FIELD OF THE INVENTION
The present invention relates to an improved cam assembly for use in harmonic drive
systems. More particularly, the invention is concerned about an improved split cam
assembly comprising plurality of uniquely symmetrically designed cam sub units which
ameliorate assembly problems and make the assembly cost effective.
The invention also relates to an improved harmonic drive system comprising the said
split cam assembly.
BACKGROUND OF THE INVENTION
The "Harmonic Drive Gears" also known as "Strain Wave Gearing" systems are 'High
Reduction Ratio' gear units. It is used in various hi-tech machineries, starting from clock,
robot to aerospace equipment. The unit (Harmonic Drive) is about fifty years old from its
first introduction by its inventor C. W. Musser (Musser, C. W., 1960, "Break Through in
Mechanical Drive design.-The Harmonic Drive", Machine Design. (April 14 Issue). Pp
160-172. And Musser, C. W., 1959, "Strain Wave Gearing". United States of America
Patent Number 2.906.143. Sept. 29. (Apparently application was filed in 1955)) in 1959.
Through its journey to this present age of computer controlled technologies it has
experienced many modifications for perfection. The inventors patented several designs
and products of harmonic drives, mainly in USA, JAPAN and Germany. Design and
manufacturing technologies are trade secret and open literatures are few. The
manufacturing of Harmonic Drive Units was pioneered by "Harmonic Drive AG,
Germany" (Product Catalogues of "Harmonic Drive AG, Germany" as in website
www.harmonicdrive.de.). The manufacturers in USA and Japan were initially a part of
the "Harmonic Drive AG, Germany" but now have become independent (New Drive,
2007, Special issue- Harmonic Drive AG, December (www.harmonicdrive.de)).
A Conventional 'Harmonic Drive (HD) Gear System', [Fig.-1] also known as 'Strain
Wave Gearing (SWG) System', consists of a rigid 'Circular Spline (CS)' of spline i.e.,
teeth Zg (say), a flexible thin rimmed 'Flex Spline (FS)' with spline or teeth number Zp
(say), usually two less than Zg , and a Strain Wave Generator (WG) Cam, elliptical in
shape, with or without a flexible thin raced ball/roller bearing (FB), mounted on it to
rotate freely inside the FS when fitted to its inside wall with a push fit. The difference in
semi major axis and semi minor axis of the ellipse, that describes the cam profile, is the
center distance between the CS and under formed FS in mesh. The transmission or
reduction ratio in a single stage, is (i) [- Zp /(Zg - Zp )] when FS is the output with CS
fixed ('-' sign indicates that input and output are in reverse directions of rotations) or (ii)
[ Zg /(Zg - Zp )] when CS is the output with FS fixed.
It was seen that the contact pattern for internal-external involute gear set in a
conventional Harmonic Drive with elliptical cam does not maintain gearing laws
perfectly if the conventional low cost (manufacturing) involute teeth are used.
The conventional HDs with pure involute teeth and ellipse shaped cam were first
introduced in 1960s (New Drive, 2007, Special issue- Harmonic Drive AG, December
(www.harmonicdrive.de)). The reason for choosing ellipse to shape the cam probably
lies in the fact that with natural deflection along diameter a circular ring resumes an
elliptical shape. Thereby the assembly of cam in flex gear is not difficult. (We have used
the term 'flex gear' instead of 'flex spline', the term usually used, as because we have
dealt with the standard and corrected involute gears in the proposed model).
In earlier designs "truncated and corrected involute teeth" were used as by that time
manufacture of involute gears were well established. The tooth difference between
internal toothed ring gear and externally toothed flex gear must be two for maximum
transmission ratio. Two major problems were with the involute gears. The "tip
interference" phenomenon (Maiti, R., 2004, A Novel Harmonic Drive with pure involute
tooth pair, ASME Journal of Mechanical Design. 126 (1) (2004) 178-182. And Maiti, R.,
and Roy, A. K., 1996, "Minimum Tooth Difference in Internal-External Involute Gear
Pair," Mechanism and Machine Theory, Vol. 31, No. 4, pp. 475-484.)restricted the
minimum tooth difference (for involute stub teeth it is minimum 7) to a higher value.
Secondly, the wave generator cam profile (Fig. 1.) had no way to maintain the gearing
laws so that the input to output could be kept to a fixed ratio throughout the contacts over
a cycle. To solve such problems researchers had been concentrating on the new conjugate
profiles for the gears (Kiyosawa, Y., et. al., 1989, "Performance of a Strain Wave

Gearing using a new Tooth Profile," Proceedings, ASME International Power
Transmission and Gearing Conference, Vol. 11, pp. 607-612. And Kondo, K., and
Takada, J., 1990, "Study on Tooth Profiles of the Harmonic Drive," ASME Journal of
Mechanical Design, Vol. 112, pp. 131-137.). This became more fascinating with the
development in profile cutting with spark erosion, wire EDM and similar technologies.
By late 1980s a major advancement in harmonic drives was made with the introduction of
a new non-involute tooth form (Product Catalogues of "Harmonic Drive AG, Germany"
as in website www.harmonicdrive.de. And New Drive, 2007, Special issue- Harmonic
Drive AG, December (www.harmonicdrive.de).). The gear pair were named as "flex
spline" (inner pinion) and "circular spline" (ring gear) as the teeth were more close to
spline than gear tooth form. In design and manufacturing "zero-backlash" drive was also
under consideration. An investigation was carried out by Kiyosawa et. al. (Kiyosawa,
Y., et. al., 1989, "Performance of a Strain Wave Gearing using a new Tooth Profile,"
Proceedings, ASME International Power Transmission and Gearing Conference, Vol. 11,
pp. 607-612.)to develop the analytical basis for the performance prediction of harmonic
drives with such a new profiled gears. Accurate kinematic and improved torsional rigidity
were achieved with such an approximate conjugate profile. A serious attempt was made
by Kondo and Takada (Kondo, K., and Takada, J., 1990, "Study on Tooth Profiles of the
Harmonic Drive," ASME Journal of Mechanical Design, Vol. 112, pp. 131-137.)to find
out the merits and demerits of various tooth profiles. In their investigation the tooth
deflection due to weak foundation effect of thin rim of flexspline was also addressed.
They studied also the pin gearing with two teeth difference. Their study on involute
profile concluded with a proposal of thinner tooth tip to avoid tip interference but with a
contact ratio mere one. Also, no analysis was provided for tooth tip interference. To
investigate kinematic errors in such gear an attempt was made by Ghorbel et. al.(
Ghorbel, F. H.; Gandhi, P. S. and Alpeter, F., 2001, "On the Kinematic Errors in
Harmonic Drive Gears," ASME Journal of Mechanical Design, Vol. 123, pp. 90-97.).
Based on such investigations and the new conjugate teeth synthesis methodology now
HI- teeth profile is in use (Product Catalogues of "Harmonic Drive AG, Germany" as in
website www.harmonicdrive.de. And Slatter, R. and Koenen, H., 2007, "Light Weight
Harmonic Drive Gears for Service Robots", A technical paper of "Harmonic Drive AG,

Germany" [www.harmonicdrive.de]. And Degen, R. and Slatter, R., 2007, "Zer-Backlash
Micro-Gears and Actuators for Microassembly applications". A technical paper of
"Harmonic Drive AG, Germany" [www.harmonicdrive.de].). Hence for the proper
gearing action of elliptical pitch curved FS's external teethed gear with CS's internal
teethed gear with circular pitch curve the conventional low cost (manufacturing) involute
teeth are replaced by a new conjugate profiles (called as 'high performance IH tooth
profile' (Product Catalogues of "Harmonic Drive AG, Germany" as in website
www.harmonicdrive.de.)). With these profiles a pair of gear set (FS & CS) may be
termed as match parts and expensive in manufacturing.
Therefore conjugate profiles (called as 'high performance IH tooth profile' (Product
Catalogues of "Harmonic Drive AG, Germany" as in website www.harmonicdrive.de.)
by Harmonic Drive AG, a leading HD manufacturer) fulfilling the gear kinematics of
elliptically flex gear matching with circular gear, are invented and introduced to enhance
the performances, both static and dynamic. Such HDs with back lash free gears are
widely used in Robotics, High precision surgical and other Medical
machines/instruments, Aero-Space Radar controller and similar appliances where very
fine rotary actuation with moderate torque and precision control are essential (Slatter, R.
and Koenen, H., 2007, "Light Weight Harmonic Drive Gears for Service Robots", A
technical paper of "Harmonic Drive AG, Germany" [www.harmonicdrive.de]. And
Degen, R. and Slatter, R., 2007, "Zer-Backlash Micro-Gears and Actuators for
Microassembly applications". A technical paper of "Harmonic Drive AG, Germany"
[www.harmonicdrive.de]) However, such a machine was of much higher cost than with
involute gear pairs, as the former type requires a specific tooth cutter set or NC and
similar high cost machining techniques. Moreover, as the gear pairs are geometrically
matched parts for better conjugate action the cutter profiles must be different for different
set of gears.
In contrast the low cost and well advantageous involute profiles have become obsolete
for Harmonic Drives with conventional (elliptical) SWG cam. Consequently the
researchers' attentions have also been shifted from design analysis of involute gears for
HDs.

Therefore to overcome the drawbacks faced by the costly hi-teeth profiles the present
inventor proposed, developed and patented a novel Harmonic Drive (Maiti, R., 1995, "An
Improved Drive System such as a Two Gear Epicyclic Drive similar to Harmonic Drive
System", Indian Patent No. 186322 of 25-10-1995 (Appln no. 1296/CAL/95).) which has
novelty in cam allowing the HD system working with most common easily
manufactureable and widely used pure involute gears. It showed also better working
features, higher torque capacity than same size conventional unit. The present inventor
had proposed in 1995, a 'novel cam' to work with 'ordinary involute gears' (Maiti, R.,
1995, "An Improved Drive System such as a Two Gear Epicyclic Drive similar to
Harmonic Drive System", Indian Patent No. 186322 of 25-10-1995 (Appln no.
1296/CAL/95). And Maiti, R., 2004, A Novel Harmonic Drive with pure involute tooth
pair, ASME Journal of Mechanical Design. 126 (1) (2004) 178-182.). Although, it is not
yet commercialized but through a project (R&D project (CHD, IIT KGP reference)
Sponsored by Department of Science and Technology, Government of India, Grant no.
SR/S3/RM-04/2002, dated: 11-07-2002.)the design has been improved, prototype has
been made and tested. It has been found that the design of this prior art has (i) better
torque capacity than that of similar size conventional unit and (ii) lower manufacturing
cost. However, the proposed circular-elliptical single piece cam, as in conventional HD's
elliptical cam, needed special fixture for assembly.
Therefore there exists a need to manufacture an improved split cam assembly for use in
drive systems such as two gear epicyclic drive, harmonic drives, and the like which
would solve not only the assembly problem of the cam faced by the prior inventions but
also provide the scope of fine adjustment of center distance (cam eccentricity) adjustment
which ameliorate assembly problems and make the assembly cost effective.
OBJECTS OF THE INVENTION
The basic object of the present invention is to overcome the disadvantages of the prior
art.
One of the objects of the present invention is to provide an improved split cam assembly
where there in a scope of fine adjustment of the center distance (cam eccentricity)
adjustment.

Another object of the present invention is to provide an improved drive system
comprising the split cam assembly.
Another object of the present invention is to eliminate the assembly problems of the drive
system.
Yet another object of the invention is to make the design and construction of the cam
assembly and the drive system simpler and of low cost with high torque capacity.
Yet another object of the invention is to provide zero backlash to the system.
SUMMARY OF THE INVENTION
An improved harmonic drive gear system comprising: at least one strain wave generator
(WG) cam ; at least one thin ring inside which the said wave generator cam is assembled;
at least one flexible bearing inside which the said thin ring is placed; at least one flex gear
which is a cup shaped hollow circular cylinder inside which the said flexible bearing is
placed; wherein said wave generator comprising plurality of U shaped identical pieces
that are trapped in between a taper adjuster; wherein said U shaped identical pieces are
placed together with said thin ring on a hub with a coupling in between and a thin nut is
also provided to regulate the said taper adjuster.
The U shaped identical pieces are two identically split halves named as split cam. The
split cam profile is a combination of circular and elliptical arcs. The said thin ring has
inner radius equal to the outer radius of the said split cam. The said flexible bearing and
said flex gear has a teeth involute of 20°. The outside of the said thin ring has equal
periphery of that of the inside of the inner race of the said flexible bearing. The said taper
adjuster is adapted to get the desired shape and size of the said split cams, when pressed
by the said adjuster. The said thin nut is adapted to adjust the center distance of said cam
(cam eccentricity) by tightening or loosening the said nut. The said split cam arrangement
being provided with zero backlash. The said thin nut is locked by a lock washer. The said
thin ring is optional and being eliminated by making the outer radius of said split cam
equal to the inner radius of said flexible bearing.

DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a proposed split cam (Fig.- lb) which has solved not only (a) the
assembly problem but also gave (b) the scope of fine adjustment of centre distance
(eccentricity).
The present inventor conceived an idea of modifying WG Cam to make it suitable for HD
gears with pure involute profiles (Maiti, R., 1995, "An Improved Drive System such as a
Two Gear Epicyclic Drive similar to Harmonic Drive System", Indian Patent No. 186322
of 25-10-1995 (Appln no. 1296/CAL/95)). Basic target was to manufacture HDs with low
costs but having higher torque capacity than HDs with new tooth profiles. Indian patent
(Maiti, R., 1995, "An Improved Drive System such as a Two Gear Epicyclic Drive
similar to Harmonic Drive System", Indian Patent No. 186322 of 25-10-1995 (Appln no.
1296/CAL/95)) was granted on this design.
The new HD with the proposed cam and teeth profile used are shown in Fig. -2. The
details of the cam are shown in Fig.-3. The proposed cam profile is a combination of
circular and elliptical arcs (Fig.- 3b). The circular portion maintains the involute teeth
contact pattern satisfying the laws of gearing and kinematic requirements. The basic idea
is to stretch the pitch circle keeping a certain amount ? of its circular portion intact, such
that the geometrical center of the new cam will coincide with the center of the whole unit,
which is also the center of ring gear. The radius of the circular portion is equal to the
pitch circle radius of the pinion. The remaining portion of the cam can be connected by
elliptical or any other suitable arcs. Another condition which is also to be satisfied for
smooth running is that the slopes of the circular and the joining arcs at their junction
points must be equal. In the present design the joining arcs are taken as a part of an
ellipse equally spread by the two sides of the minor axis. The center of the considered
ellipse is found to be situated at a certain distance (Maiti, R., 2004, A Novel Harmonic
Drive with pure involute tooth pair, ASME Journal of Mechanical Design. 126 (1) (2004)
178-182.) away from the center of the unit. The cam profile is inwardly shifted curve,
which is parallel to pitch curve. This means that the curve is shifted by a constant
difference along the radius vector of the curvature of the pitch curve at any point on it.

The amount of shift depends on the rim thickness of the flex gear and the radial thickness
of flexible roller bearing or bush bearing or the diameter of roller (in case only the rollers
with out any race are used as bearing element) or as the case may be. The geometric and
kinematic designs of this cam are detailed in reference (Maiti, R., 2004, A Novel
Harmonic Drive with pure involute tooth pair, ASME Journal of Mechanical Design. 126
(1) (2004) 178-182.).
In the original proposed design (Maiti, R., 1995, "An Improved Drive System such as a
Two Gear Epicyclic Drive similar to Harmonic Drive System", Indian Patent No. 186322
of 25-10-1995 (Appln no. 1296/CAL/95). And Maiti, R., 2004, A Novel Harmonic Drive
with pure involute tooth pair, ASME Journal of Mechanical Design. 126 (1) (2004) 178-
182.) the cam was made a single piece. The outer periphery was equal to the periphery of
the inner race of the flexible bearing. But it was very difficult to assembly in contrary to
that with conventional elliptical cam. A split cam design is found to be a good solution to
eliminate assembly problem.
The novelty in the split cam concept is that it makes the design simpler and
manufacturing easier and low cost while solving the assembly problem that was with the
earlier proposal of the novel Harmonic Drive. The present inventor proposed, developed
and patented a novel Harmonic Drive which has novelty in cam allowing the HD system
working with most common easily manufactureable and widely used pure involute gears.
It showed also better working features, higher torque capacity than those are with
conventional unit of same size. However, the proposed circular-elliptical 'single piece'
cam needed special fixture for assembly contrary to easy assembly in conventional unit.
To make the assembly easier the new split cam is proposed.
The proposed Split Cam Concept for SWG Cam is the original idea of the inventor. As in
the prior art in case of conventional Harmonic Drive or Strain Wave Gearing (SWG) the
cam is elliptical. It is made single piece cam and can be inserted easily in flex spline.
However, the conventional one does not work well with involute gears and new
conjugate profiles are used which leads to separate design of profiles for each set of gear
pairs. In an earlier design by the same inventor (Indian Patent No. 186322 of 25-10-1995)
a new 'single piece' cam profile having circular arcs at two working zones and elliptical

or any other suitable curves at other zones, is used. It had assembly difficulties contrary
to the conventional HD as in later case the circular flex spline and circular flex bearing
races take a natural elliptical shape when deflected diametrically at any circumferential
position. The problem is solved by introducing two pieces split cam and a taper adjuster,
as in the present invention. The taper adjuster also helps in center distance adjustment.
Advantages:
The proposed WG Cam with involute profile has several advantages detailed in earlier
patent (Maiti, R., 1995, "An Improved Drive System such as a Two Gear Epicyclic Drive
similar to Harmonic Drive System", Indian Patent No. 186322 of 25-10-1995 (Appln no.
1296/CAL/95)). The experimental results support those earlier claims. The present
invention solves the WG cam assembly problem that was in the proposed model. The
distinct advantages are.
(i) The problem in assembly of single piece cam is solved by splitting the
cam.
(ii) An introduction of taper adjuster completes the cam assembly as well
as facilitates centre distance or eccentricity adjustment. With the same
adjuster one can make cam of another size and eccentricity by simply
changing the two pieces (circular parts. No. I in Fig.3d & 4b). The
split cam arrangement will also help in initial backlash adjustment.
(iii) Unlike the single piece conventional 'Elliptical' or the proposed
'Circular-Elliptical' cams the 'Split Cam components 'do not require
special machining.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates conventional harmonic drive.
Figure 2 illustrates proposed new harmonic drive.
Figure 3(a) illustrates Subassembly of the Proposed Cam Photographic view (Without
bearing)
Figure 3(b) illustrates a typical Profile of the New Proposed CAM
Figure 3(c) illustrates Subassembly of the Proposed Cam Sectional view (With Flexible
bearing)
Figure 3(d) illustrates Components of the proposed cam (Coupling is not shown)
Figure 3(e) illustrates Detail drawing of a typical set
Figure 4(a) illustrates Exploded views explaining assembly sequences of elliptical cam
subassembly, and then in flex gear, of commercial unit.
Figure 4(b), illustrates Exploded views explaining assembly sequences of the proposed
cam inside the flexible bearing and flex gear together.
Figure 5 illustrates the strain developed in flex gear with elliptical and proposed new
cam.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Assembly of the conventional cam of elliptical shape is not a problem. For clarity the
exploded views of both conventional elliptical cam assembly as well as the new proposed
cam assembly are shown in Fig. 4(a) and 4(b).
In the case of elliptical cam (1) a solid single piece can be cut out of plate. It is put on a
hub (2) with a coupling (3) (like an Oldham coupling) in between. Then a circlip (4) is
put to fix the subassembly. This assembled cam can easily be inserted inside the inner
race of ball bearing (5) with thin and flexible inner and outer races specifically made for
such Harmonic drive units. Finally the sub-assembled cam unit is put easily inside the
cup shaped flex gear (6), which is simply little pressed diametrically by hand for easy
insert of the cam subassembly. It is to be attributed to the fact that the natural deflection
of a circular ring takes a shape of ellipse. For the whole assembly of the conventional
Harmonic Drive the final subassembly of the flex gear with the cam subassembly inserted
inside, can be pushed in radial direction inside the ring gear to have the gear pair in mesh
at two places along the extension of the major axis of the elliptical cam with pitch points
on that extended lines. This means that before the final assembly the conventional HD
unit will have three separate parts, namely- (i) cam subassembly, (ii) FS & (iii) CS (see
Fig.-1).

The proposed new cam if made a single piece is, however, difficult to insert in the
flexible bearing and in the flex gear. This is because the shape of the periphery is a
combination of circular and elliptical or similar arcs which does not take place in natural
deflection of a circular ring. To overcome this assembly problem the cam has been split.
The exploded views in Fig.-4(b) will help understanding the assembly sequence of the
new cam with the bearing and flex gear. Referring to the illustrations in Fig.-2 to Fig.-
4(b) the assembly method is as follows.
Two U shaped identical pieces, named as split cam (7), having outer surfaces of circular
arc of a spread slightly less than ? (Fig.- 1 b). They are placed inside a thin ring (8). The
ring has inner radius equal to the outer radius of the split cam. The split cams and the ring
are placed on the hub (9) (which is different from that (2) in elliptical cam. In the case the
same hub with circlip is used for new split cam a fixture will be required for assembly)
with the coupling (3 or 13, also see Fig.-3 d) in between (see Fig.- 4 b). The inside edges
of these split cams are tapered in such a way that when pressed by the adjuster (10) in
between the two pieces they move apart to give the desired shape of the new cam. The
centre distance can be adjusted by tightening or loosening a thin nut (11), which is finally
locked by the lock washer (12) (similar to a nut as used for bearing locking). The outside
of the thin ring has the equal periphery of that of the inside of the inner race of the
bearing i.e. equal to the conventional elliptical cam. The whole assembly process is to be
conducted inside the inner ring of the flexible bearing (5) put inside the flex gear (14).
The thin ring is optional and it may be eliminated by making the outer radius of split cam
equal to the inner radius of the inner race of the bearing or inside radius of bush bearing
as the case may be. Over the assembly facility such a split cam is having the advantage of
center distance adjustment, which can control the backlash. Backlash means the
difference between the circular pitches of gear tooth (CS) and pinion tooth (FS). In
commercial Harmonic Drives the backlash is made zero by controlling the dimensions in
manufacturing. Whereas, in the present invention it can be done by adjusting the centre
distance. In case of internal gearing if the centre distance is made maximum such that
both the flanks of pinion (in case of harmonic drive the FS) tooth touch both the flanks of
the ring gear (in case of harmonic drive the CS), while in contact, the gear pair becomes

backlash free (i.e. zero backlash). For final assembly the whole subassembly of FS
including the cam can be pushed into the CS as in case of conventional HD. However,
contrary to the conventional HD the proposed one will have two components, namely- (i)
the FS subassembly with split cam and bearing and (ii) the CS (See Fig.-2).
Figure 5:
Testing:
Tests on Performance
Tests were conducted (R&D project (CHD, IIT KGP reference) Sponsored by
Department of Science and Technology, Government of India, Grant no. SR/S3/RM-
04/2002, dated: 11-07-2002.) to examine the strains developed in the flex gear of both the
commercial unit and the proposed unit. A sample result is shown in Fig.- 5. The strain
gages were fixed inside the flex gear cup i.e. in thin wall, in circumferential direction and
it was very close to the teeth (zone 3, Inset Fig.- 4). Apparently the cup wall is more
strained when operate with the new cam. But the trend is that with the increase in torque
the strain near the pitch point reduces i.e. approaching zero in case of new cam where as
it increases in negative direction in the case of elliptical cam. The strain will reverse its
sign at a certain higher torque. On the other hand the strain will be higher in same
direction for that torque with the conventional elliptical cam. This means that for that
torque the proposed unit will have better performance. We are further investigating it.

We Claim
1. An improved harmonic drive gear system comprising:
(a) at least one strain wave generator (WG) cam ;
(b) at least one thin ring inside which the said wave generator cam is assembled;
(c) at least one flexible bearing inside which the said thin ring is placed;
(d) at least one flex gear which is a cup shaped hollow circular cylinder inside
which the said flexible bearing is placed;
wherein said wave generator comprising plurality of U shaped identical pieces
that are trapped in between a taper adjuster;
wherein said U shaped identical pieces are placed together with said thin ring on a
hub with a coupling in between and a thin nut is also provided to regulate the said
adjuster.
2. The system as claimed in claim 1 wherein said U shaped identical pieces are two
identically split halves named as split cam.
3. The system as claimed in claim 2 wherein said split cam profile is a combination
of circular and elliptical arcs.
4. The system as claimed in claim 1 wherein the said thin ring has inner radius equal
to the outer radius of the said split cam.
5. The system as claimed in claim 1 wherein said flexible bearing and said flex gear
has a teeth involute of 20°.
6. The system as claimed in claim 1 wherein outside of the said thin ring has equal
periphery of that of the inside of the inner race of the said flexible bearing.
7. The system as claimed in claim 8 wherein said taper adjuster is adapted to get the
desired shape and size of the said split cams, when pressed by the said adjuster.

8. The system as claimed in claim 1 wherein said thin nut is adapted to adjust the
center distance of said cam (cam eccentricity) by tightening or loosening the said
nut.
9. The system as claimed in claim 1 wherein said split cam arrangement being
provided with zero backlash.
10. The system as claimed in claim 1 wherein said thin nut is locked by a lock
washer.
11. The system as claim in claim 1 wherein the said thin ring is optional and being
eliminated by making the outer radius of said split cam equal to the inner radius
of said flexible bearing.
12 The improved harmonic drive gear system as herein substantially described and
illustrated with the accompanying drawings.

An improved harmonic drive gear system comprising: at least one strain wave generator
(WG) cam ; at least one thin ring (8) inside which the said wave generator cam is
assembled; at least one flexible bearing inside which the said thin ring (8) is placed; at
least one flex gear (14) which is a cup shaped hollow circular cylinder inside which the
said flexible bearing (5) is placed; wherein said wave generator comprising plurality of U
shaped identical pieces (7) that are trapped in between a taper adjuster (10); wherein said
U shaped identical pieces (7) are placed together with said thin ring on a hub (9) with a
coupling (13) in between and a thin nut (11) is also provided to regulate the said taper
adjuster (10).