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HIGH INTENSITY PHOTOCURING SYSTEM
BACKGROUND OF THE INVENTION
The present invention generally relates to a method and 5 apparatus for curing photosensitive materials, and more particularly to a method and apparatus for intensifying and routing light, such as ultra-violet light, generated by light emitting diodes for the purpose of curing photosensitive materials. 10
One typical environment where photosensitive curing technology is encountered is in the curing of ultra-violet (UV) photosensitive materials during the manufacture of electronic components. The photocuring systems found in such environments typically use mercury-arc lamps to flood the UV sensitive material with UV light. While mercury-arc lamp technology is widely used, such technology has several disadvantages. The most obvious disadvantage is the life span of the mercury bulbs used in the mercury-arc lamps. 2Q Mercury bulbs have a relatively short life, typically 100-1000 hours. Further, the mercury bulb degrades nonlinearly during its lifetime. As a result, conventional mercury-arc photocuring systems often require means to monitor and adjust the output power as the mercury bulb ^ degrades. Further, mercury-arc lamps are typically powered on even during stand-by periods because they require cumbersome warm-up and cool-down cycles; as a result, much of the life of the mercury bulbs may be lost during these stand-by periods. Another disadvantage involves the broad 3Q spectrum of the light radiated by the mercury-arc lamp. A mercury-arc lamp radiates UV and infra-red (IR) light. Typically, UV band pass niters transmit the portion of the UV spectrum required for curing a particular photosensitive material. In addition, heat-rejecting IR niters are usually 3J employed to prevent heating of the cure surface. Because the IR radiation creates a very hot lamp housing, transmission optics proximate to the lamp housing must be made of temperature resistant, UV-transmissive materials.
The introduction of UV light emitting diodes (LEDs) has 40 created new alternatives for curing some UV sensitive materials. LED technology offers several advantages over the traditional mercury-arc technology. First, typical LEDs last between 50,000 to 100,000 hours, providing a significant lifespan improvement over mercury-arc technologies. 45 Second, UV LEDs do not emit significant IR radiation, so heat-rejecting IR filtration is not required. As an added benefit, the reduced heat generation allows the use of economical UV transmitting polymers for lenses.
LED sources can also be turned on and off as required 50 because LEDs do not require the warm-up and cool-down periods common in mercury-arc lamp systems. Some LED curing systems may implement driver circuits to control the current supplied to the LEDs. These circuits typically use a closed-loop system to monitor and control the output power 55 of the LEDs, by controlling the drive current, to provide a stable and reliable UV source. These circuits may also define different curing cycles for different photosensitive materials, such as emitting a specific output power for a specific length of time. go
Unfortunately, conventional LED sources and LED systems have relatively low output power compared to traditional mercury-arc lamps. While the lower output power LED photocuring systems have proven to be sufficient for some dental applications, many commercial and industrial 65 UV sensitive materials require higher output powers, such as 0.5 to 3 J/cm2, to cure properly. For example, some UV
sensitive materials require between 100 to 600 mW/cm2 of optical intensity to initiate and complete a five second cure. Historically, these intensities have not been achieved with LED-based curing systems.
U.S. Patent Application Publication 2001/0046652 to Ostler, et al., entitled "Light Emitting Diode Light Source for Curing Dental Composites," describes use of UV LEDs for curing of dental composites. The Ostler device increases the output intensity of UV light generated by an array of relatively low-power LEDs by concentrating collimated light generated by the array to a desired spot size at a desired location. While the Ostler system increases the output intensity of a UV curing system, the Ostler approach has several disadvantages. First, the Ostler LED array comprises a fixed array of LED chips and therefore does not allow replacement of individual LED units within the array. As a result, new entire units must be purchased to change the wavelength of the emitted optical power, or to replace one or more damaged or defective LEDs. Second, the Ostler cooling system is both complicated and likely insufficient for cooling the higher power UV LEDs now available on the market. Lastly, the Ostler publication does not discuss any methods or apparatus for capturing and redirecting any stray UV light to further intensify the output light at the desired location.
Therefore, there remains a need for high intensity LEDbased curing systems that addresses one or more problems outlined above.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for curing photosensitive materials. A photocuring assembly uses LEDs and an optical concentrator to generate high optical power intensities. An LED array, comprising one or more LED assemblies, generates collimated light. An optical concentrator, e.g., a collection lens, focuses the collimated light to a desired spot size at a desired location.
In one embodiment, the photocuring assembly includes a cooling plenum at least partially defined by the collection lens. The LED array of the photocuring assembly is at least partially disposed in the cooling plenum. Therefore, a cooling fluid, such as air, cools the LED array by flowing through the cooling plenum defined by the collection lens.
In another embodiment, each LED assembly comprises a base and an LED insert detachably coupled to the base. In yet another embodiment, the LED assemblies are detachably coupled to a mounting surface, such as a PCB. Both embodiments enable a user to modify the operating wavelength of the photocuring assembly by replacing one or more LED inserts or assemblies having a first operating wavelength with one or more LED inserts or assemblies having a second operating wavelength. In addition, damaged or defective LED inserts and/or assemblies may be replaced without necessitating the replacement of the entire LED array.
In another embodiment, the photocuring assembly includes a redirecting assembly disposed between the collection lens and the desired location. Due to the emission properties of conventional LEDs, the LED assembly may not collimate some minority of the light. As a result, the collection lens does not properly focus the non-collimated light exiting the LED array. The redirecting assembly uses refraction or optical reflection techniques to redirect at least a portion of any unfocused light to the desired location to increase the intensity at the desired location.
Other embodiments of the present invention may include photocuring assemblies that comprise one or more of the
above embodiments. For example, the photocuring assembly may include the cooling plenum bounded by the collection lens and the detachably coupled LED assemblies.
BRIEF DESCRIPTION OF THE DRAWINGS 5
FIG. 1 illustrates a photocuring apparatus according to the present invention.
FIG. 2 illustrates electrical interconnections for the exemplary photocuring apparatus of FIG. 1. 10
FIG. 3 illustrates an exemplary cooling plenum.
FIG. 4 illustrates an exemplary element of an LED assembly.
FIG. 5 illustrates an element of an LED assembly collimating LED light. 15
FIG. 6 illustrates a conventional light guide.
FIG. 7 illustrates an exemplary redirection assembly.
FIG. 8 illustrates exemplary light propagation according to the present invention. 20
FIG. 9 illustrates an exemplary photocuring gun.
DETAILED DESCRIPTION OF THE
The present invention relates to a photocuring system that intensifies light emitted from one or more LEDs. The intensified light may be delivered to a remote location to induce a change in a photosensitive material 12 at the remote location, such as to cure the photosensitive material 12. 3Q Because one application for the present invention is curing UV curable materials, the discussions below use UV LEDs to illustrate the invention. However, it should be understood that the present invention is not limited to UV light or UV photocuring technologies. 35
An exemplary photocuring system according to the present invention, generally indicated at 10, is shown in FIGS. 1-8. The photocuring system 10 includes an electrical assembly 200 and an optical assembly 300, both enclosed in a suitable housing 100. In addition to providing the mechani- 40 cal structure, the housing 100 also provides a safety feature by isolating any potentially hazardous optical energy from a user. As shown in FIG. 1, the housing 100 may advantageously include an internal wall 110 that functions as a light baffle to isolate the portion of housing containing the main 45 components of the electrical assembly 200 from any stray optical energy generated in the optical assembly 300. It should be noted that while FIG. 1 shows a single common housing 100 for the electrical and optical assemblies 200, 300, these assemblies may be mounted in separate intercon- 50 nected enclosures, if desired.
The electrical assembly 200 supplies power to, and controls the operation of, the photocuring system 10. Referring to FIG. 2, the electrical assembly 200 may include a power supply 210, a current controller 220, a timer 230, and a 55 cooling fan 240. The power supply 210 performs customary power supply functions, such as converting the incoming AC power to DC voltage and current, providing DC current to the current controller 220, providing DC power to the cooling fan 240, and the like. The current controller 220 60 adaptively controls the power delivered to an LED array 330 in the optical assembly 300 to enable the LED array 330 to generate stable, constant UV light. In addition, the current controller 220 may vary the power supplied to the LED array 330 to vary the optical power generated by the LED array 65 330 as desired. The timer 230 and optional cycle start switch 232 provide for further control of the operation of the LED
array 330 to advantageously allow for triggered starts to the curing cycle, and optionally for adjustable time intervals for the curing cycles. The cooling fan 240 acts to pull cooling fluid, such as air, through the photocuring system 10 to avoid overheating the LED array 330. While discussed in greater detail below, the air is in general pulled into the housing intake 120, routed through the optical assembly 300, through the internal wall 110 to the electronic assembly 200, and then pushed out of the housing 100 by the cooling fan 240 via the housing exhaust 140.
The optical assembly 300 includes a collection lens 320, an LED array 330, a converging chamber 380, and a cooling plenum 310, as shown in FIG. 1. The LED array 330 generates high-power UV light. While an array of LEDs is used herein to illustrate the invention, it will be understood by those skilled in the art that the invention described herein applies equally well to a photocuring system using a single LED. As such, the term "LED array" as used herein is intended to mean one or more LEDs, such as a single LED or a plurality of LEDs arranged as desired. The collection lens 320 intensifies the light generated by the LED array 330 by focusing the light to a desired spot size at a desired location within the converging chamber 380. An optional redirection assembly 382 may be positioned in the converging chamber 380 to redirect light rays outside of the converging beam to the desired location to further intensify the light at the desired location, as discussed further below. The UV light intensified by the optical assembly 300 may then be delivered to the photosensitive material 12 at the remote location by coupling the intensified UV light into a light guide, such as an optical fiber 384, secured on one end to the housing 100 with a suitable fitting 150.
The LED array 330, which is discussed further below, is at least partially disposed in the cooling plenum 310, as shown in FIG. 3. For the FIG. 3 configuration, an electrical substrate 312, brackets 314, and the collection lens 320 bound the cooling plenum 310. Cooling air enters the cooling plenum 310 via intake port 316 and flows along cooling plenum 310 past LED array 330. The collection lens 320 confines the airflow to the cooling plenum 310 and forces the airflow past the LED array 330. The airflow exits the cooling plenum 310 via the exhaust port 318.
The LED array 330 comprises a plurality of LED assemblies 340. FIG. 4 illustrates an exemplary LED assembly 340 of the present invention. Each LED assembly 340 includes an LED insert 360 coupled to a collimator base 350. The collimator base 350 includes a heatsink 352 and a reflective cavity 354. The reflective cavity 354 may be shaped as a curve and functions to generally collimate and direct the diffuse LED light towards the collection lens. In a preferred embodiment, the reflective cavity 354 is shaped as a parabola. The reflective cavity 354 should be fabricated from a metal or metal alloy, e.g., an aluminum alloy, and should be highly polished to efficiently reflect the optical energy radiated at the LED's operational wavelength. In a preferred embodiment, the collimator base 350 is a single unit formed from a solid piece of material. Alternatively, the heatsink 352 and reflective cavity 354 are separately manufactured and joined together to form the collimator base 350.
The LED insert 360 includes an LED 362, LED base 364, thermal conductive adhesive 366, LED terminals 368, and a thermal post 370. An LED die (not shown) emits radiant energy at an operational wavelength preferably within the range of 315 nm to 450 nm. The LED die is typically positioned on a metalized ceramic standoff (not shown) that electrically isolates the LED die from the LED base 364, although this is not required. The standoff, or its equivalent,