## 1 Introduction  
Thanks to ongoing advancements in micro manufacturing technology over the past several decades, demand for micro-products, such as micro bio-medical and optical devices and MEMS (Microelectromechanical Systems) products, has been increasing significantly. To enhance manufacturing efficiency and improve quality for micro-products, high accuracy measuring devices are essential for micro fabrication technology. Conventional measuring devices, such as the Vernier calipers and micrometers, are incapable of measuring delicate micro-components. While a wide variety of optical measuring methods have been developed for measurement of micro-products, non-contact methods have yet to be developed for measuring the lateral-wall, high-aspect ratio and high reflection in micro-parts. More recently, in order to measure the geometry of micro-products, the micro coordinate measuring machine (\(\upmu\)-CMM) and a number of delicate tactile triggering structures have been developed [1; 2; 3]. However, the dimension of micro spherical stylus tips is one of the critical challenges for micro-CMMs. Although the micro tactile spherical styli with a diameter of 0.125 mm are commercially available, they are sold less often. To utilize a spherical stylus of such a small dimension, a micro-CMM with a high sensitive probing structure is necessary [3]. Due to the limitations of the stylus dimension, micro-CMMs still face some challenges when measuring the geometry of micro-components, such as micro-holes or micro-slots with a high aspect ratio. Micro ball-ended stylus tips, accomplished by a glue assembly process, held great precision with an eccentric deviation from 0.6 \(\upmu\)m to 1 \(\upmu\)m [4]. In our previous study, OPED (One Pulse Electrical Discharge) and gluing processes were successful to fabricate micro spherical stylus tips with a diameter of less than 0.1 mm [5]. To keep the strength of adherence sufficient for the micro-triggering touch, a Wire Electrical Discharge Grinding (WEDG) process was successful in producing micro stylus tips with diameters of less than 0.15 mm and the roundness of less than 1 \(\upmu\)m, respectively, for the purpose of controlling the amount of glue applied between the glass ball and the stem [6]. The other critical problem with the micro-CMM is a sensing structure system. In the contact measuring, the stylus tip makes contact with the micro-object to trigger an electric signal. At the same time, the impact force is generated instantaneously. There is a correlation of size and fragility being the smaller the stylus, the more fragile it is. In our previous study, a micro stylus tip with a 40 \(\upmu\)m stem diameter fractured when the impact force exceeded 11 mN [7]. To prevent them from breaking and fracturing easily during the measuring process, the sensing structure should have a sufficient stiffness in all direction [8]. [PERSON] et al. applied 1 mN contact force to assess variable stiffness in the \(z\)-direction [9]. In addition, previous researchers reported various tactile sensing mechanisms of micro-CMM probing heads. However, these delicate triggering structures depended upon MEMS processes [10; 11], which makes the probing heads so costly that they are not commercially available in the market. Our previous study reported a tri-switches tactile probing structure, focusing on only the vertical directional tactile triggering and few applications [12]. Subsequently, our other previous work enhanced both fabrication of micro-styli and multi-directional tactile triggering structure, facilitating the exploration of diverse measurement strategy [13]. Through system advancements, [PERSON] et al. defined an associated measurement strategy for a specific probe [14; 15] with stiff and flexible modes. It is observed that such an integral strategy is customized to a developed micro-CMM system while some benchmark parameters associated with the triggering scenarios are affected by the stiffness of a micro-probe, and are transferable among micro-CMMs.