Application of stepping motor in packaging machinery

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After nearly 20 years of development, Chinese packaging machinery has made considerable progress, but compared with other 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 Fucan from Wenzhou University and Wu Longqi from Henan University of Science and Technology, wrote a series of articles on the research content they are engaged in, hoping to inspire relevant people in the industry.

1. Working principle of stepper motor

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

Given an electrical pulse signal, the rotor of the stepper motor rotates through a corresponding angle, and this angle is called the step angle of the stepper 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). Take the step angle of 0.9 degrees for the progressive motor, when we give an electrical pulse signal to the stepper motor, the stepper motor will rotate through 0.9 degrees; for two pulse signals, the stepper motor will rotate through 1.8 degrees. By analogy, if the pulse signal is continuously given, the stepper motor can run continuously. Because of the linear relationship between the electric pulse signal and the rotation angle of the stepper motor, the stepper motor has been widely used in speed control and position control.

The use of stepping motors requires at least three aspects of cooperation. (1) Electric pulse signal generator, which repeatedly transmits electric pulse signals to the stepping motor according to the given settings. At present, most of these signals are made by programmable controllers or Single-chip microcomputer to complete; (2) driver (signal amplifier), in addition to amplifying the electric pulse signal and driving the stepper motor to rotate, it can also improve the performance of the stepper motor. In fact, it is in the stepper motor system. It plays an important role. Generally, a stepper motor can have multiple drivers according to different working conditions; (3) A stepper motor has a variety of control principles and models. The commonly used ones are reactive, inductive, and Mixed type and so on.

The speed control of the incoming motor is realized by the speed of the input pulse frequency. When the frequency of the pulse is reduced, the speed of the stepper motor decreases; when 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 the stepping motor is controlled by a given number of pulses. Given a pulse, turning a step angle, when the stop position is determined, it also determines the number of pulses that the stepper motor needs. In the packaging machine control, the number of given pulses is also related to the parameters of the mechanism, such as the diameter of the screw.

In packaging machinery, it is necessary to control the operating speed and operating position of the actuator in many cases. Previously, it was done mechanically or by other means, and the mechanism was complicated and difficult to adjust. After switching to a stepper motor, not only the packaging machinery structure becomes simple, the adjustment is convenient, the reliability is increased, and the thickness will be greatly improved.

2. Application of stepping motor in material measurement

(1) Measurement of powdery materials

Screw metering is a commonly used volumetric metering method. It is measured by the number of turns of the screw. In order to achieve the purpose of adjusting the size of the measurement and improving the measurement accuracy, the screw speed is required to be adjustable and the position positioning is accurate, and the step is used. The motor can meet these two requirements at the same time.

For example, the metering of the powder packaging machine uses a stepping motor to control the speed and number of revolutions of the screw, which not only simplifies the mechanical structure, but also makes the control very convenient. In the case of no overload, the speed and stop position of the stepper motor depends only on the frequency and pulse number of the pulse signal, and is not affected by the load change. Compared with the screw measurement controlled by the electromagnetic clutch, it has obvious accuracy. Advantages, more suitable for the measurement of materials with relatively large changes in specific gravity.

The stepping motor and the screw are directly connected, with simple structure and convenient maintenance. It is worth pointing out that, if the overload capacity of a stepper motor is relatively new, considerable noise will appear when it is slightly overloaded. Therefore, after the measurement conditions are determined, a larger overload factor must be selected to ensure the balanced work of the stepper motor.

(2) Measurement of viscous materials

The stepper motor controlled gear pump can also achieve precise metering. Gear pumps have been widely used in conveying viscous materials, such as syrup, bean paste, white wine, oil, tomato sauce, etc. At present, piston pumps are mostly used in the measurement of these materials, which have disadvantages such as difficulty in adjustment, complicated structure, inconvenient maintenance, high power consumption, and inaccurate measurement.

The gear pump metering is measured by a pair of gears meshing and rotating, and the material is forced from the feed port to the discharge port through the space between the teeth. The power comes from a stepper motor. The position and speed of the stepper motor are controlled by a programmable controller. The metering accuracy is higher than that of the piston pump.

The stepper motor is suitable for running at low speed. When the speed increases, the noise of the stepper motor will increase significantly, and other economic indicators will decrease significantly. For gear pumps with a relatively high speed, it is better to choose a speed-up structure. We started to adopt the structure of a stepper motor directly connected to the gear pump on the viscous packaging machine. As a result, the sound is difficult to avoid and the reliability is reduced. Later, a spur gear was used to increase the speed to reduce the speed of the stepper motor, the noise was controlled, the reliability was also improved, and the measurement accuracy was guaranteed.

Third, the application of stepping motor in the supply and delivery of packaging film

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

(1) Used for intermittent packaging machine

The intermittent packaging machine uses a stepping motor to supply the film, and the reliability can be improved. The previous packaging film supply and delivery mostly used the crank connecting rod mechanism intermittent pulling method, which was complicated in structure and difficult to adjust. Especially when the product needed to be replaced, it was not only difficult to adjust, but also a lot of waste of packaging film. Adopting a stepping motor and a pulling belt roller to directly connect the pulling belt, not only the structure is simplified, but also the adjustment is extremely convenient. It can be realized only through the buttons on the control panel, which saves adjustment time and packaging materials.

In the intermittent packaging machine, the supply of packaging materials can be controlled in two modes: bag length control mode and color code control mode. The bag length control mode is suitable for packaging film without color code. It is realized by pre-setting the speed of the stepper motor, and the setting of the emptying ratio can be realized through the DIP switch. The color code mode is equipped with a photoelectric switch. The photoelectric switch detects the position of the color code. When the color code is detected, it sends a control switch signal. After the stepper motor receives the signal, it stops rotating. After a certain delay, it rotates the film supply, and the cycle repeats. , To ensure that the film length is fixed according to the position of the color code.

(2) Used for continuous packaging machine

In the continuous industrial packaging machine, the stepping motor is continuously rotating, and the packaging film is uniformly and continuously transported. When the bag length is changed, it can be realized only by the dial switch.

Fourth, the application of stepping motor in horizontal sealing

In the continuous packaging machine, the horizontal seal is a very important executive mechanism, and it is also one of the more complicated mechanisms in the packaging machine. Especially for the packaging film of color grade, the 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 troublesome and reliable to adjust. The disadvantage of low sex. The main reason for these shortcomings is that the process requires the horizontal sealing wheel to be sealed at a constant speed and positioned to cut off.

The stepping motor directly drives the horizontal sealing wheel to achieve speed synchronization. The film supply wheel of the continuous packaging machine supplies the film continuously. The linear speed of the horizontal sealing is required to be synchronized with the speed of the film supply during horizontal sealing, so as to avoid tearing the film and film accumulation, because the diameter of the horizontal sealing wheel is constant Yes, when changing the bag length, you need to change the rotation speed of the horizontal sealing wheel, but the horizontal sealing requires a certain time, that is, it takes a constant time for the horizontal sealing wheel and the film to leave, otherwise the sealing is noisy. The total time of each rotation of the horizontal sealing wheel and the time required for horizontal sealing are constant. To meet the requirements of speed synchronization, the speed of the stepper motor can be divided into two parts. One part first meets the requirements of speed synchronization. In addition, the unloaded part meets the requirements of the total time of a week.

In order to achieve a good sealing quality, a stepping motor can also be used to achieve a non-constant speed control mode for the horizontal sealing wheel, that is, to achieve speed synchronization at each point of the horizontal sealing. Due to space limitations, it will not be described here.

The characteristics of stepper motors are mainly attributed to three aspects, (1) Good overload. Its speed is not affected by the size of the load. Unlike ordinary motors, when the load increases, the speed will decrease. Therefore, stepper motors are used in occasions that have strict requirements on speed and position; (2) Convenient control. The stepper motor rotates in units of "steps", and the digital features are more obvious, which brings great convenience to computer control. Conversely, the appearance of computers has also opened up a broader market for stepper motors. ; (3) The whole structure is simple. The traditional mechanical speed and position control structure is more complicated and difficult to adjust. After using a stepper 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 some of the uses described above, they are also used in printing, filling, pouching, etc. It has been applied, and I believe that in a relatively short period of time, my country's packaging machinery industry will surely be able to leap to a new level on the stepper motor technology platform.

Sales Tel: +86-13689242098 (Jane) QQ: 524622981 WeChat: +86-13689242098 E-mail: [email protected] WhatsApp: +86-13689242098