Rotation position detection unit

An apparatus comprising:

• a holder that is configured to hold a treatment tool that is configured to be inserted into a patient during surgery;
• a motor;
• a drive-side pulley that is connected to the motor and rotationally driven by the motor around a drive shaft of the motor;
• a driven-side pulley that rotates around a first axis of rotation;
• a transmission belt that transmits a rotational drive of the drive-side pulley to the driven-side pulley;
• a rotary encoder that is connected to the first axis of rotation and detects a rotation angle of the driven-side pulley;
• and
• a controller that controls drive of the motor and to which a detection result by the rotary encoder is input,
• wherein the holder rotates in association with a rotation of the drive-side pulley,
• a diameter of the drive-side pulley is smaller than a diameter of the driven-side pulley, and
• the controller calculates a rotation position of the holder based on the rotation angle of the driven-side pulley and a pulley ratio of the diameter of the drive-side pulley to the diameter of the driven-side pulley.

An apparatus comprising:

• a motor having a drive shaft extending along a first axis;
• a drive-side pulley that is connected to the drive shaft of the motor;
• a holder that is configured to hold a treatment tool that is configured to be inserted into a patient during surgery, the holder rotating in association with the drive-side pulley;
• a driven-side pulley that rotates around the first axis, a diameter of the drive-side pulley being smaller than a diameter of the driven-side pulley;
• a transmission belt that transmits a rotational drive of the drive-side pulley to the driven-side pulley;
• a rotary encoder that is provided on the first axis and detects a rotation angle of the driven-side pulley;
• and
• a controller that calculates a rotation position of the holder based on the rotation angle and based on a pulley ratio of the drive-side pulley to the driven-side pulley, and controls the motor based on the rotation position.