William D. Ewart, the founder of the Link-Belt Machinery Company of Chicago, Illinois was an investor to Elmer Ambrose Sperry (Sperry Electric Mining Machine Company). Sperry had finanicial issues launching his company and looked to Link-Belt for capital and continuous improvement to his products. The U.S. Patent USCC64553 was filed on May 31st 1894 and published on March 20th of 1900. Clearly shows the "Bi-Polar" electric mine locomotive design. The chief engineer at the time was Charles E. Davis. 

American Industrial Mining Co.
Preserving Our Mining and Industrial Heritage
Non-profit preservation, restorations and education

In our archives are the rare Link Belt builder photographs for the early
"Bi-Polar" designs.