Multi-purpose vacuum clamp table

In one embodiment, an apparatus for constraining an object includes a first clamping surface configured to apply a first holding force to a first surface of the object; a second clamping surface configured to apply a second holding force to a second surface of the object; and an actuator configured to selectively move the second clamping surface relative to the first clamping surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to vibrational analysis and, more specifically, to a multi-purpose vacuum clamp table.

2. Description of the Related Art

Vibrational modal analysis can be accomplished by constraining at least one degree of freedom of a structure and introducing a forcing function to the structure. Generally, one or more control points on a structure are constrained to a fixed acceleration.

In the manufacture of structures where harmonic resonance is an important characteristic, it is necessary to provide fixtures that constrain a work piece in a certain manner to test for resonant frequencies. In a typical manufacturing cycle, the resonant frequencies of a work piece are first measured. Then, precise machining operations make changes to the work piece in response to the measured resonant frequencies. Finally, the vibrational modal analysis is checked again to determine if the structure has the correct harmonic resonance.

One drawback to this approach is that machining operations require the fixture to provide a rigid base to constrain movement of the work piece during machining. However, accurate vibrational modal analysis requires uniform clamping characteristics on the boundary of the work piece, such as along the perimeter. Traditionally, this would be accomplished by moving the work piece between different fixtures for each of the operations. Changing the fixtures between phases takes time and reduces the manufacturing efficiency for creating the finished products. For example, with each change of the fixtures between phases, the boundary constraints on the work piece for vibrational modal analysis are also changed.

As the foregoing illustrates, what is needed in the art is a fixture that can be configured to constrain a work piece with one set of constraints and efficiently reconfigured to constrain the work piece with a second set of constraints.

SUMMARY OF THE INVENTION

In one embodiment, an apparatus for constraining an object includes a first clamping surface configured to apply a first holding force to a first surface of the object; a second clamping surface configured to apply a second holding force to a second surface of the object; and an actuator configured to selectively move the second clamping surface relative to the first clamping surface.

In another embodiment, a method of constraining an object includes applying a first holding force to the object to hold the object against a first clamping surface; performing a first vibrational modal analysis on the object; applying a second holding force to the object to hold the object against a second clamping surface; changing a resonant characteristic of the object; releasing the second clamping surface from the object; and performing a second vibrational modal analysis on the object.

In another embodiment, a method of constraining an object includes applying a first holding force to the object to hold the object against a first clamping surface; applying a second holding force to the object to hold the object against a second clamping surface; and moving the second clamping surface relative to the first clamping surface. The second clamping surface may be moved to a coplanar position with the first clamping surface.

DESCRIPTION

The preferred embodiment of the multi-purpose vacuum clamp table according to the present invention is illustrated in the attachedFIGS. 1-5. The multi-purpose vacuum clamp table100may be used with a machine for performing vibrational modal analysis of a musical instrument soundboard.

In the preferred embodiment, the multi-purpose vacuum clamp table100comprises6components. The multi-purpose vacuum clamp table100is illustrated inFIG. 1. The first component is an inner vice assembly110that includes an inner machined plate115used for applying a clamping force to a work piece. The top surface of the inner vice assembly110has an array of holes210drilled through the inner machined plate115that connect to a series of channels220on the back side of the plate115. The front and back surfaces of the inner machined plate115are illustrated inFIGS. 2A and 2B, respectively. A back-plate (not shown) is attached to the back surface of the inner machined plate115to seal the channels220of the inner machined plate115.

The second component is the outer vice assembly120. The outer vice assembly120includes an outer machined plate125configured with a cutout in the center of the outer machined plate125in the shape of the inner vice assembly110. The outer vice assembly120has a vacuum channel400cut into the top of the outer machined plate125. The vacuum channel400may be disposed around the perimeter of the cutout. In one embodiment, the machined vacuum channel400is concentric to the cutout in the outer machined plate125, as illustrated inFIG. 4. Two shoulder bolts510and compensating springs520connect the outer machined plate125of the outer vice assembly120to a support plate135of the outer vice assembly120, as illustrated inFIG. 5. The compensating springs520force the support plate135of the outer vice assembly120to rest against the cam lobes320of a camshaft310. Although the inner vice assembly110is shown to be substantially similar in shape to the cutout in the outer vice assembly120, it is contemplated that the inner vice assembly110may have a different shape from the cutout so long as it provides sufficient support to the work piece during the machining process.

The third and fourth components are a camshaft310assembly and two bearing housings330, respectively.FIG. 3is an illustration of an isometric view of the multi-purpose vacuum clamp table100with a hidden inner vice assembly110and a transparent outer vice assembly120. The camshaft310and the cam lobes320are used to move the inner vice assembly110relative to the outer vice assembly120. The camshaft310is constrained by two bearing housings330bolted to the bottom surface of the outer machined plate125of the outer vice assembly120. Two cam lobes320are attached to the camshaft310. The cam lobes320ride against the bottom surface of the support plate135of the outer vice assembly120. The inner vice assembly110is located in the cutout in the outer machined plate125of the outer vice assembly120and rests on top of the support plate135of the outer vice assembly120. When the camshaft310is rotated to its top-dead-center position, the top surface of the inner vice assembly110is coplanar to the top surface of the outer vice assembly120. When the camshaft310is rotated to its bottom-dead-center position, the top surface of the inner vice assembly110is below the top surface of the outer vice assembly120. The support plate135is configured to limit movement of the inner vice assembly110to a predetermined height, such as when the inner vice assembly110is coplanar with the outer vice assembly120. In one embodiment, the support plate135may be in the shape of a rectangle having dimensions larger than the cutout. The support plate135may contact the bottom of the outer machined plate125to prevent the inner vice assembly110rising higher, thereby ensuring the top surface of the inner vice assembly110is coplanar with the outer vice assembly120.

In alternative embodiments, alternative mechanisms for actuating the inner vice assembly110are contemplated. For example, the inner vice assembly110could be actuated by a screw, bellows, pneumatic or hydraulic cylinders, or any other mechanism that could raise and lower the inner vice assembly110in relation to the outer vice assembly120.

The fifth components are gaskets used to seal the vacuum clamp surfaces of the inner and outer vice assemblies110,120.FIG. 4is an enlarged partial view of the outer machined plate125of the outer vice assembly120. As shown, a gasket410,411is placed in concentric channels on both sides of the vacuum channel400of the outer vice assembly120. In the preferred embodiment, the gaskets410,411are made of a conventional vacuum gasket material having a rectangular cross-section. In alternative embodiments, other suitable sealing materials for vacuum sealing and different cross-sections may be employed, such as gaskets with a circular cross-section. The vacuum channel400is connected to a vacuum pressure through a fitting in the back of the outer machined plate125of the outer vice assembly120. The gaskets410,411provide a seal between the top surface of the outer vice assembly120and a work piece placed on top of the outer vice assembly120. A third gasket140, of similar construction, is shown inFIG. 1andFIG. 2Aaround the outer edge of the inner vice assembly110. The third gasket140provides a seal between the top surface of the inner vice assembly110and a work piece placed on top of the inner vice assembly110.

The sixth component is the frame structure that connects to the bottom of the outer vice assembly120. In the preferred embodiment ofFIG. 1, the frame160includes of four vertical legs161and two base cross-members162. A front leg161is connected to one of the back legs161by either end of one of the base cross-members162. The four legs161are connected with bolts to the bottom surface of the outer machined plate125of the outer vice assembly120. Other suitable frame structures suitable for supporting the inner and outer vice assemblies110,120are also contemplated.

In the preferred embodiment, the multi-purpose vacuum clamp table100is used as a fixture in a manufacturing process that includes a first testing stage, a machining stage, and a second testing stage. In the first testing stage, a vibration modal analysis is performed on a work piece clamped to the multi-purpose vacuum clamp table100. The camshaft310is rotated to the bottom-dead-center position, causing the top surface of the inner vice assembly110to drop below the top surface of the outer vice assembly120. A vacuum pressure is applied to the vacuum channel400in the outer vice assembly120to clamp the work piece to the outer vice assembly120around the perimeter edge of the work piece. The work piece does not touch the inner vice assembly110when the inner vice assembly110is in the lowered position. Therefore, the clamp table100is optimally configured for performing vibrational modal analysis by placing uniform constraints along the perimeter of the work piece while leaving the lower surface of the work piece unconstrained.

Next, vibrational modal analysis is performed to determine if machining operations are required to change the resonant characteristics of the work-piece. If the results of the vibrational modal analysis determine a change to the resonant characteristics of the work piece is necessary, then the machining stage is performed. Initially, a machinist rotates the camshaft310to its top-dead-center position. The support plate135of the outer vice assembly120and the inner vice assembly110are moved up such that the top surface of the inner vice assembly110is coplanar with the top surface of the outer vice assembly120. A vacuum pressure connected to the inner vice assembly110is switched on so that the work piece is clamped to the top surface of the inner vice assembly110. The work piece is now clamped to both the inner and the outer vice assemblies110,120. The top surface of the inner vice assembly110and the top surface of the outer vice assembly120provide a rigid, coplanar support for the work piece during machining operations.

After the machining operations are complete, the vacuum is disconnected from the inner vice assembly110, thereby releasing the clamping force between the work piece and the inner vice assembly110. The machinist rotates the camshaft310to its bottom-dead-center position, thereby lowering the top surface of the inner vice assembly110below the top surface of the outer vice assembly120. Subsequently, a second vibrational modal analysis is performed to check the new resonant characteristics of the work piece.

By not disconnecting the vacuum pressure from the outer vice assembly120during the test-machine-test cycle, the boundary constraints on the work piece are maintained throughout the cycle. Therefore, the second vibrational modal analysis is performed using the same boundary conditions as the first vibrational modal analysis. This allows for accurate comparison of the results of the second vibrational analysis to the results of the first vibrational analysis. However, it is contemplated that the clamp table may be used for one or more of the two testing phases and the machine phase.