Design of Compliant Mechanism Microgripper Utilizing the Hoekens Straight Line Mechanism
TL;DR: The article introduces the cartwheel type of flexure hinges, as cartwheel-type Flexure hinges are more suitable to achieve rotational deformation, values approximating nearly to that of the traditional revolute joint when it transfers motion between fixed and moving links.
Abstract: Precision engineering industries demand devices with high-precision motion, the manipulation of micro-objects in particular, which is a highly challenging task. The microgripper is an essential device during the micromanipulation of objects. Precision manipulations of objects entirely depend on the design of the microgripper and are complicated to achieve using the conventional rigid link mechanism. The compliant mechanism is found to overcome the complexities of the rigid link mechanism in precision applications. The micro-object may slip or slide during gripping and releasing, which can be controlled through parallel movement of the gripping jaws. This research article focuses on the design of a compliant microgripper with parallel moving jaws by employing the Hoekens straight line mechanism. The Hoekens mechanism consists of binary and ternary revolute joints, which demand a special type of flexure hinges. Hence, the article introduces the cartwheel type of flexure hinges, as cartwheel-type flexure hinges are more suitable to achieve rotational deformation, values approximating nearly to that of the traditional revolute joint when it transfers motion between fixed and moving links. The outer rim of the cartwheel is modified to allow ternary and binary joints between moving links. Cartwheel is designed with curved flexure arms that are limited to eight numbers of flexures. The structural behavior of the cartwheel is analyzed by varying numbered flexures from 1 to 8. The minimum number of flexure arms required for having better rotational performance is determined through Finite Element Analysis (FEA). An appropriate type of cartwheel is positioned in the mechanism. The structural performance of the designed microgripper is carried out through FEA, and its parallel movement is verified. The microgripper is fabricated from structural steel through wire Electrical Discharge Machining (EDM) technique and actuated using Shape Memory Alloy wire. The displacement of the microgripper jaw is experimentally measured, and the results show a promising improvement.
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TL;DR: A compact compliant mechanism that enables in-principle straight-line parallel jaw motion is obtained, by combining the Scott–Russell mechanism and the parallelogram mechanism, for micro-manipulation applications.
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TL;DR: The model of Oelschläger is extended and verified to consider the degradation behavior over the whole lifetime and it is shown that it is possible to simulate the longterm behavior of the stroke for one of the two load scenarios.
Abstract: One of the greatest challenges in the design of shape-memory elements (mostly binary Nickel-Titanium wires) is to ensure that the required travel (stroke) is achieved, as this is subject to variation due to various influencing factors. One way of predicting the stroke is to use a suitable energy model. In the past, for example, a model was developed by Oelschläger with which the stroke can be calculated on the basis of the electrical energy. However, so far no model takes into account the change of the phase transformation temperature. In this study, the model of Oelschläger is extended and verified to consider the degradation behavior over the whole lifetime. For this purpose, fatigue tests of 52 wires (2 different load scenarios) were performed. Based on these tests and the application of statistical methods (distribution models, goodnes-of-fit tests etc.), a target model was developed for each load scenario, which is used to verify the extended energy model. The energy model was applied to wires of both load scenarios to simulate the stroke progression. The verification of the extended simulation model shows that it is possible to simulate the longterm behavior of the stroke for one of the two load scenarios. The second load scenario shows deviations between the target model and the simulation, which is due to problems in the area of measurement equipment, convection, and temperature distribution in the wire. Nevertheless, a decisive modeling approach could be developed, which can be used to consider the long-term behavior of the phase transformation temperature of wires in simulations.