I. Field of the Invention
The present invention relates generally to the field of quill drives for machine tools and, in particular, to quill drives having an infinitely variable feed.
II. Description of the Prior Art and Prior Art Statement
Constituted in the prior art are the following U.S. Pat. Nos. 3,955,629, 3,160,033, 3,711,212, 2,905,440, 2,768,539, 3,640,147, 3,740,161, 3,561,544, 3,859,001, and 3,885,635. All of the above patents do not anticipate the present invention in that they use a multiplicity of motors for varying feed rate, or use planetary gears and clutches to vary feed rate, or use an offset feed mechanism, or they drive a ball nut arrangement to accomplish the feed function.
In the opinion of the Applicant U.S. Pat. Nos. 3,859,001 and 3,885,635 constitute the most relevant prior art to the present invention in that a ball nut disposed in the longitudinal center of the unit is driven to achieve the feed operation. The mechanical complexity of this arrangement renders its design more expensive. U.S. Pat. No. 3,885,635 drives a ball nut in the longitudinal center of the unit as well to achieve the feed drive, and in addition, U.S. Pat. No. 3,885,635 uses two feed drive motors operating at different speeds with clutches to vary the feed rate. Clearly, the two patents cited as the closest art are far more complex than the present invention and more costly in their construction.