US3539153A - Electronic dishwasher control system with condition responsive cycling - Google Patents

Description

United States Patent [72] Inventors Allan L. Wennerberg 2,779,937 1/1957 Pellerin et a1 134/57X St. Joseph; 2,824,385 2/1958 Toma 68/19X Kenneth F. Cargo, Benton Harbor, 3,049,133 8/1962 Jacobs 134/57 Michigan 3,152,462 /1964 Elliott et a1. 68/ 12 [21] Appl. No. 566,160 3,194,250 7/1965 Delapena 134/57 [22] Filed July 18,1966 3,267,303 8/1966 Meyer et al.. 307/141 [45] Patented Nov. 10,1970 3,279,481 10/1966 Sones et a1... 134/57 [73] Assignee Whirlpool Corporation 3,398,295 8/1968 Fathauer 307/ 141.4

Benton Harbor a corporanon Primary Examiner-Robert L. Bleutge of Delaware [54] ELECTRONIC DISHWASHER CONTROL SYSTEM WITH CONDITION RESPONSIVE CYCLING 14 Claims, 3 Drawing Figs. [52] US. Cl. 259/1, 68/12; 134/57;307/l41 [51] Int. Cl G05b 13/02; B011 3100 Field of Search 259/1; 68/12,19; 134/57(D),58(D):307/141(lnq) 141.4, 141.8 (lnq) [56] References Cited UNITED STATES PATENTS 2,430,668 11/1947 Chamberlin 68/ 12 Attorney-William l-louseal, James S. Nettleton, Charles D. Putnam, Burton H. Baker, ThomasE."Turcotte, Francis L. Snyder, Gene A. Heth and Donald W. Thomas, and Sughrue, Rothwell, Mion, Zinn and Macpeak ABSTRACT: An electronic control system for dishwashers and other cyclically operated home washing appliances which lends itself to integrated or printed circuit fabrication. The circuit employs solid state timer circuits thus eliminating the mechanical timer, as well as tri-level liquid sensing means to control and initate the functional advance through the appliance's cycle of operation.

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x $51 orrarszur 30 J useeusza s4 ll2-'\ w a "21.111 536 J DISPENSER s20 mum VALVE see 833 32 s 837 .11. A J1. J'L A L 3 A 110 s23 0 o 0 B2 $34 ea 36 84 Patented Nqv. 10, 197O 3 of 3 Y Sheet FIG. 28

T0 T0 T0 SCR? SCRB SCRQ SCRI3 61%E 6%E 6%5 6%E RINSE l DRY ONLY 264% ONLY T0 T0 SCRS SCRS GATE GATE sowr TO SCR4 GATE 258 260 INVENTORS. ALLAN L. WENNERBERG KENNETH F CARGO ATTORNEYS ELECTRONIC DISHWASHER CONTROL SYSTEM WITH CONDITION RESPONSIVE CYCLING This invention relates in general to an electronic control system for an article washing apparatus, and more specifically to a novel automatic dishwasher control system featuring condition responsive cycle initiation and termination. While this invention is particularly adapted to automatic dishwashers, it is not limited thereto, and has equal application to all cycle controlled article washing or laundering appliances and other cyclically controlled systems and processes.

For many years the accepted technique employed throughout theindustry for implementing cycle control in automatic dishwashers has involved the use of mechanical timers. While the fixed time method may be generally satisfactory for controlling wash and rinse cycles, where few variables are involved, serious problems have arisen with respect to time controlled water fill, water drain and drying cycles. Tap water pressures vary over a wide range from one locale to another, for example, as does the volume of dishes loaded into a machine during each operation, and when fixed timer means alone are used to control water fill cycles, the fill levels attained naturally vary over a proportionately wide range. Considering the fact that all dishwashers are designed for optimum effectiveness and durability at a given water fill level, the deleterious effects of fill level variations become apparent. Similarly, the time required to completely drain a fluid filled chamber is a function of its fill level and the drain line suction. Since timer controlled fill levels are variable, and since line suction varies from one drain system to another, it is obvious that timer controlled drain cycles give no assurance of complete drainage. The consequence of an incomplete drain directly relates to the performance of a subsequent wash or rinse cycle using dirty and/or soapy water. Also the water remaining in the machine at the end of any cycle is a source for the growth of bacteria and other germs.

Another problem attendant with the prior art dishwasher control systems arises from the fact that the degree of preload cleaning varies greatly from one operator to another and further in that certain foods, i.e. potatoes, eggs, etc., are more adherent and difficult to dislodge than others. Thus, when a single prerinse cycle is employed, in many cases the food deposits are merely softened rather than being rinsed away, which greatly reduces the effectiveness of subsequent wash cycles.

Another problem with the prior art cyclically operated machines is that a mechanical timer having contacts operated by an electrical motor is used to control the cyclic operation of the machine, and these timers are subject to mechanical fatigue and failure, Also, when used with an article washing machine, the contacts and motor are subjected to moisture and high humidity, further increasing the incidence of failure.

It is therefore a primary object of this invention to provide an electronic control system for an article washing apparatus which overcomes the above and other disadvantages attendant with the prior art systems by employing condition responsive means to both initiate and terminate many of the operational cycles involved.

It is a further object of this invention to provide such a system in which the condition responsive means senses the water level at three separate levels within the fluid chamber of the washing apparatus.

lt is a further object of this invention to provide such a system in which the condition responsive means senses the air temperature within the fluid chamber to determine the dryness of the articles therein.

it is a further object of this invention to provide such a system which includes means for sensing the turbidity of the fluid discharge stream from the prerinse cycle, and means responsive thereto for repeating the prerinse cycle until the discharged stream is sufficiently clear.

It is a further object of this invention to provide such a system in which the normal cycle program may be selectively modified by the operator, and in which any program may be interrupted at-any time and the system reprogrammed.

It is a further object of this invention to provide such a control system which employs exclusively solid-state active elements and which therefore lends itself readily to integrated and/or printed circuit fabrication, with attendant compactness and reliabilityQFurthermore, owing to its reduced size and low signal levels, the control system may be mounted in any convenient location on the washing apparatus or at some remote location.

It is a further object of this invention to provide such a system which includes bistable memory devices to both store or retain an indication of the state of program execution and to condition further memory devices for subsequent operation.

It is a further object of this invention to provide such a system which eliminates the need for a-mechanical timer for controlling the'cyclic operation of the machine.

It is a further object of this invention to provide such a system which comprises logic circuit means to implement the execution of programmed operating cycles according to predetermined sequences and in a positive and error-free manner.

The foregoing and other objects, features and advantages of the invention .will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings, in which:

FIG. 1 shows a block diagram of an electronic control system constructed in accordance with the teachings of this in vention, and

FIG. 2 (A and B) shows a schematic circuit diagram of the block diagram of FIG. 1, including some additional circuitry for implementing selective programming functions.

Referring now to the drawings, the block diagram of FIG. 1 is mainly comprised of AND gates, OR gates and inverters. The functioning of these logic components is well known in the art and will not be described here in detail. Suffice to state that AND gates produce an output only when all inputs are present, OR gates produce an output when any input is present, and inverters produce an output when no input is present.

Following through a-normal operating cycle, the closing of start switch 12 produces a signal S1 which actuates OR gate 14. The latter generates an output signal S2 which energizes the motor 16 and actuates OR gate 18. The output signal S3 from OR gate 18 energizes the control circuit 20, which includes a switch (not shown) connected in parallel with the start switch 12 to maintain power to the system when the start switch is released. The motor 16 in this instance is a continuously running, unidirectional pump motor that implements both the recirculate and drain functions, depending upon the level of water in the chamber and the energization of the drain valve. Water is admitted to the chamber by water line pressure when the water valve 24 is energized. When neither of the valves are energized, the water in the machine is recirculated.

With power supplied to the system and signal S17 not present at the input of inverter 22, it produces an output signal S4 which energizes the water valve 24, and the machine begins to fill with water for the prerinse cycle. The other inverters 32, 46, 72 and 94, in the system also produce output signals at this point, but they are all applied to AND gates as conditioning signals, and hence have no immediate effect. As the water level rises, output signals are sequentially produced by the low level sensor 26, the medium level sensor 28 and the high level sensor 30. These sensors may be of any well known type, such as electrode gap, capacitive, thermal, optical, etc., and are mounted in a manner to sense the water level in the machine chamber. When the low level sensor 26 is actuated, it produces a signal-S5 which is applied to inverter 32, AND gate 34 and'AND gate 36. lnverter 32 has no effect since it merely drops its previously raised conditioning signal S6, while AND gates 34 and 36, whose inputs are as yet incomplete, are conditioned by signal S5. When the medium level sensor 28 is actuated, its output signal S7 causes an output signal S8 from OR gate 38 which conditions AND gates 40 and 42. In addition,

signal S7 and signal S9 from inverter 46 actuate AND gate 44,

whose output signal S further combines with signal S7,to actuate AND gate' 48. The output signal S11 from the latter initiates a time delay 50, which will be assumed to be set for approximately 5 minutes. When the machine chamber becomes filled to its optimum operating level, the high level sensor 30 is actuated and produces an output signal S12. This is applied to OR, gate 52 whose output signal S13 combines with signal S8 to actuate AND gate 42. The output signal S14 from this gate is fed back to OR gate 52 in a latching mode and also energizes the heating unit 54. This heating unit not only helps maintain the water temperature during the wash and rinse cycles, but also supplies heat for the drying cycle. Signal S12 is also applied'to OR gate 56 whose output signal S15 actuates AND gate 34, which was previously conditioned by signal 85 from the low level sensor 26. AND gate 34 produces an output signal S16 which is applied to OR gate 56 in a latching mode and to OR gate 58. The output signal S17 from OR gate 58 is fed to inverter 22 which then lowers it output signal S4 to close the water valve 24. At this point the machineis in the prerinse cycle with a full water level, the heating unit is on,

' and since the motor 16 is energized the water is being recirculated. The recirculation of the water started as soon as the water level in the chamber became high enough to be recirculated by the pump motor 16. I

it will be noted that AND gate 42, whose output energized the heating unit 54 was first conditioned by the medium level sensor 28 and then finally actuated and immediately latched by the high level sensor 30. The reason for this is that during the till period the water in the machine chamber is turbulent due to recirculation and tends to splash against the level sensors, thus actuating them intermittently. The conditioning and latching technique employed assures positive turnon and turnoff under these circumstances.

At the expiration of the predetermined'period time delay 50 produces a pulse signal S18. This is applied to OR gate 60 whose output signal S19 combines with signal S5 to actuate AND gate 36. The output signal S20 from AND gate 36 is fed back to OR gate 60 in a latching mode, applied to AND gate 62 as a conditioning signal, and energizes the drain valve 64. Signal S20 is also applied to inverter 46 which drops its output signal S9 to'deenergizc AND gates 44 and 48, thus dropping signal S11 and preventing the initiation of another time period by time delay 50. The pulse signal S18 is also applied to OR gates 66, 68 and 70, but no circuit action takes place since the outputs from these OR gates are all applied to unconditioned AND gates.

Signal S20 also combines with signal S21 from inverter 72 to actuate AND gate 74, whose output signal S22 triggers an approximately 15 second time delay 76. At the end of this time delay a pulse signal S23 is produced which is applied to OR gate 78, turbidity sensor 80 and OR gates 82 and 84. OR gate 78 produces an output signal S24 which combines with signal'S20 to actuate AND gate 62 and generate output signal S25. Signal S25 is fed back to OR gate 78 in alatching mode and is also applied to inverter 72, which drops its output signal S21 to deenergize AND gate 74 and prevent the initiation of another time delay (approximately 15 seconds).

if the drain water is sufficiently clear, turbidity sensor 80 generates an output signal S26 which actuates OR gate 86 to produce an output signal S27, This is appliedto a first bistable memory 88 whose output signal S28 is fedback to OR gate 86 in a latching mode and applied to AND gates 90 and 92. AND gate 90 is merely conditioned since its second input signal S32 obtained from OR gate 66 by pulse signal S18 is no longer present, but AND gate 92 is actuated due to the presence of signal S29 from inverter 94. AND gate 92 generates an output signal S30 which conditions AND gate 96 and energizes time delay 98. This time delay 98 is also set for approximately 5 minutes, but does not have any immediate effect since its circuit is coupled with that of time delay 50. The purpose of time delay 98 is to add its delay to thatof time delay 50 the next time the latter is actuated, thus providing for a longer wash eycle.

Signal S28 which is generated by first memory 88 throug OR gate 86 in response to an output from the turbidity sensor 80, thus conditions the machine for a wash cycle by energizing the additional time delay 98 and conditioning AND gate 96 whose output causes the detergent dispenser to be operated and dump the detergent. lfthe drain water is turbid,'indicating that loose food deposits may still be present on the dishes or in the machine, turbidity sensor 80 does not produce its output signal S26 and the prerinse cycle, including the till, recirculate and drain functions, is repeated automatically in the same manner previously described.

Assuming that turbidity sensor did produce its signal S26, the water drains out of the machine due to drain valve 64 being energized by signal S20, and the high level sensor 30 is deenergized and drops its output signal $12. This has no irnmediate effect, however, since both of the AND gates 34 and 42 to which this signal is ultimately applied are latched in their existing states by feedback signals. When the medium level sensor 28 is decnergized its output signal 57 drops, which in turn causes OR gate 38 to drop signal S8 and deenergize AND gate 42. This drops signal 814 and dcenergizes the heating unit 54. The dropping ofsignnl 88 also deconditions AND gate 60, while the dropping of signal S7 deconditions AND gates 44 and 48. When the low level sensor 26 is finally dcenergized its output signal S5 drops which causes inverter 32 to produce signal S6 and recondition AND gate 40, and deenergizes or resets AND. gates 34 and 36. The resetting of AND gate 36 S16 and S17 allowing inverter 22 to raise signal S4 again. This energizes water valve 24 to open the latter and initiate a refill, and also actuates previously conditioned AND gate 96 whose output signal S31 energizes detergent dispenser 100 which allows detergent to be dumped or washed into the machine chamber. i

The prerinse cycle is now completed and the machine is entering the wash cycle with the water valve opernthe drain valve closed and the detergent dispenser open. When the water level reaches the low level sensor 26, it is energized and its output signal S5 is raised which, once again, drops output signal S6 from inverter 32, and conditions AND gates 34 and 36. When the water level rises sufficiently medium level sen sor 28 is energized whose output signal S7 actuates AND gates 44 and 48 to energize time delay 50 and causes OR gate 38 to raise signal S8 which conditions AND gates 40 and 42. When the high level sensor 30 is energized, it raises signal S12 which ultimately energizes heating unit 54 through AND gate 42 and deencrgizes water valve 24 through AND gate 34, OR gate 58 and inverter 22 to shut off the water supply.

Since pump motor 16 is continuously energized through OR gate 14, as soon as the water level is high enough, the soapy wash water is recirculated to effect the desired cleaning action. At the expiration of the period provided by time delays 98 and 50, time delay 50 generates its pulse output signal S18 which through OR gate 60 actnatesand latches AND gate 36 to open drain valve 64 and actuate AND gate 74. The output signal S22 from the latter initiates time delay 76. Pulse signal S18 is also applied to OR gate 66 whose output signal S32 actuates previously conditioned AND gate 90, whose output signal S33 in turn latches the AND gate by means ofa feedback signal through OR gate 66, causes inverter 94 to drop its output signal S29 which resets AND gate 92 to deenergizc time delay 98 and decondition AND gate% to prevent any further operations of the detergent dispenser and conditions AND gate 102. The latched AND gate 90 constitutes the second bistable memory of the system.

At the expiration of the time period ol time delay 76, pulse signal S23 is produced which actuates and latches AND gate 62 through OR gate 78, and actuates OR gate 82 whose output signal S34 in turn actuates AND gate 102 and latches it through OR gate 82. The latched AND gate 102 constitutes the third bistable memory of the system and its output signal S35 conditions AND gate 104.

With the drain valve open the high level sensor 30 is first deenergized whose dropped output signal S12 has no immediate effect, as described earlier. When the medium level sensor 28 is deenergized output signal S7 is dropped which resets AND gate 42 to deenergize heating unit 54, and deconditions AND gates 44 andt48 to prevent the initiation of another time delay. When signal S5 is dropped in response to the deenergization of low level sensor 26 the drain valve 64 is closed through the resetting of AND gate 36 and the water valve 24 is opened through the resetting of AND gate 34 and the action of inverter 22. The wash cycle has now been completed, and the machine is entering the first rinse cycle.

Once again, as the water level rises and the sensors 26, 28 and 30 are energized in sequence, the time period of time delay 50 is initiated by the medium level sensor 28, the water valve 24 is closed by the high level sensor 30 and the heater 54 is energized by the high level sensor 30. At the expiration of the time period oftimc delay 50 during which period the water is recirculated in the chamber to rinse the dishes, time delay 50 produces another pulse signal S18 which opens the drain valve 64 through AND gate 36, initiates the time period of time delay 76 through AND gate 74, and actuates conditioned AND gate 104 through OR gate 68. AND gate 104, which constitutes the fourth bistable memory of the system, is latched in its energized state through OR gate 68 by means of a feedback of its output signal S36, and its output signal S36 conditions AND gates 106 and 108. After the time period of time delay 76 expires, pulse signal S23 prevents the initiation of a further time delay by energizing AND gate 62 through OR gate 78 and energizes AND gate 108 through OR gate 84.

AND gate 108 constitutes the fifth bistable memory of the system and its output signal S37 conditions AND gate 110 and latches itself through OR gate 84. As the rinse water flows out of the open drain valve 64 the high level 30, medium level 28 and low level 26 sensors are sequentially deenergized. As before, the medium level sensor 28 causes the heating unit 54 to be deenergized and the low level sensor 26 causes the drain valve 64 to close and the water valve 24 to open. In addition, the raising of signal S4 in response to the deenergization of the low level sensor actuates previously conditioned AND gate 106 whose output signal S38 in turn actuates the wetting agent dispenser 112. The latter discharges a measured amount of wetting agent into the machine chamber to aid the final rinse cycle and promote film-free drying. The first rinse cycle has now been completed and the machine is filling for the second rinse cycle.

As the water level rises the low level, medium level and high level sensors are sequentially energized asbefore. This actuates time delay 50, energizes heating unit 54 and closes water valve 24. In addition, the dropping of signal S4 resets AND gate 106 which prevents the dispensing of additional wetting agent. The rinse water is recirculated until the expiration of the time period of time delay 50. At this point pulse signal S18 is again produced which opens drain valve 64, initiates the time period of time delay 76, and actuates previously conditioned AND gate 110 through OR gate 70. AND gate 110 constitutes the sixth bistable memory of the system and its output signal S39 is applied to OR gates 38, 58 and 70. As the water discharges through open drain valve 64, the high level, medium level and low level sensors are again sequentially deenergized. The deenergization of medium level sensor 28 has no effect, however, since OR gate 38 is held on by signal S39 and its output signal S8 maintains AND gate 40 conditioned and keeps the heating unit 54 energized through AND gate 42. When the low level sensor 26 is deenergized AND gate 34 is reset as before, but since OR gate 58 is now held on by signal S39, signal S4 from inverter 22 remains down and water valve 24 is not energized and opened. When signal S5 from the low level sensor drops, however, inverter 32 raises signal S6 which actuates previously conditioned AND gate 40. The output signal from the latter causes inverter 114 to drop its output signal S40, which in turn deenergizes OR gate 14 and drops signal S2 to shut off the motor 16. Power is maintained on control unit 20 at this point by signal S14 acting through the normally closed thermostat 116 and OR gate 18. The second rinse cycle has now been compieted and the machine is entering the dry cycle. When the temperature within the machine chamber has risen to a sufficient level to indicate that the dishes are dry, thermostat 116 opens which drops output signal S3 from OR gate 18 and deenergizes control unit 20. This removes all power from the system and terminates the drying cycle, thus completing the entire normal operating cycle of the machine. Actually, the temperature within the machine chamber does not immediately drop, but falls off gradually, which prolongs the effective drying action until all ofthe moisture has been removed.

In the control system described above, it will be noted that allof the operational components of the machine shown on the right in FIG. 1, Le. the heating unit, water valve, drain valve, dispensers, etc., are energized and deenergized according to a predetermined sequence in response to the level sensors, the turbidity sensor and the thermostat. While the time delays 50, 76 and 98 also exercise a certain measure of control, their role is a more passive one since they are each initiated by the level sensors. This mode of operation completely eliminates all of the guess work" attendant with pure timer controls and assures optimum machine functioning independent of such variables as water pressure, drain suction, preload cleaning, load volume, etc.

Turning now to the more detailed schematic circuit diagram of FIG. 2, in which the reference numerals of FIG. 1 have been used where applicable, the momentary closing of start switch 12 applies a negative DC signal of 24 volts from the rectifying power supply 124 to the entire control system. At this point, all of the silicon controlled rectifiers SCRI-SCR13 are in their nonconducting states. With power appl es to the system, transistor 01 is immediately saturated by the voltage drop across resistor 126, which energizes the motor relay 128 through resistor 130. The motor relay, as well as the others shown in H6. 2, are all reed relays, whose associated contacts are in the power circuits of the actual components. In this manner, the control system operates exclusively on low or logic level signals which reduces its power requirements and permits miniaturization using printed and integrated circuit techniques. When transistor 01 is saturated, transistor 02 is also saturated due to the lowering of its base potential through resistor 132, which energizes control relay 134 through resistor 136 and Zener diode 138. The energization of control relay 134 closes its associated switch 140 connected in parallel with start switch 12 to maintain power to the system when the start switch is released.

Transistor Q3 is also saturated at this time, since its base is tied to ground through resistors 142 and 144, and it conducts through water relay 146 to open the water valve and begin filling the machine chamber. The alternate conduction paths for transistor 03 through detergent relay 148 and transistor Q4, and through wetting agent relay 216 are blocked by the nonconduction of SCR4 and SCR7, respectively. As the water level rises in the machine chamber, low level sensor 26 is first actuated to saturate transistor Q5, which in turn causes transistor O6 to conduct through resistor 150. When the medium level sensor 28 is actuated, transistor Q7 saturates to provide a charging path for capacitor 152 through door switch 154 and resistors 156 and 158. The completion of this charge path corresponds to the initiation of time delay 50 in FIG. 1. When the high level sensor 30 is actuated, transistor 08 saturates and fires SCR] and SCR13. The firing of SCRI increases the voltage drop across resistor 142 which renders transistor Q3 nonconducting and deenergizes water relay 146, while the firing of SCR 13 allows transistor 09 to conduct through Zener diode I60 and heater relay 162, thus energizing the I heating unit. The conducting of Q9 raises the base potential of transistor 015 through resistor 266, allowing transistor Q15 to conduct through Zener diode 138, resistor 136 and control relay 134. Transistor Q9 was previously primed for conduction when transistor 07 saturated by the raising of its base I potential through resistors 164, 166 and 168. At this point, the

machine chamber is filled with water which is being recirculated for the prerinse cycle, the heating unit is on, the drain valve is closed, and the time delay network is energized.

When the charge on capacitor 152 reaches a sufficient level, approximately minutes after its charge path is completed, unijunction transistor Q is fired, which in turn fires SCR2 to energize the drain relay 170 through Zener diode 172. The firing of transistor Q10 also tends to fire sequently it cannot charge. The firing of SCR2 also permits capacitor 176 to begin charging through the path including diode 178, transistor 05, resistor 180 and diode 182. The completion of this charging path corresponds to the initiation of the time delay 76 (approximately 15 seconds) in FIG. 1.

A short time later, the accumulated charge on capacitor 176 fires unijunction transistor Q11 which in turn fires SCR3. The latter is clamped in its conductivestate through resistor 184, while diode 186 clamps the emitter of transistor Q11 to a sufficiently negative potential to prevent the generation of another pulse. The firing of transistor Q11 tends to turn on SCR4, SCR6 and SCR8, but the latter two are blocked by nonconducting transistors Q12 and Q13,'respectively.

Assuming that the drain water is sufficiently clear, the light from source 188 passing through a transparent portion of the drain pipe 190 lowers the resistance of photoresistor 192 to the point where the pulse from the transistor Q11 fires SCR4, thus implementing the turbidity check. Note that with SCR4 conducting through resistor 194, a collector path is now available for transistor Q4.

When the water drains below the high level sensor 30, transistor Q8 is turned off, which has no immediate effect. When the medium level sensor 28 is deenergized, transistor 07 is turned off which renders transistor Q9, and hence SCR13, nonconductive and deenergizes the heater relay 162. When the low level sensor 26 is deenergized, transistor O5 is turned off which renders transistor Q6, and hence SCRl, nonconductive and also deenergizes drain relay 170. At the same time transistor O3 is again saturated to energize the water relay 146. This time, however, the drop across resistors 196 and 198 through SCR4 renders transistor Q4 conductive, which energizes detergent relay 148 and implements the detergent dispensing action. With transistor Q4 conductive, a charging path for capacitor 200 exists through diode 202, and since both capacitors 152 and 200 must now be charged before transistor Q10 fires, the longer (approximately 10 minutes) time delay has been conditioned.

At this point the prerinse cycle has been completed with s satisfactory turbidity check and the machine is entering the wash cycle, with the drain valve closed, the water valve open, the detergent dispensed and the long time delay conditioned.

When the low level sensor 26 is energized, transistors 05 and Q6 saturate as before. When the medium level sensor 28 is energized, transistor Q7 saturates, transistor O9 is condi- .tioned, and capacitors 152 and 200 begin charging. When the high level sensor 30 is energized, transitor Q8 saturates which fires SCRl and SCR13. As before, the heater relay 162 is now energized through transistor Q9 and transistor O3 is cutoff to deenergize the water relay 146. At the expiration of the long time period, transistor Q10 fires which in turn fires SCR2 and energizes drain relay 170. At the same time, SCRS is fired and conducts through SCR4, which renders transistor O12 conductive and cuts off transistor O4 to prevent any further detergent dispensing. With SCR2 conductive, capacitor 176 begins to recharge and after approximately 15 seconds, transistor O11 fires which in turn fires and latches SRC3. The pulse from transistor Q11 now fires SCR6, which conducts through transistor Q12. By reconciling FIGS 1 and 2, it is apparent at this point that SCR4 constitutes the first bistable memory of the system, SCRS is the second memory, SCR6 is the third memory, SCR7 is the fourth memory, SCR8 is the fifth memory and SCR9 is the sixth memory.

As the wash cycle water drains out of the machine chamber, the three level sensors are sequentially deenergized as before to deenergize the heating unit, close the drain valve, and open the water valve. This completes the wash cycle and as the water fills for the first rinse cycle, the sensors are sequentially energized again to turn on the heating unit, close the water valve and initiate another 5 minute delay. Note that with transistor Q4 held off by the conduction of transistor Q12, capacitor 200 can no longer charge and the machine reverts to its original 5 minute delay period.

At the expiration of this period, transistor Q10 is fired which fires SCR2 to energize the drain relay and permit capacitor 176 to begin charging. The pulse from transistor 010 also fires SCR7, the fourth memory, which conducts through resistor 204 and SCR6. The drop across resistor 204 renders transistor Q13 conductive through a collector path including resistors 206, 208, 210 and 212, and reprogram switch 214. When the charge on capacitor 176 reaches a sufficient level, transistor Q11 and SCR3 are fired, and the pulse from transistor 011 also fires SCR8 which conducts through resistor 206 and transistor Q13.

As the sensors 26, 28 and 30 are deenergized in response to the lowering water level, the heating unit is again turned off, the drain valve is closed and the water valve is opened. This time, however, when transistor Q3 saturates in'response to the cut off of transistor 06 at the end of the drain cycle, the wetting agent relay 216 is energized through diode 218, SCR7 and SCR6. thus dispensing a measured amount of wetting agent into the machine chamber. At this point, the first rinse cycle has been completed and the machine is entering the second and final rinse cycle.

The fill and recirculate portions of this rinse cycle are the same as for the first rinse cycle, except that the firing of transistor Q10 at the expiration of the time delay fires SCR9 which now has a conductive path available through SCR8. With SCR9 conductive diode 220 becomes forward biased and clamps the base of transistor O3 to a level just above the negative supply potential. This prevents Q3 from becoming conductive again when the low level sensor 26 is deenergized and thus assures the continued deenergization of the water relay, the detergent relay and the wetting agent relay. The conduction of SCR9 also creates a drop across resistor 222 at the base of transistor 07, which maintains the latter saturated when the medium level sensor 28 is deenergized to keep transistor Q9 on and the heater relay 162 energized.

As the water drains out of the machine chamber at the end of the second rinse cycle, and the low level sensor 26 is deenergized to cut off transistor 05, transistor Q14 is saturated through the path including diode 178, transistor Q7, diode 224, resistors 226 and 228, drain relay 170 and SCR2. When transistor Q14 saturates, transistor 01 is cut off which deenergizes the motor relay 128 and cuts off transistor 02. Transistor 09 remains on to maintain control relay 134 energized.

With the machine chamber drained, the water valve closed, the heating uniton, and the motor off, the machine now enters the drying cycle. This continues until the temperature reaches a sufficient level to open the normally closed thermostat 116. When the thermostat opens, the voltage across resistor 230 fires SCR12, and the resulting current path though diode 178, transistor Q7, resistor 164, diode 232, SCR12, SCR9 and SCR8 creates a large drop across resistor 164 which cuts off transistor Q9 and deenergizes the heater relay 162. This in turn shuts off transistor Q15, and, since parallel transistor Q2 was previously cut off when the motor relay was deenergized, the control relay 134 is now deenergized. When this occurs, holding switch 140 opens to interrupt the power supply to the system and terminate the entire normal operating cycle.

The circuitry described thus far corresponds to that shown in the block diagram of FIG. 1. In addition, FlG. 2 includes some further circuitry for effecting reprogramming and/or selective programming, as described in detail below. The reprogramming feature permits the operator to interrupt the normal operating cycle at any stage of completion and restore the machine to its initial condition, upon which the' normal cycle may be repeated. Alternately, a series of optional programs are available, and these may be selected before the initial turn on or after reprogramming.

To reprogram the system, all of the fired memory SCRs must be reset and the chamber drained, if it is filled with any water. This is accomplished by opening the normally closed reprogramming switch 214. When this switch is opened, SCR4-SCR12 are reset since their cathode circuits are broken, thus erasing all memory functions. This does not effect SCR], SCR2, or SCR3, since they are isolated by diodes 234, 236 and 238, respectively. At the same time, however, the opening of switch 214 raises the anode potentials of these three diodes and this increased voltage fires SCRl through resistor 240, SCR2 through resistor 242 and SCR3 through re sistor 244. This closes the water valve, opens the drain valve and prevents capacitor 176 from charging, thus returning the machine to its initial condition.

If the drip-dry or no-final-heat option is exercised by the closing of switch 248, SCRll is fired and conducts through resistors 250 and 252. This has no effect on the system until SCR9 is fired at the beginning of the drain portion of the final rinse cycle, at which time diode 254 becomes forward biased. This completes a path through diode 178, transistor Q7, resistor 164, diode 232, SCRll and diode 254, which shunts away most of the current that would otherwise flow through resistors 166 and 168. When the drop across resistor 168 falls below the breakdown potential of Zener diode 160, the baseemitter junction of transistor 09 becomes reverse biased, the transistor is cut off and heater relay 162 is deenergized to shut off the heating unit. At the same time, transistor 015 is cutoff, and, when the motor is shut off at the end of the final rinse drain, the control relay is deenergized and the system is shut down. By eliminating the drying cycle in this manner, the contents of the machine are permitted to drip-dry through natural evaporation.

The soft wash option calls for a program that eliminates the prerinse cycle and prevents the heating unit from ever being turned on, and is particularly suited for the washing of delicate items that might otherwise be harmed by excessive heat and rinsing. This option is selected by closing switch 256 which fires SCRlO and permits diode 232 to shunt most of the current away from resistors 166 and 168. As described above, with respect to the drip-dry option, this holds transistor Q9 off and prevents the heating relay from becoming energized. When the soft wash switch is closed, SCR4 is also fired through diode 258 and resistor 260, which conditions the machine to enter directly into the wash cycle.

In the rinse only option, the prerinse and wash cycles are omitted from the program and the machine enters directly into the first rinse cycle followed by the final rinse and drying cycles. This option may be exercised by closing switch 262 which fires SCR4, SCRS and SCR6. The firing of SCRS saturates transistor Q12 whose collector potential holds transistor 04 off, thus preventing the detergent relay from becoming energized and capacitor 200 from charging. Under these conditions, the machine proceeds directly into the first rinse cycle with the subsequent circuit operation identical to that described above for the normal program.

The dry only option includes only the drying cycle and is used primarily to ,warm serving dishes. This program is implementcd by closing switch 264, which gates on SCR4-SCR9 and SCR13. Under these conditions only the control relay 134 and the heater relay R62 are energized, and the resulting drying cycle is terminated as before when thermostat 116 opens.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. An electronic control system for a washing apparatus having a liquid chamber for holding articles to be washed, comprising: liquid inlet means for the chamber, liquid outlet means for the chamber, circulation means for circulating the liquid within the chamber, sensing means for detecting the presence of liquid within the chamber at at least three separate levels, means including an electronic logic network for controlling the liquid inlet means, the liquid outlet means and the circulation means in response to the sensing means in accordance with a predetermined normal program of cyclic operation, and means to automatically disconnect the control system from a power source at the end of the program.

2. An electronic control system as defined in claim 1 wherein the-controlling means includes time delay means initiated by the sensing means for controlling the duration of selected cycles in the normal program.

3. An electronic control system as defined in claim 2 further comprising heating means for the chamber controlled by the controlling means in response to the sensing means.

4. An electronic control system as defined in claim 3 wherein the normal program includes a drying cycle and further comprising thermostatic means for cleenerglzing the heating means to terminate the drying cycle.

5. An electronic control system as defined in claim 3 wherein the normal program includes a predetermined sequence of rinsing, washing and drying cycles, and further comprising means for selectively altering the normal program to omit one or more of the cycles.

6. An electronic control system as defined in claim 2 wherein the normal program includes a wash cycle and further comprising means responsive to the controlling means for dispensing detergent into the chamber during the wash cycle.

7. An electronic control system as defined in claim 1 wherein the normal program includes a prerinse cycle followed by a wash cycle and further comprising means for sensing the turbidity of the drain liquid from the prerinse cycle, and means responsive thereto for enabling the wash cycle if the drain liquid is sufficiently clear and for repeating the prerinse cycle if the drain liquid is not sufficiently clear.

8. An electronic control system as defined in claim 1 wherein the normal program includes a final rinse cycle and further comprising means responsive to the controlling means for dispensing a wetting agent into the chamber during the final rinse cycle.

9. An electronic control system as defined in claim 1 wherein the controlling means includes a plurality of bistable memory elements for'storing the stage of program completion as the apparatus proceeds through the execution of the predetermined program, and wherein the controlling means includes reed relays having associated contacts in the power circuits of the liquid inlet means, liquid outlet means and the circulating means.

10. An electronic control system as defined in claim 9 further comprising means for interrupting the program at any stage of completion and restoring the apparatus to its initial condition, including the resetting of any of the memory elements that were previously set, and means for selectively modifying the program.

11. An electronic control system as defined in claim 1 wherein the electronic logic network primarily comprises a plurality of AND gates, OR gates and inverters.

12. An electronic control system for a washing apparatus having a liquid chamber for holding articles to be washed, comprising: low level, medium level and high level sensors wherein the logic circuit means includes time delay means initiated by one of the level sensors for opening the outlet means.

14. An electronic control system as defined in claim 13 wherein the logic circuit means includes an AND gate conditioned by one of the level sensors and actuated by a second of the level sensors for energizing the heating means.

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