Improvements in hand trucks with pivotally connected, spreadable, wheel-supported, auxiliary support frames

A method of operating a hand propelled hand truck having an upright main frame, including brace-connected side rails, with a handle part at its upper end;

• a forwardly extending nose platform for the lower end of the main frame for supporting a load thereon which rests back against the main frame when the main frame is in vertically rearwardly tilted position;
• and a wheel and axle assembly connected to the lower end of the main frame to support it for travel;
• there being an attachment frame, having at least one ground engaging wheel at its lower end, pivotally connected near its upper end to an upper portion of said main frame for movement out away from the general plane of said main frame to a spread divergent position with respect thereto;
• rearwardly extendible first link structure having a pivot pivotally connecting said first link structure to said main frame at a location spaced downwardly from the pivotal connection of the attachment frame to the main frame;
• forwardly extendible second link structure having a pivot pivotally connecting said second link structure to said attachment frame;
• a swingable link pivot in a first position in front to rear alignment with both said pivots in an alignment plane pivotally connecting said first link structure to said second link structure for movement from a position in which said link pivot is in a second position on one side of said alignment plane when the attachment frame is folded to said main frame through said alignment plane to an over-center third position in which said link pivot is on the opposite side of said alignment plane;
• and force exerting compressible spring mechanism having a first spring pivot connecting said spring mechanism pivotally to one of said main frame and attachment frame at a first point and a second spring pivot connecting said spring means to one of said link structures at a second point lying inboard in the front to rear direction of the pivot of said one of said main frame and attachment frame when the link pivot is in said third position and said attachment frame is in spread position;
• comprising the steps of:
• a. pulling the attachment frame outwardly against the restraining force exerted by said spring mechanism toward spread position and moving the link pivot toward said alignment plane while moving said first and second link structures from a folded position toward a more in-line position;
• b. by pulling the attachment frame outwardly, moving the second spring pivot from an initial position on one front to rear side of the pivot of said one of the main frame and attachment frame in which said spring mechanism exerts force through a moment arm to resist unfolding of the first and second link structures to a position on the other front to rear side of said second spring pivot;
• and
• c. thereby releasing the force of said spring mechanism through a moment arm sufficient to move said link pivot through said alignment plane to over-center third position, and to resist movement of said link pivot back out of said third position.