Food processor motor controller

Details Food processor motor controller Food processor motor controller

1999-12-29

2001-09-11

Ip, Paul (Department: 2837)

Electricity: motive power systems

Induction motor systems

Primary circuit control

C318S811000, C318S701000, C318S785000

Reexamination Certificate

active

06288516

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a food processor and, in particular, to a motor controller and to a method for controlling an induction motor for both normal loading tasks and for heavy loading tasks.
DESCRIPTION OF THE ART
Food processors typically include an electrical motor that drives an impeller with blades disposed in a container for processing food items. When the food items present a heavy load on the impeller, the motor speed declines enough that the motor may stall. To compensate, prior art food processors have used a voltage controller that responds to a higher loading or torque by increasing the current or voltage applied to the motor. For example, U.S. Pat. No. 4,673,860 discloses a motor controller for a food processor that controls motor speed regardless of load or torque fluctuations by increasing the electrical current or voltage applied to the motor.
U.S. Pat. No. 4,691,870 discloses a food processor in which motor speed is controlled with a motor speed detector that senses a counter electromotive force (emf) of the field winding, the counter emf being proportional to motor speed.
Some food processors have used an induction motor as its speed/torque characteristic is such that the motor will not stall when processing food items, such as vegetables. The induction motor is said to have normal loading and typically operates with a motor speed in a range of about 1,780 rpm to about 1,450 rpm. However, the induction motor stalls at about 1,450 rpm when processing food items that create heavy loading.
An object of the present invention is to provide a food processor motor controller that, during heavy loading, allows the motor to operate without stalling over substantially the same torque range as for normal loading.
Another object of the present invention is to provide a method of operating a food processor motor that, during heavy loading, allows the motor to operate without stalling over substantially the same torque range as for normal loading.
SUMMARY OF THE INVENTION
A food processor according to the present invention has an induction motor coupled to an impeller. The induction motor has a main winding and a starter winding. A motor controller has a motor speed detector coupled to the motor to produce a speed signal proportional to motor speed. A voltage controller, when enabled, controls electrical energy delivered to the motor's main winding to control the speed of the motor. When the motor speed is less than a set speed, a signal processing circuit connects the starter and main windings in circuit with an electrical power source and disables the voltage controller. When the motor speed is equal to or greater than the set speed, the signal processing circuit disconnects the starter winding from the electrical power source and enables the voltage controller. Thus, the motor is energized by the starter and main windings during motor start operations and during high torque conditions in which the motor speed declines below the set speed.


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