Patent GB-877553-A (GB)
Title: Improvements in or relating to control systems for clothes drying apparatus
IPC: D06F34/08
Filed: 1960-07-05
Abstract: 877,553. Tumbler driers. MAYTAG CO. July 5, 1960 [April 14, 1960], No. 23454/60. Class 34(2) A tumbler clothes drier comprises a rotatable drum, heating means for drying the clothes in the drum, electrodes positioned for contacting and completing an electric circuit through the tumbled clothes to measure the electrical conductivity or resistance for determining the condition of dryness of the clothes, and an automatic control circuit which includes. means for initiating termination of the drying operation and sensing means controlling the terminating means for preventing termination of the drying operation when the electrical resistance through the clothes is below a predetermined amount and for initiating termination of the drying operation when the resistance is above a predetermined amount during a period of time of sufficient length for random pieces of the clothes to contact the electrodes. The drum 10, Fig. 1, is driven by a motor 34, electric 'heating elements 75 heat air from a blower 76 also driven by the motor for passage through apertures 69 in the drum, and the electrodes 80, 81 are positioned on clothes elevating baffles 66 secured to the imperforate walls of the drum for contacting and completing the circuit through the tumbled clothes. The automatic control circuitry comprises a timing cam stack 94, Fig. 3, having cam switches 95-99 which control the heater, timer motor, drive motor, sensing circuit, and damp-dry settings respectively, energised by power lines L 1 , L 2  and N and controlled by an off-on switch 100. A centrifugal switch 104 in the motor 34 is centrifugally closed to energise the heating elements 75 whenever the motor is operating. The sensing circuit from switch 98 through lines 108, 111, has a rectifier 112 connected to a capacitor 115 through a series resistor 113 and the electrodes 80, 81 within the drum are connected across the capacitor by lines 90, 91 so that when the capacitor is charged with D.C. current. from the rectifier 112 it may be discharged by any damp clothes placed across and shorting the electrodes 80, 81. The other side of the capacitator is connected to the power line N through a series resistor 116. A gaseous discharge tube, e.g. a neon lamp 120, is connected across the capacitator, the gas therein being ionized to produce visible discharge when the charge on the capacitator reaches a predetermined valve, which visible discharge affects a light sensitive cell 122 connected by a line 123 to the line 108 and by a relay 125 to the power line N to complete the circuit to energise the relay 125. The relay 125 in turn operates a switch 126 to complete a holding circuit in order to maintain the relay 125 energised after the cell 122 has been excited. The timer motor is energised through the cam switch 96 to advance the cam stack 94 every three minutes to start the drying operation until the drier is under the control of the sensing element when it is de-energised and the timer motor remains de-energised until energised by the action of the switch 127 to terminate the drying operation. The cam stack can be manually adjusted by a knob (not shown) to vary the sensing means to change the predetermined resistance of the clothes and thereby the degree of dryness attained to achieve a "damp dry" result the resistor is connected in parallel to the resistor 113 to reduce the total resistance in series with the capacitator 115 which is thereby charged at a greater rate and the neon lamp 120 is fired when the clothes are still damp and having less resistance. Moreover, the switch 127 energises the timer motor 102 earlier and results in less heated air being passed into the drum. In a modification, the sensing circuit, which includes a rectifier Fig. 4, (not shown) and capacitator, fires a gaseous discharge tube when the resistance of the clothes sensed by the electrodes reaches a predetermined value. In an other form, Fig. 5 (not shown), the capacitator is connected to a rotor switch having a switch blade successively and alternately engaging contacts which respectively connect the rectifier to charge the capacitator, connect the capacitator across the circuit to the electrodes and connect the capacitator across the circuit which has in series a gaseous tube which discharges when the capacitator has built up a certain charge. In a further modification of the sensing circuit a motor 180, Fig. 6, constantly rotates a shaft 181 which in turn drives a spring- urged shaft 181 through a slip clutch 182 and splined faces 185, 186 and an arm 188 thereon to contact a variable resistance 187 to decrease the resistance in series with a relay 210 to nil. A gaseous tube 199 fires to energise a solenoid 200 and disengage the clutch 182 by a solenoid armature 205 which activates a spring urged lever 207 maintaining the faces 185, 186 in contact as long as the clothes are wet. When the clothes are dry the clutch is engaged to allow the arm 188 to energise the relay 210 to close a contact 211 to maintain the relay energised and also to close a contact 212 to energise the timing motor 213 which initiates the termination of the drying operation.