A flexible manufacturing cell requires an amalgam of conventional manufacturing skills and computer expertise. The mixture of equipment and techniques in the cell impose demands that are best solved by an eclectic group. The skills described below will be needed most while the cell is developed. After the cell is running smoothly they will occasionally be in demand for trouble-shooting and modifying the cell.
The mechanical equipment can be treated in much the same way as high-volume automated machinery is debugged and maintained today. Instead of compiling an exhaustive list of all the mechanical tasks involved in setting up, debugging, and maintaining a cell we focus on those that are not found in more conventional forms of production. The main features that distinguish equipment in a cell from other pieces of automated machinery are their complexity, their flexibility, and their physical interaction. For example, installing and maintaining robots requires some knowledge of the controller, the servo system, and the mechanical components. If something goes wrong it is important to know which of these systems is most likely at fault. Furthermore, the robot in this cell is not a stand-alone machine; it communicates with a host computer and it interacts physically with other pieces of equipment. Itis important to have a global view of the robot as, well as a robot repair technician’s view, when working on the robot.
The cell we have described produces precision parts, and this calls for special attention to how errors accumulate as a part moves from one process to the next. For instance, when the perpendicularity of two surfaces on a part starts to deteriorate there are many possible contributors to the problem. The axis feedback on the milling machine might be in error, or the end mill might be deflecting. The fault may lie with the fixturing on the mill. The fixturing can slightly shift with respect to the mill, or the sensors on the fixture can indicate that the part is aligned when, in fact, it is not. If the sensors on the fixturing do indicate a problem then the robot, or its gripper, may be at fault. The part may be poorly aligned during its acquisition by the robot.
The gripper is equipped with sensors to detect this condition, but they can fail. The possibilities continue beyond this list. The problem is to find the things which can be re-adjusted to improve the final accuracy of the part. Its solution is greatly aided by a thorough understanding of how the processes and equipment interact. Much of this Understanding will have to be acquired during the initial operation of the cell.
When the cell is first set up there will be a large amount of mechanical de-bugging to do. The design of fixtures is expected to be an ongoing and iterative process.
The development of the software and hardware to control the cell will require skills that are needed in any computer environment. The exceptional requirements for an application such as this are centered on the problem of integrating the computer and the machining worlds. For example, there will be development problems getting from the cell host into the machine controllers. The creation of the protocols and programs to achieve this will entail a great deal of initial effort. The effort can be eased by people with skills involving low-level interfacing of computers. The cell host will have the responsibility of assuring that no un-toward physical interaction occurs (like the robot running into the mill table). The software to support this duty will not be simple and will require the skills of a high-level program designer. The amount of programming to be done in the cell is large and will require several programmers. The managers for this project will be required to understand and communicate with people from two very different backgrounds: computers and machining.
