Advanced Manufacturing Industrial Robots

Dr. L. K. Gaafar

This presentation uses information from: http://www.glue.umd.edu/~aksamuel/academic/Viewgraph_files/frame.htm

“A robot is a programmable, multifunction manipulator designed to move material, parts, tools, or special devices through variable programmed motions for the performance of a variety of tasks”

Robot Institute of America

Industrial Robots Definition

A robot is a programmable arm simulator

Motivation for using robots to perform task which would otherwise be performed by humans.

• Safety• Efficiency• Reliability• Worker Redeployment• Cost reduction

The Advent of Industrial Robots

– Arm or Manipulator

– End effectors

– Drive Mechanism

– Controller

– Custom features: e.g. sensors and transducers

Main Components of Industrial Robots

Arm or Manipulator

• The main anthropomorphic element of a robot.

• In most cases the degrees of freedom depends on the arm

• The work volume or reach mostly depends on the functionality of the Arm

End Effectors

Grippers

– Mechanical Grippers– Suction cups or vacuum cups– Magnetized grippers– Hooks– Scoops (to carry fluids)

Device attached to the robot’s wrist to perform a specific task

Tools

– Spot Welding gun– Arc Welding tools– Spray painting gun– Drilling Spindle– Grinders, Wire brushes– Heating torches

End Effectors

Device attached to the robot’s wrist to perform a specific task

Sensors in robotics

Types of sensors :

– Tactile sensors (touch sensors, force sensors, tactile array sensors)

– Proximity and range sensors (optical sensors, acoustical sensors, electromagnetic sensors)

– Miscellaneous sensors (transducers and sensors which sense variables such temperature, pressure, fluid flow, thermocouples, voice sensors)

– Machine vision systems

Sensors in robotics

Uses of sensors:

– Safety monitoring

– Interlocks in work cell control

– Part inspection for quality control

– Determining positions and related information about objects

Sensors in robotics

Desirable features of sensors:

Accuracy

Operation range

Speed of response

Calibration

Reliability

Cost and ease of operation

Physical Configuration

Cartesian Cylindrical

Polar (Spherical) Jointed Arm

Physical Configuration

•Manual Cams, stops etc

•Walkthrough (Lead-through) Manually move the arm, record to memory

• Manual teachingTeach pendant

• Off-line programming Similar to NC part programming VAL, RAPT

Programming Robots

• Material Handling/Palletizing• Machine Loading/Unloading• Arc/Spot Welding• Water jet/Laser cutting• Spray Coating• Gluing/Sealing• Investment casting• Processing operations• Assembly• Inspection

Applications

• Size of the working envelope

• Precision of movement– Control resolution

– Accuracy – Repeatability

•Lifting capability

•Number of robot axes

•Speed of movement– maximum speed– acceleration/deceleration time

•Motion control– path control– velocity control

•Types of drive motors– hydraulic– electric– pneumatic

Performance Specifications of Industrial Robots

Determined by– Physical configurations– Size– Number of axes– The robot mounted position (overhead gantry, wall-

mounted, floor mounted, on tracks)– Limits of arm and joint configurations– The addition of an end-effector can move or offset the

entire work volume

Work VolumeSpatial region within which the end of the robot’s wrist can be manipulated

Depends on the position control system, feedback measurement, and mechanical accuracy

Spatial Resolution

Smallest increment of motion at the wrist end that can be controlled by the robot

• One half of the distance between two adjacent resolution points

• Affected by mechanical Inaccuracies

• Manufacturers don’t provide the accuracy (hard to control)

AccuracyCapability to position the wrist at a target point in the work volume

• Repeatability errors form a random variable.

• Mechanical inaccuracies in arm, wrist components

• Larger robots have less precise repeatability values

Repeatability

Ability to position back to a point that was previously taught

• The lifting capability provided by manufacturer doesn’t include the weight of the end effector

• Usual Range 2.5lb-2000lb

• Condition to be satisfied:

Load Capability > Total Wt. of workpiece +Wt. of end effector + Safety range

Weight Carrying Capacity

•Acceleration/deceleration times are crucial for cycle time.

•Determined by

– Weight of the object – Distance moved – Precision with which object must be positioned

Speed of Movement

Speed with which the robot can manipulate the end effector

• Path control - how accurately a robot traces a given path (critical for gluing, painting, welding applications);

• Velocity control - how well the velocity is controlled (critical for gluing, painting applications)

• Types of control path:

- point to point control (used in assembly, palletizing, machine loading); - continuous path control/walkthrough (paint spraying, welding).- controlled path (paint spraying, welding).

Motion Control

• Hydraulic– High strength and high speed– Large robots, Takes floor space– Mechanical Simplicity– Used usually for heavy payloads

• Electric Motor (Servo/Stepper)– High accuracy and repeatability – Low cost – Less floor space – Easy maintenance

• Pneumatic – Smaller units, quick assembly– High cycle rate – Easy maintenance

Type of Drive System

Robot Location and Workspace

x

y

L1

L2 (x, y)

)sin(sin 21211 LLx

)cos(cos 21211 LLy

22122

21

22 cos2 LLLLyx

Location:

Workspace:

211

211

22 )cos()sin( LyLxL

Positioning:

21

22

21

221

2 2cos

LL

LLyx

2-link polar robot

221

22

21

221

22

11

2coscos

yxL

LLyx

yx

y

Robot Applications (Configurations/Characteristics)

SCARA Robot

(Selective Compliance Assembly Robot Arm)

Characteristics:

•Repeatability: < 0.025mm (high) •No. of axes: min 4 axes • Vertical motions smoother, quicker, precise (due to dedicated vertical axis) • Good vertical rigidity, high compliance in the horizontal plane. •Working envelope: range < 1000mm •Payload:10-100 kg •Speed: fast 1000-5000mm/s

Applications: •Precision, high-speed, light assembly

Robot Applications (Configurations/Characteristics)

Cylindrical Coordinate Robot Characteristics:

•Wide range of sizes •Repeatability: vary 0.1-0.5mm •No. of axes: min 3 arm axes (2 linear)•Working envelope: typically large (vertical stroke as long as radial stroke) • The structure is not compact. •Payload: 5 - 250kg •Speed: 1000mm/s, average •Cost: inexpensive for their size and payload

Applications:

•Small robots: precision small assembly tasks •Large robots: material handling, machine loading/unloading.

Robot Applications (Configurations/Characteristics)

Vertical Articulated Arm Robot

Characteristics: •Repeatability: 0.1-0.5mm (large sizes not adequate for precision assembly) •No. of axes: 3 rotary arm-axes, 2-3 additional wrist axis (excellent wrist articulation) •Working envelope: large relative to the size, Structure compact, but not so rigid •Payload: 5-130kg •Tool tip speed: fast 2000mm/s

Applications: Welding, painting, sealing, deburring, and material handling

Robot Applications (Configurations/Characteristics)

Spherical Coordinate Robot Characteristics: •Repeatability: poor 0.5-1mm •No. of axes: 3 arm-axes (1 linear radial), 1-2 additional wrist-axes. •Working envelope: large vertical envelope relative to the unit size •Payload: 5-100 kg •Speed: low (linear motions are not smooth and accurate- require coordination of multiple axes)

Applications: Material handling, spot welding, machine loading

Robot Applications (Configurations/Characteristics)

Cartesian Coordinate Robot Characteristics: •Repeatability: high (0.015-0.1) •No. of axes: 3 linear arm-axis, •Working envelope:relative large •Payload:5- 100kg •Speed: fast

Applications: Precise assembly, arc welding, gluing, material handling

Robot Applications (Configurations/Characteristics)

Gantry Robot Characteristics: •Repeatability: 0.1-1mm •No. of axes: 3 linear traverse-axes, 1-3 additional wrist axes •Working envelope: very large •Payload: vary function of size, support very heavy 10-1000kg •Speed: low for large masses

Applications: Handling very large parts, moving material on long distances, welding, gluing.

• Simple Repetitive operations.

• Cycle times greater than 5s.

• Parts can be delivered in proper locations/orientation.

• Part weight is suitable.• One or two persons can be replaced in 24 hr period.

• Setups and changeovers are not frequent.

What to Automate

Robot Implementation Planning

Identify Objectives (Benefits)

• Increase productivity • Reduce labor cost • Reduce cycle time • Eliminate undesired jobs• Safety reasons: protect from exposure to hazardous conditions • Increase product quality

Robot Implementation Planning

•Consider Drawbacks

• The impact upon the workers • The impact upon production schedule and maintenance • Questions of potential model changes or process changes

Fixed automation:

ExpensiveCan become obsolete early (dedicated for a single task)Large inventoriesDifficulties in commissioning and high maintenance costsFaster and more accurate

Flexible (robot) automation:Reprogrammable for different tasksQuick to commissionEasy to maintainCheaper to design.

Robot Implementation PlanningFixed versus Flexible Automation