Servo hydraulic press

Abstract

The present invention relates to a servo hydraulic press for sheet metal forming. The press comprises a hydraulic cylinder, at least two servo motors and at least two pumps for supplying pressurized fluid to the hydraulic cylinder, where each servo motor drives at least one pump. The servo motors are operable at variable speed, and the first servo motor and first pump are operable in an opposite direction to the second servo motor and the second pump. With this arrangement, the servo hydraulic press may be operated at low speed without causing damage to the pumps or motors.

Claims

1. A servo hydraulic press for sheet metal forming comprising: a hydraulic cylinder; a first servo motor and a second servo motor; a first pump and a second pump for supplying pressurized fluid to the hydraulic cylinder, wherein the first servo motor drives the first pump, and the second servo motor drives the second pump, and wherein the servo motors are operable at variable speed, and the first pump and the second pump together provide a total flow of pressurized fluid in a closed loop supply to an upper chamber of the hydraulic cylinder; and a controller configured to operate the first servo motor and the first pump to flow pressurized fluid in an opposite direction to the flow of pressured fluid from the second servo motor and the second pump such that a reduced total flow of pressurized fluid to the upper chamber of the hydraulic cylinder is provided by the first pump and the second pump.

2. The servo hydraulic press according to claim 1, wherein each servo motor and/or pump is operable in two directions.

3. The servo hydraulic press according to claim 1, wherein the servo motors are reluctance motors.

4. The servo hydraulic press according to claim 1, further comprising a control valve.

5. The servo hydraulic press according to claim 4, wherein the control valve is manually operated.

6. The servo hydraulic press according to claim 4, wherein the control valve is automatically operated.

7. A method for controlling a hydraulic cylinder in a servo hydraulic press for forming sheet metal, the method comprising the steps of supplying pressurized fluid in a closed loop supply to an upper chamber of the hydraulic cylinder comprising a first servo motor that drives a first pump and a second servo motor that drives a second pump, operating the servo motors at variable speed, and operating the flow of pressured fluid of the first servo motor and the first pump in an opposite direction to the flow of pressurized fluid from the second servo motor and the second pump such that a reduced total flow of pressurized fluid to the upper chamber of the hydraulic cylinder is provided together by the first pump and the second pump.

8. The method according to claim 7, further comprising the step of controlling a flow of the pressurized fluid by use of a control valve.

9. The method according to claim 8, wherein the step of controlling the control valve is by manual operation.

10. The method according to claim 8, wherein the step of controlling the control valve is by automatic operation.

11. The servo hydraulic press according to claim 1, wherein the closed loop supply is configured by an internal valve in the hydraulic cylinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This and other aspects of the present invention now be described more in detail, with reference to the appended drawings showing a currently preferred embodiment of the invention.

(2) FIG. 1 shows a schematic view of a servo hydraulic press.

(3) FIG. 2a shows a schematic view of an internal valve in an open position.

(4) FIG. 2b shows a schematic view of an internal valve in a closed position.

DETAILED DESCRIPTION

(5) The present invention will be described more fully hereinafter with reference to the accompanying drawings. In the drawings, like numbers refer to like elements.

(6) The servo hydraulic press 1 according to the invention is schematically illustrated in FIG. 1. The servo motors 4a, 4b drive the pumps 3a, 3b. The motors are reluctance motors. The control valves 2 are used to rinse the system and add security to the system by manual or automatic control. The cylinder comprises an upper cylinder 6 and a lower cylinder 7. One end of the lower cylinder comprises an area 8 where the workpiece for working the sheet metal is fixed. When the press is in working mode, the cylinder is moved in the direction D, lowering the workpiece towards the sheet metal. The cylinder comprises an internal valve 5 which controls the flow of the fluid such that the fluid is in a closed loop system. In FIG. 1 the internal valve 5 is illustrated in an open position.

(7) The servo motors 4a, 4b drive the pumps 3a, 3b and can be operated in opposite directions and with variable speed. When the press is in idle mode, the first motor and corresponding pump or pumps on the first motor shaft are operated in an opposite direction in relation to the second motor and its corresponding pump or pumps. When the motors are operating in opposite directions the first motor may serve as a motor and the second motor may serve as generator, driven by the flow and pressure from the first motor. Operation in opposite directions allows the servo hydraulic press to be operated at low speed while the pumps and motors are operated at higher speed as the resultant speed is the difference between the two opposing speeds. I.e. the resulting fluid flow to the hydraulic cylinder may be lower than the fluid flow from each hydraulic cylinder since the resulting fluid flow of the two hydraulic cylinders operating in opposite directions becomes lower. The fluid flow from one of the hydraulic pumps cancel out a part of the fluid flow from the other hydraulic pump operating in an opposite direction.

(8) When the press is in operation, the first and second motors are operated in the same direction such as to achieve sufficient pressure for operation.

(9) The hydraulic system is a closed system comprising an internal valve for regulating the pressing operation. FIGS. 2a and 2b illustrate the internal valve 5 in the hydraulic press 1 in an open position in FIG. 2a and in a closed position in FIG. 2b. In the open position, the pressurized fluid flows from the upper chamber 9 to the lower chamber 10. When the cylinder is at work and in a certain position, the valve is moved into a closed position, as illustrated in FIG. 2b. In the closed position, the pressurized fluid is transported by use of the pumps 3a, 3b from the lower chamber 10 to the upper chamber 9, hence generating and exerting a force in the direction D towards which the cylinder is moved such that a sheet metal is formed by pressing. When the work is done, the valve returns to the open position and the pressurized fluid is transported from the upper chamber 9 to the lower chamber 10.

(10) In the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims.