Robotics

Definition of Robot

Robot: A reprogrammable, multifunctional manipulator designed to move material, parts, tools, or specialized devices through various programmed motions for the performance of a variety of tasks.

Industrial Robot: An automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes, which may be either fixed in place or mobile for use in industrial automation applications.

Key Characteristics

1. Reprogrammable: Can be programmed to perform different tasks
2. Multifunctional: Capable of various operations
3. Manipulator: Physical mechanism for moving and positioning
4. Programmable motions: Follows programmed paths
5. Versatile: Performs variety of tasks

Robot Anatomy

Main Components:

1. Manipulator/Mechanical Unit

   • The physical structure that performs the work
   • Consists of links and joints
   • Provides movement and positioning

2. Power Supply

   • Provides energy for robot operation
   • Types: Electric, Hydraulic, Pneumatic

3. Controller

   • The "brain" of the robot
   • Stores programs and controls movements
   • Processes sensor data

4. End Effector

   • Tool attached to the end of the manipulator
   • Performs the actual work
   • Examples: Grippers, welding torches, spray guns

Robot Joints and Links

Joints (Axes)

• Linear Joint (Type L): Sliding motion along an axis
• Orthogonal Joint (Type O): Rotational motion perpendicular to adjacent joint
• Rotational Joint (Type R): Rotational motion around an axis
• Twisting Joint (Type T): Rotational motion parallel to adjacent joint
• Revolving Joint (Type V): Rotational motion around a vertical axis

Links

• Rigid members connecting joints
• Provide structural support
• Determine reach and workspace

Robot Configurations

1. Cartesian/Gantry Robot (TTT or LLL)

• Three linear joints (X, Y, Z axes)
• Rectangular work envelope
• High precision and repeatability
• Easy to program
• Applications: Pick and place, assembly, material handling

2. Cylindrical Robot (TLR or LLR)

• One rotational joint at base
• Two linear joints
• Cylindrical work envelope
• Good for assembly operations
• Applications: Assembly, machine loading, spot welding

3. Spherical/Polar Robot (TRR or RRL)

• One rotational joint at base
• Two rotational joints
• Spherical work envelope
• Large reach
• Applications: Material handling, machine loading, spot welding

4. Articulated/Jointed-Arm Robot (TRR or RRR)

• Three rotational joints
• Most flexible configuration
• Complex work envelope
• Resembles human arm
• Applications: Welding, painting, assembly, material handling

5. SCARA Robot (Selective Compliance Assembly Robot Arm) (RRT)

• Two rotational joints in horizontal plane
• One linear joint (vertical)
• Rigid in Z-axis, compliant in XY plane
• Fast and accurate for assembly
• Applications: Assembly, pick and place, packaging

6. Parallel/Delta Robot

• Multiple arms working together
• Very high speed
• Limited workspace
• Excellent for pick and place
• Applications: Packaging, sorting, high-speed assembly

Degrees of Freedom (DOF)

Degrees of Freedom: The number of independent motions a robot can make.

• Minimum DOF for positioning: 3 (X, Y, Z)
• Minimum DOF for positioning and orientation: 6 (X, Y, Z, Roll, Pitch, Yaw)
• Redundant DOF: More than 6, provides flexibility and obstacle avoidance

DOF Breakdown:

• 3 DOF: Position in 3D space (X, Y, Z)
• 3 DOF: Orientation (Roll, Pitch, Yaw)
• Total: 6 DOF for complete spatial control

Work Envelope/Work Volume

Work Envelope: The three-dimensional space within which the robot can position its end effector.

Factors affecting work envelope:

• Robot configuration
• Link lengths
• Joint ranges
• Physical constraints

Different configurations produce different shaped envelopes:

• Cartesian: Rectangular box
• Cylindrical: Cylinder
• Spherical: Sphere
• Articulated: Complex irregular shape

Robot Drive Systems

1. Electric Drive

Advantages:

• High precision and repeatability
• Easy to control
• Clean operation
• Low maintenance
• Energy efficient

Disadvantages:

• Limited power for heavy loads
• More expensive for high power

Applications: Assembly, electronics, precision work

2. Hydraulic Drive

Advantages:

• High power-to-weight ratio
• Can handle heavy loads
• Smooth motion
• Good for large robots

Disadvantages:

• Requires hydraulic system (pump, reservoir, lines)
• Potential for leaks
• Higher maintenance
• Noisy operation

Applications: Heavy material handling, forging, large-scale operations

3. Pneumatic Drive

Advantages:

• Simple and inexpensive
• Fast operation
• Clean (if air leaks)
• Safe in explosive environments

Disadvantages:

• Limited precision
• Difficult to control position accurately
• Limited to light loads
• Compressibility of air causes issues

Applications: Pick and place, simple assembly, light material handling

End Effectors

Types:

1. Grippers

• Mechanical Grippers: Fingers that close mechanically
  • Two-finger grippers
  • Three-finger grippers
  • Multi-finger grippers
• Vacuum Grippers: Use suction to hold objects
• Magnetic Grippers: Use magnets for ferrous materials
• Adhesive Grippers: Use adhesive materials

2. Tools

• Welding torches: For arc welding, spot welding
• Spray guns: For painting, coating
• Drilling tools: For drilling operations
• Cutting tools: For cutting, trimming
• Grinding tools: For finishing operations

3. Sensors

• Force/Torque sensors: Measure forces and torques
• Vision systems: For inspection and guidance
• Proximity sensors: Detect object presence
• Tactile sensors: Sense touch and pressure

Robot Control Systems

Control Levels:

1. Joint-Level Control

• Controls individual joint positions
• Basic level of control
• Uses feedback from joint encoders

2. End-Effector Control

• Controls position and orientation of end effector
• Requires coordinate transformation
• More intuitive for programming

Control Methods:

1. Point-to-Point (PTP) Control

• Robot moves from one point to another
• Path between points not controlled
• Fastest method
• Used for pick and place, spot welding

2. Continuous Path (CP) Control

• Entire path is controlled
• Smooth motion along trajectory
• Used for welding, painting, sealing

3. Controlled Path

• Combination of PTP and CP
• Specific points with controlled segments

Robot Programming Methods

1. Lead-Through Programming/Teaching

• Operator physically moves robot through desired path
• Robot records positions
• Simple and intuitive
• Limited to simple tasks

2. Powered Lead-Through/Walk-Through

• Use teach pendant to move robot
• Record positions and motions
• Most common method
• Good for complex paths

3. Off-Line Programming

• Program created on computer
• Simulation before actual use
• No production downtime
• Requires accurate models
• More complex but more flexible

4. Task-Level Programming

• High-level commands
• Robot determines how to accomplish task
• Requires AI and advanced sensors
• Still under development

Robot Sensors

1. Internal Sensors

• Position sensors: Encoders, resolvers
• Velocity sensors: Tachometers
• Acceleration sensors: Accelerometers
• Monitor robot's own state

2. External Sensors

• Vision systems: Cameras for object recognition
• Force/Torque sensors: Measure interaction forces
• Proximity sensors: Detect nearby objects
• Tactile sensors: Sense contact
• Range sensors: Laser, ultrasonic for distance
• Monitor environment and workpiece

Robot Accuracy and Repeatability

Accuracy

• How close the robot gets to the commanded position
• Affected by:
  • Mechanical tolerances
  • Calibration
  • Thermal effects
  • Load variations

Repeatability

• How consistently robot returns to same position
• Usually better than accuracy
• Typical values: ±0.05mm to ±0.5mm
• Critical for manufacturing applications

Note: Repeatability is typically much better than accuracy in industrial robots.

Applications of Industrial Robots

1. Material Handling

• Pick and place: Moving parts between locations
• Machine loading/unloading: Feeding machines
• Palletizing: Stacking products on pallets
• Packaging: Placing items in containers

2. Processing Operations

• Spot welding: Joining metal sheets
• Arc welding: Continuous weld seams
• Spray painting: Coating surfaces
• Cutting: Laser, water jet, plasma cutting
• Grinding/Deburring: Surface finishing
• Drilling: Making holes

3. Assembly

• Part insertion: Placing components
• Fastening: Screwing, riveting
• Adhesive application: Applying glue
• Press fitting: Forcing parts together

4. Inspection

• Visual inspection: Using cameras
• Dimensional measurement: Checking sizes
• Quality control: Verifying specifications

Advantages of Industrial Robots

1. Increased productivity: Work 24/7 without breaks
2. Improved quality: Consistent performance
3. Flexibility: Reprogrammable for different tasks
4. Safety: Handle dangerous operations
5. Reduced labor costs: Long-term cost savings
6. Precision: High accuracy and repeatability
7. Harsh environments: Work in extreme conditions
8. Reduced waste: Consistent operation reduces errors
9. Space efficiency: Can work in confined spaces
10. Data collection: Monitor and record operations

Disadvantages and Limitations

1. High initial cost: Expensive to purchase and install
2. Programming complexity: Requires skilled personnel
3. Maintenance requirements: Regular servicing needed
4. Limited flexibility: Compared to humans for complex tasks
5. Job displacement: Reduces need for human workers
6. Power requirements: Need reliable power supply
7. Safety concerns: Require safety measures and barriers
8. Limited sensory capability: Less adaptable than humans
9. Downtime impact: Breakdown affects production
10. Integration challenges: Must fit into existing systems

Robot Safety

Safety Measures:

1. Physical barriers: Fences, cages around work area
2. Light curtains: Invisible barriers that stop robot
3. Pressure mats: Floor sensors detect human presence
4. Emergency stops: Easily accessible stop buttons
5. Slow speed zones: Reduced speed near humans
6. Collaborative robots (Cobots): Designed to work safely with humans
7. Safety training: Proper operator training
8. Lockout/Tagout: Procedures for maintenance
9. Warning signs: Clear marking of robot work areas
10. Regular inspections: Check safety systems

Collaborative Robots (Cobots)

Cobots: Robots designed to work alongside humans safely.

Features:

• Force limiting: Stop when encountering resistance
• Speed limiting: Operate at safe speeds
• Rounded edges: No sharp corners
• Lightweight: Less mass reduces impact force
• Easy programming: User-friendly interfaces
• Sensors: Detect human presence
• No barriers needed: Can work in shared space

Applications:

• Assembly assistance
• Quality inspection
• Machine tending
• Packaging
• Material handling

Future Trends in Robotics

1. Artificial Intelligence: Smarter decision-making
2. Machine Learning: Robots that improve with experience
3. Advanced sensors: Better perception of environment
4. Cloud robotics: Shared learning and data
5. Soft robotics: Flexible, compliant robots
6. Swarm robotics: Multiple robots working together
7. Human-robot collaboration: More cobots
8. Mobile manipulation: Robots that move and manipulate
9. Autonomous systems: Self-directed robots
10. Digital twins: Virtual models for simulation and optimization

Economic Considerations

Factors in Robot Justification:

1. Labor savings: Reduced workforce costs
2. Productivity increase: Higher output
3. Quality improvement: Reduced defects and rework
4. Flexibility: Ability to change products
5. Safety benefits: Reduced injuries and insurance costs
6. Consistency: Predictable performance
7. Payback period: Time to recover investment
8. Return on Investment (ROI): Overall financial benefit

Cost Components:

• Capital cost: Robot purchase price
• Installation cost: Setup and integration
• Programming cost: Initial programming
• Training cost: Operator training
• Maintenance cost: Ongoing servicing
• Operating cost: Energy, consumables
• Downtime cost: Lost production during failures