Pinch roller assembly

Abstract

An easily adjustable and automatically aligning pinch roller assembly for use in a graphics plotter. A movable carriage hangs from a supplemental inverted T-shaped track below the main carriage track of the plotter. The pinch roller is pivotally attached to an arm from the carriage. A leaf spring on the carriage pulls the carriage loosely into positional alignment with the pinch roller aligned with the drum while allowing translational movement easily. A second bias spring urges the pinch roller down and the carriage into gripping engagement with the supplemental track with sufficient force to prevent translational movement thereof. A release bar holds the pinch roller off the drum and releases the gripping force to allow the carriage to be slid for adjustment.

Wherefore, having thus described my invention, I claim: 
     
       1. In a graphics plotter having a rotatable drum, a pinch roller for holding a writing medium against the surface of the drum for longitudinal movement thereby, and a carriage track disposed above and parallel to the drum for supporting a pen block carriage for traverse movement, the improvement comprising: (a) a supplemental track carried by the carriage track and extending downward therefrom, said supplemental track being an inverted T-shape in cross section;   (b) a pinch roller carriage having a pair of spaced parallel side members, each having a pair of facing L-shaped gripping members extending upward therefrom, said gripping members being adapted to fit loosely about said supplemental track whereby said pinch roller carriage hangs therefrom and is easily slideable traversely along said supplemental track;   (c) a first pivot pin disposed between said side members and normal thereto at about the location of the ones of said gripping members closest to the drum;   (d) a pivot arm pivotally mounted on said first pivot pin and extending between said side members, one end of said pivot arm terminating above the drum in a yoke having a pair of parallel spaced side pieces lying in planes normal to said pivot pin, the other end of said pivot arm extending past the portion of said supplemental track furthest from the drum;   (e) a second pivot pin disposed between said side pieces and normal thereto;   (f) .[.a.]. .Iadd.the .Iaddend.pinch roller.Iadd., which is .Iaddend.mounted on said second pivot pin for rotational movement;   (g) first bias means carried by said pinch roller carriage for pushing against said supplemental track to urge said gripping members closest to said drum against the edge of said supplemental track closest to the drum whereby said second pivot pin is placed in longitudinally parallel alignment with the longitudinal axis of the drum, said urging being with a force sufficiently small to allow the easy translational sliding of said pinch roller carriage along said supplemental track;   (h) second bias means operably connected between said pinch roller carriage and said pivot arm for urging said pinch roller down against the surface of the drum and said gripping members into pinching engagement with said supplemental track with sufficient force to prevent translational movement of said pinch roller carriage; and,   (i) bias release means for selectively holding said pinch roller off said drum and releasing said pinching engagement against the force of said second bias means to allow translational movement of said pinch roller carriage and thereby the position of said pinch roller along the length of the drum.   
     
     
       2. In a graphics plotter having a rotatable drum, a pinch roller for holding a writing medium against the surface of the drum for longitudinal movement thereby, and a carriage track disposed above and parallel to the drum for supporting a pen block carriage for traverse movement, the improvement comprising: (a) a supplemental track carried by the carriage track and extending downward therefrom, said supplemental track being an inverted T-shape in cross section;   (b) a pinch roller carriage having a pair of spaced parallel side members, each having a pair of facing gripping members extending upward therefrom to form a groove of T-shaped cross section, said gripping members being adapted to fit loosely about said supplemental track with said track disposed within said groove whereby said pinch roller carriage hangs from said supplemental track and is easily slideable along said supplemental track;   (c) a first pivot pin disposed between said side members and normal thereto at about the location of the edge of said groove closest to the drum;   (d) a pivot arm pivotally mounted on said first pivot pin and extending between said side members, one end of said pivot arm terminating above the drum in a yoke having a pair of parallel spaced side pieces lying in planes normal to said pivot pin, the other end of said pivot arm extending past the portion of said supplemental track furthest from the drum;   (e) a second pivot pin disposed between said side pieces and normal thereto;   (f) .[.a.]. .Iadd.the .Iaddend.pinch roller.Iadd., which is .Iaddend.mounted on said second pivot pin for rotational movement;   (g) first bias means carried by said pinch roller carriage for pushing against said supplemental track to urge said gripping members closest to said drum against the edge of said supplemental track closest to the drum whereby said second pivot pin is placed in longitudinally parallel alignment with the longitudinal axis of the drum, said urging being with a force sufficiently small to allow the easy translational sliding of said pinch roller carriage along said supplemental track;   (h) second bias means operably connected between said pinch roller carriage and said pivot arm for urging said pinch roller down against the surface of the drum and said groove formed by said gripping members into pinching engagement with said supplemental track with sufficient force to prevent translational movement of said pinch roller carriage; and,   (i) bias release means for selectively holding said pinch roller off said drum and releasing said pinching engagement against the force of said second bias means to allow translational movement of said pinch roller carriage and thereby the position of said pinch roller along the length of the drum.   
     
     
       3. In a graphics plotter having a rotatable drum, a pinch roller for holding a writing medium against the surface of the drum for longitudinal movement thereby, and a carriage track disposed above and parallel to the drum for supporting a pen block carriage for traverse movement, the improvement comprising: (a) a supplemental track carried by the carriage track and extending downward therefrom;   (b) a pinch roller carriage having a pair of spaced parallel side members, each having a pair of gripping members extending upward therefrom, said gripping members being adapted to mate with said supplemental track whereby said pinch roller carriage is suspended from said supplemental track and is easily slideable traversely along said supplemental track;   (c) a first pivot pin disposed between said side members and normal thereto at about the location of the ones of said gripping members closest to the drum;   (d) a pivot arm pivotally mounted on said first pivot pin and extending between said side members, one end of said pivot arm terminating above the drum in a yoke having a pair of parallel spaced side pieces lying in planes normal to said pivot pin, the other end of said pivot arm extending past the portion of said supplemental track furthest from the drum;   (e) a second pivot pin disposed between said side pieces and normal thereto;   (f) .[.a.]. .Iadd.the .Iaddend.pinch roller.Iadd., which is .Iaddend.mounted on said second pivot pin for rotational movement;   (g) first bias means carried by said pinch roller carriage for pushing against said supplemental track to urge said gripping members closest to said drum against the edge of said supplemental track closest to the drum whereby said second pivot pin is placed in longitudinally parallel alignment with the longitudinal axis of the drum, said urging being with a force sufficiently small to allow the easy translational sliding of said pinch roller carriage along said supplemental track;   (h) second bias means operably connected between said pinch roller carriage and said pivot arm for urging said pinch roller down against the surface of the drum and said gripping members into gripping engagement with said supplemental track with sufficient force to prevent translational movement of said pinch roller carriage; and,   (i) bias release means for selectively holding said pinch roller off said drum and releasing said pinching engagement against the force of said second bias means to allow translational movement of said pinch roller carriage and thereby the position of said pinch roller along the length of the drum.   
     
     
       4. The improvement of claim 3 wherein: (a) said supplemental track is shaped as an inverted T in cross section; and,   (b) said gripping members are L-shaped in cross section and create a pair of parallel T-shaped grooves in which said T-shaped supplemental track is disposed.   
     
     
       5. The improvement of claim 4 wherein: said first bias means comprises a pair of leaf springs carried by said pinch roller carriage in sliding relationship with and pushing against the rearmost surface of said T-shaped supplemental track. .Iadd.   
     
     
       6.  In a graphics plotter having a rotatable drum and a pinch roller for holding a writing medium against the surface of the drum for longitudinal movement thereby, the improvement comprising: (a) a track having track surfaces extending generally parallel to the axis of the drum adapted to engage complementary track-engaging surfaces of a pinch-roller carriage;   (b) a pinch-roller carriage, which carriage includes track-engaging surfaces complementary to the track surfaces and slidably mounting the carriage on the track for sliding of the carriage longitudinally with respect to the track, the track-engaging surfaces being sized and shaped to mount the carriage loosely when the carriage is in a normal orientation with respect to the track but to be urged with force against the track surfaces to tend to bind the carriage to the track when the carriage is pivoted from the normal orientation with respect to the track;   (c) a pivot arm, carrying the pinch roller and being pivotably mounted on the carriage for pivoting about a pivot axis spaced from the axis of the pinch roller, for bringing the pinch roller into and out of engagement with the drum by the pivoting of the pivot arm;   (d) bias means acting between the carriage and the pivot arm to exert a torque about the pivot axis to tend to pivot the pivot arm to urge the pinch roller against the drum and, when the pinch roller has engaged the drum or a medium disposed thereon, to tend to pivot the carriage with respect to the pivot arm and thus with respect to the track and thereby exert a force urging the track-engaging surfaces against the engagement surfaces on the track so as to increase the static friction therebetween and prevent sliding of the carriage with respect to the track, whereby the carriage and pinch roller can be relatively easily slid along the track when the pivot arm has been pivoted against the torque exerted by the bias means but are held in place when the bias means is allowed to urge the pinch roller against the drum. .Iaddend. .Iadd.7. The improvement of claim 6 wherein:   (a) the track and track-engaging surfaces include complementary orienting portions that the loose fit of those surfaces allows to be spaced from each other but that can be brought into abutment;   (b) the pinch roller is mounted for rotation about a roller axis that is substantially parallel to the drum axis when the complementary orienting portions abut each other; and   (c) the improvement further includes a second bias means for exerting between the carriage and the track a force that urges the complementary orienting portions against each other so as to keep the roller axis parallel to the drum axis, the force applied by the second bias means being low enough that the static friction caused thereby between the orienting portions does not prevent easy sliding of the carriage with respect to the track. .Iaddend. .Iadd.8. The improvement of claim 7 further including bias release means operable to resist the torque of the first-mentioned bias means to hold the pinch roller off the drum.   
     
     
        .Iaddend. .Iadd.9.  The improvement of claim 6 further including bias release means operable to resist the torque of the first-mentioned bias means to hold the pinch roller off the drum. .Iaddend.