分段插值算法在注塑机背压控制中的应用

注塑机螺杆在回退储料过程中,要求回油背压尽可能低且稳定。市面上的PQ阀和比例溢流阀的起调压力普遍偏高,很难实现零背压控制。为了实现极低背压控制的目的,设计了一种基于分段插值算法的注塑机背压控制系统,分析了根据注射油缸回退速度和设定回油压力调节比例换向阀开度控制回油背压的原理公式;根据公式得到以流量和压力为坐标的表格;再根据流量曲线斜率对表格进行分段插值,斜率较大时采用拉格朗日插值,曲线平稳时采用最邻近插值,从而减少了表格的数据容量;通过联合仿真对算法进行了验证,结果表明,该系统最低背压小于0.1 MPa,压力精度达到0.005 MPa,接近闭环的控制性能,具有较大的实用价值。

Application of Piecewise Interpolation Algorithm in Back Pressure Control of Injection Molding Machine

The back pressure of the injection molding machine is required to be stable in the return process. The starting pressure of PQ valve and proportional overflow valve on the market is generally high, so zero back pressure control cannot be realized. An open-loop look-up table back pressure control system with piecewise interpolation algorithm is designed to realize the control of very low backpressure. The formula of controlling the return oil back pressure according to the return speed and set pressure is deduced. The table with flow and pressure as coordinates is obtained, and then the table is interpolated according to the slope of flow curve. Lagrange interpolation is used when the slope is large, and the nearest neighbor interpolation is used when the slope is stable, which reduces the capacity of the table. The algorithm is verified by joint simulation. The results show that the system can realize the control of very low back pressure, the performance is close to the closed loop, and has strong application value.