1.1.1 Distinguishing characteristics,

 

• An automatic materials handling subsystem links machines in the system and provides for automatic interchange of workpieces in each machine

 

• Automatic continuous cycling of individual machines

 

• Complete control of the manufacturing system by the host computer

 

• Lightly manned, or possibly unmanned

 

• Characteristics of application,

- Medium product mix

- Medium production volume

- Allows fast changeover on products

 

• Various measures of flexibility,

- Able to deal with slightly, or greatly mixed parts.

- Variations allowed in parts mix

- Routing flexibility to alternate machines

- Volume flexibility

- Design change flexibility

 

• Major historical developments,

- Weaving Looms with paper tapes,

- NC machines with paper tapes

- Hard wired NC machines

- Computer controlled NC machines (CNC)

- Direct Numerical Control (DNC)

 

• Components of FMS Systems,

- Robotics

- Material Handling / Transport

- Machines

- Manual / Automated Assembly Cells

- Computers

- Controllers

- Software

- Networks

- Interfacing

- Monitoring equipment

 

• Humans are not without function in an FMS cell,

- loading and unloading workparts to and from the system

- changing tools and settings

- equipment maintenance and repair

 

• Computers provide essential support in a workcell for,

- CNC - Computer Numerical Control

- DNC - Direct Numerical Control of all the machine tools in the FMS. Both CNC and DNC functions can be incorporated into a single FMS.

- Computer control of the materials handling system

- Monitoring - collection of production related data such as piece counts, tool changes, and machine utilization

- Supervisory control - functions related to production control, traffic control, tool control, and so on.

 

• FMS systems are intended to solve the following problems,

- Production of families of workparts, often based on group technology

- Random launching of workparts into system is OK, because setup time is reduced with FMS.

- Reduced manufacturing lead time - this is possible because FMS has organization, and fast setup.

- Reduced work in process

- Increased machine utilization

- Reduced direct and indirect labor

- Better management control

 

 

• The most common problems in an FMS are,

- Scheduled maintenance

- Scheduled tool changeovers

- Tooling problems (failures and adjustments)

- Electrical Failures

- Mechanical Problems (e.g., oil leaks)

 

• Implementation Strategies,

- find and identify a champion (someone who will push for automation)

- spend time to educate workers and engineers on FMS

- invest in the planning stages

- look at others in industry

- use employee involvement from the start

- install in stages - don’t try to implement all at once

 

• Things to Avoid when making a decision for FMS,

- ignore impact on upstream and downstream operations

- allow the FMS to become the driving force in strategy

- believe the vendor will solve the problem

- base decisions solely on financials

- ignore employee input to the process

- try to implement all at once (if possible)

 

• Justification of FMS,

- consider “BIG” picture

- determine key problems that must be solved

- highlight areas that will be impacted in enterprise

- determine kind of flexibility needed

- determine what kind of FMS to use

- look at FMS impacts

- consider implementation cost based on above

 

• Factors to consider in FMS decision,

- volume of product

- previous experience of company with FMS

- product mix

- scheduling / production mixes

- extent of information system usage in organization (eg. MRP)

- use of CAD/CAM at the front end.

- availability of process planning and process data

* Process planning is only part of CIM, and cannot stand alone.

 

 

1.1.2 General Concepts

 

• Manufacturing requires computers for two functions,

- Information Processing - This is characterized by programs that can operate in a batch mode.

- Control - These programs must analyze sensory information, and control devices while observing time constraints.

 

• A CIM system is made up of Interfaced and Networked Computers. The general structure is hierarchical,

 

• The plant computers tend to drive the orders in the factory.

 

• The plant floor computers focus on departmental control. In particular,

- synchronization of processes.

- downloading data, programs, etc., for process control.

- analysis of results (e.g., inspection results).

 

• Process control computers are local to machines to control the specifics of the individual processes. Some of their attributes are,

- program storage and execution (e.g., NC Code),

- sensor analysis,

- actuator control,

- process modeling,

- observe time constraints (real time control).

 

• The diagram shows how the characteristics of the computers must change as different functions are handled.

 

 

• To perform information processing and control functions, each computer requires connections,

- Stand alone - No connections to other computers, often requires a user interface.

- Interfaced - Uses a single connection between two computers. This is characterized by serial interfaces such as RS-232 and RS-422.

- Networked - A single connection allows connections to more than one other computer. May also have shared files and databases.

 

• Types of common interfaces,

- RS-232 (and other RS standards) are usually run at speeds of 2400 to 9600 baud, but they are very dependable.

 

• Types of Common Networks,

- IEEE-488 connects a small number of computers (up to 32) at speeds from .5 Mbits/sec to 8 Mbits/sec. The devices must all be with a few meters of one another.

- Ethernet - connects a large number of computers (up to 1024) at speeds of up to 10 Mbits/sec., covering distances of km. These networks are LAN’s, but bridges may be used to connect them to other LAN’s to make a WAN.

 

• Types of Modern Computers,

- Mainframes - Used for a high throughput of data (from disks and programs). These are ideal for large business applications with multiple users, running many programs at once.

- Workstations (replacing Mini Computers) - have multiprocessing abilities of Mainframe, but are not suited to a limited number of users.

- Micro-processors, small computers with simple operating systems (like PC’s with msdos) well suited to control. Most computerized machines use a micro-processor architecture.