转动副间隙对曲柄摇杆式分插机构性能的影响分析与试验

Analysis and test of influence of revolute joint clearance on performance of crank-rocker style transplanting mechanism

为了研究转动副间隙对曲柄摇杆式分插机构的影响,该文基于动力学理论及Lankarani-Nikravesh接触力模型,建立了含转动副间隙的曲柄摇杆式分插机构的动力学模型,并通过四阶龙格库塔法求解动力学模型。通过MATLAB仿真分析了转动副间隙对秧针尖的轨迹、速度、加速度和取秧位置的影响以及不同间隙大小和不同转动副含间隙对秧针尖加速度的影响。仿真分析结果表明,转动副间隙对秧针尖轨迹、速度和取秧位置的影响较小,对加速度的影响较大;随着转动副间隙的增大,分插机构取秧位置的偏离会增大,秧针尖的加速度的幅值和波动幅度会增大;在分析的3个转动副中,曲柄与连杆之间的转动副含间隙对秧针尖加速度的影响最大。通过试验与仿真对比得到基于Lankarani-Nikravesh接触力模型比基于连续接触模型更适用于含转动副间隙机构的分析。试验结果验证了基于Lankarani-Nikravesh接触力模型的仿真分析的正确性。研究结果为分插机构的结构优化设计和精度分配提供了参考。

Generally, revolute joints are considered to be ideal in dynamic analysis of crank-rocker type transplanting mechanism. However, in reality, clearances in revolute joints are unavoidable due to uncertainties such as manufacturing tolerances, assembly errors and wear. When a revolute joint clearance is introduced, the relative position of the axle pin and axle cover is uncertain, which will affect the dynamic responses of the transplanting mechanism. In order to investigate the influence of the revolute joint clearance on the crank-rocker type transplanting mechanism, the dynamic model of the crank- rocker type transplanting mechanism with a revolute joint clearance was established based on the dynamics theory and the Lankarani- Nikravesh contact force model. The revolute joint clearance will introduce 2 extra degrees of freedom, and a stable solution cannot be obtained by solving the dynamic directly, so the dynamic model wassolved by the four-order Runge-Kutta method. The parameters of the simulation calculation were obtained according to the actual parameters of transplanting mechanism and literatures. The influence of revolute joint clearance on trajectory,velocity, acceleration and taking seedling position of the needles to take seedlings was analyzed by Matlab. The results showed that the revolute joint clearance had little influence on trajectory, velocity and taking seedling position of the needles to take seedlings, and the revolute joint clearance had great influence on acceleration of the needles to take seedlings; with the increase of revolute joint clearance, the deviation of taking seedling position of transplanting mechanism would be greater, and the amplitude and fluctuation range of acceleration of the needles to take seedlings would increase. In order to quantitatively describe the influence of various revolute joint positions with clearance on acceleration of the needles to take seedlings, the average acceleration was used as the evaluation criterion of the influence. In addition to the revolute joint connected to the drive, the average accelerations of 3 various revolute joints with various clearances were obtained by simulation analysis. For the 3 revolute joint clearances, the revolute joint clearance between the crank and the connecting rod had the greatest influence on acceleration of the needles to take seedlings according to the comparison result of the average accelerations. The continuous contact model was also used to analyze the influence of the revolute joint clearance on acceleration. In order to verify the correctness of the simulation analysis and to select the simulation model whose calculation results were more in line with the actual ones, a test bench was established. An accelerometer and a data acquisition and analysis system were used to measure acceleration of the needles to take seedlings. In the test, the rolling bearing was regarded as ideal revolute joint, and the fit between sliding bearing and shaft with different radii was regarded as the revolute joint with clearance. The average acceleration of the test was larger than that of the simulation under the same condition due to some factors such as manufacturing tolerances, clearance of the rolling bearing and vibration. The conclusion that the revolute joint clearance between the crank and the connecting rod has the greatest influence on acceleration can be also obtained according to the test. By comparing the test and simulation results, the Lankarani-Nikravesh contact force model is more suitable for the analysis of the mechanism with revolute joint clearance than the continuous contact model. The relative errors of average acceleration between simulation based on the Lankarani- Nikravesh contact force model and test were within3.6% under revolute joint C or D with clearance. The relative errors of average acceleration were within 8.1% under revolute joint B with clearance. The same conclusions can be obtained with the average accelerations of simulation and the average accelerations of test. So the correctness of simulation analysis based on the Lankarani- Nikravesh contact force model was verified by the test results. This research provides the reference for structural optimization design and accuracy allocation of crank-rocker type transplanting mechanism.