Friction drive for metering device

In a fluid metering system, wherein a plunger actuated syringe is mounted in a housing and is coupled to at least one source of fluid, a highly accurate and precise linear friction drive mounted in the housing and coupled to the plunger comprising:

• a rack, having a flat side;
• a rotatable pinion pressed against the flat side of the rack for moving the rack by friction;
• opposed guide rollers, one of which is fixed relative to the housing, engaging a portion of the rack opposite the flat side in straddling relation with the pinion for urging the rack intimately thereagainst;
• a moveable swing arm having one end mounted for rotatable motion about a point and moveably supporting the other of the guide rollers against the rack;
• a force exerting means operating at a free end of the swing arm for leveraging the guide roller carried by the swing arm against the rack and transmitting the force to the pinion;
• and means for securing the swing arm in a plane perpendicular to the flat side of the rack, preventing lateral motion of the swing arm from being transmitted to the rack and pinion, for suppressing cyclical variation in the relative motion between the same.