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.
