Purpose The purpose of this paper is to carry out an assembly tolerance analysis by means of a combined Jacobian model and skin model shape. The former is based on small displacements modeling of points using 6 × 6 transformation matrices of open kinematic chains in robotics. The latter easily models toleranced features with all kinds of geometric deviations. Design/methodology/approach This paper presents the procedure of performing tolerance analysis by means of the Jacobian model and skin model shape for assemblies. The point cloud-based discrete representative is able to model the actual toleranced surfaces instead of the ideal or associated ones in an assembly, which brings the simulation tools closer to reality. Findings The proposed method has the advantage of skin model shape which is suitable for geometric tolerances management along the product life cycle and contact analysis of kinematic small variations, as well as, with the Jacobian, enabling transformation of locally expressed parts deviations to globally expressed functional requirements. The result of the case study shows the accuracy of the method. Research limitations/implications The proposed approach has not been developed fully; other functional features such as the pyramid are still ongoing challenges. Practical implications It is an effective method for supporting design, manufacturing and inspection by providing a quantitative analysis of the effects of multi-tolerances on the final functional key characteristics and for predicting the quality level. Originality/value The paper is original in taking advantages of both Jacobian model and skin model shape to consider all geometric tolerances in assembly.

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A 20 nanometer palladium-silver (Pd/Ag) ultra-thin film was used for hydrogen gas sensing. The atomic ratio of Pd: Ag was 3:1, the thin film was evaporated on the optical glass, the Pd/Ag alloy could increase the life and provide the stability of the sensing film. The artificial neutral network was used for processing the data collected from the optical fiber bundle hydrogen sensor, which could enhance the measuring accuracy, at the same time, the intrinsic and extrinsic influences were eliminated mainly. Experimental results and numerical simulation show the training method available, a linear precision of 0. 1% for the optical hydrogen sensor is achieved.Hydrogen gas detection in different measuring environments has recently become a very important problem [1] , lots of efforts have been made to develop high-performance hydrogen sensors with safety and longer life, optical sensors and especially fiber optic sensor technology provide opportunities for applications of optical sensors. Most of the optical fiber sensors use palladium (Pd) film as transducer to detect the concentration of hydrogen. Nonetheless, although pure palladium sensors could provide the good hydrogen sensitivity, there are some drawbacks associated with pure palladium. During the process of absorption and adsorption in hydrogen, pure palladium film suffers the embrittlement phenomenon, the morphology of pure palladium undergoes the phase transformations, and the process is irreversible. After several cycle of exposure to hydrogen, the palladium breaks off from the substrate. So in order to overcome the problem, a great of experiment reports introduce other metals to form palladium alloy. The Pd/Ag alloy could overcome the problem of hydrogen embrittlement. So far, Pd/Ag is perhaps the mostly studied alloy for hydrogen sensing [1] . Wang Min fabricated a zigzag-shaped microstructure of Pd-Ag plated on alumina substrate, the sensing performance of the mixed metal film is much better than that of pure palladium film [2] . In this paper we adopt 20 nm Pd 75 Ag 25 ultrathin films evaporated on the float glass substrates in the optical fiber bundle sensor to overcome the well-known problem of hydrogen embrittlement.The optical fiber sensor is affected by the intrinsic and extrinsic influences, so the optical hydrogen sensor has the characteristics of non-linearization in the whole output process. The paper presents a key technology-artificial neural network (ANN) to process the output signal from the sensor probe, ANN enhances the detection accuracy and adjusts the output non-linearity in the hydrogen sensor.The preparation of Pd/Ag alloy membranes is carried out in a commercial magnetron sputtering machine (FJL560) equipped with dc and rf power sources and adjustable substrate stage(with heating capability up to 400 o C) . Fig.1 is a schematic representation of the magnetron sputtering deposition unit. Before actual deposition, pre-sputtering is done Fig.1 Schematic representation of magnetron sputtering deposition system

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Based on the theory of gas molecular absorption spectrum, a transmission type gas cell based on cascaded GRIN lens has been designed. The gas cell is the kernel of the optical fiber gas sensor system. The system performance is relative to rationality of gas cell structure. By using GRIN lens couple in gas cell, we can solve the problems of optical discrete components. We use GRIN lens with pigtail fiber as collimating or focusing lens for transmission type of gas cell. To shorten sensor's size and length, and enhance sensor's sensitivity, we present a method by using cascaded GRIN Lens couples to compose a gas cell. With this method, the optical path length is increased and the detection sensitivity of the gas cell is greatly increased. This transmission type of gas cell based on cascaded GRIN lens couples have been applied to our system of absorption spectrum optical fiber gas sensors. We designed and manufactured a gas cell with cascaded GRIN lens couples. Experimental results show that transmission gas cell based on cascaded GRIN lens couples has a good detecting effect.