Three-dimensional finite-time guidance laws are proposed in this paper. Differing from the traditional approach that considers homing guidance problems as two identical and perpendicular channels, guidance laws proposed in this paper employ the coupled three-dimensional engagement dynamics to improve the guidance precision. A new reaching law is adopted to guarantee guidance laws continuous, which eliminates the chattering phenomenon caused by discontinuous terms. Moreover, the guidance law accelerates the convergence rate of closed-loop systems and avoids the singularity. Afterwards, the paper discusses the problem that the upper bound of the lumped uncertainty including the target information is unavailable. Therefore, to deal with this problem, another adaptive guidance law is presented, which can also guarantee the finite-time convergence of guidance systems. Numerical simulations have demonstrated that the two guidance laws have effective performance and outperform traditional terminal sliding mode guidance laws.
To determine the planar motion of a 6-DOF precision stage, a measurement system based on three Hall sensors is adopted to obtain the X, Y, Rz motions of the stage. The machining and assembly errors in the actual mechanical system, which are difficult to measure directly, cause the parameters in the model of the Hall measurement system to deviate from their designed values. Additionally, the vertical movement of the stage will render the measurement model nonlinear. To guarantee the accuracy of the measurement, the parameters in the measurement model should be estimated and the nonlinearity compensated. In this paper, a novel approach based on self-adaptive hybrid TLBO (teaching-learning-based-optimization) is proposed to estimate the parameters in the Hall measurement model. The influences of zero deviations and vertical movements on the measurement accuracy are analyzed and compensated. The effectiveness of the proposed method is validated by experimental results obtained on a 6-DOF precision stage. Thanks to parameter estimation and calibration, the measurement error of the Hall sensor array is reduced to 6 micrometers.
A new calibration procedure was proposed for strap down inertial measurement unit (IMU) in a body reference frame which was independent of the turntable. The proposed methodology required no precise mechanical platform for the calibration of the accelerometer and the rate-gyros. Error models of IMU parameters were derived from the physical characteristic of three accelerometers and three rate gyros, which taked into account the sensor axis misalignments, scale factor, gyro constant drifts, and biases inherent in the manufacture of IMU. Least squares method was used to evaluate the accelerometers and gyros model coefficients. According to the experimental results, we can see that the proposed algorithms is less affected by turntable's accuracy, process is simplified.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.