Work holders – With fluid means – Cylinder-piston means in series with additional positioning...
Reexamination Certificate
1998-07-29
2001-03-27
Scherbel, David A. (Department: 3723)
Work holders
With fluid means
Cylinder-piston means in series with additional positioning...
C269S032000
Reexamination Certificate
active
06206353
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a clamping device or fastening device for structural components.
2. Description of the Related Art
Fastening devices of this type are used for various technical applications for temporarily securing or holding workpieces. These devices must operate quickly and reliably and must ensure frequent load changes without maintenance over long periods of time.
In this regard, known in the prior art from DE 35 28 337 C2 is a clamping device for structural components in which a clamping rod is a component of a piston which is acted upon by a pressurized fluid, such as air or hydraulic liquid, and is axially displaceable in a cylinder. The end of the clamping rod facing away from the piston is connected to a bolt which supports two pairs of rollers. The rollers of the outer pair of rollers travel in straight slots which extend parallel to the longitudinal axis of the clamping rod. The rollers of the inner pair of rollers travel in arc-shaped slots of a clamping arm which can pivot about an axis. The guide slot may also possibly be curved in an arc-shaped manner.
This configuration is supposed to prevent uncontrollably high clamping forces when self-locking occurs in the end position. However, this construction requires a complicated mechanism and, consequently, its manufacture is also complicated Because of the presence of the guide slot, this clamping device has a large structural width. Because of the direct lever transmission, the travel distance of the piston is long and, thus, the construction of the device is inevitably also long. The bent-lever principle is employed in a modified form in this case.
In order to reach the self-locking position in a clamping device operating in accordance with the bent-lever principle, it is necessary to move the bracket forming a component of the bent-lever arrangement above the upper dead center position. This causes the force in the bracket to be increased theoretically up to infinity. In practice, the force is limited by the elastic deformations in the entire system. However, this means that the system is subject to wear. Moreover, it cannot be ensured that in the case of high clamping forces the clamping arm is actually pivoted past the dead center point. The maximum clamping force is determined by the available energy, particularly compressed air. If the cylinder force prevailing in a compressed air cylinder is not sufficiently great in order to apply the necessary clamping force to the clamping arm, the bracket does not move past the dead center point and, thus, does not travel into the self-locking position.
DE 31 30 942 A1 discloses a clamping device for structural components which operates in accordance with the bent-lever principle. A bracket of resiliently yielding construction is hinged to the free end of a piston rod which is connected to a piston which is acted upon by a pressure medium. The bracket is additionally connected to a rigid bent lever which is coupled 90° offset to a clamping arm. The bracket is constructed in such a way that the distance of the coupling joints to the piston rod and the lever is adjustable.
The resilient bracket has the purpose of preventing infinitely high clamping forces. Consequently, only the clamping force can be limited in this clamping device, while a self-locking position cannot be reached. In addition, the fatigue strength and the durability of the bracket should pose problems. The bracket is also difficult to manufacture. Furthermore, the force limitation is dependent on the spring constant and the spring travel.
SUMMARY OF THE INVENTION
Therefore, it is the primary object of the present invention to provide a clamping device for structural components of the above-described type which is of simple construction and makes it possible to limit the force increase by using the bent-lever principle, while still ensuring that in the clamping position the self-locking action guarantees the clamping position even when the clamping energy fails.
In accordance with the present invention, the clamping device includes a clamping rod which can be displaced by pneumatic, hydraulic or electrical energy, and a clamping arm which can be pivoted from a clamping position into a ready position and vice versa. A rigid lever is rigidly connected through a pivot shaft to the clamping arm. A rigid bracket is rotatably coupled to the lever and to an end of the clamping rod The length of the rigid bracket between the coupling joints is greater than the distance between the coupling joint of the bracket with the lever and the longitudinal axis of the clamping rod in the ready position. The coupling joint between the bracket and the end of the clamping rod is supported on at least one roller which rolls on a forced guide means. The forced guide means has a length portion corresponding to the pivoting angle of the clamping arm between the ready position and the clamping position, wherein this length portion extends in a straight line parallel to the longitudinal axis of the clamping rod in the ready position, and an end portion which is concave toward the coupling joint between the lever and the bracket with the coupling joint being in the dead center position thereof. The concave end portion begins in front of a plane which extends through the coupling joint between the bracket and the lever when the coupling joint is in the dead center position thereof and perpendicularly of the longitudinal axis of the clamping rod in the ready position and the concave end portion ends behind this plane.
At the core of the present invention is the fact that the forced guide means for at least one roller arranged at the end of the clamping rod is provided with an end portion which is concave toward the coupling joint between the lever and the bracket in the dead center point thereof. This concave end portion begins a short distance in front of the plane which extends through the coupling joint between the lever and the bracket when this coupling joint is in the dead center point determined by the clamping position of the clamping arm, and this concave end portion ends behind this plane.
When the coupling joint between the bracket and the clamping rod reaches the beginning of the concave end portion in front of this plane, the clamping arm is in the clamping position and the maximum clamping force has been built up. No further force increase takes place. However, the clamping force which still continues to act on the clamping rod causes the coupling joint between the bracket and the clamping rod to be moved past the plane until this coupling joint has reached the end of the concave end portion located behind the plane. The maximum clamping force is always maintained during this movement. Behind the plane, the bracket is in the self-locking range. However, when the clamping energy is taken away in this position, the complete clamping force is maintained without losses.
Consequently, the special advantage provided by the invention is the fact that the force limitation is ensured in a simple manner by the concave end portion. This ensures a problem-free, self-locking action after passing the dead center point. In addition, the clamping device is of a very compact construction because the distance transmission between the lever and the bracket according to the present invention only requires a short travel distance of the clamping rod.
The present invention also makes it possible to adjust the pivoting angle of the clamping arm between the ready position and the clamping position as desired. Opening angles of especially 45°, 60°, 90° and 115° up to a maximum opening angle of 135° can be provided merely by using movement-limiting pieces or by replacing the clamping rod. Moreover, the clamping device can be provided without problems with an integrated position monitoring device.
The housing for supporting the clamping arm, the lever, the bracket and the clamping rod is constructed in such a way that an abutment cooperating with the clamping arm for securing the
Becker Karsten
Borgolte Uwe
Kordtomeikel Josef
Scherbel David A.
Shanley Daniel G.
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