United States Patent
`US 6,629,011 B1
`(10) Patent No.:
`(12)
`Calderon et al.
`(45) Date of Patent:
`Sep. 30, 2003
`
`
`US006629011B1
`
`(54) AUTOINITIALIZATION IN A THREE-
`DIMENSIONAL MODELING MACHINE
`
`(75)
`
`Inventors: Joseph L. Calderon, Carlsbad, CA
`.
`*
`.
`teetaOALeee
`au
`:
`Batchelder, Somers, NY (US)
`.
`;
`(73) Assignee: Stratasys, Inc., Eden Prairie, MN (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`US.C. 154(b) by 410 days.
`
`(21) Appl. No.: 09/618,169
`(22)
`Filed:
`Jul. 17, 2000
`
`Tint, C17 eccccccccseescseseecseseeeeeesenes GO6F 19/00
`(SL)
`(52) US. Ch. ee 700/119; 264/401; 425/375;
`700/192; 700/195
`(58) Field of Search o0...i eee 700/57, 60-62,
`700/64, 114, 117-119, 123, 124, 160, 163,
`186, 190, 192-195, 302, 98; 702/33, 105,
`168; 425/135, 375: 264/497, 308, 401
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,328,553 A *
`4,642,752 A *
`4,749,347 A
`5,099,090 A *
`
`......... 700/192
`5/1982 Fredriksen et al.
`.......... 700/160
`2/1987 Debarbieri et al.
`
`.-. 425/135
`6/1988 Valavaara .........
`3/1992 Allan et al. oo, 174/257
`
`6/1992 Crump oo... eee 700/119
`5,121,329 A
`5,271,896 A * 12/1993 Jakubowicz etal. .......... 422/63
`
`5,303,141 A
`4/1994 Batchelderet al.
`............ 700/29
`aaa “
`Stoos smessnpoe seoto
`402,
`atchelder et al.
`.........
`5.428.548 A *
`6/1995 Pilboroughetal. ......... 700/195
`......... 700/196
`6/1998 Batchelderet al.
`5,764,521 A
`5,939,008 A
`8/1999. Combet al.
`ceseesseesssees 264/308
`5,968,561 A * 10/1999 Batchelder et al.
`......... 425/375
`6,004,124 A * 12/1999 Swansonet al. «2... 425/375
`
`* cited by examiner
`Primary Examiner—Leo Picard
`Assistant Examiner—Paul Rodriguez
`(74) Attorney, Agent, or Firm—Kinney & Lange, P.A.
`(57)
`ABSTRACT
`tee
`Soe
`.
`Disclosed are a method and apparatus for initializing an
`additive process computer-controlled three-dimensional
`modeling machine which builds models on a modeling
`platform. The method, without operator intervention, senses
`the top surface of a substrate or other object mounted on the
`platform at a variety of preselected x, y locations and records
`the z-axis positions of the platform corresponding to the
`sensing of the object. Using the recorded z-axis positions, a
`z-start position for the modeling platform is calculated. The
`platform can be automatically placed at the calculated z-start
`position. The recorded z-axis positions can further be used
`to define a plane fitted to the substrate top surface.
`Optionally, the model can be built in a coordinate system
`defined by the plane.
`
`27 Claims, 5 Drawing Sheets
`
`SWITCH PLLINGER FROM STORED
`
`70 ACTUATED POSITION
`
`
`
`POSITION PLUNGERABOVE A
`
`PRESELECTED LOCATION OF SUBSTRATE
`
`
`
`
`ELECTRICALLY RECORD Z-AXIS POSITION OF
`PLATFORM CORRESPONDING TO SIGNAL CHANGE
`NE
`
`
`
`
`REPEAT STEPS: B-E ATADDITIONAL
`PRE-SELECTED SUBSTRATE LOCATIONS
`
`SWITCH PLLINGER BACK JO STORED POSITION
`
`[~G
`
`ALERT OPERATOR 70 RE-LOAD SUBSTRATE[>2
`AND REPEAT INITIALIZATIONROUTINE
`
` COMPARE RECORDED Z-AXIS POSITIONS TO
`
`DETERMINE WHETHER TOP SURFACE OF
`SUBSTRATE IS PARALLEL 10 XY-PLANE
`
`
`
`
`IE NO,
`
`
`
`
`
`USE RECORDED Z-AUS POS/TIONS TO
`CALCULATE Z-START POSITION
`
`7-/
`
`POSITION PLATFORM AT Z-START POSITION
`
`Shenzhen Tuozhu 1009
`
`1
`
`Shenzhen Tuozhu 1009
`
`

`

`U.S. Patent
`
`Sep. 30, 2003
`
`Sheet 1 of 5
`
`US 6,629,011 BI
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`

`

`U.S. Patent
`
`Sheet 2 of 5
`
`Sep. 30, 2003
`
`US 6,629,011 B1
`
`3
`
`

`

`US 6,629,011 BI
`
`Sheet 3 of 5
`
`Sep. 30, 2003
`
`U.S. Patent
`
`D4
`
`184
`
`782
`
`FIG.)
`
`4
`
`

`

`U.S. Patent
`
`Sep. 30, 2003
`
`Sheet 4 of 5
`
`US 6,629,011 B1
`
`
` SWITCH PLUINGER FROYT STORED
`
`
`JO ACTUATED POSITION
`
`
`
`
`POSITION PLUNGER ABOVE A
`PRESELECTED LOCATION OF SUBSTRATE
`
`
`RAISE PLATFORM 70 DRIVE PLUNGER
`UPWARD BY CONTACT WITH SUBSTRATE
`
`
`
`MONITOR CHANGE / SENSOR OUTPUT SIGNAL
`
`\'D
`
`ELECTRICALLY RECORD Z-AXIS POSITION OF
`PLATFORM CORRESPONDING TO SIGNAL CHANGE
`
`|E
`
`REPEAT STEPS: B-E AT ADDITIONAL
`PRESELECTED SUBSTRATE LOCATIONS
`
`F
`
`SWITCH PLUNGER BACK JO STORED POSITION
`
`|~G
`
`COMPARE RECORDED Z-AXIS POSITIONS TO
`DETERMINE WHETHER TOP SURFACE OF
`SUBSTRATE 1S PARALLEL TO XY-PLANE
`
`IP YEE
`Hf
`
`:
`
`If NO,\
`
`ALERT OPERATOR 70 RE-LOAD SUBSTRATE
`AND KEPEAT INITIALIZATION ROUTINE
`
`f
`
`USE RECORDED ZAMS POSITIONS 70
`CALCLLATE Z-START POSITION
`
`}~/
`
`POSITION PLATFORM AT Z-START POS/TION
`K
`
`FIG. 6
`
`5
`
`

`

`U.S. Patent
`
`Sep. 30, 2003
`
`Sheet 5 of 5
`
`US 6,629,011 BL
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`52,
`
`[42
`
`F | G 7A
`
`154
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`6 144
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`190LE
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`

`

`US 6,629,011 Bl
`
`1
`AUTOINITIALIZATION IN A THREE-
`DIMENSIONAL MODELING MACHINE
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to the fabrication of three-
`dimensional objects using additive process modeling tech-
`niques. More particularly, the invention relates to modeling
`machines which form three-dimensional objects by depos-
`iting modeling material onto a substrate mounted to a
`modeling platform.
`Additive process modeling machines make three-
`dimensional models by building up a modeling medium,
`usually in planar layers, based upon design data provided
`from a computer aided design (CAD) system. A mathemati-
`cal description of a physical part to be created is split into
`(usually) planar layers, and those layers are individually
`shaped and applied to produce the final part. Three-
`dimensional models are used for functions including aes-
`thetic judgments, proofing the mathematical CAD model,
`forming hard tooling, studying interference and space
`allocation, and testing functionality. The dominant applica-
`tion of layered manufacturing in recent years has been for
`rapid prototyping.
`Examples of apparatus and methods for making three-
`dimensional models by depositing solidifiable modeling
`material are described in Crump U:S. Pat. No. 5,121,329,
`Batchelder, et al. U.S. Pat. No. 5,303,141, Crump U’S. Pat.
`No. 5,340,433, Batchelder, et al. U.S. Pat. No. 5,402,351,
`Crumpet al. U.S. Pat. No. 5,503,785, Abramset al. U.S. Pat.
`No. 5,587,913, Danforth, et al. U.S. Pat. No. 5,738,817,
`Batchelder, et al. U.S. Pat. No. 5,764,521 and Combetal.
`US. Pat. No. 5,939,008, all of which are assigned to
`Stratasys, Inc.,
`the assignee of the present invention. An
`extrusion head extrudes solidifiable modeling material in a
`fluentstrand (also termed a “bead”or “road”) from a nozzle
`onto a base. The base comprises a modeling substrate which
`is removably affixed to a modeling platform. The extruded
`material is deposited layer-by-layer in areas defined from the
`CAD model, as the extrusion head and the base are moved
`relative to each other by mechanical meansin three dimen-
`sions. The finished model is removed from the substrate. A
`
`solidifiable material which adheres to the previous layer
`with an adequate bond upon solidification is used as the
`modeling material. Thermoplastic materials have been
`found particularly suitable for these deposition modeling
`techniques.
`Other additive process manufacturing techniques include
`depositing UV curable polymers as in Masters U.S. Pat. No.
`5,134,569; jetting of droplets of material as in Helinski U.S.
`Pat. No. 5,136,515; extruding a settable plastic in vertical
`strips as in Valaaara U.S. Pat. No. 4,749,347; laser welding
`deposition as in Pratt U.S. Pat. No. 5,038,014; stacking and
`adhering planar elements as in DiMatteo U.S. Pat. No.
`3,932,923; and applying shaped layers of paper as in Hull
`USS. Pat. No. 5,192,559.
`In additive process three-dimensional modeling machines
`utilizing manufacturing techniques such as those described
`above, the modelis built up on a base typically comprising
`a substrate mounted on a modeling platform. The material
`being deposited must adhere to the substrate to form a
`foundation layer over which the remaining layers of the
`object are deposited. The substrate stabilizes the model asit
`is built up, and facilitates removal of the model from the
`modeling machine when the model is complete.
`It
`is preferred that parts deposited on the modeling
`substrate be strongly adhered thereto to overcome two
`
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`effects. First, strains generated within the extruded material
`tend to warp the deposited structures unless the structures
`are supported in their correct orientation. The substrate is
`important in serving to avoid localized shrinkage in the
`foundation layer. Second,
`in some deposition processes,
`there are forces such as pull from an extrusion nozzle and
`centripetal acceleration on parts that are not stationary, that
`tend to distort the deposited structures. A delamination of the
`foundation layer from the substrate during the building of
`the object could result in a total failure in forming the object.
`Further, since the removable substrate becomes a defining
`surface for the object being built,
`it must be held in a
`well-defined configuration. Typically, the substrate is held in
`a configuration approximating a plane.
`The Crump °329 and °433 patents disclose a foam plastic
`material for use as a modeling substrate.: A blue polystyrene
`material manufactured by Dow-Corning Corp under that
`name and having a compression strength of 30 psi
`is
`identified as particulary suitable coarse, porous structure.
`The Crump °329 and ’433 patents also disclose modeling on
`a wire mesh sandpaper substrate, and on a water soluble
`wax. The Batchelder et al. °521 patent discloses a sheet of
`magnetic material for use as a modeling substrate, wherein
`the modeling platform includes a magnet for attracting the
`sheet, while the Comb ’008 patent discloses a flexible sheet
`substrate held down by vacuum forces.
`In rapid prototyping systemssold in the past by Stratasys,
`Inc., a preferred substrate material has been a polymer foam.
`A foam slab substrate has proven particularly suitable for
`supporting models made by extrusion-based deposition
`modeling techniques. The porosity and compressibility of
`foam allows foundation layers of modeling material to be
`buried into the foam, which increases stability of the model
`as is it built up.
`Before building up a model in commercially available
`modeling machines which build a model on a substrate
`mounted to a platform which moves along a z-axis, the
`z-axis position of the platform requires initialization. For
`example, in the Stratasys FODM® modeling machines, the
`operator manually moves the modeling platform up or down
`to place an extrusion nozzle at a correct position with respect
`to the substrate. Nozzle tip depth is typically set at one
`location of the substrate. In the Stratasys FODM® machines
`that built the model on a foam slab substrate, the optimal
`position of the extrusion nozzle is below the top surface of
`the foam, al a depth so that the first two extruded layers of
`modeling material will be buried in the foam. Thefirst two
`layers extruded into the foam substrate provide a foundation
`to stabilize a modelasit is built up. The z-axis accuracy for
`building on the foam should be +5-10 mils. For rigid
`substrates, the z-axis accuracy desired in a Stratasys FOM®
`modeling system is +2—4 mils.
`Unfortunately, achieving the correct position of a model-
`ing platform by a manual or “eyeball” method can be
`unreliable and time-consuming. As proper positioning
`requires operator judgment, it can be difficult for inexperi-
`enced users to identify the correct position. In the Stratasys
`FDM®machines,if the top surface of the substrate is not in
`an xy plane, nozzle tip depth will be incorrect at some
`locations of the substrate. This results in “modeling in air”
`or in too much “plowing” by the tip.
`in failure in
`An incorrect z-start position can result
`forming a modcl. Additionally,
`if the substrate is not
`mounted flat to the platform, or if the substrate is deformed
`or improperly mounted so that it lacks a horizontal planar
`surface, the model quality will be adversely affected regard-
`
`7
`
`

`

`US 6,629,011 Bl
`
`3
`less of the z-start position selected. There exists a need for
`a z-axis initialization routine that does not require operator
`intervention or judgment.
`SUMMARYOF THE INVENTION
`
`invention is an automated apparatus and
`The present
`method for initialization of a computer-controlled modeling
`machine that builds up three-dimensional objects on a
`substrate supported by a modeling platform.
`An autoinitialization method of the present invention will
`calculate a z-start position for the platform based upon
`z-axis positions of the platform obtained by sensing the
`substrate surface at multiple x, y positions. A method for
`determining the z-start position includes the steps of (a)
`positioning a plunging means above a pre-selected x, y
`location of a substrate mounted on the platform; (b) raising
`the platform to drive the substrate against the plunging
`means; (c) electrically detecting contact by the substrate
`against
`the plunging means and responsive providing a
`detection indication; (d) responsive to the detection indica-
`tion of step (c), electrically recording the z-axis position of
`the platform corresponding to the detected contact between
`the substrate and the plunging means; (e) repeating steps (a)
`through (d) at a plurality of other pre-selected x, y locations
`of the substrate to obtain a plurality of recorded z-axis
`positions; and (f) using the plurality of recorded z-axis
`positions to calculate a z-start position of the platform. The
`modeling machine can then automatically position the plat-
`form at
`the calculated z-start position, without operator
`intervention. In optional additional steps, the method com-
`pares the recorded z-axis positions to verify that the sub-
`strate top surface is parallel to an xy-plane, and notifies the
`operator to re-load the substrate if the substrate surface does
`nol approximate a horizontal plane. Or, step (f) can include
`a step of performing calculations based on the recorded
`z-axis positions to define a coordinate system fitted to the
`substrate surface. The model can then be built up in the
`coordinate system of the substrate.
`the autoinitialization
`In an alternative embodiment,
`method of the present
`invention is used to determine
`whether a previously built model remains in the modeling
`machine by sensing and evaluating the z-height of the
`substrate or object carried by the platform. In a further
`alternate embodiment,
`the method is used to determine
`coordinates at which to continue building a model in the
`event of a power outage during the build process.
`Asensor assembly for use in performing the method of the
`present invention includes a plunger, a sensor and an actua-
`tor. ‘he plunger has a raised stored position and a lowered
`actuated position. The actuator switches the plunger from its
`stored position to its actuated position for use in executing
`the z-axis initialization routine and switches the plunger
`backto its stored position upon completion of the routine. In
`its actuated position, the plunger is movable by application
`of an upward force to a sensing location a predetermined
`distance above the actuated position. The sensor detects the
`presence of the plungerat the sensing location, providing an
`output signal when the plungeris detected. Upward force by
`the substrate against a downward facing tip of the plunger
`will drive the plunger up the predetermined distance. The
`sensor assembly can be mountedto the extrusion head of an
`extrusion-based modeling machine.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic of a representative generic
`extrusion-based, layered modeling system.
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`FIG. 2 is a perspective view of a preferred embodimentof
`the sensor assembly of the present invention in an actuated
`position, mounted to the extrusion head of an extrusion-
`based layered modeling machine and positioned over a
`pre-selected location of a substrate.
`FIG. 3 is a cross-sectional view of the sensor assembly of
`FIG. 2, with the plunger in a stored position.
`FIG. 4 is a cross-sectional view of the sensor assembly of
`FIG. 2, with the plunger in an actuated position.
`FIG. 5 is a rear view of the actuator.
`
`FIG. 6 is a process flow diagram illustrating the steps
`executed in performing a z-axis initialization routine accord-
`ing to the present invention.
`FIGS. 7a and 7b depict the operation of step A of FIG. 6.
`FIGS. 8a and 8b depict the operation of step G of FIG. 6.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`FIG. 1 shows a generic representation of a extrusion-
`based layered modeling system 106, of a type knownin the
`art, with which the present
`invention may be used. A
`computer aided design (CAD) program resident in a pro-
`cessor 108 generates a file describing the geometry of a part
`109 to be created. A slicing program (shownas resident in
`processor 108 but which may alternatively be resident in a
`separate processor) algorithmically subdivides the file into
`volume elements 110 corresponding to shapes that can be
`extruded from a nozzle. Additional volume elements 112 are
`added as necessary to provide mechanical support to a part
`during its construction. The volume elements are sequen-
`tially ordered so that deposited material is supported appro-
`priately.
`in response to receiving
`An electronic controller 116,
`three-dimensional shape data from processor 108 over line
`114, controls the extrusion of modeling material
`in an
`xyz-coordinate reference frame so that beads of modeling
`material are extruded layer-by-layer in a pattern defined by
`the volume elements 110 and 112. Controller 116 calculates
`
`and maintains in an associated memory 119 data represen-
`tative of movements required to build the model. Based on
`this data, controller 116 sends control signals to an xy axis
`translator 118, a z-axis translator 120 and an extrusion pump
`122, over output signal lines 117a, 117b and 117c, respec-
`tively. X-y axis translator 118 is an electromechanical device
`that moves a robotic arm 124, so as to sequentially position
`an extrusion head 126 carried by the arm 124 within an
`xy-plane with respect to a modeling substrate 128. Extrusion
`pump 122 synchronously provides modeling material from
`a material supply 130 to extrusion head 126. The extrusion
`head 126 terminates in a nozzle 132 through which the
`modeling material is extruded.
`The modeling material is extruded from nozzle 132 onto
`the substrate 128, which is removably mounted onto a
`modeling platform 134 and is located in a modeling enve-
`lope 138. Modeling platform 134 moves in a z-direction
`under the control of z-axis translator 120. The z-axis as
`
`shownis oriented radially away from the earth’s surface. In
`other implementations, however,
`it can be towards the
`ground or at some other chosen angle. Z-axis translator 120
`incrementally lowers modeling platform 134 following
`deposition of a layer of modeling material, to build up a
`model 136 layer-by-layer on the substrate 128. After the
`model 136 is created, the model 136 is removed from the
`modeling system 106 and from the substrate 128.
`An autoinitialization apparatus and method is now
`described which has application for finding the initial ver-
`
`8
`
`

`

`5
`tical position (“z-start” position) of a modeling platform in
`a three-dimensional modeling system, such as the type
`described above and shown in FIG. 1.
`It should be
`
`US 6,629,011 Bl
`
`6
`corresponding to the instant in time at which the signal
`changeis detected. By monitoring the signal on line 166 and
`recording a z-axis position of platform 147 at which the
`change in signal is detected, the controller 116 is able to
`determine the z-axis coordinate of the platform 147 at which
`the top surface of substrate 146 contacted the plunger 148.
`The controller 116 uses this known z-axis position at which
`contact occurred to calculate the z-start position of platform
`147, as described in more detail below.
`FIGS. 3 and 4 show detail of one embodiment of the
`
`understood, however, that the teaching of this invention is
`not limited for use only with an extrusion-based layered
`manufacturing system of the type shown. That is, the inven-
`tion has use also in other three-dimensional modeling sys-
`tems which build up an object on a substrate removably
`mounted to a modeling platform.
`Asensor assembly 140 of the present invention, mounted
`sensor assembly 140. FIG. 3 showsthe plungerin a stored
`to an extrusion head 142 of an extrusion-based layered
`position, while FIG. 4 shows the plunger in an actuated
`modeling system, is shown in FIG. 2. The extrusion head
`position. As depicted in FIGS. 3 and 4, plunger 148 com-
`142 is shown positioned over a substrate 146 which is
`prises a sub-housing 170 supporting a metal rod 172 embed-
`supported by a platform 147. Extrusion head 142 movesin
`ded in a transparent casing 174. Casing 174 has a cylindrical
`an xy-plane and platform 147 moves along a z-axis, as
`body 176 terminating in a flat downward-facing tip 178. Tip
`described above with respect to FIG. 1. Extrusion head 142
`178 should have a contact area large enough that the force
`terminates in a nozzle 144, from which modeling materialis
`of contact of the tip 178 against the substrate 146 does not
`extruded onto substrate 146. As shown, substrate 146 is a
`exceed an elastic yield limit of the substrate. A retaining clip
`slab substrate, such as foam. It should be noted, however,
`179 wraps around the casing 174 and a spring 180 is coupled
`that while the apparatus and method ofthe present invention
`between the clip 179 and the subhousing 170. As shown in
`are particularly useful in finding a z-start position when
`FIGS. 3 and 4, sensor 162 is an optical sensor which
`modeling on a slab substrate, the present invention also has
`generates an electrical output signal indicating whether a
`use when modeling on other types of bases, as will be
`light beam emitted from a light generating part of the sensor
`appreciated by those skilled in the art.
`is incident upon a light receiving part of the sensor. Suitable
`Sensor assembly 140 includes a plunger 148, a housing
`optical sensors are available from OPTEK Technologies, for
`152, an actuator 154, and a sensor 162 (shown in FIGS. 3
`example, modcl OPB380T51. The clectrical output signal
`and 4). Plunger 148is reciprocably mounted to housing 152,
`from sensor 162 changes state when the light beam of sensor
`so as to move vertically through an open bottom of the
`162 is occluded by plunger 148.
`housing. Actuator 154, which is generally in the shape of a
`A pin 182 and a spring 183 (not shown) couple the
`bar, is bounded between an upper guide 156 and a lower
`plunger 148 to the actuator 154, through a vertical slot in
`guide 158 of the housing 152 and slides horizontally from
`housing 152. Pin 182 slides in a ramped groove 184 along
`side-to-side in the housing 152 in response to application of
`the back side of actuator 154, as shown in ['IG. 5. When pin
`horizontal force. Actuator 154 has a rightward position at
`182 is positioned at
`the upper level of groove 184,
`the
`which it extends past the extrusion head onaright side
`plunger is held in the stored position. When pin 182 is
`thereof, and a leftward position at which it extends past the
`moved to the lower level of groove 184, plunger 148 is
`extrusion head onaleft side thereof. The side-to-side motion
`moved downto the actuated position.
`Those skilled in the art will recognize that many other
`embodiments of a sensor assembly are possible which may
`be used interchangeably with sensor assembly 140.
`Particularly, sensor 162 may be interchanged with any
`sensing means which can detect and signal contact between
`the plunger and the substrate, and need not be limited to an
`optical sensor. In other embodiments, sensor assembly 140
`may, for example, use a magnet proximity switch, a Hall
`sensor, a Wiegand wire, a reed switch, a capacitive sensor or
`an inductance sensor. Likewise, plunger 148 may be inter-
`changed with any plunging means which can be driven
`upward a predetermined distance by force of contact with
`the substrate such as a cam, pawl, cantilever, screw or
`membrane, or other mechanical structure. Or, contact
`between the plunger and the substrate can be sensed at their
`initial contact, in which case the plunging means need not
`move upward in response to contact with the substrate. For
`example, in one alternative embodiment, a pzt; voice coil or
`similar transducer is used to vibrate the plunger at a rela-
`tively high frequency (greater than 100 Hz, preferably
`greater than 10 kHz) and the transducer serves also as a
`sensing means to monitor the magnitude of the vibration.
`Contact
`is detected by the snubbing of the vibrational
`motion of the plunger.
`Sensing techniquesthat do not necessarily involve the use
`of a plunging means can also be used in practice of the
`method of the present invention. Any manner of sensing a
`surface at selected coordinates to detect the corresponding
`z-axis coordinate may be used in practice of the invention.
`Suitable sensing meansinclude butare notlimitedto, visible
`
`of actuator 154 alternately lowers and raises plunger 148.
`Actuator 154 moves plunger 148 from a stored, raised
`position during periods of non-use, to a lowered, actuated
`position for use in executing a z-axis initialization routine
`whichfinds the z-start position for the platform 147. In its
`actuated position, the plunger 148 is movable by application
`of an upward force to a sensing location located a prede-
`termined distance X above the actuated position. The sensor
`162, which is mounted within housing 152, detects the
`presence of plunger 148 at the sensing location.
`In FIG. 2, plunger 148 is shownin its actuated position,
`at which it protrudes from the bottom of the housing 152. A
`set of four connectors 160 mount the sensor assembly 140 to
`a backside of extrusion head 142. Sensor assembly 140 is
`mounted at a height such that plunger 148 in its actuated
`position extends a predetermined distance Y beneath the tip
`of nozzle 144.
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`Whenplatform 147 is raised upward along the z-axis and
`plunger 148 is in its actuated position, a top surface of
`substrate 146 contacts plunger 148 and drives it up into
`housing 152. Sensor 162 senses whenthe plunger 148 has
`traveled upward the predetermined distance to the sensing
`location, and provides a signal indicating detection of the
`plunger. The signal from sensor 162 is provided on a signal
`line 166, which is coupled to controller 116 via one of
`terminals 164 of housing 152. Controller 116 monitors
`signal linc 166. A change in the signal provided by sensor
`162 indicates to the controller 116 that plunger 148 has
`moved the predetermined distance X. Controller 116 elec-
`trically records the z-axis coordinate of the platform 147
`
`9
`
`

`

`US 6,629,011 Bl
`
`7
`imaging devices, tactile detection devices and pneumatic
`detection devices. Examples of such devices are shown and
`discussed in Batchelder, et. al. U.S. Pat. No. 5,303,141 (see
`col.8, line 39 through col. 10,
`line 61), which is hereby
`incorporated by reference herein.
`
`EXAMPLE1
`
`Referring now to the process flow diagram of FIG. 6,
`there is described a z-axis initialization routine in accor-
`
`dance with the present invention. The routine is performed
`after a substrate is loaded onto platform 147 and before
`model building is begun. Before executing the routine, the
`plunger 148is typically in its stored position. In a first step
`(A), plunger 148 is switched from its stored position to its
`actuated position. In the embodiment described herein, this
`step is performed by moving the extrusion head 142 in the
`x-direction so as to drive actuator 154 against a first sta-
`tionary block 190 located outside of the modeling envelope
`138 to the right of extrusion head 142. The force of block
`190 against actuator 154 pushes the actuator 154 to its
`leftward position. This operation is depicted in FIGS. 7a and
`7b.
`
`In a secondstep (B), the plunger 148 is positioned above
`a substrate 146 at a first pre-selected x,y location at which
`it is desired to locate a top surface of the substrate. For a
`square or rectangular substrate, a preferred location is
`towards one of the four corners, as shownin FIG. 2. A third
`step (C) is to raise platform 147 so that the top surtace of
`substrate 146 contacts the tip 178 of plunger 148 and drives
`plunger 148 upward. A next step (D) is to detect movement
`of the plunger 148 to the sensing location. This is done by
`monitoring a changein the output signal from sensor 162. In
`the cmbodiment shown herein, controller 116 monitors
`signal line 166. A change in the signal signifies that plunger
`148 hasinterrupted the light beam of sensor 162. In a step
`(E), the controller 116 electrically records in memory 119
`the z-axis coordinate of platform 147 corresponding to the
`time at which the output signal changed. Once step (E) is
`completed, platform 147 can be lowered. In the embodiment
`described, when substrate 146 is no longer pushing up
`against plunger 148, spring 180 will force plunger 148 back
`to its actuated position.
`In the absence of spring 180,
`however, the plunger could be lowered in another manner,
`such as by force of gravity or by repeating step (A).
`Astep (F)is to repeat steps (B) through (E)at a plurality
`of additional pre-selected x,y locations. In the case of a
`square or rectangular substrate, steps (B) through (E) are
`preferably repeated at locations in the vicinity of the three
`other corners of the substrate, to obtain four recorded z-axis
`positions corresponding to four sets of x,y coordinates.
`When values have been recorded at all pre-selected sub-
`strate locations, the plunger 148 is switched back up to its
`stored position, in a step (G). In the embodiment shown, this
`step is executed by moving the extrusion head 142 in the
`x-direction towards a second stationary block 192 located
`outside of the modeling envelope 138, to the left of extrusion
`head 147. The force of block 192 against actuator 154
`pushes the actuator 154 to its rightward position. The
`operation of step (G) in the described embodiment is shown
`in FIGS. 8a and 8b.
`
`When a z-axis position has been recorded for each pre-
`selected x, y location, step (H) is performed. In step (H), a
`“Find-Z” software program loaded into controller. 116 com-
`pares the recorded z-axis positions to determine whether the
`top surface of substrate 146 is approximately parallel to a
`horizontal, xy-plane. Step (H) is particularly useful for a
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`8
`modeling system that uses a slab substrate. If the result of the
`comparison showsthat the substrate top surface does not
`closely enough approximate a horizontal plane, that result
`indicates either that the substrate 146 was not mountedflush
`to platform 147,or that the substrate 146 has a deformity. In
`such a case, in a step (1), controller 116 provides a notifi-
`cation to the operator, alerting the operator to reload the
`substrate 146 onto platform 147 and then repeat the z-axis
`initialization routine. The notification is preferably by way
`of a written message on a system display screen (not shown).
`If the comparison of step (H) showsthat the substrate top
`surface is parallel to the xy-plane, a step (J) is executed, in
`which the “Find-Z” software, program uses the recorded
`z-axis positions to calculate a z-start position of platform
`147. The Find-Z program uses known, constant system
`parameters to derive the actual z-axis position of platform
`147 at the time of initial contact between substrate 146 and
`plunger 148 and to thereby determine an appropriate z-start
`position of platform 147 with respect to the extrusion head
`nozzle 144. In the case of a foam slab substrate, step (J) can
`be executed using the following algorithm:
`(1) Subtract the constant value X, representing the pre-
`determined distance of the sensing location above the
`actuated position of plunger 148, from each recorded
`z-axis position. The result of this subtraction is a set of
`actual z-axis positions of platform 147 at the instant
`that substrate 146 contacted plunger 148.
`(2) Select the lowest of the actual z-axis positions.
`(3) Add the constant value Y, representing the predeter-
`mined distance of the tip of nozzle 144 above the tip
`178 of plunger 148, to the selected actual z-axis posi-
`tion. This result of this calculation is the z-axis position
`at which substrate 146 will contact the tip of nozzle
`144.
`
`(4) Add a constant value Z, representing the desired depth
`of the tip of nozzle 144 below the top surface of
`substrate 146, to the result of step (3), to arrive at the
`z-start position.
`It will be apparentto those skilledin the art that the above
`algorithm is but one example of an algorithm that may be
`used for calculating the z-start position based upon the
`recorded z-axis positions using the method of the present
`invention. For instance, steps (1)-(4) may be combined or
`performed in a differ