Dynamic responses of a 2R manipulator in zero-gravity state excited by ender impacts and base motions

In this paper dynamic responses of a 2R manipulator which operates in zero-gravity state of out-space station are studied, specially considering both the impacts which are applied on its link ender and the base motion excitation. The ender impact and joint impact refer to the forces induced by capturing free-flying target or sudden locked of joint respectively, whereas the base motion excitation of the manipulator refers to the motion of its attached spacecraft. Firstly the governing equations of the 2R manipulator subjected to above two categories of excitations are established. The joint frictions are also included and expressed by Stribeck friction model together with flexible stiffnesses of joints. Numerical simulations of the dynamic model of the system under different cases of impact and base motion excitations show that the dynamic behaviors of the ender of the manipulator are differently described by both transient trajectories in time-domain and amplitude-frequency spectra in frequency domain

Multi-body dynamic simulation and vibration transmission characteristics of dual-rotor system for aeroengine with rubbing coupling faults

In this paper, a dual-rotor system multi-body dynamic model with rubbing coupling faults is established for practical aero-engine. In the model, the rubbing fault simulation method is introduced, the coupling effect between the internal and external rotor is considered. The numerical simulations of rotor vibration are accomplished by the utilization of multi-body dynamic platform, where the simulation model consists of discs unbalances and local rub-impact between discs and casing shells. The time-domain responses, the frequency spectra and the shaft-center trajectories of dual-rotor with different unbalance and different rubbing positions are obtained. The vibration and its transmission characteristics of the inner and outer rotors are calculated. Finally, the simulation results are compared with the measured vibration of a dual rotor tester with rubbing fault. The simulation results are consistent with the measured results, which confirms the feasibility of the established model and the multi-body dynamics simulation method in this paper. The application of multi-body dynamics simulation method in aero-engine can deepen the understanding of the internal operation nature and laws of aero-engine, reduce the repetition of physical tests, greatly improve the efficiency and quality of development, accelerate the research and manufacture process

The calibration of sinusoidal excitation force of piezoelectric ceramic exciter

Piezoelectric ceramic exciter (PCE) have been used to experimentally study on the inherent and damping characteristics of thin-walled structures. However, due to its unknown excitation force level, it can not be applied on more practical cases in which accurate test of dynamic response is urgently needed. This research combines theory with experiment to calibrate sinusoidal excitation force generated by PCE. Firstly, a feedback attenuator was developed to help data acquisition instrument securely capture high-voltage excitation signal applied on PCE by high-voltage piezoelectric amplifier; Secondly, experimental research was conducted using a PCE, of type P-885.10 produced by PI in Germany, as object based on the PCE excitation feedback system to experimentally analyze its major influences on linear excitation capability, consequently a linear excitation equation was proposed to better regulate PCE to produce linear sinusoidal excitation signal; thirdly, a calibration method was proposed to exactly determine the level of sinusoidal excitation force of PCE based on the dynamics model of the cantilever beam excited by PCE, and its calibration principle and calibration process was explained in details. Finally, practicability and effectiveness of this calibration method was demonstrated by a calibration case. The results showed that if both of output signal voltage and excitation frequency meet the linear excitation equation, the concerned sinusoidal excitation force of PCE has a linear relationship with output signal voltage

Modeling and experiments of rotor system with oil-block inside its drum cavity

A few volume of lubricate oil leaking inside the cavity of the rotating drum can cause severe vibrations, which have been observed on-site at aero-engine compressors. This paper proposes a modeling method for the rotor system which is excited by the oil-block. Firstly, the differential equations of the lumped dynamic system of a representative rotor system with a congregated oil-block inside the drum are deduced, in which the external excitation force caused by oil-block is modeled equivalently by both inertial force and sliding frictional force. Then, numerical simulations are carried out to demonstrate the transverse vibration behaviors of the rotor system and both rotating speeds and mass of the oil-block are taken into account. The obtained nonsynchronous whirling vibrations of the rotor system caused by the oil-block are validated by experimental measurements of transverse vibrations of the shaft on a rotor test rig. The results show that, when the rotating speed runs up to the first critical speed, the oil-block will slide along the inner wall of the drum and keep on rotating with the drum delayed in a slowly changing phase angle, and the amplitudes and frequency spectra of the nonsynchronous whirling vibrations of the shaft are found to be sensitive to the oil mass and viscous damping coefficients of the system

Study of vibration characteristics of the short thin cylindrical shells and its experiment

The short thin cylindrical shells are important component used in rotating machinery and its function is to connect shafts and transmitted torque. The kind of components is always destroyed due to vibrational state, so it is necessary to further research on the vibration characteristics. In this paper, the vibration characteristics of short thin cylindrical shells are solved using the beam function method, the transfer matrix method and the finite element method respectively. The solving results of three calculating methods are compared by simulation in the clamped-free and clamped-clamped boundary conditions. The simulation results show that the solving results of the transfer matrix method are close to the results of finite element method, but the deviation of the results of the beam functions method is larger than the other two methods. Furthermore, the experiments of the short thin cylindrical shell in the clamped-free boundary conditions are studied. The experimental results verify that the transfer matrix method and the finite element method are applicability to solve the vibration characteristics of the short thin cylindrical shells

Study on bearing mechanical and thermal characteristic evolvement rules affected by higher ambient temperature

In this paper, the bearing mechanical characteristics and thermal characteristics as it is running under constant speed (2400 r/min) and constant temperature (100 ℃) adopting bearing mechanical-thermal coupling model built on the basis of quasi-statics and elastohydrodynamic lubrication theory are discussed. Among which, the contact deformation between ball and inner/outer ring has same evolution law, besides, the same as the amplitude. Whose curve shape changes in the form of “circular-oblique D”, its amplitude rearches minimum value at 10thd3h between the location of 120° and 270°. The curve shapes belonging to contact angular between ball and inner/outer ring are similar to “circular”. There is opposite trend of them within the range of 90-300°. The amplitude of contact angular between ball and outer ring is the minimum at 10thd3h and 11thd1h. At the same time, the amplitude of that between ball and inner ring is the maximum. The evolution rules of contact stiffness between ball and inner/outer ring are generally consistent, which are similar to “crab”. But the amplitude of that between ball and outer ring is dominant. The maximum value of them occurs at 10thd3 and 11thd1h. The evolvement tendency of node temperatures maintains stable. Thereinto, the temperature of inner ring equals to that of contact location between ball and inner ring, which is the maximum value. It is obvious that ME, MD, MS, MCB, MCR and MOil devote themselves to heat production, the contribution rates of ME, MS, MCB and MCR are 100 %, the contribution rate of MD ranges from 52.6 % to 65.2 %. However, the amplitudes of friction moments have the opposite trend compared to “heat contribution factor”. The expansion amount owing to heat production is dominant in displacement variation and the effect of clearance on displacement can be ignored, whose evolution rules are contrary. The evolution rules of oil film thickness and oil film stiffness between ball and inner/outer ring are alike. Among which, the oil film thickness between ball and outer ring is dominant, its maximum value emerges at 10thd3h. The curve shapes of oil film stiffness between ball and outer/inner ring are oblique “D”, their amplitudes reach the maximum at 11thd1h-11thd3h

DETC2008-49059 RESEARCH ON PARAMETRIC SIMULATION TECHNOLOGY BASED ON COMPLICATED MECHANISM DESIGN

ABSTRACT A new method is proposed, which is the core of parametric simulation based on complicated mechanism design. Furthermore, the connotation of parametric simulation is affirmed and the flow of parametric simulation based on complicated mechanism design is put forward. At last, taking a parallel mechanism as example, the technology of parametric simulation proposed is applied to the simulation study used ADAMS, which consist of analyzing mechanism, parametric modeling, creating GUI, creating menu and parametric simulation. The practice indicates that the method is effectual. INTRODUCTION The mechanism design is key part of the mechanical design. During the mechanism design, the rationality of the structure parameter decides the comprehensive function of the whole mechanical product directly. Therefore, how to select the structure parameter is a very important problem. Usually, these parameters will be confirmed through the calculation of the kinetics and dynamics. For the complicated construction (for example, the space parallel mechanism), these analytic calculation processes are very complicated. And we usually can't acquire ideal solution because it's hard to establish the correct analytic mathematics model. The above questions can be resolved by simulation method effectively. Simulation method is that kinematical model is set up according to mechanism kinematical theory and then researched for confirming reasonable structure parameter. However, during the practical design, the structure parameters of the model usually need to be modified constantly and simulated repeatedly for getting ideal solution. The efficiency of simulation study is decreased by fussy operation. If mechanism model and relative constraint are completely parametric, namely by building parametric model, can improve the efficiency of simulation evidently. In the paper, a new method about mechanism design is proposed, which is the core of parametric simulation. On the basis of it, a 3-TPT parallel mechanism is taken as example, the technology of parametric simulation proposed is applied to the simulation study used ADAMS. THE CONTENT OF PARAMETRIC SIMULATION The parametric simulation includes two meanings: one is the parametric model, that is the totally parameterization of the shape and constraint to make the whole simulation model completely confirming by a few parameters, so that it is easy to reconstruct the model; The other is the whole parametric simulation flow, namely in the process of simulation, dynamically change the value of parametric variables for determining the optimum parameter in the condition of satisfying constraint. It is clear that the parametric simulation model is the precondition of parametric simulation process. For the mechanical product, which has the complicated mechanism, it is usually difficult to assure suitable structure parameter at the first stage. But the application of parametric simulation technology can make the dimension as parameter, further establishing parametric simulation model to carry on simulation research. As a result, the parametric simulation is particularly suitable for the complicated mechanism design

The calibration of sinusoidal excitation force of piezoelectric ceramic exciter

Piezoelectric ceramic exciter (PCE) have been used to experimentally study on the inherent and damping characteristics of thin-walled structures. However, due to its unknown excitation force level, it can not be applied on more practical cases in which accurate test of dynamic response is urgently needed. This research combines theory with experiment to calibrate sinusoidal excitation force generated by PCE. Firstly, a feedback attenuator was developed to help data acquisition instrument securely capture high-voltage excitation signal applied on PCE by high-voltage piezoelectric amplifier; Secondly, experimental research was conducted using a PCE, of type P-885.10 produced by PI in Germany, as object based on the PCE excitation feedback system to experimentally analyze its major influences on linear excitation capability, consequently a linear excitation equation was proposed to better regulate PCE to produce linear sinusoidal excitation signal; thirdly, a calibration method was proposed to exactly determine the level of sinusoidal excitation force of PCE based on the dynamics model of the cantilever beam excited by PCE, and its calibration principle and calibration process was explained in details. Finally, practicability and effectiveness of this calibration method was demonstrated by a calibration case. The results showed that if both of output signal voltage and excitation frequency meet the linear excitation equation, the concerned sinusoidal excitation force of PCE has a linear relationship with output signal voltage

Periodic and Chaotic Motions of a Two-Bar Linkage with OPCL Controller

A two-bar linkage, which is described in differential dynamical equations, can perform nonlinear behaviors due to system parameters or external input. As a basic component of robot system, the investigation of its behavior can improve robot performance, control strategy, and system parameters. An open-plus-close-loop (OPCL) control method therefore is developed and applied to reveal and classify the complicated behaviors of a two-bar linkage. In this paper, the conception and stability of OPCL are addressed firstly. Then it is applied to the dynamical equations of two-bar linkage. Different motions including single-periodic, multiple-periodic, quasiperiodic, and chaotic motions are unfolded by numerical simulations when changing the controller parameters. Furthermore, the obtained chaotic motions are sorted out for qualitative and quantificational study using Lyapunov exponents and hypothetic possibilities of surrogate data method