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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