GB2087269A - Paint spraying apparatus for moving vehicle bodies - Google Patents

Abstract

Vehicle bodies (11) are moved through a paint spraying system which comprises an electrostatic sprayhead (14) mounted for vertical, horizontal and rotational movements in a common plane. This plane is vertical with respect to the path of movement of the bodies and parallel to that path. The said common plane passes through the bodies. The apparatus includes drive means and control means for controlling the movement of the spray head. The spray head moves in a predetermined path, which depends on the shape and speed of movement of the bodies, so that the spacing between the bodies and spray head is maintained constant throughout spraying. The movement of the sprayhead enables the vertical front and rear surfaces of the bodies to be sprayed as well as the upper surfaces thereof. <IMAGE>

Description

SPECIFICATION Paint spraying apparatus This invention relates to apparatus for spray painting vehicle bodies.

During the manufacture of a vehicle it is desirable to perform automatically as many of the manufacturing functions as possible. The spray painting of the vehicle body as it moves along the vehicle assembly track has, in recent times, been the subject of attempts at automation. It is, for example, known in an attempt to replace manual spraying to provide a spraying station in which a pair of guns spray each side of the vehicle body as it passes the guns, and simultaneously a pair of guns suspended above the track and movable vertically spray the bonnet, the roof, and the boot lid of the vehicle. The guns of this latter pair are reciprocated at right angles to the direction of movement of the vehicle body to spray the horizontal surfaces of the body.However manual spraying by operators using hand held spray guns is still necessary in respect of the substantially vertical front and rear surfaces of the vehicle body.

The development of electrostatic, high speed bell spray guns gave rise to a modification of this prior proposal in which the air powered spray guns of the prior proposal were replaced by electrostatic guns.

The use of electrostatic, high speed bell guns does away with the need to reciprocate the two top guns in a direction transverse to the track, and also provides an improvement in the quality of the finish of the paint coating. Nevertheless, the need for manual spraying of the front and rear surfaces using hand held guns still applies and it is an object of the present invention to provide a paint spraying apparatus wherein this problem is mitigated.

According to the present invention in a paint spraying apparatus an electrostatic spray head is carried by means permitting at least three modes of movement of the head in a common plane containing the axis of the spray head, said common plane being vertical relative to the horizontal path of movement of the body to be sprayed, and being parallel to the direction of said path of movement so that said plane passes through said body to be sprayed, said three modes of movement comprising a rotationalmode wherein the head is revolved about a horizontal axis lying at right angles to said vertical plane, a vertical mode wherein the head can be raised and lowered relative to said path of movement of the body, and a horizontal mode wherein the head can be moved generally parallel to said path, and, the apparatus further including drive means for moving said head in said modes, and control means controlling said drive means, said control means causing said head to follow a path of movement, predetermined in relation to the shape and speed of movement of the body to be sprayed, such that the spray head can deliver paint to the generally vertical front and rear surfaces, and the body and such that while spraying the spacing between the spray head and the body, measured in the direction of the spray head axis, is maintained substantially constant.

Preferably the control means is capable of being preprogrammd whereby selectively, the head can be moved through any one of a number of different paths, the different paths being related to different body shapes.

Desirably the control means also controls at least one operating parameter of the spray head thus permitting the ratio of paint to body area to varied in accordance with predetermined requirements of the body being sprayed.

Conveniently operating parameters of the spray head controlled to effect control over the paint to body area ratio are selected from the group comprising, flow rate of paint to the head, volume of shroud air supplied to the head, rotational speed of the atomiser disc of the head, and the voltage applied between the body and the head.

Preferably the apparatus includes means whereby a signal representative of at least the vertical position of the head in relation to a fixed datum point is supplied periodically to said control means, and said control means is arranged to halt the spraying operation in the event that at predetermined intervals after the commencement of the operation the head is not in appropriate predetermined positions.

Desirably associated with the spraying apparatus is a detection system which senses certain predetermined parameters of the body to be sprayed, and which supplies signals in accordance with the presence of said predetermined parameters to said control means, said control means being arranged to commence the spraying operation only after receipt of all of the appropriate parameter signals.

Conveniently the parameters sensed by the detection system include the arrival of the body at a predetermined start position, the shape of the body, whether or not the body is electrically earthed, and whether or not doors, the boot, and the bonnet of the vehicle body are closed.

Preferably the spraying apparatus includes a second electrostatic spray head spaced laterally of the direction of movement of the vehicle body from the first mentioned spray head, the second spray head moving in unison with the first mentioned spray head, and spraying the body generally to one side of the longitudinal centre line of the body while the first mentioned spray head similarly sprays the body generally to the other side of the longitudinal centre line.

Preferably the apparatus includes a further pair of electrostatic spray heads, the heads of the further pair being positioned on opposite sides respectively of the path of movement of the body, and being arranged to spray at least part of the two opposite sides of the body as it passes between the heads.

One example of the present invention is illustrated in the accompanying drawings, wherein: Figure 1 is a diagrammatic representation of a paint spray booth for spraying vehicle bodies; Figure 2 is a diagrammatic plan view of the booth of Figure 1; Figure 3 is a side elevational view of part of the spraying apparatus incorporated in the booth of Figure 1; Figure 4 is a front elevation view of the part of the apparatus shown in Figure 3; Figure 5 is a plan view of the apparatus shown in Figures 3 and 4to an enlarged scale; Figure 6 is a diagrammatic representation of the movement of the spray head of the apparatus shown in Figures 3,4 and 5 during spraying of the part of a vehicle body; Figure 7 is a view similar to Figure 6 illustrating the spraying of a further part of the vehicle body; and Figures 8 and 9 are diagrammatic views illustrating the approximate path and paint flow rates of individual spray heads of the booth shown in Figure 1.

Referring to the drawings, Figures 1 and 2 illustrate a spray booth in the production line ortrack of a vehicle assembly plant. Vehicle bodies 11 pass along the track, each body 11 being carried on a support cradle 12 of the track. The bodies 11 are arranged with their longitudinal centre line parallel to the direction of movement of the track, and the spray booth 13 has six electrostatic spray heads arranged in three pairs 14,15; 16,17; and 18,19. The electrostatic spray heads themselves are of known form, and deliver electrically charged paint droplets to the region of the body 11 which is electrically earthed so as to attract the droplets to it.As will be described in more detail hereinafter the spray heads 14, 15 spray respectively generally on opposite sides of the longitudinal centre line of the vehicle, and serve to spray the front and rear vertical surfaces of the body together with the horizontal surfaces, that is to say the bonnet, the roof and the boot lid. The spray heads 16, 17 are fixed in use and spray the upper parts of the side surfaces of the body 11, and the spray heads 18, 19 are movable vertically relative to the body 11 in use and spray the lower parts of the side surfaces of the body, being moved vertically so as to follow the major mass of metal thus spraying above and into, rather than solely into, the wheel arches. The combined action of the six spray heads is sufficient to spray the whole of the exterior of the body 11.

Generally the six heads 14-19 will be operated to supply paint to the body at a predetermined volume of paint to body area ratio. However it is possible to alter thins ratio by varying one or more of the following parameters: 1. The rate at which paint is supplied to the head.

2. The rate at which shroud air is delivered from the head (it being understood that generally speaking a reduction in the rate at which shroud air is delivered leads to an increase in the cone angle of the spray pattern and thus a decrease in the paint volume to body area ratio).

3. The rotational speed of the atomiser disc or turbine of the head.

4. The voltage difference between the head (and thus the paint droplets) and the body.

The mechanism whereby the head 14 is supported and moved is illustrated in Figures 3,4 and 5, and since the mechanism of the head 15 is identical to that of the head 14 only the mechanism of the head 14will be described. In Figure 3 the arrow A illustrates the direction of movement of the body 11 relative to the support structure of the head 14. The support structure of the head 14 includes a platform 21 which is positioned at the side of the path of movement of the cradle 12 so as not to impede movement of the cradles 12 and bodies 11 through the booth. During spraying the platform 21 is fixed in position, although the platform 21 does include supporting wheels 22 located on rails 23 extending transverse to the direction of movement of bodies 11 through the booth.The wheels 22 and rails 23 permit withdrawal of the assembly of the head 14 from the booth for servicing, and for adjustment to accommodate different vehicle body widths.

Upstanding from the platform 21 is a rigid column assembly 24 comprising a pair of parallel vertically extending rectangular beams 25. Guided and supported for vertical movement by the beams 25 is a carriage 26 including a plurality of rollers 27 which bear on the beams 25. Vertical movement of the carriage 26 relative to the platform 21 is generated by an electric motor 28 supported on the platform 21 or by some alternative drive unit for example an hydraulic or pneumatic drive unit. The motor 28 can drive a reduction mechanism 29 which in turn supplies power to a chain drive mechanism the chain 31 of which extends vertically between the beams 25 and runs over a chain wheel 32 rotatably mounted by the column assembly 24 at its top.The chain 31 is connected to the carriage 26, and thus operation of the reduction mechanism 29 generates movement of the chain 31 thus raising or lowering the carriage 26 relative to the platform 21.

Extending outwardly from the carrige 26 at rightangles to the beams 25 (and thus horizontal in use) are a pair of rigid rods 33 anchored at one end to the carriage 26 and carrying an oscillating arm assembly at their opposite ends. The oscillating arm assembly includes an oscillating arm 34 supported by the rods 33 for pivotal movement about a horizontal axis 35.

The axis 35 extends parallel to the rails 23, that is to say at right angles to the horizontal path of movement of bodies 11 through the spray booth. The arm 34 hangs downwardly from the rods 33 and at its lowermost end carries a spray head support 36. The spray head support 36 extends at right angles to the arm 34 parallel to the axis 35 and at its end remote from the arm 34 the support 36 carries the spray head 14. The spray head 14 has its spraying axis at right angles to the axis of the support 36 and by virtue of the support 36 the spray head 14 is rotatable about the axis of the support 36 through approximately 110 degrees to either side of a position wherein the axis of the spray head 14 is pointed vertically downwards. It will be seen that in Figure 3, in dotted lines there is shown the limits of movement of the arm 34 relative to the rods 33 about the axis 35, and also the limits of rotational movement of the head 14 about the axis of the support 36.

It will be recognised that the support 36 projects well beyond the edge of the platform 21 in the direction of the rails 23, and thus the head 14 overlies the track along which the bodies 11 move. In some instances however it may be preferred to mount the support 36 for movement in a horizontal plane at right-angles to the track to permit retraction of the head 14 to a rest position in which it does not overlie the track. Such horizontal movement could then be utilized to permit adjustment of the horizontal location of the head in relation to the track centreline to accommodate different body widths.

A second electric motor 37 is mounted on the platform 21 and the motor 37 can cause rotational movement of an elongate rectangular sectioned bar 38 which extends parallel to the beams 25 and which is mounted at its lower end in a drive collar 39 capable of being driven by the motor 37, and mounted at its upper end in a bearing member 41.

The bar 38 can thus be rotated about its longitudinal axis which is vertically orientated. A link arm 42 supported by the carriage 26 is slidably mounted on the bar 38, and thus as the carriage 26 moves up and down the beams 25 the link arm 42 moves similarly in relation to the bar 38. However, when the bar 38 is moved rotationally about its longitudinal axis the link arm is similarly moved. The link arm 42 is connected through a push rod 43 to a drop arm 34a rigidly connected to the arm 34. Thus angular movement of the bar 38 about its longitudinal axis generates swinging movement of the arm 34 about the axis 35. The rotational movement of the head 14 relative to the arm 34 is generated by an electric motor within the support 36, although it is to be understood that in some instances it may be preferred to use pneumatic or hydraulic drive means.

It will be recognised therefore that the support structure of the spray head 14 accommodates three specific modes of movement of the head 14, all three modes of movement being movements in a common vertical plane, which plane in parallel to the direction of movement of bodies 11 through the spray booth. The first mode of movement of the head 14 is revolution of the head about the axis of the support 36, the second mode of movement of the head 14 is generally horizontal movement of the head accomplished by swinging the arm 34 about the axis 35, and the third mode of movement is vertical movement of the head accomplished by moving the carriage 26 along the beams 25.Not only can movement in the three modes be performed individually, but movement in these three modes can be performed in various combinations so that the path of movement of the head 14 within the vertical plane can be extremely complex.

As previously mentioned the spray head 95 is supported by a similar support structure to that described with reference to the spray head 14, the support structure of the spray head 15 being on the opposite side of the track from, and being a mirror image of, the support structure of the head 14. The spray heads 16 and 18 are carried by a common support structure which in many ways is similar to the support structure of the head 14. Thus the support structure of the heads 16, 18 is closely adjacent the support structure of the head 14 in the direction of movement of bodies 11 through the booth. However, neither of the heads 16, and 18 has the freedom of movement of the head 14, since such freedom of movement is not necessary in respect of the heads 16 and 18.In practice, the head 16 is completely fixed in position during spraying, and during spraying the only movement of the head 18 which is possible is a small range of vertical movement to effect spraying into and above the wheel arches. In actual fact both the head 16 and the head 18 are capable of rotational movement so that their axes can be pointed vertically downwards during flushing of the spray heads with cleanser in preparation for a change in the material to be sprayed.Vertical movement of the head 18 on its support structure is effected by a mechanism extremely similar to that used to move the carriage 26 on the beams 25, although the range of vertical movement of the head 18 is considerably less than that of the head 14 since the purpose of the head 18 is to spray only the lower part (approximately the lower half) of one side of the vehicle body, following the major mass of metal.

The vertical position of head 16 in relation to the head 18 is set for a given body size and will not vary between body styles of the same general size.

However if bodies of different size are to be sprayed then adjustment of the vertical spacing of the head 16 and the midpoint of the range of movement of head 18 is required. Conveniently this adjustment is performed automatically as a feature of the control system of the apparatus, the control system applying the adjustment by moving one of the heads as a result of receipt of a signal indicating the presence of a body of a size other than that for which the head 16 and 18 are set.

A support structure similar to that of the heads 16, 18 supports the heads 17,19 on the opposite side of the track. In effect therefore one longitudinal half of the vehicle is sprayed by the heads 14, 16, 18 while the opposite longitudinal half is similarly sprayed by the heads 15, 17, 19.

twill be recognised that during spraying, particularly spraying with top coat paint it is extremely desirable that the spray head remains at a substantially constant distance from the surface being sprayed. Insofar as the side surfaces of the body are concerned this presents no problem, since the side surfaces are sufficiently close to parallel to the direction of movement of the body through the booth that the spacing between the head 16-19 and the surfaces which they spray remains substantially constant throughout the length of the vehicle. In order however that the heads 14, 15 can spray those parts not sprayed by the heads 16-19 the head 14,15 are moved in a complex path in relation to each body passing through the booth.

Since the path of movement of the head 15 is identical to that of the head 14, (the two longitudinal halves of the vehicle being mirror images of one another) only the movement of the head 14 will be described. Parts of the path of movement of the head 14 are illustrated in Figures 6 and 7. Figures 6 and 7 illustrate the path of movement of the head 14 relative to the body 11 on the basis that the body 11 is fixed and therefore that the support structure of the head 14 traverses the length of the body at a constant rate. This of course is not the case, in practice the support structure being fixed and the body 11 travelling past the support structure at a constant rate.The path of movement of the head 14 in both Figures 6 and in Figure 7 is illustrated a number of spaced points in time, and it is to be recognised that the head 14 may not atually be spraying at each of the positions shown. In Figures 6 and 7 the cross (+) illustrates the position of the axis 35 while the support dot (.) illustrates the position of the axis of the support 36. It can be seen therefore that there is always a fixed distance between the axis 35 and the axis of support 36, and similarly there is always a fixed distance between the axis of the support 36 and the spray head 14.However as a result of rotating and swinging movement of the head 14the relative positions of the straight line joining axis 35 and the axis of 36 and the straight line joining the axis of support 36 and the head 14 vary, and the position of the whole assembly varies in a vertical direction by virtue of vertical movement of the carriage 26.

In between spraying operations, that is to say as one body 11 is leaving the booth and a subsequent body 11 is approaching the booth the spray head 14 occupies a rest position illustrated at the extreme right of Figure 6 wherein the carriage 26 occupies its lowermost position, the arm 34 is at the centre of its range of swinging movements, and so is vertical, and the head 14 is at the centre point of its rotational movement relative to the arm 34 and so has its axis pointed vertically downwards. It is in this rest position that flushing of the head 14 can take place.

The head 14 is of course in the path of movement of the body, or more accurately in the path of movement of the carriage 12 since the head 14 is in its lowermost position. At the commencement of the spraying cycle the head moves from position A to position B. In moving from A to B the head 14 has been rotated about the axis of the support 36 through its fullest extent so that the head 14 points slightly upwardly, and in the opposite direction to the direction of travel of the body 11 so that the head 14 is spraying paint at the lower front edge of the body 11.However, since the body is moving towards the head 14 then in order to maintain the spacing between the head 14 and the part of the body to be sprayed the movement from A two B is accompanied by the commencement of swinging movement of the arm 34 about the axis 35, in a direction such that the head is moved in the same direction as the body.

The swinging and rotational movements of the head 14 from position Ato position B are accompanied by a vertical movement of the carriage 26 so that the spraying of the body 11 commences at the lowermost point of the frontedge and then progresses up the front face of the body. In moving from position B to position C it will be seen that although the spacing between the body 11 and the axis 35 has been reduced the spacing between the body and the head has remained constant, since in moving from B to C further swinging movement of the arm 34 has occurred thus moving the head in the same direction as the body 11 to maintain the spacing. Also in moving from B to C the carriage 26 has raised so that the head 14 has continued to traverse the front face of the body 11 in the vertical direction.Movement from position C to position D, and from position D to position E is accompanied by further swinging movement of the arm 34 about the axis 35 to maintain the spacing between the body 11 and the head 14, and of course includes further vertical movement of the carriage 26 to continue the vertical traverse of the front face of the body by the head 14.

At position E the region of the front face of the body where the vertical front face blends into the near horizontal bonnet is being sprayed, and in following this curve (positions F, G and H) the head starts to rotate back towards the position wherein its axis is aligned with the length of the arm 34, and the arm 34 starts to swing back about the axis 35 towards the vertical position. These two movements of course tend to lower the position of the head 14 relative to the body 11, and to counter this lowering the movements are accompanied by continued vertical movement of the carriage 26. The time interval between positions E and H is the same as the time interval between positions A and D, and it will be recognised therefore that in effect the head 14 is caused to hold station over the curved region between the bonnet and the front surface of the vehicle body.During this period therefore in order to avoid overspraying this region of the body the head 14 is operated at a much reduced paint volume to body area ratio by reducing the rate at which paint is supplied to the spray head 14. Indeed, spraying may actually cease at positions F and G is required. At position H the head 14 has been rotated back to a position wherein its axis is aligned with the length of the arm 34, but the arm 34 has not yet swung back to the vertical position. Between positions H and I however the arm 34 swings back to the vertical position so that the relative positions of the arm 34 and the head 14 are the same as in the rest position.

However, the carriage 26 is raised considerably by comparison with the rest position. Thereafter spraying of the bonnet occurs in positions I, J, K and L, the only movement of the head being a raising movement effected by movement of the carriage 26, so that the head 14 follows the slope of the bonnet of the body 11. It will be seen therefore that by virtue of the compound movement of the head 14 the head 14 maintains a constant spacing from the region of the body 11 being sprayed notwithstanding the fact that the body 11 is moving at a constant speed past the fixed platform 21 of the support structure of the head 14.

After position L the bonnet has been completely sprayed and the head approaches the aperture where the windscreen will be fitted. At this point spraying ceases since there is no need to spray paint through the windscreen aperture in the body. After position L, and while spraying is interrupted, the head 14 is moved vertically higher so as to be spaced at the correct distance above the roof line of the body. Thus at position M, which position is maintained during spraying the whole of the roof, the head 14 is spaced above the roof, and the relative position of the arm 34 and head 14 are exactly as in the rest position, that is to say the arm 34 and the axis of the spray head 14 are vertical.

As can be seen in Figure 7 position M is maintained until the rear edge of the roof line has passed beneath the head 14 at which point spraying ceases.

Position M is maintained for a predetermined length of time (indicated by positions M*) during which period the body is moving away from the head. In order that the head 14 can then spray the rear surface of the body the carriage 26 starts to descend, the head 14 starts to rotate to point towards the rear of the vehicle body, and the arm 34 starts to swing about the axis 35 in a direction to move the axis of support 36 in a direction opposite the direction of movement of the body. This swinging movement of the arm 34 coupled with the rotation of the head 14 and descending movement of the carriage 26 is continued between position N and position 0 thus maintaining the spacing between the head 14 and the rear of the body.At position 0 the maximum rotational movement of the head 14 has occurred, and by position P the maximum swinging movement of the arm 34 about the axis 35 has occurred.

These relative positions are maintained until position Q, but are accompanied by continued descending movement of the carriage so that the head 14 traverses the upper, inclined, rear surface of the body 11. It will be seen that adjacent position Q the rear surface of the body becomes vertical, and in order to reserve the required spacing between the head and the body, as the body moves, and as the carriage 26 descends, the arm 34 is caused to swing back towards its vertical position without rotational movement of the head 14 relative to the arm 34. This movement continues progressively through positions R, Sand T, and at position T the spraying of the body is complete, and the flow of paint to the spray head 14 is halted. Between position T and position U the arm 34 achieves its vertical positioning, and the head 14 is rotated relative to the arm 34to a vertical orientation.Also in position U the carriage 26 is at its lowermost position and thus the parts are in the rest position in readiness for flushing if necessary prior to commencement of the spraying of a subsequent body 11.

It will be recognised that Figures 6 and 7 are only diagrammatic, and that while it is desirable to maintain the spacing between the head 14 and the part of the body being sprayed absolutely constant, in practice a slight variation in position is acceptable, such slight variations being accommodated by the nature of the electrostatic spraying process.

While the head 14 is performed the spraying sequence described above the head 15 is performing exactly the same spraying sequence on the opposite half of the vehicle body. Simultaneously of course the spray heads 16-19 are spraying the side surfaces of the body.

Figure 8 indicates diagrammatically the paint volume to body area ration of paint sprayed during the path of the head 14 in relation to the whole of the body 11. The thicknes of the line adjacent the body 11 indicates the volume to area ratio. Thus it will be seen that at the commencement (the left-hand lower corner of Figure 8) the head 14 is operated at a large volume of area ratio by initially increasing the rate at which paint is supplied to the spray head to coat the lower front edge of the body 11. As the spray head traverses the vertical front surface of the body 11 the rate of supply of paint is reduced and as the spray head reaches the front corner between the vertical front surface and the bonnet spraying ceases.The volume to area ratio during traverse of the bonnet is maintained constant, and again spraying ceases between the bonnet and the roof line owing to the aperture in the body for receiving the windscreen.

Spraying of the roof is performed at constant volume to area ratio, and then spraying ceases as the head 14 traverses the upper half of the rear surface of the body since there will be an aperture in the body to accommodate the rear window. As the head 14 sprays the lower half of the rear surface of the body the volume to area ratio is increased, by increasing the rate at which paint is delivered to the head, as the head 14 sprays the lowermost trailing edge of the body.

Figure 9 is similar to Figure 8 in that it illustrates the path of, and volume to area ratio of the spray heads 16, 17 and 18,19. It can be seen from Figure 9 that the spray heads 16, 17 are fixed in position, and have an on-off spraying pattern. Thus the spray head 16, 17 commence spraying as the A-post approaches, and deliver a constant volume of paint until the A-post has passed whereupon spraying ceases until the heads are approached by the B-post again constant volume spraying occurs until the rear window aperture intervenes whereupon spraying ceases until the rear quarter of the vehicle body approaches whereupon again constant volume of spraying occurs until this part of the body has passed whereupon spraying ceases.

It can be seen however that the spray head 18, 19 follow a path involving vertical movement relative to the body. Thus initially (lower left-hand edge of Figure 9) a large volume to area ratio is applied via the spray heads 18, 19 but then the spray heads are raised and the paint volume delivered to the heads is reduced to spray above the front wheel arch. The spray heads remain in a raised condition to spray the front wings of the body, and thereafter the spray heads 18, 19 are lowered and the spray volume to area ratio is increased by increasing the rate at which paint is delivered to the heads in order to spray the large surface area of the side of the vehicle below the window line.Subsequently the volume to area ratio is reduced, and the heads are raised to spray over the rear wheel arches, and the heads are then lowered and the volume to area ratio increased prior to shut down, to spray the rear end of the side surfaces.

It will be recognised that the complex path followed by the spray heads 14,15, the less complex path followed by the spray heads 18, and the quantity of paint delivered/unit body area at any given instant by any one of the spray heads 14-19 will be dependent upon the nature of the body being sprayed. To take a simple example, if the body being sprayed is a van body, rather than a saloon car body then there will be no rear side windows, and the head 1G, 17 will continue to spray, within increased volume, between the B-post and the rear of the vehicle body.

A microprocessor control unit has control over all of the variable parameters of the spraying apparatus. Thus inter alia the unit has control over the position of the heads 14, 15 and 18, 19, the speed at which the drive units of the heads are operated, the rate at which paint is delivered to each head, the rate at which shroud air issues from each head, the speed of rotation of the atomiser of each head and the voltage of each head. The control unit includes a memory store in which is stored the predetermined required "value" of each parameters for a given one or more body styles at a large number of sequential positions of the body relative to a fixed datum point.

The body, passing through the spraying booth, operates a pulse generator which thus produces sequential pulses in accordance with body position rather than body speed. After receipt of a start signal the unit counts the positional pulses. Expressed in simple terms, upon receipt of each pulse the stored "values" of each of the parameters of the operation relevant to that positional pulse are read and applied to the apparatus to, for example, move the heads 14, 15 at a predetermined speed about their axes 35 while raising them vertically, and reducing the rate of supply of paint to the remaining heads. Upon receipt of the next pulse the appropriate store location is read and the next "values" of the parameters are applied to the apparatus. in this way the parameters of the spraying operation are controlled in accordance with the position of the body in the booth and not the body speed.However, the "values" of the parameters are predetermined assuming a particular track speed and the spraying operation is aborted, if the track speed varies beyond predetermined acceptable limits. For this purpose the control unit includes a timing facility which monitors the time interval between positional pulses.

Immediately preceding the spray booth is a detector station which provides signals to the control unit.

As a body reaches the detection station sensors, or probes are utilized to detect a number of factors.

Firstly it is necessary to determine the body style, and the detection station thus includes an array of photoelectric sensors linked to the control unit. The unit is preprogrammed to identify predetermined body styles as a result of the combination of signals received from the sensors when the body in question is at a predetermined position relative to the array of sensors. Thus the sensors operate either to recognise a particular body style approaching the booth, so that the control unit can then select the appropriate spray programme, or alternatively to cause the control unit to stop operation and to warn the operator that the body is not of a style for which the control unit is currently programmed.

The detection station also detects whether or not the body is correctly electrically earthed, since this is a basic requirement for the electrostatic spraying process, and also, by means of mechanical probes, detects whether or not the bonnet lid, boot lid, and the doors of the vehicle are closed. In the event that any of the doors, the boot, or the bonnet are open, or in the event that the body is not correctly electrically earthed, then again the track is stopped and a warning is given to the operator of the fault situation so that it can be remedied before the body passes into the spray booth.It will be understood that the probes for sensing the open or closed condition of the doors, boot and bonnet also provide secondary body style check since if the probes are positioned for a given body style and a different style is present then it is probable that a door, boot or bonnet open indication will be given because of the wrong body shape even though the doors, boot and bonnet may be closed.

Having satisfied the detector station the body moves to the spray booth, and as the cradle 12 passes a fixed datum point of the spray booth it operates a pair of switches simultaneously. Operation of this pair of switches simultaneously supplies a signal to a control unit to initiate the spraying operation.

With certain previously proposed spraying arrangements problems have arisen as a result of the vertically movable spray heads either approaching too closely the surface to be sprayed, or alternatively not moving out of the way of the body, and being damaged as the body passes through the booth. It is usual to provide a photocell and light source carried for vertical movement with the spray head, the beam between the light source and the photocell being horizontal, and being below the level of the spray head. In the event that the body cuts the light beam, then either the spray head is automatically raised until the beam is re-established, or alternatively the track is stopped, and a fault warning is given to the operator.Such systems have proved problematic in that the cloud of paint spray particles tends on occasions to breakthe light beam, thus giving a false warning of the proximity of the body to the head. It has been proposed to try to overcome the problems of a light source with photocell be replacing the conventional light source with a low energy laser. However, there is considerable operator resistance to such lasers.

The control unit memory store, as mentioned above, contains a series of "values" representative of the required vertical position of the heads 14, 15 in relation to given body styles, and the position of the body along the length of the spray booth. Associated with the chain wheels 32 of the support structure of each of the heads 14 and 15 is a pulse generator which transmits a signal back to the control unit as a result of up and down movement of the carriage 26.

Each time each carriage is moved vertically to a new location the signal supplied from the pulse generator is compared within the control unit with "value" stored in the memory for that position of the body relative to the datum. If the signal representative of the actual position of the carriage does not agree with the intended position stored in the memory then the operation is halted and a warning is given.

Thus the unit includes a check on the vertical position of the carriage 26 each time the position of the carriage 26 is required to be changed, and if at any time the position of the carriage 26 does not conform to the required position then the track is halted, the spraying ceases and an alarm signal is generatd notifying the operator that there has been a failure resulting in the carriage 26, and therefore the head 14 or 15 occupying an incorrect vertical position relative to the body 11. In practice the control unit compares the signal from the pulse generator of head 14 with that of head 15 and if there is not parity between these two signals the "shut down" is initiated. If there is parity then the check is made for parity with the intended position "value" stored in the memory.This arrangement achieves a fine control over the position of the carriages 26 of both heads 14, 15. In a similar, but coarser, manner control is achieved over the swinging movement of the arm 34 and the rotating movements of the head 14 or 15 about the support 36. Microswitches associated with the centre positions and two limit positions of the swinging movement of the arm and rotational movement of the head 14 provide signals to the control unit representative of the position of the arm and the head, and these are compared with the signals of the microswitches of the head 15 and, if parity exists, with the stored positional "values". In the absence of parity "shut down" is initiated.

The checking of the vertical positions of the heads 14, 15 is of great importance and if desired each carriage 26 can have associates with it a back-up pulse generator driven independently of the first pulse generator. The control unit can be designed to look also for parity between the signals of the back-up generators, and between the first and back-up generators.

It is to be understood that although it is preferred to effect horizontal movement of the heads 14, 15 in the direction of the track, by means of oscillating arm 34 (so that the movement is actually arcuate but approximating sufficiently closely to horizontal), the movement could be effected by mounting the supports 36 on respective carriages in turn mounted for linear horizontal movement along the length of the rods 33.

In the above-described embodiment, the sprayers in at least the heads 14 and 15 are turbine-driven, high speed bell-type electrostatic sprayers, for example of the type manufactured by SAMES, a Division of AIR INDUSTRIES, and sold under the Trade Mark "GIGASTATRON".

Claims (10)

1. A paint spraying apparatus cqmprising an electrostatic spray head carried by means permitting at least three modes of movement of the head in a common plane containing the axis of the spray head, said common plane being vertical relative to the horizontal path of movement of the body to be sprayed, and being parallel to the direction of said path of movement so that said plane passes through said body to be sprayed, said three modes of movement comprising a rotational mode wherein the head is revolved about a horizontal axis lying at right angles to said vertical plane, a vertical mode wherein the head can be raised and lowered relative to said path of movement of the body, and a horizontal mode wherein the head can be moved generally parallel to said path, and, the apparatus further including drive means for moving said head in said modes, and control means controlling said drive means, said control means causing said head to follow a path of movement, predetermined in relation to the shape and speed of movement of the body to be sprayed, such that the spray head can deliver paint to the generally vertical front and rear surfaces, and the generally horizontal surfaces, of the body and such that while spraying the spacing between the spray head and the body, measured in the direction of the spray head axis, is maintained substantially constant.

2. Apparatus as claimed in claim 1 wherein, said control means is capable of being programmed whereby selectively, the head can be moved through any one of a number of different paths, the different paths being related to different body shapes.

3. Apparatus as claimed in claim 1 or claim 2 wherein, the control means also controls at least one operating parameter of the spray had thus permitting the ratio of paint to body area to varied in accordance with predetermined requirements of the body being sprayed.

4. Apparatus as claimed in anyone of the preceding claims wherein, operating parameters of the spray head controlled to effect control over the paint to body area ratio are selected from the group comprising, flow rate of paint to the head, volume of shroud air supplied to the head, rotational speed of the atomiser disc of the head, and the voltage applied between the body and the head.

5. Apparatus as claimed in anyone of the preceding claims wherein, the apparatus includes means whereby a signal representative of at least the vertical position of the head in relation to a fixed datum point is supplied periodically to said control means, and said control means is arranged to halt the spraying operation in the event that at predetermined intervals after the commencement of the operation the head is not in appropriate predetermined positions.

6. Apparatus as claimed in anyone of the preceding claims wherein, associated with the spraying apparatus is a detection system which senses certain predetermined parameters of the body to be sprayed, and which supplies signals in accordance with the presence of said predetermined parameters to said control means, said control means being arranged to commence the spraying operation only after receipt of all of the appropriate parameter signals.

7. Apparatus as claimed in claim 6 wherein, the parameters sensed by the detection system include the arrival of the body at a predetermined start position, the shape of the body, whether or not the body is electrically earthed, and whether or not doors, the boot, and the bonnet of the vehicle body are closed.

8. Apparatus as claimed in anyone of the preceding claims wherein there is further provided a second electrostatic spray head spaced laterally of the direction of movement of the vehicle body from the first mentioned spray head, the second spray head moving in unison with the first mentioned spray head, and spraying the body generally to the other side of the longitudinal centre line.

9. Apparatus as claimed in claim 8 including a further pair of electrostatic spray heads, the heads of said further pair being positioned on opposite sides respectively of the path of movement of the body, and being arranged to spray at least part of the two opposite sides of the body as it passes between the heads.

10. A paint spraying apparatus substantially as hereinbefore described with reference to the accompanying drawings.