Patent Description:
<CIT> describes a method for moving a tailstock at a temporary pressing speed and pressing the tailstock against a workpiece, and when an electric current value of a servo motor that moves the tailstock exceeds a threshold, the tailstock is pressed at a control speed that is lower than the temporary pressing speed.

In the method described in <CIT>, there is a problem that the target pressing force cannot be accurately controlled by the servo motor, because distortion of the workpiece and/or the tailstock that occurs when pressed at the temporary pressing speed cannot be eliminated.

Further known methods for pressing a tailstock of a machining apparatus are, for example, shown in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

It is the object of the present invention to provide a method for pressing a tailstock of a machining apparatus, a machining apparatus, a computer program, and a computer-readable storage medium, which are capable of pressing the tailstock with a desired target pressing force, while suppressing distortion of a workpiece and/or the tailstock.

The object of the present invention is achieved by a method for pressing a tailstock of a machining apparatus having the features of claim <NUM>, a machining apparatus having the features of claim <NUM>, a computer program having the features of claim <NUM>, and a computer-readable storage medium having the features of claim <NUM>.

A method for pressing a tailstock of a machining apparatus according to an advantage of the present invention includes setting a target pressing force for pressing the tailstock against a workpiece attached to a spindle in a first direction along a rotation axis of the spindle. The method includes driving an actuator for controlling a movement of the tailstock and a pressing force for pressing the tailstock against the workpiece to move the tailstock in the first direction at a first speed. The method includes detecting pressing of the tailstock against the workpiece based on a change in an input amount into the actuator. The method includes, upon detection of the pressing, controlling the actuator to stop the movement of the tailstock. The method includes driving the actuator to move the tailstock by a first distance in a second direction opposite to the first direction. The method includes driving the actuator to move the tailstock in the first direction at a second speed lower than the first speed. The method includes controlling the actuator to stop the tailstock, upon the input amount into the actuator becoming a value corresponding to the target pressing force while the tailstock is moving at the second speed. The target pressing force and the first speed are desirably determined, based on the material and the shape of the workpiece, the machining condition, and the like. Regarding the second speed, an impact force when the tailstock abuts the workpiece at the second speed desirably falls within a predetermined range.

Preferably, the first distance is larger than a theoretical value of a distortion amount of the workpiece that occurs due to the pressing.

Preferably, a threshold of the input amount for detecting the pressing is optionally settable. It is to be noted that the threshold of the input amount is desirably set, based on the material and the shape of the workpiece, the machining condition, and the like.

Preferably, the method further includes driving the actuator to move the tailstock at a third speed higher than the first speed to a position separate from the workpiece by a predetermined distance in the second direction, before moving the tailstock at the first speed.

Preferably, the actuator is a servo motor, and the input amount is an electric current value supplied to the servo motor.

Preferably, the method further includes attaching one end of the workpiece to the spindle for the workpiece to rotate together with the spindle about the rotation axis of the spindle.

Preferably, the method further includes upon detection of the pressing, opening a workpiece holder by an allowable amount, the workpiece holder being configured to hold the workpiece, and after opening the workpiece holder, closing the workpiece holder again to hold the workpiece.

Preferably, the workpiece holder includes a chuck, and one end of the workpiece is attached to the spindle via the chuck.

Preferably, the actuator presses the tailstock against another end of the workpiece on an opposite side to the one end of the workpiece in an axial direction of the rotation axis of the spindle.

Preferably, the workpiece holder further includes at least one steady rest, and each of the at least one steady rest is configured to support an intermediate portion of the workpiece between the one end and the another end for the workpiece to be rotatable about the rotation axis.

According to another advantage of the present invention, a machining apparatus includes a spindle, a tailstock, an actuator, and means for performing the method according to the present invention. To the spindle, one end of a workpiece is attached, and the spindle is configured to rotate together with the workpiece about a rotation axis. The tailstock is arranged to face the spindle in an axial direction along the rotation axis, is configured to be movable in the axial direction, and is configured to be pressed against another end of the workpiece on an opposite side to the one end of the workpiece. The actuator is configured to control a movement of the tailstock and a pressing force for pressing the tailstock against the workpiece. The means for performing the method may include an electronic circuit. The electronic circuit may include a processor.

According to a further advantage of the present invention, a machining apparatus includes a spindle, a tailstock, an actuator, a workpiece holder, and means for performing the method according to the present invention. To the spindle, one end of a workpiece is attached, and the spindle is configured to rotate together with the workpiece about a rotation axis. The tailstock is arranged to face the spindle in an axial direction along the rotation axis, is configured to be movable in the axial direction, and is configured to be pressed against another end of the workpiece on an opposite side to the one end of the workpiece. The actuator is configured to control a movement of the tailstock and a pressing force for pressing the tailstock against the workpiece. The workpiece holder is configured to hold the workpiece. The means for performing the method may include an electronic circuit. The electronic circuit may include a processor.

A computer program according to a further advantage of the present invention includes an instruction for causing the machining apparatus to perform the method according to the present invention.

A computer-readable storage medium according to yet a further advantage of the present invention records the computer program.

In the method according to the present invention, the machining apparatus including the means for performing the method, the computer program including the instruction for causing the machining apparatus to perform the method, and the storage medium storing the computer program, upon detection of the pressing of the tailstock against the workpiece, the tailstock is separated from the work, and the tailstock is caused to abut the workpiece at the second speed lower than the first speed. This eliminates distortion of the workpiece and/or the tailstock that occurs when the workpiece is pressed at the first speed, and the target pressing force is accurately controlled by the actuator. In addition, the tailstock is initially moved nearer to the workpiece at a high speed, and then the tailstock is caused to abut the workpiece at a low speed from the vicinity of the workpiece. Therefore, the time for abutting the tailstock against the workpiece can be shortened and production efficiency can be improved.

Preferably, after the pressing of the tailstock against the workpiece is detected, the tailstock is reliably separated from the workpiece.

Preferably, an optimum threshold can be set, based on the axial length of the workpiece, the material of the workpiece, the required accuracy, and the like.

Preferably, the tailstock can be moved to the vicinity of the workpiece at a high speed, and therefore the machining time of the workpiece can be shortened.

Preferably, the servo motor can be used as the actuator, and therefore the tailstock can be moved at a high speed.

Preferably, the workpiece is automatically attachable, and therefore mass production of the workpieces can be efficiently conducted.

Preferably, the workpiece is attachable to the workpiece holder with high accuracy.

Preferably, the workpiece is attachable to the spindle with high accuracy.

Preferably, in order to press the workpiece against the spindle from the opposite side of the spindle, the workpiece is attachable to the spindle with higher accuracy.

Preferably, the workpiece is attachable to the steady rest with high accuracy. Advantageous Effects of Invention.

According to the technique disclosed in the present application, a method for pressing a tailstock of a machining apparatus, a machining apparatus, a computer program, and a computer-readable storage medium are provided, which are capable of pressing a tailstock with a desired target pressing force, while suppressing distortion of a workpiece and/or the tailstock.

This invention will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.

<FIG> is an external configuration diagram of a machining apparatus <NUM> according to an embodiment of the present invention. The machining apparatus <NUM> is, for example, a composite machining lathe. The machining apparatus <NUM> includes a base <NUM>, a workpiece headstock <NUM>, a spindle <NUM>, a chuck <NUM>, a steady rest <NUM>, a carriage <NUM>, a tool headstock <NUM>, a tool spindle <NUM>, and a tailstock <NUM>. The workpiece headstock <NUM> is provided at one end of the base <NUM>. The workpiece headstock <NUM> supports the spindle <NUM> to be rotatable about a rotation axis Ax. That is, one end of a workpiece W is attached to the spindle <NUM>, and the spindle <NUM> is configured to rotate about the rotation axis Ax together with the workpiece W. In the following description, a direction along the rotation axis Ax will be referred to as a Z-axis direction, a direction along the rotation axis Ax and the height direction of the machining apparatus <NUM> will be referred to as an X-axis direction, and a direction perpendicular to the Z-axis direction and the X-axis direction will be referred to as a Y-axis direction. In addition, the Z-axis direction may be simply referred to as an axial direction.

The chuck <NUM> is provided on the spindle <NUM>. The chuck <NUM> is configured to rotate together with the spindle <NUM> about the rotation axis Ax. The chuck <NUM> is configured to hold one end of the workpiece W. That is, one end of the workpiece W is attached to the spindle <NUM> via the chuck <NUM>. The steady rest <NUM> is configured to support an intermediate portion of the workpiece W for the workpiece W to be rotatable about the rotation axis Ax. This configuration prevents chatter vibration during machining of the workpiece W, in particular, in a case where the workpiece W has a long shape. The intermediate portion of the workpiece W is located between the above-described one end of the workpiece W and the other end thereof on an opposite side to the above-described one end of the workpiece W in the axial direction. In the following description, the chuck <NUM> and the steady rest <NUM> will be collectively referred to as a workpiece holder WS. Therefore, the workpiece holder WS is configured to hold the workpiece W, and includes at least the chuck <NUM>. It is to be noted that the workpiece holder WS may include the steady rest <NUM>. In addition, although one steady rest <NUM> is illustrated in <FIG>, the number of the steady rests <NUM> may be two or more.

The carriage <NUM> is provided on the base <NUM>, and is movable in the Z-axis direction. The carriage <NUM> slides on a rail, not illustrated, provided on the base <NUM>. The tool headstock <NUM> is mounted to be movable on a surface, of the carriage <NUM>, facing the workpiece W. The tool headstock <NUM> is movable in the X-axis direction and the Y-axis direction, and is rotatable about a B axis, which is parallel to Y axis, and which serves as a rotation axis passing through a specific point of the carriage <NUM>. The tool spindle <NUM> is provided on the tool headstock <NUM>. A tool T is attachable to the tool spindle <NUM>, and the tool spindle <NUM> is configured to drive the rotation of the tool T.

The tailstock <NUM> is provided on the other end side of the base <NUM>, and is arranged to face the workpiece headstock <NUM> in the axial direction along the rotation axis Ax. The tailstock <NUM> includes a tailstock spindle <NUM>. The tailstock spindle <NUM> is rotatable about the rotation axis Ax relative to the tailstock <NUM>, and is configured to press the workpiece W, which is held by the workpiece headstock <NUM>. The machining apparatus <NUM> includes an actuator ACT and a linear motion mechanism LMM for moving the tailstock <NUM> in the axial direction. The actuator ACT is, for example, a servo motor <NUM>. The servo motor <NUM> generates a rotational force for moving the tailstock <NUM>. The linear motion mechanism LMM includes a linear guide <NUM> and a ball screw <NUM>. The linear guide <NUM> is provided on the base <NUM>, and extends in parallel with the Z-axis direction. The ball screw <NUM> is disposed on the base <NUM> such that its longitudinal direction is parallel to the Z-axis direction. The ball screw <NUM> is connected with the servo motor <NUM>, and converts the rotational force of the servo motor <NUM> into a drive force in the Z-axis direction of the tailstock <NUM>. It is to be noted that a speed reduction mechanism, not illustrated, may be added to the output shaft of the servo motor <NUM>, and the servo motor <NUM> and the ball screw <NUM> may be connected with each other via the speed reduction mechanism. It is to be noted that regarding the Z-axis direction, a direction from the tailstock <NUM> toward the spindle <NUM> will be referred to as a Z-axis negative direction or a first direction D1, and its reverse direction will be referred to as a Z-axis positive direction or a second direction D2.

The machining apparatus <NUM> further includes a servo driver <NUM> and a sensor <NUM> (for example, an encoder) for controlling the rotation speed and the torque of the servo motor <NUM>. Thus, the actuator ACT is configured to control the movement of the tailstock <NUM> and the pressing force for pressing the tailstock <NUM> against the workpiece W. In addition, the tailstock <NUM> is configured to be movable in the axial direction and to be pressed against the other end of the workpiece W on an opposite side to one end thereof.

The machining apparatus <NUM> includes a cover, not illustrated, for covering instruments, and an operation panel <NUM>. The operation panel <NUM> includes a display for displaying information through images for a user and/or a speaker for providing information through sounds for the user. Other than this, the operation panel <NUM> also includes a servo driver <NUM>, a controller CL for controlling the machining apparatus <NUM>, and an input device for receiving an input from the user. The servo driver <NUM> may be disposed outside the operation panel <NUM>. The controller CL is a so-called numerical value controller. The detailed configuration of the controller CL will be described later.

<FIG> is a block diagram illustrating an internal configuration of the controller CL. Referring to <FIG>, the controller CL includes a processor <NUM> and a memory <NUM>. That is, the machining apparatus <NUM> further includes the processor <NUM> and the memory <NUM>. The processor <NUM> is, for example, an electronic circuit such as a central processing unit (CPU). The memory <NUM> is configured to store a control program PG for controlling the machining apparatus <NUM> and to also store control data DAT. Such a control program PG is a computer program including instructions to be executed by the machining apparatus <NUM>. By reading the control program PG from the memory <NUM> and executing the control program PG, the processor <NUM> controls the spindle <NUM>, the tool spindle <NUM>, the chuck <NUM>, the steady rest <NUM>, the actuator ACT (servo motor <NUM>), and the like. The control data DAT includes predetermined parameters for controlling the movement of the tailstock <NUM>.

The controller CL further includes a first Input-Output interface <NUM>, a second Input-Output interface <NUM>, a bus <NUM>, a power supply, not illustrated, and the like. The first Input-Output interface <NUM> is connected with the operation panel <NUM>. The first Input-Output interface <NUM> outputs images and sounds on the operation panel <NUM>, and receives an input from a key, a touch panel, or the like of the operation panel <NUM>. The bus <NUM> connects the processor <NUM>, the memory <NUM>, the first Input-Output interface <NUM>, the second Input-Output interface <NUM>, and the like to one another.

The second Input-Output interface <NUM> is connected with the servo driver <NUM>, the chuck <NUM>, the steady rest <NUM>, and the like. In the present embodiment, in order to conduct speed control or position control of the servo motor <NUM>, the processor <NUM> outputs a command signal S1 for communicating a speed command value or a position command value to the servo driver <NUM> via the second Input-Output interface <NUM>, while executing the control program PG. The servo driver <NUM> outputs a drive current to the servo motor <NUM> by use of a well-known method such as PID control, so that the rotation speed or the rotation angle corresponding to the command signal S1 is achieved. In such a situation, the servo driver <NUM> receives an input of a signal from the sensor <NUM>, and controls the drive current through feedback control. The servo driver <NUM> outputs a feedback signal S2 for communicating the value of the controlled drive current to the second Input-Output interface <NUM>. Such a feedback signal S2 is sent to the processor <NUM>. It is to be noted that since the function of the servo driver <NUM> as described above is well known, a detailed description thereof will be omitted.

The speed command value of the command signal S1 described above is a value corresponding to the rotation speed of the servo motor <NUM>. The feed rate of the tailstock <NUM> is proportional to the rotation speed of the servo motor <NUM>. Here, it is assumed that Nm [min-<NUM>] denotes a rotation speed of the motor, P [mm] denotes a lead of the ball screw <NUM> (the distance that the tailstock <NUM> travels per one rotation of the ball screw <NUM>), A denotes a reduction ratio of the speed reduction mechanism that decelerates the output of the servo motor <NUM>, and Vf [mm/min] denotes a feed rate of the tailstock <NUM>. In this situation, the following formula is satisfied. [Mathematical Formula <NUM>] <MAT>.

In the above formula, in a case where the speed reduction mechanism is not applied to the servo motor <NUM>, A = <NUM> may be set. In this manner, by outputting the command signal S1, the processor <NUM> is capable of controlling the feed rate of the tailstock <NUM>. In addition, it is known that the servo motor <NUM> outputs torque proportional to a drive current value. Therefore, by multiplying a drive current value extracted from the feedback signal S2 by a torque multiplier or the like specific to the servo motor <NUM>, the processor <NUM> is capable of calculating the output torque of the servo motor <NUM>.

Furthermore, it is known that when the servo motor <NUM> applies the torque to the ball screw <NUM> and rotates the ball screw <NUM>, a thrust force (thrust) received by the tailstock <NUM> from the ball screw <NUM> is proportional to the torque of the servo motor <NUM>. For example, it is assumed that Tm [N·mm] denotes torque generated by the motor, P [mm] denotes a lead of the ball screw <NUM>, η denotes efficiency, and Fa [N] denotes a thrust force received by the tailstock <NUM>. It is to be noted that the efficiency η is efficiency in consideration of all conversion mechanisms that convert a rotational motion of the servo motor <NUM> into a linear motion of the tailstock <NUM>, and in a case where the conversion mechanism includes the speed reduction mechanism that decelerates the output of the servo motor <NUM>, the efficiency η results in a value obtained by multiplying the reduction ratio A. In this situation, the following formula is satisfied. [Mathematical Formula <NUM>] <MAT>.

While the tailstock <NUM> is in abutment with the workpiece W, the thrust force Fa corresponds to the pressing force for pressing the tailstock <NUM> against the workpiece W. Therefore, the processor <NUM> is capable of estimating the magnitude of the pressing force from the feedback signal S2. In addition to the above description, while executing the control program PG, the processor <NUM> outputs a signal for controlling opening or closing of the chuck <NUM> to the chuck <NUM> via the second Input-Output interface <NUM>. While executing the control program PG, the processor <NUM> outputs either a signal for closing the clamp of the steady rest <NUM> or a signal for opening the clamp of the steady rest <NUM> to the steady rest <NUM> via the second Input-Output interface <NUM>.

Next, the relationship between the drive current of the servo motor <NUM> and the pressing force by the tailstock <NUM> will be described. In <FIG>, instead of the workpiece W, a load cell is attached to the spindle <NUM>, the command signal S1 is sent from the processor <NUM> to the servo driver <NUM> so as to move the tailstock <NUM> in the first direction D1 at feed rates of (<NUM>) <NUM>/min, (<NUM>) <NUM>/min, (<NUM>) <NUM>/min, and (<NUM>) <NUM>/min. When a drive current having a drive current value corresponding to a target pressing force (<NUM> kN) is supplied from the servo driver <NUM> to the servo motor <NUM>, and in a case where the command signal S1 is sent from the processor <NUM> to the servo driver <NUM> so as to stop the movement of the tailstock <NUM>, temporal changes in the pressing force received by the load cell from the tailstock <NUM> are illustrated. For convenience in comparison among the cases (<NUM>) to (<NUM>), time <NUM> indicates the time when the drive current having the drive current value corresponding to the target pressing force (<NUM> kN) is supplied from the servo driver <NUM> to the servo motor <NUM>.

Referring to <FIG>, as the speed of the tailstock <NUM> when the tailstock <NUM> abuts the workpiece W is faster, the workpiece W is deformed by an impact force (impact) at the time of abutment. Then, even though the movement of the tailstock <NUM> is stopped, the servo motor <NUM> will press the tailstock <NUM> against the workpiece W with a pressing force higher than the target pressing force. Specifically, it is assumed that the workpiece W has a cylindrical shape, that is, a cross-section perpendicular to the axial direction of the workpiece W is circular and uniform. In addition, it is assumed that A [mm<NUM>] denotes a cross-sectional area of the workpiece W, l [mm] denotes the axial length of the workpiece W, E [MPa] denotes Young's modulus of the material of the workpiece W, M [kg] denotes a mass of the tailstock <NUM>, V [mm/sec] denotes a feed rate of the tailstock <NUM> when the tailstock <NUM> abuts the workpiece W, and σe [MPa] denotes stress applied to the workpiece W. In this situation, the following formula is satisfied. [Mathematical Formula <NUM>] <MAT>.

By solving this, σe is obtained by the following formula. [Mathematical Formula <NUM>] <MAT>.

Such stress σe is applied to the workpiece W, in addition to the above-described thrust force Fa. Hence, as illustrated in <FIG>, the pressing force by the tailstock <NUM> when the tailstock <NUM> abuts the workpiece W will deviate from the target pressing force, as the feed rate of the tailstock <NUM> increases. For this reason, after causing the tailstock <NUM> to abut the workpiece W, the machining apparatus <NUM> according to the present embodiment causes the tailstock <NUM> to move backward in the second direction D2 by a distance larger than an amount of distortion in which the workpiece W is distorted in the axial direction by an impact force (impact) at the time of abutment of the tailstock <NUM>. Then, the machining apparatus <NUM> moves the tailstock <NUM> in the first direction D1 at a low speed to reduce a distortion amount ΔLe of the workpiece W distorted in the axial direction, and presses the tailstock <NUM> against the workpiece W.

The distortion amount ΔLe, in which the workpiece W is distorted in the axial direction, is obtained as follows. First, distortion εe, in which the workpiece W is distorted in the axial direction by the impact force (impact) at the time of abutment of the tailstock <NUM>, is obtained by the following formula. [Mathematical Formula <NUM>] <MAT>.

Then, the distortion amount ΔLe, in which the workpiece W is distorted in the axial direction by the impact force (impact) at the time of abutment of the tailstock <NUM>, is obtained by the following formula. The distortion amount ΔLe will be referred to as a theoretical value of the distortion amount. [Mathematical Formula <NUM>] <MAT>.

The control data DAT includes the following data [<NUM>] to [<NUM>] in order to control the movement of the tailstock <NUM>.

An operator is able to optionally set the above data [<NUM>] to [<NUM>]. The target pressing force of [<NUM>] is determined beforehand by the operator, based on the material and the shape of the workpiece W, the machining condition, and the like. The first speed V<NUM> of [<NUM>] is determined beforehand by the operator, based on the material and the shape of the workpiece W, and the machining condition (production time), and the like. For the second speed V<NUM> of [<NUM>], the speed (<NUM>/min in <FIG>) at which the stress σe (impact force) obtained by the formula (<NUM>) falls within a predetermined range (the influence of the impact force is substantially eliminated) is determined beforehand by the operator. The threshold of the input amount of the actuator ACT of [<NUM>] is determined beforehand, based on the material and the shape of the workpiece W, the machining condition, and the like. For the first distance of [<NUM>], the value obtained by adding an offset to the theoretical value ΔLe of the distortion amount that has been calculated based on the first speed V<NUM> is determined beforehand by the operator. That is to say, the first distance is longer than the theoretical value ΔLe of the distortion amount of the workpiece W that occurs due to the pressing. It is to be noted that details of the position command value corresponding to the first distance will be described later.

It is to be noted that each piece of the data [<NUM>] to [<NUM>] may be calculated by the processor <NUM>, based on the material and the shape of the workpiece W, the machining condition (production time) that have been input beforehand by the machining program for the machining apparatus <NUM> to machine the workpiece W, and various parameters for calculating the formulas (<NUM>) to (<NUM>). In such a case, the control data DAT may further include the material and the shape of the workpiece W, the machining condition (production time), and various parameters for calculating the formulas (<NUM>) to (<NUM>).

In the following, a method for controlling the pressing of the tailstock <NUM> will be described. <FIG> is a flowchart illustrating a processing flow of a first pressing method for pressing the tailstock <NUM> in the present embodiment. The first pressing method is a method for pressing the tailstock <NUM>, in a case where the operator manually attaches the workpiece W to the spindle <NUM> and then presses the tailstock <NUM> against the workpiece W. Each step in the first pressing method is achievable by the processor <NUM> executing the control program PG.

In step S11, the method sets, in the axial direction of the rotation axis Ax of the spindle <NUM>, a target pressing force for pressing the tailstock <NUM> in the first direction along the rotation axis Ax on the other end of the workpiece W on an opposite side to one end thereof that is attached to the spindle <NUM> so as to rotate together with the spindle <NUM>. The setting of such a target pressing force may be input into the controller CL by the operator by use of the operation panel <NUM>. The target pressing force that has been input in this manner is stored as the control data DAT in the memory <NUM>. It is to be noted that in step S11, instead of the target pressing force, the torque of the servo motor <NUM> and/or the drive current value for the servo motor <NUM>, as indicated in the data [<NUM>], may be set. Even though these values are set, each setting of these values is substantially the same as the setting of the target pressing force.

In step S12, the method drives the actuator ACT (servo motor <NUM>) that controls the movement of the tailstock <NUM> and the pressing force for pressing the tailstock <NUM> against the workpiece W so as to move the tailstock <NUM> in the first direction D1 at the first speed V<NUM>. Specifically, the processor <NUM> reads, from the memory <NUM>, either the first speed V<NUM> or the speed command value corresponding to the first speed V<NUM>, stored as the control data DAT. Then, the processor <NUM> generates a command signal S1 for moving the tailstock <NUM> in the first direction D1 at the first speed V<NUM>, based on the data that has been read, and sends the command signal S1 to the servo driver <NUM>.

In step S13, the method detects pressing of the tailstock <NUM> against the workpiece W, based on a change in the input amount into the actuator ACT (servo motor <NUM>) for moving the tailstock <NUM>. In a case where the pressing is not detected (No in step S13), step S13 is repeated. The input amount is a current value supplied to the servo motor <NUM>. Specifically, in a case where the drive current value extracted from the feedback signal S2 exceeds a threshold, the processor <NUM> determines that the pressing of the tailstock <NUM> has been done against the workpiece W. It is to be noted that in step S13, instead of the threshold of the drive current value, the pressing may be determined, based on the thrust force corresponding to the threshold of the drive current value indicated in the data [<NUM>] and the value of the torque of the servo motor <NUM> corresponding to the threshold of the drive current. Even though the pressing is determined with these values, it is substantially the same as the determination based on the change in the input amount into the actuator ACT (servo motor <NUM>).

In step S14, upon detection of the pressing (Yes in step S13), the method controls the actuator ACT (servo motor <NUM>) to stop the movement of the tailstock <NUM>. Specifically, the processor <NUM> generates a command signal S1 including a speed command for setting the speed of the tailstock <NUM> to zero, and sends the command signal S1 to the servo driver <NUM>.

In step S15, the method drives the actuator ACT (servo motor <NUM>) to move the tailstock <NUM> by the first distance in the second direction D2, which is opposite to the first direction D1, along the rotation axis Ax. Specifically, it is assumed that L<NUM> [mm] denotes the first distance, P [mm] denotes the lead of the ball screw <NUM>, A denotes the reduction ratio of the speed reduction mechanism that decelerates the output of the servo motor <NUM>, and θ [deg] denotes a rotation angle of the servo motor <NUM>. In this situation, the rotation angle θ [deg] of the servo motor <NUM> necessary for the tailstock <NUM> to move by the first distance L<NUM> [mm] is expressed by the following formula. [Mathematical Formula <NUM>] <MAT>.

The processor <NUM> reads the first distance L<NUM> from the memory <NUM>, calculates the rotation angle θ, based on the formula (<NUM>), generates a command signal S1 including a position command value for rotating the servo motor <NUM> by the rotation angle θ, and sends the command signal S1 to the servo driver <NUM>. It is to be noted that in a case where the control data DAT includes the position command value to be output to the servo driver <NUM> for moving the tailstock <NUM> by the first distance L<NUM>, the processor <NUM> may read the position command value from the memory <NUM>, may generate the command signal S1 including the position command value, and may send the command signal S1 to the servo driver <NUM>.

In step S16, the method drives the actuator ACT (servo motor <NUM>) to move the tailstock <NUM> in the first direction D1 at the second speed V<NUM>, which is lower than the first speed V<NUM>. Specifically, the processor <NUM> reads, from the memory <NUM>, either the second speed V<NUM> or the speed command value corresponding to the second speed V<NUM>, stored as the control data DAT. Then, the processor <NUM> generates a command signal S1 for moving the tailstock <NUM> in the first direction D1 at the second speed V<NUM>, based on the data that has been read, and sends the command signal S1 to the servo driver <NUM>.

In step S17, the method determines whether the input amount (drive current value) into the actuator ACT (servo motor <NUM>) has become a value corresponding to the target pressing force, while the tailstock <NUM> is moving at the second speed V<NUM>. In a case where the input amount (drive current value) has not become the value corresponding to the target pressing force (No in step S17), step S17 is repeated. Specifically, the processor <NUM> reads the data [<NUM>] from the memory <NUM>. In a case where the data [<NUM>] is not the drive current value corresponding to the target pressing force, the processor <NUM> calculates the drive current value corresponding to the target pressing force, based on the formula (<NUM>) or the like. Then, the processor <NUM> determines whether the drive current value extracted from the feedback signal S2 has reached the drive current value corresponding to the target pressing force.

In step S18, in a case where the input amount (drive current value) into the actuator ACT (servo motor <NUM>) has become a value corresponding to the target pressing force (Yes in step S17), the method controls the actuator ACT (servo motor <NUM>) to stop the movement of the tailstock <NUM>. Specifically, the processor <NUM> generates a command signal S1 including a speed command for setting the speed of the tailstock <NUM> to zero, and sends the command signal S1 to the servo driver <NUM>.

In the first pressing method for pressing the tailstock <NUM>, when the pressing of the tailstock <NUM> against the workpiece W is detected, the tailstock <NUM> is separated from the workpiece W, and the tailstock <NUM> is caused to abut the workpiece W at the second speed V<NUM>, which is lower than the first speed V<NUM>. This eliminates the distortion of the workpiece W and/or the tailstock <NUM> that occurs when the workpiece W is pressed at the first speed V<NUM>, and the actuator ACT (servo motor <NUM>) controls the target pressing force with accuracy. In addition, the tailstock <NUM> is initially moved nearer to the workpiece W at a high speed and then the tailstock <NUM> is caused to abut the workpiece W at a low speed from the vicinity of the workpiece W. Therefore, the time for causing the tailstock <NUM> to abut the workpiece W can be shortened, and production efficiency can be improved.

<FIG> is a flowchart illustrating a processing flow of a second pressing method for pressing the tailstock <NUM> in the present embodiment. The second pressing method is a method for pressing the tailstock <NUM>, in a case where the machining apparatus <NUM> automatically attaches the workpiece W to the spindle <NUM>, machines the workpiece W, and automatically detaches the workpiece W from the spindle <NUM>. Each step in the second pressing method is achievable by the processor <NUM> executing the control program PG. In <FIG>, the same processes as those illustrated in <FIG> are denoted by the same reference numerals. Detailed description of such processes will be omitted.

After step S11 ends, the second pressing method performs step S21. In step S21, the method attaches one end of the workpiece W to the spindle <NUM> so that the workpiece W rotates together with the spindle <NUM> about the rotation axis Ax of the spindle <NUM>. Specifically, the processor <NUM> controls a workpiece carrier to carry the workpiece W to a position where one end of the workpiece W is engageable with the chuck <NUM>. The processor <NUM> controls the chuck <NUM> to close so that the chuck <NUM> holds the workpiece W. In a case where the workpiece holder WS includes the steady rest <NUM>, the processor <NUM> also controls the clamp of the steady rest <NUM> to close and hold the workpiece W. In this control, for example, when the processor <NUM> sends a control signal for closing the chuck <NUM>, the reaction force received from the workpiece W at the time when the chuck <NUM> holds the workpiece W exceeds a predetermined threshold, and in this case, it can be considered that the chuck <NUM> is closed. In addition, when the processor <NUM> sends a signal for closing the clamp of the steady rest <NUM>, the reaction force that the clamp of the steady rest <NUM> receives from the workpiece W exceeds a predetermined threshold, and in this case, it can be considered that the clamp of the steady rest <NUM> is closed.

In step S22, the method drives the actuator ACT (servo motor <NUM>) to move the tailstock <NUM> in the first direction D1 at a third speed V<NUM>, which is higher than the first speed V<NUM>. In a case where the workpiece W is automatically attached to the spindle <NUM>, the tailstock <NUM> is located at an initial position largely apart from the spindle <NUM>. For this reason, from the viewpoint of the production efficiency, the third speed V<NUM> is desirably a high feed rate that has been determined beforehand in the machining apparatus <NUM>. The control data DAT includes a speed command value corresponding to either the first speed V<NUM> or the third speed V<NUM>. Specifically, the processor <NUM> reads, from the memory <NUM>, either the third speed V<NUM> or a speed command value corresponding to the third speed V<NUM>, stored as the control data DAT. Then, the processor <NUM> generates a command signal S1 for moving the tailstock <NUM> in the first direction D1 at the third speed V<NUM>, based on the data that has been read, and sends the command signal S1 to the servo driver <NUM>.

In step S23, the method determines whether the tailstock <NUM> has reached a position separate from the workpiece W by a predetermined distance in the second direction D2. More specifically, the method determines whether the tailstock <NUM> has reached the position separate from the other end of the workpiece W by a predetermined distance in the second direction D2. In a case where the position is not separate by the predetermined distance (No in step S23), the processing of step S23 is repeated. It is desirable that the predetermined distance be approximately <NUM> on an empirical basis. The position separate from the other end of the workpiece W by the predetermined distance in the second direction D2 can be calculated from the shape of the workpiece W. Specifically, the control data DAT includes the predetermined distance and the shape of the workpiece W. The processor <NUM> reads, from the memory <NUM>, the predetermined distance and the shape of the workpiece W, which are stored as the control data DAT, and calculates the position separate from the other end of the workpiece W by the predetermined distance in the second direction D2. Then, in the same manner as in step S15, the processor <NUM> calculates the rotation angle of the servo motor <NUM>, generates a command signal S1 including the position command value for rotating the servo motor <NUM> by the rotation angle, and sends the command signal S1 to the servo driver <NUM>.

In step S24, when the tailstock <NUM> reaches the position separate by the predetermined distance (Yes in step S23), the method controls the actuator ACT (servo motor <NUM>) to stop the movement of the tailstock <NUM>. Specifically, the processor <NUM> generates a command signal S1 including a speed command for setting the speed of the tailstock <NUM> to zero, and sends the command signal S1 to the servo driver <NUM>. After step S24, the method performs steps S12 to S18.

After step S18, the method waits for the end of machining of the workpiece W by the machining apparatus <NUM>, in step S25. After machining of the workpiece W ends, the method drives the actuator ACT (servo motor <NUM>) to move the tailstock <NUM> to the initial position in the second direction D2 at the third speed V<NUM>, as in step S22. Then, the method controls the chuck <NUM> to open so as to detach one end of the workpiece W from the spindle <NUM>. In a case where the workpiece holder WS includes the steady rest <NUM>, the processor <NUM> also controls the steady rest <NUM> to be detached from the workpiece W. In addition, the processor <NUM> controls the workpiece carrier to carry the workpiece W out of the machining apparatus <NUM>.

The second pressing method for pressing the tailstock <NUM> drives the actuator ACT (servo motor <NUM>) to move the tailstock <NUM> at the third speed V<NUM>, which is higher than the first speed V<NUM>, to the position separate from the other end of the workpiece W by a predetermined distance in the second direction D2, before moving the tailstock <NUM> at the first speed V<NUM>. Therefore, the tailstock <NUM> can be moved to the vicinity of the workpiece W at a high speed, and the machining time for machining the workpiece W can be shortened.

<FIG> is a flowchart illustrating a processing flow of a third pressing method for pressing the tailstock <NUM> in the present embodiment. The third pressing method includes processing of temporarily opening the workpiece holder WS by an allowable amount and then closing again, while pressing the tailstock <NUM> against the workpiece W, in order to attach the workpiece W to the spindle <NUM> with high accuracy. Each step of the third pressing method is achievable by the processor <NUM> executing the control program PG. In <FIG>, the same processes as those illustrated in <FIG> are denoted by the same reference numerals.

After step S14 ends, the third pressing method performs step S31. In step S31, the method opens the workpiece holder WS at the time of detecting the pressing of step S13. Specifically, the processor <NUM> controls the chuck <NUM> to open so that the chuck <NUM> releases holding of the workpiece W. In a case where the workpiece holder WS includes the steady rest <NUM>, the processor <NUM> may also control the clamp of the steady rest <NUM> sandwiching the workpiece W to open.

In step S32, the method determines whether the workpiece holder WS is opened from the workpiece W by an allowable amount. The workpiece holder WS being opened by the allowable amount means that the chuck <NUM> and the clamp of the steady rest <NUM> are opened to a predetermined allowable amount from a state where the workpiece holder WS holds the workpiece W. In a case where they are not opened by the allowable amount (No in step S32), the processing of step S31 is repeated. Specifically, in a case where it is possible to designate an amount (opening degree (divergence)) for moving the workpiece holder WS in a signal for opening the workpiece holder WS to be sent from the processor <NUM> to the workpiece holder WS, the processor <NUM> sends in step S31, to the workpiece holder WS, a signal in which the opening degree corresponding to the allowable amount is designated for opening the workpiece holder WS. In step S32, when a predetermined period of time has elapsed since the signal is sent, the processor <NUM> may determine that the workpiece holder WS is opened from the workpiece W by the allowable amount. Alternatively, in a case where it is possible to send a reply that the workpiece holder WS has reached the designated opening degree (divergence), the processor <NUM>, by receiving a signal of the reply, may determine that the workpiece holder WS is opened from the workpiece W by the allowable amount. Furthermore, in a case where it is possible for the workpiece holder WS to send a reply of a signal indicating the opening degree to the processor <NUM>, the processor <NUM> may determine whether the workpiece holder WS is opened from the workpiece W by the allowable amount, based on the signal indicating the opening degree.

In step S33, when the workpiece holder WS is opened by the allowable amount (Yes in step S32), the method closes the workpiece holder WS again. Specifically, the processor <NUM> controls the chuck <NUM> to close so that the chuck <NUM> holds the workpiece W. In a case where the workpiece holder WS includes the steady rest <NUM>, the processor <NUM> may control the clamp of the steady rest <NUM> to close so that the clamp of the steady rest <NUM> holds the workpiece W. The control in step S33 is the same as the control in step S21.

In the third pressing method for pressing the tailstock <NUM>, the workpiece holder WS configured to hold the workpiece W is opened by the allowable amount, when the pressing is detected in step S13. The workpiece holder WS is opened by the allowable amount, and then the workpiece holder WS is closed again to hold the workpiece W. Therefore, the workpiece W can be attached to the workpiece holder WS with high accuracy. After step S33 is performed, step S15 is performed.

The servo motor <NUM> illustrated in the present embodiment is an example of the actuator ACT. The actuator ACT may be another actuator. <FIG> illustrates a machining apparatus 1A including a tailstock <NUM> in a case where a hydraulic cylinder <NUM> is used as the actuator ACT. The tailstock <NUM> corresponds to a cylinder body of the hydraulic cylinder <NUM>. The machining apparatus 1A includes an external tube <NUM>, which receives the tailstock <NUM>. Since the external tube <NUM> guides the tailstock <NUM> so that the tailstock <NUM> moves in the axial direction, the external tube <NUM> corresponds to the linear motion mechanism LMM. A plurality of bearings <NUM> are interposed between the tailstock <NUM> and the tailstock spindle <NUM>, and the tailstock spindle <NUM> is rotatable about the rotation axis Ax relative to the tailstock <NUM>.

The hydraulic cylinder <NUM> includes the tailstock (cylinder body) <NUM>, a piston <NUM>, and a rod <NUM>. The tailstock (cylinder body) <NUM>, the piston <NUM>, and the rod <NUM> form a first oil chamber C1 and a second oil chamber C2. <FIG> illustrates a case where the volume of the first oil chamber C1 is the smallest. A first oil passage P1 and a second oil passage P2 are formed in the rod <NUM>. Hydraulic oil is fed to the first oil chamber C1 through the first oil passage P1, and the hydraulic oil is discharged from the first oil chamber C1 through the first oil passage P1. The hydraulic oil is fed to the second oil chamber C2 through the second oil passage P2, and the hydraulic oil is discharged from the second oil chamber C2 through the second oil passage P2. When the hydraulic oil is fed to the first oil chamber C1 through the first oil passage P1 and the hydraulic oil is discharged from the second oil chamber C2 through the second oil passage P2, the tailstock <NUM> moves toward the workpiece W. When the hydraulic oil is fed to the second oil chamber C2 through the second oil passage P2 and the hydraulic oil is discharged from the first oil chamber C1 through the first oil passage P1, the tailstock <NUM> moves away from the workpiece W. The feed rate of the tailstock <NUM> is adjustable by, for example, adjusting the flow rate of an aperture provided in the oil passage for discharging the hydraulic oil. The pressing force of the tailstock <NUM> is adjustable by adjusting the hydraulic pressure of the hydraulic oil. Therefore, the input amount of the actuator ACT described above corresponds to the size of the aperture or the hydraulic pressure of the hydraulic oil, in the present modification. Also in such an actuator ACT, the movement control of the tailstock <NUM> similar to the above-described embodiment is enabled.

In addition, the actuator ACT may be another actuator capable of linearly moving the tailstock <NUM> or <NUM>. When the tailstock <NUM> or <NUM> moves at the first speed V<NUM> or the second speed V<NUM>, the torque may be controlled by the servo driver <NUM> so that the drive current supplied to the servo motor <NUM> is equal to or smaller than a drive current value corresponding to the target pressing force. The first pressing method for pressing the tailstock <NUM> may include step S21. In such a case, step S21 may be performed manually by the operator.

Some or all of the functions of the above-described control program PG may be achieved by a dedicated processor or integrated circuit. The control program PG, without being limited to the memory <NUM> built in the controller CL, may be recorded in a storage medium that is detachable from the controller CL and that is readable by the controller CL, and examples of the storage medium include disks such as a floppy disk, an optical disk, a CD-ROM, and a magnetic disk, an SD card, a USB memory, and an external hard disk. The controller CL is an example of a computer.

In the present application, the term "comprise" and its variations are intended to mean open-ended terms, not excluding any other elements and/or components that are not recited herein. The same applies to the terms "include", "have", and their variations.

Also in the present application, a component suffixed with a term such as "member", "portion", "part", "element", "body", and "structure" is intended to mean that there is a single such component or a plurality of such components.

Also in the present application, ordinal terms such as "first" and "second" are merely used for distinguishing purposes and there is no other intention (such as to connote a particular order) in using ordinal terms. For example, the mere use of "first element" does not connote the existence of "second element"; otherwise, the mere use of "second element" does not connote the existence of "first element".

Also in the present application, approximating language such as "approximately", "about", and "substantially" may be applied to modify any quantitative representation that could permissibly vary without a significant change in the final result obtained. All of the quantitative representations recited in the present application shall be construed to be modified by approximating language such as "approximately", "about", and "substantially".

Also in the present application, the phrase "at least one of A and B" is intended to be interpreted as "only A", "only B", or "both A and B".

Claim 1:
A method for pressing a tailstock (<NUM>, <NUM>) of a machining apparatus (<NUM>, 1A), the method comprising:
setting a target pressing force for pressing the tailstock (<NUM>, <NUM>) against a workpiece (W) attached to a spindle (<NUM>) in a first direction (D1) along a rotation axis (Ax) of the spindle (<NUM>);
driving an actuator (ACT, <NUM>) for controlling a movement of the tailstock (<NUM>, <NUM>) and a pressing force for pressing the tailstock (<NUM>, <NUM>) against the workpiece (W) to move the tailstock (<NUM>, <NUM>) in the first direction (D1) at a first speed (V<NUM>);
detecting pressing of the tailstock (<NUM>, <NUM>) against the workpiece (W) based on a change in an input amount into the actuator (ACT, <NUM>) for moving the tailstock (<NUM>, <NUM>);
upon detection of the pressing, controlling the actuator (ACT, <NUM>) to stop the movement of the tailstock (<NUM>, <NUM>);
driving the actuator (ACT, <NUM>) to move the tailstock (<NUM>, <NUM>) by a first distance in a second direction (D2) opposite to the first direction (D1);
characterised by:
driving the actuator (ACT, <NUM>) to move the tailstock (<NUM>, <NUM>) in the first direction (D1) at a second speed (V<NUM>) lower than the first speed (V<NUM>); and
controlling the actuator (ACT, <NUM>) to stop the tailstock (<NUM>, <NUM>), upon the input amount into the actuator (ACT, <NUM>) becoming a value corresponding to the target pressing force while the tailstock (<NUM>, <NUM>) is moving at the second speed (V<NUM>).