Sucker adsorption-type workpiece fixing device for machine tool

Abstract

To ensure holding of a positioning state of a workpiece placed on a table in a chamfer machine.SOLUTION: A workpiece 5 is adsorbed and fixed on a table upper surface 9 by a vertically moving sucker 7. The sucker 7 is adsorbed in the workpiece in an adsorption recess 12 and has an air hole 15 formed in a center base 13 so as to communicate with the adsorption recess 12. The sucker 7 is stored in a sucker storage recess 16 opened in the table upper surface 9. The adsorption recess 12 of the sucker is positioned below a workpiece lower surface 19 in a state where the workpiece is placed on the table upper surface so as to cover an upper end opening 17 of the sucker storage recess 16. The workpiece lower surface 19 is absorbed on the upper end opening of a sucker storage part through suction at the air hole 15. In this state, the raised sucker sucks the workpiece lower surface. When the center base 13 is pulled downward in the sucked state, the workpiece is pulled downward via the sucker, and the workpiece is fixed on the table upper surface in a real adsorption state.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a suction cup type workpiece fastening device in a machine tool. [Background technology]

[0002] Patent Document 1 discloses an example of a machine tool that is configured to fix a workpiece on a table to the table using an air suction method when the workpiece is subjected to machining such as chamfering using a milling cutter.

[0003] The machine tool includes a table on which a workpiece is placed, a clamping device disposed in front of the table, and a milling cutter disposed in front of the table for performing machining such as chamfering on the workpiece, the clamping device having upper and lower clamping pieces for clamping from above and below a protruding portion of the workpiece placed on the table that protrudes as required from the front edge of the table. Prior to performing the machining, the machine tool positions the workpiece placed on the table in the left-right and front-back directions as required, fixes the positioned workpiece to the table, and then moves the table as required and clamps the protruding portion that protrudes as required from the front edge of the table with the upper and lower clamping pieces. Then, in a workpiece clamping state in which the protruding portion is clamped by the upper and lower clamping pieces, the milling cutter performs machining on the processed portion of the workpiece that is in front of the clamped portion.

[0004] With the protruding portion clamped as described above, one processing surface of the workpiece is machined.

[0005] After the machining of one of the workpiece surfaces is completed, the upper and lower clamping pieces release the protruding portion from the clamping position. In this released state, the table is rotated 90 degrees to machine a new workpiece surface.

[0006] The fixing means for the workpiece on the table described in Patent Document 1 has shallow recesses on the front and rear of the top surface of the table, and a number of air holes are provided in the bottom surface of the recesses in the vertical direction. The upper ends of the air holes open on the top surface of the bottom surface, and the lower ends are connected to an air suction device that sucks in air.

[0007] After the required positioning of the workpiece placed on the table has been completed, the air is sucked out from the space formed between the recess and the underside of the workpiece in order to fix the workpiece to the table.

[0008] However, in the past, if the roughness and flatness of the bottom surface of the workpiece were not good enough, there was a problem that outside air was drawn in and the workpiece was not completely fixed. In particular, in the case of a thin-walled and warped workpiece, the above-mentioned space was in communication with the outside at the warped part, so that the workpiece did not adhere well to the top surface of the table and the workpiece could not be fixed to the table.

[0009] If the fixation is incomplete in this way, after the required positioning of the workpiece placed on the table is completed, the fixation of the workpiece to the table may become uncertain due to the acceleration / deceleration of the table when the table starts to advance or when the table stops, or due to the acceleration / deceleration of the table when the table starts to rotate 90 degrees or when the table rotation stops, and the workpiece may shift from the set position on the table, which may cause a problem that the workpiece cannot be machined accurately. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Publication No. 2012-106327 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been developed in consideration of the above-mentioned problems in the conventional art, and has as its object to provide a suction cup type workpiece fastening device for a machine tool which, when a workpiece is placed on a table in a required position and subjected to machining such as chamfering, can reliably maintain the positioning state and perform machining such as chamfering with high precision. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention employs the following means. That is, in a first aspect of the suction cup type workpiece fastening device for a machine tool according to the present invention, a workpiece is suction-fixed to the top surface of a table by a suction cup that moves up and down, the suction cup is made of rubber and is adapted to be suctioned to the workpiece by a suction recess in a skirt-shaped suction part for vacuum suction, an air hole communicating with the suction recess is provided in the central base of the suction part, and the suction cup is housed in a suction cup accommodating recess that is provided at a required part of the table and opens on the top surface of the table with the suction recess opening upward. With the workpiece placed on the table so as to cover the upper end opening of the suction cup accommodating recess, the suction recess of the suction cup is located below the lower surface of the workpiece, and in this state, suction by the air hole acts to obtain a preliminary suction state in which the lower surface of the workpiece is suctioned by the upper end opening of the suction cup accommodating recess. The suction cups are adapted to rise in the preliminary suction state, and while the workpiece suction action in the preliminary suction state prevents the workpiece from floating up from the table top surface, the peripheral portion of the suction recess presses the underside of the workpiece upward so that the peripheral portion is suctioned to the underside of the workpiece. Then, while in this suction state, the central base of the suction cups is elastically pulled downward, thereby obtaining a downward tension state of the workpiece via the suction cups, and thus the workpiece is fixed to the table top surface in the main suction state.

[0013] A second aspect of the suction cup type workpiece fastening device for machine tools according to the present invention is characterized in that, in the first aspect, a vertical guide hole is connected to the bottom of the suction cup accommodating recess, an air pipe is inserted into the vertical guide hole and the air pipe can move up and down while being guided by the vertical guide hole, an air passage is provided in the air pipe in its axial direction, an upper part of the air passage is connected to the air hole of the suction cup, and the air passage is connected to an air supply source which supplies negative pressure air or positive pressure air to the air hole, and the air pipe is moved up and down by a vertical movement device so that the suction cup can be moved up and down.

[0014] A third aspect of the suction cup type workpiece fastening device for a machine tool according to the present invention is the first aspect, further comprising: a vertical guide hole connected to the bottom of the suction cup accommodating recess, an air pipe inserted into the vertical guide hole, the air pipe being guided by the vertical guide hole to move up and down, an air passage provided in the air pipe in its axial direction, an upper part of the air passage connected to the air hole of the suction cup, and the air passage connected to an air supply source which supplies negative pressure air or positive pressure air to the air hole. Also, a piston is provided at the bottom of the air pipe so as to be able to move the suction cup up and down, the piston can move up and down in a cylinder provided in the table, the vertical movement of the piston is configured to be performed by controlling the supply of the positive pressure air or the negative pressure air to upper and lower ports provided at upper and lower parts sandwiching the cylinder and capable of communicating with the cylinder, and the upper port is also connected to the air passage, and has the following configuration. (1) When the upper end of the suction cup accommodating recess is covered with the workpiece and the piston is in contact with the bottom of the cylinder or moved toward the bottom, negative pressure air is supplied to the upper port, thereby obtaining the preliminary suction state in which the underside of the workpiece is adsorbed to the upper opening of the suction cup accommodating recess. (2) While the pre-suction state is being maintained with negative pressure air being supplied to the upper port, positive pressure air is supplied to the lower port to raise the air pipe, causing the suction cup to rise and the peripheral portion of the suction recess to be adhered to the underside of the workpiece. (3) When negative pressure air is supplied to the lower port while the workpiece is in this suction state, the piston descends, and while the suction state is maintained, the central base of the suction cup is elastically pulled downward, and the workpiece is pulled downward via the suction cup, thereby fixing the workpiece to the table top in this suction state. (4) By supplying negative pressure air to the lower port and positive pressure air to the upper port, the workpiece is released from the suction cup in the suction state.

[0015] A fourth aspect of the suction cup type workpiece fastening device for machine tool according to the present invention is characterized in that, in any one of the first to third aspects, the workpiece is placed on the table so as to cover the upper end opening of the suction cup accommodating recess, and the suction recess of the suction cup is positioned below the lower surface of the workpiece, and positive pressure air is supplied from the air hole into the suction recess to eject air at the upper end opening of the suction cup accommodating recess, thereby allowing the workpiece to be floated and moved above the table surface. Effect of the Invention

[0016] The suction cup type work fastening device for machine tools according to the present invention is configured using suction cups which are made of rubber and have good adhesion, so that when a workpiece is placed on a table in a required position and machined such as chamfering is performed on the workpiece, the positioning can be reliably maintained, and machined such as chamfering can be performed with high precision, thereby providing a suction cup type work fastening device for machine tools which can reliably maintain the positioning when the workpiece is placed on the table in a required position and can perform machined such as chamfering. [Brief description of the drawings]

[0017] [Figure 1] 1 is a plan view illustrating a suction cup type workpiece fastening device of a machine tool according to the present invention; [Diagram 2] FIG. 4 is a plan view showing the arrangement of suction cups provided on a table. [Diagram 3] FIG. 2 is a cross-sectional view for explaining the configuration of a suction cup type workpiece fastening device of a machine tool. [Figure 4] FIG. 13 is an explanatory diagram illustrating the range of vertical movement of the suction cup. [Diagram 5] FIG. 13 is an explanatory diagram illustrating a preliminary suction state of the suction cup. [Figure 6] 11 is an explanatory diagram illustrating a state in which the suction cup rises and the peripheral portion of the suction cup is attached to the underside of the workpiece when the suction cup is in a preliminary suction state; FIG. [Figure 7] FIG. 13 is an explanatory diagram illustrating a main suction state of the suction cup. [Figure 8] FIG. 13 is an explanatory diagram illustrating a state in which the fixation in the adsorbed state of the suction cup is released. [Figure 9] 1 is a side view showing a state in which the upper and lower clamping pieces are clamping a workpiece and the milling cutter is chamfering the workpiece. FIG. [Figure 10] FIG. 11 is a plan view showing a process of performing measurements for positioning a workpiece using a movable measuring device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0018] 1 and 2, a suction cup type workpiece fastening device (hereinafter also referred to as a workpiece fastening device) 1 for a machine tool according to the present invention is applied to a machine tool 2, for example a chamfering machine 2a that performs chamfering on a workpiece 5 placed on a table 3 with a milling cutter 6, and suction-fixes the workpiece 5 to a table upper surface 9 via suction cups 7 that move up and down. In this embodiment, as shown in Fig. 2, the suction cups 7 are provided at both sides in plan view at each of the four corners 10, 10, 10, 10 of the table 3 that has an octagonal shape in plan view.

[0019] As shown in Figs. 3 and 4, the suction cup 7 is adapted to be attached to the lower surface 19 of the workpiece 5 by a suction recess 12 of a skirt-shaped suction portion 11 that expands in diameter toward the upper end for vacuum suction, and an air hole 15 communicating with the suction recess 12 is provided in a central base 13 of the suction portion 11. The suction cup 7 is accommodated in a suction cup accommodating recess 16 that is provided in a required portion of the table 3 and opens on the table upper surface 9, with the suction recess 12 opening upward. With the workpiece 5 placed on the table 3 so as to cover the upper end opening 17 of the suction cup accommodating recess 16, as shown in Fig. 4, the suction recess 12 of the suction cup 7 is configured to assume a lower position located below the lower surface 19 of the workpiece 5 (hereinafter also referred to as the workpiece lower surface). The suction cup 7 in the lower position can be raised to assume an upper position protruding above the table upper surface 9, as shown by the dashed line in Fig. 4. In this embodiment, it can be raised by about 1 mm.

[0020] As shown in Fig. 5, when the suction recess 12 is in the lower position, suction is applied by the air holes 15, resulting in a preliminary suction state 20 in which the workpiece lower surface 19 is suctioned to the upper end opening 17 of the suction cup accommodating recess 16. In the preliminary suction state 20, the suction cups 7 rise to the upper position shown by the dashed line in Fig. 4, and as shown in Fig. 6, the peripheral portion 21 of the suction recess 12 presses the workpiece lower surface 19 upward while preventing the workpiece 5 from floating up from the table upper surface 9 due to the workpiece suction action in the preliminary suction state 20 (Fig. 5). This pressing causes the peripheral portion to be suctioned to the workpiece lower surface 19.

[0021] 6, the central base 13 of the suction cup 7 is elastically pulled downward while in the suction state 22 (FIG. 6), whereby a downward pulling state of the workpiece 5 is obtained via the suction cup 7. As a result, the workpiece 5 is fixed to the table upper surface 9 in the main suction state 23.

[0022] 4, in this embodiment, the suction cup accommodating recess 16 has an upper end 26 of a circular recess 25 capable of accommodating the central base portion 13 of the suction cup 7, and an expanding diameter circular recess 27 capable of accommodating the skirt-shaped suction portion 11 of the suction cup 7, which is connected to the upper end 26 of the circular recess 25 and shares a common axis with the circular recess 25. Also, a vertical guide hole 29 having a smaller diameter than the circular recess 25 is connected to the bottom central portion of the circular recess 25 and shares a common axis with the circular recess 25.

[0023] 4, an air pipe 30 is inserted into the vertical guide hole 29, and the air pipe 30 is guided by the vertical guide hole 29 so that it can move up and down. An air passage 31 is provided in the air pipe 30 in the axial direction, and the upper part of the air passage 31 is connected to the air hole 15 of the suction cup 7 via a connecting pipe member 32, and the air passage 31 is connected to an air supply source (not shown) that supplies negative pressure air or positive pressure air to the air hole 15. is connected to

[0024] 4, the air pipe 30 is moved up and down by a vertical movement device 28 so that the suction cup 7 can be moved up and down. In this embodiment, the vertical movement device 28 is provided with a piston 33 at the bottom of the air pipe 30. The piston 33 can move up and down in a cylinder 35 provided inside the table 3. The vertical movement of the piston 33 is achieved by controlling the supply of the positive pressure air or the negative pressure air to upper and lower ports 36, 37 which are provided at upper and lower positions sandwiching the cylinder 35 and can communicate with the cylinder 35, and the upper port 36 is also communicated with the air passage 31.

[0025] Next, the operation of the suction cup type workpiece fastening device 1 having such a configuration will be described with reference to Figures 4 to 7. The arrows shown in Figures 5 to 8 indicate the direction of air movement. Figure 4 shows the initial state, in which the workpiece 5, which has been positioned as required in the left-right and front-rear directions on the table 3 and placed on the table top surface 9, is immediately before being suction-fixed to the table top surface 9, with the upper end opening 17 of the suction accommodation recess 16 being covered by the workpiece 5.

[0026] FIG. 5 shows the preliminary suction state 20 in which the upper end opening 17 is covered with the workpiece 5 and the piston 33 is in contact with the bottom 34 of the cylinder 35, and negative pressure air is supplied to the upper port 36, thereby causing the workpiece underside 19 to be suctioned to the upper end opening 17 of the suction cup accommodating recess 16.

[0027] FIG. 6 shows a state in which, while maintaining the preliminary suction state 20 (FIG. 5) in which negative pressure air is being supplied to the upper port 36, positive pressure air is supplied to the lower port 37 to raise the air pipe 30, thereby causing the suction cup 7 to rise and the peripheral portion 21 of the suction recess 12 to be suctioned to the underside 19 of the workpiece.

[0028] FIG. 7 shows the state in which, while in this suction state, negative pressure air is supplied to the lower port 37 to lower the piston 33, and while in this suction state, the central base 13 of the suction cup 7 is elastically pulled downwards, and the workpiece 5 is pulled downwards via the suction cup 7, and the workpiece 5 is fixed to the table upper surface 9 in this suction state 23.

[0029] 8 shows a state in which the fixation by the suction cups 7 in the suction state is released by supplying negative pressure air to the lower port 37 and positive pressure air to the upper port 36. By releasing the fixation, the workpiece 5 can be removed from the table 3.

[0030] Next, in the case where the workpiece fastening device 1 according to the present invention is applied to a chamfering machine 2a, the process of positioning the workpiece 5 on the table 3, the process of suction cup adsorbing the workpiece 5 to properly maintain the positioned state, the process of clamping the workpiece 5 while maintaining the positioned state, and the subsequent process of chamfering the workpiece 5 will be described.

[0031] First, as shown in Fig. 1 and Fig. 9, the chamfering machine 2a includes a table 3 on which a workpiece 5 is placed, a positioning device 40 (Fig. 1) for positioning the workpiece 5 on the table 3, a clamping device 41 disposed on the front side of the table 3, and a milling cutter 6 disposed on the front side of the table 3 for machining the workpiece 5. As shown in Fig. 9, the clamping device 41 includes upper and lower clamping pieces 45, 46 for clamping from above and below an overhanging portion 43 of the workpiece 5 placed on the table top surface 9, which overhangs from a front edge portion 42 of the table 3. In a work clamping state in which the upper and lower clamping pieces 45, 46 clamp the overhanging portion 43, the milling cutter 6 performs chamfering on a processed portion 47 (Figs. 9(A)(B)) of the workpiece 5 that is in front of the clamped portion.

[0032] In the chamfering machine 2a, the table 3 has a table upper surface 9 which is horizontal, and can be rotated as required about an axis in the vertical direction by an indexing device.

[0033] The lower clamping piece 46 can take an elevated position protruding above the table top surface 9, a lowered position lower than the table top surface 9, and a clamping position in which it abuts against the lower surface 19 of the workpiece 5, and when the lower clamping piece 46 is in the elevated position, the workpiece 5 placed on the upper surface of the table 3 is advanced so that the front surface of the workpiece 5 abuts against the lower clamping piece 46, thereby forming the protruding portion 43. Then, after the table 3 advances a required amount with the lower clamping piece 46 in the lowered position, the lower clamping piece 46 rises to assume the clamping position, and the protruding portion 43 is clamped by the upper and lower clamping pieces 45, 46.

[0034] (1) Workpiece positioning process on the table The workpiece 5 placed on the table 3 has a required thickness and is square, rectangular, octagonal, or the like in plan view. The workpiece shown in Fig. 1 has a rectangular parallelepiped shape, and is formed into a square with a side length of 150 to 500 mm in plan view, for example, 300 mm.

[0035] Fig. 1 is a plan view showing the workpiece 5 placed on the table 3. With the table 3 separated rearwardly from the upper and lower clamping pieces 45, 46 (Fig. 9), the workpiece 5 is suspended onto the table upper surface 9. As shown in Figs. 1 and 4, the lower surface 19 of the workpiece 5 covers the upper end openings 17 of the suction cup receiving recesses 16 arranged at required intervals on the table 3. Prior to fixing the workpiece 5, the workpiece 5 is positioned as required on the table 3. The positioning is performed using the positioning device 40 (comprising a positioning tool 49 and a measuring device 50 shown in Fig. 1).

[0036] FIG. 1 shows the process of roughly positioning the workpiece 5 in the left-right and front-rear directions. The positioning is performed by pressing one corner 52 of the workpiece 5 against a right-angle positioning portion 51 formed by the positioning piece 49a of the advanced positioning tool 49 and the lower clamping piece 42 (FIG. 9) extending in a direction perpendicular to the axial direction of the positioning tool 49.

[0037] FIG. 10 shows a process of positioning the workpiece 5 using a measuring device 50 so that the front surface 5a of the workpiece 5 is correctly parallel to the left-right direction F (the horizontal movement direction of the milling cutter 6).

[0038] FIG. 10 shows a procedure for making appropriate corrections based on the measurement results by the measuring device 50 in order to improve the accuracy of the chamfering. In this embodiment, as shown in FIG. 10, the measuring device 50 has a movable probe 50a that can be advanced and retreated, mounted on a moving frame 54 that can move in the left-right direction (the moving direction of the milling cutter) F. The measuring device 50 advances the probe 50a when positioned at the left and right ends of the work 3, and the tip 50b of the probe 50a abuts against the front surface 5a of the work 5. This measures the distance between the tip 50b of the probe 50 in the retreated state and the front surface 5a at the left and right ends. If the two distances are not the same, the table 3 is rotated by a required angle around its axis to adjust the two distances to be the same. This allows the work 5 to be positioned on the table 3 prior to the clamping so that the front surface 5a of the work 5 is correctly parallel to the left-right direction F.

[0039] Incidentally, when performing the operation of pressing the one corner portion 52 (FIG. 1) against the right-angle positioning portion 51 (FIG. 1) in this manner, it is advisable to supply positively pressurized air from the air hole 15 (FIG. 4) of the suction cup 7 into the suction recess 12 and eject the air at the upper end opening 17 of the suction cup accommodating recess 16. This allows the workpiece 5 to be floated and moved above the table top surface 9, facilitating the movement of the workpiece 5 on the table top surface 9. This movement of the workpiece 5 can be performed without the peripheral portion 21 (FIG. 4) of the suction recess 12 of the suction cup 7 protruding from the upper end opening 17 of the suction cup accommodating recess 16, so that it can be performed smoothly and without hindrance.

[0040] Thereafter, as shown in FIG. 10, appropriate corrections are made based on the results of the measurements made by the measuring device 50, so that the workpiece 5 is positioned as required on the table 3 prior to the clamping.

[0041] (2) Suction cup attachment process for the workpiece The workpiece 5 thus positioned is fixed to the table 3 in accordance with the steps described above with reference to FIGS.

[0042] (3) Workpiece clamping process After the workpiece 5 is positioned in this manner, the table 3 is advanced a required amount (for example, 10 to 20 mm degrees) taking into consideration the size (depth) of the chamfer. Thereafter, as shown in Fig. 9, the overhanging portion 43 is held by the upper and lower holding pieces 45, 46, thereby clamping the workpiece 5.

[0043] (4) About the workpiece chamfering process In this workpiece clamped state, the milling cutter 6 performs chamfering on the edge portion of the workpiece 47, as shown in FIG.

[0044] The chamfering process according to the present invention is carried out through the above steps, and when used according to the present invention, the two problems described above in Patent Document 1 can be solved, and machining, for example chamfering, can be performed on a wide range of workpieces. The two problems referred to here are the first and second problems described below. (1) First problem If the roughness and flatness of the bottom surface of the workpiece are not good enough, outside air will be drawn in, causing the workpiece to be incompletely fixed to the table. (2) The second problem In the case of a thin-walled warped workpiece, the space is open to the outside at the warped portion, which causes poor adhesion of the workpiece to the top surface of the table, making it impossible to fix the workpiece to the table.

[0045] The reason why the work fastening device 1 according to the present invention can solve the first problem is that the work fastening device is configured using suction cups made of rubber that have good adhesion, and therefore the effects of the surface roughness and flatness of the work are mitigated compared to conventional devices.

[0046] The reason why the workpiece fastening device 1 can solve the second problem is that the present invention has the following configuration: "the suction at the air holes 15 acts to obtain the preliminary suction state 20 (FIG. 5) in which the workpiece underside 19 is suctioned at the upper end opening 17 of the suction cup accommodating recess 16, the suction cups 7 rise in the preliminary suction state 20 (e.g., rise by about 1 mm), the workpiece 5 is prevented from floating up from the table top surface 9 by the workpiece suction action in the preliminary suction state 20, and the peripheral portion 21 of the suction recess 12 presses the workpiece underside 19 upward to be suctioned to the workpiece underside 19, and the central base portion 13 of the suction cup 7 is elastically pulled downward while maintaining the suction state, thereby obtaining a downward tension state of the workpiece 5 via the suction cup 7, and thus the workpiece 5 is fixed to the table top surface 9 in the main suction state."

[0047] As a result, even if the workpiece is thin and warped, the lifting action of the suction cups can reliably suck the workpiece and fix it to the table, allowing the workpiece to be accurately machined. [Explanation of symbols]

[0048] 1 Workpiece fixing device 2 Machine tools 3 Tables 5 Work 6 Milling 7 sucker 9 Table top 11 Adsorption part 12 Adsorption recess 13 Central base 15 Air Vents 16 Suction cup receiving recess 17 Top opening 20 Pre-adsorption state 21 Periphery 23 Adsorption state 29 Guide hole 30 Air Pipe 31 Air passage 33 Piston 35 Cylinder Ports on 36 37 Lower Port 45 Upper clamping piece 46 Lower clamping piece

Claims

1. A suction cup type workpiece fastening device for a machine tool that suction-fixes a workpiece to a table top surface via a suction cup that moves up and down, The suction cup is made of rubber and is attached to the workpiece by a suction recess in a skirt-shaped suction portion for vacuum suction, and an air hole communicating with the suction recess is provided in the central base of the suction portion. The suction cup is accommodated in a suction cup accommodating recess that is provided in a required portion of the table and opens on the top surface of the table, with the suction recess opening upward. a state in which the workpiece is placed on the table so as to cover an upper end opening of the suction cup accommodating recess, and the suction recess of the suction cup is located below a lower surface of the workpiece, In this state, suction through the air hole acts to obtain a preliminary suction state in which the lower surface of the workpiece is suctioned by the upper end opening of the suction cup accommodating recess, the suction cup rises in the preliminary suction state, and the workpiece is prevented from rising from the top surface of the table by the workpiece suction action in the preliminary suction state, while a peripheral portion of the suction recess presses the lower surface of the workpiece upward, so that the peripheral portion is suctioned to the lower surface of the workpiece, a suction cup type workpiece fastening device for a machine tool, characterized in that the central base of the suction cup is elastically pulled downward while maintaining the suction state, thereby obtaining a downward pulling state of the workpiece via the suction cup, thereby fixing the workpiece to the table upper surface in this suction state.

2. A vertical guide hole is provided in the bottom of the suction cup receiving recess, an air pipe is inserted into the guide vertical hole, the air pipe is guided by the guide vertical hole and can move up and down, an air passage is provided in the air pipe in its axial direction, an upper part of the air passage is connected to the air hole of the suction cup, and the air passage is connected to an air supply source which supplies negative pressure air or positive pressure air to the air hole, 2. A suction cup type workpiece fastening device for a machine tool according to claim 1, further comprising a vertical movement device for moving said air pipe up and down so that said suction cup can be moved up and down.

3. A vertical guide hole is provided in the bottom of the suction cup receiving recess, an air pipe is inserted into the guide vertical hole, the air pipe is guided by the guide vertical hole and can move up and down, an air passage is provided in the air pipe in its axial direction, an upper part of the air passage is connected to the air hole of the suction cup, and the air passage is connected to an air supply source which supplies negative pressure air or positive pressure air to the air hole, A suction cup type workpiece fastening device for a machine tool as set forth in claim 1, further comprising: a piston provided at a lower portion of said air pipe so as to be able to move said suction cup up and down, said piston being able to move up and down within a cylinder provided within said table, said piston being able to move up and down by controlling the supply of said positive pressure air or said negative pressure air to upper and lower ports which are provided at upper and lower portions sandwiching said cylinder and which can communicate with said cylinder, said upper port also being connected to said air passage, and comprising the following configuration: (1) When the upper end of the suction cup accommodating recess is covered with the workpiece and the piston is in contact with the bottom of the cylinder or moved toward the bottom, negative pressure air is supplied to the upper port, thereby obtaining the preliminary suction state in which the underside of the workpiece is adsorbed to the upper opening of the suction cup accommodating recess. (2) While the pre-suction state is being maintained with negative pressure air being supplied to the upper port, if positive pressure air is supplied to the lower port to raise the air pipe, the suction cup will rise and the peripheral portion of the suction recess will be adhered to the underside of the workpiece. (3) When negative pressure air is supplied to the lower port while the workpiece is in this adsorbed state, the piston descends, and while the workpiece is still in this adsorbed state, the central base of the suction cup is elastically pulled downward, and the workpiece is pulled downward via the suction cup, thereby fixing the workpiece to the table top in this adsorbed state. (4) By supplying negative pressure air to the lower port and positive pressure air to the upper port, the workpiece is released from the suction cup in the suction state.

4. 4. A suction cup type workpiece fastening device for a machine tool as set forth in any one of claims 1 to 3, characterized in that, with the workpiece placed on the table so as to cover the upper end opening of the suction cup accommodating recess, and with the suction recess of the suction cup positioned below the lower surface of the workpiece, positive pressure air is supplied from the air hole into the suction recess, causing air to be ejected at the upper end opening of the suction cup accommodating recess, thereby allowing the workpiece to be floated and moved above the table surface.

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