Design of Quantitative Package Control System Based on DSP

Electronic quantitative packaging system is a dynamic quantitative weighing system developed on the basis of electronic weighing technology. It is an automatic intelligent measuring and weighing equipment integrating mechanical, electrical, automation and computer technology. According to the specific control procedure, electronic quantitative packaging equipment automatically divides large parts of materials into predetermined small parts. The equipment has been widely used in food processing, food packaging, cement packaging, medical packaging and other fields because of its advantages of intelligent automatic weighing, high production efficiency and labor force liberation. Whether the electronic quantitative packaging system is stable has a direct impact on the economic benefits of the enterprise. If the system can operate stably, it can make the enterprise obtain the best economic benefits. In order to improve the packaging speed and precision of the quantitative weighing packaging machine, this paper proposes an intelligent weighing and packaging control system based on touch screen and DSP. The hardware structure of the system is introduced in detail. On the basis of the hardware structure, the software of the control system is developed.

1. Quantitative weighing and packaging machine

1.1 Structure introduction

The quantitative weighing packaging machine mainly includes automatic control system, blanking device, feeding device, weighing device, bag clamping device and finished product conveying device.

The storage bin is funnel-shaped structure, which is mainly used to store the materials to be weighed and packed. Two material detection sensors are installed on the side of the storage bin, which is mainly used to detect the quantity of materials in the bin, so as to ensure that there are enough materials in the bin. When the low level material sensor detects that the material is insufficient, the signal is transmitted to the lower machine, and the lower machine sends the command to the actuator for feeding. When the high-level material sensor detects the material, it sends the signal to the lower machine, and the lower machine sends the command to the actuator to stop feeding. The feeding tank is mainly used to transfer the materials falling from the bin. The chute vibrates with electromagnet to shake the animal material and then falls into the weighing bucket evenly. A high-precision pressure sensor is connected at the back end of the weighing bucket. When the sensor detects that the material quality falling into the weighing bucket reaches the set value, the signal is transmitted to the controller quickly. The electromagnet stops vibration, and the unloading motor starts to move to open the material baffle and send the material into the packaging bag, so as to complete the weighing package.

1.2 Principle of quantitative packaging control

On the basis of the existing quantitative packaging machine, the secondary feeding method is still adopted. The so-called secondary feeding refers to the fast feeding speed in the initial stage. When the feeding amount reaches about 90% of the set value, the feeding speed is reduced to improve the weighing accuracy of the system. In the initial stage, the error of quantitative weighing is relatively large. At this time, the feeding speed should be considered first, so constant speed control is adopted to realize the fast feeding; When the feeding amount reaches a certain value or the weighing error is less than the set value, the control mode is adjusted to neural network control to ensure the accuracy of quantitative weighing.

2. Hardware system design

According to the process of quantitative weighing and packaging, the control mode of "HMI + DSP" is adopted in this paper. The hardware of the quantitative weighing control system is mainly composed of human-computer touch screen, DSP signal processing module, analog input module, analog output module and digital input and output module.

The main platform for touch screen development or operator to contact the control system. Some parameters can be set or modified through touch screen, such as weighing quality, blanking speed, discharge speed, etc. In addition, the real-time parameters in the weighing and packaging process can also be displayed by the human-computer interface, which is convenient for relevant personnel to monitor and set the parameters. The control system adopts the eview mt4300c series touch screen, which supports simultaneous communication of multiple serial ports, 64 K color display mode and C language macro code. RISC can handle 200 MHz, and has the characteristics of flexibility and easy to use.

Considering the control requirements of the weighing package, a DSP based main controller is designed. The DSP chip is Motorola dsp56f807, and its core is 32-bit programmable digital signal processor; The peripheral function module mainly includes: asynchronous serial communication module SCI, which is used for touch screen communication; GPIO, a general i/o module, is used to receive button and detect trigger signal of sensor; Counter module, used for servo motor control; ADC, which collects the signal of weighing sensor; Can bus module, used to control solenoid valve, signal lamp, etc; Phase detector for detecting encoder signal; JTAG interface, etc. The controller uses PC to write application program, and downloads and debugs it through JTAG interface.

3. Software system design

The control system mainly realizes the accurate control of material flow. Through collecting the analog signal of weighing sensor, it can feedback to the controller to realize the action of the actuator, and then control the material flow. The control process is to start the quantitative weighing system to make it enter the operation state. When the weighing start-up conditions are met (whether there is any material in the weighing bucket and whether the discharge door is closed), the weighing will start. The lower limit sensor detects whether there is any material. If there is no material, the storage bin starts to feed. When the material in the storage bin is detected by the upper limit sensor, the material bin stops feeding. The materials in the discharge bin are transported to the weighing bucket along the conveying tank with the vibration of the vibrating electromagnet. When the pressure sensor detects that the material quality reaches the target value, the vibration electromagnetic stops the vibration. After delay of 1.5 s, the discharge motor moves to open the discharge baffle under the weighing bucket, so that the material enters the packing bag along the hopper, and then completes a cycle of packing weighing, When the sensor detects the next bag is in place, repeat the above actions to continue weighing.

Based on the human-computer interface, the operator or developer can communicate and process data and information with the main controller. In addition, the human-computer interface can monitor and display the running state of the system in real time. If there is a fault in the process of operation, the cause of the fault will be displayed on the human-computer interface, which is very helpful to the system fault resolution. After entering the main interface, the monitoring interface, alarm interface and system interface will appear. The monitoring interface can be used for the selection of operation mode, namely, system alarm reset, operation parameter setting, start automatic control, stop manual control, start manual control, etc; Automatic operation; Manual operation, namely, emergency stop of packaging, manual bagging, bag rising start, manual quick adding and manual slow adding; Real time data display, namely the speed of servo motor, i/o point status, packaging material quality, unqualified packages, qualified packages, packaging completed packages, etc. The alarm interface can be used for system emergency stop alarm, material jam alarm, motor failure and over error fault lamp.

4. Analysis of experimental data

In order to verify the feasibility and effectiveness of the control method, a control system is built and relevant tests are carried out. The set value of packaging quality is 25 kg per bag. According to the experimental results, the weighing value of the weighing device is (25) under the control of DPS quantitative weighing ± 0.0063) kg, standard deviation 0.0063kg, maximum relative error 0.6%. The experimental results show that the relative error of the control system based on DSP is small and can meet the design requirements.

5. Conclusion

The control system of quantitative weighing and packaging is designed, which takes Motorola dsp56f807 as the control core and the touch screen eview mt4300c as the operating screen. The mechanical structure and working principle of the quantitative weighing and packaging machine are introduced. The hardware structure based on DSP and touch screen is discussed in detail. Based on the hardware structure, the software of the control system for quantitative weighing packaging is developed. The control system improves the accuracy, reliability and operability of the quantitative weighing and packaging machine.

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