Car stretcher is an important medical care equipment, in the process of transporting patients can play an important role. Seriously ill patients in physical and psychological state of extreme discomfort, driving bumps in the process of vibration will not only exacerbate the discomfort of patients, and may even increase the patient's condition. When the vehicle is running, the random vibration will occur due to the random unevenness of the road surface. The vibration will be transmitted to the stretcher through the floor and the stretcher support, which will cause the vibration of the patient's body. Therefore, it can ensure the smoothness of the stretcher during driving. Stability of the patient's condition is important. In order to solve the vibration problem of vehicle stretchers, some scholars have carried out active or passive vibration and vibration isolation control on the vehicle and stretcher system. In order to understand the vibration characteristics of the stretcher caused by floor vibration, a 6-degree-of-freedom 6-DOF vibration mechanics model of vehicle and stretcher system was established, and the stiffness and damping coefficient were analyzed. Factors on the vibration characteristics of the stretcher. Therefore, a theoretical foundation is put forward for the purpose of adopting vibration-damping and vibration-isolation measures for the vehicle stretcher.
The main form of the stretcher vibration is vertical vibration and pitch vibration. The vertical vibration and pitch vibration of vehicle body caused by the random roughness of road surface are taken into account in the analysis, and the 6-degree-of-freedom vibration mechanics model is established.
The random excitation of road surface is usually caused by the randomness of the road surface. In order to reflect the real situation of the road surface random vibration spectrum in the low frequency range, white noise filtering method is usually used to simulate the road random excitation. White noise filtering is a commonly used stochastic process numerical simulation method. It is an ideal stochastic process with constant power spectral density. The designed system can be simulated by band-limited noise which satisfies the specified spectral characteristics Random Excitation of Pavement.
Based on the established road surface roughness excitation time domain model and 1/2-vehicle stretcher 6-DOF vibration dynamic model, the simulation model was established by MATLAB / Simulink.
In order to reduce the vibration of the vehicle stretcher, we can improve the ride comfort of the vehicle and improve the road grade, reduce the randomness of road roughness, but the time and economic cost are high. The influence of these three factors on the vibration characteristics of the vehicle stretcher is analyzed, which is helpful to control the vehicle according to the different degree of influence.
4.1 Influence of Vehicle Speed on Vibration Characteristics of Vehicle Stretcher
In urban and suburban environments, the actual vehicle speed is about 60km / h. Therefore, the influence of vehicle speed on the vertical vibration characteristics and pitch vibration characteristics of vehicle stretchers was analyzed by taking vehicle speeds of 10km / h, 20km / h, 30km / h, 40km / h, 50km / h and 60km / h respectively. The maximum value of the acceleration of the pitching vibration increases with the speed, but when the vehicle speed is close to 60km / h, the curve gradually becomes gentle, and the maximum value of the vibration angular acceleration is always less than 0.3rad / s2, indicating that when the vehicle speed is increased to A certain threshold value, the tilt of the vehicle stretcher will tend to stabilize.
4.2 Stretcher support stiffness on the impact of the characteristics of the stretcher
Simulation of vehicle driving conditions set: urban and suburban C-class road, speed as the commonly used speed of 50km / h. In order to analyze the effect of the support stiffness coefficient of the stretcher on the vibration characteristics of the stretcher, the vertical stiffness of the stretcher and the vibration angle of the pitching vibration were analyzed by taking 0.25, 0.5, 0.75, 1, 1.25, 1.5 and 1.75 times of the support stiffness coefficients The influence of the stiffness coefficient of the stretcher on its vibration characteristics was studied.
4.3 The influence of stretcher support damping on the vibration characteristics of the stretcher
Also set the vehicle driving conditions: urban and suburban C-class road, speed as the common speed of 50km / h. The results show that the damping coefficient of the stretcher is 0.25 times, 0.5 times, 0.75 times, 1 times, 1.25 times, 1.5 times and 1.75 times as that of the stretcher support damping coefficient. By analyzing the changes of the vertical acceleration and pitch acceleration, Influence of Damping Coefficient on Vibration Characteristics.
(1) Through the modeling analysis of the vehicle stretcher, it is found that the vertical vibration of the stretcher is more violent than the pitching vibration, indicating that the main vibration occurs in the vertical direction. (2) The vehicle speed has a great influence on the vibration characteristics of the stretcher, especially in the vertical direction, the vertical vibration of the stretcher increases linearly with the increase of the vehicle speed. (3) The influence of the stiffness and damping coefficient of the stretcher on the vibration characteristics of the stretcher is analyzed. The following conclusions are obtained: ¢Ù Stiffness coefficient has a limited effect on the vibration characteristics of the stretcher, and both the stiffness and the vertical vibration , But the stiffness of the stretcher support structure can only be reduced if the stiffness coefficient is reduced to reduce the strength of the stretcher support structure. ¢Ú The damping coefficient has great influence on the vibration characteristics of the stretcher, and its vertical vibration and pitch vibration are weakened with the increase of the damping coefficient of the stretcher support. Therefore, the damping control of the stretcher can be realized by increasing the damping of the stretcher.
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