Study On The Mechanism And Touch Trigger Probe System Of Micro/nano Coordinate Measuring Machine

With the development of ultra-precision machining technology, 3D measuring machines with high resolution are needed to meet the miniature components. Coordinate Measuring Machines (CMMs) with small size and micro/nano meter resolution are developed via breaking through the bottleneck. Based on the projects of developing micro/nano CMM, the author focused on the research of mechanical bridge, the precision 2D positioning stage, and the touch trigger probe system. Independent experiences from designing, processing and testing of every system constitute the important part during the research.Innovative arch-bridge structure was proposed to replace the conventional rectangular-bridge structure. The arch-bridge structure has much better stability; the deformation because of pressure coming from Z-spindle was decreased more than 1/3. Harmonic analysis results proved its superior dynamic performance. Finite Element Analysis (FEA) and optimization method were extended employed in this research, a pagoda-bridge was developed to strength its rigidity and stability because of the symmetry in space. Both the bridges supply metrology referring base for the precision measurements. Coplanar concept was developed during the research of the 2D precision positioning stage. It means the guide planes in X- and Y- are in the same height, as well as the measuring plane and the plane of workpiece carrier. As a result, the Abbe's error and the cumulative error can be reduced. The symmetric structure is another highlight in this design to eliminate the structure deformation by force and temperature change. The stage was driven by nano motor with nanometer resolution and its displacement was detected by precision Linear Diffraction Grating Interferometer (LDGI). Experimental results show that XY stage can travel 25 mm with 1nm resolution and the positioning repeatability is less than 30nm.Conventional CMMs restrict the possibilities for measuring micro mechanical products and noncontact optical measuring methods are not suitable for true three-dimensional measurements. The integrated combination of optical sensors and mechanical transducers employed in this research makes an ideal low cost and high precision touch trigger probe possible to measure miniature components. This touch probe is composed of a stylus with a fiber sphere and a sensor integrated floating plate. The ball tip is fabricated using optical fiber with melting and solidification processes. Based on Taguchi method, the fusing process parameters are optimized. Fine fiber sphere with 310μm diameter and less than 1μm roundness and center offset can be fabricated. The stylus is attached to a floating plate, which is connected to the probe housing via four micro wires. The shape and dimension of the floating plate, as well as the length and diameter of the micro wire, are determined according to the selected contact forces. When the probe tip is displaced the wires will perform elastic deformation and four mirrors mounted onto the four-legged plate will amplify the up/down displacement at each mirror position. These displacements can be detected by four corresponding laser focus probes based no DVD pickup heads. Experiments were carried out to test the characteristics of the touch trigger probe. The standard deviation of unidirectional touch trigger repeatability is less than 10nm. The pre-travel variation along 360°in XOY plane is less than 15nm. The average trigger force is 110μN in XOY plane and 59μN in Z-direction when the threshold voltage is 10mV.The mechanism systems and touch trigger probe system developed in this thesis have been integrated in the projects of Non-contact Nano-CMM and the Nano-CMM with touch trigger probe.