Assembly of thermocouple sensor fitted to iron tip

A thermocouple sensor is fitted to an iron tip of an electric soldering iron provided with a temperature controller. The sensor can detect the temperature of the iron tip and supply it to the temperature controller, which then adjusts the temperature to a desired value. The thermocouple sensor is formed of a pair of non-covered sensor wires. A contact point part of the thermocouple sensor is secured to a nose of the iron tip. The wires are laid along the surface of the nose in the rearward direction and introduced into a hollow portion through a lead-in hole opened in the vicinity of the boundary between the nose and a columnar base of the iron tip. Then, the wires are inserted into and through a pair of guide holes, respectively, formed in a cylindrical insulating support of a heater. The distal ends of the wires are coupled to a socket, which is an end portion for receiving a signal representing the detected temperature of the iron tip to supply it to the temperature controller.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an assembly of a thermocouple sensor 
fitted to an iron tip of an electric soldering iron provided with a 
temperature controller, so that the sensor can detect the temperature of 
the iron tip and supply it to the temperature controller, which then 
adjusts the temperature to a desired value. 
2. Description of the Related Art 
In order to properly perform electric soldering of electric wiring, it is 
necessary, in particular, to precisely set and maintain the temperature of 
an iron tip of an electric soldering iron. 
To achieve this, electric soldering irons have been conventionally provided 
with a temperature controller which is constructed to be capable of 
adjusting the temperature of the iron tip. 
A conventional electric soldering iron 1 of this type is constructed as 
shown in FIG. 8, by way of example. A heat-radiating plate 4 is secured to 
the forward end of a grip 2 via a heat-radiating nut 3. An iron tip 5 is 
fit in the radiating plate 4 via a heater cover 6 and a cover nut 7. The 
heater cover 6 only covers the columnar base of the tip 5, while leaving 
the nose portion thereof uncovered. The cover nut 7 is screwed onto a male 
thread formed around the outer periphery of the forward end of the 
radiating plate 4, while holding the rear end of the heater cover 6. 
As has been mentioned above, the iron tip 5 comprises the tapered nose and 
the columnar base extending from the rear end of the nose. The columnar 
base is formed hollow from the rear end to the portion adjacent to the 
boundary between the base and the nose. A heater 8 shown in FIG. 7 is 
disposed in the hollow portion. An insulating support 9 of the heater 8 is 
provided with a pair of guide holes passing from the forward end to the 
rearward end of the support 9. A ceramic element 12 having a contact point 
part 11, which is a heat-sensitive part of a thermocouple sensor 10, 
embedded in the element 12 is disposed at the forward end of the 
insulating support 9. A pair of sensor wires of the thermocouple sensor 10 
are respectively inserted into and through the guide holes, and the distal 
ends of the wires are coupled to a socket, which is an end portion for 
receiving a signal representing the temperature of the iron tip, connected 
to the distal ends of signal lines extending from a temperature 
controller. 
In the conventional electric soldering iron 1 constructed as described 
above, soldering is carried out by supplying power to the heater 8 which 
then generates heat and applies it to the iron tip 5. During this 
soldering operation, the following temperature control is performed. Since 
the contact point part 11, which is a heat-sensitive part of the 
thermocouple sensor 10, is securely fixed to the forward end of the heater 
8 by being embedded in the ceramic element 12, the thermocouple sensor 10 
naturally ends up detecting the temperature of the heater 8. The detected 
temperature is then converted by the temperature controller into a value 
representing the temperature of the iron tip 5, and the converted 
temperature is compared with a desired temperature (reference temperature) 
of the iron tip. If the converted temperature is lower than the reference 
temperature, the amount of power supplied to the heater 8 is increased, 
and vice versa, thus controlling the temperature of the iron tip 5. 
Therefore, when controlling the temperature of the iron tip 5 of the 
conventional electric soldering iron 1 of this type, the temperature of 
the iron tip 5 is not directly detected, but the temperature of the heater 
8, which is a heating means, is detected. Then, the temperature controller 
executes the following processing. From the detected temperature of the 
heater 8, the temperature of the iron tip 5 is inferred, and based on this 
inferred value, the amount of power supplied to the heater 8 is adjusted 
so as to control the temperature of the iron tip 5. Because the inferred 
value may not be the actual temperature of the iron tip, the tip may be 
disadvantageously regulated to an incorrect temperature. 
In other words, when using the conventional electric soldering iron 1, the 
temperature of the iron tip 5 and that of the heater 8 maintain a constant 
relationship in which the temperature values approximate each other during 
the idling state, i.e., prior to use. It is thus possible to make 
adjustments to the temperature of the iron tip in a relatively correct 
manner. However, when the actual soldering operation is started, the iron 
tip 5 is cooled by solder or parts to be soldered, and a certain time lag 
occurs before the thus-lowered temperature of the iron tip can be 
reflected by the heater. Hence, during the actual soldering operation, the 
temperature of the iron tip 5, which has been converted from the 
temperature of the heater 8 based on a predetermined calculation formula, 
does not coincide with the actual temperature of the iron tip 5, thereby 
making it impossible to realize correct adjustments to the temperature of 
the iron tip 5. 
More specifically, a temperature drop of the iron tip caused by contact 
with solder or parts to be soldered will not be immediately reflected by 
the temperature of the heater. Thus, only after the temperature of the 
iron tip 5 drops considerably, i.e., after a lapse of a comparatively long 
time in terms of the overall soldering operation, will the temperature of 
the heater 8 eventually drop. Only after the temperature drop is detected, 
is the control system eventually actuated to compensate for such 
temperature drop. As a consequence, with the above-described conventional 
electric soldering iron, a temperature drop of the iron tip cannot be 
correctly detected in real time, thereby causing a poor response by the 
control system operable to compensate for the temperature drop, resulting 
in unsatisfactory soldering. 
In particular, for properly soldering electric parts which are increasing 
in better performance and becoming more highly integrated, without causing 
damage thereto, it is necessary to adjust the temperature of the iron tip 
of the electric soldering iron with high accuracy. 
In order to solve the above-described problems, the applicant of this 
invention filed in the Japanese Patent Office an application for an 
electric soldering iron which is constructed in such a manner that the 
temperature of the iron tip can be correctly controlled with good response 
(Japanese Patent Application No. 5-203001, Japanese Patent Laid-Open No. 
7-40037, hereinafter referred to as "the second conventional technique"). 
The applicant also filed an application in the United States Patent Office 
as a basis of a priority ensured by the Paris Convention for the 
Protection of Industrial Property, and obtained a United States patent 
(U.S. Pat. No. 5,412,178). 
The electric soldering iron of the above-described second conventional 
technique will now be explained, in particular, referring to the Japanese 
patent application. 
That is, the electric soldering iron, which is operable by heating an iron 
tip with a heater, makes adjustments to the temperature of the iron tip by 
the following process. The amount of power supplied to the heater is 
adjusted by control means, based on the detected temperature of the iron 
tip, thereby adjusting the temperature of the tip to a desired value. 
The electric soldering iron is characterized in that a temperature sensor 
for detecting the temperature of the iron tip is attached to or near the 
forward end of the iron tip. 
In this electric soldering iron, the temperature sensor may be formed of, 
for example, a thermocouple sensor, in which case, it is required that a 
pair of sensor wires constituting the thermocouple sensor be 
insulation-coated. Then, a groove is formed in the boundary between the 
forward end of the iron tip and the columnar base thereof. Through this 
groove, a pair of sensor wires extending from a contact point part of the 
sensor secured to the forward end of the iron tip are introduced to the 
portion between the outer periphery of the columnar base and the heater 
cover. The wires are further extended to be pulled out from the portion 
between the columnar base and the heater cover, and a plug is coupled to 
the distal ends of the wires. 
When controlling the temperature of the iron tip during actual soldering 
operations by use of this soldering iron constructed as described above, 
the amount of power supplied to the heater is adjusted by the control 
means based on the temperature of the iron tip detected by the 
thermocouple sensor, thereby regulating the iron-tip temperature to the 
reference temperature set by the user. 
The heat-sensitive part of the thermocouple sensor is disposed at or near 
the forward end of the iron tip, without anything intervening 
therebetween. With this arrangement, the temperature of the forward end of 
the iron tip is directly detected while soldering is performed, thus 
making it possible to correctly detect the actual temperature of the iron 
tip. Control is then executed based on the thus-detected correct 
temperature so that the amount of power supplied to the heater can be 
properly adjusted. Hence, it is possible, not only during idling but 
actual soldering operations, to correctly regulate the temperature of the 
iron tip, in particular, the forward end thereof, with good response. 
In the manner described above, the foregoing problems inherent in the 
former type of the conventional soldering iron can be solved by the 
electric soldering iron of the second conventional technique. 
In this electric soldering iron, the sensor wires of the thermocouple 
sensor whose contact point part is attached to the forward end of the iron 
tip are insulation-coated, as has been discussed above. This is because of 
the following assumption. The sensor wires may be brought into contact 
with each other while passing through the iron tip, resulting in a short 
circuit therebetween. In such a case, a contact point is newly produced in 
the short-circuited portion, and information on the temperature of the 
newly-produced contact point is disadvantageously added to the temperature 
of the iron tip, which disturbs the detection of the correct temperature 
of the iron tip. Or, because it is possible that the sensor wires may be 
brought into contact with the heater cover, the portions of the iron tip 
other than the forward end, or other elements, a short circuit may also be 
generated, which inevitably creates a plurality of contact points, thus 
similarly making it impossible to detect the correct temperature of the 
iron tip. 
Thus, in the electric soldering iron of the second conventional technique, 
the insulation-coated sensor wires are used for the thermocouple sensor to 
prevent the above-described possible short circuit, but on the other hand, 
because of this arrangement, other types of various problems are newly 
created. 
That is, for preventing damage to the insulation coatings deposited on the 
wires caused by burning or the like, the sensor wires are extended in the 
rearward direction through the narrow portion between the heater cover and 
the columnar base of the iron tip, which is at a comparatively low 
temperature. In order to allow the sensor wires to pass through such a 
narrow portion, the wires should be made narrow in diameter. This further 
brings about an easy occurrence of a wire break by an external force, and 
accordingly, protection means should be provided for the uncovered portion 
of the wire located at the forward end of the iron tip. Additionally, the 
distal ends of the sensor wires, which should be made narrow in diameter, 
cannot be directly inserted into the socket, which is an end portion for 
receiving a signal representing the temperature of the iron tip, connected 
to the distal ends of the signal wires extending from the control means. 
It is thus required that a plug be first coupled to the distal ends of the 
wires and then connected to the socket. 
As a consequence, although the second conventional technique is superior in 
quality since it employs the thermocouple sensor as a temperature sensor, 
it somewhat increases the complexity of the construction, which inevitably 
increases the number of working and assembling processes and also leads to 
an increase in cost. 
SUMMARY OF THE INVENTION 
Accordingly, a first object of the present invention is to solve the 
above-described problems inherent in the electric soldering iron of the 
second conventional technique, and more specifically, to eliminate the 
necessity of constructing the sensor wires in a complicated manner, which 
has been conventionally required for allowing the wires to pass through 
the iron tip in order to protect the insulation coatings deposited on the 
wires from burning or the like. This also obviates the need for making the 
wires small in diameter, which further solves the problem of a wire break 
and also makes it possible to connect the wires to a jack or the like 
without requiring the attachment of a plug to the distal ends of the 
wires. Additionally, without having to take a possible wire break into 
consideration, protection means for protecting the uncovered portion of 
the wires is not required. 
A second object of the prevent invention is to provide an electric 
soldering iron which is simply constructed, thereby eliminating the number 
of working and assembling processes. 
In order to achieve the above objects, the present invention provides an 
assembly of a thermocouple sensor fitted to an iron tip, the sensor 
detecting a temperature of the iron tip and supplying a signal indicative 
of the detected temperature to temperature control means which then 
controls an amount of power supplied to a heater used for heating the iron 
tip. The thermocouple sensor has a pair of non-covered sensor wires, which 
provides a heat-sensitive part to be fixed to a nose of the iron tip. The 
pair of sensor wires are constructed to be received in a hollow portion of 
a columnar base extending from the rear end of the nose, without 
application of either an external force to bring the wires into strong 
contact with each other or to bring the wires into forceful contact with a 
conductive element including the iron tip. The wires also are constructed 
to be connectable to an end portion or member which is disposed in the 
rearward direction of the columnar base so as to receive a signal 
representing the detected temperature of the iron tip and to supply it to 
the temperature control means. 
In order to enable the above-described construction in which the sensor 
wires are attached to the iron tip and connected to the temperature 
control means, the following construction is further provided by way of 
example. 
That is, the pair of sensor wires may be constructed to be laid along the 
iron tip toward the rear of the nose so as to be received in the hollow 
portion formed in the columnar base via a lead-in hole opened in the 
vicinity of the boundary between the nose and the columnar base, and the 
wires may be further constructed to be inserted into and through a pair of 
guide holes, respectively, which are formed in a cylindrical insulating 
support of the heater to be disposed in the hollow portion, the distal 
ends of the wires being constructed to be connectable to a socket, which 
is an end portion disposed at the distal ends of the guide holes so as to 
receive a signal indicative of the detected temperature of the iron tip 
and supply it to the temperature control means. 
In order to construct the structure for fitting a thermocouple sensor to an 
iron tip in the manner described above, it is not necessary to use special 
types of temperature control means, heater and other elements, and known 
elements used for an electric soldering iron of a conventional type may be 
sufficiently employed. With respect to the heater, however, it is required 
that a pair of guide holes be formed in the cylindrical insulating support 
of the heater in such a way that they pass from the forward end to the 
rear end of the insulating support. 
A pair of non-covered sensor wires are employed for the thermocouple 
sensor, as described above, in which case, the largest possible diameter 
wires should be suitably used. More specifically, the wires are required 
to have a diameter of 0.32 mm or greater, and more preferably, 0.45 mm or 
greater. 
Since the structure of the present invention is constructed in the manner 
described above, an electric soldering iron formed by application of this 
structure can be used and operated as follows. 
It is needless to say that the electric soldering iron obtained by 
application of this invention carries out soldering by supplying power to 
the heater which then generates heat and applies it to the iron tip. 
During soldering operations, the amount of power supplied to the heater is 
adjusted by temperature control means, based on the temperature of the 
nose of the iron tip detected by the thermocouple sensor, thereby 
regulating the temperature of the tip nose to the reference temperature 
set by the user. 
In this electric soldering iron, the heat-sensitive part of the 
thermocouple sensor is directly secured to the nose of the iron tip, 
without anything intervening therebetween. With this arrangement, the 
temperature of the nose of the iron tip is directly detected while 
soldering is performed, thus making it possible to correctly detect the 
actual temperature of the iron tip. Based on the thus-detected correct 
temperature, the temperature of the heater is suitably adjusted, as has 
been discussed above. Hence, it is possible, not only during idling but 
also during actual soldering operations, to correctly regulate the 
temperature of the nose of the iron tip with good response. 
In this soldering iron, although the non-covered sensor wires are employed 
for the thermocouple sensor, an abnormality does not occur in detecting 
the temperature of the nose of the iron tip, thereby making it possible to 
correctly regulate the temperature of the nose of the iron tip with good 
response. 
The foregoing advantages are because of the following reasons. The electric 
soldering iron by application of this invention is constructed to enable 
the below-mentioned attachment of the sensor wires to the iron tip and the 
connection thereof to the control means. A pair of non-covered sensor 
wires extending from the heat-sensitive part secured to the nose of the 
iron tip are introduced to the hollow portion in the columnar base 
extending from the rear end of the nose, without application of either of 
external force to bring the wires into strong contact with each other or 
to bring the wires into strong contact with a conductive element, such as 
the iron tip. Also, the wires are coupled to an end portion, which is 
disposed in the vicinity of the rear end of the columnar base so as to 
receive a signal representing the detected temperature of the iron tip and 
supply it to the temperature control means. With the above-described 
construction, the sensor wires can be protected from a short circuit 
therebetween, which would otherwise cause an abnormality in detecting the 
temperature. 
A pair of sensor wires may be brought into light contact with each other 
while passing through the iron tip. Because of this contact, a short 
circuit may appear to occur between the wires. Also, a short circuit may 
seem to occur since the wires may come into contact with a part of the 
iron tip or other elements. However, if this type of contact occurs with 
merely a light touch, it does not actually cause an abnormality in 
detecting the temperature. This idea has been validated by a number of 
experiments. 
This may be because of the following assumption. An electrical resistance 
of approximately 500 to 1k.OMEGA. or higher can still be maintained 
between the wires by this degree of light contact. This resistance is 
further increased by an oxide film thermally produced on the surfaces of 
the wires. 
That the possible contact between the wires does not cause a short circuit 
may also be because the insulation established by the oxide film produced 
on the surfaces of the wires is not easily destroyed by a 
thermally-generated voltage as much as approximately 10 mV, which is 
usually generated in the thermocouple sensor. 
As described above, the electric soldering iron by application of the 
present invention is constructed to enable the below-mentioned attachment 
of the sensor wires to the iron tip and the connection thereof to the 
temperature control means. Without application of either external force to 
bring a pair of non-covered sensor wires into strong contact with each 
other or to bring the wires into forceful contact with a conductive 
element, such as the iron tip, the sensor wires extending from the 
heat-sensitive part are introduced to the hollow portion formed in the 
columnar base which extends from the rear end of the nose of the iron tip. 
Also, the sensor wires are coupled to the end portion, which is disposed 
in the vicinity of the rear part of the columnar base so as to receive a 
signal indicative of the detected temperature of the iron tip and supply 
it to the temperature control means. 
The above-described attachment of the sensor wires to the iron tip and the 
connection thereof to the temperature control means can further be 
achieved by enabling, for example, the following construction. 
That is, the above-described pair of non-covered sensor wires forming the 
thermocouple sensor whose heat-sensitive part is securely fixed to the 
nose of the iron tip are laid along the iron tip toward the rear of the 
nose so as to be introduced to the hollow portion in the columnar base via 
a lead-in hole opened in the vicinity of the boundary between the nose and 
the columnar base. Then, the wires are inserted into and through a pair of 
guide holes, respectively, which are formed in a cylindrical insulating 
support of the heater to be disposed in the hollow portion, and the distal 
ends of the wires are coupled to a socket, which is an end portion 
disposed in the vicinity of the rear ends of the guide holes so as to 
receive a signal indicative of the detected temperature of the iron tip 
and supply it to the temperature control means. 
With this arrangement, although non-covered sensor wires are employed for 
the thermocouple sensor, an abnormality does not occur in detecting the 
temperature of the nose of the iron tip, thereby enabling correct 
adjustments to the temperature of the iron-tip nose with good response. 
Namely, in the above-described electric soldering iron, without application 
of either of external force to bring a pair of non-covered sensor wires 
into strong contact with each other or to bring the wires into forceful 
contact with a conductive element, such as the iron tip, the wires 
extending from the heat-sensitive part secured to the nose of the iron tip 
are introduced to the hollow portion of the columnar base through the 
lead-in hole. Then, the wires are guided toward the rear of the columnar 
base through guide holes formed in the insulating support of the 
insulating heater. Further, the wires are coupled to the socket connected 
to the distal ends of the signal wires extending from the temperature 
control means. With this construction, a short circuit is not produced 
between the pair of sensor wires, which would otherwise cause an 
abnormality in detecting the temperature of the iron tip. 
If a pair of sensor wires are brought forcefully into contact with each 
other or with a part of the iron tip, while passing through the iron tip, 
a short circuit may outwardly appear to occur between the wires. However, 
if this type of contact occurs with merely a small force, it does not 
actually cause an abnormality in detecting the temperature. The reason has 
already been explained in the above description. 
As has been discussed above, the present invention is constructed in such a 
manner that the thermocouple sensor is formed of non-covered sensor wires, 
and the wires are not forced to pass through the narrow space, such as the 
portion between the columnar base of the iron tip and the heater cover, 
thus making it possible to make the diameter of the sensor wires as large 
as possible. With this arrangement, it is possible overcome the drawback 
of an easy occurrence of a wire break inherent in the second conventional 
technique, which further eliminates the necessity of providing protection 
means for protecting the sensor wires from a wire break. 
Additionally, the strength of the sensor wires is increased due to the 
larger diameter thereof. Accordingly, without requiring the attachment of 
a plug to the distal ends of the wires, they can be directly coupled to 
the socket, which is an end portion for receiving a signal representing 
the detected temperature of the iron tip to supply it to the temperature 
control means. This decreases the number of assembling processes and also 
eliminates the need for a plug, which further leads to a reduction in cost 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will now be described in detail with 
reference to the drawings. 
Although the present invention will be described in the form of the 
following preferred embodiment which is limited by various technically 
preferable restrictions, it is not intended to limit the scope of the 
invention by any of these preferred modes, unless otherwise specified in 
the following description. 
As shown in FIGS. 1-4, the electric soldering iron is provided with an iron 
tip 21 at the forward end thereof. The iron tip 21 has a generally-tapered 
nose 21a at its forward end portion and a columnar base 21b at its base 
end portion. Further, the outer periphery of the base 21b is removed to 
form a smaller-diameter joint tubular portion 21c at the rear of the base 
21b. The joint tubular portion 21c can be securely screwed to a 
generally-cylindrical tip holder 22 by the following process. The joint 
tubular portion 21c is first detachably inserted into an opening at the 
forward end of the tip holder 22, and a tip-setting screw 23 is inserted 
from the outer periphery of the tip holder 22 so that the forward end of 
the tip holder 22 can be pressed against the outer periphery of the joint 
tubular portion 21c. Accordingly, when the screw 23 is loosened, the joint 
tubular portion 21c can easily be removed from the tip holder 22. 
Further, as illustrated in FIGS. 1-4, a contact point part 24a, which is a 
heat-sensitive part of a non-covered thermocouple sensor 24, is secured to 
the nose 21a of the iron tip 21. As particularly shown in FIG. 2, 
non-covered sensor wires 24b, 24b extending from the contact point part 
24a are further laid on the outer surface of the tip nose 21a toward the 
columnar base 21b in such a way that they are slightly separated from each 
other. Also, as illustrated in FIG. 1, the sensor wires 24b, 24b are 
introduced into a hollow portion 21e within the columnar base 21b through 
a lead-in groove 21d which is opened in the boundary between the tip nose 
21a and the base 21b. The wires 24b, 24b further pass into and through 
guide holes 25a, 25a which are longitudinally formed in the vicinity of 
the center of an insulating support 25d of a heater 25 which is to be 
inserted into the hollow portion 21e. The distal ends of the sensor wires 
24b, 24b projecting from the rear end of the insulating support 25b of the 
heater 25 are in the state of being coupled to a socket 26. The socket 26 
is connected to a signal processor 28 of a temperature controller 27 via 
signal wires. 
As shown in FIGS. 1 and 4, a coupling connector 30 is inserted into the 
opening at the forward end of a grip 29, and the socket 26 is fixed in the 
center of the rear portion of the coupling connector 30. Moreover, 
electric power contact pins 31, 31 are provided in predetermined positions 
of the outer peripheral portion of the socket 26, and a ground contact pin 
32 is also provided in a farther outward predetermined position than the 
contact pins 31, 31. 
As illustrated in FIGS. 1 and 4, the forward ends of electrodes 25b, 25b of 
the heater 25 are inserted into the electric power contact pins 31, 31 so 
that they can be electrically connected and mechanically supported to/by 
the pins 31, 31. 
As shown in FIG. 1, the coupling connector 30 is provided with a groove 30a 
formed in a ring-like shape in a position corresponding to the ground 
contact pin 32 so as to receive a ground spring 33. This groove 30a thus 
serves to receive one end of the ground spring 33 and also to allow a lead 
wire 33a of the end of the spring 33 to be inserted into the contact pin 
32 so as to establish an electrical connection therebetween. 
The rear ends of the power contact pins 31, 31 are connected to a power 
supply 34 of the temperature controller 27 via power lines, and the ground 
contact pin 32 is connected to the ground of the temperature controller 27 
via a ground line. 
As shown in FIGS. 1 and 4, a male thread 29a projects from the forward end 
of the grip 29, and a heat radiating nut 35 is detachably fit around the 
male thread 29a. The tip holder 22 is further fixed to the forward end of 
the radiating nut 35 via a flange portion at the rear end of the holder 22 
and via screws 36, 36 . . . used for securing the flange portion to the 
radiating nut 35. With this construction, since the forward end of the 
ground spring 33 is held by the flange portion of the tip holder 22, the 
coupling connector 30 is pressed toward the rear via the spring 33 so that 
it can be fixed within the forward portion of the grip 29. 
The above-described heater 25 is constructed in such a manner that a 
heat-emitting portion 25c is held by the cylindrical insulting support 25d 
formed of a ceramic material and is provided for only a part near the 
outer periphery of the front half of the heater 25. It is needless to say 
that the heat-emitting portion 25c is electrically connected to the two 
electrodes 25b, 25b provided at the rear end of the insulating support 
25d. 
As has been discussed above, a pair of guide holes 25a, 25a are 
longitudinally formed in the vicinity of the center of the cylindrical 
insulating support 25d of the heater 25 so as to allow the non-covered 
sensor wires 24b, 24b of the thermocouple sensor 24 to pass into and 
through the holes 25a, 25a from the forward end to the rear end. The 
socket 26 is fixed in the rear of the rear ends of the guide holes 25a, 
25a while being located by the coupling connector 30. Further, the distal 
ends of the sensor wires 24b, 24b passing through the holes 25a, 25a are 
guided into connecting holes of the socket 26. 
Since the above-described thermocouple sensor 24 is formed of non-covered 
wires, and since the wires are not forced to pass through a narrow space, 
it is possible to enlarge the diameter of the sensor wires 24b, 24b as 
needed, 0.5 mm-diameter wire rods being used in this embodiment. The 
sensor wires 24b, 24b thus have a sufficient strength and are not easily 
bent with a small force, and accordingly, they can be inserted into the 
socket 26 without requiring the connection of a plug to the distal ends of 
the wires 24b, 24b. 
The temperature controller 27 used in this embodiment is a typical 
apparatus which compares the temperature of the iron tip 21 detected by 
the thermocouple sensor 24 with the reference temperature set by the user 
and then makes adjustments to the amount of power supplied to the heater 
25, thereby controlling the temperature of the iron tip 21 to match the 
reference temperature. 
In FIG. 4, reference numeral 37 denotes a cable formed by integrating the 
above-described signal wires, power wires and the ground wire. 38 
indicates a female connector; 39 designates a male connector provided for 
the temperature controller 27; and 40 represents a cable. 
The electric soldering iron of this embodiment constructed as described 
above, as well as typical soldering irons of this type, supplies power to 
the heater 25 from the power supply 34 of the temperature controller 27 
via the power lines so as to allow the heater 25 to emit heat and apply it 
to the iron tip 21, thereby performing a soldering operation. 
In this electric soldering iron, the contact point part 24a, which is a 
heat-sensitive part, of the thermocouple sensor 24 is secured to the nose 
21a of the iron tip 21 so as to detect the temperature of the nose 21a of 
the iron tip 21. The thus-detected temperature information in the form of 
an electric signal is transmitted to the signal processor 28 of the 
temperature controller 27 via the sensor wires 24b, 24b and the signal 
wires connected thereto. The temperature controller 27 executes the 
following process to control the nose 21a of the iron tip 21 to reach the 
reference temperature. Upon processing being executed by the signal 
processor 28, the amount of power is determined in the power supply 34 so 
as to be supplied via the power lines to the heater 25 in which an 
appropriate heating action is performed so that the nose 21a of the iron 
tip 21 can reach the reference temperature. 
It is needless to say that signal processing executed by the signal 
processor 28 is performed based on the information on the detected 
temperature of the nose 21a of the iron tip 21, which information can be 
received in real time, and also based on the reference temperature set by 
the user. 
In performing an actual soldering operation by use of this electric 
soldering iron, the iron tip 21, in particular, the nose 21a, as well as 
those elements of the other types of electric soldering irons, may be 
cooled by solder or parts to be soldered, such as electric parts. 
In this embodiment, as described above, the contact point part 24a used as 
a heat-sensitive part of the thermocouple sensor 24 is attached to the 
nose 21a of the iron tip 21 so that the temperature of the nose 21a of the 
iron tip 21 can be directly detected. With this arrangement, the 
temperature of the nose 21a of the iron tip 21 can be detected without 
producing a time lag and be transmitted to the signal processor 28 of the 
temperature controller 27. The temperature is then compared with the 
reference temperature in the signal processor 28 and, upon this 
comparison, the amount of power supplied to the heater 25 can be 
determined in the power supply 34. With this arrangement, the temperature 
of the nose 21a of the iron tip 21 can be regulated without delay. 
As a result, correct adjustments can be made to the temperature of the nose 
21a of the iron tip 21 in real time, which further enables correct 
adjustments of the exact soldering temperatures required for performing 
soldering operations for precision electric parts. 
On the other hand, the non-covered sensor wires 24b, 24b are used as wires 
for the thermocouple sensor 24 of the electric soldering iron of this 
embodiment. However, the wires 24b, 24b of this type do not cause any 
abnormality in the detection of the temperature of the nose 21a of the 
iron tip 21, and it is still possible to correctly adjust the temperature 
of the nose 21a of the iron tip 21 with good response. 
That is, this seeming contradiction arises from the fact that even though 
the sensor wires 24b, 24b are non-covered, a short circuit does not occur 
between the wires 24b, 24b, which otherwise would cause an abnormality in 
detecting the temperature. 
More specifically, the sensor wires 24b, 24b in some cases may be brought 
into contact with each other while passing through the iron tip 21. 
Because of this contact, a short circuit may appear to occur between the 
wires 24b, 24b. Also, a short circuit may seem to occur between the wires 
24b, 24b since the wires may come into contact with a part of the iron tip 
21 while passing through the iron tip 21. However, this type of contact 
occurs with merely a light touch, that is, a great force does not 
particularly act upon the wires 24b, 24b when they are brought into 
contact with each other or with a part of the iron tip 21. Thus, this does 
not bring about a short circuit to such a degree as to cause an 
abnormality in detecting the temperature. 
Further, this may be because of the following reason. An electrical 
resistance of approximately 500 to 1k.OMEGA. or higher can be still 
maintained between the wires 24b, 24b by this degree of light contact. 
This resistance is further increased by an oxide film thermally produced 
on the surfaces of the wires 24b, 24b. 
That the contact between the wires 24b, 24b does not cause a short circuit 
may also be because the insulation established by the oxide film produced 
on the surfaces of the wires 24b, 24b is not easily destroyed by a 
thermally-generated voltage as much as approximately 10 mV, which is 
usually generated in the thermocouple sensor 24. 
As in the manner described above, the electric soldering iron of this 
embodiment is constructed as follows. The contact point part 24a, which is 
a heat-sensitive part of the thermocouple sensor 24, is securely attached 
to the nose 21a of the iron tip 21. A pair of non-covered sensor wires 
24b, 24b are laid and extended on the surface of the nose 21a from the 
contact point part 24a while being slightly separated from each other so 
as to be introduced into the hollow portion 21e of the columnar base 21b 
via the lead-in hole 21d which is opened in the vicinity of the boundary 
between the nose 21a and the base 21b. The wires 24b, 24b are further 
allowed to be inserted into and through the guide holes 25a, 25a, 
respectively, and the distal ends of the wires 24b, 24b projecting from 
the rear ends of the holes 25a, 25a are inserted into the connecting holes 
of the socket 26. 
With the above-described construction, the sensor wires 24b, 24b are not 
usually brought into contact with each other with a great force, and also, 
they are protected from forcefully coming into contact with any part of 
the iron tip 21. If a particular operation is performed, for example, if 
the sensor wires 24b, 24b are simultaneously pressed against the tip of a 
flat-blade screwdriver with a great force, an abnormality in detecting the 
temperature may be caused, which extreme case will be described 
hereinafter. However, it is very unlikely that an accident similar to this 
will occur during actual soldering operations. It can thus be concluded 
that the sensor wires 24b, 24b can be usually protected from the 
occurrence of a short circuit therebetween while passing through the guide 
holes 25a, 25a of the heater 25, thus allowing the thermocouple sensor 24 
to continue to detect the correct temperatures. 
FIG. 5 is a diagram showing a change in the temperature of the nose of the 
iron tip when a soldering operation is performed to solder a 1/4 W carbon 
resistor to a glass epoxy resin substrate by use of the electric soldering 
iron of this embodiment under the following conditions. The power capacity 
of the heater 25 used in the electric soldering iron is 40 W, and the 
reference temperature which is targeted in this soldering operation is 
320.degree. C. This operation is performed manually by the user. 
FIG. 6 is a diagram given for comparison with FIG. 5, and shows a change in 
the temperature of the nose of the iron tip when a soldering operation is 
performed to solder. a 1/4 W carbon resistor to a glass epoxy resin 
substrate under the following conditions by use of an electric soldering 
iron which is formed by application of the above-described second 
conventional technique. The power capacity of the heater used in the 
soldering operation is also 40 W, and the reference temperature which is 
targeted in this operation is also 320.degree. C. This operation is 
performed manually by the user. 
The iron tip of the latter soldering iron (the one which is formed by 
application of the invention of the second conventional technique) is 
formed in nearly the same shape as that of the embodiment of this 
invention, both iron tips being equal in diameter and length, although 
they cannot be exactly identical, for example, the iron tip of the latter 
soldering iron is not provided with a hole equivalent to the lead-in hole 
21d provided for the soldering iron of the embodiment. 
As shown in FIGS. 5 and 6, a sharp decrease in the temperature for an 
instant can be detected between 60 and 75 seconds and between 90 and 105 
seconds. This is because the iron tips of both the soldering irons were 
cleaned with a water-soaked sponge. 
FIGS. 5 and 6 indicate that no substantial difference can be detected 
between a change in the temperature of the nose of the iron tip according 
to the present invention and that of the second conventional technique. 
This verifies that the use of the non-covered sensor wires 24b, 24b as the 
thermocouple sensor 24 does not cause an abnormality in detecting the 
temperature. 
In the electric soldering iron of this embodiment, if an extreme operation 
is carried out, for example, if the portions of the sensor wires 24b, 24b 
which are laid on the rear part of the nose 21a of the iron tip 21 are 
simultaneously pressed against the forward end of a flat-blade 
screwdriver, a sharp temperature drop by approximately 100.degree. C. is 
detectable. This symptom may arise from the fact that a short circuit has 
been produced at the portions of the sensor wires 24b, 24b which are 
pressed against the flat-blade screwdriver, and the information on the 
temperature of the short-circuited portions is disadvantageously 
transmitted. The amount of decrease in the temperature varies depending on 
the part to be forcefully pressed against the flat-blade screwdriver. It 
is certain that the abnormality in detecting the temperature can be 
immediately eliminated by quitting the above-described pressing operation 
with the screwdriver. 
Conversely, it can be understood that the constant operation of detecting 
the correct temperatures can be ensured unless any extreme action, such as 
simultaneously pressing the sensor wires 24b, 24b with the forward end of 
the flat-blade screwdriver, is performed. In fact, however, it is very 
unlikely that such an extreme action will be made during actual soldering 
operations. It can thus be confirmed that an abnormality hardly occurs in 
detecting the temperature during the usual soldering operation. 
In the electric soldering iron of this embodiment, the thermocouple sensor 
24 is formed of the non-covered sensor wires 24b, 24b which are not forced 
to pass through a narrow space, such as a groove formed between the 
columnar base of the iron tip 21 and the heater cover. With this 
construction, the sensor wires 24b, 24b can be formed of a larger 
diameter, and accordingly, the 0.5 mm-diameter sensor wires 24b, 24b are 
used in this embodiment, as has been discussed above. 
The sensor wires 24b, 24b, in particular, the portions exposed to the 
exterior from the nose 21a of the iron tip 21, are likely to be brought 
into contact with solder or parts to be soldered during soldering 
operations or other occasions. However, even if they come into contact, 
there is very little possibility of producing a wire break because of the 
thus-formed larger wires. This eliminates the necessity of providing 
protection means or the like for preventing a break of the sensor wires, 
which are generally necessitated for the wires of the thermocouple sensor 
used in the electric soldering iron of the second conventional technique. 
Also, as described above, since the diameter of the sensor wires 24b, 24b 
of the thermocouple sensor 24 is made as large as 0.5 mm, the strength of 
the wires themselves is increased. Given this advantage, the sensor wires 
24b, 24b can be directly connected, without requiring the attachment of a 
plug to the distal ends of the wires, to the socket 26, which is an end 
portion for receiving a signal indicative of the temperature of the iron 
tip to supply it to the temperature controller 27. This further decreases 
the number of assembling processes and eliminates the need for a plug, 
which gives rise to a reduction in cost. 
For the replacement of the worn iron tip 21 with a new one, it is essential 
only that the tip-setting screw 23 is first loosened from the tip holder 
22 so as to detach only the iron tip 21 together with the thermocouple 
sensor 24 secured thereto, and then, a new iron tip 21 which is also 
provided with a thermocouple sensor 24 is coupled to the tip holder 22 
while the sensor wires 24b, 24b of the thermocouple sensor 24 are inserted 
into the guide holes 25a, 25a. In this manner, the replacement operation 
of the iron tips can be extremely simplified. In other words, since the 
sensor wires 24b, 24b possess a sufficient strength, they can be merely 
inserted into the guide holes 25a, 25a of the heater 25 so that they can 
be guided into the socket 26 and properly coupled thereto. 
In contrast, for the replacement of iron tips of the electric soldering 
iron according to the second conventional technique, it is necessary that 
the cover nut be first detached to remove the worn iron tip and the 
thermocouple sensor attached to the tip, and then, the heat-radiating nut 
be detached in order that a plug connected to the distal end of the 
thermocouple sensor of a new iron tip can be coupled to the socket 
connected to the distal ends of the signal wires of the temperature 
controller. It is obvious that the replacement operation necessitated by 
the present invention is much simpler than that by the second conventional 
technique. 
As will be clearly understood from the foregoing description, the present 
invention offers the following advantages. 
The temperature of the iron tip of the electric soldering iron is directly 
detected by the thermocouple sensor so as to regulate the temperature of 
the heater, thereby achieving correct adjustments to the temperature of 
the iron tip with good response even during actual soldering operations. 
Additionally, even though the thermocouple sensor is formed of non-covered 
sensor wires, it is constructed such that an external force does not act 
upon the wires, thus inhibiting an easy occurrence of a short circuit 
between the wires and preventing the generation of an abnormality in 
detecting the temperatures. 
Since the thermocouple sensor is formed of non-covered sensor wires, and 
since the wires are not forced to pass through a narrow space, the wires 
can be enlarged in diameter, thus inhibiting an easy occurrence of a wire 
break. This further obviates the necessity of protecting the thermocouple 
sensor from a wire break. Also, even though the sensor wires are brought 
into contact with the surrounding parts or the parts to be soldered, they 
can be prevented from being damaged even without being provided with 
protection means. With this advantage, the user is able to carry out a 
soldering operation without concern for damage to the wires. As a 
consequence, there can be an improvement in the workability of soldering. 
Moreover, the sensor wires of the thermocouple sensor possess increased 
strength because of the larger diameter thereof. Accordingly, the wires 
can be directly coupled, without requiring the attachment of a plug or the 
like to the distal ends of the wires, to a connector such as a socket or 
the like, which is an end portion for receiving a signal indicative of the 
temperature of the iron tip to supply it to the temperature controlling 
means. The plug or the like is not required so that the number of 
assembling processes can be decreased and a reduction in cost can be also 
achieved. 
Further, for the replacement of the worn iron tip with a new one used in 
the soldering iron constructed as described in the foregoing embodiment, 
it is essential merely that only the iron tip together with the 
thermocouple sensor attached thereto be detached from the tip holder, and 
then, a new iron tip which is also provided with a thermocouple sensor is 
attached to the tip holder while the sensor wires of the thermocouple 
sensor are inserted into the guide holes of the heater. In this manner, 
the replacement operation is extremely simplified. In other words, since 
the sensor wires have a sufficient strength, they can be simply inserted 
into the guide holes of the heater so that they can be guided into the 
socket, and the distal ends thereof can be properly coupled to the socket.