Induction Motor Slip Constant Estimation via Acceleration Variation

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Solution Overview

Problem

Existing methods for controlling induction motors, such as those used in machine tools and industrial robots, face difficulties in determining the slip constant, especially when it is unknown, due to complex processing requirements and the need for torque measurement, which complicates the adjustment of drive parameters.

Innovation Solution

A parameter determination support device and method that automatically measures acceleration characteristics during motor startup to a predetermined speed, allowing estimation of the slip constant with the smallest variation, enabling linear approximation and identification of the appropriate slip constant without direct torque measurement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If torque measurement methods are used to determine slip constant, then measurement precision improves, but device complexity and processing complexity increase

Engineering Contradiction:

Improveslip constant determination accuracyVSAvoidprocessing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces direct torque measurement (mechanical measurement system) with electrical signal analysis (current waveform analysis). By analyzing the relationship between stator current and rotor speed during motor startup, the system determines the slip constant without requiring torque sensors or complex mechanical measurement apparatus, thus reducing device complexity while maintaining measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces electrical current as an intermediary parameter to indirectly determine the slip constant. Instead of directly measuring torque, the system measures stator current and uses the correlation between current magnitude and motor speed to infer the slip constant, simplifying the measurement process while maintaining accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If torque measurement is required for slip constant determination, then measurement precision improves, but ease of operation deteriorates

Engineering Contradiction:

Improveslip constant determination accuracyVSAvoidparameter adjustment ease

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The motor system performs self-diagnosis by using its own operational parameters (current and speed) to determine the slip constant. The system automatically analyzes its own current waveform characteristics during startup to identify the slip constant, eliminating the need for external torque measurement equipment and complex adjustment procedures, thereby improving ease of operation.

Inventive Principle:

Principle #25Self-service

3Measurement precision

If complex torque measurement and correlation analysis are used, then measurement precision improves, but productivity deteriorates

Engineering Contradiction:

Improveslip constant determination accuracyVSAvoidparameter determination speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent extracts only the essential information needed for slip constant determination from the motor operation data. By focusing solely on the correlation between stator current magnitude and rotor speed during the startup phase, the system eliminates the need for complex torque measurement and extensive correlation analysis, significantly reducing processing time while maintaining determination accuracy.

Inventive Principle:

Principle #2Taking out (Extraction)

4Stability of the object's composition

If slip constant is set too large, then motor acceleration stability improves, but torque linearity deteriorates

Engineering Contradiction:

Improveacceleration stabilityVSAvoidtorque linearity

Core Design Contradiction:

Stability of the object's compositionVSManufacturing precision

Solution Approach 1:

The patent automatically determines the optimal slip constant parameter by analyzing the motor's current-speed characteristics during startup. This measured slip constant value optimizes the balance between acceleration stability and torque linearity, eliminating the need for manual trial-and-error adjustment and ensuring both stability and linearity are maintained within acceptable ranges.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11048236B2Parameter determination support device, parameter determination supporting method, and program

Publication Date: 2021.06.29 FANUC LTD

AI summary

The determination of a slip constant is simplified upon driving a motor for which the slip constant is unknown, based on variation of acceleration when accelerating an induction motor from start up to a predetermined speed. A parameter determination support device for motor driving includes: an automatic measurement part which automatically measures characteristic information including a speed during acceleration and acceleration upon driving an induction motor to accelerate from start up to a predetermined speed set in advance which is no more than a base speed of the induction motor, relative to each slip constant, based on a plurality of slip constants set in advance; and an estimation part which estimates, as a slip constant of the induction motor, a slip constant having the smallest variation in acceleration, among a plurality of slip constants, based on the characteristic information.