抵抗スポット溶接機のための非対称サーボ弁と単動シリンダを用いた高速空気圧-力制御

第2報 非対称電空サーボ弁の実験解析と閉ループ圧力制御系のハードウエア補償

抄録

To develop a very high-speed closed-loop pressure control system, an asymmetric servovalve, whose downstream port width is twice of the upstream one, is proposed here as hardware direct compensations to overcome the response differences in pneumatics where step-down response takes a very long settling time when the gain is adjusted to be suitable for step-up response.
The handmade asymmetric valve achieved -3dB bandwidth of 260Hz, whereas the frequency at phase -90 degree is 190 Hz, and achieved rise time less than 1ms and dead time 0.9ms for a step voltage input which corresponds to spool stroke 0.2mm.The flow capacity of the asymmetric valve at exhaust side (i. e., x=-400μm, w_d=-337NL/min) is twice of that at supply side (i. e., x=400μm, w_u=+191NL/min) for the same valve openings.The spool saturation ranges are also discussed. The flow capacity of the downstream side of asymmetric valve (-337NL/min) is about twice of that of the symmetric valve (-171NL/min). The theoretical results agreed well with the experimental ones.
It is clear experimentally that an asymmetric servovalve is effective for speeding up the step-down response of the closed-loop pressure control system to equalize the step-up and step-down response speeds. For the closed-loop system with the symmetric valve, rise time attained 5.7ms for the step response but 14ms for step-down response. Therefore, an asymmetric valve is proposed to overcome this problem. By using the asymmetric valve and a proportional controller, rise time for the step response was adjusted to be 5.7ms (the same as the case using the symmetric valve) with no overshoot and rise time for the step-down response became 7ms. Rise time for step-down responses improved from 14 to 7ms.