Lapping station for a robotic island for finishing semi-finished pieces, in particular tibial bases of knee prostheses

Abstract

A robotic island (100) for finishing cobalt-chrome tibial bases of a knee prosthesis comprises a lapping station (120) with lapping plates (328) elastically supported, grinding apparatuses (108; 110) with a grinding group (140) having two grinding wheels (142) on the same motor shaft (146), a gripping hand (200) with a gripper (208) for the tibial base, and piece-holder containers (180) for housing tibial bases of different sizes.

Description

Technical field

[0001] The present invention relates to the field of apparatuses for performing finishing operations on semi-finished pieces; in particular, the subject of the present invention is a lapping station, a grinding apparatus, a gripping hand and a piece-holder container for a robotic island for performing finishing operations on semi-finished pieces. More specifically, the present invention finds application in the field of lapping biomedical prosthesis components, for example a tibial base, for example in cobalt-chrome alloy.Background art

[0002] A semi-finished product for a tibial base is usually obtained by forging a raw piece in a cobalt-chrome alloy; the semi-finished piece is then tool-machined, preferably by milling, in order to obtain an upper pocket, and finally subjected to finishing, in particular grinding and lapping.

[0003] Currently, finishing operations are performed manually, relying on the work of specialized operators who, thanks to their skill and experience, are able to ensure the extremely tight tolerances required for finished biomedical prosthesis components.Object of the invention

[0004] The object of the present invention is to automate the lapping of semi-finished pieces, in particular cobalt-chrome tibial bases, ensuring the tolerances required for the finished piece. This object is achieved by a lapping station, a grinding apparatus, a gripping hand and a piece-holder container, as defined in the independent claims. The dependent claims identify further embodiments of the invention.Brief description of the figures

[0005] The features and advantages of the present invention will be apparent from the following description, provided by way of example and without limitation, in accordance with the figures of the attached drawings, in which: Figure 1 schematically illustrates a knee prosthesis with a femoral base and a tibial base; Figure 2 represents a tibial base; Figures 3a and 3b illustrate a robotic island according to an embodiment of the present invention; Figures 4a, 4b and 4c show a grinding apparatus according to an embodiment of the present invention; Figures 5a, 5b, 5c and 5d illustrate a piece-holder container according to an embodiment of the present invention; Figures 6a, 6b and 6c illustrate a gripping hand according to an embodiment of the present invention; Figures 7a, 7b and 7c show a gripping hand with a tibial base according to an embodiment of the present invention; Figures 8a, 8b and 8c illustrate a lapping station according to an embodiment of the present invention; Figure 9 illustrates a lapping unit according to an embodiment of the present invention; Figures 10a to 10e illustrate a centring station and a survey station according to an embodiment of the present invention. Detailed descriptionPreliminary notes

[0006] For clarity of exposition, the following description explicitly mentions a cobalt-chrome tibial base; it is understood that the present invention is applicable to the finishing of any component, regardless of its function as a biomedical prosthesis component or the material of which it is made. However, in the case of machining cobalt-chrome tibial bases, the invention proves to be particularly advantageous.

[0007] In the following, explicit reference will be made to a lapping operation, that is, a controlled abrasion process to improve the surface finish of a piece, correcting any flatness or geometric defects, carried out by means of an abrasive lapping tape on which the piece is made to slide with slow and controlled movements.

[0008] Sometimes, this machining process is referred to as "lapidation". However, it is considered that, in the field of finishing metal pieces, the term "lapping" is the most appropriate, while the term "lapidation" is confined to the field of jewellery or gemstones, sometimes involving the modification of the shape or the enhancement of the brilliance of the piece.Tibial base

[0009] A knee prosthesis 1 comprises a femoral base 2, applied to the lower end of the femur 4, a tibial base 6, applied to the upper end of the tibia 8, and a polymeric disc 10, fixed to the tibial base 6 and arranged between the tibial base 6 and the femoral base 2.

[0010] The tibial base 6 is made in a single piece, usually in a cobalt-chrome alloy, and comprises an upper region 8 and a lower region 10.

[0011] The lower region 10 comprises a stem 10a having a tibial base axis Z and provided with a terminal stem portion 10b of truncated-cone shape, coaxial with the tibial base axis Z, and a pair of ribs 10c that connect the stem 10a to the lower part of the upper region 8, outside the terminal stem portion 10b.

[0012] The upper region 8 has instead a pocket 8a, intended for housing the polymeric disc 10. The pocket 8a is peripherally delimited by a pocket side wall 8b having an outer peripheral surface 8c and an inner peripheral surface 8d, parallel to the tibial base axis Z, and an upper face 8e lying on a plane orthogonal to the tibial base axis Z.

[0013] Furthermore, preferably, the pocket side wall 8b peripherally has one or more peripheral recesses 8f.Finishing island

[0014] According to one aspect of the present invention, a robotic island 100 for finishing a tibial base 6 preferably comprises a cabin 102 comprising a cabin side wall 104 that peripherally encloses a cabin space 106, inside which are housed a first grinding apparatus 108, a second grinding apparatus 110, a storage magazine 112 for pieces to be machined, a storage magazine 114 for machined pieces, and an anthropomorphic robot 116. The island 100 further comprises a lapping station 120 at least partially accommodated in the cabin space 106, as will be better illustrated below.

[0015] According to an example of a machining cycle, the robot 116 picks up a piece to be machined from the storage magazine 112, brings it near the first grinding apparatus 108 for performing a first grinding operation, then brings it near the second grinding apparatus 110 for performing a second grinding operation, then brings it to the lapping station 120 for performing a lapping or polishing operation, and finally releases the machined piece into the storage magazine 114 for finished pieces.Grinding apparatus

[0016] Preferably, at least the first grinding apparatus 108 and / or the second grinding apparatus 110 each comprise a grinding device with abrasive wheels and belts.

[0017] According to one embodiment, a grinding device comprises a plurality of grinding group, for example three in number, vertically overlapping, in which each grinding group comprises a single grinding wheel and a single electric motor provided with a related motor shaft on which the respective grinding wheel is secured. Preferably, said grinding wheels are vertically aligned, that is, the median planes of the grinding wheels lie on the same imaginary plane orthogonal to the motor shafts, which are parallel to one another.

[0018] According to a further embodiment, a grinding device comprises a plurality of grinding assemblies 140, for example three in number, vertically overlapping, in which each grinding assembly 140 comprises at least two grinding wheels 142, preferably coaxial, each of which is associated with the related grinding tape, and a single electric motor 144 provided with a related motor shaft 146 on which the respective grinding wheels 142 are secured, axially spaced apart and on the same side as the electric motor.

[0019] Each grinding assembly 140 further comprises a belt tensioning mechanism 148 for each grinding wheel 142 of said grinding assembly 140; for example, the belt tensioning mechanism 148 comprises an idle roller 150 for returning the grinding tape. Preferably, the idle rollers 150 of the belt tensioning mechanisms 148 of a predetermined grinding assembly are arranged vertically overlapping and axially offset, so as to be each aligned with the respective grinding wheel 142. In an alternative embodiment, said idle rollers have different axial lengths or oversized axial lengths, so as to support axially offset belts.

[0020] Advantageously, a grinding assembly with multiple wheels as described above makes it possible to considerably increase, for example double, the number of grinding wheels for each grinding apparatus, while keeping the overall dimensions of the apparatus unchanged. In the specific field, a high number of grinding wheels is a highly desirable feature, since materials of very high hardness, such as cobalt-chrome alloys, are involved, and grinding tapes are subject to very rapid wear; having multiple grinding wheels therefore makes it possible to have multiple grinding tapes ready for use, thereby increasing the time interval between interventions on the apparatuses and thus their downtime.Piece-holder container

[0021] The storage magazine 112 for pieces to be machined and the storage magazine 114 for machined pieces are preferably equipped with a plurality of piece-holder containers 180 for housing, respectively, the pieces to be machined and the machined pieces. Preferably, said containers are made in a single piece of polymer material.

[0022] For example, the piece-holder container 180 consists of a body having the shape of a right prism, preferably rectangular or square, having a container compartment 182, delimited at the bottom by a container bottom 184 and peripherally by a container side wall 186.

[0023] Internally, the container side wall is shaped with steps 188, for example on all sides or preferably on three of the four sides (on the two short sides and on one long side). In this way, on the container bottom 184, a smaller standing area 190 is delimited by the lowest step, while above it an annular larger standing area 192 is delimited, constituted by the tread of the highest step. Between the smaller standing area 190 and the larger standing area 192, the various intermediate standing areas 191 are arranged in succession.

[0024] Preferably, furthermore, the body of the piece-holder container 180 has a protrusion 194 extending inwardly from the container side wall 186, for example at one of the longer sides (for example, the one without steps).

[0025] The piece-holder container 180 is intended in particular for the stable accommodation of the upper region 8 of the tibial base 6, so that the upper face 8e of a tibial base 6 rests on a standing area 190, 191, 192 depending on the size of said tibial base 6.

[0026] Usually, in fact, in order to adapt to human anatomy, tibial bases are usually provided in a predetermined number of sizes, differing in the dimensions of the upper region 8. Advantageously, the piece-holder container described above makes it possible to accommodate tibial bases to be machined and machined tibial bases of different sizes: depending on the size of its upper region, a tibial base will rest on the smaller standing area, on one of the intermediate standing areas, or on the larger standing area.

[0027] Advantageously, furthermore, the protrusion 194 is suitable for housing the peripheral recess 8f of the upper region 8 of the tibial base 6, creating a form coupling that stabilizes the support of the piece.Gripping hand

[0028] For handling the pieces, the robot 116 comprises a gripping hand 200 suitable for being applied to an arm of the robot.

[0029] The gripping hand 200 comprises a distributor 202 for fluid connection with the pressurized fluid distribution system, preferably air. For this purpose, the distributor 202 comprises a first connector 204 and a second connector 206.

[0030] The gripping hand 200 further comprises a gripping body 203, supported by the distributor 202 and fluidly connected thereto, actuable in rotation about a gripping axis W, which preferably constitutes the sixth axis of the robot 116.

[0031] The gripping body 203 comprises an actuator 207, actuable in translation, for example pneumatically, between a retracted position (figures 6b and 7b) and an advanced position (figures 6c and 7c), in which it protrudes from the gripping body 203 relative to the retracted position.

[0032] The gripping hand 200 also comprises a gripper 208, applied to the gripping body 203. The gripper 208 comprises a gripper support 210, which extends mainly along a gripper axis X, parallel to the gripping axis W, between a proximal end 212, mechanically connected to the gripping body 203, and a distal end 214. Preferably, the actuator 207 is translatable along a direction that intersects the gripper axis X, for example orthogonally

[0033] The gripper 208 further comprises a fixed jaw 216, secured to the gripper support 210 at the distal end 214. Preferably, said fixed jaw 216 extends axially beyond the support 210 and has a pair of prongs 218.

[0034] Furthermore, the gripper 208 comprises a movable jaw 220, hinged to the support 210, for example on a hinge axis 222 orthogonal to the gripper axis X, so as to be rotatable between a closed position (figures 6b and 7b), in which it cooperates with the fixed jaw 216 to grasp the piece, and an open position (figures 6c and 7c) .

[0035] In particular, the movable jaw 220 comprises a block 222 that extends toward the prongs 218 of the fixed jaw 216 and cooperates therewith for gripping the piece; preferably, the block 222 is shaped with a concave recess so as not to interfere with the terminal stem portion 10b of the lower region 10 of the tibial base 6.

[0036] For example, the tibial base 6 is gripped by the gripper 208 at the lower region 10 and in particular so that the ribs 10c are gripped between the fixed jaw 216 and the movable jaw 220, and more specifically between the block 222 and the prongs 218, without interfering with the terminal stem portion 10b.Lapping station

[0037] The lapping station 120 comprises a station support 302 and a structure 304, supported rotatably by the station support 302 about a vertical station axis Y; the lapping station 120 further comprises a first electric station motor, for example housed in or by the station support 302, for driving the structure 304 in rotation.

[0038] The lapping station 120 further comprises a horizontal standing table 306, on board the structure 304 and rotationally integral therewith, and a plurality of lapping units 310, supported by the standing table 306, preferably arranged symmetrically with respect to an imaginary plane containing the station axis Y.

[0039] For example, the standing table 306 is square-shaped and four lapping units are provided, two arranged in one half of the standing table 306 and the other two arranged in the other half of the standing table 306.

[0040] The lapping station 120 is positioned in the robotic island 100 so that, in a first working configuration, some lapping units 310c, 310d are located inside the island 100, that is, in the cabin space 106, and the remaining lapping units 310a, 310b are located outside the island 100, that is, outside the cabin space delimited by the cabin side wall 104 of the cabin 102. In a subsequent configuration, instead, reached due to the rotation of the structure 304, for example by 180°, the first lapping units 310c, 310d are located outside the island and the remaining lapping units 310a, 310b are located inside the island.

[0041] Advantageously, this allows interventions on the lapping units located outside the island for any maintenance activities or for the replacement of consumable materials, such as the lapping tapes, without interrupting the operation of the island.

[0042] A lapping unit 310 comprises an electric lapping motor 320 having a motor shaft 322 having a vertical lapping axis K, which extends between a lower end 324 and an upper end 326, projecting above the standing table 306.

[0043] The lapping unit 310 further comprises a lapping plate 328 arranged above the standing table 306, having a flat upper face 330, preferably ground, and a lower face from which a plate stem 332 protrudes, fixed to the motor shaft 322 at the upper end 323 thereof.

[0044] The lapping plate 328 is rotatable and actuatable in rotation about the lapping axis K and is supported by an adjustment table 334, arranged above the standing table 306 and raised from it.

[0045] The lapping unit 310 is provided with elastically yielding support means for the cushioned support of the adjustment table 334.

[0046] According to a preferred embodiment, said elastically yielding support means comprise a plurality of elastic elements 336 supported by the standing table 306 and configured to operate permanently on the adjustment table 334, pushing it upward, that is, away from the standing table 306. For example, an elastic element 336 consists of an axially compressible small tube, made of a polymer material.

[0047] Said elastically yielding support means further comprise at least one fixed abutment 338 that defines an upper end of stroke for the adjustment table 334, against which said adjustment table 334 is pushed by said elastic elements 336.

[0048] For example, the lapping plate 328 is rotatably supported by a rolling bearing 340, for example a ball bearing, mounted coaxially to the plate stem 332; for example, the inner race of the bearing 340 is fitted onto the plate stem 332, while the outer race is supported by a plate 342, which is in turn fixed to the adjustment table 334.

[0049] Furthermore, the lapping unit 310 is provided with adjustment means suitable for modifying the height of the upper face 330 of the lapping plate 328.

[0050] For example, said adjustment means comprise a linear adjustment actuator 350, preferably pneumatically actuated, having a regulating stem 352 connected to the adjustment table 334, for example through a spacer 354, for example tubular. The adjustment means further comprise a proportional valve for controlling the pressure of the air supplied to the linear actuator.

[0051] To adjust the height of the upper face 330 of the lapping plate 328, the adjustment actuator 350 is operated so as to pull the adjustment table 334 toward the standing table 306, counteracting the resistance exerted by the elastic elements 336 of the elastically yielding support means.

[0052] In other words, when it is necessary to lower the height of the upper face 330 relative to the standing table 306, the pulling action exerted by the adjustment actuator 350 on the adjustment table 334 overcomes the resisting action exerted by the elastic elements, causing the adjustment table 334 to lower and the elastic elements 336 to compress, until the force equilibrium is re-established at the desired height.

[0053] According to a preferred embodiment, a plurality of elastic elements 336 is provided, interacting with the adjustment table 334 at first connection zones 335 arranged at the vertices of a first regular polygon P1, and a plurality of adjustment actuators 350, interacting with the adjustment table 334 at second connection zones 349 arranged at the vertices of a second regular polygon P2; the vertices of the first polygon P1 are interposed with the vertices of the second polygon P2 (figure 8c).

[0054] The lapping unit 310 is further provided with a lapping tape covering the upper face 330 of the lapping plate 328, preferably adhered to it by means of a non-permanent adhesive, which allows replacement of the tape when worn. For example, the lapping tape has a particularly hard abrasive material, for example consisting of ceramic oxides such as aluminum oxides.

[0055] Preferably, the stator of the lapping motor is mechanically connected to and supported by the adjustment table, so that the lapping unit forms a preassembled device mounted on the structure of the lapping station.

[0056] Advantageously, the lapping unit described above is particularly effective for performing lapping with extremely tight machining tolerances, as it enables fine, repeatable, and easily adjustable adjustment of the position of the lapping tape relative to the gripping hand of the robot that carries the piece to be lapped, in particular with reference to the upper face 8e of the pocket side wall 8b.Centring station

[0057] According to a preferred embodiment, the island 100 further comprises a centring station 400 for the controlled gripping of the tibial base 6.

[0058] For example, the centring station 400 comprises a centring device 402 comprising a centring device base 404 and elastically yielding support means 406 for the elastically yielding support of the centring device base 404. In particular, the centring device base 404 consists of a horizontal plate, for example discoidal, and the support means 406 elastically support in a yielding manner said centring device base 404.

[0059] According to an example of a machining cycle, the robot 116 picks up a piece to be machined from the storage magazine 112, transports it toward the centring station 400 and places it on the centring device base 404, releasing it.

[0060] The gripper 208, in the open position, acts against the centring device base 404, pushing it downward against the elastic action of the support means 406, until the centring device base reaches an abutment.

[0061] The gripper 208 then moves to the closed position, gripping the tibial base 6 again, still at the lower region 10, without interfering with the terminal stem portion 10b.

[0062] The gripping of the tibial base by the gripper is therefore controlled, in the sense that the position of the tibial base at the moment of closing the gripper is uniquely determined.Survey station

[0063] According to a preferred embodiment, the island 100 further comprises a survey station 500 for detecting dimensional parameters P of the tibial base.

[0064] For example, the survey station 500 comprises a probe 502.

[0065] According to an example of a machining cycle, the robot 116, having gripped the tibial base from the centring station 400 or, in an alternative embodiment, coming directly from the storage magazine 112 for pieces to be machined, brings the tibial base 6 toward the survey station 500, so as to cooperate with the probe 502, thus detecting the dimensional parameters P, relating for example to the dimensions of the upper region 8 of the tibial base 6, for example its peripheral dimensions.

[0066] The island 100 further comprises: storage means for storing master dimensional parameters M relating to the dimensions of reference or master tibial bases used as production references, for example for different sizes; electronic management means operationally configured to acquire the dimensional parameters P of the specific tibial base 6 to be ground, acquire the master dimensional parameters M of a master tibial base of the same size as the tibial base being machined, and process the dimensional parameters P and the master dimensional parameters M to determine machining parameters L; electronic control means configured to acquire the machining parameters L and control the lapping station 120 and / or the grinding apparatus and / or the robot as a function of said machining parameters L.

[0067] Advantageously, this makes it possible to comply with extremely tight tolerances, since the various machining operations, for example the grinding operations, are carried out depending on how much certain dimensional parameters P of the tibial base being machined, or a reprocessing thereof, deviate from the master dimensional parameters M of the corresponding reference tibial base.

[0068] The lapping station, the grinding apparatus, the gripping hand and the piece-holder container, and in general the robotic island described above, satisfy the needs of the field and overcome the aforementioned drawbacks, since they allow the finishing operations to be carried out in an automated manner while complying with very tight machining tolerances.

Claims

1. A lapping station (120) for a robotic island (100) for finishing semi-finished pieces, in particular tibial bases (6) of knee prostheses (1), for example made of cobalt-chrome, comprising: - a substantially horizontal standing table (306); - at least one lapping unit (310), comprising: a) a lapping plate (328), electrically actuable in rotation about a vertical lapping axis (K), wherein said lapping plate (328) has a flat upper face (330) intended to support a lapping tape; b) an adjustment table (334) supporting rotatably the lapping plate (328), said upper face (330) being arranged at a predefined height above the standing table (306); c) elastically yielding support means for the elastically yielding support of the adjustment table (334) on the standing table (306).

2. A lapping station according to claim 1, wherein said elastically yielding support means comprise a plurality of elastic elements (336) operating between the standing table (306) and the adjustment table (334), configured to operate permanently against the adjustment table (334), pushing it away from the standing table (306).

3. A lapping station according to claim 2, wherein an elastic element (336) consists of a body, for example a small tube, axially compressible, made of a polymer material.

4. A lapping station according to any one of the preceding claims, wherein said elastically yielding support means comprise at least one fixed abutment (338) defining an upper end of stroke for the adjustment table (334), against which said adjustment table (334) is pushed by said elastically yielding support means.

5. A lapping station according to any one of the preceding claims, wherein the lapping unit (310) further comprises d) adjustment means suitable for modifying the height of the upper face (330) of the lapping plate (328) against the action exerted by said elastically yielding support means.

6. A lapping station according to claim 5, wherein said adjustment means comprise at least one linear adjustment actuator (350) connected to the adjustment table (334) and a proportional valve for controlling the pressure of the air supplied to the linear actuator, said adjustment actuator (350) being configured to pull the adjustment table (334) toward the standing table (306).

7. A lapping station according to claim 6, when dependent on claim 2, wherein - a plurality of elastic elements (336) is provided, wherein said elastic elements (336) interact with the adjustment table (334) in first connection zones (335) arranged at the vertices of a first regular polygon (P1); and - a plurality of adjustment actuators (350) is provided, wherein said adjustment actuators (350) interact with the adjustment table (334) in second connection zones (349) arranged at the vertices of a second regular polygon (P2); - wherein the vertices of the first polygon (P1) are interposed with the vertices of the second polygon (P2).

8. A lapping station according to any one of the preceding claims, wherein the lapping plate (328) is supported rotatably by a rolling bearing (340), supported by the adjustment table (334).

9. A lapping station according to any one of the preceding claims, comprising at least one lapping motor (320) for electrically driving the lapping plate (328) in rotation, said lapping motor (320) being provided with a vertical drive shaft (322) coaxial with the lapping axis.

10. A lapping station according to claim 9, wherein the drive shaft (322) is mechanically connected to the lapping plate (328).

11. A lapping station according to claim 9 or 10, wherein a stator of the lapping motor (320) is mechanically supported by the adjustment table (334).

12. A lapping station according to any one of the preceding claims, wherein the standing table (306) is rotatable on command about a vertical station axis (Y) and said lapping station comprises a plurality of lapping units (310) on board the standing table (306).

13. A robotic island (100) for finishing semi-finished pieces, in particular tibial bases of knee prostheses, for example made of cobalt-chrome, comprising at least one lapping station (120) according to any one of the preceding claims.

14. A robotic island (100) for finishing semi-finished pieces, in particular tibial bases of knee prostheses, for example made of cobalt-chrome, comprising: - at least one lapping station (120) according to claim 12; - at least one anthropomorphic robot (116) suitable for cooperating with the lapping station (120); - a cabin (102) comprising a cabin side wall (104) that peripherally encloses a cabin space (106) in which the robot (116) is housed, said lapping station (120) being partially accommodated in the cabin space (106), such that i) in a first working configuration, first lapping units (310; 310c, 310d) are located in the cabin space (106) and second lapping units (310; 310a, 310b) are outside the cabin space (106); and ii) in a subsequent working configuration, in which the standing table (306) is rotated with respect to the position assumed in the first working configuration, said first lapping units (310; 310c, 310d) are outside the cabin space (106) and said second lapping units (310; 310a, 310b) are in the cabin space (106).

15. A grinding apparatus (108; 110) for a robotic island (100) for finishing semi-finished pieces, in particular tibial bases of knee prostheses, for example made of cobalt-chrome, comprising a grinding device with abrasive wheels and tapes, wherein said grinding device comprises a plurality of vertically overlapping grinding groups (140), wherein each grinding group (140) comprises at least two grinding wheels (142), each associated with a respective grinding tape, and a single electric motor (144) provided with a respective motor shaft (146) on which said grinding wheels (142) are secured, axially spaced apart and on the same side as the electric motor.

16. A gripping hand (200) for a robot (116), comprising: - a distributor (202) for fluid connection with a compressed air distribution system; - a gripping body (203), supported by the distributor (202) and fluidly connected thereto, actuable in rotation about a gripping axis (W), comprising a linear actuator (207) actuable in translation between a retracted position and an advanced position; - a gripper (208) applied to the gripping body (203), comprising: i) a gripper support (210), extending mainly along a gripper axis (X), parallel to the gripping axis (W), between a proximal end (212), mechanically connected to the gripping body (203), and a distal end (214), said actuator (207) being translatable along a direction that intersects the gripper axis (X); ii) a fixed jaw (216), secured to the distal end (214) of the gripper support (210), wherein said fixed jaw (216) extends axially beyond the gripper support (210) and has a pair of prongs (218); iii) a movable jaw (220), hinged to the gripper support (210) orthogonally to the gripper axis (X), engaged with the linear actuator (207) to be operated in rotation between a closed position, in which it cooperates with the fixed jaw (216) to grasp a workpiece, and an open position.

17. A piece-holder container (180) for housing different sizes of workpieces or machined pieces, comprising a single-piece polymer body having a container compartment (182), delimited at the bottom by a container bottom (184) and peripherally by a container side wall (186), wherein, internally, the container side wall (186) is shaped with steps (188) descending toward the container bottom (184), forming at the container bottom (184) a smaller standing area (190) for smaller sizes and, above, a larger standing area (192) for larger sizes and, between these, intermediate standing areas (191).

18. A robotic island (100) for finishing semi-finished pieces, in particular tibial bases of knee prostheses, for example made of cobalt-chrome, comprising: - at least one lapping station (120) and / or at least one grinding apparatus (108; 110); - at least one anthropomorphic robot (116); - a survey station (500) for detecting dimensional parameters (P) of the semi-finished piece; - electronic management means operationally configured to acquire the dimensional parameters (P) and process the dimensional parameters (P) on the basis of master dimensional parameters (M) of a master semi-finished piece to determine machining parameters (L); - electronic control means configured to acquire the machining parameters (L) and control the lapping station (120) and / or the grinding apparatus (108; 110) and / or the robot (116) as a function of said machining parameters (L).

19. A robotic island (100) for finishing semi-finished pieces, in particular tibial bases of knee prostheses, for example made of cobalt-chrome, comprising: - at least one lapping station (120) and / or at least one grinding apparatus (108; 110); - at least one anthropomorphic robot (116); - a centring station (400) comprising a centring device base (404) and elastically yielding support means (406) for the elastically yielding support of the centring device base (404); - an abutment defining a end of stroke for the centring device base (404).

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