System Level Design

Team Vision for System-Level Design Phase

Team plan for system-level design phase:

• A list of all functions and sub-functions completed, a solid understanding of current solutions, a concept that exceeds current solutions, a flowchart of the system. 
• Well written documentation, up-to-date Gantt chart and risk management.

Team accomplishments for system-level design phase:

• A list of all functions and sub-functions
• A concept that exceeds current solutions
• A flowchart of the system
• Well written documentation
• Updated risk management
• Created simple prototypes of various sub-functions

Functional Decomposition

The overall goal and function of our project is to create art for the students. With this main function in mind a functional decomposition was done to determine what sub-functions need to be completed in order to achieve our ultimate goal. As we move down the functional decomposition we answer the question of, how? Answering this question allows us to determine sub-functions for all the functions and gives a better understanding of what all of our subsystems must do. When moving up the decomposition, we answer the question, why? This is a check to make sure that each sub-function serves a purpose in completing the function above it. With these functions we can get a better idea of what systems we need to design, and develop.

Benchmarking

Benchmarking of the entire system was carried out to determine the currently available technology that could be used to partially or fully solve the problems presented by the client. Various elements of the solutions discovered were compared with each other to determine preferability of one solution against the other and these solutions were then compared to the team solution to ensure that the team solution was better suited to address the client requirements than any other available solutions.

Benchmarking of entire system:

The team solution was determined by comparing a variety of individual components used to carry out specific functions, and these components were benchmarked to determine the viability of each component in order to produce a generally efficient, overall system. Several factors were discussed and considered when choosing the ideal components for the system, such as cost, availability, complexity for the team, complexity for the user, etc. The chosen components best satisfied the given factors.

Benchmarking of individual components:

Feasibility: Prototyping, Analysis, Simulation

Feasibility Questions

How much power we will need to supply?

Need to further design the electrical systems to determine exact applications. The device will run off the power from the school, not a battery. The benchmarked microcontroller take voltages in the range of 5-12V.

How much space will it take up and how heavy will it be?

The device needs to fit on the large desk (36" x 23") and on the teacher's cart (36" x 24"). The device will need to accommodate 14" x 20" paper.

What ranges of art utensil will it support?

• Pencil

• Large marker

• Small marker

• Colored pencil

• Crayon

• Bingo dotter/stamp

• Maybe paint

• Maybe scrape paint

What motors and servos will be used?

Need to further design the systems and source components before we can answer this question. The belts will most likely be driven by motors and a servo with an arm to move the utensil up and down.

Best way to gather user student input?

Both light push buttons and joysticks will be able to be used with the device. The user inputs will be separate from the device to allow them to be place within reach of the student or attached to a wheelchair. The buttons and joystick will be rearrangeable to allow for optimal placement for each student. 

Paper Securing prototypes

Two methods of securing a sheet of paper to the device were prototyped.

Both prototypes involved the use of a border similar to a clip board.

To test each prototype a pencil was used to make a mark on each corner of the paper. The prototypes were evaluated on how well they prevented the paper from moving

Prototype 1:

Paper was secured on the shorter sides of the paper. The paper moved slightly when marking the corners.

Prototype 2:

Paper was secured on the longer sides of the paper. The paper did not move when marking the corners.

Results:

Two long clip board style clips will be used on each long edge of the paper. One clip will be fixed to the device, the other clip will be movable to accommodate different paper sizes.

The clips will be 20 inches long to accommodate the largest paper size desired.

Belt Movement Prototype

To prototype the belt movement for the device, an image of a 3 belt system was found. This image was used to demonstrate the different components that will be needed to implement a belt system on our device. An example parts list was also created.

Gripper Prototype

The refined list of gripper options separated into two categories: powered and manual. Listed are a few available off the shelf options that would be easy to implement into the machine. The powered options would be driven by servos and the manual options by either spring or thumb screw.

Morphological Chart

The sub-functions determined by the functional decomposition are listed on the left most column and the solutions brainstormed for each sub-function are in the corresponding row. This morphological chart will be used to generate concepts by choosing one solution from each row to create many different combinations. The solutions are color coded based on their priority, green - high priority, yellow - medium priority, and red - low priority.

The live document can be found here.

Concept Development

Inputs

Tool Change

Concept Selection

Concept Generation

Concept 1

Concept 2

Concept 3

Concept 4

Concept 5

Concept 6

Concept 7

Concept 8

Concept 9

Concept 10

Concept 11

Concept 12

Concept 13

Concept 14

Concept 15

Concept Screening

The AxiDraw v3 was selected as the datum for the concept comparison. The AxiDraw v3 is an x-y plotter compatible with writing utensils such as pens and markers and draws based off a drawing sent from a graphics program. This product costs around $500 and works similar to a printer, where the drawing is not completed in real time. 

The selection criteria used to compare the concepts is the following

• Can be Completed in 2 Semesters - The project needs to be completed by the end of MSD II.
• Budget - The team has a limited budget of $1000 to build the device.
• Ease of Use for the Client - The device must be easy to use by students with varying abilities. 
• Safety - The device must be safe for everyone to use.
• Weight - The device should be portable and not very heavy, as it will be moved from classroom to classroom.
• Repairability - For a long lifetime, the device must be easily repaired by the client.
• See the Work Being Done - The students should be able to easily see the work being done. There shouldn't be many parts obstructing the view.
  
  

The live document can be found here .

Concept Improvement

The best parts of the above concepts were combined into a final improved concept.

Systems Architecture

The systems architecture provides an overview of the subsystems and how each subsystem connects to other subsystems.

• User Interface subsystem
  • Allows for student input as well as teacher/aide input
  • Teacher input is powered by the power supply
  • Both inputs are fed into the microcontroller
• Control subsystem
  • Accepts the input from the user interface subsystem
  • Accepts the input from the x and y encoders
  • Processes inputs into commands for the motor controller, Z servo and gripper servo
  • Powered by the power supply
• Motion subsystem
  • The powered mechanical components of the device
  • Uses the output of the control subsystem
  • Powered by the power supply
• Mechanical subsystem
  • The non-powered mechanical components of the device
  • Allows for proper functioning of the device
• Power subsystem
  • Regulates and distributes power to subsystems

Designs and Flowcharts

The high level flowchart shows how each system will interact with one another and the signals needed to communicate.

Red arrows represent external signals that will be outside the device.

Black arrows represent internal signals that will be contained within the device.

As the design of the device becomes more detailed the flowchart will be updated to reflect the more detailed design.

Risk Assessment

The risks associated with this project are examined in the table below. This details what the risk is, what effects it could have and how to minimize each risk. The likelihood of the problem happening and how severe the issue would be are rated on a 1, 3, 9 scale and the risk and severity values were multiplied together to get the importance of each risk. The risks all fall into one of three categories, technical, safety, or resource.

Design Review Materials

System Level Design Review

Plans for next phase

Team Plan

• Preliminary bill of materials
• Prototypes of paper securing system, gripper and belt system
• Test plans written
• Subsystem drawings
• Subsystem flowcharts
• Well written documentation, up-to-date Gantt chart and risk management.

Individual Plans

• Andrew Pasek
  
• Josh Kolosick
• Allison Morgan
• John Owens
• Dylan Lebedin