Grating Retroreflector for Compact Position Measurement

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional position-measuring devices with prism-based retroreflector elements are costly and voluminous, leading to an enlarged scanning unit, which is undesirable for compact construction.

Innovation Solution

The use of grating structures with a simple reflector element to achieve a retroreflector and scanning grating functionality, allowing for a planar and cost-effective assembly, where the grating structures provide defined lens effects and deflecting effects to facilitate compact construction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If prism-based retroreflector elements are used, then retroreflection functionality is achieved, but the scanning unit becomes voluminous and costly

Engineering Contradiction:

Improveretroreflection functionalityVSAvoidscanning unit size

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The retroreflector functionality is segmented into multiple independent components: a flat reflector element and separate first and second grating structures. This segmentation replaces the monolithic prism structure with distributed functional elements that achieve the same optical effect while reducing volume and manufacturing cost.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The grating structures serve multiple functions simultaneously: they provide the retroreflection effect, act as scanning gratings for position measurement, and create the necessary lens effects for beam focusing and collimating. This multi-functionality eliminates the need for separate optical components, reducing overall system volume.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If prism-based retroreflector elements are used, then retroreflection functionality is achieved, but manufacturing cost increases

Engineering Contradiction:

Improveretroreflection functionalityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention replaces expensive, precision-machined prism components with cheaper alternatives: a simple flat reflector element and grating structures that can be manufactured using standard diffraction grating fabrication techniques. These components are less costly to produce while maintaining the required optical functionality.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The mechanical prism structure is replaced with an optical system based on diffraction gratings and a flat reflector. This substitution transitions from mechanical precision components to optical elements that achieve the same retroreflection effect through wave optics principles, reducing manufacturing complexity and cost.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Volume of moving object

If grating structures with lens effects are used, then compact construction is achieved, but optical alignment precision is required

Engineering Contradiction:

Improvescanning unit sizeVSAvoidoptical alignment precision

Core Design Contradiction:

Volume of moving objectVSManufacturing precision

Solution Approach 1:

The grating structures are merged with the flat reflector element into a single integrated assembly. This merging ensures that the relative positions and orientations of the grating structures to the reflector are fixed during manufacturing, eliminating the need for complex field alignment and reducing the practical alignment precision requirements during installation.

Inventive Principle:

Principle #5Merging (Combining)

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 enables a compact scanning unit with reduced size and cost, maintaining the necessary optical functionality for position measurement while eliminating the need for complex prism-based retroreflector elements.

Implementation Method 1

beams of rays impinging on the measuring graduation propagate diffracted in the direction of the scanning unit, where they pass through first grating structures

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

the partial beams of rays impinge on the reflector element, from which a back reflection takes place in the direction of the measuring graduation

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS7471397B2Position-measuring device

Publication Date: 2008.12.30 DR JOHANNES HEIDENHAIN GMBH

AI summary

In a position-measuring device for recording the relative position of a scanning unit and a measuring graduation that is movable with respect to the latter in at least one measuring direction, the scanning unit includes a plurality of grating structures as well as at least one reflector element. The elements in the scanning unit are arranged such that the beams of rays diffracted by the measuring graduation pass through first grating structures in the scanning unit, subsequently impinge on the reflector element, from which there takes place a retroreflection in the direction of the measuring graduation, and the partial beams of rays then pass through second grating structures and then once again impinge upon the measuring graduation. The first and the second grating structures are arranged such that, upon the first and second passing through of the partial beams of rays, a defined lens effect on the partial beams of rays results.