Abstract: An apparatus and a process for detecting an absolute positional value relating to mechanical movement of a member to be measured from a reference point. The apparatus includes a detecting means with a plurality of detectors having periods which are different from one another. Each detector generates an electric signal having a period corresponding to the movement of the member. The signals are stored in a memory. Then, the absolute value of mechanical movement between one of the detectors and the member is specified by using two values. The first value is derived by multiplying the period of the signal corresponding to the one detector by an integer N. The second value is stored in the memory and corresponds to the one detector's partial movement which is less than one period thereof. The value of the integer is decided by using periods and stored values corresponding to other detectors.

Abstract: The rotation of a motor is converted into a swinging movement of an ultrasonic transducer by a conversion mechanism. The relationship between a rotation angle .theta. of the motor and a swinging angle .eta. of the ultrasonic transducer can be expressed by .eta.=tan.sup.-1 (sin.theta.). The rotation of the motor is detected by a rotation detector of a reluctance type having an eccentric rotor. A signal having a nonlinear relationship with respect to an actual rotation angle .theta. of the motor, which can be expressed by the following equation, is supplied to a motor driver from the rotation detector:.theta..sub.D =.theta.+K sin 2.theta..A dummy rotation angular velocity .omega..sub.D which is a rate of change with respect to a time of a dummy rotation angle .theta..sub.D is obtained by the driver. The motor is servo-driven with reference to a deviation value between the dummy rotation angular velocity .omega..sub.D and a velocity setting value .omega..sub.M.

Abstract: A plurality of detectors, i.e., encoders, are prepared each of which generates an output signal representing an absolute value below one period at a predetermined period with respect to a given rotational or linear displacement. A displacement associated with a rotational or linear displacement of an object of detection is provided to each detector and one period of each detector is established in such a manner that one such period corresponds to one of mutually different predetermined amounts of displacement of the object. As a result, the output signal of each detector changes at a rate which is different from one another with respect to the displacement of the object and a combination of values of the output signals of the respective detectors is sufficient to identify an absolute position of the object.