The 2D Polar Printer
Objective:
We were to design, build, program, and document a radial-arm plotter. The plotter had to move a pen, cutter, or other useful implement in a plane parallel to a work surface using one rotational axis of motion and one linear axis of motion. There needed to be another “half axis” of motion which engaged and disengaged the implement. Our device had to be able to accept a specification from a file on a PC and produce a drawing or part based on the data in the file.
Our Mechanical Design:
The design we came up with consisted of a rotating arm that could linearly actuate a pen on a solenoid. One motor would rotate the arm, and the other would actuate the pen across a whiteboard. We decided to use a belt and lazy-susan bearing to rotate the arm and a lead screw to actuate the pen.
Our final design was created in Solidworks to make any measurements for hole placements as well as hardware decisions easier once manufacturing began. Solidworks would also easily allow us to use files for the laser cutter (a primary tool that we used to cut down on the time required for hardware construction). The first design that was created in Solidworks can be seen in one of the figures above. Once the assembly model had been finalized, we worked to create individual part files that could be used on the laser cutter. All parts that needed to be laser cut were done using ¼ inch plywood. Plywood was chosen over acrylic or other materials mainly because plywood is less expensive; However, plywood still offered the stiffness properties and manufacturability that would be needed for our final design to be functional.
The Electrical Design:
The only electrical component of the design that needed to be accounted for was the operation of the solenoid. In order to make this happen, a basic MOSFET was used as a switch component. The circuit diagram in the figures above was built on a breadboard and placed out of the way of the rotary axis motor. When the circuit was first built, the resistance of the grounded resistor was too large and did not allow for the solenoid to discharge its current fast enough to be useful. The resistance was chosen after trial and error to give us the best results. The purpose of the diode was to allow the current to dissipate through this wire and prevent the self generated back-emf from damaging the MOSFET or the microcontroller after the microcontroller pins turns off the solenoid.
The Programming:
We were required to program our microcontroller using python. For the design of the program we created a task diagram as well as finite state machines for each task. Listed above is the schematic of our program through the task and state diagrams.
Conclusion:
Overall, our project was able to successfully take an HPGL file of a drawing, parse it and draw a picture that resembled the HPGL file. The contraption operated safely and reliably at the time of presentation. We also succeeded to spend less than $25 per person on the project. The project also served as a very valuable learning experience that taught both of us how to better design products that require the integration of software with electrical and mechanical systems.
If time permitted it, our project could be improved by spending more time on programming the path management of the drawing. Our plotter took at least a couple of minutes to parse the HPGL file and then do all the kinematic analysis to create points that the plotter could draw on a whiteboard.
This is the project that made me love robotics. The satisfaction when all is said and done and you see the robot execute your design/program is unmatched. When our robot started to draw its first scribbles I was so proud. Designing/programming robots is what I want to do.
We were to design, build, program, and document a radial-arm plotter. The plotter had to move a pen, cutter, or other useful implement in a plane parallel to a work surface using one rotational axis of motion and one linear axis of motion. There needed to be another “half axis” of motion which engaged and disengaged the implement. Our device had to be able to accept a specification from a file on a PC and produce a drawing or part based on the data in the file.
Our Mechanical Design:
The design we came up with consisted of a rotating arm that could linearly actuate a pen on a solenoid. One motor would rotate the arm, and the other would actuate the pen across a whiteboard. We decided to use a belt and lazy-susan bearing to rotate the arm and a lead screw to actuate the pen.
Our final design was created in Solidworks to make any measurements for hole placements as well as hardware decisions easier once manufacturing began. Solidworks would also easily allow us to use files for the laser cutter (a primary tool that we used to cut down on the time required for hardware construction). The first design that was created in Solidworks can be seen in one of the figures above. Once the assembly model had been finalized, we worked to create individual part files that could be used on the laser cutter. All parts that needed to be laser cut were done using ¼ inch plywood. Plywood was chosen over acrylic or other materials mainly because plywood is less expensive; However, plywood still offered the stiffness properties and manufacturability that would be needed for our final design to be functional.
The Electrical Design:
The only electrical component of the design that needed to be accounted for was the operation of the solenoid. In order to make this happen, a basic MOSFET was used as a switch component. The circuit diagram in the figures above was built on a breadboard and placed out of the way of the rotary axis motor. When the circuit was first built, the resistance of the grounded resistor was too large and did not allow for the solenoid to discharge its current fast enough to be useful. The resistance was chosen after trial and error to give us the best results. The purpose of the diode was to allow the current to dissipate through this wire and prevent the self generated back-emf from damaging the MOSFET or the microcontroller after the microcontroller pins turns off the solenoid.
The Programming:
We were required to program our microcontroller using python. For the design of the program we created a task diagram as well as finite state machines for each task. Listed above is the schematic of our program through the task and state diagrams.
Conclusion:
Overall, our project was able to successfully take an HPGL file of a drawing, parse it and draw a picture that resembled the HPGL file. The contraption operated safely and reliably at the time of presentation. We also succeeded to spend less than $25 per person on the project. The project also served as a very valuable learning experience that taught both of us how to better design products that require the integration of software with electrical and mechanical systems.
If time permitted it, our project could be improved by spending more time on programming the path management of the drawing. Our plotter took at least a couple of minutes to parse the HPGL file and then do all the kinematic analysis to create points that the plotter could draw on a whiteboard.
This is the project that made me love robotics. The satisfaction when all is said and done and you see the robot execute your design/program is unmatched. When our robot started to draw its first scribbles I was so proud. Designing/programming robots is what I want to do.
1 Likers
