Patent Description:
In machine working in a radial direction, in a case where a narrow dimensional tolerance, for example, a dimensional tolerance of <NUM> or less is demanded, it is common to perform turning with a grinding allowance left with respect to a target dimension beforehand and then repeat grinding and dimension measurement to keep the finished dimension within a tolerance of the target dimension. On the other hand, in order to perform machine working in the radial direction with high accuracy by only turning, it is necessary to conduct control for correcting an error in relative movement between a spindle apparatus and a turning tool.

For example, <CIT> discloses, in machining a key groove, a machining apparatus (combined lathe) into which a mechanism for finely adjusting the distance from a tool post to the rotation axis of the spindle is incorporated, so that a worn amount can be corrected without exchanging a tool (turning tool) that is worn. A machine stand attached to be slidable vertically and horizontally with respect to the direction of the rotation axis of the spindle is provided on a cross slide that is slidable in the direction of the rotation axis, and a rod-shaped tool is arranged and fixed on the tool post mounted on the machine stand so as to extend in a direction perpendicular to the rotation axis. In such an apparatus, by moving the rod-shaped tool forward or backward in a static or dynamic manner in its longitudinal direction, the outer diameter dimension and the roundness of a workpiece are made to be finely adjustable.

In the machine working for which the above-described narrow dimensional tolerance is demanded, in the method described in <CIT>, in a case where the dimension that has been measured after machining does not fall within the tolerance, the distance from the tool post to the rotation axis of the spindle is finely adjusted for a workpiece to be subjected to machining next. However, a thermal displacement that changes the positional relationship between the rotation axis and the tool post occurs in accordance with a temperature rise due to operations for machining. Hence, in the next machining, an appropriate distance cannot be always ensured by the same adjustment amount. Furthermore, since the distance is finely adjusted from the dimension that has been measured after machining, it is difficult to make a workpiece to be subjected for machining for the first time fall within the dimensional tolerance. In order to eliminate this, although grinding is performed after the above-described turning, a long machining time is needed to perform grinding in addition to turning. Therefore, machine working to be enabled in a short period of time by only turning is desired.

<CIT> shows a known turning method for a rotatable workpiece, in which a turning tool can be moved by means of a first movement apparatus in a radial direction of the rotation axis of the workpiece to locate a cutting edge of the turning tool in the radial direction, and a table can be moved by means of a second movement apparatus in parallel with the rotation axis for performing rough turning on the workpiece. Thereafter, the rough-processed dimension of the workpiece is measured, and then, based on the measured dimension of the rough-processed workpiece, the turning tool is moved by means of the first movement apparatus in the radial direction of the rotation axis of the workpiece as well as the table is moved by means of the second movement apparatus in parallel with the rotation axis for performing finish turning on the workpiece.

<CIT> shows a common turning method in which a tool fitted to a tool spindle is radially and axially moved for performing rough turning on a workpiece, thereafter the rough-processed dimension of the workpiece is measured, and then the tool fitted to the tool spindle is again radially and axially moved for performing finish turning on said workpiece based on the detection/correction results of the dimension of the workpiece measured.

Another turning method according to the prior art is shown in <CIT>.

<CIT> shows a mounting state inspection state for detecting the clamping state of a tool holder by the presence or absence of air leakage.

It is the object of the present invention to provide a turning method, a turning program, and a turning system that are capable of providing improved machine working for which a narrow dimensional tolerance is demanded.

The object of the present invention is achieved by each of the claimed subject-matters as defined by the independent claims.

Further advantageous developments according to the present invention are defined in the dependent claims.

A turning method according to the present invention is a turning method for a workpiece rotatable about a rotation axis, and the turning method for the workpiece includes: driving a first movement apparatus for moving a turning tool in a radial direction of the rotation axis to locate a cutting edge of the turning tool at a first radial position in the radial direction; driving a second movement apparatus for moving the turning tool in parallel with the rotation axis, performing turning on the workpiece, and then moving the turning tool in a reverse direction to retract the turning tool from the workpiece; measuring a processed dimension of the workpiece, and calculating an error between the processed dimension that has been measured and a target dimension; driving a third movement apparatus for moving the turning tool relative to the first movement apparatus in the radial direction of the rotation axis to locate the cutting edge of the turning tool at a second radial position so as to correct the error; and driving the second movement apparatus to move the turning tool in parallel with the rotation axis, and performing turning on the workpiece.

In addition, a machining system according to the present invention is a machining system for a workpiece, and the machining system includes: a machining apparatus configured to perform turning on the workpiece; a measuring apparatus configured to measure a processed dimension of the workpiece; and a controller configured to control driving of the machining apparatus and the measuring apparatus. The machining apparatus includes: a spindle apparatus configured to rotate the workpiece about a rotation axis; a first movement apparatus configured to move a turning tool in a radial direction of the rotation axis; a second movement apparatus configured to move the turning tool in parallel with the rotation axis; and a third movement apparatus having a movable range smaller than a movable range of the first movement apparatus in the radial direction of the rotation axis, and configured to move the turning tool relative to the first movement apparatus in the radial direction of the rotation axis. The controller controls the driving of the machining apparatus and the measuring apparatus to perform the above-described turning method for the workpiece.

In addition, a machining program according to the present invention is a machining program including an instruction for causing a machining apparatus to perform the above-described turning method, and the machining apparatus includes: a first movement apparatus configured to move a turning tool in a radial direction of a rotation axis of a workpiece; a second movement apparatus configured to move the turning tool in parallel with the rotation axis; and a third movement apparatus configured to move the turning tool relative to the first movement apparatus in a radial direction of the rotation axis.

In addition, another turning method according to the present invention is a turning method for a workpiece rotatable about a rotation axis, and the turning method for the workpiece includes: driving a second movement apparatus for moving a turning tool in parallel with the rotation axis to locate a cutting edge of the turning tool at a first axial position in a direction parallel to the rotation axis; driving a first movement apparatus for moving the turning tool in a radial direction of the rotation axis, performing turning on the workpiece, and then moving the turning tool in a reverse direction to retract the turning tool from the workpiece; measuring a processed dimension of the workpiece, and calculating an error between the processed dimension that has been measured and a target dimension; driving a fourth movement apparatus for moving the turning tool relative to the second movement apparatus in parallel with the rotation axis to locate the cutting edge of the turning tool at a second axial position so as to correct the error; and driving the first movement apparatus to move the turning tool in the radial direction, and performing turning on the workpiece.

In addition, another machining system according to the present invention is a machining system for a workpiece, and the machining system includes: a machining apparatus configured to perform turning on the workpiece; a measuring apparatus configured to measure a processed dimension of the workpiece; and a controller configured to control driving of the machining apparatus and the measuring apparatus. The machining apparatus includes: a spindle apparatus configured to rotate the workpiece about a rotation axis; a first movement apparatus configured to move a turning tool in a radial direction of the rotation axis; a second movement apparatus configured to move the turning tool in parallel with the rotation axis; and a fourth movement apparatus having a movable range smaller than a movable range of the second movement apparatus in a direction parallel to the rotation axis, and configured to move the turning tool relative to the second movement apparatus in parallel with the rotation axis. The controller controls the driving of the machining apparatus and the measuring apparatus to perform the above-described another turning method.

In addition, another machining program according to the present invention is a machining program including an instruction for causing a machining apparatus to perform the above-described another turning method, and the machining apparatus includes: a first movement apparatus configured to move a turning tool in a radial direction of a rotation axis of a workpiece; a second movement apparatus configured to move the turning tool in parallel with the rotation axis; and a fourth movement apparatus configured to move the turning tool relative to the second movement apparatus in parallel with the rotation axis.

According to the invention, machine working for which a narrow dimensional tolerance is demanded can be provided by only turning, without depending on grinding. Brief Description of Drawings.

Hereinafter, a turning method, a machining system, and a machining program for a workpiece according to the present invention will be described in detail with reference to <FIG>.

First, a configuration of the machining system will be described with reference to <FIG>.

As illustrated in <FIG>, a machining system <NUM> includes a processing machine <NUM> and a controller <NUM>, which controls operations of the processing machine <NUM>. The controller <NUM> is capable of driving the processing machine <NUM> in accordance with a machining program <NUM>, which has been stored beforehand, can causing the processing machine <NUM> to automatically perform turning on a workpiece W. In addition, a robot <NUM>, which serves as a measuring apparatus for measuring a processed dimension of the workpiece W, is provided outside the processing machine <NUM>, and the controller <NUM> controls the driving of the robot <NUM> in a similar manner. Here, the controller <NUM> may be installed in a plurality of locations, and may include a control circuit connected with a communication unit. For example, some or all of control processes for driving the robot <NUM> may be conducted by a control circuit that is installed in another location different from the location where a control circuit for controlling the driving of the processing machine <NUM> is installed.

The processing machine <NUM> includes: a spindle apparatus <NUM>, which holds the workpiece W and which rotates the workpiece W about a rotation axis A; a tool post <NUM>, such as a turret, to which a turning tool <NUM> is fixed; a first movement apparatus <NUM>, which moves the turning tool <NUM> together with the tool post <NUM> in a radial direction of the rotation axis A to adjust the position of a cutting edge 12a of the turning tool <NUM>; and a second movement apparatus <NUM>, which moves the turning tool <NUM> together with the first movement apparatus <NUM> and the tool post <NUM> in parallel with the rotation axis A to adjust the position of the cutting edge 12a of the turning tool <NUM>. In addition, a third movement apparatus <NUM>, which is capable of moving the turning tool <NUM> relative to the tool post <NUM>, is provided between the tool post <NUM> and the turning tool <NUM>. It is to be noted that the turning tool <NUM> is disposed to extend substantially in parallel with the rotation axis A.

Here, the second movement apparatus <NUM> includes a carriage <NUM>, a linear guide <NUM>, a ball screw <NUM>, and a servomotor <NUM>. The carriage <NUM> is attached to the two rails of the linear guide <NUM>, which are provided on a base <NUM> of the processing machine <NUM>, and which extends in parallel with the rotation axis A. The carriage <NUM> is slidable along the linear guide <NUM>, and is further screwed by the ball screw <NUM>, which extends in parallel with the rotation axis A. The ball screw <NUM> is connected with the servomotor <NUM>. By driving the servomotor <NUM>, the ball screw <NUM> is rotated to enable the carriage <NUM> to move in parallel with the rotation axis A.

Furthermore, the first movement apparatus <NUM> includes: a tool post base <NUM>, which is connected with the tool post <NUM>; a linear guide <NUM>; a ball screw <NUM>; and a servomotor <NUM>. The tool post base <NUM> is attached to the two rails of the linear guide <NUM>, which are provided on the carriage <NUM> of the second movement apparatus <NUM>, and which extend in the radial direction of the rotation axis A. The tool post base <NUM> is slidable along the linear guide <NUM>, and is further screwed by the ball screw <NUM>, which extends in parallel with the linear guide <NUM>. The ball screw <NUM> is connected with the servomotor <NUM>. By driving the servomotor <NUM>, the ball screw <NUM> is rotated to enable the tool post base <NUM> of the first movement apparatus <NUM> to move relative to the carriage <NUM> of the second movement apparatus <NUM> in the radial direction of the rotation axis A.

The first movement apparatus <NUM> causes the turning tool <NUM> to be movable in the radial direction of the rotation axis A with respect to the workpiece W to be subject to turning, and a radial position of the cutting edge 12a is adjusted. In addition, the second movement apparatus <NUM> causes the turning tool <NUM> to be movable in a direction parallel to the rotation axis A with respect to the workpiece W to be subject to turning, and an axial position of the cutting edge 12a is adjusted. Thus, the cutting edge 12a of the turning tool <NUM> is adjusted to a cutting position, and it becomes possible to give a feed in turning. For the first movement apparatus <NUM> and the second movement apparatus <NUM>, a sufficient amount of movement corresponding to the size of the workpiece W has to be ensured in a feed accompanied by such turning and retraction to be described later. The first movement apparatus <NUM> and the second movement apparatus <NUM> each may have a movable range equal to or larger than <NUM> millimeters, for example.

Further, the third movement apparatus <NUM> is capable of moving the turning tool <NUM> relative to the first movement apparatus <NUM> in the radial direction of the rotation axis A. The third movement apparatus <NUM> is preferably higher in positional accuracy than the first movement apparatus <NUM>, and is smaller in movable range than the first movement apparatus <NUM>. The third movement apparatus <NUM> has a movable range in which an error of a processed dimension caused by semi-finishing processing of the workpiece W based on the positional accuracy of the first movement apparatus <NUM> is correctable in finishing processing, and is capable of determining the position of the cutting edge 12a with high accuracy. It is to be noted that the movable range of the third movement apparatus <NUM> may be equal to or smaller than one millimeter, for example. That is, the movable range of the third movement apparatus <NUM> may be <NUM>/<NUM> or less the movable range of the first movement apparatus <NUM>. Thus, the position of the cutting edge 12a, which has been adjusted by the first movement apparatus <NUM>, is further finely adjustable in the radial direction of the rotation axis A. Examples of the method for driving the third movement apparatus <NUM> may include elastic deformation of a tool holder by use of hydraulic pressure, the use of a linear motor, the use of a slider screwed with a ball screw rotated by a servomotor.

The robot <NUM>, which serves as a measuring apparatus, includes a measuring instrument <NUM> at a tip end of a robot arm <NUM>, inserts its tip end into the inside of the processing machine <NUM> from the outside of the machine in accordance with a drive command from the controller <NUM>, and is thus capable of measuring the processed dimension of the workpiece W, which is held by the spindle apparatus <NUM>. For example, an air gauge using an air micrometer of pneumatic type can be suitably used for the measuring instrument <NUM>.

Next, as an operation of the machining system <NUM>, a method for performing turning on an outer surface or an inner surface of the workpiece W will be described with reference to <FIG> together with <FIG> and <FIG>. It is to be noted that the workpiece W is held by the spindle apparatus <NUM>, in a state in which rough processing has been completed on the workpiece W.

Referring to <FIG> together with <FIG>, the workpiece W, which is held by the spindle apparatus <NUM>, is rotated about the rotation axis A. Then, the first movement apparatus <NUM> (see <FIG>) is driven to locate the cutting edge 12a of the turning tool <NUM>, which is attached to the tool post <NUM>, at a cutting position for the semi-finishing processing of the workpiece W, and positioning is performed (S <NUM>). Here, the cutting position for the semi-finishing processing is specified by a radial position in which a finishing allowance is left with respect to a target dimension in the finishing processing in consideration of the positional accuracy of the first movement apparatus <NUM> in the radial direction, and an axial position for starting a feed in performing turning in the axial direction parallel to the rotation axis A. Such an axial position is adjusted by the second movement apparatus <NUM>.

Then, as illustrated in <FIG>, the second movement apparatus <NUM> is driven to move the turning tool <NUM>, which is attached to the tool post <NUM>, together with the first movement apparatus <NUM> in a first direction DR1 toward the spindle apparatus <NUM> along a movement axis A', which is parallel to the rotation axis A, and turning as the semi-finishing processing is performed on the workpiece W (S2).

Here, as illustrated in <FIG>, after turning is performed to a predetermined position, the third movement apparatus <NUM> is preferably driven to separate the cutting edge 12a from the surface of the workpiece W.

Next, as illustrated in <FIG>, the second movement apparatus <NUM> is driven to move the tool post <NUM> in a second direction DR2, which is a reverse direction to the first direction DR1 along the movement axis A', which is parallel to the rotation axis A, and the turning tool <NUM> is retracted from the vicinity of the workpiece W (S3). In this situation, the driving of the first movement apparatus <NUM> is locked, and the first movement apparatus <NUM> does not move in the radial direction of the tool post <NUM>. In the retraction in this manner, as described above, the third movement apparatus <NUM> is driven to separate the cutting edge 12a from the surface of the workpiece W, so that an occurrence of a return mark can be prevented. It is to be noted that the occurrence of the return mark may not necessarily be prevented, and the driving of the third movement apparatus <NUM> for separating the cutting edge 12a from the surface of the workpiece W may be omitted.

Next, as illustrated in <FIG>, the processed dimension of the workpiece W is measured (S4). Here, the measurement is conducted by driving the robot <NUM>, which serves as the measuring apparatus, to insert the robot arm <NUM> from the outside of the processing machine <NUM> and bring the measuring instrument <NUM> into close proximity to the workpiece W. Since the turning tool <NUM> has been retracted as described above, the measuring instrument <NUM> can be brought into close proximity to the workpiece W. It is to be noted that, instead of the robot <NUM>, a measuring instrument provided in the machine may be used, or the measurement may be conducted manually by an operator. The processed dimension that has been measured is input, as a measurement result, into the controller <NUM>.

The controller <NUM> calculates a radial position of the cutting position for next finishing processing, based on the measurement result of the processed dimension of the workpiece W (S5). In detail, the radial position is determined to correct an error between a target value of a finished dimension and the processed dimension that has been measured. Then, the third movement apparatus <NUM> is driven to adjust the position of the turning tool <NUM> so as to locate the cutting edge 12a at the radial position that has been determined.

Next, as illustrated in <FIG>, as the finishing processing, the second movement apparatus <NUM> is driven to move the turning tool <NUM>, which is attached to the tool post <NUM>, again in the first direction DR1 along a movement axis A', which is parallel to the rotation axis A, and turning is performed on the workpiece W (S6).

Then, as illustrated in <FIG>, turning is performed to a predetermined position, and the finishing processing ends. After the finishing processing ends, the third movement apparatus <NUM> may be driven to separate the cutting edge 12a from the surface of the workpiece W.

Furthermore, the turning tool <NUM> is retracted (S7), and the finished dimension is measured (S8). Here, in a case where the finished dimension falls within a dimensional tolerance, the first movement apparatus <NUM> and the second movement apparatus <NUM> are returned to the original positions, and the turning processing ends (S9; Yes). In this situation, a correction value for the third movement apparatus <NUM> to correct an error in the finished dimension may be calculated to be used for next finishing processing.

In a case where the finished dimension does not fall within the dimensional tolerance, the remainder of the machining allowance is checked (S9; No). In a case where the finished dimension that has been measured is smaller than a predetermined one and no machining allowance remains (S10; Yes), an alarm is issued and then the processing ends. On the other hand, in a case where the finished dimension is larger than the predetermined one and the machining allowance remains (S10; No), the processing returns to the calculation of the cutting position in the finishing processing (S5), and performs the calculation again. It is to be noted that the driving of the processing machine10 and the driving of the robot <NUM> are each based on a command from the controller <NUM> in accordance with the machining program <NUM>.

By performing turning in the above-described method, the turning tool <NUM> is not moved by the first movement apparatus <NUM>, after the positioning in the semi-finishing processing (S1) until the finishing processing (S6). In other words, the position of the first movement apparatus <NUM> remains fixed at least until the finishing processing (S6). This makes the dimensional accuracy in the radial direction irrelevant to the positional accuracy of the first movement apparatus <NUM> in the finishing processing, and makes the dimensional accuracy in the radial direction dependent on the positional accuracy of the third movement apparatus <NUM>. As described above, the third movement apparatus <NUM> is higher in positional accuracy than the first movement apparatus <NUM>, and turning is enabled with such high positional accuracy. This also meets the demand for a narrow dimensional tolerance of, for example, <NUM> or less. That is, machine working for which the narrow dimensional tolerance is demanded is achievable by only turning, without depending on grinding.

It is to be noted that in a case of performing turning on a plurality of workpieces W successively, it is conceivable that the first movement apparatus <NUM> is not made to move, the movement is limited to only the direction parallel to the rotation axis A by the second movement apparatus <NUM>, and the finishing processing is performed by use of an identical correction value to omit the dimension measurement after the semi-finishing processing. However, a thermal displacement of the processing machine <NUM> caused by repeated machining and/or a plurality of times of repeated movements of the second movement apparatus <NUM> in the direction parallel to the rotation axis A can be assumed to degrade the dimensional accuracy in the radial direction. For this reason, the dimension measurement (S4) after the semi-finishing processing is preferably performed on each workpiece W every time.

In addition, the thermal displacement caused by successively performing turning on the plurality of workpieces W can also occur in the third movement apparatus <NUM>. On the other hand, as described above, the third movement apparatus <NUM> has a smaller movable range. Hence, the thermal displacement that occurs in the third movement apparatus <NUM> is much smaller than the thermal displacement in the first movement apparatus <NUM> or the second movement apparatus <NUM>, each of which has a larger movable range. Therefore, even in the case where the thermal displacement occurs due to successive machining, the machine working for which a narrow dimensional tolerance is demanded is achievable, according to the above-described turning method.

In addition, as illustrated in <FIG>, the turning tool <NUM> is also preferably arranged to extend substantially in parallel with the rotation axis A. Such an arrangement also enables turning to be performed, in the above-described method, on the inside of a circular recess C, which is centered around the rotation axis A in the workpiece W. That is, the cutting edge 12a of the turning tool <NUM> is inserted into the recess C to perform turning on the respective wall surfaces of an inner surface side and an outer surface side. Therefore, even though it is difficult to insert a grinding wheel into the recess or the like of the workpiece, or even though the grinding wheel is insertable but grinding requires time and labor, the machine working for which a narrow dimensional tolerance is demanded is achievable automatically and successively.

As illustrated in <FIG>, in the case of performing turning on the workpiece W having a long size in the direction along the rotation axis A, it is desirable to arrange a steady rest <NUM>, which supports the workpiece W, between the spindle apparatus <NUM> and the cutting position of the turning tool <NUM> for cutting the workpiece W, in a similar manner to other cases of turning. Such an arrangement also enables turning to be performed in a similar manner as described above.

It is to be noted that even in a case of performing only finishing processing without performing the semi-finishing processing, by applying the same method from the measurement of the processed dimension (S4) that has been described above, the machine working for which a narrow dimensional tolerance is demanded is achievable by only turning. In addition, the turning method that has been described above is usable for performing turning on the inner surface and the outer surface of the workpiece. The processing machine <NUM> may be another type of processing machine, such as the turret lathe or the combined processing machine described above.

Next, a turning method for performing turning on an end surface that is a surface orthogonal to the rotation axis A in the workpiece will be described. First, a configuration of the processing machine will be described.

As illustrated in <FIG>, a processing machine <NUM>' is common to the processing machine <NUM>, which has been described above, except some components. What is mainly different is that a fourth movement apparatus <NUM>', which moves a turning tool <NUM>' in parallel with the rotation axis A, is provided instead of the third movement apparatus <NUM>, which moves the turning tool <NUM> in the radial direction of the rotation axis A. Specifically, in contrast to the processing machine <NUM>, in the processing machine <NUM>', with regard to the tool post <NUM>, the entire movement apparatus including the turning tool is exchanged. In a case where a turret is used as the tool post <NUM>, such a turret is rotated to complete this exchange. The other components such as the first movement apparatus <NUM> and the second movement apparatus <NUM> are similar to those of the processing machine <NUM>.

The fourth movement apparatus <NUM>' is also higher in positional accuracy than the second movement apparatus <NUM>, as in the case of the third movement apparatus <NUM>. Therefore, the fourth movement apparatus <NUM>' preferably has a movable range smaller than that of the second movement apparatus <NUM>. The fourth movement apparatus <NUM>' has a movable range in which an error of the processed dimension caused by the semi-finishing processing on the workpiece W based on the positional accuracy of the second movement apparatus <NUM> is correctable in the finishing processing, and the position of a cutting edge <NUM>'a can be determined with high accuracy. It is to be noted that the movable range of the fourth movement apparatus <NUM>' may be equal to or smaller than one millimeter, for example. That is, the movable range of the fourth movement apparatus <NUM>' may be <NUM>/<NUM> or less the movable range of the second movement apparatus <NUM>.

Other details of the fourth movement apparatus <NUM>' are similar to those of the third movement apparatus <NUM>, and thus the descriptions will be omitted.

Next, a turning method for performing turning on an end surface of the workpiece W by use of the processing machine <NUM>' will be described.

Referring to <FIG> together with <FIG>, the workpiece W, which is held by the spindle apparatus <NUM>, is rotated about the rotation axis A. Then, the second movement apparatus <NUM> (see <FIG>) is driven to locate the cutting edge <NUM>'a of the turning tool <NUM>', which is attached to the tool post <NUM>, at a cutting position for the semi-finishing processing of the workpiece W, and positioning is performed (S <NUM>). Here, the cutting position for the semi-finishing processing is specified by an axial position in which a finishing allowance is left with respect to a target dimension in the finishing processing in consideration of the positional accuracy of the second movement apparatus <NUM> in the axial direction parallel to the rotation axis A, and a radial position for starting a feed in performing turning in the radial direction of the rotation axis A. Such a radial position is adjusted by the first movement apparatus <NUM>.

Then, as illustrated in <FIG>, the first movement apparatus <NUM> is driven to move the turning tool <NUM>', which is attached to the tool post <NUM>, in a third direction DR3 toward the rotation center of the rotation axis A in the workpiece W and along a movement axis R in the radial direction of the rotation axis A, and turning as the semi-finishing processing is performed on an end surface of the workpiece W (S2).

Here, as illustrated in <FIG>, after turning is performed to a predetermined position, the fourth movement apparatus <NUM>' is preferably driven to separate the cutting edge <NUM>'a from the surface of the workpiece W.

Next, as illustrated in <FIG>, the first movement apparatus <NUM> is driven to move the turning tool <NUM>', which is attached to the tool post <NUM>, in a fourth direction DR4, which is a reverse direction to the third direction DR3, along the movement axis R in the radial direction of the rotation axis A, and the turning tool <NUM>' is retracted from the vicinity of the workpiece W (S3). In this situation, the driving of the second movement apparatus <NUM> is locked, and the second movement apparatus <NUM> does not move in a direction parallel to the rotation axis A of the tool post <NUM>. In the retraction in this manner, the fourth movement apparatus <NUM>' as described above is driven to separate the cutting edge <NUM>'a from the surface of the workpiece W, so that an occurrence of a return mark can be prevented. It is to be noted that the occurrence of the return mark may not necessarily be prevented, and the driving of the fourth movement apparatus <NUM>' for separating the cutting edge <NUM>'a from the surface of the workpiece W may be omitted.

Next, as illustrated in <FIG>, the processed dimension of the workpiece W is measured (S4). For example, the distance between end surfaces is measured by a measuring instrument <NUM>' having a caliper-like shape, so that the distance can be set as a processed dimension. The processed dimension that has been measured is input, as a measurement result, into the controller <NUM>.

The controller <NUM> calculates an axial position of the cutting position for next finishing processing, based on the measurement result of the processed dimension of the workpiece W (S5). In detail, the axial position is determined to correct an error between a target value of the finished dimension and the dimension that has been measured. Then, the fourth movement apparatus <NUM>' is driven to adjust the position of the turning tool <NUM>' so as to locate the cutting edge <NUM>'a at the axial position that has been determined.

Next, as illustrated in <FIG>, as the finishing processing, the first movement apparatus <NUM> is driven to move the turning tool <NUM>', which is attached to the tool post <NUM>, again in the third direction DR3 along the movement axis R in the radial direction of the rotation axis A, and turning is performed on the workpiece W (S6).

Then, as illustrated in <FIG>, turning is performed to a predetermined position, and the finishing processing ends. Other details of the turning method are similar to those of the turning method by the above-described processing machine <NUM>, and thus the descriptions will be omitted.

By performing turning in the above-described method, the turning tool <NUM>' is not moved by the second movement apparatus <NUM>, after the positioning in the semi-finishing processing (S1) until the finishing processing (S6). In other words, the driving of the second movement apparatus <NUM> remains locked at least until the finishing processing (S6). This makes the dimensional accuracy in a direction parallel to the rotation axis A irrelevant to the positional accuracy of the second movement apparatus <NUM> in the finishing processing, and makes the dimensional accuracy dependent on the positional accuracy of the fourth movement apparatus <NUM>'. As described above, the fourth movement apparatus <NUM>' is higher in positional accuracy than the second movement apparatus <NUM>, and turning is enabled with such high positional accuracy. This also meets the demand for a narrow dimensional tolerance of, for example, <NUM> or less. That is, machine working for which the narrow dimensional tolerance is demanded is achievable by only turning, without depending on grinding.

While exemplary embodiments according to the present invention and accompanying variations thereof have been described above, the present invention is not limited thereto, i.e. the scope of the present invention is defined by the appended claims.

Claim 1:
A turning method for a workpiece (W) rotatable about a rotation axis (A), the turning method comprising:
driving a first movement apparatus (<NUM>) for moving a turning tool (<NUM>) in a radial direction of the rotation axis (A) to locate a cutting edge (12a) of the turning tool (<NUM>) at a first radial position in the radial direction;
driving a second movement apparatus (<NUM>) for moving the turning tool (<NUM>) in parallel with the rotation axis (A), performing turning on the workpiece (W), and then moving the turning tool (<NUM>) in a reverse direction to retract the turning tool (<NUM>) from the workpiece (W);
measuring a processed dimension of the workpiece (W), and calculating an error between the processed dimension that has been measured and a target dimension;
characterised in that the turning method further comprises :
driving a third movement apparatus (<NUM>) for moving the turning tool (<NUM>) relative to the first movement apparatus (<NUM>) in the radial direction of the rotation axis (A) to locate the cutting edge (12a) of the turning tool (<NUM>) at a second radial position so as to correct the error; and
driving the second movement apparatus (<NUM>) to move the turning tool (<NUM>) in parallel with the rotation axis (A), and performing turning on the workpiece (W).