Problem Statement
This section willfocus on the design and construction of the manipulator, which should lower, open, and grab an object, then rotate and place the object on a drop-off surface 90 degrees relative to the pick-up surface. Ideally, the end effector should be perfectly synchronized with the rotating linkage system, opening as the linkage system expands and closing as the linkage system contracts. For reference purposes, a diagram of the linkage system, end effector system, and its various components are provided below.
Linkage System First Iteration End Effector Second Iteration End Effector Concept
Red- lower scissor lift links Orange- end effector links Dark blue- end effector links
Blue- upper scissor lift links Tan - T slot Green- L bracket
Pink- input link Red- lower scissor lift links Light pink- secondary links
Green- path slot Dark purple- manipulator path slot Dark purple- input link
Critical points (1, 2) are numbered in orange Light purple- input bracket
Ideal Profiles
An ideal mechanism path would achieve perfect linear motion of the output point as the linkage system reaches 90 degrees and 0 degrees relative to the ground, allowing for the isolation of the grabber mechanism movement relative to the rotational component of the overall system. This ideal linkage system input path is demonstrated in the curved slot and full linkage system below.
The force profile/mechanical advantage of the end effector should ideally peak at the maximum close position to maintain adequate contact with the object being picked up. The plot below demonstrates a possible ideal plot of mechanical advantage, with a peak mechanical advantage at small linear displacements (indicating a closed configuration for iteration one). For future iterations, a better alternative would be to design a system that achieves a mechanical advantage that approaches infinity as the linear displacement decreases.
Mobility Analysis
Positonal Analysis
We chose to focus on the kinematic/position analysis for the overall linkage system because its motion determines the opening/closing/position of the end effector and the rotation/displacement of the package volume.
Through prototyping, it was found that the ideal motion path was not possible using a sharp-cornered curved slot. Thus, kinematic analysis was performed on a similar system using a constant radius slotted input link to simulate the effect of the linear component of the ideal path. The position analysis and generated positional graphs of the output point below are obtained through MotionGen.
Position Analysis of Output Point
Associated Displacement, Velocity, and Acceleration Graphs
The results of the kinematic analysis demonstrate that using a constant radius input link without a linear component to the path results in poor synchronization between the end effector and the rotating linkage system. It can be easily seen from the animation that the relative distance between the critical points changes throughout the entire rotation path, indicating that the end effector will open and close while the linkage system is not in its optimal 90 degree and 0 degree position (pick up and drop off position). Moving forward, we would like to explore the effects of a multi-radius slot path that is both manufacturable and isolates change in distance between critical points to optimal points in the rotation.
Mechanical Advantage Analysis
The analysis below will focus on the end effector. We chose to focus on the mechanical advantage of the end effector because the main goal of the end effector is to maintain adequate package contact through force applied from the end effector links.
First Iteration Animation Second Iteration Animation
First Iteration Mechanical Advantage Second Iteration Mechanical Advantage
From the graphs above, it can be seen that the second iteration has a slightly more favorable mechanical advantage trend than the first iteration does. With the first iteration, the mechanical advantage peaks when the mechanism opens and drops when the mechanism closes. This is validated by the fact that the mechanism moves quickly when approaching the vertical portion of the curved slot as the vertical input force aligns with the direction of motion. The second iteration continues to have the same issue, where mechanical advantage peaks at an open configuration. It's worth noting that the reason for iteration was purely as a proof of concept for a redesign due to manufacturing concerns with slots overconstraining the system and providing excess friction.
For future iterations, the movement of the joints constraining end effector link motion needs to be inverted, initially moving with a vertical downward portion of the arc and ending with the horizontal portion of the arc for opening and vice versa for closing. To further increase the mechanical advantage, we would like to pursue lever stacking, in which multiple levers are coupled together to vastly increase the force output. As the second iteration proved, slots overconstrain the design of our system, which means that our project will likely not include slotted pathways in the final iteration.
Physical Prototype Design Process
Workflow:
- Identify constraints
- Construct ideal input pathways
- Establish general trends (kinematic, force)
- Design prototype using general trends
- Construct prototype
- Conduct in-depth analysis for areas of interest
- Iterate on prototype design using analysis
Timeline moving forward:
Week of 11/10-11/13: Design iteration, final design changes, final analyses conducted
Week of 11/13-11/17: Begin physical iteration of prototype
Week of 11/20-11/24: Finalize iterations of the prototype, begin constructing the final product
Week of 11/27-11/29: Final product construction complete
11/29: Demo Day
Physical Prototype of First Iteration End Effector
Physical Prototype of Second Iteration End Effector
Prototyping Reflection
Bill of Materials: