industrial robotics

Industrial RoboticsIndustrial Robotics

IntroductionRobot configurationProgrammingEnd effectorsSensorsIndustrial applications

IntroductioIntroductionn

Brief history of developmentDefinition of the ‘Robot Institute of

America’:A robot is a programmable, multi-function manipulator designed to move material, tools or special devices through variable programmed motions for the performance of a variety of tasks

Robot Physical ConfigurationRobot Physical Configuration

1. Polar coordinate configuration2. Cylindrical coordinate configuration3. Jointed arm configuration4. Cartesian coordinate configuration

Polar coordinate configuration

• Also called Spherical Coordinate configuration• Ex: Unimate 2000 series

Cylindrical coordinate configuration

Ex: Unimate 3000 series

Jointed arm configuration

• Cincinatti Milacron T model• Unimate PUMA model

Cartesian coordinate configuration

• Rexroth robotic system

Robot motions: six degrees of freedom

Cartesian Robot

Cartesian robot is formed by 3 prismatic joints, whose axes are coincident with the X, Y and Z planes.

Gantry Robot

Cartesian coordinate robots with the horizontal member supported at both ends are sometimes called Gantry robots.

Parallel Robot

Parallel robot is a complex mechanism which is constituted by two or more kinematics chains between, the base and the platform where the end-effectors are located. Good examples are the flying simulator

Spherical Robot

It is still in the research laboratory, the Spherical robot is actually a spherical shape robot, which has an internal driving source.

Configuration Advantages Disadvantages

Cartesian coordinates

3 linear axes, easy to visualize, rigid structure, easy to program

Can only reach front of itself, requires large floor space, axes hard to seal

Cylindrical coordinates

2 linear axes +1 rotating, can reach all around itself, reach and height axes rigid, rotational axis easy to seal

Can’t reach above itself, base rotation axis as less rigid, linear axes is hard to seal, won’t reach around obstacles

SCARA coordinates 1 linear + 2 rotating axes, height axis is rigid, large work area for floor space

2 ways to reach point, difficult to program off-line, highly complex arm

Spherical coordinates

1 linear + 2 rotating axes, long horizontal reach Can’t reach around obstacles, short vertical reach

Revolute coordinates

3 rotating axes can reach above or below obstacles, largest work area for least floor space

Difficult to program off-line, 2 or 4 ways to reach a point, most complex manipulator

Other Technical Other Technical FeaturesFeatures

Work volumePrecision of movementSpeed of movementPayload capacityType of drive system

Accuracy and Repeatability

Robot Programming

1. Manual method

2. Walkthrough method

3. Leadthrough method

4. Off-line programming

Manual method

• It is more like setting up the machine rather than programming

• Used for simple robots

• Involves setting stops, cams, switches and relays

• Uses low technology for short work cycles

Walkthrough method

• The programmer manually moves the robot’s arm and hand through the motion sequence of the work cycle

• Each movement is recorded into memory for subsequent playback during production

• Once the motion sequence is recorded, the speed of movement can be controlled independently

• Appropriate for spray painting, arc welding, etc

Leadthrough method

• Uses a teach pendent to power drive the robot through its motion sequence

• Each motion is recorded into memory for future playback during the work cycle

• Popular because it is easy and convenient

Off-line programming

• Uses off-line programming language

• Since programming is done off-line, it means higher utilisation of the robot and the equipment with which it operates

• Ensures integration of the robot with FMS and CIM systems

Robot Programming Languages

VAL

• Developed by Victor Scheinman for the PUMA robot

• Stands for Victor’s Assembly Language

• Two types of statements: Monitor commands and Programming instructions

• Program instructions are written in VAL, while various point locations are defined using a teach pendent

Monitor Commands

• Preparing the system for the user to write programs

• Defining points in space

• Commanding the robot to execute a program

• Listing programs on the CRT

• Examples: EDIT, EXECUTE, SPEED, HERE, etc

Program Instructions

• MOVE: Moves the robot to the location and orientation specified by the symbol

• MOVES: Moves the robot along a st.-line trajectory, to the specified location

• APPRO: Moves the end effector to the position defined, but offset along the Z-axis by the specified distance in mm

• APPROS: Similar as above, but along a st.-line trajectory

• DEPART: Moves the tool the distance given along the current Z-axis of the tool

• OPENI: Opens the gripper immediately

• CLOSEI: Closes the gripper immediately

• EXIT: Exits from the program and transfers control to monitor mode

VAL Programming Example

TASK:

• Pick and place operation

• Robot should pick up a part from one conveyor (Point A)

• Place the part on another conveyor (Point B)

VAL Programming Example

• PROGRAM PICK

1.APPRO A, 502.MOVES A3.CLOSEI 4.DEPART 505.APPRO B, 506.MOVES B7.OPENI 8.DEPART 50

LISTL AX/JT1 Y/JT2 Z/JT3 P/JT4 Q/JT5-105.5 87.8 119.0 -25.6 100.9

LISTL BX/JT1 Y/JT2 Z/JT3 P/JT4 Q/JT5-50.0 115.8 55.5 -10.7 100.2

End Effectors

• It is a device which is attached to the robot’s wrist to perform a specific task

• It is a special purpose tooling which enables the robot to perform a particular job

• It is usually custom engineered for the job

• Most robot manufacturers have engineering groups which design and fabricate end effctors or provide advice to their customers on end effector design

• There are two types of end effectors: Grippers and tools

Grippers

• Mechanical Grippers: Friction or the physical configuration of the gripper retains the object

• Suction cups: also called vacuum cups, used for flat fragile objects

• Magnetic Grippers: for ferrous objects

• Hooks: to lift parts off conveyors

• Scoops/Ladles: for handling fluids, powder, pellets, or granular substance

Grippers

Pivot action Gripper

Grippers

Slide action Gripper

Grippers

Double Gripper Pivot action mechanism

Grippers

Vacuum Gripper

Tools as End Effectors

• Spot welding gun

• Arc welding tools (and wire-feed mechanism)

• Spray painting gun

• Drilling head

• Routers, grinders, wire brushes

• Heating torches

SENSORS IN SENSORS IN ROBOTICSROBOTICS

Internal: for controlling position and veleocity of

various joints. Ex: optical encoders,

potentiometers, etc

External: for workcell control.

Types of Sensors in Types of Sensors in RoboticsRobotics

Tactile and Proximity sensors

Voice sensors

Machine vision

Tactile and Proximity sensors

• Provides the robot with capability to respond to contact forces with other objects within the work volume

• Two types: Touch sensors and stress sensors (tactile sensors)

• touch sensors will simply indicate that a contact has been made with an object. A simple micro switch can serve the purpose

• Stress sensors measure the magnitude of the contact force. Starin gauges are the most popular choice

• Tactile sensors are useful in assembly and inspection operations.

• In assembly, the robot can perform delicate part alignment and joining operations

• In inspection, touch sensing would be useful in gauging operations and dimensional measuring activities

• Proximity sensors are used to sense when one object is close to another

Voice sensors

• Used for voice programming

• A speech recognition system analyses the voice inputs and compares it with a set of stored word patterns

• when a match is found between the input and the stored vocabulary word, the robot performs some action which corresponds to that word

• It can speed up robot programming

Machine Vision

Machine vision can be defined as the acquisition of image data, followed by processing and interpretation of this data by computer for some useful application

Classification: 2D and 3D vision systems

Basic Functions of Vision system

• Image acquisition and

digitisation

• Image processing and analysis

• Interpretation

Image Acquisition and Digitization

A camera captures the image

Image is obtained by dividing the viewing area into a matrix of discrete picture elements(pixels)

Each pixel has a value that is proportional to the light intensity of that portion of the scene

The intensity value for each pixel is converted into equivalent digital value by an ADC

Selection of appropriate lighting system is important to establish contrast between the object and the background


Binary vision: light intensity of each pixel is ultimately reduced to either of two values, white or black, depending on whether light intensity exceeds some threshold level

Gray scale system: capable of distinguishing and storing different shades of gray in the image. It can highlight the object’s texture and colour.

Each set of pixel values is referred to as a frame and stored in computer memory as frame buffer

The process of reading all the pixel values in a frame is performed with a frequency of 25-30 times per second

Cameras used: Vidicon and Solid-state

Types of illumination: front lighting, back lighting and side lighting


The data for each frame must be analysed within the time required to complete one scan (1/30 sec)

Segmentation: define and separate regions of Interest within the image

segmentation techniques: thresholding and edge preparation

Feature extraction: length, width, perimeter, c.g., aspect ratio, etc


Interpretation

Object/pattern recognition

Template matching

Feature weighting


Machine Vision Applications

1. Inspection

2. Part identification

3. Visual guidance and control

4. Safety monitoring

Robotic Applications

Material handling: material transfer and machine loading/unloading

Processing operations: spot welding, continuous welding, spray painting, drilling, grinding, laser cutting, riveting, etc

Assembly and inspection

industrial robotics

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