Linear Motor Magnet Skew Angle Impact on Thrust Ripple

Overview of Technical Issues:

The magnet skew angle configuration insufficiently smooths the magnetic flux distribution transmitted to the coil assembly, resulting in periodic flux variation that generates thrust ripple and degrades motion smoothness and positioning precision; the goal is to optimize the skew angle to minimize thrust ripple while maintaining adequate thrust output.

Solution directions generated for this problem

Problem Direction 1 :

ImproveMagnetic flux distribution uniformity
VS
ConstraintThrust output magnitude

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Vertical takeoff and landing (VTOL) unmanned aerial vehicle (UAV)
Innovative Solution Refine solution

Graded magnetization skew array for smooth high-force linear motor

Grade magnet strength along skew
How to solve :
  • Use segmented NdFeB magnets with constant geometric skew but graded remanence, raising Br 6–10% at skew-loss zones by pulse magnetizing 2–3 subsegments per pole
  • Bond magnets on low-carbon steel back iron, target skew 0.7–0.9 pole pitch, magnet gap tolerance ±0.02 mm, magnetization angle error ≤1.0°, then map air-gap flux with Hall scan and trim by local re-magnetization
  • Set QC by FFT of back-EMF and thrust test: fundamental force ≥98% baseline, 3rd+5th flux harmonics ≤40% of baseline, thrust ripple ≤1.5%, air-gap flux deviation within ±3%, inspect with CMM, gaussmeter, dynamometer
Expected Effect : Ripple −50 to −70%, force loss <2%, positioning stability +30% vs uniform-skew arrays
Risk Control :
  • segment demag from overpulse
  • adhesive creep shifts skew
  • remanence grading drift between batches

Problem Direction 2 :

ImproveThrust ripple amplitude
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Plastic lens barrel, camera module and electronic devices
Innovative Solution Refine solution

Graded magnetization intensity magnet array for ripple suppression without precision increase

Use magnets with spatially varying magnetization strength to compensate flux loss from skewing
How to solve :
  • Employ graded magnetization intensity magnets where edge zones have 15–25% higher remanence (1.35–1.45 T) than center zones (1.15–1.25 T) to offset flux linkage reduction from skew angle, maintaining thrust output while achieving harmonic cancellation
  • Magnetize standard NdFeB N42 grade magnets using programmable magnetization fixtures with segmented coil arrays (8–12 zones per magnet), applying localized field pulses of 3.5–4.2 T to create the intensity gradient without requiring tighter assembly tolerances (±0.3 mm positioning acceptable)
  • Implement post-assembly flux mapping using Hall sensor array (0.5 mm pitch) to measure actual flux distribution, then apply software-based current compensation (±5% modulation) to cancel residual ripple from manufacturing variations, achieving <2% thrust ripple without tightening mechanical tolerances
Expected Effect : Thrust ripple <2%, positioning tolerance ±0.3mm maintained, thrust output preserved within 5% of non-skewed baseline
Risk Control :
  • magnetization gradient uniformity control
  • flux measurement accuracy and calibration drift
  • software compensation algorithm convergence time

Problem Direction 3 :

ImprovePositioning precision
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #28 Mechanics substitution
Cross-domain applicability Assess applicability
Control device, control method, and microscope device for operation
Innovative Solution Refine solution

Closed-loop position feedback compensation system for magnet skew ripple cancellation

Replace precision magnet skew with sensor-based ripple compensation
How to solve :
  • Install linear encoder (resolution ≤0.1μm) and Hall effect sensors (3-phase, 120° spacing) to measure real-time position and flux phase
  • During commissioning, execute automatic ripple characterization — drive coil through full stroke at constant velocity 50mm/s, record thrust variation vs position, generate ripple compensation table with 0.5mm spatial resolution stored in controller EEPROM
  • Implement feedforward current modulation — controller reads position, retrieves corresponding ripple amplitude and phase from table, injects compensating current (±15% rated current) into coil phases 180° out-of-phase with measured ripple, achieving real-time cancellation with <2ms latency
Expected Effect : Positioning precision ±0.5μm; magnet tolerance relaxed to ±0.3mm; ripple reduced 85%
Risk Control :
  • sensor noise coupling to compensation signal
  • temperature drift altering ripple profile
  • controller computation bandwidth insufficient
Patsnap Eureka Solution