Hardware-Software Trade-Offs in the Computer Control of Groups of Machine Tool

The design of direct computer control systems for groups of NC machine tools involves the determination of an optimum hardware-software configuration for the given task. For the case of continuous path control four basic configurations are: 1 Fully software interpolation by the control computer 2 Centralized /possibly time-shared/ interpolation by special hardware 3 Simplified local hardware interpolation, where preparatory simplification is done by central computer software 4 Full local hardware interpolation. The first alternative saves on specialized interpolation hardware but requires very high computing speed, severely restricts the number of controllable axes and needs expensive, broad bandwidth linkage with the machine tools in a noisy environment. The second requires special hardware and the same broad bandwidth linkage but saves on computer capacity. For the third and fourth alternatives there is increasing local hardware in an unfavourable environment, but simpler communication and better computer utilization. The choice between the possible configurations has generally been an empirical one, based on the equipment available. The authors have attempted, by balancing the advantages and disadvantages, to achieve a hardware-software equilibrium which will ensure optimal real-time conditions. To this end a FORTRAN simulation program of the direct computer control of groups of machine tools has been written and run on a CDC 3300 computer. The paper describes the structure of the program and the parameters it considers. In conclusion the paper describes a control system built in the authors’ Institute, incorporating the results of the above trade-off optimalization.