| China is one of the world’s wood resource-poor countries, which timber resources are distribution, small amount and poor quality. Due to the large population, timber resources share is far lower than the world average level.According to the basic situation in our country, how to use of wood reasonablely and improve the rate of wood utilization has became one of the key problems of woodworking industry, the grading of wood is a large foundation to realize the reasonable use and improve the utilization ratio of wood.Wood according to their strength performance index can be divided into several grades, called wood strength grade classification, referred to as the lumber grading. The purpose of this paper is to develop a simple and accurate lumber stress grading test machine, performance prediction should stress grading test machine, reduce mechanical stress grading costs, promote mechanical grading technology. The lumber stress grading test machine, whose structure is mainly composed of a machine frame, a motor, a roller assembly, a pressing frame, a cylinder, a loading device and a base of such components. Formation of the structure with lumber stress grading test specimen mechanical drawings and confirmed by the upper and lower respectively loading mode, in order to ensure the rationality of data acquisition, formed a design scheme of grading equipment structure.Based on the foreign advanced timber grading machine, have certain innovation, complete the spontaneous development of the lumber stress grading test machine. The equipment adopts continuous feed mechanism, can realize the lumber of displacement and force control on-line, real-time control, increase the classification accuracy. Variable speed drive, to meet the different needs of the floating structure;overall, double cylinder support clamping support roller to ensure continuous through the timber, meet the rapid quality requirements; adopts the industrial control computer and Labview acquisition control mode, realization of data acquisition and processing, anti interference is strong, operation interface is friendly; the cylinder loading convenient, and the measuring accuracy is not received the cylinder system, improve the work efficiency of wood testing.Grading test machine is driven by an electric motor driving wheel to rotate the cylinder number, to control the tightening frame control pressure roller pressure Sawn Timber Press, loading apparatus is applied constant load, the sawn timber deformation occurred, a support base for supporting the whole sets of equipment. The device is provided with a force sensor corresponding, the data measured by the sensor is transmitted to the computer system, wood bending modulus data using this structure is calculated, and the data and the data set for classification were compared to the measured structure, make the strength grade of wood, and the the grading results output.This paper mainly study of wood mechanical stress grading technology and equipment, for the lumber stress grading provides a new technical support and introduce the main structure of lumber stress grading test machine and its features. SolidWorks software is applied to set up and assemble the three-dimensional model about the stress grading machine of lumber developed by Beijing forestry Machinery Research Institute. Meanwhile carrying out motion simulation analysis by using software Solidworks Motion.The simulation is under the working conditions, and through comparative analysis of three different feed speed of lumber, which testifies to the rationality and correctness of the structure design about the Stress grading machine of lumber. Using different wood feed speed of movement simulation, results show that feed rate of500mm/s is appropriate, provide wood feed speed reliable design stress grading test machine, provides the basis for determining the transmission speed grading test machine of the driving wheel.When the feed speed of lumber reaches1000mm/s, violent fluctuation of contact force happens with lumber and loading roller, and also the impact of stress rated machine of lumber is larger, so working statement of the stress rated machine of lumber is instable, therefore the timber into the speed the detection performance of the testing machine. We should focus on testing wood feed rate in the subsequent experimental studies for the next step. So it can provide a theoretical basis to carry out the timber stress rated machine finite element analysis and optimization design.As the main bearing structure frame should stress rating test machine, has an important influence on precision and security of its stability and reliability of the whole equipment. The main structure of the aluminum frame assembly and welding molding, aluminum is the aluminum rod by hot melt, aluminum material extrusion can obtain different section shape. Has the characteristics of light weight, high strength, beautiful appearance, convenient assembly. The frame is foundation of all force grading test machine parts installation, installation position of loading device and a sensing device, and to install position related auxiliary machinery parts timber flexural bending working condition. In order to ensure the parts and reliable installation and testing result precision, frame also must have certain strength and stiffness. The deformation of a direct impact on the loading conditions to test whether the normal operation of. The frame structure is the connection form is single, the welding and bolt connecting two forms.From the SolidWorks Motion simulation of multi span wood should be stress grading equipment can be seen in various stress situation is relatively smooth, the obvious regularity, it is concluded that the classification equipment for multiple span wood stress grading, and the grading equipment performance is good, can satisfy the different span work.SolidWorks Motion as a platform to create virtual prototype in the computer to simulate the motion of complex mechanical system, so as to improve the design quality, cost saving, time saving objective, method is advanced, reliable, high efficiency, avoiding the design, manufacture of grading test equipment modification of the repeated tests and design procedure. Through the computer software platform, the lumber stress grading test machine working state of motion simulation analysis, can timely and accurately detect design flaws in the link, and modified in real time according to the analysis results, for further analysis and optimization to lay the foundation, has the very high practical significance. Through the analysis and calculation of SolidWorks Simulation simulation module should frame force grading test machine of sawn timber, get the natural resonance modal of the frame, using dynamic display can observe the vibration mode, deformation, displacement distribution, the result is very intuitive, considering the inherent modal and vibration type frame in the wood mechanical grading process, avoid resonance, affect the transmission efficiency.At the same time, conducting the wood stress rated equipment for frame finite element modal analysis, get the rack order4basic modal,modal vibration mode and at the same time find frame each order modal point of maximum stress and maximum deformation,4modal part frame contrast has a certain symmetry. The conclusions to prevent the resonance and subsequent harmonic response analysis and transient dynamic analysis and dynamic characteristics of the structure optimization design provides a theoretical basis.In stress grading test machine of lumber working process, the external excitation is mainly from the motor vibration. Motor vibration modal is lower than the timber should be minimum order natural modal of stress grading test machine, so that the frame structure in the motor running process, not with the motor resonance.Analysis of stress grading test machine modal results can be seen from the timber, timber stress grading test machine smaller deformation, to meet the requirements of stability design. The importance of modal analysis is not only to avoid the structure resonance occurs at work, foundation and analysis of dynamic response of the structure and other dynamic characteristics. |
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