Patent Application
20230398002
The invention relates to a prosthetic knee joint with a joint lower part, a joint upper part and a hydraulic system with at least one switch valve, wherein
Such a prosthetic knee joint is known from DE 10 2018 111441 A1.
Prosthetic knee joints have been known from the prior art for many years. They are important components of leg prostheses and should imitate the functions of a human leg as naturally as possible. In this context, a human knee is able to allow movements in some situations and to block them in others. This is important in order to provide the required stability whenever possible. The versatility of the human knee presents a challenge for a prosthetic knee. To be able to perform movements at different speeds and with different degrees of damping, prosthetic knees are often equipped with a hydraulic system. A prosthetic knee in which a hydraulic system is installed usually has two hydraulic chambers, a so-called extension chamber and a flexion chamber, which are fluidically connected to each other. For this purpose, at least one connecting line is provided. Both chambers contain a piston that can move inside the chamber and thus alter the volume of the respective chamber. It can be designed as a single piston. In this case, the two chambers are arranged on two opposite sides of the piston, which is preferably designed as a rotary piston. This causes the volume of the one chamber to reduce when the volume of the respective other chamber increases. Of course, two pistons can also each be arranged in a cylinder and each limit one chamber in the respective cylinder.
The joint upper part is mounted relative to the joint lower part such that it can be pivoted about a pivot axis.
The flexion describes a bending of the knee, i.e. a movement of the joint upper part relative to the joint lower part in a first direction, referred to as the flexion direction. During this movement, hydraulic liquid, for example a hydraulic oil, flows from the flexion chamber into the extension chamber. During the reverse movement, referred to as extension, the knee joint is extended. In the process, the hydraulic liquid flows from the extension chamber into the flexion chamber. In this case, the extension chamber is the chamber in which the pressure increases during extension, and the flexion chamber is the chamber in which the pressure increases during flexion.
The speed at which the hydraulic fluid moves from the one chamber into the other chamber is decisive for the speed of the movement of the joint, i.e. the movement of the joint upper part relative to the joint lower part. It depends, among other things, on the flow cross-section of the connection line. DE 693 12 771 T1 discloses a device that can be used to control a hydraulic system in an upper leg prosthesis.
Different speeds are advantageous at different phases in the gait cycle, so that a switch valve is integrated into the prosthetic knee joint. It is thus possible, for example, to switch between two different connection lines with different flow cross-sections and therefore different flow resistances. The switch valve features a valve housing in which a switch element is located. The switch element is designed, for example, as a displaceable piston or slide. The switch element is a component which, by displacing it into a first position or into a second position, can change a flow cross-section or a flow velocity within the hydraulic system and/or can open or close a hydraulic line or fluid connection. The valve housing is the component of the prosthetic knee joint in which the switch element can be displaced into the first and second position. It can also be designed as a separate component. Alternatively, another component of the prosthetic knee joint, such as the joint lower part or the joint upper part, can form the valve housing. For this purpose, a cavity or a bore is provided in the respective component, for example, in which the switch element moves.
This switch element can be brought into a first position and into a second position relative to the valve housing. When in the first position, the valve is in a first state which, for example, opens a first connection line. In a preferred embodiment, this connection line has a high flow resistance, so that the movement of the knee joint is heavily damped. As a result, only a slow and load-bearing movement of the joint upper part relative to the joint lower part is possible, which is advantageous, for example, in the stance phase while walking, when sitting down, or descending stairs or a slope.
If, however, the switch element is brought into the second position relative to the valve housing, the switch valve is in a second state in which another path is opened for the hydraulic liquid. This may be a second connection line, for example. Preferably, the damping of the movement of the knee joint in this state of the valve is weaker, which can be achieved, for example, by the second connection line having a lower flow resistance than the first connection line. This second state is advantageous in the swing phase of a step, for example, as in this phase the knee does not bear any load and heavy damping would in this case be unphysiological.
The switch element of a prosthetic knee joint according to the preamble divides the interior of the valve housing into a first chamber and a second chamber. The switch element is preferably located completely inside the valve housing and is preferably completely surrounded by the respective hydraulic fluid.
To be able to move the switch element from the first position into the second position and thus switch the switch valve, an actuation mechanism is preferably provided, by means of which a force can be applied to the switch element. The switch element is pre-tensioned by at least one pre-tensioning element, for example in the form of a spring, particularly a coil spring. The pre-tension is preferably directed towards the first position of the switch element, which causes the stronger damping.
The first position of the switch element relative to the valve housing can depend on a large number of parameters. Among other factors, it can depend on the magnitude of the pre-tension, the hydraulic pressure in the hydraulic system, possible flow paths that the hydraulic liquid can take through the system, particularly from one chamber to the other, the general dimensions of the prosthesis, especially the prosthetic knee, the type of prosthetic knee, to name but a few parameters. The exact determination of the first position of the switch element relative to the valve housing is, however, very significant, as it determines the displacement path required along which the switch element must be displaced in order to go from the first position into the second position. As such, it also determines how quickly the switch valve reacts and, for example, at which point in a step cycle the switch valve is switched from the first state, in which the switch element is in the first position, into the second state. However, the pre-tensioning element is unfortunately only located inside the valve and therefore mostly inside the hydraulic system and often in the hydraulic liquid, so that it is difficult or even impossible to access. The remaining parameters are often not obtained until assembly of the knee joint and are difficult or impossible to determine beforehand. The adjustment of the first position of the switch element relative to the valve housing is therefore barely possible or only with considerable effort.
The prosthetic knee joint also has a spring element, which is also configured to apply a force, namely the counter-force, to the switch element. This can happen directly, for example by the spring element being in mechanical contact with the switch element, or indirectly, by the spring element transmitting the force to an intermediate component and the force being transmitted from there directly or indirectly to the switch element. If no further force is applied to the spring element, thus strengthening the counter-force, the pre-tension is greater than the counter-force and the switch element is in the first position. In this position, the flow resistance that counters the flow of the hydraulic liquid through the hydraulic system and in particular through the switch valve is greater than in the second position of the switch element. As such, the standard setting of the valve ensures a high resistance that opposes a pivoting of the joint upper part relative to the joint lower part.
If an external force is applied to the spring element that enhances the counter-force, it can overcome the pre-tension and displace the switch element from the first position into the second position. If the external force decreases at a later point in time or disappears completely, the counter-force also reduces so that it is once again smaller than the pre-tension. The pre-tension then displaces the switch element back into the first position. The greater the overall force resulting from pre-tension and counter-force, the faster this happens.
The invention therefore aims to improve a prosthetic knee joint in such a way that a first position suitable for controlling the knee joint can be easily achieved.
The invention solves the addressed task by way of a prosthetic knee joint according to the preamble of claim 1, characterized in that, within the valve housing and/or the switch element, at least one fluid connection is arranged between the first chamber and the second chamber. If, for example, an external force is now applied to the spring element that opposes the pre-tension of the pre-tensioning element, the spring element is preferably tensioned, particularly compressed, and thus charged with potential energy. As a result, it exerts a force on the switch element. This can occur directly by, for example, an end of the spring element resting on the switch element, or indirectly by the spring element initially transmitting its force to one or multiple further components of the prosthetic knee joint, which transfer the force directly or indirectly to the switch element.
If the switch element is to avoid this force, it must be displaced against the pre-tension of the pre-tensioning element. As a result, one of the two chambers within the valve housing becomes smaller and the other chamber becomes larger. At least part of the hydraulic liquid must therefore leave the chamber that reduces in size. At the same time, hydraulic liquid has to flow into the chamber that increases in size. The at least one fluid connection between the first chamber and the second chamber is provided for this purpose, said connection being located, according to the invention, inside the valve housing. The cross-section of the at least one fluid connection is decisive for the amount of hydraulic fluid that flows from the reducing chamber, through the fluid connection and into the enlarging chamber. Due to the fact that the fluid connection, which can also be referred to as a bypass, is arranged inside the valve housing, no additional installation space is required, which is usually limited in prosthetic knee joints. Preferably, multiple, for example at least three, fluid connections are provided. The fluid connections can be designed to be identical. For example, they are the same length and/or have the same cross-section, for example circular or polygonal, and/or the same cross-sectional area, preferably less than 1 mm2, especially preferably less than 0.5 mm2 and especially preferably less than 0.385 mm2. Preferably, they generate the same flow resistance. This does not necessarily require an identical length or an identical cross-section or an identical cross-sectional area, but it is advantageous. The fluid connections can also be designed to be different and, for example, generate flow resistances that are not identical.
If the valve is to be switched, a force must be applied to the switch element and the latter moved from the first position into the second position or vice-versa. According to the invention, the movement of the switch element inside the valve housing is damped due to the interior of the valve housing being divided into two chambers by the switch element, the two chambers being filled with hydraulic fluid. To move the switch element, it is therefore necessary to guide fluid from the one chamber into the other chamber. This is only possible through the fluid connection, regardless of the switch state of the valve, i.e. the position of the switch element, so that the cross-section of this connection is decisive for the speed at which the switch element can react to an external force impact.
The damping of this reaction means that brief force impacts, which should not usually lead to a change in the switch state of the valve, do not persist for long enough to transfer a sufficient amount of the fluid between the two chambers inside the valve housing in this time and to switch the valve.
In a preferred embodiment, the multiple fluid connections are designed in such a way that they are effective in different positions of the switch element. To this end, multiple indentations, such as notches, grooves or flutes, are arranged in the inner wall of the valve housing, which is preferably in contact with the switch element. These indentations preferably differ in length. On the one hand, this can mean that such an indentation is closed by the switch element moving from the first position into the second position. On the other hand, such a fluid connection can also be opened by the moving switch element.
To ensure that an indentation in the inner wall of the valve housing can form a fluid connection between the first chamber and the second chamber, one end of the indentation must lie in the area of the inner wall that limits the first chamber and the other end in the area of the inner wall that limits the second chamber. When the switch element is displaced from the first position into the second position or vice-versa, the one chamber gets bigger and the other smaller. This also causes the parts of the inner wall that limit the first chamber and the second chamber to change.
Preferably, at least one fluid connection extends through the switch element. Particularly preferably, the at least one fluid connection is a bore arranged in a surface of the switch element that is perpendicular to the direction of displacement of the switch element. Preferably, multiple identical or differently designed fluid connections are provided. Alternatively or additionally, indentations are preferably arranged on the outside of the switch valve.
Alternatively or additionally, at least one fluid connection extends through the valve housing. Particularly preferably, such a fluid connection is arranged as an indentation, notch or channel in a wall of the valve housing that limits the interior of the valve housing. In this embodiment, the cross-section of the fluid connection is also decisive for the amount of fluid that is pushed by the force exerted by the spring element from the reducing chamber into the enlarging chamber.
Alternatively or additionally, at least one fluid connection extends between the valve housing and the switch element.
Irrespective of the design and/or number of the fluid connections provided, the smaller the overall cross-section of all available fluid connections, the greater the resistance to movement of the switch element due to the flow resistance of the at least one fluid connection.
If the switch element is in the first position, the hydraulic system provides a large resistance to a movement of the joint lower part relative to the joint upper part. In this state, the movement is heavily damped. In the second state of the switch valve, the switch element is in the second position and the movement of the joint lower part relative to the joint upper part is gently damped. The prosthetic knee joint also comprises at least one spring element that applies a counter-force to the switch element, which is oriented against the pre-tension.
Preferably, the cross-section of at least one fluid connection, preferably all fluid connections, cannot be changed and/or the respective fluid connection, preferably all fluid connections, cannot be closed.
The at least one spring element is preferably arranged in such a way that the switch element can be brought from the first position into the second position by applying a force to the at least one spring element for at least a predetermined period of time. Particularly preferably, the switch element cannot be brought from the first position into the second position by applying a force to the spring element for less than the predetermined time period. This embodiment means that a brief force impact, which is shorter than the predetermined time period, does not cause the switch element to move from the first position into the second position. Such a force impact can occur, for example, when the wearer of the prosthetic knee joint trips or bumps into an object. This usually happens during the swing phase, i.e. when the foot that is connected to the wearer's body via the prosthetic knee joint is not in contact with the ground. As a result of the force impact, the at least one spring element is compressed and thus charged with energy. For example, the force impact is applied to the spring pin of the cartridge in which the at least one spring element is arranged. As soon as the force is no longer applied, the stored energy discharges and the spring pin moves back into the starting position. In this case, the time in which the at least one spring element is charged with mechanical energy is too short to displace the switch element far enough to reach the second position. It should be noted that this does not mean that the switch element is not moved. A movement can occur, but it does not lead to the second position being reached.
Preferably, a force must be exerted on the at least one spring element in order to bring the switch element from the first position into the second position. There is preferably no other way to move the switch element.
To reduce noise that may occur, in particular, when one component, for example a spring sleeve, strikes another component, such as the cover of the spring cabinet or the spring housing, at least one bushing is arranged between two respective components that come into contact with each other in this manner, said bushing preferably being made of a plastic, especially a thermoplastic material. For example, the polyoxymethylene group, often shortened to POM, is well-suited to this.
Particularly preferably, the prosthetic knee joint is or can be produced according to one of the methods described here. In particular, the counter-force applied by the at least one spring element is preferably set.
In the following, an embodiment example of the invention will be explained in more detail with the aid of the accompanying figures. They show:
On the way from the extension chamber 10 into the flexion chamber 8 and/or vice-versa, the hydraulic fluid also flows through the switch valve 6. The switch valve 6 has a switch element 14, which can be brought into a first position and into a second position.
The switch element 14 is pre-tensioned via a pre-tensioning element 32. In the embodiment example shown, the pre-tensioning element 32 is designed as a compression spring and pushes the switch element 14 downwards. The pre-tensioning of the pre-tensioning element 14 thus opposes, among other things, a force applied by the spring pin 22. Depending on which of the two forces is greater, the switch element 14 moves into the first or the second position.
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 129 644.4 | Nov 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/080973 | 11/8/2021 | WO |
