Dishwasher Pump Cavitation Detection via Motor Current FFT

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing techniques for detecting a water fill level in dishwashers are inefficient and require costly adjustments to the pump motor rotor to accurately identify cavitation, leading to errors in water level detection.

Innovation Solution

A dishwasher system that includes a controller monitoring the current drawn by the motor, performing frequency analysis using Fast Fourier Transform to detect the water fill level, and generating a signal to control the fill valve, thereby accurately determining when the water level is sufficient.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If gradient of current drawn by pump motor is used to detect cavitation, then water fill level detection is achieved, but costly increase in pump motor rotor fine balance is required

Engineering Contradiction:

Improvewater fill level detection accuracyVSAvoidpump motor rotor fine balance

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical approach of rotor fine balancing with an electrical/electronic solution using frequency analysis of motor current. Instead of mechanically adjusting the rotor to eliminate vibrations, the system uses a processor to analyze current waveforms and identify cavitation conditions through frequency spectrum analysis, thereby detecting water fill levels without requiring precise mechanical rotor balance.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If frequency analysis is performed on motor current, then accurate water fill level detection is achieved, but without costly rotor balancing

Engineering Contradiction:

Improvewater fill level detection accuracyVSAvoidpump motor assembly simplicity

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent substitutes complex mechanical rotor balancing procedures with a computational approach using Fast Fourier Transform (FFT) analysis of motor current. This allows the pump motor to be manufactured without special balancing requirements, while still achieving accurate cavitation detection through electronic signal processing of the current waveform frequencies.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent transforms the detection approach by changing from monitoring mechanical vibrations (which require balanced rotors) to analyzing electrical current parameters. By examining frequency components of the motor current using FFT, the system detects cavitation-induced load variations on the motor, providing accurate water level detection without modifying mechanical manufacturing processes.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If current fluctuations from unbalanced rotor are used for cavitation detection, then detection is possible, but error in cavitation detection occurs

Engineering Contradiction:

Improvecavitation detection accuracyVSAvoiddetection error rate

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent eliminates the reliability issue caused by unbalanced rotors by replacing mechanical vibration-based detection with electrical current analysis. Since the detection method uses frequency analysis of motor current rather than mechanical vibrations, unbalanced rotors do not create false signals, thereby improving detection reliability while maintaining accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This method effectively detects the appropriate water fill level without the need for costly rotor balancing, ensuring accurate water level detection and efficient operation of the dishwasher.

Implementation Method 1

The controller performs a frequency analysis on the current to detect a water fill level in the tub

Methodology Applied

Scientific EffectFrequency analysis:

Implementation Method 2

performing frequency analysis using Fast Fourier Transform to detect the water fill level

Methodology Applied

Scientific EffectFast Fourier Transform:

Implementation Method 3

When the pump motor stops cavitating there is an appropriate water fill amount in the dishwasher

Methodology Applied

Scientific EffectCavitation: Cavitation

Data Source

PatentUS8277571B2Methods and apparatus for detecting pump cavitation in a dishwasher using frequency analysis

Publication Date: 2012.10.02 HAIER US APPLIANCE SOLUTIONS INC

AI summary

Water fill level detection techniques are provided for a dishwasher system. A dishwasher system includes a tub; a fluid circulation system for circulating water in the tub and a controller. The fluid circulation system includes at least one motor and at least one fill valve. The controller monitors a current drawn by the motor to control an operation of the fill valve. The controller performs a frequency analysis on the current to detect a water fill level in the tub.