ABSTRACT
These transducers are similar to AC electric motors in that they are electromechanical devices. These sensors have two stator windings that are physically located 90 degrees to each other. Another winding is attached to the device's rotor. Electrical excitation of the unit with an alternating current coupled with motion between the rotor and stator produces an electrical output signal that defines the degree of rotary motion. These rotary sensors are used in many of the same applications as optical encoders. However, because of their relatively coarse resolution (with respect to an encoder), they are frequently used with mechanical gearing, as shown in Figure 5.3, to obtain the desired positioning resolution. (This figure also shows one technique for utilizing a leadscrew correction-cam to mechanically correct axial positioning errors on a machine slide. This is accomplished by modifying the position of the resolver body with a compensation-cam bar linkage. This alteration in the feedback information induces an adjustment in the slide location which corrects the previously calibrated positioning errors.) External electronic circuitry is usually required to excite these devices and to process the output signal, although some units exist that are as simple to use as an encoder. A typical pulse resolution value for a resolver system is 4,000 counts per revolution. For the system shown in Figure 5.3, with a 0.250 pitch leadscrew and 6.25: 1 feedback gearing, this would provide a linear resolution of 10 microinches .
