Industrial robotics

Lesson 1Fundamentals of Robot

Robot:

A robot is a mechanical agent resembling a human being guided by a computer program with electronic circuitry and capable of performing all sorts of industrial actions in an automated way. A robot may convey a sense of intelligence or thought of its own. The branch of technology that deals with robots is called robotics.

Robot anatomy:

Robot anatomy usually has 3 physical configurations:- Body Arm Wrist In many industries the robots are usually stationary

mounted on a base. The body is attached to the base, arm is attached to the body and wrist is attached to the arm. Relative motion is achieved by movements of body, arm and wrist.

The wrist is the important component bearing the tool or work. It is usually called as end effectors. The relative movements can be rotating or sliding or the combination of both according to the need.

Co-ordinate system:

The robots used in the industry have various sizes, shapes and configurations. The common co-ordinate systems in robots are:-

Polar co-ordinate system Cylindrical co-ordinate system Cartesian co-ordinate system Jointed arm co-ordinate system

Robots with its own configuration:

Polar co-ordinate system:

The features of polar co-ordinate robots are:- It uses a telescopic arm which can be raised or

lowered about a horizontal pivot. The pivoted arm is mounted on a rotating base. The above pivot mounted rotating configuration

allows the robot to move the arm in a spherical space.

Hence it is also called as spherical co-ordinate system.

Unimate 2000 series and MAKER 110 are the robots working on polar co-ordinate system.

A polar Robot:

Cylindrical co-ordinate system:

It has a vertical column that can slide up and down along the column.

The robot arm is attached to the vertical column.

The robotic arm can rotate radially with respect to the column.

The robot work space resembles a cylinder and hence called as cylindrically co-ordinate robot.

GMF model robots are cylindrical co-ordinate type.

A cylindrical Robot:

Cartesian co-ordinate system:

This uses the mutually perpendicular axes (x, y and z respectively).

The arm is mounted in a vertical column such that it can make any kind of motion with the permissible limits of x, y, and z axes.

Hence this robot is also called as xyz robot or rectilinear robot.

By moving the arm it can surround a work area which resembles a rectangular envelope.

IBM RS-1 robots are this type.

A Cartesian robot:

Jointed arm robot configuration:

The configurations are:- This kind of robot resembles a human arm. It has two components corresponding to human

forearm and upper arm. The fore arm is connected to upper arm by an

elbow joint. The upper arm is connected to the body by a

shoulder joint. A wrist is connected to the forearm to perform

operations. SCARA model type of robots is jointed arm

type.

A jointed arm robot:

Work envelope:

It is the space within which the robot can manipulate its wrist end. The work volume is defined by the following characteristics:

Robots physical configuration Sizes of arm, body and wrist components Limits of the joints The polar configured robot has the work envelope

of sphere, the cylindrical type has cylinder envelope, Cartesian co-ordinate has a rectangular and the jointed arm has spherical envelope. The dimensions of the work envelope are defined by dimensions of the links and type of joints.

Classification of robots:

The broad classifications of robots are based on the following methods:

Configuration (same as above) Shape of workspace (same as above) Type of power-drive (electric,

pneumatic and hydraulic) Type of technology( low-level, medium

level and high level) Type of motion (linear, rotational,

extensional, twisting)

Type of power drive:

The movements of the body, arm and the wrist of the robots are determined by the power drive system. It also determines the speed, strength and performance of robots. Even drive system varies according the applications. The drive systems are:-

Hydraulic Electric Pneumatic

Hydraulic drive system:

The robots working on hydraulic power have some common features:

They are usually large type (unimate series). The essential advantage is greater speed and

strength. The disadvantage is the requirement of more

floor space, leakage etc. They usually actuate rotary and linear

movements. Rotary vane pump is employed for rotary

motion and hydraulic pistons for linear movement.

Electrical drive system:

Common specifications of electrical drive robots are:-

Do not provide as much speed and power compared to hydraulic system.

Accuracy and repeatability are far better. Requires less floor space and suitable for precise

applications. MAKER 110 is of this type. They employ stepper and servo motors for rotary

movements and telescopic arms for linear movements.

The cost of the electric robot is very much proportional too its size.

Pneumatic drive system:

The pneumatic robots have the following features:

Smaller robots with fewer degrees of freedom (2-4).

Often has application in pick and place operations.

More suitable for linear and sliding motions.

It can also be used in rotary applications.

Type of technology:

From the time of discovery of robotic technology various advancements have been made till now and the developments in technology is going on. Based on technology, the robots are classified as

Low level Medium level High level

Low-level:

Mostly used for material handling. Could carry out loading-unloading

and simple assembly operations. Fewer degrees of freedom with

movements at (2-4 axes). Have a payload of 25 pounds.

Medium level:

Mostly used for pick and place applications.

Carry out loading-unloading and common assembly operations.

Degrees of freedom is limited from (4-6) axes.

Has the payload up to 300 pounds.

High level:

Finds application in industrial manufacturing tasks.

Degrees of freedom is limited from (6-9) axes.

Has the payload from 300 pounds.

Specifications:

Robots are specified by the following terms:

Pitch Yaw Roll Joint notation Speed of motion Payload.

Roll-pitch-yaw:

Roll: The wrist of the robotic arm is

capable of rotating about its arm axis. It is called roll or swivel.

Pitch: With the wrist rotating about an axis,

the up and down motion of the wrist is called pitch.

Yaw: With the wrist rotating about an axis,

the left and right rotation of the wrist is called yaw.

Roll-pitch-yaw:

Joint notation:

The configuration of the robot can be represented by notations or symbols. (L, R, T, V)

L- Linear R- Rotation T- Twisting V- Revolving A polar configured robot is of type TRL

while a cylindrical robot can be of type TLL, LTL, LVL.

Speed:

The speed of the robot is essentially measured by a robot extending its arm to a maximum distance from the vertical axis and the speed is measure at the end of the wrist.

The maximum speed of the industrial robots is about 1.7m/s.

It determines how quickly a job can be accomplished.

It minimizes the cycle time for a given task.

Factors depending speed:

Speed depends upon 3 factors; Accuracy Accuracy has inverse relationship with speed. At

higher speeds, the robot could not locate the position accurately.

Weight of the object Weight of an object also has inverse relation on

speed. When heavy objects are moved due to inertia, it lacks its stability.

Distance to be moved Distance is directly proportional to speed. When

the robot has to travel a greater distance, it can reach its maximum possible speed.

Speed vs. distance:

0 1 2 3 4 5 6 70

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Series1; 0

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SPEED

SPEED

Pay load:

The weight carrying capacity of the robot determined by its weakest position is called payload. It depends upon size, configuration, drive system etc. if the rated load capacity of the robot is 5 kg and the end effectors load is 2kg then the pay load is 3kg.