JPH04244940A - Grasping apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gripping device used in a tensile tester, a compression tester, or the like.

0002

[Prior Art] For example, a ram cylinder device for loading a test specimen, a pair of columns erected on the sides of the ram cylinder device, and a device that is held movably up and down by a rotating nut on the pair of columns. BACKGROUND ART Material testing machines have been known that include a lower crosshead, a table that is raised and lowered by a ram cylinder device, and an upper crosshead that is held by a support that stands above the table. This material testing machine grips both ends of the specimen between the upper and lower crossheads,
A tensile test is performed with the table raised.

FIG. 3 shows a schematic configuration of a gripping device built into the crosshead of this material testing machine. This gripping device consists of a hydraulic gripper 10 built into the crosshead and a gripper hydraulic circuit 20. Gripping tool 1
0 has a pair of grip teeth 11 and a hydraulic cylinder 12 that opens and closes the left and right grip teeth 11, respectively. In this type of material testing machine, for example, a tensile testing machine with a capacity of 100 tf generally requires about 1.5 times as much gripping force. Therefore, the hydraulic circuit 20 includes a hydraulic pump 21, a pressure reducing valve 22 that reduces the discharge pressure of the hydraulic pump 21 at an arbitrary pressure reduction ratio, and a pressure intensifier 23 that increases the output pressure of the pressure reducing valve 22. , the hydraulic cylinder 12 is made smaller. The pressure intensifier 23 has a large diameter piston and a small diameter piston, and increases the pressure of the pressure oil from the pressure reducing valve 22 according to the area ratio of the pistons, and applies the pressure to the hydraulic cylinder 12. The greater the applied load, the greater the pressure reduction ratio, and therefore, the greater the applied load applied to the test piece, the greater the gripping force. 24 is a direction switching valve that switches the direction of pressure oil flowing to the hydraulic cylinder 12 and opens and closes the gripping teeth 11; 25 is a pilot operated check valve provided in a circuit communicating with a chamber on the gripping pressure holding side of the hydraulic cylinder 12; 26 is a relief valve that sets the circuit maximum pressure, and 27 is an electric motor that drives the hydraulic pump 21.

0004

[Problems to be Solved by the Invention] However, in such a conventional device, it is necessary to change the pressure reduction ratio of the pressure reducing valve 22 according to the applied load, and the operation is complicated. It is difficult to predict the applied load, and there is a possibility that the optimum pressure reduction ratio, that is, the gripping force cannot be obtained.

[0005] An object of the present invention is to provide a gripping device whose gripping force is automatically changed according to the applied load.

[0006]

[Means for Solving the Problems] The present invention will be explained in conjunction with FIG. 1 which is an embodiment.
33 and a gripping force control means 23 that controls the test piece gripping force in proportion to this load signal, the above-mentioned object is achieved.

[0007]

[Operation] The gripping force control means 23 is controlled by a load signal corresponding to the applied load, and the gripping force is controlled according to the applied load. Therefore, for example, as the tensile load increases, the gripping force also increases, and slippage is prevented.

[0008] In the sections of the means for solving the above-mentioned problems and the section of operation that explain the structure of the present invention, figures of embodiments are used to make the present invention easier to understand. It is not limited to the examples.

[0009]

[Embodiment] An embodiment of the present invention will be described based on FIG. Note that the same reference numerals are given to the same parts as in FIG. 3 to simplify the explanation. The material testing machine shown in Fig. 1 is a so-called universal testing machine, and includes a bed 1 and a ram cylinder device 2 that is installed on the bed 1 and loads a test piece.
A pair of screw supports 3 are erected on the bed 1 on the sides of the ram cylinder device 2, a lower crosshead 4 is held on the supports 3 so as to be movable up and down via a rotating nut, and the ram cylinder device 2 Table 5 that goes up and down and this table 5
It includes a pair of pillars 6 erected above and an upper crosshead 7 horizontally suspended over the pillars 6. The lower crosshead 4 and the upper crosshead 7 are provided with grippers 1 similar to those shown in FIG.
0 is built-in, and is driven to open and close by the gripper hydraulic circuit 20A.

Reference numeral 30 denotes a hydraulic circuit for the ram cylinder device 2, which includes a hydraulic pump 32 driven by a motor 31 and a manually operated load control valve 33. The load control valve 33 keeps the differential pressure between its inlet pressure and outlet pressure constant (for example, 10 kg/cm2) regardless of the load pressure on the outlet side.
Therefore, if the load by the ram cylinder device 2 is small, the pump discharge pressure will be low, and if the load is large, the pump discharge pressure will be correspondingly high. This pump discharge oil is guided to the input port of the pressure booster 23 by a circuit 28. Here, the pressure increase ratio of the pressure intensifier 23 is set to 3, and the pump discharge pressure is increased from 15 to
If it is 240Kg/cm2, the output pressure of the pressure intensifier 23 will be 45 to 720Kg/cm2, so the hydraulic cylinder 1
2 can be made small enough to be built into the crosshead.

[0011] A test procedure using such a material testing machine will be explained. A test piece TP is inserted between the grip teeth of each gripper 10 built into the upper and lower crossheads 4 and 7, and the directional control valve 2
4 to the position shown. As a result, hydraulic cylinder 1
2 is applied with pressure oil at a pressure set by a relief valve 26, and the test piece is gripped with a gripping force corresponding to the pressure. The load control valve 33 is manually operated while looking at a load indicator (not shown), and the applied load is increased at a desired speed. As the load acting on the test piece increases, the pump discharge pressure increases, and the pressure applied to the pressure intensifier 23 increases. As a result, the output pressure of the pressure intensifier 23 also increases, and the gripping force increases with the applied load.

[0012] Therefore, there is no need for an operation to set the gripping force according to the applied load, which improves work efficiency, and even when the applied load cannot be predicted in advance, the gripping force can be automatically adjusted according to the applied load. Since the output is output, there is no slippage of the test piece, and accurate test results can be obtained.

FIG. 2 is a diagram showing another embodiment. In this embodiment, the pressure reduction ratio of the electromagnetic proportional pressure reducing valve 41 is controlled according to the pump discharge pressure which is proportional to the applied load, thereby controlling the pressure applied to the pressure intensifier 23 and increasing the supply pressure to the hydraulic cylinder 12. It is something to control. Therefore, the pump discharge pressure is measured by the pressure sensor 42, the output of this sensor 42 is input to the controller 43, and the controller 43 changes the pressure reduction ratio of the electromagnetic proportional pressure reducing valve 41 in proportion to the pump discharge pressure. Therefore, the same effects as the embodiment shown in FIG. 1 can be obtained. In this case, the load control valve 3 of the constant differential pressure control method
3 may be replaced with a normal flow rate control valve, that is, a valve whose opening area is controlled in proportion to the stroke amount regardless of the pressure difference between the front and rear sides.

Although the gripping device built into the universal material testing machine has been described above, the present invention can also be applied to a gripping device installed separately from the material testing machine. Further, although the hydraulic type has been described, the present invention can also be applied to a gripping device that opens and closes the gripping teeth using an electric motor. Furthermore, although the applied load on the test piece was detected by the hydraulic pressure of the ram cylinder, if the test piece loading mechanism is not hydraulic, a signal from a detector such as a load cell that detects the applied load acting on the test piece may be used. The electromagnetic proportional pressure reducing valve may be controlled by

In the above embodiment, the hydraulic pump 32, the load control valve 33, the pressure sensor 42 and the electromagnetic proportional pressure reducing valve 41
respectively constitute a load signal generation means, and the pressure intensifier 23 constitutes a gripping force control means.

[0016]

[Effects of the Invention] According to the present invention, the specimen gripping force is controlled in accordance with the applied load, so that the gripping force in accordance with the applied load is automatically output without any particular operation by the operator. This not only improves work efficiency, but also allows for highly accurate testing without slippage, even on test specimens made of materials whose applied loads are difficult to predict.

[Brief explanation of the drawing]

[Fig. 1] Overall configuration diagram showing one embodiment of a material testing machine incorporating a gripping device according to the present invention.

[Figure 2] Overall configuration diagram showing another embodiment

[Figure 3] Diagram showing the schematic configuration of a conventional hydraulic gripping device

[Explanation of symbols]

1 Bed 2 Ram cylinder device 3. Support 4 Lower cross head 7 Upper cross head 10 Hydraulic gripping tool 11 Grasping teeth 12 Hydraulic cylinder 20 Hydraulic circuit for gripping tool 21 Hydraulic pump 22 Pressure reducing valve 23 Pressure booster 30 Hydraulic circuit for ram cylinder device 32 Hydraulic pump 33 Load control valve 40 Solenoid proportional pressure reducing valve

Claims (1)

[Claims] Claim 1: A method comprising: signal generation means for generating a load signal corresponding to the applied load on the test piece; and gripping force control means for controlling the test piece gripping force in proportion to this load signal. gripping device.