Ultrasonic transmitting unit and manufacturing method of ultrasonic transmitting unit

1. An ultrasonic transmitting unit which extends along a longitudinal axis and which is configured to transmit an ultrasonic vibration from a proximal direction toward a distal direction and thereby configured to vibrate at a predetermined resonance frequency, the ultrasonic transmitting unit comprising:

a vibration generating portion which is configured to generate the ultrasonic vibration;

a proximal side transmitting member to which the vibration generating portion is attached and to which the ultrasonic vibration is configured to be transmitted from the vibration generating portion, the proximal side transmitting member including a proximal side abutment portion which forms a distal end of the proximal side transmitting member;

a distal side transmitting member connected to the proximal side transmitting member to which the ultrasonic vibration is transmitted from the vibration generating portion, the distal side transmitting member including a distal side abutment portion on which the proximal side abutment portion of the proximal side transmitting member abuts when the distal side transmitting member is connected to the proximal side transmitting member;

a projecting portion protruding from the distal side abutment portion toward the proximal direction in the distal side transmitting member, the projecting portion including a protruding end located a predetermined protruding dimension apart from the distal side abutment portion; and

a depressed portion which is depressed from the proximal side abutment portion toward the proximal direction and which includes a bottom portion spaced a depression dimension equal to or more than the predetermined protruding dimension apart from the proximal side transmitting member, the depressed dimension being set in accordance with a Young's modulus of the proximal side transmitting member based on a relation between the Young's modulus of the proximal side transmitting member and the depression dimension so that the proximal side transmitting member and the distal side transmitting member vibrates at the predetermined resonance frequency where an antinode position of the ultrasonic vibration is located within a range in which a cavity portion formed between the protruding end of the projecting portion and the bottom portion of the depressed portion in a situation in which the ultrasonic transmitting unit transmits the ultrasonic vibration.

2. The ultrasonic transmitting unit according to claim 1 , wherein

in the situation in which the ultrasonic transmitting unit vibrates at the predetermined resonance frequency, the proximal side abutment portion and the distal side abutment portion are located at positions different from the antinode positions and node positions of the ultrasonic vibration, and

a reference antinode position which is an antinode position located between the protruding end of the projecting portion and the bottom portion of the depressed portion in the situation in which the ultrasonic transmitting unit vibrates at the predetermined resonance frequency is a proximate antinode position closest to the proximal side abutment portion and the distal side abutment portion among the antinode positions of the ultrasonic vibration.

3. The ultrasonic transmitting unit according to claim 1 , wherein the proximal side transmitting member includes a horn which is configured to increase the amplitude of the ultrasonic vibration.

4. The ultrasonic transmitting unit according to claim 1 , wherein

the projecting portion includes an external thread portion, and

the depressed portion includes an internal thread portion which is screwed to the external thread portion to engage the projecting portion with the depressed portion.

5. A manufacturing method of an ultrasonic transmitting unit which extends along a longitudinal axis and which is configured to transmit an ultrasonic vibration from a proximal direction toward a distal direction and thereby configured to vibrate at a predetermined resonance frequency, the manufacturing method comprising:

forming a vibration generating portion which is configure to generate the ultrasonic vibration;

forming a proximal side transmitting member to which the ultrasonic vibration is configured to be transmitted from the vibration generating portion and forming a distal end of the proximal side transmitting member by a proximal side abutment portion;

attaching the vibration generating portion to the proximal side transmitting member;

forming a distal side transmitting member to which the ultrasonic vibration is configured to be transmitted from the proximal side transmitting member;

connecting the distal side transmitting member to the distal direction side of the proximal side transmitting member so that the proximal side abutment portion of the proximal side transmitting member abuts on a distal side abutment portion of the distal side transmitting member;

forming a projecting portion protruding from the distal side abutment portion toward the proximal direction in the distal side transmitting member, and forming a proximal end of the distal side transmitting member by a protruding end of the projecting portion which is located a predetermined protruding dimension apart from the distal side abutment portion toward the proximal direction;

forming a depressed portion which is depressed from the proximal side abutment portion toward the proximal direction in the proximal side transmitting member, setting a depression dimension equal to or more than the predetermined protruding dimension from the proximal side abutment portion to a bottom portion of the depressed portion accordance with a Young's modulus of the proximal side transmitting member based on a relation between the Young's modulus of the proximal side transmitting member and the depression dimension, and then forming the depressed portion having the set depression dimension from the proximal side abutment portion to the bottom portion;

forming a cavity portion having a space between the protruding end of the projecting portion and the bottom portion of the depressed portion inside the proximal side transmitting member when the distal side transmitting member is connected to the proximal side transmitting member and then the depressed portion is engaged with the projecting portion; and

connecting the distal side transmitting member to the proximal side transmitting member in which the depression dimension is set so that the proximal side transmitting member and the distal side transmitting member vibrates at the predetermined resonance frequency where an antinode position of the ultrasonic vibration is located within a range in which the cavity portion is formed between the protruding end of the projecting portion and the bottom portion of the depressed portion when the ultrasonic transmitting unit transmits the ultrasonic vibration.

6. The manufacturing method according to claim 5 , wherein forming the depressed portion in the proximal side transmitting member includes

measuring a measurement resonance frequency that is a resonance frequency at which a temporary vibration unit including the proximal side transmitting member vibrates by the ultrasonic vibration, and

determining the Young's modulus of the proximal side transmitting member based on the measured measurement resonance frequency.

7. The manufacturing method according to claim 6 , wherein measuring the measurement resonance frequency of the temporary vibration unit includes

attaching the vibration generating portion to the proximal side transmitting member to form the temporary vibration unit, and

generating the ultrasonic vibration by the vibration generating portion.

8. The manufacturing method according to claim 6 , wherein measuring the measurement resonance frequency of the temporary vibration unit includes

forming a temporary depressed portion which is depressed from the proximal side abutment portion toward the proximal direction in the proximal side transmitting member, and locating a temporary bottom portion of the temporary depressed portion a temporary depression dimension smaller than the depression dimension of the depressed portion apart from the proximal side abutment portion toward the proximal direction,

attaching a vibration generator separate from the vibration generating portion to the proximal side transmitting member via the temporary depressed portion to form the temporary vibration unit, and

generating the ultrasonic vibration by the vibration generator, and

forming the depressed portion in the proximal side transmitting member includes deforming the temporary depressed portion on the basis of the Young's modulus of the proximal side transmitting member.

9. The manufacturing method according to claim 8 , wherein forming the temporary depressed portion includes forming the temporary depressed portion so that the temporary depression dimension is smaller than the predetermined protruding dimension of the projecting portion.