<p>In this paper, a fuzzy adaptive predefined time output feedback control method is given for a class of flexible joint robots system (FJRs) with output constraints. In this paper, a fuzzy logic system (FLS) is used to approximate an unknown nonlinear dynamic function and a fuzzy logic system-based state observer is constructed to estimate the unmeasured state. In addition, a barrier Lyapunov function is introduced to solve the output constraint problem and the computational complexity is reduced by constructing a predefined time filter. With this strategy, predefined time stabilization of the closed-loop system is achieved. Finally, the effectiveness and superiority of the control strategy are verified by a series of simulation results.</p>