Note: Descriptions are shown in the official language in which they were submitted.
~4~373~
Bl~CK R UND OF_E INVENTION
1. Field of tha Invention:
The pr~s~nt invention generally r~:lates to impact
printers and, more oarticularly, to a h~mmer bank controller
for controllably moving and positioning a ban~ of print
hammers in an im~act ~rinter.
2. ~escript~on of the ~rior Art:
Impac~ printers are well known in the data processing
field for providing hard copy computer output. Typically, such
printers comprise a t~pe surface, such as a character drum
or chain, which continually moves past a printing station,
comprised of a bank of aligned individually actuatable
hammers. A paper web and an ink web are disposed between the -
hammer bank and the type surface. Printing is accomplished by -::
actuating each hammer at the appropriate time to propel it
against the type surface when the charact~r to be printed moves
into alignment with the hammer stri~in~ ace.
Typically, the number of hammers in the bank is e~ual
to ~he number of characters print~ble on each line. The
spaci~g between the centers of adjacent hammers, re~erred ~o
a6 hammer spacing is e~ual to the desired spacing hetween the
centers of adjacent characters or the character spacing. For
example~ if ~he character spacing is .100 inch, the hammer
spacing is .100 in. In a printer with a ca~ability of printing
136 characters per line, 136 hammers are required~ Each hammer
is used or printing a character at a different-print position
along the print line. The print posi~ions can be though~ of
as a sequence~o odd and even positions,with the odd hammers
in tha bank being aligned with odd positions and the even
hammers being aligned with the even positions~
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The co~t o~ fabricating and maintaining a ban~ with
a lar~e numbar of hammers which are closel~ and accurately
s~aced is quite high r thereby inc~eac2in~ the c~verall cost of
the im~act printer.
S[l~IMARY OF THE INVE,NTION
____
In view ~ the foregoing an object of the present
invention is ko provide an impact printer with a r~duced
number of hammers without reducing the number of print
stations, i.e., the number of characters prin~able per line.
Another object of the invention is to provide a
printer with a hammer bank and a hammer bank controller whereby
each hammer is accurately positionable at either of two pr~nt
positions thereby serving at more than one print position,
resulting in halfing the number of hammers in the bank.
15 ` A further object of the invention is to provide a
hammer bank controller ~or moving a hammer bank between two
positions and for accurately positioning the hank at ei~h~r
position each hammer is aligned with an even print position.
These and other objects of the invention are achieved
by pro~iding in one embodiment of an impact printer a hammer
bank in which the hammer spacing, i.e., the spacing between
adjacent hammers' centers is twice the spacing be~ween
adjacent print station centers or the print stat~on spacing
which represents the character spacing. The ban]c is movable
under the control of a multimode hammer ban~ controller betwe~n
two precise positions spaced apart a distance equal t:o the
~rint station spacing. In one ban~ position the hammers are
aligned with selected print stations, e.g., the odd stations.
In the other bank position, the hammers are aligned with the
other stations, e.g., the even stations. Thus, ~ach hammer i5
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succ~.ssively ali~nahle w.ith an odd and an even ~rint
station. The controller, respc)nslve to a command signal
includes m~an~ Eor movina~ the bc~k in a velocity mode from one
bank position to the other bank position, at a controlled
velocity profile. ~s the bank position to which ~he ban~ is
moved is approached, the bcm~ velocity i5 re~uced until it
reaches the desired position. Thereat the controller switches
to a position mode in which the bank is controlled to be
precisely positîoned and maintained at the dasired station.
A subse~uently received command signal actlvates the controller
`~ D~o~
to rèturn the bank to ~he othe~ in the velocity mode and
thereafter hold it thereat in the position mods.
In an embod~ment ~o be described hereinafter means
ara included ~or initializing the system to initially drive
the bank to one o~ the two bank positions and ther~a~ter move
it between the two positions in respone to each received
command sianal. In this embodiment means are provided in the
controller to sense, automatically, the bank positions at which
the ba~k is positioned and to provide an indication thereof
2 0 to the printer logic section which controls all the pr~ nter's
operations. :
BRIEF DESCRIPTION OF THE DRAWINGS
. . _ . _ .
Figure 1 is an isometric view of an impact printer
of ~he type in which the present invention is incorporated;
Figure 2 is a par~ial view of the hammer bank c~d some
of the circuit~ ~orming part of the hammer bank controller;
Figure 3 is a hlock diagram of the novel hammer bank
controller;
Figure 4 is a multiline waveform diagram u~eful in
explaining the operation of the novel hammer bank controller;
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Fic3ure 5 is a diagram of a ~ovel po~ition trans-
ducer used in the present invention;
Fi~ure~ 6 and 7 are combination block and schema'cic
diagrams oE circuits shown in Fi~ure 3; and
Figure 8 is a cross seCtiorl diagram of a Voice-coi
type motor used in the nove 1 controller .
DESCRIPTION OF THE P~E~ERRED EMsoDIMENTs
Attention is now called to Figure 1 which illus-
trates a hi~h speed impact-printer exemplary of the type
~enerally employed for data processing application~ Briefly,
the printer of Fi~ure 1 is comprised of a first frame ln
supporting-a hammer bank 12 and a paper stepping system,
~enerally comprised o~ motor 14 driving trackor chains 16.
The chains 16 oull edge p~rorated paper 18 from a supply
stack 20 past the hamrner :Eaces 22 of hammers 23 of the hammer
bank 12. The printer of Figure l also includes a second
frame 25 which is hinged with respect to ~he rame io. The
~rame 25 supports a movable type bearing surface such as a
horizontally oriented multitrack drum 26 which i~ rotated
~about its axis by a motor 28. Means are provided for passing
a printing ribbon 29 between the rotating charac~er drum 26
and ~he hammer faces 22.
In the operation of the printer of~Fi~ure 1, the
edge perforations of the paper 18 are engaged with the
sprockets of the chains 16 to thus enable the motor 14 to
pull the paper past the hammer faces 22. Normally, ~he
motor ~4 steps the papex one line at a time. prihting~
of course, can be accomplished only ~hen the frame-25 is
pivoted to a closed position relative to the frame 10 and
locked thereto/ as by cooperating latch portions 31 and 32
In this closed operative position, the hammer faces 22
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will ~e disposed very close to the paper ~rhich in tur~ will
be disposed very close to ~he printing ribbon 29.
As the character drum 26 rotates, it cyclically
passes different raised charact~rs in front o each hammer
face. By actuating a hammer at an appropriate time, the
hammer face is propelled against the backside o~ the paper,
forcing ths paper against the ribbon 29 and drum 25 to thus
print a character on the Eront side of the paper.
Each character along the line is p~intable at a
different print station. Typically, in prior art printers,
the number of hammers in the hammer bank 12 i~ equal to the
number of print stations, one ham~er per ~rint stationO For
example, for 136 characters per ~ine, i.e., in a printQr with
136 print stations with a character (sta~ion) spacing o~
0.100 in. a bank of 136 hammers with a hammer spacing of
0.100 inch is re~uired.
The present invention is directed to a printar ~ith
a hammer bank with ~ewer hammers than the numher o~ print
stations and with a bank controller for moving the bank
precisely between different positions, so that each hammer
i5 alignable successively to serve a~ more ~han one print
station.
In accordance with the present invention tha hammer
bank xather than beinq rigidly supported in structure 10 is
movable ~herein along the print line direction represented in
Figure 1 by num ral 50. To facilitate bank movement ~he end
plates 51 and 52 of hammer bank~12 are sho~n in Figure~ 1 ~nd
2 respectively, supported by flex pivots fil and 62, on structure
63 which forms part of frame 10. Figure 2 i~ a partial view
oE the bank and some o~ the parts included in bank controller
in accordance with the inven~ion. The bank is moved by a
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~037~1Z
voice coil motor 64. The bank velocity is sensed by a
magnetic velocity transducer, e.g., tachometer 65, which as
will be explained hcreinafter, pro7ides a dc output whose
amplitude is related to the bank velocity and whose polarity
is related to movement direction. A~ optical positioner
transducer 66, hereinafter referred to as the position trans-
ducer, is also included. As will be explained hereinafter, the
output of the latter is used to maintain the bank at one of
its desired positions, once reaching the position9 as well as
to control the motion of the bank between positions.
The novel hammer bank controller of the present
invention in addition to the motor 64, the velocity transducer
65 and the position transducer 66, which together can be
regarded as forming allhammer bank motor assembly~ also includes
circuitry best described in conjunction with Figure 3j which
is a block diagram of circuitry actually reduced to proctice.
The circuitry~ shown in Figure 3, will be explained in conjunc- `
tion with a multiwaveform diagram shown in Figure 4. The
circuitry includes a move clock generator and initialize
control unit, hereinafter referred to as input unit 70g a
function generator 72, a level detector 74, an output unit
,
75, consisting of a clock generator 76 and a clock gate 77, a ~ i~
position detector 78~ an analog switch 80, a crossover ;~
detector 82, a third crossover detector ~4, a summing amplifier ~ ;
86, a power amplifier 88 and a position amplifier 90O ~ -
The circuitry may best be described by assuming
that the hammer bank 16 is movable between a RIGHT position
and a LEFT position and that at a time to (see figure 4)~
the hammer bank is at t~e RIGHT position. The fact ~hat the
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bank ls ~t the PIGEIT position i~ indicated hy a hiyh bank
position (sP) output of position detector 78 on line l.00
~Figure 3) as represented by 101 in line i Figure 4.
direction flip flop in generator 72 is shown in a set st~te,
as represQnted by 102 in line c. ~s will be pointed out, this
1ip flop changes state each time th~ controller is commanded
to move the ban~ from one position to the other or during
initialization. When the bank is at the RIGHT ~osition ~or
the LEFT) the output signal on line 104 (Figure 3) ram
generator 72 to amplifier 86 is zero, as represented by 105
in line d. This output represents a velocity command signal
~HBCV). It is also supplied to level detector 74, whose output
represen~s a position mode signal (HBPM), which is supplied
to switch 80. When HBCV is zero, HBPM is high, a5 indicated
b~ 106 in line j. When HBPM is high, th~ controller is in the
position mode, and is in the velocity mode when HBPM is low,
as represented by 107 in line j.
When HBPM is high, sw~tch 80 is enabled. It supplies
the position signal HBPOS of position amplifier 90 to su~ming
amplifier 86. Ampli~ier 90 only amplifies~ ~he output o~ the
posi~ion transducer 66. As will be pointed out hereina~ter,
when the bank is at either position the ou~put of the trans- . :
ducer 66 is zero. Xt is positive or negative respectively
when the bank deviates to right or left of the desired
:position. Any deviation is amplified by amplifier 90 and
~is applied throu~h switch 80 to sU~ming ~mplifier 86. It
sums HBPOS with the tachometer output HBTS on line 110, (as
well as HBCV which is zero in the position mode), to prov~.de
an error signal HBEV to amplifier 88. .The latter drives
` 30 motor 64 to reduoo the bank deviation from the des~red
.
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position ~nd therehy m~intain the bank at the desired position.
The change in the bank position from one position
to the next is commanded by ~he printer logic section 115
(Figure 3~ by providin~ a hammer bank move command signal H~M* .
to input unit 70 on line 116. The p~inter logic section 115
is a part of the printer which controls all the printer's
operations. It is not part of tlle pre~ent invention. The
command is re~resented by a high-to-low transition 117 shown
in line a at time tl. Unit 70~ upon sensing a low on line
116 provides a move clock pulse [HMBC) on line 118 to function
generator 72. One HMBC pulse is represented by 120 in line b.
Its leading edge 121 drives the direction flin flop in
generator 72 (see line c) from the set sta~ assumed to be
present prior to tl and represented by 102 in line c, to its
reset state, as represented by 123. Whe~ reset, the ge~era~or
72 generates the HBCV (line d) which ramps up from ~ero as
represented by 124 in line d, until it reaches a desired level
125, As HBCV increases above zero,.the output HBPM of:
level de~ector 74 goes low tsee line j3 thereby indica~ing the
end o~ ~he position mode and the start of the veloci~y mode.
When HBPM goes low switch 80 is d~sab1ed. Thus, the po~.ition .~.
signal HBPOS is not applied to the summing amplifler 8Ç.
The velocity command signal (HBCV) is applied Yia
line 104 to the summing amplifier 86~ whose output HREV feeds
the power amplifier 88 which drives the hammer bank via the
motor 64. The bank velocity is sensed by the ~achometer 65
which develops a tachometer signal (HBTS) which i5 of opposite
polarity and essentially of equal magnitude compared to the ~ .
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applied velocity command signal. The tachoMeter signal (~IBTS),
shown in line e, is fed back to the summing amplifiex which
sums lt algebraically together with the velocity command
signal HBCV to generate the error signal, ilBEV. The error
signal thPrefore is proportional to the difference between the
applied velocit~ command signal and tne tachometer signal which
is fed bac,c to ~he summing ampl.ifier. Due to this basic servo
feedback action, ~he error signal HBEV applied ~o the power
amplifier 88 is automatically of the desired strength so that
when amplified by the power amplifier 86~ i~ drives the motor
64 with suffici~nt strength to cause the hammer bank to move
at the commanded velocity level.
As previously pointad out when the bank is at the
RIGHT (or LEFT) position, the output of the position trans-
ducer 66 and there~ore the output of ampli~ier 90 i9 zero.
The txansducer is designed so that a5 the bank moves ~rom -~:
one bank position to the other, its output crosses the ~ero
level threa times. The output of the amplifier 90, which is
the positio~ signal HBPOS, corresponding to the position
tran~ducer output, is shown in line f. As the velocity co~mand
signal first ramps up ~line l24 in line d) after tl and then
reaches its desired level 125, the b~nk is first accelerated
and ~hen m~ved a~ a constant velocity toward the ~EFT position.
Consequently, the output HBPOS crosses the zero level several
25 times. Each crossing is detected by crossover detector 82
which provides a correspond m g crossover pulset desi~nated
in line g by ~30.
Each of these pulses is counted by the detector 84~ .
The latter is assumed to be initially reset by ~BM* bein~
.~ 30 high during time to (see line a) to a low level as represented
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by 131 in lin~ h. Upon counting the third pulse its output
goes high as represented by 1330 The position transducer 66
is designed so that crossover detector 82 produces ~he third
pulse when the bank is close to the desired position.
The low to high transition of the output of detector
84 (see line h~ causes several things to take place. Most import-
antly~ it provides a rese-t control signal to the generator
72. The latter ramps, as represented by 135, from level
125 (see line d) to zero, which causes the velocity of
the bank to decelerate to zero velocity~ Also, the low to ;~
high transition of the output of detector 84 activates the
position detector 78. The position detector 78 in essence
monitors the polarity of the position signal, HBPOS. As will
be e~plained hereinafter when the bank moves to the LEFT
position during the deceleration time of the bank~ the
polarity of HBPOS is positive as designated by-136 in line f~ ~ ;
and is negative when the bank decelerates towards the RIGHT
position. When the position detector 78 is activated and the
position signal HBPOS is positive thereby indicating that the
bank approaches the ~EFT position the detector output BP goes
low as indicated by 137 in line i. However, if after the
third pulse the position signal HBPOS is negative the output
BP goes high.
The generator 72 is desi~ned so that after being
reset by detector 84 in response to third pulse, it ramps back
to zero (135 in line d) at a rate so that when its output,
i.e., H~CV, reaches zero, the bank is at the desired position~
LEFT, in the present example. When the velocity command signal
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I~CV decreases to zero at t2~ the output HBPM of le~el
detector 74 ~oes high, as re~ressented by 138 in line j,
thereby indicating th~ end oE the velocity m~de and the start
of the posit70n mode. In thi.s mode, as pre~iously pointed out,
S the switch 80 is enabled so tha~ the output of ~-IBPOS o:E
position ampli~ier 90, togethe.r with the tachometer si~nal
HBTS are supplied to the summing ampli f ier 86 along wit~ the
velocitv command signal (now zero) to control the error signal
aa~d thereby the bank position.
In the posi tion mode, the servo loop re~ponds to
the position signal HBPOS, corresponding to the actual bank :~-
position ~t or near the desired position, and the ~ed back
tachometer signal, ~IBTS. In this mode like in the velocity
mode, the velocity command signal HBCV is also sup~lied to
the summing amplifier 86~ Since HBCV is zero, baslc servo
feedback theory dictates tha~ b~th.the HBPOS`and HBTS si~nals
also be zexo. Any deviation rom zero producas an error s~gnal,
HBEV, which will cause an appropriate correction in the bank's
position so as to reduce the error. This basic feedback
correction thereby establishes and thereafter maintains the ~-
desired posi-tion which is the LEFr position in the present
example.
. When the HBPM goes h1gh at t2 (line ~) it ~lso
indicates the completion o the desi.red ban~ movement~ I~
activates the clock genQrator 76 in output unit 75 to send
a move complete clock pulse HBCLK*, represented by 139 in
line Q to ~rinter logic section 115. Its reception by section
115 indicates tha~ the ban~ i9 at one of the two desired
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p~sitions (I~T irl the present example). The specific
posi-~ion is indicated hy the level o~ the output BP o~ the
position d~tector 7û which is al50 ~;upplied to the section 115
via line 100. Briefly, O~ltpUt unit 75 produces the HACLK*
5 pulse ~rhen HBPM goes hi~h, the output o~ detector 84 is high
indicating the reception of three cxossover pulse 130 ~ ~d
signal on line 70a (s~a Figure 3) is hiyh. The latter is
high only if the o~her two signals occur within a fixed time
from the star~ o~ the move command signal HBM*.
AEter receiving the move complete clock HBCLK* the
printer logic section 115 sets its output line 116 to high
as indicated in Figure 4, line a at time t3 ~here~y acknow-
ledging the bank position. The bank is maintained at ~he
LEFT position by the position servo loop in the position mode
until a subsequent bank move command HBM* is rec~ived, which
is repre~ented hy another low level on line 116 . As long
~s the bank is a~ the LEFT position, the direction flip floP
in generator 72 is in its reset state; as represent d by 123
in line c. Also, the outpu~ BP of the detector 78 is low
(see line i) to thereb~ indicate to the printer logic sect~on
115 that the bank is at the LE~T position.
To move the hank from the LRFT to the RIGHT position
ano1ther HBM* is supplied by the printer lo~ic section 115 to
input u~it 70. In response thereto, input unit 70 produces
another pulse 120 which switches the state of the d~rection
flip flop in generator 72~ Since the lat~er was in its
raset state, it is driven to ~he se~ state. As a result,
the velocity co~mand signal HBCV, produced by ~he generator 7~,
ramps down ra~her ~han up, until it reaches a desired negative
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level with re~pect to zero. As soon as ~IBCV deviates Erom
~ero, level detector 7~ produces a 1~ ~IsPM which disable~
s~itch 80. Thus, the system is switched to the velocit~ mode.
The shape of the generator output HBCV and that of the
tachomete~ output HBTS when the controller is in the velocit~
mode when moving the ban~ ~rom left to right are t~e reverse
of their shapes when the bank is moved from right to
left,as shown in lines d and e.
When the third crossover is sensed, the detector 84
resets the runction generator 72 to ra~p back to zero and
thereby decelerate the bank. Also, the detector 84 activates
the po.sition detector 78 whose output BP changes from low to
high to indicate that the bank is approaching the R~GHT
position. When the HBCV reaches zero, HBPM goes high enabling
switch 80 and thereby switching ~he co~troller rom the
velocity mode to the position mode to hold the bank at the
~IGHT position. When HBPM goes high, the output unit is
activated to produce the move complete clock HBC~K* which i
supplied to the printer logic section 115. The latter then
returns the level of line 116 to high~ Since BP on lin~ 100
is high, it indicates that the bank is at the RIGHT position.
From ~he foregoing, it should be apparent that once
a bank position is reached, the controller holds the bank at ~:.
the position by means of ~he position servo loop. The actual
position o~ the bank is known by the printer logic section
115 by the level o~ the bank position BP output of position
detector 78. Position change takes place by providing ~he
controller with ~he hammer ban~ move command, HBM*. Upon
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receiving the command th~ contro~ler ~utomatically switches
to its velocity mode in ~rhich the bank i.~ driven from one
~os-tion, e.g., the Rl~,~IT to the other, e.g., LEFT. The
motion is controll~d by ~he velocit~ servo loop in which the
output of the power ~mplifier 88, which drives the motor 64
to dri~e the hammer bank, is a unction of the velocity command
signal HBCV from ~he function generator 74 which is compared
~summed) with the fed back tachometer signal ~IBTS by the
summing amplifier 86. In the velocity mode, switch 80 is
opened and therefore the ~o~ition ~ignal is inhibited from
reaching the summin~ amplifier.
Before describing other novel asp~cts of the
invention, attention is directed to Figu.re 5, useful in
expla;ning the novel position transducer 66 which drives the
position amplifier 900 The transducer ~6 includes a posit~ n
encoder ~PE) track which is mounted on a sha~t 150 (s~e
Figures 2 and 5) which is in turn coupled to ~he movable
; hammer bank. Thus, whenever ~he latter moves the po~ition PE
track moves in the same direction. Fixedly ~ositionad on one
side of the PE track is a light source such as a light emittin~
diode (LED), whîch is not ~hown, and a pair of photocells
PCl and PC2, also referred to as the top PC and bottom PC,
respectively. They are fixedly positioned on the other
side of the PE track. The track, which has top and bottom
-25 halves, de~ines a light and dark pattern. The dark pattern
areas are represented by the cross hatched areas in Figure 5.
Light from the light source reaches the to~ PC (or bottom PC)
only when a light Pattern area of the top ~or bottom) half
of the track is between it and the light source, while a dark
area of the top (or bottom) half blocks off any light from
the top (or bottom)`~C.
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The ~wo PC ' s are interconnected as show~ in Fi~ure
5. I,ines 151-153 together represent the input l.ine to the
position amplifier 90 whose O-ltpUt HBPOS is a function of the
rela~ive position of the P~ track ~ith r~spect to the PCs.
5 Whenever the PE track is at point A (with respect to the PCs),
only the top PC is the recipient oE li~ht, since light tr~ck
area 1~5 is between it ~nd the LED, while all light -to the
bottom PC is blocked off under these conditions~ EIBPOS is
assumed to be pos itive as represented bv 156. C'onversely,
10 whenever the bottom PC is sensing the li~htl such as when the
PE track is at point K and area 157 is between it and the LED
~hile light to the top PC is blocked off, the positio~ signal
is negative, as represented by 158.
The PE track pattern i5 designed and attached to
15 the shaft 15~ so that when point B is aligned with the two
- PCs the ha~ er banlc 12 is exactly at the RIGHT position,
and ~hen point ~ is alignPd with the PCs, the bank is
exactly at the ~EFT position. The distance betw~en points B
and J is the h a r stroke distance which is equal to the
20 desired character spacing, e.g., 0.100 in~h. Whenever any of
points B, D, F, H, or J is aligned with the two PCs both PCs
receive equal amouhts of light and therefore the si~na1
ampl~tude is zero. It is positive (or hi~h) when the track
is at any of points R~ A, E or I and is negati~e ~or low)
at points C, G, K and L. Points R and L respectively represent
positions of the track when the bank abuts against right and
left bumpers, whose functions will be explained later~ From
the foregoing, it should be appreciated that as the bank ~oves
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between the RIGHT and LEFT p0SitiOIIS (between points B and J)
only three ~ero crossings of HBPOS occur. It is these three
zero crossings which are converted by detector 82 into the three
pulses 130 which are counted by detector 84.
From the foregoing description and particl~arly
Figure 5, it should be apparcnt that when the bank is at the
RIGHT position (point B3 or the LEFT position (point J),
deviations of the bank to the right or left result in a
positive or negative position signal, respectively. The
positive or negative position signals when fed to the summing
amplifier cause the power amplifier to drive the bank to the
left or right respectively to reduce the position signal to
zero. Thus, the position servo loop maintains the bank at
the desired bank positions. To insure that the position
signal is positive or negative when the bank is to the right
or left respectively of each position, the track pattern has
~o be designed to produce an odd number of crossover points.
From Figure 5 it is also seen that the ~ero cross-
over points between positions such as points D, F and H are
equally spaced between the two positions. Actually, due to
their spacing each crossover pulse occurs after the hammer bank -~
is moved 1/4 the stroke or distance between the two positions.
When the hammer bank is moved from the LEFT position (point
J) to the RIGHT position (point B), the third pulse occurs
at point D when the hammer bank is 1/4 stroke distance from
the RIGHT position. Conversely when moved from right to left
the third pulse occurs at point H when the hammer bank is 1/4
stroke distance from the LEFT position (point J). Thus~ the
function generator resetting occurs when the hammer bank is 1/4
the stroke distance away from the position to which it is
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l~lnen the power to the printer is ~irst turned O~
the controll~ is in the ~ositiol~ ~ode. F~owever, the e~act
position of the bank is not known. The position servo loop
may lock the bank a~ any of poinlts B, F or J, i.e., at any
point in which the position si~nal i5 zero with a positive
polarit~ adjacently to the ri~ht and a ne~ative po:Larit~
adiacently to the left. Since only points B and J represent
desired bank positions, it is necessary to initialiæe the
controller to drive the bank to either the RIGHT p~sition (point
B) or the LEFT position (point ~). The input unit 70 includes
logic circuitry designed to au~omatically`drive the bank to
one of the desired positio~s. The position detector 78 is
designed ~o sense to which of t~e t~o desired positions
the bank is approaching or at which it is positioned to
provide an appro~riate out~ut ~BP~ for use by the ~rinter logic
section 115. The input unit is designed such that the bank
continues to move alternately between the LEFT and RIGHT
posltions until the integrity o~ posi~ion de~ector can be
assured.
Attention is now directed to ~igure 6 wherein the
input uniS 70 is diagrammed in block form. The unit consists
of a dual triggerable one shot, which together with related
circuitry i5 desi~nated by U106~ a trig~erable one shot U112
and a la~ch circuit consisting o~ two gates U108. The
operation of the input unit may best be described in conjunction
with Figure 4. The initialization is star~ed b~ ~a hammer
bank move commcmd HBM* (line a) which is applied by the printer
logic section llS by driving line 116 low. In Figure 4, ~his
command is assumed to start at time t When HBM* is applied,
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~L~373~
i.e., line 116 ~oes low, U111-12, renresen~:in~ the output
at p;n 12 of Ulll ~oes hiqh. I t triggers th~ re~riggerable
one S~lOt 106 causin~ pin 13 (U106-13) to go high, as repre-
sented in line al in Fi~ure ~. This in turn tri~gers the other
half of the dual retri~gerable one shot 106 so that U106-5
goes high fo.r a sh~rt duration, representin~ the move clock
(HBMC) pulse 120 shown on line b.
U106-5 is connected to the direction flip ~lop,
designated U103 in the function ~enerator 72. Ba~ically, the
HBMC (pulse 120~ switches the flip flop U103 from its previous
state to its other state. As shown in ~igure 4~ it is
assumed that prior to tx, U103 is set (see line c). Thus,
at tx it is reset. As a result, ~he function generator 72
output, HBCV ramps up (line d) thereby driving the bank to the
left. For explanatory purposes, let it be assumed that at
tx the bank was initially locked at point F (Figure 5)~
Therefore, as the bank moves to the left only two pulses 130
will be produced (see line J) as points H and ~ are crossed~
The bank is drive~ past the desired LEFT position until it
reaches a left bumper,~represented in Figure 5 as point L.
The left bumper prevents an~ farther leftward motion of the
bank, even though the function generator 72 continues to
provide the velocity command signal. The bank is assumed to
reach the left bum~er at time t~. ~t time tz, ~106-13 ti~es
o~t. U106-4 gving high at this time (see line a2) trig~rs
U112 50 that U112-5 goes high (line bl). T~is is so since
U106-4, having been low during the preceding time ~eriod, had
set the associated latch circuit comprising of gates U108-8
and U108-6, which removed the reset level to U112.
-19- ::
~, .
. , - . . . . ~ ~
~ /37~
~L~37~%
When IJ:L12-5 goes high, it acti~tes an Or gate U104
in the function ~enerator 72 to reset both rlip ~lops u101-5
and u101-9 in the Eunction ~enerator. These two flip flops
~Jhen both are reset cause the integr~tor-amplifier 180 in
the function ~enerator 72 to rarnp back to zero from its
previous level. In the particu:Lar example, the voltage ramp~
down thereby ~ ~ing the bank t~ return ~r~m th~ lQft bumper
toward the LEFT position during the ensuing posi~ion mode.
The length o:E time that U112-5 is high is chosen ~o 'chat after
the HBCV reaches zero (line d) and the con~roller is in the
position mode the controller remains in this mode long
enough to drive the hank to the LEFT position, assumed to be
reached at time tp. The duration that U112-5 is high repre-
sents a ~orced voltage reset pulse FHBR shown in line bl~
Although the bank is now (tirr.e tq) ~t a valid
position (LEFT in this example), the status o~ the position
detector is uncertain. This is true since the operation of ~he
position detector (as described previously) is dependent
upon the detection of three crossover pulses 130 during bank
~0 movements~ Consequently, an additional HBMC 120 is ~enerated
at time tq so as to initiate an additional bank movement.
This is accomplished by U112-5 tline bl) going 1.~ while
U111-12 is high which tri~gers U106-13 (line a2). U106-13
~oing high in turn triggers U106-5, the output of which is
HB~C (line b).
For the LEFT to RI OEIT bank movement initiated at
time tq, three crossover pulses 130 are produced beore it
reaches the RIG~T position just like in normal operationD
Thus, the output of de~ector 84 goes high at time tr which
30 resets the function ~enerator 72 causing HBCV to ramp towards
-~0 - .
l~ ~ 73/372
, _
~ 3~ LZ
æero. At time t HBCV reaches zero and therefore HBPM goes
high. It now acti~ates the output unit 75. Since the output
of detector 84 is hi~h (line h) and since one shot IJ106-13
did not time out ~t to acti~ate U112-5, the output unit
produces the IIBCLK* pulse to the printer logic section 115.
The la~ter then sQtS line 116 at: time tt to high~ This in
turn resets U106-13 so that it cannot time out to trigger
U112-5. Thus, the initialization o~eration is completed and
the position servo loop holds the bank at the RIGHT position.
In the present invention, the on-time of U106-13 .
desi~nated as D in line al is chosen to be greater than the
period from the instant the bank move com~and HBM* is normally
received until tha move is acknowledged through receipt o
HBCLK* by ~he printer logic and line 116 returns to high.
The on-time of U112 designated D1 in line bl, is chosen to
drive the bank during the initialization process from one of
the bumpers to the adjacent desired position, first by ~he
velocity signal which ramps bac~ to zero, and then by the
position sexvo 103p.
It snould be pointed out that the initialization
process is independent of the positian of the bank at the
time the process starts or ~he state of the d.irection flip
flop. In the foregoing, it was assumed that the airection
flip ~lop was set prior to the initialization at t . Thus,
the ban~ was driven to the lef bumper. If the flip flop is `
reset prior to initialization, ~he first HBMC pulse drives
the bank to ~he riaht bumper assumed to be at point R (see
Figure 5).
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~373~2
Attention is again directed to Figure 6 in connection
with which the function gener~tor 72 will now be described
in fuxther detail. The ~enerator 72 in addition to direction
flip flop U103 and gate U104-4 includes a left flip flop U101-5
and a right flip ~lo~ U101-9 and an integrator-amplifier 180.
The integrator amplifier 180 ~r:hich is basically a closed
loop integra~or circuit is comprised of a summiny amplifier
U115-1 and an operational ampl.ifier U115-7. ~hen the bank is
at either the LEFT or RIGHT position both U101-6 and U101-8 are
high, since both flip flops are in a reset state, and the
output HBCV of circuit 180 is 2éro. When the bank is at the
LEFT position, U103,-5 i5 low and when the bank is at the
~IGHT position U103-5 is high (see line c).
Assuming that the bank is at the RIGHT posi~ion as
shown at time ~1 in line f Figure 4, U103-5 is ~igh and
U103-6 is low (see line c). Also both U101-~ and U101-8 are.
high slnce both flip flops were previously reset, see lines cl
and c2. When the next HBMC pu~se 120 is applied to initiate
a bank mOVemQnt~ pulse 120 clocks both U101 flip flops~ Since
U103-5 is high, it sets the left U101-5 flip flop so that
U1~1-6 goes low. U101-8 remains high. Also, the HBMC pulse ~-
toggles U103-5 so that U103-5 no~ goes low (after setting
U101-5 to high and U106-6 to low). -
Since U101-6 is low and U101-8 is high, Ulll-6 and
Ulll-5 axe high and low, respectively. When V111-6 goes
hi~h, a posit:ive voltage is reflected at U115-2 while U115-3
is at zero ~olts. This imbalance of the e~uilibrium co~dition
of ~he summing amplifier forces U115-1 to go low. This in
tuxn sets up a charging path via Rl to the low level at
-22-
, .
,~,,
, .. ,~. ...._...
.
.
-
:L~1373~;~
U115-1 for integrating capacitor Cl which comprises the
feedback loop of operational amplifier U115-7. As Cl begins
to charge up the output at U115-7~ which represents HB W~ -
begins to ramp up~ as represented in line d by 124~ HBCV
continues to ramp up until HBCV, fed back to pin 3 of U115
via R2 equals the potential at U115--2. When this condition
is established V115-1 goes to zero~ te~mating the charging
of the integrating capacitor. Thus, HBCV remains at a
constant level ~125 in line d). When the third crossover pulse
(130) is detected by detector 84 it activates via line 200
Nor gate U104 so that U104-4 goes low, clearing or resetting ~ ,
both UlQl flip flops. Thusg U101-6 goes highg U101-8 remains
high since it was previously in a reset state.
When U101-6 goes high, U111-6 goes low and therefore
U115-2 returns to zero volts. Since the voltage at U115-3 is
still high (equali~ed at the previous high potential of
U115-2 during the ramp up)~ U115-1 goes high. This then sets ~ ;
up a ~ scharga path via Rl for Cl~ Thus, HBCV ramps down `
until the voltage at U115-3 is equal to the zero volts at ~`
U115-2. This occurs when HBCV is back at zero volts, at ;~ ;
which time the position mode is initiated.
The function generator 72 functions in an analo
manner when the bank is at the LEFT position and the move ~;
command HB~ is received to move the bank to the right. When
in the LEFT position, U103-6 is high. Thus, when clocked by
HBMC pulse 120, the right flip flop U101-8 goes low. U101-6
remains higho When U101-8 goes low, U111-4 goes high and a
positive voltage is applied at U115~3. Since U115-2 is at
zero, the imbalance condition causes U115-1 to go high~ This
- , ~ . . ~ , : .
:., ~ . ,: .,. - : ~- .
. . . .
.. . . . . . . . . . .
73/37~
, . ,~,
73~
sets up a discharge path via ~1 to U115~1 for Cl. Conssquently,
~I~CV at U115-7 ram~s down. It continues to ramp down unt11
- th~ potential at U11$-3 decreases to zero to e~ual the
potential at U115-2~ Thus, HBCV remains at a constant level.
It rema.ins at this level until U10~-4 goes low again (when
the third crossover pulse is detected) resetting U101-8 to
high and therefore U111-4 to low. As a result, U115-3 ~oes
to a voltage slightly more negative than zero volts. Since
U115-2 is at zero volts U115-1 goes low. This sets up a
charging path via Rl to thereby charge up Cl. Thus, HBCV
at U115-7 ramps up toward zero vol~s, at which ti~e U115-3
is at zero volts as is U115-2. This causes U115-1 to return
to zero there~y terminating the charging of Cl and HBCV
remains a~ zero volts.
As s~own in Fi.gure 6, U101-5 and U101-9 are con~ected
to a Nand gate 201, which together.with the output HBCV of
generator 72 at U115-7 are applied to the level det~ctor 74~ -
As previously explained the latter's output, HBPM is high ~ ;
(line j) when HBCV is at tor near~ zero volt and i5 ~ OW when
HBCV is other ~han zero volts. After the third crossover
pulses hoth U101-5 and U101-9 are low since both flip flops are
reset by U104-4 going low. Thus, the output o~ 201 is high.
This output is shown supplied to one input of a.comparator 203.
Comparator 203 compares HBCV with zero volts as well as
~5 comparing the out~ut of gate 201 with ~ero. If either of
these inputs are sufficiently different from zero the output
from the compara~or is low. This output is HBPM, which when
high indicates tha~ the controller is in the position mode. :
.. ..
-24-
... . ...
- , .: : ,, : ~ : . . .. :: .
. :- -: -, : : . ., :
. - . . : . . ..
~L~373~
As previously e~plained HBPM, when high, is used to enable
switch 80 to enable to position signal HBPOS to reach the
summing amplifier for the position servo loop. HBPM is also
supplied to the output unit 75 which produces the move complete
pulse HBCL~* (see line ~
As previously explained ~CLK~ when received by the
printer logic section 115 indicates that the bank movement is
complete. ~hich position the bank is at is indicated by the
BP level on line 100. In accordance with the present
invention às previously pointed QUt HBCLK~- is produced only
when the bank reaches one of the positions in a normal manner (as
defined as having su~cessfully detected three crossover
pulses 130 during the bank movement). Note that HBCLK~ is not
produced when the bank reaches one of the positions from one -
of the end bumpers during the initialization process. For
example, HBCLK* is not produced when the bank reaches ~he
LEFT position at time tp. ' ' ' !
As shown in Figure 3, HBPM which is the output of
comparator 203 is applied to clock generator 76 which in
essence is one shot. It is triggered by 203 going high `~
to produce a clock pulse HBDOS shown in line k, and applied
to the clock gate 77. The later is actually a three-input
gate. If during the duration of HBDOS, U112-12 is high ~which ;
is the case as long as U106-13 did not time out) and the third
crossover detec*or having sensed the third pulse switches
from low to high as shown in line h, gate 77 produces the
HBCLK* pulse. This is the case in normal operations. However,
if during the move operation, such as during initialization, ;~
~112-5 is triggered (see Figure 4, line bl at time t2) U112-12
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.. ... .. . . . .. .
73/372
1~(33~73~'~
goes low. Thus, when H~PM goes high ~line j) after t and
~ before tp even though clock 76 produces the HBDOS pulse n
,' (line k), ~a~e 77 does not produce the ~BCLK* pulse (line 1).
A~ previously indicated the crossover detector 82
responds to the position signal HBPOS from position amplifier
90 and produc~s a pulse 130 (line g) e ch time the position
signal crossea zero in either direction. Thus, it can be
implemented as a zero-crossing detector well known in the
art. Detector 84 is in essence a counter which produces a
high output (line h) after three puls2s are coun~ed by it.
For explanatory purposes5 it may be deemed to be reset to
provide a low output (see line h) whenever ~BM* goes high.
As previously indicated the position that the bank
is approaching or is located at is indic~ted by the BP output
of detac~or 78 (line i). It is high when the bank approaches
or is at the RIGHT position and is low when the hank approaches
or is at the LEFT position. In simplest form, the detector
84 can be thought of as comprising a flip flop 210 and
comparators 211 and 212 as shown in Figure 7. FF 210 is
clocked by the low to high transition of the output of detector
84. If the position signal HBPOS is below zero, comparator 211
provides a high output causing FF 210 to be drive~ to its
set state so that its Q output which is BP is high. On the
other hand, when ~BPOS is above 2ero, comparator ~12 provides
a high output causing FF 220 to be reset. Thus, BP goes low.
Attention is now directed to Figures 1 and 2. As
previously explained the bank movement is achieved by means
of the motor 64 which is driven by the output of the powsr
amplifier 88 (see Figura 3)~ Since the bank 12 is ~upported
-26-
3'73~Z
by the ~lex pivots 61 and 62 very little driving force is
required. Also~ since the distance between the two desired
positions which is the stroke distance is only the character
spacing typically 0.100 in. the distance which the bank has
to be driven is very small. In practice, any small reversible
motor can be used as motor 64. In one embodiment actuall~
reduced to practice a voice-coil type motor or actuator was
used as motor 64. As used h~rein a voice coil motor or
actuator refers to a unit in which a movable member on which
a coil is wound is located in a magnetic field. The motion
of the movable member and its direction are a function of
the current amplitude and direction of ~low respectively.
An embodiment of such a voice_~oil motor 64 is shown !~
,'. : :, .
in cross~section in Figure 8. The motor includes a member 230 `-~
which is connected to the bank end plate 51. Member 230
houses a m~ti-turn conductor coil 231.
The member 230 which is the moving part of the motor
is supported between an upper magnetic structural member 235
and a lower magnetic structural member 238 which supports a
pair of bar magnets 240 and 241. The magnet configuration
produces a magnetic flux path, generally represented by dashed
line 246. It extends across the gap between magnets 240
and 241 and the member 235, a gap in which member 230 with
coil 231 are located. As should be readily apparent the motion
of the member 230 in the plane in which it is supported is
a function of the current and its flow direction in coil 231.
As shown in Figure 8, end plate 51 of the hammer bank 12 is
connected to member 230. Thus, the hammer bank 12 is moved
by member 230 of motor 64.
-27-
' ~ ' . ,
~37 '' ~
From the foregoing, it is thus seen that in
accordance with the presel~t invention, a prin~er is provided
in which the entire hammer bank is m~vable under the control
of the hammer bank controller. As described, the hammer bank
a~ter initiali~ation is moved between two positions (RIGHT
and LEFT). By spacing the positions of distance equal to the
character spacing, each hammer in the bank may be positioned
at either of two print stations. In the hammer bank the
hammer spacing is twice the character spacing so that when the
bank is at one position the hammers are aligned with hal~ the
print station, e,g., odd stations, and in the other position
the hammers are aligned with the even stations. Thus, the
number of required h a ers is only half the number of printable
characters per line.
Although the invention has been described with
positioning the hammer bank at two stations, it should be ;~
apparent that the teachings may be modified to position the
hammers at more than two stations and thereby further reduce -
the number of required hammersr For example, with three -
hammer bank positions and with a hammer spacing of three times
the character spacing each hammer can be positioned successi~ely
at three print stations to reduce the number of required
hammers to one third the number of characters per line. For
three position controls the dimensions of the PE track pattern
(see Figure 5) may be modified so that the distance between
point B row representing the RIGHT position and po mt F equals
a character spacing and the distance between point F and point ;
J, now representing the LEFT position is equal to one character
spacing. In such an embodiment only one crossover pulse will
be produced between positions. It can be used rather than
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73/372
.. ..
10373:a2
the -third crossover pulsR hereinbefore discussed. In ~uch
an emhodiment the ~osition to which the hammer b~nk is driven
may be determined in the printer ~o~ic section by counting
the number of HBM ~ulses from the time of initialization
5 rather th~n from the position detector.
Although particular embodiments o-E the invention
have been described and illustrated herein, it is recognized
that modifications and varia~ions may readily o~cur to those
skilled in the ar~ and consequently, it is intended that the
claims be interpreted to cover such modiEicat}ons and ~.
equivalents.
.;
-29- .;
~ ' .
