Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
1998-10-22
2001-11-20
Wachsman, Hal (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S064000, C702S065000, C219S110000
Reexamination Certificate
active
06321167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a power supply apparatus for resistance welding, and more particularly to a power supply apparatus of a type using transistors for the control of a welding current.
2. Description of the Related Art
In order to provide a control of a welding current discharged from a capacitor for storing a welding energy, a transistor-type resistance welding power supply apparatus makes substantial use of only transistors intervening between the capacitor and welding electrodes without interposing a welding transformer therebetween. This system is considered to be advantageous for use in fine spot welding due to rapid build-up properties of the welding current and to an arbitrary provision of upslope or downslope waveform control.
Such a power supply apparatus ordinarily provides a feedback constant power control so as to allow the amount of welding heat to be kept at a certain value in spite of a possible change in the welding current or a voltage across welding electrodes during the weld time. For the provision of this feedback control, a shunt resistor is disposed in a power supply circuit to detect the welding current, with voltage sensor leads connected to the welding electrodes or their support members to detect a voltage between the welding electrodes so that the welding power is computed from the welding current detection value and the voltage detection value. Note that the transistor is in the form of a transistor group including several tens of transistors which are connected in parallel to one another, each transistor being a power transistor such as an FET or IGBT which withstands a large amount of current.
Such a conventional resistance welding power supply apparatus causes the transistor group to act as a kind of variable resistor between the capacitor and the welding electrodes so that provision is made of a control of the welding current so as to allow the welding power to coincide with the set value, for example, as described above. For this reason, there arises a problem that the transistor group may consume as the resistance heat in vain most of the energy discharged (fed) from the capacitor, resulting in a poor power supply efficiency. Furthermore, such a poor efficiency may prevent an acquisition of a large amount of current or elongated weld time.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the above problems. It is therefore the object of the present invention to provide a capacitor-type resistance welding power supply apparatus ensuring an improved power supply efficiency as well as an acquisition of a large amount of welding current and longer weld time.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a resistance-welding power supply apparatus for resistance welding materials to be welded by causing a welding current to flow through a pair of welding electrodes which are in press contact with said materials to be welded, the resistance-welding power supply apparatus comprising a capacitor having one end electrically connected to one of the pair of welding electrodes, for storing a welding energy in the form of electric charge; charging means for charging the capacitor; a transistor having a first terminal electrically connected to the other end of the capacitor and having a second terminal electrically connected to the other of the pair of welding electrode; and control means electrically connected to a control terminal of the transistor, for providing a switching control of the transistor at a predetermined frequency during a preset weld time.
In the above configuration, the transistor may comprise a plurality of transistors which are connected in parallel with one another.
According to a second aspect of the present invention, there is provided a resistance-welding power supply apparatus for resistance welding materials to be welded by causing a welding current to flow through a pair of welding electrodes which are in press contact with the materials to be welded, the resistance-welding power supply apparatus comprising a capacitor for storing a welding energy in the form of electric charge; charging means for charging the capacitor; a first transistor having a first terminal electrically connected to one of the pair of welding electrodes and having a second terminal electrically connected to one end of the capacitor; a second transistor having a first terminal electrically connected to the other end of the capacitor and having a second terminal electrically connected to the other of the pair of welding electrodes; a third transistor having a first terminal electrically connected to the other of the pair of welding electrodes and having a second terminal electrically connected to the one end of the capacitor; a fourth transistor having a first terminal electrically connected to the other end of the capacitor and having a second terminal electrically connected to the one of the pair of welding electrodes; control means electrically connected to the first to fourth transistors via their respective control terminals, for providing a switching control of the first and second transistors or of the third and fourth transistors at a predetermined frequency during a preset weld time.
In the above configuration, the first to fourth transistors may each comprise a plurality of transistors which are connected in parallel with one another.
Preferably, the charging means include a transformer for stepping down an AC power supply voltage having a commercial frequency to a predetermined voltage; and a rectifying circuit for rectifying the AC voltage from the transformer into a DC voltage for the output.
Preferably, the control means provide a switching control of the first and second transistors, with the third and fourth transistors remaining off, during a first weld time constituting each weld time together with a second weld time for resistance welding, and the control means provide a switching control of the third and fourth transistors, with the first and second transistors remaining off, during a second weld time constituting each weld time together with a first weld time for resistance-welding.
The control means may include current measuring means for measuring the welding current during the weld time; current setting means for providing a desired welding current set value; current comparing means for comparing a welding current measurement value from the current measuring means with the welding current set value to obtain a comparison error for each unit cycle of the frequency; and pulse width control means for providing a control of a pulse width for a switching-on time in the next unit cycle in response to the comparison error.
The control means may include voltage measuring means for measuring a voltage between the pair of welding electrodes during the weld time; voltage setting means for providing a desired interelectrode voltage set value; voltage comparing means for comparing an interelectrode voltage measurement value from the voltage measuring means with the interelectrode voltage set value to obtain a comparison error for each unit cycle of the frequency; and pulse width control means for providing a control of a pulse width for a switching-on time in the next unit cycle in response to the comparison error.
The control means may include current measuring means for measuring the welding current during the weld time; voltage measuring means for measuring a voltage between the pair of welding electrodes during the weld time; power computing means for figuring out a welding power fed in between the pair of welding electrodes, on the basis of a welding current measurement value from the current measuring means and of an interelectrode voltage measurement value from the voltage measuring means; power setting means for providing a desired welding power set value; power comparing means for comparing a welding power computed value from the power computing means with the welding power set
Jochi Takashi
Watanabe Mikio
Miyachi Technos Corporation
Wachsman Hal
Wenderoth , Lind & Ponack, L.L.P.
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