Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2002-03-06
2004-04-13
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S248000, C219S257000, C038S082000
Reexamination Certificate
active
06720537
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
This application claims the priority benefit of German patent application DE 101 10 993.8 filed on Mar. 7, 2001.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
BACKGROUND OF THE INVENTION
The present invention relates to a device for detecting, monitoring and controlling the operating status of an electric iron or flat-iron. Commonly, the user is accustomed to receiving an optical signal, such as a light, indicating a supply of energy to a heating element of the electric iron. Usually, a glow lamp is used for this purpose, and the glow lamp, with a resistor connected in series therewith, is connected in parallel to the heating element.
Some commercially available steam irons furthermore comprise an electronic assembly which conducts and/or switches the heating current. Often, the electronic assembly is provided with additional optical or acoustic indicator means for indicating further characteristics of the operating status of the electric iron. The indicator means are controlled by a control unit provided in the electronic assembly which also comprises a low voltage power supply for energizing the additional indicator means and the control unit.
FIG. 1
shows a circuit diagram of a prior art steam iron which is provided with the above mentioned glow lamp indicator and an electronic assembly having additional indicator means. The circuitry comprises a so-called safety shut-off device such as, for example, implemented in a steam iron TDA 7550 of Bosch.
As shown in the circuit diagram of
FIG. 1
, the electronic assembly
1
comprises a low voltage power supply
2
which is energized by the line voltage supply L, N without galvanic isolation via an impedance
3
connected in series therewith. The low voltage power supply energizes a control unit
4
and a LED-indicator unit
5
. The control unit
4
controls a power switch
6
which is a component of the electronic assembly
1
, and is connected in series with an electric heating circuit L,
7
,
10
, N of the iron for opening the electric heating circuit.
The output of the control circuit
4
driving the power switch
6
is depending on delay timers (not shown), optionally in combination with a sensor system (not shown) for detecting different positions (upright, horizontal) and/or movements of the electric iron or flat iron. The present operating status of the electronic assembly
1
and, hence, of the iron, is displayed by indicator unit
5
which comprises a light-emitting diode providing an alarm indication by flashing when the power switch
6
has been opened by means of control unit
4
depending on the delay timers and/or the movement and position status sensor.
The electric heating circuit of the iron comprises a heating element
10
and a power switch
7
being connected in series therewith and constituting the primary ON/OFF-switch for the heating element
10
. Power switch
7
is provided outside of the electronic assembly
1
and, for this reason, is called hereafter “external” power switch. The external power switch
7
corresponds to the thermostat at the iron sole and is switched (closed and opened) by the usual thermostat adjustment with a temperature sensor and a manually selectable temperature range.
The power switch
6
being integrated in the electronic assembly
1
and, for this reason, being called hereafter “internal” power switch, allows a safety shut-off of the energized iron in addition to the thermostatically controlled ON/OFF-switching by means of external power switch
7
. The safety shut-off is initiated a predetermined fixed time after an initial switch-on of the iron's thermostat or when the above mentioned position and movement sensor system has not detected a movement of the iron over a predetermined time period. The above alarm indication within indicating unit
5
is exclusively given when the heating element current can no longer flow due to a forced shut-off of the heating element current by controlled opening of the internal power switch
6
.
A glow lamp
80
, together with a series resistor
90
, is connected in parallel to the heating element
10
. The glow lamp
80
illuminates when the external power switch
7
in the form of the thermostat of the iron soleplate is switched on provided that the internal power switch
6
is closed. Hence, glow lamp
80
indicates whether a voltage is applied to the heating element
10
or not. Commonly, glow lamp
80
and associated dropping resistor
90
are provided outside the electronic assembly
1
. In case of the above mentioned steam iron of Bosch, the glow lamp
80
is provided in the rear left portion of the grip handle. As indicated in dashed lines, the glow lamp can also be mechanically integrated into the electronic assembly
1
.
As known, glow lamps are very sensitive to climatic changes. Furthermore, glow lamps can only be energized from the line voltage via a high-resistance dropping resistor. Even in case the glow lamp would be replaced by a light-emitting diode being energized by means of the low voltage power supply of the electronic assembly it would be necessary to provide a voltage tap between the external power switch
7
and the heating element
10
.
BRIEF SUMMARY OF THE INVENTION
It is a general object of the invention to provide a reliable and low-priced device for detecting, monitoring and controlling the operating status of an electric iron.
According to a first aspect, the invention provides a device for detecting, monitoring and controlling the operating status of an electric iron which is provided with at least one electric heating circuit having a heating element and a first power switch of the iron connected in series to the heating element. The device includes a control unit being provided as an integrated circuit. A second power switch which is controlled by the control unit depending on the operating status of the electric iron is connected in series with the electric heating circuit. An indicator unit having at least one optical indicator element indicates the heating status of the electric iron. A low voltage power supply energizes at least one of the above units. A low-impedance measuring resistance is connected in series with second power switch, and provides an indirect detection means for the switching status of both power switches. The device further includes means for supplying a voltage drop arising at the measuring resistance as an input signal to the control unit for evaluating the input signal, and means for supplying a control signal to the indicator unit for indicating a present heating status of the electric iron by means of the indicator unit.
Accordingly, the inventional device avoids the common series connection of a glow lamp and resistor in parallel to the at least one heating element. In addition, the wiring in the form of a voltage tap “behind” the thermostat i.e. between the first power switch and the heating element is avoided. By means of detecting a voltage drop on the measuring resistance the switching status of the first or thermostatic power switch of the iron and of the second or internal power switch of the electronic assembly, as well as, the heating status of the electric iron and its heating element(s) are indirectly detected. Therefore, the heating status of the electric iron and its heating element(s) can be indicated by an indicator element of the indicator unit. This solution is a low-cost solution but nevertheless very reliable and any break and malfunction of the heating element can be detected. In contrast thereto, the glow lamp
80
of
FIG. 1
indicates a voltage even in case of a current interruption within the heating element
10
itself and thus falsely indicates supply of energy to the heating element.
Furthermore, the measurement of the current through the low-impedance measuring resistance allows a more refined analysis of the present status of the electric iron. For example, the control unit of the electronic assembly can detect by analyzing the current value of the measured heating current whether or not a
Jeffery John A.
Quarles & Brady LLP
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