This article introduces the application of a photoelectric diameter control system in a fiber filter rod forming machine, and provides a detailed explanation of the control scheme and principle for the filter rod diameter. 1. Introduction A fiber filter rod forming machine is an essential piece of equipment for manufacturing cigarette filters. The filter rods it produces are cut to meet specific requirements for cigarette filters. The quality of the cigarette filters directly affects the taste of the cigarette and the filtration of harmful substances in the smoke. The diameter of the filter rod is a crucial standard for evaluating its quality, and controlling the fluctuation of the product diameter directly affects the effectiveness of subsequent production processes. With the rapid development of tobacco equipment, tobacco factories are constantly raising their requirements for filter rod quality, and the development of new diameter control systems has gradually become an important topic in the forming process. 2. Introduction to the Pneumatic Diameter Detection/Control System The ZL22D fiber filter rod forming machine is a relatively new filter rod forming unit independently designed based on imported German technology. It adopts a servo control system from Lenze, significantly improving the unit's performance. However, the detection and control system for the filter rod diameter of this unit still relies on the detection method of using a thyristor to detect air pressure. The working principle diagram is shown in Figure 1: When the unit is in normal production, filter rods are continuously fed into the detection chamber. The solenoid valve opens, and a stable flow of compressed air is supplied from the air source to the detection chamber and the diameter controller. The air pressure in the detection chamber indirectly reflects the diameter of the filter rod. The air pressure and diameter values ​​are linearly related within a certain range. Subsequently, the diameter control device converts the air pressure signal into a voltage signal through a converter. The voltage signal is sent to the calculation circuit for processing, and the output of relay K1 or K2 is determined by the thyristor. This controls whether the motor M is running in the forward or reverse direction. The motor raises or lowers the forming gun to adjust the diameter of the filter rod. The output shaft of the motor has a large-proportion reducer, and the motor displacement calculation has high resolution, enabling high-precision control of the row spacing to adjust the diameter of the filter rod. [IMG=Figure 1 Pneumatic Diameter Control Principle Diagram]/uploadpic/THESIS/2007/11/2007111611313576654X.jpg[/IMG] Figure 1 Pneumatic Diameter Control Principle Diagram [IMG=Figure 2 Photoelectric Diameter Controller Principle Diagram]/uploadpic/THESIS/2007/11/2007111611285655273Q.jpg[/IMG] Figure 2 Photoelectric Diameter Controller Principle Diagram uses such a pneumatic pressure detection device, but in actual use, it faces many difficult problems: (1) The pneumatic circuit is complex to build and takes up a lot of space. After long-term use, various air pipes will age, and the reduction of the pneumatic circuit sealing performance will easily affect the control accuracy. (2) With long-term use, dust will easily accumulate in the pneumatic pressure detection chamber, thereby reducing the detection accuracy, and frequent cleaning and maintenance are required. (3) Although the calculation circuit has a fast response, the control method is relatively backward. (4) The noise generated by the pneumatic circuit is very loud during normal operation. (5) The pneumatic circuit is greatly affected by environmental factors. The ambient temperature and humidity will affect the expansion and density of the gas, thus affecting the normal operation of the diameter control. Due to the shortcomings of the pneumatic controller, this modification decided to eliminate the detection components of the pneumatic control system and adopt a photoelectric diameter control system. The internal calculation circuit board was eliminated and replaced by PLC control and calculation of internal parameters. The execution components of the pneumatic control were retained. 3 Selection of Photoelectric Diameter Detection Devices Using a photoelectric detector as the detection element of the diameter controller can indeed make up for many shortcomings of the pneumatic control. The photoelectric detector has a simple structure, is easy to install, has a long service life, is not easily affected by the environment, and is noiseless during operation. Most importantly, the photoelectric detector can provide various forms of voltage signals to the PLC at the expense of a certain tolerable speed. The PLC's powerful computing power can be used to implement a control strategy with high automation control capability, which can improve the system's fast response speed and stability. The following factors need to be considered when selecting a photoelectric detector: The photoelectric detector must be able to operate in a dark room; the detection accuracy of the photoelectric detector must not be lower than 0.01mm; the size of the photoelectric detector has certain limitations. After repeated comparisons and consultations, the KEYENCE LS-7000 series sensor was finally selected. Its static accuracy is 0.2μm, dynamic accuracy is 2μm, and the maximum sampling speed is 4096 times/s. 4. Theoretical Basis of Unidirectional Photoelectric Diameter Detection The roundness of the filter rod is actually ensured by adjusting the shape of the filter rod forming cavity. The expansion or contraction of the filter rod after forming obviously follows the principle of expansion. This change in shape should have the same vector value in all directions in space, that is, the deformation of expansion or contraction in all directions on a certain cross-section is the same. Although the influence of gravity and the impact deformation caused by subsequent cutting by the cutter head must also be considered, it can still be confirmed that the cross-section of the filter rod is circular or approximately circular. Therefore, the data obtained by unidirectional detection must be its diameter data. The control method adopted previously is not the most suitable control method. Since the filter rod is made of pressed filament bundles, and the density of the filament bundles is not constant and varies in size, the diameter also varies. This variation is not a continuous linear variation, but a continuous nonlinear variation, which cannot be represented by a linear function, but a nonlinear function. [IMG=Figure 3 Main program of diameter control part]/uploadpic/THESIS/2007/11/20071116114908858997.jpg[/IMG] Figure 3 Main program of diameter control part [IMG=Figure 4 Diameter control parameter interface]/uploadpic/THESIS/2007/11/20071116114956151474.jpg[/IMG] Figure 4 Diameter control parameter interface 5 System design of photoelectric diameter control In the new photoelectric diameter control system, the overall design scheme is as follows: (1) It is proposed to use a set of photoelectric sensors to replace the current detection unit: the sensor detects the diameter of the filter rod (X direction), and the obtained signal is input to the PLC in the form of voltage. Operators can set parameters and provide data feedback through the human-machine interface (HMI). (2) Starting circuit and diameter control execution unit of diameter control motor: The diameter control execution unit retains the original design, and the input control of diameter control motor is controlled by the PLC I/O through the original circuit. (3) Mechanical components of diameter control device: Most mechanical components will not be replaced, but the relevant protective components and diameter measurement components of the unit must be redesigned. (4) Original air circuit components: All removed. 5.1 Hardware design The hardware design schematic diagram of this modification is shown in Figure 2. The control system designed in this modification is based on the original pneumatic system. The original complex diameter control circuit, solenoid valve, detection air chamber, and air circuit components have been removed, and a set of photoelectric detectors has been added. After the filter rod is formed, it passes through the photoelectric detection device. The photoelectric detection transmitter emits a light curtain to the photoelectric detection receiver. After the filter rod passes through the light curtain, it blocks part of the light reception. The difference between the emitted light and the received light reflects the diameter of the filter rod. When the diameter of the filter rod increases, the amount of light blocked by the filter rod increases, and the amount of light received by the photoelectric detector decreases. The photoelectric detector converts the difference between the emitted and received light into an analog signal and transmits it to the upper PLC. The PLC performs relevant analog control calculations and outputs a digital signal to control relays K1 to engage and K2 to disengage. This causes the diameter control motor to rotate forward and press down on the forming gun, thus reducing the diameter of the filter rod. Conversely, when the diameter of the filter rod decreases, the amount of light blocked by the filter rod decreases, and the amount of light received by the photoelectric detector increases. The photoelectric detector converts the difference between the emitted and received light into an analog signal and transmits it to the upper PLC. The PLC performs relevant analog control calculations and outputs a digital signal to control relays K1 to disengage and K2 to engage. This causes the diameter control motor to rotate in reverse and press down on the forming gun, thus increasing the diameter of the filter rod. 5.2 Software Control Design Process Because the density of the filament bundle is not uniform and exhibits nonlinearity, the diameter change of the filter rod after passing through the forming cavity is also nonlinear. Based on this, the control method adopted must be designed to address this nonlinear change. First, let's analyze the change in the diameter of the filter rod. After the filter rod is formed by opening the filament bundle, its diameter is the same at the moment it leaves the forming cavity, assuming the forming cavity remains unchanged. However, due to the different densities of the filament bundle wrapped around the filter rod, the diameter changes. That is, although the vectors in all directions of expansion or contraction are equal at a certain cross-section, the vectors corresponding to different cross-sections are not equal. Combined with the influence of factors such as paper rolls and glue, this results in a non-linear change in the filter rod diameter. The calculation formula is as follows: D(x, t) = f(x) * [1 + c(t) + ∑ei(t)] Formula 1: Calculation formula for filter rod diameter change. In the formula, x and t represent the position and time values ​​of the forming cavity, respectively. D(x, t) is the diameter change formula, f(x) is the linear equation for the diameter change caused by the position of the forming cavity, c(t) is the non-linear equation for the diameter change caused by the filament bundle density corresponding to time, and ∑ei(t) represents the system of linear and non-linear equations for the diameter change caused by other factors corresponding to time. Secondly, we need to clarify our control object. Since ∑ei(t) can be considered as an error, it can be treated as a disturbance factor rather than a controlled object in control, simplifying the formula to: D(x, t) = f(x) * [1 + c(t)] Equation 2 Simplified formula for filter rod diameter change. Therefore, our controlled object is the linear equation of diameter change with respect to the forming cavity position and the nonlinear equation of diameter change with respect to the fiber density over time. Finally, we need to design the control system based on the controlled object. The linear equation of diameter change with respect to the forming cavity position can be regarded as a first-order proportional equation. Although the density change is nonlinear, it can be determined that it follows a Poisson distribution. Therefore, the result of the nonlinear equation of diameter change with respect to the fiber density over time also follows a Poisson distribution. Therefore, the adaptive control algorithm is used for the overall design of the control program. The main program is shown in Figure 3. At the same time, in order to make it easier for users to set various diameter control parameters and display the current filter rod diameter value and change status in real time, a new page needs to be added to the original human-machine interface, as shown in Figure 4. This page displays the current filter rod diameter, converts it to a circumference value, and sets the given diameter value and upper/lower limits of the allowable range. For ease of use, the page includes forward and reverse buttons, allowing operators to directly control the motor to raise or lower the filter gun to control the diameter, facilitating easy adjustments for deviations. The interface design retains the basic functions of pneumatic control as much as possible, enabling operators to learn and use the new device more easily and quickly. 6. Debugging and Summary After assembly and debugging, the improved equipment entered the trial run phase. The device performed well, accurately controlling the filter rod diameter and overcoming the shortcomings of the original device. During the test, it was found that to ensure the operation of the photoelectric diameter controller, the shape of the forming gun must be precisely adjusted to ensure the roundness of the filter rod. This indicates that the device places new demands on the mechanical adjustment of the unit. 7. Conclusion The rapid development of electronic control systems has brought about various new detection methods and instruments, as well as new control concepts and methods. The photoelectric detection/control system for filter rod diameter represents a completely new design attempt for tobacco equipment: independently analyzing and designing the entire control system without relying on external forces. Furthermore, replacing the currently used control motor with a 0.25kW AC servo motor from Lenze will further improve the control accuracy and capability of the unit. (Proceedings of the 2nd Servo and Motion Control Forum; Proceedings of the 3rd Servo and Motion Control Forum)