4. DESCRIPTION
BACKGROUND
Planetary gear trains are used for speed reduction in various applications. However, a certain amount of backlash is inherent in the use of simple planetary gear trains. The inherent backlash is often undesirable when planetary gear trains are used in high precision drives. In order to reduce the inherent backlash in the planetary gear trains, all the gears that form part of a planetary gear train are usually manufactured to very precise dimensions. High precision manufacture of the gears and the subsequent assembly of the planetary gear trains are very expensive processes involving the use of expensive machines and highly skilled laborers.
Zero backlash in a drive system is commonly achieved by using two gearboxes with independent drives. The independent drives driving the gearboxes are electrically counter-torqued to achieve zero backlash operation. The use of electrical counter-torquing and independent drives to drive the gearboxes require expensive and complicated control systems. Such control systems require simultaneous control of torque in the independent drives.
Hence, there is a need for a mechanical counter-torque drive that operates with zero backlash during continuous operation without the necessity for expensive and complicated control systems.
SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts in a simplified form that are further described in the detailed description of the invention. This summary is not intended to identify key or essential inventive

concepts of the claimed subject matter, nor is it intended for determining the scope of the claimed subject matter.
The mechanical counter-torque drive and method disclosed herein addresses the above stated need for planetary gear trains that operate with zero backlash during continuous operation without the necessity for expensive and complicated control systems. The mechanical counter-torque drive disclosed herein comprises a driving pinion, multiple input gears, multiple planetary gear trains, a driven bull gear, and a loading assembly. The driving pinion, the input gears, and the planetary gear trains are enclosed within a casing. A driving element, for example, a prime mover, rotationally drives the driving pinion. The input gears are drivably connected to the driving pinion. The input gears are, for example, one or more of spur gears, helical gears, herringbone gears, and a combination thereof In an embodiment, the mechanical counter-torque drive disclosed herein further comprises a bevel gear drive between the driving element and the driving pinion.
Each of the planetary gear trains is drivably connected to one of the input gears. The planetary gear trains are identical in structure. Each of the planetary gear trains comprises one or more stages and an output pinion. The stages of the planetary gear trains are connected to each other. The driven bull gear is drivably connected to the output pinion of each of the planetary gear trains. The loading assembly is connected to one of the planetary gear trains for preloading the mechanical counter-torque drive. The preloading induces equal and opposite torques on the connected stages of the planetary gear trains. The mechanical counter-torque drive therefore operates with zero backlash due to the induced equal and opposite torques.
The loading assembly comprises a rack, a loading member, and an adjusting member. The rack meshes with a ring gear of one of the stages of one of the planetary gear trains for the preloading. The loading member is connected to

the rack. The loading member is, for example, a spring, a hydraulic device, a pneumatic device, an electro-mechanical device, etc. The adjusting member, for example, a screw thread mechanism, is connected to the loading member for adjusting magnitude of the preload to be applied on the ring gear.
Each of the stages of each of the planetary gear trains comprises a sun gear shaft, a sun gear, a ring gear, multiple planet gears, and a planet carrier. The sun gear shaft is connected to one of the input gears through a locking assembly. The locking assembly holds in position each of the input gears with respect to the sun gear shaft of a first stage of each of the planetary gear trains. The sun gear is fixed to the sun gear shaft. The sun gear is mounted coaxially with the sun gear shaft. The sun gear shaft comprises a first end and a second end. The first end of the first sun gear shaft is connected to one of the input gears and the second end of the sun gear shaft is connected to the sun gear. The ring gear is mounted coaxially with the sun gear shaft. The ring gear comprises internal teeth or a combination of internal teeth and external teeth.
The planet gears are drivably connected to the sun gear. The planet gears are in engagement with the ring gear and the sun gear. The planet gears are meshed with the sun gear and internal teeth of the ring gear. The planet gears rotate within the planet carrier. The planet carrier is drivably connected to another one of the stages of each of the planetary gear trains or connected to the output pinion through an output shaft. For example, if each of the planetary gear trains comprises one stage, the planet carrier of that stage is directly connected to the output pinion through the output shaft. If each of the planetary gear trains comprises more than one stage, the planet carrier of the first stage is connected to the sun gear of the second stage and the planet carrier of the final stage is connected to the output pinion through the output shaft.
The output shaft comprises a first end and a second end. The first end of the output shaft is connected to the planet carrier of the final stage of the planetary

gear trains and the second end of the output shaft is connected to the output pinion. The output pinion is connected along the output shaft.
The external teeth of the ring gear of any one of the stages of one of the planetary gear trains meshes with external teeth of a corresponding ring gear of the same stage of the other planetary gear train.
In an embodiment, the mechanical counter-torque drive disclosed herein further comprises a double-sided rack meshed with external teeth of each ring gear of any one of the stages of the planetary gear trains. In another embodiment, the mechanical counter-torque drive disclosed herein further comprises a pair of idler gears meshed with external teeth of each ring gear of any one of the stages of the planetary gear trains. The double-sided rack and the idler gears reduce space occupied by the mechanical counter-torque drive.
Disclosed herein is a method of operating a mechanical counter-torque drive with zero backlash, comprising: providing the mechanical counter-torque drive disclosed herein; loosening the locking assembly and rotating the sun gear shaft held in position by the locking assembly for removing backlash from the mechanical counter-torque drive; tightening the loosened locking assembly; introducing the preload to the mechanical counter-torque drive by tightening the adjusting member on the loading assembly, wherein the preload induces equal and opposite torques on the connected stages of the planetary gear trains; and driving the driving pinion by the driving element, wherein the input gears are rotated in a direction opposite to direction of rotation of the driving pinion, wherein the input gears translate the rotation to each of the planetary gear trains that drive the driven bull gear connected to the output pinion on the output shaft; whereby the driving of the driving pinion rotates the planetary gear trains enabling the mechanical counter-torque drive to drive the bull gear with zero backlash.
BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the invention, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, exemplary constructions of the invention are shown in the drawings. However, the invention is not limited to the specific methods and instrumentalities disclosed herein.
FIG. 1 exemplarily illustrates a sectional view of a mechanical counter-torque drive for zero backlash operation.
FIG. 2 exemplarily illustrates an isometric view of a mechanical counter-torque drive with a single stage planetary gear train.
FIG. 3 exemplarily illustrates an orthogonal end view of the mechanical counter-torque drive showing each output pinion meshing the driven bull gear and a cut¬away sectional view of the loading assembly.
FIG. 4 exemplarily illustrates a side perspective view of a single stage of one of the planetary gear trains showing a ring gear with external teeth and internal teeth, planet gears, a sun gear, and a planet carrier.
FIG. 5 exemplarily illustrates a line diagram representation of a first embodiment of the mechanical counter-torque drive.
FIG. 6 exemplarily illustrates a line diagram representation of a second embodiment of the mechanical counter-torque drive, wherein a bevel gear drive is provided between a driving element and a driving pinion.
FIG. 7 exemplarily illustrates a sectional view of the second embodiment of the mechanical counter-torque drive, wherein a bevel gear drive is provided between the driving element and the driving pinion.

FIG. 8 exemplarily illustrates a sectional view of the bevel gear drive.
FIG. 9 exemplarily illustrates a line diagram representation of a third embodiment of the mechanical counter-torque drive, wherein a bevel gear drive is provided between the driving element and the driving pinion on both sides of the driving pinion.
FIG. 10 exemplarily illustrates a line diagram representation of a fourth embodiment of the mechanical counter-torque drive, wherein a double-sided rack meshing with external teeth of the ring gear of one of the stages of the planetary gear trains is provided.
FIG. 11 exemplarily illustrates a line diagram representation of a fifth embodiment of the mechanical counter-torque drive, wherein a pair of idler gears meshing with each other and with the external teeth of the ring gear of one of the stages of the planetary gear trains is provided.
FIG. 12 illustrates a method of operating the mechanical counter-torque drive with zero backlash.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 exemplarily illustrates a sectional view of a mechanical counter-torque drive 100 for zero backlash operation. The term "backlash", used herein, refers to the amount of clearance or play between the gear teeth of mating gears. The mechanical counter-torque drive 100 removes the backlash present between the gear teeth of mating gears. The mechanical counter-torque drive 100 disclosed herein comprises a driving pinion 101, multiple input gears 102, multiple planetary gear trains 104, a driven bull gear 301, and a loading assembly 105. The driving pinion 101 is rotationally driven by a driving element, for example, one or

more prime movers. The prime movers are, for example, electric motors. The driving element is connected to the driving pinion 101 using, for example, a spur gear drive, a bevel gear drive, etc. The driving pinion 101 drives the input gears 102 drivably connected to the driving pinion 101. The input gears 102 are, for example, spur gears, helical gears, herringbone gears, and any combination thereof. The driving pinion 101, the input gears 102, and the planetary gear trains 104 are enclosed within a casing 106. The casing 106 protects the planetary gear trains 104 from external contamination and minimizes noise generated during the operation of the mechanical counter-torque drive 100. The mechanical counter-torque drive 100 disclosed herein is, for example, used in antenna drives, where only one driving element is needed to be controlled.
Each of the planetary gear trains 104 is drivably connected to one of the input gears 102. The planetary gear trains 104 are identical in structure. Each of the planetary gear trains 104 comprises one or more of multiple stages 104a and an output pinion 104g. The stages 104a of the planetary gear trains 104 are connected to each other. The input gears 102 transmit rotational motion to the planetary gear trains 104. The number of stages 104a of the planetary gear trains 104 used depends on, for example, the total speed reduction needed with respect to the speed of rotation of the driving pinion 101. An isometric view of the mechanical counter-torque drive 100 with a single stage planetary gear train is exemplarily illustrated in FIG. 2. Each of the stages 104a of each of the planetary gear trains 104 comprises a sun gear shaft 104b, a sun gear 104c, a ring gear 104e, and multiple planet gears 104d within a planet carrier 104h. The sun gear shaft 104b is connected to one of the input gears 102 through a locking assembly 103. The sun gear 104c is fixed to the sun gear shaft 104b and mounted coaxially with the sun gear shaft 104b. The sun gear shaft 104b comprises a first end 104i and a second end 104j, The first end 104i of the sun gear shaft 104b is connected to one of the input gears 102 or a planet carrier 104h of a preceding stage of a planetary gear train 104. The second end 104j of the sun gear shaft 104b is connected to the sun gear 104c. The locking assembly 103 holds each of the input gears 102 in

position with respect to the sun gear shaft 104b of first stage of each of the planetary gear trains 104.
The ring gear 104e of each of the stages 104a of each of the planetary gear trains 104 is mounted coaxially with the sun gear shaft 104b. The ring gear 104e comprises internal teeth 104p or a combination of Internal teeth 104p and external teeth 104iii. The external teeth 104m of the ring gear 104e of one of the stages 104a of one of the planetary gear trains 104 is meshed with the external teeth 104m of a corresponding ring gear 104e of a corresponding stage of another one of the planetary gear trains 104, thereby connecting at least one of the stages 104a of each of the planetary gear trains 104 together.
The planet gears 104d of each of the stages 104a of each of the planetary gear trains 104 are drivably connected to the sun gear 104c corresponding to the stages 104a. The planet gears 104d are in engagement with the sun gear 104c and the ring gear 104e. The planet gears 104d are meshed with the sun gear 104c and the internal teeth 104p of the ring gear 104e that form part of the planetary gear trains 104 comprising the planet gears 104d. Rotation of the sun gear 104c induces the planet gears 104d to rotate in a direction opposite to the direction of rotation of the sun gear 104c.
The planet carrier 104h is drivably connected to another one of the stages 104a of each of the planetary gear trains 104 or connected to the output pinion 104g through an output shaft 104f. For example, if each of the planetary gear trains 104 comprises one stage, the planet carrier 104h of that stage is directly connected to the output pinion 104g through the output shaft 104f. If each of the planetary gear trains 104 comprises more than one stage 104a, the planet carrier 104h of the first stage in a planetary gear train 104 is connected to the sun gear 104c of the second stage of the planetary gear train 104 and the planet carrier 104h of the final stage of the planetary gear train 104 is connected to the output pinion 104g through the output shaft 104f.

The first end 104k of the output shaft 104f is connected to the planet carrier 104h of the final stage of the planetary gear trains 104 and the second end 1041 of the output shaft 104f is connected to the output pinion 104g. The output pinion 104g is connected along the output shaft 104f.
The driven bull gear 301 is drivably connected to the output pinion 104g of each of the planetary gear trains 104. The output pinion 104g of each of the planetary gear trains 104 drives the bull gear 301 as exemplarily illustrated in FIG. 3. The driven bull gear 301 is herein referred to as a "bull gear". Each output pinion 104g meshes with the bull gear 301 and rotation of each output pinion 104g induces rotation of the bull gear 301 in a direction opposite to the direction of rotation of the output pinion 104g. For a bull gear 301 with internal teeth, the rotation of each output pinion 104g induces rotation of the bull gear 301 in the same direction of rotation as that of the output pinion 104g
The loading assembly 105, as exemplarily illustrated in FIG. 3, is connected to one of the planetary gear trains 104 for preloading one of the stages 104a of one of the planetary gear trains 104, thereby enabling the output pinion 104g driving the bull gear 301 to operate with zero backlash. The loading assembly 105 comprises a rack 201, a loading member 202, and an adjusting member 203. The rack 201 of the loading assembly 105 meshes with a ring gear 104e of one of the stages 104a of one of the planetary gear trains 104 for the preloading. The loading member 202 is connected to the rack 201 of the loading assembly 105. The loading member 202 is, for example, a spring, a hydraulic device, a pneumatic device, an electro-mechanical device, and a combination thereof The adjusting member 203 is connected to the loading member 202 for adjusting magnitude of preload to be applied on the ring gear 104e of one of the stages 104a of the planetary gear trains 104. The adjusting member 203 is a screw thread mechanism, for example, a threaded spindle that pulls and pushes the rack 201 of the loading assembly 105.

Preloading one of the stages 104a of one of the planetary gear trains 104 induces equal and opposite torques on the connected stages 104a of the planetary gear trains 104, thereby enabling the mechanical counter-torque drive 100 to operate with zero backlash.
On application of load, the torque increases on one side of the mechanical counter-torque drive 100 and decreases the torque on the other side of the mechanical counter-torque drive 100 by an equal amount. At a definite load determined by the amount of preload, one planetary gear train 104 carries the total load. Backlash free operation is possible up to the definite load. The backlash is not affected by wear and tear in the gears. The preload ensures the meshing of the gears by pushing against each other at all times.
The sun gear shaft 104b of each of the stages 104a of the planetary gear trains 104 rotates at a lower speed of rotation compared to the sun gear shaft 104b of the preceding stage 104a or the input gears 102 driving the planetary gear trains 104. Each sun gear shaft 104b drives the sun gear 104c connected to the sun gear shaft 104b. The sun gear 104c drives the planet gears 104d meshed with the sun gear 104c. The planet gears 104d rotate in a direction opposite to the direction of rotation of the sun gear 104c. The planet gears 104d drive the planet carrier 104h thereby enabling the planet carrier 104h to drive the subsequent stages 104a of the planetary gear train 104. The rotation of the output pinion 104g connected to the planetary gear trains 104 drives the bull gear 301.
In an embodiment, the mechanical counter-torque drive 100 disclosed herein further comprises a double-sided rack meshed with external teeth 104iii of each ring gear 104e of any one of the stages 104a of the planetary gear trains 104. In another embodiment, the mechanical counter-torque drive 100 disclosed herein further comprises a pair of idler gears meshed with external teeth 104m of each ring gear 104e of any one of the stages 104a of the planetary gear trains 104. The

double-sided rack and the idler gears reduce space occupied by the mechanical cuuriler-luri|ue drive 100.
Consider an example where an electric motor is used as a prime mover for rotating the driving pinion 101. The driving pinion 101 drives the input gears 102, and induces the input gears 102 to rotate in a direction opposite to the direction of rotation of the driving pinion 101. The input gears 102 drive the sun gear shaft 104b connected to the input gears 102, hence translating the motion of the driving pinion 101 to the planetary gear trains 104, The sun gear shaft 104b drives the corresponding sun gears 104c connected to the sun gear shaft 104b. The sun gear 104c drives the planet gears 104d meshed with the sun gear 104c. The rotation of the planet gears 104d is in a direction opposite to the direction of rotation of the sun gear 104c. The rotation of the planet gears 104d tends to rotate the ring gears 104e, whose equilibrium is maintained by the loading assembly 105. The sun gear shaft 104b, the sun gear 104c, the planet gears 104d, and the ring gears 104e so connected comprise the first one of the stages 104a of the planetary gear trains 104. The driving pinion 101, the input gears 102, the sun gear shaft 104b, the ring gears 104e, and the output shafts 104f are each supported on one or more bearings. The bearings are, for example, deep groove ball bearings, angular contact ball bearings, needle bearings, roller bearings, tapered roller bearings, spherical roller bearings, thrust bearings, etc.
Any one of the stages 104a of each of the planetary gear trains 104 is connected to each other by meshing the external teeth 104m of the ring gears 104e together. The ring gears 104e of the other stages 104a are fixed. The external teeth 104m of each of the ring gears 104e induce equal and opposite torques on the external teeth 104m of the connected ring gears 104e.
The total torque provided by the driving pinion 101 is split equally between the different planetary gear trains 104. In one embodiment, two planetary gear trains 104 are used and the first one of the stages 104a of each of the

planetary gear trains 104 are connected to each other by splitting the total torque into two equal parts by the externally meshed ring gears 104e of the connected stages 104a. If one of the ring gears 104e, for example, a driving ring gear 104e provides a driving torque, the ring gear 104e connected to the driving ring gear 104e provides an equal and opposite braking torque, hence locking the ring gears 104e together. When the ring gears 104e lock together, the planet gears 104d connected to the ring gears 104e transmit all of the driving torque induced by the sun gear 104c to the sun gear shaft 104b of the subsequent stages 104a of the planetary gear trains 104.
The planet gears 104d rotate at a slower speed of rotation compared to the speed of rotation of the sun gear 104c meshed with the planet gears 104d. Hence the speed of rotation of the sun gear shaft 104b of the next stages 104a of the planetary gear trains 104 is always lower than the speed of rotation of the sun gear shaft 104b of the preceding stages 104a. The speed reduction depends on, for example, the size, number of teeth, etc. of the sun gear 104c, the planet gears 104d, and the ring gears 104e. The number of stages 104a in the planetary gear trains 104 used depends on, for example, the speed reduction required. Each of the stages 104a of the planetary gear trains 104 transmits the rotation of the preceding stage. The output shaft 104f connected to the planetary gear trains 104 transmit the rotation of the stages 104a of the planetary gear trains 104 to the output pinion 104g drivably connected to the output shaft 104f. The output pinion 104g drives the bull gear 301 meshed with the teeth 104n of the output pinion 104g.
FIG. 3 exemplarily illustrates an orthogonal end view of the mechanical counter-torque drive 100 showing each output pinion 104g meshing the bull gear 301 and a cut-away sectional view of the loading assemblylOS. The rack 201 of the loading assembly 105 meshes with a ring gear 104e of one of the stages 104a of one of the planetary gear trains 104. When the adjusting member 203, for example, a threaded spindle, is tightened, the loading member 202, for example, a spring, is compressed for pushing the rack 201 of the loading assembly 105

downwards. The teeth 104o of the rack 201 of the loading assembly 105 exerts force on the external teeth 104m of the ring gear 104e, thereby applying a preload to the ring gear 104e and the planetary gear trains 104 connected to the ring gear 104e. The magnitude of the applied preload depends on the adjustment of the adjusting member 203, for example, the number of turns applied to the threaded spindle. The preload applied on one of the ring gears 104e induces equal and opposite torques on each of the planetary gear trains 104. This enables backlash free operation of the mechanical counter-torque drive 100 under load.
FIG. 4 exemplarily illustrates a side perspective view of a single stage of one of the planetary gear trains 104 showing a ring gear 104e with external teeth 104m and internal teeth 104p, planet gears 104d, a sun gear 104c, and a planet carrier 104h. The planet gears 104d mesh with the internal teeth 104p of the ring gear 104e and the sun gear 104c. The planet carrier 104h carries the planet gears 104d. The ring gear 104e is stationary. The rotation of the sun gear 104c rotates the planet gears 104d in the opposite direction to that of the sun gear 104c. Since the ring gear 104e is stationary, the planet gears 104d move the planet carrier 104h in the same direction as the sun gear 104c. The planet carrier 104h is connected either to the sun gear shaft 104b of the subsequent stages 104a of each of the planetary gear trains 104 or to the output shaft 104f of each of the planetary gear trains 104.
FIG. 5 exemplarily illustrates a line diagram representation of a first embodiment of the mechanical counter-torque drive 100. The driving element, herein referred to as the "motor" drives the driving pinion M which drives the input gears II and 12. The direction of rotation of each of the input gears II and 12 is represented in FIG. 5 by the curved arrows. In the first embodiment, two planetary gear trains Gl and G2 are used. The first stage of the planetary gear trains Gl and G2 is represented by the sun gears SI and S2, the planet gears PI and P2, and the ring gears Rl and R2. The ring gears Rl and R2 are meshed with each other to connect the first stages of the planetary gear trains Gl and G2

together. The second stage of the planetary gear trains Gl and G2 are represented by the sun gears SI' and S2', the planet gears PI' and P2', and the ring gears Rl' and R2'.
A loading assembly S is connected to the ring gear Rl of the first stage of the planetary gear train Gl. The loading assembly S preloads the ring gear Rl and hence induces a preload on the sun gears SI and S2, the planet gears PI and P2, and the ring gear R2 of the first stage of the planetary gear trains Gl and G2, Preloading the first stage of the planetary gear trains Gl and G2 also preloads the second stage of the planetary gear trains Gl and G2.
Each of the planetary gear trains Gl and G2 are driven by the input gears II and 12. The sun gear shaft 104b of the first stage of each of the planetary gear trains Gl and G2 is driven by the input gears II and 12. The sun gear shafts 104b drive the sun gears SI and S2. The planet gears PI and P2 are driven by the sun gears SI and S2 in a direction opposite to the direction of rotation of the sun gears SI and S2. The planet gears PI and P2 rotate with lesser speed compared to the sun gears SI and S2 owing to the nature of the connection between the sun gears SI and S2, and the planet gears PI and P2. The planet gears PI and P2 tend to rotate the ring gears Rl and R2. The ring gears Rl and R2 exert equal and opposite torques on each other, hence getting locked together. The planet carriers 104h drive the sun gears SI' and S2' of the second stage of the planetary gear trains G1 and G2. The sun gears S I' and S2' drive the planet gears PI' and P2'. The direction of rotation of the planet gears PI' and P2' is opposite to the direction of rotation of the sun gears SI' and S2'. The ring gears Rl' and R2' meshed with the planet gears PI' and P2' are fixed on the casing 106. Hence, the ring gears Rl' and R2' do not rotate in any direction. Therefore, the planet carriers 104h drive the output shafts 104f that drive the output pinions 01 and 02. The output pinions Ol and 02 drive the bull gear B. The bull gear B rotates in a direction opposite to the direction of rotation of the output pinions 01 and 02.

FIG. 6 exemplarily illustrates a line diagram representation of a second embodiment of the mechanical counter-torque drive 100. In this embodiment, a bevel gear drive comprising two bevel gears B1 and B2 is introduced between the driving pinion M and the motor. A sectional view of the second embodiment of the mechanical counter-torque drive 100, wherein a bevel gear drive 701 and 702 is provided between the driving element and the driving pinion M is exemplarily illustrated in FIG. 7. The bevel gear 702 is split and spring loaded to eliminate the backlash between the bevel gear drive 701 and 702. As illustrated in FIG. 6, the bevel gear Bl is connected to the motor and the bevel gear B2 is connected to the driving pinion M. The bevel gears Bl and B2 mesh with each other to enable the motor to drive the driving pinion M. This embodiment is used when the motor is fixed with the axis of the drive shaft of the motor perpendicular to the axis of rotation of the driving pinion M. The bevel gears Bl and B2 drive the driving pinion M. A sectional view of the bevel gear drive 701 and 702 is exemplarily illustrated in FIG. 8, showing the bevel gears Bl and B2 and the driving pinion M. The working of the mechanical counter-torque drive 100 from the driving pinion M to the output pinions 01 and 02 is disclosed in the detailed description of FIG. 5.
FIG. 9 exemplarily illustrates a line diagram representation of a third embodiment of the mechanical counter-torque drive 100, wherein a bevel gear drive is provided between the driving element and the driving pinion M on both sides of the driving pinion M. Two motors are used to drive the input gears II and 12 directly without driving the driving pinion M. In the embodiment, the driving pinion M acts like an idler gear connecting the input gears II and 12. Each of the motors is connected to the input gears II and 12 using the bevel gear drive. The bevel gear Bl is connected to motor I and the bevel gear B2 is connected to the input gear II. The bevel gears Bl and B2 mesh with each other to enable the motor to drive the input gear 11. The bevel gear B1' is connected to motor II and the bevel gear B2' is connected to the input gear 12. The bevel gears Bl' and B2' mesh with each other to enable the motor to drive the input gear 12. However, the

motors can also be connected to the input gears 11 and 12 using, for example, spur gears, helical gears, herringbone gears, etc. The working of the mechanical counter-torque drive 100 from the driving pinion M to the output pinions 01 and 02 is disclosed in the detailed description of FIG. 5.
FIG. 10 exemplarily illustrates a line diagram representation of a fourth embodiment of the mechanical counter-torque drive 100, wherein a double-sided rack D meshing with external teeth 104m of the ring gear Rl or R2 of one of the stages 104a of the planetary gear trains Gl and G2 is provided. As exemplarily illustrated in FIG. 10, the double-sided rack D is meshed with the external teeth 104m of the ring gears Rl and R2 of the planetary gear trains Gl and G2. The double-sided rack D acts as a connector between the ring gear Rl and the ring gear R2. Providing the double-sided rack D allows the use of a smaller diameter ring gear 104e, thereby reducing the space occupied by the planetary gear trains Gl and G2. The working of the mechanical counter-torque drive 100 from the driving pinion M to the output pinions 01 and 02 is disclosed in the detailed description of FIG. 5.
FIG. 11 exemplarily illustrates a line diagram representation of a fifth embodiment of the mechanical counter-torque drive 100, wherein a pair of idler gears CI and C2 meshing with each other and with the external teeth 104m of the ring gear Rl or R2 of one of the stages 104a of the planetary gear trains Gl and G2 is provided. As exemplarily illustrated in FIG. 11, an idler gear CI is meshed with the external teeth 104m of the ring gear Rl of the planetary gear train Gl. The idler gear C2 meshes with the idler gear CI and the external teeth 104m of ring gear R2 of the planetary gear train G2. The two idler gears CI and C2 connect to ring gear Rl and ring gear R2 respectively which allows the use of a smaller diameter ring gear 104e, thereby reducing the space occupied by the planetary gear trains Gl and G2. The working of the mechanical counter-torque drive 100 from the driving pinion M to the output pinions 01 and 02 is disclosed

in the detailed description of FIG. 5 with the connection between the two ring gears Rl and R2 formed using the idler gears CI and C2.
The mechanical counter-torque drive 100 self adjusts in response to wear and tear, operates free of play, and provides high gear stiffness. The preload induced on the mechanical counter-torque drive 100 causes an additional torque on the gears inside the mechanical counter-torque drive 100. This additional torque on the gears compensate for the wear and tear caused on the gears due to continuous operation. The additional torque also ensures that the planetary gear trains 104 operate free of play by compensating for any play with the additional torque induced by preloading. Benefits derived from using the mechanical counter-torque drive 100 comprise, for example, lower maintenance requirements, improved reliability, and simplicity of operation.
FIG. 12 illustrates a method of operating the mechanical counter-torque drive 100 with zero backlash. A mechanical counter-torque drive 100, as disclosed and illustrated in the detailed description of FIG. 1, is provided 1201. The locking assembly 103 is loosened 1202 and the sun gear shaft 104b held in position by the locking assembly 103 is rotated for removing backlash from the mechanical counter-torque drive 100. The loosened locking assembly 103 is then tightened 1203. A preload is introduced 1204 to the mechanical counter-torque drive 100 by tightening the adjusting member 203 on the loading assembly 105. The preload induces equal and opposite torques on the connected stages 104a of each of the planetary gear trains 104. The driving pinion 101 is driven 1205 by the driving element which causes the input gears 102 to rotate in a direction opposite to the direction of rotation of the driving pinion 101. The input gears 102 translate the rotation to each of the planetary gear trains 104 that drive the bull gear 301 connected to the output pinion 104g on the output shaft 104f. The driving of the driving pinion 101 rotates the planetary gear trains 104 enabling the mechanical counter-torque drive 100 to drive the bull gear 301 with zero backlash.

The foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention disclosed herein. While the invention has been described with reference to various embodiments, it is understood that the words, which have been used herein, are words of description and illustration, rather than words of limitation. Further, although the Invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may effect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention in its aspects.

1. A mechanical counter-torque drive operating with zero backlash, comprising:
a driving pinion rotationally driven by a driving element;
a plurality of input gears drivably connected to said driving pinion;
a plurality of planetary gear trains, each of said planetary gear trains drivably connected to one of said input gears, wherein each of said planetary gear trains comprises one or more stages and an output pinion;
a driven bull gear drivably connected to said output pinion of each of said planetary gear trains; and
a loading assembly connected to one of said planetary gear trains for preloading said mechanical counter-torque drive, wherein said stages of said planetary gear trains are connected to each other, and wherein said preloading induces equal and opposite torques on said connected stages of said planetary gear trains;
whereby said mechanical counter-torque drive operates with said zero backlash due to said induced equal and opposite torques.
2. The mechanical counter-torque drive of claim 1, wherein one of said one or more stages of each of said planetary gear trains comprises:
a sun gear shaft connected to one of said input gears through a locking assembly;

a sun gear fixed to said sun gear shaft, wherein said sun gear is mounted coaxially with said sun gear shaft;
a ring gear mounted coaxially with said sun gear shaft, wherein said ring gear comprises one of internal teeth and a combination of internal teeth and external teeth;
a plurality of planet gears drivably connected to said sun gear, wherein said planet gears are in engagement with said ring gear and said sun gear, wherein said planet gears rotate within a planet carrier; and
said planet carrier drivably connected to one of another one of said one or more stages of said each of said planetary gear trains and said output pinion connected through an output shaft.
3. The mechanical counter-torque drive of claim 2, wherein said sun gear shaft comprises a first end and a second end, wherein said first end of said sun gear shaft is connected to said one of said input gears and said second end of said sun gear shaft is connected to said sun gear.
4. The mechanical counter-torque drive of claim 2, wherein said planet gears are meshed with said sun gear and said internal teeth of said ring gear.
5. The mechanical counter-torque drive of claim 2, wherein said external teeth of said ring gear of any one of said one or more stages of one of said planetary gear trains meshes with external teeth of a corresponding ring gear of said one of said one or more stages of said another one of said planetary gear trains.
6. The mechanical counter-torque drive of claim 2, a first end of said output shaft is connected to said planet carrier of a final one of said one or more stages of

said planetary gear trains and a second end of said output shaft is connected to said output pinion, wherein said output pinion is connected along said output shaft.
7. The mechanical counter-torque drive of claim 2, wherein said locking assembly holds in position each of said input gears with respect to said sun gear shaft of a first one of said stages of each of said planetary gear trains.
8. The mechanical counter-torque drive of claim 2, further comprising a double-sided rack meshed with external teeth of each said ring gear of any one of said one or more stages of said planetary gear trains for reducing space occupied by said mechanical counter-torque drive.
9. The mechanical counter-torque drive of claim 2, further comprising a pair of idler gears meshed with external teeth of each said ring gear of any one of said one or more stages of said planetary gear trains for reducing space occupied by said mechanical counter-torque drive.
10. The mechanical counter-torque drive of claim 1, wherein said loading assembly comprises:
a rack meshing with a ring gear of one of said one or more stages of one of said planetary gear trains for said preloading;
a loading member connected to said rack, wherein said loading member is one of a spring, a hydraulic device, a pneumatic device, an electro¬mechanical device, and a combination thereof; and
an adjusting member connected to said loading member for adjusting magnitude of said preload to be applied on said ring gear.

11. The mechanical counter-torque drive of claim 10, wherein said adjusting member is a screw thread mechanism.
12. The mechanical counter-torque drive of claim I, further comprising a bevel gear drive between said driving element and said driving pinion.
13. The mechanical counter-torque drive of claim 1, wherein said input gears are one or more of spur gears, helical gears, herringbone gears, and a combination thereof.
14. The mechanical counter-torque drive of claim I, wherein said planetary gear trains are identical in structure.
15. The mechanical counter-torque drive of claim 1, wherein said driving pinion, said input gears, and said planetary gear trains are enclosed within a casing,
16. A method of operating a mechanical counter-torque drive with zero backlash, comprising:
providing said mechanical counter-torque drive comprising:
a driving pinion rotationally driven by a driving element;
a plurality of input gears drivably connected to said driving pinion;
a plurality of planetary gear trains, each of said planetary gear trains drivably connected to one of said input gears, wherein each of said planetary gear trains comprises one or more stages and an output pinion, wherein each of said one or more stages of said planetary gear trains comprises a sun gear fixed to a sun gear shaft;

a locking assembly for locking said input gears to said sun gear shaft of a first one of said stages of each of said planetary gear trains;
a driven bull gear drivably connected to said output pinion of each of said planetary gear trains; and
a loading assembly connected to one of said planetary gear trains for preloading said mechanical counter-torque drive, wherein said stages of said planetary gear trains are connected to each other, and wherein said loading assembly comprises an adjusting member for adjusting magnitude of preload to be applied on said connected stages;
loosening said locking assembly and rotating said sun gear shaft held in position by said locking assembly for removing backlash from said mechanical counter-torque drive;
tightening said loosened locking assembly;
introducing said preload to said mechanical counter-torque drive by tightening said adjusting member on said loading assembly, wherein said preload induces equal and opposite torques on said connected stages of said planetary gear trains; and
driving said driving pinion by said driving element, wherein said input gears are rotated in a direction opposite to direction of rotation of said driving pinion, wherein said input gears translate said rotation to each of said planetary gear trains that drives said driven bull gear connected to said output pinion on said output shaft;

whereby said driving of said driving pinion rotates said planetary gear trains enabling said mechanical counter-torque drive to drive said driven bull gear with said zero backlash.
17. The method of claim 16, wherein said one of said one or more stages of each
of said planetary gear trains comprises:
said sun gear fixed to said sun gear shaft, wherein said sun gear shaft is connected to one of said input gears through said locking assembly, and wherein said sun gear is mounted coaxially with said sun gear shaft;
a ring gear mounted coaxially with said sun gear shaft, wherein said ring gear comprises one of internal teeth and a combination of internal teeth and external teeth;
a plurality of planet gears drivably connected to said sun gear, wherein said planet gears are in engagement with said ring gear and said sun gear, wherein said planet gears rotate within a planet carrier; and
said planet carrier drivably connected to one of another one of said one or more stages of said each of said planetary gear trains and said output pinion connected through an output shaft.
18. The method of claim 16, wherein said loading assembly further comprises:
a rack meshing with a ring gear of one of said one or more stages of one of said planetary gear trains for said preloading; and
a loading member connected to said rack, wherein said loading member is one of a spring, a hydraulic device, a pneumatic device, an electro¬mechanical device, and a combination thereof

19. The method of claim 16, further comprising meshing external teeth of each
said ring gear of any one of said one or more stages of said planetary gear
trains using a double-sided rack for reducing space occupied by said
mechanical counter-torque drive.
20. The method of claim 16, further comprising meshing external teeth of each
said ring gear of any one of said one or more stages of said planetary gear
trains using a pair of idler gears for reducing space occupied by said
mechanical counter-torque drive.