CA2585997C - Adjustable rotation radius articulated joint for gym machines and knee tutors - Google Patents

Abstract

An adjustable rotation radius articulated joint for a gym machine and knee tutor situated in correspondence of the knee of a user, comprising a first plate; a second plate; and a group composed of a third plate; first and second plate segments forming a fourth plate; and third and fourth plate segments forming a fifth plate. The first plate and the third plate segment each have an arm. The third plate segment and the second plate segment are fixed to the third plate.

The first plate segment and the fourth plate segment are rotatably fixed to the third plate. The fourth plate segment has a second slot which continues into the third plate segment. A center pin is fixed on the first plate. The first plate has a peripheral pin slidably engaged in the second slot. An adjustment screw is engaged between the third plate segment and the fourth plate segment to personalize the joint for use on a knee of a user.

Description

Adjustable rotation radius articulated joint for gym machines and knee tutors.
This application is a division of copending Canadian Application Serial No.:

2,252,221 filed April 11, 1997.
Technical Field This invention can be profitably employed in the fields of medicine and sports as it is an indispensable component of knee tutors and of machines used to strengthen or in rehabilitation to restore the muscles of the knee to their former healthy condition.
The knee is the intermediate articulation of the lower limbs. As shown in the figures 1-3 and 6, the movement whereby the knee is extended (RE), or rather, the movement of extending the leg from the thigh is performed by means of the quadricep muscle (QM), which is inserted in the foretuberosity of the tibia, a couple of centimeters below the knee. The movement of bending the knee, that is to say the movement of flexing (F/E) the leg from the thigh is performed by means of the hind muscles of the thigh (HMT). as illustrated in figure 1. The flexion-extension movement is always executed at the fore-hind plane.
The articular surfaces that come into contact in the knee are the femoral condyles (FC) (the distal, i.e. farther, part of the femur), and the tibia plate (TP) (the proximal, i.e. closer, part of the tibia), as illustrated in figure 2.
The femoral condyles consist in round surfaces with a bending radius which is rather narrow but which varies; indeed their profile is very similar to a spiral. The tibia plate, or rather the glenoid cavity of the tibia, has a much wider bending radius than the femoral condyles.
The articular mechanics of the knee is therefore complex, and the type of movement that is made is in direct relation to the angle at which the knee is open. Let us consider an extended leg to be the starting point at a 0 angle.
In the first 201-251 of the bend (i.e.: the angle of ordinary walking) the articulation's mechanics entail a sheer rotation between the two articular surfaces: each point of the femoral condyles is in contact with a corresponding point on the tibia plate. If the flexing continues, in the subsequent 1100-1150, approximately, there is a combined sliding and I I =II III 1 rotating movement of the tibia with reference to the femur. As the leg flexes further the sliding movement gradually progresses end eventually prevails over the over the rotation and a sheer sliding movement occurs: the femoral condyles slide without rotating on the tibia plate. The knee's ligaments (KL) limit the articular caps during these sliding movements and ensure the knee's fore-hind stability, enabling the execution of hinge movements whereby the articular surfaces remain in contact.
Thus, in the flexion-extension mechanics of the knee there is no fixed centre of rotation. When the leg is flexed starting from an extended position, in the 1o first 20 there is a centre of rotation located 60 mm from the tibia's articular surface. However, as the bending movement continues, the point of rotation moves on and, at the same time, the radius grows narrower, until it reaches a minimum distance of approximately 12 mm from the tibia (as can be seen in figure 2).
This variation in the radius is transformed into a variation in the distance between a point located in the centre of the femoral condyle which has been identified by tests in the first 20 -25 of the flexion-extension and another point situated on the external malleolus. Indeed, by measuring this distance, experiments reveal that in extending from 135 to 00 the variation can increase from 15 to 40 mm (distance Rg-RA), as can be seen in figure 3. The extent of the variation depends on the conformation of the knee in question.
With reference to physiotherapeutic or rehabilitation problems, when it is necessary to support and follow the knee in its movements, one usually resorts to particular mechanical devices which are strapped to the thigh and leg by means of a system of belts (a sling) which guide the articulation in its movements.
These devices are used in knee tutors, in the machines used for passive gymnastics, and in the gym machines for specific muscle training known as 1, I M I I

leg curl and leg extension machines.
These mechanical devices, which are thus bound to the limb, are hinged to an articulated joint which generally has a fixed centre of rotation and which therefore is unable to provide the combined sliding and rotating movements and change the centre of rotation, thereby producing anomalous tensions.
The latter are caused by the different trajectories of the articulated joint's mechanical devices (circle arc) compared to the one theoretically accomplished by the leg (spiral arc). Indeed, as previously described, the leg reduces its radius when it flexes (the above mentioned RB-RA); this causes w the mechanical device to rub against the leg, bringing about a friction which is passed on to the belts of the sling and results in a compressive force.
When the leg is extended, the mechanical device tends to withhold the leg along a circular path, while the leg reduces its rotation radius, and therefore tends to be drawn away from the knee. These compressive and tractive 15 forces, which are proportional to the speed of the movement and to the distance of the knee's sling, are then released on the knee caps and on the articulation's cartilage (compressive -force), and on the knee's ligaments (tractive force) respectively.
The most sophisticated versions of the knee tutors currently used in sports 20 feature a complex articulated joint which does indeed try to simulate the compromise between the rotation and sliding movements that typically occur in the knee. Knee tutors featuring a double centre of rotation are rather common; however in the positions ranging between 00 and 30 and between 90 and 135 they do not conform to the knee's mechanical physiology.
Indeed, in the first arc (0 -30 ) no single centre of rotation is identified, whereas in the second (90 -135) the sliding movement does not increase to the point of becoming exclusive. Consequently, at these angles, the knee tutor transmits tractive and compressive forces to the articulation which are released onto the ligaments as anomalous tensions.
u Attempts to solve this problem have been described in the European Patent Publication No. EP 0 361 405, in the International Patent Publication No. WO
92/15264, and in the International Patent Publication No. WO 84/03433.
The knee joint described in the European Patent Application No. EP 0 361 405 is based on the physiological concept whereby the flexing of the knee consists in the fore movement of the femoral condyles with reference to the tibia condyles, followed by a sheer rotation between the condyles of the above mentioned bones. This joint features three plates, of which the two outer ones feature coaxial holes, while the inner one features two slots where a pair of pins that fit through the above mentioned holes in the outer plates are lodged and guided. One of the slots is small and extends transversally across the longitudinal axis of the tibia and femur, while the other slot is large and is shaped like a circular segment with one end growing wider towards the top.
The first slot is linear and has the function of reproducing the first fore movement of the femur with reference to the tibia, while the second slot serves the purpose of guiding the subsequent rotation movement.
The upper end of the circular second slot is placed on the extension of the longitudinal axis of the arm of the central plate which passes through the centre of the pin lodged in the linear first slot, precisely when the pin is halfway through the stroke performed by the pin inside this slot. The centre of the circular segment that constitutes the circular second slot consists in the centre of the pin lodged in the linear first slot when the pin itself is at the end of the said first slot, which is the one farthest from the circular second slot. When the leg flexes, in the first 25 the pin lodged in the circular second slot compels the pin in the linear first slot to move from its starting position (closer to the circular second slot) to its final position (at the end of the linear first slot that lies farthest from the circular second slot).

As the distance between the centres of the pins is equal to the radius of the circular second slot, in this first part of the movement performed by the pin lodged in the linear first slot, the pin lodged in the circular second slot performs a small vertical movement within and outside the widened part that constitutes the upper part of the circular second slot. In this first phase of the flexing movement of the two outer plates slide forward with respect to the inner plate (traction or pulling apart phase of the two plates).
Subsequently the two outer plates rotate onto the inner one as the pin at the end of stroke position in the linear first slot acts as a fulcrum and compels the pin lodged in the circular second slot to move (sheer rolling phase).
The joint described in the International Patent Publication No. WO 92/15264 features an improvement of the afore described European Patent Publication EP 0 361 405. As in the previous case, at first there is a horizontal translation of the pin lodged in the linear slot for an angle al of approximately 25 -35 of the flexing movement, with the leg outstretched in the starting position. As a result, the tibia is made to slide back with reference to the femur. In this joint too in the first phase of the flexing movement the pin lodged in the circular slot moves up and down by a Y quantity at the upper end of the circular slot when the pin lodged in the linear slot passes through the latter.
This first phase of the movement is then followed by a second phase for an angle a2 which goes as far as 120 -135 of the flexing movement. This second phase is characterised by an essentially single-centered movement: the pin, which at the end of the stroke is positioned in the linear slot acts as a fulcrum and compels the pin lodged in the circular slot to translate inside the latter.
Compared to the European Patent Publication EP 0 361 405, the improvement of the present joint consists in the attempt to modify the shape and/or the position of the openings whenever the conditions of a given patient should make this advisable.

The bend of the circular groove which extends beyond 350 of the flexing movement is thus made flatter and the linear groove is extended slightly towards the distal (i.e. farther) end from the circular groove. In the first phase of the flexing movement (from 0 to 25 , angle al), the pin lodged in the linear groove moves distally, as a result of which the tibia is made to slide behind the femur in this first phase. Subsequently, from 25 to 35 of the flexing movement (angle a2) the latter pin stays still and thus will constitute the fulcrum around which the pin inside the circular groove will rotate.
Lastly, from 90 to approximately 135 of the flexing movement (angle a3), the pin in the linear groove will be forced to draw closer to the circular one when the other pin moves downwards in the flattened part of the circular groove, thereby producing a multi-centred movement in which the tibia moves in front of the femur.
Even without engaging in a controversy with the inventor of the aforementioned Patents with reference to his conceptual hypothesis on the physiological movement of the knee, it must be said that although his patents have attempted to tackle these kinds of problems they have not hit the mark. The basic model of the joint he has invented is based on the initial movement of the pin lodged in the linear groove in all its length and simultaneously on the upward and downward movement (Y) of the other pin. Indeed, in its basis model the joint features two centres - one that performs a rotation whose median axis runs vertically, and the other whose median axis runs horizontally.
The first phase of the movement between the plates occurs around the pin lodged in the circular groove (in this phase, in order to move, the plates are subjected to a traction and are drawn apart from one another).
On the other hand, the second phase of the flexing movement (between 25 and 135 ), features the rotation of the pin that is lodged in the circular groove with the other pin as its fulcrum. In this phase the pin snaps over the pin lodged in the linear groove, around which the joint develops the second part of its trajectory.

By applying this mechanical principle inside the knee, one might suppose that the latter functions with a series of jerks. This is far from true, as the movement that occurs between the articular caps features no jerks at all and is mostly a rotation movement onto which a sliding movement progressively prevails.
The movement performed by the plates is not continuous. the personalization of the curve for each individual patient is therefore absolutely uncertain.
The knee tutor joint described in the International Patent Publication No. WO
84/03433 consists of five plates. The two outer ones connected to the supporting elements of the lower leg, each feature a hole and a linear slot.
The two intermediate plates also feature a hole and a linear slot each, but in the opposing position compared to the holes and slots of the outer plates.
The central plate, which is connected to the supporting elements of the upper leg, features a central hole and a bending opening which extends completely within the plate itself and which simulate the crosswise course of a flexing point on a given patient's knee.
The plates are locked onto one another and they can each pivot around one another and around the central shaft. This shaft extends through the linear slots in the outer plates and the central holes of the intermediate and central plates.
A pin passes through the peripheral holes of the two outer plates, the linear slots in the intermediate plates and the bending opening of the central plate.
The central shaft and the pin lock the plates onto one another in such a way II I 4 , 1 , -$-that the restricted movement of the pin inside the bending groove limits the movements of the supporting elements of the lower leg with respect to those of the upper leg: hence, the flexing and extension of the patient's lower leg is limited.
The bending groove lodges some flexible pistons, which act as springs.
These can move and are fastened to the ends of the grooves in order to limit the movement of the pin and, consequently, the width of the flexing movement. These flexible pistons are locked by two threaded bolts next to each of which lies an indicator that moves longitudinally to the pistons Iu themselves. The function of the indicators is to indicate the degrees of movement allowed in the flexing and extension movements: from 0 to 140 .
If one postulates that the central plate stays still, in this joint the intermediate plates rotate and move with respect to the central one. The outer plates rotate along with the intermediate ones but they move to the side of the I i latter plates along the axis in the direction of the linear grooves in the intermediate and outer plates. In this system the outer plates move (rotate and slide) with respect to the central plate.
The central shaft and the pin that passes through the peripheral holes of the outer plates also change distance in accordance with the angle of the joint in 2u the flexing movement and in accordance with the bending groove, located on the central plate, which simulates the crosswise course of a flexing point on a given patient's knee.
However, there is no prior identification of the centre of the knee; this centre ought to be aligned with the central shaft. Furthermore, the possibility of 25 personalising the bending groove is not described other than by referring to the extreme limits imposed on the movements.
In the machines currently used for passive gymnastics, I 1 II Ii AI

the hinge rotates around a fixed centre and cannot accompany the flex/extension movement with a physiological trajectory. Hence, anomalous tractive and compressive tensions are formed and released onto the ligaments.
Weight-lifting machines are used to strengthen groups of muscles in a voluntary way. As previously mentioned, the machines currently used for the muscles in the knee are the leg curl and leg extension machines. The former selectively strengthens the knee's flexor muscles, while the latter focuses on the extensor muscles.
lo A leg extension machine is very similar to a rather high chair. When seated upon it the feet cannot touch the ground and the thighs are bound to the seat by means of straps or other constraints. A mobile load arm L (figure 6) is located in the centre of the seat (see figure 4), or beside it (see figure 5), and runs vertically, along the. longitudinal axis of the leg, rotating around a fixed centre C, which constitutes the fulcrum of the entire system. Its rotation axis "c" ought to correspond to the horizontal axis which passes through the femoral condyles (which is believed to be the centre of the knee).
An M-shaped horizontal rod is attached to the distal (farther) part of this mobile arm L, and the distal part of the leg exerts pressure on this very rod.
The leg's extension from the thigh, which makes the arm L rotate around axis "c" is withstood by the resistance of weight P, featured by the machine.
This weight P can be connected by means of a transmission system (ropes and pulleys) to mobile load arm L itself (as can be seen in figure 3), or to a rotation mechanism (figure 5). In the latter case, a driving shaft N (with a rotation axis that coincides with the aforementioned "c" axis) connects the mobile arm L to the articulated joint.
When the lower part of the leg stretches, with the thigh bound to the machine's seat and the lower part of the leg free to move, mechanical shear and bending stresses are exerted.
When the flex/extension movement of the lower part of the leg occurs, a number of rebound phenomena take place which are proportional to the load (weight P) and to the velocity with which the load itself is lifted.
In order to avoid exerting these stresses, especially in patients who have just undergone surgery in the crossed ligaments, the lower part of the leg should also be bound in several points by some sort of sling (see figure 7), so as to make it as integral as possible to mobile load arm L. The latter, which is hinged to the frame of the weight-lifting machine, releases rebound phenomena on the central rotation pin, thereby sparing the crossed ligaments.
iu The major flaw in the machines currently on the market lies in the fact that the leg sling (figure 7) cannot be made to rotate around a fixed centre because the knee, as previously stated, has no single centre of rotation and therefore cannot, as it moves, run along a circular path, but rather must perform a spiralling movement towards the centre. Hence, if the limb is fixed to mobile arm L of the machine, it exerts its rotating movement onto the leg, tugging it as it flexes (when the leg gradually reduces the radius of its trajectory, and, vice versa, compressing it as it stretches, thereby creating anomalous tensions which are released on the crossed ligaments, the knee caps and the articulatory cartilage.
In this specific sector some devices are known to exist that are capable of reducing the tensile stresses exerted on the leg. The one described in US
Patent No. 5,020,797 is aimed at allowing a leg injured in the knee to exercise, by applying a resistance force onto the leg. The leg can be extended against this resistance in a given direction, at the same time it is able to prevent a sub-dislocation in another direction close to the abovementioned knee.
This device includes a fastening device connected to a mobile arm which, in turn, is connected to an exercise machine, two shafts, each with its own fulcrum, connected to the aforementioned device, a sling connected to the .)o fastening device to perform a pivoting movement around the first shaft, and another sling that is also connected to the fastening device for pivoting around the second shaft and a lever mechanism.
The latter features an upper arm connected to the first sling, a lower arm connected to the second sling, and a lever coupling in proximity to the adjacent ends of the above mentioned arms used to pivot.
The first sling is connected to a protruding part of the upper arm of the lever.
One must first apply a supporting force in one direction next to one end of the above mentioned first bone, as this first end is close to the above mentioned articulation. The second sling is connected to a protruding part of the lower lo arm of the lever. This is where a second resistance force is to be applied in another direction close to another end of the above mentioned first bone.
This device serves the purpose of avoiding a sub-dislocation through means that are applied next to the lower part of the leg. It is entirely unrelated to leg tractions having the knee as the fulcrum.
Indeed, this patent enables the tibia to advance "properly" in the extension movement which turns out to have been "proper" only when the starting position is "improper", that is to say if the centre of the knee is set back (but not excessively so) with reference to the centre of the machine. Should the centre of the knee be casually placed (indeed, no description of how to identify it is available) and therefore be aligned to the centre of the machine or advanced, the above mentioned system brings about the advancement of the tibia and exerts a stress on the fore crossed ligament.

Another device known to exist is described in the published trench Model No.
FR
2.550.708, which allows the reduction of the pressure in the knee's joint when exercising the quadriceps muscles. This device features an arm endowed with weights pivoted onto a joint, a horizontal shaft that passes through the joint itself and a load arm.
Special slings keep the patient still on a chair so that one thigh is fastened.
The rod of the load arm is replaced by a special w fastening shoe which features fastening strips whereby the patient's foot is locked to the shoe itself. The latter is locked onto a staff which is connected to the free end of an arm that constitutes a part of a three-arm lever that can rotate around the shaft.
One of the three arms consists in an indicator that indicates on an angular scale the traction or rotation movement of the foot. The said scale is rigidly borne by a sleeve, which can be moved to the resistance arm in an arbitrary position by means of a screw. An elastic component is mounted on a pin which in turn is rigidly fixed to the said sleeve.
icy When the patient is exercising the quadriceps muscle and extends the leg, and makes the foot rotate upward the immobilising shoe is pulled upward and toward the left. This exerts a tensile stress on the foot of the patient.
This traction or rotation movement brings about a compression of the elastic component. The width of the compression, which depends on the upward movement of the shoe, is indicated in the angular scale of the abovementioned indicator.
Hence, a traction occurs in the longitudinal direction of the lower part of the leg. Thus the pressure in the articulation of the knee diminishes and no pain is felt in the knee when taking exercise. The traction is brought about automatically when the patient extends the leg or moves the lower part of it around the articulation of the knee. The width and the variation of this traction depend both from the characteristics of the elastic component and from the distance between, on the one hand, the trajectory of a point that coincides with the fastening elements of the lower part in the patient's leg rotating around the articulation of the knee, and, on the other, the trajectory of a point that coincides with the immobilising shoe rotating around the axis of the same joint (that is to say, the distance of the position of the rotation axis of the resistance arm with reference to the position of the articulation of the knee).
so By placing the rotation axis of the resistance arm of this training device I 14i~, forward and above the articulation of the knee, it is possible to vary the traction curve in such a way that the maximum traction is achieved for a pre-established position (angular) in the movement between the position wherein the knee is completely bent (900) and the one wherein it is completely extended (0 ).
By placing the two axes eccentrically in a given position with reference to one another the traction force can be made to increase gradually with the pressure in the articulation.
This device constitutes an attempt to solve the problems related to moving the knee by using a lever mechanism which is applied to the patient's foot. It rightly assumes that the alignment between the rotation axis of the device's resistance arm and the rotation axis of the articulation of the knee is essential, but instead of acting on the knee itself it tries to increase the tensile stress on the articulation.
This last patent brings about a traction of the leg with respect to the thigh during the flex-extension. This occurs in order to counterbalance the cohesive stresses caused by the quadriceps muscle which can contract painfully. The modulation of this tension occurs by placing the centre of the knee in correspondence with the centre of the machine. Hence a system for 2( the exact identification of the centre of the knee is required.
The problem then consists in accompanying the knee while it moves without allowing other mechanical stresses to interfere in its movement. In this case, once again, we have no personalisation of the trajectory even though each subject has its own flex-extension trajectory.
In conclusion to all of the above it can be said that each one of the examined patents has made an attempt to find a solution to a given atypical problem observed in the flex-extension mechanics of the knee.
None of the inventors has thus addressed the issue by making considerations which could connect all these phenomena and identify a W common denominator. This very common denominator can be found in the I II I h ,i1 ~

definition of an efficient methodology for the assessment of the articulation which must, at first, envisage the identification of an anthropometric point of reference, and subsequently its alignment with a measuring device. This point must always be found in as much as it is essential not just for a correct assessment but also to align properly any device to be connected to the knee itself (knee tutor, passive gymnastics machines, weight-lifting machines).
Furthermore, the definition of an efficient methodology enables the correct identification of the trajectory made by the knee in the flex-extension, a w trajectory which must surely be accompanied by a drawing of the articular surfaces of the tibia and femur and the succession whereby the rotation and sliding movements are combined.
The above considerations hold true with reference to an average knee.
However, the length of the crossed ligaments, their proportions and their point of insertion (features which characterise articular surfaces), differ considerably from one individual to the next. This means that the spiralling movement made by the knee differs in every individual. In order to examine the actual articular profile of a given knee it is therefore necessary to take X-rays or to measure the distance between the knee and the malleolus of the individual.

Disclosure of Invention A feature of this invention is to provide users with an articulated joint endowed with a mobile arm L that is capable of guiding the flex/extension movements of the leg along a trajectory which may reproduce as naturally and faithfully as possible the movement that is made performed by the knee's articular surfaces: sheer rotation, sliding-rotation and sheer sliding.
Another aim is that of creating a device that can easily be modified, so that it may be adapted to the anthropometric characteristics of each subject.
These and other objectives are indeed achieved by this invention, which consists in an articulated joint with a variable and controllable rotation radius to be installed in weight-lifting machines (leg extension and leg curl), on machines for the passive gymnastics of the lower limbs, and on knee tutors (knee guides).
The articulated joint consists of a mechanical first component preferably shaped as round plate, and a group composed by a third plate and four plate segments, preferably shaped like a disc, or like a fraction of a disc, and overlapping.
First plate can move independently of the group of plate and plate segments, as is the case in knee tutors and/or in machines used for passive gymnastics.
Even when applying the multiple plate articulated joint to leg extension and leg curl machines, two versions are possible, according to the type of transmission of the resistance (weight P) featured by the machine. The following two cases are therefore possible: a multiple plate articulated joint with the load on mobile arm L, or a multiple plate articulated joint with the load on the pin of the joint. In a multiple plate articulated joint used on a weight-lifting machine in which the resistance (weight P) is applied directly to the mobile load arm, first plate is constrained by a fastener, such as a bar on the leg extension and leg curl machines; a second plate is in turn fastened to first plate and acts as a cover.
The remaining plate and plate segments are connected to one another and are free to rotate between first and second plates with reference to a horizontal axis "c", which must correspond to the one crossing the femoral condyles of the subject when seated.

The four plate-segments arranged in overlapping couples are fastened onto third plate, a little farther away from first plate (close to second plate).
These four plate segments have a particular conformation. Third plate segment which is close to first plate features a central, rectangular first slot. The first slot is located in the centre and develops lengthwise; it is rectangular in shape and the shorter sides should preferably be rounded; this slot is made by extending an ideal hole and constitutes the axis of symmetry of mobile load arm. One of the plate segments is endowed with a mobile arm. When the two plate segments, which are closer to first plate are side by side they feature a peripheral second slot. The ends of the second slot, located peripherally, should preferably be rounded. The centre of one of the ends of this second slot is located on a point located at a distance "I" from the centre of the aforementioned ideal hole, and lying on radius "b", at a right angle to radius "a"
and on the same plane. The centre of the other end of the second slot is located at 130-1400 with reference to radius "b".
The second opening had specific shape: initially, for the first 15-45 with reference to the aforementioned radius "b", it is a circumference whose centre coincides with that of an ideal central hole and whose radius is equal to "I";
subsequently, for the remaining 85-125 , it is a spiral which returns towards the centre of the ideal hole. The sequence of points forming the longitudinal axis of this spiral is derived from the sequence of points of one end of a section of length "I", whose other end moves along the longitudinal axis of the first slot.
A radius "d" divides the second slot in two parts: a first part containing the circle arc and a second part containing the spiral arc. An ideal point of rotation is located on radius "d", at a distance "I" from the ideal central hole.
The aforementioned plate segments are cut according to axis "e" which goes from this point of rotation to the point of intersection of radius 'f' with the outer edge. Radius "f' is therefore in a position which is diametrically opposite to radius "b".

These plate segments are arranged in overlapping couples first and second plate segments and third and fourth plate segments; their overlooking edges have not been cut precisely along the axis "e" but rather (considering the aforementioned ideal point of rotation to be the starting point), they diverge for a few degrees from axis "e" in the direction of the mobile arm, or in the opposite direction. Hence, a distance is created in correspondence with the intersection of axis "e" with radius 'f' between the two groups of semi-plates first and fourth plate segments and second and third plate segments; this allows the rotation of the couple composed by the first and fourth plate segments on the couple composed by the second and third plate segments, with the aforementioned ideal point of rotation as the rotation fulcrum. By means of a screw, it is possible to adjust to the micrometer the distance between the two couples of plate segments.
In other words, first plate segment which is fastened to second plate only by means of the pin located in the aforementioned ideal point of rotation, can rotate with reference to second plate segment, which is permanently fastened to second plate. As fourth plate segment is fastened to first plate segment, and third plate segment to second plate segment, fourth plate segment can rotate with reference to third plate segment. Given that fourth segment features the spiraling part of the peripheral second slot, the latter's position may vary (owing to the rotation around the above mentioned ideal point of rotation) with reference to the concentric part of the peripheral second slot itself.
First plate features two holes, one located in the centre, and the other peripherally at a distance equal to "I" with reference to the central hole. In the latter a central pin is inserted which is lodged in the central first slot of third plate segment; this pin simply acts as a fulcrum around which third plate and plate segments move. A peripheral pin is placed in the second hole and is lodged in the peripheral second slot formed by third and fourth plate segments.
By adjusting the micrometric screw which is connected to third and fourth plate segments, it is possible to change the distance between these plate segments (as well as the position of the spiral side of the peripheral second slot), so that the rotation of third and fourth plate segments on first plate (by means of the pins featured by the latter) may correspond as much as possible to the flex/
extension of the leg of the subject in question.
If the multiple plate articulated joint is used on a machine in which the resistance (weight P) is applied directly to the pin of the joint, the previously described third plate and plate segments maintain the same function, even though their position is changed. Third plate and second and third plate segments are fastened to the machine by means of a fastener, such as a bar, while first plate and the first pin can move freely. First and fourth plate segments being connected to third plate, are also fastened to the machine, but may rotate partially on third plate and second and third plate segments, thanks to the pin located on the ideal point of rotation.
Where the load is attached to the pin of the joint, first plate constitutes the proximal (nearer) part of mobile arm L, and is endowed with the aforementioned central, rectangular first slot formerly features by third plate segment. Furthermore, there is the previously described central pin/propeller shaft, featuring the feather key lodged in the opening of first plate, and a threaded area onto which a second plate is screwed, or a bolt acting as a cover for the entire system.

Third plate and second and third plate segments are crossed by a hole whose centre must correspond to the centre of the previously mentioned ideal hole in which the central pin/propeller shaft will be lodged and allowed to move freely.
The motion of the propeller shaft does not affect third plate and second and third plate segments, which are fastened to the machine by means of a fastening bar; rather, the motion Is transmitted by means of the feather key inserted in the central opening of the first plate to first plate itself. The latter, in turn, will follow the previously described movement of the peripheral opening on third and fourth plate segments, compelled to do so by the presence of the second pin that is fastened to first plate and lodged in the peripheral hole.
Irrespective of the number of plates and of the fastening system used to bind them to the machine in the proximal part of the mobile arm, an opening is made in which a mechanical hook is inserted allowing it to run along the opening itself. On this mechanical system the sling to be used for the shins will be fastened, approximately below the knee.
Furthermore, the mobile arm features another opening located distally, wherein a feather key is lodged which is allowed to run freely between axis "a" of the mobile arm itself. The foot rest is attached onto this feather key; an pin can lock the feather key to the mobile arm.
The above mentioned foot rest consists in the blade or plate which is bent on the end at 900 or by two joined blades or plates united at 90 . The vertical part of the rest is joint to the mobile arm, while the horizontal part is the place where the foot actually rests, locked in position by means of a small belt.

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In the weight-lifting machines where the load is applied on the pin of the articulated joint, the articulated joint can be modified when the central pin/
propeller shaft is wider than first plate.
In this case, a guide is milled on the central pin/propeller shaft, where first plate is placed; the latter's ideal central hole corresponds to the centre of the central pin/propeller shaft, the latter featuring a threaded hole.
A three-part screw featuring head, body and thread, and whose threaded part is engaged in the threaded hole of the central pin/propeller shaft, keeps first plate within the guide, with its non-threaded section going beyond the central first slot. The head of the screw prevents the separation of the two mechanical parts.
When the leg transmits the motion to arm L, which is fastened to first plate, the proximal part of first plate, which is inserted in the guide of the central pin/
propeller shaft, transmits this motion to the central pin/propeller shaft itself through the contact of the sides of first plate with the internal surfaces of the central pin/propeller shaft guide.
The second pin featured by first plate, which is lodged in the peripheral second slot, makes first plate and arm L, which is connected to it, go along a trajectory with a varying radius, parallel to the one of the leg in the sling of arm L.
This variation in the radius during the flextextension trajectory of the leg from the thigh makes first plate within the guide translate, the screw/pin, which in turn is inserted in the central first slot, does not hamper this translation.
In using a multiple plate articulated joint on weight-lifting machines, a degree angular scale is to be drawn in an appropriate spot on a plate. The 0 position will correspond to the longitudinal axis of the mobile arm when the latter is the extension of the bar which joins the device to the machine. The scale develops in the opposite direction in which the peripheral opening is developed.
Parallel to the distal opening in the mobile arm, on the outer edge or on the side opposite that to which the leg is fastened, a verification linear millimeter scale is located, whose ideal zero is the ideal central hole.
The above mentioned pins inserted in the central first slot and peripheral second slot can be ellipsoidal. In order to ease their longitudinal motion within the aforementioned openings.
Third plate and second and third plate segments can consist in a single piece.
The device which is the object of this patent application can be used on the machines that exist at present and on future machines by removing the traditional rotation device.
It can also be used as an accessory in combination with the traditional mechanism, thereby making the machine more functional. Lastly, the device may also be used as an accessory on other types of machines (or seats), thereby endowing them with the same function as leg extension and leg curl machines. In the latter case, the fastening bar will be locked onto the machine (or onto the seat) by means of those components that are known to achieve this aim.
The use of this invention on weight-lifting machines permits the strengthening or re-education of the extensor and/or flexor muscles of the leg with reference to the thigh, so that the anomalous physiological stresses (shear, flex, rebound, tensile and compressive), which occur during motion may be prevented from releasing harmful tensions on the ligaments. Its use in knee tutors (knee guides) similarly avoids that the same types of anomalous physiological stresses be released on the knee's ligaments, on the knee-covers, on the articular cartilage of people who have suffered an injury in their knees, or athletes, as they walk, do sports or perform rehabilitation exercises.
Indeed, this articulated joint is made in order to permit its component parts to make movements which reproduce as faithfully as possible the sequence that occurs in the variation of the knee's centre of rotation and the progression of the rotation and sliding movements. Hence, the leg and arm lo L which is connected to the leg remain on trajectories that coincide perfectly, so that in each phase of the flex/extensor movement there is a perfect correspondence between every point of contact between the leg and arm L.
This prevents any kind of slipping between the mechanical device and the limb, thereby avoiding the aforementioned anomalous tensions.

A Brief Description of the Drawings Other characteristics and advantages of the invention will be more evident with the description of some specific and preferred but not exclusive configurations of the articulated joint, indicatively illustrated in the enclosed drawings in which:
figure 1 illustrates the position of the muscles of the thigh and the flexing and extension movements;
- figure 2 shows the articular surfaces of the knee;
- figure 3 illustrates the variation in the distance between the femoral condyle and the malleolus which occurs during the extension of the leg;
- figure 4 shows the type of weight-lifting machine that exists at present, called leg extension machine, where the weight is placed on the mobile arm,-- figure 5 shows a leg extension machine where the weight is placed on the articulated joint;
~o figure 6 illustrates the movement of the mobile arm on a leg extension machine;
- figure 7 shows the constraints placed on the slinged leg in a leg extension machine;
- figure 8 shows an exploded view of the articulated joint with multiple plates;
- figure 9 illustrates a frontal view of the articulated joint and the mobile arm;
- figure 10 shows a lateral view of the same articulated joint and its respective mobile arm;
- figure 11 illustrates the lateral view of the articulated joint and makes its structuring theory explicit;
- figure 12 illustrates a prospective view of the part of the articulated joint which is connected to the weight t-lifting machine;
- figure 13 illustrates the first plate of the mobile part of the articulated joint;
- figure 14 shows the first semi-plate of the mobile part of the articulated joint;
- figure 15 illustrates the second semi-plate of the mobile part of the articulated joint;
- figure 16 shows the third semi-plate of the mobile part of the articulated joint which overlaps the one shown in figure 14;
- figure 17 shows the fourth semi-plate of the mobile part of the articulated joint which overlaps the one shown in figure 15;
- figures 18, 19 and 20 show three different arrangements of the plates of the articulated joint, when the leg is in the extended, flexed at 900, and flexed at 1350 positions;
- figure 21 shows the articulated joint applied to a leg extension machine where the weight is placed on the mobile arm;
- figure 22 shows the articulated joint applied to a leg extension machine where the weight is placed on the pin of the articulated joint;
- figure 23 shows an exploded view of the articulated joint illustrated in figure 22;
- figure 24 illustrates a view of a knee tutor featuring the articulated joint which is the object of this patent application.

Mode for Carrying Out the Invention In a configuration applied to a leg extension weight-lifting machine with a resistance (P) constrained to mobile arm L, the articulated joint is formed by a first plate 1, by a second plate 8 and by a group composed of a third plate 3, a first plate segment 4, a second plate segment 5, a third plate segment 6 and a fourth plate segment 7. The plate segments are shaped like a fraction of a disc and overlapping. Plate 1 features two pins 1.2 and 1.3, whose longitudinal axis is at a right angle to the rotation surfaces of plates 1 and 2. These pins are located at a distance equal to "I". Pins 1.2 and 1.3 are cross-through pins.
These plate 3 or plate segments 4, 5, 6, 7 are connected to one another and are free to rotate onto the first plate 1 and second plate 8 (which acts like a cover), with reference to a horizontal axis "c", which passes through the femoral condyles of the subject when seated.
The plate segments 4, 5, 6, 7, in overlapping couples, are fastened to third plate 3, which is the farthest from first plate 1 of all. Third 3 features a threaded hole 3.1 in correspondence with the point of rotation of first plate segment 4, onto which a pin 4.1 is screwed, allowing the rotation of first plate segment with reference to third plate 3. Furthermore, two threaded holes 3.2 are made on third plate 3 towards semi-arm 3.3, which lock second plate segment 5 and third plate segment 6 onto third 3 by means of adequate screws. First and second plate 1,8 are fastened to the weight-lifting machine by means of a bar 1.1.
Plate segments 4, 5, 6, 7 are shaped in a particular manner. An examination of the latter two reveals that third plate segment 6 features a first slot 9.
This first slot 9 is obtained by extending an ideal hole 9.1, which is located at the centre of the third plate segment 6, towards the outside, along a radius defined as "a", which constitutes the longitudinal axis of symmetry of the mobile arm 6.1 featured by plate segment 6. This mobile arm 6.1 is connected to the weights.
When the third and fourth plate segments 6, 7 are side by side they feature a second slot 10. The ends of the second slot 10 are shaped like a circle. The centre of one of the ends of this second slot 10 is situated on a point located at a distance "I" from the centre of the aforementioned hole 9.1, and lying on radius "b", at a right angle to radius "a", which passes through the centre of the aforementioned hole 9.1 and on the same plane. The centre of the other end is located at 135 with reference to the above mentioned right angled radius "b".
The second slot 10 has specific shape: initially, for the first 200 (angle a) with reference to the aforementioned right angled radius "b", it is a circumference whose centre coincides with that of the centre of ideal hole 9.1 and whose radius is equal to "I", subsequently, for the remaining 1150 (angle 13), it is a spiral which returns towards the centre of ideal hole 9.1. The sequence of points forming the longitudinal axis of this spiral is derived from the sequence of points of one end of a section of length "i", whose other end moves along the longitudinal axis of the first slot 9 (from ideal hole 9.1 radially towards the outside along radius "a").
In second slot 10 considerable importance is played by radius "d", which divides second slot 10 into two parts: a first part 10.1, containing the circle arc of third plate segment 6 and a second part 10.2, containing the spiral of fourth plate segment 7. Radius "d" is inclined by 200 (on the same plate) with reference to radius "b". A point 11 is located on radius "d" at a distance "I"
from the hole 7.1 Plate segments 4, 5, 6, 7 are cut according to an axis "e which goes from point 11 to the point of intersection of radius 'f' with the outer edge (of plate segments 4, 5, 6, 7); radius 'f' is in a position which is diametrically opposite to radius "b".
Getting back to the details of the various components, it will appear that second plate segment 5 is fastened, as previously described, in the proximal part of semi-arm 3.3 of third plate 3. It features two holes 5.1 where as many screws, having the same interaxis as holes 3.2, pass through. The side which faces first plate segment 4 features indentation 5.2 which is slightly shorter than half the circumference and whose centre is in point 11.
First plate segment 4 is fastened onto third plate 3, next to second plate segment 5. From the side overlooking second plate segment 5 a half circumference 4.2 (whose centre is in point 11) protrudes from first plate , segment 4, whose diameter is lesser than indentation 5.2 of semi-plate 5, so as to allow it to be inserted in the latter. Pin 4.1 is inserted inside hole 4.3 located at the centre of the half circumference 4.2 (endowed with a countersink on the side overlooking fourth plate segment 7) placed in correspondence with point 11, around which first plate segment 4 rotates. This rotating pin 4.1 is screwed into hole 3.1 of third plate 3. It consists in three parts: head (which is inserted in indentation 4.4 of the half circumference 4.2), body (which is smooth and occupies hole 4.3) and thread (which is to be engaged in hole 3.1).
First plate segment 4 also features a threaded hole 4.5, located in the centre, where a screw fastening fourth plate segment 7 to first plate segment 4 itself can be inserted.
Third plate segment 6 is fastened to second plate segment 5 and to third plate 3 by means of screws that cross holes 6.1, 5.1 and 3.2. At the centre of third plate segment 6 first slot 9 opens up, while in the farther end (distal) from mobile arm 6.1 in the direction of point 11, first part 10.1 of opening 10 opening up; the latter originates from radius "b" at a distance "I" from hole 9.1, and develops with a constant radius along a circle arc until it intersects with radius "d".
Pin 1.2 is inserted in first slot 9; the former can be locked in correspondence with ideal hole 9.1. In the channel formed by first slot 9 spring 12 is inserted;
the latter is withheld by a distal spring-lock 13 (which is crossed lengthwise by hole) and by proximal spring-lock 14. The later acts on a bushing 15, within which pin 1.2 is lodged. The latter's internal diameter corresponds to the outer diameter of pin 1.2 and the outer diameter to the size of first slot 9. The mechanical finishing of bushing 15 must enable it to rotate freely on pin 1.2, an to slide freely into first slot 9. Proximal spring-lock 14 can be pushed by a peg 16, which is lodged in mobile arm 6.1 within an indentation 17 that features two locked positions; when one end of peg 16 is inserted in the proximal locked position 17.1 bushing 15, pushed from the other end by peg 16 itself (after crossing distal spring-lock 13), is compelled to place itself on ideal hole 9.1; on the other hand, when peg 16 is inserted in the distal locked position 17.2 bushing 15 is free to move within first slot 9.

Fourth plate segment 7 is fastened onto first plate segment 4 by means of a screw which crosses a countersunk hole 7.1 which is to be engaged in hole 4.5.
Second part 10.2 of second slot 10 is carved onto fourth plate segment 7; the former extends from radius "d" until the complete development of second slot itself.
Second plate segment 5 and third plate segment 6 feature an edge overlooking 10 first plate segment 4 and fourth plate segment 7 which is not, however, cut exactly along axis "e" but rather, considering point 11 to be the starting point of the edge, diverges by a few degrees from axis "e" in the direction of mobile arm 6.1. First and fourth plate segments 4,7 also feature an edge overlooking second and third plate segments 5,6 which is not cut exactly along axis "e"
but, unlike the latter plates, and, again, considering point 11 to be the starting point of the edge, rather diverges by a few degrees from axis "e" in the opposite direction from mobile arm 6.1.
As the edge of first plate segment 4 and fourth plate segment 7 and that of second plate segment 5 and third plate segment 6 share the same centre but has sides that open in the opposite direction, a distance is formed where axis "e" intersects with the external edge which permits first and fourth plate segments 4,7 to rotate on second and third plate segments 5,6; point 11 is the centre of this rotation movement.
A wing 6.3 and 7.2 is fastened onto third plate segment 6 and fourth plate segment 7, in proximity to the outer edge. A threaded, cross-through hole 6.4 is features by wing 6.3, while wing 7.2 features a non threaded cross-through hole (with the same interaxis). A screw 18 is inserted through the latter hole;
screw 18 is endowed with a bolt 18.1 which is to be engaged in hole 6.4. By acting on this screw 18 it is therefore possible to adjust the distance between third plate segment 6 and fourth plate segment 7 (and, consequently, also between first and second plate segments 4,5); it is possible to adjust this distance to the micrometer.
A pin 1.3, which crosses threaded hole 1.4 (which is on first plate 1) is inserted in second slot 10. It is made of three sectors: a handwheel with a knurled edge, which makes it easier to lock it manually on first plate 1, a threaded section which is screwed inside hole 1.4, and a non threaded cylinder section which slides inside second slot 10 and protrudes from the side opposite the one featuring the handwheel.
Furthermore, first plate 1 also features a second hole 1.5, located centrally, with a longitudinal axis at a right angle to the rotation surfaces of plates 1, 3 and plate segments 4, 5, 6, 7, and located at a distance equal to "I" with reference to hole 1.4, within which a central pin 1.2 is inserted. The latter is cross-through and its distal end is lodged inside bushing 15, thereby crossing first slot 9. Pin 12 also consists in three parts: a handwheel with a knurled edge, a threaded sector which is screwed inside hole 1.5, and a non threaded cylinder section which slides inside first slot 9.
In the section closer to mobile arm 6.1 lies an opening 19 which is rectangular in shape (and which follows the direction of axis "a"), inside which a mechanical system 20 with screws is inserted, allowing this system to move longitudinally along opening 19.
A small, semi rigid belt 21 is fastened onto mechanical system 20 to be tied around the distal part of the belt, approximately below the knee; the possibility to move mechanical system 20 makes it possible to identify the exact point in which this constraint is to be fastened according to the anthropometric dimensions of the user of the invention.
Mobile arm 6.1 also features another opening 22, located distally, which is also rectangular in shape (possibly with rounded sides) which follows the direction of axis "a".
A feather key 23 is lodged inside opening 22; the former is externally wider than opening 22 and it is thicker than mobile arm 6.1; however, it is allowed to slide freely along axis "a" of mobile arm 6.1. The foot rest is fastened to feather key 23 by means of screws; a pin 24 fastens feather key 23 to mobile arm 6.1.
The aforementioned foot rest consists in two blades 25 fastened to one another at 90 . The vertical blade allows the connection to mobile arm 6.1 by means of screws which engage in feather key 23; the horizontal blade allows the foot to rest by coming into contact with a large portion of the bottom of the foot.
The foot resting in this location is fastened to blade 25 by means of a small belt 26, so as to maintain the position it is in at the start throughout the flex/
extension movement.
A degree angular scale 1.6 is drawn at the periphery of first plate 1. The 0 position is located in correspondence with radius "a" in the position in which mobile arm 6.1 constitutes the extension of bar 1.1; the scale develops in the opposite direction compared to the direction in which pin 1.3 is located. A
verification linear millimeter scale is located parallel to opening 22. A 0 reference point is drawn on the outer edge of feather key 23.
The 0 of this millimeter scale 27 is located on ideal hole 9.1 and, consequently, the scale only shows values that are higher than a certain level, for instance centimetres. The distance between the centre of ideal hole 9.1 and the fiducial mark of the millimeter scale 27 is called radius "R". The above mentioned plate 8 acts as a cover; it is connected to first plate 1 by means of three screws 28;
these screws 28 are inserted inside specific spacing bar 29 which prevent first and second plates 1 and 8 from getting excessively close to one another.
These two plates are tightly fastened to plate segments 3, 4, 5, 6, 7 (by means of screws 28), preventing them from being drawn apart from first plate 1.
Third plate 3 and plate segment 4, 5, 6, 7 are allowed to slide onto first and second plates 1, 8 thanks to the use of self-lubricating substances for contacting surfaces.
As previously described, the length of the knee's crossed ligaments and their point of insertion are individual anthropometric characteristics which shape the knee's articular surfaces and which therefore differ from one individual to the next. In order to analyse these characteristics and to personalise the articulated joint a functional assessment is the common approach.
In order to carry out a correct assessment it is first of all indispensable for the knee to be placed on the machine in a precise position; that is to say, the axis which crosses the knee, around which the first 15-20 of the flex/extension take place (axis "c") correspond perfectly to axis "c" of the device, which crosses the centre of ideal hole 9.1 This alignment of the centre of both the knee and the machine, called self-centring, must be performed before any other step and must be performed again every time that the same subject places him/herself on the machine and need to return to the same working conditions.
The subject is made to sit down with his leg on the leg extension machine. The thigh belts and belts 21, 26 on the distal part of the leg are fastened.
Mechanical system 20 and pin 24 are released, so that the former may be free to slide into opening 19 and feather key 23 into opening 22.
After having removed pin 1.3 from first plate 1 and having locked pin 1.2 in the central position (by means of peg 16 which is located in the proximal locked position 17.1 which locks bushing 15 onto ideal hole 9.1), mobile arm 6.1 is used as an arm rotating around a fixed centre (whose centre is ideal hole 9.1 and which is coaxial to axis "c" of the device).
The subject, with the leg outstretched, performs some small flex/extension movements of approximately 30 , readable in the degree angular scale 1.6. If when the subject is seated with his limb outstretched the measure of radius R
differs from the measure taken when the limb is slightly flexed, the knee is not centred and the latter's axis "c" will not coincide with the axis "c" of the device.
For instance, if the measure of radius R increases, the knee will be in a forward position with reference to axis "c" crossing the centre of ideal hole 9.1. If the measure decreases, the knee will be behind or below axis "c".
Once the perfect correspondence between axis "c" of the knee and that of the device has been found, it is possible to trace the articular route of the tibia as it rolls and slides onto the femur. Starting from an outstretched position a few readings are taken, particularly in the last 90 of the movement, i.e. as the leg flexes between 45 and 135 , The measurements to be taken are the flexing angle (to be read on degree scale 1.6) and the corresponding variation of radius R (to be read on linear millimeter scale 27).
Having taken a number of such coupled readings, it is possible to compute mathematically the curve interpolating the points read at the maximum flexing and thus identify the second part 10.2 of the second slot 10 which best suits the subject being examined.
The subsequent personalization of second part 10.2 is performed on millimetric screw 18 which is hinged to wings 6.3 and 7.2 of third and fourth plate segments 6 and 7. By adjusting this screw 18, the distance between third and fourth plate segments 6, 7 (and first and second plate segments 4, 5) can be adjusted, as a consequence of which the position of second part 10.2 of the second slot 10 with reference to first part 10.1 will also be adjusted. Pin 4.1 is the fulcrum of the rotation of second part 10.2.
When second part 10.2 has been adjusted to suit the characteristics of the subject being examined, peg 16 is placed in the distal locked position 17.2, thereby releasing bushing 15. Peripheral pin 1.3 is then screwed into hole 1.4 of first plate 1, feather key 23 is locked (by means of pin 24) into opening 22 in correspondence with the reference spot of the foot, and mechanical system 20 is locked in opening 19, thereby definitively fastening the distal part of the leg to mobile arm 6.1.
At this stage, having personalised second part 10.2 of second slot 10, the subject may start performing normal flex/extension exercises. The movements of the multiple plate articulated joint will be similar to those of the two plate articulated joint. The subject starts from a flexed position to perform an extension of the leg from the thigh, thereby compelling mobile load arm 6.1 to rise.
This comprises third plate 3 and plate segments 4, 5, 6, 7 to move. The particular shape of first slot 9 and second slot 10 gives rise to different movements depending on the position of mobile load arm 6.1. Indeed, in the first phase of the extension (the first 115 ; angle 13), since first part 10.2 is shaped like a spiral that returns towards the centre of third plate segment 6, and the distance between the two pins is still "I", plate 3 and plate segments 4, 5, 6, 7 will be compelled to translate upwards and, at the same time, rotate onto first and second plates 1, 8. Arm 6.1, which is fastened to third plate segment 6, logically follows these movements.

Subsequently (for the remaining 15-200 of the extension: angle a), as first part 10.1 of second slot 10 is a circumference whose centre coincides with the centre of hole 9.1, plate 3 and plate segments 4, 5, 6, 7 will simply rotate onto first and second plates 1,8, the fulcrum being ideal hole 9.1.
On the other hand, the following description concerns a configuration of an articulated joint with multiple plates and the resistance of the machine on the rotating device.
In this case, central pin 1.2 constitutes the end of a shaft having a longitudinal axis placed on the extension of the knee's axis "c" Third plate 3 and plate segments 4, 5, 6, 7 maintain the same function, even though their position is changed. Plate 3, second plate segment 5 and third plate segment 6 are fastened to the machine; first plate segment 4 and fourth plate segment 7, being fastened to third plate 3 by means of pin 4.1 and by the screw crossing holes 4.5 and 7.1, also remain fastened to the machine, but may rotate partially onto third plate 3 and second plate segment 5 and third plate segment 6, thanks to the aforementioned pin 4.1 located on the ideal point of rotation.
First plate 1 constitutes the proximal part of mobile arm 1.1 which replaces the mobile arm 6.1 of the previous multiple plate version; it features central, rectangular first slot 9, formerly featured by third plate segment 6. Plate 1/arm 1.1 is free to rotate onto plate 3 and plate segments 4, 5, 6, 7.
As previously described, central pin 1.2 here constitutes one end of the propeller shaft, which features on the other end a feather key 30 which is lodged in the central, rectangular first slot 9 of first plate 1 in order to prevent pin 1.2/shaft from slipping out of plate 3 and plate segments 4, 5, 6, 7, the latter is endowed with a threaded area, in proximity to feather key 30, onto which second plate 8 is screwed, thereby acting as a cover for the entire system.
Central first slot 9 remains unchanged in its engineering, compared to the description made in the first case for third plate segment 6, with the ideal hole 9.1 as the main locating spot. However, the length of this first slot 3 is increased vertically according to the size of feather key 30, whose point of symmetry (where the transverse and longitudinal axes meet) must coincide with the ideal hole.
Plate 3 and second plate segment 5 and third plate segment 6 are crossed by a cross-through hole 31 whose centre corresponds to the centre of ideal hole 9.1, where the central pin 1.2/propeller shaft is lodged and allowed to rotate freely.
The motion of the pin 1.2/propeller shaft does not affect plate 3 and plate segments 5, 6 which are fastened to the machine, rather, it transmits this motion to first plate 1 by means of feather key 30 which is located in first slot 9.
The latter, in turn, will follow the motion suggested by the second slot 10 on plate segments 6, 7, compelled to do so by the presence of the second pin 1.3 that is fastened to first plate 1 and lodged in second slot 10.
The invention thus made is subject to several modifications and variations, all of which pertain to the inventive concept. Furthermore, all details may be replaced with other technically equivalent ones.

Claims (24)

1. An adjustable rotation radius articulated joint for a gym machine and knee tutor situated in correspondence of the knee of a user, comprising:
a first plate;
a second plate; and a group composed of a third plate, first and second plate segments forming a plate; third and fourth plate segments forming a plate;
the first plate and the third plate segment each having an arm;
the third plate segment and the second plate segment are fixed to the third plate;
the first plate segment and the fourth plate segment are rotatably fixed to the third plate;
the third plate segment having a first slot;
the fourth plate segment having a second slot which continues into the third plate segment;
a center pin fixed on the first plate engaged in the first slot;
the first plate has a peripheral pin slidably engaged in a second slot; and an adjustment screw engaged between the third plate segment and the fourth plate segment to personalize the joint for use on a knee of a user.

2. The articulated joint according to claim 1, wherein the fourth plate segment and the first plate segment rotate together around a pin fixed to the third plate.

3. The articulated joint according to claim 1, wherein the first slot provided on the third plate segment extends from a center of the third plate segment along a longitudinal axis of the arm of the third plate segment.

4. The articulated joint according to claim 1, further comprising:
a first slot provided on the first plate extending from a center along a longitudinal axis of the arm of the first plate.

5. The articulated joint according to claim 3, wherein the center pin is rotatably engaged in a bushing located in the first slot and wherein spring-lock means are provided having a spring engaged in the first slot against the bushing for fixing the bushing at the center of the third plate segment when fixed at a first position and permitting the bushing to slide in the first slot against the spring when fixed at a second position.

6. The articulated joint according to claim 5, wherein the spring-lock means comprises the spring, a first end portion, a second end portion and a peg, the spring engaged against the first end portion and the second end portion and the peg;
the peg slidably extending through the first end portion to press the second end portion against bushing in the first position when the peg is secured in a first notch on the third plate segment; and wherein, when the peg is secured in a second notch on the third plate segment in the second position the bushing is slidable in the first slot.

7. The articulated joint according to claim 1, wherein the adjustment screw is inserted through a through hole in a first wing on the fourth plate segment and held in the through hole by a bolt, wherein when the adjustment screw is threaded in a threaded hole on a second wing on the third plate segment a distance between the first and second wings is adjusted.

8. The articulated joint according to claim 1, wherein the third plate segment, the second plate segment and the third plate are formed as a single unit.

9. The articulated joint according to claim 1, wherein the first and fourth plate segments are formed as a single unit.

10. The articulated joint according to claim 3, wherein the second slot has a specific shape; initially for the first 150-450 has a circular form, whose center coincides with the center point with a radius equal to "I"; subsequently, for the remaining 90°-120°, it forms a spiral which develops towards the center point;
one end of the first slot lies on a radius "b"; that is at a right angle to radius "a";
the center point is one end of the first slot; the other end of the second slot is located at a distance "I" from the other end of the first slot.

11. The articulated joint according to claim 10, wherein a radius "d" - that is inclined by 15°-45° with reference to radius "b" divides the second slot in two parts; a circular part located on the third plate segment and a spiral part located on the fourth plate segment; and a fulcrum is located on radius "d".

12. The articulated joint according to claim 1, wherein a distance between the pins fixed on the first plate is equal to "I".

13. The articulated joint according to claim 10, wherein the first plate segment, the second plate segment, the third plate segment and the fourth plate segment each have a periphery; the first plate segment is spaced from the second plate segment, and the third plate segment is spaced from the fourth plate segment along an axis "e" which goes from a fulcrum to a point where a radius "f" intersects the peripheries of the first plate segment and the second plate segment and the peripheries of the third plate segment and the second plate segment and the peripheries of the third plate segment and the fourth plate segment; the radius "f' is diametrically opposite to radius "b";
the first plate segment, the second plate segment, the third plate segment and the fourth plate segment each has an edge that extends generally along the axis "e", but the edge of the first plate segment diverges from the edge of the second plate segment and the edge of the third plate segment diverges from the edge of the fourth plate segment starting from the fulcrum and ending at the peripheries of the plate segments, so that a distance is created between the first plate segment and the second plate segment and between the third plate segment and the fourth plate segment adjacent the intersection of axis "e"
with radius "f'.

14. The articulated joint according to claim 3 or 4, wherein a belt is fixed adjustably along a longitudinal axis of the arm adapted to constrain a calf of a user against the arm.

15. The articulated joint according to claim 3 or 4, wherein the arm features a rectangular opening located distally which develops along a longitudinal axis "a" inside which a feather key is lodged, fixed adjustably along the rectangular opening by means of a pin; a foot rest is blocked by the feather key; the foot rest having a belt adapted to constrain a foot of the user on the foot rest.

16. The articulated joint according to claim 15, wherein a linear scale is provided along an edge of the arm opposite an adjustment distance of the foot rest on the arm, a zero point of the linear scale corresponding to the center of the third plate segment.

17. The articulated joint according to claim 1, wherein the movement of rotation of the joint arises around axis "c", at a right angle to rotation surfaces of the joint itself.

18. The articulated joint according to claim 1, wherein the first and second plates are fixed together in spaced relationship and the first plate has an arm for attachment to the gym machine or to the thigh of the user;
the arm of the third plate segment is a distal arm; the second plate segment, the third plate segment and the third plate all fixed together to rotate between the first and second plates;
the first plate having the peripheral pin inserted in a peripheral hole slidably engaged in the second slot.

19. The articulated joint according to claim 1, wherein:
the third plate segment has a femorial arm for attachment to the gym machine or to the thigh of the user.

the second plate is fixed to one end of a center pin; the femorial arm having a longitudinal axis of symmetry;
said third and second plate segments and third plate being fixed together to rotate between the second plate and an element fixed to the other end of the center pin; wherein:
the first plate has a first slot that extends the longitudinal axis of symmetry of the arm of the calf of the user;
the third and second segments of plate and third plate are each provided with a cross-through hole, all of said cross-through holes being coaxial with one another; and the center pin has a feather key lodged in the first slot, the center pin serving as a center of rotation on the first plate for the third and second segments of plate and third plate.

20. The articulated joint according to claim 18, wherein a degree angular scale is provided along the periphery of the first plate to indicate an angle between the longitudinal axis of the femorial arm and the longitudinal axis of the arm for the calf of the user.

21. The articulated joint according to claim 19, wherein the first plate has a central hole located at a distance equal to "I" from a peripheral hole.

22. The articulated joint according to claim 19, wherein the center pin is lodged in the cross-through holes of the third and second segments of plate and of the third plate.

23. The articulated joint according to claim 19, wherein the center pin has, in proximity to the feather key, a threaded area onto which the second plate is fastened to act as a cover for the joint.

24. The articulated joint according to claim 19, wherein the center pin constitutes a propeller shaft to which a load is applied.