Currently, the application of industrial robots is rapidly increasing, with a focus on welding, palletizing, and painting, while the application of robots in bending processes is relatively limited. However, sheet metal bending is a high-demand task that involves certain risks and labor intensity. Therefore, the market prospects for robot bending are very promising, and there have been many successful cases both domestically and internationally. Currently, 40% to 50% of bending machines in sheet metal processing workshops in the European and American markets are equipped with robot automatic bending systems, indicating that bending automation is just beginning. In the next few years, the demand for bending robots is expected to increase sharply.
The bending workstation mainly consists of six processes: loading, unloading, centering, flipping, bending, and stacking.
1. Loading: Operators manually stack the sheets to be bent on the loading table. The loading table is equipped with sheet detection switches to prevent the robot from gripping the pallet after all the sheets have been bent.
2. Unloading: The robot moves to the loading position and uses an ultrasonic sensor mounted on the gripper to detect the height of the sheet. Based on the detection results, the robot automatically moves to the appropriate position to grab the sheet. After gripping the sheet, the thickness of the sheet is measured to avoid picking up multiple sheets at once, which could cause processing errors. Once the thickness measurement is completed, the robot prepares for centering.
3. Centering: The robot moves the product to the positioning table and places the sheet on the positioning table for precise alignment. After alignment, the sheet is gripped again in preparation for bending.
4. Flipping: Depending on the process requirements, a flipping frame may be used to flip the sheet. If necessary, the robot moves to the flipping frame position, places the sheet on the flipping frame, releases the product, and steps aside. Once the flipping is completed, the sheet is gripped again.
5. Bending: The robot moves to the bending machine position and places the sheet flat on the lower die of the bending machine. Precise positioning is achieved using a bending machine backgauge sensor. Once the positioning is completed, the robot sends a bending signal to the bending machine and coordinates with it to perform the bending operation. The robot determines whether to perform consecutive bends based on the need for additional bending. Bending is a critical step, and the challenge lies in the coordination between the robot and the bending machine, particularly in bending follow-up actions. When gripping or supporting the sheet during bending, the robot needs to follow a specific trajectory algorithm to perform arc-following motions and maintain a relatively fixed position relative to the sheet.
6. Stacking: The robot moves to the unloading table position. Depending on the formed workpiece, various stacking processes may be required, such as conventional matrix stacking, single or double-layer cross stacking, or positive and negative interlocking stacking.
6-axis or 7-axis robots are paired with 6+1 or (7+1, 8+1) axis electro-hydraulic servo-controlled CNC bending machines for fully automatic bending of metal sheets. These machines are equipped with accessories such as centering tables and flipping frames to meet the requirements of automatic bending.
Advantages of robot bending systems include labor savings, elimination of safety hazards, suitability for long continuous operations, and consistent workpiece precision.
Currently, whether it is a general standard 6-axis robot or a bending-specific robot with optimized arm reach or form, bending follow-up algorithms are needed at the lower level to support the bending process. The need for non-following bending is rare. Without good follow-up performance, poor trajectory tracking by the gripper or suction cup can cause deformation and wrinkles in the sheet, affecting the quality of the formed workpiece. Establishing an accurate robot bending follow-up motion model helps develop excellent trajectory tracking algorithms and achieve superior follow-up performance.
