JP2008111468A - Ball screw device, wear amount detection method thereof, and electric injection molding machine including the same - Google Patents

Abstract

Provided is a means for accurately detecting a relative displacement amount between a nut and a screw shaft of a ball screw device due to peeling or wear.
A screw shaft 3 having a helical shaft raceway groove 4 formed on an outer peripheral surface 3a, a nut 5 having a nut raceway groove 6 opposed to the shaft raceway groove 4 formed on an inner peripheral surface, and a shaft raceway groove 4; In a ball screw device 1 having a plurality of balls 2 screwed together with a nut raceway groove 6, a contact sensor 11 having a contact 13 opposed to the shaft raceway groove 4 via a clearance C is provided on the nut 5. The contact of the contact 13 with the shaft raceway groove 4 is detected by the thing contact sensor 11.
[Selection] Figure 3

Description

  The present invention relates to a ball screw device used for positioning and power transmission of a machine device such as a machine tool, an electric injection molding machine, and an electric press molding machine, a wear amount detection method thereof, and an electric injection molding machine including the same. .

  In the conventional ball screw device, a shaft raceway groove formed in a spiral shape on the outer peripheral surface of a screw shaft and a nut raceway groove opposed to the shaft raceway groove formed on an inner peripheral surface of a nut are screwed together via a plurality of balls. The load applied to the nut is supported by balls rolling on the load path formed by the nut raceway groove and the shaft raceway groove arranged opposite to each other, and both ends of the load path such as a ball return path provided on the nut. The rotational movement of the screw shaft is converted into the linear movement of the nut while circulating the ball through the connecting path connecting the two (see, for example, Patent Document 1).

In such a ball screw device, when the rolling surface of the shaft raceway groove and the nut raceway groove or the ball is peeled or worn due to fatigue life or lubricant life, the relative position between the screw shaft and the nut changes. .
This change in relative position is due to the fact that a preload type ball screw device is used in machine tools and measuring devices that use the ball screw device mainly for positioning purposes, and the ball is elastically deformed by the preload. Therefore, as long as there is no wear corresponding to the amount of elastic deformation, no play is generated during positioning. In addition, when play occurs, a predetermined positioning accuracy cannot be obtained, and it is possible to detect the degree of deterioration relatively easily during operation of the ball screw device due to deterioration of accuracy of a processed product and deterioration of measurement accuracy. .

  On the other hand, in a mechanical device such as an electric injection molding machine or a press molding machine that uses a ball screw device mainly for the purpose of transmitting driving force, a ball screw of a gap product in which a gap exists between the ball and the rolling surface. Since the device is used and the screw shaft is driven by a motor or the like until the measured value of the pressing force by the pressure sensor reaches a predetermined value, the nut is fed, so if wear occurs, the amount corresponding to the wear amount The increase in the feed amount does not cause a mechanical problem, and it becomes difficult to find the degree of deterioration during operation of the ball screw device.

For this reason, if the amount of increase in the rotation angle of the motor is measured using an encoder, it is considered possible to measure the amount of wear of the ball screw device. However, in fact, the resin used for injection molding has a damper effect. Since the variation in the amount of resin injected at one time is large, the wear amount is absorbed in the range of the variation, and it is difficult to quantitatively measure the wear amount.
In addition, if the discovery of the deterioration of the ball screw device due to wear or the like is delayed, the ball screw device is damaged and the mechanical device stops, and it takes time to obtain a replacement ball screw device, which reduces the operating efficiency of the mechanical device. Problem arises.

  In order to predict such deterioration due to wear and the like, in the conventional trapezoidal screw wear measuring device, when measuring the wear of the trapezoidal screw shaft and trapezoidal screw nut used for opening and closing the needle valve, the trapezoidal screw shaft and the trapezoidal screw Both nuts are equipped with end face position measuring devices based on the base, and preventive maintenance is performed by periodically measuring the amount of wear of each trapezoidal screw according to the amount of change from the initial state in the closed position of the needle valve. (For example, refer to Patent Document 2).

In addition, when detecting damage to rolling bearings or deterioration of lubricant, the average value of the background noise component of the electrical signal of the vibration sensor provided on the outer ring and the periodic peak of the rotational speed proportional component are used. In some cases, the damage of the rolling bearing or the deterioration of the lubricant is detected and the abnormality is diagnosed (for example, see Patent Document 2).
Japanese Patent Application Laid-Open No. 2004-156767 (page 7, paragraph 0025 to page 8, paragraph 0029, FIG. 2) Japanese Patent Laid-Open No. 10-234155 (2nd page, paragraph 0009-3rd page, paragraph 0012, FIG. 3) Japanese Unexamined Patent Publication No. 2004-347401 (page 4, paragraph 0016 to page 5, paragraph 0019, FIG. 5)

  However, in the technique of Patent Document 2 described above, since the amount of wear from the initial state of the end face position at the closed position of the needle valve is measured with reference to the base, this is used as a ball screw device for screw shaft rotation. In the case of replacement, since the axial movement of the screw shaft is fixed and the stroke of the nut is not constant, there is a problem that the position of the nut changes depending on use conditions, and accurate measurement is difficult.

  Further, in the technique of Patent Document 3, damage or deterioration of the lubricant is detected by vibration of the outer ring of the rolling bearing. When this is replaced with a ball screw device, a vibration sensor provided on the nut is used. Although it is possible to detect vibration when the ball passes through a flaw such as a peeling that has occurred on the rolling surface, in the case of a ball screw device, the ball shaft is circulated through a connection path provided in the nut while the screw shaft is being circulated. Since the rotational motion is converted into the linear motion of the nut, the vibration when the ball passes through this connecting path is large, and the relative displacement between the nut of the ball screw device and the screw shaft due to peeling or wear of the rolling surface etc. There is a problem that it is difficult to accurately detect the quantity.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide means for accurately detecting a relative displacement amount between a nut of a ball screw device and a screw shaft due to peeling or wear.

  In order to solve the above problems, the present invention provides a screw shaft in which a spiral shaft raceway groove is formed on an outer peripheral surface, a nut in which a nut raceway groove facing the shaft raceway groove is formed on an inner peripheral surface, and the shaft In the ball screw device including a plurality of balls for screwing the raceway groove and the nut raceway groove, the nut is provided with a sensor having a contact element facing the shaft raceway groove via a clearance, The contact of the contact with the shaft raceway groove is detected.

  As described above, according to the present invention, the amount of wear due to wear or peeling of the rolling surface of the ball screw device or the like can be directly detected by the sensor provided on the nut, and the nut and screw shaft of the ball screw device associated with wear can be detected. The relative displacement amount can be accurately detected.

  Embodiments of a ball screw device according to the present invention will be described below with reference to the drawings.

1 is an explanatory view showing a cross section of the ball screw device of the first embodiment, FIG. 2 is an explanatory view showing a side surface of the contact sensor of the first embodiment, and FIG. 3 is an explanatory view showing an installation state of the contact sensor of the first embodiment. is there.
FIG. 3 is an enlarged view of part A of FIG.
In FIG. 1, 1 is a ball screw device. The ball screw device 1 of the present embodiment is a gap-type ball screw device used in an electric injection molding machine.

Reference numeral 2 denotes a ball as a rolling element of the ball screw device 1, which is a sphere made of a steel material such as alloy steel.
Reference numeral 3 denotes a screw shaft of the ball screw device 1, which is a rod-shaped member made of a steel material such as alloy steel, and has two arc-shaped concave surfaces 4a and 4b shown in FIG. A shaft raceway groove 4 which is a Gothic arc groove arranged in the above is formed in a spiral shape with a predetermined lead.

Reference numeral 5 denotes a nut of the ball screw device 1, which is a cylindrical member made of a steel material such as alloy steel, and has two arc concave surfaces 6a and 6b shown in FIG. A nut raceway groove 6, which is a gothic arc groove arranged and formed, is formed with the same lead as the shaft raceway groove 4.
Reference numeral 7 denotes a flange portion, which is provided at one end portion of the outer peripheral portion of the nut 5 and is fixed to a moving table or the like of a mechanical device (not shown).

A load path on which the ball 2 rolls is formed by the shaft raceway groove 4 of the screw shaft 3 and the nut raceway groove 6 of the nut 5 opposed thereto, and both ends thereof are connected by a connection path such as a return tube (not shown). Thus, a circulation path is formed.
The circulation path is filled with a plurality of balls 2 and a predetermined amount of lubricant, for example, grease, and the shaft raceway groove 4 and the nut raceway groove 6 are screwed together via the balls 2 to rotate the screw shaft 3. Accordingly, the ball 2 circulates in the circulation path, and the ball 2 rolling on the load path supports the load applied to the nut 5 so as to freely reciprocate, and the nut 5 linearly reciprocates along the axial direction of the screw shaft 3. Supported as possible. Thereby, the rotational motion of the screw shaft 3 is converted into the linear motion of the nut 5.

In FIG. 2, reference numeral 11 denotes a contact sensor as a sensor, which is a mechanical sensor in which a triangular screw 12 is formed on the outer peripheral surface and a contactor 13 is provided at one end in the axial direction so as to be able to protrude and retract. When the tip 13a of the contactor comes into contact with the object, the electrical contact or the like is turned on and has a function of outputting a contact signal, which is an electrical signal, from the lead wire 14.
Further, the contact sensor 11 is provided with a dead zone so that a contact signal is generated when the contact 13 is immersed in the axial direction of the contact sensor 11 and moved by a certain amount due to the contact of the tip 13a of the contact 13 ( The amount of movement corresponding to this dead zone is called the shrinkage allowance).

  As shown in FIG. 1, the contact sensor 11 has a mounting seat 16 in which one end portion of the outer peripheral surface of the nut 5, in this embodiment, the opposite end portion of the flange 7 is cut out in parallel to the axial direction. The triangular screw 12 of the contact sensor 11 is screwed into the mounting screw hole 17 formed in the radial direction of the nut 5 and the clearance C (see FIG. 3) is adjusted to a predetermined value, and then fixed by the lock nut 18 and attached. ing.

Further, as shown in FIG. 3, the mounting position in the axial direction of the nut 5 of the contact sensor 11 is such that the ball 2 has a contact angle θ due to the axial force F applied to the nut 5 for mold clamping or the like. The position at which the tip 13a of the contact 13 loosely fits into the shaft raceway groove 4 when sandwiched between the arcuate concave surface 6a of the raceway groove 6 and the arcuate concave surface 4b of the shaft raceway groove 4, that is, clearance C (tip 13a And the arc concave surfaces 4a and 4b of the shaft raceway groove 4 are measured in the direction of the contact angle θ). Moving surface P (refers to a belt-like region along the axial raceway groove 4 in the range covered by the contact ellipse formed on the arc concave surface 4b by the force F at this time when the ball 2 comes into contact with the arc concave surface 4b. ).

The contact 13 of the contact sensor 11 of this embodiment is formed in a cylindrical shape, and its tip 13a is formed in a hemisphere, and the radius of curvature of the hemispherical spherical convex surface is when the radius of the ball 2 is Ra. 0.9 Ra or more and 1.0 Ra or less.

  Thereby, a clearance C within 10% of the ball radius Ra is formed between the tip 13a of the contact 13 and the arc concave surfaces 4a, 4b of the shaft raceway groove 4, and the arc concave surface 4b and nut of the shaft raceway groove 4 are formed. The amount of wear due to wear or delamination generated on the rolling surface P and the ball 2 formed on the arcuate concave surface 6a of the raceway groove 6 exceeds the amount corresponding to the clearance C, and the shrinkage allowance of the contact 13 of the contact sensor 11 When the contact sensor 11 is compressed, the contact signal is issued from the contact sensor 11 to notify that the relative displacement amount between the screw shaft 3 and the nut 5 of the ball screw device 1 exceeds the limit.

Further, when the screw shaft 3 is inclined due to wear or the like, when the groove bottom portion of the shaft raceway groove 4 comes into contact with the tip 13a of the contact 13 and the contraction allowance of the contact 13 is reduced, the contact sensor 11 makes contact. A signal is emitted.
The reason why the clearance C is set to 10% or less of the ball radius Ra is that the inner radius of the connection path for circulating the ball 2 is normally about 110% of the ball radius Ra, and the wear amount is the ball radius Ra. If it exceeds 10%, the ball 2 may collide with the upper part of the connecting path of the return tube or the like to be damaged.

Also, if the clearance C is 0% or more of the ball radius Ra, that is, the curvature radius of the tip 13a of the contactor 13 is 100% or less of the ball radius Ra, the nut 5 is moved in the opposite direction to open the mold. This is to prevent a contact signal from being generated beyond the contraction allowance of the contact 13 of the contact sensor 11.
Since the ball screw device 1 of this embodiment is a gap ball screw device 1 used in an electric injection molding machine, the preset clearance S shown in FIG. 3 exceeds the contraction allowance of the contact 13. If so, the upper limit of the radius of curvature of the tip 13a of the contact 13 may be set in consideration of the clearance S and the contraction allowance of the contact 13. That is, the upper limit of the radius of curvature of the tip 13a of the contact 13 is preferably a value obtained by subtracting S / cos θ or more from the ball radius Ra.

Further, when the present embodiment is applied to the positioning ball screw device 1 to which preload is applied in advance, the relative movement between the screw shaft 3 and the nut 5 accompanying the reciprocating movement of the nut 5 is so small that it can be ignored. As described above, the radius of curvature of the tip 13a of the contact 13 is preferably 90% or more and 100% or less of the ball radius Ra.
As described above, the nut 5 of the ball screw device 1 of the present embodiment is provided with the contact sensor 11 having the tip 13a opposed to the rolling surface P of the shaft raceway groove 4 via the clearance C. When the amount of wear of the ball screw device 1 due to peeling or peeling increases, both the axial play and the radial play can be directly detected by the ball screw device 1 alone.

Further, in the ball screw device 1 of the present embodiment, the triangular screw 12 provided in the contact sensor 11 is screwed into the mounting screw hole 17 provided in the nut 5 to adjust the clearance C and is fixed by the lock nut 18. Since the adjustment mechanism is provided, the clearance C can be adjusted easily.
Further, since the contact sensor 11 of this embodiment is a mechanical contact sensor 11 in which the contact protrudes and protrudes in the axial direction, it is not easily affected by contact with grease or foreign matter, and prevents erroneous detection and wear amount. Reliability in detection can be increased.

Further, since the tip 13a of the contact sensor 11 of this embodiment is not always in contact with the shaft raceway groove 4, the tip 13 is prevented from being worn without using a special material for the contactor 13, and the shaft raceway groove is thereby prevented. The amount of wear such as 4 can be accurately detected.
As described above, in this embodiment, the nut of the ball screw device is provided with a contact sensor having a contact member facing the shaft raceway groove via the clearance C, and this contact sensor causes the contactor to be turned into the shaft raceway groove. By detecting the contact, it becomes possible to directly detect the wear amount of the rolling surface P or the like of the ball screw device 1 due to wear or peeling, and the nut and screw shaft of the ball screw device accompanying the wear. Can be accurately detected, and appropriate preventive maintenance can be performed to improve the operation efficiency of the machine.

This is particularly effective in the case of a mechanical device that uses a ball screw device mainly for the purpose of transmitting driving force, such as an electric injection molding machine.
Further, by providing an adjustment mechanism for adjusting the clearance C between the contact and the shaft raceway groove in the ball screw device, the clearance C can be easily adjusted.
In the above embodiment, the contact sensor is described as being provided at the end on the opposite side of the flange portion of the nut. However, the contact sensor may be provided at the end on the flange portion side or at both ends. . In this case, if the contact sensors are provided at both ends, it is possible to more accurately detect the radial play due to the inclination between the nut and the screw shaft.

As shown in FIG. 4, a plurality of contact sensors 11 may be provided in the circumferential direction of the nut 5 (in the example of FIG. 4, the contact sensors 11 are arranged at 90 degrees equally). Even in this way, the play in the radial direction due to the inclination of the nut 5 and the screw shaft 3 can be detected more accurately. 4 is a view as seen from the direction of arrow B in FIG.
In this case, if the clearance C between the tip 13a of each contact sensor 11 and the shaft raceway groove 4 is set stepwise for each angular position within the above range, the contact is made stepwise according to the amount of wear. A contact signal is issued from the sensor 11, and the amount of wear of the ball screw device 1 can be detected in stages, and the progress of wear in the ball screw device 1 is grasped and more appropriate preventive maintenance is performed. be able to.

Also, if the sensor is a ring-shaped sensor that emits a contact signal when the inner surface made of metal comes into contact with the screw shaft and is attached to the end surface of the nut, it becomes possible to grasp the amount of wear more accurately. .
Furthermore, in the above-described embodiment, the contact sensor that emits a contact signal ON-OFF when the tip contacts the object is installed with the clearance C away from the shaft raceway groove, and this is used as the sensor. Alternatively, a mechanical distance sensor incorporating a potentiometer or the like that continuously outputs the amount of movement of the contact tip may be used as a sensor, and the amount of wear may be measured by always contacting the shaft raceway groove. In this way, it is possible to continuously grasp the progress of the relative displacement amount between the nut of the ball screw device and the screw shaft accompanying wear, and further appropriate preventive maintenance can be performed.

  In this case, it is preferable that the tip of the contactor has a hardness comparable to that of the ball used in the ball screw device by a quenching process such as induction quenching or carburizing quenching.

FIG. 5 is an explanatory diagram illustrating an installation state of the contact sensor according to the second embodiment.
FIG. 5 is an enlarged view showing the same portion as FIG. 3 of the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
As shown in FIG. 5, the contact sensor 11 according to the present embodiment has a cylindrical portion of the contact 13 formed thinner than the contact 13 according to the first embodiment, and also detects a wear amount by the tip 13 a of the contact 13. Is set at a boundary portion K which is a band-like region along the shaft raceway groove 4 between the shoulder 21 between the outer peripheral surface 3a of the screw shaft 3 and the shaft raceway groove 4 and the rolling surface P. It is installed so that the tip 13a of the contact 13 faces the boundary K.

In this case, the axial mounting position of the nut 5 of the contact sensor 11 is such that the interval T between the cylindrical portion of the contact 13 and the shoulder portion 21 of the screw shaft 3 is 0% or more and 10% or less of the ball radius Ra. It is installed to become.
If the contact sensor 11 installed in this way is used, the ball 2 does not roll on the boundary K, so that it is not affected by the wear of the rolling surface P of the arc concave surface 4b of the shaft raceway groove 4. Thus, it becomes possible to measure the wear amount more accurately.

Further, since the contact 13 is formed to be thin, the interval T is set without considering the preset gap S (see FIG. 3) even in the case of the gap ball screw device 1. It becomes possible.
As described above, in this embodiment, in addition to the same effects as those of the first embodiment, the detection portion by the contact of the contact sensor is the boundary portion K between the outer peripheral surface of the screw shaft and the shaft raceway groove. Thus, the wear amount can be measured more accurately without being affected by the wear of the rolling surface P.

  In each of the above embodiments, a case where the present invention is applied to a ball screw device using a tube-type circulation system that circulates a ball by a return tube has been described as an example, but a top type, an end cap type, a deflector type, etc. Even if the present invention is applied to a circulation type ball screw device, the same effect can be obtained.

Explanatory drawing which shows the cross section of the ball screw apparatus of Example 1. Explanatory drawing which shows the side surface of the contact sensor of Example 1. FIG. Explanatory drawing which shows the installation state of the contact sensor of Example 1. Explanatory drawing which shows the installation state of the contact sensor of Example 1. Explanatory drawing which shows the installation state of the contact sensor of Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ball screw apparatus 2 Ball 3 Screw shaft 4 Shaft raceway groove 4a, 4b, 6a, 6b Arc concave surface 5 Nut 6 Nut raceway groove 7 Flange part 11 Contact sensor 12 Triangular screw 13 Contact 13a Tip 14 Lead wire 16 Mounting seat 17 Installation Screw hole 18 Lock nut 21 Shoulder

Claims (9)

A screw shaft having a spiral shaft raceway groove formed on the outer peripheral surface, a nut having a nut raceway groove facing the shaft raceway groove on the inner peripheral surface, and a plurality of screwing the shaft raceway groove and the nut raceway groove. In a ball screw device provided with
The nut is provided with a sensor having a contact that faces the shaft raceway groove through a clearance,
A ball screw device, wherein the contact of the contact with the shaft raceway groove is detected by the sensor. In claim 1,
A ball screw device, wherein a radius of curvature of a tip of the contact is 90% or more and 100% or less of a radius of the ball. In claim 1 or claim 2,
A ball screw device comprising an adjustment mechanism for adjusting a clearance between the contact and the shaft raceway groove. In any one of Claims 1 to 3,
The ball screw device characterized in that the detection part by the contactor is a boundary part between the outer peripheral surface of the screw shaft and the shaft raceway groove. A screw shaft having a spiral shaft raceway groove formed on the outer peripheral surface, a nut having a nut raceway groove facing the shaft raceway groove on the inner peripheral surface, and a plurality of screwing the shaft raceway groove and the nut raceway groove. In a ball screw device provided with
The nut is provided with a sensor having a contact that contacts the shaft raceway groove,
A ball screw device that continuously detects the amount of movement of the contact by the sensor. In any one of Claims 1 thru | or 5,
The ball screw device according to claim 1, wherein the sensor is provided at both ends of the nut in the axial direction. In any one of Claims 1 thru | or 6,
A ball screw device comprising a plurality of sensors provided in a circumferential direction of the nut. A screw shaft in which a spiral shaft raceway groove is formed on the outer peripheral surface, a nut in which a nut raceway groove facing the shaft raceway groove is formed on the inner peripheral surface, and the shaft raceway groove provided on the nut via a clearance. And a wear amount detecting method for a ball screw device comprising: a sensor having contacts facing each other; and a plurality of balls for screwing the shaft raceway groove and the nut raceway groove,
Detecting that the contact has contacted the shaft raceway groove;
A wear amount detection method for a ball screw device, wherein a relative displacement amount between the screw shaft and the nut is detected by detecting the contact.   An electric injection molding machine comprising the ball screw device according to any one of claims 1 to 7.