Process and an apparatus for measuring an angle

Apparatus for measuring the angle which two members enclose with respect to an axis of rotation about which they are rotatable with respect to each other, comprising a rotating mark carrier having marks disposed thereon at a certain distance apart in the direction of rotation, said mark carrier being attached to one of the two members so as to rotate about their mutual axis and of being driven by a drive means for rotating said mark carrier continuously independent of the rotation movement of the two members, a pair of sensors, one of said sensors being attached to the same member as the mark carrier and the other being attached to the other member, said sensors emitting a signal corresponding to each of said marks, and a measuring and evaluating circuit comprising an identification circuit which identifies the marks belonging to the signals emitted by the sensors, a time measuring unit which measures the time distances of the signals emitted by the sensors and a calculation and storage circuit which, after receiving a corresponding command signal, calculates and stores the angular distances, with respect to a zero point of the angular measurement, between the marks from the time distance values for signals assigned to identified marks and coming from the various sensors, from stored calibrating values for the absolute angular distances of identified marks, and from the instantaneous angular velocity of the mark carrier and which, upon subsequent rotations of the mark carrier, calculates the instantaneous angle between the two members from the time distance values for signals assigned to identified marks and coming from the various sensors, and from the stored angular distances of these marks, said angular distances being with respect to the zero point of the angular measurement, and from the instantaneous angular velocity of the mark carrier.

Apparatus for measuring an angle formed between a first member and a second member rotatable about a common axis comprising:

• a mark carrier disposed for rotation about said axis;
• means for rotating said mark carrier;
• means attached to said first member for sensing the position of marks of said carrier relative to said first member;
• means attached to said second member for sensing the position of marks of said carrier relative to said second member;
• one of the marks viewed by said first sensor being configured differently than the other ones of said marks to serve as a first reference mark;
• one of the marks viewed by said second sensor being configured differently than the other ones of said marks to serve as a second reference mark;
• and
• means coupled to said first and said second sensors for processing signals produced by said sensors in response to sensings of said marks to determine the relative angular position between said first and said second members;
• said processing means including timing means for timing the occurrences of said sensor signals, and means coupled to said timing means for calculating the speed of rotation of said carrier;
• said processing means further comprising means responsive to said first and said second reference marks and to said speed of rotation for computing the angular position between said first and said second members based on the patterns of marks sensed by respective ones of said sensors during a complete revolution of said carrier, whereby the angular measurement is independent of deviations in the shapes and/or sizes of substantially equal marks.