Title:
Telautograph
United States Patent 2338949


Abstract:
The present invention relates to an electric telautograph, by means of which, for instance, a drawing made by hand at a transmitting station is rendered visible substantially at the same time at the receiving station. In this case the remote transmission may be effected either by the wireless...



Inventors:
Karl, Kupfmuller
Kurt, Reche
Application Number:
US36238840A
Publication Date:
01/11/1944
Filing Date:
10/23/1940
Assignee:
Karl, Kupfmuller
Kurt, Reche
Primary Class:
International Classes:
G08C21/00
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Description:

The present invention relates to an electric telautograph, by means of which, for instance, a drawing made by hand at a transmitting station is rendered visible substantially at the same time at the receiving station. In this case the remote transmission may be effected either by the wireless method or over lines. The present invention is particularly suitable in reproducing at the same time in the receiving apparatus the text written at the transmitting apparatus.

A known method for facsimile transmission of images with the aid of a cathode ray tube consists in scanning line by line the drawing or the text (television). It is true that in this case the advantage is presented that the images or text may practically be reproduced when transmitting the same. However, this method has the drawback that a very wide frequency band determined by the number of image points per unit of area is necessary for the remote transmission.

To avoid this drawback the electron ray is guided according to another known method by suitable deflecting devices in the same manner as the stylus of the transmitter. The text written is reproduced on a photographic plate (telautograph). Although the advantage of a narrow frequency band is thereby obtained, the lastmentioned method presents nevertheless the drawback in that the drawing to be transmitted is only visible when developed by the photographic method.

According to the known telewriting method the coordinates are either represented by resistances and potentiometers which are mechanically controlled by the stylus or the change in resistance between the stylus and the fixed points is utilized on the writing plate consisting of resistance material to characterize the coordinates. The first method has the disadvantage that the stylus is prevented from being moved by the mechanical parts cooperating therewith, whereas the second method encounters difficulties as to the linearity of the transmission and as to the fact that resistance values cannot be directly transmitted over great distances.

The present invention combines the advantages of the above-mentioned methods and avoids the disadvantages thereof. This may be accomplished by the fact that the electron ray of a cathode ray tube for reproducing pictures is controlled in accordance with the movements of the stylus of the transmitter and that each image point is visible on the fluorescent screen during the time necessary for writing the text, i. e., for instance, for 15 seconds to 2 minutes.

S The arrangement according to the invention may preferably be designed in the manner that an extinction or ignition of the electron ray corresponds to a removal of the stylus from the writing plate or to a placing of the same thereon.

The electron ray cooperates with the stylus in such a manner that the position of the stylus on the writing plate is characterized by two potentials which are a measure for the coordinates of the point where the stylus is placed on the plate.

These two coordinate potentials are represented by alternating voltages of different frequency.

They serve to deflect the ray in both coordinate directions. In this manner a position of the luminous point on the fluorescent screen corresponds to the position of the stylus on the writing plate. The frequency band necessary for the transmission is not determined by subdividing the image but only by the speed with which the text is written and is accordingly very narrow (about 5 to 10 cycles/sec. as compared to more than 106 cycles/sec. as is the case with known telewriting methods).

Further details of the invention will be apparent from the description taken in connection with the accompanying drawing, in which Fig. 1 shows the construction of the transmitting apparatus.

Fig. 2 shows a modified construction of the transmitting apparatus.

Fig. 3 shows the receiving apparatus in diagrammatic form.

Fig. 4 shows a schematical representation of the arrangement with two transmitting and two receiving apparatus.

Figs. 5 and 6 show desirable modifications of the general arrangement shown in Fig. 4.

According to the invention two homogeneous fluxes crossing each other and having the frequencies fI and 12 are produced according to the invention on a conducting or semi-conducting writing plate. Each point may then be characterized by two potentials with these frequencies. Rectangular coordinate systems or also a curvilinear cooordinate system may be employed.

In the case of rectangular coordinate systems x and y, the amplitudes of the two alternating voltages which are tapped off by the stylus when placing it on the writing plate are linearly dependent upon x and y, i. e., UI =ao+aix with the frequency fi U2=bo+biy with the frequency f2 These alternating voltages vary when writing the 85 text in accordance with time with varying x and y. They are supplied to the transmission system, for instance, to a telephone line or to a radio channel.

The linearity between the voltages UI and U2 and the coordinates x and y expressed by the two equations presupposes that the flow of current in the writing plate be homogeneous. This is accomplished according to the invention by designing the current leads in the form of extensions of the writing plate so that in the case of rectangular coordinates the cross-shaped type shown in Fig. 1 is obtained. The arms A serve to connect the poles of the alternating-current sources through the highly conducting bridging members; B is the writing plate proper. If the arms A were short the two fluxes would become very distorted by the adjacent bridging members C, since these bridging members would absorb a great portion of the lines of flow of current as a result of their high conductivity. This disturbing effect disappears the sooner the longer the arms are made; but even in the case of very long arms A there would remain a residual distortion, since the lines of flow of current of the field enter the arms of the other field. The lines of flow of current running in the direction as indicated by the arrows enter, for instance, the horizontal arms as indicated by the dash lines shown in Fig. 1. According to the invention the arms serving as current leads are besides slotted in the longitudinal direction so as to increase the reactance of the arms to a considerable extent and the lines of flow of current are prevented from entering the horizontal arms (cf. Fig. 2).

Even in the case of comparatively short arms, i. e., in the case of a relatively compact arrangement, the longitudinal slots bring about an approximately homogeneous flux.

In the arrangement shown in Fig. 1, the two energy sources are connected as indicated at P with one another and with the writing plate as well as with one pole of the transmission system E. The electrically conducting stylus D is connected to the other pole of the transmission system. In this manner there results at the input of the transmission system two alternating currents of different frequency which characterize the point where the stylus is to be placed on the writing plate, after the stylus has been brought into engagement with any point of the writing plate. However, the common point P establishes also a connection between the two adjacent bridging members C which in turn lead to a distortion of the two fluxes. Thus, for instance, the lines of flow of current running in the downward direction partly enter the right horizontal arm.

This distortion may be eliminated according to the invention by giving both fluxes a common potential point as will be apparent from Fig. 2.

Here the centers of the two secondary windings of the energy source repeaters are connected with each other as indicated at P, at which point the potential coincides with the potential at the center of the writing surface. In this manner a mutual influence of the two fluxes is avoided. The voltages at the points of the writing surface which lie symmetrically to the center differ, however, from one another only as regards to the phase and not to the amplitude. In order that the above-mentioned equations hold good it is necessary to add through the repeaters UI and U2 a predetermined amount of the two voltages to the tapping voltages.

Another possibility of avoiding a disturbing influence of the fluxes consists in employing a point of the writing surface, for instance, a corer point or a center point as a common point for connecting the transmission system.

The fact that the voltage applied to the transmission system disappears when removing the stylus from the writing plate may be utilized to extinguish and ignite the luminous point in the receiving tube. However, according to the invention an energy source having the frequency f3 may be connected as shown in Fig. 2 in series with the stylus so that the disappearance and the appearance of the current of this frequency may bring about an extinction and ignition respectively.

When the stylus is brought into engagement with the writing plate the distribution of potential of the fluxes must not be disturbed. The conditions of resistance must therefore be chosen accordingly. Under circumstances it may be preferable to insert a sufficiently high resistance in series with the stylus.

In Fig. 3 is shown the construction of the receiving apparatus. The operation thereof is as follows: The oscillations having a frequency fl, /2 andf3 are separated from one another by the three filters FI, F2, and F3 and rectified in GI, G2 and G3. The two voltages obtained by rectifying the alternating voltages of the frequency fI and f2 are supplied to the deflecting systems PI and P2 of a cathode-ray tube. The voltage obtained by rectifying the alternating voltage of the frequency 13 serves to control the intensity of the electron ray of the cathode-ray tube, for instance, through the Wehnelt-cylinder W. A complete transmission system according to the invention is shown in Fig. 4 in diagrammatic form. To each end of,the transmission system T is connected a transmitting apparatus S as well as a receiving apparatus E so that the operator is always able to observe in his own receiving apparatus the text written by him. In this case he may also ascertain to what extent the lines which have already been drawn disappear again in order to redraw them if necessary.

re When using the same frequency for the two directions it is also possible for the other operator to complete the drawing. To facilitate the completion of the drawing and the reproduction of the same the writing plate may be brought ac5o cording to the invention to coincide with the luminous image. This coincidence may, for instance, be effected by the optical method. This may be accomplished in a simple manner by projecting the fluorescent screen in the cathode ray 5 tube R on the writing plate B with the aid of a lens L and mirror M, as shown in Fig. 5. Another possibility of coinciding the reproduction with the drawing consists in designing the writing plate in the form of a plate permeable to light so 0that it may be placed on the fluorescent screen, as shown in Fig. 6. In this case the writing plate may be made, for instance, in the form of a wire gauze or in the form of a metal layer permeable to light and applied to a glass plate preferably by the spraying method. The control means and amplifier lying in the circuits are then preferably so adjusted that the reproduction coincides with the drawing so that when bringing the stylus into engagement with the writing plate the luminous point is directly visible thereunder.

With the aid of gain adjusting devices in both circuits PF GI and F2 G2 of the receiving apparatus the coincidence of the reproduction with 7b the drawing may easily be adjusted.

What is claimed is: 1. Image transmitting apparatus comprising a writing plate formed of conducting material, two current paths extending through said plate at right angles to each other, two transformers having their secondary windings in series with said current paths, respectively, means for supplying alternating currents of different frequencies to the primary windings of said transformer, a transmission circuit including a common conductor connected to corresponding points on the secondary windings of said transformers and a stylus adapted to contact various points on said writing plate and cause currents of said different frequencies to flow in said circuit in accordance with the voltages between such points and said conductor, and means for superimposing voltages of said different frequencies on said transmission circuit in order to shift the points of zero voltage for each circuit path toward or beyond the margins of the writing area on said plate.

2. In a two way image transmitting system, a writing plate of conducting material at each end of the system, means for supplying alternating currents of a certain frequency to both plates for maintaining points of both plates at different potentials corresponding with the ordinates of such points, means for supplying alternating currents of a certain different frequency for maintaining said points at different potentials in accordance with their abscissae, means including a stylus for each plate for picking up said potentials, cathode ray tubes responsive to the potential picked up by the respective styluses concurrently with the tracing thereof and means including an optical arrangement at each end of the system to project the image formed by the cathode ray on the associated writing plate.

3. In a two way image transmitting system a writing plate of conducting material at each end of the system, means for supplying alternating currents of a certain frequency to both plates for maintaining points of both plates at different potentials corresponding with the ordinates of such points, means for supplying alternating currents of a certain different frequency for maintaining said points at different potentials in accordance with their abscissae, means including a stylus for each plate for picking up said potentials, cathode ray tubes and associated screens responsive to the potentials picked up by the respective styluses concurrently with the tracing thereof and means at each end of the optical system to project the image formed by the tube on the screen, the screen and plate being parallel and the screen being permeable to light, whereby the image produced on the screen can be seen through the plate.

4. Image transmitting apparatus comprising a writing plate formed of conducting material, means for passing alternating currents of different frequency through the plate in directions which are at right angles to each other and parallel to the surface of the plate, said means including extensions of the writing plate for conducting the alternating currents to and from the plate, said extensions being slotted in the direction of current flow to prevent distortion of the current paths in the writing plate, and means including a stylus for outlining the image to be transmitted and for simultaneously picking up voltages from the surface of said plate which vary in amplitude in proportion to the coordinates of different points on the image.

5. Image transmitting apparatus comprising a writing plate formed of conducting material, means including transformers for passing alternating currents of different frequency through said plate in directions which are at right angles to each other and parallel to the surface of the plate, means including a stylus for outlining the images to be transmitted and for simultaneously picking up voltages from the surface of said plate which vary in amplitude in proportion to the coordinates of different points on the image, a com301 mon return conductor for said voltages and adjustable taps connecting the secondaries of said transformers with said conductor to enable the conductor to be connected to points on the secondaries which have the same potential as a selected point on the writing plate.

6. In an image transmitting apparatus, a writing plate formed of conducting material, means for passing alternating currents of different frequency through said plate in directions which are at right angles to each other and parallel to the surface of the plate, said means including transformers having tapped secondary windings, a stylus for outlining the image to be transmitted and for simultaneously picking up voltages from the surface of said plate, a transmission circuit extending from the tapping points of said secondary windings to said stylus, and a third transformer for placing biasing voltages on said transmission circuit, said third transformer having a secondary winding connected in series in said circuit and two primary windings connected to the alternating current sources, respectively.

KARL KOPFMViLLER.

KURT RECHE.