Plotter with drive rollers having variable radial contact surfaces

In a plotter having a recording surface, a pen carriage which grasps a writing utensil or a cutter and which moves in a lateral direction of the recording surface on a sheet placed on this recording surface, and drive rollers, each of which has its outer peripheral surface formed for preventing slip of the sheet, as well as pinch rollers which are made of an elastic material and which are rotatably supported by bearings, respectively, the drive rollers and the pinch rollers forming sets in each set of which the drive roller and the corresponding pinch roller are held in opposition to each other and are respectively disposed at both sideward parts of the recording surface, wherein in a state in which both side edges of the sheet are respectively held between the drive rollers and the corresponding pinch rollers, the drive rollers on both sides of said recording surface are synchronously rotated by a driving motor, thereby to move the sheet in a rotating direction of the drive rollers on the recording surface, the improvement comprising:

• pressure regulation means for regulating respective pressures pressing said pinch rollers on both sides of said recording surface against a surface of the sheet, the peripheral surfaces of the drive rollers being of a noncircular configuration;
• sensing means for sensing a direction and a degree of wobbling of the sheet as the sheet moves in the rotating direction of said drive rollers on said recording surface, and
• control means for controlling said pressure regulation means in accordance with the direction and degree of the wobbling of the sheet sensed by said sensing means, thereby to regulate the respective pressures pressing said pinch rollers at both of the sideward parts of said recording surface against the sheet surface.

An improved sheet moving mechanism for contacting a moving sheet of material to place indicia on the surface or for cutting the sheet into patterns, comprising:

• means for moving the sheet material including at least one set of rollers having a drive roller;
• means for varying the relative position of the material along a radial distance from a center of rotation of the drive roller to vary a tangential speed of the material relative to the center of rotation of the drive roller while maintaining a driving contact with the drive roller;
• means for monitoring the position of the sheet material, and
• means for controlling the relative position of the material to the radial distance of the drive roller by operating the means for varying in response to the monitoring means to maintain a desired movement of the sheet material.