Optical distance sensor

Details Optical distance sensor Optical distance sensor

1994-06-17

1995-09-05

Evans, F. L.

Optics: measuring and testing

By polarized light examination

With light attenuation

25055929, 356376, G01B 1106, G01B 1124

Patent

active

054483590

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an optical distance sensor according to the confocal optical imaging principle for the determination of height values and for three-dimensional surface measurement. Preferred fields of application are, especially, the inspection of soldered joints and the monitoring of the component quality in the case of high-density electronic printed circuit boards, such as for example multi-chip modules.
2. Description of the Related Art
In the inspection of the soldered joints or components of a printed circuit board, an investigation is essentially carried out for conductor track constrictions, impurities due to particles, soldered joint quality, correct placing of connecting pads, short circuits etc. As a result of the increasing intensification of the packing density of components in microelectronics, the inspection of three-dimensional objects with high resolution and at high speeds of inspection is becoming necessary. In particular, unequipped and equipped micromotherboards are to be automatically inspected.
Previously known devices for the recording of height raster images, which comprise a multiplicity of three-dimensionally existing points of object surfaces, are essentially based on the so-called triangulation method. In this method, a laser beam scans the surface of the object. The two planar space coordinates of a determined surface point are known by the relative position between scanning beam or illumination beam and the printed circuit board. The height coordinate of the surface point which is currently being measured is acquired by at least one laterally disposed objective in conjunction with a position-sensitive detector. In this way, it is possible to determine the three-dimensional space coordinates of a multiplicity of surface points. By the comparison of a recorded surface image with an ideal surface image and with consideration being given to specified error criteria, defects on printed circuit boards can be automatically recognized.
The abovementioned triangulation method has been further developed in various respects, but exhibits particular fundamental disadvantages: the reflected light from surface points of the object which do not correspond to the current point of incidence. In the case of very glossy surfaces, this may lead to considerable errors of measurement.
Small objects which are situated very close to relatively large objects or in depressions cannot in every case be sensed, as a consequence of shadows.
In order to observe the Scheimpflug condition, in most cases a non-enlarging imaging onto the detector is required. In the case of small measurement spot sizes, this leads to high power densities. A high power density on the detector surfaces in the case of lateral photodiodes places an upper limit upon the speed of scanning. The use of photodiode arrays does not increase the data rate.
It is hitherto not known to vary the imaging scale and thus the resolving power by simple exchange, for example, of an objective on the sensor system.
Commercially available measuring systems according to the triangulation method exhibit particular refinements by means of which the abovementioned disadvantages are in part avoidable. Thus, the company Robotic Vision Systems (536 Broadhollow Road, Melville, N.Y. 11747, USA) has employed linear photodiode arrays in place of lateral photodiodes for the purpose of avoiding erroneous measurements due to secondary reflexes. Erroneous measurements are recognized and eliminated by appropriate evaluating software. In total, however, the data rate of the system is reduced so greatly that this system is not suitable for a full inspection in a processing line.
In order to cope with the problems in the application of a lateral photodiode, the company Matsushita Kotobuki Electric Co., Ltd. (2131 Ohara-minamikata, Kawauchi-machi, Onsen-gun, Ekimeken 791-03, Japan) has developed a system with which observation takes place from eight directions. An evaluation of the detector signals is execu

REFERENCES:
patent: 4798469 (1989-01-01), Burke
"Chromatic Focusing Technique", IBM Technical Disclosure Bulletin, vol. 27, No. 12, May 1985, pp. 6850-6851.
"Optische Hohenmessung uber eine Linie", 592 Neues aus der Technick, May 1986, No. 2, Wurzburg, Deutschland, pp. 5-6.
Robotic Vision Systems, Inc., one page. undated.
"Vision Systems for PCB Manufacturing", Papers for IECON '90 Special Session of Yano, et al., one page.
"Vision Systems for PCB Manufacturing", Papers for IECON '90 Special Session by Muraoka, one page.
"Vision Systems for PCB Manufacturing", Papers for IECON '90 Special Session by Kobayashi, et al., one page.
"3-D Profile Detection of Etched Patterns Using a Laser Scanner (3D-Scan Detection) for Automatic Inspection of Printed Circuit Boards", reprint from the Proceedings of SPIE-The International Society for Optical Engineering, vol. 389, Jan. 20-21, 1983, pp. 44-52.

Affiliated with

Also associated with

Rating

Optical distance sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical distance sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical distance sensor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-476741