Optical quality FMS.
A development project for an extensive flexible production system for manufacturing and testing prismatic workpieces has recently been completed at Carl Zeiss Co, Oberkochen, West Germany. It was funded by the West German Ministry for Research and Technology, and is the country's first such system for the precision optical industry. It uses a Zeiss coordinate-measuring machine as the key control element.
The objective of the Zeiss installation, according to Guenther Modrich, head of production, is to reduce setup time, achieve shorter production runs, and maximize the availability of machine tooling by automating both the flow of material and the flow of information.
The term flexible production system (flexible fertigungssystem of FFS in German) is understood to be a series of production devices linked to a common control and conveyor system to completely automate production runs and allow different machining to be done on different workpieces. (We will use the more familiar US term FMS hereafter). Of all the FMSs worldwide, less then 100 truly fit this description, they feel.
Yet, there are presently something less than 200 FMSs of a looser definition operating or under construction in the Federal Republic of Germany (FRG). That either of these two numbers is so low, they feel, is testimony to the fact that there are two sides to the FMS dilemma: the desire to reduce production time and increase productivity versus the need to fully weigh investment costs, make extensive work projections, and measure cost effectiveness.
"Anyone willing to yield to competitive pressures and make long-term investments must be willing to make that investment in new production technologies,' Modrich says. "It is very important to have started at the right time.'
Planning a parts spectrum
The planning for the Zeiss FMS began in 1979 in cooperation with the Research Institute for Control Technology of Machine Tools and Production Facilities of the University of Stuttgart. The first step, selection of a parts spectrum, is a key factor in an economical application of FMS technology.
Zeiss makes over 50,000 different mechanical parts. In the FMS planning stages, a computer was used to initially select 666 prismatic parts suitable for NC machining. Further geometry and machining-requirement analysis narrowed this to 122 parts. Because of the number of filigree parts requiring many precision-machining operations, work-piece clamping requirements had to be considered in this selection process. Size limits were approximately 10, and a typical part is shown in Figure 1.
An underlying principle in their FMS planning was to use modular components readily available on the market. In 1981, four Steinel machining centers were installed, making it possible for programs, tools, and clamping devices to be tested independently of the total system. Steinel was responsible for linking the machines and became the general contractor for the mechanics of the system. The control system, developed in cooperation with the University of Stuttgart, included the control unit for DNC operation, controls for material flow, and the processing of operating data.
Now in full production, the key system components are the four Steinel BZ20 horizontal machining centers (each with 40-tool magazines), Siemens Sinumerik System 7 M controls, and a Zeiss UMC 850 CNC 3-D coordinate-measuring machine with stationary granite clamping table. The CMM determines correction values for tools and NC data. Linking the system is a work-piece-handling unit of modular design that runs on a circular track and transports the clamped workpieces to the pallet changer of the machining centers from a single row of magazines with a total of 30 fixed stations. Figure 2 shows the system layout.
The hub of the software system is a central production data processor, a DEC PDP 11/24 with a 512K main memory, two disc memories (10M), two alphanumeric-display terminals, one operating terminal with printer, and interfaces for the four CNC controls and the Siemens Primo-S transporter control unit. The production data processor controls the input and output of NC programs (DNC), and the movement of the coded pallets in the loading/unloading station, Figure 3, and to the four machines and CMM, and back.
Interfacing the man
The operating program is an essential element of the central control system. The objective is to free the operator from having to make a large amount of input and to guide him through the program. Also important is a safety mechanism that safequards against erroneous operation.
The operating program is designed for a standard display-screen terminal to allow for much of the output of information and instructions for the operator. The system is controlled by key functions with program controlled softkeys and by screen masks.
The system has these operating modes:
For manual operation without the production processor, the transportation commands for the material-handling control are entered in the manual-control station, and the NC programs are transmitted directly to the machine to start operation.
For semiautomatic operation with the production processor, the shift foreman enters all of the transportation commands into the production processor and re-records and starts the necessary NC programs. This operating mode is required for the CMM and for moving a workpiece onto a machine so long as a definite machine assignment plan is not available for input.
For automatic operation, the shift foreman enters the machine assignment plan into the production processor and initiates the automatic startup of a particular machine. The central control system issues the necessary transporting commands, records, and starts the pertinent NC programs. They only time intervention by the shift foreman is required is in case of breakdown. The semiautomatic and automatic operations can be combined. The shift foreman can also call on the production processor for information regarding all of the system's operating conditions, such as current NC programs in operation, loading conditions on the pallets and machining stations, as well as upcoming transportation commands.
Economics of operation
The application of a system such as this requires a considerable capital investment. According to a Zeiss spokesman, "We will keep a keen eye on the project to make sure that the installation of the FMS will increase productivity.' Shortly after startup, the 4 percent increase in machine usage on which the system's economics were based, was attained. Because the FMS permitted the extension of two-shift operation by 2 hr, the point of amortization has been predicted at between 2.8 and 3.5 years.
The system has been in operation since March of 1982. An extension of the two-shift operation is planned. An expansion of the data link between the CMM measuring station and the production processor is planned to permit direct data transfer. Also planned is coupling of the production processor to the in-house computer center, equipped with a Cyber 720. This would allow data to be transmitted from the programmer terminal to the in-house computer and to the production processor (DNC) and then on to the equipment controls for on-line operation.
The system has operated so far to everyone's satisfaction. It is felt that the modular design and system construction can be used as a guideline for systems in other applications. According to Zeiss, the employment of a general contractor for equipment and linkup, and the cooperation of the Stuttgart Institute FISW that developed the software have proved to be most advantageous.
Photo: 1. One typical part in the 122-part family machined on the Zeiss FMS.
Photo: 2. Layout of the system.
Photo: 3. Tooling and loading station shows the wide variety of workpieces and tooling on the coded pallets.
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|Title Annotation:||flexible manufacturing system|
|Publication:||Tooling & Production|
|Date:||Sep 1, 1984|
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