Patent Application
20120025079
The present disclosure is related to thermal imaging, and particularly to an LED array for a flash thermography based thermal imaging device.
When inspecting parts for quality control, one aspect reviewed for quality is the thickness of the part. Various techniques are used in the art to determine thickness, and thereby determine if the work piece meets quality control standards. One technique used is thermal imaging via flash thermography. Flash thermography based thermal imagers operate by subjecting the work piece to a short flash of light (a “pulse”) from a flash lamp such as an xenon strobe. A sensor in the thermal imaging device detects Infra-Red (IR) radiation from the heat being emitted from the part, and determines the magnitude of the sensed IR radiation. A controller then creates a thermal image of the work piece based on the magnitude of the sensed IR radiation and the time of maximum occurrence.
Disclosed is a thermal imaging device which has an LED flash array, a sensor capable of detecting IR radiation, and a controller. The controller is coupled to the LED flash array and the sensor. The controller is capable of causing the LED flash array to emit a pulse of radiation.
Also disclosed is an LED flash array. The LED flash array has a substantially cylindrical component with a first opening, a substantially cup shaped component with a second opening, and a passageway through the substantially cup shaped component and the substantially cylindrical component that joins the two components, such that electromagnetic radiation may pass through the LED flash array. Arranged about the cup shaped component is a plurality of LED sockets.
Also disclosed is a method for creating a thermal image which has the steps of generating an IR pulse using an array of LEDs which are controlled by a controller, sensing emitted IR radiation using a sensor, and determining the thickness of an object based on the magnitude of the emitted IR radiation.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
Schematically illustrated in
The sensor 40 detects the magnitude of the IR portion of the emitted electromagnetic emissions, and communicates the magnitude to a controller 20 such as a computer, a microprocessor, or programmable logic controller. The controller 20 also determines the magnitude of the emitted IR radiation from the pulse based on the duration of the pulse and the magnitude of power provided to the flash source 30 during that duration. The controller 20 determines the thickness of the work piece 50 by calculating the Temperature-time curve of the sample surface temperature decay history. The controller 20 can then generate a thermal image of the work piece 50 using known techniques.
IR radiation covers wavelengths of approximately 770 nm to 1 mm, whereas the spectrum emitted by xenon strobe light, as is used in conventional systems, covers the full visible spectrum and ultraviolet spectrum as well as the IR portion of the electromagnetic spectrum. Therefore, when using a xenon strobe to create the IR pulse, a full spectrum burst containing high levels of visible light and UV light along with the IR radiation is created. Such a burst requires a large expenditure of energy creating the pulse in the portions of the electromagnetic spectrum aside from the IR portion. Contrary to the burst created by a xenon strobe, a flash source 30 which is constructed out of an array of IR LEDs will emit minimal radiation outside of the IR portion of the electromagnetic spectrum, thereby reducing energy spent generating electromagnetic radiation outside of the IR portion of the spectrum. IR LEDs are LEDs which emit no visible light and UV light when an electric charge is applied, yet still emit a high magnitude of IR radiation.
The sensor 140 is aligned with the cylindrical component 134 such that IR radiation 142 from a pulse that is reflected off the work piece 150, will pass through the cylindrical component 134 and strike the sensor 140. Multiple IR LEDs are arranged on the inside of the cup shaped component 132, and are angled such that emitted IR radiation 136 strikes the work piece 150 at a single focal point 280 which is shared by all the IR LEDs. When the IR radiation 136 strikes the work piece 150, a large portion of the IR radiation is absorbed by the work piece 150, and a small portion reflects off the work piece 150. The sensor 140 senses the magnitude of the emitted IR radiation 142.
The sensor 140 is connected to the controller 120. The controller 120 receives a signal from the sensor 140 when the emitted IR radiation 142 strikes it and determines the magnitude of the emitted IR radiation 142. The controller 120 may also include a simple electrical control circuit for providing and limiting power to the IR LED array 130. The control circuit can be constructed according to any number of known principles using standard components. The controller 120 can additionally determine the magnitude of the IR radiation 136 which was output from the IR LED array 130 based on the duration of the pulse as well as the magnitude of electrical power which was transmitted through the control circuit during the pulse.
Spaced around the cup shaped component 134 are multiple LED sockets 272. In the illustrated example of
While the LED sockets 272 are arranged such that they share a focal point 280 while illuminated, it is understood that an alternate arrangement could be used which causes a broader beam without a single focal point, thereby encompassing the entire part, and generating an image based on the IR reflection from the broader beam. While the cup shaped component 132 and the cylindrical component 134 are illustrated having concentric circular cross sections, other shaped cross sections could be used, as well as non-concentric cross sections.
Referring again to
Illustrated in
During the IR radiation pulse, the IR radiation impacts a work piece which is in front of the thermal imager and a portion of the thermal radiation by the work piece 50 is radiated back toward the thermal imager. The emitted portion of the IR radiation is sensed using a sensor within the thermal imager in the Sense Emitted IR Radiation step 320. The controller is communicatively coupled to the sensor and receives the sensed data. Based on the sensed data, the duration of the pulse, and the magnitude of the electrical power provided during the duration the thermal imager can determine the thickness of the work piece according to known thermal imaging techniques in the Determine Thickness Based on emitted IR Radiation step 330.
While an example method has been illustrated above, it is understood that minor variations to the apparatus or method fall within this disclosure. Such variations include varying the duration of the pulse time, and varying the portion of the electromagnetic spectrum, which is used in the imaging process.
Although example embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.
