Gripping force measuring method and measuring jig

Abstract

To provide a gripping force measuring method capable of measuring a gripping force to a workpiece in a machine tool having an inner diameter gripping type chuck device, and a measuring tool used for the gripping force measuring method.SOLUTION: A gripping force measuring method is used for a machine tool including a chuck device that grips a workpiece by expanding a tubular collet outward in a radial direction in a hollow portion of the workpiece. The method includes a positioning step of inserting and positioning a collet into a hollow portion of a cylindrical measuring jig, a deformation step of elastically deforming a gripping force receiving portion of the measuring jig by expanding the collet outward in a radial direction and applying a gripping force from the collet to the gripping force receiving portion, and a conversion step of measuring a deformation amount of the gripping force receiving portion in the radial direction and converting the measured deformation amount into a gripping force of the chuck device.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a machine tool equipped with a chuck device that grips a workpiece by inserting a collet into a hollow portion of the workpiece. [Background technology]

[0002] In machine tools, a workpiece is gripped by a chuck device provided on a workpiece spindle device, and the workpiece is rotated together with the chuck device, and the workpiece is machined with a tool. Patent Document 1 describes a machine tool having a so-called inner diameter gripping type chuck device, in which a cylindrical collet is inserted into a hollow portion of the workpiece and the collet is deformed in the radial direction to grip the workpiece from the inside. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-70010 Summary of the Invention [Problem to be solved by the invention]

[0004] In an internal-diameter gripping chuck device, if the gripping force applied to a workpiece is weaker than desired, the position of the workpiece relative to the workpiece spindle device may shift during machining, resulting in a risk of reduced machining accuracy. However, with an internal-diameter gripping chuck device, although it is possible to visually confirm that the workpiece is being gripped, there is no way to measure and evaluate the value of the gripping force applied to the workpiece.

[0005] In order to solve the above problems, the present invention aims to provide a gripping force measurement method capable of measuring the gripping force applied to a workpiece in a machine tool having an internal diameter gripping type chuck device, and a measuring jig used in the gripping force measurement method. [Means for solving the problem]

[0006] In order to solve the above problems, the gripping force measurement method of the present invention is used in a machine tool equipped with a chuck device that grips a workpiece by expanding a cylindrical collet radially outward within the hollow portion of the workpiece, and includes a positioning step of inserting and positioning the collet into the hollow portion of a cylindrical measuring jig, a deformation step of elastically deforming the gripping force receiving portion of the measuring jig by expanding the collet radially outward and applying a gripping force from the collet to the gripping force receiving portion, and a conversion step of measuring the amount of radial deformation of the gripping force receiving portion and converting the measured amount of deformation into the gripping force of the chuck device. [Effects of the Invention]

[0007] According to the above configuration, a gripping force is applied to the gripping force receiving portion of the measuring jig by the collet inserted into the hollow portion of the measuring jig, causing the gripping force receiving portion to elastically deform. The amount of deformation of the gripping force receiving portion in the radial direction is measured, and the gripping force of the chuck device is calculated from the measured amount of deformation, thereby making it possible to measure the gripping force. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a machine tool. [Figure 2] FIG. [Figure 3] FIG. 2 is a cross-sectional view of the chuck device. [Figure 4] FIG. 10 is a diagram illustrating a measuring jig. [Figure 5] 10 is a flowchart illustrating the procedure of a gripping force measurement method. [Figure 6] 10A and 10B are diagrams illustrating the relationship between deformation of the measurement jig and the gripping force. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of a machine tool according to the present invention will be described below with reference to the drawings. Figure 1 is a diagram illustrating the interior of a machine tool 1. In the machine tool 1, a workpiece spindle device 11 and a turret device 12, which are machining devices, are covered by a machine body cover (not shown), and a machining chamber in which a workpiece is machined is configured inside.

[0010] The turret unit 12 has a tool rest 13 to which a plurality of tools are attached, and a carriage 14. Tools are attached to the tool mounting surface of the tool rest 13 via tool holders such as cutting holders and rotary tools. The turret unit 12 is designed to select a specific tool attached to the tool rest 13 by swivel indexing according to the machining content. The carriage 14 of the turret unit 12 is attached to a slide device that can change the position of the tool rest 13 relative to the bed 16. The turret unit 12 is configured so that during machining, the swivel-indexed tool can be moved and the workpiece gripped by the work spindle unit 11 can be machined with the tool.

[0011] The workpiece spindle device 11 rotatably holds a spindle extending along the width direction of the machine body inside. The width direction of the machine body parallel to the spindle is the Z axis, and the vertical direction perpendicular to the Z axis is the X axis. A chuck device 20 for gripping a workpiece is attached to the spindle of the workpiece spindle device 11 via a flange plate (not shown), and the workpiece gripped by the chuck device 20 is rotated by driving a spindle motor.

[0012] A rotary valve (not shown) is attached to the workpiece spindle device 11, and is configured to feed hydraulic oil to the rotating spindle and the chuck device 20. The spindle, which is a hollow rod, has multiple flow paths formed therethrough in the axial direction, and each flow path is connected to a flow path formed in the chuck device 20.

[0013] FIG. 2 is an enlarged perspective view of the chuck device 20. FIG. 3 is a cross-sectional view of the chuck device 20 taken along a plane along the vertical direction. The chuck device 20 is an internal-diameter gripping type chuck device that holds a workpiece by inserting a collet 40 into a hollow portion formed in the workpiece. The chuck device 20 has a piston 25 therein that moves hydraulically, and the movement of the piston 25 back and forth generates a gripping force for gripping the workpiece. In this embodiment, in the chuck device 20, the side where the collet 40 is located in the direction parallel to the center line O1 is referred to as the "front" and the opposite side is referred to as the "rear."

[0014] At the rear side of the chuck device 20, a cylinder member 24 is fixed to a ring member 23 with bolts to form a cylinder space within which a piston 25 is inserted. The cylinder spaces provided on both sides of the piston 25 define pressurizing chambers 26 through which hydraulic oil is supplied and discharged. The cylinder member 24 and the ring member 23 are formed with a clamping passage 27 and an unclamping passage 28, which are passages for feeding hydraulic oil into the pressurizing chamber. In this embodiment, the clamping passage 27 is a passage formed in the ring member 23, and hydraulic oil flowing through this clamping passage 27 is supplied into the pressurizing chamber and acts to pressurize the piston 25 rearward. Meanwhile, the unclamping passage 28 is a passage formed in the cylinder member 24, and hydraulic oil flowing through this unclamping passage 28 is supplied into the pressurizing chamber and acts to pressurize the piston 25 forward.

[0015] A bushing member 22 is fixed by a bolt to the front side of the ring member 23, and a mandrel 30 fixed to the piston 25 via a threaded portion passes through this bushing member 22 to be held slidable along the center line O1. A restriction groove 32 extending in the longitudinal direction is formed in the mandrel 30, and the tip of a stopper 33 fixed to the bushing member 22 is inserted into this restriction groove 32, thereby restricting the range of movement of the mandrel 30 in the front and rear directions.

[0016] The mandrel 30 has at its tip an expansion portion 31 for radially deforming the collet 40. The expansion portion 31 is a portion whose outer diameter increases toward the front in a cross-sectional view, and has an expansion tapered surface 31A formed on its outer periphery.

[0017] A front cover 21 having an opening 21A at its front is fixed by bolts to the front of the bushing member 22. A portion of the mandrel 30 including the expansion portion 31 protrudes from the opening 21A of the front cover 21, and a cylindrical collet 40 is attached to this portion. Specifically, the collet 40 is held from the front and rear by the expansion tapered surface 31A of the expansion portion 31 and the restricting tapered surface 36 provided on the bushing member 22, with its hollow portion penetrated by the portion of the mandrel 30 that protrudes from the front cover 21.

[0018] A front gripping portion 41 and a rear gripping portion 42 are formed on the front and rear ends of the collet 40. The front gripping portion 41 has a gripping surface 41A on its outer periphery that comes into contact with the workpiece to apply a gripping force, and a tapered surface 41B on its inner periphery that comes into contact with and faces the expanding tapered surface 31A of the mandrel 30. The rear gripping portion 42 has a gripping surface 42A on its outer periphery that comes into contact with the workpiece to apply a gripping force, and a tapered surface 42B on its inner periphery that comes into contact with and faces the restricting tapered surface 36 of the bushing member 22.

[0019] A plurality of slits 43 extending along the center line O1 are formed on the outer periphery of the collet 40, and the portions sandwiched between two slits 43 are configured to be independently deformable in the radial direction. The front gripping portion 41 and the rear gripping portion 42 described above are also configured to be independently deformable in the radial direction by being divided by the slits 43. In this embodiment, slits extending to the front end of the collet 40 and slits extending to the rear end of the collet 40 are alternately formed on the circumference of the collet 40. The collet 40 is not limited to the one shown in FIG. 2 as long as the portions sandwiched between the slits are configured to be independently deformable in the radial direction.

[0020] In the machine tool 1 configured as described above, when a workpiece having a hollow portion is gripped by the chuck device 20, the collet 40 held in front of the mandrel 30 is first inserted into the hollow portion of the workpiece to position the workpiece. Next, hydraulic oil is supplied to the clamping passage 27 to pressurize the piston 25 from the front side, moving the mandrel 30 rearward. As the mandrel 30 moves rearward, the tapered spreading surface 31A of the spreading portion 31 spreads the front gripping portion 41 of the collet 40 radially outward. As the spreading portion 31 continues to move rearward, not only the front gripping portion 41 but also the rear gripping portion 42 spreads radially outward, causing each gripping surface 41A, 42A to apply a gripping force to the workpiece. On the other hand, when the gripping of the workpiece by the chuck device 20 is released, hydraulic oil is supplied to the unclamping passage 28 to pressurize the piston 25 from the rear side, moving the mandrel 30 forward. As the mandrel 30 moves forward, the front gripping portion 41 and the rear gripping portion 42 of the collet 40 return to their radially inward positions, and the gripping force applied to the workpiece is released.

[0021] In the machine tool 1 configured as described above, if the gripping force applied to the workpiece by the chucking device 20 is smaller than expected, the workpiece may shift position relative to the collet 40 during machining, potentially reducing machining accuracy. For example, while it is possible to visually confirm whether the collet 40 is gripping the workpiece, it is not possible to evaluate the value of the gripping force applied to the workpiece. On the other hand, if the hydraulic pressure flowing through the clamping flow path 27 is set to a high value in anticipation of a weak gripping force, the gripping force applied by the collet 40 may deform the workpiece. Therefore, in this embodiment, the gripping force of the chuck device 20 of the machine tool 1 is measured using a measurement method that employs a measuring jig 60. The measured gripping force is then used to evaluate the gripping force of the chuck device 20.

[0022] Next, a measuring jig 60 used to measure the gripping force of the chucking device 20 will be described. FIG. 4(a) is a perspective view of the measuring jig 60. FIG. 4(b) is a cross-sectional view of the measuring jig 60 in the front-rear direction. The measuring jig 60 is a cylindrical member having a hollow portion 61 into which the collet 40 can be inserted, and is made of an elastically deformable metal such as aluminum or copper. The measuring jig 60 has a pair of gripping force receiving portions 62, 63 each having a diameter that increases from a center line O2 of the measuring jig 60. In this embodiment, the pair of gripping force receiving portions 62, 63 are located at both ends of the measuring jig 60 in the longitudinal direction, spaced a predetermined distance apart. Gripped surfaces 62A, 63A that receive the gripping force from the collet 40 are formed on the inner peripheries of the gripping force receiving portions 62, 63.

[0023] The measuring jig 60 has a thin-walled portion 64 that is interposed between a pair of gripping force receiving portions 62, 63 and is thinner than the gripping force receiving portions 62, 63. As shown in FIG. 4(b), the thin-walled portion 64 has a larger inner diameter and a smaller outer diameter in a cross-sectional view than the gripping force receiving portions 62, 63. This makes it easier to deform the gripping force receiving portions 62, 63 radially outward when a radially outward gripping force is applied to the gripping force receiving portions 62, 63 from the collet 40 inserted into the hollow portion 61. Note that the thin-walled portion 64 may have the same inner diameter as the gripping force receiving portions 62, 63 in a cross-sectional view, but may have a smaller outer diameter and be thinner than the gripping force receiving portions 62, 63.

[0024] Next, a method for measuring the gripping force of the chuck device 20 using the measurement jig 60 will be described. Fig. 5 is a flowchart illustrating the gripping force measurement method. For example, the gripping force measurement method shown in Fig. 5 is performed by an operator or the like prior to the machining of workpieces by multiple machine tools 1.

[0025] In step 10, a positioning process is performed in which collet 40 of chuck device 20 is inserted into hollow portion 61 of measuring jig 60, and gripping portions 41, 42 are positioned opposite gripped surfaces 62A, 63A of gripping force receiving portions 62, 63. Hereinafter, step will also be referred to as "S." At this time, because the pair of gripping force receiving portions 62, 63 have a larger diameter than thin-walled portion 64, their shapes serve as markers, making it easier to align gripped surfaces 62A, 63A of gripping force receiving portions 62, 63 with gripping portions 41, 42 of collet 40.

[0026] In S11, a deformation process is performed in which the collet 40 is spread radially outward, and the gripping forces from the gripping portions 41, 42 are applied to the gripping force receiving portion 62 of the measuring jig 60, thereby elastically deforming the gripping force receiving portion 62. As shown in FIG. 6( a), the rearward movement of the spreading portion 31 causes the front gripping portion 41 of the collet 40 to be spread radially outward in accordance with the inclination of the spreading tapered surface 31A, and applies a gripping force to the gripping force receiving portion 62 of the measuring jig 60. Therefore, the gripping force receiving portion 62 is deformed radially outward by the applied gripping force. As the front gripping portion 41 continues to spread radially outward due to the rearward movement of the spreading portion 31, the rear gripping portion 42 also spreads radially outward. As a result, rear gripping portion 42 applies a gripping force to opposing gripping force receiving portion 63, deforming gripping force receiving portion 63 radially outward. At this time, front gripping portion 41 is directly pushed open in the radial direction by pushing-opening tapered surface 31A, so the gripping force (indicated by arrows in FIG. 6(a)) applied by front gripping portion 41 to gripping force receiving portion 62 is greater than the gripping force applied by rear gripping portion 42 to gripping force receiving portion 63.

[0027] In S12, the amount of radial deformation of the gripping force receiving portions 62, 63 is measured while the gripping force from the chucking device 20 is being applied to the measuring jig 60. Specifically, the amount of deformation of each of the gripping force receiving portions 62, 63 of the measuring jig 60 is measured separately using a strain gauge or the like. This is because, as described in FIG. 6(a), the amount of deformation of each of the gripping force receiving portions 62, 63 differs due to the difference in the gripping forces applied from the front gripping portion 41 and the rear gripping portion 42. At this time, it is desirable to measure the amount of radial deformation multiple times while changing the measurement location for each of the gripping force receiving portions 62, 63, and calculate the average value of the measurement results as the amount of deformation.

[0028] In S13, the gripping force of the chuck device 20 is converted from the measured deformation amounts of the gripping force receiving portions 62, 63. FIG. 6(b) is a diagram illustrating the correspondence relationship between the radial deformation amounts of the gripping force receiving portions 62, 63 and the gripping force applied by the chuck device 20. If the radial deformation of the gripping force receiving portions 62, 63 is within an elastic deformation range lower than the elastic limit of the measuring jig 60, the deformation amounts of the gripping force receiving portions 62, 63 are proportional to the applied gripping force, and the gripping force can be converted from the deformation amounts. Note that it is desirable to select a material for the gripping force receiving portions 62, 63 so that they elastically deform within the range of the gripping force applied by the chuck device 20.

[0029] As an example of a method for converting the amount of deformation into the gripping force, a computing device such as a PC stores table information that defines the correspondence between the amount of deformation within the elastic deformation range of the measuring jig 60 and the gripping force. Then, by inputting the measured amount of deformation of each of the gripping force receiving portions 62, 63 into the computing device, the computing device converts the gripping force corresponding to the input amount of deformation using the table information. In this embodiment, steps S12 and S13 are an example of a conversion step.

[0030] In S14, an evaluation step is performed to evaluate whether the converted gripping force falls within an appropriate range for the gripping force of the chuck device 20. In this embodiment, the gripping force of the front gripping portion 41 and the gripping force of the rear gripping portion 42 are evaluated separately to evaluate whether an abnormality has occurred in the gripping force of either the front gripping portion 41 or the rear gripping portion 42. If the gripping forces of the front gripping portion 41 and the rear gripping portion 42 are within the appropriate range, machining of the workpiece by the machine tool 1 can be started. Note that the gripping force receiving portions 62, 63 are deformed within the elastic deformation range due to the gripping force, and therefore return to their original shape when the gripping force is released. On the other hand, if the gripping force of either the front gripping portion 41 or the rear gripping portion 42 is not within the appropriate range, machining of the workpiece by the machine tool 1 will not be started. In this case, inspection of the machine tool 1, etc. will be performed.

[0031] In addition, since the gripping force of the front gripping portion 41 is greater than the gripping force of the rear gripping portion 42, in S14, the gripping force of the chuck device 20 may be evaluated using only the gripping force of the front gripping portion 41 out of the converted gripping forces.

[0032] The present embodiment described above can achieve the following effects. In the gripping force measurement method, collet 40 is inserted into hollow portion 61 of cylindrical measuring jig 60, and gripping surfaces 62A of gripping force receiving portions 62 of measuring jig 60 are positioned opposite gripping portions 41, 42 provided on the outer periphery of collet 40. Grip portions 41, 42 of collet 40 are deformed radially outward, and gripping forces from gripping portions 41, 42 are applied to gripping force receiving portions 62, 63 of measuring jig 60, thereby elastically deforming gripping force receiving portions 62, 63. The amount of radial deformation of gripping force receiving portions 62, 63 is then measured, and the gripping force of chuck device 20 is calculated from the measured amount of deformation. This makes it possible to measure the gripping force of inner diameter gripping type chuck device 20, and evaluate the gripping force of chuck device 20.

[0033] The measuring jig 60 has a pair of gripping force receiving portions 62, 63 spaced a predetermined distance apart in the longitudinal direction, and has a thin portion 64 interposed between the pair of gripping force receiving portions 62, 63. This makes it easier for the thin portion 64 to elastically deform the gripping force receiving portions 62, 63 on the radially outer side when a gripping force is applied to the measuring jig 60.

[0034] Gripping force receiving portions 62, 63 have a shape in which the outer diameter expands from center line O2 of measuring jig 60. This makes it easy to position gripping force receiving portions 62, 63 to the respective gripping portions 41, 42 of collet 40 using expanded diameter gripping force receiving portions 62, 63 as markers, allowing measuring jig 60 to function properly.

[0035] Although one embodiment of the present invention has been described above, the present invention is not limited to this and various modifications are possible without departing from the spirit of the present invention. In the embodiment described above, the collet 40 includes a front gripping portion 41 and a rear gripping portion 42, and in the positioning step, a pair of gripping force receiving portions 62, 63 of the measuring jig 60 are disposed opposite each of the gripping portions 41, 42. Alternatively, the collet 40 may include only one gripping portion extending along the longitudinal side, and in the positioning step, the pair of gripping force receiving portions 62, 63 of the measuring jig 60 may be disposed opposite the single gripping portion.

[0036] When the collet 40 includes only the front gripping portion 41, the measuring jig 60 may be configured to include one pressure receiving portion disposed opposite the front gripping portion 41. [Explanation of symbols]

[0037] 1...machine tool, 11...workpiece spindle device, 12...turret device, 20...chuck device, 30...mandrel, 40...collet, 41...front gripping portion, 42...rear gripping portion, 60...measuring jig, 61...hollow portion, 62, 63...gripping force receiving portion, 64...thin-walled portion

Claims

1. The present invention is used in a machine tool having a chuck device that grips a workpiece by expanding a cylindrical collet radially outward within a hollow portion of the workpiece, a positioning step of inserting the collet into a hollow portion of a cylindrical measuring jig and positioning it; a deformation step of elastically deforming the gripping force receiving portions of the measuring jig by spreading the collet outward in the radial direction and applying a gripping force from the collet to the gripping force receiving portions; a conversion step of measuring a deformation amount of the gripping force receiving portion in the radial direction and converting the measured deformation amount into a gripping force of the chuck device.

2. The measuring jig is A pair of the gripping force receiving portions are provided spaced apart by a predetermined distance in the longitudinal direction, The gripping force measuring method according to claim 1 , further comprising a thin-walled portion interposed between the pair of gripping force receiving portions and having a thickness thinner than the gripping force receiving portions.

3. The gripping force measuring method according to claim 1 , wherein the gripping force receiving portion has a shape in which an outer diameter thereof increases from a center line of the measuring jig.

4. The present invention is used in a machine tool having a chuck device that grips a workpiece by expanding a cylindrical collet radially outward within a hollow portion of the workpiece, A cylindrical shape having a hollow portion into which the collet can be inserted, A measuring jig having a gripping force receiving portion that is elastically deformable in the radial direction upon receiving a gripping force from the collet inserted in the hollow portion.

5. A pair of the gripping force receiving portions are provided spaced apart by a predetermined distance in the longitudinal direction, The measuring jig according to claim 4 , further comprising a thin-walled portion interposed between the pair of gripping force receiving portions and having a thickness thinner than the gripping force receiving portions.

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