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This paper presents an adaptive robust posture controller for a pneumatic muscles driven parallel manipulator with a redundant degree-of-freedom (DOF). The symmetric geometric structure of the parallel manipulator driven by identical pneumatic muscles studied in this paper makes the rotation angle of the manipulator along its axial direction negligible and a non-factor in using the manipulator. As such, the axial rotation angle is normally not measured and controlled when these types of manipulator are used in practice, leading to a single DOF redundancy in synthesizing the precise posture controller for rotation angles along other axes. To make full use of this redundancy as well as effectively tackle severe uncertainties in the system dynamics, an equivalent average-stiffness-like desired constraint is introduced in the development of adaptive robust posture controller to achieve precise posture tracking while reducing control chattering due to measurement noise. Experimental results are obtained to verify the validity of the proposed controller for the pneumatic muscles driven redundant parallel manipulator.