Modelling and validation of impact response in compliant nechanisms: Using pseudo-rigid-body modelling and rigid body dynamics

Modelling and validation of impact response in compliant nechanisms: Using pseudo-rigid-body modelling and rigid body dynamics

Boersma, S.

Herder, J.L. (mentor)
Tolou, N. (mentor)

Mechanical, Maritime and Materials Engineering

Precision and Microsystems Engineering

2015-05-07

Modelling of the behaviour of compliant mechanisms leads to a better understanding and synthesis of designed mechanisms. Static and dynamic responses for compliant mechanisms have been researched extensively. While impact modelling is a well known field in rigid body dynamics, impact modelling in compliant mechanisms research is lacking. By combining the fields of dynamic modelling of compliant mechanisms using the pseudo-rigid-body model and rigid body impact modelling a technique is proposed. The efficiency of the impact is considered as the amount of energy fed back into the first mode shape, for which the compliant mechanism was designed. Energy is expected to be lost higher frequency vibrations of the system. Modelling and experiments were done for a case study to show the effects of impacting in line with and outside of the centre of mass with varying impact angles. Results for an increasing impact angle show less energy returned to the fundamental mode shape. Impacting outside of the centre of mass shows asymmetric results and impacting closer to the base from the centre of mass results in less energy loss than further from the base. Using rigid body impact modelling on the pseudo-rigid-body dynamic model (PRBDM) provides quick simulations including impact. The single degree of freedom of the PRBDM does not capture the effects of higher mode shapes outside of extra energy losses from the first mode. Therefore a two rotation pseudo-rigid-body model (2R-PRBM) is converted into a dynamic model and is applied to the case study including impact equations. This model has multiple degrees of freedom and can therefore contain the higher frequencies in which energy is lost. The dynamic 2R-PRBM provides the same response for an impact in line with the centre of mass and straight path and shows energy moves to higher frequencies at a shifted impact position or angle. The amount of energy loss currently does not match the experiments. Expected cause are assumptions made by the impact modelling.

http://resolver.tudelft.nl/uuid:a6789688-cf5e-41aa-96ef-938df61db88a

Student theses

master thesis

(c) 2015 Boersma, S.