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Fab.in.a.box - Fab Academy: Machine Design

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  • 1. Fab Academy: Machine Design Ilan Moyer 4/7/2010
  • 2. FAB-IN-A-BOX: WORKFLOW Eagle .PNG CAD.PY .RML .PY Virtual Machine Environment FABNET Stepper Control multifab
  • 3. MTM MULTIFAB Ilan Moyer and Maxim Lobovsky
  • 4. XY STAGE Z FRAME
  • 5. X AXIS Y AXIS Shuttle/ Tool Holder THE XY STAGE: KINEMATICS
  • 6. Four C-Chanel Extrusions THE XY STAGE: STRUCTURE Symmetric Bolt Pattern
  • 7. THE XY STAGE: MECHANISM Stepper MotorSynchronization Shaft Drive Shaft Drive Pulleys Shuttle Bushings Rollers Idler Pulleys Drive Belts Belt Tensioner
  • 8. THE XY STAGE: MECHANISM
  • 9. THE Z AXIS: DRIVE MECHANISM Stepper Motor Guide Rail (x2) Leadscrew Helical Beam Coupler Leadnut Bushings Thrust Bearing Assy Tube
  • 10. THE Z AXIS:TABLE Sub-Frame Sub-Table Mounting Working Surface Leveling
  • 11. TOOL-HEADS AND CAPABILITIES
  • 12. 5 AXIS TRUNNION
  • 13. STRENGTHS WEAKNESSES •Low Inertia -> High Acceleration •Direct Drive -> High Speed •200mm^3 WorkVolume •Fixed Table -> Tall 3D Prints •Low Stiffness -> No Heavy Milling •Low Basic Resolution: 0.0035” (~0.0015 with half stepping.)
  • 14. STEPPER MOTOR SELECTION Lin Engineering 4209M-02P Resistance = 2.35 Ohms Inductance = 3.2 mHenries Lin Engineering 4209L-03P Resistance: 58 Ohms Inductance: 82 mHenries NOTE: t_rise is the time for motor current to reach 100%.
  • 15. DRIVEVOLTAGE SELECTION Current Rise Time: 12V Max Speed: 12V 41% Power @ 400mm/s Max Speed: 24V 75% Power @ 400mm/s
  • 16. DRIVE ELECTRONICS Allegro A3967 Allegro A3982 - 8 uSteps/Step - 750mA/Phase - 2 uSteps/Step - 2A/Phase
  • 17. THE NETWORK Stepper Motor Control DC Motor Control RC Servo Control Virtual Machine Environment NETWORK + POWER
  • 18. GENERAL PACKET FORMAT [ [UNICAST|MULTICAST] [SOURCE IP][SOURCE PORT] [DEST. IP][DEST PORT] [LENGTH] [----PAYLOAD----] [CRC CHECKSUM] ]
  • 19. MOTION CONTROL Virtual Machine Object Control Firmware http://mtm.cba.mit.edu/fabinabox/vm/076-001e.py WWW
  • 20. MOTION CONTROL VM Environment on PC MICRO-CONTROLLER MOTION CONTROL CODE MACHINE DESCRIPTION VM Object Firmware
  • 21. FIRMWARE •PACKET HANDLING •BRESENHAM LINE ALGORITHM •CIRCULAR QUEUE •ANTI-BACKLASH
  • 22. BRESENHAM LINE ALGORITHM RULE #1:Always step along major axis. RULE #2: Step in minor axis if error > 0.5 steps.
  • 23. BRESENHAM ALGORIGTHM...THE TRICK: How do you know when the error is > 0.5? Don’t you need to know the slope? Y STEPS X STEPS ALWAYS STEP IN X AXIS. SLOPE = (Y STEPS) / (X STEPS) ERROR = (Y STEPS) ACCUMULATE ERROR EACH X STEP. WHEN ERROR > 0.5(X STEPS),TAKE A STEP INY. OR,WHEN 2 x ERROR > X STEPS.
  • 24. VIRTUAL MAJOR AXIS FOR DISTRIBUTED MOTION CONTROL VIRTUAL STEPS = 8 = MAXIMUM STEPS X STEPS = 8 Y STEPS = 3 Z STEPS = 1 2-AXIS CONTROLLER 1-AXIS CONTROLLER mtm.move(8,3,1)
  • 25. CIRCULAR BUFFER: ACCOUNTS FOR RAPID SERIES OF MOVES, SUCH AS WHEN GOING AROUND AN ARC.COMMANDWIDTH Read Pointer Write PointerSLOT0 SLOT1 SLOT2 SLOT3 SLOT4 SLOT5 SLOT6 SLOT7 SLOT8 SLOT9 SLOT10 SLOT11 SLOT12 SLOT13
  • 26. 3 AXIS MOTION CONTROL mtm.move(x,y,z,rate) VME Machine Hardware Description i.e. step angle, linear reduction, control system topology, etc... vmo.spin(x_steps, y_steps, z_steps, move_time) PC-BASED FIRMWARE Does complex calculations such as floating point and division. VMO [key, dir., max_steps, x_steps, y_steps, z_steps, counter_top] MCU-BASED FIRMWARE Does timing-critical calculations and I/O control. MCU
  • 27. mtm.cba.mit.edu/fabinabox/