Basic Concepts Of Robotics 2t4c5e

Automation and Robotics Basics

Contents History of Robotics  Robotics Application  Robot anatomy and Work Volume  Robot Configuration and work Space  End-effectors: Grippers and Tools  Robot Actuators and Drive Systems  Safety Consideration 

Who introduced the word robot? o

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The term robot was first introduced by a Czech dramatist, Karel Capek in his 1921 play "Rossum's Universal Robots". He was referring to a perfect and tireless worker performing manual labour jobs for human beings. Isaac Asimov, coined the word robotics as the science of the study of robots, in his science fiction stories about robots in 1940s.

Definition Robot term from Webster’s dictionary:- An automatic device that performs function ordinarily ascribed to human being  'Automation' refers to a mode of operation in which any machine or piece of equipment is capable of working without human intervention. 

Automation is generally regarded as being able to be divided into 3 types: 1. 2. 3.

Fixed automation Flexible automation Programmable Automation

Fixed automation 

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Used when the volume of production is very high and it is, therefore, appropriate to design specialized equipment to process products at high rates and low cost Eg: automobile industry, where highly integrated transfer line are used to perform machine operation on engine and transmission components

Flexible automation 

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Most suitable for the mid-volume production range. Typically consists of a series of workstation that are interconnected by materialhandling and storage equipment to process different product configuration at the same time to control manufacturing system Eg: Flexible Manufacturing System (FMS), Computer Integrated Manufacturing (CIM)

History of Robotics Date

Development

mid‑ 1 700s

J. de Vaucanson built several human‑sized mechanical dolls that played music.

1971

The ‑Stanford Arm," a small electrically powered robot arm, developed at Stanford University.

1979

Development of S.CARA type robot (Selective Compliance Arm for Robotic Assembly) at Yamanashi University in Japan for assembly. Several commercial SCARA robots introduced around 1981

Robot anatomy and Work Volume Robot anatomy deals with:  the types and sizes of these ts and links  and other aspects of the manipulator’s physical construction

What is a t? 

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A t of robot is similar to a t in the human body Each t gives the robot with a degree-offreedom(d.o.f)of motion In the nearly all cases, only 1 d.o.f is allowed to a t

What is a robot link? 

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Links are rigid components that form a chain connected together by ts Each t has two links, known as an input link and an output link

Types of robot ts 1. 2. 3. 4.

Linear t Rotational t Twisting t Revolving t

Linear t The relative movement between the input link and the output link is a linear sliding motion, with the axes of the two links being parallel

Rotational t This type provides a rotational relative motion of the ts, with the axis of rotation perpendicular to the axes of the input and output links

Twisting t This t also involves a rotary motion, but the axis of rotation is parallel to the axes of the two links

Revolving t In this types, the axis of the input link is parallel to the axis of rotation of the t, and the axis of the output link is perpendicular to the axis of rotation

This t‑link numbering, scheme is shown below.

GENERAL CLASIFICATION OF ROBOTS o o o

Low technology Medium technology High technology

Low technology  Material

handling, using simple assembly  2 to 4 axes of movement  Stop at extreme

Medium technology Pick-and-place  Material handling  4 to 6 axes 

High technology Material handling  Pick-and-place  Loading and unloading  Painting and welding  6 to 9 axes 

Robot Classification Based On Kinematic Structure Normally, robot manipulators are classified according to their arm geometry or kinematic structure. The majority of these manipulators fall into one of these four configuration: 1. 2. 3. 4.

Cartesian Type Configuration (PPP) Cylindrical Type Configuration (RPP) Spherical Type Configuration (RRP) SCARA Type Configuration (RRP or PRR)

Cartesian Type Configuration (PPP)

Cartesian Type Configuration (PPP) 

Manipulator whose first three ts are prismatic are known as a Cartesian manipulator.. Cartesian manipulator are useful for table‑top assembly applications and, as gantry robots for transfer of material and cargo

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Advantages: - 3 linear axes - Easy to visualize - Rigid structure - Easy to program off‑line - Linear axes make for easy mechanical stops Disadvantage: - Can only reach in front of itself - Requires large floor space for size of work envelop - Axes hard to seal

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Cylindrical Type Configuration (RPP)

Cylindrical Type Configuration (RPP)  

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For cylindrical type manipulator, its first t is revolute which produces a rotation about the based, while its second and third ts are prismatic. Advantages: - 2 linear axes, 1 rotating axis - Can reach all around itself - Reach and height axes rigid - Rotational axis easy to seal. Disadvantages: - Cannot reach above itself - Base rotation axis is less rigid than a linear axis - Linear axes hard to seal - Will not reach around obstacles - Horizontal motion is circular

Spherical Type Configuration (RRP)

Spherical Type Configuration (RRP) The first two ts of this type of manipulators are revolute, while its third t is prismatic.  Advantages: - 1 linear axis, 2 rotating axes - Long horizontal reach  Disadvantages: - Cannot reach around obstacles - Generally has short vertical reach 

SCARA Type Configuration (RRP or PRR)

SCARA Type Configuration (RRP or PRR) 

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The word SCARA stands for Selective Compliant Articulated Robot for Assembly. There are two type of SCARA robot configuration: either the first two ts are revolute with the third t as prismatic, or the first t is revolute with the second and third ts as prismatic. Advantages: - 1 linear axis, 2 rotating axes - Height axis is rigid - Large work area floor space - Can reach around obstacles - Two ways to reach a point Disadvantages: - Difficult to program off‑line - Highly complex arm

Robot Actuators and Drive Systems What is actuator? The commonly used actuators are: 1. Stepper motors 2. DC servomotors 3. AC servomotors 4. Hydraulic pistons 5. Pneumatic pistons

Electric Drive 

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Small and medium size robots are usually powered by electric drives via gear trains using servomotors and stepper motors. Advantages - Better accuracy & repeatability - Require less floor space - More towards precise work such as assembly applications

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Disadvantages - Generally not as speedy and powerful as hydraulic robots - Expensive for large and powerful robots, can become fire hazard

Hydraulic Drive Larger robots make use of hydraulic drives.  Advantages: 

- more strength‑to‑weight ratio - can also actuate at a higher speed

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Disadvantages: - Requires more floor space - Tendency to oil leakage.

Pneumatic Drive  For

smaller robots that possess fewer degrees of freedom (two‑ to fourt motions).  They are limited to pick‑and‑place tasks with fast cycles.

Direct Drive Robots  In

1981 a "direct‑ drive robot" was developed at Carnegle‑Mellon University, USA. Is used electric motors located at the manipulator ts without the usual mechanical transmission linkages used on most robots.  The drive motor is located contiguous to the t.  Benefits:  

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Eliminate backlash and mechanical defiencies Eliminate the need of a power transmission (thus more efficient) t backdrivable (allowing for t‑space force sensing)

End-effectors: Grippers and Tools What is gripper? What is tool?  Mechanical grippers  Vacuum systems  Magnetic Pickups  Tools

Cam‑operated hand It can easily handle heavy weights or bulky objects. It is designed to hold the object so that its center of gravity (CG) is kept very closed to the wrist of hand. The short distance between the wrist and the CG minimizes the twisting tendency of a heavy or bulky object.

Special hand with modular gripper This special hand, with pair of pneumatic actuators, is one of the many special hand designs for industrial robots. It is suitable for parts of light weight.

Special hand for glass tubes This hand is specially designed for industrial robots to securely grasping of relatively short tubes.

Simple vacuum cup hand This simple vacuum cup hand is suitable for Handling fragile parts such as cathode ray tube face plates (Illustrated).

Magnetic Pick up Magnetic handling is most suitable for parts of ferrous contents. Magnets can be scientifically designed and made in numerous shapes and sizes to perform various tasks.

Ladle Ladling hot materials such as molten metal is a hot and hazardous job for which industrial robots are well suited. In piston casting permanent mold die casting and related applications, the robot can be programmed to scoop up and transfer the molten metal from the pot to the mold, and then do the pouring.

Spray gun Ability of the industrial robot to do multi spraying with controlled velocity fits it for automated application of primers, paints, and ceramic or glass frits, as well as application of masking agents used before plating. For short or medium‑length production runs, the industrial robot would often be a better choice than a special purpose setup requiring a lengthy change‑over procedure for each different part. Also the robot can spray parts with compound curvatures and multiple surfaces.

Tool changing A single industrial robot can also handle several tools sequentially, with an automatic tool‑changing operation programmed into the robot's memory. The tools can be of different types or sizes, permitting multiple operations an the same workpiece

Safety Consideration When?  Practice it as soon as starting robotics project  Must be built into robotics system at the outset  Do not risk injuries by robots

What Dangers? Repairing a robot  Training/programming robot  Normal operation  Power supply 

What sort of injuries? Bodily impact  Pinching-caught in grippers or ts  Pining human against a structure 