INFLUENCE OF THE GEOMETRY OF THE CRANK MECHANISM ON THE ERROR IN CALCULATING THE SPEED OF THE SIEVE MILL OF THE GRAIN CLEANING MACHINE
The crank gear is the most widespread in technique. So, in graincleaning machines the crank gear is used in sieve boot drive. In engineering and scientific studies the kinematics of the mechanism assume that when the crank is rotates uniformly, the reciprocating motion of the sieve boot is a harmonic oscillation. In this case, such kinematic characteristics of the motion as displacement, speed, acceleration as well as inertia forces are described by simple sine or cosine functions. It is generally accepted that the error caused by this idealization of the process is insignificant. It is known that the magnitude of the error in the calculations is greater, the smaller the length of the connecting rod l and greater the eccentricity e in comparison with the crank length r. As parameters that determine the magnitude of the error we chose: the relative length of the connecting rod L= and the eccentricity ratio E =. As a criterion we chose fractional error D showing how many times the actual value of the maximum speed is greater than the value calculated by adopted approximate formula. Using the mathematical program MathCAD the calculation for 32 cases of combination of the relative sizes of connecting rod L and eccentricity E was made. The calculation results are given in the table, which makes it possible to determine the magnitude of the error of the approximate formula for any parameters of crank gear by the interpolation method. Based on the calculated data the graphical dependence of this criterion is presented in the form of the response surface where the parameters are L and E.