Electric Linear Actuator Position Control via Carrier Detection

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Solution Overview

Problem

In electric brake systems, the accuracy of controlling the axial position of the outer ring member in electric linear motion actuators deteriorates due to slippage between the rotary shaft and planetary rollers, leading to reduced responsiveness and potential wear issues.

Innovation Solution

The use of a revolution sensor to detect the rotation angle of the carrier, allowing accurate control of the outer ring member's position, with additional redundancy through a rotation angle detecting means for the electric motor, and an abnormality detecting system to alert for slippage, ensuring precise positioning and fault detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the clearances between the brake disk and the friction pads are reduced to improve responsiveness, then the brake responsiveness is improved, but the friction pads may contact the brake disk due to run-out, causing abnormal wear

Engineering Contradiction:

Improvebrake responsivenessVSAvoidabnormal wear of friction pads

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary adjustment of the axial position of the outer ring member to set the clearance between the friction pads and brake disk to an optimal value before normal operation. This preliminary positioning prevents both excessive clearance (which would reduce responsiveness) and insufficient clearance (which would cause abnormal wear due to run-out contact), thereby resolving the technical contradiction between responsiveness and wear prevention.

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If the clearances between the brake disk and the friction pads are increased to prevent abnormal wear, then the wear prevention is improved, but the brake responsiveness is deteriorated

Engineering Contradiction:

Improveabnormal wear of friction padsVSAvoidbrake responsiveness

Core Design Contradiction:

Object-affected harmful factorsVSSpeed

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

3Ease of operation

If the position of the outer ring member is controlled based on the rotation angle of the electric motor, then the axial position control is achieved, but the position accuracy deteriorates due to slippage between the rotary shaft and planetary rollers

Engineering Contradiction:

Improveaxial position controlVSAvoidposition accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent introduces a carrier as an intermediary element that directly connects the planetary rollers to the position detection system. The carrier's position is detected to control the axial position of the outer ring member, rather than directly detecting the rotary shaft's rotation angle. This intermediary approach eliminates the slippage error between the rotary shaft and planetary rollers, as the carrier moves synchronously with the planetary rollers without slippage, thereby resolving the contradiction between ease of control and position accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system implements feedback control by detecting the position of the carrier (which directly reflects the actual position of the outer ring member) and using this information to control the axial position. This feedback mechanism ensures that the control system receives accurate position information free from slippage errors, resolving the contradiction between ease of operation and measurement precision.

Inventive Principle:

Principle #23Feedback

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 enables accurate and reliable control of the outer ring member's axial position, maintaining system responsiveness and preventing wear, even with slippage occurring between the rotary shaft and planetary rollers, and provides redundancy for continued operation.

Implementation Method 1

torque is transmitted from the rotary shaft to the respective planetary rollers using friction between the rotary shaft and the respective planetary rollers

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS9353837B2Electric linear motion actuator

Publication Date: 2016.05.31 NTN CORP

AI summary

An electric linear motion actuator includes: a rotary shaft to be driven by an electric motor; a plurality of planetary rollers kept in rolling contact with a cylindrical surface formed on an outer periphery of the rotary shaft; a carrier which retains the planetary rollers such that the planetary rollers are rotatable about axes thereof while revolving around the rotary shaft, and of which axial movement is restricted; and an outer ring member surrounding the planetary rollers and supported so as to be slidable in an axial direction. Helical ribs are formed on an inner periphery of the outer ring member; and circumferential grooves are formed on an outer periphery of each of the planetary rollers so as to be engaged with the helical ribs. A rotation of the rotary shaft is thus converted to a linear motion of the outer ring member.