GB2074312A - Measuring Surface Distances - Google Patents

Abstract

A measuring instrument, for example for measuring maps or plans, has a body 3 with a movable surface- contacting element 5, a transducer to convert increments of movement of the movable element into electrical changes, and an electrically-operable display 7 for indicating a dimension which is in a function of a number of increments of movement performed by the movable element 5. In a preferred embodiment, the movable surface-contacting element 5 is a wheel carrying one graticule of a Moiré fringe assembly, the other graticule being on the body. The fringe pattern is read by an electro-optical sensor and produces a train of signals which are shaped to pulses and actuate a liquid crystal display 7 through a micro-chip circuit providing memory re-call, zero-setting addition/subtraction and conversion capabilities, amongst others. <IMAGE>

Description

SPECIFICATION A Digital Map and Plan Measuring Instrument This invention relates to an instrument which, when moved along a path in contact with a surface, gives an indication which is a function of the length of the movement. Although it is not limited to such use, the invention is hereinafter particularly described in relation to such an instrument primarily intended for use as a means for measuring distances on a map or dimensions on a plan.

A conventional form of map or plan measuring instrument comprises a body to be held in the hand, a wheel journalled in the body and protruding from it for contacting the surface of the map or plan, a dial exposed on the body, and a rotatable pointer cooperating with the dial and coupled to the wheel by a suitable gear train.

Such an instrument is subject to considerable disadvantages and limitations in practice. For instance (i) its effective maximum direct measuring capacity is limited to one rotation of the pointer; and (ii) there can only be limited provision for a scale or scales on the dial, and these scales cannot readily be changed, so that the instrument is effectively limited to a single conversion factor, or a few conversion factors, and for any other dimension which it is desired to indicate a separate arithmetical conversion must be carried out by the user, e.g. with the use of a set of scale conversion tables, as between metric and imperial units for instance.

It is accordingly the object of the present invention to provide an improved movement measuring instrument which avoids the inconvenience referred to above and which has many other advantages which will be apparent from the following description.

According to the present invention a measuring instrument comprises, in combination, a body, a surface-contacting element carried in movable manner on the body, a transducer actuatable by relative movement between the movable element and the body and adapted to convert increments of movement of the movable element into changes of electrical state, an electrically-operable display means, and electrical circuitry coupling the transducer and display means and arranged such that the display means indicates a dimension which is a function of a number of increments of movement performed by the movable element. In a preferred form, the surface-contacting element is a wheel journalled to the body.

The electrical circuitry and the display means may be physically separate from the body, but linked to the transducer by a cable or raio link, but in a preferred form they are included in the body so that an entirely self-contained instrument is provided.

The electrical circuitry preferably includes provision for introducing any desired conversion factor between the incremental output of the movable element and the dimension shown on the display. It also preferably includes provision for zero-setting the display, and means for memorizing any dimension which has been displayed, particularly a dimension which is displayed at the moment of zero-setting.

Advantageously there is provision for memory re-call, e.g. for the purpose of adding two or more dimensions, each of which may have required a conversion en route.

The movable surface-contacting element may be coupled to a member of the transducer directly or through speed-change means, or the movable element may itself carry a member of the transducer. Further, the movable element may be coupled by speed-increasing means to a movable member cooperating with the transducer, thereby to increase the sensitity of the device by diminishing the size of the smallest increment which can be sensed. Suitable rotational damping is advantageously included.

In one form, the transducer operates electromagnetically and has a large number of magnetic poles spaced at equal intervals along the periphery of the movable element, e.g. about the axis of rotation of a wheel, a sensing means such as a pole piece with a coil thereon being positioned adjacent the movable element for magnetic energising by each pole as it passes during movement of the movable element. In another form, the transducer operates optically, and has a large number of optically-varied (e.g.

light and dark) zones spaced along the periphery of the movable element, e.g. angularly about a wheel, to cooperate with an optical pick-up such as an optical having a first end positioned opposite to the zones of the movable element, and a second end terminating at a photosensitive means. Means may be included to illuminate the zones.

In a third form, the transducer includes means to produce a Moor6 fringe pattern and to read the pattern optically, as set forth in detail with reference to the accompanying drawings.

In general it is convenient if the changes of electrical state produced by the transducer are in the form of pulses, and preferably square waves or at least steep-fronted pulses, adapted for triggering of relay circuits so that switching functions may be derived from the changes of electrical state.

Means for sensing reverse movement are advantageously provided, both to give an indication when reverse movement has inadvertently occurred, and to cause automatic subtraction, from a dimension being measured, of any back-tracking which may occur inadvertently, or purposely to enable the user to go back to a correct re-starting point. Such means might be, for instance, a friction brake or friction clutch permanently engaged with the wheel, and capable of limited reverse movement to actuate a switch, or in the case of optical or magnetic transducing, a plurality of sensors cooperating with respective optical zones or magnetic poles, or Moiré fringe graticules, in such a manner that a logic circuit connected thereto can sense, and act on, signals appearing in reverse order.

The electrical circuitry may most conveniently be in the form of microprocessor or logic circuit chip technology as generally well known for calculator construction. With a key board having push-button switches for manual operation, provision may readily be made for introduction of any desired conversion factor, for zero-setting, for memorizing, or for carrying out any other function including (i) provision of an indication (visual or oral) of the inadvertent reverse movement of the movable element during the taking of a dimension, and (ii) calculating and displaying results other than linear dimensions, e.g.

calculating angles, bearings, declinations and distances when used in conjunction with a beam compass attachment.

Provision is advantageously made for tapping from the transducer and/or the electrical circuitry for feeding a separate computing means and/or display means as well as that included in the device, or a print-out device.

The display means is advantageously in the form of a liquid-crystal display giving a digital read-out of the dimension processed through the electrical circuitry.

In order that the nature of the invention may be readily ascertained, an embodiment of measuring of measuring instrument in accordance therewith, and a modification of that instrument, are hereinafter particularly described by way of nonlimiting example with reference to the accompanying drawings.

In the drawings: Fig. 1 is an elevation of one major face of the instrument; Fig. 2 is an elevation of the other major face of the instrument; Fig. 3 is an elevation of one side of the instrument; Fig. 4 is a block schematic of a basic instrument; Fig. 5a is an elevation of parts of a transducer system utilising Moiré fringe effect; Fig. Sb is an elevation of a detail of a fixed interference grid used in the system of fig. 5a; Fig. Sc is an elevation of a detail of moving Moor6 fringe element used in the system of fig. 5a; Fig. 6 is a diagrammatic edge elevation of a measuring wheel and associated parts used in the system of fig. 5a; Fig. 7 is a schematic diagram to show the processing of a photocell output signal;; Fig. 8 is a perspective elevation of parts of a key pad assembly, with the parts shown in separated condition; Figs. 9a, 9b and 9c show details of construction of a push button; Fig. 10 is a diagram to show matrix key board configuration; Fig. 11 is a system control diagram.

Reference is made firstly to figs. 1 to 4 of the drawings.

The instrument of the present invention is intended primarily for use by surveyors in reading dimensions of maps and plans, but many other possible uses are available.

The instrument comprises a body 1 in the form of a housing with a portion of portions removable for access.

At the upper part of the body there is secured, in removable manner, a handle 2 which is preferably knurled for better gripping. At the lower part of the body there is an extension 3 which carries a journal 4 for a surface-contacting wheel 5, and adjacent the wheel there is a small needle pointer or index 6 which provides a guide to the user when aligning the instrument with the beginning and end of a line to be traversed. The wheel cooperates with an increment-of-rotation transducer (not visible) within the extension 3, connected to a micro-processor.

In the body there is a liquid crystal display unit 7 which is driven by the micro-processor within the body, and which has permanent markings for denoting, for example, inches, feet, yards, miles, millimeters, centimeters, meters, and kilometers, and the arrangement is such that a bar appears above that unit which is temporarily in use. The dimension, as a number with a decimal point if necessary, appears below the permanent markings. A ietter "F" may be caused to appear to indicate that a special function is being used in the conversion, and a letter "M" may be caused to appear to indicate that the memory of the device is in use.

The instrument is powered by a conventional battery which is housed in a compartment having a closure 8.

Referring to Fig. 2, the other face of the instrument has a panel 9 with push-buttons 10 which are preferably recessed so as to be operable only by application of a pointed instrument, e.g. a pencil or a ball-point pen, and thereby avoid inadvertent operation when handling or when being laid down, or carried.

Buttons are provided, by way of example, for numbers from "1" to "9", "memory", "memory clear", "memory recall", "addition from memory", "subtraction from memory", and for the insertion into the conversion of any special function "F".

A further push-button switch 11 is provided on the periphery for use as an "on-off" switch, and/or for use as a "cancel" switch. A further button 12 is provided on the periphery for automatic insertion into the calculator of a predetermined change of units, e.g.; imperial to metric. A still further button 1 3 is provided for verifying the scale and memory units, e.g. by causing an appropriate indication to appear on the display.

Reference is now made to figs. 5 to 11 which give more detail of a preferred transducer system, photocell output signal processing, key pad construction, push button construction, keyboard matrix, and system control.

For high accuracy it is preferred to utilise a Moor6 fringe interference pattern technique for producing output pulses from a moving object.

Figs. 5a, 5b, 5e and 6 illustrate such a system.

The measuring wheel 5 could be manufactured of glass, or of a plastics material of sufficient stability to permit photographic reduction and etching of radial striations 14 used in producing a fringe pattern. A grid 15 on a fixed viewing window 16 would be produced in similar manner.

A photocell 17, mounted on the fixed viewing window 1 6 "looks" through the fixed gradations 1 5 at the moving graticule 14 of the measuring wheel 5. As the measuring wheel rotates, the interference pattern generated by the coincidence of the fixed and moving grids is detected as light and dark lines detected by the photocell. A light emitting diode 1 8 serves to illuminate the pattern on the measuring wheel as it passes in front of the viewing window.

Any movement of the measuring wheel is detected as an output, irrespective of its direction of movement. Accordingly, errors might occur, of an additive nature, due to the wheel rotating in a wrong direction. To avoid this, it is possible to use a further photocell, and the use of two photocells permits the system to take into account the direction of rotation of the wheel, and to result in subtraction occurring when the wheel is reversed.

A plasticised edge, or a tyre, 1 9 is fitted or provided on the measuring wheel 5, to give a more positive frictional grip on the surface being measured. Felt pads 20 are fitted at one or both sides of the wheel 5 to bear against its side surfaces and thus to damp rotation of the wheel and at the same time ensure that the optical surface is kept clean.

The photocell 1 7 produces a signal proportional to the light which falls upon it. The output from the photocell is passed to a level detector and pulse shaper circuit 21. The level detector detects the threshold of the light-to-dark transition of the photocell output, and the pulse shaper squares this signal to produce a uniform pulse train 22 suitable for passing to a main control system.

Reference is now made to fig. 8 which shows the construction of a keyboard, used for converting and saving measurements and adjusting scales and units. A key cap 23 is a simple moulding of a "top hat" shape which passes through a hole in the panel 9 of the instrument, and is retained within the confines of the panel by its rim. The cap 23 is in contacting with a matting 24 made from a non-conductive rubber compound or other material. The key cap 23 bears directly on the domes section 25 of the matting. On the underside of the dome 25 is attached a slug 26 of carbon-based electricallyconductive material. The slug 26 is located above a switch contact of a printed circuit switch 27.

The small center section of switch tracking is advantageously plated with a few microns of gold to ensure good electrical contact at all times.

As a key cap 23 is depressed, the domed section 25 of the matting is flattened, thus moving the slug 26 towards the contact area of the switch 27, thus prcviding a signal to the control system. When the key cap is released, the dome 25 resumes its original shape, thus providing a spring return for the switch. The rubber matting 24 also provides some protection against the ingress of liquid and other foreign matter.

Fig.10 shows the connection of a typical matrix keyboard. The switches 27 are connected as shown to a keyboard scanner 28 and receiver.

The scanner 28 "free runs", sending a signal down each row of switches in turn. If a key 23 is depressed, the output from the scanner 28 is connected to an input of the receiver 29. As the row is known at the time of contact, the depression of any one switch will give a specific column. This row and column address will define only one key, each key having a unique address.

As all mechanical switches tend to bounce upon contact, i.e. a period of time when the contacts are making and breaking, there is a possibility that this period may be interpreted as several key strokes. Accordingly, a de "debounce" delay circuit 30 is inserted to provide a time delay while the switch contacts settle after making contact. The switching of the key is thus only seen as one key stroke.

Fig. 11 shows a simplified circuit diagram of the control system. Control is based upon the use of a microprocessor 31 which has direct access to the peripheral circuits such as the keyboard 10, liquid crystal display 7, and measuring wheel signal processor, via a control and data bus 32.

The control system components are as follows: The microprocessor 31 performs all arithmetic and logic functions, and controls the flow of data between the peripheral circuits and the internal memories 33, 34. The processor program memory 33 is a non-volatile memory, i.e. it always contains program information, whether the power is switched on or not. It contains the program information necessary to direct the microprocessor 31 in the operation of its tasks.

The memory contains program routines for the conversion of measurements from imperial to metric and from metric to imperial, and routines for the scaling of the measurements obtained. The memory also contains routines for the control of the peripheral circuits.

The measurement memory 34 contains the result of previous measurements saved by the operator by use of the memory function keys on the keyboard.

The measurement signal buffer 35 is used as follows: as the rate of measurement pulses obtained from the measuring wheel may exceed the processing rate of the microprocessor 31 , the buffer 35 holds measurement pulses whilst the microprocessor catches up with the output of the measuring wheel.

The microprocessor, memories and peripherals are inter-connected by the common control and data bus 32 to allow the passing of data between all parts of the system under the control of the microprocessor.

Although the components of the control system are shown and discussed as separate items, it would be possible using the VLSI (Very large scale integration) production techniques available to manufacture the system on a single integrated ciruit.

Claims (10)

Claims

1. A measuring instrument comprising a body, a surface-contacting element carried in movable manner on the body, a transducer actuatable by relative movement between the movable element and the body and adapted to convert increments of movement of the movable element into changes of electrical state, an electricallyoperable display means, and electrical circuitry coupling the transducer and the display means and arranged such that the display means indicates a dimension which is a function of a number of increments of movement performed by the movable element.

2. A measuring instrument, as claimed in claim 1, wherein the surface-contacting element is a wheel journalled to the body.

3. A measuring instrument, as claimed in either of claims 1 and 2, wherein the coupling circuitry includes provision for introducing a conversion factor between the incremental output of the movable element and the dimension shown on the display.

4. A measuring instrument, as claimed in any one of the preceding claims, wherein the coupling circuitry includes provision for introducing a zeroset function.

5. A measuring instrument, as claimed in any one of the preceding claims, wherein the coupling circuitry includes provision for memorizing a dimension and for memory re-call.

6. A measuring instrument, as claimed in any one of the preceding claims, wherein the transducer is a More' fringe assembly having a first graticule on the body anda second graticule on the movable member, and a photosensitive means for reading the Moor6 fringe pattern.

7. A measuring instrument, as claimed in claim 6, including a level detector and pulse shaper receiving output signals from the photosensitive means and producing an output train of squared pulses.

8. A measuring instrument, as claimed in either of claims 6 and 7, wherein the electrical circuitry comprises a plurality of key switches connected in rows and columns, a keyboard scanner connected to the rows, and a keyboard receiver connected to the columns.

9. A measuring instrument, as claimed in any one of claims 6 to 8, comprising a signal processing circuit connected to the photosensitive means and adapted to produce an output train of squared pulses synchronised with output signals from the photosensitive means, a signal buffer connected to receive output from the signal processing circuit, a microprocessor, a liquid crystal display and driver, a keyboard matrix and control, a processor program memory, a measurement memory, and a processor control and data bus interconnecting the buffer, microprocessor, display and driver, keyboard matrix and control, and memories.

10. A measuring instrument substantially as described herein with reference to the figures of the accompanying drawings.