One of the most important areas in the design of Robot systems is the design of end effectors[4]. Most of the problems that occur in production are caused by badly designed tooling and not by faults in the robots. There are many different types of gripper available along with the vast number of specialist tools for nut running, arc welding, paint spraying etc. These grippers are not used solely with Robots however. They can be used for fixturing components anywhere in an automated or semi-automated line.

Gripper Types
The most commonly used grippers are finger grippers. These will generally have two opposing fingers or three fingers like a lathe chuck. The fingers are driven together such that once gripped any part is centred in the gripper. This gives some flexibility to the location of components at the pick-up point. Two finger grippers can be further split into parallel motion or angular motion fingers.
For some tasks however where flexible or fragile objects are being handled the use of either vacuum or magnetic grippers is preferable. With these the surface of the gripper is placed in contact with the object and either a magnetic field or a vacuum is applied to hold them in contact. Any errors in placement of the object at the pick-up point will be reflected in a similar error at the destination so these grippers are not usually used for high accuracy applications.

Accessories
Along with a wide range of standard grippers being available there are also a number of standard accessories for mounting them. If motion of the gripper is required which cannot easily be provided by the robot then this can be provided in the end effector. Linear and rotary units are available in many different configurations. The linear units tend to be used where reaching into confined spaces is required while the rotary units are often used where more than one gripper is mounted to switch from one to the other.
Another mechanism that is frequently used is a collision detection system. A collision detection unit works in the same manner as a probe on a co-ordinate measuring machine. It is attached between the robot flange and the end effector. The device consists of two plates held together by a spring. The two plates contact each other at three electrical contacts arranged in a triangle. These contacts are wired in series such that any motion of one plate relative to the other will cause the circuit to break. This circuit can then be wired either to the emergency stop circuit of the robot or an interrupt in the program.
Where more than one job is being performed by a robot and all of the necessary tools cannot be assembled together, it may be necessary to use a tool changer. Devices exist such that all of the services to the tools (electricity, air, etc.) can be fed through the changer so that a tangle of different wires, pipes etc does not have to exist for each different tool. Where possible however it is preferable not to use tool changers as they add weight to the end-effectors and cause an increase in cycle time when changes are required.

Gripper Drives
The same options are available for grippers as for robots. The most popular one here is pneumatic however because of the ease with which it can be supplied to the end of a robot arm and controlled. The only disadvantages of pneumatics are that it has a slightly lower Power to weight ratio than hydraulics and it is not as controllable or easy to feed as electricity. In most situations however these are not important.

Next >> Types of directional Co-ordinate Systems

Tech Materials (Free)

Robot Behaviors Exploring the T-Maze: Evolving Learning-Like Robot Behaviors using CTRNNs
Humanoid Robotics A Biochemical Subsystem for a Humanoid Robot
Industrial Automation Systems Applying Agents for Engineering of Industrial Automation Systems
Robot Team Cooperation A Descriptive Model of Robot Team and the Dynamic Evolution of Robot Team Cooperation
Kuka Robots For ONU ONU Robotics Technology Center of Excellence, powered by KUKA Robotics Corporation
Augmented reality Annotation System for Robotic Application
Modular Robots Self-Reconfiguration Planning Of Identical Modules
Autonomous robots A New Approach To Robotics
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Calibration of Industrial Robots A Photogrammetric Robot Calibration System Based On Off-The-Shelf Low Cost Hardware Components

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Amazon Books

	Creative Projects with LEGO Mindstorms by Benjamin Erwin Buy new: $20.64 / Used from: $13.00 A good place to start, especially for kids, with Lego Mindstorms
	A Practical Guide to Behavior-Based Robotics by Joe Jones Buy new: $20.67 / Used from: $15.13 Very good for programming not so much behavior as control. Language and controller agnostic