Shaft holding device

Abstract

To provide a shaft gripping device with improved accuracy in detecting gripping force. [Solution] A shaft gripping device that grips the cylindrical portion of a shaft 31 by pressurizing a sealed liquid, comprising a piston 8, a strain-sensitive resistor 12, and a locking / closing part 4, wherein the locking / closing part 4 grips or releases the shaft 31 by pressurizing / depressurizing the liquid inside the sealed liquid chamber, the piston 8 is inserted into the liquid chamber having a thin-walled portion that defines a part of the liquid chamber, the strain-sensitive resistor 12 is attached to the thin-walled portion and detects the deformation strain of the thin-walled portion caused by pressurization by the locking / closing part 4.

Description

Technical Field

[0001] The present invention relates to a shaft gripping device for gripping a shaft.

Background Art

[0002] Conventionally, a so-called hydrotype tool holder that grips a machining tool by providing a liquid chamber that pressurizes the cylindrical surface of the machining tool with a liquid such as oil through a thin sleeve has been used in machine tools.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a hydrotype tool holder, whether the shaft is held by the tool holder with a predetermined gripping force affects machining accuracy, so it is necessary to inspect at least periodically. Therefore, until now, the gripping force has been estimated and operated by measuring the amount of screwing or torsional torque of a screw that pushes a piston provided in the liquid path of the liquid pressure, and thus there is room for improvement in the detection accuracy of the gripping force because it includes the friction of the seal added to the piston and the friction of the lead of the screw.

[0005] In view of such problems, an object of the present invention is to provide a shaft gripping device with improved detection accuracy of the gripping force.

Means for Solving the Problems

[0006] A shaft gripping device according to an aspect of the present invention is a shaft gripping device that pressurizes a sealed liquid including a piston, a strain gauge resistor, and a lock opening / closing part to grip a cylindrical part of a shaft, in order to achieve the above object. ​The locking mechanism grips or releases the shaft by pressurizing / depressurizing the liquid inside the sealed liquid chamber. The piston has a thin-walled portion that defines a part of the liquid chamber and is inserted into the liquid chamber. A strain-sensitive resistor is attached to the thin-walled section and detects the deformation and strain of the thin-walled section caused by pressure applied by the locking mechanism. [Brief explanation of the drawing]

[0007] [Figure 1] This is a cross-sectional view of a shaft gripping device according to the first embodiment of the present invention. [Figure 2] This is a cross-sectional view of a shaft gripping device according to a second embodiment of the present invention. [Figure 3] This is a cross-sectional view of a shaft gripping device according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0008] The following is a detailed description of the shaft gripping device according to an embodiment of the present invention, based on the drawings. Figure 1 is a cross-sectional view of the shaft gripping device 1a and shaft (tool) 31 according to the first embodiment of the present invention.

[0009] The shaft gripping device 1a is a tool holder used to grip machining tools in machine tools such as machining centers. The shaft gripping device 1a grips the shaft (tool) 31 by pressurizing it using a liquid such as oil filled in liquid chambers 2e and 2f provided within the main body 2.

[0010] The main body 2 has a shaft gripping portion 2a and a shank portion 2b. A sleeve 3 is inserted from the negative x direction into the shaft gripping portion 2a on the side of the main body 2 that grips the shaft (tool) 31 (positive x side). The sleeve 3 has flanges 3b to 3d on its outer circumference and is fitted into the main body 2. The outer diameters of flanges 3b to 3d are designed to fit with a small gap between them and the inner diameter of the main body 2. A groove is provided in flange 3b, into which an O-ring 13 is fitted to maintain a liquid-tight seal in the liquid chamber 2f defined by the main body 2 and the sleeve 3. The main body 2 and the sleeve 3 may be fixed together at their positive x ends by adhesive or welding.

[0011] On the side of the main body 2 into which the sleeve 3 is fitted, in the minus x direction, there is an ATC holding portion 2c for moving the shaft gripping device 1a by the machining center's automatic tool changer (ATC). Further to the minus x side of the ATC holding portion 2c, there is a tapered shank portion 2b for mounting and fixing to the spindle of the machining center.

[0012] A machined hole 2d is provided at the end of the shank portion 2b. The machined hole 2d leads to the inner wall of the main body portion 2 into which the sleeve 3 is inserted. At the end of the shank portion 2b, there is a hole with a larger diameter than the machined hole 2d. A sphere 6 is placed in the stepped portion of this hole, and a sealing portion 5 is provided that pushes the sphere 6 in the +x direction to close the machined hole 2d. The radial outer circumference of the sealing portion 5 is threaded externally, and the inner wall of the hole in the main body portion 2 opposite to it is threaded internally. Therefore, by turning the bottomed hexagonal hole of the sealing portion 5 with a wrench or the like, its end can be brought into contact with the sphere 6, thereby closing the liquid chamber 2e.

[0013] A hole is provided radially between the ATC holding portion 2c and the tool gripping portion of the main body 2. A locking / closing screw 4a and a locking / closing piston 4b are inserted into this hole to form the locking / closing portion 4. A groove is provided on the cylindrical surface of the locking / closing piston 4b into which a sealing member 7 is fitted, and the sealing member 7 is attached thereto. The locking / closing screw 4a has a male thread, and the hole in the main body 2 has a female thread. Therefore, by turning the bottomed hexagonal socket of the locking / closing screw 4a with a wrench or the like, the locking / closing piston 4b can be moved radially, and the pressure of the liquid in the liquid chambers 2e and 2f can be adjusted.

[0014] On the other hand, a piston 8a, a sensor cover 11, and a connector 15 are provided opposite the lock opening / closing piston 4b.

[0015] The piston 8a has a cylindrical section with a relatively large diameter and a cylindrical section with a relatively small diameter. A groove is provided on the cylindrical surface of the relatively large diameter section into which a sealing member 7 is fitted. A bottomed hole is provided at the axial center of the cylindrical section of the piston 8a, and the relatively small diameter section is a thin-walled cylinder. This bottomed hole forms a liquid chamber 2e. A strain-sensitive resistor 12 is bonded to the outer circumferential surface of the relatively small diameter section. The strain-sensitive resistor 12 is at least one so-called strain gauge, forming a Wheatstone bridge circuit that outputs the detected strain amount as an analog voltage signal.

[0016] The sensor cover 11 is a hollow cylindrical shape, and for example, it has a flange portion and a male threaded portion with a smaller diameter than the flange. The sensor cover 11 restricts the piston 8a in the radial direction. The sensor cover 11 also seals the strain-sensitive resistor 12 of the piston 8a from the outside, protecting it from water droplets and the like. An O-ring 13 is fitted into a groove near the flange of the sensor cover 11 to keep the strain-sensitive resistor 12 tightly sealed. A hole is provided in the center of the sensor cover 11 for passing a wire 14 that connects the strain-sensitive resistor 12 and the connector 15. The wire 14 is fixed with adhesive, and the hole is also sealed with this adhesive. On the side of the sensor cover 11 opposite the flange, a recess is provided to cover the strain-sensitive resistor 12, and its end abuts against the piston 8a, restricting the radial position of the piston 8a.

[0017] Connector 15 is a relay section that relays wiring, and is, for example, a waterproof type with a round outer shape, which is a receptacle connected to a plug (not shown). Connector 15 is not limited to this, and may also be a type in which metal terminals are insert-molded into insulating resin, and the probe terminals are pressed against the metal terminals to extract electrical signals. Connector 15 is fixed in a recess facing the outside of the sensor cover 11.

[0018] The sensor cover 11 and connector 15 are designed to protect the strain-sensitive resistor 12 from environments in which liquids such as coolant used in the shaft gripping device 1a may be scattered.

[0019] In this configuration, the shaft gripping device 1a is assembled by inserting and fixing the sleeve 3 into the main body 2, attaching the piston 8a and sensor cover 11, installing the lock opening / closing piston 4b and lock opening / closing screw 4a in predetermined positions (positions for releasing the shaft), injecting a liquid such as oil, and inserting the sphere 6 and sealing part 5. The liquid such as oil is pressurized by the lock opening / closing screw 4a, causing it to flow from the liquid chamber 2e through the machined hole 2d into the liquid chamber 2f, thus filling the chamber.

[0020] When using the shaft gripping device 1a, loosen the lock opening / closing screw 4a to put the sleeve 3 in an open state, insert the shaft (tool) 31 into the inner diameter of the sleeve 3, and rotate the lock opening / closing screw 4a in the inward direction of the main body 2. Then, the oil in the liquid chambers 2f and 2e is pressurized, and the shaft 31 is gripped by the shaft gripping device 1a.

[0021] When the oil in the liquid chambers 2f and 2e is not pressurized by the lock opening / closing piston 4b, or when the shaft 31 is pressurized to such an extent that it can be inserted into the sleeve 3, the thin-walled portion of the piston 8 is in a state where it is not elastically deformed or is in a slightly elastically deformed state. On the other hand, when the oil in the liquid chambers 2f and 2e is pressurized by the lock opening / closing piston 4b and the shaft 31 is gripped inside the sleeve 3, the thin-walled portion of the piston 8a is in a relatively large elastically deformed state. Therefore, the strain gauge resistor 12 attached to the thin-walled portion of the piston 8a detects the change in resistance value due to the difference in the inertial deformation state. The diameter of the gripped portion of the shaft 31 has a slight error inherent to the shaft, and the gripping state of the shaft (tool) 31 can be detected by the strain signal output from this strain gauge resistor 12. When detecting this gripping state, it is performed by connecting to an external power source and an amplifier via the connector 15. Then, the minute analog signal of the strain output from the strain gauge resistor 12 is amplified by the amplifier. The amplified analog signal by the amplifier is digitized by an analog-to-digital converter, and based on this digital signal, it may be configured to be calculated by the central processing unit CPU (Central Processing Unit) through the input means and the result is displayed on the display.

[0022] FIG. 2 is a cross-sectional view of the shaft gripping device 1b and the shaft (tool) 31 according to the second embodiment of the present invention. The shaft gripping device 1b is a device used for, for example, a lathe. Since the shaft gripping device 1b has the same configuration as the sleeve 3 portion of the shaft gripping device 1a according to the first embodiment of the present invention, the description regarding the sleeve 3 is omitted.

[0023] In the shaft gripping device 1b, the sealing portion 5 and the sphere 6 are arranged radially along the shank portion 2b. The sealing portions 5 and 6 can close the liquid chamber 2e, similar to the first embodiment. The locking / closing piston 4b can open and close the grip on the shaft 31 by moving it forward and backward radially along the shank portion 2b using the locking / closing screw 4a. The sealing portion 5 and the locking / closing piston 4b may be facing each other in a straight line, but are not limited to this arrangement.

[0024] A machined hole 2d is provided in the axial direction, i.e., the x-axis direction, connecting liquid chamber 2e and liquid chamber 2f. The opening of the machined hole 2d has a hole wall with a relatively larger diameter than the tip, and a larger recess is provided.

[0025] A piston 8b is positioned in a hole with a relatively larger diameter than the tip. Similar to the piston 8a in the first embodiment, the piston 8b has a groove on its outer circumference to accommodate the seal member 7. The piston 8b also has a projection with a smaller diameter than the portion where the seal member 7 is positioned on its outer circumference. The bottom of the hole forming the liquid chamber 2e in this projection is thin-walled, and a strain-sensitive resistor 12 is attached opposite the bottom of the hole. Therefore, this thin-walled portion is elastically deformed by the pressure of the liquid chamber 2e, and the strain-sensitive resistor 12 attached to the thin-walled portion detects the strain caused by the elastic deformation.

[0026] The sensor cover 11 and connector 15 have the same configuration as the shaft gripping device 1a according to the first embodiment, so their description will be omitted. The shaft gripping device 1b according to the second embodiment has the function of amplifying the analog signal output from the strain-sensitive resistor 12, converting it to digital, and then transmitting it to the outside from the shaft gripping device 1b in a non-contact manner.

[0027] The strain-sensitive resistor 12 constitutes a Wheatstone bridge circuit, and the signal output from the Wheatstone bridge circuit is transmitted to the sensor board 23 via the wiring 14 and connector 15. The sensor board 23 is mounted in a recess of the main body 2 via a board holder 21 and has an amplification circuit, an analog-to-digital conversion circuit, an arithmetic circuit, a memory circuit, a modulation circuit, a transmission circuit, a rectifier circuit, and a charging circuit. The sensor board 23 is a printed circuit board and electronic components mounted on this printed circuit board.

[0028] The amplification circuit amplifies the analog signal output from the Wheatstone bridge. The analog-to-digital conversion circuit converts the amplified analog signal into a digital signal. The arithmetic circuit uses the digital signal and information stored in the memory circuit to calculate the pressure value of the liquid chamber. The modulation circuit modulates the liquid chamber pressure value calculated by the arithmetic circuit into an optical signal. The transmission circuit 22 then transmits the optical signal modulated by the modulation circuit using a light-emitting element or the like. The optical signal is, for example, infrared light, but it is not limited to an optical signal; it could also be an electrical signal transmitted by radio waves. Since the main body 2 is made of metal, the window 27 is made of resin, allowing light or radio waves to pass through easily.

[0029] A battery 26 is mounted on the sensor board 23. The battery 26 is, for example, a rechargeable battery and can be charged by the charging circuit of the sensor board 23. Furthermore, a coil 25 is arranged on the sensor board 23 in an axial direction, and together with an external coil (not shown), it can form a transformer. Therefore, by passing current through the external coil, current is generated in the coil 25, and power can be transmitted to the sensor board 23 without contact. The sensor board 23 rectifies the power transmitted from the coil 25 and charges the battery 26 by the charging circuit. A cover 24 is attached to the main body 2 to protect the coil 25 and the sensor board 23 from the external environment. The cover 24 is not limited to this, and may be fixed to the main body 2 with screws with a sealing member in between.

[0030] In this configuration, the transmission circuit 22 of the sensor board 23 can continuously or intermittently transmit information about the pressure value of the liquid chamber to the outside. Therefore, even when the shaft gripping device 1b is placed on a machining tool, it is possible to know whether the shaft (tool) 31 is securely gripped by the shaft gripping device 1b. If there are multiple shaft gripping devices 1b, each sensor board 23 can transmit the information about the pressure value of the liquid chamber along with the identification information of the shaft gripping device 1b, thereby allowing the pressure value of the liquid chamber of each shaft gripping device 1b to be determined. Furthermore, the battery 26 can be charged when the shaft gripping device 1b is in storage or in the standby position of the machine tool, and the state of the liquid chamber of the shaft gripping device 1b can be determined without stopping the machine tool.

[0031] Figure 3 is a cross-sectional view of the shaft gripping device 1c and shaft 32 according to a third embodiment of the present invention.

[0032] The shaft gripping device 1c is a bushing that supports the shaft. The main body 9 of the shaft gripping device 1c is a hollow cylindrical shape consisting of approximately two diameters, one large and one small. The sleeve 3 has flanges 3b to 3d on its outer circumference and is fitted into the main body 9. The outer diameters of flanges 3b to 3d are designed to fit with a small gap between them and the inner diameter of the main body 9. A groove is provided in flange 3b, into which an O-ring 13 is fitted to maintain liquid tightness between the liquid chambers 2e and 2f defined by the main body 9 and the sleeve 3. The main body 2 and the sleeve 3 may be fixed at both ends in the x direction by adhesive or welding. The smaller diameter cylindrical part of the main body 9 contains a sealing part 5 and a sphere 6. The larger diameter cylindrical part of the main body 9 contains a locking / unlocking piston 4b and a locking / unlocking screw 4a. The larger diameter cylindrical part of the main body 9 contains a piston 8a, a sensor cover 11, and a connector 15. The roles of the sealing part 5, the lock opening / closing part screw 4a, the lock opening / closing part piston 4b, the piston 8a, and the sensor cover 11 are the same as those of the shaft gripping device 1a in the first embodiment.

[0033] In this configuration, the shaft 32 can be inserted by loosening the locking screw 4a, and then the shaft 32 can be fixed to the shaft gripping device 1c by tightening the locking screw 4a. The gripping state of the shaft 32 can be detected by strain detection by the strain-sensitive resistor 12, which outputs a voltage signal from the wiring 14 to the connector 15.

[0034] In each embodiment, the arrangement of the sealing part, piston, lock opening / closing piston, etc., can be appropriately changed according to the intended use of each shaft gripping device.

[0035] According to the present invention, since a configuration for detecting strain is provided in the thin-walled portion of the piston inserted into the liquid chamber, the liquid pressure can be measured directly, making it possible to provide a shaft gripping device with improved accuracy in detecting gripping force.

[0036] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Industrial applicability]

[0037] Examples of applications of this invention include its use in hydraulic chucks and bushings. [Explanation of symbols]

[0038] 1a~1c: Axis gripping device 2: Main body 2a: Shaft grip part 2b: Shank section 2c:ATC held part 2d: Machining hole 2e:Liquid chamber 2f:Liquid chamber 3: Sleeves 3b~3d: Flange 4: Lock opening / closing mechanism 4a: Screw for opening and closing the lock 4b: Lock opening / closing piston 5: Sealing section 6: Sphere 7: Sealing material 8a, 8b: Piston 9: Main body 11: Sensor cover 12: Strain-sensitive resistor 13: O-ring 14: Wiring 15: Connector (intermediate section) 21: PCB holder 22: Transmitter Circuit 23: Sensor board 24: Lid 25: Coil 26:Battery 27: Window 31: Axis (tool) 32: Axis

Claims

1. A shaft gripping device that grips the cylindrical portion of a shaft by pressurizing a sealed liquid, which includes a piston, a strain-sensitive resistor, and a locking / closing mechanism, The locking mechanism grips or releases the shaft by pressurizing / depressurizing the liquid inside the sealed liquid chamber. The piston has a thin-walled portion that defines a part of the liquid chamber and is inserted into the liquid chamber. The strain-sensitive resistor is attached to the thin-walled portion and is used in a shaft gripping device that detects the deformation of the thin-walled portion caused by pressure applied by the locking / closing portion.

2. The shaft gripping device according to claim 1, wherein the wiring from the strain-sensitive resistor is connected to the outside via a relay section.

3. Furthermore, it is equipped with a printed circuit board, The shaft gripping device according to claim 1, wherein the printed circuit board is equipped with a circuit that is electrically connected to the strain-sensitive resistor, amplifies the analog signal of strain, converts it into a digital signal, and transmits information about the gripping state of the shaft to the outside.

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