DESC:FIELD OF INVENTON
The present invention relates to design of a gear teeth-rolling machine and rolling method thereof and more particularly relates to design of gear teeth rolling machine and gear rolling method having gear tool with internal teeth.
CROSS-REFERENCE TO RELATED APPLICATIONS
This invention takes priority from an earlier filed provisional patent application no. 202121031646 filed on July 14, 2021; which is incorporated herein as reference.

BACKGROUD OF THE INVENTION
Normally the gear teeth manufacturing comprise two main steps. First is gear teeth cutting and second is gear teeth surface finishing. The gear teeth are cut by various methods such as milling, hobbing, shaving, broaching, sintering, and alike. The teeth surface of the cut gear is further processed with finishing operation for more dimensional accuracy and improving surface finish. The finishing operation is carried out by methods such as grinding, honing, hard skiving, shaving and rolling and alike. The finishing operation is used for producing more accurate surface profile of gear teeth flanks. The accurate profile is required to control the gear noise at higher gear speeds.

The gears are of two types. External teeth gear and internal teeth gear. Refer figure 1 and 2. The external teeth gear (1) has teeth outside the circumference of gear, away from the centre of gear. The internal teeth gear (3) has teeth inside the circumference of gear, towards the centre of gear.

In the known gear teeth rolling method for finishing operation, an external teeth rolling gear tool is used to finish external teeth of job gear (i.e. work piece). The known external gear teeth rolling method has a major disadvantage of lower contact ratio, such as, up to 1.7. The contact ratio is the number of teeth in contact of job gear and rolling tool gear during rolling operation. Due to the low contact ratio, the unit contact force on gear teeth is high which reduces the stability in rolling method. Therefore, a higher desired accuracy of gear teeth surface profile is not achieved.

For achieving higher contact ratio, such as, above 2.0 for process stability, a bigger size (bigger diameter) external rolling tool is required which in turn increases the centre distance between job gear and tool gear, thereby making system bulky and increasing the cost of the machine making it economically unviable.

OBJECT OF THE INVENTION
The object of the present invention is to solve the above-mentioned problems.

Another object of the present invention is to design gear teeth rolling machine and method to carry out finishing of gear teeth with high accuracy and improved surface finish.

Yet another object of the invention is to design gear teeth rolling machine and method with higher contact ratio of job gear and tool gear during gear rolling operation and lower centre distance between job gear and tool gear.

Still another object of the invention is to impart higher stability and consistency in the process.

Another object of the invention is to design low cost teeth rolling machine, which requires less processing cost as compared to other teeth finishing operations.

SUMMARY OF INVENTION
To avoid the problems and achieve objects mentioned above, the applicant designed a gear teeth-rolling machine in which the rolling tool gear have internal teeth. The configuration of present invention provides rolling of external teeth of a job gear through internal teeth of rolling tool gear. During rolling process, teeth of both the gears are engage and the gear teeth contact ratio is higher, such as, 2.1. The higher contact ratio will lead to lower unit force per area of gear teeth flank imparting higher stability and consistency in the rolling process. The higher contact ratio helps to do finishing of gear teeth with high accuracy and improved surface finish.

According to one embodiment of the invention, a gear teeth rolling machine includes
a base structure, a job gear spindle to hold a job gear, a tool gear spindle to hold a tool gear, the tool gear engages with the job gear for rolling the job gear, a tailstock spindle assembly linearly coupled with a tailstock motor, a first motor coupled with a transmission mechanism to rotate the tool gear, a second motor coupled with a feed mechanism of the tool gear spindle for axial movement of the tool gear relative to the job gear, a third motor coupled with a resistive transmission mechanism to supply resistive torque to the job gear during rolling, and a controller electronically controlling rolling of the job gear. The tool gear includes a plurality of internal teeth to engage with a plurality of external teeth of the job gear mounted on the job gear spindle of the gear teeth rolling machine.

In the exemplary embodiment of the invention, the tailstock motor linearly moves the tailstock spindle assembly to locate the job gear by a taper collet of the tailstock spindle assembly. The tailstock motor linearly moves the tailstock spindle assembly to clamp the job gear on a bore of the job gear by a collet expanding mandrill of the tailstock spindle assembly. Further, the tailstock spindle assembly clamps a face of the job gear through a face clamp.

In the exemplary embodiment of the invention, the transmission mechanism to rotate tool gear is of timer belt and pulley type.

In the exemplary embodiment of the invention, the feed mechanism (18) is of ball and screw type.

In the exemplary embodiment of the invention, the gear teeth rolling machine comprises a lubrication system that provides lubrication between the tool gear and the job gear during rolling the job gear.

In the exemplary embodiment of the invention, the controller of the gear teeth rolling machine electronically controls the operation of the first motor, the second motor, the third motor, and tailstock motor for rolling the job gear on the gear teeth rolling machine. Further, the controller maintains correct synchronisation between one or more elements of the gear teeth-rolling machine during rolling of the job gear.

In the exemplary embodiment of the invention, the plurality of internal teeth of the job gear and the plurality of external teeth of the tool gear are engaged with each other with keeping a centre distance between them at a higher value than a calculated value of centre distance as per gear geometry.

In the exemplary embodiment of the invention, the plurality of internal teeth of the job gear and the plurality of external teeth of the tool gear are engaged with each other at a contact ratio of 2.1.

In another exemplary embodiment of the invention, a method of rolling on a gear teeth rolling machine comprises steps of:
1- loading a job gear, on a locator in a base structure of the gear teeth rolling machine.
2- linearly moving a tailstock spindle assembly, by a tailstock motor, to locate and clamp the job gear on the tailstock spindle assembly.
3- moving a tool gear linearly towards the job gear, by a feed mechanism, to rotatably engage the tool gear with the job gear;
4- rotating the tool gear, by a transmission mechanism, to rotate the job gear.
giving a forward linear feed to the tool gear, by the feed mechanism, for rolling the job gear.
5- applying a resistive torque to the job gear, by a resistive transmission mechanism, to start and to carry on the gear rolling operation.
6- stopping the rotation of both the job gear and the tool gear, and disengaging the job gear and the tool gear by moving the tool gear linearly away from the job gear.
In above-mentioned exemplary embodiment of the invention, the method of rolling includes rolling of the job gear by engaging a plurality of external teeth of a job gear with a plurality of internal teeth of a tool gear mounted on the gear teeth rolling machine.

In the exemplary embodiment of the invention, the method of rolling on a gear teeth rolling machine includes steps of rotating the tool gear in a clockwise direction to rotate the job gear in a first cycle of rolling, and rotating the tool gear in an anti-clockwise direction to rotate the job gear, in a second cycle of rolling.

BRIEF DESCRIPTION OF DRAWINGS:

Figures 1 is a schematic view of a rolling technique of gear teeth, according to a prior art.

Figure 2 is a schematic view of a rolling technique of gear teeth, according to one embodiment of the present invention.

Figure 3 is a schematic front view of a gear teeth rolling machine, according to one embodiment of the present invention.

Figure 4 is a schematic cross section view of a gear teeth rolling machine, according to one embodiment of the present invention.

Figure 5 is a schematic close view of mounting and clamping of job gear in a gear teeth rolling machine, according to one embodiment of the present invention.

Figure 6 is a schematic close view of mounting and clamping of tool gear in a gear teeth rolling machine, according to one embodiment of the present invention.

Figure 7 is a schematic close view of tool feed arrangement in a gear teeth rolling machine, according to one embodiment of the present invention.

Figure 8 is a schematic top view of a gear teeth rolling machine, according to one embodiment of the present invention.

Figure 9 is a schematic view showing the positions of pitch circles of job gear and tool gear during rolling operation by gear rolling machine, according to one embodiment of the present invention.

Figure 10 is a schematic method of rolling on a gear teeth rolling machine, according to one embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Figures 1 is a schematic view of an external rolling technique of gear teeth according to prior art. A work piece (1) is an external gear and a rolling tool (2) is an external gear. In the known external gear teeth rolling technique, an external rolling gear tool (2) is used to finish teeth of external work piece (1). The known external rolling technique has a major disadvantage of lower contact ratio, such as, up to 1.7. The contact ratio is the number of teeth in contact of work piece (1) gear and rolling tool (2) gear during rolling of both the gears. Due to the low contact ratio, the unit contact force on gear teeth is high which reduces the stability in rolling technique. Thus, a higher desired accuracy of gear teeth surface profile is not achieved.

Figure 2 is a schematic view of an internal rolling technique of gear teeth according to one embodiment of the present invention. A work piece or a job gear (1) is an external teeth gear and a rolling tool gear (3) is an internal teeth gear. During rolling process, teeth of both these gears are engage and the gear teeth contact ratio is higher, such as, 2.1. The higher contact ratio will lead to lower unit force per area of gear teeth flank imparting higher stability and consistency in the rolling process. Thus, the higher contact ratio helps to do finishing of gear teeth with high accuracy and improved surface finish.

Embodiments of present invention will now be explained with the help of figures herein below. All the aspects described herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope herein without departing from the spirit and scope thereof, and the present invention herein includes all such modifications.

Referring to figure 3 to 8, according to one embodiment of the present invention, a gear teeth rolling machine (100) comprises a base structure (11) on which a plurality of elements of the gear teeth rolling machine (100) are mounted and the base structure (11) is rigid to absorb the forces developed during the rolling. The plurality of elements of the gear teeth rolling machine (100) includes a job gear spindle (12), a tool gear spindle (13), the tailstock spindle assembly (14), a plurality of motors and a plurality of transmission systems and a controller.
The job gear spindle (12) holds and locates a job gear (1) precisely (the gear piece which is to be finished). The job gear spindle (12) is sufficiently rigid to eliminate any deflection during rolling operation.
The tool gear spindle (13) holds and locates the tool gear (3) precisely. The tool gear spindle (13) is rigid to avoid any deflection due to rolling forces and remain stable at conditions during rolling.
The tailstock spindle assembly (14) is provided with a collet (15) to locate the job gear and a face clamp (25) to provide clamping force during rolling. A tailstock motor (27) moves the tailstock spindle assembly (14), linearly in a forward and a backward direction. The tailstock motor (27) is preferably a servo or a stepper motor.
A transmission mechanism (16), preferably a timer belt and pulley type, rotates the tool gear (3), which intern rotates the job gear (1). A first motor (17), preferably a high torque synchronous servomotor, supplies rotational power to the tool gear (3) through the belt and pulley based transmission mechanism (16). The first motor (17) is to provide precise movement, and to provide for holding torque during rolling.
A feed mechanism (18) driven by a second motor (preferably a servomotor) provides precise relative axial movement between the job gear (1) and the tool gear (3). The feed mechanism (18) is preferably ball screw (19) type to providing the desired minute feed in linear direction during rolling.
A resistive transmission mechanism (20) provides resistive torque to the job gear (1). The resistive transmission mechanism (20) is preferably timer belt and pulley transmission mechanism. A third motor (26), preferably a high torque synchronous servomotor, provides resistive torque during rolling. A lubrication system [not shown] provides lubrication between the tool gear (3) and the job gear (1) during rolling.
A controller (22) electronically controls the operation of the first motor (17), the second motor (18), the third motor (26), and the tailstock motor (27) for rolling the job gear (1) on the gear teeth rolling machine (100). The controller maintains correct synchronisation between one or more elements of the gear teeth rolling machine (100) during rolling of the job gear (1).

In an exemplary embodiment of the invention, the first motor (17), the second motor (18), the third motor (26), and the tailstock motor (27) are replaced with any other mechanical, hydraulic or pneumatic systems for controlled rotation or translation motions.

Further, a method (10) for gear teeth rolling on the gear teeth-rolling machine (100), as illustrated in figure 10, is described below:
Step 101: Load the job gear (1) on the locator or rest block (23) provided in the base structure (11). The loading is manual or robotic. During loading, the plurality of teeth of the job gear (1) and the plurality of teeth of the tool gear (3) are engaged with each other with keeping centre distance between them slightly more than a desired centre distance as per gear geometry. In an exemplary embodiment, the central distance is such as, 2 mm.
Step 102: Tailstock spindle assembly (14) is moved forward by the tailstock motor (27), to locates the job gear (1) by the taper collet (15), and to clamp the job gear on the bore of the job gear (1) by the collet expanding mandrill (24). The face clamp (25) clamps the job gear (1) on the face of the job gear (1).
Step 103: The tool gear (3) is moved towards the job gear (1) by the first motor (17) and the ball screw arrangement of the feed mechanism (18) until gear teeth of both the gears are engaged with each other. The centre distance between the job gear (1) and the tool gear (3) is kept slightly more than the desired centre distance as per gear geometry. In an exemplary embodiment, the central distance is 0.32 mm more than the desired centre distance.
Step 104: The tool gear (3) started rotating in clockwise direction with the help of the first motor (17) with a desired torque. In an exemplary embodiment, the desired torque is 11 Nm. Due to gear teeth engagement, the job gear (1) is also starts rotating.
Step 105: When the rotational speed of tool gear (3) reached at a desired value, a feed is given to the tool gear (3) to move towards the job gear (1) for a desired time. In an exemplary embodiment, the desired value of the rotational speed of tool gear (3) is 100 RPM, and the desired time is 4 seconds.
Step 106: When the tool gear (3) moves by desired value (in an exemplary embodiment 0.32 mm), a resistive torque (in an exemplary embodiment 4 Nm) is applied to the job gear (1) by the third motor (26) to start a gear rolling operation. Thereafter, the pitch circle (31) of the job gear (1) and pitch circle (32) of tool gear (3) touches to each other [as shown in the figure 9]. The above-mentioned gear rolling operation is done for desired time. In an exemplary embodiment, the desired time is 0.5 seconds.
Step 107: Both the gears are stopped rotating and gear teeth are disengaged by moving the tool gear (3) away from the job gear (1) by a desired value (in an exemplary embodiment 0.32 mm)
Step 103 to step 107 includes two cycles of operation, in first cycle, the tool gear (3) is rotated in a clockwise direction to rotate the job gear (1) and in second cycle, the tool gear (3) is rotated in an anti-clockwise direction to rotate the job gear (1). Once the two cycles of operations are completed, the tailstock assembly (14) retracts de-clamp the job gear (1) and the job gear (1) is unloaded. All above activities are synchronised and controlled by the controller (22).

Conclusively, the gear teeth rolling machine (100) with above mentioned modifications and method of operation, provides high finishing to the internal teeth of the job gear (1) by the tool gear (3) having external teeth. Locating and clamping arrangement are provided on the gear teeth rolling machine (100) for the job gear (1) having internal teeth. An axial moving arrangement is provided for tool gear (3) having external teeth. The controller (22) is configure to give desire torques to the tool gear (3) and job gear (1). With such techniques, the gear teeth rolling machine (100) is applicable for finishing the internal teeth of job gear (1) by a tool gear (3) having external teeth.

Although the invention has been described with regard to its embodiments, specific embodiments, and various examples, which constitute the best mode presently known to the inventors, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. All changes that come with meaning and range of equivalency of the claims are to be embraced within their scope.
,CLAIMS:1. A gear teeth rolling machine (100) comprising:
a base structure (11);
a job gear spindle (12) to hold a job gear (1);
a tool gear spindle (13) to hold a tool gear (3), the tool gear (3) engages with the job gear (1) for rolling the job gear (1);
a tailstock spindle assembly (14) linearly coupled with a tailstock motor (27);
a first motor (17) coupled with a transmission mechanism (16) to rotate the tool gear (3);
a second motor coupled with a feed mechanism (18) of the tool gear spindle (13) for axial movement of the tool gear (3) relative to the job gear (1);
a third motor (26) coupled with a resistive transmission mechanism (20) to supply resistive torque to the job gear (1) during rolling; and
a controller (22) to electronically control rolling of the job gear (1),
wherein a plurality of internal teeth of the tool gear (3) engages with a plurality of external teeth of the job gear (1) mounted on the job gear spindle (12) of the gear teeth rolling machine (100).

2. The gear teeth rolling machine (100) as claimed in claim 1,
wherein, the tailstock motor (27) linearly moves the tailstock spindle assembly (14) to locate the job gear (1) by a taper collet (15) of the tailstock spindle assembly (14),
wherein, the tailstock motor (27) linearly moves the tailstock spindle assembly (14) to clamp the job gear (1) on a bore of the job gear (1) by a collet expanding mandrill (24) of the tailstock spindle assembly (14), and
wherein, the tailstock spindle assembly (14) clamps a face (1) of the job gear (1) through a face clamp (25).

3. The gear teeth rolling machine (100) as claimed in claim 1 wherein, the transmission mechanism (16) to rotate tool gear (3) is of timer belt and pulley type.

4. The gear teeth rolling machine (100) as claimed in claim 1 wherein, the feed mechanism (18) is of ball and screw type.

5. The gear teeth rolling machine (100) as claimed in claim 1 wherein, the gear teeth rolling machine (100) comprises a lubrication system that provides lubrication between the tool gear (3) and the job gear (1) during rolling the job gear (1).

6. The gear teeth rolling machine (100) as claimed in claim 1,
wherein the controller (22) of the gear teeth rolling machine (100) electronically controls the operation of the first motor (17), the second motor (18), the third motor (26), and tailstock motor (27) for rolling the job gear (1) on the gear teeth rolling machine (100), and
wherein, the controller maintains correct synchronisation between one or more elements of the gear teeth rolling machine (100) during rolling of the job gear (1).

7. The gear teeth rolling machine (100) as claimed in claim 1 wherein, the plurality of internal teeth of job gear (1) and the plurality of external teeth of tool gear (3) are engaged with each other with keeping a centre distance between them at a higher value than a calculated value of centre distance as per gear geometry.

8. The gear teeth rolling machine (100) as claimed in claim 1 wherein, the plurality of internal teeth of the job gear (1) and the plurality of external teeth of the tool gear (3) are engaged with each other at a contact ratio of 2.1.

9. A method (10) of rolling on a gear teeth rolling machine (100) comprising steps of:
loading (101) a job gear (1), on a locator (23) in a base structure (11) of the gear teeth rolling machine (100);
linearly moving a tailstock spindle assembly (14), by a tailstock motor (27), to locate and clamp (102) the job gear on the tailstock spindle assembly (14);
moving a tool gear (3) linearly towards the job gear (1), by a feed mechanism (18), to rotatably engage (103) the tool gear (3) with the job gear (1);
rotating the tool gear (3), by a transmission mechanism (16), to rotate (104) the job gear (1);
giving a forward linear feed (105) to the tool gear (3), by the feed mechanism (18),for rolling the job gear (1);
applying a resistive torque (106) to the job gear (1), by a resistive transmission mechanism (13), to start and to carry out the gear rolling operation;
stopping the rotation (107) of both the job gear (1) and the tool gear (3), and disengaging the job gear (1) and the tool gear (3) by moving the tool gear (3) linearly away from the job gear (1);
wherein rolling of a job gear (1) is carried out by engaging a plurality of external teeth of a job gear (1) with a plurality of internal teeth of a tool gear (3) mounted on the gear teeth rolling machine (100).

10. The method (10) of rolling on the gear teeth rolling machine (100) as claimed in claim 9, the method (10) of rolling comprises steps of:
rotating the tool gear (3) in a clockwise direction to rotate the job gear (1) in a first cycle of rolling, and
rotating the tool gear (3) in an anti-clockwise direction to rotate the job gear (1), in a second cycle of rolling