Robotics Unit1

7/30/2019 Robotics Unit1

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RoboticsRobotics andand AutomationAutomation

MFET5023

Dr. Sang-Heon LEE

School of Advanced Manufacturing and Mechanical Engineering

University of South Australia

Lecture 2-2

Industrial Robot Components

Lecture Outline

This lecture will cover major components of industrial robots (Chapter 2, Section 3.4)

.

2. End-effector

3. Drives

4. Controller

5. Sensor

Major components of industrial robots

Major components of industrial robots 1. Arms (Manipulator)

A mechanical linkage connected by joints to forman open kinematic chain

capable of movements in various directions

Perform the work of robot

Most important part of robot.



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1. Arms (Manipulator)

Many different ways of positioning – degree of freedom.

Each direction of joint usually gives 1 degree of ree om. o reac any poss e po n s n sworking envelop, 6 DOF required.

Two motions of robots

9 Arm and body motions-usually determine itsposition.

9 Wrist motions-usually determine itsorientation.

1.1 Arm and body motions

Vertical traverse – up-and-

Determine the position of the end-effector.

own mo on o e arm.

Radial traverse – extensionand retraction of the arm(in-and-out movement).

Rotational traverse –rotation about the verticalaxis (right or left swivel).

1.1 Wrist motions

Wrist swivel – rotation of the

Determine the orientation of the end-effector.

wr s .

Wrist bend – up-and-down

movement of the wrist, whichalso involves a rotationalmovement.

Wrist Yaw – right-or-left swivelof the wrist.

1.1 Motions of arms

1.2 Arms-example 2. End-Effector A “device” attached to

the robot manipulator tomanipulate a workpieceand to perform the task.

A tool to grip, hold andtransport objects andposition them in adesired location.

Sometimes called end-of-arm-tooling (EOAT)



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2. End-Effector

A robot can become aproduction machineonly if an end-effector

mechanical arm bymeans of the tool-mounting plate.

Tool-mounting plate isfor the interfacebetween end-effectorand the controller.

2. End-Effector Many possible types-usually custom built.

9 Process end-effector: welder, spray gun, grinder, drill,depth gauge, nut driver, etc.

9 Grippers:

• Mechanical grippers: friction or physicalconfiguration to be used to retain the objects.

• Magnetised grippers

• Suction cups (vacuum cups)

• Adhesive devices – to hold flexible materials

Some robots can change its end-effector and beprogrammable for different tasks - Tool exchangerrequired.

Grippers are used to hold workpiece using mechanicalopen-close mechanism.

Should consider the followings:

2.1 Gripper

9 Large mass at the end of robot arm requires aconsiderable amount of force to halt the movement.

9 Changing direction of movement is difficult at highspeeds with heavy loads.

9 The workpiece should remain secured in the grippereven when the power of the grips is removed (safetyreason).

2.1 Grippers-examples

Tools as a end-effector: in most applicationswhere the robot manipulates the tool.

he tools are attached to the robot wrist and

2.2 Process End-effectors

become an end-effector.

Example: welding gun, spray painting, drilling,grinding, heating, etc.

Movie file 1:polisher

Movie file Welding

Movie file Sealing



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2.2 Process End-effectors: example

2.3 Consideration of end-effectors

Change in the size of parts (shape, weight)between operations

Size variation in parts

Surface of part, Scratching and/or distortion of part for fragile materials

Grasping force, friction between part and gripper

Weight of object

Centre of mass (stability)

Speed and acceleration of robot arm

2.4 Advanced End-effectors 2.4 Advanced End-effectorsMovie file 1

Movie file 2

Movie file 4

Movie file 5: tiny gripper

Movie file 6:parallel link gripper

The origin of the coordinate system or the pointof action of the tool attached to the robot arm.

Usin forward kinematics, we could find the

2.5 Tool Centre Point (TCP)

coordinate system in the base to the coordinatesystem attached on the tool-mounting plate of the arm. All movements of the manipulator arereferenced from this location in space.

If an end-effector is added to the mountingplate, the origin of coordinate system moved to anew location, which is called the TCP.

2.5 Tool Centre Point (TCP)



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3. Drives (actuators)

It is an “Engine” that drives the links into thedesired positions.

ransmission of power from actuator to themanipulator’s joints are mostly done byelectromagnetic motors, gears, ball-screw orpulley drives.

Drives are powered by air pressure (Pneumatic),oil pressure(Hydraulic) or electric motors.

3.1 Electrical Drives

Stepper motors or servo motors used in mostindustrial robots – most common.

Easy to control – more repeatable positioning.

Fast and accurate control.

Relatively inexpensive.

High speed with low torque-gear trains or otherpower transmission units are required: Limited inresolution and tend to be noisy.

Limited payload capability.

3.1 Electrical Drives 3.2 Pneumatic Drives

Compressible air is used – position control problem.

Usually used in relatively low-cost with low-carryingcapacity.

mp e con ro – ea or gr pper

Mechanical stops are usually used to control the

actuator position – simple stop-to-stop motions, ex.pick and place application.

3.2 Pneumatic Drives Disadvantages:

9 Usually more sophisticated valve required to reducethe error – limited accuracy.

9 Noise pollution from exhausts.

9 Low efficiency especially at reduced loads.

9 Low stiffness.

Advantages

9 High speed and relatively high power to weight ratio

9 Very low cost

9 No contamination of work space (no oil leak)

9 Light weight.

3.2 Pneumatic Drives-Examples

Pneumatic control robot arm

http://www.ks.uiuc.edu/Research/Neural/robot.html



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3.3 Hydraulic Drives

Using high pressure oil

Mechanically relatively simple (familiar tomaintenance personnel)

High strength and high speed for relatively smallsize (high power to weight ratio) – ideal formoving moderate to high loads at reasonablespeeds and moderate noise level.

Stiffer than electrical motors, resulting greateraccuracy and better frequency response

Smoother response in low speed.

3.3 Hydraulic Drives

Expensive for small or medium sized robot with limitedaccuracy.

Required additional energy storage unit including pumpsan accumu a ors.

Susceptible for oil leaks – frequent cleaning andmaintenance required and environment issues.

Highly nonlinear movement

Digital encoder and highly capable feedback controlsystem can provide better accuracy and repeatabilitycompared to electrical drives but required verysophisticated control.

3.3 Hydraulic Drives-examples

Unimate 2000 series robot (Spherical coordinate)

http://www.ar2.com/uninfo.html

3.4 Power transmissionelements

Power created from actuators has to be transmitted tocreate the desired movement.

Gears, Screw drives, pulley systems, linkages andbearings are used.

3.4 Power transmissionelements 4. Controller Controller is the brain of the robot

9 Provide “intelligence” to make the manipulatorperform the desired tasks in the desired manner

9 Initiate and terminate the motions

9 Store positions and sequence data

9 Interface with outside world



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4. Robot Control System 4.1 Type of Control

Non-servo: Open loop

Servo-controlled: closed loop

4.1.1 Non-servo

Open loop control system.

Each axis will continue to move until it reachesits limit.

Path is not controlled: only the end point is

limited by9 Mechanical stops

9 Pneumatic valves

9 Electrical relays

Closed loop system.

The information about the position, velocity,acceleration is continuously monitored.

4.1.2 Servo-controlled

e esire va ues an t e actua va ues arecompared and the difference are reduced bycontrol action.

4.1.2 Servo-controlled



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5. Sensors

Provide the controller about the status of themanipulator for proper control.

Continuously monitoring position, velocity andacce eration

Internal and external sensors

5. Sensors

5. Sensors - Examples

Sonar Sensor

Vision Sensor

Vision Sensor

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Robotics Unit1