Compared to serial robots, parallel robots offer advantages such as higher stiffness, higher precision, heavier load capacity, and easier control. Three-degree-of-freedom spherical parallel mechanisms are an important type of parallel mechanism, enabling three rotational degrees of freedom around the mechanism's center of rotation. These mechanisms can be used as joints in robots such as the waist, shoulder, hip, and wrist, and also in satellite antennas and camera positioning devices, demonstrating significant application value. Among the numerous spherical parallel mechanisms, the 3-3R spherical parallel mechanism (where R represents a revolute joint) has the simplest structure. Therefore, compared to other spherical parallel mechanisms, the 3-3R spherical parallel mechanism has certain advantages in design, analysis, manufacturing, and assembly, leading to its widespread research and application. In the footwear industry, due to the high toxicity of adhesives used for leather bonding, automated adhesive spraying equipment has become an effective way for footwear companies to reduce labor costs and increase productivity. In shoe manufacturing adhesive spraying systems, the object to be sprayed is the sole surface of a shoe last with a three-dimensional spatial curved surface. Processing such a surface requires at least five degrees of freedom. Existing industrial robots, specifically serial single-unit structures, suffer from drawbacks such as low speed and small load capacity. Considering the characteristics of the sanding and adhesive spraying process, the control of the spray gun and sanding head primarily focuses on position and orientation, with limited space for orientation changes. Therefore, a combination of a three-dimensional XYZ guide rail serial structure and a three-degree-of-freedom spherical rotation parallel mechanism is adopted, as shown in Figure 1. The position of the workpiece is controlled by the three-dimensional guide rail, while the orientation of the spray gun is controlled by the spherical three-degree-of-freedom parallel mechanism. Since the movements of the three-dimensional XYZ guide rail serial structure in the x, y, and z directions are independent and uncoupled, position control is very simple. The main work focuses on the design and control of the three-degree-of-freedom spherical rotation parallel mechanism. [align=left]This paper designs a control system for a 3-3 R spherical parallel glue spraying device. Based on the kinematic characteristics of the parallel mechanism and the glue spraying process requirements of the shoemaking industry, a Googol GT-400-SG-PCI-G motion control card is adopted, and its hardware connection and software design methods are given. A user-friendly and interactive glue spraying system control software was developed. The control software implements modules such as single-axis control, coordinate system control (multi-axis coordinated control), and trajectory control. The entire system consists of five parts: a 3-3 R spherical parallel mechanism, a spray gun, a motor and drive device, a motion control card, and control software. The host computer control software calls the API functions of the motion control card to send control commands to the host computer's motion control card. The motion control card generates pulse and direction signals according to the commands to drive the motor. The motor is equipped with gears, which drive the parallel mechanism to rotate through gear meshing, thereby enabling the spray gun to reach the specified position or orientation. R Spherical Parallel Mechanism. Mechanical Structure[/align] A simplified diagram of the R spherical three-degree-of-freedom parallel mechanism is shown in Figure 2. In the 3-3R spherical three-degree-of-freedom parallel mechanism kinematic chain shown in the figure, the axis of the revolute joint is parallel to the fixed platform. Furthermore, in all three branches, the axes of all revolute joints and the central axis of the annular prismatic joint on the chassis, composed of meshing large and small gears, intersect at a single point, called the mechanism's center point. This center point is also the center of rotation of the moving platform. When the prismatic joints in each branch move at the same speed, the moving platform can rotate around the z-axis. The control system hardware implementation consists of four parts: a GT-400-SG-G motion control card (manufactured by Googol Technology), an SH2024A stepper motor driver and stepper motor, the three-degree-of-freedom parallel mechanism, and a spray gun. The core of the motion control card includes an ADSP 2181 and an FPGA, enabling high-performance control calculations and generating a wide pulse bandwidth. As a slave controller, it is based on the PCI bus protocol. The PC exchanges information with the GT-400-SG motion control card through the PCI communication interface, including issuing motion control commands to the motion control card and obtaining the current status and relevant control parameters of the motion control card through this interface. The master controller (computer) can synchronously control multiple motion axes by calling Googol's API functions to achieve multi-axis coordinated motion (driving a three-degree-of-freedom parallel mechanism requires three motion axes). CN5 on the control card's terminal board is the motion axis interface, and it has multiple dedicated and general-purpose inputs and outputs. Dedicated inputs include drive alarm signals, origin signals, and limit signals, and dedicated outputs include drive enable and drive alarm reset. The control card has a direction/pulse output signal mode and a positive and negative pulse output signal mode. This system uses the direction/pulse output signal mode. In this mode, the terminal on the terminal board (CN5~CN8) is connected to the CP terminal of the motor driver, and the DIR+ terminal is connected to the driver's terminal. The hardware connection uses an SH2024A stepper motor driver. This driver has a wide operating voltage range, is DC powered, and has a voltage value of 15-36V. The phase current is adjustable, ranging from 0.5 to 2A. It operates in two-phase eight-beat half-step mode, with a step angle of 0.9 degrees and a rotation of one revolution every 400 pulses. Motor interface: For two-phase four-wire motors, connect directly to the driver. OPTO: Common terminal for input signals, connected to an external system. If VCC is +5V, it can be connected directly; otherwise, a current-limiting resistor must be connected. Pin 7 of CN5 on the motion control card's terminal board is the +5V output; connecting OPTO to this pin drives the motor. DIR: Direction level input terminal, connected to DIR+ of CN5 to control the forward and reverse rotation of the motor. CP: Step pulse signal, connected to PULS E+; FREE: When this terminal is low, the motor stops. This terminal is not used; connect it to a +5V high level. Figure 3 shows the hardware connection diagram of the motion control card terminal board, stepper motor driver, and stepper motor (direction/pulse output signal mode). The ALM pin (pin 2) of CN 5 on the control card terminal board is specifically used to detect drive alarm signals. The driver used in the system is relatively simple and does not have this signal; short it to ground (Note: It must be shorted to ground, otherwise the control card will not operate normally; this is a hardware requirement of the control card). The control system software design follows this control logic: Communication between the PC and the motion control card is achieved using a dynamic link library; the user calls the corresponding library functions through the host program to pass relevant parameters and motion trajectory descriptions from the motion control card to the motion control card; the motion control card automatically completes complex calculations and operations such as trajectory planning, safety detection, and sampling refresh according to the host's requirements; finally, the calculation results are converted into pulses to control the stepper motor movement. The main functions provided by the 3-3R robot control software include: axis-based control, coordinate system-based control, and trajectory-based control. For axis-based control, when controlling a single axis, first select the current axis to be controlled, confirm the validity of the axis's limit switches, set motion parameters such as motion mode, speed, acceleration, and target position, and then refresh the parameters to start the axis's movement. The motion of the spherical parallel platform prototype in single-axis control mode is shown in Figure 4. In coordinate system control mode, the origin of the base coordinate system is located at the center point of the parallel mechanism. First, select all axes to participate in the motion (this control system requires control of 3 axes), input the position or direction in the user interface (the workspace of the spherical parallel mechanism is a spherical range, and points on the sphere uniquely determine the position and attitude of the moving platform relative to the base coordinate system), set the motion mode, speed, acceleration, and other motion parameters, and after pressing the "Reach Specified Position or Direction" button, the parallel mechanism can reach the target point according to the specified requirements. The coordinate system-based control interface is shown in Figure 5. In trajectory-based control mode, the origin of the base coordinate system remains at the center point of the parallel mechanism. However, the coordinate system of the tool (spray gun) on the parallel mechanism needs to be transformed to the coordinate system of the working target (shoe last). This is achieved by transforming the tool coordinate system relative to the base coordinate system into equal transformation from the target coordinate system to the base coordinate system. This equation can be transformed into a transformation of the tool coordinate system relative to the target coordinate system. Any transformation of the tool (direction and position) after transformation is relative to the target shoe last coordinate system. Importing trajectory data into the software and clicking the "Run Along Trajectory" button allows the tool to successively reach each trajectory point from its initial position according to the given interpolation algorithm, thus completing the specified trajectory. The trajectory control program flow is shown in Figure 6. In conclusion, the attitude change space of the spray gun in the glue spraying process is small, conforming to the characteristics of a spherical parallel mechanism. Compared with the traditional series structure, the 3-3R spherical parallel glue spraying device can achieve higher precision in glue spraying operations under high speed and high load. The use of motion control cards makes it easier to design modular systems and upgrade and maintain equipment hardware and software. The control system has a user-friendly human-machine interface and can realize control methods based on multiple modes. References: Huang Zhen, Kong Lingfu, Fang Yuefa. Parallel Robot Mechanism Theory and Control [M]. Beijing: Machinery Industry Press, 1997. He Leiying, Wu Chuanyu, Ni Yong. Development of Intelligent Sorting Experimental Device Based on RPPR Robot [J]. Industrial Instrumentation and Automation Device, 2007, 70-72. Li Qinchuan, Wu Chuanyu, Hu Xudong. Spherical Three-Degree-of-Freedom Parallel Attitude Control Mechanism with Ring Guide Rail: China, CN 1631612 [P]. 2005-06. Zhu Longbiao, Zhu Zhisong, Zhang Xingguo. 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