Research on Combined Weighing Technology in Quantitative Packaging

[Abstract] Weighing is a key part of quantitative packaging. Combined weighing can achieve high-speed, high-precision quantitative packaging. This paper introduces the working principle of combination weigher, expounds the hardware composition of control system based on advanced PIC microcontroller and analyzes the design method of control software.

Keywords: high-level PIC microcontroller; combination scale; combinatorial calculation

With the development of electronic technology and computer technology, electronic weighing scales are widely used for quantitative packaging of products, especially for small-scale quantitative packaging, which requires high measurement accuracy, high packaging speed, and high reliability. The conventional quantitative packing scale is a single scale, that is, a weighing hopper with a maximum packing speed of 20-30 bags/min, which has a higher requirement for the fluidity and uniformity of the material particles, but for sugar-like blocks and dried fruits. Non-uniform articles such as potato chips are also weighed on a single scale, which makes it difficult to meet production requirements in terms of accuracy and speed of weighing. The computerized combination scale based on the combined weighing technology can effectively improve the measurement accuracy and speed, and solve the problem of measurement and packaging of uneven articles. There are 8, 10, 14, 16, 20, 24, and 28 heads of computer combination scales according to the number of hopper heads, and 10, 12, or 14 are more commonly used. Each head usually includes a spare hopper and a weighing hopper. The hopper capacity is 200, 300, 500 ml, etc. The mass can reach 500 kg at the maximum, the minimum scale is ± 0.1 g, and the weighing speed can reach 350 bags/min at the fastest. The computer combination scale is a smart combination quantitative automatic weighing instrument in the weighing industry. The combined weighing technology develops a simple weighing of the weight of an item to adjust the weight of the product to meet the needs of mass production and expands the weighing function and application scope. The concept of weighing adds new content.

1 How does the combined weighing work?

The combination scale consists of a number of independent weighing components and microcomputers with the same performance. Weighing process shown in Figure 1, in order to save costs, so that the computer combination scale is commonly used in small and medium-sized enterprises, weighing the use of 10 here, the material through the electromagnetic vibration feeder into the reserve hopper temporary, prepared The material gate of the hopper is opened, the material enters the weighing hopper for weighing, the simultaneous measurement is performed with the help of the microcomputer system, and the best calculated value of the near or slightly large sub-calibration value is automatically selected as the output of the material. Therefore, rapid and accurate weighing packaging can be achieved for certain high-value bulk materials such as coarse granules or small lumps.

The feeding process generally obeys the normal distribution. Although the dispersion is large, if there are enough combinable numbers, multiple units can be combined to obtain a high-precision whole. The result of feeding is a combination of weighing and calculation. This is essentially different from traditional measurement methods. Utilizing this high-tech working principle, it can be superior to the speed and accuracy of ordinary automatic dosing devices. Moreover, not only irregular blocks can be measured, but all flowable materials can be quantified using a computerized combination weigher.

The weighing hopper is equipped with a weighing sensor and a control gate. The weighing sensor measures the weight of the material in the weighing hopper, and sends it in the form of an electric signal to a computer, and the computer performs screening and combination. After the system performs the combination calculation according to the set value of the parameters, it obtains an optimal combination result within the target weight range of the product. If there are n hoppers, there are 2n - 1 combination modes, from which the combination mode that is closest to the target weight is selected, that is, the best combination. The system then marks the selected weighing hopper. If a weighing hopper is selected, the microcomputer issues a command to open the gate of the hopper that participates in the best combination and discharges the material. The product in the hopper is released into a centralized hopper and transported to a packaging machine for packaging. If the weighing hopper is not selected, the hopper material is weighed and the weighing hopper is left in the next working cycle and the weighing hopper is still directly involved in the combination calculation. This cycle until artificially stopped. If a weighing hopper is not selected for 30 consecutive working cycles, the weighing hopper is forcibly selected once, the best combination is selected in the combination containing the weight of the weighing hopper, and the weight of the weighing hopper is unloaded. The sensor is automatically zeroed. The opening and closing of the material door is driven by a stepping motor, which finely adjusts the opening and closing speed of the material according to the characteristics of the material to prevent breakage and jamming. The action is smooth and the service life is long.

When a general single-head weigher is about to reach the target weight, the feeding speed cannot be too fast in order to ensure the accuracy, and the computer combination weigher can feed the hopper quickly. The feeding amount of each hopper is usually set as 1/3 to 1/ of the target weight. 5. When combined weigh scales are used for combination calculation, only some combinations are used. Based on the number of heads participating in the combination, the computer can calculate the number of combinations by the following formula. Where: m is the total number of weighing hoppers and i is the number of buckets participating in the combination. Usually m, i increase, the number of possible combinations increases, the greater the possibility of obtaining qualified products. However, although the operation speed of the microcomputer is very fast, the excessive number of combinations may cause the packaging speed to decrease and increase the cost. From the perspective of rationality and economy, m usually takes 8 to 16, and i generally takes 3-5. The computer control system of the combination scale is shown in Figure 2.