The need to position an article rapidly and accurately with respect to an operative tool is a basic requirement in today's automated machinery. For a programmable computer-controlled sewing machine, the workpiece must be quickly and accurately positioned relative to a reciprocating sewing needle. The actual movement of the workpiece must be accomplished during that portion of the reciprocating needle cycle when the needle is disengaged from the workpiece. As the size of the workpiece (which may in and of itself consist of a number of separate pieces to be joined together) increases, the problem of achieving the desired accuracy within the finite period of time allowed for positioning by the reciprocating needle becomes more difficult. The ever increasing weight of workpieces may pose special problems for a positioning apparatus designed to accommodate less heavy articles. For example, the structure of the positioning apparatus may be too flexible to accommodate heavier workpieces so as to result in vibration and excessive overshoot during rapid positioning movements.
One approach to the aforementioned problem of accurately positioning a heavy workpiece is to merely scale up the structure present in existing positioning apparatus. This however results in very large and heavy types of structure which even further add to the weight to be moved by a motorized drive source. This furthermore may result in apparatus that cannot be easily manufactured or thereafter adjusted.