Biomedical finger assembly with ratcheting lock
This disclosure provides systems, apparatuses, and devices for a prosthetic digit usable with persons with amputations at or proximal to the metacarpophalangeal joint. The device restores prehension in a person with missing fingers or thumb by providing opposition to forces in the extension direction via a spring-loaded pawl and locking rack ratchet mechanism, thereby allowing an individual to manipulate or stabilize objects. The digit may be spring-loaded in the extension direction by a torsion spring or other biasing member. The pawl may be automatically disengaged from the rack when the digit reaches full flexion, and the full flexion disengage stop may be adjustable. The pawl may be automatically engaged with the rack when the digit reaches full extension, and the extension stop may be adjustable. The pawl may contain a lateral feature that creates interference with the anchoring linkage under load and limits deflection of the structure.
1 . A prosthetic digit, comprising:
a first linkage coupled to a base, wherein the first linkage comprises a plurality of rack teeth;
a second linkage coupled to the base in an overlapping arrangement with the first linkage, wherein the first linkage and second linkage are each configured to pivot with respect to the base during flexion and/or extension of the prosthetic digit; and
a pawl operably coupled to the second linkage, wherein the pawl is movable between—
a first engaged position in which a distal nose of the pawl abuts a first one of the plurality of rack teeth,
a second engaged position in which a distal nose of the pawl abuts a second one of the plurality of rack teeth different from the first one of the plurality of rack teeth, and
a disengaged position in which the distal nose is spaced away from and does not contact the rack teeth during flexion and/or extension of the prosthetic digit.
2 . The prosthetic digit of claim 1 , further comprising
a third linkage pivotably coupled to a distal end of the first linkage, wherein the third linkage comprise a stop surface, and
wherein the pawl is configured to abut the stop surface to return the pawl to the first engaged position.
3 . The prosthetic digit of claim 1 , further comprising a pawl dog, and wherein, when the pawl is in the first engaged position, the pawl dog extends from the distal nose of the pawl to engage a side of the first linkage.
4 . The prosthetic digit of claim 3 wherein the pawl dog is configured to contact the first linkage during loaded articulation of the prosthetic digit.
5 . The prosthetic digit of claim 1 , further comprising:
a third linkage pivotably coupled to the base and a proximal end of the first linkage; and
a fourth linkage pivotably coupled to the base and a proximal end of the second linkage.
6 . The prosthetic digit of claim 5 wherein pivotable movement of the first elongate linkage in a first direction with respect to the base causes pivotable movement of the third elongate linkage in a second, opposite direction.
7 . The prosthetic digit of claim 1 wherein the first linkage and second linkage are pivotably coupled to the base.
8 . The prosthetic digit of claim 1 , further comprising an anchor configured to be affixed to or embedded in a socket of a user's hand, and wherein the base is fixedly coupled to the anchor.
9 . The prosthetic digit of claim 1 , further comprising a biasing member positioned to rotationally urge a distal end of one of the first and second linkages toward a distal end of the other of the first and second linkages.
10 . The prosthetic digit of claim 9 wherein the biasing member is positioned to urge the prosthetic digit toward an extended position, abutting the distal nose against the first one of the plurality of the rack teeth in the first engaged position of the pawl.
11 . The prosthetic digit of claim 10 , further comprising an adjustable flexion member carried by the first linkage, wherein the adjustable flexion member is positioned to rotate the pawl to the disengaged position when the prosthetic digit reaches a set maximum flexion position.
12 . The prosthetic digit of claim 1 , further comprising an adjustable extension member configured to abut a surface to limit the rotation of the prosthetic digit at a maximum extension position.
13 . The prosthetic digit of claim 1 , further comprising a detent member configured to contact one of (a) a concave disengaged surface on the pawl to retain the pawl in the disengaged position and (b) a convex engaged surface on the pawl to retain the pawl in the first engaged position.
14 . The prosthetic digit of claim 1 , further comprising a fairing coupled to and covering at least a portion of the first linkage and the second linkage.