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  • Open access
  • 39 Reads
Predictivity of CNC machine-induced vibrations on inter-story floors based on coupled experimental-numerical investigations

Machine-induced vibrations and their control represent, for several reasons, a crucial design issue for industrial buildings. A special attention is required, at the early design stage, for the structural and dynamic performance assessment of the load-bearing members, given that they should be optimally withstand potentially severe machinery operations. To this aim, however, the knowledge of the input vibration source is crucial, in the same way of a reliable description of the structural system to verify. In this paper, a case-study eyewear factory built in Italy during 2019 is investigated. The poor customer / designer communication on the final equipment of the factory resulted in various non-isolated Computer Numerical Control (CNC) vertical machinery centers mounted on the inter-story floor, that started to suffer for pronounced resonance issues. Following the past experience, the paper investigates the efficiency of a coupled experimental-numerical method for generalized predictive and characterization studies. Based on on-site experiments, the most unfavorable machine-induced vibration source and operational conditions are first described, among the available working processes. The experimental outcomes are then assessed and integrated with the support of Finite Element (FE) numerical simulations, to explore the resonance performance of the floor. The predictability of marked resonance issues is thus analyzed, with respect to the reference performance indicators.

  • Open access
  • 41 Reads
Anlysis of Ball Screw Pair Jamming Mechanism in EMAs
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With the development of the more electric aircraft (MEA), electromechanical actuator (EMA) are gradually becoming a popular alternative to traditional hydraulic actuators. The electromechanical actuator (EMA) brings weight reduction, improved maintenance and becomes more feasible to realize integrated control for flight control executive system. However, regarding the utilization of EMAs in the primary control surface, the major concern is the mechanical jamming, which is critical and potentially disastrous for aircraft. The mechanical jamming mainly refers to the ball screw pair which is widely used in EMAs. Therefore, the jamming mechanism and jam-tolerant capability of the ball screw transmissions are researched and discussed in this paper to find the fact that causes jam failure.

Firstly, the structure composition and working principle of the ball screw pair is introduced, and gives possible reasons for jam phenomenon. Then the kinetic and dynamic model is built when the ball moves in the raceway and through the inverter considering elastic-plastic contact deformation. Meanwhile the load distribution and deformation compatibility between adjacent balls are considered, as the viscous damping force and centrifugal force are also contained. Accordingly, the friction self-locking condition for the ball in the raceway is proposed, which could be seen as a criterion for the occurrence of the jam. The variation of contact angle and friction coefficient in different operating conditions of load, velocity and frequency are analyzed and compared. The structure parameters as altitude intercept between the raceway and inverter, the returning spiral curve are also discussed. Finally, optimized design and improved operating parameters are suggested from the view of reducing the probability of jamming.

  • Open access
  • 39 Reads
Online unbalanced vibration suppression of a flexible rotor supported by active magnetic bearing

A rotor supported by active magnetic bearing could offer various advantages over conventional bearings, but due to their limited force capacity, and moreover, the rotor has a mass unbalance. The vibration originated from the rotor's unbalance mass impacts on the dynamic properties, and even cause major accidents. Large unbalance is typically responsible for high energy vibrations and the consequent decrease in machine life. So unbalance compensation on the rotating machine is necessary, especially for the high speed flexible rotor. While the unbalanced vibration suppression need shutdown and phase sensor. To solve the problem of online suppress the unbalance vibration without adding additional hardware equipment in active magnetic bearing-rotor system, this paper proposes an online unbalanced vibration suppression based on the cross-correlation method and influence coefficient method. The amplitude and phase are achieved by cross-correlation method and feedback tracking control method in steady state. The active magnetic bearings are used to simulate the unbalanced excitation, the compensation amplitude of unbalance vibration signal are calculated by the influence coefficient method. The method was found to be effective and practical. An online test program was performed on a flexible rotor based on based on the Matlab/Simulink and a dSPACE real time system, which showed that the unbalanced vibration suppression could satisfy the performance and required precision of rotating machine, and the amplitude of the fundamental frequency of the unbalance vibration is significantly reduced.

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