GB2092313A - Automatic drawing apparatus - Google Patents

Abstract

Automatic drawing apparatus comprises a surface (3) to receive drawing paper, film or other medium to be drawn on, an arm (4) movable over the drawing surface, a carriage (5) movably mounted on the arm and carrying an instrument for drawing on said medium. The arm is cantilevered from one end from a bearing carriage 15 where it is connected with backing rolls 18, 19, 20 which are in engagement with a ferromagnetic stationary guide rail 24 extending in the intended direction of movement of the arm. The said one end of the arm is pivotally mounted so that the arm can be raised from a drawing position in which the free end of the arm lies close to the drawing surface to a raised position in which the free end of the arm is situated further away from the drawing surface, thereby facilitating the insertion of drawing medium below the arm and onto the drawing surface. The arm is urged into the drawing position by a magnet mounted in a recess in the carriage 15. <IMAGE>

Description

SPECIFICATION Automatic drawing apparatus This invention relates to an automatic drawing apparatus.

Drawing apparatus, in the form of so-called table plotters has been proposed and comprises an arm which supports a carriage for receiving a drawing instrument, and which is movable over a drawing surface of the apparatus. The arm is cantilevered from one end where it is connected with backing rolls, which are in engagement with a stationary guide rail extending in the intending in the intended direction of travel of the arm. The fact that the arm is cantilevered enables drawing paper, drawing film or other medium to be drawn on, to be slipped through underneath the free end of the arm onto the drawing paper or drawing film does not, of necessity, have to be applied in the intended direction of movement of the arm and precisely between its ends, and the drawing paper or drawing film can jut out laterally over the drawing surface.In such previously proposed drawing apparatus, the backing rolls are braced such that through fixed installation on the stationary support rail they prevent sideways play of the arm in a plane parallel to the drawing surface and they prevent the free end of the arm from being lifted, and thus ensure that the arm is guided free from play.

However, it has been found that users of such drawing apparatus frequently attempt to raise the free end of the arm, so as to create more free space for the insertion of drawing paper or drawing film, leading to damage to the bearing arrangement of the arm.

Although such drawing apparatus may be used with the drawing paper or drawing film in sheet form, it has been proposed to mount a roll of drawing paper or drawing film externally to the side of a housing of the apparatus, so that the paper or film can be drawn offfrom this roll and can be applied onto the drawing surface. Usually with this arrangement there are guides or supports in the region of the two lateral ends of the drawing surface, with which the drawing material in strip form is held evenly on the drawing surface.

A disadvantage in this arrangement is that the roll supparted externally an the housing can be intrusive in operation of the drawing apparatus and that in particular when carrying out other work in the proximity of the drawing apparatus the edges of the freely supported roll can be damaged, so that the paper or film which is to be pulled off from it is dam- aged at its edges.

It is an object of the invention to provide an automatic drawing apparatus which may be used with drawing paperordrawing film in sheet form or which may, if desired, be adapted to be used with the drawing paper or drawing film in roll form.

Accordingly, the present invention provides an automatic drawing apparatus, wherein the apparatus conprises a housing, a drawing surface to receive drawing paper, film of other medium to be drawn on, an arm movable over the drawing surface, means for moving the arm, a carriage movably mounted on the arm and adapted to receive a drawing instrument for drawing on said medium and means for moving the carriage along the arm, and wherein the arm is cantilevered from one end where it is connected with backing rolls which are in engagement with a stationary guide rail extending in the intended direction of movement of the arm, the said one end ofthe arm being pivotally mounted such that the arm can be raised from a drawing position in which the other and free end of the arm lies close to the drawing surface to a raised position in which the free end of the arm is situated further away from the drawing surface than in the drawing position, there being magnetic means for urging the arm into the drawing position by means of magnetic forces between the guide rail and a part of the apparatus carrying said backing rolls.

In the present drawing apparatus therefore, sufficient play is available to tilt the arm from its drawing position, whereby the user can create appropriate free space for the insertion of drawing paper or drawing film, whilst the magnetic force pushes the arm back from the raised position into a clearly defined drawing position and keeps it there in operation, so that a support in this direction free from play is ensured.

The part carrying the backing rolls is preferably a support carriage which is rigidly connected with the arm and which extends transversely over the surface ofthe guide rail facing the arm and embraces the guide rail, and in this case the magnetic means is so located that magnetic force attracts the region of the support carriage extending transversely over the face of the guide rail facing the arm towards this face of the guide rail, i.e. attracts the arm into its drawing position. Since the support carriage embraces the guide rail, this embracing section comes to rest on the guide rail when the free end of the arm is raised, and limits the raising movement. When the arm is released it is returned by magnetic force into the drawing position, and reliably held in this position.

On the region of the support carriage transversely over the surface of the guide rail facing the arm, a permanent magnet can be fixed adjacent to the guide rail, and the guide rail can consist of for romagnetic material, so that the permanent magnet, and hence the corresponding region of the support carriage, is attracted to the guide rail. In addition, oscillations of the support arrangement and of the other parts as a result of resonances at low step frequency of the driving motor are effectively attenuated by eddy currents occurring as a result of the movement of the magnetic field.

In order that the present apparatus may be adapted for use with drawing paper or drawing film in roll form, at least one holder for a roll of drawing paper or drawing film is provided and comprises a trough provided adjacent to the drawing surface and beneath the level of the latter, in the housing of the a wing apparatus, with the longitudinal axis of the trough running parallel to the longitudinal axis of the arm. Preferably, a plate element is provided as covering for the trough, and is hingedlymounted on the housing of the drawing apparatus.

In this embodiment of the present drawing apparatus, the roll is therefore not supported laterally outside the housing, but in a trough within the housing, so that it is surrounded by the housing and is protected from damage. In addition, this also produces a particularly advantageous aesthetic impression, since the drawing apparatus does not need to comprise additional parts arranged externally on the housing.

In order to keep as short a swivel movement as possible for the opening and closing of the trough, the trough can be situated between the hinge axis of the plate element and the drawing surface, so that the hinge axis therefore runs parallel to the longitudinal axis of the roll situated in the trough and the plate element only needs to be hinged in its width covering the trough, therefore in raised position does not project very far over the plane of the drawing surface.

If the hinge axis of the plate element, however, is located at the end of the plate element nearer to the driven end of the arm and extends vertical to the longitudinal axis of the trough, the plate element can then project in a raised position very far upwards, but large size drawing paper, which is broader than the length of the plate element can be slid under thins and underthe cantilevered arm and can be drawn upon, whereby it then projects over the dimensions in particular the width of the drawing surface.

The plate element can be held in its covering position in a simple manner by means of magnetic force, for which purpose, for example, on the plate element or on the housing ofthe drawing apparatus a strip of magnetic material may be provided and on the housing or on the plate element a strip ferromagnetic material may be provided.

When the plate element is resting in its covering position on its side adjacent to the drawing surface on the housing of the drawing apparatus, the plate element can also serve at the same time to affix the strip material, which is situated on the drawing surface and connected with the roll, in its position on the drawing surface.

In order to obtain as compact a construction as possible of the drawing apparatus as a whole, the plate element for the covering of the trough can also hold a control keyboard for the apparatus, so that no additional space is required for this control keyboard at other positions on the drawing apparatus housing.

In previously proposed automatic drawing apparatus, a carriage bearing the writing instrument is moved over a drawing surface by a worm gear. A difficulty with such a worm gear is to design the drive to be as free from play as possible, in order to obtain accurately reproducible carriage movements on movement in one direction and in order to prevent backlash of the carriage on reversal of the direction of motion.

For this, generally a nut acting as a threaded element was designed to be as difficult as possible to move on the spindle, without actually impairing its mobility. An essential disadvantage in this, however, lies in that in operation both the thread of the spindle and also the thread of the nut are subject to abrasion, whereby the play between them, which in itself is to be avoided, unavoidably arises after some time, so that then the spindle andlor the threaded element must be exchanged.

In order to overcome this disadvantage and to create a worm gear free from play, in which even if an abrasion of the threads in engagement with each other occurs, the freedom from play remains, it is preferred that the means for moving the carriage along the arm of the present apparatus should comprise a worm gear having a spindle with a trapezoidal thread which is in engagement with a correspondingly formed threaded element connected to the carriage and that the threaded element should only be in threaded engagement with the spindle over one quarter to one half of the spindle circumference and should be urged by spring tension into such engagement with the spindle. The threaded element preferably has substantially the shape of a quarter two a half nut.

In this worm gear, a threaded element is therefore used, which is only in threaded engagement over a portion of the circumference of the spindle. If abrasion of the thread of the spindle and the thread element occurs after prolonged operation, the corresponding threaded region of the threaded element is simply pressed further inward into the thread of the spindle by spring tension and in this way the connection is maintained free from play. This is easily possible, because in a trapezoidal thread the radially outward surface of the turns of the one thread is situated at a certain distance from the groove base of the other thread; therefore a displacement of the type mentioned is possible until there is direct contact of the radially outward surface of the one thread turn and the groove base of the other thread turn.

Through the spring tension acting on the threaded element, it can happen that the spindle is deflected, for instance if the spindle is relatively long and has a relatively small diameter. If in this case the threaded element has the form of a quarter to a half nut, then the region of the spindle lying opposite the thread engagement region of this threaded element is freely accessible, and an outer support can abut it which is fixed on the carriage which also bears the threaded element. Preferably, the outer support as a part extending tangentially to the threaded turns of the spindle. The provision of such an outer support serves to prevent deformation of the spindle as a result of the spring tension acting on the threaded element.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Figure 1 is a perspective view of an automatic drawing apparatus in the form of a table plotter, Figure 2 is a longitudinal section through an arm of the drawing apparatus, parts of a housing of the apparatus being omitted, Figure 3 is a section along the line Ill-Ill in Figure 2, Figure 4 is a section along the line IV-IV in Figure 3, Figure 5 is a section along the line V-V in Figure 1, Figure 6 is a section along the line VI-VI in Figure 2, and Figure 7 is a diagrammatic representation of the engagement of thread elements.

Referring now to the drawings, Figure 1 shows a drawing apparatus 1 in the form of a so-called table plotter with a control keyboard 2, a work surface 3 to receive the drawing paper, and an arm 4, which bears a carriage 5. Drawing instruments, such as tube point writing pens, are mounted in the carriage 5, and the carriage can be moved along the arm 4 by means of a worm gearwhich can be seen in Figure 2 and which will be described in greater detail with reference to Figures 6 and 7. The arm 4 is movable by means of another worm gear in the longitudinal direction of a section 2' of a housing of the apparatus and hence over the work surface 3.

As can be seen from Figure 2, a spindle 6 with a trapezoidal thread (c.f. Figure 7) is supported in the arm 4, between a bearing 7, illustrated diagrammatically at the free end of the arm, and an output shaft 8 of a stepping motor 9 at the other end of the arm.

The carriage 5, only parts of which are shown in Figure 2, is in driving engagement with the spindle 6 via a threaded element 10 pressed by a spring 11 against the spindle 6, so that upon rotation of the spindle 6 the carriage moves in the axial direction of the spindle.

Whilst the arm 4 as shown in Figure 2 is cantilevered from its left hand end, its right hand end is therefore free and situated above the work surface 3 and does not rest on it. The left hand end of the arm from which it is cantilevered is rigidly fixed on a bearing plate 12 of the motor 9. This bearing plate 12 extends, as shown in Figure 2, beneath the drawing surface 3, and carries a stop block 13 to which a threaded element (not shown) is fixed, the element being pressed by spring pressure against the trapezoidal thread of a spindle 30, so that upon rotation of the spindle 30 the arm 4 is moved over the drawing surface 3 in a direction normal to its longitudinal direction.

A bearing carriage is fixed by means of bolts 14 on the bearing plate 12 and has a region 15 running between the arm and a fixed guide rail 24 which is rectangular in cross section and which extends in the direction of motion of the arm. A U-shaped crosssectional element 16 is fastened on the region 15 on the side opposite to the bearing plate 12 by means of bolts 21. As shown in Figure 2, the free shank 17 of this element 16 embraced the bearing rail 24. Backing rolls 19 are arranged on the bearing carriage and rest on the surface of the guide rail 24 facing the arm 4, the pivot axes of the rolls 19 lying vertical to the longitudinal direction of the guide rail 24. In addition, backing rolls 18 and 20 engage on the lateral surfaces of the guide rail 24, namely two backing rolls 18 on the left hand side in Figure 2 and one backing roll 20 on the right hand side in Figure 2.In this way, as shown in Figure 3 where the guide rail 24 is shown in dot-and-dash lines, a three-point bearing of the bearing carriage and, consequently, of the arm 4 results, whereby the distance between the backing rolls 18 on the one hand and the backing roll 20 on the other hand is set with the aid of spring band 25 which is held by bolts 26 and which extends between these bolts and presses a backing roll 21 against the guide rail 24, such thatthethree-point bearing is free from play, and the arm 4 therefore cannot be swivelled in a plane running parallel to the drawing surface 3.

It can be seen that as a result the bearing carriage holds the arm 4 in the position shown in Figure 2 with the aid of the various backing rolls, and that the free end if the arm 4 can be raised, until the upper face in Figure 2 of the shank 17 of element 16 comes to rest on the lower face of the guide rail 24, i.e. the free end of the arm 4 is movable upward from the drawing position shown in Figure 2, whereby additional free space is produced for the insertion of drawing paper.

As illustrated in Figures 3 and 4, the bearing carriage has a recess 22 in the region 15, in which a permanent magnet 23 is fixed, so that its magnetic south pole is facing the guide rail 24, which consists of ferromagnetic material, but so that between the guide rail 24 and the permanent magnet 23 there is a small air gap through which adhesion of the magnet to the guide rail is avoided. The magnet 23 therefore constantly draws the region 15 of the bearing carriage towards the guide rail 24 and therefore urges the arm 4 into its drawing position, in which all the backing rolls rest on the appropriate face of the support rail 24.This pulling action is further strengthened in that the region 15 consists of ferromagnetic material and, as Figure 4 shows, a narrow air gap is formed, beyond the recess 22, between the region 15 itself and the guide rail 24, so that there is a closed path of low magnetic resistance for the magnetic lines of force of the permanent magnet 23. By this arrangement, the eddy currents occurring on movement of the magnetic field in the ferromagnetic material give rise to a particularly good damping of the oscillations of the driving system which in themselves are unavoidable.

If the end of the arm 4 lying to the right in Figure 2 is raised by the user, the backing roll 19 adjacent to the backing roll 20 can be raised from the surface of the guide rail 24, without damage occurring to the bearing arrangement. As soon as the arm 4 is released again, it returns to its drawing position and is held in this position securely and free from play through the magnetic force brought about by the permanent magnet 23.

Referring now to Figures 1 and 5, the control keyboard 2 for the table plotter comprises a plate element 31 which, as shown in Figure 5, is mounted on a bearing 32 fixed on the housing of the drawing apparatus 1, so that its pivot axis 33 runs parallel to the longitudinal direction of the arm 4. Beneath the plate element 31 in the housing of the drawing apparatus is a trough 34, the longitudinal extent of which coincides with the longitudinal extent of the arm 4, and into which a roll of drawing paper or film 35 is inserted.

As Figure 5 particularly shows, aftertiltingthe plate element 31 upward about the pivot axis 33 frem the position illustrated in Figure 2, a strip 36 can be drawn off from the roll 35 and can be brought to rest on the drawing surface 3, whereby then the free end of the strip 36 is brought underneath the support bar 37 (Figure 1), so as to fix the strip down on this side in relation to the drawing surface 3. After the strip 36 has been drawn off and iaid down, the plate element 31 is pivoted back into the position shown in Figure 5, where a strip 38 of elastic material such as rubber, provided on the left side (Figure 5) of the lower surface of the plate element 31, comes to rest on the strip 36.Underneath the strip 38, in the housing of the drawing apparatus 1, in alignment with the drawing surface 3, a strip 39 (indicated by dashes) of permanent magnetic material is incorpprated, which attracts elements of ferromagnetic material (not shown) attached on the plate element 31. In this way the strip 38 and consequently the plate element 31 are pressed firmly against the strip 36 and hold it firmly in the desired position, so that no displacement of the strip on the drawing surface 3 can occur.

Referring now in particular to Figures 2, and 7, the threaded element 10 has the form of a half nut which has a trapezoidal internal thread corresponding to the trapezoidal external thread of the spindle 6. The trapezoidal internal thread of the half nut only extends over a circumferential range of 1 80" of the spindle but serves to couple the carriage 5 with the spindle and hence to produce the required drive connection. This half nut 10 rests on a bearing sheet 40, which is fastened by means of a bolt 41 between a stop block 42 and a support element 43 of the car riage 5. Beneath the support element 43 a carrier plate 44 is arranged by means of the bolts 41 and one end ofthe pressure spring 11 rests on the carrier plate and urges the bearing sheet 40 and hence the half nut 10 against the thread of the spindle 6.In this way it is ensured that the threads of the half nut 10 and the spindle 6 always mesh with each other free from play. An outer support 45 rests above the half nut on the spindle 6, and consists of a U-shaped bracket which is fixed to the support element 43, this outer support preventing the spindle from being deflected upward as a result of the pressure of the spring 11.

As already mentioned, the bearing sheet 40 is fastened between the support element 43 and a stop block 42, and a corresponding stop block 42 is arranged by means of a bolt 41 on the side opposite the first stop block 42 on the support element.

Upon movement of the carriage 5 along the spindle 6 each of these stop blocks will come into engagement with an associated stop pin 46 which radially projects from an end ofthe spindle 6, and through which further movement ofthe carriage is prevented and the spindle 6 is stopped. So that no damage is caused to the stepping motor 9, the motor and spindle can be connected with each other via a slipping clutch orthe motor can be designed such that it can be brought to rest without damage when the spindle stops revolving.

As already mentioned above, in conventional trapezoidaI threads which are in engagementwiíh each other, between the radially outward faces of the thread turns of the one thread and the groove base of the otherthread there is a clearance 47 which enables the two threads to be pressed deeper into each other, if an abrasion of the flanks occurs. It is readily clear that in the case of the worm gear described, these clearances 47 can be larger than in conventional trapezoidal threads, so as still to ensure freedom from play of the worm gear, if for example a relatively strongly abrasive material is used for one of the trapezoidal threads.

Claims (15)

1. An automatic drawing apparatus, wherein the apparatus comprises a housing, a drawing surface to receive drawing paper, film or other medium to be drawn on, an arm movable over the drawing surface, means for moving the arm, a carriage movably mounted on the arm and adapted to receive a drawing instrument for drawing on said medium and means for moving the carriage along the arm, and wherein the arm is cantilevered from one end where it is connected with backing rolls which are in engagement with a stationary guide rail extending in the intended direction of movement of the arm, the said one end of the arm being pivotally mounted such that the arm can be raised from a drawing position in which the other and free end of the arm lies close to the drawing surface to a raised position in which the free end of the arm is situated further away from the drawing surface than in the drawing position, there being magnetic means for urging the arm into the drawing position by means of magnetic forces between the guide rail and a part of the apparatus carrying said backing rolls.

2. Apparatus as claimed in Claim 1, wherein the part carrying the backing rolls is a bearing carriage which is rigidly connected with the arm, and which extends transversely over the face of the guide rail facing the arm and embraces the rail, and wherein the magnetic means is so located that magnetic force attracts the region of the bearing carriage extending transversely over the face of the guide rail facing the arm towards this face of the guide rail.

3. Apparatus as claimed in Claim 2, wherein the guide rail consists of ferromagnetic material and a permanent magnet is fixed on the region of the bearing carriage which extends transversely over the face of the guide rail facing the arm adjacent to the guide rail.

4. Apparatus as claimed in any one of Claims 1 to 3, wherein at least one holder for a roll of drawing paper or film comprises a trough provided adjacent to the drawing surface and beneath the level of the latter, in the housing of the drawing apparatus, with the longitudinal axis of the trough running parallel to the longitudinal axis of the arm.

5. Apparatus as claimed in Claim 4, wherein the trough is covered by a plate element hingedly mounted on the housing of the drawing apparatus.

6. Apparatus as claimed in Claim 5, wherein the trough is situated between the hinge axis of the plate element and the drawing surface.

7. Apparatus as claimed in Claim 5, wherein the hinge axis of the plate element is located at the end of the plate element nearer to the driven end of the arm and extends vertical to the longitudinal axis of the trough.

8. Apparatus as claimed in any one of Claims 5 to 7, wherein the plate element is urged into its covering position by magnetic force.

9. Apparatus as claimed in any one of Claims 5 to 8, wherein the plate element in its covering position rests on its side adjacent to the drawing surface on the housing of the drawing apparatus.

10. Apparatus as claimed in any one of Claims 5 to 9, wherein the plate element holds a control keyboard for the drawing apparatus.

11. Apparatus as claimed in any one of Claims 1 to 10, Wherein the means for moving the carriage along the arm comprises a worm gear having a spindle with a trapezoidal thread which is in engagement with a correspondingly formed threaded element connected to the carriage, and wherein the threaded element is only in threaded engagement with the spindle over one quarter to one half of the spindle circumference and is urged by spring tension into such engagement with the spindle.

12. Apparatus as claimed in Claim 11, wherein the threaded element has substantially the shape of a quarter to a half nut.

13. Apparatus as claimed in Claim 11 or 12, wherein an outer support, fixed to the carriage, abuts the spindle on the side of the spindle lying opposite the region engaged bythethreaded element.

14. Apparatus as claimed in Claim 13, wherein the outer support has a part extending tangentially to the threaded turns of the spindle.

15. An automatic drawing apparatus substantially as hereinbefore described with reference to the accompanying drawings.