摘要
随着人们对众多工业产品小型化、集成化的不断需求,微操作技术日益凸现其重要性,在微电子工程、精密制造、生物工程等诸多领域均具有广阔应用前景。微纳米技术近年来的快速发展,推动着各类功能化的微器件在多种微操作系统中应用;另一方面,制造组件更加微小、功能更加集成的微光机电系统也对微操作技术提出了更高的要求。
由于尺度效应作用,在微米尺度下各种表面粘着力的作用开始占据主导地位。粘着力常会干扰微操作过程,影响微操作的可靠性和高效性,制约着微操作技术的推广应用。本文针对上述问题,结合国家杰出青年基金项目和国家高技术研究发展计划项目,对微操作中构件间的粘着机理和粘着接触模型进行研究,并基于所建立的模型,研究基于粘着力控制的微操作方法。
针对微操作中构件间广泛存在的粘着现象,从尺度效应着手,在分析原子和分子间作用力的基础上,获得微操作中各种粘着作用力的机理和特性。在此基础上,分析了在进行微操作工具优化设计和路径规划时考虑粘着现象的方法,并以简化的典型微构件操作配置为例,研究了微构件间范德华作用力的近程作用特性和毛细作用力的环境依赖性。
粘着现象是多种作用力共同作用的结果,而每种作用力具有不同的特征。为了定量认识微操作中构件之间的粘着作用力,必须对各种粘着力进行分别分析。本文考虑到实际微构件操作中的配置,重点研究了微构件之间的范德华粘着力和微构件之间的毛细作用力。
针对实际表面均不是理想光滑表面的特点,采用分形几何描述对粗糙表面建模,基于单微突体的粘着接触模型建立粗糙表面间的粘着接触模型,并在此基础上分析影响范德华粘着作用力的各种因素。分析结果表明,随着粗糙表面分形维数变大,粗糙表面间的粘着力显著增加;随着分形粗糙度参数的增大,粗糙表面间的粘着力减小;随着固体材料弹性模量增大,粗糙表面间的粘着力减小;随着两表面间粘着能的增大,粘着力急剧增大。
另外,基于圆形轮廓近似建立了微构件之间的毛细作用力模型。与基于Laplace方程的复杂数值模型比较结果显示,所建立的模型在构件间距离较小时,具有较高的精度。分析表明:在微观尺度表面张力通常对毛细作用力具有不可忽略的贡献;弯月面轮廓半径对毛细作用力具有重要影响,液体在两微构件上的接触角及构件几何形状也会影响毛细作用力。
针对常规微夹持工具和真空吸附式作业工具的不足,考虑到微尺度下粘着力的主导地位,提出了基于粘着力控制的微操作方法。拾取和释放操作中分别需要增强和减弱操作工具和微构件之间的粘着力,为此提出利用粘弹性材料工具通过速度控制改变粘着力,从而实现微构件拾取和释放操作。在微构件转移过程中,依靠粘着力大于重力的特性保持工具和微构件的相对位置。为了可靠释放,提出了利用毛细作用力控制液体种类和体积的方法执行微构件释放操作。
为了验证所建立的相关模型和提出的基于粘着力的微操作方法,进行了系列的实验研究。首先测量了粘弹性材料工具和微构件之间的粘着力,表明了其相对于重力的主导地位。其次验证了粘弹性材料工具和固体材料之间的粘着迟滞作用,说明了可以利用运动速度控制执行微构件操作。另外测量了微构件之间的毛细作用力,验证了所提出的毛细作用力模型的正确性。最后,进行了基于粘着力控制的微操作实验,验证了所提出的基于粘着力控制执行微操作任务的有效性。
Trends of miniaturization and integration of numerous industry products are continually increased recently. Micromanipulation, as an enabling technology, is being widely used in many fields, such as microelectronic engineering, precision manufacturing, bioengineering. The rapid developments of micro and nanotechnology are making more and more functionized microdevices being uitilized in micromanipulation system, on the other hand, higher demands are proposed to manufacture microsystems with smaller dimensions and more functions.
Due to the scale effects, various surface forces begin to dominate in the micro meter scales. Adhesion forces often disturb the process of micromanipulation and affect the reliability and efficiency of it, thus restrict their wide applications. Supported by the National Science Funds for Distinguished Young Scholar and the High Technolgy Research and Development Programme of China, this paper focuses on the adhesive contact model between microparts and the micromanipulations methods based on controlling adhesion forces.
Considering a mass of adhesion phenomema in micromanipulation, this paper starts from the scale effects in micrometer scales. By analyzing the forces between atoms and molecules, the mechanism and properties of adhesion forces are identified. Then the effects of adhesion forces on tools design and path planning in micromanipulation are investigated. The configurations of manipulating typical microparts are analysed to discuss the properties of adhesion forces.
Adhesion is a result of multiple forces with different characters, so that is necessary to distinguish them. Van der Waals adhesion and capillary adhesion are focused in this paper for considering the actual conditions in micromanipulation. For the usual rough surfaces, the fractal geometry methods are adopted to describe the rough surfaces. The adhesive contact model between them is developed based on the elastic contact model of single asperities. The capillary force model between microparts is also developed based on the circle approximation and the parameters that affect the force are discussed in detail.
Due to disvantages of the usual microgripper and vacuum tool, the micromanipulation methods based on adhesion force control are proposed according to the predominance of adhesion forces in micro meter scale. In picking process, strengthening the adhesion is positive, so a method using the viscoelastic tool with fast velocities are proposed. The transferring process will be stable if the adhesion force is larger than the gravity of the microobject. To realize the reliable release, a method of controlling capillary forces is suggested.
To verify the developed model and methods, a series of experiments are performed. The adhesion force between PDMS tool and microparts are measured to make sure that it is more dominate than the gravity. The adhesion hysteresis is verified to show that it is suitable to strengthen the adhesion with velocity control. The capillary force between microspheres and flats are also measured to verify the developed model. Finally, the micromanipulation experiments based on adhesion force control are performed and the results show that the feasibility of proposed methods.
引文
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