Fundamentals of factory communications.
A 1978 study sponsored by the Computer & Automated Systems Association of the Society of Manufacturing Engineers (CASA/SME) projected that an integrated factory-communication system would provide the following:
* Reduced workstation delays, resulting in less worker- and machine-idle time as well as additional operating capacity.
* Reduced lead times for shop orders, which can reduce work-in-process stock.
* Reduced schedule variances and improved customer service.
* More efficient cube use, which can open up valuable plant-floor space.
The study also projected that, in a worst case, an integrated system would return its investment within three years.
Approximately 100 computer vendors now offer products suitable for integrated factory communications, and it's predicted that the current $50-million market will explode to $250 million by 1990.
A LAN is a private data-communications system covering a limited geographical area (usually less than two miles). Distributed data processing using a LAN allows microcomputer users within a factory hierarchial network to communicate with other levels, share data bases and high-speed or special-purpuse output devices, and access remote mainframes within a corporate network.
A generic full-blown factory-communications system consists of four management levels: factory, department, workcenter, and operation, Figure 1. At the factory level, mainframes talk with other mainframes as part of a geographically distributed network; factory mainframes also can talk to department-level minicomputers. The department's computers may interface with workcenter micros and programmable controllers at the operations level by means of an industrial-strength LAN.
A shop-floor LAN generally has three main elements--monitors, servers, and workstations.
Monitors provide machine-to-machine communications, such as programmable controllers interfaced with sensors, electronic counting scales interfaced with NC machines, and AMH&S equipment (including robots) for workpiece transfers.
Servers, typically micro- or mini-computers, provide acceess to shared hard-disk data bases as well as to high-speed printing and communications devices. Material-flow system activities use monitors and workstations interfaced with information-flow servers on the LAN. Shop-floor production instruction and document files, for example, can be downloaded to a communications server acting as a LAN gateway node supporting communications between the department and factory levels. Such files may be loaded to a data-base server awaiting a request from a printer server, and/or transmitted to a workstation data-base management system (DBMS) or directly to NC and AMH&S-system monitors.
A shop's production status then may be uploaded to a workstation DBMS. The information is either forwarded to the LAN-data-base server for periodic workcenter reporting, or transmitted to the LAN gateway server for on-demand reporting to department- and factory-management levels.
Workstations provide human communications at the workcenter level by means of inteeligent and nonintelligent terminals. The former are capable of supporting a floppy-disk data base and a character printer.
Although AMH&S systems can physically link islands of automation, a software interface with shop-floor controllers is needed to integrate material and information flow in a factory. Physical (i.e., equipment) interfaces are relatively easy to establish. Integrating AMH&S and SFC systems into a unified communications system, however, is difficult.
A major problem is linking devices for monitoring, sensing, handling, and storing material in a way that effectively addresses the needs of the four management levels. This is complicated by a confounding array of design alternatives. Because vendors differ in their approaches, their offerings may not be compatible.
Moreover, because LANs are new, few vendors have the experience needed to resolve the problems of fully integrating a factory. most vendors have either a mechanics or an electronics background.
Mechanical vendors (e.g., manufacturers of NC machine tools, robots, and automated storage and retrieval systems) have extensive experience in solving shop problems. In contrast, electronics vendors (e.g., computer manufacturers) are experienced in solving data-processing and communications problems. The few firms expert in both areas are usually industrial giants (such as General Motors), or computer companies that have developed robots or programmable controllers.
At present, no vendor can be a sole supplier of an integrated factory.
Private automatic branch exchange (PABX), baseband, and broadband are the major LAN technologies. A PABX transmits messages to and from the public telephone network, which uses analog media. To accomodate digital-computer communications, microprocessor-controlled digital switching devices provide the PABX with integrated voice- and data-transmission capabilities.
The advantages here are economy and flexibility of using existing telephone lines, and relatively high transmission speeds (more than 50K bits/sec). The high cost of switching devices, however, plus an inability to handle numerous file transfers at peak data rates, are some disadvantages.
Broadband and baseband LANs also differ in capabilities and cost. Broadband analog signals are frequency modulated so multichannel voice, data, and video communications can be transmitted simultaneously, which isn't possible with baseband. Broadband systems can cover distances up to 50 kM, with data-transmission rates exceeding 100M bits/sec; baseband systems generally are limited to 2.5 kM and speeds of 10M bits/sec. Although baseband technology is generally cheaper, for more than 100 attached devices, broadband becomes more economical.
LAN systems for factory communications most likely will be a hybrid of these network approaches, with bridges between alternative transmission nodes and gateways to external long-distance public and/or private telecommunications networks. The LAN long-distance main trunk may be a broadband bus coaxial cable system interfaced with dedicated baseband bus coaxial cable systems that integrate communications between individual machine-control systems on the shop floor and an AMH&S system.
Network configuration determines organization of nodes, incidentally, and distances between nodes determines transmission medium (e.g., wire, cable, fiber optics). LANs can operate within distributed data-processing networks with geographical (Figure 2) and/or hierarchial (Figure 3) schemes.
Typically, coaxial cable is used for long distances (geographical networks) and twisted-pair wire is used for short distances (hierarchial networks). Because coaxial cable permits faster transmission than does twisted-pair wire, the choice of medium also impacts system response time. (See accompanying box, "LAN configurations," and Tooling & Production, July 1984, pg 67, "Introduction to local-area networks."
Can't get a word in?
The most common Lan access methods are carrier sense multiple access with collision detection (CSMA/CD) for bus configurations, and token passing for most ring designs. CSMA/CD, developed by Xerox Corp for Ethernet, has been adopted as the baseband interface standard by DEC, Intel, and others.
CSMA/CD works with two basic rules: Listen before talking, and listen while talking. A device won't initiate a message if another device is transmitting. While transmitting, a device listens for other messages; if its message collides with another, both devices discontinue transmission for randomly established delay times and then begin again. Random delays minimize the chance that the devices will begin transmission simultaneously.
CSMA/CD works well in networks with frequent burst (i.e., intermittent) transmission. Retransmission delays, however, can cause unacceptable irregular response times. Also, CSMA/CD limits data-packet size to minimize the time for a pulse (or level transmission) to travel through a device (called network propagation delay).
In token passing, on the other hand, the network transmits a short message (a token) to indicate that its communication lines are idle; a communication device picks up the token, transmits its message, then releases the token for another device to pick up.
For token passing, network control is centralized among sepecial-purpose nodes. although centralized control adds a potential source of system failure, it supports both regular transmissions and frequent burst traffic. Token passing doesn't limit data-packet size.
Need for standards
Interface standards are needed to ensure that multivendor elements will communicate with each other. Although no universal standard exists yet, several development efforts are in progress. The Computer & Business Equipment Manufacturers Association, for example, is developing LAN standards, and the Electronic Industries Association is standardizing formats and protocols for communications between NC machines and AMH&S equipment (also robots).
In addition, the International Standards Organization--with its US representative, the American National Standards Institute--is developing standards for industrial automation. They have established a reference model for open system interconnection (OSI).
This model defines seven layers of material, and information-flow integration: physical, link, network, transport, session, presentation, and application. Layering, a universally accepted network architecture concept, creates data-communications protocols that function at all levels.
The physical layer is the actual cable wires and plug connectors; standards already in use include RS-232 cable/connectors for low-speed serieal transmission and RS-422 cable/connectors for low-speed serial transmission and RS-422 twisted-pair wires/connectors for high-bandwidth transmission.
Intermediate layers perform error detection and correction (link), as well as routing and data switching (network). The Institute of Electrical and Electronics Engineering (IEEE) standard 802 specifies a LAN's physical and link layers. Commercial vendors typically support layers one through three. higher layers provide data pathways and format translation for communication between specific applications programmed by data-terminating-equipment vendors.
To support the physical and link layers of the OSI model, the IEEE 802 standard specifies that a baseband LAN use a bus configuration with 50-ohm coaxial cable; user devices interface with the network controller using RS-232.
Baseband systems using IEEE 802 transmit at 1M, 5M, and 10M bits/sec over a maximum interstation distance of 2.5 kM. The 802 broadband standard requires a bus with 75-ohm coaxial cable to support transmission rates of 1M, 5M, 10M, and 20M bits/sec; it uses the single-cable CATV standard for midfrequency and half-duplex or full-duplex transmission.
Factory LAN's must be able to operate in a hostile environment. Electrical interference from machines, caustic chemicals, and dust can jumble information transmission, thereby inviting disaster. Several vendors have developed industrial-strength LANs, however.
For example, DEC offers Dataway, an Ethernet-compatible, baseband bus system using coaxialcable and CSMA/CD access control. Transmission rate is 10M bits/sec. hewlett-Packard also supports an Ethernet-compatible system.
General Electric's GEnet is a broadband system that uses CATV coaxial cable and transmits at 1M to 5M bits/sec. This LAN offers a family of I/O interface modules including RS-232 and RS-422 twisted-pair wires, 8-bit parallel and serial asynchronous lines, and gateways to alien computers. CSMA/CD is currently used, but token passing has been announced. GEnet, by the way, conforms to the IEEE 802 LAN standard and specifies the physical, link, network, and transport OSI layer.
Thre programmable-controller vendors also have introduced factory LANs: Allen-Bradley's Data Highway, Gould's Modbus and Modway, and Texas Instruments' TIWAY I and TIWAY II. Although Modbus and TIWAY I also are supervisory master/slave networks, the Data Highway's approach promises better system reliability.
In the Data Highway, any of 64 programmable controllers in the network can serve as a master controller. Messages can be transmitted at 56K bits/sec over 10,000 ft (maximum). Interface communications software supports DEC's PDP-11 computers.
Modway and TIWAY II are peer-to-peer systems. Modway is a broadband, masterless (peer-to-peer, token-passing) control system; it transmits at 1.54M bits/sec up to 15,000 ft and interfaces with Gould's SEL computers. TIWAY II transmits data at rates exceeding 1M bits/sec and interfaces with Texas Instrument mini- and micro-computers. All three vendors offer gateways to other computer networks (such as GM's MAP).
A MAP for the future?
Last July, at the National Computer Conference (Las Vegas), General Motors unveiled a multivendor demonstration of its Manufacturing Automation Protocol (MAP). Participating companies and products included an Allen-Bradley Vistanet Data Gateway, A Digital Equipment VAX--11/750, A Gould Concept 32/2705, A Hewlett-Packard HP 1000, an IBM Series I, and a Motorola VME/10. All of this computer equipment communicated via a Concord Data Systems Token/Net Interface Module.
Recenty, R J Eaton, GM's VP of Advanced Product & Manufacturing Engineering, spoke on the value of factory communications, and specifically on why GM is pushing MAP. Here is some of what he had to say-- It's no secret that General Motors, and the rest of US industry for that matter, must continue improving quality and efficiency if we are to remain internationally competitive. Computers, or programmable devices from our perspective, in the hands of highly motivated workers appear to be a solution to many manufacturing challenges. Installing stand-alones on the plant floor to control single or multiple processes, however, won't solve long-term manufacturing problems.
Presently, GM uses approximately 40,000 programmable devices on its plant floors; only 15 percent communicate beyond their own processes, thereby creating islands of automation. By 1990, we expect to be using 200,000 such devices. This makes it critical that communications barriers between machines from different computer and controls companies be torn down quickly. GM must have automation that works in harmony, and communicates readily, with other plant functions.
With this objective, in 1980 we formed a task force with representation from 15 divisions. After substantial research, this group recommended adopting MAP, which we formally did in October 1982.
Getting from here to there
MAP is a seven-layer, broadband, token-bus-based communications standard for the factory. It incorporates elements developed by the US National Bureau of Standards, the International Standards Organization, the Institute of Electrical and Electronic Engineers, and the American National Standards Institute. We're counting heavily on MAP being accepted widely because it incorporates existing or emerging nonproprietary communications standards.
MAP specifies a coaxial cable that will be the backbone of our plant network. Eventually, this will permit ridding ourselves of the burden of twisted-pair, which would become intolerable as programmable devices proliferate on plant floors.
Next year we will employ MAP to help manufacture front-drive axles at our Saginaw Steering Gear Div, Saginaw, MI. Saginaw will be a multivendor, computer-integrated two-phase project. Forty manufacturing cells will be operational by late 1985; and by 1987, these cells will be integrated into a factory-control system and the plant's CAD/CAM systems.
In addition, over 60 robots will be running in the 70,000-sq-ft plant. Material will be automatically stored, retrieved, and transported throughout the factory on automatic guided vehicles.
Changeovers will be scheduled through factory controllers; new programs will be automatically loaded into the cells. All information will be electronically stored and transmitted, making Saginaw a truly paperless factory.
Flexibility is the key motivator for this venture. Our goal is to change over any cell in less than 10 min.
Saginaw will be a working laboratory to speed implementation of advanced manufacturing technology throughout GM. Other divisions are planning to purchase MAP compatible equipment to kick off their own multivendor local-area networks.
all future plant-floor programmable devices at General Motors must be able to communicate beyond their processes, therefore we will require that they be MAP compatible.
LAN joint venture
Ungermann-Bass Inc, Santa Clara, CA, and the General Electric Co, Charlottesville, VA, have signed a letter of intent to form an independent joint-venture company. Its purpose will be to develop, manufacture, and market local-area networks (LAN) for interconnecting industrial-automation equipment, and other intelligent devices such as CAD/CAM systems, regardless of brand.
Products of the venture will be sold to industrial-equipment manufacturers, including GE, on an OEM basis. GE will market the products as components of its industrial-automation systems.
All products will be compatible and interconnectable with Ungermann-Bass' general-purpose LANs, and will be in accordance with General Motors' MAP spec (IEEE 802.4).
GE will provide funding, while Ungermann-Bass will contribute technology from its current product line and be responsible for initial staffing.
Solid-modeling enhancements for GEOMOD are offered
General Electric CAE International Inc, Milford, OH--A joint venture of General Electric and Structural Dynamics Research corp (SDRC)--has introduced enhancements to the SDRC GEOMOD solid-modeling software.
The enhancements include several new visualization and modeling capabilities for engineering analysis; 20 percent faster response throughout the dual data structure; lower-cost pricing options for VAX, IBM, and Apollo computers; and the support of additional graphics terminals.
The NEW GEOMOD solid modeler version 2.5 is available for immediate delivery. It has been in beta test with divisions of such clients as Hughes, General Electric, Aerojet, and Ford for the past six months.
These clients have used GEOMOD in such applications as packaging of automotive, aerospace, and electronic equipment; product visualization and technical marketing; geometry preparation for finite element analysis; geometry definition for kinematic and dynamic analysis; creation of family-of-parts geometries, and geometry preparation for numerical control machining.
For details, circle E19.
According to the Society of Manufacturing Engineers, flexible manufacturing systems are to the 1980s what industrial robots were to the 1970s--a rapidly advancing technology that is having a dramatic impact on the way your company manufacturers its products. The society suggests that you prepare for this revolution now, with the newest book in the Manufacturing Update Series, Flexible Manufacturing Systems. It gives an overview of FMS equipment and includes background data and in-depth investigations of actual systems in use producing heavy construction equipment, machine tools, etc.
Chapters give information on various elements of an FMS, such as factory communications, data-base requirements, robotics, sensors, NC, and programmable controllers. There are discussions of systems engineering and simulation to help with questions of productive capacity, storage and buffer requirements, routing options, etc. The cost is $39 (only $34 for SME members) from SME, P O Box 930, Dearborn, MI 48121.
Unique licensing for FMS control
Rick Lussier, a VP at Automation Intelligence, Orlando, FL, has announced a unique licensing approach for FMS supervisory control. "Normal licensing limits the use of software to a specific manufacturer's CPI, and, indeed, to a specific serial number of that CPU. This severely limits the customer's future flexibility should the underlying computer hardware become obsolete or orphaned. Even though FMS is relatively new, already there are examples of customers with an FMS based on older 16-bit supervisory systems who find it impractical to update."
Mr Lussier adds, "AI has taken a two-step approach to resolve this problem. First, our FMS software license specifcally allows the customer to transfer from his current computer to a replacement CPU at no additional license fee. For example, if our current VAX customers find they prefer a different hardware platform in the future, they are free to replace it.
"Our second step makes this substitution a practical reality for the first time. Until now, FMS suppliers used CPU vendor proprietary operation systems and support. Such systems present a big obstacle to hardware replacemtn because, as a rule, they are not transportable. However, AI's VAX-based FMS will use only UNIX-based operating software. Through this use, future replacement of hardware becomes much easier. Thus our package provides good technology while protecting te user from future obsolescence." For more information, circle E28.
CNC gantry changes turning tools and loads workpieces
New flexible turning system is billed as a practical and affordable solution to total factory automation. The system employs standard modular units as building blocks and adds a multpurpose gantry loader for more-flexible automation. The building-block concept allows easy expansion, including upgrading the loading system to handle more machine tools or work stations, and linking several small systems to logically plan a fully automated production line.
The key to the flexible turning system is an Emag MSC 22 two-spindle CNC lathe that turns shafts and flange-type parts in both first and second operations. It has a four-axis CNC unit, two 33-hp spindle drives, tool probes, a tool monitoring system, and an indexing tail-stock.
The CNC four-arm gantry loader operates above the mechine and other stations, performing several functions during the machining cycle. These include automatic tool changing, part gaging, and part palletizing. The gantry works with a dual-arm tool-changing unit to select tools from a 96-station magazine (shown).
Becuase all the functions take place during the machining cycle, no time is lost by the machine waiting for the loader. Once the loader performs its task, it waits directly above the spindles for the machining cycle to end, at which time the two machined parts are inserted into holding devices.
After new parts are automatically loaded into the machine, the gantry delivers both first- and second-operation parts to the gaging station, where they are automatically checked. Dimensional corrections are transmitted to the CNC. The parts are then placed on the turnaround station and indexed 180 degrees. The finished part is returned to the pallet, while the first-operation part is retained by the gantry for insertion in the second-operation spindle during the next autoload cycle.
Perhaps the most important expansion capability of the system is the CNC pallet system. Pallet stacks containing rough and finished machined parts are automatically transported to the machine pick-up point, other operations, or storage. Because the CNC gantry places parts on a staging station before replacement in the pallet, very dense storage patterns are possible in the pallet; the space required for opening the part gripper is eliminated. Also, once parts are oriented and aligned for automatic loading, considerable money can be saved by keeping them in alignment for subsequent operations. The CNC pallet system thus eliminates the need for realignment at each additional station or machine down the line.
The two-axis pallet carriage presents a pallet of rough parts to the CNC gantry. As the parts are machined, they are returned to the pallet until it is full. The pallet is then stacked with others containing finished parts, and a new pallet of rough parts is presented to the gantry. When the stacks of rough and finished parts require transport to other positions, cells, or work areas, a CNC-directed transport cart will accomplish the task automatically.
For information from UMA Corp, Houston, TX, circle E25.
GM gets flexible production
The first "production" flexible manufacturing system in a General Motors plant is in use at Detroit Diesel Allison Div, Indianapolis, IN, according to the company. The FMS occupies about 12,000 sq ft of floor space and consists of eight machine tools, one inspection machine, 15 load-unload stations, and a sophisticated material-handling system that features two automated shuttle cars operating on a 250-ft track. The FMS can machine 43 different parts, primarily cast-iron housings for DDA's off-highway vehicle transmission line. Each station can machine several different parts, allowing quick response time to schedule changes and customer needs.
Robotics in Metalworking
Nine-axis robot control
The CIMROC 2 is a new nine-axis, continuous-path robot control developed by GCA/Industrial Systems Group, Naperville, IL. It drives six axes simultaenously plus another three axes concurrently for applications with slides, positioning tables, or other servocontrolled fixturing or process devices. Enhanced-accuracy software permits smoother, more precise location of the robot arm.
The system has 16-bit distributed processing, 128-K bytes of available memory, and the capacity for 256 digital or analog inputs/outputs.
For more information, circle E58.
Lasers and robots for FMS
The new Laserflex technology allows lasers to be used with robots in flexible manufacturing systems that require cutting, welding, and heat treating. The system is a first step in the evolution of a technology that combines the power and precision of lasers with the flexibility of robots, according to VP Michael E Kahn, who is division manager of Spectra-Physics' Industrial Laser Div, San Jose, CA. He says, "This combination allows industrial manufacturers to produce smaller volumes and a wider variety of complex parts economically, without the time and expense of hard tooling." For more information, circle E31.
Arc-welding work cell
The cyro 1000 robotic arc-welding work cell employs a new articulated-arm robot. The five-axis, all-electric robot has a work envelope 60 percent greater than the current Cyro 820 work cell. Working-envelope radius has been increased to 1037 mm, granting maximum wrist flexibility at or near the extremes of the working envelope.
Harmonic drives and ball screws provides smooth motion, and the robot averages 3500 hr mean time between failure (MTBF). The work cell uses a Cyro C-30 controller with program shift and translation features designed to reduce programming time. Its nonvolatile memory requires no battery backup, and a built-in CRT screen displays English diagnostic messages and helpful production data. An expanded teach pendant includes all programming and control commands, eliminating the need for a keyboard. The C-30 controls both the robot and the positioner. Coordinated motion is available for a single axis. Advanced Robotics Corp, Columbus, OH. Circle E21.
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|Author:||Heisterberg, Rodney J.|
|Publication:||Tooling & Production|
|Date:||Nov 1, 1984|
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