JP2016055269A - Electrostatic coating apparatus and electrostatic coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve productivity by avoiding the suspension of electrostatic coating due to generation of metal bridges while securing safety.SOLUTION: An electrostatic coating apparatus comprises: a nozzle that sprays coating; a high-voltage output part that outputs high voltage for electrifying the coating sprayed out of the nozzle; a high-voltage generation part that supplies high voltage to the high-voltage output part; a current detection part that detects current flowing through the high-voltage generation part; and a control part that controls voltage supplied to the high-voltage generation part on the basis of the current detected by the current detection part. The control part performs constant current control when a current value detected by the current detection part becomes equal to or more than a threshold value set to a value lower than a current value which causes overcurrent anomaly and suspends voltage supply to the high-voltage generation part when the constant current control is continued over a predetermined period.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to an electrostatic coating apparatus and an electrostatic coating apparatus program.

  In the field of coating, the use of paints mixed with conductive particles, for example, so-called metallic paints containing metal particles such as aluminum flakes, is increasing from the viewpoint of decorativeness and functionality. When such a paint is used, a so-called metal bridge is often a problem in electrostatic painting in which a high voltage is applied to the sprayed paint. The metal bridge is a phenomenon in which the insulation resistance of the paint is extremely reduced by the metal particles dispersed in the paint staying in the paint path and being connected in a chain form. When a metal bridge occurs, an electric current flows through the paint in the paint path, thereby causing an overcurrent to flow through the circuit in the electrostatic coating apparatus, resulting in an overcurrent abnormality.

  On the other hand, an overcurrent abnormality may also occur when an electrode for applying a high voltage to a paint and a grounded object are close to each other, or when an internal circuit has failed. It is not preferable in terms of safety to continue the electrostatic coating by outputting a higher voltage in a state where an overcurrent abnormality has occurred. For this reason, the conventional electrostatic coating apparatus stops the electrostatic coating by stopping the output of the high voltage when an overcurrent abnormality occurs.

  However, the metal bridge is easily eliminated in a relatively short period of time by dividing the metal particles connected to the chain shape by causing a flow in the paint. In addition, metal bridge is a phenomenon that occurs irregularly and relatively frequently because it is likely to occur when spraying of paint is interrupted, such as between work and breaks. Therefore, if electrostatic coating is stopped each time a metal bridge is generated, work is delayed and productivity is also reduced.

JP 2000-246168 A

  Therefore, an electrostatic coating apparatus and a program for an electrostatic coating apparatus are provided that can prevent the stop of electrostatic coating due to the occurrence of a metal bridge and improve productivity while ensuring safety.

(Claim 1)
The electrostatic coating apparatus according to claim 1, a nozzle that sprays paint, a high-voltage output unit that outputs a high voltage for charging the paint sprayed from the nozzle, and a high voltage to the high-voltage output unit A high voltage generator that supplies current, a current detector that detects a current flowing through the high voltage generator, and a control that controls a voltage output from the high voltage generator based on the current detected by the current detector A section. The control unit performs constant current control when the current value detected by the current detection unit is equal to or higher than a threshold value set to a value lower than a current value causing an overcurrent abnormality, and performs the constant current control for a predetermined period. When it continues, the output of the voltage from the high voltage generator is stopped.

  According to such a configuration, even if a metal bridge occurs in the paint path and the current flowing through the high voltage generation unit is likely to exceed the threshold, the control unit performs high current generation by performing constant current control. It is possible to prevent the current flowing through the portion from exceeding the threshold value. That is, the control unit performs constant current control so that the current flowing through the high voltage generation unit does not reach a current value that causes an overcurrent abnormality. Thereby, the control part can avoid that electrostatic coating stops by an overcurrent abnormality, and can continue electrostatic coating.

  In addition, the metal bridge is eliminated in a relatively short time. In other words, the factor that causes the value of the current flowing through the high-voltage generating unit to be continuously greater than or equal to the threshold value is likely to be a factor other than the metal bridge. Therefore, when the constant current control is continued for a predetermined period, the control unit stops the supply of voltage to the high voltage generation unit, that is, stops electrostatic coating. Thereby, when overcurrent abnormality arises by factors other than a metal bridge, electrostatic coating can be stopped and safety can be ensured.

(Claim 2)
The electrostatic coating apparatus according to claim 2, wherein the control unit switches to constant voltage control when the current value detected by the current detection unit becomes less than a threshold value after starting the constant current control. When the metal bridge is eliminated, the insulation resistance of the paint becomes larger than when the metal bridge is generated. Therefore, when the constant current control similar to that at the time of occurrence of the metal bridge is performed even though the metal bridge is eliminated and the insulation resistance of the paint is increased, for example, the following inconvenience occurs.

  That is, if the constant current control is to be continued even after the metal bridge is eliminated, the control unit attempts to set the current value detected by the current detection unit to the same current value as that when the metal bridge is generated. In this case, since the insulation resistance of the paint is increased due to the elimination of the metal bridge, the voltage generated by the high voltage generation unit is larger than when the metal bridge is generated. Therefore, the control unit always tries to generate a maximum output voltage from, for example, a high voltage generation unit. As a result, an excessive load is applied to the high voltage generator and the like. Therefore, when the current flowing through the electrode becomes less than the threshold value, the control unit determines that the metal bridge has been eliminated and switches to constant voltage control. Thereby, it is suppressed that the maximum output voltage is always output from the high voltage generator. As a result, it is possible to suppress overload on the high voltage generation unit and the like.

(Claims 3 and 4)
A program for an electrostatic coating apparatus according to a third aspect realizes the electrostatic coating apparatus according to the first aspect. A program for an electrostatic coating apparatus according to a fourth aspect realizes the electrostatic coating apparatus according to the second aspect. By executing the program for an electrostatic coating apparatus with an existing electrostatic coating apparatus, the function as the electrostatic coating apparatus according to the present invention described above can be added to an existing electrostatic coating measure.

  According to these electrostatic coating apparatus and the electrostatic coating apparatus program, it is possible to avoid the stop of electrostatic coating due to the occurrence of a metal bridge and improve productivity while ensuring safety.

The figure which shows typically an example of the electrical constitution of the electrostatic coating apparatus by one Embodiment The flowchart which shows the control content performed by a control part This figure shows the detected current value and output voltage when performing electrostatic coating. (1) is normal, (2) is when a metal bridge is generated, and (3) is when a failure occurs.

Hereinafter, embodiments will be described with reference to FIGS. 1 to 3.
First, the configuration of the electrostatic coating apparatus 10 will be described with reference to FIG. The electrostatic coating apparatus 10 includes a spray gun 20 and an electrostatic controller 30. The main body of the spray gun 20 is made of, for example, a synthetic resin such as polyacetal resin or fluorine resin having electrical insulation. The spray gun 20 includes a paint valve 21, a paint path 22, an air valve 23, an air path 24, a nozzle 25, a trigger 26, a high voltage generation unit 27, a high voltage output unit 28, and the like.

  The paint valve 21 and the air valve 23 are opened by pulling the trigger 26. The paint valve 21 is connected to a paint pump 40 and a paint tank 41 as a paint supply source via a paint path 22. The paint in the paint tank 41 is supplied to the paint valve 21 through the paint path 22 by the paint pump 40. The paint path 22 is configured by, for example, a synthetic resin hose having electrical insulation. The air valve 23 is connected to the compressor 42 via the air path 24. Compressed air generated in the compressor 42 is supplied to the air valve 23 through the air path 24.

  The nozzle 25 is provided at the tip of the spray gun 20 main body. Inside the nozzle 25, although not shown in detail, a paint supply port, an atomizing air hole, and a pattern forming air hole are provided. The output side of the paint valve 21 is connected to the paint supply port of the nozzle 25. The output side of the air valve 23 is connected to the atomizing air hole and the pattern forming air hole of the nozzle 25. When the trigger 26 is pulled to release the paint valve 21 and the air valve 23, the paint is supplied to the nozzle 25 through the paint valve 21 and compressed air is supplied through the air valve 23. The coating material supplied to the nozzle 25 is atomized by the compressed air discharged from the atomizing air holes and sprayed by being formed into a shape suitable for coating, that is, a coating pattern by the compressed air discharged from the pattern forming air holes. Is done.

  The high voltage generator 27 is called a so-called cascade, and outputs a high DC voltage proportional to the input AC voltage. In the present embodiment, the high voltage generator 27 boosts the input voltage by about 5000 times and outputs the boosted voltage. The spray gun 20 and the electrostatic controller 30 are connected by a cable 11. The cable 11 includes a power line 111 and a current detection line 112. The power line 111 is for supplying an alternating voltage to the spray gun 20. The current detection line 112 is for detecting a current flowing through the high voltage generator 27. Further, the outer periphery of the cable 11 is protected by a protection tube 12.

  The high voltage generator 27 includes an input transformer 271, a voltage doubler rectifier circuit 272, and an output resistor 273. The input transformer 271 electrically insulates between the electrostatic controller 30 and the voltage doubler rectifier circuit 272 and outputs the AC voltage Vac supplied from the electrostatic controller 30 to the voltage doubler rectifier circuit 272. The voltage doubler rectifier circuit 272 is constituted by, for example, a Cockcroft-Walton type booster rectifier circuit. The voltage doubler rectifier circuit 272 boosts and rectifies the AC voltage input from the input transformer 271 and converts it to a DC high voltage.

  The DC high voltage output from the voltage doubler rectifier circuit 272 is supplied to the high voltage output unit 28 via the output resistor 273 and is output from the high voltage output unit 28 as a DC output voltage Vdc. The high voltage output unit 28 is configured by a pin-shaped metal electrode, for example, and is provided in the vicinity of the nozzle 25. Therefore, the DC output voltage Vdc output from the high voltage output unit 28 is applied to the fine particles of the paint sprayed from the nozzle 25.

  The voltage doubler rectifier circuit 272 can set the polarity of the output voltage to either positive or negative with respect to the ground potential by changing the direction of a diode (not shown) in the circuit. In the case of the present embodiment, the polarity of the output voltage of the voltage doubler rectifier circuit 272 is configured to be negative with respect to the ground potential. Therefore, the finely divided paint is charged to a negative high voltage. In the present specification, the value of the output voltage Vdc is expressed as an absolute value for the sake of convenience without distinguishing between positive and negative.

  The electrostatic controller 30 includes a current detection unit 31, a power supply unit 32, a control unit 33, a storage unit 34, an air flow switch 35, and an operation panel 36. The current detection unit 31 is connected to the high voltage generation unit 27 via the current detection line 112. The current detection unit 31 detects the magnitude of the current I flowing through the high voltage generation unit 27 and gives the detection result to the control unit 33. In this case, the current detection unit 31 functions as a current detection unit. In the following description, the current detected by the current detection unit 31 is referred to as a detection current I. The power supply unit 32 is connected to the high voltage generation unit 27 via the power line 111. The power supply unit 32 includes two switching elements 321, an output transformer 322, a DC power supply unit 323, and an oscillation circuit 324. The power supply unit 32 functions as a power supply unit that supplies a voltage to the high voltage generation unit 27.

  The two switching elements 321 are constituted by semiconductor switches such as MOSFETs, for example, and the conduction state can be controlled by energization. The switching element 321 has a gate side connected to the oscillation circuit 324, a drain side connected to the primary end of the output transformer 322, and a source side grounded to the power supply ground.

  The DC power supply unit 323 is configured by a so-called switching power supply, and can arbitrarily output a DC voltage of about 2V to 20V, for example. The negative electrode side of the DC power supply unit 323 is grounded to the power supply ground. The positive side of the DC power supply unit 323 is connected to the primary side of the output transformer 322 and is grounded to the power supply ground via the switching element 321.

  The oscillation circuit 324 outputs a drive signal to each of the two switching elements 321. The switching element 321 changes its energization state in conjunction with the drive signal input from the oscillation circuit 324. The oscillation circuit 324 alternately outputs a drive signal at a timing at which the conduction states of the two switching elements 321 do not overlap each other, thereby switching the conduction states of the two switching elements 321 alternately. Therefore, the direction of the voltage applied from the DC power supply unit 323 to the primary side of the output transformer 322 is alternately switched in conjunction with the drive signal. As a result, an AC pulse voltage Vac in which, for example, positive and negative pulse voltages are alternately switched is generated on the secondary side of the output transformer 322 as an output of the power supply unit 32. In the case of this embodiment, the drive signal is set so that the frequency of the AC pulse voltage Vac is about 20 kHz.

  The control unit 33 includes a microcomputer (not shown), a microcomputer having a ROM, a RAM, and the like. The storage unit 34 is configured by, for example, a nonvolatile memory and is connected to the control unit 33. The control unit 33 functions as a control unit that controls the output of the power supply unit 32. The control unit 33 controls the output and stop of the drive signal of the oscillation circuit 324, so that the value of the output voltage Vdc output from the high voltage generator 27 of the spray gun 20 and the output and stop of the output voltage Vdc are controlled. Control.

  The CPU of the control unit 33 causes the electrostatic controller 30 to perform various operations by executing a program stored in the ROM or the storage unit 34. In addition, the electrostatic controller 30 can store a new electrostatic coating program in the storage unit 34 by connecting to an external personal computer, for example.

  The air flow switch 35 is provided in the middle of the air path 24 that connects the air valve 23 and the compressor 42. The air flow switch 35 operates when air flows through the air path 24 and outputs a signal to the control unit 33. A signal output from the airflow switch 35 at this time is referred to as a trigger detection signal. When a trigger detection signal is input from the airflow switch 35 during normal operation, that is, when no overcurrent abnormality has occurred in the high voltage generator 27, the controller 33 outputs a drive signal for the oscillation circuit 324. As a result, the output voltage Vdc is output from the high voltage generator 27.

  The operation panel 36 includes a plurality of switches 361 and a display 362. The operator performs various settings by operating the switches 361. The display unit 362 displays the setting contents, the current operation status, and the like. Moreover, the electrostatic controller 30 may have an alarm device such as a buzzer (not shown).

Next, the usage aspect of the electrostatic coating apparatus 10 in this embodiment is demonstrated with reference also to FIG.2 and FIG.3. In addition, the vertical axis | shaft of the graph shown in FIG. 3 is a voltage value or an electric current value, and a horizontal axis is time.
The control unit 33 executes the processing shown in FIG. 2 when the electrostatic coating apparatus 10 is turned on. Note that the control unit 33 constantly monitors the value of the detected current I detected by the current detection unit 31 separately from the processing of FIG. When the value of the detected current I reaches a preset abnormal current value Ia, the control unit 33 determines that an overcurrent abnormality has occurred due to a failure in the power supply unit 32, the high voltage generation unit 27, or the like. When the control unit 33 determines that an overcurrent abnormality has occurred, the control unit 33 stops the output of the power supply unit 32 regardless of the processing of FIG. The abnormal current value Ia is set to 80 μA, for example, as shown in FIGS. When an overcurrent abnormality occurs, the control unit 33 notifies the operator by displaying on the display 362 that the overcurrent abnormality has occurred.

  When the process of FIG. 2 is started, the control unit 33 first determines whether or not there is a trigger detection signal from the airflow switch 35 in step S11. The control unit 33 stands by until a trigger detection signal is detected (NO in step S11). When the trigger 26 is pulled by the operator, the paint valve 21 and the air valve 23 are opened. As a result, paint is sprayed from the nozzle 25 and a trigger detection signal is output from the airflow switch 35.

  When detecting the trigger detection signal (YES in step S11), the control unit 33 operates the power supply unit 32 in step S12. As a result, the control unit 33 outputs the output voltage Vdc from the high voltage generation unit 28. The high voltage output unit 28 outputs the output voltage Vdc and charges the paint sprayed from the nozzle 25. Thereby, electrostatic coating is started with respect to the article 100 to be coated. In this case, the control unit 33 controls the power supply unit 32 so that the output voltage Vdc finally reaches the ultimate target voltage value Va. The target target voltage value Va is a preset value, and is set to be a negative high voltage of, for example, −60 kV.

  As shown in FIGS. 3A to 3, the control unit 33 sets a threshold value Ib of the detection current I in advance. The threshold value Ib is set to a value slightly larger than the value of the detected current I when the output voltage Vdc output from the high voltage output unit 28 reaches the target target voltage value Va and smaller than the abnormal current value Ia. ing. In the present embodiment, the threshold value Ib is set to 40 μA, for example. In the normal state where no metal bridge or failure has occurred, the value of the detected current I when the output voltage Vdc reaches the target voltage value Va is as shown in the period P3 to P6 in FIG. And less than the threshold value Ib.

  On the other hand, when a failure such as a metal bridge or a short circuit has occurred, if no countermeasure is taken, the value of the detected current I when the output voltage Vdc reaches the target voltage value Va is set to the threshold value Ib. The abnormal current value Ia may be reached. However, as described above, the metal bridge is eliminated in a relatively short period of time as the paint flows. Therefore, when the detection current I reaches the threshold value Ib due to the metal bridge, the value of the detection current I becomes less than the threshold value Ib in a relatively short period of time as the metal bridge is eliminated. Therefore, when a metal bridge occurs, the necessity of stopping the electrostatic coating by stopping the operation of the power supply unit 32 and the high voltage generation unit 27 is low. On the other hand, when the detected current I is greater than or equal to the threshold value Ib due to a failure of the power supply unit 32 or the high voltage generation unit 27, the power supply unit 32 or the high voltage generation unit 27 is secured in order to ensure safety. There is a high need to stop the electrostatic coating to stop the operation.

  Therefore, in the present embodiment, the control unit 33 executes the processes of steps S13 to S18 shown in FIG. In the present embodiment, the control unit 33 repeats steps S13, S14, and S15 when no metal bridge or failure has occurred. When the metal bridge has occurred, the control unit 33 repeats steps S13, S16, S17, and S15. After the metal bridge is eliminated, the control unit 33 returns to normal and repeats steps S13, S14, and S15. On the other hand, when a failure other than the metal bridge has occurred, the control unit 33 repeats steps S13, S16, S17, and S15, and then executes step S18.

  Specifically, when the control unit 33 starts electrostatic coating by the operation of the power supply unit 32 and the high voltage generation unit 27 (step S12), in step S13, it is determined whether or not the detected current I is less than the threshold value Ib. to decide. When the value of the detected current I is less than the threshold value Ib (YES in step S13), the control unit 33 determines that the state is normal and proceeds to step S14. And the control part 33 performs constant voltage control with respect to the power supply part 32 in step S14. In this case, the constant voltage control is a control in which the AC voltage Vac output from the power supply unit 32 is constant, that is, the cycle and effective value of the AC voltage Vac are constant, or the output output from the high voltage output unit 28. This is to control the power supply 32 so that the voltage Vdc, that is, the voltage generated by the high voltage generator 27 is maintained at a constant value. In the case of the present embodiment, when constant voltage control is performed, the control unit 33 controls the output voltage of the power supply unit 32 so as to maintain the output voltage Vdc at, for example, the ultimate target voltage value Va. Thereby, for example, as shown in the period from P3 to P6 in FIG. 3A, electrostatic coating is performed at a constant output voltage Vdc, in this case, the ultimate target voltage value Va.

  The operator cancels the pulling operation of the trigger 26 and ends the electrostatic coating. When the pulling operation of the trigger 26 is released, the paint valve 21 and the air valve 23 are closed. Thereby, the spraying of the paint from the nozzle 25 is stopped, and the output of the trigger detection signal from the air flow switch 35 is stopped. In step S15, the controller 33 determines whether or not the trigger detection signal is continuously detected. When the trigger detection signal is not detected (NO in step S15), the control unit 33 determines that the pulling operation of the trigger 26 by the operator is released and the electrostatic coating is finished, and the process proceeds to step S19. The control unit 33 stops the operation of the power supply unit 32 and the high voltage generation unit 27 in step S19. Thereby, as shown in the period after P6 of FIGS. 3 (1) and 3 (2), the output voltage Vdc from the high voltage output unit 28 is stopped, and the electrostatic coating is terminated.

  On the other hand, when the control unit 33 determines in step S13 that the value of the detected current I is greater than or equal to the threshold value Ib (NO in step S13), the control unit 33 proceeds to step S16 and performs constant current control on the power supply unit 32. The constant current control refers to control for changing the voltage generated by the high voltage generator 27, that is, the output voltage of the power supply unit 32, so that the value of the detection current I is kept constant. In the case of the present embodiment, when constant current control is performed, the control unit 33 controls the output voltage of the power supply unit 32 so that the value of the detection current I is maintained at the threshold value Ib. In this case, as shown in the period P2 to P4 in FIG. 3 (2) or the period P2 to P5 in FIG. 3 (3), the output voltage Vdc is maintained at a value lower than the ultimate target voltage value Va. That is, in this case, the electrostatic coating is performed at a voltage lower than the normal output voltage Vdc, that is, the target reached voltage value Va.

  Thereafter, the control unit 33 proceeds to step S17. In step S17, the control unit 33 determines whether or not a predetermined period Tb has elapsed since the start of the constant current control. That is, in step S17, the control unit 33 determines whether or not the period during which the constant current control is continuously performed has reached the predetermined period Tb. In this case, if the average time required to eliminate the metal bridge, that is, the average time from the start of spraying paint when the metal bridge occurs until the metal bridge is eliminated is Ta seconds, the predetermined period Tb is, for example, Tb ≧ 2 × Ta seconds are set.

  In other words, if the value of the detection current I is greater than or equal to the threshold value Ib due to a metal bridge, the spraying of the paint, that is, the flow of the paint is started, and in almost all cases when the period twice as long as Ta seconds elapses. The bridge is considered to be eliminated. Therefore, if the detection current I is still greater than or equal to the threshold value Ib even after the spraying of the paint, that is, the flow of the paint has started and a period of twice Ta seconds has elapsed, the value of the detection current I is caused by a factor other than the metal bridge. It can be estimated that it is Ib or more. Note that Ta is, for example, about 50 milliseconds, but may be appropriately changed according to the type of the paint.

  When it is determined that the predetermined period Tb has not elapsed since the start of the constant current control (NO in step S17), the control unit 33 proceeds to step S15 and repeats steps S15, S16, and S17. On the other hand, when the predetermined period Tb has elapsed since the start of the constant current control (YES in step S17), the control unit 33 determines that an abnormality other than the metal bridge has occurred, and proceeds to step S18. Then, the control unit 33 notifies the operator by causing the display 362 to display that an abnormality other than the metal bridge has occurred. As a result, the operator can know that an abnormality has occurred, and can cancel the pulling operation of the trigger 26 and stop spraying the paint.

  Thereafter, the control unit 33 stops the operation of the power supply unit 32 and the high voltage generation unit 27 in step S19. Thereby, as shown in the period after P5 in FIG. 3 (3), the output voltage Vdc from the high voltage output unit 28 is stopped, and the electrostatic coating is terminated.

  In the said embodiment, the control part 33 of the electrostatic coating apparatus 10 is when the electric current I detected by the electric current detection part 31 becomes more than the threshold value Ib set to the value lower than electric current value Ia used as an overcurrent abnormality. Perform constant current control. And the control part 33 stops operation | movement of the power supply part 32, and stops supply of the voltage with respect to the high voltage generation part 27, when constant current control is performed continuously for the predetermined period Tb. Thereby, the output of the high voltage from the high voltage output part 28 is stopped, and electrostatic coating is stopped.

  According to this, even when a metal bridge is generated in the paint path 22 and the current I flowing through the high voltage generation unit 27 and the high voltage output unit 28 is likely to exceed the threshold value Ib, the control unit 33 performs the constant current control. By performing the above, it is possible to prevent the current I flowing through the high voltage generation unit 27 and the high voltage output unit 28 from exceeding the threshold value Ib. That is, the control unit 33 performs constant current control so that the current I flowing through the high voltage generation unit 27 and the high voltage output unit 28 does not reach the current value Ia that causes an overcurrent abnormality. Thereby, the control part 33 can avoid that electrostatic coating stops by an overcurrent abnormality, and can continue electrostatic coating.

  Moreover, the control part 33 stops the output of the high voltage Vdc from the high voltage output part 28, and stops electrostatic coating, when constant current control is continued for the predetermined period Tb. Thereby, when overcurrent abnormality arises by factors other than a metal bridge, electrostatic coating can be stopped and safety can be ensured. As a result, while ensuring safety, it is possible to avoid the stop of electrostatic coating due to the occurrence of a metal bridge and improve productivity.

  Further, after starting the constant current control, the control unit 33 switches to the constant voltage control when the current value I detected by the current detection unit 31 becomes less than the threshold value Ib. When the metal bridge is eliminated, the insulation resistance of the paint becomes larger than when the metal bridge is generated. Therefore, when the constant current control similar to that at the time of occurrence of the metal bridge is performed even though the metal bridge is eliminated and the insulation resistance of the paint is increased, for example, the following inconvenience occurs.

  That is, if the constant current control is to be continued even after the metal bridge is eliminated, the control unit 33 tries to set the current value I to the same current value as that when the metal bridge occurs, that is, the threshold value Ib. In this case, since the insulation resistance of the paint is increased by eliminating the metal bridge, the output voltage Vdc is larger than when the metal bridge is generated. Therefore, the control unit 33 maximizes the output voltage of the power supply unit 32, for example, always trying to output the maximum output voltage from the high voltage generation unit 28. As a result, an excessive load is applied to the power supply unit 32, the high voltage generation unit 27, and the like. Therefore, when the current I flowing through the high voltage generator 27 becomes less than the threshold value Ib, the controller 33 determines that the metal bridge has been eliminated and switches to constant voltage control. According to this, for example, it is suppressed that the maximum output voltage is always supplied to the high voltage generator 27, for example. As a result, it is possible to suppress overload on the high voltage generation unit and the like.

(Other embodiments)
The paint valve 21 and the air valve 23 may be electromagnetic valves that are operated based on an electrical signal, for example, and may be connected to the control unit 33. In this case, the control unit 33 can perform control to close the paint valve 21 and the air valve 23 when an abnormality is detected in step S18 of FIG. According to this, when an abnormality is detected in step S18, not only the voltage output from the high voltage output unit 28 but also the spraying of the paint from the nozzle 25 can be stopped. As a result, when an abnormality is detected in step S18, the coating is not performed due to the electrostatic coating not being performed, that is, the coating is sprayed from the nozzle 25 but the voltage is not applied. It is possible to reduce coating defects caused by this.

The said embodiment is not restricted to what is operate | moved by an operator's manual operation like the electrostatic coating apparatus 10. FIG. The above-described embodiment can also be applied to an electrostatic coating apparatus that is incorporated in a production line and automatically operated.
The paint used is not limited to a so-called metallic paint containing metal particles, and may be a so-called functional paint containing conductive particles such as carbon.
The embodiments of the present invention are not limited to the above-described embodiments shown in the drawings, and can be implemented with appropriate modifications without departing from the spirit of the invention.

  In the drawing, 10 is an electrostatic coating apparatus, 25 is a nozzle, 27 is a high voltage output unit, 28 is a high voltage generation unit, 31 is a current detection unit, and 33 is a control unit.

Claims (4)

A nozzle for spraying paint;
A high voltage output unit for outputting a high voltage for charging the paint sprayed from the nozzle;
A high voltage generator for supplying a high voltage to the high voltage output unit;
A current detection unit for detecting a current flowing in the high voltage generation unit;
A controller that controls the voltage output from the high voltage generator based on the current detected by the current detector;
The control unit performs constant current control when the current value detected by the current detection unit is equal to or higher than a threshold value set to a value lower than a current value causing an overcurrent abnormality, and performs the constant current control for a predetermined period. If it continues, stop the output of the voltage from the high voltage generator,
Electrostatic coating equipment. The control unit switches to constant voltage control when the current value detected by the current detection unit is less than a threshold value after starting the constant current control.
The electrostatic coating apparatus according to claim 1. A nozzle for spraying paint;
A high voltage output unit for outputting a high voltage for charging the paint sprayed from the nozzle;
A high voltage generator for supplying a high voltage to the high voltage output unit;
A current detection unit for detecting a current flowing in the high voltage generation unit;
A program for an electrostatic coating apparatus that is executed by a computer incorporated in an electrostatic coating apparatus comprising:
In the computer,
A process of executing constant current control when the current value detected by the current detection unit is equal to or greater than a threshold value set to a value lower than the current value causing an overcurrent abnormality;
A process of stopping output of the voltage from the high voltage generator when the constant current control is continued for a predetermined period;
A program for electrostatic coating equipment that executes In the computer,
A process of switching to constant voltage control when the current value detected by the current detection unit is less than a threshold value after starting the constant current control,
The program for an electrostatic coating apparatus according to claim 3, wherein the program is executed.

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