| The research background is the study of the large wheelbase and synchronous transmission of dryer in papermaking equipment,and parallelogram mechanism.Themotion feasibility and certainty of crank group mechanism areanalyzed.Its kinematics and dynamics equations of the mechanism arederived,and a new method of fast dynamic balancing is presented for crank group mechanism.The research content is the basic theory research of light industry equipment,and the research conclusion has important theoretical significance for the innovative of large wheelbase synchronous drive mode of innovative dryer.The dissertation's main works are listed as follows.(1)The characteristics of the synchronous transmission mode of the traditional dryer group are analyzed,and a new method of the synchronous transmission of the dryer group is put forward.The drying process of paper determines that the paper has different linear speed in different parts of the drying part.Therefore,the drying part of the existing paper machine generally adopts the group transmission mode of dryer.The line speed of different dryer groups is different,but the line speed of each dryer inside the same dryer group is the same.In general,the synchronous transmission between the dryers inside the dryer group is realized by the transmission gear between the dryers,the single motor and the reducer.But the gear drive will cause the structure of the dryers to be too complex.Therefore,this paper puts forward a new method of using the crank group mechanism to replace the gear mechanism to realize the synchronous transmission of the dryer group.(2)A method for calculating the degree of freedom of a crank group mechanism based on a link truss is proposed.If the linkage between any two cranks is regarded as an independent member,the structure of the crank group mechanism is various,which is unfavorable for the further research of the crank group mechanism.In this dissertation,after analyzing the basic structural characteristics of crank group,the concept of link truss is proposed.Because the motion of all the linkages of the crank group mechanism are completely consistent,all the linkages can be regarded as a member,namely the link truss.Structure of crank mechanism group is further clarified by link truss.Crank group mechanism may be regarded as a kind of special planar parallel mechanism.At the same time,the numbers of members of crank group mechanism is only related to the number of cranks by the truss,that is to say,the structure of crank group mechanism is simplifiedby the truss.The calculation of degree of freedom of the crank group mechanism avoids the analysis and calculation of the composite hinge.Based on the screw theory,the motion screw system and the constraint screw system of the crank group mechanism are derived,and the freedom of the crank group mechanism with any number of cranks is unifieddescribed.It is proved that the degree of freedom of the crank group mechanism is 1.The degree of freedomhas nothing to do with the position and spatial layout of the mechanism,and when a drive is applied to the crank mechanism,the crank mechanism is a planar mechanism with a definite motion.It is possible to use crank group mechanism in synchronous drive of dryer.(3)The kinematics model of crank group mechanism based on screw theory is constructed.Based on the parallelogram structure,the position solution and velocity solution of the truss are obtained by using the exponential product formula.It is proved that the link truss is only translational motion,and it is deduced that the solution of the truss is only related to the rotation angle of the crank.The position and velocity of the driven crank are obtained by the inverse solution method of the series mechanism.(4)The dynamic equations of crank group mechanisms based on redundant constraints are established.According to the kinematic characteristics of the crank group mechanism,there are two kinds of membersmovement forms.One is the same rotational motion of all cranks,and another is the translational motion of the truss.Since all the forces between the crank group members are located at the two hinge joints of the crank,all cranks have similar dynamic equations.In addition,the crank structure needs to be designed with elastic structure to compensate for the machining and assembling errors of the members to avoid the phenomenon of clamping mechanism,so obtaining the force of the hinge pointis a basic goal to establish the dynamic equations of the crank group mechanism.In this dissertation,the dynamic equations of the active crank,the driven cranks and the truss are established by the Newton Euler dynamic equation.(5)A new method for dynamic balancing of crank group mechanism is presented.In general,it is sufficient to complete only the static balance in the plane of motion for planar mechanism.However,in order to ensure that there is no interference between the truss and the crank shafts,and can't increase the complexity of the structure,the truss is often arranged on the end of the crank shaftin practice.At this time,the motion plane of the truss is not coplanar with that of the cranks.So it is necessary to research the dynamic balancing of the crank group mechanism.A general dynamic balancing method is presented for crank group mechanism with arbitrary cranks.In this dissertation,a new method is proposed for the dynamic balancing of the crank group mechanism,which is named three point real field mass substitution method based on the generalized mass substitution method.Compared with the generalized mass substitution method,the method of three point real field mass substitution increases the number of substitution positions,but avoids the tediouscalculation and judgment of the mass moment's phase angle.Only when the balance mass is arranged in the 180 degree direction of the substitution mass,the mass moment of balance mass can be obtained conveniently,and the mass solution of the real field is easier to understand than the generalized mass.Based on the three point real fieldmass substitution,the concept of crank unit is proposed,and all cranks in the crank group mechanism are divided into two crank units.The first class is named ? crank unit,which includes the substitution mass of the truss,the crank and the crank shaft,and the second class is named ?crank unit that does not have an alternative mass,including only the crank and crank shafts.The concept of crank unit not only simplifies the dynamic balancing of the crank group mechanism,but also has the instruction function to the modular design of the crank group mechanism.The example shows the effectiveness and simplicity of the three point real field method to realize the dynamic balancing of the crank group mechanism.On the one hand,the three point real field mass substitution method can solve the crank group dynamic balancing problems in the structure design,on the other hand,simplify dynamic balancing process,and laid the foundation for the structure design module and standardization of the crank groupmechanism.The dynamic balancing verification experiment of crank group mechanism is completed.It is proved that the method is correct.It has important theoretical significance for further reducing the vibration of dryer?... |
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