Chapter 4

Industrial Robot

System and Control

Reference:

James G. Keramas, Robot Technology Fundamentals, Delmark Publishers,

1999.

** Part of this ppt are reproduced from other sources.

Industrial Robot Defined

A general-purpose, programmable machine possessing

certain anthropomorphic characteristics

Hazardous work environments

Repetitive work cycle

Consistency and accuracy

Difficult handling task for humans

Multishift operations

Reprogrammable, flexible

Interfaced to other computer systems

Robot Anatomy

Manipulator consists of joints and links

Joints provide relative motion

Links are rigid members between joints

Various joint types: linear and rotary

Each joint provides a “degree-of-

freedom”

Most robots possess five or six

degrees-of-freedom

Robot manipulator consists of two

sections:

Body-and-arm – for positioning of

objects in the robot's work volume

Wrist assembly – for orientation of

objects

Base

Link0

Joint1

Link2

Link3Joint3

End of Arm

Link1

Joint2

Manipulator Joints

Translational motion

Linear joint (type L)

Orthogonal joint (type O)

Rotary motion

Rotational joint (type R)

Twisting joint (type T)

Revolving joint (type V)

Joint Notation Scheme

Uses the joint symbols (L, O, R, T, V) to designate joint

types used to construct robot manipulator

Separates body-and-arm assembly from wrist assembly

using a colon (:)

Example: TLR : TR

Common body-and-arm configurations …

Polar Coordinate

Body-and-Arm Assembly

Notation TRL:

Consists of a sliding arm (L joint) actuated relative to the body, which can rotate about both a vertical axis (T joint) and horizontal axis (R joint)

Cylindrical Body-and-Arm Assembly

Notation TLO:

Consists of a vertical column,

relative to which an arm

assembly is moved up or down

The arm can be moved in or out

relative to the column

Cartesian Coordinate

Body-and-Arm Assembly

Notation LOO:

Consists of three sliding joints,

two of which are orthogonal

Other names include rectilinear

robot and x-y-z robot

Jointed-Arm Robot

Notation TRR:

SCARA Robot

Notation VRO

SCARA stands for Selectively

Compliant Assembly Robot

Arm

Similar to jointed-arm robot

except that vertical axes are

used for shoulder and elbow

joints to be compliant in

horizontal direction for vertical

insertion tasks

Wrist Configurations

Wrist assembly is attached to end-of-arm

End effector is attached to wrist assembly

Function of wrist assembly is to orient end effector

Body-and-arm determines global position of end

effector

Two or three degrees of freedom:

Roll

Pitch

Yaw

Notation :RRT

Example

Sketch following manipulator configurations

(a) TRT:R, (b) TVR:TR, (c) RR:T.

Solution:

T

R

T

V

(a) TRT:R

R

T

RT R

TR

R

(c) RR:T(b) TVR:TR

Joint Drive Systems

Electric

Uses electric motors to actuate individual joints

Preferred drive system in today's robots

Hydraulic

Uses hydraulic pistons and rotary vane actuators

Noted for their high power and lift capacity

Pneumatic

Typically limited to smaller robots and simple material

transfer applications

Types of Motion

Slew Motion

Each joint travels at a default speed from its initial position to the required

final destination.

Joint Interpolated Motion

Required the robot controller to calculate the time it will take each joint to

reach its destination at the commanded speed. Then it selects the

maximum time among this values and uses it as the time for the other axes.

Straight-line Interpolation motion

Requires the end of the end effector to travel along a straight line path

determined in rectangular coordinates.

Circular interpolation motion

Requires the robot controller to define the points of a circle in the workplace

based on a minimum of three specified positions. Normally consist of short

straight-line segments.

Path Control

Limited-sequence robots

Not use servo-control to indicate relative positions of the joint.

Instead, they are controlled by setting limit switches and/or

mechanical stops together with a sequencer to coordinate and time

the actuation of the joints. This control system is intended for simple

motion cycles, such as pick and place application.

Pick and place robot

– best choice for simple jobs,

lowest level of control & least

expensive

Path Control

Point-to-point robots

Point-to-point robots is the most commonly used. Can move from

one specified point to another but cannot stop at arbitrary points not

previously designated. Driven by servos and often controlled by

potentiometers set to stop the robot arm at a specified point. Point

to point robots can be programmed to move from any point within

the work envelope to any other point within the work envelope.

Point-to-

point

motion

Path Control

Controlled Path

Part of the 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 points. Controlled path

robots can generate straight lines, circles, interpolated curves, and

other path with high accuracy. Only start and finish coordinates and

the path definition are required for control.

Continuous-path motion

An extension to point to point method. Involves the utilization of

more points and its path can be an arc, a circle, or a straight line. A

continuous path program can have several thousand points and the

distance between points are extremely close.

Path Control

Comparison of controlled-path and noncontrolled-path operation

Intelligence Level

Robot systems are usually classified as low-technology and high-

technology groups.

Low-technology robots do not use servo control to indicate relative

positions of the joints.

High-technology robots are servo-controlled systems that accept

more sophisticated sensors and complex programming languages.

The intelligent control robot is capable of performing some of the

functions as tasks carried out by human beings. It can detect

changes in the work environment by means of sensory perception.

Aims of the intelligent robot systems: Performing tasks such as

moving among a variety of machines and equipment on the shop

floor and avoiding collision; recognizing, picking, and properly

gripping the correct raw material or work piece; transporting a

workpiece to a machine for processing or inspection; and

assembling the components into final product.

Control System

Control systems can be divided into two types, called open-loop or

closed-loop systems.

Stepper motor is an example of open-loop system where the control

signals directly position the motor without feedback.

Two types of closed-loop systems in industrial robot are servo and

non-servo. Servo refers to a continuous position-controlling device.

A non-servo robot may use a limit switch to indicate that the robot

has reached the desired position.

Both open-loop and closed-loop system may be used in overall

robot manipulator.

Control System

5 different classes of robot controllers:

Control System

5 different classes of robot controllers:

Control System

Closed loop for non-servo robot

Controller

Valve

Actuator

axis

The controller sends

a drive signal to a

valve that energizes

the actuator. When

the axis reaches the

desired position, a

signal is sent back to

the controller to

close the valve.

Control System

Servo Robot Operation

The servo robot has a basic controlled system that receives its

reference position signal from the sequence controller.

Comparison between the desired and current position produces

error signal.

The error signal converted to the proper form and applied to the

actuator.

With proper design, the action of this feedback is very smooth and

reliable.

Control System

Servo-controlled robot can move to any point within its work

envelope.

Control of velocity, acceleration, and deceleration between program

points is also possible.

Programming may be accomplished by teach pendant, by external

control or off-line programming.

The memory of the computer is usually sufficient to store thousands

of program points.

The characteristics of a servo-controlled robot may be observed in

the smooth motions with control of speed and acceleration.

Servo-controlled robot has a greater flexibility and ability to

accomplish variety of tasks.

Control System

Robot and workcell control system

Most robot control units today are based on a microcomputer

system, which can sense, evaluate, make decisions, and interact

with their environment.

When a robot executes a stored program for instructions that

defines the sequence of motions, and positions in the work cycle,

the program may also include instructions for other functions, such

as interacting with external equipment, responding to sensors, and

processing data.

The activities of such coordination must be established by means of

control-system requirements and workcell control.

Control System

Robot and workcell control system

Control System

Programmable Logic Controller

Originally designed to replace relay logic and to provide flexibility in

control based on programming and executing instructions.

The advantages of PLCs:

Easy to program and install

The speed with internal timers operate in much faster than

conventional time-delay relay systems.

Access to PLCs is restricted by hardware features, such as

keylocks, and by software features, such as password.

Problem-solving with PLCs is a major advantage over any other

type of control system.

Control System

PLCs can be designed with communications capabilities that

allow them to converse with local and remote computer systems

or to provide human interfaces.

PLCs are extremely reliable and easier-to-maintain control

devices and can be obtained in forms that can survive and

function in harsh conditions.

PLCs require less floor space than relay logic controls.

Control System

Block diagram of a PLC

Programming

terminal

Input CPU Memory Output

Power supply

Input

devicesOutput

devices

Control System

Input/Output

The input interface provides a connection to the machine or process being

controlled. The principal function of this interface is to receive and convert

field signals into a form that can be used by the CPU.

The output interface performs the opposite function of the input interface. It

takes signals from the CPU and translates them into forms that are

appropriate to produce control actions by external devices such as

solenoids, motor starters and so on.

Memory & CPU

Memory and CPU provide the main intelligence of a PLC. Fundamental

operating information is stored in memory as a pattern of electrical charges

(bits) that is organized into basic working groups called words. Each word

stored in memory is a piece of data, an instruction, or part of an instruction.

The CPU performs logical decisions, drives the outputs, and continually

refers to the program stored in memory for instructions concerning its next

action for reference data.

Control System

Programming language have many forms and each PLC

manufacture uses a slightly different language.

Most of PLC languages are based on ladder logic, which is

advanced form of relay logic.

Control System

Relay logic diagram

A typical relay logic diagram with a Stop/Start station and a

Control Relay (CR) operating a solenoid. In this circuit,

when CR1 is OFF, the solenoid is energized

Control System

Ladder logic diagram

The same diagram drawn in ladder logic. The input and

output devices are now represented by numbers. These

numbers are referred to as address

Control System

The basic points regarding ladder logic diagram.

All devices that represent resistive or inductive loads to the circuit are

shown at the right of the diagram.

All devices that represent or make or break electrical contacts are shown at

the left of the diagram.

Devices connected in parallel with other devices are often called branches.

Each complete horizontal line of a ladder diagram is typically referred to as

a rung.

Electrical devices are shown in their conditions. An NC contact would be

shown as normally closed, or represented as XIO (examine if open), and an

NO contact would appear as a normally open device or represented as XIC

(examine if closed). All contacts associated with a device will change state

when the device is energized.

Devices that perform a start function are connected in series; devices that

perform a start function are connected in parallel

The two parallel vertical lines where all rungs are connected provide power

to the components.

Control System

Programming terminal

A programming device, or programming terminal, allows a user to

enter instructions into memory in the form of a program. The

programming device produces the pattern of electrical signals that

correspond to the symbols, letters, or numbers entered by the user.

Many PLCs can now be programmed, using a teach pendant or

personal computer (PC).

Power Supply

The power supply provides all the voltage levels needed to operate

the PLC.

Control System

Why PLC?

PLC is a microprocessor based high end thoroughly developed

Product for Industry.

It can be programmed through high end programming software

uses its different simple to understand Ladder programming

Language.

Control System

Proportional-Integral-Derivative (PID)

Continuous process cannot be accomplished fast enough by a PLC

On-Off control.

PID control is the most often used in continuous process.

Many medium-size PLCs and all large PLCs have PID control

functions, which are able to execute process control effectively.

PID control keeps the output at a set level even though varying

process parameters may tend to cause the output to vary from the

desired set point.

PID promptly and accurately changes the process level from one

set point to another set point level.

Control System

Proportional-Integral-Derivative (PID)

The Characteristics of P, I, and D controllers

A proportional controller (Kp) will have the effect of reducing the rise time

and will reduce, but never eliminate, the steady-state error.

An integral control (Ki) will have the effect of eliminating the steady-state

error, but it may make the transient response worse.

A derivative control (Kd) will have the effect of increasing the stability of

the system, reducing the overshoot, and improving the transient

response.

Control System

Proportional Control

By only employing proportional control, a steady state error

occurs.

Proportional and Integral Control

The response becomes more oscillatory and needs longer to

settle, the error disappears.

Proportional, Integral and Derivative Control

All design specifications can be reached.

Control System

CL RESPONSE RISE TIME OVERSHOOT SETTLING TIME S-S ERROR

Kp Decrease Increase Small Change Decrease

Ki Decrease Increase Increase Eliminate

Kd Small Change Decrease Decrease Small Change

The Characteristics of P, I, and D controllers

Control System

Control System

Microprocessor Unit

The microprocessor plays a dominant role in computer technology

and has contributed uniquely in the development of many new

concepts and design techniques for modern industrial systems.

The development of the microprocessor has allowed the robot

industry to develop to its present state.

Control System

Universal Robot Controller

Programs for robots can be divided into two areas; operating

system and application programs.

Operating systems, sometimes called control programs are

developed by the manufacturer and are fixed for each robot model

and cannot be changed or exchanged with other manufacturers’

robots.

Operating systems supply the intelligence that enables the robot to

receive, understand, and carry out tasks that are given.

Application programs are known as user’s program.

These programs contain positional data, axis velocity, geometric

axis moves, gripper instruction, and interface instructions to other

devices and equipment.

Control System

Interfacing

Interfacing is the communication between various components of

the robot workcell that establishes a link between the peripheral

devices, the controller, and the manipulator’s end effector.

The interfacing operation requires the programmer of the robot to

assign various lines as either input lines or output lines.

The interfacing operation may be developed through a remote

connection, this process allows the operator of the workstation to

control different work cells from a central location.

Status signals from the robot can be sent to the remote workstation,

and signals from the remote workstation can be sent to the robot

controller.

In many high-technology automated systems, computer are

interfaced with the controller. The program are written on the

computer and then downloaded to the robot controller.

Control System

Workcell Control

A robotic workcell may be defined as a cluster of one or more

robots and several machine tools or transfer lines that are

interconnected in such a way that they work together

simultaneously.

The workcell controller performs several important functions in the

robot installation. These functions can be divided into three main

categories:

Sequence control

Operator interface

Safety monitoring

Control System

Workcell Control

Typical workcell: A robot is positioned to service a number of machine clusters

Control System

Sequence Control

The sequence is determined not only by controlling the activities as

a function of time, it is also determined by using interlocks to ensure

that certain elements of the work cycle are completed before other

elements are started.

In a loading and unloading application input/output, interlocks in

sequence control are used for purposes such as the following:

Making sure that the part is at the pickup location before the

robot attempt to grasp it.

Ensuring that the part is properly loaded into the machine before

the processing cycle begins.

Indicating to the robot that the machine cycle is completed and

the part is ready for unloading.

Control System

Operator Interface

Means for the operator to interact with the robot cell must be

provided. Reasons for establishing such interface include the

following:

Programming robot

Participation in the workcell. An operator and the robot each

perform a portion of the workcell in the cell. The operator

typically accomplished tasks that require judgment or sensory

capabilities that the robot does not possess.

Data entry, such as part identification or part dimension.

Emergency stopping of the cell activities.

Control System

Safety Monitoring

A more automatic and reliable means of protecting the cell

equipment and people who might wander into the work zone is

called safety monitoring.

Safety monitoring is a workcell control function in which sensors are

used to monitor the status and activities of the cell and detect the

unsafe or potential unsafe conditions.

Various sensors can be used to implement a safety monitoring

system in a robot cell that may include limit switch, temperature

sensors, pressure-sensitive floor mats, light beams combined with

photosensitive sensors, and machine vision systems.

Control System

Safety Monitoring

The safety monitoring system is programmed to respond to various

hazard conditions in different ways. These responses might include

one or more of the following:

Complete stoppage cell.

Slowing down the robot speed to a safe level.

Warning buzzers to alert maintenance personnel of a safety

hazard in the cell.

Special program subroutines to permit the robot to recover from

a particular unsafe event.

Robot Programming

Leadthrough programming

Work cycle is taught to robot by moving the

manipulator through the required motion cycle and

simultaneously entering the program into

controller memory for later playback

Robot programming languages

Textual programming language to enter

commands into robot controller

Simulation and off-line programming

Program is prepared at a remote computer

terminal and downloaded to robot controller for

execution without need for leadthrough methods

Leadthrough Programming

1. Powered leadthrough

Common for point-to-

point robots

Uses teach pendant

Some of the key

applications are spot

welding, machine

loading & unloading,

and part transfer

process.

Leadthrough Programming

2. Manual leadthrough

Convenient for

continuous path control

robots

Human programmer

physical moves

manipulator

This method is best for

spray painting and arc

welding operations.

Leadthrough Programming

Advantages

Advantages:

Easily learned by shop personnel

Logical way to teach a robot

No computer programming

Disadvantages:

Downtime during programming

Limited programming logic capability

Not compatible with supervisory control

Robot Programming

Textural programming languages

Enhanced sensor capabilities

Improved output capabilities to control external equipment

Program logic

Computations and data processing

Communications with supervisory computers

Coordinate Systems

World coordinate system Tool coordinate system

Motion Commands

MOVE P1

HERE P1 - used during lead through of manipulator

MOVES P1

DMOVE(4, 125)

APPROACH P1, 40 MM

DEPART 40 MM

DEFINE PATH123 = PATH(P1, P2, P3)

MOVE PATH123

SPEED 75

Interlock and Sensor Commands

Interlock Commands

WAIT 20, ON

SIGNAL 10, ON

SIGNAL 10, 6.0

REACT 25, SAFESTOP

Gripper Commands

OPEN

CLOSE

CLOSE 25 MM

CLOSE 2.0 N

Simulation and Off-Line Programming

END