5.1 Serial and parallel manipulator architectures

Manipulator architectures form the backbone of robotic systems, shaping their capabilities and applications. Serial manipulators offer flexibility and reach, while parallel manipulators excel in precision and stability. Understanding these differences is crucial for effective robot design and deployment.

Kinematics, degrees of freedom, and design considerations play vital roles in manipulator development. By analyzing these factors and using simulation tools, engineers can create robots tailored to specific industrial needs, balancing performance metrics like accuracy, speed, and payload capacity.

Manipulator Architectures

Serial vs parallel manipulator architectures

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  Dynamic Modeling and Torque Feedforward based Optimal Fuzzy PD control of a High-Speed Parallel ... View original

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  MS - Mechanism design and parameter optimization of a new asymmetric translational parallel ... View original

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• Serial manipulators
  • Open kinematic chain with joints connected in series forms structure
  • Large workspace allows for greater reach and flexibility in task execution
  • High dexterity enables complex movements and orientations (6-axis industrial robot arm)
  • Versatility in task execution adapts to various applications (welding, painting, assembly)
  • Lower payload capacity limits handling of heavy objects
  • Reduced accuracy due to error accumulation along the kinematic chain
  • Lower stiffness results in potential vibrations and deflections under load
• Parallel manipulators
  • Closed kinematic chain with multiple links connecting base to end-effector creates structure
  • Higher precision and accuracy achieved through distributed load and error compensation
  • Greater stiffness and stability ideal for high-precision tasks (machining, 3D printing)
  • Higher payload capacity supports heavy-duty applications (flight simulators, satellite positioning)
  • Limited workspace constrains operational range
  • More complex kinematics and control require advanced algorithms and computational power
  • Potential for singularities within workspace may cause loss of control or damage

Kinematics of robotic manipulators

• Degrees of freedom (DOF)
  • Number of independent parameters defining manipulator configuration
  • $DOF = n - j - 1$, n represents number of links and j represents number of joints
• Serial manipulators
  • Common configurations include:
    • 3-DOF SCARA robot for planar pick-and-place operations
    • 6-DOF articulated robot arm for complex spatial movements
  • Kinematic analysis involves:
    • Forward kinematics determines end-effector position from joint angles
    • Inverse kinematics calculates joint angles for desired end-effector position
• Parallel manipulators
  • Common configurations encompass:
    • Delta robot (3-DOF) for high-speed pick-and-place tasks
    • Stewart platform (6-DOF) for motion simulation and precision positioning
  • Kinematic analysis comprises:
    • Direct kinematics solves for platform pose given actuator lengths
    • Inverse kinematics determines actuator lengths for desired platform pose

Design of manipulator configurations

• Simulation software options

  • ROS (Robot Operating System) for comprehensive robotics development
  • MATLAB Robotics Toolbox for algorithm prototyping and analysis
  • V-REP (Virtual Robot Experimentation Platform) for realistic simulations

• Design process entails:

  1. Define manipulator specifications based on application requirements
  2. Create 3D models of robot components using CAD software
  3. Implement kinematic and dynamic models in simulation environment
  4. Develop control algorithms for desired manipulator behavior

• Simulation tasks encompass:

  • Workspace analysis to determine reachable space
  • Path planning and trajectory generation for efficient movements
  • Collision detection and avoidance to ensure safe operation
  • Performance evaluation under various conditions (load, speed, accuracy)

Suitability for industrial applications

• Performance metrics for evaluation:
  • Accuracy and repeatability measure precision of positioning
  • Workspace volume and shape define operational range
  • Payload capacity determines maximum load handling
  • Speed and acceleration affect cycle times
  • Stiffness and compliance influence stability and force control
• Industrial applications include:
  • Assembly and pick-and-place operations (electronics manufacturing)
  • Welding and painting (automotive industry)
  • Machining and material removal (aerospace components)
  • Packaging and palletizing (consumer goods)
• Application-specific considerations involve:
  • Task requirements (precision for microassembly, speed for packaging)
  • Environmental factors (cleanroom conditions, extreme temperatures)
  • Cost and maintenance considerations (initial investment, downtime)
  • Flexibility and reconfigurability needs (product line changes)
• Case-based evaluation process:
  1. Analyze task requirements and constraints
  2. Compare manipulator characteristics to application needs
  3. Consider trade-offs between different architectures (workspace vs precision)
  4. Recommend optimal manipulator type for given application based on analysis