Proposal (07)

 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.

Current robots with brachiating capabilities, however, are difficult to control due to their dynamic behavior, very slow moving across the ceiling, and built with a lot of motors. These drawbacks severely handicap brachiating robots from becoming commercially viable options for industrial applications.

Through this project, we aim to overcome the disadvantages mentioned in the current brachiating robot. Our goal is to introduce a 1 DOF swinging arm mechanism that follows a set motion profile to reduce control complexity and use significantly fewer motors. By doing so, we expect the price of the robot to decrease and the speed of traversing to increase.

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.

Future work that is beyond the scope of this project includes adding adjustable linkages for different bar spacing, modifying the robot to move both forwards and backward across the bars, and adding a system that moves the robot sideways along the bars.

The most important preliminary analysis will be the position and velocity analyses of the arm linkages. The design of the linkage will be determined through a combination of analytical and experimental methods. Existing walker mechanisms will be analyzed to evaluate their feasibility for this project. From there, variations on the mechanisms will be tested to find the configuration that best meets the design requirements. This analysis will be performed primarily through simulation tools such as MotionGen.

Structural analysis will also be necessary for the final design. The maximum loads on each component will be determined and geometries will be chosen to ensure the mechanism can successfully operate under these loads. The design will be tested using finite element analysis, such as through SolidWorks.

The most exciting part of this project is the opportunity to emulate a complex robotic mechanism using simple linkages and a single motor. This design is a perfect opportunity to demonstrate the advantages of linkage design over traditional robotics.

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.