Background
Brachiation is a complex dynamic maneuver involving swinging and switching the swinging arms. This motion allows for an interesting method to traverse without floor space with a great deal of freedom. Compared to a commercially available OHT (Overhead Hoist Transport), which travels rapidly only where there are tracks, brachiation is superior in moving through unstructured environments freely without being bound to the tracks. Due to this property, robots with this kind of ability have potential applications in warehouse operations, search and rescue missions, and agriculture.
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https://arxiv.org/pdf/2305.08373.pdf
Design Complexity
To traverse equally spaced bars while suspended, the robot must latch onto the bars. Previous robots that traverse in this manner solve this problem using either individually actuated “claws” or precisely controlled 2-degree-of-freedom arms. Those approaches both require digital control of individual mechanisms. Alternatively, a linkage system that is capable of releasing, moving, and hooking onto the next bar eliminates the need for a digital control system.
The motion profile required to achieve the three-part action (release, move, hook) is quite complex. Simply moving a linkage from one bar to the next and back is simple enough with a 4-bar linkage. However, two problems arise. Firstly, the simple oscillatory motion of a 4-bar linkage does not provide a method for hooking and releasing a bar. Secondly, as the linkage moves from one bar to the next, it must remain below the horizontal plane occupied by the bars. Finally, the three end effectors must be roughly collinear during the brief moment when all three are in contact with the bars.
Proposed solution mechanism
The proposed design features a series of identical linkage mechanisms anchored to a central body containing the power supply, controller, and motor. These linkages would function as the robot’s “arms” and allow it to grasp the overhead bars. The arms would lie in two vertical planes, on the left and right sides of the body, with three on each side for a total of six. Having the arms in two planes ensures that the robot will not rotate about its forward and vertical axes, while having three arms per side ensures that there are always two points of contact per plane, preventing rotation about the horizontal axis. Each arm would be driven by the same central motor, positioned out of sync with each other to achieve a smooth walking motion.
Scope of work for final project
Our aim for this project is to design and construct a robot that can traverse a set of evenly-spaced overhead bars. The linkages will be designed around a specific distance between the bars. The robot will only be expected to move forward.
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The most challenging part will likely be the specifics of how the arms grip and release the overhead bars. Using a linkage for locomotion restricts our control over the angle of the end effector, which complicates the grasping process.
Preliminary design ideas
The above mechanism is a variation on a six-bar walker. The end effector would attach to the end of link 6. On the left side of the highlighted path, the arm approaches the bar from below and grabs onto it. It then moves in a straight line to the right while holding the bar, propelling the body to the left. At the rightmost end, it lifts up and releases the bar before circling back around to repeat the process.