The most popular speed regulation system of extrud

  • Detail

Extruder speed control system based on machine vision

1 introduction

machine vision system is a system that uses machine to replace human vision for measurement and judgment. The basic principle is to convert the captured object into image signal through image pickup device (CMOS and CCD) and transmit it to the special image processing system. According to the pixel, just make a general foundation according to the foundation map and leave the anchor screw hole for pouring, then the brightness, color and other information can be distributed and converted into digital signal; The image system carries out various operations on these signals to extract the characteristics of the target, and then controls the field equipment action according to the discrimination results. Machine vision has been developing for nearly 20 years since its inception. It should be said that machine vision, as a branch of automation technology, its functional characteristics are gradually improved and developed with the development of the whole industrial automation. In Europe and the United States, machine vision has been applied in the industry by Guangji south new era assaying Instrument Co., Ltd., which has independently developed a shoe anti-skid experimental machine. In China, with the improvement of supporting infrastructure and the accumulation of technology and capital, the demand for intelligent control using image and machine vision technology has begun to appear widely in all walks of life

the profile factory of a domestic cemented carbide Group Co., Ltd. is currently the largest bar production base in China. The imported Sandvik extruder (d-120/250) can extrude a variety of bars: 0.5mm, 1mm bars, double hole 1mm, double hole 1.5mm, double hole 2mm bars, 7 × 2.0、6 × 2.5、6 × 0.4、5.5 × 0.5 pipe, 3 × 10、1.5 × 4 flat materials, etc. The performance of the speed regulation system is very important to the quality of the bar. If the speed regulation effect is not good, it is easy to break or pile up the bar. Beijing Hollysys Electric Co., Ltd. applied machine vision and motion system based on servo motor to transform the speed control system of extruder, which greatly improved the performance of the speed control system, thus improving the product quality and output of the factory

2 introduction to hardware

(1) the speed regulation system must have high sensitivity and wide speed regulation range

(2) simple and reliable operation

(3) convenient for system upgrade and expansion

(4) it has self-protection function in case of emergency

(5) high performance price ratio

based on the above overall considerations, the hardware structure of the system is shown in Figure 1, which mainly includes: embedded image processing system with sub-pixel accuracy, AC servo motor system with good fast response, PLC control system with flexible programming and convenient upgrading, industrial touch screen with convenient viewing and modification of system parameters, overvoltage and overcurrent protection system

Figure 1 system hardware structure

3 software part

3.1 control principle

the main purpose of the speed regulation system is to stabilize the extruded bar in a certain area. Figure 2 shows the schematic diagram of the speed regulation system, that is, to control the bar edge points detected by the image processor in the balance area. In this way, the bar can be extruded normally without breaking and stacking. At the same time, it can also ensure the uniformity of the extruded bar

Fig. 2 Schematic diagram of speed regulation system

the extrusion speed of the extruder has a great relationship with the strength of the hydraulic part, the amount of material it loads, the quality of material and the thickness of bar. It is difficult to establish a linear model, and it is difficult to obtain a good control effect with simple PID control. Facing the actual situation, we use three control methods to adjust the extrusion speed of the extruder: fuzzy modeling, differential control and balance zone control

(1) firstly, through the field speed regulation test of the extruder, we summarized its fuzzy model - parabolic model. The closer to the ideal position, the less the speed adjustment is, the farther away from the ideal position, the greater the speed adjustment is, and the difference between the speed adjustment and the ideal position is a power relationship, as shown in Figure 3:

Figure 3. The characteristic curve of the extruder speed control system

(2) the author found in the field test that in case of emergencies, the speed will change sharply, seriously affecting the stability of the system, The stability of the system is improved by adding the differential link. For example, due to the hydraulic system, the extrusion speed suddenly becomes faster. At this time, the system requires acceleration, but accelerating it according to its parabolic model is far from meeting the system requirements. At this time, the system will generate stacking and add a differential link. After predicting this situation, the system will adopt multiple acceleration to improve the sensitivity of the system and meet the requirements

(3) the balance zone control is adopted. It is specified that a certain range near the ideal position is the balance zone, and it is considered that the system at this time meets the control requirements. When the bar enters the balance zone from the acceleration zone or the deceleration zone, the author reversely adjusts the speed according to the change of the edge position. This can play a buffer effect, so that the bar can stay in the balance zone in the shortest time. For example, when the edge point is at the upper limit of the balance zone (see Figure 2), the speed regulating system will reduce the speed to make the edge point of the bar drop. When it enters the balance zone, the balance zone control will start to work and the edge position will drop, Increase the speed value according to the change amount of the edge position (the specific situation here is that the edge position drops and the change amount is negative; the edge position rises and the change amount is positive. At the same time, the change amount can reflect the distance of the position change), so as to prevent the speed drop from rushing through the balance area too quickly and causing the system vibration

3.2 overall design

the main function of this system is to follow the extrusion speed of the extruder, so as to ensure the normal operation of the extruder. The software design is divided into three parts:

(1) machine vision: the position information of the extruded bar is obtained through the image processor

(2) PLC control part: prepare control program according to the control principle in Section 3.1

(3) touch screen: it allows users to easily view and modify system parameters and monitor the operation of the system

3.3 software design of visual part

as shown in Figure 2, use the image software to find the gray edge and get the position of the extruded bar. The obtained position quantity (digital quantity) is transmitted to PLC at the baud rate of 115200bps by serial communication through the serial port

3.4 software design of PLC

plc software has built the first rubber bearing isolation residential building in the world and the first isolation building in China. The design is divided into two parts: manual mode and automatic mode. In manual mode, the speed regulation system is operated manually and is not affected by the control law described in Section 3.1. The operating speed can be changed by modifying the speed parameters through the touch screen. In automatic mode, the speed regulation system adjusts the speed according to the control principle described in Section 3.1. Automatic mode and manual mode can be switched freely

3.5 the interface design of the touch screen

is shown in Figure 4. The interface design includes four parts: manual, automatic, parameter viewing and alarm

Figure 4 touch screen interface

(1) Manual: manual mode interface. When the manual mode is used, this interface can display the operation of the system and set the operation speed of the system

(2) automatic: interface of automatic mode. When the automatic mode is used, this interface can display the system operation and modify the control parameters of the automatic control law

(3) parameter view: you can view the parameter values of system operation

(4) alarm: when the system operates abnormally, it will give alarm information and clear some faults

4 conclusion

this system has realized the perfect combination of motion and vision. It has been debugged and operated on the user's site. The site operation is stable, the operation is simple, and the speed control has reached the performance of actual production. (end)

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