SURVEYOR'S DRAFTING AID

Abstract: A surveyor's drafting aid comprising a follower (18) movable by hand along the surface of a structure to be surveyed, and lines (14, 16) connecting the follower to a base station which has a paper support (36) and a marking element (48) cooperating with the paper support, the marking element being drivable from a shaft (40) which is in turn driven from a rotatable carriage (12) rotatably carrying bobbins (20) receiving the lines from the follower.

Description: Title Surveyor's Drafting Aid Field of the invention This invention relates to a surveyor's drafting aid. Background to the invention Currently, a surveyor drafts a plan of a building structure by first drawing a very rough plan by eye, then using a tape measure to evaluate principal distances and angles, and finally drafting a more accurate plan by imposing the measured distances and angles on the rough plan. The operation is time consuming andexpensive, and the final plan often contains inaccuracies arising from errors of trueness such as walls which are not exactly straight and corners which are not strictly right-angled. The invention According to the invention, there is provided a surveyor's drafting aid comprising a follower to be moved by hand along the surface of a structure to be surveyed, and a line means connecting the follower to a portable base station, the base station comprising a paper support, a displaceable marking means for cooperation with a paper on the paper support, a rotatable bobbin means on which is wound the line means from the follower, a rotatable carriage carrying the bobbin means, and means connecting the carriage and the rotatable bobbin means with the marking means so that the marking means is caused to mark on the paper a scaled down reproduction of the path of the follower. The line means preferably comprises a pair of lines extending from the follower, respectively winding in opposite directions around the bobbin means. The bobbin means therefore conveniently comprises a pair of bobbins inter¬ connected, as by means of differential gearing, to rotate equally in opposite angular directions relative to the carriage. A spring retraction means is preferably provided, acting on the bobbins to pull the follower inwardly towards the base station, sufficiently strongly to keep the lines taut. The bobbins are preferably of a substantial diameter such that a useful reach of the follower from the base station, say about 7.5 metres, can be achieved, whilst at the same time, when the follower is adjacent the base station, the lines are taken up in relatively few turns, say about five turns, on each bobbin whereby, for the avoidance of errors, the lines can readily be constrained so that this relatively small number of turns is disposed in a single layer on each bobbin. In an embodiment, the paper support is a fixed part of the. base part of a housing which itself is adapted to connect hingedly with the top of a tripod or stand for the entire base station. By turning the housing base, and thus the complete drafting aid, through 90 degrees about a horizontal axis, the drafting aid can be used to map a vertical section of a structure instead of a horizontal section. The upper part of the housing is rotatably mounted on the base part, and constitutes the carriage which carries the bobbins. The two bobbins are mounted within the upper part of the housing (which is openable relative to the base part to provide access to the paper support), respectively on opposite.sides of a centre disc which constitutes a fixed part of the upper housing. Gearing is interposed between the two bobbins and the centre disc, so that the bobbins rotate equally and oppositely relative to said centre disc. The centre disc is formed integrally with a central shaft which provides for rotation of the upper part of the housing relative to the base part. This central shaft extends downwardly into the base part of the housing to carry a slider housing for a slider carrying a drafting pen or pencil which constitutes the marking means. The slider housing thus rotates, above the paper support, with the upper part of the housing. Additionally, the said central shaft is hollow, to allow an inner drive shaft to extend through it from the upper bobbin (or the lower bobbin) to drive the slider in the slider housing. The drafting pen or pencil is therefore moved inwardly and outwardly along the slider housing in accordance with the rotation of the upper bobbin, which is in turn in accordance with inward and outward movements of the follower being moved along the structure being worked upon, whilst the slider housing itself rotates, in accordance with the.. * rotation of the upper part of the housing, which is in turn in accordance with the displacement of the follower around the structure being worked upon. The spring retraction means is preferably embodied in the centre disc, the spring retraction force being applied through a line which winds on pulleys associated with each of the bobbins. Alternatively, clock springs may be provided on the axis of the main shaft, one for the upper bobbin and one for the lower bobbin. The follower preferably has a small push button associated with it, for lifting the drafting pen or pencil on and off the paper on the paper support. The connection between the two is conveniently effected electrically, the lines connecting the follower with the base station being of electrically conductive material and the on/off signal being carried from the bobbins to the pen or pencil through the central shaft assembly. Description of embodiments A practical embodiment of the surveyor's drafting aid in accordance with the invention will now be described with reference to the accompanying drawings, in whic : - Figure 1 is a perspective view of the drafting aid when in operation; Figure 2 is a perspective view of the drafting aid with the upper part of the housing and parts of an upper bobbin and centre disc cut away; Figure 3 is a vertical cross section through the base station of the drafting aid; Figures 4A and 4B show details of a bobbin forming part of the drafting aid; Figure 5 diagrammatically shows the manner of opening of the housing to enable paper insertion; Figure 6 is an explanatory diagram to assist understanding of the manner of operation of the drafting aid; Figure 7 shows detail of a pinch wheel; Figures ε ' and 9 are respectively pictorial views of a modified embodiment, in closed and open condition; Figure 10 is an axial cross-section through the modified embodiment, the housing being removed; Figure 11 is a perspective underside view of the modified embodiment, again with the housing removed; and Figure 12 shows a detail of the modified embodiment. Referring to Figures 1 to 7 of the drawings, the drafting aid comprises a base station constituted by a housing have a base part 10 and an upper part 12 rotatable relative to the base part. Two lines 14, 16 extend out of slots in the upper part 12 and converge to a follower 18, which is moved by hand, generally in a horizontal plane, to follow the surface of a structure to be surveyed. The upper part of the housing houses a pair of rotatable bobbins, principally of similar construction to one another, on which the lines 14, 16 are wound, whilst the base part of - - the housing includes a paper support and houses a drafting pen. Within the housing, all as later described, the bobbins are connected with the drafting pen so that, as the follower is moved around the structure surface, accompanied by rotation of the upper part of the housing relative to the base part and rotation of the bobbins within and relative to said upper part, the drafting pen maps a scaled down reproduction of the path of the follower. Referring to Figures 2, 3 and 4, the two bobbins comprise an upper bobbin 20 and a lower bobbin 22, generally similar to one another, each in the form of a disc of substantial diameter and respectively located above and below a centre disc 24 which constitutes a fixed part of the upper part 12 of the housing. The lines from the follower wind in opposite senses on peripheral pulleys 26 forming parts of the upper and lower discs 20, 22, and these discs have circular racks 28 meshing with cogs 30 mounted on shafts fixed to the centre disc 24, whereby the bobbins 20, 22 rotate equally in opposite angular directions relative to the centre disc. Casings 31 forming an integral part of the centre disc 24 house spiral retraction springs which connect with lines which emerge from said casings to pass over free pulleys 32 and then wind on inner pulleys 34 forming parts of the upper and lower discs 20, 22, thereby to urge the upper and lower discs in the respective rotational senses which cause the follower to be urged into a retracted condition close to the base station (housing 10, 12). In use, therefore, a light pulling force has to be maintained on the follower as it is moved around the structure surface being surveyed. Typically, the follower may have a reach of about 7.5 metres from the base station, and the relatively large diameter of the peripheral pulleys 26 on the upper and lower discs 20, 22, enables this length of line to be accommodated in relatively few turns, say about five turns. It is thus possible, by suitably guiding the entrance of the lines into the upper part 12 of the housing, to ensure that the lines wind on the pulleys 26 in a single layer of turns, which is important for the avoidance of small errors. Assistance in this respect can also be gained by use of a spring loaded pinch wheel 35 urged against the winding on the peripheral pulleys 26 on the upper and lower discs 20, 22, as indicated in Figure 7. It should. also be mentioned that the base part 10 of the housing is adapted for mounting to the top cf a tripod or pedestal-type support with a freedom for rotation through 90 degrees about a horizontal axis. This turns the base station into a vertical orientation, enabling the drafting aid to map a vertical section of a structure instead of a horizontal section. The base part 10 of the housing includes a paper support 36, and accommodates a drafting pen mechanism later described. It also has a hinged cover plate 38 below which is hinged a horse-shoe shaped member 40 employed for the purpose of clamping a piece of paper on the paper support 36 (see also Figure 5). The upper part 12 of the housing opens away from the base part 10 when the hinged cover plate 38 is lifted The lower bobbin or disc 22 has stabilising wheels 39 which run on the cover plate 38. The centre disc 24 in the upper part 12 of the housing is integrally formed with a hollow central shaft 41 supported by a bearing 42 in the hinged cover plate 38 of the base part 10, thus affording the means by which the entire upper part 12 can rotate relatively to the base part 10. The central shaft 41 extends downwardly through the bearing 42 into the base part 10 of the housing, and at its lower end fixedly carries an elongate housing 44 for a slider 46 carrying the drafting pen 48. The slider housing 44 therefore rotates with the upper part 12 of the main housing, and thus always points towards the follower. An inner shaft 50 driven from the upper bobbin or disc 20 extends downwardly through the hollow shaft 41 and at its bottom end within the base part of the main housing connects with the slider 46 by means of a toothed rubber belt 52. The pen 48 carried by the slider 46 is thus driven forwards and backwards along the slider housing 44 in accordance with the rotational movements of the upper disc 20. The overall operation of the drafting aid may be better understood by reference to Figure 6. First, the base station is set up generally at the centre of a room. As the follower 18 is pulled out from the base station and moved by hand, generally in a horizontal plane, around the room, following the contours of corners, windows and the like, the resultant force acting on the bobbin assembly 20, 22, 24 is such as to cause this assembly to rotate, keeping balanced forces and equal extensions of the lines 14, 16. As the centre disc 24 is fixed to the slider housing 44, this housing also rotates, and always points towards the follower 18. The pen thus moves relative to the paper on the paper support in accordance with the movement of the follower around the room. However, the follower will also move in and out relative to the bobbin assembly 20, 22, 24 as it follows the contours of the room, i.e. as the distance of the follower 18 from the bobbin assembly increases and decreases. The changing extensions of the lines 14, 16 cause the bobbins 20, 22 to rotate relative to the centre disc 24. However, the upper bobbin 20 is connected with the pen slider 46 in the slider housing, so that the in and out movements of the follower relative to the base station are reproduced as in and out movements of the pen slider along the slider housing. The pen thus also moves relative to the paper in accordance with the slider movements, and the resultant or total movement of the pen is thus a reproduction of the path of the follower around the room. The reproduction is at a reduced scale, say about 50:1, determined by the mechanics of the arrangement, such as the diameter of the bobbin assembly relative to the diameter of the central shaft assembly, and it is readily ensured that the reduction ratio arising from rotation of the upper bobbin is equal to that arising from rotation of the complete bobbin assembly. It should also be mentioned that, when a complete building is being surveyed, it will be necessary to map different rooms and parts of the building successively, setting up the base station appropriately for each map that is to be drawn. Between the successive mappings, the paper on the paper support 36 is displaced appropriately to position the drawn maps relative to one another on the paper, or if necessary a fresh piece of paper can be inserted. Movement of the paper is readily facilitated by opening the cover plate and upper part 12 of the housing away from the base part 10, and temporarily releasing the paper clamp 40. Additionally, although not shown in the embodiment of Figures 1 to 7, the hand held follower 18 may carry a push button for lifting the pen on and off the paper, as may be required when an obstacle not to be drawn is encountered while moving the follower around a room. The push button may conveniently be operative in an electrical circuit which connects, via the lines 14, 16 and the central shaft assembly, with a small battery powered motor driving a holder for the drafting pen. In this case the lines 14, 16 are essentially made of electrically conductive material. Apart from drafting a plan of the surface of a structure much more quickly and therefore less expensively than conventional practice, the drafting aid of the invention is considerably more accurate, reproducing errors in straight- nesε of walls and deviations from right angles of corners, which are typical of errors which arise with conventional mapping techniques. The modified embodiment of Figures 8 to 12 differs only in minor respects from that of Figures 1 to 7, and similar reference numbers given the suffix A are therefore employed for similar parts. Figures 8 and 9 show the exterior appearance of the modified embodiment, from which it will be apparent that the base part 10A of the housing, relative to which the upper part 12A rotates, is of rectangular shape and has a carrying handle 54. The base 10A is also adapted to receive a roll 56 of drafting paper, from which paper can be drawn as successive rooms and parts of a building are surveyed, as hitherto explained. The follower 18A takes the form of a handgrip, and has a push-button 58 by operation of which the marking means can .be lifted from and engaged with the drafting paper, also as hitherto mentioned. Figure 10 shows the working parts of the device within the housing. These parts are arranged generally in the previously described manner, except that, in this embodiment, it is envisaged that the retraction means will be constituted by clock springs acommodated in housings 60 around the central shaft assembly. Accordingly, the retraction means 31, 32, 34, which in the embodiment of Figures 1 to 7 is associated with the disc assembly 24, 20, 22, is omitted. However, in practice, the retraction means of Figures 1 to 7 is preferred. Reference 62 denotes one of four line guides through which the lines 14A, 16A from the follower 18A enter the upper housing . It can also be seen in Figure 10, and likewise in Figure 11, that the marking assembly is somewhat modified. A marking pencil 62 is employed instead of a marking pen 48. The pencil lead 62 is held by a pencil sleeve 63, collet 64 and lift clip 65 associated with a pencil lift roller 66, and can be lifted from or engaged with the paper by means of a small motor 68 (powered by batteries in a housing 70), which drives a pencil lift beam 72 through a rotor 74, lift worm 76 and lift gear 78. Operation of the motor is controlled by the aforesaid push button 58 on the follower 18A, the circuit path between the follower and the base station being completed through the lines 14A, 16A, which are constituted by thin conductive cables. The entire marking assembly is balanced about the central shaft assembly to facilitate operation in a vertical plane, when in use the device is rotated through 9C degrees on its tripod mounting, as hitherto mentioned. As shown in Figure 12, the inner shaft 50A drives ' the toothed belt 52A, which in turn drives the slider 46A through a gear clip 79 and belt clip 80. The pencil 62 is located on the centre line of the belt 52A, and the geometry of the arrangement is designed to match, on a reduced scale, the geometry of the follower lines 14A, 16A, so as to avoid errors in reproduction as the angle between the lines 14A, 16A changes with movement of the follower towards and away from the base station. In Figure 10, reference 82 denotes the pulley at the outer end of the slider housing 44A, which housing is terminated by an end cap 84. Various modifications of the above-described and illustrated arrangerr.er.t-s are possible within the scope of the invention defined by the appended claims.

Claims: Claims 1. A surveyor's drafting aid comprising a follower to be moved by hand along the surface of a structure to be surveyed, and a line means connecting the follower to a portable base station, the base station comprising a paper support, a displaceable marking means for cooperation with a paper on the paper support, a rotatable bobbin means on which is wound the line means from the follower, a rotatable carriage carrying the bobbin means, and means connecting the carriage and the rotatable bobbin means with the marking means so that the marking means is caused to mark on the paper a scaled down reproduction of the path of the follower. 2. A drafting aid according to claim 2, in which the bobbin means comprises a pair of bobbins interconnected to rotate equally in opposite angular directions relative to the carriage, and the line means comprises a pair of lines extending from the follower, respectively winding in opposite directions around the respective bobbins. 3. A drafting aid according to claim 1 or claim 2, including a spring retraction means acting on the bobbins to pull the follower inwardly towards the base station, sufficiently strongly to keep the lines taut. 4. A drafting aid according to any of claims 1 to 3, in which the bobbins are of a substantial diameter such that a useful reach of the follower from the base station is achieved, whilst at the same time, when the follower is adjacent the base station, the lines are taken up in relatively few turns on each bobbin whereby, for the avoidance of errors, the lines are constrained so that this relatively small number of turns is disposed in a single layer on each bobbin. 5. A drafting aid according to any of claims 1 to 4, in which the paper support is a fixed part of the base part of a housing which itself is adpated to connect hingedly with the top of a tripod or stand for the entire base station, and the upper part of the housing is rotatably mounted on the base part, and constitutes the carriage which carries the bobbins. 6. A drafting aid according to claim 5, in which the upper part of the housing is openable relative to the base part to provide access to the paper support. 7. A drafting aid according to claim 5 or claim 6, in which the two bobbins are mounted within the upper part of the housing respectively on opposite sides of a centre disc which constitutes a fixed part of the upper part of the housing, and gearing is interposed between the two bobbins and the centre disc so that the bobbins rotate equally and oppositely relative to said centre.disc. 8. A drafting aid according to claim 7, in which the centre disc is formed integrally with a central shaft which provides for rotation of the upper part of the housing relative to the base part, and said central shaft extends downwardly into the base part of the housing to carry a slider housing for a slider carrying the marking means, whereby the slider housing rotates, above the paper support, with the upper part of the housing. 9. A drafting aid according to claim 8, in which the said central shaft is hollow, to allow an inner drive shaft to extend through it from the upper bobbin (or the lower bobbin) to drive the slider in the slider housing. 10. A drafting aid according to claim 8 or claim 9, in which the follower has a push button associated with it, for lifting the marking means on and off the paper on the paper support, and the connection between the button and the marking means is effected electrically, the lines connecting the follower with the base station being of electrically conductive material and the on/off signal being carried from the bobbins to the marking means through the central shaft assembly.

Inventors: TOWNEND DAVID COLIN, TOWNEND, DAVID, COLIN
Applicants: TOWNEND DAVID COLIN, TOWNEND, DAVID, COLIN
Application year: 1991
Main classification: B43L13
IPC codes: B43L13