Fabrication of higher precision planer multi-joint positioning mechanism using high-performance joint elements and research on its limit of positioning accuracy

平面多关节定位机构（SCARA型机械手）在精密装配线上有着广泛的应用，但现有机械手的定位精度远低于笛卡尔型定位机构。然而，它们具有上级可用性，因为它们在如此小的设置区域内具有如此广泛的工作范围。它们有望在装配线上作为坐标测量机工作。本研究利用高性能关节元件开发了一种新型平面多关节机构，以实现在300 × 200 mm工作范围内具有1 μm级定位精度的SCARA型机械手。研究了SCARA型机构在经过严格的杆件参数标定后的定位精度极限，所研制的机构臂长为L_1=250 mm，L_2 =250 mm，臂长为L_1=250 mm，臂长为L_2 = 250 mm。2=147 mm，关节轴采用精度为0.05 μm的高精度空气轴承，关节驱动采用摩擦驱动机构和直流调速器。设计了一种能够检测实际关节角度的超高分辨率旋转编码器。编码器的分辨率对于θ_1为720×10^4 ppr，对于θ_2为144×10^4 ppr。另外，将手臂结构布置成重心与关节轴重合，并以参考角度轨迹控制关节角度进行实验。确认关节角度被控制以在分辨率角度的偏差内解决。该机构30次定位重复精度的测量误差范围在±3.5 μm（3σ）以内，并验证了其误差椭圆面积减小到传统机构的10%。链路参数的校准和更详细的定位精度评估计划在下一阶段进行。

Though planer multi-joint positioning mechanism (SCARA-type manipulators) are in great demand on precision assembly lines, the positioning accuracy of current manipulators is much lower than Cartesian-type positioning mechanism. However, they have superior availability to assembly lines in factories because they have such a wide work range for such a small setting area. And they are expected to work as coordinate measuring machines in assembly lines. This study develops an novel planer multi-joint mechanism using high-performance joint elements, so as to realize an SCARA-type manipulator with 1 μm level positioning accuracy over working range of 300 × 200 mm. Moreover, it aims at researching the limits of positioning accuracy by the SCARA-type mechanism after strict calibration of link parameters.The arm length of the developed mechanism is L_1=250 mm and L_2=147 mm. A high precision air bearing with accuracy of 0.05 μm is adopted to guide the joint axis, and a friction drive mechanism and a DC servomotor are devised to drive joint. And a rotary encoder with ultra-high resolution is devised that can detect the actual joint angle. The encoder resolution is 720×10^4 ppr for θ_1 and 144×10^4 ppr for θ_2. Moreover, the arm structure is arranged so that the center of gravity coincides with the joint axis.The experiments are performed to control the joint angle with reference angle trajectory. It is confirmed that the joint angles are controlled to settle within the deviations of resolution angle. The dispersion range of the measured repeatability of 30 times positioning is within about ±3.5 μm (3σ), and it is verified that the area of dispersion ellipse is decreased to 10 % of conventional mechanism. The calibration of link parameters and more detailed evaluation of positioning accuracy are scheduled to perform on the next stage.