WO2015027938A1

WO2015027938A1 - Desktop robot

Info

Publication number: WO2015027938A1
Application number: PCT/CN2014/085405
Authority: WO
Inventors: Christopher Thomas Elsworthy; Christopher James White
Original assignee: CEL Technology Ltd
Current assignee: CEL Technology Ltd
Priority date: 2013-08-28
Filing date: 2014-08-28
Publication date: 2015-03-05
Anticipated expiration: 2016-02-28
Also published as: CN203713074U

Abstract

A desktop robot comprises an interchangeable tool having at least one electrically-powered component; a tool mount for mounting the tool, the robot being operable to control relative movement between the tool mount and an object in three dimensions; complementary first and second electrical couplings on the tool mount and tool respectively, for making an electrical connection to the at least one electrically-powered component of the tool, and complementary first and second tool-less mechanical couplings on the tool mount and tool respectively, for mechanically connecting the tool mount and tool. The desktop robot is arranged to at least improve various performance aspects of known 3D printers, including printing speed, reduced warping due to shrinking of printed articles, and user safety, among others.

Description

DESKTOP ROBOT

Technical field

The present invention relates generally to robotic tools, such as desktop manufacturing robots, and particularly, but not exclusively, to desktop robots for three-dimensional (3D) printing. Background of the Invention

In the past, computer-aided manufacturing technologies were really only affordable to large manufacturers, and smaller businesses could gain access to them through service bureaux. These sorts of technologies include 3D scanning to produce electronic models, or converting electronic models into prototypes, or finished products, using 3D printing, computer-controlled mills, routers and laser cutters, and the like. However, in recent times cost reductions in design software and computer-aided manufacturing have been a benefit for technologists who wish to design and rapidly manufacture products. While presently small businesses, and many ordinary hobbyists, can own an affordable desktop robot for 3D printing, laser cutting or routing, it would be advantageous if cost savings could be achieved to make these technologies still more accessible. Fused Filament Fabrication (FFF) is a type of 3D printing in which a robotic tool lays down material in layers to build up a three-dimensional object. US patent no. 5,121,329 describes a 3D printer using this technology, wherein a filament is fed to a melt chamber where it is melted, and then ejected from an extrusion nozzle in the printer head in fluid form while the printer head moves. The build material may be deposited upon a lower layer with which it is welded, before solidifying to define the final form of the object being printed. A 3D printer typically needs regular calibration to make sure that it is possible to safely move the print head to and from positions within the working envelope, and that the output is accurate. While locations of the printing head and printing bed are roughly known within a general area, the exact location and orientation varies due to the accumulation of manufacturing tolerances. Distortions during shipping or "crashes" into tool frames also disrupt the original orientation. On a 3-axis printer, calibration ensures that various parts are parallel and orthogonal to each other, and usually is done by hand. Manual calibration is dependent upon the visual acuity and visual access of the skilled expert. Furthermore, manual calibration is time-consuming, costly and inconsistent. Sometimes satisfactory observation of printing head motions is difficult. It will therefore be understood that there is a need for improved systems and methods for calibrating 3D printers. It will also be understood that there is a need to improve various performance aspects of known 3D printers, including printing speed, reduced warping due to shrinking of printed articles, and user safety, among others. It is furthermore an object of the invention to address these needs or, more generally, to provide an improved desktop robot.

Disclosure of the Invention A desktop robot comprising: an interchangeable tool having at least one electrically -powered component; a tool mount for mounting the tool, the robot being operable to control relative movement between the tool mount and an object in three dimensions; complementary first and second electrical couplings on the tool mount and tool respectively, for making an electrical connection to the at least one electrically-powered component of the tool, and complementary first and second tool-less mechanical couplings on the tool mount and tool respectively, for mechanically connecting the tool mount and tool.

By providing an interchangeable tool according to the invention, the desktop robot is provided with a degree of modularity, allowing it to be readily reconfigured for different purposes. Preferably the desktop robot comprises a controller for controlling the movement of the tool mount, and the tool comprises a memory device holding tool data characterizing the tool, such that with the tool connected to the tool mount the controller can read the tool data. In this manner, the desktop robot may be readily reconfigured for performing different functions, thus providing faster setup and greater versatility of operation. Preferably the desktop robot is a 3D printer, and the interchangeable tool comprises a print head including a nozzle for discharging a build material, and the at least one electrically-powered component comprises an actuator for controlling opening and closing of the nozzle.

Preferably the tool comprises at least one of: a scanner head with an electrically-powered component in the form of a scanner; a laser cutter head with an electrically-powered component in the form of a laser; a rotary cutter head with an electrically-powered component in the form of a motor driving a rotary cutting tool holder; a prehensile robotic gripper head with an electrically-powered component in the form of a power-actuated gripper; an airbrush head with an electrically-powered component in the form of a valve actuator; a power shear head with an electrically-powered component in the form of a drive for power shears; a vacuum robotic gripper head with an electrically-powered component in the form of a valve actuator and a pen plotter head with an electrically-powered component in the form of a powered pen actuator, wherein each of the heads is adapted for mechanical and electrical connection to the tool mount and includes a second electrical coupling complementary to the first electrical coupling, and a second mechanical coupling complementary to the first mechanical coupling, such that by joining the first and second mechanical couplings the first and second electrical couplings are also joined simultaneously.

The scanner head provides for 3D scanning of physical objects, i.e. the creation of 3D computer models. The scanner is preferably a 3D optical scanner, but most other types of 3D scanners can also be used, such as touch probe scanners, laser range scanners, MR, MRI, CT, x- rays, ultra sound, range cameras, time-of-flight sensors or optical scanners based on silhouettes, structure and motion, shape from shading, shape from texture or colour keying.

Optionally, it will be understood that to further expand the capabilities of the desktop robot for performing other tasks, tool heads without an electrically-powered component may also be used interchangeably, such tool heads may include, for instance, a blade, as for vinyl cutting.

The robot is preferably a Cartesian robot, but other robot configurations, such as cylindrical robots, polar robots, delta robots and articulated robot arms may also be used for moving the tool mount within the three-dimensional operating envelope.

Preferably the robot includes: at least one X rail elongated along a first horizontal axis, the tool mount being connected to move along the X rail; a pair of substantially upright Z rails, each of the Z rails connected to an opposing end of the X rail for raising and lowering the X rail; and a substantially horizontal print bed that holds the object, and is connected to move along a Y rail elongated along a second horizontal axis substantially perpendicular to the first horizontal axis.

Preferably the at least one X rail comprises two X rails elongated parallel to the first horizontal axis, the tool mount being engaged with both of the X rails. Preferably the tool mount comprises a filament-receiving fixture through which a fusible filament is directed to the print head. Preferably the filament-receiving fixture clamps an end of a Bowden tube in which the fusible filament is received.

The first and second mechanical couplings are tool-less couplings that can be quickly connected without tools, and may comprise complementary parts, such as a projection and a complementary recess that, when connected, substantially rigidly unite the tool and tool mount, isolating movement between tool mount and tool head in all degrees of freedom. The projection may be resilient, so as to provide a snap fit.

Preferably the first and second mechanical couplings comprise clamping means, for clamping the tool to the tool mount. Preferably the clamping means comprises a screw, the first mechanical coupling comprising a wheel fixed to rotate with the screw, and the second mechanical coupling comprises an internally threaded aperture complementary to the screw. Optionally, other clamping means such as a cam, or spring may be used. Preferably the screw projects from an interface of the tool mount, and the wheel is disposed on a side of the tool mount opposite the interface. Preferably the screw extends between the two X rails. Preferably the first mechanical coupling further comprises a recess in the tool mount, and the second mechanical coupling further comprises a projection of complementary form to the recess.

Preferably the first and second electrical couplings supply power to the at least one electrical component, but they may also serve to communicate control signals. Preferably one of the first and second electrical couplings comprises an array of connector pins having axes substantially parallel to the screw, and the other of the first and second electrical couplings comprises an array of contacts for engaging the connector pins. Preferably each of the pins has a telescopic construction, with tips spring-biased to an extended position, such as so-called "Pogo pins".

According to still another aspect, the invention provides a desktop robot comprising: a print head assembly including a nozzle for discharging a build material; a Cartesian robot operable to position the print head assembly at any position within a three- dimensional operating envelope, the Cartesian robot including: at least one rail elongated along a first horizontal axis, the print head assembly being connected to move along the at least one rail; and a substantially horizontal print bed that holds the build material; pivoting means compliantly supporting the print head assembly such that contact between the print bed and the nozzle applies a torque to the print head assembly about the pivoting means; an abutment face on the print head assembly for abutting a stop to restrain rotation of the print head assembly about the pivoting means in a first direction when the torque is applied to the print head assembly, but to permit rotation of the print head assembly about the pivoting means in a second direction opposite the first direction; a displacement sensor mounted to the print head assembly providing an output indicative of displacement of the abutment face away from the stop, and a controller that calibrates the robot in response to the output from the displacement sensor. Preferably the at least one rail comprises first and second rails elongated parallel to one another along the first horizontal axis, the pivoting means comprises a linear bearing supporting the print head assembly on the first rail, the first rail being offset from the nozzle such that contact between the print bed and the nozzle applies a torque to the print head assembly about the linear bearing; and the stop comprises the second rail, which abuts the abutment face to restrain rotation of the print head assembly about the first rail.

The displacement sensor may be in the form of a circuit which is closed when the abutment face abuts the stop, and open when the abutment is spaced apart from the stop. Preferably the second rail is an electrical conductor connected in the circuit, and the abutment face is provided on an electrical contact connected in the circuit. Optionally, other types of displacement sensor may be employed.

Preferably the centre of gravity of the print head assembly is offset from the first rail, such that gravity tends to hold the abutment face against the second rail. Alternatively, resilient means may be provided to urge the abutment face against the second rail, such as a poylytetrafluroethylene moulded spring for low friction. Preferably the first and second rails are X rails elongated parallel to a first horizontal axis, and the Cartesian robot further comprises a pair of substantially upright Z rails, each of the Z rails connected to opposing end of the first and second X rails for raising and lowering the first and second X rails; and wherein the print bed is connected to move along a Y rail elongated along a second horizontal axis substantially perpendicular to the first horizontal axis. Preferably a respective Z-actuator is provided for raising and lowering the opposing ends of the first and second X rails, and the controller calibrates the robot by differential operation of the Z-actuators to vary the inclination of the first and second X rails.

Preferably the 3D printer further comprises: a frame member that generally underlies the print bed, the frame member having a reference surface elongated parallel to the Y rail, the print bed including a foot cooperating with the Y rail for supporting the print bed, and in sliding engagement with the reference surface.

Preferably the Y rail is disposed near one edge of the print bed, and the foot is disposed near an opposing edge of the print bed. In yet another aspect the invention provides a 3D printer for FFF, including an interchangeable filament cartridge having: a reel about which the filament may be wound; a hub extending generally centrally through the reel for supporting the reel, such that the reel rotates relative to the hub; a non- volatile memory device mounted to the hub for storing filament-related data, and a communications interface on the hub for allowing data transfer between the non-volatile memory device and the controller.

Preferably the reel has a central axis and comprises two parts, each part including a cylindrical portion and an end flange; an internal circumferential channel is formed between the two parts of the reel when they are fixed together, and the hub includes at least one circumferential rib protruding from the cylindrical surface and received in the circumferential channel.

Preferably the FFF 3D printer has an axle with a fixed end and opposing free end, the free end being adapted to be received in the hub for supporting the hub, and a detent mechanism in the free end for coupling the hub to the axle. Preferably the detent mechanism comprises opposing apertures in the free end disposed for registration with respective openings in the hub, a spring for urging pins to project from the apertures into the openings. Preferably the non-volatile memory device comprises an EEPROM, and the filament-related data includes data defining at least one of: filament material, filament colour, filament diameter and filament length.

Preferably the communications interface comprises an electrical coupling. Alternatively, a wireless communications interface may be provided. Preferably a printed circuit board is mounted to the hub, and the non-volatile memory device is mounted to the printed circuit board, and the electrical coupling comprises one of a pin connector mounted to the printed circuit board for engagement with an array of electrical contacts mounted to the robot.

Preferably the robot further comprises a filament feeder to feed filament to a printer head, the filament feeder comprising: a driving gear meshed with a driven gear; a respective friction wheel rotationally fast with the driving gear and driven gear, whereby the filament is gripped between the friction wheels.

According to another aspect, there is provided a 3D printer for FFF, comprising: an interchangeable print head having a melt chamber in communication with a nozzle for discharging a fluid build material; a print bed for supporting an object to be printed; a translation mechanism for providing relative movement between the print head and the print bed in three dimensions along mutually orthogonal X, Y and Z axes; and a filament feeder to feed filament to a printer head, the filament feeder comprising: a driving gear meshed with a driven gear; a respective friction wheel rotationally fast with the driving gear and driven gear, whereby the filament is gripped between the friction wheels.

Preferably the driven gear is resiliently biased toward the driving gear for clamping the filament between the friction wheels. Preferably the driven gear is mounted to an arm supported by a pivot for rotation toward and away from the driving gear. Preferably the filament feeder further comprises an encoder for providing a feedback signal indicative of the speed of movement of the filament. Preferably the encoder comprises a rotary encoder that cooperates with an idler wheel supporting the filament.

Preferably the filament feeder further includes a filament sensor disposed at a position along a filament path through the feeder to provide a signal indicative of the presence or absence of a filament at the position.

The filament path between the idler wheel and friction wheels may be curved.

The filament feeder provides for accurate feed speed control under high loadings, for corresponding high print speeds. In still another aspect the invention provides a method of controlling a FFF 3D printer, comprising interlocking a door in the housing with the heating element, such that the heating element is prevented from operating unless the door is closed.

Preferably the method further comprises automatically latching the door closed with a latch when the door is closed by a user, and releasing the latch to allow the door to be opened once the internal temperature has dropped below a threshold temperature.

Preferably releasing the latch comprises translating the print bed to abut the latch.

This door interlocking and unlatching provides for improved user safety.

In yet another aspect the invention provides a 3D printer for FFF, including at least two filament feeders, each filament feeder configured to direct filament to a melt chamber that feeds one or more fluid-dispensing nozzles on a print head.

By controlling two filament feeders in this manner seamless changeover from one filament to another may be achieved and, where build materials of different colours are used, colour variations may be provided throughout the object being printed.

Brief Description of the Drawings Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein:

Figure 1 is a perspective view of a desktop robot for 3D printing according to the invention; Figure 2 is a perspective view of a Cartesian robot of the desktop robot of Fig. 1 ;

Figures 3 and 4 are front and rear perspective views respectively, of a tool mount of the desktop robot of Fig. 1 ;

Figure 5 is a perspective view of a print head of the desktop robot of Fig. 1 ; Figure 6 is a section through a print head assembly of the desktop robot of Fig. 1 ;

Figure 7 is a perspective view of the underside of a print bed of the desktop robot of Fig. 1 ;

Figure 8 is a is an exploded perspective view of a wall assembly and filament cartridge;

Figure 9 is a section through the wall assembly and filament cartridge of Fig. 8; and

Figure 10 is a schematic perspective view of a filament feeder of the desktop robot of Fig. 1. Description of the Preferred Embodiments

Referring to Figs. 1 and 2, a desktop robot 10 suitable for performing Fused Filament Fabrication on a desktop may include a housing 13 for holding a Cartesian X-Y-Z translation mechanism 11. The housing 13 has a door 14 which generally opens a front and upper portion of the build chamber 75. Incorporated into one wall of the housing 13 is a wall assembly 65. A print head assembly 15 is moved by the translation mechanism 11 within a three-dimensional operating envelope to print out an object (not shown), the object comprising a build material supported on a print bed 16.

The print head assembly 15 includes a tool mount 17 to which a print head 18 may be attached. The print head 18 is interchangeable with other print heads, or with other like "plug-and-play heads" by simply attaching the print head 18 to the tool mount 17, whereby an electrical connection to the print head 18 is completed at the same time as the mechanical connection, thereby providing power for the operation of valve actuators, heating elements and fans on the print head 18.

The tool mount 17, with reference to an orthogonal XYZ coordinate system, may slide along parallel X rails 12a, 12b, thus moving the tool mount 17 and print head 18 along an X axis of the translation mechanism 11. The tool mount 17 is fixed to a belt 27 driven by a rotary motor 26, whereby the tool mount 17 is reciprocated along the X axis. Opposing ends of the X rails 12a, 12b are fixed to carriages 20a, 20b that slide along respective Z rails 19a, 19b which are substantially upright. A rotary actuator 21 rotates each of the two Z screws 22 for raising and lowering carriages 20a, 20b and attached X rails 12a, 12b. The print bed 16 is disposed below X rails 12a, 12b in a substantially horizontal or XY plane, and is connected to move along a Y rail 23 elongated along a Y axis perpendicular to the X axis. A base frame member 24 is an important structural element in the translation mechanism 11, as it supports both the Z rails 19a, 19b and Y rail 23. The frame member 24 underlies the print bed 16 and is fixed to the housing 13, and also includes planar a reference surface 25 elongated parallel to the Y rail 23. Accordingly, the XZ displacement of the tool mount 17, combined with the Y displacement of the print bed 16, provides the three-dimensional operating envelope relative to the print bed 16 on which the printed object is supported.

As shown in Figs 3 and 4, the tool mount 17 includes an aperture in which a linear bearing 30 is located for receiving the lower X rail 12b, and a concave face 31 for abutting the upper X rail 12a. Disposed between the linear bearing 30 and face 31 is a through-extending opening 28 through which the lower run of the belt 27 passes freely, and a fixture 29 for clamping the tool mount 17 to the upper run of the belt 27. A clamping wheel 32 may be fixed to rotate with a screw 33 that extends between the two X rails 12a, 12b and projects from an interface 34 of the tool mount 17 between the two X rails 12a, 12b. The wheel 32 is disposed on a side 35 of the tool mount 17 opposite the interface 34. A recess 36 in the interface 34 is aligned with a filament-receiving fixture 37 having a central aperture 38. A fusible filament (not shown) may pass through the aperture 38 to the print head 18. The filament-receiving fixture 37 clamps an end of a Bowden tube (not shown) in which the fusible filament is received. An electrical coupling 39 on the interface 34 may comprise an array of connector pins 40 having axes substantially parallel to the screw 33. Surfaces of the recess 36 may also be in the form of a trapezoidal pyramid, for assisting in proper alignment of the print head 18. The rail 12a and an electrical contact 43 are electrically connected in a displacement sensor circuit (not shown), and effectively form a switch. The contact 43 may be mounted to project from the concave face 31 , and has an outer abutment face for abutting the X rail 12a. The rail 12a is electrically conductive , as is the contact 43, and the circuit they are connected in thus provides an output indicative of displacement of the abutment face of the contact 43 away from the X rail 12a which provides an open circuit when electrical contact with the X rail 12a is broken. Connectors 41, 42 may be mounted to the rear side 35 and electrically connected to the electrical coupling 39, contact 43 and to cables (not shown) for transmitting power and electrical signals from a controller (not shown).

The print head 18 is shown separately in Fig. 5 and, in section, mounted to the tool mount 17 in Fig. 6. A body 45 of the print head 18 holds a fan 46 in an opening at its upper side, and a nozzle 47 for dispensing the build material projects from a lower side of the body 45. A projection 49 formed in the body 45 is of complementary form to the recess 36 in which it is received and located. An internally threaded aperture 48 is complementary to the screw 33. An electrical coupling 51 comprises an array of contacts 52 for abutting the connector pins 40, which are preferably so-called "Pogo pins", having a telescopic construction, with tips spring-biased to an extended position. A channel 50 is located for registration with the filament-receiving aperture 38 for directing the filament into a melt chamber 53 heated by a resistance element 54. An actuator 55 controls the opening and closing of valves (not shown) for permitting the build material to flow from the melt chamber 53 to the nozzle 47. A centre of gravity 56 of the print head assembly 15 is offset from the lower X rail 12b, such that gravity applies a torque about the lower X rail 12b that tends to hold the contact 43 against the upper X rail 12. However, if the nozzle 47 abuts a horizontal surface then the resulting force F applies an opposite torque that displaces the contact 43 away from the second rail 12a, and the resulting electrical discontinuity indicates this displacement.

Referring to Figs 1, 2 and 7, the print bed 16 overlies the frame member 24 and its uppermost reference surface 25, and is supported on the Y rail 23. More specifically, a bearing assembly 58 is fixed to the print bed 16 near one of its edges 59 and slidingly engages with, and reciprocates on, the Y rail. The print bed 16 may be coupled by a clamp to one of the runs of a belt 60 elongated parallel to the rail 23 and driven by a rotary drive 161. Near an edge 61 opposite the edge 59, proximate its midpoint, a foot 62 may project from a lower side 63 of the print bed 16. The foot 62 is supported upon the reference surface 25 parallel to the Y rail 23, across which it slides during movement of the print bed 16. The foot 62 may be made from, or include, a low-friction material, such as poly tetr afluroethylene .

Fig. 8 illustrates the construction of the wall assembly 65, and of a filament cartridge 66 which is mounted in part to the wall assembly 65 during use. The wall assembly 65 comprises two shells 67, 68 which are connected together to enclose a drive and electronics chamber 69, and which also define an open reel chamber 70. The shell 68 has a wall 73 bounding an inner side of the build chamber 75. The shell 67 has an outer wall 72 in which an opening 71 is provided for passing the filament cartridge 66 through into the reel chamber 70. An axle 88 may be formed on the shell 68 in a cantilever manner, such that its free end 89 projects into the reel chamber 70.

The filament cartridge 66 may comprise a reel 78 which the filament (not shown) may be wound, and made from reel parts 79, 80 supported upon a hub 81. Each of the parts 80, 81 may include a respective cylindrical portion 79a, 80a integral with a respective end flange 79b, 80b. The hub 81 extends generally centrally through the reel 78 and is fixed, while the reel 78 rotates about the hub 81. The hub 81 includes a cylindrical surface 82 and a circumferential rib 83 that protrudes from the cylindrical surface 82. Opposing apertures 95 are provided in the free end 89 and disposed for registration with respective openings 94 in the hub 81. The detent spring 93 urges pins 96 to project from the apertures 95 into the openings 94.

A non- volatile memory device such as an EEPROM 86 is mounted on a circuit board 186 that is, in turn, mounted to the hub 81. The EEPROM 86 stores filament-related data, including filament material type, melting point, batch number, manufacture date, filament colour, filament diameter and filament length etc.

A communications interface 87 on the axle 88 allows data transfer between the EEPROM 86 and the controller of the robot 10. The communications interface 87 includes a printed circuit board 100 mounted to the hub 81. An array of Pogo-pins 187 is disposed on the printed circuit board 100 for contacting an array of contacts (not shown) on the circuit board 186. As shown in Fig. 9, an internal circumferential channel 84 is formed between the two parts 79a, 80a of the reel 78 when they are fixed together, and the circumferential rib 83 is received in the circumferential channel 84, supporting the reel 78 for rotation and restricting its axial movement along axis 85. A cavity 90 in the rear side of the hub 81 receives the free end 89 of the axle 88 to locate and support the hub 81 and reel 78. A push-button 92 is mounted for axial movement in a hole 98 in the free end 89 and for operating a switch 103 mounted to the printed circuit board 100. The switch 103 sends a signal to the controller to actuate the heater for the melt chamber 53.

A filament feeder 105 for feeding filament 106 to the print head 18 is illustrated in Fig. 10 and generally includes a pair of contra-rotating friction wheels 107, 108 turning about generally parallel axes and gripping opposing sides of the filament 106. A rotary drive 111 rotates a worm 113 about axis 112 to turn the worm wheel 114 to which the wheel 107 is fixed by a drive shaft 115. A driving gear 109 is also fixed to the drive shaft 115 and meshed with a driven gear 110 for transmitting torque to the wheel 108. The driven gear 110 is mounted to an arm 116 supported by a pivot 117 for rotation toward and away from the driving gear 109. Springs (not shown) bias the driven gear 110 toward the driving gear 109 for clamping the filament 106 between the friction wheels 107, 108. A rotary encoder 120 may cooperate with an idler wheel 121 supporting the filament 106 at an input side of the feeder 105 for providing a feedback signal indicative of the speed of movement of the filament 106. The rotary encoder 120 may comprise circumferentially spaced lobes 122 on the idler wheel 121 which engage a microswitch 123, or other known types of rotary encoder, such as optical, magnetic or capacitive rotary encoders. By providing this feedback signal correct and accurate operation is ensured, while errors such as slipping between the filament 106 and friction wheels 107, 108 can be detected. The filament feeder 105 pushes the filament 106 in the output direction 125 toward the print head 18. A filament sensor 124 may be provided at a position along a filament path through the feeder 105, more particularly at a position displaced from the friction wheels 107, 108 in the output direction 125. The filament sensor 124 may comprise a micros witch projecting into the filament path to provide a signal indicative of the presence or absence of a filament at the position. This filament sensor 124 allows the controller to determine the position of the end of the filament when loading a new filament into the machine.

The filament path between the idler wheel 121 and friction wheels 107, 108 may be curved. To ensure that the filament displacement produced by the feeder 105 is reproduced at the print head 18 the filament 106 is restrained within a Bowden tube (not shown).

In operation, the user may first select one from a number of interchangeable heads for fixing to the tool mount 17 according to a task to be performed, such as scanning, vinyl cutting, routing, laser cutting and pen plotting. However, for the purposes of the following description it is understood that the user will select one print head 18, perhaps from a number of different print heads, according to the requirements of a 3D printing task, such as the build material and desired printing speed or resolution. In either case the attachment to the tool mount 17 is alike, and by turning the clamping wheel 32, the print head 18 is simultaneously clamped and electrically connected to the robot 10. A non-volatile memory apparatus (not shown) may be provided in the print head 18 for storing print head data. For instance, the non-volatile memory apparatus may identify the nozzle diameter and position, such that following proper connection to the tool mount 17 no corresponding inputs need be made by the user as a consequence of the selection of the print head 18, and no manual or automated calibration is needed before starting printing.

In a similar manner, the user may select an interchangeable filament cartridge 66 according to the 3D printing task. The filament cartridge 66 is readily installed by inserting it through the opening 71 and pushing the hub 81 over the free end 89 in one of two orientations 180 degrees apart. By storing the filament-related data in the EEPROM 86 the controller may, for example, confirm that the reel 78 holds sufficient filament to complete the printing task and confirm the compatibility of the filament with the print head 18 and adjust other operating parameters such as feed speed and melt temperature accordingly. This, as in the case non-volatile memory apparatus on the print head 18, also provides a "plug-and-play" functionality that allows for quick set up and commencement of operation, without the delay and possible errors introduced by to prompting the user to input the filament-related data. Operation of the robot 10 is controlled by an electronic controller (not shown), the controller controlling the print head 18, and translation mechanism 11, as well as the other components of the system, according to a predefined programme. Following fastening of the print head 18 and closing of the door 14, the controller may perform a calibration routine. In this routine, the controller calibrates the robot in response to the output from the displacement sensor circuit to set the Z axis home position. This calibration routine may comprise lowering the print head 18 to touch the print bed 16 in one position in the XY plane, or at multiple positions in the XY plane. If calibration is performed at multiple positions, the controller can establish whether or not any errors in parallelism are present across the print bed 16, thus when printing an object compensation can be made for these errors. Each of the two rotary actuators 21 rotates a respective one of the Z screws 22, thus by controlling the rotary actuators 21 independently, to provide differential rotation between the screws 22, the angle of inclination between the rails 12a, 12b and the print bed 16 may be varied to make this compensation.

Upon receipt of the signal generated by the actuation of the switch 103, the controller actuates the heater for the melt chamber 53. The controller waits for the melt chamber 53 to reach the correct temperature for the specific filament 106 being used, then actuates the filament feeder 105 to push the filament 106 in the output direction 125 until the output switch 124 is activated, indicating that the end of filament 106 has left the friction wheels 107, 108. A pre-defined angle of rotation of the friction wheels 107, 108 defines the distance the end of the filament 106 must travel from the output switch 124 to the melt chamber 53, and the controller actuates the filament feeder 105 to drive the end to the melt chamber 53 in preparation for the start of printing.

Prior to 3D printing, the controller also operates a heating element (not shown) under the print bed 16, this heating element heats the print bed 16 to an optimum level for adhesion of the build material. The controller modulates the internal temperature to generally maintain a setpoint by selectively operating a fan (not shown) to extract air from the build chamber. Owing to the elevated temperatures of the print bed 16 and nozzle 47, automatic latching of the door 14 when it is closed, ensures that access is restricted until a safe surface temperature has been reached. When the printing process has been completed, the fan may be actuated for cooling, before translating the print bed to abut and release the latch.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.

Claims

1. A desktop robot comprising:

an interchangeable tool having at least one electrically-powered component;

a tool mount for mounting the tool, the robot being operable to control relative movement between the tool mount and an object in three dimensions;

complementary first and second electrical couplings on the tool mount and tool respectively, for making an electrical connection to the at least one electrically-powered component of the tool, and

complementary first and second tool-less mechanical couplings on the tool mount and tool respectively, for mechanically connecting the tool mount and tool.

2. The desktop robot of claim 1 further comprising a controller for controlling the movement of the tool mount, wherein the tool comprises a memory device holding tool data characterizing the tool, such that with the tool connected to the tool mount the controller can read the tool data.

3. The desktop robot of claim 1 wherein the interchangeable tool comprises a print head

including a nozzle for discharging a build material and the at least one electrically-powered component comprises an actuator for controlling opening and closing of the nozzle.

4. The desktop robot of any one of claims 1 to 3 further comprising at least one of: a scanner head with an electrically-powered component in the form of a scanner; a laser cutter head with an electrically-powered component in the form of a laser; a rotary cutter head with an electrically- powered component in the form of a motor driving a rotary cutting tool holder; a prehensile robotic gripper head with an electrically-powered component in the form of a power-actuated gripper; an airbrush head with an electrically-powered component in the form of a valve actuator; a power shear head with an electrically-powered component in the form of a drive for power shears; a vacuum robotic gripper head with an electrically-powered component in the form of a valve actuator and a pen plotter head with an electrically-powered component in the form of a powered pen actuator, wherein each of the heads is adapted for mechanical and electrical connection to the tool mount and includes a second electrical coupling complementary to the first electrical coupling, and a second mechanical coupling complementary to the first mechanical coupling, such that by joining the first and second mechanical couplings the first and second electrical couplings are also joined simultaneously.

5. The desktop robot of any one of claims 1 to 3 wherein the robot is a Cartesian robot.

6. The desktop robot of claim 5 wherein the robot includes:

at least one X rail elongated along a first horizontal axis, the tool mount being connected to move along the X rail;

a pair of substantially upright Z rails, each of the Z rails connected to an opposing end of the X rail for raising and lowering the X rail; and

a substantially horizontal print bed that holds the build material, and is connected to move along a Y rail elongated along a second horizontal axis substantially perpendicular to the first horizontal axis.

7. The desktop robot of claim 6 wherein the at least one X rail comprises two X rails elongated parallel to the first horizontal axis, the tool mount being engaged with both of the X rails.

8. The desktop robot of claim 6 wherein the tool mount comprises a filament-receiving fixture through which a fusible filament is directed to the detachable print head.

9. The desktop robot of claim 8 wherein the filament-receiving fixture clamps an end of a Bowden tube in which the fusible filament is received.

10. The desktop robot of any one of claims 1 to 3 and 6 to 9 wherein the first and second

mechanical couplings comprise clamping means, for clamping the tool to the tool mount.

11. The desktop robot of claim 10 wherein the clamping means comprises a screw, the first

mechanical coupling comprising a wheel fixed to rotate with the screw, and the second mechanical coupling comprises an internally threaded aperture complementary to the screw.

12. The desktop robot of claim 11 wherein the screw projects from an interface of the tool mount, and the wheel is disposed on a side of the tool mount opposite the interface.

13. The desktop robot of claim 12 wherein the screw extends between the two X rails.

14. The desktop robot of any one of claims 1 to 3 and 6 to 9 wherein the first mechanical coupling further comprises a recess in the tool mount, and the second mechanical coupling further comprises a projection of complementary form to the recess.

15. The desktop robot of any one of claims 1 to 3 and 6 to 9 wherein one of the first and second electrical couplings comprises an array of connector pins having axes substantially parallel to the screw, and the other of the first and second electrical couplings comprises an array of contacts for engaging the connector pins.

16. A desktop robot of any one of claims 1 to 3 and 6 to 9:

wherein the tool comprises a print head assembly including a nozzle for discharging a build material; and further comprising:

a Cartesian robot operable to position the print head assembly at any position within a three- dimensional operating envelope, the Cartesian robot including: at least one rail elongated along a first horizontal axis, the print head assembly being connected to move along the at least one rail; and a substantially horizontal print bed that holds the build material;

pivoting means compliantly supporting the print head assembly such that contact between the print bed and the nozzle applies a torque to the print head assembly about the pivoting means; an abutment face on the print head assembly for abutting a stop to restrain rotation of the print head assembly about the pivoting means in a first direction when the torque is applied to the print head assembly, but to permit rotation of the print head assembly about the pivoting means in a second direction opposite the first direction;

a displacement sensor mounted to the print head assembly providing an output indicative of displacement of the abutment face away from the stop, and

a controller that calibrates the robot in response to the output from the displacement sensor.

17. The desktop robot of claim 16 wherein the at least one rail comprises first and second rails elongated parallel to one another along the first horizontal axis; the pivoting means comprises a linear bearing supporting the print head assembly on the first rail, the first rail being offset from the nozzle such that contact between the print bed and the nozzle applies a torque to the print head assembly about the linear bearing; and the stop comprises the second rail, which abuts the abutment face to restrain rotation of the print head assembly about the first rail.

18. The desktop robot of claim 16 wherein the displacement sensor comprises a circuit which is closed when the abutment face abuts the stop, and open when the abutment is spaced apart from the stop.

19. The desktop robot of claim 18 wherein the second rail is an electrical conductor connected in the circuit, and the abutment face is provided on an electrical contact connected in the circuit

20. The desktop robot of any one of claims 17 to 19 wherein the centre of gravity of the print head assembly is offset from the first rail, such that gravity tends to hold the abutment face against the second rail.

21. The desktop robot of claim 17 wherein the first and second rails are X rails elongated parallel to a first horizontal axis, and the Cartesian robot further comprises a pair of substantially upright Z rails, each of the Z rails connected to opposing end of the first and second X rails for raising and lowering the first and second X rails; and wherein the print bed is connected to move along a Y rail elongated along a second horizontal axis substantially perpendicular to the first horizontal axis.

22. The desktop robot of claim 21 wherein a respective Z-actuator is provided for raising and lowering the opposing ends of the first and second X rails, and the controller calibrates the robot by differential operation of the Z-actuators to vary the inclination of the first and second X rails.

23. The desktop robot of claim 21 or claim 22 further comprising: a frame member that generally underlies the print bed, the frame member having a reference surface elongated parallel to the Y rail, the print bed including a foot cooperating with the Y rail for supporting the print bed, and in sliding engagement with the reference surface.

24. The desktop robot of claim 21 or claim 22 wherein the Y rail is disposed near one edge of the print bed, and the foot is disposed near an opposing edge of the print bed.

25. A desktop robot of any one of claims 1 to 3 and 6 to 9, including an interchangeable filament cartridge having:

a reel about which the filament may be wound;

a hub extending generally centrally through the reel for supporting the reel, such that the reel rotates relative to the hub;

a non- volatile memory device mounted to the hub for storing filament-related data, and a communications interface on the hub for allowing data transfer between the non-volatile memory device and the controller.

26. The desktop robot of claim 25 wherein the reel has a central axis and comprises two parts, each part including a cylindrical portion and an end flange;

an internal circumferential channel is formed between the two parts of the reel when they are fixed together, and

the hub includes at least one circumferential rib protruding from the cylindrical surface and received in the circumferential channel.

27. The desktop robot of claim 26 further including an axle with a fixed end and opposing free end, the free end being adapted to be received in the hub for supporting the hub, and a detent mechanism in the free end for coupling the hub to the axle.

28. The desktop robot of claim 27 wherein the detent mechanism comprises opposing apertures in the free end disposed for registration with respective openings in the hub, a spring for urging pins to project from the apertures into the openings.

29. The desktop robot of claim 26 wherein the non-volatile memory device comprises an EEPROM, and the filament-related data includes data defining at least one of: filament material, filament colour, filament diameter and filament length.

30. The desktop robot of claim 26 wherein the communications interface comprises an electrical coupling.

31. The desktop robot of claim 26 wherein a printed circuit board is mounted to the hub, and the non- volatile memory device is mounted to the printed circuit board, and the electrical coupling comprises one of a pin connector mounted to the printed circuit board for engagement with an array of electrical contacts mounted to the robot.

32. The desktop robot of any one of claims 1 to 3 and 6 to 9 further comprising a filament feeder to feed filament to a printer head, the filament feeder comprising:

a driving gear meshed with a driven gear;

a respective friction wheel rotationally fast with the driving gear and driven gear, whereby the filament is gripped between the friction wheels.

33. The desktop robot of claim 32 wherein the driven gear is resiliently biased toward the driving gear for clamping the filament between the friction wheels.

34. The desktop robot of claim 32 wherein the driven gear is mounted to an arm supported by a pivot for rotation toward and away from the driving gear.

35. The desktop robot any one of claims 33-34 wherein the filament feeder further comprises an encoder for providing a feedback signal indicative of the speed of movement of the filament.

36. The desktop robot of claim 35 wherein the encoder comprises a rotary encoder that cooperates with an idler wheel supporting the filament.

37. The desktop robot of any one of claims 33-34 wherein the filament feeder further includes a filament sensor disposed at a position along a filament path through the feeder to provide a signal indicative of the presence or absence of a filament at the position.

38. The desktop robot of claim 37 the idler wheel supports the filament at an input side of the feeder, and the friction wheels support the filament at an output side of the filament feeder, and the filament path between the idler wheel and friction wheels is curved.

39. A desktop robot of any one of claims 1 to 3 and 6 to 9, including at least two filament feeders, each filament feeder configured to direct filament to a melt chamber that feeds one or more fluid- dispensing nozzles on a print head.