JP2016061631A - Screw groove shape measurement device and tool machine using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw groove shape measurement device measuring a screw groove shape of a screw shaft constituting a ball screw with higher accuracy than before, and a tool machine using the screw groove shape measurement device.SOLUTION: In a screw groove shape measurement device 2, a displacement sensor 62 detects displacement in an irradiation direction of a laser beam or displacement in an axial direction of a probe, by irradiating the surface of a screw shaft 80 constituting a screw ball with the laser beam or contacting with the probe. When the axial direction of the screw shaft 80 is defined as a first direction Z, and a direction perpendicular to the first direction Z is defined as a second direction X, a control unit 60 measures the shape of each screw groove of the screw shaft 80 with a displacement sensor 62, in a state of revolving the displacement sensor 62 or fixing a revolution angle of the displacement sensor 62, so that a displacement measurement direction to be the irradiation direction of the laser beam or the axial direction of the probe is inclined to the second direction X.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a thread groove shape measuring apparatus for measuring the thread groove shape of a screw shaft constituting a ball screw, and further relates to a machine tool provided with the thread groove shape measuring apparatus.

  As a method for measuring the cross-sectional shape of the thread groove of the screw shaft constituting the ball screw, for example, a technique described in Japanese Patent No. 3579728 is known. According to this document, first, the axial cross-sectional shape is obtained by measuring the screw groove of the screw shaft in the axial direction, and then the cross-sectional shape projected in the direction perpendicular to the screw groove using the lead angle is obtained. In this document, a contact-type measuring device using a probe (probe) is disclosed, but a non-contact type measuring device such as a laser displacement sensor can also be used.

Japanese Patent No. 3577728

  When measuring the thread groove shape while moving the contact or non-contact type displacement sensor along the axial direction of the screw shaft as described above, the displacement measurement direction (perpendicular to the axis) compared to the amount of movement in the axial direction As the amount of displacement increases, there will be a difference in density between the measurement points. As a result, there arises a problem that accurate data cannot be obtained near the edge of the thread groove (near the thread) compared to near the bottom of the thread groove.

  The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a thread groove shape measuring device capable of measuring the thread groove shape of a screw shaft constituting a ball screw with higher accuracy than before. Is to provide.

  The present invention is a thread groove shape measuring apparatus for measuring the shape of each thread groove of a screw shaft constituting a ball screw, and includes a displacement sensor, a drive mechanism, and a control unit. The displacement sensor detects a displacement in the irradiation direction of the laser light or a displacement in the axial direction of the probe by irradiating the surface of the screw shaft with a laser beam or bringing a probe into contact therewith. The drive mechanism can move the displacement sensor relative to the screw shaft and can turn the displacement sensor about at least one axis. The control unit controls the displacement sensor and the drive mechanism. Here, the axial direction of the screw shaft is defined as the first direction, and the direction perpendicular to the first direction is defined as the second direction. The control unit fixes the turning angle of the displacement sensor while turning the displacement sensor so that the displacement measurement direction, which is the laser light irradiation direction or the probe axial direction, is inclined with respect to the second direction. In this state, the displacement sensor is configured to measure the shape of each screw groove of the screw shaft.

  By inclining the displacement measurement direction as described above, it is possible to measure with high accuracy up to the vicinity of the edge of the thread groove, and it is possible to prevent the density of the measurement points from occurring.

  In a preferred embodiment, the control unit moves the displacement sensor relative to the first direction in a state where the inclination angle of the displacement measurement direction with respect to the second direction is fixed, while the displacement sensor moves each of the screw grooves of the screw shaft. Configured to measure shape.

  In another preferred embodiment, the control unit is configured in a direction inclined in the direction opposite to the displacement measurement direction with respect to the second direction for each screw groove in a state where the inclination angle of the displacement measurement direction with respect to the second direction is fixed. The displacement sensor is configured to measure the shape of each screw groove while relatively moving the displacement sensor.

  By making the movement direction of the displacement sensor oblique as described above, the variation in the distance from the displacement sensor to the measurement point can be further reduced, so that the measurement accuracy can be further increased.

  In the other embodiments described above, the angle formed by the relative movement direction of the displacement sensor for each screw groove and the displacement measurement direction is preferably in the range of 85 degrees to 95 degrees.

  In the above-described embodiment and the other embodiments, the inclination angle of the displacement measurement direction with respect to the second direction is preferably in the range of 40 degrees to 50 degrees.

  By setting the displacement measurement direction to such an angle, the most accurate measurement can be performed near the contact point between the ball and the thread groove.

  In still another preferred embodiment, the control unit relatively moves and displaces the displacement sensor for each screw groove so that the displacement measurement direction is orthogonal to the surface of the screw groove at the laser light irradiation position or the probe contact position. While turning, the shape of each screw groove is measured by a displacement sensor.

  As described above, the displacement measurement direction and the surface of the thread groove are orthogonal to each other at the laser beam irradiation position or the probe contact position, thereby enabling highly accurate measurement.

  In still another embodiment described above, preferably, when the control unit assumes that the ball screw ball is in contact with the thread groove, the displacement sensor is positioned concentrically with the ball and the center of the laser beam or the probe is used. The shape of each screw groove is measured by the displacement sensor while the displacement sensor is relatively moved and turned for each screw groove so that the axis passes through the center of the ball.

  In another aspect, the present invention is a machine tool including any one of the above-described thread groove shape measuring devices.

  According to this invention, the thread groove shape of the screw shaft constituting the ball screw can be measured with higher accuracy than before.

It is a perspective view which shows typically the structure of the machine tool provided with the thread groove shape measuring apparatus by 1st Embodiment. It is a block diagram which shows the functional structure of the thread groove shape measuring apparatus of FIG. It is a figure which shows the structure of a laser displacement sensor typically. It is a side view of a screw shaft. It is a flowchart which shows the measurement procedure of the thread groove shape by 1st Embodiment. It is a schematic diagram for demonstrating the measuring method of the thread groove shape by 1st Embodiment. It is a schematic diagram for demonstrating the measuring method of the thread groove shape of the screw shaft by a comparative example. It is a flowchart which shows the process sequence of the measured thread groove shape data. It is a figure for demonstrating step S215, S220 of FIG. It is a figure for demonstrating step S225 of FIG. 8, S230. It is a figure for demonstrating step S235 of FIG. FIG. 9 is a diagram for explaining step S235 in FIG. 8 when the thread groove shape is a Gothic arch. It is a flowchart which shows the measurement procedure of the thread groove shape by 2nd Embodiment. It is a schematic diagram for demonstrating the measuring method of the thread groove shape by 2nd Embodiment. It is a flowchart which shows the measurement procedure of the thread groove shape by 3rd Embodiment. It is a schematic diagram for demonstrating the measuring method of the thread groove shape by 3rd Embodiment. It is a schematic diagram for demonstrating the measurement of the thread groove shape using a contact-type displacement sensor as a modification of 1st-3rd embodiment.

  Hereinafter, each embodiment will be described in detail with reference to the drawings. Hereinafter, a machine tool incorporating a thread groove shape measuring device will be described as an example, but the present invention is not limited to a machine tool. The same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

<First Embodiment>
[Schematic configuration of machine tool]
FIG. 1 is a perspective view schematically showing a configuration of a machine tool 1 provided with a thread groove shape measuring apparatus 2 according to the first embodiment. The machine tool 1 of FIG. 1 includes an NC (Numerical Control) device 40, an ATC (Automatic Tool Changer) 44, and a computer 64 in addition to the processing device 10.

  FIG. 2 is a block diagram showing a functional configuration of the thread groove shape measuring apparatus 2 of FIG. 2 shows an X-axis drive mechanism 34, a Y-axis / B-axis drive mechanism 36, a Z-axis drive mechanism 38, chucks 28 and 29 provided in the NC device 40, the ATC 44, the computer 64, and the machining device 10. , And the rotation drive mechanism 30 of the headstock 20 is shown. In this specification, the X-axis drive mechanism 34, the Y-axis / B-axis drive mechanism 36, and the Z-axis drive mechanism 38 are collectively referred to as the drive mechanism 32. Hereinafter, the machining apparatus 10 and the NC apparatus 40 will be briefly described with reference to FIGS. 1 and 2.

  The processing apparatus 10 includes a tool rest 24, a spindle stock 20 that supports a workpiece (in this embodiment, a screw shaft 80), an auxiliary spindle stock (or tailstock) 22 that supports a tip of the workpiece, The turret 26 and the machine body 12. When the processing apparatus 10 is viewed from the front, the vertical direction, the front-rear direction, and the left-right direction are respectively defined as an X-axis direction, a Y-axis direction, and a Z-axis direction. Three orthogonal axes are constituted by the X, Y, and Z axes orthogonal to each other. When distinguishing upward and downward in the X-axis direction, a description is given with reference numerals such as + X direction and -X direction. The same applies to the Y-axis direction and the Z-axis direction.

Headstock 20 grips the workpiece by the chuck 28, rotates the grasped workpiece in the direction indicated by the arrow C ₁ by the rotation mechanism 30. Auxiliary headstock 22 is disposed opposite with respect to the headstock 20 is movable parallel to the Z-axis direction Z ₁ axial direction. Chuck 29 of the auxiliary spindle stock 22, as shown by the arrow C _2, is rotatable gripping the workpiece.

A plurality of tools for turning the workpiece held by the chuck 28 of the head stock 20 are attached to the turret 26. Turret 26 includes a parallel X ₁ axis direction X-axis direction, is movable respectively parallel to the Z-axis direction Z ₂ axial direction.

  A tool 25 for turning or cutting a workpiece held by the chuck 28 of the headstock 20 is detachably mounted on the main spindle 25 provided on the tool rest 24. The tool of the spindle 25 is changed by an ATC (automatic tool changer) 44.

  The Z-axis moving unit 18 provided in the machine main body 12 of the processing apparatus 10 is driven by the Z-axis drive mechanism 38 and moves in the Z-axis direction. The X-axis moving unit 14 provided in the Z-axis moving unit 18 is driven by the X-axis drive mechanism 34 and moves in the X-axis direction. The Y-axis moving unit 16 provided in the X-axis moving unit 14 is driven by the Y-axis / B-axis drive mechanism 36 and moves in the Y-axis direction.

The tool post 24 is attached in front of the Y-axis moving unit 16. The tool post 24 is driven by the Z-axis moving unit 18, the X-axis moving unit 14, and the Y-axis moving unit 16 to move in the Z-axis direction, the X-axis direction, and the Y-axis direction, respectively. The central axis of the Y-axis moving unit 16, that is, the B axis is parallel to the Y axis. As shown by the arrow B ₁ , the tool post 24 is driven by the Y-axis / B-axis drive mechanism 36 and can turn around the B-axis.

  The machine tool 1 has a lathe function of turning a workpiece with the tool of the tool rest 24 and the tool of the turret 26 and a function of a machining center for cutting the workpiece with the tool of the tool rest 24. When the machine tool 1 is used as a lathe, the tool mounted on the spindle 25 does not rotate, and the workpiece is rotated and turned with the tool. Alternatively, a tool attached to the turret 26 is used, the workpiece is rotated, and turning is performed with this tool. When the machine tool 1 is used as a machining center, the tool is rotated by the spindle 25 to cut a non-rotating workpiece. The tool post 24 at this time exhibits a function as a spindle head of the machining center.

  The NC device 40 includes a PLC (Programmable Logic Controller) 42 that controls the overall operation of the machine tool 1. For example, the PLC 42 controls the X-axis drive mechanism 34, the Y-axis / B-axis drive mechanism 36, the Z-axis drive mechanism 38, and the rotational drive mechanism 30 of the headstock 20 shown in FIG. 2. The PLC 42 further controls the moving mechanism of the auxiliary headstock 22, the moving mechanism of the turret 26, and the ATC 44.

[Configuration of thread groove shape measuring device]
The basic function of the thread groove shape measuring apparatus 2 is to measure the thread groove shape of the screw shaft constituting the ball screw by cooperating with the drive mechanism 32 of the processing apparatus 10 and the PLC 42 of the NC apparatus 40. Further, the thread groove shape measuring device 2 calculates the thread shaft lead and the like based on the measured thread groove shape data 76 and the thread shaft design data 78.

  As shown in FIG. 2, the thread groove shape measuring apparatus 2 includes a measurement head 62, a drive mechanism 32, and a computer 64. The computer 64 and the NC device 40 constitute a control unit 60 for controlling the measuring head 62 and the drive mechanism 32.

  In the case of this embodiment, the measuring head 62 is a wireless head that communicates with the computer 64 by wireless communication, and is detachable that is attached to the spindle 25 of the tool post 24 by the ATC 44. Alternatively, a wired measuring head that is fixedly attached to the tool post 24 and communicates with the computer 64 via a signal line may be used.

  The measuring head 62 measures the distance DM from the reference point 33 outside the screw shaft 80 (in this embodiment, the reference point 33 is located on the B axis) to the surface of the screw shaft 80, that is, the thread groove shape. A displacement sensor. The displacement sensor provided in the measurement head 62 may be a contact type that measures the displacement of the surface of the measurement object by contacting the measurement object, or is non-contact using laser light, ultrasonic waves, electromagnetic waves, or the like. It may be a non-contact type that measures the displacement of the surface of the measurement object.

  In this embodiment, the example which measures the displacement of the surface of the screw shaft 80 by a laser displacement sensor as an example is shown. The laser displacement sensor irradiates the surface of the measurement object with the laser light L, and the distance from the laser displacement sensor to the irradiation position of the laser light L based on the reflected light of the laser light L, that is, the laser beam direction of the measurement object. Measure the displacement in the (displacement measurement direction).

  The drive mechanism 32 can move the measurement head 62 (displacement sensor) relative to the measurement object (screw shaft 80) and can turn the measurement head 62 (displacement sensor) about at least one axis. . In the case of the present embodiment, the measuring head 62 can be moved in the X-axis direction, the Y-axis direction, and the Z-axis direction by the drive mechanism 32, and therefore can be moved in any direction by combining movements in at least two axes. is there. Furthermore, the measuring head 62 can turn around the B axis parallel to the Y axis (the turning angle is ψ). The screw shaft 80 is fixed by the chucks 28 and 29 so that the direction of the central axis 82 is parallel to the Z-axis direction (the rotational drive mechanism 30 of the headstock 20 is not used when measuring the thread groove shape). .

  The computer 64 includes a processor 66, a memory 68, an input / output interface (not shown) with the NC device 40, and a communication device 70 that performs wireless communication with the measurement head 62. The processor 66 functions as a measurement control unit 72 that measures the thread groove shape of the screw shaft 80 by executing a measurement control program. The measurement result (thread groove shape data 76) is stored in the memory 68. The processor 66 further functions as a data processing unit 74 that performs arithmetic processing on the thread groove shape data 76 based on the design data 78 of the screw shaft.

  When measuring the thread groove shape of the screw shaft 80, the PLC 42 controls the drive mechanism 32 based on a command from the processor 66 of the computer 64 and outputs a trigger signal to the communication device 70 at a predetermined cycle. When the communication device 70 receives the trigger signal, it transmits a measurement command f to the measurement head 62. The measuring head 62 measures the distance DM along the displacement measurement direction (the direction of the laser beam 162) from the reference point 33 to the screw shaft 80 in accordance with the measurement command f. Data F of the measured distance DM is transmitted from the measurement head 62 to the processor 66 of the computer 64 via the communication device 70.

  The PLC 42 further acquires the position information (X, Y, Z) of the reference point 33 and the information of the turning angle ψ from the drive mechanism 32 in accordance with the timing of the distance measurement by the measurement head 62 described above. Is sent to the processor 66 of the computer 64. Based on the position information (X, Y, Z) of the reference point 33, the information of the turning angle ψ, and the measured value of the distance DM, the processor 66 obtains the position information of the measurement point (laser beam irradiation position) of the thread groove. The calculated position information of the measurement point is stored in the memory 68 as the thread groove shape data 76.

[Outline of laser displacement sensor]
Next, the structure of the laser displacement sensor incorporated in the measurement head 62 will be described.

  FIG. 3 is a diagram schematically showing the structure of the laser displacement sensor. Referring to FIG. 3, laser displacement sensor 100 includes a light emitting unit 110, a condensing lens 118 as an optical system, and a linear image sensor 120 as a light receiving unit. The light emitting unit 110 includes a laser diode 112 and a lens 114.

  The laser beam 116 emitted from the laser diode 112 is shaped into substantially parallel light by the lens 114 and is irradiated onto the measurement object 130. The light diffusely reflected on the measurement object 130 is collected by the condenser lens 118 on the linear image sensor 120 arranged in the angle direction of the laser beam 116 and γ. As a result, on the linear image sensor 120, data indicating a Gaussian luminance level is obtained. A distance from the light emitting unit 110 to the laser spot (laser beam irradiation position) 132 on the measurement object 130 is calculated based on the triangulation from the barycentric position of the luminance data. That is, the displacement of the measurement object 130 in the direction 134 of the laser beam 116 (referred to as the displacement measurement direction 134 in this specification) is measured.

  The linear image sensor 120 is preferably disposed at an angle based on a Scheimpflug Condition. That is, the detection surface of the linear image sensor 120 and the main surface of the condenser lens 118 intersect with each other in a straight line, and the angle formed by these surfaces is β. A surface including the laser beam 116 is a subject surface. With this arrangement, even if the distance between the measurement object 130 and the laser displacement sensor 100 changes, the laser spot 132 is imaged on the linear image sensor 120 without being blurred.

  The beam size of the laser beam 116 emitted from the laser diode 112 actually changes according to the distance from the laser diode 112. Specifically, the position of the beam waist determined by the focal length of the lens 114 is the reference position. In this specification, the distance from the laser diode 112 to the reference position is referred to as a reference distance. The most accurate measurement is possible at the reference position, and the laser spot size increases and the measurement error increases as the position deviates from the reference position. The measurable range is limited by the size of the detection surface of the linear image sensor 120.

[About Ball Screw]
Next, the ball screw that is the measurement target will be briefly described.

  A ball screw is a mechanical element that converts rotational motion into linear motion or converts linear motion into rotational motion, and is composed of a screw shaft, a nut, a ball (steel ball), a circulating component, and the like. When the ball rolls between the screw shaft and the nut, the screw shaft or the nut can be rotated very lightly. The circulating component is configured to circulate the ball indefinitely.

  FIG. 4 is a side view of the screw shaft. FIG. 4 shows a screw shaft 80 having a thread groove 86 with an inclination angle θ (that is, a lead angle θ). With reference to FIG. 4 (A), the outer diameter of the thread 84 portion of the screw shaft is referred to as a nominal diameter D1. When the ball 88 is in contact with the thread groove 86 of the screw shaft at an ideal contact point, the diameter of the cylinder including the center 90 of the ball 88 is referred to as a pitch circle diameter D2. In FIG. 4A, the distance between the centers of adjacent balls 88 corresponds to the lead LL.

  A procedure for measuring the lead LL of the screw shaft will be briefly described with reference to FIG. (i) First, the surface shape of the screw shaft is measured while moving the measurement point in the axial direction 92 of the screw shaft (that is, along the straight line 92 in FIG. 4B). (ii) Next, by multiplying the Z-axis coordinate of each measurement point by the cosine (cos θ) of the lead angle θ, the measured surface shape is perpendicular to the thread groove 86 (the direction of the straight line 94 in FIG. 4B). ) To the surface shape. (iii) Next, based on the surface shape after conversion, it is assumed that the ball 88 is ideally in contact with the thread groove 86, and the distance between the centers of adjacent balls at this time is obtained. (iv) Next, the obtained distance between the centers of the balls is divided by the cosine (cos θ) of the lead angle θ. As a result, the lead LL of the ball screw is obtained. Hereinafter, the measurement of the surface shape in the procedure (i) will be described in more detail.

[Method for measuring surface shape of screw shaft]
FIG. 5 is a flowchart showing a procedure for measuring the thread groove shape according to the first embodiment. FIG. 6 is a schematic diagram for explaining the thread groove shape measuring method according to the first embodiment. The schematic diagram of FIG. 6 shows a cross-sectional view of the screw shaft 80 cut along a cross section passing through the central axis. In FIG. 6, the screw shaft 80 is fixed so that the axial direction thereof is the Z-axis direction, and the cross section of the screw shaft 80 is parallel to the XZ plane. Measurement points MP by the laser displacement sensor 100 are indicated by circles in the figure.

  With reference to FIGS. 2, 5, and 6, first, the processor 66 controls the drive mechanism 32 via the NC device 40 to set the turning angle of the measurement head 62 (laser displacement sensor 100) to a predetermined angle. Set (S100). Specifically, as shown in FIG. 6A, the direction of the laser beam 116 (that is, the displacement measuring direction 134) is the axis of the screw shaft by an angle ψ1 from the direction perpendicular to the screw shaft axis (X-axis direction). It is tilted in the direction (Z-axis direction). In this case, the inclination angle ψ1 is preferably 40 to 50 degrees (typically around 45 degrees). In the first embodiment, the turning angle is fixed.

  Next, the processor 66 controls the drive mechanism 32 via the NC device 40 and moves it relative to the screw shaft 80 to thereby measure the first thread groove as shown in FIG. The measuring head 62 (laser displacement sensor 100) is moved to the start position 140 (S105).

  Next, the processor 66 controls the drive mechanism 32 via the NC device 40, thereby moving the laser displacement along the moving direction 148 that is a direction inclined to the side opposite to the displacement measuring direction 134 with respect to the X-axis direction. While moving the sensor 100, the shape of the thread groove 86 to be measured is measured by the laser displacement sensor 100 (S110). In this case, the moving direction 148 is preferably an angle range in a direction (85 ° to 95 °) substantially orthogonal to the displacement measuring direction 134. Specifically, in the case of FIG. 6A, the laser displacement sensor 100 moves linearly in an oblique direction from the measurement start position 140 to the measurement end position 142, and has a shape on one side (+ Z direction side) of the thread groove 86. Measure. Note that such movement of the laser displacement sensor 100 in the oblique direction can be realized by simultaneously performing movement in the X-axis direction and movement in the Z-axis direction.

  When measuring the shape of the next adjacent thread groove (YES in step S115), the above procedure is repeated with the turning angle of the laser displacement sensor 100 fixed at the inclination angle ψ1. That is, the processor 66 moves the laser displacement sensor 100 to the measurement start position 144 of the next thread groove 86 by controlling the drive mechanism 32 via the NC device 40 (S105). Further, the processor 66 controls the drive mechanism 32 via the NC device 40 to move the laser displacement sensor 100 while moving the laser displacement sensor 100 linearly in an oblique direction from the measurement start position 144 to the measurement end position 146. The shape of the slope on one side (+ Z direction side) of the thread groove 86 to be measured is measured by the sensor 100 (S110).

  As described above (until NO in step S115), the shape of the inclined surface on one side (+ Z direction side) of the plurality of screw grooves 86 arranged along the Z-axis direction is changed in the arrangement order of the screw grooves 86 (from the + Z direction to − Measured in the order of Z direction).

  Thereafter, the processor 66 causes the laser to pass through the NC device 40 so that the displacement measuring direction 134 is inclined in the direction opposite to that in the step S100 with respect to the X-axis direction (that is, the inclination angle ψ2). The turning angle of the displacement sensor 100 is set (S120). Then, the processor 66 measures the shape of the inclined surface on the other side (−Z direction side) of the plurality of screw grooves 86 with the laser displacement sensor 100 while moving the laser displacement sensor 100 in the direction opposite to that in the case of step S110. .

  Specifically, as shown in FIG. 6B, the processor 66 moves the laser displacement sensor 100 to the measurement start position 140 of the first thread groove 86 (S125). Next, the processor 66 linearly and obliquely extends from the measurement start position 140 to the measurement end position 142 (a direction 148 that forms an angle of 85 ° to 95 ° with respect to the displacement measurement direction 134, preferably the displacement measurement direction 134. While moving the laser displacement sensor 100 in the orthogonal direction, the shape of the inclined surface on the other side (−Z direction side) of the thread groove 86 to be measured is measured by the laser displacement sensor 100 (S130).

  When measuring the shape of the next adjacent thread groove (YES in step S135), the above procedure is repeated with the turning angle of the laser displacement sensor 100 fixed at the inclination angle ψ2. That is, the processor 66 moves the laser displacement sensor 100 to the measurement start position 144 of the next thread groove 86 by controlling the drive mechanism 32 via the NC device 40 (S125). Subsequently, the processor 66 controls the drive mechanism 32 via the NC device 40 to move the laser displacement sensor 100 linearly in an oblique direction from the next measurement start position 144 to the measurement end position 146, while moving the laser. The shape of the slope on the other side (−Z direction side) of the thread groove 86 to be measured is measured by the displacement sensor 100 (S130).

  As described above (until NO in step S130), the shape of the slope on the other side (+ Z direction side) of the plurality of screw grooves 86 arranged along the Z-axis direction is in the reverse order of steps S105 to S115 (-Z Measured from the direction to the + Z direction).

[effect]
Next, the effect of the above-described measuring method of the thread groove shape will be described in comparison with the measuring method of the comparative example.

  FIG. 7 is a schematic diagram for explaining a method for measuring a thread groove shape of a screw shaft according to a comparative example. 2 and 7, in the measurement method of the comparative example, the processor 66 controls the drive mechanism 32 via the NC device 40 to change the direction of the laser beam 116 (that is, the displacement measurement direction 134). It is made to correspond to the direction (X-axis direction) perpendicular to the axis of the screw shaft. In this state, the processor 66 controls the drive mechanism 32 via the NC device 40 to move the laser displacement sensor 100 in a direction parallel to the axis of the screw shaft (Z-axis direction), while moving the laser displacement sensor 100. Then, the shape of each thread groove is measured in order. In this case, there are the following problems.

  First, in the case of the comparative example, there is a problem that the fluctuation range of the measured value is relatively large. Specifically, in FIG. 7, the fluctuation range of the measurement value is the difference between the measurement value L5 when the measurement point MP is the bottom of the thread groove 86 and the measurement value L4 when the measurement point MP is the edge of the thread groove 86 as L6 = L5−L4. Given. On the other hand, as shown in FIG. 6, the fluctuation range of the measured value in the first embodiment is obtained by L3 = L2−L1, and is smaller than the fluctuation range L6 of the comparative example.

  As already described, the measurement range of the laser displacement sensor has a limit, and the measurement error increases with distance from the reference position. According to this embodiment, since the fluctuation range of the measured value can be further reduced as compared with the comparative example, the measurement accuracy can be improved and the possibility of exceeding the measurement limit can be reduced.

  Another problem in the case of the comparative example is that the change in the measured value becomes larger than the amount of movement of the laser displacement sensor 100 in the axial direction (Z-axis direction) of the screw shaft 80 (specifically, the screw groove 86 In the vicinity of the edge), the interval between the measurement points MP becomes too wide and accurate measurement cannot be performed. As a result, as shown in FIG. 7, the distance between the measurement points MP becomes dense between the vicinity of the edge of the screw groove 86 and the bottom of the screw groove 86. In the present embodiment, such an inconvenience hardly occurs, and accurate shape data can be obtained in the vicinity of the contact point between the screw groove 86 and the ball, which is particularly important (when the inclination angle from the X axis is about 45 degrees).

  Further, in the case of the comparative example, there is a possibility that the laser beam 152 is subjected to multiple reflection near the edge of the thread groove 86. As a result, the scattered light of the multiple-reflected laser beam 152 is incident on the light receiving portion of the laser displacement sensor 100, so that there is a problem that the measurement accuracy is unavoidably lowered. On the other hand, according to the present embodiment, there is a low possibility of erroneously detecting scattered light of the laser beam that is multiply reflected near the edge of the thread groove 86.

[Calculation method of screw shaft lead]
Next, a procedure for calculating the lead of the screw shaft based on the measured thread groove shape data will be described.

  FIG. 8 is a flowchart showing a processing procedure of measured thread groove shape data. 9-12 is a figure for demonstrating each step of FIG. Specifically, FIG. 9 is a diagram for explaining steps S215 and S220 of FIG. FIG. 10 is a diagram for explaining steps S225 and S230 of FIG. FIG. 11 is a diagram for explaining step S235 in FIG. FIG. 12 is a diagram for explaining step S235 in FIG. 8 when the thread groove shape is a Gothic arch. 9 to 12, the <Z> direction means a direction perpendicular to the thread groove, and the <Y> direction means a direction perpendicular to both the X direction and the <Z> direction.

  Referring mainly to FIGS. 2 and 8, first, the processor 66 first determines the data measured during the movement of the laser displacement sensor in the −Z direction (in step S110 in FIG. 5) and the laser displacement sensor in the approximately + Z direction. Are integrated with the data measured in step S130 of FIG. 5 (S200).

  Next, as described with reference to FIG. 4B, the processor 66 multiplies the coordinates in the Z-axis direction at each measurement point by the cosine (cos θ) of the lead angle θ, thereby measuring the measured shape data in the Z-axis direction. Is converted into shape data perpendicular to the thread groove (S205).

  Next, the processor 66 divides the converted measurement data for each thread groove (S210), and then extracts the thread portion data for each divided data to calculate the height of the thread (S210). ). Specifically, the processor 66 extracts a predetermined number of measurement points MP (in the case of FIG. 9, three measurement points with hatching) from both ends as data of the thread portion. In FIG. 9, a recess for releasing oil during grinding is formed at the bottom of the thread groove.

  Next, the processor 66 extracts the data of the thread groove portion to be used for the approximate calculation of the provisional circle in each divided data (S215). Specifically, as shown in FIG. 9, the processor 66 uses the height of the screw thread calculated in step S210 as a reference, and the distance from the reference height of the measurement points MP below the reference height is L7 or more. Measurement points below L8 are extracted. This excludes the measurement points near the thread and the measurement points at the bottom of the thread groove. The values of L7 and L8 are determined based on ball screw design data.

  Next, the processor 66 determines a provisional circle 166 by least square approximation based on the measurement points extracted in step S215 (S225). Ball design data is used for the radius of the provisional circle 166. Further, based on the determined provisional circle 166, the processor 66 further extracts a measurement point MP near the contact point between the ball and the screw groove (S230). Specifically, as shown in FIG. 10, data in the range where the angle formed with the X-axis direction 170 from δ1-δ2 to δ1 + δ2 when viewed from the center 168 of the provisional circle 166 is extracted. For example, δ1 is selected in the range of 40 ° to 50 °, and δ2 is selected in the range of 5 ° to 10 °.

  Next, based on the data extracted in step S230 (data in the vicinity of the contact point between the ball and the screw groove), the processor 66 finally uses the least square approximation to finally obtain the cross-sectional profile of the screw groove (see FIG. 11). The center 174 of the circle 172 is determined (S235).

  If the cross-sectional shape of the thread groove is a Gothic arch, the processor 66 approximates the least squares based on the measurement point MP on one side (the right side in the figure) with respect to the bottom of the thread groove, as shown in FIG. To obtain a circle 176 (center 178), and a circle 180 (center 182) by least square approximation based on the measurement point MP on the other side (left side in the figure). The processor 66 then determines the final cross-sectional profile (circle center 184) based on the circle centers 178 and 182.

  Next, the processor 66 converts the cross-sectional profile of the thread groove determined in step S235 into a cross-sectional profile in the axial direction of the screw shaft (S240). Specifically, the obtained <Z> coordinate of the center of the circle is divided by the cosine (cos θ) of the lead angle θ. In the cross-sectional profile after conversion, the distance between the centers of adjacent circles corresponds to the lead.

[Summary]
As described above, according to the first embodiment, it is possible to improve the measurement accuracy of the thread groove shape of the ball screw as compared with the prior art and to prevent the measurement points from being densely and densely formed. Further, measurement errors can be prevented from occurring due to the multiple reflected laser beams.

  5 and 6, it has been described that the laser displacement sensor 100 is first moved approximately in the -Z direction and then the laser displacement sensor 100 is moved generally in the + Z direction. However, the present invention is not limited to this. If the measurement is performed twice when the displacement measuring direction 134 is inclined toward the + Z direction and when the displacement measuring direction 134 is inclined toward the −Z direction, the movement direction of the laser displacement sensor 100 is approximately + Z in both directions. Or the opposite direction.

<Second Embodiment>
In the second embodiment, the moving direction of the laser displacement sensor during measurement of the surface shape of the screw shaft is different from that in the first embodiment. Specifically, in the second embodiment, the laser displacement sensor is moved in parallel with the axial direction (Z-axis direction) of the screw shaft. It is the same as the first embodiment in that the displacement measurement direction (laser beam direction) is fixed in a state where it is tilted from the X-axis direction (direction perpendicular to the axis of the screw shaft). Hereinafter, specific description will be given with reference to the drawings. Since the configuration of the thread groove shape measuring apparatus is the same as that described with reference to FIG. 2, description thereof will not be repeated.

  FIG. 13 is a flowchart showing a procedure for measuring the thread groove shape according to the second embodiment. FIG. 14 is a schematic diagram for explaining a thread groove shape measuring method according to the second embodiment. The schematic diagram of FIG. 14 corresponds to FIG. 6 of the first embodiment, and shows a cross-sectional view of the screw shaft 80 cut along a cross section passing through the central axis. In FIG. 14, the screw shaft 80 is fixed so that the axial direction thereof is the Z-axis direction.

  With reference to FIGS. 2, 13, and 14, first, the processor 66 controls the drive mechanism 32 via the NC device 40 to set the turning angle of the measurement head 62 (laser displacement sensor 100) to a predetermined angle. Set (S300). Specifically, as shown in FIG. 14A, the direction of the laser beam 116 (that is, the displacement measuring direction 134) is the axis of the screw shaft by an angle ψ1 from the direction perpendicular to the screw shaft axis (X-axis direction). It is tilted in the direction (Z-axis direction). In this case, the inclination angle ψ1 is preferably 40 to 50 degrees (typically around 45 degrees). Also in the second embodiment, the turning angle is fixed.

  Next, the processor 66 controls the drive mechanism 32 via the NC device, and moves the laser displacement sensor 100 in the axial direction (−Z direction) of the screw shaft 80 while changing the shape of each screw groove 86 to the laser. Measurement is performed by the displacement sensor 100 (S310). As a result, the shape of the slope on one side (+ Z direction side) of each thread groove 86 is measured.

  Next, the processor 66 is driven via the NC device 40 so that the displacement measuring direction 134 is inclined in the direction opposite to that in the step S300 with respect to the X-axis direction (that is, the inclination angle ψ2). The turning angle of the laser displacement sensor 100 is set by controlling the mechanism 32 (S320). Then, the processor 66 moves the laser displacement sensor 100 in the + Z direction, which is the opposite direction to that in the case of step S310, while the laser displacement sensor 100 moves the slopes on the other side (−Z direction side) of the plurality of screw grooves 86. The shape is measured (S330).

  According to the measurement method described above, by tilting the direction of the laser beam 116 (that is, the displacement measurement direction 134) from the X-axis direction, the density of measurement points can be reduced and the measurement accuracy can be increased. Furthermore, errors due to multiple reflections of the laser beam can be avoided. Since the movement of the laser displacement sensor 100 is simpler than that of the first embodiment, it is easy to create a measurement program.

  However, as shown in FIG. 14, since the fluctuation range L9 of the distance from the laser displacement sensor 100 to the measurement point MP is given by L8-L7 and becomes relatively large, when a laser displacement sensor with a narrow measurable range is used. The measurement method of the first embodiment is more desirable.

  In the above description, it has been described that the laser displacement sensor 100 is first moved in the −Z direction and then the laser displacement sensor 100 is moved in the + Z direction. However, the present invention is not necessarily limited thereto. If the measurement is performed twice when the displacement measurement direction is inclined toward the + Z direction side and when the displacement measurement direction is inclined toward the −Z direction side, the movement direction of the laser displacement sensor 100 is the + Z direction and the −Z direction. Either one does not matter.

<Third Embodiment>
The third embodiment is characterized in that the screw groove shape is measured by the laser displacement sensor while moving the laser displacement sensor relative to the screw shaft and turning the laser displacement sensor. Thus, the direction of the laser beam (displacement measurement direction) during measurement of the thread groove shape is made to be substantially orthogonal to the surface of the thread groove. Desirably, the distance from the laser displacement sensor to the measurement point is kept constant. Hereinafter, specific description will be given with reference to the drawings. Since the configuration of the thread groove shape measuring apparatus is the same as that described with reference to FIG. 2, description thereof will not be repeated.

  FIG. 15 is a flowchart showing the procedure for measuring the thread groove shape according to the third embodiment. FIG. 16 is a schematic view for explaining a thread groove shape measuring method according to the third embodiment. The schematic diagram of FIG. 16 corresponds to FIG. 6 of the first embodiment and FIG. 14 of the second embodiment, and shows a cross-sectional view of the screw shaft 80 cut along a cross section passing through the central axis. . In FIG. 16, the screw shaft 80 is fixed so that the axial direction thereof is the Z-axis direction.

  With reference to FIGS. 2, 15, and 16, first, the processor 66 measures the height of the thread 84 adjacent to the thread 86 to be measured by the laser displacement sensor 100 (S400). Specifically, as shown in FIG. 16A, the processor 66 controls the drive mechanism 32 via the NC device 40 so that the direction of the laser beam 116 (displacement measurement direction) becomes the X-axis direction. The height of the thread 84 is measured by the laser displacement sensor 100 while moving the laser displacement sensor 100 in the −Z direction parallel to the axis of the screw shaft 80. In this case, the distance L10 from the laser displacement sensor 100 to the screw thread 84 is set to be a reference distance that allows the most accurate measurement.

  Next, the processor 66 controls the drive mechanism 32 via the NC device 40 to measure the shape of the thread groove to be measured by the laser displacement sensor 100 while relatively moving and turning the laser displacement sensor 100 ( S410). More specifically, as shown in FIG. 16B, when it is assumed that the ball 88 is in contact with the thread groove 86 to be measured, the processor 66 determines whether the ball 88 is assumed during the measurement of the thread groove shape. The laser displacement sensor 100 is moved so as to be positioned on a circle 190 concentric with the outer periphery, and the laser displacement sensor is rotated so that the laser beam 116 passes through the center 90 of the ball 88. Also in this case, the distance L10 from the laser displacement sensor 100 to the measurement point MP on the surface of the thread groove 86 is set to be a reference distance that enables the most accurate measurement.

  After the measurement of the thread groove shape to be measured, the processor 66 measures the height of the thread 84 on the opposite side to the case of step S400 by the laser displacement sensor 100 (S420). Since the specific measurement method is the same as that in step S400 shown in FIG. 16A, description thereof will not be repeated. When measuring the next adjacent thread groove shape (YES in step S430), the above steps S400, S410, and S420 are repeated.

  According to the measurement method described above, since the distance from the laser displacement sensor 100 to the measurement point is adjusted to be the reference distance, the thread groove shape can be measured with the highest accuracy. Further, since the laser displacement sensor 100 is swung so that the laser beam 116 passes through the assumed center of the ball, the laser beam 116 enters the surface of the thread groove almost perpendicularly. As a result, it is difficult for roughness to occur at the measurement points, and the surface shape of the thread groove can be accurately measured. There is no risk of errors due to multiple reflections of the laser beam. Furthermore, in the first and second embodiments, two measurements with different displacement measurement directions are required for the same thread groove, whereas in the case of the third embodiment, a laser displacement sensor. By measuring while turning 100, there is an advantage that only one measurement is required for the same thread groove.

  Although the above is an ideal case, the same effect as described above can be obtained even if the moving path of the laser displacement sensor 100 is slightly deviated from the concentric circle of the ball.

<Modification>
In the first to third embodiments, the example in which the surface shape is measured using the laser displacement sensor has been described, but a scanning contact displacement sensor may be used instead of the laser displacement sensor.

  FIG. 17 is a schematic diagram for explaining the measurement of the thread groove shape using a contact-type displacement sensor as a modification of the first to third embodiments. The schematic diagram of FIG. 17 corresponds to FIG. 6 of the first embodiment, FIG. 14 of the second embodiment, and FIG. 16 of the third embodiment, and passes the screw shaft 80 through its central axis. The cross-sectional view cut along the cross-section is shown.

  Referring to FIG. 17, contact displacement sensor 200 is configured to detect displacement in the direction of central axis 204 of probe 202 by bringing probe 202 into contact with the surface of the measurement object. In this case, the direction of the central axis 204 of the probe 202 corresponds to the direction of the laser beam 116 in the first to third embodiments (that is, the displacement measuring direction 134).

  As shown in FIG. 17B, when the direction of the central axis 204 of the probe 202 (that is, the displacement measuring direction 134) is perpendicular to the axis of the screw shaft 80 (X-axis direction), the measurement point is a thread groove. Since the inclination of the surface of the thread groove 86 becomes steeper as it approaches the edge of 86, there exists a problem that a measurement precision falls. Furthermore, when the surface shape of the thread groove 86 is measured while moving the contact-type displacement sensor 200 in the Z-axis direction, the measurement points become dense near the edge and the bottom of the thread groove 86.

  As shown in FIG. 17A, by tilting the central axis 204 of the probe 202 from a direction (X-axis direction) perpendicular to the axial direction (Z-axis direction) of the screw shaft, the vicinity of the edge of the screw groove 86 is also obtained. The surface shape can be measured with high accuracy, and the density of the measurement points is less likely to occur. In the case of the third embodiment, the measurement accuracy can be improved by turning the contact-type displacement sensor 200 so that the center axis 204 of the probe 202 passes through the assumed center of the ball.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Machine tool, 2 Thread groove shape measuring apparatus, 10 Processing apparatus, 25 Spindle, 32 Drive mechanism, 33 Reference point, 34 X axis drive mechanism, 36 Y axis / B axis drive mechanism, 38 Z axis drive mechanism, 40 NC device, 60 control unit, 62 measuring head, 64 computer, 66 processor, 68 memory, 70 communication device, 80 screw shaft, 82, 204 central axis, 84 thread, 86 thread groove, 88 ball, 100 laser displacement sensor 116, 152, 162 Laser beam, 130 Measurement object, 132 Laser spot, 134 Displacement measuring direction, 148 Moving direction, 200 Contact displacement sensor, 202 Probe.

Claims (8)

A thread groove shape measuring device for measuring the shape of each thread groove of a screw shaft constituting a ball screw,
A displacement sensor for detecting displacement in the irradiation direction of the laser light or displacement in the axial direction of the probe by irradiating the surface of the screw shaft with laser light or bringing a probe into contact therewith;
A drive mechanism capable of moving the displacement sensor relative to the screw shaft and capable of turning the displacement sensor about at least one shaft;
A controller for controlling the displacement sensor and the drive mechanism,
When the axial direction of the screw shaft is the first direction and the direction perpendicular to the first direction is the second direction, the controller is configured to apply the laser light irradiation direction or the probe axial direction. Each of the screw shafts is moved by the displacement sensor while the displacement sensor is turned or in a state where the turning angle of the displacement sensor is fixed so that a certain displacement measuring direction is a direction inclined with respect to the second direction. A thread groove shape measuring device configured to measure the shape of a thread groove.   The controller is configured to move each displacement sensor in the first direction relative to the second direction while fixing the inclination angle of the displacement measurement direction with respect to the second direction. The thread groove shape measuring device according to claim 1, configured to measure the shape of the thread groove.   In a state where the inclination angle of the displacement measurement direction with respect to the second direction is fixed, the control unit is configured to tilt the screw groove in a direction inclined to the opposite side of the displacement measurement direction with respect to the second direction. The thread groove shape measuring device according to claim 1, configured to measure the shape of each thread groove by the displacement sensor while relatively moving the displacement sensor.   The thread groove shape measuring apparatus according to claim 3, wherein an angle formed by a relative movement direction of the displacement sensor for each thread groove and the displacement measuring direction is included in a range of 85 degrees to 95 degrees.   The thread groove shape measuring apparatus according to any one of claims 2 to 4, wherein an inclination angle of the displacement measuring direction with respect to the second direction is included in a range of 40 degrees to 50 degrees.   The control unit relatively moves and turns the displacement sensor for each screw groove so that the displacement measurement direction is orthogonal to the surface of the screw groove at the laser light irradiation position or the probe contact position. The thread groove shape measuring device according to claim 1, wherein the displacement sensor is configured to measure the shape of each thread groove.   Assuming that the ball of the ball screw is brought into contact with the thread groove, the control unit has the displacement sensor positioned concentrically with the ball and the axis of the laser beam or the probe is the center of the ball The thread groove shape measuring device according to claim 1, wherein the shape of each thread groove is measured by the displacement sensor while relatively moving and turning the displacement sensor for each thread groove so as to pass through the thread groove. .   A machine tool comprising the thread groove shape measuring device according to any one of claims 1 to 7.

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