JPH07204992A - Device for and method of measuring displacement - Google Patents

Abstract

PURPOSE:To provide a device for and a method of measuring a displacement, which can be rapidly and precisely measure a displacement value such as a thermal displacement value of a machining head in an NC machining unit or the like. CONSTITUTION:A displacement sensor 18 is rotated by a rotary member 10 while several points on a reference surface 31 of a measurement reference jig 27, and the result of the measurement is delivered to a computing and processing unit for calculating a displacement value such as a thermal displacement value of a machining head. Further, the displacement sensor 18 is three- dimensionally moved on the reference surface 31 through the rotation of the rotary member 10 so as to measure the measuring surface 31, for detecting a displacement value of a machining head for carrying out three-dimensional machining.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring device capable of quickly measuring a displacement amount of a tool position due to thermal displacement of an NC machine tool or the like.

[0002]

2. Description of the Related Art When machining a work in an NC machine tool or the like, thermal displacement occurs in the machine tool due to heat from a motor, friction heat with the work generated when machining the work, friction heat generated in a spindle, or the like. In some cases, a cooling device is installed in the part where heat is generated to prevent thermal displacement, but the installation of the cooling device increases the size of the machine tool and the running cost, and in particular requires extremely precise machining. In that case, a processing error will occur even if the cooling device is provided.

For this reason, in recent years, even if the machining reference point of a tool for machining a work is displaced by the thermal displacement, the machining reference point is mainly corrected according to the displacement amount. When correcting the machining reference point, it is necessary to measure the displacement due to heat or the like, but as an example of this displacement measuring device, conventionally, a sensor (touch probe) is directly attached to a machining head to which a tool is attached, and a reference is used. The reference ring is placed facing the machining head, the sensor is brought into contact with multiple points on the reference ring before machining, the machining reference point is determined from the measured values, and the sensor is also contacted with the reference ring after thermal displacement. It is known that the displacement from the processing reference point is obtained by doing so.

[0004]

However, in the above-mentioned conventional displacement measuring device, when the sensor measures the reference ring, it is necessary to operate the machining head to measure a plurality of points. In addition to this, the sensor must be accurately attached to the processing head during the measurement, and thus there is a problem that this replacement operation is troublesome. In addition, in the measurement by the sensor and the reference ring, only the two-dimensional displacement amount can be measured, and when measuring the three-dimensional displacement amount, a device for measuring the position (height) of the ring must be provided separately. However, there is also a problem that the price of the device itself rises.

The present invention has been made in view of the above circumstances, and it is possible to quickly and accurately measure the amount of displacement of a machining head of an NC machine tool or the like due to thermal displacement, etc., and a simple and inexpensive displacement measuring device. The purpose is to provide a measurement method.

[0006]

In order to achieve the above object, a displacement measuring device according to a first aspect of the present invention is provided with a measuring head mounted on a machining head of a machine tool and facing the measuring head. A measurement reference jig, and an arithmetic processing unit connected to the measurement head, wherein the measurement head is provided rotatably around a horizontal axis;
An actuator capable of rotating the rotating body and detecting the rotational position and a displacement sensor provided at the tip of the rotating body so as to intersect the axis of the rotating body, The tool body and a reference surface formed on a surface of the jig body facing the rotating body, the reference surface having a conical shape with which the measuring head can come into contact and the axis of which is horizontally oriented, and The arithmetic processing unit is configured to calculate the displacement amount of the machining head based on information obtained from the actuator and the displacement sensor.

According to another aspect of the displacement measuring apparatus, a measuring head attached to a machining head of a machine tool, a measurement reference jig provided to face the measuring head, and an arithmetic process connected to the measuring head. And a plurality of displacement sensors provided at a front end of the head body at predetermined intervals around a horizontal axis, the measurement head comprising: The reference jig,
The jig main body and a reference surface formed on a surface of the jig main body facing the rotating body and having a conical shape with which the measuring head can come into contact and the axis of which is oriented horizontally, The arithmetic processing unit calculates the displacement amount of the machining head based on information obtained from a plurality of displacement sensors.

A displacement measuring method according to a third aspect is a method of measuring a displacement using the displacement measuring apparatus according to the first or second aspect, wherein the displacement sensor of the measuring head is used to previously determine the reference surface of the measurement reference jig. The processing head is obtained by measuring and obtaining the reference point, measuring the reference surface by the displacement sensor after the displacement of the machining head to obtain the reference point after the displacement, and comparing and computing the reference points before and after the displacement by the arithmetic processing unit. The feature is that the displacement amount of is calculated.

[0009]

In the displacement measuring device according to claim 1 of the present invention,
The displacement amount of the machining head due to thermal displacement is calculated by measuring several points on the reference surface of the measurement reference jig while rotating the displacement sensor by the rotating body and inputting the result to the arithmetic processing unit for calculation. Further, the displacement sensor moves three-dimensionally on the reference surface by the rotation of the rotating body and measures the reference surface to measure the amount of displacement of the processing head that performs three-dimensional processing.

In the displacement measuring device according to the second aspect, when the displacement is measured, the displacement sensor is opposed to the reference surface of the measurement reference jig, and several points of the reference surface are instantaneously measured. The displacement amount of the processing head due to thermal displacement is calculated by inputting the result to the arithmetic processing unit and performing arithmetic operation.

In the displacement measuring method according to the third aspect, the three-dimensional processing is performed by comparing and calculating the reference point previously measured by the displacement sensor of the measuring head and the reference point after the displacement by the arithmetic processing unit. Quickly and reliably calculate the amount of displacement of the machining head to be performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the displacement measuring device of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an NC machine tool to which a displacement measuring device of the present invention is attached. In the figure, reference numeral 1 indicates a column for supporting a machining head 2. The column 1 is movably provided in a horizontal plane (XZ plane) and is moved by a drive mechanism (not shown). The processing head 2 is a column 1
Further, it is provided so as to be able to move up and down in the Y direction, and is moved up and down by a drive mechanism (not shown).

A tool 4 is mounted on the tip of the processing head 2 via a tool holder 3, and this tool 4
Is designed to process a work. The measuring head 5 has a mounting member 6 near the tip of the processing head 2.
Installed by. The measuring head 5 is configured as follows.

That is, as shown in FIG. 2, a cylindrical body portion 7 is supported by the mounting member 6 with its axis being horizontal. Bearings 8, 8 are fitted inside the body portion 7, and a rotating body 10 is supported by the bearings 8, 8 coaxially with the body portion 7 and rotatable about an axis. A hole 11 is formed in the base end surface of the rotating body 10 coaxially with the rotating body 10, while a flow hole 12 is formed in the tip end surface of the rotating body 10 coaxially with the rotating body 10 and in the axial center of the rotating body 10. It is formed to extend to the part.

An inner flange 13 is formed at the base end of the body portion 7, and a rotary actuator (actuator) 14 is fixed to the inner flange 13, and the rotary shaft 14a of the actuator 14 is It is inserted into the hole 11 and is joined by a key 15.
The actuator 14 rotates the rotating body 10 about its axis, and a cam type switch 16 capable of detecting the amount of rotation turns ON / OFF the displacement measurement point during rotation.

A tip portion of the rotating body 10 projects from the body portion 7 by a predetermined length, and the tip portion is formed in a truncated cone shape. The tapered surface 17 formed in this frustoconical shape
A mounting hole is formed in the mounting hole, and the displacement sensor 18 is mounted in the mounting hole.
Are fixed by crossing the axis of the rotating body 10 by a predetermined angle. The displacement sensor 18 is attached to the sensor main body 18a and the sensor main body 18a, and the taper surface 17 is provided.
It is composed of a contactor 18b that can freely move in and out of the sensor body, and when the contactor 18b moves in and out of the sensor body 18a,
The amount of movement is detected.

A concave groove 1 is formed on the outer peripheral surface of the rotating body 10.
9 is formed so as to extend in the circumferential direction, and a communication hole 20 that is connected to the flow hole 12 is formed at a predetermined position of the groove 19. Further, a plurality of blow holes 21 that open to the flow holes 12 are formed in the tip portion of the rotating body 10 and the tapered surface 17. Further, on the outer peripheral surface of the body portion 7, an air supply hole 2 that extends to the concave groove 19 and is connected to the concave groove 19.
2 is formed, and the air supplied from the air supply hole 22 is ejected from the blow holes 21 ... Through the concave groove 19, the communication hole 20, and the flow hole 12. Therefore, when the rotating pair 10 is brought close to the measurement reference jig 30 described later and the reference surface 31 is measured, the dust and the like adhering to the reference surface 31 can be blown away by the air and removed. A measurement can be made. Note that reference numerals 23 and 24 in the figure denote sealing members.

Further, a protective cover 25 is attached to the tip of the body 7. The protective cover 25 covers the tip of the rotating body 20 excluding the tapered surface 17,
It plays the role of dustproof and wiring protection. Also, the rotating body 2
A dustproof shutter 26 is openably and closably provided on the taper surface 17 of the front end portion of 0, and is closed while the work is being processed by the tool 4. A cable 27 is connected to the displacement sensor 18 via a brush 27a, and the cable 27 extends through the protective cover 25.

A measurement reference jig 30 is provided on the base B in front of the measuring head 5 having the above-described structure (to the right in FIGS. 1 and 2) so as to face the measuring head 5.
That is, the support base 28 is fixed to the front of the column 1 on the base B, and the jig base 29 a is placed and fixed on the support base 28. This jig base 29a
A mounting block 29b is fixed to the upper surface of the, and the measurement reference jig 30 is mounted on the mounting block 29b.

The measurement reference jig 30 has a rectangular parallelepiped shape, and a jig body 30b whose front surface 30a is a vertical plane,
A reference surface 3 having a frustoconical shape formed on a surface (front surface) 30a of the jig body 30b facing the rotating body 10.
It is composed of 1 and 1. The reference surface 31 is arranged such that its conical axis is oriented horizontally and is coaxial with the axis of the rotating body 10 before thermal displacement of the processing head 2. Further, the inclination angle of the reference surface 31 with respect to the conical axis and the inclination angle of the tapered surface 17 at the tip of the rotating body 10 are set to be substantially equal. In addition, a blow hole 33 is provided at the center of the bottom surface 32 that is connected to the reference surface 31.
It is formed so as to be opened on the back surface of the blower, and air is supplied from this opening and ejected from the blow hole 33. Therefore, bring the rotating body 10 closer to the measurement reference jig 30,
When measuring the reference surface 31, dust and the like adhering to the reference surface 31 can be blown away by air and removed, so that accurate measurement can be performed. Then, when the displacement amount is detected, the measurement reference jig 30 having the above configuration is
By moving the column 1 forward and raising and lowering the processing head 2, the rotating body 1 of the measuring head 5 is moved.
The tip of 0 is brought closer to the contact 18 of the displacement sensor 18.
b is brought into contact with the reference surface 31.

Further, an arithmetic processing unit 35 is connected to the measuring head 5. That is, the arithmetic processing unit 35
A cam type switch 16 which is a detector of the actuator 14 and a displacement sensor 18 are connected to the actuator, and the displacement amount of the machining head 2 is calculated based on information obtained from the switch 16 and the displacement sensor 18. There is.

Next, a method of calculating the displacement amount by the calculation processing unit 35 will be described below. In this calculation method, the deviation of the mechanical coordinate system of the machine tool after thermal displacement is measured by the measurement reference jig 30.
The displacement amount is detected by measuring the reference surface 31 of No. 1 by the displacement sensor 18. FIG. 4 shows a conical reference surface 31.
The master coordinate system is a coordinate system that represents a position on the reference plane 31, and before thermal displacement, the Z axis of the master coordinate system and the axis of the rotating body 10 coincide with each other. First, the master coordinate system is determined by measuring the reference surface 31 with the displacement sensor 18 before thermal displacement. However,
It is assumed that the X axis and the Y axis of the master coordinate system and the mechanical coordinate system before deformation are coincident with each other, and the Z axis is deviated in the axial direction.

When thermal displacement occurs, the rotating body 10
Is rotated, several points on the reference plane 31 are measured by the displacement sensor 18, and the coordinate system at this time is set as the mechanical coordinate system after deformation (the axis of the rotating body 10 is on the mechanical coordinate system). In the measurement by the displacement sensor 18, the position data by the reciprocal movement of the contact 18b and the position data by the rotation of the rotary actuator 14 are input to the arithmetic processing unit 35. Then, the displacement of the mechanical coordinate system after deformation with respect to the master coordinate system is calculated from the cross-sectional profile as follows.

The cross section of the cone (reference surface 31) before deformation is a circle because the Z axis of the master coordinate system and the axis of the rotating body 10 coincide with each other. After the deformation, the cross section of the cone is likely to be an ellipse, and the difference between the elliptic profile after the deformation and the circular profile before the deformation is first obtained. The profiles before and after the deformation are shown in FIG.
As shown in (a), the pre-deformation displacements S1 to S4 are
As shown in FIG. 5B, the post-deformation displacements S′1 to S′5 are measured, and the displacement amount is calculated as follows.

Before deformation, the equation of the circle is given by X ² + Y ² = ((S1 + S2 + S3 + S4) / 4) ² (1). After transformation, the virtual coordinate system X ′,
Consider Y '. It is assumed that this coordinate system has the center of the ellipse as the origin and is inclined by an unknown angle θ with respect to the mechanical coordinate system after deformation. Letting the major axis length be α and the minor axis length be β, the elliptic equation in the virtual coordinate system is given by the following equation. (X '/ α) ² + (Y' / β) ² = 1 (2) When this equation is transformed into the mechanical coordinate system after deformation,

[Equation 1] From equations (2) and (3), (X ″ COSθ + Y ″ SINθ + c) ² / α ² + (− X ″ SINθ
+ Y ″ COSθ + d) ² / β ² = 1 ... (4) gives the elliptic equation, and when the coordinates from S′1 to S′5 are given to the equation (4), simultaneous equations hold. , By solving this equation by numerical analysis, the center coordinates (c, d) of the ellipse in the mechanical coordinate system X ″, Y ″ after deformation, the major axis length α, the minor axis length β, and the major axis inclination θ
Ask for.

Since the major axis intersects the central axis of the cone, that is, the origin of the mechanical coordinate system before deformation, the inclination θ of the major axis is the deviation angle of the mechanical coordinate system after deformation with respect to the X axis of the mechanical coordinate system before deformation.

As shown in FIG. 6, the points of the major and minor axes (on the conical surface) when the elliptical plane is fitted to the cone are P1 (x ₁ , y).
₁ , z ₁ ), P2 (x ₂ , y ₂ , z ₂ ), P3 (x ₃ , y ₃ ,
z ₃ ), P 4 (x ₄ , y ₄ , z ₄ ), where the vectors from the origin of the master coordinate system are vector P 1, vector P 2, vector P 3, respectively.
Assuming the vector P4, the relational expression between the major axis length α and the minor axis length β is as follows.

[Equation 2]

Further, as described above, since the major axis intersects the central axis of the cone, as shown in FIG. 7, considering a plane including the major axis and the apex of the cone, from the cosine theorem, the major axis length α is ^{α = (Z0-Z1) 2} (a 2 / Z0 2 +1) + (2aZ3 / Z
^{0) 2 -4a (Z3 / Z0} ) (Z0-Z1) (a 2 / Z0 2 +
1) ^1/2 x sin (tan ^-1 (a / Z0)) (9), and Z1 can be expressed by a function of Z3. Z1 = f (Z3) (10) Further, the lengths of the vectors P1 and P3 are

[Equation 3] Becomes

As described above, in the post-deformation mechanical coordinate system, the angle between the long axis and the pre-deformation mechanical coordinate system X-axis, that is, the master coordinate system X-axis is θ, so the unit vector ex of the master coordinate system X-axis is = (0,1,0) and the relationship between the long axis and the short axis,

[Equation 4] Becomes Further, consider a normal mapping vector P'1 (x ₁ , y ₁ ) of the vector P 1 on the master coordinate system XY.

[Equation 5] The cone equation is given by (x / a) ² + (y / a) ² −z ² = 0 (16), and the coordinates P1 to P4 are substituted. (5)-(16)
The coordinate values of P1 to P4 and the equation AX + BY + CZ + D = 0 (17) can be calculated by solving the simultaneous equations of P1 to P4.

Next, the relationship between the deformed mechanical coordinate system and the master coordinate system will be described below. As shown in FIG. 8, first, the normal unit vector Qe on the elliptical plane is obtained. Assuming that the elliptical plane is π, π: AX + BY + CZ + D = 0 (X, Y, Z are master coordinate systems), so the normal unit vector Qe is Qe = (A / (A ² + B ² + C ² ) ^1/2 , B / (A ² + B ² +
C ² ) ^1/2 , C / (A ² + B ² + C ² ) ^1/2 ), and the normal unit vector Q passing through the mechanical coordinate origin after deformation
think of.

The position vector P0 on the master coordinate system of the mechanical coordinate origin O ″ after deformation is

[Equation 6] Given the unit vector Q of the vector P0O given by

[Equation 7] Therefore, the position of the mechanical coordinate origin is OO ″ = ZmQ + P0 (Zm: distance to the sensor center in the mechanical coordinate system), and the angular deviation of the mechanical coordinate system X ″, Y ″, Z ″ is Qe. Is given by the direction cosine of. θx = cos ⁻¹ Qex θy = cos ⁻¹ Qey θz = cos ⁻¹ Qez (where Qex, Qey, and Qez indicate x, y, and z components of Qe)

As described above, the relationship between the mechanical coordinate system and the master coordinate system is obtained, and by this relationship and the elliptic equation in the mechanical coordinate system obtained from the cross-sectional profile, the mechanical coordinate of the machine tool after thermal displacement is obtained. By calculating the deviation of the system, the amount of displacement after thermal displacement is obtained, and the machine tool is corrected by this amount of displacement to realize highly accurate machining.

According to the above-described embodiment, while the displacement sensor 18 is rotated by the rotating body 10, several points on the reference surface 31 of the measurement reference jig 30 are measured, and the result is input to the arithmetic processing section 35 to be calculated. Since the displacement amount of the machining head 2 due to the thermal displacement can be calculated only by itself, the displacement amount due to the thermal displacement or the like of the machining head can be measured quickly and accurately as compared with the conventional case.

The displacement sensor 18 of the measuring head 5 is also provided.
Is provided so as to intersect the axis of the rotating body 10, and the measurement reference jig 3
The reference plane 31 of 0 has a conical shape whose axis is oriented horizontally,
Since the displacement sensor 18 is rotated by the rotation of the rotating body 10 to measure the reference plane 31, the displacement sensor 18 moves three-dimensionally on the reference plane 31 to measure the reference plane 31. Therefore, it is possible to measure the amount of displacement of the machining head, such as a machining center, which performs three-dimensional machining, and correct the displacement.

9 and 10 show another embodiment of the displacement measuring device of the present invention. The displacement measuring device shown in these figures is different from the displacement measuring device of the first embodiment in the configuration of the measuring head. Therefore, this point will be described, and other common parts will be denoted by the same reference numerals. The description is omitted. In the displacement measuring device shown in FIGS. 9 and 10, the measuring head 40 is mainly composed of a head main body 41 and four displacement sensors 18 provided at the tip of the head main body 41 around the horizontal axis at predetermined intervals. Has been done. In this embodiment, the head body 41 is composed of the rotating body 10 of the displacement measuring apparatus of the first embodiment, and is rotatably provided around the axis, but the head body 10 is a columnar body that does not rotate. But it's okay. Further, the arithmetic processing unit 35 measures the displacement amount in the same manner as described above, but in this case, the information from the rotary actuator 14 is not required unlike the first embodiment.

Since the displacement measuring device having such a configuration is provided with a plurality of displacement sensors 18, the displacement sensor 18 is swung when the displacement is measured as in the displacement measuring device of the first embodiment. Since there is no need to bring the displacement sensors 18 into contact with the reference surface 31 of the measurement reference jig 30, there is an advantage that the measurement time can be further shortened. The displacement sensor 18 is not limited to the contact sensor as shown in the above embodiment, but a proximity sensor may be used.

[0037]

As described above, according to the first aspect of the present invention.
According to the displacement measuring device, the displacement sensor of the measuring head is rotated by the rotating body to measure several points on the reference surface of the measurement reference jig, and the result is input to the arithmetic processing unit to perform the calculation. Since the displacement amount of the machining head due to the displacement can be calculated, the displacement amount due to the thermal displacement of the machining head or the like can be measured more quickly and accurately than in the conventional case. In addition, the measuring head has a simple structure including a rotating body and a sensor, and thus is inexpensive.

Further, the displacement sensor of the measuring head is provided so as to intersect with the axis of the rotating body, and the reference surface of the measurement reference jig has a conical shape with its axis oriented horizontally. Since the measurement is performed by rotating the rotating body to rotate, the displacement sensor moves three-dimensionally on the reference surface and measures the reference surface three-dimensionally. Therefore, the three-dimensional measurement of the machining center or the like is performed. It is possible to measure the amount of displacement of the processing head that performs the mechanical processing and correct the displacement.

According to the displacement measuring device of the second aspect, the measuring head includes a head main body which is horizontally provided and a plurality of displacement sensors which are provided at a tip portion of the head main body around the horizontal axis at predetermined intervals. Since it is configured, when the displacement is measured, the displacement sensor only needs to be opposed to the reference surface of the measurement reference jig, which has an advantage that the measurement time can be further shortened.

According to the displacement measuring method of the third aspect, the displacement amount of the machining head is calculated by the displacement measuring apparatus of the first or second aspect, and the reference surface of the measurement reference jig is measured by the displacement sensor of the measuring head. The processing reference point before displacement is obtained, the reference surface is measured by the displacement sensor after the displacement of the processing head, the processing reference point after displacement is obtained, and the processing reference points before and after the displacement are compared and calculated by the arithmetic processing unit. Therefore, the displacement amount of the processing head that performs three-dimensional processing can be calculated quickly and reliably.

[Brief description of drawings]

FIG. 1 is a side view showing a schematic configuration of an NC machine tool to which a displacement measuring device according to an embodiment of the present invention is attached.

FIG. 2 is a side sectional view showing a displacement measuring device according to an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of the same.

FIG. 4 is a diagram schematically showing a conical reference surface of a measurement reference jig.

FIG. 5 is a diagram showing circles and ellipses in a mechanical coordinate system before and after deformation measured by a displacement sensor.

6 is a diagram when the elliptical plane in FIG. 5 is fitted to a cone.

7 is a view of the cone in FIG. 6 taken along a plane including its axis.

FIG. 8 is a diagram showing a positional relationship between a mechanical coordinate system and a master coordinate system.

FIG. 9 is a side sectional view showing a displacement measuring device according to another embodiment of the present invention.

10 is a view on arrow A in FIG.

[Explanation of symbols]

 2 Processing Head 5 Measuring Head 10 Rotating Body 14 Rotary Actuator (Actuator) 18 Displacement Sensor 30 Measurement Reference Jig 30b Jig Main Body 31 Reference Surface 35 Arithmetic Processing Section 40 Measurement Head 41 Head Main Body

Claims (3)

[Claims] 1. A displacement measuring device for measuring the amount of displacement of a machining head of a machine tool, the measuring head being attached to the machining head of the machine tool, and a measurement reference jig provided facing the measuring head. And a processing unit connected to the measuring head, wherein the measuring head is capable of detecting a rotational position while rotating the rotating body provided rotatably around a horizontal axis. An actuator and a displacement sensor provided at the tip of the rotating body so as to intersect the axis of the rotating body, the measurement reference jig is a jig body and the rotating body of the jig body. A conical reference surface that is formed on opposing surfaces and that can contact the measurement head and has its axis oriented horizontally, and the arithmetic processing unit uses information obtained from the actuator and the displacement sensor. The processing A displacement measuring device for calculating the amount of displacement of a head. 2. A displacement measuring device for measuring the amount of displacement of a machining head of a machine tool, the measuring head being attached to the machining head of the machine tool, and a measurement reference jig provided facing the measuring head. And an arithmetic processing unit connected to the measuring head, wherein the measuring head is provided horizontally on the head body, and is provided at the tip of the head body around the horizontal axis at a predetermined interval. The measurement reference jig is composed of a plurality of displacement sensors, and the measurement reference jig is formed on a jig body and a surface of the jig body facing the rotating body, and the measurement head can come into contact with the axis of the jig horizontally. A displacement measuring device, comprising: a reference surface having a conical shape that is directed, wherein the arithmetic processing unit calculates an amount of displacement of the machining head based on information obtained from a plurality of displacement sensors. 3. A method for measuring a displacement using the displacement measuring device according to claim 1, wherein a displacement sensor of a measuring head measures a reference surface of a measurement reference jig to determine a processing reference point in advance. Obtaining the displacement amount of the processing head by measuring the reference surface by the displacement sensor after the displacement of the processing head to obtain the reference point after the displacement, and comparing and computing the reference points before and after the displacement by the arithmetic processing unit. Displacement measuring method characterized by.