Patent ID: 9638219
Date: 2017-05-02
CPC Classifications: B21C,F15B

Claim:
1. A method of controlling a hydraulic system, the hydraulic system comprising: a ram cylinder unit having a cylinder and a ram; and a hydraulic pump and a reservoir used to supply hydraulic fluid to the cylinder, and hydraulically driving the ram using the hydraulic fluid supplied to the cylinder by the hydraulic pump so as to cause the ram to move against a specific load, wherein: a main ram is movably received in the cylinder; the ram unified into a front side of the main ram is disposed to be movable in an axis direction of the ram cylinder unit; in the cylinder of the ram cylinder unit, a first pipe and a second pipe for supplying and discharging the hydraulic fluid to and from the cylinder are connected to a peripheral wall on a front side and a peripheral wall on a rear side; the first pipe is connected to the reservoir; the second pipe is connected to the hydraulic pump; the hydraulic pump is attached to a portion in which the reservoir and the second pipe are connected; and the hydraulic fluid staying in the cylinder in the front side of a position of the main ram can be returned to the reservoir via the first pipe with a advancing of the main ram, the method comprising: determining what a present state is one of an initial state, a proportional steady state, and a later state, wherein the initial state is a state where the hydraulic pump supplies the hydraulic fluid via the second pipe to the rear side of the cylinder to compress the hydraulic fluid in the cylinder and to control the moving speed of the ram by the use of the pressure of the hydraulic fluid including volume loss due to the compression, the proportional steady state is a state where a predetermined correlation is maintained depending on a pumping rate supplied to the cylinder and the moving speed of the ram is controlled after the compression of the hydraulic fluid in the cylinder is completed, and the later state is a state where the pressure decreasing by decompressing the hydraulic fluid compressed in the cylinder and by returning the hydraulic fluid to the reservoir via the second pipe and the hydraulic pump is added to the pressure of the hydraulic fluid supplied to the cylinder and the moving speed of the ram is controlled by the use of the resultant pressure; controlling the pumping rate, which is obtained by adding the flow rate corresponding to the volume loss due to the compression of the hydraulic fluid thereto, to control the moving speed of the ram to a target ram speed in the initial state; controlling the pumping rate, which is obtained by subtracting the flow rate corresponding to volume recovery of the hydraulic fluid due to the relief of compression of the hydraulic fluid therefrom, to control the moving speed of the ram to the target ram speed in the later state; numerically calculating the pumping rate corresponding to the present ram speed based on the relationship between the moving speed of the ram and the pumping rate, which is expressed as the correlation in the proportional steady state which has been calculated in advance through a test under a specific load condition acting on the ram in the initial state, and calculating a pumping rate value obtained by adding the pumping rate corresponding to the target ram speed to the flow rate corresponding to the volume loss due to the compression of the hydraulic fluid thereto in the initial state corresponding to a difference between the pumping rate of the hydraulic pump in the initial state and the pumping rate corresponding to the present ram speed; numerically calculating the pumping rate corresponding to the present ram speed based on the relationship between the moving speed of the ram and the pumping rate, which is expressed as the correlation in the proportional steady state which has been calculated in advance through the test under the specific load condition acting on the ram in the later state, and calculating a pumping rate value obtained by subtracting the flow rate corresponding to volume recovery of the hydraulic fluid due to the relief of compression of the hydraulic fluid therefrom in the later state corresponding to a difference between the pumping rate of the hydraulic pump in the later state and the pumping rate corresponding to the present ram speed from the pumping rate corresponding to the target ram speed.