The spline screw in the SCARA (Selective Compliance Assembly Robot Arm) four-axis robot is a key transmission component, mainly used to achieve high-precision linear motion and rotational motion (θ axis, usually the fourth axis) of the robot in the vertical direction (Z axis). The following is its detailed use and description: 1. Main use Z-axis lifting motion: The spline screw converts the rotational motion of the motor into precise linear motion, driving the end effector of the robot arm (such as grippers, suction cups, etc.) to move up and down in the vertical direction. Rotational motion transmission: The spline structure transmits torque at the same time to achieve the rotation of the fourth axis (such as the rotation of the end tool), meeting the needs of assembly, screw tightening and other operations. High precision and rigidity: Suitable for scenarios that require repeatable positioning accuracy (such as ±0.01mm) and resistance to lateral forces (such as precision assembly and handling). Synchronous motion: When the Z-axis lifting and rotational motions work together (such as inserting parts), the spline screw can ensure the synchronization of the two motions. 2. Structural description Spline part: The external spline cooperates with the internal spline sleeve to transmit the rotational torque (θ axis), while allowing the shaft to slide up and down in the spline sleeve (Z axis), realizing the combination of rotation and linear motion. Screw part: The precision ball screw converts the rotation of the servo motor into linear motion, providing high-precision, low-friction lifting drive. Integrated design: The spline and the screw are usually integrated on the same shaft, saving space and simplifying the transmission chain. 3. Core features High load capacity: The spline structure disperses torque and radial force, suitable for cantilever loads (such as horizontally extended robotic arms). Low backlash: The preloaded ball screw and spline cooperate to reduce the motion gap and improve the repeatability. Compactness: The integrated design reduces external transmission components and adapts to the narrow joint space of the SCARA robot. Durability: Hardened steel or coating technology is used, which is wear-resistant and has a long life (such as more than 20,000 hours). 4. Typical application scenarios Electronic assembly: PCB board plug-in, chip handling (requires Z-axis precision lifting + rotation alignment). Automated production line: screwing, gluing (rotation and pressing action). Medical equipment: reagent packaging, test tube operation (dust-free, low vibration requirements). 5. Comparison with other transmission methods Characteristics Spline screw Timing belt + guide rod Linear motor Accuracy High (μm grade) Medium (affected by belt elasticity) Very high Load capacity High (suitable for heavy loads) Medium-low Medium Cost Medium Low High Maintenance complexity Regular lubrication Belt replacement Almost maintenance-free 6. Selection considerations Accuracy level: Select C3/C5 screw according to the task. Dust-proof design: Sealed spline sleeve prevents dust from entering (such as IP54 protection). Lubrication method: Automatic lubrication or maintenance-free grease design. Through the composite function of the spline screw, the SCARA robot can efficiently complete complex movements with limited degrees of freedom, becoming the mainstream choice in 3C, automotive electronics and other fields.