Abstract:Abstract:Micro-scale probing systems are used on specialist micro-coordinate measuring machines to measure small, intricate and fragile components. Probe stiffness is a critical property of micro-scale probing systems; it influences contact force, robustness, ease of manufacture, accuracy and dynamic response. Selecting the optimum stiffness, therefore, represents a significant design challenge, and often leads to undesirable compromises. For example, when contacting fragile surfaces the probe stiffness should… Show more
“…As well as determining the effect that switching from stiff to flexible mode has on sensitivity, it was also necessary to determine any unwanted stylus tip position offset error. This was determined with the knowledge that the load applied to the beams will result in a deflection of the stylus tip, which is most dominant in the z direction [ 12 ]. If the probing system was not able to return to the same initial zero offset when switched to flexible mode, it would directly impact the probing system error.…”
“…Controlling the magnitude of the compressive force, therefore, allows the probe stiffness to be controlled. A full description of the design and working principle behind the variable stiffness probing system is presented elsewhere [ 11 , 12 ].…”
When designing micro-scale tactile probes, a design trade-off must be made between the stiffness and flexibility of the probing element. The probe must be flexible enough to ensure sensitive parts are not damaged during contact, but it must be stiff enough to overcome attractive surface forces, ensure it is not excessively fragile, easily damaged or sensitive to inertial loads. To address the need for a probing element that is both flexible and stiff, a novel micro-scale tactile probe has been designed and tested that makes use of an active suspension structure. The suspension structure is used to modulate the probe stiffness as required to ensure optimal stiffness conditions for each phase of the measurement process. In this paper, a novel control system is presented that monitors and controls stiffness, allowing two probe stiffness values (“stiff” and “flexible”) to be defined and switched between. During switching, the stylus tip undergoes a displacement of approximately 18 µm, however, the control system is able ensure a consistent flexible mode tip deflection to within 12 nm in the vertical axis. The overall uncertainty for three-dimensional displacement measurements using the probing system is estimated to be 58 nm, which demonstrates the potential of this innovative variable stiffness micro-scale probe system.
“…As well as determining the effect that switching from stiff to flexible mode has on sensitivity, it was also necessary to determine any unwanted stylus tip position offset error. This was determined with the knowledge that the load applied to the beams will result in a deflection of the stylus tip, which is most dominant in the z direction [ 12 ]. If the probing system was not able to return to the same initial zero offset when switched to flexible mode, it would directly impact the probing system error.…”
“…Controlling the magnitude of the compressive force, therefore, allows the probe stiffness to be controlled. A full description of the design and working principle behind the variable stiffness probing system is presented elsewhere [ 11 , 12 ].…”
When designing micro-scale tactile probes, a design trade-off must be made between the stiffness and flexibility of the probing element. The probe must be flexible enough to ensure sensitive parts are not damaged during contact, but it must be stiff enough to overcome attractive surface forces, ensure it is not excessively fragile, easily damaged or sensitive to inertial loads. To address the need for a probing element that is both flexible and stiff, a novel micro-scale tactile probe has been designed and tested that makes use of an active suspension structure. The suspension structure is used to modulate the probe stiffness as required to ensure optimal stiffness conditions for each phase of the measurement process. In this paper, a novel control system is presented that monitors and controls stiffness, allowing two probe stiffness values (“stiff” and “flexible”) to be defined and switched between. During switching, the stylus tip undergoes a displacement of approximately 18 µm, however, the control system is able ensure a consistent flexible mode tip deflection to within 12 nm in the vertical axis. The overall uncertainty for three-dimensional displacement measurements using the probing system is estimated to be 58 nm, which demonstrates the potential of this innovative variable stiffness micro-scale probe system.
“…To prevent the undesirable elastic deformation of the bending stylus impeding the triggering accuracy, the stylus of 5 mm was used. Although using a finite element model (FEM) to study the relationship between applied sensing load and probe stiffness is not within the scope of the study, a trend of using FEM facilities has led to a similar development approach [15]. …”
Section: Mechanism Structurementioning
confidence: 99%
“…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, Alblalaihid 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 transferrable among micro-CMMs.…”
This paper describes the fabrication of a series of micro ball-ended stylus tips by applying micro-EDM (Electrical Discharge Machining) and OPED (One Pulse Electrical Discharge) processes, followed by a manual assembly process of a static tri-switches tactile structure on a micro-CMM (Coordinate Measuring Machine). This paper further proves that the essential performance of the proposed system meets an acceptable benchmark among peer micro-CMM systems with a low cost. The system also adjusts for ambient temperature and humidity as the ordinary lab environmental conditions. For demonstration, several experiments used a randomly selected glass stylus with the diameters of stem and sphere of 0.07 mm and 0.12 mm, respectively. By leveraging research guidelines and common practice, this paper further investigates the probing relationship between measurement accuracy and its associated critical characteristics, namely triggering scenarios and geometric feature probing validation. The experimental results show that repeated detections in the uncertainty, in vertical and horizontal directions of the same point, achieved as small as 0.11 µm and 0.29 µm, respectively. This customized tri-switches tactile probing structure was also capable of measuring geometric features of micro-components, such as the inner profile and depth of a micro-hole. Finally, extensions of the proposed approach to pursue higher accuracy measurement are discussed.
“…However, the inertial mass of this microprobe combined with its low stiffness prohibits its integration in a conventional CMM because the low resonance frequency renders movements of the probing system impossible. Previous works include a probing system with a variable stiffness [10], which is able to achieve close to isotropic mechanical behavior (1.3) by using a special suspension structure and applying piezo-electric compressive loads. Furthermore, three-legged suspension structures for low-probing forces have been also investigated [11].…”
Different kinds of piezoresistive microprobes based on silicon have been developed to enable measurement with high accuracies. However, the typical mechanical anisotropy of such systems leads to the slip of the tip, when probing inclined surfaces. Here, a novel microprobe design is presented, which can be tailored to provide a range of anisotropy or even a perfect isotropy. In the first approach, the microprobe is composed of two stacked silicon membranes. In the second approach, a stainless steel suspension in the form of a laser structured foil is stacked on a silicon membrane. Geometrical parameter studies were carried out by mechanical FEM simulations to determine their influence on the stiffnesses in all spatial directions and to predict anisotropies. Microsystems with selected geometries were fabricated and stacking was obtained through selective adhesive transfer and bonding on a wafer level. Prototypes with anisotropies between 3 and 0.4 were characterized confirming the simulations.Keywords -3D micro probing system, piezo-resistive effect, tactile coordinate measurement, laser structuring, wafer-level bonding and tailored mechanical anisotropy.I.
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