With the development of robot technology, automatic assembly technology based on industrial robots has been greatly applied. Considering the high-precision automatic grasping of heterogeneous products, robot grasping detection technology is put forward. Although the current method of using camera is relatively mature, it is greatly affected by the ambient light and the surface material of the object, resulting in the limited versatility. Since the 3D structured light method based on the laser scanning galvanometer has the characteristics of high speed and high accuracy, strong environmental adaptability and weak influence by the surface material of the object, the structured light equipment using laser scanning galvanometer was installed at the end of the robot to realize the grasping detection of the products. Through hand eye calibration, point cloud acquisition, point cloud processing, point cloud matching and other links, the point cloud collection and accurate matching of local features are realized. The experiment shows that the grasping detection accuracy is less than 0.32mm. It can not only achieve accurate grasping of different products, but also has the characteristics of strong adaptability to surface materials, environmental lighting, and high accuracy.
Ultrasonic elliptical vibration cutting (UEVC) is attracting much attention in ultra-precision machining of brittle materials as it was found be able to increase the critical depth of cut (dc) of brittle materials. However, there are few studies on the prediction of dc for UEVC of brittle materials. In this study, a predictive model was developed for the prediction of dc in microgroove plunge-cutting with respect to several factors, including the distance from transient surface to target surface (DTSTS), the actual undeformed chip thickness (UCT), the critical UCT (tc) and crack length (Cm). Experiments on plunge-cutting of KDP crystal were conducted. Results showed the predicted dc matches well with the experimental ones.
Potassium dihydrogen phosphate (KDP) is a type of nonlinear optical crystal material. To Inhibit the transverse stimulated Raman scattering of laser beam and then enhance the optical performance of the optics, the edges of the large-sized KDP crystal needs to be removed to form chamfered faces with high surface quality (RMS<5 nm). However, as the depth of cut (DOC) of fly cutting is usually several, its machining efficiency is too low to be accepted for chamfering of the KDP crystal as the amount of materials to be removed is in the order of millimeter. This paper proposes a novel hybrid machining method, which combines precision grinding with fly cutting, for crackless and high efficiency chamfer of KDP crystal. A specialized machine tool, which adopts aerostatic bearing linear slide and aerostatic bearing spindle, was developed for chamfer of the KDP crystal. The aerostatic bearing linear slide consists of an aerostatic bearing guide with linearity of 0.1 μm/100mm and a linear motor to achieve linear feeding with high precision and high dynamic performance. The vertical spindle consists of an aerostatic bearing spindle with the rotation accuracy (axial) of 0.05 microns and Fork type flexible connection precision driving mechanism. The machining experiment on flying and grinding was carried out, the optimize machining parameters was gained by a series of experiment. Surface roughness of 2.4 nm has been obtained. The machining efficiency can be improved by six times using the combined method to produce the same machined surface quality.
KEYWORDS: Spindles, Control systems, Feedback signals, Crystals, Servomechanisms, Signal detection, Surface roughness, Data transmission, Analog electronics, Radium
In the paper, The problem about stability in low speed of the air bearing stage driven by a linear motor was investigated to satisfy the ultra-precision fly-cutting of KDP crystals. First of all, the modal of the servo system with the permanent magnet synchronous linear motor was analyzed. In the system of the low speed linear motor driver, the main interferences came from cutting force f Load , the friction of chain and cable f n , the ripple thrust f ripp , and motor friction f fric. Secondly, the factors about low speed stability were analyzed: the key to improve the system’s stability is to control the interference forces; Another important issue is to develop an advanced control strategy. Thirdly, some optimization experiments about low speed stability were developed as follows: the influence of feedback element, the influence of Power converter, speed optimization of damping feed-forward control, speed optimization of Spindle vibration, speed optimization based on disturbance observer. Finally the experimental results: the lowest speed of the stage can reach 0.2 mm/min; the error of the speed is less than 0.06mm/min when running between 1mm/min and 10 mm/min. The cutting experiment of KDP with the size of 330mm × 330mm × 10mm, was proceeded on the Fly-cutting machine by the feeding velocity of 1mm/min. The results about the surface roughness show that the value of Rq is 3.3nm and the value of Ra is 2.6nm.
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