Open-loop light intensity calibration systems and methods

Details Open-loop light intensity calibration systems and methods Open-loop light intensity calibration systems and methods

1999-12-30

2001-05-29

Vu, David (Department: 2821)

Electric lamp and discharge devices: systems

With radiant energy sensitive control means

C250S252100

Reexamination Certificate

active

06239554

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to lighting systems for vision systems.
2. Description of Related Art
The light output of any device is a function of many variables. Some of the variables include the instantaneous drive current, the age of the device, the ambient temperature, whether there is any dirt or residue on the light source, the performance history of the device, etc. Machine vision instrument systems typically locate objects within their field of view using methods which may determine, among other things, the contrast within the region of interest where the objects may be found. To some degree, this determination is significantly affected by the amount of incident light or transmitted light.
Automated video inspection metrology instruments generally have a programming capability that allows an event sequence to be defined by the user. This can be implemented either in a deliberate manner, such as programming, for example, or through a recording mode which progressively learns the instrument sequence. The sequence commands are stored as a part program. The ability to create programs with instructions that perform a sequence of instrument events provides several benefits.
For example, more than one workpiece or instrument sequence can be performed with an assumed level of instrument repeatability. In addition, a plurality of instruments can execute a single program, so that a plurality of inspection operations can be performed simultaneously or at a later time. Additionally, the programming capability provides the ability to archive the operation results. Thus, the testing process can be analyzed and potential trouble spots in the workpiece or breakdowns in the controller can be identified. Without adequate standardization and repeatability, archived programs vary in performance over time and within different instruments of the same model and equipment.
Conventionally, as illustrated in U.S. Pat. No. 5,753,903 to Mahaney, closed-loop control systems are used to ensure that the output light intensity of a light source of a machine vision system was driven to a particular command level. Thus, these conventional closed-loop control systems prevent the output light intensity from drifting from the desired output light intensity due to variations in the instantaneous drive current, the age of the light source, the ambient temperature, or the like.
SUMMARY OF THE INVENTION
This invention is especially useful for producing reliable and repeatable results when using predetermined commands to the illumination system , such as when the command is included in a part-program that will be used on a different vision system, and/or on the same or a different vision system at a different time or place.
The input light settings in many vision systems often do not correspond to fixed output light intensities. Moreover, the output light intensity can not be measured directly by the user. Rather, the output light intensity is measured indirectly by measuring the brightness of the image. In general, the brightness of the image is the average gray level of the image. Alternatively, the output light intensity may be measured directly using specialized instruments external to a particular vision system.
In any case, the lighting behavior, i.e., the relationship between the measured output light intensity and the commanded light intensity, is not consistent between vision systems, or within a single vision system over time. Rather, the relationship between the measured output light intensity and the commanded light intensity depends on the optic elements of the vision system, the particular light source being used to illuminate a part, the particular bulb of that light source, and the like. For example, a first vision system having its stage light source set to an input light intensity command value of 30% may produce the same output light intensity as a second vision system having its stage light source set to an input light intensity command value of 70%.
FIGS. 1-3
graphically illustrate this inconsistency of the lighting behavior between different vision systems, inconsistency within a single vision system when using different optical elements, and inconsistency within a single vision system when using the same optical elements and different light sources or when using the same optical elements and light source and different bulbs or lamps in that same light source.
These examples are given to show how different the lighting behaviors may be depending on the particular vision system, optical elements and light sources. By design, the same lighting behavior cannot be expected to occur on different classes of vision systems or on the same vision system when using different optical elements and/or light sources. In practice, the illumination may also vary on different particular vision systems of the same class of vision system due to variations in components and/or alignment.
This inconsistency of the lighting behavior makes it difficult to interchange part-programs between even similar particular visions systems of the same class of vision systems. When a part program is developed on one particular vision system, that part program often does not run on another particular vision system, even when that other particular vision system is the same class as the first vision system. That is, a part program with a fixed set of commanded light intensity values might produce images of varying brightness on different vision systems. However, many measurement algorithms, such as algorithms using edge detection, depend on the brightness of the image. As a result, because the brightnesses of resulting images generated using different vision systems are almost assured to be different, part programs do not run consistently on different vision systems.
This invention provides lighting calibration systems and methods that enable open loop control of light sources of vision systems.
This invention additionally provides lighting calibration systems and methods that can be implemented entirely in software and/or firmware.
This invention separately provides lighting calibration systems and methods that calibrate a particular vision system to a reference vision system.
This invention additionally provides lighting calibration systems and methods that use reference lighting curves for each particular class of vision systems.
This invention further provides lighting calibration systems and methods that provide different reference lighting curves for each of the different light sources of each particular class of vision systems.
This invention separately provides lighting calibration systems and methods that ensure uniformity between different vision systems of each particular class of vision systems.
This invention separately provides lighting calibration systems and methods that permit repeated re-calibration.
This invention separately provides lighting calibration systems and methods that ensure the light output intensity of a light source of a particular vision system remains uniform over time.
This invention additionally provides lighting calibration systems and methods that ensure the output light intensity remains uniform over time by re-calibrating a particular light source of a particular vision system.
In various exemplary embodiments of the lighting calibration systems and methods according to this invention, a reference lighting curve for each lighting source of a particular class of vision systems is created. Each reference lighting curve is generated by providing, for a particular light source, an input light intensity command value and measuring the resulting output light intensity that reaches the light sensor of the vision system. The light sensor maybe the camera of the vision system. The amount of light reaching the light sensor of the vision system will be an essentially nonlinear function of the lamp output when driven at the input light intensity command value and any attenuation of the intensity of the light as output from the light source, i.e., a

Affiliated with

Also associated with

Rating

Open-loop light intensity calibration systems and methods does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Open-loop light intensity calibration systems and methods, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Open-loop light intensity calibration systems and methods will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2455767