Machine tool, method for detecting clamping force of chuck, and method for setting fastening amount of chuck

Abstract

The invention provides a technology capable of properly controlling the clamping force of a chuck. A machine tool includes a spindle that includes a chuck for clamping a workpiece, and acquires a clamping force of the chuck on the workpiece in a closed state on the basis of a magnitude of a difference between a first time and a second time when the chuck is brought from an open state to a closed state by an opening / closing means closing the chuck, the first time is the time from when the control unit sends a control signal of a closing operation to the opening and closing unit to when the sensor detects that the chuck is no longer in the open state, and the second time is the time from when the control unit sends the control signal to the opening and closing period to when the sensor detects that the chuck is in the closed state.

Description

Technical Field

[0001] The invention relates to a method for detecting the clamping force of a chuck in a machine tool. Background Art

[0002] In a machine tool that rotates a spindle holding a workpiece and moves a processing tool forward and backward relative to the rotating workpiece to perform processing, it is an important factor affecting the working accuracy that the chuck (clamping claw) properly clamps the workpiece. Patent document 1 discloses a scheme that controls the clamping force of the chuck by controlling the rotation angle of the spindle motor by obtaining in advance the relationship between the tightening amount generated by the rotation of the spindle motor from the time when the chuck abuts against the workpiece until a predetermined clamping force is generated and the clamping force of the chuck.

[0003] (Prior art literature)

[0004] (Patent Document)

[0005] Patent Document 1: Japanese Patent Application Publication No. 2001-096409 Summary of the invention

[0006] (Problems to be solved by the invention)

[0007] As described above, it is difficult to directly measure the clamping force of the chuck, so a method of grasping the clamping force of the chuck based on the control amount of the unit that moves the chuck is adopted. However, in many cases, the relationship between the control amount and the clamping force is not necessarily a constant relationship due to various reasons such as the advancement of chuck wear and changes in lubrication conditions.

[0008] An object of the present invention is to provide a technology that can appropriately control the clamping force of a chuck.

[0009] (Measures taken to solve the problem)

[0010] In order to achieve the above object, the machine tool of the present invention has:

[0011] A spindle having a chuck for holding a workpiece;

[0012] an opening and closing unit that moves the chuck to place the chuck in either a closed state for clamping a workpiece or an open state for attaching or detaching the workpiece;

[0013] a sensor for detecting whether the chuck is in the closed state and whether the chuck is in the open state; and

[0014] a control unit for controlling the opening and closing unit,

[0015] The machine tool includes an acquisition component, which acquires the clamping force of the chuck on the workpiece in the closed state based on the difference between a first time and a second time when the opening and closing unit causes the chuck to perform a closing action and the chuck changes from the open state to the closed state, wherein the first time is the time from the control unit sending a control signal of the closing action to the opening and closing unit to the sensor detecting that the chuck is no longer in the open state, and the second time is the time from the control unit sending the control signal to the opening and closing period to the sensor detecting that the chuck is in the closed state.

[0016] Furthermore, in order to achieve the above-mentioned object, a method for detecting the clamping force of a chuck of the present invention is a method for detecting the clamping force of a chuck on a workpiece when the chuck of a spindle of a machine tool clamps the workpiece.

[0017] The detection method comprises:

[0018] In a first step, an opening and closing unit causes the chuck to perform a closing action so that the chuck changes from an open state in which the workpiece can be attached and detached to a closed state in which the workpiece is clamped;

[0019] A second step is to obtain a first time from when the control unit sends a control signal for the closing action to the opening and closing unit until the sensor detects that the chuck is no longer in the open state and a second time from when the control unit sends a control signal to the opening and closing unit until the sensor detects that the chuck is in the closed state in the first step; and

[0020] In a third step, the clamping force is obtained based on a correlation among a magnitude of a difference between the first time and the second time, an amount of tightening of the workpiece by the chuck in the closed state adjusted by an adjustment unit, and the clamping force.

[0021] Furthermore, in order to achieve the above-mentioned object, a method for setting a tightening amount of a chuck of the present invention is a method for setting a tightening amount of a workpiece by a chuck when a chuck provided on a spindle of a machine tool clamps the workpiece.

[0022] The setting method comprises:

[0023] In a first step, when the amount of tightening of the chuck on the workpiece by the chuck in the closed state where the chuck clamps the workpiece is adjusted to a first tightening amount by the adjustment unit, the opening and closing unit causes the chuck to close so that the chuck changes from the open state where the workpiece can be attached and detached to the closed state;

[0024] A second step is to obtain, in the first step, a first time from when the control unit sends a control signal for the closing action to when the sensor detects that the chuck is no longer in the open state, and a second time from when the control unit sends a control signal to the opening and closing unit to when the sensor detects that the chuck is in the closed state;

[0025] A third step of obtaining a second tightening amount for obtaining a desired clamping force based on a correlation among a magnitude of a difference between the first time and the second time, a tightening amount of the chuck on the workpiece in the closed state adjusted by an adjustment unit, and a clamping force of the chuck on the workpiece in the closed state; and

[0026] In a fourth step, the adjustment unit adjusts the tightening amount to the second tightening amount obtained in the third step.

[0027] (Effects of the Invention)

[0028] According to the present invention, the chuck clamping force can be appropriately controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of a machine tool equipped with a workpiece recovery device according to an embodiment of the present invention.

[0030] Figure 2 Schematic cross-sectional view of the main structure around the main axis.

[0031] Figure 3 Schematic cross-sectional view of the main structure around the main axis.

[0032] Figure 4 It is a schematic cross-sectional view of the chuck jaws, bobbin, and surrounding structure of the chuck frame.

[0033] Figure 5 It is a schematic cross-sectional view of the chuck jaws, bobbin, and surrounding structure of the chuck frame.

[0034] Figure 6 It is a timing diagram of the chuck closing signal and the sensor response timing.

[0035] Figure 7 This is a graph showing the relationship between the tightening amount of the adjustment nut (nut angle) and the BA period.

[0036] Figure 8 This is a block diagram schematically showing an example of the structure of the machine tool according to the present embodiment.

[0037] Fig. 9 A diagram showing an example of the functional structure of the control unit.

[0038] Fig.10 Flow chart for producing clamping force related data.

[0039] Fig.11 Flow chart for detecting clamping force.

[0040] Fig.12 This is the timing diagram of the chuck open signal and the sensor response timing.

[0041] Fig.13 Flow chart for calibrating the clamping force. DETAILED DESCRIPTION

[0042] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments described below are merely exemplary of preferred structures of the present invention and are not intended to limit the scope of the present invention to these structures. In addition, unless otherwise specified, the hardware structure and software structure of the device, manufacturing conditions, functions, materials, shapes, relative configurations, etc. of the structural components in the following description are not intended to limit the scope of the present invention. In addition, in principle, the same reference numerals are given to the same components, and repeated descriptions are omitted.

[0043] (Example)

[0044] Figure 1 It is a schematic diagram schematically showing the structure of a machine tool 1 according to an embodiment of the present invention. Figure 1 The machine tool 1 shown is a so-called automatic lathe, which is a device that rotates a workpiece W such as a long bar as a workpiece and brings a cutting tool (processing tool) into contact with the workpiece W to perform cutting processing (turning processing).

[0045] The machine tool 1 generally includes a spindle unit 100 disposed on a base 2 and a tool rest 300. The spindle unit 100 has a spindle 101. The rotation axis direction of the spindle 101 is set as the Z axis direction, the direction parallel to the vertical direction in the direction orthogonal to the axis direction is set as the X axis direction, and the direction parallel to the horizontal direction in the direction orthogonal to the axis direction is set as the Y axis direction. Figure 1 This is a schematic diagram of the structure of the machine tool 1 when viewed in the Y-axis direction.

[0046] The spindle unit 100 includes: a spindle box 102 that can rotatably support the spindle 101, and a drive unit 103 for moving the spindle box 102 along the Z-axis direction on the base 2. As the drive unit, for example, a ball screw drive unit composed of a motor, a ball screw, a guide rail, etc. as a drive source can be used. In addition, the spindle unit 100 can also include a drive unit that moves the spindle box 102 not only along the Z-axis direction, but also along the Y-axis direction and the X-axis direction. The spindle 102, for example, includes a built-in motor (not shown), and is configured to be able to rotationally drive the spindle 101 by the rotational driving force of the built-in motor.

[0047] The spindle 101 has a hollow structure and is provided with a chuck, a chuck sleeve, a guide bush, etc. for clamping the workpiece W (a state in which the axes are aligned and the axial movement is restricted). The hollow structure has a workpiece holding hole for holding or clamping the workpiece W. The workpiece W is inserted from the spindle rear end opening of the workpiece holding hole in the axial direction, supplied to the workpiece holding hole, and clamped by the chuck at a specified insertion position. The portion of the workpiece W exposed from the spindle front end opening of the workpiece holding hole becomes the portion where turning processing is applied by the cutting tool 301 supported on the tool holder 300. The above-mentioned guide bushing not shown in the figure is, for example, arranged at the spindle front end opening of the workpiece holding hole, and maintains the posture of the workpiece W near the opening of the workpiece holding hole. In addition, the support structure of the workpiece W formed by the guide bushing can be a structure independent of the spindle unit 100.

[0048] exist Figure 1 The chuck and chuck sleeve not shown in the figure are structured as follows: the chuck sleeve is connected to the chuck structure whose movement in the axial direction is restricted from the rear through the tapered surface. The details will be described later. Figure 1 The chuck is moved in the axial direction by the force of the cylinder (not shown), thereby applying a force including a component force in the direction of the axis to the chuck, and a tightening force is generated in the chuck to close the gap provided in the chuck. Thus, the workpiece W is clamped.

[0049] The tool rest 300 is provided with a plurality of cutting tools 301 which are selectively prepared according to the type of target processing. The tool rest 300 is configured to be movable forward and backward along the X-axis direction relative to the workpiece W under the action of a driving unit (not shown), and a selected cutting tool 301 is brought into contact with the workpiece W to perform the desired cutting processing (turning processing) on ​​the workpiece W.

[0050] The machine tool 1 includes a control unit 200, which is composed of a computer having a processor such as a CPU (central processing unit) and a memory. The control unit 200 controls various operations of various parts of the machine tool 1, such as the spindle unit 100, the tool rest 300, a workpiece supply unit (not shown), an actuator 60 (described later), and a display unit 70.

[0051] Figure 2 , Figure 3 Each of them is a schematic cross-sectional view showing an enlarged view of the main structure around the main shaft 101 . Figure 2 The structure of each part in a state where a collet chuck 41 is closed (that is, a state where the workpiece W is clamped) is shown. Figure 3 The structure of each part in the state where the collet chuck 41 is opened (that is, in the state where the workpiece W can be attached to and detached from the main spindle 101) is shown. Figure 4 , Figure 5 These are schematic cross-sectional views showing enlarged main structures around a chuck jaw 47 , a bobbin 48 , and a chuck holder 50 . Figure 4 The structure of each part in the posture where the chuck jaws 47 are closed (that is, the closed state where the collet chuck 41 clamps the workpiece W) is shown. Figure 5 The structure of each part in a state where the chuck jaws 47 are opened (that is, in an open state where the workpiece W can be attached to and detached from the collet chuck 41 ) is shown.

[0052] like Figure 2 , Figure 3 As shown, the spindle 101 is rotatably assembled to the spindle box 102 via bearing devices 121, 122, and 123. The collet chuck 41 is assembled to the front end side of the axial direction of the spindle 101. The collet chuck 41 includes a hollow cylindrical body 411 capable of accommodating a workpiece W therein, and a clamping portion 412 provided on the front end side of the cylindrical body 411 in the direction of the central axis L (length direction).

[0053] The clamping portion 412 has a so-called slot structure and is configured to be able to elastically change the inner diameter size based on the central axis L1. That is, the clamping portion 412 is provided with a slit 413 extending from the end face of its front end side toward the rear end side and along the axial direction with a prescribed length. The slit 413 is formed to radially cut the clamping portion 412 relative to the central axis L, and a plurality of slits 413 are provided, for example, at equal intervals in the circumferential direction around the central axis L. A longitudinal segment 414 capable of achieving displacement in a radial direction centered on the central axis L1 is formed between these multiple slits 413. Each longitudinal segment 414 is configured to be in the shape of a leaf spring that can be elastically deformed in the above-mentioned radial direction with its base end as a fulcrum.

[0054] The inner surface of each longitudinal segment 414 facing the central axis L1 is a concave curved surface, and cooperates with each other to form a substantially cylindrical workpiece clamping surface 415 in the clamping portion 412. In addition, the outer surface of each longitudinal segment 414 includes an inclined surface inclined with respect to the axial direction, and the inclined surfaces cooperate with each other to form a tapered force-bearing surface 416 whose diameter gradually increases toward the front end in the axial direction. In addition, a shoulder surface 417 extending perpendicularly to the central axis L1 is formed at a position closer to the front end in the axial direction of each longitudinal segment 414 than the force-bearing surface 416.

[0055] The plurality of longitudinal split pieces 414 exert radially inward external forces through the force-bearing surface 416, thereby causing elastic deflection, and the diameter of the workpiece clamping surface 415 is reduced until it is in close contact with the workpiece W, thereby firmly and fixedly clamping the workpiece W. If the radial pressure on the clamping portion 412 is released, each longitudinal split piece 414 elastically recovers and the diameter of the workpiece clamping surface 415 is expanded, so that the workpiece W is released from the clamping portion 412.

[0056] A cap nut 42 is mounted at the front end of the workpiece holding hole of the spindle 101. The cap nut 42 has a stopper surface 421, which is an end surface facing the rear end side in the axial direction and abuts against the shoulder surface 417 of the collet chuck 41 in the axial direction. In addition, a chuck sleeve 43 as a second acting member is assembled in the workpiece holding hole of the spindle 101 in such a manner that the spring chuck 41 is sandwiched between the cap nut 42 and the cap nut 42.

[0057] The chuck sleeve 43 is a hollow cylindrical body capable of accommodating the workpiece W and the collet chuck 41 surrounding the workpiece W. The chuck sleeve 43 has a force-applying surface 431 on its inner surface for applying force to the force-bearing surface 416 of the collet chuck 41, and is assembled with a compression coil spring 44 as an elastic member applying force in the axial direction to the collet chuck 41. The chuck sleeve 43 has a spring receiving surface 432, and the compression coil spring 44 is compressed in the axial direction between the spring receiving surface 432 and the axial rear end surface of the collet chuck 41. Under the action of the urging force of the compression coil spring 44, the shoulder surface 417 of the collet chuck 41 abuts against the stop surface 421, and the collet chuck 41 is pressed against the cap nut 42 in the axial direction.

[0058] The force-applying surface 431 is a tapered surface whose diameter gradually increases toward the front end in the axial direction, and faces the surface that abuts against the force-receiving surface 416 in the axial direction along the central axis L1 and in the radial direction centered on the central axis L1. The force-applying surface 431 applies a radially inward force to the force-receiving surface 416, thereby performing the action of the clamping portion 412 of the collet chuck 41 clamping the workpiece W as described above.

[0059] In the workpiece holding hole of the spindle 101, a chuck opening and closing sleeve 45 and a balance sleeve 46 are provided at the rear end side in the axial direction of the chuck sleeve 43, which are hollow cylindrical bodies capable of accommodating the workpiece W therein. The chuck sleeve 43, the chuck opening and closing sleeve 45 and the balance sleeve 46 are configured such that they are arranged in series in the axial direction, are joined to each other in the axial direction, and can be displaced in the axial direction as a second acting member. The rear end in the axial direction of the balance sleeve 46 is provided with an acted surface 461 that receives an acting force.

[0060] The spindle 101 is provided with a chuck jaw 47 as a first acting member, and the chuck jaw 47 is a member for applying an acting force to the acted surface 461 of the balance sleeve 46. A plurality of chuck jaws 47 are provided around the central axis L1, for example, at equal intervals. Each chuck jaw 47 has an acting portion 471 that abuts against the acted surface 461 along the axial direction, and is configured to be rotatable relative to the spindle 101 around a rotation axis 472, which is an axis along a tangent direction of an imaginary circle centered on the central axis L1. The plurality of chuck jaws 47 are integrally supported by a chuck frame 50, and the plurality of chuck jaws 47 are mounted on the spindle 101 through the chuck frame 50.

[0061] The chuck jaw 47 rotates in a manner that allows the action portion 471 to be in a closed posture in which the action portion 471 advances in the front side in the axial direction and in an open posture in which the action portion 471 retreats in the rear side in the axial direction. The chuck jaw 47 has an acted portion 473 that receives a driving force for realizing the above-mentioned posture change. A bobbin 48 is installed on the cylindrical wall of the main shaft 101 as a direct-transport type action member that applies a driving force to the acted portion 473, and the bobbin 48 can achieve displacement in the axial direction. Specifically, the bobbin 48 is configured as a part of a bearing device 123 that can be displaced in the axial direction relative to the main shaft 101. The bearing device 123 is displaced in the axial direction relative to the main shaft 101 under the action of the driving force from the actuator 60 as a driving unit. Under the displacement of the bearing device 123 in the axial direction, the bobbin 48 can move between an action position that makes the chuck jaw 47 in a closed posture and an acted position that makes the chuck jaw 47 in an open posture.

[0062] The bobbin 48 has an action portion 481, which is a substantially conical outer peripheral surface extending in a manner that the diameter gradually decreases toward the rear end in the axial direction. When the bobbin 48 is in the action position, the chuck jaw 47 is in a state where the action portion 473 contacts the action portion 481 and mounts on the bobbin 48, and becomes a closed posture due to rotation during the mounting process. In addition, when the bobbin 48 is in the action position, the action portion 473 separates from the action portion 481 and contacts the outer peripheral surface of the spindle 101, so that the chuck jaw 47 and the bobbin 48 are in a non-contact state, and becomes an open posture due to rotation during the process of descending from the bobbin 48.

[0063] The actuator 60 includes a cylinder 61 and an arm 62 connecting a rod 610 of the cylinder 61 and a bearing device 123. The arm 62 is mounted on the spindle housing 102 so as to be rotatable around a rotation axis 622, and is rotatably connected to the rod 610 via a rotation axis 621, and is rotatably connected to the bearing device 123 via a rotation axis 623. The rod 610 of the cylinder 61 reciprocates in the direction along the central axis L, and the arm 62 rotates around the rotation axis 622 by the reciprocating motion of the rod 610. For example, the rotation axis 623 connecting the bearing device 123 and the arm 62 is configured to be displaceable in the longitudinal direction of the arm 62, and is displaced in the longitudinal direction of the arm and in the direction along the central axis L by the rotation of the arm 62. As a result, the bearing device 123 is displaced in the axial direction on the spindle 101, and the relative position of the bobbin 48 in the axial direction with respect to the chuck jaws 47 changes.

[0064] When the chuck jaws 47 are changed from the open position to the closed position, the acting portion 471 presses the acted surface 461 toward the front side in the axial direction, and the balance sleeve 46, the chuck opening and closing sleeve 45, and the chuck sleeve 43 are pressed toward the front side in the axial direction in sequence. As a result, a force toward the radial inside is applied from the force applying surface 431 of the chuck sleeve 43 to the force receiving surface 416 of the collet chuck 41, so that the amount of tightening of the collet chuck 41 on the workpiece W increases, and the workpiece W is firmly and fixedly clamped in the closed state.

[0065] When the chuck jaws 47 are changed from the closed posture to the open posture, the action portion 471 retreats in the axial direction rearward, and the chuck sleeve 43, the chuck opening and closing sleeve 45, and the balance sleeve 46 are pressed in sequence in the axial direction rearward under the urging force of the compression coil spring 44. As a result, the radially inward force from the force-applying surface 431 of the chuck sleeve 43 to the force-receiving surface 416 of the collet chuck 41 is released, so that the amount of tightening of the collet chuck 41 on the workpiece W is reduced, and the workpiece W is in the open state in which it can be freely attached to and detached from the collet chuck 41.

[0066] The air cylinder 61 is provided with a chuck open position sensor 71 and a chuck closed position sensor 72. The chuck open position sensor 71 is configured to be in a retracted position ( Figure 2 ) when the chuck closed position sensor 72 is configured to react when the stroke of the rod 610 is in the extended position ( Figure 3 ) The structure of the sensors 71 and 72 may include, for example, an optical sensor for detecting a mark provided on the rod 610, but an existing well-known sensor may be used as appropriate.

[0067] like Figure 4 , Figure 5 As shown in the figure, an adjustment nut 51 is screwed on the cylindrical wall of the spindle 101 at the rear end side in the axial direction of the chuck frame 50. The chuck frame 50 is provided so as to be movable in the axial direction on the outer peripheral surface of the spindle 101 by a guide unit (not shown) provided on the cylindrical wall of the spindle 101. The adjustment nut 51 abuts against the chuck frame 50 in the axial direction against the applied force of the compression coil spring 44 applied via the chuck sleeve 43, the chuck opening and closing sleeve 45, the balance sleeve 46, the chuck claw 47, and the chuck frame 50. The adjustment nut 51 is configured so as to be able to adjust the position in the axial direction relative to the spindle 101 by tightening or loosening it relative to the spindle 101. Therefore, by adjusting the position in the axial direction of the adjustment nut 51, the position in the axial direction of the chuck frame 50, that is, the position in the axial direction of the chuck claw 47 can be adjusted. By adjusting the position of the chuck jaws 47 in the axial direction (adjusting the tightening amount of the adjustment nut 51 ), the tightening amount of the workpiece W by the collet chuck 41 in the closed state can be adjusted.

[0068] Here, the inventor of the present invention has found through careful research that the difference in the tightening amount (nut angle) of the adjustment nut 51 will cause the difference between the timing when the above-mentioned chuck open position sensor 71 responds and the timing when the chuck closed position sensor 72 responds to be different.

[0069] When the rod 610 is in the retracted position (or exceeds the prescribed retracted reference position), the chuck open position sensor 71 outputs an open (ON) signal, and when the rod 610 deviates from the retracted position due to the stroke (or does not reach the retracted reference position), the chuck open position sensor 71 outputs a closed (OFF) signal. Similarly, when the rod 610 is in the extended position (or exceeds the prescribed extended reference position), the chuck closed position sensor 72 outputs an open (ON) signal, and when the rod 610 deviates from the extended position due to the stroke (or does not reach the extended reference position), the chuck closed position sensor 72 outputs a closed (OFF) signal. Therefore, in the stroke of the rod 610, there is a transition period in which the chuck open position sensor 71 and the chuck closed position sensor 72 do not respond (both output closed (OFF) signals). The length of this transition period varies according to the tightening amount of the adjustment nut 51.

[0070] Figure 6This is a timing chart showing the timing of the control unit 200 sending a chuck closing signal to the actuator 60 and the reaction timing of the chuck open position sensor 71 and the chuck closed position sensor 72. When the actuator 60 closes the collet chuck 41 and changes the collet chuck 41 from an open state to a closed state, the period from when the control unit 200 sends a control signal for the closing operation to the actuator 60 until the output of the chuck open position sensor 71 switches from open (ON) to closed (OFF) (first time) is set as A. In addition, if the period from when the control unit 200 sends a control signal for the closing operation to the actuator 60 until the output of the chuck closed position sensor 72 switches from closed (OFF) to open (ON) (second time) is set as B, a period BA (difference time) as a transition period is generated.

[0071] During period A, i.e., until the output of the chuck open position sensor 71 switches from open (ON) to closed (OFF), the position is where no load is applied during the chuck action, so the detection timing is substantially constant regardless of the tightening amount of the adjustment nut 51. In contrast, during period B, i.e., until the output of the chuck closed position sensor 72 switches from closed (OFF) to open (ON), the action period is where a load is applied during the chuck action, so the detection timing may deviate depending on the tightening amount of the adjustment nut 51. Therefore, the size of the period BA, which is a transition period, changes.

[0072] Figure 7 : is a graph showing an example of changes in the BA period when the tightening amount (nut angle) of the adjustment nut 51 is changed. Figure 7 As shown, when the nut angle changes to 30°, 60°, 90°, 120°, and 150°, the BA period is plotted as 0.068, 0.075, 0.082, 0.088, and 0.102, respectively. From these results, it can be seen that the tightening amount of the adjustment nut 51 and the BA period have a substantially linear relationship.

[0073] Regarding the adjustment of the clamping force, the reference point of the angle (axial position) of the adjustment nut 51 is usually determined first, and then the tightening angle relative to the reference point is adjusted to set the desired clamping force. As an existing method for determining the reference point, for example, there is a method of adjusting the axial position of the adjustment nut 51 to a state in which the front end of the acted portion 473 touches the acting portion 481 when the chuck claw 47 is not mounted on the bobbin 48, and setting the nut angle at this time as the reference angle. However, it is difficult to achieve such a setting of the reference point uniquely and always constantly. In contrast, as in the present embodiment, the adjustment amount of the adjustment nut 51 (the tightening amount of the collet chuck 41) is set in association with the time difference of the sensor detection timing, thereby making it easy to grasp the clamping force regardless of the setting of the reference point.

[0074] Figure 8 This is a block diagram schematically showing an example of the structure of the machine tool according to the present embodiment.

[0075] The control unit 200 has a general computer structure. The control unit 200 has: a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202, a RAM (Random Access Memory) 203, and an input / output interface 204. In addition, the control unit 200 has an input unit 81 and an output unit 82. These components are connected to each other through a bus. The bus is connected to various sensors including a chuck open position sensor 71 and a chuck closed position sensor 72 through the input / output interface 204, and signals from these sensors are input to the control unit 200. On the other hand, the bus is connected to an actuator for driving the spindle unit 100 and the tool rest 300, an actuator 60 for opening and closing the collet chuck 41, etc. through the input / output interface 204, and control signals are sent from the control unit 200 to these devices.

[0076] The CPU 201 controls the machine tool 1 and performs various information processing calculations. The ROM 202 and RAM 203 as storage components store an operating system (OS), various programs, various work tables, etc. Each component is controlled by executing the stored program. Thus, the control unit 200 realizes functions that meet the prescribed purpose. In addition, the control unit 200 can be a single computer or a component formed by the cooperation of multiple computers.

[0077] The input unit 81 is a component for receiving input operations performed by the user, and may include, for example, a touch panel, a mouse, a keyboard, or a microphone. The output unit 82 is a component for presenting information to the user, and may include, for example, an LCD (Liquid Crystal Display), an EL (Electroluminescence) panel, a speaker, a lamp, etc. In addition, the input unit 81 and the output unit 82 may also constitute a touch screen display.

[0078] Fig. 92 is a diagram showing an example of the functional structure of the control unit 200. The control unit 200 includes, as functional components, a processing control unit 211, a clamping force acquisition unit 212, and a clamping force correction unit 213. The processing control unit 211, the clamping force acquisition unit 212, and the clamping force correction unit 213 are functional components provided by, for example, causing the CPU 201 of the control unit 200 to execute various programs stored in the ROM 202 and the RAM 203.

[0079] The machining control unit 211 controls the machine tool 1 when machining the workpiece W. The machining control unit 211 performs control such as cutting the workpiece W by fastening the workpiece W by the collet chuck 41, rotating the spindle 101, and moving the cutting tool 301 of the tool holder 300, thereby cutting the workpiece W. The machining control of the workpiece W performed by the machining control unit 211 can use a known technique.

[0080] The clamping force acquisition unit 212 acquires the clamping force of the collet chuck 41 on the workpiece W in the closed state based on the magnitude of the above-mentioned BA period. The clamping force is acquired based on the correlation between the above-mentioned BA period and the nut tightening amount. That is, the above-mentioned BA period and the nut tightening amount (based on the adjustment amount of the adjustment nut 51) are linearly correlated with each other, and the nut tightening amount is linearly correlated with the tightening amount of the collet chuck 41 on the workpiece W in the closed state. For example, a plurality of specific numerical values ​​in kilogram-force (kgf) can be acquired in advance by installing a torque sensor on the collet chuck 41 in an experiment and detecting it, and the clamping force corresponding to the nut tightening amount can be calculated / acquired based on the plurality of measured values ​​and according to the above-mentioned linear relationship. As a notification to inform the user of the clamping force, in addition to prompting a specific numerical value, the nut tightening amount can also be divided into a plurality of stages according to a specified numerical range, and a level display of the strength level of the clamping force can be shown in each stage.

[0081] Fig.10 This is a flow chart of the preparation of clamping force related data based on the clamping force acquisition unit. It is preferred to prepare the clamping force related data in the preparation and adjustment stage before starting the actual product processing. That is, as the workpiece W used in this process, a prepared workpiece W can be used instead of the workpiece W processed as the actual product.

[0082] First, the control unit 200 sends a chuck closing motion signal to the actuator 60, so that the collet chuck 41 performs a closing motion to grip the workpiece W (S101). Then, at this time, a period A from the issuance of the closing motion control signal to the detection by the chuck open position sensor 71 that the collet chuck 41 is no longer in the open state and a period B from the issuance of the closing motion control signal to the detection by the chuck closed position sensor 72 that the collet chuck 41 is in the closed state are acquired (S102, S103). The control unit 200 stores the acquired periods A and B and the period BA acquired through the periods A and B in the storage unit.

[0083] When the data of the number of periods A and B required for obtaining the clamping force and obtaining the correlation between the BA period and the nut tightening amount (clamping force) have been obtained (S104, "Yes"), the correlation data between the BA period and the clamping force are prepared (S107). When the number of data of the periods A and B is insufficient (S104, "No"), the data is obtained again. That is, the collet chuck 41 is opened (S105), the angle of the adjustment nut 51 is changed, and the position of the chuck jaws 47 is changed (S106). The change in the adjustment amount of the adjustment nut 51 can be made manually by the user, and when it can be adjusted automatically, it can be changed on the device side. Repeat S101 to S106 until the required data is prepared.

[0084] Fig.11 For use through Fig.10 Flow chart of the chuck clamping force detection to obtain the clamping force data. The clamping force detection can be Fig.10 Similarly, it can be performed in the adjustment stage before processing the actual product, or it can be performed when processing the actual product.

[0085] A chuck closing action signal is sent from the control unit 200 to the actuator 60, causing the collet chuck 41 to close and grip the workpiece W (S201). At this time, the angle of the pre-adjusted adjustment nut 51 can be set to an angle with a specified margin compared to the actual angle during processing. That is, here, the tightening amount of the collet chuck 41 adjusted by the adjustment nut 51 is a temporary tightening amount (first tightening amount) for obtaining the optimal tightening amount (second tightening amount). Then, a period A from the issuance of the closing action control signal to the detection by the chuck open position sensor 71 that the collet chuck 41 is no longer in the open state and a period B from the issuance of the closing action control signal to the detection by the chuck closed position sensor 72 that the collet chuck 41 is in the closed state are obtained (S202, S203). Then, the BA period obtained based on the obtained periods A and B is compared with the period B obtained in Fig.10The corresponding clamping force is obtained by comparing the obtained correlation (clamping force data) with the clamping force or calculating based on the correlation, thereby obtaining the corresponding clamping force (S204). Then, the obtained clamping force is notified to the user through the output unit 82 as a notification component (S205).

[0086] Through the above processing, the user who has been notified of the clamping force can adjust the nut 51 to the desired clamping force based on the notified clamping force when necessary. In addition, when notifying the user in S205, the correlation between the nut adjustment amount and the clamping force can be displayed together. Alternatively, when the desired clamping force is input in advance through the input unit 81, the nut adjustment amount (second tightening amount) required to obtain the desired clamping force can also be obtained in S204 and prompted to the user in S205.

[0087] The clamping force correction unit 213 corrects the correlation between the obtained BA period and the clamping force (clamping force data). As described above, period A is a position where basically no load is applied (no significant change in load) during the chuck action, and the detection timing becomes a substantially constant timing regardless of the tightening amount of the adjustment nut 51. However, for example, in the case of long-term use, there is a situation where changes occur due to the influence of changes in the state of the gas supply pressure of the cylinder 61, the state of the lubricating oil between the chuck claw 47 and the barrel 48, etc. For example, when the gas supply pressure of the cylinder 61 drops from the standard 0.5MPa to 0.4MPa, time A will be extended, and along with it, period B will also be extended. In order to cope with such changes in the device action over time, it is better to correct the clamping force. Therefore, in this embodiment, the delay time (coefficient) is obtained based on the offset time (CD period) of the sensor detection timing when the closing action is performed over time, and the offset time (BA period) in the closing action is corrected.

[0088] Fig.12 This is a timing chart showing the timing of the control unit 200 sending the chuck opening signal to the actuator 60 and the reaction timing of the chuck opening position sensor 71 and the chuck closing position sensor 72. When the actuator 60 closes the collet chuck 41 and changes the collet chuck 41 from the closed state to the open state, the period from when the control unit 200 sends the opening control signal to the actuator 60 to when the output of the chuck closing position sensor 72 switches from open (ON) to closed (OFF) (third time) is set as C. In addition, if the period from when the control unit 200 sends the opening control signal to the actuator 60 to when the output of the chuck opening position sensor 71 switches from closed (OFF) to open (ON) (fourth time) is set as D, a DC period (differential time) as a transition period is generated.

[0089] As described above, the DC period as the transition period may change due to changes in the device operation over time. Therefore, by comparing the DC period in the new state with the DC period in the state where the device has been operated to a certain extent (i.e., a state where wear and tear has occurred), it is possible to obtain a coefficient (delay time) for correcting the clamping force data. By correcting the clamping force data using this coefficient, it is possible to obtain the optimal clamping force.

[0090] Fig.13 This is a flowchart of the correction of the clamping force related data by the clamping force acquisition unit. After the reference clamping force related data when the device is in a new state is created, this operation is performed when the clamping force related data is acquired again every time the device has been operated for a predetermined number of times.

[0091] First, the control unit 200 sends a chuck opening motion signal to the actuator 60, so that the collet chuck 41 performs an opening motion to release the workpiece W (S301). Then, at this time, the period C from the issuance of the opening motion control signal to the detection of the collet chuck 41 being no longer in the closed state by the chuck closed position sensor 72 and the period D from the issuance of the opening motion control signal to the detection of the collet chuck 41 being in the open state by the chuck open position sensor 71 are acquired (S302, S303). The control unit 200 stores the acquired periods C and D and the DC period acquired through the periods C and D in the storage unit.

[0092] When the data of the periods C and D required for the correlation between the DC period and the nut tightening amount (clamping force) required for obtaining the clamping force have been obtained (S304, "Yes"), the correlation data between the DC period and the clamping force are prepared (S307). When the number of data of the periods C and D is insufficient (S304, "No"), the data is obtained again. That is, after changing the angle of the adjustment nut 51 and changing the position of the chuck jaws 47 (S305), the collet chuck 41 is closed (S306) and the workpiece W is gripped again. The change in the adjustment amount of the adjustment nut 51 can be made manually by the user, and when it can be adjusted automatically, it can be changed on the device side. Repeat S301 to S306 until the required data is prepared.

[0093] The latest clamping force data (C', D') obtained by the above processing is compared with the reference clamping force data (C, D) obtained at the beginning of use to obtain the delay time (coefficient), and the clamping force data corresponding to the BC period is corrected (S308). For example, C' / C = α is used as the coefficient to correct BA in the latest clamping force data (α (BA)). In this way, by using the corrected clamping force data, a more appropriate clamping force setting that reflects the time-varying changes of the device can be achieved.

[0094] As described above, according to the present embodiment, the adjustment amount of the adjustment nut 51 (the tightening amount of the collet chuck 41) is set in association with the time difference of the sensor detection timing, thereby enabling the optimal clamping force to be set regardless of the setting of the reference point. That is, the clamping force of the chuck can be appropriately controlled, and the processing accuracy can be improved.

[0095] Furthermore, according to this embodiment, there is no need to add an additional device structure, and the clamping force of the chuck that is difficult to directly obtain (digitize) can be more appropriately obtained using the device structure of the machine tool itself, thereby achieving digitization.

[0096] In addition, the specific structures of the spindle unit, the collet chuck, the chuck sleeve, the chuck jaws and the like, the actuator for operating the units, the opening and closing sensors and the like shown in the present embodiment are only examples. That is, other existing known structures may be appropriately adopted.

[0097] (Explanation of Reference Numerals)

[0098] 1: machine tool; 100: spindle unit; 101: spindle; 102: spindle box;

[0099] 103: driving unit; 2: base; 200: control unit; 300: tool holder;

[0100] 301: cutting tool; 41: collet chuck; 43: chuck sleeve;

[0101] 44: Compression coil spring; 45: Chuck opening and closing sleeve; 46: Balance sleeve;

[0102] 47: chuck jaws; 48: bobbin; 60: actuator; W: workpiece.

Claims

1. A machine tool comprising: A spindle having a chuck for holding a workpiece; an opening and closing unit that moves the chuck to place the chuck in either a closed state for clamping a workpiece or an open state for attaching or detaching the workpiece; a sensor for respectively detecting whether the chuck is in the closed state and whether the chuck is in the open state; as well as A control unit controls the opening and closing unit, characterized in that: The machine tool includes an acquisition component, which acquires the clamping force of the chuck on the workpiece in the closed state based on the difference between a first time and a second time when the opening and closing unit causes the chuck to perform a closing action and causes the chuck to change from the open state to the closed state, wherein the first time is the time from the time the control unit sends a control signal for the closing action to the opening and closing unit to the time the sensor detects that the chuck is no longer in the open state, and the second time is the time from the time the control unit sends the control signal to the opening and closing period to the time the sensor detects that the chuck is in the closed state.

2. The machine tool according to claim 1, wherein: The machine tool also has: an adjustment unit capable of adjusting a tightening amount of the chuck to the workpiece in the closed state; and A storage component stores the correlation between the magnitude of the difference, the tightening amount, and the clamping force.

3. The machine tool according to claim 2, wherein: The machine tool also includes: a correction component, which corrects the correlation based on the change over time of the size of the second difference between a third time and a fourth time when the opening and closing unit causes the chuck to perform an opening action and causes the chuck to change from the closed state to the open state, wherein the third time is the time from the control unit sending the control signal of the opening action to the opening and closing unit to the sensor detecting that the chuck is no longer in the closed state, and the fourth time is the time from the control unit sending the control signal to the opening and closing period to the sensor detecting that the chuck is in the open state.

4. The machine tool according to claim 1, wherein: The machine tool further includes a notification unit configured to notify the outside of the information including the clamping force.

5. The machine tool according to claim 2, wherein: The opening and closing unit comprises: A first acting member, which is disposed on the spindle and can act on the chuck to bring the chuck into the closed state and the open state; a second acting member, which is provided on the main shaft and can displace the relative position with respect to the first acting member in the direction of the rotation axis of the main shaft, so as to realize a closed position in which the first acting member is in the closed posture by acting on the first acting member and an open position in which the first acting member is in the open posture by acting on the first acting member; as well as The driving unit includes an air cylinder and moves the second acting member between the open position and the closed position.

6. The machine tool according to claim 5, wherein: The adjustment unit changes the tightening amount of the chuck by changing the position of the first acting member relative to the spindle in the rotation axis direction.

7. The machine tool according to claim 6, wherein: The sensor detects whether the driving unit is in a state where the second acting member is located at the closed position and whether the driving unit is in a state where the second acting member is located at the open position.

8. A method for detecting the clamping force of a chuck, which detects the clamping force of a chuck on a workpiece when the chuck of a spindle of a machine tool clamps the workpiece, characterized in that: The detection method comprises: In a first step, an opening and closing unit causes the chuck to perform a closing action so that the chuck changes from an open state in which the workpiece can be attached and detached to a closed state in which the workpiece is clamped; A second step is to obtain a first time from when the control unit sends a control signal for the closing action to the opening and closing unit until the sensor detects that the chuck is no longer in the open state and a second time from when the control unit sends a control signal to the opening and closing unit until the sensor detects that the chuck is in the closed state in the first step; and In a third step, the clamping force is obtained based on a correlation among a magnitude of a difference between the first time and the second time, an amount of tightening of the workpiece by the chuck in the closed state adjusted by an adjustment unit, and the clamping force.

9. The method for detecting the clamping force of a chuck according to claim 8, wherein: The detection method further comprises: In a fourth step, the opening and closing unit causes the chuck to open so that the chuck changes from the closed state to the open state; A fifth step is to obtain a third time from when the control unit sends a control signal for the opening action to the opening and closing unit to when the sensor detects that the chuck is no longer in the closed state and a fourth time from when the control unit sends the control signal to the opening and closing unit to when the sensor detects that the chuck is in the open state in the fourth step; and In a sixth step, the correlation is corrected based on a change over time in the magnitude of a difference between the third time and the fourth time when the fourth step and the fifth step are repeated.

10. A method for setting the tightening amount of a chuck, which is a method for setting the tightening amount of a workpiece clamped by a chuck provided on a spindle of a machine tool, wherein: The setting method comprises: In a first step, when the amount of tightening of the chuck on the workpiece by the chuck in the closed state where the chuck clamps the workpiece is adjusted to a first tightening amount by the adjustment unit, the opening and closing unit causes the chuck to close so that the chuck changes from the open state where the workpiece can be attached and detached to the closed state; A second step is to obtain, in the first step, a first time from when the control unit sends a control signal for the closing action to when the sensor detects that the chuck is no longer in the open state, and a second time from when the control unit sends a control signal to the opening and closing unit to when the sensor detects that the chuck is in the closed state; A third step of obtaining a second tightening amount for obtaining a desired clamping force based on a correlation among a magnitude of a difference between the first time and the second time, a tightening amount of the chuck on the workpiece in the closed state adjusted by an adjustment unit, and a clamping force of the chuck on the workpiece in the closed state; and In a fourth step, the adjustment unit adjusts the tightening amount to the second tightening amount obtained in the third step.

Images