JPH1038779A - Material testing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material test machine being driven through a servo valve which is actuated and stopped according to a command signal. SOLUTION: When a hydraulic pump 2 is actuated, hydraulic cylinder 5 is driven according to a command signal to a pilot servo valve 4 by feeding a pressurized oil to a main servo valve 3 through an on/off valve 7 after the delivery pressure from the hydraulic pump 2 exceeds a controllable level. A check valve and an accumulator are interposed between the hydraulic pump 2 and the pilot servo valve 4 so that the pressure being supplied to the pilot servo valve 4 exceeds a controllable level until the pressure being supplied from the hydraulic pump 2 to the main servo valve 3 drops below a predetermined level when the hydraulic pump 2 is stopped. When the hydraulic pump 2 is stopped, pressure to be supplied to the main servo valve 3 drops. Pressure being supplied to the pilot servo valve 4 is controlled by means of the check valve and the accumulator and it is kept at least higher than the controllable level until the hydraulic pressure being fed from the hydraulic pump 2 to the main servo valve 3 drops down to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a material testing machine driven by a hydraulic circuit having a main servo valve and a pilot servo valve.

[0002]

2. Description of the Related Art In a material testing machine for performing a fatigue test on a test piece by repeatedly applying a load to the test piece by a return hydraulic cylinder, the drive of the hydraulic cylinder is controlled by a servo valve.
For example, as shown in FIG. 4, pressure oil from a hydraulic pump 2 whose maximum pressure is restricted by a relief valve 1 is supplied to a main servo valve 3 and a pilot servo valve 4, and
In some cases, the hydraulic cylinder 5 is driven by controlling the oil amount. In this circuit, when a command signal is applied to the pilot servo valve 4, a pilot flapper (not shown) of the pilot servo valve 4 is driven in accordance with the command signal, and the main flapper of the main servo valve 3 is controlled by the hydraulic pressure controlled by the pilot flapper. Is controlled, and the amount of oil according to the command signal is supplied from the main servo valve 3 to the hydraulic cylinder 5. The hydraulic pump 2 is driven by a motor 6.

In this case, when the hydraulic pump 2 is started, pressure oil is supplied to both the main servo valve 3 and the pilot servo valve 4 at the same time, so that the main flapper of the main servo valve 3 driven by the pilot servo valve 4 issues a command. Since hydraulic oil is supplied to the main servo valve 3 before it is controlled to the correct position according to the signal, the hydraulic cylinder 5 performs a movement that is not correlated with the command signal immediately after the start. That is, the flapper of the pilot servo valve 4 is not controlled to the position corresponding to the command signal unless the hydraulic pressure becomes equal to or higher than the controllable pressure. The cylinder 5 may move.

As shown in FIG. 5, an on-off valve 7 is provided between the hydraulic pump 2 and the main servo valve 3, and the hydraulic pump 2 is started to supply hydraulic oil having a controllable pressure or higher to the pilot servo valve 4. By opening the on-off valve 7 after that and supplying the pressure oil to the main servo valve 3, the undesired movement of the hydraulic cylinder 5 at the time of the above-mentioned startup is prevented.

[0005]

However, when the hydraulic pump 2 is stopped, for example, by operating an emergency stop button, the supply pressure of the main servo valve 3 and the supply pressure of the pilot servo valve 4 are simultaneously reduced. If the pressure of the pump 2 becomes equal to or lower than the controllable pressure of the pilot servo valve 4, the main servo valve 3 may move uncorrelated with the command signal.

An object of the present invention is to provide a material testing machine driven by a servo valve that moves in correlation with a command signal both at the time of starting and at the time of stopping.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIG. 1. A material testing machine according to the present invention responds to a command signal when a hydraulic pump 2 and a pressure oil higher than a controllable pressure are supplied. Servo valve 4 driven and controlled
A material comprising: a main servo valve 3 driven and controlled by the pilot servo valve 4; and a hydraulic actuator 5 driven by hydraulic oil from the hydraulic pump 2 passing through the main servo valve 3 to load the specimen. Applies to testing machines. The above-described object is to open and close the oil passage between the hydraulic pump 2 and the main servo valve 3 and to stop the hydraulic pump 2 when the hydraulic pump 2 is stopped.
Pressure control means 11 and 12 are provided between the hydraulic pump 2 and the pilot servo valve 4 so that the pressure supplied to the pilot servo valve 4 exceeds the controllable pressure until the hydraulic pressure supplied to the pilot servo valve falls below a predetermined value. This is achieved by:

At the start-up, if hydraulic oil is supplied to the main servo valve 3 by the on-off valve 7 after the discharge pressure of the hydraulic pump 2 becomes equal to or higher than the controllable pressure, the hydraulic actuator 5 is controlled by the pilot servo even at the start-up. It can be driven in correlation with a command signal to the valve 4. When the hydraulic pump 2 stops, the pressure supplied to the main servo valve 3 decreases. The supply pressure to the pilot servo valve 4 is controlled by a pressure control means 11,
The control unit 12 controls the hydraulic pressure supplied from the hydraulic pump 2 to the main servo valve 3 to be equal to or less than a predetermined value, for example, zero, until the hydraulic pressure becomes zero.

In the section of the means for solving the above problems, the present invention has been described with reference to the embodiments, but the present invention is not limited to the embodiments.

[0010]

FIG. 1 is a diagram showing a servo valve circuit of an embodiment of a material testing machine according to the present invention. The same parts as those in FIG. 4 are denoted by the same reference numerals and differences are mainly described.

An opening / closing valve 7 is provided in an oil passage between the hydraulic pump 2 and the main servo valve 3 as in the case of FIG. On the other hand, a check valve 11 is provided in an oil passage between the hydraulic pump 2 and the pilot servo valve 4, and a circuit pressure in the oil passage is provided between the check valve 11 and the pilot servo valve 4 for a predetermined time. Is provided with an accumulator 12 that can maintain at least a controllable pressure or higher.

The operation of such a circuit will be described. (1) At startup At startup, the on-off valve 7 is in the closed position and the main servo valve circuit is closed. Therefore, when the hydraulic pump 2 is started, the pressure oil is supplied from the check valve 11 to the pilot servo valve 4. If the command signal applied to the pilot servo valve 4 is zero, after the pressure supplied to the pilot servo valve 4 has reached the controllable pressure or more, the pilot flapper of the pilot servo valve 4 moves to the position where the command signal is zero. The main flapper of the main servo valve 3 is also driven to the position where the command signal is zero. At this time, the pressure is accumulated in the accumulator 12.

Thereafter, when the operator operates the on-off valve 7 to the open position to open the main servo valve circuit, the pressure oil of the hydraulic pump 2 is supplied to the main servo valve 3. At this time, since the main flapper is at the position where the command signal is zero, the hydraulic cylinder 5
No hydraulic oil is supplied, and the hydraulic cylinder 5 is not driven.
That is, the hydraulic cylinder 5 holds the stopped state in correlation with the command signal.

When a predetermined command signal is applied to the pilot servo valve 4, the pilot flapper is controlled to a position corresponding to the command signal. As a result, the main flapper of the main servo valve 3 is similarly moved to a position corresponding to the command signal. Is controlled to
The flow rate of the discharge oil of the hydraulic pump 2 is controlled so that the hydraulic cylinder 5
And the hydraulic cylinder 5 is driven.

(2) At the time of stop When the hydraulic cylinder 5 is driven at a flow rate according to the command signal, for example, when the hydraulic pump 2 is stopped by an emergency stop button, the pressure applied to the main servo valve 3 becomes the characteristic line of FIG. Although the pressure drops as shown in FIG. A, the pressure to the pilot servo valve 4 is maintained by the accumulator 12 at a controllable pressure P1 or more for a predetermined time as shown in a characteristic diagram b. As shown in FIG. 2, at time t1 when the discharge pressure of the hydraulic pump 2 becomes zero, the supply pressure of the pilot servo valve 4 is equal to or higher than the controllable pressure P1. Therefore, the pilot flapper of the pilot servo valve 4 is controlled to the position corresponding to the command signal from the emergency stop to the time t1, and the main flapper is controlled to the position corresponding to the command signal until the time t1 at which the flow rate into the main servo valve 3 becomes zero. The main flapper of the servo valve 3 is also controlled to a position according to the command signal. As a result, until the oil pressure becomes zero, the hydraulic cylinder 5 moves in correlation with the command signal, and does not move undesirably.

If the supply pressure of the pilot servo valve 4 decreases in accordance with the same characteristic diagram a as the supply pressure of the main servo valve 3, the hydraulic pump 2 is applied to the main servo valve 3 even after the pressure becomes equal to or less than the controllable pressure P1. Supplies that pressure. As a result, if the pressure becomes equal to or less than the controllable pressure P1 and the position of the pilot flapper of the pilot servo valve 4 is controlled to a position not corresponding to the command signal, the position of the main flapper of the main servo valve 3 is inevitably included in the command signal. This means that the hydraulic cylinder 5 is controlled to a non-corresponding position, and the hydraulic cylinder 5 performs an undesired movement that is not correlated with the command signal. In this regard,
According to the present invention, as described above, it is possible to prevent the main servo valve 3 from becoming uncontrollable at both start-up and stop.

The command signal is, for example, a current value corresponding to a deviation between a target value of the load or displacement applied to the specimen and an actual detected value of the load or displacement.

As shown in FIG. 3, even if a slow return valve 21 is used in place of the check valve 11 and the accumulator 12, the decrease in the supply pressure to the pilot servo valve 4 during an emergency stop can be reduced by the supply pressure of the main servo valve 3. This can be made slower than the decrease, and the same operation and effect as the embodiment of FIG. 1 can be obtained. The slow return valve 21 is a check valve 21.
a and an aperture 21b.

Furthermore, the present invention includes various forms of pressure control means for slowing down the supply pressure to the pilot servo valve 4 using various hydraulic devices and valves other than those shown in FIGS. It is a thing. Further, the hydraulic actuator is not limited to the hydraulic cylinder. Further, at time t1 in FIG.
In the above description, the supply pressure to the main servo valve 3 is zero, but the pressure value at the time point t1 may not be zero as long as the hydraulic cylinder 5 does not hinder movement.

[0020]

As described above in detail, according to the present invention, by providing the on-off valve for opening and closing the oil passage between the hydraulic pump and the main servo valve, the discharge pressure of the hydraulic pump is reduced at the time of startup. If pressure oil is supplied to the main servo valve by the on-off valve after the pressure becomes equal to or higher than the controllable pressure, the hydraulic actuator can be driven in correlation with the command signal to the pilot servo valve. When the hydraulic pump is stopped, the hydraulic pump and the pilot servo valve are controlled so that the supply pressure to the pilot servo valve exceeds the controllable pressure until the hydraulic pressure supplied from the hydraulic pump to the main servo valve becomes equal to or less than a predetermined value. Since the pressure control means is provided between the control valve and the pump, when the pump is stopped, the supply pressure to the main servo valve is equal to or less than a predetermined value, for example, a pressure equal to or more than the controllable pressure is supplied to the pilot servo valve until the pressure becomes zero. The hydraulic actuator is driven in correlation with a command signal to the pilot servo valve.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a material testing machine according to the present invention.

FIG. 2 is a diagram illustrating a pressure drop in a hydraulic circuit in FIG. 1;

FIG. 3 is a hydraulic circuit diagram showing another embodiment of the material testing machine according to the present invention.

FIG. 4 is a hydraulic circuit diagram showing a conventional example.

FIG. 5 is a hydraulic circuit diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Relief valve 2 Hydraulic pump 3 Main servo valve 4 Pilot servo valve 5 Hydraulic cylinder 6 Motor 7 On-off valve 11 Check valve 12 Accumulator 21 Slow return valve

Claims (1)

[Claims] 1. A hydraulic pump, a pilot servo valve driven and controlled in accordance with a command signal when a pressure oil equal to or higher than a controllable pressure is supplied, and a main servo valve driven and controlled by the pilot servo valve. A hydraulic actuator that is driven by pressure oil from the hydraulic pump passing through the main servo valve to load a specimen, wherein a hydraulic path between the hydraulic pump and the main servo valve is provided. An on-off valve that opens and closes, when the hydraulic pump stops, the supply pressure to the pilot servo valve exceeds the controllable pressure until the hydraulic pressure supplied from the hydraulic pump to the main servo valve becomes equal to or less than a predetermined value. A material testing machine characterized in that pressure control means is provided between the hydraulic pump and the pilot servo valve as described above.