The perpetual day of the month
Any typos are as a result of direct translation of the
original French.
The perpetual day of the month gives the same indications that the simple day of
the month, but it holds account, automatically, the various lengths of month as
well as leap years.
To explain operation we will take one perpetual day of the month Audemars-Piguet.
Operation:
Indication of the moon phase:
The 12 hours reference (2) involves the entraîneuse wheel of day of the month
(3) which carries the finger of day of the month (4).
The finger first of all makes advance moon star (5)
Indication of the days of the week:
The finger of day of the month (4) meets the lower end of the large rocker (6)
and pushes the latter upwards.
The opposite end of the large rocker, the nozzle of 7 (ã) thus actuates the
star of the days (7), the needle or the disc which are associated indicating the
next day then for him.
Indication of the day of the month:
By the intermediary of the small pawl (8), the star of the day of the month is
in its turn moved of a tooth towards the line, the corresponding needle jumping
then over the next day of the month.
Indication of the months:
Fixed on the lower part of star of day of the month (17), is then the cam of day
of the month (9).
The lower end (the feeler) of the rocker of the months (10) slips on the curve
of the cam, until this which arrives on the high part of the latter at the end
of the month.
At this time the feeler will fall on the low part of the cam and, by the
intermediary of the pawl of the months (10a), the rocker will actuate then star
of the months (11), which will move the corresponding needle about the next
month.
Here how the mechanism of the calendar for the 31 days functions months.
The characteristic of the perpetual day of the month lies however in the fact
that all the indications concerning the date remain correct until year 2100,
taking account of the months of 28, 29, 30 and 31 days.
One needs for that an additional mechanism.
This mechanism is composed of a cam of the month (12), interdependent of star of
the months determining the duration of the latter, a bissextile cam (13), of a
feeler (14), large pawl (15) and large rocker.
The essential part of an everlasting calendar is the cam of the months over
which the various monthly durations are programmed.
The projecting sections of its circumference represent the 31 days months, the
notches those 30 days.
It presents moreover a circular cutting in which the bissextile cam (13) is
moved once per year of 90 degrees by the mechanism of the calendar.
Three sides of this cam define the nonbissextile years February 28 days), while
the fourth, excentré compared to the axis of the part, indicates to it February
29 days.
This star of the months makes a turn in 1 year.
The small rectangle must thus carry out a turn in four years.
 This
result is obtained in the following way:
The gun of the rectangle swivels freely in star; it ends in a square on which a
"Maltese cross is added" to four teeth.
The Maltese cross is maintained by a screw.
It is thus interdependent of the small rectangle, but Maltese crosses and
rectangle turn freely in star.
A finger is fixed firmly on the tenon of swivelling of star.
When the star turns, the finger thus remains motionless.
During this rotation, the Maltese cross will meet the finger this one will
engage in a "entry" (between two teeth) of the Maltese cross and will
oblige it to turn of a quarter of turn.
By this device, the rectangle will also turn of a quarter of turn per annum.
Every four years, its "excentré" side comes to be placed as the image
of
the complete part indicates it, ensuring correct operation, at the time of
the leap year.
Auto-correction of the end of month:
The feeler of the large rocker (14) reads permanently on the bissextile cam the
duration of the month in progress.
In the months cash less than 31 days, it falls into the notches from the cam the
months; so the lower end of the large rocker moves more on the left.
At the end of the month, the point of the large pawl (15), which does not have
an other function that the correction of the days at the end of the month meets
the stage of the cam of the days (16) associated star of day of the month (17).
When the finger of day of the month (4) actuates the large rocker (6), it is the
large pawl (15), and not the small one, which will make turn star of day of the
month (17), via the cam of the days (16), of two, three or four teeth, so that
the needle moves over 1st next month.
As for the change of month, it intervenes at the same time, in the way described
above .
The saltires (18) are intended to prevent an unexpected displacement of
postings.
Thanks to the correctors (19), it is possible to manually modify the posting of
the day of the month, the day and the phases of the moon.
Positions of the large pawl of large rocker in the notch of the cam of day
of the month compared to the month:
One can see on the image opposite:
That the part has a cam 48 which makes a turn in 4 years. That the feeler is in
a notch of February 28.
That the large pawl (C ' ') is ready to push the cam (one is on February 28).
That the finger trainer of the months (31 ' ') is not supported yet against a
tooth of star of the months.
In the neighborhood of 22h30 the day of the month returns in catch.
The large rocker being in the major notch it will have a great displacement to
be able to leave the latter.
The finger trainer of day of the month will push the large rocker and by the
intermediary of the large pawl which is in the low part of the cam will catch up
with the lost days: 28 to the 29, 29 to the 30, 30 to the 31.
At this time the finger trainer of the months (31 ' ') is supported against the
tooth of star of the months and the feeler (m) completely left the notch.
The day of the month continues its progression, the large pawl will carry out
the passage of the 31 with 1st and the finger trainer of the months (31 ' ')
will make turn star of February at Mars.
For one 30 days month for example the displacement of the additional pawl on the
cam will be less significant, therefore it will fall at the bottom from the
notch only during the passage from the 29 to the 30 and will catch up with the 2
days which remains the following night.
The corrector of day of the month (multiple correction)
 The
corrector of day of the month works with the large rocker, which, using its
pawls and of the arm of 7, corrects the days (purple), the day of the month, the
month and the year (if the day of the month is at the end of the month or year).
The corrector of the months initially works with the large rocker in order to
release it from the cam of the months (in red) and then with star of the months
for the correction of the months (in green).
In every perpetual day of the month, the corrections cannot be done enters 22
hours and 1 hour of the morning because the mechanism is under full operation.
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