WO1992011541A1

WO1992011541A1 - Image acquisition system for use with a printed circuit board test apparatus

Info

Publication number: WO1992011541A1
Application number: PCT/US1991/008999
Authority: WO
Inventors: Mahesh Parshotam; Bill Hunt
Original assignee: Huntron Instruments, Inc.
Priority date: 1990-12-21
Filing date: 1991-11-27
Publication date: 1992-07-09

Abstract

An image acquisition system is part of a printed circuit board automatic test apparatus (10). It includes a housing (38) which has extending therefrom a swivel assembly (44, 48) in which is mounted a light-emitting diode assembly (54) which emits light at a wavelength of 660 nanometers, directed toward a selected portion of the printed circuit board to be tested. The system also includes an optical filter (65) and a lens (68) which collects reflected light from the circuit board. The optical filter (65) is a band-pass filter having a center frequency of 660 nanometers. The light from the lens (68) is focused on a charge-coupled device (76), which converts light energy to electrical signals. The electrical signals are applied to a camera assembly (80), and from there to a personal computer which produces the desired image of the circuit board to be tested.

Description

IMAGE ACQUISITION SYSTEM FOR USE WITH A PRINTED CIRCUIT

BOARD TEST APPARATUS

Technical Field

This invention relates generally to automatic test apparatus for printed circuit boards and the like and more specifically concerns an image acquisition and display system therefor.

Background of the Invention In the art of automated circuit board testing, the location of each of the particular points to be tested on a given circuit board must be programmed into the test probe control portion of the test apparatus. The location of the test points on the board is typically accomplished by an operator, either through direct visual observation of the board when it is mounted in the test apparatus or by observation of an image of the board displayed on a monitor or the like. In each case, the test probe is moved by the operator to the successive test points on the board and the X-Y-Z coordinates of the test probe are determined and then stored. The direct observation method is often cumbersome and inconvenient for the operator, and frequently leads to programming errors. The visual display method requires a background light source as well as a visual acquisition device, such as a miniature television camera, adjacent the test probe. This method has not produced very good results for a number of reasons, including inadequacy of the light source as well as the arrangement of the other necessary elements in the vicinity of the test probe device. In one device, a small halogen lamp is used as the light source. However, halogen lights have a high power draw, are expensive, have a relatively short lifetime, and are subject to operational problems due to the vibration of the test probe assembly as it moves in normal operation. Hence, there is a significant need in the automated test equipment art for an image acquisition system which is reliable, cost effective and provides a clear, sharp image so that operators will be able to conveniently use a monitor for location test point programming. Such a system will improve the overall accuracy of the programming for the automated movement of the test probe.

Disclosure of the Invention

Accordingly, the present invention is an apparatus for obtaining an image of a printed circuit board for use by a test apparatus for the board, including a narrow bandwidth illumination means which has a selected center frequency, illumination means being positioned so as to illuminate a portion of the circuit board to be tested; an optical band-pass filter having said selected center frequency, the filter being positioned to receive light from the illumination means which has been reflected from the board; a lens for focusing light from the optical filter; and means for converting focused light energy from the lens to electrical signals which are capable of being used to produce an image on a display device.

Brief Description of the Drawings Figure 1 is a general schematic view of the image acquisition system of the present invention shown as part of an illustrative circuit board test apparatus.

Figure 2 is a perspective view showing the image acquisition system of the present invention in combination with a portion of a test assembly.

Figure 3 is an elevational view of the image acquisition system of Figure 2. Figure 4 is an exploded view of the image acquisition system of Figures 2 and 3.

Best Mode for Carrying Out the Invention Figure 1 shows a representative automatic test apparatus for printed circuit boards, generally at 10. The apparatus 10 includes a frame portion 12 within which is mounted a printed circuit board 1^'4 which is to be tested. The board 14 is held in the frame portion 12 by means of support elements shown generally at 16. Mounted on opposing sides of the frame 12 are two test probe supports 18 and 20, which move in unison in a first direction (front/rear) along frame 12 by means of pulley combinations 22 and 24 and associated timing belts which are driven by a motor 26. A test probe assembly 28 is mounted on a rail 30 which extends between probe supports 18 and 20. Probe assembly 28 moves along rail 30, in a second direction (side to side) at a right angle to the first direction, by means of pulley combinations 31 and associated timing belt 33, driven by a motor 35. The probe assembly 28 includes an elongated test probe 32 which is capable of vertical movemen .

The above system is described in more detail in U.S. Patent Application Serial No. 430,873, in the name of Mahesh Parshotam, et al, which is owned by the same assignee as that of the present invention, and is hereby incorporated by reference. It should be understood that while the image acquisition system of the present invention is described in relationship to the test apparatus shown in Figure 1, the use thereof is not limited to such a test apparatus, but rather is possible in a wide variety of circuit board test apparatus applications. In the above test apparatus 10, the test probe

32 is moved to selected points on the board, by a combination of movements in three orthogonal directions, one direction by virtue of the movement of the probe supports 18 and 20, another direction along rail 30 and the third direction by virtue of the vertical movement of the test probe 32 within the test probe assembly 28. Connected to the test probe assembly 28 is a circuit board tester of some kind, such as shown and described in the '873 application. The tester itself is not shown in Figure 1, for simplicity of illustration. In an automatic circuit board tester, the successive positions of the test probe or the circuit board to be tested must be programmed into the apparatus prior to test operations. This process of programming the control portion of the apparatus relative to movement of the test probe is referred to generally as "learning the board." This is typically done by the operator moving the test probe to each desired test point on the board in turn and, at each location, programming the X-Y-Z coordinate information of the test probe into the apparatus. At the end of this learning process, the test sequence for the probe is completely programmed for a particular board and the tester then carries out its test procedure in a rapid automatic manner for that particular circuit board.

Referring now to Figures 2, 3, and 4, the image acquisition system of the present invention is shown in detail. The test probe assembly includes a body portion 36 to which is attached by screws or the like a housing 38 for the image acquisition system. At one side of the housing 38 is a first swivel element 44 which is mounted on a swivel pin 42 which extends out from housing 38. Swivel element 44 is mounted so that it is rotatable about pin 42. Swivel element 44 includes a depending portion 47 which includes a split or gap 45 (Figure 5) . A threaded opening 46 extends through the depending portion across gap 45. Forcing the depending portion closer together by closing the gap results in swivel element 44 being tightened on pin 42. A similar swivel element 48 also has a threaded opening therethrough which extends across a gap therein. Swivel element 48 is oriented at a right angle to swivel element 44 but such that the respective threaded openings of the two swivel elements are in registry. A threaded rod 50 with a tightening knob on one end thereof extends through the threaded openings in both swivel elements 44 and 48, joining them together such that rotation of the threaded rod 50 in one direction tightens both swivel elements and rotation of the threaded rod 50 in the other direction loosens both swivel elements, permitting swivel element 44 to rotate about pin element 42 in one plane and swivel element 48 to rotate about threaded rod 50 at a right angle to the one plane.

Held in swivel element 48 is a light-emitting diode assembly shown generally at 54. The LED assembly 54 (Figure 4) includes an LED housing 56, an LED holder 58, the LED 60, and an LED reflector 62. In the embodiment shown, the particular LED 60 selected emits light at 660 nanometers, i.e. in the "red" range. An LED is advantageous in the embodiment shown as it is sufficiently rugged to withstand the vibrational effect of the apparatus and has a long life. An LED also provides adequate light for the image acquisition system to produce a sharp, clear image, by illuminating successive portions of the board to be tested as the test probe assembly 28 is moved. With the system of the present invention, it is not necessary to illuminate the entire board, but only successive, relatively small portions thereof.

Also provided in housing 38 is a filter and lens assembly 64. The actual filter 65 in the embodiment shown is a bandpass, i.e. notch, filter which accepts optical frequencies at 660 nanometers +- 10 nanometers and filters out other optical frequencies. Hence, optical filter 65 is matched to the wavelength of the light emitted by LED 60. The combination of LED 60 and optical filter 65 at 660 nanometers is that the effect of any background illumination, such as florescent lighting, in the vicinity of the test apparatus is completely eliminated. Background lighting has proven to be a persistent problem with existing devices. In applicant's invention, a sharp, distinct image is obtained. The optical filter 65 is provided with a filter cover 66. Behind optical filter 65 is a lens 68. In the embodiment shown, lens 68, which has a 10 mm focal length, is conventional. Lens 68 is contained within a lens housing 70, which in turn is positioned in housing 38. The focus position of lens 68 is controlled via a focus adjustment shaft 72 which includes at one end thereof a knob 74. Movement of knob 74 and hence adjustment of shaft 72 in one direction or the other will change the position of the lens 68 relative to the board being tested, thus changing the focus of the image seen by the operator.

To the rear of lens 68 is a charge-coupled device 76 which is positioned so that the light from the lens 68 impinges thereon. The charge-coupled device 76 is conventional and in the embodiment shown acts as a detector for the light energy reflected from the board and gathered by lens 68. Charge-coupled device 76 converts the light energy which impinges thereon to a corresponding electrical signal. Device 76 is connected via a flexible ribbon cable 78 (Figure 1) to a miniature television camera 80 which is positioned at the rear of the frame 12. The camera is conventional and may be obtained for example from Electrorim Corporation. Camera 80 functions like a miniature television camera; the electrical signals from the charged coupled device 76 are applied to the camera 80. In normal operation of the camera, the charge coupled device is part of the camera; in this case, the charge coupled device is physically separate from the remainder of the camera.

The signal output of the camera is transmitted via a cable 81 to a video display device such as a personal computer 82. In operation, as probe assembly 28 moves, successive portions of the circuit board beneath the probe assembly are illuminated and displayed on the monitor of the personal computer. The image on the monitor is clear and distinct, due to the use of the image acquisition system of the present invention. Since the camera 80 is mounted on the frame 12, it is not subject to the vibration of the probe assembly. Hence, the image acquisition system of the present invention tends to be durable in operation.

As pointed out above, in actual use the operator will move the probe assembly to each desired test point on the board in turn. The image presented on the monitor by the image acquisition system of the present invention will assist in this process being accomplished quickly and accurately, as all points on the board within the field of view of the lens are clearly illuminated and displayed. There is thus no need for the operator to refer directly to the board to locate the test points, but may instead use the monitor image exclusively, which may be magnified to some extent relative to the actual size of the board. At each selected point, the X-Y-Z coordinates for the probe are determined and programmed into the control memory. At the conclusion of learning all of the test points, the programming is complete for movement of the test assembly relative to a particular circuit board.

Although a preferred embodiment of the invention has been disclosed for illustration, it should be understood that various changes, modifications and substitutions may be incorporated in such embodiment without departing from the spirit of the invention as defined by the claims which follow.

Claims

1. An apparatus for obtaining an image of a printed circuit board for use by a test apparatus for the board, comprising: a narrow bandwidth illumination means having a selected center frequency positioned so as to illuminate at least a portion of a printed circuit board to be tested; an optical band-pass filter having said selected center frequency, positioned so as to receive light from said illumination means reflected from the board; a lens for focusing light from the optical filter; means for converting focused light energy from the lens to electrical signals which are capable of being used to produce an image on a display device.

2. An apparatus of Claim 1, wherein the converting means includes a camera means and wherein the apparatus includes means responsive to the electrical signal from the camera means for displaying the image of said portion of the printed circuit board.

3. An apparatus of Claim 2, wherein the display means is a personal computer.

4. An apparatus of Claim 2, including means for moving the apparatus relative to the printed circuit board being tested.

5. An apparatus of Claim 1, wherein the illumination means is a light-emitting diode and the center frequency is 660 nanometers +- 10 nanometers.

6. An apparatus of Claim 1, including a housing member and a swivel element which extends outwardly from the housing member, the swivel element having the capability of rotational movement in two orthogonal directions, and wherein the swivel element includes means for holding the illumination means.

7. An apparatus of Claim 1, wherein the image apparatus is mounted on an assembly which contains a test probe which in operation contacts successive test points in the circuit board to be tested, wherein the test probe assembly is adapted for movement in two orthogonal directions and wherein the test probe is adapted for movement within the assembly at a right angle to said two orthogonal directions.

8. An apparatus of Claim 2, wherein converting means includes a charge-coupled device which converts light energy impinging on it from the focusing lens to corresponding electrical signals, wherein the camera means processes the electrical signals from the charge coupled device and applies them to the display device to produce the image, and wherein the camera means is mounted remotely from the image apparatus.

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