Method and apparatus for detecting the presence or absence of a pen in pen recorder

A method for sensing whether a pen is in the grasp of pen claw of a drawing arm of a plotter or other graphics mechanism, the graphics mechanism also having a reference stop, the pen including an annular ring extending therefrom, the pen claw defining a reference ring by systematically positioning the pen so that the annular ring defines a pen reference ring, the pen reference ring being present with respect to the pen claw regardless of the existence of the pen, the pen claw being vertically movable a reference distance between an upward position and a downward position, said method comprising the steps of:

• first, positioning the reference ring proximate to the reference stop;
• second, energizing the pen claw to move vertically so that the reference ring moves in a direction toward the reference stop;
• and
• third, observing whether the pen claw is substantially impeded in the third step when the reference ring is adjacent to the reference stop.

A method for sensing whether a pen is in the grasp of a pen claw of a drawing arm of a plotter or other graphics mechanism, the pen and the pen claw defining a horizontally-extending shoulder at a fixed vertical distance with respect to the pen claw when the pen is in the grasp of the pen claw, the pen claw not defining the shoulder at the fixed vertical distance when the pen is not in the grasp of the pen claw, said pen claw being vertically movable between a storage position and a writing position, said method comprising the steps of:

• first, providing a pen stop on the plotter or other graphics mechanism;
• second, positioning the pen claw so that the shoulder, if present, is proximate to the pen stop;
• third, energizing the pen claw to move vertically so that the shoulder, if present, will be substantially impeded by the pen stop;
• and
• fourth, observing whether the pen claw is substantially impeded in its vertical movement in the third step.

An apparatus for sensing whether a pen is in the grasp of a pen claw of a drawing arm of a plotter or other graphics mechanism having a control device, the pen claw being vertically movable with respect to the drawing arm between an upward position and a downward position, said apparatus comprising:

• a shoulder extending from the pen claw when a pen is in the grasp of the pen claw, said shoulder not extending from the pen claw when a pen is not in the grasp of the pen claw;
• a stop connected to the plotter mechanism in a position to engage with said extended shoulder when the pen claw is proximate to the pen stop, so that the engagement between the stop and the shoulder impedes vertical movement of the pen claw within a portion of its vertical movement;
• a means for measuring the distance of vertical movement of the pen claw, and for providing an output indicative of the distance of vertical movement;
• whereby a pen is sensed by energizing the pen claw to move the shoulder towards the stop until the movement of the pen claw is substantially impeded and measuring the distance of vertical movement.

A method for sensing whether a pen is in the grasp of a pen claw of a drawing arm of a plotter or other graphics mechanism, the pen or the pen claw being an impediment at a fixed distance with respect to the drawing arm when the pen is in the grasp of the pen claw, the pen or the pen claw not defining the impediment at the fixed distance when the pen is not in the grasp of the pen claw, said pen claw being movable relative to said plotter, said method comprising the steps of:

• first, providing a pen stop on the plotter or other graphics mechanism;
• second, positioning the pen claw so that the impediment, if present, is proximate to, and positioned vertically above, the pen stop;
• third, energizing the pen claw to move in a downward direction so that the movement will be substantially impeded by the pen stop if said impediment is present;
• and
• fourth, observing whether said movement of said pen claw is substantially impeded in said third step.