Presses – Methods
Patent
1983-01-12
1984-02-07
Wilhite, Billy J.
Presses
Methods
100 43, 100 53, 192129R, B30B 1528
Patent
active
044296274
DESCRIPTION:
BRIEF SUMMARY
The present invention relates in general to presses, and, in particular, to a tool guard for presses. More precisely, the present invention relates to a method and an apparatus for monitoring the pressure stroke in a press with the intention of preventing damage to the press, the press tool or the workpiece.
Presses which operate with high or extremely high forces are sensitive in so far as relatively simple operating errors may result in destruction of the press tool, and, in certain cases, of the press itself. In view of the fact that capital costs for a single tool for such presses may amount to tens of thousands of dollars, it is, naturally, desirable that such operating errors be prevented or at least that the press be stopped before such an error has caused any damage to the tool, the press and/or the workpiece.
Thus, there is a clearly documented need of a protective device for such presses, a need which has persisted for a considerable time. Nevertheless, no satisfactory solution to this problem has been put forward in the art.
Granted, it is previously known in the art to sense the force exerted by a press during its stroke and to compare this force with a maximum permitted force in the press for the purposes of arresting the pressure stroke as soon as the sensed force exceeds that permitted. Unfortunately, this technique does not prevent destruction of the press tool, since a considerably weaker force than the maximum permitted may give rise to such undesirable damage during a considerable part of the pressure stroke. This prior art technique can possibly provide protection for the press itself but, thus, not for the tool, nor for the workpiece.
The object of the present invention is, therefore, among other things to realize a method and an apparatus of the type disclosed by way of introduction, these making it possible to prevent damage to the tool, press and workpiece.
According to the invention, the press force exercised by the press is continually sensed during each pressure stroke. Moreover, the instantaneous value of the force is compared with a previously produced reference force value at each one of mutually subsequent positions of the one press platen of the press in relation to its other press platen during the entire stroke. Finally, the press motion is directly arrested if, on comparison, the sensed force value in any position deviates from the reference force value of that position by more than a predetermined amount.
The apparatus for reducing this method to practice comprises at least a first measuring transducer which continuously measures the force exerted by the press during the pressure stroke thereof, at least one positional transducer which continuously senses the position of the one press platen of the press in relation to its other press platen, and a monitoring unit containing a memory, said unit being connected to said transducers, being operative, during the press motion, to compare the instantaneous values of the force with a previously produced, memory-stored reference value at each one of mutually subsequent positions of the one press platen of the press in relation to its other press platen during the pressure stroke, and being operative to directly discontinue the press motion if, on such comparison, the sensed force value at any position deviates from the reference value by more than a predetermined amount.
The nature of the present invention and its aspects will be more readily understood from the following description of the accompanying drawings, and discussion relating thereto.
In the accompanying drawings:
FIG. 1 is a block diagram of one embodiment of the apparatus according to the present invention;
FIGS. 2a and 2b are diagrams showing the pressure increase during a pressure stroke, as well as the motion differences of the upper press platen; and
FIG. 3a and 3b are flow diagrams showing the mode of operation of one embodiment of the apparatus according to the present invention.
The embodiment of the apparatus according to the present invention shown in FIG.
REFERENCES:
WO81/00824 (Spalthoff), Apr. 2, 1981.
Hapgood Cyrus S.
Wilhite Billy J.
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