U.S. patent application number 09/761192 was filed with the patent office on 2001-07-19 for ac waveform inverter power supply apparatus for metallic member joining or reflow soldering.
Invention is credited to Jochi, Takashi, Moro, Kyoji.
Application Number | 20010008487 09/761192 |
Document ID | / |
Family ID | 18537151 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008487 |
Kind Code |
A1 |
Jochi, Takashi ; et
al. |
July 19, 2001 |
AC waveform inverter power supply apparatus for metallic member
joining or reflow soldering
Abstract
The number of cycles R of a fundamental frequency <SET>F
(Hz) for a set value Tw (ms) of a set weld time [WELD] is first
found as a real number. The number of cycles R conforms to the
number of times (real number) of repetition of the fundamental
frequency <SET>F cycle in the interval of the set weld time
Tw and is given as Tw.times.<SET>F (step B.sub.1). An AC
waveform cycle set value Ns (integer) for the set weld time Tw is
then determined as an integer Min [N] that is equal to the number
of cycles R or to the least one (i.e., the integer closest to R) of
larger integers (N) than R (step B.sub.2). An AC waveform cycle set
frequency Fs (Hz) and a period Ts (ms) for the set weld time Tw is
then found from the set number of cycles Ns. The set frequency Fs
and the period Ts are given as Fs=1/Ts and Ts=Tw/Ns, respectively
(step B.sub.3). The thus obtained values (data) of the set
frequency Fs and set number of cycles Ns are stored in the memory
at predetermined storage positions thereof and are indicated on a
setting screen (step B.sub.4).
Inventors: |
Jochi, Takashi; (Chiba-ken,
JP) ; Moro, Kyoji; (Chiba-ken, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
18537151 |
Appl. No.: |
09/761192 |
Filed: |
January 18, 2001 |
Current U.S.
Class: |
363/98 |
Current CPC
Class: |
B23K 11/257
20130101 |
Class at
Publication: |
363/98 |
International
Class: |
H02M 003/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2000 |
JP |
8940/2000 |
Claims
What is claimed is:
1. An AC waveform inverter power supply apparatus for metallic
member joining, comprising: a rectifying circuit which converts an
AC voltage of a commercial frequency into a DC voltage; an inverter
which converts said DC voltage output from said rectifying circuit
into a pulsed voltage of a high frequency; a transformer having
primary terminals and secondary terminals, said primary terminals
being electrically connected to output terminals of said inverter,
said secondary terminals being electrically connected to
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
said set weld time into a plurality of AC waveform cycles; and
inverter control means arranged to provide a control of switching
operations of said inverter in such a manner as to allow said
inverter to issue said high-frequency pulses with one polarity in
the former half cycle of divided each AC waveform cycle but to
issue said high-frequency pulses with the other polarity in the
latter half cycle thereof.
2. An AC waveform inverter power supply apparatus for reflow
soldering, comprising: a rectifying circuit which converts an AC
voltage of a commercial frequency into a DC voltage; an inverter
which converts said DC voltage output from said rectifying circuit
into a pulsed voltage of a high frequency; a transformer having
primary terminals and secondary terminals, said primary terminals
being electrically connected to output terminals of said inverter,
said secondary terminals being electrically connected to terminals,
respectively, of a reflow soldering heater tip, without
intervention of any rectifying circuit; current-supplying time
setting means arranged to set a current-supplying time by the unit
of time; AC waveform cycle setting means arranged to divide said
set current-supplying time into a plurality of AC waveform cycles;
and inverter control means arranged to provide a control of
switching operations of said inverter in such a manner as to allow
said inverter to issue said high-frequency pulses with one polarity
in the former half cycle of divided each AC waveform cycle but to
issue said high-frequency pulses with the other polarity in the
latter half cycle thereof.
3. An AC waveform inverter power supply apparatus according to
claim 1, wherein said AC waveform cycle setting means include means
arranged to equally divide said set weld time into a plurality of
AC waveform cycles.
4. An AC waveform inverter power supply apparatus according to
claim 2, wherein said AC waveform cycle setting means include means
arranged to equally divide said set current-supplying time into a
plurality of AC waveform cycles.
5. An AC waveform inverter power supply apparatus according to
claim 3, wherein said AC waveform cycle setting means include set
frequency computing means arranged to determine as a set frequency
the frequency allowing an equal division of said set weld time into
a least number of AC waveform cycles, among frequencies equal to or
higher than a predetermined fundamental frequency.
6. An AC waveform inverter power supply apparatus according to
claim 4, wherein said AC waveform cycle setting means include set
frequency computing means arranged to determine as a set frequency
the frequency allowing an equal division of said set
current-supplying time into a least number of AC waveform cycles,
among frequencies equal to or higher than a predetermined
fundamental frequency.
7. An AC waveform inverter power supply apparatus according to
claim 1, wherein said AC waveform cycle setting means include means
arranged to divide said 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 said first AC waveform
cycle(s) from said 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 said fundamental frequency.
8. An AC waveform inverter power supply apparatus according to
claim 2, wherein said AC waveform cycle setting means include means
arranged to divide said set current-supplying time into a single or
a plurality of first AC waveform cycles each having a predetermined
fundamental frequency and arranged to divide a remaining
current-supplying time obtained by subtracting a current-supplying
time corresponding to said first AC waveform cycle(s) from said set
current-supplying time into a single or a plurality of second AC
waveform cycles having a frequency which is higher than and most
approximate to said fundamental frequency.
9. An AC waveform inverter power supply apparatus according to any
one of the preceding claims, further comprising: AC waveform cycle
setting information display means arranged to provide indications
of the setting contents of said AC waveform cycle determined by
said AC waveform cycle setting means.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Description of the Related Arts
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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 number of
cycles, e.g., four cycles [80 ms (or 66.4 ms)].
[0008] 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.
[0009] 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
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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., number of cycles
setting and frequency setting, etc.) determined by the AC waveform
cycle setting means. Such configuration ensures the user management
of the set weld time by the number of cycles, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The above and other objects, aspects, features and
advantages of the present invention will become more apparent from
the following detailed description when read in conjunction with
the accompanying drawings, in which:
[0017] FIG. 1 is a block diagram showing the structure of an AC
waveform inverter power supply apparatus for resistance welding in
accordance with an embodiment of the present invention;
[0018] FIGS. 2A and 2B illustrate setting screens included in the
power supply apparatus of the embodiment;
[0019] FIG. 3 shows key switches of an entry unit included in the
power supply apparatus of the embodiment;
[0020] FIG. 4 is a flowchart showing the processing procedure
effected by a control unit for schedule mode in the embodiment;
[0021] FIG. 5 is a flowchart showing the processing procedure
effected by the control unit for secondary AC waveform
frequency/cycle setting in the embodiment;
[0022] FIGS. 6A and 6B are waveform diagrams showing the secondary
AC frequency/cycle setting method of the embodiment;
[0023] FIG. 7 shows welding sequence timings or waveforms that
correspond to the setting example (numerical values) appearing on
the setting screen of the embodiment;
[0024] FIG. 8 is a flowchart showing the processing procedure
effected by the control unit for current-supplying control in the
embodiment;
[0025] FIGS. 9A and 9B are waveform diagrams at the parts showing
the inverter control method of the embodiment;
[0026] FIGS. 10A to 10C illustrate an example of the fusing process
of the embodiment;
[0027] FIG. 11 is a block diagram showing the structure of an AC
waveform inverter power supply apparatus for reflow soldering in
accordance with another embodiment of the present invention;
[0028] FIG. 12 shows an example of the reflow soldering process of
the embodiment;
[0029] FIGS. 13A and 13B are waveform diagrams showing the
secondary AC frequency/cycle setting method of a variant of the
embodiment;
[0030] FIG. 14 shows an example of the setting screen indications
corresponding to the setting method of FIG. 13;
[0031] FIGS. 15A and 15B are waveform diagrams showing the
secondary AC frequency/cycle setting method of another variant of
the embodiment;
[0032] FIGS. 16A and 16B are waveform diagrams showing the
secondary AC frequency/cycle setting method of a further variant of
the embodiment;
[0033] FIGS. 17A and 17B are waveform diagrams showing the weld
time setting methods of conventional AC single-phase and AC
waveform inverter power supply apparatus; and
[0034] FIGS. 18 is waveform diagram showing the inconvenience which
may occur when the weld time is defined by the time in the AC
waveform inverter power supply apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The present invention will now be described with reference
to FIGS. 1 to 16A and 16B which illustrate presently preferred
embodiments thereof in a non-limitative manner.
[0036] FIG. 1 depicts the structure of an AC waveform inverter
power supply apparatus in accordance with an embodiment of the
present invention.
[0037] The power supply apparatus comprises a power supply unit
generally designated at 10. The power supply unit 10 includes a
three-phase rectifying circuit 14, an inverter 16 and a step-down
welding transformer 18. The three-phase rectifying circuit 14
consists of e.g., six diodes that are three-phase bridge connected
to each other and serves to full-wave rectify a three-phase AC
voltage (R, S, T) of a commercial frequency input from a
three-phase AC power terminal 12, into a DC voltage. The DC voltage
output from the three-phase rectifying circuit 14 is smoothed out
by a capacitor 20 and then fed to input terminals [La, Lb] of the
inverter 16.
[0038] The inverter 16 consists of four transistor switching
elements 22, 24, 26 an 28 in the form of, e.g., GTRs (giant
transistors) or IGBTs (insulated gate bipolar transistors).
[0039] Of the four switching elements 22 to 28, a first set of
(positive side) switching elements 22 and 26 are simultaneously
switching (ON/OFF) controlled at a predetermined inverter frequency
(e.g., 1 kHz) in response to in-phase inverter control signals
G.sub.1 and G.sub.3 that are fed via a driving circuit 30 from a
control unit 32. A second set of (negative side) switching elements
24 and 28 are simultaneously switching (ON/OFF) controlled at the
inverter frequency in response to in-phase inverter control signals
G.sub.2 and G.sub.4 that are fed via the driving circuit 30 from
the control unit 32.
[0040] The inverter 16 has output terminals [Ma, Mb] that are
electrically connected to opposite ends, respectively, of a primary
coil of the welding transformer 18. A pair of electrodes 34 and 36
for resistance welding are electrically connected via only
secondary conductors 38 to opposite ends of a secondary coil of the
welding transformer 18, without intervention of any rectifying
circuit.
[0041] The electrodes 34 and 36 are made of a metal having a high
thermal conductivity, e.g., a copper alloy and are releasably
attached to upper and lower electrode support members 42 and 44,
respectively, of a pressing unit 40. The pressing unit 40
incorporates a pressure driving unit not shown having an air
cylinder for example, to drive, e.g., the upper electrode support
member 42 in response to a press control signal FC from the control
unit 32 such that the upper electrode 34 is abutted and pressed
from above against workpieces (46, 48) mounted on the lower
electrode 36.
[0042] The control unit 32 of the power supply apparatus is
comprised of a microcomputer that includes a CPU, a ROM (program
memory), a RAM (data memory), an interface circuit, etc. The
control unit 32 provides not merely all intra-apparatus controls,
e.g., current-supplying control (especially inverter control),
various welding conditions setting or display process but also
provides desired controls to the pressing unit 40 or other external
associated devices. A clock generating circuit 50 sends a clock
signal CK.sub.tc to the control unit 32, the clock signal CK.sub.tc
defining fundamental or unit cycle tc for the switching control of
the inverter 16.
[0043] An entry unit 52 includes a keyboard or key switches
disposed on an operation panel not shown of the power supply
apparatus, for use in setting and entry of various conditions for
resistance welding. A display unit 54 includes a display, e.g., a
liquid crystal display disposed on the operation panel to indicate
set values, measured values, etc., of various conditions under the
control of the control unit 32.
[0044] To ensure the execution of the current feedback in the
current-supplying control, the power supply apparatus is provided
with a current sensor 56 in the form of a current transformer
attached to the primary circuit conductors (it may also be attached
to the secondary side) of the power supply unit 10 so that from an
output signal of the current sensor 56 a current measuring circuit
58 can acquire a primary current I.sub.1 or secondary current
I.sub.2 measured value (e.g., effective value, mean value or peak
value) as an analog current measurement signal SI, which in turn is
converted by an A-D converter 60 into a digital signal and fed to
the control unit 32.
[0045] Description will then be made of the function and operation
setting major welding conditions for a single welding sequence in
the power supply apparatus.
[0046] FIG. 2A depicts a "schedule" screen appearing on the display
of the display unit 54. On the "schedule" screen the user is
allowed to set and input various time parameters and current
parameters for the single welding sequence.
[0047] In the shown example, time parameter setting items appearing
on the "schedule" screen include initial squeeze time [SQ], first
weld time [WELD1], cooling time [COOL], secondweld time [WELD2] and
hold time [HOLD], whilst current parameter setting items include
current values [HEAT] (Is) in the first and second weld times
[WELD1] and [WELD2]. The set values for these setting items are
collectively managed by schedule numbers or codes [SCH#].
[0048] On the "schedule" screen there also appears separately set
fundamental frequency <SET>F. The fundamental frequency
<SET>F is normally set to a value in the vicinity of a rated
frequency (e.g., 50 Hz) of the welding transformer 18, or instead,
it may be set to any value desired by the user.
[0049] As shown in FIG. 3, the keyboard of the entry unit 52 is
provided with e.g., cursor keys 62 to 68, plus (+) and minus (-)
keys 70 and 72, and an enter key (ENTER) 74. The user vertically or
horizontally moves a cursor on the screen by means of the cursor
keys 62 to 68 to select a desired setting item. The user then
selects or modifies the setting item value by the plus (+) and
minus (-) keys 70 and 72 and finally determines (enters) the input
set value by the enter key (ENTER) 74.
[0050] FIG. 4 depicts the procedure of processings effected by the
control unit 32 in a "schedule" screen mode. When the schedule mode
is selected, the control unit 32 allows the "schedule" screen as
shown in FIGS. 2A and 2B to appear on the display of the display
unit 54 (step A.sub.1) and, in response to key entries (step
A.sub.2) from the above key buttons 62 to 74 of the entry unit 52,
executes predetermined processing (steps A.sub.3 to A.sub.8).
[0051] More specifically, each time one of the cursor keys 62 to 68
is pressed, the control unit 32 executes cursor move processing
(step A.sub.3) to move the cursor toward the direction instructed
by the key entry. When the plus (+) key 70 is pressed, the control
unit 32 executes plus (+) key entry processing (step A.sub.4),
whilst when the minus (-) key 72 is pressed, it executes minus (-)
key entry processing (step A.sub.5). In these key entry display
processes, the numerical value at the cursor position is
incremented or decremented by one for updating, and the updated
numerical value is displayed on the screen with the numerical value
data being retained in an appropriate storage region or register
within the memory. When the enter key (ENTER) 74 is then pressed,
the control unit 32 carries out key entry execution processing
(step A.sub.6) to determine the numerical value at the cursor
position as a set input value for the associated setting item, to
thereby store the numerical value data at a predetermined storage
position within the memory.
[0052] In the setting example shown in FIG. 2B, selected as the
schedule number [SCH#] is 001 under which the initial squeeze time
is set to 120 (ms), the first weld time [WELD1] to 20 (ms), the
cooling time to 30 (ms), the second weld time [WELD2] to 66 (ms),
and the hold time [HOLD] to 200 (ms), with the current values
[HEAT] (Is) of the first weld time [WELD 1] and the second weld
time [WELD2] being set to 600 (A) and 750 (A), respectively.
[0053] After the completion of the key entry execution process
(step A.sub.6), the control unit 32 judges whether the currently
set and entered setting item is the weld time (WELD) (step
A.sub.7), and if affirmative, then enters into the routine (step
A.sub.8) for "frequency/number of cycles setting processing".
[0054] FIG. 5 depicts the procedure of the "frequency/number of
cycles setting processing" effected in this embodiment.
[0055] In this routine, the number of cycles R of the fundamental
frequency <SET>F (Hz) for the set value Tw (ms) of the set
weld time [WELD] is first found as a real number. This number of
cycles R conforms to the number of times (real number) of
repetition of the fundamental frequency <SET>F period or the
AC waveform cycle in the interval of the set weld time Tw and is
given as Tw.times.<SET>F (step B.sub.1).
[0056] From the thus obtained number of cycles R, the AC waveform
cycle set value Ns for the set weld time Tw is then determined as
an integer value. In this embodiment, selected as the set number of
cycles Ns is an integer Min[N] that is equal to R or to the least
one of larger integers (N) than R (i.e., an integer closest to R)
(step B.sub.2).
[0057] The set frequency Fs (Hz) and the period Ts (ms) of the
secondary AC waveform cycle for the set weld time Tw is then found
from the set number of cycles Ns. The set frequency Fs and the
period Ts are given as Fs=1/Ts and Ts=Tw/Ns, respectively (step
B.sub.3).
[0058] The thus obtained values (data) of the set frequency Fs and
set number of cycles Ns are stored in the memory at predetermined
storage locations thereof and, as shown in FIG. 2B, indicated in
the items [F] and [CYCLE], respectively, on the "schedule" screen
(step B.sub.4). Although the set period Ts is not indicated, the
value (data) of Ts or Ts/2 is also stored in the memory since the
unit current-supplying period (Ts/2) corresponding to the half
cycle of the secondary AC waveform is an indispensable parameter
value in the inverter control.
[0059] In the example of FIG. 2B, the first weld time [WELD1] and
second weld time [WELD2] are 20 (ms) and 66 (ms), respectively,
relative to the fundamental frequency <SET>F of 50 Hz.
[0060] In such a case, in the "frequency/number of cycles setting
processing" for the set value Tw (20 ms) of the first weld time
[WELD1], the set number of cycles Ns is 1 due to the number of
cycles R of the fundamental frequency <SET>F being 1, and
hence the set frequency Fs results in 50.0 Hz that is equal to the
fundamental frequency <SET>F.
[0061] On the other hand, in the "frequency/number of cycles
setting processing" for the set value Tw (66 ms) of the second weld
time [WELD2], the number of cycles R of the fundamental frequency
<SET>F is a decimal 3.3, so that the set number of cycles Ns
results in 4 with the set frequency Fs of 60.6 Hz.
[0062] FIGS. 6A and 6B depict a method of the "frequency/number of
cycles setting processing" in this case. Provided that the
frequency of the AC welding current I is equal to the fundamental
frequency 50 Hz with respect to the set value Tw (66 ms) of the
second weld time [WELD2] selected by the user, then 6 ms is left
over as shown in FIG. 6A.
[0063] However, by selecting the set frequency Fs and set number of
cycles Ns of the AC welding current (secondary current) I to 60.6
Hz and 4, respectively, for the set value Tw (66 ms) of the second
weld time [WELD2] through the "frequency/number of cycles setting
processing", an AC waveform of a certain cycle can be obtained
without any remainder.
[0064] FIG. 7 depicts welding sequence timings or waveforms
corresponding to the setting example (numerical values) of FIG. 2B.
Squeeze-on time T.sub.F conforms to the sum of set values of the
squeeze time [SQ], first weld time [WELD1], cooling time [COOL],
second weld time [WELD2] and hold time [HOLD].
[0065] In this embodiment, when the user sets and enters a desired
set value Tw by the unit of time (ms) for the first and secondweld
time [WELD1] and [WELD2], the power supply apparatus sets a
frequency F.sub.2 of a secondary AC waveform cycle of which
integral multiples coincide with the set weld time Tw, for each
weld time [WELD] by the above "frequency/number of cycles setting
processing". The set frequency F.sub.2 is then defined as a value
equal to or slightly higher (at most several tens of %) than the
set fundamental frequency Fs. This will substantially obviate any
adverse effect on the characteristics of the welding transformer
18.
[0066] It is to be noted that the common welding transformers are
remarkably apt to become degraded or break upon supply of the AC
power having a frequency lower than each specific rated frequency,
as compared with the case of supply of the AC power of a frequency
higher than the rated frequency.
[0067] The control unit 32 starts a single welding sequence in
response to receipt of a predetermined start signal from an
external device such as a welding robot.
[0068] Previous to the start of the welding sequence, the control
unit 32 identifies the schedule number SCH# to be executed, from
set values on the screen of the display unit 54 or from data
attendant on the start signal. The control unit 32 then retrieves
all required set values of conditions (data) managed by the thus
identified schedule number SCH# and carries out the welding
sequence in accordance with the set condition values.
[0069] In case of the setting example of FIG. 2B, the control unit
32 provides a control of the parts at the welding sequence timings
as depicted in FIG. 7. First, the control unit 32 allows the weld
force control signal FC to go active (high) so that the pressing
unit 40 can start its pressing operation. The pressing unit 40
lowers the upper electrode support member 42 to press the upper
electrode 34 against the workpieces W (46, 48) mounted on the lower
electrode 36 to squeeze them. At a predetermined timing after the
arrival of the weld force at a predetermined value, i.e., after the
elapse of the squeeze time [SQUEEZE] from the start of the
squeezing operation, the power supply unit 10 starts the supply of
current for the first weld time [WELD1].
[0070] FIG. 8 depicts the current-supplying control procedure for
each weld time [WELD] in this embodiment.
[0071] First, set into respective predetermined registers are
required set condition values related to the supply of welding
current in the first weld time [WELD1], such as the current value
Is (600 A), the secondary AC waveform set frequency Fs (50.0 Hz),
the set number of cycles Ns (1), and unit current-supplying period
Ts/2 (10 ms) (step C.sub.1).
[0072] Due to conformity of the AC waveform half cycle to the unit
current-supplying period Ts/2 in the AC waveform inverter power
supply apparatus, the value (2Ns) obtained by multiplying the set
number of cycles Ns by 2 is set as a set value of count in a
current-supplying cycle counter for counting the number of times of
repetition of the supply of current in the unit current-supplying
period. Furthermore, the initialization for supply of current may
include setting of the inverter polarity in the first unit
current-supplying period and setting of the initial values of the
pulse width, etc., of the first high-frequency pulse in each unit
current-supplying period.
[0073] The control unit 32 then selects a predetermined polarity,
e.g., positive polarity in the first unit current-supplying period
Ts/2 (10 ms) and feeds switching signals G.sub.1 and G.sub.3 having
an initial pulse width via the driving circuit 30 to the positive
side (first set of) switching elements 22 and 26 of the inverter
16, to turn on the switching elements 22 and 26 (step C.sub.2). The
negative side (second set of) switching elements 24 and 28 remain
OFF.
[0074] When a welding current I (secondary current I.sub.2) and a
primary current I.sub.1 flow through the secondary and primary
circuits, respectively, of the welding transformer 18 during the
first switching cycle, the current sensor 56 provides as its output
a current detection signal indicative of an instantaneous value of
the primary current I.sub.1 so that the current measuring circuit
58 can acquire a measured value of current (effective value or mean
value) Si of the primary current I.sub.1 or of the secondary
current I.sub.2 in this switching cycle.
[0075] The control unit 32 fetches a measured value of current Si
from the current measuring circuit 58 by way of the A-D converter
60 (step C.sub.3) and compares the measured value of current Si
with a current set value [HEAT] (Is) to determine a pulse width
(switching-ON period) tp in the next switching cycle from the
comparison error (step C.sub.4).
[0076] In the second switching cycle, the control unit 32 feeds the
switching control signals G.sub.1 and G.sub.3 having the pulse
width tp to the positive side switching elements 22 and 26 of the
inverter 16, to turn on the switching elements 22 and 26 (steps
C.sub.6, C.sub.2).
[0077] In this manner, during the first unit current-supplying
period Ts/2 (10 ms), only the positive side switching elements 22
and 26 of the inverter 16 undergo continuous switching operations
at a high frequency (1 kHz) under the feedback pulse width control
(step C.sub.2 to C.sub.6). For the duration, the negative side
switching elements 24 and 28 are kept OFF. This allows the
secondary current I.sub.2 (welding current I) that is
constant-current controlled so as to substantially coincide with
the set value of current [HEAT] (Is) (600 A) to flow in the
positive direction through the secondary circuit of the welding
transformer 18 (FIGS. 9A and 9B).
[0078] After the ending of the first unit current-supplying period
(Ts/2), the control unit 32 increments the current-supplying cycle
counter by one (step C.sub.7) and reverses the inverter polarity
flag to its negative side (step C.sub.9), to move to the control of
the second unit current-supplying period Ts/2.
[0079] In the second unit current-supplying period Ts/2 (10 ms),
the control unit 32 subjects only the negative side switching
elements 24 and 28 to continuous switching operations at a high
frequency (1 kHz) under the feedback pulse-width control while
keeping OFF the positive side switching elements 22 and 26 of the
inverter 16 (steps C.sub.2 to C.sub.6). This allows the secondary
current I.sub.2 (welding current I) that is constant-current
controlled so as to substantially coincide with the set current
value [HEAT] (Is) (600 A) to flow in the negative direction through
the secondary circuit of the welding transformer 18 (FIGS. 9A and
9B).
[0080] After the ending of the second unit current-supplying period
(Ts/2) (10 ms), the count value of the current-supplying cycle
counter reaches the set value 2Ns (the value is 2) whereupon the
first weld period [WELD1] comes to an end (steps C.sub.8 to
C.sub.10).
[0081] The control unit 32 then measures the cooling time [COOL] by
means of a predetermined timer and thereafter commences the
current-supplying control of the second weld time [WELD2]. In the
second weld time [WELD2] as well, the parts are controlled in
accordance with the same procedure (FIG. 8) as in the above first
weld time [WELD1]. Note that individual set values of conditions
are given through the initialization (step C.sub.1). In particular,
the set value of current [HEAT] (Is) is given as 750 A, the
secondary AC waveform set frequency Fs as 60.6 Hz, the set number
of cycles Ns as 4, and the unit current-supplying period Ts/2 as
8.25 ms. The control unit 32 provides the current-supplying control
depending on these set values of conditions (steps C.sub.2 to
C.sub.9).
[0082] As a result, the feedback control allows the secondary
current I.sub.2 (welding current I) substantially coinciding with
the set current value [HEAT] (Is) (750 A) to flow, in the form of a
substantially trapezoidal current waveform, in the positive
direction during the former unit current-supplying period Ts/2
(8.25 ms) of each AC waveform cycle but in the negative direction
during the latter unit current-supplying period Ts/2 (8.25 ms).
[0083] Upon the ending of the eighth unit current-supplying period
Ts/2 (8.25 ms), the count value of the current-supplying cycle
counter reaches the set value 2Ns, whereat the second weld time
[WELD2] is terminated (steps C.sub.8 .fwdarw. C.sub.10).
[0084] The control unit 32 then measures the hold time [HOLD] by
means of the predetermined timer and thereafter ceases to issue the
weld force control signal FC to the pressing unit 40 (to allow the
signal FC to go low), to thereby release the workpieces W from the
compression of the electrodes 34 and 36. A nugget is formed at a
weld portion between the workpieces W, i.e., two metallic members
46 and 48 to obtain a metallurgical joint.
[0085] In the AC waveform inverter power supply apparatus of this
embodiment, as described above, when the user sets and enters a
desired set value Tw by the unit of time (ms) for each weld time
[WELD], the power supply unit automatically sets as a set value Tw
for that weld time [WELD] the frequency Fs of the optimum secondary
AC waveform cycle which is integral multiples of the cycle of the
set fundamental frequency <SET>F so that the
current-supplying control can be effected at that set frequency Fs.
Thus, any setting of the weld time would ensure the alternate
positive and negative current supply without inducing any excessive
residual magnetic flux in the welding transformer 18.
[0086] The user can freely and more precisely set the weld time.
The increased degree of freedom (range of selection) of the weld
time will contribute to the weld quality diversification and level
enhancement.
[0087] This embodiment further enables the user to grasp or manage
the weld time by the number of cycles since the secondary AC
waveform set frequency Fs (Hz) and set number of cycles Ns obtained
by the power supply unit are indicated for the user input set weld
time Tw (ms) on the setting screen (FIG. 2B).
[0088] The AC waveform inverter power supply apparatus of the above
embodiment has been directed to the resistance welding. However,
solder plating or tinning may be applied on the joint surfaces of
the workpieces W, i.e., of the two members 46 and 48 so that the
two members 46 and 48 can be soldered together by the same supply
of current as the above.
[0089] The above embodiment AC waveform inverter power supply
apparatus may be used as a power supply apparatus for fusing
processing.
[0090] FIGS. 10A to 10C depict an example of the fusing processing.
In this fusing processing, a coated wire 62 and a plate-like
terminal 64 made of copper alloy are electrically and physically
connected together.
[0091] First, as shown in FIG. 10A, the workpieces W are the
terminal 64 having a hooked portion or a bent portion 64a and the
coated wire 62 placed inside of the hooked portion 64 and
consisting of an insulator 62a and a conductor 62b. The workpieces
W are interposed between the two electrodes 34 and 36, with the
lower electrode 36 providing a support for the underside of the
electrode hooked portion 64a in position, and with the upper
electrode 34 abutting against the top surface of the terminal
hooked portion 64a so that the pressing unit 40 can press down the
upper electrode by a predetermined electrode force F. At the same
time, the power supply unit 10 applies an AC waveform secondary
voltage across the two electrodes 34 and 36.
[0092] Then, a current I first flows between the two electrodes 34
and 36 through the terminal hooked portion 64a serving as a current
path, to allow the terminal hooked portion 64a to generate Joule
heat. As a result, the insulator 62a of the coated wire 62 is
melted by the Joule heat and is removed from the conductor 62b as
shown in FIG. 10B.
[0093] Once the insulator 62a is removed, the current I can flow
between the two electrodes 34 and 36 by way of the conductor
(typically copper) 62b of the coated wire 62 as shown in FIG. 10C.
During the current-supplying period, the electrode force F is
continuously applied across the two electrodes 34 and 36 so that
the terminal hooked portion 64a and the coated wire conductor 62b
are joined through pressure welding or squash by the Joule heat and
the electrode force F. This allows the two members, i.e., the
coated wire 62 and the terminal 64 to electrically and physically
firmly connected together. No nugget (weld joint) will appear
between the coated wire conductor 62b and the terminal 64 due to
the extremely small resistance of the coated wire conductor 62b and
of the terminal 64.
[0094] The AC waveform inverter power supply apparatus is available
also as a power supply apparatus for reflow soldering.
[0095] FIGS. 11 depicts the structure of the AC waveform inverter
power supply apparatus for reflow soldering in accordance with
another embodiment of the present invention. The same reference
numerals are sent to substantially the same features and functions
as those of the power supply apparatus for resistance welding (FIG.
1) described hereinabove.
[0096] Referring to FIG. 11, the apparatus comprises a heater tip
80 having opposite terminals 80a and 80b that are connected only
via secondary conductors 82 to associated ends of the secondary
coil of the transformer 18 without intervention of any rectifying
circuit.
[0097] The heater tip 80 is made of a metal resistor having high
heat generation properties, e.g., molybdenum, and when a current
flows between the two terminals 80a and 80b, generates heat by
resistance heating. A thermocouple 84 acts as a temperature sensor
and is attached to the vicinity, e.g., side faces of a point 80c of
the heater tip 80. The thermocouple 84 issues an electric signal
(temperature detection signal) indicative of the temperature near
the point 80c.
[0098] The heater tip 80 is releasably attached to a tip support
member 86 of the pressing unit 40. In response to a pressure
control signal FC from the control unit 32, the pressing unit 40
drives the tip support member 86 to press the heater tip 80 against
the workpieces W for pressing.
[0099] To provide a feedback control of the heating temperature of
the heater tip 80, this power supply apparatus comprises an
amplifying circuit 88 which amplifies an analog temperature
detection signal St from the thermocouple 84 attached to the heater
tip 80, the thus amplified analog signal St being converted by the
A-D (analog-to-digital) converter 90 into a digital signal and fed
to the control unit 32.
[0100] In this power supply apparatus as well, similar to the power
supply apparatus for resistance welding (FIG. 1) described
hereinbefore, the user sets a desired current-supplying time by the
unit of time (ms) whilst the apparatus determines an optimum
secondary AC waveform set frequency Fs depending on the set
fundamental frequency <SET> F and the set current-supplying
time to provide a current-supplying control on the basis of the set
frequency Fs. The heater tip 80 generates heat by resistance
heating as a result of supply of current, and as shown in FIG. 12,
heats and presses the sites H to be soldered of the workpieces W
(92, 94) by use of its point 80c. Cream solder is previously
applied onto the joint surfaces of the sites H to be soldered so
that the cream solder can melt under the pressure and heating from
the heater tip 80. When the pressure is cancelled after the
termination of the supply of current, the solder solidifies and the
sites H to be soldered of the workpieces W (92, 94) are physically
and electrically connected to each other by way of the thus
solidified solder.
[0101] In the process example of FIG. 12, one member 92 of the
workpieces W is a coil and the other member 94 is a terminal. The
lower end portion of the tip support member 86 is made of an
electrically conductive material, e.g., copper and is coupled to
the two terminals 80a and 80b of the heater tip 80 by bolts 96 and
98, respectively. The lower end portion of the tip support member
86 serves also as part of the secondary conductors 82 of the power
supply unit 10. The secondary conductors 82 have their respective
electrically conductive end portions 82a and 82b that are
electrically insulated from each other by an insulating material
100.
[0102] The modes of setting (setting methods, setting items, etc.,)
effected on the "schedule" screen (FIGS. 2A and 2B) of the above
embodiments are merely by way of example, and may variously be
modified. For example, the weld time may be set not only by the
unit of millisecond (ms) but also by other units of time such as
second (s) or .mu.s (microsecond).
[0103] In the above embodiments, the power supply apparatus has set
the optimum frequency Fs and the number of cycles Ns adapted for
the set fundamental frequency, relative to the arbitrarily user set
and entered weld time or current-supplying time. These optimum set
frequency Fs and set cycle count Ns will normally suffice. The
apparatus configuration may however be such that the user can vary
the set frequency or the set number of cycles as the user
desires.
[0104] In the setting example of FIG. 2B, the power supply
apparatus finds the optimum set frequency Fs (60.6 Hz) and set
number of cycles Ns (4) adapted for the set fundamental frequency
<SET>F (50 Hz), relative to the set value Tw (66 ms) of the
second weld time [WELD2], and indicates the thus found set values
on the screen. From this setting information, the user may be able
to vary the set number of cycles Ns to 5 for example. In this case,
the power supply apparatus again computes the set frequency Fs and
provides the indication of a re-set value 75.7 (Hz) on the
screen.
[0105] Although in the above embodiments the set weld time Tw has
equally been divided into a plurality of (integral multiples of) AC
waveform cycles, it may be divided into a plurality of AC waveform
cycles each having a different frequency. In this unequal division
method, another setting technique may be employed as depicted in
FIGS. 13A and 13B, 15A and 15B, and 16A and 16B for example, in
which the set weld time Tw preferably includes a single or a
plurality of fundamental AC waveform cycles having the set
fundamental frequency <SET>F, with the remaining weld time Tg
equally divided into a single or a plurality of second AC waveform
cycles having a frequency different from the fundamental frequency.
The second AC waveform cycles preferably have a frequency higher
than and most approximate to the basic frequency for the remaining
weld time Tg.
[0106] More specifically, in the setting example of FIGS. 13A and
13B, the set weld time Tw (66 ms) includes three fundamental AC
waveform cycles (which correspond to 60 ms) having the fundamental
frequency <SET>F (50 Hz), with the remaining weld time (6 ms)
including a single 167 Hz AC waveform cycle.
[0107] In the setting example of FIGS. 15A and 15B, the set weld
time Tw (66 ms) includes two fundamental AC waveform cycles (which
correspond to 40 ms) having the fundamental frequency <SET>F
(50 Hz), with the remaining weld time (26 ms) including two 76.9 Hz
AC waveform cycles.
[0108] In the setting example of FIGS. 16A and 16B, the set weld
time Tw (66 ms) includes a single fundamental AC waveform cycle
(which corresponds to 20 ms) having the fundamental frequency
<SET>F (50 Hz), with the remaining weld time (46 ms)
including three 65.4 Hz AC waveform cycles.
[0109] FIG. 14 depicts, byway of example, indications on the
"schedule" screen corresponding to the setting example of FIGS. 13A
and 13B. As seen in this indication example, in case of setting the
single set weld time Tw (66 ms) by a plurality of AC waveform
cycles each having a different frequency, the setting contents
(frequency, number of cycles, weld time, etc.,) for the respective
AC waveform cycles may be listed for display in order to notify the
user of the setting information.
[0110] This unequal division method may also enable the user to
vary the AC waveform cycle setting contents provided from the
apparatus, as the user desires, in the same manner as the above
equal division method.
[0111] Although in the above embodiments, the three-phase
alternating current of a commercial frequency has been converted
into a direct current for the supply to the inverter 16, the
conversion into the direct current may be made of a single-phase
alternating current having the commercial frequency. The circuit
configuration of the inverter 16 is merely shown by way of example
and may variously be modified. The current waveform in each unit
current-supplying period is not limited to the trapezoidal one as
in the above embodiments, but instead may be controlled to any
current waveform.
[0112] Although the current-supplying control of the above
embodiments has employed the PWM (pulse width modulation) method
for the feedback constant-current control, another method may be
used such as a current peak-value control or limiter control method
by allowing the current peak value to conform to the set value for
each inverter frequency cycle.
[0113] According to the AC waveform inverter power supply apparatus
for metallic member joining or reflow soldering of the present
invention, as set forth hereinabove, it is possible to arbitrarily
set and manage the desired weld time by the unit of time without
inducing any abnormality or degradation in the transformer, as well
as to achieve the enhanced processing quality and improved quality
control by allowing more precise setting of the weld time.
[0114] While illustrative and presently preferred embodiments of
the present invention have been described in detail herein, it is
to be understood that the inventive concepts may be otherwise
variously embodied and employed and that the appended claims are
intended to be construed to include such variations except insofar
as limited by the prior art.
* * * * *