INSPECTION METHOD

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a technique for an electrostatic coating apparatus and, more particularly, to a technique for inspecting the grounding condition of an object having a low electrical conductivity.

2. Description of Related Art

[0002] In an existing art, there is known a technique that, when a component having a low electrical conductivity, such as a resin component, is electrostatically coated, a conductive primer that is a material for imparting electrical conductivity to the component is applied onto a coated surface to ensure electrical conductivity and then the component is electrostatically coated. Then, after the conductive primer is applied, it is necessary to check whether the electrical conductivity is ensured (that is, whether the component is grounded), so an exclusive device for checking the grounding condition is generally provided in a coating line for electrostatically coating the component. The technique for such a device for checking the grounding condition is, for example, described in Japanese Patent Application Publication No. 2005-58998 (JP-A-2005-58998) and is publicly known.

[0003] In the related art described in JP-A-2005-58998, a device for inspecting the grounding condition of a coated surface of an electrostatically coated object. The device includes an electric charge application device that applies electric charge to the coated surface in a noncontact manner; an electric charge amount measurement sensor that measures the amount of electric charge of the coated surface of the coated object, to which electric charge is applied, in a noncontact manner; and a determining device that determines whether the amount of electric charge measured by the electric charge amount measurement sensor falls within a predetermined range.

[0004] However, the inspection device according to the related art described in JP-A-2005-58998 is an exclusive device for checking the grounding condition and needs to provide an additional process for inspecting the grounding condition, so this leads to a long coating line, a long period of coating time, an increase in cost of coating equipment, and the like.

SUMMARY OF THE INVENTION

[0005] The invention provides an electrostatic coating apparatus and grounding condition inspection method that are able to inspect a grounding condition in a short period of time without using an exclusive device for inspecting the grounding condition.

[0006] A first aspect of the invention provides an electrostatic coating apparatus. The electrostatic coating apparatus includes: a coating gun that is used to spray a coating material toward an object; a robot arm that displaceably supports the coating gun; a high-voltage generating device that generates high voltage to be applied to the coating gun, and that adjusts the generated high voltage in such a manner that a discharge current generated when an electric field is formed between the coating gun and the object is detected, wherein, in a state where a coating material is not sprayed toward the object by the coating gun, an electric field is formed from the coating gun toward the object to charge the object with electric charge, and in a state where high voltage is not applied to the coating gun by the high-voltage generating device, the high-voltage generating device is used to detect the discharge current generated between the coating gun and the object on the basis of the electric charge that is charged on the object.

[0007] According to the above aspect, the grounding condition of the object may be inspected without using an exclusive device. In addition, by so doing, it is possible to reduce the length of the coating line, the inspection time, the cost of coating equipment, and the like. [0008] In the first aspect, when the high-voltage generating device is used to detect the discharge current generated between the coating gun and the object on the basis of the electric charge that is charged on the object in a state where high voltage is not applied to the coating gun by the high-voltage generating device, a distance between the coating gun and the object may be set so as to be shorter than a coating distance during electrostatic coating.

[0009] According to the above aspect, the surface potential of the object is further reliably detected to make it possible to improve the inspection accuracy of the grounding condition.

[0010] In the first aspect, when the electric field is formed from the coating gun toward the object to charge the object with electric charge, a displacement distance of the coating gun may be set so as to be shorter than a displacement distance of the coating gun during electrostatic coating.

[0011] According to the above aspect, a time during which electric charge is applied is reduced to make it possible to reduce an inspection time.

[0012] In the first aspect, when the high-voltage generating device is used to detect the discharge current generated between the coating gun and the object on the basis of the electric charge that is charged on the object in a state where high voltage is not applied to the coating gun by the high -voltage generating device, a displacement distance of the coating gun may be set so as to be shorter than a displacement distance of the coating gun during electrostatic coating.

[0013] According to the above aspect, a time during which the surface potential is detected is reduced to make it possible to reduce an inspection time.

[0014] An electrostatic coating apparatus may include the two first and second electrostatic coating apparatuses according to the first aspect, and the electric field may be formed from the coating gun of the first electrostatic coating apparatus toward the object to charge the object with electric charge, and the high-voltage generating device of the second electrostatic coating apparatus may be used to detect the discharge current generated between the coating gun of the second electrostatic coating apparatus and the W 2 object on the basis of the electric charge that is charged on the object.

[0015] According to the above aspect, a waiting time after application of electric charge is reduced to make it possible to further reduce an inspection time.

[0016] A second aspect of the invention provides a grounding condition inspection method that, after a conductive primer is applied onto an object, high voltage is applied to the object and a surface potential of the object is measured to inspect a grounding condition of the object. The grounding condition inspection method includes: using at least one electrostatic coating apparatus to apply high voltage to the object and to measure the surface potential of the object.

[0017] According to the above aspect, the grounding condition of the object may be inspected without using an exclusive device. In addition, by so doing, it is possible to reduce the length of the coating line, the inspection time, the cost of coating equipment, and the like.

[0018] In the second aspect, the first and second electrostatic coating apparatuses may be used, and the first electrostatic coating apparatus may be used to apply high voltage to the object, and the second electrostatic coating apparatus may be used to measure the surface potential of the object.

[0019] According to the above aspect, a waiting time after application of electric charge is reduced to make it possible to further reduce an inspection time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic view that shows the overall configuration of an electrostatic coating apparatus according to a first embodiment of the invention;

FIG. 2 is a schematic view that shows a state where an electric field is formed from the electrostatic coating apparatus according to the first embodiment of the invention toward an object; FIG. 3 is a schematic view that shows the configuration of a high-voltage generating device of the electrostatic coating apparatus according to the first embodiment of the invention;

FIG. 4A and FIG. 4B are schematic views that show a state where a grounding condition is inspected by the single electrostatic coating apparatus according to the first embodiment of the invention, in which FIG. 4A is a schematic view that shows a state where a voltage is applied and FIG. 4B is a schematic view that shows a state where a surface potential is detected;

FIG. 5 is a schematic graph that shows a time variation of the surface potential; _ of a grounding

condition inspection method performed by the single electrostatic coating apparatus according to the first embodiment of the invention;

FIG. 7A and FIG. 7B are schematic views that show a state where a coating gun is displaced with respect to the object in the electrostatic coating apparatus according to the first embodiment of the invention, in which FIG. 7A is a schematic view that shows a state where the coating gun is displaced during inspection of the grounding condition (when the voltage is applied and the surface potential is detected) and FIG. 7B is a schematic view that shows a state where the coating gun is displaced during electrostatic coating;

FIG. 8A and FIG. 8B are schematic views that show the overall configuration of a coating line, in which FIG. 8A is a schematic view that shows the configuration of the coating line when the electrostatic coating apparatus according to the first embodiment of the invention is used to inspect the grounding condition and FIG. 8B is a schematic view that shows the configuration of the coating line when an existing exclusive inspection device is used to inspect the grounding condition;

FIG. 9 is a schematic view that shows a state where the grounding condition is inspected by two electrostatic coating apparatuses according to a second embodiment of the invention; and

FIG. 10 A and FIG. 1 OB are inspection flowcharts that show the flow of a grounding condition inspection method using the two electrostatic coating apparatuses according to the second embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0021] A first embodiment of the invention will be described. First, the overall configuration of an electrostatic coating apparatus according to the embodiment of the invention will be described with reference to FIG. 1 and FIG. 2. As shown in FIG. 1 and FIG. 2, the electrostatic coating apparatus 1 according to the first embodiment of the invention includes a coating gun 3, a robot arm 4, a high-voltage generating device 9, and the like,. and . is able to electrostatically coat an object 2. The -object 2 is a component, such as a resin bumper, and has a low electrical conductivity such that the as-is object 2 cannot undergo electrostatic coating.

[0022] The coating gun 3 is used to spray a coating material onto the object 2, and includes a bell cup 3a. The coating gun 3 is a rotary atomizing coating device that is able to atomize a fluid coating material spread on the inner surface of the bell cup 3a with centrifugal force by rotating the bell cup 3a using a driving device, such as an air motor (not shown).

[0023] As shown in FIG. 1, the robot arm 4 is formed of a vertical arm 5 and a horizontal arm 6. The vertical arm 5 is pivotably coupled to a base portion 7 at its lower portion. The horizontal arm 6 is pivotably coupled to the upper portion of the vertical arm 5 at its rear end portion. The coating gun 3 is provided at the distal end portion of the horizontal arm 6. The vertical arm 5 and the horizontal arm 6 are pivoted On their pivot axes to thereby make it possible to displace the coating gun 3 with respect to the object 2.

[0024] In addition, the horizontal arm 6 is formed of a first arm portion 6a, a second arm portion 6b and a third arm portion 6c. A coupling cylinder 3b of the coating gun 3 is coupled to the distal end portion of the first arm portion 6a. The first arm portion 6a is coupled to the distal end portion of the second arm portion 6b. The second arm portion 6b is coupled to the distal end portion of the third arm portion 6c. The vertical arm 5 is pivotably coupled to the rear end portion of the third arm portion 6c.

[0025] In addition, the first arm portion 6a has two bending portions 6d and 6e, and the first arm portion 6a is bent at the bending portions 6d and 6e. By so doing, the angle of the coating gun 3 may be changed in the clockwise direction or counterclockwise direction in FIG. 1 and FIG. 2.

[0026] In addition, the coupling cylinder 3b, to which the coating gun 3 is attached at its distal end, is driven for rotation about its axis with respect to the first arm portion 6a, and the coating gun 3 is able to change its angle about the axis of the coupling cylinder 3b. By so doing, the angle of the coating gun 3 with respect to the object 2 may be freely set. . . .

[0027] In addition, the high-voltage generating device 9 is electrically connected to the coating gun 3. As shown in FIG. 1 and FIG. 2, the high-voltage generating device 9 is used to generate high voltage to be applied to the coating gun 3. The high-voltage generating device 9 includes a voltage generating portion 21 and a voltage step-up portion 22. The voltage generating portion 21 is used to generate and control voltage. The voltage step-up portion 22 is used to step up voltage generated by the voltage generating portion 21.

[0028] Then, in the present embodiment, the voltage step-up portion 22 of the high-voltage generating device 9 is arranged inside the second arm portion 6b, and the voltage generating portion 21 of the high-voltage generating device 9 is arranged outside the robot arm 4. Then, a low-voltage cable 23 is wired inside the portions 6b and 6c of the robot arm 4 and the vertical arm 5 and then the low-voltage cable 23 is drawn outside in the middle of the vertical arm 5 to thereby connect the voltage generating portion 21 to the voltage step-up portion 22 using the low-voltage cable 23.

[0029] In addition, a high-voltage cable 10 is wired inside the portions 6a and 6b of the robot arm 4 and the coating gun 3 to thereby connect the voltage step-up portion 22 to the coating gun 3 using the high-voltage cable 10. By so doing, high voltage is applied to the coating gun 3.

[0030] Then, the coating gun 3 is able to negatively charge particles of a coating material sprayed from the coating gun 3 in such a manner that negative electrostatic high voltage is applied by the high-voltage generating device 9. Then, the electrostatic field (hereinafter, referred to as electric field E) shown in FIG. 2 is formed between the negatively charged coating material and the grounded (that is, the potential is 0 V) object 2, and the electric field E is utilized to electrostatically coat the object 2.

[0031] Next, the high-voltage generating device 9 provided for the electrostatic coating apparatus 1 will be described in further detail with reference to FIG. 3. As shown in FIG. 3, the high-voltage generating device 9 includes the voltage generating portion 21, the voltage step-up portion 22, the low-voltage cable 23, and the like.

[0032] The voltage generating portion 21 is used, to generate voltage that is the source of high voltage to be applied to the coating gun 3 and the robot arm 4. The voltage generating portion 21 includes a power supply portion 27, an amplifier 28, a CPU 29, a RAM 30, a relay 31, a push-pull oscillator 32, a voltage sensor 33, a current sensor 34, band pass filters 35 and 36, and the like.

[0033] The voltage step-up portion 22 is used to step up voltage generated by the voltage generating portion 21. The voltage step-up portion 22 includes a high-voltage transformer 24, a Cockcroft^Walton circuit (CW circuit) 25, and the like. The CW circuit 25 is a rectifier and multiplier for generating high voltage, and is formed of a combination of a plurality of capacitors, a plurality of diodes, and the like. In addition, the high-voltage transformer 24 includes a primary winding 24a and a secondary winding 24b. The CW circuit 25 is connected to the secondary winding 24b.

[0034] Then, the voltage generating portion 21 includes an output terminal 21a, an output terminal 21b and an output terminal 21c. The output terminal 21a is used to output operating voltage to the center phase (hereinafter, referred to as CT phase) of the primary winding 24a. The output terminal 21b is used to output a drive signal to the drive A phase (hereinafter, referred to as DA phase) of the primary winding 24a. The output terminal 21c is used to output a drive signal to the drive B phase (hereinafter, referred to as DB phase) of the primary winding 24a. Furthermore, the voltage generating portion 21 includes an input terminal 21d, an input terminal 21e, a grounding y

terminal 21f, and the like. The input terminal 21d is used to input a current feedback signal (hereinafter, referred to as IM signal) that indicates a total current value generated by the CW circuit 25 to the CPU 29. The input terminal 21e is used to input a voltage feedback signal (hereinafter, referred to as VM signal) that indicates a high voltage value stepped up by the CW circuit 25 to the CPU 29. The grounding terminal 21f is used to ground the voltage generating portion 21.

[0035] In addition, the voltage step-up portion 22 includes an input terminal 22a, an input terminal 22b and an input terminal 22c. The input terminal 22a is connected to the CT phase of the primary winding 24a of the high-voltage transformer 24. The input terminal _22bjs connected I tt^ the DA phase _. of Jhe _. primary .winding. 24a. The input terminal 22c is connected to the DB phase of the primary winding 24a. Furthermore, the voltage step-up portion 22 includes an output terminal 22d, an output terminal 22e, a grounding terminal 22f, and the like. The output terminal 22d is used to output the IM signal that indicates the total current value generated by the CW circuit 25. The output terminal 22e is used to output the VM signal that indicates the high voltage value stepped up by the CW circuit 25. The grounding terminal 22f is used to ground the CW circuit 25.

[0036] In the voltage step-up portion 22, the CW circuit 25 is connected to the grounding terminal 22f to dissipate electric charge that is charged on the coating gun 3, and the like. Then, a bleeder resistor 26 is connected in a grounding line that connects the CW circuit 25 to the grounding terminal 22f. The bleeder resistor 26 is used to suppress leakage current. Then, furthermore, a high-voltage output terminal 22g is provided in the voltage step-up portion 22. The high-voltage output terminal 22g is used to output high voltage generated by the CW circuit 25.

[0037] The low-voltage cable 23 is a bundle of various cables that are used to electrically connect the voltage generating portion 21 to the voltage step-up portion 22. The low-voltage cable 23 is formed of a CT input line (CT) 23a, a DA input line (DA) 23b, a DB input line (DB) 23c, an IM signal line (IM) 23d, a VM signal line (VM) 23e, a common line (COM) 23f, and the like. [0038] The CT input line 23a is used to input the operating voltage generated by the voltage generating portion 21 to the CT phase of the primary winding 24a. The CT input line 23a is connected between the output terminal 21a of the voltage generating portion 21 and the input terminal 22a of the voltage step-up portion 22.

[0039] The DA input line 23b is used to input the drive signal generated by the voltage generating portion 21 to the drive A phase of the primary winding 24a. The DA input line 23b is connected between the output terminal 21b of the voltage generating portion 21 and the input terminal 22b of the voltage step-up portion 22.

[0040] The DB input line 23c is used to input the drive signal generated by the voltage generating portion 21 to the drive B phase of the primary winding 24a. The DB input line 23c is connected between the output terminal 21c of the voltage generating portion 21 and the input terminal 22c of the voltage step-up portion 22.

[0041] The IM signal line 23d is used to input the IM signal generated by the voltage step-up portion 22 to the CPU 29. The IM signal line 23d is connected between the input terminal 21d of the voltage generating portion 21 and the input terminal 22d of the voltage step-up portion 22.

[0042] The VM signal line 23e is used to input the VM signal generated by the voltage step-up portion 22 to the CPU 29. The VM signal line 23e is connected between the input terminal 21e of the voltage generating portion 21 and the input terminal 22e of the voltage step-up portion 22.

[0043] Furthermore, the common line 23f is used to set a common reference potential (0 V) by grounding the voltage generating portion 21 and the voltage step-up portion 22. The common line 23f is connected between the grounding terminal 21f of the voltage generating portion 21 and the grounding terminal 22f of the voltage step-up portion 22.

[0044] Here, a state where high voltage is generated by the high-voltage generating device 9 will be described with reference to FIG. 3. The voltage generating portion 21 generates operating voltage in such a manner that the output voltage generated by the power supply portion 27 is adjusted by the amplifier 28 in response to a command value from the CPU 29. The operating voltage generated here is adjusted by the CPU 29 so as to bring operating voltage into coincidence with a command value in such a manner that measured values measured by the voltage sensor 33 and the current sensor 34 that are connected in a line for supplying the operating voltage are fed back to the CPU 29.

[0045] In addition, the command value from the CPU 29 to the amplifier 28 is obtained in such a manner that the above described IM signal and VM signal are fed back to the CPU 29 and then the CPU 29 executes computation on the basis of feedback signals, conditions stored in the RAM 30, and the like. The IM signal, the VM signal, and the like, are input to the CPU 29 via the band pass filters 35 and 36, and the like.

[0046] In addition, the voltage generating portion 21 generates the drive signals to be input to the drive phases of the primary winding 24a using the push-pull oscillator 32 in response to the command value from the CPU 29. In addition, the command value from the CPU 29 to the push-pull oscillator 32 is obtained in such a manner that the above described IM signal and VM signal are fed back to the CPU 29 and then the CPU 29 executes computation on the basis of feedback signals, conditions stored in the RAM 30, and the like.

[0047] With the above configuration, a predetermined alternating-^current voltage may be supplied to the primary winding 24a of the high-voltage transformer 24. By so doing, the CW circuit 25 connected to the secondary winding 24b is used to step up the operating voltage supplied to the primary winding 24a by a predetermined multiplication factor in response to the number of stages of the connected capacitor and diode, and a direct-current high voltage having a predetermined voltage value may be generated between the points a and β of the CW circuit 25 in FIG. 3.

[0048] Here, in the voltage step-up portion 22, the output terminal 22g connected to the output point β is a terminal used to output high voltage to be applied to the coating gun 3. Then, the high-voltage output terminal 22g is connected to the coating gun 3 by a high-voltage cable 10.

[0049] In addition, in a state where high voltage is not applied to the coating gun 3 by the high-voltage generating device 9, when an electric field is formed from the object toward the coating gun 3 by electric charge that is charged on the object and then a discharge current flows from the output terminal 22g toward the grounding terminal 22f, a signal that indicates the voltage of the discharge current (hereinafter, referred to as IS signal) is input to the VM signal line 23e. Then, as the IS signal is input to the CPU 29, the CPU 29 executes computation based on the IS signal to thereby make it possible to detect the surface potential of the object.

[0050] Next, a method of measuring a surface potential in the case where the single electrostatic coating apparatus 1 is used as a first embodiment of the invention will be described with reference to FIG. 4A to FIG. 5. As shown in FIG. 4A, in a state where the object 2 is arranged on a conveyor 11 connected to a ground and a conductive primer is applied onto the object 2, the robot arm 4 is used to displace the coating gun 3 to keep the distance between the bell cup 3a of the coating gun 3 and the object 2 at a distance LI. Then, in this state, as high voltage is applied to the coating gun 3 by the high-voltage generating device 9, an electric field El is formed between the bell cup 3a and the object 2, and electric charge is imparted to the object 2.

[0051] In this way, a time variation of the surface potential in the object 2 in the case where electric charge is applied to the object 2 is as shown in FIG. 5. As shown in FIG. 5, as electric charge is applied to the object 2 having a surface potential V0 from time tO to time tl by the high-voltage generating device 9, the surface potential of the object 2 at time tl is VI.

[0052] Then, when the grounding condition of the object 2 is ideal, as application of electric charge by the high-voltage generating device 9 is stopped at time tl, the surface potential of the object 2 steeply decreases after time tl as indicated by the curve Gl. On the other hand, when the grounding condition of the object 2 is not appropriate, the surface potential of the object 2 gently decreases after time tl as indicated by the curve G2.

[0053] In addition, when the grounding condition of the object 2 is ideal, at time t2 after application of electric charge is stopped at time tl, the surface potential of the object 2 becomes reliably lower than a preset potential Vk. On the other hand, when the grounding condition of the object 2 is not appropriate, the surface potential of the object 2 is kept at a potential higher than the preset potential Vk.

[0054] Then, in the present embodiment, the surface potential of the object 2 at time t2 that is a predetermined time after application of electric charge using the high-voltage generating device 9 is stopped (that is, time tl) is detected to determine whether the grounding condition is good.

[0055] Specifically, at time t2 shown in FIG. 5, the robot arm 4 is used to keep the distance between the bell cup 3a of the coating gun 3 and the object 2 at a distance L2 that is As the coating gun 3 (more specifically, the bell cup 3a) connected to a ground via the bleeder resistor 26 is brought close to the object 2, electric charge that is charged on the object 2 is discharged toward the bell cup 3a. In the electrostatic coating apparatus 1 according to the present embodiment, a discharge current generated at this time is measured to detect the surface potential of the object 2 and determine whether the grounding condition is good.

[0056] Then, the discharge current value may be measured by the CPU 29 of the high-voltage generating device 9 on the basis of the IS signal as described above. Therefore, in the present embodiment, it is possible to inspect the grounding condition using only the electrostatic coating apparatus 1 without using another exclusive inspection device.

[0057] That is, the electrostatic coating apparatus 1 according to the first embodiment of the invention includes the coating gun 3 that is used to spray a coating material toward the object 2; the robot arm 4 that displaceably supports the coating gun 3; and the high-voltage generating device 9 that generates high voltage to be applied to the coating gun 3 and that adjust the generated high voltage in such a manner that a discharge current generated when the electric field El is formed between the coating gun 3 and the object 2 is detected. In a state where a coating material is not sprayed toward the object 2 by the coating gun 3, the electric field El is formed from the coating gun 3 toward the object 2 to charge the object 2 with electric charge, and, in a state where high voltage is not applied to the coating gun 3 by the high-voltage generating device 9, the high-voltage generating device is used to detect the discharge current generated between the coating gun 3 and the object 2 on the basis of the electric charge that is charged on the object 2. With the above configuration, it is possible to inspect the grounding condition of the object 2 without using an exclusive device. In addition, by so doing, it is possible to reduce the length of the coating line, the inspection time, the cost of coating equipment, and the like.

[0058] Next, the grounding condition inspection method using the electrostatic coating apparatus 1 will be described with reference to FIG. 4A to FIG. 8B. As shown in JFIG.4A and_FJG^ the electrostatic coating apparatus 1 according to the present embodiment, only the already existing single electrostatic coating apparatus 1 is used to inspect the grounding condition.

[0059] In the grounding condition inspection method using the electrostatic coating apparatus 1, first, as shown in FIG. 6A and FIG. 6B, the conveyor 11 for transporting the object 2 is operated to arrange the object 2, onto which the conductive primer has been applied, at a predetermined inspection position (S101). Then, when the object 2 is arranged at the predetermined inspection position, the conveyor 11 is stopped (SI 02).

[0060] Subsequently, in a state where the object 2 is arranged at the predetermined inspection position, the high-voltage generating device 9 is turned on to apply high voltage to the coating gun 3 as shown in FIG. 4A (S103). At this time, the electric field El is formed from the coating gun 3 toward the object 2, and electric charge is applied to the object 2. Note that, at this time, a coating material is not sprayed by the coating gun 3, and the distance between the coating gun 3 and the object 2 is the distance LI.

[0061] After that, the robot arm 4 is used to displace the coating gun 3 along a predetermined trajectory in a predetermined position (S104). As shown in FIG. 7A, when the range in which electric charge may be applied by the coating gun 3 is a circular range S, the coating gun 3 is displaced so as to draw a trajectory R at a constant speed from a state where the center of the range S coincides with a start position P so as to apply predetermined electric charge to portions (that is, so as to substantially equalize the time at which electric charge is applied to each portion) while not forming a slit in a range to which electric charge is applied.

[0062] As shown in FIG. 7B, the trajectory R may be shorter in displacement distance by an amount by which the overlap width of the range S may be reduced than a trajectory Rs drawn by the coating gun 3 when the electrostatic coating apparatus 1 is used to electrostatically coat the object 2. Therefore, a time required to apply electric charge may be shorter than a time required to perform electrostatic coating.

- [0063] Then, the coating gun 3 is displaced to a predetermined end position Q while the coating gun 3 is used to apply electric charge to the object 2 and the center of the range S draws the predetermined trajectory R (S105). In addition, when the center of the range S reaches the predetermined end position Q, the high-voltage generating device 9 is turned off (S106). Up to here, the process of applying electric charge to the object 2 using the electrostatic coating apparatus 1 is complete. Then, from here, the process proceeds to the process of detecting a surface potential using the electrostatic coating apparatus 1.

[0064] That is, in the electrostatic coating apparatus 1 according to the first embodiment of the invention, when the electric field El is formed from the coating gun 3 toward the object 2 to charge the object 2 with electric charge, the displacement distance of the coating gun 3 is shorter than the displacement distance of the coating gun 3 during electrostatic coating. With the above configuration, a time during which electric charge is applied is reduced to make it possible to reduce an inspection time.

[0065] When a predetermined period of time (that is, a time from time tl to time t2 shown in FIG. 5) elapses after application of electric charge to the object 2 is completed (S107), it is determined whether the high-voltage generating device 9 is off (S108).

[0066] Subsequently, the robot arm 4 is used to displace the coating gun 3 along the predetermined trajectory in the predetermined position (S109). Note that, in the present embodiment, on the assumption that the range in which electric charge may be applied by the coating gun 3 when the distance between the coating gun 3 and the object 2 is the distance LI and the range in which the surface potential may be detected by the coating gun 3 when the distance between the coating gun 3 and the object 2 is the distance L2 both are equal to the range S, the trajectory at this time is equal to the trajectory R shown in FIG. 7A, and the coating gun 3 is displaced at a constant speed from the start position P to the end position Q so as to detect the surface potential in all the range while not forming a slit in the range in which the surface potential is detected. That is, the trajectory (displacement distance) of the coating gun 3 at the time of applying electric charge and the trajectory (displacement distance) of the coating gun 3 at the time of measuring the surface potential may be set so as to be different from each other.

[0067] Then, under such displacement condition, while the robot arm 4 is used to displace the coating gun 3 with respect to the object 2, the surface potential is measured in the mode shown in FIG. 4B (S110), and then determination based on the measured surface potential is made (Sill). In addition, at this time, the surface potential is measured in such a manner that the distance between the coating gun 3 and the object 2 is set to the distance L2 that is shorter than the coating distance to bring the coating gun 3 further close to the object 2 to thereby further accurately measure the surface potential. , ^{■ "} ■

[0068] That is, in the first embodiment of the invention, when the high-voltage generating device 9 is used to detect a discharge current that is generated when the electric field is formed between the coating gun 3 and the object 2 on the basis of electric charge that is charged on the object 2 in a state where high voltage is not applied to the coating gun 3 by the high-voltage generating device 9, the displacement distance of the coating gun 3 is shorter than the displacement distance of the coating gun 3 during electrostatic coating. With the above configuration, a time during which the surface potential is detected is reduced to make it possible to reduce an inspection time.

[0069] In addition, in the first embodiment of the invention, when the high-voltage generating device 9 is used to detect the discharge current generated between the coating gun 3 and the object 2 on the basis of the electric charge that is charged on the object 2 in a state where high voltage is not applied to the coating gun 3 by the high-voltage generating device 9, the distance L2 between the coating gun 3 and the object 2 is shorter than the coating distance during electrostatic coating. With the above configuration, the surface potential of the object 2 is further reliably detected to make it possible to improve the inspection accuracy of the grounding condition.

[0070] The determination here is made on the basis of whether the measured surface potential is lower than or equal to the preset potential Vk as shown in FIG. 5. When the measured surface potential V2 is lower than the preset potential Vk, it is -determined thatJhe._grounding_condition.of ...the objecL2 is. good, and the determination is continuously repeated until the position of the coating gun 3 becomes the predetermined end position Q (SI 12).

[0071] Alternatively, when the measured surface potential V2 exceeds the preset potential Vk, it is determined that the grounding condition of the object 2 is abnormal and the measurement is stopped (SI 14), after which the process in case of abnormality is executed (S115). The abnormality process here is, for example, the process of checking the object 2 that has been determined to be abnormal for a grounding condition, or the like, of a grounding clip. Then, when the abnormality process is completed, determination as to the abnormal state is reset (S116).

[0072] Then, after measurement of the surface potential is complete (SI 13) or the abnormal state is reset (S116), the conveyor 11 is operated to remove the object 2 from the inspection position (SI 17). Thus, inspecting the grounding condition using the electrostatic coating apparatus 1 is completed.

[0073] That is, in the grounding condition inspection method according to the first embodiment of the invention, after the conductive primer is applied onto the object 2, high voltage is applied to the object 2 and the surface potential of the object 2 is measured to thereby inspect the grounding condition of the object 2, and the electrostatic coating apparatus 1 is used to apply high voltage to the object 2 and measure the surface potential of the object 2. With the above configuration, it is possible to inspect the grounding condition of the object 2 without using an exclusive device. In addition, by so doing, it is possible to reduce the length of the coating line, the inspection time, the cost of coating equipment, and the like.

[0074] Then, the coating line in the case where the electrostatic coating apparatus 1 is used to inspect the grounding condition in this way is configured as shown in FIG. 8A. With this configuration, the process and device for checking a grounding condition may be, for example, also used as the process and device for applying a base coat, so, in comparison with the existing coating line shown in FIG. 8B, the process and device for checking a grounding condition may be omitted, and the coating line may be made compact. - ~

[0075] Next, a method of measuring a surface potential in the case where the two electrostatic coating apparatuses 1 are used as a second embodiment of the invention will be described with reference to FIG. 4A to FIG. 5 and FIG. 9. As shown in FIG. 4 A and FIG. 4B, when the grounding condition is inspected by the single electrostatic coating apparatus 1, the process cannot proceed to measuring the surface potential until application of electric charge has been totally completed. Then, in the present embodiment, the two adjacent electrostatic coating apparatuses 1 are used to make it possible to conduct inspection in a further short period of time.

[0076] As shown in FIG. 9, in a state where the object 2 is arranged on the grounded conveyor 11 and the conductive primer is applied onto the object 2, a first robot arm 4X that is the robot arm 4 of a first electrostatic coating apparatus IX that is the first electrostatic coating apparatus 1 is used to keep the distance between the bell cup 3a of a first coating gun 3X of the first electrostatic coating apparatus IX and the object 2 at the distance LI. Then, in this state, as a first high- voltage generating device 9X that is the first high-voltage generating device 9 of the first electrostatic coating apparatus IX is used to apply high voltage to the first coating gun 3X, the electric field El is formed between the bell cup 3a and the object 2 and electric charge is imparted to the object 2.

[0077] In this way, a time variation of the surface potential in the object 2 in the case where electric charge is applied to the object 2 is as shown in FIG. 5 as described above. That is, as shown in FIG. 5, as electric charge is applied to the object 2 having a surface potential VO from time tO to time tl by the first high-voltage generating device

9X, the surface potential of the object 2 at time tl is VI.

[0078] Then, when the grounding condition of the object 2 is ideal, as application of electric charge by the first high-voltage generating device 9X is stopped at time tl, the surface potential of the object 2 steeply decreases after time tl as indicated by the curve Gl. On the other hand, when the grounding condition of the object 2 is not appropriate, the surface potential of the object 2 gently decreases after time tl as indicated by the curve G2.

[0079] In addition, when the grounding condition of the object 2 is ideal, at time t2 after application of electric charge is stopped at time tl, the surface potential of the object 2 is reliably lower than a preset potential Vk. On the other hand, when the grounding condition of the object 2 is not appropriate, the surface potential of the object 2 is kept at a potential higher than the preset potential Vk.

[0080] Then, in the present embodiment, a second electrostatic coating apparatus 1Y that is the second electrostatic coating apparatus 1 is used to determine whether the grounding condition is good for portions to which application of electric charge using the first high-voltage generating device 9X has been completed before application of electric charge using the first high-voltage generating device 9X has been totally completed and, therefore, detecting a surface potential is started before time t2 at which application of electric charge is totally completed.

[0081] Specifically, for example, at time t3 shown in FIG. 5, a second robot arm 4Y of the second electrostatic coating apparatus 1Y is used to keep the distance between the bell cup 3a of a second coating gun 3Y that is the second coating gun 3 of the second electrostatic coating apparatus 1Y and the object 2 at the distance L2 that is shorter than the distance LI as shown in FIG. 9. Here, although time t3 is earlier than time t2, the surface potential at this point in time is sufficiently lower than the preset potential Vk, so the surface potential V3 at time t3 shown in FIG. 5 may be used to determine the grounding condition. 2U

[0082] As the second coating gun 3Y (more specifically,, the bell cup 3a) connected to a ground via the bleeder resistor 26 is brought close to the object 2, electric charge that is charged on the object 2 is discharged toward the bell cup 3a. In the second electrostatic coating apparatus 1Y according to the present embodiment, the discharge current value is measured to detect the surface potential of the object 2 and determine whether the grounding condition is good.

[0083] Then, the discharge current value may be measured by the CPU 29 of the second high-voltage generating device 9Y of the second electrostatic coating apparatus 1Y on the basis of the IS signal as described above. Therefore, in the present embodiment, it. is_possible to. inspect Jhe grounding condition jjsing the already existing two electrostatic coating apparatuses IX and 1 Y without using another exclusive inspection device.

[0084] That is, in the second embodiment of the invention, the two first and second electrostatic coating apparatuses IX and 1Y are provided, an electric field E2 is formed from the first coating gun 3X of the first electrostatic coating apparatus IX toward the object 2 to charge the object 2 with electric charge, and the second high-voltage generating device 9Y of the second electrostatic coating apparatus 1Y is used to detect a discharge current generated between the second coating gun 3Y of the second electrostatic coating apparatus 1Y and the object 2 on the basis of the electric charge that is charged on the object 2. With the above configuration, a waiting time after application of electric charge is reduced to make it possible to further reduce an inspection time.

[0085] Next, a grounding condition inspection method using the two electrostatic coating apparatuses IX and 1Y will be described with reference to FIG. 9, FIG. 10A and FIG. 10B. As shown in FIG. 10A and FIG. 10B, in the grounding condition inspection method using the two electrostatic coating apparatuses IX and lY, first, the conveyor 11 for transporting the object 2 is operated to arrange the object 2, onto which the conductive primer has been applied, at a predetermined inspection position (S201). Then, when the object 2 is arranged at the predetermined inspection position, the conveyor 11 is stopped (S202).

[0086] Subsequently, in a state where the object 2 is arranged at the predetermined inspection position, the first high-voltage generating device 9X of the first electrostatic coating apparatus IX is turned on to apply high voltage to the first coating gun 3X of the first electrostatic coating apparatus IX (S203). At this time, as shown in FIG. 9, the electric field El is formed from the first coating gun 3X toward the object 2, and electric charge is applied to the object 2. Note that, at this time, a coating material is not sprayed by the first coating gun 3X.

[0087] After that, the first robot arm 4X of the first electrostatic coating apparatus IX is used to displace the first coating gun 3X along a predetermined trajectory in a predetermined position (S204). At this time, as well as the case where only the single electrostatic coating apparatus 1 is used, as shown in FIG. 7A, when the range in which electric charge may be applied by the first coating gun 3X is a circular range S, the first coating gun 3X is displaced so as to draw a trajectory R at a constant speed from a state where the center of the range S coincides with a start position P so as to apply predetermined electric charge to portions (that is, so as to substantially equalize the time at which electric charge is applied to each portion) while not forming a slit in a range to which electric charge is applied.

[0088] Then, the process proceeds to the process of detecting the surface potential using the second electrostatic coating apparatus 1Y at the time when the first coating gun 3X is started to be displaced by the first robot arm 4X.

[0089] On the other hand, the process of applying electric charge using the first coating gun 3X continues, and electric charge is applied to the object 2 while the first coating gun 3X is displaced to the predetermined end position Q (S205). In addition, at the time when the first coating gun 3X reaches the predetermined end position Q, the first high-voltage generating device 9X is turned off (S206). Up to here, the process of applying electric charge to the object 2 using the first electrostatic coating apparatus IX is complete.

[0090] Then, after a predetermined period of time (that is, a period of time from time tl to time t3 shown in FIG. 5) elapses from when the first coating gun 3X is started to be displaced (S301), the second robot arm 4Y of the second electrostatic coating apparatus 1Y is used to displace the second coating gun 3Y of the second electrostatic coating apparatus 1Y along a predetermined trajectory in a predetermined position (S302). That is, in the present embodiment, the process is able to proceed to the process of detecting the surface potential earlier than when only the single electrostatic coating apparatus 1 is used.

[0091] In addition, as well as the case where only the single electrostatic coating apparatus 1 is used, on the assumption that the range in which electric charge may be applied by the first coating gun 3X when the distance between the first coating gun 3X and the object 2 is the distance LI and the range in which the surface potential may be detected by the second coating gun 3Y when the distance between the second coating gun 3Y and the object 2 is the distance L2 both are equal to the range S, the trajectory along which the second robot arm 4Y is used to displace the second coating gun 3Y at this time is equal to the trajectory R shown in FIG. 7 A, and the second coating gun 3Y is displaced at a constant speed from the start position P to the end position Q so as to detect the surface potential in all the range while not forming a slit in the range in which the surface potential is detected.

[0092] Then, under such displacement condition, while the second robot arm 4Y is used to displace the second coating gun 3Y with respect to the object 2, the surface potential is measured in the mode shown in FIG. 9 (S303), and then the determination based on the measured surface potential is made (S304). In addition, at this time, the surface potential is measured in such a manner that the distance between the second coating gun 3Y and the object 2 is set to the distance L2 that is shorter than the coating distance to bring the second coating gun 3Y further close to the object 2 to thereby further accurately measure the surface potential.

[0093] The determination here is made on the basis of whether the measured surface potential is lower than or equal to the preset potential Vk as shown in FIG. 5. When the measured surface potential V3 is lower than or equal to the preset potential Vk, it is determined that the grounding condition of the object 2 is good, and the determination is continuously repeated until the second coating gun 3Y reaches the predetermined end position Q (S305).

[0094] Alternatively, when the measured surface potential V3 exceeds the preset potential Vk, it is determined that the grounding condition of the object 2 is abnormal and the measurement is stopped (S307), after which the process in case of abnormality is executed (S308). The abnormality process here is, for example, the process of checking the object 2 that has been determined to be abnormal for a grounding condition, or the like, of a grounding clip. Then, when the abnormality process is completed, determination as to the abnormal state is reset (S309).

[0095] Then, after measurement of the surface potential is complete (S306) or the abnormal state is reset (S309), the conveyor 11 is operated to remove the object 2 from the inspection position (S310). Thus, measuring the surface potential using the second electrostatic coating apparatus 1Y is completed, and inspecting the grounding condition using the two electrostatic coating apparatuses IX and 1 Y is completed.

[0096] That is, in the grounding condition inspection method according to the second embodiment of the invention, the first and second electrostatic coating apparatuses IX and 1Y are used, and the first electrostatic coating apparatus IX is used to apply high voltage to the object 2, while the second electrostatic coating apparatus 1Y is used to measure the surface potential of the object 2. With the above configuration, a waiting time after application of electric charge is reduced to make it possible to further reduce an inspection time.