Load detector, and winding apparatus for crane comprising said detector

A load detector for detecting a load of a hanging cargo, in a crane including:

• a winch drum around which a wire rope for hanging the hanging cargo is wound;
• a motor configured to drive the winch drum to achieve lowering or hoisting:
• a speed reducer configured to adjust torque of the motor at a predetermined speed reduction ratio and transfer the torque to the winch drum;
• and a power converter configured to supply a current for driving the motor to the motor, the load detector comprising:
• an output-torque estimation unit configured to obtain, from the power converter, a value of the current supplied to the motor and estimate output torque of the motor from the obtained value of the current;
• a number setting unit configured to set the winding number of the wire rope;
• and
• a load estimation unit configured to estimate a load value of the hanging cargo based on an estimated output torque value resulting from estimation by the output-torque estimation unit, the speed reduction ratio, an effective radius of the winch drum, and the winding number that is set by the number setting unit,
• wherein the load estimation unit obtains a rotation angle of the motor from the power converter and calculates a first fluctuation amount that is an amount of fluctuation of the estimated output torque value due to inertial forces of the hanging cargo, the winch drum, and the motor at a time of hoisting or lowering, based on the obtained rotation angle and moments of inertia of the winch drum, the motor, and the speed reducer, corrects the estimated output torque value by subtracting the first fluctuation amount from the estimated output torque value at a time of acceleration, and adding the first fluctuation amount to the estimated output torque value at a time of deceleration, and estimates the load value of the hanging cargo using the estimated output torque value that is corrected.