Impact rotary tool, torque estimation method, and non-transitory recording medium

A torque estimation method of estimating a torque value generated by an impact rotary tool including:

• a driver configured to perform a turning operation;
• a drive shaft configured to be turned by the driver;
• a hammer configured to be fitted to an outer perimeter of the drive shaft such that the hammer is movable in an axial direction of the drive shaft and rotatable in a turning direction in which the drive shaft turns;
• an anvil configured to receive impact applied by the hammer in the turning direction, the torque value being produced by the impact;
• and a controller configured to control the driver in accordance with vector control, the torque estimation method comprising:
• a travel distance measurement step of measuring a parameter relating to a hammer travel distance through which on application of the impact to the anvil by the hammer, the hammer moves away from the anvil along the axial direction from a location of the application of the impact to the anvil by the hammer;
• and
• a torque estimation step of estimating, based on at least the parameter, a torque value generated by the impact, wherein
• the driver is configured to be supplied with a torque current in accordance with the vector control performed by the controller, and
• the travel distance measurement step includes
• measuring a variation amount of the torque current in a period from when the hammer applies impact to the anvil to when the hammer next applies impact to the anvil and
• measuring, as the parameter, the hammer travel distance itself, the hammer travel distance being measured based on the variation amount.