Search

The existence of ball-raceway relative motion imposes the simultaneous occurrence of spinning motion about an axis parallel to the normal in the contact point and a rolling motion about an axis contained in the common tangent plane intersecting the axis of the ball bearing. For the separate characterization of the two friction torques - spinning and rolling moments, the devices to be used must be specially designed. For finding the spin torque or the rolling torque, the test-rigs used must contain a housing washer and a ball between which only spinning or rolling motion, respectively, exists. A test rig for evaluation of the spinning moment assumes ensuring the rotation motion about the normal in the contact point and additionally allows for estimation of the friction torque. The main inconvenience of such a device is the necessity of bearings capable to ensure a fixed position for the axis of rotation of the ball. The work proposes a simple and precise method for estimation of the spin moment by analyzing the motion of an axi-symmetric body that is in contact with the housing washer of a thrust ball bearing. The experimental data are interpolated using a parabolic function which is a function characteristic to the rotation motion with constant friction torque. The (constant) angular acceleration is found from the law of motion and together with the moment of inertia of the body is used in estimation of the spinning torque. This moment is assumed equal to the one found experimentally and thus results the value of the coefficient of friction from the contact area. The concordance between the value of the coefficient of friction obtained by the present method and the values from literature validates the proposed technique.

In rigid dynamics theory the gyroscope has a special role, as one of the bodies with the most complex motion, having three degrees of freedom. As consequence of the complexity of the motion is the fact that only for three situations, the equations of motion can be analytically integrated. For all the three situations, it is assumed that the principal moments of inertia (PMI) with respect to the principal axes that are normal to the rotation axes, are equal, condition fulfilled by the shape of body of revolution of the gyroscope. The paper analyses the case when the two principal moments of inertia are unequal. The equations of motion are numerically integrated for different values of the ratio between the two PMI. The effect of the disparity between the two PMI upon the motion of the gyroscope is proved by comparison with the motion of the axisymmetric gyroscope, both obtained by numerical integration.

The swash plate mechanism is one of the most exploited mechanisms from technical applications due to its constrictive simplicity. The kinematical analysis supposes establishing the motion of the plunger as function of the motion of the plate and of the constructive characteristics of the mechanism. The work presents the kinematical analysis of the mechanism performed by two methods. In the first way, the mechanism is replaced by a mechanism with lower pairs to which the Hartenberg-Denavit procedure is applied. In the second way, the definition conditions of the pair of first class, plunger-plate, are used. The results are obviously identical for the two methods but for the second approach, the labour required for the analysis is significantly reduced. The main outcome of the paper refers to the scheme of kinematical solving of a mechanism. The type of pairs should be a criterion and for the higher pairs, the use of direct condition of the structural definition is recommended.