Using custom made experimental apparatus, the art of electrochemical etching was systematically studied for fabricating micro/nano tungsten probes with controllable tip profiles of exponential, conical, multidiameter, and calabashlike shapes. The characteristic parameters of probe including length, aspect ratio, and tip apex radius could also be well defined. By combining of static and dynamic etching, the conical-shape probe with length up to several millimeters, controllable tip apex radius, and cone angle could be fabricated. In addition, by continuously lifting the tungsten wire up during the electrochemical etching with different speeds and distances, the multidiameter shape probe could be fabricated. Finally by controlling the anodic flow, the multiple “neck-in” could be realized creating a calabashlike probe. The aspect ratio of probes depends on (i) the effective contact time between the surrounding electrolyte and the wire, (ii) the neck-in position of immersed tungsten wire. Under the optimized etching parameters, tungsten probes with a controllable aspect ratio from 20:1 to 450:1, apex radius less than 20 nm, and cone angle smaller than 3° could be achieved. The technique is well suited for the tungsten probe fabrication with a stabilized stylus contour, ultra-sharp apex radius, and high production reproducibility. The art for preparing microprobes will facilitate the application of such microprobes in diverse fields such as dip-pen nanolithography, scanning probe microscopy, micromachining, and biological cellular studies.

This paper presents the methodology for design and control of a high-stiffness fast tool servo (FTS) system for practical application in diamond machining of freeform surfaces. The electromechanical model of the FTS system is established by combining the piezoelectric actuator and flexure hinge mechanism for the formulation of the control methodology. In order to accommodate the system nonlinearity, cutting force disturbances as well as to realize fast and accurate tracking of designated tool path required for diamond machining of freeform surfaces, a novel adaptive terminal sliding mode (NATS) control strategy capable of online self-tuning of the system gain and reach time related parameters are developed. Stability analysis of the proposed NATS controller is performed. The convergence behavior of tracking error in the presence of model parameter variations and cutting force disturbance is analyzed. Experimental verification was conducted to validate the effectiveness and robustness of the NATS control. By comparing with other related control methods, it shows significantly improved performance. The percentage of tracking error was only 0.1% for the varying trajectories on machining water-drop surface. Taking advantages of the excellent tracking performances of the FTS prototype on a diamond turning machine, various freeform surfaces were successfully produced with high quality.

Ultra-Precision Machining (UPM) is a kind of highly accurate processing technology developed to satisfy the manufacturing requirements of high-end cutting-edge products including nuclear energy producers, very large-scale integrated circuits, lasers, and aircraft. The information asymmetry phenomenon widely exists in the design and control of ultra-precision machining. It may lead to inconsistency between the designed performance and operational performance of the UPM equipment on stiffness, thermal stability, and motion accuracy, which result from its design, manufacturing, and control, and determine the form accuracy and surface roughness of machined parts. The performance of the UPM equipment should be improved continuously. It is still challenging to realize the real-time and self-adaptive control, in which building a high-fidelity and computationally efficient digital twin is a valuable solution. Nevertheless, the incorporation of the digital twin technology into the UPM design and control remains vague and sometimes contradictory. Based on a literature search in the Google Scholar database, the critical issues in the UPM design and control, and how to use the digital twin technologies to promote it, are reviewed. Firstly, the digital twins-based UPM design, including bearings module design, spindle-drive module design, stage system module design, servo module design, and clamping module design, are reviewed. Secondly, the digital twins-based UPM control studies, including voxel modeling, process planning, process monitoring, vibration control, and quality prediction, are reviewed. The key enabling technologies and research directions of digital twins-based design and control are discussed to deal with the information asymmetry phenomenon in UPM.

The atomic force microscope (AFM) possesses a unique capability for three-dimensional, high-resolution imaging down to the atomic level. It operates without the needs of additional requirements on sample material and environment, making it highly valuable for surface measurements. Recent advancements have further transformed AFM into a precision machining tool, thanks to its exceptional force measurement capability and positioning precision. High-speed AFM (HS-AFM) is a specialized branch of AFM that inherits the advantages of high spatial resolution of typical AFM but with significantly improved time resolution down to the sub-second level. In this article, instead of delving into extensive research progress enabled by HS-AFM in the broad fields of biology, biophysics, and materials science, we narrow our focus to the specific applications in the domain of ultra-precision surface machining and measurement. To the best of the authors’ knowledge, a comprehensive and systematic summary of the contributions that HS-AFM brings to this field is still lacking. This gap could potentially result in an underappreciation of its revolutionary capabilities. In light of this, we start from an overview of the primary operating modes of AFM, followed by a detailed analysis of the challenges that impose limitations on operational speed. Building upon these insights, we summarize solutions that enable high-speed operation in AFM. Furthermore, we explore a range of applications where HS-AFM has demonstrated its transformative capabilities. These include tip-based lithography (TBL), high-throughput metrology, and in-line inspection of nanofabrication processes. Lastly, this article discusses future research directions in HS-AFM, with a dedicated focus on propelling it beyond the boundaries of the laboratory and facilitating its widespread adoption in real-world applications.