Method for aligning the phase of machine tools and hobs

Abstract

This invention provides a machine tool and a method for aligning the phase of a hob with a gear using a simple configuration. [Solution] The machine tool has an encoder (176) and includes a servo motor (171) for rotating the hob (61) and a control device (200). The hob (61) and the gear (71) are positioned relative to each other such that the cutting edge (62) of the hob (61) faces the first tooth (72A) and the second tooth (72B) of the gear (71) with a gap in the axis direction of rotation of the hob (61). When the hob (61) is rotated with the servo motor (171) in the servo-off state, the control device (200) is configured to make available a first rotational position (Pa) when the cutting edge (62) contacts the first tooth (72A) and a second rotational position (Pb) when the cutting edge (62) contacts the second tooth (72B), which are obtained based on the output from the encoder (176).

Description

Technical Field

[0001] This invention relates to a machine tool and a method for aligning the phase of a hob.

Background Art

[0002] For example, Japanese Unexamined Patent Application Publication No. 2003-165024 (Patent Document 1) discloses an initial alignment device and an initial alignment method for a gear grinding machine that performs alignment at the initial meshing of a grinding tool and a workpiece in order to grind the workpiece with a grinding tool having helical grooves engraved thereon.

[0003] The initial alignment device includes a servo gain setting unit that sets the servo gain of the workpiece axis, a correction pulse addition unit that adds correction pulses to the output of an encoder for the workpiece axis that detects the rotational angle of the workpiece axis, a buildup pulse setting unit that sets a reference value for the buildup pulses, and a contact position detection unit that obtains contact position data of the workpiece axis when the tooth surface of the workpiece and the grinding surface of the grinding tool come into contact and the buildup pulses increase and reach the reference value.

[0004] Also, Japanese Unexamined Patent Application Publication No. 2019-118977 (Patent Document 2), Japanese Unexamined Patent Application Publication No. 2019-115948 (Patent Document 3), and Japanese Unexamined Patent Application Publication No. 4-193414 (Patent Document 4) disclose various gear processing devices.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

[0006] In the initial phase alignment method for a gear grinding machine disclosed in the aforementioned Patent Document 1, the initial phase alignment process is automated by adding a correction pulse to the output of the work axis encoder to rotate the work axis, and obtaining contact position data of the work axis when the tooth surface of the workpiece and the grinding surface of the grinding tool come into contact when the accumulated pulses reach a reference value.

[0007] However, implementing such a method requires the installation of the contact position detection unit and other components mentioned above, making it impossible to easily configure a gear grinding machine. In particular, when processing gears using a general-purpose machine tool rather than a dedicated gear processing machine, there is a need to avoid preparing a configuration in the machine tool that is used solely for initial phase alignment.

[0008] The objective of this invention is to provide a machine tool and a method for aligning the phase of a hob with a gear using a simple configuration. [Means for solving the problem]

[0009] The machine tool according to this invention is a general-purpose machine tool capable of machining gears using a hob and also capable of machining workpieces other than gears. The machine tool has an encoder, a servo motor for rotating the hob, and a control device for controlling the machine tool. The gear has a first tooth and a second tooth adjacent to each other in the circumferential direction of the gear. The hob has a cutting edge. The hob and gear are positioned relative to each other such that the cutting edge faces the first tooth and the second tooth with a gap in the rotation axis direction of the hob, and when the hob is rotated with the servo motor in the servo-off state, the control device is configured to make available a first rotational position when the cutting edge contacts the first tooth and a second rotational position when the cutting edge contacts the second tooth, which are obtained based on the output from the encoder.

[0010] The hob phase alignment method according to this invention is a method for aligning the phase of a hob with respect to a gear in a general-purpose machine tool capable of machining gears using a hob and also capable of machining workpieces other than gears. The machine tool has an encoder, a servo motor for rotating the hob, and a control device for controlling the machine tool. The gear has a first tooth and a second tooth that are adjacent to each other in the circumferential direction of the gear. The hob has a cutting edge. The hob phase alignment method includes the steps of: positioning the hob and gear relatively such that the cutting edge faces the first and second teeth with a gap in the rotation axis direction of the hob; setting the servo motor to a servo-off state; rotating the hob with the servo motor in the servo-off state to bring the cutting edge into contact with the first and second teeth; identifying a first rotation position when the cutting edge contacts the first tooth and a second rotation position when the cutting edge contacts the second tooth, which are obtained by a control device based on the output from an encoder; and calculating a third rotation position located at the center of the first and second rotation positions. [Effects of the Invention]

[0011] According to this invention, it is possible to provide a machine tool and a method for aligning the phase of a hob with a gear using a simple configuration. [Brief explanation of the drawing]

[0012] [Figure 1] This is a front view showing a machine tool according to an embodiment of the present invention. [Figure 2] This figure shows the finishing process of gears in a machine tool, as shown in Figure 1. [Figure 3] This figure shows a magnified view of the workpiece and hob within the area enclosed by the dashed line III in Figure 2. [Figure 4] Figure 1 is a block diagram showing the configuration for gear machining in a machine tool. [Figure 5] This figure shows the input / output relationship (servo-on state) between the control unit, display unit, and CT axis servo motor in Figure 4. [Figure 6] FIG. 4 is a diagram showing the input / output relationship (servo-off state) among the control device, display unit, and servo motor for the CT axis. [Figure 7] FIG. 5 is a diagram showing the first step of measuring the cutting edge position. [Figure 8] FIG. 6 is a diagram showing the second step of measuring the cutting edge position. [Figure 9] FIG. 7 is a diagram showing the third step of measuring the cutting edge position. [Figure 10] FIG. 8 is a flowchart showing the flow of the hob alignment method. [Figure 11] FIG. 9 is a functional block diagram showing the control device in FIG. 4. [Figure 12] FIG. 10 is a functional block diagram showing the control device when automatically calculating the third rotation position. DETAILED DESCRIPTION OF THE INVENTION

[0013] Embodiments of the present invention will be described with reference to the drawings. In the drawings referred to below, the same or corresponding members are denoted by the same reference numerals.

[0014] FIG. 1 is a front view showing a machine tool in an embodiment of the present invention. In FIG. 1, the inside of the machine tool 100 is shown by looking through a cover body 52 forming the exterior of the machine tool 100.

[0015] Referring to FIG. 1, the machine tool 100 in the present embodiment is a general-purpose machine tool capable of machining gears using a hob and also capable of machining workpieces other than gears. The machine tool 100 is not a dedicated machine for gear machining intended only for gear machining.

[0016] Machine tool 100 is a multi-tasking machine equipped with a turning function that processes a workpiece by bringing a tool into contact with a rotating workpiece, and a milling function that processes a workpiece by bringing a rotating tool into contact with the workpiece. Machine tool 100 is an NC (Numerically Controlled) machine tool in which various operations for workpiece processing are automated by computer numerical control.

[0017] In this specification, for the convenience of explaining the configuration of the machine tool 100, the axis parallel to the rotation axis of the workpiece and extending horizontally is referred to as the "Z-axis," the axis perpendicular to the Z-axis and extending horizontally is referred to as the "Y-axis," and the axis extending vertically is referred to as the "X-axis."

[0018] First, the overall structure of the machine tool 100 will be described. The machine tool 100 has a bed 41, a first workpiece spindle 11, a second workpiece spindle 16, a tool spindle 21, and a tool post 31.

[0019] The bed 41 is a base member for supporting the first work spindle 11, the second work spindle 16, the tool spindle 21, and the tool post 31, etc., and is installed on the floor of a factory or similar facility. The bed 41 is made of a metal such as cast iron.

[0020] The first work spindle 11 and the second work spindle 16 are capable of holding a workpiece. The first work spindle 11 and the second work spindle 16 face each other in the Z-axis direction. The first work spindle 11 and the second work spindle 16 are mainly provided to rotate the workpiece during turning operations using a fixed tool. The first work spindle 11 is rotatable around a rotational axis 101 parallel to the Z-axis. The second work spindle 16 is rotatable around a rotational axis 102 parallel to the Z-axis. The first work spindle 11 and the second work spindle 16 are each provided with a first chuck mechanism 13 and a second chuck mechanism 18 for gripping a workpiece so that it can be attached and detached.

[0021] The machine tool 100 further includes a servo motor 161 (see Figure 4 below). The servo motor 161 is installed on the first workpiece spindle 11. The servo motor 161 corresponds to the motor for rotating the first workpiece spindle 11 around the rotational axis 101. The rotational axis 101 corresponds to the "C-axis" indicated next to the servo motor 161 in Figure 4.

[0022] The first workpiece spindle 11 is fixed on the bed 41. The second workpiece spindle 16 is movable in the Z-axis direction by various feed mechanisms, guide mechanisms, and motors.

[0023] The machine tool 100 may have a tailstock instead of a second workpiece spindle 16 to support the rotation center of the workpiece held by the first workpiece spindle 11. In this case, the tailstock is positioned opposite the first workpiece spindle 11 in the Z-axis direction.

[0024] The tool spindle 21 is capable of holding a tool. The tool spindle 21 is rotatable around a rotational axis 103 parallel to the X-axis in the reference position described later. The tool spindle 21 has a built-in clamping mechanism (not shown) for detachably holding a tool.

[0025] The tool spindle 21 is also capable of rotatable around a pivot axis 104 parallel to the Y-axis (B-axis rotation). The rotation range of the tool spindle 21 is, for example, ±120° with respect to a reference position (shown in Figure 1) where the spindle end face 23 of the tool spindle 21 faces downward.

[0026] The tool spindle 21 is supported on the bed 41 by a column (not shown). The tool spindle 21 is movable in the X-axis, Y-axis, and Z-axis directions by various feed mechanisms, guide mechanisms, and motors provided on the column.

[0027] The tool post 31 is capable of holding tools. The tool post 31 is located below the tool spindle 21. The tool spindle 21 is positioned above the rotation axis 101 of the first work spindle 11 and the rotation axis 102 of the second work spindle 16, while the tool post 31 is positioned below the rotation axis 101 of the first work spindle 11 and the rotation axis 102 of the second work spindle 16. The tool post 31 is a so-called turret type, and multiple tools are mounted radially to perform rotary indexing.

[0028] The tool post 31 has a swivel section 32 and a plurality of tool holders (not shown). The swivel section 32 is rotatable around a pivot axis 105 parallel to the Z-axis. The swivel section 32 as a whole has a disc shape in which the axial direction of the pivot axis 105 is the thickness direction. The plurality of tool holders (not shown) consist of block bodies capable of holding tools. The plurality of tool holders are attached to the outer circumferential surface of the swivel section 32. The plurality of tool holders are arranged in the circumferential direction of the pivot axis 105. As the swivel section 32 rotates around the pivot axis 105, the tools held in the tool holders move in the circumferential direction. The tools used for workpiece machining are indexed to a predetermined angular position in the circumferential direction of the pivot axis 105.

[0029] The tool post 31 is equipped with a milling function for rotating the tool held in the tool holder. The tool post 31 further includes a servo motor 171 (see Figure 4 below) and a power transmission mechanism (not shown). The servo motor 171 is built into the swivel section 32. The power transmission mechanism is built into the tool holder. During milling with the tool held in the tool post 31, the rotational motion output from the servo motor 171 is transmitted to the tool via the power transmission mechanism (not shown).

[0030] The tool post 31 is movable in the X-axis and Z-axis directions by various feed mechanisms, guide mechanisms, and motors.

[0031] The machine tool 100 further includes a servo motor 181 and a servo motor 191 (see Figure 4 below). Servo motor 181 corresponds to a motor for moving the tool post 31 in the X-axis direction. Servo motor 191 corresponds to a motor for moving the tool post 31 in the Z-axis direction.

[0032] The tool spindle 21 and the tool post 31 both have the common function of holding the tool. The tool spindle 21 may be called the first tool post, and the tool post 31 may be called the second tool post.

[0033] The machine tool 100 further includes a cover body 52. ​​The cover body 52 forms the external appearance of the machine tool 100 and also demarcates the machining area 51. The machining area 51 is the space where the workpiece is machined, and the cover body 52 seals it to prevent foreign matter such as chips or cutting oil generated during workpiece machining from leaking out of the machining area 51.

[0034] Although not shown in Figure 1, the machine tool 100 is further equipped with an automatic tool changer (ATC) for automatically changing the tool held on the tool spindle 21, and a tool magazine for storing replacement tools.

[0035] Figure 2 shows the finishing process of a gear in the machine tool shown in Figure 1. Figure 3 is a magnified view of the workpiece and hob within the area enclosed by the dashed line III in Figure 2. Referring to Figures 1 to 3, the machine tool 100 is capable of machining the gear 71 using the hob 61.

[0036] The first workpiece spindle 11 holds a workpiece W on which a gear 71 has been formed. The gear 71 has a plurality of teeth 72. The plurality of teeth 72 are provided on the outer circumferential surface of the workpiece W. The plurality of teeth 72 are arranged in the circumferential direction of the rotational axis 101.

[0037] For example, workpiece W is a Curvic coupling for the table of a machine tool, and gear 71 meshes with a gear for inputting rotational motion from a motor into the Curvic coupling. Gear 71 may be a spur gear. Gear 71 may have a diameter of 300 mm or more. The type of gear machined using the present invention is not particularly limited.

[0038] A hobbing unit 60 is mounted on the tool post 31. The hobbing unit 60 has a hob 61 and the aforementioned power transmission mechanism (not shown). The hob 61 is rotatable around a rotational axis 106 that is inclined with respect to the Y axis by the advance angle of the hob 61. The hob 61 has a threaded cutting edge 62. The cutting edge 62 extends intermittently in a spiral shape around the rotational axis 106. When gear machining is performed by the hobbing unit 60 held on the tool post 31, the rotational motion output from the servo motor 171 is transmitted to the hob 61 via a power transmission mechanism (not shown).

[0039] The rotational axis 106 corresponds to the "CT axis" indicated next to the servo motor 171 in Figure 4.

[0040] The process for manufacturing the gear 71 is described below. First, the gear 71 is formed on the outer surface of the workpiece W by rough machining. Next, the workpiece W with the formed gear 71 is removed from the machine tool 100. Next, the workpiece W is subjected to a hardening treatment. Finally, the hardened workpiece W is put back into the machine tool 100 and mounted on the first workpiece spindle 11.

[0041] Next, to remove the distortion caused by the heat treatment, the gear 71 is subjected to finishing. Figures 1 to 3 show the finishing process of the gear 71. As shown in Figure 3, the gear 71 has a first tooth 72A and a second tooth 72B that are adjacent to each other in the circumferential direction of the rotational axis 101. The cutting edge 62 of the hob 61 is positioned in the valley between the first tooth 72A and the second tooth 72B. The cutting edge 62 meshes with the first tooth 72A and the second tooth 72B. The cutting edge 62 is in contact with the tooth surfaces of the first tooth 72A and the second tooth 72B. The gear 71 is finished by synchronously rotating the gear 71 and the hob 61 around the rotational axis 101 and the rotational axis 106, respectively.

[0042] As described above, in order to mesh the gear 71 with the cutting edge 62 of the hob 61, it is necessary to align the phase of the hob 61 with that of the gear 71 before finishing the gear 71.

[0043] More specifically, a touch probe is attached to the tool spindle 21, and the phase of the teeth 72 on the gear 71 is measured using the touch probe. The phase measurement of the teeth 72 on the gear 71 is performed each time a hardened workpiece W is fed into the machine tool 100. In addition, the cutting edge position of the cutting edge 62 of the hob 61 is measured so that the cutting edge 62 of the hob 61 is positioned at the center of the valley portion of the teeth 72 on the gear 71. The cutting edge position of the cutting edge 62 is measured each time a new hob 61 is mounted on the tool post 31.

[0044] Next, the method for aligning the phase of the hob 61 with respect to the gear 71 will be explained in detail. Figure 4 is a block diagram showing the configuration for gear machining in the machine tool shown in Figure 1. Figure 5 is a diagram showing the input / output relationship (servo-on state) between the control device, display unit, and CT axis servo motor shown in Figure 4.

[0045] Referring to Figures 4 and 5, the machine tool 100 further includes a control panel 120. The control panel 120 includes a display unit 140 and an operation unit 130. The display unit 140 is, for example, a liquid crystal panel. The display unit 140 displays various information related to machining in the machine tool 100. The operation unit 130 is, for example, a touch panel, switches, or other input interface. The operation unit 130 receives various commands or information input from the operator of the machine tool 100.

[0046] The machine tool 100 further includes a control device 200. The control device 200 controls the operation of the machine tool 100.

[0047] Each component of the control device 200 is realized by hardware including a CPU (Central Processing Unit) and various computer processors, memory or storage devices, and wired or wireless communication lines connecting them, as well as software stored in the storage devices that supplies processing instructions to the arithmetic units. The computer program may consist of device drivers, an operating system, various application programs located at a higher layer, or libraries that provide common functions to these programs.

[0048] The control device 200 includes a numerical control device 110. The numerical control device 110 executes a pre-designed machining program. The machining program is written using an NC (Numerical Control) program. The numerical control device 110 controls the servo drivers 151, 152, 153, and 154 (described later) according to the machining program, and machines the workpiece W held on the first workpiece spindle 11.

[0049] The servo motor 171 has an encoder 176. The encoder 176 converts the rotation angle of the servo motor 171 into an electrical signal and outputs it to the control device 200 as a feedback signal. The encoder 176 may be optical or magnetic. The encoder 176 may be incremental or absolute.

[0050] The control device 200 further includes a servo driver 151. The servo driver 151 controls the power supply to the servo motor 171 so that the servo motor 171 rotates according to commands from the numerical control device 110, including a target rotational speed or target position.

[0051] More specifically, the servo driver 151 sequentially calculates the actual rotational speed and actual rotational position of the servo motor 171 based on the output from the encoder 176, and controls the power supply to the servo motor 171 so that, for example, if the actual rotational speed is less than the target rotational speed, the rotational speed of the servo motor 171 increases, and if the actual rotational speed is greater than the target rotational speed, the rotational speed of the servo motor 171 decreases.

[0052] The control device 200 controls the display on the display unit 140. The control device 200 causes the actual rotational speed and actual rotational position of the servo motor 171 to be displayed on the display unit 140.

[0053] The control device 200 further includes a servo driver 152, a servo driver 153, and a servo driver 154. The servo drivers 152, 153, and 154 are provided in correspondence with the servo motors 181, 191, and 161, respectively. The servo motors 181, 191, and 161 each have encoders 186, 196, and 166, respectively.

[0054] The configurations of servo drivers 152, 153, and 154 are the same as those of servo driver 151. The configurations of encoders 186, 196, and 166 are the same as those of encoder 176.

[0055] Figure 6 shows the input / output relationship (servo-off state) between the control unit, display unit, and CT axis servo motor in Figure 4.

[0056] The servo-on state of the servo motor 171 shown in Figure 5 is a state in which feedback control of the servo motor 171 by the servo driver 151, based on the output from the encoder 176, is in operation. When power is supplied to the machine tool 100, a servo-on signal is input to the servo driver 151, and the servo-on state of the servo motor 171 is obtained. In the servo-on state, when the servo motor 171 stops, feedback control is activated to maintain the rotational position, so the rotating shaft of the servo motor 171 is locked.

[0057] The servo-off state of the servo motor 171 shown in Figure 6 is a state in which the feedback control of the servo motor 171 by the servo driver 151, based on the output from the servo driver 151, is stopped. By operating a specific button provided on the operation unit 130, the input of the servo-on signal to the servo driver 151 is turned off, and the servo-off state of the servo motor 171 is obtained. A command to put the servo motor 171 into the servo-off state may be written into the NC program input to the numerical control device 110. In the servo-off state, since the feedback control is stopped, the lock state of the rotating shaft of the servo motor 171 is released.

[0058] Furthermore, in this embodiment, even when the servo motor 171 is in the servo-off state, the encoder 176 is configured to output an electrical signal indicating the rotation angle of the servo motor 171 to the control device 200. Based on the output from the encoder 176, the control device 200 calculates the actual rotation speed and rotation position of the servo motor 171 and displays the calculated actual rotation speed and rotation position of the servo motor 171 on the display unit 140.

[0059] Figures 7 to 9 show the steps for measuring the cutting edge position. The ranges shown in Figures 7 to 9 correspond to the range shown in Figure 3. Figure 10 is a flowchart showing the flow of the hob phase alignment method.

[0060] Referring to Figures 1, 4, and 6 to 10, in the machine tool 100 of this embodiment, the hob 61 and the gear 71 are positioned relative to each other such that the cutting edge 62 faces the first tooth 72A and the second tooth 72B with a gap in the axial direction of the rotational center axis 106 (CT axis) of the hob 61. When the hob 61 is rotated with the servo motor 171 in the servo-off state, the control device 200 is configured to make available the first rotational position Pa when the cutting edge 62 contacts the first tooth 72A and the second rotational position Pb when the cutting edge 62 contacts the second tooth 72B, which are obtained based on the output from the encoder 176.

[0061] As shown in Figures 1 and 10, first, the hardened workpiece W is mounted on the first workpiece spindle 11, and the hobbing unit 60 is mounted on the tool post 31 (S101).

[0062] Next, the phase measurement of the gear 71 formed on the workpiece W is performed (S102). In this step, a touch probe is attached to the tool spindle 21. By moving the tool spindle 21 in the X, Y, and Z axis directions, the contact of the touch probe is positioned in the valley portion of the tooth 72 between the first tooth 72A and the second tooth 72B. The workpiece W is rotated in one direction and the other around the rotation center axis 101 (C axis), and the contact of the touch probe is brought into contact with the first tooth 72A and the second tooth 72B to acquire position data of the first tooth 72A and the second tooth 72B.

[0063] The touch probe outputs the acquired position data of the first tooth 72A and the second tooth 72B to the control device 200. Based on the position data from the touch probe, the control device 200 calculates the center angle of the first tooth 72A and the second tooth 72B.

[0064] Next, the cutting edge position of the cutting edge 62 of the hob 61 is measured. As shown in Figures 7 and 10, first, the cutting edge of the cutting edge 62 of the hob 61 is positioned relative to the gear 71 (S103).

[0065] In this step, the cutting edge 62 of the hob 61 is positioned between the first tooth 72A and the second tooth 72B of the gear 71 by moving the tool post 31 in the X-axis and Z-axis directions. As shown in Figure 7, the cutting edge 62 faces the first tooth 72A and the second tooth 72B with a gap in the axial direction of the rotational axis 106 (CT axis) of the hob 61. The tip 62t of the cutting edge 62 may be positioned radially outward from the rotational axis 101 (C axis) than the reference circle 76 of the gear 71. The tips 72t of the first tooth 72A and the second tooth 72B may be positioned radially inward from the rotational axis 101 (C axis) than the reference circle 66 of the cutting edge 62.

[0066] As shown in Figures 6 and 10, the next step is to set the servo motor 171 to the servo-off state (S104). In this step, for example, an operator sets the servo motor 171 to the servo-off state by operating the control unit 130. This stops the feedback control of the servo motor 171 and releases the locked state of the rotating shaft of the servo motor 171.

[0067] As shown in Figures 6, 8, and 10, the hob 61 is then rotated manually to bring the cutting edge 62 into contact with the first tooth 72A, thereby determining the first rotational position Pa when the cutting edge 62 contacts the first tooth 72A (S105).

[0068] In this step, the operator grips the hob 61 and rotates it in one direction around the rotational axis 106 (CT axis) to bring the cutting edge 62 into contact with the first tooth 72A. Because the servo motor 171 is in the servo-off state, the lock state of the servo motor 171's rotation shaft is released, allowing the operator to rotate the hob 61 manually.

[0069] While the hob 61 rotates, the encoder 176 outputs an electrical signal to the control device 200 indicating the rotation angle of the servo motor 171. Based on the output from the encoder 176, the control device 200 calculates the rotation position of the servo motor 171 and displays the calculated rotation position on the display unit 140. The operator identifies the first rotation position Pa when the cutting edge 62 contacts the first tooth 72A through the display on the display unit 140.

[0070] As shown in Figures 6, 9, and 10, the hob 61 is then rotated manually to bring the cutting edge 62 into contact with the second tooth 72B, thereby determining the second rotational position Pb when the cutting edge 62 contacts the second tooth 72B (S106).

[0071] In this step, the operator grips the hob 61 and rotates it in the other direction around the rotational axis 106 (CT axis) to bring the cutting edge 62 into contact with the second tooth 72B. The operator identifies the second rotational position Pb when the cutting edge 62 makes contact with the second tooth 72B through the display unit 140.

[0072] For example, when the hob 61 is rotated by the servo motor 171, and the cutting edge 62, in the opposite direction to that during normal gear machining, comes into contact with the first tooth 72A or the second tooth 72B, there is a problem that the cutting edge 62 can easily break off. In contrast, in step S104, the servo motor 171 is set to the servo-off state, and in steps S105 and S106, the hob 61 is rotated manually, bringing the cutting edge 62 into contact with the first tooth 72A and the second tooth 72B. This prevents excessive force from being applied from the gear 71 to the hob 61. This effectively prevents the cutting edge 62 from breaking off.

[0073] As shown in Figure 10, the third rotation position Pc, which is located at the center of the first rotation position Pa and the second rotation position Pb, is then calculated and input to the control device 200 (S107).

[0074] In this step, the operator calculates the third rotation position Pc based on the first rotation position Pa identified in step S105 and the second rotation position Pb identified in step S106. For example, if the first rotation position Pa is 75° and the second rotation position Pb is 77°, the third rotation position Pc is 76°. The operator displays the common variable input screen on the display unit 140 and operates the operation unit 130 to input the third rotation position Pc as a parameter for identifying the cutting edge position of the hob 61.

[0075] The above steps complete the process of aligning the phase of the hob 61 with respect to the gear 71.

[0076] Figure 11 is a functional block diagram showing the control device in Figure 4. Referring to Figure 11, the control device 200 includes a signal acquisition unit 211, a display control unit 212, and a parameter acquisition unit 213.

[0077] The signal acquisition unit 211 acquires signals from the encoder 176. The display control unit 212 controls the image display on the display unit 140. The parameter acquisition unit 213 acquires various parameters that are referenced in the NC program for operating the machine tool 100.

[0078] In steps S105 and S106 in Figure 10, while the hob 61 rotates, the encoder 176 sequentially outputs an electrical signal indicating the rotation angle of the servo motor 171 to the control device 200. The signal acquisition unit 211 acquires the signal from the encoder 176. Based on the signal from the encoder 176 acquired by the signal acquisition unit 211, the display control unit 212 displays the constantly changing rotation position of the servo motor 171 on the display unit 140.

[0079] The operation unit 130 receives an input operation for the third rotation position Pc from the operator and outputs the operation signal to the control device 200. The parameter acquisition unit 213 acquires the third rotation position Pc as a parameter for determining the cutting edge position of the hob 61 based on the operation signal from the operation unit 130.

[0080] In this embodiment, the display on the display unit 140 was described as an example of how the control device 200 utilizes the first rotation position Pa and the second rotation position Pb, but the machine tool in this invention is not limited to this. For example, the control device 200 may be configured to automatically calculate a third rotation position Pc located at the center of the first rotation position Pa and the second rotation position Pb.

[0081] Figure 12 is a functional block diagram showing a control device for automatically calculating the third rotation position. Referring to Figure 12, the control device 200 includes a signal acquisition unit 211, a first / second rotation position identification unit 216, a third rotation position calculation unit 217, and a parameter acquisition unit 213.

[0082] In step S105 in Figure 10, the operator grips the hob 61 and rotates it in one direction around the rotation center axis 106 (CT axis) to bring the cutting edge 62 into contact with the first tooth 72A. While the hob 61 rotates, the encoder 176 sequentially outputs an electrical signal indicating the rotation angle of the servo motor 171 to the control device 200. The signal acquisition unit 211 acquires the signal from the encoder 176. When the cutting edge 62 contacts the first tooth 72A, the change in the rotation angle of the servo motor 171 stops. The first / second rotation position identification unit 216 identifies the rotation position corresponding to the rotation angle of the servo motor 171 when the change stopped as the first rotation position Pa.

[0083] In step S106 in Figure 10, the operator grips the hob 61 and rotates it in the other direction around the rotation center axis 106 (CT axis) to bring the cutting edge 62 into contact with the second tooth 72B. While the hob 61 rotates, the encoder 176 sequentially outputs an electrical signal indicating the rotation angle of the servo motor 171 to the control device 200. The signal acquisition unit 211 acquires the signal from the encoder 176. When the cutting edge 62 contacts the second tooth 72B, the change in the rotation angle of the servo motor 171 stops. The first / second rotation position identification unit 216 identifies the rotation position corresponding to the rotation angle of the servo motor 171 at the time the change stopped as the second rotation position Pb.

[0084] In the step corresponding to S107 in Figure 10, the third rotation position calculation unit 217 calculates the third rotation position Pc, which is located at the center of the first rotation position Pa and the second rotation position Pb, based on the first rotation position Pa and the second rotation position Pb identified by the first / second rotation position identification unit 216. The parameter acquisition unit 213 acquires the third rotation position Pc calculated by the third rotation position calculation unit 217 as a parameter for identifying the cutting edge position of the hob 61.

[0085] To summarize the configuration of the machine tool 100 in the embodiment of this invention described above, the machine tool 100 in this embodiment is a general-purpose machine tool capable of machining a gear 71 using a hob 61 and also capable of machining workpieces other than gears. The machine tool 100 has an encoder 176, a servo motor 171 for rotating the hob 61, and a control device 200 for controlling the machine tool 100. The gear 71 has a first tooth 72A and a second tooth 72B that are adjacent to each other in the circumferential direction of the gear 71. The hob 61 has a cutting edge 62. The hob 61 and gear 71 are positioned relative to each other such that the cutting edge 62 faces the first tooth 72A and the second tooth 72B with a gap in the axial direction of the rotational center axis 106 of the hob 61. When the hob 61 is rotated with the servo motor 171 in the servo-off state, the control device 200 is configured to make available the first rotational position Pa when the cutting edge 62 contacts the first tooth 72A and the second rotational position Pb when the cutting edge 62 contacts the second tooth 72B, which are obtained based on the output from the encoder 176.

[0086] With this configuration, the control device 200 can determine the cutting edge position of the hob 61's cutting edge 62 relative to the gear 71 by utilizing the first rotational position Pa when the cutting edge 62 contacts the first tooth 72A and the second rotational position Pb when the cutting edge 62 contacts the second tooth 72B. In this case, when the hob 61 is rotated with the servo motor 171 in the servo-off state, the control device 200 obtains the first rotational position Pa and the second rotational position Pb based on the output from the encoder 176, so it is sufficient to use the original function of the encoder 176. Therefore, the phase alignment of the hob 61 relative to the gear 71 can be performed with a simple configuration.

[0087] Furthermore, the machine tool 100 is further equipped with a display unit 140. The control device 200 displays the first rotation position Pa and the second rotation position Pb on the display unit 140.

[0088] With this configuration, the operator can identify the first rotation position Pa and the second rotation position Pb through the display on the display unit 140.

[0089] Furthermore, the control device 200 may calculate a third rotational position Pc located at the center of the first rotational position Pa and the second rotational position Pb. With such a configuration, the third rotational position Pc, which is used as a parameter for determining the cutting edge position of the cutting edge 62 of the hob 61 relative to the gear 71, can be obtained more easily.

[0090] Furthermore, the encoder 176 is configured to output an electrical signal indicating the rotation angle of the servo motor 171 to the control device 200 when the servo motor 171 is in the servo-off state. With this configuration, the hob 61 can be rotated manually by turning off the servo motor 171, and the control device 200 can acquire the first rotation position Pa and the second rotation position Pb based on the output from the encoder 176 while the hob 61 is rotating.

[0091] Furthermore, the machine tool 100 includes a first work spindle 11 as the work spindle, a turret-type tool post 31, and a hobbing unit 60 mounted on the tool post 31 and holding the hob 61.

[0092] With this configuration, phase alignment between the gear held on the first workpiece spindle 11 and the hob 61 held by the hobbing unit 60 mounted on the tool post 31 can be performed with a simple setup.

[0093] The machining unit that holds the hob 61 may be mounted on the tool spindle 21. The embodiment in which the hobbing unit 60 is mounted on the tool post 31 is suitably applied to machining large-diameter gears such as Curvic couplings for machine tool tables, due to the machining stroke.

[0094] Furthermore, the hob phase alignment method in this embodiment is a method for aligning the phase of the hob 61 with respect to the gear 71 in a general-purpose machine tool 100 that is capable of machining the gear 71 using the hob 61 and is also capable of machining workpieces other than gears. The hob phase alignment method includes the steps of: positioning the hob 61 and the gear 71 relatively (S103) such that the cutting edge 62 faces the first tooth 72A and the second tooth 72B with a gap in the axial direction of the rotational center axis 106 of the hob 61; setting the servo motor 171 to a servo-off state (S104); rotating the hob 61 with the servo motor 171 in the servo-off state to bring the cutting edge 62 into contact with the first tooth 72A and the second tooth 72B (S105 / S106); identifying a first rotational position Pa when the cutting edge 62 contacts the first tooth 72A and a second rotational position Pb when the cutting edge 62 contacts the second tooth 72B, which are acquired by the control device 200 based on the output from the encoder 176 (S105 / S106); and calculating a third rotational position Pc located at the center of the first rotational position Pa and the second rotational position Pb (S107).

[0095] With this configuration, the phase alignment of the hob 61 with respect to the gear 71 can be performed with a simple setup.

[0096] In this embodiment, the machine tool in the present invention has been described as a multi-tasking machine comprising a first work spindle 11 and a second work spindle 16, a tool spindle 21 (first tool post), and a tool post 31 (second tool post), but it is not limited to this. The machine tool in the present invention may also be a lathe comprising a work spindle and a second tool post.

[0097] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0098] 11 First work spindle, 13 First chuck mechanism, 16 Second work spindle, 18 Second chuck mechanism, 21 Tool spindle, 23 Spindle end face, 31 Tool post, 32 Swivel section, 41 Bed, 51 Machining area, 52 Cover body, 60 Hobbing unit, 61 Hob, 62 Cutting edge, 62t, 72t Tip section, 66, 76 Reference circle, 71 Gear, 72 Teeth, 72A First tooth, 72B Second tooth, 100 Machine tool, 101, 102, 103, 106 Rotation center axis, 104, 105 Swivel center axis, 110 Numerical control device, 120 Control panel, 130 Operating section, 140 Display section, 151, 152, 153, 154 Servo driver, 161, 171, 181, 191 Servo motor, 166, 176, 186, 196 Encoder, 200 Control device, 211 Signal acquisition unit, 212 Display control unit, 213 Parameter acquisition unit, 216 Second rotation position determination unit, 217 Third rotation position calculation unit, Pa First rotation position, Pb Second rotation position, Pc Third rotation position, W Workpiece.

Claims

1. A general-purpose machine tool capable of machining gears using a hob, and also capable of machining workpieces other than gears, A servo motor having an encoder for rotating the hob, The machine tool is equipped with a control device for controlling the machine tool, The gear has a first tooth and a second tooth that are adjacent to each other in the circumferential direction of the gear. The hob has a cutting edge, A machine tool in which the hob and the gear are positioned relative to each other such that the cutting edge faces the first tooth and the second tooth with a gap between them in the rotation axis direction of the hob, and when the hob is rotated with the servo motor in the servo-off state, the control device is configured to make available a first rotation position when the cutting edge contacts the first tooth and a second rotation position when the cutting edge contacts the second tooth, which are obtained based on the output from the encoder.

2. It also includes a display unit, The machine tool according to claim 1, wherein the control device displays the first rotation position and the second rotation position on the display unit.

3. The machine tool according to claim 1, wherein the control device calculates a third rotation position located at the center of the first rotation position and the second rotation position.

4. The machine tool according to claim 1 or 2, wherein the encoder is configured to output an electrical signal indicating the rotation angle of the servo motor to the control device when the servo motor is in the servo-off state.

5. A workpiece spindle for rotating the workpiece, A turret-type tool rest, The machine tool according to claim 1 or 2, further comprising a hobbing unit mounted on the tool post and holding the hob.

6. A general-purpose machine tool capable of machining gears using a hob and also capable of machining workpieces other than gears, wherein the hob is phase-aligned with the gear, The aforementioned machine tool is A servo motor having an encoder for rotating the hob, The machine tool is equipped with a control device for controlling the machine tool, The gear has a first tooth and a second tooth that are adjacent to each other in the circumferential direction of the gear. The hob has a cutting edge, The method for aligning the phase of the hob is as follows: The steps include positioning the hob and the gear relative to each other such that the cutting edge faces the first tooth and the second tooth with a gap between them in the rotation axis direction of the hob, The steps include setting the servo motor to the servo-off state, The steps include: rotating the hob while the servo motor is in the off state, thereby bringing the cutting edge into contact with the first tooth and the second tooth; The steps include determining, based on the output from the encoder, a first rotational position when the cutting edge contacts the first tooth and a second rotational position when the cutting edge contacts the second tooth, which are obtained by the control device, A method for aligning the phase of a hob, comprising the step of calculating a third rotation position located at the center of the first rotation position and the second rotation position.

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