Note: Descriptions are shown in the official language in which they were submitted.
~C~5531~
This invention relates to sewing machlnes and in particular to
a low inertia work holder control system ~or an automatic sewing machine.
In an automatic sewing machine, apparatus must be provided for
moving a work piece relative to the sewing needle. GenerallyJ it is
the work piece that is moved. The speed at which the work piece is moved
is limited by the inertia of the moving parts of the translation system.
In particular, with respect to movement of the work pieceJ the inertia
of the translation system and work holder may prevent rapid acceleration
and deceleration which are required to move the work piece over a distance
quickly.
In prior automatic sewing machines having a work holder moving
in either a linear coordinate system or a polar coordinate system, the
inertia of the moving parts has prevented rapid acceleration and decelera-
tion of the work holder. It is therefore one object of this invention to
provide an automatic sewing machine with an improved work holder support
and translation system which overcome the defects of known prior art
devices. It is another object of this invention to provide an apparatus
having a lower inertia characteristic and greater acceleration and de-
celeration characteristics than prior known devices. Further other and
additional objects of the invention will become apparent from the descriptionJ
drawing and claims which follow hereinafter.
The invention discloses two cable systems connected to the work
holder and adapted to move the work holder in two coordinate directions.
The power to move the work holder is derived from two stepping motors
ixed in position with respect to the sewing needle, each of which is
connected in a driving relationship to its respective cable system. The
work holder is connected to an e~tendable arm carried on a pivoting arm.
The latter pivots about a pivot point to a specified angular position con-
trolled by the first cable system. The extendable arm moves radially over
the pivoting arm and its position on that arm is controlled by the second
~L~S53~6 : ~
cable system.
Also disclosed is a compensating coordinate system. This coordin-
ate system is neither polar nor rectilinear although it moves the work
holder relative to th~ s~wing needle in what approximates, within predefined
limits, a rectilinear coordinate system. A first pulley connected to the
cable system which drives the extendable arm is located so that a line from
the point where oneend of the cable is connected to the extendable arm near
the work holder to the point where the pivotable arm pivots is parallel to
the portion of the cable from the connection point to the pulley when the
pivoting ar~ is at the center of its travel. In addition, the needle lies
on the line from the connection poin~ to the pivot point at the pivoting
arm's center of travel. The other end of the cable may be connected either
to a spring tension device to keep the cable taut or to the extendable arm.
According to one aspect the invention is an automatic sewing
machine comprising a sewing needle, a work holder for holding in place a
material to be sewn, the work holder being movable with respect to the needle,
first driving means to move the work holder in a first coordinate direction,
second driving means to move the work holder in a second coordinate direction,
a homing assembly for positioning said work holder at a predetermined home
position in said first coordinate direction, said homing assembly being
driven in positional synchronism with movement of the work holder in the
first coordinate direction, said homing assembly comprising an adjustable
position indicating means, saîd position indicating means being connected
to and driven by one of said driving means, and a position reading means
providing an output signal in response to the position indicating means,
adjustment of said indicating means causing a change in said home position.
According to a second aspect the invention is a homing assembly
for positioning the work holder of an automatic sewing machine at a predeter-
~ined home position, comprising: a work holder; a support assembly; a shaft
rotatably received in said support assembly; a position indicating element
secured to and rotatably movable with said shaft, means mounted at: a pre-
selected rotational position relative the rotational axis of said shaft for
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determining the rotatable position of said element and for generating a
signal; means for adjusting the relative angular position of the indicating
element and determining means for a given positi.on of the work holder to
select said home position; means for moving said work holder in positional
synchronism with the movement of said position indicating element toward
said predetermined home position; and means responsive to said signal of
the determining means for stopping the work holder at said predetermined
home position.
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l~S53~6
~.
,~
~ er features, objects, and advantages of the invention ~:.
will be described below in connection with the following drawings in
which: ;~
Figure l is a side elevation view of portions of a sewing
machine incorporating the invention; ~ -~
Figure 2 is a sectional top view of a portion of the sew-
ing machine taken along line 2-2 of Figure l with certain parts
removed;
Figure 3 shows one of the novel stepping motor pulleys;
Figure 4 is a pictorial drawing of the extendable por-
tion of the arm and work holder assembly; ~.
Figure S shows the extendable arm bracket for the lower
clamp;
Figure 6 is a perspective view of the pivotlng arm portion
of the work holder assembly;
Figure 7 is an exploded pictorial of the synchronizer
unit; ' .
Figure 8 is a block diagram of the electrical signal ..
flow paths for the machine;
Figure 9 is an exploded pictorial of the homing and
limit assembly; ` :~
,
Figure lO is a cross sectional view of tlhe extendable and
pivoting arm assemblies taken along line 10-10 in Figure 2; :
Figure 11 is a cross sectional view taken along line
11-11 in Figure 2 showing the homing and limit assembly;
Figure 12 is an enlarged view of the spring loaded strip- ~ .
per mounted on the needle bar; and : ~:
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3~553~
Figure 13 is a hlock diagram of the central control logic.
Referring to Figurc 1, the mechanical portion of a program con-
trolled sewil1g machine according to the invention includes an overhanging
arm 12 which carries mechanical power to a sewing needle 14. The work
piece to be sewn (not shown) is held generally in a work holder 16 which
is moved in a horizontal plane by a novel power translation system. This
system is driven by a pair of stepping motors 18, 20 which supply driving
power to move the work holder in two coordinate directions. The power
translation system acts to translate the rotary drive of the stepping
motors to movement of the work holder in its two coordinate directions.
The stepping motors are driven by electrical signals from novel
electrical circuitry. These signals are synchronized to the movement of
the needle 1~ into and out of the work piece by a novel electromechanical
synchronization ~mit 22. Unit 22 :is connected to and driven by a con-
ventional hand wheel 24 of the sewing machine and supplies synchronization
signals to the electrical circuitry.
In this particular embodiment, the work holder is moved in a pre-
determined pattern relative to the movement of the sewing machine needle.
A sequence of instructions describing the desired pattern of movement and
stitching of the work holder 16 is stored in a storage element having a
plurality of randomly addressable storage locations. Preferably, the
storage element is a programmable read only memory. In such devices the
instructions stored in the various storage locations may be changed to
describe a desired new pattern of movement, The storage element may also
be, for example, a randomly addressable read only memory in which the
stored instructions may not be changed to describe a new pattern of move-
ment. Solid state memory elements of both types are available and are
preferred.
Electrical control circuitry is provided which reads information
3~ from as many of the addressable locations of the storage element as
.. . . .
l~S5~
necessary to obtain a complete instruction for each movement o~ the work
holder. It also converts each instruction into a sequence of pulses to be
applied to the stepping motors, and thus drives the motors at a time when,
as indicated by the synchronizing unit 22~ the needle 14 is not engaged
in the work piece. In this way, movement of the work holder is timed not
to adversely affect the movement of the sewing needle 14.
Referring to Figure 2, the power translating system used to trans-
mit power from stepping motors 18, 20 to the work holder 16 comprises two
cable systems, one for each coordinate direction. The cable systems are
arranged as follows. Pulleys 26, 28 are attached to shafts 30, 32 of
stepping motors 18, 20. Cables 34, 36 are secured around pulleys 26, 28
respectively by screws 38, 40 respectively. In this manner, the rotational
movement of the stepping motor shafts 30, 32 is converted into linear move-
ment of the cables 34, 36.
Referring now to Figure 3, each of pulleys 26, 28 has a groove 42
in which a cutout 44 is formed. The cutout extends a distance circumferen-
tially on the core 42 of the pulley between its ends so that at least part
of a turn of the cable is made above the cutout 44 and part of a turn of
the cable is made below it. Between these turns, the cable drops into the
cutout 44 where it is secured, for example, in pulley 26 by a screw 38.
In this way, the appropriate cable is rigidly secured to each pulley.
At one end, cable 36, which pivots the work holder about the pivot
pin 68 (see figure 10), is attached to a base plate 46 of the sewing machine
by a hook and shoulder screw 48. The cable is then threaded around a free
turning pulley 50 attached to the underside of a pivoting arm 52 ~see also -~
Figure 6). The cable is then threaded around a free turning pulley 53
also attached to the base plate 46, from which the cable makes a complete
turn around a large pulley 54 secured to a homing and limit assembly 55.
The cable is then threaded around pulley 28 of stepping motor 20, as pre-
3~ viously described, and then around a free turning pulley 56 attached to the
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~mderside of the pivoting arm 52. The end of the cable is then secured
to a tension assem~ly 58 which includes a compression spring 60, one end
of tlle spring bearing against a support 62 secured to the base 46 and the
other end of the spring bearing against a draw bar assembly 64 to which
the cable 36 is secured. The draw bar assembly has a nut 66 which to-
gether with ~he spring 60 regulates the tension on cable 36 to insure
that no part of the cable becomes slack.
In operation, as stepping motor 20 rotates pulley 28 the cable
36 pulls one of the pulleys 50, 56, depending on the direction of cable
movement away from a center line between the needle and the pivot
pin 68 and thus rotates the arm 52 about the pin 68 to one side or the
other of the clamp's center position shown in Figure 2. Pivoting arm 52
carries with it, as it pivots, an extendable arm 70 (Figures 4 and 10),
to one end of which is affixed the work holder 16. Thus, as a~m 52
rotates about pivot pin 68, so do arm 70 and work holder 16.
Affixed to a post 72 at the opposite end of the arm 7Q from the
work holder is one end of the cable 34 which controls the radial movement
of the arm 70 ~see Figures 2 and 10). From there, the cable is threaded
around a free turning pulley 74, attached to base plate 46 by means of a
shoulder screw 76, and then around a free turning pulley 78 which is
attached to the base plate 46 by means of a shoulder screw 80. The
cable is next threaded around a free turning pulley 82 of a cable ten-
sioning pulley assembly 84, also mounted on the plate 46, from which it is
trained around pulley 26 for 2-1/4 turns. The cable is secured to the
pulley 26 by a screw 38 as previously described. Cable 34 is then threaded
completely around a large pulley 86 attached to a homing and limit assembly
88. From there, the cable then extends around a free turning pulley 90
attached to the base plate 46 by a shoulder screw 92. The cable terminates
at the underside of the extendable arm 70 at a connecting point 94 mounted
at a point on the underside of the arm 70 which lies on a line between the
~5533~G
pivot pin 68 and the scwing necdle 1~ when the pivoting arm 52 is in its
center position. Pulley 90 has a circumferential groove (not shown) for
the cable 34.
Cable 3~ is maintained under continuous tension by the cable
tensioning pulley assembly 84. This assembly consists of a compression
spring 96, a support 98, a draw bar 100, and a nut 102. Instead of ~he ?
hook of assembly 58, the reaction force which tensions cable 34 is trans-
mitted from the draw bar to the cable through a pulley block 104 and
pulley 82. In this particular embodiment, pulley assembly 84 is advan-
tageously placed, as shown, physically separated from arms 52, 70, first,
because this arrangement decreases the weight of pivoting ar~ 52 and
extendable arm 70, thereby reducing their inertia, and second because,
as shown, assembly 8~ is more accessible for maintenance and adjustment.
In operation, when stepping motor 18 turns, the rotational motion
of the motor is translated into linear cable motion and this in turn moves
the extendable arm 70 carrying the work holder 15 radially with respect to
the pivot pin 68.
Though, at first glance, the coordinate system in which the work
holder moves appears to be polar, thàt is, a coordinate system having a
radial component delivered by moving the extendable arm 70 over the `
pivoting arm 52, and an angular component, delivered by rotating the
pivoting arm 52 about pivot pin 68, there is built into the system means
for causing the work holder to move in what closely approximates a rec-
tangular coordinate system with respect to the needle 14.
This means includes apparatus whereby, when the wor~ holder is
rotated about pivot pin 63, the circular line of stitching which would
normally result from such movement is modified to approximate a straight -
line of stitching such as would be created in a rectangular coordinate
system. This approximation of a straight line of stitching is accomplished
automatically by shortening the effective length of the extendable arm 70
f
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~LC)S53~6
by amounts depell~ent Oll t~c ~mount o~ rotational movement imparted
to the work hol~er by the pivoting arm 52. rhe alnount by which the
effective length of the e~tendable arm is shortened for a particular
angular position of arm 52 is determined by (1) the distance from the
co-mecting point 94 to both the needle 14 and the pivot pin 68, (2)
the distance from the axis about which pulley 90 rota~es to the connecting
point 94 and (3~ the radius of the pulley 90 at the inside o~ the cir-
cumferential groove. Pulley 90 is spaced to one side of a line between
the pivot pin 68 and needle 14, a distance equal to the radius of the
pulley plus one-half the thickness of the cable.
With the structure shown in the drawings, connecting point 94,
for a fixed position of stepping motor 18 traces a path called the in-
volute of a circle (the circle being the inner circumference of pulley 90),
and the result is to pull the connecting point 94 radially inward more
and more as the angle through which the arm 52 is rotated increases from
its center position. As already discussed, the amount of radially inward
movement required is such as to have the needle sew along a path which
approximates a straight line when only a rotational movement is imparted
to the work holder by the cable 36.
This is accornplished in this particular embodiment by making the
distance between the pivot pin 68 and a tangent point 106 between the
cable 34 and the pulley 90, 3.470 inches, by making the distance between
tangent point 106 and cable connection point 94, 1.623 inches, and by
making the distance between the pivot pin 68 and the needle 9.000 inches.
These dimensions can be scaled up or down in larger or smaller equipment
as long as the relationship between them remains the same.
As pivoting arm 52 pivots about pin 68 from its center position,
the cable 34 winds or unwinds about the pulley 90, for clockwise or
counterclockwise rotation, respectively. As a result, for the same angular
rotation of arm 52 from the center position, the compensatory effect will
1~5~i316
vary depending upon thc direction of rotation from the center position.
In orcler to maintain the compensation as symmetrical as possible, it is
necessary to keep the radius of pulley 90 as smal] as possible, consistent
with proper handling of the cable 34 Accordingly, in the preferred
embodiment of tlle invention, the radius for this pulley is about .328
inches.
In this particular embodiment, there are two homing assemblies
and two limit assemblies, one of each being combined to operate from the
same rotating shaft. As heretofore referred to these are homing and
limit assemblies 55 and 88. Both homing and limit assemblies 55, 88
perform the same two functions. One is to position the work clamp at a
predetermined location ("home") and the other is to provide an indication,
in this particular embodiment a contact closure, that the work holder is
being moved beyond the predetermined allowed limits. Both limit assemblies
also provide firm physical resistance to movement beyond the predetermined
allowed limits. The homing assembly is intended to prevent cumulative
errors in reference position from occurring from cycle to cycle and to
al~ays maintain registration. An additional function of the homing
assembly is to insure extremely accurate start or end point positioning
~0 ~o enable auxiliary devices, such as slitting knives to cut buttonholes,
to be actuated and to perform repeatedly with a high degree of positional
accuracy.
~ eferring to Figure 11, only homing and limit assembly 88 for
limiting travel and effecting homing of arm 70 in the radial direction will
be described in detail, assembly 55 having a similar operation and construc-
tion for the rotational coordinate direction. Pulley 86 of the homing and
limit assembly 88 has a sufficiently large diameter that the maximum
allowable cable travel for moving the work holder in a radial direction
results in less than a complete revolution of the pulley. By thus limiting
3~ the angular rotation of a shaft 108 on which the pulley 86 is mounted to
n~ _ .. _.. _. _. __._._. . . ... , __ _ . . .: . . . ... .. . ., _ _ ........... . . . .
lOS53~6
less than a full revolutioll, adjustable limit switclles, secured in an
operative relation to shaft 108, allol~ full range of radial movement of
~he wor~ holder wllile providing a con~act closure to electrical control
circuitry to indicate tilat the work holder is being moved beyond the
present limits.
ReferTing to Figures 9 and 11, the limit assembly portion of
homing and limit assembly 88 includes a sleeve 110l with bearings 112 and
114 pressed into its ends. The sleeve is held in a support assembly 116
by means of a screw 118. Limit switch brackets 120 and 122 fit around
sleeve 110 and are held in position by clamps 124, 126 against a disc 128
of the support assembly 116 with screws 130, 132 respectively. Limit
switch assemblies 134, 136 are held on brackets 120, 122 respectively by
means o~ screws 138. A trigger 140 for the homing and limit assembly,
but used only for the limit function 88 is secured to the underside of
pulley 86 by means of screws 142. Pulley 86 mates with and is rotatable
: on shaft 108 above disc 128 of the support assembly 116. Trigger 140 moves
in an arc between limit switch assemblies 134 and 136 as pulley 86 rotates
in response to movement of cable 34.
In normal operation, the work holder does not travel beyond the
predetermined allowed limits because the instruction sequence controlling
; movement of the work holder does not instruct the drive circuitry to
move the wo~k holder that far. However, if for any reason the stepping
motors continue to drive the work holder beyond the allowed range of move- -
ment and therefore into potential contact with the sewing machine needle,
` possibly damaging the needle or the work holder, trigger 140 engages the
contacts 154 or 156 of limit switch assembly 134 or 136 causing them to
close~ Closure of normally open contacts 154 or 156 signals the electrical
control circuitry to prevent further stepping of the corresponding stepping
motor until the direction of travel for that motor is reversed.
As an extra safety, should the limit switches, the wiring to them,
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~553~6
or relatecl electrical circult ~ail so that the motor continues to be
clriven furtller out of the allo~ed limits, trigger l40 urges contacts 15~,
156 against one of the bac~up screws 158 which have a fixed position with
respect to support assembly 116. This prevents further movement of the
trigger 140, and therefore of pulley 86, cable 34, and stepping motor 18.
Further movement of the extendable arm 70 is thereby prevented and damage
to the sewing needle 14 or the work holder is avoided. Backup screws 158
are preferably adjusted to stop contacts 154, 156 one motor step after
the contacts have actuated. Similar apparatus is used for limiting travel
.
of the work holder in the other coordinate direction.
The homing assembly portion of the homing and limit assembly 88
positions the work holder,upon command, to a predetermined location, the
location being anywhere within the working range of the two-coordinate
system. Because of the nature of the coordinate system in this embodiment,
it is p~eferable to have the home position at the center of polar travel --
and near that limit of radial travel at which the extendable arm is most
extended.
The apparatus for sensing the home position is located at the
lower portion of the homing and limit assemblies, and includes apparatus
having indlcating portions driven by the cable 34 via the pulley 86 and
shaft 108 whose motion is thus synchronized to the movement oE the cor-
responding cables driving the work holder. Only the homing assembly por-
*ion of the homing and limit assembly 88 will be described in detail, the
homing assembly portion of homing and limit assembly 55 being substantially
the same in operation and structure.
The homing assembly includes a notched homing disc 160 and an
optical sensor 162 arranged so that the sensor detects the presence or
absence of the notch. In this particular embodiment, the optical sensor
162 is a light-emitting diode and an interrupter type phototransistor
3~ mounted as one unit which is supported on a bracket 164 by screws 166.
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~05~3~tj
Bracket 16~l is securecl to the lowcr section of support assembly 116. The
homing disc 160 is secured to tile lower end of shaft 1O8J and rotates in
union l~ith pulley 86 ~YIlich is coupled to the upper end of shaft 108 by means
of pin 1~16~ lever 14~, adjusting scre~ 150 and bracket 148 affixed to pulley
86. ~urning the adjusting screw 150 rotates homing disc 160 with respect
to the cable 34 and the work piece of that easy and precise adjustment of
the home position is possible.
In operation, an output signal from the optical sensor 162 deter-
mines the direction in which stepping motor 18 must be rotated to move edge
168 of homing disc 160 into alignment with the sensor. As soon as the edge
reaches alignment, it causes a signal output change and the motor to stop.
If the motor overshoots proper alignment, the motor can be reversed by the
electrical control circuitry and the disc brought into more precise alignment
with its aligned position. A similar apparatus is used for the other co-
ordinate direction.
Referring now to Figure 6, pivoting arm 52 is provided with free
turning rollers 170, 172S attached to pivoting arm 52 by means of screws
174, and free turning rollers 176, 178 attached to levers 180, 182 res-
pectively by means of screws 184. Levers 180, 182 are attached to pivoting
arm 52 by screws 186 about which they can freely pivot. A compression spring
188 fits between levers 180, 182 and is held in place by lugs 190, 192
on levers 18n, 182 respectively. This construction makes rollers 176, 178
movable and spring loaded. The extendable arm 70 rides on rollers 170, 172,
176, 178 as will be further described below.
Extendable arm 70 (Figure 4~ rides on tracks formed by triangular
shaped portions 194, which allow the arm to ride on rollers 170, 172, 176,
178. ~ffixed on the underside of extendable arm 70 is a bracket 196 ~Figures
and 5) to which a lower clamp jaw 198 of the work holder is attached by means
of two screws 200. An UM er clamp member 202 is pivotally mounted about its
rear end around an axle 204. Upper clamp member 202 is urged downwardly
.
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~5S3~6
about tlle a~lc by a compression spring 206 tllat fits around a s~ld portion
208 of-the bracket 196. A thulllbscre~ 210 is used to adjust the spring force.
~ ssem~led, thc forward part of extendable arm 70, the part nearest
the work holder, rides on rollers 170, 176 while tlle trailing part of the
arm 70 ri~es on rollers 172, 178. The ~York holder, attached to the exten-
dable arm 70, pivots with pivoting arm 52 around pivot pin 68 by means of an
opening in pivoting arm ~2 through which pin 68 extends. As previously des-
cribed, pivotal movement is controlled by cable 36, driven by stepping motor
20. E~tendable arm 70 riding on the rollers 170, 172, 176, 178 in tracks
1~4 moves along the pivoting arm in a substantially radial direction with
respect to pivot pin 68. As previously described, cable 34, driven by
stepping mo*or 18, controls the radial movement of the extendable arm 70.
Thus, depending on the direction of motor rotation, one end of the cable at
stud 72 pulls while the other end of the cable at connecting point 94 relaxes,
or vice versa. In this way, there is always a positive drive to control
radial movement of the extendable arm.
Upper clamp 202, as noted above, is urged downward by spring 206.
In this way, the work piece is clamped and held in position between upper
and lower clamp jaws 220, 198. At the beginning of a sewing cycle when the
2~ work piece is placed in the work holder, and at the end of the sewing cycle
when the work piece is removed from the work ho]der, the clamp 202 must be
raised. Referring to Figure 1, the apparatus for raising the upper clamp
includes a svlenoid actuated air valve 214 which, in response to a signal
from the electrical circuitry at an appropriate time in a sequence of instruc-
tions, lS energized and thereby admits air under pressure to a cylinder 216.
In response, cylinder 216 pulls on cable 218 to lift clamp 202. At the
beginning o a cycle~ after the operator has placed the work piece in the
work holder, the clamp will, in response to a manual or pedal switch, close
as solenoid valve 214 is de-energized causing cylinder 216 to extend its
3~ piston by means of an internal spring ~not shown) and relax the cable 218.
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3~6
Spring 206 thereby urges upper clamp 202 to pivot about axle 204 to forcibly
engagc tlle work piec~ bet~Yeell lower clamp jaw l~S and upper clamp jaw 220.
As a safety precaution, a clalnp closed sensor 296 is provided to
prevent au~o~atic machi]le operation until the clamp has completely closed.
Closure of the upper clamp is sensed by cable tension sensing assembly 222
~Figure 1). ~en ~he cla~p is fully closed~ the cable relaxes and in res-
ponse thereto a switch ~not shown) in the assembly 222 resets by its own
internal spring.
For p~oper operation of the apparatus, the movement of the work
holder must be synchronized to the stitching cycle so that the work holder
is moved only ~hen the needle is not in the work piece. Furthermore, the
sewing ~achine must stop at the end of a sewing cycle with the needle in the
up position so that the work holder may be moved to the home position and
so that the work piece may be removed from the work holder after the upper
cl~mp is raised. Thread cutting is also done as part of this "needle-up"
sequence. These functions are perfor~ed by a commercial apparatus, Quick,
Model No. 800-ST-362 ~not shown), which is modified somewhat for this par-
ticular application.
Referring to Figure 7, the electromechanical synchronization unit 22
2a includes a rotating slip ring assembly 224 which is affixed to the sewing
machine hand wheel 24 by means of an adapter 226, A stationary portion 228
of assembly 224 includes electrical brushes 230, 232, 234, 236 affixed to a
bracket ~not sllo~m). Insulating portions 238, 240 and 242 provide electrical
inte-rruptions in ~hree slip rings 244, 246 and 248 when these portions are
contacted by bTushes 230, 232~ 236 respectively. Brush 234 is used ~o
supply electrical current to the slip rings. Current from the three active
slip rings is usad in a conventional manner to activate a commercial "needle
positioner" ~Quick, Moael No. 800-ST-362 mentioned above). A pulley 252 and
a belt 254 ~Figure l) connect to a pulley ~not shown) on the sewing machine
needle positioner. ~y ~eans of suitable gearing in the needle positioner and
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1C35531~ii
in response to elcctrical inputs from tlle elcctromecllanical synchroni~ation
nit 22 and from -the clcctrical control circuitry, the needle positioner
~ill cause tllc se~/ing machine: ~a) to run at fast speed or slow speed; (b)
to act~Jate a solenoid powered thread c~lt~er (not shown) and a thread tension
release solenoid (not sho~n); and (c) to stop the machine with the needle up.
This apparatus is all commercially available and it is mentioned here only
for the purpose of adequately describing certain additions which follow.
The synchronizer 22 includes a photo-reflective transducer 256,
its holder 25~, a mounting strap 260, a photocell commutator ring 262, a ~ -
a set screw 264 retaining ring 262 at any chosen angular position on the -
asse~bly 224, a cover 266, and a scale 268 either imprinted on the cover or
separately printed and affixed by adhesive. In uperation, light emitted by
transd~lcer 256 strikes the s~rface of ring 262 and is reflected to an optical
sensing portion of transducer 256 creating an output current. The output
current remains constant except at a notched portion 270 of ring 262 at
1 ~hich ~he amoumt of reflected light and therefore the output current are
I greatly diminished. The notched portion and the corresponding signal change
initiate the beginning of a time period in which the work holder can be moved
without damaging the needle, that is, the beginning of the time period
immediately after the needle has been withdrawn from the work piece. The
needle positioner, although commercially designed for actuation by treadle,
is made fully automatic by attaching an air cylinder (not shown) to its
actua~ing lever. The air cylinder is controlled through an electric air
valve ~not shown) by current from the electrical control circuitry.
Referring to Figure 12, the presser foot of the sewing machine
has been replaced b~ a spring loaded stripper mounted on a needle bar con-
sisting of a stripper 272 and a compression spring 274. One end of the spring
is affixed to the lower end of the needle bar and the other end is affixed to
~ the top side of the stripper 272. ~le stripper holds the material down
! 30 against the throat plate to allow a needle thread loop to form as the needle
j .
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1~553~6
l-l begins to rise and ~o be picked up by the sewing machine's rotary hoo~
~not shown).
As noted above, the addressable storage element whicll is preferred
in this embod;ment is a programMable read only memory ~PRO~I). With the
proper equipment, the operator of an automatic sewing machine according
to this invention can change or add programs (i.e., instructions or a sequence
of instruc~ions) ~o a PR~M. Depending on the information capacity of each
Storage location and the information content of each instruction, a single
inctruction ~ay be stored in a single storage location. On the other hand,
in the preferred embodiment of the invention, each instruction requires more
than one storage location. The sequence of instructions stored describes a
patte~ which the automatic sewing machine work holder will follow. In
this particular embodiment, the PROM has a randomly addressable eight binary
digit ~bit~ word in each storage location and a total of 256 such locations.
Each instruction includes a command and work holder positioning
data. In the preferred embodiment there are four commands. The first
command directs movement of the work holder without stitching; the second
directs ~ovement of the work holder while stitching slowly; the third directs
movement of the work holder while stitching at a fast rate; and the fourth
indicates the end of the sequence of instructions and directs movement of
the work holder to its home position. Each of the first three commands
recited above re~uires two groups of positioning data to form a complete
instruction. Each data group includes directional and stepping information
necessary for a different one of the two coordinate directions to determine
the next position of the work holder. While there are many possible ways
of providing this infoTmation, it is preferred to construct each data group
as a signed number which indicates the number of steps and the direction
in which the work holder is to be moved. Thus, this particualr embodiment
of the invention utili~es an open loop system, that is, the work holder is
moved from place to place during a sewing operation without any feedback
-16-
~1~5S31~
to indicate its present position. In this particular embodilllent, the maximum
allo~rablc number of stcps in each coordinate direction is twelve per instruc-
tion ~rilen stitching,and fifteen pcr instruction when the work holder is
moved lrithout stitching.
In this embodiment, each instruction, when written in binary requires
twelve bits. The designation of the command portion of each instruction re-
quires two bits and the trork holder positioning data requires five bits for
each coordinate direction, one for the direction ~positive or ~egative) and
four bits to designate the number of steps. Thus, each instruction of the
sequence requires more than one addressable location ~in the PR0~1.
Once the PROM has been programmed, that is, once the PROM contains
a sequence of instructions in a predetermined order to describe a desired
setring pattern, the sewing machine is ready :Eor operation If the programs
are short enough, two or more programs may be stored in a single storage
element. In this case, switches, for example on the front panel of the
sewing machine, may be manually operated to choose which of thé programs
is to be used.
Referring to Figure 8, ~he operation of the sewing machine is con-
trolled by a central control logic 276. First the operator places a work
piece in the proper position in the work holder 16. Then, when a foot pedal
278 of the sewing machine is depressed half way by the operator, a first
slritch ~not shown~ is closed causing the central control logic 276 by means
not shown to generate a signal which causes solenoid 214 to lower upper
clamp 202 to engage and hold the work piece. After the clamp is lotrered, .-
the foot pedal is fully depressed by the operator and, if the clamp 202
is fully closed, automatic operation of the machine begins. In normal
operation, a "homing" cycle is first initiated. Thereafter, the first in-
str~lction is read from the storage element 280, here shown as a PROM,
according to the program selection switches ~not shown) on the front panel
282 by the central control logic 276. This logic responds by providing the
-17-
l~SS3~
corrcct n~u~ r of ~ cs for movillg thc l~ork 1lokler and, after a signal fron
electromc~cl~;lllica~ syncllrolli7ation ~mlt 22, transrllits thcsc pulscs to motor
drivc logic~ '~4 and 2SG. Drivc logics 28~-~, 286 drive respectively po~er
drivers 2S8, 290 ~hicll in turn drive stcpping mo~ors 18, 20 in the desired
direction and tllrougl~ the desircd rotation.
Thc pulses to the drive logics 284, 286 are arranged to be
aperiodic to increase the machine cycle rate and to prevent unwanted oscilla-
tions and therefore unwanted feeding of the work piece againstthe needle.
The \~ork piece thus moves in a true intermittent motion, the work piece being
stationary when the needle is inserted into it. More particularly, the cen-
tral control logic 276 includes means for spacing the first three pulses of
a serics of pulses and the last two pulses of the series further apart than
any remaining intermediate pulses. Where the number of pulses to a stepping
motor is less than three, the amount of current from the power drivers 288,
290 is reduced ~by known means not shown) to further minimi~e oscillations in
the stepping motors. The next instruction is then read and carried out,
followed by the one after that, etc., until the last instruction has been
implcmented. In response to the last instruction which will be a stop command,
the central control logic causes the needle positioner to halt the sewing
machine~ causes the thread to be cut, and then initiates a second "homing"
cycle.
The "houing" cycle is controlled by the central control logic
which, in response to the signals from optical sensors 162, 294, cycles the
stepping motors to return the work holder to its radial and rotational "home"
location.
~ther inputs to the central logic are from the limit switch
asscmblies 134, 136, of both coordinate directions, clamp sensor 296 of ck~mp
tension sensing assembly 222,and cutter circuitry 297. Cutter circuitry 297
signals the control logic after the thread llas been cut. There is also
included a needle/thread break sensor 298 which signals the control logic
~553~6
276 ol a l)rc.lk in thc ncedlc t~lrcad. Ui)on rcceipt of a break sigll.ll from a
sellsor 298, thc control logic 276 C.lUSCS the needle positioner to halt the
sewing mac}~ e an~l inh;~its an~ furtller movemont of the work holcler by stop-
ping -the ;ncrementatioll of an acldress counter 372 (Figure 13) ~hich sequential-
ly addresses the storage element~ Tllus, the address in address co-lnter 372
is prescrved and the control logic 276 waits for a restart signal from the
front panel before starting up again. As will be explained hereafter, once
tlle thread or needle has been repaired and replaced, the operator may restart
the machine at the beginning of the sewing pattern or restart it at the
instruction following the instruction at which the break occurred.
Depending upon whether an instruction requires slow or fast stitch-
ing, the control logic 276, in response to that lnstruction, will signal,
through driver 300, a control box 306 of a "Quick" needle positioner (not
sho~m) to cause machine to stitch at the required speed. If a stop command
is read, control logic 276, in response to that instruction, deactuates
through driver 304, brake clutch valve solenoid 308 in the needle positioner
to stop the sewing machine.
Referring to Figure 13, the control logic 276 (Figure 8) is shown
in greater detail. A sequencing circuitry 322 monitors over the cable labelled
"W~ECKS": (a) inputs from synchronization unit 22; (b) clamp sensor 296; (c)
needle/thread break sensor 298; ~d) cutter circuitry 297; (e) limit switch
assemblies 134, 136; (f~ front panel 282; and (g) optical sensors 162, 2~4
for both coordinate directions. Signals from foot treadle 278 are read over
the line labeled "START". Gating logic circuits provided within the sequencing
circuitry serve ~o halt machine and work holder operation if the proper
operating conditions are not maintained. When the operator fully depresses
the treadle~ this causes an enabling signal on line 324 to appear and initiate
the first "homing'l cycle when the clamp sensor indicates the work holder is
closed. This homing insures that the work holder will be at a predetermined
initial position at the beginning of a sewing sequence.
- 19 -
~C~553~L~
lloming circuitry 3~6 operatcs togcther ~Yitll hol~ lg alld limit
assemblics 55, 8S to preset the l~ork holclor at the desired locations Eor se~Y-in~ in e~lch of the tlYO coordinate direct;ons. ~or convenience, the coordinate
directions will be called ~ and Y, corresponcling to a rectilinear coordinate
system~ although in the preferred embodiment the coordinate system is based on
polar coordinates modified to appro~imate a rectilinear system The homing
circuitry, in response to the enabling signal over line 324 from the sequenc-
ing c;rcuitry 322, provides output signals over lines 332 and 334 to a direc-
tion steering circuitry 336, based upon the inputs from optical sensor 162,
294 over lines 328, 330. These ou~put signals indicate the direction in which
the s*epping motors should be moved. Direction steering circuitry 336 gates
the signals on lines 332, 334 to the motor drive logics 284, 286 to control
the direction of movement of the motors 18, 20. These signals are also gated
to ~ limit circuitry 342 over lines 338 and 340 whose operation will be
described below. The homing circuitry 326 also enables a pulse modifier
circuitry 344 by a signal over line 345 so it is in condition to be enabled ~
to provide output electrical pulses over lines 346 and 348 from the low speed -
oscillator 368. After the first homing approach, this output is preferably
reduced in frequency by a rate modifier circuitry 349 to motor drive logics
28~, 286, as will be explained hereinafter, by the signals over a command line
351 from homing circuitry 326.
Pulse modifier circuitry 344 is enabled to gate these pulses to
the motor drive logic by signals from a run/sew circuitry 350 over lines 352
and 354. Signals on one of these lines control the gating of pulses to one of
the motors 18, 20 while signals on tlle others control the gating of pulses to
the other motor. The signals on lines 352, 354 are provided by the run/sew
circuitry 350 in the homing mode by a set of input signals over lines 356 and
358 from homing circuitry 326 whell there exists an enabling signal over line
324 from the sequencing circuitry 322. The absence of signals over one of
lines 356, 358 and thus one of lines 352, 354 causes the pulse ;nodifier cir-
- 20 -
. . .
.. . . .
~5533L6
cuitry to inili~it pulsing to the corrcspondillg stcpping motor. Tlli; occ~lrs
~henevcr tlle homc position for the correspo]~ g coordinate directioll has been
acllieve~ or proper operation o~` tllc pulsc modifier circuitry during the
homing cyclc, there must be enabling signals over line 3~5 and one or both of
lillc~ 35Z, 354.
In all cases, the stepping motors overshoot the home posiiion.
IYhen this occurs the optical sensors generate a signal whicll causes tlle motor
involved to reverse and "zero in" on the correct home position. This is done
by changing the signals over lines 332 and/or 33~ according to information
from the optical sensors to reverse the direction of one or both stepping
motors. rhe homing circuitry also includes additional logic circuitry for
ensuring that the final approach of each motor to its home position is all~ays
from the s~le direction irrespective of the initial position of the wor~
holde~ prior to homing. In addition, all homing motion after the first home
approach is accomplished at a reduced rate generated by rate modifier circuitry
349. Means in the homing circuitry 326, responsive to the optical sensor
outputs~ provide the signal over command line 351 for causing the stepping
rate to be reduced. This mixture of stepping rates creates an optimally fast
homing cycle.
In this particular embodiment there is always at least one change
of direction of approach to the "home" position for each motor. If, after
reversing the motor, the second approach direction is not the same as an
approach direotion predetermined in advance, the direction of motor rotation
is automatically reversed again by logic in the homing circuitry which senses
the direction of approach and a third and final approach is made from the
predetermined approach direction. In this ~ay, greater accuracy in position-
ing the wor~ holder is achieved.
~len the first homing cycle has been completed a signal is placed
by the homing circuitry on line 360 from the homing circuitry 326 to the
sequencing circuitry 322. In response to this signal~ the enable level on
1~553~6
line 32~1 is i~mnedi.~tely rcmoved by tile se~lucncing circuitry tllereby prcventing
furthel movclllen-t of tlle work ~loldcr. llle sequencing circuitry thcn initiates
a memory cycle by generatillg an enable sig~ l level over a line 362. This ~ -
signal lcvel allows worcls ~rom storage elemcnt 280 to be addressed and read
as follows. The Outp~lt of a high speed oscillator 366 is reduced by a counter
here labeled lo\~ speed oscillator 368 whose output is one-tenth the frequency
of the high speed oscillator. The low speed oscillator 368 provides periodic
pulses which determine the rate at which the stepping motors will be driven.
The enable signal on line 362 enables the address counter 372 whose output on
lines 374 represents the address of the word which is going to be read from
the storage element. The enable signal on line 362 also enables a count to
three counter 376 whose outputs determine which of three units portions of a
word of storage are read into. The three units comprise a storage unit 378
wh:ich receives the command portion of the instruction and the signs of the
coordin~te directions, upcounter 380 and upcounter 382. These two upcounters
respectively receive the work holder positioning data for each coordinate
direction in inverted form after it is inverted b~ an inverter 384 comprising
several inYerting gates. ~`
In operation, the first clock pulse output of the high speed
oscillator 366, after line 362 is enabled increments address counter 372
resulting in a new four bit word being available from the storage element over
lines 3~0. The same clock pulse also increments tlle count to three counter
which causes an enabling signal to appear on one of its output lines, namely
line 392 corresponding to a count of one. This in turn enables the upcounter
382 *o store the four bit word in inverted form. The inverted four bit word
is entered into the upcounter 382 by the trailing edge of the same first clock
pulse over line 393.
In the same fashion, the next clock pulse from the high speed
oscillator ~corresponding to a count of two) increments counters 372 and 376
and causcs the inverse of the next addressed four bit word to be reacl into
- ~2 -
,., .. _, . ~ ~ ., .. _ .. , ... .. _ .. , _ . .. , . _ . _. ., . ,.. . , , .. ", . _.. . , .. , _ . . .
,
.: , . :, -
,, ,
~C~553 3L6
upcourltcr 3~0 as dctc~ incd by a1l cnab:l ing signc11 fro11l count to three counter
over 1ine 39~1. Tllis corresponcls to a co~lnt of two.
T11e t11ird cloc~ pu1se from the l1igh speed oscillator again in-
cremcnts countcrs 372 cmd 37G and causes the next addresscd four bit word to
be read into storage unit 37S as determined by an enabling signal from the
co~mt to three counter over line 396. This corresponds to a count of three.
The enabling signal on line 396 is also provided by a connection, not shown,
to the sequencing circuitry 322 in response to which the enabling signal on
line 362 is removed. As a result, the count to three counter 376 is reset to
zero, and address counter 372 cannot be incremented. By this time, one com-
plete instruction has been read from the memory and is stored, parts in each
of upcounters 380, 382 and storage unit 378.
All that remains to utili~e this instruction is to translate it
into movement o the stepping motors 18, 20 and into motion of the sewing
machine, if required. Where the previous instruction required a sewing opera-
tion, this is accomplished by a signal from the synchronizing unit 22 which is
connected to the sequencing circuitry over one of the lines entitled "CHECKS"
and which causes the sequencing circuitry to provide an enabling signal over
line 397 indicating that the needle is clear of the work piece. ~Vhere the
previous instruction did not require stitching, for example when the work
holder is positioned for sewing following the first homing operation, the
equivalent of the needle disengage signal is generated internally by logic
means within the sequencing circuitry to produce an enabling signal over line
397 a short time after the new instruction is read into storage. In either
instance, the enabling signal over line 397 is connected to the pulse modifier
cir~litry 344 which allows the stepping motors to be driven in accordance with
I the outputs of upcounters 380, 380, 382 whenever appropriate signals are
.! present on lines 352, 354, 442, 444. The latter two lines (from limit cir-
cuitry 342) will always have appropriate signals on them for this purpose unless
the work holder is outside of its permitted range of movement.
- 23 -
,, , ,, ,, ~
1~35S31 E;
A~ter thc ena~ling signal is proyi~cd on llnc 397, cloc~ signals
~rom the low spccd oscillator increlllent upcounters 3~0, 3~2 through a count
enable circuitry 40n over lincs 402, '10'1. At tile same timc, -the samo clocl~
signals from the low spcecl oscillator are connected to pulse modifier circuitry
344. Pulse trains from the pulsc modifier circuitry to drive each stepping
Motor are derived from these low speed clock signals from each coordillate
direction.
The outputs of upcounters 380, 382 determine the number of output
pulses there will be *o step each motor in a given coordinate direction. The
directions are deteTmined by the direction indicating portions of the word
stored in s~orage unit 378. ~le direction indicating portions are gated to
the stepping motor drive logic and the limit circuitry by direction steering
logic 336. The number of output pulses to each motor corresponds to the data,
the inverse of which was initially stored in the upcounters. ~le upcounters
are constructed so that, when they have been incremented a number of times
equal to the number of steps specified in the instruction, a carry output
appears on lînes 406, 408. The carry outputs are sent to the run/sew circuitry
and affect ~he pulse modifier circuitry 344 by run/sew circuitry 350 response
over lines 35~, 354. As noted above, signals over one or the other of lines
352, 35~ indicate that a proper number of input pulses from the low speed
oscillator have been received for a particular coordinate direction. When
both carry outputs appear ~and, of course, they need not appear in the same
clock cycle~ the sequencing circuitry 322 causes the enable signal on line
397 to be removed thereby indicating that the information contained in the
instruction las~ read from the memory has been utilized.
As long as the work holder is within the limits that are mechani~
cally set in the ]imit portion of the homing and limit assemblies, the pulse
modi~ier circuitry operates as follows. During the homing cycle when there IS
the enabling signal on line 345, pulses from the low speed oscillator are
applied to the stepping motors in the coordinate direction or directions in-
- 24 -
.. . . . . _ . ... . ... ......
553~6
~licilted h~ thc signals on lincs 332, 33~ c O-ltpll~ L~ulse tr,l:ins arc
yerioclic. During tl~at port;on of the loglc operation when thcre is an enabl-
;ng slgnal on line 397 dlle to a single instruction bcing utilized, the periodic
pl~lses from tl1e low spced oscillator 368 are gated accordillg to the clata
stored in the upcounters 380, 382 to provide pulse trains to the stepping
motor driYe log;cs over lines 3~6, 348. If the number of steps in a coordin-
ate direction is at least three, the pulse train for that direction is
derived as follows.
After *he enable signal on line 397 appears~ the first clock
signal from the low speed oscillator is passed through the pulse speed oscil-
lator is passed ~hrough the pulse modifier circuitry to the drive logic. The
second and third clock signals from the low speed oscillator are blocked and
an initial delayed pulse is added by the pulse modifier circuitry approximately
equ:iclistant between what would originally have been the second and third clock
signals. The clock signals from the low speed oscillator after the third
cloc~ signal pass through circuitry 344 essentially unchanged as long as
there is no change in signal level over whichever one of lines 352 or 354 cor-
responds to the coordinate direction concerned. After a change in signal level
on one of lines 352, 354 further clock signals from ~he low speed oscillator
are blocked from forming part of the output pulse train for that coordinate
direction. Thereafter an additional terminal delayed pulse is automatically
added by the pulse modifier to the otherwise terminated output pulse train.
This pulse is added a predetermined interval of time following the last pulse
in the ~rain, the time interval being greater than the time between pulses
from the low speed oscillator. As a result~ the drive pulses to the stepping
motors are aperiodic, having a somewhat lower frequency at both the beginning
and end of the pulse train and a higher frequency in the middle of the pulse
train. This allows an increased machine cycle rate l~ith smaller oscillations
and therefore more accurate positioning.
l~en the information from storage element 280 was entered into up-
- 25 -
l~)SS3
,~
coullters 3S0 an(l 3S2, if the n-~lber of stops spec:ified for eithor coorclinate
dircction was one or tl~O, this information l~as storecl in decode circuitry 3~8
and is immediately m~(le available to the pulse modificr circuitry over lines
40~ ne pulse modifier circuitry in response to this information from decode
circuitry 39S alters i-ts normal operation, described above~ so that, i only
two stepping pulses are required, only the initial delayed pulse is added
; and if only 03le pulse is required neither the initial nor the terminal delayed ~ ;
pulses are added.
l~hen the called ~or number of X and Y steps has been obtained, as
indicated by a change in the carry signals from the upcounters, the enable
signal 397 is removed and the sequencing circuitry, after a short delay starts
a new memory cycle and provides an enable signal over line 362 to read the
next instruction from memory. ~le operation of control circuitry 276 then
repeats until an end of program signal :is encountered.
~le limit circuitry 342 discussed briefly above operates so that,
if the limit switches indicate that the work holder has reached a boundary, a
signal from limit circuitry 342 to pulse modifier circuitry 344 over one of
lines 442, 444, depending upon the coordinate direction involved, acts to in-
hibit further drive pulses to the corresponding stepping motor until the
direction of stepping has been reversed, as indicated by the signals over
lines 338 or 34V from direction steering circuitry 336. The only effect this
has on the operation of the sewing machine or the electrical control circuitry
is to halt movement of the work holder in the coordinate direction concerned.
The central control logic and the sewing machine continue to operate mormally
except for inhibiting drive pulses to the stepping motor concerned.
Storage element 378 stores a command and direction infiormation as
described above. Each bit of the command is connected to decode circuitry
430. Each output line of decode circuitry 430 collectively labeled 432 is i
associate~ with a particular command. The decode circuitry decodes the command
stored in unit 378 and provides an enabling signal level on the one of its
:`
26 -
.,
~: '
J~553~6
OUtpllt lillc~ ~32 associ.ltcd witll that con~ ncl. Output lines 432 are connected
to tho se~lJcncillg circuitry 2~22 ~ crc thcy arc amplificd before bcing sent on
to the "Quick" unit 306 over line ~67 to control the operation of the sewing
macll;lle .
The sequoncing circu;try utilizes the signals over llnes 432 for
two purposes. First to differentiate between stitch and no stitch commands
to effect proper operation o the needle positioner and second, in response to
a "stop" command, to provide end of program sequencing which includes signal-
ling cutter circuitl~ 297 t^ cut the thread and return the work holder to its
"home" position. To accomplish the latter operation, an enabling signal on
a line 324 is generated in response to an "end of cut" signal from the cutter
circuitry 297 in the presence of an "end of program" signal or command over
one of the lines ~32. After this second homing cycle is completed, the upper
clamp is rais~d in response to a signal from central control logic 276 to a
solenoicl actuated air valve 214 through driver 302 so that the work piece can
be removed.
The Quick unit 306 utilizes the signals over lines 467 from the
sequencing circuitry 322 to stitch fast or slow and to initiate a needle up and
trim in response to the stop command.
In the particular embodiment shown in Figure 13, storage element
280 is a PROM. In many circumstances the program describing a pattern will
not occupy all o the memory and in fact may not occupy even half of the memory.
As a rosult, ~he PROM is split into two portions, an odd and an even portion
and switches on the front panel determine whether the PROM is used in its
split mode (odd or even) or in a full complement mode. In the preferred em-
bodiment, each location in the PROM contains eight bits as mentioned above.
These bits may be numbered for convenience 1, 2, 3, ..., 8. The odd half of
the memory is defined here as the bits of each word numbered 1, 3, 5, 7, and
the even half is defined as the bits numbered 2, 4, 6, 8. In other embodi-
ments of the invention there will be other acceptable divisions of the memory.
~553:~L6
Pro~ra1n selcct circ~itry 4GO in response to thc front panol switches has an
output over l;nc ~162 whic1l inclic,ltes to tl~e l'ROI~l whcther to choose the program
storccl in the odd or even storage locations. When a program occupies the
entire PRO~I, it is written in the PROM so that, b~ sequencing first through
the instructions as if it were an "even" program and then throl1gh the
instructions as thoug}1 it were an "odd" program, the entire program is read.
In ~his case, a carry signal from address counter 372 over line 364 tells the
program select circuitr~ when to switch from "even" to "odd".
~ther embodiments will occur to those skilled in the art and are
wlthin the following claims.
'' ,,
.
~ .
..
