I. PLC (Programmable Logic Controller) and Real-time Control
PLC Overview
- Control computer specifically designed for industrial environments
- Characteristics: industrial-grade reliability, modular structure, cyclic scan working mode (typical scan cycle 10-100ms)
- Typical applications: automotive assembly lines, packaging machinery, building automation
Role of PLC in Robot Control
- Production line level control: coordinate multiple robot workstations, manage peripheral devices, implement safety interlock
- Collaborate with robot controller: communicate via industrial buses (ProfiNet, EtherCAT)
Communication Protocol Comparison
| Protocol Type | Transmission Rate | Typical Applications |
|---|---|---|
| Modbus TCP | 100Mbps | Simple device control |
| EtherNet/IP | 1Gbps | Automotive production line |
| PROFINET IRT | Real-time <100μs | Precision synchronized control |
Real-time Control Architecture
| Layer | Control Cycle | Responsibilities |
|---|---|---|
| Upper PLC | 10-100ms | Production process management, exception handling, data collection |
| Lower motion controller | 0.1-1ms | Multi-axis interpolation, torque compensation, vibration suppression |
II. Embedded and Distributed Architecture
Distributed Joint Control
- Represented by UR5 collaboration, each joint integrates independent drive and control modules (STM32H7+DRV8320)
- Data exchange with main controller via CANopen/EtherCAT
- Three major advantages: simplified electrical wiring, distributed computing load, easy maintenance
Safety Control Integration
- Collaborative robot safety standard ISO/TS 15066 requires collision detection response within 10ms
- Mainstream solutions use dual closed-loop design: position loop (1kHz) + torque loop (8kHz bandwidth)
Real-time Requirements
- Hard real-time system: control cycle jitter <50μs, bus communication delay <1ms
- Key technologies: time-triggered architecture (TTA), priority preemptive scheduling, memory locking mechanism
III. Operating System (ROS)
Functional Completeness
- Complete communication mechanisms (topics, services, actions)
- Rich function packages (navigation, motion planning, vision processing)
- Typical applications: SLAM mapping, robotic arm grasping, autonomous navigation
Development Convenience
- Cross-platform support (Linux, Windows, MacOS)
- Over 100,000 developers globally
- Saves 30%-50% time compared to traditional development
Notes
- ROS itself is not a hard real-time system
- Communication delay typically in milliseconds
- Typical layering in industrial applications: high-level ROS for task planning + low-level RTX/control card for servo control
IV. Control Algorithms
Basic Components
- PID closed-loop control for each joint motor
- Most robot joint servo systems use PID or its improved versions
Performance Enhancement Technologies
- Model feedforward control (based on robotic arm dynamics model)
- Friction compensation technology
Advanced Algorithms
- Sliding mode control, H∞ control, adaptive control
V. MPC (Model Predictive Control)
Core Principle
- Real-time solving of optimization problems at each control cycle
- Calculate optimal control inputs by predicting future system behavior
Main Advantages
- Can explicitly handle system constraints (joint torque/speed limits, avoid singular poses)
- Can optimize various control performance indicators
Typical Applications
- Robotic arm obstacle avoidance trajectory tracking: maintain high precision in complex assembly paths
- Robotic arm force control: dynamically adjust force in pin insertion assembly
VI. Force and Compliance Control Technology
Impedance Control and Admittance Control
- Core principle: introduce spring-damping model, enabling robotic arm to intelligently adjust when contacted with external forces
- Relies on real-time force sensor feedback
- Achieve constant force pressing or flexible obstacle avoidance functions
Application Scenarios
- Assembly, grinding, polishing and other processes
- Collaborative robot millisecond-level force release protection mechanism
VII. Safety Control System
Motion Monitoring System
- Dynamic limits: single axis speed not exceeding 120% of rated value, acceleration 0.5-2m/s²
- Electronic fencing function: preset workspace geometric boundaries through 3D modeling
Collision Protection Mechanism
- Based on motor current ripple analysis (10kHz sampling, identification within 5ms)
- Three-level response: contact warning (50N) → deceleration buffer (150N) → emergency stop (300N)
Collaborative Safety Configuration
- Complies with ISO/TS 15066 standard
- Maximum power limit below 80W
- End effector linear velocity ≤0.25m/s
Safety System Verification
- V-shaped development process
- FMEA analysis during design phase
- 1,000-hour durability testing during prototype phase
- MTBF can reach 50,000 hours