US3769716A

US3769716A - Variable timer runout control for dryer

Info

Publication number: US3769716A
Application number: US00198354A
Authority: US
Inventors: D Janke; R Marcade; J Karklys
Original assignee: Whirlpool Corp
Current assignee: Whirlpool Corp
Priority date: 1971-11-12
Filing date: 1971-11-12
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06
Also published as: AU462478B2; AU4529572A; CA950072A

Abstract

Apparatus for controlling the operation of a dryer includes a circuit to sense for a predetermined dryness condition during a drying operation, a circuit for determining the elapsed time interval in attaining that condition and means for extending the drying operation by an interval determined in accordance with the elapsed sensed drying time to improve repeatability in percent moisture retention particularly with respect to loads which are difficult to dry.

Description

United States Patent Janke et al. 1 Nov. 6, 1973 [5 VARIABLE TIMER RUNOUT CONTROL 3,662,186 5/1972 Karklys 34/45 FOR DRYER 3*???323 131323 32112 ers i r [75] Inventors: g0naldI;E-h.lla aB 1t rlli 3,392,350 7 19 3 Griffin 328/48 oque arca e, evensvi e;

Joseph Karklys, St. Joseph, all of I Mich Primary ExammerWlll1am F. O Dea Assistant ExaminerPaul Devinsky Assigneei whirlpool Corporation, Benton Attorney-James S. Nettleton et al.

Harbor, Mich.

[22] Filed: Nov. 12, 1971 [57] ABSTRACT [21] Appl. No.: 198,354

Apparatus for controlling the operation of a dryer includes a circuit to sense for a predetermined dryness [52] US. Cl 34/33, 34/45,33243//543 condition during a y g operation, a Circuit for dew mining the elapsed time interval in attaining that condigjga g i g tion and means for extending the drying operation by 2 an interval determined in accordance with the elapsed sensed drying time to improve repeatability in percent moisture retention particularly with respect to loads [56] UNlTE S T ;S :;:ENTS which are difficult to dry.

3,702,030 11/1972 Janke 34/33 9 Claims, 11 Drawing Figures 6M2 f6 7 24 I 77M/A/6 PULSES //EA 752 CLOCK 3/ t/554102); 22:107'06 DHYA/f-SS X/N M54102) sflvsoe (600N752) 5X E c u r -M,qsrEe 5Y$7'EM OED /NPU7- 77MF LOG/C h I l l 4 i 2.9 I I l 3 L l l l 39 L L 1 i l l J ME/waey #550 sac/a PAT/l5 PAIENIEBnuv emu 3,769,716

summer 5 VARIABLE TIMER RUNOUT CONTROL FOR DRYER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for Y controlling the operation of a dryer and is particularly concerned with the provision of a dryer control comprising means for extending the dryer operation beyond the point at which a predetermined dryness condition is sensed by an interval which is related to the amount of time accumulated in reaching the predetermined condition.

2. Description of the Prior Art It is generally known that certain fabrics, for example, fabrics composed of manmade synthetic fibers, tend to dry easier than other fabrics. Accordingly, dryer cycles were provided to accommodate the difference in basic types of fabric by providing a selection of drying times and temperatures. It is also generally known that towels, rugs, work clothes, and other heavy articles are generally harder to dry due to pockets, seams, nap or upstanding fibers extending from a core. Articles of this type present a substantially different drying problem in that the exterior of an article which According to a preferred embodiment of the invention, a moisture sensing circuit is employed .to sense for a predetermined moisture level which is conventionally used for terminating operation of a dryer, and means are provided for extending the drying operation in accordance with the time accumulated in sensing for the predetermined moisture level. The means for extending the drying operation includes an extended timing logic circuit which reads the output of a clock system to determine elapsed drying time and inhibits termination of the drying operation for an extended interval determined by the amount of drying time read.

A time override circuit is provided which reads the output of the clock system and is operable to terminate a drying operation whenever such an operation proceeds for an extended time without the occurrence of a termination signal from the dryness sensor. 'Therefore, this circuit fixes a limit to the amount of sensed drying time available andwillterminate the drying operation in the event that the dryness sensor fails, or in the event that a timed rather than an automatic cycle is selected.

contacts the moisture sensor of a dryer has less moisture retention than the interior of the article so that a predetermineddesired moisture retention level'may be prematurely sensed by the moisture sensor causing a premature termination of the drying operation. One remedy is of course to perform a second drying operation. This remedy is, however, undesirable in that it requires additional work for the operator and the requisite additional drying time is an unknown variable. Another solution known in the art is to add drying time after a sensed drying period through the provision of a fixed timerrunout. This technique also has" drawbacks in that there is no flexibility in providing for a predetermined moisture retention with the result that some fabrics may become excessively dry'while others may still be insufficiently dry.

SUMMARY OF THE INVENTION The primary objectof the present invention is to provide an improved method and apparatus for operating a dryer to obtain a desired moisture retention in the load undergoing drying.

Another object of the invention is to improve the repeatability inpercent moisture rentention from load to load for a given setting of the dryer whereby hard to dry loads are dried to. generally the same moisture retention as easy to dry loads.

The foregoing and other objects of the invention are realized through the provision of control techniques which include sensing for a predetermined dryness condition, determining the time accumulated in reaching that predetermined dryness condition and variably extending the drying operation for an interval beyond the point at which the predetermined dryness condition is sensed in accordance with the accumulated time interval. The extension of the drying operation may have any desired relationship with respect to the duration of the sensed drying interval including a proportional relationship or a stepped relationship wherein a certain amount of time is added whenever the sensed drying operation extends beyond predetermined times.

Although the preferred embodiment of the invention described herein relates to a dryer having means for sensing the dryness condition of the fabric load by way of a fabric conductivity sensor, it should be appreciated that other variables which provide an indication of the load dryness condition may be sensed for purposes of practicing the invention. For example, rather than sensing fabric conductivity, it may be desirable to sense for static electricity which isincreasingly generated by the load as it becomes dry, and extend the drying operation beyond. the point at which a predetermined static signal is detected by an interval which is dependent .on the elasped drying time prior to the static signal. Alternatively, the time required to reach a predetermined temperature or humidity condition within a dryer could be used as the basis for determining the interval by which a drying operation is tobe extended.

BRIEF DESCRIPTION OF TH DRAWINGS Other objects, features and advantages of the invention, its organization, construction and operation, will best be understood fromthe following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a graph illustrating typical performance for electronic moisture sensing dryer controls and the desired performance of such controls wherein percent moisture retention is plotted with respect to drying difficulty;

' FIG. 2 is a program chart illustrating a program for adding time to the drying operation in accordance with the principles of the present invention;

FIG. 3 is a schematic diagram of a dryer having an electronic control circuit, including a front view of the FIGS. 6a and 6b, oriented as illustrated in FIG. 7, form a schematic logic circuit diagram of a dryer control constructed in accordance with the principles of the present invention;

FIG. 8 is an explanatory truth table utiized as a legend for understanding the operation of the NOR gates of FIGS. 6a and 6b;

FIG. 9 is a chart describing the various switch inputs which the present control utilizes; and

FIG. 10 is a chart illustrating the dryer function which corresponds to each memory state.

. DESCRIPTION OF THE PREFERRED EMBODIMENT Although'the present invention is applicable to other types of dryer control systems, it will be discussed below in the environment of a digital dryer control system such as disclosed by Donald E. Janke in his United States patent application entitled"Digital Dryer Control Circuit, Ser. No. 129,008, filed Mar. 29, 1971 now. US. Pat. No. 3,702,030, and assigned to the same assignee as the present invention.

Referring to FIG. 1, the typical performance for some prior electronic moisture sensing controls is plotted as percent moisture retention with respect to drying difficulty. This curve illustrates that the dryer performance degrades as loads are encountered which are increasingly difficult to dry. Drying difficulty for a particular load is primarily dependent upon the size of the load and the type of material. For example, towels and blankets are difiicult to dry because the upstanding'fibers at the surface prevent the sensor electrodes from contacting the body portion of an article which may retain considerable moisture at the time the surface fibers become dry. .As illustrated in FIG. 1, there is a tendency toward increased moisture retention for loads of increased drying difficulty. The present embodiment of the invention comprises a drying technique which adds on a variable amount of drying time after the sensor indicates that some predetermined moisture level has been attained The amount of added drying time increases as the duration of the sensed drying period increases in order to achieve the desired performance level indicated in'FIG. 1. I I V Referring toFIG. 2, a program for adding time to the drying operation, as suggested in FIG. 1, is illustrated. By way of example, no additional drying time is. provided for sensed drying periods of less than 35 minutes duration, in accordance with the first portion of the performance curve of FIG. 1 .--Beyond the initial 35 minute period the drying operation is extended by 'one minute for each additional 5 minutes of sensed drying time, until 60 or more minutes of drying time is accu- "mulated after which a fixed 6 minute additional drying "interval is provided. This program is only representative of add-on times and any particular program is primarily determined by the amount of departure between the desired and actual moisture retentions as suggested in FIG. 1. Improved drying performance has also been obtained by using a program of add-on times which are proportional to the sensed drying operation.

outlet duct 16 having a filter 17 therein. The flow of air 14 is heated by a heater 18 disposed in the inlet duct 15.

The tumbling load periodically contacts a sensor 19 having a pair of

electrodes

20 and 21 which are connected to a control circuit 22. The control circuit 22 also receives 60 Hz timing signals and controls the operation of the dryer by way of a plurality of outputs including an output 23 connected to the motor 12, an output 24 connected to the heater l8 and an output 25 for controlling the application of power to the dryer.

FIG. 4 is a block diagram of the control circuit 22 of FIG. 3. The control circuit 22 includes a clock system 26 which receives the 60 Hz timing pulses and the input signals from the drynesssensor, and a memory indexing circuit 27 operated by the clock system 26 to index a memory 28 which provides the outputs 23-25 for controlling the operation of the dryer. The memory 28 includes feedback circuits 29 and 30 to the memory indexing circuit 27 and the clock system 26 for indicating the operational state of the memory to these circuits. The foregoing is generally the system disclosed in the aforementioned Janke application Ser. No. l29,008. The present invention may be employed in such a system through the provision of an extended time logic circuit 31 which is connected between the clock system 26 and the memory indexing circuit 27 to control operation of the memory indexing circuit 27 and thus prevent termination of the drying operation for an extended period. The extended time logic circuit 31 also has a feedback connection 32 from the memory 28.

. The memory circuit 28 may be a'shift register or a binary counter having a plurality of independent states which correspond to various operations of a drying cycle. The memory is indexed sequentially through a program of memory states by the memory indexing circuit which receives input signals from the clock system 26. The clock system 26 is a digital counter which receives timing pulses which may be derives from a conventional 60 Hz linejThe clock system 26 provides a signal to the extendedtime logic circuit 31 at such time as the sensor signal is received. The logic circuit 31 reads the amount of time accumulated duringthesens'ed drying operation from a portion of the clock system 26 and allows the drying operation to continue for an amount of time which is determined by the sensed drying time accumulated before the signal which initiates operation Referring to FIG. 3, a dryer is generally illustrated at 10 as comprising a drum 11 having a rear wall Illa. The

drum 1] is rotated by a motor 12 via a belt 13 to tumble a load. The motor 12 is also utilized to drive a fan (not shown) for effecting a flow of air, as indicated at 14,

through the drum 11 by way of an inlet duct 15 and an of the memory indexing circuit 27. When energized, the memory indexing circuit develops a pulse for sequencing the memory to its next logic state.

FIG. 5 is a more detailed block diagram of the control circuit 22. In FIG. 5, the clock system'is seen to comprise three separate counters, an S counter 33, an A counter 34 and an F & T counter 35. The S counter 33 is associated with the sensor circuit and is operated by the 60 Hz pulses to reset theA counter 34 upon the accumulation of a predetermined number of pulses, unless such accumulation is prevented by the receipt of a reset pulse from the sensor circuit. Therefore, repetitive reset pulses from the sensor circuit to the S counter 33 will permit the A counter 34 to operate without reset. The remaining portions of the clock system provide the time base for both the sensed drying operation and a conventional timed drying operation and their functions will be best understood from the description below related to the logic circuit of FIGS. 6a and 6b.

In addition to the extended time logic circuit 31, a timed dry circuit 36 is provided between the F & T counter and the memory indexing circuit 27. An override circuit is also provided which is operable to terminate the drying operation whenever such an operation proceeds for a predetermined period of time without the occurrence of a terminating signal from the dryness sensor. This circuit therefore limits the amount of sensed drying time andwill terminate the drying operation in the event that the dryness sensor or a circuit driven thereby fails.

Referring to FIGS. 6a-8, a schematic logic circuit is illustrated wherein the control circuit 22 is further broken down to better illustrate the operation of the invention. The clock system 26 (FIG. 6a) includes a shaping circuit.40 for shaping a 60 Hz waveform to provide 60 Hz pulses to the S counter 33. These pulses are also supplied to a C counter 39 which may be viewed as a common front end for both the A counter 34 and the F counter 37. Timing pulses derived from the aforementioned 60 Hz pulses are thus applied to the A counter 34, the F counter 37 and the T counter 38 by way ofthe C counter 39. A plurality of inverters and NOR gates 41-46, 48, 49 and a bistable circuit 47, whose functions will be appreciated from the operational description, make up the remainder of the clock system 26.

The

counters

33, 34, 37, 38 and 39 have a plurality of outputs and complementary outputs (not shown). The S counter 33 includes a plurality of outputs S1-S4, the A counter 34 includes a plurality of outputs A1-A9, theC counter 39 includes a plurality of outputs C1-C6, the F counter 37 includes a plurality of outputs Fl-F9, and the T counter 38 includes a plurality of outputs T1- T5. The extended time logic circuit 31 comprises a plurality of NOR gates 50-63 and a plurality of inverters 6411-66. The NOR gates 50-53 and -59 are employed to read the outputs, primarily the complementary outputs, of the F counter 37 and the T counter 38. In addition, the gate 53 includes an input D from a cycle selection switch and the gate 54 includes an input from the C counter 39. The gate 61 receives logical imputs from the memory 28 and servesas a resetting control input for the F counter 37 by way of the

gates

46 and 44. The gate 63 serves as an output device to control indexing at the memory indexing circuit 27.

In FIG. 6b, the memory 28 is illustrated as having a plurality of outputs Ml-M3. Each of these outputs has I a complementary output (not shown). The memory indexing circuit 27 includes a plurality of NOR gates 67-73 and a bistable circuit 74. Each of the gates 67-72 has a plurality of inputs for reading the outputs of-the

counters

34, 37, 38 and the memory In addition, switch inputs E, F and G are provided. The memory indexing circuit therefore reads the outputs of these counters and the switch inputs'for indexing the memory by way of the gate 73. The gate 73 includes an input from the gate 63 of the extended time logic circuit 31. Therefore, the elapsed time read by the extended time logic circuit 31 determines subsequent indexing of the memory 28 in that the counters are not reset until termination of the additional drying time. Gate 71 of the memory indexing circuit 27 provides the aforementioned sensor override function, receiving inputs only from the last two stages of the T counter 38 such that a signal, to initiate memory indexing will be provided whenever 80 minutes of sensed drying time are accumulated. Gate 72 serves to initiate memory indexing when anti-wrinkle operation (described in the aforementioned Janke application) is not desired, and gate 70 terminates the anti-wrinkle operation after a period of 2 hours.

The elapsed time is transformed into additional drying time by the decoding of the gates 55-59 whose outputs carry additional time designations of l min., 2 min., 3 min., 4 min. and 6 min. as an example of binary information transformed'into minutes. This information is utilized by way of the gates 62, 63 and 73 to cause indexing of the memory by the bistable circuit 74 after the predetermined additional time has been run. At such time, the output of the gate 73 together with a shaped pulse to the trigger input of the bistable circuit by way of the shaping circuit 40 and the inverter 41 operate the bistable circuit to index the memory and reset the F counter 37 and the T counter 38 by way of the inverter 45 and the gate 44 and the

gates

48, 49 respectively. The F counter 37 has been continuously driven from the overflow of the C counter 39, while the T- counter 38 has been indexed at 5 minute increments effected by way of the gate 43 which reads the output of the F counter 37, and subsequent Hz trigger pulses from the shaping circuit 40 by way of the inverter 41.

FIG. 6b also includes gates 84 and 85, and inverter 86 for controlling the operation of the motor 12 in accordance with the state of the memoryv 28 and the state of the F counter 37. A similar circuit may control the heater 18. For the circuit shown, the output of inverter 86 goes high whenever the motor 12 is to be energized. Appropriate power switching devices (not shown) are, of course, necessary to directly operate the'motor 12 and the heater 18. v

The timed dry circuit 36 is also illustrated in FIG. 6b as comprising a plurality of NOR gates 75-83 which are connected to read the outputs of the T'counter 38 and the outputs of a dryness selector switch wherein A, B, C are independent outputs of such a switch for giving eight possible combinations of binary data. The selection of any one of these gates sets an indicated predetermined amount of available drying time, here 10 min. min., and the gate 83 serves to read such drying time in combination with the state of the memory 28 and the cycle selection switch input D, and serves as an input to the gate 73 of the memory indexing circuit 27. Therefore, whenever the cycle selection input D to gate 83 is low and the memory output M2 is also low indicating that the dryer is in the drying part of a cycle, gate 83 becomes operative and will provide a signal to gate 73 to index the memory 28 at a time which is deter- Y mined by gates -81. Once indexed, memory 28 shifts to a state which disables the timed dry logic circuit 36.

In operation, a 60 Hz waveform is supplied to the shaping circuit 40 to derive 60 Hz pulses. These 60 Hz pulses are employed to drive the S counter 33, the C counter 39 and, by way of the C counter, the F counter 37 and the A counter 34. In addition, these 60 Hz pulses are fed by way of an inverter 41 to the trigger input of a bistable circuit 47 for pulsing the T counter 38 once every five minutes, as read from the F counter -"37 by the NOR gate 43. The overflow operation of the which also reads the state of the memory 28 and the state of the cycle selection :iwitch D. It should be noted that the

counters

33, 34 and 38 and the memory M are provided with a preset (resetting) signal upon initiation of operation. This may be by any technique such as the well known RC reset circuit technique.

The sensor 19 is associated with a circuit such as disclosed by Alvin J. Elders in his U. S. Pat. No. 3,471,938, assigned to the same assignee as the present invention, which operates to provide resetting pulses to ture level above that desired predetermined moisture level, the C counter 39, the F counter 37, and the T counter 38 have been driven to provide a reading of elapsed time, which reading is decoded by the extended time logic circuit 31 which translates the elapsed drying time into a desired extended drying time by means of an add on interval. Ordinarily, upon detection of the desired predetermined moisture level, the

counters

34, 39 would effect indexing from a memory state which effects heater energization; however, in the embodiment of theinvention illustrated in FIGS. 6a and 61) only a preparatory indexing step in such a direction is permitted until performance of the additional, variably extended drying time is achieved.

As the drying operation progresses, and repetitive resetting of the S counter 33 permits continued pulse accumulation by the C counter 39 and the A counter 34, and eitherof the gates 68, 69 of the memory index circuit 27 have been selected by appropriate switches to provide dryness inputs E and F thereto, all inputs to the gate 73 are conditioned such that the change of state of the selective gate 68, 69 causes a change of state of the gate 73 which in turn operates the bistable circuit 74 in conjunction with a trigger pulse from the shaper circuit 40 by way of the inverter 41. Operation of the binary circuit' 74 causes the memory to be indexed as v a preparation step to heater turn off from a memory state of 000 to a memory state of 100. The gate 61 of the extended time logic circuit 31 reads this memory state and conditions the memory index circuit 27 by way of the inverter 66 and the gate 63 which supply an input to the gate 73. It should be noted that although this particular illustratedembodiment has employed a 34 sec. output of the gate 69 or a l min. 9 sec. output of the gate 68 as an indirect signal from the sensor to effect preparatory indexing, other time signals could be employed. As described in the aforementioned Janke application Ser. No. 129,008, now US. Pat. No. 3,702,030, the greater the time interval which must be accumulated by the counter associated with the sensor (the A counter) before the memory is indexed, the dryer the clothes load will be at the end of the sensed drying operation. 7

The gate 61 also has its output connected to a gate 46 of the clock system 26. The gate 46 is interposed between the Q output of the bistable circuit 47 anda reset input of the F counter 37 by way of a gate 44. Therefore, every min. read from the F counter 37 bythe gate 43 effects resetting of that counter for continued pulse accumulation by the overflowof the C counter 39 upon its continued accumulation of the 60 Hz pulses from the shaper circuit 40. It should be noted, however, that the T counter 38 is only stepped once every 5 min. so that during latching of the indexing circuit 27, the outputs of the T counter 38 are frozen so to speak for such an interval so that these outputs are available for reading along with the changing states of the F counter 37. The gates of the extended time logic circuit therefore transform the elapsed time interval set in the T counter into an extended time interval at the gates 50-59 whereupon the gates 62 and 63 respond to effect indexing of the memory 28 by way of the gate 73 and thebistable circuit 74. Upon indexing, the bistable circuit 74 provides a reset signal to the F counter 37 and the T counter 38 by way of the inverter 45 and the gate 44 and the

gates

48, 49 to clear these counters in conjunction with the change of state of the memory from 100 to 101 which also causes de-energization of the heater by way of a circuit (not shown) similar to that of the gates 84, and inverter 86 for effecting control of the motor 12.

In conclusion, there has been disclosed a variable timer run-out control wherein a sensing means is provided for detecting a predetermined load dryness condition, timing means are employed to detect the amount of time accumulated in achieving the predetermined dryness condition and further means are pro-' vided for continuing the drying operation for a time interval which is determined by the accumulated drying time so that repeatability in percent final moisture retention from load to load is improved for a given setting of the dryer. I

Although we have described our invention by reference to a particular illustrative embodiment thereof, many changes and modifications of our invention may become apparent to those skilled in the art without departing from the spirit and scope of our invention, and it is to be understood that we intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of our contribution to the art.

We claim: Y

l. A method of operating a fabric drying apparatus pulses accumulated and stored in reaching the predetermined condition; and terminating the fabric drying operation at the end of the extended interval.

2. A method of operating a fabric drying apparatus comprising the steps of:

presetting the fabric drying apparatus to a desired maximum drying time; initiating a fabricdrying operation;

sensing the dryness condition of the fabric during the drying operation; 1 producing timing pulses;

accumulating and storing the timing pulses to measure the time required for the fabric load to reach a predetermined sensed dryness condition;

extending the drying operation beyond the time at which said predetermined condition is reached by an interval which is dependent upon the timing pulses accumulated and stored in reaching the predetermined dryness condition; and

terminating the fabric drying operation at the end of a predetermined period constituted by the first to occur of (1) the end of the extended interval and (2) the preset maximum time.

3. A fabric drying apparatus comprising:

a chamber for'receiving a fabric load to be dried;

heating means for supplying heat to said chamber;

and

control means for controlling the drying operation,

said control means comprising: sensing means for sensing the moisture content of the fabric in said chamber, and

means responsive to the period of time required before a preselected moisture content is sensed for extending the drying operation by an interval which is dependent upon said period of time, in-

cluding means for producing timing pulses,

means responsive to said timing pulses to accumulate time and responsive to said sensing means to stop accumulating time, and

means for transforming the accumulated time into an interval for extending the drying operation.

4. A fabric drying apparatus according to claim 3, including means for presetting the drying operation for a maximum drying time and means connected to said time accumulating means for terminating the drying operation upon the accumulation of the preset maximum time.

5. In a dryer control of the type including an indexable memory device having a plurality of states which correspond to a program of dryer operations, means for indexing said memory, moisture sensing means, and a source of timing signals used to control dryer operations which are not sensed, the improvement comprising:

a first time accumulating circuit operable to accumulate and store a signal indicative of the time required for the sensing means to indicate that the fabric load has attained a predetermined apparent moisture content;

a second time accumulating circuit operable to accumulate time after the sensing means indicates said moisture level has been obtained; and

circuit means connected to said first and second time accumulating circuits and operable to produce a signal for indexing said memory to terminate the drying operation when said second time accumulating circuit has accumulated an amount of time which is dependent upon the amount of time stored in said first time accumulating circuit.

6. The dryer control of claim 5 wherein said first and second time accumulating circuits comprise first and second digital counters respectively, and said circuit means comprises a logic circuit including a plurality of logic gates.

7. The dryer control as defined in claim 6, wherein said first and second counters are connected to said source of timing signals and said logic circuit-means is connected to said memory indexing means.

8. A fabric drying apparatus comprising: a chamber for receiving a fabric load to be dried; heating means for supplying heat to said chamber;

and 7 control means for controlling the drying operation,

said control means comprising: sensing means for sensing the moisture content of the fabric in said chamber; and means responsive to the period of time required before a preselected moisture content is sensed for extending the drying operation by an interval which is dependent upon said period of time, including pulse means for producing timing pulses, means responsive to said timing'pulses to accumulate time and responsive to said sensing means to stop accumulating time including first timing means for timing a first period, second timing means for timing intervals greater than said first period in conjunction with said first timing means,'and means for resetting said first timing means upon timing of said first period, said first and second timing means providing digital outputs corresponding to the time accumulated thereby, means for reading the digital outputs of said first and second timing means, including means for transforming said outputs into a corresponding proportional time interval, and means for extending the energization of said heating means for said proportional time interval. 9. A fabric drying apparatus comprising: a chamber for receiving a fabric load to be dried; heating means for supplying heat tosaid chamber;

and control means for controlling the drying operation, said control means comprising: 7

sensing means for sensing the moisture content 0 interval required to achieve said preselected moisture content, means for transforming the time accumulated by said timing means into an interval of time for addition to the accumulated time, including a plurality of logic gates for reading said digital time signal and producing a signal to terminate the drying operation after an interval which is determined by said digital timesignal, and means'for continuing energization of said heating means for said added time interval.

Claims

1. A method of operating a fabric drying apparatus comprising the steps of: initiating a fabric drying operation; sensing the dryness condition of the fabric during the drying operation; producing timing pulses; accumulAting and storing the timing pulses to measure the time required for the fabric load to reach a predetermined sensed condition; extending the drying operation beyond the time at which said predetermined condition is reached by an interval which is dependent upon the timing pulses accumulated and stored in reaching the predetermined condition; and terminating the fabric drying operation at the end of the extended interval.

2. A method of operating a fabric drying apparatus comprising the steps of: presetting the fabric drying apparatus to a desired maximum drying time; initiating a fabric drying operation; sensing the dryness condition of the fabric during the drying operation; producing timing pulses; accumulating and storing the timing pulses to measure the time required for the fabric load to reach a predetermined sensed dryness condition; extending the drying operation beyond the time at which said predetermined condition is reached by an interval which is dependent upon the timing pulses accumulated and stored in reaching the predetermined dryness condition; and terminating the fabric drying operation at the end of a predetermined period constituted by the first to occur of (1) the end of the extended interval and (2) the preset maximum time.

3. A fabric drying apparatus comprising: a chamber for receiving a fabric load to be dried; heating means for supplying heat to said chamber; and control means for controlling the drying operation, said control means comprising: sensing means for sensing the moisture content of the fabric in said chamber, and means responsive to the period of time required before a preselected moisture content is sensed for extending the drying operation by an interval which is dependent upon said period of time, including means for producing timing pulses, means responsive to said timing pulses to accumulate time and responsive to said sensing means to stop accumulating time, and means for transforming the accumulated time into an interval for extending the drying operation. 20

5. In a dryer control of the type including an indexable memory device having a plurality of states which correspond to a program of dryer operations, means for indexing said memory, moisture sensing means, and a source of timing signals used to control dryer operations which are not sensed, the improvement comprising: a first time accumulating circuit operable to accumulate and store a signal indicative of the time required for the sensing means to indicate that the fabric load has attained a predetermined apparent moisture content; a second time accumulating circuit operable to accumulate time after the sensing means indicates said moisture level has been obtained; and circuit means connected to said first and second time accumulating circuits and operable to produce a signal for indexing said memory to terminate the drying operation when said second time accumulating circuit has accumulated an amount of time which is dependent upon the amount of time stored in said first time accumulating circuit.

7. The dryer control as defined in claim 6, wherein said first and second counters are connected to said source of timing signals and said logic circuit means is connected to said memory indexing means.

8. A fabric drying apparatus comprising: a chamber for receiving a fabric load to be dried; heating means for supplying heat to said Chamber; and control means for controlling the drying operation, said control means comprising: sensing means for sensing the moisture content of the fabric in said chamber; and means responsive to the period of time required before a preselected moisture content is sensed for extending the drying operation by an interval which is dependent upon said period of time, including pulse means for producing timing pulses, means responsive to said timing pulses to accumulate time and responsive to said sensing means to stop accumulating time including first timing means for timing a first period, second timing means for timing intervals greater than said first period in conjunction with said first timing means, and means for resetting said first timing means upon timing of said first period, said first and second timing means providing digital outputs corresponding to the time accumulated thereby, means for reading the digital outputs of said first and second timing means, including means for transforming said outputs into a corresponding proportional time interval, and means for extending the energization of said heating means for said proportional time interval.

9. A fabric drying apparatus comprising: a chamber for receiving a fabric load to be dried; heating means for supplying heat to said chamber; and control means for controlling the drying operation, said control means comprising: sensing means for sensing the moisture content of the fabric in said chamber; and means responsive to the period of time required before a preselected moisture content is sensed for extending the drying operation by an interval which is dependent upon said period of time, including timing means for timing the drying operation up to the point in time when said sensing means senses said preselected moisture content, including a source of repetitive timing pulses, and a digital counter for receiving said pulses and storing a digital signal indicative of the time interval required to achieve said preselected moisture content, means for transforming the time accumulated by said timing means into an interval of time for addition to the accumulated time, including a plurality of logic gates for reading said digital time signal and producing a signal to terminate the drying operation after an interval which is determined by said digital time signal, and means for continuing energization of said heating means for said added time interval.