted processing of work pieces in a manufacturing line may be provided. A plasma-assisted process can include any operation, or combination of operations, involving the use of a plasma. The work pieces can be plasma-processed continuously, periodically, in batches, in sequence, or any combination thereof.
Plasma-assisted processes consistent with this invention can include, for example, sintering, annealing, normalizing, spheroiding, tempering, age hardening, case hardening, or any other type of hardening or process that involves heat-treatment. Plasma-assisted processing can also include joining materials that are the same or different from one another. For example, plasma-assisted processing can include brazing, welding, bonding, soldering, and other types of joining processes. Additional plasma-assisted processes, such as doping, nitriding, carburizing, decrystallizing, carbo-nitriding, cleaning, sterilizing, vaporizing, coating, and ashing, can also be included consistent with this invention.
FIGS. 10-13 show various views of illustrative apparatus 300 for plasma-assisted sintering. It will be appreciated, however, that apparatus 300 can be used to perform any other plasma-assisted process consistent with this invention as well.
FIG. 10 shows a perspective view of illustrative apparatus 300 for plasma-assisted processing of one or more work pieces consistent with this invention. Apparatus 300 can include, for example, radiation source 305, radiation waveguide 307 through which radiation passes from source 305 toward irradiation zone 325, and conveyor 310 for sequentially moving work pieces 320 into and out of irradiation zone 325 adjacent waveguide 307. Apparatus 300 can also include one or more gas ports (not shown) for conveying a gas in, out, or through zone 325 to enable plasma formation there.
FIG. 11 shows another perspective view of apparatus 300, taken along line 11-11 of FIG. 10. Any of radiation source 305 and power supply 335 (not shown) for powering source 305 can be located in housing 330. It will be appreciated, however, that source 305 and supply 335 can be located anywhere in relation to the floor plan, or to meet any other physical or dimensional requirement, of plasma-assisted processing apparatus 300. This includes separating source 305 from supply 335, in or out of housing 330.
Source 305 can irradiate zone 325 from any direction. For example, radiation source 305 can be located above, below, or in the same horizontal plane as zone 325 and waveguide 307 can be used to direct the radiation from source 305 to zone 325. If radiation source 305 is capable of directing radiation in the form of a beam (e.g., a diverging, converging, or collimated beam), then waveguide 307 can be eliminated and the zone can be irradiated simply by directing the radiation beam toward zone 325. In another embodiment, source 305 can supply radiation to zone 325 via one or more coaxial cable (not shown). In yet another embodiment, the radiation output of source 305 can directly irradiate zone 325.
When apparatus 300 includes waveguide 307, waveguide can have any cross-sectional shape to selectively propagate any particular radiation mode or modes. For example, as shown in FIG. 10, waveguide 307 can have a rectangular cross-section, but could also have a round, oval, or other shape capable of propagating radiation. Also, waveguide 307 can be linear, arched, spiral, serpentine, or any other convenient form. In general, waveguide 307 can be used to couple radiation source 305 to a radiation zone (e.g., a cavity) for forming a plasma and performing any type of plasma-assisted process.
A conveyor can include at least one carrier portion for conveying work pieces. As used herein, a carrier portion can be any portion of a conveyor adapted to carry, support, hold, or otherwise mount one or more work pieces. As shown in FIG. 11, for example, carrier portions 340 and 342 can be circular plates on which one or more work pieces can be placed and conveyed. FIG. 12, for example, shows a top plan view of conveyor 310, including six holes 350 on which carrier portions 340 and 342 can be positioned. Although conveyor 310 has been configured to hold up to six carrier portions, conveyor 310 can be configured to hold more or less carrier portions, if desired. It will be appreciated that a carrier portion consistent with this invention can also be integral with the conveyor or with the work piece.
Conveyor 310 need not include holes 350 consistent with this invention. For example, as shown in FIG. 14, upper surface 360 of conveyor 362 can include one or more recesses 364 in which one or more work pieces 366 can be placed while conveyor 362 rotates or otherwise moves. Alternatively, a conveyor consistent with this invention can have raised portions or even no surface features at all (not shown). That is, the supporting surface of the conveyor can be substantially flat and one or more work pieces can be placed in any convenient orientation on the surface. In this way, differently shaped work pieces can be used with the same conveyor consistent with this invention.
Any number of work pieces can be carried by carrier portions consistent with this invention. FIGS. 11 and 13, for example, show that carrier portions 340 and 342 each carry a single work piece. In this case, the work piece can be a powdered metal part to be sintered using a plasma. Also, as shown in FIG. 13, carrier portions 340 and 342 can be configured or shaped to fit in or otherwise attach to conveyor 310. For example, the sides of carrier portions 340 and 342 can be tapered so that they precisely fit into holes 350. In addition, the upper surface of the carrier portions can be customized or otherwise adapted so that one or more work pieces are carried or supported in a predetermined position. For this purpose, one or more adaptors can be used with the same carrier portion so that it can be used for differently shaped work pieces and plasma-assisted processes.
A waveguide and at least one carrier portion can cooperate to form a plasma-processing cavity consistent with this invention. For example, FIG. 11 shows tip portion 370 of waveguide 307 facing downward at work piece 320, which is located on carrier portion 342. Thus, work piece 320 can be located between tip portion 370 and carrier portion 342 that, together, form cavity 369 (shown in FIG. 13) in which a plasma can be formed. It will be appreciated that cavity 369 can be open or closed and the �openness� of the cavity depends on the relative position of tip portion 370 with respect to carrier portion 342.
As shown in FIGS. 11 and 13, for example, work piece 320 can be lifted by carrier portion 342 toward tip portion 370 by actuator 372, making the size and openness of cavity 369 smaller. In one embodiment, the gap between tip portion 370 and carrier portion 342 is reduced such that cavity 369 is essentially closed before a plasma is ignited, essentially trapping gas and forming a plasma with that gas. In another embodiment consistent with this invention, a gap remains before, during, or after plasma processing, permitting a gas to flow through the cavity.
In any case, cavity 369 can have the appropriate dimensions to substantially confine the plasma and prevent plasma formation outside cavity 369. Thus, work pieces 320, which can be carried by carrier portions 340 and 342, can be conveyed sequentially into a plasma processing station below tip 370 by rotating conveyor 310 with motor 374.
To prevent gas and plasma from traveling up through waveguide 370, radiation-transmissive plate 373 (e.g., made from quartz or ceramic), can be used as shown in FIG. 13. In this case, plate 373 can act as an upper surface of plasma cavity 369. Waveguide tip 370 can include lip 371, which may be cylindrical, conical, or any other shape configured to form a suitable plasma cavity. During operation, lips 371 can be positioned around part 320 to form the sides of cavity 369. Finally, carrier portion 342, part 320, or conveyor 310 can be used to form the lower part of cavity 369. FIG. 11 illustrates how radiation 345 can be directed toward part 320 into cavity 369 from waveguide tip 370. In practice, however, the distance between tip 370 and part 320 could be reduced to perform a plasma process, thereby making cavity 369 less open.
In another embodiment (not shown), a work piece can be lowered or otherwise positioned at a plasma-processing station using the carrier portion. And, once again, a processing cavity can be formed between either the work piece or the carrier portion and a waveguide tip. Alternatively, as shown in FIG. 1, a plasma-processing cavity can be formed in a substantially radiation-transmissive vessel. In this case, neither the carrier portion nor the waveguide necessarily forms a portion of the plasma cavity. In another embodiment, the waveguide housing can be replaced with a radiation-transmissive housing and used to form a plasma cavity similar to the cavity shown in FIG. 1A, for example. In other words, the waveguide need not be coupled directly to the plasma-processing cavity. It can be coupled to a larger radiation cavity in which the plasma cavity is positioned.
Although work pieces can be carried into place by carrier portions, those work pieces need not carry or otherwise support the work pieces during processing. That is, carrier portions can place the work pieces in a plasma cavity and then remove them from the cavity after processing. The same or different carrier portions can also be used to remove the work pieces after they have been plasma-processed.
As used herein, a conveyor can be any device capable of moving work pieces from one location to another, and in particular to and from a plasma-processing station. Thus, in addition, or as an alternative, to the rotatable table-type conveyors shown in FIGS. 10-14, a conveyor consistent with this invention can include, for example, a belt, a track, a robot, a turntable, a roller, a wheel, a chain, a bucket, a tray, a guide rail, a lift, a screw, a push bar, a ribbon screw, a rail system, an under floor system, a roller system, a slider system, a slat system, a gravity feed system, a chain on edge system, a cable system, a magnetic conveyor, a pulley system, a reciprocating conveyor, or any other moving and positioning mechanisms.
Conveyor 310, as well as plasma-processing cavity 325, can be located in radiation chamber 304 to prevent potentially harmful radiation from escaping the processing station. Radiation chamber 304 can be substantially reflective or otherwise opaque to the radiation supplied by source 305 and being used to form the plasma. Chamber 304 can be particularly useful when one or more of the components that form cavity 325 are substantially transmissive to the radiation supplied by source 305 or when cavity 325 is at least partially open. It will be appreciated, however, that if cavity 325 is sealed (e.g., by waveguide tip 370 and carrier portion 320) potentially harmful radiation can not escape cavity 325 during plasma-assisted processing and chamber 304 may be redundant However, chamber 304 may still be used to trap the processing gas.
Apparatus 300 can include one or more ports for moving work pieces in and out of apparatus 300. For example, apparatus 300 can include entrance port 380 for moving parts 320 into apparatus 300 for plasma-assisted processing. Entrance port 380 can be part of gas lock 384 that substantially isolates a processing gas (e.g., argon, helium, nitrogen, etc.) in chamber 304 from a gas (e.g., air) outside chamber 304. Similarly, apparatus 300 can include exit port 382 for removing parts 320 from apparatus 300 after plasma-assisted processing is complete. Exit port 382 can also be part of gas lock 386 that substantially isolates the processing gas from the gas outside chamber 304. Mechanical arms or guides (not shown) can be used to assist in the loading of parts onto, and the unloading of parts off of, conveyor 310, if desired.
As described more fully above, an active or passive plasma catalyst can be used to ignite, modulate, or sustain a plasma at pressures below, at, or above atmospheric pressure consistent with this invention. Because these catalysts have already been described in detail above, they will not be described again here. In addition, sparking devices, and other devices for inducing a plasma, can also be used consistent with this invention. In any case, the plasma catalyst can be placed in an operable location to relax, or improve, the plasma-ignition requirements. In one embodiment, the plasma catalyst can be located on and carried by a carrier portion or the work piece itself. In another embodiment, the plasma catalyst can be attached or otherwise positioned adjacent to waveguide tip 370.
FIG. 15 shows a flow-chart for illustrative method 400 of plasma-processing a plurality of work pieces consistent with this invention. The method can include: placing each of the plurality of work pieces in a plurality of movable carriers in step 405, sequentially moving each of the movable carriers on a conveyor into an irradiation zone in step 410, flowing a gas into the zone in step 415, igniting the gas in the zone by subjecting the gas to radiation to form a plasma in step 420, sustaining the plasma for a period of time sufficient to plasma-process at least one of the work pieces in the zone in step 425, and advancing the conveyor to move the at least one processed work piece out of the zone in step 430.
A plasma-processing method consistent with this invention can selectively expose one or more of the work pieces to a plasma. This includes exposing one or more work pieces for a relatively long period of time compared to the others, or to a higher temperature plasma for the same period of time, or a combination thereof. For example, as shown in FIG. 10, work pieces located in radiation zone 325 will be exposed to a plasma while the others work pieces within chamber 304, but not in zone 325, will not be so exposed. Moreover, the rate of rotation of conveyor 310 can be varied or the length of time that a work piece remains in zone 325 can be varied. Moreover, as shown in FIG. 11, the height of carrier 342 and tip 370 can be varied to change the radiation intensity in zone 325 and therefore the plasma intensity there.
In one embodiment, an electric bias can be applied to one or more of the work pieces within an irradiation zone to produce a more uniform and rapid plasma-assisted process. For example, a potential difference can be applied between an electrode (e.g., suspended in a plasma cavity) and a work piece. The work piece can be connected to a voltage source directly, or through one of the moveable carriers. The voltage source can be outside the applicator or irradiation zone and the voltage can be applied through a microwave filter to prevent, for example, microwave energy leakage. The applied voltage can, for example, take the form of a continuous or pulsed DC or AC bias. In the case of a plasma-assisted coating process, the applied voltage may attract charged ions, energizing them, and facilitate coating adhesion and quality.
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