Patent Application
20160039148
This invention is directed to a three-dimensional printer, and more specifically a three-dimensional printer having motion sensors attached to or monitoring both the print head and the build platform in order to provide a closed feedback loop to a motion controller.
Through increased use of computer aided design (CAD) solid modeling systems have developed which translates CAD output data into a structural component. Forming objects automatically in three-dimensions is useful in testing for input CAD errors, part functionality, assessing aesthetics, mold formation by subtractive wax, and small production runs. While some of these applications are somewhat insensitive to short and long range dimensional errors, such as assessing of aesthetics, other applications are moderately sensitive to error, such as testing part functionality. Still other applications, such as mold manufacturing, are extremely sensitive to dimensional errors.
Automated three-dimensional part printing techniques that are currently available exhibit generally poor long range dimensional tolerance. In addition three-dimensional printing, also known as additive manufacturing, currently suffers from poor surface finish on the printed part that requires post processing such as sanding to improve the finish. Part of the reason that the surface finish is rough is due to the inherent processing needs, which induce unwanted motion into the print head and the build platform. Consequently a need exists to improve motional compensation for one or both of the print head or the build platform to improve the print quality.
The present invention provides a three-dimensional printer incorporating motion sensors which monitor or are attached to both a print head and a build platform in order to provide a closed feedback loop to a motion controller such that the relative motion between the build platform and the print head is minimized and unwanted positional error is minimized in the x-y printing plane. The motion sensors can be accelerometers, optical motion sensors or piezoelectric sensors. Providing motional compensation and adjustments to both the print head and the build platform improves print quality.
The 3-D printer includes a nozzle for extruding a material, apparatus for controllably positioning the nozzle in accordance with the specification; and apparatus for generating a feedback signal that is indicative of at least one characteristic of a most recently extruded portion of the material. In one embodiment the feedback generating apparatus includes a visual or infrared emission imaging system. In another embodiment the feedback generating apparatus includes a proximity detecting apparatus such as a capacitive sensor, tactile sensor, or pneumatic sensor. The positioning apparatus is responsive to a nozzle movement list stored within a controller for translating the nozzle horizontally within an x-y plane and further comprising an object supporting stage that is translated vertically along a z-axis. The positioning apparatus is also operable for translating the nozzle in the z-axis.
The material may be comprised of, but is not limited to adhesives, waxes, thermoplastic polymers, thermoset polymers, resins, metallic alloys, glasses, epoxy resins, silicone adhesives, and combinations thereof. The material may also include combinations containing dissimilar materials added to impart a desired electrical or structural characteristic to the material.
Referring to
Coupled to nozzle 12 is a nozzle heater 26 which is connected to a source of heater power 28. The heat sensing means, such as a thermocouple 30, contacts the nozzle 12 for maintaining the desired temperature, which is a function of the material being extruded. A conduit 32 is connected to the nozzle 12 and provides for a flow of melted material to be provided to the nozzle 12. This material is held in a heated reservoir 34 that is coupled, via a conduit 36, to a source of compressed air operating at a desired pressure. Conduit 32 has an associated heater 38 and reservoir 34 as an associated heater 40 both of which are connected to a source of heater power 42. A heat sensing means, such as a thermocouple 44, as provided for maintaining the reservoir within a predetermined range of temperatures. The range of temperatures is a function of the melting point of the selected material.
Coupled to the x-y axis translator 14, the z-axis translator 18, and to the needle valve air cylinder 22 is a controller 46. Controller 46 may be embodied in a personal computer data processing system. Connection to the translators 14 and 18 may be made by any suitable means such as a parallel communications port or a serial communications port. Controller 46 has an input for receiving three-dimensional shaped data from a CAD system and has a memory 48 for storing data representative of the structure being extruded by the nozzle.
For certain extrusion materials the various heaters shown may be eliminated altogether. In addition, for those materials that are heated during or after extrusion, a local source of air or some other gas has been found to speed cooling of the material. By example, a duct 47 having a plurality of openings is coupled to a source of air and is disposed such that it provides substantially uniformed flow of cooling air to the plane where extrusion is occurring.
The printer 10 may include a deposition feedback system comprised of a feedback sensor 60 which operates near the tip of nozzle 12 and which provides a feedback signal to the controller 46. This feedback signal is indicative of a characteristic of the extruded bead. More specifically, the feedback sensor 60 detects a position or other characteristic of a most recently extruded portion of the material. By example, the sensor 60 may detect the position of the extruded bead relative to a positional reference system, the bead position being monitored by the controller 46 so as to make adjustments, if required to the nozzle 12 position during extrusion. This technique advantageously permits a finer control of the geometry of the extruded structure and results in a structure that more closely approaches that defined by the three-dimensional shape data. The feedback signal, depending upon the particular type of sensor 60 that is employed, may also provide other information, such as temperature of the extruded bead or a dielectric characteristic thereof.
The feedback provided by the sensor 60 is important and that a number of different mechanisms may operate that result in the extruded material having dimensions other than those intended. For example, when the extruded bead is applied around a convex or concave contour the bead, while still hot enough to be pliable, tends to distort to minimize its length. Also, and depending on the distance from the nozzle to the underlying material, the extruded bead may change its deposited cross-section as a function of this distance. Also, it has been found that back pressure from already deposited material that is near the nozzle may reduce the flow rate out of the nozzle. Also, changes in temperature or composition of the material to be extruded may change the rate at which the material flows out of the nozzle and, as a result, the rate at which the material solidifies to its final dimension.
The feedback sensor 60 may be embodied by a number of different devices that are either fixed to the frame of the system or which are translated with the nozzle 12. In general, the feedback sensor 60 may be embodied within imaging devices or within proximity sensing devices. In either case, the sensors function to provide information regarding the most recently extruded material. More specifically, suitable sensors include, but are not limited to, visible imaging devices, infrared emission imaging devices, capacitive detection devices, tactile detection devices, and pneumatic detection devices.
In addition to sensor 60 which may be attached to nozzle 20, a second sensor 62 is attached to the table 16 for sending a signal to the controller 46. Both sensors 60 and 62 can be high bandwidth motion sensors such as accelerometers, optical motion sensors, piezoelectric sensors which are physically attached or can monitor both the print head and the build platform to provide a closed loop feedback signals 61, 63 to the controller 46 such that the relative motion between the build platform and the print head is minimized thereby eliminating unwanted positional error in the x-y printing plane.
As also shown in
Although the present invention has been described and illustrated with respect to an embodiment thereof, it is to be understood that changes and modifications can be made therein which are within the full intended scope of the invention as hereinafter claimed, for example, the nozzle can be translated in the z-axis and the build platform can be translated in the x-y axis.
