Loading features for ultrasonic surgical instrument

1. A surgical instrument comprising:

(a) a body;

(b) a shaft assembly extending distally from the body;

(c) an end effector coupled with a distal end of the shaft assembly, wherein the end effector is operable to manipulate tissue;

(d) a transducer assembly, wherein the transducer assembly is operable to convert electrical power into ultrasonic vibrations, wherein a distal end of the transducer assembly is configured to removably couple with a proximal end of the shaft assembly; and

(e) a loading assembly, wherein the loading assembly comprises an actuator configured to selectively move from a first position to a second position to thereby couple the distal end of the transducer assembly with the proximal end of the shaft assembly, wherein the loading assembly is configured to rotatably drive the transducer assembly successively through a first stage of rotation and a second stage of rotation when moving the actuator from the first position to the second position, wherein the loading assembly during the first stage of rotation is configured to rotatably drive the transducer assembly with a first rotational speed and a first rotational torque, wherein the loading assembly during the second stage of rotation is configured to rotatably drive the transducer assembly with a second rotational speed and a second rotational torque, wherein the second rotational speed is less than the first rotational speed, and wherein the second rotational torque is greater than the first rotational torque for coupling the distal end of the transducer assembly with the proximal end of the shaft assembly.

2. The instrument of claim 1 , wherein the loading assembly comprises a first spur gear and a second spur gear, wherein the second spur gear has a larger diameter than the first spur gear.

3. The instrument of claim 2 , wherein the loading assembly comprises a first rack and a second rack, wherein the first rack is configured to engage the first spur gear and the second rack is configured to engage the second spur gear.

4. The instrument of claim 3 , wherein first rack is translatable to rotate the first spur gear, wherein the second rack is translatable to rotate the second spur gear, wherein the first spur gear is configured to rotate at a higher speed than the second spur gear, wherein the second spur gear is configured to rotate at a higher torque than the first spur gear.

5. The instrument of claim 3 , wherein the first rack extends along an arcuate path, wherein the second rack extends along an arcuate path.

6. The instrument of claim 2 , wherein the first rack is configured to engage the first spur gear during the first stage of rotation, wherein the second rack is configured to engage the second spur gear during the second stage of rotation.

7. The instrument of claim 6 , wherein the first rack is configured to disengage the first spur gear during the second stage of rotation.

8. The instrument of claim 1 , further comprising a bevel gear secured to a portion of the shaft assembly, wherein the bevel gear is configured to engage the loading assembly.

9. The instrument of claim 1 , wherein the actuator is configured to translate relative to the body.

10. The instrument of claim 9 , wherein the actuator is operable to translate through a first range of longitudinal motion to provide the first stage of rotation of the transducer assembly, wherein the actuator of the loading assembly is operable to translate through a second range of longitudinal motion to provide the second stage of rotation of the transducer assembly.

11. The instrument of claim 1 , wherein the shaft assembly defines a longitudinal axis, wherein the actuator is rotatable about an axis that is perpendicular to the longitudinal axis.

12. The instrument of claim 1 , wherein the loading assembly comprises a rotation locking member configured to selectively prevent rotation of the shaft assembly relative to the body.

13. The instrument of claim 12 , wherein the loading assembly comprises a feature configured to selectively disengage the rotation locking member, to thereby permit rotation of the shaft assembly relative to the body.

14. The instrument of claim 1 , wherein the actuator comprises a lever that is pivotable relative to the body to couple the distal end of the transducer assembly with the proximal end of the shaft assembly.

15. The instrument of claim 1 , wherein the actuator is translatable relative to the body to couple the distal end of the transducer assembly with the proximal end of the shaft assembly.

16. The instrument of claim 1 , wherein the loading assembly comprises a ratcheting feature configured to provide one or both of user feedback or one-way movement restriction during actuation of the loading assembly.

17. The instrument of claim 1 , wherein at least a portion of the loading assembly is housed within the body.

18. The instrument of claim 1 , wherein the end effector comprises an ultrasonic blade and a pivoting clamp arm.

19. A surgical instrument comprising:

(a) a shaft assembly;

(b) a transducer assembly, wherein a distal end of the transducer assembly is configured to removably couple with a proximal end of the shaft assembly; and

(c) a loading assembly, wherein the loading assembly comprises an actuator that is configured to move through a first range of motion and a second range of motion, wherein the loading assembly is configured to couple the distal end of the transducer assembly with the proximal end of the shaft assembly at a first speed and a first torque during the first range of motion, wherein the loading assembly is configured to couple the distal end of the transducer assembly with the proximal end of the shaft assembly at a second speed and a second torque during the second range of motion, wherein the second speed is less than the first speed, and wherein the second torque is greater than the first torque.

20. A method of operating a surgical instrument, wherein the instrument comprises a shaft assembly, a transducer assembly configured to removably couple with a proximal end of the shaft assembly, and a loading assembly, the method comprising the step of:

(a) positioning a proximal end of the shaft assembly adjacent to a distal end of the transducer assembly;

(b) actuating the loading assembly to couple the shaft assembly with the transducer assembly at a first speed and a first torque; and

(c) actuating the loading assembly to couple the shaft assembly with the transducer assembly at a second speed and a second torque, wherein the second speed is slower than the first speed, and wherein the second torque is greater than the first torque.