Systems and methods for controlling a surgical stapling and cutting instrument

1. A surgical stapling instrument, comprising:

a handle;

a shaft extending distally from the handle;

an end effector positioned at a distal end of the shaft, the end effector comprising:

a firing member translatable proximally and distally along a longitudinal axis of the end effector from a stroke begin position to a stroke end position distal of the stroke begin position;

a knife coupled to the firing member;

a staple cartridge comprising a wedge sled positioned to be actuated by distal translation of the firing member; and

a position sensor positioned to sense a position of the firing member;

a motor coupled to the firing member to translate the firing member between the stroke begin position and the stroke end position during a firing stroke;

a motor controller to receive a motor set point and provide a drive signal to the motor;

an energy storage device electrically coupled to provide energy to the motor;

a Coulomb counter electrically coupled to the energy storage device to measure energy provided by the energy storage device; and

a control circuit comprising at least one processor and a memory device in communication with the at least one processor, wherein the memory device comprises instructions that, when executed by the at least one processor, causes the at least one processor to;

receive a first firing signal;

at a first time and in response to the first firing signal, set the motor set point to a first motor set point value while allowing at least one other motor parameter to drift, wherein the drift is based on a tissue characteristic;

at a second time, receive from the position sensor an indication that the firing member has traversed a predefined initial distance between the stroke begin position and the stroke end position, wherein an open-loop portion of the firing stroke is defined as a period beginning at the first time and ending at the second time;

receive, from the Coulomb counter, first energy data describing a first energy provided from the energy storage device during the open-loop portion, wherein the first energy is reflective of a tissue characteristic;

determine that the first energy exceeds a threshold energy wherein the threshold energy correlates to a tissue thickness;

modulate the motor to draw a first constant power from the energy storage device based on the first energy, and the corresponding tissue characteristic, from the open-loop portion of the firing stroke; and

maintain the first constant power draw from the motor between the initial distance and the stroke end position.

2. The surgical stapling instrument of claim 1 , wherein the memory device further comprises instructions that, when executed by the at least one processor, causes the at least one processor to:

receive a second firing signal;

at a third time and in response to the second firing signal, set the motor set point to a second motor set point value;

at a fourth time, receive from the position sensor an indication that the firing member has traversed the initial distance between the stroke begin position and the stroke end position;

receive, from the Coulomb counter, second energy data describing a second energy provided from the energy storage device between the third time and the fourth time;

determine that the second energy is less than the threshold energy; and

modulate the motor to draw a second constant power higher than the first constant power.

3. A surgical instrument comprising:

an end effector, the end effector comprising:

a firing member translatable proximally and distally along a longitudinal axis between a stroke begin position to a stroke end position distal of the stroke begin position; and

a knife coupled to the firing member;

a position sensor configured to sense a position of the firing member and indicate that the firing member has traversed a predefined distance from the stroke begin position;

an energy sensor;

a motor coupled to the firing member to translate the firing member between the stroke begin position and the stroke end position; and

a control circuit comprising at least one processor and a memory device in communication with the at least one processor, wherein the memory device comprises instructions that, when executed by the at least one processor, causes the at least one processor to:

begin a firing member stroke by providing an initial motor setting to the motor while allowing at least one other motor parameter to drift, wherein the drift is based on a mechanical resistance to the firing member from tissue;

maintain the initial motor setting for an open-loop portion of the firing member stroke, wherein the open-loop portion is defined by a predetermined portion of the firing member stroke from the stroke begin position to the predefined distance;

receive, from the energy sensor, firing member energy data describing a firing member energy provided to the motor during the open-loop portion of the firing member stroke, wherein the firing member energy is reflective of a tissue characteristic;

compare the firing member energy to a threshold energy wherein the threshold energy correlates to a tissue characteristic;

select a firing control program based on the firing member energy, and the corresponding tissue characteristic from the open-loop portion; and

after the open-bop portion of the firing member stroke, drive the firing member according to the selected firing control program to the stroke end position.

4. The surgical instrument of claim 3 , wherein the open-loop portion of the firing member stroke is from a beginning of the firing member stroke to an end of an initial time period.

5. The surgical instrument of claim 3 , wherein the predefined distance is about 1/6 of a distance between the stroke begin position and the stroke end position.

6. The surgical instrument of claim 3 , wherein providing the initial motor setting to the motor comprises providing a first motor set point to a motor control circuit.

7. The surgical instrument of claim 3 , wherein the initial motor setting is a voltage of a motor drive signal provided to the motor.

8. The surgical instrument of claim 3 , wherein the drive of the firing member according to the firing control program comprises driving the firing member to a first constant speed.

9. The surgical instrument of claim 3 , wherein the drive of the firing member according to the firing control program comprises driving the firing member with a constant power.

10. The surgical instrument of claim 3 , wherein the open-loop portion is a first open-loop portion, wherein the firing member stroke is a first firing member stroke, wherein the firing control program is a first firing control program, wherein the memory device further comprises instructions that, when executed by the at least one processor, causes the at least one processor to:

begin a second firing member stroke by providing the initial motor setting to the motor;

maintain the initial motor setting for a second open-loop portion of the second firing member stroke;

receive second firing member energy data describing energy provided to the motor during the second open-loop portion of the second firing member stroke;

select a second firing control program based on the energy of the firing member during the second open-loop portion of the second firing member stroke; and

after the second open-loop portion of the second firing member stroke, drive the firing member according to the second firing control program.

11. The surgical instrument of claim 10 , wherein the second firing member energy data indicates that more energy was provided to the motor during the second open-loop portion of the second firing member stroke than was provided to the motor during the first open-loop portion of the firing member stroke, wherein the drive of the firing member according to the first firing control program comprises driving the firing member at a first constant power, and wherein the drive of the firing member according to the second firing control program comprises driving the firing member at a second constant power less than the first constant power.

12. The surgical instrument of claim 10 , wherein the second firing member energy data indicates that more energy was provided to the motor during the second open-loop portion of the second firing member stroke than was provided to the motor during the first open-loop portion of the firing member stroke, wherein the drive of the firing member according to the first firing control program comprises driving the firing member to a first constant speed, and wherein the drive of the firing member according to the second firing control program comprises driving the firing member to a second constant speed lower than the first constant speed.

13. The surgical instrument of claim 3 , further comprising a Coulomb counter electrically connected to sense energy provided to the motor.

14. A surgical stapling instrument, comprising:

a handle;

a shaft extending distally from the handle;

an end effector positioned at a distal end of the shaft, the end effector comprising:

a firing member translatable proximally and distally along a longitudinal axis of the end effector from a stroke begin position to a stroke end position distal of the stroke begin position during a firing stroke;

a knife coupled to the firing member;

a staple cartridge comprising a wedge sled positioned to be actuated by distal translation of the firing member; and

a position sensor positioned to sense a position of the firing member;

a motor coupled to the firing member to translate the firing member between the stroke begin position and the stroke end position;

a motor controller to receive a motor set point and provide a drive signal to the motor;

an energy storage device electrically coupled to provide energy to the motor;

an energy measuring device electrically coupled to the energy storage device to measure energy provided by the energy storage device; and

a control circuit comprising at least one processor and a memory device in communication with the at least one processor, wherein the memory device comprises instructions that, when executed by the at least one processor, causes the at least one processor to:

receive a first firing signal;

at a first time and in response to the first firing signal, set the motor set point to a first motor set point value while allowing at least one other motor parameter to drift, wherein the drift is based on a tissue condition:

at a second time, receive from the position sensor an indication that the firing member has traversed a predefined initial distance between the stroke begin position and the stroke end position, wherein an open-loop portion of the firing stroke is defined as a time period beginning at the first time and ending at the second time;

receive first energy data describing a first energy provided from the energy storage device during the open-loop portion, wherein the first energy data determines tissue thickness from the open-loop portion; and

at or after the second time, modulate the motor to maintain a constant power draw from the energy storage device, based on the determined tissue thickness from the open-loop portion, between the initial distance and the stroke end position.