WO2016084351A1

WO2016084351A1 - Method and apparatus for forming stereoscopic object

Info

Publication number: WO2016084351A1
Application number: PCT/JP2015/005770
Authority: WO
Inventors: Satoru Yamanaka; Tatsuya Tada; Kenji Karashima; Hirokazu Usami; Takashi Kase
Original assignee: Canon Kabushiki Kaisha
Priority date: 2014-11-28
Filing date: 2015-11-18
Publication date: 2016-06-02

Abstract

The present invention relates to a method for forming a stereoscopic object (S). The method includes the steps of forming at least one powder layer by disposing forming powders (M) based on slice data, forming a material layer from the at least one powder layer, and laminating the material layer on a stereoscopic object (S) being produced. The powder layer is formed so as to have a thickness of less than twice a volume mean diameter of the forming powders (M) and to have a projection area percentage of 90% or higher per unit area. '

Description

METHOD AND APPARATUS FOR FORMING STEREOSCOPIC OBJECT

The present invention relates to a technique for forming a stereoscopic object and, in particular, relates to a sheet lamination stereoscopic-object forming apparatus and a method for controlling the same.

A technique for forming a stereoscopic object called additive manufacturing (AM) has recently been attracting attention. The AM technique is a technique for forming a stereoscopic object by slicing three-dimensional (3D) data on a stereoscopic object to generate a plurality of slice data items and by repeating the process of disposing a forming material based on the slice data and gluing it to form a stereoscopic object.

The AM technique has the convenience of needing no mold and an advantage in that a product of complex shape can be formed. Thus, the AM technique is used in producing a prototype for checking the action and shape of a component and in producing discrete components and small-lot items. This technique also allows production of components of complex shape that cannot be produced with molds and products of high-quality design that require much time and effort.

Main examples of the method for laminating and fixing successive layers of material include stereolithography, powder bed fusion, material jetting, and fused deposition modeling. The example techniques require much time to create a product because they adopts a system in which a forming material is deposited while being fixed directly onto a laminated object in process in a traversal manner or line by line.

PTL 1 discloses a method for forming a stereoscopic object by disposing material powders in two dimensions on a belt on the basis of slice data using an electrophotographic process to form material layers, heating the powders into films, and laminating successive layers of material on the laminated object on a stage. The AM technique using the electrophotographic process allows lamination of a forming material layer by layer, allowing a stereoscopic object to be produced in a relatively short time as compared with other systems.

U.S. Patent No. 5,088,047 Japanese Patent Laid-Open No. 2014-133414 (WO 2014/092205) Japanese Patent Laid-Open No. 2014-115518

If the amount of powders per unit area coated in forming a material layer is small, the AM technique disclosed in PTL 1 causes clearances among the powders. When the material layer is made into a film in the state in which there are clearances among the powders, the film is bored due to the clearances among the powders. Once the thin film having holes is laminated, part of a thin film laminated on the film may be positioned cavities (the holes of the preceding thin film).

This can cause deposition failures, for example, causes part of the upper thin film corresponding to the holes to remain on the belt without being laminated and part of the upper thin film to be drawn by the part remaining on the belt, thus damaging the thin film.

The present invention eliminates or reduces the deposition failures in the AM technique.

A method for forming a stereoscopic object according to an aspect of the present invention includes the steps of forming a material layer by disposing forming powders based on data and laminating the material layer on a stereoscopic object being produced. The material layer is formed so as to have a thickness of less than twice a volume mean diameter of the forming powders and to have a projection area percentage of 90% or higher per unit area.

A stereoscopic-object forming apparatus according to another aspect of the present invention includes a material-layer forming unit and a lamination unit. The material-layer forming unit includes a powder-layer forming section that disposes forming powders based on data to form at least one powder layer and a transfer section that forms a material layer by transferring the at least one powder layer to a transferred member. The lamination unit receives the material layer from the material-layer forming unit and laminates the material layer in sequence. The material-layer forming unit forms a powder layer having a thickness of less than twice a volume mean diameter of the forming powders and having a projection area percentage of 90% or higher per unit area.

According to an embodiment of the present invention, a stereoscopic object can be efficiently formed by eliminating or reducing lamination failures that occur during a forming process using a stereoscopic-object forming apparatus.

Fig. 1 is a schematic diagram illustrating the overall configuration of a stereoscopic-object forming apparatus according to an embodiment of the present invention. Fig. 2A illustrates the arrangement of powders of a powder layer and a thin film formed from the powder layer in cross sectional view. Fig. 2B illustrates the arrangement of powders of a powder layer and a thin film formed from the powder layer in cross section view. Fig. 3 is a diagram illustrating the problem to be solved by the present invention. Fig. 4A is a diagram illustrating clearances formed among powders of the same diameter that are disposed densely. Fig. 4B is a diagram illustrating clearances formed among powders of the same diameter that are disposed densely. Fig. 5A is a diagram illustrating an example of the arrangement of powders of the same diameter. Fig. 5B is a diagram illustrating a VB-VB cross section of the powders in Fig. 5A. Fig. 6A is a diagram illustrating an example of the arrangement of powders of different diameters. Fig. 6B is a diagram illustrating a VIB-VIB cross section of the powders in Fig. 6A. Fig. 7A is a schematic diagram illustrating a powder-layer forming section according to a first embodiment of the present invention. Fig. 7B is a schematic diagram illustrating a developing device according to the first embodiment of the present invention. Fig. 7C is a cross-sectional view of a toner conveying member in the developing device. Fig. 8 is a schematic diagram illustrating a state in which forming powders are being conveyed. Fig. 9A is a cross sectional view of forming powders illustrating the arrangement after being developed. Fig. 9B is a diagram illustrating the arrangement of the forming powders after being developed. Fig. 9C is a cross sectional view of forming powders illustrating the arrangement before being developed. Fig. 9D is a diagram illustrating the arrangement of the forming powders before being developed. Fig. 10 is a flowchart of an operation sequence in determining the projection area percentage of a material layer per unit area using an image detection sensor. Fig. 11A is a schematic diagram illustrating a developing device for use in a second embodiment. Fig. 11B is a graph illustrating the relationship between a potential difference and the efficiency of recovery. Fig. 12 is a schematic diagram illustrating a developing device for use in a third embodiment. Fig. 13 is a schematic diagram illustrating a developing device for use in a fourth embodiment.

Embodiments of the present invention will be described hereinbelow with reference to the drawings. The sizes, materials, shapes, and the relative arrangement of the components of the apparatuses described in the embodiments, the procedures, control parameters, and target values of various control operations are given for mere illustration and are not intended to limit the scope of the invention unless otherwise noted.

Overall Configuration of Stereoscopic-object Forming Apparatus

First, the overall configuration of a stereoscopic-object forming apparatus according to an embodiment of the present invention will be described. Fig. 1 is a schematic diagram illustrating an example of the overall configuration of the stereoscopic-object forming apparatus. The stereoscopic-object forming apparatus adopts an additive manufacturing (AM) system for producing a stereoscopic object by repeatedly a laminating material layer in which material powders are disposed in two dimensions.

As illustrated in Fig. 1, the stereoscopic-object forming apparatus roughly includes a control unit U1, a material-layer forming unit U2, and a lamination unit U3. Fig. 1 illustrates a configuration example in which two kinds of forming powder, Ma and Mb, are used.

The control unit U1 is a unit that plays the role of controlling a process of generating slice data (cross-section data) on a plurality of layers from three-dimensional-geometry data on an object to be produced and the role of controlling the components of the stereoscopic-object forming apparatus.

The material-layer forming unit U2 is a unit that forms material layers made of forming powders using an electrophotographic process. Specifically, the material-layer forming unit U2 respectively forms powder layers made of forming powders Ma and Mb with powder-

layer forming sections

10a and 10b on the basis of the slice data generated by the control unit U1. The powder layers formed by the powder-

layer forming sections

10a and 10b are respectively transferred to an intermediate bearing member 111 by

transfer devices

110a and 110b to form a material layer made of the forming powders Ma and Mb, and the material layer is conveyed to the lamination unit U3.

The material layer passed from the material-layer forming unit U2 to a second intermediate bearing member 30 of the lamination unit U3 is conveyed to a lamination position without being changed or after being melted into a film by a heater (not shown) halfway through. At the lamination position, the second intermediate bearing member 30 on which the thin film is born is held between an opposing member 33 including a built-in heater and a stage 34, so that the thin film is laminated and fixed on an object S being produced on the stage 34.

Amount of Forming Powders Coated

The amount of forming powders coated on the material layer formed by the material-layer forming unit U2 will now be described. Fig. 2A illustrates a case in which powders M are sufficiently coated to form a material layer in which the powders are densely disposed. Fig. 2B illustrates a case in which the powders M are not sufficiently coated to form a material layer in which the powders are sparsely disposed.

As illustrated in Fig. 2A, the powder layer in which the forming powders M are densely disposed is transferred to the intermediate bearing member 111 to form a material layer. The material layer is transferred to the second intermediate bearing member 30 and is melted into a film. If the forming powders M are densely disposed, the powders melted into a film can fill the clearances among the powders M, allowing a thin film without holes to be formed. Laminating thin films without holes every time, as illustrated Fig. 2A, allows a dense high-quality stereoscopic object to be produced.

In contrast, if the forming powders M are sparsely disposed to generate a large clearance between the powders M, as illustrated in Fig. 2B, the powders M melted into a film do not spread to fill the clearance between the powders, thus forming a thin film having a hole. A thin film having holes can be laminated without particular problems if the surface of the object to be coated in the lamination has no cavity. However, the following problem occurs when the next material layer is laminated.

Fig. 3 illustrates a case in which a thin film La having no hole is laminated on the object S on which a thin film Lb having a hole is laminated. The thin film La having no hole is laminated from the second intermediate bearing member 30 onto the surface of the object S on which the thin film Lb having a hole is laminated. The thin film La having no hole is laminated on the object S in process, is fixed to the object S with heat, and is peeled from the second intermediate bearing member 30. At that time, a force Fb of holding the thin film La toward the stage 34 is smaller than an adhesive force Fa between the second intermediate bearing member 30 and the thin film La above the cavity due to the hole of the thin film Lb. This causes lamination failures; for example, the thin film La cannot be laminated on the cavity, so that part of the thin film La remains on the second intermediate bearing member 30, the other part of the thin film La is drawn by the part remaining on the second intermediate bearing member 30, thus damaging the thin film, and the lamination position of the thin film La is shifted.

The inventors examined the amount of coated powders M of a forming material in the AM technique using the electrophotographic process. Material layers have to be formed of a sufficient amount of coating powders to form thin films having no hole, so that powder layers need to be formed of a sufficient amount of coating powders. The examination showed that even if powders M disposed at a projection area percentage per volume smaller than a given value are melted, the clearances among the powders M cannot be filled, causing holes in the thin film.

Fig. 4A illustrates a powder layer in which forming powders having a substantially equal diameter are disposed most densely, viewed from a direction perpendicular to the disposition plane. If forming powders have a substantially equal diameter, the clearances among the powders can be filled when the powders are melted by disposing the powders in such a manner that the clearances among the powders, viewed from a direction perpendicular to the powder disposition plane, is smaller than the clearance with the disposition in Fig. 4A.

Figs. 5A and 5B illustrate another example of the disposition of forming powders with a substantially equal diameter. Fig. 5A is a diagram illustrating the state of powders viewed from a direction perpendicular to the powder disposition plane. Fig. 5B illustrates a VB-VB cross section.

As illustrated in Fig. 5A, each of the powders is disposed so as to be in contact with four powders in the same plane. At that time, as illustrated in Fig. 5B, there are large clearances among the powders in the first layer, but powders not in the first layer are fitted in the clearances of the first layer. Thus, there is no clearance as viewed from a direction perpendicular to the powder disposition plane. Such a state allows the clearances to be filled with the powders that fit in the clearances of the first layer, thus providing a thin film having no hole.

Figs. 6A and 6B illustrate an example of disposition of forming powders having different diameters. Fig. 6A is a diagram illustrating the state of powders viewed from a direction perpendicular to the powder disposition plane. Fig. 6B illustrates a VIB-VIB cross section.

As illustrated in Fig. 6B, powders having small diameters are partly fitted among powders having large diameters. This can achieve small clearances as viewed from a direction perpendicular to the powder disposition plane. Thus, also in the case of Figs. 6A and 6B, the clearances are filled with the powders fitted in the clearances of the first layer when the powders are melted into a film, thus providing a thin film having no hole.

Thus, setting the projection area percentage of the powders M equal to or smaller that of Figs. 4A and 4B allows a thin film having no hole to be formed.

The projection area percentage of the powders M per unit area with the powder disposition in Figs. 4A and 4B will be calculated. As illustrated in Fig. 4B, which is a partially enlarged view of Fig. 4A, the powders are disposed in such a manner that each powder is in contact with six powders.

The projection area percentage of the powders M per unit area is expressed as (πr²/2)/(√3r²) = π/(2√3), and π/(2√3) is approximately equal to 0.9, where r is the radius of each powder M. Accordingly, a projection area percentage of the powders M per unit area of 90% or higher can prevent or reduce holes formed in the thin film.

To control the shape of the object to be produced at high accuracy, the thicknesses of the laminated material layers need to be uniform. Forces by which powders M are attracted to a developing roller have the relationship, F₂ is approximately equal to F_n, and F_n is much smaller than F₁, where F₁ is a force by which the powders M in the first layer are attracted to the developing roller, F₂ is a force by which the powders M in the second layer are attracted to the developing roller, and F_n is a force by which the powders M in the nth layer (n is a real number larger than 2) are attracted to the developing roller. That is, forces by which powders in the second layer and subsequent layers are sufficiently smaller than the force by which the powders M in the first layer are attracted to the developing roller, and the difference between the forces is sufficiently small.

This makes it difficult to control the material layer, for example, to two layers, for example, to perform delicate control so as to remove powders M in the third layer, with powders M in the second layer left. In other words, it is very difficult to control a material layer in which two or more powder layers are stacked to a uniform thickness.

In an embodiment of the present invention, a material layer with a substantially uniform thickness is obtained by controlling the thickness of the powder layer to be less than twice the volume mean diameter MV of the powders Ma.

Thus, to produce a high-accuracy object by reducing lamination failures in the AM technique, powder layers with a thickness less than twice the volume mean diameter of the forming powders and with a projection area percentage of 90% or higher per unit area is formed. This allows a material layer with a projection area percentage of 90% or higher per unit area to be formed.

A stereoscopic-object forming apparatus according to an embodiment of the present invention and a method for forming a stereoscopic object using the same will be described in detail hereinbelow.

First Embodiment

A stereoscopic-object forming apparatus according to an embodiment of the present invention and a method for forming a stereoscopic object according to an embodiment of the present invention will be described in detail.

Control Unit

The configuration of the control unit U1 will be described. As illustrated in Fig. 1, the control unit U1 includes a three-dimensional-geometry-data input section U10, a slice-data calculation section U11, a material-layer-forming-unit control section U12, and a lamination-unit control section U13.

The three-dimensional-geometry-data input section U10 has the function of receiving three-dimensional-geometry data on an object to be produced from an external device (for example, a personal computer). Examples of the three-dimensional-geometry data include data generated by and output from a three-dimensional CAD, a three-dimensional modeler, and a three-dimensional scanner. For example, a stereolithography (STL) file format may be used, although any file formats can be used.

The slice-data calculation section U11 has the function of slicing the target object expressed as three-dimensional-geometry data at a predetermined pitch, calculating the cross-sectional shapes of individual layers, and generating image data (referred to as slice data) for use in forming material layers with the material-layer forming unit U2 on the basis of the cross-sectional shapes. The slice data is generated by calculating the cross-sectional shape of a support material that is necessary for forming the target object and is added to the target object expressed as three-dimensional-geometry data. The support material is a material temporarily provided to support the structural material of an overhang portion of the stereoscopic object and is finally removed. The structural material is a material that constitutes the stereoscopic object. The structural material and the support material are collectively referred to as a forming material.

The material-layer forming unit U2 of this embodiment allows forming of a material layer with a plurality of kinds of material. Thus, the slice data includes data corresponding to powder layers of the individual materials. To prevent images of different materials from overlapping, the positions and shapes of the powder layers in the slice data are adjusted. This is because overlapping of the images causes variations in the thicknesses of the material layers, leading to a decrease in the dimension accuracy of the stereoscopic object. Examples of file formats of the slice data include multi-valued image data (the individual values indicate the kinds of material) and multi-plane image data (the individual planes correspond to the kinds of material).

The material-layer-forming-unit control section U12 controls the material-layer forming process in the material-layer forming unit U2 on the basis of the slice data generated by the slice-data calculation section U11. The control unit U1 also controls a developing device, described later, so that forming powders constituting a powder layer are disposed to satisfy predetermined conditions. The lamination-unit control section U13 controls the lamination process in the lamination unit U3. Details of the control performed by the individual units U1 to U3 will be described later.

The control unit U1 further includes an operating section, a display section, and a storage section (not illustrated). The operating section has the function of receiving instructions from a user. Examples of the instructions include instructions on on/off of the power source, various settings, and operations. The display section presents information to the user. Examples of the information include various setting windows, error messages, and operating states. The storage section has the function of storing three-dimensional-geometry data, slice data, and various setting values.

The control unit U1 may be, in terms of hardware, a computer including a central operating unit (CPU), a memory, auxiliary storage devices (for example, a hard disk and a flash memory), an input device, a display device, and various interfaces. The functions of the above sections U10 to U13 are implemented by reading the programs stored in the auxiliary storage devices and controlling necessary devices with the CPU. Part or all of the functions may be configured with circuits, such as an application specific integrated circuit (ASIC) and a field programmable gate array (FPGA), or may be implemented by another computer using cloud computing, grid computing, or any other technique.

Material-Layer Forming Unit

Next, the configuration of the material-layer forming unit U2 will be described. The material-layer forming unit U2 in Fig. 1 is a unit that forms a material layer composed of forming powders using an electrophotographic process. Electrophotography is a technique for forming a desired image through a series of processes of charging a photoconductor, forming a latent image through exposure, and depositing developing powders on the latent image to form a developed image. The principle of electrophotography is common to the principle used in 2D printers, such as a copying machine, but the properties of a material for use as a developer differ from the properties of a toner material for use in 2D printers. Therefore, process control and component structures in 2D printers cannot be used without any change in many cases. Fig. 1 illustrates an apparatus that uses the electrophotographic process, whereas an ink-jet system may be used as disclosed in PTL 2.

As illustrated in Fig. 1, the material-layer forming unit U2 includes a first powder-layer forming section 10a, a second powder-layer forming section 10b, and a transfer section 11. The first powder-layer forming section 10a is a powder-layer forming unit configured to form powder layers with the first powder material Ma and includes an image bearing member 100a, a charging device 101a, an exposing device 102a, a developing device 103a, and a cleaning device 105a. The second powder-layer forming section 10b is a powder-layer forming unit configured to form powder layers with the second powder material Mb and includes an image bearing member 100b, a charging device 101b, an exposing device 102b, a developing device 103b, and a cleaning device 105b.

The transfer section 11 includes the

transfer devices

110a and 110b, the intermediate bearing member 111, an intermediate bearing-member cleaning device 112, and an image detection sensor 113. The powder layers formed by the powder-

layer forming sections

10a and 10b are transferred to the intermediate bearing member 111 by the

transfer devices

110a and 110b to form a material layer. If one kind of forming powder is used, the formed material layer is the same as the powder layer, and if a plurality of kinds of forming powder are used, the formed material layer is formed of a plurality of powder layers.

Suppose that the first powder material Ma is a structural material, such as a thermoplastic water-insoluble resin, and the second powder material Mb is a thermoplastic water-soluble support material. Examples of the structural material include polyethylene (PE), polypropylene (PP), acrylonitrile butadiene styrene (ABS), and polystyrene (PS). Examples of the support material include carbohydrate, polylactic acid (PLA), polyvinyl alcohol (PVA), and polyethylene glycol (PEG). The diameters of the powders of the individual materials are preferably 5 μm or more and 50 μm or less.

The powder-

layer forming sections

10a and 10b are disposed along the surface of the intermediate bearing member 111. Although the powder-layer forming section 10a for a structural material in Fig. 1 is disposed upstream in the conveying direction, the powder-

layer forming sections

10a and 10b may be disposed in any order. The number of powder-layer forming sections is not limited to two and may be increased or decreased in accordance with the number of kinds of forming material.

If heat generated in the lamination unit U3 is transmitted to the material-layer forming unit U2, the powder materials before production can be softened, or conditions for the powder-layer forming processes in the powder-

layer forming sections

10a and 10b and conditions for the transfer process in the transfer section 11 can be changed. This may possibly preclude stable forming of material layers. Thus, the material-layer forming unit U2 and the lamination unit U3 are configured to be separated except during the process of transferring a material layer.

The entire material-layer forming unit U2 may be moved or the entire lamination unit U3 may be moved, although Fig. 1 does not illustrate a mechanism for changing the distance between the material-layer forming unit U2 and the lamination unit U3. However, the mechanism for moving the whole of one of the units is large-scaled. In terms of preventing the mechanism from becoming large-scaled, a mechanism for moving a secondary transfer roller 31 in the lamination unit U3 to change the distance between a roller 114 and the secondary transfer roller 31.

The configurations of the components of the material-layer forming unit U2 will be described in detail hereinbelow. In descriptions common to the powder-

layer forming sections

10a and 10b, subscripts a and b in the reference signs of the components are omitted; the components are referred to as, for example, a powder-layer forming section 10 and an image bearing member 100.

Image Bearing Member

Fig. 7A is a diagram illustrating the configuration of the powder-layer forming section 10. Fig. 7B is a diagram illustrating the detailed configuration of a developing device 103. Fig. 7C illustrates a cross-sectional shape of a toner conveying member 1032a of a developing roller 1032.

The image bearing member 100 is a member for bearing an electrostatic latent image. In this case, the image bearing member 100 is a photosensitive drum having a photosensitive layer having photoconductivity on the outer circumference of a metal cylinder made of aluminum or the like. Examples of the photosensitive member include an organic photoconductor (OPC), an amorphous-silicon photoconductor, and a selenium photoconductor. Any other photoconductors may be selected according to the application and required functions for the stereoscopic-object forming apparatus. The image bearing member 100 is rotatably supported by a frame (not shown). During image formation, the image bearing member 100 rotates clockwise in the drawing at a constant speed by a motor (not shown).

Charging Device

A charging device 101 is a charging unit configured to uniformly charge the surface of the image bearing member 100. This embodiment employs a non-contact charging system using corona discharge but may employ another charging system, for example, a roller charging system in which a charging roller is brought into contact with the surface of the image bearing member 100.

Exposing Device

An exposing device 102 is an exposing unit configured to expose the image bearing member 100 with light in accordance with image information (slice data) to form an electrostatic latent image on the surface of the image bearing member 100. The exposing device 102 includes a light source, such as a semiconductor laser and a light-emitting diode, a scanning mechanism including a polygon mirror that rotates at high speed, and an optical element, such as an image-forming lens.

Developing Device

The developing device 103 is a developing unit configured to visualize an electrostatic latent image by supplying forming powders (powders including a structural material or a support material, hereinafter also referred to as toner) to the image bearing member 100 using a known single-component contact developing method. In this specification, visualization with forming powders is referred to as development, and the visualized image is referred to as a powder layer.

Fig. 7B illustrates the detailed configuration of the developing device 103. The developing device 103 includes a developer container 1030 that contains a developer, a recovery roller 1031 disposed in the developer container 1030, and the developing roller 1032 that bears the developer and supplies the developer to the image bearing member 100. The developing device 103 further includes stirring supply rollers 1034 that stir the developer to bring the forming powders and the magnetic powders into contact with each other to charge the forming powders and supply the charged forming powders to the developing roller 1032. The developing device 103 further includes a scraper 1035 for scraping the developer and the magnetic powders adhering to the surface of the recovery roller 1031. A portion at which the forming powders adhere from the developing roller 1032 to the image bearing member 100 is referred to as a developing portion, and the forming powders and the magnetic powders are collectively referred to as a developer.

The recovery roller 1031 is disposed close to the developing roller 1032, upstream from the developing portion in the moving direction of the developing roller 1032. The recovery roller 1031 includes a rotatable developer conveying member and a permanent magnet secured in the developer conveying member.

The developing roller 1032 includes the rotatable toner conveying member 1032a and a permanent magnet 1032b secured in the toner conveying member 1032a. The surface of the toner conveying member 1032a has a plurality of recesses of a size corresponding to the diameters of the forming powders. Fig. 7C illustrates a cross-section of the toner conveying member 1032a taken along the rotating direction. Specifically, the recessed structure illustrated in Fig. 7C extends along the axis of rotation of the developing roller 1032 and has grooves with a width larger than or equal to the diameters of the forming powders and smaller than the diameters of the magnetic powders. The depth D of the recessed structure (the height of the projections) satisfies the relationship, r/2 is less than or equal to D, and D is less than or equal to r, where r is the diameter of the forming powders. The shape of the recessed structure is given for mere illustration. For more details, refer to PTL 3.

The permanent magnet 1032b and the permanent magnet disposed in the recovery roller 1031 form a magnetic field in cooperation with each other. In the developing device 103 illustrated in Fig. 7B, the individual permanent magnets are disposed so that the magnetic flux density increases with an increasing distance from the toner conveying member 1032a to the developer conveying member. Therefore, magnetic powders between the toner conveying member 1032a and the developer conveying member cause a magnetic force from the toner conveying member 1032a toward the developer conveying member. This causes a brush of magnetic powders to be formed along the magnetic field directed from the permanent magnet 1032b toward the recovery roller 1031.

The developer conveying member is configured to rotate in the same direction as the rotating direction of the toner conveying member 1032a. This allows the magnetic powders held on the surface of the developer conveying member by the magnetic force to be given a conveying force from the developer conveying member into the developer container 103 due to the force of the magnetic field and a frictional force between the magnetic powders and the surface of the developer conveying member.

The magnetic powders held on the surface of the developer conveying member are scraped by the scraper 1035, which is retained by the developer container 103 at one end, back into the developer container 103. The magnetic powders recovered into the developer container 103 are mixed with the non-magnetic forming powders by the stirring supply rollers 1034 and are conveyed again to the surface of the recovery roller 1031.

The non-magnetic forming powders are stirred and charged by the stirring supply rollers 1034 and are held on the surface of the magnetic powders. The forming powders held on the surface of the magnetic powders are brought into contact with the toner conveying member 1032a in the process in which the magnetic powder brush is formed and held on the developer conveying member and is conveyed by the developer conveying member. At that time, the forming powders come into multipoint-contact with the recessed structure of the surface of the toner conveying member 1032a to coat the inside of the recessed structure.

This structure in which the forming powders come into multipoint-contact with the toner conveying member 1032a allows the toner conveying member 1032a to be coated using a smaller electromagnetic adhesive force than a force generated when the forming powders come into point-contact with a flat surface. In other words, the amount of forming powders that coat the inside of the recessed structure is stable against changes in the discharge amount of the forming powders as compared with the flat structure.

Fig. 8 is a schematic diagram illustrating a state in which the forming powders M that have separated from magnetic powders MM onto the toner conveying member 1032a are being conveyed. The magnetic powders MM used generally have a diameter several or more times the diameters of the forming powders M, and the widths of the recesses are smaller than the diameters of the magnetic powders. This allows the forming powders M adhering to the recessed structure on the top of the toner conveying member 1032a to be secured in the recessed structure which the magnetic powders MM cannot enter even if a magnetic brush MB passes therethrough.

The arrangement of the forming powders M that have once adhered to the toner conveying member 1032a is not disturbed because the forming powders M are restrained in movement and rotation and are not scraped by the magnetic powders MM. This allows the toner conveying member 1032a to convey the forming powders M that uniformly coat the recessed structure to the developing portion at which the toner conveying member 1032a and the surface of the image bearing member 100 are opposed.

Between the toner conveying member 1032a and the image bearing member 100, a developing bias voltage is applied by an electric-field applying section (not shown). Thus, the forming powders M conveyed to the developing portion adhere to the image bearing member 100 due to the developing bias voltage, thus forming a latent image on the image bearing member 100 with the forming powders M. Examples of the developing method include a reversal developing method in which a developer is deposited on a portion at which electric charges are removed by exposure and a normal developing method in which a developer is deposited on an unexposed portion, any of which may be used.

Figs. 9A and 9B illustrate the state of the developed forming powders M adhering to the image bearing member 100 in the vicinity of the developing portion. Figs. 9C and 9D illustrate a state in which the forming powders M adhering to the toner conveying member 1032a is being conveyed. In the cross-sectional view in Fig. 9C, the toner conveying member 1032a is uniformly coated with the forming powders M secured in the recessed structure. However, in the plan view of Fig. 9D, there are clearances between the forming powders M by an amount corresponding to the difference between the diameters of the forming powders M and the pitch of the recessed structure in the rotating direction. Thus, if the latent image on the image bearing member 100 is developed in this disposition state, the clearances are left between the powders of the developed image on the image bearing member 100 in the powder-layer conveying direction.

Thus, in this embodiment, the control unit U1 controls the toner conveying member 1032a and the image bearing member 100 so as to rotate at different speeds. Specifically, the toner conveying member 1032a is rotated a slightly larger distance than the difference between the pitch of the recessed structure and the diameters of the forming powders M relative to the image bearing member 100. This causes the latent image on the image bearing member 100 to be developed such that the forming powders M are pushed by the subsequent forming powders M, so that the clearances between the forming powders M formed on the toner conveying member 1032a are filled, as shown in Figs. 9A and 9B. This allows forming of a powder layer in which the forming powders are closely arranged in a single layer.

The developing device 103 may have a so-called developing cartridge structure detachably mounted in the material-layer forming unit U2. This is because the developer (the structural material and the support material) can easily be refilled or changed by replacing the cartridge. The image bearing member 100, the developing device 103, and the cleaning device 105 may be combined into one cartridge (a so-called process cartridge), so that the image bearing member itself can be replaced. If the wear and life of the image bearing member 100 are particular concerns because of the kind, hardness, and diameters of the structural material and the support material, the process cartridge configuration is advantageous in terms of practical use and convenience.

The transfer section 11 includes the transfer device 110 that transfers the powder layer on the image bearing member 100 onto the surface of the intermediate bearing member 111. The transfer device 110 is disposed on the opposite side from the image bearing member 100 with the intermediate bearing member 111 therebetween. The transfer device 110 electromagnetically transfers the powder layer on the image bearing member 100 to the intermediate bearing member 111 by applying voltage with a polarity opposite to the polarity of the powder layer. The transfer from the image bearing member 100 to the intermediate bearing member 111 is also referred to as primary transfer. Examples of a method of transfer include a corona discharge transfer method and a roller transfer method.

Cleaning Device

The cleaning device 105a is a unit configured to recover developer powders left on the image bearing member 100 without being transferred to clean the surface of the image bearing member 100. Although the blade cleaning device 105a of this embodiment employs a blade type that scrapes developer powders with a cleaning blade in counter-contact with the image bearing member 100; a brush cleaning device or an electrostatic-attraction cleaning device may be used.

Intermediate Bearing Member

Powder layers formed by the individual powder-layer forming sections 10 are transferred to the intermediate bearing member 111. A powder layer formed of the forming material is transferred from the upstream powder-layer forming section 10a, and then a powder layer formed of the support material is transferred from the downstream powder-layer forming section 10b to form a single material layer on the surface of the intermediate bearing member 111.

The intermediate bearing member 111 is an endless belt made of, for example, resin and polyimide, and is stretched between the

rollers

114 and 115, as illustrated in Fig. 1. In addition to the

rollers

114 and 115, a tension roller may be provided so that the tension of the intermediate bearing member 111 can be adjusted. At least one of the

rollers

114 and 115 is a drive roller for rotating the intermediate bearing member 111 counterclockwise in Fig. 1 using the driving force of a motor (not shown) during image formation. The roller 114 forms a secondary transfer nip between the roller 114 and the secondary transfer roller 31 of the lamination unit U3.

Bearing-Member Cleaning Device

The bearing-member cleaning device 112 is a unit configured to clean a material adhering to the surface of the intermediate bearing member 111. Although the bearing-member cleaning device 112 of this embodiment employs a blade type that scrapes the material with a cleaning blade in counter-contact with the intermediate bearing member 111, a brush cleaning device or an electrostatic-attraction cleaning device may be used.

Image Detection Sensor 1

The image detection sensor 113 is a unit configured to detect a powder layer born on the surface of the intermediate bearing member 111. The result of detection performed by the image detection sensor 113 is used to align the material layer, control of timing with the downstream lamination unit U3, detection of abnormality of the material layer (for example, an undesired image, absence of an image, a large variation in thickness, positional misalignment of an image), and so on.

The image detection sensor 113 may have a function of determining the projection area percentage of the material layer per unit area. Specifically, the image detection sensor 113 may have a function of processing a gray image acquired by applying light to the material layer.

Determining the projection area percentage of the material layer per unit area to detect abnormality when the percentage is less than 90% can prevent formation of a thin film having holes, thereby eliminating or reducing lamination failures. The projection area percentage per unit area detected by the image detection sensor 113 is transferred to the control unit U1, where it is determined whether abnormality has occurred. The control unit U1 controls the state of contact between the material-layer forming unit U2 and the lamination unit U3 in accordance with the result of determination.

Specifically, if a material layer with a projection area percentage of 90% or higher per unit area is detected, the control unit U1 brings the material-layer forming unit U1 and the lamination unit U2 into contact with each other to transfer the material layer from the intermediate bearing member 111 to the second intermediate bearing member 30. If a material layer with a projection area percentage of less than 90% per unit area is detected, the control unit U1 does not bring the material-layer forming unit U1 and the lamination unit U2 into contact to hold the material layer on the intermediate bearing member 111. The material layer that is removed with the bearing-member cleaning device 112 for the intermediate bearing member 111 and is not transferred to the second intermediate bearing member 30 is reformed.

Fig. 10 is a flowchart of a specific operation sequence in determining the projection area percentage of the material layer per unit area with the image detection sensor 113 using the stereoscopic-object forming apparatus illustrated in Fig. 1.

A powder layer formed of structural material powders is formed in the powder-layer forming section 10a (S500), and a powder layer formed of support material powders is formed in the powder-layer forming section 10b (S501). These powder layers are sequentially transferred to the intermediate bearing member 111 to form a material layer (S502). The material layer is conveyed to the lamination unit U3 by the intermediate bearing member 111, during which a projection area percentage of the material layer per unit area is determined by the image detection sensor 113 (S503).

Information on the projection area percentage per unit area determined by the image detection sensor 113 is transferred to the control unit U1. If the projection area percentage per unit area is 90% or higher, it is determined that the material layer is normal, and if the projection area percentage per unit area is less than 90%, it is determined that the material layer is abnormal (S504). If the material layer is determined to be normal, the control unit U1 controls the material-layer forming unit U2 and the lamination unit U3 so that they come into contact with each other (S505), so that the material layer on the intermediate bearing member 11 is transferred to the second intermediate bearing member 30 (S506). Upon completion of the transfer of the material layer to the second intermediate bearing member 30, the material-layer forming unit U2 and the lamination unit U3 are separated (S507), and the material layer is conveyed to the lamination position by the second intermediate bearing member 30 (S508).

When the material layer reaches the lamination position, the second intermediate bearing member is stopped (S509), and the stage 34 is elevated (S510), so that the material layer is laminated on an intermediate product on the stage 34 (S511). Upon completion of the lamination, the stage 34 moves downward (S512), and it is determined whether a predetermined number of material layers have been formed (S513).

If the control unit U1 determines that the material layer is abnormal (S504), the control unit U2 controls the material-layer forming unit U2 and the lamination unit U3 be held at the separate positions (S514). Then, the material layer on the intermediate bearing member 111 is not transferred to the second intermediate bearing member 30 and is removed by the bearing-member cleaning device 112 (S515).

This is an example in which material layers are laminated as they are; the material layers may be welded into thin films before the material layers reach the lamination position.

Although the image detection sensor may detect one portion of the material layer, a plurality of image detection sensors may be disposed in a direction crossing the direction in which the material layers are conveyed to detect a plurality of portions of the material layer.

Lamination Unit

Next, the configuration of the lamination unit U3 will be described. The lamination unit U3 is a unit configured to form a stereoscopic object by receiving the material layers formed in the material-layer forming unit U2 from the intermediate bearing member 111 and laminating and fixing the material layers in sequence.

As illustrated in Fig. 1, the lamination unit U3 includes the second intermediate bearing member 30, the secondary transfer roller 31, the image detection sensor 32, the heater (the opposing member) 33, and the stage 34. The configurations of the components of the lamination unit U3 will be described in detail hereinbelow.

Second Intermediate Bearing Member

The second intermediate bearing member 30 receives material layers formed in the material-layer forming unit U2 from the intermediate bearing member 111 and conveys the material layers to the lamination position. The lamination position is a position at which the process of laminating the material layers on a stereoscopic object being produced. In the configuration in Fig. 1, the lamination position corresponds to a portion at which the second intermediate bearing member 30 is held between the heater 33 and the stage 34.

The second intermediate bearing member 30 is an endless belt made of, for example, resin and metal, such as polyimide and stainless steel. As illustrated in Fig. 1, the second intermediate bearing member 30 is stretched across the secondary transfer roller 31 and a plurality of

rollers

301, 302, 303, and 304. At least one of the

rollers

31, 301, and 302 is a drive roller, which rotates the second intermediate bearing member 30 clockwise in Fig. 1 using the driving force of a motor (not shown). The

rollers

303 and 304 are a roller pair that plays the roll of adjusting the tension of the second intermediate bearing member 30 and holding the second intermediate bearing member 30 (that is, the material layer being laminated) passing through the lamination position parallel to the stage 34.

Secondary Transfer Roller

The secondary transfer roller 31 is a transfer unit configured to transfer a material layer from the intermediate bearing member 111 of the material-layer forming unit U2 to the second intermediate bearing member 30 of the lamination unit U3. The secondary transfer roller 31 and the opposing roller 114 of the material-layer forming unit U2 nip the intermediate bearing member 111 and the second intermediate bearing member 30 to form the secondary transfer nip. A bias opposite in polarity to the material layer is applied to the secondary transfer roller 31 by a power source (not shown) to transfer the material layer to the second intermediate bearing member 30.

The lamination unit U3 may further include, between the secondary transfer roller 31 and the roller 304, a heater for melting the material layer received on the second intermediate bearing member 30 into a film before lamination.

Image Detection Sensor 2

The image detection sensor 32 is a detection device configured to read the material layer born on the surface of the second intermediate bearing member 30. The result of detection performed by the image detection sensor 32 is used for alignment of the material layer and for controlling the timing of conveying the material layer to the lamination position.

Heater

The heater 33 is a temperature control device configured to control the temperature of material layers conveyed to the lamination position. Examples of the heater 33 include a ceramic heater and a halogen heater. Not only the heater but also a configuration for promoting decrease of the temperature of the material layers by heat radiation or cooling may be provided. The lower surface of the heater 33 (a surface adjacent to the second intermediate bearing member 30 is flat so as to also serve as a guide for the second intermediate bearing member 30 passing through the lamination position and as a pressing member for applying uniform pressure to the material layer.

Stage

The stage 34 is a flat mount on which a stereoscopic object is produced. The stage 34 can be moved vertically (in a direction perpendicular to the surface of the second intermediate bearing member 30 by an actuator (not shown). A material layer conveyed to the lamination position is sandwiched between the stage 34 and the heater 33 and is heated and pressed (the heat is radiated or cooled as needed) so that the material layer is transferred from the second intermediate bearing member 30 onto the stage 34. The first material layer is directly transferred onto the stage 34, and the second and subsequent material layers are laminated on the object in process on the stage 34. In this embodiment, the heater 33 and the stage 34 constitute a unit for laminating the material layers, as described above.

Although the stage 34 in Fig. 1 can be moved only in the vertical direction, the stage 34 may be moved back and forth in the conveying direction of the second intermediate bearing member 30. This configuration allows the material layers to be laminated on the intermediate product while moving the stage 34 and the second intermediate bearing member 30 in synchronization. This configuration eliminates the need for stopping the second intermediate bearing member 30 at the lamination position. This allows the material layers formed by the material-layer forming unit U2 to be transferred to the second intermediate bearing member 30 at all times, allowing efficient lamination without being restricted by the lamination process.

The units U1 to U3 may either be accommodated in a single casing or be accommodated in a plurality of casings. The configuration in which the units U1 to U3 are accommodated in a plurality of casings facilitates combination and replacement of the units U1 to U3 in accordance with the application of the stereoscopic-object forming apparatus, requirements, the forming material, the installation space, and failures. This offers enhanced flexibility and convenience of the apparatus configuration. In contrast, the configuration in which all the units U1 to U3 are accommodated in a single casing has the advantage of reducing the size and cost of the entire apparatus. The unit configuration in Fig. 1 is given for mere illustration, and any other configurations may be adopted.

As described above, the first embodiment of the present invention allows a powder layer with a thickness of less than twice the volume mean diameter of the forming powders and with a projection area percentage of 90% or higher per unit area to be formed with stability. Sequential lamination of such powder layers prevents or reduces lamination failures, thus allowing efficient production of a stereoscopic object.

Second Embodiment

In a second embodiment, a method for forming a powder layer with a thickness of less than twice the volume mean diameter of forming powders and with a projection area percentage of 90% or higher per unit area using another developing device will be described. Description of components and methods other than the developing method will be omitted because they are the same as those of the first embodiment.

Fig. 11A illustrates a developing device 103 for use in this embodiment. The developing device 103 in Fig. 11A adopts a hybrid developing method.

The developing device 103 includes a developer container 1030 that contains a developer, a recovery roller 1031 disposed in the developer container 1030, and a developing roller 1032 that bears the developer and supplies the developer to an image bearing member 100. The developing device 103 further includes stirring supply rollers 1034, a scraper 1035, a magnetic roller 1036, and a height defining member 1037.

The magnetic roller 1036 includes a rotatable developer conveying member, a permanent magnet secured in the developer conveying member, and a conductor capable of applying a desired potential V1 and is disposed close to the developing roller 1032. A magnetic brush of magnetic powders that hold forming powders stirred by the stirring supply rollers 1034 to become charged is formed on the surface of the developer conveying member.

The height of the magnetic brush is defined by the height defining member 1037 with the same potential as the potential of the magnetic roller 1036 before the forming powders are supplied to the developing roller 1032. The height defining member defines the height of the magnetic brush, allowing forming powders supplied to the developing roller 1032 to be set to a fixed amount.

The developing roller 1032 includes a rotatable toner conveying member 1032a and a conducting member 1032b capable of applying a desired potential. The conducting member 1032b is given a potential V2 at which an electric field that attracts the forming powders from the magnetic roller 1036 toward the developing roller 1032.

For example, if the forming powders are negatively charged, the developing roller 1032 is given a potential higher than a potential for the magnetic roller 1036. This causes an electric field directed from the developing roller 1032 to the magnetic roller 1036 between the developing roller 1032 and the magnetic roller 1036, thus allowing the forming powders to be selectively deposited on the developing roller 1032. If the forming powders are positively charged, potentials may be applied to the rollers so as to generate an opposite electric field.

The amount of forming powders to be attached to the developing roller 1032 may be freely determined by adjusting the potential difference V21 = (V2 - V1) (the absolute value) between the magnetic roller 1036 and the developing roller 1032. In this embodiment, a potential difference at which one or more forming powder layers adhere to the developing roller 1032 is given to hold a sufficient amount of forming powders on the developing roller 1032.

The forming powders adhering to the developing roller 1032 are conveyed to a position facing the recovery roller 1031 disposed downstream of the rotation of the developing roller 1032.

The recovery roller 1031 is disposed away from the developing roller 1032 by a distance twice the diameters of the forming powders and can recover forming powders of two or more layers adhering to the developing roller 1032.

The recovery roller 1031 includes a rotatable recovery conveying member and a conducting member capable of applying a desired potential V3. The conducting member is given the potential V3 at which an electric field that attracts forming powders from the developing roller 1032 toward the recovery roller 1031 is generated.

Fig. 11B is a graph illustrating a relationship between the potential difference V32 = (V3 - V2) (the absolute value) between the recovery roller 1031 and the developing roller 1032 and the efficiency of attraction of forming powders adhering to the developing roller 1032 to the recovery roller 1031 for recovery. As is apparent from the graph, the amount of forming powders recovered from the developing roller 1032 can be freely determined by adjusting the potential difference V23.

Thus, the potential V3 that applies a voltage Vx for achieving a recovery efficiency of 50% to the conducting member of the recovery roller 1031 to recover the second layer of forming powders adhering to the developing roller 1032 with the recovery roller 1031. The recovered forming powders are recovered into the developer container 1030 with the scraper 1035.

As described above, the second embodiment of the present invention allows a powder layer with a thickness of less than twice the volume mean diameter of the forming powders and with a projection area percentage of 90% or higher per unit area to be formed, thus offering the same advantageous effects as those of the first embodiment.

Third Embodiment

In a third embodiment, a method for forming a powder layer with a thickness of less than twice the volume mean diameter of forming powders and with a projection area percentage of 90% or higher per unit area using still another developing device will be described. Description of components and methods other than the developing method will be omitted because they are the same as those of the first embodiment.

Fig. 12 schematically illustrates a developing device 103 for use in this embodiment. The developing device 103 in Fig. 12 also adopts a hybrid developing method. The developing device 103 includes a developer container 1030 that contains a developer, a magnetic roller 1036 disposed in the developer container 1030, a height defining member 1037, and a stirring supply roller 1034. The developing device 103 further includes a heater-built-in roller 1038 opposed to the magnetic roller 1036, an elastic rubber roller 1039, and a rotatable thermosensitive adhesive belt 1040 stretched between the heater-built-in roller 1038 and the elastic rubber roller 1039.

The heater-built-in roller 1038 includes a rotatable belt conveying member and a heater secured in the belt conveying member. The heater-built-in roller 1038 is disposed close to the magnetic roller 1036 to which an AC bias is applied. The temperature of the heater in the roller 1038 is controlled by a heater control unit 1042. The elastic rubber roller 1039 is a rotatable belt conveying member having an elastic rubber layer on the surface. The elastic rubber roller 1039 is disposed in contact with the image bearing member 100. Although the material of the elastic rubber layer of this embodiment is urethane, another elastic material, such as silicone rubber, may be used.

The thermosensitive adhesive belt 1040 is a resin belt on which a material whose viscosity changes according to the temperature. An example of the thermosensitive adhesive belt 1040 is a cool-off type Intelimer tape (made by Nitta Corporation) that exhibits viscosity when heated to 55°C or higher.

Forming powders reciprocate between a magnetic brush and the thermosensitive adhesive belt 1040, due to the effect of the AC bias, at a portion at which thermosensitive adhesive belt 1040, which is heated to 55°C or more by the heater-built-in roller 1038, and the magnetic roller 1036 are opposed. Most of forming powders that have reached the thermosensitive adhesive belt 1040 are drawn back to the magnetic roller 1036 due to the AC bias. However, since the surface of thermosensitive adhesive belt 1040 exhibits viscosity, the powders in the first layer in contact with the surface of thermosensitive adhesive belt 1040 are held with the viscosity of the thermosensitive adhesive belt 1040, thus remaining on the surface of thermosensitive adhesive belt 1040 without being drawn back to the magnetic roller 1036.

The surface of thermosensitive adhesive belt 1040 to which the forming powders adhere is cooled to less than 55°C by a belt cooling unit 1041, thus losing viscosity. Furthermore, the forming powders are conveyed toward the image bearing member 100 between the elastic rubber roller 1039 and the image bearing member 100 by application of a DC bias. As described above, the third embodiment of the present invention allows a powder layer with a thickness of less than twice the volume mean diameter of the forming powders and with a projection area percentage of 90% or higher per unit area to be formed. Thus, lamination of the powder layers formed using the developing device 103 according to the third embodiment offers the same advantageous effects as those of the first and second embodiments.

Fourth Embodiment

In a fourth embodiment, a method for forming a powder layer with a thickness of less than twice the volume mean diameter of forming powders and with a projection area percentage of 90% or higher per unit area using still another developing device will be described. Description of components and methods other than the developing method will be omitted because they are the same as those of the first embodiment.

Fig. 13 illustrates a developing device 103 for use in this embodiment. The developing device 103 in Fig. 13 adopts a method of depositing forming powders on an image 36 made of liquid output from an ink-jet printer.

The developing device 103 includes a developer container 1030 that contains a developer, a developing roller 1032 disposed in the developer container 1030, a magnetic roller 1036, a height defining member 1037, and a stirring supply roller 1034.

A roller 302 is opposed to the developing roller 1032. A belt-like intermediate bearing member 30 stretched between the roller 302 and a roller 301 can convey the forming powders on the surface of the intermediate bearing member 30 with the

rollers

301 and 302.

An ink-jet cartridge 35 is disposed upstream in the conveying direction of the intermediate bearing member 30 from the position at which the roller 302 and the developing roller 1032 are opposed.

The ink-jet cartridge 35 is filled with liquid and ejects the liquid to a portion of the intermediate bearing member 30 on which forming powders are arrayed, thereby forming the image 36. The image 36 formed on the intermediate bearing member 30 is conveyed to the position at which the roller 302 and the developing roller 1032 are opposed. As in the first embodiment, the surface of the developing roller 1032 bears one or more layers of forming powders. When the image 36 reaches the position at which the roller 302 and the developing roller 1032 are opposed, the uppermost layer of forming powders on the developing roller 1032 are attracted to the image 36, thus moving to the intermediate bearing member 30. Forming powders in the second and subsequent layers remain on the developing roller 1032 because the adhesive force between the developing roller 1032 and forming powders is generally stronger than the adhesive force among the forming powders.

As described above, the fourth embodiment of the present invention allows a powder layer with a thickness of less than twice the volume mean diameter of the forming powders and with a projection area percentage of 90% or higher per unit area to be formed. Thus, lamination of the powder layers formed using the developing device 103 according to the fourth embodiment offers the same advantageous effects as those of the other embodiments.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2014-242522, filed November 28, 2014 and No. 2015-197994, filed October 5, 2015, which are hereby incorporated by reference herein in their entirety.

U1 Control unit
U2 Material-layer forming unit
U3 Lamination unit
10, 10a Powder-layer forming section (Powder-layer forming unit)
111 Intermediate bearing member
113 Image detection sensor
30 Second intermediate bearing member

Claims

A method for forming a stereoscopic object comprising the steps of:
forming at least one powder layer by disposing forming powders based on slice data;
forming a material layer from the at least one powder layer; and
laminating the material layer on a stereoscopic object being produced,
wherein the powder layer is formed so as to have a thickness of less than twice a volume mean diameter of the forming powders and to have a projection area percentage of 90% or higher per unit area.
The method for forming a stereoscopic object according to Claim 1, wherein the powder layer is formed through an electrophotographic process using a single-component contact developing method.
The method for forming a stereoscopic object according to Claim 1 or 2, further comprising the step of:
determining whether the material layer has a projection area percentage of 90% or higher per unit area before the step of laminating the material layer on the object being produced,
wherein if the projection area percentage per unit area is not 90% or higher, the material layer is not laminated on the stereoscopic object being produced.
The method for forming a stereoscopic object according to one of Claims 1 to 3, wherein the material layer is melted into a film before the step of laminating the material layer on the stereoscopic object being produced.
The method for forming a stereoscopic object according to one of Claims 1 to 4, wherein the forming powders comprises a plurality of kinds of powder.
A stereoscopic-object forming apparatus comprising:
a material-layer forming unit including a powder-layer forming section that disposes forming powders based on slice data to form at least one powder layer and a transfer section that forms a material layer from the at least one powder layer; and
a lamination unit that receives the material layer from the material-layer forming unit and laminates the material layer in sequence,
wherein the material-layer forming unit forms a powder layer having a thickness of less than twice a volume mean diameter of the forming powders and having a projection area percentage of 90% or higher per unit area.
The stereoscopic-object forming apparatus according to Claim 6, wherein the material-layer forming unit includes at least one sensor that detects a projection area percentage of the powder layer per unit area.
The stereoscopic-object forming apparatus according to Claim 7, wherein the at least one sensor comprises a plurality of sensors in a direction crossing a direction in which the material layer is conveyed.
The stereoscopic-object forming apparatus according to Claim 7 or 8, further comprising:
a control unit that controls an operation of the material-layer forming unit and an operation of the lamination unit,
wherein the control unit controls a state of contact between the material-layer forming unit and the lamination unit in accordance with information from the at least one sensor.
The stereoscopic-object forming apparatus according to one of Claims 7 to 9, wherein the powder-layer forming section forms the power layer using a electrophotographic process.