Variable transmission for assistive prosthesis device

An assistive device, comprising:

• an artificial joint;
• an actuation mechanism coupled to the artificial joint and operable to rotate the artificial joint;
• a first motor configured to operate the actuation mechanism;
• and
• a transmission mechanism coupled to the artificial joint, the transmission mechanism including a crank having a variable configuration such that in a first configuration of the crank, in which the crank has a first crank length, the artificial joint is configured to operate at a first torque profile and a first speed profile, and in a second configuration of the crank, in which the crank has a second crank length, the artificial joint is configured to operate at a second torque profile and a second speed profile that are different from the first torque profile and the first speed profile, respectively, wherein the crank comprises a pivot shaft that is movable about and between a first position in which the crank is in the first configuration and a second position when the crank is in the second configuration,
• wherein the transmission mechanism comprises a passively variable element that is connected to the artificial joint and to the actuation mechanism, wherein the passively variable element is variable as the crank moves between the first and second configurations in response to a power input, wherein the passively variable element is configured to store potential energy as a result of varying in response to the power input, and is operable to assist in powering rotation of the artificial joint through release of the stored potential energy,
• wherein the passively variable element extends to the pivot shaft of the transmission mechanism.