JPH03239403A - Return method to origin of c-axis in opposed-spindles lathe - Google Patents

Abstract

PURPOSE:To return each of main spindles to the C-axis origin while a work is held by two spindles, by storing a turning angle positional data with its renewing by a storing means with the signal of the turning angle detection means provided on 1st, 2nd spindles and controlling each of work spindles. CONSTITUTION:The turning angle positional data AD2 of a storing means are reset when the C-axis origin arrival of a spindle 15 is known by the signal CP2 transmitted from an angle detection means 17b by holding a work 12 with the spindles 15, 5 and driving the spindle 5 by making the spindle 15 in a free state. The detection is continued while renewing it and the turning angle positional data AD1 in a storing means 27a are reset when the C-axis origin arrival of the spindle 5 is known by the signal CP2 transmitted from an angle detection means 7b. A spindle control part 30 decelerates a motor 6 by a control part 27 when C-axis origin return complete signals CF1, CF2 are input from control parts 27, 37, the turning angle positional data AD, AD are stored in counters 27a, 37a with their being renewed in order by the signal to be input from angle detectors 7b, 17b according to the rotations of spindles 5, 15 and a main control part 30 executes the C-axis control at the C-axis angle position of the main spindles 5, 15 stoppage time.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention is directed to an opposed spindle lathe in which two workpiece spindles face each other, in which one workpiece is held by the two workpiece spindles. The present invention relates to a C@origin return method when performing machining involving C-axis control on the workpiece.

(b), Conventional Technology In an opposed spindle lathe, one workpiece is held by two workpiece spindles, and machining such as milling that involves C-axis control is sometimes performed on the workpiece. Conventionally,
When performing machining with C-axis control under such conditions,
Only one workpiece spindle is controlled by the C-axis, and the other workpiece spindle is allowed to rotate freely.

(c) 2 Problems to be Solved by the Invention As mentioned above, the method of performing machining by controlling only one workpiece spindle along the C-axis has disadvantages such as twisting of the workpiece. , the two workpiece spindles are each C
One possible method is to perform machining by controlling the axis.

In the case of C-axis control of two workpiece spindles, it is necessary to perform C-axis home return for the two workpiece spindles separately before performing C-axis control of each workpiece spindle.

However, when one workpiece is held by two workpiece spindles, that is, when the two workpiece spindles are connected via the workpiece, each workpiece spindle cannot be rotated independently. Therefore, first, the holding of the workpiece by one workpiece spindle is released, the two workpiece spindles are not connected via the workpiece, and each workpiece spindle is rotated independently to perform the C-axis return to origin. A possible method is to hold the workpiece again with two workpiece spindles. However, in this case, when returning the C-axis of the workpiece spindle to its origin, a relatively time-consuming operation of releasing and re-holding the workpiece must be performed, resulting in a problem that the machining time becomes longer.

In view of the above-mentioned circumstances, the present invention has been devised to suitably control each workpiece spindle while holding one workpiece by two workpiece spindles.
It is an object of the present invention to provide a method for returning to the C-axis origin in a counter-spindle lathe that can return to the 8M point.

(d) Means for Solving Problem 1 The present invention provides an opposed spindle lathe (1) in which a first work main shaft 1 (15) and a second work main shaft (5) are provided facing each other. Each of the workpiece spindles (5, 15) is provided with a rotation angle detection means (7b, 17b) for detecting the rotation angle of the 1 ft. (5, 15) of the workpiece main shaft. Rotation angle detection means (7b, 1
Rotation angle position storage means (27a, 37a) that updates and stores the rotation angle position data (AD2) of the workpiece spindle (5, 15) based on the rotation angle signal (AP, AP,) from 7b). and each work main # (5, 1
5), the rotation angle position storage means (27a, 37a);
Drive control means (6, 1) capable of rotationally driving the workpiece spindle (5, 15) based on rotation angle position data (AD machining, AD2) of the workpiece spindle (5, 15) stored in the
6, 27, 37), and with the workpiece (12) held by the first workpiece spindle (15) and the second workpiece spindle (5), C@origin of each workpiece spindle (5, 15). When performing the return, the first or second work spindle (5,
15), one of the workpiece spindles (15) is brought into a free rotating state, and the other workpiece spindle (5) is rotationally driven;
Cm of each workpiece spindle (5, 15)! The rotation angle detection means (17b) on the first work main # side performs a point detection operation.
When it is determined that the first work spindle (15) has reached the C-axis origin based on the detection signal (cpz) from the The rotation angle position data (AD2) of the first workpiece spindle is reset, and the rotation angle position data (AD2) of the first workpiece spindle is reset.
is the rotation angle detection means (17b) on the first work spindle side.
), the C-axis origin detection operation of the second work spindle (5) is continued while updating based on the rotation angle signal (APE) from the rotation angle detection means (7b) on the second work spindle side. Based on the detection signal (CP), the second workpiece spindle (
5) is configured to reset the rotation angle position data (ADl) on the second workpiece spindle side in the rotation angle position storage means (27a) when it is determined that C@ has reached the origin. .

Numbers in parentheses are for convenience and indicate corresponding elements in the drawings, and therefore, this description is not limited to the descriptions in the drawings. r (e) below
The same applies to the column ``, action''.

(e) 1 Effect With the above-described configuration, while the workpiece (12) is held by the first workpiece spindle (15) and the second workpiece spindle (5), the C@ of each workpiece spindle (5, 15) It acts to perform a return to origin.

(f), Example Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing an example of an opposed spindle lathe to which the present invention is applied, and FIG. 2 is a time chart showing an example of a C-axis home return program.

As shown in FIG. 1, the opposed spindle lathe 1 has a machine body 2.
The machine body 2 has a headstock 3 and a headstock 13 facing each other, each of which can be driven independently to move in the directions of arrows E and F, which are the direction of the spindle axis (Z-axis direction). (In addition, since the two headstocks 3 and 13 only need to be able to move relatively in the directions of arrows E and F in order to transfer the workpiece, either the headstock 3 or the spindle base 3 One side is aircraft 2
).

The headstock 3 has five workpiece spindles and a drive motor 6.
A chuck 5a is attached to the right end of the workpiece spindle 5 in the figure, and a chuck 5a is attached to the right end of the workpiece spindle 5 in the figure. On the left side of the figure.

A rotation speed detector 7 capable of detecting the rotation speed of the workpiece spindle 5
a, and a rotation angle detector 7b capable of detecting the rotation angle of the workpiece spindle 5.

Further, similar to the headstock 3, a workpiece spindle 15 is provided on the headstock 13 so as to be rotatably driven in the directions of arrows G and H in a manner that is integrated with the output shaft of a drive motor 16. A chuck 15a is attached to the left end of 15 in the figure. In addition, the workpiece spindle 15 includes the workpiece spindle 1
5 rotation speed detector 17a, and a rotation angle detector 1 that can detect the rotation angle of the workpiece main shaft 15.
7b is provided.

A turret 10 is provided between the headstock 3 and the spindle metalwork 3. The tool rest 20 is connected to the headstock 3. The tool rest 10.20 is provided movably in the J direction (X-axis direction) in a manner corresponding to the headstock 13, and a plurality of turning tools or rotary tools 10a, 20a are detachably attached to the tool rest 10.20. (In addition, if either the headstock 3 or the headstock 13 is fixed to the machine body 2, at least the machine body 2 is fixed so that the headstock and the turret can move relatively. The turret (turret 10 or turret 20) corresponding to the headstock (headstock 3 or 13) fixed to the headstock is also movable in the arrow E and F directions (Z-axis direction).

Further, the opposed spindle rotary l1111 has a main control section 30, and the main control section 30 is connected to a system program memory 21, a computer program memory 31, a tool post control section 22 via a bus line 30a. .32, headstock feed control section 23.33, spindle control section 27.37, etc. are connected.

The tool rest 10 is connected to the tool rest control section 22, and the head stock 3 is connected to the head stock feed control section 23. Further, a counter 27a, a dynamic motor 6, a rotation speed detector 7a, and a rotation angle detector 7b are connected to the main shaft control section 27.

Further, the tool rest 20 is connected to the tool rest control section 32, and the head stock 13 is connected to the head stock feed control section 33. In addition, the main shaft control section 37 includes a counter 37a, a llJl upper mover 16, and a rotation speed detector 17a.
, and a rotation angle detector 17b are connected thereto.

Opposing spindle #:! Since l has the above configuration, by the opposing spindle group Ill.

When machining a long workpiece 12 as shown in FIG. 1, both left and right ends of the workpiece 12 in the figure are gripped by the chuck 5a on the workpiece spindle 5 and the chuck 15a on the workpiece spindle 5. Performs processing involving C-axis control such as turning or milling.

First, when performing turning processing on the workpiece 12, the main control section 30 reads the machine tool program PRO from the tool program memory 31, and controls the spindle control section 27.37 based on the tool program program PR○. The two workpiece main shafts 5.15 are rotated together with the workpiece 12 via the workpiece 12. That is, Lord ##
The controllers 27, 37 drive and control the drive motor 6.16 based on the rotational speed signals R5, R32 input from the rotational speed detectors 7a, 17a, and rotate the workpiece spindle 5.15 to the first position.
It is synchronously rotated in the direction of arrow G (or H) in the figure at a predetermined number of rotations instructed by the Ni program PRO. In addition, the main control section 30 appropriately moves the tool rest 10 (or 20> in the arrow direction and J direction via the tool rest control section 22 (or 32), and further controls the headstock feed control section 23.33. The amphibious spindle heads 3 and 13 are synchronously moved and driven in the directions of arrows E and F, and turning is performed using the turning tool 10a (or 20a) on the tool rest 10 (or 20). If either the amphibious spindle 3.13 or the headstock 13 is fixed to the machine body 2, the amphibious spindle 3.13 is not moved in the directions of arrows E and F, and the turret 10 (or the turret 13 is fixed). 20) is suitably moved in the direction of the arrow J, and also in the directions of the arrows E and F to carry out the turning process.

Furthermore, when processing the workpiece 12 with C-axis control such as milling, each workpiece spindle 5, 15 is returned to its origin in cm prior to processing.

That is, when the main control unit 30 determines that the content of the machine program PR○ is machining involving C-axis control, it reads the C-axis return-to-origin program ROP from the system program memory 21, and executes the program based on the C1ll return-to-origin program ROP. , the workpiece spindles 5 and 15 are returned to the C8M point via the spindle control units 27 and 37.

First, as shown in the time chart of the CI origin return program ROP in FIG.
7.37, the drive motor 6.16 is speed controlled to set each workpiece spindle 5.15 at a low home return speed A V
Rotate with c.

Then, in the time T machining shown in Fig. 2, the workpiece spindle 5
．． When the rotation speed AV of No. 15 reaches the home return speed AVc, the main control section 30 rotates one of the workpiece spindles at the home return speed AVc via the spindle control section 27.37, and Let the other workpiece spindle freely rotate. For example, the workpiece spindle 5 is rotationally driven, and the workpiece spindle 1
5 into a free rotation state. That is, the spindle control section 27 supplies power to the drive motor 6 to control the speed of the drive motor 6, thereby rotating the workpiece spindle 5 at the origin return speed A V c. Further, the spindle control unit 37 stops supplying power to the drive motor 16, and brings the workpiece spindle 15, which is rotationally driven by the drive motor 16, into a free rotation state in which it can be rotated from the outside. Then, since the workpiece spindle top 5 is connected to the workpiece spindle 5 via the workpiece 12, it rotates together with the workpiece spindle 5. In the Unknown M document, the free rotation state is a state in which the drive motor of the workpiece spindle is free without any current flowing through it, and as described later, when the -degree C-axis origin detection signal is picked up, the rotation angle is detected and A state in which the rotation angle position data is updated and the rotational speed from the C-axis origin does not lose its position even if the output shaft (workpiece spindle) is rotated externally, and from a free rotation state to C-axis control. In the case of a shift, the shift to C-axis control can be made directly by simply supplying current to the active motor and starting position control without performing a CM return to the origin. The drive motor 16 (the same applies to the active motor 6) has a built-in structure in which the output shaft is integrated with the workpiece spindle top 5, as shown in FIG. Can be easily rotated from the outside,
The workpiece spindle 15 is driven by the drive motor 6 of the workpiece spindle 5.
can be smoothly rotated around the workpiece spindle 5.

Then, the main control section 30 controls both work spindles 5 and 15 to be set to CI! via the spindle control section 27 and 37, as will be described later. III
The workpiece spindle 5 is driven to rotate at a constant origin return speed AVc until the workpiece spindle 5 returns to the origin, and the workpiece spindle 5 is rotated in a free rotation state.

In addition, each spindle control section 27.37 has each rotation angle detector 7.
The C-axis origin detection signal CP outputted from the terminals b and 17b is set to an acceptance permission state, and the C-axis origin detection operation for each workpiece spindle 5.degree. 15 is performed.

Then, at time T2 when the workpiece spindle 5.15 has rotated by a certain angle, when the C-axis origin of the workpiece spindle 15 is detected and the C-axis origin detection signal CP2 is output from the rotation angle detector 17b, the C-axis origin is detected. The spindle control unit 37 of the workpiece spindle 15 to which the signal CP2 is input is configured so that the workpiece spindle top 5 is C.
It is determined that the axis origin has been reached, and the rotation angle position data AD stored in the counter 37a is reset. Further, the main shaft control section 37 outputs a C-axis home return completion signal CF to the main control section 30. In this way, the workpiece spindle 1
When the return to the C-axis origin of step 5 is completed, the drive motor 6 becomes in a position controllable state, but the spindle control unit 37 does not supply power to the drive motor 16 and keeps the workpiece spindle 15 in a freely rotating state. Make it. In addition, although the main spindle control unit 37 is in a state where the drive motor 16 is inactive, the rotation angle detection operation is always performed, and when the work spindle 15 rotates with the rotation of the work spindle 5, the one rotation angle detector Based on the rotation angle signal AP2 input from b, the counter 37
5 on the workpiece spindle reset as described above in a.
The rotational angle position data AD regarding the rotational angle position data AD is sequentially updated based on the detected C-axis origin.

Then, at time T when the workpiece spindle 5.15 has further rotated by a certain angle, the CM origin of the workpiece spindle 5 is detected and the C-axis origin detection signal CP1 is output from the rotation angle detector 7b. The spindle control unit 27 of the workpiece spindle 5 to which the detection (y number CP□ is input) determines that the workpiece spindle 5 has reached the C-axis origin and resets the rotation angle position data AD□ stored in the counter 27a. Also,
The main shaft control section 27 outputs a C-axis home return completion signal CF to the main control section 30.

The main control unit 30 receives a C-axis home return completion signal CF1. from the amphib axis control unit 27.37. When CF2 is input, it is determined that the return to the CIIIgX point of each of the work spindles 5 and 15 has been completed, and a stop command is output to the spindle control section 27. Then, the main shaft control section 27 controls the drive motor 6.
is decelerated to stop the workpiece spindles 5, 15 and workpiece 12. At this time, the spindle control unit 27.37 detects rotation angle detectors 7b, 17b as the workpiece spindles 5, 15 rotate.
Based on the rotation angle signals AP1, AP, input from the counters 27a, 37a, rotation angle position data AD1. AD, is sequentially updated based on the origin of each CI#.

Therefore, when both workpiece spindles 5.15 stop at time T, the counters 27a and 37a contain the rotational angular position data AD and the C-axis angular position when each workpiece spindle 5.15 stopped. It is stored as AD.

Then, the main control section 30 outputs a C-axis control start command to the main spindle control section 27.37, and the main spindle control section 27.37 controls the position of each drive motor 6 and king 6 to control the position of each workpiece spindle. 5. Based on the C-axis angular position at the time of stop of ↓5, the subsequent C-axis control of the workpiece spindle 5.15 is performed, that is, the counter 2
The rotational angle position data AD□ of the workpiece spindle 5 in 7a,
The rotation angle position data AD of the workpiece spindle 15 in the counter 37a do not match because there is a phase difference in the C-axis angular position of both workpiece spindles 5.15.

Both workpiece main shafts @5.15 are connected via the workpiece 12, and rotation angle position data AD of both workpiece main shafts 5.15
Since the difference, that is, the phase difference, is always constant, based on the rotation angle position data AD.

C-axis control of both workpiece spindles 5.15 can be performed.

In this way, the C-axis origin return of each workpiece spindle 5.15 can be performed while the workpiece 12 is held at both workpiece spindles 5.15, so the workpiece holding can be released for the C-axis origin return. Since there is no need to perform relatively time-consuming operations such as , re-holding, processing time can be shortened.

In this way, when the C-axis control of both workpiece spindles 5.15 is started, the main control section 30 controls both workpiece spindles 5.15 via the spindle control section 27.37 based on the cannibal program PR○.
15 is synchronously rotated under C-axis control, and the workpiece 12 held by both workpiece spindles 5 and machining machine 5 is transferred to the machining program P.
Position it at the predetermined C-axis angle position instructed by RO,
Or rotate at a predetermined angular velocity indicated by the nitrogram PR○. At this time, since there is a certain phase difference between the C-axis angular positions of both workpiece spindles 5.15, the main control unit 30
When a predetermined C-axis angle position is specified in the cannibal program PRO, for one of the two work spindles 5 and 15, the C-axis angle specified in the cannibal program PRO is set with respect to the work spindle as a reference. The C-axis is controlled based on the position, and for the other workpiece spindle, the C-axis angular position is calculated by adjusting the phase difference with respect to the C-axis angular position specified by the machine program PR○.
The C-axis is controlled based on the angular position of the axis.

Then, the spindle control section 27 sequentially updates the rotation angle position data AD1 of the workpiece spindle 5 in the counter 27a based on the rotation angle signal AP□ input from the one-rotation angle detector 7b according to instructions from the main control section 30. At the same time, the drive motor 6 is drive-controlled based on the rotational angle position data AD1, and the workpiece main shaft #I5 is synchronously moved to a predetermined C-axis angle while maintaining a constant phase difference with the workpiece main shaft 15, which will be described later. 5 or rotate at a predetermined angular velocity. Also,
The main shaft control section 37 follows instructions from the main control section 30.
Rotation angle signal AP input from rotation angle detector 17b
, while sequentially updating the rotational angle position data AD of the workpiece spindle 15 in the counter 37a based on the rotational angle position data AD, drive control of the drive motor 6 is performed based on the rotational angle position data AD, so that the rotational angle position data AD of the workpiece spindle 15 is kept constant with the workpiece spindle 5 described above. The workpiece spindle 15 is synchronously positioned at a predetermined C-axis angular position or rotated at a predetermined angular velocity while maintaining the phase difference. Further, the main control section 30 appropriately moves the tool rest 10 (or 20) in the arrow direction and J direction via the tool rest control section 22 (or 32), and further controls the headstock feed control section 23.33. The amphibious spindle head 3.13 is synchronously moved and driven in the directions of arrows E and F through the turret 10 (or 20), and the rotary tool 10a (or 20a) on the tool rest 10 (or 20) performs processing that involves C-axis control such as milling. (If either the headstock 3 or the headstock 13 is fixed to the machine body 2, do not move the amphibious spindle 3.13 in the directions of arrows E and F. Tool rest 10 (
Alternatively, the tool rest 20) is suitably driven to move in the directions of the arrows J and E, and is also suitably driven to move in the directions of arrows E and F to perform machining accompanied by C-axis control. At this time, since the workpiece 12 is rotationally driven by the two workpiece spindles 5.15, the inertia of the other free-rotating workpiece spindle is the same as when the conventional workpiece is rotationally driven by only one workpiece spindle. The workpiece 12 can be suitably machined without any twisting occurring in the workpiece due to the workpiece main shaft being rotated or rotated.

In the above-described embodiment, the workpiece spindle 5 is rotationally driven and the workpiece spindle top 5 is rotated in a freely rotating state. It is also possible to have them rotate around with each other depending on the state.

Further, in the above embodiment, the workpiece spindle 15 is
The case where the workpiece spindle is the workpiece spindle and the workpiece spindle 5 is the second workpiece spindle, that is, the case where the workpiece spindle 15 is first returned to its C-axis origin, and then the workpiece spindle 5 is returned to its C-axis origin. However, the workpiece spindle 5 is better than the workpiece spindle 15.
If the C-axis origin is detected earlier, the workpiece spindle 5 is set as the first workpiece spindle, and the workpiece spindle 5 is set as the second workpiece spindle.
Of course, the workpiece spindle 5 may be returned to its C-axis origin first, and then the workpiece spindle 15 may be returned to its origin.

In addition, in the above embodiment, each workpiece spindle 5.15
The drive motor 6.16 of each workpiece spindle 5.15 has a built-in structure.
16 does not necessarily have to be a built-in structure.

(g) 8 Effects of the Invention As explained above, according to the present invention, the workpiece spindle 1
Opposed spindle rotation ff in which a first workpiece spindle such as 5 etc. and a second workpiece spindle such as workpiece spindle 5 face each other
1l, each workpiece spindle is provided with rotation angle detection means such as rotation angle detectors 7b and 17b for detecting the rotation angle of the workpiece spindle, and each workpiece spindle is provided with a rotation angle signal from the rotation angle detection means. Based on AP□, AP, rotation angle position data AD□, A of the workpiece spindle
Rotational angle position storage means such as counters 27a and 37a for updating and storing D2 are provided, and each workpiece spindle is provided with rotational angle position data AD, AD2 of the workpiece spindle stored in the rotational angle position storage means. , a drive motor 6.16 capable of rotationally driving the workpiece spindle, and a spindle control section 2
7, 37, etc. are provided, and when the workpiece 12 is held by the first workpiece spindle and the second workpiece spindle, and the C-axis origin return of each of the workpiece spindles is performed, the first or second drive control means is provided. Among the workpiece spindles, one of the workpiece spindles is set in a free rotation state, and the other workpiece spindle is rotationally driven to perform a C-axis origin detection operation of each of the workpiece spindles, and a rotation angle detection means on the first workpiece spindle side. When it is determined that the first workpiece spindle has reached the C@origin based on the C-axis origin detection signal from the
The rotational angle position data AD2 on the workpiece spindle side is reset, and the rotational angle position data AD2 on the first workpiece spindle side is reset.
, based on the rotation angle signal AP from the rotation angle detection means on the first work spindle side, the CM origin detection operation of the second work spindle is continued, and the rotation of the second work spindle side is updated. When it is determined that the second workpiece spindle has reached the origin C@ based on the first detection signal such as the CNM inspection point detection signal C from the angle detection means, the second workpiece in the rotation angle position storage means is Since the configuration is such that the rotational angle position data AD on the spindle side is reset, 2 on the workpiece is
The C-axis origin return of each workpiece spindle can be performed while the workpiece spindle is held by the second workpiece spindle and the second workpiece spindle. Therefore, when performing the C-axis home return of each workpiece spindle, there is no need to release the holding of the workpiece by one workpiece spindle and bring both workpiece spindles into a state where they are not connected.
Since there is no need to perform relatively time-consuming operations such as releasing and re-holding the workpiece, the machining time does not become long, and the C-axis origin return of each workpiece spindle can be suitably performed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an opposed spindle lathe to which the present invention is applied, and FIG. 2 is a time chart showing an example of a C-axis home return program. l...Opposed spindle lathe 5...Second work spindle (work spindle) 6...
... Drive control means (drive motor) 7b ...
Rotation angle detection means (rotation angle detector) Work 2... Work 15... First work spindle (work spindle) 16
...... Drive control means (drive motor) 17b...
...Rotation angle detection means (rotation angle detector) 27... Drive control means (spindle control section) 27a.
... Rotation angle position storage means (counter) 37 ... Drive control means (spindle control section) 37a ...
...Rotation angle position storage means (counter) AD...Rotation angle position data AP...Rotation angle signal

Claims (1)

[Claims] In an opposed spindle lathe in which a first workpiece spindle and a second workpiece spindle are provided facing each other, each workpiece spindle is provided with rotation angle detection means for detecting the rotation angle of the workpiece spindle. and each of the workpiece spindles is provided with a rotational angle position storage means for updating and storing the rotational angle position data of the workpiece spindle based on the rotational angle signal from the rotational angle detection means; Drive control means capable of rotationally driving the workpiece spindle based on rotational angular position data of the workpiece spindle stored in the angular position storage means, and the workpiece is held by the first workpiece spindle and the second workpiece spindle. In this state, when performing the C-axis home return of each of the workpiece spindles, one of the first or second workpiece spindles is brought into a free rotation state, and the other workpiece spindle is rotationally driven, and each of the above-mentioned workpiece spindles is When the C-axis origin detection operation of the workpiece spindle is performed and it is determined that the first workpiece spindle has reached the C-axis origin based on the detection signal from the rotation angle detection means on the first workpiece spindle side, the above-mentioned Resetting the rotation angle position data on the first work spindle side in the rotation angle position storage means, and converting the rotation angle position data on the first work spindle side into the rotation angle position data on the first work spindle side from the rotation angle detection means on the first work spindle side. The C-axis origin detection operation of the second workpiece spindle is continued while updating based on the angle signal, and the second workpiece spindle is updated based on the detection signal from the rotation angle detection means on the second workpiece spindle side.
A method for returning a C-axis to an origin in an opposed spindle lathe, wherein when it is determined that the axis has reached the origin, the rotation angle position data of the second workpiece spindle in the rotation angle position storage means is reset.