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Room 3-470 77 Massachusetts Ave. Cambridge, MA 02139. Phone: (617) 253-1953 Fax: (617) 258-6427 http://pergatory.mit.edu/. The Standard MiniMill™ Stiffness Calculations. By: Roger Cortesi rcortesi@mit.edu http://pergatory.mit.edu/rcortesi/. Precision Engineering Research Group
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Room 3-470 77 Massachusetts Ave. Cambridge, MA 02139 Phone: (617) 253-1953 Fax: (617) 258-6427 http://pergatory.mit.edu/ The Standard MiniMill™ Stiffness Calculations By: Roger Cortesi rcortesi@mit.edu http://pergatory.mit.edu/rcortesi/ Precision Engineering Research Group Massachusetts Institute of Technology, Mechanical Engineering Department
Types of Stiffness Calculations • Ball Screw Stiffness • Servo Stiffness • Carriage Translation Stiffness • Carriage Roll Stiffness
The ball screw is really a wedge Standard MiniMill™ Servo Stiffness
Star Linear™ Steel Truck Short (left) and Standard Truck (right) Standard MiniMill™ Carriage Translation Stiffness The carriage stiffness in the UP DOWN and SIDE directions in 4 times the truck stiffness in each of these directions.
Lb Lt Tool Force 2 Trucks 2 Trucks Center of Stiffness Standard MiniMill™ Carriage Roll Stiffness
Carriage Stiffness Comparison Between The Standard and Modified MiniMill™ Axial Stiffness 1 is the servo stiffness. Use if a linear encoder is used Axial Stiffness 2 is the stiffness of the ball screw, use if a rotary encoder is used See the Modified MiniMill™ Stiffness Presentation for the calculation of the its stiffness values
Overall Machine Stiffness Estimates Between The Standard and Modified MiniMill™ • The Standard MiniMill™ has an estimated Machine Stiffness of: • 10 N/micron (57,000 lbf/inch) • This can be doubled by upgrading from short trucks (0.02 C Preload) • to Standard Trucks (0.08 C Preload) The Modified MiniMill™ has an estimated Machine Stiffness of: 5 N/micron (27,000 lbf/inch) The machine stiffness was estimated from the deflection due to the rolling of Y Carriage and Deflection of the Z Axis. See the Modified MiniMill™ Stiffness Presentation for the calculation of the its stiffness values