US3507052A - Tumble pattern sensor and method of drying - Google Patents

Description

April 2l, 1970 w. F. RQBANDT. .Y ,3,507,05

TUMBLE PATTERN SENSOR AND METHOD OF DRYING v Filed March 2o, i968 w 3 sheets-sheet 1 E 75 El 2g-Z TUMBLE PATTERN SENSOR AND METHOD OF DRYING F11-ed March 2o, 1968 April 21, 1970 w. F. RQBANbT INVENTOR.

3 Sheets-Sheet Z April 21, 1970 A w. F. RQBANDT A 3,507,052 l TUMBLE PATTERN- sEN'soR Nn METHODOF DRYING- l 3 Sheets-Sheet 3 INVENTOR.

\ gm F'- gamma Filed March 20, 1968 d y'. ATTORNEYS United States Patent Office 3,507,052 Patented Apr. 21, 1.970

,507,052 TUMBLE PATTERN SENSOR AND METHOD F DRYING William F. Robandt, St. Joseph, Mich., assignor to Whirlpool Corporation, St. Joseph, Mich., a corporation of Delaware Filed Mar. 20, 1968, Ser. No. 714,581 Int. Cl. F26b 7/00, 13/10 U.S. Cl. 34-12 25 Claims ABSTRACT OF THE DISCLOSURE A dryer apparatus in which materials are tumbled in a treatment zone and wherein sensing means sense variations in the tumble pattern of the materials so that the drive motor may be driven at a speed insuring an optimum tumble pattern. The control is effected by regulating either motor speed or by actuating a magnetic slip clutch as a function of changes in tumble pattern. Moisture sensing controls are also provided.

CROSS REFERENCE TO RELATED APPLICATION The tumble pattern sensor and method of drying of this invention is applicable to dryers such as described in the application entitled Hold Circuit for a Dryer, invented by William F. Robandt and Keith D. Salisbury and assigned to the assignee of this invention, Ser. No. 718,432, filed Apr. 3, 1968.

BACKGROUND OF THE INVENTION Field of the invention The invention relates in general to dryers, as for example, clothes dryers formed with rotary drums or other mechanical means which tumble clothing or other material through a drying air stream. A control system has sensing means in the air outlet of the dryer 4which controls the tumble speed and turns off the dryer when a preset moisture level has been obtained. The tumble speed is controlled so that the articles being dried follow an optimum tumble pattern.

Description of the prior art U.S. Patent 3,072,386 sets the drum speed of a clothes dryer in response to the weight of clothing added. U.S. Patent No. 3,266,168 has a preset table motor speed control which holds drum speed at a single speed throughout a cycle of operation.

SUMMARY OF THE INVENTION In accordance with the present invention, sensing means are provided to sense variations in a tumbling pattern within a treat-ment zone. The resultant signal is used to control drum speed, thereby to insure that an optimum tumbling pattern is obtained. For example, the tumble pattern is sensed within a treatment zone -by determining conditions at two or more discrete locations in a tumbling drum. Such determination is effected by temperature sensing means, air pressure responsive means or photoelectric means. The drum speed is then controlled as a function of variations in the tumble pattern by either controlling the speed of the drive motor or controlling the operation of a magnetic slip clutch.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE l is a somewhat schematic front elevational view of a dryer embodying the features of the present invention;

FIGURE 2 is a side elevational view of the dryer of FIG. l;

FIGURE 3 is an enlarged view of a control panel of the dryer;

FIGURE 4 is a fragmentary cross sectional view taken on line IV-IV of FIGURE 2 showing the back wall of a dryer constructed in accordance with this invention and showing various tumble patterns which exist in the treatment zone prescribed by the machine of FIGURES l and 2;

FIGURES 5a and 5b are additional detailing schematics of the control system of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGUR-ES 1 and 2 are schematic views of a clothes dryer 11 which has a cabinet 12 with a door 13. The dryer 11 is of the so-called stationary bulkhead type more particularly disclosed and claimed in U.S. patent application S.N, 425,302; led Jan. 13, 1965, and assigned to Whirlpool Corporation, assignee of the present invention. A control panel 15 is attached to the top of the cabinet 12 and has a moisture control knob 14 and a start button 16. Asbest shown in FIGURE 3 the knob 14 has a pointer 17 that may be set against indicia 20 to control the shut-olf point of the dryer in accordance with a preset selection depending on the degree of dryness desired by the operator. In a stationary bulkhead dryer of the type shown only schematically herein, a stationary rear wall 18 forms one wall of a treatment zone. The peripheral contines of the zone are formed by a rotatable drum wall 19 driven by a motor 21 and a belt 22. With such an arrangement, a batch of clothes or other material placed within the treatment zone will be tumbled for exposure to a stream of air directed therethrough.

It is well known that the speed of rotation of a drum has a profound effect on the tumble pattern in the treatment zone. For example, if the drum is rotated at a speed suiciently high that it is beyond a critically determinative speed for the diameter of the drum, the materials will merely adhere to the surface of the drum in the form of an annulus and will not tumble at all.

On the other hand, if the drum is rotated at slow speed, the materials will merely roll over in the bottom of the drum. Under such circumstances clothes tend to ball and will not be properly exposed to drying currents of air as to promote evaporation of the entrained moisture.

In accordance with this invention it is contemplated that an optimum tumbling pattern will be achieved. The optimum pattern is such as will permit the materials in the drum to be elevated by the rotating drum wall through a lower quadrant of a cylindrical zone inwardly of the drum wall and on upwardly into an upper quadrant of the cylindrical zone. The speed of the drum is closely regulated so that the dynamic forces imparted to the materials being tumbled will elevate the materials to an optimum discrete location in the upper quadrant whereupon the gravitational forces acting on the materials will overcome the applied dynamic forces and the materials will fall in a trajectory extending more or less diametrically y y 3 acrossvrthe V,cylindricalzone for maximum exposure to currents of drying air circulating through the zone. The materials impact against an oppositely disposed lower quadrant of the drum wall, whereupon they are once again acted upon by the rotating drum wall.

An inlet orifice 23 and an outlet orifice 24 are fformed in the bulkhead 18, A heater 10 is mounted in a duct (not shown) leading to the inlet orifice 23 and a Vblower motor 26 with a suitable impeller is mounted in a duct (not shown) leading from the outlet orice 24 to draw a supply of heated drying air in the form of a stream through the dryer. Although FIGURE 4 illustrates a totally stationary bulkhead, it will be understood that only a portion of the bulkhead may be made stationary if it is so desired.

As shown in FIGURE 4, and in accordance with this invention the outlet orifice 24 is generally above center and to one side of the dryer. At a first discrete predetermined location arrows X, Y, and Z illustrate various paths which articles in the dryer -will take depending on corresponding drum speed. For example, arrow X shows a path where the materials being tumbled begin the gravitational trajectory near the top of the orifice and results when the drum speed is relatively high. The arrow Y depicts a trajectory which passes generally over the center of the outlet orifice 24. When the material to be dried follows a path between trajectories X and Y, optimum drying performance results since this path maximizes the exposure of tumbling materials to currents of drying air. The arrow Z illustrates a path wherein the gravitational trajectory begins below the orifice 24 and corresponds to a drum speed which is too slow for optimum drying conditions. Thus, to maintain an optimum tumbling speed, the drum speed must be continuously adjusted throughout the drying cycle so clothing always follows the path between arrows X and Y in tumbling through the heated air circulated through the drum. An additional benefit of this control system is that as the drum speed is continuously varied to induce clothing or other tumbled materials to follow the trajectory between arrows X and Y, the changing speed breaks up any regular tumbling pattern the clothing might establish thereby causing it to ball This balling effect is highly detrimental to proper drying since the clothing on the inside of the ball is not exposed to heated air and comes out damp while the clothing on the fringes of the load are over-dried.

j In order to maintain the articles being dried in the band shown between arrows X and Y to obtain optimum drying, the speed of the drum motor 21 is controlled to maintain the material in this band by means of sensing means determining the tumble pattern at two discrete lo- :ations inwardly of the drum wall. A pair of transducers 28 and 29 are mounted in the outlet orifice 24 with transducer 29 mounted adjacent the top of the orifice and transducer 28 mounted adjacent the bottom of the orifice. Transducers 28 and 29 may be thermistors, for example, although the invention is not to be limited to thermistors as other forms of sensing means such as thermostats, air Jresfsure switches, photocells or lamp sensors could be Jsed.lIf clothing follows the arrow Y, heated air must pass through damp clothing before going out the portion 3f thegrill in which thermistor 28 is located. However, heated air does not go through the clothing load before passing `by thermistor 29. Thus, if clothing follows, the arrow Y, thermistor 28 typically runs about 10 F. cooler :han thermistor 29. To control the drum speed so that the pathbetween arrows X and Y is followed by the clothing, therefre, a` speed control circuit for the motor receives inputs from thermistors 28 and 29 and continuously varies die drum speed so that the temperature differential be- ;ween thermistors 28 and 29 is maintained at the deterninable maximum as evidenced between the two discrete locations.

As the clothing within the drum begins to dry, hot air Jassing through the partially dried clothing no longer is cooled as much as it was at the beginning of the cycle when the clothing was completely soaked. Thus, near the end of the drying cycle thermistor 28 begins to approach thermistor 29 in temperature. I have determined that the temperature differential between thermistors 28 and 29 is linearly related to the percent moisture retention of the load when it follows the path intermediate arrows X and Y. Thus, by using the temperature differential between the two thermistors, a source of signal for an extremely accurate dry control responsive to variations in the tumble pattern is obtained.

In a typical operation of a domestic clothes dryer controlled by the circuitry of theinstant invention, the housewife sets knob 14 to the desired moisture retention and presses start button 16 to start the dryer. As -best shown in FIGURES 5a and 5b commonly available A.C. power, as for example volts, is connected between terminals B and N of the dryer. A 220 volt supply is connected between terminals B and C. A door switch 31 is connected to terminal B and is open when the door 13 is open. When the door 13 is closed, the switch 31 closes to connect terminal B with contact 32 of switch 16. Contact 32 is connected to a thermostat switch 33 which is in series with a centrifugal switch 34, actuated when motor 21 comes up to normal operating speed, a relay actuated heater switch 36 and the heater 10. The outer side of the heater 10 is connected to terminal C.

A second terminal 37 of switch 16 is connected to a hold relay 38 which has its other side connected to terminal N. The relay 38 has an armature which moves the linkages 35 to control the switches 36 and 39.

The switch 39 has one contact connected to the contact 32 of the switch 16. A second contact 41 is connected to a lead 42. A cool-down thermostat 43 is connected between the contact 32 and the lead 42.

A normally closed switch 44 has one contact connected to contact 41 and a second contact 46 connected to one side of relay 38. The motor 21 has a run winding 47 and a start winding 48. First sides of these windings are connected to the lead 42. The other side of the winding 48 is connected to a centrifugal switch 49 which opens when the motor comes up to speed and has its other side connected to a capacitor C1. The other side of the capacitor C1is connected to terminal N. A condenser C2 is connected from the terminal N to the winding 48. A triac 51 has the anode thereof connected towinding 47 and its cathode connected to terminal N. The gate lead 52 of triac 51 is connected to a resistor R1 and the anode of a diode D1. The cathode of diode D1 is connected to the secondary 53 of a transformer T1. The other sides of secondary 53 and resistor 'R1 are connected to the terminal N.

A full wave bridge 54 comprising diodes D2, D3, D4 and D5 is connected between terminal N' and a resistor R3. The other side of resistor R3 is connected to lead 42.

A resistor R2 is connected between diodes D2 and D3 and.

lead 54. A lead S6 is connected between diodes D4 and D5. A Zener diode D6 is connected v.between leads 54 and 56. A capacitor C3 is connected across Zener diode D3.

The primary 57 of transformer T1 is connected to line 54 and to the collector of a transistor T10. The emitter of transistor T10 is connectedto a resistor which has its other side connected to lead S6. A resistor R5, a unijunction transistor T3 and a resistor R6 are connected in series between leads 54 and 56.

A variable resistor R7 and a capacitor C11 are connected between lines 54 and 56. The emitter Lelectrode of transistor T3 is connected to the point betweenl resistor R7 and capacitor C11. A diode D7 has its cathode also connected to this point and its anode connected to resis? tors R8, R9 and the collector of transistor T2. The other side of resistor R8 is connected to lead 54. A resistor R11 is connected between the emitter of transistor T2 and lead 56. The other side of resistor R3 is connected to the base of transistor T2.

A resistor R19 isalso connected to the base of transistor T2 and to point H. A condenser C4 is connected between point H and lead 56.

Referring to FIGURE 5b it will be noted that points D, E, H, F and G correspond to the same points in FIG- URE 5a.

The motor 21 has an output shaft 58 which drives a tachometer 61. The tachometer 61 provides an A.C. input voltage to a bridge 62. The tachometer 61 has an output coil 63 connected across points M and O of bridge 62. Resistor R13 is connected between points Q and O yand Resistor R14 is connected between points O and P. Thermistor 28 is connected between points M and P and thermistor 29 is connected between points M and A resistor R12 is connected between point Q and lead 56. A wiper contact 65 engages resistor R12 and is connected to the anode of diode D14. The cathode of diode D14 is connected to resistor R19. A resistor R15 and capacitor C12 are connected in series between point Q and the base of a transistor T3.

A transformer T29 has its primary 64 connected between leads 42 and 56. The secondary 66 of transformer T29 is connected across a full wave bridge 67 having diodes D5, D9, D19, and D11. A resistor R15 is connected between diodes D9 and D19 and to lead 68. A capacitor C5 and Zener diode D12 are connected in parallel between leads 68 and 69.

Resistors R17 and R19 are connected in series across leads 68 and 69. A condenser C5 is connected across resistor R19. The junction point between resistors R17 and R19 is connected to the base of transistor T3. Resistor R13 is connected from lead 68 to the collector of transistor T3, and a resistor R29 is connected between the emitter of transistor T3 and lead 69.

Resistor R21 and capacitor C3 are connected in series between leads 68 and 69. Resistor R22 is connected between the emitter of transistor T3 and the junction point between resistor R21 and capacitor C9. Capacitor C7 is connected across R21.

A resistor R23, transistor T5 and capacitor C19 are connected in series between leads 68 and 69. A resistor R25 is connected across condenser C19. A resistor R25 is connected between lead 68 and the base of transistor T5.

A Zener diode D13 and resistor R24 are connected in series between the collector of transistor T5 and the point between resistor R21 and condenser C5.

A capacitor C9, transistor T4 and relay 71 are connected in series between leads 68 and 69. The base of transistor T4 is connected to capacitor C19.

The relay 71 controls linkage 59'. A wiper arm 72 is connected to the emitter of transistor T4 and forms a part of potentiometer 73. This is the moisture control element and knob 14 is connected by shaft 74 to control the position of wiper arm 72. A resistor VR27 is connected between line 68 and potentiometer 73. 3

In operation, the speed of motor 21 is maintained so that an optimum tumbling pattern is established. The user places clothing or other articles to be dried in the dryer and sets pointer 17 by knob 14 to the desired final moisture content of the articles. This sets wiper arm 72 of potentiometer 73 to a particular resistance.

The door 13 is closed which closes door switch 31 and the start button 16 is momentarily depressed to engage contacts 32 and 37. This supplies power to relay 38 which closes switches 36 and 39. Switch 39 supplies holding current to relay 38 through normally closed switch 44.

The heater 10 will be energized through normally closed safety thermostat 33 and centrifugal switch 34 when the motor 21 comes up to speed.

Switch 39 also provides power on line 42 to a motor speed control circuit and a dry control circuit. Normally open thermostat switch 43 is open unless the temperature in the exhaust stack of the dryer reaches a high temperature as, for example, 110 F.

Both the motor speed control and the dryer control receive signals from the bridge circuit 62.

The motor 21 starts with normally closed centrifugal switch 49 allowing current to pass through the start winding 48. As the motor comes up to speed, switch 49 opens and the run winding 47 continues to energize the motor.

The tachometer 61 is driven by motor 21 through shaft 58. The tachometer induces a voltage in winding 63 which varies in frequency and magnitude with the speed of motor 21.

Bridge 62 includes thermistors 28 and 29 (see FIG' URE 4 for their mounting positions) and resistors R13 and R14. Resistor R13 has a lower resistance than resistor R14. When the dryer starts the resistance of thermistors 28 and 29 are the same due to their resistance versus temperature curves being identical. Thus, at the initiation of the cycle, a signal voltage appears at point Q. Also, any time that the resistance of thermistor 28 approaches the resistance of thermistor 29, a signal voltage will appear at point Q because of the initial unbalance of the bridge. It should be remembered that the voltage at point Q. of the bridge depends on two factors, (l) the speed of motor 21 and (2) the temperature diiference between thermistors 28 and 29.

The signal voltage at point Q is utilized to regulate the speed of motor 21 so that if the tumbling pattern is maintained at the optimum, this signal controls the firing point of triac 51 which regulates power supplied to run winding 47 in the following manner.

Voltage for the motor speed control is supplied by line 42 through resistor R3. This is full wave rectified by bridge circuit. The full wave rectied A.C. then passes through a current limiting resistor R2 and is applied to iilter capacitor C3 whose output voltage is clipped by Zener diode D5.

Capacitor C3 has a small capacitance so that it does not maintain a set level of ripple-free D C. voltage on line 54. Instead, this voltage rises and falls, giving a generally clipped full wave signal, as shown by curve 78 above line 54. This is important because triac 51 must be fired at a controlled point in each half cycle of A.C. power and the firing point must be synchronized to power on the A.C. line.

Wiper arm 65 is set on resistor R12 to preset a desired voltage. This voltage is half wave rectified by diode D1.,= and furnished to lter capacitor C4. The voltage across capacitor C4 is thus proportional to the signal voltage at point Q.

The voltage on capacitor C4 supplies base drive to transistor T2.

If the signal voltage at point Q is high, transistor T2 will be driven into saturation and the voltage appearing at its emitter will be low. Thus, current passing through resistor R9 each time the voltage rises at point Q is shunted to ground through transistor T2 and does not pass through diode D7 to capacitor C11. All charge current to capacitor C11 must pass through resistor R7. Resistor R7 is set such that the voltage level on capacitor C11 builds at a slow rate. At a predetermined level, the voltage on capacitor C11 res unijunction transistor T5 and the charge dumps from capacitor C11 through transistor T5 and resistor R5. This creates a voltage drop across resistor R5 which biases switching transistor T19 on. A current pulse is then drawn through the primary 57 of pulse transformer T1. This generates a pulse across the secondary 53 ofthe pulse transformer and triac 51 is fired through diode D1. Once triac 51 fires, power is delivered to the motors run winding 47. Note that a high magnitude of signal voltage at point Q results in delayed tiring of triac 51 and motor 21 is caused to run at a low speed.

If the output voltage at point Q is low (which is the case when bridge 62 is balanced due to thermistor 29 being hotter than thermi-stor 28 thereby insuring that its resistance is lower than thermistor 28, or when the motor is rotating slowly causing tachometer 61 to generate a low voltage) capacitor C4 will have a low voltage appearing across it. This biases transistor T2 to a nonconductive state and current passes to capacitor C11 via re-sistor R8 and diode D7, as well as through resistor R11. This insures that unijunction transistor T is red early in each half cycle and thus triac 51 tires early in each half cycle. The motor 2.1 now runs at a higher rate of speed due to the increased power supplied to run winding 47. In summary, with signal voltage low at point Q, thc motor runs at a relatively high rate of speed.

As shown in FIGURE 4, it is to be noted that the tumble pattern of the clothing should follow a trajectory lying somewhere between the arrows'X -and Y. The control circuit of this invention assures this in the following manner. When the drying cycle is initiated, thermistors 28 and 29 are of cour-se, at equal temperatures. This causes the bridge 62 to be unbalanced and the output at point Q tends to be high due to the effect of the thermistors. This effect alone would tend to slow the motor down and the clothing would be expected to follow the arrow Z. AHowever, with the clothing following the arrow Z, the motor is rotating at such a low speed that tachometer 61 applies a very small voltage to bridge 62. Although the thermistor bias tends to slow the motor down, the input to the bridge is so low that no appreciable signal appears at point Q. Thus, the motor control circuit applies ring pulses to triac 51 early in each half cycle of the A.C. line and motor 21 speeds up. The clothing is thus not allowed to follow the path of arrow Z simply because bridge 62 will be supplied with insufcient voltage to produce an output of any magnitude at point Q with the motor rotating at such a slow speed.

Assuming the rnotor is rotating at a higher speed, which causes the clothing to follow the trajectory of arrow X, both thermistors 28 and 29 are covered by the clothing. Thus, their temperature and resistance become equal. Due to the different resistance of resistors R15 and R14, a high signal voltage appears at point Q. Also, since motor speed is high, the magnitude of tachometer output is high causing the input to the bridge to be high. Thus, both bridge unbalance and high motor speed cause the output at point Q to be high. Capacitor C11 now charges to a high value and saturates transistor T2. This insures that the tiring pulse delivered to triac 51 via pulse transformer T1 is delayed in each half cycle of A.C. line voltage, causing motor 21 to slow down. Thus, clothing no longer follows the path of the arrow X.

When the clothing follows the path of arrow Y, the thermistor 28 is shielded from hot air passing through orifice 24 while thermistor 29 receives hot air. This Causes thermistor 29 to heat above thermistor 28 and its resistance value drops. Bridge 62 now tends toward balance and the output voltage at point Q decreases.

The charge level on capacitor C4 decreases correspondingly and transistor T2 begins to go out of saturation. This allows earlier charging of capacitor C11 in each half cycle of A.C. line voltage and the triac 51 is iired earlier. Thus, the motor speeds up. By this action, the clothing is caused to continuously oscillate in a band lying between arrows X and Y.

It should be noted that when clothing is rst placed in the dryer, the drum sped for an optimum tumble pattern is different than the drumspeed for an optimum tumble pattern near the end of the drying cycle after the clothing has nearly dried. It has been found that the average drum speed must increase as the cycle progresses to keep the clothing in the band defined by arrows X and Y. The speed control of this invention regulates the average drum speed such that it does increase throughout the cycle of operation thereby maintaining an optimum tumble pattern throughout the cycle. It is also noted, that since the clothing is forced to oscillate in a band between arrows X and Y, any established tumbling patterns are broken up and the clothing is always placed directly in the path of the heated air. This not only assures minimum drying time but also assures that the clothing will not ball which would lead to overdrying of the outside of the load while the inside remained damp.

The dry control portion of the invention is shown in FIGURE 5b. The voltage at -point Q is also used to control the termination point of the drying cycle. Power on line `42 passes through the primary 64 of stepdown transformer T20 and -appears on the secondary 66 at -a reduced voltage. Bridge circuit 67 full wave recties the output of transformer T20 and applies it to a filter capacitor C5 via current limiting resistor R15. Zener diode D12 regulates the voltage across capacitor C5 to a D.C. level con-sistent with the ratings of components within the dry control circuitry.

Potentiometer 73 forms part of a voltage divider consisting of a fixed resistor R21, potentiometer 73, and relay coil 71. Thus, the initial setting of potentiometer wiper 72 determines the emitter voltage of transistor T4. Transistor T4 is connected in a regenerative fashion with transistor T5. If a voltage of magnitude greater than the emitter voltage of transistor T4 appears at the base of transistor T4 it begins to conduct. This draws base current from transistor T5 which also begins conduction. As transistor T5 goes into conduction, the base drive to transistor T4 is reinforced and the pair of transistors cascade into conduction. When these two transistors -become conductive, the drying cycle is terminated as described below.

The time when transistors T5 and T4 cascade into conduction is controlled by the signal voltage at point Q which is A.C. coupled to the base of transistor T3 via a resistor R15 and capacitor C12. As long as the clothing within the drum is damp, the motor speed control insures that it oscillates within the band dened by arrows X and Y. When clothing follows arrow Y, output at point Q is low and the voltage coupled to transistor T3 is correspondingly low. Thus, transistor T3 does not conduct and charge does not pass to capacitor C3 through resistor R22. When clothing follows the path of arrow X, output at point Q causes transistor T3 to conduct and charge begins to accumulate on capacitor C5. However, as long as clothing within the drum is damp, it cools thermistor 28 when clothing follows arrow Y. This assures that the charge applied to capacitor C5 while the clothing followed arrow X is bled away from the capacitor while the clothing follows arrow Y.

This alternate charging and discharging of capacitor C8 does not allow the voltage at point U to rise to a level exceeding the Zener voltage of Zener diode D13 and thus current does not pass through Zener diode D13 and resistor R24 to circuit point V. This assures that with damp clothing in the dryers drum, transistors T4 and T5 are not cascaded into conduction. However, as the clothing begins to dry, thermistor 28 is not cooled by clothing following arrow Y and the resistance of the two thermistors begins to equalize. Now the signal voltage at point Q remains at a high level for an extended period of time. This signal voltage is continuously coupled to transistor T3 and it remains conductive on a continuous basis. Thus, the charge level on capacitor C3 builds until it rises above the Zener voltage of Zener diode D13. Current now passes to circuit point V and transistors T4 and T5 cascade into conduction. The amount of current which must be supplied at point V to cascade the two transistors is determined by the emitter bias on transistor T4 which is, of course, preset by potentiometer 73. This permits the termination point of the drying cycle to be varied by potentiometer 73 and thus the final moisture retention of the clothing may be varied.

When transistors T4 and T5 cascade into conduction, relay coil 71 is energized, thereby opening switch 44 and breaking power to relay coil 38. When relay coil 38 drops out, contacts 36 and 39 open. This breaks power to the machines heater 10. However, note that normally open cool-down thermostat 43 has closed during the drying cycle since the exhaust stack temperature has risen. Power continues to be supplied through thermostat 43 to line 42. This keeps rotor 21 running until the exhaust stack temperature drops far enough for thermostat 43 to open, whereupon the cycle of operation is terminated and the clothes may be removed from the machine.

The following modifications could be made to the system described above without departing from the spirit and scope of the invention.

(l) Thermistors 28 and 29 could be replaced with appropriately calibrated thermostats which would allow the motor speed to be varied between two distinct levels in accordance with the tumble pattern of clothing sensed within the drum.

(2) Thermistors 28 and 29 could be replaced with pressure switches which sense the velocity of exhaust air passing through different locations in the exhaust outlet. These switches could then mechanically control potentiometers in bridge circuit 62 to control motor speed in the same manner as thermistors 28 and 29.

(3) Thermistors 28 and 29 could be replaced with photocells and appropriate light sources to sense the tumble pattern within the drum. As clothing blocked light from the photodiodes in a selective manner, motor speed would be controlled to give an optimum tumble speed.

(4) The control circuit could be used to control a magnetic clutch interposed between drive motor 21 and the dryers drum. This clutch would slip an amount dependent on the firing angle of triac 51.

The principles of the invention explained in connection with the specific exempliiications thereon will suggest many other applications and modifications of the same. It is accordingly desired that in construing the breadth of the appended claims, they shall not be limited to the specific details shown and described in connection with the exempliiications thereof.

Although various modifications might be suggested by those versed in the art, it should be understood that I wish to embody Within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are deiined as follows:

1. A drying apparatus comprising:

(a) means forming a treatment zone including tumbling means for tumbling articles to be dried,

(b) driving means connected to the tumbling means,

(c) .control means for said driving means and comprising sensing means associated with the tumbling means and sensing the path of travel of the articles to be dried and connected to the driving means to control its speed so that the articles to be dried travel in a path which is optimum for drying.

2. A drying apparatus according to claim 1 and further characterized by means forming an air inlet and an air outlet for said treatment zone, air translation means for supplying a stream of drying air into said treatment zone through said air inlet and out through said air outlet and said sensing means being placed in said air outlet.

3. Apparatus according to claim 1 wherein the sensing means is temperature responsive and controls the driving means as a function of temperature changes in said treatment zone.

4. Apparatus according to claim 2 wherein the sensing means is responsive to air pressure and controls the driving means as a function of air pressure changes in the treatment zone.

S. Apparatus according to claim 1 wherein the sensing means is responsive to radiant energy and controls the driving means as a function of radiant energy changes in the treatment zone.

6. Apparatus according to claim 1 wherein the sensing means comprises a pair of sensors with the lirst sensor mounted in a first position in said treatment zone such that it has an output which varies as a function of the moisture in the articles being dried, and the second sensor is moved in a second position in said treatment zone such that its output does not vary as a function of the moisture in the articles to be dried when the articles are following the desired optimum pattern.

7. Apparatus according to claim 2 wherein said air outlet is positioned within the dryer such that articles travelling in an optimum path for drying will be dispersed in the path of air directed into the outlet.

8. Apparatus according to claim 7 wherein the sensing means comprises a pair of sensors with the first sensor mounted in the air outlet at a position which is normally covered by articles travelling in an optimum drying path, and the second sensor mounted in the air outlet at a position which is normally not covered by articles travelling in an optimum drying path.

9. Apparatus according to claim 6 and further characterized by a driving means control circuit including a bridge circuit and wherein iirst and second sensors are mounted in the bridge circuit.

10. Apparatus according to claim 9, a tachometer connected to the driving means and producing an output proportional to the speed of the driving means and connected to the bridge circuit to energize it.

11. Apparatus according to claim 10 wherein the driving means control circuit includes a power gating circuit with its output controlling the driving means and receiving an input from the bridge circuit so that the driving means runs at a speed to maintain the articles being dried in an optimum path.

12. Apparatus according to claim 11 wherein the power gating circuit includes a power supply and gate means connected to circuit with the driving means, and the gate means controlling power to the driving means in response to the output of the bridge circuit.

13. Apparatus according tod claim 12, a dryer terminating circuit comprising, switch means connected in circuit with the power supply, and the dryer terminating circuit connected to control the switch means to turn the dryer off.

14. Apparatus according to claim 13, moisture content set means forming a portion of the dryer terminating circuit to turn the dryer off when a preset moisture level is obtained.

15. Apparatus according to claim 14, the power supply coupled to the moisture content set means, a relay connected to the switch means and the moisture content set means, and a second gating circuit connected in circuit with the moisture content set means and relay and receiving an input from the bridge circuit to turn the driving means olf when the preset moisture content has been reached.

16. Apparatus for terminating the drying cycle of a tumble-type dryer comprising, a plurality of sensors mounted at distinct locations in the dryer for determining variable drying conditions as a function of the tumble pattern, and a dryer terminating circuit connected to said sensors to turn the dryer oif when the conditions detected by the sensors reach predetermined values.

17. Apparatus according to claim 16 wherein the dryer has an air outlet and iirst and second sensors are mounted at different locations within said air outlet.

18. Apparatus according to claim 17 wherein the first and second sensors are temperature responsive and the variable condition comprising changes in temperature.

19. Apparatus according to claim 17 wherein the first and second sensors are pressure responsive and the variable condition comprising changes in pressure.

20. Apparatus according to claim 17 wherein the first and second sensors are responsive to radiant energy and the variable condition comprises variations in the level of radiant energy.

21. The method of controlling the speed of a dryer wherein materials are tumbled by successively elevat.

ing the materials upwardly and gravitationally accelerating the materials downwardly through a tumble pattern including a gravitational trajectory which includes the step of sensing the tumble pattern of articles within the drum at two distinct locations to develop a control signal as a controlling variable which is a function of changes in the tumble pattern.

22. The method of claim 21 wherein the tumble pattern is sensed as a function of changes in pressure.

23. The method of claim Z1 wherein the tumble pattern is sensed as a function of changes in temperature.

24. The method of claim 21 wherein the tumble pattern is sensed as a function of changes in radiant energy.

25. The method of controlling a dryer as defined in claim 21 wherein the materials are successively elevated and gravitationally accelerated by rotatably driving a drum and confining the materials in the drum and further characterized by controllingA the speed of the driving means as a function of changes in the tumble pattern so that the articles follow an optimum tumble pattern for drying.

References Cited UNITED STATES PATENTS JOHN J. CAMBY, Primary Examiner U.S. Cl. X.R. 34-52

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