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ROBOTICS TECHNOLOGY
Robots
According to Robotics Industries Association (RIA)
"An industrial robot is a re-programmable, multi-functional manipulator designed to move materials, parts, tools, or special devices through variable programmed motions for the performance of a variety of task.
TYPES OF JOINTS
1) Linear Joint (L-joint):
The relative motion between the input and the output link is a linear sliding motion, with the axes of the two links being parallel.2) Orthagonal Joint (O-joint):
This is also a linear sliding motion, but the input and output links are perpendicular to each other during the move.3) Rotational Joint (R-joint):
This type of joint provides a rotational relative motion of the joints with the axis of rotation perpendicular to the axes of the input and output links.4) Twisting Joint (T-joint):
This joint also involves a rotary motion but the axis of rotation is parallel to the axes of two links.5) Revolving Joint (V-joint):
In this joint type, the axis of the input link is parallel to the axis of rotation of the joint, and the axis of the output link is perpendicular to the axis of rotation.
Control Resolution CR
CR refers to the capability of the robot controller and positioning system to divide the range of the joint into closely spaced points that can be identified by controller. These points are called addressable points.
Therefore CR is defined as the distance between adjacent addressable points.
Number of Addressable points = 2n
CR = Joint Range / 2n
Spatial Resolution (SR)
It combines the CR with the mechanical error in the joints and associated links. Mechanical error arise from such factors as gear backlash, deflection of the links etc.
SR = CR + 6 (Std. deviation of Mechanical Error)
Accuracy
Accuracy is a measure of the robots ability to position the end of its wrist at a desired location.
Accuracy = CR/2 + 3s
Repeatability
It is a measure of the robot's ability to position its end wrist at a previously taught point in the work volume.
Repeatability = 6s
END EFFECTORS
It is defined as the special device that attached to the manipulator wrist to enable the robot to complete a specific task. Because of wide variations in tasks that are performed by robot, the end effectors must usually be custom engineered and fabricated for a specific job. In the case of gripper, the part shape and size will vary for different application, this will influence the design of gripper.
Tools and grippers are two general categories of end effectors uses in robotics.
Tools are used in those application where the robot must perform some processing operation on the workpart. Examples of tools used as a end effector are
- Spot Welding gun
- Arc Welding tool
- Spray painting
- Heating torch
- Water jet cutting tool
Grippers are end effectors used to grasp and manipulate objects during the work cycle. the objects are usually workpart that are moved from one location to another. Machine loading and unloading applications fall in this category.
Examples of grippers are
- Mechanical grippers
- Vacuum gripper
- Magnetized devices
- Adhesive devices
SENSOR IN ROBOTICS
Sensors can be classified into two categories.
INTERNAL SENSORS
Used for controlling position and velocity of various joints. Typical sensors used to control the position of the robot are include potentiometer and optical encoder. And for speed of the robot arm, tachometer are used.
EXTERNAL SENSORS
These sensors are used to coordinate the operation of the robot with the other equipment in the cell. These sensors are relatively simple devices such as limit switches that determine whether the part has been positioned properly in the fixture.
SOME COMMONS SENSORS
* Tactile Sensors:
These sensors are used to determine whether contact is made between the sensor and the object. It is divided into two categories.
- Touch Sensors:- that indicate simply that contact has been made with the object.
- Force Sensors:- are used to indicate the magnitude of the force with the object. This might be useful in grippers to determine the magnitude of the force.
* Proximity Sensor
It is used to determine the actual distance of the object also called Range Sensors.
* Optical Sensor:
These sensors are used to detect the presence of the object.
CHARACTERISTICS OF ROBOT APPLICATION
The general characteristics of an industrial work which have tended to promote the substitution of a robot for human labor are the following:
1) Hazardous Work Environment:
When the work environment is unsafe, unhealthful, hazardous, or otherwise unpleasant for people, this is a reason to consider an industrial robot for the work. For example, in forging, spray painting, continuous arc welding, spot welding etc.
2) Repetitive Work Cycle:
If the sequence of element in the cycle is the same and the element consists of relative simple motions, a robot is usually capable of performing the work cycle with greater consistency and repeatability.
3) Difficult Handling for Human Beings
Parts or tools that are too heavy for human beings to handle conveniently are well within the load carrying capacity of a large robot.
4) Multi-shift operation
In manual operation, sometime industry require more than one shifts, substitution of a robot will provide a much faster financial payback. Instead of replacing one worker, the robot replaces two or three worker.
ROBOT CELL DESIGN
There are three basic types of workcell layout.
1) Robot Centered Cell
The robot is located at the approximate center of the cell, and the other pieces of equipment are arrange around it. The layout is shown in figure. This type of layout is suited to installation in which there is a single robot servicing one or more production machines. Machine loading and unloading applications are example of this case.
2) In-Line Robot Cell
This is the arrangement in which one or more robots are located along an in-line conveyor or other material transport system. The work is organized so that parts are presented to the robots by the transport system, and each robot performs some processing or assembly operation on each part.
3) Mobile Robot Cell
In this arrangement, the robot is provided with a means of being transported within a cell to perform various processing operations at different location in the cell. The transport mechanism consist of either a floor mounted track or overhead rail system that allows the robot to be moved along a linear path. This is suitable where the robot serve more than one production machine at different location, and the workstation cannot be located around the robot.
ROBOTS APPLICATIONS
The application can be classified into three categories
1) Material Handling
2) Processing Operation
3) Assembly & Inspection
1) Material Handling
Material handling application are those in which the robot moves material from one location to another. To accomplish this, the robot is equipped with gripper type end effector. The gripper must be designed to handle the specific part or parts to be move in the application.
Material Handling operation are divided into two categories.
a) Material Transfer
Primary purpose of robot is to pick up parts at one location and place them at a new location. Transferring parts from one conveyor to another is an example.
b) Material Loading and Unloading
There are three cases
i) Machine Loading: in which the robot loads the parts into the production machine, but the parts are unloaded by some other means.
ii) Machine Unloading: In this type, the raw material or a part being machine is fed or load into the machine without the use of robot. But the unloading of the finished part is accomplish by the robot.
iii) Loading and Unloading: In this case, both loading and unloading of the raw material and finished part is accomplish by robot. The robot centered cell is most commonly used for this application category.
2) Processing Operations
Processing applications are those in which the robot performs a processing operation on the part. A distinguishing characteristics of this category is that the robot is equipped with some type of tool as its end effector. In some application, more than a single tool must be used during the work cycle. In these instances, a quick change mechanism of tool is used to exchange the tools during the work cycle.
Examples lie in this categories are :
- Spot Welding
- Continuous arc welding
- Spray painting
- Drilling
- Grinding
- Water Jet cutting
- Laser cutting
3) Assembly & Inspection
Assembly and inspection can involve both the handling of materials and the manipulation of a tool. For example, assembly operation typically involve the addition of components to build the product, which requires material handling.
Assembly and Inspection are traditionally labor intensive activities industry. They are highly repetitive and often boring.
The inspection which are performed by industrial robots can be classified as follows
- The robots performs loading & unloading task to support inspection testing machine.
- The robots manipulates the inspection device such as mechanical probe test the product.
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