The undesired synchronous vibration due to rotor mass imbalance is a main disturbance source in all rotating machinery including active magnetic bearing (AMB)-rotor systems. In the AMB-rotor system, imbalance compensation, which causes the AMB actuators to spin a rotor about its geometric axis, and automation balancing, which spins a rotor about its inertial axis, are two kinds of common control aim for the rotor imbalance control. In this study, the internal relation between the imbalance compensation and the automation balancing is analyzed and a uniform control method is proposed. With the identical control algorithm, the proposed control method can realize the automation balancing or the imbalance compensation, respectively, by switching the controller’s junction position in the original control loop. The proposed control method does not depend on the dynamic plant model, because its algorithm is based on the real-time identification for the Fourier coefficient of the rotor imbalance disturbance. In this paper, the process of identification algorithm is given in detail and all the possible junction forms of the controller are illustrated. By the simulations, the identification performances of the control algorithm are compared in the conditions with three variable factors, including the signal noise ratio (SNR), the imbalance phase and the identification delay time. The noise level has considerable influence on the identification precision, but the imbalance phase has little. To prolong the identification delay time will be of benefit to improve the identification precision but slow down the identification process. Experiments, which are carried out on an AMB-rigid rotor test rig, indicate that by switching the junction position of the controller in control loop, both kinds of rotor imbalance control can achieve the good effectiveness.
Advances in quantum computers pose great threats on the currently used public key cryptographic algorithms such as RSA and ECC. As a promising candidate secure against attackers equipped with quantum computational power, multivariate public key cryptosystems (MPKCs) have attracted increasing attention in recently years. Unfortunately, the existing MPKCs can only be used as a multivariate signature scheme, and it remains unknown how to construct an efficient MPKC enabling secure encryption. Furthermore, some multivariate signature schemes have been shown insecure in recent years, and it is also not trivial to build MPKC which can serve as a secure signature scheme. By employing the basic MQ-trapdoors, this paper proposes a novel MPKC and shows how it can be used as a multivariate signature scheme and a multivariate encryption scheme, respectively. The goal is achieved by incorporating our new hash authentication techniques and some modification methods such as the Shamir's minus method. Thorough analysis shows that our schemes are secure and efficient. Our MPKC gives a positive response to the challenges in multivariate public key cryptography.
This study proposes a novel active screw-drive in-pipe robot that can adapt the circular-type and square-type pipe structure. The pipe robot is composed of four driving units and a wall-pressing suspension mechanism. Each driving unit contains a motor, a transmission train, and an electromagnetic brake, which is for switching the motion transmission route. DC motors drive the helical wheels, and the incline angle of the helical wheels can be adjusted by using the electromagnetic brake. The wheels of the driving unit exhibit rolling and steering motion. Thus, the robot is capable of translation movements, rotation movements, and screw motions with respect to the axis of the pipe according to the different positions of the helical wheels. The robot can avoid obstacles by using the rotation and screw modes. Moreover, the wallpressing mechanism is analyzed and modified, and a criteria for entering a reduction pipe reducer are derived for the double scissor-like suspension mechanism. We also analyze the robot motion in curved pipes in two typical postures. The simulation experiments reveal the relationship between the translation and rotation motion of the robot and indicates that the steering angle of the wheels can be regarded as a regulator to adjust the movement speed of the robot aside from tuning the posture of the robot. Elbow experiments are conducted to verify the effectiveness of the motion strategy. The robot can be adapted for both circular and square tube pipes without any change in its structure due to the special configuration.
The evolutionary cryptosystem is a new cryptosystem. This paper studies its security level resisting against differential cryptanalysis. It is shown that the evolutionary cryptosystem possesses higher resistance than its initial fixed cryptosystem against differential cryptanalysis. On the basis of the relationship among the data complexity, the bit advantage and the success rate of differential cryptanalysis, it is proven that more data is needed for attacking the evolutionary cryptosystem when the bit advantage and success rate are identical. Moreover, it is shown that the time complexity for attacking the evolutionary cryptosystem is higher than that of differential attacking its initial fixed cryptosystem with the same amount of plaintext-ciphertext pairs. The research indicates that the evolutionary cryptosystem is more robust than its initial fixed cryptosystem against differential cryptanalysis.
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