System Level Design

Team Vision for System-Level Design Phase

The plan going into the System-Level Design Phase was to complete all relevant MSD assignments for this phase, progress in our individual studies for the project, and to research/review the previous team's materials.  We, as a team, accomplished all the relevant MSD assignments for this phase and they are shown below. We also progressed significantly in our individual studies and we have reviewed a large portion of the previous team's materials. A lot of progress was made during this phase with the design of the printer, specifically the Z-axis. The team put together the X-Y axis of the printer and the prototype frame from the previous team and we got a better understanding of the size the printer will take up. This leads to adjustments within the engineering requirements, specifically in regards to the disassembly and storage of the printer. 

Functional Decomposition

Functional Decomposition is analytical method where a complex process is dissected in order to examine the individual elements. Each major function is broken down into smaller process steps to make the parts into more comprehensible units. Each team member was tasked with individual brainstorming before group collaboration. This aided in a thorough development a functional decomposition. Individual functional decomposition can be found in our File List- Functional Decomposition.

The team compared and contrasted our individual decompositions. There were overlaps at times. Discussion led to discovering some gaps missed the fight time through. Below is our group Functional Decomposition. This is broken down to the interfacing the user interacts with and internal mechanical/programmed printer steps. This was extremely helpful in establishing Morphological Charts and Concept Generation since each main function of the printer is now clearly laid out. 

Benchmarking

Concept Development

Now that the team has a foundational understating of the decomposition and how similar products functions, a table was developed breaking down possible options for each of the main functions. The team level concept generation chart can be found here. Along with the concepts that were developed, individual selection criterion were also developed to measure these concepts. These selection criterion were used in the Pugh Chart used for Concept Selection. 

Feasibility: Prototyping, Analysis, Simulation

As the group developed some concepts for the 3D concrete printer, the feasibility of these features must be considered. Each member produced preliminary work where they applied their 3D printer and field knowledge. They established feasibility questions and possible solutions. The group's combined live Feasibility Questions document can be found here. 

Below are a few feasibility testing/analyses possible at this time. 

REBA Analysis

The REBA Assessment is focused on determine the safety of a movement for the user. This was developed based on the following assumptions: User was 5'4 ft, lifting +40 lbs object above head to a high surface. 

Concrete Working Time Analysis

Individual Morphological Charts

We each individually took the concept generation chart and selected concepts that we thought would be worth discussing. These individual morphological charts can be found here.

Below are the rationales for the starting concepts from each member of the team. 

Derek's Concept Rationale:

Concept 1: I think a peristaltic pump/hopper design would work perfectly with the water dosing to maintain concrete moisture. The peristaltic pump requires concrete to be pumped into it from the hopper or reservoir, which can be achieved by an auger in the reservoir. This auger will also serve to mix in the water dosage, the peristaltic pump will act as a backup mixing system. G-code is often transferred by SD card if there are any concerns about WiFi transfer. Acme rods and stepper motors are standard in many CNC and 3D printing systems.

Concept 2: An auger in the extruder could control the flow of concrete out of the nozzle (this is already a common setup). With a sealed reservoir and moisture sensor the user can monitor the moisture needs and manually add it when necessary. With this level of moisture control we can hopefully maintain the proper viscosity to rely on gravity to feed the extruder. The concrete would be user mixed and added, then mixed and rewet when necessary. The Duet board supports WiFi. Stepper motors can be used with threaded rods to control the motion of the axes.

Tyler's Concept Rationale:

Concept 1: This method allows the user to predetermine the mixture before inserting it into the system and test the concrete's slump and consistency before hand. It also avoids a complex system of mixing the concrete at the extruder.

Concept 2: This method prevents premature setting of the concrete and allow for change in mixture as the print progresses, if that is deemed to be a valuable trait. The upload to the printers memory means easier repeatability of prints, even with extended amount of time between prints.

Anthony's Concept Rationale:

Concept 1: I think that parts of this concept, like mixing concrete and water at the nozzle warrant further investigation because it would solve some issues with reservoir design. Also, I selected robotic arms as the motion solution because they have the most versatility.

Concept 2: This design is close to what the previous concRIT team did. The rationale behind this concept is that a lot of the components are already purchased and in the cubicle, so we might as well experiment with them and see if they are optimal or if they can be improved upon.

Meghan's Concept Rationale: 

Concept 1: One method could be a design modeled after syringe. The syringe body would be reservoir. Once loaded a cap will be put on to lock in moisture. The cap will have the mixer attached. The motor will be turned on for the lid. This will begin mixing the material and put pressure on the top layer of the concrete. This will push the concrete through the system. Once some material has flowed the machine will be initiated by the team members and it will follow the path provided in the USB file. The machine will use motors and grooved tracks to move about the plane.

Concept 2: Students will use a template on a computer near the machine to create and upload the GCode. Concrete will be placed in a funneled reservoir. A Drill will be placed over the reservoir to mix the materials. Gravity will be used to push the material from the funnel into the extruder system. Students will check moisture levels. If the mixture is getting dry, students will spray water on top. The printing will start. The machine will slide on tracks to move about the plane.

Nicola's Concept Rationale:

Concept 1: Utilizing a auger system to extrude the concrete would allow for the concrete to be mixed within the extruder.  Having the concrete mixed in the extruder removes the worry of wet concrete setting in the reservoir or delivery system limiting the clean up.  A dosing roller pump would allow a controlled amount of dry concrete mixture to be moved into the extruder with very tight controls well as water ensuring the mixture is always at the right hydration.  Motion of the extruder being controlled by threaded rods allows for the extruder motion to be very precise. WIFI uploading to the printer can aid in the printers ease of use.

Concept 2: Utilizing a auger system to extrude the concrete would allow for a less liquid concrete mixture to be pushed through the extruder reducing curing time on the print bed.  Having the wet curing blanket gives a simple an din expensive solution to keeping the concrete from curing within the reservoir.  Utilizing gravity to deliver the concrete from the reservoir to the extruder can help to simplify  our design limiting the possible points of failure in the design.  Motion of the extruder being controlled by threaded rods allows for the extruder motion to be very precise. WIFI uploading to the printer can aid in the printers ease of use

Concept Selection

The team level concept selection as well as selection criterion can be found here. The selection criterion along with the rationales for each one are listed in the table below.

Design Concepts:

The team took the top concepts and using the selection criterion, ranked them via a Pugh Chart:

Systems Architecture

Manual System Architecture

 The manual architecture's key feature is that the concrete is mixed by the user and then poured into the reservoir. The concrete mix ratios are put into the mixing container and the user manually mixes through whatever preferred method. Once the concrete is thoroughly mixed it is placed into the reservoir where the reservoir keeps the concrete moving to prevent setting. The reason the user mixes the concrete then pours it in is because mixing concrete takes a lot more energy than keeping it moving to prevent setting. Some benefits of this architecture is that it is less complex to design and to repair if something goes wrong. Also, it is cheaper to build, which could be a consideration moving forward once the bill of materials is compiled.

Automatic System Architecture

The automatic system architecture has separate reservoirs for the water and powder mix, which are released/deposited into the mixing chamber where the mixing motors take over and mix the concrete. The concrete mix is then transported to the auger. An obvious benefit to this architecture is that the user has much less work to do. However, the trade-off is that the system is now more complex and if something where to go wrong, it would be more expensive and difficult to fix.

Sub-functions Systems Architecture

Sub-functions can be found here. 

Design Review

The next phase is the Preliminary Detailed Design phase and ideally, the design concept will be cemented and a bill of materials will be compiled. The two potential design concepts that we can pursue need to be prototyped and tested for feasibility. Simulations also need to be done to determine and finalize some items on the bill of materials, such as motors. Test plans will also be developed in regards to concrete testing in the Soils and Materials Lab, complying with safety protocols and COVID protocols. Our individual 3 week plans have progressed significantly and once it comes time to design test plans and put pieces together, they will definitely be helpful. Immediate next steps are to submit peer evaluations and to design CAD models, schematics, and flowcharts of the system.