Development of a Miniaturized Gripper driven by a Magnetic Shape Memory Single Crystal Actuator

Development of a Miniaturized Gripper driven by a Magnetic Shape Memory Single Crystal Actuator

Categories Konferenz
Year 2007
Authors Guldbakke, J. M.; Rolfs, K.; Mecklenburg, A.; Raatz, A.; Schneider, R.; Hesselbach, J.
Published in MRS Fall Meeting, Boston, 2007

The development of grippers for the handling of microparts must solve special requirements, for example very high preciseness, adhesion, sensitive parts, moderate dynamics and clean room conditions. Because only few conventional grippers can meet all of these requirements, a mechanical miniature gripper having flexure hinges and a magnetic shape memory (MSM) actuator is developed. The design of the gripper is simple, but it is capable of gripping small objects with high precision. This could be realized by using a frictionless mechanism.The gripping mechanism is a so-called compliant mechanism. This term has been defined as a mechanism which gains the whole or a part of its mobility from the relative flexibility of its members rather than from rigid body motion. This means that conventional rotational bearings which connect two rigid bodies are replaced by flexure hinges. A flexure hinge is a type of bending beam which is used in mechanical systems as a revolute joint. Compliant mechanisms are strongly recommendable for precise applications because in opposite of conventional bearings they do not have undesired friction and wear effects. Further on the mechanisms consist of only one part and can easily be machined in small dimensions. However, there are some restrictions one has to take into account for a successful design of a compliant mechanism. First, flexure hinges reach only small angular displacement, limiting the motion of the whole compliant mechanism. This is not a general drawback for microgrippers, since the objects to be handled are only small in size. Second, flexure hinges have restoring forces. Therefore the actuator has to exert not only the desired gripping force, but additionally the restoring forces of the mechanism. Third, unlike rigid-body-links the instantaneous center of velocity is not fixed but changes its position during the movement of the link. As an actuator a 5M-Ni-Mn-Ga single crystal is used. This MSM crystal was produced at the Hahn-Meitner-Institute Berlin. Before the integration of the single crystal as the actuation element into the gripper, the properties of the MSM alloy have to be examined. Therefore test devices were developed and set-up. With these devices temperature dependent stress-strain curves of the single crystals can be determined as well as the magneto-stress-strain behaviour of MSM alloys. The integrated crystal works at temperatures up to 65°C, has a stress plateau under 1 MPa and exhibits a stress induced strain of approximately 7 %. Furthermore the MSM sample can be activated with magnetic fields less than 0.6 T. For the layout of the coil system to generate the required magnetic field the finite element program ANSYS was used.