[b]0 Introduction[/b] Although the research on robotic arms is not a new topic, how to minimize manufacturing costs and shorten manufacturing cycles while maintaining high positional accuracy remains a problem worth exploring. Traditional industrial robotic arms are mostly designed in series, that is, by directly mounting the drive and transmission components (such as motors, reducers, etc.) near the rotating joint. Although this design is simple and direct, the drive components themselves become the load of the robotic arm, which can greatly reduce the effective load of the robotic arm and also produce adverse effects such as vibration, reducing the positioning accuracy of the robotic arm. To this end, a wire transmission mechanism is proposed to realize the power transmission from the drive components to the end load. This design can minimize the impact of the drive components themselves on the load capacity of the robotic arm. At the same time, the elasticity of the wire itself also gives the robotic arm a certain degree of flexibility, realizing a certain adaptive function. Due to the position adjustment of the transmission components, the design of the control system requires accurate feedback control of the final end position of the robotic arm. [b]1 Degree of Freedom Robotic Arm Mechanical System[/b] The four-degree-of-freedom robotic arm discussed in this paper is intended for application in small and medium-sized logistics systems. The basic design requirements are: practicality, relatively large working space, gripping weight not less than 2.5 kg, repeatability not exceeding a certain value, lightweight, and neat appearance. For ease of operation and practicality, the design incorporates four degrees of freedom: waist rotation, upper arm pitch, forearm pitch, and wrist rotation. The overall structure adopts a gravity-folding unfolding configuration, with the upper arm pitch and forearm pitch forming a single planar degree of freedom, as shown in Figure 1. The robotic arm primarily utilizes a wire rope transmission mechanism, placing the additional loads such as the motor and gear reducer of the forearm pitch joint on the robotic arm base. This reduces the requirements for other joint drive components and the overall power consumption of the robotic arm, lowers its weight, and increases its external work capacity and efficiency. This robotic arm not only meets the performance requirements of being lightweight and having a large external work capacity, but also boasts advantages such as simple manufacturing and low cost, facilitating its widespread industrial application. The new embedded wire rope tensioning device allows for easy on-site adjustment of tension, solving various problems associated with wire rope transmission and effectively improving the repeatability of the robotic arm. The weight-to-load capacity ratio reaches 4:1. Regarding the control system architecture, an upper-lower-lower-level model using an industrial control computer and a motion control card is adopted. This approach facilitates the calculation of complex robotic arm movements and the design of control software. The overall structure of the control system is shown in Figure 2. Control System Design and Implementation: Hardware Design. After comprehensively considering the project's mechanical structure requirements, functional objectives, and development cycle, the following scheme is proposed for the control system design: For the degrees of freedom of the chassis (waist), upper arm pitch, and lower arm pitch, a closed-loop control system is constructed using servo motor drives and encoder feedback. Due to the project's high positioning accuracy requirements, position control (i.e., pulse control) is selected for the servo motor control method. Therefore, a PCI-8134 supporting the LabVIEW platform is chosen as the motion controller for the servo motor. For the control of wrist rotational freedom and the opening and closing of the gripper, considering that this part of the mechanism is mainly located near the end load and requires a small size, a DC motor with a gear reducer was chosen, and the angle value is indirectly measured by the voltage value of a linear potentiometer. Correspondingly, the PCI-9114DG, which supports the LabVIEW platform, was selected as the digital I/O controller. LabVIEW itself has extensive digital signal processing capabilities, which can effectively solve signal interference and filtering problems commonly encountered in control systems. Using LabVIEW can shorten the project development cycle, allowing for rapid completion of mechanical design, material processing, and control system hardware and software design, which are also important reasons for prioritizing it as the system development platform. Software Design: After considering the overall technical requirements of the robotic arm, the main functions of the control system software can be roughly divided into the following categories: system hardware information feedback, motion parameter setting, manual and automatic motion control, capture and reproduction of the robotic arm's spatial position, and file operations. It should be noted that servo motor position detection primarily obtains feedback on the actual position by reading the corresponding servo motor encoder. At extreme positions, a Hall sensor transmits a trigger signal to the PCI-1 to achieve extreme position detection, and the robot arm's motion status is fed back by periodically reading the I/O register values. DC motor position detection, on the other hand, indirectly measures the DC motor's rotation angle by measuring the voltage of a linear potentiometer fixed to the gear reducer. When the DC motor potentiometer input voltage is affected by AC interference signals, LabVIEW's built-in signal processing functions can effectively suppress the influence of interference signals on the program's decision logic. When a physical filter cannot be quickly obtained on-site, software filtering can be considered. File operations are frequently encountered during program development, requiring functions such as adding, saving, deleting, and retrieving data. In development platforms such as VC or VB, file operations are relatively complex due to the design of document template structures, file pointer operations, and message mapping. In this context, it utilizes document controls such as WebView, spreadsheets, VIs, table controls, and array operations. Click here to download the document: Design of a Four-DOF Robotic Arm Motion Control System Based on LabVIEW. Edited by: He Shiping