March 2009 – March 2013
flexure mechanisms, elastic mechanisms, compliant mechanisms, finite element based multibody modeling, large stroke, precision positioning in vacuum, design principles, 2-3 DOFs stage.
Accurate large stroke positioning mechanisms are increasingly applied in extreme conditions such as vacuum. Traditionally, roller-bearings are used in these positioning mechanisms, but they suffer from drawbacks such as contamination, friction and hysteresis. Therefore alternative solutions are desirable to satisfy vacuum condition requirements. In MOVET two possible solutions will be researched. One is to improve tribology in vacuum conditions. The second possible solution is the use of elastic mechanisms. The research conducted in Mechanical Automation and Mechatronics if focused at elastic mechanisms. Such a mechanism consists of rigid and elastic elements where the elastic elements typically behave like hinges. An example of an elastic mechanism is shown in figure 1. Here three degrees of freedom (DOFs) are constrained and three DOFs are compliant.
Figure 1: Concept three DOFs elastic mechanism
These mechanisms have the advantage that they operate without contaminating the vacuum and are friction/hysteresis free. However, such mechanisms are traditionally only applied in short stroke applications, because the elastic elements suffer from a significant decrease in stiffness when the deflection is relatively large. This causes the dynamics of the whole mechanism to change depending on the deflection of the elastic elements. In figure 2 this decrease in stiffness is illustrated for a clamped/free leaf spring, where the stiffnesses in the three translation directions are plotted as a function of the rotation angle Rz.
Figure 2: Normed stiffnesses of a leaf-spring deflected in the Rz-direction. The relative dimensions are: l/h = 4, l/t = 300, h/t = 75
The main objective of this project is to be able to accurately and efficiently model the position dependent dynamics of elastic mechanisms with a relatively large stroke. The models should be applicable for a fast evaluation of various mechanism designs as well as to evaluate its closed-loop performance. It is expected that accurate and fast simulations can be realized by combining sound modeling techniques (SPACAR) and model reduction techniques. The research also aims at designing flexure elements that principally maintain a high stiffness at deflection. One solution has been proposed in .
During the first year of the research a first proof-of-principle 2 DOFs precision stage will be modeled, designed and fabricated, based on the current knowledge. A conceptual design of this stage is shown in figure 1. The elastic elements will be interchangeable so that a wide variety of design solutions for minimal position dependent dynamics can be tested in practice. During the second and third year the modeling techniques will be improved for faster analysis and optimization. The insight both from modeling and the first proof-of-principle demonstrator will be used for a final optimized stage.
- A literature study on model reduction techniques for the creation of efficient and accurate dynamical models
- Two mechanisms are researched. The orientation and the stiffness characteristics of the elastic elements in two mechanisms is evaluated based on the end-effector natural frequency.
- A reduced model of the curved hinge flexure has been built in SPACAR
- Researching elastic hinges which exhibit less stiffness changes under bending conditions
- Continuing the development of the test setup, which will result in a redesign of the original test setup
- Applying promising model reduction techniques found in the literature study
- Investigating control strategies for non-linear position dependent dynamical systems
Journal papers (refereed)
Conference proceedings (refereed):
- D.M. Brouwer, J.P. Meijaard, J.B. Jonker, Elastic element showing low stiffness loss at large deflection, Proceedings of the 24th annual meeting of the American Society of Precision Engineering, 4-9 Oct 2009, Monterey, pp30-33, ISBN978-1-887706-51-3 http://www.aspe.net/aspe_member/php/abstracts/absdisplay.php?Abstract_ID=2859.
- S.E. Boer, R.G.K.M. Aarts, D.M. Brouwer, J.B. Jonker, Multibody modelling and optimization of a Curved Hinge Flexure, The 1st Joint International Conference on Multibody System Dynamics, May 25–27, 2010, Lappeenranta, Finland, Accepted
- S.E. Boer, D.M. Brouwer and R.G.K.M. Aarts, Elastic Hinge for Large Deflection, EM symposium (poster), Lunteren (NL), October 28-29, 2009