How do you get a good future in sonic CD 1993

To get a good future in an act, you must go to the past and destroy a robot generator. If you did it in acts 1 and 2, then act 3 (boss act) will have a good future as well.

To the best ending, collect all the time stones (in the special stages), or by getting a good future in all acts. If you collect all the time stones, then you will have a good future for the rest of the game.