Doctoral Degrees (Mechanical and Mechatronic Engineering)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/780

Browse

Browsing Doctoral Degrees (Mechanical and Mechatronic Engineering) by Subject "Actuators -- Design"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Generative design procedure for embedding complex behaviour in pneumatic soft robots
    (Stellenbosch : Stellenbosch University, 2020-03) Ellis, David Rostin; Venter, Martin P.; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Soft pneumatic actuators form part of the growing field of soft robots being used in areas not suited to conventional hard-linked robots. Applications include low-cost automation, wearable technology, and the handling of easily damaged produce/goods. Typically these actuators are manufactured as cast silicone bodies and are powered by compressed air. This research set out to develop methods whereby these actuators can be designed to best represent a desired behaviour and behavioural responses not previously possible. A bimodal actuator was developed where the bending direction can be altered by changes to the internal pressure. This allows non-trivial behaviour whilst using a single pressure source. A layer of a specially developed bilinear material facilitates this response. This bilinear material utilises a strain limiter crimped to an initial condition. As the paper layer decrimps, the response becomes stiffer and approximates that of the reinforcing paper layer. This change in stiffness allows for the preferential bending direction of the actuator to change. An additional stream of research focused on a modular actuator construction made up of smaller articulating units in series. These units are constructed to have a preferential bending direction. By changing the orientation of each unit, a different deformed actuator shape can be made. A design tool was developed where a genetic algorithm was coupled with a nonlinear finite element solver. This design tool optimises the design using the genetic information available in the initial population over multiple generations and presents a candidate that best resembles a desired profile specified as the objective function. A 2D reduced-order model was developed that reduces the time for each function evaluation from ≈ 20 min for a 3D numerical analysis, to ≈ 45 s. The design tool was tasked to solve design targets ranging from sin and cos functions of various amplitudes to final actuator tip positions. In each case, the inflated actuator resembled the desired profile. Five of these designs were manufactured using an aluminium mould with ±0.02 mm tolerances. The inflated actuators were 3D scanned and qualitatively compared to their numerical counterparts. The overall deformation shape of the physical models closely resembled that of the numerical models.