Patent ID: 7168771

Claim:
A method of evaluating soundness of a hydraulic drive device, wherein the hydraulic drive device comprises a pressure generator for generating a flow of a pressurized hydraulic fluid, a pressure-variable accumulator for accumulating the pressure of the pressurized hydraulic fluid supplied from the pressure generator, and a pressure control unit that is arranged and constructed to receive the pressurized hydraulic fluid from the accumulator and to control the pressure of the pressurized hydraulic fluid in response to an input from an external device, so that the pressurized hydraulic fluid having the controlled pressure is used for driving an operation device, comprising: detecting a first pressure of the hydraulic fluid within a flow path of the hydraulic fluid by a first pressure sensor, wherein the flow path extends between the pressure control unit and the operation device, and the first pressure sensor is coupled to the flow path, detecting a second pressure of the hydraulic fluid discharged from the accumulator by a second pressure sensor, wherein the second pressure sensor is coupled to the accumulator, determining a stabilization time by an operation control unit, wherein the stabilization time is a time when an absolute value of a pressure gradient per unit time of the pressurized hydraulic fluid supplied from the accumulator becomes smaller than a predetermined value during the supply of the hydraulic fluid from the pressure control unit to the operation device, and the operation control unit receives detection signals from the first and second pressure sensors, determining a pressure drop of the second pressure during a period between a time prior to starting the operation of the pressure control unit and the stabilization time, determining the first pressure at the stabilization time or at a time immediately after the stabilization time, and comparing the determined pressure drop with a pressure drop under a normal condition and comparing the detected first pressure at the stabilization time with a value under normal condition of the first pressure at stabilization time or at a time immediately after the stabilization time.