ES341727A1 - Improvements in or relating to laundry machines - Google Patents

Abstract

Field windings 98, 99, of motor 30 are selectively energized to control the movement of the basket 28 or the agitator 29 of a washing machine. When capacitor 112 is charged from source 72 to the level required for firing unijunction transistor 111, a pulse is developed which fires two of the silicon controlled rectifiers 82-85 and supplies power to one of the field windings to drive the motor. Switches 129, 130, are cam-operated to a " spin " position by timer motor 56 to energize field winding 99 only, a switch 107 short-circuiting a portion of the field winding for operation at higher speed. Gating pulses for the controlled rectifiers are derived from transformer primary windings 126, 127, associated with magnetic reed switch 128 controllable in accordance with the position of either the agitator or the basket. Sensor 74 detects excessive motor current to reduce the voltage applied to the motor. Circuit 79 provides an input to transistor 119 proportional to motor voltage. If this voltage increases, the conduction of transistor 119 is increased to extend the charging time of capacitor 112 and so delay the triggering of the unijunction transistor 111. A sensor 76 also increases the conduction of transistor 119 with increased line voltage. A motor speed sensor comprises a bridge circuit including the armature 97 and resistors 100, 134-136. Variations in the output of this circuit are amplified by transistor 119 to control the speed. When switch 137 is actuated to the " spin " position, the resistor 136 is adjusted to allow increased speed. A delay pulse circuit is connected between the firing angle control circuit 77 and the motor reversing circuit 78, so that, when the reed switch 128 is being changed-over, a delay pulse restricts the firing of the unijunction transistor 111 until the switch is in a position for allowing pulses to be applied to the appropriate transformer winding. In another embodiment, the motor reversing circuit 78 and the delay pulse circuit are replaced by a flip-flop circuit associated with a relaxation oscillator circuit. The speed of the motor may be detected by a tachometer generator the output of which is filtered and compared with the voltage of a Zener diode for firing angle control. The supply voltage for the motor 30 may be rectified initially so that only two silicon controlled rectifiers are required in the motor circuit. The armature current is detected for controlling the firing angle of the rectifiers. In a modified form of the motor circuit, a single field winding is connected in series with the armature which is in a bridge arrangement of four controlled rectifiers. The driving motor may be of the split-phase type the auxiliary winding of which is centre-tapped and connected to alternate pairs of controlled rectifiers. In a system for a D.C. shunt motor, the armature is in a bridge circuit comprising both controlled and uncontrolled rectifiers, the field winding being split and associated with further controlled rectifiers whose gating is determined by the reed switch. In other embodiments, the drive motor for the washing machine is of the three-lead reversible A.C. type or of the permanent magnet type. Alternatively, a universal motor may be employed for this purpose. The motor circuit may comprise a multi-layer switching device which allows conduction in either direction when a voltagepulse is developed across its terminals of sufficient value, the maintaining voltage being at a lesser value.