There are various ways of measuring static unbalance of a rotary member, such as a grinding wheel, motor vehicle wheel and the like. One form of such a procedure, as disclosed in DE 29 45 819 A1 and Hofmann News 8 (05.85 D) and 11 (10.88) involves determining the axial moment of inertia of the rotary member when mounted pivotably in a horizontal position, that is to say with the axis of rotation of the rotary member extending vertically. In that procedure, in dependence on a deviation of the rotary member from its initial horizontal position, a return force effective to return the rotary member to its horizontal position is produced in a regulating circuit as a control parameter, and the value of the static unbalance from which the rotary member suffers is formed from the measured return force. To perform that procedure, the rotary member to be measured is placed with its axis of rotation vertical, on a horizontal balancing tray member or plate which is mounted in such a way as to be pivotable, preferably by means of a gimbal or Cardan-type mounting arrangement. If the rotary member suffers from an unbalance, that means that the center of gravity of the rotary member is shifted and a moment corresponding to the static unbalance from which the rotary member is suffering is operative about the pivot mounting axis of the balancing tray member or plate. If the balancing tray member or plate is subjected, at a constant spacing from the pivot mounting axis thereof, to a force which causes the balancing tray member or plate to return to its horizontal position, the force applied, being proportional to the static unbalance, makes it possible to determine the unbalance of the rotary member.
In an apparatus for carrying out that procedure, the deviation of the balancing tray member or plate is detected by suitable means and, in dependence on the deflection signal, an electronic measuring and regulating system produces an electrical current and supplies it to a return or restoring means which includes an electromagnet unit and which is operable to return the weighing tray member or plate into its horizontal position. The current forming the control parameter for the regulating circuit is proportional to the force applied by the return or restoring means and is thus also proportional to the static unbalance of the rotary member to be tested.
The above-outlined operating procedure and the apparatus for carrying out same enjoy the advantage that the fact of using the described compensation principle means that there is no residual deflection of the balancing tray member or plate, and thus the unbalance measurement result is not falsified in that way. When measuring rotary members which are of different weights however it is not possible to adhere to a specific cycle time for carrying out the unbalance measuring operation as the regulator involves constant regulating parameters and depending on optimum adjustment of the regulator, positioning of the balancing tray member or plate in its horizontal position, when dealing with different types of rotary member which involve different weights, requires different positioning times. Hitherto, optimum adjustment of the system has been effected in relation to a low rotary member weight in order to avoid the generation of high control parameter signals which could result in the regulating circuit suffering from instabilities. When measuring types of rotary member which are of relatively high weight however, it has to be accepted in that situation that the time for the balancing tray member or plate to return to its horizontal position and thus the cycle time involved in carrying out the rotary member unbalance measuring procedure is increased.