Abstract: The positioner is one of the important pieces of equipment in robot production lines and robot stations. As there are variations in workpiece shape and size, its structure becomes more flexible and diverse. This paper introduces the basic requirements, types, and common structures of the positioner, providing a reference for the design of dedicated workpiece positioners. Keywords: Robot Positioner In certain applications of industrial robots, especially in welding operations, the relative posture of the welding torch held by the robot and the weld seam of the workpiece is a crucial factor in ensuring welding quality. Since the robot's structure and workspace are fixed, and the weld seam positions and shapes of various workpieces vary greatly, their positions relative to the robot may be distributed in various directions. Furthermore, the shape of the workpiece and the components on the fixture may affect the correct positioning of the welding torch, inevitably leading to situations where the position is unsatisfactory or welding is impossible. How to transform the weld seam position of each part of the workpiece to the location most favorable for the robot's welding torch positioning and welding has become a crucial problem that must be solved in robotic welding and other operations. After years of practice, workpiece position changing machines with different structural forms suitable for different operating scenarios have emerged, effectively solving the problem of relative position transformation between the robot and the workpiece. I. Basic Requirements of Positioning Machines Workpieces in different applications vary greatly, and the corresponding fixtures are also diverse. Workpiece position changing machines (hereinafter referred to as positioners) must adapt to the requirements of the workpiece, fixture, and operation. Here, we summarize different types of positioners and generally discuss their basic requirements. ① The positioner must be able to transform the workpiece to the optimal position to ensure that the robot tool (such as the welding torch) is in the most reasonable working state. ② The positioner should meet the requirements of all working positions as much as possible. For positions that are truly difficult to achieve or machining dead zones, manual handling or alternative clamping methods can be used in the next workstation. ③ The positioner should have high repeatability to ensure the consistency and stability of workpiece machining quality. ④ The positioner should minimize robot waiting time. By using a two- or multi-station structure, the manual processing time and robot working time can be combined to shorten the processing cycle and improve productivity. ⑤ The positioner should have sufficient strength and rigidity to resist normal external forces, ensuring that the overall deformation does not affect the normal operation of the robot or the welding quality of the workpiece. ⑥ When the positioner is running, the problem of destructive entanglement of electrical wires and air hoses must be solved. Necessary lead wires and air intake devices should be installed to protect the wires and pipes from damage. ⑦ When the positioner is used for welding operations, the negative electrode of the welding probe should be as close as possible to the workpiece being welded, and the current should not pass through mechanical parts with few or small contact points, such as bearings, to ensure good arc quality and avoid damage to mechanical moving parts. ⑧ For operations with significant vibration, the positioner should be integrated with the robot body via a base or other structural components to ensure the relative positional accuracy between the robot and the positioner. II. Common Types of Positioners Positioners come in many varieties, each with its own characteristics in terms of drive, positioning, and structure, depending on the workpiece shape, size, drive method, positioning method, and number of position dwell points. Common drive methods for positioners include pneumatic drive, AC motor drive, and AC servo motor drive. Corresponding positioning methods include pneumatic pin positioning, stop-feed positioning, and position servo positioning. Pneumatic and AC motor drives are low-cost and often used for operations with a small number of position dwell points and moderate accuracy requirements; while position servo motor drives are more expensive. They can be used as external axes of the robot, controlled by an additional robot control unit, and are often used in operations with a large number of position dwell points, requiring coordinated movement between the positioner and the robot, and demanding high positioning accuracy. Commonly used structural forms include single-axis cantilever type, double-axis cantilever type, single-axis double-support type, double-axis double-support type, double-axis tilt type, rotary table type, 4-axis lifting type and composite type, etc. Various positioners are shown in the table. [align=center] [/align] In practical applications, these basic types of positioners have evolved into various composite types of positioners based on usage requirements, manual operation and productivity improvement. Figure 1 shows some typical examples. (8) is a three-axis double-support type positioner formed on the basis of the single-axis double-support type; (b) and (c) are two types of positioners generated by the rotary table type; (d) is a double-axis tilt type positioner placed on a linearly movable slide and sequentially sent into the robot's workspace. These positioners share a common feature: they have two mounting stations, capable of clamping two workpieces. Through rotation or movement, one workpiece is alternately positioned within the robot's workspace, while the other is positioned at the manual operating station. This allows for simultaneous workpiece loading/unloading and robot operations, significantly reducing auxiliary time and improving the robot's efficiency. III. Positioner Structure In summary, the positioners selected and designed for robot workstations are highly flexible. Their effectiveness depends on various factors such as operational requirements, workpiece shape and size, drive method, and positioning method. Furthermore, the type and performance of the positioner greatly influence the work quality, thus requiring sufficient attention. Specific problems must be analyzed specifically to design the optimal workpiece position changing machine. The positioner 2 is a three-axis, dual-pivot positioner. We will analyze its specific mechanical structure. An H-shaped support is mounted on a turntable, which can rotate 180 degrees to change the positions of the two clamping bodies. Two dual-pivot rotation systems are mounted on the H-shaped support, driving the two clamping bodies respectively, allowing the robot to find the optimal working position relative to the workpiece. Four cylinders are mounted on the platform below the four corners of the H-shaped bracket. These cylinders drive positioning pins and support pins to accurately position the H-shaped bracket and prevent deformation of the H-shaped bracket under external forces such as operating forces, which would affect the robot's work quality. The turntable structure is shown in Figure 3. An AC servo motor drives the main shaft to rotate the H-shaped bracket through an RV reducer and gear pair. At the 0° and 180° positions, proximity sensors, over-limit switches, and stops are used to detect and locate the stopping position and faults. There is a through hole in the middle of the main shaft, and the lower end is equipped with a wire and hose support. The wires and hoses are led from bottom to top through the main shaft core into the H-shaped bracket and delivered to the respective wiring and connection points. A flexible chain-type tubing protective sleeve is used between the wire and hose support and the bracket fixed on the housing. The structure of the double-pivot rotation system of the safety clamp is shown in Figure 4. The gripper is mounted on the active and passive side connectors. The AC servo motor on the active side drives the gripper to rotate via an RV reduction gear. The driven shaft is hollow, with a rotary air intake connector installed at the tail. Compressed air is drawn from the tail and exits from the front face of the shaft. The negative terminal of the welding power supply is fixed to a pressure block on the right side of the bearing housing. Under the action of a spring, the pressure block is always in close contact with the shaft, ensuring good conductivity and preventing current from passing through the bearing. The wheel at the front of the shaft is a device for releasing and collecting electrical wires. The extreme positions of the gripper's rotation are detected by two proximity switches. If the proximity switches malfunction, the stop block at the rear of the active side connector will be stopped by a dead stop block. In summary, the positioner is an important piece of equipment in robot application engineering. Its form and design requirements are flexible and varied, and its performance directly affects the production quality and efficiency of the robot workstation and production line.