Multiphase Planar Motor Coil Pitch Layout for Low Force Ripple
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Solution Overview
Problem
Conventional multiphase linear or planar motors used in lithographic apparatuses experience significant ripple in motor constant due to varying positions of magnets relative to coils, leading to undesirable force variations, especially at high accelerations where forces are large and constant force is not feasible.
Innovation Solution
A multiphase motor design featuring a coil system with non-zero gaps between adjacent coil assemblies and a magnet system with magnets of opposite polarity, where the magnet assembly's dimension is adjusted to match the coil assembly's dimension plus half the gap, reducing ripple by extending the magnet assembly to compensate for manufacturing and serviceability constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the magnet assembly dimension is increased to cover gaps between coil assemblies, then manufacturing and serviceability constraints are satisfied, but the motor constant ripple increases
Solution Approach 1:
The patent applies parameter changes by adjusting the magnet assembly dimension to a specific value that is a function of the coil assembly dimension and gap size. The formula Lm = Lc + g/2 establishes an optimal parameter relationship that balances manufacturing constraints with performance requirements, reducing motor constant ripple while accommodating practical manufacturing and serviceability needs.
2Productivity
If high acceleration forces are generated, then productivity is improved, but force variation due to ripple becomes unacceptable
Solution Approach 1:
The patent implements feedback by using position-dependent current adjustment to compensate for motor constant ripple. The control system continuously monitors the magnet position relative to coil assemblies and adjusts the phase currents accordingly, providing feedback control that maintains constant force output even at high accelerations where ripple would normally cause unacceptable force variations.
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
The solution significantly reduces the ripple in motor constant, achieving a consistent force generation across different positions, improving the design freedom and performance of the motor, particularly at high accelerations where ripple was previously up to 8%, now reduced to below ±0.5%.
Implementation Method 1
the coil system is configured to generate magnetic fields interacting with the magnet system to cause driving forces in the first main driving direction to move the magnet system relative to the coil system
Data Source
AI summary
An electromagnetic motor is described, the electromagnetic motor comprising: a magnet assembly configured to generate a two-dimensional alternating magnetic field having a pitch Pm1 in a first direction and a pitch Pm2 in a second direction; a coil assembly configured to co-operate with the magnet assembly to generate a first force in the first direction and a second force in the second direction, wherein the coil assembly comprises a first coil set comprising a plurality of first coils for generating the first force and a second coil set comprising a plurality of second coils for generating the second force, wherein a ratio R1 of a coil pitch Pc1 in the first coil set in the first direction over Pm1 is different from a ratio R2 of a coil pitch Pc2 in the second coil set in the second direction over Pm2.