FIELD OF THE INVENTION

The present invention generally relates to printing systems and specifically to a 3D printing nozzle calibration system. CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims priority from and is related to U.S. Provisional Patent Application Serial Number 62/467,258, filed 03/06/2017, this U.S. Provisional Patent Application incorporated by reference in its entirety herein.

BACKGROUND 3D printing or Additive Manufacturing (AM), Fuse Depositing Modeling (FDM) and Fused Filament Fabrication (FFT) refer to any of the various processes for printing a three-dimensional object. Primarily additive processes are used, in which successive layers of material are laid down under computer control. These objects can be of almost any shape or geometry, and are produced from a 3D model or other electronic data source. Different types of 3D printers were developed over the years, such as 3D FDM (Fused Deposition Modeling) extrusion printers. 3D FDM extrusion printers are mostly based on melting a filament, e.g. plastics, in a printer head.

While printing with high melting temperature printing materials, such as, glass, metal, etc., it is desirable to maintain a high temperature in the printing area in order to avoid cracks or breakages due to thermal stresses on the printed part. For that purpose, the printing process has to be performed in a hot environment e.g., inside a heated chamber/furnace.

Height calibration of the printing nozzle relative to the printing base plate is very important, especially for the first layer. If the nozzle (printing head) is placed too close to the printing base plate, the first layer may be very thin and hard to adhere. If the nozzle is placed too far from the printing base plate, the first layer will not adhere at all. The printing base plate is not perfectly flat so it is important to calibrate the nozzle height relative to the printing base plate in a number of points of the printing base plate area.

The Height calibration is much more critical while printing at high temperatures because of the significant thermal expansion.

Existing solution use distance sensor installed near the printing nozzle.

While moving the printing base plate on XY plane to a number of determined points, the base plate moves up and down on Z axis until the distance sensor recognize the printing base plate. Performing this process in a number of determined points enables the printer controller to generate a mapping file of the nozzle's height relative to the printing base plate for the whole printing base plate area.

Since the important value is the distance between the nozzle and the printing base plate (not the distance between the distance sensor and the printing base plate), another measurement is required, the distance between the nozzle and the printing base plate at least at one of the determined points. This measurement may be done manually by moving the nozzle towards the printing base plate. By using this method, there is a risk of damaging the nozzle by crashing it into the printing base plate. The heated chamber/furnace raises a problem of how to calibrate the nozzle's height while the nozzle's tip is mounted in a very hot environment (e.g., 600 deg C) inside the heated chamber/furnace where it is impossible to use standard electronic

devices/distance sensors, etc. Therefore, there is a need for a system enabling to calibrate the height of a printing nozzle while the nozzle's tip is mounted in a hot (or very hot) environment. BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a

fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings:

Fig. 1 is a schematic view of a 3D printing nozzle calibration system, printing using a fixed printing head/nozzle and a moving printing base plate according to embodiments of the present invention;

Fig. 1A is a schematic side view of the 3D printing nozzle calibration system of Fig. 1;

Fig. 2 is a flowchart showing the nozzle's calibration process performed by the system of Fig. 1 according to embodiments of the present invention;

Fig. 3 is a schematic view of a 3D printing nozzle calibration system, printing with a moving printing head/nozzle and a fixed base plate, according to embodiments of the present invention;

Fig. 3A is a schematic side view of the 3D printing nozzle calibration system of Fig. 3; and

Fig. 4 is a flowchart showing the nozzle's calibration process performed by the system of Fig. 3 according to embodiments of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the

phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

The present invention provides a system for calibrating a 3D printing nozzle while the nozzle's tip is mounted in a hot (or very hot) environment (e.g., 600 deg C). Throughout the description, 3D printing materials printed inside a heated chamber, such as, glass, metal or any other printing material requiring high melting temperature may be referred to as printing material(s).

It will be appreciated that the calibration process of the present invention is performed in a system printing using a fixed printing head/nozzle and a moving printing base plate, but this process may also be performed similarly in a system printing using a moving printing head/nozzle and a fixed printing base plate or any other combination of a moving printing nozzle and a moving printing base plate. It will be appreciated that the terms "fixed printing nozzle" and "fixed printing base plate" are related to the printing process. During calibration the printing nozzle and/or the printing base plate may be fixed or not.

Fig. 1 is a schematic view of a 3D printing nozzle calibration system 100, printing using a fixed printing head/nozzle and a moving printing base plate, according to

embodiments of the present invention, comprising: a heated chamber/furnace 105, a printing head (nozzle) 110 partially mounted inside the heated chamber 105, a moving substrate/printing base plate 120 mounted inside the heated chamber 105, moving means 106 for moving the printing base plate 120 in the XYZ planes, a moving carriage 140 to which the printing nozzle 110 is connected, at least one linear guide rail 150 (two are shown) on which the moving carriage 140 is sliding up and down, a hard stop 160 connected to the moving carriage 140, a fixed part 170, defining the nozzle's tip position (the working position), on which the hard stop 160 is resting, and a printer controller (not shown).

The upper side of the nozzle 110 is mounted outside the heated chamber 105 and the lower side (the nozzle's tip) is mounted inside the heated chamber 105. The nozzle 110 is connected to the moving carriage 140 which is mounted outside the heated chamber 105. The carriage 140 slides on at least one linear guide rail 150, parallel to "Z" axis, and enables the nozzle 110 to move up if exposed to a vertical pushing force. The hard stop 160 connected to the carriage 140 rests against the fixed part 170 and defines the nozzle's tip position (the working position).

According to embodiments of the present invention, the hard stop 160 is connected to one polarity of a simple electric circuit and the fixed part 170 is connected to the other polarity of the same electric circuit. As long as the hard stop rests against the fixed part 170, the electric circuit is closed, namely, the nozzle's tip is at the lower position - working position. When the nozzle moves up, the hard stop 160 disconnects from the fixed part 170 and the electric circuit is opened. When the disconnection happens, the electric circuit sends a signal to the printer controller to record the exact height of the printing base plate.

Fig. 1A is a schematic side view of the 3D printing nozzle calibration system 100 of Fig. 1

Fig. 2 is a flowchart 200 showing the nozzle's calibration process performed by the system 100 according to embodiments of the present invention. In step 210, the printer controller sends a command to the printing base plate moving means to move the printing base plate 120 in the XY plane to a determined point. In step 220, when the printing base plate is at the determined point, the printer controller sends a command to the printing base plate moving means to move the printing base plate 120 up in the Z axis. When the nozzle's tip touches the printing base plate, the nozzle 110 is pushed up by the printing base plate and the hard stop 160, which is connected to the same moving carriage as the nozzle 110, also moves up and disconnects from the fixed part 170. In step 230, due to the disconnection, the electric circuit is opened, sends a signal to the printer controller to record the printing base plate's height and the controller sends a signal to the printing base plate moving means to stop moving up. This Z height parameter is stored in the printer controller.

It will be appreciated that this process may be repeated as desired, in a number of determined points, in order to create a mapping file of the distances between the printing base plate and the nozzle's tip at each one of the determined points of the printing base plate.

It will be appreciated that the system 100 may include, instead of the electric circuit, a load cell as the fixed part on which the hard stop is resting. In such a case, the printer controller measures the force made on the load cell and detects degradation of the force when the printing base plate touches the nozzle's tip.

It will be appreciated that other solutions such as a distance sensor, a capacitive base sensor, an IR sensor, laser based sensor, etc. may also be used instead of the electric circuit to detect the disconnection of the hard stop 160 from the fixed part 170.

As mentioned before, the hard stop defines the nozzle's tip lower position (working position). Sometimes during printing, a retraction of the printing material is required. The retraction involves a force that may pull the nozzle up, if the nozzle is free to move up on its carriage. According to embodiments of the present invention, in order to prevent that movement, during printing (not during height calibration), an electromagnet (e.g. 180 of Fig.1) or any other type of locking mechanism which can prevent this movement, may be used in order to keep the nozzle's tip locked at working position (e.g., mechanical). In some cases, the electromagnet may be the fixed part (170 of Fig. 1) on which the hard stop is resting. In such a case, the hard stop should be formed from a magnetic material (ferromagnetic). According to embodiments of the present invention, a cleaning station may be used before or during the calibration in order to prevent cases where molten material which stuck to the nozzle's tip causes the height measurement to be inaccurate. According to embodiments of the present invention, the height calibration process may be performed on a non-planar printing base plate or surface. Since the process may be repeated as desired, a comprehensive mapping file may be generated by calibrating in a large number of points. According to the mapping file, the printer controller may send Z axis corrections to the printing base plate while printing.

As mentioned above, the described calibration process may be performed in a system printing with a fixed printing head/nozzle and a moving printing base plate and in a system printing with a moving printing head/nozzle and a fixed printing base plate or any other combination of a moving printing nozzle and a moving printing base plate.

Fig. 3 is a schematic view of a 3D printing nozzle calibration system 300, printing with a moving printing head/nozzle and a fixed printing base plate, according to embodiments of the present invention, comprising: a heated chamber/furnace 305, a moving printing head (nozzle) 310 partially mounted inside the heated chamber, a substrate/printing base plate 320 mounted inside the heated chamber, a moving carriage 340 to which the printing nozzle 310 is connected, at least one linear guide rail 350 on which the moving carriage is sliding up and down (two are shown), a board 355 on which the at least one linear guide rail 350 is mounted, a hard stop 360 connected to the moving carriage 340, a resting part 370 connected to the board 355, defining the nozzle's tip position (the working position), on which the hard stop 360 is resting, a printer controller (not shown) and moving means (365 of Fig. 3A) for moving the board 355 in the XYZ planes along with the printing nozzle 310, the carriage 340, the hard stop 360, the at least one linear guide rail 350 and the resting part 370.

As mentioned before, the hard stop defines the nozzle's tip lower position (working position). Sometimes during printing, a retraction of the printing material is required. The retraction involves a force that may pull the nozzle up, if the nozzle is free to move up on its carriage. According to embodiments of the present invention, in order to prevent that movement, during printing (not during height calibration), an electromagnet (e.g. 380 of Fig.3) or any other type of locking mechanism which can prevent this movement, may be used in order to keep the nozzle's tip locked at its current working position (e.g., mechanical). In some cases, the electromagnet may be the resting part (370 of Fig. 3) on which the hard stop is resting. In such a case, the hard stop should be formed from a magnetic material (ferromagnetic). Fig. 3A is a schematic side view of the 3D printing nozzle calibration system 300 of Fig. 3

Fig. 4 is a flowchart 400 showing the nozzle's calibration process performed by the system 300 according to embodiments of the present invention. In step 410, the printer controller sends a command to the printing nozzle moving means to move the printing nozzle in the XY plane to a determined point. In step 420, when the printing nozzle is at the determined point, the printer controller sends a command to the printing nozzle moving means to move the printing nozzle down in the Z axis. When the nozzle's tip touches the printing base plate, the nozzle is pushed up by the printing base plate and the hard stop, which is connected to the same moving carriage as the nozzle, also moves up and disconnects from the resting part. In step 430, due to the disconnection, the electric circuit is opened, sends a signal to the printer controller to record the nozzle's height and the controller sends a signal to the printing nozzle moving means to stop moving up. This Z height parameter is stored in the printer controller.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the appended claims and includes combinations and sub-combinations of the various features described hereinabove as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description.