Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~i4~aiOl
The present invention relates to an engagement
mechanism for engaging conveyance containers to a plurality
of endless chains in a continuous conveyance system where
a large volume of bulk load, such as crushed rock, sand or
the like, can be continuously conveyed to any elevation,
and more particularly relates to an improvement of the
engagement mechanism of the type in which two lines of inner
endless chains are engaged directly to the front support
positions on both side walls of the conveyance container,
and two lines of outer endless chains are engaged indirectly
to the rear support positions on both side walls of the
conveyance container.
As means for conveying to an elevated position
loose bulk, such as granular material, crushed rock and
others, there is known typically a bucket conveyor compris-
ing a series of buckets engaged to endless chains which
are passed round a pair of upper and lower sprocket wheels,
said endless chains being driven in circulation by means of
a power source, such as an electric motor. According to
the conventional bucket conveyor system as described above,
however, the loose bulk accumulated at a lower position is
immediately lifted up to an elevated position by the
buckets, so that it is impossible with this conveyor system
to continuously receive and convey to an elevated position
bulk load continuously supplied from a belt conveyor.
In fact, the inventors invented a new and unique
container circulating type continuous conveyance system
which is quite free from the drawbacks inherent to the
conventional bucket conveyor system and by which loose
bulk load continuously supplied by means of a belt conveyor
can be conveyed to an elevated location in the vertical
direction. They filed a patent application with the
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Japanese Patent Office on November 15, 1976, and a patent
was granted to them on June 6, 1980 under Patent Publication
No. 20,946/80.
The conveyance system to which a patent was issued
contains a first 180 degrees turn-over section where loose
bulk is received, a first horizontal transfer section, a
first pair of 90 degrees rotary sections, an upward moving
section, a second pair of 90 degrees rotary sections, a
second horizontal trans~er section, a second 180 degrees
turn-over section where loose bulk is discharged, a first
horizontal return-section, a first return 90 degrees rotary
section, a downward return section, a second return 90
degrees rotary section and a second horizontal return
section, wherein two pairs of inner and outer endless chains
are extended through the respective sections as listed
above to drive conveyance containers in circulation there-
through. A first pair of inner endless chains are engaged
to the respective conveyance containers in position at
their front part and a second pair of outer endless chains
~0 are engaged to the respective conveyance containers in posi-
tion at their rear part so that the conveyance containers
are aligned one after another. It is to be noted that the
sprocket wheels located at the inside 90 degrees rotary
section have the inner endless chains carried thereon, and
the sprocket wheels located at the outside 90 degrees
rotary section have the outer endless chains carried thereon
so that the conveyance containers move upwards with their
horizontal posture maintained throughout the upward moving
section while they keep a certain distance one above
another. The respective conveyance containers have an
engagement plate fixedly secured thereto, said engagement
plate of resilient material being effective in preventing
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bulk load received therein from falling down through a
clearance between the two adjacent conveyance con-tainers.
The respective conveyance containers turn over at the first
180 degrees turn~over section to receive loose bulk
material from a charging hopper with the:Lr posture reversed
by 180 degrees, move along the first horizontal transfer
section, change the direction of their movement at the
first pair of 90 degrees rotary sections to move upwards
throughout the upward moving section with their horizontal
posture maintained, then move along the second horizontal
transfer section and finally discharge loose bulky material
at the second 180 degrees turn-over section.
In fact, the present invention is intended to
eliminate the drawbacks inherent to the conventional
conveyance system as described above and make it possible
to ensure smooth movement of a series of conveyance con
tainers through 180 degrees turn-over sections as well as
at 90 degrees rotary sections with the aid o-f an engagement
mechanism for-~the conveyance containers without any p:Lvotal
, 20 means such as pivotal links which are fixedly secured to
the side walls of the.respective conveyance containers at
their front support positions in the conveyance system as
well as to construct the engagement mechanism in such a
manner that unbalanced distribution of weight load to be
- carried by the inner and outer endless chains is ade~uately
compensated. Specifically, the engagement mechanism for
the conveyance containers in accordance with the present
invention is such that stationary front shafts on the both
side walls of the conveyance container at the front support
position are engaged directly to tWQ lines of inner endless
chains and a movable rear shaft transversely extending
through the conveyance container at the rear support
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iOl
position is engaged to two lines of outer endless chains
displaceably within a certain extent. During downward
movement of the conveyance containers, their weight load
i9 carried by the outer two endless chains which are
engaged to the movable rear shaft which abuts against a
stopper of a defining member. As time elapses, the afore-
said two lines of outer endless chains are gradually elon-
gated and thereby the distance between both engagement
positions where the inner and outer endless chains are
engaged to the conveyance container is reduced corres-
pondingly. As a result, the weight load carried by the
movable rear shaft via the stopper in the defining member
is decreased and the stationary front shaft in turn begins
to participate in carrying the weight load, resulting in
elongated inner endless chains. Thus, elongation of the
two inner endless chains and the two outer endless chains
is alternately produced whereby unbalanced distribution of
weight load to be carried by them is satisfactorily compen-
sated. Further, owing to the structural arrangement that
the relative distance between the engagement positions
where the inner and outer endless chains are engaged to
the conveyance container is adjustable with the use of the
engagement mechanism of the invention, the distance between
both support shafts at the front and rear portions of the
conveyance container is changed in dependence on the arc
length of the endless chains, when the conveyance containers
pass through 180 degrees turn-over sections as well as
through 90 degrees rotary sections with the result that
they move therethrough without any trouble and noisy sound.
In accordance with a preferred embodiment of the
invention, the movable shaft at the rear support position
of the conveyance container is arranged such that it moves
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back and forth within a certain limited extent by means of
a combination of a pair of upper and lower guide plates
extended at a right angle to the side wall of the conveyance
container along the periphery of an elongated opening
formed thereon and a stopper extended at a right angle to
the side wall of the ~onveyance container and located
behind the rear part of the elongated opening. In other
words, the rear shaft is movable within the extent of the
longitudinal diameter of the elongated opening.
In order to prevent bulk load received in the
respective conveyance containers from falling away through
the elongated opening on both side walls thereof, there is
provided preventive means comprising a tubular spacer cover
encasing the movable rear shaft and blind plates fixedly
secured to the tubular spacer cover at both ends thereof.
Further in accordance with another preferred
embodiment of the invention, the movable rear shaft at the
rear support position of the conveyance container is
arranged such that it pivotally moves back and forth within
a certain limited extent defined by means of a combination
of a bracket extending downwards from an arched elongated
opening to be fixedly secured to the side wall of the
conveyance container, a link pivotally connected to said
bracket at the lower end thereof and a stopper formed on
the upper portion of said bracket and located behind the
rear part of the elongated opening. In this embodiment,
the rsar shaft is movable within the extent of the longi-
tudinal diameter of the arched elongated opening.
Hence, it is a principal object of the present
invention to provide an engagement mechanism for conveyance
containers in the S-shaped conveyance system which is
effective in compensating unbalanced weight load distribution
~144~
on both inner and outer endless chains to which the respec-
tive conveyance containers are engaged and which is
adjustable in the center distance between both stationary
front shafts and movable rear shaft when they pass through
180 degrees turn-over sections as well as through 90 degrees
rotary sections.
It is another object of the present invention to
provide an engagement mechanism for conveyance containers
which is simple in structure and easy to be manufactured.
It is another object of the present invention to
provide an engagement mechanism for conveyance containers
which is free from a fear that bulk load received in the
containers falls down through the engagement mechanism.
Other objects and advantageous features of the
present invention will become apparent from the following
detailed description of the invention and the appended
claims.
The characteristic features and other peculiarities
of the present invention will ~e easily understood from the
following description of the invention when taken in
conjunction with the accompanying drawings in which like
reference numerals are used throughout to designate like
parts and components.
Figure 1 is a schematic side elevational view
illustrating conceptionally the struc-
tural mechanism of the conventional S-
shaped conveyance system,
Figure 2 is a partial front view illustrating the
arrangement of sprocket wheels and
endless chains at the 180 degrees turn-
over sections C and D as well as at the
90 degrees rotary sections A and B, as
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1~44~01
seen in the direction at a right angle
to that in Figure l;
Figure 3 is a schematic side elevational view of
another conventional S-shaped conveyance
system similar to Figure 1,
Figure 4 is a schematic side elevational view of
an S-shaped conveyance system similar to
Figure 3, wherein a conveyance container
engagement mechanism in accordance with
the present invention is employed therefor;
Figure 5 is a perspective view of the conveyance
container with the engagement mechanism
of the invention incorporated therein,
wherein the front and rear support shafts
and both inner and outer endless chains
are illustrated in a disassembled state
and the side wall of the container is
partially cut away;
Figure 6 is a partial vertical sectional view of
the engagement mechanism at the front
support shaft of the container;
Figure 7 is a partial vertical sectional view of
the engagement mechanism at the rear
support shaft of the container;
Figure 8 is a partial schematic view of the
conveyance system with the engagement
mechanism employed therefor, wherein
elongations of both inner and outer
endless chains are compensated alternately;
Figure 9 is a perspective view of the conveyance
container similar to Figure 1, wherein
the engagement mechanism in accordance
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with another embodiment of the invention
is incorporated therefor; and
Figure 10 is a partial vertical sectional view of
the engagement mechanism at the rear
support shaft similar to Figure 7, said
engagement mechanism being as shown in
Figure 9.
The above conventional continuous conveyance system
will be described in greater detail in t~e following. Figure
1 is a schematic side view of the conventional continuous
conveyance system as described above. The 180 degrees turn-
over section C is provided with a shaft 4, inside sprocket
wheels 2 and 2 and outside sprocket wheels 2' and 2', said
inside and outside sprocket wheels being secured to the
shaft 4 at both end parts thereof, as illustrated in Figure
2. Further, the shaft 4 has bearings 3 and 3 at both ends
thereof, said bearings 3 and 3 being disposed in a casing
(not shown). Further, the shaft 4 is rotatably carried by
a bearing 13 which is adapted to slide within a mounting
frame 12, said bearing 13 being adjustable by means of an
~ adjustment screw 14 screwed through a support wall 12' of
`~ the mounting frame 12, whereby the endless chains have the
optimum tension adjusted with the aid of the screw means 14.
The 90 degrees rotary section C' i5 constructed in the same
manner as the aforesaid 180 degrees turn-over section C,
whereas the 90 degrees rotary section C " is constructed
also in the same manner as the aforesaid 180 degrees turn-
over section C with the exception that the inner sprocket
wheels 2 and 2 are formed with cutouts at the positions
where engagement pieces for engaging the outer endless chains
1' to the conveyance containers E might interfere with the
sprocket wheels. ~his ensures smooth movement of the
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~k41~1~
conveyance containers when they pass through the 90 degrees
rota.ry section C ", because the engagement pieces enter into
the aforesaid cutouts of the inner sprocket wheels 2 and 2.
The second 180 degrees turn-over section D is constructed in
the same manner as that of the first 180 degrees turn-over
section C with the exception that the shaft 4 is provided
with a driving sprocket wheel 2 " fixed at its one end which
is operatively connected to a motor M so that the whole
conveyance system is driven in circulation by means of the
motor M.
Further, in the 90 degrees rotary section A, the
shafts 4 and 4 with the outer sprocket wheels 2' and 2'
mounted thereon are supported by means of both bearings 3 and
3, whereas in the 90 degrees rotary section B, the shafts
4' and 4' with the inner sprocket wheels 2 and 2 mounted
thereon are supported by means of both bearings 3 and 3. It
is to be noted that two pairs of 90 degrees rotary sections
A and B as well as A' and B' are spaced from one another by
the same distance as that between the front and rear support
shafts of the respective conveyance containers E.
As illustrated in Figure 1, the conveyance system
is constructed such that both inner and outer endless chains
1 and 1' are passed round both inner and outer sprocket
wheels at the first and second 180 degrees turn-over sections
C and D, and 90 degrees rotary sections A, B, A', B', C' and
C " and the inner endless chains 1 and 1 are engaged to the
conveyance containers at the front part while the outer
endless chains 1' and 1' are engaged to the conveyance
containers at the rear part thereof so that the respective
conveyance containers E are arranged end to end during their
horizontal movement through the horizontal transfer and
return sections. In the meanwhile, in the upward movement
B
1:~4~
section, the respective conveyance containers are lifted up
with the horizontal posture maintained. Thus, owing to the
structural arrangement as described above, a series of
conveyance containers are driven by means of the motor M
to circulate through the whole conveyance system.
As described above, the sprocket wheels at the 90
degrees rotary sections A and B as well as A' and B' are
spaced by the same distance as the distance 1 between the
front and rear support axes. The conveyance containers E
keep horizontal posture with their open side faced upwards
during movement from the first 180 degrees turn-over section
C through the 90 degrees rotary sections A, B, A' and B'
to the second 180 degrees turn-over section D and then turn
over at the second 180 degrees turn-over section D. When
entering into return movement, they keep horizontal posture
with their open side faced downwards through the first and
second horizontal return sections while they pass through
the downward movement section with their vertical posture
maintained and then they turn ove~ at the first 180 degrees
turn-over section C to restore the original horizontal
posture with the open side faced upwards, whereby a single
conveyance cycle is completed. Subsequently a next conveyance
cycle starts.
Since both inner and outer endless chains are
engaged to the respective conveyance containers E at the
front and rear parts thereof by a fixed distance equal to
the center distance 1 between the front and rear support
shafts of the conveyance containers E, it happens that a
difference in length is generated between the arch length
of the endless chains round the sprocket wheels and the
linear length 1' between both ends of the aforesaid arch
which connects the front support shaft to the rear support
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114410~
shaft, said linear length 1' being a little shorter than the
arch length that is equal to the distance 1 between the
front and rear support shafts, when the conveyance con-
tainers pass through the first and second 180 degrees turn-
over sections C and D as well as through the 90 degrees
rotary sections C' and C''. Thus, troubles take place often
with the conventional conveyance system when the conveyance
containers pass through these turn-over and rotary sections.
- To resolve the technical problem as described above, the
inventors proposed that the front support shafts of the
conveyance containers are pivota~ly connected to the inner
endless chains by way of pivotal links arranged in position
on both side walls thereof so that the dimensional differ-
ence between the distance between the engagement positions
where the inner and outer endless chains are engaged to the
conveyance contains and the distance between the front and
rear support shafts thereof is adequately compensated by
way of pivotal movement of the pivotal links when they pass
through the first and second 180 degrees turn-over sections
C and D as well as through the 90 degrees rotary sections
C' and C ". Figure 3 is a schematical side view of another
conventional conveyance system with the above proposal
embodied therefor, shown in a larger scale than Figure 1.
The pivotal link which constitutes an essential component
of the above proposal is identified by the reference numeral
15.
In fact, another technical problem is found out
with the conventional conveyance system in spite of the fact
that smooth movement of the conveyance containers at the
180 degrees turn-over sections and 90 degrees rotary sections
is ensured owing to the above proposal. As readily under-
stood from Figure 3, driving power exerted on the conveyance
-- 11 --
~44~(?1
containers in the horizontal direction as well as their
weis~ht load during downward return movement are carried
only by tw~ lines of outer endless chains l' and 1' directly
connected to the conveyance containers at the rear part
thereof, whereas two lines of inner endless chains l and 1
pivotally connected to the conveyance containers at the
rear part thereof by way of the pivotal links 15 participate
in carrying a part of the weight load of the conveyance
containers E during upward movement. As a result, the outer
endless chains l' and 1' are elongated more than the inner
endless chains 1 and 1 as time elapses. This will cause
the loosened endless chains to be disengaged from the
'sprocket wheels. Sometimes it is found that the conveyance
containers move upwards with their inclined postureimain-
tained throughout the upward movement section, said inclined
posture being caused due to the enlarged distance between
the engagement positions where both inner and outer endless
chains are engaged to the conveyance containers in position
at the front and rear parts thereof.
-20 ~ow the present invention will be described in
more detail with reference to the accompanying drawings
which illustrate two preferred embodiments of the invention.
Specifically, Figure 4 is a schematic side view of the
whole S-shaped conveyance system with the conveyance
container engagement mechanism of the invention employed
therefor. Since the structure and function of the convey-
ance system itself are similar to those of the conventional
S-shaped conveyance system shown in Figures l and 3 except
the engagement mechanism for the conveyance container, the
same reference numerals are given to similar parts and
components. In view of simplification, repeated description
of the similar parts and components will be neglected.
~ '
~1441~1
Figure 5 is a partially cut-away perspective view
of a conveyance container E and outer and inner endless
chains 1 and 1' which are to be engaged to said conveyance
container E with the aid of the engagement mechanism of the
invention, Figure 6 is a partial vertical sectional view
of the engagement mechanism at the front support shaft, and
Figure 7 is another partial vertical sectional view of the
engagement mechanism at the rear support shaft. The convey-
ance container E is made of steel plates, having a boat-
shaped cross-section taken in the longitudinal direction.
Further, the container is provided with a plate 16 made of
resilient material, said plate being fixedly secured to the
tail end portion of the conveyance container in such a manner
as to cover the leading end portion of the subsequent
conveyance container in order that bulk load to be charged
in the conveyance container through the lower bulk load
feeder F does not fall down through a clearance between-the
two adjacent conveyance containers. Otherwise, there will
be a danger that scattered material is deposited on the
travelling endless chains, causing the whole conveyance
system to be damaged. Moreover, the conveyance container
- is formed with a rectangular opening at the bottom thereof and
said rectangular opening is covered with a separate bottom
plate 16' made of resilient material such as rubber or the
like. As readily understood from Figure 4, said resilient
bottom plate 16' is squeezed upwards by means of the roller
R on the driven shaft of the sprocket wheel located at the
180 degrees turn-over section D, when the conveyance
container E passes therethrough. As a result, bulk load
adhesively deposited on the bottom plate 16' is completely
discharged.
The reference numeral 17 designates a bracket on
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~44I(9i
both side walls of the conveyance container E at the front
supporting location, said bracket 17 having a shaIt 18 of
which one end is fixedly secured thereto by tightening a
nut 181 al d the other end is engaged to the inner endless
chain 1. A split pin 182 is provided for preventing the
inner chain 1 from being disconnected from the shaft 18.
In the rear support position is formed an elongated opening
19 on both side walls of the container E. Further along the
both upper and lower periphery oî said elongated opening 19
are provided a pair of parallel guide plates 201 and 202,
whereas at the rear part of the opening 19 is provided a
stopper 203, said guide plates 201 and 202 as well as
stopper 203 extending in the horizontal direction at a right
angle to the side walls of the conveyance container. The
reference numeral 21 designates a longitudinally displaceable
shaft which extends through the elongated openings 19 with a
tubular spacer cover 22 arranged over said shaft 21.
Further rectangular sliding bearings 204 are arranged
displaceably in the longitudinal direction within the area
20 defined by means of both upper and lower guide plates 201
and 202 as well as rear stopper 203. Thus, a defining member
20 is constituted by a combination of the guide plates 201
and 202 and stopper 203 on both side walls of the container.
It is to be noted that the elongated opening 19 is dimen-
sioned a little larger than the diameter of the movable
shaft 21, and thus the movable shaft 21 is supported by
means of both upper and lower guide plates 201 and 202 as
well as stopper 203 with the aid of the sliding bearing 204,
resulting in no opportunity that the movabie shaft 19 comes
30 in contact with the periphery of the elongated opening 19.
The reference numeral 23 designates a bracket for engaging
the movable shaft 21 with the outer endless chain 1', said
E~ 14 ~
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bracket 23 being bridged over the inner endless chain 1.
The bracket 23 is formed with a drilled hole 231 at its one
side wall through which the threaded portion 211 of the
movable shaft 21 extends to be tightened by means of a nut
212. In the meanwhile, the bracket 23 has the outer endless
chain 1' engaged thereto by means of a combination of a bolt
232 and nut 233. In this connection, it is to be noted that
the distance between both engagement positions where the
inner and outer endless chains are engaged to the conveyance
containers is dimensioned substantially equal to the distance
between the front stationary shafts 18 and the rear movable
shaft 21 in such a working condition that the sliding
bearing 204 abuts against the rear stopper 203. Further,
the reference numeral 24 designates a displaceable blind
plate which is fixed to the tubular spacer cover 22 for the
purpose of preventing bulk material from falling down through
the clearance between the elongated opening 19 and movable
shaft 21.
Owing to the fact that the engagement mechanism is
constructed for the respective conveyance containers in the
above described manner, it follows that both front and rear
shafts 18 and 21 carry substantially the same weight load
during upward movement of the conveyance containers E and
just the rear movable shaft 21 carries the whole weight of
the conveyance container E via the sliding bearing 204
which abuts against the rear stopper 203 during downward
movement of the conveyance containers E, resulting in
elongation of the outer endless chains 1' engaged to the
movable shaft 21 due to the weight load on them. This causes
the distance between the engagement positions where the
inner and outer endless chains are engaged to the conveyance
containers to be relatively reduced. As a result, the
01
weight load imparted to the stopper 203 via the sliding
bearing 204 becomes decreased and the front stationary
shafts 18 in turn participate in gradually carrying the
weight load whereby the inner endless chains 1 are elongated.
~ ow the above-mentioned operational behavior will
be described in greater detail with reference to Figure 8.
In the beginning, the distance between both front and rear
shafts in the conveyance container amounts to 1 in such a
working condition that the s.liding bearing 20~ abuts
against the stopper 203, whereas the distance between both
engagement positions where the inner and outer endless chains
are engaged to the conveyance container amounts to 1 also.
In the meanwhile, the distance between the engagement posi-
tions where the rear shafts of the réspective conveyance
containers E, E' and E " are engaged to the outer endless
chains 1' is assumed L. As the outer endless chains 1' are
elongated due to the weight load thereon, the aforesaid
. , ., ~ .
distance L becomes another distance L' which is a little
longer than L. When considering this elongation from a view-
point of the conveyance container E, the working distancebetween the engagement points where the inner and outer
endless chains are engaged to the conveyance container E'
is reduced to 1 - (L' - L), whereas the working distance
between the engagement points where the inner and outer
endless chains are engaged to the next conveyance container
. E " is also reduced to 1 - 2 x (L' - L). Because of the
shortened distances as described above, it follows that the
sliding bearing 204 moves away from the stopper 203 and
thereby the weight load to be carried is gradually trans-
ferred from the outer endless chains 1' to the inner endlesschains 1 with the result that the latter is elongated.
Since the above-described load transference is effected
- 16 -
11441(3~
gradually and alternately, elongation of the outer endless
chains 1' and inner endless chains 1 is compensated alter-
nately. Thus, it is ensured that operational trouble such
as wrong engagement of endless chain to sprocket wheel due
to unbalanced elongation of one of the inner and outer
endless chains, disengagement of endless chain from sprocket
wheel, declination of conveyance container caused during
upward movement thereof or the like does by no means take
place and that smooth movement is effected without any noisy
sound when the conveyance containers E pass through the 180
degrees turn-over sections C and D or 90 degrees rotary
sections C' and C'' owing to the fact that the distance
between the engagement positions where the inner and outer
endless chains are engaged to the conveyance container is
adequately adjusted-by way of forward displacement of the
movable shaft 21.
On the contrary, there is a case that the distance
between the engagement positions where the inner and outer
endless chains are engaged to the conveyance containers is
dimensioned less than the distance between the front sta-
tionary shaft 18 and rear movable shaft 21 and thereby chain
engagement is effected in such a working condition that the
sliding bearing 204 does not abut against the stopper 203.
In this case, first the front stationary shafts 18 undertake
carrying of the weight load of the conveyance container,
causing the inner endless chains 1 to be elongated. As a
result, the distance between the engagement positions where
the inner and outer endless chains are engaged to the
conveyance container becomes another distance which is longer
than the former, whereby the sliding bearing 204 gradually
approaches toward the stopper 203 until the former abuts
against the latter. Thus, elongations of the outer and
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inner endless chains are mutually compensated in the same
manner as described above.
Figures 9 and 10 illustrate another embodiment of
the defining member 20 by way of perspective view and verti-
cal sectional view. In this modified embodiment, the
conveyance container E has a bracket 25 fixedly secured
thereto at the rear support location, said bracket 25
extending downwards from an elongated opening 19' and having
a pivotal link 201 I pivotally connected thereto at the lower
end by means of a pin 20r2 1~ Said pivotal link 201' carries
the movable shaft 21 at the upper end. It is to be noted
that the elongated opening 19' is different from the elon-
gated opening 19 in the preceding embodiment in that the
former is shaped in the form of an arch having a radius
equal to the center distance of the pivotal link 201'. A
stopper 203' is provided behind the elongated opening 19'
at the upper portion of the hracket 25. Thus in this
embodiment of the engagement mechanism, the defining member
20' is constituted by a combination of the pivotal link 20
pin 202' and stopper 203'. In this embodiment, the movable
shaft 21 moves back and forth, scribing a trace of arch
having a radius equal to the center distance of the pivotal
link 201', whereas in the preceding embodiment the movable
shaft 21 moves back and forth under straight guiding by
means of the defining member 20. Thus, more smooth movement
of the movable shaft 21 is ensured owing to the definitive
pivotal movement of the pivotal link 201' with the aid of
the pin 202'. Other structure and functions of the engage-
ment mechanism are the same as those in the preceding
embodiment of the invention.
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