US3548419A - Electrically driven prosthetic elbow - Google Patents

Description

Dec. 22, 1970 R. KATSUREN ELEQTRICALLY DRIVEN PROSTHETIC ELBOW Filed Dec. 10, 1968 INVENTOR ROY I. K ATSUREN ATTORNEY United States Patent O US. Cl. 3-1.1 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved electrically driven prosthetic elbow wherein the elbow is capable of being rigidly locked into place in any desired position, and upon driving the arm to the fully extended position, the elbow is automatically unlocked.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION The use of external power in human upper extremity prosthesis is rapidly becoming more important for the rehabilitation of the severely handicapped. Electrically powered prosthetic elbows that have been developed to date are generally self-locking in all functional positions which is not the most advantageous design since the amputee in certain situations can experience discomfort, inconvenience and embarassment due to the inability to unlock the elbow. For example, in the simple act of sitting at a table, a locked prosthetic arm in the fully extended position will contact the chair before the amputee. In order to avoid this awkward movement, the amputee must either swing his arm at the shoulder and let the arm hang over the side of the chair, or he must drive the elbow to a convenient flexed position. The choice of letting the arm hang over the side of the chair presents an unnatural position for the amputee and is thus undesirable. With the elbow flexed, however, the amputee must keep in mind that he cannot leave the table by standing directly, but must first be sure that his artificial arm will miss the table. Besides the inconvenience of having to keep these thoughts in mind, the fact that the amputee would probably stand with his prosthetic arm in an uncosmetic flexed position presents another undesirable alternative. The present invention is designed to overcome these prior art inconveniences by allowing the amputee to manipulate his artificial limb in a lifelike manner with the ability to lock his artificial limb into any desired position.

SUMMARY OF THE INVENTION The present invention directs itself to an electrically powered prosthetic elbow which is designed to overcome the disadvantages of existing electrically driven prosthetic mechanical elbows in that the present elbow provides for a simple locking means which will lock in any desired position and which automatically unlocks when the arm is placed in the fully extended position. This unlocking feature permits the amputee to simulate normal movement of his prosthesis and thus overcome the major disadvantage of existing prior art prosthetic elbows,

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cut-away side view of the mechanical elbow depicting the locking mechanism in the locked position.

FIG. 2 is an isometric view of the mechanical elbow in the unlocked position.

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DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularly to the drawings, in

FIGS. 1 and 2, a reversible direct current motor 1 is connected to speed reducer 3 through connector 2. The motor 1 drives the speed reducer 3 which in turn drives worm 5 through a coupling 4. The worm 5 is covered by the worm cage 6. The motor 1, connector 2, speed reducer 3, coupling 4, worm 5 and worm cage 6 are all located in a cavity in the stump attachment of the prosthetic arm located above the elbow. The worm 5 drives gear 7, the combination being self-locking if exterior forces tend to drive the system. Gear hub 8 and its assembly (limiting ring 13, locking lever 10, bracket 17 and bar 11) and shaft 9, which is mounted in the elbow cavity, rotate independently of each other about axis II except when locking lever 10 rests within cavity 26 and bar 11 is in its locking position (FIG. 1). Plate 27 is affixed to gear hub 8 and prevents bar 11 from moving below its locking position. Unlocking stud 12 is capable of rotating bar 11 about fastening pin 24. Locking lever 10 is also capable of rotating about fastening pin 28. Spring 16 is aflixed to fastening pin 24. One end of spring 16 is afiixed to pin 18 which is rigidly affixed to bracket 17. The other end of spring 16 is affixed to pin 19 which is rigidly afiixed to bar 11. Limit switch actuators 14 and 22 are designed to actuate switches 15 and 23 when limit lobes 20 and 21 respectively of limiting ring 13 come into contact with the switch actuators.

In the preferred embodiment of the invention, a prosthetic hand and forearm are attached to the elbow such that the vertical motion of the hand and forearm corresponds to the clockwise and counterclockwise rotation of shaft 9 about axis II. A cavity 26 for receiving locking lever 10 exists within shaft 9 as does a cavity opening 25 exist within gear hub 8. In the unlocked position, FIG. .2, shaft 9 is capable ofv rotation about center axis II independent of gear hub assembly 8, 10, 11, 13 and 17. Limiting ring 13, bracket 17 and gear hub 8 are affixed so that they jointly rotate about axis II when driven by power train 1, 2, 3, 4, 5, 6 and 7. Support pins 18 and 19 and fastening pin 24 form the spring holding assembly for spring 16. Locking lever 10 and bar 11 are rotatably attached to limiting ring 13 by fastening pins 28 and 24 respectively as shown in FIGS. 1 and 2.

In normal operation, the patient starts with the elbow fully extended with the artificial arm hanging by his side. FIG. 2 represents the physical relationships of cavity 26, bar 11, locking lever 10, limiting ring 13 and unlocking stud 12 at this fully extended free swing position. In this position limiting lobe 20 of limiting ring 13 has contacted limit switch actuator 14 which in turn actuated limit switch 15. Limit switch 15 stopped motor 1 thus ending any further rotation about axis II in a counterclockwise direction of limiting ring 13, locking lever 10, bar 11, gear hub 8- and shaft 9. At this position, bar 11 has been forced to rotate in a clockwise manner about fastening pin 24 as a direct result of the force applied by unlocking stud 12 to the end of bar 11. The resultant force, applied by unlocking stud 12 to the end of bar 11, is sufficient to overcome the counterclockwise torque about fastening pin 24 applied to bar 11 by spring 16. The result is the unlocking of locking lever 10. With bar 11 rotated out of its locking position, locking lever 10 is free to rotate about locking pin 28 and out of cavity 26. Gear hub 8, worm gear 7, limiting ring 13, locking lever 10 and bar 11 depend upon the activation of motor 1 for their rotation about axis II. However, shaft 9, whose rotation about axis II is representative of the movement of the artificial forearm and hand, is not dependent upon motor 1 for movement when bar 11 is 3 forced out of its locking position as depicted in FIG. 2. In this unlocked position, the patient is able to place his artificial arm into any desired position, and upon driving the gear hub 8 and its assembly into a locking position, lock the elbow at that new position.

As the patient begins to place his arm from its fully extended position into a desired position, shaft 9 begins to rotate clockwise about axis II. In so doing, the walls of cavity 26 force locking lever 10 to rotate counterclockwise about fastening pin 28. Since bar 11 has been forced to rotate out of its locking position, locking lever 10 is capable of counterclockwise movement about fastening pin 28. When the patient has his artificial arm in the desired position, shaft 9 has been rotated clockwise about axis II and thus cavity 26 has also been rotated and is no longer in aligment to receive locking lever 10. To lock the elbow into the new position, the patient actuates motor 1 to cause worm gear 7, gear hub 8 with its cavity opening 25, limiting ring 13, locking lever 10 and bar 11 to rotate clockwise about axis II. As the assembly rotates clockwise about axis II, bar 11 is no longer brought into contact with unlocking stud 12. As a result, the overbalancing force applied by unlocking stud 12 to bar 11 is removed and the tension of spring 16 forces bar 11 to rotate counterclockwise about fastening pin 24. In this position, bar 11 applies a force to locking lever 10 causing locking lever 10 to rotate clockwise about fastening pin 28. The blunt end of locking lever 10 is thus forced through gear hub cavity opening 25 and is pressed against shaft 9 as locking lever 10 and the rest of the gear hub assembly rotate about axis II seeking to bring locking lever 10 and gear hub cavity opening 25 into alignment with relocated cavity 26. The patient continues to actuate motor 1 causing the rotation of the gear hub assembly until locking lever 10 locks into place within cavity 26. At this moment, the patient stops the motor and the elbow is now locked into place. In this position, gear hub cavity opening 25 has aligned itself with cavity 26, the blunt end of locking lever 10 is no longer sliding along the circumference of shaft 9 but rather has been fitted into cavity 26 by the force applied to it by bar 11, and bar 11 has rotated counterclockwise about fastening pin 24 and has come to rest at its locking position. Plate 27 prevents rotation of bar 11 about fastening pin 24 beyond the desired locking position. In this locked position, with the motor off, counterclockwise rotation of shaft 9 and thus upward rotation of the artificial arm about the elbow is prevented due to the inability of shaft 9 to rotate independently of the gear hub assembly when locking lever 10 rests within cavity 26. Clockwise rotation of shaft 9 and thus downward rotation of the artificial arm about the elbow is prevented due to the inability of locking lever 10 to be rotated out of cavity 26 when bar 11 is in the locked position. In both of these cases, power train 1, 2, 3, 4, 5, 6 and 7 provides the locking effect as it is directly coupled to the elbow mechanism, and in the deenergized state, the power train provides great frictional resistance to any external attempts at moving the system. In the locked position, the movement of shaft 9 and thus the positioning of the artificial arm is directly controlled by motor 1. The patient can either raise or lower his arm depending upon how he operates motor 1. Limits, however, are imposed upon this movement by the interaction of limiting ring 13 with its lobes 20 and 21, limit switch actuators 14 and 22 and limit switches 15 and 23. One limit of movement is being approached in FIG, 1. FIG. 1 represents the approaching of the fully extended arm position. As the limit is reached, lobe of limiting ring 13 comes into contact with switch actuator 14 which in turn activates switch 15. Switch 15 in turn causes motor 1 to shut off. The other extreme limit of movement for the elbow is the position represented by the bending of the elbow to bring the artificial arm and hand up towards the shoulder. In this position lobe 21 of limiting ring 13 comes into contact with switch actuator 22 causing switch actuator 22 to actuate switch 23. Switch 23 will also cause motor 1 to shut off. Diodes are placed across switches 23 and 15 to permit current to flow in a reverse direction thus enabling the patient to mechanically drive the elbow in an opposite direction after one of the extreme positions has been reached.

I claim:

1. An electrically driven prosthetic elbow comprising:

(a) an inner rotatable shaft representative of the rotational movement of a prosthetic elbow;

(b) an electrically driven gear hub, said gear hub being independently rotatable about said inner shaft;

(0) locking means capable of securing said inner shaft to said gear hub;

((1) switching means capable of controlling the limits of angular movement of said gear hub; and

(e) means for automatically unlocking said gear hub from said inner shaft at one of the limit positions of said gear hub.

2. An electrically driven prosthetic elbow as described in claim 1 wherein:

(a) said inner shaft contains a cavity;

(b) said gear hub contains an opening capable of alignment with the cavity of said inner shaft;

(c) a limiting ring is attached to said gear hub;

(a) a first pin is attached to said limiting ring;

(e) a locking lever is rotatably attached to said first pin and aligned so as to be capable of insertion through said gear hub opening into said inner shaft cavity;

(f) a second pin is attached to said limiting ring;

(g) a bar is rotatably attached to said second pin and in relationship with said locking lever so as to have a common surface with said locking lever; and

(h) a spring is carried by said second pin and in relationship with said bar so as to cause said bar to place a constant force upon the common surface with said locking lever.

3. An electrically driven prosthetic elbow as described in claim 2 wherein the switching means comprises:

(a) limit lobes attached to said limiting ring, said limit lobes being offset from each other; and

(b) a limit switch in alignment with each of said offset limit lobes, said switches capable when actuated of cutting out an electrical power source.

4. An electrically driven prosthetic elbow as described in claim 3 wherein the unlocking means consists of an unlocking stud aligned with said bar so as to force said bar to rotate out of contact with said locking lever when said limiting ring approaches one of its limits.

References Cited On the Use of Electricity in Upper Extremity Prostheses, by Colin A. McLaurin, The Journal of Bone and Joint Surgery, vol. 47B, No. 3, August 1965, pp. 448452.

RICHARD A. GAUDET, Primary Examiner R. L. FRINKS, Assistant Examiner s. 01. X.R. 3-12.3; 28714, 99; 74 527

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