Pressing device for joining workpieces

Details Pressing device for joining workpieces Pressing device for joining workpieces

1998-02-20

2001-03-20

Hughes, S. Thomas (Department: 3726)

Metal working

Means to assemble or disassemble

With means to regulate operation by use of templet, tape,...

C029S702000, C029S709000, C029S714000, C029S720000, C029S508000, C072S015100

Reexamination Certificate

active

06202290

ABSTRACT:

The invention concerns a pressing device for joining workpieces, in particular press fittings to a pipe, having an electric drive and a pressing tool attached replaceably thereto.
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 pressed radially together, 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. An electric drive, which can be combined with a hydraulic unit, is provided for this movement.
In the case of the known pressing devices, the jaw drive always travels toward a specific, constant final force. Final force limiters, for example in the form of an overpressure valve in the case of a hydraulic pressure cylinder, a torque coupling in the case of a rotating drive, or an overcurrent release in the case of an electric motor, are provided for this purpose. To ensure that a complete pressing takes place in all circumstances, the final force is set sufficiently high that it lies above the maximum force which normally occurs. The reason is that inaccuracies in the final force limiter have a strong effect on the final force that can actually be attained, since final force limiters do not measure directly the force proceeding from the drive, but rather a converted magnitude which represents only a fraction of the actual drive force. The high final force leads to wear on the bearing points of the pressing jaws, and on all parts acted upon by the drive.
The problems described above occur even if the drive is matched to the particular pressing tool joined to it, and also to the workpieces to be pressed therewith. Usually, however, a specific drive is used for a tool set made up of a plurality of pressing tools which are configured for pressing different press fittings. For this purpose, the drive can easily be detached from the particular pressing tool and attached to another pressing tool. In order for the drive to be usable for all the pressing tools of a tool set, the drive and the final force limiter are designed so that the drive and the final force achievable therewith are sufficient for pressing with even the largest pressing tool. The problems described above occur even with these pressing tools. They become more serious as the pressing tool becomes smaller, and thus as the deformation work to be performed decreases. The final force at which the drive is shut down is then far greater than the actual force needed. As a result, the pressing tools for small workpiece diameters must be grossly overdimensioned, i.e. they are heavier and more costly than necessary, and are subject to severe wear. But since it would be even more expensive to provide a matched drive for each pressing jaw unit (not to mention transport problems), this is perforce accepted. In previously unpublished German Patent Application 196 33 199.4, the applicant proposes, in order to eliminate the aforesaid problems, equipping the control device of the drive with an output control device which generates an output profile for the drive such that the pressing tool has, at least at the completion of pressing, less kinetic energy than without an output controller. In addition, a limit switch is provided in order to shut down the drive, at the latest, when the final pressed position is reached. The result of this feature is that the maximum force which acts on the parts moved by the drive is substantially reduced, and ideally is the same as the maximum force to be applied when deforming the workpieces. Because the jaw drive is shut down as a function of position and not as a function of force, and because the kinetic energy is reduced and ideally equals zero at the completion of pressing, high forces resulting from kinetic energy still present at that time do not occur after shutdown of the drive. The pressing tools can accordingly, in particular in the lower size range, be of much lighter dimensions, and wear is also considerably less.
In an exemplifying embodiment, the output controller is concretely influenced by a clearance sensor on the pressing tool, which detects the clearance between the end faces of the pressing jaws of the pressing tool. The result, with a corresponding circuit device, is that the output of the electric drive is reduced in a first phase by way of the phase angle. The switchover to the time phase without such reduction occurs later, the smaller the masses moved by the drive and the softer the combination of press fitting plus pipe, i.e. the smaller the diameter of said combination. Each pressing tool thus has associated with it an individually matched clearance sensor which, when the drive is connected to the particular pressing tool, ensures an appropriately matched output profile for the drive, with the purpose of building up as little kinetic energy as possible, toward the completion of pressing, in the masses moved by the drive.
It is the object of the invention to configure a pressing device of the kind cited initially in such a way that the pressing device experiences less load and is subject to less wear than the known pressing devices.
This object is achieved according to the invention, in a first alternative, by the fact that control parameters for the drive are stored on the pressing tool, preferably in a memory chip.
This approach opens up the possibility of associating with each pressing tool optimally matched control parameters for an output controller, with the goal of minimizing the load on the pressing tool by means of an output profile which is matched to the particular pressing tool. In this context, the term “control parameters” is to be understood generally. It can refer, for example, to certain coefficients which are associated with a function stored in the drive. The term “control parameters” can also, however, go further, and for example can also comprise the variables of a function or the function itself, which then, when the pressing tool and drive are connected, are passed on to the latter. The output profile can also be stored in the form of points, or in any other desired form. All that is important is that the control parameters are suitable for influencing the drive, for example by way of the phase angle, in such a way that a desired output is achieved.
The connection between the memory chip and a part of an output controller located on the drive can be accomplished by means of an electrical circuit which is automatically closed when the respective pressing tool is attached to the drive. There also exists, however, the possibility of a wireless transfer of control parameters, for example electromagnetically or optically.
There theoretically also exists the possibility of configuring the entire program for influencing the output profile, but at least the control parameters, in downloadable fashion in a control memory of an output controller. The memory chip then, however, requires a relatively large memory capacity.
In a second alternative, the object is achieved, according to the invention, by the fact that multiple output profiles are stored, one of which can in each case be set. This can be done, for example, by providing a manually actuable switch arrangement for setting the relevant output profile. It is preferred, however, for setting to be accomplished automatically, and, for this purpose, for the pressing tool to have a code which determines the output profile when the code is detected. The code defines which of the stored output profiles is utilized for the drive. This also opens up the possibility o

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