Note: Descriptions are shown in the official language in which they were submitted.
7~6~-53
EIAND HELD DIGITAL MEASURING DEVICE
Field of the Invention
This invention is directed to a hand held measuring
05 device which provides a digital display. It is more
specifically directed to a motcrized tape measure which
digitally measures the tape extension and displays the
reading in various units.
Background of the Invention
Various forms of measuring devices have been in use for
hundreds of years. The ruler, yardstick or meter stick is
quite efficient and can accurately measure dimensions within
reasonable accuracy limits. ~owever, the major problem with
these types of measuring devices is that they are cumbersome
and hard to handle, carry or store.
Because of these common problems various ways have been
tried to make a measuring device compact and easily handled
and carried. The two most common devices that have evolved
are the folding measuring ruler which is commonly used by
carpenters and the convenient hand-held tape measure.
One of the attributes of the hand-held tape measure is
that it is generally light weight and easily stored and
used. The tape is compactly coiled within the housing and is
spring biased to retract into the housing when not in use.
This device provides an additional feature in that the tape
as it is extended has a slightly concave cross-sectional bow
which allows the tape to extend outwardly, in a
self-supporting configuration for a substantial distance. In
addition, another common feature of this type of device is
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that the length of the housing behind the extension point of
the tape is usually a standard set dimension so that the
device can be used for measuring inside dimensions by merely
adding the set length of the case to the measurement shown
05 on the tape face.
The primary drawback with this type of device is that
only relatively coarse and inaccurate measurements can
actually be made. These measuremPnts are also limited to the
units to w~ich the tape is graduated. The accuracy of the
readings depends upon how small these units are divided and
how accurately they are interpreted by the user. Naturally,
the size of the graduation will determine how well they can
be seen, especially under poor lighting conditions.
The present invention is directed to a way of
conveniently extending or retracting the tape from the
housing and at the same time providing an extremely accurate
and convenient measurement reading. This reading can even be
obtained where there is only limited light. At the same
time, the present invention can instantly convert the
displayed measurement reading to fractional or decimal units
of either the English or metric system. All of this can be
done in a matter of a few seconds.
Information Disclosure Stateme~lt
The following patents which are believed to be
pertinent to the subject matter of this invention are
presented in compliance with the inventor's duty to disclose
all materials of which he is aware.
The Soule patent (U.S. 4,031,360) discloses an
0 electronic tape measuring device comprising an electronic
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digital display unit connected to an electronic calculator.
The device has a rachet wheel type sensing means for
detecting the unwinding and winding of the tape on the reel.
The readout in this device can be set to read in English or
05 metric units. A manual electric switch is provided for
operating the readout portion of the device.
The Grant patent (U.S. 4~242,574) discloses a digital
display tape measure wherein the tape is optically encoded.
As the tape passes op~ical fiber bundles, its indicia are
read by electronic logic circuitry and exhibited on the
digital display. There is a capability proviaed in this
device for measuriny lengths in either centimeters or inches
as desired.
The Iwase patent (U.S. 4,181,848) and Tateishi, et al.
(U.S. 4,181,960) discloses digital tape measures which
incorporate a memory circuit. These devices are capable of
performiny addition and subtraction operations during the
measuring functiorl. In Tateishi, et al., a photo detector
determines the length of the tape by noting the rotation of
the spring loaded tape reel.
In the German patent which issued to Reller (DT 28 46
915), the length of the tape is shown in either centimeters
or millimeters on a digital display. In addition, a
magnifyinq glass is provided for reading the fine divisions
on the tape. Electronic scanning markers can be provided for
reading the measurement which is being made with the device.
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S~nmary of the Invention
This invention is directed to a hand-held digital
measuring device, which includes a motorized tape which has
an electronic digital sensor.
05 The tape is mounted within a suitable housing and is of
the common thin metal variety which is wrapped or coiled on
a rotatably mounted reel or shaft. A small reversible motor
is connected to the shaft by a series of reductisn gears
with a belt drive connec~ion to the tape shaft. A suitable
operating switch can be utilized for energizing the motor in
either the extend or retract direction~ The motor can also
be of the variable speed type so that the actual speed of
the tape can be easily controlled. In addition, the high
gear reduct7on will help to hold the tape in the extended
position when the motor is deenergized.
The actual tape used in this device has an additional
feature which is not found in most conventional tape
measuring devices. A series of small equally spaced holes
are provided along the longitudinal center of the tape. The
surface of the tape can be left blank or marked with the
usual indicia. A rotatable sprocket having pins or teeth
which closely fit and engage the tape holes is suitably
mounted within the housing. The sprocket is connected by
speed increasing gears to an encoding disk which is
rotatably mounted between oppositely positioned optical
switches. The encoding disk, gears and sprocket are designed
to have minimum or no backlash so that the rotation of the
encoding disk will closely follow the lineal movement of the
tape. A fine adjustment knob can be connected to the
sprocket shaft and arranged to extend beyond the side of the
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housing whereby a precise length of the tape can be easily
obtained.
The encoding disk is utilized in conjunction with at
least two optical coupler switches to produce an electronic
05 digital output that is arranged in direct proportion to the
movement of the tape in either direction. This disk is
composed of an even number of alternating segments or slots.
In the present example, the segments are each 45 degrees
making a total of eight segments. Four of the segments are
transparent and allow infrared light to pass while the
alternating four are opa~ue. This can be accomplished by
cutting alternating segments out of a solid disk or forming
the disk out of clear plastic and coating the alternating
segments with a material which i~ opaque so as to block
infrared or other light energy. The optical coupler switches
are each composed of an infrared or light emitter on one
side of the disk and a silicon collector on the opposite
side which is sensitive to the generated energy. Usually,
when the energy strikes the collector, current is allowed to
flow resulting in an "on" condition or output. Optîcal
switches, Model No. TIL143, manufactured by Texas
Instruments, have been found to be quite satisfactory for
this purpose.
One switch is offset one half of the width of a segment
which would be 22~ in this example. Thus, the outputs from
the coupler switches are out of phase by 22~ in either
direction depending upon which direction the tape is moving.
The pulses in the outputs from both switches are added and
fed to an integrated circuit counter which processes the
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outputs to add or subtract to -~he display count or determine
the final display reading~
The speed ratio between the sprocket and the encoding
disk is arranged in the present example to 1:4. By the same
token, the diameter of the sprocket in the present example is
sized so that the sprocket makes one revolution for each two-
inch lineal movement of the tape. Thus, in this example herein
the display readout can be given in fractions as small as
1/32nd of an inch.
It is to be understood that this device is not
limited to the number of segments and gear ra,ios as described
herein. The present arrangement has intended for English units
but can be arranged to provide any desired units or divisions
merely by changing the number of segments on the encoding disk,
the gear ratio between the sprocket and the disk and the
diameter of the sprocket. In this way, any desired measuring
scales, divisions or units in either the English or metric
system can be provided as well as the display given in decimal
or fractions with the degree of accuracy desired.
The invention also includes various other features
such as a fence lu~ to be used in conjunction with the rip
fence on a table saw. This feature can be used when the
ripping dimension is less than the length of the tape housing.
In addition, various electrical switches can be provided on the
housing which will allow the digital readout to be reversed
from one side to the other as well as electronic conversion of
the readout from either English or the metric units. At the
same time, the circuitry can be provided with a memory switch
whereby measurements can be added or subtracted or reset as
desired during a measuring function. Measurements
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longer than the total length of the tape can be made by
electronically adding multiples of the total length of the
tape to the actual tape reading to obtain the final
dimension.
05 As an additional feature, the power switch can also
include a lock which extends over the end of the tape when
the switch is in the off position. This prevents the tape
from extending when the power is off and can provide an
automatic reset for the digital display.
other features and advantages of the present invention
will become apparent from the following detailed description
of the invention when it is considered in conjunction with
the accompanying drawings.
Brief Description of the Drawinqs
Figure 1 is a perspective cutaway view of a hand-held
digital tape measure according to the present invention;
Figure 2 is a right side cross-sectional view showing
the internal arrangement of the components;
Figure 3 is a top plan view with the tape slightly
extended;
Figure 4 is a left cross-sectional view;
Figure 5 is a front view showing the marking device
along the right edge;
Figure 6 is a rear view of the device;
Figure 7 is a pictorial enlarged view of the encoding
disk showing the energy opaque and transparent segments;
Figure 8 shows the output wave form and phase
relationship ~etween the coupler switches during the forward0 and reverse rotational movement of the encoding disk; and
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Figure 9 is a block diagram of the electronic circuitry
used in the present invention.
Detailed Description of the Drawings
05 Turning now more specifically to Figure 1, the
hand-held digital measuring dev;ce 10 according to the
present invention, includes a case or housing 12, digital
display 14, and measuring tape 16. The free end 18 of the
measuring tape 16 extend5 through an elongated slot 20
provided at one end of the housing 12. A hook or clip 22 is
suitably mounted on the end of the tape 18. The tape which
can have any desired total length, such as 12 or 16 feet, is
suitably coiled or wound on a reel or shaft 24 which is
rotatably mounted within the housing 12. An electrical power
source or battery 44 and small variable speed, reversible
electric motor 26 are mounted within the housing. The motor
26 includes a pinion gear 28 connected to its output shaft.
Speed reducing gears 30, 32 suitably mounted within the
housing are arranged to engage the pinion gear 28 and drive
the reel 24 by means of the pulleys 34, 36 and belt 38. As
can be easily seen, the speed of the motor through the gears
30, 32 and pulleys 34, 36 is greatly reduced for driving the
reel 24. This provides two important results, one being that
the reel or shaft is essentially locked when the motor is
deenergized preventing the extended end 18 of the tape 16
from moving in either direction once the measurement has
been established. The other is that the actual speed of the
tape in or out of the housing can be precisely controlled by
varying the rotational speed of the motor 26.
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The switch 40 is a master switch which disconnects ~he
motor and electronic circuitry from the electrical power
source. This switch can also include a lock (not shown )
which engages the end of the tape when in the off or
05 deenergized position. This lock provides an additional
restriction which prevents the tape from moving out of the
housing when the motor is deenergized~ The motor 26 is
engaged by a noramlly "off"~ momentary switch 65. A variable
resistant switch may be used for this purpose which would
allow control over the speed of extension and retraction and
also the direction of the tape movement.
The battery 44 for pow~ring the motor is mounted
within the housing and is arranged to be easily removed or
replaced. The battery can be of the alkaline type,
nickel-cadmium type or some other which will provide long
service life and possibly can be recharged. If desired, the
battery can be permanently mounted in the housing and
recharged by a suitable case connection to an external
charger. The battery also provides electrical power to the
solid state electronic circuitry which is provided in
conjunction with the digital display 14. It is anticipated
that the electronic circuitry will include a prepackaged
micro-computer circuit which will be mounted as a unit with
the display 14 to compactly fit within the upper portion of
the housing 12.
Along the upper surface 45 of the housing 12 are
arranged a number of push button or rocker type control
switches 46, 48, 50 and 52. Switch 46 provides an
inside/outside measurement function while switch 52 provides
the mode selection. Switch 48 can be utilized for resetting
the display measurement to zero while control switch 50 can be
utilized for the extended measurement function thereby units of
the tape length can be added to the display reading for per-
forming measurements longer than the single tape length. An
additional switch 47 can be provided to reverse the display so
that it can be read from either side of the housing. Other
switches can be added or individual switches can perform dual
functions if additional features are desired.
A spring biased marker 54 is mounted on the side of
the housing 12 adjacent to and in line with the edge of the
housing to mark the exact location where the measurement is
taken. This marker includes a pointed plunger 56 which is
biased in the raised position by the spring 58.
A unique and sensitive tape sensing device 60 is
suitably mounted within the housing 12. The sensing device 60
includes a rotatably mounted shaft 62 having a sprocket ring 64
mounted thereon. The sprocket includes a number of outwardly
extending equally spaced teeth or pins 66. The tape 16 has a
series of equally spaced holes 68 which are centrally arranged
along the longitudlnal axis of the tape over its entire length.
The sprocket pins 66 have the same pitch or spacing as the
pitch of the holes 68 so that they precisely engage and rotate
the sprocket in response to any lineal movement of the tape end
18. In addition, the pins 66 can be tapered or pointed and the
holes 68 si~ed slightly smaller than the base of the pins so
that as the holes are engaged by the pins there will be a close
fit to eliminate any backlash or relative movement between the
tape and the sprocket. If desired, a rotatable Teflon or nylon
roller
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(not shown) can be suitably mounted below the tape to hold it
in proper position against the sprocket. This roller as well
as possibly several additional rollers can also help to reduce
the friction between the tape and the inside surface of the
housing.
The sensing device 60 further includes a gear 70
which is mounted on the sprocket shaft 62. The gear 70 engages
a pinion gear 72 which is suitably mounted on a shaft which
also contains an encoding disk 74. Mounted on either side and
surrounding the encoding disk 74 are optical coupling switches
76 and 78. The gear ratio between the gear 70 and 72 is
arranged so that one revolution of the sprocket 64 will produce
four revolutions of the encoding disk 74. It is to be under-
stood, however, that any desired ratio can be provided
depending upon the desired sensitivity and accuracy of the
sensing device. Thus, as can be readily understood as the free
end 18 of the tape 16 either extends out of or is retracted
into the housing 12 the sprocket 64 rotates following the pre-
cise movement of the tape. The rotational movement of the
sprocket 64 is transmitted through the gears 70, 72 and is
accurately transLated into rotational movement of the encoding
disk 74. An adjusting knob 63 can be arranged on the end of
the sprocket shaft 62 so that it will protrude through an
opening in the side of the housing 12. By turning the knob 63
a fine adjustment can be made to the length of the extended
tape to make a precise measurement.
The coupler switches 76, 78 can be of the infrared
digital output type. In these devices, infrared energy is
generated on one side of the encoding disk with an infrared
sensor provided on the opposite side. As can be seen in
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Fig~re 7 the encoding disk can be equally divided into seg-
ments. Half of the segments are co~ered with a material which
is opaque to the infrared energy and alternate with the other
half which are transparent to this energy. As shown in this
example eight segments are provided with each encompassing a
circular angle of 45 degrees. The coupler switches 76, 78 are
mounted so as to straddle the edge of the encoding disk 74 and
are arranged so that they are one half of a segment width or
22~2 degrees out of phase with each other as illustrated in
Figure 7. As can be easily seen one coupler switch 76 is
shown at a position which is precisely at the transition point
between two segments. The second coupler switch 78 is posi-
tioned at the exact midpoint of a subsequent segment. The
angular offset of the couplers with respect to each other is
important and not the actual type of the respective segments.
The signal output from the coupler switches is an on or off
condition depending upon whether the associated segment is
opaque or transparent. Thus, the output from each switch is
essentially a series of square wa~e pulses with the electrical
output of one switch being out of phase one half of the width
of a pulse compared to the other.
In Figure 8 the phase relationship between coupler
switch 78 and coupler switch 76 is either leading or lagging
depending upon which direction the encoding disk 74 is
rotating. The counterclockwise rotation of the encoding disk 74
as shown by arrow A is designated for the purpose of illustra-
tion as being the forward direction. This is a condition in
which the tape end 1~ is being extended from the housing 12.
Upon reversal of the direction of the tape 16 and its retrac-
tion into the housing the rotational
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direction of the encoding disk 7~ is reversed 50 that the
cyclic OUtp~lt of the second switch is actually lagging behind
the output of the first.
In Figure 9 is shown a block diagram of the circuitry
which can be utilized for obtaining the actual digital display.
The outputs from the individual coupler switches are fed into
an integrated circuit which includes a logic input circuit for
determining the phase shift of the two signals to determine
whether the tape is extending or retracting with respect to the
housing. The other input circuit provides a counting function
for counting the input pulses that are generated by both of the
coupler switches. As previo~sly mentioned, as the tape extends
or retracts exactly two inches, the sprocket 64 makes exactly
one revolution. Due to the speed increasing gears 70, 72 the
encoding disk is caused to rotate precisely four times or four
revolutions for each revolution that is made by the sprocket
64. The unique combined outputs from both switches during the
angular rotation of the disk for one transparent and one opaque
segment cycle results in four binary output functions or
counts. Thus, the four revolutions of the encoder disk for the
present illustration causes the production of 64 binary
functions for both switches. For each inch of tape travel a
precise total of 32 "on" or "off" binary functions or counts
are produced for each coupler switch. Thus, each count is
equal to precisely l/32nd of an inch travel of the tape end
18. In this way, these binary on/off functions produce the
digital input to the electronic circuitry.
As previously stated the outputs from the optical
coupler switches are fed directly to an up/down logic circuit
84 which identifies ~he phase relationship of the
4~i8~)
outputs. From here the output goes through a counter 86
which feeds the resulting count directly into a divider 88.
The divider 88 divides by 32. The output of this counter
which is in whole inches, in turn, is split and fed into two
os divide circuits. One circuit 90 divides by 12 while the
second 92 divides by 256. The output of the divider 90
splits with the residual output designated as inches
connected directly to the address multiplex 96. The other
output which represents units of feet is fed to ~ divider 94
which divides by 16 to convert the units of feet into units
of total t~pe length. In the example ~hat is provided in
this application, the length of the tape is anticipated to
be 16 feet. Thus, the output from this divider is fed
directly to the address multiplexer 96 and represents a
whole number or decimal fraction of the total length of the
tape for that particular measurement. If greater than a
whole number, the whole number can be stored and added to
the next measurement to provide a reading for a measurement
longer than the actual length of the tape. The other output
of the 32 divider 88 represents the residual fractional part
in inches of the total count which is fed directly into the
Read Only Memory (ROM) 98. The output of the divider 92
which is in units of inches is also fed directly into the
address multiplexer 96.
A display format selector switch such as switch 52
which determines the mode of operation for the device
actuates an input to the address multiplexer 96 as well as a
si~nal directly into the ROM 98 and the display driver 100.
An output from the address multiplex circuit 96 is fed into
the ROM 98 for later processing or comparison for conversion
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from English to metric units or vice versa. Any fractional
parts of the original count from divider 88 is added in the
ROM. Thus the output from the address multiplexer is
compared with the previously stored information concerning
05 fractions or decimals for the conversion from English to
metric units. The output from this device is then fed
directly into the display driver which in turn conditions
the results for direct display by the liquid crystal diodes
(~CD) which are provided in the display 102.
As can be easily seen, the described circuitry allows
for an up or down counting depending upon which direction
the tape is actually moving. Thus, when the tape is
retracted into the housing the count is reversed or down
counts from the original display measurement~ In this way,
the reading when the tape is completely retracted into the
housing should return to exactly zero. In this way, a
determination can be made as to ~he accuracy or tolerance
that exists within measuring device. If the inaccuracy is
extreme, then it is necessary to recalibrate or repair the
unit prior to further use.
It is to be understood that the electrical power source
for powering this device can be a replaceable or
rechargeable battery or even a solar cell. A solar cell,
especially for outside use can be used to directly power the
unit or recharge an internal battery. The rechargeable
battery can be permanently mounted within the housing and
the housing connected directly to a suitable charger or a
separate battery charger can be connected by a suitable
jack.
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While a hand held digital tape measure has been shown
and described in detail in this application, it is to be
understood that this invention is not to be limited to the
exact form disclosed and changes in detail and construction
05 of the invention may be made without departing from the
spirit thereof.
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