Design and optimization of large stroke flexure mechanisms
Due to the COVID-19 crisis the PhD defence of Mark Naves will take place online (until further notice).
The PhD defence can be followed by a live stream.
Mark Naves is a PhD student in the research group Applied Mechanics (AM). His supervisor is prof.dr.ir. D.M. Brouwer from the Faculty of Engineering Technology (ET).
Flexure-based mechanisms are widely used in many small stroke precision applications because of the absence of play and friction, resulting in highly deterministic and predictable behavior. However, for large stroke applications, flexure-based mechanisms are often avoided due to the strong decrease in support stiffness and load-bearing capacity when subjected to large deflections. The performance of flexure-based mechanisms for large range of motion applications can be improved by using more complex geometries to maintain high support stiffness at larger deflections. However, due to the complex relation between the geometry of the flexures and the performance of the system, particularly in the presence of large deformations, designing a “good” flexure mechanism suited for large stroke applications is not trivial.
For this reason, a strategy for the optimization of large stroke flexure-based mechanisms is presented in this thesis. This strategy takes advantage of a Nelder-Mead based shape optimization algorithm combined with design principles for flexure-based systems in order to synthesize new design topologies for flexure-based equivalents of traditional bearings. This optimization strategy is supplemented by a collision detection scheme to enable the optimization of complex spatial mechanisms while avoiding collision of the flexures. This approach has been used to devise and optimize a new design for a large stroke flexure-based revolute joint with a range of motion of ±45 degrees rotation, a universal joint with a range of motion of ±25 degrees tip-tilt motion and a spherical joint with a range of motion of ±30 degrees tip-tilt and ±10 degrees pan motion. The obtained designs break through the traditionally considered maximum deflection angles of only a few degrees and provide unmatched support stiffness at large deflections. As a result, these flexure joints can be used as a “stand-in” replacement of traditional bearings for systems which require enhanced precision and large rotation angles.
In order to demonstrate the potential of these large range of motion joints, a fully flexure-based hexapod robot with 6 degrees of freedom has been designed and optimized. By utilizing the obtained designs for the large range of motion universal and spherical joints, an unprecedented range of motion for a flexure-based hexapod robot is obtained. This hexapod allows for a translational range of motion of ±100 millimeter and more than ±10 degrees of rotation in each direction combined with a base radius of 0.43 meter and a height of 0.42 meter. Furthermore, a dedicated low pivot shift flexure-based design for the actuators enable the use of high actuation forces without impairing precision, allowing for end effector accelerations exceeding 10 g and force feedback at the actuators.
Topology and shape optimization show new possibilities for large stroke flexure mechanisms by enabling higher support stiffness at large deflection. This allows for applications with a larger range of motion or improved mechanism volume to workspace ratio without suffering from a strong reduction in support stiffness when deflected. Furthermore, the increased range of motion allows for a broadening of the scope of application, expanding the potential for the use of flexures-based mechanisms.