Abstract:
A superfinishing system and method, wherein an abrasive is employed to process a workpiece, and wherein the system simultaneously mounts a plurality of workpieces in a diagonal turret, or mounts a plurality of different types of workpieces in a plurality of chucks for different operations thereon, or performs a plurality of different operations on the same workpiece without remounting. The system improves throughput by allowing flexibility in the operation and multitasking.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to high throughput cup wheel superfinishing systems and methods therefore, in particular relating to workpiece identification, loading, unloading and repositioning.  
         [0003]     2. Description of the Prior Art  
         [0004]     Superfinishing is a well known process in which an outer surface of a workpiece is removed, using a process which generates little heat or surface stress, to produce a smooth surface having a precise contour and properties similar to the bulk material.  
         [0005]     A superfinishing operation can be performed on almost any previously machined surface which may have a flat, cylindrical, spherical or other specific configuration. It improves the finish of the previously machined surface by removing surface material or “smear metal” left by the previous machining operation, and by cutting off ridges on the base metal surface of the workpiece. Superfinishing can also effect small corrections in the dimensions or shape of the workpiece. A superfinished surface is also characterized by a pattern of minute scratch marks which are beneficial for purposes of lubrication. Such scratch marks may take the form of a cross-hatched pattern cut by a combination of workpiece and stone movements.  
         [0006]     Known processes employ, for example, a fine abrasive cup wheel to produce an abrasive pattern having a relatively constant relative velocity, which due to the rotation of the cup and workpiece, acts on the surface at in an area contact at nearly right angles, producing the characteristic cross hatch surface pattern. The process is typically controlled to apply a constant force on the workpiece surface, with the cup wheel spinning rapidly and the workpiece moving slowly, so that the cup wheel provides a treatment to all regions of the surface at least once (and in general, many times). This arrangement is useful for finishing planar or spherical surfaces.  
         [0007]     A conventional superfinishing stone is formed as a block of solid abrasive material and relies on a coolant, commonly of relatively high viscosity, flooded over the stone and workpiece surface by means of external supply nozzles or by immersion. Such conventional stones are specially compounded to the user&#39;s specifications as to size, grit material, bond and hardness.  
         [0008]     Typically, a superfinishing operation is controlled based on a pressure of the abrasive on the workpiece. This provides uniformity of treatment over corresponding parts of respective workpieces, and to the extent topological issues are resolved, globally uniform treatment, regardless of original surface configuration. This, in turn, requires a close loop servo feedback control system, to position the workpiece and abrasive in accordance with their relative force.  
       SUMMARY OF THE INVENTION  
       [0009]     With the foregoing considerations in mind, a first object of the present invention is to provide a superfinishing system and method which provides automated loading, positioning, and unloading of the workpiece into the apparatus.  
         [0010]     By providing an automated workpiece handing system, the process is facilitated and manual efforts eliminated. This automation therefore potentially allows greater productivity, both of the machine which works continuously, and of the human operator, who can manage a number of workcenters simultaneously or perform other tasks.  
         [0011]     A turret (i.e., a diagonal turret) provides a set of elements which have axes which are inclined with respect to each other, and thus a workpiece in one turret location has both a different position and a different inclination than a workpiece in another turret location. An index table, on the other hand, maintains the axes of the workpieces in parallel relation.  
         [0012]     While machining turrets are known, typically these are provided for machining tools, not workpieces, and are typically designed with the tool in an active tool position facing horizontal or vertically downward. The turret may be fluid filled, and include hydraulic elements, so that a change in orientation from a downward tool direction may result in difficulties in operation. Likewise, the turret, though typically designed to be tolerant to cooling fluid, is typically not designed to be bathed in fluid, as would be expected if the turret is used to mount a workpiece for a superfinishing operation, which requires a substantial fluid flow. A turret design provides a relatively open space in the same plane as the vertical spindle, since the opposite spindle is horizontal, facilitating visualization of the process, and loading and unloading of non-machining spindles. The use of a turret may result in a space savings on the base of the machine, and therefore occupy less floor space than an index table design.  
         [0013]     Known superfinishing systems which employed index tables were not capable of handling different types of workpieces, although a system was known which processed opposite faces of a single type of workpiece sequentially, in different chucks, with an automated system for inserting the workpiece, flipping it, and then extracting it to a finished workpiece area. This type of system is specially designed for a single application, and thus is not particularly adaptable. The present invention advances this system by providing for the use of an incremental rotatory index table, for example a direct drive index table, to selectively control an offset between the cup wheel axis and workpiece axis, to avoid or mitigate the need for control over this offset on the cup wheel drive mounting, and allow different positions of workpiece axis relative to the machining axis. This control also allows processing of two different surfaces of a workpiece (or a plurality of workpieces simultaneously) without remounting.  
         [0014]     A second object of the invention provides automated superfinishing of two different surfaces of the workpiece according to different processing parameters.  
         [0015]     In various embodiments, it is possible to provide a mechanism for replacing or interchanging a cup wheel, although the changeover time may mitigate the advantages of the present system. For example, an index table or turret may be provided to mount the cup wheel as well.  
         [0016]     In processing two surfaces whose tolerance are to be tightly held relative to each other, the present invention provides a system and method wherein first and second operations are chained in a sequential process, without unmounting the workpiece, so that the surface as actually produced in the first process serves as a positional reference for the second surface. Since a servo-drive may be employed for advancing the cup wheel along its axis, the position information may be acquired from this system, alleviating the need for a separate gauge or gauging operation.  
         [0017]     A third object provides a multiposition turret having a chuck at each position for rotating a workpiece during superfinishing, wherein different positions are adapted for different workpieces or use of different superfinishing parameters. Each chuck may be encoded, so that the system will automatically recognize the workpiece and its associated processing parameters.  
         [0018]     Another advantage of a turret system is that it allows “live spares”. That is, in the event that a workpiece chuck or spindle is damaged, another chuck may be enlisted to serve its purpose. Since the changeover may be automated, this can improve the reliability and/or “uptime” of the system, an important characteristic for superfinishing machines, which are often used in high production environments.  
         [0019]     A fourth object of the invention provides a robotic arm for loading and unloading of the workpiece, e.g., at a non-machining location of the turret, wherein the robotic arm is mounted on a common base with the workpiece drive spindle. This arrangement reduces alignment issues as compared to separate bases. In this case, it is important to provide a splash guard which blocks most of the cooling fluid from washing over the robotic arm, while allowing free access to the loading position. Since the preferred turret is a 45 degree diagonal turret, a splash guard may be provided which has a lower angled plate which divides the turret between upper and lower portions, with the upper portion being subjected to cooling fluid spray and the lower portion isolated from it. The angled play may have apertures corresponding to the shape of the turret and spindles, leaving only a small opening for fluid to leak out. The robotic arm and bottom portion of the turret may be housed within a secondary cabinet, to maintain all fluid within the system, and to protect the operator from harm during operation.  
         [0020]     A fifth embodiment of the invention provides an index table, that is, a set of workpiece holders mounted having spindle axes parallel to each other, on a rotatable plate, allowing the different workpiece holders to move between various positions. According to the present invention, the index table may be driven to an arbitrary position, rather than a mechanically predetermined stop position, allowing selectively controllable offset between a workpiece axis and a cup wheel axis. Since this offset is controllable from the workpiece side, there is no need to provide control over this axis from the cup wheel side, potentially simplifying the construction and control of the system.  
         [0021]     According to the first object, a turret, having a plurality of positions and at least one active position in which a spindle is driven for rotation, is employed to hold, position and rotate the workpiece with respect to the cup wheel. For example, a workpiece may be loaded into the turret at a first position, superfinished at a second position, and unloaded at a third position. Alternately, the workpiece may be loaded and unloaded at the same position. Advantageously, the turret may be a standard machining turret, configured to rotate the workpiece rather than a tool. The superfinishing abrasive cup is provided on a second spindle, which is controlled by a process feedback controller.  
         [0022]     Typically available turrets have only a single driven spindle position; however, in a modified turret design, a plurality of workpieces may be rotatably driven at a single time, potentially allowing superfinishing of a plurality of workpieces in a single apparatus. This may be advantageous, for example, where a single set of workpiece loading/unloading systems is provided for multiple working positions, where a single workpiece is to be processed under a plurality of sequential conditions (e.g., different cup wheel, etc.), or otherwise.  
         [0023]     It is noted that in typical milling and drilling machining operations, in which such turrets are normally applied, the turret supports the cutting tool, and not the workpiece.  
         [0024]     According to the second object, two surfaces, for example a flat end surface and an annular planar surface projecting from a cylinder, are both to be superfinished. Typically, these would be treated as two different operations, since the parameters of optimal treatment differ. According to the present invention, a plurality of sets of control parameters are sequentially employed by the control, to first treat one surface, and then treat the other surface, without unloading the workpiece.  
         [0025]     Typically, the surfaces to be superfinished are at different depths. Traditionally, one would gauge the relative depth between surfaces or absoluter depth of each surface, and index the cup wheel to the appropriate position. On the other hand, according to the present invention, the fact that the process is process feedback controlled allows the system to reposition the abrasive with respect to the surface in the plane of the surface, and to then allow the control to find the working depth by itself.  
         [0026]     Thus, according to this embodiment, the control must store and appropriately employ two different control parameter sets for each workpiece, which is not the norm for superfinishing systems.  
         [0027]     According to the third embodiment, a single machine may be placed within multiple workflows, without a change in setup. A multiposition turret is provided, which is preferably associated with one or more automated feeds and/or removal mechanism to insert the superfinishing machine into an automated flow. Typically, a superfinishing machine is set up for a single type of workpiece, which is inserted and extracted from the chuck in its normal operating position. According to the present embodiment, a plurality of chucks are provided on a turret, which is automatically controlled. Each chuck can be adapted for a different workpiece, so, without a change in setup, the machine can operate on different workpieces with different superfinishing processes, simply by calling a superfinishing operation associated with a particular chuck (turret position). A sensor may be provided to determine whether a chuck is occupied. After completion of processing, the workpieces may be extracted into separate workflows, for example by having separate automated insertion and extraction mechanisms for the different chucks or chuck types.  
         [0028]     Another advantage of the index programming embodiment is that it facilitates “just in time” production methods, since the workflow through the machine can be efficiently allocated between jobs on a piece by piece basis. Even if a separate automated mechanism is not available for loading and unloading the chuck, the embodiment still has merit, since adjusting or replacing the feed may be less cumbersome than retooling the entire operation.  
         [0029]     It is noted that the cup wheel selection and replacement may also be automated, using either a single spindle or turret design. A single spindle is preferred.  
         [0030]     The control for the superfinishing system and method therefore includes a memory for storing a plurality of processing programs or parameters therefore, which are selectively retrieved and loaded based on a required superfinishing operation as determined by a type of workpiece, a surface of a workpiece, and/or other parameters.  
         [0031]     The embodiments of the present invention are designed to work in conjunction with existing elements of superfinishing machines, including the products of Supfina Machine Co., Inc. (N. Kingstown, R.I.), and in conjunction with workcenter automation systems of known types.  
         [0032]     In general, a first type of automation system employs relatively special purpose single axis or double axis mechanisms which, using a simple sequence, load or unload, or in some cases, both load and unload, workpieces from the chuck. In order to reduce complexity, it is preferred that the loading and unloading occur at different locations, using different mechanisms. Such automated systems may be relatively low cost and small, but are limited in functionality and flexibility. This type of mechanism can be especially efficient for small workpieces which are arrayed in a line or tube.  
         [0033]     A second type of automation system employs a general purpose automated mechanism, such as an industrial robot, which can be programmed to perform multiple operations and provide sophisticated motion control and sensing. Such systems are generally more expensive than dedicated mechanisms, but through programming can affect a variety of operations. Due to this flexibility, loading and unloading may be affected at a single position. This type of mechanism is well suited for larger workpieces, or those which are arrayed in a tray or otherwise require manipulation for insertion or extraction.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]      FIG. 1  shows a prior art superfinishing apparatus having a first spindle and chuck rotating the workpiece and a second spindle rotating the abrasive cup wheel, and wherein the processing must be interrupted for loading and unloading of the workpiece;  
         [0035]      FIG. 2  shows a first embodiment according to the present invention in which the workpiece chuck is mounted on a turret, and therefore loading, unloading and certain types of gauging may proceed concurrently with the processing of another workpiece;  
         [0036]      FIG. 3  shows a first automated insertion and extraction system in which workpieces are inserted and extracted at different locations of the turret;  
         [0037]      FIG. 4  shows a second automated insertion and extraction system in which workpieces are inserted and extracted at the same turret location;  
         [0038]      FIG. 5  shows a third embodiment of the invention in which multiple turret locations correspond to different processing operations, allowing the superfinishing machine to perform a plurality of different processing operations on different workflows without alternate setup;  
         [0039]      FIGS. 6A, 6B  and  6 C show a fourth embodiment of the invention in which a single workpiece is processed on different surfaces with respectively different processing parameters while mounted in the same chuck;  
         [0040]      FIG. 7  shows a first index table embodiment of the invention wherein different workpieces are processed using different cup wheels simultaneously, and wherein the rotational axis of the index table can be continuously controlled;  
         [0041]      FIG. 8  shows a robotic arm embodiment of the present invention with a splash guard in place to protect the arm from a spray of cooling fluid; and  
         [0042]      FIG. 9  shows a flowchart of a chained processing sequence in which a first surface is finished, and the position of the first surface used to form the second surface with high relative accuracy.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Prior Art  
       [0043]      FIG. 1  shows a typical cup wheel superfinishing apparatus. In this type of system, a cup wheel  2  spins rapidly, for example 10,000 RPM. The workpiece  1  also moves relative to the cup wheel  2 , so that the entire surface  1 ′ to be treated contacts the cup wheel  2 . In this case, the workpiece  1  also rotates, for example at 500-3500 RPM. The axis of the cup wheel  7  is offset from the axis of the workpiece  8 , and depending on the relative angles, produces a spherical surface with positive (convex), or negative (concave) curvature, or having an infinite radius (planar). There are thus a number of mechanical adjustments, in addition to selection of the cupwheel  2 , including the advancement of the cup wheel along its axis  7 , the radial displacement of the cup wheel axis  7  and the workpiece axis  8 , and the angle of the cup wheel axis  7  with respect to the workpiece axis  8 .  
         [0044]     In general, the type of superfinishing operation encompassed by the preferred embodiments of the present invention provide a spinning cup wheel  2  on a different axis  7  (which may be parallel or inclined) than a spinning axis  8  of the workpiece  1 . The workpiece  1  typically spins more slowly than the cup wheel  2 , and the process is controlled by a constant force or pressure, or other control system (not shown) to provide a constant pressure between the cup wheel  2  and the workpiece  1 , which leads to a controlled removal of material. The workpiece  1  material removal is typically controlled based on a gauge measurement, but in some cases where tolerances are not critical, the gauge may be dispensed with. If the axes of the cup wheel  7  and workpiece  8  are parallel, the resulting processed surface is planar, while if the axes are inclined, a spherical surface is produced. Because the cup wheel  2  has a leading and trailing edge in contact with the workpiece  1 , a characteristic cross-hatch pattern is produced on the workpiece  1 . Typically, a stream of coolant (not shown) is provided to lubricate, rinse and cool the workpiece  1  during processing, and it is possible to monitor acoustic emissions into this stream to analyze and control aspects of the process. Other possible control parameters include normal force, torque, deflection, and vibration sensing of the mechanism.  
         [0045]     In  FIG. 1 , the abrasive wheel  2  is rotated by a spindle motor  5  at a high speed. The chuck  3  is mounted on a spindle (not shown), which rotates the workpiece  1  at a speed lower than that of the abrasive cup wheel  2 . The chuck  3  is pressed towards the cup wheel  2  by means of pressure caused by a feed system  4  with a lead screw (not shown) so that the surface  1 ′ to be worked of the workpiece  1  is brought into contact with the cup wheel  2  surface.  
         [0046]     The process is controlled to provide a minimum processing of all portions of the workpiece  1 , which is maintained until the appropriate amount of material removal or other parameter is met.  
         [0047]     As shown in  FIG. 1 , the feed system  4  is mounted on a wall  6 , which is rigidly connected to a base  9 , to maintain critical position and alignment through the process. A spray of cooling fluid is provided on the workpiece  1  and exterior of the cup wheel  2 , by a nozzle (not shown).  
       First Embodiment  
       [0048]      FIG. 2  shows a superfinishing apparatus having a set of chucks  3  mounted on respective spindles of a turret  10 . In this arrangement, the superfinishing operation can proceed simultaneously with loading and unloading, and/or a gauging process may be conducted prior to, during an intermediate step, or after the process, by a gauge  17  located in conjunction with a workpiece  13  in a non-machining chuck, without unduly reducing process throughput. Of course, gauging may also be conducted in-process by a gauge  16  located in conjunction with a workpiece  1  in a machining chuck. Thus, the superfinishing process may proceed while secondary operations are performed at different turret stations.  
         [0049]     The preferred turret is a Pibomulti  256 ,  356 , or  358 , which provides a single electrical servomotor to both position the turret and drive the spindle in at single turret location. The turret  10  permits loading and unloading through a hydraulically clamp at a single position.  
         [0050]     As shown in  FIG. 2 , the abrasive wheel (cup wheel) is designated at  2 . The chuck  3  or clamping fixture shown in  FIG. 1  is placed on a turret  10 , which is rotationally driven by a spindle (not shown), internal to the turret  10 . The chuck  3  is, for example, operated hydraulically. The cup wheel  2  is moved quickly along its axis  7  toward the workpiece  1  until there is contact, in order to speed processing and reduce cycle times. Typically, the initial contact or “crash” is detected through a sensor or process parameter change, and the feed rate of the feed system  4  is slowed to appropriate processing speed(s) until the process is complete. The process is, for example, controlled based on a process parameter correlated to the cutting force, to ensure the process remains within appropriate limits. If the material removal is attempted at too high a speed, heat is generated which can damage the cup wheel  2 , or alter the characteristics of the workpiece  1  in an undesired fashion, or simply produce an unacceptable finish. Slow speeds result in prolonged processing, decreasing throughput.  
         [0051]     The turret  10  may have any number of positions, for example holding six workpieces  1 ,  11 ,  12 ,  13 ,  14 ,  15 . Typically, only a single chuck  3  of the turret  10  is driven for rotation, although turrets with multiple driven spindles may be employed. The turret  10  may include various sensors, such as chuck loading status, turret position, rotational speed, torque, force, vibration, and the like, which may advantageously be employed by the control system (not shown). Typically, a single control system is employed to control the superfinishing operation, in particular the advancement of the feed system  4  and turret  10 , although separate but coordinated systems may be implemented.  
         [0052]     Another advantage of a turret  10  mechanism is that it provides possible redundancy of workpiece chucks  3 , and therefore allows a machine to remain operational even if one turret  10  position becomes defective or unavailable.  
         [0053]      FIG. 3  shows a first automated insertion and extraction system in which workpieces  1 , inside of chuck  3 , are inserted and extracted at different location chucks  12 ,  14  of the turret  10 . In this case, relatively simple single axis loading  23  and unloading  21  mechanisms may be employed. To load a workpiece  1 , an empty chuck  14  is positioned at a loading station. Once in position, a workpiece  1 , from a linear array of workpieces in chute  24 , is presented with its axis aligned with the chuck  14 , moved into the chuck  14 , and the chuck  14  clamped (or otherwise closed) to hold the workpiece  1 . To unload a workpiece  1 , the turret  10  is positioned with the chuck  12  at an unloading station, and a mechanism  22  extended to grasp or catch the workpiece  1 . The chuck  12  is then unlatched or released, and the workpiece  1  extracted from the chuck  12 . In this type of system, the control for the loading and unloading may be closely or loosely integrated with the turret  10  control. As appropriate, sensors for turret position, availability of a new workpiece  1  in the loading chute  24  or space for a subsequent workpiece after extraction in the unload chute  25 , state of alignment of insertion/extraction mechanism with chuck axis, and insertion/extraction status may be employed.  
         [0054]      FIG. 4  shows a second automated insertion and extraction system, in which workpieces  1  are inserted and extracted at the same turret  10  location. In this case, a single coordinated mechanism  31  inserts and extracts workpieces  1 . Such mechanisms, exemplified by robotic arms, typically have a large number of degrees of freedom, and are typically controlled in both time and space to follow a predefined path. In contrast to the embodiment shown in  FIG. 3 , the system does not require that the workpieces  1  be precisely arrayed, and indeed they can be presented on a conveyor belt or tray. Workpieces  1  may be irregularly shaped or otherwise difficult to feed using a tube, chute, or ramp.  
         [0055]     Also shown in  FIG. 4  are that the robotic arm mechanism  31  and base  20  of turret  10  are mounted on a common base  9 , which is rigidly connected to the vertical wall  6  supporting the cup wheel  2  positioning mechanism  30 .  
         [0056]     Since the robotic arm mechanism  31  requires sophisticated motion control, the control is typically separate from the turret  10  control and superfinishing control. Thus, the separate control may communicate over a link or network, such as Profibus, Ethernet (802.x), RS-232, RS-485, IEEE-1488, I2C, USB, IEEE-1394, IEEE-1451, or other known communication standard, or through a communication bus.  
       Second Embodiment  
       [0057]      FIG. 5  shows a second embodiment of the invention in which multiple turret  10  locations correspond to different processing operations, allowing the superfinishing machine to perform a plurality of different processing operations on different workflows without additional changeover.  
         [0058]     This embodiment is structurally similar to the first embodiment shown in  FIG. 2 , except perhaps that multiple flows of workpieces  41 ,  42 ,  43 ,  44 ,  45 ,  46  may interact with the turret  10 , to load and unload the respective chucks. However, from a control standpoint, this embodiment is somewhat different.  
         [0059]     In prior systems, control complexity was limited by providing a system which was set up and run to perform a single operation. The cup wheel  2  and workpiece  1  each rotated about a defined axis, and the control used its process parameter sensor or a position sensor to initiate contact. Thereafter, the process was controlled to produce a finish on the workpiece with the desired parameters, which were, for example, dimensional, surface finish quality, or the like.  
         [0060]     In this embodiment, the control has a program which is selected based on the turret  10  position of the respective workpiece  41 ,  42 ,  43 ,  44 ,  45 ,  46 . Thus, with a six position turret  10 , it is possible to have six different programs selected accordingly. By loading the workpiece  41 ,  42 ,  43 ,  44 ,  45 ,  46  into an appropriate chuck on the turret  10 , the superfinishing process appropriate for that workpiece  41 ,  42 ,  43 ,  44 ,  45 ,  46  may be initiated and controlled.  
         [0061]     According to another example, incoming parts may be gauged for various dimensions and parameters, and binned accordingly. Depending on the classification, the part may be selectively inserted into a respective turret  10  position, which will then trigger the appropriate processing conditions for that part. This alleviates the need to electronically communicate a new control program (or parameters thereof) to the control for each workpiece  41 ,  42 ,  43 ,  44 ,  45 ,  46 .  
         [0062]     Of course, the process control parameters need not be determined only by the turret  10  position, and a parameter associated with a part may be communicated to the process control independently of turret  10  position.  
       Third Embodiment  
       [0063]      FIGS. 6A, 6B  and  6 C show a third embodiment of the invention in which a single workpiece  1  is processed on different surfaces  1 ′,  1 ″ with respectively different processing parameters while mounted in the same chuck  3 . In this case, the control employs respectively different control parameters, if for nothing else, to define the offsets A, B of the various surfaces to be treated, but likely also in-process conditions as well. Accordingly, during processing, the control causes the cup wheel  2  to contact a first surface  1 ′ and applies a respective treatment, until completed. After the first surface  1 ′ is treated, a second processing program is triggered which then realigns the axes  7 ,  8  of the cup wheel  2  and workpiece  1 . In some instances, the cup wheel  2  is replaced with a different abrasive, appropriate for the subsequent operation. Using the next set of processing parameters, the subsequent surface  1 ″ is treated. These sequential operations, calling sequential sets of control parameters, are repeated until all surfaces are treated. Therefore, a large number of surfaces on the same workpiece may be sequentially and efficiently processed. Because the feed system  4  is mounted on plate  36 , with inclination adjustment  39 , which, in turn is positioned by X axis servo  37  and Z axis servo  38 , a high degree of precise control is available over the sequential processes. Further, the cup wheel repositioning mechanism allows precise and repeatable relative movements, ensuring that the surfaces  1 ′,  1 ″ of the workpiece  1  are accurately spaced relative to one another.  
         [0064]     This process is shown in the flowchart of  FIG. 9 . The process starts  100  with a fast approach  102  to the first surface  1 ′. Initial contact of the cup wheel  2  with the workpiece  1  is detected  104 , and the advance of the feed motor is immediately slowed. An axis register is set to zero  106 , and a predetermined amount of material is removed from the workpiece  1  by advancing  108  the cup wheel  2  along its axis  7 , until it reaches a depth corresponding to a desired material removal of the first surface  1 ′. The advance of the cup wheel  2  is then stopped  110 , in a process step also known as spark out, and the forces between cup wheel  2  and workpiece  1  are allowed to drop to zero. The final axis position of the first surface  1 ′ is then registered  112 . The cup wheel  2  is then retracted  114  from the first surface  1 ′ until clear of the workpiece  1 , typically a predetermined distance.  
         [0065]     The cup wheel  2  axis  7  is then repositioned  116  for finishing the second surface  1 ″. The feed system  4  then advances the cup wheel  2  with a fast approach  122  toward the second surface  1 ″. Contact with the second surface  1 ″ is detected  124 , and an amount of material is removed from the workpiece  1  by advancing  128  the cup wheel  2  along its axis  7 , until it reaches a depth corresponding to a desired depth of the second surface  1 ″, which is calculated relative to the first surface  1 ′ registered final axis position  112 , and which is typically compensated by a cup wheel  2  wear factor, if necessary to achieve a final tolerance. The advance of the cup wheel  2  is then stopped  130 , and the forces between cup wheel  2  and workpiece  1  are allowed to drop to zero. The cup wheel  2  is then retracted  134  from the second surface  1 ″ until clear of the workpiece  1 . The workpiece  1  may then be changed to a new, unprocessed one, and the process repeated.  
       Fourth Embodiment  
       [0066]     As shown in  FIG. 8 , a shield may be provided around the cup wheel  2  and machining station of the turret  10 , separating the machining space internal to the cabinet formed by front face  61 , sides  60 , rear support  68 , and shield  63 , from the loading and unloading space. This protects the robotic arm mechanism  31  from large flows of cooling fluid, and permits superfinishing to be conducted simultaneously with these ancillary operations. As shown in  FIG. 8 , the robotic arm mechanism  31  is mounted on the same table or base  9  as the turret  10 , providing improved dimensional stability over a separate stand design.  
         [0067]     The shield is part of a cabinet, with an inclined bottom  63 , having a plane which generally bisects the turret  10 . The shield  63  has, for example, cutouts  64  which conform to the shape of the turret  10  and chucks  3 ,  35 . In this arrangement, and due to the right angle inclination of the bottom chuck  35  with respect to the top chuck  3 , the loading and unloading operations may be readily separated from machining, even in close confines.  
         [0068]     The robotic arm mechanism  31  preferably has a pair of grippers  32 ,  33 , to allow insertion and extraction of workpieces  1  in a coordinated set of movements of the arm. Typically, the loading and unloading space is also enclosed in a guard (not shown) which, for example, provides operator safety and contains residual coolant spray, which drains into trough  67 .  
         [0069]     The control electronics for the apparatus are contained in a cabinet  65  on the rear of the rear support  68 .  
       Fifth Embodiment  
       [0070]      FIG. 7  shows a direct drive index table  50  embodiment having two simultaneous machining positions  52 ,  55  for respectively different machining operations, for example, different operations on a workpiece. Because the index table  50  is direct drive, the axis of rotation of the workpiece  52 ,  54  may be controllably offset from a nominal position, providing an additional degree of freedom for machining. Thus, the cup wheel  56 ,  61  axes  7 , driven by spindle motors  57 ,  58  may remain fixed in position, and the workpiece  52 ,  55  axis  8  offset in controlled manner, potentially simplifying the cup wheel positioning mechanisms  59 ,  60  to allow then to simply advance the cup wheel  56 ,  61 .  
         [0071]     In  FIG. 7 , it is seen that during processing of workpieces  52  and  55 , workpieces  53  and  54  are accessible for gauging, insertion and extraction, or other operations.  
         [0072]     While certain representative embodiments of the invention have been described herein for the purpose of illustration, it will be apparent to those skilled in the art that modifications therein may be made without departing from the spirit and scope of the invention.