US 3402478 A
Description (OCR text may contain errors)
Sept. 24, 1968 I HETRICK 3,402,478
DRYER CONTROL Filed June 20, 1966 i 5 Sheets-Sheet l WITNESSES INVENTOR W14 fW George L. Hetrick J W; fi AGENT Se t. 24, 1968 G. L. HETRICK DRYER CONTROL Filed June 20, 1966 5 Sheets-Sheet 2 LOW HEAT NO HEAT 0 REGULAR HEAT P 1968. G. L. HETRICK 3,402,478
DRYER CONTROL Filed June 20, 1966 5 Sheets-Sheet 5 samba OF A M Y Q A All VOLTAGE DRUP ACROSS ELECTRODES OF TIME /0 OF CONTACT TIME OF MOIST PARTS OF LOAD TO SENSOR INTEGRATING TiMER RUNOUT TIME TIME
United States Patent 3,402,478 DRYER CONTROL George L. Hetrick, Washington Township, Mansfield, Ohio, assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed June 20, 1966, Ser. No. 558,951 8 Claims. (CI. 3453) ABSTRACT OF THE DISCLOSURE An automatic timer for a clothes dryer which includes a sensing portion which generates signals representative of moisture content in the clothes as a function of electrical conductivity therethrough. The timer is characterized in that the signals generated are manifested as a mechanical displacement of a conventional cam rotated by a conventional timer motor, accordingly, there is an electromechanical integration of the electrical signals generated.
This invention relates, in general, to clothes dryers and more particularly to an automatic or moisture sensing timer control for use therewith.
Clothes drying apparatus at an early date, utilized timers 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 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, for example, weighing scales, have been suggested and tried in order to better establish this estimate, the result being only to reduce the limits of error of the unaided estimate, however, not the total elimination of the error.
Many principles and related constructions have been tried to overcome the forging problem. All approaches appear to have paved the way for the latest principle which is based on the measurement of moisture content remaining in the clothes as a function of electrical conductivity or resistance. One of the first and probably the most typical controls of this type utilizes a moisture sensor in conjunction with an electromechanical timer motor which advances a cam between on and off positions. The moisture sensor provides an electrical signal which triggers means for starting the timer motor. With such an arrangement the run-out time of the timer motor and cam represents a fixed amount of quantity, therefore the timer motor must be calibrated such that the largest load will be completely dried. This, as will be obvious, presents a problem of overdrying where it is desired to dry a relatively small load of clothes utilizing such a control.
Accordingly, it is the general object of this invention to provide a new and improved automatic moisture sensing control for clothes or fabric dryers.
It is a more particular object of this invention to provide a new and improved automatic moisture sensing control for clothes dryers wherein varying electrical signals generated in the dryer basket are mechanically integrated by means of a conventional timer motor.
Another object of this invention is to provide a new and improved automatic moisture sensing control for clothes dryers comprising an electromechanical motor, the run-out time of which is a function of both moisture content in the clothes and the contact time of sensing electrodes by the moist portions of the clothes.
A further object of this invention is to provide a new "ice and improved clothes dryer control, the run-out time of which, for the purpose of damp drying, may be either a function of variable time or variable resistance.
Briefly, the present invention accomplishes the abovecited objects by providing mechanical integrating means in the form of a conventional clothes dryer timer motor and associated cam structure for integrating or storing electrical signals generated in a clothes dryer basket by means of electrodes bridged by wet clothes contained in the basket. The signals are indicative of moisture content, below a predetermined level, remaining in the clothes and are a function of the electrical conductivity through the clothes. Additionally, the signal is indicative of bridging or contact time of the clothes with the electrodes. As a result of those two characteristics the initial signals generated are not continuous but they are intermittent. Accordingly, switch means interposed between the signal generating means and the mechanical integrating timer is provided for advancing the timer motor in response to a signal generated and stopping advancement of the timer motor in the absence of a signal. (The cam associated with the motor is carried by the shaft of the motor or driven by a gear train such that it is advanced at the same rate as the motor.) Advancement of the cam is between a first position wherein the cam cooperating with a cam follower is effective to initiate operation of the dryer and a second position wherein the cam and its associated follower are effective to terminate operation of the dryer.
Other objects and advantages of the present invention will become more apparent when considered in view of the following detailed description in which:
FIGURE 1 is a perspective view, partly broken away, of a domestic clothes dryer incorporating the invention;
FIG. 2 is a cross-sectional view on the line IIII of FIG. 1;
FIG. 3 is a schematic wiring diagram incorporating the invention;
FIG. 4 is a top plan view of a sensor incorporated in the invention;
FIG. 5 is a side elevational view of a sensor pick-up incorporated in the invention; and
FIGS. 6-8 represent a set of curves illustrating functional characteristics of the invention.
Referring to the drawings, especially FIG. 1, reference character 10 designates generally a domestic clothes dryer comprising a metallic clothes receptacle or drum 11 having a generally cylindrical shape including an imperforate annular wall 12 and a perforate rear wall 13 opposite a front wall 14. The front wall 14 has an opening 16 providing access to the interior of drum 11 for insertion or removal of clothes.
A bearing structure 17 journalled in the rear wall 13 and a peripheral flange 18 framing the opening 16 serve to support the drum 11 for rotation about a substantially horizontal axis within a cabinet 15. The drum is rotated by means of a conventional motor 19 through a flat drive belt 21 encircling the annular wall 12 and a pulley 22 fixed to one end of the output shaft of the motor 19.
An impeller means 23 including blades mounted on the other end of the motor output shaft serves to circulate moisture removing air through the clothes and out of the dryer. The circulating air may be heated by means of an electrical resistance heater 24 as the air is induced thereacross by the impeller means 23, After being warmed by the heater 24 the air then flows through the perforate rear wall 13, the clothes in the drum 11, through a perforate rear panel 26 of the dryer door structure 27, through lint trap 28, front air duct 29, through the air impeller means 23 and out of the dryer through an exhaust duct (not shown).
To provide the user with a choice of operation, therefore, with heat or without heat, a manually operable selector switch 31, connected in a control circuit 30 (illustrated schematically in FIG. 3), is adapted to connect a power supply line L with a conductor L to place 230 volts across the heater 24. Alternately, the switch 31 is adapted to connect the supply line L with a neutral conductor (N) to place 115 volts across the heater 24. The dryer 10 may be operated without heat by placing the switch 31 in the No Heat position which as can be seen moves the heater from the circuit 31.
Mounted on an inner surface 32 of the annular wall 12 are a plurality of clothes tumbling vanes 33, made from any suitable insulating material, for example, phenolic. There are preferably three such vanes and they are preferably equally spaced one from the other.
Secured to the inner surface 32 partially subadjacent each of the vanes 33 is a sensor structure 34 in the form of a printed circuit comprising an insulator board 36 and two sets of electrical conductors or electrodes 37 and 38. Each sensor 34 is secured to the annular wall 12 by means of metal fasteners 39 and 40. The head of the fastener 39 contacts the electrode 37 and the metallic drum 11 and is, therefore, effective in grounding the electrode 37 to the cabinet 15 of the dryer 10 through the drum 11 and the bearing structure 17. The fastener 40 comprises a screw 41 and a speed nut 42, the latter being in good contact with the electrode 38 and the former being suitably insulated from the drum 11 by means of an insulator bushing 43.
The head of each of the screws 41, of which there are three, projects outwardly from the annular wall 12 and contacts a continuous metal band 44 supported on the annular wall of the drum 11. The band 44 is insulated from the drum by means of a felt pad 46 suitably bonded to the drum 11 and disposed intermediate the band and the drum.
A sensor pick-up structure 47 (see FIGS. 1 and is mounted, by means of an insulating bracket 48, to a flange 49 of the cabinet 15 such that a carbon brush 51 carried by a spring arm 52 engages the band 44. The spring arm 52 is provided with an electrical terminal 53 for connecting the sensor pick-up 47 to the control circuit 30 by means of an electrical lead 54.
It will be understood that the electrodes 37 and 38 of any one of the sensor structures 34 are so positioned as to be simultaneously bridged by clothes 55 tumbling in the drum 11 thereby providing a current flow path from the latter to the former, the latter being supplied with electrical energy from the power supply lead L through a resistor 57 the resistance valve of which may be normally varied by the user for a purpose which will be discussed hereinafter, in conjunction with a damp dry cycle of operation. The clothes 55 together with the electrodes 37 and 38 constitute a variable resistor, or load sensing element, the resistance or conductivity of which is a function of the moisture content in the clothes. Therefore, when the moisture content is high the resistance is low and conversely when the moisture content is low the resistance is high.
A timer motor 58 indicated schematically in FIG. 3 carries a generally circular cam structure 59 on the output shaft thereof. The cam structure 59 is provided with a high portion 61 constituting the major part of the periphery thereof and an indented portion 62 having a pair of steps 63 and 64. The cam 59 is adapted to be normally positioned by the operator by means of a program control knob 66 associated with an indicia bearing dial 65 carried by a back control panel 67. When the control knob 66 is positioned by the operator a cam follower 68 rides on the high portion 61 and is cammed thereby to effect closure of a first pair of contacts 69 and 70 which completes a circuit from L to N through the motor 19 and to ground through the variable resistor 57 and the clothes 55. Simultaneously, the cam follower 68 effects closure of a second pair of contacts 71 and 72 thereby completing a circuit from L to L or N through the heater 24, that is if the circulated air is to be heated, otherwise, no circuit will be established through the heater when the switch 31 is in the No Heat position.
The timer motor 58 is preferably an AC sixteen pole hysteresis type synchronous motor rated at 2.5 watts, 125 v. as marketed by International Register Company. In accordance with the present invention it is desired that operation of the motor 58 be delayed initially, immediately following closure of the contacts 69 and 70, consequently, it is connected in series with a half wave rectifier or diode 73 and, therefore, will only operate upon firing of a thyristor or controlled rectifier 74 which bypasses the diode 73 in the oppostie polarity. An example of a suitable thyristor is type TSW23C (manufactured by the Transitron Co.) rated at 200 ma. with a gate sensitivity of 0.4 ma. The gate 76 of the rectifier 74 is connected to the electrode 38 through a voltage sensitive switch herein illustrated as a neon lamp or glow discharge tube 77. Such a device is marketed by the Signalite Co. under type No. A-173-A. As is well known in the art such devices are nonconductive until a predetermined break down voltage is impressed thereacross. With such an arrangement the rectifier 74 is fired only when the voltage across the electrodes 37 and 38, which with the clothes 55 constitute one leg 56 of a voltage divider consisting of the variable resistor 57 and the former, reaches the firing voltage of the neon lamp 77. When the clothes are wet, the resistance and, therefore, voltage across the electrodes is low, consequently, a predetermined amount of moisture, for example, 80%, must be removed to raise the voltage across the electrodes 37 and 38 thereby changing the divider ratio the required amount for firing the neon bulb 77.
Theoretically, the design of the electrodes and sensor pick-up may be such that there would be enough stray capacity to fire the thyristor 74, however, a capacitor 78 connected across the electrodes 37 and 38 serves to store sufficient energy to fire the rectifier 74. A 220 pf. capacitor was satisfactorily rused in practicing the present invention.
A diode 81 protects the gate 76 against reverse polarity. A resistor 79 is provided to turn off (thyristor) in the absence of a firing signal. Other protective devices, shown schematically in FIG. 3, comprise an exhaust air thermostat 82 serving to control the general air temperature in the dryer, and a safety thermostat 83 adapted to monitor the inlet and temperature in the vicinity of the heater 24 and to prevent overheating of the apparatus.
It will be appreciated that during a cycle of operation, of the dryer 10, the moisture level at which firing of the neon lamp 77 takes place can be either raised or lowered by adjusting the variable resistor 57 by means of a dampness control knob 84 having indicia 85 indicative of degree of dampness. This changes the divider resistance ratio such that the voltage to the neon lamp 77 is either higher or lower for any given moisture. The higher the moisture at which the firing voltage of the lamp bulb 77 is reached the more moisture will be left in the clothes according to the degree of dampness and as indicated on the scale 85.
It will be readily understood by those skilled in the art that in lieu of using variable resistance for controlling dampness variable time in the form of differential increments of distance on the surface of a cam associated with the timer motor 58 may be employed.
To illustrate the operation of the present invention, reference may be had to FIG. 6 wherein a graph 86 depicts the relationship of the voltage drop across the electrodes 37 and 38 as an electrical signal generated thereby and occurring during a cycle of operation of the dryer 10. A straight line curve 87 represents the firing voltage of the neon bulb 77. As will be apparent from the graph 86, during the early part of the drying cycle when the clothes are very wet, the voltage across the electrodes 37 and 38 is low and fairly smooth, but as the clothes begin to dry, the moisture becomes more uneven and the clothes load lightens thereby producing a noisy signal with ever increasing periods of high voltage (i.e., voltage which exceed the firing voltage of the neon bulb 77 as represented by the straight line 87) until the voltage drop across the electrodes 37 and 38 finally levels off above the firing voltage of the neon bulb 77.
Since the controlled rectifier 74 is fired, thereby advancing the timer motor, only during the periods when the voltage drop across the electrodes 37 and 38 exceeds the firing voltage of the neon lamp, the run-out or percent on time of the timer motor 58 is inversely proportional to the contact time of the moist portions of the clothes 55 with the electrodes. This characteristic of the invention is illustrated in FIG. 7 by a curve 88 representing percent contact time of the moist portions of a relatively large load of cothes with the electrodes versus percent on time" of the timer motor with respect to time. As indicated by the flat or horizontal portion of the curve 88, the clothes 55 are initially very wet, consequently, the wet clothes contact the electrodes 37 and 38 100% of the time. Once some of the moisture has been removed the contacting of the electrodes by the wet clothes becomes less and less as indicated by the sloped portion of the sensor 88. It should be apparent that with relatively smaller loads of clothes, the contact time will be somewhat less than 100% of the time. Consequently the present invention compensates the load size.
Another way of illustrating the run-out characteristic of the timer motor 58 is by a curve 89 which is a plot of timer run-out or on time versus time. As can be seen on the first portion of the curve (no slope), the clothes being very wet and the contact time very high, the timer motor does not run. When this foregoing condition exists no signal is generated. As the clothes become dryer and the contact time as represented by the second portion of the curve 89 (very shallow slope) the voltage exhibited across the electrodes 37 and 38 intermittently exceeds the firing voltage of the neon bulb 77 but does not remain above that level. Once this voltage or signal exceeds the firing voltage and remains at that level as represented by the third portion of the curve 89 (i.e., very steep slope) the timer motor 58 remains energized and functions as a straight time run-out type of motor.
It will be understood that each time the timer motor 58 is advanced as a result of a signal generated by the sensors 34, the cam 59 is advanced between contact closing and contact opening positions. In other words the cam advances between a point on the high portion 61 of the cam contacted by the cam follower 68 and the step 64 wherein both sets of contacts 69, 70 and 71 and 72 are opened to terminate operation of the dryer. It should therefore, be appreciated that the cam structure 59 is storing or mechanically integrating the electrical signals generated by the sensor structure 34.
Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.
I claim as my invention:
1. In fabric drying apparatus including a fabric sup porting drum and means for rotating said drum to tumble said fabrics, control structure comprising:
means for generating signals indicative of the condition of said fabrics,
signal integrating means operable between a first condition for initiating operation of said drum rotating means and a second condition for terminating operation of said drum rotating means,
and means responsive to said signal generating means for progressing said signal integrating means from said first condition to said second condition,
said generating means generating electrical signals and said integrating means being electromechanical,
said electromechanical integrating means comprising an alternating current motor and cam means supported for rotation thereby,
rectifier means in series with said motor, said means responsive to said signal generating means comprising a bistable element connected to said motor such that it bypasses said rectifier means in the opposite polarity.
2. Structure as specified in claim 1, wherein said signal generating means comprises sensing means supported in said drum and voltage sensitive switch means.
3. Structure as specified in claim 2, wherein said sensing means comprises a plurality of electrodes adapted to be bridged by the fabrics in said drum and said bistable element comprises a thyristor having its gate connected to said voltage sensitive switch means.
4. In a fabric dryer including a fabric containing drum and means for rotating the drum during a complete cycle of operation, means for controlling at least a part of said cycle of operation, said control means comprising:
signal generating means,
and means responsive to said signal generating means for rendering operable said integrating means,
said generating means generating electrical signals and said integrating means manifesting the integrated signals as a mechanical displacement,
said integrating means comprising an alternating current device and said means for rendering said integrating means operable comprising a half wave rectifier connected in series with said alternatmg current device and a bistable device connected to said alternating current device such that it bypasses said half wave rectifier in the opposite polarity.
5. Structure as specified in claim 4, wherein said signal generating means comprises sensing means and voltage sensitive switch means the triggering voltage of which serves to create a signal each time said triggering voltage is sensed.
6. Structure as specified in claim 5, wherein said sensing means comprises at least one set of electrodes supported in the drum and adapted to be bridged by the fabrics in said drum and said bistable device comprises a thyristor controlled rectifier having its gate connected to said voltage sensitive switch.
7. Structure as specified in claim 6, wherein said voltage sensitive switch means comprise a glow discharge tube.
8. Structure as specified in claim 7, for manually varying the duration of noncontrolled part of the cycle of operation.
References Cited UNITED STATES PATENTS 3,248,799 5/ 1966 Worst 3453 XR 3,248,800 5/1966 Pierce 3453 XR 3,324,568 6/1967 Nelson et al. 34-45 FREDERICK L. MATTESON, 111., Primary Examiner.
A. D. HERRMANN, Assistant Examiner.