P1 Humanoid Arm: Technical Engineering Brief
Validated Design: Actuator Sizing, Reliability, and Kinematic Structure
Core Mechanical Performance Targets
At full 900mm extension
Shoulder to Gripper Tip
3 Shoulder, 3 Elbow, 2 Wrist, 1 Gripper
Design Basis (Endurance Testing)
Kinematic Architecture & Modular Breakdown
The arm is modularized into four main assemblies, each housing actuators and sensors to achieve the total 9 Degrees of Freedom. This structure is critical for simplified manufacturing and repair.
Component Cost Segmentation
The majority of the $\$2,045$ unit cost is concentrated in high-precision, low-backlash actuation components. This intentional expenditure ensures the joint life and high payload capacity requirements are met.
- Precision Gearing (Harmonic Drives)
- Frameless Motors (Shoulder/Elbow)
- Servos (Wrist/Gripper)
- Structural/Electronics
Actuator Sizing and Safety Factor Validation
The required continuous torque to hold the $5.0\text{ kg}$ payload at $900\text{ mm}$ reach is $\mathbf{0.562\text{ Nm}}$ at the motor shaft. The revised $\mathbf{1.0\text{ Nm}}$ continuous motor ensures a robust $\mathbf{1.78\times}$ safety margin.
Shoulder Torque Demand vs. Reach
The blue curve shows the required torque to hold a 5kg payload (static load) as a function of arm extension. The green dashed line indicates the continuous capacity of the motor (C11-01) mapped back to the joint, confirming significant operational headroom.
Actuator Safety Margin Audit
Comparison of loads vs. motor ratings. The **Continuous Rated** torque (1.0 Nm) provides $1.78\times$ the required holding torque (0.562 Nm), exceeding the $1.5\times$ requirement. Peak margin is $2.79\times$.
Risk Reduction: FMEA & DfR Actions
The Failure Mode and Effects Analysis (FMEA) highlighted "Cable Chafe" and "Fastener Loosening" as critical risks with high initial Risk Priority Numbers (RPN > 100). The implementation of Design for Reliability (DfR) actions, such as reinforced cable conduit and standardized thread-locking procedures, drastically reduced these risks.
Design Verification Testing (DVT) Roadmap
The DVT plan is segmented into four phases to ensure complete verification against all mechanical and environmental specifications before mass production approval.
Phase 1: Environmental
Verify material stability and component function across operational extremes.
- Thermal Cycle: -40°C to 85°C
- Humidity: 95% RH for 96 Hrs
Phase 2: Shock & Vibration
Validate fastener and connector integrity under typical transportation and operational forces.
- Shock: 30g, 11ms Half-Sine
- Vibration: 0.04 g²/Hz Random
Phase 3: Endurance Cycling
Simulate lifetime operation to confirm the 1M cycle target and assess wear on gears/bearings.
- Target: 30,000 Cycles (Accelerated)
- Load: 5.0 kg Full Payload
Phase 4: Functional Audit
Final performance metrics measured on the tested units.
- Hysteresis: $\le 5$ arcmin
- Repeatability: $\le 0.1\text{ mm}$
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