ELECTRONIC MEASURING TAPE

Abstract: An electronic tape measure (10) comprises a flexible, fabric tape (11) frictionally engaging an optical encoder shaft (44) which rotates as the tape is withdrawn or retracted, and for desired measurement positions the encoder output is supplied to a computer. The tape (11) has an end bar (14) and a friction grip saddle (16) to define respective end positions. For measuring a circumferential dimension, the bar (14) fits in hooks (21) of the saddle (16). A recess (33) is provided at the exterior of housing (32); when the tape (11) is withdrawn from the housing so that the bar (14) and saddle (16) just fit in the recess, the known length of tape enables a calibration measurement to be undertaken.

Description: Electronic Measuring Tape The present invention relates to an electronic measuring tape, for example a flexible tailor's tape measure. A conventional fabric tape measure requires user judgement in accurate reading and user reliability in recording correctly the measurements which have been taken. The readings can also be subject to user bias, unintentional or otherwise, and mistakes can be made in recording a large number of measurements. Electronic measuring tapes are known. For example, EP-A-0740126 discloses a digital tape measure with regularly-spaced markers which are detected by electronic sensing means. In addition, US-A-5, 743,021 discloses a digital length gauge with a tape having a series of uniformly spaced holes which drive pins on a sprocket connected to an optical encoder. The need to provide markers and/or holes in a tape imposes limitations on the weight, thickness, strength and flexibility of the material used for the tape. The present invention seeks to overcome or reduce one or more of the disadvantages of the prior art. According to a first aspect of the present invention, there is provided an electronic tape measure device comprising a tape which passes around a rotatable shaft, the shaft being connected to an encoder device for measuring the amount of tape withdrawn, characterised in that means are provided for constraining the tape to engage the shaft in a frictional manner. An advantage of this arrangement is that a plain tape can be used. Moreover, a fabric tape of the type used by tailors or in dressmaking may be used. Over a period of time it is possible for the tape to stretch and/or for tape slippage to develop and/or for the measuring accuracy of the device to drift. In order to calibrate prior art electronic devices, it would be necessary to measure known distances with the devices, which could be a long and complicated procedure. The present invention also seeks to provide a quick and simple calibration method. According to a second aspect of the present invention there is provided an electronic tape measure device comprising a tape arranged to be withdrawn from a housing and having at or adjacent its free end at least one member, characterised in that the exterior of the housing has a formation relative to which, after a length of tape has been withdrawn and wrapped around the periphery of the housing, the member may be accurately located in a repeatable manner. The formation is preferably a recess in the housing. An advantage of such an arrangement is that no separate calibration artefacts need to be provided. The formation may alternatively be a saddle member attached to the housing, eg by pivotal arms. According to a third aspect of the present invention, there is provided a method of calibrating an electronic tape measure device comprising a tape arranged to be withdrawn from a housing and having at or adjacent its free end at least one member, characterised in that the method comprises the steps of withdrawing a length of tape and wrapping it round a defined peripheral path on the exterior of the housing, locating the member accurately relative to a formation on the exterior of the housing, and undertaking a calibration measurement. The preferred device is a hand-held measuring tape on a spring loaded reel, similar in mechanical operation to a carpenter's steel tape measure but made of a soft, pliable and substantially non-stretchable material which can be safely applied to human skin and which remains flexible after repeated bending. The amount of tape pulled out from the device is detected electronically by an encoder and the measurements made by the device are fed directly into a computer when triggered by a push button. The output from the encoder may be treated in the same way as the output from the encoders in a conventional PC mouse and is fed by flexible cable to a standard COM port on a PC in the same way that a mouse is connected to a PC. A further option is to fit telemetry electronics to the case and the PC in order to obviate the need for a cable. The device is supplied with software modules to interpret the signals arriving at the COM port according to user need. One or more push buttons on the device may signal the beginning and end of a measurement. A thumb operated push button may be located on the device and computer software provided which interprets one push of the button as a zero reading with the tape retracted and the next push as a measurement. The electronic pulses from the device, detected by the PC, are converted to length measurements by a calibration factor stored in the computer program. It is also envisaged that communication with a computer could be wireless, for example by infra-red, ultrasound or radio frequency signals. The calibration factor is determined by using the device to measure known distances; one such distance being part of the periphery of the device itself. Alternatively, calibration artefacts such as cylinders of known circumference could be supplied with the device. Data handling can be customised to user need through supply of appropriate software modules. Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a perspective view of an electronic measuring tape device in accordance with a first embodiment of the present invention; Figure 2 is a cross-sectional side view, or an enlarged scale, of the device of Figure 1; Figure 3 is a sectional plan view of the device of Figure 1 ; Figure 4 shows one method of use of the device of Figure 1; Figure 5 is a schematic perspective view of an electronic measuring tape device in accordance with a second embodiment of the present invention; Figure 6 is a view of the device of Figure 5 in self-calibration mode; Figure 7 is a cross-sectional side view of a modified tape device; and Figure 8 is a perspective view of the device of Figure 7 with the tape extended. Referring now to the drawings, Figs. 1 to 4 show a measuring device 10 comprising a tape 11 which is of plain, unmarked, flexible fabric material and which can be withdrawn from and returned to a housing 12. Typical dimensions of housing 12 are: length 115 mm, width 78.8 mm and depth 52 mm. Tape 11 is typically 15-20 mm wide. The end of the tape 11 is provided with a fixed round bar member 14. A saddle or bracket member 16 is arranged to slide along the tape 11 with a frictional grip, so that, when moved by a user, it remains in the same position on the tape until it is adjusted again. Bracket member 16 comprises a rounded end 18 nearer the housing 12, and a hooked end 20 nearer to member 14, the hooked end housing two hook elements 21 each with an inner curve 22 matched to the curvature of the bar member 14. To receive the tape 11, the member 16 is provided with an interior through slot extending between ends 18 and 20. Housing 12 comprises two interfitting halves which define a front surface 28 with a slot 30 for passage of the tape 11. The housing has a curved side edge 32 which extends substantially all the way around from the bottom of front surface 28 to the top of the front surface. Edge 32 is slightly wider than the tape 11 and has, at its end adjacent the top of front surface 28, a recess 33 with curved ends 34, 35. The curvature of front curved end 34 corresponds to the curvature of the bar member 14. The curvature of the rear curved end 35 corresponds to the curvature of the rounded end 18 of the saddle 16. Housing 12 also has buttons 36, 38 for controlling operation of the device, and a five metre length of cable 39 with a plug 40 for connection to a power supply and communication with a computer (not shown). Inside the housing 12, the tape 11 is wound around a sprung storage drum 41, Figure 2. From here it passes around an idle roller or pulley 42 and then around a knurled shaft 44 which is fixedly attached to an encoder wheel 45. The wheel 45 is part of an encoder device, the output of which is connected to cable 39. In a preferred embodiment, the shaft 44 has a diameter of 6.366 mm so that one revolution of the shaft corresponds to 20 mm of linear movement of the tape 11. An optical encoder with apertures at spacing of 0.5 mm enables a resolution of better than 1mm to be obtained. In another embodiment a larger shaft with a diameter of up to 25 mm may be used. The tape 11 then passes between the inner surface of a floating collar 46, in the form of an almost-closed ring, and the knurled surface of shaft 44; this serves to keep the tape in non-slipping contact with the shaft. It will be seen that the collar 46 constitutes a tape capture mechanism. The tape then passes past a spring biased element 48 forming the exit slot 30. Element 48 serves as a governor, ie as a device to restrict the speed at which the tape 11 passes. Element 48 also serves to reduce the amount of dirt entering the housing 12. In case any dirt does enter the housing 12, it may be taken apart and shaft 44 may be removable for cleaning purposes to prevent any deterioration in the performance of the encoder. As shown in Figure 3, button 36 acts against a leaf spring 50 to actuate a corresponding micro switch 51. In a preferred arrangement, button 36 operates to reset the electronic measurement function of the device. Not visible in Figure 3 is button 38, which has its respective leaf spring and micro switch and preferably serves to actuate a "data send" operation of the device or to indicate a gap between different sets of data. In use, the bar member 14 is successively placed at the two extremeties of a dimension to be measured, and the buttons 36, 38 are operated to supply the relevant encoder information to the computer. In cases where the device 10 itself can be maintained stationary at one of the extremeties (or in line with the measurement), this operation is straightforward. It can be of assistance to place the saddle member 16 against the end of an article or dimension to be measured which is nearer to the device 10, but the distance between the device 10 and the saddle member needs to be kept constant throughout the process. This could be conveniently arranged by keeping end 18 tight against slot 30. For other measuring processes, the method illustrated in Figure 4 can be used. Here, the circumference of circle 60 represents a dimension to be measured, e.g. the waist measurement of a person. The datum level for this measurement is set by retracting the tape 11 into the device 10 as far as possible so that only members 14 and 16 are visible with the end 18 of the latter engaging slot 36. A length of the tape 11 is then withdrawn from the device and wrapped around the person's waist, bar member 14 is latched in the hook elements 21, and the tape is then suitably tightened around the waist by moving saddle member 16 along the tape. Upon completion the of the fitting, bar member is released and the tape can be gently fed back onto drum 41 until end 18 engages slot 30, care being taken to ensure that saddle member 16 does not move along the tape during this process. The output of the device now represents the required dimension. Note that it is not necessary to locate the housing 12 directly against the person's waist, which could be inconvenient. Alternatively, the datum level could be set at or after the end of the measurement procedure, by moving the end 20 of the saddle member 16 against the person being measured; of course the length of saddle member 16 and/or the length correction required when member 14 is placed in hook elements 21 may be automatically compensated for in the computer software. From time to time, it may be necessary to undertake a calibration process. The device 10 provides a convenient facility for this to define a known distance, by wrapping the tape around the side edge 32 to the position 11' illustrated in Figure 2. Here, the saddle member shown as 16' and the bar member shown as 14' fit precisely in recess 33 between curved ends 34, 35. It may be detected how many encoder pulses correspond to a fixed distance, e.g. to detect whether any tape slippage is occurring. The above-described device has several advantages. The use of a fully flexible fabric tape allows difficult measurements to be taken, e.g. of human beings or animals. Other awkward dimensions may also be measured. The employment of frictional engagement between the tape and the shaft 44 means that a plain unmarked tape can be used without holes or other openings. The use of both the end member 14 and the saddle member 16 to define the extremeties of a dimension to be measured improve both the accuracy and the convenience of the measurement process. Moreover, the device may be used with a standard personal computer. In addition the provision of dimension of known extent, ie the length of edge 32, provides an extremely convenient self-calibrating feature and avoids the need to provide separate measurement standards. Various modifications can be made to the above-described arrangement. For example, saddle member 16 can be omitted, in which case the front surface 28 of the housing 12 can be used to define one extremity of the dimension to be measured. Only part of the periphery of the housing 12, or the dimension of some other part may be used to calibrate the device; alternatively the calibration feature may be omitted completely. The device may comprise one or more lights and/or sound emitting elements (eg giving an electronic beep) to indicate satisfactory operation, in particular completion of a data transfer process. Further control members, eg an on-off switch may also be provided. Instead of a frictional collar 46, the tape 11 may be urged against the encoder shaft by a pinch wheel (not shown). Instead of a spring-biased member 48 being provided, the tape 11 may emerge for the housing between two relatively-small guide rollers. Any suitable rotary encoder means may be used in association with shaft 44. Recess 13 may be dimensioned to receive bar member 14 alone. The tape may be of other materials e.g. of metal. Figures 5 and 6 show a device 70 in accordance with a second embodiment of the present invention. The device 70 has a rounded shape that is designed to fit comfortably in the palm of the hand. It has a flexible tape 71 , intended to be similar in use and feel to a conventional tailor's fabric measuring tape. The tape is manufactured in a material with properties of softness, non-toxicity, strength, flexibility and minimal stretching. There need be no markings on the tape, though a conventional scale may be added. The tape has a generally flat rubber end stop 74. In this embodiment, a light but sturdy saddle 76 is hinged by arms 78 to the housing 72 at 77 and resets on the tape. A zero measurement is deemed to be when the end stop 74 rests at the end of the saddle 76, ie when the tape is retracted. In use, the end of the saddle 76 marks one end of the distance to be measured and the end stop marks the other end. Circumferential measurements are made by drawing the tape from its zero position, around the object to be measured and touching the end stop on the end of the saddle again. The measured distances could be introduced, for example, into a spreadsheet for easy manipulation of the data. In this embodiment, the housing 72 can be used as a calibration check by folding the saddle 76 upwards against the exterior periphery 82 of the housing and drawing the tape 71 around the housing until the end stop 74 touches the end of the saddle 76. The device 70 is supplied with a calibration value for this measurement. As with device 10, further calibration standards can be supplied with the device if required. The device has a push button 83 and an indicator light 84. It is envisaged that a display may also be provided on the housing 72 and that there may also be a degree of data processing within the unit, possibly to the extend of enabling the unit to be totally self- contained in terms of distance measurement and display. The features and modifications of the first and second embodiments may be interchanged as desired. In a further modification, not shown, a saddle of similar shape to saddle 16 is fixedly attached to the housing of the device. In this case the free end of the saddle can be used to locate one extremity of a dimension to be measured. In a calibration measurement, member 14 may fit in the hook elements 21, as with the circumferential measurements of the first embodiment. In yet another modification, Figures 7 and 8, to replace the hook elements 21, a device 90 has recesses 100 formed in projections 101 from the sides of the front surface 28 of a housing 92. Attached to the end of tape 111 is a shaped member 114. The end 120 of member 114 which is nearer to the housing 92 has a circular bar member 124 which matches the curvature of recesses 100. Thus member 124 fits in recesses 100: (i) in the storage position shown in Figure 7; (ii) in a calibration position in which a length of tape 111 is wrapped once around the entire periphery of housing 92; and (iii) in a circumferential measurement position, e.g. when measuring a person's waist.

Claims: Claims 1. An electronic tape measure device (10, 70, 90) comprising a tape (11, 71, 111) which passes around a rotatable shaft (44), the shaft being connected to an encoder device (45) for measuring the amount of tape withdrawn, characterised in that means (46) are provided for constraining the tape to engage the shaft in a frictional manner. 2. A device according to claim 1, wherein the constraining means comprises a collar (46) arranged around the shaft (44) and the tape passes between the collar and the shaft. 3. A device according to claim 1 or 2, wherein the tape (11) has a fixed end member (14) and a relatively-movable member (16) which is movable by a user along the tape but remains in an adjusted position relative to the tape. 4. A device according to claim 3 wherein the relatively-moveable member (16) includes hook means (21), the end member (14) being arranged to fit within said hook means. 5. A device according to any preceding claim, wherein the device comprises a housing (12, 22) the exterior of which defies a path (32, 82) along which the tape may be placed to define a known dimension for calibration purposes. 6. A device according to claims 3 and 5 wherein the end of the path is defined by a recess (33) which is dimensioned to fit either the end member (14) or a combination of the end member (14) and the relatively-movable member (16) in contact with each other. 7. A device according to claim 1 or 2, wherein the device comprises a housing (72) and a member (76) is attached to the housing to define a measuring position. 8. A device according to claim 7, wherein the member (76) is pivotally attached to the housing (72). 9. A device according to claim 7 or 8, wherein the exterior of the housing (72) defines a path (82) along which the tape (71) may be placed to define a known dimension for calibration purposes. 10. A device according to claims 8 and 9 wherein said member (76) is pivotable to a first position for defining said measuring position and pivotable to a second position to define the end of said exterior calibration path (82). 11. A device according to claim 7, wherein said member is fixedly attached to the housing. 12. A device according to claim 11, wherein the said member includes hook means. 13. A device according to claim 11 wherein the member comprises one or more recesses arranged at or adjacent the portion (28) of the housing from which the tape (111) emerges. 14. A method of measuring a distance using a device (10, 70) according to any preceding claim. 15. A method of calibrating a device (10, 70) according to any of claims 1 to 12 comprising the steps of moving the end of the tape (11, 71, l ll) to a known position on the exterior of the device and then undertaking a calibration measurement process. 16. An electronic tape measure device comprising a tape (11, 71, 111) arranged to be withdrawn from a housing (12, 72, 92) and having at or adjacent its free end at least one member (14, 16, 114), characterised in that the exterior of the housing has a formation (33, 76, 100) relative to which, after a length of tape has been withdrawn and wrapped around the periphery (32, 82) of the housing, the member may be accurately located in a repeatable manner. 17. A method of calibrating an electronic tape measure device comprising a tape (11, 71, 111) arranged to be withdrawn from a housing (12, 72, 92) and having at or adjacent its free end at least one member (14, 16, 114), characterised in that the method comprises the steps of withdrawing a length of tape and wrapping it round a defined peripheral path (32, 82) on the exterior of the housing, locating the member accurately relative to a formation (33, 76, 100) on the exterior of the housing, and undertaking a calibration measurement.

Inventors: TURNER NICHOLAS PAUL, TURNER, NICHOLAS, PAUL
Applicants: SECRETARY TRADE IND BRIT, TURNER NICHOLAS PAUL, THE SECRETARY OF STATE FOR TRADE & INDUSTRY, TURNER, NICHOLAS, PAUL
Application year: 2000
Main classification: G01B3
IPC codes: G01B3, G01B21