Work holders – Work-underlying support – Support mounting means
Reexamination Certificate
2000-04-12
2001-08-14
Watson, Robert C. (Department: 3723)
Work holders
Work-underlying support
Support mounting means
Reexamination Certificate
active
06273410
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a support element for holding or supporting a workpiece in a machine tool, on a platform or the like. Such elements include a support bolt slideably mounted in a housing for supporting an unstable work piece.
BACKGROUND INFORMATION
U.S. Pat. No. 5,915,679 (KOHLERT) describes a workpiece holding element with a support bolt slideably movable and guided in a bore of a housing. Once the support bolt has reached its clamping or rather support position in response to an air stream, a locking piston is pressed, for example by a hydraulic force, against the support bolt in a direction perpendicularly to the longitudinal bolt axis to hold the support bolt in place.
When clamping unstable work pieces on a machine tool or on pallets, it is necessary to perform the clamping in such a way that the work pieces are not deformed and that a located workpiece is not displaced out of its precise, located position. Thus, excessive forces may not be applied to the work pieces. However, it is nevertheless necessary that the work pieces are in a stable position for the machining operation. Especially for unstable work pieces a repeatable, fine adjustment of the force applied to the workpiece to keep it in place is required and such requirement can be satisfied only by special support elements. Normally, more than three support points are required. The support elements must be so constructed that the support bolt can easily be positioned to contact the workpiece and then to lock the support bolt in the workpiece contacting position without deforming the and without displacing the workpiece.
Other conventional workpiece holding elements are equipped with screws, springs or wedges for adjusting and holding the support bolt. These elements are mechanically operated, whereby so-called stretch belts may be used. However, hydraulically operated support elements are also known. Generally, the locking takes place either by maintaining the pressure that moves the support bolt or by a laterally extending force applied to the support bolt. In the above mentioned U.S. Patent to Kohlert the support bolt is mounted in a housing and pneumatically movable into a workpiece contact by air that is introduced into the housing bore that guides the support bolt. The air that moves the support bolt is passing through special guide channels and develops a determinable or controllable contact force between the support bolt and the work piece. The locking of the support bolt is accomplished by a hydraulically operated locking piston extending perpendicularly to the length of the support bolt and pressing the support bolt against the wall of the housing bore.
The hydraulic forces effective through the locking piston on the support bolt during a machining operation assure an absolutely safe holding or locking of the support bolt. This feature means that the frictional forces which are effective on the support bolt by the pressure exerted by the piston must be larger than the reaction forces from the workpiece.
The supporting element of my earlier invention performs its function well. However, there is room for improvement, especially with regard to simplifying the construction and avoiding the need for both a hydraulic source of pressure and a pneumatic source of pressure.
OBJECTS OF THE INVENTION
In view of the above it is the aim of the invention to achieve the following objects singly or in combination:
to construct a workpiece support element that is capable of placing a support bolt into contact with the workpiece without a pneumatic source of pressure;
to assure that contacting the workpiece by the support bolt will not disturb in any manner the work piece;
to make sure that the sum of all frictional pressure forces caused by the locking force applied to the support bolt by the locking piston is larger at all times than the pressure force applied to the locking piston;
to lock the locking piston in the cocked state in such a way in the housing that the locking piston becomes in effect a fixed element of the housing so that it will maintain the locking pressure without any elastic reaction by the locking piston and/or the support bolt so that a precise maintenance of the workpiece position is assured at all times.
SUMMARY OF THE INVENTION
A supporting element according to the invention is characterized by the combination of the following features. A support bolt or pin is movably guided in a housing and maintained in a workpiece supporting position by a locking piston which is movable in a direction at right angles relative to the support direction. The support bolt or pin is guided in a preferably dead-end bore of the housing. The bore such as a dead-end bore is provided with a recess in the housing wall extending along the dead-end bore over the range of movement of the support bolt. The recess has a circumferential width that is smaller than the diameter of the support bolt. The recess has edges that are preferably provided with a concave bevel or chamfer to form two housing pressure surfaces or housing pressure take-up members in contact with the support bolt. The locking piston is provided with a second recess also having a diameter smaller than the diameter of the support bolt so that two locking piston segments are formed having inwardly directed edges extending lengthwise of the support bolt in the motion direction of the support bolt when it is brought into a working position or removed out of a working position. The inwardly directed edges of the piston segments are also preferably concave to form two piston pressure surfaces or piston pressure take-up members for contacting the support bolt. Thus, in the locking position of the locking piston, the support bolt is clamped between the housing pressure take-up members and the piston pressure take-up members. These pressure take-up members provide relatively small contact areas between the support bolt and the housing and between the support bolt and the locking piston. These small surface areas of the pressure takeup members assure a substantially larger pressure force application to the support bolt than is possible when the locking force is distributed over the full cylindrical surface of the support bolt. This feature of the invention takes advantage of the fact that the pressure, expressed as force per surface area, becomes larger when the surface area becomes smaller.
It is an advantage of the invention that in the clamping state due to the reaction forces, a moment is applied to the locking segments of the locking piston. This moment bends the locking segments radially outwardly until the support projections of the locking segments solidly contact the cylinder wall in the housing for arresting the locking piston in the cylinder of the housing.
REFERENCES:
patent: 5915679 (1999-06-01), Kohlert
Fasse W. F.
Fasse W. G.
Watson Robert C.
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