GB2241060A - "Electronic tape measure" - Google Patents

Abstract

An electronic tape measure has a casing A, a calculator, and LCD displays. A microprocessor incorporated within the casing A controls the displays to provide measurement readings. The movement of the tape is detected by sensors 24 which read movement of holes 10 in the tape wound on a reel 23 and sensors 18 which detect movement of incremental markings 19 on a disc 15 which rotates with the reel. Markings 17 on the disc also provide output signals for a level meter when the disc is allowed to freely rotate by being declutched from the reel. The disc is mechanically biassed by a weight 16 to adopt a particular orientation with respect to gravitational forces when free to rotate. <IMAGE>

Description

Tape Measure The invention relates to tape measures.

The invention relates more particularly to a tape measure which can be combined with a level meter and/or a calculator. Tape measures have already been proposed which provide a digital read out of distance measured and include a microprocessor, or other calculating electrical circuit, for providing read-outs of area and volume based on measurements of different dimensions of an object or space made using a same tape measure. Compact tape measures which include multiple functions including level measuring have not so far been proposed and/or use the same measuring type of arrangements for both functions.

Tape measures and level meters are often required at the same location by the same user and yet must be conventionally provided of necessity by separate devices.

According to the invention there is provided an electronic tape measure having a casing and a retractable tape in the casing wound on a spool provided with a circular disc having readable incremental markings distributed therearound, in which the tape has evenly distributed apertures along its length, a first reader for reading movement of the incremental markings corresponding to small movement of the tape in and out of the casing and providing first incremental output signals corresponding to passage of the markings past the reader, a second reader for sensing the apertures on the tape and providing second output signals corresponding to the passage of the apertures past the second reader, a microprocessor arranged to receive and programmed to combine the first and second output signals and drive a readable display to indicate the length of tape extending from the casing.

The spool may be freely rotatable and arranged to orient in a particular rotational position with respect to gravitational forces, so that markings on the disc relative to the orientation of the casing can be used to determine whether the casing is level or not and/or to what extent the casing is not level.

A generally conventional digital calculator may be mounted on the casing in which the display of the calculator is arranged to be controlled as required for displaying tape measurements or other output signals from the microprocessor.

The microprocessor may be programmed to generate and control the display to indicate total lengths of sequential different measurements, areas by combining two sequential measurement or volumes by combining three sequential measurements.

An electronic tape measure according to the invention will now be described by way of example with reference to the accompanying drawings in which: Figures 1 and 2 are different perspective views of the tape measure; Figure 3 is a perspective exploded view of the tape measure; Figure 4 is a block diagram of a circuit for the tape measure; Figures 5 and 6 are flow charts showing functions of the circuit; and Figure 7 shows measuring interval patterns used in the tape measure.

The tape measure to be described is combined in one device with a calculator, and a level meter.

Referring to the drawings, in Figures 1 and 2 a plastics casing A is provided with LCD display 1, a sliding tape mechanical locking button 2, an ENTER key 3 for use in entering a tape measurement to store the measurement in a memory. A tape 4 which has a conventional tip 4A is used to measure distances between the tip 4A and a mouth 5 of the casing A. A (+case) key 6 when pressed adds the length of the casing A to any measurement so the tape measure can be used to measure from the tip 4A to the rear of the casing opposite the mouth 5.

A power switch 7 turns the power ON and OFF and also selects electrically, according to its position, the units of measurement to be displayed by the tape measure. The position of the switch 7 is also used to select whether the device is to be used for measurement or as a level meter. An LCD display 8 is for use with a generally conventional calculator mounted in the side of the casing A having a usual keyboard as shown for use with the calculator. A key 9 is provided for circular computations. If a circle diameter is measured by the tape and the key 9 pressed once, the circumference of the circle will be displayed on display 1, if the key 9 is pressed twice, the area of the circle will be displayed.

The tape 4 is provided with apertures 10 at intervals of 1 centimetre. A SELECT key 11 is mounted on the side of the casing A.

The LCD displays 1 and 8 are used to conveniently display the current measurement of the tape or act as a level meter, and for showing calculation results, respectively.

Measuring an object is carried out using the tape measure placing its tip 4A at one end of the object to be measured and the mouth 5 of the plastic casing at the other end of the object and then pressing the ENTER key 3. The measurements are shown instantaneously on the measurement display 1 while moving the tape. Pressing ENTER key 3 causes the measurement at that instant to be stored in a memory. The locking button 2 prevents the tape from retracting back into the case.

While the calculator can be used as an ordinary 8-digit-display calculator with four fundamental functions, percentage computation, All Clear (AC), Clear Entry (CE), and Memory Recall (MR), it can also be used interactively with the tape measurements.

This is without having to transfer from a certain mode to another or having to re-enter the measurements manually on the numeric keyboard.

After entering a tape measurement by pressing the ENTER key 3, the measurement can be readily multiplied or divided with a certain number or be included in a series of computations by simply pressing Memory Recall (MR) since the tape measurement is automatically stored in the memory once ENTER key 3 is pressed.

This electronic measure features five selectable functions. The default function is single entry.

Everytime ENTER key 3 is pressed the memory is overwritten with the current tape measurement.

Pressing SELECT key 11 the first time leads to function two which performs the summation of lengths. This means that pressing ENTER will add the current tape measurement to the previous entered measurement, and the next entry will be added to the sum of the previous ones and so on. Pressing SELECT key 11 the second time will lead to function three which is area computation. That is, the second tape measurement entry will be multiplied to the first one. Pressing again SELECT key 11 will lead to function four which is volume computation. This is similar to function three but can accommodate up to three entries unlike function three which is limited to two entries only. Pressing SELECT key 11 the fourth time will finally lead to function five. This function is a combination of the summation of lengths and volume computation.This is useful in measuring large volumes or areas of objects with very long sides that exceed the whole length of the measuring tape. Pressing again SELECT key 11 will lead back to function one. In all these five functions, the current tape measurement is displayed on the tape measurement display 1 while the current computed value is displayed in the display 8. The computed value is stored automatically in the memory.

The +CASE key 6 is provided for wall to wall measurements which adds the length of the plastic casing of the tape measure to the actual tape reading for accurate measurements.

The tape measure is capable of measuring in either Metric or Imperial units. The power switch 7 is slid to select the desired unit of measurement. The metric system has a resolution of 1 millimeter and Imperial system has a resolution of 1/16 inch, as will be explained below.

The power switch is also used to select the level meter function. The level meter uses the same display as that of the tape measure.

The tape measure has an auto-power-off timer which activates when the device is left idle for five minutes. If no keys are pressed, or the tape is not being drawn in a out of the casing, or the level meter is not being used for a complete span of five minutes the power will be switched OFF automatically.

In Figure 3 a mechanical calibration switch 12 is mounted near the mouth of the casing and used to reset a counter of a microprocessor to zero when the tape is totally retracted back into the casing A. A battery compartment 14 holds three AA batteries to provide a power supply. It has a plastic casing 22 which houses the extensible tape 4 would around a spring-loaded spool 23 to enable the tape to retract by itself into the casing A. Guide rollers 20 are mounted on springs and used to press against the tape and the spool to make sure that the tape is wound around the spool uniformly as it retracts back into the casing. This tape has holes 10 in it placed every one centimeter. An optical sensoring device 24 is positioned near the mouth of the casing to detect every pass of a hole and produce a signal to be inputted to the microprocessor.The microprocessor will either increment or decrement its counter depending on the movement of the tape, whether the tape is being drawn out or retracted back into the casing respectively.

It will be noted that counting the holes 10 can only provide a one centimeter resolution. To be able to measure to a resolution of 1 millimeter a disc 15 with "millimeter" marks is attached to the spring-loaded spool so that everytime the tape is drawn from or retracted into the casing, the disc rotates together with the spool. This disc has light and dark marks 19. Each pair of which represents one millimeter. As the disk rotates together with the spool, an optical sensoring device 18 near the disk translates the light and dark marks to digital signals which are then passed through a decoder 31 (Figure 4) that analyzes if the counter should count up or down depending on the direction of the rotation of the marks, i.e. whether the disc is rotating clockwise or counter clockwise. The same decoder determines if the holes 10 are being drawn out or retracted back into the casing A.The decoded signals are inputted to the microprocessor which will either increment or decrement its counter and then drive the measurement display 1 to show the current tape measurement reading.

Since the rotational distance produced by the disc varies according to the inner diameter of the spool plus the thickness of the remaining extensible tape would around it, a correction factor should be implemented to eliminate the error due to the increasing displacement as the inner diameter of the spool decreases as the tape is pulled out. The number of marks on the disc is used to compensate for this error. The disc is designed in a way that when the tape is pulled out with a horizontal distance of nine millimeter it will also move a rotational distance that covers nine marks regardless of the amount of the tape would around the spool.

This is achieved by taking the diameter dl of the spool when all of the tape is drawn out (spool is empty) and the diameter d2 of the spool when all of the tape is wound around it (spool is full). The average of the circumferences is: (di x pi) + (d2 x pi) (pi = tape thickness) 2 The number of marks on the disc must be equal to the value of the average. It is evident that the number of marks on the disc directly depends on the inner diameter of the spool and the length and the thickness of the tape being used. So everytime these dimensions are changed for a certain device, the number of marks on the disk must also vary. This method would be applicable only for as long as the maximum error produced due to the difference between the inner and outer diameters is less than 1 mm, which is the smallest unit of resolution.The longer the tape is the thinner its thickness must be to compensate for the error.

This tape measuring device can count both in Metric and Imperial system with just one disc due to a repetitive interval pattern being followed.

EQUIVALENT INTERVALS IN MILLIMETER IN MILLIMETER O in = O mm ar O mm lmm 1/16 in = 1.5875 mm # 1 mm 2mm 1/8 in = 3.175 mm # 3 mm lmm 3/16 in = 4.7625 mm Ac4 mm 2mm 1/4 in = 6.35 mm # 6 mm 2mm 5/16 in = 7.9375 mm # 8 mm lmm 3/8 in = 9.525 mm # 9 mm 2mm 7/16 in = 11.1125 mm # 11 mm lmm 1/2 in = 12.7 mm # 12 mm 2mm 9/16 in = 14.2875 mm # 14 mm 2mm 5/8 in = 15.875 mm # 16 mm lmm 11/16 in = 17.4625 mm # 17 mm 2mm 6/8 in = 19.05 mm # 19mm lmm 13/16 in = 20.6375 mm # 20 mm 2mm 7/8 in = 22.225 mm # 22mm 2mm 15/16 in = 23.8125 mm # 24mm lmm 1 in = 25.4 mm # 25mm It can be seen from above that counting in units of 1/16 of an inch, when converted to millimeters, follows a certain interval pattern: 1 2 1 2 2. This interval pattern is translated into a string of binary bit pattern that is ANDed with the signals from the decoder, thus, producing signals that are actually counting in units of 1/16 of an inch. Using this approach any unit of measurement is possible with with to measure in Imperial units after a bit pattern has been determined based in the millimeter units.

Figure 7 shows the complete interval pattern used.

The complete pattern is composed of four sets of sub-patterns: SET A, SET B, SET AB, and SET C.

First, pattern SET A is repeated three times then pattern SET B follows. The two pattern sets are collectively labelled SET AB. SET AB is repeated four times then pattern SEC C follows. This pattern goes on endlessly except for one exception which is at the very start. At the start of this repetitive pattern, SET AB is repeated only two times and SET C immediately follows.

To convert the tape measure to act as a level meter, a clutch 21 is provided to release the disc 15 from the spool 23 and enable it to rotate freely. A weight 16 is embedded on the disk so that the disc will take up a fixed orientation with respect to gravitational forces. The level meter is now operational and the disc is freely rotatable. The method of counting is the same as that of the tape meter. The method of detecting the position of the disc is similar to before but a different set of marks 17 on the disc and a different sensoring device 18 are used. Each mark represents 1 degree of tilt.

The sensor assembly 18 contains two pairs of optical sensors, one pair for the tape measure and the other for the level meter.

A separate speech processor 40 is controlled by the microprocessor to read out the contents of the measurement and the calculator displays. Connected to this speech processor is an amplifier 41 and a speaker 42.

Figure 4 shows a block diagram of the electronic circuit which comprises one pair of sensors 26 for the level meter, another pair of sensors 27 for the tape meter, and one sensor 28 to count the holes 10 in the tape. The sensors detect the rotational angle of the disc (for the level meter) or the travelled distance of the extensible tape (for the tape meter) by counting the marks on the disc or the holes on the tape with the aid of light emitting diodes and light receiving elements that produce signals corresponding to the number of pairs of light and dark marks detected from the disc or the number of holes on the tape that pass the sensors.

Schmidt triggers 29 transforms since wave signals from the sensors to square wave signals before passing them to a signal select circuit 30. The signal select circuit ensures that only the signals from the sensors of the level meter will be passed through the decoder 31 when the device is used as a level meter and only the signals from the sensors of the tape measure will be passed through the decoder when the device is used as a tape measure. A decoder circuit analyzes the signals from the signal select circuit, and according to which they are, count-up or count-down signals, processes them to be acceptable to the timing requirements of the microprocessor 32.

The microprocessor 32 is programmed to control all its functions, performs all the mathematical computations , and drive the measurement display 33 and the calculator display 34.

Aside from the decoder circuit, inputs are provided for the microprocessor from the numeric keyboard 35, the ENTER key 37, the function SELECT key 39, the calibration switch 38, the METRIC/IMPERIAL/LEVEL METER switch 36, or from the Auto-power-off Timer 43. Everytime an input signal is received, the program directs the microprocessor to perform the necessary procedures to produce the required output which can be viewed from the displays.

Figure 5 shows a system flowchart of the stored program in the microprocessor. As mentioned earlier, POWER switch is slidable to the desired unit of measurement (Metric or Imperial) or to select the level meter. The first thing that the program does is to test the POWER switch setting to determine what unit of measurement it will use in counting and to initialize the LCD displays properly. If the level meter is chosen, the microprocessor will wait for signals of count-up or count-down or just stay in its idle position waiting for an input. The calculator can be used at anytime.

If the tape measure is chosen, that is, the POWER switch is either set to METRIC or IMPERIAL, a function may be selected by pressing SELECT key 11, a number of times depending on the desired function, or the counter can be initialized to the size of the tape meter casing by pressing +CASE key 6, or the calculator can be used, or tape measurement can be carried out immediately without setting anything (this will run under function 1).

A separate speech processor 40 is controlled by the microprocessor to read out the contents of the measurement and the calculator displays. Connected to this speech processor is an amplifier 41 and a speaker 42.

The methods of computation for each function are the following: 1. Function 1 (Single Entry) - store measurement X to memory.

MEM = X l.a Circumference - multiply memory by value of pi.

MEM = MEM x 3.14159 l.b Circular area - multiply memory by measurement X which is actually the diameter then divide it by four.

MEM = (MEM x X) / 4 2. Function 2 (Summation of Lengths) - store first measurement X to memory MEM = X Then add the next measurement X to memory.

MEM = MEM + X Add again the next measurement X to memory.

MEM = MEM + X And so on.

3. Function 3 (Area Computation) - store first measurement X to memory.

MEM = X 4. Function 4 (Volume Computation) - store first measurement X to memory.

MEM = X Then multiply the second measurement X to memory.

MEM = MEM x X Multiply again the third measurement X to memory.

MEM = MEM x X 5. Function 5 (combination of Function 2 & 4) store first measurement X to memory then do the Summation of Lengths routine until the x key is pressed. The total length will then be considered as the length of first side X1 and the memorywill be cleared for the second side X2. After pressing he x key the second time, the product of X1 and X2 is computed and the memory will again be cleared for the third side X3. After pressing the x key the third time, the product of X2 and X3 is computed.

after 1st entry X, MEM = X after 2nd entry X, MEM = MEM + X after 3rd entry X, MEM = MEM + X after x key is pressed, X1 = MEM after 1st entry X, MEM = X after x key is pressed X2 = MEM MEM = X1 x X2 X2 = MEM after 1st entry X, MEM = X after 2nd entry X, MEM = MEM + X after x key is pressed, X3 = MEM MEM = X2 x X3

Claims (5)

1. Claims 1. An electronic tape measure having a casing and a retractable tape In the casing wound on a spool provided with a circular disc having readable incremental markings distributed therearound, in which the tape has evenly distributed apertures along its length, a first reader for reading movement of the incremental markings corresponding to small movement of the tape in and out of the casing and providing first incremental outputs signal corresponding to passage of the markings past the reader, a second reader for sensing the apertures on the tape and providing second output signals corresponding to the passage of the apertures past the second reader, a microprocessor arranged to receive and programmed to combine the first and second output signals and drive a readable display to indicate the length of tape extending from the casing.
2. 2. An electronic tape measure according to claim 1, in which the spool is freely rotatable and arranged to orient in a particular rotational position with respect to gravitational forces, so that markings on the disc relative to the orientation of the casing can be used to determine whether the casing is level or not and/or to what extent the casing is not level.
3. 3. An electronic tape measure according to claim 1 or 2, including a generally conventional digital calculator mounted on the casing in which the display of the calculator is arranged to be controlled as required for displaying tape measurements or other output signals from the microprocessor.
4. 4. An electronic tape measure according to any one of claims 1 to 3, in which the microprocessor is programmed to generate and control the display to indicate total lengths of sequential different measurements, areas by combining two sequential measurement or volumes by combining three sequential measurements.
5. 5. An electronic tape measure substantially as herein described with reference to any one or more of Figures 1 to 7 of the accompanying drawings.