TECHNICAL FIELD The present invention relates to a mechanical gripping organ intended to be secured to an amputated lower arm or an amputated hand of an amputee so as to simulate the movements of a human hand. The invention furthermore proposes a method for using the aforementioned organ in order to simulate and perform the most important gripping manipulations that a human hand can execute.

PRIOR ART Many attempts have been made to produce a suitable prosthesis for use as a mechanical hand. On account of the unique movements that are possible by using the fingers together with the opposing thumb, the hand has been regarded as an extremely difficult limb to simulate or imitate by means of an artificial prosthesis. The second consideration that has to be taken into account when designing an artificial hand is that the arrangement must have a weight that is the same as that of the original hand and the movements of the fingers including the thumb must be quick, while still exerting a sufficient gripping force so that it can be used in practice as a prosthesis.

When the movements performed by a real hand in executing various gripping operations are examined, three important gripping operations that the actual hand can perform may in particular be distinguished, in which the movements of the hand and finger elements in these gripping operations become very important so they can be simulated with the help of a prosthesis, so that thereby the same movement patterns can be executed with finger elements when carrying out these gripping operations. The important distinguishable gripping operations may be characterised as a precision grip, a power (force) grip and a key (opening) grip. An important area to investigate when the human hand executes the

aforementioned gripping operations are the movements of the human thumb.

In the precision grip the thumb is pivoted by a certain angle about its own axis, whereupon the inside of the thumb faces the inside of the remaining fingers. In this way it is possible for the tip of the thumb to touch the tips of the remaining fingers, in particular the tips of the index finger and middle finger, or to touch both the tips of the index finger and middle fingers simultaneously. By employing the precision grip the hand can hold small objects and tools, such as for example a pen or small tools for precision work.

In the power grip the thumb is pivoted until it is opposite the remaining fingers, with the inside of the thumb facing towards the latter. The power grip is exerted when the fingers are forcibly bent towards the inside of the palm of the hand or towards the facing thumb, whereupon an object can be held with a strong force exerted by the fingers with or without the contribution of the thumb.

In the third of the aforementioned gripping operations, i. e. the key grip, all the fingers are slightly bent and support one another laterally, while at the same time the thumb is pivoted about its own axis so that it can be held via its tip on the inside of the latter, facing the side of the index finger. A simple example of a hand executing a key grip is when the hand holds a key with the aim of turning it in a door. When using the key grip the wrist is usually pivoted at the same time relative to the lower arm in order to exert turning forces on the whole object.

With all the three types of grip hand movements can furthermore be combined with a tilting of the hand at the wrist in an inwardly or outwardly executed turning movement. The inward movement in this case involves a direction in which the hand is tilted so that the palm of the hand is bent towards the lower arm, i. e. so that the angle between the palm of the hand and the lower arm decreases. In a similar manner, with outward movements of the hand the outside of the hand is bent towards the lower

arm, i. e. so that the angle between the outside of the hand and the lower arm decreases.

Up to now no hand prosthesis exists in which a composite hand has the ability to execute properly as desired any of the three aforedescribed types of grip (including when the thumb is pivoted about its own axis).

Accordingly, as a consequence of this none of the mechanical hands described in the prior art can execute as desired any of the aforementioned types of grip and in particular the type of grip in which the hand at the same time is able to be pivoted or tilted relative to the lower arm.

There is furthermore a great desire among amputees provided with hand prostheses that the latter should appear as natural as possible. Thus, a hand prosthesis should be the same size as a human hand, have a middle hand (metacarpus), fingers and thumb that resemble the corresponding elements in a real, human hand as far as possible as regards length and appearance. The movements of the hand elements should follow a natural movement pattern. As an example of known technology, reference may be made here to an arrangement proposed in US patent specification 5 080 682, which discloses a mechanical hand of natural size, five fingers, a thumb and a middle hand, in which furthermore the length of the fingers and the size of the individual parts of the hand appear natural and in good proportion to one another. However, the known mechanical hand has limitations. The thumb cannot pivot about its own longitudinal axis, and accordingly the ability to execute natural gripping movements like a normal hand in the correct manner, as described above, does not exist. As an example, it is not possible to exert a pure power grip with the thumb involved with the aforedescribed hand. The thumb can only bend from the side towards and underneath the other fingers, and accordingly the other fingers can bend towards the thumb with the side of the thumb facing towards the aforementioned fingers, with the thumb and other fingers in almost the same plane. In this connection no force can be exerted by the thumb on the inside of the remaining fingers. This is a consequence of the restriction that the inside of the aforesaid thumb cannot pivot about its own axis, so that the inside of the thumb faces towards the remaining

fingers when the power grip is exerted, and accordingly it is not possible by using the hand according to the aforementioned specification to exert a firm and natural power grip with the inside of the thumb facing towards the remaining fingers around an object in a true and natural power grip.

Furthermore, a known mechanical hand is disclosed in US patent specification 4 792 338, in which a hand is described that is capable of exerting a precision grip.

The hand in the aforedescribed arrangement employs fingers and a thumb that are not able to bend with the aid of joints along the fingers, which means that all the fingers are stiff and therefore creates an unnatural appearance in certain positions, since such a hand cannot be held flat for example. A key grip can furthermore not be exerted with this known mechanical hand.

Hitherto neither has a mechanical hand been available with the movements in all associated parts of a hand involved in movements that are controlled in a co-ordinated manner, so that the pattern of movements in the parts of the hand resemble those movements in a human hand when executing corresponding gripping operations. An object of the present invention is to provide such a mechanical hand.

DESCRIPTION OF THE INVENTION One object of the present invention is to provide a method for simulating the movements in a human hand by means of a mechanical gripping arrangement that is to be secured preferably on the lower arm of a person. The arrangement has a supporting platform that corresponds to the metacarpus of the human hand. The platform has a front side for accommodating at least two finger organs, namely a first finger organ corresponding to the index finger and a second finger organ corresponding to the middle finger of a human hand. The said finger organs are pivotably arranged with respect to the said platform. The finger organs can be bent around at least one finger joint. The gripping organ furthermore has a thumb finger corresponding to the thumb of a human hand, secured on

one side of the platform adjacent to the said first finger organ. The aforementioned method comprises the following steps: - the thumb is arranged so as to be pivotably movable about a thumb base axis that is inclined at an angle a that is less than 90° with reference to a longitudinal axis through the lower arm, - the movements in each movable finger element are produced by means of drive arrangements controlled by control signals, - the gripping organ is arranged to execute as desired any of the gripping operations, namely precision grip, power grip and key grip by a co-ordination of the drive arrangements by means of control signals that control a) bending movements of finger elements at their joints and turning movements of finger elements at their pivotable securements on the platform, and b) pivoting movements of the thumb finger for an integrated and co-ordinated execution of the movements that are included in the pattern of movements in the chosen gripping operation.

A further object of the invention is to provide a mechanical gripping organ that can perform the movements according to the method defined above with the gripping organ characterised according to the independent arrangement claim.

In the following description the term"finger"is sometimes used instead of the"mechanical finger organ of the hand", and the term"thumb"is sometimes used instead of the"thumb finger"or the"thumb finger organ" when this can be done without any risk of confusion with the natural corresponding element of the hand.

The performance of the new mechanical hand is achieved with the aid of a number of new solutions. One of these is that the finger organ of the hand has drive arrangements, i. e. its drive motors and machinery turning the finger element together with the transmission means, incorporated in the respective finger organ. The property of having individually powered fingers gives the user in principle two functional advantages. First and

foremost it allows the fingers to adapt to the shape of an object and helps to produce a more stable grip at the same time as eliminating the need for powerful squeezing forces. In addition it allows the practical power grip to be employed in order to hold different objects. The finger organ is flexibly secured to the palm of the hand both for cosmetic reasons and for longer durability. The provision of power supply means in the fingers means in addition that the hand prosthesis equipped in this way is perfectly adequate for a hand prosthesis that comprises only part of a hand, which is not possible in mechanical gripping means that have a large number of drive arrangements and control means in the platform itself that corresponds to the middle hand.

The middle hand, i. e. the supporting platform, includes the control unit for the mechanical gripping means and may also include a lightweight battery pack. Since the transmission means and motors are encapsulated in the fingers, the space in the middle hand can simply be used for control units, control devices and batteries, which is not possible with arrangements according to the known technology.

The hand, i. e. the mechanical gripping device, is equipped with power and sliding sensors that are connected to the control unit of the hand. When an object is first grasped with the hand, a light grip is first of all applied, i. e. the squeezing forces between the fingers and the opposing thumb or palm of the hand are small. If the object begins to slip from the grasp the squeezing force increases automatically. The user can however ignore this function in every case and consciously control the gripping force.

The mechanical hand is of course intended for use with a glove made of a material that is extremely resistant to influences of various kinds. The glove is available in different sizes and with different pigmentation so as to create a natural appearance in combination with the hand described hereinbefore, which for its part provides natural hand movements.

The bendable, and with respect to the middle hand, pivotable fingers have an improved function and cosmetic appearance compared to conventional hand prostheses. In contrast to the latter, the hand described hereinbefore

has a natural thumb length, which imparts a more natural appearance to the hand. The hand also looks more natural when its parts move.

All finger organs (apart from the thumb) can turn about a joint between the middle hand and the said finger organ. The said finger organ has per se only two separate finger bones, which are mutually pivotably combined, i. e. they are combined in a finger joint. The front end of each finger organ is slightly bent since the natural fingers on a human hand are usually held in such a position. This facilitates the use of finger organs in the aforedescribed gripping operations. Research has shown that there is no serious limitation on the gripping capability of a hand that does not additionally employ a finger joint in every finger, since it is not absolutely necessary to bend the outermost part of a finger in a natural hand in order to achieve a desired grip. However, the front end of the finger organ has to be slightly modified so that the said grip can be executed without a further joint in the front part of the finger.

Some of the advantages of the mechanical hand according to the invention are the following: it is possible to exert different grips for different activities, it is possible to grip and handle objects of different sizes and shapes, it is possible to grip and turn a lock for example, and it is possible to exert a sufficient grip, i. e. that is not too hard or too forceful.

If, as preferred, the hand is equipped with five fingers and is furthermore provided with a cosmetic glove it bears a great resemblance to and is like a human hand. There is a degree of freedom for the finger organ to move.

Multiple fingers can react according to the size and shape of an object in a manner that is more adapted to the object compared to a two-finger or three-finger hand, and permit a firmer grip without the need for unnecessarily large gripping forces.

DESCRIPTION OF THE DRAWINGS Figs. la and 1b show diagrammatically in two perspective views from two different directions a complete mechanical hand according to the invention.

Fig. 2 shows a simplified hand with the thumb finger secured to the middle hand and with the possible pivotings of the thumb clearly shown.

Fig. 3 is a front view of thumb pivoting movements along the axis of pivoting of the base of the thumb.

Figs. 4a and 4b illustrate in two different views the precision grip exerted by the tip of the thumb touching the tips of both the index finger and middle finger.

Figs. 5a and 5b illustrate two different views of the power grip without the use of an opposing thumb.

Figs. 6a and 6b show two different views of the key grip in operation.

Fig. 7 diagrammatically illustrates a drive arrangement installed in a finger organ.

Figs. 8a and 8b show the enforced bending of a front finger bone in a finger organ, partly in the straight position and partly in the bent position.

Fig. 9 shows details of the transmission parts for executing, in relation to the lower arm, the tilting of the hand and pivoting of the hand joint at the wrist.

DESCRIPTION OF IMPLEMENTATION Some examples of the implementation of the invention are described hereinafter with the aid of the accompanying drawings.

Figs. la and b show an example of a mechanical hand 1 according to the invention. In the said hand the reference numeral 2 refers to a platform that simulates the palm of a human hand. For the sake of simplicity the platform 2 will be referred to as the middle hand (metacarpus) 2. A hand joint 4 is secured to the rear end 3 of the middle hand. The front part of

the hand joint will be referred to as the carpus 5. The rear part of the hand joint is in the present case termed the prosthesis connection 6, whose axis of symmetry is intended to be an extension of the longitudinal axis of an amputated human lower arm.

All the fingers with the exception of the thumb are termed ordinary fingers and are identified by the following reference numerals : index finger 10, middle finger 11, ring finger 12 and little finger 13. The ordinary fingers 10 - 13 are mounted in the front side 14 of the middle hand 2. Every one of the ordinary fingers is pivotably arranged at the base of the finger on an attachment to the middle hand 2 by means of a pivotable joint formed round an axis 15 that is for the most part parallel to the said front side 14 on the middle hand 2 with the said joint axis 15 in the finger base position substantially in a plane that forms an elongated section of the middle hand 2. The pivotable joints on the axis 15 allow the innermost finger bone on every finger 10-13 to bend about 90° from a substantially rectilinear direction to an angle of about 90° towards the palm of the hand, i. e. the inside 2b of the middle hand 2. The ordinary fingers have a second finger bone 10b-13b that corresponds to a combination of both the second and third finger bone in a human hand. The second finger bone 10b-13b on each finger organ 10-13 is joined to the first finger bone via a pivotable finger joint 9. The front part of the second finger bone 10b-13b on each finger organ 10-13 corresponding to the furthermost, third finger bone in a human hand is secured to the rear part of the said second finger bone 10b-13b in a slightly downwardly bent position. This serves to simplify the mechanism since there is no need for drive arrangements for a joint in each finger organ. The disadvantage of such a solution is not very serious since, as has already been mentioned in connection with investigations on human hand grips, it is found that the third finger bone on each ordinary finger is scarcely bent when the human hand executes one of the gripping operations described above. The second finger bone 10b-13b on each ordinary finger organ 10-13, with the exception of the fourth finger organ, is bent by means of a pantograph rod 16 secured to the finger joint 9 and, relative to the axis of the finger joint 9, towards the parallel extended axis. The said pantograph rod 16 is furthermore secured at its second, inner end, i. e. the rear end, to an axis that is extended parallel

with respect to the joint axis 15, whereby the pantograph rod 16 acts on the said second finger bone 10b-13b so that the said second finger bone is forced to bend inwardly when the associated ordinary finger is pivoted relative to the middle hand.

The thumb finger 17, hereinafter called the thumb for the sake of simplicity, is shown in more detail in Figs. 2 and 3. The all-round gripping capability that is provided with the aid of the new hand according to the invention is due in large part to the unique flexibility of the thumb 17.

Accordingly, the configuration of the thumb and the securement of the thumb to the hand will be described in more detail. The unique movement pattern in the thumb 17 is primarily achieved by means of a mounting installed on a thumb base 18 formed by a cylinder located on the mechanical hand in a position corresponding to the position of the thumb base (metacarpus 1) in the human hand. The thumb base 18 is consequently accommodated in the lower part of one side of the middle hand 2 adjacent to the first finger organ 10. The axis of symmetry 19 of the cylinder that forms the thumb base 18 is fixed and forms an angle a relative to the longitudinal axis 20 of the lower arm. In order to imitate the position of the thumb base in the human hand, the angle a in the said axis of symmetry 19 corresponds to the angle by which the thumb base in the human hand in a normal position deviates from the longitudinal axis of the lower arm, which means that the value of the angle a is preferably in the range 0° to 45°. The angle a may of course be increased up to 90°, but in this case the mounting of the thumb 17 would look unnatural and anaesthetic.

The thumb 17 is secured to the thumb base 18. The human hand has two finger bones. According to the invention the thumb 17 is not provided with these two separate finger bones that can be pivoted relative to one another. Instead, the two finger bones in the human thumb are simulated by a single integral thumb that projects at an angle from the circumferential surface of the cylinder that forms the thumb base 18. The said thumb 21 does not have any joints, but instead is bent in an arc that simulates the average curvature of a human thumb for various types of grip.

In order to impart a natural appearance to the thumb mounting, the angle a in the thumb base 18 is such that the axis of symmetry 19, in the forward direction of the hand, is at an increasing distance from the plane of the palm of the hand. In other words, this means that the axis of the base of the thumb 19 is somewhat downwardly inclined in the forward direction. In order to achieve the strong thumb grip that the hand should exert, the inner part of the thumb, here called the thumb root 21, is inclined upwardly from the thumb base 18 at an angle y, which may arbitrarily be chosen in the range 0° < y < 90°, but which conveniently may be in the range 30° < y < 60° so that it gives the hand a natural appearance when a glove is worn. The size of y depends of course on the angle that is chosen for the thumb base, i. e. the angle a.

The cylinder 18 of the thumb base is pivotably arranged. The cylinder can be pivoted about its own axis of symmetry 19 by means of an electric motor installed in the cylinder.

By means of the said arrangement of the thumb root 21 and thumb base 18 the thumb 17 enjoys a large degree of flexibility. When the motor inside the thumb base 18 is activated by means of control signals and in addition a voltage from a voltage source inside the middle hand 2 is applied to the motor, the thumb 17 pivots about the axis of symmetry 19.

On pivoting of the thumb in this way the tip of the thumb 17 describes a circle 22 as shown in Figs. 2 and 3.

When the thumb 17 pivots and at the same time one or both of the first finger organ 10 (index finger) and the second finger organ (middle finger) 11 is/are bent, it can be seen from the Figures that the thumb 17 and one or both of the said finger organs 10,11 can meet one another somewhere on the periphery of the circle 22. In this connection the precision grip can be exerted as shown in Figs. 4a and 4b. As can also be seen in Fig. 3, the inside of the front of the thumb 21 together with the tip of the thumb face the finger organs 10-13 when the thumb 17 is pivoted outwardly towards the finger organs in the same way as during the corresponding movement in a human thumb, when the same type of grip is exerted. This

is important as the pattern of movements should appear natural as if performed by a human hand.

The power grip exerted by a thumb in order to grip an object between the ordinary fingers and the thumb may also, like the precision grip, be exerted by a pivoting of the thumb 17 in the direction towards the fingers 10-13 along the path that is described by the circle 22, while at the same time the ordinary fingers 10-13 can be bent so as to touch the object, the thumb 17 acting on the object from the opposite side. The power grip is exerted by bending the fingers towards the inside of the palm of the hand without using the thumb 17, as can be seen in Figs. 5a and 5b.

The key grip is illustrated in Figs. 6a and 6b. It can be seen from these Figures that the ordinary fingers 10-13 are bent inwardly, as a result of which the thumb 17 is pivoted towards the side of the index finger 10. In this connection the front part of the thumb 17 comes into contact with the side of the index finger 10 during pivoting of the thumb 17, so that the thumb can be held with the desired force against the side of the index finger. In this way a key or other similar object can be held by the hand with sufficient force.

The arrangement for one of the ordinary fingers 10-13 is shown in Figs.

7 and 8. The innermost finger bone 10a corresponding to the index finger and taken by way of example comprises an electric motor 23 that has a shaft 24 that projects through a conical toothed wheel 25. The said conical toothed wheel 25 rests against a toothed gear ring 26. Since the toothed gear ring is fixed in relation to the middle hand 2 of the hand 1, the whole finger 10 is bent downwardly, which means that the angle between the inside 2b of the middle hand 2 and the finger 10 decreases when the motor 23 is activated in a first direction of rotation. At the same time as the finger 10 is bent downwardly, the pantograph rod 16 is caused to act on the second finger bone 10b on the finger 10 since the pantograph rod 16 is mounted eccentrically on the joints and both ends of the said first finger bone 10b and the innermost pantograph rod shaft 27 is fixedly mounted relative to the palm of the hand 2 as has been described

hereinbefore. The second finger bone 10b is thus forced to bend inwardly towards the palm of the hand when the inner finger bone 10a is bent downwardly by the drive action of the motor 23. When the finger 10 is already bent downwardly and the motor 23 is activated to rotate in the opposite direction, the finger straightens out. The remaining finger organs that correspond to the middle finger and the ring finger are constructed in a similar way.

The finger organs 10-13 are designed so they can be secured in a snap- fit manner to the middle hand 2 by means of snap fastenings 28 that engage in corresponding openings in the front side 14 of the middle hand for the said snap fastenings 28. The power connection and control signal connections engage one another when the finger organs 10-13 and the middle hand are connected in this way. The finger organs are suitably fastened to the middle hand 2 by means of fixing means, for example a screw, a locking pin, a rivet or an equivalent device that is inserted into a hole 29 adapted for this purpose.

The functions of the pivoting and tilting possibilities of the hand 1 are diagrammatically illustrated in Fig. 9. Here the arm rod 30 is an extension of the aforementioned prosthesis connection 6. The rod 30 is designed so that it can be fixed securely to the lower arm on an amputated arm. The front end of the arm rod 30 is connected in front (at the hand 1) to a conical toothed wheel 31, which forms part of a differential gear consisting of the said conical toothed wheel 31, a first differential toothed wheel 32, a second differential toothed wheel 33 and a differential shaft 34. The differential shaft 34 is divided into two parts, a first part 34a and a second part 34b. The said first wheel 32 is mounted on the said first shaft part 34a and the said second wheel 33 is mounted on the said second shaft part 34b. A pair of electric motors 35,36 are arranged inside the carpus 5. Each of the motors 35,36 is connected to a set of toothed wheels, respectively a first set of toothed wheels 37 and a second set of toothed wheels 38. When the first motor 36 is actuated, the first wheel set 37 causes the first differential shaft part 34a to rotate. In the same way, when the second motor 35 is actuated the second wheel set 38 causes the second differential shaft part 34b to rotate. If now both motors 36,35 are

operated so that they have the same direction of rotation, both sets of toothed wheels 37,38 cause the differential shaft parts 34a and 34b to rotate in the same direction. Accordingly, both the first and second differential toothed wheels 32 and 33 rotate in the same direction. Since both the first and second differential toothed wheels 32 and 33 rest against the same conical toothed wheel 31 on the rod 30, the said conical toothed wheel 31 cannot be caused to rotate without locking. On account of the locking action the front part of the carpus 5 is forced to tilt by an angle 8 upwardly or downwardly, principally within an angle of 180°C. If on the other hand the motors 36,35 are caused to rotate in different directions, then the differential causes the whole carpus 5 to pivot around the arm rod 30 by an angle, which is preferably in an angular range of 180°, in which the said pivoting of the carpus 5 can take place in both directions of pivoting depending on the directions of rotation in the motors.

Depending on the degree of loss of the hand or arm, the size of the mechanical hand can be adapted as appropriate. The hand joint 4 may for example be omitted if the human hand joint is still available and accessible. The size of the platform 2 may be reduced if the shortened human hand still has a part of the palm of the hand remaining. This variant is made possible by the hand 1 according to the invention, since the drive arrangements of the finger organ are localised inside the said finger organ.

The control of the various elements of the mechanical hand 1 by means of control signals may be effected by the transmission and reception of myogram signals from muscles in for example the human arm. The said muscles are stimulated depending on nerve signals from the human brain, so that the muscles can exert a grip according to commands from the brain. Through movements of the muscles myogram signals are transmitted and received and are converted in a control unit into control signals that are used to activate the intended finger organs 10-13 and to actuate the appropriate motors so as to drive the said finger organs according to the desired pattern. The tilting and pivoting movements of the hand part may be controlled in a similar way. The control unit is

accommodated inside a storage space in the platform 2 that forms the middle hand. Power is supplied to the motors from lightweight batteries that can likewise be accommodated in the space in the middle hand. The hand 1 is furthermore provided with pressure sensors and sliding sensors for detecting that sufficient forces are applied in order to exert the desired grip.