Thermoforming apparatus with improved press

A thermoforming apparatus including a press, a preheat oven preheating plastic sheet material to be formed into shaped articles in said press, means for feeding sheet material through said oven and into said press, means for creating a differential pressure acting on said sheet material to force said sheet material against tooling in said press to be formed, said press including;

• a machine frame;
• an upper platen;
• a lower platen;
• said machine frame including a top structure and a bottom structure connected together by four corner posts extending therebetween, said upper and lower platens confined within said corner posts for movement towards and away from each other to bring thermoforming tooling together to form an article and to separate said thermoforming tooling to allow loading of sheet material into said tooling and to remove a formed article:
• said upper and lower platen each guided by linear bearing means on an inside surface of each of said four corner posts and outside surfaces of sides of said upper and lower platens to guide movement thereon during said platen movement towards and away from each other;
• an upper platen drive means including a set of four toggle linkages drivingly connected to an upper side of said upper platen in a rectangular pattern to establish four points of support for said upper platen to resist forces generated by thermoforming of said articles;
• said upper platen drive means further including motor means driving said set of linkages drivingly connected to said upper platen to cause movement of said upper platen towards and from said lower platen;
• lower platen drive means including a set of four toggle linkages drivingly connected to a lower side of said lower platen in a rectangular pattern to establish four points of support for said lower platen to resist forces generated by thermoforming of said articles;
• said lower platen drive means further including lower platen motor means driving said set of four toggle linkages connected to said lower platen to cause said movement of said lower platen toward, and away from said upper platen;
• said upper platen motor means including two separate servo drive motors each having an output shaft drivingly connected to respective pairs of said four linkages connected to said upper platen, and said lower platen motor means including two separate servo motors each having an output shaft drivingly connected to respective pairs of said four linkages connected to said lower platen;
• and
• further including a positive driving interconnection between said output shafts of said two servo motors of each of said upper and lower platen drive means positively constraining simultaneous rotation of said output shafts of said upper platen and lower platen drive means, whereby if one servo motor stalls, the other servo motor in said respective upper or lower platen drive is stopped.