China's packaging machinery after nearly 20 years of development, has made great progress, but compared with foreign countries, there is a relatively large gap, gap space in what place? We think it's mostly about control. As a result, two experts, Yang fushi of wenzhou university and wu longqi of henan university of science and technology, have written a series of articles on their research, hoping to inspire people in the industry.

　　1. Working principle of stepping motor

　　Stepper motor is an open-loop control element that converts the given electrical pulse signal into angular displacement or linear displacement.

　　Given an electrical pulse signal, the rotor of the stepping motor rotates at the corresponding Angle, which is called the stepping distance Angle of the stepping motor. At present, the stepper pitch Angle of commonly used stepper motor is mostly 1.8 degrees (commonly known as a step) or 0.9 degrees (commonly known as a half step). For the progressive motor with a step distance Angle of 0.9 degrees, when we give the stepping motor an electric pulse signal, the stepping motor will turn around 0.9 degrees; Give two pulses and the stepper motor turns 1.8 degrees. Similarly, given a continuous pulse signal, the stepper motor can be continuously running. by

　　The linear relationship between the electric pulse signal and the stepper motor Angle makes the stepper motor widely used in speed control, position control and other aspects.

　　The use of stepper motor requires at least three aspects of cooperation, one is the electrical pulse signal generator, it is repeated in accordance with the given Settings for the stepper motor transmission of electrical pulse signal, at present, most of the signal by the programmable controller or single-chip microcomputer to complete; 2 it is to drive (amplifier), which in addition to electrical pulse signal amplification, driving a stepper motor rotation, through which can also improve the use of stepper motor performance, in fact it in the stepping motor system plays an important role, usually a stepper motor can be according to the different working conditions with multiple drives; Third, the stepper motor, it has a variety of control principles and models, now commonly used reaction type, inductor type, hybrid stepper motor speed control is through the input pulse frequency fast and slow to achieve. When the frequency of pulse decreases, the speed of stepping motor will decrease. As the frequency increases, the speed increases. The speed or position accuracy of stepping motor can be improved by changing the frequency.

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

　　In packaging machinery, in many cases, the need to control the speed and position of the actuator, the former is through mechanical or other ways to complete, complex mechanism, adjustment is not easy. Using stepper motor, not only can make the structure of packaging machinery become simple, easy to adjust, reliability increased, and the roughness will be greatly improved.

　　The application of stepper motor in material measurement

　　1. Measurement of powdery materials

　　Screw measurement is a commonly used volumetric measurement method, it is through the screw rotation of the number of turns to achieve the number of measurement, in order to achieve the measurement size can be adjusted to improve the accuracy of measurement purposes, the screw speed can be adjusted position positioning is accurate, the use of stepper motor can meet the requirements of both aspects.

　　For example, the measurement of powder packaging machine adopts stepping motor to control the screw speed and revolution, which not only simplifies the mechanical structure, but also makes the control very convenient. In the case of no load, the speed and stop position of the stepper motor only depend on the frequency and pulse number of pulse signal, and is not affected by the change of load, which has an obvious precision advantage over the electromagnetic clutch control screw metering, more suitable for material metering with large proportion change.

　　The stepper motor and the screw adopt the direct connection way, the structure is simple, the maintenance is convenient. It is worth pointing out that, for example, when the stepper motor is slightly overloaded, it will produce considerable noise. Therefore, after determining the metering condition, it is necessary to select a larger overload coefficient to ensure the balance of the stepper motor.

　　2. Measurement of viscous materials

　　Stepping motor control gear pump can also achieve accurate measurement. Gear pump in the transport of viscous body has been widely used, such as syrup, bean paste, white wine, oil, ketchup and other transport. At present, piston pumps are mostly used in the measurement of these materials, which are difficult to adjust, complex structure, inconvenient maintenance, high power consumption, inaccurate measurement and other shortcomings.

　　Gear pump metering is based on a pair of gears meshing rotation metering, material through the tooth and tooth space is forced from the feeding port to the discharge port. Power from the stepper motor, stepper motor rotation position and speed by the programmable controller control, measurement accuracy is higher than the piston pump measurement accuracy.

　　The stepper motor is suitable for running at low speed. When the speed increases, the noise of the stepper motor will increase obviously, and other economic indicators will decrease significantly. For high speed gear pump, the choice of speed structure is better. We began to use in the viscous packaging machine is the stepping motor direct gear pump structure, the result is difficult to avoid noise noise, reliability decline. Later, the speed of stepping motor was reduced by means of straight gear speed increase, noise was controlled, reliability was improved, and measurement accuracy was guaranteed.

　　Application of stepping motor in packaging film supply and delivery

　　In the bag making, filling, sealing as one of the packaging machine, packaging with plastic film positioning long supply, whether intermittent supply or continuous supply, can be used to step motor to complete reliably.

　　1. Used for intermittent packaging machine

　　The reliability of intermittent packing machine can be improved by using stepping motor to supply film. In the past, the packaging film is mainly supplied by the intermittent belt pulling mode of crank linkage mechanism, which is complicated in structure and difficult to adjust. Especially when the product needs to be replaced, it is difficult to adjust and waste a lot of packaging film. Stepper motor and pull-belt roller are directly connected to the pull-belt, which not only simplifies the structure, but also makes the adjustment extremely convenient. As long as the buttons on the control panel can be realized, the adjustment time and packaging materials can be saved.

　　In batch packaging machine, two modes can be used to control the delivery of packaging materials: bag-length control mode and color-coded control mode. The bag length control mode is suitable for packing film without color mark, which can be realized by presetting the speed of stepping motor, and the setting of air ratio can be realized by dialing code switch. The color code mode is equipped with photoelectric switch, which detects the position of the color code. When the color code is detected, the control switch signal is sent out. After the stepping motor presses the signal, it stops rotating.

　　2. Used for continuous packaging machine

　　In the continuous industrial packaging machine, the stepping motor is continuous rotation, packaging film is uniform continuous transport, when changing the length of the bag, only through the code switch can be achieved.

　　Application of stepping motor in horizontal seal

　　In the continuous packaging machine, horizontal seal is a very important executive mechanism, but also one of the more complex mechanisms in the packaging machine. Especially for the color file 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, etc., but these mechanisms are very difficult to adjust, low reliability of the shortcomings. The main reason for these defects is that the process requires the horizontal sealing wheel to be fixed speed and position cutting.

　　The speed synchronization can be realized by direct driving of horizontal sealing wheel by stepping motor. Continuous type of packaging machine for membrane is continuous membrane, horizontal transverse sealing requirement when sealing the linear velocity of synchronization with the speed of the film for, in order to avoid has the tear film and film accumulation situation, due to the lateral sealing the diameter of the wheel is constant, when change the bag length, by changing the horizontal sealing wheel speed is required to change, but the transverse seal need a certain amount of time, that is horizontal wheel and sealing film from contact to leave takes constant time, otherwise the sealing noisy. In order to meet the requirement of speed synchronization, the speed of the stepping motor in one week can be divided into two parts. One part first meets the requirement of speed synchronization, while the other part without load meets the requirement of total time in one week.

　　In order to achieve good sealing quality, non-uniform speed control mode can be achieved by stepping motor on transverse sealing wheel, that is, speed synchronization can be achieved at every point of transverse sealing. Due to limited space, it is not stated here.

　　The characteristics of stepper motor are mainly attributed to three aspects, one is good overload. Its speed is not affected by the size of the load, unlike ordinary motor, when the load will increase the speed will decline, so the stepper motor is used in the speed and position of the occasion have strict requirements; Second, convenient control. Stepper motor is "step" as the unit of rotation, digital characteristics are more obvious, so it brings great convenience to the computer control, in turn, the emergence of the computer has opened up a broader market for the use of stepper motor; Third, the structure of the machine is simple. Traditional mechanical speed and position control structure is more complex, difficult to adjust, the use of stepper motor, the structure of the whole machine becomes simple and compact.

　　Stepper motor in the use of packaging machinery has just started, many traditional mechanical control mode can use stepper motor to replace, in addition to some of the USES described above, it is still in print, filling and bursa bag, etc, the application of trust in a relatively short period of time, China's packaging machinery industry will have on the stepper motor technology platform onto a new level.