Patent Publication Number: US-6666164-B2

Title: Automatic coating method and apparatus

Description:
This application is a Division of application Ser. No. 09/601,344 filed on Aug. 17, 2000; which is a 371 of PCT/JP99/06920 filed on Dec. 9, 1999. 
    
    
     TECHNICAL FIELD 
     This invention relates to an automatic coating method for carrying out coating operations in various colors automatically by selectively loading and unloading paint cartridges of different colors into and from a coating apparatus, and an automatic coating apparatus therefor. 
     BACKGROUND ART 
     Generally, for coating objects like vehicle bodies, for example, rotary atomizing head type coating apparatus which are equipped with a rotary atomizing head have been in wide use. Lately, coating apparatus of this sort are increasingly required to meet demands for reductions of the amounts of paint and solvent to be discarded at the time of color changes and for capability of coping with a large number of paint colors. 
     As a first example of the prior art of this category, Japanese Laid-Open Patent Publication No. H8-229446 describes a rotary atomizing head type coating apparatus which is so arranged as to reduce the amounts of discarding paint and solvent and which can cope with an increased number of paint colors. This rotary atomizing head type coating apparatus employs paint cartridges which are filled with different paint colors and adapted to be selectively and replaceably mounted on the coating apparatus in the course of a coating operation on vehicle bodies. However, no description is given in this prior art with regard to an apparatus for changing the paint cartridges. 
     As a second example of the prior art, there has been known an automatic coating apparatus (e.g. from Japanese Laid-Open Patent Publication No. S63-175662) which is arranged to perform a coating operation automatically according to programmed procedures. According to this prior art automatic coating apparatus, paint cartridges of various colors are located within a working area of a coating robot or other working mechanism, and, at the time of cartridge replacement, the working mechanism is operated to serve as a cartridge changer. Therefore, in this case each one of the paint cartridges needs to be located within a reach of the working mechanism. However, actually there is a limit to the number of paint cartridges which can be located within a working area of a working mechanism. 
     Further, as a third example of the prior art, there has been known an automatic coating apparatus as described in International Gazette WO97/34707. This third prior art coating apparatus is comprised of a working mechanism such as a coating robot which is provided in a coating area, a coating machine which is mounted on the working mechanism and provided with a rotary atomizing head adapted to be put in high speed rotation by an air motor for atomizing paint into finely divided particles, a number of paint cartridges which are filled with paint of different colors and adapted to be replaceably mounted on the coating machine, and a cartridge changer which is arranged to support the respective paint cartridges and mount and dismantle a paint cartridge on and from the coating apparatus for cartridge replacement. 
     In this case, the cartridge changer is provided with a round support table which is arranged to support a large number of paint cartridges in an annular array. The cartridge support table is turned by a drive motor or the like to bring a paint cartridge to be used for a coating operation, to a predetermined pick-up position. 
     In the case of the third prior art automatic coating apparatus which is arranged in the manner just described, paint is supplied from a cartridge to a coating machine of the coating apparatus to spray the paint toward a coating object. At this time, the working mechanism is put in operation to move the coating apparatus along contours of coating surfaces of a coating object. 
     When changing the paint color, the working mechanism is moved to bring the paint cartridge on the coating apparatus to a predetermined cartridge changing position of the cartridge changer. Then, a cartridge gripper which is provided on the side of the cartridge changer is operated to remove a consumed or empty paint cartridge from the coating apparatus and return same to the cartridge support table. Nextly, a fresh paint cartridge which is filled with a next color is picked up from the cartridge support table and mounted on the coating apparatus. 
     The cartridge changer according to the prior art just mentioned is arranged to locate a selected one of the paint cartridges on the cartridge support table in a predetermined pick-up position by turning the support table, and mounted on the coating apparatus in place of a cartridge of a previous color. 
     However, the cartridge support table, which carries a large number of paint cartridges in an annular array, is necessarily large in size and weight. It follows that, for driving the cartridge support table, the cartridge changer is required to have a drive motor with large driving power. Needless to say, a cartridge changer of a large size is disadvantageous in that it invites increases in cost. 
     DISCLOSURE OF THE INVENTION 
     In view of the above-mentioned problems with the prior art, it is an object of the present invention to provide an automatic coating method and apparatus for putting the method into practice, in which a large number of paint cartridges of different colors are arranged and located in such an efficient manner as to facilitate cartridge replacements and to realize reductions in size and cost of the coating apparatus in addition to improvements in working efficiency. 
     In order to achieve the above-stated objective, according to the present invention, there is provided an automatic coating method which is applied by the use of a working mechanism located in a coating area, a coating apparatus mounted on the working mechanism and adapted to be replaceably loaded with paint cartridges of various colors, and a cartridge changer including a paint replenishing means for replenishing paint into the paint cartridges and a cartridge gripper means having a couple of gripper members for gripping paint cartridges separately thereon and adapted to hand over paint cartridges to and from the coating apparatus to replace an empty paint cartridge on the coating apparatus by a replenished paint cartridge. 
     The automatic coating method according to the present invention comprises: coating step of coating object by the coating apparatus loaded with a replenished paint cartridge and moved by the working mechanism; a replenished paint cartridge picking up step of picking up said replenished paint cartridge of a color to be used in a next coating operation from a paint replenisher means by the use of one of the gripper members of the cartridge gripper means; an empty paint cartridge unloading step of unloading said empty paint cartridge from the coating apparatus by the use of the other one of the gripper members of the cartridge gripper means having the replenished paint cartridge still gripped in one gripper member; the replenished paint cartridge loading step of loading said replenished paint cartridge into the coating apparatus by one gripper member of the cartridge gripper means having the empty paint cartridge still gripped on the other gripper member; and returning the unloaded empty paint cartridge to the paint replenishing means. 
     With the arrangements just described, in the coating step, the working mechanism is put in motion to perform a coating operation by the coating apparatus which is loaded with a replenished paint cartridge. In the step of picking up a replenished paint cartridge, a replenished paint cartridge is gripped and picked up from the paint replenishing means by one of the gripper members of the cartridge gripper means. Nextly, in the empty cartridge unloading step, the empty paint cartridge is picked up from the coating apparatus by the other gripper member of the cartridge gripper means while gripping the replenished paint cartridge by one of the gripper members of the cartridge gripper means. In the replenished paint cartridge loading step, the replenished paint cartridge is loaded into the coating apparatus by one of the gripper members of the cartridge gripper means while gripping the empty cartridge by the other gripper member of the cartridge gripper means. Thus, in the empty cartridge returning step, a replenished paint cartridge and an empty paint cartridge are exchanged between the coating apparatus and the cartridge changer. 
     According to the present invention, there is also provided an automatic coating apparatus suitable for putting the above-described method into practice, which basically includes a working mechanism located in a coating area, a coating apparatus mounted on and moved by the working mechanism and adapted to be replaceably loaded with paint cartridges of various colors, and a cartridge changer arranged to hand over paint cartridges to and from the coating apparatus to replace an empty paint cartridge on the coating apparatus by a replenished paint cartridge. 
     The cartridge changer used in the automatic coating apparatus according to the present invention comprises: a paint replenishing means having a number of paint replenishers correspondingly for different paint colors, each adapted to support and replenish a paint cartridge of a corresponding color; a cartridge transfer means arranged to transfer paint cartridges in the directions of three perpendicularly intersecting axis; and a cartridge gripper means supported on the cartridge transfer means and adapted to grip and transfer paint cartridges between the coating apparatus and the paint replenishing means. 
     With the arrangements just described, upon finishing a coating operation, the coating apparatus with an empty paint cartridge is located at a cartridge replacing position, whereupon the cartridge means is actuated to move the cartridge gripper means toward that position. At this time, the cartridge gripper means is operated to transfer and exchange an empty paint cartridge and a replenished paint cartridge of a next color between the coating apparatus and the paint replenishing means. Besides, in preparation for use in a next coating operation, the empty paint cartridge which has been handed over to and set on the paint replenishing means is replenished with paint concurrently with a coating operation by the coating apparatus. 
     The coating apparatus to be used in the present invention is preferably constituted by a cartridge mount portion to be replaceably loaded with paint cartridges, and a coating machine with a rotary atomizing head for atomizing and spraying paint supplied from a paint cartridge loaded in the cartridge mount portion. 
     With the arrangements just described, as soon as paint is spurted out from a paint cartridge which is loaded in the cartridge mount portion, it is atomized into finely divided particles and sprayed toward a coating object by the rotary atomizing head of the coating machine. 
     Further, preferably, the paint cartridges to be used in the present invention are each constituted by a container to be filled with paint, and a feed tube extended axially from one end of the container, and the paint replenishing means is adapted to replenish paint into the container of the paint cartridge through a fore end of the feed tube. 
     With the paint cartridge construction just described, paint can be replenished into the container of a paint cartridge which has been handed over to and set on the paint replenishing means, thereby utilizing the fore end of the feed tube as a replenishing port. 
     In this instance, preferably, the paint cartridges are each constituted by a container to be filled with paint and a feed tube axially extended from a fore end of the container, and the paint replenishing means is constituted by a plural number of replenishing stools for replenishment of various paint colors, each having a feed tube passage hole formed axially therein to receive the feed tube of a corresponding paint cartridge, and a connector member located in the replenishing stool located in a deeper position than the feed tube passage hole to connect the fore end portion of the feed tube to a paint supply passage. 
     With the arrangements just described, when an empty paint cartridge is returned to a replenishing stool, the feed tube of the cartridge is inserted into the feed tube passage hole on the side of the stool until its fore end is connected to the connector member for communication with the paint supply passage. Therefore, paint which is supplied to the paint supply passage is replenished into the container via the connector member and the feed tube. 
     Further, preferably the cartridge transfer means to be used in the present invention is constituted by a first transfer mechanism arranged to move the cartridge gripper means in a longitudinal or transverse direction of the paint replenishing means, a second transfer mechanism arranged to move the cartridge gripper means in a transverse or longitudinal direction, and a third transfer mechanism arranged to move the cartridge gripper means in a vertical direction, and the cartridge gripper means is supported on the third transfer mechanism. 
     With the arrangements just described, the cartridge gripper means is moved in longitudinal, transverse and vertical directions by the first to third transfer mechanisms and located in the cartridge replacing position or in a cartridge pick-up position over a selected one of paint cartridges which are supported on the paint replenishing means. In addition, the cartridge gripper means is moved vertically up or down by the third transfer mechanism at the time of lifting up or lifting down a paint cartridge from or onto the coating apparatus or paint replenishing means. 
     Further, preferably the cartridge gripper means to be used in the present invention is provided with a couple of gripper members side by side to grip a couple of paint cartridges separately and independently of each other. 
     With the arrangements just described, a replenished paint cartridge is gripped in one of the gripper members of the cartridge gripper means at the time when an empty paint cartridge is unloaded from the coating apparatus by the other one of the gripper members at the time of replacement. Therefore, the replenished paint cartridge can be loaded into the coating apparatus immediately after removal of the empty paint cartridge. 
     Further, according to the present invention, the cartridge changer is provided with a shock absorber provided between the cartridge transfer means and the cartridge gripper means to permit movements of the cartridge gripper means relative to the cartridge transfer means when brought into abutting engagement with a paint cartridge. 
     With the arrangements just described, when the cartridge gripper means is moved toward and abutted against a paint cartridge by the cartridge transfer means, the shock absorber permits the cartridge gripper means to move for buffering the impacts of abutment. 
     Further, according to the present invention, the automatic coating apparatus further comprises a washer means which is located in the vicinity of a cartridge replacing position of the cartridge changer for washing the coating apparatus each time when replacing an empty paint by a replenished paint cartridge of a different color. 
     With the arrangements just described, when the coating apparatus is located in a cartridge replacing position for cartridge replacement, deposited previous color on the coating apparatus can be washed off by the washer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a front view of an automatic coating apparatus with a cartridge changer embodying the present invention; 
     FIG. 2 is an enlarged vertical sectional view of a rotary atomizing head type coating apparatus shown in FIG. 1; 
     FIG. 3 is an enlarged vertical sectional view of a rotary atomizing head shown in FIG. 1; 
     FIG. 4 is a vertical sectional view of a paint cartridge on an enlarged scale; 
     FIG. 5 is an enlarged front view of a cartridge changer shown in FIG. 1; 
     FIG. 6 is a plan view of the cartridge changer of FIG. 5; 
     FIG. 7 is a left-hand side view of the cartridge changer of FIG. 5; 
     FIG. 8 is an enlarged vertical sectional view of a paint replenisher shown in FIG. 1; 
     FIG. 9 is a vertical sectional view of the paint replenisher in an operational stage of replenishing a paint cartridge; 
     FIG. 10 is an enlarged schematic view of a cartridge gripper shown in FIG. 7; 
     FIG. 11 is a schematic illustration explanatory of a coating operation by the coating apparatus; 
     FIG. 12 is a schematic illustration explanatory of an operation of picking up a replenished paint cartridge from the paint replenisher; 
     FIG. 13 is a schematic illustration explanatory of an operation of locating the coating apparatus to a cartridge changing position by the cartridge changer; 
     FIG. 14 is a schematic illustration explanatory of an operation of washing the rotary atomizing head and a fore end portion of a feed tube by an atomizing head washer; 
     FIG. 15 is a schematic illustration explanatory of an operation of dismantling an empty paint cartridge from the coating apparatus; 
     FIG. 16 is a schematic illustration explanatory of an operation of positioning a replenished paint cartridge over the coating apparatus; 
     FIG. 17 is a schematic illustration explanatory of an operation of mounting the replenished paint cartridge on the coating apparatus; 
     FIG. 18 is a schematic illustration explanatory of an operation of returning a dismantled empty paint cartridge to the paint replenisher; and 
     FIG. 19 is an operational time chart of the cartridge changer. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereafter, the automatic coating apparatus according to the present invention is described more particularly by way of its preferred embodiments with reference to FIGS. 1 through 19 of the accompanying drawings. 
     In the drawings, indicated at  1  is a coating robot employed as a working mechanism. The coating robot  1  is largely constituted by a base  2 , a vertical arm  3  which is rotatably and pivotally supported on the base  2 , a horizontal arm  4  which is pivotally connected to a fore end portion of the vertical arm  3 , and a wrist  5  which is provided at a fore distal end of the horizontal arm  4 . 
     Indicated at  11  is a rotary atomizing head type coating apparatus (hereinafter referred to simply as “coating apparatus  11 ” for brevity) which is mounted on the coating robot  1 . As shown in FIG. 2, the coating apparatus  11  is largely constituted, as described in greater detail hereinafter, by a housing  12 , feed tube passage holes  17  and  24 , a coating machine  18 , a paint cartridge  25 , a paint valve  35 , and a thinner valve  43 . 
     Indicated at  12  is the housing which is formed of engineering plastics such as PTFE, PEEK, PEI, POM, PI, PET and the like, and which is detachably attached to the fore end of the wrist  5 . The housing  12  constitutes a cartridge mount portion along with the coating machine  18 , and includes a neck portion  13 , which is detachably attached to the distal end of the wrist  5  of the coating robot  1 , and a head portion  14  which is formed integrally at the fore end of the neck portion  13 . 
     In this instance, the housing  12  is provided with a coating machine mount portion  15  and a cartridge mount portion  16 , each in the form of a cylindrical cavity, on the front and rear sides of the head portion  14 , respectively. Further, female and male coupling portions  16 B and  16 C are provided separately at the bottom  16 A of the cartridge mount portion  16  for fitting engagement with male and female coupling portions  26 A and  26 B which are provided on the side of a container  26  as will be described hereinafter. The female and male coupling portions  16 B and  16 C on the cartridge mount portion  16  function to orient the container  26  into position in the circumferential direction as the container  26  is mounted on the cartridge mount portion  16 . 
     Indicated at  17  is the feed tube passage hole which is provided on the side of the housing and formed between and in communication with the coating machine mount portion  15  and the cartridge mount portion  16 . This feed tube passage hole  17  on the side of the housing is composed of a front portion in the form of a feed tube passage portion  17 A of a small diameter and a rear portion in the form of a conically converging portion  17 B. In this instance, the feed tube passage portion  17 A is formed in coaxial relation with the feed tube passage hole  24  which is provided on the side of the coating machine as will be described hereinafter. On the other hand, the conically converging portion  17 B is brought into abutting and fitting engagement with a conical projection  27  which is provided on the side of the paint cartridge  25  as will be described hereinafter, for orienting the paint cartridge into position in both axial and radial directions. 
     Indicated at  18  is the coating machine which is set in the coating machine mount portion  15  of the head portion  14 . In this instance, the coating machine  18  is largely constituted by an air motor  19  including a motor case  19 A, rotational shaft  19 B, air turbine  19 C and air bearing  19 D, a rotary atomizing head  20  to be put in rotation by the air motor  19  for centrifugally atomizing supplied paint into finely divided particles and spraying same toward a coating object  106  which will be described hereinafter, and a shaping air ring  21  which is provided on the front side of the air motor  19 . 
     On the other hand, as shown in FIG. 3, the rotary atomizing head  20  is constituted by: a bell cup  20 A which is formed in a bell-like shape; a circular disk-like hub member  20 B which is fitted in a center portion on the front side of the bell cup  20 A; a paint spreading surface  20 C which is formed on outer peripheral portions on the front side of the bell cup  20 A for spreading paint in a thin film; a paint reservoir  20 D which is defined on the rear side of the hub member  20 B, a plural number of wash fluid inlet holes  20 E which are formed in center portions of the hub member  20 B to let a wash fluid to flow into the paint reservoir  20 D from the front side of the hub member  20 B; and a large number of paint outlet holes  20 F which are formed in outer peripheral portions of the hub member  20 B to guide paint, which is spurted out from the feed tube  28 , toward the above-mentioned paint spreading surface  20 C. 
     The shaping air ring  21  is bored with a multitude of shaping air outlet holes  21 A on its outer peripheral side for spurting shaping air toward paint releasing edges of the rotary atomizing head  20  to shape released paint particles into a predetermined spray pattern. 
     Designated at  22  is a high voltage generator which is provided on the neck portion  13  of the housing  12 . For example, the high voltage generator  22  is constituted by a Cockcroft circuit which is adapted to elevate a source voltage from a power supply (not shown) to a high voltage of from −60 kv to −120 kv. The output side of the high voltage generator  22  is connected, for example, to the air motor  19  to apply a high voltage to the rotary atomizing head  20  through the rotational shaft  19 B of the air motor  19  for directly charging paint particles. 
     Indicated at  23  are a plural number of air passages which are provided on the neck portion  13  of the housing  12  and are connected from a control air source (not shown), for supplying turbine air, bearing air and brake air to be supplied to the air motor for the control thereof, in addition to shaping air to be supplied to the shaping air ring for shaping the paint spray pattern. In the drawings, only one air passage is shown to represent various air passages just mentioned. 
     Indicated at  24  is the feed tube passage hole which is provided on the side of the coating machine, axially through the rotational shaft  19 B of the air motor  19 . This feed tube passage hole  24  on the side of the coating machine has its base end opened into a feed tube passage portion  17 A of the feed tube passage hole  17  on the side of the housing and its fore end opened into the paint reservoir  20 D of the rotary atomizing head  20 . Further, the feed tube passage hole  24  on the side of the coating machine is formed in coaxial relation with the feed tube passage portion  17 A of the feed tube passage hole  17  on the part of the housing. The feed tube  28  of the paint cartridge  25  is extractably passed into these feed tube passage holes  17  and  24 . 
     Denoted at  25   a,    25   b,  . . .  25   n  are paint cartridges of different colors (hereinafter referred to simply as “cartridges  25 ” for brevity) which are filled with paint of different colors a, b, . . . n to be supplied to the rotary atomizing head  20 . As shown in FIG. 4, each one of these cartridges  25  is largely constituted by a container  26 , a conical projection  27  which is provided at a front end of the container  26 , a feed tube  28  which is extended out axially forward from the conical projection  27 , a piston  29  which is fitted in the container  26 , and a thinner passage  32  which is provided on the side of the paint cartridge to supply therethrough thinner as a paint extruding liquid. 
     The container  26  of the paint cartridge  25  is formed of engineering plastics, for example, similar to the housing  12 , and provided with a cylindrical body (a cylinder) of a diameter which can be removably fitted in the cartridge mount portion  16  on the housing. Further, the container  26  is provided with male and female coupling portions  26 A and  26 B on its front end face in confronting positions relative to the female and male coupling portions  16 B and  16 C on the side of the cartridge mount portion  16 , respectively. The container  26  is closed at its base or rear end, and provided with a knob  26 C of an outwardly diverging shape integrally at the rear end. This knob  26 C is adapted to be gripped by a cartridge gripper  100  which will be described in greater detail hereinafter. 
     The above-mentioned male and female coupling portions  26 A and  26 B serve to orient the container  26  into position in the circumferential direction when the latter is set in the cartridge mount portion  16 . These male and female coupling portions  26 A and  26 B also serve to orient the container  26  into position in the circumferential direction when the container is set on a container support portion  61  of a paint replenisher  55  which will be described hereinafter. 
     Indicated at  27  is a conical projection which is formed integrally at the fore end of the container  26 . This conical projection  27  is brought into abutting and fitting engagement with the conically converging portion  17 B when the container  26  of the paint cartridge  25  is set in the cartridge mount portion  16  of the housing  12 , for orienting the container  26  into position in both axial and radial directions. Also, the conical projection  27  is brought into abutting and fitting engagement with the inwardly converging conical portion  60 A which is formed on a feed tube passage hole  60  on the side of the replenishing stool, when the paint cartridge  25  is set in a container support portion  61  of a paint replenisher  55 , for orienting the container of the paint cartridge  25  into position in both axial and radial directions. 
     The feed tube  28  which is provided at the distal end of the conical projection  27  is internally provided with a coaxial paint supply passage  28 A, which has its base end connected to a paint reservoir chamber  30 , which will be described hereinafter, and has its fore end opened toward the rotary atomizing head  20 . Further, provided on the inner periphery of a fore end portion of the feed tube  28  is a valve seat  28 B which is formed by reducing the diameter of part of the above-mentioned paint supply passage  28 A. A valve member  35 B of the paint valve  35 , which will be described hereinafter, is seated on and off the valve seat  28 B. The feed tube  28  is arranged in such a length that its fore end is extended into the rotary atomizing head  20  when the paint cartridge  25  is set in position within the cartridge mount portion  16 . 
     In this instance, the feed tube  28  allows paint to flow into the paint supply passage  28 A from the paint reservoir chamber  30  and to flow out toward the rotary atomizing head  20  from the fore distal end of the paint supply passage  28 A. Further, at the time of replenishing paint into the paint reservoir chamber  30 , the fore distal end of the feed tube  28  is connected to a connector member  63  of a paint replenisher to serve as a replenishing port for the cartridge. 
     On the other hand, the piston  29  is axially slidably fitted in the container  26  to divide the internal space of the container  26  into a paint reservoir chamber  30 , which is in communication with the paint supply passage  28 A of the feed tube  28 , and a thinner chamber  31  to which thinner is supplied as a paint extruding liquid. 
     Indicated at  32  is a thinner passage on the side of the paint cartridge, the thinner passage  32  being extended axially through an outer peripheral portion of the container  26  and having one end opened in the distal end face of the male coupling portion  26 A of the container  26  and the other end communicated with the above-mentioned thinner chamber  31 . As thinner is supplied to the thinner chamber  31  through this thinner passage  32  on the side of the paint cartridge, the piston  29  is pushed toward the feed tube  28  thereby to extrude paint in the paint reservoir chamber  30  toward the rotary atomizing head  20 . 
     In this regard, thinner to be employed as a paint extruding liquid should be of a type which has electrically insulating properties or high electric resistance, in order to prevent the high voltage from the high voltage generator  22  from leaking through thinner. In case thinner is used as an extruding liquid, it contributes to retain inner wall surfaces of the container  26  always in a wet state as the piston  29  is displaced within the container  26 , preventing paint from getting dried up and solidifying on the inner wall surfaces and stabilizing frictional resistance between the piston  29  and the inner wall surfaces of the container  26  to ensure smooth movement of the piston  29 . Besides, it also contributes to enhance the tightness of the seal between the piston  29  and inner wall surfaces of the container  26 . 
     Indicated at  33  is a quick coupling which is provided within the male coupling portion  26 A of the container  26 , at an open end of the thinner passage  32  on the side of the paint cartridge. When the paint cartridge  25  is set in position within the cartridge mount portion  16 , bringing the male coupling portion  26 A into engagement with the female coupling portion  16 B, a valve in the quick coupling  33  is opened to communicate the thinner passage  32  on the side of the cartridge with the thinner passage  39  on the side of the housing which will be described hereinafter. On the other hand, when the container  26  is removed from the cartridge mount portion  16 , thereby disengaging the male coupling portion  26 A from the female coupling portion  16 B, the thinner passage  32  on the side of the paint cartridge is closed by the action of a valve spring to prevent thinner from flowing out of the thinner passage  32 . Also, the opening and closing operations of the quick coupling  33  are performed in case of loading or unloading the paint cartridge to the container support portion  61  of the replenishing stool  56  which will be described hereinafter. 
     Indicated at  34  is a paint valve accommodating portion which is provided in a front end portion of the container  26 , and at  35  a paint valve which is received in the paint valve accommodating portion  34 . In this instance, the paint valve  35  is constituted by an air-piloted directional control valve, including a piston  35 A which is slidably fitted in the paint valve accommodating portion  34  in such a way as to define a spring chamber and a pressure receiving chamber on its opposite sides, an elongated valve member  35 B which is connected to the piston  35 A at its base end and extended into the paint supply passage  28 A of the feed tube  28  at its fore end to seat on and off the valve seat  28 B, and a valve spring  35 C which is provided in the spring chamber of the paint valve accommodating portion  34  and adapted to act on the valve member  35 B through the piston member  35 A urging the valve member  35 C to seat on the valve seat  28 B . 
     Normally, the valve member  35 B of the paint valve  35  is seated on the valve seat  28 B of the feed tube  28  under the influence of the biasing action of the valve spring  35 C, thereby closing the paint supply passage  28 A and suspending paint supply to the rotary atomizing head  20 . On the other hand, as soon as pilot air is supplied to the pressure receiving chamber in the paint valve accommodating portion  34  from a pilot air source through a pilot air piping system (both not shown) via the pilot air passage  38  on the side of the housing and the pilot air passage  36  on the side of the paint cartridge, the valve member  35 B is unseated from the valve seat  28 B against the action of the valve spring  35 C to start supply of paint from the paint reservoir chamber  30  to the rotary atomizing head  20 . In this instance, one end of the pilot air passage  36  is opened in an inner peripheral surface of the female coupling portion  26 B of the container  26 , while the other end is communicated with the pressure receiving chamber of the paint chamber  34 . 
     Indicated at  37  is a thinner passage which is provided on the side of the housing  12 . The thinner passage  37  is extended axially through and within the neck portion  13  and bent backward in an L-shape at a position behind the female coupling portion  16 B. One end of this thinner passage  37  on the side of the housing is connected to a thinner supply device (not shown), while the other end is opened in a bottom portion of the female coupling portion  16 B on the cartridge mount portion  16 . The angularly bent portion of the thinner passage  37  on the side of the housing is arranged to provide a valve seat  37 A for seating and unseating a valve member  43 B of a thinner valve  43  which will be described hereinafter. 
     Denoted at  38  is a pilot air passage which is provided on the side of the housing  12 . One end of this pilot air passage  38  is connected to a paint valve pilot air source through pilot air piping (both not shown). The other end of the pilot air passage  38  is opened in a circumferential surface of the male coupling portion  16 C, which is provided at the bottom  16 A of the cartridge mount portion  16 , at a position which confronts the pilot air passage  36  on the side of the paint cartridge. 
     Indicated at  39  is an air suction passage which is provided in the housing  12  and opened in the bottom portion  16 A of the cartridge mount portion  16 . This air suction passage  39  is connected to a vacuum source through vacuum piping (both not shown). This air suction passage  39  functions to suck air out of a vacuum space  40 , which is formed at a deep portion of the cartridge mount portion  16  on the inner side of the container  26 , to fix the paint cartridge  25  in the cartridge mount portion  16  with suction force. 
     Further, indicated at  41  is an ejection air supply passage which is provided in the housing  12  and opened at the bottom  16 A of the cartridge mount portion  16 . This ejection air supply passage  41  is connected to an ejection air source through air piping (both not shown). Through this ejection air passage  41 , ejection air supplied to the vacuum space  40  to cancel the suction grip on the paint cartridge  25 , thereby permitting to dismantle the paint cartridge  25  from the housing. 
     Indicated at  42  is a thinner valve accommodating portion which is provided in the head portion  14  of the housing  12 , and at  43  a thinner valve which is provided in the thinner valve accommodating portion  42 . In this instance, substantially in the same manner as the paint valve  35 , the thinner valve  43  is arranged as an air-piloted directional control valve, including a piston  43 A which is slidably fitted in the thinner valve accommodating portion  42  in such a way as to define a spring chamber and a pressure receiving chamber on its opposite sides, a valve member  43 B which is connected to the piston  43 A at its base end and extended into the thinner passage  37  on the side of the housing at its fore end to be seated on and off the valve seat  37 A, and a valve spring  43 C which is provided in the valve chamber of the thinner valve accommodating portion  42  and adapted to act on the valve member  43 B through the piston  43 A, urging the valve member  43 B into a seated position. 
     Normally, the valve member  43 B of the thinner valve  43  is seated on the valve seat  37 A in the thinner passage  37  on the side of the housing under the influence of the biasing action of the valve spring  43 C, thereby closing the thinner passage  37  to suspend thinner supply to the thinner chamber  31 . On the other hand, as soon as pilot air is supplied to the pressure receiving chamber from the thinner valve pilot air source via pilot air piping (both not shown) and through the pilot air passage  44 , the valve member  43 B is unseated from the valve seat  37 A against the action of the valve spring  43 C to start thinner supply to the thinner chamber  31 . In this instance, one end of the pilot air passage  44  is connected to the thinner valve pilot air source through pilot air piping, while the other end is communicated with the pressure receiving chamber of the thinner valve accommodating portion  42 . 
     Referring now to FIGS. 5 to  7 , there is shown a cartridge changer which is arranged to store a plural number of paint cartridges for different paint colors and to replaceably mount a selected one of the paint cartridges on the coating apparatus, in the manner as described below. 
     Namely, indicated at  51  is the cartridge changer according to the present embodiment of the invention. This cartridge changer  51  is located outside the working area of the coating robot  1  and in the vicinity of a washing apparatus  103  which will be described hereinafter. The cartridge changer  51  is largely constituted by a paint replenishers  55 , a cartridge transfer system  77  and a cartridge gripper  100  as described below. 
     Indicated at  52  is a deck which provides a main frame structure of the cartridge changer  51 , and which is largely constituted by four legs  53  which are erected in spaced positions in four corner portions of the rack, and a rectangular deck plate  54  which is supported on the legs  53  at its four corners and at vertically intermediate portions of the legs. 
     Indicated at  55   a,    55   b,  . . .  55   n  are paint replenishers for paint colors a, b, . . . n (hereinafter referred to collectively as “paint replenisher  55 ” for brevity) which are provided on the rectangular deck plate  54  of the deck  52 . As shown in FIG. 6, the paint replenishers  55  are arranged in rows and columns. Each one of the paint replenishers  55  are largely constituted, as will be described in greater detail hereinafter, by a replenishing stool  56 , a feed tube passage hole  60  on the part of the replenishing stool, a connecting member  63 , and a replenishing valve  65 . 
     In this instance, the respective paint replenishers  55  are located under a longitudinal transfer mechanism  78  and a transverse transfer mechanism  86  of the cartridge transfer system  77  and outside a working area of the coating robot  1 . Paint cartridges are handed over to and from the paint replenishers  55  and the coating apparatus  11  of the coating robot  1  by the cartridge transfer system  77 , and each paint cartridge  25  is mounted into and dismantled from the housing  12  of the coating apparatus  11  by the cartridge gripper assembly  100  which is provided on a vertical lift mechanism  93 . 
     Designated at  56   a,    56   b,  . . .  56   n  are replenishing stools which constitute the respective paint replenishers  55  of different colors (hereinafter referred to collectively as replenishing stools  56 ). As shown in FIG. 8, each one of the replenishing stools  56  is largely constituted by a foot portion  57  which is fixed on the deck plate  54  of the deck  52  by the use of bolts or other fixation means, a column portion  58  which is extended vertically upward from the foot portion  57 , and a seating block portion  59  which is formed by bulging an upper end portion of the column portion  58 . 
     Indicated at  60  is the feed tube passage hole on the side of the replenishing stool, which is formed internally of and vertically through the column portion  58  of the replenishing stool  56  to receive therein the feed tube  28  of the paint cartridge  25 . Provided at the upper end of the feed tube passage hole  60  on the part of the replenishing stool is an inwardly converging conical portion  60 A which serves to hold the container  26  in position on the replenishing stool in axial and radial direction, by coupling engagement with the conical projection  27  at the fore end of the container  26 . 
     Indicated at  61  is the container support portion which is provided at one axial end (on the upper side) of the seating block portion  59  to support the container  26  of the paint cartridge  25  therein. This container support portion  51  is in the form of a recessed cylindrical cavity in communication with the upper open end of the feed tube passage hole  60  on the side of the replenishing stool. As seen in FIG. 9, female and male connector portions  61 B and  61 C are separately formed at the bottom  61 A of the container support portion  61  for fitting engagement with the male and female coupling portions  26 A and  26 B on the part of the container  26 , respectively. These female and male connector portions  61 B and  61 C serve to set the container  26  in a predetermined position in the circumferential direction when the container  26  is mounted on the container support portion  61 . 
     Indicated at  62  is a connector receptacle bore which is formed in an axially opposite end portion of the replenishing stool  56 , at a deeper position than the feed tube passage hole  60 . Namely, the connector receptacle bore  62  is in the form of a cylindrical cavity which is formed by widening the diameter of a deeper portion of the feed tube passage hole  60 . The lower end of the connector receptacle bore  62  is reduced in diameter in the downward direction through a stepped portion  62 A. 
     Denoted at  63  is a connector member which is vertically movably provided in the connector receptacle bore  62 . The connector member  63  is formed in the shape of a tube, which internally defines a paint passage  63 A and which is provided with a flange-like spring seat  63 B of an increased diameter at the upper end thereof. The paint passage  63 A of the connector member  63  is brought into liquid-tight fitting engagement with a fore end portion of the feed tube  28  at the time of supplying paint into the container  26  through the feed tube  28 . Further, the paint passage  63 A is connected to a replenishing valve  65  through a hose  67  as will be described hereinafter. 
     Indicated at  64  is a coil spring which is provided around the outer periphery of the connector member  63 . More particularly, the coil spring  64  is interposed between the spring seat  63 B of the connector member  63  and the stepped portion  62 A of the connector receptacle bore  62  to bias the connector member  63  in the upward direction toward the feed tube passage hole  60  on the side of the replenishing stool. 
     Thus, the connector member  63  is movable vertically in the upward and downward directions, and constantly urged toward the feed tube  28  by the biasing action of the coil spring  64 . Therefore, even if the feed tube  28  is located in a deviated position in the upward or downward direction, the positional deviation of the feed tube  28  can be absorbed by an upward or downward movement of the connector member  63 . Besides, by the action of the coil spring  64 , the feed tube  28  can be securely brought into fitting engagement with the connector member  63 . 
     Indicated at  65  is a replenishing valve which is connected to the connector member  63 . The replenishing valve  65  is connected to a paint supply line (not shown) of a paint source on its upstream side through a paint conduit  66 . The downstream side of the paint replenishing valve  65  is connected to the connector member  63  through a flexible paint hose  67  which constitutes a paint supply passage. The replenishing valve  65  is normally closed, and opened at the time of paint replenishment to a paint cartridge  25 , permitting paint from the paint supply line to flow toward the connector member  63 . 
     Indicated at  68  is a thinner discharge passage which is provided in the seating block portion  59  of the replenishing stool  56 . This thinner discharge passage  68  is opened at one end thereof into the female coupling portion  61 B of the container support portion  61 , and connected at the other end to a thinner reservoir tank (not shown) through a thinner conduit  69 . Through the thinner discharge passage  68 , the thinner which flows out of the thinner chamber  31  of the paint cartridge  25  at the time of paint replenishment is discharged to the thinner reservoir tank. 
     Indicated at  70  is a pilot air passage on the side of the replenishing stool, which is provided in the seating block portion  59 . One end of the pilot air passage  70  is connected to a paint valve pilot air source (not shown) through a pilot air conduit  71 . The other end of the pilot air passage  70  is opened in a circumferential surface of the male coupling portion  61 C of the container support portion  61  in a confronting position relative to the pilot air passage  36  on the side of the paint cartridge. Consequently, when the paint cartridge  25  is mounted on the container support portion  61  of the replenishing stool  56 , the pilot air passage  70  on the side of the replenishing stool is communicated with the pilot air passage  36  on the side of the paint cartridge to supply pilot air from the paint valve pilot air source to the paint valve  35 . 
     Indicated at  72  is an air suction passage which is provided in the seating block portion  59  and opened in a bottom portion  61 A of the container support portion  61 . This air suction passage  72  is connected to a vacuum source (not shown) through a vacuum conduit  73 . Through the air suction passage  72 , air is sucked out of a vacuum space  74  which is formed between a deep bottom portion of the container support portion  61  and the container  26  of the paint cartridge  25 , so that the paint cartridge  25  is fixedly gripped in the container support portion  61  by suction force. 
     Designated at  75  is an ejection air supply passage which is also provided in the seating block portion  59  and opened in a bottom portion  61 A of the container support portion  61 . This ejection air supply passage  75  is connected to an ejection air source (not shown) through an air conduit  76 . At the time of dismantling the paint cartridge  25  from the container support portion  61 , air is supplied from the ejection air passage  75  to the vacuum space  74  thereby to release the paint cartridge  25  from the paint replenisher  56 . 
     Indicated at  77  is a cartridge transfer system which is provided over the deck  52  to transfer a cartridge gripper unit  100 , which will be described hereinafter, in the directions of three perpendicularly intersecting axes, namely, in longitudinal, transverse and vertical directions of the deck  52 . For this purpose, the cartridge transfer system  77  is largely constituted by a longitudinal transfer mechanism  78 , a transverse transfer mechanism  86  and a vertical transfer mechanism  93 . By way of these three transfer mechanisms of the cartridge transfer system  77 , a paint cartridge  25  is transferred and handed over to and from the paint replenisher  55  and the coating apparatus  11  which is mounted on the coating robot  1 . 
     Designated at  78  is a first or longitudinal transfer mechanism which is mounted on top of the legs  53  of the deck  52 . In this instance, as shown in FIGS. 5 to  7 , the longitudinal transfer mechanism  78  is largely constituted by: front and rear rail support beams  79  which are extended in parallel relation between and securely fixed on right and left legs  53  on the front and rear sides of the arrayed paint cartridges  25  of the paint replenishers  55 , respectively; a pair of longitudinal rails  80  which are provided on each one of the front and rear rail support beams  79 ; a couple of sliders  81  which are mounted on the longitudinal rail support beams  79  for movements longitudinally in the rightward and leftward directions on and along the longitudinal rails  80 ; a pair of pulleys  82  which are rotatably mounted on right and left end portions of each longitudinal rail support beam  79 ; elongated timing belts  83  which are respectively extended in the longitudinal direction and around the pulleys  82  and securely connected to the sliders  81  at a predetermined portion; a connecting rod  84  which is extended in the transverse direction to connect the pulleys  82  on the right ends of the rail support beams  79 ; and a drive mechanism  85  for moving the sliders  81  in the rightward and leftward directions along the rails  80 . 
     In this instance, the drive mechanism  85  includes another pulley  85 A which is mounted on the connecting rod  84 , and a drive motor  85 C which is connected to the pulley  85 A through a short timing belt  85 B. 
     According to the extent of rotation of the drive motor  85 C of the drive mechanism  85 , the sliders  81  of the longitudinal transfer mechanism  78  are moved through the timing belts  83  either in the rightward direction or in the leftward direction along the longitudinal guide rails  80 . As a consequence, the cartridge gripper unit  100  is moved to the right or to the left through the transverse transfer mechanism  86  and the vertical transfer mechanism  93  which are supported on the respective sliders  81 . 
     Indicated at  86  is the second or transverse transfer mechanism which is provided on the longitudinal transfer mechanism  78 . In this instance, the transverse transfer mechanism  86  is largely constituted by: a transverse rail support beam  87  which is extended in the transverse direction and supported on the sliders  81  of the longitudinal transfer mechanism  78  at its opposite ends; a pair of transverse guide rails  88  which are provided on the transverse rail support beam  87 ; a slider  89  which is movably mounted on the transverse guide rails  88  for movements therealong; a male screw member  90  which is rotatably mounted on the transverse rail support beam  87  and extended between and along said transverse guide rails  88 ; a female screw member  91  which is mounted on the slider  89  and held in threaded engagement with said male screw member  90  through a large number of steel balls (not shown) to form a ball screw together with the male screw member  90 ; and a drive mechanism  92  for moving the slider  89  back and forth along the transverse guide rails  88 . 
     In this instance, the drive mechanism  92  is constituted by a pulley  92 A which is mounted on an end portion of the male screw member  90 , and a drive motor  92 C which is connected to the pulley  92 A through a timing belt  92 B. 
     According to the extent of rotation of the drive motor  92 , the male screw member  90  is turned relative to the female screw member  91  to move the slider  89  along the transverse guide rails  88  of the transverse transfer mechanism  86 . Accordingly, the transverse transfer mechanism  86  moves the cartridge gripper assembly  100  in a transverse direction through the vertical transfer mechanism  93  which is mounted on the slider  89 . 
     Indicated at  93  is the third or vertical transfer mechanism which is mounted on the transverse transfer mechanism  86 . In this instance, the vertical transfer mechanism  93  is largely constituted by: a post  94  which is fixedly attached to the slider  89  of the transverse transfer mechanism  86  and extended in vertical direction; a pair of vertical guide rails  95  which are provided on the post  94 ; a slider  96  which is movably mounted on the vertical guide rails  95  for movements therealong; and a drive mechanism  97  for moving the slider  96  along the vertical guide rails  95 . 
     In this instance, the drive mechanism  97  is largely constituted by a piston-cylinder  97 A which is mounted on the post  94  and internally provided with a free piston (not shown) for sliding movements therein; and a lift member  97 B which is provided on the outer peripheral side of the cylinder  97 A and adapted to move up and down following movement of the free piston. The lift member  97 B is connected to the slider  96 . In this manner, the drive mechanism  97  is arranged as a rodless cylinder which can stop the slider  96  in predetermined upper and lower positions. 
     Thus, the slider  96  of the vertical transfer mechanism  93  is moved in upward and downward directions along the vertical guide rails  95  as the lift member  97 B of the drive mechanism  97  is moved along the cylinder  97 A. As a consequence, the cartridge gripper assembly  100  which is attached to the slider  96  is moved vertically in the upward or downward direction along with the slider  96  of the vertical transfer mechanism  93 . 
     Indicated at  98  is one shock absorber which is constituted, as shown in FIG. 10, by a rectangular top plate  98 A which is projected froward from the front side of the slider  96 , four rod members  98 B which are pendant from the top plate  98 A and are loosely fitted in the top plate  98 A for vertical movements relative to the latter, a bottom plate  98 C which is securely fixed to lower ends of the rod members  98 B, and coil springs  98 D which are fitted around the rod members  98 B between the top and bottom plates  98 A and  98 C. Attached to the bottom plate  98 C is one of gripper members  101  of the cartridge gripper assembly  100 . 
     Further, indicated at  99  is the other shock absorber which is provided side by side with the above-described one shock absorber  98 . Similarly to the first-described shock absorber  98 , the other shock absorber  99  is constituted by top plate  99 A, rod members  99 B, bottom plate  99 C and coil springs  99 D. Attached to the bottom plate  99 C is the other one  102  of the gripper members of the cartridge gripper assembly  100 . 
     The shock absorbers  98  and  99  are located between the vertical transfer mechanism  93  and the gripper members  101  and  102  of the cartridge gripper assembly  100 . Therefore, at the time when the grippers  101  and  102  are lowered toward and abutted against paint cartridges  25  by the vertical transfer mechanism  93 , the shock absorbers  98  and  99  permit upward displacements of the grippers  101  and  102  to buffer impacts of abutting contact. In addition, the shock absorbers  98  and  99  permit downward displacements of the grippers  101  and  102  to absorb relative positional deviations of paint cartridges  25 , if any. 
     The cartridge gripper assembly  100  is mounted on the vertical transfer mechanism  93  through the shock absorbers  98  and  99  as cartridge gripper means, and largely constituted by a couple of gripper members  101  and  102  to simultaneously grip a couple of paint cartridges  25  side by side. 
     Indicated at  101  is one of the gripper members, which is supported on the vertical transfer mechanism  93  through one shock absorber  98 . This one gripper member  101  is attached to the bottom plate  98 C of one shock absorber  98 , and largely constituted by a drive section  101 A which has an actuator (not shown) built into its housing, and a pair of gripper claws  101 B which are provided in the drive section  101 A and adapted to be moved toward and away from each other by the actuator. The gripper claws  101 B of the first gripper member  101  are moved toward or away from each other by the actuator of the drive section  101 A at the time of gripping or releasing a knob portion  26 C of a container  26 . 
     The other or second gripper member  102  which is provided wide by side with the first gripper member  101  is similarly constituted by a drive section  102 A which is mounted on the lower side of the bottom plate  99 C of the other shock absorber  99 , and a pair of gripper claws  102 B which are provided on the drive section  102 A. 
     On the other hand, indicated at  103  is a washer which is located within a working area of the coating robot  1  and in the vicinity of the cartridge changer  51 , for the purpose of washing clean the rotary atomizing head  20 . In this instance, the washer  103  is largely constituted by a waste liquid recovering container  104  to be located under the coating apparatus  11  when the coating apparatus  11  is moved to a predetermined cartridge replacing position, and washing nozzles  105  which is provided within the waste liquid recovering container  104  to spurt out a wash liquid toward the rotary atomizing head  20  in a washing step of a coating operation. 
     More particularly, after the coating apparatus  11  is located in a cartridge replacing position of the cartridge changer  51  and the housing  12  of the coating apparatus  11  is located within the waste liquid recovering container  104 , a wash fluid is spurted toward the front end of the rotary atomizing head  20  from the washing nozzles  105  of the washer  103 . 
     With the arrangements as described above, the automatic coating apparatus according to the present embodiment can perform coating and cartridge (color) changing operations automatically, in the manner as described below with reference to FIGS. 11 through 18 and to the time chart of FIG.  19 . In the operational conditions as illustrated in FIGS.  11  through  18 , the two grippers  101  and  102  are located in overlapping positions and only one of the two grippers  101  and  102 , which is on the proximal side, is visible. However, the two grippers  101  and  102  are shown separately in these figures for the purpose of explaining movements of the respective grippers. 
     Firstly, in the case of a coating operation, the automatic coating apparatus is operated according to an uploaded coating program, which specifies the order of paint colors to be used in the coating operation. Therefore, concurrently with a coating operation with a first paint color, the cartridge changer  51  is operated to pick up a replenished paint cartridge  25  of a next color from the paint replenisher  55  to attain higher efficiency of cartridge replacing work. 
     Firstly, in a coating step, the arms  3  and  4  of the coating robot  1  are operated as shown in FIG. 11 to turn the coating apparatus  11  with a paint cartridge  25   a  of color a, for example, toward a coating object  106 . In this state, the air motor  19  is actuated, thereby putting the rotary atomizing head  20  in high speed rotation, spurting out shaping air through the shaping air outlet holes  21 A on the shaping air ring  21 , and applying a high voltage to the paint from the high voltage generator  22 . Then, thinner is supplied as a paint extruding liquid quantitatively to the thinner chamber  31  in the container  26 , thereby pushing forward the piston  29  to supply the paint of color a from the paint reservoir chamber  30  to the rotary atomizing head  20  through the feed tube  28 . As a result, the paint is sprayed in finely atomized particles from the rotary atomizing head  20  toward the coating object  106 . 
     Now, in order to change to paint color from a to b, the cartridge changer  51  is operated to pick up a replenished paint cartridge  25   b  of next color bconcurrently with a coating operation with a preceding color a as mentioned hereinbefore. 
     In the step of picking up a replenished paint cartridge of a next color, the longitudinal and transverse transfer mechanisms  78  and  86  of the cartridge changer  51  to locate one gripper member  101  of the cartridge gripper assembly  100 , which is supported on the vertical transfer mechanism  93 , in a position over the paint cartridge  25   b  which is supported on the replenishing stool  56 b of the paint replenisher  55   b.  Then, the vertical transfer mechanism  93  is operated to lower the gripper member  101  along with the slider  96  toward the paint cartridge  25   b  and to grip the knob portion  26 C of the paint cartridge  25   b  by the gripper claws  101 B of the gripper member  101 . 
     When the cartridge gripper assembly  100  is lowered by the vertical transfer mechanism  93  as described above, one gripper member  101  is abutted against the paint cartridge  25   b.  At this time, however, one shock absorber  98  buffers the impacts of abutment by letting the gripper member  101  move in the upward direction. The shock absorber  98  which permits vertical upward or downward movement of the gripper member  101  also contributes to absorb a vertical positional deviation of the paint cartridge  25   b,  if any. The same applies to the other shock absorber  99  as well as the other gripper member  102 . 
     As soon as the paint cartridge  25   b  is gripped by one gripper member  101 , the cartridge gripper assembly  100  is lifted up by the vertical transfer mechanism  93 . As a result, the replenished paint cartridge  25   b  is picked up from the replenishing stool  56   b  by one gripper member  101 . Then, through the longitudinal and transverse transfer mechanisms  78  and  86 , the gripper member  101  which grips the replenished paint cartridge  25   b  of color b in one gripper member  101  is further transferred until the other gripper member  102  is located in a standby position over the washer  103  as shown in FIG.  12 . 
     A step of coating color a is followed by a washing step to wash off deposited color a from the coating apparatus  11 . For this purpose, as shown in FIG. 13, the coating robot  1  is operated to move the coating apparatus  11  to a position above the washer  103 , thereby putting the rotary atomizing head  20  of the coating apparatus  11  in the waste liquid recovering container  104  of the washer  103 . As a result, the coating apparatus  11  is located in a cartridge replacing position over the washer  103 . 
     Then, the fore end of the coating apparatus  11  on the side of the rotary atomizing head  20  is inserted into the waste liquid recovering container  104  of the washer  103  to wash the rotary atomizing head  20  clean. In this washing step, as shown in FIG. 14, a wash fluid is spurted out from the respective washing nozzles  105  to wash away deposited previous color a from fore end portions of the housing  12  and rotary atomizing head  20 . 
     As a consequence, the wash fluid which is spurted out from the wash nozzles  105  is supplied to the front side of the rotary atomizing head  20  to wash off deposited paint P 1  of color a from the paint spreading surfaces  20 C. Further, part of the wash fluid is allowed to flow into the paint reservoir  20 D through the respective wash fluid inlet holes  20 E to wash off deposited paint P 2  of color a on inner wall surfaces of the bell cup  20 A as well as deposited paint P 3  of color a on fore end portions of the feed tube  28 . 
     At the end of the washing step, after washing off the previous color a, air is supplied to the vacuum space  40  between the housing  12  and the paint cartridge  25   a  to cancel the suction air grip on the paint cartridge  25   a.    
     Following the above-described washing step is an empty paint cartridge unloading step as shown in FIG. 15, in which the empty paint cartridge  25   a  is unloaded from the housing  12 . More specifically, in this step, the cartridge gripper assembly  100  which grips the replenished paint cartridge  25   b  in one gripper member  101  is lowered by the vertical transfer mechanism  93  to grip the empty cartridge  25   a  on the coating apparatus  11  in the other gripper member  102 . In this state, the cartridge gripper assembly  100  is lifted up by the vertical transfer mechanism  93  as shown in FIG. 15 to extract the empty paint cartridge  25   a  out of the housing  12  of the coating apparatus  11  by the other gripper member  102 . 
     After removing the empty paint cartridge  25   a  from the housing  12  in this manner, the cartridge gripper assembly  100  is moved in a transverse direction by the transverse transfer mechanism  86  as shown in FIG. 16 to locate the replenished paint cartridge  25   b  in one gripper member  101  in a position above the cartridge mount portion  16  of the housing  12 . 
     The empty paint cartridge unloading step is followed by a replenished cartridge loading step as illustrated in FIG.  17 . In the replenished paint cartridge loading step, the cartridge gripper assembly  100  which still grips the empty cartridge  25   a  in the other gripper member  102  is lowered by the vertical transfer mechanism  93 . As a result, as seen in FIG. 17, the replenished paint cartridge  25   b  which is gripped in one gripper member  101  is fitted and set in the cartridge mount portion  16  of the housing  12 . At this time, air in the vacuum space  40  is sucked out through the air suction passage  39  to grip the paint cartridge  25   b  fixed in the housing  12  by vacuum force. 
     As soon as the paint cartridge  25   b  of color bis loaded in the cartridge mount portion  16  of the coating apparatus  11 , the operation advances to an empty paint cartridge returning step as illustrated in FIG.  18 . In the empty paint cartridge returning step, the empty paint cartridge  25   a  which has been unloaded from the coating apparatus  11  is returned to a replenishing stool  56   a  of the paint replenisher  55   a  as shown in FIG.  18 . At this time, the feed tube  28  of the empty paint cartridge  25   a  is placed in the feed tube passage hole  60  on the side of the replenishing stool, and its container  26  is set on the container support portion  61  of the stool. Further, a fore end portion of the feed tube  28  is fitted into the connector member  63  and therefore becomes communicable with the paint hose  67 . 
     In the meantime or concurrently with the empty paint cartridge returning step, a coating operation is carried out by the coating apparatus  11  which is loaded with the replenished paint cartridge  25   b  of color b. Therefore, the coating apparatus  11  with the fresh and replenished paint cartridge  25   b  is moved to a coating standby position by the coating robot  1  to start coating in color b as soon as a coating object  106  is transferred to a predetermined position. 
     Now, the description is directed to a paint replenishing step of the operation. In this step, paint is replenished into a cartridge immediately before a coating operation by that cartridge for the purpose of preventing separation and sedimentation of pigment components in the paint. Therefore, the timing for starting replenishment varies widely depending upon the frequency at which a particular paint color is used or other factors. In this particular embodiment, a paint replenishing operation is started by way of example at a time interval from the end of the empty paint cartridge returning step as described above. 
     The paint replenishing step is started by opening the replenishing valve  65  of the paint replenisher  55   a  as shown in FIG. 9 to supply and replenish paint of color a into the container  26  of the paint cartridge  25   a  through the paint hose  67  and the paint passage  63 A of the connector member  63  and through the fore end of the feed tube  28 . 
     In this manner, according to the present embodiment, for example, a replenished paint cartridge  25   b  of a next color b is gripped in one gripper member  101  prior to cartridge replacement. Therefore, the replenished paint cartridge  25   b  on one gripper member  101  can be loaded on the coating apparatus  11  immediately after unloading the empty paint cartridge  25   a  from the coating apparatus  11  by the other gripper member  102 . It follows that, in replacing the paint cartridge  25 , it suffices for the cartridge transfer system  77  to reciprocate the cartridge gripper assembly  100  between the paint replenisher  55  and the coating apparatus  11  just for once each time. Therefore, it becomes possible to shorten the time period required for the cartridge replacement, and to enhance the productivity. 
     Besides, the cartridge changer  51  is constituted by the paint replenishers  55   a,    55   b,  . . .  55   n  which are arranged to support the paint cartridges  25   a,    25   b,  . . .  25   n  of various colors in rows and columns, the cartridge transfer system  77  which is located above the paint replenisher  55  and adapted to transfer the paint cartridge  25  in longitudinal, transverse and vertical directions, and the cartridge gripper assembly  100  which is provided on the cartridge transfer system  77  and adapted to pick up replenished and empty paint cartridges. Thus, the cartridge changer  51  has the paint cartridges  25  located efficiently in rows and columns so that it can be reduced in size and installed compactly in a small space. Besides, since the cartridge gripper assembly  100  is moved by the cartridge transfer system  77 , smaller motors can be used for the drive motors  85 C and  92 C for the purpose of cost reductions. 
     In addition, the cartridge changer  51  utilizes the stools  56  of the respective paint replenishers  55  as seats for the paint cartridges  25 . Therefore, when an empty paint cartridge  25  is returned to the cartridge changer  51 , it can be replenished with paint by a paint replenisher  55  without a need for a transfer, for example, to a separately located paint replenisher. 
     Further, the vertical transfer mechanism  93  is provided with the shock absorbers  98  and  99  on the slider  96 , so that, as the gripper members  101  and  102  of the cartridge gripper assembly  100  are lowered and abutted against the paint cartridge  25 , the impacts of abutment are buffered by the shock absorbers  98  and  99  to lessen abrasive wear or damages and to enhance the durability of contacting parts. Additionally, since the shock absorbers  98  and  99  can absorb deviations in vertical position of the cartridge  25 , the vertical transfer mechanism  93  suffices to be a two-position control type which is less costly. 
     Further, the washer  103  for washing the rotary atomizing head  20  of the coating apparatus  11  is located at a cartridge replacement position of the cartridge exchanger  51 , so that deposited previous color on the rotary atomizing head  20  can be washed off at the time of each cartridge replacement in such a way as to enhance working efficiency. 
     Although in the foregoing embodiment the rotary atomizing head type coating apparatus  11  is mounted on the coating robot  1  which is typical of working mechanisms, it is to be understood that the present invention is not limited to the particular arrangement shown. For example, the coating apparatus  11  may be mounted on a reciprocator or other working mechanisms if desired. 
     Further, in the foregoing embodiment, the cartridge transfer system  77  is systematically provided with transfer mechanisms for transferring the cartridge gripper assembly  100  in the longitudinal, transverse and vertical directions, including the longitudinal transfer mechanisms  78 , the transverse transfer mechanism  86 , and the vertical transfer mechanism  93  which is supported on the transverse transfer mechanism  86 . However, in this regard, it is to be understood that the present invention is not restricted to the particular arrangements shown. For example, there may be employed a modified cartridge transfer system, in which the longitudinal transfer mechanism is mounted on the transverse transfer mechanism and the vertical transfer mechanism is mounted on the longitudinal transfer mechanism. 
     Further, although in the foregoing embodiment thinner is employed for pushing the piston  29  in the paint cartridge  25 . However, water or other extruding liquid may be employed depending upon properties of paint or upon the type of the high voltage application system. 
     On the other hand, to cope with coating operations in which one and same color is coated continuously, the cartridge changer may be modified to hold two or more paint cartridges  25  for each color or for a particular color. 
     Industrial Applicability 
     As described in detail hereinbefore, the automatic coating method according to the present invention is comprised of: coating step of a coating object by a coating apparatus loaded with a replenished paint cartridge and operated through a working mechanism; a step of picking up a replenished paint cartridge of a color to be used in a next coating operation from a paint replenisher means by the use of one of gripper members of a cartridge gripper means; a step of unloading an empty paint cartridge from the coating apparatus by the use of the other one of the gripper members of the gripper means with the replenished paint cartridge still gripped in one gripper member; a step of loading the replenished paint cartridge on the coating apparatus by one gripper member of the cartridge gripper means with the empty paint cartridge on the other gripper member; and a step of returning the unloaded empty paint cartridge to a paint replenisher. Accordingly, an empty paint cartridge on the coating apparatus can be replaced by a replenished paint cartridge in an efficient manner, i.e., by reciprocating the cartridge gripper means only for once between the coating apparatus and a paint replenishing means. 
     Further, as described hereinbefore, the automatic coating apparatus according to the present invention employs a cartridge changer, which is comprised of: a paint replenishing means having a number of paint replenisher units for different paint colors, each adapted to support and replenish a paint cartridge of a corresponding color; a cartridge transfer means adapted to transfer paint cartridges in the directions of three perpendicularly intersecting axis; and a cartridge gripper means supported on the cartridge transfer means and adapted to grip and transfer paint cartridges between the coating apparatus and the paint replenishing means. Therefore, when the coating apparatus with an empty or consumed paint cartridge is located at a predetermined cartridge replacing position for cartridge replacement after finishing a coating operation in one color, the cartridge gripper means is moved by the cartridge transfer means to hand over a paint cartridge to and from the coating apparatus and the paint replenishing means. In addition, the empty paint cartridge is supported by and replenished with paint by the paint replenishing means in preparation for next use.