Chapter 6

Automated Manufacturing Systems

Objectives

• Types of automation.• Computer based control systems.• Integration of product design software and

manufacturing systems software.

Introduction

• Building blocks of automation:• 1. A repeatable manufacturing operation or

process.• 2. A control system.• 3. A material placement system.• If automation is to be successfully

implemented, all sources of variability must be controlled.

The Nature of Automation

• Before interchangeability can be accomplished components and materials must be standardized.

• To achieve interchangeability you must control variability.

• The primary goal of automation is to improve productivity.

• Productivity is dependent on the reliability, availability, and maintainability of the hardware and tooling of the automated system.

Control Systems

• In a manual control system the operator is required to start, stop, or adjust the process by pushing buttons, turning knobs, or engaging levers on the machine.

• Automated control systems must be able to start, stop, and sequence production (advance parts). They must simultaneously monitor the quality of the product and the functioning of the system.

Open and closed loop systems

• An open loop control system attempts to meet a preset standard without monitoring the output or taking corrective action.

• Examples are dishwashers and clothes dryers.• A closed loop system consists of an input,

error detector, controller, actuator, output and a feedback circuit.

• Feedback: The output is measured and compared to a preset standard or reference.

On/Off Control

• Most actuators are on/off devices such as motors, solenoid valves, and relays.

• Relay logic, a system based on opening and closing electro-mechanical relays served for many years as the basis for a majority of the on/off control systems.

• Now programmable logic controllers (PLCs) have almost completely replaced relays in automatic control systems.

Control System Design• If the operation requires variation of speed,

tension, or temperature , proportional control should be considered.

• Steps in control:• 1. Identify the output devices that must be

activated or controlled.• 2. Determine the states of the output devices.• 3. Identify the input that would cause the control

system to activate the output device and result in the desired change in state.

Numerical Control• Numerical control (NC)is a type of programmable

machine tool automation.• A numerical control program contains precise

instructions for each move along each machine axis.• The programmer determines the moves, sequence,

tools, and overall motions that the machine tool uses in machining the part.

• Under NC, the primary responsibility of the machine operator is monitoring the machine tool’s operation.

• With Computer Numerical Control (CNC) a microprocessor is built in to the control panel of the machine tool.

Adaptive Control

• Adaptive control systems can respond to conditions being encountered by a particular machining operation and make necessary changes in feed rates and other factors.

• Adaptive control became possible with the advent of miniaturized sensors and transducers that could measure the forces and temperatures created by the cutting tool.

Computer Integrated Manufacturing

• Computer Integrated Manufacturing (CIM) involves using computers to link together the various control systems that are found in manufacturing.

• CIM is now viewed by many manufacturing firms as an essential strategy for remaining competitive in a global market.

• Large production lots are not necessary – with CIM the ideal lot or batch size is one.

Material Handling Systems

• Three major types of material handling systems: bulk systems, feeding/orienting devices, and magazine feeders (fig. 6-7, page 103).

• Bulk systems are designed to dispense liquids, gases, and granular solids.

• A feeder system contains and conveys discrete components while simultaneously orienting and sorting them.

• Magazine systems are material handling systems that contain and convey pre oriented parts.

Summary• The primary goal of automation is to improve productivity.• Productivity is dependent on the reliability, availability, and maintainability of the hardware

and tooling of the automated system.• Automated control systems must be able to start, stop, and sequence production (advance

parts). They must simultaneously monitor the quality of the product and the functioning of the system.

• An open loop control system attempts to meet a preset standard without monitoring the output or taking corrective action.

• A closed loop system consists of an input, error detector, controller, actuator, output and a feedback circuit.

• Feedback: The output is measured and compared to a preset standard or reference.• Now programmable logic controllers (PLCs) have almost completely replaced relays in

automatic control systems.• With Computer Numerical Control (CNC) a microprocessor is built in to the control panel of

the machine tool.• Computer Integrated Manufacturing (CIM) involves using computers to link together the

various control systems that are found in manufacturing.

Home Work

• 1. What is the primary goal of automation?• 2. What is productivity dependent on?• 3. What should automated control systems be

able to do?• 4. Define an open loop control system.• 5. Define a closed loop system.• 6. What is feedback?