Ratcheting for master alignment of a teleoperated minimally invasive surgical instrument
A minimally-invasive surgical system includes a slave surgical instrument having a slave surgical instrument tip and a master grip. The slave surgical instrument tip has an alignment in a common frame of reference and the master grip, which is coupled to the slave surgical instrument, has an alignment in the common frame of reference. An alignment error, in the common frame of reference, is a difference in alignment between the alignment of the slave surgical instrument tip and the alignment of the master grip. A ratcheting system (i) coupled to the master grip to receive the alignment of the master grip and (ii) coupled to the slave surgical instrument, to control motion of the slave by continuously reducing the alignment error, as the master grip moves, without autonomous motion of the slave surgical instrument tip and without autonomous motion of the master grip.
1. A method comprising:
characterizing, by a ratcheting system in a surgical system, a first alignment error that is a difference between a first alignment of a master grip of the surgical system and a first alignment of a slave surgical instrument tip of a slave surgical instrument of the surgical system;
determining, by the ratcheting system, a new alignment error that is a difference between a second alignment of the master grip and the first alignment of the slave surgical instrument tip; and
using, by the ratcheting system, the new alignment error to control motion of the surgical instrument tip only if the new alignment error is smaller than the first alignment error.
2. The method of claim 1 :
wherein the first alignment error comprises a first orientation error: and
wherein the new alignment error comprises a new orientation error.
3. The method of claim 2 , wherein the first orientation error comprises an angle.
4. The method of claim 3 :
wherein the angle (θ e ) is expressed as:
θ e =cos −1 [0.5*( R Δ11 +R Δ22 +R Δ33 −1)], and
wherein R Δ11 , R Δ22 , R Δ33 are diagonal elements of a relative rotation matrix R Δ-first .
5. The method of claim 3 , wherein the angle is one Euler angle in a set of Euler angles.
6. The method of claim 2 , wherein the new orientation error comprises an angle.
7. The method of claim 6 :
wherein the angle (θ e ) is expressed as:
θ e =cos −1 [0.5*( R Δ11 +R Δ22 +R Δ33 −1)], and
wherein R Δ11 , R Δ22 , R Δ33 are diagonal elements of a relative rotation matrix R Δ-new .
8. The method of claim 6 , wherein the angle is one Euler angle in a set of Euler angles.
9. The method of claim 1 , further comprising:
constraining, by the ratcheting system, roll motion of the slave surgical instrument tip if a joint limit is reached during motion of the slave surgical instrument tip.
10. The method of claim 1 , further comprising:
introducing, by the ratcheting system, a control system error in the new alignment error to speed up convergence of alignment between the slave surgical instrument tip and the master grip.
11. The method of claim 1 , further comprising:
determining, by the ratcheting system, a first orientation solution closest to an orientation of the master grip from multiple orientation solutions; and
using the first orientation solution to determine the new alignment error.
12. The method of claim 1 , the master grip comprising an unpowered master grip.
13. The method of claim 1 , further comprising:
performing the determining and the using the new alignment error while the master grip is used to control the slave surgical instrument tip.