Cutting mechanism with constant-force retraction and bailout

A surgical tool, comprising:

• a drive housing;
• a drive input rotatably mounted to a bottom of the drive housing;
• a capstan assembly arranged within the drive housing and including a drive gear operatively coupled to the drive input such that rotation of the drive input correspondingly actuates the drive gear;
• a longitudinally driven gear arranged within the drive housing and engageable with the drive gear such that the longitudinally driven gear translates between a proximal home position and a distal extended position in response to actuation of the drive gear;
• a drive rod coupled to the longitudinally driven gear and extending from the drive housing to an end effector of the surgical tool;
• and
• at least one biasing member mounted to the drive housing and operatively coupled to at least one of the capstan assembly or the longitudinally driven gear to bias the longitudinally driven gear toward the proximal home position with a constant force,
• wherein:
• the at least one biasing member comprises a constant-force spring constructed from a band of spring material and defining a coil supported within the drive housing, and
• the band is operatively coupled to the longitudinally driven gear such that translation of the longitudinally driven gear toward the distal extended position unwinds the band from the coil;
• and
• further comprising a mounting plate carried by the longitudinally driven gear and the band is coupled to the mounting plate.

A surgical tool, comprising:

• a drive housing;
• a drive input rotatably mounted to a bottom of the drive housing;
• a capstan assembly arranged within the drive housing and including a drive gear operatively coupled to the drive input such that rotation of the drive input correspondingly actuates the drive gear;
• a longitudinally driven gear arranged within the drive housing and engageable with the drive gear such that the longitudinally driven gear translates between a proximal home position and a distal extended position in response to actuation of the drive gear;
• a drive rod coupled to the longitudinally driven gear and extending from the drive housing to an end effector of the surgical tool;
• and
• at least one biasing member mounted to the drive housing and operatively coupled to at least one of the capstan assembly or the longitudinally driven gear to bias the longitudinally driven gear toward the proximal position with a constant force,
• wherein:
• the band is operatively coupled to the capstan assembly and winds and unwinds from the capstan assembly to coil and uncoil the band from the coil;
• and
• the capstan assembly includes a coupler that includes a hook for securing the band to the coupler.

A surgical tool system, comprising:

• a drive housing having a drive input rotatably mounted to a bottom thereof and operably couplable to a tool driver;
• a shaft extending distally from the drive housing and terminating at an end effector;
• a capstan assembly arranged within the drive housing and including a drive gear operatively coupled to the drive input such that rotation of the drive input correspondingly actuates the drive gear;
• a longitudinally driven gear arranged within the drive housing and engageable with the drive gear such that the longitudinally driven gear translates between a proximal home position and a distal extended position in response to actuation of the drive gear;
• a drive rod coupled to the longitudinally driven gear and extending through the shaft to a knife;
• and
• at least one constant force spring mounted to the drive housing and extending to at least one of the capstan assembly or the longitudinally driven gear,
• wherein the at least one constant force spring constantly biases the longitudinally driven gear toward the proximal home position, and
• wherein the at least one constant force spring is operable to move the longitudinally driven gear to the proximal position in response to decoupling the drive housing from the tool driver.