The mechanical design of humanoid robots begins with understanding human biomechanics and anthropometry. WIA-ROB-019 establishes design guidelines based on human proportions, ensuring robots can navigate human environments and use human tools effectively.
The standard defines three size categories to accommodate different applications and design constraints:
| Category | Height Range | Weight Range | Applications |
|---|---|---|---|
| Compact | 100-140 cm | 15-40 kg | Research, education, child interaction, confined spaces |
| Standard | 150-180 cm | 40-80 kg | Service, healthcare, general applications |
| Industrial | 180-210 cm | 80-150 kg | Heavy manipulation, construction, disaster response |
Within each category, proportions should approximate human ratios to maintain natural appearance and functional compatibility:
Proper mass distribution is critical for balance and energy efficiency. The center of mass should be located approximately at the hip joint level (50-55% of total height from ground) with the robot in a neutral standing position. This placement minimizes the energy required to maintain balance and facilitates natural walking dynamics.
Each joint must provide sufficient range of motion (ROM) to enable natural human-like movement. WIA-ROB-019 specifies minimum ROM for each major joint:
| Joint | Motion | Minimum ROM | Typical ROM | Human ROM |
|---|---|---|---|---|
| Hip | Flexion/Extension | -20° to 90° | -30° to 120° | -30° to 140° |
| Hip | Abduction/Adduction | -15° to 30° | -20° to 45° | -30° to 50° |
| Hip | Internal/External Rotation | -20° to 20° | -30° to 30° | -45° to 45° |
| Knee | Flexion | 0° to 110° | 0° to 130° | 0° to 140° |
| Ankle | Dorsiflexion/Plantarflexion | -25° to 25° | -30° to 45° | -45° to 50° |
| Ankle | Inversion/Eversion | -10° to 10° | -20° to 20° | -35° to 25° |
| Joint | Motion | Minimum ROM | Typical ROM | Human ROM |
|---|---|---|---|---|
| Shoulder | Flexion/Extension | -30° to 120° | -45° to 180° | -60° to 180° |
| Shoulder | Abduction | 0° to 90° | 0° to 180° | 0° to 180° |
| Shoulder | Internal/External Rotation | -45° to 45° | -70° to 90° | -90° to 90° |
| Elbow | Flexion | 0° to 120° | 0° to 145° | 0° to 150° |
| Wrist | Flexion/Extension | -45° to 45° | -75° to 75° | -85° to 85° |
| Wrist | Pronation/Supination | -60° to 60° | -90° to 90° | -90° to 90° |
Material selection for humanoid robots involves balancing multiple competing requirements: strength, weight, cost, manufacturability, and aesthetic considerations. WIA-ROB-019 provides guidelines for appropriate material choices:
All structural components must undergo FEA to verify they meet safety factors under expected loading conditions. WIA-ROB-019 requires:
After FEA, critical components require physical testing to validate simulation results. This includes static load testing to 150% of maximum expected load, dynamic testing with representative load profiles, and accelerated fatigue testing. Documentation of all test results is required for WIA-ROB-019 certification.
Robot joints must provide controlled motion, support structural loads, and integrate sensors for position and force feedback. WIA-ROB-019 recognizes three primary joint architectures:
Motor directly connected to joint without gearing. Advantages include zero backlash, high bandwidth, and excellent force control through current sensing. Disadvantages are lower torque and higher cost due to larger motors. Primarily used in research platforms and applications requiring high-fidelity force control.
Design requirements:
Most common architecture, using harmonic drives, planetary gears, or cycloidal reducers to amplify motor torque. Reduction ratios typically 50:1 to 200:1. Harmonic drives offer zero backlash and high reduction ratios in compact packages but have limited backdrivability.
Design requirements:
Compliant element (spring) placed between motor/gearbox and joint output. The spring deflection is measured to determine applied torque, enabling precise force control and impact absorption. Particularly valuable for safe human-robot interaction.
Design requirements:
WIA-ROB-019 defines minimum actuator performance requirements for each joint class:
| Joint Class | Peak Torque | Continuous Torque | Max Speed | Power |
|---|---|---|---|---|
| Ankle (each axis) | 100-150 Nm | 40-60 Nm | 180°/s | 200-400 W |
| Knee | 150-250 Nm | 60-100 Nm | 240°/s | 300-600 W |
| Hip (each axis) | 150-250 Nm | 60-100 Nm | 180°/s | 300-600 W |
| Shoulder (each axis) | 40-80 Nm | 15-30 Nm | 240°/s | 100-250 W |
| Elbow | 40-80 Nm | 15-30 Nm | 240°/s | 100-250 W |
| Wrist (each axis) | 10-20 Nm | 4-8 Nm | 360°/s | 40-100 W |
| Hand (per finger) | 2-5 Nm | 0.5-2 Nm | 180°/s | 5-20 W |
Human hands perform diverse grasping strategies. WIA-ROB-019 identifies essential grasp types that humanoid robot hands should support:
The standard recognizes three hand complexity levels:
Simple parallel-jaw or adaptive gripper with 1-2 DOF. Suitable for structured environments with known objects. Cost-effective, reliable, limited versatility.
Specifications:
Underactuated design with 3-5 active DOF and passive compliance. Conforms to object shapes automatically. Good balance of capability, simplicity, and cost.
Specifications:
Anthropomorphic design with 12-20 active DOF enabling human-like manipulation. High cost and complexity, suitable for research and applications requiring fine manipulation.
Specifications:
The foot is critical for maintaining balance during standing and walking. WIA-ROB-019 specifies requirements for foot design:
The foot must incorporate force-torque sensors to measure ground reaction forces. Sensor placement options include:
Some degree of ankle compliance improves stability and reduces impact forces. Three approaches are recognized:
The torso houses critical components (batteries, computers, power electronics) while providing structural support and flexibility for natural motion.
WIA-ROB-019 recognizes two primary torso configurations:
Single rigid structure, simple and mechanically robust. Suitable for applications not requiring torso articulation. All body motion achieved through hip, shoulder, and neck joints.
Multiple segments (typically 2-3) connected by spine joints enabling:
Articulated torsos extend workspace, improve balance recovery, and enable more natural human-like motion. Trade-offs include added complexity, weight, and cost.
The torso must efficiently package heavy components while maintaining proper mass distribution:
The head serves primarily as a sensor platform housing cameras, microphones, and communication interfaces. Design priorities include:
The neck enables camera pointing and enhances social interaction through head gestures. Minimum requirements:
Proper cable management is essential for reliability and maintenance. WIA-ROB-019 requires:
Accurate kinematic models are essential for motion planning and control. Forward kinematics calculate end-effector position from joint angles using Denavit-Hartenberg parameters or equivalent representations. Inverse kinematics solve for joint angles to achieve desired end-effector poses—often with multiple solutions requiring optimization to select preferred configurations.
Dynamic models relate joint torques to motion, incorporating inertial properties, gravity, velocity-dependent effects (Coriolis, centrifugal), and friction. The equations of motion for an n-DOF robot:
M(q)q̈ + C(q,q̇)q̇ + G(q) + F(q̇) = τ
Where:
These models enable model-based control, simulation, and performance prediction. WIA-ROB-019 requires that dynamic models be validated through physical testing, with prediction accuracy within 10% of measured values for torques and 5% for energy consumption.
This chapter covered the mechanical design and biomechanical principles underlying humanoid robot development according to WIA-ROB-019. We examined anthropometric design guidelines, material selection, joint architecture, and specialized subsystems including hands, feet, torso, and head mechanisms.
Proper mechanical design is fundamental to achieving the performance, safety, and reliability required for real-world humanoid robot deployment. The specifications and guidelines in WIA-ROB-019 reflect accumulated best practices from decades of research and development.
In Chapter 3, we'll explore control systems and locomotion algorithms that bring these mechanical systems to life, enabling stable walking, balance recovery, and coordinated whole-body motion.