High-Precision Control of Servomechanism Using Traction Drive

与减速齿轮相比，牵引传动具有优良的传动特性。在高频范围内，牵引传动的间隙可以忽略不计，传动误差的频率分量很小。实际上，牵引传动只包含低频传动误差。这对于获得高精度的伺服机构具有重要意义，因为与齿轮减速器相比，可以更容易地补偿传动误差。因此，井村将牵引驱动应用于恒速伺服机构。研制了一种高精度的伺服机构，并通过实验结果验证了高精度伺服机构的牵引传动的性能。牵引传动通过两个滚子之间形成的液膜粘性力传递扭矩。牵引传动的扭矩传递伴随着两个滚子之间的打滑。扭矩传递特性对伺服机构是非常重要的。牵引传动在POSI…上的应用对于更多的伺服机构，必须对输出轴的转角进行反馈控制。这意味着滑移发生在反馈回路内，并影响伺服机构的性能。因此，重要的是要了解扭矩传递特性与滑移率的关系。然而，已有的研究成果大多只涉及静态特性，动态特性尚未阐明，这是因为动态特性难以测量，另一方面，扭矩传递的动态特性对伺服机构的动态性能非常重要，因此，我们通过实验研究了传递特性与滑移率的关系。两个滚子之间的滑移量非常小，因此很难使用常规方法进行高精度检测，特别是在高速旋转时。Emura建议使用非正弦两相锁相环来实现高分辨率的滑移速度检测。该方法使用两个编码器，分别安装在输入轴和输出轴上。通过干涉两个编码器的相位，我们能够高精度和高分辨率地检测两个滚子之间的旋转速度差。然而，滚子的偏心和跳动会对速差产生较大的波动，检测电路的输出含有较大的误差。因此，为了精确研究扭矩传递的频率特性，本研究采用互相关法消除这种误差，实验结果表明扭矩传递特性具有很大的非线性，线性范围很小。扭矩传递的非线性会导致伺服机构产生振荡等不稳定现象，对负载波动的鲁棒性变差。为了提高系统的稳定性和负载特性，提出了一种基于实测扭矩传递特性的转差速度反馈控制方案。实验结果表明，该伺服机构的稳定性和负载特性均有明显改善。较少

Traction drive has excellent transmission characteristics compared with reduction gear. Backlash of traction drive is negligible and the frequency components of transmission error are small in high frequency range. Actually, traction drive contains only transmission error that has low frequency. This is significant for obtaining high-precision servomechanisms because the transmission error can be compensated more easily compared with gear reducers. Therefore, EMURA applied traction drive to a constant-velocity servomechanism. We developed a high-precision servomechanism and demonstrated the performance of traction drive for high-precision servomechanisms by experimental results.Traction drive transmits torque by viscous force of fluid film formed between two rolling rollers. Torque transmission of traction drive is accompanied with slip between the two rollers. The torque transmission characteristics versus slip are very important to the servomechanisms. Applying traction drive to posi … More tioning servomechanisms, we have to carry out feedback control of rotary angle of output axis. This means that the sliptakes place inside feedback loop and affects the performance of the servomechanisms. Therefore it is important to know torque transmission characteristics versus slip. However, most of reported results are only about static characteristics and the dynamic characteristics have not yet clarified, because it is difficult to measure the dynamic characteristics, On the other hand, the dynamic characteristics of torque transmission are very important to the dynamic performance of servomechanisms.Therefore, we investigated the transmission characteristics versus slip by experiments. Slip between the two rollers is very small so that it is difficult to detect with high accuracy by using conventional methods, in particular, at a high-velocity rotation. Emura proposed to use non-sinusoidal 2-phase type PLL for high-resolution detection of slip velocity. This method used two encoders mounted on input axis and output axis respectively. Byinterpo lating the phase of the two encoders, we are able to detect the difference of rotary velocity between the two rollers with high accuracy and high resolution. However, the eccentricity and run-out of rollers induce large ripples to the velocity difference, and the output of detection circuits contains large error. Therefore, in this study, cross correlation method was used to remove such error for precise investigation of the frequency characteristics of torque transmission.The experimental results showed that the torque transmission characteristics have large nonlinearity and the linear range is very small. The nonlinearity of torque transmission induces unstableness like oscillations to servomechanisms and the robustness for load fluctuation becomes poor. To improve the stability and load characteristics, we proposed a slip-velocity feedback control to the servomechanism based on the measured torque transmission characteristics. The experimental results showed that the stability and load characteristics of the servomechanism were significantly improved. Less