Linear Motor Ironless Coil Structural Support Design

Overview of Technical Issues:

The structural support framework in an ironless coil linear motor insufficiently constrains the coil assembly position during dynamic operation, causing coil deflection under electromagnetic and inertial forces, leading to air gap variation, force ripple, and reduced positioning accuracy; the goal is to optimize the support structure design to maintain precise coil positioning while preserving the ironless configuration's advantages of zero cogging force and low moving mass.

Solution directions generated for this problem

Problem Direction 1 :

ImproveSupport framework structural stiffness
VS
ConstraintMoving assembly mass

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Support frame and rail carriage for transporting bulk material on rail transport system
Innovative Solution Refine solution

Functionally-segmented hybrid-stiffness coil support frame with load-adaptive zones

Divide frame into high-load and low-load zones with differentiated stiffness design
How to solve :
  • Segment the coil support frame into three functional zones: high-stiffness central zone (carbon fiber composite ribs, 15mm height) where electromagnetic force peaks, transition zones (aluminum honeycomb, 8mm height) for moderate loads, and minimal-mass end zones (thin-wall aluminum, 3mm) for low-stress regions — each zone independently optimized for local load conditions
  • Apply topology optimization to each segment: central zone designed for 50N peak load with deflection ≤0.025mm (safety margin included), transition zones for 20N with ≤0.05mm deflection, end zones for 5N structural integrity only — total frame mass maintained at 0.78kg through material removal in low-stress areas
  • Implement modular snap-fit assembly with self-aligning kinematic couplings (three-point V-groove contacts at segment interfaces) — each module fabricated to ±0.08mm tolerance, assembly achieves ±0.03mm overall alignment through geometric constraint, eliminating need for precision machining of entire frame
Expected Effect : Deflection reduced to 0.025mm; mass 0.78kg; cost -30%
Risk Control :
  • segment interface fatigue under cyclic loading
  • kinematic coupling wear causing alignment drift
  • carbon fiber delamination in high-stiffness zones

Problem Direction 2 :

ImproveCoil position constraint force
VS
ConstraintMoving assembly mass

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Actuator devices, power-assisted robots, and humanoid robots
Innovative Solution Refine solution

Distributed micro-constraint node array for coil positioning

Replace centralized constraint with distributed micro-nodes
How to solve :
  • Deploy 12–16 micro-constraint nodes around coil perimeter, each node providing 3–5N localized constraint force via spring-loaded ceramic ball contacts (total 40–60N constraint capacity)
  • each node mass 8–12g, fabricated from titanium alloy Ti-6Al-4V with ceramic Si₃N₄ ball tips (hardness HV1800), total added mass ≤0.15kg maintaining 0.8kg baseline
  • nodes positioned at 30° intervals, contact preload 2–4N adjusted via micro-screws (±0.01mm pitch), ensuring distributed load path that collectively constrains coil displacement to ≤0.05mm under 50N electromagnetic force and 3g acceleration
Expected Effect : Constraint force +100% (20N→40N), mass +18.75%, deflection −67%
Risk Control :
  • node contact wear causing preload loss
  • assembly alignment complexity across 12+ nodes
  • ceramic ball fracture under shock loads

Problem Direction 3 :

ImproveSupport framework structural stiffness
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #1 Segmentation
Cross-domain applicability Assess applicability
Offset control for assembling an electronic device housing
Innovative Solution Refine solution

Modular self-aligning coil support frame with independent stiffness zones

Divide frame into snap-fit modules with zone-specific stiffness
How to solve :
  • Segment support frame into 3-5 independent modules — high-stiffness ribs (carbon fiber composite, 15mm height) at peak electromagnetic load zones, lighter sections (aluminum alloy, 8mm height) elsewhere, each module tolerance ±0.08mm
  • Design kinematic coupling interfaces between modules using three-point V-groove contact (120° spacing, contact sphere diameter 6mm, hardness HRC58-62) that self-align during snap assembly to achieve overall ±0.03mm deflection without tight individual part tolerances
  • Apply liquid shim adhesive (epoxy, viscosity 500-800 cPs, cure time 24h at 23°C) at module interfaces after preliminary alignment on reference jig — adhesive fills gaps 0.05-0.15mm, locks alignment, then final cure under 2N clamping force per joint
Expected Effect : Deflection ≤0.03mm under 50N load; individual module tolerance relaxed to ±0.08mm; assembly time <15min; total mass maintained at 0.8kg
Risk Control :
  • V-groove contact wear over cycles
  • adhesive thickness variation affecting stiffness
  • module interface fatigue under dynamic loads

Problem Direction 4 :

ImproveCoil positioning stability
VS
ConstraintMoving assembly mass

Inspiration 1 : Cross-domain reference

Application Principle: #2 Taking out
Cross-domain applicability Assess applicability
Positioning system
Innovative Solution Refine solution

Stationary-side cable constraint system for coil positioning

Transfer position constraint from moving coil to stationary frame using cable system
How to solve :
  • Mount pre-tensioned cable constraint network on stationary stator frame, with cables extending to coil assembly perimeter at 4–6 anchor points, providing lateral constraint force ≥30N while adding <0.05kg to moving mass
  • Use high-modulus UHMWPE cables (diameter 0.8–1.2mm, tensile strength ≥2GPa) with adjustable tensioners on stator side, pre-tension set at 15–25N per cable to maintain taut geometry during 3g acceleration
  • Integrate cable length auto-compensation mechanism using spring-loaded pulleys (spring constant 50–80 N/m) on stator frame to maintain constant tension across ±10mm travel range, limiting coil position variation to <0.05mm
Expected Effect : Position variation reduced to 0.04mm; moving mass increase <6%; constraint force 35N
Risk Control :
  • cable fatigue under cyclic loading
  • tension uniformity across multiple cables
  • cable-coil attachment point wear

Problem Direction 5 :

ImproveCoil positioning stability
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #10 Preliminary action
Cross-domain applicability Assess applicability
Bracket assembly for multi-component vision systems in electronic devices
Innovative Solution Refine solution

Pre-calibrated modular coil cartridge with kinematic coupling interface

Pre-calibrate coil-frame assembly at factory with kinematic coupling interface
How to solve :
  • Design coil assembly as pre-calibrated cartridge module — factory-tuned to ±5μm positioning accuracy, sealed as matched unit
  • Integrate three-point kinematic coupling (120° distributed conical seats + spherical contact balls) at mounting interface — self-locating repeatability ±0.01mm without field adjustment
  • Relax individual component tolerances to ±0.08mm, achieve final positioning stability through deterministic contact geometry rather than cumulative dimensional precision
Expected Effect : Position variation <0.04mm; field assembly time -70%; manufacturing tolerance relaxed to ±0.08mm
Risk Control :
  • kinematic contact wear over cycles
  • thermal expansion mismatch at coupling
  • contamination affecting repeatability
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