In the robot systems and intelligent machines, the gear-box or mechanisms are connected with the motor to transmit the actuator torque to a distant joint. Generally, its elasticity causes resonance frequency in the system. By using the conventional PID controller, this method cannot perform well in this situation. Much research has proceeded with the aim of reducing vibration. A new effective control method, the resonance ratio control, has been introduced as a new way to guarantee the robustness and suppress the oscillation during task executions for a position and force control. In this paper, two techniques are proposed for improving the performance of resonance ratio control: 1) A new multi encoder based disturbance observer (MEDOB) is shown to estimate the disturbance force on the load side. The proposed observer is not necessary to identify the nominal spring coefficient. 2) A coefficient diagram method (CDM) has been applied to calculate a new gain controller. A new resonance ratio gain has been presented as 2. The effectiveness of the method is verified by simulation and experimental results.