电机在包装机械中的应用

This article discusses the working principle and usage characteristics of the motor, introduces several application examples of the motor in packaging machinery, and points out the broad application prospects of the motor in packaging machinery.

1. Working principle of the motor

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

Given an electrical pulse signal, the motor rotor rotates a corresponding angle, which is called the step angle of the motor. At present, the step angles of commonly used motors are mostly 1.8 degrees (commonly known as one step) or 0.9 degrees (commonly known as half a step). For a progressive motor with a step angle of 0.9 degrees, when we give the motor an electrical pulse signal, the motor rotates 0.9 degrees; when we give two pulse signals, the motor rotates 1.8 degrees. By analogy, the motor can run continuously if the pulse signal is given continuously. Due to the linear relationship between the electrical pulse signal and the motor angle, the motor has been widely used in speed control, position control and other aspects.

The use of motors requires at least three aspects of cooperation. The first is the electric pulse signal generator, which repeatedly transmits electric pulse signals to the motor according to the given settings. At present, most of these signals are completed by programmable controllers or single-chip microcomputers; the second is the driver (signal amplifier), which can not only amplify the electric pulse signal and drive the motor to rotate, but also improve the performance of the motor. In fact, it plays an important role in the motor system. Generally, a motor can have multiple drivers according to different working conditions; the third is the motor, which has multiple control principles and models. The commonly used ones are reactive, inductive, and hybrid.

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

The position control of the motor is controlled by the given number of pulses. Given a pulse, turn a step angle, and when the stop position is determined, the number of pulses required by the motor is determined. In the control of the 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, it is often necessary to control the running speed and running position of the actuator. In the past, this was done by mechanical or other means, with complex mechanisms and difficult adjustment. After switching to motors, not only can the packaging machinery structure become simple, easy to adjust, and reliable, but also the roughness will be greatly improved.

2. Application of motors in material metering

1. Measuring of powdered materials

Screw metering is a commonly used volumetric metering method. It achieves the amount of metering by the number of turns of the screw. In order to achieve the purpose of adjustable metering size and improve metering accuracy, the screw speed is required to be adjustable and the position is accurate. The use of motors can meet these two requirements at the same time.

For example, the metering of powder packaging machines uses motors 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 motor only depend on the frequency and number of pulses of the pulse signal, and are not affected by load changes. Compared with the screw metering controlled by the electromagnetic clutch, it has obvious accuracy advantages and is more suitable for the metering of materials with relatively large specific gravity changes.

The motor and the screw are directly connected, with a simple structure and easy maintenance. It is worth pointing out that if the overload capacity of the motor is relatively large, when it is slightly overloaded, considerable noise will occur. Therefore, after the metering condition is determined, a larger overload coefficient should be selected to ensure the balanced operation of the motor.

2. Metering of viscous materials

Motor-controlled gear pumps can also achieve accurate metering. Gear pumps have been widely used in conveying viscous materials, such as syrup, bean paste, liquor, oil, ketchup, etc. At present, piston pumps are mostly used for metering these materials, which have the disadvantages of difficult adjustment, complex structure, inconvenient maintenance, high power consumption, and inaccurate metering.

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

The motor is suitable for running at low speed. When the speed increases, the noise of the motor will increase significantly, and other economic indicators will decrease significantly. For gear pumps with relatively high speed, it is better to use a speed-up structure. We initially used the structure of the motor directly connected to the gear pump in the viscous packaging machine, but the noise was difficult to avoid and the reliability decreased. Later, the method of spur gear speed increase was adopted to reduce the speed of the motor, the noise was controlled, the reliability was improved, and the metering accuracy was guaranteed.

3. Application of motor in supplying packaging film

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

1. For intermittent packaging machine

Intermittent packaging machines use motors to supply film, and the reliability can be improved. In the past, the packaging film supply mostly adopted the intermittent belt pulling method of the crank connecting rod mechanism, which had a complex structure and was difficult to adjust. Especially when the product needs to be replaced, it is not only difficult to adjust, but also a lot of packaging film is wasted. The motor is directly connected to the belt pull roller, which not only simplifies the structure, but also makes the adjustment extremely convenient. It can be achieved by pressing the button on the control panel, which saves both adjustment time and packaging materials.

In intermittent packaging machines, the feeding control of packaging materials can adopt two modes: bag length control mode and color mark control mode. Bag length control mode is suitable for packaging films without color marks. It is realized by presetting the motor speed. The setting of the speed-to-air ratio can be realized by the dial switch. The color mark mode is equipped with a photoelectric switch. The photoelectric switch detects the position of the color mark. When the color mark is detected, a control switch signal is issued. After the motor receives the signal, it stops rotating. After a certain delay, it rotates to supply the film again, and repeats the cycle to ensure that the film is supplied at a fixed length according to the position of the color mark.

2. Used in continuous packaging machines

In continuous packaging machines, the motor rotates continuously, and the packaging film is evenly and continuously conveyed. When the bag length is changed, it can be realized by simply using the dial switch.

4. Application of motors in horizontal sealing

In continuous packaging machines, horizontal sealing is a very important actuator and one of the more complex mechanisms in packaging machines. Especially for packaging films with colored strips, the requirements for sealing and cutting positions are extremely strict. In order to improve the accuracy of cutting, people have developed eccentric sprocket mechanisms, crank guide rod mechanisms, etc., but these mechanisms have the disadvantages of being very troublesome to adjust and having low reliability. The main reason for these disadvantages is that the process requires the transverse sealing wheel to seal at a constant speed and cut at a fixed position.

The motor directly drives the transverse sealing wheel to achieve speed synchronization. The film supply wheel of the continuous packaging machine is a continuous film supply. When sealing horizontally, the linear speed of the transverse sealing is required to be synchronized with the speed of film supply to avoid tearing the film and film accumulation. Since the diameter of the transverse sealing wheel is constant, when the bag length is changed, it is necessary to change the speed of the transverse sealing wheel. However, transverse sealing requires a certain amount of time, that is, the transverse sealing wheel and the film need a constant time from contact to separation, otherwise the sealing is tight. The total time of each rotation of the transverse sealing wheel is constant with the time required for transverse sealing. To meet the requirements of speed synchronization, the speed of the motor in one cycle can be divided into two parts. One part first meets the requirements of speed synchronization, and the other unloaded part meets the requirements of the total time of one cycle.

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

The characteristics of the motor are mainly attributed to three aspects. First, it has good overload resistance. Its speed is not affected by the load size. Unlike ordinary motors, when the load increases, the speed will decrease. Therefore, the motor is used in occasions with strict requirements on speed and position; second, it is easy to control. The motor rotates in "steps" and has obvious digital characteristics, which brings great convenience to computer control. In turn, the emergence of computers has opened up a wider market for motors; third, the whole machine structure is simple. The traditional mechanical speed and position control structure is relatively complex and difficult to adjust. After using the motor, the structure of the whole machine becomes simple and compact.

The use of motors in packaging machinery has just begun. Many traditional mechanical control methods can be replaced by motors. In addition to some of the uses introduced above, it has also been used in printing, filling, and packaging. I believe that in a relatively short period of time, my country's packaging machinery industry will be able to leap to a new level on the platform of motor technology.