U.S. patent number 3,583,314 [Application Number 04/750,845] was granted by the patent office on 1971-06-08 for postal franking machine.
This patent grant is currently assigned to Roneo Limited. Invention is credited to John Brian Gillender, Leslie Harrold Smith.
United States Patent |
3,583,314 |
Gillender , et al. |
June 8, 1971 |
POSTAL FRANKING MACHINE
Abstract
A franking machine of the kind having a rotatable printing head
with teeth which are movable radially outwards in respect of the
axis of rotation of the head in correspondence with the value to be
printed and to be registered, while the register drum for each
digit is driven by a toothed wheel which engages the said movable
teeth, the toothed wheel being held resiliently in each of its
positions corresponding to the values transmitted to the register
drum by the movable teeth by a spring loaded pawl, with the
exception of the value given by the last tooth in which case the
pawl is held rigidly engaged with the toothed wheel by a lever
mechanism operated by a cam rotated with the printing head to
prevent rotation of the toothed wheel due to inertia when it
becomes free of the last tooth. The pawls of the toothed wheels are
mounted upon a common shaft to which is fastened a lever having a
pin opposite each pawl, and which is engageable with the pawl to
hold it engaged with the toothed wheel while one end of the shaft
has a cam follower mounted upon a lever which engages the edge of a
disclike cam fastened to the printing head.
Inventors: |
Gillender; John Brian (Essex,
EN), Smith; Leslie Harrold (Essex, EN) |
Assignee: |
Roneo Limited (Croydon,
EN)
|
Family
ID: |
10400456 |
Appl.
No.: |
04/750,845 |
Filed: |
August 7, 1968 |
Foreign Application Priority Data
Current U.S.
Class: |
101/91;
235/101 |
Current CPC
Class: |
B07C
3/18 (20130101); G07B 17/00508 (20130101); F16D
11/06 (20130101); F16H 37/12 (20130101); G07B
2017/00548 (20130101); Y10T 74/1555 (20150115) |
Current International
Class: |
F16H
37/12 (20060101); F16H 37/00 (20060101); B07C
3/00 (20060101); B07C 3/18 (20060101); F16D
11/06 (20060101); F16D 11/00 (20060101); G07B
17/00 (20060101); B41l 047/46 () |
Field of
Search: |
;101/91,92,93,99
;235/101 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Penn; William B.
Claims
It is to be understood that the above description is by way of
example only and that details for carrying the invention into
effect may be varied without departing from the scope of the
invention we claim.
1. A franking machine of the kind including a rotatable printing
head, said head having teeth movable radially outwards in respect
to the axis of rotation of the head in correspondence with the
value to be printed and recorded, value recording means for each
digit, a rotatable intermediate transfer gear engageable with said
movable teeth and operably related to said recording means to drive
the same, means resiliently holding said transfer gear in each of
its positions corresponding to the values transmitted to the
recording means by the movable teeth, said holding means comprising
a movable pawl, spring means urging said pawl into engagement with
said gear except for the value given by the last tooth, a lever
mechanism operably related to said pawl, a cam rotatable with the
printing head, and actuating means between the cam and lever
mechanism operative to move the lever mechanism and pawl into
engagement with the transfer gear to prevent rotation of the gear
due to inertia when the gear becomes free of the last tooth.
2. The franking machine as claimed in claim 1 including a shaft on
which said pawl is rotatably mounted, said lever mechanism
including a lever secured to the shaft, a pin on the lever
engageable with the pawl to hold the pawl in engagement with the
transfer gear, and said actuating means comprising a lever carried
by the shaft and a cam follower supported by said last named lever
for engaging said cam.
3. The franking machine as claimed in claim 2 including a plurality
of sets of movable teeth, recording means and transfer gears, all
of said pawls being mounted on said shaft and each pawl having the
lever and pin associated therewith.
Description
BACKGROUND OF THE INVENTION
The invention relates to franking machines of the kind which
besides being capable of franking envelopes, is adapted to provide
printed labels for attachment to postal packets which cannot be
inserted into the machine for franking in the normal way, while the
object of the invention is to provide a franking machine of the
kind above referred to, which is positive in action, and is more
reliable in use than machines heretofore proposed.
SUMMARY OF THE INVENTION
The invention consists in a franking machine of the kind having a
rotatable printing head with teeth which are movable radially
outwards in respect of the axis of rotation of the head in
correspondence with the value to be printed and to be registered,
while the register drum for each digit is driven by a toothed wheel
which engages the said movable teeth, characterized in that the
toothed wheel is held resiliently in each of its positions
corresponding to the values transmitted to the register drum by the
movable teeth, by a spring loaded pawl, with the exception of the
value given by the last tooth, where the pawl is held rigidly
engaged with the toothed wheel by a lever mechanism operated by a
cam rotated with the printing head to prevent rotation of the
toothed wheel due to inertia when it becomes free of the last
tooth.
The invention still further consists in a franking machine as set
forth in the preceding paragraph in which the pawl is rotatably
mounted upon a shaft to which is fastened a lever having a pin
which is engageable with the pawl to hold it engaged with the
toothed wheel, one end of the shaft having a cam follower mounted
upon a lever which engages the edge of a disclike cam fastened to
the printing head.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings show, by way of example only, one
embodiment of the invention in which:
FIG. 1 is a view in perspective of the label paper feed
mechanism;
FIG. 2 is a view in perspective of the other side of the frame
illustrated in FIG. 1;
FIG. 3 is a view in perspective, partly broken away, of the slogan
control;
FIG. 4 is a view in perspective of the interlock;
FIG. 5 is a perspective view of the clutch with the outer ring
removed for clarity;
FIG. 6 is a perspective view of the value change mechanism;
FIG. 7 is a perspective view of the meter locking means;
FIG. 8 is a general perspective view of the machine showing the
relationship of the mechanisms shown in FIGS. 1 to 7;
FIG. 9 is a view in perspective along the lines of FIG. 8
illustrating the manner in which the printing head is driven, via a
clutch, by an electric motor;
FIG. 10 is a diagrammatic view in elevation of the mechanism for
changing the position of the printing wheels;
FIG. 11 is a view taken along line 11-11 of FIG. 10, the view
looking in the direction of the arrows; and
FIG. 12 is a view taken along line 12-12 of FIG. 10, the view
looking in the direction of the arrows.
DETAILED DESCRIPTION OF THE INVENTION
It may be seen from FIG. 8 that the machine comprises a hollow box
like base member A which forms a common support for the internal
mechanisms of the machine. There is provided a horizontal plate B,
upon which, at the nearer end, the piece of mail to be franked is
placed, and along which it is conveyed to pass under a printing
head C.
The printing head C is driven by an electric motor, mounted, below
a clutch D, and connected thereto by a gear drive (FIG. 9). The
motor runs continuously and the drive is initiated by the clutch D
during each cycle of operation.
The value to which the printing wheels in the head C are selected
by means of selector wheels, of which one E is shown.
To ensure that the total of the values printed are correct and no
errors can be introduced, the register meter is locked by means of
a pawl and cam mechanism F.
Besides franking pieces of mail such as envelopes, the machine is
adapted to print upon labels cut from a roll of paper G. The paper
strip is fed to the printing head C by a feed and cutting mechanism
H which is adapted to provide labels of two different lengths, and
also to control the printing of a slogan or other advertising
display upon each label at the choice of the operator of the
machine.
The mechanism of the machine is protected by a cover J which is
removable for servicing of the machine.
The features of the machine above referred to are each described in
detail hereinafter with reference to the respective FIGS. 1--7.
The label paper feed mechanism and the slogan control and interlock
device are provided in order that one can obtain long or short
labels according to the setting of a hand control, and includes
means for suppressing the printing of the slogan or advertising
display when short labels are selected.
FIG. 1 shows a main bearing side frame 34 with the nearer part of
the mechanism in view, and FIG. 2 shows the assembly on the other
side of the main frame. A drum 1, FIG. 2, is mounted integrally on
the shaft 5, as also is disc 3 which has two notches 3A cut to
180.degree.. The drum 1 is of such diameter that its periphery is
equal to the length of a long label. Half its periphery is equal to
a short label. By operating a hand set lever 35 a camshaft 30 can
be rotated, raising and lowering levers 26 and 28 respectively. The
bearings of pressure rollers 25 and 27 are mounted in these levers
so that the rollers are lifted clear from the drum 1 for purposes
of loading the machine with paper. The free end of a roll of paper
on a mounting, not shown, is threaded around the drum 1 and over a
"see saw" pallet 23. The pressure of rollers 25 and 27 is then
restored.
With the power switched on, a gear 36 rotates continuously. A
clutch sprag 2 rotates with this gear and is pivotally mounted on a
stud 37 which is integral with the gear 36. The gear 36 is free to
move around the shaft 5. A tooth 2B of the sprag 2 would engage in
the notch 3A in the disc 3 but for the presence of a lobe 4 on
lever 11. The top end of lever 111 passes through side frame 34,
FIG. 1, having a slotted hole and a strong spring 22 urging it to
the right hand of the figure as shown. The spring 38, FIG. 2, is
not strong enough to overcome the pressure existing at the lobe 4,
and so that the tooth 2B on sprag 2 would "jump" or ride clear of
the notch 3A in disc 3. Similarly, the presence of a double lobed
cam 9 on shaft 10 prevents engagement of the sprag in second and
180 opposite notch. No drive will therefore be transferred to the
drum shaft 5.
Drum shaft 5 comes through a disc 13 with a grooved hub which is
capable of being moved laterally to and fro having a key, not
shown, which engages with a slot in the shaft 5. The disc 13
therefore revolves with the drum 1 and shaft 5. Disc 13 has four
pins, two long ones 15, one not being visible, and two short ones
14. These pins 14 and 15 engage in radial slots 16A in a Geneva
wheel 16. The Geneva wheel 16 is fixed to the shaft 10, which is
integral with cam 9, see FIG. 2, and knife assembly 7.
The knife assembly 7 has a double edged blade 7A (only one side of
which is shown); with sharp V-shaped points at two opposite
180.degree. apart. The drum 1 has two inserts diametrically
opposite (only one of which is shown); which have V grooves exactly
complementary to the serrations of blade 7A. These two inserts 73
are locked into drum 1, but have springs underneath urging them
outwards. The blade 7A is of such a size as to interfere slightly
piercing the label paper to the maximum extent. Damage to the
insert is avoided because of the give in the spring insert.
In FIG. 6 there is illustrated the mechanism for changing the
printing wheel within the printing head C with a change of setting
of the value required to be printed by the selective wheel 201.
While this figure illustrates but one such selective wheel 201, it
is to be understood that a selective wheel 201 is provided for each
printing wheel and each selective wheel is operated by a similar
mechanism. In this position, short pins 14 cannot engage in the
slots 16A of the Geneva wheel 16.
The action which occurs on the demanding of a "long" label is as
follows:
A slide 12, FIG. 1, has a slotted hole behind washer 39. The slide
can therefore be moved by hand operation to the left by a thumb
knob not shown, with stepped end at 40 also carrying lever 11 to
the left. Lobe 4, FIG. 2, ceases to influence sprag 2 which now
engages disc 3 and rotates the shaft 5 with the drum 1 in a
counterclockwise direction. After 90.degree. only of revolution,
the pin 15, FIG. 1, on the underside of disc 13 approaches one of
the radial slots 16A in the Geneva wheel 16.
During the next 90.degree. of revolution, Geneva wheel 16 is
rotated also through 90.degree., taking with it shaft 10, cam 9 and
the knife blade assembly 7. By virtue of the cam 9 rotating in a
clockwise direction, it clears lobe 2A of sprag 2, thus allowing
sprag 2 to continue driving disc 3. Should the hand operation of
slide 12 have been unnecessarily prolonged, no repeat can occur
while slide 12 is raised clear of lever 11 by the action of pins 15
as they revolve with disc 13.
The drum 1, shaft 5 and disc 13 continue to rotate until sprag 2
has again become engaged by the restored presence of lobe 4 and
lever 11. During the last 90.degree. of revolution, the pin 15,
FIG. 1, will have passed the Geneva wheel 16 causing blade 7A, FIG.
2, to become engaged with the paper and the insert 73 in drum 1.
The paper becomes perforated severely, but not quite separated. At
the moment of piercing, the leading edge of the paper has entered
the first feed rolls of the printing head feed, not shown, and is
pulled tightly over the pallet 23, FIGS. 2 and 4. This member is
mounted on a single shouldered stud which is offset, so that when
the paper tightens thereover, it "see saws" raising one side. This
occurs when the perforation passes over it, thus triggering off a
tear, which is then easily completed by the tug of the feed
rolls.
The paper thus is separated before it passes under the franking
head. The length of paper is equal to the total circumference of
the drum 1. In this setting, it is assumed that a slogan or display
is to be printed. Feed rolls 60 and 61 carry the label forward to
the printing drum head, and have thereabove, as shown in FIG. 4,
flexible pressure bands 62 and 63, which are pressed downwards by
spring 64 between support bracket 65 and the carriage 66. The
rotation of the printing drum head is initiated by the contacting
of the arm of a switch 67, either by a label, when these are being
used, or by an envelope when it is inserted into the pinch or nip
of the roll 60. A roll 68 of paper strip is housed in a means 69 in
the side of the machine, and passes over guide pins 70, 71 and 72
and thence around the feed drum 1 as previously described. The
method of demanding the slogan printing automatically is now
described:
In FIG. 3 is seen the part of a printing drum head 42 provided with
a slogan die carrier 41. The carrier 41 is pivoted at 43, and its
underside rides on cam 44, mounted on shaft 49, while also on shaft
49 are two wheels 47 and 48, each having two teeth projecting at
180.degree. opposite. These wheels are set at 90.degree. to one
another. As previously mentioned in the description relating to
FIG. 1 for demanding a "long" label, the plate 18 and the lug 20 do
not close the microswitch 19. Therefore, the electrical circuit is
not closed and electromagnet 50, FIG. 3, is not energized. The
armature therefore is at rest in the position shown.
When the printing head is operated, it revolves counterclockwise.
The lower extremity of armature 51 lies in the path of wheel 47,
and as it sweeps past it will be revolved in a clockwise direction,
turning shaft 49 through 90.degree. raising the slogan die carrier
41 by means of the cam 44. This is retained by springs 46. A die
41A, mounted on the carrier 41, is now in its raised or printing
position, and will remain so, during further cycles of operation,
because the tooth of wheel 47 is over to the right-hand. Also,
because the shaft 49 has been moved through 90.degree., tooth 52 of
the nearer wheel 48 is now around in a position where it will
engage the tip of armature 51 should the magnet 50 become
energized.
The setting of a short label is now described in reference to FIG.
1. The control knob 74, is operated and turns the cranked rod 17
through 90.degree. to bring the lug 20 around to close the
microswitch 19 which causes the operation of the electromagnet 50,
FIG. 3. The disc 13, FIG. 1, moves nearer to the Geneva wheel 16.
The short pins 14 now operate in the radial slots 16A of the Geneva
wheel 16, in addition to the long pins 15. With the hand operation
of slide 12 which pushes lever 11, this operates the sprag 2, FIG.
2, after the manner previously described, and the drum 1 revolves.
During the first 90.degree. of rotation, pin 14 moves the Geneva
wheel 16, shaft 10 and knife assembly 7, FIG. 2, and also cam 9.
During the next 90.degree. of rotation, the Geneva wheel 16, FIG.
1, is again moved. The result of this repeated operation in the
first 180.degree. of revolution of drum 1, FIG. 2, is that the cam
9 now presents a high portion in the path of sprag 2 and also the
knife assembly 7 serrates the paper. Sprag 2 is disengaged from the
disc 3 and drum 1 comes to rest after 180.degree. movement only.
Enough paper feed only for a short label is half the circumference
of the drum 1. The paper is parted as before described. The slogan
die 41A does not print ink on the impression roller because the
magnet armature 51, being attracted, has caused wheel 48 to turn
shaft 49 and cam 44 back to low position.
In FIG. 1, detent spring member 21 retains the Geneva wheel 16, so
that it remains in the true position for the entry of the pins 14
and 15. The plate 18 is so shaped that the slide 12 can only be
operated in the correct settings of shaft 17. Detent member 31
retains drum 1 and shaft 5 in the true at rest position and avoids
overthrow when the sprag 2 is disengaged.
The printing head C is driven by an electric motor, FIG. 9, by way
of clutch D. The motor runs continuously while the machine is in
use, and each franking process is initiated by the engagement of
the clutch D. The clutch is operated remotely, and it is of vital
importance that the printing and recording head should make one
revolution and that it should be arrested at a precisely
predetermined position, and be prevented from rotating further
until demanded to do so by the remote control.
Details of the clutch are shown in FIG. 5 in which outer toothed
ring 101 is shown separated, so that the pawl mechanism housing may
be clearly seen. The outer ring 101 is driven continuously by the
electric motor and fits freely over pawl housing 103 which contains
and retains four driving pawls 104a, 104b, 104c and 104d, each of
which is urged in an outward direction by a spring, not shown,
under each pawl. Screws 106 secure pawl housing 103 to drive plate
102, and also secure pawl housing 103 and drive plate 102 to the
end face of a printing/recording head shaft, not shown, which is
required to make only one revolution before being arrested by means
of projections 109 and 110 being caught under hooked end of pawl
111.
A pawl control plate 105 is located between pawl housing 103 and
the drive plate 102, and is free to move radially by a
predetermined amount, in relation to drive plate 102 and pawl
housing 103. Pawl control plate 105 is cut away internally to
provide four internal cam faces 107a, 107b, 107c and 107d, of which
only the first can be seen, and each of which engages a projection
provided on the inner face on the four driving pawls 104a, 104b,
104c and 104d retained in the slots in the pawl housing 103.
A trigger stop 111 is pivoted on a shaft 118 and the hooked end of
this trigger stop is urged away from the clutch components 102,
103, and 105 by a torsion spring 112.
When the shaft to which the pawl housing 103 and drive plate 102
are rigidly attached, is required to make one revolution, an
electric current passing through coil 114 energizes magnet 113,
which then attracts the horizontal portion of armature 115, pivoted
on shaft 116, thereby withdrawing the top end of the vertical
portion of armature 115 from under a projection 119 on trigger stop
111.
When the top end of armature 115 is withdrawn from under the
projection 119 on trigger stop 111, torsion spring 112 causes the
hooked end of trigger stop 111 to move away from the projection 109
on pawl housing 103 and the projection 110 on drive plate 102.
One end of spring 108 is secured to pawl plate 105, and the other
end of the spring is secured to drive plate 102. When the hooked
end of the trigger stop 111 is withdrawn from projection 109 and
projection 110, spring 108 causes pawl plate 105 to rotate in a
clockwise direction to the limit provided by an internal stop, and
the internal cam faces 107a, 107b, 107c and 107d, in pawl control
plate 105 permit the four driving pawls 104a, 104b, 104c and 104d
to be urged upwards and outwards, each by its own spring, not
shown, against the inner toothed bore of outer ring 101.
The pawls 104a, 104b, 104c and 104d, are unequally spaced around
pawl plate 103, and are positioned in such a manner that only one
of the four pawls 104a, 104b, 104c and 104d, can locate against any
one of the internal ratchet teeth in the outer ring 101.
The pawls are spaced so that the radial difference between each
pawl is equal to one-fourth of the pitch of the internal teeth in
outer ring 101. If, therefore, one pawl just misses contact with
the radial face of any one of the internal teeth in outer ring 101,
the next pawl will engage one-fourth of a pitch of the internal
teeth in the outer ring 101 later.
When any one of the pawls 104a, 104b, 104c and 104d engage in any
one of the internal teeth in outer ring 101, the constantly
rotating outer ring 101 drives the printing head via one of the
pawls and causes the printing head to rotate.
When the hooked end of trigger stop 111 is withdrawn from
projections 109 and 110, the pointed end of trigger stop 111 is
advanced towards the peripheries of pawl control plate 105 and the
drive plate 102, the pointed end of trigger stop 111 advances to
within an appropriate distance such that when during the rotation
of the printing head the projections 109 and 110 impinge on the
pointed end of trigger stop 111, the projections 109 and 110 cause
trigger stop 111 to partially rotate around its spindle 118, and
cause hooked end of trigger stop 111 to be placed in the path of
projections 109 and 110.
The vertical portion of armature 115 is urged by torsion spring 117
against the projection 119 of trigger stop 111. When the hooked end
of trigger stop 111 is urged inwards by projections 109 and 110,
pushing the tail end of trigger stop 111 forward, the extreme end
of the vertical portion of armature 115 is able to move under
projection 119, on the back face of trigger stop 111, and hold this
component in such a position that the hooked end trigger stop 111
is held firmly in the path of the rotating projections 109 and
110.
At the commencement of rotation of the shaft, the projection 109
has been moved radially out to the line with respect of projection
110 by virtue of the spring 108 which is secured at one end to the
pawl plate 105 and at the other end to the drive plate 102 rotating
by a small amount. Consequently, the projection 109 can reach the
underside of the hooked end of trigger stop 111 in advance of the
projection 110 on the drive plate 102 and when the projection 109
meets the undersurface of the hooked end of the stop 111, the
projection is arrested in such position and thus causes the slots
104', 104" , 104'" and 104"" in the pawl control plate 105 to be
rotated out of line with the slots in the pawl housing 103. This
action forces downwardly the pawls 104a, 104b, 104c and 104d into
the pawl housing whereby the projecting rim of the plate 105
retains the pawls in their downward position and out of engagement
with the internal teeth in the outer toothed ring 101. Drive plate
102 continues to rotate until the projection 110 also contacts the
underface of the hooked end of trigger stop 111.
When the projection 110 meets the underface of the hooked end of
trigger stop 111, drive plate 102 is arrested, and as this plate is
rigidly attached to the printing head shaft, the printing head is
also arrested in a desired position. When the printing head and
drive plate 102 are arrested by the underface of the hooked end of
trigger stop 111, a pawl, not shown, engages in one of the teeth on
the periphery of the drive plate 102 and prevents the drive plate
rotating in an anticlockwise direction.
FIGS. 6 and 10 to 12 show the mechanism for changing the position
of the printing wheels within the printing head C with change of
setting of the value required to be printed by means of selector
wheel 201, only one is shown in FIG. 6, while in fact one is
provided for each printing wheel (see FIGS. 10 and 11), each
operated by a similar mechanism.
When a value selecting wheel 201 is rotated by an appropriate
amount, to change the value to be printed upon a piece of mail
passed through the machine, printing wheel 210 prints a value
identical with the number selected. It will be observed that the
value selector wheel 201 and the printing wheel 210 rotate about
axes which are at right angles to one another.
The value selecting wheel 201, which has on one face a pinion 202
and on the other face a projecting drum on the periphery of which
are numerals indicating values required to be printed, is one of a
number of wheels mounted coaxially with one another, and each
meshes with the teeth on the periphery of a disc 204, coaxial with
one another, and rotates it by an appropriate amount. Each disc 204
engages its internal teeth 211 with a gear 212 on the end of a
screw 205 provided with one or more coarse helical grooves.
A nut 206 with a corresponding thread is located on the screw 205,
and moves along the latter with rotation of the value selecting
wheel 201. There is a screw 205 for each wheel 201 and disc 204,
which are spaced circumferentially around the axis of the disc 204
and each nut 206 carries a rack 207 attached thereto by screw 208,
and engages a pinion 209 of a printing wheel 210. All the printing
wheels are on the same axis (FIG. 10).
The gear ratio of pinions 202, discs 204, screws 205, and toothed
ends 207A of the racks 207 and pinions 209, are so chosen that when
the value selecting wheel 201 is moved a certain amount, the
printing wheels 210 rotate a corresponding amount precisely related
to the amount of rotation of the value selecting wheels 201.
One or more of the mechanisms illustrated in FIG. 6 may be used in
each postal franking machine allowing a plurality of value
selecting wheels 201 to be used independently or collectively to
operate one or a plurality of printing wheels 210.
In FIG. 7, there is shown a locking mechanism associated with the
register meter, which indicates the total value which has been
printed by a machine, and is provided in order to prevent errors in
the readings given. The printing head is provided in known manner
with a toothed wheel, in which the number of teeth which project
are caused to correspond to the value to which the associated
printing wheel is set. The means for permitting radial movement of
the teeth is by a cam track and pins and reference is made to U.S.
Pat. No. 2,727,687. For example, in FIG. 7 there are four teeth
projecting, of which the last tooth is tooth 301. Consequently,
when the printing head is rotated in an anticlockwise direction
during the franking process, gear 302 is moved four teeth, with the
tooth 301 having just left the gear 302. The gear 302 engages the
gear beside the numbered drum and the latter has just moved four
units.
In order to prevent any overthrow taking place after the last tooth
301 (which is at all times the last tooth to pass the intermediate
transfer gear 302 which engages with a gear integral with the value
recording wheels 309) has left the gear 302, a disc 303 is provided
with a cam 303A thereon, which engages follower 304A on a lever 304
which is fixed to the shaft 307, on which there is also provided a
lever 306 with a pin 305, which engages the back of pawl 308, and
positively prevents further rotation of the gear 302. Prior to the
last tooth 301 passing gear 302, the pawl 308 is held in mesh by
spring 310. The timing of the cam is such that the pawl 308
commences to engage between two teeth of the gear 302 before the
last rising tooth 301 has left the gear 302, thus ensuring that no
overthrow is possible.
* * * * *