Autonomous Robots with Four Bar Lifting Mechanism
Summary
In this project, I worked with a team of four to design, manufacture, assemble, and program two robots capable of lifting aluminum plates off of rooves and placing them on a staging platform. I used SOLIDWORKS to design four-bar mechanisms capable of moving a gripper to three desired positions. I manufactured all the components of the robots using 3D printing and laser cutting.
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Skills Learned/Used
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SOLIDWORKS CAD
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Stress Analysis
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PTC Mathcad
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Laser Cutting
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3D Printing
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Step 1: Linkage Synthesis
The first step was to perform a linkage synthesis to determine the lengths and positions of the rocker and crank links so that they would move the gripper, the connector link, to the appropriate positions.
Step 3: Modeling the Robot
Next, I modeled the entire robot based on what we learned from the previous steps. This assembly video shows how one of our robots was put together.
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Force and velocity analysis was also done on all parts of the mechanism to ensure structural integrity.
Step 5: Assembly
Having manufactured all the parts, my teammates and I assembled our robots. The image to the right shows one of our partially assembled robots.
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Step 6: Programming
Having built the robots, it was time to program them to autonomously accomplish the task. The team utilized ultrasonic sensors, reflectance sensors, and potentiometers to do this. After much trial and error, our robots could accomplish the task aptly, as demonstrated by one of our robots in the video..
The programming stage of our project took much effort, as a large portion of time was set aside to fine-tune the various sensors and debug code.
The Challenge
As part of the RBE 2001 class I took during the first term of my sophomore year, a team of three others and I were tasked with building two robots that could autonomously pick up and place metal "solar panels" from roofs of two different angles as well as a staging platform.
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As my skills were suited to mechanical design, I was largely responsible for designing the four bar linkage mechanism and the gear train that operated it. I also manufactured the needed parts.
Step 2: Motion Study
To determine the torque required to operate this four bar mechanism and lift the aluminum plate, I used SOLIDWORKS motion analysis to determine the maximum torque needed. This torque was then used to calculate the required gear ratio. Due to packaging reasons, we used a 3-stage transmission for our first robot and a 2-stage transmission for our second robot.
Step 4: Manufacturing
After finalizing the design in SOLIDWORKS, I began 3D printing and laser cutting the major components. The gripper, L-brackets, and motor and sensor mounts were 3D printed, while the ground planes, rockers, and cranks were laser cut using acrylic. The images to the left show one of our grippers, operated by a screw, gripping onto a plate.
Post Assembly
It took us around four weeks to design and assemble the first robot (left) since it was our first time going through the design of the robot. Learning from our mistakes, we designed and built the second robot (right) in under a week.
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One challenge we faced in the assembly process was the tolerances of the 3D-printed parts. As our design contained many holes that needed to be mated to each other, hole tolerances were important. We solved this by printing test parts so we can determine the suitable dimensions for holes.
The team demonstrated the robots capabilities to the professor of the course through a live demonstration and through a presentation. If you would like to learn aobut the development of our robots in more detail, please feel free to review our final presentation.