Piezo actuators and giant magnetostrictive actuators are widely used in micropositioning and micromanipulating devices. Due to their limited output stroke, flexure-based displacement amplifiers are usually employed to meet the large-stroke requirements. Although amplifiers increase the stroke of the actuators, they lower the resolution of the motion, making it difficult to obtain positioning of nanometer or even sub-nanometer resolution. To achive very high resolution from these actuators, a compact flexure-based displacement reducer, which shows the capability of obtaining very large reduction ratio, is proposed in this work. The reducer contains two bridge-type flexure mechanisms connected in a way that the output of the reducer equals the difference of the outputs of the two mechanisms (thus is called the bridge-type differential displacement reducer). If the two bridge-type flexure mechanisms are identical, no matter how large the input is, the output will always be 0, indicating an infinite reduction ratio theoretically. Therefore, introducing a slight difference between the two mechanisms can yield a very large reduction ratio. A kinetostatic model for the reducer is developed, base on which a reducer exhibiting a reduction ratio of 100 is designed and prototyped. The results of the kinetostatic model, the finite element model and the experiment agree well with each other, validating the effectiveness of the proposed reducer and the correctness of kinetostatic model.

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