GB2171508A - Apparatus for sensing movement - Google Patents

Abstract

A measuring tape is provided with a sensor (66) for detecting movement of the tape (55) into and out of a housing (53) and for indicating the total movement. A light source (46) transmits a beam on a scale on the surface (31) of the tape and light sensors (2, 8, 9) detect the light reflected from the surface (31) and the output of the sensors is used to derive the total tape movement. The output is applied to a micro- computer (70) which processes the output to energise a visual display (57) indicating tape movement. The indication may be in metric or imperial units, and the micro-computer also includes a calculating facility to enable a user to perform calculations which may be based upon a movement of the tap. <IMAGE>

Description

SPECIFICATION Apparatus for sensing movement This invention relates to apparatus for sensing movement and has particular reference to apparatus for sensing movement of a surface passed the apparatus. The apparatus is particularly applicable to measuring tapes where it is used to sense movement of the tape and to provide an output indicative of movement of the tape and which can be used to obtain measurement of the amount of movement.

According to one aspect of the present invention apparatus for sensing movement comprises a source of light for directing light on to the surface, a first detector for detecting light reflected by a first part of the surface from the source, and a second detector for detecting light reflected from a second part of the surface spaced from the first part along the surface in the direction of movement, and means for detecting changes in the outputs of first and second detectors.

Preferably, the surface carries a series of equi-spaced areas of alternate light reflective and non-reflective properties, the series lying in the direction of movement of the surface.

In that case, the second part of the surface is spaced from the first part by a distance about equal to one half of the distance about equal to one half of the distance between adjacent light reflecting areas.

Preferably, the apparatus also includes a third detector responsive to light reflected from a third part of the surface. The third part may be spaced from the first part by a distance about equal to three times the distance between the first and second parts. The light may lie in the range of visible light or in the infra-red range.

According to another aspect, the present invention comprises a sensing head supporting a source for directing light on to a surface movable relatively to the head, a first detector for detecting light reflected by a first part of the surface from the source, and a second detector for detecting light reflected by a second part of the surface from the source.

The head may also support a third detector for detecting light reflected by a third part of the surface from the source.

The head may have at least one passage for the passage of light from the source to the surface, and first and second passages for allowing light reflected from the first and second parts of the surface to reach the first and second detectors.

The head may also have a third passage for allowing light reflected by the third part of the surface to reach the third detector.

The passages may terminate at one end in a groove in a face of the head across which the surface is movable.

The groove may lie in a direction that is transverse to the direction of movement of the surface, and is of substantially V-shaped cross section in said transverse direction.

The or each first mentioned passage may terminate in one of the inclined faces of the groove while the third passage terminates in the other inclined face of the groove.

The first and second passages may terminate in the base of the groove.

The head may be adapted to accommodate the light source and each detector.

Apparatus for sensing the movement of a surface may comprise a sensing head as hereinbefore specified together with means for detecting the response of each detector to light reflected from the parts of the surface.

The detecting means may comprise a circuit arrangement for converting the detector responses into electrical impulses and means for counting the impulses in dependence upon the direction of movement of the surface relatively to the head.

The circuit arrangement may comprise circuit means responsive to the electrical impulses and which operates to indicate an error when a specified pattern or patterns of impulses is received.

The invention also envisages a tape measure including means programmed to receive inputs indicating the pulses and the direction of movement and to energise a visual display to indicate tape movement.

The means may also be programmed to increase the displayed movement by an amount equal to a specified dimension when so required by a user.

The programmed means may be a microcomputer which may also be programmed to adjust the displayed movement in dependence upon an indication of ambient temperature inputted to the microcomputer by a user.

Preferably, the microcomputer is also programmed to adjust the displayed movement in dependence upon the tape movement to correct for catenary errors when required to do so by a user.

The microcomputer may also include user available memories for storing information as determined by a user.

By way of example only, an embodiment of the invention and a measuring tape incorporating the embodiment will now be described in greater detail with reference to the accompanying drawings of which: Fig. 1 is an explanatory diagram, Fig. 2 is a perspective view of part of a surface, Fig. 3 is an explanatory diagrammatic representation of part of the apparatus, Fig. 4 is an explanatory waveform diagram, and Fig. 5 is a circuit diagram, Fig. 6 is an explanatory perspective view of a surface, Fig. 7 is a circuit diagram in logic form, Figs. 8A, 8B and 8C are, respectively, side elevation, plan view, and end view of a component, Figs. 9, 10 and 11 are explanatory perspective views of different arrangements of components, Fig. 12 is a perspective view of an embodiment of the invention, Fig. 13 is a plan view of the embodiment of Fig. 12, Fig. 14 is a plan view of the embodiment of Fig. 12, and, Fig. 5 is a circuit diagram in block schematic form.

Referring first to Fig. 1, a movement detector comprises a source 1, for example a light emitting diode, arranged to project radiation for example radiation in the visible light range or in the infra red range on to a surface 3.

The area of the surface 3 that is illuminated will depend upon the accuracy of detection desired and will normally be small. The angle of incidence of the radiation on the surface is A", and a receiver 2 arranged to detect radiation from the source 1 reflected by the surface 3 at an angle of B". The receiver may incorporate a photo-diode or a phototransistor.

Preferable angle A equals angle B and each should be greater than 0 but less than 40".

Both light source 1 and detector 2 may incorporate means, for example optical fibres, for collimating radiation emitted from the source 1 and radiation received by the receiver 2. Such means are indicated at 4 and 5 respectively in Fig. 1 and both terminate close to the surface 3 to minimise losses due to scattering.

To enable the detector to detect movement of the surface relative to the detector, the surface carries a series of light and dark transverse bands 6 and 7 as shown in Fig. 2.

The bands are of equal width as measured in the direction of movement of the surface.

Thus, with the detector shown in Fig. 1, passage of the surface results in a series of alternative high and low outputs from the receiver 2 and these can be used as an indication of the movement. The area of the surface illuminated by the light source will be small and may comprise a circular area whose diameter is a little greater than the width of one of the areas 6 or 7.

However, in many cases, for example if the surface is that of a measuring tape, it is necessary also to be able to detect the direction of movement of the tape and for this purpose an additional receiver is necessary.

The additional receiver is arranged to produce an output that is 90" out of phase with respect to receiver 2. This is illustrated in Fig. 3 where the additional receiver is referenced 8.

Receiver 8 is arranged to respond to a different part of the area illuminated by the light source, the part being chosen to produce the phase difference between outputs as mentioned above.

In the example given above, the part of the illuminated area to which receiver 8 responds is spaced about 0.25 mm from that part of the area to which receiver 2 responds, the distance being measured in the direction of movement of the surface. In Fig. 3, the receivers are shown diagrammatically only and they would be inclined as in Fig. 1.

In many cases, for example a measuring tape, it is also necessary to be able to indicate the extent of movement and this can be obtained from the outputs of the receivers.

Preferably, the widths of areas 6 and 7 are equal and the width selected in dependence upon the minimum movement to be detected.

For example, if the minimum movement to be detected is 1 mm, this can be achieved with areas of 0.50 mm in width separated by 0.50 mm gaps, both distances measured along the length of the surface or tape.

The extent of movement can then be obtained by counting the number of pulses emitted from receiver 2 and then multiplying by, in the example quoted above, 1 mm. However, allowance has to be made for any reversal of the direction of movement of the tape that may have occurred during a measurement and an appropriate correction made to the calculated value.

Idealised waveforms representing the outputs of receivers 2, 8 are shown in Fig. 4 for the case in which the surface is moving in direction C (Fig. 3). If those outputs are applied to a suitable circuit for example that shown in Fig. 5, then appropriate correction of an indicated pulse count is possible.

In Fig. 5, the output of receiver 2 is applied to Schmitt trigger inverters 10 and 11 which produce a square waveform output from the receiver 2 output which is necessarily far from square. The output of inverter 10 is applied to a monostable oscillator represented by block 12 which effects a further "squaring" of the waveform for application to NAND Schmitt trigger 13.

The output of inverter 11 is applied via another Schmitt trigger inverter 14 to a second monostable oscillator represented as block 15 to a second NAND Schmitt trigger 16.

The output of receiver 8 is applied to Schmitt trigger inverter 17 whose output forms a second input to triggers 13 and 16.

The outputs of triggers 13 and 16 are applied respectively via Schmitt trigger inverters 18, 19 to NAND gates 20, 21. The inputs of the gates 20, 21 are connected together as shown so that the gates act simply as inverters.

Finally, the outputs of the gates 20, 21 are combined by NAND gate 22 whose output is applied to a counting circuit not shown.

The counting circuit is such that it will count both up and down, the counting direction being determined by the output of a set-reset (SR) latch comprising NAND gates 23, 24 as shown.

Both monostable multivibrators 12 and 15 are rising edge triggered i.e. O to 1). The condition for an upcount is when the output from receiver 8 = logic '0' and the output from receiver 2 changes from logic '0' to logic '1'.

At this time monostable multivibrator 15 initiates a pulse. Also at this time, the output of receiver 8 equals logic '0' and that output, after passing through the inverter 17, enables NAND gates 13 and 16. Due to that enabling, NAND gate 16 passes the monostable, pulse to inverter 19 and this results in a count pulse from NAND gate 22. The output from inverter 19 also sets the SR latch (NAND gates 23 and 24) to logic '1' which signifies the direction of the count, i.e. either up or down.

The condition for a downcount is that when the output from receiver 8 is a logic '0' and the output from receiver 2 changes from a logic '1' to a logic '0'. This then produces an output of a logic '0' from the SR latch.

Thus, the output of the counting circuit gives the amount of movement of the surface in millimetres to an accuracy of 1 mm.

The surface 3 may be liable to contamination affecting the pulse count and this will give rise to errors. For example, dirt on the surface may result in no response or only a partial response by a receiver to light bands 6. Also, damage to the surface may result in complete or partial removal of a dark band 7 and again such damage will result in errors.

The existence of such contamination or damage can be detected by means of a third receiver 9 so arranged with respect to receiver 8 that the outputs from the two receivers are in anti-phase, i.e. the receivers are 1800 apart, or, in the example noted above, receiver 9 responds to a part of the area illuminated by source 1 that is 0.75 mm from the part of that area to which receiver 2 responds.

The output of receiver 9 is also shown in Fig. 4 and, in the absence of contamination of or damage to the surface 3, it will be observed that the output of receiver 9 is always in anti-phase with that of receiver 8.

Fig. 6 is a perspective view of a surface bearing contamination at 10 which extends over a dark area 7 and into the light area 6 on both sides thereof. If such contamination lies within the area of the surface scanned by the receivers, it may change the pulse count but it will also change the phase of the output signals from receiver 9 relatively to those of receiver 8. Thus, if at any instant the outputs of receivers 2, 8 and 9 are the same, there is contamination or damage to the surface sufficient to affect the count.

The outputs of receivers 2, 8 and 9 can, therefore, be combined to produce an error signal and one way of achieving this is shown in Fig. 7.

The condition of a logic '1' or a logic '0' from all of the receivers 2, 8 and 9 indicates an error due, for example, to contamination on or wear of the markings on the tape.

The light source and receivers are associated with a sensing head comprising a mounting head that provides mounting apertures for the source and heads. Figs. 8A-C show one form of mounting head.

A block 25 of metal or other suitable material, for example aluminium or a plastics material, has a groove 26 on its lower face of inverted V shape. The block is drilled or formed to allow passage of light from the source 1 to pass and the relevant drawings show a passage 27 for radiation from source 1. Passage 27 exits on one of the inclined faces of the groove 26. Similar passages 28, 29 and 30 are provided for the receivers. The latter passages are disposed in such manner that the receivers are responsive to light reflected from the respective parts of the surface referred to above.

As can be seen in Fig. 8B, passage 28 is centred on a transverse axis that passes across the head 25 slightly ahead of the centre of passage 29. That provides the lateral offset of the parts of the illuminated area to which receivers 2 and 8 respond. The point at which the passage 30 exits into the groove 26 determines the location of that part of the illuminated area of surface 31 to which receiver 9 responds.

In the form of head shown in Figs. 8A-C, flat upwardly-inclined faces are provided on the upper surface of the block. As has been stated, passage 27 exits on one 27A of those faces while passages 28, 29 and 30 exit respectively from faces 28A, 29A and 30A.

The arrangement gives greater accessibility to the passages for mounting purposes and provides better separation of control leads etc.

The longer inclined side of the groove 26 is preferably inclined to the horizontal at an angle of about 30 whilst the inclination to the horizontal of the shorter horizontal side is about 60".

The longitudinal axis of the passages 27 and 30 are inclined to the vertical at equal angles of about 30". The passages 28 and 29 are similarly inclined.

This arrangement is found to produce effective illumination of the tape surface and acceptable reflection therefrom.

Passageway 27 has an upper part of increased diameter as compared with the lower part in order to receive a suitable light source which transmits light through the lower part of the passage 27 on to the surface 31 arranged to lie closely beneath the block.

In similar manner, passages 28, 29 and 30 also have enlarged upper parts to accommodate receivers to which light reflected from the surface passes via the lower parts of the passages. If desired, optical fibres accommodated in the lower parts of the passages 28, 29, 30 may be used to transmit reflected light from the surface 31 to the receivers.

With the arrangement shown in Figs. 8A8C, the source is arranged to produce an illuminated area on the surface 31 large enough to be "visible" to the three receivers and this is shown in diagrammatic form only in Fig. 9, the block 25 being omitted.

The light source 32 energised via leads 33 directs light by means of an optical system (not shown) or otherwise on to the surface 31 shown in Fig. 9. Reflected light is conveyed to the receivers 2, 8, 9 via optical fibres 34, 35, 36 that terminate close to the surface 31 to receive light reflected from the parts thereof corresponding with the receiver positions shown in Fig. 3. Both the source 32 and the receivers 2, 8 and 9 and fibres 34, 35 and 36 are accommodated in the block 25 in the manner described above.

An alternative arrangement of light source and receivers is shown diagrammatically in Fig. 10. Three separate light sources 37, 38 and 39 are used each transmitting light on to the parts of the surface 31 via respective optical fibres 40, 41 and 42. Fibres 40, 41 and 42 terminate adjacent surface 31 in positions corresponding to those of receivers 2, 8 and 9 shown in Fig. 3. Closely adjacent the ends of fibres 40, 41 and 42 are the ends of receiving fibres 43, 44 and 45 respectively which convey to their associated receivers 2, 8 and 9 respectively light reflected from the surface 31.

Yet another alternative is shown in digrammatic form only in Fig. 11. A single light source 46 transmits light via three optical fibres 47, 48 and 49 on to the difference parts of the surface 31 at positions corresponding with those of the receivers 2, 8 and 9, Fig. 3. Each of the fibres 47, 48 and 49 terminates close to those parts of the surface 31 and closely adjacent the ends of the fibres 47, 48 and 49 are the ends of receiving fibres 50, 51 and 52 which convey to their associated receivers 2, 8, 9 light reflected from the surface 31.

The alternatives of Figs. 10 and 11 will require a form of mounting block generally similar to the block 25 described above, suitable modifications being required to accommodate the different arrangement of the light source.

It is not essential that, during use, the light source or light sources be continuously energised. It is preferable, when the power source is a battery, to pulse the light source(s) thereby conserving battery power. A duty cycle of from 15%60% may be employed as the pulsing rate.

Where the light source(s) is pulsed some modification of the receiver is required to ensure that the output of the latter comprises only one pulse for each burst of pulsed energisation of the source(s) for each light area of the surface.

It will be appreciated that the surface can be that of other components than tape measures. For example, the stroke of a piston can be monitored and measured as can the movement of step and repeat tables and other moving members of industrial machines and equipment. The output of the receivers can be used to control and limit the extent of movement of a moving component.

The invention is, however, of particular application to tape measures, especially surveyor's tape measures. A surveyor's tape measure embodying the invention will now be described in greater detail with reference to Fig.

12.

A housing 53 is provided, at one end, with a carrying handle 54 and, at the opposite end, with an exit for a measuring tape 55.

The housing accommodates an electronic calculator and microcomputer control, the calculator keyboard being indicated at 56. A display 57, preferably of the liquid crystal kind, is connected to be responsive to inputs from the keyboard or from the microcomputer as will be explained in more detail later. Further control keys at 58 provide additional inputs to the microcomputer and calculator which comprise the movement sensing facility, memory, printer facility, trigonometrical functions, catenary and temperature corrections.

Adjacent the keyboard 56, the housing has a window 59 beneath which is located a paper roll 60 for a printer 61. Paper emerges from the roll from a slot 62 in the housing just above the window 59, a serrated edge cutter 63 being located along one edge of the slot to enable a length of paper to be detached from the roll.

The housing also accommodates a reel 64 rotatable in the housing about an axis transverse to the sides thereof. A winding handle (not shown) located externally of the housing enables a user to rotate the reel and reel on or off a measuring tape accommodated on the reel. Preferably, the tape is of metal sheathed with a protective plastics coating and carried, in addition to the conventional human-readable visual scale, the light and dark areas 6, 7 referred to above.

As can be seen from Fig. 14, the tape 55 passes into the housing through wiper blades 65 which remove most of the surface contamination from the tape. The tape then passes beneath a sensing head 66 of the form described above with reference to Fig. 8 and includes a light source and receiver of one of the forms described above with reference to Figs. 9, 10 or 11. After passing round a tensioning roller 67, the tape is wound to the reel 64. At the lower part of the housing adjacent the wiper blades 65 and the sensing head 66 are located batteries 68 that power the electronic components.

The output of the receivers in the head 66 is fed via conductors 69 to the microcomputer located beneath the keyboards where the output is processed and the results exhibited on the display 57.

Fig. 14 shows in block schematic form the principal functional components of the microcomputer 70 and its associated controls. Also included is a low power sensing circuit 71 which, via the microcomputer and display 57, indicates to a user when the battery potential has reached an unacceptably low value. The microcomputer may be Type 7503 manufactured by NEC.

Also included but not shown in Fig. 14 is an output port that enables the microcomputer to be connected to another external computer for the transfer of information between the microcomputer and the external computer.

The microcomputer is programmed to operate in either metric or imperial units, to correct a displayed length in respect of catenary errors, to correct a displayed length for variations in ambient temperature when the value of the latter is inputted by a user. The microprocessor is also programmed to allow for the location of the sensing head with respect to the exit for the tape and to add-on a length representing the length of the housing when required. Memories are also provided to receive specified measurements and to store these for use recall when necessary.

Facilities may also be provided for carrying out trigonometrical surveying and the calculations involved.

Further details of the housing etc. are provided in co-pending Patent Application No.

(Case I) the contents of which are hereby incorporated into this Application.

Compensation may also be provided which may be user controlled or automatic in dependence upon a sensor level of ambient light.

It is not essential to include all the facilities just referred to. The sensing head may drive a display programmed to exhibit a measured length in metric or imperial units and to modify a displayed length by the addition of the housing length when required. In such case, a simpler microcomputer will be used having facilities sufficient to deal with the measurements just mentioned. In that way, there is provided a relatively inexpensive pocket tape measure.

Claims (27)

1. Apparatus for sensing movement of a surface relatively to the head comprising a source of light for directing light on to the surface, a first detector for detecting light reflected by a first part of the surface from the source, and a second detector for detecting light reflected from a second part of the surface spaced from the first part along the surface in the direction of movement, and means for detecting changes in the outputs of first and second detectors.

2. Apparatus as claimed in claim 1 in which the surface carries along its length a series of spaced transverse equi-spaced areas of alternate light reflective and non-reflective properties, and in which the second part of the surface is spaced from the first part by a distance about equal to one half of the distance between adjacent light reflecting areas.

3. Apparatus as claimed in claim 1 or 2 in which the apparatus comprises a third detector responsive to light reflected from a third part of the surface.

4. Apparatus as claimed in claim 3 when appended to claim 2 in which the third part is spaced from the first part by distance about equal to three times the distance between the first and second parts.

5. Apparatus as claimed in any one of the preceding claims in which the light lies in the range of visible light or in the infra-red range.

6. A sensing head supporting a source for directing light on to a surface movable relatively to the head, a first detector for detecting light reflected by a first part of the surface from the source, and a second detector for detecting light reflected by a second part of the surface from the source.

7. A head as claimed in claim 6 which also supports a third detector for detecting light reflected by a third part of the surface from the source.

8. A head as claimed in claim 6 or 7 which has at least one passage for the passage of light from the source to the surface, and first and second passages for allowing light reflected from the first and second parts of the surface to reach the first and second detectors.

9. A head as claimed in claim 8 when appended to claim 7 which also has a third passage for allowing light reflected by the third part of the surface to reach the third detector.

10. A head as claimed in claim 8 or 9 in which the passages terminate at one end in a groove in a face of the head across which the surface is movable.

11. A head as claimed in claim 10 in which the groove lies in a direction that is transverse to the direction of movement of the surface, and is of substantially V-shaped cross section in said transverse direction.

12. A head as claimed in claim 11 in which the or each first mentioned passage terminates in one of the other inclined faces of the groove.

13. A head as claimed in claim 12 in which the first and second passages terminate in the base of the groove.

14. A head as claimed in any one of claims 6-13 in which the head is adapted to accommodate the light source and each detector.

15. Apparatus for sensing movement of a surface comprising a sensing head as claimed in any one of claims 6-14 and means for detecting the response of each detector to light reflected from the parts of the surface.

16. Apparatus as claimed in claim 15 in which the means comprise a circuit arrangement for converting the detector responses into electrical impulses and means for counting the impulses in dependence upon the direction of movement of the surface relatively to the head.

17. Apparatus as claimed in claim 15 in which the circuit arrangement comprises circuit means responsive to the electrical impulses and which operates to indicate an error when a specified pattern or patterns of impulses is received.

18. A tape measure comprising apparatus as claimed in claims 16 or 17 including a means programmed to receive inputs indicating the counted pulses and the direction of movement and to energise a visual display to indicate tape movement.

19. A tape measure as claimed in claim 18 in which the means are also programmed to display tape movement in metric or imperial units as determined by a user.

20. A tape measure as claimed in claim 19 in which the means is also programmed to increase the displayed movement by an amount equal to a specified dimension when so required by a user.

21. A tape measure as claimed in any one of claims 18-20 in which the programmed means is a microcomputer also programmed to adjust the displayed movement in dependence upon an indication of ambient temperature imputted to the microcomputer by a user.

22. A tape measure as claimed in claim 21 in which the microcomputer is also programmed to adjust the displayed movement in dependence upon the tape movement to correct for catenary errors when required to do so by a user.

23. A tape measure as claimed in claim 21 or 22 in which the microcomputer includes user available memories for storing information as determined by a user.

24. Apparatus for sensing movement as claimed in any one of claims 1-5 substantially as herein described with reference to and as illustrated by Fig. 1-3 of the accompanying drawings.

25. A sensing head as claimed in any one of claims 5-14 substantially as herein described with reference to and as illustrated by Figs. 8A, 8B, 8C and 9-11 of the accompanying drawings.

26. Apparatus as claimed in any one of claims 15-17 substantially as herein described with reference to and as illustrated by Figs. 111 of the accompanying drawings.

27. A tape measure substantially as herein described with reference to and as illustrated by Figs. 1-15 of the accompanying drawings.