26-12-2012, 04:27 PM
CAM Systems & CNC Machine
CAM Systems.ppt (Size: 400.5 KB / Downloads: 358)
History
1955 - John Parsons and US Air Force define a need to develop a machine tool capable of machining complex and close tolerance aircraft parts with the same quality time after time (repeatability). MIT is the subcontractor and builds the machine for the project.
1959 - MIT announces Automatic Programmed Tools (APT) programming language
1960 - Direct Numerical Control (DNC). This eliminates paper tape punch programs and allows programmers to send files directly to machine tools
Control Systems
Open-Loop Limitations
Control unit “assumes” desired position is achieved
No positioning compensation
Typically, a lower torque motor
Open-Loop Advantages
Less complex, Less costly, and lower maintenance costs
Closed-Loop Advantages
DC motors have the ability to reverse instantly to adjust for position error
Error compensation allows for greater positional accuracy (.0001”)
DC motors have higher torque ranges vs.. stepper motors
Closed-loop limitations
Cost
CNC vs. NC Machine Tools
Computer Numerical Control (CNC) - A numerical control system in which the data handling, control sequences, and response to input is determined by an on-board computer system at the machine tool.
Machining Centers
A machining center can be defined as a machine tool capable of:
Multiple operation and processes in a single set-up utilizing multiple axis
Typically has an automatic mechanism to change tools