Maglev Wafer Handler Position Sensing Without Distributed Sensors
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Solution Overview
Problem
Conventional substrate processing equipment, such as wafer handlers, face challenges with accuracy errors due to robotic kinematic errors like mechanical hysteresis, vibration, and thermal expansion. Additionally, magnetically levitated wafer conveyors require a network of distributed sensors that increase the tool's footprint and cost.
Innovation Solution
The proposed solution involves a substrate processing apparatus that uses actuator coils to track the absolute position of a levitating body or base of the wafer handler without dedicated position feedback sensors. This system employs alternating current voltage and current sampling to determine the position, reducing complexity and cost while maintaining accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetically levitated wafer conveyors use a network of distributed sensors for position determination, then position tracking accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The electromagnets serve dual functions: both propulsion/levitation and position sensing. The position determination is achieved by monitoring the electrical characteristics (current, voltage, impedance) of the electromagnets themselves, eliminating the need for separate sensor systems. The system uses its own actuation components for measurement purposes.
Solution Approach 2:
The electromagnets perform multiple functions simultaneously: they provide magnetic levitation, propulsion, and position feedback. By using the same components for both actuation and sensing, the system reduces overall device complexity while maintaining measurement precision.
2Measurement precision
If magnetically levitated wafer conveyors employ distributed sensors within the sealed environment, then position feedback is achieved, but manufacturing complexity increases due to specialized machining requirements
Solution Approach 1:
The electromagnets serve as both actuators and sensors, eliminating the need for separate sensing components that would require specialized machining and integration within the sealed environment. This self-service approach simplifies manufacturing significantly.
Solution Approach 2:
The position sensing function is extracted from the sealed environment by using the electromagnets' electrical characteristics for measurement. This eliminates the need to place sensors inside the sealed chamber, thereby removing the associated manufacturing complexities.
3Measurement precision
If conventional robotic manipulators use position feedback sensors mounted on actuator shafts, then end effector position is determined, but accuracy errors increase due to mechanical hysteresis, vibration, and thermal expansion
Solution Approach 1:
The patent replaces mechanical position sensing (which is susceptible to mechanical errors) with electrical field-based sensing. By monitoring the electrical characteristics of the electromagnets, the system determines position without relying on mechanical sensors that are affected by hysteresis, vibration, and thermal expansion.
Solution Approach 2:
The electrical characteristics of the electromagnets serve as an intermediary for position determination. Instead of directly measuring mechanical position with sensors, the system uses electrical parameters (current, voltage, impedance) as a mediator to infer position, thereby avoiding direct exposure to mechanical errors.
4Measurement precision
If a network of distributed sensors is used for position feedback, then position tracking is achieved, but tool footprint increases due to space competition with electromagnets
Solution Approach 1:
The patent merges the actuation and sensing functions into a single component system. The electromagnets are used for both propulsion and position determination, eliminating the need for separate sensor networks and their associated wiring harnesses. This consolidation reduces the overall tool footprint.
Solution Approach 2:
The electromagnets perform multiple functions simultaneously, including propulsion, levitation, and position sensing. This multi-functionality eliminates the need for dedicated sensor components and wiring, thereby reducing the space required and minimizing the tool footprint.
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 enhances the accuracy and reduces the cost of substrate processing by eliminating the need for a network of distributed sensors and simplifying the mechanical design, while maintaining precise position tracking and propulsion control.
Implementation Method 1
an array of electromagnets configured to effect levitation and propulsion of the wafer handler base
Implementation Method 2
The array of electromagnets is employed for position determination of the wafer handler base in addition to effecting levitation and propulsion
Data Source
AI summary
A linear electrical machine including a frame with a level reference plane, an array of electromagnets connected to the frame and coupled to an alternating current power source energizing each electromagnet, at least one reaction platen of paramagnetic, diamagnetic, or non-magnetic conductive material disposed to cooperate with the electromagnets of the array of electromagnets so that excitation of the electromagnets with alternating current generates levitation and propulsion forces against the reaction platen that controllably levitate and propel the reaction platen along at least one drive line, in a controlled attitude relative to the drive plane, and a controller operably coupled to the array of electromagnets and the alternating current power source and configured so as to sequentially excite the electromagnets with multiphase alternating current with a predetermined excitation characteristic so that each reaction platen is levitated and propelled with up to six degrees of freedom.