Domestic appliance with control means

Dec. 24, 1968

Η. T. THUNANDER

3,417,480

DOMESTIC APPLIANCE WITH CONTROL MEANS

Filed Oct. 14, 1965

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FIG.3.

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NO

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INVENTOR

Hans T Thunander

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AGENT

3,417,480

Patented Dec. 24, 1968

United States Patent Office

3,417,480

DOMESTIC APPLIANCE WITH CONTROL MEANS

Hans T. Thunander, Mansfield, Ohio, assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania

Filed Oct. 14, 1965, Ser. No. 496,047

Claims. (CI. 34—45)

ABSTRACT OF THE DISCLOSURE

Clothes drying apparatus having a control including electrodes disposed in the rotating basket, which electrodes, together with the clothes, constitute a varying resistance which is measurable as a function of moisture content in the clothes. The control is more specifically characterized by the incorporation of means capable of producing various signals representative of moisture content which serve to either extend operation of the dryer or to terminate operation thereof, the extended operation including both a drying portion with heat and a cool-down portion without heat.

The invention relates, in general, to domestic clothes dryers and, more particularly, to electronic controls therefor.

Domestic clothes drying apparatus, at an early date, utilized a timer that could be manually set in order to establish the duration of the drying cycle so as to accommodate the drying of different size loads of clothes to different degrees of dryness as desired by the user.

While such an arrangement is reasonably satisfactory, the end result is dependent entirely upon the judgment of the operator with respect to his or her estimate as to the time required to dry the particular load of clothes to the desired degree of dryness. The use of many mechanical aids have been suggested and tried in order to better establish this estimate, the result being only to reduce limits of error of the unaided estimate.

As a solution to the guessing problem attendant with the clothes dryers of the type dicussed above, control means such as a thermostat was added, for automatically shutting down the dryer when the clothes are dry. The thermostat is so located within the dryer as to respond fairly well to a completely dry condition, however, it is not capable of automatically shutting off the dryer when the clothes are still damp enough for ironing. Such being a desirable feature, many attempts have been made to design such a control. Such controls, heretofore, attempted, have been based on the fact that, as the clothes dried below a certain moisture content, the rate of drying falls off, this being reflected in various phenomena in the dryer, such as exhaust temperature, heat utilized for vaporization, and humidity in the exhaust air, etc. A relatively large number of seemingly unrelated control schemes are based on this fundamental principle, i.e. rate of drying, and efforts have been directed at finding qualities such as temperature, time, etc., and combination of qualities, which respond as purely as possible to the rate of drying. Unfortunately, most of these qualities also respond to ambient temperature, line voltage, load size, air flow, initial amount of water present in the clothes, heating and cooling of dryer parts, etc. Such controls, although not infeasable tend to be either inadequate or cumbersome and expensive. Furthermore, the fundamental principle is not entirely correct. For instance, the correlation between rate of drying and moisture content is not the same for heavy fabrics as for light fabrics, nor for cotton as for rayon or nylon.

Accordingly, an entirely new approach, based on a principle which is independent of the drying process and of the dryer, has been utilized in more recent dryer constructions. It is based on measurement of moisture content remaining in the clothes. As this measurement is independent of whether or not the clothes are drying, most of the variables that render the previously mentioned control schemes unsatisfactory are eliminated. One such arrangement for measuring the moisture content, utilizes the correlation between cooling effect of the clothes on a heated body and moisture content. In other words, clothes having a relatively high moisture content and, hence, high heat conductivity, will remove a greater amount of thermal energy from the heated body than clothes in the damp-dry or completely dry condition. The decreased heat removal by the clothes can be readily utilized directly or indirectly to effect termination of heated air supplied to the clothes.

Such an arrangement as just discussed has been used in a control which is intended primarily for clothes which are to be removed from the dryer with sufficient moisture retained therein to render them suitable for ironing. However, any commercially acceptable clothes dryer, must also be able to dry clothes completely and automatically. A thermal arrangement similar to that discussed supra, cannot be relied upon to accurately sense moisture remaining which is less than, say, 20%, accordingly with such an arrangement it is necessary to extend the drying time beyond the control point of the thermal control. This can be done by providing a timer motor which can be started and stopped in response to a signal from the thermal control used in conjunction therewith. The timer normally may be started and will run for a predetermined period of time after a specific percentage of moisture, sensed by the thermal control, remains in the clothes.

The thermal type of sensing device used is usually located at a point on the basket and, therefore, makes contact with the clothes at the most, once during each rotation. Since the signal produced by such an arrangement is neither smooth nor continuous it is desirable from the standpoint of sensitivity, reliability, and repeatability, to provide a sensing device which contacts the clothes continuously. A continuous sensor not only produces a smoother signal but in the case of extremely small clothes loads or single items, a useable signal is available when anyone point in the basket might be missed for several revolutions. It will be understood by those skilled in the art that known thermal sensors are not suitable for continuous sensing and that the portions of the control used in conjunction with thermal sensors are not suitable for use with continuous sensors.

Accordingly, it is the general object of this invention to provide new and improved clothes drying apparatus.

It is a more particular object of this invention to provide new and improved electronically controlled clothes drying apparatus.

Another object of this invention is to provide a control system for clothes dryers suitable for damp drying and complete drying automatically.

Still another object of this invention is to provide a new and improved sensing and control system which measures moisture content as a function of electrical conductivity.

Briefly, the present invention accomplishes the abovecited objects by providing, in a domestic clothes dryer, an electronic control comprising a relay actuated timer motor, which relay is responsive to an electrical signal resulting from the electrical conductivity level of the clothes load, the level or degree of electrical conductivity of the clothes being a function of the moisture content thereof. The clothes therefore, act as a variable resistance which is connected in the circuitry of the control

3,417,480 by means of a pair of spaced apart continuous electrodes extending the entire distance around the inside of the dryer basket and a pair of slip rings. It will be apparent to those skilled in the art that one or more point sensors, i.e. electrodes confined to small areas may be employed in lieu of continuous electrodes. The voltage across the clothes serves to fire a gas diode at a moisture level in the clothes determined by the resistance values in the voltage divider and by the parameters of a low-pass filter inserted between the voltage divider and the gas diode. The voltage divider is adjustable to effect firing of the gas diode at various moisture levels and the firing of the gas diode is used either to effect immediate termination of operation or extended operation, the extended operation including a period with heat and a period without heat.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a front elevational view of a clothes dryer, partly broken away, representing the invention;

FIG. 2 is an enlarged fragmentary section of the basket of the dryer, illustrated in FIG. 1 and portions of the electrodes carried thereby;

FIG. 3 is a schematic diagram of the dryer control.

Referring to the drawings, especially FIG. 1, reference character 10 designates generally a clothes drying machine comprising a casing structure 11 having a generally cylindrical baffle 12 supported therein and enclosing a drying chamber or receptacle 13. The drying chamber is provided with an air inlet duct 14 for directing heated air thereto and an air discharge duct 16 for directing moisture laden air therefrom. A generally open end cylindrical basket 17 is supported within the drying chamber 12. A cylindrical sidewall 15 of the basket 17 may be perforate substantially throughout its circumferential extent for the passage of air from the air inlet duct 14 through the clothes in the basket 17 to the discharge duct 16. The basket 17 is preferably provided with a plurality of radially inwardly extending vanes 18 for the tumbling of the clothes during the drying operation. The casing 11 is provided with an opening (not shown) which is in registry with the open end (not shown) of the basket 17 for providing access to the interior of the basket through a door (not shown) for insertion and removal of clothes.

The basket 17 is suitably journaled in the casing 11 for rotation about a horizontal axis and is driven by a sheave 19 belted, as shown at 21, to an electric motor 22 mounted on the bottom of the casing 11. The motor 22 also serves to drive the rotor 23 of a blower 24. The blower is provided with an air intake opening 26 communicating with the space within the casing 11, which space receives air from the surrounding atmosphere through openings (not shown) formed in the casing sidewalls. The blower 24 discharges into the air inlet duct 14 and passes over an electric heater 27 provided for heating the air before it is circulated through the clothes in the basket 17.

Consonant with conventional practice the heater 17 is connected to an Edison three-way single phase circuit having main conductors LI and L2 and a neutral conductor N (see FIG. 3). It is understood that the potential between the main conductors LI and the neutral conductor is 115 volts and the potential across LI and L2 is 230 volts.

Referring to FIG. 3, there is shown schematically an electronic control generally indicated 28 which comprises a timing mechanism 29 having a timer motor 31 and provided with a manually adjustable knob 32 by which the user may set the timer 29 in an active range of operation designed to start the dryer motor 22 and to, itself, operate for a desired period of time, say 50 minutes after a predetermined delay, which will be hereinafter discussed in detail. The timer 29 is so constructed that when it reaches the end of the selected period, it will shut itself off by returning to its inactive position. Alternately the control knob 32 may be used to set the timer 29 to an inactive position designed to start the dryer motor 22 and in which the timer motor will not run at the end of a corresponding delay period. It will be apparent that the timer motor may be of any known type; for example, electric, hydraulic, pneumatic, or thermal, etc.

The knob 32, as best shown in FIG. 3, is provided wtih an annular scale 33 comprising indicia indicating an “off” position, “damp,” “dry,” regular heat and “dry,” low heat. A selector switch 34 (see FIG. 3) serves to connect conductor LI to the neutral conductor N, for supplying 115 volts to the heater 27 or, alternately, to connect the conductor LI to the conductor L2 to supply 230 volts to the heater 27. To set the timer 29, the control knob 32 is rotated counterclockwise, the degree of rotation determining the duration for which the timer motor 31 will run when actuated. As the timer runs, the control knob 32 gradually rotates in a clockwise direction, so that, by the time the selected period, represented by the setting of the knob, has nearly terminated, switch actuating means (not shown), serves to open a heater switch 36 for deenergizing the heater 27 and when the selected period has terminated, the switch actuating means serves to open a dryer motor switch 37 for stopping rotation of the motor 22. The above outlined procedure will take place for all settings of the control knob 32, with the exception of the “damp” dry setting the function of which will become apparent hereinafter.

A conventional door actuated safety switch 38 is connected in series with the motor switch 37, thereby serving to stop the motor 22 and, consequently, deenergize the heater 27 at any time the dryer door (not shown) is open.

The control 28 is provided with means 41 for sensing the electrical conductivity of the clothes load within the basket 17. The sensing means 41 comprises a pair of continuous electrodes 42 and 42' made from any suitable material, for example, stainless steel, which are secured in a suitable manner within the interior of the basket 17 to insulating material 40 secured to the cylindrical sidewall 15 for the entire length thereof and pass under the vanes 18 (see FIG. 2). Under one of the vanes 18, electrical conductors (not shown) are connected to one of the other of the electrodes. One of the conductors is, in turn, connected to the basket 17 while the other conductor is, in turn, connected to the sensing circuit via a conventional slip ring 43 shown schematically in FIG. 3. The conductor connected to the basket is connected to the casing 11 and the sensing circuit by means of a conventional slip ring 44, also shown schematically in FIG. 3. The foregoing arrangement will be obvious to one skilled in the art. The wet clothes and the electrode 42 appear to the circuit as a variable resistor 46, the electrical conductivity of which is a function of the moisture in the clothes. The resistance is low when the clothes are wet and increases to a very high value when the clothes are completely dry. Typical resistances are (approximate magnitude only): 100% water—1000 ohms, 25% water—0.5 megohm, 10% water—50-100 megohms, and 0% water—500-5000 megohms (including insulation leakage). The resistance represents a useable signal upon which there may be superimposed some very strong noise signals, ranging in frequency from a few cycles per hour to several thousand cycles per second. One important problem, the solution of which is accomplished by the present invention as will be apparent, is that of extracting the desired signal (i.e. those having frequencies ranging from one cycle per minute to a few cycles per day) from the background noise signals, the most troublesome of which occur when the clothes have a moisture suitable for ironing.

3,417 . . ⁵

The sensing circuit 41 further comprises a fixed resistor 47 which together with the variable resistor 46 forms a voltage divider which has a very low output until there is a specific amount of moisture, say, 15-20% remaining in the clothes. With the value of the resistor 47 5 equal to 66 megohms and as long as the variable resistor 46 remains below 5 megohms, there is a very low voltage across the variable resistor 46. At this point the voltage begins to rise rapidly and within a couple of minutes, it rises to half the supply voltage applied to conductor 48. ₁₀At this point the voltage is rising at its greatest speed and represents a detectable signal which is utilized to start the timer motor 31 to thereby extend drying time. Variations in supply voltage or the exact level of voltage across the resistor 46 when the circuit triggers has a nominal effect 15 on the instant when the relay 39 closes. This is important in order to achieve good repeatability with wide tolerance components which may be used to minimize cost. The value of the fixed resistor 47 is, therefore, selected to be nearly equal to the resistance across variable resistor 46 20 when the moisture content in the clothes is at the desired level and when the relay 39 is to be triggered. Actually, the relay triggers somewhat later due to an unavoidable delay to be described later.

A fixed resistor 49 and a variable resistor 51 connected 25 in series, may also be coupled with the variable resistor 46 by means of a selector switch 52 operable by the control knob 32 at the “damp” setting to form another voltage divider. The variable resistor 51 is preferably a rheostat having a logarithmic taper and a maximum resistance 30 of at least two megohms. The variable resistor 51 may also be a selector switch having a number of fixed resistances. The resistor 51 may be adjusted by means of a control knob (not shown). The fixed resistor 49 may have a resistance in the range from 50,000¹ to 300,000 ohms 35 and serves to prevent the resistance between the variable resistor 46 and the power supply across the variable resistor 51 from being set to zero. The resistance valves of resistors 49 and 51 are dependent on the specific electrode design and the desired latitude of settings. Since the re- 40 sistance of the resistor 47 is much greater (66 megohms) than the resistors 49 and 51 (300,000 ohms max. plus 2 megohms max.) it need not be disconnected. When the resistance of the variable resistor 46 is equal to the resistance of the resistor 49 plus the resistor 51 approxi- 45 mately one half of the supply voltage will appear across the variable resistor 46. Triggering of the relay 39 takes place at this point, however, instead of starting the timer motor 31 for extending drying time as in the case of the “dry” setting, the operation of the dryer 10 is terminated 50 by stopping the dryer motor 22 as will be apparent hereinafter. Alternatively, a very short run-out time could be set on the timer motor.

The sensing circuit 41 is fed by a half-wave power supply 53, which also supplies the rest of the control circuit 55 28. The power supply 53 comprises a rectifier 54, a filter capacitor 56 and a surge limiting resistor 57. The sensing circuit 41 is therefore, supplied with about 150 volts negative voltage as will be understood by those skilled in the art. The half-wave power supply 53 permits utilization of 60 high voltage in the sensing circuit and minimizes the effect of galvanic phenomena at the electrodes 42 which may be present to a lesser or greater extent, depending on a material from which the electrodes are made. Moreover, the effect of capacitive currents on alternating current is not 65 a problem with this direct current type of arrangement.

A fixed resistor 58 and a fixed capacitor 59 having resistance and capacitance values, respectively, of 22 megohms and two microfarads, form a low-pass filter with a cut-off frequency of about 0.25 cycle per minute. 70 This is a compromise between the desirability of even lower cut-off to more effectively eliminate background noise on damp settings and the unavoidable longer delay, at the lower cut-off frequency. The delay is about 45 seconds on a steadily rising input signal which delay is 75 ,480 ⁶ tolerable. Since the sensing circuit on the “damp” setting has a very low resistance compared to that of the resistor 58, it has very little effect on the cut-off frequency of the filter. However, a much higher output impedance is produced, on “dry” settings, in the sensing circuit (i.e. between 20 to 40 megohms), which impedance effectively appears in series with the resistance across resistor 58 thereby lowering the cut-off frequency of the filter to one-tenth cycle per minute, the delay of the signal being increased by about one and two-thirds minutes. Both of these effects are beneficial since the lower cut-off frequency results in greater repeatability and the increased delay allow the selection of less running time of the timer motor 31. The size of the capacitor 59 is determined by the pulse energy required by the circuitry following and the resistor 58 is chosen to give the frequency response described above for “damp” settings. It will be understood that a larger capacitor would give more of a pulse, larger delays on dry settings and would permit use of cheaper components down stream. The choice of a two microfarad capacitor may be changed if warranted by the cost savings.

An electrically actuated switch 61, herein shown as a gas diode, in the form of a small neon lamp is adapted to be fired when the capacitor 59 has been charged to the breakdown voltage of the switch 61. At this point a portion of the charge on the capacitor 59 is discharged through a resistor 62, the base-emitter junction of a P-N-P, germanium transistor 63 and a resistor 64. The resistor 62 serves to limit the amplitude of the pulse and also determines its duration. A resistor 66 serves to bypass any collector leakage around the base-emitter junction while the resistor 64 causes a reverse bias thereon. Together the resistors 66 and 64 prevent thermal runaway of the transistor 63.

It will be apparent to those skilled in the art that the wider the differential is between the breakdown voltage of the gas diode 61 and its extinguishing voltage, the more of the charge on the capacitor 59 can be utilized. For example, the commercially available gas diode NE-83 has a relatively large differential compared to the NE-2 gas diode, consequently, a smaller capacity and a less sensitive relay may be used, a matter of considerable economy. Accordingly, numerous combinations of components can be employed, the selection of which may be governed by such variables as cost, reliability, etc.

The transistor 63 amplifies the pulse or signal so that a rather powerful relay 39 which can handle the motor current directly can be utilized thereby eliminating the need for a slave relay. The transistor has a current gain of about 50 in the grounded emitter configuration and a collector-emitter voltage rating of 25 volts. In the absence of a signal or a pulse a voltage divider comprising resistors 67 and 68 and the resistor 64 applies about 22 volts to the collector of the transistor. With the relay 39 having closing time of 14 milliamps or less, a coil resistance of about 1000 ohms and a pull-in time of about 20 milliseconds, the transistor should be maintained saturated for at least 20 milliseconds. In lieu of the transistor 63 a Silicon-controlled rectifier (SCR) has been successfully utilized, resulting in significant advantages for example, a less sensitive relay may be used, less pulse is required from the gas diode, no contact is needed for “lock-in,” and the relay and SCR operate on the full voltage of capacitor 56 without the need for a voltage divider.

The amplified signal or pulse fed to the coil 69 of the relay 39 causes the relay to close momentarily, but as soon as the relay switch 71 closes the transistor 63 is bypassed, however, the relay is locked in for as long as the power supply 53 delivers current. The moisture level or conductivity level at which this occurs of course, depends, on the setting of the switch 52 and the variable resistor 51. For the “dry” setting, regular heat the switch 52 is opened and the relay 39 closes when about 10-15% moisture remains in the clothes. For the “damp” setting

3,417,480 the switch 52 is closed and the moisture level of the clothes depends on the setting of the variable resistor 51 by means of a knob (not shown) which can be set by the user as desired.

As indicated above, the selector switch 52 is actuated by the control knob 32, the switch 52 being operatively connected to a second two position selector switch 72 which is simultaneously actuated with the switch 52. For example, when the control knob 32 is set to one of the “dry” settings the switch 52 is opened while the switch 72 is simultaneously closed and vice versa. The switch 72 by-passes a switch 73 of the relay 39 and the dryer motor 22 continues to run after the pulse from the transistor 63. The relay switch 73, which was open prior to the pulse, closes, thereby starting the timer motor 31. The moisture in the clothes is removed to an extent determined by the timer setting which in the case of the “dry” setting, regular heat, is fifteen minutes. This works well, regardless of load size, at low moisture levels because diffusion rates, rather than available heat, determines the drying rate. When about five minutes are left on the timer the heater switch 36 opens, deenergizing the heater 27. The air flow from the blower 24 continues thereby cooling the dryer. After five minutes the dryer motor switch 37 opens thereby deenergizing the dryer motor 22.

When the knob 32 is set at “damp” dry, the switch 52 is closed and the switch 72 is open. Now the pulse from the transistor 63 causes the relay 39 to lock in as before, but when the relay switch 73 opens the dryer motor 22 is deenergized immediately opening centrifugally actuated switches 26 and 27 thereby deenergizing the dryer motor and the heater 27. In this instance, therefore, there is no running-out of the timer motor 31 after the pulse as in the case of the “dry” setting.

The dryer 10 may be controlled by the timer 31 independently of the sensing circuit 41 and the relay 39. To this end a manually operated selector switch 78 is provided which serves to by-pass the relay 39. With the switch 78 in the closed position, the control knob 32 may be set anywhere in the “time range” and the dryer 10 will operate in the conventional manner under the control of the thermostat and timer contacts.

Contrary wise, when the selector switch 78 is opened, then, drying is accomplished “automatically” through the relay 39 as hereinabove discussed. If for any reason the operator, at the termination of a “damp” dry cycle, desires to run the dryer for a minute or two, he or she may do so by means of an override switch 79 in the form of a spring biased push-button. As long as the button is depressed by the user the dryer motor 22 and the heater 27 will be energized thereby serving to further dry the clothes load. This can be carried out with or without heat depending on the position of the switch 34. By releasing the push-button the override switch 79 opens, however, the motor 32 continues to run momentarily until a pulse is generated by the sensing circuit 41 to open the relay switch 73, at which time the motor 22 is immediately deenergized due to the switch 72 being in the opened position.

An outlet thermostat 80 is suitably mounted in the exhaust air stream in a conventional manner and serves to control the general air temperature in the dryer. As a safety precaution against dangerous overheating another thermostat 82 is mounted, also in a conventional manner, in the inlet air stream in the vicinity of the heater 27.

Normally the electrical codes governing installations of dryers similar to that of dryer 10 allow grounding, thereof, through the neutral conductor or line wire N, which grounding may be accomplished by means of a conventional grounding strap (not shown). Where the electric codes do not allow grounding as discussed above, the grounding strap (not shown) may be replaced by a separate ground wire which, for example, may be attached in a well known manner to a water pipe. In the latter grounding arrangement, the sensing circuit 41 is completed ⁸ to the neutral line N by means of a resistor 83 having a suitable resistance value of, say 100,000 ohms, which resistor provides a potential difference between the neutral and ground thereby limiting the current flow to the rest of the circuit to a safe value.

It will be apparent that there has been disclosed a dryer and an electronic control therefor in which it is not necessary to guess which of a plurality of settings should be used in conjunction with the automatic drying operation, as is in the case of prior art constructions. In other words, the same setting is used for all load sizes and all fabrics, consequently, the necessity of having settings, which tell the control what kind of load it has to work with, are eliminated. Moreover, the control disclosed herein minimizes the harshness, stiffness and shrinkage caused by overheating of the clothes, commonly caused when an exhaust thermostat is used to determine end of drying. Furthermore, the dryer herein disclosed works very well on low or with restricted air flow, which operation is most unsatisfactoy with thermostatically controlled dryers, and gives satisfactory results on installations for 115 volts.

While there has been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.