Portable appliance motor control with speed-based current limitation

Patent metadata

Field	Value
Publication number	US-9780718-B2
Application number	US-201013882203-A
Country	US
Kind code	B2
Filing date	Nov 2, 2010
Priority date	Nov 2, 2010
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

A method of controlling a portable appliance includes measuring an input current supplied to a motor of the portable appliance and measuring a rotational speed of a shaft of the motor. The method also includes determining a current limit based on the rotational speed of the shaft using a substantially continuous function which relates a domain of rotational speeds to a range of current limits. The method further includes reducing, when the input current exceeds the current limit, the rotational speed of the shaft incrementally along the substantially continuous function until the input current is approximately equal to the current limit.

First claim

What is claimed is:

1. A method of controlling a portable appliance, the method comprising:
providing a user control that is configured to permit a user to input a desired rotational speed;
measuring an input current supplied to an electric motor of the portable appliance utilizing a current sensor comprising an amplifier that measures voltage across a resistor coupled in series with the electric motor;
measuring a rotational speed of a shaft of the electric motor utilizing a revolutions-per-minute (RPM) sensor;
determining a current limit for the measured rotational speed of the shaft using an electronic controller based on the rotational speed of the shaft using a substantially continuous function which relates a domain of nonequal rotational speeds to a range of predefined nonequal current limits using the measured rotational speed of the shaft of the electric motor as the only input to the substantially continuous function; and
regulating, when the input current does not exceed the current limit determined by the electronic controller, a rotational speed of a shaft of the electric motor to maintain a desired rotational speed that has been input;
reducing, when the input current exceeds the current limit, the rotational speed of the shaft according to the substantially continuous function until the input current is approximately equal to the current limit for the measured rotational speed of the shaft using the electronic controller;
wherein measuring the input current supplied to the electric motor comprises periodically sampling, at a first sampling rate, an output signal of the current sensor;
wherein measuring the rotational speed of the shaft of the electric motor comprises periodically sampling, at a second sampling rate, an output signal of the revolutions-per-minute (RPM) sensor; and
wherein the first and second sampling rates each have a greater frequency than a periodic drive signal used to drive the electric motor.

2. The method of claim 1 , wherein:
using the electronic controller to determine the current limit using the substantially continuous function comprises calculating the output of a linear function with the rotational speed of the shaft as the input.

3. The method of claim 1 , wherein:
using the electronic controller to determine the current limit using the substantially continuous function comprises calculating the output of a non-linear function with the rotational speed of the shaft as the input.

4. The method of claim 1 , wherein:
using the electronic controller to determine the current limit using the substantially continuous function comprises retrieving a value which corresponds to the rotational speed of the shaft from a look-up table.

5. The method of claim 1 , wherein:
using the electronic controller to reduce the rotational speed of the shaft along the substantially continuous function comprises, iteratively, (i) reducing the rotational speed of the shaft by an increment, (ii) measuring a new rotational speed of the shaft, (iii) measuring a new input current, and (iv) determining a new current limit based on the new rotational speed of the shaft using the substantially continuous function, until the new input current is approximately equal to the new current limit.

6. The method of claim 5 , wherein:
each iteration of steps (i)-(iv) is performed within a period of a periodic drive signal used to drive the motor using the electronic controller.

7. The method of claim 1 , further comprising:
operating the motor using a proportional-integral-derivative (PID) algorithm of the electronic controller to maintain the rotational speed of the shaft at a desired speed setting, until the input current equals the current limit.

8. The method of claim 7 , further comprising:
increasing a previously reduced rotational speed of the shaft, when the input current is less than the current limit and until the rotational speed of the shaft is approximately equal to the desired speed setting using the electronic controller.

9. A mixer comprising:
a user control operable to generate an input signal indicative of a desired speed setting for the mixer;
an electric motor having a shaft configured to provide motive power to a mixing element, the electric motor defining a range of nonequal current limits that, if exceeded, damage the electric motor;
a current sensor operable to generate an output current signal indicative of an input current supplied to the electric motor, the current sensor comprising an amplifier that measures voltage across a resistor coupled in series with the electric motor;
a revolutions-per-minute (RPM) sensor operable to generate a speed signal indicative of a rotational speed of the shaft of the electric motor;
an electronic controller operable to (i) generate a motor control signal such that the rotational speed of the shaft corresponds to the desired speed setting, (ii) calculate a current limit based on the speed signal using a substantially continuous function which relates a domain of nonequal rotational speeds of the shaft to a range of nonequal current limits, wherein the motor speeds of the substantially continuous function decrease with increasing motor electrical current, and (iii) modify the motor control signal, when the output current signal exceeds the current limit, such that the rotational speed of the shaft is reduced according to the substantially continuous function while increasing electrical current to the electric motor until the output current signal is approximately equal to the current limit;
wherein the controller is operable to measure the input current supplied to the electric motor by periodically sampling, at a first sampling rate, an output current signal of the current sensor;
wherein the controller is operable to measure the rotational speed of the shaft of the motor by periodically sampling, at a second sampling rate, a speed signal of the revolutions-per-minute (RPM) sensor; and
wherein the first and second sampling rates each have a greater frequency than a periodic drive signal used to drive the electric motor.

10. The mixer of claim 9 , wherein:
the output current signal exceeding the current limit is associated with a pinch point between the mixing element and a mixer bowl that receives the mixing element.

11. The mixer of claim 9 , wherein:
the substantially continuous function comprises one of a linear function, non-linear function, and a look-up table.

12. The mixer of claim 11 , wherein:
the electronic controller is further operable to, at least once during each period of the periodic drive signal, (i) calculate a new current limit based on the speed signal using the substantially continuous function and (ii) modify the motor control signal, when the output current signal exceeds the new current limit, such that an average current of the periodic drive signal is reduced relative to an output current signal that would be required to maintain the rotational speed of the electric motor at the desired speed setting.

13. The mixer of claim 9 , further comprising:
a driver circuit operable to generate a periodic drive signal to drive the electric motor in response to the motor control signal.

14. A tangible, machine readable medium comprising a plurality of instructions that, in response to being executed, result in an electronic controller:
receiving an input signal from a user control indicative of a desired speed setting for a portable appliance having a motor;
receiving a speed signal indicative of the rotational speed of the shaft from a revolutions-per-minute (RPM) sensor;
receiving a current signal indicative of an input

Assignees

• Barfus Dan Christian
• Conard Wayne Weaver
• Lai Alex
• Xiao Rainman
• Whirlpool Co

Inventors

• Barfus Dan Christian
• Conard Wayne Weaver
• Lai Alex
• Xiao Rainman

Classifications

• H02P29/028 Primary

  the motor continuing operation despite the fault condition, e.g. eliminating, compensating for or remedying the fault · CPC title

• A47J43/08 Primary

  Driving mechanisms · CPC title

• B01F15/00389

  Operations & Transport · mapped topic

• H02P29/032

  Preventing damage to the motor, e.g. setting individual current limits for different drive conditions · CPC title

• B01F7/00325

  Operations & Transport · mapped topic