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

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

  1. 1. Fab Academy: Machine Design Ilan Moyer 4/7/2010
  2. 2. FAB-IN-A-BOX: WORKFLOW Eagle .PNG CAD.PY .RML .PY Virtual Machine Environment FABNET Stepper Control multifab
  3. 3. MTM MULTIFAB Ilan Moyer and Maxim Lobovsky
  4. 4. XY STAGE Z FRAME
  5. 5. X AXIS Y AXIS Shuttle/ Tool Holder THE XY STAGE: KINEMATICS
  6. 6. Four C-Chanel Extrusions THE XY STAGE: STRUCTURE Symmetric Bolt Pattern
  7. 7. THE XY STAGE: MECHANISM Stepper MotorSynchronization Shaft Drive Shaft Drive Pulleys Shuttle Bushings Rollers Idler Pulleys Drive Belts Belt Tensioner
  8. 8. THE XY STAGE: MECHANISM
  9. 9. THE Z AXIS: DRIVE MECHANISM Stepper Motor Guide Rail (x2) Leadscrew Helical Beam Coupler Leadnut Bushings Thrust Bearing Assy Tube
  10. 10. THE Z AXIS:TABLE Sub-Frame Sub-Table Mounting Working Surface Leveling
  11. 11. TOOL-HEADS AND CAPABILITIES
  12. 12. 5 AXIS TRUNNION
  13. 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. 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. 15. DRIVEVOLTAGE SELECTION Current Rise Time: 12V Max Speed: 12V 41% Power @ 400mm/s Max Speed: 24V 75% Power @ 400mm/s
  16. 16. DRIVE ELECTRONICS Allegro A3967 Allegro A3982 - 8 uSteps/Step - 750mA/Phase - 2 uSteps/Step - 2A/Phase
  17. 17. THE NETWORK Stepper Motor Control DC Motor Control RC Servo Control Virtual Machine Environment NETWORK + POWER
  18. 18. GENERAL PACKET FORMAT [ [UNICAST|MULTICAST] [SOURCE IP][SOURCE PORT] [DEST. IP][DEST PORT] [LENGTH] [----PAYLOAD----] [CRC CHECKSUM] ]
  19. 19. MOTION CONTROL Virtual Machine Object Control Firmware http://mtm.cba.mit.edu/fabinabox/vm/076-001e.py WWW
  20. 20. MOTION CONTROL VM Environment on PC MICRO-CONTROLLER MOTION CONTROL CODE MACHINE DESCRIPTION VM Object Firmware
  21. 21. FIRMWARE •PACKET HANDLING •BRESENHAM LINE ALGORITHM •CIRCULAR QUEUE •ANTI-BACKLASH
  22. 22. BRESENHAM LINE ALGORITHM RULE #1:Always step along major axis. RULE #2: Step in minor axis if error > 0.5 steps.
  23. 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. 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. 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. 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. 27. mtm.cba.mit.edu/fabinabox/

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