Angular Frequency Extractor for Brushed DC Motor Control

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Solution Overview

Problem

DC motors exhibit manufacturing variations that affect their angular frequency, making it difficult to achieve precise control, as friction and other factors inconsistently impact motor speed, limiting their application in applications requiring tight speed control.

Innovation Solution

An apparatus comprising a motor driver, current sense unit, and angular frequency extractor that detects discontinuities in the motor's electrical current amplitude to determine the time period for one complete rotor revolution, generating a feedback signal to control the motor's angular frequency, allowing for precise speed adjustment without relying on back electromotive force (BEMF) voltage measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If DC motors are used for applications requiring tight speed control, then manufacturing variations and friction inconsistencies cause angular frequency deviations, but the patent implements a feedback control system using current amplitude discontinuities to detect rotor position and regulate speed, resolving the contradiction between manufacturing variability and precise speed control

Engineering Contradiction:

Improveangular frequency measurement precisionVSAvoidmotor manufacturing variations

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent implements a feedback control system that continuously monitors current amplitude discontinuities to detect rotor position and angular frequency, then adjusts the motor drive signal to maintain precise speed control despite manufacturing variations. The system measures actual angular frequency and compares it to a reference value, applying corrective feedback to compensate for friction and manufacturing inconsistencies.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces traditional mechanical sensors (such as encoders or Hall effect sensors) with an electrical measurement approach that detects rotor position through current amplitude discontinuities. This substitution eliminates the need for additional mechanical components while achieving precise angular frequency measurement and control.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If traditional BEMF voltage measurement methods are used for angular frequency extraction, then periodic motor cessation is required and unknown conversion factors are needed, but the patent uses current amplitude discontinuities to enable continuous operation with known parameters

Engineering Contradiction:

Improvecontinuous motor operationVSAvoidmotor cessation time

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent replaces BEMF voltage measurement with current amplitude discontinuity detection, enabling continuous motor operation without requiring periodic cessation. The system extracts angular frequency information from the timing of current discontinuities that occur naturally during commutation, eliminating the need to stop the motor for measurement.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent utilizes the motor's own operational characteristics (current amplitude discontinuities during commutation) as the measurement signal, rather than requiring external measurement signals or modifying the motor operation. The motor's natural commutation process provides the feedback information needed for control.

Inventive Principle:

Principle #25Self-service

3Measurement precision

If BEMF voltage measurement is used for angular frequency control, then conversion factors from voltage to angular frequency are required but are unknown, but the patent uses current amplitude timing with known parameters to eliminate this issue

Engineering Contradiction:

Improveangular frequency measurement accuracyVSAvoidunknown conversion factors

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent replaces BEMF voltage-based measurement with current amplitude-based measurement, using the timing of current discontinuities to directly determine angular frequency. This approach uses known electrical parameters (current amplitude, switching frequency) rather than requiring unknown conversion factors between voltage and angular frequency.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the measurement parameter from BEMF voltage to current amplitude discontinuity timing. By measuring the time between current discontinuities and using the known switching frequency, the system calculates angular frequency using known parameters without requiring empirical conversion factors.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9628006B2Angular frequency extractor for controlling a brushed DC motor

Publication Date: 2017.04.18 TEXAS INSTRUMENTS INC

AI summary

An apparatus includes a motor driver configured to drive a motor across a pair of input terminals to the motor and a current sense unit configured to sense the motor's electrical current amplitude. Further, an angular frequency extractor is operatively coupled to the motor driver and the current sense unit and configured to detect discontinuities in the motor's electrical current amplitude. The angular frequency extractor also is configured to determine a time period for one complete revolution of a rotor of the motor and to generate a feedback signal based on the determined period to control an angular frequency of the motor. The feedback signal may be used to adjust how the motor is being driven (e.g., to slow the motor down or speed it up).