Detailed Description
Linear Motors Need a Different Cable
A rotary servo motor is bolted to a fixed frame. The cable connects a stationary cabinet to a motor that does not move. All the motion is internal to the motor — the cable is fixed.
A linear motor is fundamentally different: the cable connects a stationary cabinet to a motor that is the moving element — the forcer/slider travels along the entire length of the axis. The cable must:
- Travel with the motor through the full stroke (1–10+ meters)
- Carry both high-power motor phase current and precision Hall sensor feedback signals in the same sheath
- Maintain signal integrity despite the PWM power conductors being millimeters from the signal conductors
- Survive millions of high-speed, long-travel cycles in a cable carrier
The Hall Sensor Challenge — Clean Signals Next to Noisy Power
Hall effect sensors detect the linear motor's magnetic pole position — they are the "encoder" equivalent for linear motors. These sensors output low-level analog or digital signals (typically 5 V or 24 V) that tell the servo drive exactly where the forcer is along the magnet track.
The problem: the power conductors carrying the motor phase current (switching at 4–16 kHz with 5 kV/μs dv/dt) are inside the same cable as the Hall sensor signal conductors, separated by only a few millimeters of insulation.
Without proper design, the PWM power waveform capacitively couples into the Hall sensor signals, corrupting the position feedback. The servo drive loses commutation — the motor loses position or faults.
Three design features prevent this:
1. Physical Separation — PET Fleece Inter-Layer
The power conductors are stranded in the cable's inner core. The signal conductors are in a separate outer layer. A PET fleece tape between the layers provides additional dielectric isolation beyond the individual core insulation.
2. Low-Capacitance Signal Insulation
The Hall sensor cores use PP or PE insulation — materials with low dielectric constants (εr ≈ 2.3) vs PVC (εr ≈ 4.5). Lower dielectric constant = lower capacitance between power and signal cores = lower coupled noise voltage.
3. Overall Shield — Tinned Copper Braid
The 85%+ coverage braid shield surrounds the entire cable assembly — both power and signal cores. The shield intercepts radiated EMI from external sources AND provides a ground reference plane that reduces capacitive coupling between the power and signal conductors inside the cable.
Typical Configurations by Motor Size
| Linear Motor Type | Typical Power | Hall Sensors | Thermal | Typical Configuration |
|---|---|---|---|---|
| Small ironless (< 200 N) | 1.5–2.5 mm² | 5 signals (3 Hall + 2 power) | 2 signals (PTC/KTY) | 4G1.5 + 7 × 0.5 |
| Medium ironless (200–500 N) | 2.5–4 mm² | 5 signals | 2 signals | 4G2.5 + 7 × 0.5 |
| Iron-core (500–2 000 N) | 4–10 mm² | 5–8 signals | 2 signals | 4G4 + 8 × 0.5 + 2 × 0.5 |
| Large iron-core (> 2 000 N) | 10–35 mm² | 8 signals | 2 signals | 4G10 + 8 × 0.5 + 2 × 0.5 |
Long-Travel Design — Beyond Standard Carriers
Standard drag chain cable is designed for travels up to 10–20 m. Linear motor axes often exceed this — semiconductor wafer stages routinely travel 2–5 m at nanometer precision, and large-format machine tools can have 10–30 m strokes.
Long-travel design considerations:
- Tensile load at the carrier take-off point: A 10 m carrier filled with cable weighs 5–15 kg. At the moving end, the entire weight of the cable in the carrier pulls on the clamp point. Kevlar tensile fillers carry this load — not the copper conductors
- Cable sag in the carrier: Long horizontal carriers experience cable sag between support points. The sag creates non-uniform bend stress. Higher tensile reinforcement and optimized carrier support spacing address this
- Heat buildup in long carriers: Friction over long travels generates heat that cannot dissipate easily from the middle of the carrier. PUR jacket is specified partly for thermal stability — it maintains mechanical properties at elevated temperature better than PVC
Why Choose Yichi Cable Linear Motor?
- Motor-specific configuration: Send us your linear motor manufacturer and model. We match the Hall sensor pinout, thermal sensor type (PTC, KTY, PT100), and power cross-section to your motor datasheet — not a generic "one-size-fits-many" cable
- Hall sensor signal integrity tested: Every production batch is tested for power-to-signal crosstalk at the motor's PWM switching frequency — we verify that the Hall sensor signals remain clean at full motor power
- PET fleece inter-layer as standard: The power-to-signal isolation layer is standard on every linear motor cable — not an extra-cost option
- Pre-assembled with connectors: Motor-specific connectors (M23, M40, M58 power + M17, M23 signal) pre-assembled and tested — plug and commission, no field wiring