Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2001-01-18
2001-11-20
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S132000, C219S130510, C219S1370PS
Reexamination Certificate
active
06320774
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an inverter power supply apparatus for metallic member joining or reflow soldering, and, more particularly, to an AC waveform inverter power supply apparatus allowing an AC waveform current to flow on its transformer secondary side.
2. Description of the Related Arts
Of late years, AC waveform inverter power supply apparatuses are prevailing as power supply apparatus for use in resistance welders. The AC waveform inverter power supply apparatuses can obviate the disadvantages of the DC inverter power supply apparatuses that flow a DC welding current on their welding transformer secondary side while keeping the advantages of the DC inverter power supply apparatuses.
More specifically, the DC inverter power supply apparatuses have a high heat generation efficiency enough to ensure stabilized resistance welding with less spatters since the length of their effective weld time is remarkably larger at all times than that of the current-unsupplied time, as compared with single-phase AC thyristor controlled power supply apparatuses. Due to their fixed current direction or polarities between a pair of electrodes clamping workpieces, however, the DC inverter power supply apparatuses may often suffer from such deficiencies that one of the pair of electrodes is liable to be degraded or wear than the other, that the workpieces tend to be magnetized, and that poor quality readily occurs because of the residual magnetism. Furthermore, high-frequency pulses from the inverter are converted into DC currents by a rectifying circuit on the secondary side of the welding transformer. Hence, the rectifying circuit and means to cool the same must be provided with a need for the high-frequency welding transformer suited to pass the AC pulses of the inverter frequency therethrough, which inconveniently makes the most prevalent commercial frequency welding transformers unavailable.
In this respect, the AC waveform inverter power supply apparatuses provide the same inverter control as the DC inverter power supply apparatuses, on their welding transformer primary side, to thereby advantageously achieve the heat generation efficiency and stability equivalent to the DC inverter power supply apparatuses, without the need for the rectifying circuit on the welding transformer secondary side, thus rendering low-frequency transformers available by flowing the AC waveform welding current (secondary current) at a low frequency substantially level with the single-phase AC power supply apparatuses.
Due to the availability of the low-frequency welding transformers in common with the single-phase power supply apparatuses as described above, the AC waveform inverter power supply apparatuses typically set the primary side AC waveform frequencies to the commercial frequency as shown in
FIGS. 17A and 17B
so that the weld time can be managed by the number of cycles of commercial frequency which has customarily been used in the single-phase AC power supply apparatuses. One cycle time being defined as one cycle 20 ms (or 16.6 ms) of the commercial frequency 50 Hz (or 60 Hz), the weld time Ta is managed by the numbers of cycles, e.g., four cycles [80 ms (or 66.4 ms)].
From experiences of the DC inverter power supply apparatuses, however, more and more users are recently hoping to arbitrarily set desired weld time by the time. Therefore, if the AC waveform inverter power supply apparatuses can set the weld time to any desired length by the time (e.g., ms), It may not merely be significantly convenient for the users but also it may be possible to further fine the weld time, i.e., one of welding condition parameter values and thus to achieve an Improved weld quality.
In the AC waveform Inverter power supply apparatuses, however, a difficulty may arise when the user desired weld time does not coincide with the integral multiples of the cycles of the welding transformer fundamental frequency. For example, when selecting the weld time to be 66 ms with respect to one cycle 20 ms of the fundamental frequency as shown in
FIG. 18
, 6 ms is left over from three cycles (60 ms). In this case, if during the remaining weld time (6 ms) the current supply Is made with one polarity only, then excessive residual magnetic flux will remain In the welding transformer, which may possibly break the inverter switching elements.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the above problems posed by the prior art. It is therefore an object of the present invention to provide an AC waveform inverter power supply apparatus for metallic member joining or reflow soldering, capable of arbitrary setting and managing of desired weld time without inducing any abnormality or degradation in its transformer.
It is another object of the present invention to provide an AC waveform inverter power supply apparatus for metallic member joining or reflow soldering, capable of finer setting of the weld time or current-supplying time to improve the work quality and quality management.
In order to attain the above objects, according to an aspect of the present invention, there is provided an AC waveform inverter power supply apparatus for metallic member joining or reflow soldering, comprising a rectifying circuit which converts an AC voltage of a commercial frequency into a DC voltage; an inverter which converts the DC voltage output from the rectifying circuit into a pulsed voltage of a high frequency; a transformer having a couple of primary terminals and a couple of secondary terminals, the couple of primary terminals being electrically connected to two output terminals, respectively, of the inverter, the couple of secondary terminals being electrically connected to a pair of electrodes, respectively, which join workpieces in the form of metallic members together, without intervention of any rectifying circuit; weld time setting means arranged to set a weld time by the unit of time; AC waveform cycle setting means arranged to divide the set weld time into a plurality of AC waveform cycles; and inverter control means arranged to provide a control of switching operations of the inverter in such a manner as to allow the inverter to issue the high-frequency pulses with one polarity in the former half cycle of divided each AC waveform cycle but to issue the high-frequency pulses with the other polarity in the latter half cycle thereof.
In the AC waveform inverter power supply apparatus of the present invention, when the user sets and enters a desired set value of each weld time by the unit of time (e.g., ms), the frequency setting means divide the set weld time into a plurality of (integer) AC waveform cycles so that the inverter control means can provide the current-supplying control by the set AC waveform cycles. Thus, applications of positive and negative currents can evenly be effected irrespective of the arbitrary weld time setting, to obviate any excessive residual magnetic flux. The user is also allowed to freely and more precisely set the weld time. The increased degree of freedom (width of selection) and the raised precision of the weld time will contribute to the process quality diversification and level enhancement.
Preferably, the AC waveform cycle setting means include means arranged to equally divide the set weld time into a plurality of AC waveform cycles. The AC waveform cycle setting means may include means arranged to divide the set weld time into a single or a plurality of first AC waveform cycles each having a predetermined fundamental frequency and arranged to divide a remaining weld time obtained by subtracting a weld time corresponding to the first AC waveform cycle(s) from the set weld time, into a single or a plurality of second AC waveform cycles having a frequency which is higher than and most approximate to the fundamental frequency.
The apparatus may further comprise AC waveform cycle setting information display means arranged to provide indications of the setting contents of the AC waveform cycle (e.g., num
Jochi Takashi
Moro Kyoji
Miyachi Technos Corporation
Vu Bao Q.
Wenderoth , Lind & Ponack, L.L.P.
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