FIELD OF THE INVENTION The present invention relates to a hand prosthetic. The invention also relates to a robotic gripping device.

BACKGROUND OF THE INVENTION Current hand-prosthetics are rather inflexible and do not allow the disabled user to have an everyday similar to a non-disabled person. The challenge in developing a functional hand-prosthetic is determined by a balanced combination of weight, speed, volume, gripping force, controllability and functionality, dictated by the capabilities and parameters of the human hand. Besides this, a hand-prosthetic has to be robust to be able to survive the scrutiny of daily usage.

The majority of today's electric hand-prosthetics are controlled by one or two signals from a patients residue muscles. Electrodes are placed externally on these residue muscles and the patient can, by contracting these muscles, open and close his prosthetic. This kind of control is known as "myo-electric control". By contracting a muscle slow or fast, the patient can control the speed and the gripping force of the prosthetics fingers. This is called "proportional control" and is used in today's electric driven hand-prosthetics. Most of hand-prosthetics today are further driven by electric actuators powered by a battery worn by the user. These hand-prosthetics are however often not very fast in displacing a moveable finger or digit nor do these hand-prosthetics provide a sufficiently strong gripping mechanism, e.g. the hand-prosthetic available from Touch Bionics.

Recently, the "Fluidhand" from Karlsruhe-based Research Center and the

Orthopedic University in Heidelberg in Germany has been disclosed, cf.

http://www.handprothese.de/handprothese.html. The "Fluidhand" is operated at a rather low pressure (9-10 bar) which means that the gripping force is relatively low. Another disadvantage is the use of externally mounted hoses and couplings which are quite vulnerable in many everyday situations. For hydraulic driven hand-prosthetics, the possibility of a sudden leakage is highly problematic for a user.

Another hydraulic-based hand-prosthetic has been presented by Oak Ridge National Laboratory (2008, www.ornl .gov) . This hand-prosthetic is using an experimentally developed piezoelectric actuated pump in their so-called

mesofluidic hand. This pump is apparently a construction of a prototype pump that has been designed, fabricated and tested earlier in 2003. The advantage of the ORNL system is that it doesn't generate much heat because of the

piezoelectric pump. This system has the possibility to deliver variable pressures with different fluid volumes. However, the design is apparently not as affective yet as a system with an electromotor because of problems with internal leakage.

Hence, an improved hand prosthetic would be advantageous, and in particular a more efficient and/or reliable hand prosthetic would be advantageous.

OBJECT OF THE INVENTION

It is a further object of the present invention to provide an alternative to the prior art.

In particular, it may be seen as an object of the present invention to provide a hand prosthetic, in particular a prosthetic with 5 displaceable digits or fingers, that solves the above mentioned problems of the prior art with providing a both fast and strong gripping mechanism in a hand prosthetic.

SUMMARY OF THE INVENTION

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a hand-prosthetic with a plurality of independently displaceable digit members, the hand-prosthetic being myo-electrically controllable by a user, the hand-prosthetic comprising :

a casing,

a plurality of displaceable digit members, each digit member being rotatably mounted on the casing, and a hydraulic circuit arranged for displacing the digit members, the hydraulic circuit comprising :

- a first pump, said first pump being arranged for low pressure, high volume operation

- a second pump, said second pump being arranged for high pressure, low volume pump operation as compared to said first pump,

- a motor for driving said first and said second pump,

- a decoupling device arranged for decoupling the first pump from the hydraulic circuit,

wherein the decoupling device is arranged to decouple the first pump from the hydraulic circuit during a closing operation of the hand-prosthetic.

The invention is particularly, but not exclusively, advantageous for obtaining a hand-prosthetic with high functionality, which can be controlled with 2 (or more) myo-electric signals from the user. The disclosed hand-prosthetic may be fast, robust, have a high gripping force, use only the volume of the natural hand and have an acceptable weight, for instance less than 450 gram. In short the present invention may enable a relatively small building volume, high power/weight ratio and economic energy consumption.

Preferably, the decoupling device may be mechanically, electrically, hydraulically or magnetorheologically (RM) controllable. Typically, the decoupling device may be a clutch of a conventional kind, where, for the hydraulic case, the system pressure may be used to generate the decoupling force.

It is to be understood that the digit members are coupled to the hydraulic circuit in the sense that the hydraulic circuit is arranged for displacing the digit members based on the pressure within the hydraulic circuit.

In one embodiment, the second high-pressure pump may be operated in a pressure regime which is at least 2 times, preferably 2.5 times, or most preferably at least 3 times higher than the pressure regime of the first low-pressure pump. More specifically, the first pump may be operable at a pressure interval of 10-30 bar, preferably 15-25 bar. Even more specifically, the second pump may be operable at a pressure interval of 50-90 bar, preferably 60-80 bar. The hydraulic circuit of the hand-prosthetic may preferably be embedded in the casing, partly or completely, in order to protect the circuit against external wear and/or chocks.

Preferably, the first pump, the second pump, the decoupling device, and/or the said motor of the hydraulic circuit may be arranged to be mounted outside of the casing on the arm portion of the user or similar parts of the user. For instance, the pumps may be fixed on an underarm of a user.

In one embodiment, each digit member may be connected to a hydraulic actuator, where each hydraulic actuator may be independently controllable by pressure control means for each digit member in order to provide realistic hand-like actuation of the hand-prosthetic. More specifically, the pressure control means for each digit member may comprise a valve in front of the hydraulic actuator, e.g. it may be electrical valves, piezo valves, or of the MEM-type, etc. It may

alternatively be a first and a second valve connected in series.

In another embodiment, an angle sensor may be mounted in relation with a digit member to determine the rotational position of the corresponding digit member to provide accurate control of the digits. Preferably, at least one digit member may have a corresponding hydraulic cylinder with a displaceable piston, the piston being longitudinally displaceable arranged in the cylinder, and the piston comprising an end portion being in a cable or gear cooperation with a gear wheel, or pulley, capable of actuating the displacement of the said digit member. Thus, a transmission may actuate one or more fingers not necessarily all fingers or digits. Typically, a resilient means may be mounted to cooperate with a digit member to provide an opening force for each digit member, e.g. a spring will force the digits to open if not countered by the hydraulics.

Preferably, hydraulic circuit, upon a closing operation of the hand-prosthetic, may be arranged for being driven by the first and the second pump, and, as the digit members come into contact with an object to be gripped, the decoupling device may be arranged to de-couple the first pump thereby allowing the second pump to drive the hydraulic circuit. Thus a closing operation is provided with, initially, a fast gripping, and, subsequently, a slower but stronger gripping in the last part of the closing operation. Preferably, a decoupling valve may be provided in front of the first pump to hydraulically close off the first pump during high pressure operation in a closing operation of the hand-prosthetic, and thereby shut off the first pump in order to prohibit the oil (pressure) from leaking away over the first pump.

An adaptive grip of the digit members is provided because of the fact that fluid in a pressurized system follows the path of least resistance. This results in all digit members to follow the contours of a gripped object before considerable gripping force is exerted by the digit members.

In one embodiment, wherein the second pump may be driven directly by the motor and the first pump is coupled to the motor by the decoupling device. In an alternative embodiment, the first and the second pump may be driven directly by the motor, and the first pump is arranged to be de-coupled by the decoupling device, e.g. by a common axis through the pumps.

In a second aspect, the present invention relates to a method for operating a hand-prosthetic with a plurality of independently displaceable digit members, the hand-prosthetic being myo-electrically controllable by a user, the method comprising :

- providing a casing,

- providing a plurality of displaceable digit members, each digit member being rotatably mounted on the casing, and - providing a hydraulic circuit arranged for displacing the digit members, the hydraulic circuit comprising :

- a first pump, said first pump being arranged for low pressure, high volume operation

- a second pump, said second pump being arranged for high pressure, low volume pump operation as compared to said first pump, - a motor for driving said first and said second pump,

- a decoupling device arranged for decoupling the first pump from the hydraulic circuit,

wherein the decoupling device is arranged to decouple the first pump from the hydraulic circuit during a closing operation of the hand-prosthetic.

In a third aspect, the present invention relates to a robotic gripping device with a plurality of independently displaceable gripping members, the device comprising : a casing,

a plurality of displaceable gripping members, each digit member being rotatably mounted on the casing, and

a hydraulic circuit arranged for displacing the gripping members, the hydraulic circuit comprising :

- a first pump, said first pump being arranged for low pressure, high volume operation

- a second pump, said second pump being arranged for high pressure, low volume pump operation as compared to said first pump,

- a motor for driving said first and said second pump, and

- a decoupling device arranged for decoupling the first pump from the hydraulic circuit,

wherein the decoupling device is arranged to decouple the first pump from the hydraulic circuit during a closing operation of the gripping device.

Though, the principle of the present invention is particularly suited for working in a hand-prosthetic, it is contemplated that the advantages of the invention may also be beneficially applied in connection with gripping devices in general, in particular gripping devices for robots of various kinds, e.g . industrial robots, domestic robots, etc. The first, second and third aspect of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE FIGURES The invention will now be described in more detail with regard to the

accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible

embodiments falling within the scope of the attached claim set.

Figure 1 is a schematic drawing of the bone parts of a human hand,

Figure 2 is a schematic drawing of an embodiment of the invention,

Figure 3 shows schematic drawings for two embodiments of the invention,

Figure 4 shows a hydraulic circuit according to the present invention, Figure 5 shows a perspective drawing of a part of a hand-prosthetic according to the present invention,

Figure 6 shows another perspective drawing of a hand-prosthetic according to the present invention, and

Figure 7 is a flow chart of a method according to the invention. DETAILED DESCRIPTION OF AN EMBODIMENT Figure 1 is a schematic drawing of the bone parts of a human hand. The drawing is included because the hand-prosthetic according to the present invention in preferred embodiments, at least to some extents, mimics or resembles the actual hand of a human being. On the outer most part the distal phalanges are located, except for the thumb digit on the right, followed by a joint to the intermediate phalanges. Next thereto the proximal phalanges and metacarpals follow; the metacarpals are integrated onto the carpals as seen in Figure 1. Thus, several anatomical parts, e.g . joints and bone parts, have corresponding parts, e.g.

mechanical joints or digit member parts, respectively, in the hand-prosthetic as it will be apparent from this description. Figure 2 is a schematic drawing of an embodiment of the invention. The drawing schematically illustrates the hydraulic circuit forming part of the hand-prosthetic. The hydraulic circuit is arranged for displacing the digit members (not shown for clarity) by actuation of three hydraulic actuators 201a, 201b, and 201c, though typically five actuators, one for each digit member of the hand-prosthetic, is applied. Each digit member is connected to a hydraulic actuator 201, each hydraulic actuator being independently controllable by pressure control means, e.g. a valve, 202a, 202b, and 202c for each digit member. The hydraulic circuit further comprises a first pump 203, said first pump being arranged for low pressure, high volume operation, e.g. the first pump is operable at a pressure interval of 10-30 bar, preferably 15-25 bar.

The hydraulic circuit also comprises a second pump 204, said second pump being arranged for high pressure, low volume pump operation as compared to said first pump 203, e.g. the second pump is operable at a pressure interval of 50-90 bar, preferably 60-80 bar.

For driving said first 203 and said second 204 pump, a motor 205 is provided and appropriately connected to each pump as schematically indicated by the arrows from the motor 205 to each of the pumps 203 and 204. The motor 205 is preferably a servo-motor. Moreover, a decoupling device 206 is arranged for decoupling the first pump 203 from the hydraulic circuit. The decoupling device may be any suitable kind of decoupling device, such as a decoupling device being mechanically, electrically, hydraulically or magnetorheologically (RM) controllable. The decoupling device is typically a clutch, preferably of a mechanical or a hydraulic kind. The decoupling device 206 is arranged to decouple the first pump 203 from the hydraulic circuit during a closing operation of the hand-prosthetic. This pump-decoupling device configuration of the hand-prosthetic enables a small building volume, high power/weight ratio and/or economic energy consumption.

Figure 3 shows schematic drawings for two embodiments of the invention showing more detailed configurations of how to arrange the decoupling device 206 and the motor 206 with respect to the first 203 and second 204 pumps. In the upper embodiment labelled A, the decoupling device 206 is positioned between the first 203 and second 204 pumps. Thus, the second pump 204 is driven directly by the motor 205, and the first pump 203 is coupled to the motor by the decoupling device 206. This is presently the preferred solution.

In the lower embodiment labelled B, the decoupling device 206 and the motor 205 are positioned between the first 203 and second 204 pumps. Thus, the first 203 and the second 204 pump are driven directly by the motor 205, the first pump being arranged to be de-coupled by the decoupling device 206. For instance, a common axis (not shown) through the pumps may be provided, the common axis having a clutch for decoupling the first pump 203.

In the context of the present invention, it is to be understood that where the terms "motor" and/or "pump" are used, the motor could comprise several motors combined or integrated into a common motor unit i.e. a "motor", and, similarly, that the pump could comprise several pumps combined or integrated into common pump unit, i.e. a "pump".

Figure 4 shows a hydraulic circuit according to the present invention in more detail compared to Figure 2, and also five digit members 401 and 402 with some mechanical components are shown.

The index- 401a, middle- 401b, ring- 401c and little 401d -finger have each three parts corresponding to the anatomical phalanges, cf. Figure 1. The rotation of these fingers proximal parts or "phalanges" is done in the four mechanical joints 403, corresponding to metacarpophelangeal joints (MCP), by means of 4 hydraulic actuators i.e. cylinders 404. The rotation of each digit members 401 is done by means of a cable 405. The cable is attached to the cylinders 404, or close thereto, and guided over a wheel to a pulley or gear wheel that is mounted in front of the cylinders 404. The digit members 401 will rotate when the pulley rotates under actuation of the hydraulic cylinders 404. The angle of rotation is determined by the ratio of the diameters of the wheel and the pulley. Thus, each digit member 401 has a corresponding hydraulic cylinder 404 with a displaceable piston, the piston being longitudinally displaceable arranged in the cylinder, and the piston comprises an end portion having a geared part 417 acting on the gear wheel. The digit member 402 corresponding to the thumb is similarly operated with hydraulic actuator 404, except that this digit member 402 has an additional degree of freedom provided by the rotational coupling 410. The coupling 410 may be manually, hydraulically or electrically operated by a user.

The hydraulic actuators 404 are provided with compensators 411 having the dual purpose of storing the extra volume of oil as the cylinder-rods translate into the cylinders, and having the function to give a positive pressure on the suction-side of the pumps 203 and 204. This positive pressure is necessary for the pumps to be able to suck in the hydraulic fluid, e.g. oil, and prevents under-pressure, as this would result in damage to the pumps. There is no compensator situated by the thumb in this embodiment, because this is not necessary because the low pressure side (left to the valves 415) is one connected subsystem. It is therefore not important where the compensator(s) 411 are situated left of the valves 415. Only the total volume of oil that the compensator(s) 411 can house or

accommodate is important. So it could alternatively be one big compensator or 2 or more smaller compensators as well. Each digit member 401 and 402 is connected to a hydraulic actuator, 404, where each hydraulic actuator is independently controllable by pressure control means, e.g. the pressure control means for each digit member may comprise a first 415a and a second 415b valve connected in series in front of each hydraulic actuator 404. The two electrical valves may be of an electric, a piezo, or a micro electrical mechanical (MEM) type, etc. Preferably, the valves 415 are micro-valves.

Typically, a normal valve always uses electro magnets that act on a steel rod to control an orifice, i.e. the actual part that controls the opening, for opening and closing of a valve. In a micro valve it will be understood that the orifice is the electric controlled part (piezo, MEM). The possible flow and pressure through direct controlled piezo, MEM-valves is very low compared to normal valves and has therefore no use in ordinary hydraulics.

Additionally, a decoupling valve 416 is provided in front of the first pump 206 to hydraulically close off the first pump during high pressure operation in a closing operation of the hand-prosthetic. When the hand-prosthetic is closing, pumps 203 and 204 can deliver a high volume at low pressure, the fingers or digits 401 and 402 will move at high speed and with low gripping force. Subsequently, the fingers 401 and 402 come in 5 contact with an desired object for gripping, the system hydraulic pressure will rise above typically 20 bars, and the decoupling device or clutch 206 will couple out the first pump 203. In affect, the second pump 204 can now use the full torque of the motor 205 to deliver high pressure (strong grip) at low volume (low speed of the fingers). Valve 416 is an electric controlled 2/2 valves, which is normally 10 closed. This valve ensures that when the first pump 203 is coupled out so that the high pressure from the second pump 204 doesn't flow back over the first pump 203.

The valves 415 and 416 are micro valves. Valve 415b is used to keep cylinders 15 404, being under a load, in a fixed position without having to use the pumps. This saves energy and results in less noise. Valve 415a is used to control which finger(s) 401 and 402 are moving at the same time.

Operation of these valves 415 and 416 is done with very little operation current 20 and they exert a relatively little opening force. They are not able to open against higher pressures than 5-10 bars. In order to be able to open such a valve under high pressure, the pump will equal out the pressure over the valve. If for example the cylinder of the thumb 402 is under high pressure, and the thumb has to be opened, it works as follows:

25

- Valve 415a is directed open (electric valve 415a is already open because of the high pressure in the cylinder of the thumb 402).

- The motor 205 gets the signal to drive the first 203 and second 204 pumps for a few microseconds to put high pressure on the system.

30 - Valve 415b will now be able to be directed open because of equal pressure on both sides of the valve.

-Motor 205 gets signal to stop.

- Valve 416 is directed open (there is no pressure in the system). - Valve 415a and 415b are now open and the motor will get the signal to drive the first 203 and second 204 pumps to transport the oil out of the cylinder of the thumb 402, resulting in an opening of the thumb. This process takes typically a few milliseconds to complete, therefore this delay of the patient's control will not be perceived. In the same manner all other fingers 401 or 402 can be opened and closed.

The micro-valves 415 and 416 are relatively small and light, and they can handle high static pressure. This makes it possible to get a high functionality in a limited space at low weight.

The hydraulic system may be considered to have a pump-unit (pumps 203 and 204) connected to 5 hydraulic cylinders 404. When 2 or more cylinders are causing rotation from the same angular position, they will rotate at the same angular speed. When one of these rotating fingers or digits 401 or 402 comes in contact with an object to be gripped, the oil-flow will follow the path of the least resistance and rotate the other finger(s) until they are in contact with the object as well. When all rotating fingers 401 and 402 are in contact with the gripped object, the system -pressure rises and gripping-force is exerted . This results in an adaptive grip, where all fingers 401 and 402 can "shape" itself to follow the contours of the gripped object. Thus, a fast and adaptive grip results of the hand- prosthetic. It ensures a tight grip on every object and exact positioning of the hand-prosthetic is not necessary. This results in less necessary visual control of the user and therefore a more user-friendly system.

The pumps 203 and 204 control the angular speed of the fingers 401 and 401 while closing and opening. These pumps can only deliver pressure as the fingers close. The force for opening the fingers is controlled by springs (not shown). The system is a servo-system which means that the fingers 401 and 402 can grip with any given force, can move at any given speed and can stop at any given position within the limits of the system.

All fingers 401 and 402 are equipped with an angle sensor 402 and 420 positioned in the joint corresponding to the metacarpophalangeal (MCP, cf. Figure) joint. The thumb 402 has an extra angle sensor 421 in the carpometacarpel joint (CMC, cf. Figure 1). In this CMC joint the oil pressure- and return-transport is done by means of a rotating coupling 410 that enables the thumb 402 to be moved into any opposed position of the fingers whilst ensuring a continuously control of the thumb.

The corresponding CMC joint of the thumb 402 preferably has a fixation

mechanism allowing the thumb to be (manually, hydraulically or electrically) placed in a number of exact positions. These positions have a fixed angle and are recognized by associated software to create a gripping-pattern when the hand- prosthetic is activated.

Examples of gripping-patterns are: - Credit-card grip: where the fingers close first and the thumb afterwards rotates down on the side of the index finger.

Pinch grip: where the index-, middle-finger and thumb touch each other at the finger tips.

Pointing with index finger: where first the middle-, ring- and little-finger close and the thumb afterwards rotates down on these fingers.

Power grip: where all fingers close at the same time and the thumb afterwards rotates down on the fingers.

This makes it possible to create advanced gripping-patterns whilst the hand- prosthetic is controlled by only 2 signals. The gripping-patterns of the hand- prosthetic in these fixed positions of the thumb, are free programmable.

Programming can be done by means of a person wearing a data-glove that "teaches" the hand-prosthetic how to move the fingers when the thumb is in a certain position. Whilst programming with the data-glove, the hand-prosthetic is copying these movements. When the gripping-pattern is complete, the data can be stored onto the hand-prosthetics microprocessor.

The positions of the thumb in between the fixed angles have no programmed pattern. When the hand-prosthetic in this situation gets a signal to close, all fingers will rotate at the same time. The patient is still able to stop the motion any finger by holding this finger or by putting it against an object. Some positions of the thumb and index finger have to be protected in order to avoid too much force on the side of the finger. The software measures the position of each finger at any time and the pressure of the pump will be limited in such a scenario. The 5 free programmable gripping-patterns give the opportunity to have each hand- prosthetic optimized and customized to a patients needs.

Figure 5 shows a perspective drawing of a part of a hand-prosthetic 600 according to the present invention . Similarly to Figure 4, the digit members 401 and 402

10 can be seen but in this Figure without the outer parts in order to provide an

improved view of the hydraulic cylinders 404, and especially the hydraulic pistons, 501 and 502. The cylinder 404' of digit 401d has been left partly open (cut in half) to provide a view of the inside. In particular, the hand-prosthetic 600 comprises a casing 503 to protect the hydraulic circuit. The hydraulic circuit is kept in place by

15 appropriate fastening means, e.g . bolts, 505 to keep the circuit in position also under high pressure operation .

The hand-prosthetic 600 is provided with a joint 504 for connecting the remaining part of the users arm. In one embodiment, the first pump 203, the second pump 20 204, the decoupling device 206, and/or the motor 205 of the hydraulic circuit is arranged to be mounted outside of the casing on an arm portion of the user, i.e. the hydraulic circuit comprises a portion located on the arm .

Figure 6 shows a full perspective drawing of a hand-prosthetic 600 according to 25 the present invention with the digit members 401 and 402 mounted . It is noted that the casing 503 preferably protects and confines all the hydraulic components, and thereby the complete circuit.

Figure 7 is a flow chart of a method for operating a hand-prosthetic with a

30 plurality of independently displaceable digit members, the hand-prosthetic being myo-electrically controllable by a user, the method comprising :

SI providing a casing 503, 52 providing a plurality of displaceable digit members 401 and 402, each digit member being rotatably mounted on the casing, and

53 providing a hydraulic circuit arranged for displacing the digit members, the hydraulic circuit comprising :

- a first pump 203, said first pump being arranged for low pressure, high volume operation

- a second pump 204, said second pump being arranged for high pressure, low volume pump operation as compared to said first pump,

- a motor 205 for driving said first and said second pump,

- a decoupling device 206 arranged for decoupling the first pump from the hydraulic circuit, wherein the decoupling device is arranged to decouple the first pump from the hydraulic circuit during a closing operation of the hand-prosthetic.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.