FR2548411A1 - METHOD AND DEVICE FOR IDENTIFYING A POINT ON THE SCREEN OF A VIEWING TERMINAL - Google Patents

Abstract

FOR THE IDENTIFICATION OF A POINT ON THE SCREEN OF A VIEWING TERMINAL, POINT 2 OF A PROBE 1 IS APPLIED ON THE SCREEN, THIS SOUNDS AN ULTRASONIC SIGNAL WITH THE FREQUENCY VARIED IN A DETERMINED WAY, THIS SIGNAL IS DETECTED AT DIFFERENT POINTS OF THE SCREEN AND THE SIGNALS OF 4 DETECTORS ARE PROCESSED TO PROVIDE THE IDENTITY OF THIS POINT.

Description

The present invention relates to display terminals intended

  to be used in so-called "interactive" systems in which it is desirable that the subject viewed can

  be modified by the operator, in a way that he can control.

  In many such systems, operating protocols require the identification or modification of part of a text or an image displayed on a display terminal. The control by cursor is awkward, and one has attempted to eliminate it by using touch-sensitive screen tops, light emitting diode arrays, and light pencils to identify displayed subjects or to enter data in visual form. a

high cost.

  The object of the present invention is to achieve a system in which the above-mentioned defects are minimized.

  The invention proposes a method for identifying a point on the screen of a display terminal, according to which the tip of a probe is applied to the screen, at the place to be identified, the emission, by the probe tip, of an ultrasonic on20 signal whose frequency is modified in a preset manner, this ultrasonic signal propagating on the surface of the screen, ultrasonic wave signals are detected at different points on the screen where detectors are placed, we analyze the

  signals thus detected to identify the point to be located, and the identity of this point is signaled to the associated equipment.

  To apply such a method, a frame with ultrasound detector attached to the screen is used, this frame being able to be added to a pre-existing display terminal, and

  a high resolution means capable of replacing devices such as touch-sensitive screens is thus obtained.

  The different objects and characteristics of the invention

  will now be detailed in the description which follows, given by way of nonlimiting example, with reference to the figure years which represent:

  Figure 1, a very schematic sketch of a system used

Saying the invention.

  FIG. 2, a block diagram representing part of the signal processing circuits used in a communication system

implementation of the invention.

  FIG. 3, a graph showing how the frequency of the transmitted ultrasonic wave varies linearly over time, in an implementation system of the invention, and FIGS. 4 and 5, graphs illustrating the detection techniques used, FIG. 4 corresponding to the case of a probe coupled to the display terminal, while FIG. 5

  corresponds to a probe not coupled to this terminal.

  In the system described below, a hand-held probe 1, comprising an ultrasonic generator transducer 2 located at its tip, is used to "mark" the screen of the display terminal which includes a device with a detector frame 3 This frame is a virtual reference frame with, in its corners, detectors such as 4 Ultrasonic waves can propagate in this frame As shown, four such detectors are provided but, in

  in some cases, only two detectors can be used. In addition, the 20 detectors can be mounted elsewhere on the frame.

  The probe includes the circuits necessary to control the transducer element located at its tip and to cause the excursion of the frequency generated in a preset frequency range. Thus, with a base frequency of 100 k Hz, the frequency varies linearly 25 out of 10 k Hz The probe also has a microswitch which is activated when this tip is pressed against the screen, in order to

  to validate the circuits which drive the transducer element.

  Thus, to "mark" the screen, we touch, with the tip of the probe, the desired location on the screen, which causes the micro30 switch in the probe to cause the vibration of the transducer element as described. higher ultrasonic signals as well

  applied to the screen propagate to the corners where the detectors are located Due to known frequency variations, the circuits to which the detectors are connected measure the propagation times, so that the point touched by the probe is "localized" .

  To measure the propagation times of detected ultrasonic waves, a signal processing technique is used which

  takes advantage of the linear excursion of frequency of the ultrasonic wave emitted.

  The difference with the ultrasonic frequency detected by each detector is obtained by a "heterodyne" operation in a DET detector, figure 2 The corresponding analog voltage which, due to the above-mentioned frequency excursion, is proportional to the distance from measure, is obtained by frequency detection, linear So the DET detector output signal passes

  by an LPF arm pass filter, a LIM limiter, a DC differentiation circuit, a RECT rectifier and an INT integrator, polar give an VR output signal.

  The analog output signal VR thus obtained by the detectors can then be processed in analog form to calculate the X and Y coordinates of the probe However, at this stage, it is

  preferable to convert the signals into digital signals and to resort to a digital processing to carry out the calculations required.

  Of course, such use of digital techniques is

  then particularly well suited if the display terminal is associated with digital equipment.

  The frequency of the ultrasonic wave signal applied to the screen by the probe varies linearly with time, as represented by the solid line graph in FIG. 3 The propagation time, therefore the distance that the wave has crossed since the probe tip to a detector can be measured by noting the difference between the frequencies of the transmitted wave and the received wave, as indicated by the dashed graph The circuits used to

  these are as described above by considering figure 2, and four30 produce a linearly varying signal, the amplitude of which is proportional to the propagation distance.

  To identify the location of the ultrasonic transmitting probe relative to the receiving detectors, data processing is simple, the nature of the calculations depending on whether or not the probe is connected to the display terminal by a

c.b 1 st driver.

  In the first arrangement, only two detectors are required.

  They can then be located one in the lower left corner, the other in the lower right corner The distances from the probe to these detectors are measured directly using the transmitted frequency as reference The coordinates of the probe reported on the screen display, can be obtained from geometric considerations, see figure 4 In figure 4, W is the screen width, h the screen height, and R 1, R 2 are the distances from the probe to the detectors We can see that the distances R 1 and R 2,

  plus the angles a and B, defining the coordinates.

  In the second arrangement, that in which the probe is not coupled to the terminal, the transmitting probe cannot be used as a frequency reference, and four detectors are required, one at each corner of the screen Measuring frequencies difference between the various pairs of frequencies reviewed, and the applicable geometric considerations are, as can be seen by considering FIG. 5, such that at each location of the probe reported on the screen also corresponds a point of intersection between 20 two hyperbolas whose main axes are located on the upper side and the lower side of the screen, and whose focal points coincide

with detectors.

  The linearly variable signals representing the coordinates of the probe can be digitized, with any desired degree of precision, before being stored in a digital configuration table having geometric ratios identical to those of the screen of the display terminal. This configuration table is explored by the image scan of the display terminal, so that the binary digits stored in said table are used to illuminate the corresponding points of the screen. Thus, one can draw or erase images.

  on the screen by moving the probe as you would with a pencil.

  It is obvious that the foregoing descriptions have

  been made by way of nonlimiting example and that many variants can be envisaged without going beyond the scope

of the invention.

Claims (4)

  1 Method for identifying a point on the screen of a display terminal, characterized in that the tip of a probe is applied to the screen, at the point to be identified, the emission by the tip of the probe of an ultrasonic wave signal whose frequency is modified in a preset manner, this ultrasonic signal propagating on the surface of the screen, ultrasonic wave signals are detected at different points on the screen where detectors are arranged, the 10 signals thus detected are analyzed to identify the point to be located, and   signals the identity of this point to the associated equipment.   2 Method for modifying an image displayed on the screen of a display terminal, characterized in that at the point where it is desired to modify the image, the tip 15 of a probe by hand, we cause the emission, by the tip of the probe, of an ultrasonic wave signal whose frequency is modified in a preset manner, this signal propagating on the surface of the screen, we detects ultrasonic wave signals at different points on the screen where detectors are arranged, the signals thus detected are analyzed to identify the point where the image must be modified, the beam of the display terminal is established on the point o the modification must be made, and   this beam is controlled in a manner corresponding to the desired modification.   3 Method according to claiml or 2, characterized in that the screen of the display terminal is provided with a virtual reference frame in which the ultrasonic waves are easily propagated, and by the fact that the tip of the probe   is designed to meet the screen of the display terminal.   4 Device for implementing the method according to one   any of claims 1 to 3.