CA2009993C

CA2009993C - Two-spindle opposed type cnc lathe

Info

Publication number: CA2009993C
Application number: CA 2009993
Authority: CA
Inventors: Kousaku Suzuki; Naoki Okuno
Original assignee: Nakamura Tome Precision Industry Co Ltd
Current assignee: Nakamura Tome Precision Industry Co Ltd
Priority date: 1989-04-19
Filing date: 1990-02-14
Publication date: 1997-03-25
Anticipated expiration: 2010-02-14
Also published as: CA2009993A1

Abstract

A CNC lathe in which a first spindle stock is secured onto a base of a slant type inclined at a down gradient on this side, a second spindle stock opposed thereto is provided movably only in the direction of the spindle, and separate turret type tool rests are arranged in deep of the spindle stocks.
A CNC device having the aforesaid construction in which both spindle stocks are respectively provided with independent spindle motors, mechanically disconnectable spindle indexing and driving devices and encoders on the spindle and indexing and driving device, a CNC lathe for rotating the index motor on the basis of a phase difference detected by the encoder to effect adjustment of phases when the spindle indexing and driving device is connected to the spindle and when the workpiece is transferred between both the spindles.
A CNC device having the aforesaid construction provided with a synchronous control device for providing output pulses of the encoders mounted on both the spindles as a unit of fine time to correct a speed command according to the magnitude relation thereof.

According to this invention, there is provided a CNC lathe in which a rigidity of the first spindle stock is high, a bar feeder having a conventional construction can be used. Work efficiency at the spindles in composite workings including indexing and work efficiency for bar working including cutting off the end of the bar can be considerably enhanced.

Description

20099~3 TITLE OF THE 1NV~N~ION

-- TWO-SPINDLE OPPOSED TYPE CNC LATHE

BACXGROUND OF THE INVENTION
1. Field of the Invention This invention relates to a machine tool for working a workpiece principally in the shape of a rotary body, and relates to a CNC (computer numerical control) lathe provided with two spindle stocks and two tool rests opposed on a single base.

2. Description of the Prior Art It has been heretofore carried out to add a milling working means to a single-spindle CNC lathe. A
spindle stock in the single-stock CNC lathe of this kind is secured to a base, the spindle being provided with a spindle motor for machining and working, a spindle index driving device capable of being connected and disengaged, a spindle orientation mechanism using a locating cam, a locating pin and the like for stopping the spindle at an angle of an original point and the like so that when the spindle is stopped at an angle of an original point, the spindle index driving device can be connected to the spindle. The tool rest is of the turret type, which can be moved and located in a direction of the spindle (hereinafter referred to as the direction of axis Z) and in a direction perpendicular to the direction of axis Z (hereinafter referred to as the direction of axis X) and which indexes the turret having a plurality of tools, such as machining tools, milling tools and drilling tools arranged in the periphery thereof to work the workpiece. The milling tool and the drilling tool are driven by a driving motor for rotating the tools.
Thereafter, there has been proposed a machine which is provided with a sub-spindle improved over a conventional tail stock for the purpose of attaining a composite working in order to meet the demand of industrial fields with the desire of obtaining a finished product by a single machine in which the workpiece held by the chuck of the spindle is subjected to machining and milling after which it is subjected to the back working by the same machine.
In the single-spindle type CNC lathe of this kind, a subspindle unit is arranged at a position of the conventional tail stock. This subspindle can be moved and located in the direction of axis Z by a hydraulic 2C~C~99~3 cylinder or an NC servo. In the back working, the subspindle is moved toward the spindle, the end of the workpiece is gripped by the chuck, the workpiece is received from the spindle, the subspindle is moved away from the spindle, the subspindle in which the workpiece is held by the chuck is rotated and driven by the subspindle motor, and the tool mounted on the turret on one and the same tool rest is used to work the back of the workpiece.
In summary, the subspindle in the aforementioned single-spindle type CNC lathe is approximately one in place of the tail stock, in which case, for working materials which are small and flange materials which require large chucks, power is often short, and the sizes of workpiece that may be worked are limited so that only the chamfering of the back and finishing thereof may be performed. Above all, the spindle remains rest during the back working, efficiency of which is not so good.
On the other hand, various improvements have been progressed in order to meet the earnest desire of the industrial field of increasing the number of composite working by the machine and apparatus of this kind to obtain various efficient and more complete 20099g3 finished products by a single machine. As the result, there has been developed a two-spindle opposed type CNC
lathe comprising a first working unit wherein a conventional spindle is used as a first spindle, a spindle stock is used as a first spindle stock and a conventional tool rest is used as a first tool rest and a second working unit wherein a subspindle is made to be powerful to the same extent as that of the first spindle to use it as a second spindle, a spindle stock is used as a second spindle stock, and a turret type tool rest equal to the first tool rest is provided to use it as a second tool rest, whereby the synchronous orientation operation of the first and second spindles and powerful composite working are rendered possible, and in addition, the continuous operation can be made while simultaneously executing the front and back working of the workpiece as well as the automatic delivery of the workpiece between both the spindles, such lathe being put to a practical use.
The two-spindle opposed type CNC lathe of this kind, in view of the mode of installation and arrangement of the spindle stocks and tool rests on the base, roughly includes the following three different types:

2009!3~

Wherein as disclosed in the specification of European patent publication No. 289,333, both the first and second spindle stocks and both the first and second tool rests are installed on the base so that they can be moved and located in the direction of axis Z and in the direction of axis X, respectively, both the tool rests being arranged deep in the base from both the spindle stocks;
wherein the first spindle stock is secured to the base, the second spindle stock can be moved and located in the direction of axis Z, and the first and second tool rests can be moved and located in the direction of axes Z and X, the second tool rest being arranged on the base so as to be positioned this side of the second spindle stock; and wherein both the first and second spindle stocks can be moved and located in the direction of axis z and both the first and second tool rests can be moved and located in the directions of axes Z and X, both the tool rests being arranged on the back of the base from both the spindle stocks.
However, among these three different types, the first type described in the European patent publication No. 289,333 and the third type are rational 2io~ 3 in construction in that the shape to be worked is determined by the synthetic operation of the movement of the first and second spindle stocks in the direction of axis Z and the movement of the first and second tool rests in the direction of axis X and have the merit in that they have a simple construction which is symmetrical to left and right. However, there gives rise to a problem in the short of rigidity in the first spindle stock and a problem in workability when a bar material is automatically supplied and worked resulting from the structure in which the first spindle stock is moved.
That is, normally, the workpiece or blank is first mounted on the first spindle, and therefore the weight of workpiece and the amount of unbalance are greatest during the entire processing step, and the first step often results in heavy cutting. Accordingly, a great rigidity is required particularly in the first spindle. However, in the construction in which the first spindle stock is moved, the problem in the short of rigidity tends to occur in the first spindle stock.
In case where a method for automatically supplying the bar material through a hollow hole in the first spindle is employed, when the first spindle stock moves, an unworked blank extending through the first spindle also moves axially, posing a problem in that most of bar feeders so far used cannot be used.
In the aforementioned second type in which the first or second tool rest is provided on this side from the firæt or second spindle, there involves a problem in that accessibility of the operator or robot arm to the spindle is bad, mounting and removing operation for workpiece are not only inconvenient but a danger is accompanied.
Furthermore, two tool rests are arranged to close to each other because it is necessary to make the machine small-size. However, in the construction in which both the tool rests may be moved only in the direction of axis X, it has no moving ability to move both the tool rests in a direction of moving away from each other, and therefore there involves a difficulty in that the workability is bad in mounting and removing the tool from the turret and in maintenance and repair of the tool rests.
Moreover, the base of the conventional machine of this kind is mostly of the flat shape, of which central portion has a chip receiving box mounted thereon so as to make the machine compact. With this, there ~n099~93 gives rise to problems in that a leak of cutting liquid caused by the inconvenience of filtration of the cutting liquid, the inconvenience in maintenance work after the tip conveyor has been mounted, and the like in view of limitation of space.

SUMMARY OF THE INVENTION
This invention has been provided in an attempt of improving various problems as noted above.
It is a primary object of this invention to provide a two-spindle opposed type CNC lathe in which a base is of a slant type inclined forwardly, and both two-tool rests are arranged in deep of both opposed spindles with the result that the accessibility to both the spindles is good, the workability during mounting and removing the workpiece is good, no danger involves in operation, monitoring of the working state can be easily made and chips and cutting liquid may be quickly discharged into the chip receiving box disposed at this side of the base, which can minimize a thermal deformation particularly of the base. It is a second object of this invention to provide a two-spindle opposed type CNC lathe in which the first spindle stock is secured to the base, whereby the sufficient rigidity 2~ 993 is given to the first spindle stock, no problem occurs in which a blank on the bar feeder moves in an axial direction during working of the bar material, and the bar feeder so far used can be used without modification.
It is a third object of this invention to provide a two-spindle opposed type CNC lathe in which connection of spindle indexing and driving devices disposed on the opposed two spindles, respectively, and adjustment of phase of two spindles can be quickly accomplished, the work effficiency in the composite continuous working including the back working and indexing can be considerably enhanced and the respective spindles can be indexed and located or rotated at low speeds by the spindle indexing and driving devices with the result that the reverse resistance of the spindles during the aforesaid working can be increased, and the lathe has a powerful working ability as well as the aforementioned increase in rigidity of the first spindle.
It is a fourth object of this invention to provide a two-spindle opposed type CNC lathe in which since a difference in phase or speed between the first spindle and the second spindle can be detected in a very short period of time without delay to continuously 2~9~9~

correct a speed command given to a spindle motor, the phase and speed of the two spindles can be accurately synchronized during rapid acceleration and deceleration as well as during the constant-speed operation, and in addition, since the control construction is simple, working can be simply done, and a synchronous control device is provided in which the set value is set by the CNC device adjusting to the size of workpiece and the working situation to thereby positively avoid hunting and a torsional stress acting on the workpiece.
It is a fifth object of this invention to provide a two-spindle opposed type CNC lathe in which the same NC program can be used in continuous working of the same workpiece by the first and second working units to reduce the trouble in preparation of programs; and if the moving directions of the first tool rest and the second spindle stock in the direction of axis Z are the same (for example, rightward movement), the relative moving relation between the tool and the workpiece is also the same (for example, the tool is in the direction away from the spindle), and therefore, erroneous operation can be avoided during manual operation and collision or the like between the workpieces resulting 2009~g3 from the erroneous operation can be positively prevented.
Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings.
For achieving the aforesaid objects, this invention provides a two-spindle opposed type CNC lathe comprising two opposed spindle stocks consisting of a first spindle stock and a second spindle stock, each spindle stock supporting a spindle for rotation about parallel spindle axes, two tool rests consisting of a first turret type tool rest forming a first working unit together with said first spindle stock and a second turret type tool rest forming a second working unit together with said second spindle stock, said two spindle stocks and said two tool rests being mounted on a common base, said lathe being provided with a CNC device for working a workpiece principally in the shape of a rotary body, characterized in that a. the base is of the slant type inclined at a down gradient;
b. the first spindle stock is secured to the base;

c. the second spindle stock is mounted on the base through a slide capable of being moved and located in the direction of the axis of its respective spindle; and d. the first tool rest is mounted on the base through a slide capable of being moved and located in the direction of the axis of its respective spindle, and in the direction perpendicular thereto, and the second tool rest is mounted on the base through a slide adapted to be moved and located only in the direction perpendicular to the axial direction of its respective spindle, said mounting position being offset from both the spindle stocks.

DESCRIPTION OF THE DRAWINGS
The drawings show e_bodiments of the two-spindle opposed type CNC lathe according to the invention of this patent application. However, in the illustration of the ~mhodiments, there is employed the way of illustration to a degree that may be easily understood by those having an ordinary knowledge in the technical field to which belongs the two-spindle opposed type CNC lathe according to the invention of this patent application, and the illustration of constituent parts that may not be greatly affected in underst~n~;ng the---------------------------------------_ A

two-spindle opposed type CNC lathe according to the invention of this patent application is made as simple as possible or omitted.
FIG. 1 is a view of arrangement of various machines and devices installed on the base, that is, principal members which constitute a two-spindle opposed type CNC lathe according to the invention of this patent application;
FIG. 2 iS a schematic sectional view of apparatus;
FIG. 3 iS a perspective view showing a chip discharge system;
FIGS. 4 and 5 are explanatory views showing the relationship with the control program;
FIG. 6 is a developed view for explaining the spindle stock;
FIG. 7 iS a detailed view of a brake device;
FIG. 8 iS a block diagram showing the control system of the brake device;
FIG. 9 iS a perspective view of a spindle indexing and driving device;
FIG. lO is a block diagram showing the control system of an indexing and driving motor;

2009~93 FIG. 11 is a block diagram showing the connection control system between the spindle and the spindle indexing and driving device;
FIG. 12 i8 a block diagram showing the control system of spindle motors;
FIG. 13 is a view showing an example of a slow/fast discriminating circuit partly omitted;
FIG. 14 is a view for explaining a spindle encoder; and FIG. 15 i8 a view showing an example of pulses generated from the slow/fast discriminating circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
Also in the description of this embodiment, the spindle direction is referred to as the Z-axis direction, and the direction perpendicular to the Z-axis is referred to as the X-axis direction.
In FIGS. 1 to 3, reference numeral 1 designates a base, 2a a first spindle stock, 2b a second spindle ~tock, 3a a first turret type tool rest, 3b a second turret type tool rest, 4 a chip receiving box, and 5 a chip discharging conveyor.
The base 1 is of a slant type with an upper surface inclined at 45 degrees to the horizontal. The first ,A'' spindle stock 2a is secured to the base 1, and supports a spindle lla for rotation about an axis ext~n~;ng in the Z-direction. The second spindle stock 2b is arranged in opposition to the first spindle stock 2a and is slidable only in the Z-axis direction through a slide 6. Spindle stock 2b supports a spindle llb for rotation about an axis exten~;ng in the Z-direction. The tool rests 3a and 3b are offset with respect to the first spindle stock 2a and the second spindle stock 2b, respectively. The first spindle stock 2a and the first tool rest 3b form a first working unit 17a, and the tools on the first tool rest 3a work a workpiece mounted on the first spindle stock 2a. The second spindle stock 2b and the second tool rest 3b form a second working unit 17b, and the tools on the second tool rest 3b work a workpiece mounted on the second spindle stock 2b.
The first tool rest 3a is mounted slidably in the z-axis direction (the spindle direction) and in the X-axis direction (the direction perpendicular to the spindle direction) by a slide 7 composed of a slides 71 and 7~, and the second tool rest 3b i~ mounted slidably only in the X-axis direction by a slide 8.
The slides 6, 7 and 8 are each provided with a feed device composed of feed motors 12b, 12a, 13a and 13b, feed screws 14b, 14a, 15a, 15b and ball nuts not shown. The rotation of the feed motors 12b, 12a, 13a and 13b is controlled by a program of a CNC device 26 to determine the feed speed of and position movement of the second spindle stock 2b, the first tool rest 3a and the second tool rest 3b.
The tool rests 3a and 3b are respectively provided with turrets 9a and 9b having a plurality of tools including rotary tools such as milling cutters, drills or the like, the turrets 9a and 9b being indexed and driven by index motors lOa and lOb so as to ~elect the desired tool. Motors 39a and 39b for milling are disposed for rotating the selected tool if the latter i~
a rotary tool.
The po~itions of the first turret 9a, the second turret 9b and the second spindle llb shown by the phantom lines in FIGS. 4 and 5 are position~ of original points. At this position of the oriqinal point, the positional relation between the turrets 9a and 9b and the spindles lla and llb is symmetrical to left and right.
The reason why the base l of the ~lant type inclined at 45 degrees is employed is that the chip~ described later are quickly discharged, that the workability of replacement of the tool on the turret is taken into consideration, that a loader or an unloader can be arranged at a ~uitable po~ition upwardly or A

2!~09g93 frontwardly of the machine, and that an excessively large eccentric load i8 prevented from being exerted on the slide surfaces of the spindle stocks 2b and the tool rests 3a, 3b. In the actual construction, three slideways are integrally cut in the upper surface of the base 1 to increase the rigidity and are formed in build-block system to thereby reduce an increase in cost.
The upper surface of the base 1 in the working area formed between both the spindle stocks 2a and 2b is covered by an expansible cover 18 mounted between the slide 6 of the second spindle stock 2b and the first spindle stock 2a.
(Chip receiving box) The chip receiving box 4 is removably arranged on the front edge of the base 1, and a conveyor 5 for discharging the chips sideward is arranged on the bottom surface of the chip receiving box 4. Accordingly, the chip~ generated in the working area slip down on the cover 18, fa}l onto the chip receiving box 4 and are promptly discharged sideward by the conveyor 5.
In the turning working, a tool capable of heavy cutting is used in order to complete rough cutting as soon as possible, and the workpiece 16 is rotated at a high speed and the tool is fed at a high speed to 20~99~

effect rough cutting. Because of this, a high working heat is generated. It is therefore an important requirement for preventing thermal deformation of the machine and the workpiece 16 to maintain a high working precision to apply a cutting liquid to cool the chips and promptly remove the latter from the working area.
Accordingly, one of most important problems in the machine of this kind is to process the chips. The lathe according to this invention employs the aforementioned construction described in connection with the embodiment to solve the problem. The chip conveyor 5 can be of the construction in which the chips are discharged rearwardly of the machine, which type however has the construction in which the chips are gathered in the center of the chip receiving box, in which case the conveyor 5 passes along the center of the base 1 and therefore, the maintenance operation is not convenient.
Generally, a number of controllers are arranged at the rear of the machine, and therefore, the aforesaid type is not preferable in terms of maintenance of the controllers.
(Spindle stock) As shown in FIGS. 1 to 6, the spindles lla and llb are rotatably mounted on the first and second 20~9gg3 . .

spindle stocks 2a and 2b, respectively, the spindles lla and llb having chucks l9a and l9b secured to first ends thereof, and having chuck cylinders 20a and 20b for opening and closing chucks mounted on the other ends thereof, respectively. The spindles lla and llb are rotated by the spindle motors 21a and 21b through V-belt~ 28a and 28b, respectively, and the angle of rotation thereof i5 detected by spindle encoders 27a and 27b through timing belts 29a and 29b. The spindle motors 21a and 21b are provided to independently drive the spindles during the high speed working such as the turning.
On the first and second spindle stocks 2a and 2b are mounted brake devices 22a and 22b later described in detail, spindle indexing and driving devices 23a and 23b, ~hift gears 24a and 24b for engaging and disengaging the spindle indexing and driving devices 23a and 23b and the spindles lla and llb, gears 25a and 25b, indexing encoders 26a and 26b and spindle encoders 27a and 27b.
(Brake devices) The brake devices 22a and 22b mounted on the spindles lla and llb have the function to freely and automatically control the braking force such that in 2~0g~93 case where the position of the spindles lla and llb need be stopped at the de~ired position, the rotation of the spindles lla and llb i9 positively braked at the desired position, and in case of milling for contouring, the rotation thereof is braked by the force half of the former. The rotational speed and the angle of rotation of the spindles lla and llb can be controlled by the pro~ram of the CNC device 46 accurately without any vibration.
As shown in PIGS. 7 and 8, the brake devices 22a and 22b in this embodiment comprise brake disks 31a and 31b secured to the spindles lla and llb, brake shoes 32a and 32b held from both sides and movable to and from the brake disks, and brake cylinders 33a and 33b for applying a holding force thereto, and are secured to the spindle stocks 2a and 2b through brackets 34a and 34b.
In the present embodiment, the braking force of the brake devices 22a and 22b can be automatically controlled by controlling the hydraulic pressure of the brake cylinders 33a and 33b. However, other constructions of brake devices can be employed as long as they have a construction in which the braking force can be automatically controlled.

The operation of the braking devices 22a and 22b will be described in detail with reference to FIG.
8. For example, where the milling for contouring is discontinuously operated, vibrations sometimes occur in the spindles lla and llb. The brake devices 22a and 22b are to damp the vibrations of this kind by applying a brake to the spindles lla and llb to vary the braking force according to the magnitude of the working reaction.
In the present invention, servo drivers 47a and 47b for controlling the index motors 40a and 40b of the spindle indexing and driving devices 23a and 23b have measuring units 36a and 36b for measuring the driving force thereof mounted thereon, and output signals therefrom are guided to brake control devices 37a and 37b. Signals outputted from the brake control devices 37a and 37b are inputted into pressure control servo valves 38a and 38b thereby regulating the oil pressures of the brake cylinders 33a and 33b.
- In this embodiment, output of the index motors 40a and 40b when the spindles lla and llb are rotated at low speeds for milling work only with braking load is set to a predetermined value (when no brake is applied, a very small output is present), therefore the brake hydraulic pressure is regulated in advance so as to balance with the output. When the load of the index motors 40a and 40b exceeds the aforesaid level, the brake hydraulic pressure is automatically regulated by the brake control devices 37a and 37b in a direction of relieving the brake through that amount. In doing so, the braking force reduces as the load increases after commencement of milling work, and the index motors 40a and 40b continue their running while maintaining an output in a fixed range. Even if the load of the milling work is varied, the torque variation in the spindle indexing and driving devices 23a and 23b will not occur, and the vibrations of the spindles lla and llb are effectively suppressed so that the working can be effected in a stable manner.
(Spindle indexing and driving devices) As shown in FIGS. 6, 9 and 10, the spindle indexing and driving devices 23a and 23b are disengageably connected to the spindles lla and llb through disengageable mechanisms 23'a and 23'b of the devices 23a and 23b. The spindle indexing and driving devices 23a and 23b are provided to rotate the spindles lla and llb during working at low speed rotation such as indexing, milling work for contouring, etc. and comprise 20~993 index motors 40a and 40b, worms 41a and 41b secured to the output shafts thereof, worm wheels 42a and 42b meshed therewith, worm wheel shafts 43a and 43b secured thereto, and disengageable mechanisms 23'a and 23'b. The disengageable mechanisms 23'a and 23'b comprise shift gears 24a and 24b axially movably mounted on the worm wheel shafts 43a and 43b with precise spline, gears 25a and 25b secured to the spindles lla and llb, shift forks 44a and 44b for engaging the shift gears 24a and 24b with the gears 25a and 25b, and shift cylinders 45a and 45b.
The shift gears 24a and 24b and the gears 25a and 25b are precise gears having the same number of teeth. In turning, the shift gears 24a and 24b are moved rightward in FIG. 9 by the shift cylinders 45a and 45b to release the engagment with the gears 25a and 25b, and the spindles lla and llb are rotated at high speeds by the spindle motors 21a and 21b. In milling or drilling, the shift gears 24a and 24b are returned to the state shown in FIG. 9 into engagement with the gears 25a and 25b, and the rotation of the index motors 40a and 40b is reduced by the worms 41a, 41b and worm wheels 42a, 42b to rotate the spindles lla and llb through the gears 24a, 24b and gears 25a, 25b whereby working can take place while effecting locating at a predetermined angle or rotation at a low speed.
A harmonic drive type reduction gear or a differential reduction gear can be also employed in place of the aforementioned worms 41a, 41b and worm wheels 42a, 42b. A large reduction ratio is used whereby an accurate angle positioning of the spindles lla and llb can be accomplished. Also, which respect to the disengageable mechanisms 23'a and 23'b of the spindle indexing and driving devices 23a and 23b, an engaging type mechanical clutch or the like can be used in place of a shift type gear, of which driving may be of air pressure type or electric type. In short, such spindle indexing and driving devices 23a and 23b are independently respectively provided on the two spindles lla and llb of the two-spindle opposed type CNC lathe.
The spindle indexing and driving devices 23a and 23b employ the construction in which the motor output is transmitted to the spindles lla and llb through a high reduction-ratio mechanism composed of the worms 41a, 41b and worm wheels 42a, 42b having a high reverse resistance to increase the reverse drive resistance of the spindles lla and llb, thus rendering possible heavy cutting milling.

2(~ 95~3 (Disengageable mechanism for the spindle indexing and driving devices) As shown in FIG. 6, the index motors 40a and 40b in the spindle indexing and driving devices 23a and 23b are provided with the indexing encoders 26a and 26b, whereby the phase and rotational speed of the shift gears 24a and 24b secured to the worm wheel shafts 43a and 43b can be detected, which are used for connection between the spindle indexing and driving devices 23a and 23b and the spindles lla and llb. That is, a control system is employed in which there is provided means for computing a position of engagement of the spindles lla and llb with the shift gears 24a, 24b and gears 25a, 25b from each four of data comprising phases of a reference position and a present position of the spindles detected by the spindle encoders 27a, 27b and phases of a reference position and a present position detected by the indexing encoders 26a and 26b so that when the spindle indexing and driving devices 23a and 23b are connected to the spindles lla and llb by the disengageable mechanisms 23'a and 23'b, the spindle indexing and driving devices 23a and 23b are rotated to the engaging position determined by said computation means on the basis of the command of the CNC device 46 to effect engagement of the shift gears 24a, 24b and the gears 25a, 25b.
As the control system, as shown in FIG. 11, the spindle encoders 27a and 27b and the indexing encoders 26a and 26b are provided with pitch counters 49a, 49b, 48a and 48b, respectively. These pitch counters 49a, 49b, 48a and 48b are counters whose maximum count number comprises the number of pulses issued by the spindle encoders 27a and 27b or indexing encoders 26a and 26b when the spindles or worm wheel shafts are rotated through an angle corresponding to a circumferential pitch of the shift gears 24a, 24b, and gears 25a, 25b, indicating phases from the engaging points of the shift gears 24a, 24b and gears 25a, 25b.
The pitch counters 49a, 49b, 48a and 48b are reset by their count up pulses and reference angle pulses of the encoders 27a, 27b, 26a and 26b (pulses outputted when the spindles and worm wheel shafts 43a and 43b assume reference phases). Accordingly, the pitch counters 49a, 49b and 48a, 48b start counting when the spindles lla and llb and the shift gears 24a and 24b assume the reference phases and are reset every time the shift gears 24a, 24b and gears 25a, 25b rotate through one circumferential pitch or one pitch portion of the 2009~3 gear to newly start counting. Therefore, if the counting number of the pitch counters 49a and 49b is equal to that of the pitch counters 48a and 48b, the phases of the spindles lla and llb are adjusted to those of the shift gears 24a and 24b and the engagement between the shift gears 24a, 24b and the gears 25a, 25b can be made at a given position. Dividers 50a and 50b are provided to roughen the divided number of the indexing encoders 26a and 26b to the divided number of the spindle encoders 27a and 27b. For example, if the divided number of the spindle encoders 27a and 27b is 3600 and that of the indexing encoders 26a and 26b is 360000, the divided number of the dividers 50a and 50b is 100. When the spindle indexing and driving devices 23a and 23b are connected to the spindles lla and llb, the CNC device 46 issues a rotation command to the index motors 40a and 40b through a difference in value between the pitch counters 49a and 48a, 49b and 48b detected by comparators 51a and 51b to engage the gears 24a, 24b and gears 25a, 25b.
Thereby, the orientation operation of the spindles lla and llb at the low speed at the time of connection to the spindle indexing and driving devices 23a and 23b is eliminated, and the spindles lla and llb are rapidly reduced in speed to stop as it is. The stopped phase is detected by the pitch counters 49a and 49b of the spindle encoders 27a and 27b. The shift gears 24a and 24b are rapidly located so as to meet the phase to render possible the operation of connecting the spindle indexing and driving devices 23a and 23b to the spindles lla and llb. Since the index motors 40a and 40b comprise servomotors, even if they are rapidly stopped, no deviation occurs in position, and the connecting operation can be terminated in a short period of time.
It is necessary for employment of the aforesaid construction to sufficiently increase the pitch accuracy of the shift gears 24a, 24b and gears 25a, 25b. When the high pitch accuracy of the shift gears 24a, 24b and gears 25a, 25b cannot be expected, the pitch counters 49a, 49b and 48a, 48b in FIG. 11 are increased in amount so that counting is made by the pitch counters 49a, 49b and 48a, 48b of the angle of rotation of gears 25a, 25b and shift gears 24a, 24b from the reference phase and the the shift gears 24a and 24b of the spindle indexing and driving devices 23a and 23b may be rotated through the count difference detected by the comparators 51a and 51b. In this case, since the ~0~)99~3 engagement of the gears 25a, 25b and shift gears 24a, 24b is always at a constant position, the accuracy may be easily maintained.
According to the above-described construction, the connecting operation with idle time considerably reduced is rendered possible, and thereby the orientation mechanism herefore required becomes unnecessary to render possible a great reduction in cost in terms of construction of machine.
While the control system shown in FIG. 11 is shown by the circuit block diagram, it is to be noted that similar operation can be carried out by the program of the CNC device. Such a device controlled by the program can be employed as the connecting mechanism of the spindle indexing and driving devices. This is also true for the following phase adjusting mechanism of spindles.
(Control mechanism for the spindle indexing and driving devices) The index motors 40a and 40b are controlled by the servo drivers 47a and 47b upon receipt of a command from the CNC device 46, as shown in FIG. 10.
Outputs of the indexing encoders 26a and 26b are inputted as speed signals into the servo drivers 47a :

2(~t)9993 and 47b to feedback control the speeds of the index motors 40a and 40b, and on the other hand, inputted as phase signals into the CNC device 46, so that when the phase signals assume a predetermined value, that is, when the spindles lla and llb are located at a predetermined angle, the CNC device issues a stop command to the servo drivers 47a and 47b.
The indexing operation is carried out at high speeds by rotating the index motors 40a and 40b at high speeds, whereas at the indexing position, the brake devices 22a and 22b are powerfully actuated to stop them at a predetermined position. In case of milling for contouring, the CNC device 46 issues a feed speed to the servo drivers 47a and 47b, which in turn cause the spindles lla and llb to be rotated at a speed instructed by the feedback control.
When the spindle indexing and driving devices 23a and 23b are used to rotate the spindles lla and llb, powerful continuous milling work can be accomplished.
At that time, the spindles lla and llb are applied with half brake by the brake devices 22a and 22b when necessary to prevent vibrations of the spindles lla and llb due to the variation in load.

2~99~3 Moreover, since the phase of the spindles lla and llb during the transfer of the workpiece can be set by the program of the CNC device 46, a variety of transfers and workings of workpiece can be executed, making it possible to provide an effective composite machine coupled with an increase in rigidity of the first spindle stock 2a aæ previously mentioned.
(Phase-adjusting device for both spindles) The phase adjustment of the spindles lla and llb when the workpiece is transferred is carried out, as shown in FIG. 11, in the procedure such that a value (a difference in indicated value between a reference phase and a present phase) of the counters 60a and 60b of the indexing encoders 26a and 26b and a rotation command is given to either index motor 40a or 40b so that both are the coincided or set phase difference, or rotation commands in both normal and reverse directions are given to both the index motors 40a and 40b so that both are the coincided or set phase difference. Further, a preferable construction is that a control device is provided so that the second spindle llb and the first spindle lla are rotated in the opposite direction to each other toward the target phase.

Z~0~993 Servo motors are used as the index motors 40a and 40b whereby the phase adjustment of the spindles lla and llb each other can be made in a very short period of time.
A specific description will be made hereinafter.
Assume that both the gears 25a and 25b of the spindles lla and llb and the shift gears 24a and 24b have the same number of teeth, the number of teeth being z, and n = 360/z, then, the number of meshing points of the gears is z every n.
It is assumed that the reference positional phase of the gear 25a on the first spindle side is normally 0, the present positional phase (stop positional phase) of the gear 25a on the first spindle side is al, the reference positional phase of the shift gear 24a on the first spindle side is 0, and the present positional phase (stop positional phase) of the shift gear 24a on the first spindle side is ~1.
It is assumed that the reference positional phase of the gear 25b on the second spindle side is normally 0, the present positional phase (stop positional phase) of the gear 25b on the second spindle side is a2, the reference positional phase of the gear Z 0~9~3 24b on the second spindle side is normally 0, and present positional phase (stop positional phase) of the shift gear 24b on the second spindle side is ~2.
In the foregoing, phase data are two sets amounting to four.
The shift gear 24a is meshed with the gear 25a of the spindle lla, and 81 is obtained from the formula below:
al - a2 = m x n + ~1 where m is an integer including 0. If the gear 24a is rotated through 81, it reaches the meshing position.
The value of 81 is normally smaller than n. That is, for example, if z is 36, 81 is less than 10. The time required for indexing is very short.
Also in case of the second spindle, similar operation is able to carry out.
The phase at the meshing position between the gears 25a and 25b and the shift gears 24a and 24b is + 81 in the first spindle, and ~2 ~ 82 in the second spindle.
In adjusting phases of the spindles lla and llb for transfer of a workpiece, an angular phase at which workpiece is transferred is set to r.

2~0~39~3 In case of r = o, that is, in case where transfer is effected with a workpiece is stopped at an original phase, the spindles are indexed and rotated by + 81 in the first spindle, and ~2 + 82 in the second spindle.
Since r may not be O unless an interference of fixtures or machinery is present, if r is not O and the transfer is effected if phases of the first and second spindles are coincided, the spindles are indexed and rotated by 1/2 of a phase difference between the first and second spindles, and a transfer phase is automatically obtained by calculation and both the spindles are indexed to that position~then Q = [ (~1 + 81) ~ 2 + ~i2) ] / 2 If indexing is made through an angle of Q, a transfer point is obtained. In this manner, an angular phase of milling executed by the first spindle is succeeded as an accurate phase angle even after a workpiece has been moved to the second spindle.
In case of a shape such that an interference occurs in a chuck jaws when a workpiece is transferred, an offset angle free from interference is predetermined, and there may be set an angle obtained by adding a 20~)~`993 required offset angle to a phase at which the first and second spindles are coincided at the time of transfer.
Let r be the offset angle, the following formula holds in place of the above-described formula.
Q + r/2 = [(~1 + ~ 2 + ~2) + r] / 2 That is, if the spindles are mutually rotated in derections of (+) and (-) through an angle of Q +
r/2, the transfer of a workpiece may be made.
(Spindle motor control mechanism) FIG. 12 shows the control system for the spindle motors 21a and 21b. When the spindle motors 21a and 21b are individually operated, the speeds thereof are individually controlled by motor control portions 52a and 52b which receive the individual speed commands from the CNC device 46. When the spindle motors 21a and 21b are synchronously operated, they are controlled by a synchronous control device 53 through switching of a switch 57.
In FIG. 12, the synchronous control device 53 encircled by the dash-dotted contour lines comprises a slow/fast discriminating circuit 54 for comparing magnitude of signals issued by both the spindle encoders 27a and 27b, a correction value setting unit 55 for setting a correction value of one unit, a correction 2~9993 command circuit 56 for causing said correction value of one unit to input as an addition or subtraction signal into speed command correction circuits 58a and 58b on the basis of the output of said slow/fast discriminating circuit 54, a switch 57, and speed command correction circuits 58a and 58b for correcting the speed command applied to the motor control portions 52a and 52b of the spindle motors 21a and 21b from the CNC device 46. The slow/fast discriminating circuit 54 counts and compares output pulses of the spindle encoders 27a and 27b in a fine time of millisecond unit to monitor whether or not a phase difference or a speed difference between the first and second spindles lla and llb occurs according to the magnitude of the output pulses.
FIG. 13 is an example showing a circuit partly omitting on the side of the second spindle llb in the aforesaid slow/fast discriminating circuit 54. A
circuit similar to that on the side of first spindle lla with an affix "a" applied thereto is also provided on the side of the second spindle llb, in which circuit, output pulses of the spindle encoders 27a and 27b are provided in predetermined width to count them by the counters 63a and 63b, and a difference therebetween is discriminated by a comparator 64. The spindle encoders 2Q~999;~

27a and 27b have phase detecting slits 65, ... for generating output pulse every predetermined angle and reference angle pulse generating slits 65' for generating reference angle pulse every predetermined angle as shown FIG. 14, the latter output pulse being inputted into AND gates 69a and 69b for providing count pulses through one shot circuits 66a, 66b, AND gates 67a, 67b and OR gates 68a and 68b.
On the other hand, acceleration signal and deceleration signal to the spindle motors 21a and 21b are formed into a common signal (acceleration and deceleration signal) P by OR gates 70a and 70b, which is fed to the AND gates 67a and 67b, and also fed to the OR
gates 68a and 68b via inverters 71a and 71b. The acceleration signal and deceleration signal may be outputted, for example, when the count value before last is compared with the previous count value of the counters 63a and 63b and the resultant value is larger or smaller than an allowable value.
A one shot circuit 72 for defining the width of count pulse is provided, which is triggered by a timing pulses TP applied at regular time intervals (sampling time intervals), outputs of which serve as input signals of AND gates 69a and 69b.

20~993 With the above-described arrangement, when the spindle lla and llb are operated at constant speed, the acceleration and deceleration signal P is at LOW level and when the inverters 71a and 71b are inverted, outputs of OR gates 68a and 68b are maintained at HIGH level, and therefore, the count pulses in pulse width of the one shot circuit 72 are provided as shown in FIG. 15(a).
If a speed difference is present between the spindles lla and llb, a difference in count value between the first counter 63a and the second counter 63b occurs, the magnitude of which is discriminated by the comparator 64. When the spindles lla and llb are being accelerated and decelerated, the timing pulse TP of the one shot circuit 72 rises, and thereafter the pulses of the one shot circuits 66a and 66b triggered by the reference angle pulse rise, after which output pulses of the spindle encoders 27a and 27b are counted. Therefore, the count start time on the side in which the phase is early becomes fast, and even if the speeds are the same, the count value on the side in which the phase is early becomes large. Accordingly, the phase difference can be discriminated by comparing the count values of the first and second counters 63a and 63b similarly to the case of 20~9993 the constant speed rotation. Thereby, hunting during the constant speed rotation can be prevented.
A speed correction value to be given every unit time interval to the correction command circuit 56 is set to the correction value setting unit 55. This correction value can be given by the NC program as previously mentioned. The correction command circuit 56 receives the output of the slow/fast discriminating circuit 54 to supply the correction value set to the correction value setting unit 55 as a subtraction command or an addition command to the speed command correction circuits 58a and 58b. Of course, correction values are supplied as a subtraction command and an addition command to the side in which phase and speed are gained and to the side in which they are delayed, respectively. The speed command correction circuits 58a and 58b adds or subtracts the correction value from the speed command supplied ~rom the CNC device 46 to supply the speed command to the motor control portions 52a and 52b.
When the first spindle lla and the second spindle llb are desired to be synchronously driven, the speed command for the first spindle lla is supplied to both the motor control portions 52a and 52b by the 20~)99~3 switch 57, and the switch 57 is switched so that the correction signal may be supplied to the speed command correction circuits 58a and 58b so that the correction value is subtracted and inputted into the side in which the phase is gained and conversely the correction value is added and inputted into the side in which the phase is delayed. This series of control cycles are repeatedly carried out at short time intervals whereby the first spindle lla and the second spindle llb can be synchronized.
While in the above-described embodiment, the synchronous control device 53 is formed from a hard structure for better understanding, it is to be noted that it may be formed from a soft ware of a computer.
Actually, the soft ware structure is preferable because it has a high flexibility.
(Procedure for working the workpiece) Working of the workpiece 16 by the two-spindle opposed type CNC lathe according to this invention is carried out in the following procedure.
First, the chuck opening and closing cylinder 20a of the first spindle lla forming the first working unit 17a is operated so that the workpiece 16 is held by the chuck l9a to effect turning operation in cooperation 2 ~ ~ ~ 3 with the first tool rest 3a. At this time, the shape of the workpiece 16 to be worked is determined according to the degree of movement of the first tool rest 3a in the Z-axis direction and in the X-axis direction. Upon termination of the turning operation, the first spindle lla is rapidly reduced in speed to be stopped without locating to a predetermined reference phase.
When milling or drilling is required in the working by the first working unit 17a, phases of connecting portions between the spindle lla and the spindle indexing and driving device 23a are adjusted, and the first spindle lla and the spindle indexing and driving device 23a are connected by the disengageable mechanism 23'a to effect indexing and milling operation of contouring.
When the first spindle lla and the spindle indexing and driving device 23a are connected by the disengageable mechanism 23'a, the index motor 40a is rotated to the engaging position between the shift gear 24a and the gear 25a on the basis of the count value from the spindle encoder 27a showing the phase of the spindle lla and the count value from the indexing encoder 26a, and the shift gear 24a is moved by the shift cylinder 45 and the shift fork 44 to engage the 2(~0~3993 shift gear 24a with the gear 25a. The thereafter indexing is carried out by rotating the index motor 40a on the basis of the count value from the indexing encoder 26a. If the servo motor normally used is used as the index motor 40, high speed locating of the spindle indexing and driving device 23a can be easily accomplished, and the connection between the first spindle lla and the spindle indexing and driving device 23a can be carried out in a few seconds.
Upon termination of the working by the first working unit 17a, the phase of the first spindle lla is made in coincidence with that of the second spindle llb, the second spindle stock 2b is moved toward the first spindle stock 2a, and the workpiece 16 is transferred from the chuck l9a to the chuck l9b by the operation of the chuck cylinders 20a and 20b.
In case where the workpiece 16 is a bar, there includes the step in which the end of the bar is held by the chuck l9b of the second spindle llb, and thereafter, the first spindle lla and the second spindle llb are synchronously rotated by the synchronous control device 53a and the workpiece 16 is cut off from the end of the bar by cutting-off operation.

ZO~)99g3 The adjustment of phases between the first spindle lla and the second spindle llb when the workpiece is to be delivered is carried out by connecting the spindle indexing and driving device 23b with the second spindle llb through the connecting mechanism, then reading the count value from the index-ing encoder 26a of the first spindle stock 2a when the indexing has been terminated, and rotating the index motor 40b till said value coincides with that of the second spindle stock 2b or assumes the designated angle difference to adjust the phases to effect the delivery of the workpiece 16. In case where the servo motor is used as the index motor 40b, the adjustment of phases at the time of delivery of the workpiece 16 can be done in a very short period of time. At this time, the adjustment of phases between the first spindle lla and the second spindle llb can be carried out by reversely rotating both the spindle indexing and driving devices 23a and 23b in an approaching direction.
In case where the workpiece 16 is a flange, the lengthwise dimension of the workpiece 16 is often relatively small, and therefore, in this case, when the workpiece 16 is approached for the transfer from the first spindle lla to the second spindle llb, there is a 2~ 33 fear that the chucks l9a and l9b collide with each other. To avoid this, it is necessary to deviate the phase of the second spindle llb from the phase of the first spindle lla through 60 degrees (in case where the chucks l9a and l9b are of three jaws). However, in the present invention, when the workpiece 16 is transferred, the amount of rotation of the first spindle lla or the second spindle llb may be corrected through a deviation portion. This phase difference will suffice to be input in the NC program.
Furthermore, rising of rotation in the state where both ends of the work are held at the time of working a bar is promptly and smoothly carried out by the synchronous control device 53. Therefore, in this respect, the working cycle can be shortened, the second spindle stock 2b is given sufficient rigidity and an excessively large torsional load is not exerted on the workpiece 16. Moreover, by the addition of the synchronous control device 53, the workpiece 16 may be transferred while synchronously rotating the first spindle lla and the second spindle llb. In case where the final working on the side of the first spindle lla is turning, such operations are carried out whereby the idle time required to once stop and again accelerate the first spindle lla can be reduced.
The synchronous control device 53 compares signals from the spindle encoders 27a and 27b so that a speed command is offset and inputted to the spindle of which speed is high or the spindle of which phase is gained in a direction of delaying it whereas a speed command is offset and inputted to the spindle of which speed is low or the spindle of which phase is delayed in a direction of advancing it to thereby make a control so as to make zero the speed difference or phase difference between both the spindles lla and llb covering the rotational characteristics and inertia characteristics.
In the system for correcting and inputting as a common command the speed command supplied from the CNC device 46 to the spindle motor control portions 52a and 52b to modify the speed difference or phase difference as described above, controlling to follow each other is effected to follow an average value between both the spindles toward the target unlike the conventional following system heretofore often used, that is, the system to cause one to follow with the other being a principal.

With this, the amount of correction per each spindle when the phase difference or speed difference is corrected will suffice to be half of the one-side following system. The prompt following operation can be effected during high speed rotation or during rapid acceleration or deceleration while suppressing servo hunting.
In the conventional controling,for the detection of the speed difference or phase difference, an amount of deviation is detected to obtain a command value corresponding to a differential thereof by computation. This requires a time for computation process and a repeated unit of period for correction cannot be shortened. Therefore, for those machines such as the lathe which rotates at high speed and is short in acceleration and deceleration time, the speed difference or phase difference between both the spindles lla and llb becomes already varied when the correction value is calculated, resulting in a rough control with time lag to fail to maintain a good synchronous accuracy. On the other hand, in the present invention, since the repeated unit of control period is shortened and therefore all the computation to obtain the correction command value from the phase difference or speed difference can be ~o~

omitted, and the slow/fast is merely discriminated to ignore the amount thereof. The set correction values are simply added or subtracted so as to obtain the command value. The correction values of one unit to be set are individually set in advance in consideration of the characteristics of individual motors, and the individual working programs are set in consideration of the mass or the like of workpiece. Thereby, the repeated period for the correcting operation is a millisecond unit. Correction can be made almost continuously. Furthermore, by setting an adequate unit correction value, prompt synchronous control can be effected without occurrence of hunting.
In the sampling of the encoder signal, the phase difference between both the spindles lla and llb is discriminated during the acceleration or deceleration to effect acceleration control, whereas the speed difference is discriminated during constant speed operation to effect speed control. In doing so, it is possible to positively prevent a large torsional torque which involves a danger acting on the workpiece during acceleration or deceleration and to effectively prevent hunting during constant speed operation.

In case where in inputting a predetermined correction value, the speed difference or phase difference is below a fixed value, an insensitive zone is provided so as not to produce a correction signal from the synchronous control device, thus preventing control hunting to stabilize the operation. In case where both the spindles lla and llb are operated at independent rotational speeds, the synchronous control device 53 is disengaged by the switch 57 whereby sufficiently coping with the independent operation of each of the spindles lla and llb.
After the workpiece 16 has been delivered to the chuck l9b of the second spindle llb, the second spindle llb is moved in the direction of moving away from the first spindle lla to work the back of the workpiece 16 in cooperation with the second tool rest 3b. At this time, the shape of the workpiece 16 to be worked is determined by the movement of the second spindle stock 2b in the Z-axis direction and the movement of the second tool rest 3b in the X-axis direction. During that period, the next workpiece 16 is supplied to the chuck l9a of the first spindle lla, and the previous workpiece 16 and the next workpiece 16 are simultaneously worked. After the working by the second 2(~ 993 working unit 17b has been terminated, the previous workpiece 16 is discharged outside the machine, and the chuck l9b of the second spindle stock 2b moves to grip the workpiece 16 which has been worked in the first spindle stock 2a. The workpieces 16 are successively worked in a similar procedure.
Cutting liquid is sprinkled over the workpiece 16 being worked, and the chips ruptured by the tools on the tool rests 3a and 3b flow down on the cover 18 together with the cutting liquid and thence fall into the chip receiving box 4 at the front edge of the base 1. The chips gathered in the chip receiving box 4 are delivered into a bucket provided laterally of the machine by means of the chip conveyor 5, the cutting liquid being filtered and circulated for use.
In the working accompanied by the transfer of the work between the first working unit 17a and the second working unit 17b, as shown in FIG. 4, a command is given to the first working unit 17a with a first working program A with a work transfer program JA added to the end thereof whereas a command is given to the second working unit 17b with a work transfer program JB
added to the head thereof.

20~3~3;3 In case where for example, the program A
portion of the working for the workpiece 16 as shown in FIG. 4 is simultaneously carried out by the first working unit 17a and the second working unit 17b, using the two-spindle opposed type CNC lathe according to this invention, a command is given with the same working program A to both the working units 17a and 17b, as shown in FIG. 5. At this time, the rightward movement of the first tool rest 3a and the rightward movement of the second spindle stock 2b are the movements of the tools in the direction of moving away from the spindles lla and llb, and the relative moving relation between the workpiece 16 and the tool is the same in the irst working unit 17a as well as in the second working unit 17b. Accordingly, if a command of movement in the X-axis direction given to the first tool rest 3a is given to the second tool rest 3b as it is, exactly the same working as that to be done in the first working unit 17a can be effected even in the second working unit by the same program. Exactly the same working program A may be given to both units.
According to this invention, since the spindle indexing and driving devices 23a and 23b having a large reverse resistance are mounted on the first spindle lla 2~0~9~3 and the second spindle llb, powerful contouring millings can be simultaneously carried out with the coincided phase of the back working, and naturally, the same rotary tool for milling as that of the first tool rest is mounted on the second tool rest 3b. In this construction, the slant type base 1 is employed to facilitate the maintenance operation of the tool, and the chip receiving box 4 is arranged frontwardly of the machine to promote quick discharge of chips and quick radiation of cutting heat.
According to the construction of the two-spindle opposed type CNC lathe of this invention, since two tools are positioned in deep of the spindles, good accessability to the spindles is obtained, good workability during mounting and removal of the work is obtained, and no danger involves in operation. These effects are further promoted by the use of the slant type base.
Furthermore, since there is employed a construction in which the first spindle stock is fixed, sufficient rigidity can be applied to the first spindle stock. During working of a bar no problem occurs that a workpiece on the bar feeder is axially moved.

2~

A conventional bar feeder can be used without modification. If the first tool rest is moved in the Z-axis direction, mounting and removal of the tool to the turret and maintenance and repair of the tool rests can be easily carried out.
Moreover, since the discharge of the chips or cutting liquid into the chip receiving box installed frontwardly of the base can be quickly done, it is possible to minimize the thermal deformation of the machine body. Various types of workpiece loaders and unloaders may be utilized without modification.
In addition, connection of the spindle indexing and driving device to the spindle and adjustment of phases of the first and second æpindles can be very quickly accomplished to considerably enhance the working efficiency in the composite one continuous operation of the workpiece including the back working and indexing. Since the index locating and low speed rotation feed can be given to the spindle by the independent spindle indexing and driving device, the reverse resistance can be increased during the working.
It is possible to provide a two-spindle opposed type CNC
lathe provided with a powerful working ability as well 200~9~

as an increase in rigidity of the first spindle stock as mentioned above.
Moreover, according to the æynchronous control device of this invention, the phase difference or speed difference between the first and ~second spindles can be detected at extremely short time intervals to correct the speed command continuously given to the spindle motor, and therefore the phases or speeds of two spindleæ can be accurately synchronized during the rapid acceleration or deceleration as well as constant speed operation. Since the control construction is simple, the machine can be operated in a simple manner. If the set value is set by the CNC device while adjusting to the size of workpiece and working situation, hunting and torsional stress acting on the workpiece can be positively avoided.
Furthermore, in the lathe of this invention, when the same workpiece is worked by the first and second working units, the same NC program can be used to thereby relieve the trouble in preparation of program.
In addition, if the moving direction of the first tool rest in the Z-axis direction is the same (for example, rightward movement) as that of the second spindle stock, the relative moving relation between the tool and the 2~)0~9~3 workpiece is also the same (for example, the direction in which the tool moves away ~rom the spindle), and therefore, erroneous operation during manual operation can be avoided, and collision or the like between the workpieces resulting from the erroneous operation can be positively prevented.

Claims

1. A two-spindle opposed type CNC lathe comprising two opposed spindle stocks consisting of a first spindle stock and a second spindle stock, each spindle stock supporting a spindle for rotation about parallel spindle axes, two tool rests consisting of a first turret type tool rest forming a first working unit together with said first spindle stock and a second turret type tool rest forming a second working unit together with said second spindle stock, said two spindle stocks and said two tool rests being mounted on a common base, said lathe being provided with a CNC device for working a workpiece principally in the shape of a rotary body, characterized in that a. the base is of the slant type inclined at a down gradient;
b. the first spindle stock is secured to the base;
c. the second spindle stock is mounted on the base through a slide capable of being moved and located in the direction of the axis of its respective spindle; and d. the first tool rest is mounted on the base through a slide capable of being moved and located in the direction of the axis of its respective spindle, and in the direction perpendicular thereto, and the second tool rest is mounted on the base through a slide adapted to be moved and located only in the direction perpendicular to the axial direction of its respective spindle, said mounting position being offset from both the spindle stocks.

2. The two-spindle opposed type CNC lathe according to claim 1, wherein the upper surface of the base between the first and second spindle stocks in the base of the slant type is covered by a cover which expands as the second spindle stock moves.

3. The two-spindle opposed type CNC lathe according to claim 1, wherein a separately placing type of a chip receiving box having a chip discharging conveyor mounted interiorly thereof is arranged at the lower portion of the front edge of the slant type base.

4. The two-spindle opposed type CNC lathe according to claim 1, wherein both the first and second spindle stocks are respectively separately provided with a spindle driving device for turning working and a spindle indexing and driving device for indexing and milling working for contouring, the spindle indexing devices and the spindles being mechanically disconnected, and said disconnecting operation, clamping and unclamping operation for the workpiece on the chuck provided at the end of the spindle of each spindle stock, rotation, stopping and indexing of each spindle and movement and locating of the second spindle stock are controlled by the CNC device individually or synchronously actuated along with the movement and locating of each tool rest and the indexing of the turret and fixing operation.

5. The two-spindle opposed type CNC lathe according to claim 4, wherein both the spindle stocks are provided with a brake device capable of adjusting a load for applying a rotational load to the spindle.

6. The two-spindle opposed type CNC lathe according to claim 4, wherein both the spindle indexing and driving devices are respectively provided with a shift gear in engagement with gears secured to the spindles of the spindle stocks, a disengageable mechanism for the gear secured to the spindle and the shift gear, a reduction mechanism and an index motor having an encoder for detecting a phase of the driving shift gear.

7. The two-spindle opposed type CNC lathe according to claim 4, wherein the first spindle and the second spindle are respectively provided with a spindle encoder for detecting a phase of the spindle and an indexing encoder for detecting a phase of the spindle indexing and driving device, and in adjusting phases of the first spindle and the second spindle on the basis of a command of the CNC device in order to effect the transfer of work between the spindles, the index motor is rotated on the basis of a difference in indicated value between a reference position phase and a present phase of said indexing encoder so that the first spindle and the second spindle are adjusted in phase to the same phase or the set phase difference.

8. The two-spindle opposed type CNC lathe according to claim 7, wherein in adjusting phases between the first spindle and the second spindle in order to effect the transfer of workpiece between the spindles, the first spindle and the second spindle are rotated in the direction opposite to each other toward the target phase.

9. The two-spindle opposed type CNC lathe according to claim 4, wherein the first spindle and the second spindle are respectively provided with a spindle encoder for detecting a phase of the spindle and an indexing encoder for detecting a phase of the spindle indexing and driving device, means is provided to detect an engaging position between the gears for the first and second spindles and the shift gears of the spindle indexing and driving device corresponding thereto from each four of data comprising a reference position phase and a present phase of the spindle detected by the spindle encoder and a reference position phase and a present phase detected by the indexing encoder, and in connecting the spindle indexing and driving device to each spindle on the basis of the command of the CNC
device, the index motor of the spindle indexing and driving device is rotated to the engaging position defined by the present phase of the spindle encoder to engage the shift gear therewith.

10. The two-spindle opposed type CNC lathe according to claims 7 or 9, wherein the spindle indexing and driving device for rotatively driving the first spindle and the second spindle for turning working is connected to a synchronous control device for synchronizing and rotating the spindle motors, said synchronous control device being adjusted in phase to effect acceleration or deceleration and turning or cutting-off working while synchronously rotating the first and second spindles which hold both ends of the workpiece.

11. The two-spindle opposed type CNC lathe according to claim 10, wherein the synchronous control device includes means for detecting slow/fast of both spindles from a difference in pulse number per unit time generated by each spindle encoder and means, when said slow/fast is detected, for making the fine correction value normal or reverse to supply it to the spindle motor control portion.

12. The two-spindle opposed type CNC lathe according to claim 10, wherein the synchronous control device comprises a spindle encoder for detecting a rotational speed and a relative phase of the first and second spindles, a slow/fast discriminating circuit for measuring signals generated therefrom by fine unit time to compare the magnitude thereof, a correction setting unit for setting a correction value of one unit, a speed correction circuit for correcting a speed command to be given from the CNC device to the motor control portion for controlling the rotation of each of the spindles, and a correction command circuit for inputting said correction value of one unit as an addition or subtraction signal to said speed correction circuit on the basis of the output of said slow/fast discriminating circuit, whereby the correction operation can be repeated at fine time intervals in the direction of delaying the phase for the side in which the phase is gained whereas in the direction of advancing the phase for the side in which the phase is delayed.

13. The two-spindle opposed type CNC lathe according to claim 10, wherein the slow/fast discriminating circuit detects and compares phase differences of the spindles when the spindles are accelerated or decelerated, whereas detects and compares rotational speed differences of the spindles when the spindles are rotated at constant speed.