The material flow control facility controls and supervises the transport of the workpiececarriers with the clamped workpiece in the flexible manufacturing cell.
The workpiece carriers are transported by the transport system of the cell between a
source station and a destination station. Source and destination station include clamping
locations, machine tools, washing and measuring machines, etc.
The transport requests are specified by the station-specific programs (e.g. machine
tool program, fixturing programme) to the MFC facility at the end of an operation and
processed by the MFC facility according to the FIFO principle (FIRST IN FIRST OUT).
In addition to the stations, each cell normally has storage locations where the workpiece
can be held if the destination station is occupied.
If this happens the transport job together with the destination and the priority is
preserved. The source station identifier is replaced by the storage location number.
Information on the source and destination is obtained by interpreting the workpiecespecific
schedule, in which among other things the sequence of operations is defined.
During transport the status data of the transport system, source and destination stations,
workpiece carrier and workpiece are updated by the MFC facility in real time.
19.9.8 MACHINE TOOL PROGRAM
In the FMC system the machine tool program undertakes all the tasks arising at the interface
to the machine tool. These tasks are online functions, so that each of the machine tools
integrated into the FMC system is assigned its own machine tool program.
The machine tool programs process:
i. NC functions
Maintaining a list of the NC programs available in the CNC
Loading a program by preparing the CNC for loading and activating program
transfer via the NC program supply module
Erasing the CNC memory
ii. Tool data
Reading the tool magazine and forwarding the contents to the tool
requirement module
Forwarding the tool offset data on loading the tool magazine
Alarms and status messages which lead to the cancellation of automatic
processing of the machine tool.
Alarms and status messages are logged by the basic software system. The relevant
status data are simultaneously updated.
Chapter 19
Flexible Manufacturing Systems 635
19.9.8.1 Synchronization
Synchronization must be carried out in the event of a restart for a machine tool in the FMC:
(i) Resetting the PLC
Interrogate alarms and status
Cancel NC programs
Read tool magazine data
(ii) Forwarding the information to the relevant program modules
(iii) Resetting the NC program supply module.
19.9.8.2 CNC Program Supply
With the aid of this module, (Fig. 19.14) CNC programs are:
transferred to the CNC of the cell,
retransferred from a CNC (updated, optimized programs),
read from floppy disk or via a host computer interface into the cell computer,
deleted from the NC program library.
CNC
PROGRAMS
TOOL
LISTS
SYSTEM OPERATION
INFORMATION
PROGRAM
TRANSMISSION
PROGRAM
EDITING
PLC CNC
NC PROGRAM
SUPPLY
MACHINE CONTROL
PROGRAM
Workpiece Carrier
Identification
Fig. 19.14 CNC Program Management
The CNC programs are held ready by a machine tool program at the interface to the
CNC and transferred if the CNC signals that it is ready to receive. Retransmission of updated
NC programs is initiated by means of operator inputs on the cell computer.
When CNC programs are transferred to the cell computer they are read into an input
file, provided with the necessary prefix and management data by the operator interacting
with the computer and transferred to the library with a particular CNC program number
and references to subroutines and tool lists. The status of the CNC program indicates
whether the program is blocked, released for production or whether it is an updated version.
By entering appropriate requests on the operator console lists information relating to:
All blocked diagrams
All programs with update versions etc.
636 CAD/CAM/CIM
19.9.9 TOOL FLOW CONTROL
Figure 19.15 shows a schematic diagram of tool flow control. The tool flow control facility
processes the bi-directional transfer of tools between the cell magazines. For each machine
tool, the tool planning function supplies the tool flow control facility with lists containing
the identification numbers of the tools required and the tools those are available.
MAGAZINE
DATABASE
CELL MAGAZINE
MANAGEMENT
Data input fo r
Manual exchange
TOOL FLOW
CONTROL
MACHINE TOOL
PROGRAM
CNC
PLC
MAGAZINE
MANAGEMENT
Fig. 19.15 Schematic Diagram of Tool Flow Control
The deciding factor is the time of requirement or the time of tool release for dismantling.
Before a workpiece arrives at the machining location of the machine tool a check is carried
out to establish whether:
All the tools required are available in the machine tool magazine, or
The tools not in the machine tool magazine are available in the cell magazine.
If the necessary tools are not available the workpiece is rejected. If the tools are in the
cell magazine, a change of tools is initiated. The time of the change of tools is notified to
the relevant machine by the PLC as follows:
From flags set in the NC programs the machine tool PLC knows if there is enough time
available for a change of tools. If a flag is set, the tool flow control facility is informed.
19.9.9.1 Tool Changing
The co-ordinates of the tool location are passed to the PLC of the handling