Preliminary Detailed Design
Team Vision for Preliminary Detailed Design PhaseDuring 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, SimulationsThis 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 DiagramsMany 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.
Electrical DiagramsThe 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.
Software DiagramsThe controller board selected included a number of diagrams to illustrate the functionality of the board.
Prototyping, Engineering Analysis, SimulationDuring this phase, all teams began creating prototypes or models of their components.
Mechanical Prototyping and SimulationsFor 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 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.
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.
Software Engineering AnalysisThe tool that will be used with the Duet board is the RepRapFirmware Configuration Tool.
Feasibility: Prototyping, Analysis, SimulationFeasibility 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.
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.
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 AnalysisFor 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.
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.
Test PlansA 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 step-by-step, detailed test strategy that anyone on the team can follow
- Testing objectives such as metrics or requirements
- A description of resources necessary for performing the test (manpower, man hours, hardware, software, cost)
- A preliminary estimation of the testing schedule (when and where it can it be performed)
A generic test plan writing procedure follows:
- Analyze the product
- Design the Test Strategy
- Define the Test Objectives
- Define Test Criteria
- Resource Planning
- Plan Test Environment
- Schedule & Estimation
- Determine Test Deliverables
Risk AssessmentThe 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.
Design Review Materials
Plans for Next PhaseThe 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.