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EP-4350279-B1 - HIGH SPEED VACUUM CYCLING EXCITATION SYSTEM FOR OPTICAL INSPECTION SYSTEMS

EP4350279B1EP 4350279 B1EP4350279 B1EP 4350279B1EP-4350279-B1

Inventors

  • SAFAI, MORTEZA
  • WANG, XIAOXI

Dates

Publication Date
20260506
Application Date
20180619

Claims (15)

  1. A method for inspecting a workpiece, comprising: obtaining a first image of a surface of the workpiece at atmospheric pressure; increasing a vacuum pressure applied to the surface of the workpiece from the atmospheric pressure to a first vacuum pressure using a vacuum system, the first vacuum pressure being a negative pressure less than the atmospheric pressure; obtaining a second image of the surface of the workpiece at the first vacuum pressure; decreasing the vacuum pressure applied to the surface of the workpiece from the first vacuum pressure to a second vacuum pressure that is lower than the first vacuum pressure and higher than the atmospheric pressure without decreasing the vacuum pressure to the atmospheric pressure, the second vacuum pressure being a negative pressure less than the atmospheric pressure; obtaining a third image of the surface of the workpiece at the second vacuum pressure; and increasing the vacuum pressure applied to the surface of the workpiece from the second vacuum pressure to a third vacuum pressure that is higher than the first vacuum pressure without decreasing the vacuum pressure to the atmospheric pressure, the third vacuum pressure being a negative pressure less than the atmospheric pressure.
  2. The method of claim 1, wherein the first image is a first reference image and the method further comprises: illuminating the surface of the workpiece using a laser beam output by a laser while the first vacuum pressure is applied to the surface; performing the obtaining of the second image while the surface is illuminated with the laser beam, wherein the second image is a first inspection image of the surface; illuminating the surface using the laser beam while the second vacuum pressure is applied to the surface; and performing the obtaining of the third image while the surface is illuminated with the laser beam, wherein the third image is a second reference image.
  3. The method of claim 2, further comprising removing the illumination of the surface by the laser beam during the decreasing of the vacuum pressure applied to the surface from the first vacuum pressure to the second vacuum pressure.
  4. The method of claim 2, further comprising comparing the first inspection image with the first reference image to detect differences between the first inspection image and the first reference image that would indicate workpiece defects.
  5. The method of claim 4, further comprising detecting differences between the first inspection image and the first reference image, wherein the differences between the first inspection image and the first reference image indicate debonding of a first workpiece layer from a second workpiece layer.
  6. The method of claim 1, wherein the increasing of the vacuum pressure from the atmospheric pressure to the first vacuum pressure comprises: moving a piston to increase a volume of a vacuum chamber and to increase a chamber vacuum pressure within the chamber; and opening a valve in fluid communication with the vacuum chamber and the surface of the workpiece.
  7. The method of claim 6, wherein the decreasing of the vacuum pressure from the first vacuum pressure to the second vacuum pressure comprises: moving the piston to decrease the volume of the vacuum chamber and to decrease the chamber vacuum pressure within the chamber; and opening the valve in fluid communication with the vacuum chamber and the surface of the workpiece.
  8. The method of claim 7, wherein the valve is a first solenoid pneumatic valve, and the method further comprises: moving a second solenoid pneumatic valve in fluid communication with the vacuum chamber from a closed position to an open position; and injecting a gas into the vacuum chamber through the second solenoid pneumatic valve in the open position.
  9. The method of claim 1, wherein the increasing of the vacuum pressure applied to the surface of the workpiece from the atmospheric pressure to the first vacuum pressure comprises moving a piston to increase a chamber volume of a vacuum chamber of the vacuum system and to increase a chamber vacuum pressure within the vacuum chamber; the decreasing of the vacuum pressure applied to the surface of the workpiece from the first vacuum pressure to the second vacuum pressure comprises moving the piston to decrease the chamber volume of the vacuum chamber and to decrease the chamber vacuum pressure within the vacuum chamber; the increasing of the vacuum pressure applied to the surface of the workpiece from the second vacuum pressure to the third vacuum pressure comprises moving the piston to increase the chamber volume of the vacuum chamber and to increase the chamber vacuum pressure within the vacuum chamber; and the increasing of the vacuum pressure from the atmospheric pressure to the first vacuum pressure, the decreasing of the vacuum pressure from the first vacuum pressure to the second vacuum pressure, and the increasing of the vacuum pressure from the second vacuum pressure to the third vacuum pressure is performed at a frequency of at least 60 hertz.
  10. The method of claim 1, wherein the second vacuum pressure is from ¼ to ¾ of the first vacuum pressure.
  11. A vacuum system (100) for inspecting a workpiece, the vacuum system being configured to conduct the method of any one of claims 1 to 10 and comprises: a housing (106) defining at least a portion of a vacuum chamber (108); a piston (112) within the housing, wherein the piston is configured to oscillate, thereby varying a chamber volume of the vacuum chamber; a first valve (118) in fluid communication with the vacuum chamber, wherein the first valve comprises a first or open position that permits an intake of a gas into the vacuum chamber and an exhaust of the gas out of the vacuum chamber, and a second closed position that prevents the intake of the gas into the vacuum chamber and the exhaust of the gas out of the vacuum chamber through the first valve; a second valve (120) in fluid communication with the vacuum chamber, wherein the second valve comprises an open position that permits the intake of the gas into the vacuum chamber and the exhaust of the gas out of the vacuum chamber, and a closed position that prevents the intake of the gas into the vacuum chamber and the exhaust of the gas out of the vacuum chamber through the second valve; and a hood (124) in fluid communication with the second valve and the vacuum chamber, wherein the second valve, in the open position, permits a flow of the gas between the vacuum chamber and the hood and, in the closed position, prevents the flow of the gas between the vacuum chamber and the hood through the second valve, wherein, preferably, the piston, the first valve, and the second valve are cooperatively configured to: increase a vacuum pressure applied to a surface of the workpiece from the atmospheric pressure to the first vacuum pressure; decrease the vacuum pressure applied to the surface of the workpiece from the first vacuum pressure to the second vacuum pressure that is lower than the first vacuum pressure; and increase the vacuum pressure applied to the surface of the workpiece from the second vacuum pressure to the third vacuum pressure that is higher than the first vacuum pressure.
  12. The vacuum system of claim 11, wherein the hood (124) is configured to be positioned on a surface (102) of the workpiece (104) during an application of a vacuum force to the surface of the workpiece by the vacuum system during the inspecting.
  13. The vacuum system of claim 11 or 12, further comprising a light source (128) configured to activate and deactivate during inspection of the workpiece (104) wherein, during the activation, the light source being configured to illuminate the workpiece, wherein it is preferred if the light source is a laser (128) which emits a laser beam (130) which illuminates a surface (102) of the workpiece.
  14. The vacuum system of any one of claims 11 to 13, further comprising a camera (132) configured to image a surface (102) of the workpiece (104) during the inspection of the workpiece, wherein it is preferred if at least one of the first valve (118) and the second valve (120) is a solenoid pneumatic valve.
  15. A shearography system for inspecting a workpiece, comprising: - a vacuum system (100), preferably a vacuum system of any one of claims 11 to 14, the vacuum system (100) comprising: -- a housing (106) defining at least a portion of a vacuum chamber (108); -- a piston (112) within the housing, wherein the piston is configured to oscillate, thereby varying a chamber volume of the vacuum chamber; -- a first solenoid pneumatic valve (118) in fluid communication with the vacuum chamber, wherein the first solenoid pneumatic valve comprises a first or open position that permits an intake of a gas into the vacuum chamber and an exhaust of the gas out of the vacuum chamber, and a second closed position that prevents the intake of the gas into the vacuum chamber and the exhaust of the gas out of the vacuum chamber through the first solenoid pneumatic valve; -- a second solenoid pneumatic valve (120) in fluid communication with the vacuum chamber, wherein the second solenoid pneumatic valve comprises an open position that permits the intake of the gas into the vacuum chamber and the exhaust of the gas out of the vacuum chamber, and a closed position that prevents the intake of the gas into the vacuum chamber and the exhaust of the gas out of the vacuum chamber through the second solenoid pneumatic valve; and -- a hood (124) in fluid communication with the second solenoid pneumatic valve 120 and the vacuum chamber 108, wherein the second solenoid pneumatic valve, in the open position, permits a flow of the gas between the vacuum chamber and the hood and, in the closed position, prevents the flow of the gas between the vacuum chamber and the hood through the second solenoid pneumatic valve; - a laser (128) configured to activate and deactivate during inspecting of the workpiece (104) wherein, during the activation, the laser emits a laser beam which illuminates the workpiece; - a camera (132) configured to image the workpiece during inspecting of the workpiece; and - a controller (134) configured to coordinate operation of the vacuum system (100), the laser (128), and the camera (132) during inspecting of the workpiece (104).

Description

Technical Field The present teachings relate to testing, inspection, and metrology, and more particularly to a vacuum system and method that can be used for testing, inspection, metrology, as well as other uses. Background Vacuum systems are commonly used in industry for testing, inspection, and metrology. A vacuum system can be used, for example, to assess whether a product design and/or a manufacturing process is sufficient to ensure that the product conforms to standards of load or stress resistance. In another use, a product surface can be exposed to cyclic loading from a vacuum to test a resistance of the product to fatigue. During destructive testing, resistance to a vacuum stress can be measured using an increasing vacuum applied to a product until the product fails. During non-destructive testing or inspection, stresses can be applied to some or all articles from a production lot using a vacuum system to ensure that the articles have been properly manufactured. A vacuum system that allows testing modes and conditions not available with conventional system designs would be a welcome addition to the art. US 5 257 088 relates to testing a vehicle, such as an aircraft, using nondestructive interferometry. An interferometer detects movements in the vehicle surface due to stress. One applies such stress by pressurizing the vehicle. In one embodiment, a hood housing the interferometer attaches to the vehicle surface with the aid of a vacuum. One can vary the pressure in the vehicle in various ways, while monitoring the interferometer for signs of defects in the structure behind the surface. The invention also includes an arrangement for substantially automating the analysis. For example, one can automatically position the interferometer according to position information received from appropriate sensors, in combination with stored information about the structure of the vehicle. One preferably uses a real-time interferometer, such as an electronic shearography camera, in the present invention. One can quickly determine the location of defects by observing fringes on a video monitor. US 2013/114088 A1 relates to a method and apparatus for the remote nondestructive evaluation of an object such as a wind turbine blade involves applying mechanical and/or thermal stress to the object and then scanning the object using long-range thermographic and/or laser interferometric imaging. The laser interferometric imaging is preferably performed by a long range shearography camera capable of imaging deformation derivatives at long distances coupled with a blade stressing mechanism incorporating either thermal or internal blade pressurization for the purpose of detecting remotely and at high speed, changes in the structural integrity of an installed wind turbine blade. JP H04 351936 A relates to running various strength tests with higher operativeness and in a shorter time by putting a container in an air tight testing room, maintaining the inside of the container at the first pressure higher than air pressure and varying pressure in a space between the inner periphery of the testing room and the outer periphery of the container from the second pressure higher than the first pressure to the third pressure higher than air pressure but lower than the first pressure. A container to be subjected to strength test such as the fuselage of a vehicle including a rolling stock is put in an air-tight testing room and the inside of the fuselage is maintained at the first pressure higher than air pressure. Air pressure between the inner periphery of the testing room and the outer periphery of the fuselage is varied from the second pressure higher than the first pressure to the third pressure higher than air pressure but lower than the first pressure to equalize the amplitude value of stress on the container to an actual load condition. As a result, the need for a vacuum pump is eliminated, a simple device is realized, forcible supply and discharge of fluid such as compressed air are only required, good operativeness is secured and a testing cycle is shortened this time. US 2001/040682 A1 relates to an apparatus for performing electronic shearography on a test object, especially a tire or retread tire. The apparatus uses a laser light source to illuminate the test object. An optical element through which electromagnetic radiation is reflected from the test object is transmitted and forms a random interference image. The random interference image can be electronically processed to provide a video animation of the effects of stress on the test object. US 5 481 356 A show a shearographic system with a hood and the but discloses no details for the pump. EP 2 523 064 A2 shows a pump with solenoid valves. Summary The following presents a simplified summary in order to provide a basic understanding of some aspects of one or more implementations of the present teachings. This summary is not an extensive overview, nor is it intended to identify