Implementing a stand-up sequence using a lower-extremity prosthesis or orthosis
Knee orthoses or prostheses can be used to automatically, when appropriate, initiate a stand-up sequence based on the position of a person's knee with respect to the person's ankle while the person is in a seated position. When the knee is moved to a position that is forward of the ankle, at least one actuator of the orthosis or prosthesis is actuated to help raise the person from the seated position to a standing position.
1 . An active orthotic or prosthetic apparatus for a wearer comprising:
a thigh member;
a lower leg member;
a knee joint for connecting the thigh member to the lower leg member;
a rotary motor comprising a motor shaft output;
a motor drive transmission assembly coupled to the motor shaft output;
a drive transmission assembly coupled to the output of the motor drive transmission assembly, with an output of the drive transmission assembly coupled to the lower leg member for applying torque to the knee joint to rotate the lower leg member with respect to the thigh member;
at least one sensor having at least one output from which a position of the knee joint with respect to an ankle joint can be determined while the wearer of the apparatus is in a seated position; and
a controller configured to:
calculate, by an inertial measurement unit, an upward and forward velocity of a hip joint, the upward and forward velocity measured as a function of a displacement of the hip joint in three-dimensional space,
determine when the knee joint is moved to a position that is forward of the ankle joint based on the least one output of the at least one sensor, and
in response to said determination, controls the rotary motor to help raise the wearer from a seated position to a standing position by increasing a torque of the knee joint, the torque increasing initially to a first relatively small value and configured to be reduced absent positive feedback confirming the user's intent to stand, and increasing gradually to a second relatively large value in accordance with the upward and forward velocity of the hip joint in the presence of the positive feedback.
2 . The apparatus of claim 1 , wherein the at least one sensor comprises an inertial sensor that measures a gravity vector in relation to a thigh coordinate system.
3 . The apparatus of claim 1 , wherein the at least one sensor detects a rotation angle of the lower leg in relation to the thigh.
4 . The apparatus of claim 1 , wherein the controller is programmed to maintain a low joint impedance in response to a determination that the wearer is in the seated position.
5 . The apparatus of claim 1 , wherein the controller controls the rotary motor so that as the wearer approaches the standing state, restorative torque is applied to assist the wearer in achieving balance while in the standing state.
6 . The apparatus of claim 1 , further comprising at least one pressure sensor configured to measure a force being applied to the wearer's foot.
7 . The apparatus of claim 1 , wherein the controller controls the rotary motor to help raise the wearer from the seated position to the standing position by increasing knee torque in accordance with a measured electromyographic signal from at least one of a knee muscle and a hip muscle.
8 . The apparatus of claim 1 , wherein the torque is configured to be reduced exponentially absent the positive feedback.
9 . A method of controlling a knee orthosis or prosthesis having at least one actuator for applying a torque to the knee joint to rotate the lower leg member with respect to the thigh member, the knee orthosis or prosthesis being worn by a wearer, the method comprising the steps of:
detecting the position of the wearer's knee with respect to the wearer's ankle while the person is in a seated position;
determining when the knee is moved to position that is forward of the ankle based on a result of the detecting step, and generating an output indicative thereof;
calculating, by an inertial measurement unit, an upward and forward velocity of a hip joint, the upward and forward velocity measured as a function of a displacement of the hip joint in three-dimensional space; and
actuating, in response to the output, the at least one actuator of the knee orthosis or prosthesis to help raise the wearer from the seated position to a standing position, the torque increasing initially to a first relatively small value and configured to be reduced absent positive feedback confirming the user's intent to stand, and increasing gradually to a second relatively large value in accordance with the upward and forward velocity of the hip joint in the presence of the positive feedback.
10 . The method of claim 9 , further comprising the step of measuring a gravity vector in relation to a thigh coordinate system.
11 . The method of claim 9 , further comprising the step of detecting a rotation angle of the wearer's lower leg in relation to the wearer's thigh.
12 . The method of claim 9 , further comprising the step of maintaining a low joint impedance in response to a determination that the wearer is in the seated position.
13 . The method of claim 9 , further comprising the step of applying restorative torque to assist the wearer in achieving balance while in the standing state.
14 . The method of claim 9 , further comprising the step of measuring a force being applied to the wearer's foot.
15 . The method of claim 9 , further comprising the step of increasing knee torque in accordance with measured electromyographic signals from at least one of a knee muscle and a hip muscle.