In the previous study, we developed a flexible pneumatic cylinder. A wrist rehabilitation device using these cylinders was also proposed and tested. To improve the position control performance of the cylinder, a disturbance observer with time-delay compensation and Smith's compensator were applied into a built-in tiny embedded controller for position control of a single cylinder. As a result, it was confirmed that 40% improvement of the mean absolute error in experiments was achieved by using

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... e proposed control scheme. In the next step, we aim to apply the improved controller into the attitude control system of the whole wrist rehabilitation device using three cylinders in which there exists an interference among three cylinders. To install the control system, it is necessary to measure lengths of bending cylinders. In this paper, we apply the disturbance observer to the attitude control of the device, and we propose a measuring method of bending tube length by using a twisted wire type linear potentiometer and a simple analytical model. Then, the proposed method is applied to the attitude control of the device.