1.Overview

Multihead weigher is a newly developed intelligent combination quantitative automatic packaging and weighing device in the weighing industry. In the past, the conventional quantitative packing scale was based on single bucket metering, and the material particles were uniform as the premise. Therefore, this type of quantitative packaging scale only need to have 0 district settings, delay sampling, advance volume setting and drop correction, can make the weighing accuracy to achieve the intended goal. And with coarse, fine feeding and a variety of judgments can improve the loading speed. In fact, however, a variety of material particles uniformity, especially in the food industry a variety of processed foods, such as dried fruit, confectionery, puffed products, local sundries, pet food and other individual weight uneven accounted for a considerable proportion. At present, with the rise of supermarkets in large and medium-sized cities in China, prepackaged food occupies a dominant position, the development of pre-packaging has promoted the development of multihead weigher, but most of the prepackaged food belongs to granular or bulk uneven type. For the packaging of such items, if the use of conventional single-bucket or multi-bucket metering packaging scales, no matter from the weighing accuracy and speed are more difficult to meet the requirements. For this reason, a high efficiency measurement of uneven products of the computer multihead weigher came into being. The following from the evolution of commodity pre-packaging see the technical development of computer multihead weigher.

2. The development of multihead weigher tech 　　

The development of computer combination scales has gone through a long period of time both at home and abroad. 　

In 70s, various types of bulk goods of sale in the shops in China is generally not pre-packaged, store retail is on-site manual packaging, on-site manual weighing, on-site manual pricing. By the 80 's, with the implementation of China's reform and opening policy, some enterprises with foresight, introduce foreign advanced electronic scale technology,electronic scales automatic weighing, valuation. However, this kind of valuation scale is a manual packaging after the measurement method. 　　

This method, such as the packaging line used in the production enterprise, the measurement speed of the average per person per minute metering less than 10 times, packaging efficiency is low. In order to improve the measurement speed, in the second half of the 80s, a single-bucket belt vibrating feeding electrical weighing and packaging machine was developed at home and abroad. Although the packaging speed can be increased to about 20 packets of/min, but the scope of application is little, for the particle uniformity requirements are higher. 　　

Sometimes, in order to meet the weighing speed need, the weighing accuracy of it is worse than the manual packaging metering. In the late 80s, with the development of the chemical industry, the need for quantitative packaging of uneven granular raw materials, as well as food manufacturers in order to meet customer requirements for packaging appearance and hygiene, the need for easy operation, with automatic quantitative weighing function, can be a variety of uneven particles and bulk items to achieve accurate, high-speed measurement of the weighing machine. 　　

At this time, in the world launched a multi-bucket weighing, through the computer symmetric bucket to achieve intelligent random combination of computer multihead weigher products, thus meet the above requirements. This stage is more representative of the introduction of computer combination scale products. First of all, its scope of application is wide. It can not only transmit large volume product, light weight of potato chips, but also can transmit and weighing the items are difficult to separate, easy to adhere to the cheese, as well as the ones difficult to separate, easy to leak, fragile, poor fluidity.

 3. Principle

The material is delivered to the storage hopper through an ascending conveyor, and when the material is added to a pre-set horizontal position, the horizontal photoelectric detector placed above the storage hopper sends a signal through detection to cause the lifting conveyor to stop feeding. When the horizontal position of the material on the storage hopper drops to a pre-set horizontal position, the horizontal photoelectric detector then emits the starting feed signal. The material entering the storage hopper is sent from the wire vibrating plate to the buffer hopper and then from the buffer hopper to the weighing hopper, and the material in the weighing hopper is weighed by the weighing sensor and the output signal is fed into the micro-processor. Because there are multiple weighing hoppers along the whole circumference direction of the weighing body, and the weighing signal is fed into the computer, the computer carries on the random combination operation, the roving detection combination finds the maximum number of weighing bucket combinations closest to the target weight at the fastest speed to carry on a combination. Select the combination of weighing hopper material from the weighing hopper opening and closing control mechanism action, material unloading, and through the finishing groove to reach the set hopper, and then into the following automatic packaging machine. At this time, in addition to the selection of the combination of weighing air bucket, the rest of the heavy weighing bucket began b combination operation, to find the closest to the target weight of the weighing bucket, and then cycle by continuous B combination ..., so as to achieve high speed, high accuracy of the quantitative weighing. The biggest feature of the computer combination scale is that multiple weighing fights are added at the same time. For example, when the heavy number is called 14, 14 weighing hoppers are added at the same time, due to the inhomogeneity of the alleged material, resulting in a considerable deviation in the weighing of each bucket. First, the precise weight of the material in each bucket is judged quickly and correctly by the weighing sensor, and then the computer uses a stochastic combination operation method, the number of operations is generally 2n-1 times, that is, the number of operations of 14 fights is 214-1 = 16,383 times. Each combination operation results in comparison with the set target weight, each combination is generally 3~5 a bucket, (if the 3~5 bucket combination is not equal to the target weight value, you can adjust the amplitude level of the line vibration plate on each weighing bucket). If the number of fights in the combination is too large, the efficiency is not high, the number of fights is less, the combination accuracy is not high. In the actual operation, the first is 14 fights at the same time feeding, the first combination of 14 fights in 3 combination bucket discharge, then the remaining 11 fights and then the second B combination, the third time by the remaining 8 fights plus the first discharge and then filled with 3 fights, that is, the third C combination of 11 fights, And then there's the fourth D combination of 11 fights ... General single-weighing process before and after the execution time is about 1200ms, of which the combined time is about 200ms, the total packaging speed can reach 80 packs/min or more. If the use of double scales, with memory bucket, weighing 20 of the structure form, the total packaging speed can be up to 240 packets/min.

4. New development of Tech used in Kenwei series multihead weigher 　　

The computer multihead weigher is completely different from the traditional quantitative packaging scale using a weighing bucket weighing, its structure uses a number of weighing, the microcomputer randomly selects the mixed weight of several of the weighing bucket, its weight is equal to the target weight. The combinatorial process is done by a micro-information processor. 　　

The data of each part controlled by the operator is displayed on the control screen, which is very convenient and concise. Kenwei Series combination scale, according to the hopper form can be divided into double row without memory bucket, three rows of memory bucket, weighing head 10 head, 14 head, 20 head, 32 head specifications. Its biggest feature is the structural integration of each weighing bucket, in which almost all intelligent components, such as weighing loadcell, stepper motors, converters, and printing bodies with dedicated integrated blocks, are set in sealed drive units. The drive unit is in the specialized production workshop, after strict inspection package, the unit adopts plug-in connection, does not need any wiring operation. The same unit is used for the same series of models. Each unit is interchangeable, and each drive unit can be easily mounted on a cylindrical machine with just 4 bolts. And the various hoppers of the drive unit index (including buffer hopper, weighing hopper) and hopper door control actuator can be simply disassembled without tools. 10-20-head model of the intelligent combination scale, as long as the availability of 1 drive units, you can complete the annual maintenance needs of the product. The same series of models of intelligent combination scales, hoppers are universal design, hopper between the interchangeability, hopper materials using a thickness of slightly more than 1.2mm mirror polished stainless steel plate, easy to clean. The hopper opening and closing mechanism adopts the stepper motor drive control mode, which greatly reduces the vibration and noise, and is conducive to improving the weighing accuracy. The machine itself meets the standards of waterproof, dustproof of IP65. Among them, the printer can be rinsed with water, the feed main vibration machine sealed in the middle seat cylinder body, reduce noise. There is no maintenance problem with all sockets and wiring in the cylindrical fuselage. Secondly, the application software is quite rich, can meet the needs of weighing different materials. The latest model of the Kenwei computer combination scale automatic detection function is as follows:

① can automatically show whether the motor operation is normal or not;

② automatically shows whether the weight is accurate or not;

③ automatically shows whether the printer is operating properly or not;

④ automatically shows whether the LAN is normal or not;

⑤ automatically check whether the memory module is normal or not;

⑥A/D conversion automatic monitoring

⑦ weighing loadcell waveform monitoring: Automatically display the fault of a weighing bucket, adaptive adjustment data, uninterrupted work;

5、Ending

Recently, the International Legal Metrology organization OIML R87,and China's State Technical Supervision Bureau 43rd order of the formal implementation of nationwide supervision spot  checks. The field of commodity pre-packaging from the low condition to high-speed, high-accuracy  direction of development. Computer multihead weigher products have begun to gradually enter China's  commodity processing, packaging industry. Some insightful enterprises, especially some of the more  large food processing plants began to use computer multihead weigher, according to incomplete  statistics, take chocolate candy weighing and packaging as an example, if the bag is100g, the price of it  is 16RMB, the bag workshop workers manual package weight is 2g exceed the actual one. but that of  computer multihead weigher is 0.5g ,less 1.5g per bag  than manual packaging weight.That saves  0.24RMB per bag.  If the factory is equipped with a computer multihead weigher. It produces 70  bags/min, 33600 bags/8h.Total 300 days in a year, then it produces 10.08 million bags a year.The  raw materials saved is up to 2.42 million RMB.  Add the savings in the labour force, more substantial economic benefits can be created.