JP2012161755A - Electrostatic coating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable uniform coating without reducing work efficiency while preventing paint from adhering to a worker or a spray gun when the spray gun is separated from an object to be coated.SOLUTION: This electrostatic coating apparatus 1 includes a spray gun 2, a cascade 3 provided in the spray gun to generate a high DC voltage, an electric current detection circuit 14 that detects a current flowing through the cascade 3, and an output mode changing device 21. The output mode changing device 21 changes the output voltage of the cascade 3 to an intermittent output mode when the detected electric current becomes a reference value of Ik or below while the cascade 3 outputs DC voltage Vdc which is high voltage in a continuous output mode, and changes the output voltage of the cascade 3 to the continuous output mode when the detected electric current becomes Ik or above while the cascade 3 is in the intermittent output mode.

Description

  The present invention relates to an electrostatic coating apparatus having a configuration in which fine particles of paint are charged to a negative or positive high voltage and sprayed.

  In electrostatic coating equipment, paint (liquid paint such as solvent paint and water-based paint or powder paint) supplied to the spray gun is atomized by compressed air when the operator pulls the trigger, and is applied as fine particles. Is sprayed on the object to be coated. At this time, the atomized fine particles of the paint (hereinafter referred to as paint particles) are charged to a negative or positive high voltage by a DC high voltage generator (cascade) provided in the spray gun and grounded to the ground ( It is applied to the surface of the object by electrostatic force acting between the object to be grounded (see, for example, Patent Document 1).

JP 2006-82064 A

  In the electrostatic coating apparatus described above, the operator pulls the spray gun trigger to generate a high voltage, atomize and spray the paint particles, and the operator directs the spray gun toward the object to be coated. Perform electrostatic coating on the workpiece.

  By the way, in order to paint the object to be coated evenly, in the state where the charged paint particles are sprayed from the spray gun (when the trigger is pulled), the spray gun is moved to one position where the object is removed. While moving to the object to be coated while maintaining an appropriate distance, it is moved at an almost constant speed while being sprayed onto the object to be coated, and then moved to the distant position on the other side of the object to be coated in sequence. .

  However, if the spray gun moves away from the object to be coated, the object to which the sprayed charged paint particles are attached is far away, and the floating charged paint particles slightly adhere back to the operator or the spray gun itself. In some cases, when the adhering paint is accumulated, the paint dripped from an operator or a spray gun, and there is a risk that the adhering paint will be adhered to the object to be coated.

  Here, as a countermeasure, the operator pulls the trigger of the spray gun at a position approaching one side of the object to be coated, and cancels the pulling operation just before leaving the other side of the object to be coated. However, if the timing of the trigger pulling operation (start of blowing) is too late, or if the trigger releasing operation (ending of blowing) is too early, uneven coating tends to occur, and the coating cannot be made clean. Further, forcing the operator to perform a trigger operation that requires such skill level results in a decrease in work efficiency. Therefore, the operation mode of pulling the trigger from one part far away from the object to be painted, passing the spray gun through the part corresponding to the object, and releasing the trigger when reaching the other part far away from the object to be painted is It cannot be changed from the viewpoint of work efficiency and prevention of uneven painting.

  The present invention has been made in view of the above-described circumstances, and its purpose is to provide electrostatic coating that can be applied without lowering the work efficiency and without uneven coating, and can further prevent adhesion of paint particles to an operator or a spray gun. To provide an apparatus.

  The present invention has been made paying attention to the following points. In electrostatic coating equipment, paint particles charged at a high voltage can be adhered to the operator or the spray gun itself when the spray gun is moved away from the object to be coated as described above. It has been found that if the output voltage of the DC high voltage generator is set to a voltage lower than the normal high voltage during the separation, the adhesion of the paint particles to the operator and the spray gun can be reduced. In this case, since it was not necessary to stop spraying the paint particles, it was found that there was no uneven coating at the start of spraying. Here, it is known that the direct current high voltage generating unit decreases the current of the direct current high voltage generating unit itself when the distance of the spray gun from the object to be coated is long. It is possible to detect the separation distance from the object to be coated.

  In consideration of the above, the present inventor has made the output voltage of the DC high voltage generating unit a normal high voltage suitable for electrostatic coating (characteristic line A) as shown in FIG. Then, it is detected that the spray gun is separated from the object to be coated (for example, 300 mm or more away) when the current (output current) flowing through the DC high voltage generating unit is less than or equal to the first reference value. The output voltage of the voltage generator is set to a low voltage (see characteristic line B). Then, in order to detect that the spray gun approaches the object to be coated again, the second reference value is compared with the detection current indicated by the characteristic line B, and the detection current becomes equal to or greater than the second reference value. We are considering the control to return the output voltage of the DC high voltage generator to a high voltage by detecting that the spray gun has re-approached the object to be coated.

  However, in the case of the above-described control, as can be seen from FIG. 6, when the output voltage of the DC high voltage generator is low, the current itself flowing through the DC high voltage generator is small and the current itself changes. The rate is also small. For this reason, it is difficult to determine what value the second reference value is set to.

  In view of this point, the invention of claim 1 comprises a spray gun for atomizing paint and spraying it from a nozzle, and a DC voltage generator provided in the spray gun for generating a DC high voltage. In the electrostatic coating apparatus in which the paint particles sprayed by the above are charged to a negative or positive high voltage by the direct current high voltage generating unit and adsorbed to the object to be coated to perform the electrostatic coating, the direct current high voltage generation Current detection means for detecting the current flowing through the part, and a reference value for determining under the high voltage that the separation distance between the spray gun and the object to be coated is a predetermined distance or more, The voltage output mode of the DC voltage generator can be switched between a continuous output mode for continuously outputting the high voltage and an intermittent output mode for outputting the high voltage every predetermined time in a predetermined time width. Electric When the generation unit is in the continuous output mode state, the current detection means switches to the intermittent output mode when the detected current is less than the reference value, and the detected current is in the intermittent output mode state. And an output mode changing means for setting the continuous output mode when the reference value is exceeded.

  In the first aspect of the invention, when the DC high voltage generator is in the continuous output mode, the mode is switched to the intermittent output mode when the current detected by the current detection means becomes less than the reference value. In other words, the fact that the separation distance of the spray gun from the object to be coated has become longer is detected when the detected current is less than the reference value, and based on this, the output voltage of the DC high voltage generator is switched to the intermittent output mode. . In this case, since the paint particles are not charged in the time zone when the output of the high voltage is stopped, the return adhesion of the paint particles to the operator or the spray gun does not occur. The paint particles are charged in a time zone during which a high voltage is output. By shortening the time, it is possible to prevent the paint particles from returning to the operator and the spray gun as much as possible. Since a high voltage is output for a short time, a current flowing through the DC high voltage generator can be detected under the high voltage, and thus a detection current with a large current can be acquired. Accordingly, the reference value for determining the reapproach of the spray gun to the object to be coated can be the same as that in the high voltage continuous output mode, the reference value can be easily set, and the spray value can be set. The distance detection accuracy between the gun and the object to be painted is also stable.

  Furthermore, since the output mode of the DC high voltage generator is automatically switched, there is no need for the operator to perform voltage switching operations one by one at the timing when the distance between the spray gun and the object to be coated is reduced, resulting in lower work efficiency. There is nothing to do.

  According to a second aspect of the present invention, the output mode changing means includes an AC power supply device that generates an AC voltage by switching a DC voltage using a switching element and inputs the AC voltage to the DC high voltage generation unit. The DC high voltage generator is set to the continuous output mode by continuously operating, and the AC high voltage generator is set to the intermittent output mode by operating the AC power supply device at predetermined time intervals (intermittent operation). It has the characteristics.

  According to this, the output mode of the DC high voltage generator can be easily changed to the continuous output mode and the intermittent output mode by continuously outputting and intermittently outputting the output AC voltage by continuous operation and intermittent operation of the AC power supply device. Can be changed.

  According to the present invention, it is possible to paint without reducing the work efficiency and without uneven painting, and further, it is possible to prevent the paint particles from adhering to the operator and the spray gun when the spray gun is separated from the object to be coated. The detection accuracy of the distance between the object and the object to be coated is not lowered.

Functional block diagram of the electrostatic coating apparatus according to the first embodiment of the present invention. Flow chart showing the control contents of the control unit Diagram showing the relationship between the distance between the spray gun and the object to be painted and the current flowing in the cascade The figure which shows an example of the change of the output mode of a cascade FIG. 2 equivalent view showing the second embodiment of the present invention 3 equivalent diagram showing a reference example

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram schematically showing an electrical configuration of the electrostatic coating apparatus 1 according to the first embodiment. The electrostatic coating apparatus 1 includes a spray gun 2, a cascade (corresponding to a direct current high voltage generation unit in the present invention) 3 built in the spray gun 2, and an alternating current connected to the cascade 3 via a connection cable 4. A control device 6 having a power supply device 5 is provided. The connection cable 4 includes power supply cables 4a and 4b for supplying an AC voltage Vac and a current detection cable 4c for a current detection circuit (current detection means in the present invention) 14.

  The spray gun 2 has a main body formed of a synthetic resin such as polyacetal resin or fluorine resin having electrical insulation, for example. The spray gun 2 has a configuration used for general electrostatic coating, and includes a nozzle 2a, an atomizing air hole and a pattern forming air hole provided in the vicinity of the nozzle 2a (both not shown). ).

  The spray gun 2 further includes a paint valve 15 and an air valve 16 inside. The paint valve 15 and the air valve 16 are operated by pulling a trigger 2b (shown schematically in FIG. 1) provided in the spray gun 2. To be released. The paint valve 15 is connected to a paint tank 18 via the paint pump 17. The air valve 16 is connected to a compressor 19, and an air flowchart switch 20 is interposed in an air piping path between the compressor 19 and the air valve 16.

  The air flowchart switch 20 is provided in the control device 6 and operates when air flows through the air piping path, and supplies an air flow detection signal, that is, a trigger operation detection signal to the control unit 13 described later. Yes.

  The compressed air supplied from the compressor 19 is discharged from the atomizing air holes and the pattern forming air holes, whereby the paint supplied from the paint tank 18 is atomized and the atomized paint particles are suitable for painting. Form into a shape (paint pattern) and spray.

  The cascade 3 includes a step-up transformer 3a, a voltage doubler rectifier circuit 3b, and an output resistor 3c, and generates a DC voltage Vdc having a magnitude proportional to the AC voltage Vac supplied from the AC power supply device 5. In other words, the AC voltage Vac input to the step-up transformer 3a is boosted and then boosted and rectified by, for example, a Cockcroft-Walton type voltage doubler rectifier circuit 3b and converted to a high voltage of about 60 kV to 100 kV. The voltage doubler rectifier circuit 3b changes the direction of a diode (not shown) in the circuit to make the polarity of the output voltage positive (plus) or negative (minus) with respect to the ground potential. Can do. In the case of the present embodiment, the polarity of the output voltage of the voltage doubler rectifier circuit 3b is configured to be negative with respect to the ground potential, and the pin-like electrode 7 provided in the vicinity of the nozzle 2a of the spray gun 2 Is supplied with a negative DC voltage Vdc (high voltage suitable for normal electrostatic coating) via the output resistor 3c.

  The AC power supply device 5 includes an oscillation circuit 8, a DC power supply 9, two switching elements 10 and 11, and an output transformer 12. The AC power supply device 5 and the control unit 13 are used to change an output mode as output mode changing means. The apparatus 21 is comprised.

  The output of the DC power supply 9 is connected to the power supply ground via the switching elements 10 and 11 on the primary side of the output transformer 12. Specifically, the output terminal of the DC power supply 9 is set to be positive with respect to the ground potential by the output transformer 12 and the switching element 10, and is set to be negative with respect to the ground potential by the output transformer 12 and the switching element 11. It is connected to the.

  The switching elements 10 and 11 are configured by semiconductor switches such as MOSFETs, for example, and the conduction state can be controlled by energization. The switching elements 10 and 11 become conductive (on) when energized, and become non-conductive (off) when energization is stopped, and on / off is controlled by the oscillation circuit 8 and the control unit 13. . The control unit 13 is configured by a microcomputer including a CPU, a ROM, a RAM, and the like (not shown), and outputs a command signal corresponding to the energization time (ON time) of the switching elements 10 and 11 to the oscillation circuit 8. . The oscillation circuit 8 generates a pulsed drive signal based on this command signal and outputs it to the respective switching elements 10 and 11.

  The switching elements 10 and 11 change their energization state in conjunction with the drive signal output from the oscillation circuit 8 and switch the output of the DC power supply 9 to the positive side or the negative side. The drive signal is output at a timing at which the ON states of the switching elements 10 and 11 do not overlap each other, and the switching elements 10 and 11 are alternately turned on and off alternately at several tens of kHz, for example, according to the pulse width of the drive signal. As a result, a low-voltage AC voltage Vac corresponding to the output voltage of the DC power supply 9 is generated on the secondary side of the output transformer 12.

This AC voltage Vac is supplied to the cascade 3 via the connection cable 4.
The cascade 3 generates a DC voltage Vdc (for example, 60 kV) that is a high voltage corresponding to the magnitude of the AC voltage Vac. This DC voltage Vdc is supplied to the electrode 7 through an output resistor.

  The AC power supply device 5 is driven (operated) in response to a drive command signal from the control unit 13, and the drive pattern includes a continuous drive mode and an intermittent drive mode. In the drive mode, the cascade 3 continuously outputs the DC voltage Vdc (continuous output mode, indicated by the symbol Mr in FIG. 4), and in the intermittent drive mode of the AC power supply device 5, the cascade 3 intermittently outputs the DC voltage Vdc. (Intermittent output mode, indicated by symbol Mp in FIG. 4). This intermittent output mode is a mode in which the DC voltage Vdc is output at a predetermined time width b (for example, 3 to 5 msec) and the output is repeatedly stopped every predetermined time a (for example, 100 msec). In FIG. 4, for the sake of convenience, the ratio of the predetermined time width b to the predetermined time a in the intermittent output mode is scaled up.

  The current detection circuit 14 detects the magnitude of the current (output current) flowing through the cascade 3 via the connection cable 4 (current detection cable 4c) and supplies it to the control unit 13. The control unit 13 When the current exceeds a preset excess current determination reference value, it is determined that there is an abnormality, and for example, the operation of the oscillation circuit 8 is stopped and the output of the AC power supply device 5 is stopped.

  Further, the control unit 13 sets a reference value Ik (see FIG. 3) in addition to the excess current determination reference value. The reference value Ik is a current determination for determining that the separation distance between the spray gun 2 and the object to be coated 22 is a predetermined distance (for example, 300 mm) or more under the DC voltage Vdc that is the high voltage. This is the reference value.

  Now, in the electrostatic coating apparatus 1 having the above-described configuration, the control unit 13 has a control program for electrostatic coating, and control contents according to the control program will be described with reference to FIG. When the operator pulls the trigger 2b after turning on the paint pump 17 and the compressor 19, the air flow switch 20 is turned on.

  When determining that the air flow switch 20 is turned on in step S1, the control unit 13 sets the drive mode for the AC power supply device 5 to the intermittent drive mode in step S2, thereby changing the initial output mode of the DC voltage Vdc of the cascade 3 to the intermittent output mode. And

  Here, the reason why the initial output mode of the cascade 3 is set to the intermittent output mode as described above by the pulling operation of the trigger 2b is that the operator initially positions the spray gun 2 at a position away from the workpiece 22. Since the trigger 2b is pulled (the spraying of the paint is started but the spraying on the object 22 is not yet reached), the output of the cascade 3 may be stopped, but the distance of the trigger 2b to the object 22 is a predetermined distance. Therefore, the DC voltage Vdc is output every predetermined time for a predetermined time width (3 to 5 msec) that is a time necessary for acquiring the detection current from the current detection circuit 14. By the way. In this case, since the cascade 3 outputs the DC voltage Vdc every 100 milliseconds with a time width of 3 to 5 milliseconds, it is possible to prevent the paint particles from adhering to the worker or the spray gun 2 as much as possible. The predetermined time width of 3 to 5 milliseconds is a time sufficient for the cascade 3 to raise and output the DC voltage Vdc.

  In step S3, whether or not the detected current from the current detection circuit 14 has become equal to or greater than the reference value Ik (whether the operator has moved the spray gun 2 away from the object 22 to be separated by 300 mm or less). If it is determined that the reference value is equal to or greater than the reference value Ik, the process proceeds to step S4, where the output voltage of the AC power supply device 5 is set to the continuous drive mode, whereby the cascade 3 is set to the DC voltage Vdc continuous output mode.

  In this continuous output mode, corona discharge sufficient for coating is generated at the electrode 7 and the paint particles sprayed from the spray gun 2 are charged. The object to be coated 22 is grounded (grounded) to become an anode, and has the same potential (ground potential) as the AC power supply device 5 and the like. The electrostatic coating apparatus 1 normally performs electrostatic coating to apply such paint particles to an earthed object 22 by electrical adsorption force by charging.

  In step S5 following step S4, it is determined whether or not the current detected by the current detection circuit 14 is less than the reference value Ik (whether the operator has separated the spray gun 2 from the object 22 by more than 300 mm). If the detected current is less than the reference value Ik, the process proceeds to step S6 to set the intermittent output mode. In this case, as described above, the output voltage of the cascade 3 is an output with a very short time width, so that it is possible to prevent the paint particles from adhering to the operator or the spray gun 2 as much as possible.

When the pulling operation of the trigger 2b is released, the above-described control operation is stopped and the air flow switch 20 is on standby.
In the above-described embodiment, when the cascade 3 is in the continuous output mode state, the mode is switched to the intermittent output mode when the current detected by the current detection circuit 14 becomes less than the reference value Ik. That is, it is detected that the separation distance of the spray gun 2 from the object to be coated 22 has been increased by detecting that the detected current is less than the reference value Ik, and based on this, the output voltage of the cascade 3 is switched to the intermittent output mode. . In this case, since the paint particles are not charged in the time zone in which the output of the DC voltage Vdc, which is a high voltage, is stopped, the return adhesion of the paint particles to the operator or the spray gun 2 does not occur. In the time zone in which the DC voltage Vdc is output, the paint particles are charged, but since the time is shortened, it is possible to prevent the paint particles from returning to the operator and the spray gun 2 as much as possible. And although it is a short time, by outputting DC voltage Vdc, the current which flows into the said cascade 3 under this DC voltage Vdc can be detected, Therefore A detection current with a large electric current can be acquired. Therefore, the same reference value Ik as that in the continuous output mode of the DC voltage Vdc can be used as the reference value Ik for determining reapproach of the spray gun 2 to the object 22 to be coated, and the setting of the reference value is easy. In addition, the distance detection accuracy between the spray gun 2 and the object to be coated 22 is also stable.

  Furthermore, since the output mode of the cascade 3 is automatically switched, it is not necessary for the operator to perform the voltage switching operation one by one at the timing when the distance between the spray gun 2 and the workpiece 22 is increased, and the work efficiency is lowered. There is nothing.

  Further, according to the present embodiment, the output mode changing device 21 includes the AC power supply device 5 that generates the AC voltage Vac by switching the DC voltage Vdc with the switching elements 10 and 11 and inputs the AC voltage Vac to the cascade 3. The cascade 3 is set to the continuous output mode by continuously operating the AC power supply device 5, and the cascade 3 is set to the intermittent output mode by operating the AC power supply device 5 at predetermined time intervals (intermittent operation). By continuously outputting and intermittently outputting the output AC voltage Vac by the continuous operation and intermittent operation of the AC power supply device 5, the voltage output mode of the cascade 3 can be easily changed to the continuous output mode and the intermittent output mode.

  As described above, according to the present embodiment, the coating efficiency can be applied without lowering the work efficiency, and the paint particles can adhere to the operator and the spray gun 2 in a state where the spray gun 2 is separated from the workpiece 22. Moreover, the detection accuracy of the distance between the spray gun 2 and the object to be coated 22 is not lowered.

  FIG. 5 shows a second embodiment of the present invention, which is different from the first embodiment in that the initial output mode of the cascade 3 is set to the continuous output mode (step T1). . In the second embodiment, it is possible to try the charge rising before the start of painting, and thereafter, the same effect as in the first embodiment can be obtained.

  The paint particles may be positively charged. In this case, the object 22 is preferably a cathode.

  In the drawings, 1 is an electrostatic coating device, 2 is a spray gun, 2b is a trigger, 3 is a cascade (DC high voltage generator), 5 is an AC power supply device, 9 is a DC power supply, 10 and 11 are switching elements, and 14 is A current detection circuit (current detection means) 21 indicates an output mode change device (output mode change means).

Claims (2)

A spray gun that atomizes the paint and sprays it from the nozzle, and a DC voltage generator that is provided in the spray gun and generates a DC high voltage. The paint sprayed by the spray gun generates the DC high voltage. In electrostatic coating equipment that performs electrostatic coating by charging to negative or positive high voltage by the part and adsorbing to the object to be coated,
Current detection means for detecting a current flowing through the DC high voltage generator;
It has a reference value for determining under the high voltage that the separation distance between the spray gun and the object to be coated is a predetermined distance or more, and the voltage output mode of the DC voltage generator is set to the high voltage When it is possible to switch between a continuous output mode for continuously outputting a voltage and an intermittent output mode for outputting the high voltage every predetermined time with a predetermined time width, and when the DC high voltage generator is in the continuous output mode state When the detected current by the current detecting means becomes less than the reference value, the mode is switched to the intermittent output mode, and when the detected current becomes the reference value or more in the intermittent output mode state, the continuous output is performed. An output mode changing means for setting a mode;
An electrostatic coating apparatus comprising:   The output mode changing means includes an AC power supply device that generates an AC voltage by switching a DC voltage with a switching element and inputs the AC voltage to the DC high voltage generator, and the DC power supply device is operated by continuously operating the AC power supply device. 2. The high voltage generator is set to the continuous output mode, and the DC high voltage generator is set to the intermittent output mode by operating the AC power supply device at a predetermined time interval every predetermined time. The electrostatic coating apparatus described.

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