Weighing controller for multihead weigher

Author: Smartweigh–Multihead Weighter

1. Composition and technical parameters of weighing controller for multihead weigher Multihead weigher is a commonly used online dynamic weighing system, which mainly consists of load belt conveyor, carrier, screening equipment, weighing controller, net weight Set up equipment and other components, with automatic identification, dynamic measurement verification and other characteristics. During work, without manual control, the load belt conveyor will automatically send the raw material to be weighed to the carrier, according to the two optical inspection components on both sides of the weighing platform to distinguish the position of the raw material to be weighed, and set up in advance according to the setting equipment. Good net weight range to carry out screening. In order to better keep the raw material being weighed on the scale according to the speed of the conveyor, it is stipulated that the weighing control panel should be fast, accurate and reliable.

The weighing controller is used to control the tread multihead weigher on the tread pressure team in the vulcanized rubber field. It is mainly composed of an automatic control system composed of 51 single-chip microcomputers, a preamplifier, a setting device, a screening result display lamp, an electronic counter, a copier, a switching power supply, and the like. Its basic principle framework is shown in Figure 1.

The preamplifier enlarges the millivolt level data signal output by the working pressure sensor, converts it into a differential signal, and sends it to the CS-51 single-chip automatic control system for data processing. The set net weight range is compared, and the comparison result is based on the opening and exit of the display lamp to display information, electronic counter to count, and start the copier to record the production data information. The weighing controller has two working modes: operation and calibration. When the calibration method is selected, it will enter the static data and display the information normally.

At this time, put the object to be weighed on the weighing platform, the control panel will display the net weight of the object to be weighed, and the scale can be calibrated. When the operation method is selected, the weighing controller will enter the dynamic weighing and screening operation. At this time, the weighing controller will check the optical data signals of the parts to be weighed on both sides of the weighing platform, identify the tread parts, and carry out dynamic weighing and screening operations.

In my country, the weighing controllers used for multihead weighers are mostly imported products, and most of the products developed and designed in China are evolved from general-purpose weighing displays. The screening category of the net weight is input by the keyboard. When everything is working normally, the actual operating staff cannot see the preset value, the image is poor, and the adjustment is inconvenient. The weighing controller developed and designed by us imitates the overseas samples, and four four-position DIP switches are set on the control panel of the control board to set the net weight screening range. The four DIP switches can be subdivided into five net weight categories according to the processing technology (see Figure 2).

The first two digits of the four-digit data represent an integer amount, and the last two digits represent a decimal. During the whole process of dynamic weighing and screening, the preset value can be adjusted anytime and anywhere. Set up corresponding display lamps and counters for each net weight on the control panel.

The actual operating staff can immediately adjust the working pressure of the tread extrusion inlet according to the trend analysis of the net weight shown by the upper error and the lower error to control the net weight of the tread. In that way, it is very visual and convenient. Each of the six six-digit registers has data information such as good weighing, upper error, lower error, upper deviation, lower deviation, production volume (including good, upper error, and lower error).

It is equipped with a copier to copy data and information such as birth output, which is convenient for production workshop management. For unqualified products with upper deviation and lower deviation, the screening equipment will be automatically activated to remove them, and an alarm will sound to remind the actual operating staff to pay attention. The weighing controller not only has the functions of sound dynamic weighing and screening operation, but also has the functions of zero-point automatic tracking, peeling, and zero-clearing, etc. It is a high-precision universal display instrument meter.

Its key performance parameters are:. Display screen: four-digit seven-segment LED digital display tube. Display screen resolution: more than 300 million. Sensor encourages switching power supply: DC15V. One 16 printer interface. Operating temperature: one 10-40 ℃. Power supply system switching power supply: AC380VsoHz Second, software development The mobile phone software of all system software is divided into background operation and reception program flow. Contents that are not very practical, such as copying, data processing methods, and net weight screening and identification, are allocated to the background management work; while the content that is more practical for collection, timing execution, etc., are allocated to the receptionist. The software development adopts a modular design structure, which is divided into several program modules according to the daily tasks, which is helpful for adjustment, expansion and transplantation.

The simplified frame diagram of the source program is shown in Figure 3. In order to carry out static data weighing and dynamic screening and weighing, the program flow mainly carries out functional analysis and anti-interference design. Each is described below.

1. Function analysis The function analysis of the mobile phone software is mainly to design various program modules, and according to this program module, carry out various essential daily tasks. In this program flow, the key functions performed by the mobile phone software may be:. Zero-point automatic tracking;. Peeling;.. Zero-point calibration;. Data collection; Timing execution;.Read key and setting;.Operation/check conversion;.Copy;.Unlock the displayed information value under the operation method;. Under the management of the system monitoring program, this program module performs static data weighing or dynamic screening and weighing according to the predetermined implementation plan.

2. Anti-interference design scheme Because the multihead weigher works in the natural environment of industrial production, there are various influences on the spot, which endanger the normal work of the scale. Therefore, in addition to the hardware configuration anti-jamming countermeasures, the mobile phone software anti-jamming countermeasures as the second defense is also very critical and indispensable. A sound system software should not only carry out functional analysis, but also carry out anti-interference design scheme to improve the reliability of the system software.

The system software selects the following two anti-interference countermeasures for mobile phone software: (1) The anti-interference electromagnetic interference of analog signal I/O safety channel is mostly burr-like, and the effect time is short. According to this characteristic, when collecting the net weight data signal, it can be continuously collected for several times, until the results of the continuous two collections are completely the same, the data signal is reasonable. If the data signal is inconsistent after several collections, the current data signal collection will be discarded.

The maximum frequency limit of each collection and the continuous same frequency can be adjusted according to specific requirements. The maximum amount collected in this program flow is 4 times, and 2 consecutive times are also reasonable collections. For the output safety channel, even if the MCU is designed to obtain appropriate output data information, the output device may obtain incorrect data information due to external influences.

On the mobile phone software, a more reasonable anti-interference countermeasure is to output the same data information repeatedly. The repetition cycle time is as short as possible, so that after receiving an affected error report, the peripheral device can't make a reasonable response in time, and an appropriate output information content has arrived again. That way, wrong posture is immediately avoided.

In this program flow, the output is placed in the timing execution interrupt, which can reasonably avoid the output error operation. (2) Digital filtering is aimed at the collected net weight data signal, which often has arbitrary influence, so it is necessary to obtain the data information close to the real value of the point from the data information series products, and obtain a result with a high degree of authenticity. In mobile phone software, the common method is digital filtering.

This program flow is divided into static data weighing and dynamic screening weighing. Due to the different weighing methods, the selected digital filtering methods are also different. The different digital filtering methods adopted by the two weighing methods are respectively indicated below.

¹Static data weighing: The key consideration of static data weighing is the reliability and precision of the system software. It is necessary to take into account the relative stability of the displayed information under stable conditions and the fast response during loading. Therefore, the reliability identification of the collected data information should be carried out first, and then the digital filtering solution should be carried out.

In the process of digital filtering procedure, the moving average filtering technique is selected to improve the actual filtering effect. The specific method is as follows: each time a sample is taken, one of the earliest data information is removed, and then the sampling value of this time and the sampling value of many previous times are averaged together, and the reasonable sampling value obtained by the individual can be delivered for use. Therefore, this improves the usability of the system software.

The selection of sampling frequency N has great harm to the actual effect of filtering. The larger N is, the better the actual effect is, but it will endanger the dynamic response of the system software. In this weighing controller, in order to improve the reliability of the system software and the ability to respond quickly, N is 32 when it is stable, and 8 when it is unstable.

Because of choosing a reasonable filtering method, the reliability and precision of the system software and its loading response time have been further improved.ºDynamic screening and weighing: In the dynamic screening and weighing, the tread is quickly based on the weighing platform. The tread is on the scale within 1.5 seconds, so sampling must be done within 1 second.

In that way, the sampling frequency is limited. In addition, because the tread will cause a certain vibration when it is quickly adjusted to the weighing platform, it will affect the sampling value. Therefore, it is very important to consider what data information is valid and what kind of digital filtering technology is selected to suppress the harm of heavy symmetry of electromagnetic interference.

According to the specific observation, the multihead weigher's weighing data signal waveform is shown in Figure 5. In the figure, from the arrival of the tread to the weighing platform until its departure is divided into three links: the first stage is the time t, segment, which is the whole process from the arrival of the tread to the weighing platform until it is completely on the weighing platform. The net weight data signal is here. The second stage is the ninth stage, the tread is completely on the weighing platform, and this period is the weighing stage; the third stage is the time t. The segment is the whole process that the tread leaves the weighing platform, and the net weight data signal slowly decreases to zero during this period.

At the beginning and end of the nine weighing sections, the weighing data signal suffers relatively heavier effects. In the mountain section, that is, when the tread is in the middle of the weighing platform, the weighing data signal is relatively stable. Therefore, it is more ideal to choose the data information of the Δt time range.

Use the placed scale to walk to the end of the photoelectric switch to start the weighing controller to receive the dynamic sampling data information, and sample within the mountain time. The sampling frequency N is related to the sampling rate. The faster the sampling speed is, the higher the collected frequency N is. The installation of the photoelectric switch must ensure that the collected visual data is the data information when the object to be weighed is located in the city of Weitaishan.

For the N data information collected, all have different influence components, so it is necessary to choose a reasonable filtering method to obtain the true value of the tread net weight. This procedure selects the composite filtering technology, that is, the application of two or more digital filtering methods is combined and applied, which is not enough to complement each other, so as to improve the actual effect of filtering, so as to achieve the actual effect that cannot be achieved by only a single filtering method. Here, the filtering method that combines the maximum value filtering method and the arithmetic mean filtering method is selected.

De-maxima filtering first removes the significant single-pulse influence value, and does not sign up for mean value calculation, so that the output value of mean filtering is closer to the true value. The basic principle of the optimization algorithm is as follows: continue to sample N times, accumulate and ask for mercy, and find the highest and minimum values ​​in it, and then subtract the highest and minimum values ​​from the accumulation and vertical, and calculate according to N one or two sampling values. mean, that is, to obtain a reasonable sampling value. The flow chart of the compound filtering procedure is shown in the waveform diagram of the weighing data signal in Fig. 5. From the arrival of the tread to the weighing platform until its departure, it is divided into three links: the first stage is the time t, segment, which is the time when the tread arrives at the scale. The whole process from the platform until it is completely on the scale platform, the net weight data signal slowly rises during this period; the second stage is the time period nine, the tread is completely on the scale platform, this period is the weighing section; the third stage That is time t.

The segment is the whole process that the tread leaves the weighing platform, and the net weight data signal slowly decreases to zero during this period. At the beginning and end of the nine weighing sections, the weighing data signal suffers relatively heavier effects. In the mountain section, that is, when the tread is in the middle of the weighing platform, the weighing data signal is relatively stable.

Therefore, it is more ideal to choose the data information of the Δt time period. Use the placed scale to walk to the end of the photoelectric switch to start the weighing controller to receive the dynamic sampling data information, and sample within the mountain time. The sampling frequency N is related to the sampling rate. The faster the sampling speed is, the higher the collected frequency N is.

The installation of the photoelectric switch must ensure that the arithmetic mean of the collected values ​​in the formula and N is the arithmetic mean of the 2 sampling values; w is the i-th sampling value; N is the sampling frequency. In order to facilitate the calculation, the sampling frequency is generally selected as 6, 10, 18 such as 2 to the power of the integer amount of 2 plus 2, which is convenient to use shift instead of division. In this program flow, the solution is selected while sampling, so there is no need to develop the data information storage area in the ruler AM.

After digital filtering, the W value is obtained, and then data processing methods such as peeling and average error conversion are carried out to obtain the tread net weight value for display information, identification and copying. After the second photoelectric switch detects that the tread has completely left the weighing platform, start the zero-point tracking assembler, select the large sample sample and drag the average filter technology, and automatically remove the tare, so as to prepare for the arrival of the next tread. Accept advance preparation. 3. Conclusion The weighing controller has perfect functions and strong anti-interference. It is not only suitable for tread screening operation in the field of vulcanized rubber, but also suitable for the operation of various multihead weighers such as eggs, coins, livestock, and industrial production lines.

At this stage, the multihead weigher introduced by some manufacturers in our country has been used for more than ten years. Some weighing controllers can no longer work normally, and are in urgent need of replacement. In addition, there are also some manufacturers who still use the pedal-type multihead weigher, which cannot be considered necessary for production and manufacturing. Therefore, the weighing controller has an extremely useful marketing promotion value today.

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