Application of Compound Metering Belt Scale

1.  Introduction

Factor affected the accuracy of belt scale measurement is more, such as the speed of belt, wandering, belt scale elastic modulus changing with temperature and time, weighing before and after the period and the operation condition of the roller group, scale structure and installation and debugging process, and the calibration method of belt scale, maintenance, management and so on are different degrees of influence on the accuracy of belt scale.The actual situation has proved that some traditional electronic belt scales can not reach the accuracy promised by the manufacturer in the field operation. Therefore, the application of high-precision metering belt scales is an effective means to solve the problems existing in the belt scales.

2. The main problems existing in the electronic belt scales

2.1 The formulation of the belt conveyor standard does not take into account the technical requirements of measurement, such as the operation condition of the weighing section and the idlers before and after it, the change of the belt tension, and the process environment of the scale frame installation point.

2.2 At present, most of the scale frames provided by manufacturers are made use of the roller frames and rollers on the field belt conveyor. As the roller sets are "rivet welded parts" according to the technical standards, the shape and position errors of the roller frames are far greater than 1.0mm, and the axial movement and radial runout of the roller are greater than the technical requirements of 0.5mm and 0.2mm.

2.3 At present, 80% of on-line metering belt scales cannot meet the technological conditions of physical inspection.Chain code, and code such as simulation load test can only simulate the belt on the whole transport state of a certain period of material transportation, not on the belt conveyor in the process of actual production the conveying belt tension is full of material and the change of the belt tension state, through the actual test results show also the chain code such as simulation test compared with physical inspection, there are still some differences.

2.4 The influence of material changes on dynamic linearity (even if the multi-point linear correction function of the secondary meter can be used to correct it, it is difficult to provide a standard quantity of multiple repeated material flows).

2.5 Whether the measurement of the electronic belt scale is accurate in the process of operation can only be determined by the physical inspection after the event.

3. The characteristics and principles of compound metering belt scales

3.1 Basic principle of system inspection

In a belt installed two performance of the same belt scale, and the two belt scale error in the same scope, USES the material inspection bar code superposition method, namely in one of the platform scale automatically add standard load, the normal delivery, after weighing the material will be two platform scale weighing result is presupposed, subtracting the result compared with the actual weight of standard load, get the corresponding relation,To achieve the purpose of belt balance check.Material bar code superposition method: zero adjustment is carried out first, and then the error value and error direction of the two scales are adjusted within the range of basic requirements (the error value is less than 0.1%);In the material bar code superposition method test, normal delivery of materials, and in one of the scale frame such as scale frame 2) bar weight added;At this time, the accumulator of 2 scales accumulates and obtains the difference of the accumulative quantity △P when the belt runs the integer circle;The adjustment coefficient K is calculated by adding relevant formulas of weights, and the coefficient is the adjustment coefficient of scale frame 2 (since the error of two scales is the same at this time, so the coefficient is also equal to the adjustment coefficient of scale 1). The test process ends.

3.2 Analysis of technical characteristics

3.2.1 double scale frame

A company in a set of weighing system selected two three roller scales (see Figure 1), with two scales can be compared at any time between the two scales of the measurement data difference, once the measurement data difference exceeds the pre-specified value and is confirmed, it is necessary to immediately stop measuring and check the scale system.

3.2.2 Group of special rollers

Increase the roundness eccentricity of the weighing roller.The roundness eccentricity of the general belt conveyor roller is about 0.1mm, while the roundness eccentricity of the weighing roller of ICSPJZ-MK4 belt scale can be as high as 0.01mm.In addition, the support frame of the weight roller has good torsion resistance, and the mechanical design is equipped with fine tuning screws for symmetrical weight roller collimation and the whole module height and height adjustment mechanism, which does not need to be aligned with gaskets as the traditional belt scale.The two three-roller suspension scales adopt 6 sets of idlers specially customized by the factory for weighing. In addition, the 3 transition idlers in front and rear and the 5 transition idlers in the middle as shown in Figure 1 are all replaced with specially customized weighing idlers, so that the total number of idlers specially customized for weighing reaches 17 sets.These idlers require that the axial channeling and radial runout are not more than 0.5mm and 0.2mm respectively. The groove error of the idlers is guaranteed by the special structure of the idlers and the movable connection of the groove bearing.

3.2.3 Weighing sensor

Because the modular sensor eliminates the traditional weighing bridge, it greatly reduces the dead load of the scale and improves the use range of the sensor.I compound belt scale adopts flat quadrilateral stress structure, weighing roller is through the upper and lower spring force to the sensor, greatly improving the anti-bias load capacity.

3.2.4 The mathematical model corresponding to the standard load distribution and the actual load distribution is established

Because the standard load is constantly superimposed in the normal conveying material, the whole circle accumulative amount of the standard load before the system calibration is obtained by using the method of two scales' whole circle accumulative subtraction, which is different from any kind of simulated load inspection method. Pro/E, CAE and other technologies are also applied.Theoretical analysis of structural mechanics, simulation and multi-flexible and multi-elastomer system dynamics was carried out on the virtual prototype model of the system. The loading method of standard load was studied, and a mathematical model corresponding to the distribution of standard load and actual load was established: G=K×∑M (L-B) /L×L to correct the test coefficient.

3.2.6 Calibration method

The material bar code superposition on-line calibration method is adopted, which is carried out in the process of normal conveyance and material measurement of belt conveyor. (it is not necessary to stop production calibration and is not restricted by installation conditions) to achieve the purpose of physical calibration.

3.2.7 The influence of belt tension and other factors on measurement and calibration is avoided

Two belt scales with the same measuring performance are installed on the same belt conveyor. When the belt conveyors the materials, the two scales are affected by the same factors such as the belt tension, and the two scales can be offset by subtracting each other when checking.

3.2.8 Solve the influence of material flow changes on dynamic linearity

Using the functions of an electronic leather belt scale measuring and inspection integrated system, it is very convenient to provide a variety of repeated material flow standard quantities while conveying materials normally:Under the normal material flow state, the error of the two scales is corrected in the same range. When the conveyor changes the throughput, the dynamic linear error of the two scales is still in the same range. At this time, it is easy to solve the problem with the instrument's multi-point linear correction function.

3.2.9 Solve the accuracy of the electronic belt scale in the operation process

In the process of operation, the use of two preset relative error alarm value, can be very easy to determine whether the system is out of tolerance, and can be tested and adjusted online at any time.

4. Application of compound metering belt scales

A set of compound belt scale produced by a company is installed on the belt conveyor. The system is easy to operate, and the on-site calibration can be carried out online without affecting the production. The "bar code superimposed material object" is calibrated for 5 times with an average error of 0.3%, and the physical object is calibrated through twice.Fruits were 0.52% and 0.45%, and the errors were ±1.0%.

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