Linear Motor Slot Pitch Selection for Force Uniformity

Overview of Technical Issues:

The slotted stator structure creates periodic disturbances in the magnetic field distribution, generating harmful force ripple and non-uniformity in the electromagnetic force output of the linear motor; the goal is to select an optimal slot pitch that minimizes these force variations and achieves uniform force generation for improved positioning accuracy and reduced vibration.

Solution directions generated for this problem

Problem Direction 1 :

ImproveMagnetic field distribution uniformity
VS
ConstraintStator tooth magnetic flux capacity

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Flat diaphragm earphone with magnetic field constraint structure and manufacturing method
Innovative Solution Refine solution

Modular stator with segmented tooth width zones for flux-uniformity balance

Divide stator into independent flux zones with optimized tooth geometry
How to solve :
  • Partition stator into three longitudinal zones: Zone A (entry/exit, 20% length) uses 5mm narrow teeth at 12mm pitch for field uniformity
  • Zone B (center, 60% length) uses 8mm wide teeth at 18mm pitch for flux capacity
  • Zone C (transition, 10% each side) uses gradient teeth 5-8mm for smooth flux handoff
  • Manufacture each zone as separate laminated modules with zone-specific stamping dies, then bolt-assemble with ±0.05mm alignment pins to form complete stator, maintaining ±0.1mm slot tolerance per zone
  • Install flux bridge connectors (soft magnetic composite strips, 2mm thick, μr=5000) between Zone A/B interfaces to equalize flux distribution and prevent 30% capacity drop, ensuring total thrust retention ≥95% while achieving <5% field variation in Zone A
Expected Effect : Field uniformity <5% in critical zones; total flux capacity maintained ≥95% vs 8mm baseline; force ripple reduced to 4-6%; positioning accuracy ±8μm
Risk Control :
  • inter-zone flux leakage at module joints
  • alignment precision during bolt assembly
  • flux bridge saturation under peak load

Problem Direction 2 :

ImproveMagnetic field distribution uniformity
VS
ConstraintSlot geometry manufacturing precision

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Dental implant, abutment for a dental implant and combination thereof and an implant set
Innovative Solution Refine solution

Two-stage slot opening machining with functional zone separation

Divide slot into precision and standard zones
How to solve :
  • Machine slot openings in two functional stages: precision-grind the top 2mm air-gap-facing zone to ±0.03mm tolerance where flux enters and field uniformity is critical
  • rough-cut the lower 6mm slot body to ±0.1mm standard tolerance where flux path geometry has minimal impact on air gap field distribution
  • Use segmented fixturing with independent datum surfaces: top zone referenced to stator outer diameter (runout ≤0.02mm), lower zone referenced to slot centerline, enabling different machining methods without cumulative error
  • Apply zone-specific tooling: CBN grinding wheel (grain size 120#) for top zone achieving Ra 0.4μm surface finish, carbide end mill for lower zone with standard Ra 1.6μm finish, reducing total machining time by 40% versus full-depth precision grinding
Expected Effect : Field uniformity <5%, machining cost -35%, cycle time -40%
Risk Control :
  • datum transition accuracy between zones
  • grinding wheel wear affecting top zone tolerance
  • thermal deformation during zone-specific processing

Problem Direction 3 :

ImproveElectromagnetic force output stability
VS
ConstraintStator tooth magnetic flux capacity

Inspiration 1 : Cross-domain reference

Application Principle: #3 Local quality
Cross-domain applicability Assess applicability
Cutting insert
Innovative Solution Refine solution

Variable-width stator tooth architecture with zone-optimized flux distribution

Divide stator into functional zones with optimized tooth geometry
How to solve :
  • Partition stator into three alternating zones: Zone A (force-smoothing) uses 5mm narrow teeth at 12mm pitch to suppress slot harmonics and reduce ripple to <3%
  • Zone B (high-thrust) uses 8mm wide teeth at 18mm pitch to maintain full magnetic flux capacity
  • Zone C (transition) uses 6.5mm intermediate teeth with 15mm pitch for smooth field coupling between zones, achieving spatial averaging of force output
  • Implement phase-shifted winding distribution across zones: offset coil placement by 120° electrical angle between adjacent zones to cancel ripple harmonics through destructive interference, while maintaining net thrust through constructive summation of fundamental force components
  • Apply silicon steel lamination with graded thickness: 0.35mm sheets in Zone A for low eddy current loss and field uniformity, 0.50mm sheets in Zone B for high saturation flux density (1.9T) and mechanical strength, laser-cut slot openings to ±0.05mm tolerance using fiber laser micromachining
  • Quality control: measure flux density distribution using Hall sensor array with 2mm spatial resolution, acceptance criteria ≤5% peak-to-peak variation
  • verify force ripple via load cell testing at 0.5m/s traverse speed, reject if ripple >3.5%
  • inspect tooth width using CMM with ±0.02mm repeatability
Expected Effect : Force ripple reduced to 2.8%, thrust maintained at 95% of 8mm-tooth baseline, positioning accuracy ±4.5μm
Risk Control :
  • zone transition field distortion causing localized ripple spikes
  • winding phase alignment error degrading harmonic cancellation
  • lamination thickness variation affecting zone-specific permeability

Problem Direction 4 :

ImprovePositioning accuracy
VS
ConstraintSlot geometry manufacturing precision

Inspiration 1 : Cross-domain reference

Application Principle: #28 Mechanics substitution
Cross-domain applicability Assess applicability
System and method for multi-microphone automated clinical document
Innovative Solution Refine solution

Adaptive current waveform shaping with real-time flux mapping for positioning accuracy enhancement

Replace geometric precision with electronic compensation
How to solve :
  • Install Hall-effect sensor arrays (spacing 5mm) along air gap to map actual flux distribution with existing ±0.1mm slot tolerances, sampling at 10kHz during motor operation
  • Implement adaptive current shaping algorithm in controller: decompose measured flux into harmonic components, calculate compensation currents at slot-passing frequency (fundamental + 3rd/5th harmonics) to cancel 8-12% force ripple in real-time
  • Apply feedforward-feedback hybrid control: pre-load motor-specific ripple signature from factory calibration, combine with real-time sensor feedback to generate corrective phase currents within 100μs response time
Expected Effect : Positioning accuracy ±5μm achieved; machining tolerance remains ±0.1mm; force ripple reduced to <3%
Risk Control :
  • sensor drift under temperature variation
  • algorithm computational latency exceeding 100μs
  • electromagnetic interference affecting Hall sensor readings
Patsnap Eureka Solution