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Ch 3 Introduction to Automation

Sections:

1. Basic Elements of an Automated System

2. Advanced Automation Functions

3. Levels of Automation

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Automation and Control Technologies in

the Production System

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Automation Defined

“Automation is the technology by which a process or

procedure is accomplished without human

assistance”

Basic elements of an automated system:

1. Power - to accomplish the process and operate

the automated system

2. Program of instructions – to direct the process

3. Control system – to actuate the instructions

It is implemented using a Program of Instructions combined with

a Control System that executes the instructions.

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Elements of an Automated System

Fig. 4.2

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Power to Accomplish the

Automated Process

Power for the process

To drive the process itself

To load and unload the work unit (proper position and

orientation)

Transport between operations

Power for automation

Controller unit

Power to actuate the control signals

Data acquisition and information processing

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Controller Unit (digital computer)

Read program of instructions

Make the control calculations

Execute instructions by transmitting the proper commands

to the actuating devices

Actuaters are electromechanical devices such as switches

and motors.

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Electricity -

The Principal Power Source

Widely available at moderate cost

Can be readily converted to alternative forms, e.g.,

mechanical, thermal, light, etc.

Low level power can be used for signal transmission, data

processing, and communication

Can be stored in long-life batteries

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Program of Instructions

“Set of commands that specify the sequence of steps in

the work cycle and the details of each step”

Example: CNC part program

During each step, there are one or more activities

involving changes in one or more process parameters

Examples:

Temperature setting of a furnace

Axis position in a positioning system

Motor on or off

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1. The actions performed by an automated process are

defined by a “Program of Instructions”.

2. A new part or parts are completed during each work

cycle.

3. The particular processing steps for the work cycle are

specified in a “Work Cycle Program” (part programs).

4. The program of instructions is repeated each work cycle

without deviation.

5. In many cases, the corresponding instructions for dealing

with variations are incorporated into the regular program.

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Decision-Making in a

Programmed Work Cycle

The following are examples of automated work cycles in which decision making is required:

Operator interaction

Automated teller machine

Different part or product styles processed by the system

Robot welding cycle for two-door vs. four door car models

Variations in the starting work units

Additional machining pass for oversized sand casting (nonstandard/unidentical parts)

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Features of a Work Cycle Program

Number of steps in the work cycle

Manual participation in the work cycle (e.g., loading

and unloading workparts)

Process parameters - how many must be controlled?

Operator interaction – is operator required to enter

processing data?

Variations in part or product styles

Variations in starting work units - some adjustments in

process parameters may be required to compensate

for differences in starting units

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Control System

The Control element of the automated system executes

the program of instructions.

The control system causes the process to accomplish its

defined function, to carry out some manufacturing

operation.

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Control System – Two Types

1. Closed-loop (feedback) control system – a system in

which the output variable is compared with an input

parameter, and any difference between the two is used

to drive the output into agreement with the input

2. Open-loop control system – operates without the

feedback loop

Simpler and less expensive

Risk that the actuator will not have the intended

effect

E.g. Car parking sensors

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Input Parameter (set point) represents the desired value of the output

The process is the operation or function being controlled (output value)

A sensor is used to measure the output variable and close the loop between input and output.

The controller compares the output with the input and makes the required adjustment in the process to reduce the difference between them.

The adjustment is accomplished using one or more actuators which are the hardware devices that physically carry out the control actions.

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(a) Feedback Control System and

(b) Open-Loop Control System

(a)

(b)

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Positioning System Using

Feedback Control

A one-axis position control system consisting of a

leadscrew driven by a dc servomotor and using an optical

encoder as the feedback sensor

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When to Use an

Open-Loop Control System

Actions performed by the control system are simple

Actuating function is very reliable

Any reaction forces opposing the actuation are small

enough as to have no effect on the actuation

If these conditions do not apply, then a closed-loop control

system should be used

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Advanced Automation Functions

1. Safety monitoring

2. Maintenance and repair diagnostics

3. Error detection and recovery

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Safety Monitoring

“Use of sensors to track the system's operation and

identify conditions that are unsafe or potentially unsafe”

Reasons for safety monitoring

To protect workers and equipment

Possible responses to hazards:

Complete stoppage of the system

Sounding an alarm

Reducing operating speed of process

Taking corrective action to recover from the safety

violation

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Safety monitoring - Examples

Temperature sensors

Heat or smoke detectors

Pressure sensetive floor pads

Vision systems

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Maintenance and Repair Diagnostics

Maintenance and Repair Diagnostics refer to the

capabilities of an automated system to assist in identifying

the source of potential or actual malfunctions and failures

of the system.

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Maintenance and Repair Diagnostics

Status monitoring

Monitors and records status of key sensors and parameters during system operation

Failure diagnostics

Invoked when a malfunction occurs

Purpose: analyze recorded values so the cause of the malfunction can be identified

Recommendation of repair procedure

Provides recommended procedure for the repair crew to effect repairs

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Errors

Random errors occur as a result of the normal stochastic

nature of the process

Systematic errors are those that result from some

assignable cause such as a change in raw material

properties

Aberrrations (disorders) result from either an equipment

failure or a human mistake

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Error Detection and Recovery

1. Error detection – functions:

Use the system’s available sensors to determine

when a deviation or malfunction has occurred

Correctly interpret the sensor signal

Classify the error

2. Error recovery – possible strategies:

Make adjustments at end of work cycle

Make adjustments during current work cycle

Stop the process to invoke corrective action

Stop the process and call for help

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Levels of Automation

1. Device level – actuators, sensors, and other hardware

components to form individual control loops for the next

level

2. Machine level – CNC machine tools and similar

production equipment, industrial robots, material

handling equipment

3. Cell or system level – manufacturing cell or system

4. Plant level – factory or production systems level

5. Enterprise level – corporate information system

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Levels of Automation