Patent Application
20070107568
The present application is related to the following applications, all of which are incorporated herein by reference as if fully set forth: U.S. patent application of Alan Campbell, Dale Ehnes, and Daniel Wertz, entitled “Cutting Tool Having Variable Movement at Two Simultaneously Independent Speeds in an X-Direction Into a Work Piece for Making Microstructures,” and filed on even date herewith; U.S. patent application of Dale Ehnes, Alan Campbell, and Daniel Wertz, entitled “Cutting Tool Having Variable Movement in a Z-Direction Laterally Along a Work Piece for Making Microstructures,” and filed on even date herewith; and U.S. patent application of Dale Ehnes, Alan Campbell, and Daniel Wertz, entitled “Cutting Tool Having Variable Rotation About a Y-Direction Transversely Across a Work Piece for Making Microstructures,” and filed on even date herewith.
The present invention relates to diamond machining of microreplication tools used in creating microreplicated structures.
Machining techniques can be used to create a wide variety of work pieces such as microreplication tools. Microreplication tools are commonly used for extrusion processes, injection molding processes, embossing processes, casting processes, or the like, to create microreplicated structures. The microreplicated structures may comprise optical films, abrasive films, adhesive films, mechanical fasteners having self-mating profiles, or any molded or extruded parts having microreplicated features of relatively small dimensions, such as dimensions less than approximately 1000 microns.
The microstructures can also be made by various other methods. For example, the structure of the master tool can be transferred on other media, such as to a belt or web of polymeric material, by a cast and cure process from the master tool to form a production tool; this production tool is then used to make the microreplicated structure. Other methods such as electroforming can be used to copy the master tool. Another alternate method to make a light directing film is to directly cut or machine a transparent material to form the appropriate structures.
Other techniques include chemical etching, bead blasting, or other stochastic surface modification techniques. However, those techniques are typically not capable of forming the sharp, precise microstructures, and the breadth of features, desired to obtain the appropriate light diffusion characteristic achieved with a cutting tool using the methods of the present invention. In particular, these methods are not capable of producing highly accurate, repeating structures because of the inherent impreciseness and unrepeatability associated with chemical etching, bead blasting, and other stochastic surface modification techniques.
A first cutting tool assembly includes a tool post and an actuator configured for attachment to the tool post and for electrical communication with a controller. A tool tip attached to the actuator is mounted for movement with respect to a work piece to be cut. The actuator provides for independent and variable control of the movement of the tool tip in an x-direction into the work piece and a z-direction laterally along the work piece for use in selectively cutting the work piece.
A second cutting tool assembly includes a tool post capable of lateral movement along a work piece to be cut and an actuator configured for attachment to the tool post and for electrical communication with a controller, the actuator including a piezoelectric stack. A tool tip attached to the piezoelectric stack is mounted for movement with respect to the work piece to be cut. The actuator provides for independent and variable control of the movement of the tool tip in an x-direction into the work piece and a z-direction laterally along the work piece for use in selectively cutting the work piece in order to make microstructures in the work piece.
The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, explain the advantages and principles of the invention. In the drawings,
Cutting Tool System
General diamond turning techniques are described in PCT Published Application WO 00/48037, incorporated herein by reference as if fully set forth. The apparatus used in methods and for making optical films or other films can include a fast servo tool. As disclosed in WO 00/48037, a fast tool servo (FTS) is a solid state piezoelectric (PZT) device, referred to as a PZT stack, which rapidly adjusts the position of a cutting tool attached to the PZT stack. The FTS allows for highly precise and high speed movement of the cutting tool in directions within a coordinate system as further described below.
System 10 is controlled by a computer 12. Computer 12 has, for example, the following components: a memory 14 storing one or more applications 16; a secondary storage 18 providing for non-volatile storage of information; an input device 20 for receiving information or commands; a processor 22 for executing applications stored in memory 16 or secondary storage 18, or received from another source; a display device 24 for outputting a visual display of information; and an output device 26 for outputting information in other forms such as speakers for audio information or a printer for a hardcopy of information.
The cutting of a work piece 54 is performed by a tool tip 44. An actuator 38 controls movement of tool tip 44 as work piece 54 is rotated by a drive unit and encoder 56, such as an electric motor controlled by computer 12. In this example, work piece 54 is shown in roll form such as a hard copper roll; however, it can be implemented in planar form and make use of other materials for machining. For example, the work piece can be alternatively implemented with aluminum, nickel, steel, or plastics (e.g., acrylics). The particular material to be used may depend, for example, upon a particular desired application such as various films made using the machined work piece. Actuator 38, and the actuators described below, can be implemented with stainless steel, for example, or other materials.
Actuator 38 is removably connected to a tool post 36, which is in turn located on a track 32. The tool post 36 and actuator 38 are configured on track 32 to move in both an x-direction and a z-direction as shown by arrows 40 and 42. Computer 12 is in electrical connection with tool post 36 and actuator 38 via one or more amplifiers 30. When functioning as a controller, computer 12 controls movement of tool post 36 along track 32 and movement of tool tip 44 via actuator 38 for machining work piece 54. If an actuator has multiple PZT stacks, it can use separate amplifiers to independently control each PZT stack for use in independently controlling movement of a tool tip attached to the stacks. Computer 12 can make use of a function generator 28 in order to provide waveforms to actuator 38 in order to machine various microstructures in work piece 54, as further explained below.
The machining of work piece 54 is accomplished by coordinated movements of various components. In particular, the system, under control of computer 12, can coordinate and control movement of actuator 38, via movement of tool post 36, along with movement of the work piece in the c-direction and movement of tool tip 44 in one or more of the x-direction, y-direction, and z-direction, those coordinates being explained below. The system typically moves tool post 36 at a constant speed in the z-direction, although a varying speed may be used. The movements of tool post 36 and tool tip 44 are typically synchronized with the movement of work piece 54 in the c-direction (rotational movement as represented by line 53). All of these movements can be controlled using, for example, numerical control techniques or a numerical controller (NC) implemented in software, firmware, or a combination in computer 12.
Work piece 54, after having been machined, can be used to make films having the corresponding microstructures for use in a variety of applications. Examples of those films include optical films, friction control films, and micro-fasteners or other mechanical microstructured components. The films are typically made using a coating process in which a material in a viscous state is applied to the work piece, allowed to at least partially cure, and then removed. The film composed of the cured material will have substantially the opposite structures than those in the work piece. For example, an indentation in the work piece results in a protrusion in the resulting film.
Cooling fluid 46 is used to control the temperature of tool post 36 and actuator 38 via lines 48 and 50. A temperature control unit 52 can maintain a substantially constant temperature of the cooling fluid as it is circulated through tool post 36 and actuator 38. Temperature control unit 52 can be implemented with any device for providing temperature control of a fluid. The cooling fluid can be implemented with an oil product, for example a low viscosity oil. The temperature control unit 52 and reservoir for cooling fluid 46 can include pumps to circulate the fluid through tool post 36 and actuator 38, and they also typically include a refrigeration system to remove heat from the fluid in order to maintain it at a substantially constant temperature. Refrigeration and pump systems to circulate and provide temperature control of a fluid are known in the art. In certain embodiments, the cooling fluid can also be applied to work piece 54 in order to maintain a substantially constant surface temperature of the material to be machined in the work piece.
The system 10 can be used for high precision, high speed machining. This type of machining must account for a variety of parameters, such as the coordinated speeds of the components and the work piece material. It typically must take into consideration the specific energy for a given volume of metal to be machined, for example, along with the thermal stability and properties of the work piece material. Cutting parameters relating to machining are described in the following references, all of which are incorporated herein by reference as if fully set forth: Machining Data Handbook, Library of Congress Catalog Card No. 66-60051, Second Edition (1972); Edward Trent and Paul Wright, Metal Cutting, Fourth Edition, Butterworth-Heinemann, ISBN 0-7506-7069-X (2000); Zhang Jin-Hua, Theory and Technique of Precision Cutting, Pergamon Press, ISBN 0-08-035891-8 (1991); and M. K. Krueger et al., New Technology in Metalworking Fluids and Grinding Wheels Achieves Tenfold Improvement in Grinding Performance, Coolant/Lubricants for Metal Cutting and Grinding Conference, Chicago, Ill., U.S.A., Jun. 7, 2000.
PZT Stack, Tool Tip Carrier, and Tool Tip
Electrical connections to the disks 74, 76, and 78, as represented by lines 80 and 82, provide electrical fields to them in order to provide for movement of post 88. Due to the PZT effect and based upon the type of electric field applied, precise and small movement of post 88, such as movement within several microns, can be accomplished. Also, the end of PZT stack 72 having post 88 can be mounted against one or more Belleville washers, which provides for preloading of the PZT stack. The Belleville washers have some flexibility to permit movement of post 88 and a tool tip attached to it. Each PZT stack in the actuators described below can also incorporate Belleville washers for preloading or, alternatively, any device mounted against each PZT stack for preloading of it.
As shown in
Other configurations of tool tip carriers are possible based, for example, upon requirements of particular embodiment. The term “tool tip carrier” is intended to include any type of structure for use in holding a tool tip for machining a work piece. Tool tip carrier 90 can be implemented with, for example, one or more of the following materials: sintered carbide, silicon nitride, silicon carbide, steel, or titanium. The material for tool tip carrier 90 preferably is stiff and has a low mass.
X-Z Actuator
As shown in
PZT stacks 118 and 116 are securely mounted in main body 112 for the stability required for precise controlled movement of tool tip 136. PZT stack 118 is secured in main body 112 by rails such as rails 120 and 122, and PZT stack 116 is secured in main body 112 by rails such as rails 124 and 126. The PZT stacks 118 and 116 can preferably be removed from main body 112 by sliding them along the rails and can be secured in place in main body 112 by bolts or other fasteners. PZT stacks 118 and 116 include electrical connections 130 and 134, respectively, for receiving signals from computer 12. The end caps of PZT stacks 118 and 116 include ports 128 and 132, respectively, for receiving cooling fluid such as oil from reservoir 46, circulating it around the PZT stacks, and delivering the oil back to reservoir 46 for maintaining temperature control of it. Main body 112 can include appropriate channels for directing the cooling fluid around PZT stacks 118 and 116, and the cooling fluid can be circulated by a pump or other device in temperature control unit 52.
While the present invention has been described in connection with an exemplary embodiment, it will be understood that many modifications will be readily apparent to those skilled in the art, and this application is intended to cover any adaptations or variations thereof. For example, various types of materials for the tool post, actuator, and tool tip, and configurations of those components, may be used without departing from the scope of the invention. This invention should be limited only by the claims and equivalents thereof.
