Patent Application
20220280265
The disclosure relates generally to a kinematic apparatus and, more specifically, to a kinematic nest having a flexure and kinematic mount embedded therein to secure and repeatedly locate a model.
Thermoforming is used in manufacturing processes to create specific shapes for a product. A sheet such as a plastic sheet is heated to a pliable forming temperature that allows it to be stretched into or onto a mold and cooled to a defined shape. After forming the defined shape, the plastic is usually picked up and placed a number of times in an automatic and/or manual process down the manufacturing line in order to create a final finished product.
In any manufacturing process, for example in an automated process, the consistency at which an arm such as a pick and place robot arm is able to complete thermoforming, assembly, quality control, packaging and other material handling processes improves the overall quality of production and reduces downtime due to errors. Speed contributes significantly to productivity, as pick and place robots move products through the manufacturing process much quicker than manual options. For example, in aligner manufacturing it is a goal to produce a plurality of aligners to desired specifications at a fast throughput. However, challenges arise when there are manufacturing errors in the sizes of molds or models on which a plastic for producing an aligner is thermoformed. With these errors, it is usually difficult to precisely locate the thermoformed plastic and/or model in a repeatable fashion throughout the manufacturing process. For example, a model in a patient treatment plan might differ from another one by, for example, one thousandths of an inch. Assuming 60 models are needed for one treatment plan, the errors in the manufacturing process can accumulate quickly resulting in an inability to precisely locate the models in a manufacturing process that involves several steps of picking up and placing the model in a determinate manner.
The illustrative embodiments provide an apparatus, method, computer system and a computer readable media.
In an aspect herein, the apparatus is any apparatus that needs to hold secure a model in a defined position for subsequent work on the model such as a thermoforming apparatus, a Computer Numerical Control (CNC) apparatus, laser marking apparatus or otherwise kinematic apparatus. The kinematic apparatus includes: a nest; a lower mount, which may be the nest or a part of the nest, that includes a plurality of pins arranged in the nest to conform to Maxwell's criterion when coupled with an upper mount such as a an external clamping method (or gravity in the absence of an upper mount), in order to repeatedly locate a model,; and a flexure embedded in the nest and connected to an alignment pin that is movable, the flexure is configured to move jointly with the alignment pin that is movable. In the apparatus, another alignment pin is embedded in the thermoforming nest, is stationary, and engages a first groove of the model. In the apparatus, the alignment pin that is movable is configured to engage a second groove of the model and move jointly with the flexure which uses a spring resistance to motion to secure the model on the mount.
In another aspect herein, any combination of the following features are provided: (i) the first and second grooves are sideways v-grooves, (ii) the plurality of pins are four, (iii) the thermoforming nest is configured to receive a 3D printed dental arch model in order to thermoform an aligner on the 3D printed dental arch model, (iv) the flexure is movable in the X direction and unmovable in the Y and Z directions, (v) the flexure is movable from an original position to a maximum position in order to secure any model size that is between a minimum and a maximum size respectively, (vi) a thickness of the flexure is designed to produce a slit in the thermoforming nest, wherein in the original position, the flexure is a first distance from a first edge of the slit and in the maximum position, the flexure is a second distance from the first edge of the slit, wherein a difference between the first and second distances is chosen to accommodate tolerances of the model, (vii) the mount is over constrained, the thermoforming disc is made of a polymer material having a substantially constant thickness.
In yet another aspect herein, a method is provided. The method includes providing a thermoforming nest with a flexure and a kinematic mount having a plurality of pins, the plurality of pins are arranged to mate with surfaces of a thermoformed disc to conform to Maxwell's criterion in order to repeatedly locate the model; providing the model with a number of v-grooves; securing the model on the kinematic mount of the thermoforming nest by using said number of v-grooves to engage corresponding pins of the plurality of pins of the kinematic mount; and. placing the first material on the model and thermoforming said first material around the model and the plurality of pins such that a negative of the model and the plurality of pins is formed in the first material. In the method, the flexure is connected to an alignment pin of the corresponding pins, the alignment pin being movable and moving jointly with the flexure such that when one v-groove of the model engages the movable pin, the flexure moves with spring resistance to motion, in order to accommodate any size of the model that is between a defined minimum and maximum size.
In another aspect, one or more combinations of the following are provided: (i) the model is a 3D printed dental arch model, (ii) the first material that is thermoformed, together with the dental arch model in the thermoforming nest forms a quasi-Maxwell kinematic coupling which is subsequently obtained by an external device and repeatedly located relative to a reference point, (iii) trimming the first material that is thermoformed on the dental arch model along a gum line of the dental arch model to produce an aligner, (iv) the providing, securing and placing steps are repeatable to produce a plurality of other aligners from a corresponding plurality of other dental arch models using the same thermoforming nest.
In yet another aspect, a computer system is provided. The computer system comprises at least one processor operable to perform the steps of: obtaining a thermoforming nest provided with a flexure and a kinematic mount having a plurality of pins, the plurality of pins are arranged to mate with surfaces of a thermoformed disc to conform to Maxwell's criterion in order to repeatedly locate the model; obtaining the model, the model being provided with a number of v-grooves; securing the model on the kinematic mount of the thermoforming nest by using said number of v-grooves to engage corresponding pins of the plurality of pins of the kinematic mount; placing the first material on the model and thermoforming said first material around the model and the plurality of pins such that a negative of the model and the plurality of pins is formed in the first material, wherein the flexure is connected to an alignment pin of the corresponding pins, the alignment ping being movable and moving jointly with the flexure such that when one v-groove of the model engages the movable pin, the flexure moves with spring resistance to motion, in order to accommodate any size of the model that is between a defined minimum and maximum size.
In an even further aspect herein, a non-transitory computer-readable storage medium is provided. It stores a program which, when executed by a computer system, causes the computer system to perform a procedure comprising: obtaining a thermoforming nest provided with a flexure and a kinematic mount having a plurality of pins, the plurality of pins are arranged to mate with surfaces of a thermoformed disc to conform to Maxwell's criterion in order to repeatedly locate the model; obtaining the model, the model being provided with a number of v-grooves; securing the model on the kinematic mount of the thermoforming nest by using said number of v-grooves to engage corresponding pins of the plurality of pins of the kinematic mount; and placing the first material on the model and thermoforming said first material around the model and the plurality of pins such that a negative of the model and the plurality of pins is formed in the first material, wherein the flexure is connected to an alignment pin of the corresponding pins, the alignment ping being movable and moving jointly with the flexure such that when one v-groove of the model engages the movable pin, the flexure moves with spring resistance to motion, in order to accommodate any size of the model that is between a defined minimum and maximum size.
To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced. Certain novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of the illustrative embodiments when read in conjunction with the accompanying drawings, wherein:
The illustrative embodiments described herein are directed to a nest having a plurality of pins and corresponding engaging surfaces that conform to Maxwell's criterion and a flexure that jointly moves with one of the pins in order to secure and locate several size of models in a repeatable manner for a manufacturing process. One or more embodiments recognize that an existing problem in manufacturing is the need for locating objects such as three-dimensional (3D) printed models repeatedly. One or more embodiments are directed to the use of kinematics to determine positions for pins in a thermoforming nest, said pins being configured to hold different sizes of 3D printed models and a thermoformed material for repeatability.
In an embodiment, one pin is connected to, and moves with a flexure that is designed to extend and contract to a maximum position and a minimum position in order to secure a maximum size and a minimum size of the model respectively. In another embodiment, the model is a model of a dental jaw, but can be any model on which a material having a substantially constant thickness is to be thermoformed. In an embodiment, an operator loads a model onto a kinematic mount of a thermoforming nest, the kinematic mount comprising at least the plurality of pins. The mount may be a part of the nest or may be the nest. The model is provided with a plurality of v-grooves that engage a number of the pins. A flexure connected to one of the pins and moving jointly with said pin is able to extend or contract in a defined degree of freedom (DOF) in order to secure the model.
Flexures allow motion through the bending elements that make up the flexure. The design of elements of the flexure ensures compliance of movements of the flexure in its degree(s) of freedom, but make the flexure relatively stiff in its degree(s) of constraint (DOC) thus allowing the provision of motion in defined directions, but constraint in other directions. Friction-less, controlled, limited-range motion is thus achieved. Designing flexures involves developing a model, using Finite Element Analysis (FEA), and verifying the model. By identifying and characterizing desired degrees of freedom/directions of travel, a flexure topology can be generated. For example, a computer can be used to iteratively synthesize the topology of a flexure by satisfying displacement and force requirements of the flexure. In another example that uses flexural building blocks, flexural elements with intersecting lines of action are designed to form a center about which a stage rotates.
In an illustrative embodiment, a flexure 602 is designed with flexure element 604 to have linear travel with a spring resistance to motion which acts as a self-centering feature for the flexure 602. By integrating movable pin 202a with the flexure 602, the movable pin is translatable to accommodate different sizes of a model 206.
Movable pin 202a is part of a plurality of pins that conform to Maxwell's criterion as described hereinafter. A plurality of pins conforming to Maxwell's criterion allows the creation of a quasi-Maxwell kinematic coupling, which is also described hereinafter.
Kinematics is a field of classical mechanics that encompasses describing the motion of objects. An aspect thereof, kinematic coupling, involves the coupling of systems together to provide precision and certainty of location. The reproducibility and precision of a kinematic coupling comes from the principle of exact constraint design which requires that the number of points of constraint should be equal to the number of degrees of freedom to be constrained. As shown in
Maxwell kinematic couplings (or kinematic mounts designed with the Maxwell Criteria) utilize some form of an arrangement of three balls in three V-grooves to locate and position a pair of parallel plates such that six degrees of freedom are held fixed.
As shown in
The Maxwell kinematic coupling 100 can thus precisely locate critical parts to critical surfaces in a repeatable manner and eliminate or substantially eliminate error due to slop or movement.
It follows then that, in the case of a planar mount coupling, a layout of 3 arbitrary v-grooves (arbitrary v-groove 110a, arbitrary v-groove 110b and arbitrary v-groove 110c), as shown in
In an illustrative embodiment, as shown in
As shown in
The illustrative embodiments recognize that, throughout the manufacturing process, the location of each model and aligner is to be known. For example, in an automated manufacturing process, aligners are repeatedly picked up by a robot arm from an assembly line for trimming. Being able to locate the aligners and the models in a repeatable manner is thus critical for the manufacturing process. For example, a conveyor system may be configured to move the plurality of assemblies in a stepwise movement sequence from a loading area to the heating system, then from the heating system to the forming system, and then from the forming system to an unloading area.
The illustrative embodiments also recognize that there are dimensional tolerances/accuracy issues inherent in 3D printing as well as other printing processes. An error, such as deviations of a printed model from base dimensions can be propagated in the printing of other models in a treatment plan, thus quickly adding up. Such errors in dimensions, if unaccounted for can prevent the models from fitting or being secured in a desired location due to the dimensions being too large or too small with respect to the desired location. Moreover, the more accurately the manufacturing process locates parts of the model, the less work needed downstream to correct errors caused by improper locating.
In an embodiment, dental model (model 206) and aligner (thermoforming disc 208) are constrained and repeatedly located by ensuring that the pins and corresponding engaging surfaces conform to Maxwell's criterion.
Dimensional differences between sideways v-grooves of one model and sideways v-grooves of another model of the same entity/patient are also accounted for by employing a flexure 602 configured to move jointly with movable pin 202a from an initial position to a final position in order to secure a minimum size of the model 206 and a maximum size of the model 206 respectively.
Further, dimensional differences between sideways v-grooves of one model and sideways v-grooves of another model of a different entity (such as an adult patient's dental arch model and a child patient's dental arch model) are accounted for by employing a flexure 602 configured to move jointly with movable pin 202a from an initial position to a final position in order to secure a minimum size of the model 206 and a maximum size of the model 206 respectively.
Thus, in order to minimize unwanted movement (ie: slop), avoid the consequential loss of positional alignment and to accommodate the part tolerance error of models on a thermoforming nest, a set of kinematic alignment features and a spring flexure are configured, embedded in the nest, to move the model back to a known and repeatable location that could be used by down-stream automation equipment. To achieve this, a quasi-Maxwell kinematic coupling is used to locate the model with a spring flexure embedded in the locating nest to accommodate the positional misalignment inherent in manufacturing large quantities of models and thermoformed parts. This provides a simple design with one moving part, passively returning the model 206 to a repeatable position on the nest without external mechanisms and with near-zero frictional effects and offering low cost of production and cost of ownership.
The main difference between a CNC nest the laser mark nest is that the laser mark nest may not include pin 202b. The laser mark nest may require the use of a backlight that shines from below and behind the nest 310 and up through the thermoformed disk 208 so that a camera (not shown) located above the nest 310 and looking down onto the disk 208, can image and capture a 2D data matrix code that is laser printed on the disk 208. To make room for that backlight, it may be necessary to remove/eliminate pin 202b (leaving an unoccupied position 312) as it would simply block the light and interfere with ability for the camera to read a code on the part (for example, a code required to track the part through the robot cell and downstream processes). Critical locating features (pins 202a, 202c and 202d) are still maintained. These 3 pins still obey the Maxwell criteria and quasi-Maxwell kinematic coupling. Further, the locating precision, repeatability and accuracy requirements of the laser marking may be much lower than that required at, say, the CNC mill nest. Therefore, a relatively small loss in precision is not detrimental to the laser marking process.
Turning now to
In an illustrative embodiment showing the interaction between the quasi Maxwell kinematic coupling and the flexure 602, a V-groove geometry pair is molded (i.e. 3D printed) into model 206 to which a matching pair of ¼″ outside diameter (OD) alignment pins mates and locates the arch. One of the pins, pin 202b is stationary on the nest. The second pin, movable pin 202a is attached to the flexure 602, the flexure 602 being cut from the nest base plate 606, and permitting the movable pin 202a to be displaced in the X direction (
The pair of ¼″ OD alignment pins are press-fit into the nest base plate 606. The nest base plate 606 includes a feature cut with CNC or Electrical Discharge Machining (EDM) that removes material from the nest base plate 606 such that what remains is a moving spring-like flexure element 604 within a part to which the top alignment pin (movable pin 202a) is attached. The thickness of the flexure 602 is designed to permit a defined but small amount (such as 1-3 mm) of movement in the X-direction and thereby a matching amount of movement by the movable pin 202a. The variance or slop being accommodated are in the distance between the V grooves that are print in the models. The 3D printing process from in the model (e.g. from arch to arch of a 3d dental model) produces small errors in the X direction in the range of, for example, ˜0.010 mm to 0.500 mm. The design of the flexure may take into consideration dimensional restrictions of the nest. The flexure may be designed to be large enough to press-fit in the movable pin 201a as well as strong enough to survive strong forces of the thermoforming process. Moreover, it may be designed to be “soft” enough to move even with 0.1 lbf (load force) applied at movable pin 202a. Also it may be designed such that X displacement in millimeters that movable pin 202a would move with a defined load force applied (such as 1 lbf) is enough to accommodate the ‘slop’ (ie the variance in the 3D printed sideways V-groves. If the distance between pins 202a and 202b is too short, the model 206 will float around on the nest 210 and possibly fall off. If that distance is too large, the arch may chip/crack during insertion or may pop out all together. The flexure compensates for that relatively large variation. Because the distance between the alignment pins (pin 202b and movable pin 202a) is configured to match the V groove features in model 206, the movable pin 202a will displace during model 206 loading on the nest base. For any out of tolerance V groove location and/or mis-location of the alignment pin locations, the flexure will self-center and self-locate the arch, retaining the arch securely during subsequent manufacturing operations. Utilizing the set of four pins arranged to provide conformity to the Maxwell criterion produces matching pockets in the thermoforming disc 208 during the thermoforming process.
The remaining slit 608 or groove left after machining is also selected to act as a self-limiting ‘bump stop’ preventing the flexure 602 from being overextended or damaged during regular usage of the nest, thereby providing the near-infinite life.
In
In
In step 906, process 900 secures the model on the quasi Maxwell kinematic mount of the thermoforming nest such that the v-grooves engage corresponding pins of the plurality of pins. The pins are the alignment pins (pin 202b and movable pin 202a). In step 908, process 900 places the first material on the model and thermoforms the first material around the model and the plurality of pins such that the a negative of the model and the plurality of pins is formed in the first material. In an illustrative embodiment, the first material is a polymer and the model 206 is a dental arch model. This allows the thermoforming of an aligner on the dental arch model.
In an alternative embodiment, a fixed pair of alignment pins is used to provide arch alignment of the model. Spacing between the alignment pins is this chosen to allow a size of a model 206 to be loaded and may useable for models of that size. In another alternative embodiment, one fixed pin and one pin attached to a coiled-spring return mechanism (not shown) are designed to produce similar results as the flexure 602 but with a defined and shorter life due ease of exceeded acceptable yield strengths. In yet another alternative embodiment, active mechanisms having external air cylinders or electrical servo motors can be used to move alignment pins and align a model on a nest. This requires moving parts, pre-alignment and tuning during build and could be more expensive.
Having described the kinematic apparatus, reference will now be made to
In one example embodiment herein, at least some components of the kinematic apparatus may form or be included in the computer system 1000 of
The display interface 1008 (or other output interface) forwards text, video graphics, and other data from the communication infrastructure 1002 (or from a frame buffer (not shown)) for display on display unit 1014. For example, the display interface 1008 may include a video card with a graphics processing unit or may provide an operator with an interface for controlling the kinematic apparatus.
The computer system 1000 may also include an input unit 1010 that may be used, along with the display unit 1014 by an operator of the computer system 1000 to send information to the computer processor 1006. The input unit 1010 may include a keyboard and/or touchscreen monitor. In one example, the display unit 1014, the input unit 1010, and the computer processor 1006 may collectively form a user interface.
One or more steps of aligning and locating a model or thermoformed disc may be stored on a non-transitory storage device in the form of computer-readable program instructions. To execute a procedure, the computer processor 1006 loads the appropriate instructions, as stored on storage device, into memory and then executes the loaded instructions.
The computer system 1000 may further comprise a main memory 1004, which may be a random-access memory (“RAM”), and also may include a secondary memory 1018. The secondary memory 1018 may include, for example, a hard disk drive 1020 and/or a removable-storage drive 1022 (e.g., a floppy disk drive, a magnetic tape drive, an optical disk drive, a flash memory drive, and the like). The removable-storage drive 1022 reads from and/or writes to a removable storage unit 1026 in a well-known manner. The removable storage unit 1026 may be, for example, a floppy disk, a magnetic tape, an optical disk, a flash memory device, and the like, which may be written to and read from by the removable-storage drive 1022. The removable storage unit 1026 may include a non-transitory computer-readable storage medium storing computer-executable software instructions and/or data.
In further illustrative embodiments, the secondary memory 1018 may include other computer-readable media storing computer-executable programs or other instructions to be loaded into the computer system 1000. Such devices may include removable storage unit 1028 and an interface 1024 (e.g., a program cartridge and a cartridge interface); a removable memory chip (e.g., an erasable programmable read-only memory (“EPROM”) or a programmable read-only memory (“PROM”)) and an associated memory socket; and other removable storage units 1028 and interfaces 1024 that allow software and data to be transferred from the removable storage unit 1028 to other parts of the computer system 1000.
The computer system 1000 may also include a communications interface 1012 that enables software and data to be transferred between the computer system 1000 and external devices. Such an interface may include a modem, a network interface (e.g., an Ethernet card or an IEEE 802.11 wireless LAN interface), a communications port (e.g., a Universal Serial Bus (“USB”) port or a FireWire® port), a Personal Computer Memory Card International Association (“PCMCIA”) interface, Bluetooth®, and the like. Software and data transferred via the communications interface 1012 may be in the form of signals, which may be electronic, electromagnetic, optical or another type of signal that may be capable of being transmitted and/or received by the communications interface 1012. Signals may be provided to the communications interface 1012 via a communications path 1016 (e.g., a channel). The communications path 1016 carries signals and may be implemented using wire or cable, fiber optics, a telephone line, a cellular link, a radiofrequency (“RF”) link, or the like. The communications interface 1012 may be used to transfer software or data or other information between the computer system 1000 and a remote server or cloud-based storage (not shown).
One or more computer programs or computer control logic may be stored in the main memory 1004 and/or the secondary memory 1018. The computer programs may also be received via the communications interface 1012. The computer programs include computer-executable instructions which, when executed by the computer processor 1006, cause the computer system 1000 to perform the methods as described hereinafter. Accordingly, the computer programs may control the computer system 1000 and other components of the kinematic apparatus.
In another embodiment, the software may be stored in a non-transitory computer-readable storage medium and loaded into the main memory 1004 and/or the secondary memory 1018 of the using the removable-storage drive 1022, hard disk drive 1020, and/or the communications interface 1012. Control logic (software), when executed by the computer processor 1006, causes the computer system 1000, and more generally the kinematic apparatus, to perform the some or all of the methods described herein.
Lastly, in another example embodiment hardware components such as ASICs, FPGAs, and the like, may be used to carry out the functionality described herein. Implementation of such a hardware arrangement so as to perform the functions described herein will be apparent to persons skilled in the relevant art(s) in view of this description.
Different features, variations and multiple different embodiments have been shown and described with various details. What has been described in this application at times in terms of specific embodiments is done for illustrative purposes only and without the intent to limit or suggest that what has been conceived is only one particular embodiment or specific embodiments. It is to be understood that this disclosure is not limited to any single specific embodiment or enumerated variation. Many modifications, variations and other embodiments will come to the minds of those skilled in the art, in view of this specification, and are intended to be and are in fact covered by this disclosure. It is indeed intended that the scope of this disclosure should be determined by a proper legal interpretation and construction of the disclosure, including equivalents, as understood by those of skill in the art relying upon the complete disclosure present at the time of filing.
