A kind of quasi-circular gait was proposed, which divided the periodic motion into three phases: start phase, middle phase and end phase. The time was equal in the start phase and the end phase, and could be adjusted with the parameter ratio. The joint trajectories of the two phases were planned by quintic polynomial, and the middle phase was still the circular gait joint trajectory. The trajectory of the proposed quasi-circular gait was simulated.

The angular velocity was continuously differentiable and 0, the angular acceleration was continuous and 0, and the end-effector trajectory became flat with the increase of ratio. The results on the physical prototype of the lower limb rehabilitation robot were principally consistent with the simulation, and the machine worked smoothly.

The proposed variable quasi-circular gait had smooth angular acceleration at the junction of periodic motions, which effectively solved the jitter problem when using circular gait for lower limb rehabilitation training and avoided secondary injury to the patients.