5.1 Serial and parallel manipulator architectures
3 min read•july 25, 2024
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, , 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 .
Manipulator Architectures
Serial vs parallel manipulator architectures
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- Serial manipulators
- Open with joints connected in series forms structure
- Large allows for greater reach and flexibility in task execution
- High 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 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
- , 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:
- determines end-effector position from joint angles
- calculates joint angles for desired end-effector position
- Common configurations include:
- 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 lengths
- Inverse kinematics determines actuator lengths for desired platform pose
- Common configurations encompass:
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
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Design process entails:
- Define manipulator specifications based on application requirements
- Create 3D models of robot components using CAD software
- Implement kinematic and dynamic models in simulation environment
- 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 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:
- Analyze task requirements and constraints
- Compare manipulator characteristics to application needs
- Consider trade-offs between different architectures (workspace vs precision)
- Recommend optimal manipulator type for given application based on analysis
Key Terms to Review (18)
Actuator: An actuator is a crucial component in robotic systems that converts energy, typically electrical or hydraulic, into physical motion. It plays a vital role in enabling robots to perform tasks by moving parts like joints or limbs. Actuators are responsible for providing the necessary force and motion, allowing robots to interact with their environment effectively and execute complex movements.
Degrees of Freedom: Degrees of freedom refer to the number of independent parameters or movements that a mechanical system can undergo. In robotics, it specifically indicates how many distinct ways a manipulator can move, which affects its ability to position and orient its end effector in space. Understanding degrees of freedom is essential for tasks like inverse kinematics, controlling velocities, assessing manipulator structures, and navigating configuration spaces with obstacles.
Dexterity: Dexterity refers to the skill and ease with which a manipulator can perform tasks, often relating to precision and control over movement. In the context of robotic manipulators, dexterity encompasses both the ability to reach and grasp objects effectively, as well as the capability to perform complex movements with finesse. This skill is crucial for applications requiring intricate manipulation and adaptation to varying tasks.
End Effector: An end effector is the device at the end of a robotic arm that interacts with the environment, serving as the tool or means by which the robot accomplishes its tasks. This can include grippers, claws, or specialized tools designed for specific applications, and understanding end effectors is crucial for designing robots capable of performing various functions. Their design and functionality significantly influence the robot's performance and effectiveness in executing precise movements.
Forward Kinematics: Forward kinematics is the process of calculating the position and orientation of a robot's end effector based on the joint parameters, such as angles and displacements. This process is crucial for understanding how movements in a robotic system relate to its physical configuration, enabling precise control and manipulation in various applications.
Industrial automation: Industrial automation refers to the use of control systems such as computers or robots for handling different processes and machinery in an industry to replace human intervention. This technology enhances efficiency, precision, and safety in manufacturing and other industrial sectors. It integrates various components, including sensors, actuators, and robots, to automate tasks traditionally performed by humans, enabling higher production rates and consistent quality.
Inverse Kinematics: Inverse kinematics is the process of calculating the joint parameters needed to place the end-effector of a robotic arm or manipulator at a desired position and orientation in space. This technique is essential for controlling robotic systems, as it allows for precise movement and positioning based on the goals set by a user or program.
Joint Limits: Joint limits refer to the maximum and minimum angles or positions that a robot's joints can achieve during movement. These limits are critical for ensuring that the robot operates safely and effectively, as exceeding them can lead to mechanical failure or damage. Understanding joint limits helps in designing robotic systems, analyzing their workspaces, and generating smooth and safe trajectories for movement.
Kinematic Chain: A kinematic chain is a series of interconnected links and joints that create a mechanical system capable of producing movement. This concept is crucial in understanding how robots and manipulators translate motion from input to output through their configurations. The arrangement and type of joints within the kinematic chain determine the degrees of freedom, which directly affect the capabilities and limitations of the robotic system.
Parallel manipulator: A parallel manipulator is a type of robotic system where multiple actuators work together to control a common end-effector, allowing for increased stability and precision. Unlike serial manipulators, where joints are arranged in a chain, parallel manipulators use parallel kinematics, enabling them to handle larger loads and achieve higher accuracy. This unique architecture makes them ideal for applications requiring high rigidity and speed.
Payload capacity: Payload capacity refers to the maximum weight a robot can carry or manipulate while performing its designated tasks. This term is essential as it determines the robot's effectiveness in various applications, influencing design choices, stability, and overall performance in real-world scenarios. The payload capacity is also closely linked to the type of actuators used, the structure of the manipulator, and the intended function of the robot.
PID Control: PID control is a widely used control loop feedback mechanism that stands for Proportional, Integral, and Derivative control. This technique helps maintain a desired output in systems by continuously adjusting the input based on the difference between the desired setpoint and the measured process variable. It is integral to effectively managing the performance of various actuators, manipulators, and robots, making it essential for achieving precise control in automation.
Repeatability: Repeatability is the ability of a robotic system to consistently return to the same position and orientation when performing the same task multiple times. This concept is crucial in robotic manipulation as it ensures that tasks can be executed with high precision and reliability, which is essential for applications in manufacturing, assembly, and automation. High repeatability often indicates that the robot’s mechanical components are functioning correctly and that the control algorithms are effectively managing its movements.
Robotic surgery: Robotic surgery is a minimally invasive surgical technique that utilizes robotic systems to assist surgeons in performing complex procedures with enhanced precision, flexibility, and control. This method allows for smaller incisions, reduced blood loss, and quicker recovery times compared to traditional open surgery. The integration of advanced technology in robotic systems connects closely with various aspects of robotics, including the manipulation of force and impedance, the structural architecture of robotic arms, and the use of visual tracking systems for improved surgical outcomes.
Serial manipulator: A serial manipulator is a type of robotic arm where each joint is connected in a series, creating a chain-like structure. This design allows for a high degree of freedom in movement, enabling the manipulator to reach various positions in its workspace. Each joint typically provides one degree of freedom, allowing the end effector to perform complex tasks by combining the movements of all the joints sequentially.
Stiffness: Stiffness is a measure of a system's resistance to deformation when subjected to an applied force. In robotics, it plays a crucial role in determining how a manipulator or system reacts to external loads, influencing control strategies and the performance of tasks. Understanding stiffness helps engineers design systems that can effectively manage forces while maintaining desired positions and movements.
Trajectory Planning: Trajectory planning is the process of determining a path for a robot or manipulator to follow, along with the timing and control inputs necessary to execute that path smoothly. It involves calculating the motion that a robot needs to perform in order to achieve desired positions, velocities, and accelerations while considering constraints like obstacles and dynamics. In relation to different manipulator architectures, trajectory planning plays a crucial role in ensuring effective and efficient operation, whether the manipulator is configured serially or in parallel.
Workspace: Workspace refers to the total volume of reachable positions that a robotic manipulator can access through its movements. Understanding the workspace is essential as it directly impacts how effectively a robot can perform tasks in its environment and helps in the design and optimization of robotic systems.