Adjustable stiffness Jack Spring actuator
View Patent ↗The present invention is a mechanical element, commonly referred to as a “Jack Spring” that is based upon the concept of adding and subtracting coils from a spring. In particular, with the method and apparatus of the present invention, by changing the number of coils in a spring, the actual or intrinsic stiffness of the spring is structurally changed. A very simple and practical method is used to adjust the number of coils. The Jack Spring actuator of the present invention is based upon adjusting the effective structure of a spring.
1. An actuator operatively coupled to a kinematic joint, the actuator comprising:
a spring including a plurality of coils;
a guiding element coupled to the spring and configured to divide the coils between active coils and inactive coils, wherein rotation of one of the guiding element and the spring relative to the other increases or decreases an amount of the active coils and causes the spring and guiding element to translate relative to each other;
a motor, the spring and guiding element being coupled between the motor and the kinematic joint, wherein the motor is configured to rotate one of the spring and the guiding element relative to the other and to add energy to or remove energy from the kinematic joint by increasing or decreasing, respectively, energy stored in the active coils of the spring.
2. The apparatus of claim 1 , wherein the spring comprises a curvilinear coiled spring.
3. The apparatus of claim 1 , wherein the guiding element extends within the spring.
4. The apparatus of claim 1 , wherein the guiding element includes a guide surface having a surface spacing that differs as compared to a coil spacing of the spring.
5. The apparatus of claim 1 , wherein the guiding element comprises at least one protuberance extending between the coils of the spring and dividing the spring between active coils and inactive coils.
6. The apparatus of claim 5 , wherein the at least one protuberance comprises a pair of pins.
7. The apparatus of claim 6 , wherein a dimension of the pins matches spacing between coils of the spring.
8. The apparatus of claim 1 , wherein the guiding element is configured to exhibit a duality of self-locking or back-drive behavior with respect to the spring.
9. The apparatus of claim 1 , wherein the spring is configured to store energy under at least one of tension, compression, bending, and shear loads.
10. The apparatus of claim 1 , wherein rotation of one of the spring and the guiding element changes an axial stiffness of the spring.
11. The apparatus of claim 1 , wherein rotation of one of the spring and the guiding element changes a bending stiffness of the spring.
12. The apparatus of claim 1 , wherein the motor is configured to rotate the one of the spring and the guiding element to control a position of the kinematic joint.
13. The apparatus of claim 1 , wherein the motor is configured to rotate the one of the spring and the guiding element to control a force and/or torque of the kinematic joint.
14. The apparatus of claim 1 , wherein the motor is configured to rotate the one of the spring and the guiding element to modulate a stiffness of the kinematic joint.
15. The apparatus of claim 1 , used in a wearable actuated system.