PATENT DOCUMENT

Publication Number: US-8550876-B2
Application Number: US-201113241084-A
Country: US
Kind Code: B2

Title: Force-controlled surface finishing through the use of a passive magnetic constant-force device

Abstract:
A constant force finishing system used to finish a surface of a workpiece includes at least a first movement device arranged to apply a first movement to a finishing tool, the first movement having a range of distance D 1 . The finishing system also includes a constant force device (CFD) in mechanical communication with the finishing tool, the CFD arranged to apply a second movement in conjunction with the first movement to the finishing tool, the second movement having a range of Δ 1 , where D 1 &gt;&gt;Δ 1 .

Claims:
What is claimed is: 
     
       1. A constant force finishing system used to finish a surface of a workpiece, comprising:
 a finishing tool on which is mounted a finishing material used to apply a finish to a workpiece; 
 a first movement device coupled to the finishing tool and arranged to apply a first movement to the finishing tool, the first movement having a range of distance D 1 ; 
 a constant force device (CFD) in mechanical communication with the finishing tool, the CFD arranged to apply a second movement in conjunction with the first movement to the finishing tool, the second movement having a range of Δ 1 , where D 1  is much greater than Δ 1 ; and 
 a chuck on which is mounted the workpiece during the finishing process, wherein the chuck moves the workpiece relative to the finishing tool, wherein during the finishing process when a surface variation of surface S of the workpiece is encountered by the finishing tool, the first movement device moves the finishing tool within the range D 1  relative to the workpiece when the surface variation is determined to have a size on the order of D 1 , and the CFD moves the finishing tool at most the distance Δ 1  when the surface variation is determined to have a size on the order of Δ 1  resulting in the finishing tool applying a constant force to a surface S of the workpiece throughout the finishing process. 
 
     
     
       2. The constant force finishing system as recited in  claim 1 , wherein the CFD is a constant magnetic device. 
     
     
       3. The constant force finishing system as recited in  claim 1 , further comprising:
 a set of linear bearings; and 
 a linear drive motor mechanically coupled to the finishing tool by way of the linear bearings, the linear drive motor arranged to move the finishing tool a distance on the order of D 1  using the linear bearings. 
 
     
     
       4. The constant force finishing system as recited in  claim 3 , wherein the CFD is mechanically coupled to the finishing tool by way of the linear drive motor. 
     
     
       5. The constant force finishing system as recited in  claim 4 , wherein the constant force applied by the CFD is mediated by the linear drive motor. 
     
     
       6. The constant force finishing system as recited in  claim 3 , wherein the CFD is mounted directly to the finishing tool. 
     
     
       7. The constant force finishing system as recited in  claim 1 , further comprising:
 a pivoting armature, the pivoting armature arranged to rotate about a first rotation axis and pivot about a first pivot axis; and 
 a translational block on which is mounted the pivoting armature, the translational block arranged to provide at least two translational degrees of freedom to the pivoting armature, wherein the chuck is directly mounted to the pivoting armature. 
 
     
     
       8. A method for finishing a workpiece by a finishing system, comprising:
 receiving a workpiece; 
 securing the workpiece to a chuck; 
 moving a finishing tool to the secured workpiece until contact; 
 starting the finishing operation; 
 
       when a surface variation on surface S of the workpiece is determined to be greater than D 1 , then use a linear motor to move the finishing tool; and
 when the surface variation of surface S of the workpiece is determined to be much less than D1, then use a constant force device (CFD) to move the finishing tool. 
 
     
     
       9. The method as recited in  claim 8 , wherein the CFD is a constant magnetic device. 
     
     
       10. The method as recited in  claim 9 , wherein the finishing system further comprises:
 a set of linear bearings; and 
 a linear drive motor mechanically coupled to the finishing tool by way of the linear bearings, the linear drive motor arranged to move the finishing tool a distance on the order of D 1  using the linear bearings. 
 
     
     
       11. The method as recited in  claim 10 , wherein the CFD is mechanically coupled to the finishing tool by way of the linear drive motor. 
     
     
       12. The method as recited in  claim 11 , wherein the constant force applied by the CFD is mediated by the linear drive motor. 
     
     
       13. The method as recited in  claim 10 , wherein the CFD is mounted directly to the finishing tool. 
     
     
       14. The method as recited in  claim 8 , the finishing system further comprising:
 a pivoting armature, the pivoting armature arranged to rotate about a first rotation axis and pivot about a first pivot axis; and 
 a translational block on which is mounted the pivoting armature, the translational block arranged to provide at least two translational degrees of freedom to the pivoting armature, wherein the chuck is directly mounted to the pivoting armature. 
 
     
     
       15. An apparatus for finishing a workpiece by a finishing system, comprising:
 means for receiving a workpiece; 
 means for securing the workpiece to a chuck; 
 means for moving a finishing tool to the secured workpiece until contact; 
 means for starting the finishing operation; 
 means for using a linear motor to move the finishing too when a surface variation on surface S of the workpiece is determined to be greater than D 1 , and 
 means for using a constant force device (CFD) to move the finishing tool when the surface variation of surface S of the workpiece is determined to be much less than D 1 . 
 
     
     
       16. The apparatus as recited in  claim 15 , wherein the CFD is a constant magnetic device. 
     
     
       17. The apparatus as recited in  claim 16 , wherein the finishing system further comprises:
 a set of linear bearings; and 
 a linear drive motor mechanically coupled to the finishing tool by way of the linear bearings, the linear drive motor arranged to move the finishing tool a distance on the order of D 1  using the linear bearings. 
 
     
     
       18. The apparatus as recited in  claim 16 , wherein the CFD is mechanically coupled to the finishing tool by way of the linear drive motor. 
     
     
       19. The apparatus as recited in  claim 18 , wherein the constant force applied by the CFD is mediated by the linear drive motor. 
     
     
       20. Non-transitory computer readable medium for storing computer code executable by a processor used to control a finishing system, the computer readable medium comprising:
 computer code for receiving a workpiece; 
 computer code for securing the workpiece to a chuck; 
 computer code for moving a finishing tool to the secured workpiece until contact; 
 computer code for starting the finishing operation; 
 
       computer code for using a linear motor to move the finishing tool when a surface variation on surface S of the workpiece is determined to be greater than D 1 ; and
 computer code for using a constant force device (CFD) to move the finishing tool when the surface variation of surface S of the workpiece is determined to be much less than D 1 . 
 
     
     
       21. The non-transitory computer readable medium as recited in  claim 20 , wherein the CFD is a constant magnetic device. 
     
     
       22. The non-transitory computer readable medium as recited in  claim 21 , wherein the finishing system further comprises:
 a set of linear bearings; and 
 a linear drive motor mechanically coupled to the finishing tool by way of the linear bearings, the linear drive motor arranged to move the finishing tool a distance on the order of D 1  using the linear bearings. 
 
     
     
       23. The non-transitory computer readable medium as recited in  claim 22 , wherein the CFD is mechanically coupled to the finishing tool by way of the linear drive motor.

Description:
This application claims priority to and the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/521,067, filed Aug. 8, 2011, entitled FORCE-CONTROLLED SURFACE FINISHING THROUGH THE USE OF A PASSIVE MAGNETIC CONSTANT-FORCE DEVICE by Brian Demers, the entire disclosure of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The described embodiment relates to a finishing process that uses an application of constant force. 
     2. Description of the Related Art 
     Precise surface finishing of metals using operations like sanding, grinding, polishing, buffing often requires the application of a repeatable force. The use of the repeatable force ensures that material removal and resulting surface finish is consistent across a variety of geometries. For example, the use of repeatable force can be quite useful when finishing surfaces have sharp geometries, such as around corners, protruding surfaces and features, and so forth. Conventional approaches to applying a repeatable force in various finishing operation include systems designed to use compliant mechanisms in a support structure of a surface finishing machine that to helps to ensure a more uniform application of force. These compliant mechanisms include for example: foams, coil springs, and air cylinders. However, only systems that incorporate air cylinders (when configured with a proper regulator and bleed valve) are capable of providing a constant force over their travel albeit with limitations. 
     Thus, in view of above, methods, apparatus and materials are desirable that facilitate the application of constant force in the finishing of work pieces having a variety of shapes. 
     SUMMARY 
     Broadly speaking, the embodiments disclosed herein describe methods, apparatus and materials for finishing a workpiece having surface features using a constant force. 
     In particular, a constant force finishing system used to finish a surface of a workpiece includes at least a first movement device arranged to apply a first movement to a finishing tool, the first movement having a range of distance D 1 . The finishing system also includes a constant force device (CFD) in mechanical communication with the finishing tool, the CFD arranged to apply a second movement in conjunction with the first movement to the finishing tool, the second movement having a range of Δ 1 , where D 1 &gt;&gt;Δ 1 . The finishing system further includes a chuck on which is mounted the workpiece during the finishing process. In the described embodiment, the chuck moves the workpiece relative to the finishing tool. During the finishing process when a surface variation of surface S of the workpiece is encountered by the finishing tool, the first movement device moves the finishing tool within the range D 1  relative to the workpiece when the surface variation is determined to have a size on the order of D 1 , and the CFD moves the finishing tool at most the distance Δ 1  when the surface variation is determined to have a size on the order of Δ 1  resulting in the finishing tool applying a constant force to a surface S of the workpiece throughout the finishing process. 
     A method for finishing a workpiece by a finishing system is described. The method is carried out by performing at least the following operations: receiving a workpiece, securing the workpiece to a chuck, moving a finishing tool to the secured workpiece until contact, starting the finishing operation. When a surface variation on surface S of the workpiece is determined to be greater than D 1 , then using a linear motor to move the finishing tool. On the other hand, when the surface variation of surface S of the workpiece is determined to be much less than D1, then using a constant force device (CFD) to move the finishing tool. 
     An apparatus for finishing a workpiece by a finishing system is described. The apparatus includes at least means for receiving a workpiece, means for securing the workpiece to a chuck, means for moving a finishing tool to the secured workpiece until contact, means for starting the finishing operation, means for using a linear motor to move the finishing too when a surface variation on surface S of the workpiece is determined to be greater than D 1 , and means for using a constant force device (CFD) to move the finishing tool when the surface variation of surface S of the workpiece is determined to be much less than D 1 . 
     Non-transitory computer readable medium for storing computer code executable by a processor used to control a finishing system, the computer readable medium is described. The computer readable medium includes at least computer code for receiving a workpiece, computer code for securing the workpiece to a chuck, computer code for moving a finishing tool to the secured workpiece until contact, computer code for starting the finishing operation, computer code for using a linear motor to move the finishing tool when a surface variation on surface S of the workpiece is determined to be greater than D 1 , and computer code for using a constant force device (CFD) to move the finishing tool when the surface variation of surface S of the workpiece is determined to be much less than D 1 . 
     Other aspects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  is a representative finishing system in accordance with the described embodiments. 
         FIG. 2  is a variation of the representative finishing system shown in  FIG. 1 . 
         FIG. 3  and  FIG. 4  shows a representative finishing system that uses a robotic arm to position and move a workpiece in accordance with an embodiment of the invention. 
         FIG. 5  is a flowchart detailing a constant force finishing process in accordance with the described embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE DESCRIBED EMBODIMENTS 
     In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the concepts underlying the described embodiments. It will be apparent, however, to one skilled in the art that the described embodiments can be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the underlying concepts. 
     This embodiments described herein relate to the use of a constant force device (CFD) acting as a compliant mechanism arranged to apply a constant force during a finishing operation carried out by surface finishing equipment, in one embodiment, the CFD can take the form of a device having constant-force magnetic springs. Particular examples of constant force magnetic springs are magnetic springs (referred to as MagSpring® manufactured by NTI AG of Spreitenbach, Switzerland. In the described embodiments, the CFD finishing system can be used to finish a surface of a workpiece with a high degree of precision regardless of the shape of the workpiece. In one implementation, the CFD finishing system can include at least a first movement device arranged to apply a first movement to a finishing tool where the first movement has a range of distance D 1  and a constant force device (CFD) in mechanical communication with the finishing tool. In the described embodiment, the CFD can apply a second movement to the finishing tool in conjunction with the first movement where the second movement has a range of Δ 1  where D 1 &gt;&gt;Δ 1 . 
     The CFD finishing system also can include a chuck on which is mounted the workpiece during the finishing process providing for the workpiece to be positioned relative to the finishing tool. During the finishing process, when the chuck places the workpiece in position, the first movement device moves the finishing tool into a contact position relative to the workpiece. In this way, the first movement device moves the finishing tool within the range D 1  relative to the workpiece, and the CFD moves the finishing tool at most the distance Δ 1  such that the finishing tool applies a constant force to the workpiece. 
     Surface finishing can be applied to a work piece through the use of a device like a belt, a wheel, or an abrasive pad. Typically the workpiece can mounted on a sliding bearing, allowing it to move in one axis, towards and away from the portion of the workpiece to be finished. In one embodiment, a CFD can be configured to provide support in this axis. In this way, the motion provided by a combination of the CFD and the sliding bearing can be used together to assure that a constant force is applied to the surface of the workpiece being finished. In other words, the sliding bearing can be used to provide an overall movement of the workpiece during the finishing process whereas the CFD can be relied upon to provide the minute corrections needed to be taken into account due to the small irregularities in the surface of the workpiece being finished. For example, when the CFD is a magnetic spring, the CFD can operate in a passive manner since the spring has no electronics and no controllers. In this implementation, the CFD outputs a constant force based on its inherent specification (which is determined by its dimensions and magnetic properties). In order for this constant force to be translated properly to a part in a surface finishing operation, the orientation of the surface finishing device can be kept constant with respect to gravity. Therefore, the part being finished will be manipulated/rotated to accommodate the fixed angle of the surface finishing device. 
     These and other embodiments are discussed below with reference to FIGS.  1 - xx . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1  is representative finishing system  100  in accordance with the described embodiments. System  100  can be used to finish surfaces of workpiece  102  mounted to chuck  104 . Workpiece  102  can take many forms. For example, workpiece  102  can take the form of housing for a portable computing device and as such workpiece  102  can be formed of metal such as aluminum, high impact plastic, and so forth. Workpiece  102  can be mounted to chuck  104  using a mechanical clasp or holder. In another implementation, workpiece  102  can be mounted to chuck  104  using a vacuum form of attachment. In any case, workpiece  102  can be secured to chuck in such a way that during a finishing process, workpiece  102  can remain essentially immobile with respect to chuck  104  thereby assuring a high degree of precision. 
     Since workpiece  102  can take any shape, in order to assure that all aspects of surface S of workpiece  102  can be properly finished, chuck  104  can have multiple degrees of freedom for moving workpiece  102 . By degrees of freedom it is meant that workpiece  102  can be translated in a pre-determined number of spatial directions and rotated about a pre-determined number of rotational axes. For example, chuck  104  can be attached to arm  106 . Arm  106  can be configured to pivot and/or rotate in rotational (U,V) space. In the described embodiment, dimensional component U represents a rotational component about pivot  108  and dimensional component V represents a rotational component about hinge  110 . In this way, chuck  104  can move workpiece  102  to any point within the rotational (U,V) space as required by surface S of workpiece  102  in order that constant force is applied normally to surface S. Additional degrees of freedom can be provided by mounting arm  106  directly to slider  112 . Slider  112  can be configured to translate both arm  106  and chuck  104  in (X,Y) space where X represents a linear translation and Y represents a translation (orthogonal) to that of X. In this way, workpiece  102  can be moved with a number of degrees of freedom represented by (U,V,X,Y) space. 
     In order to finish workpiece  102 , finishing material  114  (for example, sand paper), can be brought in direct contact with surface S of workpiece  102 . In one embodiment, finishing material  114  can be secured to linear motion device  118 . Linear motion device  118  can translate finishing material  114  in ±Z dimension relative to workpiece  102  thereby providing an additional degree of freedom. In the described embodiment, linear motion device  118  can include linear motor  120  connected to finishing material  114  by way of linear bearings  122 . In the described embodiment, constant force device (CFD)  124  can be arranged in such a way that constant force F const  is exerted by finishing material  114  on surface S of workpiece  102  during a finishing operation. In particular, when linear motor  120  is activated, finishing material  114  can be brought into direct contact with surface S of workpiece  102  by moving finishing material  114  in the −Z direction until a sensor (not shown) indicates initial contact. Once initial contact has been detected, the motion of finishing material  114  can be stopped at which point the finishing process can commence. 
     However, due to the nature of the direct contact between finishing material  114  and CFD  124 , force applied to workpiece  102  by finishing material  114  remains essentially constant regardless of the geometry of surface S. This is particularly true in those situations where workpiece  102  has an irregularly shaped surface, protuberances, or other features that heretofore makes it difficult or impossible to apply a constant finishing force. For example, in a first motion, motor  120  can move finishing material  114  a distance D 1  associated with a course adjustment used to, for example, bring finishing material  114  in direct contact with workpiece  102 . However, in those instances where minute variations in surface S characteristics would cause a conventional finishing process or apply a non-uniform force to surface S, the use of CFD  124  can cause finishing material  114  to move a second distance Δ 1  (where D 1 &gt;&gt;Δ 1 ) corresponding to any minute variations in the geometry of surface S. Such variations can be due to, for example, an irregular shape of surface S, variations in thickness of workpiece  102 , and so on. CFD  124  can therefore cause finishing material  114  to apply constant finishing force F const  to surface S of workpiece  102  regardless of any surface irregularities or surface geometries having a size scale on the order of Δ 1 . 
       FIG. 2  shows another embodiment of finishing system  100  in the form of constant force finishing system  200  in accordance with the described embodiments. Constant force finishing system  200  can be arranged in such a way the constant force device (CFD)  202  can in placed in direct contact with finishing material  114 . By reducing the distance between CFD  202  and finishing material  114 , any delay due to the mechanical nature of motor  120  can be reduced due to the proximity of CFD  202  to finishing material  114 . In this way, the amount of time between a change in surface S geometry and a resulting change in force applied by CFD  202  to finishing material  114  on surface S of workpiece  102  can be substantially reduced. 
       FIG. 3  and  FIG. 4  show additional embodiments of finishing system  100 . For example,  FIG. 3  shows constant force finishing system  300  that includes robotic arm  302 . In this embodiment, robotic arm  302  can be operated by a computing system programmed to move workpiece  102  by varying a speed and direction of motion of chuck  104 . For example, robotic arm  302  can be controlled by a computing system that can be programmed to move robotic arm  302  in any of six degrees of freedom (DOF). In this way, a more accurate and precise movement of chuck  104  (and therefore workpiece  102 ) can result in a finer, more detailed finishing operation. In some embodiments, the computing system that controls robotic arm  302  can also provide control signals to linear motor  120  and/or CFD  124 . In this way, the movement of finishing material  114  can be co-ordinated with that of chuck  104  and force F const  applied by CFD  124 . More particularly, finishing system  300  makes use of robotic armature  302  on which to support workpiece  304 . Robotic armature  302  can have as many as six degrees of freedom (DOF). 
       FIG. 5  shows a flowchart detailing process  500  of finishing a workpiece using a constant force device (CFD) in accordance with the described embodiments. Process  500  can be performed by receiving a workpiece at  502  and secured to a chuck at  504 . Once the workpiece is secured to the chuck, a finisher is moved towards the secured workpiece at  506 . The finisher can include a finishing material that can be used to finish a surface S of the workpiece. Accordingly, the finishing material can take many forms such as abrasives along the lines of steel wool, sand paper, and so on as well as finer materials such as lamb&#39;s wool, cotton, etc. In any case, once it has been determined at  508  that contact between the finisher and surface S of the workpiece has taken place; the finishing process can begin at  510 . The finishing process can involve movement of the finisher (and associated finishing material) in relation to surface S of the workpiece. Due to contours in the surface S of the workpiece (due to design protuberances, for example), a surface variation can be encountered and if at  512 , the dimension of the surface variation in on the order of linear size D1, then a linear motor is used to move the finisher in relation to the encountered surface variation at  514 . If, however, it is determined at  516  that the surface variation has a size on the order of Δ 1  that is much smaller than D1, then a constant force device (CFD) mechanically coupled to the finisher is used to move the finisher a distance commensurate with Δ 1  at  518 . At  520 , the finishing operation is completed when surface S is determined to be within design limitations called out in a specification associated with the finished workpiece. 
     The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, DVDs, magnetic tape, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     The many features and advantages of the present invention are apparent from the written description and, thus, it is intended by the appended claims to cover all such features and advantages of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, the invention should not be limited to the exact construction and operation as illustrated and described. Hence, all suitable modifications and equivalents may be resorted to as falling within the scope of the invention.

Metadata:
Filing Date: 20110922
Publication Date: 20131008
Grant Date: 20131008
Priority Date: 20110808
Inventors: DEMERS BRIAN
Assignee: APPLE INC
CPC Classifications: [{"code": "B24B49/16", "inventive": true, "first": true, "tree": "[]"}, {"code": "B24B49/16", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 47677814