Research Of Three-Dimensional Parallel Vibrating Screen For Grain Cleaning

As an important part of the combine harvester, Cleaning unit’s performance directly affects the whole machine characteristic. The wind-sieve cleaning unit is widely used in combine harvester, and its cleaning effect is influenced by many factors. Among which, one of the important factors is the form of movement of vibrating sieve’s surface driving device. Most of the current, the plane linkage mechanism is being applied, where the cleaning effect of sieving is subject to greater impact of the planar motion of sieve surface; At the same time, the structure and shape of the sieve surface also have an impact on the cleaning effect. It is easily lead to the sieve pore clogging and affects the permeability of sieving while cereals likely tend to gather together, when the common flat-sieve surface is being used. So, the research of an efficient vibration sieving-cleaning unit, focus on the effect of the form of sieve surface movement and break through the traditional main body and the sieve structure of vibrating sieve to improve sieving efficiency and reduce the loss rate of the cleaning etc, has important practical significance and academic value. Based on this background, and combined with the implementation of the project in the national scientific and technological support. We have carried out the grain cleaning parallel vibrating sieve theoretical and experimental research, which take the optimization variable drive into parallel mechanism as the main body of vibrating sieve. The major research work includes:1. Based on the analysis of grain composition, characteristics and sieving features, we put forward the optimization design principle of multidimensional parallel vibrating sieve machine, that suitable for grain sieving. According to those optimization principles,4types of7kinds3-DOF parallel vibrating sieve main mechanism have been designed, and their structural characteristics also been analyzed. Meanwhile, designed a less convex column sieve surface suitable for grain sieving, which lay the foundation for further optimize the parallel vibrating sieve main mechanism.2. The collision model between the grain and grain or grain contact the wall is established, which based on the discrete element method (DEM). Rice materials group on the sieve surface, that include flat-reciprocating and8kinds of space multi-dimensional vibration types, through the sieve and the law of motion curve is numerically simulated. To complete the work, the discrete element method and application software-EDEM need to be used. The simulation results show that:①Form of the sieve surface’s motion have a greater impact on the state of through sieve and the law of motion of grain;②Compared to multi-dimensional vibrating sieve, the sieving efficiency and cereal cleaning rates of a reciprocating sieve are both lower;③Among the8kind of multi-dimensional vibration type, those new model of parallel mechanism with the motion in the form of za(3, xza, xyz multidimensional vibrating sieve, simultaneously having higher grain cleaning rate and sieving efficiency, should be preferably choose.④The numerical simulation results of surface grain beating regular,which using a flat-reciprocating vibrating sieve, is consistent with the theoretical conclusions; Simultaneously, experiments verified that the test results of the multidimensional sieve with the form of zαβmotion and simulation results are basically the same. This verified the feasibility of the numerical simulation in a variety of sieve surface’s motion by EDEM, and provides a basis for the design of parallel vibrating cleaning sieve.3. The effect of number of driver on the screen output and pass sieves characteristic are studied and attained:①Calculation by MATLAB software of the3-DOF、2-DOF and1-DOF parallel kinematic sieve with same output type and dimension shows that:screen motor output between2-DOF and1-DOF parallel kinematic sieve are relatively close; and simulation analysis by EDEM software shows that the pass sieves effect of grain between3-DOF and1-DOF parallel kinematic sieve are relatively close;②Construction Simplicity and low-cost principle of the machine are taken into account,l-DOF parallel mechanism is chosen for optimization models of parallel kinematic sieve and grain sieving experiment are conducted, the numerical calculation results and the experimental results matched; Grain sieving need not high accuracy,l-DOF parallel mechanism is chosen for parallel kinematic sieve has a lot benefits, such as structure simple, achieved reliability, low-cost and casy-to-handle, etc. 4. Put forward the concept of driving the three dimensional parallel vibrating screen with variable speed (rotation direction) input and designed a kind of variable voltage/frequency speed control system, for three-phase ac asynchronous motor. Employ the special motor chip ARM-LPC1752as the core of the frequency controlled system, and while use Intelligent Power Module PS21865as an inverter, which reduced lots of the system’s complexity and improved the reliability; According to the speed requirements about three-dimensional vibrating sieve deal with grain cleaning, designed the speed and current double closed-loop variable frequency control system based on SPWM. The dynamic response and the control precision of the speed control system can satisfy the actual speed requirements.5. In order to ensure the screening effect, put forward the concept of controlling the grain feeding amount of vibrating screen by adjusting the speed of transmission system. Design the vibrating load and transmission speed double closed-loop control system. Transmission speed controller use the traditional PID control, and vibration load controller use the dual mode control with fuzzy control and traditional PID control combined. Parameter self-tuning control is adopted in the fuzzy controller. The test results of grain distribution density step disturbance show that the controller can effectively restrain the disturbance, and achieve the desired control effect.6. Carrying on the comparison experiment to grain sieving between traditional straight kinematic sieve and1-DOF parallel kinematic sieve, experimental results show that:①Sieving efficiency and the rate of pass sieves of parallel kinematic sieve is higher than that of straight kinematic sieve;②Whether parallel kinematic sieve or straight kinematic sieve, the sieving efficiency based on less convex column sieve is significantly higher than that based on planar sieve, convex column of sieve is useful to loose and prevent blocking grain.7. Based on the3-DOF parallel mechanism, a grain cleaning device designed, and orthogonal experiment is done to analyze the effect factors of sieving result, we concludes that:①The interaction between motor speed and the rate of sieve pore and convex column significantly affected cleaning rate, sieve size and the rate of Convex column also significantly affected cleaning rate; sieve size and motor speed significantly affected loss rate.②The best optimizing combination of various factors: sieve size is8*8mm the rate of Convex column is1%、motor speed is1400r/m and motor’s rotary direction is reverse.