Hollow Rotary Direct Drive Motors (also called Hollow Shaft DDR Motors or Hollow Bore Torque Motors) eliminate mechanical transmission components (gears, belts, couplings) by directly integrating torque generation into a rotating assembly with a central bore. These motors are widely used in precision automation, robotics, semiconductor equipment, and medical devices.
Hollow Bore Diameter: Must accommodate cables, pipes, or optical paths (typical range: 20mm–300mm).
Rotor/Stator Configuration:
• Outer Rotor Design (common): Higher torque density, better heat dissipation.
• Inner Rotor Design: Compact, suitable for limited-space applications.
Bearing System:
• Crossed Roller Bearings (high rigidity, axial/radial load support).
• Angular Contact Bearings (high-speed applications).
Torque Density: High-torque permanent magnet (PM) designs (up to 500 Nm+).
Cogging Torque Minimization: Critical for smooth motion (skewed magnets/slotless designs).
Cooling Methods:
• Natural Convection (low-power).
• Liquid Cooling (high-power industrial use).
Encoder Feedback: High-resolution absolute encoders (e.g., 23-bit) for precision.
Compatibility: Direct mounting to stages or robotic joints (flange standards: ISO 9409-1).
Drive Electronics: Requires matched servo amplifier (e.g., EtherCAT/CANopen).
|
Application |
Key Requirements |
Example Motor Specs |
|
Semiconductor Wafer Handling |
Ultra-clean, high precision |
50 Nm, 0.1 arc-min repeatability |
|
Robotic Joint (Cobot Arm) |
Compact, low cogging |
10 Nm, hollow Ø40mm |
|
Optical Rotary Stage |
High angular accuracy |
20 Nm, ±1 arc-sec error |
|
Medical Imaging (CT/MRI) |
Non-magnetic, backlash-free |
Titanium housing, 5 Nm |
► Torque (Continuous/Peak) – Determines load capacity.
► Hole Diameter – Must fit internal cabling.
► Speed (RPM) – Trade-off with torque (higher speed = lower torque).
► Accuracy/Repeatability – Encoder-dependent (e.g., ±0.001°).
► Mounting Interface – Flange type (e.g., H7 tolerance hub).
• IP Rating (e.g., IP65 for dust/water resistance).
• Vacuum Compatibility (semiconductor tools).
• Temperature Range (e.g., -20°C to 80°C).
|
Brand |
Series |
Notable Features |
|
Kollmorgen |
DDR (e.g., DDR-060) |
High torque (up to 400 Nm), modular design |
|
ETEL |
TMB+ |
Ultra-low cogging, <1 arc-min ripple |
|
Yaskawa |
SGM7G (Hollow Shaft) |
EtherCAT support, 1,000–3,000 RPM |
|
Hiwin |
HR Series |
Cost-effective, Ø30–200mm bore |
|
Beckhoff |
AM8000 |
Integrated servo drive, 50–250 Nm |
Alignment: Use dowel pins/laser alignment to minimize eccentricity.
Load Mounting: Avoid overhung loads to prevent bearing wear.
Cable Routing: Use slip rings if continuous rotation >360° is needed.
EMI Shielding: Critical for encoder signal integrity.
Bearing Lubrication: Grease life typically 20,000+ hours.
Encoder Cleaning: Prevent dust buildup in optical encoders.
|
Motor Type |
Pros |
Cons |
Price Range |
|
Standard Hollow DDR |
Balanced performance |
Moderate cogging |
$2,000–$10,000 |
|
Ultra-Precision |
<0.5 arc-min error |
3–5× higher cost |
$15,000–$50,000 |
|
Budget (Hiwin/Lead) |
Low cost, Ø<50mm |
Limited torque/speed |
$800–$3,000 |
• For Precision Automation: ETEL TMB+ (best accuracy).
• For Robotics: Kollmorgen DDR (modular, high torque).
• Cost-Sensitive OEMs: Hiwin HR Series.
Would you like help matching a motor to a specific payload or motion profile? Contact with us for your direct drive motor request.
