Method of phasing threaded grinding stone, as well as device therefor

Provided is a method of phasing a threaded grinding stone, as well as a device therefor, the aforementioned method and device being such that contact or non-contact of a threaded grinding stone with a disk dresser can be detected with high accuracy, with the result that the phasing of the threaded grinding stone can be accurately performed. For the purpose of achieving the above, a threaded grinding stone (14) is phased with respect to a disk dresser (32) prior to the engagement of the threaded grinding stone (14) with the disk dresser (32) during dressing. In performing this phasing, it is determined whether or not the threaded grinding stone (14) contacted the disk dresser (32), on the basis of a voltage (V) which is commensurate with the amplitude of the elastic wave generated in the threaded grinding stone (14) at the time when the threaded grinding stone (14) contacted the disk dresser (32). In a case where the voltage (V) does not exceed a threshold value (Vo) even if the threaded grinding stone (14) contacts the disk dresser (32), then the rotational speed of the disk dresser (32) is increased, with the result that there is forcibly created a situation where it is determined that contact occurred. Subsequently, the threaded grinding stone (14) is positioned, on the basis of the resulting phase thereof, in an intermediate phase where the aforementioned engagement is feasible.

TECHNICAL FIELD

The present invention relates to a phasing method and a phasing device for a threaded grinding wheel used to phase a threaded grinding wheel with a dresser ahead of the meshing of the threaded grinding wheel with the dresser at the time of dressing.

BACKGROUND ART

Heretofore, gear grinding machines are provided to efficiently finish the tooth surfaces of a workpiece, which is a heat-treated gear to be machined, by grinding the workpiece with a grinding wheel, which is a grinding tool. In such a gear grinding machine, the workpiece is ground in a state in which the grinding wheel and the workpiece are being rotated in synchronization while meshing with each other. Accordingly, insufficient precision of meshing may cause uneven grinding on the tooth surfaces of the workpiece and may reduce the life of the grinding wheel due to an excessive load thereon.

For the above-described reasons, in a gear grinding machine of this type, phasing is performed ahead of meshing at the time of grinding in order to mesh a grinding wheel with a workpiece with high precision. In the phasing, the grinding wheel and the workpiece are positioned so that the cutting edges (peaks and valleys) of the grinding wheel and the roots (peaks and valleys) of the teeth of the workpiece have an appropriate phase relationship. Such a phasing method for phasing a grinding wheel with a workpiece is disclosed in, for example, Patent Document 1.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese Patent Application Publication No. Hei 5-138438

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In the above-described conventional phasing method, a grinding wheel is slid on a workpiece in the axial direction thereof, and an AE (acoustic emission) sensor detects the instant of occurrence of contact and the instant of loss of contact when the grinding wheel crosses a thread groove of the workpiece. The workpiece is moved in the axial direction thereof so that the grinding wheel faces an intermediate position in the thread groove which is found based on the results of the detection. In this way, the grinding wheel and the workpiece are phased with each other. However, in the conventional method, the precise detection of contact or non-contact of the grinding wheel with the workpiece is difficult because the detection is performed in an instant.

In addition, in the gear grinding machine, it is considered that the same problem occurs not only in the phasing of the grinding wheel with the workpiece during grinding but also in the phasing of the grinding wheel with a dresser during dressing, because the workpiece is ground by use of the grinding wheel dressed by the dresser.

Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a phasing method and a phasing device for a threaded grinding wheel which enable detection of contact or non-contact of the threaded grinding wheel with high precision and precise phasing of the threaded grinding wheel.

Means for Solving the Problems

A phasing method for a threaded grinding wheel according to the first invention that solves the problems is a phasing method for a threaded grinding wheel, in which the threaded grinding wheel is phased with a dresser prior to the engagement of the threaded grinding wheel with the dresser during dressing, the method characterized by comprising:

rotating the threaded grinding wheel in one direction;

detecting elastic waves generated when one of thread surfaces of the threaded grinding wheel comes into contact with a corresponding one of blade surfaces of the dresser;

increasing the number of rotations of the dresser until a measured value on one direction side corresponding to the elastic waves exceeds a predetermined value in a case where the measured value on the one direction side does not exceed the predetermined value even if the threaded grinding wheel comes into contact with the dresser;

storing a phase on the one direction side of the threaded grinding wheel once the measured value on the one direction side exceeds the predetermined value;

rotating the threaded grinding wheel in the other direction;

detecting elastic waves generated when the other one of the thread surfaces of the threaded grinding wheel comes into contact with the other one of the blade surfaces of the dresser;

increasing the number of rotations of the dresser until a measured value on the other direction side corresponding to the elastic waves exceeds the predetermined value in a case where the measured value on the other direction side does not exceed the predetermined value even if the threaded grinding wheel comes into contact with the dresser;

storing a phase on the other direction side of the threaded grinding wheel once the measured value on the other direction side exceeds the predetermined value; and

positioning the threaded grinding wheel at a phase where the engagement is feasible, on the basis of the phase on the one direction side and the phase on the other direction side of the threaded grinding wheel.

A phasing device for a threaded grinding wheel according to the second invention that solves the problems is a phasing device for a threaded grinding wheel, with which the threaded grinding wheel is phased with a dresser prior to the engagement of the threaded grinding wheel with the dresser during dressing, the device characterized by comprising:

detection means for detecting elastic waves generated when the threaded grinding wheel rotates and comes into contact with the dresser;

determination means for determining that the threaded grinding wheel has come into contact with the dresser in a case where a measured value corresponding to the elastic waves detected by the detection means exceeds a predetermined value;

dresser rotation number setting means for setting the number of rotations of the dresser so that the measured value exceeds the predetermined value, in a case where the threaded grinding wheel comes into contact with the dresser and the measured value does not exceed the predetermined value; and

grinding wheel phase control means for positioning the threaded grinding wheel at a phase where the engagement is feasible, on the basis of the phase of the threaded grinding wheel when the detection means determines that the contact has occurred.

A phasing device for a threaded grinding wheel according to the third invention that solves the problems is characterized in that the dresser rotation number setting means increases the number of rotations of the dresser in a stepwise manner.

Effects of the Invention

In the phasing method and the phasing device for a threaded grinding wheel according to the present invention, a determination is made whether or not the threaded grinding wheel has come into contact with the disc dresser, on the basis of a measured value corresponding to elastic waves generated in the threaded grinding wheel when the threaded grinding wheel comes into contact with the dresser. In a case where the measured value does not exceed a predetermined value even if the threaded grinding wheel comes into contact with the dresser, the number of rotations of the dresser is increased. Accordingly, contact or non-contact of the threaded grinding wheel can be detected with high precision, and thus the threaded grinding wheel can be phased with the dresser precisely.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a phasing method and a phasing device for a threaded grinding wheel according to the present invention will be described in detail with reference to the drawings.

Embodiment

A gear grinding machine1to which the phasing device for a threaded grinding wheel according to the present invention is applied is used to grind a workpiece (gear to be machined) W as a material of an internal gear with a barrel-shaped threaded grinding wheel14as shown inFIG. 2. Further, the gear grinding machine1has the dressing function of dressing the threaded grinding wheel14with a disc dresser32as shown inFIG. 1.

As shown inFIGS. 1 to 3, a grinding wheel head11is movably and turnably supported in the gear grinding machine1. A spindle12is rotatably supported by this grinding wheel head11. At the tip of this spindle12, a grinding wheel arbor13is formed. Further, to the tip of the grinding wheel arbor13, the threaded grinding wheel14is removably attached. Thus, driving the grinding wheel head11causes the threaded grinding wheel14to be rotationally driven through the grinding wheel arbor13of the spindle12.

In front of the grinding wheel head11, a rotary table21is rotatably supported. To an upper surface of this rotary table21, the workpiece W is removably attached through an unillustrated installation jig. Thus, driving the rotary table21causes the workpiece W to be rotationally driven.

At a side of the rotary table21, a dresser drive unit31is movably supported. To this dresser drive unit31, the disc dresser32is removably attached. Thus, driving the dresser drive unit31causes the disc dresser32to be rotationally driven.

On the tip surface of the grinding wheel head11, an AE (Acoustic Emission) fluid sensor (detection means)42of an acoustic emission type is supported through a bracket41. This AE fluid sensor42is configured to detect, through jetted fluid, elastic waves generated in a material due to vibration, friction, and the like, and to process the elastic waves as an AE signal. The AE fluid sensor42has a jet orifice42afor jetting coolant C as the fluid to a predetermined measurement point on the grinding wheel arbor13and a detection unit42bfor detecting elastic waves propagating through the coolant C from the measurement point. Furthermore, the jet orifice42aof the AE fluid sensor42has a coolant tank43connected thereto, and the detection unit42bhas an AE sensor amplifier44connected thereto.

It should be noted that the coolant C supplied from the coolant tank43to the AE fluid sensor42is, for example, grinding oil, and that the coolant pressure and the jetting flow rate of the coolant can be adjusted in accordance with the distance between the AE fluid sensor42and the measurement point.

Specifically, in the AE fluid sensor42, elastic waves generated in the threaded grinding wheel14by jetting the coolant C supplied from the coolant tank43from the jet orifice42ato the measurement point on the grinding wheel arbor13are detected by the detection unit42bthrough the coolant C, and these detected elastic waves are then inputted as an AE signal to the AE sensor amplifier44. In the AE sensor amplifier44, as shown inFIG. 4, the inputted AE signal is converted into voltage V (measured value), and this voltage V is displayed as needed.

Moreover, in the gear grinding machine1, an NC unit (determination means, dresser rotation number setting means, grinding wheel phase control means)50is provided. This NC unit50is connected to, for example, the grinding wheel head11, the rotary table21, the dresser drive unit31, the AE sensor amplifier44, and the like. The NC unit50controls the grinding of the workpiece W with the threaded grinding wheel14and the dressing of the threaded grinding wheel14with the disc dresser32based on inputted workpiece specifications and machining conditions. Ahead of meshing (gear meshing operation) at the time of the above-described grinding or dressing, the NC unit50determines whether or not there is a contact between the threaded grinding wheel14and the workpiece W or the disc dresser32, based on the amplitude of elastic waves detected by acoustic emission fluid sensor42, thus phasing the threaded grinding wheel14.

The grinding of the workpiece W with the threaded grinding wheel14starts with moving the threaded grinding wheel14into the workpiece W attached to the rotary table21as shown inFIG. 2. After the threaded grinding wheel14is moved to the workpiece W side, the phasing between the threaded grinding wheel14and the workpiece W is roughly performed (rough phasing) before the threaded grinding wheel14and the workpiece W are meshed with each other so that the thread tips of the threaded grinding wheel14and the tooth tips of the workpiece W do not interfere with each other. In such a roughly phase-matched state, the threaded grinding wheel14and the workpiece W are rotated in synchronization, and the coolant C is jetted from the jet orifice42aof the AE fluid sensor42toward the measurement point on the grinding wheel arbor13. Then, the detection of elastic waves generated in the threaded grinding wheel14is started by the detection unit42bof the AE fluid sensor42.

When the detection of elastic waves by the AE fluid sensor42is started as described above, the AE sensor amplifier44converts the inputted AE signal into the voltage V to display the change thereof with time as shown inFIG. 4. It should be noted that at the same time as the detection of elastic waves by the AE fluid sensor42is started, the voltage V is measured as the maximum voltage Vf of the threaded grinding wheel14in non-contact conditions, and a threshold value Vo larger than this voltage Vf is automatically set. This threshold value Vo is used when an undermentioned contact determination is made on the threaded grinding wheel14.

Subsequently, only the rotation speed (number of rotations) of the workpiece W is increased to cause a loss of synchronization between the threaded grinding wheel14and the workpiece W. Thus, one of tooth surfaces of the workpiece Ware brought into contact with corresponding one of thread surfaces of the threaded grinding wheel14. As a result, elastic waves generated in the threaded grinding wheel14due to the contact are propagated to the grinding wheel arbor13. These elastic waves propagated to the grinding wheel arbor13are detected by the AE fluid sensor42through the coolant C. At this time, as shown inFIG. 4, in the AE sensor amplifier44, the waveform of the voltage V changes in accordance with the inputted AE signal. When this voltage V (Vf) exceeds the predetermined threshold value Vo, the NC unit50determines that the workpiece W has come into contact with the threaded grinding wheel14, and stores the phase of the threaded grinding wheel14of this time.

On the other hand, only the rotation speed (number of rotations) of the workpiece W is decreased to cause a loss of synchronization between the threaded grinding wheel14and the workpiece W. Thus, the other one of the tooth surfaces of the workpiece W are brought into contact with the other one of the thread surfaces of the threaded grinding wheel14. As a result, elastic waves generated in the threaded grinding wheel14due to the contact are propagated to the grinding wheel arbor13. These elastic waves propagated to the grinding wheel arbor13are detected by the AE fluid sensor42through the coolant C. At this time, as shown inFIG. 4, in the AE sensor amplifier44, the waveform of the voltage V changes in accordance with the inputted AE signal. When this voltage V (Vf) exceeds the predetermined threshold value Vo, the NC unit50determines that the workpiece W has come into contact with the threaded grinding wheel14, and stores the phase of the threaded grinding wheel14of this time.

Then, the NC unit50finds an intermediate phase from the two stored phases of the threaded grinding wheel14. The intermediate phase is between the two stored phases. After that, phasing is performed precisely (precise phasing) by positioning the threaded grinding wheel14so that the phase thereof is the intermediate phase. Subsequently, in such a precisely phase-matched state, the threaded grinding wheel14is meshed with the workpiece W, and the threaded grinding wheel14and the workpiece W are rotated in synchronization. As a result, the one of the tooth surfaces of the workpiece W are ground by the corresponding one of the thread surfaces of the threaded grinding wheel14.

What should be noted here is that the use of the threaded grinding wheel14to grind a certain number of workpieces W causes a decrease in sharpness of the threaded grinding wheel14due to the wear of the thread surfaces thereof. To address this decrease, the dressing of the threaded grinding wheel14needs to be carried out on a regular basis with the disc dresser32.

The dressing of the threaded grinding wheel14with the disc dresser32starts with moving the threaded grinding wheel14to the disc dresser32side as shown inFIG. 1. After that, the phasing between the threaded grinding wheel14and the disc dresser32is roughly performed (rough phasing) before the threaded grinding wheel14and the disc dresser32are meshed with each other so that the thread tips of the threaded grinding wheel14and the blade edge of the disc dresser32do not interfere with each other. Subsequently, in such a roughly phase-matched state, the disc dresser32is rotated while the rotation of the threaded grinding wheel14is kept stopped, and the coolant C is jetted from the jet orifice42aof the AE fluid sensor42toward the measurement point on the grinding wheel arbor13. Then, the detection of elastic waves generated in the threaded grinding wheel14is started by the detection unit42bof the AE fluid sensor42.

Note that the number of rotations of the disc dresser32at this time is set to an intermediate value between the minimum number of rotations and the maximum number of rotations. The minimum number of rotations is the number that allows an operator to hear contact sound when the threaded grinding wheel14comes into contact with the disc dresser32. The maximum number of rotations is the number that allows any of the threaded grinding wheel14and the disc dresser32not to be broken when the threaded grinding wheel14comes into contact with the disc dresser32.

When the detection of elastic waves by the AE fluid sensor42is started as described above, the AE sensor amplifier44converts the inputted AE signal into the voltage V to display the change thereof with time as shown inFIG. 4. It should be noted that at the same time as the detection of elastic waves by the AE fluid sensor42is started, the voltage V is measured as the maximum voltage Vf of the threaded grinding wheel14in non-contact conditions, and a threshold value Vo (predetermined value) larger than this voltage Vf is automatically set. This threshold value Vo is used when an undermentioned contact determination is made on the threaded grinding wheel14.

Then, the threaded grinding wheel14is rotated forward so that one thread surfaces thereof are brought into contact with one blade surface of the disc dresser32. As a result, elastic waves generated in the threaded grinding wheel14due to the contact are propagated to the grinding wheel arbor13. These elastic waves propagated to the grinding wheel arbor13are detected by the AE fluid sensor42through the coolant C. At this time, as shown inFIG. 4, in the AE sensor amplifier44, the waveform of the voltage V changes in accordance with the inputted AE signal. When this voltage (a measured value on one direction side) V exceeds the predetermined threshold value Vo, the NC unit50determines that the threaded grinding wheel14has come into contact with the disc dresser32, and stores the phase (a phase on the one direction side) of the threaded grinding wheel14of this time.

Subsequently, the threaded grinding wheel14is rotated reversely so that the other thread surfaces thereof are brought into contact with the other blade surface of the disc dresser32. As a result, elastic waves generated in the threaded grinding wheel14due to the contact are propagated to the grinding wheel arbor13. These elastic waves propagated to the grinding wheel arbor13are detected by the AE fluid sensor42through the coolant C. At this time, as shown inFIG. 4, in the AE sensor amplifier44, the waveform of the voltage V changes in accordance with the inputted AE signal. When this voltage (a measured value on other direction side) V exceeds the predetermined threshold value Vo, the NC unit50determines that the threaded grinding wheel14has come into contact with the disc dresser32, and stores the phase (a phase on the other direction side) of the threaded grinding wheel14of this time.

Then, the NC unit50finds an intermediate phase from the two stored phases of the threaded grinding wheel14. The intermediate phase is intermediate between the two stored phases. After that, phasing is performed precisely (precise phasing) by positioning the threaded grinding wheel14so that the phase thereof is the intermediate phase. Subsequently, in such a precisely phase-matched state, the threaded grinding wheel14is meshed with the disc dresser32, and the disc dresser32is rotated. As a result, the thread surfaces of the threaded grinding wheel14are dressed by the blade surfaces of the disc dresser32.

It should be noted that though the workpiece W as a material of an internal gear has been employed in this example, a workpiece as a material of an external gear may be employed. Moreover, though the common threshold voltage Vo has been used in a contact determination between the threaded grinding wheel14and the workpiece W or the disc dresser32, different threshold values may be used. With respect to these threshold values, different values can be set for different materials, different machining conditions, and the like.

Here, when the threaded grinding wheel14comes into contact with the disc dresser32by rotating forward or reversely as described above, in a case where the voltage V does not exceed the threshold value Vo even after a predetermined time has passed although the threaded grinding wheel14are in contact with the disc dresser32, the NC unit50performs control so that the number of rotations N of the disc dresser32increases. Specifically, as shown by the dotted line inFIG. 4, in a case where the measured voltage V exceeds the maximum voltage Vf in non-contact conditions and is equal to or lower than the threshold value Vo, the number of rotations N of the disc dresser32is increased in a stepwise manner at a constant rate until the voltage V exceeds the threshold value Vo (seeFIG. 5), and thereby the elastic waves of the threaded grinding wheel14are forcibly amplified. This improves the detection sensitivity of the AE fluid sensor42and ensures the contact determination to be made on the threaded grinding wheel14.

With regard to the method for setting the number of rotations N of the disc dresser32in a stepwise manner, the increase rate of the number of rotations N may be set as constant as shown by the solid line inFIG. 5, or may be set as variable. For example, the increase rate may be set to be gradually smaller as shown by the dotted line inFIG. 5.

Next, a process of setting the number of rotations of the disc dresser32by the NC unit50is described usingFIG. 6.

First, the maximum voltage Vf in non-contact conditions of the threaded grinding wheel14is measured in Step S1, and next in Step S2, the threshold value Vo is set to a value larger than the maximum voltage Vf measured in Step S1, the threshold value Vo used for determining that the threaded grinding wheel14has come into contact with the disc dresser32.

Then, in Step S3, an intermediate value between the minimum number of rotations and the maximum number of rotations is set as the number of rotations of the disc dresser32. The minimum number of rotations is the number that allows an operator to hear contact sound when the threaded grinding wheel14comes into contact with the disc dresser32. The maximum number of rotations is the number that allows the threaded grinding wheel14not to be broken when the threaded grinding wheel14comes into contact with the disc dresser32. After that, in Step S4, phasing of the threaded grinding wheel14with the disc dresser32is started.

Next, in Step S5, a determination is made whether or not the threaded grinding wheel14has come into contact with the disc dresser32. If YES in Step S5, the phasing of the threaded grinding wheel14is continued in Step S6, and the phasing ends in Step S7. If NO in Step S5, the number of rotations N of the disc dresser32is increased in Step S8and then the process returns to Step S5.

Accordingly, in the phasing method and the phasing device for a threaded grinding wheel according to the present invention, the threaded grinding wheel14is phased with the disc dresser32prior to the engagement of the threaded grinding wheel14with the disc dresser32during dressing. In performing this phasing, a determination is made whether or not the threaded grinding wheel14has come into contact with the disc dresser32, on the basis of the voltage V corresponding to the amplitude of the elastic waves generated in the threaded grinding wheel14when the threaded grinding wheel14has come into contact with the disc dresser32. In a case where the voltage V does not exceed a threshold value Vo even if the threaded grinding wheel14comes into contact with the disc dresser32, then the number of rotations of the disc dresser32is increased and a determination is forcibly made that the contact has occurred. Subsequently, the threaded grinding wheel14is positioned, on the basis of the resulting phase thereof, in an intermediate phase where the engagement is feasible.

Industrial Applicability

The present invention can be applied to a gear grinding machine which enables a reduction of non-machining time.