Machine tool

Abstract

The invention provides a machine tool capable of improving the precision of a stop position of a driven object under the condition of performing semi-closed-loop control. A machine tool (1) is provided with: a guide mechanism (30) for driving an object that is a guide tool (TO1) and / or a workpiece (W1); a servo motor (40) that moves the drive object guided by the guide mechanism (30); and a control unit (U1) that performs semi-closed-loop control on the servo motor so as to move the drive object from the initial position (P1) to the target position (P2). A control unit (U1) performs semi-closed loop control so as to apply a vibration component (Vc) to the movement of a drive object from a midway position (P3) between an initial position (P1) and a target position (P2) to the target position (P2), the vibration component (Vc) repeating a forward motion (M1) toward the target position (P2) and a backward motion (M2) opposite to the forward motion (M1).

Description

Technical Field

[0001] The invention relates to a machine tool performing semi-closed loop control. Background Art

[0002] As a machine tool, there is known an NC (Numerical Control) lathe that uses a tool to cut a workpiece held by a spindle. The NC lathe includes a guide mechanism for a tool or workpiece as a driven object, a servo motor with an internal encoder, a servo amplifier, an NC device, and the like. The servo amplifier performs semi-closed loop control on the servo motor based on a position command from the NC device and a feedback signal from the internal encoder (for example, refer to Patent Document 1).

[0003] [Background Technology Literature]

[0004] [Patent Document]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-25474 Summary of the invention

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

[0007] However, although the output of the internal encoder indicates that the driven object has reached the target position, in reality, the driven object may stop slightly away from the target position. Adding a sensor for detecting the position of the driven object in order to improve the accuracy of the stop position of the driven object will increase the cost. Therefore, it is desired to improve the accuracy of the stop position of the driven object when performing semi-closed loop control without adding a position detection sensor.

[0008] Furthermore, the above-mentioned problem is not limited to lathes, but exists in various machine tools such as cutting machines.

[0009] The invention discloses a machine tool capable of improving the accuracy of the stop position of a driven object under the condition of semi-closed loop control.

[0010] [Technical means to solve the problem]

[0011] The machine tool of the present invention has the following aspects, that is, it processes a workpiece using a tool and comprises:

[0012] A guiding mechanism for guiding a driven object, wherein the driven object is at least one of the tool and the workpiece;

[0013] a servo motor to move the driving object guided by the guide mechanism; and

[0014] A control unit performs semi-closed loop control on the servo motor to move the driven object from an initial position to a target position; and

[0015] The control unit performs the semi-closed loop control in a manner that applies a vibration component to the movement of the driven object from a midway position between the initial position and the target position until the target position is reached, wherein the vibration component is a repeated forward movement toward the target position and a backward movement opposite to the forward movement.

[0016] [Effects of the invention]

[0017] According to the present invention, it is possible to provide a machine tool capable of improving the accuracy of the stop position of a driven object when performing semi-closed loop control. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a diagram schematically showing a configuration example of a machine tool.

[0019] Figure 2 This is a block diagram schematically showing a configuration example of a circuit of a machine tool.

[0020] Figure 3 is a block diagram schematically showing an example of a semi-closed loop control system.

[0021] Figure 4 1 is a diagram schematically showing an example of the relationship between a controlled position x1 and an actual position x2 of a driven object.

[0022] Figure 5 1 is a diagram schematically showing an example of region division of the control position x1 centered at the reference position 0 in the semi-closed loop control.

[0023] Figure 6 This is a diagram schematically showing an example in which a vibration component is added to the movement of the driven object from the intermediate position to the target position.

[0024] Figure 7 It is a diagram schematically showing an example of a vibration component.

[0025] Figure 8 1 is a diagram schematically showing an example in which the driven object continues to vibrate for a set period of time after reaching the target position.

[0026] Fig. 9 : is a flowchart schematically showing an example of the vibration condition determination process.

[0027] Fig.10 FIG. 1 is a diagram schematically showing a current command with a scanning frequency variation.

[0028] Fig.11 It is a diagram schematically showing an example of the amplitude magnification M with respect to the frequency f.

[0029] Fig.12Schematically showing an example of phase delay φ with respect to frequency f.

[0030] Fig.13 : is a flowchart schematically showing an example of frequency determination processing. DETAILED DESCRIPTION

[0031] The following will describe embodiments of the present invention. Of course, the following embodiments are merely examples of the present invention, and not all of the features shown in the embodiments are essential to the solution means of the invention.

[0032] (1) Technical overview of the present invention:

[0033] First, refer to Figures 1 to 13 The examples shown are used to illustrate the technical overview of the present invention. In addition, the figures of this application are schematic diagrams of examples, and sometimes the magnifications of the directions shown in these figures are different, and there are situations where the figures are inconsistent. Of course, the elements of this technology are not limited to the specific examples shown by the symbols.

[0034] In addition, in the present application, the numerical range "Min to Max" means a range from a minimum value Min to a maximum value Max.

[0035] [Form 1]

[0036] picture Figures 1 to 3 As illustrated, a machine tool 1 according to one embodiment of the present technology is a machine tool 1 for machining a workpiece W1 using a tool TO1, and is provided with a guide mechanism 30, a servo motor 40, and a control unit U1. The guide mechanism 30 guides a driven object, and the driven object is at least one of the tool TO1 and the workpiece W1. The servo motor 40 moves the driven object guided by the guide mechanism 30. The control unit U1 performs semi-closed loop control on the servo motor 40 so that the driven object moves from an initial position P1 to a target position P2 (for example, refer to Figure 3 ).picture Figure 6 As illustrated in the examples above, the control unit U1 performs the semi-closed loop control by applying a vibration component Vc to the movement M0 of the driven object from the midway position P3 between the initial position P1 and the target position P2 until it reaches the target position P2, wherein the vibration component Vc is a repeated forward action M1 toward the target position P2 and a backward action M2 opposite to the forward action M1.

[0037] If semi-closed loop control is performed without applying the vibration component Vc to the movement M0 of the driven object, strain will be generated in the structure from the servo motor 40 to the driven object, resulting in residual internal stress in the structure, and the actual stop position of the driven object sometimes deviates from the target position P2. In the semi-closed loop control of the form, the vibration component Vc is applied to the movement M0 of the driven object from the midway position P3 to the target position P2, so the internal stress generated in the structure is released and the driven object reaches the target position P2. As a result, the residual internal stress in the structure is reduced, and the actual stop position of the driven object is close to the target position P2. Therefore, the form can suppress the increase in the cycle time of the command to move the driven object and improve the accuracy of the stop position of the driven object. In addition, the residual internal stress in the structure is reduced, and the torque generated by the servo motor when the driven object stops becomes smaller, thereby reducing the standby power.

[0038] Here, the machine tool includes a lathe, a cutting machine, and the like.

[0039] The guide mechanism can guide the driven object so that the driven object moves in a specified direction, and can also guide the driven object so that the driven object rotates around a specified axis.

[0040] Moving the driven object includes moving the driven object along the indicated moving direction, rotating the driven object along the indicated direction, and the like.

[0041] The servo motor may move a tool as a driving target, may move a workpiece as a driving target, or may move both the tool and the workpiece as driving targets. When the driving targets are both the tool and the workpiece, the guide mechanism guides both the tool and the workpiece.

[0042] The above-mentioned supplementary remarks are also applicable to the following forms.

[0043] [Form 2]

[0044] picture Figure 8 As illustrated, the control unit U1 may perform the semi-closed loop control in the following manner, i.e., the vibration component Vc is applied to the driven object within a set period 202 within the period (e.g., stop period 201) during which the driven object stops at the target position P2 after reaching the target position P2.

[0045] In the above case, the internal stress remaining in the structure from the servo motor 40 to the driven object is further reduced, thereby further improving the accuracy of the stop position of the driven object.

[0046] [Form 3]

[0047] picture Fig. 9As illustrated, the control unit U1 may also perform the semi-closed loop control in a vibration condition determination mode for determining the vibration condition (e.g., frequency or amplitude) of the vibration component Vc, using each candidate i of the plurality of candidates i of the vibration condition (e.g., frequency fi or amplitude Ai) as the vibration condition, so as to detect the torque (e.g., torque value TR1i) generated by the servo motor 40 when the driven object stops at the target position P2. The control unit U1 may determine a candidate among the plurality of candidates i when the torque (TR1i) is lower than a reference torque (e.g., reference torque value TR0) as the vibration condition.

[0048] In the case where internal stress remains in the structure from the servo motor 40 to the driven object, when the driven object stops at the target position P2 in the semi-closed loop control, the servo motor 40 generates a torque (TR1i) corresponding to the internal stress of the structure. Therefore, if the vibration condition of the vibration component Vc is determined in such a way that the torque (TR1i) generated by the servo motor 40 when the driven object stops is lower than the reference torque (TR0), the internal stress remaining in the structure when the driven object stops is reduced. Therefore, the above-mentioned form can provide a better example of improving the accuracy of the stop position of the driven object.

[0049] [Form 4]

[0050] The frequency of the vibration component Vc may be included in a resonant frequency band that allows the portion of the machine tool 1 holding the driven object (e.g., the tool rest 20 or the spindle box 10) to resonate. In addition, the frequency measured when resonance occurs has a range, so the resonant frequency band refers to the range of frequencies in which resonance may occur. Fig.13 The resonance frequency fr exemplified in is included in the resonance frequency band.

[0051] In the above case, the vibration component Vc of the resonance frequency band is applied to the movement M0 of the driven object from the intermediate position P3 to the target position P2 in the semi-closed loop control, so the internal stress generated in the structure from the servo motor 40 to the driven object is easily released, and the internal stress remaining in the structure is further reduced. Therefore, the above form can provide a better example of improving the accuracy of the stop position of the driven object.

[0052] [Form 5]

[0053] picture Fig.13 As illustrated, the control unit U1 may also input a current instruction 300 having a change in scanning frequency into the semi-closed loop in a vibration condition determination mode for determining the frequency of the vibration component Vc to detect the resonance frequency fr generated by the part of the machine tool 1 that holds the driven object, and determine the detected resonance frequency fr as the frequency of the vibration component Vc.

[0054] If the current command 300 with a sweep frequency change is input to the semi-closed loop, the portion of the machine tool 1 that holds the driven object vibrates at the sweep frequency of the current command 300. If the resonance frequency fr generated in this portion is detected, the detected resonance frequency fr is determined as the frequency of the vibration component Vc. As a result, the internal stress remaining in the structure from the servo motor 40 to the driven object is further reduced. Therefore, the above-described embodiment can provide a preferred example of improving the accuracy of the stop position of the driven object.

[0055] (2) Specific example of the structure of the machine tool:

[0056] Figure 1 The configuration of a lathe as an example of the machine tool 1 is schematically illustrated. Figure 2 A circuit configuration of a lathe as an example of the machine tool 1 is schematically illustrated. Figure 1 , 2 The machine tool 1 shown is an NC automatic lathe equipped with an NC (numerical control) device 70 that numerically controls the machining of a workpiece W1 held by a spindle 11. The computer 100 is not an essential element of the machine tool 1, and therefore, the external computer 100 may not be connected to the machine body 2.

[0057] Figure 1 The machine tool 1 shown is an NC machine tool including a spindle box 10 in which a spindle 11 is assembled, a tool holder 20 for directly or indirectly holding a tool TO1, a guide mechanism 30 for the spindle box 10 or the tool holder 20, a servo motor 40, and an NC device 70. Here, the front spindle box 10A and the back spindle box 10B, which is also called the opposing spindle box, are collectively referred to as the spindle box 10. The front spindle 11A and the back spindle 11B, which is also called the opposing spindle, are collectively referred to as the spindle 11. Figure 1 The illustrated spindle head 10 is provided with a motor 13 , for example, a built-in motor, which rotates the spindle 11 about the spindle center axis AX1 . Figure 1 The spindle 11 shown has a holding portion 12 such as a suction nozzle. The comb-shaped tool holder 21 and the hexagonal tool holder 22 are collectively referred to as the tool holder 20. Figure 1 The comb-shaped tool holder 21 shown is provided with a rotary unit 25 assembled with a plurality of tools TO1. The guide mechanism 31 for guiding the spindle box 10 and the guide mechanism 32 for guiding the tool holder 20 are collectively referred to as the guide mechanism 30. The guide mechanism 32 includes a rotary guide mechanism for guiding the rotation of the rotary unit 25. The servo motor 41 for moving the spindle box 10 and the servo motor 42 for moving the tool TO1 are collectively referred to as the servo motor 40. The servo motor 42 includes not only a servo motor for moving the tool holder 20 but also a servo motor for rotating the rotary unit 25.

[0058] Figure 1The control axes of the machine tool 1 shown include the X-axis shown by "X", the Y-axis shown by "Y", the Z-axis shown by "Z", and the B-axis shown by "B". The Z-axis direction is the horizontal direction along the spindle centerline AX1 that is the rotation center of the workpiece W1. The X-axis direction is the horizontal direction orthogonal to the Z-axis. The Y-axis direction is the vertical direction orthogonal to the Z-axis. The B-axis is a reference axis for controlling the rotation angle of the rotary unit 25, for example, a control axis along the vertical direction of the Y-axis. In addition, the Z-axis and the X-axis may not be orthogonal as long as they intersect, the Z-axis and the Y-axis may not be orthogonal as long as they intersect, and the X-axis and the Y-axis may not be orthogonal as long as they intersect. In addition, the drawings referred to in this specification only represent examples for illustrating the present technology and do not limit the present technology. In addition, the description of the positional relationship of each part is only an example. Therefore, making the left and right opposite or the rotation direction opposite is also included in the present technology. In addition, the sameness of direction or position is not limited to strict consistency, and includes situations where there is deviation from strict consistency due to errors.

[0059] Figure 1 The machine tool 1 shown is a spindle-moving lathe, and both the front spindle box 10A and the back spindle box 10B move in the Z-axis direction. The guide mechanism 31 guides the spindle box 10 along the Z-axis. When the holding portion 12 holds the workpiece W1, the guide mechanism 31 guides the workpiece W1 along the Z-axis. In addition, the machine tool 1 can be a spindle-fixed lathe in which the front spindle box 10A does not move, or the back spindle box 10B does not move while the front spindle box 10A moves in the Z-axis direction. Of course, the spindle box 10 can also move in the X-axis direction, etc.

[0060] The spindle 11 releasably holds the workpiece W1 through the holding portion 12. The motor 13 rotates the spindle 11 and the workpiece W1 together around the spindle centerline AX1. In the case where the workpiece W1 before processing is, for example, a cylindrical (rod-shaped) long strip of material, the spindle 11A can be rotated from the rear end ( Figure 1 The workpiece W1 is supplied to the holding portion 12. In this case, the front side of the front spindle 11A ( Figure 1 The workpiece W1 is provided with a guide sleeve (right side in the middle) to support the workpiece W1 so that it can slide in the Z-axis direction. In the case where the workpiece W1 before processing is a short material, the workpiece W1 can also be supplied to the holding portion 12 from the front end of the front spindle 11A. The workpiece W1 after the front processing is handed over from the front spindle 11A to the back spindle 11B, and becomes a product after the back processing.

[0061] The tool holder 20 is directly or indirectly mounted with a plurality of tools TO1 for processing the workpiece W1, and is movable in the X-axis direction and the Y-axis direction. The guide mechanism 32 guides the tool holder 20 and the tool TO1 along the X-axis and the Y-axis. Of course, the tool holder 20 can also move in the Z-axis direction. The plurality of tools TO1 include turning tools including cutting tools, rotary tools such as rotary drills or end mills, etc. The rotary unit 25 provided on the comb-shaped tool holder 21 is capable of rotating around the B-axis together with the tool TO1. It can also be said that the comb-shaped tool holder 21 has a guide mechanism 32 for guiding the tool TO1 and the rotary unit 25 around the B-axis. The hexagonal tool holder 22 distributes the tool TO1 by rotating around the rotary axis AX2 along the Z-axis.

[0062] The guide mechanism 30 may use a rolling guide mechanism such as a ball screw or a linear guide, a sliding guide mechanism such as a combination of a dovetail and a dovetail groove, or the like.

[0063] like Figure 2 As shown, the NC device 70 is connected to an operating unit 80, a servo amplifier 50, a rotation drive unit (not shown) of the spindle 11, a drive unit (not shown) of the holding unit 12, etc. Here, the servo amplifier 51 for the spindle box 10 and the servo amplifier 52 for the tool holder 20 are collectively referred to as the servo amplifier 50. The servo amplifier 50 and the NC device 70 are examples of the control unit U1. The servo amplifier 50 is connected to a servo motor 40 having an encoder 43 inside. The NC device 70 has a CPU (Central Processing Unit) 71 as a processor, a ROM (Read Only Memory) 72 as a semiconductor memory, a RAM (Random Access Memory) 73 as a semiconductor memory, a clock circuit 74, an I / F (interface) 75, etc. Therefore, the NC device 70 is a type of computer. Figure 2 In FIG. 7 , I / Fs such as the operation unit 80 , the servo amplifier 50 , and the external computer 100 are collectively represented as I / F 75 .

[0064] The control program PR1 for interpreting and executing the processing program PR2 including a plurality of commands CM1 is written in the ROM 72. The ROM 72 may also be a semiconductor memory capable of rewriting data. The processing program PR2 created by the operator is rewritable in the RAM 73. The processing program is also called an NC program. The CPU 71 uses the RAM 73 as a work area to execute the control program PR1 recorded in the ROM 72, thereby realizing the functions of the NC device 70. Of course, some or all of the functions realized by the control program PR1 may also be realized by other methods such as ASIC (Application Specific Integrated Circuit).

[0065] The operation unit 80 includes an input unit 81 and a display unit 82, and functions as a user interface of the NC device 70. The input unit 81 includes, for example, a button or a touch panel for accepting operation input by an operator. The display unit 82 includes, for example, a display that displays the contents of various settings accepted by the operator or various information related to the machine tool 1. The operator can store the machining program PR2 in the RAM 73 using the operation unit 80 or the computer 100.

[0066] The servo amplifier 51 controls the position and moving speed of the workpiece W1 and the spindle box 10 as the driven objects according to the instruction 57 from the NC device 70. The servo motor 41 controlled by the servo amplifier 51 rotates according to the torque instruction 59 from the servo amplifier 51, and moves the spindle box 10 together with the workpiece W1 via the guide mechanism 31. For example, in the case where the spindle box 10 is a front spindle box 10A that can move along the Z axis, the servo amplifier 51 controls the position and moving speed of the front spindle box 10A in the Z axis direction according to the instruction 57 from the NC device 70. The servo motor 41 moves the front spindle box 10A in the Z axis direction via the guide mechanism 31 according to the torque instruction 59 from the servo amplifier 51.

[0067] The servo amplifier 52 controls the position and moving speed of the tool TO1 and the tool rest 20 as the driven objects according to the command 57 from the NC device 70. The servo motor 42 controlled by the servo amplifier 52 rotates according to the torque command 59 from the servo amplifier 52, and moves the tool rest 20 together with the tool TO1 via the guide mechanism 32. For example, when the tool rest 20 is a comb-shaped tool rest 21 that can move along the X-axis and the Y-axis, the servo amplifier 52 for the X-axis controls the position and moving speed of the comb-shaped tool rest 21 in the X-axis direction according to the command 57 from the NC device 70, and the servo amplifier 52 for the Y-axis controls the position and moving speed of the comb-shaped tool rest 21 in the Y-axis direction according to the command 57 from the NC device 70. The servo motor 42 for the X-axis moves the comb-shaped tool rest 21 in the X-axis direction according to the torque command 59 from the servo amplifier 52 via the guide mechanism 32, and the servo motor 42 for the Y-axis moves the comb-shaped tool rest 21 in the Y-axis direction according to the torque command 59 from the servo amplifier 52. The servo amplifier 52 for the B axis controls the position and rotation speed of the tool TO1 and the rotary unit 25 as the driven objects according to the command 57 from the NC device 70. The servo motor 42 for the B axis rotates according to the torque command 59 from the servo amplifier 52, and rotates the rotary unit 25 together with the tool TO1 via the guide mechanism 32.

[0068] Figure 3A semi-closed loop control system is schematically illustrated. The semi-closed loop control system has a loop that feeds back the position detected by the encoder 43 provided on the servo motor 40. Since the encoder 43 is located inside the servo motor 40, in the semi-closed loop control system, the position obtained by detecting the actual position of the driven object is not fed back.

[0069] Figure 3 The control system shown is set up separately for the Z-axis movement of the front spindle box 10A, the Z-axis movement of the back spindle box 10B, the X-axis movement of the comb tool holder 21, the Y-axis movement of the comb tool holder 21, the B-axis rotation of the rotary unit 25, the X-axis movement of the hexagonal tool holder 22, the Y-axis movement of the hexagonal tool holder 22, etc.

[0070] The NC device 70 can output the command 57 to the servo amplifier 50. When the command 57 is a position command of the driven object (tool TO1 or workpiece W1), the subtraction unit 55 of the servo amplifier 50 inputs the position command from the NC device 70, inputs the position feedback signal SG1 based on the output from the encoder 43 of the servo motor 40, and outputs the position deviation SG2 to the position gain 53. The position deviation SG2 is a difference signal between the position command of the driven object and the position feedback signal SG1. The position gain 53 inputs the position deviation SG2 from the subtraction unit 55, and outputs the speed command 58 to the subtraction unit 56 based on the position deviation SG2. The subtraction unit 56 inputs the speed command 58 from the position gain 53, inputs the speed feedback signal SG3 based on the output from the encoder 43, corrects the speed command 58 based on the speed feedback signal SG3, and inputs it to the speed gain 54. The speed gain 54 inputs the corrected speed command from the subtraction unit 56, and outputs the torque command 59 to the servo motor 40 based on the corrected speed command. The torque of the servo motor 40 is proportional to the current flowing through the servo motor 40 , and therefore the torque command 59 corresponds to the value of the current flowing through the servo motor 40 .

[0071] According to the above, the NC device 70 and the servo amplifier 50 perform semi-closed loop control on the servo motor 40 according to the command CM1 for moving the driven object, so that the driven object moves from the initial position to the target position. For example, when the command CM1 is a fast feed command for moving the tool TO1 along the X-axis, the NC device 70 and the servo amplifier 52 for the tool perform semi-closed loop control on the servo motor 42 in such a way that the tool TO1 moves from the initial position to the target position along the X-axis straight line. In addition, the fast feed command is different from the cutting feed command accompanying the cutting of the workpiece W1, and is a command for moving the tool TO1 without the cutting of the workpiece W1. The command CM1 can also be a command for moving the tool TO1 along multiple axes, such as the X-axis and the Y-axis. When the command CM1 is a fast feed command for rotating the tool TO1 around the B-axis, the NC device 70 and the servo amplifier 52 perform semi-closed loop control on the servo motor 42 in such a way that the tool TO1 rotates around the B-axis from the initial position to the target position. When the command CM1 is a command to move the workpiece W1 along the Z axis, the NC device 70 and the servo amplifier 51 for the headstock perform semi-closed loop control on the servo motor 41 so as to move the workpiece W1 linearly along the Z axis from the initial position to the target position.

[0072] In addition, the NC device 70 can output a current command as a command value for current control to the servo amplifier 50 as a command 57. The current command is an input value that does not receive feedback from the current control, and the torque command 59 input to the servo amplifier 50 is an output value that receives feedback from the current control. If there is no feedback signal (SG1, SG3), the torque command 59 becomes a current command.

[0073] Furthermore, the servo amplifier 50 can output a torque value corresponding to the torque command 59 to the NC device 70. The torque value corresponds to the current value flowing in the servo motor 40. The NC device 70 can output a torque value acquisition command for acquiring the torque value from the servo amplifier 50 to the servo amplifier 50. The servo amplifier 50 that receives the torque value acquisition command outputs the torque value to the NC device 70.

[0074] The encoder 43 is located inside the servo motor 40 and indirectly detects the position of the driven object. Since friction is generated by the guide surface of the guide mechanism 30 or the sealing O-ring, when the structure from the servo motor 40 to the driven object is strained and becomes a state where internal stress remains, the detected position based on the encoder 43 will deviate from the actual position of the driven object. In addition, the structure is the guide mechanism 30, the spindle box 10, the tool rest 20, etc.

[0075] As described above, although the output of the encoder 43 in the servo motor 40 indicates that the driven object has reached the target position, in reality the driven object may slightly deviate from the target position and stop.

[0076] Figure 4 The following schematically shows an example of the relationship between the control position x1 output by the encoder 43 and the actual position x2 of the driven object when the control unit U1 performs semi-closed loop control to move the driven object from the initial position P1 to the target position P2. Figure 3 The semi-closed loop control position of the position feedback signal SG1 shown. For example, in the case of X-axis movement of the driven object, the control position x1 represents the control position on the X-axis, and the position x2 represents the actual position on the X-axis. In addition, no internal stress remains in the structure at the initial position P1.

[0077] The friction force acts on the guide surface of the guide mechanism 30. When the servo motor 40 starts to move the driven object, the structure generates strain, causing the position where the driven object actually starts to move to become the action start point Ps slightly delayed from the initial position P1 under control. When the driven object moves, the friction force also acts on the guide surface of the guide mechanism 30, and the strain of the structure remains. Even if the controlled position of the driven object reaches the target position P2, the internal stress will remain due to the strain of the structure, so that the actual position of the driven object will generate an error Er relative to the strict target position P2. Adding a sensor to detect the actual position of the driven object in order to eliminate the error Er will increase the cost.

[0078] The same can be said about the B-axis rotation of the rotation unit 25 .

[0079] Figure 5 The following schematically shows an example of area division of the control position x1 in semi-closed loop control centered at the reference position 0. The control position x1 indicates the target position of the driven object in the moving direction of the driven object, with the right side from the reference position 0 indicating a positive position and the left side from the reference position 0 indicating a negative position.

[0080] Since the friction force acts on the guide surface of the guide mechanism 30, even if the control is performed to move the driven object within the range of the first area AR1, the actual position of the driven object does not change. In the first area AR1, only a force smaller than the friction force is applied to the driven object in the moving direction of the driven object with the reference position 0 as the center. This is because the strain of the structure from the servo motor 40 to the driven object does not exceed the friction of the guide surface. The positive side boundary of the first area AR1 corresponds to Figure 4The action start point Ps shown. The second areas AR2 and AR3 located on both sides of the first area AR1 in the moving direction of the driven object are areas where the actual position of the driven object changes by controlling the moving of the driven object in the moving direction of the driven object, and the strain of the structure is reduced by the vibration centered on the reference position 0. The third areas AR4 and AR5 located on both sides of the second areas AR2 and AR3 in the moving direction of the driven object are areas where a large amount of strain remains in the structure due to the movement in the positive and negative directions during the vibration process centered on the reference position 0, because the position of the driven object changes greatly in the moving direction of the driven object. It can also be said that moving from the third area AR4 on the positive side to the third area AR5 on the negative side will cause a large amount of internal stress to remain, and moving from the third area AR5 on the negative side to the third area AR4 on the positive side will cause a large amount of internal stress to remain. Therefore, the vibration that reduces the residual stress of the structure is preferably repeated in the moving direction of the driven object from the second area AR2 on the positive side to the second area AR3 on the negative side and from the second area AR3 on the negative side to the second area AR2 on the positive side.

[0081] In this specific example, a micro-vibration component is applied to the movement of the driven object to the extent that the moving driven object moves back and forth between the second areas AR2 and AR3 before reaching the target position P2, thereby suppressing the increase in the cycle time of the command CM1 and reducing the residual stress of the structure. As a result, when the semi-closed loop control is performed, the actual stop position of the driven object is close to the target position P2, and the accuracy of the stop position of the driven object is improved.

[0082] Figure 6 A case where a vibration component Vc is added to the movement of the driven object from the midway position P3 between the initial position P1 and the target position P2 until the target position P2 is reached is schematically illustrated. Figure 7 The vibration component Vc is schematically illustrated. Figure 6 , 7 In the figure, the horizontal axis is time t and the vertical axis is the control position x1. Figure 6 2 shows that control is performed to start moving the driven object from the initial position P1 at t=0, and control is performed to stop the driven object at the target position P2 when time t is the movement stop time t1. Figure 7 The t=0 and Figure 6 The t=0 shown is different.

[0083] For example, when the tool TO1 moves linearly along the X-axis, the control position x1 indicates the control position of the tool TO1 (particularly, the tool tip) along the X-axis.

[0084] The command CM1 is a fast feed command for moving the tool TO1 from the initial position P1 to the target position P2. In this case, the servo amplifier 52 for the tool performs semi-closed loop control on the servo motor 42 by applying a vibration component Vc to the movement of the tool TO1 (the movement M0 of the driven object) from the intermediate position P3 to the target position P2. The vibration component Vc is a repeated forward movement M1 toward the target position P2 and a backward movement M2 opposite to the forward movement M1. Figure 6 As shown, the vibration component Vc is not applied to the movement of the tool TO1 from the initial position P1 to the intermediate position P3, and the vibration component Vc is applied to the movement of the tool TO1 from the intermediate position P3 to the target position P2. By adding the vibration component Vc, the internal stress generated in the structure from the servo motor 42 for the tool to the tool TO1 is released, and the internal stress remaining in the structure is reduced when the tool TO1 reaches the target position P2. As a result, the actual movement stop position of the tool TO1 approaches the target position P2, and the accuracy of the movement stop position of the tool TO1 is improved. The vibration component Vc can also be said to be a micro-vibration component in which the internal stress generated in the structure from the servo motor 40 to the driven object is released when the driven object stops at the target position P2. By reducing the internal stress remaining in the structure, the torque generated by the servo motor 42 when the movement of the tool TO1 stops becomes smaller, and the standby power is reduced. In addition, by not applying the vibration component Vc to the movement of the tool TO1 from the initial position P1 to the intermediate position P3, the power consumption can be suppressed. The same can be said about the B-axis rotation of the rotary unit 25 , the Z-axis movement of the workpiece W1 , and the like.

[0085] The intermediate position P3 may also be a position at a specified distance from the target position P2, for example, a position in position with the target position P2 as a reference. In position means a set position at which the driven object is considered to have reached the target position. In addition, the intermediate position P3 may be a position at which the rotation speed of the servo motor 40 becomes less than a specified rotation speed, or a position at a time specified before the movement stop time t1 expected to reach the target position P2, etc.

[0086] Figure 7 The vibration component Vc shown is a sine wave with a period of T and an amplitude of A. Therefore, during the period t=0-T, a component of the forward motion M1 is applied to the movement of the tool TO1 between 0-(1 / 4)T and (3 / 4)T-T, and a component of the backward motion M2 is applied to the movement of the tool TO1 between (1 / 4)T-(3 / 4)T. In addition, the vibration component Vc is not limited to a sine wave, but may also be a triangular wave, a rectangular wave, or the like. Since the triangular wave or the rectangular wave contains a harmonic component, it is presumed that the effect of releasing the internal stress generated in the structure when the driven object is stopped is improved.

[0087] NC device 70 can output amplitude A and frequency (f) of vibration component Vc as arguments to servo amplifier 50. Servo amplifier 50 receiving amplitude A and frequency f performs semi-closed loop control so as to apply vibration component Vc of amplitude A and frequency f to movement M0 of the driven object.

[0088] The amplitude A of the vibration component Vc of the control position x1 is preferably 1 to 100 μm. If the amplitude A is 1 μm or more, the vibration component Vc is likely to exceed Figure 5 If the amplitude A is less than 100 μm, the vibration component Vc will not reach the first area AR1 and enter the second area AR2 and AR3. Figure 5 The vibration component Vc can be regarded as a component of micro vibration, and the vibration actually generated can be regarded as micro vibration.

[0089] The frequency f=1 / T of the vibration component Vc is preferably 100 to 1000 Hz. If the frequency f is above 100 Hz, the number of vibrations from the intermediate position P3 to the target position P2 increases, thereby facilitating the release of the internal stress generated in the structure when the driven object stops. If the frequency f is below 1000 Hz, the vibration of the driven object is easy to follow the control, thereby facilitating the release of the internal stress generated in the structure when the driven object stops.

[0090] In addition, in order to facilitate the release of the internal stress generated in the structure, the vibration conditions including the frequency f and the amplitude A may be changed to perform semi-closed loop control for moving the driven object, and the vibration conditions under which the internal stress generated in the structure when the driven object stops is released as much as possible are searched. In the case where internal stress remains in the structure when the driven object stops, the servo amplifier 50 controls the servo motor 40 in a manner that generates a torque that eliminates the internal stress of the structure. Therefore, the magnitude of the torque generated by the servo motor 40 when the driven object stops corresponds to the magnitude of the residual stress of the structure. Therefore, the vibration conditions may be changed to perform semi-closed loop control for moving the driven object, and the vibration condition under which the torque value obtained from the servo amplifier 50 when the driven object stops is minimized is set as the vibration condition of the vibration component Vc. For example, when Figure 2 When the vibration condition is stored in the ROM 72 shown, the NC device 70 can output the vibration condition stored in the ROM 72 as an independent variable to the servo amplifier 50. Thus, the vibration component Vc is applied to the movement M0 of the driven object so that the internal stress generated in the structure when the driven object stops is released as much as possible. The vibration condition can also be searched under the standard amplitude A = 1 to 100 μm and the standard frequency f = 100 to 1000 Hz.

[0091] The vibration conditions to be searched may also include waveforms such as triangular waves or rectangular waves.

[0092] like Figure 8 As shown, the servo amplifier 50 can also perform semi-closed loop control in the following manner, that is, after the driven object reaches the target position P2, within the set period 202 within the stop period 201 at the target position P2, the vibration component Vc is applied to the driven object. The set period 202 refers to the period from the moving stop time t1 when the driven object reaches the target position P2 until the vibration stop time t2, which is shorter than the stop period 201. The set period 202 is not particularly limited, and is 1 to 1000 milliseconds, etc. By continuing to vibrate within the set period 202 after the driven object reaches the target position P2, the internal stress remaining in the structure from the servo motor 40 to the driven object when the driven object is at the target position P2 can be made smaller. As a result, the accuracy of the stop position of the driven object can be further improved.

[0093] Figure 2 The machine tool 1 shown may have a vibration condition determination mode for determining the vibration condition of the vibration component Vc in addition to the machining mode for machining the workpiece W1 with the tool TO1 according to the machining program PR2 .

[0094] Fig. 9 The vibration condition determination process performed by the NC device 70 in the vibration condition determination mode is schematically illustrated. When the operation unit 80 receives an operation for selecting the vibration condition determination mode, the NC device 70 starts the vibration condition determination process. The vibration condition determination process will be described below using the movement of the tool TO1 as an example.

[0095] When the vibration condition determination process starts, the NC device 70 sets a candidate i for obtaining the torque value TR1i when the tool TO1 stops moving from among a plurality of candidates i for the vibration condition (step S102). The candidate i for the vibration condition is, for example, a combination of a frequency fi and an amplitude Ai. A waveform such as a triangular wave or a rectangular wave, Figure 8 The setting period 202 shown in the figure may also be included in the factors of candidate i. Next, the NC device 70 causes the servo amplifier 52 for the tool to perform semi-closed loop control so as to apply the vibration component of candidate i from the intermediate position P3 to the movement of the tool TO1 from the initial position P1 to the target position P2 (movement M0 of the driven object) (step S104). After the movement of the tool TO1 stops and the addition of the vibration component also stops, the NC device 70 obtains the torque value TR1i from the servo amplifier 52 (step S106).

[0096] As described above, the NC device 70 and the servo amplifier 52 perform semi-closed loop control using the candidate i as the vibration condition, and detect the torque generated by the servo motor 42 when the tool TO1 stops at the target position P2.

[0097] After obtaining the torque value TR1i, the NC device 70 determines whether to end the search for the vibration condition (step S108). For example, the NC device 70 may determine that the search is ended when the torque value TR1i is lower than the reference torque value TR0 corresponding to the reference torque, or may determine that the search is ended when the torque value TR1i has been obtained for all candidates i. If the NC device 70 determines that the search for the vibration condition is not ended, it repeats the processing of steps S102 to S108. If the NC device 70 determines that the search for the vibration condition is ended, the candidate i whose torque value TR1i is lower than the reference torque value TR0 is determined as the vibration condition of the vibration component Vc (step S110), and the vibration condition determination processing is ended. In step S110, the NC device 70 may also determine the candidate i with the smallest torque value among the obtained torque values ​​TR1i as the vibration condition of the vibration component Vc.

[0098] As described above, the NC device 70 and the servo amplifier 52 determine, among the plurality of candidates i, the candidate in which the torque generated by the servo motor 42 when the movement of the tool TO1 stops is lower than the reference torque as the vibration condition of the vibration component Vc.

[0099] When the tool TO1 stops at the target position P2 in the semi-closed loop control, the servo motor 42 generates a torque corresponding to the internal stress of the structure up to the tool TO1. If the vibration condition of the vibration component Vc is determined in such a way that the torque generated by the servo motor 42 is lower than the reference torque when the tool TO1 stops moving, the internal stress remaining in the structure when the tool TO1 stops moving is reduced. Therefore, the accuracy of the moving stop position of the tool TO1 in the machining mode is improved by the vibration condition determination process. Of course, the accuracy of the stop position of the driven object in the machining mode is also improved by similar actions regarding the B-axis rotation of the rotary unit 25 and the Z-axis movement of the workpiece W1.

[0100] The frequency of the vibration component Vc may be included in a resonant frequency band that can cause the portion of the machine tool 1 that holds the driven object to resonate. When the driven object is the tool TO1, the portion that holds the driven object includes at least the tool holder 20, and may also include at least a portion of the guide mechanism 32 as a portion that generates resonance. When the driven object is the workpiece W1, the portion that holds the driven object includes at least the spindle box 10, and may also include at least a portion of the guide mechanism 31 as a portion that generates resonance. The resonant frequency (set as fr) generated in the portion that holds the driven object is measured, for example, by a hammer test before the machine tool 1 is put on the market, and is written into the ROM 72. Since the measured resonant frequency fr has a range, the range is set to ±Δf (Δf>0), and the resonant frequency band refers to a range of frequencies that may generate resonance, such as (fr-Δf) to (fr+Δf).

[0101] When the frequency of the vibration component Vc is included in the resonance frequency band, the structure from the servo motor 40 to the driven object vibrates relatively strongly by applying the vibration component Vc of the resonance frequency band to the driven object from the midway position P3 to the target position P2. In addition, the amplitude A of the vibration component Vc is small, about 1 to 100 μm, and the vibration component Vc can only be applied to the movement M0 of the driven object from the midway position P3. Therefore, the reduction in the position accuracy of the driven object caused by the resonance itself generated in the part holding the driven object can be suppressed. In particular, when the command CM1 is a fast feed command without cutting of the workpiece W1, the resonance will not cause the position accuracy of the driven object to be reduced. By vibrating the structure relatively strongly, the internal stress generated in the structure is easily released, thereby further reducing the internal stress remaining in the structure. Therefore, when the frequency of the vibration component Vc is included in the resonance frequency band, the accuracy of the stop position of the driven object can be further improved.

[0102] Figure 2 The machine tool 1 shown in the figure can also determine the frequency of the vibration component Vc as the frequency of the resonance frequency band in the vibration condition determination mode. The resonance frequency fr included in the resonance frequency band can be determined by Fig.10 The current command 300 with the scanning frequency variation illustrated in FIG. 1 is input to the servo amplifier 50 and measured. Fig.10 In FIG. 5 , the horizontal axis is time t and the vertical axis is command value CV. The NC device 70 can use the current command 300 as Figure 3 The command 57 shown is output to the servo amplifier 50 .

[0103] The sweep frequency is the frequency that changes continuously from the start frequency to the end frequency. Fig.10 The sweep frequency with a continuously increasing frequency is shown in . The amplitude Ac of the current command 300 is constant regardless of the frequency.

[0104] Fig.11 The following schematically shows an example of the amplitude magnification M of vibration relative to the frequency f when an external force is applied to a mass point of a vibration system to cause it to vibrate. The amplitude magnification M is the ratio of the amplitude of output vibration to the amplitude of the external force. Fig.12 An example of a phase delay φ of the output vibration relative to the frequency f when an external force is applied to a mass point of the vibration system to cause it to vibrate is schematically shown. The phase delay φ is the phase difference between the external force and the output vibration, and the delay of the phase of the output vibration is expressed as a negative value with respect to the phase of the external force. In addition, the mass point corresponds to the portion of the machine tool 1 that holds the driven object, the external force corresponds to the current command 300 input to the servo amplifier 50, and the output vibration corresponds to the torque command 59 that has been fed back. Therefore, the amplitude magnification M corresponds to the ratio of the amplitude of the torque command 59 to the amplitude Ac of the current command 300.

[0105] like Fig.11 As shown in , the amplitude multiplier M reaches a peak value near the natural vibration frequency fn of the particle. The reason is that resonance occurs. The peak value of the amplitude multiplier M depends on the damping ratio of the vibration system. The larger the damping ratio, the lower it is. Fig.12 As shown, the phase delay φ of the output vibration relative to the frequency f is greater than -90° when f<fn, is -90° when f=fn, and is less than -90° and greater than -180° when f>fn.

[0106] According to the above, when the current command 300 with the sweep frequency variation is input to the servo amplifier 50, the frequency at which the phase delay φ of the torque command 59 that vibrates by receiving feedback becomes -90° becomes the resonance frequency fr. Therefore, the resonance frequency fr may be determined as the frequency of the vibration component Vc in the vibration condition determination mode.

[0107] Fig.13 The frequency determination process performed by the NC device 70 in the vibration condition determination mode is schematically illustrated. When the operation unit 80 receives an operation for determining the frequency of the vibration component Vc in the vibration condition determination mode, the NC device 70 starts the frequency determination process. The frequency determination process is described below using the movement of the tool TO1 as an example.

[0108] When the frequency determination process starts, the NC device 70 uses the current command 300 with a sweep frequency change that continuously changes from the start frequency to the end frequency as Figure 3 The command 57 shown in FIG. 1 is output to the servo amplifier 52 (step S202). The servo amplifier 52 inputs the current command 300 into the semi-closed loop, detects the phase delay φ of the torque command 59 that vibrates by receiving feedback, and outputs the scanning information indicating the change of the phase delay φ with respect to the frequency of the current command 300 to the NC device 70. The scanning information becomes a range from the starting frequency to the ending frequency. Fig.12 The NC device 70 that has received the scanning information acquires the frequency of the current command 300 when the phase delay φ is -90° as the resonance frequency fr (step S204).

[0109] In the above manner, the NC device 70 and the servo amplifier 52 input the current command 300 to the semi-closed loop to detect the resonance frequency fr generated in the portion of the machine tool 1 that holds the tool TO1 .

[0110] In addition, the detection of the resonance frequency fr is not limited to the detection based on the phase delay φ. For example, the frequency at which the amplitude magnification M relative to the frequency of the current command 300 is the maximum may be detected as the resonance frequency fr. In addition, when the tool holder 20 is provided with a vibration sensor, the vibration of the tool holder 20 relative to the frequency of the current command 300 may be detected by the vibration sensor, and the frequency at which the amplitude of the tool holder 20 is amplified to the maximum may be detected as the resonance frequency fr.

[0111] After detecting the resonance frequency fr, the NC device 70 determines the resonance frequency fr as the frequency of the vibration component Vc (step S206 ), and ends the frequency determination process.

[0112] By determining the detected resonance frequency fr as the frequency of the vibration component Vc, the structure from the servo motor 42 to the tool TO1 is relatively strongly vibrated by using the vibration component Vc of the resonance frequency fr applied to the driven object from the intermediate position P3 to the target position P2. By relatively strongly vibrating the structure within a range that can suppress the reduction in the position accuracy of the tool TO1 caused by the resonance itself, the internal stress generated in the structure is easily released, thereby further reducing the internal stress remaining in the structure. Therefore, the accuracy of the moving stop position of the tool TO1 is further improved. Of course, with regard to the B-axis rotation of the rotary unit 25, the Z-axis movement of the workpiece W1, etc., the accuracy of the stop position of the driven object in the processing mode is also improved through similar effects.

[0113] Furthermore, in order to determine vibration conditions other than the frequency, such as the amplitude of the vibration component Vc, the NC device 70 may also perform Fig. 9 The vibration conditions shown determine the treatment.

[0114] As described above, when the driven object moves from the intermediate position P3 to the target position P2 in the semi-closed loop control, the vibration component Vc is applied to the movement M0 of the driven object, so the internal stress generated in the structure from the servo motor 40 to the driven object is released, and the driven object reaches the target position P2. By reducing the residual stress of the structure when the driven object stops, and the actual stop position of the driven object is close to the target position P2, the accuracy of the stop position of the driven object is improved. By releasing the internal stress of the structure when the driven object moves, the increase in the cycle time of the command CM1 can be suppressed. Therefore, this specific example can suppress the increase in the cycle time of the command CM1 and improve the accuracy of the stop position of the driven object. In addition, by reducing the residual stress of the structure, the torque generated by the servo motor 40 when the driven object stops becomes smaller, thereby reducing the standby power.

[0115] (3) Variations:

[0116] The present invention contemplates various variations.

[0117] For example, the control unit U1 may include not only the machine body 2 but also the machine body 2 and the computer 100 .

[0118] The command CM1 for moving the driven object is preferably a rapid feed command for moving the driven object without cutting the workpiece W1 , but may be a cutting feed command for moving the driven object while cutting the workpiece W1 .

[0119] (4) Conclusion:

[0120] As described above, according to the present invention, a technology such as a machine tool that can improve the accuracy of the stop position of a driven object when performing semi-closed loop control can be provided in various forms. Of course, the technology consisting only of the constituent elements of the claims can also obtain the basic functions and effects.

[0121] In addition, it is also possible to implement a configuration in which each configuration disclosed in the above examples is replaced or modified, a configuration in which a known technology and each configuration disclosed in the above examples are replaced or modified, etc. The present invention also includes these configurations, etc.

[0122] [Explanation of Symbols]

[0123] 1: Machine tools

[0124] 2: Mechanical body

[0125] 10: Spindle box

[0126] 11: Spindle

[0127] 12: Holding part

[0128] 13: Motor

[0129] 20: Knife holder

[0130] 21: Comb knife holder

[0131] 22: Hexagonal tool holder

[0132] 25: Rotary unit

[0133] 30, 31, 32: Guidance mechanism

[0134] 40, 41, 42: servo motor

[0135] 43: Encoder

[0136] 50, 51, 52: Servo amplifier

[0137] 57: Instructions

[0138] 58: Speed ​​command

[0139] 59: Torque command

[0140] 70:NC device

[0141] 201: Stop period

[0142] 202: Setting period

[0143] 300: Current command

[0144] A. Ai: Amplitude

[0145] AR1: First Area

[0146] AR2, AR3: Second area

[0147] AR4, AR5: Third area CM1: Command

[0148] CV: Command value

[0149] Er: error f, fi: frequency

[0150] fn: natural vibration frequency fr: resonance frequency

[0151] M: Amplitude magnification

[0152] M0: Movement of the driven object M1: Forward motion

[0153] M2: Backward movement

[0154] P1: Initial position

[0155] P2: Target position

[0156] P3: Midway position

[0157] Ps: Action starting point

[0158] PR1: Control Program

[0159] PR2: Processing program

[0160] SG1: Position feedback signal SG3: Speed ​​feedback signal t1: Movement stop time t2: Vibration stop time TO1: Tool

[0161] TR0: Reference torque value TR1i: Torque value

[0162] U1: Control unit

[0163] Vc: Vibration component

[0164] W1: Workpiece

[0165] x1: Control position

[0166] x2: actual position φ: phase delay.

Claims

1. A machine tool that uses a tool to process a workpiece and has: A guiding mechanism, used for guiding a driven object, wherein the driven object is at least one of the tool and the workpiece; a servo motor to move the driving object guided by the guide mechanism; and A control unit performs semi-closed loop control on the servo motor to move the driven object from an initial position to a target position; and The control unit performs the semi-closed loop control in a manner that adds a vibration component to the movement of the driven object from an intermediate position between the initial position and the target position until the target position is reached, wherein: The vibration component repeatedly performs an advance motion toward the target position and a retreat motion opposite to the advance motion. 2 . The machine tool according to claim 1 , wherein the control unit performs the semi-closed loop control by applying the vibration component to the driven object for a set period within a period during which the driven object stops at the target position after reaching the target position.

3. A machine tool according to claim 1 or 2, wherein the control unit, in a vibration condition determination mode for determining the vibration condition of the vibration component, uses each of a plurality of candidates for the vibration condition as the vibration condition to perform the semi-closed loop control so as to detect the torque generated by the servo motor when the driven object stops at the target position, and determines a candidate among the plurality of candidates when the torque is lower than a reference torque as the vibration condition. 4 . The machine tool according to claim 1 , wherein the frequency of the vibration component is included in a resonance frequency band that causes a portion of the machine tool that holds the driven object to resonate.

5. A machine tool according to claim 1 or 2, wherein the control unit inputs a current instruction with a change in scanning frequency into the semi-closed loop in a vibration condition determination mode for determining the frequency of the vibration component to detect the resonant frequency generated by the part of the machine tool that holds the driven object, and determines the detected resonant frequency as the frequency of the vibration component.

Images