DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Hereunder, a surface finishing apparatus and its related method of each of various embodiments according to the present invention are described below in detail with reference to the accompanying drawings. In the following description, directional terms, such as “laterally”, “horizontally” and “vertically”, are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention. Also, for the sake of convenience of explanation, an axial direction (a lateral direction, for example, as viewed in FIG. 1 ) of a workpiece is assigned to be an X-direction, a lateral or horizontal direction (perpendicular to a page space, for example, in FIG. 1 ) perpendicular to the X-direction a Y-direction and a vertical direction perpendicular to the X-direction a Z-direction. Also, in the following description of surface finishing apparatuses and related methods of various embodiments of the present invention, by the term “surface finishing” is meant the surface processing including lapping or roller burnishing.

First Embodiment

[0056] Referring now to FIGS. 1 and 2 , there is shown a surface finishing apparatus, in the form of a lapping apparatus 1 , of a first embodiment of the present invention. FIG. 1 is a schematic front view of the lapping apparatus, and FIG. 2 is a schematic view corresponding to a cross section taken on line 2 - 2 of FIG. 1 .

[0057] As shown in FIGS. 1 and 2 , the lapping apparatus 1 of the presently filed embodiment serves to finely lap a workpiece W, in the form of a crankshaft, in given surface finish subsequent to preceding rough surface machining operation, such as cutting using a machining tool, heat treatment and grinding operation. That is, the lapping apparatus 1 serves to lap a target shaped periphery of the workpiece W, such as a journal portion or a pin portion of the crankshaft, in a desired surface quality with a surface profile formed in a mid-concave shape. The lapping apparatus 1 is shown to include a workpiece supporting mechanism WS that supports the workpiece W having the target shaped periphery of the workpiece W to be finely lapped in a given surface finish, a pressure applying mechanism 10 operative to apply a pressure force to a surface finish tool, in the form of a lapping film 11 , such that the lapping film 11 is held in pressured contact with the target shaped periphery of the workpiece W with the pressure force exhibiting a distribution pattern depending upon an axial direction of the workpiece W, an actuator 30 associated with the pressure applying mechanism 10 , a drive mechanism 40 driving the crankshaft W to allow the lapping film 11 to lap the target shaped periphery of the crankshaft into a desired geometrical profile, and a tool shifting mechanism 50 , in the form of an oscillating mechanism, that laterally shifts at least one of the lapping film 11 and the workpiece W.

[0058] More particularly, in the lapping apparatus 1 of the presently filed embodiment, the workpiece supporting mechanism WS comprises a base 49 A, a workpiece support table 49 disposed on the base 49 A for sliding movements in the X-direction, a biasing member 52 resiliently coupled to the workpiece support table 49 to allow the same to be horizontally oscillated as described below, a first slidable table 47 disposed on the workpiece support table 49 and a second slidable table 48 disposed on the workpiece support table 49 , with the first and second slidable tables 47 , 48 being slidable in the Y-direction, a headstock 42 carried on the first slidable table 47 and rotatably supporting a spindle 41 by which a chuck 43 is connected to grip one end of the workpiece W, and a tailstock 46 having a center 46 a to support the other end of the workpiece W.

[0059] In the lapping apparatus 1 , a target shaped periphery of the workpiece W is lapped using the lapping film 11 in a manner described below. The lapping film 11 includes a thin-walled base member 11 a (as shown FIG. 3 described later) that is non-extensible and deformable and has an entire surface covered with abrasive material with an abrasive face 11 b (as shown FIG. 3 described later) of the thin-walled base member being placed to face the target shaped periphery of the workpiece W to be lapped. Although the lapping film 11 can be classified into various types and, in the presently filed embodiment, the thin-walled base member is formed of non-extensible material, such as polyester resin, formed in a strip-like structure with a given width and a thickness “t” (as shown FIG. 3 described later) ranging from approximately 25 μm to 150 μm. Formation of such a lapping film 11 using the thin-walled base member that is non-extensible and deformable allows the target shaped periphery of the workpiece W to be smoothly lapped in a preferable fashion.

[0060] In the lapping film 11 , the thin-walled base member has a surface provided with a large number of abrasive grains, such as aluminum oxide, silicone carbide and diamond, with a grain diameter ranging from approximately several micron meters to 200 μm, with the abrasive grains (such as aluminum oxide, silicone carbide and diamond) being fixed to the thin-walled base member by adhesive. The lapping film 11 may take a structure wherein the abrasive grains are adhered to an entire surface of the thin-walled base member or a structure wherein non-abrasive regions, each with a given width, that are intermittently formed along a length of the thin-walled base member. It is a usual practice for the other surface of the thin-walled base member to be applied with a back coating layer composed of resisting material (not shown) such as rubber or plastic resin, but non-slip surface treatment may be carried out on the other surface of the thin-walled base member if desired.

[0061] As best shown in FIG. 2 , the lapping film 11 is stretched between a supply reel 15 and a winding reel 16 that are rotatably supported on a frame body (not shown) of the lapping apparatus 1 , and the winding reel 16 is operatively connected to and driven by a drive motor M 3 . Disposed between the supply reel 15 and the winding reel 16 is a tensioned guide roller R 5 that is pulled in a given tensioned force. Operating the motor M 3 to rotate the winding reel 16 to cause the lapping film 11 to be pulled out from the supply reel 15 and guided by a plurality of guide rollers R 1 to R 10 to be wound by the winding reel 16 .

[0062] Disposed in the vicinity of the supply reel 15 and the winding reel 16 are lock mechanisms (not shown) which are selectively actuated to cause the lapping film 11 to be entirely applied with a given tension and to remain tensioned for lapping operation.

[0063] As best shown in FIG. 2 , the pressure applying mechanism 10 is comprised of a tool holder 28 including an upper shoe case 28 A, carrying therein a plurality of shoes 21 A, and a lower shoe case 28 B carrying therein a plurality of shoes 21 B, with the shoes 21 A and 21 B serving as tool holding elements and disposed on a rear side of the lapping film 11 to allow the abrasive face of the lapping film 11 , serving as the surface finishing tool, to be held in a pressured contact with the target shaped periphery of the workpiece W to be lapped. Each of the shoes 21 A, 21 B is formed of rubber or plastic material in structure with a relatively increased rigidity and has an inside portion formed in a circular arc surface to fit the target shaped periphery of the workpiece W to be lapped while an outside portion is retained by the shoe case.

[0064] In addition, the pressure applying mechanism 10 further includes an upper presser arm 22 and a lower presser arm 23 which are pivotally supported by upper and lower pivot shafts 24 , 24 , respectively, to allow front end portions 22 a, 23 a to be moved into or out of operative positions, respectively. The actuator 30 is comprised of a fluid cylinder 25 (adapted to be actuated by hydraulic pressure or air under pressure) operatively disposed between rear end portions 22 b, 23 b of the upper presser arm 22 and the lower presser arm 23 , respectively, to selectively apply shoe pressure forces to the front end portions 22 a, 23 a, respectively, through a rod. 26 such that the shoes 28 A, 28 B are held in pressured contact with the target shaped periphery of the workpiece W to be lapped at given pressure forces.

[0065] With such a structure of the pressure applying mechanism 10 , upon actuation of the fluid cylinder 25 , both the presser arms 22 , 23 move about the centers of the pivot shafts 24 , 24 for opening and closing capabilities. Opening and closing movements of both the presser arms 22 , 23 are carried out in association with the lapping film 11 and, during closing movements of both the presser arms 22 , 23 , the shoes 21 A, 21 B are brought into pressured contact with the workpiece W by means of the lapping film 11 whereas, during opening movements of both the presser arms 22 , 23 , the shoes 21 A, 21 B are brought out of abutting engagement between the workpiece W and the shoes 21 A, 21 B.

[0066] Moreover, the lapping apparatus 1 further includes shoe pressure force adjusting units 31 A, 31 B as shown in FIG. 2 by which spring forces of compression springs (not shown) to be applied to the shoe cases 28 A, 28 B are adjusted by cams 35 A, 35 B. However, the present invention is not limited to such a particular shoe pressure force adjusting structure and may take an alternative structure in which the spring forces are adjusted through the use of screw members.

[0067] During lapping operation, heat builds up in the shoe cases 28 A, 28 B and a cooling unit 70 is disposed on a front side of the pressure applying mechanism 10 to supply coolant to cooling areas proximate to the workpiece W and the lapping film 11 associated therewith for cooling these components.

[0068] Turning back to FIG. 1 , the drive mechanism 40 includes a main drive motor M 1 that is connected to and drive the spindle 41 through a belt 44 to rotate the workpiece W for lapping operation.

[0069] With the structure set forth above, the workpiece W is set between the headstock 42 and the tailstock 46 . Then, the main motor M 1 is operated and the workpiece W is rotated through the spindle 41 and the chuck 43 for lapping operation. Operatively coupled to the spindle 41 is a rotary encoder S 1 that detects a rotary position of the workpiece W during lapping operation and delivers a detection signal, indicative of the rotary position of the workpiece W, to a controller 100 . The controller 100 is responsive to this detection signal to allow a rotational speed of the main motor M 1 to be varied to enable the workpiece W to be driven at a workpiece rotational speed Vw of a given value.

[0070] Moreover, the oscillating mechanism 50 , serving as the tool shifting mechanism, oscillates the workpiece W along a horizontal axis thereof for a specific reason as will be described below in detail. To this end, the oscillating mechanism 50 is comprised of an eccentric rotary element 51 rotatably supported by the frame body in abutting engagement with a distal end of the workpiece support table 27 , a motor M 2 connected to and drive the eccentric rotary element 51 for oscillating the workpiece support table 49 and the urging unit 52 that urges the workpiece support table 49 in the lateral direction to cause the eccentric rotary element 51 into abutting engagement with the distal end of the workpiece support table 49 . Cooperation between rotation of the eccentric rotary element 51 , caused by the motor M 2 , and the urging unit 52 enables the workpiece support table 49 to be operated in reciprocating movements in an X-direction such that the entirety of the workpiece W is oscillated in the X-direction. Additionally, for the purpose of detecting an oscillating position of the workpiece W relative to the lapping film 11 during oscillating operation in the X-direction, a rotary encoder S 2 is mounted for detecting a rotary position of the eccentric rotary element 51 to allow resulting detection signal to be delivered to the controller 100 .

[0071] An oscillating stroke in which the workpiece W travels in a lateral direction is determined based on eccentric displacement of the eccentric rotary element 51 with respect to an axis of an output shaft of the motor M 2 . The rotary position of the eccentric rotary element 51 is detected by the rotary encoder S 2 , and adjustment of eccentric displacement may be executed by inserting one or more number of adjustor plates into an engaged area between the motor M 2 and the eccentric rotary element 51 or by using a hydraulic unit.

[0072] Also, while the presently filed embodiment has been described above with reference to a particular example wherein the oscillating mechanism 50 oscillates the workpiece W along the X-direction, the present invention is not limited to such a particular structure. The oscillating mechanism 50 may be modified in such a way as to directly oscillate the lapping film 11 along a longitudinal direction thereof. This is achieved through the use of a structure wherein the lapping film 11 is pulled out from the shoes 21 A, 21 B in a radial direction once to be wound on a roller whereupon the lapping film 11 is restored to the initial position near the shoes 21 A, 21 B, with the roller being connected to an oscillating means to be oscillated in the radial direction.

[0073] Incidentally, as shown in FIG. 2 , lubricating liquid LU such as lubricating oil is supplied toward the lapping film 11 and the shoes 21 A, 21 B.

[0074] FIG. 3 is a schematic structural view of an essential part of the crankshaft W for illustrating how the target shaped periphery of the crankshaft W is lapped in the lapping apparatus of the presently filed embodiment to provide a mid-concave profile on the target shaped periphery, FIG. 4 is a cross sectional representation taken along line 4 - 4 of FIG. 3 and FIG. 5 is an enlarged front view of a part of the crankshaft for illustrating a surface profile formed in the mid-concave shape as a result of lapping operation.

[0075] Especially, the presently filed embodiment contemplates to provide an arrangement in which the upper and lower shoes 21 A, 21 B are offset in contact position, in which the lapping film 11 is urged, with the target shaped periphery with respect to a center line thereof to enable the target shaped periphery of the crankshaft W to be lapped in the mid-concave profile. Here, by the term “target shaped periphery W1 of the crankshaft W” is meant the outer circular-arc shaped periphery between the fillet portions Wf.

[0076] As shown in FIGS. 3 and 4 , the lapping apparatus 1 of the presently filed embodiment employs an even number of shoes 21 A, 21 B which are mutually offset with respect to the target shaped periphery W 1 of the workpiece. With such an arrangement, the two upper shoe components are able to be held in contact with the target shaped periphery W 1 at a contact region A and the two lower shoe components are held in contact with the target shaped periphery W 1 at a contact region B such that the contact regions A, B overlap in a central region C lying at a center line O-O and do not overlap in terminal regions D, D closer to the fillet portions Wf, Wf. Also, hereinafter, the term “contact” refers to a phase in that the upper and lower shoes 21 A, 21 B are held indirect abutting contact with an outer periphery (target shaped periphery) W 1 of the workpiece W through the lapping film 11 , and by the term “contact region” is meant the region in which the upper and lower shoes 21 A, 21 B are held in indirect abutting contact with the outer periphery W 1 of the workpiece W through the lapping film 11 .

[0077] With such an offset arrangement of the upper and lower shoes 21 A, 21 B with respect to the target shaped periphery W 1 of the workpiece W, the lapping film 11 is apt to be pressured against the central region C of the target shaped periphery W 1 of the crankshaft W through all of the upper and lower shoes 21 A, 21 B to increase a lapping time interval for the target shaped periphery W 1 of the crankshaft W whereas, in the terminal regions D of the target shaped periphery W 1 , the lapping film 11 is intermittently brought into pressured contact with the target shaped periphery W 1 with the upper and lower shoes 21 A, 21 B, resulting in reduction in the time interval for which the workpiece W is lapped.

[0078] As a result, the target shaped periphery W 1 of the crankshaft W has a surface profile having the central region C formed in a concave profile Wa and the terminal regions each formed in a convex profile Wb, resulting in formation of an entire structure with a mid-concave profile as shown in FIG. 5 .

[0079] The surface profile of the workpiece W was tested to provide quantitative results in terms of offset displacement between the upper and lower shoes 21 A, 21 B in a manner as described below.

[0080] When conducting tests, use was made of the lapping film 11 with a width N in compliance with a width S of the target shaped periphery W 1 of the workpiece W and the even number of shoes 21 A, 21 B formed in the same width S that was made smaller than the width S of the target shaped periphery W 1 to be lapped as shown in FIG. 3 . The upper and lower shoes 21 A, 21 B were offset by a value δ in opposite directions with respect to the center line O-O of the lapping width S of the workpiece W. Here, the offset displacement δ was expressed in a percentage (100×δ/L%) with respect to the lapping width L.

[0081] Then, operations were carried out to lap the target shaped periphery W 1 of the workpiece W in offset displacement at differing values of 3, 6, 9, 12%, respectively, and straightness were measured for respective surface profiles resulting from lapping operations, with measured results being shown in FIG. 6 .

[0082] FIG. 6 is a view illustrating straightness of resulting surface profiles of the workpiece in terms of various offset displacements with abscissa indicating a position of the resulting surface profile of the workpiece W while the coordinate representing the straightness of the surface profiles, resulting from lapping operations, that is, in a value (μm) equivalent to a depth m of the mid-concave portion Wa.

[0083] With respect to the results shown in FIG. 6 , in consideration of a result deemed to be preferable when the depth m of the mid-concave portion Wa of the workpiece W falls in a value equal to or greater than 5 μm and equal to or less than 20 μm, it appears that desired surface profiles resulting from lapping operations are obtained under a condition where the offset displacement between the associated shoes 21 A, 21 B lies in a value equal to or greater than 3 and equal to or less than 12%. Especially, with the arrangement described above in which the even number of the shoes 21 A, 21 B with the same width S are used and disposed in offset positions with respect to the center line O-O of the target shaped periphery W 1 of the workpiece W, the target shaped periphery W 1 of the workpiece W can be formed in the surface profile to have the mid-concave profile around the center line O-O of the target shaped periphery W 1 of the workpiece W. Also, the upper and lower shoes 21 A, 21 B can be placed in the offset positions in an easy and precise fashion and even when concurrently carrying out the lapping operations on multiple target peripheries, the multiple target shaped peripheries of the workpiece W can be precisely lapped at the respective central regions, enabling formation of desired mid-concave portions of the target shaped peripheries of the workpiece W in a uniform profile with a resultant improved product quality.

[0084] Further, as set forth above, with the lapping apparatus 1 of the presently filed embodiment having the oscillating mechanism 50 enabling the workpiece W to oscillate in the X-direction, it is preferable for the relationship between the oscillating stroke, provided by the oscillating mechanism 50 , and the offset displacement δ such that the offset displacement δ is made smaller than the oscillating stroke. However, it is preferable for the shoes 21 A, 21 B associated with the lapping film 11 not to be dislocated from the target shaped periphery of the workpiece W even when the shoes 21 A, 21 B are disposed in the offset positions with respect to the lapping film 11 .

[0085] In operation, both the presser arms 22 , 23 are brought into the open condition and under such a condition, the lock unit associated with the supply reel 15 is locked whereupon the motor M 3 is operated to rotate the winding reel 16 . This causes the lapping film 11 to be moved in a given length with a new abrasive surface of the lapping film 11 being set to face the target shaped periphery W 1 of the workpiece W while applying the lapping film with a given tension.

[0086] And, when locking the lock unit associated with the winding reel 8 , the lapping film 11 is applied with tension to fall in a stretched state with no looseness.

[0087] Under such a circumstance, the workpiece W is set between the headstock 42 and the tailstock 46 . After such setting operation, the fluid cylinder 25 is actuated and the both presser arms 22 , 23 are brought into the closed condition. When this takes place, the lapping film 11 is set onto the target shaped periphery W 1 of the workpiece W, with both shoes 21 A, 21 B being brought into abutting engagement with the target shaped periphery W 1 of the workpiece W with a given urging force. In the presently filed embodiment, the workpiece W takes the form of the crankshaft that has a plurality of pins with the target shaped peripheries, respectively, and the lapping films 11 are set onto these target shaped peripheries in pressured contact, respectively.

[0088] Then, the main motor M 1 is operated and the workpiece W is rotated, causing the target shaped peripheries of the workpiece W to be lapped with the associated abrasive surfaces of the lapping films 11 . Depending on shapes of the pin portions, a probability occurs in which some of the pin portions eccentrically rotate with accompanied rocking movements of both the presser arms 22 , 23 in a normal practice, with resultant lapping operations being similarly executed on the associated pin portions.

[0089] In the presently filed embodiment, particularly, due to the presence of the shoes 21 A, 21 B disposed in the offset positions with respect to the center line O-O of the target shaped periphery W 1 of the workpiece W, the contact regions A of the shoes 21 A, 21 B held in contact with the target shaped periphery W 1 overlap one another at the central region C of the target shaped periphery W 1 of the workpiece W and do not overlap one another at the terminal regions D. When this takes place, in the central region C of the target shaped periphery W 1 of the workpiece W, both the shoes 21 A, 21 B are effective to press the lapping film 11 onto the target shaped periphery W 1 of the workpiece W to allow the central region C of the target shaped periphery W 1 to be lapped at a greater rate than those at which the other regions are lapped, resulting in the workpiece W having surface profiles each formed in a mid-concave profile.

[0090] Thus, when carrying out lapping operation to provide the target shaped periphery formed in the mid-concave profile, it is extremely advantageous in that the number of processing steps is decreased to a lower value than that required in using a burnishing roller and no specific roller is required in use with a resultant decrease in a cost performance. Additionally, no probability occurs in the workpiece to have a surface roughness formed in an undesirably smoothed extent and thus, an oil sump area is advantageously formed in the central region of the target shaped periphery of the workpiece to be highly advisable in a lubricating capability.

[0091] In the meantime, during lapping operation of the lapping apparatus 1 , the motor M 2 is operated to allow the eccentric rotary element 51 of the oscillating mechanism 50 to rotate against the biasing force of the urging unit 52 , thereby oscillating the workpiece support table 49 in the X-direction to cause the workpiece W to oscillate in the X-direction.

[0092] During oscillating operation of the oscillating mechanism 50 , there occurs an increase in a distance in which the target shaped periphery W 1 of the workpiece W and the abrasive grains of the lapping film 11 are held in contact, resulting in an increase in the number of abrasive grains acting upon the target shaped periphery per unit time for thereby enabling lapping operation to be achieved within a shortened time interval to surface finish the workpiece at an increased efficiency. Due to the presence of the offset displacement δ between the associated shoes 21 A, 21 B to be made smaller than the oscillating width, the oscillation and lapping operation can be reliably performed.

[0093] Further, as shown in FIG. 3 , since the workpiece W has the journal portion and the pin portion each formed with fillet portions Wf at both ends of the target shaped periphery to allow the fillet portions Wf to be used for providing spaces to enable the workpiece W to oscillate and the associated shoes to be placed in the offset positions, it becomes possible to provide an improved operability. Also, during such lapping operation, no crushing or wearing, that would otherwise occur in roller burnishing operation, occur in the vicinity of the fillet portions Wf, enabling the workpiece W to be machined at a desired straightness.

[0094] FIG. 7 is a schematic view illustrating a surface, in an exaggerated form, of the target peripheries shown in FIG. 5 . When performing lapping operation in a manner set forth above, the surfaces of the mid-concave portion Wa and the terminal portions Wb appear to have axially contoured configurations, as viewed in cross section, in which sharp edges T 1 and valley portions T 2 are alternately formed as shown in FIG. 7 .

[0095] With such concave and convex portions being filled with lubricating oil, the concave and convex portions serve as desired oil reservoirs, exhibiting a desired function to provide am improved lubricating capability while preventing the journal or pin portions from being seized. However, in actual practice to provide a final product, it is preferable for the sharp edges T 1 to be subjected to burnishing operation so as to remove the sharp edges T 1 such that the sharp edges T 1 is lowered to some extent. In so doing, it becomes possible to prevent the sharp edges T 1 , that would otherwise be caused during an initial stage of start-up of an engine from being worn, with a resultant increase in a durability.

[0096] The present invention is not limited to the presently filed embodiment set forth above, and various alterations may be made. While the presently filed embodiment has been described with reference to a particular structure where the pin portions of the crankshaft are mainly processed, lapping operations may be performed not only for the pin portions but also for the journal portions of the crankshaft and, if the occasion demands, lapping operation may be carried out on the target shaped peripheries with non-complete round shape in cross section, such as cam lobe portions or journal portions of a cam shaft. In addition, the present invention may also be applied to the other objective with a target profile in other circular-arc shaped configuration.

[0097] Further, while the surface finishing apparatus of the presently filed embodiment has been shown and described in conjunction with an structural example wherein the tool shifting mechanism is comprised of the oscillating mechanism 50 that is arranged to oscillate the workpiece support table 49 by which the workpiece W is oscillated in the lateral direction, the tool shifting mechanism may be modified such that the main spindle 41 is oscillated to cyclically move the workpiece along the axis thereof. In another alternative, the tool shifting mechanism may take a structure to directly oscillate the lapping film 11 or to directly oscillate both workpiece W and the lapping film 11 . Also, the oscillating mechanism 50 is not limited to the particular structure that employs the eccentric rotary element 51 , and the oscillating mechanism 50 may include an ultrasonic oscillator.

[0098] While the surface finishing apparatus of the presently filed embodiment has been shown and described in conjunction with an structural example wherein the oscillating position of the workpiece W is detected based on the rotational position of the eccentric rotary element 51 through the use of the rotary encoder S 2 , the surface finishing apparatus may take a modified structure upon using an optical sensor to directly detect the terminal end of the workpiece W for thereby detecting the oscillating position of the workpiece W.

[0099] Moreover, the surface finishing apparatus of the presently filed embodiment has been shown and described in conjunction with a structural example that includes the convex-shaped shoes, the surface finishing apparatus may use other types of shoe configurations.

Second Embodiment

[0100] A surface finishing apparatus 1 A of a second embodiment of the present invention is described below with reference to FIGS. 8 to 14 and FIGS. 15A and 15B . FIG. 8 is a schematic view illustrating the surface finishing apparatus 1 A of the second embodiment of the present invention. FIG. 9 is a schematic view, with a positional relation in correspondence with FIG. 2 , showing a pressure applying mechanism 10 A, forming part of the surface finishing apparatus 1 A, by which upper and lower presser arms, that are operative to assume open positions and closed positions, are retained in the closed positions. FIG. 10 is a schematic view showing the pressure applying mechanism 10 A by which the upper and lower presser arms are retained in the open positions. FIG. 11 is an enlarged partly cross sectional view showing the presser mechanism, forming an essential part, of the surface finishing apparatus 1 A of the presently filed embodiment. FIG. 12 is a view illustrating the relationship between a cam position and an oscillating angle. FIG. 13 is a schematic view showing a structure equivalent to a structure of the pressure applying mechanism 30 . FIG. 14 is a view illustrating the relationship between a presser force and an eccentric angle of a cam. FIG. 15A is a perspective view showing an example of a workpiece in the form of a cam shaft to be machined. FIG. 15B is a perspective view showing another example of a workpiece in the form of a crankshaft to be machined.

[0101] The surface finishing apparatus 1 A of the second embodiment differs from the surface finishing apparatus 1 of the first embodiment in that a cam shaft is employed as a workpiece and a controller 100 A is arranged to control a pressure force to be applied by a pressure applying mechanism 10 A in dependence on an oscillating position of the workpiecee resulting from a rotational position, indicative of an oscillating angle θc, of an eccentric rotary element 51 of an oscillating mechanism 50 . In the presently filed embodiment, the same component parts as those of the surface finishing apparatus of the first embodiment bear like reference numerals and the surface finishing apparatus 1 A is described below aiming at differing points in structure with explanation for the same component parts being simplified or omitted.

[0102] Referring to FIGS. 9 and 10 , there is shown the pressure applying mechanism 10 A operative to apply a pressure force to a surface finish tool, in the form of the lapping film 11 , with the pressure force exhibiting a distribution pattern depending upon an axial direction of the workpiece such that the lapping film 11 is held in pressured contact with the target shaped periphery, with the pressure force exhibiting a distribution pattern depending upon an axial direction of the workpiece W. The lapping film 11 extends between the supply reel 15 and the winding reel 16 and is guided with the guide rollers R 1 to R 10 . The guide rollers R 1 and R 10 are supported on the frame body (not shown) of the surface finishing apparatus 1 A. Further, the guide rollers R 3 to R 5 are supported on the upper presser arm 22 , and the guide rollers R 6 to R 9 are supported by the lower presser arm 23 . A pair of guide rollers R 3 and R 4 are located on a front portion of the forward end 22 a of the upper presser arm 22 , and the guide roller R 5 is located in an inside area of the upper presser arm 22 at a position close proximity to the upper pivot shaft 24 .

[0103] Likewise, a pair of guide rollers R 7 and R 8 are located on a front portion of the forward end 23 a of the lower presser arm 23 , and the guide roller R 6 is located in an inside area of the upper presser arm 23 at a position close proximity to the lower pivot shaft 24 . With such an arrangement, the lapping film 11 is pulled out from the supply reel 15 and guided with the pair of first guide rollers R 3 and R 4 , the second guide roller R 5 , the third guide roller R 6 and the pair of fourth guide rollers R 7 and R 8 whereupon the lapping film 11 is taken up on the winding reel 16 .

[0104] Supported in an intermediate area of the upper presser arm 22 between the guide roller R 4 and the guide roller R 5 is an upper shoe 21 A, and supported in an intermediate area of the lower presser arm 23 between the guide roller R 6 and the guide roller R 7 is a lower shoe 21 B. A cam lobe portion 61 of the cam shaft WA, that is rotatably supported with the headstock 42 and the tail stock 46 (see FIG. 8 ), remains at a central area between the upper and lower presser shoes 21 A, 21 B for a purpose to be described below.

[0105] Connected to the winding reel 16 is a motor M 3 . With the motor M 3 being operated, the winding reel 16 is rotated and the lapping film 11 is progressively fed from the supply reel 15 . In order to detect the amount of lapping film 11 delivered from the supply reel 16 , a rotary encoder S 3 is mounted onto a shaft of the winding reel 16 as a detection unit to detect rotational displacement thereof. The lock units are mounted to the frame body (not shown) in the vicinity of the supply reel 15 and the winding reel 16 , respectively, and operative to apply the given tension force to an entirety of the lapping film 11 .

[0106] The pair of upper and lower presser arms 22 and 23 are pivotally supported on the upper and lower pivot shafts 24 , 24 to allow the forward end portions 22 a, 23 a of the upper and lower presser arms 22 , 23 to be movable with respect to one another in the Z-direction for opening and closing capabilities. The upper and lower presser arms 22 and 23 are actuated by the fluid cylinder 25 . With such a structure, if the piston rod 26 of the actuator 30 protrudes from a retracted condition, the upper and lower presser arms 22 , 23 are pivoted in a direction to allow the forward end portions 22 a, 23 a of the upper and lower presser arms 22 , 23 to fall in the closed position shown in FIG. 9 . In the meantime, if the piston rod 26 is retracted from the protruding condition, the upper and lower presser arms 22 , 23 are pivoted in the other direction to allow the forward end portions 22 a, 23 a of the upper and lower presser arms 22 , 23 to fall in the open position shown in FIG. 10 . Pivoting movements of the upper and lower presser arms 22 , 23 allow the lapping film 11 to be moved in the same directions as the upper and lower presser arms 22 , 23 . Pivoting movements of the upper and lower presser arms 22 , 23 in the closing directions allow the shoes 21 A, 21 B to be brought into abutting engagement with the cam lobe portion 61 by means of the lapping film 11 . Also, pivoting movements of the upper and lower presser arms 22 , 23 in the opening directions allow the shoes 21 A, 21 B to be brought out of abutting engagement with the cam lobe portion 61 .

[0107] Although the upper and lower presser shoes 21 A, 21 B may be classified into convex type shoes and concave type shoes depending on outer profiles of the forward end portions of the shoes, in the illustrated second embodiment, the upper and lower presser shoes 21 A, 21 B are shown as concave type shoes, respectively, each of which has a concave distal end portion formed with plural lobes (shown as two lobes in the second embodiment) that are selectively brought into abutting engagement with a target shaped periphery of the cam lobe portion 61 by means of the lapping film 11 . The distal end of each shoe is indented but has a pair of engaging surfaces per se, which mate with the workpiece WA, that are formed in convex circular arc configurations in cross section, respectively. Thus, the upper and lower presser shoes 21 A, 21 B are able to be brought into abutting engagement with the target shaped periphery of the cam lobe portion 61 at two line contacts though the lapping film 11 is intervened. Due to the presence of the cam lobe portion 61 being supported with the upper and lower presser shoes 21 A, 21 B at four contact points, the cam lobe portion 61 can be rotated in a stable and reliable fashion. Here, by the term “contact” used in the presently filed embodiment is meant that the upper and lower presser shoes 21 A, 21 B are brought into indirect abutting engagement with the target shaped periphery of the workpiece WA via the lapping film 11 , and by the term “contact surface area” is meant the surface area in which the upper and lower presser shoes 21 A, 21 B are brought into indirect abutting engagement with the target shaped periphery of the workpiece WA via the lapping film 11 .

[0108] As shown in FIG. 11 , the forward end portions 22 a, 23 a of the upper and lower presser shoes 21 A, 21 B are formed with vertically inward cavities 27 A, 27 B, respectively, in which shoes cases 28 A, 28 B carrying the upper and lower shoes 21 A, 21 B, respectively, are slidably accommodated for protruding and retracting capabilities with respect to the workpiece WA. Disposed inside cavities 28 a, 28 b of the shoe cases 28 A, 28 B are upper and lower shoes 21 A, 21 B that are supported on pivot shafts 29 A, 29 B, respectively, for rocking movements. The upper and lower pivot shafts 29 A, 29 B are arranged to be aligned on a line segment intersecting a center 0 of the cam shaft 60 and to cause shoe pressure forces P to be efficiently applied to the lapping film 11 . Also, reference numeral 70 a designates a nozzle of the cooling unit 70 by which coolant is injected to an area close proximity to the target shaped periphery of the workpiece WA.

[0109] The pressure applying mechanism 10 A includes upper and lower pressure adjusting units 31 A, 31 B associated with the forward end portions 22 a, 23 a, respectively, of the upper and lower presser arms 22 , 23 for enabling the shoes 21 A, 21 B to hold the lapping fill 11 in pressured contact with the target shaped periphery, i.e., the cam lobe portion 61 , of the workpiece W under the given pressure distribution pattern. Also, as conceptually shown in FIG. 13 , each of the upper and lower pressure adjusting units 31 A, 31 B includes a connecting rod 32 whose distal end is connected to the shoe case ( 28 A, 28 B), a workpiece clamp spring 33 made of a coil spring, a presser rod 34 causing the workpiece clamp spring 33 to be resiliently compressed with respect to a rear end of the connecting rod 32 , an eccentric rotary element ( 35 A, 35 B), serving as a lift adjustment element, held in abutting engagement with a head portion of the presser rod 34 , and a presser motor M 4 rotating and driving the eccentric rotary element 35 . The connecting rod 32 and the presser rod 34 are slidably accommodated in a through-hole ( 22 c, 23 c ) formed in the presser arm ( 22 , 23 ). With the shoe cases 28 A, 28 B being depressed, the shoes 21 A, 21 B retained by the respective shoe cases 28 A, 28 B are pressed, thereby causing the abrasive grain surface of the lapping film 11 to be depressed against the cam lobe portion 61 . A cam lift h of the eccentric rotary element 35 is equal to a product in which a base circle diameter is subtracted from a total height H of a cam, and the cam lift h defines a dimension to enable the presser rod 34 to move in the maximum distance. Thus, the workpiece clamp spring 33 , the presser rod 34 , the eccentric rotary element 35 and the presser motor M 4 form each presser force adjusting unit ( 31 A, 31 B) for adjusting a shoe pressure force P.

[0110] As shown in FIG. 14 , the shoe pressure force P varies in dependence on the rotational position of the eccentric rotary element 35 to allow the lapping film 11 to be applied with the shoe pressure forces P in a distribution pattern depending upon an axial direction of the workpiece WA. That is, an initial position (eccentric angle θe=0 degree) is assigned to be a position in which the base circle is brought into abutting contact with the head of the presser rod 34 . When rotating the eccentric rotary element 35 from such an initial position through the eccentric angle θe of 180 degrees, the presser rod 34 is shifted by the cam lift h to cause the workpiece clamp spring 33 to be further resiliently deformed and, as a result, the shoe pressure force P takes the maximum value. If the eccentric rotary element 35 is further rotated through the eccentric angle θe of 360 degrees, the presser rod 34 is restored to the initial position and the shoe pressure force P is also restored to the same presser force as that of the initial position. In order to detect variation of such a shoe pressure force P, a rotary encoder S 4 is mounted to detect the rotational position of the eccentric rotary element 35 (see FIG. 11 ).

[0111] FIG. 16A is a view conceptually showing a shifted condition of the workpiece WA together with the lapping film 1 , when applied with the oscillating motion. FIG. 16B is a view conceptually illustrating a degree of damage D encountered by the abrasive grains 12 , suffered from edges We of the workpiece WA that moves accompanied by oscillation thereof, and a geometric shape along the axis of the workpiece WA, shown in an exaggerated form, as a result of lapping operation in a comparative example in which the shoe pressure force P is made constant regardless of the oscillating position of the workpiece WA.

[0112] Also, FIG. 17A conceptually shows the relationship between a removal quantity of the target shaped periphery W 1 per unit time, resulting from the abrasive grains 12 of the lapping film 11 , and the shoe pressure force P. FIG. 17B conceptually shows the relationship between the degree of damage D encountered by the abrasive grains 12 caused by the edges We of the workpiece WA that moves due to oscillation, and the shoe pressure force P. FIG. 17C conceptually shows the relationship between the removal quantity of the target shaped periphery W 1 per unit time resulting from the abrasive grains 12 of the lapping film 11 and the degree of the damage D of the abrasive grains under a condition where the shoe pressure force P is kept constant.

[0113] In FIG. 16A, a solid line indicates a status wherein the target shaped periphery W 1 of the workpiece WA assumes a central position with respect to the lapping film 11 , a single dot line indicates a status wherein the target shaped periphery W 1 of the workpiece WA is deviated to the leftmost end in the X-direction with respect to the central position of the workpiece WA and a double dot line indicates a status wherein the target shaped periphery W 1 of the workpiece WA is deviated to the rightmost end in the X-direction with respect to the central position of the workpiece WA. In FIG. 16A, a reference symbol “Lw” designates a width of the target shaped periphery W 1 along the axis of the workpiece WA, the reference symbol “Lo” indicates a width in which the workpiece WA is oscillated and the reference symbol “Ao” indicates an oscillating width of oscillation.

[0114] The abrasive grains 12 of the lapping film 11 encounter damages, such as cracks or fallouts in the worst case, resulting from the edge portions We, We of the workpiece WA that moves in oscillation. For this reason, as shown in FIG. 16 B, the degree of the damage D encountered by the abrasive grains 12 due to the edge We of the workpiece WA substantially equals zero in the contact region of the lapping film 11 that is held in pressured contact with the target shaped periphery W 1 of the workpiece WA at all times, and the degree of damage D of the abrasive grains increases in a region in which the edge portion We of the workpiece WA shifts. Such a degree of the damage D of the abrasive grains is assigned to be “a”.

[0115] Here, the removal quantity of the target shaped periphery W 1 of the workpiece WA per unit time due to the abrasive grains 12 of the lapping film 11 increases with an increase in the shoe pressure force P (see FIG. 17A ). The damage D in the abrasive grains increases with an increase in the shoe pressure force P (see FIG. 17B ). Under a condition where the shoe pressure force P is kept constant, the removal quantity of the target shaped periphery W 1 per unit time caused by the abrasive grains 12 decreases with an increase in the damage D in the abrasive grains (see FIG. 17C ).

[0116] Accordingly, in the comparative example, as shown in FIG. 16 B, wherein the shoe pressure force P is held constant (as expressed as P=P 0 ) regardless of the oscillating position of the workpiece WA, the removal quantity of the target shaped periphery W 1 relatively increases at the central portion as compared to the both end portions, resulting in formation of the geometric shape into the mid-concave profile along the X-direction. Upon formation of the geometric shape into the mid-concave profile along the X-direction in such a manner, it is hard for the target shaped periphery W 1 to have a straightness at a desired level, resulting in a fear of occurrence of defective surface finish.

[0117] Therefore, the surface finishing apparatus 1 A of the second embodiment contemplates the provision of a structure wherein the rotational position (the oscillating angle θc) of the eccentric rotary element 51 using the rotary encoder S 2 and the oscillating position of the cam shaft 60 is detected using the oscillating position θc whereupon the controller 100 A operates to variably control the shoe pressure force P, to be applied to the lapping film 11 in the given distribution pattern depending upon the axial direction of the workpiece WA, in dependence on the oscillating position of the workpiece WA during surface finishing operation for thereby enabling the target shaped periphery W 1 to be formed into a desired geometric profile along the axis of the workpiece WA.

[0118] A basic sequence of operations in control set forth above is described in detail with reference to FIG. 18 and FIGS. 19A to 19 C. FIG. 18 shows a schematic block diagram illustrating a control system of the surface finishing apparatus 1 A of the presently filed embodiment, and FIGS. 19A to 19 C show control examples to indicate how the shoe pressure forces P are variably controlled in dependence on the oscillating position of the workpiece WA during surface finishing operation to allow the shoe pressure forces P to be applied to the target shaped periphery W 1 of the workpiece WA, with the pressure force exhibiting the given distribution pattern depending upon the axial direction of the workpiece WA such that the target shaped periphery W 1 is surface finished in a desired geometrical profile, contoured along the axial direction of the workpiece WA in cross section.

[0119] Referring to FIG. 18 , the control system includes the controller 100 A, that is mainly comprised of a CPU and memories, to which the rotary encoders S 1 to S 4 are connected to receive detection signals related to the rotational position of the cam lobe portion 61 , the rotational position of the eccentric rotary element 35 with the shoe pressure force P being varied, and the rotational position of the eccentric rotary element 35 applied with oscillation, respectively. Also, the controller 100 A is applied with detection signals related to the rotating speed of the main motor M 1 by which the workpiece rotating speed Vw is determined and the rotating speed of the oscillating motor M 2 , by which the oscillating speed Vo is determined, respectively.

[0120] The controller 100 A is responsive to the detection signal related to the rotational position of the eccentric rotary element 51 delivered from the rotary encoder S 2 and discriminates to find whether the oscillating position of the cam shaft 60 is located. And, the controller 100 A variably controls the shoe pressure forces P to be applied to the shoes 21 A, 21 B in dependence on the oscillating position of the cam shaft 60 along the axial direction thereof.

[0121] The shoe pressure forces P are variably controlled by the controller 100 A in a manner described below. As shown in FIG. 19 A, the controller 100 A controls the operation of the pressure applying mechanism 10 A, involving the pressure adjusting units 31 A, 31 B including the eccentric rotary elements