GB2067283A

GB2067283A - Determining relative movement

Info

Publication number: GB2067283A
Application number: GB8100508A
Authority: GB
Original assignee: Gamon Eng Co Ltd V C
Current assignee: Gamon Eng Co Ltd V C
Priority date: 1980-01-10
Filing date: 1981-01-08
Publication date: 1981-07-22

Abstract

A device for determining relative movement has a scale 6, and a reading means 7 with reading elements 10 spaced along the scale 6 by increments less than the spacing between adjacent markers 8, the reading elements 10 being also spaced from each other in a direction transverse to the scale 6 whereby in particular the device may be used to determine increments which are small relative to the dimensions of the reading elements 10. A scaling apparatus for use with a drawing board has two such devices, the scale of the second device being carried on a cursor of the first device, and the readings of the two cursors being indicated on a display which may incorporate a conversion factor. <IMAGE>

Description

SPECIFICATION Determining relative movement This invention relates to the determination of extent of movement of an item relative to a reference point, for example to permit display of that extent of movement in units.

A first object of the invention is to provide a device for the determination of movement of a reading means relative to a scale having spaced markers, adapted to facilitate determination of very small increments of movement which may be less than the spacing of the markers.

A second object of the invention is to embody such a device in apparatus for use with a drawing board.

According to the present invention, a device for determining relative movement comprises a scale having a plurality of markers with a respective space between each pair of adjacent markers, and a reading means adapted to react differently to: (i) a marker, and (ii) a space between adjacent markers, the reading means including plural reading elements which are spaced in the direction along the scale by an increment less than the spacing between adjacent markers, each reading element being spaced from the next reading element in a direction transverse to the direction along the scale, the scale and the reading means being relatively movable in the direction along the scale.

The term "spaced" as used herein is applied to the centre of the reading element. More than two reading elements may be arranged serially, each adjacent pair of reading elements being spaced in the same sense in that direction transverse to the direction along the scale. Preferably, the product of (a) the spacing of the reading elements, in the direction along the scale, and (b) the number of reading elements, is equal to the spacing between two adjacent markers.

Conveniently, the markers and spaces are optically different to permit reading by optical sensors, and in a preferred embodiment, the reading elements are each one end portion of an optical fibre having its other end associated with a respective light-responsive device of the reading means.

To provide summation of the increments of relative movement, there may be provided a counter coupled to the reading means, and means may be included for applying a conversion factor to the count provided by the counter. For convenience of reading the device may have a numerical display, such as a digital display.

With such an arrangement, relative movement of the reading means from one marker to the next marker will involve presentation of one of those markers to each of the reading elements in turn, and the reading elements may activate a display related to the number of incremental units involved in the movement. Preferably there is provision for setting of the display to zero at any desired point of the scale, and for inclusion of a memory such that any departure of a selected new zero point, from an absolute or fixed starting point of the scale, may be recalled and taken into account.

Further according to the invention, an apparatus comprises first and second devices as claimed in any one of claims 1 to 9, the direction along the scale of the first device being different from the direction along the scale of the second device, e.g. the respective scales being linear and disposed one at a right angle to the other.

By way of example the apparatus is used for both of the two scales, disposed at an angle, of a drawing board. Thus, a scaling structure for a drawing board may comprise a first scale, a first cursor including a reading member, means for guiding said first cursor such that its reading member travels along the first scale, a second scale on the first cursor transverse to the direction of the first scale, a second cursor including a reading member, means for guiding said second cursor such that its reading member travels along the second scale, and means for displaying increments of travel of the respective cursors.

Preferably, the display means comprises a single display device regulable to display one or the other or both of the increment quantities. In a convenient arrangement, the display device is incorporated with the second cursor.

In order that the nature of the invention may be readily ascertained, a device for determining relative movement, and an embodiment of electronic scale structure for a drawing board incorporating said device, are hereinafter particularly described with reference to the figures of the accompanying drawings, wherein: - Fig. 1 is a diagram to illustrate the manner of disposition of reading elements relative to a scale; Fig. 2 is an elevation of a portion of a scale, and a reading head to coact therewith; Fig. 3 is an elevation of an apparatus for use on a drawing board; Fig. 4 is a block diagram of an electronic circuit for the apparatus of Fig. 3, and Fig. 5 is an elevation of a possible layout of microprocessor key and display board for use in the apparatus of Figs. 3 and 4.

Fig. 1 illustrates the basic elements, and their inter-relationship, in a device for determining relative movement.

A scale 1 has markers 2 with equal spacings 3 between neighbouring markers. A reading means incorporates reading elements 4, and a series of five such elements are arranged on a line "A" which is transverse to the longitudinal axis "B" of the scale 1. The line "A" is not precisely at a right angle to axis "B" but is offset from the normal to "B" by a small angle such that the respective centre points of the series of elements 4 may all lie within the spacing between two next adjacent markers 2. The arrangement is such that the spacing of the centre points of two adjacent elements 4, measured in the direction "B", multiplied by the number of elements 4, equals the spacing between two adjacent markers 2.This spacing of the elements 4 along the line "A" has particular advantage where the cross-sectional dimension of the elements 4 is large compared with the increments tG be measured, such that it would be impossible to space the elements 4 along the line "B" and still have their centre points all disposed between two next adjacent markers 2. In the drawing there are shown, by way of example only, some comparative dimensions, e.g.

the spacing of the markers 2 is 1 mm, the width of each element 4 is 0.5 mm, the spacing along line "A" of the elements 4 is 2 mm, the "offsetting" along axis "B" of adjacent elements 4 is 0.2 mm, and the angle which line "A" makes with the normal to axis "B" is 5.7C The elements 4 are all mounted in fixed relative position on a reading member (not shown), and the reading member would traverse along axis "B". Starting from the position shown in Fig. 1, and assuming that the reading elements are moved in the direction of the arrow 5, it will be seen that each increment of 0.2 mm, of travel of the reading elements will cause a respective one of the reading elements to read the marker 2, and the same action is repeated for each marker 2.

Thus, increments of 0.2 mm can be read by elements which are themselves 0.5 mm in width.

Reference is now made to Fig. 2 which shows details of a scale 6 and pick-up 7 of a reading member The scale 6 has marks 8 on a contrasting background 9. The marks are linear and are equally spaced. The pick-up 7 has a face presented closely adjacent to the scale. At that face there terminate five optical fibres, the ends 10 of the fibres being positioned along a straight line which is inclined (here shown exaggeratedly) with respect to the normal to the scale 6. By this means, an effective spacing between the ends 10 of the optical fibres, in the direction of motion along the scale is achieved, although the fibres themselves, for dimensional reasons, are a greater distance apart.The five optical fibres terminate at their other end at an optical/electronic transducer 11 adapted to produce electric pulses at each time of passage of a mark 8 in front of an end 10 of an optical fibre in the pick-up 7.

Fig. 3 shows apparatus for application to a drawing board. A horizontal guide rail 12 incorporates a scale 13 for indicating horizontal position. The scale might be for example 1500 millimetres long and marked off in millimetres, and with the possibility of reading increments as small as 0.2 mm.

On the guide rail 12 there is slidable a first cursor 14 which also includes a scale 1 5 for indicating vertical position. This latter scale could again be 1500 millimetres long, and marked in millimetres. On the cursor 14 there is slidable a second cursor 1 6 which carries a horizontal rule 17 and a vertical rule 18 and an angular display 1 9. There is also present, on the second cursor 16, a digital display and control board 20 explained in detail below.

The first cursor 14 carries a pick-up 21 to coact with the scale 13 for determining horizontal position of the first cursor. The second cursor 1 6 carries a pick-up 22 to coact with the scale 1 5 for determining vertical position of the second cursor.

Each of the associated scales and pick-ups could be as described with reference to Fig. 2.

Reference is now made to Fig. 4. The information (pulses) supplied from the pick-up 21 of the first cursor 14 is fed in at 23, and represents horizontal position of the first cursor. The information (pulses) supplied from the pick-up 22 of the second cursor 1 6 is fed in at 24, and represents vertical position of the second cursor.

These respective inputs are fed to a microprocessor 25 having a memory 26 and under the control of a keyboard 27. Output from the microprocessor is taken to a display drive circuit 28 operating one or more digital displays 29. Items 25 to 29 are incorporated in second cursor 1 6.

Reference is now made to Fig. 5. It is desirable to have a display 30 for horizontal position, and a display 31 for vertical position. It is also desirable to be able to calculate various items, e.g. when scaling or introducing a factor of increase or reduction, and this may be displayed at 32.

Buttons 33 are provided, and may advantageously include the usual controls for a multi-function calculator. The calculator equipment of Fig. 4 is incorporated in the board 20 of Fig. 3.

In normal drawing board practice, for the preparation of a drawing, a draughtsman will use a scale to establish all dimensions. If information is to be transferred from one drawing to another, and if the two drawings are scaled differently, two scales will probably be used. The use of scales in this manner is time consuming and prone to error.

It is therefore desirable to be able not only to read off accurately distances along each of two scales, but also if necessary to introduce a factor, variable at will, between the distance actually moved along a scale and the distance which is read off.

If a drawing board is provided with the apparatus as described with reference to Figs. 3-5, having horizontal and vertical movement of the drawing head 17, 18, 19, built into the drawing board, it is possible to provide an electronic digital display on the displays 20, 31 showing both horizontal and vertical position. This can, for example, eliminate the need for scales in drawing work, and a single apparatus fixed to the board can serve for all requirements.

Digital indication in this manner offers the additional advantages of automatic scaling, e.g.

the respective displays 30, 31, could indicate actual dimensions whereas the respective cursor movement would be the corresponding scaled dimension. For example, if it was required to mark off an actual distance of 1 1.35 metres on a drawing with a scale of 1/25, "11.35" on the digital display would correspond to a cursor movement of 454 millimetres. Further development of the system could include a planimeterfunction and a curve length measuring feature.

As each pick-up 21, 22 travels along its respective scale the output from any one optical fibre (plus the transducer) will be one pulse for every one millimetre of travel along the scale.

However, pulses from consecutive fibres will correspond to 0.2 millimetres of travel. By counting the pulses from the transducer, the position of the respective cursor is known at all times, with reference to a zero, e.g. one end of the scale. Direction of travel of the cursor along the scale may be established by determining the order in which the five fibres originate a pulse, i.e.

n, n + 1 denotes "forward", and n, n - 1 denotes "reverse", where n is the fibre reference.

The scales 13 and 1 5 may conveniently be manufactured by photo-anodizing on aluminium with the following advantages: - (i) lines on the scale are clearly defined, and black on an aluminium background provides ample contrast for optical sensor operation; (ii) such a scale is not brittle, and thus handling problems prior to fixing are avoided; (iii) such a surface can readily be treated to give a scratch- and chemical-resistant finish; (iv) the scale may be manufactured with a selfadhesive back surface, to facilitate fixing on a board; (v) the cost is low; (vi) length changes due to temperature variations are insignificant, e.g. less than 0.0007% per OC.

The pick-ups 21, 22 may have a body formed as a moulded plastics block into which passes an optical cable carrying five optical fibres and two electrical conductors. The fibres disperse in the block so as to have input end portions at the required locations at the undersurface of the block. Each fibre, of say about 0.5 millimetre diameter, terminates at the bottom face so that light impinging on that bottom surface passes up the fibre. The bottom surface of the block may also have a lamp enclosure for a lamp fed through the two conductors. The other ends of the fibres connect to a proprietory five-channel optoelectronic converter unit. Five electrical outputs from the unit, one for each of the fibres, are connected to the electronic circuitry, as at 23, 24, in Fig. 4.Alternatively, the opto-electronic convertors could be mounted in the pick-up so that only electrical conductors for lamp would need to be connected to the head.

It is necessary to transfer power to the first cursor 14, and to transfer power and horizontal position information to the second cursor 1 6.

Power for the horizontal cursor 14 may be derived from a power supply unit mounted, for example, under the drawing board or in other convenient position, and transferred by means of a trailing cable (not shown) at the rear of the drawing board.

Power and horizontal position information may be transferred to the second cursor 1 6 by means of a helical type flexible cable running in a trough within the body of the first cursor 14.

The electronic processing should desirably include counting, calculating, memory and display driving functions, e.g. using a microprocessor.

Because a keyboard for the microprocessor would in any event require many of the keys normally found on a simple multi-function calculator, a normal calculator function could be incorporated at only small extra cost.

The electronic processing means desirably provides the following functions:- (a) setting an absolute zero position for both horizontal and vertical movement, and continuously monitoring of movement relative to these positions, even if the display is being used temporarily for other purposes, as explained below, and recalling of the absolute position, relative to the absolute zeros, at any time; (b) setting one or both of the horizontal and vertical position displays to zero so that a fixed distance can be moved, without interfering with the absolute position monitoring, as in (a) above, and with updating of the memories containing the absolute positions. For example, the absolute horizontal position may be "942.4", measured from absolute zero, e.g. the left-hand edge of drawing.If it is then required to move 38.6 millimetres to the left, the horizontal position display must be set to zero, and movement implemented until "38.6" appears on the horizontal display. This is clearly simpler than subtracting 38.6 from 942.4 = 903.8, and then moving the cursor until 903.8 appears in the display.

(c) storing a scale and processing all horizontal and vertical position information so that the displays show actual dimensions but cursor movement corresponds to the scaled value, e.g. if a scale of 1:100 is programmed, a reading of 1000 millimetres on the display would be the equivalent to 10 millimetres of actual cursor movement.

(d) provision for working in both imperial and metric units.

(e) provision for functioning as a calculator.

Where information from at least one reading means is fed electronically to a display, e.g. to a calculator means, provision may be made for feeding thereto other information derived from a detector of absolute or differential angular relative positioning relative to a reference. The read-out to be obtained would be a function of the increments to be moved and the angle relative to the reference, and any conversion factor which it is desired to introduce.

Claims

1. A device for determining relative moment, comprising a scale having a plurality of markers with a respective space between each pair of adjacent markers, and a reading means adapted to react differently to (i) a marker, and (ii) a space between adjacent markers, the reading means including plural reading elements which are spaced in the direction along the scale by an increment less than the spacing between adjacent markers, each reading element being spaced from the next reading element in a direction transverse to the direction along the scale, the scale and the reading elements being relatively movable in the direction along the scale.

2. A device, as claimed in claim 1, wherein more than two reading elements are arranged serially, each adjacent pair of reading elements being spaced on the same sense in that direction transverse to the direction along the scale.

3. A device, as claimed in either of claims 1 or 2, wherein the product of (a) the spacing of the reading elements in the direction along the scale, and (b) the number of reading elements, is equal to the spacing between two adjacent markers.

4. A device, as claimed in any one of claims 1 to 3, wherein the markers and spaces are optically different.

5. A device, as claimed in claim 4, wherein the reading elements are each one end portion of an optical fibre having its other end associated with a respective light-responsive device of the reading means.

6. A device, as claimed in any one of the preceding claims, including a counter coupled to the reading means.

7. A device, as claimed in claim 6, including means for applying a conversion factor to the count provided by the counter.

8. A device, as claimed in any one of the preceding claims, including a numerical display.

9. A device, as claimed in claim 8, wherein the display is a digital display.

10. An apparatus comprising first and second devices as claimed in any one of claims 1 to 9, the direction along the scale of the first device being different from the direction along the scale of the second device.

11. An apparatus, as claimed in claim 10, wherein the respective scales are linear and are disposed one at a right angle to the other.

12. Apparatus, as claimed in either of claims 10 and 11, comprising a first scale, a first cursor including a reading means, means for guiding said first cursor such that its reading means travels along the first scale, a second scale on the first cursor transverse to the direction of the first scale, a second cursor including a reading means, means for guiding said second cursor such that its reading means travels along the second scale, and means for displaying increments of travel of the respective cursors as determined by their respective reading means.

13. Apparatus, as claimed in claim 12, wherein the displaying means comprise a single display device regulable to display one or the other or both of the increment quantities.

14. Apparatus, as claimed in either of claims 12 and 13, wherein the display device is incorporated with the second cursor.

15. A device for determining relative movement, as claimed in claim 1, substantially as described herein with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

1 6. Apparatus substantially as described herein with reference to Figs. 3 to 5 of the accompanying drawings.