Method and apparatus to monitor position of a rotatable shaft
View Patent ↗A rotatable shaft is equipped with a measurement device that generates output signals corresponding to discrete angular positions of the shaft. Rotational angles of the shaft are measured for a complete rotational period. A true angular velocity of the shaft is determined. Angular velocity is calculated between contiguous pairs of the discrete angular positions. A velocity correction is determined, and a rotational angle error term is determined based upon the velocity correction.
1. Method for monitoring rotational position of a rotatable shaft, comprising:
generating output signals corresponding to a plurality of discrete rotational angles of the shaft;
monitoring the output signals and elapsed times corresponding to the discrete rotational angles of the shaft for a complete rotation during which rotational speed of the shaft is substantially constant;
determining a true angular velocity of the shaft for the complete rotation during which the rotational speed of the shaft is substantially constant;
calculating angular velocities between contiguous pairs of the discrete rotational angles;
determining a velocity correction based upon the calculated angular velocities and the true angular velocity;
determining an error in measurement of the rotational angle of the shaft based upon the velocity correction; and
determining a rotational angle error term combinable with the discrete rotational angles of the shaft.
2. The method of claim 1 , wherein angular velocities are calculated between contiguous pairs of the discrete rotational angles for the complete rotation of the shaft, and wherein a velocity correction is determined for each of the contiguous pairs of discrete rotational angles.
3. The method of claim 2 , wherein a rotational angle error term is determined for each of the contiguous pairs of discrete angular positions.
4. The method of claim 2 , wherein velocity corrections are determined by dividing each of the calculated angular velocities by a mathematical average of the calculated angular velocities between contiguous pairs of the discrete rotational angles for the complete rotation of the shaft.
5. The method of claim 1 , further comprising correcting the discrete rotational angles of the shaft based upon the rotational angle error terms.
6. The method of claim 1 , further comprising equipping the shaft with a measurement device operative to generate the output signals corresponding to the plurality of discrete rotational angles of the shaft.
7. The method of claim 6 , comprising determining the rotational angle error term for the measurement device based upon the velocity correction.
8. Method for measuring a true rotational angle of a rotatable shaft, comprising:
fixedly attaching a resolver rotor to the shaft;
providing a resolver stator to generate a resolver stator signal corresponding to rotational angles at discrete angular positions of the rotor;
rotating the shaft and monitoring the resolver stator signal;
measuring the rotational angles and elapsed times therebetween for a complete rotation of the shaft during which rotational speed of the shaft is substantially constant;
determining a true angular velocity of the shaft for the complete rotation during which the rotational speed of the shaft is substantially constant;
calculating an angular velocity between contiguous pairs of the discrete angular positions for the complete rotation of the shaft;
determining a velocity correction between the calculated angular velocity and the true angular velocity;
determining a rotational angle error term based upon the velocity correction; and
correcting the measured rotational angle with the rotational angle error term.
9. The method of claim 8 , wherein a velocity correction is determined for each of the contiguous pairs of discrete rotational angles.
10. The method of claim 9 , wherein the rotational angle error term is determined for each of the contiguous pairs of discrete angular positions.
11. The method of claim 8 , comprising determining the velocity correction by dividing each of the calculated angular velocities by a mathematical average of the calculated angular velocities between each of the contiguous pairs of the discrete angular positions for the complete rotation.
12. The method of claim 11 , further comprising measuring rotational angles of the shaft corresponding to the discrete angular positions for a plurality of complete rotations during which the rotational speed of the shaft is substantially constant.
13. Method to determine an error in measurement of an angular position of a rotatable shaft, comprising:
determining rotational angles corresponding to discrete angular positions of the shaft;
rotating the shaft and measuring the rotational angles corresponding to the discrete angular positions for a complete rotation of the shaft during which rotational speed of the shaft is substantially constant;
determining a true angular velocity of the shaft for the complete rotation during which rotational speed of the shaft is substantially constant;
calculating angular velocities between contiguous pairs of the discrete angular positions for the complete rotation of the shaft;
determining a velocity correction between the calculated angular velocity and the true angular velocity for each of the contiguous pairs of discrete angular positions; and
determining a rotational angle error term based upon the velocity correction for each of the contiguous pairs of discrete angular positions.
14. The method of claim 13 , wherein the velocity corrections are determined by dividing each of the calculated angular velocities by a mathematical average of the calculated angular velocities between each of the contiguous pairs of the discrete angular positions for the complete rotation.
15. The method of claim 14 , further comprising correcting the measured rotational angles of the shaft based upon the rotational angle error terms.