Figure 1 Robot motion axis system

In the automotive painting process, spraying robots are increasingly used. Its significant advantage is that it can be mixed on the same production line at the same time. A variety of models improve the automation and production efficiency of painting. Its six- or seven-axis motion axis system is more flexible than traditional reciprocating machines and automatic spraying machines.

In the automobile painting production line, any new model needs to set process parameters or modify equipment, such as spreader fulcrums and mechanized skid systems, before trial production and mass production. , robot spraying profiling and parameter setting, etc. Among them, robot spraying profiling and parameter setting are particularly important, because the middle coating, topcoat layer and varnish layer on the white body are all sprayed by robots. The following mainly introduces the automobile painting line New robot model profiling and parameter settings.

The robot's spraying action is carried out according to the preset trajectory program and process parameters, and its curved surface movement is carried out through multiple LIN points, such as LIN(P1)→LIN(P2)→LIN(P3)→ LIN(P...), the operation between each LIN point, the robot program defaults to linear movement. Each LIN point is composed of the robot's "WORLD" coordinate system (X, Y, Z). At the same time, the paint spraying parameters on the car body surface are carried out according to the preset values ??of the process.

Robot motion axis system

Based on the complexity of the workpiece processed and the requirements of the motion profiling coordinate system (X, Y, Z), the robot motion axis system is generally divided into the following seven axes (See the table in the text and Figure 1, which vary according to different robot manufacturers and parameters)

Robot coordinate system

Robot systems usually use the "WORLD" coordinate system (see Figure 2), which The coordinate system has the following two characteristics: the X, Y, and Z axes are at right angles to each other; the forward direction of the mechanized conveyor chain is aligned with the +X direction.

Figure 2 "WORLD" coordinate system

As shown in Figure 3, in the robot "WORLD" coordinate system, the meanings of each coordinate system are as follows:

+ Follow the mechanization to the right;

+Z: The top direction of the spray booth;

-Z: The floor (grid) direction of the spray booth.

Figure 3 The meaning of each coordinate system

Machine profiling program settings

Based on the above robot motion axis system and coordinate system, the following is based on a certain robot manufacturer Take the profiling program as an example to explain the robot's profiling program settings.

There are 4 robots in this station, which are arranged on the left and right sides. The robots on the left are R11 and R12, and the robots on the right are R21 and R22. The profiling settings are:

.

..

…(omitted)

STARTPROG(“DOOR”)

Start DOOR program

SELECT(“R11”)

Select R11 robot

S E L E C T

SELECT SETTOOL(HT_BELL250)

Load robot cup parameter TOOL data

SETTOOL SETOBJECT(HP)

SETOBJECT

LOADBRUSHFILE()

Load brush file

VEL(V 650)

Set robot TCP speed

ACC(A2500)

Set robot TCP acceleration

OVERLAP(NODEC50)

Load related robots Motion parameter values

SETTRIGGERPAR(G50)

Load robot trigger parameter values

MOVE(“DOOR”)

Start ROOD simulation Shape path

MOVE LIN(P1)

Robot TCP moves straight to point P1

SETBRUSH(Gun1 1 PO3 TRG3)

Settings Brush file

SETBRUSH GUN (Gun1 GunOn PO6 TRG6)

Main Gun is on

LIN (P4) Move to P4 point

LIN(P5) Move to point P5

LIN(P6) Move to point P6

LIN(P7) Move to point P7

GUN( Gun1 GunOff P9 TR3) Main Gun is closed

LIN(P10) Move to P10 point

WAIT_PAINTPOSITION(180.0)

Wait until the mechanization feedback value reaches 180mm

GUN(Gun1 GunOn P12 TR4)

Main Gun is on

LIN(P13) moves to P13 point

LIN(P14) Move to point P14

LIN(P15) Move to point P15

LIN(P16) Move to point P16

LIN(P17) Move to point P17

LIN(P18) Move to point P18

LIN(P19) Move to point P19

GUN(Gun1 GunOff P73 TR14)

Main Gun is closed

LIN(P22) Move to P22 point

END MOVE(“DOOR”)

DOOR path Completion and termination

RELEASE("R11") R11 robot operation completed

ENDPROG("DOOR") program

DOOR ended

RETURN Return to the main program

As mentioned above, after the program is compiled, the robot trajectory diagram shown in Figure 4 is generated on the robot's industrial computer. At this point, the profiling of the robot R11 has been set up. Use the same The program sets R12, R21 and R22, and finally uses the main program to connect the sub-programs of the four robots in series to form the robot's motion profiling program.

Figure 4 Robot trajectory

The above method is an online profiling measurement method using a real vehicle on site. In practical applications, due to the continuous improvement of three-dimensional digital models and robot application software for vehicle model development, With the development of the industry, it is completely possible to use software (such as FANUC's "PAINTPRO" software, DURR's "3-D ONSITE" software, etc.) for offline programming of profiling programs. Track points are set on the surface to implement programming (see Figure 5). The most commonly used three-dimensional digital analog data of new car models is CATIA's IGS and CGR format model data, which are input into the application software for programming. After programming, the profiling data is input to the robot industrial computer to complete the profiling program setting of the body, shortening It shortens the robot profiling production cycle and reduces on-site debugging of scrapped vehicles.

Figure 5 Setting track points on the car body surface

Robot process parameter value setting

After the motion profiling program is set, the robot cannot completely spray the Qualified paint body also needs to set the following process parameters:

1. High voltage value of the robot atomizer

The principle of the robot electrostatic spraying machine is to ground the surface to be painted. The object is the positive electrode, and the rotating cup (spray gun) is the negative electrode, thus forming a high-voltage electrostatic field between the object to be coated and the atomizer. According to the principle of same-sex repulsion and opposite-sex attraction, the negatively charged paint is adsorbed on the parts to be painted under the action of the electrostatic field. Therefore, the value of the high voltage directly affects the electrostatic effect, paint rate and coating rate of electrostatic coating. film uniformity. If the distance between the atomizer and the car body is certain, the increase in the high voltage value will strengthen the electric field force of the electrostatic field. At this time, the density of magnetic field lines on the surface of the object being painted is higher, which increases the coating rate of the paint and the thickness of the film layer. . However, the higher the high voltage value, the better. During spraying, when the electric field intensity exceeds 4500V/cm, spark discharge will occur. At the same time, sags, bubbles and blooms are prone to occur at the corners and sharp corners of the car body. and other paint defects. When the voltage value is too low, the paint rate will be too low. At this time, the sprayed paint will form snowflake-like clusters, resulting in the backflow of the conical spray paint flow, and too little paint will cover the surface of the car body.

The suitable high-voltage parameter range for car painting is 50 to 80kV, which varies according to metallic paint, mid-coat paint and varnish. Due to the low resistance value and good conductivity of the original paint, the metallic paint is usually set at 50-65kV, and the mid-coat and varnish are set at 60-75kV. For the corners, in order to avoid the electrostatic effect at the corners, it is usually set to 45~50kV.

2. The amount of shaping air of the robot atomizer

The shaping air of the atomizer is generally called shaping air. It is sprayed from the evenly distributed small holes on the back side of the rotary cup. Out, its main function is to limit the size and shaping range of paint flow. When other parameters are kept constant and the molding air volume is adjusted individually, the greater the molding air volume, the narrower area will be formed when the paint flow is sprayed out, and the coating thickness in the center of the spray paint flow will increase significantly; the molding air volume The smaller it is, the width of the conical spray paint stream is expanded, resulting in a thinner paint film thickness in the area. The molding air volume should be within a certain range, and its size setting is related to the following two parameters:

(1) Paint flow rate: It is directly proportional to the molding air volume. The greater the paint flow rate, the greater the molding air volume. also increased accordingly.

(2) Rotating cup speed: proportional to the amount of molding air. The molding air volume is generally set to 100~350NL/min according to the above parameters. When it is too low, it will easily cause a low paint application rate and a decrease in paint utilization, and it will also cause paint mist pollution in the rotary cup; when it is too high, it will easily lead to low paint application rate and reduced paint utilization. , due to the large compressed air flow, air flow interference occurs, causing the paint to adhere to the atomizer, which will cause quality defects on the paint film surface and cause adverse effects.

Robot motion axis system

3. Robot paint flow

In the robot rotary cup system, 75% of the paint is sprayed from the annular gap of the rotary cup. 25% of the paint is sprayed out from the center hole of the rotary cup. The paint flow rate of robot electrostatic spraying is generally adjustable in the range of 0 to 500 ml/min, and is accurately controlled through a gear metering pump, with a metering accuracy of ±1.5%. In unit time, the larger the paint flow parameter setting is, the width of the conical spray paint flow will increase, the total number of paint particles will increase, and the density of the paint particle flow will increase, resulting in a larger paint film thickness, and vice versa. When the paint flow rate of the paint is too large, it will affect the atomization effect of the rotary cup, causing difficulty in atomization, coarse paint particles, and paint defects such as paint dripping, sagging, and bubbles. Its size is mainly related to the following factors:

(1) Paint solid content: When the required film thickness is the same, the higher the solid content of the paint, the smaller the paint flow setting value.

(2) The size of the mechanized chain speed: It is directly proportional to the paint flow rate. When the chain speed increases, the paint flow rate also increases accordingly.

(3) Requirements for coating film thickness: For example, the requirement for varnish is 35~50μm, the requirement for metallic paint is 12~18μm, and the requirement for medium paint is 30~45μm. The film thickness requirements are different. The parameter values ??are also different.

The paint flow rate calculation formula for each rotary cup of the robot spray station is as follows:

P=[Sxδ/(TxNV)]/N

Where:< /p>

P—Paint flow rate, in ml/min;

S—Spraying area on the outer surface of the new model, in m2;

δ—Dry coating film thickness , the unit is μm;

T—paint coating rate (utilization rate), generally 80% to 90% (different robot manufacturers use different values);

NV—the solid content of paint construction;

N—the number of robots at the station (number of rotary cups).

Usually, the theoretical calculation value is set during the debugging stage, and the actual deviation from the optimal paint flow value after on-site debugging and optimization has a certain range (about 10%).

4. Rotary cup speed of the robot

The main function of the rotary cup speed is to atomize the sprayed paint at a speed of up to 25,000 to 60,000 revolutions per minute. It reaches a certain atomization fineness. The setting of the rotating cup speed is related to the following factors:

(1) Paint coating requirements: For example, intermediate paint, color paint and varnish require different speeds. Taking solvent-based paint as an example, The rotation speed of varnish is 35000~45000 r/min, and the speed of mid-coat and base paint is slightly lower, 30000~35000 r/min.

(2) Paint flow rate of paint: When other parameters remain unchanged, the greater the paint flow rate, the higher the required rotating cup speed.

Normally, the greater the rotating cup speed, the thicker the paint film thickness and the better the atomization effect. However, if the parameter setting value is higher than 45000 r/min for a long time, it will cause the rotary cup to become damaged. Damage, such as excessive wear of bearings, increases the replacement cost of equipment spare parts.

5. Main Gun control parameters

The function of the main gun is to control the switch of paint, solvent and compressed air in the color change valve when the robot is spraying. Take the top spray robot as an example. When spraying the body of a car with a sunroof on the roof, it can be seen from the profiling data that the position of the sunroof is point 252~276 (the automatic machine uses the body at the grating acceptance position as point 0). When the top spray machine is running When it reaches the starting point 252 of the skylight position, set the main needle to close. When it reaches point 276, set the main needle to open. Its function is equivalent to the needle in a manual spray gun. The needle opens, the paint sprays out, and the needle closes. The paint is not sprayed, so that the robot does not spray paint at the skylight position.

In addition, the main needle can also define the on and off points of the time of each atomization device area, as well as the starting points of the cleaning program and the paint injection program. When setting the main needle parameters, special attention should be paid to the fact that the main needle must be closed at the appropriate position before starting the cleaning process. At the same time, pay attention to the gap between the bodies and place the cleaning program at the appropriate position (flushing time) to prevent The machine with overlapping main needles reports a malfunction.

6. Overload percentage of parameters

The overload percentage can define various parameters such as: conveyor chain speed, paint flow (P), forming air volume (LL) and high voltage value (HT ) and other parameters. This parameter setting value can make many parameter settings of the robot very simple on some occasions.

(1) Example 1: The existing chain speed of the topcoat line is 2.6m/min. Due to the demand for production line capacity, it needs to be increased to 2.86m/min. Then the paint consumption per unit time It must be increased accordingly, otherwise the car body will have paint defects such as less paint and orange peel. We can also increase the paint volume, forming air volume and other parameters of each area in the parameter modification window. However, compared to one color and one car model, the parameters are as high as 90 areas, and more than 200 parameters need to be reset. Adjustment results in large parameter modifications. By modifying the overload percentage of parameters, you only need to set the chain speed overload percentage value in the "Conveyor Chain Speed" adjustment window to: (2.86-2.6)/2.6×100%=10% to achieve the goal.