Graphic recorder

Abstract

4. An instrument for graphically recording information by providing a visually perceptable image on a web of flexible, wide sheet material comprising: a pair of spools with flexible wide sheet material extending therebetween, a head for graphically transferring information onto said flexible material, means for displacing said head in two different transverse directions across at least a portion of the width of said flexible material during transferring of information, a driving means located opposite said head for contacting said flexible material between said spools and for moving said flexible material in two different longitudinal directions past said head during transferring of information, said directions being perpendicular to the displacement of said head, said driving means including a control spindle of low rotational inertia and having a minimum diameter compatible with the flexibility of said flexible material, and air pressure means to hold said flexible material against a portion of the surface of said control spindle and applied between said control spindle and each of said pair of spools forming loops therebetween and isolating said control spindle from the inertial action of said spools, whereby said control spindle and said air pressure means cooperate to positively control movement of said flexible material past said head without the use of any other drive means for said flexible material. The present invention has for its object a graphic recorder intended to operate automatically from numerical inputs. The graphic recorders of this kind which exist at the present time comprise a tracing head capable of moving in two opposite directions above a sheet of paper which can in turn be moved by means of a driving drum in two opposite directions which are however perpendicular to the movements of the tracing head. A paper unwinding and winding device comprises two driving rollers having two directions of rotation and, following a known arrangement, the rollers and the driving drum are each located at one of the apices of a triangle. The tracing head reproduces the ordinates and the driving drum forms the abscissae. The numerical impulses are applied to two independent reversible motors which drive step-by-step the tracing head and the driving drum. This driving drum generally has a relatively large diameter, which presents a non-negligible problem of inertia, and it is known that the polar inertia of a drum or cylinder is equal to 0.098d 4 where d is the diameter. The graphic recorder in accordance with the invention comprises a driving cylinder of small diameter which reduces the phenomenon of inertia to a very considerable extent. This reduction in the diameter of the driving cylinder is made possible by the device of two intermediate loops formed in the paper on each side of the driving cylinder. In order to render the driving cylinder completely independent of reciprocal action of the rollers on each other through the intermediary of the sheet of paper, the recorder according to the invention comprises a device for reading and correcting loops. This reading and loop corrector device has for its purpose to keep constantly in balance the two loops which are drawn-in by a suction system. The device for reading and correcting loops can be constituted by at least two pairs of photo-electric cells arranged in pairs at different levels, the position of the tops of the loops varying between two limits defined by the two levels of the cells. The suction device may be constituted by a simple fan of adequate power, and contributes in obtaining maximum winding of the paper on the driving cylinder of small diameter and therefore of low inertia.

I claim: .[.1. In an instrument for recording information comprising: 
     
        movement of said flexible material between said spools..]. .[.2.  A device in accordance with claim 1, further characterized by said air pressure means acting in a direction substantially opposing the direction in which said portion of the surface of said control spindle contacting the flexible material faces..]. .[.3. A graphic recorder intended to operate automatically from numerical inputs, said recorder comprising:   a recording head,   means for displacing said head transversely in two different directions about a sheet of flexible material having perforations in said flexible material,   a driving spindle adapted to move said sheet of flexible material in two different directions but perpendicular to the displacement of said recording head,   unwinding-winding spools supporting said sheet of flexible material on each side of said driving spindle,   said spindle being of low rotational inertia and a minimum diameter compatible with the flexibility of said material and having projections engaging the perforations in said flexible material,   air pressure means for maintaining a uniform pressure contact area of said flexible material against and around a sector of said driving spindle,   the axis of said spindle and the axes of said unwinding-winding spools spaced from and parallel to each other and spaced from each other a distance sufficient to produce two intermediate loops formed in said sheet of flexible material on each side of said driving spindle,   a device for reading and correcting said loops formed in said flexible material whereby the driving spindle is rendered totally independent of any interaction of said winding-unwinding spools..]. .Iadd. 4. An instrument for graphically recording information by providing a visually perceptable image on a web of flexible, wide sheet material comprising:   a pair of spools with flexible wide sheet material extending therebetween,   a head for graphically transferring information onto said flexible material,   means for displacing said head in two different transverse directions across at least a portion of the width of said flexible material during transferring of information,   a driving means located opposite said head for contacting said flexible material between said spools and for moving said flexible material in two different longitudinal directions past said head during transferring of information, said directions being perpendicular to the displacement of said head,   said driving means including a control spindle of low rotational inertia and having a minimum diameter compatible with the flexibility of said flexible material,   and air pressure means to hold said flexible material against a portion of the surface of said control spindle and applied between said control spindle and each of said pair of spools forming loops therebetween and isolating said control spindle from the inertial action of said spools, whereby said control spindle and said air pressure means cooperate to positively control movement of said flexible material past said head without the use of any other drive means for said flexible material. .Iaddend. .Iadd. 5. A device in accordance with claim 4, further characterized by:   said air pressure means acting in a direction substantially opposing the direction in which said portion of the surface of said control spindle contacts the flexible material faces. .Iaddend..Iadd. 6. A device in accordance with claim 4, including reversible motor means to rotate said driving means in either direction in accordance with the input signal received by the reversible motor means. .Iaddend..Iadd. 7. A device in accordance with claim 6, further characterized by projections extending from said spindle for engaging perforations in said flexible material. .Iaddend. .Iadd. 8. The instrument of claim 4 wherein said flexible material includes perforations, and said control spindle includes projections for engaging the perforations in said flexible material and wherein said air pressure means causes said flexible material to be sufficiently draped around said control spindle to enable said projections to engage said perforations. .Iaddend.