Linear Motor Thrust Ripple Correction via Induced Voltage Measurement
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Solution Overview
Problem
Existing methods for measuring and correcting thrust ripple in linear motors used in semiconductor exposure apparatuses are inaccurate due to external disturbances and complexity, leading to positional deviations and reduced throughput, and there is a need for a method to efficiently measure and correct thrust ripple before the motor is incorporated into the apparatus.
Innovation Solution
A moving control apparatus and method that includes a driver with a movable element and a stator, a position detector, a measurement unit to measure induced voltage, and a correction calculator to calculate and apply a thrust ripple correction value, allowing for accurate measurement and correction of thrust ripple, as well as abnormality detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high thrust is applied to increase speed and acceleration for high throughput, then productivity is improved, but the influence of thrust ripple is magnified causing increased positional deviation and longer stabilization time
Solution Approach 1:
The system performs preliminary measurement of thrust ripple characteristics before actual production operation. A correction table is pre-calculated and stored based on measured thrust ripple data, allowing the control system to compensate for thrust variations during high-speed operation without real-time measurement delays
Solution Approach 2:
The system uses feedback from position detectors to monitor actual stage position and compares it with commanded position. The measured positional deviation due to thrust ripple is fed back to adjust the control commands, enabling continuous compensation during acceleration and constant-speed scanning phases
2Measurement precision
If thrust ripple correction is performed during actual stage driving by recording current values, then correction is applied, but external disturbances such as friction resistance and other forces make accurate measurement difficult
Solution Approach 1:
The system extracts and separates the thrust ripple measurement from the actual production operation. By performing measurements during dedicated calibration phases with controlled conditions and minimal external disturbances, the system isolates the thrust ripple characteristics from confounding factors like friction and gravitational forces
Solution Approach 2:
Thrust ripple characteristics are measured and correction tables are generated in advance before normal production operation begins. This preliminary calibration is performed when the stage is stationary or moving minimally, eliminating the influence of friction resistance and other motion-dependent disturbances during the measurement phase
3Reliability
If multiple parameters are estimated by adaptation mechanism to correct thrust ripple, then correction is attempted, but the number of parameters increases making accurate determination difficult
Solution Approach 1:
The system extracts and focuses on measuring only the essential thrust ripple characteristics rather than attempting to model all possible parameters. By directly measuring the relationship between commanded current and actual thrust output, the system determines correction factors without requiring complex multi-parameter adaptation
Solution Approach 2:
The system transforms the correction approach from estimating multiple physical parameters (friction coefficients, gravitational forces, inertial effects) to directly measuring and storing empirical correction factors in a lookup table. This parameter transformation simplifies the problem from complex physical modeling to direct empirical measurement
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 solution enables accurate measurement and correction of thrust ripple, improving positional accuracy and throughput, and allows for efficient detection of abnormalities such as coil breakage or magnet demagnetization, even when the motor is not yet incorporated into the apparatus.
Implementation Method 1
Four movable magnets 105 are arranged on the table top plate 101 such that the polarities of the magnets are alternately changed with respect to a vertical direction of the surface of the drawing. The movable magnets 105 and coils 104 arrayed at equal intervals in a moving direction of the table top plate 101 form a liner motor.
Implementation Method 2
a position detector which detects a relative position between the movable element and the stator in the driver
Data Source
AI summary
A moving control apparatus comprising: a moving member provided movably at least in one direction; a driver having a movable element connected to the moving member and a stator to displace the movable element; a controller which energizes the driver to cause the movable element to generate a thrust; a position detector which detects a relative position between the movable element and the stator in the driver; a measurement unit which drives the movable element of the driver and measures an induced voltage generated in the driver; and a correction calculator which calculates a thrust ripple correction value to correct a thrust ripple as a variation of a thrust generated in the driver from the measured induced voltage and the relative position in the driver, and multiplies a command to the driver by the correction value.