Knee assistance for stroke patients with gait disorder is essential for everyday walking, which leads to better quality of life(QOL). Since hemiplegic patients still have motor functions in the lower limb, it is very important that assistance is made in the way that it does not make resistance to natural movement of the patient. End effector design of the knee assistance robot is suggested in this paper that does not have restriction on natural movement of the knee. The hardware parameters were optimized to minimize force that disrupts the natural movement and harms the knee.