US2836893A - Apparatus for making perspective drawings - Google Patents

Description

June 3, 1958 R. A. BARNETT I 2,836,893

APPARATUS FOR MAKING PERSPECTIVEDRAWINGS Filed Sept. 19, 1956 I 6 Sheets-Sheet 1 June 3, 1958 R. A. BARNETT 2,836,893 APPARATUS FOR MAKING PERSPECTIVE DRAWINGS Filed Sept. 19, 1956 6 Sheets-Sheet 2 June 3, 1958 R. A. BARNETT APPARATUS FOR MAKING PERSPECTIVE DRAWINGS Filed Sept. 19, 1956 6 Sheets-Sheet 3 June 3, 1958 R. A. BARNETT APPARATUS FOR MAKING PERSPECTIVE DRAWINGS Filed Sept. 19, 1956 6 Sheets-Sheet 4 June 3, 1958 E. A. BARNETT APPARATUS FOR MAKING PERSPECTIVE. DRAWINGS Filed Sept. 19; 1956 6 Sheets-Sheet 5 ,0, In I05 June '3, 1958 R. A. BARNETT APPARATUS FOR MAKING PERSPECTIVE DRAWINGS Filed Sept. 19, 1956 6 Sheets-Sheet 6 United States Patent APPARATUS FOR MAKING PERSPECTIVE DRAWINGS Robert A. Barnett, Germiston, Transvaal, Union of South Africa Application September 19, 1956, Serial No. 610,865

Claims priority, application Union of South Africa August 9, 1954 24 Claims. (Cl. 33-18) This invention relates to perspective drawing rnachines of the kind in which the movements imposed on a tracing point are transmitted to a drawing point associated with a flat drawing surface, through an arm pivoted at the fixed station point. The station point is the equivalent of the eye of the observer and the object looked at is located to be scanned by the tracing point. In most cases the object is a plan view the altitudes of the various points of which are known and which is orientated in relation to the station point in conformity with the perspective view to be drawn. For convenience, the plan is usually laid on a horizontal surface and the tracing point is the lower extremity of a vertical column to which the arm is secured at a variable level. Altering the point of attachment of the arm to the column is equivalent to variation of the angle of sight in the vertical plane.

The basis upon which these machines proceed, in relation to the preparation of a perspective view derived from a plan and given data on altitudes, is that perspective projections are made in several horizontal planes at difierent altitudes, the inclinations of the arm being varied from plane to plane in conformity with the altitude of each plane. The several perspective views thus obtained are then amalgamated into a single perspective drawing by inserting the lines which are vertical or have a vertical direction component. In some cases the verticals are drawn by movement along the column end of the arm; in other cases the verticals are interpolated manually on the perspective drawing.

When the object is three-dimensional, the procedure is simplified in that, with the arm made variable in length and including the tracing point, the latter is caused to scan the object in the three-dimensions, as the eye does, and the drawing point produces the perspective view, as it is produced on the retina of the eye.

The failure of these machines to win generalacceptance among architects and enginneers can probably be ascribed to any one or more of three factors; high cost due to complexity, complication in the use of the machine and disadvantages in the design of simple machines. These disadvantages may be inherent. For instance the persepective view may be produced on too large or' too small a scale, or in reverse; or the drawing being made may not be visible to the operator while he is at work at the tracing position. 7

The object of the present invention is to produce a machine which eschews mechanical complication so that its cost is moderate, which is easy to operate, in which the scale of the perspective drawing is within the control of the operator, and in which the drawing being made is in the operators view as he causes the tracing point to scan the object.

A perspective drawing machine according to the invention comprises a horizontal table, a vertical drawing board, an extensible tracing arm and an extensible drawing arm at right angles to one another in plan, a vertical column, a plinth supporting the column and standing Patented June 3, 1958 movably on the table, means swivellably connecting an end of the tracing arm to the column and movable up and down the column, a tracing point provided by the plinth, a writing instrument mounted at one end of the drawing arm, a coupling, rotatable about a vertical axis, connecting the drawing and tracing arms one above the other and constraining them against relative movement in the horizontal plane while permitting relative pivotal movement in vertical planes, a vertical post rigidly fixed to the table, means to support the coupling on the post at an adjustable height, and additional coupling means connecting the drawing and tracing arms, displaced in plan from the vertical axis of the coupling, spanning the vertical distance between them and comprising a universal joint.

Other features will be apparent from the following description of various embodiments of the invention.

Several embodiments of the invention are illustrated by way of example in the accompanying drawings in which Figurel is a perspective View of one embodiment;

Figure-2 is an elevation, partly in section, of a counterbalancing means for the drawing arm;

Figure 3 is an elevation of the coupling device;

Figure 4 is a horizontal section on the line 44 of Figure 3;

Figure 5 is a view of a partly completed drawing;

Figure 6 is a detail view of part of the tracing column;

Figure 7 is a perspective view of another form of the invention;

Figure 8 is a fragmentary side view, partly in section of the coupling means of Figure 7;

Figure 9 is a perspective view of an alternative form of tracing column;

Figure 10 is a perspective view of another form of tracing column; and I Figure 11 is a perspective view of yet another form of tracing column.

In the drawings, 10 denotes a table on which the machine stands. Ona section 11 of the table surface the object from or of which a perspective view is to be made is mounted. In the drawing this is shown as a plan view 12 of the building 13 shown in Figures 1, 5 and 7.

A vertical pillar v14 is mounted on the table and the tracing arm 15 is carried by it in a coupling device later to be described.

In the case of a flat object such as the plan view 12, the tracing point is provided at the lower end of a vertical tracing column 16 to which an end of the tracing arm 15 is secured by a swivelling clevis 17 engaging, through pivot pins 18, a collar 19 that rotates around a core 19a that slides on the column 16.

To ensure verticality of the column 16, it is based on a broad plinth 249, preferably of transparent material, on which the tracing point occurs as a spot 21.

The collar 19 is attached to one bight of an endless band 22, that passes around pulleys 23 mounted towards the ends of the column 16. One pulley is rotatable by means of a knob 24, operation of which varies the height of the collar 19 above the table level and thus the inclination of the arm 15.

The collar is associated with a scale 25 calibrated in units of height, for instance the scale is applied to the band 22.

To allow for lost motion between the tracing point 21 and the pivot of the arm 15the station point-in the coupling device, the arm consists of a sleeve 26 held by the device and a rod 27 slidable in it; that is, so that the drawing arm will be unresponsive to movements of the point 21 transverse to the drawing arm and to the components of movement of the point in that direction.

The drawing point is a writing instrument 31 that ter- .minat'es a drawing arm 32, which is carried by the 'erator.

9 V al t couplingdevice. The arm, =like the the instrument 31, and consists in a sleeve 33 held by the device, and a rod 34 slidable in it and carrying the instrument 31. The latter is biassed towards a flat, jupright, drawing board 35 mounted on the table by a tension spring 36 or an elastic band, and is capable of retraction from the board against the resistance of the spring 36 or the band.

The outer end of the arm 32 may carry the counterbalance weight,- shown in Figure 2 and described later;

The board 35 has a piece of drawing paper 38 pinned to it, on which the perspective view is-to bernade; and is mounted on posts 39. V

The core of the invention is the separation of tracing V "arm and drawing arm, and the motion-transmitting means between them that ensures that the-drawing arm, despite the separation, will be the slave of the tracing In all embodiments, the arms are at right angles to one another and the drawing arm '32, being the slave of the tracing arm' 15, remains at right angles to it whatever the'behaviour'of the tracing arm.

that it imposes on the drawing instrument 31 movement that causes the instrument to depict the perspective drawing right side up and in free and close view o'f the op- The device' consists in an open framework 41 that is pivotally supported on a vertical axis AA by pin-bear- 'ings 42 provided by a yoke 43 that is mounted on the pillar 14 by means of a slidable 'collar 44, that can be locked in any position on the pillar by a locking screw 45. The sleeve 26 of the tracing arm is connected to the framework by a horizontal spindle 46 that con- 1 strains it against'all movement relatively to "the frame other than pivotal movement aboutthe axis ofthepspindlc. Similarly the sleeve 33 of the drawing arm 32 is pivoted ion a horizontal spindle 47, set atan angle to the spindle 46 which,-inthe embodiment being discussed, is aright angle. 7 '5' a 1 The ,arms15 and 32 are directly connected together through the Hookes joint device 48. [,Gne "element 49 of the outer member of the Hookefsjoin't isscctn'edto a link '51 that extends parallel with the tracing arm 15 tracing arm 1'5,'is 7 constructed to allow lost motion between the vdevice and transmitted to the drawing instrument 31'as a horizontal movement.

Movement'of the point 21. in the direction parallel to 7 the edge 59 eitherJare ineffective to aflfect the drawing armi32 if the tracing arm 15 is horizontal i. e.if the line of sight is horizontal, and the arm 15 is itself parallel to the edge 59. If the arm 15 is inclined (i. e. if the line of sight is up ordown), movements of the point 21 cause the tracing arm. '15 progressively to vary its inclination to the horizontal asthe distance between the column 16 and the station'point progressively increases or decreases; that is, as the angle of the arm to the horizontal changes whereupon the linkages between the. arms 15, 32 '(without moving the framework 41) cause the drawing arm 32 to tilt correspondingly, upwardly,

if the point 21 is approaching the station point (that is, if the angle of the arm 15 to the horizontal is increasing), downwardly if it is receding from it (that is, if the angle of the arm to' t'he horizontal is decreasing).

Thus, every movement of the spot 21in the plane of' I of motion are concerned, 'the vertical and horizontal angular variations respectively of the arm 15 only are transmitted, irrespective of the distance in the plane of the table traversed by the spot, it follows that true recession of planes is achievediand that the instrument 31 will draw a true perspective representation of the twodimensional plan 12 as seen from the station point.

The 'counterbalancing means mentioned, above and shown in Figure 2 is necessary to counteract thetendency of the rod .34 of the drawing arm 32 from being gravitationally projected towards or away from the board 35 when the angle of inclination of the arm 32 to the 'hori-' zontal exceeds the angle at which the rod 34 will slide gravitationally within the sleeve. 1 Q

The rod 34 is shown as mounted for sliding movement within-thetsleeve '33 on ro'llers81, which are journaled in the sleeve. The sleeve carries an extension arm :82 on whicha wheeled carriage 83 runs. The carriage and the other element 50 is secured to a link 52 that ex- 2 tends parallel with the drawing arm 32. Each-link 51, "52 is connected to its arm 15,32 bya clevised strap 53 that straddles the arm and is pivotally secured 'to it by cross pins 54. The links are so connected to the straps by means of a head 55 that is rotatable 'on the reduced extremity 56 of each arm, the head being pivoted to the straps by spindles 57 held by thestraps.

'I-n order'to transmit tilting movement of the tracing arm 15 to the drawing arm 32; the limb'58a of the central member 580i the Hookes joint '48 is pivoted to the frame about a horizontal axis that is inclined to the axis of both arms 15-and 32, to maintain the arms in their prescribed angular relationship. As this relationship is a right'angle, the member is at an angle of 45 to each axis.

Consideration will show that the linkages described tie the arms 15, 32 together in a'rigid relationship in which neither arm is capable 'of movement notimposed on it by the other. ,Thus,when the tracing spot 21 is moved in the 'direction'normal to the edge 59 of the table 10,

the motion is transmitted via the spindle 46 to the framework 41, and by the framework to the. drawing arm 32 through the spindle 47. Assuming the arm 15 to be horizontal, as this motion is wholly normal to the .planes ot the pivotal movement permittedthe arms 15,

32 about the spindles 46, 41, the Hookes joint 48.:plays supports a weighted pendulum.'84, the carriage and the pendulum being substantially equivalent in weight to the rod 34 and its attachments. a

The carriage and the rod 34 are both tied to, an endless cord85 *which passes round pulleys 86, 87, oneI86 of which is mounted on the sleeve 33 and the other on the I extensionarm 82. V i a When the 'arm 32 is inclined downwardly it urges the bight a of the cord downwardly, and the bight 85b thus tends to propel the carriage 83 upwardly. Contrariwise when the arm 32 is inclined upwardly the' carriage tends to 'be propelled downwards; so that in both cases a state of equilibrium of forces exists.

Without a compensating device of this sort, the drawpaper 38 or falls 7 ing instrument 31- either digs into the away from it. 7 V

In the embodiment of Figures 7 and 8, ;the motiontransmitting means includes a coupling 88, which is 7 through the upper slot 9.0 and is .pivotally connected to j the coupling by the horizontal cross pin 92;

Thus both arms 15 and32 are constrained against movements relatively to the coupling, otherwisethan in vertical planes at right angles to one another. Movements of the tracing arm in the horizontal plane or movements having a horizontal direction component cause rotation of the coupling about the axis A-A, which rotation is transmitted to the drawing arm 32 and causes corresponding horizontal displacement of the arm.

The motion-transmitting means includes also a pair ofmembers which in the drawing are shown as contacting cylinders 93, 94; one, 93, mounted on a horizontal arm 95 projecting rigidly from and at right angles to the sleeve 26 of the tracing arm 15, and the other 94 mounted on a horizontal arm 96 projecting rigidly from and at right angles to the sleeve 33 of the drawing arm 32.

The centre of gravity of the arm 32 and the structure it carries is located between the pivot pin 92 and the board 35, so that the two cylinders are held gravitationally in contact with one another. Thus each cylinder provides one element of a pair of contact surfaces held together and free to move in contact with one another as the movements of the tracing arm 15 dictate.

The members'93, 94, are such that the distance a-a Fig. 8, which is the vertical distance between the horizontal planes containing the two arms 95, 96, is substantially the same at all times as the vertical displacement of the pin 92 above the pin 91. This condition is satisfied by forming the members 93, 94 as cylinders, as illustrated, but could also be satisfied by making them conical with opposed tapers, or for that matter as flat contacting plates universally pivoted to the arms 95, 96. However, the simplest form is that illustrated; and to minimise friction the cylinders, in the embodiment being described, are rollers.

it could also be that the members 93, 94 are held in contact by a spring if they are not biassed gravitationally together, but this again would introduce complexity.

As in the case of the embodiment of Figures 1-3 the structure described ties the arms 15, 32 together in a rigid relationship in which the drawing arm 32 is constrained to movement imposed on it by the tracing arm 15. When the tracing spot 21 is moved in the direction normal to the edge 59 of the table 10, the motion is transmitted via the pin 91 to the coupling 88 and by the coupling to the drawing arm 32 through the pin 92. As this motion is wholly normal to the planes of the pivotal movement permitted the arms 15, 32 about the pins 91, 92, the members 93, 94, play no active part therein and the arms are solidly locked together. Movement of the spot 21 normal to the edge 59 is thus transmitted to the drawing instrument 31 as a horizontal movement.

Movements of the point 21 in the direction parallel to the edge 59, if the arm is inclined, cause the tracing arm 15 progressively to vary its inclination to the vertical as the distance between the column 16 and the station point progressively increases or decreases; whereupon the members 93, 94 act to cause the drawing arm 32 to tilt correspondingly, upwardly, if the point 21 is approaching .the station point, downwardly if it is receding from it, without movement of the coupling 83.

Apart from the coupling means, the construction of the machine of Figures 7 and 8 is identical with that of Figures 13.

After the explanatory comments made above, the method of use of either apparatus will be reasonably clear.

The perspective angle having been decided, the plan 12- is correspondingly oriented in relation to the station point. The yoke 43 is adjusted on the pillar 14 to correspond to the altitude of the station point, and the spot 21 and the collar 19 set for the co-ordinates of a central point of the drawing to be made. The collar 15 is moved to the altitude of the plane first to be regarded, the spot 21 is moved to scan the plan in the first plane; the collar is moved to the altitude of the next plane, the plan at that plane is scanned; and so on until all the necessary planes have been dealt with.

There then follows the amalgamation of the perspective plans. In so far as true vertical lines are concerned these are integrated into the perspective view by stationing the spot 21 on the appropriate point on the plan and turning the knob 24 to move the arm 15 upwandly or downwardly for the distance on the scale corresponding to the height of the lines.

As to lines having both vertical and horizontal components, these are necessarily interpolated into the perspective drawing manually, although, in the case of curved lines, a series of points in horizontal planes at different levels may be plotted to facilitate their insertion in the perspective drawing. Since at least in the case of an architectural drawing the preponderance of upward lines are truly vertical, the necessity to interpolate lines into the perspective drawings by hand is seldom burdensome.

Taking, as an example of the procedure discussed above, the house shown in perspective view in Figure l, the plan view, shown in the tracing position in Figure 1, is prepared to show (at 61a, 62a, 63a) the location of the door 61, the window 62 and the door 63 in the lean-to 64. The plan is mounted on the table 10 in the determined orientation. Selecting a station point at, say lintel of the window 62, the arm 15 is set on the pillar 14 at its altitude. The collar 19 is then dropped to ground level and the ground plan of the house is scanned, bearing in mind of course that portions of the plan will be hidden from sight by the superposed structure. The arm is then raised successively to the altitude of the window sill, the window lintel, the door lintels, the upper and lower roof levels of the lean-to, the roof and the chimney top. This will produce a perspective drawing as shown in Figure l or Figure 7.

The verticals are then introduced by location of the spot 21 successively at the corners of the building, and of the chimney 65 and at the stiles of doors and win dows, and moving the arm 15 the distances appropriate to the several altitudes. The resulting perspective drawing, shown in Figure 1, or Figure 7 is complete save for the manual operation of adding the sloping roof of the lean-to.

As each successive operation in the preparation of a perspective drawing is completed, the writing instrument 31 is withdrawn from the paper 38 against the resistance of the biassing spring or band 36. This may be done manually but it will be appreciated that a draftsman who has both hands employed in directing the tracing spot 21 along the object 12 will waste time and tend to lose concentration if his observation of the object and of the emerging perspective drawing be interrupted by the necessity to retract the instrument 31 by hand.

There is the provision of means whereby retraction of the instrument is effected by the foot. To this end, the rear end 71 of the arm 34 has attached to it a Bowden cable 72 which is led below the table 10 close to floor level, where it is attached to a foot pedal 73. The operator, by treading on the pedal causes the instrument to be retracted without the necessity to disturb his concentration on the work in hand.

Many of the advantageous features of the invention have already been noted. Others which may be stressed are the compactness of the design, and the fact thatthe perspective drawing being made is under the observation of the draftsman at close hand, due to the mounting of the drawing arm 32 at an angle to the tracing arm 15 and of the board in an upright position facing the operator, a disposition which applicant believes to be new in the art. Furthermore, the scale of the perspective drawing vis-a-vis the object is infinitely variable over a Wide range within the control of the draftsm-an merely by adjustment of the ratio of the effective lengths of the arms 15 and 32, this adjustment being possible by reason of the slidability of the rods composing the arms within their sleeves.

The machine is'highly flexible in that any perspective i protractor .102.

view, exterior or'interior, can be drawn in a fraction of .theifirne necessary to do so by ordinary drafting methods. 1

Q .Aiword may. be said about three-dimensional objects.

Whiihthe'se are to be drawn, the object may be located on the table ,10, the'tracing arm 15 is withdrawn from' spot 21 is kept stationary at the point on the plan 651) appropriate .to the vertical line. If, however, the line be inclined -t o1the ver.tical, it cannot be thus translated to the drawingarm32.- The reason for this is that given above, ethat-machineslof the kind in question produce perspective 'viewspf :thelobject being drawn in a number of horizontal planes intersecting the object, and the drawing is com-. pleted by .connecting the series of views together by lines 'corresponding to the extent of the object in the third The verticality of the tracing column thus Iconfines those lines which can be drawn by the machine itself to lines which are themselves verticalgso that the lutmost .aidithat themachine can give for inclined lines dimension.

is tofacilitatelplotting of the points of intersection of'the .lines with a succession of horizontal planes, the points then being joined together manually.

i If the inclined lines be rectilinear this procedure presents no difficulty as has been seen, but this is not so when a they are curvilinear. Thus the drawing in'perspective of .a circle .(which'is the usual curvilinear line encountered) that does not lie in a horizontal plane is beyond thescope .of the machine. V i w The arrangements of Figures 9 to '11 are designed to rdealwith non-vertical and especially curvilinear lines, and each proceeds upon the basis that it provides means defining a path that is a simulacrum of the line, means to orientate the path in space in'conformity with a plan view;of the line, and means to constrain the tracing point .of the tracing arm tomove along the path. .Since the normal .PIOCCdUI'JWlll be first to scan the plan view, the orientation of the path will customarily ;be related to aplan view already located and scanned.

will be apparent that the basis of the devices of IEigu'res 9 toll is .thesimulation of a three-dimensional object, the plan representing two of the dimensions and the path the third. It follows that any line in the thirddimens ion, be it.recti-..or curvilinear, can'be translated to the drawing arm :32, within the practical limitations of defining-the path. V V

.In.Figures 9 to. 11 there is seen the end of a tracing column which in Figure 9.is like that illustratedinlFigures Land T7, butis simplified in Figures lO'andll. In Figures '9-1'1, reference numbers. similar to those .used in Figs; 7

and 8 are employed, with the'addition of the'sutfix'es X,

In Figure '10 the collar'19y is'moved "up or down "directlyfby'hand and'can be secured at any height on the columnby a'th umbscrew-97. V a

In Figure9 the collar 19xcarries aplate 9S'that is mounted on the collar 19x by means'of a yoke 99 to which 'theplate is secured by wing nuts' 100 that screw 01110? screw-"threaded studs ltlLprojectihgfrorn the plate .QSithrOnghitheIi-mbS- f the yoke 99. The inclina'tion'of the plate .tortheyertical maybe adjusted by tilting-the plate about thehorizontal pivotal axis, provided by the ;studs .-101,-the.angle;of inclination ibeing indicated on a The plate i98 has cutintoit a seriesJof concentric.cir- .cular grooves .103, the radii of which correspond to the 155 'arm,.,1f5, .16 represents in all figures the vertical-tracing 8 A radii .of circular lines most likely to be encountered in drawings of thekind to be dealt with.

Two or more plates may be provided, each withiits series of grooves, if the series catered for in one plateis insuflicient to deal with a-ll probabilities, the appropriate plate being mounted on the column 16.76., i V

In use the column is located on the table x, over, the circle or are that appears on the planview which is drawnon the paper 651 7 By means of a set-square,lthe groove of appropriate diameter .on the plate 9 8 is alljusted (by rotation v.of the column 16x and tilting of the plate 93) to occupy in space the same orientationas the circular or arcuate line to be drawn. Thereupon, the

pointed end'15a of the tracing arm x is projected to enterthe groove andthe tracing arm 15x is rotated for the end to traverse the groove or such portion of it as is appropriate.

Thedeyice of Figure 10 is advantageousin that the circles that can be dealt with are of infinitelyjvarifible radiusand not merely any one of a prescribed series.

The device consists in a' graduated crank arm 103;.held. slidably in a guide 104 that is 'rotatably mounted, on i the collar 19y. One end of the arm 103 carries a peg 105 pocked at 106 to receive the pointed end 15;: .of the tracingarmlSy. 7 y l r lnuse the crank arm 103 is adjusted in the guide 104 describedin connexion with Figure 9, the end..15a is 'held engaged in .the pock 196 and the arm 103 is rotated.

No provision is made in the device of Figure lOfor tilting of .the crank arrn103. -Thus, as it is drawn,-the 7 device deals only with circles and arcs in vertical'planes. However, the arm 103 could be mounted for tilting, like, the plate 98 of Figure 9.

. In Figure 11, the vertical column 16z is made up of twoparallel-rails 1611,1612 of T section that act as guides for a saddle 107 which can be clamped at anyposition along the height of the column by a thumbscrew 108. T heheight of the saddle is set by means of a pointer 10? associated with a graduated'scale 110.

' The device is mounted on the saddle for rotation about a horizontal pivot pin '111 and may be clamped in any angular orientationto the vertical by means of W a thumbscrew behind the saddle. 'The angular position :is indicated by a pointer 112 associated with aprotractor {The device comprises a disc 114 which is rotatable about its axis on a spindle .115, within a sleeve 116. The sleeve is carried at the'end of a cranked bracket 117 of" which the crank-arm 118 is mounted for rotation about the pivot pin 111. V

. 'The bracket 117 is; such that in all angular positionsof thedisc 114 the centre "of the disc lies vertically above the :tracing point Zlz.

On the face of the disc 114 is pivotally mountedza pointer 119, associated with anarcuate scale 120. The

:pointerzhas a peck 121 which is designed to be engaged by the pointed end 15oz of the tracing arm 15z.

In use the plinth base Ztlz, is placed on the plan drawn :onthe paper b and the disc 114 is adjusted at the correct altitude on the column 16 and in the correctorientation to conform .with the circle or are to be drawn. The pointer 119 is moved along'the scale 120 held in engagement while the disc 114 is rotated. Thus by orientation of the disc 114 and pointer 119 in space, a simulacrum of the circle or are to be drawn is in effectdefined'and is'translated by the tracing arm to the drawing arm.

If an object of irregular shape is to be scanned, a plan view thereof may be drawn and applied to the'disc 114, which is then orientated. Tre tracing point 15az is then caused to scan the lines of the drawing. To ensure that the plan is held immobile while this is happening, the spindle 115 may be clamped to the sleeve by means of a thumbscrew 122.

I claim:

1. A perspective drawing machine comprising a horizontal table, a vertical drawing board, an extensible tracing arm and an extensible drawing arm at right angles to one another in plan, a vertical column,'a plinth supporting the column and standing movably on the table, means swivellably connecting an end of the tracing arm to the column and movable up and down the column, a tracing point provided by the plinth, a writing instrument mounted at one end of the drawing arm, a coupling rotatable about a vertical axis, connecting the drawing and tracing arms one above the other and constraining them against relative movement in the horizontal plane while permitting relative pivotal movement in vertical planes, a vertical post rigidly fixed to the table, means to support the coupling on the post at an adjustable height, and additional coupling means connecting the drawing and tracing arms, displaced in plan from the vertical axis of the coupling, spanning the vertical distance between them and comprising a universal joint.

2. The machine of claim 1 including a yoke slidably mounted on the post and means to clamp the yoke to the post, in which the arms of the yoke are horizontal and in which the coupling is mounted between the arms.

3. A perspective drawing machine comprising a horizontal table, a vertical drawing board, an extensible tracing arm and an extensible drawing arm at right angles to one another in plan, a vertical column, a plinth supporting the column and standing movably on the table, means swivel-lably connecting an end of the tracing arm to the column and movable up and down the column, a tracing point provided by the plinth, a writing instrument mounted at one end of the drawing arm, a coupling rotatable about a vertical axis, connecting the drawing and tracing arms one above the other and constraining them against relative movement in the horizontal plane while permitting relative pivotal movement in vertical planes, a vertical post rigidly fixed to the table, means to support the coupling on the post at an adjustable height, and additional coupling means connecting the drawing and tracing arms and consisting in two parts each providing one element of 'a pair of surfaces biassed into contact but free to move relatively to one another, the parts being one above the other and such that their vertical displacement remains substantially constant in all positions of the drawing and tracing arms.

4. The machine of claim 3 in which the surfaces are biassed gravitationally into contact with one another.

5. The machine of claim 4 in which the contact surfaces are provided by the peripheries of two cylinders the axes of which are parallel with the tracing arm and the drawing arm respectively.

6. The machine of claim 5 in which the cylinders are rollers mounted on short beams projecting from the arms.

7. The machine of claim 6 in which the arms are at an angle to one another and the beams at right angles to the arms, and in which the rollers are located substantially on the line bisecting the angle formed by the two arms.

8. The machine of claim 1 in which the coupling is a body with two vertical slots, one above the other and at right angles to one another, and in which the drawing and tracing arms extend one through each slot and are pivoted on the slots about horizontal axes.

9. The machine of claim 1 in which the coupling is an t 10 open frame to which each arm is attached for pivotal movement in a vertical plane.

10. The machine of claim 9 in which the universal joint comprises a Hookes joint, the central member of which is arranged vertically, with a horizontal limb fixed on the frame for pivotal movement about its axis which axis is inclined to the axes of both arms to transmit to one arm tilting movements of the other arm.

11. The machine of claim 10 including a link parallel with and pivoted to each arm and each fast with one of the outer members of the Hookes joint.

12. The machine of claim 11 in which each link is arranged to be permitted rotational movement about its own axis relatively to its arm.

13. The machine of claim 1 including a collar on the column to which the tracing arm is swivellably connected, pulleys at the top and bottom of the column, an endless band around the pulleys, an operating knob for rotating one pulley to drive the band, and a calibrated scale on the band, the collar being attached to one bight of the band.

14. The machine of claim 1 including counterbalancing means mounted on the drawing arm consisting in a wheeled carriage that runs on the drawing arm, two spaced pulleys mounted on the drawing arm and an endless cord around the pulleys, one bight of which is secured to the carriage and the other to the rod.

15. A perspective drawing machine comprising a horizontal table, a vertical drawing board, an extensible tracing arm comprising a tracing point; and an extensible drawing arm at right angles to one another in plan, a vertical column, a plinth supporting the column and standing movably on the table, a tracing point provided by the plinth, a writing instrument mounted at one end of the drawing arm, a coupling rotatable about a vertical axis, connecting the drawing and tracing arms one above the other and constraining them against relative movement in the horizontal plane while permitting relative pivotal movement in vertical planes, a vertical post rigidly fixed to the table, means to support the coupling on the post at an adjustable height, additional coupling means connecting the drawing and tracing arms, displaced in plan from the vertical axis of the coupling, spanning the vertical distance between them and comprising a universal joint; and a device for translating to the drawing arm lines that are curved in plan view, consisting in means defining a path that is a simulacrum of the line mounted on the column and movable up and down on it; means to orientate the path in space in conformity with a plan view of the 'line, and means to constrain the tracing point of the tracing arm to move along the path.

16. The machine of claim 15 in which the defining means is a disc mounted for its height and for its orientation to be adjustable.

17. The device of claim 16 in which the defining means is a plate with a series of concentric grooves cut into it, and in which the tracing point is a stylus adapted to be engaged in any one of the grooves and to be constrained by the groove to move around the selected groove.

18. The machine of claim 16 in which the defining means is a disc mounted for rotation about its axis, and a means to engage the end of the tracing arm arranged on the face of the disc for its radial distance to be adjustable.

19. The machine of claim 18 in which the engaging means comprises a pointer associated with a scale graduated to show radial distances, and a peck in the pointer and in which the tracing arm has a pointed end that is adapted to be engaged in the pock in the pointer.

20. The machine of claim 19 including a spindle mounted on the column journalled in a cranked bracket that is adjustable in respect of its angular orientation to the vertical.

that is adjustable in respect of its angular orientation to the -vertical andc-in which the disc'is rotatably mounted V on the spindle.

22. The machine of claim 15 in which the defining means is' a crank arm having m'eans to engage the drawing point and in which the throw of the crank-arm is adjustable. a

23. The device of claim 21 in which the engaging means is a peck in which a stylus on the tracing armis e e assassa 24. The machine of claim 1 including a spring biasing V the writing instrument 'into contact with the drawing board, and means tn retract the instrument from the board comprising a pedal and a Bowden cable between 1 the pedal and the instrument. 7

- Beferences Cited in the file o f this taatent UNITED STATES PATENTS 704,307 Eichenb'erger 'I y 8,1902 888,249 Meyer -May 19,1908 7' 962,439 Kirk June 28, 1910 F ORE IGN PATENTS V r 17,733 Switzerland Oct. 3,1898

176,067 Switzerland c June 17, 1935

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