There are many applications where it is desired to provide feedback information for information displayed on a CRT screen. For example, it has become common practice with the use of computers to display on the screen a choice for the user to select from. The user is typically instructed to operate specific keys, on a keyboard or similar device, to select from among a menu of possible choices. In response to the user operating the selected key the menu is changed and the user is given a new choice, again making the choice by operating a particular key. Such an arrangement is tedious since a user must first look at the screen and then go to a separate keyboard to find the proper key. This is time consuming and requires costly separate equipment.
One possible solution to the problem has been to arrange the menu of choices along a side of the viewing screen and to arrange next to the screen a series of buttons. As the labels on the screen change the buttons become dynamically relabeled. While this solves some of the problems, it does not allow the complete flexibility of the visual display and still requires an artificial arrangement of the display.
Several attempts have been made to solve the problem, one such being the use of a light pen which is held over the point on the CRT screen corresponding to the desired response. Light from the CRT raster then enters the pen and the position of the raster is determined by comparing the signal output from the pen to the position of the raster beam at the time of the signal. This arrangement, while performing properly, has the disadvantage of requiring the user to hold a pen and to properly direct the pen to the proper place on the screen.
Other touch sensitive screens used cross wires, crossed beams of infrared light, reflection of acoustic surface waves, current division in resistive sheets, force balancing, or mechanical buttons on which a display image was superimposed by a half silvered mirror. When used with a CRT display, the foregoing methods require careful calibration to establish correspondence between points on the touch screen and points on the display. The need for special transducers or many electrical connections increase complexity and cost.
An exciting advance in the art is disclosed in two copending priorly filed applications, one in the name of L. R. Kasday (Ser. No. 333,744) filed Dec. 23, 1981, which is a continuation of application Ser. No. 140,715, filed Apr. 16, 1980, and one in the name of J. B. Mallos (Ser. No. 140,716) filed Apr. 16, 1980, now U.S. Pat. No. 4,346,376, dated Aug. 24, 1982. The Mallos application discloses a solid device into which signals are injected by total internal reflections. The Kasday application discloses a similar device where a flexible overlay is said to enhance the injection of signals into the device. Kasday also discloses the injection of the signals directly into the overlay. While both of these arragements operate properly, it is desired to arrange the device to both increase the amount of light (signal) energy which reaches the edges of the device and to provide a tactible sense of touch for the user. The problem with light signal strength is that common soda lime glass (as opposed to a high transmission glass) is a poor signal conductor in the longitudinal direction. Thus, signals which are introduced by total internal reflection must travel through the glass medium before arriving at a detector and thus are attenuated significantly thereby requiring sophisticated detector electronics to process the output signal.