JP7845139B2 - Actuator, actuator runout measurement mechanism, and actuator runout measurement method - Google Patents

Description

This invention relates to an actuator, a mechanism for measuring the runout of an actuator, and a method for measuring the runout of an actuator.

For example, Patent Document 1 describes an actuator comprising a ball screw shaft that rotates with the help of a motor, a ball screw nut that moves linearly due to the rotation of the ball screw shaft, a sliding part to which the ball screw nut is fixed, a groove along the direction of linear motion, rolling elements that roll in the groove to support the sliding part so that it can move, and a working shaft fixed to the sliding part.

Furthermore, for example, Patent Document 2 describes a ball screw type actuator comprising a screw shaft, a nut member screwed onto the screw shaft via a first rolling element, a movable body movable together with the nut member, a guide means for supporting the movable body so as to be movable in the axial direction in which the screw shaft extends, and a connecting means for axially connecting the nut member and the movable body, having a groove for arranging a second rolling element in the circumferential direction of the screw shaft.

Furthermore, for example, Patent Document 3 shows a robot in which parallel links are connected in series.

Furthermore, for example, Patent Document 4 describes an inspection method for a ball screw mechanism.

Japanese Patent Publication No. 2020-041706 Japanese Patent Publication No. 2017-053431 German Utility Model Publication No. 212013000250 Japanese Patent Publication No. 2018-179713

The actuators shown in Patent Documents 1 and 2 work by having a screw shaft rotate, causing a nut to move along the screw shaft, and thereby moving the operating shaft and movable parts that move in conjunction with the movement of the nut.

As an alternative to the actuators shown in Patent Documents 1 and 2, an actuator that rotates the nut and moves the screw shaft can be considered. While a nut-rotation type actuator can achieve highly accurate positioning by converting the rotation of the nut into axial thrust of the screw shaft, and can realize a relatively small actuator, it is desirable to suppress the runout of the ball screw shaft.

For example, in the case of a robot like the one shown in Patent Document 3, high precision is required at a work point located far from the actuator that drives it. In such cases, it is crucial for the single-axis actuator to move in a straight line to achieve high precision, and it is necessary to suppress the swing of the single-axis actuator.

Furthermore, in order to meet the required precision of actuators, inspections such as those described in Patent Document 4 are necessary. Even in nut-rotating actuators, high-precision measurement of the runout of the ball screw shaft is desired to meet precision requirements.

This disclosure has been made in view of the above-mentioned problems, and aims to provide an actuator capable of accurately measuring the runout of a ball screw shaft in a nut-rotating type actuator, a runout measuring mechanism for the actuator, and a method for measuring the runout of the actuator.

To achieve the above objective, an actuator according to one aspect of the present disclosure includes a housing, a rotor rotatably mounted on the housing around a central axis, a ball nut fixed to the hollow portion of the rotor, a ball screw shaft extending axially and inserted into and engaged with the ball nut, and movable in the axial direction as the ball nut rotates, a guide portion provided on the housing that guides the movement along the axial direction and to which the tip of the ball screw shaft is attached, a first fixing portion provided on the guide portion to which a runout detector is fixed that detects the amount of radial runout of the tip of the ball screw shaft in synchronization with the axial movement of the ball screw shaft, and a second fixing portion provided on the guide portion to which a restraint is fixed that restrains only the relative axial movement of the ball screw shaft with respect to the guide portion and the relative rotation of the ball screw shaft with respect to the guide portion around the ball screw shaft.

In a preferred embodiment of the actuator described above, the first fixing portion comprises at least two first fixing holes.

In a preferred embodiment of the actuator described above, the second fixing portion comprises at least two second fixing holes positioned with the tip of the ball screw shaft in between.

A preferred embodiment of the actuator further includes a measuring section provided on the ball screw shaft and having a circumferential measuring surface formed coaxially with the ball screw shaft.

A preferred embodiment of the actuator further includes a through-hole provided in the guide portion into which the ball screw shaft is loosely inserted.

To achieve the above objective, an actuator runout measuring mechanism according to one aspect of the present disclosure comprises: a housing; a rotor rotatably mounted on the housing around a central axis; a ball nut fixed to the hollow portion of the rotor; a ball screw shaft extending axially, inserted into and engaged with the ball nut, and movable in the axial direction as the ball nut rotates; and a guide portion provided on the housing, which guides the movement along the axial direction and to which the tip of the ball screw shaft is attached. The mechanism includes: a runout detector fixed to the guide portion and detecting the radial runout of the tip of the ball screw shaft in synchronization with the axial movement of the ball screw shaft; a rotation detector provided on the rotor and detecting the rotation angle of the rotor; and a restraint attached to the guide portion that restricts only the relative axial movement of the ball screw shaft with respect to the guide portion and the relative rotation of the ball screw shaft with respect to the guide portion around the ball screw shaft.

In a preferred configuration of the actuator runout measurement mechanism described above, the restraint has an extension formed in a folded shape to surround the guide portion, with one end of the extension attached to the guide portion so as to be movable only in the axial direction, and the other end of the extension provided to be separated from the guide portion and fixed to the tip of the ball screw shaft.

In a preferred embodiment of the actuator runout measurement mechanism described above, the restraint device comprises a cylindrical main extension and a rod-shaped sub-extension loosely inserted inside the main extension. One end of the main extension and one end of the sub-extension inserted inside the main extension are fixed to each other, the other end of the main extension is fixed to the guide, and the other end of the sub-extension is fixed to the tip of the ball screw shaft. The guide has a through-hole into which the other end of the main extension is loosely inserted.

To achieve the above objective, a method for measuring the runout of an actuator according to one aspect of this disclosure comprises: a housing; a rotor rotatably mounted on the housing around a central axis; a ball nut fixed to the hollow portion of the rotor; a ball screw shaft extending axially, inserted into and engaged with the ball nut, and movable in the axial direction as the ball nut rotates; and a guide portion provided on the housing, which guides the movement along the axial direction and to which the tip of the ball screw shaft is attached. The method for measuring the runout of an actuator includes the steps of: connecting the ball screw shaft to the guide portion by restraining only the relative axial movement of the ball screw shaft with respect to the guide portion and the relative rotation of the ball screw shaft with respect to the guide portion around the ball screw shaft using a restraint device; detecting the amount of radial runout of the tip of the ball screw shaft in synchronization with the axial movement of the ball screw shaft using a runout detector fixed to the guide portion; detecting the rotation angle of the rotor using a rotation detector provided on the rotor; and obtaining the runout of the ball screw shaft based on the detected runout amount and rotation angle.

According to this disclosure, the runout of the ball screw shaft can be measured with high accuracy in a nut-rotation type system.

Figure 1 is a perspective view showing an example of the actuator configuration of the embodiment. Figure 2 is a cross-sectional view showing an example of the actuator configuration of the embodiment. Figure 3 is a perspective view showing a first configuration example of the actuator runout measurement mechanism according to the embodiment. Figure 4 is a side view showing a first configuration example of the actuator runout measurement mechanism according to the embodiment. Figure 5 is a perspective view showing a second configuration example of the actuator runout measurement mechanism according to the embodiment. Figure 6 is a side view showing a second configuration example of the actuator runout measurement mechanism of the embodiment. Figure 7 is an exploded perspective view showing a second configuration example of the actuator runout measurement mechanism according to the embodiment. Figure 8 is a partial cross-sectional view showing a second configuration example of the actuator runout measurement mechanism according to the embodiment. Figure 9 is a flowchart illustrating the method for measuring the runout of the actuator according to the embodiment. Figure 10 is a schematic diagram showing the results of the runout measurement of the actuator according to the embodiment. Figure 11 is a schematic diagram showing the results of the runout measurement of the actuator according to the embodiment.

The embodiments for carrying out the invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, the components in the embodiments described below include those that are easily conceivable by those skilled in the art, those that are substantially identical, and those that fall within the so-called equivalent range. Moreover, the components disclosed in the embodiments described below can be combined as appropriate.

The actuator of this embodiment can be applied, for example, to robots that require precise positioning accuracy, such as medical devices and industrial equipment.

As shown in Figures 1 and 2, the actuator 1 is configured as a nut-rotating type and includes an actuator body 2 and a guide section 3.

The actuator body 2 includes a housing 2A, a motor 2B (which is the drive source), a ball nut 2C, a ball screw shaft 2D, and an encoder (rotation detector) 2E.

The housing 2A is rectangular and box-shaped. It is elongated in one direction, which is the Z-direction. Furthermore, the housing 2A is formed in two directions perpendicular (intersecting) to the Z-direction, which are the X-direction and the Y-direction, respectively, forming a roughly square shape in these X and Y directions. Note that the housing 2A is not limited to a box shape; it can be configured to support the motor 2B, ball nut 2C, and encoder 2E.

As shown in Figure 2, the motor 2B is housed inside the housing 2A. The motor 2B has a rotor 2Ba and a stator 2Bb. The rotor 2Ba is attached to the housing 2A via a bearing 2F and is rotatable around a central axis CL that extends in the Z direction. The Z direction in which the central axis CL extends is also called the axial direction. The rotor 2Ba has a hollow portion 2Baa formed on the central axis CL, consisting of a circular through hole that penetrates in the Z direction. Permanent magnets 2Bab are fixed to the outer circumferential surface of the rotor 2Ba. Multiple permanent magnets 2Bab are arranged at intervals in the circumferential direction around the central axis CL. The stator 2Bb is formed in a cylindrical shape centered on the central axis CL so as to surround the rotor 2Ba. Electromagnetic coils are wound around multiple core portions of the stator 2Bb, which are provided at intervals in the circumferential direction around the central axis CL, with insulating material in between. Therefore, the motor 2B is driven to rotate around the central axis CL by energizing the electromagnetic coil of the stator 2Bb.

The bearing 2F that attaches the rotor 2Ba to the housing 2A is provided on one side in the Z direction (the side where the ball nut 2C is located) and the other side in the Z direction (the side where the encoder 2E is located). The bearing 2F on the one side in the Z direction restricts the movement of the rotor 2Ba relative to the housing 2A by being sandwiched between a stepped portion 2Aa and a projection 2Ab formed on the inner circumferential surface of the housing 2A. The bearing 2F on the one side in the Z direction restricts the movement of the rotor 2Ba relative to the rotor 2Ba by being sandwiched between a projection 2Bac protruding from the outer circumferential surface of the rotor 2Ba and a fixing ring 4 provided on the outer circumferential surface of the rotor 2Ba. The fixing ring 4 has an annular shape with a female thread formed on its inner circumferential surface, and is screwed into the female thread formed on the outer circumferential surface of the rotor 2Ba and tightened in the Z direction. As a result, the relative movement of the rotor 2Ba and the housing 2A in the Z direction is restricted via the bearing 2F.

As shown in Figure 2, the ball nut 2C is integrally connected to the rotor 2Ba of the motor 2B. The ball nut 2C integrally has a cylindrical body portion 2Ca that is loosely fitted into the hollow portion 2Baa of the rotor 2Ba on one side in the Z direction, and an annular flange portion 2Cb that abuts against one end of the rotor 2Ba in the Z direction. That is, the body portion 2Ca of the ball nut 2C is fitted into the hollow portion 2Baa of the rotor 2Ba with a gap that allows for movement between them. The flange portion 2Cb of the ball nut 2C is connected to the rotor 2Ba via a fixing screw 5 fastened to the fixing ring 4. Therefore, the ball nut 2C is rotationally driven around the central axis CL by the drive of the motor 2B. The ball nut 2C has a helical groove 2Cc formed around the central axis CL along the Z direction, and balls are arranged in the groove 2Cc, and is provided so that the balls roll in the groove and circulate when rotated. Furthermore, as shown in Figure 2, the actuator 1 may have a gap 6 formed between the ball nut 2C and the rotor 2Ba in the Z direction. A spacer 7 is interposed in this gap 6, and the ball nut 2C and rotor 2Ba are tightened and fixed in the Z direction with the spacer 7 in between using a fixing screw 5.

As shown in Figure 2, the ball screw shaft 2D is housed inside the housing 2A, with a portion extending outside the housing 2A. Inside the housing 2A, the ball screw shaft 2D is inserted and engaged with the ball nut 2C, and a portion of it is inserted into the hollow portion 2Baa of the rotor 2Ba of the motor 2B. A helical groove 2Da is formed on the outer circumferential surface of the ball screw shaft 2D, along the central axis CL, and the balls of the ball nut 2C are rotatably engaged in this groove 2D. Therefore, the ball screw shaft 2D is movable in the Z direction along the central axis CL by the rotational drive of the ball nut 2C.

The encoder 2E is located outside the housing 2A. The encoder 2E is connected to the rotor 2Ba, which extends from the inside to the outside of the housing 2A. The encoder 2E detects and outputs the rotational speed of the rotor 2Ba, which rotates around the central axis CL driven by the motor 2B. That is, the encoder 2E detects and outputs the rotational speeds of both the rotor 2Ba and the ball nut 2C. While the encoder 2E is configured as a rotary encoder, other encoders, such as a linear encoder (not explicitly shown in the figure), may also be used. These encoders may detect the movement of the connecting member 3A (described later) and calculate the rotation angle from that movement and the lead of the ball screw shaft 2D.

As shown in Figure 1, the guide section (guiding section) 3 is attached to the actuator body 2 and includes a connecting member 3A, a guide rail 3B, a first linear guide 3C, and a second linear guide 3D.

The connecting member 3A has a connecting portion 3Aa and a support portion 3Ab. The connecting portion 3Aa is connected to one end of the ball screw shaft 2D that protrudes from the ball nut 2C (housing 2A). The connecting portion 3Aa is formed extending in one direction in the X direction from the end of the ball screw shaft 2D. The support portion 3Ab is integrally connected to the connecting portion 3Aa and extends in the Z direction, bending from the X-direction-extending end of the connecting portion 3Aa, and is positioned along the outside of the housing 2A. Therefore, the connecting member 3A is provided to be movable in the Z direction along the central axis CL together with the ball screw shaft 2D. The connecting member 3A is supported by the housing 2A via the guide rail 3B, the first linear guide 3C, and the second linear guide 3D.

The guide rail 3B is fixed to the support portion 3Ab. The guide rail 3B extends in the Z direction along with the support portion 3Ab. Two guide rails 3B are provided parallel to each other in the Z direction, and are positioned in opposite directions in the Y direction with the support portion 3Ab in between. Therefore, the guide rail 3B is provided to be movable in the Z direction along the central axis CL together with the ball screw shaft 2D via the connecting member 3A.

The first linear guide 3C is fixed to the housing 2A via a fixing member 3E. The fixing member 3E is fixed to one side of the housing 2A in the X direction, and two fixing pieces 3Ea rising in the X direction are arranged opposite each other in the Y direction. Therefore, the fixing member 3E is formed in an overall U shape so as viewed from the Z direction, it opens to one side in the X direction by an L-shaped member and a plate member. The fixing member 3E is also provided with a cover 3Eb (see Figures 3 to 7) that closes the opening. Two first linear guides 3C are provided on the opposing surfaces of each fixing piece 3Ea of the fixing member 3E, facing each other in the Y direction. When viewed from the X direction, each first linear guide 3C is in a symmetrical position in the Y direction with respect to the ball screw shaft 2D (central axis CL). Each first linear guide 3C engages with each guide rail 3B and supports the guide rail 3B so that it can move in the Z direction. Therefore, the first linear guides 3C guide the movement of the guide rail 3B in the Z direction. In other words, the first linear guide 3C guides the movement of the ball screw shaft 2D in the Z direction via the guide rail 3B and the connecting member 3A.

The second linear guide 3D is fixed to the housing 2A via a fixing member 3E. The second linear guide 3D is configured similarly to the first linear guide 3C and guides the movement of the ball screw shaft 2D in the Z direction via the guide rail 3B and connecting member 3A.

The first linear guide 3C and the second linear guide 3D are fixed to the fixing member 3E side by side in the Z direction. The first linear guide 3C is positioned on the side in the Z direction where the ball screw shaft 2D protrudes from the ball nut 2C (housing 2A), while the second linear guide 3D is positioned on the side in the Z direction where the ball screw shaft 2D retracts into the ball nut 2C. In other words, the first linear guide 3C is positioned on one side of the housing 2A in the Z direction, and the second linear guide 3D is positioned on the other side of the housing 2A in the Z direction.

Actuator 1, in the configuration example described above, is configured to accommodate runout measuring mechanisms 101 and 102, as shown in Figures 3 to 7. Runout measuring mechanisms 101 and 102 are used to measure the runout of the ball screw shaft 2D in actuator 1. Specifically, runout measuring mechanisms 101 and 102 measure the inclination of the central axis CL relative to the ball nut 2C and rotor 2Ba. They also measure the parallel position of the central axis CL relative to the ball nut 2C and housing 2A. The inclination of the central axis CL relative to the ball nut 2C and rotor 2Ba, and the parallel position of the central axis CL relative to the ball nut 2C and housing 2A, are determined for each actuator 1. Details of runout measuring mechanisms 101 and 102 are described below.

Figure 3 is a perspective view showing a first configuration example of the actuator runout measurement mechanism according to the embodiment. Figure 4 is a side view showing a first configuration example of the actuator runout measurement mechanism according to the embodiment.

The runout measuring mechanism 101 of the first configuration example includes the actuator 1, the runout detector 8, and the restraint 9 described above.

The actuator 1 is the configuration example described above and includes an encoder 2E, which is a rotation detector that detects the rotation angle of the rotor 2Ba. The rotation detector is necessary for runout measurement in this embodiment, and in addition to the encoder 2E, the motor 2B is a pulse motor such as a stepping motor, thus including it in the configuration of the runout measurement mechanism 101.

The runout detector 8 detects the amount of radial runout (perpendicular to the axial direction) at the tip of the ball screw shaft 2D in synchronization with the axial movement of the ball screw shaft 2D. The runout detector 8 includes a first runout detector 8A and a second runout detector 8B.

The first runout detector 8A detects the amount of runout at one end of the ball screw shaft 2D, which is mounted on the rotor 2Ba via a ball nut 2C. Specifically, the first runout detector 8A consists of an electric micrometer, with a measuring probe 8Ab extending from the outside of the detector body 8Aa, which houses a differential transformer. The first runout detector 8A detects the amount of runout of the ball screw shaft 2D by contacting the measuring probe 8Ab with one end of the ball screw shaft 2D. A measuring section 2Db is formed at one end of the ball screw shaft 2D. The measuring section 2Db has a measuring surface 2Dba that is coaxial with the ball screw shaft 2D and polished circumferentially around a central axis CL. The measuring probe 8Ab contacts the measuring surface 2Dba of this measuring section 2Db.

In this embodiment, the actuator 1 moves the ball screw shaft 2D to be detected in the Z direction relative to the rotor 2Ba (ball nut 2C). Therefore, the first runout detector 8A needs to move in the Z direction together with the ball screw shaft 2D so that the measuring probe 8Ab remains positioned at a predetermined location (measuring surface 2Dba) at one end of the ball screw shaft 2D. To this end, the detector body 8Aa of the first runout detector 8A is fixed to the connecting member 3A in the guide section 3. In this embodiment, the detector body 8Aa of the first runout detector 8A is fixed to the connecting member 3A via a fixing arm 10A. One end of the fixing arm 10A is fixed to the connecting member 3A, and the detector body 8Aa is fixed to the other end. The connecting member 3A has a first fixing hole (first fixing part) 3Ac in which a screw is inserted or tightened so that one end of the fixing arm 10A can be fixed. The first fixing hole 3Ac is formed in the connecting member 3A at the end of the support portion 3Ab extending in one direction in the Z direction, where the connecting portion 3Aa is provided, penetrating in the Y direction. In this embodiment, a total of four first fixing holes 3Ac are formed, two in the X direction and two in the Z direction. In this way, the first vibration detector 8A is mounted so as to be movable in the Z direction together with the ball screw shaft 2D by fixing the detector body 8Aa to the first fixing hole 3Ac of the connecting member 3A via the fixing arm 10A, and the measuring probe 8Ab is positioned at a predetermined position (measuring surface 2Dba) at one end of the ball screw shaft 2D. Although not explicitly shown in the figure, the fixing arm 10A is configured to be freely bendable by providing a joint in the middle, and the position of the measuring probe 8Ab can be adjusted as appropriate by the joint.

The second runout detector 8B detects the amount of runout at the other end of the ball screw shaft 2D, which is on the opposite side in the Z direction from the position of the ball nut 2C as detected by the first runout detector 8A. Specifically, the second runout detector 8B consists of an electric micrometer, with a measuring probe 8Bb extending from the outside of the detector body 8Ba, which houses a differential transformer. The second runout detector 8B detects the amount of runout of the ball screw shaft 2D by contacting the other end of the ball screw shaft 2D with the measuring probe 8Bb. A measuring section 2Dc is attached to the other end of the ball screw shaft 2D. The measuring section 2Dc has a measuring surface 2Dca that is polished circumferentially around the central axis CL and is coaxial with the ball screw shaft 2D. The measuring probe 8Bb of the second runout detector 8B contacts the measuring surface 2Dca of this measuring section 2Dc. The measuring section 2Dc is detachably mounted on the ball screw shaft 2D and is removed when the actuator 1 is in use.

In this embodiment, the actuator 1 moves the ball screw shaft 2D to be detected in the Z direction relative to the rotor 2Ba (ball nut 2C). Therefore, the second runout detector 8B also needs to move in the Z direction together with the ball screw shaft 2D, similar to the first runout detector 8A. Thus, the detector body 8Ba of the second runout detector 8B is fixed to the connecting member 3A in the guide section 3. In this embodiment, the detector body 8Ba of the second runout detector 8B is fixed to the connecting member 3A via a fixing arm 10B. One end of the fixing arm 10B is fixed to the connecting member 3A, and the detector body 8Ba is fixed to the other end. Similar to the first runout detector 8A, the second runout detector 8B is mounted so as to be movable in the Z direction together with the ball screw shaft 2D by fixing the detector body 8Ba to the first fixing hole 3Ac of the connecting member 3A via the fixing arm 10B, and the measuring probe 8Bb remains positioned at a predetermined position (measuring surface 2Dca) at the other end of the ball screw shaft 2D. Although not explicitly shown in the diagram, the fixed arm 10B is configured to bend freely by having a joint in the middle, and the position of the measuring probe 8Bb can be adjusted as needed using the joint.

Thus, in this embodiment, the actuator 1 is provided with a first fixing hole (first fixing part) 3Ac in the connecting member 3A of the guide part (guiding part) 3, to which the vibration detector 8 is fixed.

The restraint device 9 restrains only the relative movement of the ball screw shaft 2D with respect to the guide portion 3 in the Z direction (axial direction) and the relative rotation of the ball screw shaft 2D with respect to the guide portion 3 around the ball screw shaft 2D. The restraint device 9 is provided on the guide portion 3 and interposed between the guide portion 3 and the ball screw shaft 2D. In the first configuration example, the restraint device 9 constitutes a U-shaped extension portion 9A that extends to one side in the Y direction when viewed from the X direction, bends in the Z direction, and then folds back to the other side in the Y direction. That is, the extension portion 9A is formed in a folded shape so as to surround the connecting portion 3Aa of the connecting member 3A in the guide portion 3. One end 9Aa of the extension portion 9A of the restraint device 9 is attached to the connecting portion 3Aa of the connecting member 3A in the guide portion 3. The connecting portion 3Aa has a second fixing hole (second fixing portion) 3Ad into which a screw 11 is tightened so that one end 9Aa of the extension portion 9A can be attached. The second fixing hole 3Ad is formed to penetrate the connecting portion 3Aa in the Z direction. In this embodiment, as shown in Figure 4, two second fixing holes 3Ad are formed side by side in the X direction at symmetrical positions with the tip of the ball screw shaft 2D in between, with the central axis CL in between. The second fixing hole 3Ad is formed as a hole approximately +0.2 mm to the screw diameter 4 mm of the screw 11. Therefore, the screw 11 can be fixed in the second fixing hole 3Ad even in the middle of being tightened into the second fixing hole 3Ad. In this way, the restraint 9 is formed in a folded shape so as to surround the connecting portion 3Aa of the connecting member 3A, so that one end 9Aa of the restraint 9 is attached to the connecting portion 3Aa of the connecting member 3A by the screw 11 so as to be able to move only slightly and in a limited manner in the Z direction (axial direction). The restraint 9 is formed such that the distance β in the Z direction between one end 9Aa and the other end 9Ab of the extension portion 9A is larger than the thickness dimension α in the Z direction of the connecting portion 3Aa. Therefore, when one end 9Aa of the restraint device 9 abuts against the connecting portion 3Aa, for example, a gap S is created between the connecting portion 3Aa and the other end 9Ab. The other end 9Ab of the extension portion 9A of the restraint device 9 is then fixed to the tip of the ball screw shaft 2D. That is, because the screw 11 is fixed to the second fixing hole 3Ad during tightening, limited and minute movement in the Z direction is permitted, while the movement of the ball screw shaft 2D relative to the guide portion 3 in the Z direction (axial direction) and the movement of the ball screw shaft 2D relative to the guide portion 3 around the ball screw shaft 2D (Z direction (axial direction)) are restricted by the two screws 11. Therefore, the actuator 1 is restrained only by the restraint device 9 in the Z direction (axial direction) and the rotational component of the ball screw shaft 2D in the Z direction (axial direction).

Figure 5 is a perspective view showing a second configuration example of the actuator runout measurement mechanism of the embodiment. Figure 6 is a side view showing a second configuration example of the actuator runout measurement mechanism of the embodiment. Figure 7 is an exploded perspective view showing a second configuration example of the actuator runout measurement mechanism of the embodiment. Figure 8 is a partial cross-sectional view showing a second configuration example of the actuator runout measurement mechanism of the embodiment.

The second configuration example of the runout measurement mechanism 102 includes the actuator 1 described above, the runout detector 8, and the restraint 12.

The actuator 1 is the configuration example described above and includes an encoder 2E, which is a rotation detector that detects the rotation angle of the rotor 2Ba. The rotation detector is necessary for runout measurement in this embodiment, and in addition to the encoder 2E, it is included in the configuration of the runout measurement mechanism 102 by using a pulse motor such as a stepping motor for the motor 2B.

The runout detector 8 detects the amount of radial runout (direction perpendicular to the axial direction) at the tip of the ball screw shaft 2D in synchronization with the axial movement of the ball screw shaft 2D. The runout detector 8 includes a first runout detector 8A and a second runout detector 8B. The configurations of the first runout detector 8A and the second runout detector 8B, and the configuration of the first fixing hole (first fixing part) 3Ac to which the runout detector 8 is fixed, are the same as in the first configuration example, and the same reference numerals are used, omitting further explanation.

The restraint 12 restrains only the relative movement of the ball screw shaft 2D with respect to the guide portion 3 in the Z direction (axial direction) and the relative rotation of the ball screw shaft 2D with respect to the guide portion 3 around the ball screw shaft 2D. The restraint 12 is provided on the guide portion 3 and interposed between the guide portion 3 and the ball screw shaft 2D. In the second configuration example, the restraint 12 has a main extension portion 12A and a sub-extension portion 12B. The main extension portion 12A is formed in a cylindrical shape extending in the Z direction. The sub-extension portion 12B is formed in a rod shape that is loosely inserted inside the cylinder of the main extension portion 12A. That is, the sub-extension portion 12B is inserted with spatial clearance relative to the main extension portion 12A. The main extension 12A and the sub-extension 12B are joined together by tightening a nut 13 onto a male screw on one end 12Ba, with the sub-extension 12B inserted into the main extension 12A, so that their respective ends 12Aa and 12Ba in the Z direction are fixed to each other. The other end 12Ab in the Z direction of the main extension 12A is fixed to the connecting portion 3Aa of the connecting member 3A in the guide portion 3. The other end 12Ab of the main extension 12A is fixed by tightening a screw 11 into the second fixing hole (second fixing portion) 3Ad. The other end 12Bb in the Z direction of the sub-extension 12B forms the end where the main extension 12A and the sub-extension 12B are connected by joining them. The sub-extension 12B is fixed to the tip of the ball screw shaft 2D by a female screw hole formed in the other end 12Bb. Specifically, the restraint device 12 has the other end 12Ab of the main extension 12A fixed to the guide portion 3, and the other end 12Bb of the sub-extension 12B fixed to the tip of the ball screw shaft 2D. The other end 12Bb of the sub-extension 12B is fixed to the tip of the ball screw shaft 2D via a spacer 14 between it and the measuring portion 2Db formed at one end of the ball screw shaft 2D, which is the tip side of the ball screw shaft 2D. The guide portion 3 has a through hole 3Ae formed in the Z direction at the connecting portion 3Aa of the connecting member 3A. The other end 12Bb of the sub-extension 12B of the restraint device 12 is loosely inserted into the through hole 3Ae. That is, the other end 12Bb of the sub-extension 12B is inserted into the through hole 3Ae with space to spare and fixed to the tip of the ball screw shaft 2D. The through hole 3Ae is formed with a diameter larger than the circumferential diameter of the measuring portion 2Db formed at one end of the ball screw shaft 2D, which is the tip side.

In a ball screw shaft 2D moving in the Z direction, the relative movement of the ball screw shaft 2D with respect to the guide portion 3 in the Z direction (axial direction) and the relative rotation of the ball screw shaft 2D with respect to the guide portion 3 (in the Z direction (axial direction)) are transmitted to the other end 12Bb of the sub-extension 12B. However, because the restraint 12 has the sub-extension 12B loosely inserted into the main extension 12A and one end 12Ba fixed, the relative movement of the ball screw shaft 2D with respect to the guide portion 3 and the relative rotation of the ball screw shaft 2D with respect to the guide portion 3 are absorbed, and transmission to the guide portion 3 to which the other end 12Ab of the main extension 12A is fixed is suppressed. Therefore, the actuator 1 is restrained only by the restraint 12 for the relative movement and rotation of the ball screw shaft 2D with respect to the guide portion 3, while relative movement in the X and Y directions and relative rotation around the X and Y directions are not restrained.

As shown in Figures 4 and 6, the runout measuring mechanisms 101 and 102 are electrically connected to the measuring instrument 21, with runout detectors 8A and 8B and an encoder (rotation detector) 2E connected to the measuring instrument 21. The measuring instrument 21 is, for example, a computer, and although not explicitly shown in the figures, it is implemented by a processing unit including a microprocessor such as a CPU (Central Processing Unit). The measuring instrument 21 measures the runout of the ball screw shaft 2D from the radial runout amount of the ball screw shaft 2D detected by the runout detectors 8A and 8B and the rotation angle of the ball screw shaft 2D detected by the encoder 2E. The following describes in detail the method for measuring the runout of an actuator using the runout measuring device including the runout measuring mechanisms 101 and 102.

Figure 9 is a flowchart illustrating the actuator runout measurement method of the embodiment. Figure 10 is a schematic diagram showing the results of the actuator runout measurement of the embodiment. Figure 11 is a schematic diagram showing the results of the actuator runout measurement of the embodiment.

As shown in Figure 9, the runout measurement method involves, in step S1, connecting the ball screw shaft 2D to the guide section 3 while restricting only its relative movement in the Z direction relative to the guide section 3 and its relative rotation around the ball screw shaft 2D relative to the guide section 3 using restraints 9 and 12. Then, in step S2, detecting the amount of runout of the ball screw shaft 2D in the Z direction (i.e., the amount of radial runout at the tip of the ball screw shaft 2D, synchronized with its axial movement) using a runout detector 8 fixed to the guide section 3. Furthermore, in step S3, detecting the rotation angle of the rotor 2Ba using an encoder 2E provided on the rotor 2Ba. Finally, in step S4, measuring and acquiring the runout of the ball screw shaft 2D based on the detected runout amount and rotation angle using a measuring instrument 21.

As shown in Figures 10 and 11, it is preferable that the central axis CL, which serves as the reference axis for the movement of the ball screw shaft 2D, is parallel to the reference axis SL, which is moved by the connecting member 3A in the guide section 3 via the guide rail 3B and linear guides 3C and 3D, so that the ball screw shaft 2D does not run out. In the runout measurement method, for example, as shown in Figure 10, if the amount of runout of the ball screw shaft 2D is large at different rotation angles relative to the central axis CL, the measuring instrument 21 measures and acquires the position at which the ball screw shaft 2D, including the ball nut 2C, is tilted and runout relative to the rotor 2Ba, based on the detection results of the amount of runout of the ball screw shaft 2D by the runout detectors 8A and 8B and the detection results of the rotation angle of the rotor 2Ba by the encoder 2E. Furthermore, in the runout measurement method, for example, as shown in Figure 11, if the runout amount of the ball screw shaft 2D increases at the same rotation angle relative to the central axis CL, based on the detection results of the runout amount of the ball screw shaft 2D by the runout detectors 8A and 8B and the detection results of the rotation angle of the rotor 2Ba by the encoder 2E, the measuring instrument 21 measures and acquires the position and degree of eccentricity of the ball screw shaft 2D, including the ball nut 2C, relative to the rotor 2Ba. In this way, the runout measuring device of this embodiment measures the inclination and eccentric runout of the ball screw shaft 2D.

The actuator 1 of this embodiment includes, as described above, a housing 2A, a rotor 2Ba rotatably mounted on the housing 2A around a central axis CL, a ball nut 2C fixed to the hollow portion 2Baa of the rotor 2Ba, a ball screw shaft 2D extending in the Z direction (axial direction), inserted into and engaged with the ball nut 2C, and movable in the Z direction as the ball nut 2C rotates, a guide portion 3 provided on the housing 2A that guides movement along the Z direction and to which the tip of the ball screw shaft 2D is attached, a first fixing portion 3Ac provided on the guide portion 3 to which a runout detector 8 is fixed that detects the amount of radial runout of the tip of the ball screw shaft 2D in synchronization with the axial movement of the ball screw shaft 2D, and a second fixing portion 3Ad provided on the guide portion 3 to which restraints 9 and 12 that restrain only the relative movement of the ball screw shaft 2D in the Z direction with respect to the guide portion 3 and the relative rotation of the ball screw shaft 2D around the ball screw shaft 2D with respect to the guide portion 3.

In this nut-rotating actuator 1, which has a hollow motor in which a ball nut 2C is fixed to the hollow portion 2Baa of the rotor 2Ba, and in which a ball screw shaft 2D is inserted and engaged with the ball nut 2C, measuring the runout of the ball screw shaft 2D is difficult because the ball screw shaft 2D is housed within the hollow motor. Furthermore, in a configuration where the ball nut 2C is rotated, it is necessary to fix only the relative movement of the ball screw shaft 2D in the Z direction relative to the guide portion 3 and the relative rotation of the ball screw shaft 2D around the ball screw shaft 2D relative to the guide portion 3. It is extremely difficult to constrain only two of the six degrees of freedom in which the ball screw shaft 2D can operate: the relative movement and the relative rotation.

Therefore, according to the actuator 1 of this embodiment, a first fixing part 3Ac is provided on the guide part 3 to which a runout detector 8, which detects the amount of radial runout at the tip of the ball screw shaft 2D in synchronization with the axial movement of the ball screw shaft 2D, is fixed, and the actuator 1 of this embodiment is configured to be movably fixed together with the ball screw shaft 2D. With this configuration, the actuator 1 of this embodiment can have a reference point for the parallel movement of the ball screw shaft 2D and can detect runout on the coordinates in which the ball screw shaft 2D is moving. Furthermore, according to the actuator 1 of this embodiment, a second fixing part 3Ad is provided to which restraining devices 9 and 12 are fixed to the guide part 3. These restraining devices restrict only the relative movement of the ball screw shaft 2D with respect to the guide part 3 in the Z direction and the relative rotation of the ball screw shaft 2D with respect to the guide part 3. This configuration prevents the aforementioned relative movement and rotation of the ball screw shaft 2D with respect to the guide part 3 from being transmitted to the guide part 3. With this configuration, the actuator 1 of this embodiment has the function of fixing the restraining devices 9 and 12 by the second fixing part 3Ad so as to restrict only the aforementioned relative movement and rotation transmitted from the tip of the ball screw shaft 2D to the guide part 3. As a result, the actuator 1 of this embodiment can accurately measure the runout of the ball screw shaft 2D in a nut rotation type.

Furthermore, in the actuator 1 of this embodiment, the first fixing portion 3Ac consists of at least two first fixing holes.

If there is only one fixing hole, the runout measuring device 8 may move around that hole, potentially preventing accurate measurement. Therefore, according to the actuator 1 of this embodiment, the runout measuring device 8 can be securely fixed by at least two first fixing holes, enabling accurate measurement.

Furthermore, in the actuator 1 of this embodiment, the second fixing portion 3Ad consists of at least two second fixing holes, each positioned with the tip of the ball screw shaft 2D in between.

In the case of a single fixing hole, the restraints 9 and 12 may swing around the fixing hole, applying torque to the ball screw shaft 2D, potentially preventing accurate measurement. Therefore, according to the actuator 1 of this embodiment, the restraints 9 and 12 can be securely fixed by at least two second fixing holes, with the tips of the ball screw shaft 2D in between, allowing for accurate measurement.

Furthermore, the actuator 1 of this embodiment further includes measuring sections 2Db and 2Dc, which are provided on the ball screw shaft 2D and have circumferential measuring surfaces 2Dba and 2Dca formed coaxially with the ball screw shaft 2D.

Therefore, according to the actuator 1 of this embodiment, the measuring units 2Db and 2Dc can provide a reference point for contacting the runout detector 8 with the ball screw shaft 2D.

Furthermore, the actuator 1 of this embodiment further includes a through-hole 3Ae provided in the guide portion 3 into which the ball screw shaft 2D is loosely inserted.

Therefore, according to the actuator 1 of this embodiment, the through-hole 3Ae prevents interference between the ball screw shaft 2D and the guide portion 3 during the connection between the restraint 12 fixed to the guide portion 3 and the ball screw shaft 2D. This allows the actuator to have a function where only the relative movement of the ball screw shaft 2D in the Z direction relative to the guide portion 3 and the relative rotation of the ball screw shaft 2D around the ball screw shaft 2D relative to the guide portion 3 are not transmitted to the guide portion 3.

The runout measuring mechanisms 101 and 102 of the actuator 1 in this embodiment include a housing 2A, a runout detector 8 fixed to the guide portion 3 and synchronized with the axial movement of the ball screw shaft 2D to detect the radial runout of the tip of the ball screw shaft 2D, an encoder (rotation detector) 2E provided on the rotor 2Ba to detect the rotation angle of the rotor 2Ba, and restraints 9 and 12 attached to the guide portion 3 that restrict only the relative movement of the ball screw shaft 2D with respect to the guide portion 3 in the Z direction and the relative rotation of the ball screw shaft 2D about the ball screw shaft 2D with respect to the guide portion 3.

According to the runout measuring mechanisms 101 and 102 of the embodiment, the runout detector 8 is configured to move together with the ball screw shaft 2D with respect to a guide portion 3 to which the tip of the ball screw shaft 2D is attached so as to guide movement along the Z direction relative to the housing 2A. This provides a reference for the parallel movement of the ball screw shaft 2D and allows detection of the amount of runout on the coordinate system in which the ball screw shaft 2D is moving. Furthermore, according to the runout measuring mechanisms 101 and 102 of the embodiment, in addition to detecting the amount of runout of the ball screw shaft 2D by the runout detector 8, the rotation angle of the rotor 2Ba is detected by the encoder 2E, allowing the rotation angle of the rotor 2Ba and the amount of runout of the ball screw shaft 2D to be measured in association. Furthermore, according to the runout measuring mechanisms 101 and 102 of the embodiment, by restricting only the relative movement of the ball screw shaft 2D in the Z direction with respect to the guide portion 3 and the relative rotation of the ball screw shaft 2D around the ball screw shaft 2D with respect to the guide portion 3 using the restraints 9 and 12, the runout of the ball screw shaft 2D can be accurately measured. As a result, the runout measuring mechanisms 101 and 102 of the embodiment of the actuator 1 can accurately measure the runout of the ball screw shaft 2D in a nut-rotating type actuator 1.

Furthermore, in the runout measuring mechanism 101 of the actuator 1 of this embodiment, the restraint 9 has an extension 9A formed in a folded shape to surround the connecting portion 3Aa of the guide portion 3. One end 9Aa of the extension 9A is attached to the connecting portion 3Aa of the guide portion 3 so as to be movable only in the Z direction (axial direction), and the other end 9Ab of the extension 9A is provided to be separated from the connecting portion 3Aa of the guide portion 3 and fixed to the tip of the ball screw shaft 2D.

Here, when constraining only the relative movement of the ball screw shaft 2D in the Z direction relative to the guide portion 3 and the relative rotation of the ball screw shaft 2D around the ball screw shaft 2D relative to the guide portion 3, if the constraint is placed at a position close to the runout measurement point, the runout being measured will also be constrained to some extent. Therefore, the measured value will be smaller than the actual runout value, making it impossible to measure an accurate value.

Therefore, according to the runout measuring mechanism 101 of the actuator 1 of this embodiment, the restraint 9 only allows movement of the ball screw shaft 2D in the Z direction (axial direction). Thus, only the relative movement of the ball screw shaft 2D with respect to the guide portion 3 in the Z direction and the relative rotation of the ball screw shaft 2D with respect to the guide portion 3 are restrained, allowing for accurate measurement of values.

Furthermore, in the runout measuring mechanism 102 of the actuator 1 of this embodiment, the restraint 12 has a cylindrical main extension 12A and a rod-shaped sub-extension 12B that is loosely inserted inside the main extension 12A. One end 12Aa of the main extension 12A and one end 12Baa of the sub-extension 12B inserted inside the main extension 12A are fixed to each other, the other end 12Ab of the main extension 12A is fixed to the connecting portion 3Aa of the guide portion 3, and the other end 12Bb of the sub-extension 12B is fixed to the tip of the ball screw shaft 2D. The guide portion 3 has a through hole 3Ae into which the other end 12Bb of the sub-extension 12B is loosely inserted.

Therefore, according to the runout measuring mechanism 102 of the embodiment, the restraint 12 transmits the relative movement of the ball screw shaft 2D in the Z direction with respect to the guide portion 3 and the relative rotation of the ball screw shaft 2D with respect to the guide portion 3 to the other end 12Bb of the sub-extension 12B. However, since the sub-extension 12B is loosely inserted into the main extension 12A and one end 12Ba is fixed, only the relative movement and relative rotation of the ball screw shaft 2D with respect to the guide portion 3 are absorbed and restrained. As a result, the runout measuring mechanism 102 of the embodiment can measure accurate values. Furthermore, according to the runout measuring mechanism 102 of the embodiment, by providing a through hole 3Ae in the guide portion 3 into which the other end 12Bb of the sub-extension portion 12B is loosely inserted, it is possible to restrict only the relative movement of the ball screw shaft 2D in the Z direction with respect to the guide portion 3 and the relative rotation of the ball screw shaft 2D with respect to the guide portion 3 at a position further away from the runout measurement point of the ball screw shaft 2D, while leaving the relative movement in the X and Y directions and the relative rotation around the X and Y directions unrestricted.

The method for measuring the runout of the actuator 1 of this embodiment is applied to an actuator 1 comprising: a housing 2A; a rotor 2Ba rotatably mounted on the housing 2A around a central axis CL; a ball nut 2C fixed to the hollow portion 2Baa of the rotor 2Ba; a ball screw shaft 2D extending in the Z direction (axial direction), inserted into and engaged with the ball nut 2C, and movable in the Z direction as the ball nut 2C rotates; and a guide portion (guiding part) 3 provided on the housing 2A that guides movement along the Z direction and to which the tip of the ball screw shaft 2D is attached. The method is applied to an actuator 1 comprising: a housing 2A; a rotor 2Ba rotatably mounted on the housing 2A around a central axis CL; a ball nut 2C fixed to the hollow portion 2Baa of the rotor 2Ba; a ball screw shaft 2D extending in the Z direction (axial direction), inserted into and engaged with the ball nut 2C, and movable in the Z direction as the ball screw shaft 2D rotates; and a guide portion (guiding part) 3 provided on the housing 2A that guides movement along the Z direction and to which the tip of the ball screw shaft 2D is attached. The process includes: connecting the ball screw shaft 2D to the guide portion 3 while restricting only its relative movement in the Z direction relative to the guide portion 3 and its relative rotation around the ball screw shaft 2D relative to the guide portion 3; detecting the amount of radial runout at the tip of the ball screw shaft 2D in synchronization with the axial movement of the ball screw shaft 2D using a runout detector 8 fixed to the guide portion 3; detecting the rotation angle of the rotor 2Ba using an encoder (rotation detector) 2E provided on the rotor 2Ba; and acquiring the runout of the ball screw shaft 2D based on the detected runout amount and rotation angle.

Therefore, according to the runout measurement method of the actuator 1 of this embodiment, the restraints 9 and 12 restrict only the relative movement of the ball screw shaft 2D in the Z direction with respect to the guide portion 3 and the relative rotation of the ball screw shaft 2D with respect to the guide portion 3, preventing transmission to the guide portion 3. Then, the amount of radial runout at the tip of the ball screw shaft 2D is detected by a runout detector 8 fixed to the guide portion 3, and the rotation angle of the rotor 2Ba is detected by an encoder 2E provided on the rotor 2Ba. Based on these runout amounts and rotation angles, the runout of the ball screw shaft 2D is obtained. As a result, the runout measurement method of the actuator 1 of this embodiment can accurately measure the runout of the ball screw shaft 2D in a nut-rotating type actuator 1.

1 Actuator 2A Housing 2Ba Rotor 2Baa Hollow section 2E Encoder (rotation detector)
2C Ball nut 2D Ball screw shaft 2Db Measuring section 2Dba Measuring surface 3 Guide section (Indicator section)
3Ac First fixing part (first fixing hole)
3Ad Second fixing part (second fixing hole)
3Ae Through hole 8 (8A, 8B) Vibration detector 9 Restraint 9A Extension 9Aa One end 9Ab Other end 12 Restraint 12A Main extension 12Aa One end 12Ab Other end 12B Sub-extension 12Ba One end 12Bb Other end 21 Measuring instrument 101, 102 Vibration measuring mechanism

Claims (9)

Housing and
A rotor is provided in the housing so as to be rotatable around a central axis,
A ball nut fixed to the hollow portion of the rotor,
A ball screw shaft extending in the axial direction, inserted into and engaged with the ball nut, and provided to be movable in the axial direction as the ball nut rotates,
A guide portion provided in the housing, which is guided to move along the axial direction and to which the tip of the ball screw shaft is attached,
A first fixing part is provided on the guide part and is fixed to which a runout detector is fixed, which detects the amount of radial runout at the tip of the ball screw shaft in synchronization with the axial movement of the ball screw shaft.
A second fixing portion is provided on the guide portion and to which a restraining device is fixed that restrains only the relative axial movement of the ball screw shaft with respect to the guide portion and the relative rotation of the ball screw shaft with respect to the guide portion about the ball screw shaft,
Actuators, including The actuator according to claim 1, wherein the first fixing portion comprises at least two first fixing holes. The actuator according to claim 1, wherein the second fixing portion comprises at least two second fixing holes arranged with the tip of the ball screw shaft in between. The actuator according to claim 1, further comprising a measuring section provided on the ball screw shaft and having a circumferential measuring surface formed coaxially with the ball screw shaft. The actuator according to claim 1, further comprising a through hole provided in the guide portion into which the ball screw shaft is loosely inserted. Housing and
A rotor is provided in the housing so as to be rotatable around a central axis,
A ball nut fixed to the hollow portion of the rotor,
A ball screw shaft extending in the axial direction, inserted into and engaged with the ball nut, and provided to be movable in the axial direction as the ball nut rotates,
A guide portion provided in the housing, which is guided to move along the axial direction and to which the tip of the ball screw shaft is attached,
A runout measuring mechanism for an actuator comprising:
A runout detector fixed to the guide portion and synchronized with the axial movement of the ball screw shaft to detect the amount of radial runout at the tip of the ball screw shaft,
A rotation detector provided on the rotor for detecting the rotation angle of the rotor,
A restraining device attached to the guide portion that restricts only the relative axial movement of the ball screw shaft with respect to the guide portion and the relative rotation of the ball screw shaft with respect to the guide portion about the ball screw shaft,
An actuator runout measurement mechanism, including the actuator. The aforementioned restraint device is
It has an extension that is folded over to surround the guide portion,
One end of the extension is attached to the guide so as to be movable only in the axial direction, and the other end of the extension is provided so as to be separated from the guide and fixed to the tip of the ball screw shaft.
The actuator runout measuring mechanism according to claim 6. The aforementioned restraint device is
A cylindrical main extension,
A rod-shaped sub-extension is loosely inserted inside the main extension,
It has,
One end of the main extension and one end of the sub-extension inserted inside the main extension are fixed to each other, the other end of the main extension is fixed to the guide, and the other end of the sub-extension is fixed to the tip of the ball screw shaft.
The aforementioned guide section is
The other end of the aforementioned sub-extension has a through hole into which it is loosely inserted.
The actuator runout measuring mechanism according to claim 6. Housing and
A rotor is provided in the housing so as to be rotatable around a central axis,
A ball nut fixed to the hollow portion of the rotor,
A ball screw shaft extending in the axial direction, inserted into and engaged with the ball nut, and provided to be movable in the axial direction as the ball nut rotates,
A guide portion provided in the housing, which is guided to move along the axial direction and to which the tip of the ball screw shaft is attached,
A method for measuring the runout of an actuator comprising:
A step of connecting the ball screw shaft to the guide portion by restricting only the axial relative movement of the ball screw shaft with respect to the guide portion and the relative rotation of the ball screw shaft with respect to the guide portion around the ball screw shaft using a restraining device,
A step of detecting the amount of radial runout at the tip of the ball screw shaft in synchronization with the axial movement of the ball screw shaft using a runout detector fixed to the guide portion,
A step of detecting the rotation angle of the rotor using a rotation detector provided on the rotor,
A step of obtaining the runout of the ball screw shaft based on the detected runout amount and rotation angle,
A method for measuring the runout of an actuator, including [the specified method].