This article introduces the application of Siemens S7-1500 PLC in the overall control system of a painting robot and its suspended walking mechanism; from the perspectives of software and hardware design, and combined with on-site debugging examples, it describes the successful implementation of key functions.
I. Project Introduction
In recent years, robotic automated painting systems have been widely used in industries such as automobiles due to their numerous advantages, including high repeatability, good coating quality, high reliability, strong applicability, and high efficiency. However, the manufacturing process for aerospace products remains labor-intensive, complex, and involves harsh working conditions, relying heavily on tooling and fixtures and primarily manual production, with insufficient automation capabilities. Against the backdrop of the national 13th Five-Year Plan and the vigorous development of "Made in China 2025," the Composite Materials Manufacturing Institute of AVIC (Aviation Industry Corporation of China) has taken a forward-looking approach, pioneering the use of robots for automated production in the painting field, accelerating the transformation and upgrading of the enterprise's production model, and improving its advanced equipment manufacturing capabilities.
This project uses a mobile, suspended 6-axis spraying robot, which is mounted on a 3-DOF Cartesian coordinate displacement crane. It can move in multiple degrees of freedom, including forward, backward, left, right, up, down, and rotation, within the spray booth area (spray booth dimensions: L30m×W9m×6.5m). The robot's arm is equipped with a spray gun, which can perform spraying operations on the outer surface of large composite material workpieces.
II. Composition of the Suspended Robotic Spraying System
The suspended robot painting system consists of a central control system, an overhead crane system (suspended traveling mechanism), a robot system, an intelligent paint supply system, and a video monitoring system. The system network diagram is shown in Figure 1.
The overhead crane system includes: one longitudinal travel mechanism (X-axis), one transverse travel mechanism (Y-axis), one lifting mechanism (Z-axis), and an electrical servo drive system, as well as auxiliary facilities such as a walkway for maintenance and inspection. (See Figure 2.)
The intelligent paint supply system consists of a siphon, diaphragm pump, material tank, filter, 2KS (heat exchange system), pressure regulator, and dry run protector, forming a complete paint supply system. It is a crucial component of the spraying system, playing a vital role in everything from raw material supply to adjusting the premixing ratio, and is a necessary prerequisite for the actuators. The materials include paint, hardener, and cleaning agent.
The project uses the Staubli TX250 series 6-axis robot, which is also the latest model. The entire robot system consists of three parts: the CS8C controller, the robotic arm (Arm), and the manual control pendant (MCP).
III. Control System Frame
The main control system of this system uses a Siemens S7-1500 PLC as the master controller, WinCC Professional V13 SP1 as the host computer interface, and TP1200 as the operation panel. The overhead crane, robot, and paint supply system each use an S7-1200 as their controller. The S7-1500 master control system communicates with the painting robot system, paint supply system, and overhead walking system via PROFINET bus to complete the overall system control, enabling real-time monitoring and operation of the system's operating status and ensuring continuous painting of the entire workpiece. The control system architecture is shown in Figure 4, and the main control system hardware equipment list is shown in Table 1 below.
IV. Functions Implemented by the Control System
The suspended robotic painting system allows for independent operation of both the overhead crane system and the robotic painting system. On-site, the overhead crane can be operated via the TP700 control panel, allowing for functions such as powering on the X, Y, and Z axis servo motors, zero-point calibration, and absolute positioning.
The TP700 field display panel of the paint supply system can display paint level, cleaning agent level, hardener level, pipeline pressure, solenoid valve status, fluid pressure regulator status, automatic mixing status of various paints in the 2KS system, pneumatic pump, and anti-dry-run protection device, etc.
The TP700 on-site display of the robot system shows the movement of the six axes: X, Y, Z, RX, RY, and RZ. The on-site teach pendant can perform offline trajectory planning for the robot.
The overall control system consists of two sets: a field control system and a remote control system. The field control system can communicate with the robot system, the suspended walking system, and the paint supply system via a bus to complete the overall system control and continuous spraying of the entire workpiece; the remote control system mainly realizes real-time monitoring and operation of the system's operating status.
The main control system can control and display the status of subsystems. It can automatically perform operations such as color changing, paint addition, and cleaning on the paint supply system. It can also correct errors generated during the movement of the suspended travel mechanism.
V. Key Technical Points of Spraying Process Flow and Control
The painting process of the suspended robot painting system is as follows:
First, the overhead crane system, paint supply system, and spraying system are ready. The workpiece enters the designated position and is positioned. → The system detects the actual position of the workpiece. → Coordinate fitting. → Teaching (manual program debugging). → Startup. The central control reads the "workpiece data" for painting and sends the "trajectory number" and "recipe confirmation" signals to the robot spraying system. → The robot spraying system reads the "trajectory number" and color "recipe number". → The robot spraying system determines that it is the current spraying recipe and sends a "spraying request" signal for position 1 to the central control. → After the three axes of the suspension system reach the designated position 1, they send a "header crane has reached the spraying position" signal to the central control. → 2KS mixing. The robot starts automatic spraying (calling spraying program 1). → Spraying area 1 of the workpiece. Spraying complete. Once completed, the robot returns to the HOME position and stops, sending a "Spraying Complete" signal to the central control unit. The central control unit reads the "Spraying Complete" signal, changes the workpiece pointer to point to workpiece data in area 2, and sends the spraying "trajectory number" and spraying "recipe confirmation" signals to the robot spraying system. The robot spraying system reads the spraying "trajectory number" and color "recipe number." If the robot spraying system confirms the current spraying recipe, it sends a "Spraying Request" signal for position 2 to the central control unit. After the three axes of the suspension system reach the designated position 2, they send a "Crane has reached spraying position" signal to the central control unit. After 2KS mixing, the robot begins automatic spraying (calling spraying program 2). It sprays workpiece area 2. After spraying is complete, the robot returns to the HOME position and stops…
Follow the above procedure to spray the workpiece in areas 3, 4, ... n, until the entire workpiece is sprayed. Then the robot returns to the zero position (HOME point), the overhead crane returns to its original position, and the workpiece is removed from the production line.
To complete the continuous spraying of the entire workpiece until the overhead crane returns to its original position, the S7-1500 controller, as the most critical core component of the entire system, coordinates and controls the operation of the overhead crane and the robot system. When manually teaching and debugging the robot program, the X, Y, and Z coordinates of the workpiece in each area, as well as the robot's trajectory number, must be manually recorded. This data is then input into the data block of the S7-1500 PLC via the TP1200 operating screen of the central control unit or on the industrial computer of the central control unit. When the system runs automatically, it automatically recalls the stored data step by step according to the process sequence.
Due to the variety of workpieces and the varying sizes of the regions divided for different workpieces, and the fact that each region contains multiple values, the data storage (DB) blocks are nested, i.e., multiple arrays. Therefore, the DB block size must be large enough to meet production requirements. Implementing data storage and retrieval using a standard S7-300/400 PLC with STEP7 programming would be difficult. Therefore, an S7-1500 PLC with TIA Portal's SCL programming method is chosen for this function, which is more convenient and easier. The implementation process is described below.
The process of creating a workpiece process data table:
(1) In the TIA Portal V13SP1 programming software, add a new "PLCdatatypes" (equivalent to the user-defined DB block created in Step7), named "Workpiece Recipe". Add "Crane X Coordinate" (defined as integer data type), "Crane Y Coordinate" (defined as integer data type), "Crane Z Coordinate" (defined as integer data type), and "Robot Trajectory Number" (defined as byte data type) to it. Also add two spare data for future customer requests to add new functions: "Paint Recipe Number" (defined as Word data type) and "Paint Flow Rate" (defined as integer data type). Currently, these two data are directly input on the screen and directly received by the paint supply system.
(2) In the TIA Portal program file, add a global type DB block with data number 8 and name "Workpiece Process Table 1". Open this data block and add a block named "Workpiece Data" with the data type of the array "Workpiece Recipe" created above, ranging from 1 to 200, as shown in Figure 9. The expanded data group is shown in Figure 10. Also, check the "Retain" option to retain data even after power failure.
(3) Writing the actual teaching form filling SCL program: Add function block FB63 to the TIA Portal program file, defining input/output interfaces, X-axis position, Y-axis position, Z-axis position, robot path number, paint number, maximum workpiece number, HMI data storage confirmation, counter pointer, and other parameters. The interface parameters are shown in Figure 11:
The main program for FB63 is written as follows:
IF #HMI confirmation pulse = 1 AND #count pointer <= #maximum workpiece number then
// Input values from the touchscreen (i.e., the subroutine's IN port) and store them in the DB process workpiece table.
“Workpiece Process Table 1”.Workpiece Data [#Count Pointer].Heavy Crane X Coordinate: =#X-axis Position;
“Workpiece Process Table 1”.Workpiece Data [#Count Pointer].Heavy Crane Z Coordinate: =#Z Axis Position;
"Workpiece Process Table 1". Workpiece Data [#Count Pointer].Robot Trajectory Number:=#Robot Path Number;
“Workpiece Process Table 1”.Workpiece Data [#Count Pointer].Paint Formula Number: =#Paint Number;
#Counter pointer := counter pointer + 1;
//After each array is entered, the pointer is incremented by 1, pointing to the next position.
END_IF;
Figure 11 Parameters of the actual teaching number filling interface
Below is a data sheet for teaching one of the large wings. It takes 17 fixed-point spraying to complete the painting of the entire part.
Serial number, X-axis coordinate value, Y-axis coordinate value, Z-axis coordinate value, robot trajectory number
Note: The units for X/Y/Z are mm.
Table 2. Teaching Data for Large Wings
Automatic multi-array reading process:
This process is quite complex, involving reading each set of data stored in the "Workpiece Process Table 1" array DB8, then transmitting the X-axis, Y-axis, and Z-axis positions to the S7-1200 PLC of the overhead crane system via PROFINET communication, and transmitting the robot trajectory number to the S7-1200 PLC of the robot system via PROFINET communication. This is executed according to the painting process sequence of the suspended robot painting system.
Writing an automatic workpiece process table SCL program: Add function block FB91 to the TIA Portal program file and define the input/output interface. The interface parameters are shown in Figure 12.
Figure 12 Interface parameters for automatically reading workpiece process table
The FB91 program is partially written as follows:
IF#start signal pulse=1 AND first step=0THEN
#oHeavy crane X coordinate: = "Workpiece process table 1".Workpiece data [#iSpecify start step].Heavy crane X coordinate;
#oHeavy crane Y coordinate: = "Workpiece process table 1".Workpiece data [#iSpecify start step].Heavy crane Y coordinate;
#oHeavy crane Z coordinate: = "Workpiece process table 1".Workpiece data [#iSpecify start step].Heavy crane Z coordinate;
#o Robot trajectory number: = "Workpiece process table 1".Workpiece data [#i Specifies the start step]. Robot trajectory number;
#o Paint formula number: = "Workpiece process table 1".Workpiece data [#i Specifies the start step]. Paint formula number;
#i specifies the starting step: =1;
#Counter pointer:=#i specifies the starting step;
#o Table lookup completes crane return to origin: =0;
END_IF;
VI. Conclusion
This project used Siemens S7-1500 PLC and TIA Portal software. The S7-SCL language was extensively used in the programming process. Compared with other programming languages for Siemens PLCs, SCL has obvious advantages in processing multi-array data, making it more convenient for control tasks that require cyclic use. It not only has a smaller program size but is also less prone to errors, and the debugging cycle is greatly shortened. Overall, the use of the S7-1500 series PLC shortened the design and debugging cycle in the project development process and improved the methods and efficiency of equipment debugging, making it a great tool for industrial equipment research and development and manufacturing.
Since its commissioning, this system has operated well, with reliable and stable control. It has shortened the coating cycle time, improved production efficiency, and achieved ideal coating thickness and uniformity on the workpieces. It has significantly reduced the labor intensity of workers and improved the working environment, earning recognition from the leadership and frontline staff of the composite materials company. This system enables aircraft manufacturing to transition from traditional manual coating operations to efficient, intelligent, and precise automated coating operations, meeting overall aircraft performance indicators, improving product quality, enhancing the rapid development and production capabilities of next-generation aircraft, and improving the core competitiveness of the aviation industry.
