DESC:FIELD OF THE INVENTION
The invention relates to machine-tool construction, particularly, to turn mill center for multiple machining. The invention relates to a machine to perform independent turning and milling operations. The invention particularly relates to a method for rotating and precise positioning of the Machine Tool spindle during metal working operations. Additionally the invention relates to an improved C-axis configuration of a Turn Mill centers.

BACKGROUND OF THE INVENTION
With ever increased demand for reduced sizes and increased complexity and accuracy, traditional machine tools have become less effective for machining components. The present invention relates to machine-tool construction, particularly, to turn/mill centers for multiple precise machining. Said machine can perform independent and combined turning and milling operations. Lathes of the general character referred are provided with and controlled by electronic, computer-numerical-controllers that control each of the functions of the lathes and that are programmable to effect the automatic manufacture of multiplicities of different cylindrical parts that such lathes are intended and capable of producing. Computer-numerical-controlled lathes are commonly called CNC lathes.

CN208826046U relates to a turning and milling compound table. The utility model discloses turning and milling compound tables, including working basic stand, the gear assembly of turning-milling complex processing component, the Turntable Assemblies for placing workpiece to be processed and the driving Turntable Assemblies rotation is installed on the working basic stand, turning-milling complex processing component includes power source and the general tool apron of the turning and milling connecting with power source. Using turning-milling complex processing component, milling cutter or lathe tool can be replaced by the general tool apron of turning and milling to realize cutter changing. The gap that disappears is realized using gear case assembly, passes through the control for controlling the motor speed realization turntable revolving speed of gear case assembly. To realize that structure is simple, and manufacturing cost is low in the enterprising driving of same turntable, milling. This model is limited to carryout turning and milling operations by means of a universal tool.

CN105834807A relates to a tool handle positioning structure with clearance removing mechanisms. The invention discloses a tool handle positioning structure with clearance removing mechanisms. The tool handle positioning structure comprises at least two limiting pins fixedly arranged on a spindle or a spindle box, and a limiting block used for being fixedly installed on a tool handle of a tool. The limiting block comprises a fixing part and at least two connecting arms. A through hole is formed in the fixing part, and each connecting arm is provided with a limiting hole. Each connecting arm is provided with a radial hole. One end of each radial hole communicates with the corresponding limiting hole. Each radial hole is internally provided with one clearance removing mechanism. Each limiting pin is correspondingly inserted in the corresponding limiting hole in a connected manner. The side wall of each limiting pin abuts against a ball. The tool handle positioning structure has the beneficial effect of being good in locking effect. Meanwhile, the connecting rigidity for positioning the tool turning tool handle through the double pins can be effectively improved. Furthermore, the shaking phenomenon caused by starting and stopping of turning is eliminated by applying static pretightening force. This model is mainly for tool positioning purpose not for the machining accepts.

CN208895590U relates to the turning and milling compound table component of high stationarity. The utility model discloses the turning and milling compound table components of high stationarity, including working basic stand, the gear assembly of turning-milling complex processing component, the Turntable Assemblies for placing workpiece to be processed and the driving Turntable Assemblies rotation is installed on the working basic stand, damper, damper is attached most importance to oil damper, and turning-milling complex processing component includes power source and the general tool apron of the turning and milling connecting with power source. Using turning-milling complex processing component, milling cutter or lathe tool can be replaced by the general tool apron of turning and milling to realize cutter changing. The gap that disappears is realized using gear case assembly, passes through the control for controlling the motor speed realization turntable revolving speed of gear case assembly. To realize in the enterprising driving of same turntable, milling, structure is simple, manufacturing cost is low, pass through the design of heavy oil damper, stability of the turntable when slowly running is improved, and utilizes stabilizing base, when slowly running, the distance between upper stabilizing base, lower stabilizing base seaming chuck are designed using oil pressure, improves the stability of turntable operation. The assembly is complex in shape and backlash cannot be controlled effectively as it is having gear drive mechanism.

CN103753351B relates to a kind of Digit Control Machine Tool backlash monitoring method of Full-closed servo system. A Digit Control Machine Tool backlash monitoring method for Full-closed servo system, utilizes lathe built-in encoder to carry out continuous sampling to motor and operating position, and taking motor position as reference position, computing reference position sequence xm(n) locate backlash sequence c (n), compare and traditional backlash method of testing, the method is without outer sensor, can realize the measurement to omnidistance backlash, with respect to representing omnidistance gap with the gap width of a point, the method can be more accurate, comprehensively test out backlash situation, method of testing automaticity is high, by Real-Time Monitoring lathe backlash situation and calculate backlash profile errors in closed-loop Digit Control Machine Tool, thereby realize monitoring and control to profile errors, guarantee the profile errors error range in allowing all the time, this monitoring method automaticity is higher, monitoring cost is lower, monitoring reliability is high. This system of integration needs high degree of automation.

KR101602941B1 relates to a machining method of Roller Gear Cam using 5-Axis CNC Machine. The present invention relates to a method for processing a roller gear cam using a five-axis computer numerical control (CNC) machine, and more specifically, to a method for processing a roller gear cam using a five-axis CNC machine comprising: an angle diagram definition step; a rough cutting step; and a fine cutting step. In the angle diagram definition step, data is extracted to form an angle between slanted surfaces on both sides of a thread (24) of a drum cam (20) to be bigger than the angle between rollers (12) of a follower (10). Moreover, in the fine cutting step, data is extracted to allow the width of a groove (22) of the drum cam (20) to be increased in a curved section of the groove (22) of the drum cam (20), compared with a linear section. Accordingly, controlling the inter-axial distance between the follower and the cam to reduce the backlash formed between the rollers of the follower and the cam is unnecessary such that the roller cam gear can be easily installed. Furthermore, the position of the follower can be stably maintained in the linear section of the groove of the cam, and stress concentrated on one of the rollers of the follower or a clearance generated on other roller can be prevented. This machine is proposed to process mainly roller gear cam using 5 axis CNC machine. whereas the submitted C axis machine is for multiple machining operations.

CN104117716B relates to a multi-Precision strengthens CNC planer type milling machine. The present invention relates to mechanical system field, more particularly to a kind of portal bench. Multi-Precision strengthens CNC planer type milling machine, including workbench, portal frame, portal frame includes at least two columns, and column is equipped with crossbeam, and crossbeam is equipped with slide carriage, slide carriage is equipped with main shaft, cutter adapter is equipped with below main shaft, main shaft uses an electro spindle, a motor is equipped with below electro spindle, as spindle motor, the shaft connection cutter adapter of spindle motor;Electro spindle upper end is fixedly connected with slide carriage. In above-mentioned design, the actuating unit of cutter adapter is set directly on main shaft, rather than by the way of traditional transmission using transmission mechanism. Reduce intermediate transmission link, the power of spindle motor is directly transferred to as far as possible on cutter, so as to greatly improve precision. It is an enhanced multi precision CNC gantry milling machine.

The background art discloses lathes with low accuracy due to transmission backlash; the present invention discloses a design of precision C-axis of a CNC Turn Mill Centre.

OBJECTS OF INVENTION
The primary objective of the invention is to develop C axis with backlash free transmission system.

Another objective of the invention is development of modular design concept to adapt for any type and range of CNC Turn Mill Centre with minimum modifications.

Another objective of the invention is in order to eliminate the backlash in the transmission system, we are applying a reverse drive with additional motor and the system will move overcoming this applied drive and this is being implemented by electrical bracing of two drives.

Another objective of the invention is the electrical bracing work on the basis of master slave control of two identical systems and master drive has higher torque in the process and slave drive work against it and this is how transmission backlash is eliminated and positional accuracy is improved.

SUMMARY OF THE INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.

It is the primary aspect of the present invention to provide a CNC turn mill center with anti-backlash modular C axis drive, comprising:
one or more C-axis drive units with one or more servo motors;
a coupling cylinder;
a main drive measurement unit;
C-axis direct measurement unit;
a coupling cylinder position sensing unit;
a master control unit in drive configuration;
a slave control unit in drive configuration;
a CNC controller;
one or more motors;
one or more drive shafts;
one or more gears; and
a spindle,
wherein an encoder of the C Axis drives (for a control circuit which is placed inside the cabinet and outside the mill center) is the direct measuring unit always remains fixed/ coupled to the C Axis drive,
wherein the rotating speed of the spindle is controlled by the servo drive controlling the rotating speed of a motor of the gear box assembly and the turning and milling is carried out on the same spindle,
a reverse drive/opposite direction rotation is applied to the master drive unit with an additional motor for anti-backlash in the transmission system and the mill center is moved overcoming this applied drive and is implemented by electrical bracing such that slave drive unit with torque between 10 Nm to 20 Nm is allowed to rotate in the opposite direction with respect to the master drive of two drives, and
the electrical bracing is implemented with the master and slave control units which are identical in rating and the master drive has torque between 520Nm to 560Nm in the process and the slave drive work against it for anti-backlash in the transmission system.

It is another aspect of the present invention, wherein the C-axis drive units with one or more servo motors comprises of two modes of operation:
the spindle is driven by the main motor with a speed of 2800 rpm and torque of 230 Nm, in the direct drive (variant A); and
once to the second mode (variant B) is activated, the C axis drive is engaged with the spindle drive and offers a speed of 45 rpm with high torque 585 Nm.

It is another aspect of the present invention, wherein the coupling arrangement is provided for the engagement of C axis drive to the spindle drive once the mode of operation is changed.

It is another aspect of the present invention, wherein the main drive measurement unit is an encoder attached to the measuring system and is integrated to measure the speed of the spindle drive.

It is another aspect of the present invention, wherein the encoder is attached to ensure the speed feedback of the C axis drive, once the variant B mode is activated.
It is another aspect of the present invention, wherein the sensing unit is attached to the C axis drive to get the feedback of the swiveling mechanism for engagement of C axis drive to the main spindle once the variant B gets activated.

It is another aspect of the present invention, wherein the C-axis drive units engage with the main spindle of the lathe machine when needed to make it a rotary axis and the drive unit from the main spindle motor is isolated from the spindle during this operation and uses the swivel mechanism to engage the C axis.

It is another aspect of the present invention, wherein the development of modular design with the swivel mechanism and the C-axis drive is adapted for any type and range of the CNC turn mill centre.

It is another aspect of the present invention, wherein the characterized driving between the shaft and gears detect and correct the backlash.

It is another aspect of the present invention, wherein the servo motors are configured as master-Slave configuration by the CNC controller.

It is another aspect of the present invention, wherein the direct measurement unit from the spindle is connected to the CNC controller for getting position feedback and the inbuilt motor encoders give the velocity feedback to the drives.

It is another aspect of the present invention to provide a method of working of the CNC turn mill center with anti-backlash modular C axis drive, comprising the steps:
starting of the machine;
activation of the spindle drive mode (Variant A);
starting of the spindle with an appropriate speed;
performing facing and turning operation of the machine;
stopping the spindle;
measurement of job and ensuring dimensional accuracy;
activation of the C-Axis drive (Variant B);
starting of the spindle with an appropriate speed;
stopping of the C Axis in the teached reference position;
moving of swivel engagement with standard pressure on fixed stop;
releasing of C Axis drive; and
activation of the new drives and C Axis positioning in master- slave-mode to compensate backlash and wear,
wherein when the machine in C-Axis mode, first reference the two servo motor to a home position,
wherein after getting this home position feedback activate the C-axis engage command and this command engages the C-Axis drive to the main spindle drive by using a hydraulic actuation mechanism and coupling feedback taken by the sensor unit,
wherein after getting the mechanical coupling feedback, the motors are electrically couple by torque coupling function in CNC System and the spindle is reference to a C-axis home position and the home position feedback is taken by the sensor unit preferably a proximity sensor, and
wherein after completing the job, the C-Axis disengage command given and deactivate the hydraulic actuation and the disengage feedback taken by the sensor unit.

It is another aspect of the present invention to provide a reverse gap monitoring method of a numerical control machine tool of a fully-closed loop servo system, comprising:
continuously sampling the positions of a motor and a workbench through the build-in encoder of the machine tool; and
taking the position of the motor as a reference position to calculate the reverse gap sequence.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, may be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and is therefore not to be considered limiting of the invention's scope as it may admit to other equally effective embodiments.
FIG. 1a and Fig 1b is the cross sectional views of the CNC turn mill center according to the present invention.
FIG.2 is the view depicting the drive configuration comprising of the master drive and the slave drive according to the present invention.
FIG. 3 is the schematic diagram of the control circuit layout for torque coupling function with two motor according to the present invention.
FIG. 4 is the graphical representation of the characteristic curves for optimized converter setting data.

DESCRIPTION FOR DRAWINGS WITH REFERENCE NUMERALS:
(10, 11) C-Axis drive motor units
(12) Coupling cylinder
(13) Main drive measurement unit
(14) C-axis direct measurement unit
(15) Coupling cylinder position sensing unit
(101) Master control unit
(102) Slave control unit
(103) Spindle
(104) CNC controller

DETAILED DESCRIPTION OF THE INVENTION
The invention relates to machine-tool construction, particularly, to turn mill center for multiple machining. The invention relates to a machine to perform independent turning and milling operations. The invention particularly relates to a method for rotating and precise positioning of the Machine Tool spindle during metal working operations. Additionally the invention relates to an improved C-axis configuration of a Turn Mill centers.

The present invention discloses a new Concept of C axis for CNC Turn Mill Centre. It attempts to address the drawback in the background art, wherein the existing machinery shows low accuracy due to Transmission backlash. The invention discloses a C-axis configuration to improve the accuracy of C axis of Turn Mill Centre to enable it be used for high precision components like Aerospace application. The design is modular to adapt for any CNC Turn Mill Centre with minor modifications.

Referring to Figure 1a and Figure 1b, cross sectional views of the CNC turn mill center according to the present invention are illustrated. Referring to Figure 2, view depicting the drive configuration comprising of the master drive and the slave drive according to the present invention is illustrated. CNC turn mill center with anti-backlash modular C axis drive, comprises one or more C-axis drive motor units (10, 11) with one or more servo motors; a coupling cylinder (12); a main drive measurement unit (13); C-axis direct measurement unit (14); a coupling cylinder position sensing unit (15); a master control unit (101) in drive configuration; a slave control unit (102) in drive configuration; a CNC controller (104); one or more motors; one or more drive shafts; one or more gears; and a spindle (103). The encoder of the C Axis drives (for a control circuit which is placed inside the cabinet and outside the mill center) is the direct measuring unit (14) always remains fixed/ coupled to the C Axis drive. The rotating speed of a rotary table is controlled by controlling the rotating speed of a motor of the gear box assembly and the turning and milling is carried out on the same rotary table. A reverse drive/opposite direction rotation is applied to the master drive unit (101) with an additional motor for anti-backlash in the transmission system and the mill center is moved overcoming this applied drive and is implemented by electrical bracing such that slave drive unit (102) with torque between 10 Nm to 20 Nm is allowed to rotate in the opposite direction with respect to the master drive of two drives, and the electrical bracing is implemented with the master and slave control units (101, 102) which are identical in rating and the master drive has torque between 520Nm to 560Nm in the process and the slave drive work against it for anti-backlash in the transmission system.

The C-axis drive motor units (10, 11) with one or more servo motors comprises of two modes of operation: the spindle (103) is driven by the main motor with a speed of 2800 rpm and torque of 230 Nm, in the direct drive (variant A); and once to the second mode (variant B) is activated, the C axis drive is engaged with the spindle drive (103) and offers a speed of 45 rpm with high torque 585 Nm. The coupling arrangement (12) is provided for the engagement of C axis drive to the spindle drive (103) once the mode of operation is changed. The main drive measurement unit (13) is an encoder attached to the measuring system and is integrated to measure the speed of the spindle drive (103). The encoder is attached to ensure the speed feedback of the C axis drive, once the variant B mode is activated. The sensing unit (15) is attached to the C axis drive to get the feedback of the swiveling mechanism for engagement of C axis drive to the main spindle (103) once the variant B gets activated. The C-axis drive units (10, 11) engage with the main spindle (103) of the lathe machine when needed to make it a rotary axis and the drive unit from the main spindle motor is isolated from the spindle (103) during this operation and uses the swivel mechanism to engage the C axis.

The development of modular design with the swivel mechanism and the C-axis drive is adapted for any type and range of the CNC turn mill centre. The characterized driving between the shaft and gears detect and correct the backlash. The servo motors are configured as master-slave configuration by the CNC controller (104). The direct measurement unit (14) from the spindle (103) is connected to the CNC controller (104) for getting position feedback and the inbuilt motor encoders give the velocity feedback to the drives (10, 11).

The method of working of the CNC turn mill center with anti-backlash modular C axis drive, comprising the steps: starting of the machine; activation of the spindle drive mode (Variant A); starting of the spindle with an appropriate speed; performing facing and turning operation of the machine; stopping the spindle; measurement of job and ensuring dimensional accuracy; activation of the C-Axis drive (Variant B); starting of the spindle with an appropriate speed; stopping of the C Axis in the teached reference position; moving of swivel engagement with standard pressure on fixed stop; releasing of C Axis drive; and activation of the new drives and C Axis positioning in master- slave-mode to compensate lash and wear.

When the machine is in C-Axis mode, first reference goes to the two servo motor (10, 11) to a home position. After getting this home position feedback, activate the C-axis engage command and this command engages the C-Axis drive to the main spindle drive by using a hydraulic actuation mechanism and coupling feedback taken by the sensor unit (15). After getting the mechanical coupling feedback, the motors are electrically couple by torque coupling function in CNC System and the spindle (103) is reference to a C-axis home position and the home position feedback is taken by the sensor unit (15) preferably a proximity sensor, and after completing the job, the C-Axis disengage command given and deactivate the hydraulic actuation and the disengage feedback taken by the sensor unit (15).

The reverse gap monitoring method of a numerical control machine tool of a fully-closed loop servo system, comprising: continuously sampling the positions of a motor and a workbench through the build-in encoder of the machine tool; and taking the position of the motor as a reference position to calculate the reverse gap sequence.

The model consist of turn-milling composite workbench .The rotary table assembly is used for containing a work piece to be machined. The gear assembly drives the rotary table assembly to rotate. A universal tool apron used to achieve turning and milling. Anti-backlash is achieved through the gear box assembly, and the rotating speed of the rotary table is controlled by controlling the rotating speed of a motor of the gear box assembly. Finally turning and milling carried out on the same rotary table. The tool handle positioning structure has the beneficial effect in locking. The connecting rigidity for positioning the tool turning tool handle through the double pins can be effectively improved. Furthermore, the shaking phenomenon caused by starting and stopping of turning is eliminated by applying static pretightening force. The automatic positioning and clamping device is applied to general and dedicated machine tools. It is particularly applied to machine tool for continuously or intermittent feeding process of a long shaft type in the axial direction. This is a back lash monitoring and rectification device. It is a reverse gap monitoring method of a numerical control machine tool of a fully-closed loop servo system. The method comprises continuously sampling the positions of a motor and a workbench through the build-in encoder of the machine tool and taking the position of the motor as a reference position to calculate the reverse gap sequence. The equipment achieves turn-milling conversion, high-precision work piece indexing. The C-axis box is suitable for feed drive during milling of the high-precision numerical control vertical-type turn-milling machining center workbench. Rotationally symmetric parts can be clamped between dog and the centering means and first angle measuring system being assigned to the dog. Then part is rotated by means of a drive. The signals from the drive side angular position are processed. The structure consists of motor, drive shafts, and gears. The characterized driving between the shaft and gears helps to detect and correct the backlash. The NC machine tool comprises chassis, a main shaft device, a translation device and the rotary work platform. Positional angles of cutters and the work pieces can be adjusted, so that the NC machining tool is enabled to be provided with a best cutting point that can be used for cutting.

Referring to Figure 3, the schematic diagram of the control circuit layout for torque coupling function with two motor according to the present invention is illustrated. “ Torque coupling, master-slave” function in 840D sl CNC controller is used for eliminating transmission backlash and a direct measurement system (14) with 40000 signal periods ~1Vpp mounted to meet high accuracy in position. The Master servo motor drive the main spindle with a high torque (~540Nm) and the slave motor rotating in opposite direction with less torque (~20Nm) to reduce the backlash of the main drive (101,102). The C-Axis control system consists of two servo motors coupled to a spindle. The servo motors are configured as Master-Slave configuration by 840D sl CNC controller. A Direct measurement system from spindle is connected to CNC controller for getting the position feedback. The inbuilt motor encoders give the velocity feedback to the drives.

Sequence of Operation:-
1. Change the CNC Machine to C-Axis mode
2. When the machine in C-Axis mode, first reference the two servo motor (10, 11) to a home position. Motor 1 and Motor 2 home position feedback were taken by using two proximity switches.
3. After getting this home position feedback activate the C-axis engage command. This command engages the C-Axis drive to the main spindle drive by using a hydraulic actuation mechanism and coupling feedback taken by using a proximity switch (15).
4. After getting the mechanical coupling feedback the motors are electrically couple by torque coupling function in CNC System and the spindle is reference to a C-axis home position. The home position feedback is taken by means of proximity switch.
5. After referencing, CNC starts the job
In the torque coupling function one motor act as master and the other is slave. The master motor drives the spindle with a high torque (~540Nm) and this high torque may create backlash in the spindle. To eliminate this backlash the slave motor rotates in opposite direction with less torque (~20Nm) with respect to the master drive.
6. After completing the job the C-Axis disengage command given and deactivate the hydraulic actuation and the disengage feedback taken by means of proximity feedback (15).

DESIGN OF C-AXIS
In reference to Fig 1, the position of each drive is just a rough orientation. The drives have to be engaged deactivated without a fixed position. They should find their position (tooth on gap) in an arc minute range without any forced moment. After that procedure, the C Axis drives will be activated and work against each other.

The encoder of the C Axis drives (for the control circuit) is the direct measuring system. The repeatability results from this direct measuring system, which always remains fixed/ coupled to the C Axis.

Standard Operation:
• The C Axis stops in the teached reference position.
• The new drives stop in the teached reference positions and must be switched of-it is just a rough reference position for the new drives.
• Move swivel engagement with standard pressure on fixed stop. The higher pressure (20 bars) ensures safely coupled drives when you need maximum torque.
• The initiator releases the C Axis drive.
• Activation of the new drives and C Axis positioning in master- slave-mode to compensate backlash and wear.

In order to eliminate the backlash in the transmission system, of conventional design, an embodiment of the present invention applies a reverse drive with additional motor. The system moves overcoming this applied drive. This is implemented by electrical bracing of two drives. Electrical bracing works on the basis of master slave control which is of two identical systems. Master drive has higher torque in the process and slave drive work against it. Thus, the transmission backlash is eliminated and positional accuracy is improved.

Design details of C axis
On CNC lathe with live tool, precise circular orientation/ contouring is required for job accuracy. The present design we are able to achieve +/-45 arc second position accuracy. If we improve accuracy level to +/- 10 arcs second it can be used in the areas of high precision manufacturing like aerospace and defense components.

The design is modular to adapt for any CNC Turn Mill Centre with minor modifications. C axis is a drive unit with 2 servo motors. It will engage with main spindle of lathe when needed to make it a rotary axis. Drive from the main spindle motor will be isolated from spindle during this operation. Otherwise C axis will be isolated. It uses swivel mechanism to engage the C axis. Hence it cab can be adapted to any machine with minor modifications. The direct measuring system gives necessary accuracy.

The specification of the C axis to be integrated is
Torque : 520 nm.
Max speed : 40 RPM
Positioning accuracy :+/-10”(As per VDI DGQ 3441)
Repeatability : +/-5” (As per VDI DGQ 3441)
Technical data of drive motor

Although, the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention.
,CLAIMS:WE CLAIM:
1. A CNC turn mill center with anti-backlash modular C axis drive, comprising:
one or more C-axis motor drive units (10, 11) with one or more servo motors;
a coupling cylinder (12);
a main drive measurement unit (13);
C-axis direct measurement unit (14);
a coupling cylinder position sensing unit (15);
a master control unit (101) in drive configuration;
a slave control unit (102) in drive configuration;
a CNC controller (104);
one or more motors;
one or more drive shafts;
one or more gears; and
a spindle (103),
wherein an encoder of the C Axis drives (for a control circuit which is placed inside the cabinet and outside the mill center) is the direct measuring unit (14) always remains fixed/ coupled to the C Axis drive,
wherein the rotating speed of the spindle is controlled by the servo drive controlling the rotating speed of a motor of the gear box assembly and the turning and milling is carried out on the same spindle,
characterized in that a reverse drive/opposite direction rotation is applied to the master drive unit (101) with an additional motor for anti-backlash in the transmission system and the mill center is moved overcoming this applied drive and is implemented by electrical bracing such that slave drive unit (102) with torque between 10 Nm to 20 Nm is allowed to rotate in the opposite direction with respect to the master drive of two drives, and
the electrical bracing is implemented with the master and slave control units (101, 102) which are identical in rating and the master drive has torque between 520Nm to 560Nm in the process and the slave drive work against it for anti-backlash in the transmission system.

2. The CNC turn mill center with anti-backlash modular C axis drive as claimed in claim 1, wherein the C-axis drive units (10, 11) with one or more servo motors comprises of two modes of operation:
the spindle (103) is driven by the main motor with a speed of 2800 rpm and torque of 230 Nm, in the direct drive (variant A); and
once to the second mode (variant B) is activated, the C axis drive is engaged with the spindle drive (103) and offers a speed of 45 rpm with high torque 585 Nm.

3. The CNC turn mill center with anti-backlash modular C axis drive as claimed in claim 1, wherein the coupling arrangement (12) is provided for the engagement of C axis drive to the spindle drive (103) once the mode of operation is changed.

4. The CNC turn mill center with anti-backlash modular C axis drive as claimed in claim 1, wherein the sensing unit (15) is attached to the C axis drive to get the feedback of the swiveling mechanism for engagement of C axis drive to the main spindle (103) once the variant B gets activated.

5. The CNC turn mill center with anti-backlash modular C axis drive as claimed in claim 1, wherein the C-axis drive units (10, 11) engage with the main spindle (103) of the lathe machine when needed to make it a rotary axis and the drive unit from the main spindle motor is isolated from the spindle (103) during this operation and uses the swivel mechanism to engage the C axis.

6. The CNC turn mill center with anti-backlash modular C axis drive as claimed in claim 1, wherein the development of modular design with the swivel mechanism and the C-axis drive is adapted for any type and range of the CNC turn mill centre.

7. The CNC turn mill center with anti-backlash modular C axis drive as claimed in claim 1, wherein the characterized driving between the shaft and gears detect and correct the backlash.

8. The CNC turn mill center with anti-backlash modular C axis drive as claimed in claim 1, wherein the servo motors are configured as master-slave configuration by the CNC controller (104).

9. The CNC turn mill center with anti-backlash modular C axis drive as claimed in claim 1, wherein the direct measurement unit (14) from the spindle (103) is connected to the CNC controller (104) for getting position feedback and the inbuilt motor encoders give the velocity feedback to the drives (10, 11).

10. A method of working of the CNC turn mill center with anti-backlash modular C axis drive, comprising the steps:
starting of the machine;
activation of the spindle drive mode (Variant A);
starting of the spindle with an appropriate speed;
performing facing and turning operation of the machine;
stopping the spindle;
measurement of job and ensuring dimensional accuracy;
activation of the C-Axis drive (Variant B);
starting of the spindle with an appropriate speed;
stopping of the C Axis in the teached reference position;
moving of swivel engagement with standard pressure on fixed stop;
releasing of C Axis drive; and
activation of the new drives and C Axis positioning in master- slave-mode to compensate lash and wear,
wherein when the machine in C-Axis mode, first reference the two servo motor (10, 11) to a home position,
wherein after getting this home position feedback activate the C-axis engage command and this command engages the C-Axis drive to the main spindle drive by using a hydraulic actuation mechanism and coupling feedback taken by the sensor unit (15),
wherein after getting the mechanical coupling feedback, the motors are electrically couple by torque coupling function in CNC System and the spindle (103) is reference to a C-axis home position and the home position feedback is taken by the sensor unit (15) preferably a proximity sensor, and
wherein after completing the job, the C-Axis disengage command given and deactivate the hydraulic actuation and the disengage feedback taken by the sensor unit (15).