Method and apparatus for determining absolute position of displacement and angle sensors

An apparatus for determining an absolute position of first and second sensors, said sensors being mechanically coupled to each other, said first sensor generating an output signal having a first number of periods within a measuring range, said second sensor generating an output signal having a second number of periods within the measuring range, said first and second numbers of periods differing by one, said apparatus comprising:

• a subtracting element for comparing the output signals of the first and second sensors generating a difference signal representative of the comparison of the output signals;
• a first adding element for adjusting the difference signal when the difference signal is negative by adding a first predetermined value thereto;
• a first computation component for determining an integer approximation of the adjusted difference signal multiplied by the first number of periods and divided by the measuring range and for generating a period number signal by multiplying the integer approximation by the measuring range;
• a second adding element for generating an absolute output signal representative of the absolute position of the first and second sensors by adding the output signal of the first sensor to the period number signal;
• a second computation component for generating an auxiliary signal as a function of the absolute output signal, said auxiliary signal being based on a difference between the absolute output signal and the adjusted difference signal multiplied by the first number of periods;
• a window discriminator for determining whether the auxiliary signal is within a predetermined range;
• and
• a third computation component for adjusting the absolute output signal when the auxiliary signal is outside the predetermined range by adding a second predetermined value thereto.

Method for determining the absolute position of two mechanically coupled sensors, a first sensor generating an output signal with a first number of periods within a measuring range and a second sensor generating an output signal with a second number of periods within the measuring range, said first and second numbers of periods differing by one, said method comprising the steps of:

• a) forming a difference signal from the output signals of the two sensors;
• b) determining whether the difference signal is negative and adding a constant value to the difference signal if the difference signal is negative to form a corrected difference signal;
• c) rounding the corrected difference signal that is multiplied by the first period number and divided by the measuring range to the next lower integer and then multiplying the integer by the measuring range to form a period number signal;
• d) adding the output signal of one sensor to the period number signal to form a highly accurate, absolute output signal;
• e) forming an auxiliary signal in the form of the difference between the absolute output signal and the corrected difference signal multiplied by the period number of one sensor;
• f) determining whether the auxiliary signal lies within a predetermined limiting range;
• and
• g) further correcting the corrected absolute output signal by adding or subtracting a predetermined value if the auxiliary signal lies outside the limiting range.