GB2361311A

GB2361311A - Method and apparatus for inspecting an object

Info

Publication number: GB2361311A
Application number: GB0100248A
Authority: GB
Inventors: Hongling Kang; Xiaolu Lou Chen; Zili Wu
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2000-01-11
Filing date: 2001-01-04
Publication date: 2001-10-17
Also published as: GB0100248D0; DE10100467A1

Abstract

Apparatus 10 and method for inspecting components, parts, and other objects 12 includes a conventional computer 14 having a memory unit 16 and operating under stored program control. The computer 14 is communicatively coupled to video sensors or cameras 13 to 26, to a selectively actuatable impacting device 28, and to a vibration sensor 30, by use of a communications bus or path 46. The computer 14 receives signals generated by cameras 18 to 26 and by the sensor 30, processes and analyzes the received signals to determine whether the object 12 is "non-conforming" or "defective", for example, whether the object 12 contains any cracks, undesirable porosity, or surface flaws.

Description

1 2361311 1 - method and Apparatus for Inspecting an Object

Field of the Invention

This invention relates to a method and an apparatus for inspecting an object and more particularly, to a method and an apparatus for inspecting a die-cast object which reliably detects defects such as cracks, porosity, and surface flaws within the object.

Backaround of the Invention

Quality inspection systems, devices, and methods are used to determine: whether produced components, assemblies, and other objects contain defects. For example and without limitation, quality inspection devices and methods are used to determine whether objects, such as die-castings, include any defects, such as undesirable cracks, porosity, and/or surface flaws.

Prior quality inspection systems for die-cast objects and components typically require a human to individually inspect each die cast object or component. Particularly, these prior systems generally require a human inspector to visually inspect each diecast object or component for cracks and surface flaws. If no defects are visually detected on the object or component, an inspector will typically strike the object or component in a certain manner, and listen for a certain tone or reverberating sound which is indicative of a non-conforming or a 1 1 2 "defective" part (e.g., a cracked die casting will typically produce a dull tone or sound). These types of prior quality inspection systems and methods are undesirably subjective (e.g., the systems rely on human audio-visual perception and interpretation, which varies from inspector to inspector). Consequently, these prior quality inspection systems are unreliable, tedious, timeconsuming, and subject to human errors. Additionally, only relatively large cracks and defects are detectable by these systems, as relatively small cracks and defects are often too small to be detected or perceived by the human eye, and/or produce tone or sound variances which are not detectable or perceptible by the human ear. As a result, many conforming or "non-defective" parts are wrongfully scrapped and many defective parts wrongfully and undesirably pass inspection, thereby resulting in a relatively large amount of waste and undesirable quality control problems.

The present invention addresses these drawbacks and provides a method and an apparatus for inspecting an object which employs multiple sensors to gather objective data relating to the cracks, porosity, surface flaws, and/or other defects within the object, and which analyzes the data to reliably determine whether the object is defective.

3 Summary of the Invention

It is a first object of the invention to provide a method and an apparatus for inspecting an object which overcomes at least some of the previously delineated drawbacks of prior systems, devices, and/or methods.

It is a second object of the invention to provide a method and an apparatus for inspecting an object which utilizes multiple sensors to determine whether any defects, such as cracks, porosity, or surface flaws, are present within a die-cast object.

It is a third object of the invention to provide a method and an apparatus for inspecting an object which utilizes visual sensors and audio or vibration sensors to reliably determine when defects are present within an object, and based upon that determination, to properly sort the object.

It is a fourth object of the invention to provide a method and an apparatus for inspecting an object which does not rely upon subjective human interpretation to determine whether any defects are present within the object.

According to one aspect of the present invention an apparatus for detecting defects within an object is provided. The apparatus includes at least one camera which selectively acquires image data from the object, and which 30 transmits a first data signal representing the acquired 4 image data; an impactor which selectively impacts the object, thereby causing the object to vibrate; at least one sensor which measures certain attributes relating to the vibration of the object and to transmit a second data signal representing the certain attributes; and a controller which is communicatively coupled to the at least one camera and the at least one sensor, which receives the first and the second data signals, and which determines whether the object contains any defects by use of the first and the second data signals.

According to a second aspect of the present invention, there is provided a method for detecting defects within an object, using at least one camera, an impactor and a controller which is communicatively coupled to said at least one camera and to said at least one sensor, wherein the method comprises the steps of:

i) using said at least one camera to selectively acquire image data from said object, and to transmit tothe controller a first data signal representing said acquired image data; ii) using the impactor to selectively impact said object, thereby causing said object to vibrate; iii) using said at least one sensor to measure certain attributes relating to said vibration of said object, and to transmit to the controller a second data signal representing said certain attributes; and iv) receiving at the controller said first and said second data signals, and then using the controller to determine whether said object contains any defects by use of said first and said second data signals.

The method may include the steps of: comparing image data to second image data, effective to whether the object contains any surface flaws; the object, thereby causing the object to emit an signal; providing a sensor for measuring the signal; and comparing the acoustic signal to data, effective to determine whether the object any cracks.

is the first determine striking acoustic acoustic acoustic contains Further objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.

Brief Description of the Drawincrs

The invention will now be further described by way of example, with reference to the accompanying drawings, in 25 which:

Figure 1 is a schematic diagram of an apparatus for inspecting an object incorporating the teachings of the preferred embodiment of the invention; 6 - Figure 2 is a block diagram of the apparatus that is illustrated in Figure 1; Figure 3 is a block diagram illustrating the operational functionality of the apparatus that is shown in Figure 1; Figure 4 is a screen displayed by the apparatus that is shown in Figure 1, and illustrating a component which is being inspected; Figure 5 is a screen displayed by the apparatus that is shown in Figure 1 and illustrating a surface flaw which has been detected on the component which is being inspected; Figure 6 is a graph illustrating the amplitude of an acoustic signal over time for a non-defective component; Figure 7 is a graph illustrating the amplitude of an acoustic signal over time for a defective or cracked component; Figure 8 is a graph illustrating the frequency response of a non- defective component; and Figure 9 is a graph illustrating the frequency response of a defective component.

Detailed Description

Referring now to Figure 1, there is shown an inspection system, assembly, or apparatus 10 for inspecting components, parts, and/or other objects 12, which is made in accordance with the teachings of the preferred embodiment of the invention. In the preferred embodiment of the invention, objects 12 comprise aluminum. or magnesium die-cast objects, which may potentially include one or more defects, such as cracks, undesirable porosity, and/or surface flaws. In other alternate embodiments, object 12 may comprise any type of object having certain visual, vibration, and/or audio characteristics, attributes or signatures, which may be indicative of defects within the object. As shown, apparatus 10 includes a conventional microprocessor, controller or computer 14 having a memory unit 16 and operating under stored program control. Computer 14 is electrically, physically, and communicatively coupled to video sensors or cameras 18 to 26, to a selectively actuatable impacting device or apparatus 28, and to a laser vibrometer or vibration sensor 30, by use of a communications bus or path 46. Cameras 18 to 26, apparatus 28 and sensor 30 are operatively mounted within an inspection enclosure housing, or chamber 32, which is insulated from vibration and acoustic noise.

Apparatus 10 further includes light sources 34, 36, which each may comprise one or more LED diffuse lighting sources and which substantially and uniformly illuminate the 8 object 12 that is being inspected. In other alternate embodiments, different or additional numbers of light sources may be used. A mirror prism 38 is operatively disposed or mounted between camera 18 and sensor 30, and allows light rays illuminating object 12 to be reflected to camera 18, and further reflects a sensing ray or laser 40 from sensor 30 to object 12 and back to sensor 30. A conventional conveyor line or assembly 42 having a conventional controller 41, which is communicatively coupled to computer 14, operatively moves and/or transports object 12 into chamber 32 for inspection. In the preferred embodiment, object 12 is coupled to a fixture 44 prior to being conveyed or transported into chamber 32.

As described more fully and completely below, controller 14 receives signals which are generated by cameras 18 to 26 and by sensor 30, and processes and analyzes the received signals to determine whether object 12 is "non-conforming" or "defective.' (e.g., whether object 12 contains any cracks, undesirable porosity, or surface flaws). Based on this determination, controller 14 selectively causes conveyor assembly 42 to direct the object 12 into a "non-conforming" or "defective,, object receptacle or bin 48, or into a "conforming" or 11nondefective,, object receptacle or bin 50. In one nonlimiting embodiment, computer 14 further displays images, defects, inspection results, and other data on a conventional display 52.

conventional In the preferred embodiment, controller or computer 14 comprises one or more commercially available and microprocessor-based computer systems operating under stored program control, and includes signal processing software and/or circuitry, which is adapted to receive, translate, and interpret the signals which are received from cameras 18 to 26 and from sensor 30. In the preferred embodiment of the invention, memory 16 is a conventional memory unit including both permanent and temporary memory, and is adapted to and does store at least a portion of the operating software which directs the operation of computer 14. Moreover, memory 16 is also adapted to selectively store other types of data or information, including information associated with the operation of the preferred embodiment of the invention and/or associated historical data, processing data, and/or operational data. As will be more fully discussed below, examples of such data include, but are not limited to, data defining specifications of the dimensional and geometrical object 12, templates, dimensional tolerances, images of conforming or "non-defective" objects, current images of object 12, vibration criteria for "defective" and "non-defective" parts, and other data which is used by computer 14 to determine whether object 12 is non-conforming or "defective,,. Moreover, as should also be apparent to those of ordinary skill in the art, computer 14 and memory 16 may actually comprise a plurality of commercially available, conventional, and disparate chips or devices, which. are operatively and communicatively linked in a cooperative manner.

- Cameras 18 to 26 comprise a plurality of conventional and commercially available "charge coupled device,,-type PCCD11) cameras, which are fixedly mounted within chamber 32, and which acquire or measure image data from object 12 from various angles or directions. More particularly, in the preferred embodiment of the invention, camera 18 selectively acquires image data from the top of object 12, and cameras 20 to 26 are disposed approximately ninety degrees apart from each other and selectively acquire image data from four ',sides" of object 12. In alternate embodiments, additional or different quantities of cameras are used to selectively acquire information from all surfaces of object 12. Each of cameras 18 to 26 transmits a data signal representing the acquired 14, which processes and utilizes these determine whether any flaws or defects surface of object 12. It should be cameras 18 devices or band pass images to computer acquired images to are present on the appreciated that to 26 may include filtering and/or processing circuits (e.g., low pass, high pass, and/or filters) which filter and/or process the measured or sensed image data prior to sending the data to computer 14.

Impacting device or apparatus 28 is a conventional and selectively acuatable 11piezo- electric transducer" or 11PZT11 impactor. Apparatus 28, which includes an impacting device or hammer 27, which is controllably actuated and which strikes object 12 with a predetermined force, and piezo- electric sensor 29, which is disposed on hammer 27 and 11 - which senses or detects the value of the actual striking or impacting force and communicates this value to controller 14.

Laser vibrometer or vibration sensor 30, is a conventional vibration measurement device or apparatus which is effective to sense the vibration characteristics, attributes or responses of object 12 once object 12 is struck by impactor 28. In the preferred embodiment of the invention, sensor 30 projects a laser beam 40 onto object 12, and senses or measures variations in the reflection of beam 40 caused by the vibration of object 12. Sensor 30 transmits a data signal to computer 14, which represents this acquired data, by use of bus 46. Computer 14 utilizes this data to determine the vibration attributes and/or characteristics of object 12, such as the primary or resonant frequencies of object 12, the vibration response of object 12, and the damping coefficient of object 12.

In one non-limiting embodiment, laser vibrometer 30 is replaced with one or more conventional microphones or acoustic sensors, which are disposed in relative close proximity to object 12, which selectively measure acoustic signals emanating from object 12, and which transmit a data signal to computer 14 representing the acquired data. Computer 14 utilizes the acquired data to determine the acoustic response and/or attributes of object 12. Sensor 30 may include filtering and/or processing devices or circuits (e.g., low pass, high pass, and/or band pass filters) which filter and/or process the measured or 12 sensed vibration/ acoustic data prior to sending the data to computer 14.

To understand the operational functionality of the preferred embodiment of apparatus 10, reference is now made to the operational flow diagram or "flow chart" 60 of Figure 3. once object 12 has been coupled to fixture 44, controller 14 transmits a signal to conveyor controller 41, which is effective to cause conveyor 42 to move object 12 into chamber 32, as shown in functional block or step 62. Chamber 32 is then sealed or closed, and inspection for surface flaws begins, as shown in functional block or step 64. Imaging data and/or images of object 12 are acquired by each of cameras 18 to 26 and are communicated to computer or controller 14 by use of communications bus or path 46, as shown in functional block or step 66. In one non-limiting embodiment, the images are acquired by cameras 18 to 26 in sequence, and are sequentially communicated to computer or controller 14. In other non-limiting embodiments, the images are acquired and transmitted substantially simultaneously or "in parallel."

In functional block or step 68, the acquired imaging data is processed and analyzed. Particularly, using conventional machine vision software and/or algorithms, computer or controller 14 compares the received data, which describes object 12, to one or more specifications, dimensions, and/or sample images, which are stored within one or more database tables of memory 16, and which represent specifications, dimensions, and/or images of - 13 conforming or non-defective objects of the same type as object 12. In the preferred embodiment of the invention, memory 16 includes different specifications, dimensions and images for different types of objects or components 5 which are inspected by system 10. Computer 14 compares the images from cameras 18 to 26, by use of conventional graphics analysis software, and automatically analyzes the differences between the images of object 12 and the stored images of a "conforming" or "non-defective,, object of the same type as object 12. Particularly, computer 14 compares the various geometrical and dimensional measurements of object 12 to the desired or "conforming" geometrical and dimensional specifications, and to acceptance criteria, which is stored within memory 16. Computer 14 also compares these stored and acquired images to determine whether any surface flaws or imperfections are present on object 12. In the preferred embodiment of the invention, the results and images generated during this inspection process are communicated to display 52. In one non-limiting embodiment of the invention, screens 90 and 94, which are respectively illustrated in Figures 4 and 5, are generated and displayed by system 10. Screen image 90 of Figure 4 illustrates the top view of an alternator housing 92, which is being inspected by apparatus 10, and screen image 94 of Figure 5 illustrates a flaw 96 which has been detected on the top surface of alternator housing 92.

AS shown in functional block or step 70, if the computer 14 determines that object 12 does not conform to the - 14 acceptance criteria, either in terms of dimensional tolerances or by the size and/or quantity of surface flaws, the object 12 is "rejected." In functional block or step 72, the rejected component or object 12 is directed or transported to the non-conforming or defective component bin or receptacle 48, by use of conveyor assembly 42. Once the object 12 has been delivered to bin 48, the testing process is 'Ire-started" or repeated, and the next object 12 within the conveyor line 42 is moved or transported into chamber 32.

If the object 12 satisfies the stored tolerances and/or acceptance criteria in terms of dimensions, geometry, and/or the size/number of flaws, computer 14 begins crack/porosity inspection, as shown in functional block or step 74. Computer 14 sends a command signal to impactor 28, which causes impactor 28 to strike object 12 with a predetermined force and velocity, as shown in functional block or step 76. The actual striking force and velocity is measured by piezo-electric sensor 29 and is communicated to computer 14 for use in the vibration and/or acoustic analysis of object 12.

In functional block or step 78, the vibration response or "signature" of object 12 is sensed and/or measured by vibrometer 30. In alternate embadiments, theacoustic response or signature of object 12 is sensed and/or measured by use of one or more microphones. The measured vibration and/or acoustic data is then communicated to computer 14 where it is analyzed, as shown in functional - is - block or step 80. Particularly, computer 14 compares the vibration and/or acoustic data that is received from object 12 to the vibration and/or acoustic data which is stored within memory 16, and which corresponds to "conforming" or "non-defective,, parts (e.g., parts having no cracks and an acceptable level of porosity). In the preferred embodiment of the invention, computer 14 compares the frequency response of object 12 to an "expected" or predetermined frequency response of a conforming object of the same type as object 12. Computer 14 further compares the '..time - domain,, response of object 12 to an "expected" or predetermined time- domain response of a conforming object. Particularly, the frequency response is analyzed for one or more primary or resonant frequency values of object 12, and is compared to one or more predetermined or known primary or "resonant" frequency values of a conforming object. Additionally, the "rate of decay" or the "exponential decay coefficient" of the time-domain response of the vibration or acoustic signal is calculated in a conventional manner and is compared to the "rate of decay" or the "exponential decay coefficient" of the vibration and/or the acoustic signal produced by a conforming object when the conforming object is struck by impactor 28 at the same force and/or velocity.

It should be appreciated that the following analysis provides a reliable indication of cracks and porosity, since the existence of cracks and porosity within an object typically alters the frequency response of the 16 object and increases damping factors. For example and without limitation, the amplitude of an acoustic signal produced by a die-cast object (e.g., an alternator housing) without cracks is illustrated in graph 100 of Figure 6, and decays at a slower rate over time than the amplitude of an acoustic signal of a similar die-cast object (e.g., an alternator housing) with cracks, illustrated in graph 110 of Figure 7. Furthermore, the primary or resonant frequency 122 of a die-cast object that does have cracks, which is illustrated in graph 120 of Figure 8, is greater than the primary or resonant frequency 132 of a similar die-cast cast object that has cracks, which is illustrated in graph 130 of Figure 9.

As illustrated in functional block or step 82, if either the primary or resonant frequency of object 12 or the exponential decay coefficient falls outside of certain acceptance criteria or tolerances, which are stored within memory 16, computer 14 determines that the object 12 is "defective', or "non-conforming" and "rejects" the part. If computer 14 determines that the object 12 is conforming, it will accept the object 12, as illustrated in functional block or step 84, and communicates. a command signal to conveyor controller 41 that is effective to cause conveyor assembly 44 to move or transport object 12 to conforming bin or receptacle 50. Once the object 12 has been delivered to bin 50, the testing process is 'Ire-started" or repeated, and the next object 12 within the conveyor line 42 is moved into chamber 32.

- 1 7 Additionally detection It should be appreciated that by use of both image and acoustic data, apparatus 10 reliably detects the existence of surface flaws, porosity. and cracks within object 12.

apparatus 10 performs this inspection or an objective manner, without relying on subjective human interpretation. Moreover, computer 14, cameras 18 to 26, and sensor 30 cooperatively allow apparatus 10 to detect relatively small defects, imperfections, and/or irregularities that would otherwise be undetectable or not perceivable by human vision or hearing.

procedure in It is understood that the various inventions are not limited to the exact construction which is illustrated and described above, but that these previously delineated inventions may be varied without departing from the scope of the inventions as described in the following claims.

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Claims

Claims:

1. An apparatus for detecting defects within an object, said apparatus comprising:

at least one camera which selectively acquires image data from said object, and which transmits a first data signal representing said acquired image data; an impactor which selectively impacts said object, thereby causing said object to vibrate; at least one sensor which measures certain attributes relating to said vibration of said object, and which transmits a second data signal representing said certain attributes; and a controller which is communicatively coupled to said at least one camera and to said at least one sensor, which receives said first and said second data signals, and which determines whether said object contains any defects by use of said first and said second data signals.

2. The apparatus of claim 1 wherein said controller determines whether said object contains any surface flaws by use of said first data signal.

3. The apparatus of claim 2 whe-rein said controller determines whether said object contains any cracks by use of said second data signal.

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4. The apparatus of claim 1 wherein said at least one sensor comprises a laser vibrometer which measures a vibration frequency response of said object.

is

5. The apparatus of claim 1 wherein said vibrating object emits an acoustic signal, and wherein said at least one sensor comprises a microphone which measures said acoustic signal.

6. The apparatus of claim 1 further comprising an insulated chamber in which said at least one camera, said impactor, and said at least one sensor are contained.

7. The apparatus of claim 1 wherein said controller compares each of said first and said second data signals to at least one predetermined specification valve to determine whether said object is defective.

8. A method for detecting defects within an object, using at least one camera, an impactor and a controller which is communicatively coupled to said at least one camera and to said at least one sensor, wherein the method comprises the steps of:

i) using said at least one camera to selectively acquire image data from said object, and to transmit to the controller a first data signal representing said acquired image data; - ii) using the impactor to selectively impact said object, thereby causing said object to vibrate; iii) using said at least one sensor to measure certain attributes relating to said vibration of said object, and to transmit to the controller a second data signal representing said certain attributes; and iv) receiving at the controller said first and said second data signals, and then using the controller to determine whether said object contains any defects by use of said first and said second data signals.

9. An apparatus for detecting defects within an object substantially as herein described, with reference to or as shown in the accompanying drawings.

10. A method for detecting defects within an object substantially as herein described, with reference to or as shown in the accompanying drawings.