[0001] The invention relates to an electronic control device for a laundry drier adapted
to permit the execution of drying cycles for determining the drying of the laundry
in a preselected manner.
[0002] Known laundry driers are designed to permit the execution of different laundry drying
cycles selected in accordance with the type and quantity of the tissues to be dried
and with the degree of dryness to be obtained. These drying cycles are adapted to
be selected by the preliminary adjustment of a respective program control unit of
the machine, which may comprise a conventional electromechanical timer or an electronic
microprocessor, or by actuating respective push-button selectors associated to an
electronic control device with which the machine is additionally provided for controlling
the degree to which the laundry is to be dried.
[0003] In particular, the execution of each drying cycle thus selected is automatically
controlled by the program control unit by successively energizing and deenergizing
the various electric components of the machine, while the pre-selected degree of dryness
of the laundry is obtained thanks to the presence of the elctronic control device
which is effective, in response to the moisture content of the laundry as detected
by means of two detector electrodes disposed in the drum of the machine, to repeatedly
energize and deenergize the heater element of the machine.
[0004] There are known control devices (German Patent Application n. 2930671) comprising
a load circuit substantially composed of a rectangular-pulse generator connected to
an electric capacitor through a differentiating element, an amplifier, a diode and
a limiting resistor, said capacitor having its terminal connected respectively to
ground and to a first detector electrode together with said charge circuit.
[0005] The second detector electrode of the machine on its part is electrically insulated
from the first detector electrode and is otherwise connected to ground.
[0006] Such control devices further comprise an electronic comparator the input terminals
of which are connected respectively to the electric capacitor, together with the
first detector electrode and said charge circuit, and to a reference voltage source
the voltage level of which is adjustable in accordance with the degree of dryness
of the laundry to be attained, the output terminal of said comparator being connected
to the heater element of the machine through a flip-flop circuit and a control relay.
[0007] In this manner the described control device is operable to constantly charge the
capacitor to a preselected voltage level through the charge circuit, while the capacitor
on its part is partially discharged to ground through the detector electrodes when
the latter are short-circuited by the wet laundry contained in the drum of the machine
and coming into contact with the electrodes during the rotation of the drum.
[0008] The actual charge voltage level of the capacitor is applied to one input of the comparator
and continually compared to the reference voltage applied to the other input of the
comparator, until the charge voltage is higher than the reference voltage, whereupon
there is no output signal at the output terminal of the comparator.
[0009] Under these conditions, the comparator causes the heater element of the machine to
be maintained in the energized state, with the result that the laundry is progressively
dried.
[0010] When on the other hand the charge voltage is lower than the reference voltage, indicating
that the laundry has been dried to the desired degree of dryness, the comparator supplies
a positive signal at its output for causing the heater element to be deenergized through
the flip-flop circuit and the control relay.
[0011] At this time the program control unit may control the energization of a blower for
the laundry cooling phase of the cycle, and for the subsequent termination of the
selected drying cycle.
[0012] With the above discussed laundry driers it is thus possible to execute the drying
of various kinds of fabrics by employing different drying temperatures by subdividing
the electric heater element of the machine into several separate sections which may
be individually energized or connected to one another in series or in parallel, depending
on the required heat output.
[0013] It is an object of the present invention to provide an electronic control device
for a laundry drier, such control device being of a simple construction and capable
of permitting the drying cycles and the drying degree of the laundry to be selected
solely by actuating the drying cycle selector push-buttons associated to a microprocessor
for controlling the execution of the respective cycles, to thereby permit the formerly
provided push-buttons for selecting the degree of dryness to be eliminated, with the
resultant simplification of the construction of the drier.
[0014] These and other objects are attained according to the invention by an electronic
control device for a laundry drier having a rotatable drum for containing the laundry
and at least one variable-output heater element, said device comprising at least one
microprocessor containing encoded informations defining the drying cycles capable
of being selected and adapted to control the execution of the selected cycles; first,
second and third selector means operable respectively to select drying cycles with
the rated output and reduced output of the heater element and to maintain said heater
element energized for a supplementary period; said devcie further comprising integrator
means composed of a plurality of electric capacitors connected in parallel to one
another to two sensor electrodes disposed in said drum and adapted to be short-circuited
by the moist laundry, and comparator means adapted to control the energization and
deenergization of said heater element through said microprocessor in response to the
comparison of the charge voltage levels of said integrator means to a predetermined
reference voltage.
[0015] A control device of this type is characterized according to the invention in that
said microprocessor is adapted to identify each drying cycle selected by means of
said first, second or third selector means through said integrator means, with the
aid of an enabling signal generated by said microprocessor and supplied simultaneously
to said integrator means and to said second and third selector means.
[0016] The characteristics of the invention will become more clearly evident from the following
description, given by way of example with reference to the accompanying drawing, the
only figure of which shows an electric circuit diagram of a control device according
to the invention for use in a laundry drier.
[0017] With reference to the drawing, there is shown an electronic control device 1 for
controlling the laundry drying process in a laundry drier, substantially comprising
a microprocessor 2 including a memory containing initially stored informations defining
all drying cycles which can be executed by the respective drier. Microprocessor 2
is also adapted to automatically control the execution of any drying cycle selected
in the manner to be described; the control device further includes first, second and
third selector means 3, 4 and 5 in the form of conventional push-button switches mounted
in the control panel of the drier and adapted to be manually and separately actuated
for selecting respective drying cycles at different drying temperatures.
[0018] In particular, for obtaining different drying temperatures the heater element 6 of
the drier may be conventionally subdivided into several separate sections (in the
present case two sections 7 and 8 adapted to be connected in parallel to one another).
These heater element sections may be energized separately or in combination as required
for generating the heat energy required for the drying process.
[0019] Heater element 6 on its part is connected to a power supply conductor 9 of the drier,
and its energization is controlled by microprocessor 2 through a switch element 10
in the form for instance of a triac, a relay or the like, microprocessor 2 being otherwise
connected to the other power supply conductor 11 of the drier.
[0020] First and second selector means 3 and 5 are both operable to select conventional
drying cycles for cotton fabrics and resistant synthetics to be executed with the
maximum heat output, to which purpose all sections of heater element 6 are interconnected
for obtaining a predetermined degree of dryness of the laundry; in the second case,
heater element 6 is maintained in the energized state for a predetermined supplementary
period so as to determine the complete drying of the laundry (these drying cycles
are denoted as "extra dry cycles").
[0021] Second selector means 4 on its part is operable to select drying cycles with reduced
heat output for drying delicate synthetic fabrics, providing for the energization
of only one section of heater element 6 for a sufficient period for attaining the
preselected degree of dryness of the laundry (these drying cycles are referred to
as "acrylic drying cycles"). The present control device further comprises an integrator
circuit 12 composed of a plurality of electric capacitors 13 connected, in parallel
to one another, to limiter resistors, diodes and other per se known electronic components
(all of which are now shown), and to two sensor electrodes 14 and 15 disposed in the
rotating drum (not shown) of the drier adapted to contain the moist laundry to be
dried, sensor electrodes 14 and 15 being connected respectively to integrator circuit
12 and to ground 16 and adapted to be short-circuited by the moist laundry to be dried.
[0022] Integrator circuit 12 is energized at a low voltage and adapted, in response to the
selection of respective drying cycles by means of first, second and third selector
means 3, 4 and 5, corresponding to predetermined degrees of dryness of the laundry,
to vary the time constant of capacitors 13.
[0023] To this purpose integrator circuit 12 is connected to first and second selector means
3 and 4, respectively, via respective conductors 17 and 18, and to third selector
means 5 via a conductor 19 itself connected to conductor 18 and to a logic inverter
20 of conventional type, the function of which will become evident as the description
proceeds.
[0024] The present control device finally comprises an electronic comparator 21 having its
input terminals 22 and 23 connected respectively to integrator circuit 12 and to a
fixed-level reference voltage source, and its output terminal 24, to a further conductor
25 adapted to connect second and third selector means 4 and 5 in parallel, and to
microprocessor 2 through an optoinsulator 26 or a similar insulating element provided
for electrically separating microprocessor 2, which is energized with the mains voltage
through the respective conductors 9 and 11, from the components energized at low voltage
(and comprising integrator circuit 12, selector means 3, 4 and 5, and electronic comparator
21).
[0025] Comparator 21 serves the purpose of comparing the charge voltage level of capacitors
13 of integrator circuit 12 as preselected by first, second or third selector means
3, 4 or 5, to the predetermined reference voltage level, for thus controlling, in
response to the result of the comparison, the energization and deenergization of
heater element 6 through microprocessor 2 and switch element 10 in the manner to be
described.
[0026] For permitting microprocessor 2 to identify each drying cycle selected in the manner
described, microprocessor 2 is arranged to furnish at its output 27 a continuous enabling
signal of rectangular shape to be applied to an associated input 28 of microprocessor
2 and simultaneously to integrator circuit 12 and second and third selector means
4 and 5, to which purpose output 27 is connected to conductors 18 and 19 through conductor
29 and a further optoinsulator 30 or a similar insulating element provided for electrically
separating microprocessor 2 from the low-voltage elements defined above.
[0027] To this purpose microprocessor 2 is responsive to the absence or presence at output
24 of comparator 21 of said enabling signal when a drying cycle to be executed has
been selected by actuating first or second selector means 3 or 4, respectively, and
of an enabling signal identical but complementary to the first-named signal, when
a drying cycle has been selected by actuating third selector means 5. In the first
case, particularly, the absence of the enabling signal at output 24 of comparator
21 results from the fact that different voltage levels are applied to the two inputs
22 and 23 of comparator 21. In the second case, the presence of the enabling signal
at output 24 of comparator 21 results from the actuation of second selector means
4. In the third case, finally, the complementary enabling signal is obtained as a
result of the presence of logic inverter 20 connected in series with third selector
means 5.
[0028] In this manner, and depending on the selected drying cycle, microprocessor 2 operates
to initiate the respective cycle by causing heater element 6 to be energized in accordance
with the required heat output and to subsequently control in an automatic manner the
execution of the selected cycle for the full duration thereof.
[0029] During the execution of the drying cycle, capacitors 13 of integrator circuit 12
are progressively charged when the enabling signal applied to integrator circuit 12
is at a high level, and are partially discharged to ground 16 via sensor electrodes
14, 15, as they are short-circuited by the moist laundry, when the enabling signal
is at a low level.
[0030] As long, moreover, as the charge voltage and the reference voltage applied to inputs
22 and 23 of comparator 21 are at different levels, there appears no signal at output
24 of comparator 21, indicating that the laundry has not yet been dried to the selected
degree, so that heater element 6 is maintained in the energized state by microprocessor
2. As soon, on the other hand, as these voltages are at the same level, comparator
21 furnishes a signal at output 24, causing heater element 6 to be deenergized by
the action of microprocessor 2 and switch element 10.
[0031] Subsequently microprocessor 2 may initiate the cooling phase by causing the blower
(not shown) of the drier to be energized to thereby cool the laundry and the metallic
parts of the drum and the housing of the drier as the conclusion of the selected drying
cycle.
[0032] The advantages of the present control device are thus fully evident.
[0033] As a matter of fact, this device permits to contemporaneously obtain, during the
selection of the drying cycle to be executed by the actuation of first, second or
third selector means 3, 4 or 5, respectively, the identification and subsequent control
of the selected cycle by microprocessor 2, and the adjustment of the degree of dryness
required for the respective laundry by the variation of the time constant of capacitors
13 of integrator circuit 12 due to the presence of the enabling signal furnished by
the microprocessor. In comparison to known solutions, the present control device is
of a simple construction eliminating the need of expensive electromechanical devices
for controlling the execution of the drying cycles, thanks to the fact that these
operations are directly controlled by the microprocessor which is energized from the
electric circuit of the drier and electrically separated by opto-insulators 26 and
30 from the low-voltage electrical components of the control device itself.
[0034] This device also permits a combined selection of the drying cycle and of the desired
degree of dryness to take place by solely acting on selector means 3, 4 and 5, thus
eliminating the need of separate push-button actuators for selecting the degree of
moisture (or of dryness) of the laundry as required in previous solutions, with the
resultant simplification of the overall construction of the laundry drier.
1. An electronic control device for a laundry drier having a rotary drum for containing
the laundry and at least one variable-output heater element, said device comprising
at least one microprocessor containing encoded informations relating to drying cycles
to be selected and adapted to control the execution of the selected cycles, first,
second and third selector means operable respectively for selecting drying cycles
at the rated output and reduced heat output of said heater element and for maintaining
said heater element in the energized state for a supplementary period, said device
further comprising integrator means composed of a plurality of electric capacitors
connected in parallel to one another to two sensor electrodes disposed in said drum
and adapted to be short-circuited by the moist laundry, and comparator means adapted
to control the energization and deenergization of said heater element via said microprocessor
in response to the comparison between the levels of the charge voltage of said integrator
means and of a predetermined reference voltage,
characterized in that said microprocessor (2) is adapted to identify each drying cycle
selected by means of said first, second or third selector means (3, 4, 5) via said
integrator means (12) with the aid of an enabling signal generated by said microprocessor
(2) and simultaneously applied to said integrator means (12) and to said second and
third selector means (4, 5).
2. A control device according to claim 1, characterized in that said microprocessor
(2) is connected to the power supply conductors (9, 11) of the drier in series with
said heater element (6) through per se known switching means (10), and has an output
(27) for said enabling signal and in input (28) for the identification of said signal,
said output (27) and said input (28) being connected via respective electric insulation
means such as opto-insulators (26, 30) or the like, to said integrator means (12)
and to the output (24) of said comparator means (21).
3. A control device according to claim 2, characterized in that said first selector
means (3) is connected to said integrator means (12), and that said second selector
means (4) is connected, in parallel to a circuit composed of said third selector means
(5) and, in series therewith, inverter means (20) adapted to generate a complementary
enabling signal, to said integrator means (12) and to said output (24) of said comparator
means (21).