Low voltage sensor for a dryer

A fabric treating apparatus, such as a domestic clothes dryer, is provided with a digital control circuit and a sensor system which cooperate to terminate a fabric treatment operation when the fabric reaches a desired condition. A digital counter receives and accumulates timing pulses. A sensing circuit repetitively charges a capacitor which is allowed to discharge through a sensor in contact with the wet fabric load. If the fabric in contact with the sensor is wet, the capacitor will quickly discharge. As the fabric dries the capacitor will discharge more slowly. After the capacitor has been allowed to discharge for a preselected period, the charge on the capacitor is read and if low, the counter is reset. As the fabric load approaches the desired dryness condition, the remaining charge on the capacitor will increase until it reaches a level which prevents the counter from being reset. Thus, the counter accumulates successively greater counts before being reset, until eventually a preselected count is accumulated in the counter which triggers cicruitry to terminate the fabric drying operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the art of sensing and control techniques for 
laundry apparatus, and is particularly concerned with methods and 
apparatus for sensing the moisture content of a clothes load within a 
dryer and controlling the operation of the clothes dryer as a function 
thereof. 
2. Description of the Prior Art 
U.S. Pat. No. 3,702,030 discloses a high voltage sensor circuit for an 
integrated circuit control that produces repetitive pulses when the 
clothes load is dryer than a given dryness level for resetting a second 
counter to prevent the second counter from resetting a first counter. The 
first counter, upon reaching a predetermined count, ends the sense portion 
of the drying cycle. Similar circuits are utilized in U.S. Pat. Nos. 
3,762,064 and 3,769,716. 
U.S. Pat. No. 3,621,293 discloses the use of a field effect transistor for 
sensing voltage buildup on a capacitor in a drying control. 
U.S. Pat. No. 3,221,417 discloses a moisture sensor control circuit. 
Rotating cams and a timer motor along with a motor driven rotor switch arm 
are utilized which successively closes circuits causing a capacitor to be 
charged. The capacitor is connected to a pair of spaced electrodes and 
then to a relay. If the charge on the capacitor does not discharge through 
the electrodes, it will remain to power the relay for terminating the 
drying operation. 
SUMMARY OF THE INVENTION 
The present invention provides a means of sensing clothes load moisture in 
a microcomputer controlled dryer based on the level of moisture retention 
measured in the clothes load. 
A low voltage sensor circuit comprising a moisture sensor, a capacitor and 
a tri-stating port on a microcomputer is used to sense the degree of 
dryness of a load of clothes within the dryer. The sensor and capacitor 
are connected in parallel to the tri-stating port. The tri-stating 
condition of the tri-stating input/output port allows for three different 
conditions at the port. First, the port can output a voltage. Second, the 
port can present a high impedance. Third, the port can read an input 
voltage. 
As utilized in the present invention, first a charge is applied to the 
capacitor by the port in the output mode. The port is then tri-stated to 
its very high impedance input stage. Thus, the capacitor can only 
discharge through the sensor which is located within the drum of the dryer 
where it can contact the clothes load. If moisture is sensed by means of 
wet clothes bridging the sensor, the capacitor will discharge rapidly. If 
the clothes load is dry or no clothes touch the sensor, the charge will 
tend to remain in the capacitor. 
Next, after a preselected time interval, the state of the port is changed 
to receive an input voltage from the capacitor. After reading the charge, 
the port outputs the voltage which recharges the capacitor and the process 
repeats. The discharge time, when the port is tri-stated, along with the 
value of the capacitor, will determine the voltage remaining on the 
capacitor for a given level of clothes dryness. 
If a low voltage is read by the input port, this represents a wet signal 
and causes a counter to be reset. If a high voltage is read, this 
represents a dry signal and the counter continues to accumulate counts. As 
the clothes load continues to dry, wet signals will decrease until a 
sufficient length of time between wet signals occurs allowing the counter 
to accumulate a preselected count. When this occurs, the sensing portion 
of the drying process will end and the control circuit will cause the 
remainder of the selected program to continue.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 there is generally shown an automatic dryer 10 having a cabinet 
12 and a control console 14 with a plurality of presettable controls 16 
thereon. Each of the controls 16 may take the form of touch control 
switches. However, the controls 16 may be of any number of types commonly 
known in the art without departing from the spirit of the invention. The 
controls 16 provide the operator with the opportunity of preselecting a 
special custom mode of operation such as fabric selection, automatic dry, 
timed dry, air and touch-up drying cycles. A range of selections are 
available in each of the automatic and timed dry cycles. 
A front 18 of the cabinet 12 has a door 20 which provides access to a 
treatment zone in the interior of the dryer 10 including a rotatable drum 
22. Provided in a rear stationary bulkhead at the rear of the drum 22 
there is an inlet aperture 26 with a screen or perforate cover plate 27 
across the aperture 26 and an air outlet aperture 28 formed by 
perforations 29 in bulkhead 24 through which a supply of temperature 
conditioned air is circulated by a blower or fan 31 during the drying 
process. 
As seen in FIG. 2, a heating element 38 is provided in the air flow path 
designated by broken arrow 40 which is selectively energized by a control 
logic circuit 60 to selectively temperature condition the air to the 
interior of the dryer 10 as required, thereby conditioning the air to take 
on increased moisture. Blower 31 is connected in an air flow relationship 
with the air inlet and outlet apertures so that air is drawn into the drum 
22 by way of the aperture 26 after first passing the heating element 38 
and is withdrawn from the drum through the aperture 28. An electric motor 
42 drives the blower 29 and is also provided to rotate the drum 22 by 
means of a drive pulley 43, a tensioning idler pulley 41 and a belt 44. 
At least one sensor 30 is provided which can be in contact with the clothes 
load during the drying operation while the drum is rotating. The sensor 30 
is comprised of two electrodes 32 and 34 which are connected by a pair of 
conductors 50, 52 to a low voltage moisture sensor circuit 36 as shown in 
FIG. 2 
A digital control circuit is generally shown at 48 and includes the sensor 
circuit 36 which is connected to the sensor electrodes 32, 34, a digital 
millisecond counter circuit 54 which is driven by a timing crystal 56, a 
memory storage 58 and the control logic circuit 60 for reading the states 
of a counter 54 and the stored values in the memory storage 58 for 
indexing the memory storage 58. 
The control logic circuit 60 includes a plurality of outputs for 
controlling various machine functions and, accordingly, for controlling 
the program of the dryer. A first output is indicated by the electrical 
connection line 61 which extends from the control logic circuit 60 to the 
heating element 38 for controlling the application of heat to the interior 
of the drum 22. A second output is indicated by means of an electrical 
connection line 62 which extends from the control logic circuit to the 
electrical drive motor 42 for controlling rotation of the drum 22 and the 
fan. 
A third output is indicated by means of an electrical connection line 63 
which extends from the control logic circuit 60 to a display circuit 64 
which controls a number of indicator lamps behind the panel on the console 
14 of the dryer 10 to indicate to the operator which drying functions have 
been selected and in which portion of the drying cycle the dryer is 
currently operating. Another output is evidenced by the electrical 
connection line 66 which may be employed, for example, as a master power 
control lead for disconnecting the circuits from the electrical supply at 
the termination of the drying program. 
As will be appreciated by those skilled in the art, the electrical 
connections 61, 62, 63, and 66 are in schematic form only, and in practice 
appropriate interface circuitry such as is well known in the art would be 
necessary to enable the relatively low level signals developed by the 
logic circuitry to be used to control the power supply to the machine 
components. 
FIG. 3 details the electrical circuitry utilized in the present invention. 
A transformer 68 is connected to a source of 120 volt alternating current 
by conductors 70 and 72. The alternating current is rectified to direct 
current by means of diodes 74 and 76. A capacitor 78 to protect against 
voltage spikes, a power supply regulator 82, and a low voltage shut down 
circuit 84 are provided in a power line conductor 80 to insure a constant 
voltage level is supplied to a microprocessor or microcomputer 86. The 
timing crystal 56 supplies a timing pulse to the microcomputer along 
conductors 88, 90. A plurality of input switches 92 are connected through 
resistors 94 and conductors 96 to the microcomputer 86 in order to alert 
the microcomputer as to certain conditions such as an open door or a 
filled lint receptacle. 
Output signals or conductors 120, 122 and 124 are sent through drivers 130, 
132 and 134 to operate relays 140, 142 and 144 which send appropriate 
signals along lines 61, 62 and 66 to the heating element, motor and master 
switch as described above. 
Output signals are also sent on a series of conductors representatively 
shown by lines 126 and 128 which are strobed through transistors 136 and 
138 alternatingly providing closed circuits along a plurality of 
conductors 129 for various LED's 146 in the display circuit 64. The lines 
126 and 128 represent any number of conductors which are multiplexed to 
reduce the power requirements of the display circuit. 
Output signals from the microcomputer 86 also are sent on a plurality of 
conductors 150 through driver amplifiers 152 and on a plurality of 
conductors 63 to energize the appropriate LED's 146. Output signals are 
also sent on a conductor 154 through drivers 156 to energize an end of 
cycle alarm 158 at the end of the drying cycle. 
A plurality of input switches 160 form a part of the controls 16 which are 
provided for the operator to make the appropriate selections of the 
various drying cycle operation options. These input signals are supplied 
to the microcomputer 86 through a plurality of conductors 162. 
The sensing circuit 36 utilizes a tri-stating input/output port 98 of the 
microcomputer 86 such as provided on the S-2000 microcomputer family 
manufactured by American Microsystems, Inc. The tri-stating port 98 is 
connected by a conductor 104 to a first terminal 99 of a capacitor 100 and 
a first terminal 101 of the moisture sensor 30. A second terminal 102 of 
capacitor 100 and a second terminal 103 of the sensor 30 are both 
connected at all times to a reference potential such as ground. 
The tri-stating condition of the port 98 allows for three different 
conditions. First, the port 98 can output a voltage. Second, the port can 
present a high impedance. Third, the port can read an input voltage. 
As utilized in the present invention, first the port 98 outputs a voltage 
on line 104 which charges capacitor 100. However, if there are wet clothes 
in contact with the sensor 30, then the current will flow through the 
sensor 30 to ground and the capacitor 100 will not fully charge. 
After the port 98 has output a voltage it then is tri-stated so that it 
presents a very high impedance. This condition is continued for a 
preselected length of time, for instance one second, during which time the 
capacitor 100 can only discharge through the sensor 30. If wet clothes are 
in contact or come in contact with the sensor 30 during this period, the 
capacitor 100 will discharge. If no clothes or dry clothes are in contact 
with the sensor 30, then the capacitor 100 will remain charged. 
At the end of the preselected time the condition of the port is changed so 
that it reads the charge on the capacitor 100. If a low voltage or charge 
is read, this is interpreted as a wet signal which causes an accumulation 
counter to be reset as will be described below. If a high voltage or 
charge is read, this is interpreted as a dry signal which allows the 
accumulation counter to continue to count. 
After the port 98 has read the charge on the capacitor 100, it again 
outputs a voltage and repeats the operation throughout the entire portion 
of the drying cycle. 
FIGS. 4a and 4b illustrate the operation of the apparatus of the present 
invention during an automatic cycle of operation. FIGS. 4a and 4b are in 
functional block diagram form, with the various blocks indicating steps 
performed in sequence during the performance of the method of the present 
invention, and also indicating the structure which is employed during the 
operation of the dryer. Although a preferred embodiment of the present 
invention employs a microcomputer controller for the performance of the 
dryness sensing controlling program, the present invention also 
contemplates an organization in which each of the blocks illustrated in 
FIGS. 4a and 4b corresponds to an individual control unit. Control of the 
operation is passed from control unit to control unit, to execute the 
program in its proper sequence. The operation proceeds by a sequence of 
steps. 
The first step in the performance of the automatic operation of the dryness 
sensing control is by control unit 200 which is periodically energized 
from a strobe line 202. The microcomputer 86 as utilized in the present 
invention has four strobing circuits under control of a strobing or K-scan 
unit 205, one of which (202) is devoted to the sensing and time dry 
portion of the drying cycle. The other three strobes control the scanning 
of the inputs and the selections of the output relays and the output 
lights. 
Control unit 200 inspects the drying cycle selections to determine if the 
drying cycle is complete. If the drying cycle is complete, then control is 
passed to unit 204 which performs the various control operations for the 
cycle selected before returning the strobe line to the K-scan unit 205. If 
control unit 200 determines that the drying cycle is not complete, then 
control is passed to unit 206. 
Control unit 206 inspects the cycle selections to determine if the dryer is 
currently in the anti-wrinkle portion of the cycle. If unit 206 determines 
that it is, then control is passed again to unit 204 which would perform 
the control operations for the anti-wrinkle portion of the cycle before 
returning the strobe line to the K-scan unit 205. If control unit 206 
determines that the dryer is not in the anti-wrinkle portion of the cycle, 
then control is passed to unit 208. 
Control unit 208 inspects the cycle selections to determine if the dryer is 
in the sensing or timed portion of the cycle. If unit 208 determines that 
it is not, then control is passed to unit 210 which inspects the cycle 
selections to determine if the cool down option has been selected. If unit 
210 determines that it has, then control is passed again to unit 204 which 
would perform the control operations for the cool down cycle prior to 
returning the strobe line to the K-scan unit 205. 
If control unit 210 determines that cool down has not been selected, then 
control is passed to unit 212 which inspects the cycle selections to 
determine if add-on time is over. If unit 212 determines that it is, then 
control is passed to unit 204 to perform the various control operations 
for the cycle selected. If unit 212 determines that the add-on time is not 
over, then control is passed to unit 214 which increments a seconds 
counter in control logic 60 which keeps track of total run time and an A 
counter in control logic 60 which is used to determine if the clothes load 
has reached a selected level of dryness. Then control is passed to a unit 
216 which stores the total run time. 
If control unit 208 determines that the dryer is in the sensing or timed 
portion of the cycle, then control is passed to unit 218 which inspects 
the cycle selections to determine if the damp dry dryness level has been 
selected. If unit 218 determines that damp dry has not been selected, then 
control is passed through a series of units ending with unit 220 which 
inspects the cycle selections to determine if the very dry level of 
dryness had been selected. 
Although only two dryness level inquiries, damp dry and very dry, have been 
shown in FIG. 4a as performed by units 218 and 220, it should be 
understood that any number of dryness levels may be utilized in the 
program which would allow an operator to select from a range of dryness 
levels for the fabrics being treated in the dryer. The following control 
unit functions would be the same for any level of dryness selected. 
If control unit 218 determines that the damp dry level has been selected, 
control would be passed to unit 222 which inspects counter A to determine 
if a preselected delay count A for damp dry has been reached. The delay 
count A is a given interval of time in which the sensor 30 has not 
recorded a valid wet signal. As an example, the delay count A for damp dry 
could be 15 seconds. 
If control unit 222 determines that delay count A for damp dry has been 
reached, then control is passed to unit 224 which stores total run time to 
be used in setting the cool down time by unit 204. Unit 224 also sets an 
add-on time in accordance with the procedure disclosed in U.S. Pat. No. 
3,762,064 issued to Carl R. Offutt on Oct. 2, 1973 and assigned to the 
Whirlpool Corporation, the disclosure of which is incorporated herein by 
reference. After control unit 224 has stored the count and set the add-on 
time, control is passed to the unit 214 which increments the seconds 
counter and the A counter and then passes control to unit 216 which stores 
the total run time. If control unit 222 has determined that the delay 
count A for damp dry has not been reached, then control is passed directly 
to unit 214. 
If any of the other levels of dryness, such as very dry, have been 
selected, the same steps would be performed by control units as are 
performed by units 218, 222, and 224. Specifically, control unit 220 
determines if the very dry level has been selected. If it has, then 
control is passed to unit 226 which inspects counter A to determine if 
delay count A for very dry has been reached. As an example, the delay 
count A for very dry could be two minutes. 
If control unit 226 determines that delay count A for very dry has been 
reached, then control is passed to unit 228 which stores the total run 
time and sets the add-on time as described with reference to unit 224. 
Then control is passed to unit 214 as described above. If control unit 226 
determines that delay count A for very dry has not been reached, then 
control is passed directly to unit 214. 
If control has passed from unit 218 through all of the various dryness 
level control units to unit 220 and control unit 220 determines that the 
very dry level has not been selected, then control is passed to unit 230 
which inspects the cycle selectors to determine which timed dry period has 
been selected and it inspects the total run time stored by unit 216 to 
determine if the time period has completely elapsed. If the control unit 
230 determines that the time has elapsed, control is then passed to unit 
232 which stores the total run time to be used by unit 204 in determining 
the cool down time and control is passed to unit 214. If control unit 230 
determiens that the time period has not completely elapsed, then control 
is passed directly to unit 214. 
As described above, control unit 214 increments the seconds counter and the 
A counter and then passes control to unit 216 which stores the total run 
time. Control is then passed to unit 234. Control unit 234 determines if 
the sensor 30 is being utilized. If unit 234 determies that the sensor is 
not being utilized, then control is returned to the K-scan. 
If control unit 234 determines that the sensor is being used, then control 
is passed to unit 238 which inspects the total run time stored by unit 216 
to determine if the dryer has been on for ten minutes. The ten minute 
initial run time allows the dryer and the clothes load to reach a minimum 
drying time required for any small clothes load. If the dryer has been on 
for less than ten minutes, then control is passed to units 239 and 240 
which rest the A counter to zero and a milliseconds count equal to zero, 
respectively. Control is then passed to unit 205 for returning the strobe 
line to the K-scan. 
If control unit 238 determines that the dryer has been on for at least ten 
minutes, then control is passed to unit 242 which increments the 
milliseconds count by one, representing four milliseconds. A millisecond 
counter is utilized to control the condition of port 98 of the 
microcomputer 86 by keeping track of the time used for each of the three 
conditions of the port. In the preferred embodiment, four strobe lines are 
utilized and each strobe uses one millisecond, therefore each time the 
K-scan storbes line 202 and passes through this portion of the program, 
four milliseconds have elapsed. Thus, control unit 242 increments the 
milliseconds by four for each increment in its count. 
Control is then passed to unit 244 which inspects the millisecond counter 
to determine if the millisecond count is equal to one. If it is, then 
control is passed to unit 246 which outputs the preselected voltage at 
port 98. Control is then pased to the K-scan unit 205. 
If unit 244 determines that the millisecond count is not equal to one, then 
control is passed to unit 248 which inspects the millisecond counter to 
determine if the millisecond count is less than 250 representing 1,000 
milliseconds. If it is, then control is passed to unit 250 which presents 
a high impedance at port 98. Control is then passed to the K-scan unit 
205. 
If unit 248 determines that the millisecond count is not less than 250, 
then control is passed to unit 252 which inspects the millisecond counter 
to determine if the millisecond count is equal to 250. If it is, then 
control is passed to unit 254 which reads the voltage level at the port 
98. Control is then passed to unit 256 which inspects the voltage read by 
unit 254 to determine if there is a wet signal. 
If unit 256 determines that there is a wet signal, the control is passed t 
o unit 239 which resets the "A" counter to zero. Control is then passed to 
unit 240 which resets the millisecond count to zero. If unit 256 
determines that there is not a wet signal, control is passed directly to 
unit 240 to reset the millisecond counter. Control is then passed from 
unit 240 to the K-scan unit 205. 
The strobing continues until the "A" counter delay has been reached 
indicating that the dryness level selected has been reached and then the 
program moves on into the add-on and cool down and/or anti-wrinkle cycle 
selected, control unit 204 performing the various control operations for 
the cycle selected. After unit 204 has performed the various control 
operations, control is passed to the K-scan unit 205. 
Thus, it is seen that there is provided a low voltage moisture sensor for a 
dryer which senses the moisture content in the clothes load and sends an 
appropriate signal to a microcomputer for use in timing and control 
functions. A first counter is utilized to measure the time since a last 
wet signal has been sent. A second millisecond counter is utilized in 
controlling the condition of the tri-stating port. The first counter is 
reset each time that a wet signal has been sent. The first counter 
continues to count, in the absence of a wet signal, until a preselected 
level of dryness has been sensed. 
As is apparent from the foregoing specification, the invention is 
susceptible of being embodied with various alterations and modifications 
which may differ particularly from those that have been described in the 
preceding specification and description. It should be understood that we 
wish to embody within the scope of the patent warranted hereon all such 
modifications as reasonably and properly come within the scope of our 
contribution to the art.