Time-Multiplexed Position Measuring System for Mass Reduction
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Solution Overview
Problem
Conventional position-measuring systems in semiconductor manufacturing face challenges with high accuracy requirements and dynamic performance, particularly due to refractive-index fluctuations in air and the introduction of electromagnetic interference and increased mass from cable trailing devices, which affect the precision and reliability of position measurements in high-speed applications.
Innovation Solution
A position-measuring system utilizing a multiplexer unit to transmit raw position signals from scanning units to sequential electronics in time multiplex operation, without converting them into position values beforehand, along with optical or electrical signal transmission via fibers or lines, and incorporating correction and error-redundant data coding to enhance accuracy and reduce system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cable trailing devices are used to transmit measurement data from scanning units to sequential electronics, then position measurement capability is achieved, but system mass and volume increase
Solution Approach 1:
The patent extracts the signal conversion function from the moving scanning units and relocates it to the stationary sequential electronics. Only the essential optical scanning components remain on the moving table, while the data conversion and processing functions are removed from the moving mass, thereby reducing system mass while maintaining measurement capability.
Solution Approach 2:
The patent transitions from transmitting multiple independent analog signals through multiple cables to transmitting a single time-multiplexed digital signal. This dimensional consolidation reduces the cable bundle from multiple parallel channels to a single communication channel, significantly reducing volume and mass.
2Reliability
If robust interference-immune line drivers and shielded signal lines are used in scanning units, then electromagnetic interference resistance is improved, but mass and unit volume of scanning units increase
Solution Approach 1:
The patent replaces the mechanical/electrical approach of using heavy shielded cables and robust line drivers with an optical-digital approach. Time-multiplexed digital signals transmitted via optical fibers or controlled impedance lines provide immune to electromagnetic interference without requiring bulky shielding, thus reducing scanning unit volume.
Solution Approach 2:
The patent changes the signal parameters from analog to digital and from simultaneous transmission to time-multiplexed transmission. This parameter transformation allows the use of simpler, lighter transmission media while maintaining or improving interference resistance through digital signal integrity.
3Measurement precision
If multiple scanning units are mounted on traversing table to measure all degrees of freedom, then complete position measurement is achieved, but inert mass and stiffness of cable trailing device increase
Solution Approach 1:
The patent merges the data output from multiple scanning units into a single time-multiplexed digital signal stream. Instead of requiring separate cable trails for each scanning unit, all measurement data are combined into one communication channel, significantly reducing the total cable mass and improving the stiffness-to-mass ratio of the trailing device.
4Measurement precision
If laser interferometers are used for position measurement, then measurement capability is achieved, but measured-value fluctuations increase due to refractive-index fluctuations in air
Solution Approach 1:
The patent replaces laser interferometry with a grating-based optical encoding system. Instead of measuring interference patterns that are sensitive to air refractive index changes, the system uses direct optical scanning of encoded position information on gratings, which is inherently immune to environmental refractive index fluctuations, thereby improving measurement stability.
Data Source
AI summary
A position-measuring system is for measuring the position of an object, movable in several degrees of freedom, relative to a stationary object. The position-measuring system includes at least one measuring graduation that is joined to one of the objects, as well as a plurality of scanning units which are joined to the other object and which generate raw position signals based on the optical scanning of the measuring graduation. Moreover, a multiplexer unit is provided, the raw position signals generated by the scanning units being supplied to the multiplexer unit, and from there, the raw position signals of the various scanning units being transmitted in time multiplex operation to a downstream sequential electronics, without converting the raw position signals into position values beforehand.