Machine tool, method for detecting gripping force of chuck, and method for setting tightening amount of chuck

Abstract

To provide a technique cable of appropriately controlling a chuck gripping force.SOLUTION: A machine tool comprises a main spindle equipped with a chuck for gripping a workpiece. A chuck gripping force with respect to the workpiece in a closed state is acquired on the basis of the size of a difference between first time from issuing of a control signal of a closed operation from the control unit to an opening / closing mechanism to detection of the opened state of the chuck by a sensor and second time from issuance of the control signal from the control signal during an opening / closing period to detection of the closed state of the chuck by the sensor when the opening / closing mechanism closes the chuck so as to change from the opened state to the closed state.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] In a machine tool that rotates a spindle that holds a workpiece and moves a processing tool forward and backward relative to the rotating workpiece to perform processing, an important factor in machining accuracy is whether the chuck (gripping jaws) can properly hold the workpiece. Patent Document 1 discloses that the relationship between the amount of fastening caused by the rotation of the spindle motor from when the chuck comes into contact with the workpiece until a predetermined gripping force is generated and the gripping force of the chuck is determined in advance, and the rotation angle of the spindle motor is controlled to control the gripping force of the chuck. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-096409 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, it is not easy to directly measure the gripping force of the chuck, and a method is used in which the gripping force is grasped from the control amount of the mechanism that operates the chuck. However, the relationship between the control amount and the gripping force is often not always constant due to various factors such as the progress of wear of the chuck and changes in the lubrication state.

[0005] An object of the present invention is to provide a technique that enables appropriate control of the chuck gripping force. [Means for solving the problem]

[0006] In order to achieve the above object, the machine tool of the present invention comprises: A spindle equipped with a chuck for gripping a workpiece; an opening / closing mechanism that operates the chuck so that the chuck is in either a closed state in which the chuck holds a workpiece or an open state in which the chuck can attach and detach the workpiece; a sensor for detecting whether the chuck is in the closed state and a sensor for detecting whether the chuck is in the open state; A control unit that controls the opening and closing mechanism; In a machine tool comprising: The present invention is characterized in that it further comprises an acquisition means for acquiring the gripping force of the chuck against the workpiece in the closed state based on the magnitude of the difference between a first time from when the control unit issues a control signal for the closing operation to the opening and closing mechanism to when the sensor detects that the chuck is no longer in the open state, and a second time from when the control unit issues the control signal during the opening and closing period to when the sensor detects that the chuck has entered the closed state, when the opening and closing mechanism performs a closing operation to change the chuck from the open state to the closed state.

[0007] In order to achieve the above object, the present invention provides a method for detecting a gripping force of a chuck, comprising the steps of: A method for detecting a gripping force of a chuck provided on a spindle of a machine tool against a workpiece when the chuck grips the workpiece, comprising: An opening and closing mechanism opens the chuck from an open state in which the workpiece can be attached and detached to a state in which the workpiece is gripped. A first step of performing a closing operation so as to achieve a closed state in which the door is closed; a second step of acquiring a first time from when the control unit issues a control signal for the closing operation to the opening / closing mechanism to when a sensor detects that the chuck is no longer in the open state, and a second time from when the control unit issues the control signal to the opening / closing mechanism to when the sensor detects that the chuck is in the closed state, in the first step; a third step of acquiring the gripping force based on a correlation between a magnitude of a difference between the first time and the second time, a clamping amount of the chuck with respect to the workpiece in the closed state adjusted by an adjustment mechanism, and the gripping force; The present invention is characterized by comprising:

[0008] In order to achieve the above object, the method for setting the tightening amount of a chuck of the present invention comprises the steps of: A method for setting a clamping amount of a chuck provided on a spindle of a machine tool with respect to a workpiece when the chuck grips the workpiece, comprising: a first step of adjusting a clamping amount of the chuck with respect to the workpiece in a closed state in which the chuck grips the workpiece to a first clamping amount by an adjustment mechanism, and causing an opening / closing mechanism to close the chuck from an open state in which the chuck is in a position to allow attachment and detachment of the workpiece to the closed state; a second step of acquiring a first time from when the control unit issues a control signal for the closing operation to the opening / closing mechanism to when a sensor detects that the chuck is no longer in the open state, and a second time from when the control unit issues the control signal to the opening / closing mechanism to when the sensor detects that the chuck is in the closed state, in the first step; a third step of acquiring a second clamping amount that provides a desired gripping force based on a correlation between a magnitude of a difference between the first time and the second time, a clamping amount of the chuck on the workpiece in the closed state adjusted by an adjustment mechanism, and a gripping force of the chuck on the workpiece in the closed state; a fourth step of adjusting the tightening amount to the second tightening amount obtained in the third step by the adjustment mechanism; The present invention is characterized by comprising: Effect of the Invention

[0009] According to the present invention, the chuck gripping force can be appropriately controlled. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of a machine tool equipped with a workpiece recovery device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the main components around the spindle. [Diagram 3]FIG. 2 is a schematic cross-sectional view of the main components around the spindle. [Figure 4] FIG. 2 is a schematic cross-sectional view of a chuck jaw, a bobbin, a chuck holder, and the surrounding structure. [Diagram 5] FIG. 2 is a schematic cross-sectional view of a chuck jaw, a bobbin, a chuck holder, and the surrounding structure. [Figure 6] 4 is a timing chart of a chuck closing signal and a sensor response timing. [Figure 7] 1 is a relationship diagram between the tightening amount (nut angle) of the adjusting nut and the BA period. [Figure 8] 1 is a block diagram illustrating an example of a configuration of a machine tool according to an embodiment of the present invention. [Figure 9] FIG. 4 illustrates an example of a functional configuration of a control unit. [Figure 10] 13 is a flowchart for generating grip force correlation data. [Figure 11] 13 is a flowchart of gripping force detection. [Figure 12] 4 is a timing chart of a chuck open signal and a sensor response timing. [Figure 13] 13 is a flowchart of gripping force correction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Preferred embodiments of the present invention will be described below with reference to the drawings. However, the embodiments described below are merely illustrative of preferred configurations of the present invention, and the scope of the present invention should not be limited to those configurations. In the following description, the hardware and software configurations of the device, manufacturing conditions, functions, materials, shapes, relative arrangements of components, and the like are not intended to limit the scope of the present invention unless otherwise specified. In addition, the same components are generally given the same reference numbers, and repeated explanations are omitted.

[0012] (Example) Fig. 1 is a schematic diagram showing the configuration of a machine tool 1 according to an embodiment of the present invention. The machine tool 1 shown in Fig. 1 is a so-called automatic lathe device, which rotates a workpiece W, such as a long bar, and brings a cutting tool (machining tool) into contact with the workpiece to perform cutting (turning).

[0013] Machine tool 1 generally includes a spindle mechanism 100 arranged on a base 2, and a tool rest 300. Spindle mechanism 100 has a spindle 101. The direction of the rotation axis of spindle 101 is defined as the Z-axis direction, and among the directions perpendicular to the axial direction, a direction parallel to the vertical direction is defined as the X-axis direction, and a direction parallel to the horizontal direction is defined as the Y-axis direction. Figure 1 is a schematic diagram of the configuration of machine tool 1 as viewed in the Y-axis direction.

[0014] The spindle mechanism 100 includes a headstock 102 that rotatably supports the spindle 101, and a drive mechanism 103 for moving the headstock 102 in the Z-axis direction on the base 2. As the drive mechanism, for example, a ball screw drive mechanism including a motor as a drive source, a ball screw, a guide rail, and the like may be adopted. The spindle mechanism 100 may also include a drive mechanism for moving the headstock 102 not only in the Z-axis direction, but also in the Y-axis direction or the X-axis direction. The headstock 102 includes, for example, a built-in motor (not shown) and is configured to be able to rotate the spindle 101 by the rotational drive force of the motor.

[0015] The spindle 101 has a hollow structure with a workpiece holding hole for holding or gripping the workpiece W, and is provided with a chuck, chuck sleeve, guide bush, etc. for holding the workpiece W (a state in which the axial center is aligned and the movement in the axial direction is restricted). The workpiece W is inserted and fed in the axial direction from the spindle rear end opening of the workpiece holding hole, and is gripped by the chuck at a predetermined insertion position. The part of the workpiece W exposed from the spindle tip opening of the workpiece holding hole is the part to be turned by the cutting tool 301 supported by the tool rest 300. The above-mentioned guide bush (not shown) is provided, for example, at the spindle tip opening of the workpiece holding hole, and holds the attitude of the workpiece W near the opening of the workpiece holding hole. The support structure of the workpiece W by the guide bush may be a structure separate from the spindle mechanism 100.

[0016] Although details will be described later, the chuck and chuck sleeve (not shown in Fig. 1) are configured such that the chuck sleeve is joined to the chuck, whose axial movement is restricted, from the rear via a tapered surface in the axial direction. The chuck sleeve receives a force from an air cylinder (not shown in Fig. 1) and attempts to move in the axial direction, exerting a force on the chuck that includes a component force in a direction toward the axis, generating a clamping force in the chuck that closes the slits provided in the chuck. This creates a state in which the workpiece W is gripped.

[0017] The tool rest 300 is equipped with a plurality of cutting tools 301 that are prepared so as to be selectable according to the type of processing to be performed. The tool rest 300 is configured to be movable forward and backward in the X-axis direction relative to the workpiece W by a drive mechanism (not shown), and a desired cutting process (turning process) is performed on the workpiece W by bringing a selected cutting tool 301 into contact with the workpiece W.

[0018] The machine tool 1 includes a control unit 200 configured by a computer having a processor such as a CPU (Central Processing Unit) and a memory. The control unit 200 controls the spindle mechanism 100, the tool rest 300, a work supply unit (not shown), an actuator 60 (described later), a display unit 70, and the like. It controls various operations of each part constituting the machine tool 1.

[0019] 2 and 3 are schematic cross-sectional views each showing an enlarged view of the main components around the spindle 101. FIG. 2 shows the configuration of each part when the collet chuck 41 is closed, i.e., when the workpiece W is gripped. FIG. 3 shows the configuration of each part when the collet chuck 41 is open, i.e., when the workpiece W is removable from the spindle 101. FIG. 4 and FIG. 5 are schematic cross-sectional views each showing an enlarged view of the configuration of the chuck jaws 47, the bobbin 48, and the chuck holder 50. FIG. 4 shows the configuration of each part when the chuck jaws 47 are in a closed position, i.e., when the collet chuck 41 is in a closed position gripping the workpiece W. FIG. 5 shows the configuration of each part when the chuck jaws 47 are in an open position, i.e., when the workpiece W is removable from the collet chuck 41.

[0020] 2 and 3, spindle 101 is rotatably mounted to headstock 102 via bearing devices 121, 122, and 123. Collet chuck 41 is mounted to the axial tip side of spindle 101. Collet chuck 41 includes a hollow cylindrical body 411 capable of receiving workpiece W therein, and a gripping portion 412 provided on the tip side in the direction of central axis L (longitudinal direction) of cylindrical body 411.

[0021] The gripping portion 412 has a so-called slotted structure, and is configured to be able to elastically change the inner diameter dimension based on the central axis L1. That is, the gripping portion 412 is provided with slits 413 extending a predetermined length in the axial direction from the end face on the tip side to the rear end side. The slits 413 are formed so as to cut out the gripping portion 412 radially with respect to the central axis L, and are provided in a plurality of slits 413, for example, at equal intervals in the circumferential direction around the central axis L. Between these plurality of slits 413, vertical split pieces 414 are formed that are able to displace in the radial direction centered on the central axis L1. Each vertical split piece 414 is configured in the shape of a leaf spring that is able to elastically deform in the radial direction with its base end as a fulcrum.

[0022] The inner surface of each vertical split piece 414 facing the central axis L1 is a concave curved surface, which cooperates with each other to form a substantially cylindrical workpiece gripping surface 415 of the gripping portion 412. The outer surface of each vertical split piece 414 includes an inclined surface inclined with respect to the axial direction, which cooperates with each other to form a tapered force receiving surface 416 that gradually expands in diameter toward the axial tip. Furthermore, a shoulder surface 417 extending perpendicular to the central axis L1 is formed on the axial tip side of the force receiving surface 416 of each vertical split piece 414.

[0023] When a radially inward external force is applied to each of the multiple vertical split pieces 414 via the force receiving surface 416, the vertical split pieces 414 elastically bend and reduce the diameter of the workpiece gripping surface 415 until it comes into close contact with the workpiece W, thereby firmly and securely gripping the workpiece W. When the radial pressure on the gripping portion 412 is released, each of the vertical split pieces 414 elastically restores its original shape, expanding the diameter of the workpiece gripping surface 415, and the workpiece W is released from the gripping portion 412.

[0024] A cap nut 42 is attached to the tip of the workpiece holding hole of the spindle 101. The cap nut 42 has an end face facing the rear end in the axial direction and has a locking surface 421 that abuts against a shoulder surface 417 of the collet chuck 41 in the axial direction. In addition, a chuck sleeve 43 as a second acting member is attached to the workpiece holding hole of the spindle 101 so as to sandwich the collet chuck 41 between the cap nut 42 and the cap nut 42.

[0025] The chuck sleeve 43 is a hollow cylindrical body capable of receiving the workpiece W and the collet chuck 41 surrounding the workpiece W therein. The chuck sleeve 43 has a force application surface 431 on its inner surface that acts on the force receiving surface 416 of the collet chuck 41, and has a compression coil spring 44 attached thereto as an elastic member that applies a biasing force in the axial direction to the collet chuck 41. The chuck sleeve 43 has a spring receiving surface 432, and compresses the compression coil spring 44 in the axial direction between the spring receiving surface 432 and the axial rear end surface of the collet chuck 41. Due to the biasing force of this compression coil spring 44, the shoulder surface 417 of the collet chuck 41 abuts against the locking surface 421, and the collet chuck 41 is pressed in the axial direction against the cap nut 42.

[0026] The force applying surface 431 is a tapered surface that gradually expands in diameter toward the axial tip, and is a surface that faces and abuts against the force receiving surface 416 in both the axial direction along the central axis L1 and the radial direction centered on the central axis L1. The force applying surface 431 applies a radially inward operating force to the force receiving surface 416, whereby the gripping portion 412 of the collet chuck 41 grips the workpiece W, as described above.

[0027] A chuck opening / closing sleeve 45 and a balance sleeve 46, which are hollow cylindrical bodies capable of receiving a workpiece W therein, are attached to the axial rear end side of the chuck sleeve 43 in the work holding hole of the spindle 101. The chuck sleeve 43, the chuck opening / closing sleeve 45 and the balance sleeve 46 are arranged in series in the axial direction in this order and are engaged with each other in the axial direction, so as to be displaceable in the axial direction as a second acting member. An acted surface 461 that receives an operating force is provided at the axial rear end of the balance sleeve 46.

[0028] The spindle 101 is provided with chuck jaws 47 as a first acting member for applying an operating force to the acting 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 acting surface 461 in the axial direction, and is configured to be rotatable about a rotation axis 472 that is tangent to a virtual circle centered on the central axis L1 with respect to the spindle 101. The plurality of chuck jaws 47 are integrally supported by a chuck holder 50, and are attached to the spindle 101 via the chuck holder 50.

[0029] The chuck jaws 47 rotate so as to be able to take a closed posture in which the acting portion 471 advances forward in the axial direction, and an open posture in which the acting portion 471 retreats backward in the axial direction. The chuck jaws 47 have an acted portion 473 that receives a driving force for the above-mentioned posture change. A bobbin 48 as a linear motion member that applies a driving force to the acted portion 473 is attached to the main shaft 101 so as to be displaceable in the axial direction on a cylindrical wall of the main shaft 101. Specifically, the bobbin 48 is configured as a part of a bearing device 123 that is displaceable 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 by a driving force from an actuator 60 as a driving means. The bobbin 48 is configured to be able to move between an acting position that causes the chuck jaws 47 to take a closed posture and an acted position that causes the chuck jaws 47 to take an open posture by the axial displacement of the bearing device 123.

[0030] The bobbin 48 has an action portion 481 which is a substantially conical outer circumferential surface that extends so as to gradually reduce in diameter toward the rear end in the axial direction. When the bobbin 48 is in the action position, the acted-on portion 473 of the chuck jaws 47 comes into contact with the action portion 481, and the chuck jaws 47 are in a state of riding on the bobbin 48, and take a closed position by rotating during the process of riding on the bobbin 48. When the bobbin 48 is in the acted-on position, the acted-on portion 473 moves away from the action portion 481 and comes into contact with the outer circumferential surface of the spindle 101, and the chuck jaws 47 are in a non-contact state with the bobbin 48, and take an open position by rotating during the process of descending from the bobbin 48.

[0031] The actuator 60 includes an air cylinder 61 and an arm 62 that connects a rod 610 of the air cylinder 61 to the bearing device 123. The arm 62 is attached to the headstock 102 so as to be rotatable about a rotation shaft 622, and is connected to the rod 610 via a rotation shaft 621 so as to be rotatable with respect to the bearing device 123 via a rotation shaft 623. The air cylinder 61 has a rod 610 that reciprocates in a direction along the central axis L, and the arm 62 rotates about a rotating shaft 622 due to the reciprocating motion of the rod 610. For example, the rotating shaft 623 that connects 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 due to the rotation of the arm 62. As a result, the bearing device 123 is displaced in the axial direction on the main shaft 101, and the relative position of the bobbin 48 with respect to the chuck jaws 47 in the axial direction changes.

[0032] When the chuck jaws 47 change from the open position to the closed position, the acting portion 471 presses the acted surface 461 forward in the axial direction, and the balance sleeve 46, the chuck opening / closing sleeve 45, and the chuck sleeve 43 are successively pressed forward in the axial direction. As a result, a radially inward force is applied from the force applying surface 431 of the chuck sleeve 43 to the force receiving surface 416 of the collet chuck 41, increasing the amount of clamping of the collet chuck 41 against the workpiece W, resulting in a closed state in which the workpiece W is firmly and fixedly gripped.

[0033] When the chuck jaws 47 change from the closed position to the open position, the action portion 471 retreats axially rearward, and the chuck sleeve 43, the chuck opening / closing sleeve 45, and the balance sleeve 46 are successively pressed axially rearward by the biasing force of the compression coil spring 44. This releases 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, reducing the amount of clamping of the collet chuck 41 against the workpiece W, and the collet chuck 41 enters an open state in which the workpiece W can be freely attached and detached.

[0034] 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 react when the stroke of the rod 610 is in a contracted position (FIG. 2) where the bobbin 48 has been moved to an operating position. The chuck closed position sensor 72 is configured to react when the stroke of the rod 610 is in an extended position (FIG. 3) where the bobbin 48 has been moved to a non-operating position. The sensors 71 and 72 may be configured, for example, as an optical sensor that detects a mark provided on the rod 610, but any conventionally known sensor may be used as appropriate.

[0035] As shown in FIG. 4 and FIG. 5, an adjustment nut 51 is screwed to the cylindrical wall of the spindle 101 at the axial rear end side of the chuck holder 50. The chuck holder 50 is provided so as to be slidable in the axial direction on the outer circumferential surface of the spindle 101 by a guide mechanism (not shown) provided on the cylindrical wall of the spindle 101. The adjustment nut 51 abuts against the chuck holder 50 in the axial direction against the biasing 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 jaws 47, and the chuck holder 50. The adjustment nut 51 is configured so that the axial position of the adjustment nut 51 relative to the spindle 101 can be adjusted by tightening or loosening the adjustment nut 51 relative to the spindle 101. Therefore, by adjusting the axial position of the adjustment nut 51, the axial position of the chuck holder 50, i.e., the axial position of the chuck jaws 47, can be adjusted. By adjusting the axial position of the chuck jaws 47 (by adjusting the amount of fastening of the adjustment nut 51), it is possible to adjust the amount of fastening of the collet chuck 41 to the workpiece W in the closed state.

[0036] Here, the inventors of the present invention have found through extensive research that differences in the amount of tightening (nut angle) of the adjustment nut 51 result in differences in the difference between the timing at which the chuck open position sensor 71 responds and the timing at which the chuck closed position sensor 72 responds, as described above.

[0037] The chuck open position sensor 71 outputs an ON signal when the rod 610 is in the contracted position (or when it has exceeded a predetermined contraction reference position), and When the rod 610 moves out of the extended position (or does not reach the retraction reference position), it outputs an OFF signal. Similarly, the chuck closed position sensor 72 outputs an ON signal when the rod 610 is in the extended position (or when it has passed a predetermined extension reference position), and outputs an OFF signal when the rod 610 moves out of the extended position (or does not reach the extension reference position) due to the stroke. Therefore, during the stroke of the rod 610, there is a transition period during which neither the chuck open position sensor 71 nor the chuck closed position sensor 72 reacts (both output an OFF signal). This means that the length of this transition period changes depending on the amount of tightening of the adjusting nut 51.

[0038] 6 is a timing chart showing the timing when the control unit 200 issues a chuck close signal to the actuator 60 and the respective response timings of the chuck open position sensor 71 and the chuck closed position sensor 72. When the actuator 60 closes the collet chuck 41 from the open state to the closed state, the period (first time) from when the control unit 200 issues a control signal for the closing operation to the actuator 60 until the output of the chuck open position sensor 71 switches from ON to OFF is defined as A. Also, if the period (second time) from when the control unit 200 issues a control signal for the closing operation to the actuator 60 until the output of the chuck closed position sensor 72 switches from OFF to ON is defined as B, a period BA (difference time) occurs as a transition period.

[0039] During period A, i.e., the period until the output of the chuck open position sensor 71 switches from ON to OFF, this is a position where no load is applied in the chucking operation, so the detection timing is approximately constant regardless of the tightening amount of the adjusting nut 51. In contrast, during period B, i.e., the period until the output of the chuck closed position sensor 72 switches from OFF to ON, this is an operation period where a load is applied in the chucking operation, so a shift in the detection timing occurs depending on the tightening amount of the adjusting nut 51. Therefore, the length of the period BA changes as a transition period.

[0040] Fig. 7 is a graph showing an example of the change in the BA period when the tightening amount (nut angle) of the adjustable nut 51 is changed. As shown in Fig. 7, when the nut angle is changed 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 there is a substantially linear relationship between the tightening amount of the adjustable nut 51 and the BA period.

[0041] The gripping force is usually adjusted by first determining a reference point for the angle (axial position) of the adjusting nut 51, and then adjusting the tightening angle from the reference point to set the desired gripping force. A conventional method of determining the reference point is, for example, to adjust the axial position of the adjusting nut 51 so that the tip of the acted portion 473 abuts against the acting portion 481 when the chuck jaws 47 are not on the bobbin 48, and the nut angle at this time is set as the reference angle. However, it is difficult to set such a reference point uniquely and always constant. In contrast, as in this embodiment, the adjustment amount of the adjusting nut 51 (the tightening amount of the collet chuck 41) is set in correspondence with the time difference of the sensor detection timing, making it easy to grasp the gripping force regardless of the setting of the reference point.

[0042] FIG. 8 is a block diagram illustrating an example of the configuration of a machine tool according to the present embodiment.

[0043] The control unit 200 has a typical computer configuration. The control unit 200 includes a central processing unit (CPU) 201, a read only memory (ROM) 202, a random access memory (RAM) 203, and an input / output interface 204. The control unit 200 also includes an input unit 81, an output The control unit 200 has a control section 82. These are connected to each other by a bus. Various sensors including a chuck open position sensor 71 and a chuck closed position sensor 72 are connected to the bus via an input / output interface 204, and signals from these sensors are input to the control unit 200. On the other hand, actuators for driving the spindle mechanism 100 and the tool rest 300, actuator 60 for opening and closing the collet chuck 41, etc. are connected to the bus via the input / output interface 204, and control signals are sent from the control unit 200 to these devices.

[0044] The CPU 201 controls the machine tool 1 and performs various information processing operations. An operating system (OS), various programs, various tables, etc. are stored in the ROM 202 and RAM 203 as storage means. Each component is controlled through the execution of the program. In this way, the control unit 200 realizes a function that meets a predetermined purpose. The control unit 200 may be a single computer or may be a combination of multiple computers.

[0045] The input unit 81 is a means for accepting an input operation performed by a user, and includes, for example, a touch panel, a mouse, a keyboard, a microphone, etc. The output unit 82 is a means for presenting information to a user, and can include, for example, an LCD (Liquid Crystal Display), an EL (Electroluminescence) panel, a speaker, a lamp, etc. The input unit 81 and the output unit 82 may be configured as one touch panel display.

[0046] 9 is a diagram showing an example of the functional configuration of the control unit 200. The control unit 200 includes, as functional components, a process control unit 211, a gripping force acquisition unit 212, and a gripping force correction unit 213. The process control unit 211, the gripping force acquisition unit 212, and the gripping force correction unit 213 are functional components provided by, for example, the CPU 201 of the control unit 200 executing various programs stored in the ROM 202 and the RAM 203.

[0047] The machining control unit 211 controls the machine tool 1 when machining the workpiece W. The machining control unit 211 clamps the workpiece W with the collet chuck 41, rotates the spindle 101, and further controls the movement of the cutting tool 301 of the tool rest 300, thereby, for example, cutting the workpiece W. A known technique can be used for the machining control of the workpiece W by this machining control unit 211.

[0048] The gripping force acquisition unit 212 acquires the gripping force for the workpiece W when the collet chuck 41 is in the closed state based on the magnitude of the BA period described above. The gripping force is acquired based on the correlation between the BA period and the nut tightening amount described above. That is, the BA period and the nut tightening amount (adjustment amount by 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 for the workpiece W when in the closed state. As the gripping force corresponding to the nut tightening amount, for example, a specific numerical value in units of kilogram-force (kgf) may be acquired in advance by, for example, attaching a torque sensor to the collet chuck 41 in an experiment or the like to detect it, and the gripping force may be calculated and acquired from the above linear relationship based on a plurality of actual measured values. In addition to presenting a specific numerical value, the gripping force may be notified to the user by dividing the nut tightening amount into stages for each predetermined numerical range, and a level display may be displayed to indicate the strength level of the gripping force for each stage.

[0049] 10 is a flowchart of the creation of gripping force correlation data by the gripping force acquisition unit. The creation of the gripping force correlation data is preferably performed in the preparation and adjustment stage before the start of actual product processing. In other words, the workpiece W used in this process may be a spare workpiece W, not a workpiece W to be processed as an actual product.

[0050] First, the control unit 200 issues a chuck closing operation signal to the actuator 60, causing the collet chuck 41 to perform a closing operation and grip the workpiece W (S101). Then, at this time, a period A from the issuance of the closing operation control signal to the chuck open position sensor 71 detecting that the collet chuck 41 is no longer in the open state, and a period B from the issuance of the closing operation control signal to the chuck closed position sensor 72 detecting that the collet chuck 41 has entered the closed state are acquired (S102, S103). The control unit 200 stores the acquired periods A and B, and the period BA acquired thereby, in a storage means.

[0051] When the number of data for periods A and B necessary for obtaining the correlation between the BA period and the nut tightening amount (gripping force) required for obtaining the gripping force has been obtained (S104, YES), correlation data between the BA period and the gripping force is created (S107). When the number of data for periods A and B is insufficient (S104, NO), data is obtained again. That is, the collet chuck 41 is opened (S105), the angle of the adjusting nut 51 is changed, and the position of the chuck jaws 47 is changed (S106). The adjustment amount of the adjusting nut 51 may be changed manually by the user, or, if automatic adjustment is possible, may be changed on the device side. S101 to S106 are repeated until the necessary data is obtained.

[0052] Fig. 11 is a flowchart of chuck gripping force detection using the gripping force data acquired by Fig. 10. This gripping force detection may be performed in the adjustment stage before machining of an actual product, as in Fig. 10, or may be performed during machining of the actual product.

[0053] The control unit 200 issues a chuck closing operation signal to the actuator 60, causing the collet chuck 41 to perform a closing operation and grip the workpiece W (S201). The angle of the adjustment nut 51 adjusted in advance at this time may be an angle with a predetermined margin from the angle during actual processing. In other words, the tightening amount of the collet chuck 41 adjusted by the adjustment nut 51 here is a provisional tightening amount (first tightening amount) for obtaining an optimal tightening amount (second tightening amount). Then, a period A from the issuance of the closing operation control signal to the chuck open position sensor 71 detecting that the collet chuck 41 is no longer in the open state, and a period B from the issuance of the closing operation control signal to the chuck closed position sensor 72 detecting that the collet chuck 41 is in the closed state are acquired (S202, S203). Then, the BA period obtained from the obtained periods A and B is compared with the correlation (grip force data) with the grip force obtained in Fig. 10, or calculated based on the correlation, to obtain the corresponding grip force (S204).Then, the obtained grip force is notified to the user via the output unit 82 as a notification means (S205).

[0054] Through the above process, the user who has been notified of the gripping force can readjust the adjustable nut 51 based on the notified gripping force, if necessary, to achieve the desired gripping force. Note that when notifying the user in S205, the correlation between the nut adjustment amount and the gripping force may also be displayed. Alternatively, in cases where the desired gripping force has been input in advance via the input unit 81, the nut adjustment amount (second tightening amount) required to obtain the desired gripping force may be obtained in S204, and presented to the user in S205.

[0055] The gripping force correction unit 213 corrects the correlation (grip force data) between the acquired BA period and the gripping force. As described above, the period A is basically a position where no load is applied (the load does not change significantly) in the chucking operation, and the detection timing is approximately constant regardless of the tightening amount of the adjustment nut 51. However, for example, in the case of long-term use, it may fluctuate due to the influence of changes in the state of the air supply pressure of the air cylinder 61 and the state of the lubricating oil between the chuck jaws 47 and the bobbin 48. For example, if the air supply pressure of the air cylinder 61 drops from the standard 0.5 MPa to 0.4 MPa, the time A will be extended, and the period B will also be extended accordingly. In order to cope with such changes in the device behavior over time, Therefore, in this embodiment, the delay time (coefficient) is obtained from the time lag (CD period) of the sensor detection timing when the opening operation is performed, and the time lag (BA period) in the closing operation is corrected.

[0056] 12 is a timing chart showing the timing when the control unit 200 issues a chuck open signal to the actuator 60 and the respective response timings of the chuck open position sensor 71 and the chuck closed position sensor 72. When the actuator 60 closes the collet chuck 41 from the closed state to the open state, a period (third time) from when the control unit 200 issues a control signal for the opening operation to the actuator 60 until the output of the chuck closed position sensor 72 switches from ON to OFF is defined as C. Also, if a period (fourth time) from when the control unit 200 issues a control signal for the opening operation to the actuator 60 until the output of the chuck open position sensor 71 switches from OFF to ON is defined as D, a period DC (difference time) occurs as a transition period.

[0057] As described above, the duration of this transition period DC may vary due to changes in device behavior over time, etc. Therefore, by comparing the period DC when the device is brand new with the period DC when the device has been in operation to a certain extent (i.e., when wear and tear have progressed), a coefficient (delay time) for correcting the gripping force data can be obtained. By correcting the gripping force data using this coefficient, it becomes possible to obtain a more optimal gripping force.

[0058] 13 is a flowchart of the correction of the gripping force correlation data by the gripping force acquisition unit. This operation is performed when the gripping force correlation data is reacquired each time the number of times the device is operated reaches a predetermined number of times after the reference gripping force correlation data is created when the device is brand new.

[0059] First, the control unit 200 issues a chuck open operation signal to the actuator 60, causing the collet chuck 41 to perform an opening operation to release the workpiece W (S301). At this time, the control unit 200 acquires a period C from the issuance of the opening operation control signal until the chuck closed position sensor 72 detects that the collet chuck 41 is no longer in the closed state, and a period D from the issuance of the opening operation control signal until the chuck open position sensor 71 detects that the collet chuck 41 has entered the open state (S302, S303). The control unit 200 stores the acquired periods C and D and the DC period acquired thereby in a storage means.

[0060] When the number of data for periods C and D necessary for obtaining the correlation between the DC period and the nut tightening amount (gripping force) required for obtaining the gripping force is obtained (S304, YES), correlation data between the DC period and the gripping force is created (S307). When the number of data for periods C and D is insufficient (S304, NO), data is obtained again. That is, after changing the angle of the adjusting nut 51 to change the position of the chuck jaws 47 (S305), the collet chuck 41 is closed (S306) and the workpiece W is gripped again. The adjustment amount of the adjusting nut 51 may be changed manually by the user, or, if automatic adjustment is possible, may be changed on the device side. S301 to S306 are repeated until the necessary data is obtained.

[0061] The latest grip force data (C', D') obtained by the above process is compared with the reference grip force data (C, D) obtained at the beginning of use to obtain a delay time (coefficient), and the grip force data corresponding to the BC period is corrected (S308). For example, BA in the latest grip force data is corrected using C' / C=α as a coefficient (α(BA)). Using the corrected grip force data in this way makes it possible to set a more appropriate grip force that reflects the changes over time of the device.

[0062] As described above, according to this embodiment, the adjustment amount of the adjustment nut 51 (the tightening amount of the collet chuck 41) is set in correspondence with the time difference of the sensor detection timing, so that the adjustment amount can be adjusted depending on the setting of the reference point. In other words, it becomes possible to appropriately control the gripping force of the chuck, thereby improving the machining accuracy.

[0063] Furthermore, according to this embodiment, the gripping force of the chuck, which is difficult to directly obtain (quantify), can be more appropriately obtained and quantified using the equipment configuration that the machine tool has traditionally had, without the need to add a separate equipment configuration.

[0064] The specific configurations of the spindle mechanism, the chuck opening / closing mechanism such as the collect chuck, chuck sleeve, and chuck jaws, the actuator for operating the mechanism, the opening / closing sensor, and the like shown in this embodiment are merely examples. In other words, other conventionally known configurations may be appropriately adopted. [Explanation of symbols]

[0065] Reference Signs List 1...machine tool, 100...spindle mechanism, 101...spindle, 102...spindle stock, 103...drive mechanism, 2...base, 200...control unit, 300...tool rest, 301...cutting tool, 41...collet chuck, 43...chuck sleeve, 44...compression coil spring, 45...chuck opening / closing sleeve, 46...balance sleeve, 47...chuck jaws, 48...bobbin, 60...actuator, W...workpiece

Claims

1. A spindle having a chuck for gripping a workpiece, an opening / closing mechanism for operating the chuck so that the chuck assumes either a closed state for gripping the workpiece or an open state for attaching / detaching the workpiece, a first sensor for detecting whether the chuck is in the open state, a second sensor for detecting whether the chuck is in the closed state, a control unit for controlling the opening / closing mechanism, in a machine tool comprising: acquisition means for acquiring the gripping force of the chuck on the workpiece in the closed state based on the magnitude of the difference between a first time, from when the control unit issues a control signal for the closing operation to the opening / closing mechanism to cause the chuck to perform a closing operation from the open state to the closed state, until the first sensor detects that the chuck is no longer in the open state, and a second time, from when the control unit issues the control signal to the opening / closing mechanism until the second sensor detects that the chuck is in the closed state. The machine tool is characterized by comprising the acquisition means.

2. an adjustment mechanism for adjusting the tightening amount of the chuck on the workpiece in the closed state, storage means for storing the correlation between the magnitude of the difference, the tightening amount, and the gripping force, The machine tool according to claim 1, further comprising the above.

3. correction means for correcting the correlation based on the temporal change in the magnitude of a second difference between a third time, from when the control unit issues a control signal for the opening operation to the opening / closing mechanism to cause the chuck to perform an opening operation from the closed state to the open state, until the second sensor detects that the chuck is no longer in the closed state, and a fourth time, from when the control unit issues the control signal to the opening / closing mechanism until the first sensor detects that the chuck is in the open state. The machine tool according to claim 2 is characterized by further comprising the correction means.

4. The machine tool according to claim 1, further comprising notification means for notifying external information including the gripping force.

5. The opening / closing mechanism is a first acting member provided on the spindle so as to be able to assume a closing posture acting on the chuck to close the chuck and an opening posture acting on the chuck to open the chuck. A second acting member capable of displacing the relative position with respect to the first acting member in the direction of the rotation axis of the main shaft, the second acting member being provided on the main shaft so as to be able to take a closed position that acts on the first acting member so as to bring the first acting member into the closed posture, and an open position that acts on the first acting member so as to bring the first acting member into the open posture. It includes an air cylinder and drive means for moving the second acting member between the closed position and the open position. The machine tool according to claim 2, characterized by comprising the above.

6. The machine tool according to claim 5, characterized in that the adjustment mechanism can change the clamping amount of the chuck by changing the position of the first acting member with respect to the main shaft in the direction of the rotation axis.

7. The first sensor detects whether or not the drive means has positioned the second acting member at the open position. The machine tool according to claim 6, characterized in that the second sensor detects whether or not the drive means has positioned the second acting member at the closed position.

8. A method for detecting the gripping force of a chuck on a workpiece when the chuck provided on the main shaft of a machine tool grips the workpiece, A first step in which an opening / closing mechanism closes the chuck from an open state in which the workpiece can be attached and detached to a closed state in which the workpiece is gripped. In the first step, a first time from when the control unit issues a control signal for the closing operation to the opening / closing mechanism until the first sensor detects that the chuck is no longer in the open state, and a second time from when the control unit issues the control signal to the opening / closing mechanism until the second sensor detects that the chuck is in the closed state are obtained. A second step. Based on the magnitude of the difference between the first time and the second time, the clamping amount of the chuck on the workpiece in the closed state adjusted by the adjustment mechanism, and the correlation between the gripping force, a third step of obtaining the gripping force. A method for detecting the gripping force of a chuck, characterized by including the above.

9. A fourth step in which the opening / closing mechanism opens the chuck from the closed state to the open state. In the fourth step, a third time from when the control unit issues a control signal for the opening operation to the opening mechanism until the second sensor detects that the chuck is no longer in the closed state, and a fourth time from when the control unit issues the control signal to the opening and closing mechanism until the first sensor detects that the chuck is in the open state are obtained in a fifth step. A sixth step of correcting the correlation based on a change over time in the magnitude of the difference between the third time and the fourth time when the fourth step and the fifth step are repeated. The method for detecting the gripping force of a chuck according to claim 8, further comprising this.

10. When the chuck provided on the spindle of the machine tool grips the workpiece, the A method for setting the tightening amount of the chuck with respect to the workpiece, comprising: In a first step, with the tightening amount of the chuck with respect to the workpiece in a closed state where the chuck grips the workpiece adjusted to a first tightening amount by an adjustment mechanism, an opening and closing mechanism closes the chuck from an open state where the workpiece can be attached and detached to the closed state. In the first step, a first time from when the control unit issues a control signal for the closing operation to the opening and closing mechanism until the first sensor detects that the chuck is no longer in the open state, and a second time from when the control unit issues the control signal to the opening and closing mechanism until the second sensor detects that the chuck is in the closed state are obtained in a second step. Based on the magnitude of the difference between the first time and the second time, the tightening amount of the chuck with respect to the workpiece in the closed state adjusted by the adjustment mechanism, and the correlation between the gripping force of the chuck with respect to the workpiece in the closed state, a second tightening amount for obtaining the desired gripping force is obtained in a third step. In a fourth step, the adjustment mechanism adjusts the tightening amount to the second tightening amount obtained in the third step. A method for setting the tightening amount of a chuck, comprising this.

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