In the semiconductor manufacturing industry, efficient operation of wafer transfer robots has a direct impact on productivity and product quality. Ball screw misalignment anomalies are a critical factor affecting precision transport of robots. Early diagnosis of these anomalies is essential to maintaining system efficiency. This study proposed a method to effectively diagnose ball screw misalignment anomalies using 1D-CNN and 2D-CNN models. This method mainly uses binary classification to distinguish between normal and abnormal states. Additionally, explainable artificial intelligence (XAI) technology was applied to interpret diagnostic decisions of the two deep learning models, allowing users to convince prediction results of the AI model. This study was based on data collected through acceleration sensors and torque sensors. It compared accuracies of 1D-CNN and 2D-CNN models. It presents a method to explain the model"s predictions through XAI. Experimental results showed that the proposed method could diagnose ball screw misalignment anomalies with high accuracy. This is expected to contribute to the establishment of reliable abnormality diagnosis and preventive maintenance strategies in industrial sites.
In this paper, we introduce a recently built screwing robotic system for the bolt assembly of elastic steel plates. The screwing robotic system consists of two vision cameras (having narrow and wide fields of view), a collaborative robot with a 10 kg payload, and a motorized screw drill with a pneumatic bolt supplier. Due to the elasticity of the steel plates, they tend to statically deform and dynamically vibrate during tasks under the conventional setting of automatic screwing, often resulting in screw failures. Thus, we designed a compliant connector device to be attached between the robot end-effector and screw drill that can absorb vibration and shock during the bolt assembly to improve the screwing quality and success rate of the bolt assembly. Upon adopting this screwing robotic system with the compliant connector, the success rate of the bolt assembly was improved from 56% to 100%.
This study aimed to determine effects of ultrasonic nanocrystal surface modification (UNSM) as a surface pre-process on performance and surface characteristics of bolts manufactured through a screw rolling process. Surface roughness, hardness, and microstructural changes after UNSM treatment were examined. Results showed no significant defects such as cracks in all fabricated samples after screw rolling of bolt pre-processed by UNSM treatment. In addition, material flow was continuously maintained without disconnection. After UNSM treatment, surface roughness was improved for both body and screw parts. The surface roughness of the UNSM treated screw part was improved the most at 43%. Hardness test showed the greatest increase in hardness on the surface hit by the UNSM ball tip, with hardness improved to about 500 μm deep from the surface. The hardness at the screw part was the highest at 471 HV, which was attributed to the fact that grains near the surface were deformed and refined by UNSM treatment followed by screw rolling. Near the surface of the screw, refined grains and high dislocation density were clearly observed by EBSD mapping. These results confirm that UNSM treatment before screw rolling is effective in improving mechanical properties of screw rolled bolts.
The study focused on the development of the CAM system restricted to the fabrication of variable pitch screws by using turning centers. To develop the dedicated CAM system at a low cost, open source programming language was used as much as possible. A commercially available 3D-CAD system was used to model variable pitch screws. The edge data of the variable pitch screw was extracted from 3D-CAD data of the variable pitch screw, and then a number of the edge data were copied by the amount of feed in the longitudinal direction of the screw to make a cutter path. The successive cutter path was repeatedly generated by reducing the size of the edge data. The advantage of this method of generating the cutter path is very simple and easy to use, compared with the conventional CAM systems. During the cutter path generation, the system can detect the collision between the cutting tool and the workpiece. As a result, the validity of the developed CAM system for variable pitch screws fabrication was confirmed from several examples of the cutter path generation.
For esthetic and functional implant prosthesis, the retention type of implant should be selected considering the oral condition of the patient. However, studies on the differences in biomechanical stability of the retention type are scarce. The purpose of this study was to evaluate the biomechanical effects between retention types in implant prosthesis using 3- dimensional finite element analysis. Two retention types (Cement and Screw-Cement) were considered for the implant complex consisting of the ComOcta abutment, SS type implant, and screw all implanted in the mandibular segment of the bone block. Static finite element analysis was performed under external loads of 200 N (Vertical Load) and 100 N (Oblique Load) to each cusp tip. We measured the von-Mises stress fields in abutment and implant, and the principal strain distribution of the mandibular bone to evaluate the risk of fatigue failure in the bone. Separations between the implant components were also evaluated. The results show that with the ComOcta abutment Cement type provided enhanced stability.
In this study, a super-twisting sliding mode controller with a non-linear disturbance observer for a ball-screw servo system was designed to obtain a precise motion and fast convergent control performance. Unknown dynamics of the servo system were approximated into pre-assumed diagonal constants for rapid controller design in the real industry to avoid expensive and time consuming experimental identification process. Moreover, uncertainties due to nonlinear friction, axis misalignment and dead zone were estimated by a nonlinear disturbance observer, which is combined with the designed super-twisting controller. The designed controller and observer systems were applied to the 2-axis ball screw servo system to verify the efficacy of the proposed control system via simulation and experiment.
The ball screw can be included in steering systems, the brake system, seat moving devices, and transmission systems of vehicles. Performance of the ball screw in these systems plays a key role in delivering agile and accurate power transmission. The purpose of this study is to improve performance by focusing on performance of the ball screw, by applying various conditions based on a design factor in the circulation system. The selected single design factor is to apply the cycloid curve to a circulation area. The circulation part to obtain a cycloid curve with highest performance, can have the smoothest ball flow. In addition, based on results, we intend to reduce failure cost that may be incurred in developing future ball screws for automobiles, and to establish databases that can be applied to developed products by deriving optimal shape.
This paper investigates the relationship between the preload level of a ball screw drive and the detected natural frequency of the system in an axial direction. A dynamic model to study the preload variation of the system is derived, and then a preload feature is proposed for extracting preload conditions based on the detected natural frequency of the system. A modified double-nut ball screw drive system with adjustable preload level is constructed. This is for the purpose of experimental verification. An accelerometer is attached to the ball screw nuts of the drive system to acquire vibration signals. The signals are analyzed to obtain the natural frequency of the ball screw drive system in an axial direction. By investigating the variation of the detected natural frequency, it is shown that the preload level can be diagnosed by the proposed preload feature. Both the experiment results and mathematical model show a direct correlation between the natural frequency and preload levels. Natural frequency increases when the preload level increases. This study provides a method to monitor the preload of a ball screw system which can be used as an indicator of the health status of the drive system.
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The parallel slider system can be configured as a parallel robot by combining with other link devices. Therefore, the degree of positioning of the parallel slider would have considerable influence on the smooth operation of the parallel robot. In order to examine the degree of positioning of each slider, the following trajectory is equally presented, and the possibility of tracking the slider trajectory examined by application of the PD and PND control. From the experimental results, the dynamic characteristics of the slider show different responses to differing equivalent frictional forces acting on the slider. The PND control can make the rise time shorter than the PD control, and the PND control and PD control can smoothly follow the same trajectory given to each slider. It is therefore anticipated that the PND control and the PD control could be successfully implemented to follow the trajectory of a parallel robot based on a parallel slider system. It would then be necessary to fabricate slider experimental equipment capable of generating torque of sufficient magnitude to successfully reduce the trajectory error of the slider.
The recent development of core techniques in the IT industry can be summarized as a technical advancement for safety and convenience, and mechanical technology for being “eco-friendly” and lightweight. Under these circumstances, research of lightweight material has become attractive. In this study, CFRP (Carbon Fiber Reinforced Plastic) laminate specimens are subjected to a tensile test using the UTM(Universal Testing Machine, AG-IS 100 kN) to estimate their mechanical properties in terms of the Hole machining impact evaluation. The FEM (Finite Elements Method) analysis method is applied and the material properties obtained from basic experiments such as the Tensile test, the compressive test, and the shear test. CFRP materials properties from a previous study, as well as a finite element analysis program for Hole machining CFRP was compared with the experiments.
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