An Innovation in Control Panels for Large Computer Control Systems

A control panel of novel design has been developed at SLAC. This panel, called a touch panel, consists of a glass plate placed in front of a computer driven cathode ray tube display. Ultrasonic surface (Rayleigh) wave (8.5 MHz) beams are transmitted in a crossing X-Y grid through the glass. The intersection points of the beams form the "buttons" on the panel. The computer furnishes legends for these buttons. The presence of an operator\´s finger on the glass "pushing" a button is detected by the absorption of an X and a Y beam. A prototype panel has been built and used successfully with an SDS-925 computer for magnet control in the SLAC beam switchyard. A second generation panel with low parallax using the glass face of the CRT itself as the medium for ultrasonic propagation has been designed and is being constructed. An extensive software system, utilizing numerous "software panels", for general control of the accelerator, the beam switchyard, and their associated subsystems is being developed. The physical principles of the device, its advantages and disadvantages over conventional devices, current hardware and software implementation, and future plans are discussed.