10. Mechanical design, machine design¶
Assignments in this week¶
Group Assignment:
- Design a machine that includes mechanism+actuation+automation+application
- Build the mechanical parts and operate it manually
- Actuate and automate your machine
- Document the group project and your individual contribution
Individual Assignment:
- Document individual contribution
Group Assignments¶
This is our team work. We have divided the work into various tasks. I am mainly responsible for the design, processing and production of circuit boards.
- Group Assignment on Machine Week
Brainstorming¶
Idea One：Food cutter¶
Idea Two：Wine Shaker¶
Idea Three：Dumplings Maker¶
At the very beginning, we had three ideas that we wanted to do. When we searched online based on the three ideas, we found that there were actually many finished products for sale. After constant discussions, we originally wanted to make a machine with Chinese characteristics - a dumpling machine. Then after confirming the idea, we will refine what work we need to do.
Problems that we need to solve¶
Step1: How to make a dumplings skin？¶
Because there are many kinds of dough-making machines on the market, the general mechanical principle is to press the dough of corresponding size into dough by extrusion, and then use some cutting dies to cut out the standard dumpling dough size and shape. The size and thickness of the dough are actually more important here.
Step2: How to mix the dumpling fillings？¶
Stirring dumpling fillings can be completed with a conventional rotary machine. The most basic requirement for this part is to rotate, stir and divide the same amount of dumpling fillings into the dumplings.
Step3: How to squeeze the dumpling fillings and make a dumpling？¶
There are usually many ways to make dumplings, and different dumplings can be made into many different shapes. The main thing here is to break down the action of pinching dumplings. The first step is to fill the dumpling dough with dumpling filling. In the second step, you need to find the creases for pinching the dumpling dough; in the third step, you need to adjust the appropriate strength to pinch the dumplings.
Step4: How to transfer and place the dumplings？¶
The last step requires a transport mechanism to transport and place the dumplings
When we find that there are so many steps that need to be broken down, we feel that there is not much time left for us.
Last Minute Decision¶
There are a total of 6 members in our team, and 3 of them do not live in the same city as us, so they can only choose to gather with us on weekends and weekends to complete the project. In addition, everyone usually has their own jobs, so the early team collaboration process was not smooth.
So when our mentor Salman finally came to China, he guided us to build a writing machine to complete teamwork more easily.
Principle of the Machine¶
The entire writing machine needs to move on a 2D plane. The X and Y axes are driven by stepper motors, which can accurately control its movement on the writing frame plane. At the same time, there should be a servo to control the up and down movement of the pen barrel.
The most important part of the project was to design a mechanical structure that could move freely in the x and y directions. However, none of the team members had any mechanical design experience. Instead, we searched online and found several options. One of the most popular structures is one that uses the x-axis and y-axis as the main axes. In other words, the system has two stepper motors, each controlling one axis.
When the x-axis motor is started, it will move along its rotation line, and the entire platform only moves on the x-axis. One of the advantages of this design is that the mathematics of motion are very simple and easy to calculate. For example, if we want to move from point (0,0) to point (10, 20) in centimeters, we only need to move one motor 10 cm at the same time and the other motor 20 cm at the same time. Another advantage is that the structure is very easy to design. It looks like the xy plotter in Figure 2. The disadvantage of this design is that since the two motors are located on different axes, one motor will be fixed and the other motor must move with the bracket that holds the pen, creating more vibration and requiring more space to increase stability.
What should to make this machine？¶
Although this is an open source project, we still need to do it ourselves from materials to processing. In order to complete this assignment faster, we disassembled the task of implementing this machine.
Mechanical design and production
In this part, we need to select appropriate aluminum profiles, find all the parts that realize mechanical movement, and assemble them according to the corresponding dimensions. The final effect we achieved is that two motors can control two slide rails to move on the X and Y axes respectively.
Electronic design and production
In this part we need to redesign and make the circuit board, record the complete design process from schematic design to PCB design, then process and make the PCB circuit board, and debug each functional module of the circuit board.
Software design and debug
This part is mainly about program design and debugging. In order to realize the entire mechanical movement, we selected the corresponding XIAO main control board and stepper motor drive module, programmed and debugged.
System integration & debugging
This step is the most important, which is the overall assembly and debugging. Because mechanical movement requires some limit settings, this can only be completed during the debugging process.
Video & Poster Promotion
The next step is to create presentation materials for our team’s assignment. Poster+Video
Team work assignment arrangement¶
Crail - Mechanical design and production
Matthew
Jiawei
Chenxin
Dion
Individual Assignment¶
In my individual assignment, I need to design and make the circuit part of the entire system.
Component Selection¶
Because this project is originally a popular open source project, there are many reference circuit diagram designs on the Internet. Based on the relevant reference circuits, we will also make our circuit diagram.
In this circuit diagram, I modified two parts.
1. One is that I changed the main controller inside from Raspberry Pi Pico to Seeed Studio XIAO RP2040.
2. The other is that I added a power conversion chip model NCP1117. Through this power conversion chip, a 12V power supply can be directly used to drive the entire main control board and circuit board.
To move the pen position in the x-y plane, we use two bipolar stepper motors. Each stepper motor consumes 12 V / 2 A.
I power the stepper motor through a 12V/2A DC power adapter, and at the same time output 5V power through the NCP1117 power conversion chip to supply power to the XIAO RP2040 main control board and 2 stepper motor drivers.
To control the stepper motors we used two A4988 stepper motor drivers. The motor driver requires 3-5 volts of power to operate.
I did not supply 5V voltage to the stepper motor driver separately, but used the same power conversion chip to supply power to the main control board and stepper motor at the same time. But before the test, I actually didn’t calculate whether this solution was feasible.
Each motor has four wires, forming two coils.
（The black and green wires make up one coil, and the red and blue wires make up the other coils. These four wires are connected to pins 1A, 1B (one coil) and 2A, 2B (one coil) in the motor driver. Each motor The drivers both take two inputs from the microcontroller: step size and direction. Whenever the step size pin changes from 0 to 1, the motor will move one step. When the direction pin receives a 1, the motor moves counterclockwise. When the direction pin receives 0, the motor moves clockwise. We also use an SG90 servo motor to control the lifting and lowering of the pen holder. The servo motor is controlled by the PWM signal sent by the microcontroller.）
Schematic Design¶
In the schematic design part, I still used the module design.
1. First define the relevant connection signal pin marks of the main control module.
2. To design the power conversion module part, refer to the reference design diagram of the power conversion chip. I must give the pins two polarity capacitors. Since there are no 10uf capacitors in my laboratory, I use 100uf capacitors in the actual circuit. This will also make my circuit more stable.
3. The last step is the circuit design of the two stepper motor drive modules. I also referred to the reference design diagram of the stepper motor drive. In order to ensure that the stepper motor drive is not burned out, I also added a capacitor to the power supply end of the motor. , thereby achieving the function of protecting the circuit.
PCB Design¶
The PCB design part is a test of design ability, because it must not only ensure complete functionality, but also ensure aesthetics. In this process, a lot of time was actually spent on arranging and laying out the components.
I made the power supply part and signal line part thicker to facilitate subsequent processing, but the pads were still too small, making subsequent processing more difficult.
Milling the PCB¶
- Export the manufacturing project file with Gber format in KiCad.
- Import the project file to generate a PNG image via Gbertopng site.
- Then import the PNG images to the Mos website to generate NC files. This process is the same as making circuit boards in the previous lessons.
- Load the generated NC manufacturing file into the software in the CNC cutting machine to start cutting.
- Due to a problem with the drilling bit in our laboratory, it was difficult to complete the drilling project when we cut the circuit board. This caused difficulties for me in subsequent soldering.
- The finished PCB board is shown below. The effect is quite satisfactory.
Soldering & Testing Circuit Board¶
- First prepare the required electronic components and the prepared circuit board. Because the drilling process is not very smooth, I cannot use a carving knife to enlarge the hole in the power supply welding part, otherwise there is no way to weld.
- The board after welding is as follows. I can only lightly fix the welded pins on the board. There is no way to drill through the holes. This will also give the stepper motor driver module, which generates serious heat, enough space for heat dissipation.
- After the welding is completed, I first measure it with a multimeter. Make sure that there is no short circuit in the circuit, and also make sure that the various signal lines of the circuit are connected according to the parts I want.
- When everything is measured, power on and measure. The board can work normally and the program can be successfully downloaded through the Arduino IED.
