Electric heating – Metal heating – By arc
Reexamination Certificate
1998-11-25
2001-05-29
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S1370PS
Reexamination Certificate
active
06239407
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to power sources. More particularly, this invention relates to inverter power sources employed in welding, cutting and heating applications.
Power sources typically convert a power input to a necessary or desirable power output tailored for a specific application. In welding applications, power sources typically receive a high voltage alternating current (VAC) signal and provide a high current output welding signal. Around the world, utility power supplies (sinusoidal line voltages) may be 200/208V, 230/240V, 380/415V, 460/480V, 500V and 575V. These supplies may be either single-phase or three-phase and either 50 or 60 Hz. Welding power sources receive such inputs and produce an approximately 10-40 volt dc high current welding output.
Welding is an art wherein large amounts of power are delivered to a welding arc which generates heat sufficient to melt metal and to create a weld. There are many types of welding power sources that provide power suitable for welding. Some prior art welding sources are resonant converter power sources that deliver a sinusoidal output. Other welding power sources provide a squarewave output. Yet another type of welding power source is an inverter-type power source.
Inverter-type power sources are particularly well suited for welding applications. An inverter power source can provide an ac square wave or a dc output. Inverter power sources also provide for a relatively high frequency stage, which provides a fast response in the welding output to changes in the control signals.
Generally speaking, an inverter-type power source receives a sinusoidal line input, rectifies the sinusoidal line input to provide a dc bus, and inverts the dc bus and may rectify the inverted signal to provide a dc welding output. It is desirable to provide a generally flat, i.e. very little ripple, dc bus. Accordingly, it is not sufficient to simply rectify the sinusoidal input; rather, it is necessary to also smooth, and in many cases alter the voltage of, the input power. This is called preprocessing of the input power.
There are several types of inverter power sources that are suitable for welding. These include boost power sources, buck power sources, and boost-buck power sources, which are well known in the art.
Generally, a welding power source is designed for a specific power input. In other words, the power source cannot provide essentially the same output over the various input voltages. Further, components which operate safely at a particular input power level are often damaged when operating at an alternate input power level. Therefore, power sources in the prior art have provided for these various inputs by employing circuits which can be manually adjusted to accommodate a variety of inputs. These circuits generally may be adjusted by changing the transformer turns ratio, changing the impedance of particular circuits in the power source or arranging tank circuits to be in series or in parallel. In these prior art devices, the operator was required to identify the voltage of the input and then manually adjust the circuit for the particular input.
Generally, adapting to the various voltage inputs in the prior art requires that the power source be opened and cables be adjusted to accommodate the particular voltage input. Thus, the operator was required to manually link the power source so that the appropriate output voltage was generated. Operating an improperly linked power source could result in personal injury, power source failure or insufficient power.
Prior art devices accommodated this problem by configuring the power source to operate at two different VAC input levels. For example, U.S. Pat. No. 4,845,607, issued to Nakao, et al. on Jul. 4, 1989, discloses a power source which is equipped with voltage doubling circuits that are automatically activated when the input is on the order or 115 VAC, and which is deactivated when the input is on the order of 230 VAC. Such sources are designed to operate at the higher voltage level, with the voltage doubling circuit providing the required voltage when the input voltage is at the lower level. This type of source, which uses a voltage doubling circuit, must use transistors or switching devices as well as other components capable of withstanding impractical high power levels to implement the voltage doubling circuit. Further, the circuitry associated with the voltage doubling circuit inherently involves heat dissipation problems. Also, the voltage doubling circuit type of power source is not fully effective for use in welding applications. Thus, there exists a long felt need for a power source for use in welding applications which can automatically be configured for various VAC input levels.
Welding power sources are generally known which receive a high VAC signal and generate a high current dc signal. A particularly effective type of the power source for welding applications which avoids certain disadvantages of the voltage doubling circuit type of power source generally relies on a high frequency power inverter. Inverter power sources convert high voltage dc power into high voltage AC power. The AC power is provided to a transformer which produces a high current output.
Power inverters for use over input voltage ranges are generally known in the art. For example, a power inverter which is capable of using two input voltage levels is disclosed in U.S. Pat. No. 3,815,009, issued to Berger on Jun. 4, 1974. The power inverter of that patent utilizes two switching circuits; the two switching circuits are connected serially when connected to the higher input voltage, but are connected in parallel to account for the lower input voltage. The switching circuits are coupled to each other by means of lead wires. This inverter is susceptible to operator errors in configuring the switching circuits for the appropriate voltage level, which can result in power source malfunction or human injury.
Other prior art welding sources that improved upon manual linking provided an automatic linkage. For example, the Miller Electric AutoLink is one such power source and is described in U.S. Pat. No. 5,319,533 incorporated herein by reference. Such power sources test the input voltage when they are first connected and automatically set the proper linkage for the input voltage sensed. Such welding power sources, if portable, are generally inverter-type power sources, and the method by which linking is accomplished is by operating the welding power source as two inverters. The inverters may be connected in parallel (for 230V, for example) or in series (e.g., for 460V). Such arrangements generally allow for two voltage connection possibilities. However, the higher voltage must be twice the lower voltage. Thus, such a power source cannot be connected to supplies ranging from 230V-460V to 380V-415V or 575V.
A 50/60 Hz transformer could be used to provide multiple paths for various input voltages. It would, however, have the disadvantage of being heavy and bulky compared to an inverter-type welding power source of the same capacity. In addition, if it was automatically linked as in the Miller AutoLink example given above, it would have to have link apparatus for each voltage. Such an automatic linkage would be complicated and probably uneconomical for the range of voltages contemplated by this invention. Thus, it is unlikely that prior art power sources that automatically select the proper of two input voltage settings will accommodate the full range of worldwide electrical input power. This shortcoming may be significant in that many welding power sources are purchased to be transportable from site to site. The ability to automatically adapt to a number of input power voltage magnitudes is thus advantageous.
It is, therefore, one object of this invention to provide a welding power source that receives any of the above-mentioned input voltages, or any other input voltage, without the need of any linkages, whether manual or automatic. Additionally, it is desirable to have such a welding power
Corrigan George R.
Illinois Tool Works Inc.
Shaw Clifford C.
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