SYSTEMS AND METHODS FOR MAINTAINING MINIMUM OPENING FORCE OF JAWS IN POSITION CONTROL MODE

1 . A method for controlling opening force generated by jaws of a gripper tool of a surgical robotic system, comprising:

determining, by a processor, based on an input jaw angle between the jaws that the jaws are in a position mode, the position mode being characterized by using a position command to position the jaws at the input jaw angle;

measuring a jaw angle and an opening force between the jaws in the position mode;

determining, by the processor, whether a jaw angle error between the input jaw angle and the measured jaw angle is larger than a jaw angle error threshold in the position mode;

determining, by the processor, whether the measured opening force is smaller than a minimum opening force threshold in response to determining that the jaw angle error is larger than the jaw angle error threshold; and

generating, by the processor, an opening force error to maintain the measured opening force above the minimum opening force threshold in response to determining that the measured opening force is smaller than the minimum opening force threshold.

2 . The method of claim 1 , wherein determining that the jaws are in the position mode comprises:

determining, by the processor, that the input jaw angle is greater than or equal to a threshold jaw angle for more than a minimum time period, wherein the threshold jaw angle comprises a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to touch each other without an object being held.

3 . The method of claim 1 , wherein determining whether the jaw angle error is larger than the jaw angle error threshold comprises:

determining, by the processor, that the input jaw angle is larger than the measured jaw angle; and

determining, by the processor, that the jaw angle error is larger than the jaw angle error threshold for at least a minimum time period.

4 . The method of claim 1 , wherein determining whether the measured opening force is smaller than the minimum opening force threshold comprises:

determining, by the processor, that the measured opening force is smaller than the minimum opening force threshold as long as the measured opening force is smaller than the minimum opening force threshold plus a margin anywhere within a time window.

5 . The method of claim 4 , wherein a length of the time window is measured by an opening force counter, wherein an operation of the opening force counter comprises:

incrementing the opening force counter by one when the measured opening force is larger than the minimum opening force threshold plus the margin every time the measured opening force is sampled; and

resetting the opening force counter when the measured opening force is smaller than the minimum opening force threshold.

6 . The method of claim 5 , wherein determining whether the measured opening force is smaller than the minimum opening force threshold further comprises:

determining, by the processor, that the measured opening force is smaller than the minimum opening force threshold for an entirety of the length of the time window equaling to the opening force counter when the measured opening force is smaller than the minimum opening force threshold plus the margin anywhere within the window.

7 . The method of claim 1 , wherein the opening force error comprises a difference between the measured opening force and the minimum opening force threshold.

8 . The method of claim 1 , wherein generating the opening force error to maintain the measured opening force above the minimum opening force threshold comprises:

generating a compensating position command by the processor from the opening force error; and

combing the compensating position command and the position command by the processor to generate an updated position command.

9 . The method of claim 8 , further comprising:

applying the updated position command to position the jaws to maintain the measured opening force above the minimum opening force threshold.

10 . An apparatus to control jaws of a gripper tool of a surgical robotic system, comprising:

a sensor configured to:

estimate an angle between the jaws to generate a measured jaw angle; and

estimate opening force generated by the jaws to generate a measured opening force;

a processor configured to:

determine that the jaws are in a position mode based on a desired jaw angle between the jaws, the position mode being characterized by an application of position commands to position the jaws at the desired jaw angle;

determine whether a jaw angle error between the desired jaw angle and the measured jaw angle is larger than a jaw angle error threshold in the position mode;

determine whether the measured opening force is smaller than a minimum opening force threshold in response to a determination that the jaw angle error is larger than the jaw angle error threshold; and

generate an opening force error to update the position command to maintain the measured opening force above the minimum opening force threshold in response to a determination that the measured opening force is smaller than the minimum opening force threshold; and

an actuator drive unit configured to apply the updated position command to position the jaws to maintain the measured opening force above the minimum opening force threshold.

11 . The apparatus of claim 10 , wherein the processor configured to determine that the jaws are in the position mode comprises:

determine that the desired jaw angle is greater than or equal to a threshold jaw angle for more than a minimum time period, wherein the threshold jaw angle comprises a jaw angle when the jaws simultaneously contact an object held between the jaws or when the jaws begin to touch each other without an object being held.

12 . The apparatus of claim 10 , wherein the processor configured to determine whether the jaw angle error is larger than the jaw angle error threshold comprises:

determine that the desired jaw angle is larger than the measured jaw angle; and

determine that the jaw angle error is larger than the jaw angle error threshold for at least a minimum time period.

13 . The apparatus of claim 10 , wherein the processor configured to determine whether the measured opening force is smaller than the minimum opening force threshold comprises:

determine that the measured opening force is smaller than the minimum opening force threshold as long as the measured opening force is smaller than the minimum opening force threshold plus a margin anywhere within a time window.

14 . The apparatus of claim 13 , wherein a length of the time window is measured by an opening force counter, wherein the opening force counter is configured to:

increment by one when the measured opening force is larger than the minimum opening force threshold plus the margin every time the measured opening force is estimated by the sensor; and

reset the opening force counter when the measured opening force is smaller than the minimum opening force threshold.

15 . The apparatus of claim 14 , wherein the processor configured to determine whether the measured opening force is smaller than the minimum opening force threshold further comprises:

determine that the measured opening force is smaller than the minimum opening force threshold for an entirety of the length of the time window equaling to the opening force counter when the measured opening force is smaller than the minimum opening force threshold plus the margin anywhere within the window.

16 . The apparatus of claim 10 , wherein the opening force error comprises a difference between the measured opening force and the minimum opening force threshold.

17 . The apparatus of claim 10 , wherein the processor configured to generate the opening force error to update the position command comprises:

generate a compensating position command from the opening force error; and

combine the compensating position command and the position command to generate the updated position command to position the jaws to maintain the measured opening force above the minimum opening force threshold.

18 . A surgical robotic system, comprising:

an end effector including a pair of jaws;

a user interface device configured to generate an input jaw angle between the jaws;

a processor communicatively coupled to the end effector, the processor configured to:

determine that the jaws are in a position mode based on the input jaw angle between the jaws, the position mode being characterized by an application of a position command to position the jaws at the input jaw angle;

measure a jaw angle and an opening force between the pair of jaws in the position mode;

determine whether a jaw angle error between the input jaw angle and the measured jaw angle is larger than a jaw angle error threshold in the position mode;

determine whether the measured opening force is smaller than a minimum opening force threshold in response to a determination that the jaw angle error is larger than the jaw angle error threshold;

generate an opening force error to update the position command to maintain the measured opening force above the minimum opening force threshold in response a determination that the measured opening force is smaller than the minimum opening force threshold; and

apply the updated position command to position the jaws to maintain the measured opening force above the minimum opening force threshold.

19 . The surgical robotic system of claim 18 , wherein the processor configured to determine whether the jaw angle error is larger than the jaw angle error threshold comprises:

determine that the input jaw angle is larger than the measured jaw angle; and

determine that the jaw angle error is larger than the jaw angle error threshold for at least a minimum time period.

20 . The surgical robotic system of claim 18 , wherein the processor configured to determine whether the measured opening force is smaller than the minimum opening force threshold comprises:

determine that the measured opening force is smaller than the minimum opening force threshold plus a margin using a debouncing algorithm.