3.2 Interface data of information systems and NCs
The appearance of PC-based NCs allows us to integrate easily the machine tools and the information systems such as process planning and production management systems. The progress of S/W methodology -- modularity and object-oriented analysis and design -- will allow us to reconfigure manufacturing systems and FA equipment. We can forecast that the following will be realized easily and cheaply.
- Change of the production line
- Metamorphic machine tools by a combination of mechanical devices
- High value-added machining and production management by using software tools on personal computers.
To change the production line and achieve metamorphic machine tools, the controller software corresponding to the mechanical devices to be changed should be also changed. For the development of controller software, it is desirable to generate it automatically based on the model and the configuration information of production lines and machine tools.
The relationship of distributed manufacturing systems and NCs in section1.3 and the function layer of NC systems in section 2.2 were mentioned above. Here, we discuss the interface data of information systems and NCs.
3.2.1 Interface Data of Information Systems and NCs.
Figure 3.2.1 shows data flow from process planning to machine tools. The process planning activity generates a process plan from the parts drawing information and the equipment model of the production line. The process plan is sent to a preparation activity and it makes the NC programs required to machine the parts.
A part of the process plan information, such as that concerning machine tools, machining time, etc., production number and due-date of the parts, are sent to an activity scheduler in order to generate a schedule, i.e., a gnat chart information. Finally, the NC programs which consist of the part geometry and the cutting conditions are passed to the operators of the machine tools, or alternatively, the machining will be done remotely by the line controller, using protocols like VMD (Virtual Manufacturing Devices). The interface data for information systems and NCs are summarized in Table 3-2-1.
Table 3-2-1 Interface data of information systems and NCs
| Activity | Function |
Data |
| CAD/CAM | Product Design | product figure, part geometry, tolerance, number of product, product cost |
| Production Design | workpiece geometry, tolerance, cutting condition, process plan (machine tools, fixtures, machining mode, machining time), NC programs |
| Production Management | Scheduling Management | process plan (machine tools, machining time), order (production number, due-date), NC programs, machine tools data, schedule |
| Quality Management | quality data, maintenance data
|
| Production Control | Production Control | schedule, NC status, alarm data |
Figure-3.2.1 Data flow from a process planning to the machine tools
3.2.2 NC Interface Protocol
The NC message protocol from remote nodes has been developed and standardized as the ISO/IEC9506-4 MMS (Manufacturing Message Specification) part 4 NC-CS (Companion Standard). The MMS NC-CS defines the services and the transfer syntax for remote control of NCs, and defines standard variables for NC information and NC controlling parameters. The NC interface protocol should be based on the MMS NC-CS.
(1) Services of NC interface
Services of the MMS NC-CS, shown in a Figure 3.2.2, are defined for the following functions.
- General Services: management of the communication environment.
- NC Program/Data Management Services: management and uploading/downloading of the NC program/data.
- NC Process Management Services: controlling of the NC process.
- NC Information and Data Transfer Services: reading of NC information and writing of NC control parameters
- NC Alarm Processing Services: monitoring and signaling of alarms.
- NC Exclusive Control Services: taking and relinquishing control of NC system.
(2) NC Variables
Standard variables of the MMS NC-CS, shown in a Figure 3.2.3, are defined for the following variables.
- Basic Information: information about the NC, such as controller voltage or controller error information.
- Device Information: information about the device, such as hydraulic pressure or device voltage.
- Process Information: information about the Controlling Process, e.g. the currently executing program block.
- Data Store Information: information about the NC data store, such as data type or memory usage.
- Probe Data Table: data about the probe system, such as probe data or probe measuring data .
- Static Data Table: dynamic data during process, such as part production timers .
- Tool Data: tooling information, such as tool data or tool magazine data, used by the milling machine.
- Setup Data: static machine parameters, such as setup data or taper trims data, used by the machine.
- Means of Production Data: means of production information, such as fixture information or parking location information, used by the FMS.
Figure-3.2.2 Sample of NC Services on NC upper interface
Figure-3.2.3 Sample of NC Variables
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