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

  1. Production line level control: coordinate multiple robot workstations, manage peripheral devices, implement safety interlock
  2. Collaborate with robot controller: communicate via industrial buses (ProfiNet, EtherCAT)

Communication Protocol Comparison

Protocol TypeTransmission RateTypical Applications
Modbus TCP100MbpsSimple device control
EtherNet/IP1GbpsAutomotive production line
PROFINET IRTReal-time <100μsPrecision synchronized control

Real-time Control Architecture

LayerControl CycleResponsibilities
Upper PLC10-100msProduction process management, exception handling, data collection
Lower motion controller0.1-1msMulti-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

  1. Can explicitly handle system constraints (joint torque/speed limits, avoid singular poses)
  2. 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