The present invention relates to a method for dimensional checking of models generated by additive manufacturing.

As is known, additive manufacturing (also known commonly as “three-dimensional printing”) is nowadays becoming widely used in many and varied sectors.

In the biomedical sector, to which the present invention particularly relates, the practice is increasingly widespread of reproducing bones or other anatomical parts of patients by way of three-dimensional printing, for example for the purposes of analysis and diagnosis of diseases, or for simulating a surgical operation.

The model is produced on the basis of a three-dimensional virtual image of the organ, which can be reconstructed starting from two- dimensional images obtained by way of computerized tomography (CT) or magnetic resonance (MRI).

Some examples of conventional technologies for three-dimensional printing are Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), stereolithography apparatus (ALS), and others.

According to the sector of use, the models produced must meet different quality standards in terms of dimensional tolerance.

With reference to the biomedical sector, a precision of a tenth of a millimeter is typically required.

Currently, dimensional checking is carried out by qualified technicians by way of manual instruments such as calipers, micrometers and the like, or by way of automated measurement apparatuses such as probes, three-dimensional scanners and the like.

However, the necessity to employ qualified technicians for dimensional checking entails high costs and practical limitations.

In particular, it would be desirable to install the three-dimensional printer directly in the place where the model produced will need to be used, typically a hospital, a clinic, a laboratory etc., with the printing process being managed remotely by a specialist technician.

However, in this case the qualified technician must still visit the place of manufacture for the dimensional checking, or the finished model must be sent to the qualified technician and, after the check, returned by the latter to the user, with evident logistical complications.

Another drawback of the conventional systems for dimensional checking is that the equipment for carrying out the measurements can have relatively high purchase costs and maintenance costs, especially for automated measurement apparatuses such as those mentioned above.

Therefore, the aim of the present invention is to provide a method for dimensional checking of models generated by additive manufacturing that is reliable and precise, and which can be carried out with high repeatability by persons without specialized training on the basis of simple instructions, so as to make it possible to manage the entire process remotely.

Within this aim, an object of the invention is to provide a method that has low execution costs.

A further object of the invention is to provide a method that can be applied indifferently to any additive manufacturing technology.

The above aim and other objects, which will become clearer from the description that follows, are achieved by a method having the characteristics recited in the appended claim 1, while the appended dependent claims define other characteristics of the invention which are advantageous, although secondary.

Now the invention will be described in greater detail, with reference to a preferred but not exclusive embodiment thereof, which is illustrated for the purposes of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a front elevation view of a generic three-dimensional printer, by way of which the method for dimensional checking according to the invention can be carried out;

Figure 2 is a side view of two bodies produced by the three- dimensional printer in Figure 1 when set up to carry out the method according to the invention, without dimensional errors;

Figure 3 shows the bodies in Figure 2 during the step of dimensional checking carried out using the method according to the invention;

Figures 4 and 5 are two views, similar to Figures 3 and 4 respectively, but in which the bodies have dimensional errors;

Figure 6 is a perspective view of two more complex bodies produced by the three-dimensional printer in Figure 1 when set up to carry out the method according to the invention;

Figure 7 is a side view of the two bodies in Figure 6 arranged on the reference plane of the three-dimensional printer;

Figure 8 shows the bodies in Figures 6 and 7 during the step of dimensional checking carried out using the method according to the invention;

Figure 9 shows a first accessory element of the method according to the invention;

Figure 10 shows a second accessory element of the method according to the invention.

For the purposes of example, the present description refers to the additive manufacturing technology known as Fused Deposition Modeling (FDM).

That notwithstanding, as will become clearer from the description below, the method according to the invention can likewise be applied to any additive manufacturing technology.

In Fused Deposition Modeling, a filament of polymeric material is heated by a heating element and extruded by way of a nozzle that can move along the three Cartesian axes with respect to a reference plane, on which the model is generated by way of superimposing layers of material.

With initial reference to Figure 1, a generic three-dimensional printer 10 using Fused Deposition Modeling comprises a base 12 that supports the reference plane 14 on a first pair of horizontal guides 16 which extend along a first horizontal axis Y. The reference plane 14 is entrained to translate along the first pair of horizontal guides 16 by first motor means 18.

A portal 22 is fixed on the base 12 and supports a crossmember 24 on a pair of vertical guides 26 which extend along the vertical axis Z. The crossmember 24 is entrained to translate along the vertical guides 26 by second motor means 28.

The crossmember 24 supports an extrusion head 30, provided with the heating element 32 and the nozzle 34 mentioned previously, by way of a second pair of horizontal guides 36 which extend along a second horizontal axis X which is perpendicular to the first horizontal axis Y. The extrusion head 30 is entrained to translate along the second pair of horizontal guides 36 by third motor means 38.

As mentioned previously, the extrusion head 30 is supplied with a filament F of polymeric material which is heated by the heating element 32 and extruded on the reference plane 14 through the nozzle 34.

In a manner that is conventional per se, a computer 42 is programmed to control the movements of the extrusion head 30 along the three Cartesian axes so as to generate, layer after layer, a model I (Figure 2) on the basis of a preset three-dimensional pattern.

As is known, the generated model can present dimensional errors due to various factors, such as: sudden changes in current during the generation of the piece, which can cause unforeseen and uncontrolled movements of the motors; anomalous behavior of the material owing to sudden changes in temperature, unevenness of the material etc.; errors in the calibration of the reference plane 14; errors in the three-dimensional pattern; and other factors. Therefore, a precise dimensional checking of the model building is required for the most critical applications.

According to the invention, the dimensional checking is carried out by producing, in parallel with the model I, at least one control element M which has a profile which coincides with that of the model I in at least two points of contact PI, P2.

Preferably, the two points of contact PI, P2 lie on a straight line R which is inclined by a first angle a with respect to the layers of material of the model I and by a second angle b which is different from the first angle a with respect to the layers of material of the control element M.

In the example in Figures 2 and 3, a dimension to be checked is the distance D between two cusps II and 12 of the model I. The control element M is therefore provided with two pointed portions Ml and M2, the ends of which, if production is correct, must coincide with the ends of the two cusps II and 12.

Figure 2 shows the model I and the control element M arranged on the reference plane 14 in the position in which they are generated, while Figure 3 shows the model I and the control element M as they are being made to line up at the points PI and P2 in order to check that the distance D is correct. In this example, the angle a has a value of approximately 60°, while the angle b is equal to 0.

While the model I shown in Figures 2 and 3 is dimensioned correctly, the model T shown in Figures 4 and 5 (where the similar parts are identified by the same reference numerals with the addition of a prime symbol) has a dimensional error along the vertical axis Z. In Figure 4, the correct profile of the model and of the control element is shown with a dotted line in order to highlight the dimensional error.

As illustrated in Figures 2 and 4, the angle a, a' comprised between the straight line R, R' that joins the two points PI, PF and P2, P2' and the layers of material of the model I, T is different from the angle b, b' comprised between the straight line R, R' and the layers of material of the control element M, M'.

As a consequence, the error generated along the axis Z during the manufacturing of the model G, as shown in Figure 4, although affecting both the model G and the control element M', can be detected from the failure of the profiled elements to coincide at the points PI' and P2' at the time of the comparison (Figure 5).

It has also been found in practice that, since the error propagates mainly along the vertical axis Z, it is preferable that the two points PI, P2 of the model to be checked are mutually spaced as far apart as possible along the axis Z in the manufacturing step, within the limits of the production requirements, so that any error is more evident.

In use, the computer is programmed to generate the model and, in parallel, the control element, using the same material. In the present description the expression “in parallel”, referring to the production of multiple pieces, means that, for each layer of a piece that is laid, before the next layer is laid, a layer of all the other pieces is laid as well, so that the different pieces “grow” in parallel until, one after the other, they are completed.

In this phase, the programming and the printing process can be managed remotely by a qualified technician. Once the printing process is complete, the model and the control element are removed from the printer and lined up by the user for the dimensional checking. Optionally, the qualified technician who manages the printing remotely can prepare simple instructions to show the user the correct assembly of the pieces for the purposes of the dimensional checking, so that this can always be carried out easily even by users with no special training.

For the sake of simplicity of explanation, in the example described above there are only two points of contact in which the control element and the generated model must line up. However, it is evident that the greater the number of points or surfaces of contact, the more precise the dimensional checking will be.

For example, Figures 6 and 7 show a complex model, in particular the model of a hip bone 100, and the respective control element 102, arranged on the reference plane 14 in the position in which they are generated.

The control element 102 has a base 104 from which three rods 106a, 106b and 106c extend perpendicularly, terminating at differentiated heights with three respective areas of contact extending in the three dimensions. The areas of contact of the control element 102 are complementarily contoured with respect to three corresponding reference surfaces of the model 100. In addition, the control element 102 has an additional, broader area of contact 108, concave in shape and also complementarily shaped with respect to a corresponding reference surface of the model 100.

Figure 8 shows the model 100 and the control element 102 while they are being lined up at the ends of the rods 106a, 106b, 106c and at the concave surface 108.

Advantageously, in addition to the control element, in parallel with the model, a flattened calibration element C, shown in Figure 9, is generated. The calibration element C has a base B, with which it rests on the surface, and raised portions and/or recesses on the opposite face, the dimensions of which can easily be measured using a manual instrument, e.g., calipers. In the example in Figure 9, the dimensions to be measured are for some recesses Fla, Fib, F2, F3 which are present on the calibration element C. Advantageously, for an immediate confirmation, the calibration element also bears the correct measurement N 1 , N2, N3 of the dimension to be checked printed thereon.

The calibration element C makes it possible to check the correct calibration of the reference plane 14 of the three-dimensional printer 10, as well as to check that the scaling factor is correct.

Although in the example described herein the calibration element C is shown as being separate from the control element and from the model, it is understood that it could be an integral part of one of them.

Advantageously, in addition to the control element and to the optional calibration element, in parallel with the model a series of modular elements Tl, T2, T3, T4, shown in Figure 10, are also generated. The modular elements Tl, T2, T3, T4 have respective base surfaces and respective lateral surfaces which extend preferably on both vertical and oblique planes and are mutually engageable by interlocking.

As illustrated in Figure 10, the interlocking profiled elements are preferably defined by simple geometric shapes such as triangles, semicircles, squares, trapezoids etc., and they can be put together in one way only.

The modular elements Tl, T2, T3, T4 make it possible to verify the correct calibration of the reference plane 14 of the three-dimensional printer 10 especially in the first layers of the print.

Some preferred embodiments of the invention have been described, but obviously the person skilled in the art may make various modifications and variations within the scope of protection of the claims.

In particular, it is evident per se that, without affecting the general principle defined in the independent claim, the shape and the dimensions of the control element, of the calibration element, and of the modular elements can all be varied widely as a function of the shape of the model to be checked and of the precision required.

The disclosures in Italian Patent Application No. 102018000002833 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.