NL2018455B1

NL2018455B1 - Three-dimensional modeling system and method

Info

Publication number: NL2018455B1
Application number: NL2018455A
Authority: NL
Inventors: Jonathan Bruggeman Thomas; Bruggeman Adrianus; Johannes Wolbers Martijn; Hendrik Jozef Voss Kevin; Kuiper Bouwe
Original assignee: Bond High Performance 3D Tech B V
Priority date: 2017-03-02
Filing date: 2017-03-02
Publication date: 2018-09-21

Abstract

A three-dimensional modeling system for creating an object comprising a three-dimensional modeling printhead, wherein the printhead is attached to positioning means spatially moving at least one of the printhead and the object being printed relative to one another. The printhead comprises a tubular feed member and a nozzle arranged at one end of the tubular feed member, the nozzle having a nozzle outlet for dispensing modeling material modeling material, and a nozzle tip, for interfacing previously deposited tracks of modeling material on the object to be created. The tubular feed member comprises a feed channel for feeding the modeling material to the nozzle outlet. The system further comprises modeling material feeding means arranged at an end of the tubular feed member opposite of the nozzle, Wherein the modeling material feeding means are arranged for exerting a pressure on the modeling material within the feed channel towards the nozzle. The system further comprises a pressure determining means for determining a parameter indicative for a pressure exerted on the modeling material. The system further comprises a control system arranged for controlling the modeling material feeding means based on the determined parameter indicative for a pressure exerted on the modeling material. A method of three-dimensional modeling using the system.

Description

DESCRIPTION

FIELD OF THE INVENTION

The invention relates to a three-dimensional modeling system for creating a three-dimensional object, and a method of three-dimensional modeling a three-dimensional object.

BACKGROUND

In three-dimensional modeling objects are formed by layering modeling material in a controlled manner such that a desired three dimensional shaped object can be created. This way of forming objects can also be referred to as additive manufacturing. Very often for three-dimensional modeling a three-dimensional modeling printer is used. The printer has a three dimensionally moveable printhead which dispenses the modeling material, while the printhead is moved over previously deposited tracks of the modeling material.

The object to be printed can be placed on a base. The printhead is movable in a three dimensional space relative to the object being modeled or printed or vice versa. In some cases, the object is movable in one or more dimensions relative to the printhead. Various combinations are possible for moving the object on which the object is modeled relative to the printhead and vice versa.

The motions of the printhead are controlled by a control system which controls in a 3-dimensionally controllable positioning system to which the printhead is attached. By means of software a pattern of tracks can be designed, which pattern is used for moving the printhead and for depositing the tracks.

The object is created on a base structure in a reference location relative to the movable printhead. The modeling material can be fused with previously formed tracks. The three-dimensional modeling material can be fed in the printhead in the form of for example filaments, granulate, rods, liquid or a suspension. The printhead dispenses the modeling material from the printhead through a nozzle and deposits it on the base in the form of tracks forming a layer of tracks, or when a previous layer of the object to be created has been deposited, on the object on previously deposited tracks where it is allowed to solidify. The modeling material can be thermally or chemically or otherwise fused with the previously deposited tracks. The chemically modeling material can be dispensed from the printhead and deposited on the previously deposited tracks and cured to solidify immediately after the deposition.

The relative motion of the base and object to the printhead in tracks and simultaneous deposition of modeling material from the printhead allow the fused deposition modeled object to grow with each deposited track and gradually attains its desired shape.

-2In current material extrusion printers (including granulate extruders, ram extruders and syringe extruders), the material is deposited in a feed forward, flow-controlled way. The flow of the modeling material is kept constant, depending on thickness of the tracks to be deposited and the print speed. As part of the machine calibration, the material flow is calibrated.

Moreover, the X-Y-Z positioning system which causes the printhead to move over the previously deposited tracks of the object being created must be calibrated in order to maintain accurate dimensions of the object to be created and especially to maintain a controlled thickness of the tracks being deposited.

When the calibration is correct, solid objects can be printed accurately using flow control. When the gap between the printhead nozzle and the previously deposited layer for example increases due to lack of calibration, the flow of modeling material can become too small to fill up the gap, thereby causing the occurrence of spaces between the printed tracks, resulting in cavities in the printed object. This is called under-extrusion.

On the other hand, when the gap between the printhead nozzle and the previously deposited layers decreases due to lack of calibration, the flow of modeling material can become too high for the track being deposited, so too much material will be extruded.. This is called over-extrusion. Over-extrusion can also occur when the track is laid between two previously deposited tracks and the space therebetween is narrowing This may result in excessive forces between the object and the printhead and in a rough surface of the object due to overflow of the modeling material. The overflow of modeling material may lead to debris or residue on the nozzle tip of the printhead which may come off the nozzle tip and fuse with the object being printed and cause potential loss of the object.

Loss of calibration may also be caused by thermal expansion and while printing and subsequent shrinking after printing of thermally fused material. When the thermal expansion and shrinking is insufficiently compensated, the gap between nozzle and previously deposited layers may not have constant dimensions. Likewise, also dimensions in directions perpendicular to the deposition direction by the printhead or nozzle may vary due to thermal effects.

Another cause of under- or over extrusion may lie in variation of the modeling material feedstock dimensions. When for example filament of modeling material is used, its diameter may vary causing variations in the amount of modeling material deposited when printing, giving cause to under-or over-extrusion when using constant flow control of the modeling material being deposited.

When performing the calibration of the X-Y-Z system and of the feeding means of the modeling material, the highest priority is to prevent over-extrusion, since this will make the

-3process unreliable. Therefore three-dimensional modeling extrusion printers usually have some degree of under-extrusion causing formation of open spaces or cavities. As a side effect, parts will not be leak-tight or pressure resistant and the strength of the part will be sub-optimal.

SUMMARY

It is therefore an object of the invention to overcome the above described problems and disadvantages.

The object is achieved in a three-dimensional modeling system for creating an three-dimensional object comprising a three-dimensional modeling printhead, wherein the printhead is attached to positioning means spatially moving at least one of the printhead and the object being printed relative to one another.

The printhead comprises a tubular feed member and a nozzle arranged at one end of the tubular feed member, the nozzle having an outlet for dispensing modeling material, and a nozzle tip, for facing previously deposited tracks of modeling material on the object to be created.

The tubular feed member comprises a feed channel for feeding the modeling material to the nozzle outlet.

The system further comprises modeling material feeding means arranged at an end of the tubular feed member opposite of the nozzle, wherein the modeling material feeding means are arranged for exerting a pressure exerted on the modeling material within the feed channel towards the nozzle.

The system further comprises pressure determining means for determining a parameter indicative for a pressure exerted on the modeling material.

The system further comprises a control system arranged for controlling the modeling material feeding means based on the determined parameter indicative for a pressure exerted on the modeling material.

By controlling the pressure, it can be sensed by the control system using the pressure determining means that the under-extrusion occurs when for example the pressure drops below a certain level. By increasing the pressure exerted on the modeling material within the tubular feed member, this under-extrusion can be compensated for. This may occur for example when a space between previously deposited adjacent tracks is widening while depositing the current track.

On the other hand, it can be sensed that over-extrusion occurs when the parameter indicative of the pressure exerted on the modeling material pressure increases above a certain level. By decreasing the pressure exerted on the modeling material within the tubular feed member, this over-extrusion can be compensated for. This may occur for example

-4when a space between previously deposited adjacent tracks is narrowing. By controlling the pressure of the modeling material, remaining spaces in the printed object will be filled well, independent of the volume of the remaining space. This will result in fusing of the track being deposited with the previously deposited adjacent tracks, causing total infill of cavities and improved bonding between adjacent tracks. Therefore, parts will have optimal leak tightness and strength.

The track thickness, determined by the gap between nozzle and previously deposited layer, is usually very small. This implies that the pressure drop over this gap is large due to viscosity of the modeling material. It requires only a distance in the order of magnitude of a millimeter for the pressure drop from the level of the pressure in or at the nozzle tip to reach ambient pressure. As the distance to the nozzle becomes larger, the pressure drop over the gap increases. When the pressure drop is equal to the overpressure in the nozzle, the flow stops and the track does not become wider. As the printhead moves over the object, this balances out to become a stable track width

The main difference with flow controlled printing is that width of the track being deposited balances out to a constant line width while filling up all the gaps nicely, while flow based printing would soon result in systematic under- or over-extrusion.

By controlling the pressure exerted on the modeling material, variations in the gap size between the nozzle and previously deposited tracks are compensated for.

In an embodiment, the control system is arranged for controlling the modeling material feeding means to maintain a pressure exerted on the modeling material between a predetermined minimum pressure value and a predetermined maximum pressure value. This allows the pressure exerted on the modeling material to be within a range ensuring that no overor under-extrusion occurs, regardless of imperfections of alignment or calibration of the positioning means.

In an embodiment, the control system is arranged for maintaining the parameter indicative for a pressure exerted on the modeling material at a constant value. This further improves tracks to be deposited between or adjacent previously deposited tracks to be filled up fully without leaving open spaces, or cavities, while preventing formation of debris and residue. Moreover, the constant pressure reduces wear in the printhead and modeling material feeding means.

In an embodiment, the modeling material feeding means comprise a controllable drive and transmission means connected to the drive for transferring a force generated by the drive to the modeling material. The controllable drive allows the control system to generate a controllable force which results in a pressure exerted on the modeling material within the tubular

-5feed means, i.e. the feed channel and a pressure exerted on the modeling material at the nozzle tip.

In an embodiment, the pressure determining means for determining a parameter indicative for a pressure exerted on the modeling material comprise pressure determining means for determining the parameter indicative of the pressure exerted on the modeling material within the feed channel. This allows for example the parameter indicative for a pressure exerted on the modeling material to be determined by the force exerted on the modeling material by the controllable drive and the transmission means. The thus determined parameter constitutes a measure indicative for the pressure exerted on the modeling material within the feed channel.

Depending on the modeling material, an appropriate drive and force transmission means can be chosen. The controllable drive is controllable by the control system. Forces at the nozzle tip and torque within the drive and transmission system can be considered indicative for a pressure exerted on the modeling material.

In an embodiment, the controllable drive comprises a rotary drive, and the pressure determining means for determining the parameter indicative of the pressure exerted on the modeling material on the modeling material within the feed channel comprise torque determining means for determining a torque exerted by the rotary drive and/or transmission. This allows the parameter indicative of the pressure exerted on the modeling material to be derived from the torque exerted by at least one of the rotary drive and the transmission.

In an embodiment, the controllable drive comprises an electric motor, and wherein the torque determination means comprise a motor current measuring means. This allows torque determination without any further torque sensor.

In an embodiment, the modeling material feeding means comprises a plunger for feeding modeling material into the modeling material feeder. The plunger allows modeling material in the form of rods to be fed into the tubular feed member.

The parameter indicative for a pressure exerted on the modeling material within the feed channel is determined by the pressure exerted on the modeling material by the plunger, and wherein the pressure determining means for determining the parameter indicative of the pressure exerted on the modeling material within the feed channel comprise a force sensor, arranged at the plunger for measuring the pressure exerted by the plunger on the modeling material.

From the exerted force, the parameter indicative for the pressure exerted on the modeling material within the feed channel can be derived. This is an alternative way to measuring motor current or torque from the drive system to easily determine the parameter

-6indicative for a pressure exerted on the modeling material within the feed channel of the tubular feed member.

In an embodiment, the pressure determining means for determining the parameter indicative of the pressure exerted on the modeling material within the feed channel comprise a pressure sensor connected to the feed channel of the tubular feed member. Thus the parameter indicative of the pressure exerted on the modeling material within the feed channel can be determined directly by the pressure sensor.

In an embodiment, the pressure determining means for determining the parameter indicative of the pressure exerted on the modeling material within the feed channel comprise a pressure sensor connected to the feed channel at the nozzle. Thus the parameter indicative of the pressure exerted on the modeling material within the feed channel can alternatively be directly determined by the pressure sensor within the nozzle.

In an embodiment, the pressure sensor arranged at the nozzle comprises a nozzle deformation sensor. This has an advantage that the sensor does not need direct contact with the flow of modeling material within the feed channel of the nozzle.

In an embodiment, the pressure determining means for determining a parameter indicative of a pressure exerted on the modeling material comprise pressure determining means for determining a parameter indicative of a pressure exerted on the modeling material within the track being deposited. This allows direct measurement and control of the modeling material within the track being deposited, thus ensuring smooth deposition of the modeling material and optimal fusing with laterally previously deposited tracks.

In an embodiment, the pressure determining means for determining a parameter indicative of a pressure exerted on the modeling material within the track being deposited comprise a pressure sensor having a fluid channel at the nozzle tip for measuring a pressure in the deposited modeling material at the nozzle tip. The fluid channel at the nozzle tip allows measuring a pressure in the deposited track outside the nozzle near the nozzle outlet. This allows direct measurement of the pressure at the nozzle tip, within the modeling material being deposited, ensuring fast and accurate pressure measurement.

In an embodiment, the pressure determining means for determining the parameter indicative of a pressure exerted on the modeling material within the track being deposited comprise a force sensor arranged between the printhead and the positioning means. The force exerted by the printhead , i.e. nozzle tip, on the modeling material of the track being deposited, can be measured by measuring a counterforce at a different location in the mechanical path from the printhead via the gantry and positioning system, base, to the object to be created, which transmits the force exerted by the printhead on the track being deposited.

-7From the determined force, the pressure exerted on the modeling material at the tip can be derived.

In an embodiment, the force sensor is arranged at an interconnection of the printhead and the positioning means. In this case the force can be measured between the printhead and positioning means, more specifically the gantry against which the printhead is mounted.

In an embodiment, the pressure determining means for determining the parameter indicative of a pressure exerted on the modeling material within the track being deposited comprises a force sensor arranged on a base of the positioning means, which is arranged for receiving the object to be created. The object to be created is located at the reference location. It can be mounted on the base. A force on the build plate can be measured, or alternatively a force between the build plate and positioning means can be measured from which the parameter indicative of the pressure can be derived.

The determined pressure can be compensated by the weight of the object being printed. This weight can for example be determined by the force sensor when the printhead is not active or withdrawn. This can be performed in time intervals during the printing process wherein the deposition of tracks is performed.

In an embodiment, the system further comprises modeling material flow determining means. This allows determination of an amount of modeling material used in depositing tracks. From the modeling material flow and printing speed a thickness of the deposited tracks can be determined.

In an embodiment the flow determining means comprise a displacement sensor for determining displacement of the modeling material feeding means, and wherein the control system is arranged for determining the flow by determining a displacement per unit in time. The modeling material feeding means push the modeling material into the tubular feed member. By measuring a displacement of the feeding means per time unit, a modeling material flow can be determined from the displacement in time and a cross section area of the tubular feeding member.

In an embodiment, the control system is arranged for alternatively controlling a flow of the modeling material using the determined modeling material flow, and controlling the pressure exerted on the modeling material.

In an alternative embodiment, the flow determining means comprise a flow sensor for determining flow of the modeling material feeding means.

In an embodiment, the flow determining means comprise a sensor for determining a rotation speed of the rotary drive. The rotary drive drives the modeling material feeding means. Displacement of the modeling material within the tubular feed member is

-8thereby linked to the rotary speed of the rotary drive. Thus from the rotary speed of the rotary drive the modeling material flow in the tubular feeding member can be derived. This has an advantage in that when an electric motor is utilized as rotary drive, the rotary speed can easily be determined from electric parameters associated with the driving of the motor. Thus no separate displacement sensor is required.

In an embodiment, the control system is arranged for controlling the positioning means and the printhead for depositing two first tracks using flow control, wherein the first two tracks are spaced apart, and wherein the control system is arranged for controlling the positioning means and the printhead for depositing an intermediate track between the two first tracks while controlling the pressure exerted on the modeling material. In this scheme, the first tracks are deposited independent of previously deposited tracks. Such tracks do not require a high filling grade for preventing spaces and cavities, thus flow control can be used. The intermediate second track to be deposited between the first two tracks however require the high filling grade leaving no cavities. Thus this third track can be deposited using pressure control.

In an embodiment, the tubular feed member is heatable by a heating element arranged around at least a lower portion of the tubular feed member adjacent to the nozzle. This allows heatable modeling material to be processed by the fused deposition modelling system. The modeling material is heated while it is pushed into the tubular feed member. When the modeling material reaches the nozzle is heated to the modeling material melting temperature. The heating element can be dimensioned and controlled to reach the required melting temperature.

In an embodiment, the nozzle is heatable by a heating element arranged around or within the nozzle. This allows the heating element of the tubular feed member to be adjusted to a lower temperature preventing the modeling material to thermally degrade as some materials can only be kept at a high temperature, i,e, melt temperature for a limited time. Only in the last part of the feed channel near the nozzle the modeling material is heated to its melting temperature, thus adequate printing is provided while the modeling material is maintained in good condition, i.e. degradation is prevented.

The object is further achieved in a method of three-dimensional modeling, comprising performing three-dimensional modeling using the system for three-dimensional modeling as described above.

The method further comprises: depositing a first track of three-dimensional modeling material, comprising • feeding the modeling material using the modeling material feeding means;

• determining a parameter indicative of a pressure exerted on the modeling material;

-9• controlling the modeling material feeding means depending on the parameter indicative of the pressure exerted on the modeling material.

In an embodiment, the controlling the modeling material feeding means depending on the parameter indicative of the pressure exerted on the modeling material comprises comparing the parameter indicative of the pressure exerted on the modeling material with a reference value, and wherein the controlling the modeling material feeding means is based on a difference between the exerted pressure and the reference value.

In an embodiment, the controlling the modeling material feeding means depending on the pressure exerted on the modeling material comprises maintaining the parameter indicative of the pressure exerted on the modeling material between a previously determined minimum pressure value and a previously determined maximum pressure value.

In an embodiment, the controlling the modeling material feeding means depending on the parameter indicative of the pressure exerted on the modeling material comprises maintaining the parameter indicative of the pressure exerted on the modeling material at a previously determined constant value.

In an embodiment, wherein the step of depositing a first track of threedimensional modeling material comprises depositing the first track in a space between a previously deposited second track of three-dimensional modeling material, and a previously deposited third track of three-dimensional modeling material, the third track being spaced apart from the second track.

In an embodiment the determining a parameter indicative of a pressure exerted on the modeling material comprises determining a parameter indicative of a pressure exerted on the modeling material within the feed channel of the tubular feed member and/or nozzle.

In an alternative embodiment, the determining a parameter indicative of a pressure exerted on the modeling material comprises determining a parameter indicative of a pressure exerted on the modeling material within the track being deposited.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 a shows a diagram of a system for three-dimensional modeling according to the state of the art.

Fig. 1 b shows a block diagram of a control system for controlling a system for three-dimensional modeling according to the state of the art.

Figs. 2a - 2c show aspects of a system for three-dimensional modeling according to the state of the art.

Figs. 3a - 3b show aspects of a system for three-dimensional modeling according to an embodiment of the invention.

- 10Fig. 4a shows a diagram of a system for three-dimensional modeling according to an embodiment of the invention.

Fig. 4b shows a block diagram of a control system for controlling a system for three-dimensional modeling according to an embodiment of the invention.

Fig. 5 shows a diagram of a system for three-dimensional modeling according to an embodiment of the invention.

Figs. 6a - 6d show aspects of a system for three-dimensional modeling according to an embodiment of the invention.

Figs. 7a - 7c show aspects of a system for three-dimensional modeling according to an embodiment of the invention.

Figs. 8a - 8b show aspects of a system for three-dimensional modeling according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In fig. 1a a system for three-dimensional modeling 100 is shown in a simplified form. The system 100 comprises a view step position modeling printhead 121 attached via a connection 107 to a gantry 106, which gantry 106 is comprised in a X-Y-Z positioning system, not shown in fig. 1a, which allows the printhead 121 and object to be printed to be moved relatively to one another while depositing layers 110 of modeling material. The printhead 121 comprises a tubular feed member 101, which acts as an extruder tube, and which is arranged for feeding modeling material 108 from one end of the tubular feed member 101 towards a nozzle 102 connected at the opposite end of the tubular feed member 101. The tubular feed member 101 can for example be made from a metal, such as stainless steel.

The tubular feed member 101 and the nozzle 102 comprise a feed channel 120a, 120b respectively. The feed channel 120b of the nozzle 102 leads to the nozzle outlet 102a at the nozzle tip 102b. During printing, the nozzle tip 102b is in contact with the modeling material being deposited 110.

The three-dimensional modeling material 108 may include thermoplastic polymers such as for example polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polycarbonate (PC) and polyether ether ketone (PEEK). These materials can be melted within the tubular feed member 101 and dispensed from the printhead nozzle 102 in subsequent tracks 109, 110, for forming an object to be created.

The tubular feed member 101 and also the nozzle can be provided with one or more heating elements, which can be arranged around the tubular feed member 101, to heat and melt modeling material feedstock in order to allow the printhead to deposit and fuse modeling material in a molten state.

- 11 Other materials for three-dimensional modeling may include pastes, suspensions or resins, which can be deposited in thin tracks 109, 110 and cured for example by exposure to ultraviolet light, air, heat, or other curing agents.

The modeling material 108 is deposited on a base in a first track, and on previously deposited tracks 109 in a successive deposition operations conducted by the X-Y-Z positioning system. The base can be a base plate, ground or any other structure suitable for initiating the deposition of tracks and building and carrying the object to be printed. The base can be fixed or movable. In some cases, the base is movable in a horizontal X_Y direction, whereas the printhead is movable in a vertical Z-direction. In other cases, the base is movable in X-Y-Z horizontal and vertical direction relative to the printhead. In again other cases, the printhead is movable in X-Y-Z horizontal and vertical direction relative to the base. In this description the latter case is provided by way of example.

While the printhead 121 is moved over the previously deposited tracks 109, a drive system comprising a drive 104, a transmission 105a, 105b for transmitting the rotary motion of the drive 104 to a longitudinal motion of a plunger 103, which pushes the modeling material within the feed channel 120a of the tubular feed member 101 towards the nozzle 102. The rotation to translation transmission 105,a, 105b, 103 can be a spindle transmission, wherein the nut 105b is driven by the rotary drive 104. The pressure exerted on the modeling material 108 by the rotation to translation transmission can be derived from the determined torque using the transfer ratio of the angular displacement of the motor axle and the longitudinal displacement of the plunger 103 attached to a spindle of the rotation to translation transmission 105a, 105b, 103. The rotary drive 104 can be a stepper motor which can be controlled digitally to proceed a discreet number of steps in a chosen direction. The rotary drive 104 can also be an electric motor, DC or AC, or servomotor, which is controllable by voltage and/or current supplied to the motor. In the latter case, an encoder connected to the motor axle may provide position information of the motor.

The plunger 103 can be provided with a displacement sensor 111, which can be arranged to measure a displacement X of the plunger 103 relative to the tubular feed member 101. The state of the art as depicted in fig. 1a is shown as an example for example feeding modeling material rods in the tubular feed member 101 to the nozzle 102. In the art alternative examples of feeding modeling material to the nozzle are available, such as feeding modeling material filament into a tubular feed member 101 using for example filament punch rollers, which can be driven by an electric motor. The deposition of tracks 110 on top of previously deposited tracks 109 performed in similar ways using a X-Y-Z positioning system whilst the modeling material filament is fed into the tubular feed member 101.

- 12The system 100 according to fig. 1a, can be controlled by a control system which is arranged to dispense three-dimensional modeling material at a rate proportional to a required track thickness and printing speed. In order to achieve this, a predetermined flow of the modeling material 108 is to be achieved. The control system controls the drive 104, and a displacement sensor 111 measures displacement X of the plunger 103. The displacement of the plunger 103 per time unit provides the flow of the modeling material 108, thereby allowing the control system to regulate the required amount of dispensed modeling material 108 in track 110.

In fig. 1 b an example of a control system is shown wherein a set value S for the required flow is provided to a subtraction unit 115, which is arranged to subtract the calculated displacement X per time unit, thereby giving an error signal which can be supplied to a regulator module 114 of the control system.

The regulator module 114 can be provided with an appropriate transfer function H1, having a proportional, proportional and integrating, or proportional integrating and differential control function. The control system controls the drive 104 and transmission unit 105,105a and the transmission of the spindle transmission from the gear 105b to the plunger 103. The drive 104, transmission 105a, 105b and associated transmission ratio of these elements are symbolically depicted in block 113 of the example in fig. 1 b. As descripted the displacement of the plunger 103 can be obtained from a displacement sensor 111, however the skilled person may find alternatives for establishing the displacement of the plunger 103.

In fig 2a. three-dimensional modeling 100 is illustrated according to the state of the art. A new track 110a of modeling material 108 is deposited on previously deposited tracks 109. In an ideal situation, the deposited tracks are continuously deposited. There are no gaps between the previously deposited tracks and tracks, neither in horizontal direction nor in vertical direction. This can be achieved when the flow of modeling material is accurately controlled relative to the required track thickness and deposition speed of the printhead 121. The degree and tightness of depositing modeling material 108 depends highly on calibration of the system or printer.

In fig. 2b, a common fault in flow controlled three-dimensional modeling is shown called under-extrusion. In under-extrusion, cavities or gaps 201 occur during the deposition of the modeling material. A track 110b is shown which is incompletely dispensed while printing on the printing on the previously deposed tracks. Such gaps 201 may occur when the threedimensional modeling system is not properly calibrated. When performing the calibration, the aim is normally to prevent over-extrusion, since this will make the process unreliable. However, perfect calibration is not possible due to random errors, therefore three-dimensional modeling systems or printers usually have some degree of under extrusion. As a side effect, parts will not be leak-tight or pressure resistant and the strength of the part will be sub-optimal.

- 13In fig. 2c, over-extrusion is represented. In over-extrusion, the flow of modeling material 108 into the deposited layer 110c is too high. As a consequence crests 202 of modeling material 108 may occur, caused by the nozzle tip 102b accumulating modeling material 108 and pushing excess modeling material to the sides, transverse to the deposition or printing direction.

In fig. 3a, track 110d of modeling material is deposited tight fitting between previously deposited tracks 109 independent of the volume of the remaining space between these tracks. Similarly in fig 3a. the space between the previously deposited tracks 109 is narrower than the tracks themselves.

In fig. 3b, the deposited track 110e is broader than the previously deposited tracks. This will result in total infill of cavities and improved bonding to adjacent and lower print tracks. Therefore parts printed in this way will have optimal leak tightness and strength, which can be achieved in a deposition modeling system as described below.

In fig. 4a a fused deposited modeling system 400 is shown similar to fig. 1a. A torque sensor 401 can be provided to measure the torque exerted by the drive 104 and transmission 105a, 105b to the plunger 103 and thereby to the modeling material 108. From the measured torque, a pressure exerted on the modeling material 108 in the tubular feed member 101 can be derived.

Alternatively, a pressure sensor may be attached to the plunger 103. The pressure sensor is arranged for measuring the pressure exerted by the plunger 103 to the modeling material 108. The plunger pressure sensor can be attached to the tip of the plunger 103 to measure the pressure exerted on the modeling material directly. The plunger pressure sensor can also be a force sensor attached to the point of engagement of the plunger 103 with the drive 104 and/or transmission system 105a, 105b. Moreover the pressure sensor can be a strain gauge attached the plunger stem. When a pressure or force is applied to the plunger 103, this pressure or force is transferred to the modeling material 108. Due to the applied pressure or force, the plunger stem will deform, which can be measured by the strain gauge. The pressure exerted by the plunger 103 on the modeling material 108 in a higher end of the tubular feed member 101 eventually results in a pressure of the modeling material within the nozzle 102.

In fig 4b, a control system is shown for performing pressure controlled threedimensional modeling with the system 400. As an example, the torque sensor 401 can provide a measured torque of the motor which drives the modeling material feed means which can be used as the measured parameter P_M indicative of the pressure exerted on the modeling material 108 within the feed channel 120a, 120b of the tubular feed member 102.. Alternatively, the motor current can be used as parameter P_M indicative of the pressure exerted on the modeling material 108 within the feed channel 120a, 120b. The motor current is proportional to the torque

- 14delivered by the motor to the transmission 105a, 105b to the plunger 103. Moreover the plunger pressure can be used as parameter P_M indicative of the pressure exerted on the modeling material 108.

The control system 412 can be arranged to compare the measured parameter P_Mto a reference parameter value P_R, by means of a subtractor 403. The measured parameter P_Mis subtracted in the subtractor 403 from the reference parameter value P_R, which difference is supplied to the regulation function module 402 having a transfer function H₂. The transfer function H₂can be proportional (P), proportional and integrating (PI), or proportional, integrating and differentiating (PID). The controller provided with a regulation module 402 controls the drive system 113.

By controlling the motor current, pressure control on the modeling material 108 within the tubular feed member 101 can be achieved.

The reference parameter value or setpoint P_R may vary depending on printhead travel speed, gap size, temperature, modeling material properties.

In fig. 5 the system corresponding to the system of fig. 4a is shown having an alternative way for establishing the parameter indicative of the pressure exerted on the modeling material 108. In the system of fig 4a, the parameter is indicative of the pressure exerted on the modeling material within the printhead 121, i.e. the tubular feed member 101. In the system of fig. 5, the parameter indicative of the pressure exerted on the modeling material is determined by the pressure exerted on the modeling material being deposited in track 110 at the tip 102b of the nozzle 102. While extruding by exerting a pressure on the modeling material 108 in the printhead 121, a pressure at the nozzle tip 102b is caused within the deposited layer 110, which results in an force which pushes the nozzle tip 102b away from the previously deposited tracks 109.

This force is propagated from the printhead 121 via the gantry 106 and X-Y-Z positioning system 503 which is connected to the base 504 whereupon the object to be modeled is placed. Alternatively, the X-Y-Z-system and gantry may be connected to ground. Thus the object to be printed can be on ground which serves as a base for the object to be printed. The force exerted on the modeling material is then measurable between the object and the ground.

The force is thus also being propagated between the gantry 106 and the printhead 121 and can for example be measured at the connection 107. The connection 107 of the printhead 121 to the gantry 106 of fig. 4a can be formed by at least one resilient connection member 502. A displacement sensor 501 can measure the deformation of the resilient connection member 502 as a measure for the force transmitted through the propagation path from the printhead to the object to be created via the X-Y-Z system and base, and thereby the

- 15pressure exerted on the feed in the deposited track 110. Alternatively, measurement of the force can also be achieved in a system according to fig. 4a, wherein the connection 107 between the printhead 121 and gantry 106 is provided with a load cell or strain gauge, which measure a pressure exerted by the printhead 121 and the track 110 being deposited.

Moreover, the force exerted on the modeling material in the layer 110 being deposited can be measured between the object and the base 504, by for example using a weight scale, or pressure pad. The force thus measured is indicative for the pressure exerted on the modeling material within the layer being deposited.

As shown in figures 6a - 6d, alternatively to measuring the pressure exerted on the modeling material within the printhead 121, as described in relation to figure 4a, i.e. the torque of the drive and transmission system or force at the plunger 103, a pressure exerted on the modeling material 108 within the tubular feed member 101, i.e. the feed channel 120a can be measured directly, as shown in fig. 6a. The pressure measured by the pressure sensor 601 can be used for controlling the drive 104 in order to obtain a pressure suitable for printing the modeling material into the track 110 to be deposited. An alternative placement of pressure sensor 602 is shown in fig. 6b, wherein the pressure sensor 602 is placed within the nozzle 102 and wherein the pressure is sensed of the feed channel 120b within the nozzle 102. An alternative for measuring the pressure within the feed channel 120b is to measure deformation of the nozzle around the feed channel 120b.

An alternative to measuring the pressure within the feed channel 120a, 120b, is to have a pressure sensor 604 as shown in fig. 6d, which is arranged within the nozzle 102 and which is fluidly connected to the nozzle tip 102. The pressure measured at the nozzle tip 102b represents the pressure exerted on the modeling material track 110. Thus this way an alternative way to for establishing a pressure exerted on the modeling material in trackl 10 is established relative to fig. 5 is provided.

Pressure sensors suitable for use in a three-dimensional modeling system as described above for measuring pressure within the printhead 121, comprise membrane sensors which have a deformable membrane. A liquid such as mercury may transfer the pressure within the modeling material channel wherein pressure is to be measured, i.e. the feed channel 120a, 120b, or at the nozzle tip 102b to the membrane. The sensor itself may be of a type including a thin film metal sensor, a conductor/strain gauge related sensor, a piezo-electric sensor, magneto-resistive sensor, laser interferometer sensor and sensor based on mechanical displacement.

As shown in figures 6a - 6d, the track 110 can be deposited next to a previously deposited track 109 using pressure control forming a continuous track of deposited modeling material. The track 110 will by the pressure exerted on it via the nozzle orifice or nozzle tip flow

- 16to the previously deposited track and fuse with the previously deposited material. In figures 7a 7c an alternative strategy is shown for deposition of tracks of modeling material using pressure control.

A first track 701 is deposited, using flow or pressure control as shown in fig. 7a.

In fig. 7b a second track 702 is shown being deposited spaced apart from the first track 701. In fig. 7c a third track 703 is shown being printed between tracks 701 and 702 using pressure control. The modeling material 108 fills the open space between the first track701 and the second track 702 and fuses with these previously deposited tracks, such that the tracks 701, 702 - 703 form a continuous layer without gaps or cavities.

In figures 8a, 8b a refinement of the printing strategy is shown, wherein a first stack of tracks 801 is deposited using flow control. Adjacent tracks 802a, 802b having a more coarse deposition profile can be deposited using pressure control as an infill.

The control system may comprise a programmable logic controller (PLC), a microcontroller or processor having a memory (RAM, ROM, EPROM, etc) comprising program instructions, which in operation cause the processor to perform the controlling as described.

The program instruction may comprise modules for calculating pressures exerted on the modeling material 108 from these indicative forces and torques as described. Moreover losses due to friction and other causes within the drive, transmission, modeling material tubular feed member 101 and nozzle may be calculated and used to compensate or correct the control loops 412 as described.

The embodiments above are descripted as examples only. Supplements and modifications can be made to these embodiments without departing from the scope as defined set out in the claims below.

REFERENCE NUMERALS

100 Three-dimensional modeling system

101 Tubular feed member

102 Nozzle

102a Nozzle outlet

102b Nozzle tip

103 Piston

104 Drive

105a, 105b Gear

106 Gantry

107 Connection bar

108 Modeling material

- 17Previously deposited tracks

Deposited FDM track

New track of modeling material

Incompletely dispensed track of modeling material

Over-extruded track of modeling material

Track of modeling material deposited in tight fitting

Track of modeling material broader than the previously deposited tracks Displacement sensor

Displacement control system

Drive system compensation

Flow regulator module

Feed channel

Printhead

Three-dimensional modeling system for pressure control within the printhead Sensor for parameter indicative of pressure within feed channel

Pressure control module

Subtractor

Control system for pressure control

Three-dimensional modeling system for pressure control at nozzle tip

Displacement sensor

Resilient member

XYZ positioning system

Pressure sensor

First track

Third track

Second track

First track using flow control

Second track using flow control

Third track using pressure control

First stack of tracks

Adjacent tracks

Flow setpoint

Displacement per time unit

Pressure setpoint

Measured parameter indicative of the pressure

Flow control transfer function

- 18‘H₂’ Pressure control transfer function

Claims

CONCLUSIONS

A three-dimensional modeling system (400, 500) for creating a three-dimensional object comprising a modeling printhead (121);

- wherein the printhead (121) is attached (106,107,502) to positioning means (503) for spatially moving the printhead (121) and the object to be created;

- wherein the printhead (121) comprises:

a tubular supply member (101);

a nozzle (102) disposed at one end of the tubular feed member (101), the nozzle (102) having a nozzle outlet (102a) and a nozzle tip (102b) for interfacing with pre-deposited tracks (109) of modeling material (108 ) on the object to be created;

- wherein the tubular supply member (101) comprises a supply channel (120a, 120b) for supplying modeling material (108) to the nozzle outlet (102a);

- wherein the system (400, 500) further comprises modeling material supply means (103, 104, 105a, 105b) disposed at an end of the tubular supply member (101) against over the nozzle (102), the modeling material supply means (103, 104, 105a, 105b) are adapted to exert a pressure on the modeling material (108) within the supply channel (120a, 120b) to the nozzle (102);

- wherein the system (400, 500) further comprises pressure determining means (401, 501,601-604) for determining a first parameter (Pm) indicative of a pressure exerted on the modeling material (108, 110);

- wherein the system (400, 500) further comprises a control system (412) adapted to control the modeling material supply means (103, 104, 105a, 105b) based on the said determined first parameter (Pm) indicative of a pressure exerted on the modeling material (108, 110), wherein the control system is adapted to control the positioning means and the print head (121) for depositing two first tracks (701, 702), said two first tracks (701, 702) spaced apart, and depositing an intermediate track (703, 110d, 110e) between said two first tracks (701, 702) while controlling the pressure exerted on the modeling material using

-20 of said first parameter (Pm) indicative of a pressure exerted on the modeling material (108, 110).

A system according to claim 1, wherein the control system (412) is adapted to control the modeling material supply means (103, 104, 105a, 105b) around said first parameter (Pm) indicative of a pressure exerted on the modeling material (108, 110) between a predetermined minimum pressure value and a predetermined maximum pressure value.

The system (400, 500) according to claim 1, wherein the control system (412) is adapted to hold said first parameter (Pm) indicative of a pressure exerted on the modeling material (108, 110) at a constant value.

A system (400, 500) according to any one of the preceding claims, wherein the modeling material supply means (103, 104, 105a, 105b) comprise an adjustable drive (104) and transmission means (105a, 105b, 103) for transferring a driving force generated by the drive (104) on the modeling material (108).

The system (400, 500) according to any of the preceding claims, wherein the pressure determining means (401, 501, 601-604) for determining said first parameter (Pm) indicative of a pressure exerted on the modeling material (108, 110) is pressure determining means (401, 501, 601-604) for determining a second parameter indicative of a pressure exerted on the modeling material (108, 110) within the feed channel (120a, 120b).

The system (400) according to claim 4 or 5, wherein the controllable drive (104) comprises a rotary drive, and wherein the pressure determining means (401, 601-604) for determining said second parameter indicative of the pressure exerted on the modeling material ( 108) within the feed channel (120a, 120b) include torque determining means (401) for determining a torque exerted by the rotary drive (104) and / or transmission means (105a, 105b).

The system (400) according to claim 6, wherein the controllable drive (104) comprises an electric motor (104) and wherein the torque determining means (401) comprises motor current measuring means.

A system (400) according to claim 5, wherein the modeling material supply means (103, 104, 105a, 105b) comprise a piston (103) for supplying modeling material rods in the tubular supply member (101), and wherein the pressure-determining means (401,601-603 ) for determining said second parameter indicative of the pressure exerted on the modeling material (108) within the supply channel (120a, 120b) include a pressure sensor mounted on the piston (103) for measuring the pressure exerted by the piston ( 103) on the modeling material (108).

A system (400) according to claim 5, wherein the pressure determining means (401, 601-603) for determining said second parameter indicative of the pressure exerted on the modeling material (108) within the supply channel (120a, 120b) pressure sensor (601 ) connected to the supply channel (120a) of the tubular supply member (101).

The system (400) according to claim 9, wherein the pressure determining means (401, 601-603) for determining said second parameter indicative of the pressure exerted on the modeling material (108) within the supply channel (120a, 120b) is a pressure sensor ( 602) connected to the supply channel (120b) at the nozzle (102).

The system (400) according to claim 10, wherein the pressure determining means (601)

603) include a nozzle distortion sensor (603).

A system (500) according to any one of the preceding claims 1-4, wherein the pressure determining means (401, 501,601-604) for determining said first parameter (Pm) indicative of a pressure exerted on the modeling material comprises pressure determining means (501,604) for determining a third parameter indicative of a pressure exerted on the modeling material within the intermediate track (703, 110d, 110e) being deposited.

The system (500) according to claim 12, wherein the pressure determining means (501)

604) for determining said third parameter indicative of a pressure exerted on the modeling material within the intermediate track (703, 110d, 110e) being deposited comprising a pressure sensor (604) with a fluid channel at the tip (102b) of the nozzle for measuring a pressure in the deposited modeling material (110) at the tip of the nozzle (102b).

A system (500) according to claim 12, wherein the pressure determining means (501, 604) for determining said third parameter indicative of a pressure exerted on the modeling material within the intermediate track (703, 110d, 110e) being deposited a force sensor (501) included between the printhead (121) and the positioning means (504, 106).

The system (500) according to claim 14, wherein the force sensor (501) is mounted on a connection (107) of the print head (121) and the positioning means (106).

The system (500) according to claim 12, wherein the pressure determining means (501, 604) for determining said third parameter is indicative of a pressure exerted on the modeling material within the intermediate track (703, 110d,

110e) that is deposited includes a force sensor mounted on a base (504) adapted to receive the object to be created.

The system (400, 500) according to any of the preceding claims, further comprising modeling material, flow determination means.

The system (400, 500) according to claim 17, wherein the flow determining means comprises a displacement sensor for detecting displacement of the modeling material supply means (103, 104, 105a, 105b), and wherein the control system is adapted to determine the flow through determining a displacement per time unit.

The system (400, 500) according to claim 17, wherein the flow determining means comprises a flow (flow) sensor for determining the flow of the modeling material.

The system (400, 500) according to claim 17 and claim 6, wherein the current determining means comprises a sensor for determining a rotational speed of the drive (104, 105a, 105b).

The system (400, 500) according to any of claims 17-20, wherein the control system (412) is further adapted to alternately control a flow of the modeling material (108) using the determined modeling material flow.

The system (400, 500) according to claim 21, wherein the control system (412) is further adapted to control the positioning means (106) and the printhead for depositing said two first tracks (701, 702) while said flow of the modeling material is controlled.

A method of three-dimensional modeling for creating a three-dimensional object, comprising:

performing three-dimensional modeling of the three-dimensional object using the system (400, 500) for three-dimensional modeling according to any of claims 1-22;

feeding the modeling material (108) using modeling material feeding means (104, 105a, 105b, 103);

determining a first parameter (Pm) indicative of a pressure exerted on the modeling material;

- controlling (412) the modeling material supply means (104, 105a, 105b, 103) depending on said first parameter (Pm) indicative of a pressure exerted on the modeling material (108, 110);

-23 depositing two first tracks (701, 702) of three-dimensional modeling material, said two first tracks (701, 702) being spaced apart, and depositing an intermediate track (703, 110d, 110e) between the said two first tracks (701, 702) while controlling the pressure exerted on the modeling material using said first parameter (Pm) indicative of a pressure exerted on the modeling material (108, 110).

The method of claim 23, wherein controlling (412) the modeling material supply means (104, 105a, 105b, 103) depending on said first parameter (Pm) indicative of the pressure exerted on the modeling material (108, 110) comprises:

comparing (403) said first parameter (Pm) indicative of the pressure exerted on the modeling material (108, 110) with a reference value (Pr); and wherein the control is based on a difference between said first parameter (Pm) and the reference value (Pr).

The method of claim 24, wherein controlling (412) the modeling material supply means (104, 105a, 105b, 103) depending on said first parameter (Pm) indicative of the pressure exerted on the modeling material (108) comprises:

holding said first parameter (Pm) indicative of the pressure exerted on the modeling material (108, 110) between a predetermined minimum pressure value and a predetermined maximum pressure value.

The method of claim 25, wherein controlling (412) the modeling material supply means (104, 105a, 105b, 103) depending on said first parameter (Pm) indicative of the pressure exerted on the modeling material (108, 110) comprises keeping said first parameter (Pm) indicative of the pressure exerted on the modeling material (108, 110) at a predetermined constant value.

The method of claim 23, wherein determining said first parameter (Pm) indicative of a pressure exerted on the modeling material comprises determining a second parameter indicative of a pressure exerted on the modeling material (108) within the feed channel (120a, 120b) of the tubular feed member (101) and / or nozzle (102).

A method according to any of claims 23-26, wherein determining said first parameter (Pm) indicative of a pressure exerted on the modeling material comprises determining a third parameter indicative of a pressure exerted on the modeling material within the track ( 110, 703) that is deposited.

5

The method of any one of claims 23 to 28, further comprising:

• determining a modeling material flow;

• alternately controlling a flow of the modeling material (108) using the modeling material flow.

The method of claim 29, further comprising:

Depositing said first two tracks (701, 702) while controlling said flow of modeling material.

-25112

FIG. 1a (State of the art)

111

FIG. 1b (State of the art) i- ': g? C (State of ih-art ·

Fig 2d, Stale or

FIG. 3b

FIG. 3a

FIG. 4b

108

701