Machine tool, gear measurement device, error measurement method, gear production method, and computer program

Abstract

A machine tool according to the present invention comprises a control device that is configured to execute an error measurement process. The error measurement process includes: determining, on the basis of the orientation of a workpiece that has been machined into a gear shape and that is held by a workpiece holding device, an approach start point and an approach direction of a touch probe held by a tool holding device; controlling an actuator to move the touch probe from the approach start point in the approach direction; obtaining the center position of a tip ball of the touch probe at the time when the touch probe comes into contact with the surface of the workpiece by the movement; determining a candidate value of an error between the gear shape and a target shape of a gear product; generating, on the basis of the candidate value, the target shape, and the orientation, a cross-sectional model representing a cross-sectional shape of a tooth surface; obtaining a minimum distance between the cross-sectional model and the center position; and changing the candidate value to determine, as the error, a candidate value at which the absolute value of the difference between the minimum distance and the radius of the tip ball is not more than an allowable value.

Description

Machine tool, gear measuring device, error measurement method, gear manufacturing method, and computer program

[0001] The present invention relates to a machine tool, a gear measuring device, an error measurement method, a gear manufacturing method, and a computer program.

[0002] In many gear manufacturing processes, a workpiece is roughly machined into a gear shape using a machine tool, the workpiece is then removed from the machine tool, and errors are measured using a dedicated gear measuring device such as that described in Patent Document 1. Based on the measurement results, the workpiece is then reattached to the machine tool and finish-machined.

[0003] One technique for solving such problems is the machine tool described in Patent Document 2. The machine tool disclosed in Patent Document 2 processes a workpiece into a gear shape, then measures errors using a touch probe attached to the machine tool, automating a series of operations from rough machining to finish machining.

[0004] JP 2006-234775 A JP 61-070401 A

[0005] In the machine tool of Patent Document 2, the hard ball at the tip of the touch probe needs to be moved until it contacts both teeth of the gear, so a touch probe with a hard ball that matches the shape of the gear must be selected.

[0006] An object of the technology disclosed in the present application is to provide a technology that can measure gear form errors using a touch probe selected regardless of the gear form, for example.

[0007] A machine tool according to a first aspect of the present disclosure includes a workpiece holding device, a tool holding device, an actuator, and a control device. The workpiece holding device is configured to hold a workpiece. The tool holding device is configured to hold one of a touch probe and at least one tool. The actuator is configured to move the tool holding device relative to the workpiece holding device. The control device is configured to control the tool holding device and the actuator and to perform an error measurement process. The error measurement process includes determining the approach start point and approach direction of the touch probe held by the tool holding device based on the attitude of the workpiece machined into a gear shape held by the workpiece holding device, controlling the actuator to move the touch probe from the approach start point in the approach direction, determining the center position of the tip ball of the touch probe when the touch probe comes into contact with the surface of the workpiece as a result of the movement, determining a candidate value for the error between the gear shape and the target shape of the gear product, generating a cross-sectional model representing the cross-sectional shape of the tooth flank based on the candidate value, the target shape and the attitude, determining the minimum distance between the cross-sectional model and the center position, changing the candidate value, and determining, as the error, the candidate value for which the absolute value of the difference between the minimum distance and the radius of the tip ball is equal to or less than a tolerance.

[0008] According to a second aspect of the present disclosure, the machine tool according to the first aspect further includes a tool changer configured to change one of the touch probe and the at least one tool held by the tool holding device for another tool.

[0009] According to a third aspect of the present disclosure, in the machine tool according to the first or second aspect, a control device controls the tool changer so that the tool holding device selectively holds a first tool, a second tool, and a touch probe among at least one tool, and is configured to receive a first command, a second command, and up to a third command. Upon receiving the first command, the control device is configured to control the actuator to machine the workpiece into a gear shape with the first tool. Upon receiving the second command, the control device is configured to execute an error measurement process. Upon receiving the third command, the control device is configured to control the actuator to adjust the movement path of the second tool based on the error to manufacture a gear product.

[0010] An error measurement method according to a fourth aspect of the present disclosure includes having a computer determine an approach start point and approach direction of a touch probe based on the attitude of a workpiece machined into a gear shape, controlling an actuator to move the touch probe in the approach direction from the approach start point, having the computer determine the center position of the tip ball of the touch probe when the touch probe comes into contact with the surface of the workpiece as a result of the movement, and having the computer calculate an error between the gear profile and a target shape of a gear product based on the center position. Having the computer calculate the error includes determining a candidate value for the error, generating a cross-sectional model representing the cross-sectional shape of the tooth flanks based on the candidate value, the target shape, and the attitude, determining the minimum distance between the cross-sectional model and the center position, changing the candidate value, and determining, as the error, the candidate value for which the absolute value of the difference between the minimum distance and the radius of the tip ball is equal to or less than a tolerance.

[0011] According to a fifth aspect of the present disclosure, in the machine tool according to the first aspect or the error measurement method according to the fourth aspect, determining the approach start point and the approach direction includes determining a contact target point of the target shape. The approach direction is determined in the direction of a normal vector of a tangent plane of the target shape at the contact target point when the gear product is placed in the attitude, or vice versa. The approach start point is determined at a position facing in the opposite direction to the approach direction from the contact target point.

[0012] According to a sixth aspect of the present disclosure, in the machine tool or error measurement method according to the fifth aspect, the contact target point is a point on the pitch circle of the gear product. When the gear product is an involute gear, the value of the parameter of the involute curve representing the pitch point is equal to the pressure angle. When the gear product is a cycloidal gear and the curve model is made up of an epicycloidal curve and a hypocycloidal curve, the pitch circle is the same as the base circle used to generate the cycloidal curve. When the gear product is a trochoidal gear and the curve model is an epitrochoidal parallel curve, the contact target point is not limited to the intersection of the trochoidal parallel curve and the pitch circle, but may also be the intersection of the trochoidal parallel curve and the root circle, or the intersection of the trochoidal parallel curve and the tip circle.

[0013] According to a seventh aspect of the present disclosure, in the machine tool or error measurement method according to the fifth or sixth aspect, a first plane that is perpendicular to the tangential plane and includes the contact target point, and a gear rotation axis when the gear product is placed in that orientation are defined. Of multiple curves represented by cutting the target shape with the first plane, a target curve that passes through the contact target point is moved in a direction away from the gear rotation axis when the gear product is placed in that orientation on the first plane, and the cross-sectional model is represented by a model curve.

[0014] According to an eighth aspect of the present disclosure, in the machine tool or error measurement method according to the seventh aspect, the first plane is a plane obtained by rotating a second plane perpendicular to the gear rotation axis around a straight line passing through the gear rotation axis or the contact target point on the second plane by a helix angle defined by the tooth profile of the target shape.

[0015] According to a ninth aspect of the present disclosure, in the machine tool or error measurement method according to the seventh or eighth aspect, the minimum distance is the distance between the central position and a neighboring point among multiple points on the model curve that has the smallest distance from the central position.

[0016] According to a tenth aspect of the present disclosure, in the machine tool or error measurement method according to any one of the seventh to ninth aspects, the model curve is a curve segment obtained by shifting a curve segment that is a target curve between a first intersection of the target curve and a root circle or base circle of the target shape centered on the gear rotation axis and a second intersection of the target curve and a tip circle of the target shape centered on the gear rotation axis by a candidate value in the separation direction. When the model curve is an involute curve, the first intersection may be a point of intersection of the target curve and one of the base circle and the root circle, whichever has a smaller radius. When the model curve is a cycloid curve, or when the model curve is a cycloid curve, the first intersection may be a point of intersection of the root circle and the target curve. Furthermore, when the curve model is an epitrochoid parallel curve and the contact target point is a point of intersection of the trochoid parallel curve and the root circle, two adjacent intersections of the tip circle and the target curve may be the first and second intersections. When the curve model is an epitrochoid parallel curve and the contact target point is an intersection point between the trochoid parallel curve and the tip circle, two adjacent intersection points between the root circle and the target curve may be set as the first intersection point and the second intersection point.

[0017] According to an eleventh aspect of the present disclosure, in the machine tool or error measurement method according to any one of the seventh to tenth aspects, the model curve can be expressed by using parameters for each coordinate in a two-dimensional coordinate system that defines a position on the first plane, and the positions of multiple points on the first plane can be found by changing the parameters by the same amount.

[0018] According to a twelfth aspect of the present disclosure, the error measurement method according to any one of the fourth to eleventh aspects includes, before contacting the touch probe with the surface of the workpiece, positioning the workpiece so that the orientation of the workpiece is a predetermined orientation, or setting a coordinate system for moving the touch probe in accordance with the orientation of the workpiece. Furthermore, according to the twelfth aspect of the present disclosure, in the machine tool according to any one of the first aspect or the fifth to eleventh aspects, the control device controls the workpiece holding device so that the orientation of the workpiece is a predetermined orientation, or sets a coordinate system for moving the touch probe in accordance with the orientation of the workpiece, before contacting the touch probe with the surface of the workpiece. The predetermined orientation is preferably a gear-shaped orientation that allows a contact target point to be analytically determined in the predetermined coordinate system. Furthermore, the coordinate system set in accordance with the orientation of the workpiece is preferably a coordinate system that allows a contact target point to be analytically determined.

[0019] A gear manufacturing method according to a thirteenth aspect of the present disclosure includes, when a first command is received by the computer of any of the fourth to eleventh aspects, causing the computer to control the actuator to machine a workpiece into a gear shape with a first tool held by a tool holding device of a machine tool. The gear manufacturing method includes, when a second command is received by the computer, causing the computer to control the actuator to move the touch probe in accordance with the error measurement method of any of the fourth to eleventh aspects, thereby calculating the error. The gear manufacturing method includes, when a third command is received by the computer, causing the computer to control the actuator to adjust a movement path of a second tool held by the tool holding device based on the error, thereby causing the second tool to manufacture a gear product.

[0020] A gear manufacturing method according to a fourteenth aspect of the present disclosure further includes, when the computer of any of the thirteenth to tenth aspects receives a first command, causing the computer to control a tool changer of the machine tool so that the tool holding device of the machine tool holds a first tool. The gear manufacturing method further includes, when the computer receives a second command, causing the computer to control the tool changer to replace the implement held by the tool holding device with a touch probe. The gear manufacturing method further includes, when the computer receives a third command, causing the computer to control the tool changer to replace the touch probe held by the tool holding device with a second tool.

[0021] According to a fifteenth aspect of the present disclosure, the gear manufacturing method according to the thirteenth or fourteenth aspect includes causing the computer to execute a process of controlling the workpiece holding device to rotate the workpiece so that its orientation is a predetermined orientation or to set a coordinate system for moving the touch probe in accordance with the orientation of the workpiece before contacting the touch probe with the surface of the workpiece. According to the fifteenth aspect of the present disclosure, in the machine tool according to the third aspect, the control device is configured to rotate the workpiece so that its orientation is a predetermined orientation or to control the workpiece holding device to set a coordinate system for moving the touch probe in accordance with the orientation of the workpiece before contacting the touch probe with the surface of the workpiece. Note that the predetermined orientation is preferably a gear shape orientation that allows the contact target point to be analytically determined in the predetermined coordinate system.

[0022] A gear measuring device according to a sixteenth aspect of the present disclosure includes a computer configured to execute the error measurement method according to any one of the fourth to twelfth aspects.

[0023] A computer program according to a seventeenth aspect of the present disclosure comprises instructions that, when executed by a computer, cause the computer to execute the error measurement method according to any one of the fourth to twelfth aspects.

[0024] A computer program according to an eighteenth aspect of the present disclosure comprises instructions that, when executed by a computer of a machine tool, cause the computer to carry out the gear manufacturing method according to either the thirteenth or fourteenth aspect.

[0025] According to a nineteenth aspect of the present disclosure, the computer program according to the eighteenth aspect includes instructions for causing the computer to execute a process of controlling the workpiece holding device to rotate the workpiece so that the orientation of the workpiece assumes a predetermined orientation before the touch probe is brought into contact with the surface of the workpiece, or to set a coordinate system for moving the touch probe in accordance with the orientation of the workpiece, wherein the predetermined orientation is preferably a gear-shaped orientation that allows a contact target point to be analytically determined in the predetermined coordinate system.

[0026] A computer-readable medium according to a twentieth aspect of the present disclosure comprises instructions that, when executed by a computer, cause the computer to carry out an error measurement method according to any one of the fourth to twelfth aspects.

[0027] A computer-readable medium according to a twenty-first aspect of the present disclosure comprises instructions which, when executed by a computer of a machine tool, cause the computer to carry out a gear manufacturing method according to either the thirteenth or fourteenth aspect.

[0028] According to a twenty-second aspect of the present disclosure, the computer-readable medium of the twenty-first aspect includes instructions for causing a computer to execute a process of controlling the workpiece holding device to rotate the workpiece so that the orientation of the workpiece assumes a predetermined orientation before the touch probe contacts the surface of the workpiece, or setting a coordinate system for moving the touch probe in accordance with the orientation of the workpiece, wherein the predetermined orientation is preferably a gear-shaped orientation in the predetermined coordinate system that allows analytical determination of the contact target point.

[0029] The machine tool according to the first aspect, the error measurement method according to the fourth aspect, the gear measuring device according to the sixteenth aspect having a computer configured to execute the error measurement method according to the fourth aspect, the computer program according to the seventeenth aspect having instructions for causing a computer to execute the error measurement method according to the fourth aspect, and the computer-readable medium according to the twentieth aspect having instructions for causing a computer to execute the error measurement method according to the fourth aspect all use a cross-sectional model to estimate the error between the gear profile and the target profile of a gear product from the position of the center of the tip ball of the touch probe when the touch probe contacts the surface of the workpiece. Therefore, since it is not necessary to move the touch probe until it contacts both teeth of the gear, it is possible to measure gear errors using a touch probe selected regardless of the gear profile.

[0030] In the machine tool according to the fifth aspect, the error measurement method according to the fifth aspect, the gear measuring device according to the sixteenth aspect comprising a computer configured to execute the error measurement method according to the fifth aspect, the computer program according to the seventeenth aspect comprising instructions for causing a computer to execute the error measurement method according to the fifth aspect, and the computer readable medium according to the twentieth aspect comprising instructions for causing a computer to execute the error measurement method according to the fifth aspect, the touch probe is brought into contact with the surface of the workpiece generally perpendicularly, making it less likely for slippage to occur after contact and enabling gear errors to be measured with high accuracy.

[0031] In the machine tool according to the sixth aspect, the error measurement method according to the sixth aspect, the gear measuring device according to the sixteenth aspect comprising a computer configured to execute the error measurement method according to the sixth aspect, the computer program according to the seventeenth aspect comprising instructions for causing a computer to execute the error measurement method according to the sixth aspect, and the computer-readable medium according to the twentieth aspect comprising instructions for causing a computer to execute the error measurement method according to the sixth aspect, when the gear product is an involute gear, the approach direction can be easily derived using the number of teeth and pressure angle of the gear specifications. When the gear product is a cycloidal gear, the approach direction is tangent to the pitch circle, making it easy to derive.

[0032] In the machine tool according to the seventh aspect, the error measurement method according to the seventh aspect, the gear measuring device according to the sixteenth aspect having a computer configured to execute the error measurement method according to the seventh aspect, the computer program according to the seventeenth aspect having instructions for causing a computer to execute the error measurement method according to the seventh aspect, and the computer-readable medium according to the twentieth aspect having instructions for causing a computer to execute the error measurement method according to the seventh aspect, when a workpiece is produced by a tool that produces a gear, such as a hob, the tooth profile surface is formed so as to shift relative to the approach direction of the hob, so that a highly accurate cross-sectional model can be produced.

[0033] With the machine tool according to the eighth aspect, the error measurement method according to the eighth aspect, the gear measuring device according to the sixteenth aspect comprising a computer configured to execute the error measurement method according to the eighth aspect, the computer program according to the seventeenth aspect comprising instructions for causing a computer to execute the error measurement method according to the eighth aspect, and the computer-readable medium according to the twentieth aspect comprising instructions for causing a computer to execute the error measurement method according to the eighth aspect, it is possible to generate with high accuracy a cross-sectional model of a workpiece having a helical gear shape.

[0034] The machine tool according to the ninth aspect, the error measurement method according to the ninth aspect, the gear measuring device according to the sixteenth aspect comprising a computer configured to execute the error measurement method according to the ninth aspect, the computer program according to the seventeenth aspect comprising instructions for causing a computer to execute the error measurement method according to the ninth aspect, and the computer readable medium according to the twentieth aspect comprising instructions for causing a computer to execute the error measurement method according to the ninth aspect, are capable of determining coordinates of an approximate solution of the contact point.

[0035] In the machine tool according to the tenth aspect, the error measurement method according to the tenth aspect, the gear measuring device according to the sixteenth aspect comprising a computer configured to execute the error measurement method according to the tenth aspect, the computer program according to the seventeenth aspect comprising instructions for causing a computer to execute the error measurement method according to the tenth aspect, and the computer readable medium according to the twentieth aspect comprising instructions for causing a computer to execute the error measurement method according to the tenth aspect, the model curve can be expressed by an involute curve in the case of an involute gear, by an epitrochoid parallel curve in the case of a trochoid gear, and by an epicycloid curve and a hypocycloid curve in the case of a cycloid gear, mathematical modeling can be facilitated.

[0036] The machine tool according to the 11th aspect, the error measurement method according to the 11th aspect, the gear measuring device according to the 16th aspect having a computer configured to execute the error measurement method according to the 11th aspect, the computer program according to the 17th aspect having instructions for causing a computer to execute the error measurement method according to the 11th aspect, and the computer-readable medium according to the 20th aspect having instructions for causing a computer to execute the error measurement method according to the 11th aspect make it possible to accurately determine an approximate solution for the contact point.

[0037] In the machine tool according to the 12th aspect, the error measurement method according to the 12th aspect, the gear measuring device according to the 16th aspect having a computer configured to execute the error measurement method according to the 12th aspect, the computer program according to the 17th aspect having instructions for causing a computer to execute the error measurement method according to the 12th aspect, and the computer-readable medium according to the 20th aspect having instructions for causing a computer to execute the error measurement method according to the 12th aspect, the coordinate system of the model curve and the center position can be determined depending on the attitude of the workpiece.

[0038] In the machine tool according to the second aspect, the touch probe and tool can be replaced by the machine tool, which reduces the burden on the user when performing an operation that combines machining and error measurement.

[0039] In the machine tool according to the third aspect, the gear manufacturing method according to the thirteenth aspect, the computer program according to the eighteenth aspect, and the computer-readable medium according to the twenty-first aspect, which includes instructions for causing a computer to execute the gear manufacturing method according to the thirteenth aspect, by loading a machining program including the first to third commands into the machine tool, it is possible to cause the machine tool to automatically execute a series of operations including rough machining, error measurement, and finish machining without removing the workpiece from the machine tool.

[0040] In the machine tool according to the third aspect, the gear manufacturing method according to the fourteenth aspect, the computer program according to the eighteenth aspect having instructions for causing a computer to execute the gear manufacturing method according to the fourteenth aspect, and the computer-readable medium according to the twenty-first aspect having instructions for causing a computer to execute the gear manufacturing method according to the fourteenth aspect, by loading the machining program including the first command to the third command into the machine tool, tool replacement can also be automated, and the machine tool can automatically execute all of the series of operations from rough machining, error measurement, and finish machining.

[0041] In the machine tool according to the fifteenth aspect, the gear manufacturing method according to the fifteenth aspect, the computer program according to the nineteenth aspect, and the computer-readable medium according to the twenty-second aspect, the coordinate system of the model curve and the center position can be determined according to the attitude of the workpiece.

[0042] According to the technology disclosed in the present application, for example, it is not necessary to move the touch probe until it contacts both teeth of the gear, and therefore it is possible to measure gear errors using a touch probe selected regardless of the gear shape.

[0043] FIG. 1 shows a schematic configuration of a machine tool according to a first embodiment. FIG. 2 is a hardware block diagram of a control device. FIG. 3 shows the state of a workpiece involved in error measurement by the control device. FIG. 4 is a flowchart showing each operation of the error measurement process by the control device. FIG. 5 is a diagram illustrating a shape model representing the cross-sectional shape of the tooth flank when the gear product is a spur gear. FIG. 6 is a schematic diagram showing the approach start point and approach direction when the gear product is a spur gear. FIG. 7 shows an example of a machining program. FIG. 8 is a flowchart showing each operation of the gear manufacturing process by the control device. FIG. 9 is a flowchart showing each operation of the gear manufacturing process by the control device. FIG. 10A is a schematic diagram showing the approach start point and approach direction when the gear product is a helical gear. FIG. 10B is a schematic diagram showing another method for determining the approach start point and approach direction when the gear product is a helical gear. FIG. 11A is a schematic diagram showing the approach start point and approach direction when the gear product is a standard bevel gear. Fig. 11B is a schematic diagram showing another method for determining the approach start point and approach direction when the gear product is a standard bevel gear. Fig. 12A is a cross-sectional view of an example of a reducer including a trochoid gear. Fig. 12B is a cross-sectional view of another example of a reducer including a trochoid gear. Fig. 13A is a schematic diagram showing the approach start point and approach direction when the external gear product as in Fig. 12A is a trochoid gear. Fig. 13B is a schematic diagram showing another method for determining the approach start point and approach direction when the external gear product as in Fig. 12A is a trochoid gear. Fig. 14 is a schematic diagram showing the approach start point and approach direction when the gear product is a cycloid gear.

[0044] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings showing embodiments thereof, in which the same reference numerals designate corresponding or substantially identical components.

[0045] <First embodiment> <Overall configuration> Fig. 1 shows a schematic configuration of a machine tool 100 according to a first embodiment. Note that the X axis shown in Fig. 1 runs along the height direction of the machine tool 100, the Y axis runs along the depth direction of the machine tool 100, and the Z axis runs along the width direction of the machine tool 100. The B direction is the circumferential direction of the Y axis, and the C direction is the circumferential direction of the Z axis.

[0046] As a rough machining operation, the machine tool 100 performs gear cutting operations such as hobbing and gear skiving on a workpiece W1 held by a workpiece spindle 122 to machine the workpiece W1 into a gear shape. However, the machine tool 100 may also machine a workpiece W1 that has been rough machined by a machine tool other than the machine tool 100 into a gear product by performing deburring and finishing operations. As shown in FIG. 1 , the machine tool 100 includes a column 110, a tool headstock 112, a workpiece headstock 120, and a tool changer 130. The column 110, the workpiece headstock 120, and the tool changer 130 are arranged on a base 140.

[0047] The column 110 is movable in the Y-axis direction and the Z-axis direction on the base 140. A tool headstock 112 is attached to the column 110. The tool headstock 112 is movable in the X-axis direction relative to the column 110. The tool headstock 112 is rotatable in the B-direction, which is the circumferential direction of a rotation axis A1 along the Y-axis direction, relative to the column 110. The machine tool 100 includes a first actuator ACT1 configured to move the tool headstock 112 in the X-axis direction and the B-direction. The first actuator ACT1 includes, for example, at least one motor and a power conversion mechanism such as a ball screw. The first actuator ACT1 may include a motor that moves the tool headstock 112 in the X-axis direction and a motor that moves the tool headstock 112 in the B-direction separately. Alternatively, the first actuator ACT1 may have separate power conversion mechanisms, one for moving the tool headstock 112 in the X-axis direction from one motor and the other for moving the tool headstock 112 in the B direction. The machine tool 100 includes a tool spindle 114. The tool spindle 114 is also referred to as a tool gripper. The tool spindle 114 is attached to the tool headstock 112. The tool spindle 114 is rotatable about a rotation axis A2 along the X-axis direction relative to the tool headstock 112. The machine tool 100 includes a second actuator ACT2 configured to rotate the tool spindle 114 about the rotation axis A2. The second actuator ACT2 is, for example, a motor. The tool spindle 114 is configured to hold one of a touch probe 150 and at least one machine tool 160. The touch probe 150 will be described in detail below.

[0048] The machine tool 100 includes a workpiece spindle 122. The workpiece spindle 122 is also referred to as a workpiece gripper. The workpiece spindle 122 is attached to a workpiece headstock 120. The workpiece spindle 122 is rotatable in a C direction, which is the circumferential direction of a rotation axis A3. The rotation axis A3 extends along the Z axis direction. The workpiece spindle 122 is configured to hold a workpiece W1. The workpiece spindle 122 may grip the workpiece W1 via a chuck or the like. The machine tool 100 includes a fourth actuator ACT4 configured to rotate the workpiece spindle 122 in the circumferential direction of the rotation axis A3. The fourth actuator ACT4 is, for example, a motor.

[0049] The machine tool 100 includes a third actuator ACT3 configured to move the workpiece headstock 120 in the Z-axis direction. The third actuator ACT3 includes, for example, a motor and a power conversion mechanism such as a ball screw. The first to fourth actuators ACT1 to ACT4 are collectively referred to as actuators ACT. Note that the functions of the first to fourth actuators ACT1 to ACT4 are not limited to those described above. For example, the first actuator ACT1 may move the tool headstock 112 in the X-axis direction and the Z-axis direction. In other words, the machine tool 100 includes actuators ACT configured to move the tool holding device (tool spindle 114) relative to the workpiece holding device (workpiece spindle 122). The first to fourth actuators ACT4 preferably include a rotation sensor such as an encoder to detect the amount of movement and rotation angle of the controlled object.

[0050] The tool changer 130 is configured to change one of the touch probe 150 and the at least one tool 160 held on the tool spindle 114 for another. Specifically, the tool changer 130 includes a magazine arm 132 and a stocker 134. The magazine arm 132 is rotatable about an axis along the Z-axis direction. The magazine arm 132 is movable in the Z-axis direction relative to the stocker 134. The stocker 134 stores the touch probe 150 and the at least one tool 160 so that the touch probe 150 and the at least one tool 160 are movable in the X-axis direction. The at least one tool 160 includes at least one of a hob, a skiving cutter, a side cutter having a tooth groove-shaped cross section, a pinion cutter, and a mill tool.

[0051] The tool change by the tool changer 130 is performed as follows: The tool headstock 112 moves in the X-axis direction and pivots in the B-axis direction so that the tool attached to the tool spindle 114 faces the tool changer 130. The column 110 approaches the tool changer 130 in the Y-axis direction and the Z-axis direction to move the tool to the tool change position. The magazine arm 132 has a first gripper at one end in the extension direction of the magazine arm 132 and a second gripper at the other end in the extension direction. The first gripper holds the tool attached to the tool spindle 114 in order to remove the tool attached to the tool spindle 114. When the magazine arm 132 moves away from the tool spindle 114 in the Z-axis direction, the tool is removed from the tool spindle 114. In order to load another tool onto the tool spindle 114, the magazine arm 132 rotates about an axis along the Z-axis direction and moves the other tool gripped by the second gripper to a tool mounting position. When the column 110 approaches the tool changer 130 in the Z-axis direction, another tool is loaded onto the tool spindle 114.

[0052] The machine tool 100 is equipped with a control device 1 for controlling rotation around each rotation axis and movement in each axial direction. The control device 1 is configured to control a tool spindle 114 (tool holding device), a work spindle 122 (workpiece holding device), and an actuator ACT. The control device 1 is connected to a base 140. The control device 1 may be connected to another location on the machine tool 100 and may be installed separately from the base 140 as long as it is capable of transmitting control signals and receiving detection results. The control device 1 is provided with a display 40 and an input interface 50. The input interface 50 may include a touch panel built into the display 40. The display 40 and the input interface 50 together form a graphical user interface. However, the display 40 and the input interface 50 may be provided separately from the control device 1.

[0053] FIG. 2 is a hardware block diagram of the control device 1. As shown in FIG. 2, the control device 1 includes a processor 10, a memory 20, a sensor control circuit 30, a display circuit 42, and an input circuit 52. The processor 10, the memory 20, the sensor control circuit 30, the display circuit 42, and the input circuit 52 are connected to each other via a bus 1A. The memory 20 stores programs and data necessary for machining. The processor 10 is a hardware processor composed of electrical circuits, and reads and executes programs stored in the memory 20. This realizes the various functions of the control device 1. The various functions realized by the control device 1 include processes such as rough machining of gears, gear phase detection, gear deburring, finishing, and tooth surface profile measurement. Because the processor 10 and the memory 20 also have the same functions as a general computer, the control device 1 may also be referred to as a computer 1C.

[0054] Specifically, the memory 20 is configured to store a machining program 22, gear data 24, an interpreter 26, an actuator control library 27, and a sensor processing library 28. The machining program 22 is written in program code, such as EIA / ISO program code, and includes commands for machining the workpiece W1 into a gear shape, detecting the orientation of the workpiece W1, and measuring the error between the gear shape of the machined workpiece W1 and the target shape of a gear product. The gear data 24 includes dimensions of the target shape (e.g., module, pressure angle, and number of teeth). The gear data 24 may be three-dimensional CAD data.

[0055] The interpreter 26 is a program for analyzing commands written in the machining program 22 and executing at least one of an actuator control library 27 and a sensor processing library 28. In other words, the control device 1 is configured to accept various commands written in the machining program 22 (e.g., first to fifth commands shown in FIGS. 8 and 9 , described later) by executing the interpreter 26. The actuator control library 27 is a program for executing commands written in the machining program 22 for controlling the tool changer 130, commands written in the machining program 22 for driving or moving the workpiece spindle 122 or the tool spindle 114, and commands for measuring the error between the gear shape of the machined workpiece W1 and the target shape of a gear product. The sensor processing library 28 is a program for executing commands for detecting the attitude of the workpiece W1 and commands for measuring the error between the gear shape of the machined workpiece W1 and the target shape of a gear product. The detected attitude of the workpiece W1 is, for example, the phase of the gear in the C direction of the workpiece spindle 122. When the interpreter 26 receives a command for controlling the tool changer 130 described in the machining program 22, the interpreter 26 calls the actuator control library 27 and executes processing for controlling the tool changer 130 so that the tool spindle 114 (tool holding device) selectively holds a first tool and a second tool among at least one machine tool and the touch probe 150. In other words, the control device 1 is configured to control the tool changer 130 so that the tool spindle 114 (tool holding device) selectively holds the first tool and the second tool among at least one tool and the touch probe 150. When the interpreter 26 receives a command for measuring the error between the gear shape of the workpiece W1 and the target shape of the gear product, the interpreter 26 calls the actuator control library 27 and executes processing for moving the touch probe 150 held by the tool spindle 114, and then calls the sensor processing library 28 and executes processing for detecting a contact state using a contact sensor attached to the touch probe 150.

[0056] When the sensor processing library 28 is executed, the sensor control circuit 30 receives a detection signal output from a contact sensor attached to the touch probe 150 to detect whether the tip ball 152 of the touch probe 150 has come into contact with an object. For example, when the first to fourth actuators ACT1 to ACT4 are motors, the actuator control circuit 32 includes an electrical circuit that generates control signals to their drivers. For example, when the actuator control library 27 outputs the target rotation speed and target torque of the motor based on commands written in the machining program 22, the actuator control circuit 32 outputs a control signal (e.g., a pulse signal) to the driver corresponding to the target rotation speed and target torque. Control signals from the control device 1 and detection signals from the touch probe 150 are transmitted and received via a cable 140C between the control device 1 and the base 140.

[0057] The display circuitry 42 is, for example, a video card, and is connected to the display 40. The display circuitry 42 controls drawing on the display 40 under the control of the processor 10. The input circuitry 52 is connected to the input interface 50. The input circuitry 52 outputs operations received by the input interface 50 to the processor 10 as operation input signals.

[0058] <Workpiece Error Measurement Process> Figure 3 shows the state of the workpiece W1 involved in error measurement by the control device 1. Area SP2 in Figure 3 is an enlarged view of area SP1. The control device 1 moves at least one machine tool 160, such as a hob or skiving cutter, in a radial direction (machining approach direction) relative to the rotation axis A3 of the workpiece spindle 122 to machine, for example, a cylindrical workpiece W1 into a gear shape. Therefore, the gear rotation axis A4 of the workpiece W1 coincides with the rotation axis A3 of the workpiece spindle 122. In Figure 3, the target shape of the gear product is indicated by a dotted line TS, and the outer shape of the workpiece W1 is indicated by the outer peripheral surface PS. Due to the nature of machining using a hob or skiving cutter, if a shape model consisting of only two adjacent teeth T1 and T2 is considered, the outer peripheral surface PS exists at a position separated from the target shape TS by an error e in the machining approach direction. While Figure 3 illustrates a case where the Y-axis direction is the same as the machining approach direction, the machining approach direction may be in another direction.

[0059] When workpiece W1 is machined into a gear shape by a hob or skiving cutter, it is unknown to machine tool 100 at what angle the tooth grooves or teeth of workpiece W1 held by workpiece spindle 122 are located in direction C, which is the circumferential direction of rotation axis A3 of workpiece spindle 122. In other words, the phase in direction C of the gear represented by the outer peripheral surface PS formed on workpiece W1 relative to workpiece spindle 122 is unknown to machine tool 100. Therefore, in order to measure error e, machine tool 100 detects the phase of the gear in direction C relative to workpiece spindle 122.

[0060] Here, the phase P of the gear represented by the outer peripheral surface PS in this embodiment is defined as follows: The phase P is the angle of any position on the C axis of the outer peripheral surface PS relative to a reference position RL on the C axis, which is the circumferential direction of the gear rotation axis A4 of the workpiece W1. The reference position RL is, for example, a position corresponding to the machining approach direction. In the following description, the reference position RL is assumed to correspond to the positive direction of the Y axis. As shown in Figure 3, the intersection CP of the pitch circle PC of the gear product and the outer peripheral surfaces PS of two adjacent teeth T1 and T2 is１ , C.P. ２ and the curved line segment CP on the outer peripheral surface PS １ CP ２ The midpoint of CP ０ Then, point CP １ , C.P. ２ , C.P. ０ The phases of each of these are P １ , P ２ , P ０ In addition, point CP １ , C.P. ２ , C.P. ０ is not limited to a point on the pitch circle PC, but may be on any circumference between the addendum circle AC and the root circle RC, the circumference being centered on the axis of rotation of the gear product.

[0061] In this embodiment, the phase P １ , P ２ and its phase P １ , P ２ The central phase of ０ By doing so, the phase P ０ can be obtained. Specifically, for example, when the X and Y coordinates of the tip sphere 152 of the touch probe 150 are positioned between the two adjacent teeth T1 and T2, the distance the touch probe 150 can be moved in the Z-axis direction is longer than the distance it can move when it comes into contact with the gear side surface SS. Utilizing this fact, the control device 1 determines the X and Y coordinates of the center position of the tip sphere 152 of the touch probe 150 so that the X and Y coordinates of the tip sphere 152 of the touch probe 150 are positioned between the two adjacent teeth T1 and T2. It is desirable that these X and Y coordinates be set at coordinates on the pitch circle PC. The control device 1 then moves the tip sphere 152 of the touch probe 150 in the Z-axis direction so that it is positioned between the two adjacent teeth T1 and T2. The point CP １ , C.P. ２ , C.P. ０ The position in the Z-axis direction is shown in the lower diagram of FIG.

[0062] Next, the fourth actuator ACT4 is driven to rotate the workpiece W1 around the rotation axis A3 (gear rotation axis A4) to the point CP １ and point CP ２ and the touch probe 150 is brought into contact with the point CP. １ and point CP ２ When contacted by the touch probe 150, the points CP are spaced apart from the center position of the tip sphere 152 of the touch probe 150 by the radius of the tip sphere 152, but are spaced apart in opposite directions by the radius of the tip sphere 152. Therefore, the points CP １ The rotation angle θ of the fourth actuator ACT4 when the fourth actuator ACT4 is brought into contact with the touch probe 150 １ and point CP ２ The rotation angle θ of the fourth actuator ACT4 when the fourth actuator ACT4 is brought into contact with the touch probe 150 ２ The rotation angle θ is exactly halfway between ０ From the above, the phase P when the rotation angle of the fourth actuator ACT4 is set to an arbitrary angle θ is ０ can be obtained.

[0063] Phase P ０ Once this is known, the control device 1 determines the point CP ０ The fourth actuator ACT4 is driven to rotate the workpiece W1 around the rotation axis A3 (gear rotation axis A4) so ​​that the point CP is located on the Y axis. ０ The X-axis and Y-axis are rotated around the Z-axis to be converted into X'-axis and Y'-axis so that the point CP is located on the Y'-axis, and the following movement of the touch probe 150 and the coordinate system of the error e are executed in the X'Y' coordinate system. ０ In the following description, it is assumed that the workpiece W1 is rotated so that the coordinates are positioned on the Y axis. However, if coordinate conversion to the X'Y' coordinate system is performed, the XY coordinate system in the following description can be read as the X'Y' coordinate system.

[0064] After carrying out the above pre-processing, the control device 1 is configured to execute the error measurement process described below. Fig. 4 is a flowchart showing the error measurement method according to this embodiment, that is, each operation of the error measurement process carried out by the control device 1 (computer 1C). When the processor 10 receives a predetermined command written in the machining program 22, it executes the actuator control library 27 and the sensor processing library 28 to execute steps S18 and S19. In step S18, the processor 10 determines the orientation of the workpiece W1. The orientation of the workpiece W1 is, for example, the orientation of the point CP described above. ０ Phase P ０ That is, the error measurement method includes causing the computer 1C to obtain the attitude of the workpiece W1.

[0065] In step S19, the processor 10 positions the workpiece W1 so that the orientation of the workpiece W1 is a predetermined orientation, or sets a coordinate system for moving the touch probe 150 in accordance with the orientation of the workpiece. In other words, the error measurement method includes having the computer 1C position the workpiece W1 so that the orientation of the workpiece W1 is a predetermined orientation, or set a coordinate system for moving the touch probe 150 in accordance with the orientation of the workpiece, before bringing the touch probe 150 into contact with the surface of the workpiece W1 for error measurement. For example, the orientation of the workpiece W1 being a predetermined orientation means that the position of the point CP ０ This means that the workpiece W1 is rotated so that the center point CP between the rotation axis A3 (gear rotation axis A4) and the adjacent teeth T1 and T2 is a point on an axis (Y-axis in the example of FIG. 3) extending in the opposite direction to the machining approach direction from the rotation axis A3 (gear rotation axis A4). In other words, arranging the workpiece W1 so that the posture of the workpiece W1 is a predetermined posture means rotating the workpiece W1 to a posture that makes it easy to calculate the error measurement process described later. Setting a coordinate system for moving the touch probe 150 in accordance with the posture of the workpiece means that the center point CP between the rotation axis A3 (gear rotation axis A4) and the adjacent teeth T1 and T2 is a point on an axis (Y-axis in the example of FIG. 3) extending in the opposite direction to the machining approach direction from the rotation axis A3 (gear rotation axis A4). ０A coordinate system (X'Y' coordinate system) based on an axis (X' axis) pointing toward the workpiece and an axis (Y' axis) perpendicular to that is set as the coordinate system for moving the touch probe 150 for error measurement. In other words, setting a coordinate system for moving the touch probe 150 in accordance with the attitude of the workpiece means setting a coordinate system for moving the touch probe 150 to a coordinate system that makes it easier to calculate the error measurement process described below.

[0066] In step S21, the processor 10 determines the approach start point APSP and approach direction APD of the touch probe 150 held by the tool spindle 114 (tool holding device) based on the posture of the workpiece W1 machined into a gear shape and held by the workpiece spindle 122 (workpiece holding device). In other words, the error measurement method involves having the computer 1C determine the approach start point APSP and approach direction APD of the touch probe 150 based on the posture of the workpiece W1 machined into a gear shape. Hereinafter, the contents of the flowchart will be explained using an example in which the gear product is an involute gear and a spur gear. Similar calculations can be performed for other gear products, and the calculation method for such cases will be described in a modified example. Figure 5 is a diagram illustrating a shape model representing the cross-sectional shape of the tooth flanks (the target shape TS of the gear product and the outer peripheral surface PS of the workpiece W1) when the gear product is a spur gear.

[0067] In this case, the coordinates (x, y) of point P on target shape TS in the XY coordinate system are expressed by the parameter α (rad) as shown in the following (Equation 1) and (Equation 2): x = Rb / cos α * sin(π / (2*N) - invA + invα) (Equation 1) y = Rb / cos α * cos(π / (2*N) - invA + invα) (Equation 2) The parameter α is an angle as shown in FIG. 5. In (Equation 1) and (Equation 2), Rb is the radius of the base circle BC. The angle A (rad) is the pressure angle. N is the number of teeth of the gear product. The radius Rp of the pitch circle PC is 1 / cosA times the radius Rb of the base circle BC. The involute angle invA is tan A - A, and the involute angle invα is tan α - α. Note that (Equation 1) and (Equation 2) utilize the fact that when the intersection of the involute curve and the base circle BC is on the Y-axis, the parameter α (rad) becomes equal to the pressure angle A (rad) at the contact target point PP(s), which is the intersection of the involute curve and the pitch circle PC.

[0068]

[0069]

[0070]

[0071] Xps=Rp*sin(π / (2*N))-L*cos(π / (2*N)+A) (Formula 4) Yps=Rp*cos(π / (2*N))+L*sin(π / (2*N)+A)(Formula 5)

[0072]

[0073] In step S23, the processor 10 determines whether or not the touch probe 150 has come into contact with the workpiece W1 as a result of the movement. In other words, the error measurement method includes determining whether or not the touch probe 150 has come into contact with the surface of the workpiece W1 as a result of the movement. Specifically, the processor 10 can determine whether or not the touch probe 150 has come into contact with the workpiece W1 based on whether or not the processor 10 has received a detection signal output from a contact sensor attached to the touch probe 150. If the touch probe 150 has not come into contact with the workpiece W1 (No in step S23), step S23 is repeated.

[0074] When the touch probe 150 comes into contact with the surface of the workpiece W1 as a result of this movement (Yes in step S23), in step S24, the processor 10 determines the center position of the tip sphere 152 of the touch probe 150 at that time. In other words, the error measurement method includes having the computer 1C determine the center position of the tip sphere 152 of the touch probe 150 when the touch probe 150 comes into contact with the surface of the workpiece W1 as a result of this movement. Specifically, the processor 10 calculates the center position SeP(s) of the tip sphere 152 from the output of the rotation sensor of the first actuator ACT1 or the third actuator ACT3 at the time the detection signal is received. In the following description, the coordinates of the center position SeP(s) are assumed to be (x(s), y(s), z(s)).

[0075] Next, in step S25, the processor 10 determines a candidate value e(i) for the error between the gear profile (outer peripheral surface PS) and the target profile TS of the gear product. That is, the error measurement method includes having the computer 1C determine the candidate value e(i). Specifically, the processor 10 determines the candidate value e(i) by increasing it by a predetermined increment from a negative predetermined value. In step S26, the processor 10 generates a cross-sectional model (i) representing the cross-sectional profile of the tooth flank based on the candidate value e(i), the target profile TS, and the predetermined posture. That is, the error measurement method includes having the computer 1C generate a cross-sectional model M(i) representing the cross-sectional profile of the tooth flank based on the candidate value e(i), the target profile TS, and the predetermined posture.

[0076] In generating the cross-sectional model M(i), a first plane CS1 (see the lower diagram in FIG. 6 ) that is perpendicular to the tangential plane TP(s) and includes the contact target point PP(s), and the gear rotation axis A4 when the gear product is placed in the specified attitude are defined. The cross-sectional model M(i) is represented by a model curve MCL(s,i) obtained by shifting a target curve TCL(s) that passes through the contact target point PP(s) on the first plane CS1 in the direction away from the gear rotation axis A4 (Y direction) from the first plane CS1. This model curve MCL(s,i) is a curve segment obtained by shifting the target curve TCL(s) between a first intersection SP(s) of the target curve TCL(s) with a root circle RC or base circle BC centered on the gear rotation axis A4 of the target shape TS and the target curve TCL(s), and a second intersection EP(s) of the target curve TCL(s) with a tip circle AC centered on the gear rotation axis A4 of the target shape TS and the target curve TCL(s) by a candidate value e(i) in the separation direction (Y direction). A first end point SP'(s,i) of MCL(s,i) is located at a position shifted by the candidate value e(i) in the Y direction from the position of the first intersection SP(s). A second end point EP'(s,i) of MCL(s,i) is located at a position shifted by the candidate value e(i) in the Y direction from the position of the second intersection EP(s).

[0077] In the example of Figure 6, the radius Rb of the base circle BC is greater than the radius Rr of the root circle RC. However, depending on the gear design, the radius Rr of the root circle RC may be greater than the radius Rb of the base circle BC. The first intersection point SP(s) is the point of intersection between the root circle RC or the base circle BC, whichever has the larger radius, and the target curve TCL(s). In the example of Figure 6, the X and Y coordinates of the first intersection point SP(s) are expressed as (Rb * sin(π / (2*N) - invA), Rb * cos(π / (2*N) - invA)). The X and Y coordinates of the second intersection point EP(s) are expressed as (Ra * sin(π / (2*N) - invA + invα1), Ra * cos(π / (2*N) - invA + invα1)). Here, Ra is the radius of the tip circle AC, α1 is a parameter for defining the coordinates of the second intersection point EP(s), and α1 = arccos(Rb / Ra).

[0078] At this time, according to (Equation 1) and (Equation 2), the XY coordinates (x(i, α), y(i, α)) of any point on the cross-sectional model M(i) (model curve MCL(s, i)) are expressed as follows: x(i, α) = Rb / cos α * sin(π / (2*N) - invA + invα) (Equation 6) y(i, α) = Rb / cos α * cos(π / (2*N) - invA + invα) + e(i) (Equation 7) (where 0≦α≦arccos(Rb / Ra)).

[0079] When the radius Rr of the root circle RC is greater than the radius Rb of the base circle BC, the X and Y coordinates of the first intersection point SP(s) are expressed as (Rr * sin(π / (2 * N) - invA + invα2), Rr * cos(π / (2 * N) - invA + invα2)). Here, Rr is the radius of the root circle RC, α2 is a parameter for defining the coordinate of the first intersection point SP(s), and α2 = arccos(Rb / Rr). In this case, the range of α in (Equation 6) and (Equation 7) is arccos(Rb / Rr) ≦ α ≦ arccos(Rb / Ra). In this way, the above-mentioned model curve (curve segment) allows each coordinate in the two-dimensional coordinate system (X and Y coordinates) that defines the position on the first plane CS1 to be expressed by parameters.

[0080] In step S27, the processor 10 calculates the minimum distance L(i) between the cross-sectional model M(i) (model curve MCL(s,i)) and the center position SeP(s). In other words, the error measurement method includes having the computer 1C calculate the minimum distance L(i) between the cross-sectional model M(i) (model curve MCL(s,i)) and the center position SeP(s). The minimum distance L(i) is the distance between the center position SeP(s) and the closest point among multiple points on the model curve MCL(s,i) that is the smallest distance from the center position SeP(s). In calculating the minimum distance, α(j) (j is from 0 to the division number - 1) is prepared by dividing α in the range 0≦α≦arccos(Rb / Ra) or arccos(Rb / Rr)≦α≦arccos(Rb / Ra) at equal intervals. Preferably, this division number is 100 or more. That is, the positions of the above-mentioned multiple points on the first plane CS1 can be found by changing the parameters by the same amount. Then, the processor 10 finds α(j) that minimizes D(i,j) expressed by (Equation 8) as αmin, and determines the square root of D(i,j) corresponding to αmin as the minimum distance L(i). D(i,j)={x(i,α(j))-x(s)} ２ +{x(i, α(j))−y(s)} ２ (Equation 8) In step S28, the processor 10 determines whether the absolute value of the difference between the minimum distance L(i) calculated in step S27 and the radius of the tip ball 152 of the touch probe 150 is equal to or smaller than a tolerance. In other words, the error measurement method includes having the computer 1C determine whether the absolute value of the difference between the minimum distance L(i) calculated in step S27 and the radius of the tip ball 152 of the touch probe 150 is equal to or smaller than a tolerance. This tolerance is determined according to the required accuracy of the gear product. If the absolute value of this difference is greater than the tolerance (No in step S28), the process returns to step S25, where the candidate value e(i+1) = e(i) + Δe (Δe is the increment described above) is determined, and steps S26 to S28 are repeated.

[0081] If the absolute value of this difference is equal to or less than the tolerance (Yes in step S28), in step S29, the processor 10 determines the candidate value e(i) as the error e. That is, the processor 10 changes the candidate value e(i) and determines, as the error e, the candidate value e(i) where the absolute value of the difference between the minimum distance L(i) and the radius of the tip sphere 152 is equal to or less than the tolerance. That is, the error measurement method changes the candidate value e(i) and causes the computer 1C to determine, as the error e, the candidate value e(i) where the absolute value of the difference between the minimum distance L(i) and the radius of the tip sphere 152 is equal to or less than the tolerance. In this way, the error measurement method causes the computer 1C to calculate the error e between the gear profile of the workpiece W1 and the target shape TS of the gear product based on the center position SeP(s).

[0082] <Coordination between Error Measurement Processing and Gear Machining Processing> The machine tool 100 is capable of executing both gear machining and error measurement processing by processing a machining program 22 in which commands for performing such error measurement processing are added to program code for machining the workpiece W into a gear shape or gear product. FIG. 7 shows an example of such a machining program 22. In FIG. 7, "line number:" is added to the left of the machining program 22 for ease of reference. The control device 1 executes an interpreter 26, an actuator control library 27, and a sensor processing library 28 to analyze the machining program 22 and perform gear manufacturing processing corresponding to the commands in the machining program 22. FIGS. 8 and 9 are flowcharts showing the gear manufacturing method according to this embodiment, i.e., the operations of the gear manufacturing processing performed by the control device 1 (computer 1C).

[0083] 7, line number 1 indicates the start of the program, line number 2 indicates the program number, line number 3 describes the sequence number used for recursive calls, and line number 4 is a command to set the work coordinate system to the offset specified by the G54 command.

[0084] The control device 1 according to this embodiment determines whether a first command has been received in step S1 of FIG. 8 . The first command is, for example, a combination of the G310 command to the G312 command shown in FIG. 7 . This determination can be made, for example, by determining whether the interpreter 26 executed by the control device 1 has read the G310 command to the G312 command. The G310 command in line number 5 and the G311 command in line number 6 are commands for inputting hob specifications and operating conditions, and the G312 command in line number 7 is a command for inputting machining conditions. The G311 command in line number 6 is an example of a first tool definition command for specifying, at Y28, a first tool (e.g., a hob, skiving cutter, or mill tool) capable of performing gear machining held by the tool spindle 114 of the machine tool 100. The first tool specified in the example of line number 6 is a hob. Note that the T number associated with the first tool definition command is not limited to a T number specifying a hob, but may also be a T number specifying another tool for gear machining.

[0085] The commands written in lines 5 to 7 are an example of a first command that controls the actuator ACT so that the first tool machines the workpiece W1 into a gear shape. In the command in line 7, the number after J represents the depth of cut in the Y-axis direction. The second command may be a command for inputting the specifications, operating conditions, and machining conditions of the skiving cutter. Furthermore, the second command may be a command for inputting the tool path and cutting conditions (rotation speed, feed rate, etc.) for machining with a mill tool. The first tool definition command may also be a separate command (e.g., M60) separated from the first command.

[0086] If the first command has not been received (No in step S1), the control device 1 waits until the first command is received. If the control device 1 receives the first command (Yes in step S1), in step S2, the control device 1 controls the tool changer 130 so that the tool spindle 114 (tool holding device) holds a first tool of the at least one tool 160. In other words, the gear manufacturing method according to this embodiment includes, when the computer 1C receives the first command, having the computer 1C control the tool changer 130 of the machine tool 100 so that the tool spindle 114 (tool holding device) of the machine tool 100 holds the first tool.

[0087] Next, when the control device 1 receives the first command (Yes in step S1), in step S3 it controls the actuator ACT so that the first tool machines the workpiece W1 into a gear shape. In other words, the gear manufacturing method according to this embodiment includes, when the computer 1C receives the first command, having the computer 1C control the actuator ACT so that the first tool machines the workpiece W1 into a gear shape.

[0088] Specifically, the processor 10 controls the movement of the column 110 in the Z-axis direction and the rotation of the tool headstock 112 about the rotation axis A1. For example, the processor 10 moves the column 110 by outputting a PWM signal to a stepping motor. Then, while rotating the work spindle 122 about the rotation axis A3 and the tool spindle 114 about the rotation axis A2, the processor 10 controls the movement of the tool headstock 112 in the Y-axis direction and the movement of the column 110 in the Y-axis direction and the Z-axis direction so that the hob comes into contact with the outer peripheral surface of the cylindrical workpiece W1. In this way, a gear is formed on the workpiece W1.

[0089] 7 is an example of a fourth command for determining the posture of the workpiece W1. In this example, the fourth command is a midpoint CP between two adjacent teeth. ０8 shows a G340 command for measuring the phase (position on the C-axis) of the tool spindle 114 of the machine tool 100. The G340 command is H38.61 and includes a fourth tool defining command for defining the touch probe 150 held by the tool spindle 114 of the machine tool 100. However, the fourth tool defining command may be a separate command (e.g., M60) separated from the fourth command. The control device 1 according to this embodiment determines whether the fourth command has been received in step S4 of FIG. 8. If the fourth command has not been received (No in step S4), the control device 1 waits until the fourth command is received. When the control device 1 receives the fourth command (fourth tool defining command) (Yes in step S4), the control device 1 controls the tool changer 130 in step S5 to replace the tool (first tool) held by the tool spindle 114 (tool holding device) with the touch probe 150. That is, the gear manufacturing method according to this embodiment includes, when computer 1C receives the fourth command, having touch probe 150 control tool changer 130 to replace the tool (first tool) held by tool spindle 114 (tool holding device) of machine tool 100 with touch probe 150. Thereafter, control device 1 executes the process of step S18 in Fig. 4. The processing result of this command is output to macro variable #802 of control device 1.

[0090] Line numbers 9 and 10 in FIG. 7 are examples of a fifth command for positioning the workpiece W1 so that the orientation of the workpiece W1 is a predetermined orientation, or for setting a coordinate system for moving the touch probe 150 in accordance with the orientation of the workpiece. Line number 9 in FIG. 7 is a command for substituting the value of macro variable #802 output by step S18 into macro variable #5245 of the control device 1. This macro variable #5245 is a variable that defines the offset of the C-axis. Line number 10 in FIG. 7 sets the value set in macro variable #5245 as the offset of the C-axis, thereby creating a coordinate system for moving the touch probe 150 (the midpoint CP between two adjacent teeth). ０ The fifth command is a command to set the intermediate point CP based on macro variable #802. ０It may also be a command to rotate the work spindle 122 so that the Y′ axis passes through the Y′ axis.

[0091] The control device 1 according to this embodiment determines whether or not a fifth command has been received in step S6 of Fig. 8 . If the fifth command has not been received (No in step S6), the control device 1 waits until the fifth command is received. If the control device 1 receives the fifth command (Yes in step S6), it executes the process of step S19 of Fig. 4 . That is, the gear manufacturing method according to this embodiment includes causing the computer 1C to execute a process of controlling the workpiece spindle 122 (workpiece holding device) so that the workpiece W1 assumes a predetermined orientation before the touch probe 150 is brought into contact with the surface of the workpiece W1 for error measurement, or to set a coordinate system for moving the touch probe 150 in accordance with the orientation of the workpiece, and causing the computer 1C to control the tool changer 130 of the machine tool 100 so that the tool spindle 114 (tool holding device) of the machine tool 100 holds the first tool.

[0092] Line number 11 in FIG. 7 is an example of a second command for executing the error measurement process related to steps S21 to S29 in FIG. 4. This example shows a G344 command for executing a process in which gear specifications are input as arguments and the above-mentioned error e is output as a remaining allowance. The G344 command further includes a second tool defining command H38.61 for defining the touch probe 150 held by the tool spindle 114 of the machine tool 100. The G344 command may also include an argument related to the approach distance L. However, the second tool defining command may be a separate command (e.g., M60) separated from the second command. In the example of FIG. 4, the second tool defining command and the fourth tool defining command specify the same touch probe 150, but they may specify different touch probes 150.

[0093] The control device 1 according to this embodiment determines whether a second command has been received in step S7 of FIG. 9 . This determination can be made, for example, by determining whether the interpreter 26 executed by the control device 1 has read the second command. If the second command has not been received (No in step S7), the control device 1 waits until the second command is received. When the control device 1 receives the second command (second tool defining command) (Yes in step S7), the control device 1 controls the tool changer 130 in step S8 to replace the tool held by the tool spindle 114 (tool holding device) with the touch probe 150. That is, the gear manufacturing method according to this embodiment includes, when the computer 1C receives the second command (second tool defining command), having the touch probe 150 control the tool changer 130 to replace the first tool held by the tool spindle 114 (tool holding device) of the machine tool 100 with the touch probe 150. In the example of FIG. 4, the second tool defining command and the fourth tool defining command are the same, so no tool change is performed. In this case, the operation of step S5 may be considered to be the same as the operation of step S8.

[0094] Furthermore, when the control device 1 receives the second command (Yes in step S7), it executes the error measurement process relating to steps S21 to S29 in Fig. 4. The control device 1 outputs the output value of this process to macro variable #784 of the control device 1. Thus, the gear manufacturing method according to this embodiment includes, when the computer 1C receives the second command, controlling the actuator ACT to move the touch probe 150 in accordance with the error measurement process relating to steps S21 to S29 in Fig. 4, causing the computer 1C to calculate the error e between the gear profile of the workpiece W1 and the target shape TS of the gear product.

[0095] 7 is a command to set the workpiece coordinate system to the offset specified by the G54 command. Line 13 sets up a process to jump to the sequence number written in line 20 and end the machining program 22 if macro variable #784 output by the G344 command is 0 or less.

[0096] In FIG. 7 , lines 14 and 15 contain the same commands as lines 5 and 6. Line 16 is almost the same command as line 7, except that the value of macro variable #784 is added to the value after J. This command indicates that the aforementioned error e is to be added to the cutting depth in the Y-axis direction. The combination of commands described in lines 14 to 16 is an example of a third command that controls the actuator ACT to manufacture a gear product using the second tool based on the error e. The G311 command in line 15 is an example of a third tool definition command for specifying a second tool (e.g., a hob, skiving cutter, or mill tool) capable of performing gear machining held by the tool spindle 114 of the machine tool 100 at Y28. In the example of FIG. 4 , the third tool definition command and the first tool definition command may specify the same hob, and the first and second tools are the same. However, they are not limited to the same hob, and other tools for gear machining may also be specified.

[0097] The control device 1 according to this embodiment determines whether a third command has been received in step S9 of FIG. 9 . This determination can be made, for example, by determining whether the interpreter 26 executed by the control device 1 has read a combination of the G310 command to the G312 command. If the third command has not been received (No in step S9), the control device 1 waits until the third command is received. Upon receiving the third command (Yes in step S9), the control device 1 controls the tool changer 130 in step S10 to replace the touch probe 150 held by the tool spindle 114 (tool holding device) with a second tool among at least one tool. In other words, the gear manufacturing method according to this embodiment includes having the computer 1C control the tool changer 130 to replace the touch probe 150 held by the tool spindle 114 (tool holding device) with the second tool when the computer 1C receives the third command. While the example in FIG. 4 illustrates an example in which the first tool and the second tool are the same, the first tool and the second tool may be the same or different tools.

[0098] Next, when the control device 1 receives the third command (Yes in step S9), in step S11, it controls the actuator ACT to adjust the movement path of the second tool based on the error and manufacture a gear product. In other words, the gear manufacturing method according to this embodiment includes, when the computer 1C receives the third command, controlling the actuator ACT to adjust the movement path of the second tool based on the error and manufacture a gear product using the second tool. <Application to Helical Gears> In the above example, the gear product is an involute gear and a spur gear, but the present invention is also applicable to helical gears, bevel gears, and cycloidal gears. In all of these cases, the cross-sectional model M(i) is expressed as a curve expressed by parameters obtained by shifting the target curve TCL(s) in a predetermined direction, and the approach direction is determined to be the direction of the normal vector of the tangent plane TP(s) of the target shape TS at the contact target point PP(s), or vice versa. In either case, once the cross-sectional model M(i), the approach direction, and the approach start point are determined, the error e can be detected using the same algorithm as in the above embodiment, and this algorithm will now be described.

[0099]

[0100] For comparison, FIG. 10A also shows the model curve MCL(s,i) for a spur gear. In addition, the target curve on the X"Y plane is represented as TCL(h), the contact target point is represented as PP(h), the tangent plane is represented as TP(h), the first intersection is represented as SP(h), and the second intersection is represented as EP(h). The first end point of MCL(h,i) is represented as SP'(h,i), and the second end point of MCL(h,i) is represented as EP'(h,i). In this case, the X"Y plane is defined as a first plane CS1 that is perpendicular to the tangent plane TP(h) and includes the contact target point PP(h). The first plane CS1 is a plane obtained by rotating the second plane CS2 (XY plane), which is perpendicular to the gear rotation axis A4, on the second plane CS2 around a straight line (Y axis) passing through the gear rotation axis A4 on the second plane CS2 by a helix angle β defined from the tooth profile of the target shape TS. The first end point SP'(h,i) of MCL(h,i) is located at a position shifted by the candidate value e(i) in the Y direction from the position of the first intersection point SP(h). The second end point EP'(h,i) of MCL(h,i) is located at a position shifted by the candidate value e(i) in the Y direction from the position of the second intersection point EP(h).

[0101] In this case, the X" coordinate of each point on the target curve TCL(h) can be obtained by multiplying the X coordinate of each point on the target curve TCL(s) by cos β. The X" coordinate of each point on the model curve MCL(h, i) can be obtained by multiplying the X coordinate of each point on the model curve MCL(s, i) by cos β. Therefore, according to (Equation 6) and (Equation 7), the X" and Y coordinates (x(i, α), y(i, α)) of any point on the model curve MCL(h, i) are expressed as follows: x(i, α) = Rb / cos α * sin(π / (2*N) - invA + invα) * cos β (Equation 9) y(i, α) = Rb / cos α * cos(π / (2*N) - invA + invα) + e(i) (Equation 10) (However, 0≦α≦arccos(Rb / Ra) (when Rb≧Rr), arccos(Rb / Rr)≦α≦arccos(Rb / Ra) (when Rb<Rr))

[0102] In this case, if the angle between the Y axis and the line where the tangential plane TP(h) and the X"Y plane intersect is θp(h), then the following equation holds: tan θp(h) = tan θp(s) * cos β (Equation 11) The X and Y coordinates of the contact target point PP(s) are expressed as (Rp * sin(π / (2*N)), Rp * cos(π / (2*N)), and therefore the X" and Y coordinates of the contact target point PP(h) can be expressed as (Rp * sin(π / (2*N)) * cos β, Rp * cos(π / (2*N)). The difference D between the Y coordinate of the approach start point APSP(s) and the Y coordinate of the contact target point PP(s) is expressed as (Equation 12) below. D = Rb / cos(A + π / (2*N)) - Rp * cos(π / (2*N)) = Rp * {cos A / cos (A + π / (2 * N)) - cos (π / (2 * N))} = Rp * sin (π / (2 * N)) * tan θp (s) (Equation 12) The difference D' between the Y coordinate of the approach start point APSP (h) and the Y coordinate of the contact target point PP (h) is expressed as in the following (Equation 13). D' = Rp * sin (π / (2 * N)) * cos β * tan θp (h) (Equation 13)

[0103]

[0104]

[0105]

[0106]

[0107]

[0108] <Application to bevel gears>

[0109] 11A, for the sake of convenience, the model curve MCL(b,i) is omitted from the illustration, and instead the relationship between the target curve TCL(s) for a spur gear and the target curve TCL(b) for a standard bevel gear is shown. The target point of contact of the standard bevel gear is represented as PP(b), the tangent plane as TP(b), the first intersection as SP(b), and the second intersection as EP(b). In this case, the XY" plane is defined as a first plane CS1 that is perpendicular to the tangential plane TP(b) and includes the contact target point PP(b). The first plane CS1 is a plane obtained by rotating the second plane CS2 (XY plane), which is perpendicular to the gear rotation axis A4, on the second plane CS2 around a straight line (X axis) that passes through the gear rotation axis A4 by a reference cone angle δ defined from the tooth profile of the target shape TS. The model curve MCL(b, i) is positioned at a position shifted by the candidate value e(i) in the Y" direction with respect to the target curve TCL(b). In other words, it is positioned away from the target curve TCL(b) by the candidate value e(i) / cos δ in the Y direction.

[0110] In this case, the Y" coordinate of each point on the target curve TCL(b) can be obtained by multiplying the Y coordinate of each point on the target curve TCL(s) by cos δ. The Y" coordinate of each point on the model curve MCL(b, i) can be obtained by multiplying the Y coordinate of each point on the model curve MCL(s, i) by cos δ. Therefore, according to (Equation 4) and (Equation 5), the XY" coordinates (x(i, α), y(i, α)) of any point on the model curve MCL(b, i) are expressed as follows: x(i, α) = Rb / cos α * sin(π / (2*N) - invA + invα) (Equation 17) y(i, α) = Rb / cos α * cos(π / (2*N) - invA + invα) * cos δ + e(i) (Equation 18) (However, 0≦α≦arccos(Rb / Ra) (when Rb≧Rr), arccos(Rb / Rr)≦α≦arccos(Rb / Ra) (when Rb<Rr))

[0111] In this case, if the angle between the Y axis and the line where the tangential plane TP(b) and the XY" plane intersect is θp(b), then the following equation holds: tan θp(b) = tan θp(s) / cos δ (Formula 19) The X and Y coordinates of the contact target point PP(s) are expressed as (Rp * sin(π / (2*N)), Rp * cos(π / (2*N)), and therefore the X and Y" coordinates of the contact target point PP(b) are expressed as (Rp * sin(π / (2*N)), Rp * cos(π / (2*N) * cos δ).

[0112] The difference D' between the Y" coordinate of the approach start point APSP(b) and the Y" coordinate of the contact target point PP(b) is expressed as the following (Equation 20): D'=Rp*sin(π / (2*N))*tan θp(b) (Equation 20)

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] FIG. 12A is a cross-sectional view of an example reducer 200 including a trochoid gear. FIG. 12B is a cross-sectional view of another example reducer 201 including a trochoid gear. The reducer 200 includes an internal gear 210 formed by a plurality of internal pins 214 rotatably attached inside an outer cylinder 212, and an external gear 220 that meshes with the internal gear 210. Speed ​​reduction is achieved by the difference between the number of internal pins 214 and the number of teeth of the external gear 220. In many cases, the number of teeth of the external gear 220 is one less than the number of internal pins 214. The external gear 220 has an outer shape defined by an epitrochoid parallel curve. The reducer 201 includes an external gear 221 formed by a plurality of external pins 224 rotatably attached inside an inner cylinder 222, and an internal gear 211 that meshes with the external gear 221. Speed ​​reduction is achieved by the difference between the number of external pins 224 and the number of teeth of the internal gear 211. In many cases, the number of external pins 224 is one less than the number of teeth of the internal gear 211. The external shape of the internal gear 211 is defined by a hypotrochoid parallel curve. The case of FIG. 12A will be described below. For the internal gear 211 shown in FIG. 12B, the epitrochoid parallel curve of the external gear 220 shown in FIG. 12A can be applied to the hypotrochoid parallel curve, and therefore a description thereof will be omitted.

[0120]

[0121] The radius of the internal pin 214 is R ＯＰ Then, the XY coordinates (x, y) of point P on the epitrochoid parallel curve are generally expressed by (Equation 24) and (Equation 25). x = x ０ +R ＯＰ cosθ (Formula 24) y=y ０ +R ＯＰ sinθ (Equation 25) (x ０ , y ０ ), cos θ, and sin θ are expressed by the following equations: ０ =-a*sinφ+Rp*sin(φ / Zb) (Formula 26) y ０ =-a*cosφ+Rp*cos(φ / Zb) (Formula 27)

[0122]

[0123]

[0124] where φ is a parameter for drawing the epitrochoid curve. Rp is the radius of the pitch circle PC (base circle BC) of the internal pin 214. Zb is the number of internal pins 214. One period of Φ is 2πZb. Za is the number of teeth of the external gear 8. x is a correction coefficient that determines the curvature of the epitrochoid curve. The radius of the rolling circle in the model that draws the epitrochoid curve is R. Ｔ Then, t and a are expressed by the following formula: t = (Rp - R Ｔ ) / Rp (Formula 30) a=Rp(1-t) / Zb=R Ｔ / Zb (Equation 31) The larger t is, the smaller the curvature of the epitrochoid curve is, and the smaller t is, the larger the curvature of the epitrochoid curve is. Here, for example, φ=2nπ+φ ０ (n: integer, 0≦φ ０ < 2π), then φ from 0 to 2π ０ The relationship between φ and t is stored in memory 20. In other words, the same value of t is applied every 2π. Once φ is determined, t is determined from the relationship, a is determined from (Equation 31), and the XY coordinates (x, y) of P are determined based on (Equations 24) to (Equations 29).

[0125] Here, point P in FIG. ０ is obtained by setting the parameter φ to 0. The point P coincides with the first intersection point SP(s) of the target curve TCL(s). ０ can be obtained from the values ​​of (x, y) when the parameter φ is set to 0. The second intersection point of the target curve TCL(s) is set to the point P １ can be calculated from the value of (x, y) when the parameter φ is set to π. The contact target point PP(s) is ２ +y ２ The value of Rp ２ The (x, y) that is closest to can be found as an approximate solution.

[0126]

[0127] The XY coordinates (x(i), y(i)) of a point on the model curve MCL(s, i) are expressed as follows based on (x, y) expressed by (Equation 24) and (Equation 25) and the candidate value e(i): x(i) = x (Equation 34) y(i) = y + e(i) (Equation 35)

[0128]

[0129]

[0130] In a cycloidal gear, the pitch circle PC and the base circle BC coincide, and the target curve TCL(s) is expressed as an epicycloid outside the base circle BC, and the target curve TCL(s) is expressed as a hypocycloid inside the base circle BC. The epicycloid is expressed by the locus of a point on a circle when an outer rolling circle of radius Re rolls on the base circle BC without slip. The hypocycloid is expressed by the locus of a point on a circle when an inner rolling circle of radius Rh rolls on the base circle BC without slip.

[0131] Therefore, the XY coordinates (x(i, θe), y(i, θe)) of any point on the epicycloid of the model curve MCL(s, i) are expressed by the following matrix.

[0132]

[0133] The XY coordinates (x(i, θh), y(i, θh)) of any point on the hypocycloid of the model curve MCL(s, i) are expressed by the following matrix.

[0134]

[0135]

[0136] ​The machine tool 100, error measurement method, interpreter 26 having instructions for causing a computer 1C to execute the error measurement method, actuator control library 27, and sensor processing library 28 according to this embodiment use the cross-sectional model M(i) (model curve MCL(h, i)) to estimate the error e between the gear profile (outer peripheral surface PS) of the workpiece W1 and the target profile TS of the gear product from the center position SeP(s) of the tip ball 152 of the touch probe 150 when the touch probe 150 contacts the surface of the workpiece W1. Therefore, since there is no need to move the touch probe 150 until it contacts both teeth of the gear, it is possible to measure the gear error using a touch probe 150 selected regardless of the gear profile.

[0137] Furthermore, the machine tool 100, gear manufacturing method, and interpreter 26, actuator control library 27, and sensor processing library 28, which are equipped with instructions for causing a computer 1C to execute the gear manufacturing method, according to this embodiment, are capable of processing the first through fifth commands. Therefore, by loading a machining program 22 including the first through fifth commands into the machine tool 100, the machine tool 100 can automatically execute a series of operations, including rough machining, error measurement, and finish machining. <Modifications> In the above embodiment, the contact target point PP(s) is located on the pitch circle PC of the gear product. However, it may be located at another point on the target curve TCL(s). In this case, the contact target point PP(s) can be determined using Equation 1, Equation 2, or the like. Furthermore, while the model of error e has been described as a model in which the target curve is shifted in the Y-axis direction, the model curve MCL(s,i) may also be generated by generating an involute curve, a trochoid parallel curve, an epicycloid curve, or a hypocycloid curve by adding an offset of error e to the base circle radius Rb. In this case, the separation direction is not limited to a specific axial direction, but may be any radial direction relative to the gear rotation axis A4.

[0138] 7 are commands for involute spur gears and helical gears, but dedicated commands applicable to involute bevel gears, trochoidal gears, and cycloidal gears are also provided, and the dedicated commands may be processed by the interpreter 26, actuator control library 27, and sensor processing library 28 of the control device 1 in the same way as the G310, G311, G312, G340, and G344 commands. Alternatively, by adding parameters specific to involute bevel gears, trochoidal gears, and cycloidal gears as arguments to the G310, G311, G312, G340, and G344 commands, these gears may be processed in the same way as involute spur gears and helical gears. Furthermore, the first through fifth commands described above may be combined into one, or at least two of the commands may be partially combined into one command. Specifically, the fourth command, the fifth command, and the second command may be integrated into one command.

[0139] A dedicated processor or integrated circuit may be used to implement some or all of the logic functions of the interpreter 26, actuator control library 27, and sensor processing library 28 of the control device 1. The interpreter 26, actuator control library 27, and sensor processing library 28 may be stored not only in the memory 20 built into the control device 1, but also in a storage medium that is removable from the control device 1 and readable by the control device 1, such as a disk such as a floppy disk, optical disk, CD-ROM or magnetic disk, an SD card, a USB memory, or an external hard disk.

[0140] The workpiece gripper may be a gripper such as a vise that can grip a workpiece, instead of the work spindle 122. In this case, the machine tool 100 may be a machine tool that processes the workpiece W into a gear shape or a gear product using a mill tool.

[0141] In the above embodiment, an example was shown in which the error detection method according to Fig. 4 is implemented when a predetermined command is received by the machining program 22 in the machine tool 100. However, the error detection method according to Fig. 4 may also be implemented by a dedicated measuring device such as that disclosed in Japanese Patent Application Laid-Open No. 2006-234775. In this case, the configuration of the computer 1C described above is provided in the dedicated measuring device. Furthermore, the error detection method according to Fig. 4 may be implemented by any input from the user, not just by a command by the machining program 22.

[0142] In this application, the term "comprises" and its derivatives are open-ended terms that describe the presence of elements and do not exclude the presence of other elements not listed. This also applies to the terms "have," "include," and their derivatives.

[0143] The terms "member," "part," "element," "body," and "structure" may have multiple meanings, such as a single part or multiple parts.

[0144] Ordinal numbers such as "first" and "second" are merely terms for identifying components and do not have any other meaning (e.g., a particular order). For example, the presence of a "first element" does not imply the presence of a "second element," and the presence of a "second element" does not imply the presence of a "first element."

[0145] Words expressing degrees such as "substantially," "about," and "approximately" can refer to reasonable deviations that do not significantly change the end result. All numerical values ​​described in this application can be interpreted to include words such as "substantially," "about," and "approximately."

[0146] In this application, the phrase "at least one of A and B" should be interpreted to include A only, B only, and both A and B.

[0147] It is apparent that various changes and modifications of the present invention are possible in light of the above disclosure, and therefore, the present invention may be practiced otherwise than as specifically disclosed herein without departing from the spirit of the present invention.

Claims

1. A system comprising: a workpiece holding device configured to hold a workpiece; a tool holding device configured to hold either a touch probe or at least one tool; an actuator configured to move the tool holding device relatively to the workpiece holding device; and a control device configured to control the tool holding device and the actuator and to execute an error measurement process, wherein the error measurement process comprises: determining an approach start point and approach direction of the touch probe held by the tool holding device based on the attitude of the workpiece machined into a gear shape held by the workpiece holding device; controlling the actuator to move the touch probe from the approach start point in the approach direction; determining the center position of the tip ball of the touch probe when the touch probe comes into contact with the surface of the workpiece by said movement; determining a candidate value for the error between the gear shape and a target shape of a gear product; generating a cross-sectional model representing the cross-sectional shape of the tooth surface based on the candidate value, the target shape and the attitude; determining the minimum distance between the cross-sectional model and the center position; varying the candidate value and determining, as the error, the candidate value for which an absolute value of a difference between the minimum distance and the radius of the tip sphere is equal to or smaller than a tolerance.

2. The machine tool according to claim 1, further comprising a tool changer configured to change one of the touch probe and the at least one tool held by the tool holding device for another tool.

3. The machine tool according to claim 2, wherein the control device is configured to: control the tool changer so that the tool holding device selectively holds a first tool and a second tool of the at least one tool and the touch probe; and to receive a first command, a second command, and up to a third command; upon receiving the first command, to control the actuator so that the first tool processes the workpiece into the gear shape; upon receiving the second command, to execute the error measurement process; and upon receiving the third command, to control the actuator so that the movement path of the second tool is adjusted based on the error to manufacture the gear product.

4. An error measurement method comprising: having a computer determine an approach start point and approach direction of a touch probe based on the attitude of a workpiece machined into a gear shape; controlling an actuator to move the touch probe from the approach start point in the approach direction; having the computer determine the center position of the tip ball of the touch probe when the touch probe comes into contact with the surface of the workpiece by said movement; and having the computer calculate an error between the gear shape and a target shape of a gear product based on said center position, wherein having the computer calculate the error comprises: determining a candidate value for the error; generating a cross-sectional model representing the cross-sectional shape of the tooth flank based on the candidate value, the target shape and the attitude; determining the minimum distance between the cross-sectional model and the center position; changing the candidate value until the absolute value of the difference between the minimum distance and the radius of the tip ball is equal to or less than a tolerance value; 5. The error measurement method according to claim 4, wherein determining the approach start point and the approach direction includes determining a contact target point of the target shape, wherein the approach direction is determined in the direction of a normal vector of a tangent plane of the target shape at the contact target point when the gear product is placed in the attitude, or the reverse of that, and wherein the approach start point is determined at a position directed from the contact target point in a direction opposite to the approach direction.

6. An error measurement method according to claim 5, wherein a first plane perpendicular to said tangential plane and including said contact target point, and a gear rotation axis when said gear product is placed in said attitude, are defined; and said cross-sectional model is represented by a model curve obtained by shifting a target curve passing through said contact target point on said first plane in a direction away from said gear rotation axis, among a plurality of curves represented by cutting said target shape with said first plane.

7. The error measurement method according to claim 6, wherein the first plane is a plane obtained by rotating a second plane perpendicular to the gear rotation axis on the second plane around the gear rotation axis or a straight line passing through the target contact point by a helix angle defined by the tooth profile of the target shape.

8. The error measurement method according to claim 6 or 7, wherein the minimum distance is the distance between the central position and a neighboring point among a plurality of points on the model curve that has the smallest distance from the central position.

9. An error measurement method according to any one of claims 6 to 8, wherein the model curve is a curve segment obtained by moving the target curve segment between a first intersection of the target curve and a root circle or base circle of the target shape centered on the gear rotation axis, and a second intersection of the target curve and a tip circle of the target shape centered on the gear rotation axis, by the candidate value in the separation direction.

10. An error measurement method according to any one of claims 6 to 9, wherein each coordinate of the model curve in a two-dimensional coordinate system that defines a position on the first plane can be expressed by a parameter, and the positions of the multiple points on the first plane can be found by changing the parameter by the same amount.

11. An error measurement method according to any one of claims 4 to 10, further comprising: before bringing the touch probe into contact with the surface of the workpiece, positioning the workpiece so that the orientation of the workpiece is a predetermined orientation, or setting a coordinate system for moving the touch probe in accordance with the orientation of the workpiece.

12. A gear manufacturing method comprising the steps of: when the computer according to any one of claims 4 to 11 receives a first command, causing the computer to control the actuator so that a first tool held by a tool holding device of a machine tool is used to machine the workpiece into the gear shape; when the computer receives a second command, causing the actuator to control the actuator to move the touch probe in accordance with the error measurement method of any one of claims 4 to 11, thereby causing the computer to calculate the error; and when the computer receives a third command, causing the computer to control the actuator so that the movement path of a second tool held by the tool holding device is adjusted based on the error, causing the second tool to manufacture the gear product.

13. A gear measuring device comprising a computer configured to execute the error measuring method of any one of claims 4 to 11.

14. A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the error measurement method of any one of claims 4 to 11.

15. A computer program comprising instructions that, when executed by a computer, cause the computer to carry out the gear manufacturing method of claim 12.

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