US3820168A - System for operating a prosthetic limb - Google Patents

Abstract

A SERVOMOTOR FOR MOVING A PROSTHETIC LIMB IS ACTUATED BY A CONTROLLER WHICH RESPONDS TO LOCAL VARIATIONS IN MUSCULAR RIGIDITY AS DETERMINED BY ONE OR MORE PRESSURE SENSORS BEARING UPON THE FLESH OF THE WEARER WITHIN AN ANNUAL FRAME CONTACTING AN AREA OF HIS BODY. THE FRAME MAY BE RESILIENTLY SUPPORTED IN A CUTOUT OF A RIGID SLEEVE BY ONE OR MORE SPRINGS URGING IT INTO CONTACT WITH AN UNDERLYING STUMP. THE CONTACTS OF THE SENSOR FORM PART OF AN ELECTROMAGNETIC VIBRATOR WHOSE OSCILLATIONS, FELT BY THE USER, ARE MODULATED BY A FEEDBACK SIGNAL CONTROLLED BY THE POSITION OR THE SPEED OF THE PROSTHETIC LIMB.

Description

llll 3,820,168

[ June 28, 1974 SYSTEM FOR OPERATING A PROSTHETIC LIMB [75] Inventor: Eduard Horvath, Duderstadt,

Germany [73] Assignee: F irma Otto Bock Orthopadische Industrie KG, Duderstadt, Germany [22] Filed: Sept. 11, 1972 [2]] Appl. No.: 288,093

Related US. Application Data [63] Continuation-in-part of Ser. No. 33,694,'May 1,

I970, abandoned.

[30] Foreign Application Priority Data Oct. l6, 1971 Germany 2l5l563 [52] US. Cl. 3/l.l-, ZOO/DIG. 2 [51] Int. Cl A6lf 1/00, A6lf H06 [58'] Field of Search 3/].1, 1.2; 200/85 R, DIG. 2

[5 6] References Cited UNITED STATES PATENTS 2,086,066 7/1937 Churchill ZOO/85 R 2,679,649 6/1954 Alderson 3/l.l FOREIGN PATENTS OR APPLICATIONS 1,917,057 [0/1969 Germany 3/l.l

163,718 l/l965 U.S.S.R 3/l.l

OTHER PUBLICATIONS Human Limbs & Their Substitutes, by Klopsted and Wilson et al., McGraw-I-Iill Book Co., Inc., N.Y., Toronto, London, 1954, pp. 39l392.

Primary ExaminerRichard A. Gaudet Assistant Examiner-Ronald L. Frinks Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno ABSTRACT A servomotor for moving a prosthetic limb is actuated by a controller which responds to local variations in muscular rigidity as determined by one or more pressure sensors bearing upon the flesh of the wearer within an annular frame contacting an area of his body. The frame may be resiliently supported in a cutout of a rigid sleeve by one or more springs urging it into contact with an underlying stump. The contacts of the sensor form part of an electromagnetic vibrator whose oscillations, felt by the user, are modulated by a feedback signal controlled by the position or the speed of the prosthetic limb.

8 Claims, 8 Drawing Figures 2Z6 REVERSE i i minnows m4 3.820.168

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nuscuz 5 22 P LL/ fl BONE I Eduard Horvafh lnreman Attorney 1 SYSTEM FOR OPERATING A PROSTHETIC LIMB This application is a continuation-in-part of my copending application Ser. No. 33,694 filed May 1, 1970 and now abandoned.

My present invention relates to the control of servoactuated prosthetic limbs.

Such prosthetic appliances, e.g., when powered by small batteries, have been controlled in the past by electromechanical systems responsive to major movements of some part of the body of the wearer such as a shoulder or the stump of an arm. More recently, sensors have been developed which are capable of detecting muscular contractions and expansions and which, therefore, can be utilized as part of a more sensitive control mechanism for a prosthetic limb. Prior devices of this nature, however, required cumbersome har- 1 nesses to maintain the proper physical correlation between the sensor and the part of the body engaged thereby.

My invention, therefore, aims at providing a simple,

efficient and sensitive controller for an extemallypowered prosthetic limb. A more particular object is to provide a controller of this description which is compact enough to be mounted on a stump socket for engagement with an underlying area of the body.

Another object of my invention is to provide means in such a controller for giving the wearer a feel of the motion of the prosthetic limb in response to voluntary muscular changes.

I have found, in accordance with the present invention, that both normal and atrophied muscles undergo distinct and mechanically detectable structural changes in response to impulses transmitted to them through the nervous system, generally in the form of a localized stiffening of the flesh. In many instances, the resistance of the body to outside pressure has a definite distribution throughout a limited area which is modified by the play of a muscle so that the resistance gradient varies in magnitude and, frequently, in sign at the willof the amputee. The resulting lateral relocation of the zone of maximumpressure resistance within a predetermined area of the body can therefore be used, pursuant to one aspect of my invention, to generate alternate command signals for the movement of the limb in one direction or the other.

Thus, a control device embodying the present improvement has a plurality of relatively movable contactors closely juxtaposable on a selected body area, in combination with output means such as a set of electrical contacts coupled with these contactors for generating the requisite command signal or signals. In a simple case, these relatively movable contactors are a single pressure sensor and a preferably annular support on which this sensor is movably mounted; a more elaborate device includes two or more independently movable pressure sensors supported on a common bodycontacting frame.

In order to report back to the controlling muscle the change in position of the controlled prosthetic limb, I

provide the sensor with an electromechanical vibrator which is included in or coupled to the energizing circuit of the limb drive so as to operate as long as that drive is active. The vibrations may be modulated, in intensity and/or in frequency, by a feedback signal from a signal generator such as a variable impedance mechanically coupled with the prosthetic limb, either directly or through the transmission linking it with its drive motor.

Advantageously,pursuant to a further feature of my invention, contacts closed by the sensor in the stiffened condition of its controlling muscle are part of an electromagnetic interrupter which acts as the vibrator. The pulsating current generated by this interrupter may be used directly or indirectly, after amplification if necessary, to energize the limb drive.

The above and other features of my invention will be described in greater detail hereinafter with reference to the accompanying drawing in which:

FIG. 1 is a perspective view of a prosthetic hand fitted onto an arm stump and provided with a controller embodying the invention;

FIG. 2 is a cross-sectional view of a controller similar to that shown in FIG. 1 but drawn to a larger scale;

FIG. 3 is a cross-sectional view taken on the line III III of FIG. 2;

FIGS. 4 and 5 diagrammatically illustrate the pressure distribution along the surface of a muscle, contacted by a single sensor, in its state of relaxation and stress, respectively;

FIGS. 6 and 7 are views similar to FIGS. 4 and 5, respectively, showing the muscle engaged by three juxtaposed sensors; and

FIG. 8 shows a circuit diagram for the control of a servomotor by the three sensors of FIGS. 6 and 7.

In FIG. I I have shown at l the stump of an arm onto which a socket or sleeve of metal or plastic material is fitted in the conventional manner. Sleeve 2 terminates in a prosthetic hand 50 which, with the aid of a servomotor not shown in this Figure, may be rotated at the wrist against the force of a restoring spring likewise not illustrated. It will be apparent that this hand could also be provided with movable fingers operated in a similar manner by a servomotor.

For the control of such a servomotor there is shown provided a controller 3 secured to the sleeve 2, in a manner more fully described hereinafter, by a bracket 4 riveted to the sleeve at 41. Sleeve 2 has a circular cutout 42 traversed with slight clearance by the controller.

Controller 3, as shown in FIGS. 2 and 3, comprises a housing 6 of plastic material topped by a lid 5 which is removably fastened thereto by screws 31 (FIG. 1). Housing 6 has a frustoconically concave bottom 6b forming a rim around a central circular recess 6c accommodating a pressure sensor in the form of a contactor 6a framed by the housing bottom. Pressure sensor 6a has a stem 6d threadedly engaged by a screw 7 whose head bears upon a surrounding guide sleeve 8 through an upper end wall thereof. A flexible diaphragm 9 is anchored to an outer ring 33, embedded in lid 5, and an inner ring 34 frictionally engaging the upper end of sleeve 8. A similar diaphragm 10 spans the annular gap between an outer ring 35, embedded in housing bottom 6b, and an inner ring 36 embracing the sleeve 8 with a friction fit. These two diaphragms, which together with housing 6 and lid 5 define a fluidtight compartment 12, are thus vertically movable with sensor 6a relatively to the housing. This movement is resisted by a spring yoke 11 with a cross-brace 37 engaged by a bolt l9'which is adjustably screwed into an internal ledge of housing 6 to vary the biasing force exerted by the free ends of the yoke upon an extension 8a of sleeve 8. Extension 8a carries a movable contact 13 confronting a fixed contact 14 on the lower surface of an arm 15 carried by the lid 5. Contacts 13 and 14 are included in a circuit, more fully described hereinafter with reference to FIG. 8, which comprises wires 16, 17 forming part of a cable 18 that leads to the servomotor 70 driving the hand 50. The energizing circuit for this servomotor further includes a magnetic armature 23, rigid with sleeve extension 8a, and a surrounding electromagnetic coil 24 fixedly secured to housing 6. I

As shown in FIG. 3, an extension 43 of the controllercarrying bracket 4 (FIG. 1) is traversed by a bolt 44 around whose projecting ends two looped springs 20 are coiled, the free ends of these springs being received in lugs 6e of housing 6. The springs 20 exert upon the controller 3 a certain pressure (downwardly in FIG. 2) urging the sensor 6a and the surrounding frame portion 6b of the housing into contact with a limited area of muscle 22 forming part of the stump I of FIG. 1.

In the operation of the device 3, a hardening of the muscle 22 in the zone engaged by sensor 6a (but unaccompanied by a corresponding stiffening in the region contaced by frame 6b) raises the sensor 6a and, with it,

, and interrupter contacts 13 and 14, thereby operating the associated servomotor and vibrating the contactor 6a with reference to housing 6. When the muscle subsequently relaxes, this circuit is broken so that the controlled prosthetic member (here the hand 50) is caused to remain in the position last reached or returns to its original position under the control of a restoring spring. The fluidtight seal around space 12 prevents any contamination of the contacts by perspiration or other extraneous matter which could interfere with the generation of the proper command signal.

This mode of operation is diagrammatically illustrated in FIGS. 4 and 5 in which the controller 3 has been shown subjected to a contact pressure P, i.e., the force exerted upon it by its mounting springs 20 (FIGS. 2 and 3). This contact pressure gives rise to a muscular reaction force p which in the relaxed condition of muscle 22 (FIG. 4) is substantially evenly distributed so that all body-engaging parts of the controller, i.e., the sensor 6a and the frame 6b, are uniformly loaded. Biasing spring 11 keeps the contacts l3, l4 separated under these circumstances so that the motor circuit remains open. When the muscle 22 is stressed (FIG. 5). the disby the muscle are normally evenly distributed as shown in FIG. 6. In the stressed state of the muscle illustrated in FIG. 7, force P exceeds the forces P, and P;; so that a larger pressure p is required to restore the balance; this involves, of course, the raising of the middle sensor 62 to increase the stress of its biasing spring, as symbolized by the lengthening of arrows p FIG. 8 illustrates the possibility of using three sets of contacts 71, 72, 73, respectively controlled by sensors 61, 62 and 63, for the selective energization of a reversible servomotor from a battery 74 to displace the movable part of the associated prosthetic limb in one or the other direction, depending on a shift in the relative magnitudes of muscular forces p p and p in FIGS. 6 and 7.

Thus, a stiffening of the left-hand portion of muscle 22 would increase the reaction forces 11,, p with reference to force 12,, thereby closing contacts 71 and 72 to drive the motor 70 in the forward direction; an increased compression resistance in the right-hand part of the muscle would increase the forces p p compared with force p, to close the contacts 72 and 73 for reverse operation. Each set of contacts 71 73 may be similar to the contacts 13, 14 shown in FIG. 2.

The operating circuit of servomotor 70 upon the joint actuation of sensors 61 and 62 can be traced from battery 74 via contacts 72, coil 24a (which corresponds to coil 24 of FIGS. 2 and 3), member 13a of contact pair 71 carrying the armature 23a'(which corresponds to coil 23 of FIGS. 2 and 3), member 14a of contact pair 71, the primary winding of a transformer 26a to ground via a potentiometer 25a driven by motor 70; the secondary winding of transformer 26a is connected to a forward input of motor 70 through a rectifier network schematically illustrated as a diode 27a. An analogous circuit, including coil 24b with armature 23b, contact members 13b, 14b, a transformer 26b, a motor-driven potentiometer 25b and a diode 27b, comes into existence upon the joint actuation of sensors 62 and 63 to drive the servomotor 70 in the reverse direction.

The frequency of the vibrations generated by interrupter 71, 23a, 24a or 73, 23b, 24b depends on the circuit impedances as well as on the mass of the movable elements and the elasticity of the stiffened muscle; this frequency can therefore be modified by varying the muscular tension. As the motor 70 advances the hand 50 from a starting position in what has been referred to above as the forward direction, the effective resistance of potentiometer 25a increases along with the time constant of the electromagnetic circuit so that the vibration frequency is reduced; in a limiting position, in which the slider of the potentiometer moves off its resistor, the current flow through transformer 25a is completely interrupted so that the motor 70 stops. Since the cadence of the pulsations passing the rectifier 27a determines the motor speed, the vibration frequency as felt by the wearer is a measure of that speed as well as an indication of the position reached by the prosthetic limb 50.

Similar considerations apply, of course, upon the reversal of the motion of motor 70 by the simultaneous operation of sensors 62 and 63. Potentiometers 25a and 25b are part of a signal generator 25, mechanically coupled with the limb 50, with transformers 26a, 26b acting as correlated responders feeding back positional information to the sensors 61, 63 in the form of physically detectable vibration changes.

It will be apparent that sensors 62 and 63 could be omitted, together with contacts 73, coil 24b,

transformer 26b, potentiometer 25b and diode 27b and with short-circuiting of contacts 72, if the shaft of motor 70 were provided with a restoring spring tending to rotate it in the direction (here counterclockwise) opposite the sense of rotation imparted to the motor by the secondary current of transformer 26a. In such a case, though, the user will have to maintain an offnormal position of limb 50 by the application of a positive force (muscular contraction).

The mechanical contacts l3, 14 of FIGS. 2 and 3 could also be replaced by electronic circuit closers such as, for example, a piezo transistor inserted between the contactor 6a and the upper housing wall 5, preferably in combination with a surrounding coil spring absorbing part of the contact pressure as disclosed in my prior application Ser. No. 33,694. In fact, any electromechanical vibrator in direct pressuretransmitting relationship with the underlying muscle may be employed, with the operating energy supplied by an external source such as battery 74.

With a normally open-circuited power supply, as described with reference to FIGS. 2 and 8, the present system dissipates energy only during actual movement of the controlled prosthetic member so that its operation is highly economical.

I claim:

1. A system for operating a proshetic limb, comprisa support provided with fastening means for placing same in contact with the body of a wearer;

electric drive means for displacing said limb;

an energizing circuit for said drive means including pressure-sensing means on said support movable relatively thereto for engagement with said body;

biasing means on said support urging said pressuresensing means into engagement with said body;

electromechanical vibrating means on said support connected in said energizing circuit and operative in the energized state of said drive means to transmit to the wearer a physically detectable oscillation upon a displacement of said limb; and

frequency-modulating means for said oscillation controlled by said drive means to signal to the wearer the speed and extent of such displacement.

2. A system as defined in claim 1 wherein said vibrating means includes a circuit closer and an electromagnetic coil in series therewith, said pressure-sensing means comprising a contactor operatively linked with said circuit closer and an armature for said coil rigid with said contactor.

3. A system as defined in claim 2 wherein said support comprises a housing enclosing said coil and said armature, said contactor projecting outwardly from said housing into a bottom recess thereof framed by an annular rim, said coil being rigid with said housing.

4. A system as defined in claim 3 wherein said circuit closer comprises a first contact fixedly mounted in said housing and a co-operating second contact mounted on an extension of said contactor.

5. A system as defined in claim 4 wherein said housing is internally provided with two partitions defining a fluidtight compartment for said contacts, at least one of said partitions being a flexible diaphragm mechanically connected with said extension for displacement with reference to said housing.

6. A system as defined in claim 5 wherein said armature and said coil are disposed in said compartment.

7. A system as defined in claim 1 wherein said support comprises a sleeve adapted to receive a stump to be fitted with said limb, said sleeve being provided with a cutout, a frame in said cutout adapted to surround a bearing area of the stump fitted into the sleeve, and spring means on said sleeve engaging said frame with an inwardly directed loading force, said pressuresensing means being positioned to confront said bearing area within said frame.

8. A system as defined in claim 7 wherein said pressure-sensing means comprises two sensors positioned to confront different parts of said bearing area, said sensors being independently actuatable with opposite effect upon the direction of displacement of said limb by said drive means.

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