Optical: systems and elements – Lens – With support
Reexamination Certificate
1999-09-10
2001-09-11
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With support
C359S704000
Reexamination Certificate
active
06288855
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a mechanical device having an axially aligned, linear axial movement between its components, and, more particularly, to a preloading arrangement that prevents backlash in the movement.
A number of types of mechanical devices include components that translate relative to each other while maintaining a precisely defined, axially aligned relationship. In an example of interest to the inventor, an optical zoom lens requires that tubular housings containing the optical elements translate along an optical axis to change the spacings of the optical elements. The housings may rotate about the optical axis, but must remain well-aligned along the optical axis so that the optical signal is not distorted.
For some zoom lenses, backlash and play in the movement is not a concern. However, in sophisticated zoom lens systems such as found in some sensing devices and display devices, there can be no backlash or play between the housings, as for example when the direction of axial movement is changed. The presence of backlash may lead to errors in the determination of the exact power of magnification of the zoom lens and in turn lead to errors in the output of the system.
Mechanical structures are available to prevent backlash in such mechanical systems having a linear axial movement. Precisely machined multi-start helicoil threads are sometimes used. In another approach, accurately positioned slot-and-pin arrangements have been employed, but these structures require post-fitting operations and extreme accuracy. These approaches are operable, but are expensive to implement because they require a high degree of precision. Additionally, the closely fitted elements may be susceptible to change when the temperature of operation changes. The latter is particularly of concern where different ones of the components are made of different materials so that the fit between them changes as a result of temperature changes.
There is a need for a simpler, less-complex, and less-expensive approach to the prevention of backlash and play in mechanical systems having a linear axial movement. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides a mechanical device having a linear axial movement between components. The device is not susceptible to mechanical backlash when the direction of movement is reversed. The structure that maintains a preload on the components is readily manufactured and assembled, and does not require a high degree of precision. It uses only one element in addition to the linearly moving components. The axial alignment of the components is precisely maintained, and the structure is temperature compensated in the sense that the preload and alignment are maintained when the temperature is changed. The structure is not susceptible to misalignment or unpredictable changes as a result of mechanical shocks and vibrations. The approach is described herein with respect to a single pair of components, but it may be extended to cover multiple pairs components aligned along a common axis.
In accordance with the invention, a preloaded device comprises a female component having a right-circular cylindrical internal surface, a first helical recess in the internal surface of the female component, a male component having a right-circular cylindrical external surface sized to be slidably received within the right-circular cylindrical internal surface of the female component, and a second helical recess in the external surface of the male component. The second helical recess has the same pitch as the first helical recess so that the second helical recess is in facing relationship along its length to the first helical recess when the male component is assembled to the female component. A spring component is received within the first helical recess and the facing second helical recess when the male component is assembled to the female component. The spring component preferably has at least one shape distortion thereon so as to press the spring component against the first helical recess and the second helical recess. Most preferably, there are three approximately equidistantly spaced shape distortions.
A stop to the helical movement is optionally provided with a notch in the male component and a stop screw in the female component positioned to engage the notch when the male part is rotated to a maximum permitted rotation.
The structure of the invention does not utilize a conventional threaded structure, with a male thread in one component engaged to a female thread in the other component. Such arrangements produce backlash due to the mechanical tolerances between the threads introduced during manufacturing. Instead, the present approach utilizes a recess in both mating components. The spring component that is received in the two recesses locks the two components together so that they may move relative to each other along a helical path. The spring component exerts a spring force between the recesses, so that there is no backlash or play in the movement. The recesses, which are preferably in the form of grooves, need not be machined with tight (small) tolerances, reducing the cost of manufacture of the device.
The ability of the present structure to function with loose (large) tolerances and with materials of different types is an important feature. For example, it may be desirable to make the female component of plastic and the male component of metal. The plastic female component is injection molded, which usually results in rather large tolerances and a relatively rough surface on the part. The coefficient of thermal expansion of the plastic is also much different from that of the metal. The approach of the invention, with the two recesses and interlocking spring component, does not require close tolerances, good surface finishes, or a close match in the coefficients of thermal expansion to be operable. It is therefore well suited to such applications.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.
REFERENCES:
patent: 2319063 (1943-05-01), Hutchinson
patent: 4302076 (1981-11-01), Hashimoto
patent: 4740065 (1988-04-01), Aoyagi
patent: 5398498 (1995-03-01), Mort et al.
patent: 5940228 (1999-08-01), Burnett
Epps Georgia
Lenzen, Jr. Glenn H.
Raytheon Company
Schubert William C.
Seyrafi Saeed
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