P20652: 3D Concrete Printer
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

During this the preliminary detailed design phase, the mechanical team planned to prototype the extrusion system using 3D printing. The electrical team planned to perform more analysis on the auger rotation stepper motor and design the power delivery system. The software team planned to perform more feasibility on the controller and control software.

Meetings were setup with various subject matter professionals and companies to ask for design financial support.

Each team was able to achieve their planned goals. The mechanical team was successful in creating an extrusion system comprised of PVC and 3D printed parts. The electrical team designed various power distribution circuits and created documents displaying additional feasibility for power supply, motors, e-stop, and edge detection components. The software team determined the workflow for using the RepRap software interface.

At this point, Duet3D has pledged to donate a Duet2 Wifi board.

Drawings, Schematics, Flow Charts, Simulations

This section includes drawings, schematics, flow charts, and simulations from the preliminary detailed design phase. This section builds upon documents from previous phases as well as introduces new content generated in the preliminary detailed design phase.

Mechanical Diagrams

Many 3D models were created for prototyping during this phase.

The base nozzle design is shown below. It is a base model so it is able to be modified to augment its functionality.

Model of the first auger.

Model of the first auger.

PVC extruder assembly model.

PVC extruder assembly model.

Auger in the extruder model.

Auger in the extruder model.

The base model of the printer nozzle.

The base model of the printer nozzle.

Electrical Diagrams

The following display some wiring schematics for the overall system and subsystems.

Figure 1: The flow of power and signals is described to demonstrate how subsystem electrical interactions are channeled. This diagram will provide insight for the design of physical subsystem and component placement, visual aid in power analysis, and general reference of the inter-connectedness of components. For the final version of the Electrical System Block Diagram see this link.

Figure 2: The E-stop proposal describes how the switch should be placed such that when activated it will de-energize the actuators.

Figure 3: Displays the systems that should be receiving an electrical supply. This diagram was used to provide a visual aid for power analysis.

Fig. 1: Overall electrical block diagram.

Fig. 1: Overall electrical block diagram.

Fig. 2: E-stop circuit diagram.

Fig. 2: E-stop circuit diagram.

Fig. 3: Power supply connection diagram.

Fig. 3: Power supply connection diagram.

Software Diagrams

The controller board selected included a number of diagrams to illustrate the functionality of the board.
Functional diagram of the Duet2 3D printing board.

Functional diagram of the Duet2 3D printing board.

I/O diagram of the Duet2 3D printing board.

I/O diagram of the Duet2 3D printing board.

Wiring diagram of the Duet2 3D printing board.

Wiring diagram of the Duet2 3D printing board.

Wiring diagram of the Duet2 3D printing board with unused details removed.

Wiring diagram of the Duet2 3D printing board with unused details removed.

Prototyping, Engineering Analysis, Simulation

During this phase, all teams began creating prototypes or models of their components.

Mechanical Prototyping and Simulations

For this stage, the Mechanical Engineering team began prototyping the extrusion system. The prototype extrusion system is comprised of a 3D printed and PVC parts. Photos of each component with a description are shown below.
The first nozzle prototype.

The first nozzle prototype.

The nozzle interface with feed system.

The nozzle interface with feed system.

The first auger prototype.

The first auger prototype.

The auger in the PVC tube.

The auger in the PVC tube.

Explanation of inputs and outputs of Extrusion System.

Explanation of inputs and outputs of Extrusion System.

Design and test flow between versions 1 and 2 of our PVC extruder assembly.

Design and test flow between versions 1 and 2 of our PVC extruder assembly.

The prototypes shown above were tested with a concrete mix. The parts were unsuccessful in depositing material from the extruder. The main issue experienced was that the auger could not be torqued as much as it needed to be in order to spin and move the mix. The auger was also originally printed too large. The mechanical team filed down the diameter of the blade to help reduce it, but this also reduced the thickness of the print wall which decreased its rigidity. The auger ultimately failed as it was being torqued with a wrench (directly fastened to plastic). New designs of the auger implement an axial square metal shaft which will provide rigidity and will allow interfacing with a wrench or drill to provide additionally torque.

Electrical Engineering Analysis and Simulations

The electrical team was able to model motors using Simulink. A range of models in varying complexity are demonstrated.

Figure 1: The Level 2 motor simulation is modeled based on equations describing the electrical and torsional mechanics of a stepper motor.

Figure 2: The Level 3 motor simulation implements pre-programmed models to simulate the stepper motor system. Interactions between and behaviors of the on-board PWM generator of the controller, the stepper drivers, the motor, and the load can be simulated effectively.

Fig. 1: Level 2 motor simulation schematic, drafted in Simulink.

Fig. 1: Level 2 motor simulation schematic, drafted in Simulink.

Fig. 2: Level 3 motor simulation schematic, drafted in Simulink.

Fig. 2: Level 3 motor simulation schematic, drafted in Simulink.

Simulation results, analysis documents, and proposals for the power supply, E-stop, and motors are documented. Some documents describe and perform the techniques used to analyze a subsystem so that it shall provide the capabilities to meet system requirements. The proposals summarize: relevant background, requirements the system/component shall meet, and a product/design recommendation.

Additional planning and information will be found below in the Feasibility section.

System Wide Power Analysis

Power Supply Proposal

Motor Selection Plan

Motor Selection Proposal

Motor Simulation Plan

Motor Simulation Results (Note: The simulations have been designed but implementation is still taking place. Analytical results will be posted.)

E-Stop Analysis and Proposal

Edge Detection Analysis Report

Software Engineering Analysis

The tool that will be used with the Duet board is the RepRapFirmware Configuration Tool.
This screen allows the user to configure the general setting for the printer. The user can configure things like power failure settings and homing settings. These settings should remain consistent throughout the life of the machine, unless the machine undergoes some structural changes.

This screen allows the user to configure the general setting for the printer. The user can configure things like power failure settings and homing settings. These settings should remain consistent throughout the life of the machine, unless the machine undergoes some structural changes.

This screen offers the ability to add an expansion board to the Duet2 in the form of the Duex2 and Duex5 that offer an additional 2 and 5 stepper motor drivers respectively. These expansion boards offer other features such as heaters, fans, and GPIO pins which are of no use in our current design but could be useful if changes are made during our time with the project or future teams.

This screen offers the ability to add an expansion board to the Duet2 in the form of the Duex2 and Duex5 that offer an additional 2 and 5 stepper motor drivers respectively. These expansion boards offer other features such as heaters, fans, and GPIO pins which are of no use in our current design but could be useful if changes are made during our time with the project or future teams.

This screen offers configuration settings for axis motors and extruder motors. These settings include direction, microstepping, steps per mm, max speed change, max speed, acceleration, motor current, and motor driver. This page also allows the user to reduce motor currents after the motor is idle for a specified time.

This screen offers configuration settings for axis motors and extruder motors. These settings include direction, microstepping, steps per mm, max speed change, max speed, acceleration, motor current, and motor driver. This page also allows the user to reduce motor currents after the motor is idle for a specified time.

Here the user can find configuration settings for different end stop devices. Settings can be chosen for X and Y axis endstops with options for active high and active low configurations. Options are also available for endstops being located at the low end or high end of the machine. There are specialty settings for Z-probe sensors such as the probe type, trigger height, and the trigger value.

Here the user can find configuration settings for different end stop devices. Settings can be chosen for X and Y axis endstops with options for active high and active low configurations. Options are also available for endstops being located at the low end or high end of the machine. There are specialty settings for Z-probe sensors such as the probe type, trigger height, and the trigger value.

This screen shows the standard user interface in which files are uploaded to the printer. The user has direct control of motors and includes an emergency stop button.

This screen shows the standard user interface in which files are uploaded to the printer. The user has direct control of motors and includes an emergency stop button.

The system editor allows the operator to change configuration files on the file in order to fine to quickly fine tune the machine.

The system editor allows the operator to change configuration files on the file in order to fine to quickly fine tune the machine.

This file shows an example of the configuration settings for the printer. Some shows include setting stepper motor settings and axis limit settings.

This file shows an example of the configuration settings for the printer. Some shows include setting stepper motor settings and axis limit settings.

The Pronterface software acts as a command line interface to the printer that allows the configuration of network settings and also allows different operation commands to be sent to the printer.

The Pronterface software acts as a command line interface to the printer that allows the configuration of network settings and also allows different operation commands to be sent to the printer.

Feasibility: Prototyping, Analysis, Simulation

Feasibility analysis was continued by each team for various systems.

Mechanical Prototyping and Simulations

To connect design decisions about the auger to the project's engineering requirements, a rudimentary analysis was completed. The figure below shows the ideal volumetric flow rate through the extruder in cubic meters per hour as the rotational speed of the auger increases from 0 to 20 rpm. Pitch of the auger is varied over a generous range from 0 to 4.75 inches, and is reflected as green to yellow in the figure, respectively (i.e. green represents smaller values for pitch while yellow represents larger values). The pitch used for prototype 1 is shown as the blue line. Finally, this is related to ER2, which designates the minimum deposition rate required from the machine. The requirement is shown as the red line. It should be noted that this analysis assumes no slip between the auger and the cement, which is entirely unrealistic. Thus, empirical data is needed to inform and improve the model.

Ideal volumetric flow rate vs auger rotational speed, as pitch varies

Ideal volumetric flow rate vs auger rotational speed, as pitch varies

Electrical Prototyping, Analysis, Simulation

The feasibility and benchmarking of the electrical systems are detailed in the documents below. These documents were produced as an initial effort to brainstorm the design and selection of some subsystems.

Power Supply Feasibility

Power Supply Benchmarking

Motor Selection Plan

Motor Selection Benchmarking

Edge Detection Feasibility

Software Feasibility Analysis

Software feasibility analysis was done to continue to verify that the Duet2 would be an appropriate choice for this application. Feasibility of this stage primarily consisted of discovering the software tools and other examples of the board in use. Previous feasibilities were focused on the hardware of the board and its ability to support the motors necessary.

A comprehensive wiki page exists that details the usage of the printer. Additionally, recommendations about appropriate stepper motors are made. The wiki can be found here.

A website is provided in order to generate a new firmware package specifically tuned to the parameters of any printer system. This website can be found here.

An video example setup using the Duet2 Wifi is found here.

Ergonomic Analysis

For the ergonomic analysis, we have performed a Biomechanical preliminary analysis to detect and act towards risks associated with work demands exceeding human capabilities.

The preliminary analysis consists of a Biomechanical 2D Static Analysis. Also, we will be performing a 3D Dynamic Model and a Design of Experiments in the 3D Static Posture. Because of the complexity of analyzing this, a 3D Static Strength prediction program will be used.

Cart Push Analysis Part 1

Cart Push Analysis Part 1

Spine Force Compression Analysis

Spine Force Compression Analysis

Spine Analysis External Moment

Spine Analysis External Moment

Spine Analyis Part 1

Spine Analyis Part 1

Cart Push Analysis part 2

Cart Push Analysis part 2

Bill of Material (BOM)

The Bill of Materials for this phase can be found here. A preview png can be found below. For the final Bill of Materials, see this link.
The BOM.

The BOM.

Test Plans

A test plan is a detailed document tool used to assist a team member in designing and performing a test. A test plan can be performed to test prototypes, verify component or system level performance, experiment with software/user interfaces, etc. A test plan should contain the following information:

A generic test plan writing procedure follows:

  1. Analyze the product
  2. Design the Test Strategy
  3. Define the Test Objectives
  4. Define Test Criteria
  5. Resource Planning
  6. Plan Test Environment
  7. Schedule & Estimation
  8. Determine Test Deliverables

Test Axes in System Test Plan

Controller_Driver_Motor Circuit Test Plan

Nozzle Geometry Test Plan

Nozzle Material Test Plan

Printhead Structures_Auger Test Plan

Cement Mixer Test Plan

Risk Assessment

The Risk Management document for this phase can be found here. A preview png can be found below. For the final Risk Management and Progress document, see this link.
Risk Management Document for Preliminary Design Review.

Risk Management Document for Preliminary Design Review.

Design Review Materials

Pre-read

Plans for Next Phase

The Gantt chart below shows a plan of tasks that need to be completed during the next phase and the tentative schedule for each task. For the final Schedule Management document, see this link.
Gantt chart for Preliminary Detailed Design.

Gantt chart for Preliminary Detailed Design.

The three week plans for the system level design review are found below.

Alex K.

Alex P.

Amiee

Chad

Joe

Mary

Nick

Seth


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