Particularity of Cardan Shaft Balance Test

1. Hard and soft shafts

There are two types of transmission torque for shaft parts: coaxial and variable axial. Coaxial transmission is rigid transfer, the shaft can be called hard shaft. Variable axis transmission is flexible transmission, its axis can be called soft shaft. The two axes are very different in structure, and the imbalance created by rotation will not be exactly the same.

When the hard shaft rotates, its size and direction are fixed. The inherent unbalance measurement can be corrected by dynamic balance test. Soft shaft - the measure of the unbalance produced by the rotation of the drive shaft has an inherent measure of the unbalance, as well as a variable measure of the unbalance. The unbalance measurement is caused by the gap between the universal joint and spline shaft sleeve when the drive shaft rotates. This is one of the characteristics of the dynamic balance test of the transmission shaft.

2. Special clamping method

Through the analysis of the vibration form of the long shaft, it is known that there is always axial force, thus causing the axial channeling when the long shaft vibrates. Axial channeling will seriously interfere the reception and conversion of radial vibration signals. Therefore, the elastic support seat of the dynamic balancing machine of hard shaft does not limit the degree of axial freedom.

The transmission shaft is a flexible shaft that transfers torque by changing the axis. The cardan shaft is a flexible shaft that in the structure, it has a spline shaft sleeve with absorbing axial channeling, but the universal joint with soft connection at both ends cannot be placed on the support seat for rotation test. At this point, the test machine must be equipped with clamps for use in connection between the two supports, and the drive shaft end with high precision bearing is ensured. Therefore, the bearing pedestal structure itself limits the axial freedom of the test shaft. So from the requirements of the test machine, the dynamic balance test of the transmission shaft is also special.

3. Fixture error in dynamic balance test of cardan shaft

The special clamping mode of the dynamic balance test of the transmission shaft determines that it must connect the universal joint protrusions at both ends with the jig in the dynamic balance test, and rotate with the driving shaft connected with the jig, before the measurement and correction work of the dynamic balance test can be carried out. At this time, the elastic support seat receives the vibration from the transmission shaft and is fed into the measuring system through the vibration pickup. This is a vibration signal produced by the integral rotation of the drive shaft, clamp, drive shaft, bearing and dial, etc. If the signal is eliminated to near zero by correction, it will only mean that the whole thing connected together is in equilibrium and not that one of them is in equilibrium. Since the drive shaft must be removed from the fixture and used separately, the signal or error received and converted by the upper support seat shall consist of the transmission shaft and the clamp and the rotating part connected with the fixture. The former is called product error and the latter is called fixture error. Through the above analysis, it is certain that it is impossible to calibrate the transmission shaft that meets the quality requirement before the fixture error is eliminated.

4. Fixture error eliminated

Eliminating fixture error is the necessary step of calibrating transmission shaft dynamic balance tester. At the same time of eliminating the fixture error, balance correction should also be performed on the test transmission shaft used for calibration, and the balance state of the transmission shaft and fixture should be verified repeatedly. Only when the clamping device and the test shaft are eliminated can the dynamic balance correction quality of the transmission shaft be guaranteed.