Note: Descriptions are shown in the official language in which they were submitted.
i~71279
The present invention relates to an extension thermo-
stat for controlling the energization of an electric heating
element, in particular for hair treatment apparatuses.
Thermostats are necessary in numerous technical ap-
paratuses, especially in warming pans, coffee machines or heating
plates.
In hair treatment apparatuses, e.g. curling irons, it
is also required to be able to regulate the heating temperature.
Such curling irons normally have a heater by which heat is
provided for curling hair, which is initially moistened and then
treated by the hair treatment apparatus. m e heating temperature
is, however, not adjustable, so that in some cases it is too high
and in other cases it is too low. A particular problem arises in
the temperature control of steam curling irons when it is desired
to control the temperature relatively accurately within a
relatively limited range of about 100C to 150C. The lower
limit temperature of 100C corresponds to the vapourization
temperature of water, while the upper temperature of 150C should
not be exceeded, otherwise the hair will be damaged.
In U.S. Patent 3,534,392, there is disclosed a curling
iron having a resistor in the form of a heater spiral functioning
as a heater. This electrical resistor is provided with a thermo-
stat which prevents over-heating of the resistor. The thermostat
comprises a bi-metallic relay which switches on and off at
predetermined temperatures. However, bi-metallic relays have
the disadvantage that they are trouble-prone and operate
inaccurately. Moreover, a thermostat of the above-described kind
is not continuously adjustable, i.e. it switches on and off only
at predetermined temperatures which cannot be altered by the
person using the curling iron.
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It is accordingly an object of the present invention to pro-
vide a novel and improved extension thermostat which enables the opera-
ting temperatures of a heat treatment apparatus to be readily adjusted.
According to the present invention, there is provided an
extension thermostat for controlling the energization of a heating
element, comprising a heat sensor, the heat sensor comprising a
sensing tube and a rod received in the sensing tube; the rod having
a co-efficient of thermal expansion different from that of the
sensing tube; the rod and the sensing tube being in secure engage-
10 ment at at least one position; and the rod or the sensing tube beingsecured to a fixed point, whereby relative movement of the rod and
the sensing tube is caused by extension and contraction of the rod or ~ -
the tube in response to temperature variations; switch means actua-
table by the relative movement of the rod and the sensing tube; a
heating element located in the vicinity of the heat sensor and hav-
ing a current circuit the energization of which is controlled by the
switch means; a double-armed lever having a first lever arm engaged
by the heat sensor and a temperature adjustment mechanism connect-
ing the second lever arm of the lever to a switch actuation member
20 forming part of the switch means.
In one advantageous embodiment of the invention, the first
lever arm is shorter than the second lever arm, and the adjustment
mechanism comprises a threaded member which can be screwed through
the second lever arm and which is arranged below the switch actua-
tion member of the switch means, the threaded member being con-
nected to part of an adjustment disc and, by a spring, to the switch
actuation member. In order to adjust the required end temperature
of the hair treatment apparatus, the user has only to adjust the ad-
justment disc to a pre-determined temperature. When the pre-set
30 temperature is reached, this can be indicated by means of a lamp.
Almost all of the operations required for effecting this take
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place automatically without the user having to undertake any
further actions.
It is a particular advantage of the invention that it
can be employed without difficulty in different technical
apparatuses requiring heat regulation, e.g. in coffee machines or
heating plates.
The invention will be more readily understood from the
following description of a preferred embodiment thereof given, by
way of example, with reference to the accompanying drawings,
in which,-
Figure 1 shows a plan view of a curling iron;
Figure 2 shows an enlarged view of an adjustment disc
forming part of the curling iron of Figure l;
Figure 3 shows 'a view of the curling iron of Figure 1
rotated through 90 about its longitudinal axis;
Figure 4 shows parts of a thermostat of the curling
iron of Figure l; and
Figure 5 is a partial view, taken in cross-section to
the curling iron of Figure 1, showing parts of the thermostat.
In Figure 1 of the drawings there is shown a curling
iron which comprises basically a hand-grip 2, a curling rod 3, a
steamer part 4 and a clamp 5. In the hand-grip 2, there is
provided a clamp actuating device 6, a lamp 7 indicating the
state of operation of the curling iron and an adjustment disc 8.
The supply of electrical energy is effected, in the illustrated
curling iron 1, through a cable 9. When it is desired to curl
hair, the hair is wound around the curling rod 3 with the clamp
5 raised and then, by releasing the clamp actuating device 6, the
hair is pressed against the curling rod. Through the cable 9, a
heater element, which is located in the curling rod 3 and which,
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for example, can have the form of a cylindrical heater spiral,
is supplied with an electrical energy and is thereby heated.
Simultaneously, a plate (not shown) located in the curling rod 3
is heated. The steamer part 4, wllich comprises essentially a
water container from which a wick extends, can now be pressed
against this plate. When the wick comes against the heated plate,
the water vapourizes and passes through the curling rod to the
hair. When the steaming process is completed, the moistened
hair is dried again with the help of the heating element disposed
in the curling rod.
When the hair treatment has been finished, the clamp
5 is released by pressure on the clamp actuating device 6, and
the curled hair can be removed from the curling rod 3.
Figure 2 shows in greater detail the adjustment disc
8 already illustrated in Figure 1. As can be seen, the adjust-
ment disc 8 has a knurled peripheral ring 10, which facilitates
manual rotary adjustment of the adjustment disc 8. In addition,
the adjustment disc 8 has a temperature range indicator 11 in the
form of a segmental annular slot provided with symbols indicating
middle, high and low temperatures. Instead of these symbols, the
Celsius scale could, of course, could be directly indicated. By -
rotations of the adjustment disc, it is possible to set the
required final temperature.
Preferably, the hand-grip 2 is provided with a fixed
mark pointing towards the temperature range indicator, and in
this way easy observation of the adjusted temperature is provided.
Figure 3 shows the same curling iron 1 as Figure 1, but
rotated through 90 about its longitudinal axis. In this position,
holes provided in the curling rod 3 for the discharge of the
steam can be very clearly seen.
Figure 4 diagrammatically illustrates the manner in
which switch actuation is effected by means o~ a sensing tube 12
having an inner rod 13. The sensing tube 12 is held at a fasten-
ing 16 and carries in its interior the rod 13, which has a
notch 15 engaged by a nose 14 connected with the sensing tube 12.
While the notch 15 and the nose 14 are provided at the lower, i.e.
left-hand, ends of the rod 13 and the sensing tube 12, the oppo-
site end of the rod 13 bears against the shorter arm of a double-
armed lever 17. The longer arm of the lever 17 bears against a
switch actuation plunger 20 of a micro switch 19, the conductors
21 of which extend to a heating element (not shown). If the
temperature around the sensing tube 12 increases, the sensing tube
12 expands. Since, however, it is fixedly secured at one end, it
can expand in only one direction, i.e. to the left as viewed in
Figure 4. By this leftward movement, the rod 13 in the sensing
tube 12 is likewise drawn to the left, since it is connected by
the notch 15 to the sensing tube 12. Since the rod 13, however,
in contrast to the sensing tube 12, is not fixedly secured at
one end, it also moves its end, which bears against the lever 17,
towards the left, whereby the force acting on the switch actuation
plunger 20 of the microswitch 19 is reduced and the current
supply is switched off. When the sensing tube 12 cools, the lever
17 pivots in the opposite direction about its pivot 18.
The arrangement of the sensing tube 12 with a high co-
efficient of thermal expansion around the rod 13 with a low co-
efficient of thermal expansion has particular advantages over the
opposite arrangement. If the inner rod 13 had the larger co-
efficient of thermal expansion and if it displaced a tube, so
that the latter actuated a switch, then a time delay would occur
before the switch actuation was effected. This time delay would
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be caused since the outer temperature would not immediately reach
the inner rod, but would firstly have to pass through the outer
tube. Since the regulator shown in Figure 4 is a two-way regula-
tor, i.e. only switches on or off, the temperature differences
between switching on and switching off would be too large and,
in extreme cases, would exceed the control range of 100C to
150C, which is important in steam curling. A temperature
deviation of plus or minus 5C should in no case be exceeded.
In order to obtain a regulation which is as exact as
possible, the heat transfer between the heating spiral or casing
on the one hand, and the sensing tube on the other hand, must of
course be sufficiently good. This is achieved by appropriate
arrangement of the sensing tube on or in the heating element.
Pre-adjustment of the final temperature to be reached
is not possible using only the parts shown in Figure 4, but is
effected by the arrangement shown in Figure 5.
Figure 5 shows the hand-grip 2 of the curling iron 1,
which hand-grip 2 contains the sensing tube 12 and the rod thirt-
een. One end of the sensing tube 12 extends into a heating element
in the curling rod 3, which is not shown in this figure, and in
this manner is exposed to the heat of this heating element. The
other end of the sensing tube 12 is fixedly secured in the
fastening 16. The shorter arm of the lever 17 is engaged by the
rod 13 projecting from the sensing tube 12. The longer arm of
the lever 17 extends from the pivot point 18 of the lever 17
initially in a downwardly inclined direction, as viewed in Figure
5, and then has a horizontal disposition. Consequently, the
shorter and longer lever arms are disposed practically perpendicu-
lar to one another, which, however, is not essential to the
invention but is merely particularly advantageous in the present
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embodiment of the curling iron~
In the horizontal part of the longer lever arm, there is
screwed a threaded bolt 25, which bears against the switch actua-
tion plunger 20 of the microswitch 19. This microswitch 19 has --
terminals 27, 28 and 29 to which corresponding conductors 30, 31
and 32 extend. By actuation of the switch actuation plunger 20,
the conductors, which extend to the heating element, can be
energized or de-energized.
The force required for actuating the switch actuation
plunger 20 is provided mainly by a spring 23, which has one end
secured to a fixed portion of the hand-grip 2 and which has its
other end engaged in the longer arm of the lever 17. By accurate
dimensioning of the spring 23, the lever 17, the sensing tube 12
and the rod 13, and by adjustment of the sensing tube 12 relative
to the lever 17, an arrangment can be provided for producing an
; accurately defined final temperature of the curling rod 3.
Alteration of the final temperature can then be obtained
by means of the adjustment disc 8. When the adjustment disc 8 is
manually rotated, then it in turn rotates a bolt 24, which is
connected to it, and thus drives a spring 22. The spring 22, in
turn, rotates the threaded bolt 25 and screws inwardly or out-
wardly of the longer arm of the lever 17. In this way, the
spacing between the longer lever arm and the switch actuation
plunger 20 is altered, which effects an earlier or later actuation
of the microswitch 19 as desired.
With the arrangement shown in Figure 5, it is not the
purpose of the spring 22 to provide a spring force in the vertical
direction; moreover, a spring is used only since, by means of the
spring, the actual displacement of the threaded bolt 25 caused by
the inward or outward screwing of the threaded bolt 25 in the
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lever arm does not affect the bolt 24. Instead of the spring, any
other element, e.g. vulcanized rubber concertina wall, which ful-
fills the same functions could be employed.
~ loreover, the use of microswitch 19 of the type illus-
trated is not absolutely essential, since any switch having a
small switching path and which can be fixed on a part fixedly
connected by a screw 26 to the hand-grip 2 may be employed.
It has been found that brass or aluminum are particu-
lar materials for the sensing tube 12, while the rod 13
preferably comprises a nickel-iron alloy. However, other
materials may be employed, provided that they differ from one
another sufficiently with respect to their co-efficients of
thermal expansion.
Although the above-described embodiment of the inven-
tion is a curling iron, the invention is in no way restricted to
curling irons, but can be employed with advantage whenever it is
required to provide a variable temperature limit.
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