The invention relates to a force sensor, particularly suitable for use in a temporary hip joint implant in order to measure the forces acting on the artificial hip joint and to use this information to improve the characteristics of a defi nite hip joint after implementation into the patient.

A problem with known force sensors that are particu larly used for measuring the forces acting on an artificial hip joint is that strain gauges cannot be used in view of its re quirement to be integrally construed with the hip joint, which hinders its application because cleaning and sterilization is virtually impossible without damaging the construction of the force sensor.

It is an object of the invention to provide a solution for this problem and to answer the need for a reliable force sensor with which the forces acting on an artificial hip joint can be measured. Eventually this leads to better solutions for the patient when he or she is provided with an artificial hip joint that is optimized in terms of its placement and its in terference with the bones of the patient.

US-Bl-10,486,314; US2006/0213287; CN-A-104568279; DE 10 2017 218 033 Al; US2014/0041461; and US2019/0025143 each disclose a force sensor which comprises a base, a table with legs mounted on the base and said table being movable with re spect to the base by a force applied to the table, wherein the force sensor is further equipped with a measuring instrument or instruments for measuring a deflection of one or more of the legs, which deflection represents a measure of said force ap plied to the table.

The force sensor of the invention has the features of one or more of the appended claims.

In the force sensor of the invention each leg is con nected to the base and is connected to the table, wherein there is a distance between the base and the table, and wherein each leg comprises a relatively thick portion and a relatively thin portion, wherein the relatively thick portion is fixed to the base and the relatively thin portion is fixed to the table, without the thick portion engaging the table and without the thin portion engaging the base, and wherein the thick portion and the thin portion are essentially parallel to each other, such that both the thick portion and the thin portion substan tially span the distance between the base and the table, and that the thin portion comprises two parallel parts, a first part connected to the table and having a first extremity dis tant from the table, and a second part connected to the thick portion proximate to the table and provided with a second ex tremity distant from the table, which first extremity and sec ond extremity merge into each other so as to arrange that a movement of the table with respect to the base that results in a corresponding movement of the first part of the thin portion that connects to the table, translates into an enlarged move ment of the first extremity and second extremity that are merged into each other distant from the table.

To say it short, a relatively small movement of the table is thus amplified into a relatively large movement at the first and second extremities that are merged into each other distant from the table. This provides a very effective means for measuring the displacement of the table which is repre sentative of the force that is applied to the table. According ly it is preferred that the measuring instrument or instruments are arranged to measure a displacement of the first extremity and second extremity that are merged into each other distant from the table.

Preferably the force sensor has three legs with which the table is mounted on the base, to provide the force sensor with three degrees of freedom for measuring.

Within the scope of the invention several types of measuring instruments can be used in the force sensor. In one embodiment the measuring instrument or instruments comprise an optical displacement sensor or sensors. In another embodiment the measuring instrument or instruments comprise a Hall effect sensor or sensors for measuring a displacement of the first ex tremity and second extremity that are merged into each other distant from the table. In that embodiment it is preferred that the measuring instrument or instruments comprise a magnet or magnets mounted on the thin portion of the leg, preferably on the first extremity and/or second extremity that are merged in to each other distant from the table. One of the benefits of the force sensor according to the invention is that it is possible to arrange that the meas uring instrument or instruments are dismountable from the force sensor to enable cleaning and/or sterilization of the respec tive parts of the force sensor.

Another benefit of the force sensor of the invention is that it is not costly to manufacture, particularly when at least one of the base, the table and the legs is made from stainless steel.

In a suitable embodiment the table connects to a ball of a hip joint implant. This opens the way to a use of the force sensor according to the invention in a hip joint implant of a patient for measuring forces acting on the hip joint im plant during movement of the patient.

The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of a force sensor according to the invention that is not limiting as to the appended claims.

In the drawing:

-figure 1 shows a three dimensional view at the force sensor of the invention, provided with a ball head;

-figure 2 shows an enlarged view of the force sensor of figure 1 with the ball head removed;

-figure 3 shows a schematic drawing of particular me chanical parts of the force sensor of the invention;

-figure 4A/4B shows a 2D representation of the force sensor of the invention; and

-figure 5A/5B shows a representation of the movements of one of the legs of the force sensor of the invention.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Making first reference to figure 2, particular details of the force sensor 1 of the invention are shown, notably a base 2, a table 3 with three legs 4 mounted on the base 2, wherein said table 3 is movable with respect to the base 2 by a force F _x , F _y , F _z (see figure 1) applied to a ball head 5 mounted on the table 3. The force sensor 1 preferably has three degrees of freedom, for which purpose the force sensor 1 is provided with the shown three legs 4 that support the table 3 on the base 2. Further there is a measuring instrument or there are measuring instruments 6, 7 for measuring a deflection of one or more of the legs 4, which deflection ultimately is representa tive for said force F _x , F _y , F _z that is applied -indirectly- to the table 3 through the ball head 5. It is possible to apply optical instruments for the measurement of said displacement, but it is preferred to apply a Hall effect sensor or sensors 6 that cooperate with magnets 7 for measuring a displacement of the legs 4. The magnets 7 are placed on the legs 4, and the Hall effect sensors 6 are stationary provided on the base 2. To achieve best results the magnets 7 are mounted on a thin por tion A'' of the legs 4, preferably on a first extremity 8' and/or second extremity 9' that are merged into each other dis tant from the table 3 as will be discussed in the next para graphs.

Specifically with reference to figure 3 and the de tailed view provided by figures 5A/5B, the cooperation of nota ble parts of the force sensor 1 of the invention can be ex plained.

Figure 3 shows that each leg 4 is connected to the base 2 and is connected to the table 3, wherein there is a dis tance d between the base 2 and the table 3. Figures 5A/5B both show one of the legs 4 separately from the base 2 and the table 3. Each leg 4 of the preferably three legs, comprises a rela tively thick portion 4' and a relatively thin portion '', wherein the relatively thick portion A' is fixed to the base 2 and the relatively thin portion A'' is fixed to the table 3, without the thick portion A' engaging the table 3 and without the thin portion A'' engaging the base 2. The thick portion A' and the thin portion A'' are essentially parallel to each oth er, such that both the thick portion A' and the thin portion A'' substantially span the distance d between the base 2 and the table 3. Further, as may be best seen in figures 5A/5B, the thin portion A'' comprises two parallel parts, a first part 8 connected to the table 3 and having a first extremity 8' dis tant from the table 3, and a second part 9 connected to the thick portion A' proximate to the table 3 and provided with a second extremity 9' distant from the table 3, wherein the first extremity 8' and the second extremity 9' merge into each other so as to arrange that a movement of the table 3 with respect to the base 2 that results in a corresponding movement of the first part 8 of the thin portion A'' that connects to the table 3, translates into an enlarged movement X of the first extremi ty 8' and second extremity 9' that are merged into each other distant from the table 3. It is at this location where the first extremity 8' and the second extremity 9' merge into each other, that the earlier mentioned magnet or magnets 7 are ap plied when the displacement measurement is carried out using a Hall sensor or sensors 6.

The difference between the construction of figure 5A and figure 5B is the following. Figure 5A relates to an embodi ment wherein the behaviour of the leg 4 depends only on the ma terial properties and its dimensions. Figure 5B is embodied with particular curvatures 10 on the thick portion 4' of the leg 4, which prevents high stress locations on weak locations of the movable thin portion '' of the leg 4, and accordingly increases the working range of the force sensor 1.

The elucidation of the previous paragraphs also ap plies to the 2D representation of figure 4A/4B depicting an in dication how a force F _z in the Z-direction and a transversal force F _x that both may act on the force sensor 1, cause a dis placement of the first extremity 8' and second extremity 9' that are merged into each other distant from the table 3. The force F _z results in a symmetrical movement -X and X of the shown legs 4, whereas the transversal force F _x leads to an asymmet rical movement of the legs 4. In these figures 4A/4B, it is al so shown that for measuring the displacement of the merged first extremity 8' and second extremity 9', an optical sensor or a Hall effect sensor or sensors 6 can be applied. When use is made of an Hall effect sensor or sensors 6, it is preferred that magnets 7 are applied on the first extremity 8' and second extremity 9' that are merged into each other distant from the table 3. Preferably further the measuring instrument or instruments are dismounta- ble from the force sensor 1 to enable cleaning and/or sterili zation of the respective parts of the force sensor 1.

It is further preferred that at least one of the base 2, the table 3 and the legs 4 is made from stainless steel.

This reduces manufacturing costs.

Preferably the ball head 5 that connects to the table 2 of the force sensor 1 is a ball of a hip joint implant. Ac cordingly the force sensor 1 of the invention can suitably be used in a hip joint implant of a patient for measuring forces acting on the hip joint implant during movement of the patient. Although the invention has been discussed in the fore going with reference to an exemplary embodiment of the force sensor of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the ap pended claims without intent to limit the claims to this exem plary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment.