This report is written for the thesis of my master Mechanical Engineering that was conducted at the department Precision and Microsystems Engineering of the Delft University of Technology. The goal of the project was to design a compliant hipback support of an exoskeleton while r
...
This report is written for the thesis of my master Mechanical Engineering that was conducted at the department Precision and Microsystems Engineering of the Delft University of Technology. The goal of the project was to design a compliant hipback support of an exoskeleton while researching how to achieve desired directional compliance on this application. This work starts with an introduction to exoskeletons and explaining their working principles. The problem is that the reduction of range of motion for wearing an exoskeleton reduces the adoption of exoskeletons in industry. The objective of this study was to solve this by creating a hipback support with compliant behaviour in torsion and lateral bending while remaining stiff in the supporting forward bending direction. For inspiration, the state of the art of current hipback supports and research projects was reviewed. Also, the characterization methods of compliant mechanisms were reviewed for inspiration, to come up with a suitable design method for developing a compliant structure for a hipback support. By tuning stiffness of the structure in distinct directions, a conventional synthesis method for compliant mechanisms could be applied, namely the Freedom and Constraint Topologies method. This was used to come up with a preliminary design. This design was extended to improve stiffness behaviour for coupled motions by researching how to change stiffness on demand. The only categories to change stiffness are shape, material, prestress and boundary condition. For each category, a promising highlevel design was worked out with improved stiffness behaviour for coupled motions. To generate an even more satisfying solution, optimization of the beam shape was applied to handle the defined rather complex kinetostatic task and to develop a lightweight structure. The objective function was to reach specified deflections where shaperelated parameters are optimized. These parameters were the spine shape of the beam, the crosssection and orientation of the crosssection. To generate a design, a selfdeveloped optimizer using beam modelling was extended and applied. The extensions were to optimize a doubleclamped beam that was loaded in the middle point and optimizing for angular deformations as a set objective function. This extended optimizer generated the final design which was a thin rectangularshaped beam with threedimensional curves. This design was not straightforward to fabricate into a prototype. Multiple manufacturing methods were evaluated and one final method was selected to fabricate a close approximation of the final design. This final manufacturing method was to produce the prototype by roll bending and manually applying a twist on a curved lasercut strip which was extracted from flattening of the spatial shape. This prototype was verified by simulations and experiments. Simulation tests were run on an original design of the back support and compared with the new optimized shape based on the requirements. The results, for similar loadings and material, are 27 times more lateral flexibility, 1.25 more torsional flexibility and a design that is four times lighter in comparison to the original design. The original relative stiffness of 1 to 1 for forward relative to lateral bending improved to 2 to 1. An important remark to note is that the beam model generated a thin section which was less suitable for 1D beam modelling of the implemented FEM. Creating an optimizer based on 2D shell modelling code might give more accurate results and can be considered for future work.