Process and Apparatus for Actuating the Ram Weight Compensation Mechanism of a Press

The present invention relates to a process and apparatus for the positive actuation of a weight compensating mechanism for the ram associated with an upper die of a press.

In case of presses of the type disclosed in British Pat. No. 1,348,627 or U.S. Pat. No. 3,115,086 having devices for compensating for the weight of the ram with upper die, equipped with an automatic device for adjusting the value required for counterbalancing the weight of the ram with upper die, for example to adjust the gas pressure in a cylinder-piston unit, there is the danger that the press is set in operation if the weight compensating mechanism for the ram with upper die is not correctly set. The incorrect setting is primarily due to the fact that the operator intentionally or inadvertently omits the operation of this automatic mechanism, which result in disturbances in the working process of the press or damage to the press.

Therefore, it is an object of the present invention to provide a process and apparatus by means of which the device for setting the correct value for the weight compensation mechanism is operated independently of the operator's will.

The present invention starts with the realization that this apparatus must be actuated if the tool set used in the press has been changed, since this results practically in all cases in an alteration of the weight to be counterbalanced. Accordingly, the invention is based on the consideration that it is necessary to positively detect the changing of the tool set and, in dependence thereon, to positively actuate the device for setting the correct value.

On the one hand, the operation of the ram adjusting mechanism of the press is a step indicating a tool set change, because an actuation of the ram adjusting mechanism is required for extending the tool set out of the press working zone and for moving the tool holding plate toward the tool set for mounting one of the tools. On the other hand, the introduction of at least one support die into the press working zone is also a step indicating a tool set change, because at least one support die must be utilized for safety reasons during a tool set change while operating within the press working zone. Furthermore, the at least one-time switching of a sensor switch at the press table or at a tool holding plate is a step indicating a tool set change, because such a sensor switch is operated only if a tool is detached from the tool holding plate or from the press table or if a tool is attached thereto. Finally, the separation of at least one plug-in connection to the tool set, serving for feeding current to at least one tool of the tool set, is a step indicating a tool set change, because only during such a procedure is there a need for severing such plug-in connections. In accordance with the present invention, the various abovedescribed steps can be utilized individually or in combination to effect the positive actuation of the device for setting the correct value.

In accordance with a feature of the present invention, a blocking mechanism is actuated which serves for preventing the engagement of the clutch and the release of the brake for the working operation. It is understood that such a blocking mechanism still makes it possible, if necessary, to move the drive into a predetermined position, e.g. upper dead center, for example in slow motion or at reduced speed or with a reduced transmittable torque as is known in the art. In this predetermined position, the setting of the correct value for the weight compensating mechanism is to be effected. However, the blocking mechanism must make it impossible to conduct operating strokes of the press by a corresponding influence on the clutch and brake.

According to the present invention the method may be effected by providing a switching arrangement, for example, at a press, wherein the operation of the ram adjusting mechanism or one of the other aforementioned operations, actuates a bistable flip-flop connected on the output side with an input of an AND gate circuit and with a switch for actuating the blocking mechanism and maintains same. The other inputs of the AND gate circuit are connected to signal generators for the existence of the remaining conditions. The output of the AND gate circuit controls the stepping or control mechanism for the weight compensating mechanism and sets the same in operation. After an operating cycle of the stepping or control mechanism has been completed, the flip-flop is reset, whereby the blocking mechanism is deactivated. Thereafter, it is possible for the press to execute working strokes triggered automatically or arbitrarily.

These and further objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention, and wherein:

the single FIGURE is a block diagram of a control system for actuating the ram weight compensation mechanism of a press.

Referring now to the single FIGURE, the control system of the present invention includes at least one signal generator 100, 101 and 102 wherein the signal generator 100, for example, provides an output in response to a tool change of the press, the signal generator 101 provides an output in response to the operation of the ram adjusting mechanism, and the signal generator 102 provides an output in response to the introduction of at least one support die into the press working zone. Alternatively, the signal generators may be individually triggered in response to the switching of a sensor switch at the press table or at a tool holding plate or the separation of at least one plug-in connection to the tool set. As shown, the signal generators are connected to a bistable multivibrator or flip-flop 103 whereby the output from any one of the signal generators serves for setting the flip-flop 103 so as to provide an output therefrom. The output of the flip-flop 103 is applied to one input of an AND gate 104 and to a switch device 105 of a blocking mechanism. The switching device is arranged to actuate the blocking mechanism so that operation of the press is prevented. The switching device 105 may be connected, for example, in the circuit of the operating elements such as electromagnets of the pressure medium valves which operate the brake and clutch mechanisms of the press. Accordingly, operation of the switch device 105 of the blocking mechanism when the flip-flop 103 provides an output, results in activation of the blocking mechanism so as to engage the brake and prevent engagement of the clutch. Suitable control circuits for a clutch and brake of a press or similar mechanism are disclosed in U.S. Pat. No. 2,816,635 and 2,939,973. As disclosed in such patents, appropriate operation of the clutch and brake controls may be effective to engage a brake and cause disengagement or relieving of a clutch.

The control circuit as illustrated in the FIGURE also includes signal generators 106, 107, 108, 109 each of which is connected with a respective input of the AND gate 104. The signal generators serve for sensing the conditions necessary for actuating the ram weight compensation device. For example, the signal generator 106 may be arranged for sensing the condition that the selector switch is in operating position and for providing an output in response to such sensed condition. The selector switch is generally a manually operated switch having a plurality of positions including an off position and at least one operating position. The signal generator 107 may be responsive to the condition that the ram is in the upper dead center position, i.e. the drive is in a predetermined position, whereas the signal generators 108 and 109 may be responsive to the conditions that the clutch is relieved or disengaged and that the brake is engaged, respectively. Here again, the signal generators 107 to 109 provide an output to the AND gate 104 in response to the sensed condition. Alternatively, the signal generators 107 or other of the signal generators may be utilized to sense other conditions such as the ram adjusting mechanism has been operated, the support die has been inserted a sensor switch has been operated or a plug-in connection has been severed with such sensed condition being preferably utilized with one or more of the other indicated sensed conditions for control purposes. It is noted that signal generators 100-102 and 106-109 may be constructed in a manner known in the art so as to be responsive to appropriately sensed conditions. When each of the signal generators 106-109 has sensed the appropriate condition and has generated an output which is delivered to the AND gate 104, the AND gate in response to the simultaneously applied input signals provides an output which activates a stepping or control mechanism 110 which may include a switch mechanism 20 for initiating a ram weight compensation device of the type disclosed for example in British Pat. No. 1,348,627, U.S. Pat. No. 3,115,086 or in the commonly assigned copending application by Eugen Waller, Rolf Kellenbenz, Burkhard Schumann, Wolfram Buchler and Franz Schneider, Ser. No. 561,166 entitled "Press With Hydraulic Overload Safety Device and Ram Weight Counterbalancing Mechanism", filed on even date with this application, the subject matter of the copending application being incorporated herein.

Upon completion of the operating cycle in which the ram weight is compensated, this completion is sensed by the stepping or control mechanism 110 and such mechanism provides an output for resetting the flip-flop 103 which in turn causes the switching over of the switch device 105 of the blocking mechanism. Accordingly, the brake is disengaged and the clutch may be engaged whereby the press is now ready again for operation. It is noted that the completion of the weight compensating operation may be sensed in a conventional manner or, for example, may be sensed in the manner as disclosed in the copending application whereby upon completion of the compensation operation, the flip-flop 103 is reset so as to enable further operation of the press.

While we have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.