Module-3-Grippers

Robot End Effectors

• Overview: Devices attached to a robot’s wrist to perform specific tasks, ranging from handling parts to spray painting.

Definition and Functionality

• Definition: End effectors are specialized tools enabling robots to execute tasks.

• Common Applications:

  • Work part handling

  • Spot welding

  • Spray painting

• Custom Engineering: Typically designed by the robot owner or the manufacturing company.

Categories of End Effectors

• Grippers: Used for grasping and manipulating objects.

• Tools: Used for performing processes, e.g., welding or painting.

Types of Grippers

General Classification

• Mechanical Grippers

• Electromagnetic Grippers

• Pneumatic Grippers

• Hydraulic Grippers

• Vacuum/Suction Cups

• Adhesive Grippers

• Hooks

• Scoops

Mechanical Grippers

• Functionality: Commonly used to grasp objects, particularly in confined spaces.

• Motion: Can move in parallel or angular paths using mechanical linkages, gears, or pneumatic actuators.

Electric Grippers

• Recent Development: New technology, becoming more cost-effective.

• Characteristics:

  • Ideal for high-speed applications and light to moderate grip forces.

  • Cleaner than pneumatic/hydraulic grippers, suitable for clean rooms.

Pneumatic Grippers

• Advantages:

  • High gripping force in a compact size.

  • Clean operation, suitable for manufacturing settings.

• Cost-Effectiveness: Common due to accessibility to compressed air.

Hydraulic Grippers

• Advantages:

  • Excellent gripping power, ideal for heavy lifting.

• Disadvantages: Higher costs, less accuracy, unsuitable for clean rooms.

Gripper Design

• Grippers may have two, three, or four fingers.

• Common Use: Two-fingered grippers are the most common; however, multi-fingered variants exist.

• Grip Mechanics:

  • Applies friction-based force to lift objects.

  • Not suitable for delicate/brittle objects.

Vacuum Grippers

• Functionality: Utilize a vacuum pump to create suction, useful for grasping flat objects.

• Specifications: Suction cups made of rubber-like material; can withstand temperatures up to 200°C.

Magnetic Grippers

• Operation: Use magnetic attraction to grasp ferrous materials; relies on electric power for operation.

• Advantages: Small size, high holding power; easy control.

• Disadvantages: Potential issues with residual magnetism and multi-sheet lifting.

Adhesive Grippers

• Material: Use adhesive substances for gripping.

• Reliability: Effectiveness diminishes over repeated use.

• Suitability: Good for limited power applications; versatile and cost-effective.

Gripper Mechanisms

• Types:

  • Pivoting Mechanism: Commonly employed in mechanical grippers for industrial robots, involving slider-crank mechanisms.

  • Translational Mechanism: Utilizes gear-and-rack configurations for finger movement.

Gripper Force Analysis

• Objective: To convert input power into required motion and force to grasp objects.

• Key Elements:

  1. Design grips that enclose objects properly.

  2. Ensure the applied force overcomes gravity and other forces during holding.

• Formula for Gripping Force:

  [ F_g = mg \sin(\theta) \mu n ]

  • where

    • m = Mass (kg)

    • g = Gravity (m/s²)

    • \mu = Coefficient of friction

    • \theta = Angle with horizontal

    • n = Number of contact surfaces

Practical Example

• Scenario: A 5 kg block lifted vertically at 1 m/s with specific conditions requires force analysis to prevent slippage:

  • Formula Application: Calculated minimum force = 194.1 N.

Tools as End Effectors

• Common tools include spot welding guns, arc welding tools, spray painting guns, and automated assembly tools.

• Tools act as end-effectors and are attached to the mounting plate for operation.

Summary of Tools

• Typical examples include:

  • Spot Welding Gun

  • Arc Welding Tool

  • Spray Painting Gun

  • Rotating Spindles for drilling

  • Automatic Screwdrivers

  • Heating Torches

  • Water Jet Cutting Tools