JP2010149244A - Main spindle device of machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a main spindle device of a machine tool predicting abnormality inside bearings and quickly detecting the abnormality occurred. <P>SOLUTION: In the main spindle device provided with two or more bearings, an encoder 9 is arranged in a retainer 15 retaining rolling elements 14 of the bearings 5-8, and a rotation sensor 10 detecting the rotational speed of the encoder 9 is arranged in a non-rotating member. Abnormality inside the bearings can be predicted and the abnormality occurred there can be quickly detected by detecting the revolving speed ratio of the retainer 15 from the rotational speed of the encoder 9 detected by the rotation sensor 10 and calculating the temperature difference between inner and outer rings of the bearing from the revolving speed ratio. Also, by calculating the load of a main spindle 1 from the revolving speed ratio of the retainer 15, setting an appropriate working condition and appropriate determination of wear of a tool can be performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spindle device of a machine tool, and is particularly suitable for a spindle of a machine tool that performs a cutting process such as a lathe, a milling machine, or a machining center.

In particular, some machine tools that perform cutting such as a lathe, a milling machine, and a machining center rotate the spindle at a high speed of 20000 rpm. In such a bearing that supports the main shaft that rotates at high speed, the lubricating oil moves from the inner ring raceway to the outer ring raceway due to the centrifugal force, and the lubricating oil film on the rolling contact surface between the inner ring and the rolling element is insufficient. There is a risk of abnormalities such as seizure. When seizure occurs, not only the bearing is damaged, but also peripheral members such as the main shaft and the housing become high temperature, which adversely affects other parts such as a motor (rotor, stator, winding).
Therefore, in Patent Document 1 below, a temperature sensor is attached to the housing of the spindle unit in which the bearing is incorporated, and when the temperature detected by the temperature sensor exceeds a threshold value, the machine tool is stopped because an abnormality has occurred in the bearing or the like. The method of doing is taken.
JP 9-79915 A

However, since it is difficult to identify an abnormal part only by the housing temperature of the main spindle unit, it is necessary to disassemble the main spindle unit, and it takes time to specify the abnormal part. Further, since the temperature rises when the rotational speed of the machine tool is increased or due to a change in the lubrication environment, it is not possible to distinguish between an abnormal state and a normal state, and there is a possibility of misjudging the abnormal state and the normal state.
The present invention has been made paying attention to the above-described problems, and provides a spindle device for a machine tool capable of predicting an abnormality inside a bearing or quickly detecting an abnormality that has occurred. It is intended to do.

  In order to solve the above-described problems, a spindle device for a machine tool according to the present invention is a spindle device for a machine tool including two or more bearings, and an encoder provided in a cage that holds rolling elements of the bearings A rotation sensor that is attached to a non-rotating member and detects the rotation speed of the encoder; and a change in the revolution speed of the cage is detected from the rotation speed of the encoder detected by the rotation sensor, and the change in the revolution speed And a detecting device for calculating a temperature difference between the inner and outer rings of the bearing.

  A spindle device for a machine tool according to the present invention is a spindle device for a machine tool having two or more bearings, an encoder provided in a cage for holding rolling elements of the bearing, and a non-rotating member And a rotation sensor for detecting the rotation speed of the encoder, and a change in the revolution speed of the cage is detected from the rotation speed of the encoder detected by the rotation sensor, and the spindle load is calculated from the change in the revolution speed. It is characterized by comprising a detection device for calculating.

The spindle device of the machine tool according to the present invention is characterized in that the change in the revolution speed is a ratio of the revolution speed of the cage to the rotation speed of the spindle.
The spindle device of the machine tool of the present invention is characterized in that the detection device detects a bearing abnormality in the spindle.
The spindle device for a machine tool according to the present invention is used for a spindle of a machine tool that rotates at high speed.

  Thus, according to the spindle device of the machine tool of the present invention, it is possible to foresee an abnormality inside the bearing or to quickly detect an abnormality that has occurred.

Next, an embodiment of a spindle device for a machine tool according to the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of a spindle unit of a machine tool according to the present embodiment, and is used for various high-speed rotation type dedicated machine tools such as a high-speed rotation general-purpose machine tool such as a lathe, a milling machine, and a machining center. Is. Reference numeral 1 in the figure denotes a main shaft, and reference numeral 2 denotes a unit housing. The main shaft 1 is inserted into the housing 2 from the left side of the figure, and is sealed with a cap 3 fixed to the left end opening of the housing 2. A stopper 4 is attached to the right end portion of the inserted main shaft 1 to prevent it from coming off.

  Between the main shaft 1 and the housing 2, two bearings 5 to 8 are interposed on the right driving side in the drawing and two on the left operating side in the drawing, respectively. Among them, an encoder 9 is attached to the cage of the rightmost bearing 5 and the leftmost bearing 8 shown in the figure, and the housing 2 has a rotation sensor 10 for detecting the rotation speed of the encoder 9. Installed. The output of the rotation sensor 10 is read by the detection device 11.

  FIG. 2 is an overall configuration diagram of a unit showing a different embodiment of the spindle device of the machine tool of the present invention, and is used for a high-speed rotary type machine tool such as a lathe or a milling machine as in the embodiment of FIG. . In this embodiment, it is a so-called motor built-in type machine tool spindle unit in which a rotor 41 is attached to the spindle 1 and a stator 42 is disposed on the outer periphery of the rotor 41 in the housing 2. Also in this embodiment, two bearings 5 to 8 are interposed on the right support side in the drawing and two on the left operation side in the drawing, respectively, and in the case of this embodiment, the second from the right on the right side in the drawing. Encoders 9 are attached to the bearings 6 and the cage of the second bearing 7 from the left on the left in the drawing, and the housing 2 is provided with a rotation sensor 10 that detects the rotational speed of these encoders. The output of the rotation sensor 10 is read by the detection device 11.

  In the spindle unit with a built-in motor, the heat of the rotor and the stator is transmitted to the bearing, the temperature difference between the inner and outer rings is likely to occur, and the bearing is easily seized. In order to suppress the temperature rise of the main shaft due to the heat generated by the motor, so-called outer cylinder cooling is performed by passing coolant through the periphery of the bearings and stator. Therefore, even if a temperature sensor is attached to the outer diameter of the outer ring, the sensor In some cases, the coolant absorbs the heat generated in the vicinity and it is difficult to detect the temperature rise of the bearing. In such a case, the temperature detection device of this embodiment functions effectively.

  FIG. 3 shows details of the bearings 5 and 8 to which the encoder 9 is attached. In the figure, reference numeral 12 denotes an outer ring, reference numeral 13 denotes an inner ring, reference numeral 14 denotes a rolling element, and reference numeral 15 denotes a cage for holding the rolling element 14. As described above, in the bearings 5 and 8 at both ends that support the main shaft 1, the encoder 9 is attached to the retainer 14, and the rotation sensor 10 that detects the rotational speed of the encoder 9 is provided at the opposite portion. The encoder 9 is a multipolar magnet encoder, for example, and generates a pulse each time the retainer 14 rotates by a predetermined angle. Such a multipole magnet encoder is described in detail, for example, in Japanese Patent Application Laid-Open No. 2008-26042 previously proposed by the present applicant. Specifically, for example, the axial end surface of the encoder 9 provided on the axial end surface of the cage 14 is magnetized alternately at N and S poles at predetermined angles, and the current when these magnetic poles pass is determined. The change is detected by the rotation sensor 10, and a pulse is generated and output from the current value of the sine waveform generated at that time.

  For example, assuming that the contact angle between the rolling element and the bearing ring during normal operation of the bearing is FIG. 3, for example, the inner and outer ring temperature difference occurs in the bearing as when the inner ring temperature becomes higher than the outer ring temperature. The contact angle between the rolling element and the race is shown in FIG. In this case, since the temperature of the inner ring is higher than that of the outer ring, a difference in thermal expansion occurs between the inner and outer rings, and the bearing internal radial gap is reduced. When the bearing internal radial clearance is reduced, the contact angle is reduced as shown in FIG. When the contact angle becomes smaller, the rotation speed of the rolling element becomes smaller than that in the normal state, and the revolution speed of the cage also becomes smaller. In addition, if only the revolution speed of the cage is detected at this time, the revolution speed may change as the rotation speed of the main spindle changes. Therefore, the ratio of the revolution speed of the cage to the rotation speed of the main spindle (hereinafter referred to as “revolution speed”) It is desirable that the evaluation is also expressed as a revolution speed ratio).

  For example, when the amount of lubricating oil changes during operation of a machine tool, the temperature of the bearing also changes. If the amount of lubricating oil is large, a cooling effect is obtained inside the bearing, and the temperature decreases. Conversely, if the amount of lubricating oil is small, the cooling effect inside the bearing is lost and the temperature rises. At this time, since it becomes a cooling effect by the lubricating oil inside the bearing, the influence of the temperature of the inner and outer rings is equivalent, and therefore, the temperature difference between the inner and outer rings hardly occurs. For this reason, a method using the characteristics of the bearing is desirable for detecting the occurrence of abnormality and for early prediction.

  When seizure occurs in the bearing, as described above, due to the lack of lubricating oil, an oil film cannot be formed between the rolling contact surfaces of the rolling elements and the raceway grooves, and metal contact occurs. For this reason, the temperature rise of the bearing is increased, but it is well known that the temperature on the inner ring side rotating in synchronization with the rotating shaft is higher than the temperature on the outer ring side. This is because the outer ring, which is a stationary wheel, is in contact with a heat-capacity housing and other members, and it is easy to dissipate heat, whereas the inner ring, which is a rotating wheel, rotates synchronously with the main shaft having a small heat capacity. This is because it is difficult to do.

When a temperature difference between the inner and outer rings occurs in which the inner ring temperature is higher than the outer ring temperature, as described above, the amount of thermal expansion in the inner ring is larger than that in the outer ring, so that the radial clearance inside the bearing is reduced. By reducing the radial gap, the contact angle between the rolling element and the raceway groove is reduced, so that the rotating speed of the rolling element is reduced and the revolution speed of the cage is reduced. By using this characteristic, it is possible to detect the temperature difference between the inner and outer rings from the revolution speed ratio by acquiring conversion data of the inner and outer ring temperature difference, radial gap change amount, contact angle change, revolution speed ratio in advance. Is possible. In addition, by setting a threshold for the temperature difference between the inner and outer rings, the machine can be stopped before seizure occurs to prevent seizure, or the machine can be stopped immediately when seizure occurs to prevent secondary damage. It becomes possible to do. Specifically, the temperature difference information between the inner and outer rings is transmitted to the control device side of the machine tool, and a threshold value for predicting seizure occurrence or a threshold value for detecting seizure occurrence is set in advance. Can be reduced or rotation can be stopped.
The relationship between the internal radial clearance of the bearing and the contact angle is expressed by the following formula (1). The change value of the contact angle α can be calculated from the changed internal radial gap Δr in the one expression.

FIG. 5 shows the relationship between the revolution speed ratio and the inner / outer ring temperature difference. As can be seen from the figure, the revolution speed ratio decreases as the temperature difference between the inner and outer rings increases. Therefore, by previously acquiring the relationship between the inner and outer ring temperature difference and the revolution speed ratio as shown in FIG. 5, it is possible to detect the temperature difference between the inner and outer rings from the revolution speed ratio.
Moreover, the axial load acting on the bearing can be detected by measuring the revolution speed ratio. During normal operation, the change in the radial gap due to the difference in thermal expansion between the inner and outer rings is small because the temperature change of the inner and outer rings is small. Here, consider a case where an axial load is generated. As shown in FIGS. 6 and 7, when an axial load is generated, a relative displacement in the axial direction occurs between the inner ring and the outer ring. Due to this axial displacement, the contact angle between the rolling elements and the rolling wheels changes. With this change in the contact angle, the rotation speed of the rolling element changes, and the revolution speed of the cage changes.

  In a machine tool, detecting a load at the time of cutting is considered beneficial for the following reasons. That is, when the cutting load is determined, it is possible to select appropriate machining conditions. For example, if it becomes possible to find a machining condition in which the amount of chips discharged is the same and the cutting load is small, it becomes an efficient machining condition, which leads to energy saving and extension of the tool life. Further, when the cutting load increases under the same processing conditions, it is estimated that the cutting performance of the tool, that is, the so-called sharpness reduction or wear has occurred, and it is possible to judge the tool replacement time and the tool life. In addition, by storing the history of the detected cutting load, it is possible to estimate the damage factor when the bearing is damaged. Examples of the damage factor obtained from the history search include cutting under an unreasonable load condition and impact load in which the tool tip collides with a workpiece.

  As a method for detecting the cutting load of the machine tool, the change in the revolution speed ratio is read in the same manner as the method used when a bearing abnormality occurs. It has been explained that when a bearing abnormality occurs, the inner and outer ring temperature difference is generated, and therefore, the bearing internal radial gap is reduced due to the difference in thermal expansion between the inner and outer rings, and the contact angle is reduced, so that the revolution speed ratio is reduced. Here, a method for detecting a cutting load will be described below.

  Since the temperature change of the inner and outer rings is small during normal operation, the variation in the radial gap due to the difference in thermal expansion between the inner and outer rings is small. That is, since the change in the contact angle due to the reduction in the radial gap is eliminated, the only factor that changes the contact angle is when the axial load changes. When an axial load is applied, the contact angle between the rolling wheel and the raceway groove is increased, and the revolution speed ratio is increased. If the relationship between the axial load and the contact angle is acquired in advance, the axial load can be detected by detecting the revolution speed ratio. FIG. 8 shows an example of the relationship between the revolution speed ratio and the axial load.

  However, accurate load detection cannot be performed when seizure abnormality occurs, but it can be used in normal times because it is a problem only at the time of abnormality. Conversely, even when there is a revolution change due to a load, an abnormality such as seizure can be detected. This is because the margin of change in the revolution speed ratio differs between the inner and outer ring temperature differences and the axial load. FIG. 9 shows the margin of change in the revolution speed ratio due to the temperature difference between the inner and outer rings and the axial load. As is clear from this figure, the amount of change in the revolution speed ratio due to the temperature difference between the inner and outer rings is about 5 to 6 times greater than the amount of change in the revolution speed ratio due to the axial load. Using this characteristic, for example, when the revolution speed ratio shown in FIG. 9 reaches a threshold value equal to or higher than the temperature, the temperature difference between the inner and outer rings becomes large, and it is sufficient to stop the machine if a bearing abnormality occurs.

  As described above, according to the spindle device of the machine tool of the present embodiment, the encoder 9 is provided in the retainer 15 that holds the rolling elements 14 of the bearings 5 to 8, and the rotational speed of the encoder 9 is detected in the non-rotating member. A rotation sensor 10 is provided, the revolution speed ratio (change in revolution speed) of the cage 14 is detected from the rotation speed of the encoder 9 detected by the rotation sensor 10, and the bearing inner and outer rings are determined from the revolution speed ratio (change in revolution speed). Therefore, it is possible to foresee an abnormality inside the bearing and to quickly detect an abnormality that has occurred.

Further, the encoder 9 is provided in the cage 15 that holds the rolling elements 14 of the bearings 5 to 8, and the rotation sensor 10 that detects the rotation speed of the encoder 9 is provided in the non-rotating member, and the encoder detected by the rotation sensor 10. Since the revolution speed ratio (change in revolution speed) of the cage 14 is detected from the rotational speed 9 and the load on the spindle 1 is calculated from the revolution speed ratio (change in revolution speed), appropriate machining conditions are set. And proper tool wear can be determined.
Further, by making the change in the revolution speed the ratio of the revolution speed of the cage 15 to the rotation speed of the main shaft 1, the temperature difference between the bearing inner and outer rings and the load on the main shaft can be properly detected.

It is a whole lineblock diagram showing one embodiment of a unit using a spindle device of a machine tool of the present invention. It is a whole block diagram which shows different embodiment of the unit using the spindle apparatus of the machine tool of this invention. FIG. 3 is a detailed view of the bearing of FIGS. 1 and 2. FIG. 3 is a detailed view of the bearing of FIGS. 1 and 2. It is explanatory drawing which shows the relationship between the revolution speed ratio of a holder | retainer, and the temperature difference of a bearing inner / outer ring. FIG. 3 is a detailed view of the bearing of FIGS. 1 and 2. FIG. 3 is a detailed view of the bearing of FIGS. 1 and 2. It is explanatory drawing which shows the relationship between the revolution speed ratio of a holder | retainer, and a load. It is explanatory drawing which shows the relationship between the revolution speed ratio of a holder | retainer, and a load.

Explanation of symbols

  1 is a main shaft, 2 is a housing, 5 to 8 are bearings, 9 is an encoder, 10 is a rotation sensor, 11 is a detection device, 12 is an outer ring, 13 is an inner ring, 14 is a rolling element, and 15 is a cage.

Claims (5)

  A spindle device of a machine tool including two or more bearings, an encoder provided in a cage that holds rolling elements of the bearing, and a rotational speed of the encoder that is attached to a non-rotating member A rotation sensor and a detection device that detects a change in revolution speed of the cage from the rotation speed of the encoder detected by the rotation sensor and calculates a temperature difference between the inner and outer rings of the bearing from the change in revolution speed. A machine tool spindle device.   A spindle device of a machine tool including two or more bearings, an encoder provided in a cage that holds rolling elements of the bearing, and a rotational speed of the encoder that is attached to a non-rotating member A rotation sensor and a detection device that detects a change in the revolution speed of the cage from the rotation speed of the encoder detected by the rotation sensor and calculates a load on the spindle from the change in the revolution speed. Machine tool spindle device.   3. The spindle device for a machine tool according to claim 1, wherein the change in the revolution speed is a ratio of the revolution speed of the cage to the rotation speed of the spindle.   The spindle device for a machine tool according to any one of claims 1 to 3, wherein the detection device detects a bearing abnormality inside the spindle.   The spindle device for a machine tool according to any one of claims 1 to 4, wherein the spindle device is used for a spindle of a machine tool that rotates at a high speed.

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