Illumination – Light source and modifier – Adjustable or repositionable light source or light source...
Reexamination Certificate
1998-02-18
2001-01-30
O'Shea, Sandra (Department: 2875)
Illumination
Light source and modifier
Adjustable or repositionable light source or light source...
C362S276000
Reexamination Certificate
active
06179448
ABSTRACT:
TECHMCAL FIELD
This invention relates generally to the field of illumination systems, and more specifically to adjusting the intensity and power of light provided by illumination devices, particularly those for use with magnification systems, such as microscopes.
BACKGROUND OF THE INVENTION
Magnification systems require an illumination source for illuminating the object to be magnified. In many situations, the intensity of the light illuminating the object must be kept uniform over a significant duration of time for proper imaging. In certain fields, such as microelectronic fabrication, uniform light intensity is critical to properly inspect the surfaces of microelectronic devices. Uniformity in the light intensity on an illuminated object is difficult to achieve for any significant duration. For example, the amount of light emitted by an illumination source, such as a light bulb, may change as the light bulb heats up, ages, etc. This is especially true when a high intensity light source is employed. The intensity of light provided by a high intensity light source begins to change almost immediately upon operation. Even if the intensity of the light from the light source is constant, the intensity of light provided by an illumination device using the light source would still vary. For example, as components and structures in the illumination device heat up, the geometry of the components, including the relative position of the light source and reflector, varies thus altering the intensity of light provided by the illumination device. Therefore, to maintain a constant intensity of light on an illuminated object, the power and the intensity of light produced by the illumination device must continually be tuned to compensate for the various changes.
A manual method is currently employed to tune the intensity and amount of light provided by an illumination device. The position of the light source is manually adjusted by a technician in an attempt to maintain the intensity of illumination constant over time. The size of an aperture in a diaphragm is likewise, manually adjusted, in an attempt to maintain a constant amount of light per unit of time, or power. This requires a skilled technician to make many time-consuming and error prone adjustments to the correctly position of the light source.
SUMMARY OF THE INVETION
An automated light tuner is provided to reduce the time and level of skill required of technicians to adjust an illumination device to achieve a uniform intensity of light on an object, such as an object being magnified or illuminated over a period of time. The automated light tuner also eliminates the error introduced by the manual method of tuning. In a first exemplary embodiment, the automated light tuner includes a housing which defines an enclosure having an opening at one end. A reflector is mounted in the enclosure, and a light source mounted in a light source receiver is positioned in the enclosure between the reflector and the opening. The light source and reflector are selectively positionable with respect to one another along at least a first axis. Preferably, the light source is selectively positionable with respect to the reflector along a first axis, a second axis and a third axis. The automated light tuner also includes a light meter which is composed of a power meter and a sensor such as a photomultiplier tube, an avalanche diode, or a silicon diode, the sensor being positioned in a light reflection path. The power meter measures the amount of light per unit of time reflected from an object which, due to the fixed area of the sensor, is proportional to the intensity of light being delivered to the illuminated object. The power meter provides a measure of the amount of light, and consequentially the light intensity, to a control mechanism in the form of a power signal. The control mechanism responds to the power signal by producing a control signal for controlling a drive assembly that positions the light source relative to the reflector. The automated light tuner may further include a diaphragm having an aperture located across the opening of the enclosure. The aperture of the diaphragm is adjustable to limit the amount of light, or power, delivered to the target position. The drive assembly, diaphragm and light meter are coupled to each other in a feedback loop to adjust the amount and the intensity of light delivered to the object to a desired value, which may be constant.
The drive assembly may include a first motor, a second motor and a third motor for positioning the light source with respect to the reflector along the first axis, the second axis and the third axis, respectively. The motors may be connected to the light source receiver by a set of drive trains. The motors may be controlled by a motor controller, which may in turn be controlled by the control mechanism.
The aperture may be adjusted by an aperture drive mechanism which may include an aperture motor and an aperture motor controller. The aperture motor controller may in turn be controlled by the control mechanism.
The control mechanism can take the form of a hard wired circuit or microprocessor, but in the exemplary embodiment is shown as a programmed general purpose computer. The control mechanism receives the measurements of amount of light and the light intensity which are produced by the light meter. The control mechanism uses these measurements to incrementally adjust the position of the light source with respect to the reflector. The position of the light source with respect to the reflector is preferably first adjusted along the first axis to achieve a maximum intensity of light at the target position. The position of the light source with respect to the reflector may next be adjusted along the second axis to again achieve a maximum light intensity. The position of the light source with respect to the reflector can then be adjusted along the third axis to again achieve a maximum light intensity at the target position. A maximum intensity along any given axis may be reached by moving the light source in incremental steps along the given axis until the light intensity begins to fall off. The light source is then moved in the opposite direction along the same axis, using a smaller incremental step, until the intensity begins to fall off. This reiterative process is performed until some minimum incremental step is achieved, signifying that the maximum illumination has been reached with respect to the given axis. Alternatively, the light source may be moved with respect to the reflector until the intensity begins to fall off. The light source may then be incremented one or less steps in the opposite direction.
Once the maximum light intensity has been achieved for all of the desired axes, the aperture of the diaphragm may be adjusted until a desired amount of light is achieved at the target position. A reiterative procedure may be used to adjust the size of the aperture to achieve the desired amount of light in which the size of the aperture is first incrementally adjusted in a first direction until the desired amount of light is overstepped. The size of the aperture is then incrementally adjusted in the second direction in an incremental step smaller than the first incremental step until the desired amount of light is again overstepped. This process is performed until some minimum increment step size is reached.
In a second exemplary embodiment, a lens may be located between the light source and the diaphragm. The lens may be selectively positioned between the light source and the drive diaphragm by a lens position drive mechanism which includes a lens holder, lens positioning motor, and lens drive train. The lens positioning motor is controlled by the control mechanism. The lens is adjustable with respect to the reflector or the light source to achieve a desired light intensity at the target position.
REFERENCES:
patent: 3639751 (1972-02-01), Pichel
patent: 3648045 (1972-03-01), Le Vantine et al.
patent: 3663109 (1972-05-01), Sharples
patent: 3706000 (1972-12-01), Retzer et al.
p
Frank Peter S.
Hatfield Robert J.
Johnson David R.
Phillips Joe L.
Dorsey & Whitney LLP
Micro)n Technology, Inc.
O'Shea Sandra
Sawhney Hargobind
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