Device for rotating the workpiece

Abstract

A device (1) for rotating a 3D printing workpiece (100). The device has a rotor (2) for rotation about a rotation axis (A) and a receptacle (8) for holding the workpiece (100). The receptacle (8) is pivotally mounted to the rotor (2) for rotation about a pivot axis (B) transverse to the rotation axis (A). The pivotable mounting allows for pivoting of the receptacle (8) between a first angular orientation relative to the rotation axis (A) and a different second angular orientation relative to the rotation axis (A). The device (1) further has a counterweight (9) movably disposed relative to the receptacle (8). The counterweight (9) is lockable at different distances relative to the receptacle (8).

Description

[Technical Field]

[0001] The present invention relates to a device for rotating a workpiece, particularly a dental workpiece, that is being constructed in an additive manufacturing process, particularly for cleaning the workpiece and removing at least some excess photocurable material that was used to construct the workpiece. [Background technology]

[0002] In various technical fields, physical or mechanical workpieces are increasingly being produced by additive manufacturing processes (also referred to herein as 3D printing).

[0003] Such additive manufacturing processes typically allow a workpiece to be built into its desired individual shape by successively adding material to create that shape, and are increasingly replacing so-called subtractive processes, in which a workpiece is machined by removing material from a larger blank.

[0004] While additive manufacturing processes are widely used in industry for rapid prototyping, the production of final products remains challenging in many areas. In particular, for producing dental restorations, it is generally necessary to use materials that are compatible for use in the human body. Furthermore, dental restorations produced by the building process must meet requirements for mechanical stability as well as aesthetic expectations, for example, regarding color shade and color tone.

[0005] Some additive manufacturing processes are based on stereolithography, which typically uses light to harden a photocurable or photopolymerizable resin. Computer-aided design and / or computer-aided manufacturing (CAD / CAM) data is used to project a light pattern onto a layer of photocurable resin. The photosensitive resin is typically hardened by exposure to light, resulting in a layer of hardened resin according to the pattern. By building up successive layers, the desired three-dimensional workpiece is created. The pattern is then controlled according to the desired geometry of the three-dimensional object.

[0006] Typically, at the interface between the workpiece and the photocurable material, some photocurable material is present on the workpiece after the workpiece is constructed. The photocurable material is typically present on the workpiece in varying amounts, depending, for example, on the viscosity of the photocurable material. This excess or extra material is generally undesirable because it forms additional structure on top of the actual shape of the workpiece, and because the photocurable material is often tacky, may contain undesirable monomers, and / or may not form a durable structure. Therefore, currently, such residual photocurable material is often post-cured to provide a solid surface on the workpiece. According to another approach, the workpiece is cleaned mechanically or with the aid of a chemical solution and, optionally, then post-cured.

[0007] While existing approaches for cleaning workpieces produced by additive manufacturing provide useful results, there remains a need to efficiently clean such workpieces while minimizing damage or impact to the workpiece during cleaning. A solution should desirably be available for a variety of different additive manufacturing processes that operate based on different chemical materials for constructing the workpieces.

[0008] EP 2216105 (B1) (Peugeot) describes a method for cleaning and drying machined parts by centrifugal movement of the machined part, the centrifugal movement comprising rotation of the machined part about at least two rotation axes inclined relative to each other.

[0009] German Patent Application Publication No. 102015120211 (A1) (Zippel) relates to a movable holding device for workpieces or machine components to be industrially cleaned, comprising at least one first drive unit having a horizontally extending first drive shaft which can be driven about a pivot axis by means of the first drive unit, a second one arranged on the first drive shaft unit having a second drive shaft which is drivable by means of the second drive unit around the first one, perpendicular to the pivot axis extending rotation axis, and a workpiece support unit having a workpiece support for holding and receiving the workpiece or machine component to be cleaned. Summary of the Invention

[0010] The present invention relates to a device for rotating a workpiece. Such a workpiece is preferably of the type produced by additive manufacturing (further referred to herein as a "3D printed workpiece," with stereolithography or digital light processing sometimes being preferred). The device comprises a rotor for rotation about an axis of rotation. The device may further comprise a receptacle for holding the workpiece. The receptacle is pivotally connected to the rotor for rotation about a pivot axis transverse to (or perpendicular to) the axis of rotation, thereby enabling rotation of the receptacle between a first angular orientation relative to the axis of rotation and a different second angular orientation relative to the axis of rotation. The device further comprises a counterweight movably disposed relative to the receptacle. The counterweight is lockable at different distances relative to the receptacle.

[0011] In one embodiment, the device includes a workpiece, and the receptacle is optional. The workpiece may be pivotally connected to the rotor for pivoting about a pivot axis transverse to (or perpendicular to) the axis of rotation, thereby enabling pivoting of the workpiece between a first angular orientation relative to the axis of rotation and a different second angular orientation relative to the axis of rotation. The device further includes a counterweight movably disposed relative to the workpiece. The counterweight is lockable at different distances relative to the workpiece.

[0012] The weight of the counterweight is typically in the range of 20 g to 100 g or 30 g to 50 g.

[0013] The distance at which the counterweight can be locked relative to the workpiece is within the range of 30mm to 150mm.

[0014] The present invention is advantageous in that it enables rotation of a workpiece in at least two different, determined angular orientations. In contrast to conventional centrifuges, in which the angular orientation results from the centrifuge's geometry and rotation speed, the device of the present invention enables at least one of two or several different angular orientations to be controlled independently of the rotation speed. Furthermore, the present invention is advantageous in that it enables effective rotation of a workpiece according to its shape. For example, the angular orientation to which the workpiece is rotated can be determined in advance during the workpiece design stage. The present invention is further advantageous in that it enables rebalancing of a workpiece during rotation, for example, when excess photohardenable material detaches from the workpiece, thereby reducing the weight of the workpiece containing the excess photohardenable material. The present invention is further advantageous in that it enables removal of excess material from a workpiece without the use of any solvents. Therefore, the quality of the workpiece is not affected by any solvents.

[0015] The viscosity of the photocurable material to be removed from the surface of the workpiece during the spinning process is typically 23°C and 1 s -1 At shear rates of 0.1 to 150 Pa * s or 1 to 100 Pa * It is within the range of s.

[0016] The rotation speed is typically in the range of 100 to 3,000 revolutions per minute (r / min), or in the range of 1,800 to 3,000 r / min, the latter range sometimes being preferred due to the higher viscosity of the photocurable material.

[0017] In one embodiment, the device comprises a workpiece (e.g., received on a receptacle). The workpiece may, in particular, comprise a dental workpiece. Such a dental workpiece may be a dental dentition model, in particular a 3D printed positive model or replica of the patient's dentition. The 3D printed positive model of the patient's dentition may be used as an alternative to a plaster model obtained from a dental impression. Furthermore, the workpiece may be a dental aligner. Such a dental aligner may have a negative shape of the patient's teeth and may be shaped to move the teeth toward a desired position.

[0018] In one embodiment, the workpiece comprises a dental restoration or multiple dental restorations, such as one or more dental crowns, one or more dental bridges, one or more dental inlays, or any combination thereof. A dental crown or bridge typically has an outer surface and an inner surface. The outer surface typically corresponds to the surfaces that are visible or accessible in the patient's mouth (e.g., the occlusal and lateral surfaces), while the inner surface typically forms a cavity for receipt over a tooth stump or dental abutment.

[0019] The workpiece typically has dimensions of 1 to 10 cm in the x and y directions and 1 to 5 cm in the z direction. The weight of the workpiece typically ranges from 0.1 g to 100 g, or from 0.2 g to 50 g.

[0020] The workpiece may further include one or more support structures for supporting the dental restoration while it is being constructed. The workpiece may also include a base structure on which the dental restoration is held (ultimately via the support structures) on the receptacle.

[0021] In one embodiment, the device may have only one receptacle and / or only one workpiece, thus facilitating rebalancing of the workpiece during rotation (e.g., due to changes in weight).

[0022] In one embodiment, the device includes an actuation drive for computer-controlled positioning of the counterweight at different distances relative to the receptacle. The actuation drive may include a motor and a spindle drivable by the motor. The spindle may have threads that engage with corresponding threads in the counterweight. The motor may include a positioning sensor for controlling the angular position of the motor toward a desired position. Thus, by rotating the motor toward a known angular position, the counterweight is displaced to a known linear position. This is because rotation of the spindle via the motor is translated into a corresponding proportional linear displacement of the counterweight. It is noted that the actuation drive is not limited to a spindle drive. Those skilled in the art will recognize alternative actuation drives, for example, based on electric linear drives or pneumatic or hydraulic cylinders.

[0023] In one embodiment, the device further comprises a sensor for sensing imbalances induced in response to rotating the rotor. The sensor may be based on an acceleration sensor. The acceleration sensor may be positioned to measure accelerations in at least one or two dimensions radial to the axis of rotation. For example, the sensor may be mechanically coupled, e.g., fixed, to the device or a component of the device. If any imbalances induced in response to rotating the rotor, the device (or a component thereof) may vibrate. The vibrations of the device may be sensed by the acceleration sensor.

[0024] Furthermore, the sensor may be based on a force sensor arranged to measure the force exerted by the rotor on the force sensor in at least one or two radial dimensions of the axis of rotation. For example, the force sensor may be arranged to sense the force exerted on a bearing supporting the rotor.

[0025] In one embodiment, the sensors may be configured to sense any imbalances that occur in response to rotating the rotor in two or three axes based on a Cartesian coordinate system.

[0026] In one embodiment, the actuation drive is controlled to position the counterweight based on the output of the sensor. For example, upon sensing an imbalance (by sensing acceleration or force), the actuation drive may be controlled to displace the counterweight in a first direction. During and / or after the displacement of the counterweight, any imbalance is preferably sensed again or continues to be sensed. If the imbalance increases, the actuation drive may be controlled to displace the counterweight in an opposite second direction. The actuation drive may be controlled to displace the counterweight in the first and second directions until the imbalance sensed by the sensor reaches a minimum. Thus, the device is configured to rebalance during rotation in response to excess material being removed from the workpiece.

[0027] In one embodiment, the device includes a pivot arm pivotally connected to the rotor for pivoting about a pivot axis. Therefore, the receptacle is preferably pivotally connected to the rotor via the pivot arm. The pivot arm may be elongated and extend along a longitudinal axis. The longitudinal axis is preferably disposed perpendicular to the pivot axis. The pivot arm preferably has a first end and a second end, with the receptacle disposed at the first end.

[0028] The pivot arm preferably has an axis of inertia extending in a dimension passing through the first end and the second end. The longitudinal axis may correspond to the axis of inertia of the pivot arm.

[0029] In one embodiment, the actuation drive is controlled to position the counterweight based on information from a computer having a data representation (or computer model) of the workpiece stored therein. Based on the computer model of the workpiece, the workpiece's axis of inertia and / or the workpiece's center of mass can be calculated. Based on the workpiece's axis of inertia, the workpiece can be positioned or constructed at a position on the receptacle such that the workpiece's axis of inertia is aligned with the longitudinal axis of the pivot arm. Furthermore, the workpiece's center of mass can be used to adjust the counterweight so that imbalance during rotation of the workpiece about the rotation axis is minimized at the second angular orientation. Thus, the device can be configured such that the workpiece's axis of inertia and / or the workpiece's center of mass can be received by the device (specifically, by the device's control unit) in the form of data from a computer.

[0030] In one embodiment, the device is configured to lock the receptacle against pivoting in at least a first angular orientation. Specifically, the receptacle can be locked against pivoting by locking the pivot arm against pivoting. Thus, the device can be configured to selectively lock or unlock the receptacle (or pivot arm) in at least a first angular orientation. When locked, the receptacle (or pivot arm) is preferably locked against pivoting about a pivot axis, whereas when unlocked, the receptacle (or pivot arm) is allowed to pivot toward a second angular orientation. Thus, the device can have a locking mechanism that can releasably lock the rotor and the pivot arm to one another in the first angular orientation. The locking mechanism can include a displaceable pin that can be pushed through a first hole in the rotor and a second hole in the pivot arm to lock the rotor and the pivot arm to one another. To release, the pin can be withdrawn from at least one or both of the first and second holes. The pin may be displaceable by an electrically controllable actuator, for example a solenoid actuator.

[0031] In one embodiment, the device comprises a control unit for controlling the operation of the device.

[0032] The control unit may electrically control the actuator to lock the rotor and pivot arm together in a first angular orientation or to release the rotor and pivot arm from each other so that they pivot relative to each other. Thus, the device may generally be configured to operate in a first operating mode in which the receptacle is in a first angular orientation and in a second operating mode in which the receptacle is in a second angular orientation. In both the first and second operating modes, the workpiece is rotated about the axis of rotation A. However, the angular orientation of the receptacle (and therefore the workpiece) is different in the first and second operating modes. Preferably, the first and second operating modes of the receptacle (and therefore the workpiece) relative to the axis of rotation differ by 90 degrees (or essentially 90 degrees) between the first and second operating modes.

[0033] In one embodiment, in the second angular orientation, the pivot arm is oriented such that the inertial axis of the pivot arm (or the longitudinal axis of the pivot arm) is inclined relative to the rotation axis at an oblique angle. The oblique angle can be 90 degrees (or essentially 90 degrees). Therefore, in the first angular orientation, the rotation axis and the longitudinal axis preferably coincide with each other. In other words, in the first angular orientation, the pivot arm is oriented such that the inertial axis of the pivot arm is aligned with the rotation axis. In the second angular orientation, the rotation axis and the longitudinal axis are preferably inclined relative to each other by 90 degrees (or essentially 90 degrees) (preferably, the rotation axis and the longitudinal axis intersect).

[0034] The first and second ends of the pivot arm are preferably arranged along or on the longitudinal axis. The pivot axis is preferably arranged at a distance from the second end. The pivot axis may further intersect the longitudinal axis. The receptacle preferably has a receiving surface for receiving a workpiece. The pivot axis is preferably arranged between the second end and the receiving surface of the receptacle. The receiving surface may be planar. The receiving surface may further be arranged perpendicular to the longitudinal axis. The receiving surface may be suitable for building a workpiece thereon. Preferably, the receptacle has an axis of inertia that coincides with the longitudinal axis of the pivot arm when the receptacle is mounted on the pivot arm. Therefore, the pivot arm including the mounted receptacle can preferably be rotated about the longitudinal axis without causing imbalance due to the rotation.

[0035] In one embodiment, the receptacle is releasably mountable or mounted to the pivot arm. Further, the receptacle may be releasably mountable within an additive manufacturing device for building a workpiece layer by layer from photocurable material. Thus, the receptacle may be selectively mountable within an additive manufacturing device or a rotational device.

[0036] The counterweight is preferably linearly guided within the pivot arm. Preferably, the counterweight is linearly guided along the longitudinal axis of the pivot arm. The counterweight may be displaceably mounted on the pivot arm for linear displacement in the dimension through the first end and the second end (or along the longitudinal axis).

[0037] In one embodiment, the workpiece has an axis of inertia and is mounted in the receptacle such that the axis of inertia of the workpiece is aligned with the axis of inertia of the pivot arm. Thus, the workpiece can be mounted in the receptacle such that the axis of inertia of the workpiece is aligned with the longitudinal axis of the pivot arm.

[0038] In one embodiment, the counterweight and the workpiece are positioned on opposite sides of the pivot axis. The counterweight is therefore positioned to counteract the weight of the workpiece that would otherwise cause a torque about the pivot axis. Furthermore, in the second angular rotation, the counterweight and the workpiece are preferably further positioned on opposite sides of the rotation axis. The counterweight is therefore positioned to counteract centrifugal forces generated by the workpiece during rotation about the rotation axis. Such centrifugal forces, if not counteracted, would otherwise cause an imbalance during rotation of the workpiece about the rotation axis.

[0039] In one embodiment, the device further comprises a vacuum chamber, which may be formed by a collection vessel and a closure for releasably closing (or sealing) the collection vessel, and the workpiece may be disposed within the collection vessel for rotation.

[0040] In one embodiment, the device comprises a rotary drive for driving the rotor, the rotary drive preferably being configured to operate at a variable rotational speed, in particular the rotary drive preferably being operable at a specific rotational speed selected from a range of rotational speeds under the control of the control unit.

[0041] In one embodiment, the rotor extends through a closure of the vacuum chamber, and a seal may be disposed within the closure for slidable sealing with a surface of the rotor. In this embodiment, the rotary drive is disposed external to the vacuum chamber.

[0042] In an alternative embodiment, the rotor and rotary drive are located within a vacuum chamber, and therefore sliding seals may not be required.

[0043] The devices described herein are particularly useful for cleaning workpieces fabricated or obtained by an additive manufacturing process involving layer-by-layer photocuring of a photocurable material (e.g., using a stereolithography process).

[0044] Therefore, there is also provided a process for cleaning such a workpiece, comprising: Providing a device as described herein; placing or securing a workpiece, particularly a dental workpiece, having a light-curable material disposed on a surface thereof, on a receptacle pivotally mounted relative to a rotor; rotating the workpiece at a rotational speed that results in removal of the photocurable material from the surface of the workpiece; A process is described, including: [Brief explanation of the drawings]

[0045] [Figure 1] 1 is a perspective view of a device for rotating a workpiece in a first angular orientation according to one embodiment of the present invention; [Figure 2] 2 is a perspective view of the device shown in FIG. 1 in a second angular orientation according to one embodiment of the present invention. [Figure 3] 3 is a different perspective view of the device shown in FIG. 2. [Figure 4] FIG. 1 is a perspective view of a receptacle including a workpiece according to one embodiment of the present invention. [Figure 5] FIG. 5 is a bottom view of a receptacle including the workpiece shown in FIG. 4. [Figure 6] FIG. 1 is a cross-sectional view of a device combined with a collection container according to one embodiment of the present invention. [Figure 7] FIG. 1 is a cross-sectional view of a device combined with a collection container according to one embodiment of the present invention. [Figure 8] FIG. 10 is a cross-sectional view of a device in combination with an alternative collection container according to one embodiment of the present invention. [Figure 9] FIG. 10 is a cross-sectional view of a device in combination with an alternative collection container according to one embodiment of the present invention. [Figure 10] FIG. 10 is a perspective view of a receptacle in combination with a further collection container according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0046] FIG. 1 illustrates a device 1 for rotating a workpiece 100. In particular, the workpiece 100 is 3D printed, and in particular, constructed from multiple layers of photocured material. During the process of building the workpiece, individual layers of specific thicknesses are formed using photocurable (uncured) material, each individual layer is cured, and then the next layer of photocurable material is added to the cured layer. For curing, each layer of photocurable material is exposed to light (e.g., UV light) that hardens the respective layer. After the workpiece 100 is built, photocurable (uncured) material may still be attached to the workpiece 100. Such attached photocurable (uncured) material (also referred to herein as "excess material") may be at least partially removed by spinning it and separating it using centrifugal force.

[0047] In this example, the workpiece 100 is a positive dental model that replicates a patient's dentition. Such a dental model may be used by a dental laboratory as a substitute for a plaster model. In another example, the dental workpiece may be a dental restoration. The dental restoration may be a dental crown or bridge, or a partial dental crown, a dental inlay, or one or more replacement teeth / teeth. Furthermore, the dental workpiece may include multiple dental restorations. The multiple dental restorations may be printed as a single unit (e.g., in an array or tree) and may be later separable from one another.

[0048] The device 1 has a rotor 2. The rotor 2 is rotatable about a rotation axis A. A swivel arm 3 is rotatably (or pivotally) suspended relative to the rotor 2. The swivel arm 3 is rotatably (or pivotally) suspended relative to the rotor 2 about a pivot axis B. In this example, the pivot axis B is arranged transversely to the rotation axis A, in particular perpendicular to the rotation axis A. The swivel arm 3 is therefore rotatable about and perpendicular to the rotation axis A. The rotor 2 in this example is fork-shaped. The rotor 2 specifically has a drive shaft 4 from which two legs 5a and 5b protrude. The drive shaft 4 extends along the rotation axis A, and the two legs 5a, 5b each extend parallel to and laterally offset from the rotation axis A. Each of the legs 5a, 5b has a free end portion 6a, 6b, respectively. The swivel arm 3 is suspended at the rotor 2 by an axle 7. The axle 7 extends through the free end portions 6a, 6b of the rotor 2 and through the pivot arm 3, thus forming a rotatable link between the rotor 2 and the pivot arm 3. The rotatable link further defines a pivot axis B. Alternatively, each of the two axles may extend through the free end portions 6a / 6b into one side of the pivot arm 3, thus forming a rotatable link between the rotor 2 and the pivot arm 3. Those skilled in the art will recognize additional designs of rotors that include pivot arms suspended from a rotor. Thus, the present invention is not limited to the design of this example.

[0049] The rotor 2 can be driven to rotate about its axis of rotation. The rotor 2, specifically the shaft 4, can therefore be coupled to a rotary drive (not shown). The rotary drive can be controlled at various rotation speeds, for example, preferably within a range of up to 3000 revolutions per minute. The rotary drive in this example is a servo motor.

[0050] The device 1 further includes a receptacle 8 for holding a workpiece 100. The receptacle 8 in this example is provided in the form of a flat platform to which the workpiece 100 can be secured. However, other shapes that provide a suitable interface for attaching a workpiece are possible. The receptacle 8 is pivotally mounted (in this example via a pivot arm 3) relative to the rotor 2 for pivoting about pivot axis B. The receptacle 8 can therefore be pivoted about pivot axis B independently of any rotation about rotation axis A. Pivoting of the pivot arm 3 (and therefore of the receptacle 8) relative to the rotor 2 is enabled between a first angular orientation relative to the rotation axis A and a different second angular orientation relative to the rotation axis A. Pivoting of the pivot arm 3 (and therefore of the receptacle 8) relative to the rotor 2 may be otherwise limited, for example, disabled outside an angular range defined between the first and second angular orientations. The first angular orientation is shown in FIG. 1 and is defined herein as a 0 (zero) degree orientation with respect to the rotation axis A. In the first angular orientation, the rotation axis A preferably coincides with the inertial axis of the workpiece 100. Therefore, the angle between the inertial axis of the workpiece 100 and the rotation axis is 0 degrees. Thus, in the first angular orientation, the workpiece 100 can be rotated about the rotation axis A without the workpiece 100 becoming unbalanced during rotation. Furthermore, in this example, the rotation axis A extends through the workpiece 100 in the first angular orientation. This is achieved in that the inertial axis of the workpiece 100 is determined during design of the workpiece in a CAD system and by mounting (or 3D printing) the workpiece 100 on the receptacle A such that the inertial axis is aligned with the rotation axis A. The CAD system may further be used to design an interface on workpiece 100 that can mate with a corresponding mating interface on receptacle 8 in one unique rotational and lateral position. Such an interface may include, for example, at least two spaced apart pins that can be received in correspondingly spaced apart and sized holes provided in the receptacle.Therefore, the workpiece 100 can be mounted so that the axis of inertia is aligned with the axis of rotation A by simply mating the interfaces of the workpiece 100 and the receptacle 8 together.

[0051] The pivot arm 3 is preferably lockable in a first angular orientation. When locked, the pivot arm 3 is prevented from pivoting from the first angular orientation. Furthermore, when the pivot arm 3 is unlocked, the pivot arm 3 is preferably freely rotatable from the first angular orientation to a second angular orientation. Thus, the device 1 can be operated in a first operating mode in which the receptacle 8 is in the first angular orientation and the device 1, and therefore the workpiece 100, is rotated about the rotation axis A. This preferably causes excess material adhering to the workpiece 100 (specifically, excess uncured photocurable material used for 3D printing of the workpiece 100) to separate from the workpiece 100 by centrifugal force. In the first operating mode, the pivot arm 3 is preferably locked from pivoting toward the second angular orientation. This prevents the receptacle 8 from automatically pivoting toward the second angular orientation by centrifugal force. It is noted that locking in the first angular orientation is useful because the workpiece may initially be rotated about its axis of inertia, but the pivoting arm 3 with the receptacle 8 will typically tend to deflect towards the second angular orientation in practice.

[0052] The device 1 can further be operated in a second operating mode in which the receptacle 8 is in a second angular orientation and the workpiece 100 is rotated about the rotation axis A. Thus, while the workpiece is still rotated about the same rotation axis A, the workpiece is oriented differently, thereby allowing different portions of excess material to be removed from the workpiece in the first and second angular orientations. The second angular orientation is shown in FIG. 2 . The second angular orientation is defined herein as an orientation that is essentially 90 degrees (or 90 degrees) relative to the rotation axis A. While the second angular orientation is desirably 90 degrees, the pivot arm 3 typically assumes an angular orientation resulting from centrifugal forces acting on the workpiece and, ultimately, gravity. Therefore, slight deviations from 90 degrees are intended to be encompassed by the term “essentially 90 degrees.” In the second angular orientation, one side of the workpiece 100 (in this example, the occlusal side of the dentition model) faces radially away from the rotation axis A. Thus, any excess material adhering to this side is urged away from the workpiece 100 due to centrifugal forces acting on the excess material during rotation about the rotation axis A. In the first angular orientation, the same side of the workpiece 100 (in this example, the occlusal side of the model dentition) faces in a direction along or axially relative to the rotation axis A. Thus, in the first angular orientation, any excess material adhering to the surface of the workpiece 100 facing radially away from the rotation axis A is urged away from the workpiece 100 due to centrifugal forces, whereas excess material adhering to the surface of the workpiece 100 facing radially toward the rotation axis is urged toward the workpiece 100. Thus, although not all of the surfaces of the workpiece 100 may be cleaned of excess material in the first angular orientation, additional surfaces of the workpiece 100 can be cleaned of excess material by further rotating the workpiece 100 at a second angular orientation.

[0053] In particular, when the workpiece 100 is a dental crown, it forms a cavity to be received on a natural tooth or abutment in the patient's mouth. Sequentially rotating the dental crown in a first angular orientation and a second angular orientation (or vice versa) results in the removal of a maximum amount of excess material. In this case, the dental crown is preferably oriented in the first angular orientation such that the cavity is open (axially) away from the receptacle 8 and in the dimension of the rotation axis A. Rotating the dental crown in the first angular orientation typically removes excess material from the dental crown that is attached to the outside of the dental crown, whereas rotating the dental crown in the second angular orientation typically removes excess material from the dental crown that is attached to the inside of the dental crown (i.e., excess material attached within the cavity). In the second angular orientation, the dental crown is preferably oriented so that the cavity is open in a direction away from the receptacle 8 and in a radial dimension about the axis of rotation A.

[0054] As shown in FIG. 3 , the pivot arm 3 is suspended from the rotor 2 at (or adjacent to) a first end 3 a of the pivot arm 3. The pivot arm 3 further has a second end 3 b opposite the first end 3 a. A receptacle 8 is attached to the first end 3 a of the pivot arm 3. A workpiece 100 is attached to the receptacle 8. A pivot axis B is disposed between the workpiece 100 and the second end 3 b of the pivot arm 3. The workpiece 100 and the second end 3 b of the pivot arm are disposed on opposite sides of the pivot axis B. The pivot arm 3 is counterbalanced so that when the workpiece 100 is attached to the receptacle 8 on the pivot arm 3 (as shown in the figure), it naturally remains in a second angular orientation. To balance the pivot arm 3, including the receptacle 8, relative to the workpiece 100, the pivot arm 3 includes a counterweight 9. The counterweight 9 is movably arranged relative to the receptacle 8. Furthermore, the counterweight 9 can be locked at different distances relative to the receptacle 8. The pivot arm 3 extends along a longitudinal axis C that is aligned with the rotation axis A in a first angular orientation and angularly offset by 90 degrees relative to the rotation axis A in a second angular orientation. The longitudinal axis C further corresponds to the axis of inertia of the pivot arm 3 and of the receptacle 8. Thus, in the first angular orientation, the pivot arm 3 and the receptacle 8 (without the workpiece) can be rotated about the rotation axis without unbalance occurring. The counterweight 9 is, in particular, displaceable along the longitudinal axis C. In this example, the counterweight 9 is linearly guided within the pivot arm 3 for movement along the longitudinal axis C. Furthermore, the counterweight 9 is engaged with a threaded spindle 13 which, when rotated, displaces the counterweight 9 along the longitudinal axis C. Due to the threaded connection between the spindle 13 and the counterweight 9, the counterweight 9 is locked in position when the spindle 13 does not rotate. The pivot arm 3 further comprises a motor 11 which is able to drive the threaded spindle 13 in both directions of rotation. The rotation of the motor 11 can further be controlled via its angular position.For example, motor 11 can be a stepper motor or another motor with a position measurement system. Thus, the linear position of counterweight 9 can be adjusted to a desired position within pivot arm 3 (via rotating spindle 13 for a particular angular rotation) under computer control. Depending on the weight and center of mass location of workpiece 100, counterweight 9 can be adjusted to an appropriate distance relative to the center of mass of workpiece 100 to minimize any imbalance during rotation of workpiece 100 in the second angular orientation. For example, the center of mass, and ultimately the weight, of the workpiece can be transmitted to device 1 (e.g., from a CAD system), and device 1 can automatically adjust the counterweight accordingly.

[0055] Alternatively, or additionally, device 1 may include a sensor 18 (shown only diagrammatically) for sensing imbalances caused by rotating rotor 2. In this example, sensor 18 is a three-axis acceleration sensor, such as that available from TDK Corp. (Japan) under the designation MPU6050. Sensor 18 is preferably mechanically coupled to device 1 so that vibrations caused by the imbalances caused by rotating the rotor are mechanically transmitted to sensor 18. This can be achieved, for example, by mounting sensor 18 to a mounting base 10 of device 1 for mounting a rotary drive (not shown). However, sensor 18 may similarly be mounted to any other component of device 1 that is mechanically coupled to rotor 2. Sensor 18 can be used to measure accelerations in at least two of the three axes along which sensor 18 can sense accelerations. In the figures, the three axes along which sensor 18 can sense accelerations are designated X, Y, and Z. When acceleration is sensed (particularly along axis X and axis Y, but eventually also along axis Z), counterweight 9 is displaced until the acceleration reaches a minimum. Thus, counterweight 9 may initially be displaced in one direction, and if the sensed acceleration increases, counterweight 9 may be displaced in the opposite direction until the sensed acceleration reaches a minimum. Device 1 can therefore be used with differently shaped and configured workpieces and is configured to automatically rebalance during rotation.

[0056] The motor 11 in this example is fixed within the pivot arm 3 via a fixing block 12. However, the motor 11 may similarly be fixed by alternative means or directly to a component of the pivot arm 3. The motor 11 in this example is electrically connected to a power supply via a current collecting ring (not shown) and ultimately to a data line. Alternatively, the motor 11 may be electrically connected to a power supply via an inductive interface and ultimately to a data line.

[0057] FIG. 4 shows the receptacle 8 with the workpiece 100 in more detail. The receptacle 8 has a flat receiving surface 14 and a plurality of tooling holes 15. The tooling holes 15 have known positions relative to the longitudinal axis C measured in the plane of the receiving surface. The positions of the tooling holes 15 can be used to design the workpiece so that it can be secured on the receptacle in a specific desired position. Typically, the workpiece is designed so that the center of mass of the workpiece is aligned with the longitudinal axis C when mounted on the receptacle 8 through the use of the tooling holes 15. Furthermore, in this example, the receptacle 8 can be used as a build platform in a 3D printing device. Accordingly, the receptacle 8 includes a fitting 17 that allows the receptacle 8 to be removably attached to the pivot arm 3. Additionally, the fitting 17 allows the receptacle 8 to be removably attached within a 3D printing device for building the workpiece 100 directly on the receptacle.

[0058] 5 shows the workpiece 100 with its center of mass 16 indicated. In this example, the center of mass 16 is located on the center of mass 101 of the receptacle 8 in a plane perpendicular to the longitudinal axis C. Any imbalance in the receptacle and workpiece 100 combination can therefore be avoided by designing the workpiece in proper relationship to the shape of the receptacle 8.

[0059] FIG. 6 shows the device 1, which in this example includes a collection container 20. The rotor 2, including the pivot arm 3, the receptacle 8, and the workpiece 8, is (partially) disposed within the collection container 20. The collection container 20 is cup-shaped and has a bottom wall 20a and a peripheral side wall 20b. The peripheral side wall 20b is disposed around the rotation axis A. Thus, any excess material centrifuged from the workpiece 100 is collected by the peripheral side wall 20b and ultimately flows toward the bottom wall 20a. The collection container 20 has an opening 20c that can be closed by a closure 21, as shown in FIG. 7. The collection container 20, in combination with the closure 21, can form a vacuum chamber. A vacuum can be generated via a vacuum pump (not shown) connected to the vacuum chamber. The vacuum can help avoid or minimize the presence of any air bubbles on the workpiece. The drive shaft 4 extends through the closure 21, and the rotary drive (not shown in FIGS. 6 and 7) can be located entirely outside the collection container 20. At least the peripheral sidewall 20b may be light-transmitting (preferably transparent). The workpiece 100 may therefore be exposed to light emitted through the peripheral sidewall 20b. This allows any (eventually small) residual photocurable material still adhering to the workpiece 100 after rotation to harden and become part of the workpiece. Furthermore, any residual photocurable material collected in the collection container 20 may be hardened. This allows the collection container 20 to be disposed of without unhardened photocurable material, which would eventually become harmful.

[0060] 8 and 9 are identical to FIGS. 6 and 7, respectively, except that the closure 21 is combined with the rotary drive 19. Again, the rotor 2, including the pivot arm 3, receptacle 8, and workpiece 8, is (partially) disposed within the collection container 20. The collection container 20 is cup-shaped and has a bottom wall 20a and a peripheral side wall 20b. The peripheral side wall 20b is disposed about the rotation axis A. The collection container 20 has an opening 20c that can be closed by the closure 21, as shown in FIG. 9. In this example, the rotary drive 19 is disposed inside the collection container 20. Therefore, a passage for the drive shaft 4 through the closure 21 is not necessary. Again, at least the peripheral side wall 20b can be light-transmitting (preferably transparent), as described above.

[0061] 10 shows an alternative collection container 20 that is placed directly on a receptacle 8 and confines a workpiece 100 therein. The collection container 20 is again cup-shaped. In this example, the receptacle 8 (in this case preferably in the form of a build platform on which the workpiece is directly built) forms a closure for the collection container 20. The collection container 20 in this example may be attached to the receptacle using a threaded connection, a bayonet fitting, a flap mechanism, a magnetic fastener, or the like.

[0062] The collection container 20 in the embodiments of FIGS. 6-10 may have an internal absorbent layer, such as a cloth or fleece, capable of absorbing and retaining liquid. Therefore, any photocurable material that separates from the workpiece and strikes the absorbent layer is absorbed and retained. This minimizes splashback back onto the workpiece 100 and maximizes cleaning of the workpiece 100. The absorbent layer is preferably light-transmitting. For example, the cloth or fleece preferably has openings through which light can pass and may be made of transparent or translucent fibers that allow additional light to pass through. Therefore, the workpiece 100 can be exposed to light to cure all residual photocurable material on the workpiece 100. At the same time, the photocurable material retained in the absorbent layer is cured. The collection container 20 including the absorbent layer, or—if separable—only the absorbent layer, can be disposed of after curing all residual photocurable material on the workpiece 100. Whether the absorbent layer with the retained light-cured material is separable from the collection container can be controlled by one skilled in the art by selecting a material for the collection container 20 that does not adhere to the light-cured material.

Claims

1. 1. A device for rotating a workpiece, comprising: a rotor for rotating about an axis of rotation; and a receptacle for holding the workpiece, the receptacle pivotally connected to the rotor for pivoting about a pivot axis transverse to the axis of rotation, thereby enabling pivoting of the receptacle between a first angular orientation relative to the axis of rotation and a different second angular orientation relative to the axis of rotation; the device comprising: a counterweight movably arranged relative to the receptacle, the counterweight being lockable, in use, at different distances relative to the receptacle on a longitudinal axis extending along a direction perpendicular to both the axis of rotation and the pivot axis.

2. The device of claim 1 , configured to lock the receptacle against rotation in at least the first angular orientation.

3. 3. A device according to claim 1 or 2, comprising an actuating drive for positioning said counterweight at said different distances relative to said receptacle under computer control.

4. The device of claim 3 , further comprising a sensor for sensing imbalance caused in response to rotating the rotor.

5. 5. The device of claim 1, comprising a workpiece, the workpiece selected from a dental dentition model, a dental aligner, or a dental restoration, the workpiece constructed in an additive manufacturing process, the workpiece comprising a light-curable material disposed on a surface of the workpiece.

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