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.sup.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.

Dependencies are inferred from the claim text.