Feed index device in universal parallel ruler or the like

A straightedge movement control mechanism for use in a universal parallel ruler or the like to provide incremental movement of a straightedge over a drawing surface, said mechanism comprising:

• a track means for guiding a straightedge;
• a movable carriage plate including said straightedge, said carriage plate being mounted on, and movable along, said track means;
• a control member mounted on said track means for rotatable reciprocal motion between an initial position and an end position;
• a linkage means coupled between said movable carriage plate and said control member for transmitting movement of said movable carriage plate along said track to said control member to thereby rotate said control member from said initial position to said end position, said linkage means including a belt to which said movable carriage plate is attached and which rides on and drives a pulley linked to said control member, said linkage means further including a clutch mechanism between said pulley and said control member for disengaging to allow said control member to move independently of said movable carriage plate back to said initial position;
• a stop member mounted on said track means located at one of said initial and end positions to stop the movement of said control member thereat;
• an adjustable means located at the other of said initial and end positions to stop the movement of said control member thereat;
• and,
• operating means linked to said movable carriage plate for moving said movable carriage plate and linked to said clutch mechanism for engaging said clutch mechanism when said operating means is activated to move said movable carriage plate and said coupled control member from said initial position to said end position, but disengaging said clutch mechanism when said operating means is deactivated.