DE9320708U1 - Elbow lifter - Google Patents

Description

Dipl.-Ing. Justus E. Funke Patent Attorney · US Registered Patent Agent

Hanns-Peter Schrammek

Otto Bock Orthopaedic

Industry Ownership and 108-153 DE-2

Verwaltungs KG

Industriestraße Date

10 Oct. 1994 37115 Duderstadt

Elbow lifter

The invention relates to an elbow lifter for an arm prosthesis, the upper arm fitting part of which is connected via at least one elbow axis to a lower arm fitting part, the pivoting of which is supported by a spring element.

In prosthetics construction, a distinction is made between active and passive prostheses depending on their performance. The group of active prostheses includes those that are controlled by the patient's own power or by external power. The arm prosthesis with power pull occupies an outstanding place among the self-powered prostheses. The arm with the hand as a gripping organ is mainly subjected to tension due to gravity. Therefore, constructive solutions must be sought that lead to tension relief. With the active arm prosthesis, the voluntary bending of the forearm is initiated by means of shoulder bandages made of elastic material in Bowden cables. This is done by shortening the bending cable, whereby the attachment between the upper and lower arm takes place at one end of the cable, and the force is introduced via the shoulder to the upper arm of the other cable.

These prosthetic systems have the disadvantage that the wearer of the prosthesis becomes tired due to the lack of compensation for the weight of the forearm; in addition, the flexion function range cannot be used optimally. Various technical solutions have been developed to compensate for the weight of the forearm.

Theodor-Heuss-Straße 1 0-38122 Braunschweig Federal Republic of Germany

Telephone 05 31/800 79 Telex 0-952 620 gramm d Fax 05 31/812 97

The most commonly used designs are spring-supported systems that are attached close to the joint point. The disadvantage of these designs is that the highest torque to support the bending movement is introduced when the forearm is extended, and that this torque decreases when the forearm is bent. The torque curve is therefore exactly the opposite of the actual needs. Another disadvantage of these previously known solutions is that if the torque is increased too much, the free swing phase is hindered and the natural appearance of the pendulum phase of the forearm is thus disturbed.

The above-mentioned object is achieved according to the invention, based on the elbow lifter described at the beginning, in that the spring element applies a tensile force directly or indirectly to the input of a gear, the output of which acts on the inner end of a tensile organ, the outer end of which can be fixed to a fixed point of the upper arm fitting part that defines a torque lever with the elbow axis, whereby the force is transmitted through the gear in such a way that the course of the torque acting on the fixed point of the upper arm fitting part is approximately parabolic depending on the bending angle of the forearm fitting part and has its lowest values in the extended position of about 5° to 25°, preferably 10° to 20°, as well as at maximum bending and its maximum at about 90°.

While the torque curve in the previously known elbow lifters decreases almost linearly from a maximum starting from the extended position of the arm to the maximum flexion angle of the forearm, the invention achieves a torque curve that corresponds exactly to the actual needs in supporting the flexion of the forearm. If the system is adjusted correctly, the swing phase of the upper arm stump can be used to bring the forearm forward and lower it. This even makes it possible to control a

♦ ·

The traction rope required to lift the forearm is no longer necessary, which allows the amputee greater freedom of movement.

In a further development of the inventive concept, it can be expedient if the spring force is changed by an electrical adjustment depending on the bending angle and the torque curve and/or increased by an electrically applied additional torque. In terms of the device, it can be advantageous if the adjustment of the spring element is carried out via a first motor controlled by a sensor. In addition, it can be advantageous if a second motor 24 is provided in the area of the elbow axis, which applies an additional torque to the forearm fitting part.

It is advantageous if the spring element is designed to be adjustable in terms of its tensile force, whereby this adjustment should be able to be carried out manually from the outside.

The spring element is preferably a spiral spring, but could also be a tension spring or a similar storage element.

The transmission of the spring force between the individual stages could in principle be carried out by rigid elements such as lever arms or by combinations of lever arms, swivel joints, gears or the like. However, it appears to be advantageous to design the gear as a cam disk gear, which can be designed in particular as follows: 30

a) The cam mechanism comprises two cams each mounted in a rotationally fixed manner on a common shaft;

b) the said force transmission element is a flexible belt or the like, which engages directly or indirectly with one end of the spring element, the first of the two cam discs with the arm extended

prosthesis and is attached with its other end to this first cam disc at a point defining the transmission input;

c) the said traction element is also designed to be flexible and is attached with its inner end to a point on the second cam disk that defines the gear output, which is increasingly wrapped around by the traction element as the forearm fitting part is bent. 10

It is useful if the traction element coming from the second cam disc is guided around a pulley approximately tangentially to the lower contour of the upper arm fitting part. In order to prevent the arm from swinging forward too quickly in the event of severe overcompensation, it is advantageous if hydrodynamic damping is built into the pulley.

Further features of the invention are the subject of the subclaims and are explained in more detail in connection with further advantages of the invention using two exemplary embodiments.

The drawing shows two exemplary embodiments of the invention. They show: 25

Figure 1 - longitudinal section and partial side view of a complete arm prosthesis with extended forearm;

Figure 2 - enlarged view of a section of the

Figure 1;

Figure 3 - the representation according to Figure 2 but with strong

bent forearm; 35

Figure 4 - an embodiment equipped with additional electric drives in a representation according to

Figure 3 and

Figure 5

three torque curves plotted against the flexion angles of the forearm.

The arm prosthesis shown in Figure 1 comprises an upper arm fitting part 1 and a lower arm fitting part 2, which are connected to one another via an elbow axis 3. To support the pivoting of the lower arm fitting part 2 into various bending positions an elbow lifter 4 is provided. This has a housing 5 that accommodates or encloses all of its components and is inserted into a suitable recess in the lower arm fitting part 2.

The elbow lifter 4 shown in Figure 2 essentially comprises a spiral spring 6, a cam disk gear 7, a force transmission element designed as a flexible belt 8 that transmits the force from the spiral spring 6 to the cam disk gear 7, and a traction element 9 that kinematically connects the cam disk gear 7 to the upper arm fitting part 1.

The cam disk gear 7 comprises two cam disks 7a and 7b, each of which is fixedly mounted on a common shaft 10.

The spiral spring 6 is fastened in a spring housing 11 and applies a torque to an output disk 12 which is located on an axle 13. The preload of the spiral spring 6 can be changed according to the weight to be balanced and acting on the forearm fitting part 2 by turning a worm gear 14, for the operation of which a manually operable rotary disk 15 accessible from the outside, a knurled wheel or the like is provided.

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The belt 8 is attached at one end to a fixed point 16 on the driven pulley 12, wraps almost completely around the outer curve contour of the first cam disk 7a and is attached at its other end to the outer circumference of this first cam disk 7a via a fixed point 17, which defines the gear input of the cam disk gear 7.

The tension member 9, which is designed to be flexible like the belt 8, is attached with its inner end to a fixed point 18 on the circumference of the second cam disk 7b, which defines the gear output, is then guided around a deflection roller 19 mounted in the housing 5 and is fixed with its outer end, which leads out of the housing 5, to a fixed point 20 of the upper arm fitting part 1, which defines a torque lever with the elbow axis 3. Figure 2 shows that the tension member 9 only wraps around the outer curved contour of the second cam disk 7b over a short section when the lower arm fitting part 2 is stretched and rests in the area between the deflection roller 19 and the fixed point 20 on the upper arm fitting part 1 on its lower, approximately circular segment-shaped contour 21.

Figure 3 shows the forearm fitting part 2 at its maximum bending angle. A comparison with Figure 2 makes it clear that starting from the stretched arm position, with increasing bending angle of the forearm fitting part 2 relative to the upper arm fitting part 1, the belt 8 is wound off the first cam disk 7a and onto the driven disk 12 driven by the coil spring 6, while the traction element 9 increasingly detaches itself from the lower contour 21 of the upper arm fitting part 1 and is wound onto the second cam disk 7b. Figure 3 also shows that the deflection roller 19 is arranged in such a way that the traction element 9 is guided almost tangentially to the contour 21.

The gear 7 is designed in conjunction with the characteristics of the spring element 6 so that the course of the torque applied to the elbow axis 3 is approximately parabolic depending on the bending angle of the forearm fitting part 2.

is (see Figure 5) and has its lowest values in the extended position of about 10° to 20° and at maximum flexion and its maximum at about 90°. This is achieved with the embodiments shown in Figures 2 and 3 by a corresponding design of the curve of the two cam disks 7a, 7b and by their assignment to one another, which also results in a corresponding compensation of the spring force characteristic curve. The adjustable range of this compensation is shown in Figure 5 by the torque lines plotted over the flexion angle of the forearm fitting part 2.

Figure 4 schematically shows that the adjustment of the spring element 6 can also be carried out by a first motor 24 controlled by a sensor 23 depending on the bending angle. The spring force can thus be changed by electrical adjustment depending on the bending angle and the torque curve. In addition, a second motor 25 can be provided in the area of the elbow axis 3, which applies an additional torque to the forearm fitting part 2. This allows the spring force to be electrically increased. Finally, Figure 4 also shows a third motor 26, with which the forearm fitting part 2 can be electrically locked in a desired bending position.

A comparable kinematics to that achieved by the two cam disks 7a, 7b could be achieved by corresponding curve formation of the output disk 12, the deflection roller 19 and/or the contour 21.
Gr/is

Claims (14)

1. Elbow lifter for an arm prosthesis, the upper arm fitting part (1) of which is connected in an articulated manner to a lower arm fitting part (2) via at least one elbow axis (3), the pivoting of which is supported by a spring element (6), characterized in that the spring element (6) applies a tensile force directly or indirectly to the input (17) of a gear (7), the output (18) of which acts on the inner end of a traction element (9), the outer end of which can be fixed to a fixed point (20) of the upper arm fitting part (1) which defines a torque lever with the elbow axis (3), the force being transmitted by the gear (7) in such a way that the course of the torque at the fixed point (20) of the upper arm fitting part (1) as a function of the flexion angle of the lower arm fitting part (2) is approximately parabolic and has its lowest values in the extended position of approximately 5° to 25°, preferably 10° to 20° and at maximum flexion and its maximum at approximately 90°. 2. Elbow lifter according to claim 1, characterized by a one-piece assembly which can be inserted into a recess of the forearm fitting part (2). 3. Elbow lifter according to claim 1 or 2, characterized in that the spring element (6) is a spiral spring. Theodor-Heuss-Straße 1 D-38122 Braunschweig Federal Republic of Germany Telephone 0531/800 79 Telex 0-952 620 gramm d Fax 05 31/812 97 4. Elbow lifter according to claim 1, 2 or 3, characterized in that the spring element (6) is adjustable with regard to its tensile force. 5. Elbow lifter according to claim 3 and 4, characterized in that the preload of the spring element (6) is adjustable via a worm wheel (14). 6. Elbow lifter according to claim 4 or 5, characterized in that the adjustment of the spring element (6) takes place via a first motor (24) controlled by a sensor (23). 7. Elbow lifter according to one of the preceding claims, characterized in that the spring element (6) acts as a rotary force on a driven disk (12) to which a force transmission element (8) connected to the gear input (17) is fixed. 8. Elbow lifter according to one of the preceding claims, characterized in that the gear (7) is a cam disk gear. 9. Elbow lifter according to claim 8, characterized by the following features: a) The cam disk gear (7) comprises two cam disks (7a, 7b) each of which is non-rotatably mounted on a common shaft (10); b) said force transmission element (8) is a flexible belt or the like, which with one end engages directly or indirectly with the spring element (6), the first (7a) of the two cam discs (7a,7b) when the arm prosthesis is extended largely wraps around and with its other end on this first cam disc (7a) at a is fixed to the point defining the drive input (17); c) the said tension member (9) is also designed to be flexible and is connected with its inner end attached to a point of the second cam disc (7b) defining the gear output (18), which is increasingly wrapped around by the pulling element (9) as the forearm fitting part (2) is bent more and more. 10 10. Elbow lifter according to claim 9, characterized in that the traction element (9) coming from the second cam disc (7b) is guided around a deflection roller (19) approximately tangentially to the lower contour (21) of the upper arm fitting part (1). 11. Elbow lifter according to claim 10, characterized in that the traction element (9) rests, when the arm prosthesis is extended, in the area between the deflection roller (19) and the fixed point (20) on the upper arm fitting part (1) on its lower, approximately circular segment-shaped contour (21). 12. Elbow lifter according to one of the preceding claims, characterized by a housing (5) accommodating or enclosing all components. 13. Elbow lifter according to one of the preceding claims, characterized in that a second motor 25 is provided in the region of the elbow axis (3), which applies an additional torque to the forearm fitting part (2). 14. Elbow lifter according to one of claims 10 to 13, characterized in that a hydrodynamic damping is built into the deflection roller (19). Patent attorneys
Grams + Lentil Gr/is