Xinjian Li

Designing micro-mechanisms that satisfy large strokes, high precision, and multiple degrees of freedom has consistently been a research focus and challenge in the field of micromanipulation systems. Linear ultrasonic motors (LUMs), with advantages such as millimeter-level travel, nanometer-level motion resolution, and power-off self-locking, significantly contribute to the advancement in the mechanism design of micromanipulation systems. However, the challenge of mechanical drift lacks a comprehensive theoretical analysis to explain its cause and limits its application. This paper presents a mechanical drift modeling method for a compliant parallel micromanipulation (CPM) driven by a LUM. The model primarily focuses on the creep characteristics of the flexure clamp element in the LUM. Based on the stiffness matrix analysis method of the compliant parallel mechanism kinematics, the mechanical drift dynamics model of the CPM is established. The influence of the main structural parameters on the CPM mechanical drift is investigated. The research indicates that the creep of flexure clamps in the CPM is the main factor leading to the mechanical drift. Optimization of mechanical drift is achieved by choosing flexure clamps with higher tangential stiffness for LUM and flexure hinge joints with greater flexibility for CPM. Finally, experimental studies reveal that under equivalent conditions, the mechanical drift of the optimized CPM was significantly reduced than before, proving the rationality of the theoretical model and optimization method.

Linear ultrasonic motors (LUMs) have advantages such as de-energized self-locking and micro-nano displacement resolution. However, their positioning and control accuracy are negatively affected by mechanical drift, which limits their application in ultra-precision fields. To date, the quantitative mechanism of LUM mechanical drift under power-off conditions remains unreported. To solve the problem, we employ the creep theory to identify the clamp stiffness parameters and consider the internal friction and stick-slip effects of the slider, thereby establishing a non-autonomous dynamic model of the LUM mechanical drift in the power-off state. Subsequently, we utilize this model to investigate how the LUM’s structural parameters influence mechanical drift and explore methods to mitigate this undesirable phenomenon. Finally, we validate the model’s validity through experimental research. Our findings reveal that structural creep is the primary cause of mechanical drift in LUMs. Increasing the tangential stiffness of the clamp component and slider internal friction proves to be an effective approach to reducing mechanical drift. This study holds substantial theoretical and practical significance as it deepens understanding of the mechanisms of mechanical drift in LUMs and offers a pathway to achieve effective mechanical drift control.

This paper proposed a three-core fiber Bragg grating (FBG) probe for sub-millinewton contact force measurement of a micromanipulator system. The probe comprises a bundle of three single-core FBGs assembled under the effect of capillary self-assembly. Theoretical relationships between Bragg wavelength and force are calculated based on the assumption of material mechanics. The experimental results show that the probe has a good linear relationship for the measurement of the radial two degrees of freedom contact force, and it is suitable for measuring the radial contact force of 0.1–1 mN. The proposed three-core FBG probe has the characteristics of simple structure, low cost, and better forming stability and sensitivity compared with the four-core structure.