Patent Application
20090044696
The present invention is related to a fluid pressure type actuator driven by supply/discharge of fluid such as air.
Recently, the use of an elastic expansion body disclosed in documents such as Patent Document 1˜Patent Document 3 (hereinafter referred to as a fluid pressure type actuator) as a drive source of the equipment has been suggested.
In the conventional fluid pressure type actuator, for example, a pneumatic actuator, the outer periphery of a rubber tube is wrapped by a non-elastic net-like wrapping body, and the diameter of the wrapping body gets increased by expansion of the tube due to supply of air. The increment of the diameter of the wrapping body leads to reduction of its length, and driving force is generated by the reduction of length.
Patent Document 1: JP-A-H7-24771
Patent Document 2: JP-A-2002-103270
Patent Document 3: WO2004/085856
The pneumatic actuator disclosed in the above-mentioned Documents has a problem that when expansion and contraction are repeated many times, the mesh of the wrapping body starts falling apart along with the increase of the number of repetitions. For example, the present inventor found out that when air is supplied to a pneumatic actuator to obtain driving force, the vicinity of opposite ends of the pneumatic actuator in longitudinal direction expand in spherical form, and the size of the mesh of the wrapping body expands larger than the intermediate portion of the actuator in longitudinal direction. In this way, when the mesh of the wrapping body is enlarged, a part of the rubber tube expanded due to supply of air protrudes from the mesh, which leads to a damage of the tube being pinched in the gaps between the mesh. For example, according to the experiment performed by the present inventor, it has been proved that a certain type of pneumatic actuator, when expansion/contraction is repeated at a frequency of 4 times/minute, gets damaged after a few tens thousands of times of repetition. When the tube is damaged, it causes leakage of the air supplied to the tube, whereby impairing the function of the pneumatic actuator.
The objective of the present invention is to solve the above-mentioned problem by improving the durability of the pneumatic actuator.
The fluid pressure type actuator of the present invention is characterized in comprising:
an expansible/contractible body which is sealed by plug members on opposite ends, and expands/contracts by supply/discharge of fluid;
a wrapping body which wraps the outer periphery of the expansible/contractible body, and having its opposite ends fastened and fixed to the plug members;
an inlet/outlet of fluid formed in the plug members; and
an auxiliary member for preventing or suppressing local deformation in which the wrapping body expands outwards when the fluid is supplied to the expansible/contractible body.
In accordance with the present invention, the number of repeated expansions/contractions until the local deformation takes place at the end portions of the wrapping body (durability) is substantially increased by comprising the auxiliary member.
Hereinafter, an embodiment of the present invention will be described referring to the diagrams.
a rubber tube (hereinafter referred to as an inner tube) 1 which expands by air supply;
rubber plugs 2 and 3 for sealing opposite ends of the inner tube 1;
an air supply/discharge tube 4 which is formed to pass through the rubber plug 2 and to reach the internal space of the inner tube 1;
a first net-like wrapping body (hereinafter referred to as a first mesh sleeve) 5 which wraps the outer periphery of the inner tube 1;
a second net-like wrapping body (hereinafter referred to as a second mesh sleeve) 6 which wraps the outer periphery of the first mesh sleeve 5; and
a stopper (not shown) which fastens and fixes the mesh sleeves 5 and 6 to the rubber plugs 2 and 3. To the air supply/discharge tube 4, an air supply/discharge device not shown in the diagram, for example, an air compressor is connected, and the pneumatic actuator is driven by the air supplied from the air compressor into the inner tube 1 via the air supply/discharge device, or by discharge of the air from the inner tube 1.
The outer periphery of the inner tube 1 is covered by the first net-like mesh sleeve 5, and the outer periphery of the first net-like mesh sleeve 5 which covers the outer periphery of the inner tube 1 is covered by the second mesh sleeve 6. These mesh sleeves 5 and 6 can have the same material and thickness of the wire rod (filament), number of wires for forming the mesh, and the diameter of the mesh. In other words, the mesh sleeves 5 and 6 form a twofold structure. The mesh sleeves 5 and 6 are braided by a resin having extremely small dilation with respect to a load, for example, a wire rod (filament) of a high tension fiber such as a nylon fiber or polyester, and the mesh is braided so as to cross from two directions having a predetermined angles in the longitudinal direction of the mesh sleeve. As for such a material for the mesh sleeve, CLEAN CUT PET (CLEAN CUT is a trademark of TECHFLEX Inc. registered in the Patent and Trademark Office in the United States) manufactured by TECHFLEX Inc. (located in New Jersey, U.S.A.) can be cited.
The inner tube 1 which is covered by the mesh sleeves 5 and 6 is plugged by the rubber plugs 2 and 3 and fixed at opposite ends of the inner tube in longitudinal direction as shown in the diagram. According to the method of fixation, the rubber plugs 2 and 3 are inserted into the inner tube 1 at both ends. Next, the inner tube being attached with the rubber plugs 2 and 3 are inserted into the mesh sleeve 5 cut in the length that is a little longer than the inner tube 1. Further, the outer periphery of the mesh sleeve 5 is covered with the mesh sleeve 6. The length of the mesh sleeve 6 is to be approximately the same as the inner tube 1. After that, the end portion of the mesh sleeve 5 is folded back in the direction toward the center and inserted into the mesh sleeve 6, and the inner tube 1 and the mesh sleeves 5 and 6 are fastened to the rubber plugs 2 and 3 by the stoppers. The end portions of the mesh sleeve 5 being folded back and fastened to the rubber plugs 2 and 3 are formed into the shape that can be connected to a hook attached to the load. In order to insert the air supply/discharge tube 4 into the rubber plug 2 covered with the mesh sleeve 5, a part of the mesh sleeve 5 is stretched out.
Endurance test for both the pneumatic actuator of the present invention configured as above and the conventional pneumatic actuator was carried out in the manner as shown in
the rated diameter of the material of the mesh sleeves 5 and 6 is 1.5 inches;
the external diameter of the mesh sleeve when unloaded is about 30 mm;
the external diameter of the mesh sleeve when loaded to the maximum is about 50 mm; and
the length of the pneumatic actuator when unloaded is 400 mm. A 30 kg of plummet is suspended from the actuator. Then as an endurance test, a method was employed to repeat the condition of
The pneumatic actuator comprising the conventional onefold mesh sleeve 5, when the test proceeds over several thousand times, the portions in the vicinity of opposite ends of the mesh sleeve 5 configuring the actuator starts to deform into a spherical form having the diameter larger than the one of the central portion (refer to
On the contrary, the pneumatic actuator comprising the double structured mesh sleeves 5 and 6 to which the present invention is applied does not cause the deformation in the vicinity of opposite ends of the mesh sleeve 5 which configures the actuator even as the endurance test proceeds. In the pneumatic actuator of the present invention, the mesh sleeve 5 expands/contracts while maintaining the uniform diameter over approximately the entire length even when the endurance test proceeds with repetition of supply and discharge of air. Therefore, even in the vicinity of opposite ends of the mesh sleeve 5, as is in the central portion, broadening of the gaps among the mesh does not take place since the length of the tube shrinks for the portion of the enlarged diameter. Consequently, damage from the friction due to the inner tube 1 being pinched in the gap of the mesh sleeve 5 can be prevented. In addition, the pneumatic actuator comprising the double structured mesh sleeve lapses into inoperable condition after repeating the operation over several hundreds of thousands of times, due to fatigue subsidiary fracture in the rubber of the inner tube 1.
As shown in the result of the endurance test in chart 1, in the pneumatic actuator of the present invention, the number of times of repeating operation from the start of the test to the breakage is improved by the degree of 5.5˜9 times compared to the pneumatic actuator covering the inner tube with only the conventional onefold mesh sleeve 5. Among the samples having the double structured mesh sleeves 5 and 6, there was one having about 10 times longer life span than the single structured actuator though not shown in chart 1. From the result of this endurance test, superiority of the pneumatic actuator to which the present invention is applied has been confirmed.
Next, the second embodiment of the present invention will be described referring to
Next, the third embodiment of the present invention will be described referring to
While the present invention has been described above based on the embodiments, various changes may be made without departing from the scope of the invention. The present invention can be summarized that it is characterized in comprising means for preventing or suppressing the local deformation in the vicinity of opposite ends of the first mesh sleeve 5. While the wrapping body (mesh sleeve) is configured having double structure as means to prevent or suppress the local deformation in opposite ends of the first mesh sleeve 5 in embodiments 1˜3, the wrapping body may have three or more layered structure. Also, the same effect as the first embodiment can be attained, when the fluid is supplied to the expansible/contractible body or in the process of supplying fluid, by covering the portions in the vicinity of opposite ends of the mesh sleeve with the member having the same rate-of-change of the diameter as the rate-of-change of the diameter in the center portion of the mesh sleeve 5 in order to prevent the local deformation in the vicinity of opposite ends of the mesh sleeve 5.
Also, while the pneumatic actuator that uses air as fluid is described in the above embodiments, the fluid to be supplied to the expansible/contractible body does not have to be limited to air, and a variety of fluids such as water, oil and gas can be used according to the purpose of usage.
The pneumatic actuator related to the present invention can be used as a driving actuator for a rehabilitative equipment (for example, CPM (Continuous Passive Motion) device) or care-giving equipment. Also, it can be used as a driving actuator for wearable robot suits, which is an artificial muscle. Further, it can be applied to industrial robots or construction equipment. Through the improvement of the durability of the fluid pressure type actuator by the present invention having such wide range of application, further expansion of its application can be expected
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-333947 | Nov 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/322075 | 11/6/2006 | WO | 00 | 5/16/2008 |
