[Show abstract][Hide abstract] ABSTRACT: Carbon fiber-reinforced thermoplastics (CFRTP) are just beginning to be utilized for various applications such as aerospace, automobiles, and sporting goods in place of CFRPs, and the demand for through-hole drilling of CFRTPs is increasing. In this study, the machinability in drilling of CFRTPs under various conditions was experimentally analyzed in terms of the material properties, and a feasibility study of ultrafast feed drilling was conducted. The results showed that delamination at the outlet surface can be significantly suppressed during high rotational drilling when the feed rate is set to more than 3000mm/min. By providing appropriate drilling conditions to prevent polymers in CFRTPs from softening, ultra-fast drilling of CFRTPs was successfully achieved under dry conditions.
[Show abstract][Hide abstract] ABSTRACT: The optical micro-resonator, which stores light at a certain spot, is essential in next-generation optical signal processing. Single-crystal calcium fluoride (CaF2) is the most suitable material for this element. Ultra-precision turning is a feasible fabrication process for CaF2 optical micro-resonators. In this study, the influence of subsurface damage on the resonator's Q factor is investigated. TEM observation shows that the subsurface layer of up to several tens of nanometers thickness changed from single-crystal to polycrystalline morphology due to ultra-precision turning. A diamond tool with 0° rake angle results in lower damage than one with negative rake angle, which enhances the resonator's performance.
[Show abstract][Hide abstract] ABSTRACT: Chatter vibration deteriorates the machining accuracy and shortens the tool life. Thus, In-process monitoring methods have been proposed by using additional sensors such as dynamometers and acceleration sensors. However, introducing additional sensors leads to high cost and reduction of machine-tool stiffness. To solve these problems, a sensor-less monitoring method applying the disturbance observer theory was proposed in our previous research which has experimentally shown that chatter vibration can be detected only from the servo information in milling. For further demand, because chatter vibration can be classified into self-excited vibration and forced vibration, an assorted detection method is required. In this study, we propose a novel frequency analysis method combining moving variance and moving Fourier transform algorithms, which can obtain the power spectrum density of each chatter vibration type separately with small computational load. The validity of the proposed method is evaluated through milling tests with different rotational speeds.
No preview · Article · Jan 2015 · Journal of the Japan Society for Precision Engineering
[Show abstract][Hide abstract] ABSTRACT: This paper deals with axial ultrasonic vibration-assisted machining with workpiece bending. It was proposed as a novel machining method for the reduction of the chippings at the machined holes during micro through-hole drilling of chemically strengthened glass. In micro through-hole drilling of chemically strengthened glass, machining accuracy and efficiency tend to be low because the material's high hardness and brittleness cause rapid tool wear and large chippings at the inlet and outlet of the machined holes. In order to machine small holes with high accuracy, the reduction of the tensile stress that causes large chippings at the outlet of the machined holes is an issue of primary importance that deserves investigation. In the proposed machining method, the glass plate is bent slightly to be convex upward through the application of a compressive stress at the posterior surface of chemically strengthened glass, with a specially designed jig. Using this proposed method that can reduce the tensile stress, the chipping size at the outlet of the machined holes was successfully reduced with applied compressive stress values of 38.9 MPa. In conclusion, it has been clear that the axial ultrasonic vibration-assisted machining with workpiece bending has the potential for achieving high-precision and high-efficiency machining for chemically strengthened glass.
Preview · Article · Jan 2015 · Journal of Advanced Mechanical Design Systems and Manufacturing
[Show abstract][Hide abstract] ABSTRACT: Electro adhesive gel (EAG) shows a unique characteristic changing its surface adhesive property according to the applied electric field, which is named as electro-adhesive effect (EA effect). Our recent research results indicated that the EAG is feasible to be applied to fixture, clutch, damping, and brake mechanisms. While the performance of EAG has been dramatically enhanced over the past decade, the individual difference caused by the production process has been still problem. In other word, adhesive area of EAGs under the same electric filed is non-uniform and uncontrollable. In this research, to ensure stable EA effect, an electro-adhesive surface (EAS) applying 3-dimensional micro structure alternative to the EAG is proposed. The proposed EAS is composed of the 3-D micro-mesh structure fabricated by the photolithography and silicone gel. The prototype of the EAS was developed and its characteristic was experimentally investigated by microscopic observation and shear test. The result obviously shows that the EAS generates larger adhesive force in higher intensity of electric filed. Furthermore, a uniform and regular pattern of adhesion area is clearly observed. From these results, EAS has a strong possibility to improve the stability of EA effect and enhance the performance of its application devices.
Preview · Article · Jan 2015 · Journal of the Japan Society for Precision Engineering
[Show abstract][Hide abstract] ABSTRACT: It is important to take countermeasures against tool collision to avoid serious damage to the machine tool. Though rapid collision detection is needed, the introduction of additional sensors to a machine tool is not desirable owing to cost, machine-tool stiffness, and failure rate considerations. In this study, a sensor-less tool collision detection method is proposed on the basis of the disturbance observer theory. It only uses the servo information of a ball-screw-driven stage and does not require external sensors. The proposed method successfully detects the collision between a tool and a workpiece in less than 3 ms with a feed rate of 50 m/min.
[Show abstract][Hide abstract] ABSTRACT: This paper addresses axial ultrasonic-vibration-assisted helical milling of chemically strengthened glass. Axial ultrasonic vibration was applied to a milling tool using an ultrasonic device to obtain longer tool life, higher machining accuracies, and improved cutting efficiency. The effects of ultrasonic vibration on microscale, through-hole helical milling of chemically strengthened glass were investigated and the impact of three cutting parameters (feed velocity, pitch per revolution, rotation speed) on the characteristics of surface chippings was evaluated. The results of the cutting tests clearly showed a reduction of chipping size and an improvement in tool life by using the proposed manufacturing method. Finally, optimum cutting conditions were proposed based on the results of the milling tests.
[Show abstract][Hide abstract] ABSTRACT: To realize ultimately efficient signal processing, it is necessary to replace electrical signal processing circuits with optical ones. The optical micro-resonator, which localizes light at a certain spot, is an essential component in optical signal processing. Single-crystal calcium fluoride (CaF2) is the most suitable material for a highly efficient optical micro-resonator. The CaF2 resonator can only be manufactured by ultra-precision machining processes, because its crystal anisotropy does not allow the application of chemical etching. However, the optical micro-resonator's performance depends definitely on the surface integrity.
No preview · Article · Nov 2014 · Precision Engineering
[Show abstract][Hide abstract] ABSTRACT: Carbon fiber reinforced plastics (CFRP) have been used for various applications such as aerospace, automobiles, and sporting goods due to their superior properties, and the demand for through-hole drilling of CFRP is increasing. A novel hybrid helical milling technique applying ultrasonic vibration and cryogenic tool cooling method is proposed in this paper, as an effective machining method for CFRP. To investigate the effects of ultrasonic-vibration-assisted machining and cryogenic tool cooling method, cutting performance evaluations based on thrust force, machining accuracy, and tool wear were conducted in this study. The results of the cutting tests clearly indicated that the proposed cutting method provides reductions in thrust force, and suppresses delamination at the machined surface.
[Show abstract][Hide abstract] ABSTRACT: In current practice, the buffing process required to finish the surface of mechanical parts is performed manually by a technical expert as it requires a delicate adjustment of the buffing force. The automation of this process is desirable in an effort to shorten the process time and reduce labor cost. To automate the buffing process, a beneficial process monitoring technique that supervises the buffing tool conditions in real time must be developed. From a practical perspective, an observer technique that does not require additional sensors would be most suitable for monitoring the tool operating condition. The authors propose a technique that estimates the buffing tool stiffness based on a disturbance observer. The validity of the proposed method as a buffing tool condition monitoring technique is verified through numerical simulations and experiments.
[Show abstract][Hide abstract] ABSTRACT: Disturbance observation is a sensorless process monitoring technique that has not yet been applied to the monitoring of tool collision in the use of machine tools. This paper presents a monitoring algorithm that detects collisions that involve the breakage of drills through observation of the disturbance force change rate. A comprehensive experimental study of diverse operator-induced collisions was conducted to analyze the collision detection potential of the disturbance observer. It was found that collision monitoring by the disturbance observer is more sensitive and responsive than that using a sensorless jerk observer.
No preview · Article · Aug 2014 · CIRP Journal of Manufacturing Science and Technology
[Show abstract][Hide abstract] ABSTRACT: Tool fracture detection is important to avoid tool breakage and ensure cutting accuracy. However, conventional tool condition monitoring methods use additional sensors that are expensive, increase the failure rate, and reduce the machine-tool stiffness. This study proposes a novel in-process method to detect tool fracture based on disturbance observer theory. It uses only servo information in a ballscrew-driven stage control system. Furthermore, a rotational digital filter is developed and applied to drilling tests to enhance the detection accuracy. Tool fracture is successfully detected without any external sensors by the proposed method.
No preview · Article · Apr 2014 · CIRP Journal of Manufacturing Science and Technology
[Show abstract][Hide abstract] ABSTRACT: To achieve maximally efficient signal processing, an electrical signal processing circuit needs to be replaced withan optical one. Optical micro-resonators, storing light at certain spots, areessential for optical signal processing. Single-crystal Calcium Fluoride (CaF2) is the most suitable materialfor highly efficient optical micro-resonators, and a resonator made of CaF2can be manufactured by ultra-precision machining. However, the performance of such optical micro-resonators depends on its surface integrity.
In this study,therelation between the crystal anisotropy and surface integrity after ultra-precision cutting was investigated. The most difficult point in the cylindrical turning of a crystalline material is thatthe crystalline plane and the cutting direction constantly vary. We analyzed crack initiation and surface integrity of the entiremachined surface from the perspective of slip system and cleavage. Subsurface damage was also observed by using the TEM and X-ray analyzersfor more efficient manufacturing of optical micro-resonators.
[Show abstract][Hide abstract] ABSTRACT: The suppression of chatter vibration is required to enhance the machined surface quality and to increase tool life. In this study, a new, conceptually active approach for chatter suppression in machining is proposed. The hybrid control method developed by applying sensorless force control with a disturbance observer enables the simultaneous and independent control of the position trajectory and band-limited forces. The proposed method is introduced to the carriage of a prototype desktop-sized turning machine, and the ability to suppress chatter is evaluated by end-face cutting tests. The results demonstrate that actively controlling a band-limited force leads to the avoidance of chatter.
No preview · Article · Jan 2014 · CIRP Annals - Manufacturing Technology
[Show abstract][Hide abstract] ABSTRACT: The on-machine measurement of a machined workpiece has numerous advantages such as reducing the man-hours and operator-dependent measurement errors, and improving work-efficiency. In this paper, we propose an external sensor-less on-machine measurement system by only utilizing internal servo information in order to add a workpiece-measurement function to ultra-precision machine tools without increasing the cost. The cutting force observer developed for monitoring the process has the ability to estimate the external force with a resolution of 0.05 N based on servo information. Sensor-less contact force control with the cutting force observer is applied to an on-machine measurement system. To evaluate the performance, several tests are carried out. The results show that the proposed on-machine measurement system is effective at measuring the accuracy of the machined form.
[Show abstract][Hide abstract] ABSTRACT: The buffing process for finishing an automobile's body is still done manually, and the final surface quality of the body depends on the skill and technique of the worker. To automate buffing, not only tool path control but also precise and fast force control is required. In this study, a novel methodology based on the sensor-less force control technique and the quarry matrix capable of the mode decoupling is proposed for a parallel mechanism polishing machine to control x–y trajectory, tool posture, and polishing force in z-direction, and its validity for automated buffing is verified.
[Show abstract][Hide abstract] ABSTRACT: This investigation reports the physical characteristics of
electrorheological (ER) gels, which are a type of functional material
having controlled surface friction. We previously developed slip
clutches using ER gels sandwiched between electrodes, and verified their
responses and controllability. We newly report the temperature and shear
rate characteristics of ER gel in this study because the input and
output electrodes of the clutch continuously slip past each other. While
the temperature of ER gels increased when energized, the shear stress
hardly changed. Instead, wearing and adaptation to the electrode affect
the property. The shear rate hardly affected the shear stress in the
high-shear-rate region. Conversely, the shear stress depended on the
shear rate in the lower region.
Full-text · Article · Feb 2013 · Journal of Physics Conference Series
[Show abstract][Hide abstract] ABSTRACT: With the development of virtual reality (VR) technology, many applications require force display systems. However, existing products are not widely used owing to their inconvenient fit and the possibility that the devices may inflict injuries on the user. This study aims to develop a VR suit that can display a force to each joint. The force is generated by a functional material, electrorheological (ER) gel. In this paper, we discuss the development of a device that attaches to the arm, and evaluate the usefulness of the ER gel wearable brake.