GB1571140A - Friction coupling for artificial limbs - Google Patents

Description

(54) FRICTION COUPLING FOR ARTIFICIAL LIMBS (71) We, FORSHUNGSINSTITUT FUR ORTHOPADIE-TECIINIll, an Austrian body Corporate, of Geigergasse 5-9, 1030 Vienna, Austria, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to improvements in a friction coupling for artificial limbs, particularly for a hand or elbow prosthesis.

Drives for artificial limbs are mounted between an electromotor and a limb to be moved, such as an albow or the fingers of a hand prosthesis, to transmit the rotary motion of the motor shaft to the limb. It is desirable for such transmissions to work quietly, efficiently and dependably, to have relatively small dimensions and to be light in weight.

Usually, toothed gear or worm gear transmissions have been used for this purpose but they are relatively noisy in operation and are not very efficient. Belt drives have also been used and Published German Patent Application No. 2335974 proposes the use of planetary gears with friction wheels, the friction wheels being pressed into frictional engagement by the elastic clamping action of the enclosing wheel. Since the friction losses are essentially directly proportional to the pressure force, the efficiency of this drive transmission is rapidly reduced with a reduction in the load.

In accordance with the present invention there is provided an artificial limb having a friction coupling for transmission of moton from a drive motor to a part of the limb, wherein the coupling comprises three rotary friction members each of which is in frictional contact with at least one of the others, the axes of rotation of the three members being substantially in the same plane, and a clamping ring enclosing the three members, one of the members being an idler and the other two serving as input and output members of the coupling.

With this very simple structure, the pressure with which the members of the coupling are brought into frictional engagement is automatically adapted to the force to be transmitted and the friction losses in the drive due to a relatively small load being applied are reduced. This produces an unchanging efficiency of the transmission even when the load decreases. Furthermore, the drive is not only simple in structure but it also operates noiselessly.

The invention will be described in more detail with the aid of an example illustrated in the accompanying drawing wherein Fig. 1 is a schemtic top view of a hand prosthesis incorporating a coupling according to the invention, Fig. 2 is an axial section of the drive, and Fig. 3 is a section along line rn-rn of Fig. 2.

Referring now to the drawing and first to Fig. 1, the power source for the drive is shown as an electric motor 1 whose output shaft is coupled to a friction coupling 2. Toothed gear 3 keyed to an output shaft of the friction coupling and, upon rotation of the output shaft of motor 1, rotary motion is transmitted to toothed gear 14 which is in meshing engagement with gear 3. Further toothed gear 15 is mounted coaxially with gear 14 and rotates herewith, gear 15 being in meshing engagement with segmental gear 17 rotatable about axis 16. Idling roller 18 is affixed to segmental gear 17 and two further guide roller 5, 5 are mounted on the prosthesis body on opposite sides of roller 18. Cable 4 is trained about rollers 5, 18 and 5, the cable ends being affixed to respective rollers 6 mounted in the region of the inner ends of fingers 8 of the prosthesis. Further cables 7 are trained over each roller 6 and the ends of cables 7 are affixed to respective fingers 8.

Depending on the direction of rotation of the output shaft of motor 1, the hand will execute an opening or dosing movement, rotation of segmental gear 17 in the direction of arrow A producing an opening movement while rotation of the gear in the direction of arrow B will produce a closing movement of the hand prosthesis.

The present invention does not deal with this prosthesis drive as such but with the structure of friction coupling 2 through which the rotary motion of the motor shaft is transmitted to segmental gear 17 of the prosthesis drive. As appears from Figs. 2 and 3, this coupling comprises friction wheel 12 keyed to a shaft 10 for rotation therewith and two rotarv friction members in tile form of shafts 9 and 11. The friction members are surrounded and enclosed by a clamping ring 13 and the entire coupling is mounted in a housing 2 in which the shafts 9, 10 and 11 are journaled for rotation. Shaft 9, which is coupled to the motor shaft, is the input member of the coupling, shaft 11 is the idler of the coupling and wheel 12, which is keyed to shaft 10, is the output member of the coupling. Shaft 9 and wheel 12 are in frictional contact with each other, as are wheel 12 and shaft 11.

Shafts 9 and 11, wheel 12 and clamping ring 13 have hardened and polished contact surfaces.

The inner diameter of clamping ring 13 is so selected that it will be elastically stretched a little when it is assembled with the friction members whereby wheel 12 and shafts 9 and 11 are pressed against each other into contact. However, the pressure exerted by the clamping ring should not be large enough to transmit substantial torque. The required frictional contact pressure will b come effective only when the drive is in operation.

When shaft 9 is driven in the direction of arrow C (Fig. 3), the rotary speed of shaft 9 exceeds that of wheel 12 and idling shaft 11, due to the slippage in the coupling. This causes clamping ring 13, which moves faster at point 19 in contact with driving shaft 9 than at point 20 in contact with idling shaft 11, to assume the eccentric position shown in broken lines in Fig. 3, thus pressing the three coupling components into frictional engage ment. This pressing force is automatically increased until the frictional force between the coupling components is sufficient for transmission of the driving force. The press ing force, which is limited only by the friction coefficient and the rigidity of clamping ring 13, is compensated by the elasticity of the clamping ring so that the storage pressures are low. This further increases the effectiveness of the coupling.

Obviously, the coupling will operate in the same manner whichever shaft is used as the input, that is to say either shaft 9, or shaft 10 may be coupled to the motor shaft.

WHAT WE CLAIM IS:- 1. An artificial limb having a friction coupling for transmission of motion from a drive motor to a part of the limb, wherein the coupling comprises three rotory friction members each of which is in frictional contact with at least one of the others, the axes of rotation of the three members being substantially in the same plane, and a clamping ring enclosing the three members, one of the members being an idler and the other two serving as input and output members of the coupling.

2. An artificial limb as claimed in claim 1 in which two of the members of the coupling are in the form of shafts and the third is wheel keyed to a shaft.

3. An artificial limb as claimed in claim 2 in which the wheel is in contact with each of the other two members of the coupling.

4. An artificial limb as claimed in claim 1 or 2 in which one of the members in the form of a shaft is the idler.

5. An artificial limb having a friction coupling substantially as described with reference to Figs. 2 and 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. B will produce a closing movement of the hand prosthesis. The present invention does not deal with this prosthesis drive as such but with the structure of friction coupling 2 through which the rotary motion of the motor shaft is transmitted to segmental gear 17 of the prosthesis drive. As appears from Figs. 2 and 3, this coupling comprises friction wheel 12 keyed to a shaft 10 for rotation therewith and two rotarv friction members in tile form of shafts 9 and 11. The friction members are surrounded and enclosed by a clamping ring 13 and the entire coupling is mounted in a housing 2 in which the shafts 9, 10 and 11 are journaled for rotation. Shaft 9, which is coupled to the motor shaft, is the input member of the coupling, shaft 11 is the idler of the coupling and wheel 12, which is keyed to shaft 10, is the output member of the coupling. Shaft 9 and wheel 12 are in frictional contact with each other, as are wheel 12 and shaft 11. Shafts 9 and 11, wheel 12 and clamping ring 13 have hardened and polished contact surfaces. The inner diameter of clamping ring 13 is so selected that it will be elastically stretched a little when it is assembled with the friction members whereby wheel 12 and shafts 9 and 11 are pressed against each other into contact. However, the pressure exerted by the clamping ring should not be large enough to transmit substantial torque. The required frictional contact pressure will b come effective only when the drive is in operation. When shaft 9 is driven in the direction of arrow C (Fig. 3), the rotary speed of shaft 9 exceeds that of wheel 12 and idling shaft 11, due to the slippage in the coupling. This causes clamping ring 13, which moves faster at point 19 in contact with driving shaft 9 than at point 20 in contact with idling shaft 11, to assume the eccentric position shown in broken lines in Fig. 3, thus pressing the three coupling components into frictional engage ment. This pressing force is automatically increased until the frictional force between the coupling components is sufficient for transmission of the driving force. The press ing force, which is limited only by the friction coefficient and the rigidity of clamping ring 13, is compensated by the elasticity of the clamping ring so that the storage pressures are low. This further increases the effectiveness of the coupling. Obviously, the coupling will operate in the same manner whichever shaft is used as the input, that is to say either shaft 9, or shaft 10 may be coupled to the motor shaft. WHAT WE CLAIM IS:-

1. An artificial limb having a friction coupling for transmission of motion from a drive motor to a part of the limb, wherein the coupling comprises three rotory friction members each of which is in frictional contact with at least one of the others, the axes of rotation of the three members being substantially in the same plane, and a clamping ring enclosing the three members, one of the members being an idler and the other two serving as input and output members of the coupling.

2. An artificial limb as claimed in claim 1 in which two of the members of the coupling are in the form of shafts and the third is wheel keyed to a shaft.

3. An artificial limb as claimed in claim 2 in which the wheel is in contact with each of the other two members of the coupling.

4. An artificial limb as claimed in claim 1 or 2 in which one of the members in the form of a shaft is the idler.

5. An artificial limb having a friction coupling substantially as described with reference to Figs. 2 and 3 of the accompanying drawings.