12.2 Project Prototype

Kinematic Analysis

The walking mechanism uses a series of interconnected linkages designed to transform rotary motion into a linear (up and down) motion for the IPad/laptop stand. The synchronized motion was driven by a single actuator.

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Figure 1: GIF of Motion

Linkage geometry and motion in Figure 1 were modeled in MATLAB in order to see the paths of motion and further prepare for variables such as step height and stride length. This design achieves linkage lengths of 125 mm, 125 mm, and 75 mm for the main connecting links with a flat base in an “L” shape that allows for obstacle clearance and a more stable structure.

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Figure 2: Position Analysis

After completing a position analysis in Figure 2, the relationship between the crank angle and the connecting rod angle as well as the final position can be visualized. From the first graph, it can be seen that as the input angle (theta 2) increases, the output angle decreases smoothly which accommodates for the crank’s rotation. The middle plot represents the vertical displacement of the slider which rises to a maximum height of 5 inches as the input angle is increased to 90 degrees. The bottom plot is essentially expressing the same as plot 2 but with regards to theta 3, therefore having an opposite effect which is an inverse relationship.

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Figure 3: Velocity Analysis

The velocity of the input angle versus the output point C oscillates around 0 since it stops momentarily to change directions for the system as seen in the first graph of Figure 3. There is a different pattern for point B because as the crank spins, the linear velocity for B rotates as motion is transferred. Finally, for point A it indicates that as the linkage extends, the output motion slows.

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Figure 4: Acceleration Analysis

Figure 4 shows acceleration for the system with regards to link B and point B. There are 2 sign changes for the first plot with peaks corresponding to when the crank is near horizontal positions. For the bottom plots, the high angular acceleration in one link compensates for the low linear motion in another which is consistent for a symmetric up and down motion.

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Figure 5: Mechanical Advantage Plots

Physical Prototype

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Figure 6: Top View of Prototype

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Figure 7: Side View of Prototype

The physical prototype was constructed utilizing wood that was leftover from previous projects. These pieces were laser cut and grooves were indented into the places where the links would slide against the “L” shaped base to allow for smooth, controlled motion. An acrylic rod was used to attach the platform, made of cardboard for this case, to the link system with enough length at the ends to act as a handle for demonstration. Each of these features were attached using a combination of tape, bearings, and screws.   

While not representative of the platform that would hold the IPad for the final product, a piece of cardboard was used to simulate this aspect. It does not hold the same structural integrity, but acts as a placeholder in order to test the motion of the stand.

Iteration Documentation

The main challenge with the prototype was the rigidity and tilting mechanism of the laptop platform. At first, the sheer size of the prototype was rapidly growing - making different link lengths needed along with different versions of the L brackets (pictured in Figure 8). Next, the structural support of the platform posed problems because the acrylic shaft used to connect the two L brackets was not only not sturdy enough, but it also rotated. There were two different two-link ideas for a tilting mechanism, one in a triangle orientation and one in a crank orientation. The triangle orientation (pictured in Figure 9 and Figure 10) showed the most promise, but did not allow for a completely flat platform when the stand was at base position, was cumbersome in its size and location, would need to be on a separate motor, and required shafts for the sliding portion to attach to. For the crank orientation (pictured in Figure 11 and Figure 12), the link lengths were the main issue because even the slightest change in length would greatly impact the maximum height of the backside of the platform. Other issues included: the mechanism being vastly ugly, the weight of the crank affecting the tilt of the platform at base position, and its support for the laptop platform being in the horizontal center.

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Figure 8: Different Link Dimensions Used for Testing

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Figure 9: Triangle Mechanism at Base Position

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Figure 10: Triangle Orientation at Top Position

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Figure 11: Crank Orientation at Base Position

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Figure 12: Crank Orientation at Top Position

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Figure 13: Tilt Profiles

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Figure 14: Lift Profiles

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Figure 15: Mechanism Concept

The initial iterations for the design process of the prototype resulted in the structure that can be seen drawn in Figure 13, Figure 14, and Figure 15. However, after consulting our designs, it was found that there was not enough structural integrity in order to hold a physical IPad/laptop, which is the goal of our mechanism. The tilting mechanism itself would have too many weight considerations to be taken into account and therefore after much testing and simulations, it was found to not work. The slider crank aspect of the bottom portion shown in Figure 14 was kept for final prototyping.

Reflection

We encountered various issues throughout our design process and brainstorming for the prototype. The most apparent issue is how to attack the motorized tilting aspect of the stand while maintaining structural integrity. For this, a strong material would be needed that is sturdy enough to hold an IPad/Laptop while a user wants to put force downward.

Initially, we tried to design a slider mechanism that would go a level above our vertical linkage system. However, this did not work due to wait and structural issues. As well, we tried to research tilting mechanisms and how they function but none were able to function and keep a sturdy surface while moving. In the future, we hope to attack this issue and possibly consider raising/lowering the system from both sides of the platform, not just one.

Bill of Materials