Analys och kompensering av system med mycket svag dämpning

In order to get a system with a very low damping, a positionservo has been provided with an inertia disc driven by spring transmission. The servo will therefore drive a mechanical oscillation unit. The motor is simulated as armature controlled by feeding back the tachogenerator signal to the existing motor which is field controlled. In a former examination work at the institution the transfer function for the motor, arranged in this manner, has been measured. In this examination work the dynamics of the transmission has been measured. As a result of the difficulties to balance the servoamplifier exactly, drift arises, when the system is open-loop. Owing to this the measurements have been achieved with the system performing in a very weak closed-loop. A simple linear model cannot explain the whole story of the transients. This mainly depends on the friction in the system is reaching a considerable value. After that an extensive analysis of the system has been executed. In this connection the transfer functions of passive networks included in the motor circuit has been determined. Now the order of the model has increased from four to seven. This model reflects reality somewhat better than the original one, but since the improvement is negligible, the simple model will be used as basus for the synthesis. The system has been compensated through cancelling with varying precision. For an acceptable result only moderate precision will be necessary. To improve the velocity a lead network has been added. This type of compensation gives an excellent result. Even feeding back the techo signal has been tried with a fine result. The stability can be improved by adding a low-pass filter in the motor circuit. Feeding back from all states has been used too. This method always gives a very fine result, but it is difficult to use in this particular case