METHOD AND APPARATUS FOR DETERMINING LOAD HOLDING CURRENT

摘要

The preset invention relates to a method for determining the amount of motor current that is sufficient to hold a load (4) in a hoisting apparatus (2), where the motor (6) is an electrical induction motor that is driven by an electrical power source (12), the load (4) is attached to a line (5) on a drum (7) that is driven by the motor (6), and where the method comprises a start step where the load (4) is accelerated, a steady state step where the load (4) is hoisted with substantially constant speed while the line (5) is winded onto the drum (7), and a breaking step where the load (4) is decelerated where the motor current (I) is measured at the end of the steady state step, from which the load holding current is determined by comparing the measured motor current (I) with an empirical table, from which the load holding current is determined in order to counterbalance the torque (T) on the motor (6) caused by the load (4). The preset invention, furthermore, relates to a hoisting apparatus (2) comprising an electric induction motor (6), a transmission system (14), a winch containing a line (5) that in one extremity is attached to a drum (7) of the winch and in the other extremity is equipped with means for attaching a load (4), where the drum (7) is driven by the electric induction motor (6), a driver which supplies the electric induction motor (6) with a current and a controller (10) for controlling the motor (6) where the electric induction motor (6) is a pulse width modulated DC electric motor, and the controller (10) is adapted to receive a measurement of the current supplied to the electric induction motor (6), and the controller (10) is equipped with an empirical table.