Electric Motor Control Device for Gravity-Axis Positioning

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Solution Overview

Problem

Electric motor control systems require excessive thrust force when driving axes to stop in the antigravity direction compared to the gravity direction, leading to inefficient energy usage.

Innovation Solution

A control device for electric motors that determines if an overrun operation is allowable and, if so, controls the motor to drive past the target position in the antigravity direction and then back to the target position in the gravity direction, reducing the thrust force required for stopping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the axis is driven to rise in the antigravity direction to stop at the target position, then the positioning function is achieved, but a wastefully large thrust force is required compared to driving the axis to fall in the gravity direction

Engineering Contradiction:

Improvepositioning accuracyVSAvoidthrust force

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

Instead of directly driving the axis to the target position in the antigravity direction, the invention inverts the approach by first driving the axis to an overrun position beyond the target, then reversing direction to drive back to the target. This inversion allows the axis to fall in the gravity direction during the return stroke, significantly reducing the thrust force required while still achieving accurate positioning at the target.

Inventive Principle:

Principle #13The other way round (Inversion)

2Measurement precision

If the thrust force command is changed according to position deviation magnitude, then the axis can be controlled to stop at the target position, but excessive thrust force is required when stopping in the antigravity direction

Engineering Contradiction:

Improveposition control precisionVSAvoidenergy consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The invention applies the inversion principle by reversing the driving direction after reaching an overrun position. This allows the axis to utilize gravity during the return stroke to the target position, reducing energy consumption while maintaining precise position control through the existing thrust force command adjustment mechanism based on position deviation.

Inventive Principle:

Principle #13The other way round (Inversion)

3Productivity

If the axis is driven to stop at the target position directly, then the positioning operation is completed, but a large thrust force equal to (gravity)+(dynamic friction force) is required when moving in antigravity direction

Engineering Contradiction:

Improvepositioning speedVSAvoidthrust force

Core Design Contradiction:

ProductivityVSForce

Solution Approach 1:

The invention segments the positioning operation into two distinct phases: first driving the axis to an overrun position beyond the target, then reversing to drive back to the target position. This segmentation allows the second phase to utilize gravity assistance, reducing the thrust force required while maintaining overall positioning speed and productivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

By inverting the driving direction after the overrun position, the invention enables the axis to fall back to the target using gravity, significantly reducing the thrust force requirement from (gravity)+(dynamic friction force) to approximately (gravity)−(dynamic friction force) during the return stroke.

Inventive Principle:

Principle #13The other way round (Inversion)

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 approach reduces the thrust force needed to stop the axis, optimizing energy usage by leveraging the difference in thrust forces between gravity and antigravity directions.

Implementation Method 1

an electric motor for driving the feed axis drives the axis to rise or fall at a constant speed and vertically moves a moving body such as a tool coupled to the feed axis, a table, or a workpiece along the gravity direction

Methodology Applied

Scientific EffectGravity: Gravitation

Implementation Method 2

the magnitude of the thrust force (torque) required for the motor is (gravity)+(dynamic friction force) when the moving body rises

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS11196367B2Control device of electric motor and method for controlling electric motor

Publication Date: 2021.12.07 FANUC LTD

AI summary

A control device of an electric motor that drives an axis influenced by gravity includes: a determination unit that determines whether an overrun operation to move past a target position of the axis is allowable; and a drive control unit that, in a case in which it is determined by the determination unit that the overrun operation is allowable and the axis is driven in an antigravity direction, controls driving of the electric motor so that, after the axis being driven to the overrun position past the target position in the antigravity direction, the axis is driven again in a gravity direction to stop at the target position.