User:Alexander L. McQuiggan/sandbox
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Undulatory Locomotion
Undulatory locomotion is a type of movement that can be described as alternating wavelength which propel an objects body in a given direction. A unique characteristic of the wave motion is that it is sinusoidal, or has equidistant positive and negative magnitudes throughout the length of a period. This allows for nice, even strokes that appear harmonious in nature when observed. Consider a sine graph, for example, the line moves evenly up and down from period to period without any disruption to an infinite length. With that in mind, think of the motion utilized by a snake, or that of the fins of a cuttlefish; the same pattern is followed, a constant wave both up and down, or side to side, that is even throughout a period of observation. Another exceptional aspect of undulatory motion is that it provides a means for balance and directional compensation as well as allowing for both frontward and backward movement [1]. Take for example a cuttlefish, the animal utilizes such motion to allow for fast lateral movement as well as forward and reverse directional movement. Also, it grants the species the unique ability to hover in any given location.
Existence in Nature
Undulatory locomotion proves most effective as a means of propulsion, and therefore it is not unexpected that it occurs most commonly in organisms which exist in aquatic environments. The wave oscillations push the water which allow for an exceptionally useful means of transportation. Undulatory locomotion, as it exists in underwater existing organisms equipped with fins, is broken into three different forms; rajiform, amiiform, and gymnotiform types [2].
Rajiform
The rajiform type is fin propulsion that is generated by passing vertical undulations along pectoral fins. This form is the type of motion that is seen in stingrays, mantas, cuttlefish, as well as in the fins of squid [2].
Amiiform
Amiiform locomotion is achieved through the use of a dorsal fin which stretches the length of most of, if not the entire body, of the fish. This fin is what propels the fish through the water while maintaining a straight body [2]. Essentially, the only aspect of the fish that is active in the motion is the dorsal fin.
Gymnotiform
The gymnotiform type of propulsion which employs the undulation of a fin located along the under-belly of the fish [2]. This fin acts in the same way as the dorsal fin in amiiform locomotion with the same result.
A forth form exists in animals that use the motion in a full body application, for example eels or snakes. Such organisms employ a full body wave oscillation from front to back which causes them to move in a motion that is commonly described as slithering [3].
Though the motions differ in appearance, some more than others, the motion is conceptually the same as it employs the same characteristics.
Robotic Application
Studies in the field of Biomimetics of undulatory locomotion as it exists in nature have led to the creation of robotic mechanisms which replicate the motion. Such robots intend to mimic the organisms and perform just as said organisms would when set in similar conditions. Therefore the robots have multiple nodes upon the axis of motion [3],[4]. Meaning, if the robot were to have a fin which employs undulatory locomotion, that fin would need to be broken up into numerous sub-sections in order to work effectively. At each of these points, the motor would be required to move the focal point of the fin in both a positive and negative direction on a timed interval. The most important feature of the fin relies on the fact that these movements correspond flawlessly with one another. Making sure that each node relays in perfect sync with every other node upon the same fin axis. This is an imperative attribute because if just one of the motors is off by any margin, the motion is compromised and the robot would not maintain an even pattern of locomotion [2].
A robot with multiple fins, replicating the body of an organism like a cuttlefish or ray, would require separate motors per each fin [2],[4]. This attribute is essential in order to properly portray such movement. If the fins were on the same motor, it would not permit the fins to move independently from one another [2],[4]. Thereby, not allowing the robot to be capable of lateral movement, the ability to balance and retain equilibrium, or the ability of rapid course correction [2],[3],[4]. All of which are unique characteristics of squid, cuttlefish, and rays.
[1] A. Willy, and K. H. Low, “Biomimetic Motion Planning of an Undulating Robotic Fish Fin.”Journal of Vibration and Control 16 May 2006: 12-1337. SAGE. Web. 1 Feb. 2011.
[2] Low, K. H, “Modelling and Parametric Study of Modular Undulating Fin Rays for Fish Robots.” Mechanism and Machine Theory March 2009: 44-3. Special Issue on Bio Inspired Mechanism Engineering. Web. 4 Feb. 2011.
[3] Hasanzadeh, S, and A. Akbarzadeh Tootoonchi, “Ground Adaptive and Optimized Locomotion of Snake Robot Moving with a Novel Gait.” Auton Robot 2010: 457-470. Springer Science+Business Media. Web. 4 Feb. 2011.
[4] M. Sfakiotakis, D. Lane, and J. Bruce C. Davies, “Review of Fish Swimming Modes for Aquatic Locomotion.” IEEE Journal of Oceanic Engineering APR. 1999: 24-2. IEEE. Web. 1 Feb. 2011.