1 Background: The emerging 2019 novel coronavirus (2019-nCoV) has pushed several 2 countries into state of emergency all over the world. The possible transmission of

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In this article, a novel sliding mode tracking control scheme for vehicle active suspension systems with matched and mismatched uncertainties is proposed based on super-twisting concept. In order to stabilize suspension deflection motion to the desired trajectory in finite time, a finite-time sliding mode controller is designed. Specifically, a novel trajectory function is proposed to adjust the suspension performances (e.g. ride comfort, tire dynamic load and suspension deflection). Compared with the first-order sliding mode control method, the proposed tracking control scheme can effectively improve the ride comfort and ensure the suspension deflection constraint. The control scheme requires only the suspension deflection and acceleration feedback and thus is easy to implement. The uncertainties of the active suspension system are considered as a total disturbance term which can be estimated online, and the estimated error can become a vanishing term in finite time using an extended super-twisting disturbance observer. Finally, the proposed control algorithm is applied to a quarter-car active suspension model, and numerical and experimental results are provided to show the merits and effectiveness of the proposed control scheme.

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The inconvenient loading and unloading of a long and heavy drill pipe gives rise to the difficulty in measuring the contour parameters of its threads at both ends. To solve this problem, in this paper we take the SCK230 drill pipe thread-repairing machine tool as a carrier to design and achieve a fast and on-machine measuring system based on a laser probe. This system drives a laser displacement sensor to acquire the contour data of a certain axial section of the thread by using the servo function of a CNC machine tool. To correct the sensor’s measurement errors caused by the measuring point inclination angle, an inclination error model is built to compensate data in real time. To better suppress random error interference and ensure real contour information, a new wavelet threshold function is proposed to process data through the wavelet threshold denoising. Discrete data after denoising is segmented according to the geometrical characteristics of the drill pipe thread, and the regression model of the contour data in each section is fitted by using the method of weighted total least squares (WTLS). Then, the thread parameters are calculated in real time to judge the processing quality. Inclination error experiments show that the proposed compensation model is accurate and effective, and it can improve the data acquisition accuracy of a sensor. Simulation results indicate that the improved threshold function is of better continuity and self-adaptability, which makes sure that denoising effects are guaranteed, and, meanwhile, the complete elimination of real data distorted in random errors is avoided. Additionally, NC50 thread-testing experiments show that the proposed on-machine measuring system can complete the measurement of a 25 mm thread in 7.8 s, with a measurement accuracy of ±8 μm and repeatability limit ≤ 4 μm (high repeatability), and hence the accuracy and efficiency of measurement are both improved.