Mechanism of “Man-nen dokei,” a Historic Perpetual ... - IFToMM

12th IFToMM World Congress, Besançon (France), June18-21, 2007
Mechanism of “Man-nen dokei,” a Historic Perpetual Chronometer
Part2 : Power Supply
Takehiro Hato * Kazuyoshi Suzuki † Yoichi Tomii ‡
Toshiba R&D Center National Science Museum Kyoto University
Kawasaki, Japan Tokyo, Japan Kyoto, Japan
Mitsunobu Yoshida § Yasuhiro Yokota ** Yuji Kubota ††
Toshiba R&D Center Toshiba R&D Center Toshiba R&D Center
Kawasaki, Japan Kawasaki, Japan Kawasaki, Japan
Abstract—The “Man-nen dokei,” which is a historic
perpetual chronometer, was made in 1851 by Hisashige Tanaka,
who founded the predecessor of Toshiba Corporation. It has six
multi-functional clock faces and a celestial globe. It is said that
it runs for almost a year with just a single winding. Man-nen
dokei was disassembled and restored in a national project. We
investigated on the mechanism of Man-nen dokei in cooperation
with this project. In this paper, we report on the mechanism of
the power supply. As a result, from mechanism constitution of
the power supply, we confirmed that maximum continual
movable days of Man-nen dokei were approximately 225 days.
But from the fusee steps and the double spiral spring
composition, it is thought that Hisashige’s goal was to make it
move for 1 year continually. The spring that generates a huge
torque became necessary to make it move for 1year, but it is
assumed that the spiral spring were wound just a little due to
strength poverty of the wooden frame. Moreover, we think the
composition of one fusee is a reasonable design to obtain
necessary torque for continuous operation with stability for 1
year, and the reason why Hisashige used two-fusee composition
remains still to be unclear.
national important cultural property in June 2006. This
clock's height is about 60 cm (excluding pedestal), weighs
approximately 38 kg, and is composed of more than 1000
parts. A "celestial globe", which demonstrate movements
of the sun and the moon, is arranged at the top of the clock
and each of six faces arranged underneath the celestial
globe has time displaying unit different each other [1], [2],
[3]. A pedestal having six legs is provided under the time
displaying unit and a chime for time telling is disposed in
it. On each face of a hexagonal pedestal (approximately
65 cm in diameter) provided underneath is decorated with
cloisonne, and four spiral springs to be used for power
generation of the Man-nen dokei are accommodated in
this hexagonal pedestal [4].
Keywords: mechanism, mechanical clock, power supply,
torque equalization, spring, fusee
I. Introduction
Man-nen dokei (Official name: Man-nen-jimei shou) is
a mechanical type clock manufactured in 1851 by
Hisashige Tanaka (referred to as Karakuri-giemon),
founder of Toshiba Corporation. This clock fused Western
technology with Oriental nature to simulate real life at that
time and realized a variety of time displaying functions by
means of complicated mechanisms, and is said to be the
masterpiece in Wadokei. This masterpiece was exhibited
at Aichi EXPO held in 2005 and was designated as the
_______________________________________
*E-mail: takehiro.hato@toshiba.co.jp
†E-mail: k-suzuki@kahaku.go.jp
‡E-mail: yoichi.tomii@viking.mbox.media.kyoto-u.ac.jp
tE-mail: mitsunobu.yoshida@toshiba.co.jp
**E-mail: yasuhiro.yokota@toshiba.co.jp
††E-mail: yuji.kubota@toshiba.co.jp
Fig. 1. Schema of power transmission

12th IFToMM World Congress, Besançon (France), June18-21, 2007
Figure 1 shows a schema of power transmission from
the spiral spring to the time display unit and the celestial
globe. Two of four spiral springs compose one set of
power, and two sets of power are provided, one for time
driving and the other is for chime striking. A power
generated by the spiral spring is transmitted to the first
wheel of time driving and of chime striking via fusees
illustrated in conical form, and is then transmitted to each
of driving parts to realize operations as the Man-nen
dokei.
It is said that the Man-nen dokei functions continuously
for one year if wound once. This description is seen in the
advertisement and literature of the Man-nen dokei [5], [6].
To realize this specification, composition of the power
supply unit plays a vital role. A combination of spiral
spring/fusee was invented in the 1500s, and used as power
for clocks in France etc. and in 1600~1800 it was used for
pocket watches [7]. In 1700s, chronometers were used for
navigation of the sea, which resulted in development of
fusee mechanism technology. In view of the above, it is
considered that around 1850 when the Man-nen dokei was
manufactured, technology of spiral spring/fusee
mechanism was promulgated to a certain extent in the
West. Apparently, power generation mechanism by spiral
spring/fusee was used in Yumihiki-doji and Shumisenngi,
achievements by Hisashige Tanaka, which were produced
prior to Man-nen dokei [8]. Although spiral spring/fusee
composition was used in the Man-nen dokei as the power,
it has two-spiral spring and two-fusee composition, which
is not seen in Western mechanical type clocks and
Hisashige's other workmanship, and this composition are
considered extremely rare.
As one of activities of national project " Inventions in
the Edo period " promoted by the Ministry of Education,
Culture, Sports, Science and Technology for the sake of
verification of technical level and creativity of Japan in
Edo period, disassembly, investigation, restoration and
duplication of the Man-nen dokei were carried out.
Although disassembly survey was attempted so far several
times [9], there is no data that deals with the details of
mechanisms and operations. For power supply unit which
might have involved many originalities and ingenuities to
realize operations for lengthy period of time, little record
is left. Consequently we attempted to identify the structure
of the power supply unit of the Man-nen dokei utilizing
data acquired by the current disassembly survey and to
investigate the mechanism. This paper reports the results
we obtained.
II. Composition of power supply unit
A. Composition of mechanism
Figure 2 shows CG perspective view and internal
mechanism CG image of the power supply unit. In the
wooden hexagonal pedestal, which is located at the
bottom of the Man-nen dokei, four spiral springs being
accommodated in a barrel drum are mounted. As shown in
Fig. 2 (b), two barrel drums are connected by a chain and
two spiral springs are composed to generate one power.
As shown in the photograph of Fig. 3, it is designed so
that shaft of one spiral spring per one power is fixed to the
X-shaped metallic plate and shaft of other spiral spring is
elongated to be connected as the output shaft to the fusee
mechanism at upper part. None of barrel drum is fixed.
With such a configuration, the sum of the number of
rotations of two springs is obtained by the output shaft.
An output shaft of the spiral spring passes through legs
of the six leg pedestal and conveys a power to the fusee
mechanism shown in Fig. 4. A downward pointing fusee
(input fusee) is directly mounted to the output shaft of the
spiral, and is connected with an upward pointing fusee
(output fusee) by a chain, and the power is then
transmitted via output fusee gear to a first wheel that
serves as the driving source of clock operations. In other
words, outputs of two spiral springs are uniformed via two
fusees and used for clock operations. When a spiral spring
is once made free, it releases its power at once, so a speed
regulating mechanism is required. For speed regulation of
time driving side, a speed regulator in the Western style
clock plays this role. For speed regulation mechanism of
chime striking side, a whizzing wheel is provided that is
turned intermittently and timing of this turning is
interlocked with Wadokei movement.
The fusee has helix profile as shown in Fig. 4 and this
profile determines how much the spiral springs output
torque could be uniformed. Fusees used in the Man-nen
dokei are handmade and therefore, profiles of each fusee
are delicately different. Table 1 shows dimensions
(diameter) of each step in the cross section passing
through the center of the fusee and the center of the hole
of hooking the chain.
(a) Perspective view
(b) Internal mechanism
Fig. 2. CG image of power supply unit
Fig. 3. Spring section of the power supply unit

12th IFToMM World Congress, Besançon (France), June18-21, 2007
The shaft of each fusee is supported by the elliptic
shaped metallic plate(fusee support plate) and the pedestal
frame. Further, as shown in Fig. 4, height of supporting at
input fusee and at output fusee is shifted by thickness of
the gear of the output fusee. So the second ~ third step
from the bottom of the input fusee and lowest step of the
output fusee are connected by the chain. The fusee support
plate is supported by four metal columns while two of
four metal columns are connected to the diagonal column
support plate extending from the pedestal. This column
support plate looks as if mounted to prevent turning of the
fusee support plate. Besides, a comma-shaped cam
configuration provided on the output fusee shaft forms a
winding amount regulating mechanism with a lever shape
part. The winding amount regulating mechanism is a
mechanism for preventing excessive winding of the spiral
spring and is normally used in spiral spring/fusee
mechanism [7].The Man-nen dokei is designed in such
that locking is applied when the output fusee is turned
about six times. The output fusee makes one turn in 37.5
days when calculated from rotational speed of the first
wheel of the Western clock. It is noticed from this that the
maximum continual movable days of the Man-nen dokei
is about 225 days from mechanism constitution. Although
it was identified by the previous disassembly survey [9],
the current study could confirm this together with reasons
for that. Although this figure is less than the number of
days of yearly operation which has been believed till date,
it is understood that a mechanism that realized an
astonishing specification in those days was manufactured
since number of days of clock operation at that time was
about 10 days at the longest.
Fig. 4. Fusee mechanism section of the power supply unit
Fusee
Fusee for
driving clock
Fusee for
striking chime Average
steps Input Output Input Output [mm]
[mm] [mm] [mm] [mm]
1 62.3 62.5 60.7 61.0 61.6
2 61.6 52.7 57.0 57.0 57.1
3 45.7 44.9 50.7 49.7 47.8
4 39.1 38.5 44.2 43.4 41.3
5 33.8 33.1 38.1 38.9 36.0
6 29.5 29.3 31.9 31.5 30.6
7 26.3 27.5 29.3 29.1 28.1
8 23.7 25.7 26.9 26.5 25.7
9 22.3 21.0 24.3 24.7 23.1
Table 1. Fusee size data
B. Forces exerted to wooden frame
The column support plate shown in Fig. 4 is supposed to
be a structure for preventing rotation of the fusee support
plate from the assembled direction and configuration.
Therefore this section reports results on how much power
is exerted to the wooden frame (six leg pedestal)
calculated from a geometrical relationship between the
fusee support plate and the wooden frame.
Figure 5 shows geometrical relationship between the
fusee support plate and the wooden frame. In Fig. 5,
length from point O to point A that is rotating center of
the input fusee is 88 [mm], length from point O to point B
that is rotating center of the output fusee is 56 [mm],
length from point O to x-component of point C (point C x )
that is column support point of fusee support plate is 37
[mm], and length from point O to y-component of point C
(point C y ) is 54 [mm]. In this case, when considering the
case where the symmetrical force interacts to Point O,
force F A
to turn the fusee support plate is expressed by
x
the following equation:
OB
FA x
= FA
= 0. 537FA
AB
A reaction force of this turning force is applied to the
column support plate and force F applied to the wooden
D
frame is expressed as follows:
OA
F = D
FA 0. 722F
x
A
OC
=
Tensile force F D
applied to the wooden frame and
x
shearing force F D
which are desired to be obtained
y
finally are represented by the following equations:
OC
y
FD = FD
= 0. 596F
(1)
x A
OC
OCx
FD = FD
= 0. 408F
(2)
y A
OC
Next, force F applied to rotating center of the input
A
fusee is obtained from generated torque of the spiral
spring. The fusee support plate, fusee and spiral spring are
in a positional relationship shown in Fig. 6 and it is
considered that force F′ generated by the spiral spring is
A
nearly equal to tensile force F exerted between fusees.
A
Torque T of the spiral spring is expressed as follows,
z
where Ω denotes maximum winding angle of spiral
spring, α denotes released angle of spiral spring and M
0
denotes torque of spiral spring per unit angle.
T Z
= M
0(
Ω −α)
(3)
Then, force F′ can be obtained by the following
A
equation:
TZ
F ≅
(4)
′A
R
If initial state (α = 0) is considered where spiral spring is
wound N times ( N denotes winding number of spiral

12th IFToMM World Congress, Besançon (France), June18-21, 2007
spring), Eq. (4) can be rewritten as follows:
2πM
0
F′ A
≅ N
(5)
R
N
From measurement of torque of the spiral spring (see
Section 3, Fig. 9),
M
0
≅ 1450[kgfmm] = 14.2[Nm]
and from measurement result R = 29.3 [mm] for spiral
1
spring wound once ( N = 1), force F′ is calculated as
A
follows:
3
F ≅ 311[kgf] = 3.05 10 [N]
A , N = 1
×
Substituting this result into Eqs. (1) and (2), tensile force
F D
and shearing force F
x
D
are obtained as follows:
y
3
F ≅ 185 [kgf ] = 1.82 10 [N]
F
D
×
x
D
≅ 127[kgf] = 1.24×
y
10
3
[N]
As shown above, a sizable force is exerted to the wooden
frame even if the spiral spring is wound only once.
Although strength of the wooden frame is unknown,
cracks are observed with the wooden frame in fact. From
this, it is considered that in practice, spiral spring could
not be turned that much.
III. Spiral springs
A. Profile and materials
It is considered that spiral springs mounted currently to
the Man-nen dokei are the third generation. The first
generation spiral spring was forged by a sword-smith
upon request by Hisashige Tanaka and the second
generation spiral spring is the replacement replaced in
1884 when the Man-nen dokei was disassembled by
S.Tanaka (disciple of 1st Hisashige Tanaka) upon request
by 2nd Hisashige Tanaka. At this time, since the cracks
were found with the spiral spring, it was replaced. The
third generation spiral spring was replaced at disassembly
survey of the Man-nen dokei carried out in 1949 by T.
Asahina et al. at National Science Museum. Also at this
survey, spiral springs were found cracked and those of the
same quality were produced and used for replacement.
Since there is no description of spiral spring replacement
other than the said replacement made twice [10], it is
considered that the third generation spiral spring is
mounted to the Man-nen dokei. Figure 7 is a photograph
showing the third generation spiral spring.
The current survey includes dimensional measurements
and analysis of materials of the third generation spiral
spring. Table 2 shows results obtained. Further, from
dimensions of the spiral spring shown in Table 2, effective
number of rotations of the spiral spring is calculated to be
about 3.8 turns.
Fig. 5. Geometrical configuration of fusee support plate and wooden
frame
Fig. 7. Spiral spring (third generation)
Fig. 8. Torque measuring apparatus
(a) Side view
(b) Top view of fusee
Fig. 6. Cross section diagram of power supply unit
Length
3050 [mm]
Width
65 [mm]
Spring Thickness
1.9 [mm]
Material
7-3 BrassCu:73.08%, Zn:26.20%,
Sn:0.35%, Pb:0.15%, Fe:0.22%
Barrel Diameter
φ120.5 [mm]
Shaft Diameter
φ 27.0 [mm]
Table 2. Size and material analysis of the spring

12th IFToMM World Congress, Besançon (France), June18-21, 2007
Fig. 10. Fusee and spring barrel composition
Fig. 9. Experimental result of spring torque
B. Torque characteristics
Next, measurement of torque of the third generation
spiral spring will be discussed. As shown in Fig. 8, the
barrel drum of the spiral spring was fixed, the spiral
spring was turned gradually from released state, and
torque at each number of rotations was measured. Results
of the measurement of torque are shown in Fig. 9.
Although outside of the barrel drum was reinforced before
current measurements, experiments were limited to 1.5
turns in fear of possible deformations of the barrel drum
having thickness of only 1 mm. Therefore, torque for
more than 1.5 turns is of estimated value. Since effective
number of turns of the third generation spiral spring is
about 3.8 turns as mentioned previously, results in Fig. 9
are for torque values up to 3.8 turns.
IV. Fusee mechanism
Torque generated by a spiral spring varies greatly when
released from wound state. Fusee was devised to make
these variations uniform. Normally, the fusee mechanism
is composed of combination of a fusee having sectional
profile close to parabola and a cylinder (in many cases,
barrel drum storing spiral springs) (Fig. 10) [7]. However,
in the case of the Man-nen dokei, two fusees are arranged
in upward and downward directions as shown in Fig. 4. In
this chapter, power characteristics of the Man-nen dokei
using two fusees are assumed and reasons for that two
fusees are employed are discussed.
A. Characteristics of Man-nen dokei power supply unit
A case where a fusee is provided to spiral spring side
too as shown in Fig.11 is considered. Suppose that a chain
is applied to radius R (α ) position of the input fusee
(which is connected to spiral spring) and at radius r (β )
position of the output fusee. Torque of the spiral spring
can be expressed by Eq. (3) and torque T conveyed to
out
the output shaft is then expressed as:
r
T out = M 0 ( Ω −α)
(6)
R
Fig. 11. Fusee composition of Man-nen dokei
If the chain is released from input fusee by a small mount
of R ⋅ dα
, the same length r ⋅ dβ
should be wound at
output fusee, then the following equation is established:
∫ α
R ( α)
dα
= ∫
β
r(
β ) dβ
(7)
0
0
If maximum number of rotations of the spiral spring is
represented by N , number of turns of the spiral spring
from the place it is winded to the maximum extent is
represented by n , and number of rotations of the output
shaft is by m , the following relationships are obtained:
Ω = 2 πN
, α = 2πn,
β = 2πm
(8)
Using Eqs. (8) in Eqs. (6) and (7), the following
relationships are obtained:
r(
m)
T out = 2π M 0 ( N − n)
(9)
R(
n)
∫ n
R n)
dn = ∫
m
0
( r(
m)
dm
(10)
0
To obtain torque characteristics of the output shaft, Eq. (9)
is simply calculated under the condition that R (n)
and
r (m) satisfy the relationship expressed by Eq. (10).
Using formula processing software Mathematica
(registered trademark of Wolfram Research, Inc.),
characteristics of the output shaft were calculated by Eqs.
(9) and (10). Profile R (n)
and r (m)
of the fusee were
obtained by supplementing actual measurements shown in
Table 2 by tertiary polynomial expression. Calculations
were made for two cases, one is a case spiral spring shaft
is turned eight times to allow continuous operation of one
year and the other is a case of five turns that is close to the
composition remained at present. Results are shown in Fig.
12 by solid line and dotted lines.
B. Discussions of use of two fusees
In this section, discussion is made on why Hisashige
Tanaka used two fusees in the Man-nen dokei. First, with
a combination of cylinder and fusee which is an ordinary
composition of the fusee mechanism, virtual design was

12th IFToMM World Congress, Besançon (France), June18-21, 2007
fusee that is ordinary composition of the fusee mechanism,
unnecessarily large power is not exerted to the wooden
frame and uniform output is obtained, and this
configuration is thus suited for the power supply system
of the Man-nen dokei. The reason why Hisashige Tanaka
used two-fusee composition remains still to be unclear.
Fig. 12. Calculated results of spring output torque
attempted to know what output characteristics would be
obtained. As the design constraint condition, that the fusee
mechanism should be accommodated within the wooden
frame (six leg pedestal) was used. Specifically, the
following equation
R + r 70 [mm]
0 8
≤
was used as the constraint condition where radius of the
cylinder is represented by R and maximum radius of the
0
fusee is represented by r 8
.
Radius of the fusee that maintains output torque
constant is obtained by the following equation [7]:
r0
r m = (11)
2r0
m
1−
R0
N
where, r is 12.3 [mm] same as that of actual fusee.
0
Further, maximum level of number of rotations m of the
output shaft is assumed to be m = 8 supposing
max
continuous operation of one year.
In promoting virtual design, it is considered that number
of rotations of the spiral spring shaft N be kept minimal
as much as possible so that large power may not act on the
wooden frame. However, if N is made smaller, R in the
0
denominator of right side member of Eq. (11) should be
made larger, which does not meet with the constraint
condition. So in this discussion, virtual design is promoted
using N = 6. If it is assumed that the spring is fully
released when the output shaft rotates eight times,
R = 32.8 [mm]
0
is obtained from the condition that the denominator of
right side member of Eq. (11) is zero. Accordingly, it is
now possible to increase r up to 37.2 [mm] from the
8
constraint condition.
From Eq. (11), r k
(k=1,2,.... ,7) are obtained as follows:
r 1 =13.1, r 2 =14.2, r 3 =15.6, r 4 =17.4, r 5 =20.1,
r 6 =24.6, r 7 =34.8 (all units are [mm])
Profiles of the fusee were supplemented by the tertiary
polynomial expression and torque characteristics of the
output shaft were calculated as shown in Fig. 12 by
dashed-dotted line. It is noticed from Fig. 12 that with one
V. Conclusion
This paper deals with clarification of mechanism of the
power supply unit of the Man-nen dokei and discussions
involved. It has been found that from composition of the
mechanism of the power supply unit, the maximum
continual movable days of the Man-nen dokei now
existing is to be about 225 days, and it is considered that
from the number of steps of fusees and devisal for
lengthening driving hours by double configuration spiral
springs, Hisashige Tanaka would have targeted
continuous operation for one year. Although spiral springs
generating a huge torque were necessary to realize a
power supply unit capable of allowing continuous one
year operation, it is assumed that the spiral spring were
wound just a little due to strength poverty of the wooden
frame. In order to attain the torque required for one-year
continuous operation in stable fashion, one-fusee
composition allows reasonable design and hence, the
reason why Hisashige Tanaka used two-fusee composition
remains still to be unclear.
Acknowledgement
We wish to express our heartiest thanks to Seiko
Precision Inc. and Sunco Spring Co., Ltd, for their great
cooperation in promoting this study.
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