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Robot application on press brake

In recent years, the application cases of industrial robots in China have increased rapidly, mainly in the fields of welding, painting, handling, etc., and there are not many applications in bending. The bending of the work piece is a widely used and dangerous work, so the market prospect of robot bending is very optimistic, and there are many successful experiences abroad. At present, 40% to 50% of the bending machines in the sheet metal processing workshops in Europe and the United States are equipped with robotic automatic bending systems, and China’s current bending automation has just started. In the next 10 years, the Domestic demand for bending robots will rise in straight line.

The CNC sheet bending flexible processing unit with robot as the core execution unit is a highly automated combination of equipment with high efficiency, high quality and high flexibility. In the bending flexible processing unit, selecting the right combination of components can provide better support for improving processing efficiency and flexibility. The bending accuracy depends on the precision of the press brake, the positioning accuracy of the robot, and the coordinated control of the robot and the press brake. The difficulty of the cooperative control is the speed matching between the robot and the press brake, and the running track of the robot supporting the work piece; The poor follow-up effect will seriously affect the forming effect of the bending angle and the flatness of the board surface, thus affecting the quality of the finished product.

Composition of the bending unit

The standard bending processing unit (Figure 1) is centered on the robot and the press brake.The gripper, feeding platform, blanking platform, positioning work table, flipping frame,hand changing device, and the various detecting sensors are auxiliary components.

Figure 1   Overall layout of the bending unit

The gripper is the “hand” for the robot to replace the manual and pick up the work piece. The gripper of a bending robot is generally constructed by mounting a plurality of suction cups on a metal frame. The feeding and blanking stations usually use stacking pallets. and also use conveyor belts or roller conveyors to transport raw materials and transport finished products. Oily board is prone to sticking, resulting in picking up multiple sheets at a time. A separate device (such as a magnetic separator) and a detection sensor can be installed beside the loading table to ensure that the plate is grabbed.

The positioning table is a tilting platform with ribs, and the micro-bumps are distributed on the table. The robot transfers the steel plate to the positioning table, and the plate slide down to the rib freely by gravity. Since the position of the positioning table and the ribs are fixed, the position of the plate and the gripper is relatively accurately fixed when the robot re-grasps the plate, which provides a reference for the next bending step.

The flipping frame is a fixed frame for the gripping device. When the robot needs to change the position to take the work piece, the work piece can be placed on the flipping frame to fix it, and the robot can re-hold the work piece in the new position. In some special cases, the gripping position can also be changed after the work piece is clamped by the press brake mold clamp.

Bending process unit work flow

The bending process unit is mainly divided into six steps: feeding, reclaiming, centering, flip side, bending and stacking, as shown in Figure 2.

Figure 2  Work flow of the bending unit

(1) Feeding

The sheet material to be processed is manually placed on the loading table. and the sheet material detecting switch is installed on the loading table to avoid the robot from grasping the tray after the sheet material is completely processed.

(2)Reclaiming

The robot runs to the loading table position, and the height of the sheet is detected by the ultrasonic sensor installed on the gripping hand. According to the test data, the sheet is automatically moved to a suitable position for the sheet material to be grasped, and after the sheet material is grasped, the board is passed through the thickness measuring device. The thickness of the material is measured to avoid the occurrence of multiple sheets of material at a time, resulting in processing failure. After the thickness is measured, the centering is prepared.

(3) Centering

The robot runs to the position of the positioning table, put the plate sheet on the positioning table for precise positioning (Figure 3). After the positioning is completed, the sheet material is grabbed again to prepare for bending.

Figure 3  sheet positioning

(4) Flip side

According to the process requirements, judge whether it is necessary to use the flipping rack. If necessary, move the robot to the position of the turning rack, place the sheet on the flipping rack. and the robot releases the sheet and runs to the other side of the plate sheet to grab the material.

(5) Bending

The robot runs to the position of the bending machine.  the sheet is laid flat on the lower mold of the bending machine.  the sensor is accurately positioned by the back finger sensor of the press brake. After the positioning is completed, the robot sends a bending signal to the press brake.  The press brake completes the bending action and determines whether it is necessary to bend again to determine whether to perform continuous bending, as shown in (figure 4).

Bending is the key link. The technical difficulty of bending is the matching action between the robot and the press brake, also called bending follow. When the robot grips or supports the sheet material to bend, the sheet is deformed. and the robot needs to follow the sheet material to perform a circular motion according to a specific trajectory algorithm, and maintain a relatively fixed position with the metal sheet.

Figure 4  sheet bending

Figure 5  Sheet Stacking

(6)Stacking

The robot runs to the position of the blanking table. Because of the forming difference of the work piece.Too much stacking process actions,such as conventional matrix stacking, single-layer cross-stacking, forward-reverse stacking, etc. as shown in (Figure 5).

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