Note: Descriptions are shown in the official language in which they were submitted.
f9 ,;~ ,d , ., 4, ;~~ w,
~,d I~l kl.. x.i c~~ >>~ °.~
_ 1
RBP File No. 2013-018
Title a 1HETHOD ~C APPAICtATjJS FOR PRI1NTI~TG POS%L'AIs CODE »INGS
FIE:L~D OF THE II~TVEIdTI0ia1
This invention relates to the printing of
machine readable markings on envelopes, for use in
automatic postal sorting and similar machinery.
Ii~.CEGRO'CJIdD OF THE 7C~7EIdTIOl~
It is the practice of postal authorities to
print machine-readable markings on envelopes which pass
through the postal system, to signify a particular sorting
or delivery code.
One common practice is that at the sorting
office 'the envelope passes through a station at which the
envelope is visually presented to a clerk; the clerk reads
the postal code written by the sender on the outside of
the envelope, and then presses the appropriate keys to
print a corresponding machine readable code, for example
a series of bars, typically of fluorescent ink, on the
envelope. In the case of window envelopes, the clerk
reads the postal code as written on the item of
correspondence that lies inside the envelope, and again
presses the keys to print the bars.
Thereafter, the' bars can be detected
automatically; consequently, once the bars have been
printed on the envelope, the envelope need not be handled
by post office personnel again until it is actually
delivered.
Fluorescent ink, as opposed to ordinary ink, is
specified by many national Post Offices for the markings
that are to be detected automatically, to make sure that
only the markings themselves are read by the automatic
detectors. In practice, there is generally no way in
which spurious fluorescent markings could appear by
accident, and be detected, on the envelopes. However,
some national 7?ost Offices specify, for example, blade
s ~ i~ ... ;:) ~;:~ i..~
ink.
The task of manually reading the postal codes,
and manually keying-in the appropriate maxkings, is
tedious, and requires a high degree of concentration on
the part of the coding clerk. Also, processing time is
relatively slow, such that a large number of clerks are
required where mail volumes are high, contributing
significantly to post office labour costs. Equipment for
the machine-reading of postal cades is in common use, at
least where the codes are printed or typewritten. The
equipment can respond to ordinary alpha-numeric
characters. The degree of accuracy of such equipment
however is only fair, and it is still necessary to employ
clerks to process the many "rejects" that the equipment
cannot read.
With window~envelopes, the problem o~ correctly
detecting and reading the characters through the window is
worse, and consequently the accuracy to be expected from
the traditional equipment falls still further.
It is the high-volume user with which the
invention is mainly concerned, in which the user sends
out, for example, a million items per month, all of a
similar nature. A typical example would be a bank which
issues credit card statements. zn a number of
jurisdictions, savings in postal rates are available if
the envelopes in which these statements are sent can be
printed, in-house, with the machine-readable code,
representative of the particular postal code, as this
eliminates a mail processing step at the post office.
Althaugh savings per piece of mail may be small, high-
volume users may achieve significant savings in postal
charges.
Further, the high-volume user, as in the example
of a bank which issues credit card statements as described
above, desires not to print up the envelope at the time
the statement is printed. The high--volume user prefers
rather that the envelope be not unique to the particular
r~ .s ~: ; ;_ ~ ,~,
la ~ .:L ~~7 ~ur ,.) v. ~
- 3 -
statement, since attempting to match the envelopes to the
letters, especially when other enclosures are required 'to
be inserted into the envelopes in addition to the
statements, is difficult. Accordingly, it is preferred to
make only the statement unique, and make use of window
envelopes. Thus it is not convenient to provide envelopes
pre-printed with the appropriate machine-readable code.
A number of patent documents were considered in
relation to the invention, these patents being listed
belowa
United States Patent No. 3,895,220
United States Patent No. 4,158,835
United States Patent No. 4,317,030
United States Patent No . 4,641,347
United States Patent No. 4,743,747
United States Patent No. 4,75?,189
United States Patent No. 4,821,195
United States Patent Na. 4,797,832
United States Patent No. 4,800,504
United States Patent No. 4,800,505
United States Patent No. 4,800,506
United States Patent No. 4,853,869
United States Patent No. 4,862,386
United Kingdom Patent No. 2,193,160
United Kingdom Patent No. 1,486,596
United Kingdom Patent No. 550,618
Eurapean Patent No. 0,076,972
United States Patent No. 4,027,142
United Kingdom Patent No. 4,306,817
United States Patent No. 3,895,220 to Nelson et
a1. is entitled SELECTIVELY ENCODABLE ENVELOPE INSERT AND
RELATED APPARATUS, and describes a magnetically readable
envelope insert provided with bars of magnetized ink
located on detachable portions of the insert. The insert
may be read while sill inside an envelope. The insert has
particular application for insertion in reply envelopes,
different portions of the insert being detached to
.~ " .;,
t~ xi ._.
_ 4 _
indicate certain orders or different methods of payment.
For an illustration of this, sea, for example, the chart
at the bottom of column 3 of the patent.
United States Patent No. 4,158,335, to Miura et
al. is entitled ARRANGEMENT FOR DETECTING A WTNDOW AREA
OF A WINDOW-HAVING MAIL ITEM and describes apparatus for
detecting the location of the window area of an envelope
using photoelectric detectors.
United States Patent No. 4,317,030 to Berghell,
entitled MAILING PACKAGE FOR FACILITATING AUTOMATIC
SORTING OF MAIL, relates to the provision of machine
readable coded arrays on 'the exterior of an envelope. The
invention has particular application for use with re
usable envelopes. When the envelope is sent out, for
example from a utility to a customer, the coded arrays are
provided by punching apertures corresponding to an address
in a sheet and placing a sheet of cowtrasting colour
behind this, such that the contrasting colour of the back
sheet is visible through the apertures, and through a
window in a containing envelope, and may be read by a
sorting machine. When the envelope is returned to the
utility; the location of the contrasting sheet of colour
is moved such that it lies behind an array of apertures ,
punched in the envelope, such that this array may be read
and used to facilitate sorting of the returning mail.
United States Patent No. 4,641,347 to Clark et
al. is entitled SYSTEM FOR PRINTING ENCRYPTED MESSAGES
WITH A CHARACTER GENERATOR AND BAR-CODE REPRESENTATION,
and relates to a postage meter for use in imprinting
various information, including a zip code or bar code, on
the exterior of an envelope or the like. The information
is entered manually by an operator. The main thrust of the
disclosed invention appears to be in the prevention of
fraud and forgery involving postal stamps.
United States Patent No. 4,743,747 to Fougere
et al. is entitled POSTAGE AND MAILING INFORMATION
APPLYING SYSTEM and discloses a system for encoding
CA 02019956 2000-10-25
information on an envelope or other piece of mail. The
patent discloses the printing of a bar code on a label,
directly on an envelope, or in an insert which is visible
through a window.
5 United States Patent No. 4,757,189 to Daboub
relates to apparatus for coding re-usable envelopes and
discloses a system for manually entering bar codes on the
outside of an envelope for internal mailing systems.
Patent Nos. 4,821,195, 4,797,832, 4,800,504,
4,800,505, 4,800,506, 4,853,869, and 4,862,388 all relate
to bulk mailing systems, in which the information which is
printed on the exterior of the envelope is extracted from a
data base.
In United Kingdom Patent Application No.
2,193,160, applicant Thorn EMI plc, entitled PRINTER, a
unit is disclosed in which means are provided for
determining whether an address signal includes a post code.
If a post code is detected, an extractor derives the
relevant information from a data store, the resultant
signal being combined with the address signal at a summer
before input to an address writer. The post code is
applied to the envelope or label in a phosphor-dot form
which is easily machine-readable. The remainder of the
address is printed in conventional form. Thus, a multi-
mode printer is provided which is capable of printing in
alphanumeric script and in machine-readable phosphor-dot
code. The printer may be a modified conventional printer
and may have an impact printing mechanism (for example, a
daisy 5 wheel arrangement) with two ribbons (one for each
form of printing), or one ribbon with two bands.
In United Kingdom Patent No. 1,486,596, granted
to Hotchkiss Brandt Mecanisation, and entitled CODING HEAD
FOR POSTAL ENVELOPES AND A CODING STATION FITTED THEREWITH,
discloses apparatus for printing a machine readable postal
code on an envelope is disclosed. The system is intended
for use in an operation where control signals
characteristic of a code marking to be printing are
E~~~.3 r~
~J i.t v.~ J
- 6 -
produced as a function of an address read by an ogerator,
who punches into a keyboard the address details and a
logic device translates 'these to the appropriate control
signals. The printing head includes an assembly for
holding an envelope to be coded in register with a
printing ribbon. A plurality of printing bars having
parallel printing heads mounted in register with a portion
of the inking ribbon are provided, the number of bars
being equal to the number of printing coding marks which
may be printed. The coding head may be manually fed with
individual envelopes by an operator or may be
automatically fed to reading position from which the
envelope is manually transferred to a coding position.
In United Kingdom Patent No. 550,618, granted to ._
Remington Rand Inc., entitled IMPROVEMENTS IN OR RELATING
TO STATISTTCAL MACHINES, a machine which reads the
information contained in a punched data card, and then
prints this information on the same card. The machine
discloses a complex mechanical arrangement for sensing the
perforations on a punched card, temporarily retaining this
information, decoding the information and printing the
decoded information onto the card at a different location
in the machine.
In United States Patent No. 4,027,142, to Paup
et al, entitled AUTOMATED PROCESSTNG OF FINANCIAL
DOCUMENTS, apparatus for the automatic processing of bank
cheques is disclosed. The cheques are encoded with a line
of alphanumeric characters and are processed by passing
through a first station for generating an item control
number unique to each document and a read station for
sensing each character in the encoded line ~to produce a
string of data signals for each document. At a print
station the control number and other data are imprinted on
'the back of each document in code form and the control
number and other data are imprinted on the face of each
document in human readable form. The read station
includes an MICR read station, an OCR read station and a
CA 02019956 2000-10-25
7
bar-code read station. The print station includes a bar
code ink j et printer, a bar code indicator, and a dual
alphanumeric ink jet printer. The MICR read station serves
to read the alphanumeric data encoded in magnetic ink on
the bottom of each cheque, while the OCR read station reads
the same line of information. This information is merged
to produce a single output data stream. The printing of
the correct information on each cheque is synchronized by
means of a central computer.
In United States Patent No. 4,306,817 to Alas,
entitled BAR CODE PRINTING MECHANISM, there is disclosed
the use of two synchronized printing heads, each spaced
apart longitudinally for printing one half a bar of, for
example, a U.S. postal code. The operation of the
forwardmost head is delayed for a period of time sufficient
to allow the target object to have moved a distance
approximately equal to the spacing between the heads.
SUNDQARY Og' THS INV'HNTION
A first aspect of the present invention provides
a method of encoding correspondence to facilitate routing
of the correspondence to a destination address by automatic
mail sorting apparatus. The method comprises the steps:
(a) marking a letter with an easily machine
readable first code being generated from and corresponding
to the human readable postal code of the destination
address;
(b) stuffing the letter into a window envelope
such that the first code is positioned within the window;
(c) machine reading the first code within the
window; and
(d) printing a machine readable second code
corresponding to the first code and the human readable
postal code of the destination address in the location and
format utilized by a particular automatic mail sorting
apparatus such that the envelope is suitable for processing
by the apparatus.
y .~~ ", ,.. ~-s
'a
f..s :,I :~i :;3 ., .
g
This method allows a volume mailer, such as a
bank or credit card company sending out monthly
statements, to provide pieces of mail for the post office
which have already undergone a first process step, that is
the marking of a machine readable marking corresponding to
the postal code on the exterior of the envelope in a
manner which permits automatic sorting of the mail. The ,
marking of the letter with the first code conveniently
takes place as the letter is marked with the destination
la address. Further, the use of window dnvelopes does not
require the matching of a letter or other correspondence
with a particular envelope, and substantially simplifies
the envelope stuffing operation, allowing this to be
carried out with easily available, conventional apparatus.
According to a second aspect of the present
invention, there is provided a method of encoding
correspondence to facilitate routing of the correspondence
to a destination address by automatic mail sorting
apparatus comprising the steps:
(a) marking a piece of mail with an easily
machine readable first code corresponding to the human
readable postal code of the destination address;
(b) machine reading the first cods; and
(c) printing a machine readable second code
2~ corresponding to the first code and the human readable
postal code of the destination address in a location and
format utilized by a particular mail sorting apparatus.
This particular aspect of the invention, not
necessarily requiring the use of window envelopes, is
advantageous, for example, where a number of envelopes are
to be sent to various different destination addresses With
the same enclosures, or where a number of similar
postcards are to be sent to different destination
addresses.
A further aspect of the invention provides an ,
apparatus for printing coded markings on an envelope. The
apparatus includes a read station and a print station, and
6A r'1 -,r :~ .,
~~ ~v .:,. .. ..
g _
a conveyor for transporting the envelope therebetween.
The read statian includes an optical sensor,
which preferably is arranged to pick up reflections from
the markings an the correspondence, and is effective to
produce a series of electrical signals in accordance
therewith. The apparatus includes computing means, a
means for transmitting the said electrical signals from
the optical sensor to the computer, a means for
transmitting resultant signals to the print station, and
a means for arranging the said signals iwto a sequence of
spaced pulses.
The privet station includes at least one signal
controlled printer, which, during normal operation of the
apparatus, remains at a fixed print point at the print
station.
In one aspect of the invewtian, the computing
means accepts signals of displacement of the passing
envelope from the print station and the read station, and
coordinates these displacements with the signals from a
read head, whereby the printer is effective to print a
mark on the envelope as the envelope passes the said print
station, and to print a series of such marks on the
passing envelope in spaced-apart sequence in accordance
with the said spaced pulses.
Preferably, each station is provided with a
revolution counter, or angular-displacement indicator,
which is set to engage with the passing envelope, whereby
the linear displacement of the passing envelope
corresponds to the angular displacement of the counter.
One of the difficulties with reading printed
markings through a window is that the read sensor tends to
read the edge of the window as one of the markings. The
first aspect of the invention is described as i~t relates
-to its application to window envelopes, but it should be
~5 noted that the said difficulty can arise also in the case
where the markings to be read are printed on a stick-on
label, wherein the read sensor has a tendency to detect
CA 02019956 2000-10-25
the edge of the label as if it were one of the markings.
The scope of the invention should be construed accordingly.
As will be described presently, the first aspect of the
invention allows the read sensor to read the markings
5 clearly and accurately, with a good deal of tolerance, and
yet enables the read sensor to ignore the edge of the
window, or the edge of the label.
In a preferred construction, for use with window
envelopes, at the read station a read head is provided with
10 a photo-detector. The photo-detector scans the window of a
passing envelope, and detects the presence of a bar printed
on the item of correspondence inside the envelope, and
visible through the window.
The window of a window envelope is, as a general
rule, provided with a pane of transparent material, such as
cellophane, and the read head must detect the presence of
the bars through the transparent material. A springy
slipper is preferably provided, for the purpose of
smoothing the pane down flat onto the item of
correspondence.
The thickness of the envelopes may vary, in the
range from less than 1 mm to about 5 mm. The read head
preferably is mounted on a parallelogram linkage, by the
operation of which the passing envelope may deflect the
read head upwards, and the read head still remains in the
correct position relative to the window. The task of
sensing markings through a transparent pane is a demanding
one, and it is recognised that the orientation of the read
head to the window is critical. A preferred manner in
which the read head may be arranged to accommodate these
aspects will be described below.
A still further aspect of the invention provides
a print station, where the bars (or other machine-readable
markings) are printed on the outside of the envelope, the
pattern of the bars being in accordance with the postal
code as read by the read sensor.
In the manual system referred to earlier the
sJ y.. e.l ~:_~~: c-..~5 ',
- 11 -
bars have been applied to the envelope by means of printer
hammers activated by solenoids: the operator presses keys
in accordance with the code he reads in, and the keys
activate the solenoids. Generally, Post Offices call for
the fluorescent bars to be about 6 mm high and about 1 mm
wide, and 'the designer of the apparatus specifies an
appropriate solenoid.
One characteristic of conventional solenoids is
that they are comparatively slow-acting, due to the
inertia of the (large) armature. The present invention is
for use with apparatus with a throughput of two or three
envelopes per second, at which speed there is a tame
interval between fluorescent bars of about 5 milliseconds.
~'or speeds like that, printing by conventional solenaids
is unsuitable.
This aspect of the invention provides a means
for printing fluorescent bars on an envelope to signify a
postal code, wherein the means for printing the
fluorescent bars comprises a pair of dot-matrix print
heads, which are arranged for printing onto the envelope
through a ribbon containing fluorescent ink. 3n the
invention, the print heads are stationary within the
apparatus, and are arranged side by side, in line along
the direction of travel of the envelope through the
apparatus. The two print heads are offset laterally with
respect to the direction of travel of the envelope,
whereby one print head prints the bottom half of the bar,
and the other prints the tog half of the bar.
A dot-matrix print head, of the configurations
which are commonly available, wall only print a bar with
a height of about 3 mm. This is the reason two print
heads are needed to print a bar 6 mm high. Dot-matrix
print heads are not made wider 'than 3 mm, because dot
matrix print heads are invariably controlled by a
computer, and, even where taller printing as needed, it is
usually of no grea-~ consequence to program the computer to
cause the print head to make more than one pass over the
~ .J ,.r.~d ~~ T" ~L~
~y ~ . °._
- 12 -
paper.
The arrangement of the invention allows
conventional dot.-matrix print heads to be used, and the
invention permits advantage to be taken of their
characteristic responsiveness, ease of programming, and
well developed reliability. ~
In conventional dot-matrix printers -- the usual
application in which dot-matrix print heads are found --
only one head is provided, and this on$ head is driven in
motion by a transporter mechanism, which moves the print
head at right angles to the motion of the paper.
In the circumstances of the presewt invention,
it would not be practicable to move the envelope laterally
(i.e. to move the envelope at right angles to the line of
its passage through the apparatus) as it passed through
the print station. In the invention, neither the
envelopes nor 'the print heads are required to move
laterally. It would indeed be almost impossible to move
either a single 3 mm head, or the envelope, laterally fast
enough to print a 6 mm high bar. Also, it is recognised
that it would be difficult to arrange for the envelope to
pass through the print station twice, which is a
possibility that might be considered by a designer> it
must be considered that, in order to print a 6 mm high
bar, it would be possible to pass the envelope twice
through a single 3 mm print unit, However, this would
drastically reduce throughput, and is not contemplated w
within thus aspect of the invention. '
Hot-matrix paint heads are computer controlled,
and it is recognised in the invention that there is no
difficulty in programming the computer to operate the two .
print heads in correct sequence.
~Rg~:F I~~~~33IFTION OF IaRAWING~
By way of further explanation o:~ the invention,
an exemplary embodiment of the apparatus of the invention
will now be described with reference to the accompanying
drawings, in whichs
~ r~ ;~~ f~
..~~ :.$ e>' a 3..~
- 13 -
Figure la is an illustration of a method of
encoding envelopes in accordance with a first aspect of
the present invention;
Figure lb is a enlarged plan view of an envelope
which has been processed in accordance with the method of
the Figure la;
Figure 2 is a side elevation of an apparatus
which is assembled and arranged for operation according to
the invention;
Figure 3 is a block diagram showing the
operative connections between the various components of
the apparatus of Figure 2;
Figure 4 is a close-up side view of a read
station of the apparatus of Figure 2;
Figure 5 is a close-up side view of a print
station of the apparatus of Figure 2;
Figure 6 is a cross-section on line fi-6 of
Figure 4;
24 Figure 4;
Figure 5;
Figure 7 is a cross-section on line 7-7 of
Figure 8 is a cross-section on line 8-8 of
Figure 9 is a broken away view of a different
form of printing station for use in a further embodiment
of the present invention;
Figure 14 is a plan view from above of the
printing station of Figure 9; and
Figure 11 is an end view of the printing station
of Figure 9.
r~~T~r.LFn ~FSC~aap~rso~ ~F ~~FE~~D Fr~so~l~~~s
Figure 1 of the drawings shows a flaw chart
illustrating the main method steps of the present
invention, which is intended far use primarily by those
involved in large volume mailing. The invention allows a
mailer to mark envelopes or other items of correspondence
with a machine readable code which is suitable for reading
by the automatic mail sorting apparatus as used by a
CA 02019956 2000-10-25
14
local, national or regional Post Office. This marking is
normally carried out by the Post Office on receipt of the
mail from the mailer. Thus, the method and apparatus of
the present invention allows the Post Office to eliminate a
major processing step on their sorting operation, and this
benefit may be passed onto the mailer in the form of a
lower postal rate.
The method of a first aspect of the invention
involves four basic steps, as illustrated in Figure 1a as
follows:
(a) marking a letter with an easily machine
readable first code generated from and corresponding to the
human readable postal code of the destination address of
the letter;
(b) stuffing the letter into a window envelope such
that the first code is positioned within the window;
(c) machine reading the first code within the
window; and
(d) printing a machine readable second code
corresponding to the first code and the human readable
postal code of the destination address in the location and
format utilized by a particular automatic mail sorting
apparatus such that the envelope is suitable for processing
by the apparatus.
The method will initially be described fairly
briefly, followed by a more detailed description of the
method and apparatus of the invention.
The machine readable first code takes the form of a
series 36 of bars 37 forming a bar code which is printed on
the correspondence, in this example a statement, which is
printed below the destination name and address at the same
time, and with the same typically black ink used to print
the destination name and address.
The letter marked in this manner is then stuffed
into a window envelope 28, together with any enclosure,
using conventional envelope stuffing apparatus, such as the
Bell and Howell MAILSTAR (Trademark). The letter is folded
CA 02019956 2000-10-25
and located in the envelope such that the address and the
bar code are visible through the window 29.
The stuffed envelope is then conveyed into an
encoding apparatus. The encoding apparatus includes a read
5 station, where the first code is read within the window.
The read code is then processed by the apparatus
and, when the envelope is conveyed to a print station
"downstream" of the read station, the second code is
printed on the envelope, the second code corresponding on
10 location, ink and format to that utilised by the particular
automatic mail sorting apparatus used by the local Post
Office. In the example illustrated, the second code is a
series 49 of bars 56 forming a bar code printed in
fluorescent ink.
15 In further embodiments, the first code may be
printed on a label or the like, for affixing to the face of
an envelope. This method of address encoding may be
particularly appropriate where the enclosures of the
envelopes are the same, and there is no need to match
particular enclosures with particular addresses.
The methods and apparatus of the invention will now
be described in more detail.
The drawings are diagrammatic, and some details of
construction have been omitted from the drawings, to
enhance the clarity of illustration.
Figure 2 depicts the overall apparatus. The
apparatus includes a fixed base frame 2, which comprises a
base plate, pillars, and a lower track frame 3. An upper
track frame 4 is, during operation of the apparatus,
unitary with the base frame 2, but is openable relative
thereto for service purposes.
A lower conveyor belt 5 is driven by a motor (not
shown). An upper conveyor belt 7 is spring loaded at
several points 8 against the lower conveyor belt 5, the
arrangement being such that the two belts are driven in
unison. The conveyor assembly may include belt tensioners
9. The arrangement of the conveyor assembly is such that an
CA 02019956 2000-10-25
16
envelope is caught between the upper and lower belts, and
is thereby transported through the apparatus.
The forward ends of the conveyor belts 5, 7 (the
right-hand end in Figure 2) do not extend right to the end
of the frame. Thus, the envelope is only picked up
between the conveyor belts 5, 7 after the envelope has
already traversed some distance into the apparatus. The
first portion of the transport of the envelope, upon
entering the apparatus, is handled by a pair of pinch
rollers 10, 12 of which the lower roller 10 is driven by an
electric motor (not shown).
The drive arrangement is that the conveyor belts 5,
7 act as if to transport the envelope at a faster rate than
do the pinch rollers 10, 12. No actual slippage
occurs, however, and the effect is limited to the creation
of an induced tension in the envelope, as it passes from
the pinch rollers to the conveyor belts. The read station
16 of the apparatus is so positioned in the apparatus that
the portion of the envelope that is being read at the read
station is subject to this induced tension.
The read station 16 is described in more detail
below. The apparatus also includes a print station 17,
which is also described in more detail below.
Positioned in the lower track frame 3, at the
read station 16, is a read-station position-sensor 18,
shown schematically in Figure 3 of the drawings and in
some detail in Figure 4 of the drawings, which comprises
a wheel 19, an associated spring-loaded follower 20, and
a revolution counter 23 (Figure 7), such as a SUNX (TM)
Rotary Shaft Encoder. The arrangement is such that as soon
as an envelope passes between the wheel 19 and the follower
20, the wheel 19 starts rotating, the rotary displacement
of the wheel 19 being a measure of the linear displacement
of the envelope as the envelope is conveyed through the
read station. The angular output reading from the counter
23 is therefore a measure of the linear displacement of the
envelope with respect to a particular point within the read
CA 02019956 2000-10-25
17
station.
A photocell 24 (Figure 3) is incorporated into the
track frame 4, for the purpose of detecting the presence of
an envelope. During normal operation of the apparatus,
when envelopes are passing continuously through the
apparatus, the wheel 19 does not stop rotating between
envelopes, and in fact, due to its inertia, the wheel
barely slows down between envelopes. Therefore, the mere
fact that the wheel 19 is revolving cannot be relied upon
as the signal that an envelope is present in the station.
Instead, the photocell 24 signifies the presence or absence
of an envelope passing through the read station 16. A
computer 25 is provided in the apparatus, the computer
being programmed to start receiving the output from the
counter 23 only after the photocell 24 has been activated.
It will be appreciated that the photocell
preferably should be so positioned, within the station,
that the envelope engages the wheel 19 before the envelope
trips the photocell 24, to ensure that the wheel is up to
speed and running, before readings from the wheel are fed
into the computer.
A similar arrangement is provided in respect of the
print station 17. A photocell 26 senses whether an
envelope is present at the print station. Again, the
computer 25 accepts output from a print-station revolution-
counter 27 only when the photocell 26 signifies that an
envelope has entered the print station.
The photocells 24 and 26 are mounted on a fence 34
(Figure 6). The fence 34 is adjustable laterally, to
accommodate different widths of envelope. The fence 34,
and the photocells 24 and 26, are not shown in Figures 4
and 5, for clarity, but their positions are signified by
the numerals 24 and 26 thereon.
The envelope 28 (Figure 2 ) , is of the kind with
which the invention is concerned, is provided with a window
29, formed by cutting through the material of the envelope.
A pane 30 of the cellophane or other suitable transparent
CA 02019956 2000-10-25
18
material is glued into the cut-out area.
The conventional arrangement with window envelopes
is that a name and address written on an item of
correspondence (in this example a credit card statement) 35
placed within the envelope 28 is visible though the window
29. In accordance with the method of the invention, as
mentioned above, a series 36 of bars 37 is printed on the
statement 35, such that the series 36 also is visible
through the window 29. The spacing and layout of the bars
37 is such that the series 36 signifies the appropriate
postal code and error-checking verification, preferably in
the form of a parity check feature. The bars 37 are
printed in ordinary black ink, and are printed on the
statement simultaneously with and adjacent to the other
personal details and destination address.
It will be described below how the invention
enables a read sensor to read the bars 37, through the pane
30, with the required degree of accuracy and sensitivity.
One difficulty that should be considered in the reading
process is that of making the sensor insensitive to the
edges 38, 39 of the window 29 -- the problem is that the
read sensor might detect the edges 38, 39 of the window as
if the edges were bars 37. Similarly, the read sensor
might detect the edges of the envelope 28 as if they were
bars.
The read sensor is signified generally by number 40
and is illustrated in some detail in Figure 4. The
difficulty, on the part of the read sensor 40, of having to
detect the difference between a bar 37 and an edge 38, 39
may be avoided in the invention. The computer 25 may be so
programmed as to ignore the readings from the read sensor
until after the envelope 28 has been displaced a
predetermined distance into the read station. Thus, the
photocell 24 is used to signify the instant when the
35 envelope 28 enters the read station 16. The output from
the read sensor 40 may then be ignored until after the
counter 23 has signified that the leading edge 38 of the
CA 02019956 2000-10-25
19
window 28 has passed a read-line 41. The read-line 41 is
the line in the read station 16 at which the sensor 40
actually scans the series 36 of bars 37.
It cannot be avoided that the item of
correspondence 35 must be given a considerable freedom of
movement within the envelope 28, in order to allow the use
of conventional envelope-stuffing machines. Also,
sometimes the envelopes 28 will be stuffed with ancillary
items of correspondence, but sometimes the envelopes will
contain only the bare statement on its own, and the
dimensions of the statement and the envelope 28 must be
acceptable for both cases. Therefore, it cannot be avoided
that the first of the bars 37 in the series 36 might
sometimes be as close as, say, 3 mm to the leading code 38,
and on other occasions the first of the bars might be 20 mm
behind the leading edge. Similarly, in the lateral sense,
the position of the bars 37 on one occasion may be
laterally displaced by as much as 10 mm from the position
of the bars 37 on another occasion. By the same token, the
series 36 may lie at an angle relative to the direction of
motion of the envelope 28.
On the other hand, there is little difficulty in
manufacturing the envelope to reasonably tight tolerances,
whereby the distance 45 from the leading edge 46 of the
envelope 28 to the leading edge 38 of the window may be
expected not to vary by more than about 1 mm. The result
is that the photocell 24, which is activated very reliably
by the edge 46 of the envelope, can be used to signify with
adequate accuracy the moment at which the leading edge of
the envelope 28 passes the photocell, and therefore to
signify, by simple addition of pre-set accurately-known
distances, the moment at which the leading edge 38 of the
window clears the read-line 41. Once that moment is past,
the computer 25 can be allowed to start to process the
readings from the sensor 40.
As mentioned earlier, the invention may be applied
to the case where the series 36 of bars 37 is printed on a
CA 02019956 2000-10-25
stick-on mailing label, rather than on an item of
correspondence to be read through a window: the same
problem arises, with a label, that the edges of the label
might be mistaken for coded markings. As the invention
5 uses the position of the window or label as the means for
indicating to the computer whether the signal from the read
head should be, or should not be, ignored, any extra
positional tolerance requirement detracts directly from the
margin over which the read head can operate accurately.
10 Thus it would be important in a "label" application that
the label be positioned accurately on the envelope.
The series 36 of bars 37 may be set so as always to
contain a set number of bars, in which case, the computer
can be programmed to look for exactly that number, and
15 then to ignore any further signals. However, it is
preferred in the invention that the computer 25 be
programmed so that the processing of signals from the
counter 23 continues only for a given displacement of the
envelope after the start of processing, that is, that the
20 signal upon which the computer 25 stops processing the
output of the read sensor 40 is simply that the envelope
has travelled a given pre-set distance since the computer
started processing the output of the read sensor. Under
this procedure, it is not possible that the trailing edge
25 39 of the window 29 could be detected as if it were a bar
37, and also under this procedure there is no requirement
that all the unique series 36 of bars 37 in all the passing
envelopes 28 should have the same number of bars 37.
As regards printing the markings on the envelopes,
the general rule is that Post Offices specify the distance
47 it requires between the leading edge 46 of the envelope
and the start point 48 of the series 49 of typically
fluorescent markings 50. The instant at which the envelope
28 enters the print station 17 is signalled to the computer
by the print-station photocell 26; the computer can be
programmed to start the printing process as soon as the
envelope has travelled a predetermined distance after that.
CA 02019956 2000-10-25
21
It may be noted that the distance specified by the
Post Office between the leading edge 46 of the envelope 28
(i.e. that edge that activates the photocell 26), and the
point at which the series 49 is to start, will in most
jurisdictions be always the same, irrespective of the size
of the envelope 28. Therefore, the print station photocell
26 may remain at a fixed site relative to the print-line 56
at the print station (Figure 8). In contrast, it will be
recalled that the photocell 24 in the read station 16 is
adjustably movable relative to the read-line 41, to cater
for the possibility that the windows 29 of one batch of
envelopes might lie at a different distance from the
leading edge 46 of the envelope than the windows 29 of
another batch. Of course, if the need arises, the position
of the photocell 26 at the print station 17 may similarly
be made adjustable.
It should be noted that it would be inadvisable to
allow just one photocell to be used to control the
operational starting points of both stations, since the
distance 45 between the leading edge 38 of the window and
the leading edge 46 of the envelope changes more often
than, and independently of, the distance 47 between the
start of the series 49 and the leading edge 46 of the
envelope.
It is possible to provide adjustability for the
various operating points at the stations either by the
preferred method of moving the read-station photocell or
alternatively by re-programming the computer, when
adjustment is required, to respond to a new value for a
measured displacement. It is recognised in the invention
that the former is much easier than the latter -- all the
technician in charge of the setting the apparatus needs to
do is to make sure that he follows this rule: that he sets
the distance 57 of the photocell 24 from the read-line 41
to be equal to the distance 45 from the leading edge of the
envelope to the leading edge of the window (plus C, where C
is an apparatus-dependent constant dimension). As
CA 02019956 2000-10-25
22
mentioned, the technician does not need to re-position the
corresponding photocell 26 at the print station 17 for each
size of envelope, because the distance 47 between the
leading edge 46 of the envelope and the start-point 48 of
the fluorescent markings produced at the print station will
generally always be required to be constant.
The construction and operation of the read sensor
40 will now be described, with particular reference to
Figure 4 of the drawings.
The read sensor 40 includes a housing 58, attached
to a parallelogram linkage 59, by which the housing 58 is
guided for up/down movement. The parallelogram linkage is
mounted from a block 60 secured to the upper track frame 4.
Attached to the housing 58 is a springy slipper 64,
which of such dimensions as to engage resiliently against
the top surface of an envelope 28 passing beneath the read
sensor 40. The housing 58 also includes a pair of legs 65,
each leg having a foot and having a ball-bearing 67 mounted
at the foot. The bearings 67 also engage the top surface
of the envelope, but there is substantially no resilience
between the bearings 67 and the housing 58.
A suspension unit 68 is provided in connection with
the parallelogram linkage 59, the purpose of the suspension
unit 68 being to act in conjunction with the weight of the
housing 58 to produce the desired downwards force on the
envelope 28.
The housing 58 contains a lens 69 and an optical-
sensor or photo-detector 70 such as a Silicon Photo-
Darlington Transistor. The housing also contains
floodlights 73. The lens 69 and detector 70 are mounted in
a focusing tube 74, which can be moved vertically within
the housing 58, and can be locked to the height at which
the detector 70 is focused on the envelope 28.
To assist in focusing, the detector 70 may be
removed from the tube 74 and replaced temporarily with a
standardised light source. A spot of light from the source
would then appear on a test sheet placed under the sensor,
CA 02019956 2000-10-25
23
and the height of the tube 74 can be adjusted until that
spot is focused.
When an envelope 28 enters the read station 16, the
leading edge 46 of the envelope strikes the ball bearing
67, thereby urging the housing 58 upwards and onto the
envelope. In other apparatus, the ball bearing 67 may be
omitted, if desired, such that the weight of the housing 58
is supported solely by the slippers 64. The springy
slipper 64 presses lightly down onto the envelope. The
main purpose of the springy slipper 64 is to smooth out the
pane 30, in order firstly to smooth out any wrinkles that
might tend to be present in the pane 30, and secondly to
ensure that the pane is in direct contact with the paper of
the statement 35.
The function of the slipper 64 is in fact critical
to the accurate operation of the apparatus. A wrinkle in
the pane 30 might not appear to be significant to a person,
because the eye ignores it, but the photo-detector 70 will
all too easily detect a wrinkle as if the wrinkle were one
of the bars 37. Therefore, the pane preferably should be
perfectly smooth and flat. No less important is the
requirement to ensure that the pane 30 is pressed into firm
contact with the paper beneath as read-sensing is taking
place: if the pane 30 were to be even slightly clear of the
paper below, the resulting scattering of light could
produce false readings.
The suspension unit 68 therefore should be such
that the combined effect of the weight of the housing and
the action of the spring within the unit 68 provides a firm
engagement action. The force of engagement should not be
too strong, however, or the envelope might tend to be
distorted. Such distortion would, if it happened,
interfere with the smooth passage of the envelope through
the read station, and one of the aims of the invention is
to create as little resistance as possible to the motion of
the envelope, since such interference would limit the rate
of throughput.
CA 02019956 2000-10-25
24
Glare and reflections from the transparent material
of the pane 30 can be troublesome if not properly dealt
with, either producing a false indication that a bar 37 is
present, or preventing a bar 37 from being detected. The
springy slipper 64 consequently is provided with only a
small hole 62, so that only a small portion of the
potentially glare-producing pane is exposed during the
reading. The inside of the focusing tube 74 is blackened,
as is the upper surface of the slipper 64, to minimize
glare. The floodlights 73 are set at an angle, to minimize
spurious reflections from the window and the surface of the
paper.
The parallelogram linkage 59 is important in
achieving the desired degree of accuracy in the performance
of the sensor 40. It might be considered that the housing
58 could be mounted on a single pivoting arm, as distinct
from the two parallel arms as shown, and such an
arrangement is contemplated. However, the position of the
pivot-point of such a notional single arm upon the frame 4
would be critical: if the pivot point were too high, the
acurate operational movement of the arm would mean that as
the housing 58 swung upwards the housing would also be
slightly displaced horizontally forwards relative to the
hole 62 in the slipper 64. If the pivot-point were a
substantial distance above the envelope 28, such an error
might not be negligible. Such an effect might be
alleviated if the pivot-point were low down, at or near the
level of the envelope, or if the arm were long, but there
is little room in the apparatus for these measures to be
taken, especially since there is generally a requirement
also that the read sensor 40 be adjustable as to its
lateral position, to cater for the window 29 not always
being in the same lateral position on the envelope 28.
In the preferred parallelogram arrangement, the
pivot-points between the block 60 and the linkage 59 are,
as shown, quite high above the envelope 28, and the linkage
59 is quite short, yet substantially no fore-aft motion
CA 02019956 2000-10-25
accompanies the up/down motion of the housing 58.
The envelope thickness can vary in the range of
about 1-5 mm. The suspension unit 68 is adjustable, and it
is usually desirable for the technician to adjust the
5 setting of the suspension unit 68 in accordance with the
nominal thickness of a particular run of envelopes; the
distance through which the housing 58 is called upon to
rise, as the envelope 28 passes beneath, is thereby kept to
a minimum. The block 60 tends to bounce upwards only very
10 slightly, as the envelope passes beneath, when the
suspension unit 68 is set correctly.
Preferably, the two legs 65 and their ball-bearings
67 should be spaced sufficiently widely apart, laterally,
that the bearings are well clear of the pane 30.
15 The block 60 is slidable in the lateral sense in a
groove in the upper track frame 4, for adjusting the sensor
in accordance with the location of the window 29 upon the
envelope 28. Such a lateral adjustment facility is
enhanced by virtue of the fact that the sensor 40 is
20 located ahead of the belts 5, 7.
The first code contains a number of bars 37
indicative of the postal code and also a parity check
feature: a count is made of the "postal code" bars 37 of
the first code and a number of further bars 37 printed in
25 the code such that a count of all of the bars 37 in the
code is of a selected first parity. Thus, a correct first
code, as presented to the read head, should have this
selected first parity. If, on reading the first code, a
count of the bars 37 of the first code reveals the code is
of a different second parity, this is detected by the
computer 25 and a command is sent to "hold" the printer and
a signal sent to downstream envelope reject apparatus to
reject the incorrectly coded envelope, that is, no second
code is printed on the envelope and the envelope is
rejected. The envelope can then be manually re-fed. In
testing of the apparatus rejects at this stage are about
five per thousand envelopes processed, and usually caused
CA 02019956 2000-10-25
26
by a poor stuff.
The construction and operation of the print station
17 (Figure 5) will now be described.
At the print station 17, two print heads 75 are
provided. These are mounted in a carriage 76, which is
mounted on a parallelogram linkage 78 for up/down movement
relative to a block 79. The block 79 is fixed to the upper
track frame 4.
Each print head 75 includes a dot-matrix print unit
80. Print unit 80 is a conventional proprietary item, such
as an Epson LX800 (TM), and will not be described in
detail. Such units are readily obtainable either with nine
or twenty-four pins. Positioned alongside the print unit
80, and on the same print-line 56, a roller-follower 81 is
provided, the axle of which is fixed firmly to the carriage
76. Both the print unit 80 and the roller-follower 81 are
arranged to bear onto a strike-roller 82, the axle of which
is fixed firmly to the lower track frame 3.
A ribbon 94 is threaded underneath the print unit
75. The ribbon 94 contains ink to be detected by the
particular automatic mail sorting apparatus used by the
Post Office, and is typically fluorescent black or other
colour ink, and is mounted in a conventional ribbon
carrying cartridge 95. The ribbon is continuously
circulated by means of a motor 96. (The ribbon has been
omitted in Figures 5 and 8).
The weight of the carriage 76, with the print heads
75 attached, is partially supported on an adjustable spring
unit 83. A leg 84 and attached bearing 85 is provided,
which is similar to that described in respect of the read-
sensor 40, and which also takes a portion of the weight of
the carriage. Thus the total weight of the carriage 76 is
divided between four points of support: the two roller
followers 81, the bearings 85, and the spring unit 83. In
addition, when the print heads 75 are being actuated, the
actuation forces on the pins in the two print heads 75 are
reacted against the weight of the carriage. In other
CA 02019956 2000-10-25
27
embodiments, the bearing 85 may be omitted.
Of these, of course, the actuation forces of the
pins are the most important; and in fact the other weight
controlling supports are arranged so that the actuation
forces of the pins can be controlled with the correct
degree of sensitivity and responsiveness.
V~hen an envelope 28, travelling along the tray 97,
enters the print station 17 (from the right, Figure 5), the
leading edge 46 of the envelope 28 engages the bearing 85,
driving the leg 84 upwards, and raising the carriage 76.
The parallelogram linkage 78 ensures that the carriage
remains horizontal during the upwards motion, and remains
so while the envelope 28 passes beneath the carriage. It
is desirable that the two print heads 75 be both positioned
at exactly the same height above the passing envelope, and
this requirement applies even though the thickness of the
envelopes may vary. An angle setting means 86 is included
as part of the carriage, and operates in combination with
the parallelogram linkage 78, whereby the angle of the
carriage 76 can be adjusted relative to the linkage 78.
The purpose of the leg 84 and its bearing 85 is to raise
the carriage 76 well before the printing operation actually
starts: after its sudden rise, which may be accompanied by
momentary bouncing, the carriage then has time to settle
down gently to its correct level, well before printing
commences .
The print pins in the print heads 75 are, as
mentioned, arranged so as to strike the envelope, reacting
against the strike-roller 82. The envelopes pass the print
head 75 at speeds in the region of 50 cm/sec. Print heads
were developed for use in dot matrix printers, wherein the
print head moves much more slowly relative to the paper
during printing; and one of the features of the invention
is the recognition that a dot-matrix print head can be used
in a manner which is so different from that for which it
was developed. To accommodate the high relative speed,
steps are taken to allow the print head 75 to move slightly
CA 02019956 2000-10-25
28
with the passing envelope 28 during the moment the pins are
striking the envelope 28, as will now be described.
As shown in Figure 8, the print unit 80 is bolted
solidly to a rail 87. The rail 87 in turn is bolted
between a pair of thin springy arms 89, which depend
downwardly from a block 90 which is bolted to the carriage
76. The effect of this arrangement is that the print head
75 has some "give", and can move (slightly) in the
direction of travel of the envelope. The fact also that
the reaction-roller 82 is moving with the envelope 28, but
is providing a solid base against which the pins can
strike, gives a very advantageous manner of printing. It
may be noted that exceptional clarity of printing is not
required, and indeed the individual dots preferably are
allowed to merge into each other, but the amount of
smudging does need to be controlled to ensure that each
fluorescent bar 50 is clearly delineated.
The bars 50 typically have a width or thickness as
produced by five pin-strikes. Thus, to produce a bar 50,
the pins are actuated five times -- when nine pins are
provided, the pins would alternate in a 5-4-5-4-5 sequence.
As mentioned, the reason two print heads 75 are
provided is that proprietary dot-matrix print heads are
normally only 3 mm high, whereas the fluorescent bar 50 is
required to be 6 mm high. The two print heads are offset
the 3 mm difference. Thus, the first print head prints the
bottom halves of the bars 50, and the second print head
prints the top halves of the bars. Naturally, it is
important that the two halves of the bars match up
exactly, and suitable inter-adjustment means (not shown) is
provided.
Provided downstream of the print station 17 may be
a verification reader 200 (Figures 2 and 3), which may take
any convenient from and which reads the bars printed by the
print heads. The signal obtained by the reader is compared
with the input data to the printer. If there is an error
in the printed code, a signal is sent to the computer 25 to
CA 02019956 2000-10-25
29
notify an envelope reject apparatus downstream of the
reader 200 to reject the incorrectly coded envelope. This
feature serves as a quality assurance feature for detection
and immediate action to reject an envelope or stop
processing if the fault is caused by for example, a faulty
print head, printer ribbon, or mechanical problem in the
transport or displacement measurement.
As stated above, the read sensor 40 is designed to
be adjustable laterally, because the position of the window
29 can vary. The print heads 75, on the other hand, do not
need to be adjustable laterally, because the fluorescent
bars 50 are required always to be the same distance from
the edge of the envelope.
The requirements of different Post Offices may
cause the fluorescent bars 50 to be at different places,
but again, once the apparatus has been designed for a given
positioning of the fluorescent bars 50, the print heads 75
would remain in that position. It is unlikely that an
apparatus would need to be built to cater for the
requirements of more than one Post Office, but such
adjustment could be provided if desired.
The apparatus shown in the drawings can be easily
serviced, because of its construction. The upper track
frame 4 is able to pivot about the conveyor belt drive
pulley 99. Upon release of a suitable catch (not shown)
the upper track frame 4 may be swung upwards, together with
all the components attached to it, including the upper
conveyor belt 5, and the read and print stations 16, 17.
As a further aid to servicing, the print station 17 is
mounted on a mounting plate 98, which during operation is
locked down to the upper track frame 4, but which can swing
upwards, for servicing, about an axis parallel to the
direction of travel of the envelope, with respect to the
upper track frame.
The modular construction of the apparatus is
apparent. Most of the components are designed to be held
in place by a single bolt.
CA 02019956 2000-10-25
As regards the spacing of the fluorescent bars 50,
this can be the same as the spacing of the ink bars 37;
alternatively the coded pattern of the bars 50 may be
different from that of the bars 37. Preferably, the
5 spacing is smaller for the first code; between 1/4 and 1/2
inch spacing is desirable between the right window edge and
the first bar, to allow for enclosure movement and clearing
of the window edge signal, and the last bar should be
spaced from the left window edge. In conventional window
10 envelopes these requirements will normally require the
first code to be "compressed" relative to the second code.
Figures 9 through 11 illustrate a somewhat
different print station 100, for use with an apparatus in
accordance with another aspect of the present invention.
15 The print station 100 is provided with two print heads 102,
(only one shown in Figures 9 and 11, and no print head
shown in Figure 10), which are separately mounted on a
carriage in the form of a printer plate 106. Each print
head 102 is mounted on a respective U-shaped printhead
20 plate 108, 100. Each plate 108, 110 is mounted to the
printer plate 106 through a parallelogram linkage for
up/down movement relative to the plate 106. Each linkage
comprises a pair of pivot arms 112, 114.
The arms 112, 114 are mounted to the plate 106 by
25 stationary pivot posts 116, 118. Posts 120, 122 extend
from the other ends of the arms 112, 114 in front of the
plate 106 (as viewed in Figure 9) to the rear of the plate
106 and one arm of the respective print head plate 108,
110. The other arm of each plate 108, 110 is provided with
30 a post which acts as a spring spacer 122. The springs 124
acting on the spacer 122 are formed of flat strips of steel
and extend from spring mounts 125 on the printer plate 106.
The springs are arranged such that an upper spring 124a
resists upward movement of the plate 108, 110, and thus
also the print head 102, 104, while the lower spring 124b
resists downward movement.
The printer cartridge (not shown) is mounted on the
CA 02019956 2000-10-25
31
front of the print plate 106 and is driven through a
coupling 126 and electric motor 126 mounted on the rear of
the plate 106.
The plate 106 is mounted on the apparatus frame
through an adjustable pivot mount 129 at one end of the
plate 106, and is provided with an adjustable bearing
portion 130.
The print heads 102, 104 of this embodiment operate
similarly to the print heads described above.
An alternative construction contemplated in the
invention is that the read and print heads are positioned
beneath the tray, in the lower track frame, and act
upwards. This arrangement would have the benefit that the
read and print heads could remain stationary as the
envelope passed: roller followers mounted in the upper
track frame could move to accommodate the thickness of the
passing envelope. Although the construction of the read
and print stations would therefore be simplified, such an
arrangement is not preferred because in that arrangement
the envelopes would travel face down: other postal
machinery requires the envelopes to be face up, so that
inverters would be needed.
Another alternative, in which the passing envelopes
are face up, is to arrange that the envelopes pass
underneath the tray, and are pressed upwards into contact
with he tray. Again, this measure would avoid the need for
the read and print heads to float, but the difficulty now
is that the ideal agency -- i.e. gravity -- for holding the
envelopes in position on the tray would not be available.
The conventional dot-matrix print heads as
mentioned will only print a height of about 3 mm, which is
why two print heads are provided in the preferred
embodiment. However, an alternative arrangement is
contemplated in the invention wherein the pins in the print
head are operatively engaged with a relatively wide strike-
bar. In this arrangement, when the pins are actuated, the
motion of the pins is transmitted mechanically to the
CA 02019956 2000-10-25
32
strike bar, which then strikes through the ribbon onto the
envelope. In that case only one print head would be
required, but a disadvantage lies in the fact that the
extra inertia of the strike-bar would slow the speed and
responsiveness of the print action.
