US2656546A - Mechanical flexion and extension wrist - Google Patents

Description

Oct. 27, 1953 Q B, ROB|N$0N i 2,656,546

MECHANICAL `FLEXl-.ON AND EXTENSION WRIST Il Filed July 2, 1952 INVENTORz George B Rob/nso Patented Qct. 27, 1953 OFFICE MECHANICAL FLEXIoN AND EXTENSION WRIST George B. Robinson, Napa, Calif.

Application July 2, 1952, Serial No. 296,980

4 Claims. (Cl. 3-12.4)

(Granted under Title 3-5, U. S. `Code (1952),

sec. 266) The invention described herein may be manufactured and used by and for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to prostheses and, more particularly, to a mechanical flexion and extension wrist.

Prior art prostheses attempting simulation of natural hand and wrist movements, have either been unduly complicated or have failed entirely to provide certain functions available in the natural member. An object of this invention is, therefore, to provide an artificial upper extremity of simple construction, which will be capable of ilexion and extension cf the wrist and, in addition, will be applicable to a hand wherein flexion and extension of the wrist automatically provides for simultaneous desired movements of the thumb relative to the palmar portion of the hand.

Other objects and many oi the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l is a plan view of an artificial hand embodying the principles of the invention;

Fig. 2 is a fragmentary view showing the Wrist of the present invention; and

Fig. 3 is a longitudinal cross-sectionl view of an artiiicial arm including the flexion and extension wrist of this invention.

Reference is made -to the drawings wherein the numeral I indicates generally the artificial hand of this invention. The hand includes a rocker I that is pivotally connected to the wrist I2 by means of a pair of spaced parallel arms I4 and I6, corresponding ends of which are xedly mounted in the wrist. Arms I4 and I6 are provided with aligned apertures and rocker I0 is also provided with aligned apertures through respective sets of which, bolts I8 and 20 are passed to constitute axles for pivotally mounting the rocker on the spaced arms. The arm I6 includes an extended offset portion 24 for a purpose to be hereinafter described.

Considering the rocker III in more detail, it is seen to comprise four spaced, sector-like plates 26, and an arcuate mounting plate 28 interconnecting the plates 26. Plates 26 are arranged in pairs, one pair of which flanks and is pivotally connected to arm i4, while the other pair lianks and is pivotally connected to arm I6. Plate 28 is perforated to form a plurality of locking apertures 30 adapted to receive a locking pin 32.

Pin 32 is longitudinally displaceable within a bore formed through wrist I2 and is biased distally into locking position by means of spring 34 bearing against washer-like disc 35 xed to pin 32. The proximal end of pin 32 is provided with an eye 33 for attaching a control cable 38 which cable is connected between the eye 36 and a point 39 on the eccentric plate 40, which point is eccentric to the elbow axis (Fig. 3). The plate 40 is normally iixed relative to the upper arm by means of a set screw 4I engaging the elbow pin which is non-rotatably mounted in the upper arm.

It will be seen that the distance between the point 39 and the wrist I2 is at its minimum when the arm is as shown in Fig. 3, exed at degrees. In the construction shown, the length of the cable 38 plus the pin 32 is made just suicient so that the pin 32 engages the apertures 30. Thus, when the arm is either flexed or extended away from the position shown in Fig. 3, the distance between the wrist and the point 39 increases and, since the cable-pin link is inextensible, it becomes too short to span the entire distance and thus, in elTect, is withdrawn from engagement with the aperture 30 in the rocker I0. The eccentricity of the point 39 and the length of the cable 33 are so related that the pin will be completely withdrawn from its normal locking position when the forearm is either fully extended or fully flexed. This is, of course, a matter of choice, and any other unlocking position can readily be obtained by displacement of the plate 40 through a desired angle.

It will be apparent that the angular position of rocker I0 relative to wrist I2 will be determined by the particular one of the locking apertures 30 in which the pin 32 is seated. It will also be apparent that the pin 32 can be withdrawn from its seated position by means of the cable 38, acting in case of flexion or extension of the forearm, and that the rocker III can then be moved by flipping the hand or by cable action or otherwise, so as to align a different locking aperture 30 with the pin. The exion and extension of the wrist is used to control thumb movement in the manner to be described. In flexion it is desirable that the thumb be swung into opposition with the palmar portion, and in extension it is desirable that the thumb be brought out of opposition to the palmar portion, the hand thus effecting a grasping movement in flexion and a releasing movement in extension. To accomplish this function, the structure in the illustrated embodiment includes a thumb, generally indicated at 32, having a rst phalange 44, attached by means of a rubber shank 46 to a proiection 48 formed integral with the rocker I 0. An intermediate point on the phalange 44 is connected to the end of offset portion 24 by a flexible cable 50, while its distal end is connected to the palmar portion 52 by means of a rubber bridge 54. As previously described, the arm i6 and hence its offset portion 24 are fixed relative to wrist I2, whereas the rocker I0 is angularly displaceable relative thereto. Thus, as the palmar portion 52 moves in the direction of flexion the thumb is swung into opposition with the palmar portion. Similarly, the thumb is swung away from the palmar portion when the palmar portion is moved in the direction of extension. This result is achieved by virtue of the fact that the rubber bridge 54 and the rubber shank 4B act on the thumb in such a way as to keep the cable 59 always in tension and, since the cable 50 is in'- extensible, its point of attachment on the thumb must always remain the same distance from its point of attachment on member I6. Thus, as the base of the thumb moves upwardly or downwardly with the rocker l0, the distal end of the first phalange of the thumb, by twisting the shank, swings in an arc to maintain the points of attachment always equidistant.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as snecically described.

What is claimed is:

l. A prosthesis comprising a wrist member;

a hand; means for pivotally mounting said hand relative to said wrist; means for locating said hand in a plurality of angularly displaced posi tions relative to said wrist, said locating means including a longitudinally displaceable locking pin concentrically positioned to extend through said wrist, and spring means for biasing said pin into engagement with said hand; and means for disengaging said pin from said hand in opposition to said spring means comprising an eccentric plate iixed to the upper arm of the prosthesis, concentric with the axis of the elbow, a tension member connected at its one end to said pin and at its other end to a point of said eccentric plate located eccentrically of the elbow axis, the length of said tension element being so related to the eccentricity of said point that said pin will be disengaged from 'said hand at at least one location when the forearm of said prosthesis rotates from a position of full iiexion to a position of full extension.

2, rihe prosthesis of claim l including means for adjusting about the axis of the elbow the location of said eccentric point of attachment of said tension member thereby varying the place at which disengagement of said pin will Occur.

3. rIhel prosthesis of claim 1 wherein said hand includes a thumb and palmar portion, and means for automatically moving said thumb into opposition with said palmar portion when said hand is iiexed and for moving said thumb out of opposition with said palmar portion when said hand is extended.

4. A prosthesis comprising an upper arm, a forearm articulated to the upper arm, an arti- :ncial hand and wrist combination including means for locking said hand in a plurality of angularly displaced positions relative to said wrist, means responsive to the rotation of the forearm relative to the upper arm for operating said locking means, said rotation responsive means comprising a plate mounted for adjustment about the elbow axis and releasably iixed to the upper arm,- a cable connected between a point on said plate eccentric to the elbow axis and the control element of said locking means, the length of said cable being so related to the eccentricity or the said eccentric point that said locking means passes through at least one unlocked position as said forearm rotates from a position or" full exion to a position of full extension.

GEORGE B. ROBINSON.

References Cited in the ille of this patent UNITED STATES PATENTS Stone Oct. 14, 1947

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