The Development And Research Of Automatic Weighing Machine

1. IntroductionThe weighing technology has been emphasized from ancient times till nowalways, especially the new technological revolution brought science's and technology's significant discovery invention and the widespread application impelled the productive forces, the production method, the life style to have the unprecedented profound transformation in the worldwide scale. Along with electronic technology development and computer's widespread application,the automatic weighing technology already became the essential part of the processing technology,the storage and transport technology, the pre-packing technique, the goods service and the retail industries. Faceing increasingly fierce market competition, during the process of product manufacturing, the accurate high speed weighing is helpful in raises the efficiency, saving resources, reduce the cost. The high speed dynamic quantitative weighing process is also precisely the direction which the famous university and the weighing apparatus manufacturing firm pursues.According to the production line's reactant filling working procedure demand, we have developed a new type of automatic weighing machines to realize automatic feeding, high speed dynamic quantitative weighing and automatic discharge. Has solved the difficult problem of present automatic weighing equipment can not matche with this production line's specification of weighing speed, precision and explosion-proof performance, it also has the profound project significance and the promoted value.2. Mechanical design and theoretical analysis of automatic weighing machine and theoretical analysis The automatic weighing machine undertakes the working procedure of weighing and filling reactant. According to overall design request, the automatic weighing machine is mainly composed of the material handling and recovery system, the vibration feed system, the weighing measuring system. Automatic weighing machine structure is designed as shown in Fig 1.Useing the vacuum pump, the material handling and ecovery system inhales material, then transports it after the pipeline from the bunker to feeding system. The bunker used the inverted cone-shape design, pipe wall after polishing treatment to ensure the smooth flow of materials. The filling equipment installed underneath the automatic weighing machine, guaranteed that all reactants can load the container correctly.The filling equipment is driven by the cylinder, which is convenient maintenance.The vibration feed system uses the high speed switch valve to drive pneumatic muscle generating vibration by periodic inflation and denflation. In order to adjust the pneumatic muscle vibration characteristic,the PLC control high speed switch valve by sending PWM signal.Measurement system is the core of the machine.The quantitative automatic scale is consisted of weighing hopper, weighing sensor, feeding system and weighing controller. The automatic weighing machine selects the parallel connection multi-scale mode to carry on the reactant weighing work.Useing the principle of the combination of coarse feeding and fine feeding .Vibration feeding system innovative using pneumatic muscle as vibration source. Based on considering main influence factors, a relatively simple but integrated mathematic model of the pneumatic muscle output force is founded as followes: Build three dimensional solid models of vibration feeding device, and analyze it by means of ANSYS software. We pick-up the five rank vibration modes, the first natural frequency is 60Hz, the feed chute translation along the vertical direction with the principal vibration spring moving, basically the same as the actual work.Then elicit the curve of material feeding velocity and frequency.By the harmonic response analysis, we found amplitude increased with increasing frequency. Through the vibration, the material is transported to the weighing system. Materials will appear four basic movement forms: relative motionless, forward gliding, backward gliding, throwing movement. Motion state of the material in the vibration feeding system can be simplified for the slider moving on the inclined plane under the external force. Through the kinematic method, we got the the start conditions of forward gliding and backward gliding:When material occurred throwing movement, the relationship between throwing start angle and throwing away angle: Theoretical average speed of throwing movememt:3. Development of automatic control system and experimental researchMeeting the technical requirements of the mechanical design is the hardware foundation, Highly integrated and highly automated equipment necessary advanced control theory and a perfect control system. We use Simens S7-300 PLC as the core of the whole system, according to the working principle, STEP7 programming software applications on the modular design of program. When design completion ,test it with on-line and off-line method. Convenient operate human-machine interface is perfect manifestation of the highly automatic system.The human-machine interface make use of inspecting and controling software SIMATIC ProTool6.0. Human-computer interface includs inputing dosing date , monitoring the production process and data records management.The human-machine interface had built the bridge which between the operators and the control system.When control system design was completed, feeding velocity experiment was conducted to study the effects of duty cycle and frequency. Through the experiment we known feeding velocity could be increases with increasing frequency, if frequency less than 40Hz the materials do not move, it is unable to achieve feeding function.When reached 50Hz, it had the fastest speed. In frequency certain situation, changed the pulse duration ratio, feeding velocity could decrease with increasing duty cycle, When reached 0.5, the materials do not move. After debugging subsystem, select three kinds of material to test the overall unit performance, recorded 900 times result, the mean pass rate exceeded 99%. Practice proved that the automatic weighing machine is running stable and reliable, fully meeting the design requirements.4. ConclusionThis paper proposed a integrated and systematic design scheme, according to the technical requirements. Aiming at mechanical system and control system carry out a scientific, safety and reliability analysis. Accomplished the whole design of the mechanical structure.Make use of pneumatic muscle as vibration source, analyzed working theory of vibration feeding system and movement state of the material. Designed the program of automatic control system and friendly human-machine interface.Through trial operation tested the performance of the equipment. The Application of Automatic weighing machine and other equipments of the production line, helped realize leaping development from the manual production to fully automated production .This also provide important theoretical basis and reference value to the similar design and manufacturing.