by Yun-Han Lin
Preface
When it comes to durability testing, most people think of the equipment IKEA uses on the furniture. IKEA uses linear actuators to squeeze and push the piece of furniture back and forth or up and down. This feature is what we need for our tester where a wooden block can be placed to move back and forth on sandpaper.
Structure / Design
1. Four-bar linkage: With a four-bar linkage as the foundation, three of them serve as revolute joints, while the *prismatic joint falls upon the place the sandpaper comes into contact with the wooded block. The whole design features a simple movable closed-chain linkage.
*A prismatic joint provides single-axis sliding and prevents the parts from rotating.
2. We used a 9V gear motor at about 90rpm. The lower the output speed, the greater torque it creates. Although there were other motors with greater torque, we just used this one as it worked fine in one of our previous projects.
3. As it was only a single-use tester, we decided to use only the simplest design and materials. There were a lot of spare wood pieces from deserted furniture, so we could use as much as we wanted.
Production Process
It took about 6 to 8 hours to complete the tester. The main obstacle was the strong friction created from the contact between the sandpaper and the wooden block, which was why there needs to be high torque. Although we used a D-shaped rotating shaft (as shown in the picture), the 3D-printed linkage arms would come loose or deform when the torque is high. It was not until we tried with the third version model that all the parts stayed intact.
- Nuts and screws are used at revolute joints, and nylon nuts are recommended so that the arms do not loosen due to frequent rotation.
- The 3D-printed parts were thickened and the motor shaft was fixed with 2 3mm screws to make sure the parts would not loosen during rotation.
- The tester should be set to only anticlockwise rotation so that the wooden block does not take too much force from up-down motion.
Conclusion
As a simple tester, the end product turned out quite well, yet there was still room for improvement:
1. The motor torque was not high enough to handle the weight of heavier blocks that resemble a real-life situation.
2. To simplify the design of the prismatic joint, we minimized the spaces where the parts could move left or right during rotation, but not so much the spaces for shaking in the up and down movement. Although the linkage arm had perfect contact with the sandpaper when it leaned forward, it often went loose when going backward, which reduced the testing efficiency.
3. We spent only 10 minutes testing each type of sandpaper. Should it take longer, there needs to be a way to remove the sawdust; otherwise, a large amount of sawdust could largely decrease the testing efficiency as well.
If you are interested in the test result and the comparison of sandpaper we sorted out, subscribe to our Youtube channel, and the video will be released soon, while there are also articles on these topics you can refer to on the vMaker website~
