The information in this section will build upon the information presented in the previous Kinematic Analysis and Prototyping section. The goal of the mechanism remains the same, though the analysis and ideal profile of the mechanism have changed as a result of reducing scope. Because the two iterations -this prototype and the one displayed in the previous section- were so different, a second page has been created to further describe the development behind the iteration that became the final prototype.
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The above model is an approximation without the presence of the slot that caused binding, simulating a close to realistic manufacturable model. The first iteration's motion profile was extremely curvilinear, with almost no linear or close to linear portion to allow the linearly actuated end effector to close before the entire system started rotating. This, along with many other factors, made the first iteration completely unrealistic for the final model. In comparison, the second and final iteration's motion profile achieves very close to linear if not linear portions at the ends of its travel, allowing for isolation of the end effector motion. The redesigned linkage system also eliminates the need for slots and the potential for binding of the system due to sharp corners and friction as the entire system is driven by rotary revolute joints.
Another useful quirk of the final redesigned mechanism is the tuneable displacements for the pick up and drop off phases. This is done by adjusting the length of the coupling link in the final four bar mechanism driving the rotation of the system. It can be seen from the positional analysis of the second iteration that the displacement for the pick up phase is larger than the drop off phase- this is done on purpose to demonstrate that the mechanism allows for partial actuation of the end effector. This becomes useful in situations where the end effector must constrain its fully open position, for example, in tight drop off or pickup zones where packages are placed closely together.
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The toothed part of the rack drives the actuation of the end effector as the pinion gear is allowed to rotate when meshed with the rack. This is the actuation phase, where any movement of the linkage system will result in actuation of the end effector. This is planned to be coupled to the linear portion of the linkage system pathway, allowing for isolation of end effector motion. The untoothed part of the rack then converts the rotational motion of the pinin gear to a linear motion as the teeth slide along the smooth rack. This is the dwell phase, where any movement of the linkage system will not result in actuation of the end effector. This is ideally coupled to the rotational quarter circle motion of the linkage system motion profile, where constant contact on the package must be maintained and consequently when the end effector must maintain its position. This end effector will be pinned to the output joint and slotted to the middle joint, taking advantage of the colinear movement as a linear input.
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