Generalized coordinate surrogates for integrated estimation and control
A robotic device includes a control system. The control system receives a first measurement indicative of a first distance between a center of mass of the machine and a first position in which a first leg of the machine last made initial contact with a surface. The control system also receives a second measurement indicative of a second distance between the center of mass of the machine and a second position in which the first leg of the machine was last raised from the surface. The control system further determines a third position in which to place a second leg of the machine based on the received first measurement and the received second measurement. Additionally, the control system provides instructions to move the second leg of the machine to the determined third position.
1. A method comprising:
receiving, by a machine having a first leg and a second leg, a first measurement indicative of a first distance along a first direction from a center of mass of the machine to a first position of the first leg when the first leg initially contacts a surface during a first stance period, the first stance period commencing when the first leg initially contacts the surface at the first position;
receiving, by the machine, a second measurement indicative of a second distance along an opposite second direction from the center of mass of the machine to a second position of the first leg when the first leg initially raises from the surface during the first stance period, the first stance period terminating when the first leg initially raises from the surface;
determining, by the machine, a third distance along the first direction from the center of mass of the machine for placing the second leg in contact with the surface at a third position during a second stance period based on the received first measurement and the received second measurement, the second stance period commencing after the first stance period terminates; and
providing instructions to move the second leg of the machine to the third position during the second stance period.
2. The method of claim 1 , further comprising:
receiving a bias value indicative of a desired influence on a direction in which the machine is moving, wherein the third distance along the first direction from the center of mass to the third position is also determined based on the received bias value to adjust the direction in which the machine is moving according to the desired influence.
3. The method of claim 1 , further comprising:
receiving a bias value that influences a yaw-heading velocity direction of the center of mass of the machine, wherein the third position distance along the first direction from the center of mass to the third position is also determined based on the received bias value.
4. The method of claim 1 , wherein the surface at the second position is at a first height, wherein the surface at the third position is at a second height, and wherein the first height is not equal to the second height.
5. The method of claim 1 , wherein determining the third distance comprises:
estimating a velocity of the machine based on a difference between the first measurement and the second measurement;
estimating an acceleration of the machine based on a sum of the first measurement and the second measurement; and
determining the third distance from center of mass for placing the second leg in contact with the surface at the third position during the second stance period based on a linear combination of the estimated velocity and the estimated acceleration.
6. The method of claim 5 , wherein determining the third distance from center of mass for placing the second leg in contact with the surface at the third position during the second stance period based on a linear combination of the estimated velocity and the estimated acceleration comprises:
determining a scaled velocity by multiplying the estimated velocity by a first scaling factor;
determining a scaled acceleration by multiplying the estimated acceleration by a second scaling factor; and
determining the third distance from center of mass for placing the second leg in contact with the surface at the third position during the second stance period position in which to place the as a sum of the scaled velocity and the scaled acceleration.
7. The method of claim 5 , wherein determining the third distance comprises:
determining a path in which the machine is expected to travel based on the estimated velocity and the estimated acceleration;
determining whether the machine is expected to collide with an object based on the determined path; and
determining the third distance from center of mass for placing the second leg in contact with the surface at the third position during the second stance period to avoid colliding with the object based on the received first measurement and the received second measurement.
8. The method of claim 5 , wherein determining the third position distance comprises:
providing a velocity value indicative of a desired speed of the machine, wherein the velocity value is different from the estimated velocity of the machine; and
determining the third distance from center of mass for placing the second leg in contact with the surface at the third position during the second stance period based on the received first measurement, the received second measurement, and the provided velocity value.
9. The method of claim 1 , wherein the first measurement takes place at a first time during the first stance period, wherein the second measurement takes place at a second time during the first stance period, and wherein the second time occurs after the first time.
10. The method of claim 9 , further comprising:
providing a velocity value indicative of a desired speed of the machine;
determining a third time during the second stance period to move the second leg of the machine to the third position based on the provided velocity value; and
providing instructions to move the second leg of the machine to the third position at the determined third time.
11. The method of claim 1 , further comprising:
determining, by the machine, a fourth distance along a third direction from the center of mass of the machine for placing the second leg in contact with the surface at the third position during the second stance period based on at least the received first measurement and received second measurement, the third direction perpendicular to the first direction and the second direction; and
determining a two-dimensional position based on (i) the determined third distance of the third position of the second leg from the center of mass along the first direction, and (ii) the determined fourth distance of the third position of the second leg from the center of mass along the third direction; and
providing instructions to move the second leg of the machine to the determined two-dimensional position during the second stance period.
12. The method of claim 1 , further comprising:
determining, by the machine, a force for the second leg to apply to the surface at the third position; and
providing instructions to move the second leg of the machine to the third position and to apply the determined force to the surface during the second stance period.
13. The method of claim 1 , wherein determining the third distance comprises determining damping values indicative of a rate in which the machine suppresses perturbations caused by external forces, and wherein the third distance is also determined based on the damping values.
14. The method of claim 1 , further comprising:
receiving, by the machine, an indication of an object in front of the machine; and
providing instructions to stop the machine responsive to receiving the indication of the object in front of the machine.