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

• US 6,466,889 B1
• Filed: 10/27/1999
• Issued: 10/15/2002
• Est. Priority Date: 10/27/1998
• Status: Expired due to Term

• Current Assignee: Bourns Incorporated
• Original Assignee: Ruf Electronics GmbH (Gentherm Incorporated)
• Inventors: Schödlbauer, Dieter
• Primary Examiner(s): Hilten, John S.
• Assistant Examiner(s): Pretlow, Demetrius R.
• Application Number:
  US09/428,180
• Time in Patent Office: 1,084 Days
• Field of Search: 702/150, 702/151, 702/152, 702/33, 702/36, 702/94, 702/95, 702/183, 33/1.PT, 324/207.2, 324/173, 324/174, 324/207.17, 324/207.25, 324/207.21
• US Class Current: 702/150
• CPC Class Codes: G01B 7/003 for measuring position, not involving coordinate determination coordinate measuring G01B7/004
• CPC Class Codes: G01B 7/02 for measuring length, width or thickness G01B7/004, G01B7/12 take precedence
• CPC Class Codes: G01B 7/30 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01D 5/24476 Signal processing G01D5/2448 - G01D5/24495 take precedence
• CPC Class Codes: G01D 5/2452 incorporating two or more tracks having an (n, n+1, ...) relationship

Abstract

A method and apparatus for determining the absolute position of displacement and angle transmitters. Two individual sensors are mechanically coupled to one another in such a way that they generate sawtooth output signals with a number of periods that differ by one within a predetermined measuring range. In a first step, a difference signal is formed from the output signals of both sensors and, if negative, is corrected by a constant value. A period number signal is obtained from the corrected difference signal by deriving an integer. This period number signal and the output signal of one sensor are added to form a highly accurate, absolute output signal. Since the absolute output signal still contains errors, an auxiliary signal is formed from the absolute output signal and the modified, corrected difference signal. A window discriminator determines whether the auxiliary signal lies within a predetermined limiting range. If not, the absolute output signal is corrected by a predetermined amount.

Claims

1. A method 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 method comprising the steps of;

comparing the output signals of the first and second sensors;

generating a difference signal representative of the comparison of tile output signals;

adjusting the difference signal when the difference signal is negative by adding a first predetermined value thereto;

determining an integer approximation of the adjusted difference signal multiplied by the first number of periods and divided by the measuring range;

generating a period number signal by multiplying the integer approximation by the measuring range;

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;

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;

determining whether the auxiliary signal is within a predetermined range; and

adjusting the absolute output signal when the auxiliary signal is outside the predetermined range by adding a second predetermined value thereto.

2. The method of claim 1 wherein the output signals are sawtooth signals.

3. The method of claim 1 wherein the measuring range is 2π

.

4. The method of claim 1 further comprising the step of driving the first and second sensors at different speed ratios.

5. The method of claim 1 wherein the first number of periods is one more than the second number of periods.

6. The method of claim 1 wherein the adjusted absolute output signal is substantially linear over the measuring range.

7. The method of claim 1 wherein the first predetermined value is 2π

.

8. The method of claim 1 wherein the predetermined range is between approximately −

π and

+π

.

9. The method of claim 1 wherein the second predetermined value is +2π

if the auxiliary signal is less than −

π and

−

2π

if the auxiliary signal is greater than +π

.

10. 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.

11. The apparatus of claim 10 wherein the output signals are sawtooth signals.

12. The apparatus of claim 10 wherein the measuring range is 2π

.

13. The apparatus of claim 10 further comprising a gear for driving the first and second sensors at different speed ratios.

14. The apparatus of claim 10 wherein the first number of periods is one more than the second number of periods.

15. The apparatus of claim 10 wherein the adjusted absolute output signal is substantially linear over the measuring range.

16. The apparatus of claim 10 wherein the first predetermined value is 2π

.

17. The apparatus of claim 10 wherein the predetermined range is between approximately −

π and

+π

.

18. The apparatus of claim 10 wherein the second predetermined value is +2π

if the auxiliary signal is less than −

π and

−

2π

if the auxiliary signal is greater than +π

.

19. 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.

20. Apparatus for implementing the method according to claim 19, wherein two mechanically coupled sensors generate an essentially linear, sawtooth output signal having a number of periods k₁, k₂, respectively, within a measuring range, said numbers of periods of both sensors differing by one, said apparatus comprising an evaluation circuit having:

a) a subtracting element for forming a difference signal from the two output signals of the sensors;

b) a comparator that determines whether the difference signal is negative;

c) a first adding element that adds a constant value to the difference signal depending on the comparison to form a corrected difference signal;

d) a first computation component that derives an integer value from the corrected difference signal multiplied by the period number of one sensor and divided by the measuring range, said first computation component multiplying the integer value by the measuring range to obtain a period number signal;

e) a second adding element for adding the period number signal and the output signal of one sensor to form a highly accurate, absolute output signal;

f) a second computation component for forming an auxiliary signal in the form of the difference between the absolute output signal minus the product of the period number of one sensor and the corrected difference signal;

g) a window discriminator that determines whether the auxiliary signal lies within a predetermined limiting range; and

h) a third computation component that alters the absolute output signal by a correction value depending on the result of the window discriminator to form an absolute output signal that is free of errors.