Programmed means for imparting compound motion to a spray gun

Sept. 20, 1971 ε. lehmann 3,606,162

PROGRAMMED MEANS FOR IMPARTING COMPOUND MOTION TO A SPRAY GUN

Filed Aug. 28, 1969 3 Sheets-Sheet 1

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Sept. 20, 1971 e. lehmann 3,606,162

PROGRAMMED MEANS FOR IMPARTING COMPOUND MOTION TO A SPRAY GUN

Filed Aug. 28, 1969 3 Sheets-Sheet 2

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Sept. 20, 1971 e. lehmann 3,606,162

PROGRAMMED MEANS FOR IMPARTING COMPOUND MOTION TO A SPRAY GUN

Filed Aug. 28, 1969

Sheets-Sheet 3

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3,606,162

Patented Sept. 20, 1971

United States Patent Office

3,606,162 PROGRAMMED MEANS FOR IMPARTING COMPOUND MOTION TO A SPRAY GUN Ernst Lehmann, St Gall, Switzerland, assignor to Gema AG Apparatebau, St. Gall, Switzerland Filed Aug. 28,1969, Ser. No. 853,911 Claims priority, application Germany, Oct. 25, 1968, P 18 05 145.1 Int. Cl. B05b 3/18 UA Cl. 239—227 3 Claims

ABSTRACT OF THE DISCLOSURE

Spraying apparatus for automatically coating workpieces with coating material applied by means of a spray gun the apparatus including a carrier head on which a spray gun is mounted for pivoting movement in a vertical plane. The carrier head is mounted on a lifting stand for vertical up and down movement and the lifting stand is placed on carriage means for movement in a horizontal plane in two directions at right angles to each other. The movements of the spray gun, lifting stand and carriage means are effected by motors controlled by program control devices adapted to be set to produce a sequence of operating steps of the spray gun, lifting stand and carriage means.

A plurality of such program controlled spraying apparatus may be mounted along a workpiece coating line to automatically perform all the required coating steps on workpieces of a complicated shape.

The present invention relates to a spraying apparatus for automatically coating workpieces with coating material by means of a spray gun.

In known apparatus for automatic operation of lacquer or powder spraying technique, the workpieces to be coated are moved by a conveyer past one or a plurality of spray guns. The guns are either stationary or are arranged to swing up and down or to and fro, the deflection and the central point of this swinging movement usually being adjustable. When workpieces are to be coated on all sides, then each individual workpiece is given an additional rotary movement while passing across the spray jet. In order to coat the insides of tubular workpieces for example, special guns are also used, which produce a conical spray jet having a wide angle of cone and which are automatically caused to enter into the tubular workpiece. However, satisfactory layers of uniform thickness cannot be produced with such or similar known devices on articles of complicated shape. In order to automatically coat workpieces of complicated shape, spraying plants composed of a plurality of individual spraying devices are used, in which the coating of each workpiece is effected in several successive stages. A spraying plant is generally designed with the aid of experimental coatings made on test workpieces, so that such a finished plant usually is suitable only for a single workpiece shape as originally provided and a conversion to coat other shapes is only possible with great difficulty. If one of the spray guns fails during operation of the plant, the coating errors thus produced must be corrected afterwards by means of hand operated spray guns.

The invention has for its object the provision of a spraying apparatus which enables the automatic coating of workpieces of complicated shape in satisfactory manner and which makes it possible to build spraying plants according to the principle of unit construction, which can be more universally used than the known plants and which avoids the necessity of having to correct by hand those coating errors produced by failures of any of the spray guns.

The spraying apparatus according to the invention comprises a carrier head, a spray gun mounted on the carrier head, a lifting stand supporting said carrier head, controllable driving means for moving said carrier head up and 5 down, and a program control device adapted to be set to a sequence of operating steps for controlling the operation of said carrier head driving means.

In order to be able to move the spray gun in a direction at right angles to the up and down movement, the lifting 10 stand is mounted on a carriage which is movable along a guide by means of a controllable carriage-drive device, said carriage drive device preferably being controlled by a program control device adapted to be set for a sequence of operating steps.

In order to be able to move the spray gun additionally in the direction of a third orthogonal space axis, the lifting stand-carriage together with its guide and its carriage drive device may be mounted on a support movable in the horizontal plane at right angles to the carriage20 guide by a controllable drive device and said support drive device may be controlled by a program control device adapted to be set to a sequence of operating steps.

The invention will be more fully described hereinafter with reference to the accompanying drawings showing by 25 way of example a spraying apparatus according to the invention.

FIG. 1 is a perspective view of a complete spray gun apparatus having program control means with a crossbardistribution device,

FIG. 2 is a view in elevation of the programming part of the control means,

FIG. 3 is a basic circuit diagram for a program control given by way of example, and

FIG. 4 is a plan view of an automatic spraying plant 35 comprising a plurality of spraying apparatus of FIG. 1.

The apparatus shown schematically in FIG. 1 comprises a spray gun 1 constructed for electrostatic powder coating. This spray gun is mounted on a carrier head 2 for rocking movement about a horizontal axis 3. In the most ⁴⁰ simple embodiment, the gun 1 may be adjusted and clamped by hand in the adjusted position so that the axis of the spray jet is situated, for example, in a horizontal plane, or is inclined at any desired angle with respect to the horizontal. The carrier head 2 is fixed to a lifting ^4j stand 4 whose lifting column 6 mounted on a base 5 is extensible and retractable in vertical direction y—y by a driving device 8. The base 5, affording a sufficiently solid stand for the lifting column 6 with the carrier head _5Q 2 and the spray-gun 1, is provided with a dust-tight housing 7, in which the driving control device 8 and ancillary parts necessary therefor are accommodated. The driving device advantageously comprises a direct current motor which can tolerate frequent switching without disturb₅₅ ances, for example, a so-called disc-armature motor. Direction of rotation, speed of rotation and running time of the motor are controlled by a program control device 9, described in detail later in this applicatin, so that the spray gun is moved up or down for a predetermined distance _βθ and at a predetermined speed. In order to determine the distance to be travelled by the gun, an electric bridge circuit is preferably used, in which a determined theoretical value is compared with the actual value given by a displacement pick-up of known construction and when _g5 the values are equal the driving control device 8 is switched out or switched over by a step-on pulse to another mode of operation.

In order to automatically coat a workpiece 10, the spray gun 1 is guided along a path of motion consisting of a 70 sequence of straight line sections with the speed of the gun and a predetermined portion of the powder dosage being allocated to each line section. In the so far described

3,606 part of the apparatus, the possible path of motion of the spray gun consists of a sequence of vertical line sections, and each line section of the sequence is determined by the ordinate value of its end point. For programming the path of motion, the control device 9 contains a cross- 5 bar distribution panel 11, on which the theoretical ordinate value, the speed of movement of the gun 1 (motor r.p.m.) and the powder dosage can be set for each of the line sections to be covered. The program control device of the entire apparatus will be explained in greater 10 detail in a particular example later in the application. From the above short description of the program control device 9, it is apparent that the part of the apparatus so far described can advantageously be used for coating workpieces of simple shape, particularly when the work- 15 pieces are moved past the spray gun at constant speed. A small spray plant, in which only workpieces of simple shape are to be coated, will therefore include one or more spray gun lifting stands 4 of the type shown, their bases 5 being placeable on wheels if the lifting stands are to be 20 easily transportable.

These spray-gun stands may easily be improved and perfected. It often is required that the axis of the spray jet shall be horizontal over a certain operating section and over another section it shall be inclined with respect 25 to the horizontal. In order to be able to adjust the spray jet axis in the vertical plane according to a given program, the axis of rotation 3 of the spray gun 1 is operatively connected to a motor 12 which is mounted on the carrier head 2 and is covered in dust proof manner by a casing 30 13, as shown in FIG. 1. In many cases, it is sufficient for obtaining satisfactory coating layers that the spray jet axis from the spray gun 1 be adjustable over a large angle in steps of for example 10°. The control of the drive motor 12 of the rotary axis 3 is then advantageously 35 effected by the crossbar distribution panel 11, so that for each operating step, the vertical inclination of the spray jet axis can also be adjusted in addition to the theoretical vertical distance of gun movement, the speed of such gun movement and the powder dosage. Instead of this, the ⁴⁰control of the drive motor 12 may also be carried out independently, each adjustment of the angle of inclination of the spray gun being considered as a separate coating step. The necessary number of step axes to be provided in the crossbar distribution panel is then greater, ₄but the mode of operation of the apparatus is also more universal and more precise. For example, cylindrical surface parts of workpieces may be coated by bringing the rotary axis 3 of the spray gun 1 in a first operating step into alignment with the axis of the cylindrical surface 59 part and then moving the spray gun about its axis in the following operating steps, so that the spray jet sweeps once or several times over the surface part to be coated. In a further construction of the lifting stand, the lifting column 6 is rotatably mounted to base 5 so as to be 55 rotatable about its axis. The rotation of the lifting column 6 is effected by a motor 12' which is accommodated in dust-pro of manner in the housing 7 located in the base of the column, and is controlled in the same manner as the driving motor 12 for the rotary axis 3 of the gun 1. 60 The spray gun may thus also effect a pivoting movement in the horizontal plane.

As is further shown in FIG. 1, the base 5 of the lifting stand 4 is mounted on a carriage 14 which is guided along the rail 24 running at right angles to the vertical axis ⁶⁵of the column 6. By shifting the carriage 14 along its guide rail, the spray gun is moved to and fro in the second orthogonal space coordinate axis x—x.

The carriage 14 is driven by means of a geared motor 15 operating through an arrangement of chains and chain wheels, the motor being controlled by the program control device 9 and coupled with a displacement pickup in order to derive a signal indicating the actual distance travelled by carriage 14. The program control device 9 75 ,162 is constructed in a manner similar to that already described briefly above.

The motor 15 with all its accessories, such as for example relays (not shown), is accommodated in housings 16 which are secured to both ends of the guide rail 24. Bellows 17 are arranged between the ends of the carriage 14 and the housings 16, which bellows, together with the housings 16, seal the drive and guide means of the carriage 14 in dust-tight manner. Any other suitable type of drive means may be chosen instead of a chain drive, such as for example a hydraulic cylinder with servo-valve.

This part of the apparatus with carriage, guide rail and drive means is advantageously constructed as a separate unit, the carriage 14 being so arranged that the lifting stand 4 may easily be secured thereon, for example, by overplugging.

In order also to be able to move the spray gun in the third orthogonal space axis z—z, carriages 14', 14 of the previously described type are mounted on a support platform 18 at a sufficient distance from one another and on parallel guide rails 24', 24, so that the assembly of carriage 14 carrying the stand 4 can be secured by its protective housings 16 to carriages 14' and 14.

FIGS. 2 and 3 show details of a program control device 9 given by way of example, having a crossbar distributor 11 of the type that has already been briefly explained hereinabove.

According to FIG. 2, the front panel of the control device 9 has a plurality of vertically and horizontally aligned holes 19. Plugs 20 may be inserted as desired into the holes and each inserted plug connects two intersecting bars of the crossbar distributor. This pattern of holes includes: The command axes B_x, B_y, B₂ for moving the spray gun in the direction of the orthogonal space axes, Βψ and Bs for rotating the spray gun about the axes x’—x' and y'—y', B_v for the advance speed and B_dfor the powder dosage, a number of theoretical value axes for setting corresponding theoretical values, only ten axes W0-W9 for a step-by-step movement of the spray gun in the direction of the orthogonal space axes having been shown in FIG. 2 for the sake of simplicity, and finally a larger number of stepping axes S1-S8 cross the command and theoretical value axes, so that by plugging a stepping axis in the section of the command axes, an operation is communicated to the operating step in question and by plugging the same stepping axis in the section of the theoretical value axis, the extent of this operation is given. FIG. 3 shows the basic circuit diagram for a control circuit of this type, but for the sake of clearness only the control of the spray gun movement in the direction of the orthogonal space axes x, y, z has been shown in detail.

Each command axis bar B_x to B_d is connected to a relay R1 to R7. Each of the stepping-bars SI to S5 crossing the command bars is connected to one of the contacts a to aS situated in a plane of a rotary switch Dr, and the wiper 21α of this rotary switch plane is connected to a current source (not shown) for energising the relays R1 to R7. Each relay R1 to R7 has a number of normally-open contacts r which are connected in the respective control circuit with the corresponding theoretical value bars. When for example no coating shall be effected at the fifth operating step, a plug is inserted in the section of the command axes at point of intersection S5-B_d and in the section of the theoretical value axes at point of intersection S5-W0. When the. wiper 21α of the rotary switch Dr then arrives on the contact aS, the relay R7 is energised and its normally-open contacts are closed to switch off the feed of powder to the spray gun. FIG. 3 shows in greater detail a D.C. follower control for the movement of the spray gun in the direction of the orthogonal space axes. Each of the stepping bars SI to S5 crossing these theoretical value bars is connected to one of the contacts bl to bS lying in another plane of the rotary switch. One end of the bleeder

3,606,162 chain Sp is connected to one pole of a control voltage source B and its other end to a series of normally-open, parallel connected contacts rll, rl2, rl3 of the relays Rl, R2, R3, connected in parallel. A lead runs from each normally-open contact to the potentiometer WG1, WG2 or WG3 of the associated displacement pick-up and from there to the other pole of the control voltage source B. The theoretical value bars WO to W6 are connected to the individual stages of a voltage divider consisting of the bleeder chain Sp, and the wiper 21b of this rotary switch plane is connected at an input, the theoretical value input, of a bridge amplifier BV, the other input of which, the actual value input, is connected to the tappings of the displacement-pickup potentiometers WG1, WG2, WG3 by a second set of operating contacts r21, r22, r23. Power amplifiers LV1, LV2, LV3 are connected to the output of the bridge amplifier BV via further normally open contacts r31, r32, r33 of the relays Rl, R2, R3, which power amplifiers control or feed the drive axes SI, S2, S3 for moving the lifting column or the carriages in the apparatus described. When, for example, the stepping axis S3 and the command axis B_z are plugged in the section of the command axes, and the theoretical value W5 is plugged in the section of the theoretical value axes, the relay R3 is energised when the wipers of the rotary switch reach the stepping bars S3, and its contacts rl3, r23, r33 close. Consequently the displacement pickup-potentiometer WG3 is switched in and the bridge amplifier receives at its two inputs the corresponding theoretical- and actual-value signals. If the two signals are different, the differential voltage is amplified in the bridge amplifier and, according to the detuning of the bridge, a polarized (left-right) signal is transmitted via the contacts r33 to the power amplifier LV3. Corresponding to this signal, the drive motors in the carriage units are set in motion and the unit with the lifting column is shifted in z-direction until the actual value signal is the same as the theoretical value signal. When the signals are equal a stepping comparator circuit pulse is transmitted by the bridge amplifier or comparator circuit BV via a second output e to the rotary selector Dr and its wipers scan the following stepping bar S4.

The technical construction of a program control device operating according to a principle of this type or like principle, is familiar to any skilled person. Circuit details are determined by special wishes or requirements and many variations are possible. Thus for example the setting of the theoretical value for the different lengths of path may be effected in decadic manner instead of in step-by-step manner, corresponding decoding devices being for example connected to the circuit, whereby the number of plug holes in the crossbar distribution panel is reduced. The program control device may also be constructed so that during an operating step, a plurality of commands may be executed simultaneously, e.g. a simultaneous movement in all three orthogonal directions, so that the spray gun is guided over an inclined path, and the advance speed, moreover, may be different in each axial direction. In such a case, a stepping pulse is only issued to the rotary switch when all partial movements have come to an end.

The mode of operation of the spraying apparatus shall now be more clearly explained by reference to a simple example of coating an article. The box Id shown in FIG. 1 which is open on one side shall be electrostatically coated with a powder. It is assumed that the box shown can be coated by moving the spray gun 1 over a continuous path 22 composed of straight line sections extending in the direction of the orthogonal space axes. This path of motion is shown as a dashed line in FIG. 1 and consists, as may be seen, of a first line section in x-direction, followed by a line section in z-direction and a line section in y-direction. Subsequently, there follows a short line section again in x-direction, a longer one in y-direction, etc. The whole program is advantageously divided into stages, and the first stage shall include for example the above-mentioned steps. In the control device, the automatic stepping action of the rotary switch Dr is for example switched off by opening a switch 23 and the rotary switch is set by hand to the individual step-by-step bars SI to S5. When the spray gun is disconnected, the first program stage is plugged step by step. For further explanation, it is assumed that the theoretical value axes WO to W9 (FIG. 2) are designed for step-by-step advance having a, step length of for example 5 cm. In the first operating step, the spray gun is brought into starting position (position I in FIG. 1), to which end it is assumed that the gun must be raised by 15 cm. On the stepping axes SI (FIG. 3), accordingly the command axis B_y and the theoretical value W3 are plugged. In the next operating step, the gun should be moved 25 cm. to the left. Therefore, the command axis B_x and the theoretical value W5 are plugged on the stepping axes S2. In the third operating step, the spray gun shall move forward in z-direction by 20 cm., and to this end, the command axes Bz and the theoretical value W4 are plugged on the stepping axes S3. The upward movement of the spray gun by for example 20 cm., desired in the fourth operating step, is obtained by plugging the command axis By and the theoretical value W7 on the stepping axis S4. In the fifth operating step, the gun shall move to the right by 10 cm., and consequently the command axis Bx and the theoretical value W3 are plugged on the stepping axis S, since, in the preceding y-step, W4 was plugged. After the first program stage has been plugged in this way, the gun is brought back and when automatic operation is switched-in, a test spraying is effected. Any possible plugging errors are then corrected and the next program stage is plugged. When the whole program has been satisfactorily plugged, the automatic coating of a series of workpieces can begin.

It may now occur that a small number of different types of workpieces have to be coated in series during a considerable period of time. In such cases, it is recommended to use, in addition to the cross-bar distribution panel 11, fixed program storage means, such as punched cards 26, punched tapes or magnetic tapes. The control apparatus then will be equipped with suitable scanning devices 25, but the desired program is firstly plugged in the cross bar distribution panel and is then transferred onto the fixed program storage means.

For workpieces of complicated shape, automatic coating plants are generally required, as has already been mentioned. As shown in FIG. 4, such an automatic coating plant may easily be assembled by making use of the above described spraying apparatus. To this end, one or more complete spraying apparatus 27 as described and also parts of such apparatus 28, 29 are arranged along a production line through which the workpieces 30 to be coated pass. At the end of the coating line, a complete apparatus 31 is arranged, which has to correct the coating errors produced for example by the failure of any one of the program stages. Should for example a spray gun in the coating line fail, the last complete apparatus 31 receives the program of this spray gun, either by being connected to the program control device of the nonfunctioning gun or by the program being plugged on its own crossbar distribution panel. The automatic seriescoating is in this way not interrupted at all or only for a short time and all workpieces leaving the line are satisfactorily coated.

A coating plant assembled from the described spraying apparatus may easily be converted, completed and enlarged, according to the actual coating requirements.