JPH0442765Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a material testing machine using a hydraulic actuator as a load device, and particularly relates to one in which the actuator is driven by a flow rate control type servo valve.

[Prior Art] In a material testing machine equipped with a hydraulic actuator as a load device, the actuator is driven by a flow rate control type servo valve, a pressure control type servo valve, a pressure/flow rate control type servo valve, or the like. Another approach is to use a servo valve in a closed loop.

[Problems to be solved by the invention] When using a flow rate control type servo valve that controls the flow rate according to the opening degree of the valve in an open loop,
As shown in FIG. 2A, a control signal is output at a ratio of 1:1 to the operating amount of the operating knob, and a flow rate proportional to the operating angle of the operating section is provided. Therefore, there was a problem in that adjustment near the zero point (hold position) was difficult and it was generally very difficult to control the pressure inside the load cylinder. Furthermore, when using a pressure-controlled servo valve, there is a problem in that the flow rate is insufficient when moving the ram stroke.
Pressure/flow control type servo valves are convenient in that they can control both, but they have the problem of being very expensive.

When using a servo valve in a closed loop, it is difficult to control the load value when a stroke signal is used as a feedback signal. When using a stroke signal as a feedback signal until a load is applied, and then switching to a load signal when a load is applied,
There was a problem that the test piece became uncontrollable when it reached the plastic region.

Therefore, this invention was devised in consideration of the problems with various servo valves as mentioned above, and it is possible to easily control pressure even when using commonly used flow rate control type servo valves. The purpose is to provide a material testing machine.

[Means for Solving the Problems] In order to solve the above problems, the present invention employs the following configuration.

In other words, the material testing machine according to the present invention uses a hydraulic actuator as a load device, and drives the actuator with a flow rate control type servo valve that is controlled by a valve opening signal output according to the amount of operation of the operation section. In this material testing machine, the shape of the sleeve port hole of the servo valve is such that the opening area at the end is small and the opening area at the center is larger than this, and the zero point of the operating section is It is characterized by the provision of signal conversion means that reduces changes in the output valve opening degree signal in response to changes in the manipulated variable in the vicinity.

[Function] By making the shape of the sleeve port hole of the servo valve so that the opening area on the end side is smaller than the center, the characteristics of the output flow rate with respect to the input current of the servo valve can be changed within a range where the input current is small. The characteristic can be such that the amount is small. Furthermore, due to the signal conversion means, the change in the output valve opening signal in response to a change in the manipulated variable is smaller near the zero point of the operating section than in other parts, making it easy to finely adjust the output near the zero point. . Pressure control can be performed with high precision by making it easy to change these output flow characteristics and finely adjust the operating section.

[Example] FIG. 1 is a block diagram showing the configuration of a material testing machine that is an example of the present invention. The test piece 1 is held by chucks (not shown) on tables 2 and 3. The lower table 3 is the ram 6 of the actuator 5.
It moves up and down in conjunction with the movement of the ram 6. The actuator 5 is driven by using pressure oil sent from a hydraulic pump 9 through a flow rate control type servo valve 8.
This is done by controlling the The displacement of the test piece 1 is detected as the displacement of the ram 6 of the actuator 5 by the ram stroke detector 10, and the stroke detection signal is input to the input/output device 14 mainly composed of the CPU to obtain the stroke value. . In addition, the load on the test piece 1 is measured by the load detector 1.
2, the load detection signal is amplified by the load amplifier 13, inputted to the input/output device 14, and the load value is determined by the arithmetic processing of the CPU.
The calculation results are displayed on the display device 22.

On the other hand, a voltage signal that is output in proportion to the operating angle of the valve opening setting knob 16 is input to the input/output device 14 . The input/output device 14 includes an A/D converter 17 that A/D converts this input voltage, and a setting knob 16 that converts the digital setting signal output from the A/D converter 17 as shown in FIG. a conversion circuit 18 that converts and outputs the change so that the amount of change is smaller near the zero point than other parts; and a D/A that converts the output signal converted by the conversion circuit 18 into an analog signal.
A converter 19 is provided. The output signal output from the conversion circuit 18 is supplied to the servo amplifier 20 as an analog signal via the D/A converter 19.
Open and close the servo valve 8.

The conversion circuit 18 is constituted by ROM, RAM, etc., and the conversion operation is performed by software through the processing of the CPU of the input/output device 14. As mentioned above, the conversion circuit 18 converts the linear output signal from the setting knob 16 shown in FIG.
As shown in Figure B, the servo valve 8 is converted into a nonlinear
The oil flow rate regulated by will also change according to the characteristic curve shown in the figure.

In addition, the shape of the port hole 33 of the sleeve 30 of the flow rate control type servo valve 8 shown in FIG. It is formed into a trapezoid shape. With such a shape of the port hole, the conventional linear characteristic of the output flow rate shown in FIG. In the figure, 40 is a spool, 41 is a coil bobbin, 42 is a nozzle, 43 is a field back spring, 44 is an armature, 45
is a yoke.

The material testing machine according to the present invention is converted to facilitate fine adjustment of the output near the zero point of the valve opening knob 16 as described above, and
The shape of the sleeve port hole of the servo valve has been changed to reduce the output flow rate near zero of the control input signal, so both of these effects make pressure control possible even when using a flow control type servo valve. can be done.

In the above configuration, when a change in pressure in the cylinder, a change in oil temperature, etc. occurs, the amount of leakage from the servo valve changes. In this case, the control signal is converted in advance by a conversion circuit, and it becomes impossible to handle the situation when the load has to be held at a position beyond the operating angle of the knob that enables pressure control. Therefore, by adding the valve leakage amount to the correction amount in advance in the conversion circuit 18 as shown in FIG. 3, the load can be held within the operating angle range where pressure control can be performed. The leakage correction amount may be calculated by setting the correction amount at the maximum load as the maximum value and being proportional to the load value.

As mentioned above, the material testing machine of the present invention is configured using a flow rate control type servo valve that controls the flow rate by the opening degree of the valve under open loop control, but it is not limited to controlling the displacement of the ram stroke. Pressure control can also be performed. In addition, when using the conventional closed-loop system, a manually operated valve was used in combination with the open-loop valve opening system, but with this example machine, a single servo valve is used. Therefore, both the valve opening method and the closed loop method (load control, stroke control, strain control) can be adopted.

[Effects of the invention] As is clear from the above explanation, the material testing machine according to the invention has the following advantages:
In addition to displacement control, it is now possible to perform pressure control as well.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention, and Fig. 2 (a) and (b) show output characteristics in which a signal output linearly according to the operating angle of the valve opening setting knob is converted into a nonlinear signal near zero. FIG. 3 is a diagram showing the output characteristics of the converted signal in the modified embodiment, and FIG.
The figure shows the structure of the servo valve, Figure 5 is a diagram explaining that the sleeve port hole is changed, and Figure 6 A and B show the output flow characteristics before and after changing the sleeve port hole of the servo valve. FIG. 5... Actuator, 6... Ram, 8... Flow control type servo valve, 9... Hydraulic pump, 14...
Input/output device, 16...Valve opening setting knob, 1
7... A/D converter, 18... Conversion circuit, 19...
...D/A converter.

Claims (1)

[Scope of utility model registration request] A material testing machine in which a hydraulic actuator is used as a load device, and the actuator is driven by a flow rate control type servo valve controlled by a valve opening signal output in accordance with the operation amount of the operation part, The shape of the sleeve port hole of the servo valve is such that the opening area at the end is small and the opening area at the center is larger than this, and the output valve is designed to respond to changes in the manipulated variable near the zero point of the operating section. A material testing machine characterized by being provided with a signal conversion means for reducing changes in an opening signal.