CN1982900B - Ground detection device and electrostatic spraying system - Google Patents

Abstract

The invention discloses a ground detection device and an electrostatic spraying system, comprising a hanger for hanging workpieces, a conveying chain and a grounding device, the hanger is fixed on the conveying chain and moves with the conveying chain, the conveying chain and the grounding The electrical connection of the device also includes a reference voltage generating circuit, a sampling circuit, a conductor and a processing circuit for calculating the external resistance value, the reference voltage generating circuit, the sampling circuit and the conductor are connected in series, and the conductor is used to contact the workpiece , the processing circuit is connected to the sampling circuit. The present invention adds a set of workpiece on-line grounding detection device on the electrostatic spraying line to eliminate the poorly grounded hanger as soon as possible, so that the workpiece is always kept well grounded, improving the efficiency of coating, the quality of the coating and the utilization rate of the coating, reducing the safety accident.

Description

Ground detection device and electrostatic spraying system

【Technical field】

The invention relates to an electrostatic spraying device, in particular to an electrostatic spraying device with a workpiece grounding detection system.

【Background technique】

The rapid development of modern industry has higher and higher requirements for spraying quality. Generally, the efficiency of brushing and spraying is low, there is a lot of waste of paint, and the quality of spraying is not good, but electrostatic spraying can overcome the above shortcomings. Compared with general brushing and spraying, electrostatic spraying has high efficiency, less paint waste, and less paint flying into the air, which improves the working environment. In the electrostatic spraying system, the usual way to ground the object to be coated is: workpiece (that is, the object to be sprayed) → hanger → conveyor chain → metal bracket → grounding. But in the production process, because the paint is easy to adhere to the hanger, and because the paint is accumulated and thickened due to repeated use, the connection point between the hanger and the workpiece is poorly conductive, and the grounding effect is not good.

In the process of electrostatic spraying, if the grounding of the metal workpiece is not good, it will also cause low utilization rate of the paint and a lot of waste of paint, which will affect the painting efficiency and the quality of the paint, and put a lot of pressure on the recycling system, making it too late to recycle the excess paint However, if it flows to the outside of the spraying room, it not only wastes the paint, but also deteriorates the environment in the operation room. Due to poor grounding, the paint is easy to accumulate charges when it adheres to the workpiece. When people and other grounding objects approach or touch it, there is a danger of spark discharge.

【Content of invention】

The main purpose of the present invention is to solve the problems existing in the prior art, to provide a grounding detection device, which can detect the grounding status of the workpiece on-line, eliminate the faults leading to poor grounding as soon as possible, and keep the workpiece well grounded all the time.

Another object of the present invention is to provide an electrostatic spraying system to solve the problems existing in the prior art, which can detect the grounding status of workpieces online, eliminate faults that cause poor grounding as soon as possible, and keep the workpieces well grounded all the time.

In order to achieve the above object, a ground detection device proposed by the present invention includes a reference voltage generation circuit, a sampling circuit, a conductor and a processing circuit for calculating an external resistance value, and the sequence of the reference voltage generation circuit, the sampling circuit and the conductor connected in series, the conductor is used to contact the object to be detected, the processing circuit includes a sequentially connected rectification unit, an A/D converter and an external resistance processing unit, the rectification unit is connected to both ends of the sampling resistor, the rectification unit The unit is connected to the sampling circuit.

Wherein the preferred scheme of each part is as follows:

The sampling circuit is a sampling resistor, and the conductor is a flexible conductor.

The external resistance processing unit includes a programmable controller, and the rectification unit is a precision rectification unit.

The reference voltage generating circuit is a sine wave generator.

In order to achieve the above object, the present invention also proposes an electrostatic spraying system, including a hanger for hanging workpieces, a conveyor chain and a grounding device, the hanger is fixed on the conveyor chain and moves with the conveyor chain, and the conveyor chain and The grounding device is electrically connected, and also includes a grounding detection device, and the grounding detection device includes a reference voltage generation circuit, a sampling circuit, a conductor and a processing circuit for calculating an external resistance value, and the reference voltage generation circuit, the sampling circuit and the conductor sequence in series, the conductor is used to contact the workpiece, the processing circuit includes a sequentially connected precision rectification unit, an A/D converter and an external resistance processing unit, the precision rectification unit is connected to both ends of the sampling resistor, the The precision rectification unit is connected with the sampling circuit.

Wherein the preferred scheme of each part is as follows:

The reference voltage generating circuit is a sine wave generator, the sampling circuit is a sampling resistor, and the conductor is a flexible conductor.

The external resistance processing unit includes an encoder and a programmable controller, the input of the programmable controller is respectively connected to the output of the A/D converter and the output of the encoder, and the shaft of the encoder is connected to the electrostatic The motor shafts of the spraying system are mechanically linked.

The conductor is located near the moving track of the hanger and can be in contact with the workpiece.

The beneficial effects of the present invention are: when the workpiece on the hanger moves along the direction of the conveyor chain, the workpiece touches the conductor, at this time, the reference voltage generating circuit of the grounding detection device passes through the conductor→workpiece→hanger→conveyor chain→ The grounding device forms a current loop, collects the voltage through the sampling circuit, calculates the external resistance of the conductor, and uses the resistance change of the external resistance to reflect whether the electrical connection between the workpiece and the rack is good, or whether the rack and the grounding device are in good condition Electrical connection, if the resistance value is greater than the set resistance value, it means that the connection between the workpiece and the hanger is not good or the connection between the hanger and the grounding device is not good, the workpiece is not well grounded, and there is a fault that needs to be dealt with. Through this solution, the grounding status of the workpiece can be detected online, and faults that cause poor grounding, such as bad hangers, can be eliminated as soon as possible, so that the workpiece is always well grounded, reducing paint waste, ensuring the quality of spraying, and reducing safety accidents.

The features and advantages of the present invention will be described in detail with reference to the accompanying drawings.

【Description of drawings】

Fig. 1 is the principle block diagram of ground detection device of the present invention;

Fig. 2 is a schematic diagram of the electrostatic spraying system of the present invention.

【Detailed ways】

As shown in Figure 1, the grounding detection device is used for online detection of the grounding status of the workpiece being sprayed. The reference voltage generating circuit is a sine wave generator 11, which is connected to a +24V DC voltage and converted into the voltage required by the circuit. various voltages. The internal signal generator circuit generates and outputs a sine wave of 100Hz and 10mA, which is amplified by the amplifier 12 and then output to the sampling resistor 13, and connected to the detected object through the conductor 14. The rectification unit 15 is connected to both ends of the sampling resistor 13 , and the output terminal of the rectification unit 15 is sequentially connected to the A/D converter 16 and the programmable controller 18 . In order to ensure that the conductor is in good contact with the object to be detected and that the conductor does not damage the object to be detected, the conductor is preferably a flexible conductor. When the conductor 14 is in contact with the object to be detected, since the object to be detected communicates with the ground, a current path is formed from the sine wave generator 11→sampling resistor 13→conductor 14→the object to be detected→ground, and the conductor can be calculated by 14 external resistance to judge whether the detected object is well grounded. In order to accurately measure the resistance value of the external resistor and reduce the influence of the rectifier unit 15 on the external resistor value, a precision rectifier unit with a small turn-on voltage is used.

The electrostatic spraying system including the above-mentioned grounding detection device and with online grounding detection of the workpiece is shown in Figure 2. The workpiece is hung on the hanger 3, the hanger 3 is fixed on the conveyor chain 1 through the boom 2, and the conveyor chain 1 is grounded through the grounding device , the grounding device is a metal bracket 4, that is, the workpiece is grounded through the hanger 3, the spreader 2, the conveyor chain 1, and the metal bracket 4. The conductor 14 is located near the moving track of the hanger, and can be in contact with the workpiece that moves near the conductor 14 . Since the workpiece is in motion, the best solution for the conductor to be in contact with the workpiece is to be designed to be fixed on the moving track of the workpiece, so that the workpiece can be in contact with the conductor when the workpiece moves to the position of the conductor. In order to avoid damage to the workpiece when the conductor rubs against the workpiece, the conductor uses a flexible conductor, such as a soft conductive belt. When the workpiece on the hanger 3 moves along the direction of the conveyor chain 1, the workpiece touches the conductive soft belt. At this time, the 100Hz sinusoidal alternating current inside the sine wave generator 11 passes through the conductor 14→workpiece→hanger 3→sling 2 → Conveyor chain 1 → Metal support 4 → Grounding, forming a loop. The AC voltage at both ends of the internal sampling resistor 13 of the ground detection device is sent to the A/D converter 16 through the internal precision rectification circuit 15, and the A/D converter 16 can use the FN2N-2AD analog-to-digital conversion module to convert the analog voltage value into a digital The amount is stored in the programmable logic controller (PLC) 18 so as to calculate the resistance value of the hanger and compare it with the set resistance data value. If the detected external resistance value is greater than the set resistance data value, it is judged that the workpiece is not well grounded . Programmable controller 18 can adopt FX2N-128MT type programmable controller. In order to know exactly which hanger has a problem, the present embodiment has adopted encoder 17, and encoder 17 is an incremental encoder, and its shaft is mechanically connected with the shaft of conveyor chain motor 19, and its signal output terminal and programmable The controller 18 is connected, the A phase of the encoder 17 is connected to the X0 terminal of the FX2N-128MT programmable controller, and the B phase is connected to the X1 terminal of the FX2N-128MT programmable controller. Every time the shaft of the encoder 17 rotates one revolution, a series of signals are output, which are output periodically with the rotation of the shaft of the encoder 17, so the programmable controller 18 can judge the conveyor chain motor 19 according to the signal output by the encoder 17. The number of revolutions of the motor can be calculated from the number of revolutions of the motor. When the hanger travels to the test position of the conductive soft belt, the programmable controller 18 controls the grounding detection device to detect the grounding state of the workpiece. The program counts the internal counter C251 of the programmable controller. By calculating and processing the data of the high-speed counter C251, it can accurately calculate the corresponding position and resistance value of each rack, and record the measured external resistance value and rack The serial number is reserved for future reference.

Its operation principle is as follows:

Because VEF/REF=(V-VEF)/R

So the external resistance value is: R=REF×(V-VEF)/VEF

In the above formula, VEF is the sampling value of the A/D converter, REF is the resistance value of the sampling resistor, V is the reference voltage output by the sine wave generator, and R is an external resistor.

When the first hanger passes through the conductive soft belt, put the calculated corresponding external resistance value into the data register D200; when the second hanger passes through the conductive soft belt, put the calculated corresponding external resistance value into into the data register D201, and so on, to reach the number of hangers deposited. When the resistance value of the detection resistor is greater than the set resistance data value, it means that the workpiece carried by the rack is not well grounded. At this time, the PLC can further drive the sound and light alarm circuit to alarm, and the register D200 can also be monitored through the touch screen. The resistance data is used as the basis for us to clean up the paint attached to the hanger or to eliminate other faults that cause poor grounding of the workpiece.

When the first hanger passes through the conductive soft belt again, the calculated detection resistance value is put into D200 again, and the resistance data in D200 is refreshed. In this way, as long as the hanger is running, the corresponding resistance data will be refreshed, so that Realize large-scale online detection.

The following experiments illustrate the effect of this scheme:

Through the above scheme, it is determined that the workpiece is poorly grounded. When the insulation resistance between the ground and the workpiece exceeds 1MΩ, it means that the workpiece is not well grounded. Its resistance value is shown in Table 1.

Table 1

Measured workpiece 1 2 3 4 5 6 Workpiece grounding resistance (MΩ) 2.5 3 2 3.5 5 3

From the measurement results in Table 1, it can be seen that the workpiece is not well grounded. At this time, the main operating process parameters are as follows:

1 Electrostatic spray gun electrostatic voltage: 65kV

2 fog type air pressure 2.5kg/cm2

3 atomization air pressure 2.0kg/cm2

4 Paint discharge volume Air pressure 1.0kg/cm2

After spraying and curing, check the quality of the paint film. Measure the thickness of 6 different workpieces at the same point of the workpiece. The measurement results are shown in Table 2.

Table 2

Measured workpiece 1 2 3 4 5 6 Workpiece painting thickness (micron) 14 13 15 12 10 13

From the data shown in Table 2, it can be seen that the thickness of the coating is very uneven, and there are pinholes in its appearance, color difference on the surface, and poor edge wrapping. This situation is especially serious for workpieces with complex shapes that require manual repainting.

The hanger is well grounded. At this time, under the condition of maintaining the original operating parameters, the coating thickness of 6 different workpieces is measured, and the data are shown in Table 3.

table 3

Measured workpiece 1 2 3 4 5 6 Workpiece painting thickness (micron) 17 18 17 17 17 18

Check the appearance of the paint film, it can be found that the paint film is thick and the surface is smooth and uniform, with good gloss and no pinholes and other defects.

It is not difficult to see from the above experimental results that adding a set of workpiece online grounding detection device to the electrostatic spraying line can eliminate the poorly grounded hanger as soon as possible, which not only improves the efficiency of coating, the quality of coating and the utilization rate of coating, The environment in the spraying operation room is also improved. Moreover, the design cost of the online workpiece grounding detection system is not high, and an excellent performance-price ratio is achieved.

Claims (10)

1. ground detection device, it is characterized in that: comprise reference voltage generating circuit, sample circuit, electric conductor and be used to calculate the treatment circuit of outer meeting resistance value, described reference voltage generating circuit, sample circuit and electric conductor are connected in proper order, described electric conductor is used to contact detected material, described treatment circuit comprises rectification unit, A/D converter and the outer meeting resistance processing unit that order links to each other, and described rectification unit links to each other with sample circuit.

2. ground detection device as claimed in claim 1 is characterized in that: described sample circuit is a sampling resistor, and described electric conductor is a flexible electrical conductors.

3. ground detection device as claimed in claim 2 is characterized in that: described rectification unit is connected the two ends of sampling resistor.

4. ground detection device as claimed in claim 3 is characterized in that: described outer meeting resistance processing unit comprises Programmable Logic Controller, and described rectification unit is the precision rectifying unit.

5. ground detection device as claimed in claim 1 is characterized in that: described reference voltage generating circuit is a sine-wave generator.

6. electrostatic coating system, comprise the hanger that is used to hang workpiece, carrier chain and earthing device, described hanger is fixed on the carrier chain and can moves with carrier chain, described carrier chain and earthing device are electrically connected, it is characterized in that: also comprise ground detection device, described ground detection device comprises reference voltage generating circuit, sample circuit, electric conductor and the treatment circuit that is used to calculate the outer meeting resistance value, described reference voltage generating circuit, sample circuit and electric conductor are connected in proper order, described electric conductor is used for contact workpiece, described treatment circuit comprises the precision rectifying unit that order links to each other, A/D converter and outer meeting resistance processing unit, described precision rectifying unit links to each other with sample circuit.

7. electrostatic coating system as claimed in claim 6 is characterized in that: described reference voltage generating circuit is a sine-wave generator, and described sample circuit is a sampling resistor, and described electric conductor is a flexible electrical conductors.

8. electrostatic coating system as claimed in claim 7 is characterized in that: described precision rectifying unit is connected the two ends of sampling resistor.

9. electrostatic coating system as claimed in claim 8, it is characterized in that: described outer meeting resistance processing unit comprises scrambler and Programmable Logic Controller, the input end of described Programmable Logic Controller links to each other with the output terminal of A/D converter and the output terminal of scrambler respectively, and the axle of described scrambler links to each other with the motor shaft machinery of electrostatic coating system.

10. electrostatic coating system as claimed in claim 6 is characterized in that: described electric conductor is positioned near the hanger motion track and can touches with workpiece.

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