Linear Motor Thermal Expansion Mounting

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Solution Overview

Problem

Conventional positioning apparatus, such as CMMs, face metrological challenges due to relative thermal expansion and contraction between linear motor components and their members, leading to inaccuracies in motion control, especially when using rotary motors and differing thermal inertias of materials.

Innovation Solution

The use of a linear motor with a decoupled stator and armature assembly that allows for longitudinal expansion and contraction, mounted via rigid and compliant assemblies to accommodate thermal changes, ensuring improved metrology by minimizing thermal mismatch effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a linear motor is rigidly mounted to moveable members, then servo stiffness is maintained, but thermal expansion and contraction cause metrological inaccuracies

Engineering Contradiction:

Improvemetrology accuracyVSAvoidservo stiffness

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The mounting system is segmented into rigid mounting portions and compliant mounting portions. The rigid portions maintain servo stiffness by providing stable mechanical support, while the compliant portions accommodate thermal expansion and contraction through controlled flexibility. This segmentation allows the system to simultaneously achieve both metrological accuracy and thermal adaptability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The compliant mounting portions are designed to change their mechanical parameters (stiffness, flexibility) in response to temperature variations. By allowing controlled parameter changes in the mounting system, the linear motor can expand and contract with thermal conditions while maintaining accurate positioning, thus resolving the contradiction between thermal stability and metrological precision.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If the stator and armature are rigidly coupled to their members, then mechanical stability is improved, but thermal mismatch between different materials causes expansion/contraction discrepancies

Engineering Contradiction:

Improvemechanical stabilityVSAvoidthermal expansion matching

Core Design Contradiction:

Stability of the object's compositionVSManufacturing precision

Solution Approach 1:

Compliant mounting portions act as intermediaries between the linear motor components and the moveable members. These intermediaries absorb thermal mismatch by providing a flexible connection that accommodates differential expansion and contraction between materials with different thermal coefficients, thereby maintaining both mechanical stability and thermal compatibility.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If conventional rotary motors with belts are used, then thermal inertial differences are reduced, but direct linear motor control provides superior positioning accuracy

Engineering Contradiction:

Improvepositioning accuracyVSAvoidthermal inertia

Core Design Contradiction:

Measurement precisionVSTemperature

Solution Approach 1:

The invention extracts and isolates the thermal management function from the positioning function. By separating the linear motor into independently mountable stator and armature assemblies with compliant mounting, the thermal effects are decoupled from the positioning mechanism, allowing direct linear motor control to achieve superior accuracy without being constrained by thermal inertia limitations of rotary motor systems.

Inventive Principle:

Principle #2Taking out (Extraction)

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 configuration enhances the accuracy and reliability of the positioning apparatus by decoupling the motor components from their members, reducing thermal expansion-related inaccuracies and maintaining servo stiffness.

Implementation Method 1

a linear motor comprising at least one elongate stator assembly and at least one armature assembly respectively mounted to the first and second moveable members for effecting relative movement of the first and second moveable members

Methodology Applied

Scientific EffectElectromagnetic force: Lorentz Force

Implementation Method 2

The positioning apparatus can be configured so at to permit longitudinal expansion and/or contraction of the at least one elongate stator assembly and/or of the at least one armature assembly relative to its respective member

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

The at least one elongate stator assembly could be mounted to its respective member at/toward a first end by a rigid mount assembly. The at least one elongate stator assembly could be mounted to its respective member at/toward its other end via a compliant mount assembly

Methodology Applied

Scientific EffectMechanical compliance: Elasticity

Data Source

PatentUS10826369B2Positioning apparatus with relatively moveable members and a linear motor mounted thereon

Publication Date: 2020.11.03 RENISHAW PLC

AI summary

A positioning apparatus comprising first and second relatively moveable members, and a linear motor comprising at least one elongate stator assembly and at least one armature assembly respectively mounted to the first and second moveable members for effecting relative movement of the first and second moveable members, configured so at to permit longitudinal expansion and/or contraction of the at least one elongate stator assembly and/or of the at least one armature assembly relative to its respective member.