Door Into Summer

It is 1970, and electronics engineer Dan Davis has finally made the invention of a lifetime: a household robot with extraordinary abilities, destined to dramatically change the landscape of everyday routine. Then, with wild success just within reach, Dan's greedy partner and even greedier fiancée steal his work and leave him penniless, and trick him into taking the long sleep—suspended animation for thirty years.  They never imagine that the future time in which Dan awakens has a very limited form of time travel, just enough that Davis can travel back and recover his research. He then again undergoes suspended animation, and awakens again in the high-tech future of the year 2000, with his reputation, fortune, and his sweetheart.