Geometrical instruments – Gauge – Collocating
Reexamination Certificate
1998-03-10
2001-04-24
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Gauge
Collocating
C033S573000, C033SDIG002
Reexamination Certificate
active
06219931
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of measuring devices and more particularly to a target base for a measuring system.
BACKGROUND OF THE INVENTION
It is common practice when measuring the surface contour of an object to take measurements of the object using an optical or laser measuring apparatus. One such method includes marking predetermined locations on the object and attaching targets to the object at each location. Conventional target bases generally utilize a magnet or multiple suction cups to attach the target to the object. Conventional target bases may also provide proper spacing of the target from the surface of the object by feet that make point contact with the object. In many applications, it is necessary to keep the targets attached to the object being measured for long periods of time, such as when two or more sub-assemblies are being assembled and their relative positions are being established prior to joining them.
Conventional target bases that utilize small suction cups generally operate by being pressed onto the surface of the object. The air is squeezed out of the suction cups and the suction cups are released whereupon they partially resile and form a vacuum within the suction cup. Suction cups have several disadvantages. For example, the force that the suction cups exert is relatively small, inasmuch as it is a function of the resiliency of the suction cup. Accordingly, even when several suction cups are used on a target, the force holding the target to the object is relatively low, and there is a chance that the target will change position or even become dislodged. In addition, suction cups must be applied with attention to making sure that all of the suction cups are evenly pressed onto the surface of the object, lest there be an uneven suction force among them, thus allowing the target to tilt in the direction of a greater suction force. Furthermore, suction cups are inherently resilient, thereby displacing the target away from the surface. Because of the displacement, or rebound, of the target from the surface of the object, the legs that set the distance of the target from the surface of the object are often not effectively engaged.
The amount of rebound the target experiences is subject to variation that is dependent upon many factors, such as environmental conditions (e.g., temperature and humidity), the orientation of the target (e.g., gravity forces opposing or aiding the suction cups), and the physical condition of the suction cups (e.g. age, wear, and the like). Other problems associated with suction cups may include creep of the sealing lips of the suction cups that allows them to loosen, and leakage that allows the suction cups to lose their vacuum over time.
In short, pressed-on suction cups provide scant assurance that the targets on the object are uniformly positioned at predetermined locations and that the offset distance and the target angle accurately reflects the surface of the object. In addition, it cannot be assured that pressed-on suction cups will not move over time or even be dislodged.
SUMMARY OF THE INVENTION
Accordingly, a need has arisen for an improved target base for a measuring system. The present invention provides a target base that substantially eliminates or reduces problems associated with the prior methods and systems.
In accordance with one embodiment of the present invention, a target base for attaching an apparatus to an object includes a substantially rigid body having a mount surface adapted to couple an apparatus or target to the body, and a base surface. A suction cup is affixed to the base surface of the body and has a suction cavity that is defined by a deformable sealing lip at the perimeter of the suction cup. The sealing lip and vacuum cavity in conjunction with the object form a vacuum chamber. A vacuum system communicates a vacuum pressure to the vacuum chamber. The target base also includes one or more contact members which are coupled to the base surface of the body to provide consistent off-set positioning of the target base with respect to the object.
In a particular embodiment, the target base includes a sight system used to accurately position the target base with respect to the object. The sight system may include a hole through the target base, a mounting sleeve assembly housed within the hole, and a reticle mounted within the mounting sleeve assembly in sealed relation. The reticle may include a targeting guide, such as a circle and cross hairs, for precise positioning of the target base over the object.
In another embodiment, a locating system is associated with the mount surface of the target base to ensure accurate mating of the apparatus with the target base in a predetermined position. A simple but highly accurate locating system may consist of two circular cylindrical bosses that project from the mount surface and have different diameters. The base may also include threaded holes in the body opening at the mount surface and adapted to receive screws by which the apparatus is attached to the target body.
In a particular embodiment of the present invention, the contact surfaces of the contact members are located within the suction cavity, primarily to maximize the area of the suction cup. The contact members may include threaded attachment shanks that pass through the suction cup and are threaded into the body and have heads configured to make substantially point contact with the surface of the object. In general, three contact members equidistant from each other and from a center axis perpendicular to a plane created by the mount surface of the target base are used. The sealing lip of the suction cup may be concentric with the center axis. The described configuration of the contact members and sealing lip of the suction cup provides a distribution of forces due to the pressure differential across the suction cup such that the centroid is along the center axis and the reaction forces on the contact members are equal.
One technical advantage of the present invention is to provide a target base for an apparatus, such as a target, to be used in optical or laser measuring systems that will support the apparatus with high accuracy over a point on an object. Another technical advantage is to provide a target base that provides accurate positioning of the apparatus relative to the point to be measured on the surface of the object, regardless of the orientation of that surface to which the target base is attached relative to the horizontal—i.e., the accuracy of the positioning of the target base is not affected by gravitational forces acting on the target base and the apparatus that it supports. Other technical advantages include stable positioning of the apparatus without movement over long periods of time.
A further technical advantage of the present invention is to provide a suction cup that is substantially coextensive with the mount surface to allow a large retention force of the vacuum created within the suction cup. The retention force of the vacuum created within a suction cup of the present invention having a large area is generally greater than that of conventional suction cups having smaller areas. Furthermore, the larger area of the suction cup of the present invention allows the target base to be attached to the object with a lower vacuum than that required for conventional suction cups.
Other technical advantages of the present invention will be readily apparent to one skilled in the art form the following figures, description, and claims.
REFERENCES:
patent: 1851028 (1932-03-01), Worrall
patent: 2148055 (1939-02-01), Blumenthal
patent: 2535051 (1950-12-01), Donohue
patent: 2565793 (1949-07-01), Weismantel
patent: 2831260 (1958-04-01), Shaw
patent: 2939671 (1960-11-01), Beekman
patent: 3540256 (1967-07-01), Thompson
patent: 3716307 (1973-02-01), Hansen
patent: 4336765 (1982-06-01), Coughlin
patent: 4898452 (1990-02-01), Kawachi et al.
patent: 4964218 (1990-10-01), Morghen
patent: 5013075 (1991-05-01), Littell
patent: 5087005 (1992-02-01)
Anderson Terry J.
Fernandez Maria
Gutierrez Diego
Hoch, Jr. Karl J.
Northrop Grumman Corporation
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