Motor Backlash Correction via Positional Error Threshold

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Solution Overview

Problem

Existing motor control systems fail to effectively correct backlash in systems using gears and belts due to the influence of belt elasticity, leading to delayed reversal of driven shafts and potential negative impacts on reversing operations.

Innovation Solution

A motor control device that includes position detection, positional error calculation, and backlash correction mechanisms, which detect the reversal of the motor position command and add a backlash correction amount to the position command only when the positional error variation or change rate exceeds a predetermined reference value, ensuring appropriate timing for correction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If backlash correction is applied immediately after motor reversal, then reversal delay of driven shaft can be corrected, but the correction becomes ineffective or negative when belt elasticity is involved

Engineering Contradiction:

Improvereversal behavior accuracyVSAvoidcorrection timing accuracy

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The control device monitors the actual positional error between motor and driven shaft in real-time, and only applies backlash correction when the error exceeds a predetermined threshold. This feedback mechanism ensures correction is applied at the appropriate moment when belt elasticity has settled, avoiding premature correction that would be ineffective or harmful.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system prepares backlash correction in advance by setting threshold values and correction amounts, but delays actual application until the positional error confirms the appropriate timing. This preliminary preparation combined with conditional execution ensures the correction is ready but not applied prematurely due to belt elasticity effects.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If backlash correction amount is added to position command, then driven shaft reversal delay is corrected, but operational stability deteriorates when applied at inappropriate timing

Engineering Contradiction:

Improveposition accuracyVSAvoidoperational stability

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The backlash correction system transitions from a static immediate-correction approach to a dynamic conditional approach. The correction amount and timing adapt based on real-time positional error conditions, allowing the system to maintain stability by applying correction only when operational conditions are appropriate rather than uniformly at all reversals.

Inventive Principle:

Principle #15Dynamics

3Ease of manufacture

If correction is applied based on fixed timing, then implementation is simple, but effectiveness decreases when belt elasticity influences the system

Engineering Contradiction:

Improvecontrol system simplicityVSAvoidcorrection effectiveness

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The system changes the control parameter from fixed timing to conditional timing based on positional error threshold. This parameter change allows the simple threshold comparison logic to replace complex timing calculations, maintaining ease of implementation while significantly improving correction effectiveness in systems with belt elasticity.

Inventive Principle:

Principle #35Parameter changes

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 allows for precise and timely backlash correction, improving the reversing behavior of driven shafts by avoiding immediate correction that can exacerbate the issue, thus enhancing the operational stability and accuracy of motor-driven systems.

Implementation Method 1

a first position detection part (for example, the first position detection part 101 described later) that detects a first position which is a position of the movable part

Methodology Applied

Scientific EffectEncoder detection:

Implementation Method 2

a second position detection part (for example, the second position detection part 103 described later) that detects a second position which is a position of the driven part

Methodology Applied

Scientific EffectEncoder detection:

Implementation Method 3

a motor (for example, the motor 20 described later) and a motor shaft (30)

Methodology Applied

Scientific EffectElectromagnetic conversion: Electromagnetic Induction

Data Source

PatentUS9958857B2Motor control device, motor control method, and non-transitory computer readable medium recording motor control program

Publication Date: 2018.05.01 FANUC LTD

AI summary

To provide a motor control device, motor control method, and non-transitory computer readable medium recording a motor control program, which add a backlash correction amount to a position command for a motor at the appropriate timing. Included are a first position detection part that detects a first position which is a position of a movable part; a second position detection part that detects a second position which is a position of a driven part; a positional error calculation part that calculates positional error, which is deviation between a converted first position detected value and a second position detected value; and a backlash correction part that adds a backlash correction amount when the absolute value for the variation of the positional error since reversal of a position command was detected exceeds the predetermined reference value.