Metal working – Means to assemble or disassemble – With means to regulate operation by use of templet – tape,...
Reexamination Certificate
1998-02-20
2001-06-05
Cuda, Irene (Department: 3726)
Metal working
Means to assemble or disassemble
With means to regulate operation by use of templet, tape,...
C029S702000, C029S706000, C029S708000, C029S282000
Reexamination Certificate
active
06240626
ABSTRACT:
The invention concerns a pressing device for joining workpieces, having a pressing tool and a motorized drive for actuation of the pressing tool over a pressing distance, and having a control device which has a drive control device for influencing the drive.
It is known, in order to join pipes, to use sleeve-like press fittings which, in order to produce a pipe joint, are slid over the pipe ends and then radially compressed, both the press fitting and the pipe being plastically deformed. Pipe joints of this kind and the pertinent press fittings are known, for example, from DE-C-11 87 870, EP-B-0 361 630, and EP-A-0 582 543.
Pressing takes place with the aid of pressing devices such as are known in various embodiments, for example from DE-C-21 36 782, DE-A-34 23 283, EP-A-0 451 806, EP-B-0 361 630, and DE-U-296 04 276.5. The pressing devices have a pressing jaw unit having at least two or sometimes more pressing jaws, which during the pressing operation are moved radially inward to form a substantially closed pressing space. The pressing tool is attached replaceably to the other part of the pressing device so that a pressing tool matching the diameter of the press fitting can be used in each case.
An electric drive, which additionally can also be combined with a hydraulic unit, is provided for movement of the pressing jaws. In the context of a pressing operation, the drive travels over a pressing distance which usually initially begins with a takeup distance before the pressing jaws come into contact against the press fitting. Over the rest of the pressing distance, the press fitting and pipe end are deformed until a final pressed position is reached. Here the drive is automatically shut down, either by means of a force limiting element, for example in the form of a torque coupling, or a hydraulic switching valve, or by means of a limit switch in combination with a jaw closure sensor on the pressing tool (DE-U-296 02 240.3).
The purpose of each pressing is to avoid mispressings, since they generally result in a leaky pipe connection, which in the case of liquid-carrying pipelines can cause major damage. Mispressings can have various causes; said causes for the most part cannot be detected with the known pressing devices, so that a mispressing effected because of such a cause goes unnoticed.
A situation of this kind exists when a pressing device is used, with a certain pressing tool, to press a press fitting which does not match the pressing tool, i.e. is either too large or too small. In both cases, mispressings occur, which can result in leaks. The mispressings cannot be noticed since both the final force and the final pressed position are reached.
Creasing can also occur in the region of the end faces of two adjacent pressing jaws. Since it usually occurs at the end of the pressing distance, it is difficult for the operator to notice, particularly if the pressing device is switched off by means of a force limiting element. Small creases may also not be noticed even if a limit switch is provided, particularly if the limit switch is arranged in the region of two pressing jaws where creasing does not occur. This applies if foreign objects such as dirt or other solid particles become lodged in the pressing tool, and jam the movement of the pressing jaws.
Mispressings can also occur if a pipe end is not inserted sufficiently into the press fitting. In pressing devices which do not have a special monitoring element for the purpose, this also goes unnoticed and usually results in a mispressing.
It may also happen that a breakage occurs in the force-affected parts of the drive. This can result in a sudden elevation in the rotation speed, causing the pressing device to constitute a hazard.
A special problem is represented by interruption of a pressing operation, for example due to a power failure. When pressing is then resumed, a long takeup distance must be covered, which takes time and, depending on how the drive is controlled, lead to the buildup of high kinetic energies, with the risk that the pressing jaws will strike abruptly against the only partly pressed press fitting.
It is the object of the invention to configure a pressing device of the kind cited initially in such a way that mispressing are eliminated with greater reliability, or at least can be recognized.
This object is achieved, according to the invention, by means of a pressing device having the following features:
the drive control device has a malfunction detection device;
the malfunction detection device has an actual value sensor;
the actual value sensor is suitable for detecting, as the actual value, a physical magnitude which is correlated with the pressing resistance;
at least one limit value profile is retained in the malfunction detection device;
the malfunction detection device has a malfunction comparison device which, during a pressing, checks whether the particular actual value lies on the permissible or impermissible side of the pertinent limit value profile;
the malfunction detection device comprises a signal device and/or a shutdown device for the drive, which are/is activated if the actual value lies on the impermissible side of the limit value.
Preferably at least one upper and at least one lower limit value profile are retained, constituting a limit value corridor. These can also be limit values which remain constant. It is preferable, however, for the limit value profiles to be matched to the profile of the actual value for a correct pressing, constituting a limit value corridor.
The basic idea of the invention is thus, in the case of a pressing device, of the species, to provide a malfunction detection device which, when a physical magnitude correlating with the pressing resistance deviates from a standard profile, leads to creation of a signal and/or to a shutdown of the drive. In this context, the signal can be created visibly or audibly, in the simplest case as the sounding or flashing of an alarm light or alarm buzzer, but also, depending on the type of malfunction, as a differentiated signal or even a display with a readable malfunction message, or in the form of a spoken output. The operator thus receives more or less specific information that a malfunction is present and that the pressing operation should therefore be interrupted for further checking. Instead of or in combination with the signal, automatic shutdown of the drive can also occur, so that the pressing operation can at least not be continued immediately. It is evident that the malfunction detection device according to the invention yields much greater protection against mispressings, which is extraordinarily important in terms of the great potential for damage as a result of such mispressings.
The physical magnitude correlating with the pressing resistance is advantageously selected to match the characteristics of the drive. For drives that are not output-controlled, an obvious choice is to detect the rotation speed of the drive, since it changes with the pressing resistance. For example, if jamming of the drive occurs before the end of the pressing distance due to creasing of the press fitting or the presence of foreign objects, the rotation speed departs from the permissible limit value corridor downward; in such cases it is advisable to activate the shutdown device. A considerable drop in rotation speed with departure from the limit value corridor is also a consequence of pressing a press fitting that is too large for the pressing jaws. The rotation speed rises, conversely, when too small a press fitting is acted upon, when the pipe end is not inserted far enough into the press fitting, or when a breakage occurs.
Instead of detecting the rotation speed as the physical magnitude, it is also possible to directly detect the force being applied, for example by means of strain gauges, or, analogously, the torque being applied. Lastly, the average electrical current is suitable as an indicator of the pressing resistance, since the former also changes along with the latter.
In a further embodiment of the invention, provision is mad
Cuda Irene
Green Anthony L.
Liniak, Berenato, Longacre & White LLC
Novopress GmbH Pressen und Presswerkzauge & Co. KG
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