Tactile sensing transfers complex interactive information in a most intuitive sense. Such a populated set of data from the environment and human interactions necessitates various degrees of information from both modular and distributed areas. A sensor design that could provide such types of feedback becomes challenging when the target component has a nonuniform, agile, high resolution, and soft surface. This paper presents an innovative methodology for the manufacture of novel soft sensors that have a high resolution sensing array due to the sensitivity of ceramic piezoelectric (PZT) elements, while uncommonly matched with the high stretchability of the soft substrate and electrode design. Further, they have a low profile and their transfer function is easy to tune by changing the material and thickness of the soft substrate in which the PZTs are embedded. In this manuscript, we present experimental results of the soft sensor prototypes: PZTs arranged in a four by two array form, measuring 1.5-2.3 mm in thickness, with the sensitivity in the range of 0.07-0.12 of the normalized signal change per unit force. We have conducted extensive tests under dynamic loading conditions that include impact, step and cyclic. The presented prototype's mechanical and functional capacities are promising for applications in biomedical systems where soft, wearable and high precision sensors are needed.
Brittle materials such as ceramics, glasses and oxide single crystals find increasing applications in advanced microengineering products. Machining small features in such materials represents a manufacturing challenge. Ultrasonic drilling constitutes a promising technique for realizing simple micro-holes of high diameter-to-depth ratio. The process involves impacting abrasive particles in suspension in a liquid slurry between tool and work piece. Among the process performance criteria, the drilling time (productivity) is one of the most important quantities to evaluate the suitability of the process for industrial applications. This paper summarizes recent results pertaining to the ultrasonic micro-drilling process obtained with a semi-industrial 3axis machine. The workpiece is vibrated at 40 kHz frequency with an amplitude of several micrometers. A voice-coil actuator and a control loop based on the drilling force impose the tool feed. In addition, the tool is rotated at a prescribed speed to improve the drilling speed as well as the hole geometry. Typically, a WC wire serves as tool to bore 200 m diameter micro-holes of 300 to 1,000 m depth in glass and ruby. The abrasive slurry contains B4C particles of 1 m to 5 m diameter in various concentrations. This paper discusses, on the basis of the experimental results, the influence of several parameters on the drilling time. First, the results show that the control strategy based on the drilling force allows to reach higher feed rates (avoiding tool breakage). Typically, a 8 um/s feed rate is achieved with glass and 0.9 m /s with ruby. Tool rotation, even for values as low as 50 rpm, increases productivity and improves holes geometry. Drilling with 1 m and 5 m B4C particles yields similar productivity results. Our future research will focus on using the presented results to develop a model that can serve to optimize the process for different applications.
This article presents a laboratory machine designed to perform orthogonal micro-cutting experiments. The machine allows an accurate control of the various cutting parameters and a direct comparison of micro-and macrocutting tool-material data bases. Research with the machine will focus on validating the application of macrocutting data to at least a range of microcutting applications and to define the limits beyond which such applications are no longer possible. The paper describes the machine and its design specifications and provides the validation of the performances claimed. The machine can cut in a reproducible manner with depths of cut as low as 1 lm, at speeds in the range 50-1000 mm/s, while measuring the cutting and thrust forces. The variability in nominal depth of cut is equal or better than 1 lm. Application examples illustrate the influence of lubrication and lead additions on the cutting process and demonstrate that the machine is indeed suitable for the application for which it was designed.
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