Screw feeding system weighing is a common dynamic on-line metering equipment in the powder and granular materials industry. Screw feeding dynamic quantitative weighing process contains time-varying, non-linear and various uncertainty factors. In the process of continuous industrial production, how to simultaneously improve the dynamic quantitative weighing accuracy and weighing speed, has been one of the enterprises and the measurement of the field of urgent need to solve the problem, quantitative packaging in the lack of advanced spiral feeding dynamic quantitative weighing control methods, so the dynamic accuracy is low, slow, restricting the development of the industry. In some industries that can not quickly online accurate weighing, in order to prevent the loss of credibility due to insufficient weight, have to use a slightly overweight weighing and loading method. In this paper, in the development of feed, flour dynamic quantitative weighing packaging, by analyzing the spiral feeding dynamic on-line quantitative weighing process, gives a new double-speed variable diameter variable pitch spiral feeding dynamic quantitative weighing control method. The feeding station adopts the control method of /first fast, then slow, and finally point 0, which better solves the contradiction between precision and speed in the dynamic quantitative weighing process. Practice has proved that the technology of feed, flour, grain, fertilizer, cement and small powder and granular material quantitative loading, quantitative packaging and weighing and batching, the effect is quite good.

1, spiral quantitative weighing structure principle

Spiral is the most commonly used hopper scales in a dynamic weighing and feeding. In the quantitative weighing device, the motor-driven spiral feeding mechatronic equipment (commonly known as the winch motor) placed between the bin and the hopper, the electronic measurement and control devices to achieve dynamic quantitative weighing of powder materials, start the winch motor, the corresponding bin of powder materials with the rotation of the spiral feeding mechanism into the hopper. The hopper and the weighing frame are equipped with three strain-type tension sensors, the weight of the hopper is directly converted into electrical signals by the tension sensor group and sent to the electronic measurement and control device, and when it reaches the set weight value, it will shut down the screw motor to stop feeding and control the hopper door to open the door for unloading, which is the completion of a dynamic feeding quantitative weighing.

2、Spiral feeding control mode research

Spiral dosing equipment is to ensure the dynamic quantitative weighing accuracy and uniformity of the important links. Due to the non-linear and strong non-self-balancing of the spiral dosing electromechanical integration device, as well as in the process of dosing the particle size of the material, humidity and silo pressure and so on will cause the instability of the dosing flow. If you speed up the weighing speed, the impact of the material on the hopper, will affect the accuracy and stability of weighing; and if you improve the weighing accuracy, you have to reduce the feeding speed.

In order to coordinate the contradiction between weighing accuracy and weighing speed, most of the dynamic on-line quantitative weighing equipment adopts two-stage charging method. This feeding method can only take into account the requirements of precision and speed to a certain extent, the precision is not high, and there is over-difference. Due to the irreversible nature of the spiral charging, the quantitative weighing overrun can not be compensated for, and can only be carried out again. Weighing mixer in order to improve the rate and solve the problem of over-difference, the use of / first fast, then slow, the last point of action 0 feeding control mode, aimed at / fast feeding 0 to shorten the charging time, improve the weighing speed; / slow feeding 0 to reduce the impact of the material, to improve the detection accuracy; and the last / point of action feeding 0 to replenish the material in order to ensure that zui the final accuracy of quantitative weighing. The control feeding process is as follows: at the beginning of weighing/fast feeding 0, when reaching the given value of fast feeding prediction Wg1 start/slow feeding 0; when reaching the given value of slow feeding prediction Wg2, delay for a period of time to wait for the air material falling into the hopper, such as not yet reached the quantitative value of the material Ws of the lower limit of the allowable error value of the system WsL, then begin to slow/spotting feeding 0, until the net material weight is greater than the WsL before opening the hopper. WsL before opening the hopper door unloading. Since each pointing charging time decreases with the decrease of the material difference value, the occurrence of over-difference is effectively avoided.

Due to the time-varying nature of the spiral mixer dosage device, and the time (t1 ~ t4) corresponding to the charging flow, when the signal is issued to feed the weighing screw feeding machine always lags for a period of time before the start of charging; when stopping the charging, the spiral feeding mechanical inertia and delay for a period of time before stopping; spiral charging stops, there are still not yet fallen into the hopper in the air of the space of the material (known as the difference between the fall B, also known as early shutdown), so that the weighing of the amount of material to be stopped. (also known as the amount of early stop), so that the weighing value increases, and the size of the increase and stop feeding before the flow is related. The longer the slow dosing time, the more stable Qg2 is and the more accurate the corresponding predicted B is, but it reduces the weighing speed. If we consider from the quantitative weighing speed, the bigger Wg1 is, the better, but the bigger Wg1 is, the shorter the slow charging time is, which will affect the quantitative weighing accuracy. Therefore, how to correctly predict B and how to dynamically correct Wg1 and Wg2 on-line is the key issue to realize the accuracy and speed of quantitative weighing at the same time.

3. Compensation algorithm for fallout

The uncertainty that affects the accuracy of dynamic quantitative weighing is mainly the randomness and unmeasurability of the falling material in the air after stopping charging, which cannot be compensated by a fixed parameter.

4、Automatic correction

The correction principle of the given value of fast feeding is adjusted according to the length of time of slow feeding, which is the given value of the kth fast feeding and slow feeding prediction, respectively; is the weight of the kth slow feeding; T2(k) is the time of the kth slow feeding; T2 is a constant, which is the optimal slow feeding time rectified by the experiment;

5. Experimental results and experimental comparison

In the feed dynamic quantitative weighing production site, with the same equipment, respectively, using the above control algorithms and conventional empirical fixed setting method for comparison experiments. A total of 5 times, each continuous sampling 10 packages, take the average value. The accuracy was improved from less than 0.2% in the empirical fixed-setting method to better than 0.1% in the predictive algorithm, and the number of pointing movements was reduced.

6, Conclusion

(1) The dynamic quantitative weighing spiral feeding control method of the weighing mixer adopts/first fast, then slow, and finally pointing 0 and introduces the control algorithm, which better solves the contradiction between the dynamic quantitative weighing accuracy and speed.

(2) weighing and feeding machine from the actual process object, using two simple prediction equations, for quantitative weighing 25kg, its measured accuracy is better than 0.1%, the speed of 8 packets of Pmin, resolution of 10g.

(3) weighing mixer technology for grain, flour, fertilizer, cement, and small powder and granular material amount of quantitative packaging has a greater potential for application and promotion value.