GB2135012A - Motor drive transmission means, especially for use in a prosthesis - Google Patents

Abstract

Motor drive transmission means comprising a motor drive shaft (40) which drives an output shaft (14) via a friction gearing arrangement (42) enclosed in a housing (44). The drive shaft (40) is surrounded by three planetary wheels or rollers (46) which are in turn enclosed by a ring or ring-like member (48) so that the rollers are resiliently urged into frictional driving contact with the drive shaft (40). Each planetary wheel has a shaft (50) projecting on either side of its flat surfaces, and these shafts are slidingly received in radial slots (52) provided in a front face plate (54) and a back face plate (56). The two plates (54) and (56) are spaced apart by three "bridges" (58) at or near their circumferences, the three bridges being equally spaced apart. <IMAGE>

Description

SPECIFICATION Motor drive transmission means, especially for use in a prosthesis This invention relates to motor drive transmission means and is especially useful in a prosthesis, such as a mechanical hand, which is operated by an electric motor.

In our prior British Patent Application No.

2,072,020A published on 30th September 1981, we have described a mechanical hand having an operating leverwhich is driven by a power unit including an electric motor, the operating lever being connected to a shaft driven by a motor in such a way that rotation of the drive shaft causes the operating leverto pivot about its pivotal axis.

The motorofthat mechanical hand is illustrated in Figure 1 of Application No. 2,072,020A and comprises a main shaft surrounded bythree planetary rollers running between two rings which are urged towards each otherbyaspring disc. Tapered internal surfaces on the rings urge the rollers radially inwards against the motor main shaft so that, when the latter rotates, it causes the three planetary rollers to rotate as well.

Each of the rollers has a centre bore which receives a respective pin carried on an end portion of an output shaft provided with an "acme" type screwthread. The output shaft has a nutthreaded on to it and this nut serves to operate one or more actuating levers of the mechanical hand itself. The drive meansforthe hand therefore comprises an electric motor having drive transmission means serving to operate one or more actuating levers ofthe hand.

Anotherform of motor drive transmission means is shown in German Patent No.1,650,741. In this construction two planetary rollers are urged into frictional contactwith a motor shaft by a ring-like member surrounding them. This ring does not however bear directly on the two planetary rollers but, instead, acts on each ofthem via two auxiliary rollers sandwiched between the ring-like member and its respective planetary roller. Each planetary roller has a shaft projecting axially on each of its two main faces, and these shafts are received in bearing blocks adaptedtoslide radiallywith respecttothe motor shaft in radial slots provided in two discs or plates arranged one on each side of the planetary rollers.

The present invention is concerned with motor drive transmission means which are especially useful in a mechanical hand or other prosthesis and which constitute an improvement over the motor drive transmission means shown in our prior British Patent Application No. 2,072,020A and that shown in German Patent No.1,650,741. In essence, the invention is a simplification ofthetransmission means shown in the said German Patent, thereby giving advantages both as regards reduced cost and less components to go wrong.

According to the invention, motor drivetransmis- sion means, especiallyfor use in a prosthesis, comprise a number of planetary rollers or wheels which are resiliently urged against a motor drive shaft by a surrounding ring or ring-like member, in which the planetary rollers or wheels are each provided with shafts projecting on both sides of the wheels with the shaft being mounted for sliding movement radially of the motor drive shaft in radial slots formed in two substantially parallel plates or discs arranged one on each sideofthe planetarywheelsorrollers,the planetary wheels being in direct contact with the inner surface ofthe surrounding ring or ring-like member.

Preferably, the plates or discs are spaced apart by bridges arranged at or near their circumferences.

Normally,three planetarywheelswill be provided and three such bridges. However, in certain circumstances it may be satisfactory to have just two planetary wheels and two bridges.

The advantage given bythe invention overthe construction shown in German Patent No.1,650,741 is thatthe auxiliary rollers provided in the latterconstruction are now omitted. This makes for simplicity of operation and reduced cost in manufacture.

An example of a mechanical hand incorporating motor drive transmission means in accordance with the invention is shown in the accompanying drawings, in which~ Figure 1 is a side view of the mechanical hand showing alternative positions for its "fingers" in broken lines; Figure 2 is another side view of the hand taken at right angles to the view shown in Figure 1; Figure 3 is a view of the hand taken from the opposite side to Figure 1; Figure 4 is a part sectional side view of the electric motor and transmission means incorporated in the hand shown in Figures 1-3; Figure 5 isa section taken on the line BB in Figure 4; Figure 6 is an enlarged sectional viewthrough part ofthe motor drive transmission means shown in Figure 4; Figure 7 is an end view of the components shown in Figure 6;; Figures 8 and 9 are details of two of the components shown in Figure7; Figure 10 is a part sectional side view of one ofthe components shown in Figure 6; and Figure 11 is an enlarged sectional view of some of the components shown in Figure 4.

Figures 1~3 showy mechanical hand having movable fingers 10, such movement being effected by a drive from an electric motor 12. The drivetransmission means between the electric motor 12 and the fingers 10 includes an output shaft 14 having an "acme" type screwthread, there being a nut 16 in the form of a trunion threaded on the shaft 14. Thus, the nut 16 has a pair of projecting journal pins 18, one on each side of the nut. Pivotally carried on these journal pins 18 are two parallel "thumb" operating levers 20 having a "thumb" 22 pivotally mounted on it at 24.

Another pair of parallel levers 26 are also mounted on the journal pins 18, and these levers are pivotally connected at 28to one or more "fingers" 30. In the case ofthe "finger" operating levers 26, an elongated slot32 is formed in them to receive the journal pins 18.

Rotation of the output shaft 1 4 therefore causes the nut 16to move a long the shaft with the result that the finger(s) and thumb are moved towards or away from each other (seethe alternative positions indicated in Figure 1) depending on the direction of rotation ofthe output shaft 14.

To allow the electric motor to accommodate itselfto the hand, the motor casing is pivotally mounted at 34 on a wrist portion 36 ofthe mechanical hand. This wrist portion 36 also supports a moulded sleeve 38 corresponding to the palm and back portion of a hand.

Thecircuitryforcontrolling operation of the motor can be quite complex and will differ according to whetherthe mechanical hand is controlled by muscle movements on the part of a wearer of the hand or by a servosystem. Further information about possible circuitry is given in ourpriorSpecifications Nos.

2,072,020A and 2,088,589A, and will not therefore be described here as the present invention is more particularly concerned with the construction ofthe drive transmission means between the motor and the output shaft 14. Preferably, a mechanical hand or other prosthesis in accordance with the present invention will also fall within the scope of the claims in Specification No. 2,070,020A and will have a control system as described and claimed in Specification No.

2,088,589A.

The construction of the drive transmission means from the motor 12 will now be described in detail with reference to Figures4~11 ofthe accompanying drawings. As will be seen from Figure 4, the motor 12 has a drive shaft 40 which drives the output shaft 14 via a form of clutch 42 enclosed in a clutch housing 44.

The drive shaft 40 is surrounded by three planetary wheels or rollers 46 which are in turn enclosed by a ring or ring-like member 48so that the rollers are urged into frictional driving contact with the drive shaft40. Each planetary wheel has a shaft 50 projecting on either side of its flat surfaces, and these shafts are slidingly received in radial slots 52 provided in a frontface plate 54 and a backface plate 56~see Figures 6 and 7. The two plates 54and 56 are spaced apart by "bridges" 58 at or neartheir circumferences, the three bridges being equally spaced apart as shown in Figure 5. The bridges can be separate pieces which are screwed or otherwise connected to the front and back face plates 54 and 56. Alternatively, the bridges can be formed integrally on one or other of the two face plates.Where that is the case, screw holes can be provided in the plate not carrying the bridges and in the bridges so that the two plates can be connected together. In the best arrangement however, the two plates and the bridges are made from one solid piece of metal which is so cast and/or machined as to producetheconstruction shown in Figure 10.

Irrespective ofthe precise way in which the plates 54 and 56 and the bridges 58 are formed,three equally spaced slots 52 are cut along radial lines at 120"to each other in both the front and back face plates 54 and 56. These slots are cut very precisely to allow the planet wheel shafts 50 to slide in the slots but leaving very little free play.

Projecting from the outer face of the front plate 54 is a shaft portion 60 which is mounted for rotation in a ball race 62 as shown in Figure 4. The output shaft 14 is connected totheshaft portion 60 or is integrally formed on it. During assemblyofthe motor drive transmission means shown in Figures 4~11, each planetwheel has its shafts positioned in the planet carrier formed by the front and back face plates 54 and 56 and the bridges 58 with the planet heel shafts lying at the bottom ofthe slots 52. Onseallthreeplanet wheels are in position, the surrounding ring 48 is positioned around the three planet wheels.The ring has a certain amount of elasticity and is preferably made of springy metal so asto urge the planetwheels resiliently into frictional contact with the motor drive shaft 40.

During rotation ofthe drive shaft40, the planet wheelsarefreefrom any radial constraining forces from the planet carrier and can therefore move radially inwards and outwards with respect to the drive shaft 40 so as to accommodate the effects of temperature on the components and/or manufacturing tolerances. As will be understood, the radial forces from the elastic ring 48 provide the radial reaction required to transmit tangential forces from the motor drive shaft 40 to the other rotating parts ofthe system.

An important advantage given by this form of construction is that the shafts or axles 50 ofthe planet wheels or rollers 46 have very little free play in a tangential direction within the confines ofthe slots 52.

This means that, when the drive is reversed, there will be practically no backlash in the system, which is an important consideration if the mechanical hand isto attain a high grade of performance.

Claims (6)

1. Motor drive transmission means, especially for use in a prosthesis, comprising a number of planetary rollers orwheelswhich are resiliently urged against a motor drive shaft by a surrounding ring or ring-like member, in which the planetary rollers orwheels are each provided with shafts projecting on both sides of the wheels with the shafts being mountedforsliding movement radially ofthe motor drive shaft in radial slots formed in two substantially parallel plates or discs arranged one on each side ofthe planetary wheels or rollers, the planetarywheels being in direct contact with the inner surface ofthe surrounding ring or ring-like member.

2. Motordrivetransmission means according to claim 1, in which the plates or discs are spaced apart by bridges arranged at or neartheir circumferences.

3. Motor drive transmission means according to claim 2, inwhich three planetarywheels are provided and three such bridges.

4. Motor drive transmission means according to any one of claims 1-3, in which the ring is made of springy metal.

5. Motor drive transmission means substantially as described herein with reference to the accompany ing drawings.

6. A prosthesis incorporating motor drive trans mission means as claimed in any preceding claim.