Apparatus utilizing planetary gearset coupled to a constant torsion spring

1. An apparatus comprising:

a. a planetary gearset, the gearset including:

i. a sun gear;

ii. a rotatable ring gear;

iii. planet gears operatively supported together by a carrier and interposed between the sun gear and ring gear,

iv. an input shaft connected to the sun gear; and

v. an output shaft connected to the carrier;

b. an idler gear rotatably engaged with the ring gear;

c. a rotatable spring shaft having a first end and a second end;

d. a spring shaft gear mounted on the spring shaft at the first end and rotatably engaged with the idler gear;

e. a first spool mounted on the spring shaft at the second end;

f. a rotatable parallel shaft to the spring shaft, the rotatable parallel shaft having a second spool mounted thereon; and

g. a metal band wrapped about the first and second spools, the metal band having a rotational range of movement between the first and second spools, whereby winding the metal band on one of the spools stores spring energy; wherein the metal band imparts an approximately constant torque to the spring shaft and, via the spring shaft gear and the idler gear, the ring gear through the rotational range of movement of the metal band between the two spools; and wherein the ring gear winds the metal band about the first spool when the torque level at the output shaft exceeds a threshold.

2. The apparatus of claim 1 , further comprising:

a. a first brake connected to the spring shaft, the first brake selectively engagable after the metal band has been wound on the first spool, and being power-on engaged; and

b. a drive brake connected to the input shaft, the drive brake being power-off engaged,

c. wherein when power is turned off, the drive brake engages to stop rotation of the input shaft and the first brake turns off allowing the wound metal band to move from the first spool to the second spool thereby rotating the spring shaft, which in turn rotates the spring shaft gear, idler gear, and the ring gear, whereby the output shaft is moved to a home position.

3. The apparatus of claim 1 , wherein the rotatable ring gear includes outer teeth that cooperatively engage with teeth located on a circumference of the idler gear and the idler gear teeth engage with teeth located on a circumference of the spring shaft gear.

4. The apparatus of claim 1 , wherein the metal band comprises a constant torsion spring.

5. An apparatus for selectively limiting output shaft torque or returning the output shaft to a home position, comprising:

a planetary gearset comprising a sun gear, planet gears, and a rotatable ring gear;

an input shaft coupled to the sun gear of the planetary gearset;

an output shaft coupled to the planet gears of the planetary gearset via a carrier; and

a constant torsion spring coupled to the ring gear of the planetary gearset; and

wherein the apparatus selectively:

a) in a first mode prevents the ring gear from moving when a torque at the output shaft is below a threshold, the ring gear winding the constant torsion spring in response to the torque exceeding the threshold, or

b) in a second mode winds the constant torsion spring, via the ring gear, using a first brake and a second brake coupled to the ring gear and the input shaft, respectively, during an initiation phase and the first and second brakes arranged and configured in a power loss to return the output shaft to the home position as the constant torsion spring unwinds.

6. The apparatus of claim 5 , wherein during the first mode, in response to the torque falling below the threshold after the winding of the constant torsion spring, the constant torsion spring unwinds and restores a positional relation between the input shaft and the output shaft.

7. The apparatus of claim 6 , wherein the constant torsion spring comprises a first spool coupled to rotate with the ring gear and a second spool that freely rotates, the first and second spools being coupled by a metal band that coils around one or both of the first and second spools.

8. The apparatus of claim 5 , wherein during the second mode:

the first brake, being coupled to the ring gear and the constant torsion spring, is arranged and configured to engage following the initiation phase and disengage in response to a loss of power; and

the second brake, being coupled to the input shaft, is arranged and configured to engage in response to the loss of power, the engagement of the second brake and disengagement of the first brake causing the constant torsion spring to drive the output shaft to the home position, wherein the engagement of the second brake prevents back-driving of the input shaft by the constant torsion spring.