Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2001-05-29
2003-05-27
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S086250
Reexamination Certificate
active
06570120
ABSTRACT:
FIELD OF THE INVENTION
The invention generally concerns an apparatus for resistance welding and more particularly an apparatus for resistance welding with different welding currents.
BACKGROUND OF THE INVENTION
A typical form of apparatus for resistance welding includes a welding transformer with a primary side and a secondary side. Arranged on the secondary side are two welding electrodes which are connected to the welding transformer. The welding electrodes are also each arranged on a respective operating or positioning arm, of which at least one is movable by way of an actuator drive. Also arranged at the primary side is a regulating arrangement with electronically controllable switching members disposed between the welding transformer and the connection to a three-phase mains network. The regulating arrangement serves to regulate the voltage at the primary side.
Such an apparatus is intended for a resistance welding procedure in which the welding electrodes are pressed with a certain contact pressure force against both sides of the articles to be welded, for a certain period of time. For example plates or sheets can be welded together with that apparatus.
Conventional arrangements for producing a welding current in the case of ac resistance welding apparatuses are well known from the state of the art. In one such arrangement a voltage is tapped off between two connections of the three-phase network and fed to the welding transformer. Provided on the primary side of the welding transformer are two thyristors which are arranged parallel to each other with opposite forward directions and which form electronic switching members. The two connections can be connected to two phases of the three-phase network or to the neutral conductor and a phase of the network which usually involves a network frequency of 50 Hz or 60 Hz.
The above-discussed arrangement with the thyristors is inexpensive and generally reliable in operation. It will be noted however that the regulating options afforded with that arrangement are limited as the thyristors are switched only once in each half-wave of the current on the primary side and are switched off only at the zero-passage of the current on the primary side. Such an arrangement also suffers from further disadvantages which are generally known in this context and which therefore do not need to be further discussed herein.
The disadvantages of the above-discussed arrangement can be avoided by a resistance welding apparatus which has been offered in the past by the present patentees and which is operable to convert alternating current into direct current. That apparatus comprises a rectifier with a B-6 circuit, that is to say a bridge circuit with six diodes, with an inverting converter, also referred to as inverter, connected on the output side. The apparatus also has a smoothing capacitor. The voltage of all three phases, which is tapped off from the three-phase network, is rectified by the rectifier and chopped and inverted by the inverter. Depending on the capacity and operational efficiency of the inverter it generates a series of rectangular pulses of alternate polarity in the medium-frequency range, which can be referred to for the sake of brevity as the MF-range, at for example 1000 Hz, or in the high-frequency range, which can be referred to for the sake of brevity as the HF-range, at for example 20,000 Hz. In those apparatuses that voltage is applied to the primary side of an MF-transformer or HF-transformer designed for the corresponding frequency. The medium-frequency or high-frequency transformer voltage is rectified on the secondary side by high-current diodes and fed to the welding electrodes. The mode of operation of that apparatus is generally known and therefore does not need to be further discussed herein.
The essential parameters in regard to resistance welding are on the one hand the welding current and on the other hand the welding time for which the welding current flows. In the above-discussed apparatuses both parameters are controlled by a welding control system. A further parameter however which also has a crucial influence on resistance welding is the contact pressure force which has already been referred to hereinbefore. Hereinafter in this specification the contact pressure force will be referred to generally as the welding force.
In the above-discussed prior apparatuses the welding force is afforded for example by a pneumatic or hydraulic actuating drive for moving one of the control arms on which one of the welding electrodes is arranged, while the other control arm with the other welding electrode is arranged fixedly and rigidly. Instead of the pneumatic or hydraulic drive however it is also possible for the control arm to be moved by means of an electric motor. In comparison with the pneumatic or hydraulic drives, an electric motor drive is faster, more precise and can be better controlled. Furthermore, the wear of the individual components which make up the welding tongs assembly formed by the control arms and the welding electrodes, and in particular the wear suffered by the welding electrodes, is less by virtue of the controllable movement and the force settings which can be achieved in that case.
The electric motor in the above-discussed prior apparatuses is controlled by a drive control system which is provided exclusively for controlling the electric motor. In that case, the drive control system co-operates with the welding control system in such a way that matching of the above-indicated parameters in order to achieve a good welding result is possible only at the cost of a relatively high level of complication. In addition, the two separate control systems, more specifically the drive control system and the welding control system, means that the costs in terms of material for producing the apparatuses in question are also high.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus for resistance welding by means of frequency inverter technology in which the drive control system for the drive is simplified so that the apparatus production costs are reduced.
Another object of the present invention is to provide an apparatus for resistance welding which is of a simplified structure generally and also in terms of its operating systems while nonetheless affording reliable operational results.
Still another object of the present invention is to provide a resistance welding apparatus capable of implementing welding procedures using different welding currents, which affords enhanced versatility of operation without the requirement for complicated operating and control systems.
Yet another object of the present invention is to provide a resistance welding apparatus which is so designed that components which are present in the apparatus can be used for more than just one operational purpose.
In accordance with the principles of the present invention the foregoing and other objects are attained by an apparatus for resistance welding, with different welding currents, comprising a welding transformer having a primary side and a secondary side, and first and second welding electrodes which are connected at the secondary side to the welding transformer and which are each arranged on a respective control or positioning arm. The apparatus has at least one drive for moving at least one of the control arms. A regulating and control arrangement which is connected on the primary side between the welding transformer and a connection to a three-phase network comprises a rectifier circuit connected to all three phases of the three-phase network and a controllable welding inverter which converts the rectified voltage into voltage pulses of alternating polarity at a predetermined frequency. At least one electronic unit of the rectifier circuit and/or the welding inverter is connected to the drive for controlling and/or powering the drive.
The at least one drive for moving at least one of the control arms may be more particularly an electric motor, and the movement of the control arms may be either a di
Heinemann Axel
Marek Udo
Matuschek Ulrich
Metzen Norbert
Pöll Karl
Choate Hall & Stewart
Matuschek Messtechnik GmbH
Shaw Clifford C.
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