Series elastic actuator, method for controlling series elastic actuator and system thereof

1. A method of controlling a series elastic actuator (SEA) comprising a motor-side rotation unit, a load-side rotation unit, and at least one elastic member, the motor-side rotation unit and the load-side rotation unit being coupled each other to transfer rotatory power of a driving motor to a load, the method comprising:

measuring relative displacement between the motor-side rotation unit and the load-side rotation unit;

calculating external torque by an external force applied to the load side based on the measured displacement and hardness (K) of the elastic member;

comparing the calculated external torque with a critical torque; and

switching a control mode of the SEA to any one of torque control and position control based on a result of the comparison.

2. The method of claim 1 , wherein the displacement is measured using a magnetic body and hall sensor respectively positioned at corresponding positions of the motor-side rotation unit and the load-side rotation unit.

3. The method of claim 1 , wherein when the calculated external torque is greater than the critical torque, the control mode switches to the torque control for controlling torque transferred to the load side.

4. The method of claim 1 , wherein when the calculated external torque is less than or equal to the critical torque, the control mode switches to the position control for controlling a rotation angle of the load side.

5. The method of claim 4 , wherein the rotation angle of the load side is controlled using a rotation angle of the fed-back motor-side.

6. The method of claim 1 ,

wherein when the external torque increases to a value greater than the critical torque, the control mode switches from the position control to the torque control, and

when the external torque decreases to a value or less obtained by subtracting given torque from the critical torque, the control mode switches from the torque control to the position control.

7. The method of claim 1 , wherein at least one pair of the elastic members is provided in spaces between the motor-side rotation unit and the load-side rotation unit.

8. The method of claim 7 , wherein any one of the pair of elastic members is compressed toward a rotation direction of the motor-side rotation unit.

9. A series elastic actuator (SEA) system, comprising:

a motor-side rotation unit coupled to a driving motor and rotated by rotatory power of the driving motor;

a load-side rotation unit coupled to the motor-side rotation unit to transfer the rotatory power of the driving motor to a load; and

at least one pair of elastic members provided in spaces between the motor-side rotation unit and the load-side rotation unit;

a sensor part configured to measure relative displacement between the motor-side rotation unit and the load-side rotation unit; and

a controller configured to calculate external torque by an external force applied to the load side using the measured displacement and switch a control mode to any one of torque control and position control based on a result of a comparison between the calculated external torque and a critical torque,

wherein the controller is further configured to:

switch the control mode from the position control to the torque control when the external torque increases to a value greater than the critical torque; and

switch the control mode from the torque control to the position control when the external torque decreases to be less than or equal to a value obtained by subtracting given torque from the critical torque.

10. The SEA system of claim 9 , wherein the controller controls a rotation angle of the load side using a rotation angle of the fed-back motor-side when the control mode is the position control.

11. The SEA system of claim 9 , wherein a frame having accommodation spaces to which the pair of elastic members is fixed is formed in any one of the motor-side rotation unit and the load-side rotation unit.

12. A series elastic actuator (SEA) system, comprising:

a motor-side rotation unit coupled to a driving motor and rotated by rotatory power of the driving motor;

a load-side rotation unit coupled to the motor-side rotation unit to transfer the rotatory power of the driving motor to a load; and

at least one pair of elastic members provided in spaces between the motor-side rotation unit and the load-side rotation unit;

a sensor part configured to measure relative displacement between the motor-side rotation unit and the load-side rotation unit; and

a controller configured to calculate external torque by an external force applied to the load side using the measured displacement and switch a control mode to any one of torque control and position control based on a result of a comparison between the calculated external torque and a critical torque,

wherein the controller controls a rotation angle of the load side using a rotation angle of the fed-back motor-side when the control mode is the position control.