FIELD OF INVENTION
This invention relates to a technique for fusing electric conductors together.
More particularly, the invention relates to an improved method and apparatus for
fusing at least two conductors, in particular during manufacture of dynamo-
electric machines such as electric motors and generators.
BACKGROUND OF THE INVENTION
Fusing (also sometimes referred to as hot staking) is a well known process used
in the manufacture of dynamo-electric machines. The purposes for fusing is to
mechanically and electrically connect the leads of armature coils to tangs on or
slots in the commutator of the armature. Fusing is similarly used for mechanically
and electrically connecting stator coil leads to terminations on the stator. The
typical fusing process involves the application of force and heat to at least one of
two (or more) electrical conductors to be connected. The heat removes
insulation (e.g., wire insulation) from the conductors. The heat helps to soften
the conductors so that they can subsequently be more easily deformed to bring
them into close and intimate contact with one another. Force is used to finally
deform the conductors such that they are finally brought into intimate contact
with one another.

A fusing operation is typically carried out by, placing a fusing electrode and a
ground electrode in contact with at least one of the conductors to be connected.
Heat is generated by, passing an electrical current through the series circuit
including the fusing electrode, the work piece, and the ground electrode. The
fusing electrode is forced against the work piece to produce required
deformation of the work piece as part of the fusing operation.
While it is important to ensure that there is enough heat and force to remove all
insulation and produce a tight mechanical and electrical connection, it is also
important to avoid any significant melting of the conductors during the fusing
operation. It may also be important to avoid overheating of those structures of
the dynamo-electric machine which are adjacent to the fusing site. For example,
the commutator bars being fused to coil leads may be embedded in a mass of
resin, which it is important not to overheat.
In recent years increasing attention has been given to the fusing step or steps
involved in the manufacture of dynamo-electric machines. This has been due to
several factors such as the need to improve the quality of fused connections, the
need to increase production rates, and the need to avoid overheating of the
more heat-sensitive resin materials now being used in place of asbestos
materials to support the commutator bars in armatures. Reducing the fusing
cycle time tends to increase production rates and may help avoid overheating of

adjacent structures, but it makes it more difficult to maintain or improve the
quality of the resulting connections. At the very least, a shorter fusing cycle time
requires more careful control of the parameters of the fusing cycle in order to
ensure that the desired mechanically tight connections of low electrical resistance
with no residual insulation remaining in the connection are produced.
OBJECTS OF THE INVENTION
It is an object of this invention to propose an improved method and apparatus
for fusing at least two conductors, which facilitates the provision of shorter, and
more efficient fusing cycles.
Another object of this invention is to propose an improved method and
apparatus for fusing at least two conductors, which provides optimized controls
for fusing operations so that the quality of the resulting connections can be
improved.
A further object of the invention is to propose an improved method and
apparatus for fusing at least two conductors which is capable of optimizing the
time to perform a fusing cycle.

SUMMARY OF THE INVENTION
These and other objects of the invention are accomplished in accordance with
the features of the invention.
According to the invention, the thermo emf of the electrical circuit including the
work piece through which electrical current is passing as part of a fusing
operation is measured. This joint temperature typically increases as the fusing
operation proceeds. The temperature at any given time is used as an indication
of how the fusing cycle is progressing. Other parameters of the fusing cycle are
then controlled based on when the thermo emf value reaches one or more
predetermined thermo emf values.
Learning mode: During learning mode, a good hot staking joint is done by
selecting a set of good fusing parameters such as current, force and time. The
Fusing operation is carried out. The thermo emf and welding current values as a
function of time are measured and stored in the memory for the given optimized
fusing duration. The hot staking is tested and the quality is ensured.
Fusing mode: During hot staking, the fusing current value and thermo emf
voltage values are measured during each of the fusing cycle. The measured

value is compared with the reference values stored during the learning mode. If
the thermo emf value is more, then the welding current for the next cycle is
reduced by a predetermined amount. If the thermo emf value is less then the
welding current value for the next cycle is increased by a pre-determined value.
Thereby the thermo emf value during the next cycle is equal to the stored values
for the next cycle.
Further features of the invention, its nature and various advantages will be more
apparent from the accompanying drawings and the following detailed description
of the preferred embodiments.
BRIEF DESCRIPTION OF THE ACQNPANYIMG DRAWINGS
FIG. 1 is a simplified view of illustrative work piece before and after hot staking.
Fig 2 is a picture of the controller used for controlling the fusing operation
Fig 3 is the recording of the thermo emf curves during learn mode and during
operation.

FIG. 4 is a simplified block diagram of electrical circuit
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in Fig. 1, an electrode (15) is disposed on a tong (13) of the a
commutator (2). The tong (13) folds one end of a wire (14). When the resistance
hot staking electrode (16) sits on the tong (13), the welding current flows
through the tong (13) and the wire (14) to be joined. The commutator (2) sits
on the tong (13). Once the fusing cycle starts, the fusing current flows through
the tong (13), one end of the wire (14) and the commutator segment (2). When
the fusing current passes, the wire insulation melts and the bare wire is joined
with the tong (13). In order to measure the thermo emf, a small tungsten tip is
fixed to the top electrode (16) of the fusing apparatus. When the temperature
increases, a small thermo emf is generated across the tungsten electrode (16)
and the copper ground electrode (15). This emf is proportional to the
temperature of the joint to be welded.
Fig 1 further shows the commutator segment (2) before carrying out hot staking
and after the hot staking operation. A copper strip (14) is folded over the end of
an armature wire (15) before hot staking. After hot staking, the bent copper strip
(14) is pressed over the end of the wire (15).

Fig.2 shows, the line diagram of a controller (17) used for controlling the hot
staking operation for dynamo electric machines. The front panel contains a set of
switches (18) for inputting the data for selection of number of cycles, values for
the welding current and time required to be set for different weld cycles like
squeeze time, current time, upset time and hold time. Provision is made to
adjust these timings to achieve a good weld. Also the front panel displays the
values of the above parameters being displayed by a LCD (19) during setting and
during operation. The status of welding cycle during operation and the error
conditions are also indicated by the LED indicators (20) provided in the front
panel
Fig 3 shows, the temperature recording during the various welding cycles. Once
a reference temperature curve is recorded and stored in the memory, further hot
staking operations follow the same pattern. This shown clearly in the above
diagram.
The fusing current and the welding voltage are measured using a toroid coil and
a voltage pick up probe. This information is taken to an Analog to Digital
converter (10) through a current conditioner (7) a temperature conditioner (8)
and an analog multiplxer (9). From the A/D converter (10) the information is
transferred to a CPU (5). The same information is also available as analog output
at the output side of a DAC (12).

Fig 4 shows the detailed block diagram of the Hot staking controller. The hot
staking machine is any regular resistance welding machine(l). The hot staking
constitutes is joining of the copper strip (14) to the commutator segment (2) The
front panel switches (18) and function status are also brought through an I/O
interface (21) in to the CPU (5). The primary voltage is sampled and taken for
reference of zero cross detection (4). This information is given through an
interrupt controller (6) to the CPU(5). The CPU first collects the data of thermo
emf values and welding current values(3) and stores them as reference values in
the memory (22) of the CPU(5) during the learn mode. During actual Hot staking
mode, the actual thermo emf and current values are measured and compared
(23) with the values stored in a memory (22) for every welding cycles and the
welding current of the subsequent cycles are modified in order to match the
temperature and the welding currents. Once the temperature crosses a value of
400 deg.C, at this temperature the insulation of the wire would have melted and
the fusing will take place. The fusing will be of good quality and the joint would
have been well bonded.

WE CLAIM:
1. An improved method of fusing at least two conductors (15, 16) in
particular during manufacture of dynamoelectric machines, comprising the
steps of:
- placing a fusing electrode (16) and a ground electrode (15) in contact
with one of the at least two connectable conductors (14, 2);
- generating heat by passing an electrical current through a series circuit
comprising the fusing electrode (16), a work piece (13), and the ground
electrode (15); and
- forcing the fusing electrode (16) against the work piece (13) in a hot
staking machine to produce a mechanically tight connection of low
electrical resistance,
characterized in that:
- the operating parameters of the fusion cycle is controlled in a hot stack
controller (17) by carrying-out the steps of:

- selecting in a learning mode a set of optimum fusing parameters such as
current, force, time and fusing duration and carrying out a fusing
operation;
- measuring the thermo electromotive force (emf) and welding current
values (3) as a function time and storing the data in a memory (22) of the
hot stack controller (17); and
- during an actual fusing mode, measuring in each cycle the real time value
of the fusing current and thermo emf voltage;
- comparing (23) the acquired real-time value with the stored value,
adjusting one of the values in opposite direction in the next fusing cycle,
and matching the real time and the stored value to produce a good quality
connection.
2. The method as claimed in claim 1, wherein passing said electrical current
to said circuit comprises applying electric power as a succession of a
plurality of pulses separated by time intervals during which substantially
no other electrical power is applied to said circuit.

3. The method as claimed in claim 1, wherein during the actual fusing mode
the joint temperature is measured and at least one parameter of said
fusing operation is controlled based at least in part on the thermo emf
measured in said measuring step and a predetermined electrical delivery
function to regulate heat so that at least one of said conductors is
softened, insulation on a portion of one of said conductors is vaporized, at
least one of said conductors is deformed to be in intimate contact with the
other, and both of said conductors are bonded together, said heat being
applied continuously while at least one of said conductors is softened, said
insulation is vaporized, and at least one of said conductors is deformed
and bonded.
4. The method as claimed in claim 3, wherein said measuring step
comprises:
measuring the amount of electrical current flowing through said circuit;
measuring the thermo emf voltage across said circuit; and calculating said
joint temperature, by calculating the thermo emf value separated from the
welding voltage.

5. The method as claimed in claim 3 or 4, comprising the step of:
determining the joint temperature of the portions of said circuit other than
said conductors; and wherein, in said calculating step, said thermo emf is
calculated by separating the thermo emf from welding voltage, wherein
when the thermo emf is equal to the reference temperature, the
predetermined welding current is selected for the next current cycle, and
wherein when the measured thermo emf during the learning mode is not
equal to the reference value, the welding current is increased or
decreased so that the thermo emf measured during the next cycle is
matched with the next reference point.
6. The method as claimed in claim 3 or 4, comprising correcting the welding
current to achieve the required joint temperature and controlling the
power passing through said circuit in response to the measured thermo
emf as corrected in said correcting step so that a predetermined amount
of power is dissipated in said conductors.
7. Apparatus for carrying - out an improved method for fusing at least two
conductors in particular during manufacture of dynamoelectric machines,
the apparatus comprising :

means for measuring the joint temperature of said circuit during fusing
operation; and means for measuring and controlling at least partly the
welding current of fusing operation based at least the joint temperature
measured and a predetermined welding current to regulate a continuous
heat so that at least one of said conductors is softened, insulation on a
portion of conductor is vaporized and both of said conductors are bonded
together.
8. The apparatus as claimed in claim 7, wherein welding current parameter
is selected from the group consisting of time of application of electrical
power, target level of electrical power, time of application of said force.
9. The apparatus as claimed in claim 7, wherein said means for measuring
comprises a first means for measuring the amount of electrical current
flowing through said circuit; and a second means for measuring the
thermo emf-voltage across said circuit.
10.The apparatus as claimed in claim 7, comprising means for measuring the
joint temperature of said circuit during fusing operation through thermo
emf measurement; and means for correcting the welding current so that
the required temperature achievement is ensured.

ABSTRACT

TITLE: 'AN IMPROVED METHOD AND APPARATUS OF FUSING AT
LEAST TWO CONDUCTORS IN MANUFACTURE OF DYNAMO ELECTRIC
MACHINES'
The invention relates to an improved method of fusing at least two conductors
(15, 16) in particular during manufacture of dynamoelectric machines,
comprising the steps of: placing a fusing electrode (16) and a ground electrode
(15) in contact with one of the at least two connectable conductors (14, 2);
generating heat by passing an electrical current through a series circuit
comprising the fusing electrode (16), a work piece (13), and the ground
electrode (15); and forcing the fusing electrode (16) against the work piece (13)
in a hot staking machine to produce a mechanically tight connection of low
electrical resistance.The operating parameters of the fusion cycle is controlled in
a hot stack controller (17) by carrying-out the steps of selecting in a learning
mode a set of optimum fusing parameters such as current, force, time and fusing
duration and carrying out a fusing operation; measuring the thermo
electromotive force (emf) and welding current values (3) as a function time and
storing the data in a memory (22) of the hot stack controller (17); and during an
actual fusing mode, measuring in each cycle the real time value of the fusing
current and thermo emf voltage; comparing (23) the acquired real-time value
with the stored value, adjusting one of the values in opposite direction in the
next fusing cycle, and matching the real time and the stored value to produce a
-good quality connection.