Patent Publication Number: US-6217944-B1

Title: Automatic coating method and apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an automatic coating method and an automatic coating system therefor, using a coating machine particularly suitable for use in coating of vehicle bodies or other articles which involve changes of paint colors. 
     2. Discussion of the Background 
     Generally speaking, prior art automatic coating systems are largely constituted by a working mechanism which is located in a predetermined coating area like a coating booth, and a coating machine which is mounted on the working mechanism and provided with a rotary atomizing head to be put in high speed rotation for spraying a paint in the form of finely atomized particles. 
     The coating machine which are used in the coating system of this sort are largely constituted by an air motor which is mounted within a housing, a hollow cylindrical rotational shaft which is passed axially through the air motor and put in high speed rotation by the air motor, a feed tube which is extended axially and internally through the rotational shaft to supply a paint or a wash fluid, and a rotary atomizing head which is mounted on and at the fore end of the rotational shaft and provided with paint releasing edges on the outer peripheral side thereof. 
     In this connection, there has been known a feed tube of the construction as described in Japanese Utility Model Laid-Open No. H2-37766. This feed tube is formed in the shape of a double wall tube providing a paint passage internally of an inner tube and a front end washing thinner passage between inner and outer tubes. The paint passage of the feed tube is connected to a color changing valve apparatus, while the thinner passage is connected to a thinner source through a thinner pipe. Thinner is spurted out through the front end washing thinner passage whenever it becomes necessary to wash off deposited paint from the outer periphery of a front end portion of the feed tube. Further, through a drain valve which is constituted by a three-way valve, one end of a waste liquid drain passage is connected to a joint portion of the paint passage of the feed tube with the afore-mentioned paint pipe. The other end of the waste liquid drain passage is connected to a waste tank. 
     In this instance, the coating machine is mounted on a working mechanism such as a coating robot, reciprocator or the like for a paint coating operation while keeping a predetermined distance from a vehicle body or an object to be coated. At the same time, paint is sprayed by the coating machine toward a coating object (e.g., a vehicle body) for coating the paint thereon. 
     Namely, while the coating machine is moved by the working mechanism, the rotary atomizing head is put in high speed rotation by the air motor. In this state, a paint from a color changing valve apparatus is supplied to the rotary atomizing head through the paint passage of the feed tube. The supplied paint is released in the form of atomized particles at paint releasing edges of the rotary atomizing head which is kept in high speed rotation. Since a high voltage is applied to the rotary atomizing head, the paint is sprayed as charged particles from the paint releasing edges of the rotary atomizing head, and urged to fly toward and deposit on the coating object under the influence of an electrostatic field which is formed between the rotary atomizing head and the coating object which is connected to earth. The coating system includes controls for the coating machine and the working mechanism to carry out a coating operation on the coating object automatically. 
     When changing the paint color, a previous color which remains in the paint pipe is washed away before supplying a fresh color thereto. In a washing stage, the drain valve is opened in the first place to secure a route from the paint feed pipe to the waste tank through the waste liquid drain passage. Then, thinner and air are alternately supplied from the color changing valve apparatus to clean the paint pipe. 
     In the next place, thinner is supplied again from the color changing valve apparatus to wash the paint passage in the feed tube and the rotary atomizing head. This thinner is flushed toward the rotary atomizing head through the paint pipe and the feed tube, thereby washing the paint passage as well as the rotary atomizing head. 
     Further, from a front washing thinner source which is provided separately from the color changing valve apparatus, thinner is supplied to the outer periphery of a fore end portion of the feed tube via thinner pipe, front washing valve and front washing thinner passage of the feed tube to wash spot-wise the outer periphery of a fore end portion of the feed tube. Thereafter, paint of a fresh color is supplied to the paint passage in the feed tube from the color changing valve apparatus in preparation for a coating operation for the new color. 
     Thus, according to the paint sprayer machine which is disclosed in Japanese Utility Model Laid-Open No. H2-37766, the paint pipe between the rotary atomizing head and the color changing valve apparatus as well as the rotary atomizing head and the outer periphery of a fore end portion of the feed tube have to be washed each time before changing the paint color. A washing operation of this sort not only takes a long time but also invites a conspicuous increase in running cost due to large consumption of thinner or wash fluid. 
     Attempts have been made to develop a coating machine which can overcome these problems, as disclosed in Japanese Patent Laid-Open No. H6-134354 and H6-269702. The prior art coating machines described in these publications are of the type which uses a bundle of feed tubes for feeding various paint colors separately from the respective paint sources through the respective paint pipes, paint valves and paint feed tubes. 
     In the case of the coating machines of the bundled feed tube type, having a bundle of feed tubes including a plural number of paint feed tubes for different paint colors and a wash feed tube which is connected to a thinner source through a thinner feed pipe having a wash valve connected within the length thereof. 
     According to the prior art coating machines of the type just mentioned, the each one of the bundled paint feed tubes is connected to a paint supply source of a specific color through a paint feed pipe and a paint valve which is provided within the length of the paint feed pipe. The paint which is supplied to a rotary atomizing head through one of the bundled feed tubes is released in the from of atomized paint particles from the rotary atomizing head which is put in high speed rotation. Since a high voltage is applied to the rotary atomizing head, the released paint particles are thereby charged and caused to fly toward and deposit on a coating object which is connected to earth. 
     On the other hand, when changing the paint color, a wash fluid like thinner is fed to the rotary atomizing head through a wash feed tube for washing away blots of previous color from the rotary atomizing head. 
     In the case of the coating machine as described in the above-mentioned Japanese Utility Model Laid-Open No. H2-37766 having a double-wall feed tube, there is an inherent problem that the machine construction is complicated due to the necessity for connecting the washing thinner passage of the feed tube to a washing thinner source through a thinner pipe separately from the color changing valve apparatus. 
     Similarly, the machine construction is complicated in the coating machines disclosed in Japanese Patent Laid-Open No. H6-134354 and H6-269702 which require to connect a wash feed tube in the bundle of feed tubes to a thinner source through a thinner feed pipe separately from other paint feed tubes which are allocated to different colors. 
     Further, each one of the above-mentioned prior art coating machines has a problem in that, when washing a rotary atomizing head, a coating area is contaminated considerably by paint and thinner which are scattered around when released from the rotary atomizing head. 
     Furthermore, in any of the above-mentioned prior art coating machines having a wash thinner passage (or a wash feed tube) located on a coating machine body, there is a possibility of an applied high voltage flowing toward the thinner source through the thinner in the wash thinner passage (or a wash feed tube). Therefore, the thinner to be used for a washing operation is required to maintain a certain level of electrical resistivity and in a large quantity because it cannot be selected from inexpensive products simply in consideration of washing capacity. 
     SUMMARY OF THE INVENTION 
     In view of the above-described problems of the prior art, it is an object of the present invention to provide an automatic coating method and an automatic coating system which can wash a rotary atomizing head from the front side thereof. 
     In accordance with the present invention, the above-stated object is achieved by the provision of an automatic coating method for a coating system including a working mechanism provided in a predetermined coating area, and a coating machine mounted on the working mechanism and having a rotary atomizing head to be put in high speed rotation by an air motor for atomizing paint into minute particles, the coating machine being moved by the working mechanism relative to a coating object while spraying paint thereon, the automatic coating method comprising the steps of: after stopping a coating operation by the working mechanism and the coating machine, locating a washing nozzle closely in front of the rotary atomizing head; and washing the rotary atomizing head from front side by supplying and spurting a wash fluid toward the rotary atomizing head through the washing nozzle. 
     With the arrangements just described, in an atomizing head washing stage subsequent to suspension of a coating operation, the washing nozzle is located closely in front of the rotary atomizing head, and a wash fluid is spurted out from the washing nozzle toward the rotary atomizing head which is put in rotation. As a result, the wash fluid is allowed to flow into and through the rotary atomizing head to wash off deposited paint therefrom. 
     According to the present invention, there is also provided an automatic coating system including a working mechanism provided in a predetermined coating area, and a coating machine mounted on the working mechanism and having a rotary atomizing head to be put in high speed rotation by an air motor for atomizing paint into minute particles, the automatic coating system comprising: an atomizing head washer having a washing nozzle adapted to spurt a wash fluid toward the rotary atomizing head from front side thereof, the atomizing head washer being located in the vicinity of the working mechanism and relatively movably toward and away from the rotary atomizing head. 
     With the arrangements just described, during a paint coating operation, the atomizing head washer is moved relatively away from the rotary atomizing head to a position which would not come into the way of the coating operation. On the other hand, at the time of an atomizing head washing operation, the atomizing head washer is moved relatively toward the rotary atomizing head and located closely on the front side of the rotary atomizing head, and then a wash fluid is spurted toward the rotary atomizing head through the washing nozzle. As a result, the rotary atomizing head is washed with the wash fluid which is supplied from the washing nozzle. 
     In this instance, according to one preferred form of the present invention, the rotary atomizing head of the coating machine is constituted by a main body formed in a bell-like or cylindrical shape, and a hub member which is located on the front side of said main body of the rotary atomizing head and provided with solvent outlet holes and paint outlet holes in central and peripheral portions thereof, respectively, and the washing nozzle is adapted to let the wash fluid flow into the rotary atomizing head through the solvent outlet holes and flow out through the paint outlet holes. 
     With the arrangements just described, in an atomizing head washing stage, the wash fluid which is spurted out through the washing nozzle is directed toward the rotary atomizing head which is in rotation. At this time, the wash fluid flows into the rotary atomizing head through solvent outlet holes in a center portion of the hub member which is barely influenced by centrifugal force of the rotary atomizing head, and flows out through paint outlet holes in peripheral portions of the hub member under the influence of the centrifugal force. As a consequence, with streams of the wash fluid flowing through the rotary atomizing head, deposited paint is washed away therefrom. 
     Further, according to the present invention, the atomizing head washer may be provided separately from the working mechanism. In this instance, the atomizing head washer is located in a position which would not come into the way of the coating operation by the coating machine. At the time of an atomizing head washing operation, the atomizing head washer is moved to a predetermined closely confronting position relative to the rotary atomizing head, and a wash fluid is spurted out through the washing nozzle toward the rotary atomizing head to wash the latter with the wash fluid. 
     In this instance, according to the present invention, the atomizing head washer may be constituted by a waste liquid collecting container located in the coating area for collecting waste liquid, and a washing nozzle provided within the waste liquid collecting container, the washing nozzle being connected to a wash fluid supply source while the waste liquid collecting container is connected to a waste liquid tank. 
     With the arrangements just described, at the time of washing the rotary atomizing head, the rotary atomizing head of the coating machine is put into the waste liquid collecting container of the atomizing head washer. In this state, a wash fluid is supplied from the wash fluid supply source to the washing nozzle and spurted out to wash the rotary atomizing head. Besides, the wash fluid used for washing the rotary atomizing head is collected into the waste liquid collecting container and allowed to flow down toward a waste liquid tank. Therefore, the wash fluid is prevented from scattering around to keep clean the coating area where the working mechanism is installed. 
     Further, according to the present invention, the atomizing head washer may be integrally mounted on the working mechanism. In this case, there will no possibility of the atomizing head washer coming into the way of the coating operation by the coating machine if it is located, for example, in front of a waiting position of the coating machine. On the other hand, at the time of washing the rotary atomizing head, the atomizing head washer is moved toward the coating machine which has been located in the waiting position, and a wash fluid is spurted out through the washing nozzle to wash the rotary atomizing head. 
     In this particular form of the present invention, the atomizing head washer may be constituted by a waste liquid collecting container located in the vicinity of the working mechanism within the coating area for collecting waste liquid therein, and a washing nozzle provided within the waste liquid collecting container, the washing nozzle being connected to a wash fluid supply source while the waste liquid collecting container is connected to a waste liquid tank. 
     With the arrangement just described, at the time of washing the rotary atomizing head, the rotary atomizing head is moved to a waiting position and then put in the waste liquid collecting container of the atomizing head washer. In this state, a wash fluid is supplied from the wash fluid supply source to the washing nozzle to wash the rotary atomizing head with the wash fluid. Used wash fluid collected in the waste liquid collecting container is allowed to flow down into the waste liquid tank. Therefore, the wash fluid is prevented from scattering around to keep clean the coating area where the working mechanism is installed. 
     Further, according to the present invention, the waste liquid collecting container may be provided movably toward and away from the working mechanism. In this case, the waste liquid collecting container is moved toward the working mechanism at the time of washing the rotary atomizing head, and moved to a position away from the working mechanism while the coating machine is in a paint coating operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of an automatic coating system which is adopted as a first embodiment of the present invention; 
     FIG. 2 is a plan view showing positional relations between the automatic coating system of the first embodiment and a conveyer; 
     FIG. 3 is an enlarged sectional view showing major components of a rotary atomizing head of a coating machine to be mounted on a coating robot; 
     FIG. 4 is a schematic illustration showing the manner in which a wash fluid, supplied from a wash nozzle, flows on and in the rotary atomizing head; 
     FIG. 5 is a front view of an automatic coating system which is adopted as a second embodiment of the present invention; and 
     FIG. 6 is a front view of an automatic coating system which is adopted as a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, the present invention is described more particularly by way of its preferred embodiments with reference to FIGS. 1 through 6 of the accompanying drawings. Firstly, reference is had to FIGS. 1 to  4  which show a first embodiment of the present invention. 
     Indicated at  1  is a coating robot which is employed as a working mechanism in the automatic coating system of the first embodiment. In this instance, as shown in FIG. 2, the coating robot  1  is largely constituted by a pedestal or base  2  which is located at one side of a conveyer A within a predetermined coating area like a coating booth, a rotary base  3  which is rotatably mounted on the pedestal  2 , a support column  4  which is rockably mounted on the rotary base  3  for back and forth rocking movements thereon, an arm  6  which is pivotally supported by a coupler  5  at the upper end of the support column  4 , and a wrist portion  7  which are attached to the fore end of the arm  6  with a certain degree of freedom. A coating machine  20  is detachably mounted on the wrist portion  7  by way of a support portion  8  as will be described hereinafter. 
     With the arrangements just described, the coating robot  1  can move the coating machine  20  in rightward and leftward directions, upward and downward direction, and forward and backward directions relative to and at a predetermined distance from a coating object, namely, a vehicle body B in this particular example. Indicated at  9  is a pipe which is connected to various passages of the coating machine  20  and to a color changing valve apparatus (not shown) which is located outside the coating area. 
     Denoted at  10  is a fixed type atomizing head washer which is used in this embodiment. The atomizing head washer  10  is largely constituted by a base  11  which is fixedly located within a coating area in the vicinity of the coating robot  1 , a support column  12  which is erected on the base  11 , a waste liquid collecting container  13  which is supported on top of the support column  12 , and a washing nozzle  14  which is projected upward and centrally through the bottom of the waste liquid collecting container  13 . The waste liquid collecting container  13  is formed in a cup-like shape which is open on the top side and converged toward a concavely curved bottom. In addition, as shown in FIG. 2, the atomizing head washer  10  is located in a suitable position within a coating area which would not come into the way of paint coating operations, for example, in a position at one side of the conveyer A. On the other hand, the washing nozzle  14  functions to spurt thinner toward a center portion of the rotary atomizing head  28  which will be described hereinafter. Consequently, the thinner which is spurted from the washing nozzle  14  is allowed to enter and flow into the rotary atomizing head  28 , barely influenced by the centrifugal force of the rotary atomizing head  28  in high speed rotation. 
     Indicated at  15  is a thinner pipe which supplies thinner as a wash fluid to the washing nozzle  14 . The thinner pipe  15  is connected to a thinner tank  16  at its base end and to the washing nozzle  14  at its fore end. A thinner pump  17  such as gear pump, plunger pump or the like is connected to the thinner pipe  15  on the side of the thinner tank  16 . Upon actuating the thinner pump  17 , a thinner (or a wash fluid) in the thinner tank  16  is spurted out through the washing nozzle  14 . 
     Denoted at  18  is a waste liquid drain pipe or tube which is connected to the lowermost bottom portion of the waste liquid collecting container  13  at one end and to the waste liquid tank  19  at the other end thereof. This waste liquid drain pipe  18  provides a flow passage to the waste liquid tank  19  for the waste liquid consisting of thinner and paint collected in the waste liquid collecting container  19 . 
     Indicated at  20  is a coating machine which is used in the present embodiment. The coating machine  20  can be turned in upward, downward, rightward and leftward directions by pivotal movements of the support members  8  in the wrist portion  7  of the coating robot  1 . In construction, the coating machine  20  is arranged as shown in FIG.  3 . 
     In that figure, indicated at  21  is a housing which defines the outer profile of the coating machine  20 . The housing  21  is formed of an insulating synthetic resin material in a cylindrical shape. Provided in the housing  21  is an air motor  24  which will be described hereinafter, along with a shaping air ring  22  which is located on the front side of the housing  21 . In this instance, similarly to the housing  21 , the shaping air ring  22  is formed of an insulating synthetic resin material in the shape of a covered cylinder with stepped peripheral walls. Opened in a front end face of the shaping air ring  22  are a multitude of shaping air outlet holes  22 A which are arranged annularly or circularly at suitable intervals. Shaping air passages  23  are provided in the housing  21  and shaping air ring  22  to supply shaping air to the air outlet holes  22 A. 
     Indicated at  24  is an air motor which is mounted within the housing  21 . The air motor  24  is formed of a conductive metallic material in a hollow cylindrical shape and internally provided with an air turbine and air bearings (both of which are not shown in the drawings) for driving a rotational shaft  25  which will be described hereinafter. Further, the air motor  24  is applied with a high voltage from a high voltage generator (not shown). 
     Denoted at  25  is the above-mentioned rotational shaft which is formed of a conductive metallic material in a hollow cylindrical shape and internally provided with a bore  25 A. The rotational shaft  25  is axially passed through and supported in the air motor  24  for high speed rotation therein. Further, the rotational shaft  25  has its base end portion fitted in the air turbine (not shown) of the air motor  24  and has its fore end projected on the front side of the air motor  24 . 
     Designated at  26  is a feed tube which is extended axially through the bore  25 A of the rotational shaft  25 . This feed tube  26  is constituted by a single tube of a conductive metallic material, internally defining a paint passage  26 A which is connected to a color changing valve apparatus through a paint pipe (both of which are not shown in the drawings). Provided within the length of the feed tube  26  is a valve member  27  of a paint valve (not shown) which functions to turn on and off the supply of paint or thinner. Further, connected to the base end of the feed tube  26  is a waste liquid drain passage which is in communication with a waste liquid tank through a waste drain valve (both of which are not shown in the drawings). On the other hand, the fore end of the feed tube  26  is projected out of the rotational shaft  25  and extended into the rotary atomizing head  28 . 
     Indicated at  28  is a bell type rotary atomizing head, which is mounted on the rotational shaft  25  on the front side of the shaping air ring  22 . The rotary atomizing head  28  is constituted by a main body  29  and a hub member  30 . 
     In this instance, the main body  29  of the rotary atomizing head  28  is constituted by a bell cup portion  29 A which is formed of a conductive metallic material in a bell-like shape spreading in the forward direction, an annular partition wall  29 B which is projected radially inward from the bell cup portion  29 A behind the hub member  30 , a paint spreading surface  29 C which is formed on a front face of the bell cup portion  29 A on the front side of the hub member  30  for spreading paint into a thin film, paint releasing edges  29 D which are provided at and around the front end of the bell cup portion  29 A for releasing as liquid threads the thin film of paint from the paint spreading surface  29 C, a mounting hole  29 E which is bored axially into a smaller diameter end of the bell cup  29 A for fitting engagement with a fore end portion of the rotational shaft  25 , and a paint reservoir  29 F which is defined between the front side of the annular partition wall  29 B and the back side of the hub member  30 . 
     The hub member  30  is mounted centrally on the inner peripheral side of the bell cup  29 A by fitting engagement with the latter. Similarly to the main body  29  of the rotary atomizing head, the hub member  30  is formed of a conductive metallic material. In this instance, the hub member  30  is constituted by a circular plate portion  30 A which closes the front side of the bell cup  29 A, and an annular rim portion  30 B which is formed along the outer periphery of the circular plate portion  30 A for fitting engagement with the front face of the main body  29  of the atomizing head. A plural number of solvent outlet holes  30 C (e.g., four solvent outlet holes) are bored in a center region of the circular plate portion  30 A of the hub member  30  to let a supply of thinner from the feed tube  26  flow out onto the front surface at the time of a washing operation (although only two of the solvent outlet holes are shown in the drawings). Besides, a plural number of paint outlet holes  30 D are bored in radially outer portions of the circular plate portion  30 A of the hub member  30 , thereby guiding paint or thinner from the feed tube onto the paint spreading surface  29 C on the main body  29  of the atomizing head. 
     Further, the rotary atomizing head  28  is mounted on the rotational shaft  25  by fitted and threaded engagement with a fore end portion of the rotational shaft  25  which is received in the mounting bore  29 E of the main body  29  of the atomizing head. When the rotary atomizing head  28  is mounted on the rotational shaft  25 , the fore end of the feed tube  26  is projected forward of the annular partition wall  29 B on the main body  29  of the atomizing head. 
     Having the construction as described above, the automatic coating system according to the present embodiment operates in the manner as follows. 
     In case of a paint coating operation using the coating machine  20  for coating an article like a vehicle body, for example, the coating machine  20  is moved by a coating robot  1  to shift its paint spraying position, keeping a predetermined distance from the vehicle body B while coating a paint on the vehicle body B. 
     More particularly, while applying a high voltage to the coating machine  20 , air is supplied to the air motor  24  to put the rotary atomizing head  20  (i.e., the rotational shaft  25 ) in high speed rotation. In this state, the valve body  27  of the paint valve is opened so that the paint from the color changing valve apparatus is allowed to flow into the paint passage  26 A of the feed tube  26  and spouted toward the rotary atomizing head  28 . As a consequence, the paint which is fed to the rotary atomizing head  28  is released from the paint releasing edges  29 D as charged paint particles. Whereupon, charged paint particles are shaped into a suitable spray pattern by the action of shaping air which is spurted out through the respective shaping air outlet holes  22 A, and urged to fly toward the vehicle body along an electrostatic field which is formed between the rotary atomizing head and the vehicle body B, which is connected to earth, and deposit on the vehicle body B. By controlling the operation of the coating robot  1  in relation with the operation of the coating machine  20  in this manner, the coating machine  20  is moved along the contours of the vehicle body B by the coating robot  1  to carry out an automatic coating operation. 
     Now, for changing the paint to a new or next color, it is necessary to wash off previous color in or on various parts of the machine, including the paint supply line from the color changing valve apparatus to the rotary atomizing head  28 , the paint passage  26 A of the feed tube  26 , and the rotary atomizing head  28 . For this purpose, the coating robot  1  is operated to shift the coating machine  20  to a predetermined position, for example, as indicated by two-dot chain line in FIG. 1, and the rotary atomizing head  28  which is in high speed rotation is relatively moved to the proximity of the washing nozzle  14 . 
     In the first place, the paint line from the color changing valve apparatus to the rotary atomizing head  28  is washed in the following manner. In this case, by opening the drain valve which is located on the upstream side of the feed tube  26 , a waste liquid drain passage is established from the paint feed pipe to the waste tank via the waste liquid drain valve and the waste liquid drain passage. In this state, thinner and air are alternately supplied from the color changing valve apparatus to flush the paint line between the color changing valve apparatus and the paint feed pipe, and waste liquid is collected in the waste tank through the above-mentioned waste liquid drain passage. 
     In the next place, residues of a previous color in the paint passage  26 A of the feed tube  26  are washed off in the manner as follows. For this purpose, the waste drain valve is closed to shut up the passage to the waste liquid tank. Consequently, the thinner from the color changing valve apparatus is fed to the feed tube  26 . This thinner flows out into the waste liquid collecting container  13  via the paint feed pipe, the paint passage  26 A in the feed tube  26 , the rotary atomizing head  28 , and the respective solvent outlet holes  30 C and paint outlet holes  30 D of the hub member  30 , thereby collecting the thinner into the waste liquid tank  19 . In this stage, it is not necessary to clean the rotary atomizing head  28  in high speed rotation, which will be washed clean in a succeeding atomizing head washing stage. Accordingly, in this stage, it suffice to consume only a small amount of thinner which is necessary for washing off the previous color remaining in the paint passage  26 A of the feed tube  26 . 
     In the next stage, the rotary atomizing head  28  is washed in the manner as follows. In this atomizing head washing stage, the thinner pump  17  is actuated to spurt thinner from the washing nozzle  14  of the atomizing head washer  10  toward the front side of the rotary atomizing head  28  which is in high speed rotation. More particularly, as indicated by arrows in FIG. 4, thinner is spurted from the washing nozzle  14  toward the center of the hub member  30  which is less influenced by the centrifugal force resulting from high speed rotation of the rotary atomizing head  28 . By the centrifugal force of the rotary atomizing head  28 , the supplied thinner is divided into two different types of streams, i.e., streams which move along the surface of the hub member  30 , and streams which flow into the rotary atomizing head through the respective solvent outlet holes  30 C and then come out through the respective paint outlet holes  30 D. 
     The thinner streams along the surface of the hub member  30  are urged to flow from radially inner to radially outward directions of the hub member  30  by the centrifugal force of the rotary atomizing head  28 , thereby washing off deposited paint P 1  from the surface of the hub member. 
     Besides, the other thinner streams, which have entered the paint reservoir  29 F on the inner side of the hub member  30  through the solvent outlet holes  30 C, are separated into streams along the inner wall surface of the annular partition wall  29 B and streams along the back side of the hub member  30 . Paint P 2  which had deposited on the outer periphery of a fore end portion of the feed tube  26  is washed off by the thinner streams along the inner wall surface of the annular partition wall  29 B, along with paint P 3  which had deposited on the surfaces between the annular partition wall  29 B and the paint outlet holes  30 D of the main body  29  under the influence of the centrifugal force on the rotary atomizing head  28 . On the other hand, paint which has deposited on the back side of the hub member  30  is washed off by the back side thinner streams. 
     Further, the thinner streams along the surfaces of the hub member  30  as well as the thinner streams coming out through the paint outlet holes  30 D of the rotary atomizing head after entrance through the solvent outlet holes  30 C are collected into the waste liquid collecting container  13 . The collected thinner is allowed to flow down through the waste liquid pipe  18  into the waste liquid tank  19 . 
     After washing the paint line, the feed tube  26  and the rotary atomizing head  28  in this manner, paint of a new color is fed to the coating machine  20  from the color changing valve apparatus in preparation for a nest cycle of coating operation. 
     Thus, according to the automatic coating system of the first embodiment as described above, when changing the paint color, the front end of the coating machine  20 , which is mounted on the coating robot  1 , is put into the waste liquid collecting container  13 , and at the same time thinner is spurted from the washing nozzle  14  against the front side of the rotary atomizing head  28 , thereby facilitating the washing operation on the rotary atomizing head  28 . 
     In this regard, in the case of prior art machines, it has been necessary to wash all of the paint pipe, feed tube and rotary atomizing head with thinner which is supplied from a color changing valve apparatus each time before changing the paint color. In contrast, according to the present embodiment of the invention, the rotary atomizing head  28  is washed by means of the washing nozzle  14  of the atomizing head washer  10  separately from washing operations for the paint pipe and feed tube  26 . Consequently, the consumption of thinner to be used for washing the paint line can be reduced to an amount which is necessary for washing the paint line and feed tube  26  alone, permitting to cut the running cost to a significant degree. 
     Further, according to the present embodiment having the atomizing head washer  10  located in the vicinity of the coating robot  1  for washing exclusively the rotary atomizing head  28 , the feed tube  26  of the coating machine  20  can be constituted by one and single tube. Therefore, the feed tube is not required to be a double wall tube internally defining a paint passage along with a front washing thinner passage as in Japanese Utility Model Laid Open No. H2-37766 mentioned hereinbefore. Besides, the present embodiment makes it possible to omit the front washing thinner passage from the feed tube, as well as the front washing valve, thinner feed pipe and thinner source which are necessarily connected to the front washing thinner passage, thereby contributing to simplify the construction of the coating machine unit. 
     Similar effects can be obtained even if the coating machine  20 , which is mounted on the coating robot in the above-described embodiment, is replaced by a coating machine having a number of bundled paint feed tubes respectively for various colors as in Japanese Patent Laid-Open No. H6-134354 mentioned hereinbefore. Even in this case, it becomes possible to simplify the construction of the coating machine by omitting not only the wash feed tube in the bundle of a plural number of feed tubes but also the front washing valve, front washing thinner feed pipe and front washing thinner source. 
     Further, in the case of the present embodiment which can obviate the front washing thinner passage (or the wash feed tube), there is no possibility of an applied high voltage flowing to the front washing thinner source via the thinner in the front washing thinner passage (or the wash feed tube). It follows that the thinner to be used for the washing operation can be selected irrespective of electrical resistance, and simply from products which have satisfactory properties in washing capacity. Besides, a substantial cut in cost can be realized by a reduction of thinner consumption in washing the paint line and the rotary atomizing head  28 . 
     Furthermore, at the time of a washing operation, the front end of the coating machine  20  is automatically put into the waste liquid collecting container  13  by operation of the coating robot  1 , and spent thinner or waste liquid resulting from the washing operation can be collected into the waste liquid tank  19  through the waste liquid collecting container  13  and the waste liquid pipe  18 , thereby preventing the thinner from scattering around in the coating area and thereby keeping the coating area clean. 
     Referring now to FIG. 5, there is shown a second embodiment of the present invention, with features in that the coating machine is mounted on a reciprocator which is employed as a working mechanism, and in that the washing nozzle is mounted on an atomizing head washer separately from the reciprocator. In the following description of the second embodiment, the component parts which are common with the foregoing first embodiment are simply designated by common reference numerals or characters to avoid repetitions of same explanations. 
     Indicated at  31  is a side type reciprocator which has been adopted as a working mechanism in the automatic coating system of the present embodiment. In this instance, the reciprocator  31  is mainly constituted by a fixed casing  32  which is located within a coating area and at one side of a conveyer (not shown), which transfers coating articles into and out of the coating area, a vertical slide slot  33  which is formed on one side of the fixed casing  32 , and a moving arm  34  which is reciprocated up and down within the slide slot  33  as indicated by arrows a. A coating machine  20  similar to the one in the foregoing first embodiment is mounted on a fore end portion of the moving arm  34 . Side surfaces of a vehicle body or the like are coated by moving the arm  34  in the directions of arrows a. Indicated at  35  is a pipe which is connected between the coating machine  20  and a color changing valve apparatus (not shown) which is located outside the coating area. 
     Denoted at  36  is a movable type atomizing head washer which is employed in the present embodiment. The atomizing head washer  36  is provided separately from the reciprocator  31  and located within the coating area. In this instance, the atomizing head washer  36  is constituted by a carriage  37  which is movable back and forth and to the right and left within the coating area, a post  38  which is erected on the carriage  37 , an arm moving mechanism  39  which is slidably mounted on the post  38  for upward and downward movements, a support arm  40  which is moved back and forth (in the directions of arrow b), a waste liquid collecting container  41  which is located in a front end position on the arm  40 , and a washing nozzle  42  which is mounted within the waste liquid collecting container  41  and projected forward from a deep center position toward a front opening of the waste liquid collecting container  41 . The waste liquid collecting container  41  is formed in a cylindrical shape which is closed on the rear side and provided with an opening on the front side thereof. Connected to the bottom or lower side of the waste liquid collecting container  41  is a waste liquid pipe  47  which will be described hereinafter. The atomizing head washer  36  is located in a position which would not come into the way of the coating machine during coating operations. 
     Indicated at  43  is a thinner pipe or tube which supplies a wash fluid such as thinner to the washing nozzle  42 . The thinner pipe  43  is connected to the washing nozzle  42  at its fore end and connected to a thinner tank  44  at its base end. At the end on the side of the thinner tank  44 , a thinner pump  45  is connected to the thinner pipe  43 . Upon actuating the thinner pump  45 , the thinner in the tank  44  is pumped up therefrom and spurted out as a wash fluid from the tip end of the wash nozzle  42 . Further, a tube take-up reel  46  is provided at a halfway point thereby to reel up or reel out the thinner tube  43 , for reducing or increasing the length of the thinner tube  43  according to movements of the atomizing head washer  36 . 
     Denoted at  47  is a waste liquid tube which has one end thereof connected to a lowermost portion of the waste liquid collecting container  41  and the other end connected to the waste liquid tank  48 . The waste liquid, including paint and thinner, which has been collected into the waste liquid collecting container  41  is allowed to flow down into the waste liquid tank  48  through the waste tube  47 . Further, a tube take-up reel  49  is provided at a halfway point to reel up or reel out the waste liquid tube  47 , thereby reducing or increasing the length of the waste liquid tube  47  according to movements of the atomizing head washer  36 . 
     With arrangements as described above, the coating system of the second embodiment operates in the manner as follows. 
     In this instance, charged paint particles which are released from the rotary atomizing head  28  of the coating machine  20  are caused to fly toward and deposit on a coating object like a vehicle body, traveling along an electrostatic field which is formed between the rotary atomizing head  28  and the vehicle body which is connected to earth. In coating side surfaces of the vehicle body, the coating machine  20  is moved by the reciprocator  31  up and down (in the directions of arrow a) relative to the vehicle body which is being transferred by the conveyer. 
     Now, when changing the paint color, the arm  34  of the reciprocator  31  is stopped at a predetermined position, and the atomizing head washer  36 , which is of a movable type in this case, is moved to the proximity of the reciprocator  31 . At this time, the thinner tube  46  and the waste liquid tube  47  on the reels  46  and  49  are reeled out or reeled up according to the movement of the atomizing head washer  30 . 
     Then, the height of the waste liquid collecting container  41  is adjusted to the same level as the coating machine  20  by vertically adjusting the position of the support arm  40  through the arm moving mechanism  39  of the atomizing head washer  36 . Again through the arm moving mechanism  39 , the support arm  40  is moved in the direction of arrow b to locate the waste liquid collecting container  41  in the position indicated by two-dot chain line, so that a fore end portion of the coating machine  20  is received in the waste liquid collecting container  41 . At this time, the fore end of the washing nozzle  42  is advanced along with the waste liquid collecting container  41  toward and into a closely confronting position relative to the rotary atomizing head  28 . 
     In this state, firstly thinner is supplied from a color changing valve apparatus to wash the paint line substantially in the same manner as described in the foregoing first embodiment. In the next place, through the washing nozzle  42  of the atomizing head washer  36 , thinner is supplied to the front side of the rotary atomizing head  28 , which is in high speed rotation, to wash off deposited paint therefrom. 
     Thus, similarly to the above-described first embodiment, this embodiment makes it possible to obviate the washing thinner passage as used in the feed tube on prior art coating machines, contributing to simplify the construction of the coating machine. 
     In addition, since the rotary atomizing head  28  is washed separately from the paint line, it becomes possible to reduce the consumption of thinner or other wash fluid and therefore to cut the running cost. 
     Further, during a washing operation, the fore end of the coating machine  20  which is mounted on the reciprocator  31  is put in the waste liquid collecting container  41 . Accordingly, the waste liquid like waste thinner which occurs during a washing operation is collected into the waste liquid tank  48  through the waste liquid collecting container  41  and waste liquid tube  47 , thereby preventing thinner from scattering around within the coating area and keeping the coating area clean. 
     Shown in FIG. 6 is a third embodiment of the present invention, with features in that, in addition to a coating machine  20 , a washing nozzle is mounted on a reciprocator  31  in a position close to the coating machine  20 . In the following description of the third embodiment, the component parts which are common with the foregoing first and second embodiments are designated by common reference numerals or characters to avoid repetition of same explanations. 
     Indicated at  51  is an atomizing head washer which is adopted in the present embodiment. The atomizing head washer  51  is located in a position which corresponds to a lowermost waiting position of an arm  34  which is moved along a sliding slot  33  of a reciprocator  31 . In this instance, the atomizing head washer  51  is mainly constituted by an arm moving mechanism  52  which is fixedly mounted in a lowermost portion of a fixed casing  32 , a support arm  53  which is moved by the arm moving mechanism  52  and upturned at its fore end, a waste liquid collecting container  54  which is formed on the upturned fore end of the support arm  53  and provided with an opening on a lateral side facing toward the reciprocator, and a washing nozzle  55  which is mounted in the waste liquid collecting container  54  and projected forward toward the opening from a deep center position in the waste liquid collecting container  54 . 
     Denoted at  56  is a thinner tube for supplying a wash fluid like thinner to the washing nozzle  55 . The base end of the thinner tube  56  is connected to a thinner tank  57 , while its fore end is connected to the washing nozzle  55 . On the side of the thinner tank  57 , a thinner pump  58  is connected to the thinner tube  56  so that, upon actuating the thinner pump  58 , thinner is pumped up from the thinner tank  57  and spurted out through a nozzle hole at the fore end of the washing nozzle  55 . 
     Indicated at  59  is a waste liquid tube which has one end thereof connected to a lowermost portion of the waste liquid collecting container  54  and the other end connected to the waste liquid tank  60 . The waste liquid containing spent thinner and paint, which has been collected in the waste liquid collecting container  54 , is allowed to flow down into the waste liquid tank  60  through the liquid tube  59 . 
     In the case of the atomizing head washer  51  with the arrangements just described, the rotary atomizing head  28  is moved into the lowermost waiting position by the moving arm  34  in an atomizing head washing stage, and then the arm  53  is moved in the direction of arrow b. As a result, the coating machine  20  and the washing nozzle  55  are shifted into the positions indicated by two-dot chain line, and the fore end of the washing nozzle  55  is located in closely confronting relation with the rotary atomizing head  28 . Then, thinner is spurted toward the front side of the rotary atomizing head  28  from the washing nozzle  55  to wash the rotary atomizing head  28 . 
     In the foregoing embodiments, the feed tube  26  is used for the supply of paint to the coating machine  20 . However, it is to be understood that the present invention is not restricted to this particular form of coating machine and can also be applied to a cartridge-type coating machine which is arranged to supply paint from cartridge-type paint tanks. In such a case, the rotary atomizing head is washed each time when a paint tank is replaced for a change of color. 
     Further, the present invention is not limited to the particular combinations shown in the above-described embodiments, i.e., the combination of the coating robot  1  and the fixed type atomizing head washer  10  in the first embodiment, the combination of the reciprocator  31  and the movable type atomizing head washer  36  in the second embodiment, and the combination of the reciprocator  31  and the movable type atomizing head washer  51  which is provided on the reciprocator. Of course, the present invention can be similarly realized by means of a combination of the coating robot  1  and the movable type atomizing head washer  36 . 
     Further, although a gear pump or a plunger pump is employed as the thinner pump  17  ( 45 ,  58 ) in the foregoing embodiments for spurting thinner through the washing nozzle  14  ( 42 ,  55 ), the present invention is not limited to the particular arrangements shown. For example, in place of a gear or plunger pump, there may be employed a pressure tank which is arranged to push thinner forward under pressure of compressed air. 
     Alternatively, if desired, the thinner pump  17  ( 45 ,  58 ) may be abolished by connecting the wash tube  15  ( 43 ,  56 ) to a thinner circulation line. 
     Further, although the present invention has been described in the foregoing embodiments by way of a direct charging type coating machine in which a high voltage is applied to the rotary atomizing head for electrically charging atomized paint particles which are released from the rotary atomizing head  28 . However, the present invention is not limited to coating machines of this sort but similarly applicable to an indirect charging type coating machine in which a corona discharge area is formed in front of a rotary atomizing head to apply a high voltage to atomized paint particles released from the rotary atomizing head, or to a coating machine with a non-electrostatic type rotary atomizing head. 
     Moreover, needless to say, the coating machine may have a tubular or cup-shaped rotary atomizing head in place of the bell type rotary atomizing head in each one of the above-described embodiments. 
     As explained in detail in the foregoing description, the automatic coating method according to the present invention comprises an atomizing head washing step in which, after stopping a coating operation by a coating machine and a working mechanism, a washing nozzle is located in a confronting position relative to a rotary atomizing head to spurt a wash fluid toward the front side of the rotary atomizing head. Being supplied from the front side, the wash fluid is allowed to enter and flow through interior passages of the rotary atomizing head, thereby making it possible to wash off deposited paint therefrom in a reliable manner and with a reduced amount of wash fluid to realize a substantial reduction in running cost. 
     The automatic coating machine according to the present invention comprises an atomizing head washer which is provided with a washing nozzle and located in the proximity of a working mechanism movably toward and away from a rotary atomizing head, for washing the rotary atomizing head with a wash fluid which is supplied through the washing nozzle of the atomizing head washer. Being supplied from the front side, the wash fluid is allowed to enter and flow through interior passages of the rotary atomizing head, thereby making it possible to wash off deposited paint therefrom reliably with a reduced amount of wash fluid. Besides, it contributes to simplify the construction of the coating machine since there is no necessity for providing a washing mechanism for the rotary atomizing head on the part of the coating machine.