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.

Abstract: About a bobbin, there are wound primary coils in axially displaced locations and wound also is a secondary coil. A core is linearly slidably provided in the bobbin. The primary coils are individually excited by AC signals which are out of phase with each other, e.g. a sine wave signal and a cosine wave signal. The secondary coil thereupon produces an output signal resulting from phase shifting the applied sine or cosine wave signal in accordance with a linear position of the core. Accordingly, the linear position can be detected by measuring phase difference between a reference AC signal and the output signal of the secondary coil. Likewise, velocity and acceleration change may be determined using the position change data.

Abstract: An electrophotographic copying machine includes a photosensitive drum rotatably mounted in a housing. The drum may be taken out from the housing through an opening formed in the top wall thereof by a supporting mechanism when a covering for closing the opening is pivoted to open the opening.