Optical: systems and elements – Mirror – With support
Reexamination Certificate
2001-03-14
2002-05-14
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Mirror
With support
C359S880000, C359S881000, C359S871000, C359S872000
Reexamination Certificate
active
06386719
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to mechanical assemblies, and in particular to a system for aligning planar surfaces of discrete components.
BACKGROUND OF THE INVENTION
Mechanical assemblies commonly include components having planar surfaces that require alignment. For example, optical assemblies often include mirrors that must be accurately positioned to provide proper imaging functionality. Typically, proper positioning of each mirror depends on the alignment of the reflective surface of the mirror with a planar reference surface in a base structure. In a conventional optical assembly, this alignment operation is generally performed using a combination spring-hook and adjustment screw mechanism.
For example,
FIG. 1
shows a cross section of a conventional optical assembly
100
, which includes a mirror
110
, a. base structure
130
, retaining hooks
140
a
and
140
b
, guide posts
141
a
and
141
b
, extension springs
142
a
and
142
b
, and adjustment screws
160
a
and
160
b
. Mirror
110
comprises a reflective surface
111
formed on the top surface of a glass substrate, and is therefore called a “front surface mirror.” Because reflected light rays do not have to pass through a layer of glass (as they would in a second surface mirror, i.e., a mirror in which the reflective surface is formed on the bottom surface of the glass substrate), undesirable aliasing and refraction effects are avoided. Base structure
130
includes a planar reference surface
131
that specifies the target plane for reflective surface
111
; i.e., the plane in which reflective surface
111
must lie for mirror
110
to provide accurate imaging.
Adjustment screws
160
a
and
160
b
are installed in, and extend through, threaded holes
132
a
and
132
b
, respectively, in base structure
130
. Retaining hooks
140
a
and
140
b
are slidably coupled to base structure
130
by guide posts
141
a
and
141
b
, respectively, and are attached to base structure
130
by extension springs
142
a
and
142
b
, respectively. When retaining hooks
140
a
and
140
b
are hooked over the edges of mirror
110
, mirror
110
is held firmly against the protruding tips of adjustment screws
160
a
and
160
b
by the retentive force of extension springs
142
a
and
142
b
. Adjustment screws
160
a
and
160
b
can then be used to adjust the vertical position and angular orientation of mirror
110
, so as to align reflective surface
111
with reference surface
131
of base structure
130
.
Unfortunately, the conventional mirror positioning technique of optical assembly
100
is subject to two significant limitations. First, it is difficult to verify the proper positioning of mirror
110
. Even though reflective surface
111
may appear to be aligned with reference surface
131
to the naked eye, even a slight amount of skew between the two surfaces can lead to significant imaging errors in sensitive or high resolution optical assemblies. Therefore, the manual alignment process required by optical assembly
100
can require a time-consuming iterative calibration sequence (i.e., adjust positioning, then test, then adjust based on results, and so on).
Secondly, optical assembly
100
requires recalibration whenever mirror
110
is replaced, due to the fact that mirrors are generally not held to tight thickness tolerances. While base structure
130
is typically made from a readily machinable material and can therefore be milled to highly accurate dimensions, lapping a glass component (such as a mirror substrate) to a precise thickness can be difficult and expensive. Therefore, if mirror
110
is replaced, adjustments will have to be made to screws
160
a
and
160
b
to accommodate the new mirror thickness. In addition, even if mirror
110
is simply removed and then reinstalled, play between the threads of adjustment screws
160
a
and
160
b
and threaded holes
132
a
and
132
b
, respectively, may necessitate a recalibration.
Accordingly, it is desirable to provide a system for accurately and repeatably aligning planar surfaces of components in a mechanical assembly that does not require an iterative calibration procedure and can accommodate deviations in the non-planar dimensions of the components.
SUMMARY OF THE INVENTION
The present invention provides a planar surface alignment system that uses the planar surfaces themselves to perform the alignment, thereby ensuring accurate positioning while eliminating the need for calibration. According to one embodiment of the present invention, a first planar surface of an auxiliary component is aligned with a reference planar surface of a base component by a retaining element having a base contact region and an auxiliary contact region. The base contact region and the auxiliary contact region are coplanar portions of the retaining element. The base contact region is clamped against the reference planar surface, and the first planar surface is held against the auxiliary contact region by a resilient force. Therefore, the base contact region is aligned with the reference planar surface, and the first planar surface is aligned with the auxiliary contact region. Because the auxiliary contact region and the base contact region are coplanar, the first planar surface is aligned with the reference planar surface.
In another embodiment of the present invention, a front surface mirror is mounted on elastic pads in a well in a base structure. The elastic pads are configured to displace the planar reflective surface of the front surface mirror away from the planar reference surface. Retaining clips having coplanar contact regions are screwed to the base structure such that portions of the coplanar contact regions are clamped against the planar reference surface, and other portions of the coplanar contact regions contact the planar reflective surface. The elastic pads deform in response to the loading from the retaining clips, allowing the contact regions to position the planar reflective surface. In this manner, the planar reflective surface is aligned to the planar reference surface via the contact regions of the retaining clips.
According to another embodiment of the present invention, the elastic pads are formed from an elastomer or other resilient material, and can have any desired cross-section. The elastic pads can be placed under all edges of the front surface mirror, or can be placed at selected locations. The elastic pads can be attached to the front surface mirror, to the base structure, or can be a completely separate component of the optical assembly. According to another embodiment of the present invention, the elastic pads can be replaced with a resilient support structure using mechanical springs. Alternatively, gas or hydraulic cylinders can be used to provide the resilient force.
According to another embodiment of the present invention, the retaining clips comprise straight elements positioned over two opposite edges of the mirror. According to another embodiment of the invention, the retaining clips comprise a plurality of smaller elements positioned at various intervals around the perimeter of the mirror. According to another embodiment of the present invention, a single retaining clip clamps along the entire perimeter of the mirror. According to another embodiment of the present invention, the screwed-down retaining clips can be replaced with retaining elements are hinged to the base structure and pulled tight against the planar reference surface by springs. According to another embodiment of the present invention, the screwed-down retaining clips can be replaced with retaining elements that are clamped against the planar reference surface by mechanical latching mechanisms.
According to another embodiment of the present invention, a camera system includes multiple camera-mirror arrangements, each camera being aimed at its associated mirror, the mirror directing the camera field of view away from a central axis of the camera system. Each of the mirrors is mounted in a resilient mounting structure, and clamped in place by a set of reta
Bever Hoffman & Harms LLP
Enroute, Inc.
Mao Edward S.
Sikder Mohammad
LandOfFree
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