Design of Pneumatic Coil Tension Control Mechanism of Packaging Machine
Abstract: Introduce a new type of packaging machine tension control machine. The mechanism uses the flexible characteristics of pneumatic actuators to enable the packaging machine to achieve high-speed unwinding, and to ensure that the tension of the packaging material is small and constant, so as to meet the requirements of modern high-speed packaging mechanism for its unwinding.
Foreword: In recent years, pneumatic technology has been widely used in the packaging machinery industry, which has made great progress in the packaging machinery industry. Due to the massive intervention of advanced technologies such as pneumatic and computer control, the mechanical structure of modern packaging machinery has been greatly simplified, the cost of equipment has been reduced, and the packaging speed and the automatic ratio and reliability of product appearance technicians have not been improved. It has been greatly improved.
The pneumatic mechanism moves briskly, does not pollute the environment, and can well meet the requirements of packaging machinery for speed and environment. Modern packaging machinery generally uses cylinders as actuators, mainly using cylinders with linear output and adjustable speed, etc., thus absorbing the traditional deceleration and conversion mechanism from rotary motion to linear motion, effectively simplifying the packaging machinery The transmission mechanism reduces the cost and shortens the production cycle. In addition, using the cylinder as the actuator, the timing requirements of the coordination work of the entire actuator can be solved by adjusting the control software. Compared with the traditional cam control mechanism, this can save a lot of installation and commissioning work, which is also an important reason for the popularity of pneumatic technology in the packaging machinery industry. Pneumatic actuators have good flexibility, or the speed and stroke of the cylinder piston can be constrained by other mechanisms. Using this characteristic of pneumatic actuators, it can be designed as a composite mechanism of pneumatic and mechanical combination to achieve accurate movement coordination and synchronization, or it can be set up as a flexible actuator. This flexible mechanism can complete some specific tasks. . Including the machine pneumatic tension control mechanism is an example of working with the flexibility of the cylinder.
1. Brief introduction of the pneumatic coil tension control mechanism of the packaging machine The pneumatic coil tension control of the packaging machine is divided into two periods:
1) Film opening period: As shown in Figure 1, the servo motor does not run, the vacuum suction cup sucks the packaging material, and the film supply roller brake cylinder releases the film supply roller brake disk. The film supply roller is in a free state and the swing lever Under the combined action of the downward pulling force of the film pulling floating cylinder, the swing rod swings downward, and the film feeding roller is rotated by the packaging material to open the film. When the swing lever runs down to the action position of the proximity switch, the sensor sends a signal, the PLC controls the brake cylinder to brake the film supply roller, and at the same time controls the solenoid valve that pulls the film floating cylinder to swing downward, and the swing lever acts on gravity Sagging naturally.
2) Film pulling period: First, the vacuum suction cup releases the vacuum and releases the packaging materials. At the same time, the two-position three-way solenoid valve that controls the upward movement of the film pulling floating cylinder is energized, so that the cylinder generates thrust for upward operation. By adjusting the pressure reducing valve (Figure 2), the upward thrust of the cylinder is smaller than the total force of the swing rod gravity acting on the cylinder rod (generally, the difference is 1.5-2Kg). At this time, the piston rod of the film pulling cylinder does not move, and the film pulling floats The role of the air cylinder at this time is to reduce the weight of the swing rod, and at the same time make the packaging material have a certain tension, and then the servo motor starts to pull the film. The motion of the servo motor pulling the film is intermittent, and the length of each film pulling is determined by the positioning color mark on the packaging material. The color marks on the packaging material are equally spaced. When the color sensor detects the positioning color mark of the packaging material, it sends a signal to the PLC. The PLC determines that the positioning film block controls the servo motor to quickly stop, and realizes the rapid fixed-length film pulling. At the same time, the solenoid valve is controlled so that the vacuum suction cup sucks the packaging material, reducing the forwarding of the packaging material, and at the same time turning off the solenoid valve that controls the upward movement of the floating cylinder, so that the swing rod sags naturally, otherwise the forward movement of the packaging material is large, although the floating cylinder The generated thrust is less than the weight of the swing rod, but because the lower chamber of the floating cylinder already has compressed air, the swing rod sometimes cannot fully fall back to tighten the wrap rod by its own weight, so the compressed air in the lower chamber of the floating cylinder needs to be temporarily released, etc. After the swing lever is fully retracted, the solenoid valve that controls the upward movement of the floating cylinder is opened to prepare for the next film pulling. This mechanism can make the packaging material have a small constant tension, and at the same time have enough film opening tension, which improves the packaging speed. This mechanism utilizes the flexible work of pneumatic actuators, which can not only force the swing rod to swing downward to open the film, but also have the characteristics of floating. The mechanism is applied to a 400g automatic nitrogen-filled milk powder packaging machine, and the use effect is very good.
2 Dynamic parameter calculation of pneumatic tension control mechanism of packaging machine 2.1 Unwinding tension calculation Rotational inertia of packaging film roll consists of two parts, one is the rotational inertia of the film expansion shaft itself, and the other is the rotational inertia of the packaging material roll itself . The rotational inertia of the expansion shaft can be calculated as a cylinder, the formula is J! == 1 / 2m · R12 (1)
In the formula; J1——the rotational inertia of the expansion shaft, Aem2;
m1——the mass of the expansion shaft, Kg;
R1——The radius of the expansion axis, m.
The rotational inertia of the film itself can be calculated according to the rotational inertia of the cylinder, the formula is J2 == 1/2 m2 (R22 + r2) (2)
In the formula, J2——the moment of inertia of the roll film, Kgm2;
m2-the quality of the roll film, Kg;
R2——outer diameter of roll film, m;
r-the inner diameter of a roll of film, m.
It should be noted that the quality and outer diameter of the roll film are gradually reduced during the work process. During the operation of the packaging machine, the rotational inertia of the roll film is changed, and the radius of the tension of the packaging material is also changed. In order to find the maximum unwinding tension, it should be calculated separately under two limit states. Take the maximum value as the basis for selecting system parameters. According to the action requirements of the packaging machine, the unwinding time t≤0.4S; the unwinding length of the packaging material L≥0.2m, calculate the tension F required for unwinding.
Design of Pneumatic Coil Tension Control Mechanism of Packaging Machine
In order to simplify the calculation and omit the influence of friction, the unwinding process is regarded as uniformly accelerated circular motion. The calculation formula for the length of each unwinding package is H == 1 / 4л · R · at2 (3)
In the formula, H——Package material length, m;
R——outer roll diameter, m:
a——Acceleration, m / S2;
t——Unwind time, s.
The formula for calculating the acceleration of circular motion is a == Mg ï¼ J == RF / J (4)
Where Mg == RF, where R—the outer diameter of the packaging material, m
F——Packing material tension, N.
Take formula (4) into (3) to get the formula for calculating the tension of the package material F == 2H · J ï¼ R2 · t2 (5)
Where J = J1 + J2—the total rotational inertia of the film roll, kgm2;
In order to determine the unwinding tension, it is necessary to calculate the unwinding tension under the two limit cases of the maximum outer diameter of the packaging material and the minimum outer diameter of the packaging material:
Unwinding tension at the maximum diameter of package material Fdmax == 14.04N
Unwinding tension at the minimum diameter of packaging material Fdmin == 50.6N
According to the above calculation results, the maximum tension occurs when the packing material is the least, so the cylinder size can be determined according to the tension when the packing material is the least.
2.2 Calculation of Cylinder Tension In Figure (3), the swing angle of the swing rod is ± 10o. The position of the swing rod varies with respect to the direction of action of the swing center. The cylinder requires the most tension in the extreme position,
The cylinder bore is calculated based on this pulling force.
The force balance equation of the swing lever is 4F · L1ï¼F1F2 ï¼F2L3 == 0 working (6)
Then the calculation formula of cylinder tension is F2 == 4F · L1 / L2-ï¼F1 · L2 / L2 (7)
In the formula F2-the pulling force generated by the cylinder, N
F-Tension of roll film. N;
F1—the mass of the swing rod, Kg;
L2—The distance between the action point of the tension of the packaging material on the swing bar and the swing center of the swing bar, m;
L1——the distance m from the center of mass of the swing rod to the swing center of the swing rod;
L3——The vertical distance between the action point of the swing rod cylinder tension and the swing center of the swing rod, m.
Table 2 The geometric and mechanical parameters of the swinging rod The working pressure of the packaging machine system is 0.65Mpa. In order to have a certain adjustment range for the pulling force of the floating cylinder, the working pressure is initially determined to be 0.5Mpa. SMC's CDM2B32-150 cylinder.
3 Installation, commissioning and use of the pneumatic coil tension control mechanism of the packaging machine The pneumatic coil tension control mechanism of the packaging machine is specially designed for the 400g automatic nitrogen-filled milk powder packaging machine, which has been officially put into production and is in good operating condition. During commissioning, the working pressure of the pressure reducing valve (2) that controls the working pressure of the pneumatic circuit pulled down by the floating cylinder is set to 0.45Mpa, and the working pressure of the floating cylinder pushes the reducing valve (1) to 0.3Mpa The actual measured uncoiling time is 0.42s, the uncoiling length is 0.23m, and the tension of the packaging material during the film-drawing period is 1.8kg. The requirements for unwinding work illustrate the feasibility of the above structural scheme and the correctness of the calculation.
4 Conclusion 1) This article gives the design criteria of the pneumatic coil tension control mechanism of the packaging machine. The production practice proves that the system has stable performance and reliable operation, and meets the requirements of modern high-speed packaging machinery for unwinding its packaging materials.
2) Because of its flexibility and cleanliness, pneumatic control is easy to form a machine electrical integration system, which will further enhance the overall level of the packaging machinery industry.
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