Brief Introduction of Working Principle and Control System of Intelligent Multihead Weigher

With the development of electronic technology and computer technology, quantitative packaging of products is widely used in all walks of life and synchronous measurement by means of a computer system. Especially for small-quantity quantitative packaging, it is required that the measurement accuracy is high, and the best calculated value of the packaging is close to or slightly larger than the calibration value as the output of the material. The conventional quantitative packaging scale is a single scale, which can barely weigh quantitatively for bulk materials with uniform and small particles, but the fastest packaging speed is 15 ~ 30 bags / min, but for sugar cubes, dried fruits, potatoes If the uneven items such as tablets are weighed with a single scale, it is difficult to meet the production requirements regardless of weighing accuracy and speed. Computer combination scales based on combined weighing technology can effectively improve the measurement accuracy and speed, and solve the problem of measurement and packaging of uneven items. The computer combination section is divided by the number of hopper heads. There are 8, 10, 14, 16, 20, 24, 28 heads, 10 and 14 heads are more commonly used. Each head usually includes a buffer hopper and a weighing hopper, the hopper capacity is 300ml, the minimum scale is ± 0.1g, the fastest weighing speed is 350 bags / min, and the computer combination scale is an intelligent combination quantitative automatic packaging in the weighing industry Weighing instruments, combined weighing technology will develop the simple weighing of items to adjust the weight of products, meet the needs of mass production, expand the weighing function and application range, and add new content to the concept of weighing.


1. Working principle of combination weigher

The material falls into the cross-cutting bucket of the combination scale through the hoist, and vibrates through the main feeder, so that the material is evenly distributed on the conical funnel to the linear feeder tray. When there is no material in the cross-cutting bucket or the material is not enough, it will be detected by the horizontal photoelectric detector, and a signal is sent to the main board, and then a feed signal is sent to the conveyor through the main board to feed the material. The vibration machine time sends the product to each buffer hopper. Then the driving equipment, that is, the stepper motor works, and the buffer hopper is opened to send the material into the weighing hopper.

In the weighing hopper, the product generates a weight signal through the sensor, and then transmits it to the main board of the control device through the lead. The CPU on the main board reads and records the weight of each weighing hopper, and then selects it through calculation, analysis and combination The combination weighing hopper closest to the target weight sends a command to start the driver to open the collecting hopper to discharge the product to the packaging machine when the CPU receives the discharge permission signal from the packaging machine, and sends a packaging signal to the packaging machine.

The feeding process generally follows a normal distribution. Although the dispersion is large, if there are enough combinations, multiple units can be combined to obtain a high-precision whole. The result of the feeding is combined by weighing and calculation. This is essentially different from traditional measurement methods. Using this high-tech working principle, it can be better than the speed and accuracy of ordinary automatic quantitative devices. Moreover, not only can irregular masses be measured, but all flowable materials can be quantified using a computer combination scale.

In general single-head scales, when the target weight is about to reach, in order to ensure accuracy, the feeding speed cannot be too fast, and the computer combination scale can quickly feed, the feeding amount of each hopper is usually set to 1/3 to 1 / of the target weight 5. When the combination scale is used for combination calculation, only part of the combination is used. The computer can calculate the number of combinations according to the number of heads participating in the combination: n = Cim = M / I (MI), where: M is the weight of the weighing hopper The total number, I is the number of buckets participating in the combination. Generally, when M and I increase and the number of possible combinations increases, the possibility of obtaining qualified products is greater. However, although the operation speed of the microcomputer is very fast, too many combinations will lead to a reduction in packaging speed and increase costs From the perspective of rationality and economy, M usually takes 8 to 16, while I generally takes 3 to 5.

2.The combined weighing control system

When the combination scale is working, it must have a capacity of more than 70 packs / min (1 pack / s), that is, it must complete weight detection, combination calculation, find the best combination, etc. at least within 1s, so as to complete a packaging, including combination calculation Relatively more time-consuming, high-performance single-chip microcomputer or PLC, can directly complete the detection, calculation, control output, which can not only meet the precision requirements of the combination scale real-time control, but also meet the packaging speed requirements, is a more effective control method. When the control system is working, a single-chip or PLC sends a signal to the multi-way switch, time-sharing selects 10 weighing sensors, the signal is amplified, A / D converted, and input to the single-chip or PLC, and the 10 input values are combined Calculate the number of a group of weighing hoppers where the best combination is located, and control the speed and direction of the corresponding stepper motor according to the number to open the material door of the group, complete the discharge, and then close the material door; the material level in the storage hopper is determined by Photoelectric detection switch detection. In addition, the system has also designed display, alarm and keyboard circuits to make the system more complete.

Combination weighing technology with its high precision and high speed represents the highest level and development direction of today's weighing technology. In the past, China mainly imported from other country. Because of its high price, it has hindered the widespread application and popularity of computer combination scales. With the rapid development of China's commodity packaging in the direction of high speed and high accuracy, computer combination scales will quickly enter China's commodity processing and packaging industry. It can be said that the development of the packaging industry has promoted the development of weighing technology. At the same time, weighing technology has also improved the level of packaging and promoted the development of the packaging industry.

At present, there are mainly two types of combination scale equipment at home and abroad: the first type of analog signal combination weigher; the second type is a digital signal combination scale. Although the combination scale is a very mature product, these different transmission signals can cause different weighing accuracy. The analog signal combination scale is just an old-fashioned imitation scale. Due to the poor processing of imitation technology, the scale mainly has problems such as unstable performance, easy-burning motherboards, and second-hand sources of IC patches. The biggest problem is the product. Because imitation has no improvement at all. Digital signal combination scales all use digital high-precision weighing signals, which are both fast and stable. These characteristics are unmatched by analog products. For example, the intelligent combination scale produced by Guangdong Kenwei Intellectualized Machinery Co.,Ltd. is a representative product of this type of product. Its products are widely favored by domestic and foreign customers with high speed and high precision. Therefore, the user must distinguish when selecting the combination weigher, otherwise it is difficult to meet the requirements of use, and the final delay in production will lead to loss of economic benefits, which is not worth the loss.

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