Welding apparatus adapted to be connected to different electric power supply networks

The present invention relates to the field of electric arc welding, and more specifically to an electric arc welding apparatus according to the preamble of Claim 1.

Welding apparatus, of both the professional and the commercial type, which use high working currents, have the characteristic feature that they draw from the electric power supply network to which they are connected a very large amount of current and therefore power.

In the case where these apparatus are connected to low-power electric networks, such as for example domestic distribution networks, and when the maximum output current of the apparatus is required, the current drawn from the distribution network may be such as to trip the thermomagnetic protection switch with which all electric networks are normally equipped.

This results in the need for the welding operator to reset the thermomagnetic switch, restoring the power supply circuit, and to set manually the output welding-current value so that the apparatus does not require too high a current consumption which cannot be supported by the network.

Disadvantageously, this latter operation requires adjustment of the welding current so as to reduce the current drawn from the network to values such that it does not trip the abovementioned protection switch. Unfortunately, manual adjustment of this current is difficult to perform and does not allow the maximum optimum welding-current values to be easily reached.

The object of the present invention is therefore to provide a satisfactory solution to the abovementioned problem, ensuring optimum adjustment of the welding current depending on the output power of the electric power supply network to which the apparatus is connected in each case.

According to the present invention, this object is achieved by means of a welding apparatus having the characteristic features which are described in Claim 1.

Particular embodiments form the subject of the dependent claims.

hi brief, the present invention is based on the principle of automatic recognition of the type of power supply network to which the apparatus is connected and automatic limitation of the maximum output current of the welding apparatus so as to limit consequently the current drawn from the electric network.

This is achieved by providing means for connecting together the apparatus and the available electric power supply network, which are different depending on the type of electric network to which they may be connected.

By way of example, a welding apparatus may be designed for connection to a "low-power" electric supply network, such as a domestic distribution network, and for connection to a "high-power" supply network, such as an industrial distribution network. In the first case the network is commonly provided with electric sockets of the 16A Shuko type, so that the apparatus connection means must be equipped with a corresponding Shuko electric plug, while in the second case the network is commonly provided with 32 A industrial electric sockets, so that the apparatus connection means must be equipped with a corresponding industrial electric plug.

Since the two connectors are not compatible with each other, the apparatus according to the invention envisages a kit of cables for connection to the power supply, which can be selectively used to connect the apparatus to a power supply network depending on the type of network available in the room or premises where the apparatus must be used. Said cables have, at the network end, a dedicated connector in compliance with the standards for the specific type of network to which they are to be connected and, at the apparatus end, a connector with a common form adapted to co-operate with a matching panel connector of the apparatus.

Each connection cable has its own electrical identification characteristic which may be detected by a recognition circuit internal to the apparatus and arranged to recognise and signal the type of network to which the machine is connected on the basis of the connection cable used, for the benefit of a following welding-current control circuit.

Advantageously, in this way a circuit for controlling and adjusting the current of the apparatus will limit the maximum value of the output welding current depending on the signal received, without requiring manual intervention on the part of the operator.

Such an apparatus is for all intents and purposes compact, light and reliable and has optimum operating features.

Further characteristic features and advantages of the invention will be described more fully in the detailed description which follows of an embodiment thereof provided by way of a non-limiting example, with reference to the accompanying drawings, in which:

Figure 1 is an overall view of the apparatus according to the invention;

Figure 2 is a simplified block diagram of the apparatus according to the invention; and

Figure 3 is a detailed block diagram of the main electric modules of the apparatus according to the invention.

In the figures 10 denotes overall an electric arc welding apparatus intended to be connected to an electric power supply network and adapted to supply a predetermined welding current to a pair of arc generating electrodes.

Such an apparatus may be, for example, a single-phase inverter welder for electric arc welding using MMA coated electrodes and for welding using the direct-current TIG method.

Reference numeral 12 denotes a pair of panel connectors for connecting the electrodes to the machine, and the welding current may be manually set to a desired value by means of a knob or similar adjusting means 14. A display 16, such as an LED display for example,

allows monitoring, in real time, of the functions of the apparatus, such as, for example, setting of the welding current, selection of the electrode diameter, the actual welding current on the electrode, the existing power supply voltage, as well as the internal overheating temperature.

Reference numeral 20 denotes overall an electrical connection kit for connecting the apparatus to a power supply network available from among a plurality of existing types of network which are distinguished by different output power limits. For example, the figures shows two connection cables 22a and 22b, respectively, for connecting the apparatus to a domestic distribution network adapted to supply 16A current, or to an industrial distribution network adapted to supply 32A current.

Each connection cable has at one end a first connector 24a, 24b suitable for an electric socket device corresponding to the type of power supply network to which the cable is intended to be connected. At the opposite end the cables have a second similar connector 26a, 26b (namely with a structure common to both cables), adapted to be connected to a power circuit of the apparatus via a matching panel connector (not shown).

With reference to Figure 2, this shows in schematic form the logic configuration of the apparatus according to the invention.

RA and R _B respectively indicate high-power and low-power supply networks which are generally available in working environments where the apparatus is used.

The block indicated by 20 represents schematically the electrical connection kit with which the apparatus is provided and which comprises apparatus connection means (the connection cables 22a, 22b) which can be selectively connected to a power circuit of the apparatus 30 arranged to generate the welding current by drawing electric power from the power supply network.

Each of the connection means is adapted to be uniquely connected to a respective type of power supply network and connection thereof to the apparatus is detected by a current

control and regulating circuit 32, which controls the welding current supplied by the power circuit 30 depending on the type of power supply network to which the apparatus is connected, which is recognised by detecting the type of connection cable (22a or 22b) currently connected to the apparatus.

The configuration and operation of the apparatus are described below with reference to the diagram in Figure 3.

The cables 22a, 22b for connecting the apparatus to the available power supply network (which are two in number in the example, but they could also obviously be greater in number) have a connector 26a, 26b for connection to the power circuit 30 of the apparatus, which has a plurality of terminals for transferring the electric power 40 (in the figures indicated using standard terminology L, GND, N for the live, earth and neutral connections) and at least one pair of identification terminals 42.

The pair of identification terminals 42 define an electric two-terminal circuit, for example a two-terminal circuit which is able to assume one of a plurality of possible configurations of the resistive, inductive or capacitive type, which have an electric identification characteristic representative of the type of connection cable with which it is associated and therefore ultimately the type of electric power supply network to which this cable may be connected. This electric characteristic consists in the value of an electric parameter of the two-terminal circuit, for example the value of the electric impedance or resistance. In the currently preferred embodiment, in which identification of one of two possible power supply networks is required, the two-terminal circuit defined between the pair of terminals may be alternately a zero-impedance two-terminal circuit, i.e. a short-circuit, when the terminals are connected together, for example by means of a jumper, or an infinite- impedance two-terminal circuit, i.e. an open circuit, when the terminals are kept floating.

The connector on the apparatus is indicated by 28 and has, correspondingly, three terminals 40' for transferring the electric power (in the figures indicated using standard terminology L, GND, N for the live, earth and neutral connections) directly connected to the power circuit 30, and a pair of terminals 42' intended for connection to the

identification terminals 42 of the connectors 26a, 26b.

The pair of terminals 42' form part of a detection circuit 50, including a stage 50' for detecting the electrical identification characteristic, and a stage 50" for signalling the type of power supply network detected, adapted to emit an electric network recognition signal.

The stage 50' for detecting the electrical identification characteristic of the connection cable includes an actuating relay 52 connected to an associated excitation source 54 which, in a preferred embodiment, is incorporated in the power circuit 30, by means of a closed current path via the two-terminal circuit defined between the pair of identification terminals 42 of the connector 26a, 26b connected to the power circuit. Rl and Dl respectively indicate a current-limiting resistor and a diode for protecting the detection stage.

By means of the actuating relay 52 the detection stage 50' is connected to the signalling stage 50".

The signalling stage 50" includes a switching device 60 controlled by the relay 52 and adapted to switch between a first and a second operating position for selective application of a respective predetermined reference voltage to a microcontroller μC forming part of the control circuit 32. A fixed contact of the switch is connected to a terminal 70 of the control circuit 32 connected to a reference potential (earth). In the first operating position (rest position) the movable contact of the switch closes onto a floating terminal 72, while in the second operating position the movable contact closes onto a terminal 74.

The microcontroller μC of the control circuit 32 is arranged to provide at a signal output 76 a welding current command signal which is supplied to the power circuit 30.

This command" signal is dependent on the desired value of the welding current within a predetermined relative scale of values, defined via means 80 for manually setting the welding current, the range of absolute admissible values of the welding current being determined depending on the type of power supply network which is recognised.

The means 80 for manually setting a desired value of the welding current essentially comprise a potentiometric regulating system as shown in the figure, which can be operated by means of the knob 14 present on the front panel of the apparatus.

During operation, the apparatus is connected to the power supply network available in the room or premises where it must be used by means of the appropriate connection cable 22a or 22b.

Connection of the cable 22a or 22b to the power circuit 30 of the apparatus via its second connector 26a, 26b, respectively, and the panel connector 28 results in one of the two possible configurations of the detection circuit 50.

With reference to the diagram shown in Figure 3, in the case where the low-power connection, and therefore the connection cable 22a, is chosen, upon connection of the associated connector 26a to the apparatus, the identification terminals 42 connected together by means of the jumper close the circuit of the detection stage 50', allowing excitation of the actuating relay 52 by means of the source 54.

Excitation of the relay 52 causes switching of the movable contact of the switch 60, from the rest position, shown in the figure, where it is closed on the floating terminal 72, into the position where it closes onto the terminal 74.

In this way the signalling stage 50" provides the microcontroller of the control circuit 32 with a recognition signal substantially corresponding to the value of the earth reference potential to which the fixed contact of the switch 60 is connected.

The microcontroller μC, depending on the value of the recognition signal received at its input, generates a given welding current command signal at the output 76 of the control circuit 32, converting the value entered by the operator in accordance with a first predetermined adjustment scale. For example, when the connection to a low-power supply network is recognised, the control circuit attributes an end-of-scale value within the range

of values which can be set for the welding current, equal to 140A.

In an alternative condition, where the apparatus is connected to an industrial power supply network via a high-power connection, the connector 26b of the connection cable 22b has its identification terminals 42 open, i.e. separated by an open circuit.

Therefore, the circuit of the detection stage 50' is interrupted and the actuating relay 52 is not excited, thus not causing any switching of the movable contact of the switch 60.

The switch 60 therefore remains in the configuration shown in the figure, namely closed on the floating line 72.

The recognition signal supplied to the microcontroller μC corresponds in value to a reference voltage which is different from the earth potential, which is for example equal to +5 V, namely extracted from the voltage available to the microcontroller.

The microcontroller μC, depending on the value of the recognition signal, generates a given welding current command signal at the output 76 of the control circuit 32, converting the value set by the operator in accordance with a second predetermined adjustment scale. For example, when the connection to a high-power supply network is recognised, the control circuit attributes an end-of-scale value within the range of values which can be set for the welding current, equal to 180A.

The welding current command signal may be of the analogue or digital type. It is preferably a PWM type signal, the pulse width of which is controlled depending on the desired current value and the type of power supply network recognised (for example, a signal with 0% width will correspond to an analogue value of OA of current at the output, while a signal with a 100% width will correspond to an analogue value of 180A of current (at the output)).

The power circuit 30 comprises a supply power conversion section, adapted to modulate the incoming current by means of the PWM welding-current command signal generated by

the control circuit 32.

Obviously, without modifying the principle of the invention, the embodiments and the constructional details may be widely varied with respect to that which has been described and illustrated purely by way of a non-limiting example, without thereby departing from the scope of protection of the present invention defined by the accompanying claims.