Introduction to Robotics

Robot ”programmable, multifunction, manipulator designed to move material parts or specialized devices through variable programmed motion for the performance of a variety of tasks. “ (Robot Institute of America)

Ideal TasksTasks which are:

• Dangerous• Space exploration• chemical spill cleanup• disarming bombs• disaster cleanup

• Boring and/or repetitive• Welding car frames• part pick and place• manufacturing parts.

• High precision or high speed• Electronics testing• Surgery• precision machining.

Automation vs. robots• Automation –Machinery designed to carry out a specific task

• Bottling machine• Dishwasher• Paint sprayer

• Robots – machinery designed     to carry out a variety of tasks

• Pick and place arms• Mobile robots• Computer Numerical Control    machines

Cost/Productivity: help increase the number of manufactured products and decrease the production of defective goods , they can produce the same quality products during the production process ,  they do not get exhausted , and they work for a long period of time. They can work at a constant speed without sleep , breaks , vacations , salaries , and  they can produce more than the human workers.

Precision: can be programmed to perform a simple task ,  they repeat that task more times , the robots work in the factory with  high degree of accuracy , and they work with constant velocity .

Strength: Without a doubt, robots can be significantly stronger than people.

Speed: Additionally, robots can be significantly faster than people too.

Environment: Robots can be designed to work in extremely harsh environments. can perform dangerous applications in hazardous settings , They  minimize the  material waste , they can save the time and effort , and their movements are always exact .

Robots Benefits

Disadvantages of robots Expense:  The initial investment to integrate robot.

Expertise:  Employees will require training program and interact with the robotic equipment.

Limited Functionality: Robots are very good at doing perfectly defined jobs, however robots typically do not handle the unexpected as well as people do.

Industrial Robot Main ComponentArm and Body: The arm and body of a robot are used to move and position parts or tools within a work envelope. 

Wrist: The wrist is used to orient the parts or tools at the work location.

Manipulator: a mechanical skeleton that serves as a rigid structural framework to support the arm and body.

Actuator: exerts force to drive the manipulator into a predetermined position and hold the joint rigid once the position is reached.

Gripper and other end effecter: the gripper secures the robot work piece while the operation is being performed.

Control unit: controls or keeps track of the time, the position of the joint, and the movement of the manipulator.

Power supply: provides the actuator and the control unit with the energy that they need to function.

Data distribution system: receives messages from the control unit and passes them on to the actuator.

Data acquisition system: receives messages from the environment and passes them on to the control unit.

Glossary of Robotic TerminologyWork cell / work envelope: the space in which the robot gripper can move with no restrictions or limitations in movement other than those imposed by the joint.

Degree of freedom: every joint or movable axis (including the arm). Example: For two joints, the degree of freedom equals 2.

Speed: the rate at which the gripper moves.

Resolution: the smallest change that a robot is able to make between two coordinate points (programmed points), and is referred to as the basic resolution unit (BRU). For IRB2000 ABB robot it is approximately 0.125 mm on linear axis.

Payload: the maximum load that the manipulator can handle (includes the weight of the gripper plus the weight of whatever the gripper carries).

Accuracy: how close a robot can position its payload to a given programmed point.

Repeatability: a measure of how close the robot returns to its previously established position on subsequent attempts.

ROBOT CLASSIFICATION• ARM GEOMETRY: RECTANGULAR;CYLINDIRICAL;SPHERICAL; JOINTED-ARM(VERTICAL);JOINED-ARM(HORIZONTAL).

• DEGREES OF FREEDOM: ROBOT ARM; ROBOT WRIST.

• POWER SOURCES: ELECTRICAL;PNEUMATIC;HYDRAULIC;ANY COMBINATION.

• TYPE OF MOTION:  JOINT-INTERPOLATION; Linear INTERPOLATION; CIRCULAR INTERPOLATION.

• PATH CONTROL: LIMITED SEQUENCE; POINT-TO-POINT; CONTINOUS PATH; CONTROLLED PATH.

• INTELLLIGENCE LEVEL: LOW-TECHNOLOGY(NONSERVO); HIGH-TECHONOLOGY(SERVO).

ARM GEOMETRY• ROBOT MUST BE ABLE TO REACH A POINT IN SPACE WITHIN THREE AXES BY MOVING FORWARD AND BACKWARD, TO THE LEFT AND RIGHT, AND UP AND DOWN.

• ROBOT MANIPULATOR MAY BE CLASSIFIED ACCORDING TO THE TYPE OF MOVEMENT NEEDED TO COMPLETE THE TASK.

RECTANGULAR-COORDINATED- HAS THREE LINEAR AXES OF MOTION.

- X REPRESENTSD LEFT AND RIGHT MOTION- Y DESCRIBES FORWARD AND BACKWARD MOTION.- Z IS USED TO DEPICT UP-AND-DOWN MOTION.

       THE WORK ENVELOPE OF A RECTANGULAR ROBOT IS A CUBE OR RECTANGLE, SO THAT ANY WORK PERFORMED BY ROBOT MUST ONLY INVOLVE MOTIONS INSIDE THE SPACE.

RECTANGULAR-COORDINATED

Characteristics

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

Advantages/Disadvantages• ADVANTAGES:

• THEY CAN OBTAIN LARGE WORK ENVELOPE BECAUSE TRAVELLING ALONG THE X-AXIS, THE VOLUME REGION CAN BE INCREASED EASILY.

• THEIR LINEAR MOVEMENT ALLOWS FOR SIMPLER CONTROLS.

• THEY HAVE HIGH DEGREE OF MECHANICAL RIGIDITY, ACCURACY, AND REPEATABILITY DUE TO THEIR STRUCTURE.

• THEY CAN CARRY HEAVY LOADS BECAUSE THE WEIGHT-LIFTING CAPACITY DOES NOT VARY AT DIFFERENT LOCATIONS WITHING THE WORK ENVELOPE.

• DISADVANTAGES:• THEY MAKES MAINTENANCE MORE DIFFICULT FOR SOME MODELS WITH OVERHEAD DRIVE MECHANISMS AND CONTROL EQUIPMENT.

• ACCESS TO THE VOLUME REGION BY OVERHEAD CRANE OR OTHER MATERIAL-HANDLING EQUIPMENT MAY BE IMPAIRED BY THE ROBOT-SUPPORTING STRUCTURE.

• THEIR MOVEMENT IS LIMITED TO ONE DIRECTION AT A TIME.

Application• PICK-AND-PLACE OPERATIONS.

• ADHESIVE APPLICATIONS(MOSTLY LONG AND STRAIGHT).

• ASSEMBLY AND SUBASSEMBLY(MOSTLY STRAINGHT).

• AUTOMATED LOADING CNC LATHE AND MILLING OPERATIONS.

• WELDING.

CYLINDRICAL-COORDINATED• HAS TWO LINEAR MOTIONS AND ONE ROTARY MOTION.

• ROBOTS CAN ACHIEVE VARIABLE MOTION.

• THE FIRST COORDINATE DESCRIBE THE ANGLE THETA OF BASE ROTATION--- ABOUT THE UP-DOWN AXIS.

• THE SECOND COORDINATE CORRESPOND TO Y--- IN OUT MOTION AT WHATEVER ANGLE THE ROBOT IS POSITIONED.

• THE FINAL COORDINATE AGAIN CORRESPONDS TO THE UP-DOWN Z POSITION.

• RESULTS IN A LARGER WORK ENVELOPE THAN A RECTANGULAR ROBOT MANIPULATOR.

• SUITED FOR PICK-AND-PLACE OPERATIONS.

CYLINDRICAL-COORDINATED

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

Advantages/Disadvantages• ADVANTAGE:

• THEIR VERTICAL STRUCTURE CONSERVES FLOOR SPACE.

• THEIR DEEP HORIZONTAL REACH IS USEFUL FOR FAR-REACHING OPERATIONS.

• THEIR CAPACITY IS CAPABLE OF CARRYING LARGE PAYLOADS.

• DISADVANTAGE:• THEIR OVERALL MECHANICAL RIGIDITY IS LOWER THAN THAT OF THE RECTILINEAR ROBOTS BECAUSE THEIR ROTARY AXIS MUST

OVERCOME INERTIA.

• THEIR REPEATABILITY AND ACCURACY ARE ALSO LOWER IN THE DIRECTION OF ROTARY MOTION.

• THEIR CONFIGURATION REQUIRES A MORE SOPHISTICATED CONTROL SYSTEM THAN THE RECTANGULAR ROBOTS.

Applications• APPLICATION:

• ASSEMBLY• COATING APPLICATIONS.• CONVEYOR PALLET TRANSFER.• DIE CASTING.• INSPECTION MOULDING.• MACHINE LOADING AND UNLOADING.

SPHERICAL COORDINATED• HAS ONE LINEAR MOTION AND TWO ROTARY MOTIONS.• THE WORK VOLUME IS LIKE A SECTION OF SPHERE.• THE FIRST MOTION CORRESPONDS TO A BASE ROTATION ABOUT A VERTICAL AXIS.

• THE SECOND MOTION CORRESPONDS TO AN ELBOW ROTATION.• THE THIRD MOTION CORRESPONDS TO A RADIAL, OR IN-OUT, TRANSLATION.• A SPHERICAL-COORDINATED ROBOTS PROVIDES A LARGER WORK ENVELOPE THAN THE RECTILINEAR OR CYLINDIRICAL ROBOT.

• ADVANTAGES AND DISADVANTAGES SAME AS CYLINDIRICAL-COORDINATED DESIGN.

SPHERICAL COORDINATED

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• APPLICATIONS:

• DIE CASTING• DIP COATING• FORGING• GLASS HANDLING• HEAT TREATING• INJECTION MOLDING• MACHINE TOOL HANDLING• MATERIAL TRANSFER• PARTS CLEANING• PRESS LOADING• STACKING AND UNSTICKING

Articulated Robots• Vertical jointed arm• Horizontal jointed arm (SCARA)

Vertical jointed armThis robot design features rotary joints and can range from simple two joint structures to 10 or more joints. The arm is connected to the base with a twisting joint. The links in the arm are connected by rotary joints. Each joint is called an axis and provides an additional degree of freedom, or range of motion. Industrial robots commonly have four or six axes.

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• material handling 

Horizontal jointed arm (SCARA)Selectively Compliant Assembly Robot Arm commonly used in assembly applications, this selectively compliant arm for robotic assembly is primarily cylindrical in design. It features two parallel joints that provide compliance in one selected plane.

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• Speed: fast 1000-5000mm/s

Applications

• Precision• High speed• Light assembly

Power Sources• ELECTRIC: ALL ROBOTS USE ELECTRICITY AS THE PRIMARY SOURCE OF ENERGY.• PNEUMATIC: THESE ARE GENERALLY FOUND IN RELATIVELY LOW-COST MANIPULATORS WITH LOW LOAD CARRYING CAPACITY.

• HYDRAULIC: ARE EITHER LINEAR POSITION ACTUATORS OR A ROTARY VANE CONFIGURATION.• Combination

Wrist Rotation• Yaw• Pitch• Roll• Bend

TYPES OF MOTIONJoint-Interpolated Motion: A method of coordinating the movement of the joints so that they all arrive at the desired location at the same time. This servo control method produces a predictable path regardless of speed and gives the fastest cycle time for a particular move.

Linear Motion: Requires the End Effectors to travel through along a straight path determine in Cartesian coordinates.

Circular-Interpolated Motion: Requires the robot controller to define the points of a circle in the workplace based on a minimum of three specified positions.

Path ControlLIMITED-SEQUENCE: DO NOT USE SERVO-CONTROL TO INDICATE RELATIVE POSITIONS OF THE JOINTS.

THEY ARE CONTROLLED BY SETTING LIMIT SWITCHES AND/OR MECHANICAL STOPS TOGETHER WITH A  SEQUENCER TO COORDINATE AND TIME THE ACTUATION OF THE JOINTS.

WITH THIS METHOD OF CONTROL, THE INDIVDUAL JOINTS CAN ONLY BE MOVED TO THEIR EXTREME LIMITS OF TRAVEL.

 POINT-TO-POINT: THESE ROBOTS ARE MOST COMMON AND CAN MOVE FROM ONE SPECIFIED POINT TO ANOTHER BUT CANNOT STOP AT ARBITRARY POINTS NOT PREVIOUSLY DESIGNATED.

CONTROLLED PATH: IS A SPECIALIZED CONTROL METHOD THAT IS A PART OF GENERAL CATEGORY OF A POINT-TO-POINT ROBOT BUT WITH MORE PRECISE CONTROL.

THE CONTROLLED PATH ROBOT ENSURES THAT THE ROBOT WILL DESCRIBE THE RIGHT SEGMENT BETWEEN TWO TAUGHT POINTS.

CONTROLLED-PATH IS A CALCULATED METHOD AND IS DESIRED WHEN THE MANIPULATOR MUST MOVE IN THE PERFECT PATH MOTION. 

CONTINUOUS PATH: IS AN EXTENSION OF THE POINT-TO-POINT METHOD. THIS INVOLVES THE UTILIZATION OF MORE POINTS AND ITS PATH CAN BE ARC, A CIRCLE, OR A STRAIGHT LINE.

BECAUSE OF THE LARGE NUMBER OF POINTS, THE ROBOT IS CAPABLE OF PRODUCING SMOOTH MOVEMENTS THAT GIVE THE APPEARANCE OF CONTINUOUS OR CONTOUR MOVEMENT.

INTELLIGENCE LEVEL• Open loop, i.e., no feedback, deterministic

• Closed loop, i.e., feedback, maybe a sense of•    touch and/or vision