JPH10202151A - Electrostatic coating system and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an electric discharge from being generated by a coating material applicator and at the same time, improve the efficiency of a high voltage power supply by controlling the increase and decrease of high voltage to be applied to the applicator based on a current sensing signal connected to an area between the applicator and a target object. SOLUTION: When high voltage generated by connecting a variable voltage drive signal to a high voltage module 200 from a control module 300, is applied to a coating material applicator 100 for giving a coating material to a target object T, a current sensing signal which represents the current filtered within the range of a change rate of current or a zone passing frequency between the applicator 100 and the object T, is generated. Further, a control signal is connected to the control module 300 by a system controller 400 in response to the current sensing signal, so that the high voltage to be sent to the applicator 100 is decreased(increase) under control when the change rate of current increases(decreases).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic coating system and method for applying a coating material to a target object.
More specifically, the present invention relates to preventing discharge from a coating material applicator of an electrostatic coating system and increasing the efficiency of a high voltage power supply that supplies a high voltage to the coating material applicator of the electrostatic coating system.

[0002]

2. Description of the Related Art Electrostatic coating systems apply an electrostatically charged fluid or powder coating material to a target object, which is stationary or moved along a conveyor, and applies the coating material to the target object. Used to adhere uniformly. These systems generally include a coating material applicator that is maintained at a high potential with respect to the target object. The coating material applicator is usually, but not always, at a negative potential, and the target object is maintained at or near ground potential. As used herein, the term coating material applicator refers to a type of device for charging powdered and fluid coating materials and applying the charged coating material to a target object. These coating material applicators are described, for example, in the "Nonincendive Rotary Atomizer" dated July 18, 1995 by Howe et al., Assigned to Lansberg Corporation, the assignee of the present invention, herein incorporated by reference. No. 5,433,387, entitled "Atomizer", and include, inter alia, a coating material application gun, a coating material application bell and a coating material application sprayer.

[0003] The relatively high voltage between the coating material applicator and the target object causes a substantial electrical discharge or spark potential between the coating material applicator and the target object, including the operator, to cause substantial voltage to the operator. Causes electric shock. In addition, many coating materials are volatile and flammable, which can ignite when discharged, leading to a risk of injury. When operating the electrostatic coating system,
Workplace safety regulations under the Safety and Health Act (OSHA) apply, and the liability insurer states that, with a few exceptions, the operation of electrostatic painting can be controlled by the National Fire Protection Association for spray finishing operations ( NFPA) requires that it be performed in accordance with the standard. Accordingly, it is desirable to prevent discharge of an electrostatic coating system to meet government ordinances and industry standards and reduce the risk of injury to the operator.

[0004]

Some progress has already been made towards reducing the risk of discharge of electrostatic coating systems. For example, Bentley, assigned to Lansberg Corporation, the assignee of the present invention, entitled "Electrostatic Coating System" dated February 5, 1980.
U.S. Pat. No. 4,187,527 entitled "System)", a short-circuit device having a low resistance discharge resistor is disclosed in US Pat.
The high voltage between the coating material applicator and the target object is rapidly reduced to zero when a spark condition is imminent. More specifically, the discharge device is enabled by a control circuit in response to detecting an excess current or an excessive rate of change of current between the coating material applicator and the target object. These detected current parameters generally depend on the distance between the coating material applicator and the target object, the size and shape of the target object, and the rate at which the target object moves relative to the coating material applicator. . Thus, Bentley prevents discharge by rapidly disabling the voltage of the coating material applicator when an electric spark is imminent. However, Bentley does not change the voltage of the coating material applicator in response to changing current parameters. Rather, the high voltage of Bentley's coating material applicator is affected by changing current parameters only when the current parameter limits are exceeded,
Voltage is completely disabled and must be reset manually.

US Patent No. 4,745,520, entitled "Power Supply", issued May 17, 1988, issued to Hughes, also assigned to Lansberg Corporation, the assignee of the present invention, An electrostatic coating system having a high voltage generator connected to a coating material applicator is disclosed. The high voltage of the coating material applicator is discharged relatively quickly when an electrical spark is imminent by substantially eliminating the high voltage output and the high resistance and high capacitance of the coating material applicator.
The high-voltage generator comprises a high-voltage transformer whose center-tapped primary winding is driven by a pulse-width-modulated drive signal, which is controlled by a fixed-frequency oscillator. Are alternately switched through the two halves of The pulse width modulated drive signal adjusts the high voltage of the coating material applicator based on the voltage feedback signal in response to the control signal. The high voltage generator removes voltage from the center tap of the primary winding and responds to the overload current detected between the coating material applicator and the target object and applies a high voltage to the coating material applicator in a series. It is disabled by discharging through a resistor. However, Hughes' system must be manually reset when the high voltage generator is disabled in response to an overload current condition. Also, the high voltage generator is momentarily disabled in response to a signal representing a corona discharge, but is only enabled if the generation of the signal representing the corona discharge is discontinuous within a particular time period. Otherwise, Hughes' system must be reset manually, as in the case of an overload current condition. Hughes also does not change the voltage of the coating material applicator in response to changing current parameters. Rather, the high voltage of Huge's coating material applicator, like Bentley, is completely disabled only when current parameter limits are exceeded. He gives automatic system recovery if the current fault is corrected within a specified time period, or the system must be manually reset.

[0006] Lans-Pa, available from Ransburg Corporation of Indianapolis, Indiana
The k®1000 power supply includes a high voltage transformer and an integral cascade transformer to provide high voltage output to the coating material applicator. The high voltage of the coating material applicator is controlled based on a number of current parameters between the coating material applicator and the target object. First, the high voltage of the coating material applicator is similar to that described above for US Pat. No. 4,745,520 to Hughes,
Disabled in response to a DC overload condition. Second
In addition, the high voltage is dynamically changed as a DC change between a DC threshold and a DC value corresponding to a DC overload condition. The high voltage is reduced along the steep load line in response to the increasing direct current as the target object approaches the coating material applicator, and the voltage decreases as the target object moves away from the coating material applicator. Is increased along the same steep load line. However, with this arrangement, the voltage is controlled over a relatively narrow range of DC changes by the steep load lines. Also, Lans-Pak (registered trademark) 1000
The power supply does not include dynamic voltage control in response to current rate fluctuations and current parameters representing corona discharge. Therefore, the Lans-Pak® 1000 power supply
The coating material applicator will undergo unnecessary disabling of the high voltage to prevent discharge.

[0007] This is also assigned to Lanceberg Corporation, the assignee of the present invention, by Huge et al., 1992.
High-voltage power supply control system (High
U.S. Pat. No. 5,159,544 entitled "Voltage Power Supply Control System" includes a coating material applicator connected to a high voltage generator that includes a high voltage transformer, wherein the high voltage generator comprises Operated at resonance frequency,
An electrostatic coating system is disclosed that provides a maximum output voltage and reduces the risk of discharge. The voltage controlled oscillator provides an output signal for driving a primary winding of a high voltage transformer. The phase comparator generates a control signal based on the output signal phase of the voltage controlled oscillator and the output signal phase of the secondary winding of the high voltage transformer. The control signal of the phase comparator is
It is used to vary the frequency of the output signal generated by the voltage controlled oscillator so that the output signal of the secondary winding of the high voltage transformer is 90 ° out of phase. Therefore,
The high voltage transformer is operated at its maximum output voltage to prevent the risk of unexpected voltage surges that can cause a discharge.

From the foregoing, it is apparent, among other things, that there is a need for improving known electrostatic coating systems and methods.

[0009]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a novel electrostatic coating system and method that overcomes the known problems. It is also an object of the present invention to provide a novel electrostatic coating system and method that reduces the risk of discharge between the coating material applicator and the target object.

It is another object of the present invention to dynamically adjust the voltage supplied to the coating material applicator based on a current sensing signal generated in a closed loop feedback system to provide a voltage between the coating material applicator and a target object. It is an object of the present invention to provide a novel electrostatic coating system and method for preventing electrostatic discharge of a sheet.

It is yet another object of the present invention to dynamically adjust the voltage supplied to the coating material applicator based on a current sensing signal generated in a closed loop feedback system, and to control the voltage between the coating material applicator and the target object. A novel electrostatic coating system and method for preventing electrostatic discharge during, wherein the current sensing signal is a direct current, a current to provide improved sensitivity to a relatively wide range of conditions indicative of an imminent discharge. It is to provide a novel electrostatic coating system and method that represents one or more of the rate of change and the filtered current in the bandpass frequency range.

It is also an object of the present invention to provide a novel electrostatic coating system and method that increases the efficiency of a high voltage power supply that supplies a high voltage to the coating material applicator of the electrostatic coating system. Another object of the invention is to provide a delay between the first and second complementary drive signals that alternately sink the variable voltage drive signal provided to the center tap of the high voltage transformer. It is an object of the present invention to provide a novel electrostatic coating system and a method for increasing the efficiency of a high voltage power supply for supplying a high voltage to a coating material applicator of an electrostatic coating system.

Another object of the present invention is to vary the driving frequency of the first and second complementary drivers which alternately sink the variable voltage drive signal supplied to the center tap of the high voltage transformer. A novel electrostatic coating system and method for increasing the efficiency of a high voltage power supply that supplies a high voltage to a coating material applicator of an electrocoating system, wherein the variable voltage drive signal is a selected voltage at the output of a high voltage transformer. To provide a novel electrostatic coating system and method that is minimized for

It is yet another object of the present invention to provide a drive frequency of a first and second complementary driver that alternately sinks a variable voltage drive signal supplied to a center tap of a high voltage transformer with a phase shift. A novel electrostatic coating system and method for increasing the efficiency of a high voltage power supply that supplies a high voltage to a coating material applicator of an electrostatic coating system by matching the resonant frequency of the high voltage transformer, comprising: It is to provide a novel electrostatic coating system and method in which the voltage at the output of the vessel is maximized.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantages of the present invention will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, in which like parts and steps are designated by the same reference numerals. . FIG. 1 is a block diagram of an electrostatic coating system 10 that generally includes a coating material applicator 100 for applying a charged coating material toward a target object T. The coating material applicator 100 is maintained at a relatively high positive or negative potential relative to the target object T, which is typically at or near ground potential. The operating voltage between the coating material applicator 100 and the target object T is
It has a DC voltage component having a magnitude of about 20 kilovolts (kV) to about 100 kV. Coating material applicator 1
The operating current between 00 and the target object T has a DC component with a magnitude of about 20 microamps (μA) to about 1000 μA. However, these operating voltage and current ranges are merely exemplary, and those skilled in the art will recognize, among other things, the conductivity of the coating material, the type of coating material applicator, the number of coating material applicators in the system, the coating material, and the like. It will be apparent that it may be larger or smaller based on a number of factors, including the distance between the applicator and the target object, and the size and shape of the target object. Further, according to one aspect of the present invention, these operating voltage and current parameters are:
As described below, the voltage applied to the coating material applicator is controlled and the coating material applicator 100 is controlled.
It is dynamically varied within and outside these ranges to control the current between it and the target object T.

[0016] The coating material applicator 100 generally comprises
A coating material application gun for applying a charged liquid or powder coating material, or a coating material application rotary sprayer, or a coating material application sprayer. In one exemplary configuration,
The coating material applicator 100 is disclosed in How et al., 1995, assigned to the assignee of the present invention, which is incorporated herein by reference.
Rotary with relatively low capacitance to reduce stored energy as disclosed in U.S. Pat. No. 5,433,387 entitled "Nonincendive Rotary Atomizer" dated July 18, 2008. It is a nebulizer. The coating material applicator 100 is more generally arranged in an electrical circuit configuration in parallel with a common high voltage power supply of the electrostatic coating system to apply the coating material to one or more target objects. 3 shows a plurality of coating material applicators. Also, as used herein, the term target object refers to an object (one or one) that forms a discharge path from the coating material applicator 100 regardless of whether the object is the intended target object of the applied coating material. Plural). Thus, for example, target objects also include operators and other objects that may be near the coating material applicator 100 and cause an electrical discharge.

The system 10 shown in FIG.
0 and output 2 connected to the coating material applicator 100
20 is provided.
In FIG. 2, the high voltage module 200 includes a high voltage transformer 230 having a primary winding and a high voltage secondary winding, the secondary winding of which is a high voltage rectifier / multiplier circuit 24.
0, which is connected to the high voltage AC of the secondary winding of the transformer.
The signal is converted to a high voltage DC output, which is provided to the coating material applicator 100. This exemplary high voltage module configuration is disclosed in U.S. Pat. No. 4, entitled "Power Supply", issued May 17, 1988, assigned to the assignee of the present invention and incorporated herein by reference.
No. 745,520. In applications where a single coating material applicator 100 is connected to the high voltage module 200, the high voltage module 200 may be integrated with the coating material applicator 100 and stored energy as disclosed in the Hughes patent, which is incorporated by reference. And can be dissipated relatively quickly. In applications where a number of coating material applicators are connected to the high voltage module 200 in a parallel configuration, the corresponding high voltage cable may connect the high voltage module 200 to the high voltage module 200.
Is connected to a number of individual coating material applicators, in this case a high voltage power supply 200 and a coating material applicator 1
The distance between 00 is generally minimized to reduce stored energy.

FIG. 1 shows a control module 300 connected to a high voltage module 200, which provides a variable voltage drive signal at an input 210 of the high voltage module and connects to a coating material applicator 100. A high voltage is generated at the output 220 of the high voltage module. The control module 300 shown in FIG. 2 includes a pulse width modulator 310 and a switching regulator 320. Pulse width modulator 310 generates a variable output signal in response to a control signal from system controller 400. In one embodiment, pulse width modulator 310 is a programmable frequency / pulse width generator that produces a variable frequency and duty cycle output signal that varies between about 40 kHz and about 60 kHz. Switching regulator 320 is connected to pulse width modulator 310 and generates a variable voltage drive signal in response to the variable output signal. The switching regulator 320 supplies a variable voltage drive signal to the center tap 232 of the high voltage primary winding to generate a variable high voltage at the output of the high voltage transformer. A first phase driver 330 is connected to the first input 234 of the primary winding of the transformer, and
The phase driver 340 is connected to the second input 236 of the primary input winding of the transformer. The first phase driver 330 generates a first signal in response to the first drive signal from the controller 400, sinks the variable voltage drive signal provided to the center tap 232, and
0 alternately generates the second signal in response to the second drive signal from the controller 400 and sinks the variable voltage drive signal provided to the center tap 232. Due to this feature of the present invention, the first signal from the first phase driver 330 and the second signal from the second phase driver 340 are also at the same frequency and 180 ° out of phase.

FIGS. 1 and 2 show a coating material applicator 10.
5 shows a voltage sensing module 500 connected to the output 220 of the high voltage module to generate a voltage sensing signal representing a high voltage between 0 and the target object T. In one embodiment, the voltage sensing signal is based on a first voltage feedback signal generated by a resistive divider circuit at the output 220 of the high voltage module. A first voltage feedback resistive divider circuit suitable for this purpose is described by Huge, assigned to the assignee of the present invention, Power Sup, dated May 17, 1988, incorporated herein by reference.
ply) "in U.S. Pat. No. 4,745,520. The voltage sensing module 500 is connected to the system controller 400 to provide a voltage sensing signal to the system controller 400. The system controller 400 generates and supplies control signals to the control module 300 in response to the voltage sensing signal, and the high voltage of the coating material applicator 100 is applied to the system controller 4.
In response to the control signal from 00, the control module 300 can adjust to the first voltage level during steady state operation. This first voltage level is generally a user-defined voltage level selected for a particular coating application,
It is entered into the system controller 400 at the user interface 30 and displayed on the visual indicator 40. In one embodiment, the voltage sensing signal comprises:
A control signal for controlling the variable voltage of the pulse width modulator, as disclosed in detail in U.S. Pat. No. 4,745,520 entitled "Power Supply", issued May 17, 1988 by Hughes, supra. Is supplied to a comparator that generates FIG.
In one embodiment, the voltage sensing signal is passed through a buffer 20 to a microprocessor-based system controller 40.
0 and the system controller 400
In response, it generates a control signal for controlling the variable output signal generated by pulse width modulator 310 and controls switching regulator 320 as described above. Accordingly, the voltage of the coating material applicator 100 is dynamically increased or decreased in response to the voltage sensing signal to provide a desired voltage to the coating material applicator 100.

The current sensing module 600 shown in FIG.
Are the direct current (I) between the coating material applicator 100 and the target object T, the current change rate (di / dt) between the coating material applicator and the target object, and Connected to the output 220 of the high voltage module to generate a current sensing signal representative of at least one of the filtered currents BP (i) in the bandpass frequency range between. In one embodiment, the current sensing signal is based on a second voltage feedback signal generated by a resistance in series with the return of the high voltage module output 220 to ground.
A second voltage feedback resistor circuit suitable for this purpose is disclosed in U.S. Pat. No. 4,745, issued May 17, 1988 to Hughes, assigned to the assignee of the present invention and entitled "Power Supply". 520. According to this aspect of the invention, the DC current is proportional to the DC component of the second voltage feedback signal corresponding to the current sense signal, and the current rate of change signal and the filtered current signal are as described below. , A second voltage feedback signal.

Also, the current sensing module 600 is connected to the system controller 400 to provide a current sensing signal to the system controller 400. The system controller 400 generates and supplies a control signal to the control module 300 in response to the current sensing signal, and the high voltage of the coating material applicator is dynamically controlled by the control module 300 in response to the control signal from the system controller 400. Can be adjusted. Therefore, the coating material applicator 10
The high voltage sent to 0 is controlled in response to both a voltage sense signal and a current sense signal. However, for the purpose of controlling the high voltage, the current sensing signal has a higher priority than the voltage sensing signal. This is because the current sensing signal generally represents an initial electrostatic discharge that can be prevented by reducing the high voltage. In the embodiment of FIG. 2, the current sensing signals are provided to a microprocessor-based system controller 400, which generates control signals for controlling a variable voltage drive signal of the control module 300, wherein the control signals are , May be generated by an analog circuit.

The rate of change of current is generally measured by sampling the current sensing signal and comparing the most recently sampled signal with the already sampled signal. In one embodiment, the second voltage feedback signal corresponding to the current sensing signal is the Bently assigned "Electrostatic Coating System" dated February 5, 1980, assigned to the assignee of the present invention, which is incorporated herein by reference. (Ele
ctrostatic Coating System)
As described in detail in US Pat. No. 187,527, the signal is supplied to a tilt detection circuit incorporating a sample and hold circuit. In the embodiment of FIG. 2, the second
Is supplied to the microprocessor-based system controller 400 via the buffer 22. In this configuration, the microprocessor-based system controller 400 continuously samples the current sense signal and compares the most recently sampled current sense signal with the already sampled current sense signal to provide a measure of the current rate of change. obtain. In one embodiment, the system controller 400 determines the current sense signal D
The C component is sampled to obtain a measure of the current change rate. Microprocessor based system controller 400
Can provide a relatively instantaneous measure of the rate of change of the current, allowing the system controller 400 to more responsively control the high voltage of the coating material applicator 100. This improved high voltage control allows the system controller 400
Reduces the high voltage of the coating material applicator 100 in response to an increase in the rate of current change before the rate of current change increases to a level at which the high voltage of the coating material applicator needs to be disabled; As described in detail below, generally improved operating efficiency can be obtained.

[0023] The filtered current in the bandpass frequency range is typically measured by filtering the current sensing signal with a bandpass filter. In one embodiment, as disclosed in detail in US Patent No. 4,745,520 to Hughes, which is incorporated by reference,
A second feedback voltage signal corresponding to the current sensing signal is provided to an analog bandpass filter circuit to generate a filtered current in a bandpass frequency range. In the embodiment of FIG. 2, the second
Are fed by a buffer 24 to a programmable bandpass filter 50 connected to a microprocessor-based system controller 400, which can be programmed by the system controller 400. In one application, the range of the bandpass filter is from about 20 Hz to about 2000 Hz with a center frequency of about 200 Hz. More generally, the frequency range may be wider or narrower, and the center frequency will vary based on the particular application. In one configuration, a number of different frequency ranges and their corresponding center frequencies are stored in memory and selected and used in different coating material applications.
In accordance with this aspect of the invention, the output signal of filter 50 corresponds to the filtered current in the bandpass frequency range and indicates the potential for corona discharge in coating material applicator 100. System controller 400
Controls the high voltage supplied to the coating material applicator 100 in response to the measured level of the filtered current in the bandpass frequency range, as described in detail below.

The high voltage supplied to the coating material applicator 100 is coupled to a current sensing signal indicative of at least one of an increase in DC current, an increase in current change rate, and an increase in filtered current in the bandpass frequency range. In response, it can be dynamically reduced. Also, the high voltage provided to the coating material applicator 100 is responsive to a current sensing signal indicative of at least one of a decrease in DC current, a decrease in current change rate, and a decrease in filtered current in the bandpass frequency range. Then, it can be dynamically increased by the control module 300.

FIG. 3 is a graph showing an exemplary load curve relationship between the high voltage supplied to the coating material applicator 100 and the DC current between the coating material applicator 100 and the target object T. According to one feature of the present invention, the high voltage supplied to the coating material applicator 100 is a first voltage.
Direct current rises above the DC current level I _1, the current rate of change increases from the first current change rate level, and at least one of the filtered current in the band pass frequency range increases from the first band-pass current level dynamically it is reduced to the first voltage level V ₁ or less in response to a current sense signal representative of the above. The high voltage of the coating material applicator
A DC current decreasing toward a first DC current level, a current change rate decreasing toward a first current change level,
And dynamically increasing toward the _first voltage level V1 in response to a current sense signal representing at least one of the filtered currents in a bandpass frequency range decreasing toward the first bandpass current level. Is done.

According to another feature of the present invention shown in FIG. 3, the high voltage supplied to the coating material applicator, a DC current exceeding a DC current limit I _max, the current change rate and a band pass beyond the change rate limit Disabled in response to a current sensing signal representing at least one of the filtered currents in a bandpass frequency range that exceeds a filter current limit. Also, the high voltage supplied to the coating material applicator
It may be disabled when the voltage decreases to a certain minimum value.

In accordance with another aspect of the present invention, the system controller 400 disables the supply of the coating material applicator 100 when the current sensing signal component that caused the fault condition disappears within a specified time. Automatically attempts to enable the voltage. In one mode of operation, for example, a disabled high voltage is enabled when the level of the filtered current in the bandpass frequency range representing the corona discharge disappears within a specified time. According to this aspect of the invention, the system controller 400 attempts to reset the system multiple times before the disabled high voltage must be manually reset.

During the initial application of power to the system 10 and during an automatic reset of the system 10, the variable voltage drive signal provided to the center tap 232 of the transformer is controlled by the system controller 400. It is ramped or increased in an up direction toward the first voltage level at a predetermined rate of increase. However, the rate of voltage increase may be reduced and eventually disabled in response to a current sense signal indicative of a discharge. The rate of voltage increase is generally not the same between the initial power-up state and the automatic system reset state, but the automatic system reset state may require more power during the initial power-up of the system. A rapid voltage increase is required.

Although the graph of FIG. 3 shows the relationship between voltage and DC current including a substantially linear operating region, the voltage-DC current relationship is generally non-linear. Similar relationships exist between voltage and current rate of change, and between voltage and the filtered current component of the current sensing signal, but each of these voltage-current relationships is generally unique. Non-linear. Although the rate of current change and the parameters of the filtered current are unique, they tend not to change from application to application as the DC current parameters change from application to application. The required DC current levels include, for example, the conductivity of the coating material, the type of coating material applicator, the distance between the coating material applicator and the target object, and the electrostatics including the size and shape of the target object, among others. It depends on a number of factors related to the configuration of the coating system and the particular application. Thus, the DC current level is a user-defined current level, selected for a particular coating application, entered into the user interface 30 and displayed by the visual indicator 40. In general, the various relationships between voltage and current are determined empirically and by reference to accepted industry standards.

In a microprocessor-based system controller, the voltage-current relationship of the current sensing signal and the voltage sensing signal to the current parameter is generally controlled by a programmed algorithm. In accordance with this aspect of the invention, the algorithm is easily revised or reprogrammed for a particular electrostatic coating system configuration or application. In addition, a number of programs with different voltage-current algorithms can be stored in memory associated with the microprocessor, to select the desired voltage-current algorithm for a particular system configuration and application, and to provide a virtual system for the electrostatic coating system. It is also possible to form a universal high-voltage power supply. Also, the microprocessor-based system controller 400 can monitor system performance and storage of performance-related data, and in particular, the fault condition of the non-volatile memory 60, which can be analyzed later to determine the voltage It can be the basis for a control algorithm revision.
A computer 70 connected to the system controller by a serial input / output port 72 can be used to download algorithms to the system controller 400 and upload data from the memory of the system controller.

Dynamically controlling the high voltage supplied to the coating material applicator 100 in response to the current sensing signal representing the current parameter represents a relatively wide range of conditions where the current parameter indicates an imminent discharge. , Resulting in significant advancements and improvements in preventing discharge of electrostatic coating systems.

According to another aspect of the present invention, the operating efficiency of the high voltage module 200 is increased, and discharge between the coating material applicator 100 and the target object is prevented.
FIG. 1 shows a phase sensing module 700 connected to an output 220 of a high voltage module to generate a phase sensing signal.
Is shown. The phase sensing module 700 is also connected to the system controller 400 to provide a phase sensing signal to the system controller 400. According to this aspect of the invention, the system controller 400 includes the first and second phase drivers 330 and 340 from the first and second phase drivers 330 and 340, respectively.
And the driving frequency of the second signal is substantially matched to the resonance frequency of the high voltage transformer 230 with a 90 ° phase shift to maximize the voltage signal at the output of the transformer. The circuit for generating the phase sensing signal at the output of the transformer and the circuit for controlling the phase and frequency are described by Huge et al., Oct. 27, 1992, assigned to the assignee of the present invention, which is hereby incorporated by reference. High Voltage Power Su
US Patent No. 5,15 entitled "Pply Control System").
No. 9,544 discloses in detail. The drive frequency and phase of the first and second drive signals of the first and second phase drivers 330 and 340 are high, which tend to change as the target object T approaches or moves away from the coating material applicator 100. It is dynamically controlled to match the resonance frequency of the voltage transformer 230. Operating the transformer 230 at its resonant frequency produces a maximum voltage at the output of the transformer, thus reducing the risk of an unexpected increase in the voltage supplied to the coating material applicator 100 resulting in a discharge. In the embodiment of FIG. 2, the phase feedback signal is provided to the microprocessor-based system controller 400 via buffer 24, and the system controller 400 includes a first and second phase driver 330.
And 340 are controlled to match the driving frequency of the first and second signals from the high frequency transformer 230. In one embodiment, the high voltage transformer 230
Is a universal wound type transformer, and the driving frequency is about 45
It varies between kHz and about 110 kHz, and this frequency range may be wider or narrower for different applications and system configurations.

In accordance with another aspect of the present invention, the operating efficiency of the high voltage transformer 230 is such that the variable voltage drive signal from the control module 300 provided to the transformer 230 is reduced and transmitted to the coating material applicator 100. It is further optimized by generating a high voltage. It also reduces the heat generated by the high voltage module, which is of particular importance in hand-held coating guns and small coating material applicators. Reducing the heat of the high voltage module 200 also reduces the stress on the voltage rectifier and the multiplier, which will extend the operating life. According to this aspect of the invention, the voltage driven sensing module 800
Are connected to the control module 300 to generate a voltage drive sensing signal. This voltage drive sensing signal is generated by the resistive divider in the variable voltage drive signal generated by the control module 300. In addition, the voltage drive sensing module 800 provides the system controller 4 with a voltage drive sense signal to the system controller 400.
00, the system controller 400 receives the first signals from the first and second phase drivers 330 and 340.
And sweeping or changing the drive frequency of the second signal;
A drive frequency at which the variable voltage drive signal from the control module 300 is minimized is determined. Accordingly, the drive frequency changes to a frequency where the variable voltage sent to the high voltage transformer 230 is at a minimum for the desired high voltage sent to the coating material applicator 100. This feature that enhances the efficiency of transformer 230 can be used alone or in combination with the frequency matching and phase shift features described above, but minimizes the variable voltage supplied to transformer 230. The effort involved varies the drive frequency within a limited range for the resonant frequency of the transformer 230, with the constraint of compromising the match between the drive frequency and the resonant frequency.

According to another feature of the present invention, the operating efficiency of the high voltage transformer 230 depends on the first and second phase drivers 33.
With a delay between the first and second signals of 0 and 340,
It is further optimized by allowing the breakdown of the electric field induced in the transformer by the variable voltage drive signal before the polarity reversal.
This reduces the variable voltage drive signal supplied to the transformer center tap 232 and reduces the heat generated by the transformer. Fig. 4 shows the center tap 2 of the transformer.
32 shows the delay or dead space between the complementary first and second phase drive signals driving the first and second phase drivers 330 and 340 to alternately sink the variable voltage drive signal provided to 32. . According to one feature of the invention, the delay between the phase drive signals is a fixed delay time. In another embodiment, the delay time is varied over a small range to determine the delay time at which the variable voltage drive signal is minimized in response to the voltage drive sense signal from switching regulator 320 for the desired output voltage. Is done. This method of increasing the efficiency of the high voltage transformer 230 may be used alone or in combination with one or more of the other efficiency improving features of the present invention described above.

From the above description, those skilled in the art will be able to make and use what is presently considered to be the best mode of the present invention, but with the spirit and spirit of the particular embodiments described herein. Various modifications, combinations, and equivalents within the scope will be readily understood. Therefore, the invention is not to be limited by the specific embodiments described above, but only by the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electrostatic coating system according to an embodiment of the present invention.

FIG. 2 is a block diagram of a microprocessor-based electrostatic coating system according to an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a load voltage and a current of the electrostatic coating system according to the present invention.

FIG. 4 shows complementary first and second drive signals generated by corresponding first and second phase drivers.
FIG. 6 is a diagram showing a second waveform.

[Explanation of symbols]

 Reference Signs List 10 electrostatic coating system 100 coating material applicator 200 high voltage module 210 input 220 output 230 high voltage transformer 232 center tap 240 high voltage rectifier / multiplier circuit 300 control module 310 pulse width modulator 320 switching regulator 330 first phase driver 340 second phase driver 400 system controller 500 voltage sensing module 600 current sensing module 700 phase sensing module 800 voltage driven sensing module

Claims (22)

[Claims] 1. An electrostatic coating system for applying a coating material to a target object, comprising: a coating material applicator for applying a charged coating material toward the target object; A high voltage module connected to the coating material applicator, and a control module connected to the input of the high voltage module, wherein the variable voltage drive signal is used to generate a high voltage sent to the coating material applicator. And a current sensing module connected to the output of the high voltage module, wherein the rate of change of the current between the coating material applicator and the target object; and At least one of a filtered current in a bandpass frequency range between the material applicator and the target object A current sensing module for generating a current sensing signal representing the current sensing signal; and a system controller connected to the current sensing module for receiving the current sensing signal generated by the current sensing module, the system controller being responsive to the current sensing signal. A system controller connected to the control module to provide control signals to the control module, wherein the high voltage sent to the coating material applicator increases the rate of current change and the filtered current in the bandpass frequency range. Decreasing by the control module in response to a current sensing signal representing at least one of the following increases:
And the high voltage sent to the coating material applicator is
The electrostatic coating system can be increased by a control module in response to a current sensing signal indicative of at least one of the reduction of the current rate of change and the reduction of the filtered current in the bandpass frequency range. . 2. The pulse width modulator connected to the system controller and generating a variable output signal in response to a control signal from the system controller, the pulse width modulator being connected to the pulse width modulator. A switching regulator for generating a variable voltage drive signal in response to a variable output signal of a pulse width modulator, the switching regulator being connected to an input of the high voltage module, and applying a variable voltage drive signal to an input of the high voltage module. And a switching regulator for providing a variable high voltage sent to the coating material applicator in response to a variable voltage drive signal from the switching regulator. . 3. The high-voltage module comprises a transformer having a primary input winding and a secondary output winding with a center tap, wherein the center tap is connected to the control module, and wherein the control module includes the primary module. Providing a variable voltage drive signal to a center tap of an input winding; wherein the control module is further a first phase driver connected to a first input of a primary input winding of the transformer;
A first phase driver for sinking a variable voltage drive signal sent to the center tap in response to a first drive signal; and a second phase driver connected to a second input of a primary input winding of the transformer. And a second phase driver for sinking a variable voltage drive signal sent to the center tap in response to a second drive signal, wherein the system controller comprises a first phase driver and a second phase driver. Connected to a phase driver, and the system controller provides a first drive signal to the first phase driver and alternately provides a second drive signal to the second phase driver, the first drive signal and the second drive signal. 2. The system of claim 1 wherein are common drive frequencies and are 180 degrees out of phase. 4. The system controller further comprises a phase sensing module connected to an output of the high voltage module for generating a phase sensing signal, the phase sensing module including a phase controller for providing the system controller with a phase sensing signal. 4. The system controller of claim 3, wherein the system controller substantially matches a drive frequency with a phase shift to a resonance frequency of the high voltage module to increase the efficiency of the high voltage module in response to a phase sensing signal. System. 5. The system of claim 3, including a delay between the first drive signal and the second drive signal, the delay increasing the efficiency of the high voltage module. 6. A voltage driven sensing module connected to a control module for generating a voltage driven sensing signal, wherein the voltage driven sensing module is configured to provide a voltage driven sensing signal to the system controller. And wherein the system controller changes the drive frequency to determine a drive frequency at which the variable voltage drive signal from the control module is reduced in response to the voltage drive sense signal.
System. 7. The system controller further includes a voltage sensing module connected to an output of the high voltage module for generating a voltage sensing signal, the voltage sensing module including a voltage sensing module for providing the voltage sensing signal to the system controller. And the system controller provides a control signal to the control module in response to the voltage sensing signal, wherein the high voltage sent to the coating material applicator is responsive to the voltage sensing signal provided to the system controller. The system of claim 1, wherein the control module can be adjusted to a first voltage level. 8. The system of claim 1, wherein the coating material applicator is a plurality of coating material applicators for applying a charged coating material to a target object. 9. The high voltage module comprises a universal wound transformer connected to a voltage multiplier, a primary winding of the universal wound transformer is connected to the control module, and The system of claim 1, wherein the output of the voltage multiplier is connected to a coating material applicator. 10. An electrostatic coating system for applying a coating material to a target object, comprising: a coating material applicator for applying a charged coating material toward the target object; and a primary input winding having a center tap. A high voltage module having a high voltage module output connected to the coating material applicator; and the high voltage module connected to the high voltage module for generating a high voltage supplied to the coating material applicator. A control module for providing a variable voltage drive signal to a center tap of the module; a variable voltage drive connected to a first input of a primary input winding of the high voltage module and sent to the center tap in response to a first drive signal A first phase driver for sinking a signal, and a second input of a primary input winding of the high voltage module. A second phase driver for sinking a variable voltage drive signal sent to the center tap in response to a second drive signal; and a system controller connected to the first phase driver and the second phase driver. Wherein the first drive signal is the first drive signal.
A system controller in which the first drive signal and the second drive signal are supplied to the phase driver alternately and the second drive signal is supplied to the second phase driver, and the first drive signal and the second drive signal have a common drive frequency and are 180 ° out of phase. And a voltage driven sensing module connected to the control module to generate a voltage driven sensing signal, the voltage driven sensing module connected to the system controller to provide the voltage driven sensing signal to the system controller. The variable voltage drive signal from the control module is reduced in response to the voltage drive sense signal by providing one delay between the first drive signal and the second drive signal and changing the drive frequency. An electrostatic coating system characterized by the following. 11. The direct current between the coating material applicator and the target object, the rate of change of current between the coating material applicator and the target object, and the DC current between the coating material applicator and the target object. A current sensing module connected to an output of the high voltage module to generate a current sensing signal representative of at least one of the filtered currents in a bandpass frequency range, wherein the system controller includes The system controller is connected to the current sensing module to receive the generated current sensing signal, and the system controller is connected to the control module to provide a control signal to the control module in response to the current sensing signal; The high voltage supplied to the applicator increases the DC current, It can be reduced by a control module in response to a current sensing signal representing at least one of an increase in flow rate change and an increase in filtered current in the bandpass frequency range, and is provided to the coating material applicator. The high voltage may be increased by the control module in response to a current sensing signal indicative of at least one of the following: a decrease in the DC current, a decrease in the rate of current change, and a decrease in the filtered current in the bandpass frequency range. The system according to claim 10. 12. The system controller further comprising a phase sensing module connected to an output of the high voltage module for generating a phase sensing signal, wherein the phase sensing module provides a phase sensing signal to the system controller. 11. The system controller of claim 10, wherein the system controller is adapted to substantially match a drive frequency with a phase shift to a resonance frequency of the high voltage module to increase the efficiency of the high voltage module in response to a phase sensing signal. System. 13. A method for applying a coating material to a target object by an electrostatic coating system, the method comprising applying a charged coating material toward a target object by a coating material applicator, wherein the coating material is connected to the coating material applicator. Supplying a high voltage to the coating material applicator by a high voltage module having an output, and applying a variable voltage drive signal to an input of the high voltage module,
A high voltage is generated at the output of the high voltage module by a control module connected to the input of the high voltage module, and a current sensing module connected to the output of the high voltage module allows a high voltage to be generated between the coating material applicator and the target object. And a current sensing signal representing at least one of a current rate of change signal and a filtered current signal in a bandpass frequency range between the coating material applicator and the target object. Providing a control signal to a control module in response to a current sensing signal by a system controller connected to the high voltage supplied to the coating material applicator, wherein the high voltage supplied to the coating material applicator is increased in the current change rate and filtered in the bandpass frequency range. The control in response to a current sensing signal indicative of at least one of the increased currents A high voltage reduced by Joules and provided to the coating material applicator is responsive to a current sensing signal indicative of at least one of a reduction in the rate of current change and a reduction in filtered current in the bandpass frequency range. Increasing by the control module. 14. The coating by the control module in response to a current sensing signal representing at least one of a current change rate exceeding a rate of change limit and a filtered current in a bandpass frequency range exceeding a bandpass filter current limit. 14. The method of claim 13, further comprising the step of disabling the high voltage provided to the material applicator. 15. A method for reducing a high voltage supplied to a coating material applicator by a control module in response to a current sensing signal representing an increase in DC current and controlling in response to a current sensing signal representing a decrease in DC current. 14. The method of claim 13, further comprising increasing a high voltage provided to the coating material applicator by the module. 16. The method of claim 15, further comprising the step of disabling a high voltage supplied to the coating material applicator by the control module in response to a current sensing signal indicative of a DC current exceeding a DC current limit. Method. 17. The method according to claim 17, wherein the high voltage supplied to the coating material applicator comprises: a DC current increasing from a first DC current level; a current change rate increasing from the first current change level;
A control module responsive to a current sensing signal representative of at least one of a filtered current in a bandpass frequency range increasing above the first bandpass current level and decreasing below the first voltage level; The high voltage supplied to the applicator is increased by a DC current decreasing toward a first DC current level, a current change rate decreasing toward a first current change rate level, and a first bandpass current level. 14. The method of claim 13, further comprising: increasing the control module toward the first voltage level in response to a current sensing signal representing at least one of the filtered currents in the decreasing bandpass frequency range. the method of. 18. The high-voltage module includes a transformer having a primary input winding and a secondary output winding with a center tap, the center tap being connected to the control module, and the control module including the transformer. A first phase driver connected to a first input of a primary input winding of the transformer; and a second phase driver connected to a second input of a primary input winding of the transformer, wherein the system controller comprises: Connected to the first and second phase drivers, the method further comprises providing a variable voltage drive signal to a center tap of a primary input winding of the transformer, the first drive signal being provided to the first phase driver. And alternately providing a second drive signal to the second phase driver;
The first drive signal and the second drive signal have a common drive frequency and are 180 ° out of phase, and are supplied to the center tap in response to the first drive signal from the first phase driver. 14. The method of claim 13, comprising: sinking a variable voltage drive signal and alternately sinking a variable voltage drive signal provided to the center tap in response to a second drive signal from the second phase driver. The described method. 19. A phase sensing signal generated by a phase sensing module connected to an output of the high voltage module, providing the phase sensing signal to a system controller, wherein the phase sensing module is connected to the system controller and driven. 19. The method of claim 18, further comprising the step of substantially matching the frequency with a phase shift to the resonant frequency of the high voltage module to increase the efficiency of the high voltage module in response to the phase sensing signal. 20. The high voltage module according to claim 1, wherein a delay is provided between the first drive signal and the second drive signal to increase the efficiency of the high voltage module.
9. The method according to 8. 21. A voltage driving sensing signal generated by a voltage driving sensing module connected to the control module, the voltage driving sensing signal being supplied to a system controller, wherein the voltage driving sensing module is connected to a system controller, 19. The method of claim 18, further comprising: changing a driving frequency to reduce a variable voltage driving signal from a control module in response to the voltage driving sensing signal. 22. A voltage sensing signal generated by a voltage sensing module connected to an output of the high voltage module, providing the voltage sensing signal to a system controller, wherein the voltage sensing module is connected to a system controller; 19. The method of claim 18, comprising providing a control signal to a control module in response to the voltage sensing signal to adjust a high voltage of the coating material applicator to a first voltage level.