GB2419949A

GB2419949A - Distance Measuring Apparatus

Info

Publication number: GB2419949A
Application number: GB0424280A
Authority: GB
Inventors: Naseem Bari; Steve Bookbinder; Colin Henderson
Original assignee: Trumeter Co Ltd
Current assignee: Trumeter Co Ltd
Priority date: 2004-11-02
Filing date: 2004-11-02
Publication date: 2006-05-10
Also published as: GB0424280D0

Abstract

The invention provides a measuring wheel instrument 1 having one or more tracks 15a, 15b, 15c with electrically conductive sectors 17 for use in determining the number of rotations or partial rotations the wheel 4 of a measuring wheel instrument makes and / or the direction of rotations of the measuring wheel. According to a first aspect of the present invention, there is provided distance measuring apparatus including a ground contacting measuring wheel 4; a first track 15a having a plurality of alternating conductive 17 and non-conductive 18 sectors; and a first electrical contact 21a, the first electrical contact and the first track 15a mutually relatively rotatable at a speed proportional to the speed of rotation of the measuring wheel, wherein, upon rotation of the measuring wheel, the first electrical contact sequentially contacts the conductive and non-conductive sectors of the first track, so as to generate a first electrical signal. Optionally a second track 15b may provide a second electrical signal out of phase with the first electrical signal in order to determine the direction of rotation of the wheel. A third conductive track 15c may be provided in constant contact with a third electrical contact 21c. Contact 21c is in electrical connection with contacts 21a and 21b. Contact with this third track may provide part of the circuit of the first and second tracks.

Description

1 2419949

DISTANCE MEASURING APPARATUS

This invention relates to ground distance measuring instruments of the wheel type such as those used by surveyors.

Measuring wheel instruments are well known in the art. A measuring wheel of known dimensions is rolled along, usually manually by means of a handle attached to either the wheel or a housing. Each rotation of the measuring wheel thus corresponds to a known distance. By pushing the wheel along and counting the number of rotations, the linear distance travelled can be measured.

A counter mechanism can be attached to the wheel to register then number of rotations. The counter mechanism can be either mechanical, as shown in US 37169219, or electronic, as shown in US 4176458. The mechanism usually includes a display to indicate the distance travelled, either as an indication of the number of wheel rotations (which can be interpreted as a distance by the user) or as an actual distance. The display can be digital or analogue, and usually has a means to reset it.

It is desirable that the counter mechanism can determine the direction in which the wheel is rotated. This can allow a displayed distance travelled to increment when the wheel is rolled in e.g. a forward' direction, and decrement when the wheel is rolled in e.g. a reverse' direction. This feature is advantageous, for example, if a user of the measuring instrument rolls the wheel forward beyond their intended finishing position for a distance measurement, If the user reverses the wheel back to the desired finishing point, the displayed distance travelled can be decremented accordingly, resulting in a correct net distance displayed at the desired finishing point.

At its most general, the present invention provides a measuring wheel instrument having one or more tracks with electrically conductive sectors for use in determining the number of rotations or partial rotations the wheel of a measuring wheel instrument makes and/or the direction of the rotations of the measuring wheel.

According to a first aspect of the present invention, there is provided distance measuring apparatus including a ground contacting measuring wheel; a first track having a plurality of alternating conductive and nonconductive sectors; and a first electrical contact, the first electrical contact and the first track mutually relatively rotatable at a speed proportional to the speed of rotation of the measuring wheel, wherein, upon rotation of the measuring wheel, the first electrical contact sequentially contacts the conductive and non-conductive sectors of the first track, so as to generate a first electrical signal.

Preferably, during contact between the first electrical contact and any of the conductive sectors, a first electrical circuit is complete, and a current flows through first electrical circuit. Preferably, during contact between the first electrical contact and any of the non- conductive sectors, the first electrical circuit is incomplete, and current is prevented from flowing through the first electrical circuit. Preferably, the first electrical signal comprises a plurality of intermittent electrical current pulses, each current pulse being produced during the period the first electrical circuit is complete. For simplicity, the current pulses are referred to in the following description as ON' pulses of the signal, and the gaps between the ON' pulses, are referred to as OFF' pulses. Preferably the ON and OFF pulses cycle' repeatedly so as to produce e.g. a square wave electrical signal. By counting the number of repeating cycles of the electrical signal, a number of complete or partial rotations the measuring wheel makes may be determined. This count can be converted into a value for the total distance travelled by the measuring wheel.

Preferably, the distance measuring apparatus further includes a second track having a plurality of alternating conductive and non-conductive sectors; and a second electrical contact, the second electrical contact and the second track being mutually relatively rotatable at a speed proportional to the speed of rotation of the measuring wheel, wherein, upon rotation of the measuring wheel, the second electrical contact sequentially contacts the conductive and non-conductive sectors of the second track so as to generate a second electrical signal.

Preferably, the second electrical signal is similar to, and is produced substantially in the same manner as, the first electrical signal. Preferably, the second electrical signal can also be used to determine the distance the wheel has travelled.

Preferably, the frequencies (number of repeating cycles per unit time) at constant speed of the wheel of the first and second electrical signals are substantially identical at any instant in time.

Preferably, the conductive sectors of the first track are offset in the direction of relative rotation from corresponding conductive sectors of the second track.

Preferably the first and second tracks are substantially circular, have different diameters and are positioned concentrically, one inside the other, and preferably the conductive sectors of the first track are circumferentially offset from corresponding conductive sectors of the second track. Preferably the conductive sectors of the first track are offset from corresponding conductive sectors of the second track such that repeating cycles of the first and second electrical signals are out of phase with respect to each other. Alternatively, the first and second electrical contacts may be offset, e.g. circumferentially offset, instead of the conductive sectors, so as to achieve the same effect. For the purposes of this description, a cycle' of either of the electrical signals is considered to be a portion of the signal between the beginning of an ON pulse and the end of the subsequent OFF pulse.

If the signals are out of phase, the cycles of the signals will begin at different times, i.e. one signal will lead' the other signal. For the purposes of this description, a signal is considered to lead' the other signal if starts its cycle whilst the other signal is more than half way through a cycle. If it starts its cycle whilst the other signal is less than halfway through a cycle, the other signal is considered to lead'. Preferably, if one signal leads' when the wheel is rotated in a first direction, the opposite signal will lead' when the wheel rotates in the opposite direction.

For example, the apparatus may be configured such that, when the measuring wheel is rotated in a first direction, the e.g. first electrical contact will contact a conductive sector of the first track, and subsequently, the second electrical contact will contact a corresponding conductive sector of the second track. If the first contact remains in contact with the conductive sector whilst the second contact begins the contact with its respective conductive sector, the first electrical signal will lead' the second electrical signal. With this configuration, when the wheel is rotated in the opposite direction, the converse preferably happens, i.e. the second electrical contact will contact a conductive sector of the second track and will remain in contact whilst the first electrical contact subsequently contacts a conductive sector of the first track. Therefore, when the wheel is rotated in this opposite direction, the second electrical signal will lead' the first electrical signal.

Preferably, the distance measuring apparatus includes circuitry for analysing the first and/or second electrical signals. Preferably the circuitry has means for comparing the first and second signals, e.g. a data processor such as a microchip.

Fig. 1 a and 1 b provide a graphical representation of how the first and second electrical signals may vary over time when input to e.g. the circuitry of the distance measuring apparatus. Fig. la, shows an example of how the electrical signals may vary when the wheel is rotated in a reverse direction. During rotation in the reverse direction, in this example, the first electrical signal leads' the second electrical signal since, when the first electrical signal begins its cycle, the second electrical signal is 3/4 of the way through a cycle. This means that the phase difference between the two signals is 1/4 of a cycle, or 90 degrees'. Fig. lb. shows how the electrical signals of Fig. la vary when the wheel is rotated in a forward direction. During rotation in the forward direction, the second electrical signal now leads' since, when the second electrical signal begins its cycle, the first electrical signal is 3/4 of the way through a cycle. Again, this means that the phase difference between the two signals is 1/4 of a cycle, or 90 degrees'.

It is preferable that the phase difference between the two signals is 90 degrees when the measuring wheel is rotated in either direction. It is not preferable that the phase difference between the two signals is 180 degrees (half a cycle) as this will result in it not being clear which signal is leading'.

Preferably, for each direction of rotation of the wheel, it is known which of the first and second electrical signals will lead'. Therefore, in use, the direction of rotation of the wheel may be determined by ascertaining which of the first and second electrical signals is leading'.

Preferably, the distance measuring apparatus includes a counting means.

Preferably, the counting means counts the number of cycles of the first and/or second electrical signals e.g. received by the receiver. Preferably, each cycle or count' corresponds to a partial, or whole rotation of the wheel, which in turn corresponds to a predetermined distance travelled by the wheel. Therefore, the total count can preferably be represented as a total distance travelled. Preferably the total distance travelled is incremented when the wheel is rotated e.g. in a forward direction, and is decremented when the wheel is rotated e.g. in a reverse direction.

The resolution of the total distance travelled (i.e. the amount by which the total may be incremented or decremented upon each count) will correspond to the predetermined distance.

To have a high resolution for the total distance travelled (i.e. to have a small predetermined distance), it is most preferable that the counting means counts the number of edges' of the first and/or second signals received by e.g. the receiver, rather than the number of cycles. Indications of the positions of edges are shown in Figs. la and lb. An edge is a point of transition between an ON pulse and an OFF pulse (or vice-versa) of the first and/or second electrical signals. A cycle of the first and/or second electrical signals typically has two edges.

Preferably the first and second tracks are components of a circuit board.

Preferably, the conductive sectors are of metal material. Preferably the metal is copper. Preferably the non-conductive sectors are of insulating material. Preferably the insulating material is plastics material. Preferably, the conductive sectors of each track are electrically connected such that e.g. a single power supply may supply all the conductive sectors at once, preferably with the same voltage. Preferably the power supply is a D.C. battery, preferably a button battery, e.g. a 3V button battery.

Preferably, the battery is mounted on the circuit board. It is understood that a mains supply could be used instead of a battery, but accompanying supply cables would limit freedom of use of the distance measuring apparatus.

Preferably, the distance measuring apparatus further includes a third electrical contact, electrically connected to both the first and second electrical contacts; and a third conductive track, the third electrical contact and the third track being mutually relatively rotatable at a speed proportional to the speed of rotation of the measuring wheel, wherein, upon rotation of the measuring wheel, the third electrical contact contacts the third conductive track. Preferably, the third conductive track is substantially circular, and is positioned concentrically with the first and second tracks, e.g. on the same circuit board.

Preferably, the third electrical contact is always in contact with the third conductive track. Preferably, the contact between the third contact and third track provides part of the first and/or second electrical circuits.

Preferably, the first, second and/or third tracks are concentric about the axis of rotation of the measuring wheel.

Preferably, the first, second and/or third electrical contacts are resiliently flexible, e.g. are spring contacts. This may allow constant contact between the contacts and the tracks during rotation of the measuring wheel when e.g. the surfaces of the tracks are not even. The tracks may not be even due to e.g. the conductive sectors being raised above the non-conductive sectors, or e.g. due to abrasion of the track occurring during use.

Preferably, the first and second electrical contacts are connected to each other and to the third electrical contact. Preferably the first, second and third contacts are a single piece part.

Preferably, the first, second and/or third tracks are fixed in position in the distance measuring apparatus and, upon rotation of the wheel, the contacts rotate.

Preferably the tracks are fixed in position with respect to a housing of the distance measuring apparatus. Nevertheless, it is understood that the contacts may instead be fixed in position, e.g. with respect to the housing, and upon rotation of the wheel, the tracks rotate.

A distance measuring apparatus, including a ground contacting measuring wheel and a counting means; wherein an electrical signal is generated upon rotation of the measuring wheel, and the counting means counts edges of the electrical signal, is considered to be a second aspect of the present invention.

An embodiment of the invention will now be described in more detail with reference to the accompanying drawings, in which: Figs. 1 a and 1 b described above show output signal graphically; Figs. 2a and 2b is a side view and a rear view respectively of a measuring wheel instrument which is an embodiment of present invention; Fig. 3 is an exploded view of the measuring wheel instrument of Figs. 2a and 2b; Fig. 4 is an exploded view of the counting device of the measuring wheel instrument of Figs. 2a and 2b; Fig. 5 is a perspective view of a disk with electrical contacts of the counting device of Fig. 4; Fig. 6 is a cross-sectional side view of the counting device of Fig. 4; and Figs. 7a and 7b is a perspective view and a front view respectively of electrical contacts and tracks according to the present invention.

Figs. 2a, 2b and 3 show a measuring wheel instrument 1 which is an embodiment of the present invention. The measuring wheel instrument 1 has a protective housing 3, which is made of two parts 3a, 3b of durable material (e.g. engineering plastics) fixed together by screws. The measuring wheel instrument 1 has a handle 2 which is fixed in between the two housing parts 3a, 3b, such that it extends away from the housing 3.

Figs. 2a and 2b show a measuring wheel 4 located at one side of the housing 3. The measuring wheel rotates, about an axis, being fixed on an axle 5 supported by a bearing in the housing 3. The measuring wheel instrument 1 has a brake 31, for inhibiting rotation of the measuring wheel 4, a stand 32 for supporting the instrument 1 when it not in use, and a pointer 33 for marking a position of the measuring wheel 4. The housing 3 encloses a counting device 6 that determines the amount of rotations or partial rotations the measuring wheel 4 makes, in use.

Figs. 4 and 5 show an exploded view and a cross-sectional side view respectively of the counting device 6. The counting device 6 has a housing 11 which is made of two parts 11 a, 11 b of durable material (e.g. engineering plastics) fixed together by one or more spring clips 111. A rim seal 16 is located between the two parts 1 la, 11 b of the housing 11, when they are fixed together, for keeping the housing 11 watertight. Components of the counting device 6 are enclosed in the housing 11. The counting device 6 includes a display, in this embodiment an LCD display 12, for displaying information e.g. the amount of rotations or partial rotations the measuring wheel 4 makes, or a corresponding distance that the measuring wheel 4 has travelled. The counter device 6 has one or more control push buttons 14 for e.g. changing the type of information that is displayed by the display 12, resetting the display 12, and/or turning the counting device 6 on or off.

The counting device 6 has a circuit board 13, having e.g. a microprocessor (not shown) for determining the number of rotations the measuring wheel makes, and determining a corresponding total distance that the measuring wheel 4 has travelled.

The microprocessor may be an application specific integrated circuit (ASIC).

The circuit board 13 has a track board 15, extending downwardly therefrom shown in Figs 7a and 7b. The track board 15 has three tracks 15a, 15b, 15c which are circular and concentric so as to provide an outer track 1 5a, a middle track 1 5b and an inner track 15c. The outer track 15a and the middle track 15b each have a plurality of uniform alternating conductive sectors 17 and uniform non-conductive sectors 18 over their entire circumferential length. The conductive sectors 17 are of metal material, in this case copper, that is printed' onto the surface of the track board 15. The non-conductive sectors 18 are exposed regions of a surface of the track board 15. The track board 15 is of insulating material, such as plastics. The inner track 15c is a continuous ring of conductive material, e.g. copper.

As can be seen in this embodiment, each of the outer and middle tracks 15a, 1 5b consists of outer and inner circular conductive elements 35, 36 intermittently joined together by the conductive sectors 17. Since all the conductive sectors 17 of each track 1 5a, 1 5b are connected, only one connection lead (not shown) is needed for each track 1 5a, 1 5b. Nevertheless, it is understood that only one of the outer and inner circular conductive elements 35, 36 is necessary to achieve this effect.

The counting device 6 has a disk 19, carried by a sleeve 20 protruding from a face thereof (as is shown in Fig. 6). An end 51 of the wheel axle 5 engages in the sleeve 20. 0-rings 52 keep engagement between the axle 5 and the sleeve 20 watertight. Since the axle 5 is engaged with the disk 19, when the axle 5 rotates, the disk 19 also rotates. The disk 19 carries three electrical contacts 21a, 21b, 21c, located on its face opposite to the face from which the sleeve 20 projects. The electrical contacts 21a, 21b, 21c are sprung sheet metal elements projecting from a metal base sheet 22. Each electrical contact 21a, 21b, 21c contacts a respective one of the three tracks 15a, 15b, 15c by wiping or brushing against the respective track when the measuring wheel 4, and therefore the disk 19, rotates. The sprung sheet metal elements 21a, 21b, 21c, have contact portions 211a, 211b, 211c at distal ends thereof, for contacting the respective tracks iSa, 15b, 15c. These contact portions 2lia, 2lib, 211c may be positioned along a same line, radial to the axis of rotation of the disk 19.

When the outer and middle electrical contacts 21a, 21b wipe against the outer and middle tracks 15a, 15b respectively, they contact the alternating conductive and non-conductive sectors 17, 18 sequentially. Meanwhile, the inner electrical contact 15c wipes against the inner track i5c, and keeps continual contact with conductive material of the inner track i5c. Each time the outer electrical contact 21a contacts any of the conductive sectors of the outer track 1 5a, a first electrical circuit is completed. Each time the middle electrical contact 21b contacts any of the conductive sectors of the middle track 15b, a second electrical circuit is completed.

The first and second electrical circuits both include a connection to a same power supply, e.g. a button battery 23. The battery is mounted to the housing ii via a clip 34.

When the first circuit is complete, current flows from the battery 23, through the contact between the inner ring 15c and the inner electrical contact 21c, through the metal base sheet 22 and through the contact between the outer contact 21a, and the outer track 1 5a. The outer track is connected to a receiver (not shown) located on the circuit board 14. The microprocessor interprets the current flow through the first electrical circuit as a first electrical signal.

When the second circuit is completed, current flows from the battery 23, through the contact between the inner ring 15c and the inner contact 21c, through the metal base sheet 22 and through the contact between the middle contact 21b, and the middle track 15b. The middle track is also connected to the receiver. The microprocessor interprets the current flow through the second electrical circuit as a second electrical signal.

The first and second electrical circuits each toggle between complete and incomplete as the outer and middle electrical contacts 21a, 21b sequentially contact the conductive and non-conductive sectors 17, 18 of the outer and middle tracks 1 5a, 15b respectively. Therefore, current flow through the first and second circuits is intermittent: it consists of a plurality of current pulses. The microprocessor interprets these current pulses as square wave signals.

The contact portions 211 a, 211 b, 211 c of the electrical contacts 21 a, 21 b, 21c, extend circumferentially along the tracks 15a, 15b, 15c. So that regular square wave signals are produced, in particular square wave signals having duty ratios of 50% as shown in Figs. la and ib, the conductive sectors 17 of the outer and middle tracks 1 5a, 1 5b are circumferentially shorter than the non- conductive sectors 18, so as to compensate for the extending contact portions 211a, 211b, 211c. As can be seen, the contact portions 211a, 211b, 211c are forked to increase their compliability.

The number of repeating cycles, or fractions of repeating cycles, of the square wave signals is proportional to the number of rotations or part rotations of the measuring wheel 4. Therefore by monitoring the number of repeating cycles, or fractions of repeating cycles, a number of rotations the measuring wheel 4 makes, or a total distance the measuring wheel 4 has travelled, is determined and displayed by the LCD display 12.

To determine the direction of rotation of the measuring wheel 4, the conductive sectors 17 of the outer track 1 5a are circumferentially offset from corresponding conductive sectors of the middle track 15b, as shown in Figs 7a and 7b, such that repeating cycles of the first and second electrical signals are out of phase with respect to each other.

The conductive sectors 17 of the outer track 1 5a, as shown in Fig 7b, are circumferentially offset from corresponding conductive sectors of the middle track 15b, such that, when the disk 19 is rotated in a clockwise direction (indicated by arrow A' in Fig. 7b) the middle electrical contact 21b will begin contacting a conductive sector 17 of the middle track 15b whilst the outer electrical contact 21a is in contact with a non-conductive sector 18 of the outer track 15a, and, as further clockwise rotation occurs, the outer electrical contact 21a will begin contact with a conductive sector 18 of the outer track 15a, whilst the middle electrical contact 21b is still in contact with the same conductive sector of the middle track 15b. The repeating cycles of the first and second square wave signals will therefore be phase shifted, with the second signal leading' the first signal, as shown in Fig. 1 b. This indicates that the measuring wheel 4 is travelling forward, and accordingly, the e.g. total distance travelled displayed on the LCD display 12 is incremented.

When the disk 19 is rotated in an anti-clockwise direction (i.e. in the direction opposite to the direction indicated by arrow A') this time the outer electrical contact 21a will begin contacting a conductive sector 17 of the outer track 15a whilst the middle electrical contact 21b is in contact with a non- conductive sector 18 of the middle track 15b, and as further anti- clockwise rotation occurs, the middle electrical contact 21b will begin contact with a conductive sector 18 of the middle track 15a, whilst the outer electrical contact 21a is still in contact with the same conductive sector of the outer track 15a. The repeating cycles of the first and second square wave signals will therefore again be phase shifted, but this time with the first signal leading' the second signal, as shown in Fig. la. This indicates that the measuring wheel 4 is travelling in a reverse direction, and accordingly, the e.g. total distance travelled displayed by the LCD display 12 is decremented.

This technique for determining the direction of rotation of the measuring wheel is a form of quadrature'.

When the measuring wheel 4 is rotated in the forward direction, the electrical contacts 21a, 21b, 21c substantially trail the point at which they contact the tracks 15a, 15b, 15c. Therefore, in the forward direction, tensile forces are predominantly exerted on the electrical contacts 21a, 21b, 21c, (as opposed to compressive forces, which will occur when the wheel rotates in the reverse direction). This configuration is desirable since the forward direction is the most common direction of rotation of the measuring wheel 4, and tensile forces cause less damage to the elements 21a, 21b, 21c than compressive forces.

The described embodiment is provided by way of example only. It will be appreciated by a skilled person in the art that the invention can be achieved in ways other than those specifically described.

Claims

Claims: 1. Distance measuring apparatus including: a ground contacting

measuring wheel; a first track having a plurality of alternating conductive and non- conductive sectors; and a first electrical contact, the first electrical contact and the first track being mutually relatively rotatable at a speed proportional to the speed of rotation of the measuring wheel; wherein, upon rotation of the measuring wheel, the first electrical contact sequentially contacts the conductive and non-conductive sectors of the first track, so as to generate a first electrical signal.
2. The distance measuring apparatus of claim 1, further including: a second track having a plurality of alternating conductive and nonconductive sectors; and a second electrical contact, the second electrical contact and the second track being mutually relatively rotatable at a speed proportional to the speed of rotation of the measuring wheel; wherein, upon rotation of the measuring wheel, the second electrical contact sequentially contacts the conductive and non- conductive sectors of the second track so as to generate a second electrical signal.
3. The distance measuring apparatus according to claim 2, wherein the first and second tracks and the first and second contacts are so arranged that the first and second signals are out of phase, whereby the direction of rotation of the wheel is

detectable.
4. The distance measuring apparatus of claim 2 or 3, wherein the conductive sectors of the first track are offset from corresponding conductive sectors of the second track such that repeating cycles of the first and second electrical signals are out of phase with respect to each other.
5. The distance measuring apparatus of claim 3 or 4, wherein the conductive sectors of the first track are offset circumferentially from corresponding conductive sectors of the second track.
6. The distance measuring apparatus of any one of claims 3 to 5, wherein the repeating cycles of the first and second electrical signals are 90 degrees out of phase with respect to each other.
7. The distance measuring apparatus of any one of claims 2 to 6, including a third electrical contact, electrically connected to both the first and second electrical contacts; and a third conductive track, the third electrical contact being rotatable relative to the third track at a speed proportional to the speed of rotation of the measuring wheel, wherein upon rotation of the measuring wheel, the third electrical contact contacts the third conductive track.
8. The distance measuring apparatus of any one of the preceding claims, wherein the third conductive track is substantially circular, and is positioned concentrically with the first and/or second tracks.
9. The distance measuring apparatus of any one of the preceding claims, wherein the track(s) are fixed in position and, upon rotation of the wheel, the contact(s) rotate.
10, The distance measuring apparatus of any one of claims 1 to 8, wherein the contact(s) are fixed in position and, upon rotation of the wheel, the track(s) rotate.
11, The distance measuring apparatus of any one of the preceding claims, wherein the track(s) are components of a circuit board.
12. The distance measuring apparatus according to any one of the preceding claims, including a counting means configured to count edges of the first and/or second signal.
13. Distance measuring apparatus, including a ground contacting measuring wheel and a counting means; wherein an electrical signal is generated upon rotation of the measuring wheel, and the counting means counts edges of the electrical signal.
14. Distance measuring apparatus substantially as described herein with reference to the accompanying drawings.