Patent Application
20230092812
This application is directed to a knee prosthesis or orthosis, and more specifically, to a knee prosthesis or orthosis that provides highly desirable transmission characteristics.
A typical gait cycle consists of a stance phase, during which the knee must support the weight of the body, and a swing phase, during which the knee allows the foot to swing forward in advance of the next stance phase. In the design of a knee prosthesis or orthosis, it is desirable for the knee joint to provide sufficient torque in the stance phase to support body weight. In swing phase, it is desirable for the knee to swing almost freely, and at much higher speeds than required during the stance phase. The knee should also provide torque in the swing phase, to support suitable knee motion, such appropriate knee flexion for clearance between the foot and ground, full knee extension at the end of swing, and damping to avoid high impact torques at full extension. Further, in the stance phase, it is desirable for the knee to support weight against knee flexion, but to freely allow knee extension, to allow straightening of the knee without the possibility of knee buckling. Further, in the knee extension portion of the swing phase, it is desirable to allow knee extension, while resisting knee flexion, so that the knee will support the user at heel strike immediately upon heel strike or foot strike. The knee must switch between these respective behaviors essentially instantaneously (e.g., within tens of milliseconds).
Recently, powered knee prostheses have emerged. These prostheses typically employ an electric motor that drives the knee joint through a high-gear transmission ratio (e.g., 200:1). With a high-gear transmission ratio, the knee can provide the high torque required for stance phase, but is generally unable to provide low output impedance required for the swing phase of gait. Also, the unidirectional behavior must be achieved via sensing (of torque) and closed-loop control, which is less reliable and functional than mechanical means. It is possible to provide low impedance also with feedback control, but this also requires other sensing (of output torque), and is less reliable and functional than mechanical means. As such, implementing these behaviors via feedback control severely compromises performance, particularly relative to systems that provide these behaviors by design. The net effect is that these systems are unable to effectively provide the behavioral characteristics of unidirectionality, low-impedance, and high-speed, and thus are compromised in all three of the above-stated behaviors.
Some other approaches for knee prostheses with variable transmission ratios have been proposed, but these change ratios slowly, and therefore are unable to make substantial changes in gear ratio within a small fraction of a stride. These systems also do not provide unidirectional characteristics. In the absence of fast changes and unidirectional behaviors in the transmission ratio, these systems are unable to provide the above discussed behaviors within a stride and, therefore, cannot provide the desirable characteristics listed above.
It would be desirable to have a new prosthesis or orthosis that provides a more seamless, smoother, reliable and quicker transition between appropriate dedicated behaviors.
The term embodiment and like terms are intended to refer broadly to all of the subject matter of this disclosure and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the claims below. Embodiments of the present disclosure covered herein are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the disclosure and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter. This summary is also not intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings and each claim.
According to one embodiment, a knee prosthesis or orthosis includes at least one moveable joint and a torque modulating unit. The torque modulating unit is configured to impose a controllable torque on the at least one moveable joint. The torque modulating unit includes at least one of a motor or brake. The at least one of the motor or brake coupled to the at least one moveable joint via an electronically-controlled transmission. The electronically-controlled transmission is a two-speed transmission.
The disclosure, and its advantages and drawings, will be better understood from the following description of exemplary embodiments together with reference to the accompanying drawings. These drawings depict only exemplary embodiments, and are therefore not to be considered as limitations on the scope of the various embodiments or claims.
While the invention is susceptible to various modifications and alternative forms, specific implementations have been shown by way of example in the drawings and will be described in further detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
According to one embodiment, a knee prosthesis or orthosis includes at least one moveable joint and a torque modulating unit. The torque modulating unit being configured to impose a controllable torque on the at least one moveable joint. The torque modulating unit includes at least one of a motor or brake. The at least one of the motor or brake being coupled to the at least one moveable joint via an electronically-controlled transmission. The electronically-controlled transmission being a two-speed transmission.
The knee prosthesis or orthosis of the present invention is advantageous in that it yields a knee joint that specifically provides: (1) high-torque, low-speed unidirectional extension torque, with little to no flexion torque (which is appropriate for the stance phase of the gait cycle); (2) low-torque, high-speed, low-impedance, bidirectional knee behavior (which is appropriate for the swing flexion phase of walking); and (3) low-torque, high-speed, low-impedance, unidirectional knee behavior in knee extension, with a simultaneous high resistance to knee flexion (which is appropriate for the swing extension phase of walking). The gear transmission ratios between the states are different by more than an order of magnitude, and the transmission is configured to change between these states under load on the order of less than 20 milliseconds, and desirably less than 15 or 10 milliseconds.
One non-limiting example of a knee prosthesis or orthosis that may be used is depicted in
The torque modulating unit 14 is configured to impose a controllable torque on the at least moveable joint 12. The knee prosthesis or orthosis 10 of
To provide a high-torque, low-speed, high-impedance behavior characteristic and also to separately provide a low-torque, high-speed, low-impedance behavior characteristic representative of knee behavior in stance and swing, respectively, the ECT used in the present invention is a two-speed transmission. Unlike common multi-speed transmissions, however, the two speeds in the ECT are spaced at least about an order of magnitude apart. For purposes of comparison, a standard automotive transmission typically changes gear ratios by a factor of 1.3 between adjacent gears. The gear transmission ratios used in the ECT of the present invention, however, should be at least about an order of magnitude different in ratio, in order to satisfy the torque, speed, and impedance differences associated with the stance and swing phases of gait. For example, in an embodiment, the gear transmission ratios in low gear and high gear should be at least a factor of 8 or at least a factor of 10 apart. In another embodiment, the transmission gear ratios should be different by a factor of 15. In a further embodiment, the transmission gear ratios should be different by a factor of 20.
In the embodiment described here, the two-speed transmission is based on a planetary gear transmission. The planetary gear transmission includes at least two transmission stages—an input planetary stage and an output planetary stage. In one embodiment, the input planetary stage includes at least an input sun gear, an input carrier link, and the output planetary stage includes an output carrier link. In this embodiment, the stages share a common ring gear (i.e., all stages share the same ring gear). Common ring gear means that the ring gears associated with each stage are rigidly coupled together.
In a typically embodiment, a sun gear, a carrier link, and at least three or more planet gears are used in each planetary stage (e.g., an input planetary stage and an output planetary stage). In this embodiment, each of the stages includes a common ring gear.
The two-speed transmission includes at least a ring clutch and a carrier clutch in one embodiment. The ring clutch and the carrier clutch are solenoid-actuated clutches in one embodiment. Both of the ring and the carrier clutches are configured independently to be either in an engaged state or a disengaged state. In the disengaged state, the ring clutch in one embodiment allows the common ring gear to rotate relative to ground. The term “ground” as used herein includes grounding to a frame, grounding to housing, or the like. In the engaged state, the ring clutch in one embodiment prevents or inhibits the common gear from rotating relative to ground. In the disengaged state, the carrier clutch in one embodiment allows the input carrier link to rotate relative to ground. In the engaged state, the carrier clutch in one embodiment prevents or inhibits the input carrier link from rotating relative to ground.
Referring to
The schematic 50 of
Both of the schematics 50, 70 of the planetary gear transmission includes a common ring gear 52, an input planet gear 56, an output planet gear 58, an input sun gear 60, and an output sun gear 62. The input planet gear 56 is connected to the output sun gear 62 via an input carrier link 64. The output planet gear 58 is connected to an output carrier link 68. The input is the input sun gear 62 and the output is the last carrier link (carrier link 68 in schematics 50, 70).
In this embodiment, the input carrier link 64 can be grounded via a carrier clutch. In this embodiment, the carrier clutch is an electromagnetic clutch. In this embodiment, the common ring gear 52 is separately grounded by a ring clutch. The ring clutch in this embodiment is a unidirectional electromagnetic clutch. The carrier and ring clutches can be engaged or disengaged in various combinations to provide: (1) a high-gear transmission ratio appropriate for stance phase; (2) a low-gear transmission ratio appropriate for swing phase; and (3) a combination thereof that enables a low-gear transmission ratio against extension and high-impedance against flexion.
In the high gear (i.e., high-gear transmission ratio) of
In addition to a two-stage planetary gear transmission such as discussed above with respect to
Both of the schematics 150, 170 of the planetary gear transmission includes an input common ring gear 152, the input planet gear 56, a second stage planet gear 156, the output planet gear 58, the input sun gear 60, a second stage sun gear 160, and the output sun gear 62. The input planet gear 56 is connected to the second stage sun gear 160 via an input carrier link 164. The second stage planet gear 156 is connected to the output sun gear 62 via an input carrier link 166. The output planet gear 58 is connected to an output carrier link 168.
In the high gear (i.e., high-gear transmission ratio) of
This general transmission configuration is configured to function for a planetary gear transmission with any number of stages provided that the ring gear of each stage is a common ring gear.
There are two defined gear transmission ratios (high-gear ratio and low-gear ratios.). In this embodiment there are two clutches (ring clutch and carrier clutch) on the transmission. In this embodiment, each of the ring and carrier clutches includes two states. The two states in the ring and carrier clutches are energized and de-energized. Because of the two gear transmission ratios and the two states, there are four possible states of transmission.
The sequence of clutch states that would be employed in a knee prosthesis or orthosis during walking are shown, for example, in
In each state, the configuration of the ring and carrier clutches produces one of four behaviors in each the flexion and extension directions: a low-gear transmission ratio (low), a high-gear transmission ratio (high), over-determined locking (lock), and under-determined motion between input and output (slip or not engaged). Each state of the transmission is described in more detail below.
In the first state 210, the ring clutch and the carrier clutch are both de-energized. The common ring gear in the first state 210 is grounded (only in one direction). The transmission is in its high gear against flexion. The high-gear transmission ratio is configured to support a weight of the prosthesis or orthosis of a user when standing on the knee prosthesis or orthosis. Because the ring clutch can only engage the transmission unidirectionally, the transmission slips against extension (i.e., does not resist extension movement). The unidirectional behavior of the transmission is configured to generate torque against knee flexion. The torque modulating unit is in the first state 210 when the prosthesis or orthosis user is standing on the prosthesis or orthosis (stance), providing support against flexion of the knee.
In the second state 220, the ring clutch is energized and the carrier clutch is de-energized. The transmission assumes its underdetermined state. Energizing the ring clutch unlocks the ring gear. With the ring gear unlocked, the transmission has an extra rotational degree of freedom, decoupling the output from the input. The motor can no longer provide torque at the knee joint. The torque modulating unit is only in the second state 220 for a few milliseconds before entering the third state 230. This is part of the transition from stance to swing, when the gear transmission ratio changes from high to low. The purpose of entering the second state 220 before entering the third state 230 is to avoid locking the transmission while it is moving, which has the potential to damage the transmission.
In the third state 230, the ring clutch and the carrier clutch are both energized. The ring gear is unlocked and free to rotate, and the first stage or input carrier link is locked to the housing, preventing or inhibiting its rotation. In this configuration, the transmission is in its low gear. The low-gear transmission ratio enables the prosthesis or orthosis to allow a knee joint to swing freely when the knee prosthesis or orthosis is not supporting the weight of the user. Because the carrier clutch provides bi-directional locking in this embodiment, the motor can provide torques in both directions at the knee. The torque modulating unit remains in the third state 230 until the prosthesis or orthosis has completed swing flexion and enters swing extension.
In the fourth state 240, the carrier clutch is energized and the ring clutch is de-energized. When the knee joint of the prosthesis or orthosis begins to extend while in swing phase, it is no longer necessary to energize the ring clutch. Because the ring clutch only provides unidirectional locking against flexion in this embodiment, and cannot resist extension, the ring clutch does not need to be energized during swing extension. The transmission is still in its low gear. If the prosthesis or orthosis is suddenly subject to a flexion load (e.g., if the prosthesis or orthosis user trips on something), then the prosthesis or orthosis automatically enters the high gear and is able to resist flexion. This mechanical fail-safe removes the lag-time from the controller that would otherwise have to switch the torque modulating unit into the high gear.
The low-gear transmission ratio is configured to have asymmetric behavior in which the two-speed transmission is configured to resist extension with a low resistance while resisting flexion with a high resistance.
In one embodiment, the two-speed transmission is configured to be in at least a first state, a second state or a third state. The two-speed transmission in the first state provides the high-gear transmission ratio when resisting flexion or providing extension, while providing little to no torque when resisting extension or providing flexion. The two-speed transmission in the second state provides the low-gear transmission ratio. The low-gear transmission ratio is bidirectional. The two-speed transmission in the third state provides the low-gear transmission ratio when resisting extension or providing flexion, while also providing a high resistance when resisting flexion or providing extension.
In another embodiment, the two-speed transmission is further configured for a fourth state. The two-speed transmission in the fourth state provides the high-gear transmission ratio. The high-gear transmission ratio is bidirectional.
In a further embodiment, the two-speed transmission is configured to be in at least a neutral state, in which the two-speed transmission is disengaged from at least one of the motor or brake.
Referring to
The motor or brake 302 is coupled to at least one moveable joint (e.g., the at least one moveable join 12 in
The torque modulating unit 300 is configured as an electromagnetic disk clutch. Thus, in this embodiment, the carrier clutch armature 342 is a ferromagnetic disk clutch armature. The carrier clutch armature 342 is collinearly fixed to the first stage carrier 312 of the planetary gear transmission 310. It is contemplated that the carrier clutch armature may be formed from materials other than ferromagnetic material.
The carrier clutch stator 346 is collinearly fixed to the electric motor/brake 302. The electric motor/brake 302 and the carrier clutch stator 346 are fixed to the housing. The planetary gear transmission 310 is supported by a pair of thin-section bearings so that it is able to freely rotate (when not constrained by the ring clutch or grounded). The wave disk spring 306 separates the carrier clutch armature 342 and the carrier clutch solenoid stator 346 when the torque modulating unit 300 is de-energized. The O-ring 336 is fixed to the carrier solenoid stator 346 and becomes compressed by the carrier clutch armature 342 when the carrier clutch 300 is energized. The plain bearing 308 encircles the carrier clutch armature 342 and the O-ring 336. The O-ring 336 in one embodiment is a medium durometer square-cross section O-ring.
When the clutch is de-energized, rotation and lateral translation of the carrier clutch armature 342 are constrained by the wave spring 306 and the plain bearing 308, respectively. When the ring clutch solenoid 334 is de-energized (i.e., in the OFF state), the spring element keeps the carrier clutch solenoid stator 346 and the carrier clutch armature 342 separated, and the O-ring 336 is not engaging the carrier clutch armature 342. When the ring clutch solenoid 334 is energized (i.e., in the ON state), the carrier clutch armature 342 is pulled to the carrier clutch solenoid stator 346 and is engaged by the O-ring 336, creating a high-friction interface between the stator 346 and the armature 342, locking the armature 342 to the stator 346, and preventing or inhibiting rotation of the armature 342. This prevents or inhibits rotation of the first stage carrier link and the second stage sun gear.
The ring and the carrier clutches desirably use friction-based locking that permits locking in any configuration. The ring and the carrier clutches desirably use solenoid-actuation permits state changes within several milliseconds, and therefore within a single stride of the gait cycle.
In one embodiment, the ring clutch is a unidirectional clutch. In the engaged state, the ring clutch allows unidirectional rotation of the common ring gear relative to ground. The unidirectional ring clutch is a capstan clutch in one embodiment.
In another embodiment, the ring clutch is selectively unidirectional or bidirectional. The ring clutch in this embodiment includes a first ring clutch and a second ring clutch. The engagement of the first and second ring clutches prevents or inhibits rotation of the common ring gear in both directions, and the selective disengagement of one of the first and second ring clutches allows unidirectional rotation of the common ring gear relative to ground in one of two directions. The selective disengagement of both the first and second ring clutches allows bidirectional rotation of the common ring gear relative to ground.
In a further embodiment, the ring clutch is a bidirectional clutch, such that in the engaged state, the ring clutch prevents or inhibits rotation of the common ring gear relative to ground in both directions.
Referring to
The design of the ring clutch 400 is beneficial in that it: (1) enables high holding torque with a low activation force, due to the exponential self-amplification property of a capstan; and (2) provides a unidirectional holding torque, which accommodates the previously described asymmetrical resistance desirable in the stance phase and late swing phase (i.e., low-impedance resistance to extension and high-impedance resistance to flexion).
The ring clutch of
The sleeve 410 is typically an aluminum sleeve. It is contemplated that the sleeve may be made of other materials, including other metallic materials. The sleeve 410 is pressed onto the common ring gear 412. The ring gear may be a ECT common ring gear. The wire rope 414 is wrapped a plurality of times around an exterior of the sleeve 410 as shown in
The spring element 420 applies tension to one end of the wire rope 414, while the other end of the spring element 420 is grounded to the housing by the adjustable anchor point 422. The adjustable anchor point 422 is adjustable via a set screw thereon that permits adjustment of the preload tension on the spring element 420. The distal ends of the spring element 420 and wire rope 414 are fixed to the solenoid armature 428. The solenoid armature 428 is located or positioned within the solenoid stator 432.
When the common ring gear 412 and the sleeve 410 are turned away from the end of the wire rope 414 that is secured to the adjustable anchor point 422, the force applied by the spring element 420 is multiplied by the capstan effect, producing a much larger holding force in the wire rope 414 secured to the anchor points. The effect is a strong holding torque that resists the motion of the rotating torque, effectively grounding the common ring gear. When a rotating torque is applied in the opposite direction (towards the ends of the wire rope 414 that is secured to the anchor point), the spring element 420 does not apply enough force to create a strong holding torque, and the drum rotates in the direction of the applied torque. This makes the ring clutch 400 a unidirectional clutch (i.e., the engagement that it provides is directionally dependent). The effect this has is similar to an overrunning clutch, where the rotating shaft inside the clutch is free to spin in one direction, but is locked in the opposite direction.
When the solenoid is de-energized (i.e., in the OFF state), the spring element 420 keeps the wire rope 414 engaged with the sleeve 410, and the common ring gear 412 can only be turned in one direction due to the capstan effect. When the solenoid is energized (i.e., in the ON state), the solenoid compresses the spring element 420, which negates the tensile force on the wire rope 414. The wire rope 414 is naturally stiff, and becomes straighter as force from the spring element 420 is removed. This causes the wire rope 414 to move away from the surface of the sleeve 410. With the wire rope 414 is no longer in contact with the drum, the clutch is disengaged, and the common ring gear 412 is free to rotate in both directions.
When the ring clutch solenoid is de-energized, the ring clutch is engaged. When the ring clutch solenoid is energized, the ring clutch is dis-engaged. When the carrier clutch solenoid is energized, the carrier clutch is engaged. When the carrier clutch is de-energized, the carrier clutch is disengaged.
It is contemplated that other ring clutches may be used than the ring clutch shown in
The ring clutch 500 of
The flexion ring clutch and solenoid provides a grounding force for the common ring gear when a resistive knee flexion torque is applied, but permits knee extension with little or no resistance. The extension ring clutch and solenoid provides a grounding force for the common ring gear when a resistive knee extension torque is applied, but permits knee flexion with little or no resistance. The ends of each capstan for both clutches are grounded.
Referring to
The foregoing description of the embodiments, including illustrated embodiments, has been presented only for the purpose of illustration and description and is not intended to be exhaustive or limiting to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art.
Although the disclosed embodiments have been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur or be known to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein, without departing from the spirit or scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents.
This application claims priority to and the benefits of U.S. Provisional Patent Application No. 62/980,861 filed Feb. 24, 2020, the contents of which is hereby incorporated by reference herein in its entirety.
This invention was made with government support under Grant No. 2018260077 awarded by the National Science Foundation. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/019079 | 2/22/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62980861 | Feb 2020 | US |
