<p>This paper explores the stabilization control problem of inverted pendulum-cart systems with unmeasurable velocities by developing a novel event-triggered fuzzy control solution that considers swing angle constraints. To surmount the design challenge posed by the underactuated mechanical structure, auxiliary variables are constructed to transform the mechanical dynamic equation into a non-strict feedback form, which effectively facilitates the implementation of the dynamic surface-based backstepping design framework. By exploiting a nonlinear mapping function and a state reconstruction method, the swing angle is constrained within a prescribed region without taking into account the rigorous feasibility condition of the virtual controller. Operational frequencies of the actuator are reduced through event-triggering, thereby mitigating excessive mechanical wear. Importantly, a high-gain observer is developed to separately recover unmeasurable velocities and the disturbance term. Based on the estimated velocity information, the fuzzy logic systems are designed to approximate the nonlinear terms derived from unmeasurable velocities in the non-strict feedback system. Finally, theoretical analyses and simulations confirm the effectiveness of the developed control solution.</p>