The invention relates to display devices for rotary balancing machines.
It is already known for example from U.K. patent specification No. 1,339,724 and the corresponding U.S. Pat. No. 3,732,737 to provide a rotary balancing machine which provides a digital output in the form of one value representative of the balance weight value required to balance a work piece and another digital value indicative of the angular position with respect to a datum at which the weight should be placed. In a wheel balancer for balancing automotive and similar wheels, it is desirable to balance the wheel in two planes to ensure that out of balance couples as well as out of balance forces are taken into consideration when balancing the wheel. The axial positions (that is radial planes) at which weights can be added are defined by the structure of the wheel so that in the case of a wheel balancer, what is required and available from the known balancers is a weight value and an angular position value for each of the two planes.
Considering for the moment only the situation within a single radial plane, it has been proposed in U.S. Pat. No. 3,550,455 that in order to standardise the value of weights which have to be made available, a pair of weights of a predetermined standard value may be employed at angular positions to either side of the nominal position at which a single weight would be placed.
In further detail, when:
W is the value of a single weight required to balance a wheel .theta. is the angle with respect to a datum at which weight W should be placed. PA0 W.sub.1 is the value of standardised weight PA0 .theta..sub.1 and .theta..sub.2 are angles with respect to the datum at which weights W.sub.1 should be placed to be equivalent of weight W at angle .theta.. PA0 .DELTA..theta. is equal to .theta.-.theta..sub.1 and equal to .theta..sub.2 -.theta.
Then: EQU .theta.=arc cos (W/2W.sub.1)
It has also been proposed in U.S. Pat. No. 4,068,532 to provide an electronic arithmetic unit to calculate from weight and basic angle signals the corresponding angle positions for weights of a single weight value to replace the single weight at the basic angular position.
The present invention is concerned with certain details of a display device for a rotary balancing machine which display device includes means for receiving signals indicative of values of W and .theta., means for calculating corresponding values of .theta..sub.1 and .theta..sub.2 for weights of predetermined value W.sub.1 and means for displaying in digital form the angles .theta..sub.1 and .theta..sub.2.