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Ching-Han Tseng Dominic Boiko Frankie Ning HaroutHedeshian Joel Meisinger 3DP PDR
Overview • Design of a 3D printer for affordable prototyping. • Prints each cross section of a 3D object layer by layer • Three axis motion in a 3x3 feet chassis for large scale modeling • Use of accurate stepping motors for high precision printing • Network communication
Objective • 25mm/s linear write speed • 0.5mm deposition resolution • 5mm3/s (0.3 in3/s) • Capable of printing a 10cm3 object • Capable of printing functional prototypes
Mechanical • Expected Dimension: 3 ft x 3ft x 3ft • 3 stepping motors
Electrical System Functional Block Diagram 5V Wall Power CDH Controller 5V 12V RS422 Bus Interrupt Motor Controller I/O Encoder Controller Extrude Header Controller
CDH Command and Data Handling
Command & Data Handling • Coordinate all events on printer • Communications interface for daughter boards • Provide a physical human interface for high level control • Platform independent and driverless communications to host computer
EPS DEBUG Power Sequencing RS232 5V 5->3.3 Buck 5->2.5 Buck RS422 Driver 6-DIN ARM Cortex M3 (Stellaris LM3S6965) Main CPU SPI 4Mb AVR MCU (ATXMEGA128A1) IO Hub RS422 Driver 6-DIN RS422 Driver 6-DIN RS232 Ethernet Reset lines GPIO I2C GPIO USB->RS232 Buzzer LCD Buttons
Choosing interface and MCU • Choosing the Stellaris: • On die Ethernet MAC and PHY • Ethernet drivers already written by TI • Have working code for MCU from prior projects • Choosing the XMEGA-A1 • Cheaper to use XMEGA than purchasing SPI-UART converters. • Allows Stellaris to be bypassed for fallback
MCU: LM3S6965 I/O: ATXMEGA128A1 • 50MHz ARM Cortex M3 • 256KB Flash • 64KB Single Cycle SRAM • On die Ethernet MAC and PHY • 3 x UART • 1 x SPI • 2 x I2C • Why the 128 and not the 64: It’s in stock • 32MHz • 128KB Flash • 8KB Single Cycle SRAM • EBI for external buffer memory • 4 x UART • 4 x SPI • 4 x I2C
Board level firmware • XMEGA: • Mostly interrupt driven custom firmware • Simple functionality acting as a “smart” I/O controller. • May use YAVRTOS • Stellaris: • FreeRTOS • uIP • Time permitting: lwIP • Using a highly modified Telnet server implementation to provide raw TCP socket for communication.
CDH Risk • Primary risk: Ethernet non-functional • Likelihood of success: 90% [Software working on dev board, hardware design untested] • Fall back to USB-UART • Secondary Risk: USB-UART non-functional • Likelihood of success: 6.022E23% [Used controller IC before and have several working designs using said device] • Fall back to UART on AVR
EPS Electrical Power System
Power Supply Power Supply • Provide each sub-system with appropriate power level • Maintain UL compliance • Isolated Power System • Reduced Shock Hazard • Continuity of power • Noise Reduction • Over-current and short circuit protection
EPS Functional Block Diagram Wall Outlet 120VAC EMI Filter CDH Feedback 5V Forward converter (Isolated) MDC Rectifier Bridge Transformer/Reset Winding Isolated PSC 12V Forward converter (Isolated) FPS SMC Metallic Enclosure For Grounding Relay(Enable)
EPS Risk Risk • Primary risk: Shock/Explosion Hazard • Example • Over-current/short current protection, metallic enclosure grounding and isolation • are part of considerations to prevent this hazard • Secondary risk: Components go “Pooof-Hazard” • Hand-made Transformers might not operate as ideal as the calculation • Fall back to more detailed analysis, calculation, component upgrade, and proper • circuit protection.
MDC Material Deposition Controller
Material Deposition Controller Purpose of Subsystem • Lay down the material of choice (ABS plastic, Epoxy) at a constant rate. • Be able to stop and start new point. • Provide system feedback CDH such as material empty signal and motor error signal.
MDC Functional Block Diagram MDC FBD EPS XMEGA MCU 3.3V DC/DC converter RS422 Driver CDH 5V Deposition Motor Driver Deposition Thermal Driver 12V Thermal Feedback Print head
Material Selection: ABS Plastic • Moderate melting point: 221°F, 105°C • ABS possesses outstanding impact strength and high mechanical strength, which makes it so suitable for tough consumer products. • Many colors. • Risk: • ABS not working for dependable deposition • Nozzle tip temperature not constant • Contingency plan: • Use other material type such as a epoxy plunger feed. • Use other tip sizes and materials.
PSC Position Sensor Controller
Position Sensor Controller • Objective • Keep track of extruder head location • Keep track of motor movements and provide limit warnings • Requirements • Supply CDH Controller with 3 axis position of the extruder within 1/200th of a rotation • Supply limit warnings and movement verification to Stepper Motor Controller
PSC Functional Block Diagram EPS PSC RS232 ISP 6 GPIO SMC RS232 Driver XMEGA MCU 3.3V DC/DC converter RS422 Driver CDH 5V RS422 Encoder Z Encoder X Encoder Y
Encoder Specifications And Considerations • Specs • Optical • Resolution (>200 count per motor cycle) • Fits ACME threaded rod • Considerations • Index preferred • Quadrature preferred • Ease of Mounting/flexibility • Max Frequency Response • Low Cost
SMC Stepper Motor Controller
Step Motor Controller • Controller for the three axis stage moving the print head • Drives three 2-phase bipolar stepper motors, one for each axis • Monitor motor current and temperature • Interface with main command and data handling module
SMC Functional Block Diagram EPS SMC RS232 ISP Temp sensor PSC 6 GPIO RS232 Driver XMEGA MCU 3.3V DC/DC converter RS422 Driver CDH 5V Motor Driver Motor Driver Motor Driver RS422 Linear Actuator X Linear Actuator Y Linear Actuator Z
Interface and control • Communication with CDH using RS-422 • I/O to Toshiba Stepper Driver IC (TB6560AHQ) that drive the motors • I/O from PSC for motor limits and motor moving information
Choosing TB6560AHQ • Single 2-phase bipolar motor driver chip • Controllable current for torque management • Capable of half stepping and microstepping • Digital control inputs • Stepping speed determined by input clock
Risk • Current stepper motors might not produce enough torque to move extrude head • Very low risk • Current spikes of the motors damaging the microcontroller • Low risk with proper opotoisolation
Schedule • Gant chart