Parametric Reverse And Dynamics Analysis Of Conjugate-cam Weft Insertion Mechanism

Weft insertion mechanism is one of the most important parts of rapier looms. Theperformance rapiers run is directly affected by design of the mechanism. There is a large gapbetween home and abroad, in aspects of design and manufacture. In order to improvecompetitive ability and independent innovation ability, in this paper, research of kinematics,dynamic analysis of rigid body, and elastic-dynamic analysis have been done. Conjugate-cambeat up mechanism is similar to conjugate-cam weft insertion mechanism, so in this paper, it hasbeen analyzed to a certain extent. The specific contents are as follows:1) In this paper, the kinematics model of the conjugate-cam weft insertion mechanism wasestablished, and a kinematics simulation interface of this mechanism was written by MATLABGUI. After importing contours of the conjugate-cam, and setting all parameters of themechanism, kinematics characteristics curves, such as displacement, velocity, acceleration andjerk of rapier can be exported. Through changing the sizes of rockers and connecting rod of thefour bar mechanism, kinematics spectrum can be obtained by simulation of the interface. Afteranalysis, the most suitable rod for defined as variable length rod when design was found. The rodwas taken as variable-length-rod for adjusting maximum displacement of rapier. With definingthe length of bar near gears as variable, the more suitable length of this rod was preferred,through kinematics atlases.2) This paper smoothed the conjugate-cam contours of weft insertion mechanism. Askinematics curves of rapier obtained in MATLAB simulation and UG simulation were notsmooth, considering data of conjugate-cam contours are only fewer points, in order to obtainsmooth kinematics curves, contours of conjugate-cam was smoothed. Because of particularity ofconjugate-cam, in order to ensure its conjugate precision, only considering the smooth-degree ofcam contour can’t obtain the result expected. In this paper, three times spline function whose twoorder continuous differentiable was used to interpolate the fewer measured value and get the liftand return curve of the cam. After getting more points of the conjugate-cam, NURBS(Non-Uniform Rational B-Splines) was used to fit all points with CAD. Smooth contour of theconjugate-cam has been obtained with this method. UG modeling and simulation proved thevalidity of this method. Moreover, this paper solved the auxiliary cam using the main cam through the relative motion relationship between them.3) This paper reversed the conjugate-cam by redesigning the acceleration curve of rapier ofthe conjugate-cam weft insertion mechanism. The acceleration curve was designed basing onmodified trapezoidal acceleration motion curve. Lines were connected by cubic spline curves. Itwas sure that in the design, the acceleration was zero when rapier reached the maximumdisplacement. After solving the rapier displacement, speed and jump variation with the camangle, basing on the kinematics model established before, using reverse method and envelopeformula, contour points of conjugate-cam were obtained.3D model of the conjugate-cam weftinsertion mechanism and the new conjugate-cam reversed was established with UG. The UGsimulation result proved the correction of reverse method and the conjugate-cam reversed before.4) Basing on mechanical analysis, the approximately proportional relationship betweentorque inputted into the cam mechanism and product of tangential velocity and tangentialacceleration of the roller was obtained. The result was extended to the conjugate-cam weftinsertion mechanism. Torque inputted into the cam mechanism and product of tangential velocityand tangential acceleration of the roller were calculated by UG simulation. After treatment byMATLAB, the result proved the correctness of relationship mentioned above. After assignmentdensity for all parts established before, weights and rotational inertia were measured with themeasurement function of UG. Total energy and rapier energy were calculated, using velocityobtained in the reversing processes, and the relationship between input-torque and product ofvelocity and acceleration of rapier were obtained. After verifying the conclusion, the mechanismis optimized with redesign the modified trapezoidal acceleration curve, using the conclusion.5) In this paper, a spring-damping-mass model of conjugate-cam weft insertion mechanismwas established basing on the lumped parameter method, after analyzing motion characters ofthis mechanism. The model was simplified by removing all translation ratio, with conservationof energy and ignoring all dampings. Vibration equations were established with Newton’s secondlaw. Using them, multi degrees of freedom system vibration equation of the whole mechanismwas established. Each order natural frequency was calculated using frequency function. Themodel, spring-damping-mass model of conjugate-cam weft insertion mechanism, was simplifiedto a single degree of freedom model. After decomposing the rapier theoretical displacementfunction with Fourier decomposition method, elastic dynamic response of this mechanism was obtained.6) Elastic-dynamics simulation has been done in this paper, and the correctness of theelastic-dynamics model established before is verified by simulation results. Beyond that, otherrelated conclusions are obtained.