Workpiece Alignment via Transmissivity Compensation
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Solution Overview
Problem
Conventional light presence sensors fail to accurately position workpieces with varying light transmission properties, such as silicon carbide wafers, leading to positioning errors due to differences in transmissivity and emissivity compared to opaque silicon substrates.
Innovation Solution
A workpiece alignment system that determines the transmissivity of the workpiece using a controller, adjusting alignment signals based on this measurement, and utilizing dual light beams with equivalent wavelengths to accurately position workpieces regardless of material, thickness, or coatings, by calculating the rotational position and two-dimensional offset of the workpiece.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional light presence sensor is used to determine workpiece position, then the system works adequately for opaque substrates like conventional silicon, but positioning accuracy deteriorates when substrates have varying transmissivity such as silicon carbide
Solution Approach 1:
The system measures the transmissivity parameter of each workpiece and uses this measured value to adjust the alignment determination process. By changing the operational parameters (light intensity compensation) based on the measured transmissivity, the system maintains accurate positioning across different substrate materials without requiring hardware changes
Solution Approach 2:
The system implements a feedback mechanism where the measured transmissivity of the workpiece is used to adjust subsequent alignment measurements. The transmissivity measurement feeds back into the alignment calculation process, allowing the system to compensate for material-specific light transmission characteristics and maintain positioning accuracy
2Measurement precision
If the alignment system is modified to accommodate different substrate transmissivities, then positioning accuracy for varying materials improves, but system complexity increases
Solution Approach 1:
The alignment system is designed to universally handle different substrate materials by measuring transmissivity and automatically adjusting alignment parameters. The same hardware configuration serves multiple functions: initial alignment detection, transmissivity measurement, and material-specific compensation, eliminating the need for separate alignment systems for different materials
Solution Approach 2:
The system performs self-characterization by automatically measuring the transmissivity of each workpiece and using this information to adjust its own alignment determination process. The system serves itself by adapting to different materials without requiring external calibration or manual intervention, reducing operational complexity
3Device complexity
If conventional alignment systems are used without transmissivity compensation, then the system structure remains simple, but positioning errors occur when changing from one substrate type to another
Solution Approach 1:
The system replaces mechanical or manual adjustment mechanisms with an optical measurement and computational compensation approach. Instead of physically adjusting alignment components for different materials, the system uses light transmission measurement and software-based compensation to maintain positioning reliability, substituting mechanical complexity with optical-electrical systems
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 system minimizes costs and ensures accurate positioning for any substrate material and thickness, reducing errors and the need for frequent system changes by accounting for varying transmissivity and emissivity.
Implementation Method 1
a beam of light is emitted by a light emitter and directed toward the workpiece concurrent to a rotation of the workpiece with respect to the beam of light. A variation in light received by a light receiver can be then used to determine the position of notch defined in the workpiece
Implementation Method 2
The transmissivity and emissivity from workpiece to workpiece can vary with the constituency, thickness and coatings disposed on the particular workpiece
Data Source
AI summary
A workpiece alignment system has a workpiece support to support a workpiece. A first light emitter directs a first light beam toward the workpiece. A first light receiver receives the first light beam. A rotation device rotates the workpiece support about a support axis. A second light emitter directs a second light beam toward a peripheral region of the workpiece. A second light receiver receives the second light beam concurrent with the rotation of the workpiece. A controller determines a transmissivity of the workpiece based on a total initial emittance of the first light beam a transmission of the first light beam through the workpiece. The controller determines a position of the workpiece with respect to the support axis based, at least in part, on a rotational position of the workpiece, a portion of the second light beam received, and the determined transmissivity.