Application of the hottest stepper motor in packag

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The application of stepping motor in packaging machinery

after nearly 20 years of development, China's packaging machinery has made considerable progress, but compared with foreign countries, there is still a relatively large gap. Where is the gap? We think it mainly lies in control. In view of this, two experts, Yang Fufen of Wenzhou University and Wu Longqi of Henan University of science and technology, wrote a series of articles on the research content they are engaged in, hoping to enlighten relevant insiders

I. working principle of stepper motor

stepper motor is an open-loop control element that converts a given electric pulse signal into angular displacement or linear displacement

given an electric pulse signal, the rotor of the stepping motor will turn the corresponding angle, which is called the step angle of the stepping motor. At present, the step angle of commonly used stepping motors is mostly 1.8 degrees (commonly known as one step) or 0.9 degrees (commonly known as half step). For the progressive motor with a step angle of 0.9 degrees, when we give an electric pulse signal to the stepping motor, the stepping motor turns 0.9 degrees; Given two pulse signals, the stepper motor will turn 1.8 degrees. By analogy, the stepper motor can operate continuously if the pulse signal is given continuously. Because of the linear relationship between the electric pulse signal and the rotation angle of the stepping motor, the stepping motor has been widely used in speed control, position control and so on

the use of stepping motor requires at least three aspects of cooperation, (1) electric pulse signal generator, which repeatedly transmits electric pulse signals for stepping motor according to the given settings. At present, most of this signal is completed by programmable controller or single chip microcomputer; (2) The driver (signal amplifier), in addition to amplifying the electric pulse signal and driving the stepper motor to rotate, can also improve the service performance of the stepper motor through it. In fact, it plays an important role in the stepper motor system. Generally, a stepper motor can have a variety of drivers according to different working conditions; (3) Stepper motor, which has a variety of control principles and models, now commonly used are reactive, inductor, hybrid and so on

the speed control of the induction motor is realized by the speed of the input pulse frequency. When the frequency of the pulse decreases, the speed of the stepping motor decreases; As the frequency increases, the speed increases. The speed or position accuracy of the stepping motor can also be improved by changing the frequency

the position control of stepping motor is controlled by the given number of pulses. Given a pulse, turn a step angle, when the stop position is determined, it also determines the number of pulses that the stepper motor needs to be given. In the control of packaging machine, the number of given pulses is also related to the parameters of the mechanism, such as the diameter of the screw

in packaging machinery, in many cases, it is necessary to control the running speed and position of the actuator, which was previously completed by machinery or other means, and the mechanism is complex and difficult to adjust. After using stepping motor, not only the packaging mechanical structure becomes simple, the adjustment is convenient, the reliability is increased, but also the coarseness will be greatly improved

II. Application of stepping motor in material measurement

(I) measurement of powdery materials

screw measurement is a commonly used volumetric measurement method, which achieves the measurement by the number of turns of the screw. In order to achieve the purpose of adjusting the measurement size and improving the measurement accuracy, it is required that the screw speed can be adjusted and the position can be accurately positioned. The use of stepping motor can meet the requirements of these two aspects at the same time

for example, the measurement of powder packaging machine adopts stepping motor to control the speed and revolution of screw, which not only simplifies the mechanical structure, but also makes the control very convenient. Under the condition of no overload, the speed and stop position of the stepping motor only depend on the frequency and number of pulses of the pulse signal, and are not affected by the change of load. This has obvious accuracy advantages compared with the screw metering controlled by the electromagnetic clutch, and is more suitable for the metering of materials with large changes in specific gravity

the stepping motor is directly connected with the screw, which has simple structure and convenient maintenance. It is worth pointing out that if the overload capacity of the stepping motor is older, when it is slightly overloaded, considerable noise will appear. Therefore, after the measurement condition is determined, a larger overload coefficient should be selected to ensure the balanced operation of the stepping motor

(II) measurement of viscous materials

step motor control gear pump can also achieve accurate measurement. Gear pump has been widely used in conveying viscous substances, such as syrup, bean paste, Baijiu, oil, tomato sauce and so on. At present, piston pumps are mostly used in the measurement of these materials, which have the disadvantages of difficult adjustment, complex structure, inconvenient maintenance, high power consumption, inaccurate measurement and so on

gear pump metering depends on the meshing and rotation of a pair of gears, but it is not the most important. Materials are forcibly sent from the feed port to the discharge port through the space between teeth. The power comes from the stepping motor. The position and speed of the stepping motor are controlled by the programmable controller, and the measurement accuracy is higher than that of the piston pump

the stepping motor is suitable for running at low speed. When the speed is accelerated, the noise of the stepping motor will increase significantly, and other economic indicators will decrease significantly. For the gear pump with high speed, it is better to choose the speed-up structure. We began to adopt the structure of step motor direct connected gear pump on the viscous body packaging machine, which made it difficult to avoid noise and reliability. Later, the method of spur gear speed-up was adopted to reduce the speed of the stepping motor, the noise was controlled, the reliability was improved, and the measurement accuracy was guaranteed

III. application of stepper motor in the supply and delivery of packaging film

in the packaging machine integrating bag making, filling and sealing, it is required that the plastic film used for packaging is positioned and supplied in fixed length. Whether intermittent supply or continuous supply, it can be reliably completed by stepper motor

(I) for intermittent packaging machine

the reliability of intermittent packaging machine can be improved by using stepping motor to supply film. In the past, the intermittent belt drawing mode of crank connecting rod mechanism was mostly used for the supply and delivery of packaging film, which was complex in structure and difficult to adjust. Especially when products needed to be replaced, it was not only difficult to adjust, but also a lot of waste of packaging film. Using the stepping motor and the tension roller to directly connect the tension belt, not only the structure is simplified, but also the adjustment is extremely convenient. It can be achieved only through the button on the control panel, which saves the adjustment time and packaging materials

in the intermittent packaging machine, the feeding control of packaging materials can adopt two modes: bag length control mode and color code control mode. The bag length control mode is applicable to the packaging film without color code. It is realized by pre setting the step-by-step electrical stiffness measurement to the rotating speed of the static stiffness measuring machine, and the setting of the rotation to air ratio can be realized through the dial switch. The color code mode is equipped with a photoelectric switch, which detects the position of the color code. When the color code is detected, the photoelectric switch sends a control switch signal. After the stepping motor presses the signal, it stops rotating. After a certain time delay, it turns the film supply again and again to ensure that the film supply length is determined according to the position of the color code

(II) for continuous packaging machines

in continuous industrial packaging machines, the stepping motor rotates continuously, and the packaging film is transported uniformly and continuously. When changing the bag length, it can be achieved only through the dial switch

fourth, the stepping motor should be used last in the horizontal sealing

in the continuous packaging machine, the horizontal sealing is a very important actuator, and it is also one of the more complex mechanisms in the packaging machine. Especially for the colored packaging film, its sealing and cutting position requirements are extremely strict. In order to improve the accuracy of cutting, people have developed eccentric sprocket mechanism, crank guide rod mechanism and so on, but these mechanisms have the shortcomings of troublesome adjustment and low reliability. The main reason for these shortcomings is that the process requires the horizontal sealing wheel to be fixed speed, horizontal sealing and positioning cut-off

speed synchronization can be achieved by directly driving the transverse sealing wheel by stepping motor. The film feeding wheel of continuous packaging machine is a continuous film feeding machine. During horizontal sealing, the linear speed of horizontal sealing is required to be synchronized with the speed of film feeding, so as to avoid tearing the film and film accumulation. Because the diameter of the horizontal sealing wheel is constant, when changing the bag length, it needs to be changed by changing the speed of the horizontal sealing wheel to the original problem in the development of plastic extruders in China, but the horizontal sealing takes a certain time, That is to say, it takes a constant time for the horizontal sealing wheel and the film to contact and leave, otherwise the sealing is noisy. The total time of each revolution of the cross sealing wheel and the time required for the cross sealing are constant. To meet the requirements of speed synchronization, the speed of the stepping motor in a week can be divided into two parts. One part first meets the requirements of speed synchronization, and the other part without load meets the requirements of the total time of a week

in order to achieve good sealing quality, you can also realize the non constant speed control mode of the transverse sealing wheel through the stepping motor, that is, to achieve speed synchronization at every point of the transverse sealing. Due to space limitation, it is not stated here

the characteristics of stepping motor are mainly attributed to three aspects: (1) good overload performance. Its speed is not affected by the size of the load. Unlike ordinary motors, the speed will decrease when the load increases, so stepping motors are used in occasions with strict requirements on speed and position; (2) Convenient control. Stepper motor rotates in steps, with obvious digital characteristics, which brings great convenience to computer control. In turn, the emergence of computer has opened up a broader market for stepper motor; (3) The whole machine is simple in structure. The traditional mechanical speed and position control structure is complex and difficult to adjust. After using the stepping motor, the structure of the whole machine becomes simple and compact

stepper motors have just begun to be used in packaging machinery. Many traditional mechanical control methods can be replaced by stepper motors. In addition to the uses described above, they have also been applied in printing, filling, packaging and other aspects. It is believed that in a relatively short time, China's packaging machinery industry will be able to leap to a new level on the platform of stepper motor technology

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