新型并联柔性约束测头的变刚度机理及自适应刚度控制

Probe is the key part of the accurate measuring equipment. Development of new types of probe with high-performance is focus of the field of precision measurement technology. Existing researches mainly focus on perfecting the measurement theory and optimizing the sensor capability, but few pay attention to the structure innovation of the probe, which greatly limits the improvement of the performance of the probe. Stiffness property is an important factor of the performance of the probe, which should have the optimum stiffness performance so as to adapt the force-measuring variation with the work piece and measurement process changing. Based on the basic property, that the kinematical characteristic and the stiffness performance change when the parallel mechanism is or near the singularity, this project constructs a new type of parallel constraint probe with variable stiffness performance using the “expanded rigid body replacement synthesis”. The models for static stiffness, measuring force, elastic dynamics, error analysis and the error correction mechanism are derived. The configuration parameters of the probe are optimized. Based on the aforementioned theoretical models, the variable stiffness mechanism of the probe is expounded and the adapt stiffness control mechanism is established. A test platform for the three-dimensional precision measurement with this new type of probe is build, on which the performance tests are accomplished. This project can further expand the area of application for parallel mechanism, develop the innovative approaches of the precision probe, perfect the performance of the probe, and advance the technology progress of the probe and the development of the precision measurement technology.

测头是精密测量设备的关键部件，开发性能优良的新型测头是精密测量技术领域关注的重点。现有研究主要关注完善测量理论和优化传感器性能，对测头本体结构创新方面研究较少，极大地限制了测头性能的提升。测头刚度特性是影响其性能的重要因素，测头应具有最优的刚度性能以适应测量对象与测量过程变化引起的测力变化。项目基于并联机构位于奇异位形及其附近区域时，机构运动学及刚度特性发生改变这一基本属性，利用“扩展刚体替换综合法”构造具有变刚度性能的新型并联柔性约束测头。建立该新型测头的静刚度模型、测力检测模型、弹性动力学模型、误差分析模型及误差修正机制等，优化其结构参数。综合各项理论模型，揭示测头变刚度机理，创建其自适应刚度控制机制。构建基于该新型测头的三维精密测量试验平台，完成测头的性能测试。本项目可进一步拓展并联柔性机构应用范围，丰富精密测头结构创新方法，完善测头性能，促进测头技术进步与精密测量技术领域的发展。

测头约束支撑机构是测头本体结构的主体，研究使得测头支撑机构在测量过程中表现出最优的刚度特性，具有非常重要的理论意义与实际价值。项目构造出若干新型类型的测头约束支撑机构，主要研究工作如下：(1)基于并联机构的运动学奇异，利用“刚体替换综合法”构造出一种新型并联柔顺约束测头。基于线几何和力雅可比矩阵零空间法简要阐明了机构具有三维测头所需的功能自由度。基于并联柔顺支撑机构的静力学及分支杆刚度模型，构造机构的整体刚度矩阵，建立测头的测力-位移模型，通过数值模拟和有限元软件验证理论分析的正确性。(2)基于虚功原理，建立附加弹簧曲柄滑块机构的运动静力学力矩-转角平衡方程。该方程表明机构工作于运动学支链奇异附近时，可产生四类非线性刚度特性。研究弹簧刚度参数对非线性刚度特性的影响，揭示各类非线性刚度特性的产生机理及其相互间的转化机制。以构造零刚度特性并以确定恒力矩区域为例，阐释创建相应的非线性刚度特性的一般性方法。该内容拓展了机构运动学奇异的应用范围，具有非线性刚度特性的柔性机构结构可应用于需要变刚度特性的测头支撑梁约束终端结构。(3)利用压电装置驱动柔顺导向机构产生位移，以改变悬丝所受的轴向张紧力，构造一种基于悬丝约束支撑的变刚度微纳测头，以解决测量过程中测头支撑机构刚度不可变问题。根据测头支撑机构在测量过程中刚度的变化，分别建立刚性和柔性模式下微纳测头Z向和横向刚度模型。对比有限元仿真和刚度理论模型，结果表明理论模型具有较高的准确性。(4)利用压电装置驱动柔顺机构变形以改变柔性支撑梁的轴向受力和横向刚度，构造出基于十字交叉型悬臂梁支撑的变刚度测头。利用最小势能原理构建测头约束支撑机构的刚度模型，基于上述模型获得所需压电驱动力大小。对比刚度理论计算值与仿真值，验证了刚度理论模型具有较高的准确性。本项研究丰富了测头本体结构的创新方法，为新型变刚度测头应用提供了理论指导，促进了测头技术进步。