Study On The Dynamic Characteristics Of Lumber Stress Grading Machine

Mechanical stress grading of sawn lumber is an important technical mean to make efficient and rational use of sawn lumber and improve the production quality of the wood structure building.The method of mechanical stress grading developed based on visual grading is more convenient for classification.It can effectively avoid the unstable drawbacks of the traditional visual grading method using mechanical stress grading to evaluate lumber strength.In this paper,the FD1146 lumber stress grading machine has been taken as the research object to analyze the dynamic characteristics and dynamic stability of the device in the process of its dynamic detection.Then this equipment and the universal mechanical testing machine both have been used to conduct static and dynamic elastic modulus detection on the same batch of lumber to verify reliability of the dynamic elastic modulus which was got from the test of the lumber stress grading machine.The main works are as follows:(1)According to the detection principle and structural characteristics of the lumber stress grading machine,its mathematical model of bending dynamic detection for lumber machine has been established to analyze the interaction among the supporting force,loading deformation and the elastic modulus of sawn lumber.Besides,Matlab has been used to operate numerical analysis on the model.It is found that the variation of loading deformation is the main factor that affects the support force.In the range of 8~16mm,the support force decreases by about 130 N.(2)ADAMS has been used to establish a simplified model of mechanical stress grading machine and simulate lumber's motion characteristics and loading conditions under different feed velocities and different loading deformations,and at the same time,analyze its mechanical performance under different operating parameters.What's more,lumber's driving force and the contact force between rollers are extracted to make comprehensive analysis on the horizontal swing speed and stability of the load in the process of feeding lumber.This analysis results canprovide some reference to the practical test and application of the lumber stress grading machine.(3)The transient dynamic analysis has been carried out on the loading unit which is under impact and inertia load to calculate the structural stiffness and strength of the system in the process of dynamic response.Beyond that,fatigue and durability analysis has been made on the leaf spring element of the loading mechanism to study the overall influence of the displacement of the joints on the loading deformation and main effect parameters of transient response characteristics of loading unit system.The results show that the reliability is 95.44%when the deformation error of the loading unit is within 5% in the test process.These provide the lumber stress grading machine a basis for the optimization of the dynamic performance.(4)The FD1146 lumber stress grading machine and universal mechanical testing machine both has been used to test three dimensions of specifications of the same batch of sawn spruce and Douglas fir and get the correlation between dynamic and static elastic modulus of the sawn lumber.Apart from this,the detection result change under different feed velocities and different loading deformations has been analyzed to make comprehensive evaluation of the detection stability and detection accuracy.The results show that the stability of the classification equipment is better,the detection accuracy is less than 5% and the lumber strength can be well evaluated by using this machine.