Design of automatic detector for missing bars in t

Design of automatic detector for cigarette box missing bars

the last process of cigarette production is cigarette packing. According to the field observation and understanding for many times, the box packer sometimes works disorderly, especially when the production flow of the box packer is large or the incoming materials are insufficient, the box packer works abnormally, and there is a lack of 1 ~ 10 cigarettes; In order not to damage the mutually beneficial relationship between customers, dealers and manufacturers, the tobacco factory sends more employees to this post to monitor, check and fill vacancies, which is a high labor intensity of workers. At the request of a factory, the author designed an automatic detector for cigarette box missing bars

1 existing equipment and defects

the existing equipment mainly uses photoelectric detection to check whether the cigarette box is missing or not. Its basic principle is to install five groups of light-emitting diodes and photoelectric receiving tubes in the cigarette packing machine, the light-emitting diodes emit light signals, and when there are cigarette sticks, the light emitted by the diodes is reflected to the photoelectric receiving tubes through the surface of the cigarette sticks. However, when there are cigarette sticks placed obliquely, the light emitted by one group of light-emitting diodes may be received by another group of photoelectric receiving tubes, and this method cannot make a reliable judgment

2 principle and circuit implementation of capacitive smoke box strip missing detector

2.1 basic principle

capacitive sensor can transform the change of non electric quantity into the change of capacitance. When designing, flat capacitor is used, and its capacitance is: (2--1)

where ε Is the dielectric constant of the medium between the plates; S is the effective area of two plates facing each other; D is the distance between plates. It can be seen from the continuous 5% annual growth rate (2-1) of formula, as long as D, s ε One of the three can change the capacitance. Figure 2-1 shows the AC bridge measurement circuit, C2 is the flat capacitance sensor, and the parameters of the other three components are known. When using the capacitance sensor to detect the smoke box, the whole smoke box is used as the medium of the capacitor. When the number of cigarettes in the smoke box changes, C2 changes accordingly, and affects the output voltage of the AC bridge. Therefore, this method can be used to make the smoke box strip missing detector

2.2 working principle of detector

system block diagram is shown in Figure 2-2. The whole instrument is divided into two parts, the dotted box is the detection part, and the rest is the data processing part. The working process is as follows: when a smoke box arrives, the proximity switch outputs a high level, which is connected to the MCU bit P1.7 and starts the sinusoidal oscillation circuit. The sinusoidal oscillation signal is added to the AC bridge and the output signal uo. In order to ensure the reliable operation of the AC measuring circuit, it is necessary to add a primary amplifier to amplify and isolate it, and then it is rectified by the precision rectifier circuit. Because the voltage here is high, it is necessary to add a sampling circuit to make the output voltage between 0 and 1oV. In addition, the singlechip P1.0, P1.1 and P1.2 output the selection signal to the electronic switch, which always remains the same. The electronic switch changes everything of the five signals to the voltage frequency of 0 At the input end of 10mpa/s speed loading rate circuit, because the input voltage is proportional to the output frequency, the output binary signal excites the LED, and the optical signal is transmitted to the photoelectric receiving circuit by the optical fiber. The binary signal is sent to the T1 count of the single chip microcomputer 8051, and the data is stored in RAM. After completion, p1.3 outputs a high level, starts electromagnet 1, moves five capacitive sensors for a certain distance (less than or equal to the width of a cigarette), and then repeats the above action. The MCU compares the collected 10 data with the internal standard data. If a certain data exceeds a certain deviation range, it will judge the corresponding pile of missing bars, output a high level from P1.4, start electromagnet 2, and push the smoke box out of the assembly line

2.3 technical methods used in design and production

(1) a box of cigarettes is divided into 5 layers and 10 stacks, a total of 50. In order to reliably judge whether there is a lack of smoke in the smoke box, if a parallel plate capacitor is used, the output voltage may be the same as that when there is no lack of smoke. In order to avoid this situation, five flat-panel capacitive sensors are used to collect the output voltage of 10 stacks of smoke as the medium twice, and the CPU can judge whether the cigarette pack is missing or not by comparing the obtained data. The first advantage of this design is that the parameters of adjacent products are relatively close; The second advantage is that the larger overall mass error of the whole box of cigarettes is dispersed into smaller individual mass errors, which can be ignored compared with the change of medium type and effective thickness; The third advantage is that the influence of temperature change on the structural stability and dielectric constant of capacitive sensor can be ignored

(2) because the cigarettes produced by a cigarette production line cannot be the same brand. In order to make the cigarette box strip missing detector applicable to the strip missing detection of various brands, a button with the function of reading standard data is designed. The operator can select five cigarettes with quality standards, and then press the read key, and the single chip microcomputer will take it as standard data; This avoids tedious debugging and setting data

(3) in order to eliminate the influence of edge effect, the structure of protective ring is adopted in the structural design of capacitive sensor, which is also the reason why 10 capacitive sensors are not directly used

(4) any capacitor is equivalent to the parallel connection of a capacitor C and a leakage resistance R, which form a complex impedance added to the measuring circuit to affect the output, which will lead to slow zero drift of the output of the sensor in serious cases. The leakage resistance R is mainly affected by the surface resistance of the capacitive sensor, so when designing and manufacturing the capacitive sensor, the ceramic and thin copper sheets are bonded together, which not only solves the problem of too small leakage resistance, but also solves the problem of heat dissipation

(5) the system only judges the lack of bars in the cigarette box, and there is no closed-loop control process. Considering the improvement of the anti-interference ability of the system, it does not use the expensive a/D converter, but uses the voltage frequency converter (V/F) and the internal hardware resources of the single chip microcomputer to replace the A/D converter to collect data, which is simple, convenient and low-cost. Figure 2-3 shows the specific circuit. LM331 and op-27 form a V/F converter. The relationship between input and output is shown in formula (2-2):