Geometrical instruments – Distance measuring – By flexible tape
Patent
1993-12-03
1995-06-27
Wirthlin, Alvin
Geometrical instruments
Distance measuring
By flexible tape
33707, G01B 310
Patent
active
054268630
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates more particularly to an electronic tape measure with a digital display.
BACKGROUND OF THE INVENTION
Electronic tape measures with a digital display are already available and often include a calculator, mounted on a case incorporating a wound tape, for use as a normal calculator and/or for use in computing various information based on one or more distances measured by the tape measure.
The distance measured in all these devices requires some arrangement for determining the length of tape which has been drawn out of the case at any time as well as determining, as the tape is moved, whether the tape is being moved out of or in to the case. A digital display is provided for displaying, usually at all times, the amount, that is the length, of tape which is currently extending out of the case.
The most direct way of monitoring the tape is to "read" optical, magnetic or other markings on the tape itself. It has already been proposed to provide equally spaced perforations in the tape and to sense movement of the tape by exposing the tape to a light source on one side of the tape and sensing light that passes through the perforations as the tape moves past the sensor. Such arrangements cannot in themselves provide an indication of which direction the tape is moving and are particularly inaccurate if the tape judders, sensitivity of the sensor varies or the intensity of the light source changes, and so on.
Further, the resolution of such arrangements cannot be very high without significantly weakening the strength of the tape, that is, other than by having very many perforations per unit length.
SUMMARY OF THE INVENTION
According to the invention there is provided an electronic tape measure comprising a case having a digital display and including a microprocessor, an extendible tape wound on a reel in the case which can be withdrawn from the case to carry out measurements, a number of equal displaced readable unit markings on the tape and a reader for reading the markings as the tape is moved out of and into the case, in which the reader has a number of separate reading devices displaced lengthwise with respect to the tape and displaced from one another to extend over a distance equal to the separation of markings on the tape for providing signals representing incremental units of movement of the tape, the markings and the reading devices being arranged so that discrete sequential incremental signals are developed by the reading devices corresponding to positions whenever a mark of the tape is read by either a single reading device or two adjacent reading devices at any one time, the outputs of the reading devices being provided to the microprocessor as the incremental unit signals.
The unit markings may comprise holes in the tape and the reading devices comprise photocells.
The unit markings may be arranged at one cm. or one inch intervals along the length of the tape.
A digital calculator may be mounted on the case having a dedicated digital display. The measurements made by the tape may be supplied to the calculator.
A combined electronic tape measure and calculator according to the invention will now be described by way of example with reference to the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of the measure and calculator;
FIG. 2 is an isometric view of the measure and calculator with one side removed;
FIG. 3 shows part of the tape;
FIG. 4 shows a schematic layout of photocells for use in the measure and calculator;
FIG. 5 shows some various possible positions of the tape relative to the photocells;
FIG. 6 shows the sequential logic of outputs received from the photocells when the tape measure is used; and
FIG. 7 is a block circuit diagram of the electric circuit for measure and calculator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, in FIG. 1 a plastics casing A is provided with an LCD display 1, a sliding mechanical tape locking button 2, an ENTER key 3 for use in ente
REFERENCES:
patent: 4161781 (1979-07-01), Hildebrandt et al.
patent: 4195348 (1980-03-01), Kakutani
patent: 4427883 (1984-01-01), Betensky et al.
Solar Wide Industrial Ltd.
Wirthlin Alvin
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