Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 31 9925
Field of the Inve~ntion
This invention relates generally to planar chart
recorders of the rotary type and charts for these. More
specifically, this invention relates to portable chart
recorders. This application is a divisional application
of copending application SN 567,519, filed May 24, 1988.
Back~round Of The Invention
Recorders of parameters such as temperature or
humidity or both are well known. Typically, a recorder
is provided with one or more pens that are directly
coupled by suitable lin~s to sensors. A replaceable
planar circular chart is used which is mounted for
rotation about an axis on a surface of the recorder
under sne or several pens. The recorder can be
entirely mechanically driven, such as with a spring-
wound motor to rotate the chart and with the stylus or
pen mounted on, for example, a coiled, bimetallic
temperature sensor that causes the pen to move along
part of a circular path to record a temperature trace
on the chart.
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" 1 31 9925
secause the pen motion is along a curved path, the
chart bears time lines that are correspondingly curved.
In this manner, parameter values can be read from a
recorded trace, though with some level of difficulty
due to the non-linear appearance of the reference time
lines. When several different parameters are to be
recorded on the same chart, the different traces,
though usually of different colors to enhance their
visual separation, are off-set in time with respect to
each other. This is due to the different pivot arm
lengths associated with the pens. As a result, the
combination of curved time lines and time off-set
between different traces makes these multiple trace
charts more cumbersome to analyze.
In practical applications, it is important that
recorders can operate reliably in the absence of
electrical power. It is important, for example, for
insurance purposes to ~now what the temperature and
humidity conditions are in a computer room after a
power failure has occurred. Also, when food is trans-
ported in a frozen state, it is desirable to have a
record of temperature conditions within the transport.
Portability of a flat chart recorder, therefore, is
an important characteristic. Fully mechanical re-
corders are portable but normally do not have suffici-
ently long operating cycles for many applications.
Battery operated flat chart recorders often have practi-
cal time limits that are below desirable operating
periods. Mechanically moved pens also tend to be
inaccurate as well as difficult to provide compensation
for.
- 1 31 9925
Field of The Invention
With a rotational planar chart recorder in accor-
dance with the invention a long-term portable operation
is achieved while accommodating one or several para-
meter measurements. Multiple parameters can be re-
corded in a visually clear manner that is convenient to
analyze. Long duration portable battery operations can
be achieved of the order of twenty-eight day cycles
while using electronically positioned pens.
This is achieved with one form for a chart recorder
in accordance with the invention by employing a trace
recording pen that moves parallel to a radius along a
line that is substantially a straight radial path
relative to the axis of rotation of the chart. The
chart i8 provided with concentric circles representing
param~ter values and with straight radial time lines.
As a result, multiple pen traces are particularly
conveniently read and interpolated.
As described herein for one preferred form of the
invention, a pair of pens are used. The pens can form
ink traces or be heat elements or any other type of
marker. Each pen is supported by an arm which is moved
by an electrically powered actuator that is aligned to
operate in parallel to the desired radial travel paths
of the pens. The pen actuators are located on opposite
sides of the travel paths and each operatively engages
an arm. The arms extend towards each other so that
their respectively-supported pens are placed in time
proximity to one another relative to the rotation of
the chart. In this manner, each pen can form a trace
that uses the full scale of the chart without
1 31 9925
interference with the other pen. Yet different traces
substantially relate to the same time as viewed along a
straight radius.
Although the pens can operate in very close proxi-
mity, some time displacement is necessary if each pen
is to move without interference with the other. In
accordance with the i~vention, even this time displace-
ment can be removed by delaying positioning of the
leading pen by an amount equal to their respeotive time
disp~acement. Alternately, pens may be placed on the
same time line, with the soft pen tips deforming around
each other during those rare occasions when the pens
must cross.
A particularly advantageous feature of a chart
recorder in accordance with the invention is that the
pens can be efficiently moved with very low electrical
power consumption. This enables long term operation on
battery power so as to record parameter values over a
twenty-eight day cycle. One such technique involves
the regular sampling of a parameter signal and then
causing pen motion from the position required by the
last sample. The sampling rate is made sufficiently
high so as to follow variations of the parameter and
yet sufficiently low to save battery power for a long
operating cycle.
It is, therefore, an aspect of the invention to
provide a rotatable planar chart recorder which pro-
vides conveniently read traces of a parameter such as
temperature, relative humidity and the like. It is a
further aspect of the invention to provide a planar
chart with a simplified scale pattern. It is still
further an aspect of th~ invention to provide a planar
chart recorder capable of lony-term battery operation,
`` 1 31 9925
- 4a -
provide accurate temperature and humidity indications
and an ability to compensate for non-linear charac-
teristics.
In yet another aspect of the invention, there is
provided a chart holder for a planar chart recorder in
which a chart is rotated by a rotating element that
extends through the center of the chart and has a
magnetically receptive flange.
The chart holder has magnet means on a side thereof
and a spindle bore sized to freely receive the spindle
on the flange so as to enable the magnet means to clamp
the chart to the flange when the chart holder is brought
into operative proximity with the flange.
The chart holder preferably has a magnet means which
is annular in shape and located around the spindle
bore. Furthermore, the magnet means may be made of a
plurality of magnetic elements.
~ hese and other aspects and advantages of the inven-
tion can be understood from the following detailed
description of a preferred embodiment for a rotational
planar chart recorder as shown in the drawings.
1 31 99~5
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Brief Description of Drawings
Figure 1 is a perspective view of a rotational
planar chart recorder in accordance with the invention;
Figure 2 is a plan view of a planar chart in accor-
dance with the invention;
Figure 3 is an enlarged perspective view of the
chart recorder of Figure 1, but with the door open;
Figure 4 is a front view in elevation and partly
broken away of the chart recorder of Figure l;
Figure 5 is a partial section view of the chart
recorder taken along the line 5-5 in Figure 4i
Figure 6 is a perspective view of the chart holder
used to mount a planar chart to the chart recorder of
Figure l;
Figure 7 is a section view of the chart holder;
Figure 8 is a perspective exploded view of the
chart holder of Figure 7;
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-- 6
Figure 9 is a block diagram of the electrical net-
work used to operate the chart recorder o~ Figure l;
Figure 10 is a flow chart for the operation of the
microprocessor used in the network of Figure g;
Figure lOA is a flow chart showing the control over
pen movements with greater detail;
Figure 11 is a flow chart showing a technique for
correcting pen position information;
Figure 12 is a section view of a magnetic chart
holder in accordance with the invention; and
Figure 13 is a bac~ view of the chart holder in
accordance with Figure 12.
Detailed De~criPtion of Drawinqs
With reference to Figure 1, a rotary planar chart
recorder 20 is shown formed with a housing 22 having a
windowed door 24 through which a planar chart 26 can be
seen. Chart 26 is rotated by a drive 28, not shown in
Figure 1 but see Figure 5, with a removable chart
holder 30 being used to lin~ the drive 28 to chart 26
and cause it to rotate about an axis 32, see Figure 2.
Drive 28 can be a mechanical drive but preferably is
electrically controlled as described herein.
Planar chart 26 is shown provided with two separate
traces 34, 36 formed by a pair of pens 38, 40. Pens
can form a trace with many different marking techni-
ques. The pens are moved under control by a micropro-
cessor along lines that are parallel straight radial
1 3 1 9925
lines. A panel 42 provides a place for a plurality of
switch controls 44, LCD displays 46 and power switches
48.1 ~on) and 48.2 (off).
The panel includes a time of day clock display 46.1
and is provided with associated time setting and time
advancing controls 44.1 and 44.2. Peak signal display
selectors 44.3 (high), 44.4 (low) are provided as well
as a peak reset switch 44.5 which erases the currently
stored peak values to enable new peak values to be
stored.
A chart rotational speed control 44.6 is provided
with three settings of one-day, seven-day and twenty-
eight-day intervals for one rotation of chart 26. A
three-position display control 44.7 enables the selec-
tion of the current temperature in Fahrenheit, F;
Celsius, C; or the percentage of relative humidity, H.
The planar chart 26 includes a central opening 60
to mount the chart on a rotating drive element such as
a drive spindle 62 (see Figure 7). Chart 26 further
carries a plurality of concentric circle 64 as is
common with rotary planar charts. Each circle repre-
sents a particular parameter value as indicated by the
numerals ad~oining the heavier circles. Chart 26 is
further provided with rstraight radial time lines 66
each of which presents a particular time within the
rotary interval represented by chart 26. In the
example, of Figure 2, chart 26 is intended to record
parameter values for one full day, though longer
intervals of seven and twenty-eight days are contem-
plated for charts 26.
Use of chart 26 is similar to conventional chart
recorders. Door 24 is opened and the chart holder 30
~ 1 3 1 9925
is released and removed to enable placement of chart 26
onto the spindle 62. The chart is rotated to align the
starting time line, such as the one that corresponds to
the actual time of day with the travel paths for pens
38, 40. The chart holder 30 is then remounted to
establish a connection between the spindle 62 with the
chart 26. With the pens 38, 40 mounted to the door 24,
an automat~c pen lift is achieved to facilitate
installation or removal of a chart.
With reference to Figures 3 and 4 the chart re-
corder 20 is shown with greater detail. The pens 38,
are mounted to travel along straight paths 70, 72
that substantially extend radially from the rotational
axis 32 and are parallel to a straight radius from axis
32. Travel paths 70, 72 are in close physical, and
thus also time, proximity to each other. Their
separation represents a small portion of the total
rotational interval of a chart 26, typically about a
minute for a 24-hour chart 26 or less than one tenth of
one percent of a whole revolution.
This is achieved by using a pair of pen actuators
74, 76 that are aligned to operate parallel to paths
70, 72 and are located on opposite sides of the paths
and chart 26 within a recess 78 of door 24. Actuators
74, 76 are of like construction and include arms 80,
80' which operatively engage lead screw 82, 82'. Arms
80, 80' extends towards each other and thus paths 70,
72 and removably support pens 38, 40. Clips 84 are
used to hold the pens 38, 40 in position. The pens 38,
40 can be positioned to produce markings along an essen-
tially common radial path where paths 70, 72 merge. In
such case, the soft pens can deform around each other
during those rare occasions when the pens must cross.
1 31 9925
g
The pen arms 80, 80' are mounted to lead screws 82,
~2' and adjoining parallel slide bars 86, 86' by way of
blocks 88, 88' having appropriate slide `bores and
threaded bores to respectively engage bars 86, 86' and
lead screws 82, 82'. Lead screws 82, 82' are journaled
in blocks 90, 90' which are affixed to door 24. Shafts
92, 92' connect drive motors 94, 94' through worm gear
arrangements 96, 96' to lead screw 82, 82' by way of
couplings 98, 98'. Shafts 92, 92' are journaled in
blocks 100, 100' that are also affixed to door 24.
Positioning of pens 38, 40 is controlled with posi-
tion sensors 102, 102' which sense the rotations of
shafts 92, 92' and thus also those of lead screw 82,
82'. The position sensors provide output signals on
lines 104, 10~' in the form of pulses, each of which
can represent a full lead screw rotation but preferably
a known fraction thereof. Since the pitches of the
lead screw 82, 82' are known, each pulse represents a
certain amount of straight radial travel along a path
70 o~ 72.
Actual positioning of the pens 38, 40 is done by
measuring the number of pulses on lines 104, 104'
relative to reference positions 106, 106' of arms 80,
80'. These reference positions are sensed when the
leading edges 108, 108' of elements 110, 110' on arms
80, 80' interrupt light beams in light sensors 112,
112' that are operatively aligned with reference
positions 106, 106'. The pen positions are thus
determined by accumulating the number of pulses from an
associated reference position.
A particularly advantageous feature of chart re-
corder 20 is that pen positioning can be done under
electrical battery power. For this appropriate space
1 31 9925
-- 10 --
is made available to store a practical number of
D-sized batteries 120. These provide sufficient elec-
trical power to maintain the chart recorder operational
for at least as long a cycle as twenty-eight days and
usually about two months. The number of batteries
carried for this purpose is limited to what is
practical to avoid excessive weight and size of the
recorder.
With reference to Figure 9, an electrical system
130 is shown to operate chart recorder 20. A micro-
processor 132 is used with a keyboard 134 that includes
the control switches previously described with refer-
ence to the panel 42 shown in Figure 1. An output to a
display 136 is provided which in this case includes the
liquid crystal displays 46.1 and 46.2. Communication
between microprocessor 132 and the keyboard 134 and
with the displays 136 involves known circuits and
protocols and typically includes additional connectors
for coupling to other remova~le external devices for
special loading and checking functions during assembly
of chart recorder 20.
A system timing circuit 138 is provided to deliver
appropriate timing pulses to a chart paper drive motor
140. These pulses are generated at a sufficient rate
to move the motor at a speed so as to rotate chart 26
once a day, in seven days, or in 28 days. Hence, the
chart speed control switch 44.6 (see Figure 3) is
coupled along several lines 142, see Figure 5, to
circuit 138 to control the pulse rate to motor 140.
Chart paper motor 140 may be a stepper-type motor which
`will advance to successive positions in response to
pulses from circuit 138 without consuming significant
electrical current during the pauses between the
-`` 1319925
pulses. Motor 140 can also be a mechanical device such
as a geneva mechanism or a spring driven motor, all of
which produce a rotating output shaft or element.
Processor 132 responds to interrupt timing pulses
on line 144 from timing circuit 138 to cause a movement
of bidirectional pen motors 94, 94' via motor drives
146, 146'. These pen actuating pulses occur at regular
intervals with the rate being a function of the rota-
tional speed of the chart paper drive motor 140. Thus,
typically, pen motions are initiated once every minute
for a 24-hour chart 26, once every seven minutes for a
seven-day chart and every 28 minutes for a 28-day
chart. Different pen actuating rates can be used with
higher rates needed when significant changes in
parameter values such as temperature or humidity occur
in shorter intervals and it is desired to record these
with the pens 38 or 40. The rates, when expressed in
terms of angle of rotation, generally would occur in
the range from about once every one-tenth to about once
every half a degree of rotation.
The advantage of periodic activation of the pens
38, 40 is that substantial power savings are obtained
resulting in much longer battery life. On the average
about four times longer battery life is obtained in
comparison with continuously moved pens.
In the chart recorder 20 two parameters are sensed,
temperature with a sensor 150 and relative humidity
with a sensor 152. These sensors can be an integral
part of recorder 20 or be placed at external strategi-
cally desired locations.
1 31 9925
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The sensors 150, 152 produce output signals that
are applied to suitable electronic circuits 154, 156
which generate appropriate output signals on lines 158,
160 at voltage levels suitable for conversion to digi-
tal format by A/D converter 162. A suitable multi-
plexer, not shown, is used to share A/D converter 162
between the different parameter signals.
Operation of A/D converter 162 is regulated by
timing signals produced on lines 164 from processor 132
and in response parameter digital data is presented on
parallel lines 166. The rate at which temperature and
humidity are sampled by processor 132 can be very high,
well in excess of what is normally required to sense
their variations.
DC electrical power is delivered on lines 168 by a
power supply monitoring and switching circuit 170.
This circuit enables an automatic changeover from AC
power available from AC transformer 172 and AC lines
174 to DC power from the battery supply 120.
Figure 10 illustrates a flow chart 180 for the
operation of recorder 20. When the recorder is turned
on by activating the panel on switch 48.1 (see Figure
2), the processor 132 responds with a reset mode at 182
in Figure 10. The reset mode commences by first
checking the voltage of the available power source.
This is done by a monitor 176 inside circuit 170 (see
Figure 9) and which generates an output signal on line
178 which is coupled to processor 132. If the voltage
is too low as tested at 184, the entire system is shut
down at 186. When the voltage level checks out OK, the
various circuits and program flags used in the system
are initialized at 188.
" 1 31 9925
The initializing operation includes at 190 the
generation of appropriate drive signals to drive motors
146, 146' (see Figure 9) so as to move the pens 38, 40
to their reference positions at 106, 106' (see Figure
4). Once the pens reach these, the reference sensors
90, 90' (see Figures 4 and 9) generate appropriate
interrupts to processor 132 to stop it from moving the
pens 38, 40 any further.
At 192 the various signals that are external to
processor 132 are read in. These include parameter
values, temperature, humidity, battery voltage and AC
power.
At 194 a test is made whether the battery power is
low. If so, a low battery power indication is entered
in display 46.2 at 196.
The values for temperature and humidity are
linearized by processor 132 at 198 and the maximum and
minimum values are stored or updated at 200. Thus,
each parameter value is compared with the stored
maximum and minimum and if the current values respec-
tively exceed or are less than these, the current value
is used to replace the stored value.
Linearizing of parameter measurements follows well
known criteria and depend upon the characteristics of
the sensors that are used. For example, microprocessor
132 may store a formula or a look-up table with which
incoming sensor signals are corrected to enable record-
ing on the linear scale of chart 26.
At 202 a test is made whether an interrupt request
was received on line 144 from timing circuit 138, see
also Figure 9. If so (as shown in Figure lOA), the
t 3 1 9925
current values of the sensor signals are at 206 first
translated into a number of pulses relative to the
reference position 106, 106'. This conversion may be
obtained by determining a scale factor by which, for
example, the number of degrees in centigrade is
directly converted to a specific number of pulses from
sensors 102, 102'. Since the chart scales increase
from left to right and the reference positions are at
the high right end of the scale, the conversion also
involves a subtraction of the specific number of pulses
from the total number of pulses needed for a pen to
travel the full length of a radial 66 on chart 26. The
final pulse number is then stored at 208, Figure lOA as
a desired pen position. This value is then compared at
210 with the current pen position. If this is at a
reference position 106 or at some other place, the
difference in pulses is stored at 212.
Each pen motor is energized at 214 until the number
of pulses detected from the appropriate lead screw
rotation sensor 102 or 102' equals the difference as
counted down as zero at 216. When this equal
comparison is detected the drive 146 or 146' to the
appropriate parameter motor is deactivated at 218 by
processor 132.
The current pen position value is then replaced at
220 with the desired value as determined at 208 and a
test is made at 222 if there is another pen to be
moved. If so, at 224 other pen values are used and the
appropriate pen flag incremented at 226 for use with
test 222. A return is then made to step 206 to cause
movement of this last pen.
By requiring an interrupt from timer circuit 138 to
initiate a pen movement, a substantial saving in
1 31 9925
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battery power is obtained since pen motors 94, 94' are
but periodically operated. Since changes in tempera-
ture and humidity usually tend to occur slowly, the
amount of pen movement required also tends to be
small. The pen motors may thus be considered to be
driven by pulses of durations commensurate with the
desired pen position change.
After the pens have been moved, the keyboard or
panel 42 is interrogated at 230 in Figure 10 for the
actuation of any of its keys. The appropriate displays
are updated at 232 and a return is then made to step
192 to repeat the previously described process.
A particular advantage of the planar chart recorder
in accordance with the invention is the ability to uti-
lize low cost DC motors 94-94'. Such motors, however,
typically tend to overshoot after power is turned off
or even when a reverse braking potential is briefly ap-
plied. As shown in Figure 11, a technique 300 is em-
ployed whereby pen motion past a desired position is
measured and used to maintain pen position control.
The routine 300 is carried out both with program
steps inside a microprocessor and the sensing of para-
meters as previously described with reference to Fig-
ures 10 and lOa. The Figure 11 is shown for a slngle
temperature recording pen such as 38 with a similar
routine being applicable to a humidity recording pen
such as 40. The steps describe the generation of
various signals as explained below.
Thus at 190' in Figure 11, like stop 190 in Figure
10, a temperature recording pen 38 is first moved to
its reference position as is needed at turn- on. If a
1 31 9925
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temperature reading was made at 192', the temperature
measurement is converted to a number of pulses, Np,
and a pen motion initiated at 214'.
When the pen reaches its desired temperature indi-
cating position, To~ as determined by test 302 where
the number of pulses N are compared to Np, the motor
is braked at 304. This can be done in different ways
such as by disconnecting electrical power to the motor
or shorting the motor leads together to use the back
emf of the motor for braking.
After electrical power is removed, the motor tends
to continue to rotate in a coasting mode to place the
pen at a temperature indicating position of Tl.
Hence, at 306, the pulses generated on line 104 during
coasting are counted and the sum stored as Nc. Since
such coasting tends to be of limited duration, the
counting of coasting pulses is limited to a maximum
interval. The coasti~g count Nc represents a correc-
tion signal indicative of the amount that a pen has
traveled past a desired parameter indicating position.
The stored position of the pen 38 is then adjusted
to include the coasting motion of the motor after its
connected pen had reached the desired position. The
stored pen position, in the number of pulses, is then
as determined at 308; note that this corresponds to a
temperature indicating position of Tl instead of
To~ No attempt is made to reverse the motor to cor-
rect for the coasting error.
However, when as indicated by test 311, a new tem-
perature, T2, measurement is to be made at 313 and
its equivalent pulse count NT2 is stored, further pen
`"` I 31 9925
motions are made relative to the actual pen position,
NTl, and not the initial desired temperature
positin~ NT0
This is implemented by first determining at tests
314 and 316 whether the new desired pen position NT2
exceeds the old position NTl by a minimum count or
number of pulses NMIN and the expected amount of
coasting pulses Nc. If not, then no pen motion is
implemented and a return is made at 318 to the main
program along line 320. In the event the new tempera-
ture position exceeds the current pen position by more
than NMIN + Nc pulses, the pen is moved after com-
parison at 322 whcih produces a signal representative
of a desired pen travel that is equal to the difference
less the amount of expected coasting pulses. A return
is made to test 302 after a flag is set at 324 to force
the subsequent coast count to be positive.
In the event the new temperature position, NT2,
requires a reversal of pen motion, as suggested in the
diagram of 326, then the pen is moved at 328 by an
amount equal to the difference less the amount of
expected coast pulses. A return is then made to test
302 after a flag is set at 330 to force the subsequent
coasting count to be negative when the pen's actual new
position is determined at 308.
Note that with this technique an automatic learning
is achieved in the amount of coasting pulses that are
involved with the motors and related pen moving ele-
ments.
As shown in Figures 5, 7 and 8, chart drive motor
140 is mounted below a chart support surface 240 and
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- 18 -
has its drive shaft 242 connected to the drive spindle
62 with a bolt 244. Spindle 62 extends above surface
240 for engagement by chart holder 30. Spindle 62 has
an annular bottom flange 246 that has its upper surface
247 aligned level with surface 240 so that chart 26 can
seat level on both surfaces.
Spindle 62 extends above surface 240 with a circu-
lar shaft 248 that terminates at a head 2~0 having a
through bore 252 and a counter bore 254 sized to
receive the head of bolt 244.
Shaft 248 has a turned down segment 256 that
terminates with an annular fulcrum surface 2~8 and at a
rim 260 just above flange 246. Rim 260 serves to
facilitate centering of a chart 26 onto spindle 62 as
shown in Figure 7.
Chart holder 30 serves as shown in Figures 7 and 8
to provide a rotational coupling of the spindle 62 with
a chart 26 in a manner that permits easy placement and
removal of a chart while providing good chart engage-
ment to reduce chart tearing during rotation. This is
achieved by forming chart holder 30 so that it can be
pressed against a chart 26 without requiring rotation
while providing an enlarged frictional surface contact.
Chart holder 30 is formed of a clamping segment
made of a pair of sections 270, 272 which are mounted
in juxtaposed spaced-apart positions with each other by
a pair of stand-off pins or screws 274. The bottom
surfaces 276 are flat and provide good frictional con-
tact with a re-enforcing ring 278 on chart 26. Sec-
tions 270, 272 each have a partial cylindrical cut-out
280 so that when pins 274 hold the segments together,
`" 1 ~t 9925
the head 250 of spindle 62 extends into them, prefer-
ably with a close tolerance fit.
Pins 274 are sized to space sections 270, 272 apart
to form a slot 282 to receive a manual actuator 284.
This has a deformable bias arm 286 which normally tends
to be straight as shown in Figure 8. Arm 286 termi-
nates at oppositely-located pivot portions 288, 288'
each of which has a bore 290 sized to freely receive a
pin 274. The parts of the arms 288, 288' below the
pins are sized and shaped to form edges 292 for seating
as shown in Figure 7 below and against annular fulcrum
edge 258 of spindle 62 while surfaces 294 align
parallel to the recessed segment 256 of spindle 62.
The distance between pins 274 is set so that arm
286 must be deformed as shown in Figure 7 to align
bores 290 with the pins. This produces a shape restor-
ing moment in the direction of arrows 296. This tends
to pivot arms 288, 288' and thus causes edges 292 to
push against fulcrum edge 258 and clamp the entire
chart holder 30 against chart 26.
A compressible spring 300 may be used to increase
the chart clamping force. Spring 300 may be seated in
a recess 302 in a platform 304 extending from segment
270 into slot 282 so as to fit below arm 286 as shown
in Figure 7.
With a chart holder 30 as illustrated in Figures 7
and 8, the removal and replacement of a chart 26 is
made very convenient. Removal requires manual squeez-
ing of the arm 286 against its natural bias thus pivot-
ing edges 292 of arms 288, 288' away and allowing the
holder 30 to ~e pulled away at the same time. The
1 31 9925
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chart 26 can ~hen be pulled away from spindle 62. When
the arm 286 is squeezed during installation of a chart,
it can then be rotated and time aligned by onè hand.
Figure 6 illustrates a pen 38 or 40 for use with
recorder 20. The pens are preferably aligned so that
the writing tips 310 project forwardly from ink contain-
ing chamber 312. This enables close placement of the
pens to minimize time off-sets between them.
Figures 12 and 13 illustrate another chart holder
350 which adheres magnetically to a flange 246' con-
nected to chart motor 140. Flange 246' is formed of
iron and has a spindle 260' shaped to fit through a
hole 60 in a chart 26. Chart holder 350 is formed of a
cylindrical plastic element having four recesses 352
arranged in an annular fashion around a central bore
354. Bore 354 is sized to freely but snugly receive
spindle 260'.
Strong magnetic elements 356 are mounted in re-
cesses 352 and project therefrom sufficiently to form
an annular magnet by which chart 26 can be firmly held
to flange 246'. Elements 356 can be ceramic type mag-
nets that are selected to provide a firm clamping force
to a chart 26 placed on the flange 246'. Elements 356
are sized to force fit in recesses 352.
By way of such magnetic chart holder, it is easy
and convenient to replace or mount a chart 26.
Having thus described a chart recorder and chart in
accordance with the invention, its advantages can be
appreciated. Variations can be implemented without
departing from the scope of the invention. For
example, the motion of the leading pen can be delayed
by storing its associated parameter values for a time
that is equivalent to the actual spacing between pens.
