Machine tools and their control methods

Abstract

A machine tool and its control method are provided, which automatically adjusts the clearance between the rotating guide sleeve and the bar stock by adjusting the opening of the rotating guide sleeve through an adjusting nut, wherein the rotating guide sleeve and the front spindle rotate synchronously. The rotating guide sleeve has an adjusting nut, which adjusts the clearance by rotating the guide sleeve body and simultaneously engages with the guide sleeve body when adjusting the clearance between the bar stock and the guide sleeve body. The control device has a guide sleeve opening determination unit, which determines the amount of clearance adjustment based on the rotation angle of the front spindle when the back spindle rotates while holding the bar stock with the back spindle and without energizing the front spindle drive motor.

Description

[Technical Field]

[0001] This invention relates to a machine tool for adjusting the gap between a bar and a rotating guide sleeve, and a control method thereof. [Previous Technology]

[0002] A machine tool with a guide bushing is known in the past. The guide bushing is disposed in front of the spindle and supports and guides the bar stock held by the spindle. In order to process the bar stock stably and with good machining accuracy, it is necessary to adjust the gap between the bar stock and the guide bushing (also known as guide bushing opening adjustment). There are known technologies for automatically adjusting the opening of the guide bushing (e.g., Patent Document 1).

[0003] Patent document 1 is Japanese Patent Application Publication No. 7-328804. [Summary of the Invention]

[0004] In the machine tool described in Patent Document 1, when adjusting the opening of the guide sleeve, an adjusting nut (also called a drawbar) screwed into the guide sleeve is used. Here, the guide sleeve of Patent Document 1 does not rotate synchronously with the spindle, but in addition to avoiding galling of the guide sleeve by the bar stock and avoiding deterioration of the surface properties of the bar stock, it is also preferable to automatically adjust the gap between the rotating guide sleeve and the bar stock in order to process the bar stock stably and with good machining accuracy.

[0005] Hereinafter, the present invention solves the problems of the prior art, that is, the object of the present invention is to provide a machine tool and a control method thereof, which automatically adjusts the gap between the rotating guide sleeve and the bar when the opening of the rotating guide sleeve is adjusted by adjusting the nut and the rotating guide sleeve is configured to rotate synchronously with the front spindle.

[0006] The invention of claim 1 is a machine tool comprising: a front spindle for rotatably holding a bar; a front spindle drive motor for rotatably driving the front spindle; an encoder for detecting the rotation angle of the front spindle drive motor; a rotary guide sleeve disposed in front of the front spindle on a guide sleeve support platform, allowing and supporting the rotation of the bar about a pivot axis and its movement in the direction of the pivot axis as it enters and exits the front spindle, and rotating synchronously with the front spindle; a back spindle disposed opposite to the front spindle and rotatably holding the bar; a back spindle drive motor for rotatably driving the back spindle; and a control device for controlling the operation of the front spindle and the back spindle. The rotary guide sleeve has a guide sleeve frame, a guide sleeve body, and an adjusting nut. The guide sleeve frame is fixed to the guide sleeve support platform. The guide sleeve body can rotate relative to the guide sleeve frame and allows and supports the rotation of the bar about the axis of rotation and the movement in the direction of the axis of rotation. The adjusting nut is used to adjust the gap between the bar and the guide sleeve body by rotating the guide sleeve body to adjust the gap, and at the same time, it is screwed into the guide sleeve body. The control device has a guide sleeve opening degree determining unit. The guide sleeve opening degree determining unit determines the amount of gap adjustment based on the rotation angle of the front spindle when the back spindle is rotated while the bar is held by the back spindle and the front spindle drive motor is not energized, thereby solving the above-mentioned problem.

[0007] The invention of claim 2, apart from the machine tool structure of claim 1, solves the above-mentioned problem by making the retaining fixture for holding the bar removable by the back spindle system.

[0008] The invention of claim 3 is, in addition to the machine tool structure of claim 1 or 2, a rotary fixture that engages with the adjusting nut of the rotary guide sleeve opposite to the front spindle and rotates the adjusting nut, and is attached to the bar between the front spindle and the rotary guide sleeve, thereby further solving the above-mentioned problems.

[0009] Claim 4's invention relates to a control method for a machine tool, the machine tool comprising: a front spindle for rotatably holding a bar; a front spindle drive motor for rotatably driving the front spindle; an encoder for detecting the rotation angle of the front spindle drive motor; a rotary guide sleeve disposed in front of the front spindle on a guide sleeve support platform, allowing and supporting the rotation of the bar about a pivot axis and its movement in the direction of the pivot axis as it enters and exits the front spindle, and rotating synchronously with the front spindle; a back spindle disposed opposite to the front spindle and rotatably holding the bar; a back spindle drive motor for rotatably driving the back spindle; and a control device for controlling the operation of the front spindle and the back spindle, the rotary guide sleeve having a guide sleeve frame, a guide sleeve body, and an adjusting nut, the guide sleeve frame being fixed to the guide sleeve support platform, and the guide sleeve body being rotatable relative to the guide sleeve frame. The tool allows and supports rotation of the bar about a pivot and movement in the direction of the pivot. The adjusting nut is used to adjust the gap between the bar and the guide sleeve body by rotating the guide sleeve body to adjust the gap, and simultaneously engages with the guide sleeve body. The control method of the machine tool includes: holding the bar with the back spindle; rotating the back spindle about a pivot; measuring the rotation angle of the front spindle drive motor generated by rotating the back spindle with the encoder; determining the adjustment amount of the gap based on the rotation angle of the front spindle measured by the encoder; and rotating the back spindle about a pivot to rotate the rotating guide sleeve relative to the adjusting nut to form the determined adjustment amount of the gap, thereby further solving the above-mentioned problems.

[0010] Effects of the invention: The machine tool according to claim 1 has a control device with a guide sleeve opening determination unit. The guide sleeve opening determination unit determines the amount of clearance adjustment based on the rotation angle of the front spindle when the back spindle is rotated, while the back spindle is holding the bar and the front spindle drive motor is not magnetized. In this way, when the back spindle holding the bar is rotated, the change in the rotation angle of the front spindle, which can rotate arbitrarily, is based only on the rotation of the bar that is driven by the rotation of the back spindle. Therefore, compared with the case where the clearance between the rotating guide sleeve and the bar is adjusted based on the load of the back spindle drive motor when the back spindle holding the bar is rotated, the signal-to-noise ratio is improved. When the opening of the rotating guide sleeve is adjusted by adjusting the nut and the rotating guide sleeve is in a structure that rotates synchronously with the front spindle, the clearance between the rotating guide sleeve and the bar can be adjusted with high precision and automatically.

[0011] In addition to the effects achieved by the machine tool of claim 1, the back spindle holds the bar by means of a detachable and retaining fixture. The retaining fixture attached to the back spindle holds the bar. Therefore, even if the back spindle cannot directly hold the bar, the bar can be indirectly held on the back spindle by selecting a retaining fixture corresponding to the bar.

[0012] The machine tool according to claim 3, in addition to the effects achieved by the machine tool according to claim 1 or 2, has a rotary fixture that engages with the adjusting nut of the rotating guide sleeve opposite to the front spindle and rotates the adjusting nut. The rod is attached between the front spindle and the rotating guide sleeve. In this way, the rod is held by the back spindle and the rotating fixture is engaged with the adjusting nut. The rod is rotated by the back spindle, and the adjusting nut of the rotating guide sleeve rotates. Therefore, the gap between the rotating guide sleeve and the rod can be adjusted with high precision and automatically.

[0013] The control method for a machine tool according to claim 4 includes the steps of measuring the rotation angle of the front spindle drive motor generated by rotating the back spindle with an encoder, determining the adjustment amount of the clearance based on the rotation angle of the front spindle measured by the encoder, and rotating the back spindle about a pivot axis to rotate the rotating guide sleeve relative to the adjusting nut to form the determined adjustment amount of the clearance. In this way, when the back spindle holding the bar is rotated, the change in the rotation angle of the front spindle, which can rotate arbitrarily, is based only on the rotation of the bar accompanying the rotation of the back spindle. Therefore, compared with the case where the clearance between the rotating guide sleeve and the bar is adjusted based on the load of the back spindle drive motor when the back spindle holding the bar is rotated by the back spindle drive motor, the signal-to-noise ratio is improved. In the case where the opening of the rotating guide sleeve is adjusted by adjusting the adjusting nut and the rotating guide sleeve is configured to rotate synchronously with the front spindle, the clearance between the rotating guide sleeve and the bar can be adjusted with high precision and automatically.

Implementation Method

[0015] The present invention comprises a machine tool comprising: a front spindle for rotatably holding a bar stock; a front spindle drive motor for rotatably driving the front spindle; an encoder for detecting the rotation angle of the front spindle drive motor; a rotary guide sleeve disposed in front of the front spindle on a guide sleeve support platform, allowing and supporting the rotation of the bar stock entering and exiting the front spindle around a pivot axis and its movement in the direction of the pivot axis, and rotating synchronously with the front spindle; a back spindle disposed opposite to the front spindle for rotatably holding the bar stock; a back spindle drive motor for rotatably driving the back spindle; and a control device for controlling the operation of the front spindle and the back spindle, wherein the rotary guide sleeve has a guide sleeve frame. The guide sleeve body and adjusting nut are included. The guide sleeve frame is fixed to the guide sleeve support platform. The guide sleeve body can rotate relative to the guide sleeve frame and allows and supports the rotation of the bar around the axis and the movement in the direction of the axis. The adjusting nut is used to adjust the gap between the bar and the guide sleeve body by rotating the guide sleeve body to adjust the gap. At the same time, it is screwed into the guide sleeve body. The control device has a guide sleeve opening degree determining unit. The guide sleeve opening degree determining unit determines the amount of gap adjustment based on the rotation angle of the front spindle when the back spindle is rotated while the bar is held by the back spindle and the front spindle drive motor is not energized. The gap between the rotating guide sleeve and the bar can be adjusted automatically. The specific implementation mode is flexible.

[0016] Furthermore, any control method for a machine tool includes: a front spindle for rotatably holding a bar; a front spindle drive motor for rotatably driving the front spindle; an encoder for detecting the rotation angle of the front spindle drive motor; a rotary guide sleeve disposed in front of the front spindle on a guide sleeve support platform, allowing and supporting the rotation of the bar entering and exiting the front spindle around a pivot axis and its movement in the direction of the pivot axis, and rotating synchronously with the front spindle; a back spindle disposed opposite to the front spindle for rotatably holding the bar; a back spindle drive motor for rotatably driving the back spindle; and a control device for controlling the operation of the front spindle and the back spindle. The rotary guide sleeve has a guide sleeve frame, a guide sleeve body, and an adjusting nut. The guide sleeve frame is fixed to the guide sleeve support platform, and the guide sleeve body... It can rotate relative to this guide sleeve frame, and allows and supports the rotation of the bar about the axis and the movement in the direction of the axis. The adjusting nut is used to adjust the gap between the bar and the guide sleeve body by rotating the guide sleeve body to adjust the gap, and at the same time engages with the guide sleeve body. The control method of the machine tool includes: the step of holding the bar with the back spindle; the step of rotating the back spindle about the axis; the step of measuring the rotation angle of the front spindle drive motor generated by rotating the back spindle with an encoder; the step of determining the amount of gap adjustment based on the rotation angle of the front spindle measured by the encoder; and the step of rotating the back spindle about the axis to make the rotating guide sleeve rotate relative to the adjusting nut to form the determined amount of gap adjustment, so as to automatically adjust the gap between the rotating guide sleeve and the bar. The specific implementation mode is arbitrary.

[0017] Example 1: The following describes a machine tool 100 according to an embodiment of the present invention based on Figures 1 to 10B.

[0018] <1. Overview of the Machine Tool> First, based on Figures 1 to 5, the overview of the machine tool 100 will be described. Figure 1 is a schematic configuration diagram of an automatic lathe according to an embodiment of the machine tool of the present invention.

[0019] Machine tool 100 is an automatic lathe, as shown in Figure 1, and has a bed 110 that is placed on the ground F and is rectangular when viewed from above. Hereinafter, the vertical direction relative to the bed 110 is referred to as the "Y direction", the direction of the long side of the bed 110 when viewed from above is referred to as the "Z direction", and the direction of the short side of the bed 110 when viewed from above is referred to as the "X direction".

[0020] The bed 110 is provided with a front spindle 120, a front spindle feed mechanism 130, a rotary guide sleeve 140, a guide sleeve support 150, a back spindle 160, and a back spindle feed mechanism 170. The front spindle 120 rotatably holds the bar W. The front spindle feed mechanism 130 feeds the front spindle 120 in the Z1 direction, which is parallel to the Z direction. The rotary guide sleeve 140 allows and supports the rotation of the bar W about the axis L and the movement in the direction of the axis L as it enters and exits from the front spindle 120. The guide sleeve support 150 is located in front of the front spindle 120 and supports the rotary guide sleeve 140. The back spindle 160 is arranged opposite to the front spindle 120 and the rotary guide sleeve 140 and rotatably holds the bar W. The back spindle feed mechanism 170 feeds the back spindle 160 in the Z2 direction, which is parallel to the Z direction, and in the X2 direction, which is parallel to the X direction.

[0021] Here, the front main shaft 120 and the bar W can move forward and backward in the Z1 direction. "Front" of the front main shaft 120 and the bar W refers to the direction in which the front main shaft 120 and the bar W approach the back main shaft 160, and "rear" of the main shaft 120 and the bar W refers to the direction in which the front main shaft 120 and the bar W move away from the back main shaft 160. Similarly, "front" of the rotating guide sleeve 140 refers to the direction in which the rotating guide sleeve 140 approaches the back main shaft 160, and "rear" of the rotating guide sleeve 140 refers to the direction in which the rotating guide sleeve 140 moves away from the back main shaft 160. Furthermore, the back main shaft 160 can move forward and backward in the X2 direction and also in the Z2 direction. "Front" of the back main shaft 160 refers to the direction in which the back main shaft 160 approaches the front main shaft 120, and "rear" of the back main shaft 160 refers to the direction in which the back main shaft 160 moves away from the front main shaft 120.

[0022] The workpiece to be processed by the machine tool 100 is a long workpiece in the shape of a round bar, namely bar W. It is supplied from the rear end of the front spindle 120 by the push head of the bar feeder (not shown). The front spindle 120 is rotatably supported by the rotating guide sleeve 140 around the rotating shaft L and is fed towards the rear spindle 160. In addition, the top end of the push head of the bar feeder is provided with a finger chuck for holding the rear end of the bar W.

[0023] Furthermore, the machine tool 100 is equipped with a control device 180 to control the operation of the front spindle 120 and the back spindle 160.

[0024] <2. Components of the Machine Tool> Next, the components of the machine tool 100 described above will be explained in detail based on Figures 1 to 5. Figure 2 is a configuration diagram of the rotating guide sleeve, the front spindle, and the back spindle; Figure 3 is a perspective view of the adjusting nut shown in Figure 2; Figure 4 is a perspective view of the retaining fixture shown in Figure 2; and Figure 5 is a perspective view of the rotating fixture shown in Figure 2.

[0025] <2.1 Front Spindle> The front spindle 120, as shown in Figure 1, includes a spindle stage 121, a front spindle body 122, a front spindle drive motor 123, and an encoder 124. The spindle stage 121 is mounted on the front spindle feed mechanism 130 and is movable in the Z1 direction. The front spindle body 122 is rotatably supported on the spindle stage 121. The front spindle drive motor 123 drives the front spindle body 122 to rotate. The encoder 124 detects the rotation angle of the front spindle drive motor 123.

[0026] The front spindle body 122 is supported on the spindle table 121 with the Z1 direction as shown in Figure 1 as its axis. As shown in Figure 2, the bar W can be rotatably held (held) around the rotation axis L by the chuck 122a. The chuck 122a is concentrically arranged with the front spindle body 122 and rotates integrally with the front spindle body 122. That is, the rotation axis L of the bar W is consistent with the rotation center of the front spindle 120.

[0027] Furthermore, the front end of the main shaft body 122 is as shown in Figure 1, and is provided with a timing pulley 122b, with the timing belt V1 wrapped around the timing pulley 122b.

[0028] The front spindle drive motor 123 has a stator and a rotor. It generates a magnetic field by rotating either one, and generates driving force by changing the magnetic field. It is called an "electric motor".

[0029] <2.2 Front Spindle Feed Mechanism> The front spindle feed mechanism 130 has a Z1 direction slide rail 131, a Z1 direction slider 132, and a Z1 direction motor 133. The Z1 direction slide rail 131 is fixed to the bed 110 and extends in the Z1 direction. The Z1 direction slider 132 is mounted on the Z1 direction slide rail 131 and can slide along the Z1 direction. The Z1 direction motor 133 causes the Z1 direction slider 132 to slide. The spindle table 121 of the front spindle 120 is disposed on the Z1 direction slider 132.

[0030] Furthermore, a self-rotating reversible shaft 134 is provided in this front main spindle feed mechanism 130. The main spindle-side timing pulley 134a, around which the timing belt V1 is wound, and the rotating guide sleeve-side timing pulley 134b, around which the timing belt V2 is wound, are connected to this reversible shaft 134. Therefore, when the front main spindle body 122 is driven to rotate by the front main spindle drive motor 123, the reversible shaft 134 rotates through the timing belt V1.

[0031] <2.3 Rotary Guide Sleeve> The rotary guide sleeve 140, as shown in Figure 1, is inserted into the guide sleeve support 150, which has a rotary guide sleeve insertion hole 150a concentric with the front spindle 120.

[0032] Furthermore, as shown in Figure 2, this rotating guide sleeve 140 has a hollow cylindrical guide sleeve frame 141, a guide sleeve assembly 142, a bearing 143, a cylindrical guide sleeve body 144, an adjusting nut 145, a timing pulley 146, an anti-loosening nut 147, and a flange 148. The guide sleeve frame 141 is inserted into and fixed in the rotating guide sleeve insertion hole 150a of the guide sleeve support platform 150. The guide sleeve assembly 142 is inserted into the guide sleeve frame 141. The bearing 143 is disposed between the guide sleeve frame 141 and the guide sleeve assembly 142. The guide sleeve assembly 142 is rotatably supported relative to the guide sleeve bracket 141. The guide sleeve body 144 is inserted into the guide sleeve assembly 142. The adjusting nut 145 is screwed into the male thread 144a formed at the rear end of the guide sleeve body 144. The timing pulley 146 is inserted into the rear end side of the guide sleeve bracket 141 and can rotate relative to the guide sleeve bracket 141. The anti-loosening nut 147 is engaged with the guide sleeve assembly 142 and prevents the timing pulley 146 from falling off. The flange 148 is fixed to the guide sleeve support platform 150 and prevents the timing pulley 146 from falling off.

[0033] The guide sleeve frame 141 has a hollow cylindrical guide sleeve frame body 141a and an annular bearing pressing member 141b. The guide sleeve frame body 141a is inserted into the rotating guide sleeve insertion hole 150a of the guide sleeve support table 150. The bearing pressing member 141b is mounted on the rear end side of the guide sleeve frame body 141a and together with the guide sleeve frame body 141a, it positions the bearing 143 in the front-rear direction.

[0034] The inner circumference of the front end portion of the guide sleeve assembly 142 has a tapered portion 142a whose inner diameter gradually decreases rearward. Furthermore, the guide sleeve assembly 142 has a screw through hole 142c in the radial direction for the insertion of a locking screw 142b. Additionally, a key 142d that engages with the timing pulley 146 is embedded in the outer circumference of the rear end portion of the guide sleeve assembly 142.

[0035] The guide sleeve body 144, as shown in Figure 2, supports and guides the rod W held by the front main shaft 120 to rotate about the axis of rotation L and move in the direction of the axis of rotation L. The front end portion of this guide sleeve body 144 has a groove 144b extending in the Z direction.

[0036] Furthermore, a tapered portion 144c is formed on the outer periphery of the front end portion of the guide sleeve body 144. The outer diameter of the tapered portion 144c gradually decreases rearward and corresponds to the taper angle of the tapered portion 142a of the guide sleeve assembly 142. A rearwardly extending groove 144d is formed behind the tapered portion 144c. This groove 144d is formed to gradually deepen rearward and extends until it reaches the male thread 144a.

[0037] Furthermore, the retaining screw 142b, which is screwed into the screw through hole 142c of the guide sleeve assembly 142, is inserted into the groove 144d. Therefore, the retaining screw 142b engages with the groove 144d, and the guide sleeve body 144 can only move forward and backward relative to the guide sleeve assembly 142 in the Z direction, and the guide sleeve body 144 and the guide sleeve assembly 142 can rotate together around the pivot L. That is, the guide sleeve body 144 can rotate relative to the guide sleeve bracket 141 when the retaining screw 142b engages with the groove 144d.

[0038] The adjusting nut 145 (also called the pull rod) is a hollow cylindrical shape and is located at the rear of the guide sleeve body 144. The adjusting nut 145 can rotate relative to the guide sleeve assembly 142. As shown in Figure 2, the inner circumferential side of the front end portion of the adjusting nut 145 has a female thread 145a with a specified pitch, which engages with the male thread 144a formed on the rear end portion of the guide sleeve body 144.

[0039] Therefore, by rotating the adjusting nut 145 around the pivot L, the guide sleeve body 144 moves forward and backward relative to the guide sleeve assembly 142. When the guide sleeve body 144 moves backward relative to the guide sleeve assembly 142, the cone 144c is pushed by the cone 142a, and the front end portion of the guide sleeve body 144 bends towards the bar W through the groove 144b, thus reducing the opening of the front end portion of the guide sleeve body 144. On the other hand, when the guide sleeve body 144 moves forward relative to the guide sleeve assembly 142, the pushing force of the cone 142a is released, and the front end portion of the guide sleeve body 144 expands outward, thus increasing the opening of the front end portion of the guide sleeve body 144.

[0040] That is, the displacement of the guide sleeve body 144 in this embodiment (the opening degree of the rotating guide sleeve 140 is the same as the opening degree of the front end portion of the guide sleeve body 144) is determined by the amount of rotation relative to the adjusting nut 145. In other words, the adjusting nut 145 can rotate the guide sleeve body 144 to adjust the size of the gap when adjusting the gap between the rod W and the guide sleeve body 144.

[0041] Furthermore, as shown in Figure 3, the rear 145b of the adjusting nut 145 has several (e.g., three) engagement holes 145b1.

[0042] The timing pulley 146 is cylindrical, as shown in Figure 2, and is rotatably inserted into the rear end of the bearing abutment 141b of the guide sleeve 141.

[0043] A key groove 146a is formed on the inner circumference of the front end portion of the timing pulley 146, which engages with the key 142d of the guide sleeve assembly 142. Furthermore, a belt positioning groove 146b is formed on the outer circumference of the timing pulley 146, and the timing belt V2 is wound around this belt positioning groove 146b.

[0044] Therefore, when the front spindle body 122 rotates, the reverse shaft 134 also rotates via the timing belt V1, and the timing pulley 134b on the rotating guide sleeve side also rotates. Thus, the timing pulley 146 of the rotating guide sleeve 140 also rotates via the timing belt V2, the guide sleeve assembly 142 rotates via the key 142d, and the guide sleeve body 144 rotates via the locking screw 142b. That is, the guide sleeve body 144 rotates synchronously with the front spindle 120, that is, it rotates around the axis L at the same rotational speed as the front spindle 120.

[0045] The female thread formed on the inner circumference of the anti-loosening nut 147 engages with the male thread formed on the outer circumference of the rear end portion of the guide sleeve assembly 142. By engaging the female thread of the anti-loosening nut 147 with the male thread of the guide sleeve assembly 142, as shown in Figure 2, the timing pulley 146 will not fall off to the rear.

[0046] The flange 148 is a ring-shaped component, as shown in Figure 2, and is fixed to the guide sleeve support platform 150 by fixing bolt B.

[0047] <2.4 Guide Sleeve Support Table> The guide sleeve support table 150 is fixed to the bed 110. Furthermore, as shown in Figure 1, this guide sleeve support table 150 internally houses the rotating guide sleeve side timing pulley 134b, which is mounted on the top of the reverse shaft 134 of the front spindle feed mechanism 130.

[0048] Furthermore, a tool post moving mechanism 151 is provided on the back spindle 160 side of this guide sleeve support platform 150, and the tool post 152 is mounted on the tool post 152. The tool post moving mechanism 151 allows the tool post 152 to move in the X or Y direction. The cutting tool 152a with its top facing the rotating shaft L is mounted on the tool post 152. Therefore, by moving the front spindle 120 in the direction of the rotating shaft L and moving the tool post 152 in the X or Y direction, the cutting tool 152a can be used to machine the bar stock W.

[0049] <2.5 Back Spindle> The back spindle 160, as shown in Figure 1, has a spindle table 161, a back spindle body 162, and a back spindle drive motor 163. The spindle table 161 is mounted on the back spindle feed mechanism 170 and can move in the Z2 and X2 directions. The back spindle body 162 rotatably supports the spindle table 161, and the back spindle drive motor 163 drives the back spindle body 162 to rotate.

[0050] The back spindle body 162 is supported on the spindle table 161 with the Z2 direction, which is parallel to the Z1 direction shown in Figure 1, as its axis. As shown in Figure 2, the bar W can be rotatably held (held) by the chuck 162a. The chuck 162a is configured to be concentric with the back spindle body 162 and can rotate freely together with the back spindle body 162.

[0051] The collet 162a is as shown in Figure 2, and the retaining fixture 164 for holding the bar W is detachably mounted on the collet 162a. This retaining fixture 164, as shown in Figures 2 and 4, consists of a C-shaped spindle connector 164a, a C-shaped bar holder 164b, and a connecting bolt 164c. The spindle connector 164a is mounted on the back spindle body 162, the bar holder 164b holds the bar W, and the connecting bolt 164c connects the spindle connector 164a and the bar holder 164b. When viewed from the front spindle side 120, the collet 162a is a C-shaped component.

[0052] As shown in Figure 2, the spindle mounting fixture 164a has an inner diameter that is almost equal to the outer diameter of the back spindle body 162. Furthermore, as shown in Figure 4, the spindle mounting fixture 164a is secured to the back spindle body 162 by inserting a fastening bolt 164d into a through hole formed in a direction orthogonal to the circumferential direction of the spindle mounting fixture 164a, and then screwing it into a threaded hole opposite to this through hole. In this way, the spindle mounting fixture 164a and the back spindle body 162 are integrated and rotate together.

[0053] A through hole extending in the Z2 direction is formed in the bar holder 164b. A connecting bolt 164c is inserted into this through hole and screwed into a threaded hole 164a1 formed on the front of the spindle mount 164a, thereby forming the bar holder 164b and the spindle mount 164a integrally. Furthermore, since this bar holder 164b is a C-ring, as shown in Figure 2, the inner diameter φ of the bar holder 164b is variable. The inner diameter of this bar holder 164b is adjusted by inserting an adjusting bolt 164e into a through hole formed in a direction orthogonal to the circumferential direction of the bar holder 164b and screwing it into a threaded hole 164b1 opposite to this through hole.

[0054] <2.6 Back Spindle Feed Mechanism> The back spindle feed mechanism 170 is as shown in Figure 1, consisting of an X2 direction feed structure 171 and a Z2 direction feed structure 172. The X2 direction feed structure 171 is mounted on the table 110, and the Z2 direction feed structure 172 is mounted on the X2 direction feed structure 171.

[0055] The X2 direction feed structure 171 has an X2 direction slide rail 171a, an X2 direction slider 171b and an X2 direction motor 171c. The X2 direction slide rail 171a is fixed to the bed 110 and extends in the X2 direction. The X2 direction slider 171b is mounted on the X2 direction slide rail 171a and can slide along the X2 direction. The X2 direction motor 171c causes the X2 direction slider 171b to slide.

[0056] The Z2 direction feed structure 172 includes a Z2 direction slide rail 172a, a Z2 direction slider 172b, and a Z2 direction motor 172c. The Z2 direction slide rail 172a is fixed to the Z2 direction slider 171b and extends in the Z2 direction. The Z2 direction slider 172b is mounted on the Z2 direction slide rail 172a and can slide along the Z2 direction. The Z2 direction motor 172c causes the Z2 direction slider 172b to slide. A spindle table 161 of a back spindle 160 is provided on the Z2 direction slide rail 172a.

[0057] <2.7 Control Device> The rotation of the front spindle 120 and the back spindle 160, and the movement of the front spindle feed mechanism 130 and the back spindle feed mechanism 170 are controlled by the control device 180. The control device 180 has a control component 181 and an input component 182, which are connected by a bus.

[0058] The control component 181 is composed of a CPU or memory, for example, loading various programs or data stored in ROM into RAM and executing the program. That is, the machine tool 100 is controlled to operate by the program loaded into the RAM control component 181. In addition, the rotation of the front spindle 120 and the rear spindle 160, the movement of the front spindle feed mechanism 130 and the rear spindle feed mechanism 170, etc., can be set by a program or by input to the input unit 182.

[0059] Furthermore, the control assembly 181 includes a motor control unit 181a, a guide sleeve opening determination unit 181b, and a data sheet 181c. The motor control unit 181a controls the operation of the front spindle drive motor 123, the back spindle drive motor 163, and the Z2 direction motor 172c, for example, when adjusting the gap between the bar W and the rotating guide sleeve 140 (i.e., the rotating guide sleeve body 144). The guide sleeve opening determination unit 181b determines the adjustment amount of the gap between the bar W and the rotating guide sleeve body 144 based on the rotation angle of the front spindle drive motor 123 measured by the encoder 124 and referring to the data sheet 181c. More specifically, the guide sleeve opening determination unit 181b estimates the size of the gap between the bar W and the rotating guide sleeve body 144 by calculating the difference between the estimated gap size and the optimal gap size, and then determines the rotation amount of the back spindle 160 based on this difference, that is, determines the adjustment amount of the gap between the bar W and the rotating guide sleeve body 144. Data sheet 181c stores data corresponding to the rotation angle of the front spindle drive motor 123 for the material and diameter of the bar W, and data corresponding to the size of the gap between the bar W and the rotating guide sleeve body 144.

[0060] <2.8 Rotary Fixture> As shown in Figure 2, the machine tool 100 is equipped with a rotary fixture 190, which rotates the adjusting nut 145 that adjusts the gap between the adjusting bar W and the rotating guide sleeve body 144.

[0061] The rotating jig 190 is a C-shaped ring as shown in Figure 5, and the bar W is inserted into the rotating jig 190 as shown in Figure 2. Furthermore, like the bar holder 164b, the inner diameter of this rotating jig 190 is variable. The inner diameter of the rotating jig 190 is adjusted by inserting a fastening bolt 191 into a through hole formed in a direction orthogonal to the circumferential direction of the rotating jig 190, and screwing it into a threaded hole 190a opposite to this through hole.

[0062] Furthermore, a locking pin 192 is provided on the front 190b of the rotating fixture 190, and the locking pin 192 engages with the locking hole 145b1 of the adjusting nut 145 of the rotating guide sleeve 140.

[0063] <3. Gap Adjustment Step> Next, based on Figures 1 to 10B, an example of an adjustment step for the gap between the bar stock W and the rotating guide sleeve 140 of the machine tool 100 according to an embodiment of the present invention, that is, the gap size between the bar stock W and the rotating guide sleeve body 144, will be described. Figure 6A is a flowchart showing the steps for adjusting the gap between the bar and the rotating guide sleeve. Figure 6B is a flowchart showing the preparation steps shown in Figure 6A. Figure 6C is a flowchart showing the steps for adjusting the gap shown in Figure 6A. Figure 7A is a schematic diagram showing the state of inserting the bar into the front spindle. Figure 7B is a schematic diagram showing the state of inserting the bar into the rotating guide sleeve. Figure 7C is a schematic diagram showing the state of advancing the front spindle to engage the rotating fixture with the adjusting nut. Figure 8 is a schematic diagram showing the state of disengaging the rotating fixture from the adjusting nut. Figure 9 is a schematic diagram showing the rotating fixture and bar shown in Figure 8 viewed in the direction indicated by arrow IX in Figure 8. Figure 10A is a schematic diagram showing the state of retracting the back spindle to engage the rotating fixture with the adjusting nut. Figure 10B is a flowchart explaining the steps for rotating the back spindle to adjust the gap between the bar and the rotating guide sleeve body. Furthermore, the steps shown below are merely an example, and the adjustment of the gap size between the bar W and the rotating guide sleeve body 144 is not limited to the following steps.

[0064] <3.1 Preparation steps> (Step S10) First, the machine tool 100 series performs the preparation steps shown in Figure 6B.

[0065] (Step S11) In the preparation step, the bar W is inserted into the rear end of the front main shaft 120 (refer to Figure 7A) by the push-out head of the bar feeder (not shown), and then sequentially inserted into the rotating fixture 190 and the rotating guide sleeve 140. At this time, the rotation center of the back main shaft 160 is aligned with the rotation center of the front main shaft 120 and the rotation center of the rotating guide sleeve 140.

[0066] (Step S12) Next, as shown in Figure 7B, the rotating fixture 190 is tightened and fixed to the bar W, so that the rotating fixture 190 and the bar W are integrated and rotate about the axis L. Furthermore, when the rotating fixture 190 is fixed to the bar W, the distance D1 from the rotating fixture 190 to the adjusting nut 145 of the rotating guide sleeve 140 is shorter than the distance D2 from the bar W to the retaining fixture 164 of the back spindle 160.

[0067] (Step S13) Next, the bar W is pushed out until the engaging pin 192 of the rotating jig 190 is inserted into the engaging hole 145b1 of the adjusting nut 145 of the rotating guide sleeve 140. By inserting the engaging pin 192 of the rotating jig 190 into the engaging hole 145b1 of the adjusting nut 145 of the rotating guide sleeve 140, the direction of the adjusting nut 145, that is, the direction of the rotating guide sleeve body 144, is set to the specified direction. Furthermore, when the engaging pin 192 of the rotating jig 190 is inserted into the engaging hole 145b1 of the adjusting nut 145 of the rotating guide sleeve 140, since the distance D1 from the rotating jig 190 to the adjusting nut 145 of the rotating guide sleeve 140 is shorter than the distance D2 from the bar W to the retaining jig 164 of the back spindle 160, if the inner diameter φ of the retaining jig 164 of the back spindle 160 is made sufficiently large beforehand, the bar W will be inserted into the retaining jig 164 of the back spindle 160 as shown in Figure 7C.

[0068] Furthermore, when the bar W is being ejected, if the positions of the engagement hole 145b1 of the adjusting nut 145 and the engagement pin 192 of the rotating fixture 190 are misaligned in the direction of rotation, the bar W (i.e., the front main shaft 120 of the bar W) is rotated until the engagement hole 145b1 of the adjusting nut 145 and the engagement pin 192 of the rotating fixture 190 are aligned.

[0069] (Step S14) Next, in this state, the retaining fixture 164 is fastened to the bar W by means of the adjusting bolt 164e of the retaining fixture 164 of the back spindle 160 and held (held) by the back spindle 160.

[0070] (Step S15) Next, the magnetic field of the electric motor, namely the front spindle drive motor 123 of the front spindle 120, is cut off, so that the back spindle 160 moves forward toward the rotating guide sleeve 140 until the rotating fixture 190 is disengaged from the adjusting nut 145, forming the state shown in Figure 8.

[0071] <3.2 Inspection Step> (Step S20) Next, in this state, the back spindle 160 is rotated in a specified direction by a specified angle. That is, as shown in Figure 9, the back spindle 160 is rotated so that the bar W rotates only by a specified angle θ from the reference angle position P to the angle position P1.

[0072] (Step S21) Here, when the magnetization of the front spindle drive motor 123 is cut off, the rotation of the timing pulley 146 of the rotating guide sleeve 140 can cause the front spindle drive motor 123 of the front spindle 120 to rotate through the timing belts V1 and V2.

[0073] Therefore, as described above, when the bar W rotates only a predetermined angle θ from the reference angle position P to the angle position P1, if the gap between the bar W and the rotating guide sleeve body 144 is narrow, the bar W and the rotating guide sleeve body 144 may come into contact. This contact with the bar W may cause the rotating guide sleeve body 144 to be driven by the bar W. By driving the guide sleeve body 144, the guide sleeve assembly 142, which is formed by the guide sleeve body 144 and the fixing screw 142b, rotates, and the timing pulley 146, which engages with the key 142d embedded in the guide sleeve assembly 142, rotates. The rotation of this timing pulley 146 is transmitted by the timing belt V2 to the reverse shaft 134, by the reverse shaft 134 to the timing belt V1, by the timing belt V1 to the front spindle body 122 of the front spindle 120, and by the front spindle body 122 to the front spindle drive motor 123, which rotates.

[0074] Conversely, when the bar W rotates only by a specified angle θ from the reference angle position P to the angle position P1, if the gap between the bar W and the rotating guide sleeve body 144 is too large, the bar W will not contact the rotating guide sleeve body 144, and the rotating guide sleeve body 144 may not rotate.

[0075] Here, in step S21, it is determined whether the rotation angle of the front spindle drive motor 123 is within the specified angle range.

[0076] When the rotation angle of the front spindle drive motor 123 is within the specified angle range, the gap size between the bar W and the rotating guide sleeve body 144 is considered to be the optimal gap size, and the adjustment of the gap size between the bar W and the rotating guide sleeve body 144 is completed.

[0077] On the other hand, if the rotation angle of the front spindle drive motor 123 does not reach the lower limit of the specified angle range, the gap between the bar W and the rotating guide sleeve body 144 is too large. Therefore, it is considered that the gap between the bar W and the rotating guide sleeve body 144 needs to be adjusted, and step S22 is entered to adjust the gap between the rotating guide sleeve body 144. Also, if the rotation angle of the front spindle drive motor 123 exceeds the upper limit of the specified angle range, the gap between the bar W and the rotating guide sleeve body 144 is too small. Therefore, it is considered that the gap between the bar W and the rotating guide sleeve body 144 needs to be adjusted, and step S22 is entered to adjust the gap between the bar W and the rotating guide sleeve body 144.

[0078] (Step S22) First, rotate the back spindle 160 until the bar W returns from angle position P1 to the reference angle position P (i.e., the reverse of step S20). Then proceed to step S30 to adjust the gap between the bar W and the rotating guide sleeve body 144.

[0079] <3.3 Gap Adjustment Step> (Step S30) Next, perform each step of the gap adjustment step shown in Figure 6C.

[0080] (Step S31) First, move the back spindle 160 back until the rotating jig 190 is inserted into the adjusting nut 145 of the rotating guide sleeve 140, forming the state shown in Figure 10A.

[0081] (Step S32) Next, the front spindle drive motor 123 is magnetized. Herein, a holding torque is applied to the front spindle drive motor 123, and the effect of this holding torque extends to the timing pulley 146 of the rotating guide sleeve 140, so that even if the timing pulley 146 is to be rotated, it will not rotate.

[0082] (Step S33) In this state, as shown in Figure 10B, with the bar W held by the back spindle 160, the back spindle 160 is rotated only by a predetermined amount in a predetermined direction based on the output of the guide sleeve opening determination unit 181b. By rotating the back spindle 160, the bar W rotates, and the rotating fixture 190 fixed to the bar W rotates only by a predetermined amount in a predetermined direction.

[0083] Here, since the timing pulley 146 does not rotate, the guide sleeve assembly 142, which engages with the key 142d, and the guide sleeve body 144, which engages with the set screw 142b, also do not rotate. However, when the rotating fixture 190 rotates, the adjusting screw 145, which engages with the rotating fixture 190, rotates. Since the guide sleeve assembly 142 and the rotating fixture 190 prevent the adjusting screw 145 from moving in the Z direction, the guide sleeve body 144, which engages with the adjusting screw 145, moves in and out in the Z direction relative to the rotation direction of the adjusting screw 145, and the gap between the bar W and the rotating guide sleeve body 144 is adjusted.

[0084] (Step S34) After the gap between the bar W and the rotating guide sleeve body 144 changes by a specified amount, the back spindle 160 is advanced, and the rotating fixture 190 is disengaged from the adjusting nut 145 of the rotating guide sleeve 140, returning to step S20.

[0085] Repeat the above steps as appropriate until the rotation angle of the front spindle drive motor 123 is within the specified angle range.

[0086] <4. Effects achieved by machine tool 100> According to the machine tool 100 described above, when the back spindle 160 holding the bar W is driven to rotate, the change in the rotation angle of the front spindle 120, which can rotate arbitrarily, is based solely on the rotation of the bar W that accompanies the rotation of the back spindle 160. Therefore, compared to the case where the size of the gap between the rotating guide sleeve and the bar is adjusted based on the load of the back spindle drive motor when the back spindle 160 holding the bar W is driven to rotate, the signal-to-noise ratio is improved. In the case where the opening of the rotating guide sleeve 140 is adjusted by adjusting the nut 145 and the rotating guide sleeve 140 and the front spindle 120 rotate synchronously, the gap between the rotating guide sleeve 140 and the bar W can be adjusted with high precision and automatically.

[0087] Furthermore, the back spindle 160 holds the bar W by means of a detachable and retaining fixture 164. The retaining fixture 164 attached to the back spindle 160 holds the bar W. Therefore, even if the back spindle 160 cannot directly hold the bar W, the bar W can be indirectly held on the back spindle 160 by selecting the retaining fixture 164 corresponding to the bar W.

[0088] Furthermore, the rotary fixture 190, which engages with the adjusting nut 145 of the rotary guide sleeve 140 opposite to the front spindle 120 and rotates the adjusting nut 145, is mounted on the bar W between the front spindle 120 and the rotary guide sleeve 140. In this way, with the bar W held by the back spindle 160 and the rotary fixture 190 engaged with the adjusting nut 145, the bar W is rotated by the back spindle 160, and the adjusting nut 145 of the rotary guide sleeve 140 rotates. Therefore, the gap between the rotary guide sleeve 140 and the bar W can be adjusted with high precision and automatically.

[0089] <Variation> The above describes a machine tool according to one embodiment of the present invention, but the machine tool of the present invention is not limited to the machine tool of the above embodiment.

[0090] For example, in the above embodiment, the front spindle drive motor 123 is mounted on the spindle table 121, but the front spindle drive motor may not be mounted on the spindle table. For example, it may be mounted on a bed and the front spindle body may be rotated and driven by a transmission mechanism. The same applies to the back spindle drive motor.

[0091] For example, in the above embodiments, the synchronous rotation of the front main shaft 120 and the rotating guide sleeve 140 has been illustrated by using a timing belt. However, the present invention is not limited to this example. Any method is acceptable as long as the front main shaft 120 and the rotating guide sleeve 140 are structurally connected and rotate synchronously.

[0092] In addition, as described below, the front spindle 120 may be electrically connected to the rotating guide sleeve 140 and the front spindle 120 and the rotating guide sleeve 140 may rotate synchronously.

[0093] That is, as shown in Figure 11, which illustrates a schematic configuration diagram of an automatic lathe according to a variation of the machine tool of the present invention, the machine tool 100A of the variation of the present invention does not have an encoder 124 and a reversing shaft 134 as described in the machine tool 100 above. Instead, a rotary guide sleeve drive motor 149 is provided on the bed 110 to rotate the guide sleeve body 144 of the rotary guide sleeve 140. The timing belt V2 is wound around a timing pulley located at the top of the rotary guide sleeve drive motor 149. Furthermore, the rotary guide sleeve drive motor 149, like the front spindle drive motor 123, is an electric motor and has an encoder 149a to detect the rotation angle of the rotary guide sleeve drive motor 149.

[0094] Furthermore, the motor control unit 181a of the control device 180 controls not only the operation of the front spindle drive motor 123, but also the operation of the rotary guide sleeve drive motor 149. In addition, in this variation, the motor control unit 181a synchronizes the rotation drive of the front spindle drive motor 123 with the rotation drive of the rotary guide sleeve drive motor 149.

[0095] In this machine tool 100A, the gap between the bar stock W and the rotating guide sleeve 140 is adjusted by detecting the rotation angle of the rotating guide sleeve drive motor 149 rather than the rotation angle of the front spindle drive motor 123. Furthermore, the steps for adjusting the gap between the bar stock W and the rotating guide sleeve 140 are the same as those for adjusting the gap between the bar stock W and the rotating guide sleeve 140 in the machine tool 100 described above, except that the detection target is set to the rotation angle of the rotating guide sleeve drive motor 149, and the magnetization target in step S32 is set to the point of the rotating guide sleeve drive motor 149.

[0096] In the machine tool 100A configured as described above, a guide sleeve opening determination unit 181b determines the amount of clearance adjustment based on the rotation angle of the rotary guide sleeve drive motor 149 when the back spindle 160 is rotating, while holding the bar W with the back spindle 160 and without magnetizing the rotary guide sleeve drive motor 149 and the front spindle drive motor 123. By having this guide sleeve opening determination unit 181b, the change in the rotation angle of the rotary guide sleeve drive motor 149, which can rotate arbitrarily when the back spindle 160 holding the bar W is rotated, is limited to... Based on the rotation of the bar W driven by the 160 rotation of the back spindle, the signal-to-noise ratio is improved compared to the case where the gap between the rotating guide sleeve and the bar is adjusted based on the load of the back spindle drive motor when the back spindle of the bar W is rotated by the back spindle drive motor. In the case where the opening of the rotating guide sleeve 140 is adjusted by adjusting the nut 145 and the rotating guide sleeve 140 rotates synchronously with the front spindle 120, the gap between the rotating guide sleeve 140 and the bar W can be adjusted with high precision and automatically using a simple structure. [Simplified Explanation of the Diagram]

[0014] [Figure 1] A schematic diagram of an automatic lathe according to an embodiment of the machine tool of the present invention. [Figure 2] A diagram showing the structure of the rotary guide sleeve, the front spindle, and the back spindle. [Figure 3] A perspective view of the adjusting nut shown in Figure 2. [Figure 4] A perspective view of the holding fixture shown in Figure 2. [Figure 5] A perspective view of the rotary fixture shown in Figure 2. [Figure 6A] A flowchart showing the steps for adjusting the gap between the bar stock and the rotary guide sleeve. [Figure 6B] A flowchart showing the preparation steps shown in Figure 6A. [Figure 6C] A flowchart showing the gap adjustment steps shown in Figure 6A. [Figure 7A] A schematic diagram showing the state in which the bar stock is inserted into the front spindle. [Figure 7B] A schematic diagram showing the state in which the bar stock is inserted until it reaches the rotary guide sleeve. [Figure 7C] A schematic diagram showing the state in which the front spindle is advanced so that the rotary fixture engages with the adjusting nut. [Figure 8] A schematic diagram showing the state of disengagement between the rotating jig and the adjusting nut. [Figure 9] A schematic diagram of the rotating jig and bar shown in Figure 8, viewed in the direction indicated by arrow IX in Figure 8. [Figure 10A] A schematic diagram showing the state of retracting the back spindle to engage the rotating jig and the adjusting nut. [Figure 10B] A flowchart illustrating the steps of rotating the back spindle to adjust the clearance between the bar and the rotating guide sleeve body. [Figure 11] A schematic diagram of the configuration of an automatic lathe, a variation of the machine tool of the present invention.

Claims

1. A machine tool comprising: a front spindle for rotatably holding a bar; a front spindle drive motor for rotary driving the front spindle; an encoder for detecting the rotation angle of the front spindle drive motor; a rotary guide sleeve disposed in front of the front spindle on a guide sleeve support platform, allowing and supporting the rotation of the bar about a pivot axis and movement in the direction of the pivot axis as it enters and exits the front spindle, and rotating synchronously with the front spindle; a back spindle disposed opposite to the front spindle and rotatably holding the bar; a back spindle drive motor for rotary driving the back spindle; and a control device for controlling the operation of the front spindle and the back spindle. The rotating guide sleeve has a guide sleeve frame, a guide sleeve body, and an adjusting nut. The guide sleeve frame is fixed to the guide sleeve support platform. The guide sleeve body can rotate relative to the guide sleeve frame and allows and supports the rotation of the bar about the axis of rotation and the movement in the direction of the axis of rotation. The adjusting nut is used to adjust the gap between the bar and the guide sleeve body by rotating the guide sleeve body to adjust the gap, and at the same time, it is screwed into the guide sleeve body. The control device has a guide sleeve opening degree determining unit. The guide sleeve opening degree determining unit determines the amount of gap adjustment based on the rotation angle of the front main shaft drive motor when the back main shaft is rotated while the bar is held by the back main shaft and the front main shaft drive motor is not energized.

2. As in request item 1, the machine tool, wherein, The back spindle system allows the retaining fixture for holding the bar to be disassembled and removable.

3. Machine tools as requested in item 1 or 2, wherein, A rotary fixture that engages with and rotates the adjusting nut of the rotating guide sleeve opposite to the front main shaft is attached to the bar between the front main shaft and the rotating guide sleeve.

4. A control method for a machine tool, the machine tool comprising: a front spindle for rotatably holding a bar stock; a front spindle drive motor for rotatably driving the front spindle; an encoder for detecting the rotation angle of the front spindle drive motor; a rotary guide sleeve disposed in front of the front spindle on a guide sleeve support platform, allowing and supporting the rotation of the bar stock entering and exiting the front spindle about a pivot axis and its movement in the direction of the pivot axis, and rotating synchronously with the front spindle; a back spindle disposed opposite to the front spindle and rotatably holding the bar stock; a back spindle drive motor for rotatably driving the back spindle; and a control device for controlling the operation of the front spindle and the back spindle. The rotary guide sleeve has a guide sleeve frame, a guide sleeve body, and an adjusting nut. The guide sleeve frame is fixed to the guide sleeve support platform. The guide sleeve body is rotatable relative to the guide sleeve frame and allows and supports rotation of the bar about a pivot axis and movement in the direction of the pivot axis. The adjusting nut is used to adjust the gap between the bar and the guide sleeve body by rotating the guide sleeve body to adjust the gap, and is screwed onto the guide sleeve body. A rotary fixture that engages with the adjusting nut of the rotary guide sleeve opposite to the front spindle and rotates the adjusting nut is mounted on the bar between the front spindle and the rotary guide sleeve. The control method of the machine tool includes: holding the bar with the back spindle; rotating the back spindle about a pivot axis; and measuring the rotation angle of the front spindle drive motor generated by rotating the back spindle with the encoder. The steps are as follows: determining the adjustment amount of the clearance based on the rotation angle of the front spindle drive motor measured by the encoder; and rotating the back spindle about the shaft and rotating the adjusting nut relative to the guide sleeve body through the rotating fixture mounted on the bar to form the determined adjustment amount of the clearance.

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