High-Precision Control of Servomechanism Using Traction Drive

与减速器相比，牵引传动具有优良的传动特性。牵引传动的间隙可以忽略不计，传动误差的频率分量在高频范围内很小。实际上，牵引传动只包含低频的传动误差。这对于获得高精度伺服机构具有重要意义，因为与齿轮减速器相比，传动误差可以更容易地补偿。因此，EMURA将牵引驱动应用于等速伺服机构。研制了一种高精度伺服机构，并通过实验验证了牵引驱动在高精度伺服机构中的性能。牵引传动通过两个滚动辊之间形成的流体膜的粘性力传递扭矩。牵引传动的转矩传递伴随着两辊之间的滑移。转矩对滑移的传递特性对伺服机构来说是非常重要的。将牵引传动应用于定位伺服机构中，需要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，了解转矩与滑移的传递特性是很重要的。然而，大多数报道的结果只是关于静态特性，动态特性尚未明确，因为很难测量动态特性，另一方面，转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输特性与滑移的关系。两辊之间的滑动非常小，因此很难用常规方法高精度地检测，特别是在高速旋转时。Emura建议使用非正弦两相锁相环进行高分辨率的滑移速度检测。该方法采用分别安装在输入轴和输出轴上的两个编码器。通过对两个编码器的相位进行插值，可以高精度、高分辨率地检测出两个滚子之间的转速差。然而，由于轧辊的偏心和跳动会对速度差产生较大的波动，检测电路的输出误差较大。因此，本研究采用互相关法去除该误差，以精确研究转矩传递的频率特性。实验结果表明，转矩传递特性具有较大的非线性，且线性范围很小。转矩传递的非线性导致伺服机构产生振荡等不稳定性，对负载波动的鲁棒性变差。为了提高伺服机构的稳定性和负载特性，提出了一种基于实测转矩传递特性的滑移速度反馈控制方法。实验结果表明，该伺服机构的稳定性和负载特性得到了显著改善。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