Interferometric Encoder Beam Routing for Compact Multi-Dimensional Measurement
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Solution Overview
Problem
Interferometric encoders face challenges in reducing size and weight while maintaining sensitivity and interference signal strength, especially in applications with limited space and accelerated stages, where small beam sizes increase sensitivity to grating errors and limit measurement range.
Innovation Solution
The solution involves routing beams to minimize space on the encoder scale by allowing multiple measurement beams to overlap and propagate through the same glass volume, using a slight angular separation between beams to direct them to separate detectors with a single focusing lens, and employing optical components like retroreflectors, waveplates, and birefringent wedge prisms to redirect and combine beams effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple measurement beams use different diffraction orders to monitor stage motion in multiple dimensions, then measurement capability in multiple dimensions is improved, but device size and weight increase
Solution Approach 1:
The patent combines multiple measurement beams into a shared optical path by diffracting a single measurement beam into multiple diffraction orders (+1, -1, +2, -2) that all interact with the same encoder scale footprint. The beams are redirected by reflectors to overlap and propagate through the same glass volume in the encoder head, allowing multi-dimensional measurement without proportionally increasing device size.
Solution Approach 2:
A single measurement beam serves multiple functions by being diffracted into multiple orders that monitor different dimensions of stage motion. The encoder scale and optical path are designed to handle multiple diffraction orders simultaneously, making the system universally capable of measuring motion in multiple directions using one beam source.
2Area of stationary object
If beam size is reduced to minimize footprint on encoder scale, then space requirements are improved, but sensitivity to grating errors increases
Solution Approach 1:
Multiple diffraction orders are combined to interact with the same encoder scale footprint, minimizing the required beam size on the scale while maintaining measurement precision. The overlapping beams share the same optical path and glass volume, reducing the overall footprint without sacrificing sensitivity.
3Volume of stationary object
If multiple measurement beams are allowed to overlap and share the same optical path, then device size is reduced, but beam separation and detection complexity increases
Solution Approach 1:
The patent introduces a slight angular separation between the overlapping measurement beams by designing the encoder head optics with asymmetric element orientations. This asymmetric angular separation allows a single focusing lens to direct the beams to separate detectors, simplifying the detection system while maintaining compact size.
Solution Approach 2:
A single focusing lens acts as an intermediary element that receives multiple overlapping measurement beams with slight angular separation and directs them to separate detectors. This intermediary component simplifies the optical path management by providing a unified method for beam separation and detection.
4Measurement precision
If glass components are used for multiple measurement beams to reduce air path, then measurement precision is improved, but device weight increases
Solution Approach 1:
Multiple measurement beams are merged to propagate through the same glass volume in the encoder head, allowing the use of glass components for all beams without proportionally increasing weight. The shared optical path through glass reduces air turbulence impact on all beams simultaneously while minimizing the total glass volume required.
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 weight and space requirements of interferometric encoders, minimizes measurement errors, and maintains sensitivity by allowing shared optical components and reduced beam splitter volume, while avoiding parasitic beam paths and substrate errors.
Implementation Method 1
an encoder scale diffracts the measurement beam into a plurality of diffracted orders
Implementation Method 2
at least two reflectors arranged to receive and redirect the once-diffracted measurement beams back toward the encoder scale
Implementation Method 3
a single focusing lens can direct the beams to separate detectors
Implementation Method 4
The beam splitter is shared among all measurement beams and is arranged to combine and separate the measurement and reference beams
Implementation Method 5
employing optical components like retroreflectors, waveplates, and birefringent wedge prisms to redirect and combine beams effectively
Implementation Method 6
Interferometric encoders can perform high precision measurements of the position of mechanical stages
Data Source
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AI summary
An encoder interferometry system includes an encoder scale arranged to receive and diffract a measurement beam. The system further includes one or more optical elements configured and arranged to receive a first diffracted measurement beam and a second diffracted measurement beam from the encoder scale and to redirect the first diffracted measurement beam and the second diffracted measurement beam toward the encoder scale such that the first diffracted measurement beam and the second diffracted measurement beam propagate along non-parallel beam paths having an angular separation α following a second diffraction at the encoder scale. The system further includes a first detector arranged to receive the first diffracted measurement beam and a second detector arranged to receive the second diffracted measurement beam.